BACKGROUND OF THE INVENTION
[0001] The present invention relates to a cleaning system to clean an image bearing member
used in electrophotographic process and an image forming system equipped with said
cleaning system.
[0002] In the field of image forming technology where images are formed by an electrophotographic
system, efforts have been made in recent years to reduce toner particle size, thereby
improving image quality. Resolution can be improved and sharp images can be formed
by reducing toner particle size. However, the following problems arise in the cleaning
process:
[0003] With the reduced size of toner particles, there is an apparent increase in adhesion
of toner to the image bearing member. This makes it difficult to clean the image bearing
member by removing it from the toner remaining after transfer. When using the cleaning
method of using only the cleaning blade, cleaning failure occurs to deteriorate image
quality. Especially when image is formed using the toner whose particles are formed
by emulsion polymerization method or suspension polymerization method, cleaning failure
called "sneaking-through" occurs, wherein remaining toner on the image bearing member
passes through the cleaning system without being scraped off by the cleaning blade
of the cleaning system. This is because the particle size is very small and toner
particles are roughly spherical in shape.
[0004] Study is currently under way in an effort to solve the problem resulting from the
reduced particle size of such toner particles. For example, Official Gazette of Japanese
Patent Laid-Open NO.52808/1999 proposes the cleaning technology wherein conductive
or semiconductive rubber is used as the material constituting the cleaning blade,
and voltage having polarity reverse to that of toner is applied to the cleaning blade,
thereby applying mechanical and electrical removing force to toner remaining on the
image bearing member.
[0005] Official Gazette of Japanese Patent Laid-Open NO.189675/1991 discloses a cleaning
technology which permits cleaning by installing a cleaning brush to apply electrostatic
force and a cleaning blade to apply mechanical cleaning force on the downstream side
of said cleaning brush.
[0006] In the image forming system based on electrophotographic method so far, a cleaning
method using an elastic cleaning blade is known as a means of cleaning toner remaining
on the image bearing member. This is extensively use for simple structure and lower
cost.
[0007] In addition to cleaning of the toner after transfer, an image bearing member cleaning
means is used to clean the surface of the image bearing member with a great deal of
toner remaining thereon without being transferred, for example, after sudden suspension
of the operation due to paper jamming or the like or on the patch created for image
adjustment or the like.
[0008] When pulverized toner created by the conventional pulverization method is used, toner
has been successfully scraped off for a long time without cleaning failure, even if
a great deal of toner has reached the cleaning blade without being transferred.
[0009] In the image forming system based on electrophotographic method, many proposals have
been put forth regarding the cleaning system laid out on the periphery of the carrier
to clean the surface of the image bearing member.
[0010] In the normal image forming process, electrostatic latent image is formed on the
image bearing member. After that, said electrostatic latent image is developed by
toner to create a toner image. After said toner image is transferred, paper powder
adhering to said carrier surface or remaining toner having failed to be transferred
is removed by the cleaning system.
[0011] Amorphous toner produced according to the conventional pulverization method (average
circularity of 0.95 or less) has been sufficiently scraped off only when the end of
an elastic plate member called a cleaning blade is brought into mechanical contact
with the surface of the image bearing member to scrape it off.
[0012] Said conventional cleaning technology, however, has the following problems:
(1) Sufficient cleaning cannot be performed when the potential distribution on the
image bearing member is not uniform.
(2) If high voltage is applied to the cleaning blade for cleaning work, electric discharge
or injection of electric charge into the image bearing member takes place. This results
in image quality or image bearing member.
(3) Toner electrostatically attached to the cleaning blade is deposited with time,
and deposited toner falls down to contaminate the image or interior of the equipment.
(4) If bias voltage applied to the cleaning roller in order to raise the cleaning
performance of said cleaning roller, toner is absent between the downstream cleaning
blade and image bearing member. This will deteriorate friction reducing effect by
toner, and is likely to cause separation of the cleaning blade.
The cleaning system disclosed in said Official Gazette allows the cleaning function
to be shared between a cleaning brush and cleaning blade, thereby ensuring improved
cleaning performance. However, it has the following problems:
(5) Since the greater part of toner is removed by the brush located on the upstream
side, the amount of toner between the toner carrier and cleaning blade can be very
small. If this occurs, friction between the image bearing member and cleaning blade
will be increased. This is likely to cause chattering where the cleaning blade vibrates,
or curling where the cleaning blade tip rotates in the reverse direction following
the image bearing member.
(6) According to an example disclosed in the Official Gazette of Japanese Patent Laid-Open
NO.189675/1991, a high voltage is applied to the upstream brush roller and the image
forming surface is likely to be damaged by electrical discharge. Especially in the
initial phase of development, foreign substances (carrier in the developer, magnetic
substance and mixed metal chip) are likely to deposit on an image former due to overshooting
of the development bias. If a brush charged with said voltage is brought in contact
with that portion, electric discharge will easily occur with the result that the image
former is damaged and image failure occurs.
(7) In the real-world usage, toner deposits over the range in excess of the image
forming area by scatters from the development device. When the disclosed art alone
is used, it may be difficult to recover the toner having dispersed over said range.
A simple countermeasure is to increase the width of the cleaning brush (roller). In
this case, electric discharge occurs from the cleaning brush (roller) to which bias
is applied to the substrate (aluminum used normally) of both image forming ends. This
makes it difficult to maintain stable cleaning performances.
(8) In keeping with improvement of image quality in an image forming system, roughly
spherical and small-sized toner is coming into use. Roughly spherical shape of toner
is effective in increasing the development quality. Small-sized toner is essential
to formation of a high resolution image. If the weight mean particle size is below
3 microns, however, deposition of toner on the image bearing member is caused by van
der Waals force, with the result that fogging is produced to deteriorate image quality.
(9) Said roughly spherical and small-sized toner can be obtained with relative ease
if it is made into polymerized toner (to be discussed later). Polymerized toner is
preferably used to ensure high quality image. It is known in the related art that,
when such polymerized toner is used, however, it is difficult to scrape said toner
off the surface of the image bearing member with the cleaning blade as a cleaning
means if much toner remains on the image bearing member.
(10) This is commonly explained by the following argument: The tip of said cleaning
blade in contact with the image bearing member surface is vibrated by the rotation
of the image bearing member, and a gap is produced between the tip of said cleaning
blade and image bearing member surface due to said vibration. Since the polymerized
toner is roughly spherical, it easily escapes through the above gap. This phenomenon
tends to occur more frequently if the cleaning blade is used for a long time and friction
of blade edge proceeds. Then cleaning failure is more likely to take place.
(11) For the reasons discussed above, there has been a problem of incomplete cleaning
when a great deal of said toner without being transferred has arrived and the number
of printings has increased.
(12) In response to the requirements for higher image quality in recent years, small
sized roughly spherical polymerized toner with high mean circularity has come into
use. Such polymerized toner with high mean circularity raises no problem when the
cleaning blade has been replaced with a new one. In time it will gradually wears out
resulting in poor contact with image bearing member. If contact pressure between cleaning
blade and image bearing member is deteriorated, toner is considered to slip easily
through the slight gap between the tip of the cleaning blade and the surface of the
image bearing member, because of spherical shape of the toner particle. It can also
be considered that both the shape and particle size are uniform and there is an increased
affinity between toner particles with respect to the image bearing member.
(13) Toner with a high mean circularity is desired to be used to ensure high image
quality. However, if cleaning of the image bearing member is not satisfactory, attached
paper powder and remaining toner will adversely affect the formation of the next image,
with the result that image quality is deteriorated.
SUMMARY OF THE INVENTION
[0013] The object of the present invention is to solve the problems in conventional cleaning
technologies as indicated above.
[0014] Accordingly, to overcome the cited shortcomings, the object of the present invention
can be attained by cleanig apparatus described as follow.
1. A cleaning apparatus, comprising; a cleaning roller being either conductive or
semi-conductive and in contact with an image bearing member carrying charged toner;
a constant current source to apply a bias voltage, having a polarity opposite to that
of toner utilized for a developing operation performed on the image bearing member,
onto the cleaning roller; and a cleaning blade contacting the image bearing member
and located at a downstream side of the cleaning roller in a moving direction of the
image bearing member.
2. The cleaning apparatus of item 1, wherein the cleaning roller rotates in such a
manner that its contact surface moves in the same direction as the moving direction
of the image bearing member at a position in contact with the image bearing member,
and the ratio between a roller moving velocity of the cleaning roller and a moving
velocity of the image bearing member at the contact surface is within a range of 0.5:1
to 2:1.
3. The cleaning apparatus of item 1, further comprising: a removing member for removing
toner from the cleaning roller by contacting the cleaning roller.
4. The cleaning apparatus of item 1, wherein the cleaning blade contacts the image
bearing member with a pressing load being within a rang of 1 to 30 grams/cm.
5. The cleaning apparatus of item 1, wherein the contact angle between the image bearing
member and the cleaning blade is within a range of 0 to 40 deg.
6. The cleaning apparatus of item 1, wherein the hardness of the cleaning blade is
within a range of 20 to 90 deg.
7. The cleaning apparatus of item 1, further comprising: a control section to control
the constant current source so as to increase an absolute value of an electronic current
applied by the constant current source according as an increase of an image-forming
amount.
8. The cleaning apparatus of item 7, wherein the image-forming amount is a number
of sheets on which images are formed.
9. The cleaning apparatus of item 1, further comprising: a control section to control
the constant current source so as to increase an absolute value of a toner-collecting
voltage applied by the constant current source according as an increase of an image-forming
amount, wherein the toner-collecting voltage is equivalent to the bias voltage.
10. The cleaning apparatus of item 9, wherein the image-forming amount is a number
of sheets on which images are formed.
11. The cleaning apparatus of item 1, further comprising: a control section to control
the constant current source so as to apply either a toner-collecting voltage or a
toner-releasing voltage onto the cleaning roller by selecting one of them in a time-sharing
manner, wherein both the toner-collecting voltage and the toner-releasing voltage
are equivalent to the bias voltage.
12. The cleaning apparatus of item 11, wherein the toner-releasing voltage is applied
at every completion of forming images on a predetermined number of sheets.
13. The cleaning apparatus of item 12, wherein the predetermined number of sheets
changes corresponding to a total number of sheets on which images are formed.
14. The cleaning apparatus of item 13, wherein the toner-releasing voltage is generated
by superimposing an alternative current voltage on a direct current voltage.
15. The cleaning apparatus of item 1, further comprising: a control section to control
the constant current source so as to increase an absolute value of a toner-collecting
voltage according as an increase of an image-forming amount, and so as to apply either
the toner-collecting voltage or a toner-releasing voltage onto the cleaning roller
by selecting one of them in a time-sharing manner, wherein both the toner-collecting
voltage and the toner-releasing voltage are equivalent to the bias voltage.
16. The cleaning apparatus of item 15, wherein the image-forming amount is a number
of sheets on which images are formed.
17. The cleaning apparatus of item 15, wherein the toner-releasing voltage is applied
at every completion of forming images on a predetermined number of sheets.
18. The cleaning apparatus of item 17, wherein the predetermined number of sheets
changes corresponding to a total number of sheets on which images are formed.
19. The cleaning apparatus of item 17, wherein the toner-releasing voltage is generated
by superimposing an alternative current voltage on a direct current voltage.
20. The cleaning apparatus of item 9, wherein the cleaning roller rotates in such
a manner that its contact surface moves in the same direction as the moving direction
of the image bearing member at a position in contact with the image bearing member,
and the ratio between a roller moving velocity of the cleaning roller and a moving
velocity of the image bearing member at the contact surface is within a range of 0.5:1
to 2:1.
21. The cleaning apparatus of item 9, further comprising: a removing member for removing
toner from the cleaning roller by contacting the cleaning roller.
22. The cleaning apparatus of item 1, wherein an average circularity of toner particles
included in the toner is within a range of 0.96 to 0.99, and a toner deposit amount
per unit area on a surface of the image bearing member is not greater than 0.25 mg/cm2 at a surface area ranging from a first position at which the image bearing member
contacts the cleaning roller to a second position at which the image bearing member
contacts the cleaning blade.
23. The cleaning apparatus of item 1, wherein an average circularity of toner particles
included in the toner is not smaller than 0.96.
24. The cleaning apparatus of item 23, wherein the cleaning roller is an elastic roller.
25. A cleaning apparatus, comprising: a cleaning roller being either conductive or
semi-conductive and in contact with an image bearing member carrying toner; an electric-power
source to apply a toner-collecting voltage and a toner-releasing voltage onto the
cleaning roller; a control section to control the electric-power source; and a cleaning
blade contacting the image bearing member and located at a downstream side of the
cleaning roller in a moving direction of the image bearing member, wherein the control
section controls the electric-power source so as to apply either the toner-collecting
voltage or a toner-releasing voltage onto the cleaning roller by selecting one of
them in a time-sharing manner.
26. An image-forming apparatus, comprising: an image bearing member; a developing
device; and the cleaning apparatus cited in item 1.
27. The image-forming apparatus of item 26, wherein the image bearing member is an
organic photoreceptor.
28. The image-forming apparatus of item 26, wherein the developing device performs
a developing operation by employing toner particles formed by a polymerization method,
in which a volume average particle size of the toner particles is within a range of
3.0 to 8.5 microns.
29. The image-forming apparatus of item 26, wherein the cleaning apparatus comprises:
a control section to control the constant current source so as to increase an absolute
value of a toner-collecting voltage according as an increase of an image-forming amount,
wherein the toner-collecting voltage is equivalent to the bias voltage.
30. The image-forming apparatus of item 26, wherein the cleaning apparatus comprises:
a control section to control the constant current source so as to apply either the
toner-collecting voltage or a toner-releasing voltage onto the cleaning roller by
selecting one of them in a time-sharing manner, wherein both the toner-collecting
voltage and the toner-releasing voltage are equivalent to the bias voltage.
31. The image-forming apparatus of item 29, wherein the control section controls the
constant current source so as to apply either the toner-collecting voltage or a toner-releasing
voltage onto the cleaning roller by selecting one of them in a time-sharing manner,
wherein both the toner-collecting voltage and the toner-releasing voltage are equivalent
to the bias voltage.
32. The image-forming apparatus of item 26, wherein the constant current source starts
applying the bias voltage onto the cleaning roller after the image bearing member
started moving and after a developing bias voltage has been applied onto the developing
device, and further, the constant current source stops applying the bias voltage onto
the cleaning roller before the image bearing member stops moving and before an operation
of applying the developing bias voltage onto the developing device is finished.
33. The image-forming apparatus of item 26, wherein dimension W1 (mm), which indicates
a width of the cleaning roller in its longitudinal direction, dimension W2 (mm), which
indicates a width of a developer feeding device employed for the developing device
in its longitudinal direction, and dimension W3 (mm), which indicates a width of the
photosensitive layer on the image bearing member, fulfill a relational expression
of
W2 < W1 < W3.
34. The image-forming apparatus of item 26, wherein the constant current source applies
the bias voltage onto the cleaning roller so that a toner deposit amount per unit
area on a surface of the image bearing member is not greater than 0.25 mg/cm2 at a surface area at which the image bearing member contacts the cleaning roller.
35. The image-forming apparatus of item 26, wherein an average circularity of toner
particles included in the toner is within a range of 0.96 to 0.99, and a mass average
particle size of the toner particles is within a range of 3 to 10 microns.
36. The image-forming apparatus of item 34, wherein a fur brushing roller is employed
for the cleaning roller.
37. An image-forming apparatus, comprising: a first image bearing member: a plurality
of developing devices arranged around a periphery of the first image bearing member;
a second image bearing member on which a toner image formed on the first image bearing
member is temporarily transferred; the cleaning apparatus cited in item 1, the cleaning
apparatus being equipped for either the first image bearing member or the second image
bearing member.
[0015] Further, to overcome the abovementioned problems, other cleaning systems, cleaning
apparatus and cleaning methods, embodied in the present invention, will be described
as follow:
a1. A cleaning system characterized by comprising: a conductive or semiconductive
cleaning roller in contact with an image bearing member carrying the charged toner;
a constant current source from which bias voltage having a polarity reverse to that
of the toner related to development on said image bearing member is applied to said
cleaning roller; and a cleaning blade contacting said image bearing member at the
downward position in the movement of said image bearing member.
a2. A cleaning system according to item a1 characterized in that the contact surface
of said cleaning roller rotates to move in the same direction as said image bearing
member at the position in contact with said image bearing member, and the ratio between
the traveling speed of the cleaning roller at the contact face and that of said image
bearing member at the contact face and is in the range from 0.5:1 to 2:1.
a3. A cleaning system according to item a1 or a2 characterized by comprising a means
of removing toner from said cleaning roller by contacting said cleaning roller.
a4. A cleaning system according to item a1 characterized in that said cleaning blade
is brought in contact with said image bearing member at the load from 1 to 30 grams/cm.
a5. A cleaning system according to any one of items a1 to a4 characterized in that
the contact angle between said image bearing member and said cleaning blade is within
the range from 0 to 40 deg.
a6. A cleaning system according to any one of items a1 to a5 characterized in that
the hardness of said cleaning blade is within the range from 20 to 90 deg.
a7. A cleaning system characterized by comprising: a conductive or semiconductive
cleaning roller in contact with an image bearing member carrying the charged toner;
a constant current source from which bias voltage having a polarity reverse to that
of the toner related to development on said image bearing member is applied to said
cleaning roller; a control means of controlling said constant current source; and
a cleaning blade located at the downward position in the movement of said image bearing
member, with said cleaning blade contacting said image bearing member; wherein said
control means is characterized by controlling said constant current source so that
said constant current source applies the current whose absolute value is changed according
to the increase in the amount of the image formed.
a8. A cleaning system according to item a7 characterized in that the amount of the
image formed is equivalent to the number of sheets for formed image.
a9. An image forming system comprising an image bearing member and a cleaning system
according to any one of items a1 to a8.
a10. An image forming system according to item a9 characterized in that said image
bearing member is an organic photoconductor.
a11. An image forming system according to item a9 or a10 characterized by comprising
a development device wherein development is performed by using the toner whose particles
are formed by polymerization method, with the volume mean particle size ranging from
3.0 to 8.5 microns.
b1. A cleaning system characterized by comprising: a conductive or semiconductive
cleaning roller in contact with an image bearing member carrying the charged toner;
a electronic-power source to apply toner-collecting voltage to said cleaning roller;
a control means of controlling said electronic-power source; and a cleaning blade
located downward of said cleaning roller in the direction of said image bearing member
movement, with said cleaning blade contacting said image bearing member; wherein said
control means is characterized by controlling said electronic-power source so that
said toner-collecting voltage whose absolute value is changed according to the increase
in the amount of the image formed is applied to said cleaning roller.
b2. A cleaning system according to item b1 characterized in that wherein the amount
of the image formed is equivalent to the amount of the image formed.
b3. A cleaning system characterized by comprising: a conductive or semiconductive
cleaning roller in contact with an image bearing member carrying the charged toner;
a electronic-power source to apply toner-collecting voltage and toner-releasing voltage
to said cleaning roller; a control means of controlling said electronic-power source;
and a cleaning blade located downward of said cleaning roller in the direction of
said image bearing member movement, with said cleaning blade contacting said image
bearing member; wherein said control means is characterized by controlling said electronic-power
source so that said toner-collecting voltage and said toner-releasing voltage are
applied selectively in terms of time.
b4. A cleaning system according to item b3 further characterized in that said tone
discharge voltage is applied at every formation of the image in specified numbers
of sheets.
b5. A cleaning system according to item b4 further characterized in that said toner-releasing
voltage is applied at every formation of the image in said specified of sheets which
changes according to the number of sheets for formed image.
b6. A cleaning system according to any one of items b3 to b5 further characterized
in that said toner-releasing voltage is composed of alternate current voltage (hereinafter,
referred to as a.c. voltage) superimposed on direct current voltage (hereinafter,
referred to as d.c. voltage).
b7. A cleaning system characterized by comprising: a conductive or semiconductive
cleaning roller in contact with an image bearing member carrying the charged toner;
a electronic-power source to apply toner-collecting voltage and toner-releasing voltage
to said cleaning roller; a control means of controlling said electronic-power source;
and a cleaning blade located downward of said cleaning roller in the direction of
said image bearing member movement, with said cleaning blade contacting said image
bearing member; wherein said control means is characterized by controlling said electronic-power
source so that said recovery voltage whose absolute value is increased according to
the amount of the image formed is applied, and said toner-collecting voltage and said
toner-releasing voltage are applied selectively in terms of time.
b8. A cleaning system according to item b7 further characterized in that the amount
of the image formed is equivalent to the number of sheets for formed image.
b9. A cleaning system according to item b7 or b8 further characterized in that said
toner-releasing voltage is applied at every formation of the image in specified numbers
of sheets.
b10. A cleaning system according to item b9 further characterized in that said toner-releasing
voltage is applied at every formation of the image in said specified of sheets which
changes according to the number of sheets for formed image.
b11. A cleaning system according to any one of items b7 to b10 further characterized
in that said toner-releasing voltage is composed of a.c. voltage superimposed on d.c.
voltage.
b12. A cleaning system according to any one of items b1 to b11 characterized in that
the contact surface of said cleaning roller rotates to move in the same direction
as said image bearing member at the position in contact with said image bearing member,
and the ratio between the traveling speed of the cleaning roller at the contact face
and that of said image bearing member at the contact face and is in the range from
0.5:1 to 2:1.
b13. A cleaning system according to any one of items b1 to b12 characterized by comprising
a means of removing toner from said cleaning roller by contacting said cleaning roller.
b14. A cleaning system according to any one of items b1 to b13 characterized in that
said cleaning blade is brought in contact with said image bearing member at the load
from 1 to 30 grams/cm.
b15. A cleaning system according to any one of items b1 to b14 characterized in that
the contact angle between said image bearing member and said cleaning blade is within
the range from 0 to 40 deg.
b16. A cleaning system according to any one of items b1 to b15 characterized in that
the hardness of said cleaning blade is within the range from 20 to 90 deg.
b17. An image forming system comprising an image bearing member and a cleaning system
according to any one of items b1 to b16.
b18. An image forming system according to item b17 wherein said image bearing member
is an organic photoconductor, said image forming system further characterized by comprising:
a charging device to charge said organic photoconductor; an exposure device to expose
said charged organic photoconductor; and a development device to form an image by
developing the electrostatic latent image formed on said organic photoconductor by
charging and exposure, and by depositing the charged toner thereon.
b19. An image forming system according to item b18 characterized in that development
is performed by using the toner whose particles are formed by polymerization method,
with the volume mean particle size ranging from 3.0 to 8.5 microns.
c1. An image forming system comprising: an image former having a photosensitive layer
on the surface thereof, a development device by making latent image on said image
former visible by means of toner; a transfer device to transfer a toner image on said
image former to the transfer image bearing member; and a cleaning system to remove
toner from the image former after transfer; said cleaning system further characterized
by comprising at least; a cleaning roller which is located in contact with image former,
rubs the image former surface and consists of a conductive or semiconductive elastic
body; a cleaning blade consisting of an elastic body located downward of said cleaning
roller in the direction of image former movement; and a electronic-power source to
apply bias potential to said cleaning roller; wherein application of bias potential
from said electronic-power source starts later than start of said image former movement
or application of bias potential to said development device, and terminates later
than termination of application of bias potential to said development device, and
earlier than suspension of said image former movement.
c2. An image forming system according to item c1 characterized in that said electronic-power
source is a constant current source.
c3. An image forming system according to item c1 or c2 characterized in that the toner
making said latent image visible is synthesized by polymerization, and has a volume
mean particle size ranging from 3.0 to 8.5 microns.
c4. An image forming system comprising: an image former having a photosensitive layer
on the surface thereof; a development device by making latent image on said image
former visible by means of toner; a transfer device to transfer a toner image on said
image former to the transfer image bearing member; and a cleaning system to remove
toner from the image former after transfer; said cleaning system further characterized
by comprising at least; a cleaning roller which is located in contact with image former,
rubs the image former surface and consists of a conductive or semiconductive elastic
body; a cleaning blade consisting of an elastic body located downward of said cleaning
roller in the direction of image former movement; and an electronic-power source to
apply bias potential to said cleaning roller; said image forming system further characterized
in that
W2 < W1 < W3, Where, W1: width of said cleaning roller in the longitudinal direction
(mm), W2: width of developer feed in the longitudinal direction in said development
device (mm), and W3: width of the photosensitive layer on said image developer in
the longitudinal direction (mm).
c5. An image forming system according to item c4 characterized in that said electronic-power
source is a constant current source.
c6. An image forming system according to item c4 or c5 characterized in that the toner
making said latent image visible is synthesized by polymerization, and has a volume
mean particle size ranging from 3.0 to 8.5 microns.
d1. An image forming method characterized in that; a mean circularity of the toner
used for image formation is 0.96 to 0.99; a cleaning blade rubbing an image bearing
member in contact therewith, and a toner recovery means installed on the upstream
side of said cleaning blade are provided to remove the remaining toner deposited on
the image bearing member after toner transfer; and cleaning is carried out when the
deposit amount per unit area of toner on the image bearing member which reaches said
cleaning blade after passing through said toner recovery means is smaller than 0.25
mg/cm2.
d2. An image forming system wherein a toner image is formed on a rotating carrier,
and toner remaining after having been transferred by a transfer means is cleaned by
a cleaning system; said image forming system comprising a cleaning blade contacting
and rubbing said image bearing member elastically and a toner recovery means located
on the upstream side of said cleaning blade; said image forming system further characterized
in that the bias voltage having a polarity reverse to the charging characteristics
of toner is applied to said toner recovery means, and the deposit amount per unit
area of passing toner is smaller than 0.25 mg/cm2.
Said image forming system is preferred to use the toner having a mean circularity
ranging from 0.96 to 0.99 and a weight mean particle size ranging from 3 to 10 microns.
The present invention provides an image forming system which ensures formation of
high quality image by excellent cleaning through the use of said toner.
e1. A cleaning system for cleaning an image bearing member to form images using toner
with a high mean circularity of 0.96 or more, said cleaning system comprising: a cleaning
blade for cleaning with its end in contact with said image bearing member; a cleaning
roller located on the upstream side of said blade with said roller cleaning said image
bearing member in contact with it; and a bias voltage application means for applying
bias voltage to said cleaning roller.
e2. A cleaning system according to item e1 wherein said cleaning roller is a conductive
elastic roller.
e3. A cleaning system according to item e1 or e2 comprising a control means for application
of bias voltage by said bias voltage application means through d.c. constant current
control.
e4. An image forming system comprising a cleaning system according to item e2 or e3.
e5. An image forming system comprising a cleaning system according to any one of items
e1 to e3 characterized in that multiple development means are installed around the
first image bearing member, a toner image formed on said first image bearing member
is primarily transferred onto the second image bearing member, and the toner image
on the secondary image bearing member having been primarily transferred in the above
step is secondarily transferred onto a recording medium; wherein the cleaning system
of said first image bearing member or said second image bearing member is the cleaning
system according to any one of items e1 to e3.
e6. An image forming method comprising: a development process for forming images in
the image bearing member using toner with a high mean circularity of 0.96 or more;
a transfer step for transferring a toner image on said image bearing member; and a
cleaning step for cleaning said image bearing member subsequent to said transfer step;
said cleaning process further characterized in that the tip of the cleaning blade
is brought in contact with said image bearing member to perform cleaning after a cleaning
roller with bias voltage applied thereto is bought in contact with the image bearing
member to perform cleaning.
e7. An image forming method according to item e6 characterized in that said cleaning
roller is a conductive elastic roller.
e8. An image forming method according to item e6 or e7 characterized in that bias
voltage is applied to said cleaning roller through d.c. constant current control.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Other objects and advantages of the present invention will become apparent upon reading
the following detailed description and upon reference to the drawings in which:
Fig. 1 is a drawing representing the image forming system as a first embodiment of
the present invention;
Fig. 2 is a drawing representing an example of the cleaning roller in the cleaning
system according to the present invention;
Fig. 3 is a chart representing the relation between bias voltage and the number of
sheets for formed image;
Fig. 4 is a chart representing the relation between toner-collecting voltage and the
number of sheets for formed image;
Fig. 5 is a drawing representing the image forming system as a second embodiment according
to the present invention;
Fig. 6 is an enlarged view representing the configuration of a cleaning system;
Fig. 7 is a drawing illustrating overshoot in development bias;
Fig. 8 is a drawing illustrating the time of starting or stopping application of bias
to a cleaning roller;
Fig. 9 is a drawing illustrating scraping of toner off the cleaning roller.
Fig. 10 is a drawing illustrating the adequate width along the length of a cleaning
roller;
Fig. 11 is a drawing illustrating the adequate width along the length of a cleaning
roller;
Fig. 12 is a drawing specifically illustrating the time of starting or stopping application
of bias to a cleaning roller;
Fig. 13 is a drawing specifically illustrating the adequate width along the length
of a cleaning roller;
Fig. 14 is a cross sectional view representing an example of the image forming system
according to the present invention;
Fig. 15 is a cross sectional view representing an example of the cleaning system shown
in Fig. 14 according to the present invention;
Fig. 16 is a chart representing the relation between the current value of bias voltage
applied to the toner recovery roller and the amount of deposited toner after passing;
Fig. 17 is a cross sectional view representing the configuration of another example
of the cleaning system;
Fig. 18 is a schematic drawing representing the relation between the cleaning system
and image bearing member according to the present invention;
Fig. 19 is a schematic drawing representing a laser printer as an example of the image
forming system equipped with the cleaning system according to the present invention;
Fig. 20 is a drawing representing the shape of toner particles and major portions
of a shape distribution measuring instrument;
Fig. 21 is a perspective view illustrating the photographing unit in Fig. 21 and the
flow of liquid sample; and
Fig. 22 is a drawing representing how to obtain circularity.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[EMBODIMENT 1]
[0017] Fig. 1 is a drawing representing an image forming system as an embodiment according
to the present invention. In Fig. 1, numeral 1 denotes a photoconductor as an image
bearing member.
[0018] From the view point of environmental conservation and cost reduction, said photoconductor
is preferred to be an organic photoconductor with photosensitive layer consisting
of resin with organic photoconductor dispersed thereon.
[0019] Numeral 2 denotes a charging device to charge said photoconductor 1 and to build
up uniform potential on the photoconductor 1. This charging device is preferred to
be a Scorotron charging device having a control grid and discharge electrode, or a
charging device based on contact charging, using a roller with voltage applied thereto.
[0020] Numeral 3 indicates a exposure device for exposing the photoconductor 1 according
to the image data. The exposure device is preferred to a scanning exposure device
with a scanning optical system consisting of a polygon mirror, lens and mirror where
a laser diode is used as a light source. Another preferred exposure device is a scanning
optical device with light emitting diode array and imaging optical fiber. Said exposure
device 3 provides dot exposure of the photosensor 1 according to the image data.
[0021] Numeral 4 indicates a development device. It stores one-component developer or two-component
developer, and carries the developer to the area of developer by means of a development
sleeve 41. It develop the electrostatic latent image on the photoconductor 1 to form
a toner image on the photoconductor 1. The development sleeve is supplied with the
d.c. development bias having the same polarity as the charging polarity of charging
device 2 or development bias having the same polarity as the charging polarity of
charging device 2 superimposed on the a.c. voltage. This is followed by the step of
reversal development where toner is attached to the portion exposed by the exposure
device 3.
[0022] Numeral 5 denotes a transfer device comprising a corona charging device. The transfer
device 5 charges the recording paper P in the polarity reverse to that of toner on
the photoconductor 1, and transfers the toner image to the recording paper P.
[0023] Numeral 6 denotes a separator comprising a corona charging device. It provides a.c.
corona charging to recording paper P to eliminate electric charge from the recording
paper P, and separate the paper from the photoconductor 1.
[0024] Numeral 7 denotes a fixing device. It fixes toner image on the recording paper P
by means of a heating roller 71 with a built-in heating source (e.g. halogen lamp)
and a heating roller 72 in contact therewith.
[0025] Numeral 8 indicates a cleaning system. Toner yet to be transferred or toner remaining
after transfer is deposited on the photoconductor 1 after transfer. To start the next
image formation step, the photoconductor 1 must be cleaned. Cleaning system 8 has
a cleaning blade 81 consisting of elastic blade such as urethane rubber and a cleaning
roller 82. The cleaning blade 81 is supported by a fixed blade holder 83, and the
tip edge is kept in contact with with the photoconductor 1 at almost the constant
pressure by the elastic property of the blade.
[0026] The blade holder 83 can be a blade holder which is rotatable about the shaft and
which provides a certain contact pressure to cleaning blade 81 through the load of
a spring or gravity.
[0027] The load of said cleaning blade 81 in the tip edge is preferred to be within the
range from 1 g/cm to 30 g/cm, and is particularly preferred within the range from
5 g/cm to 25 g/cm.
[0028] If the load is smaller than 1 g/cm, cleaning force will be insufficient, and incomplete
cleaning, hence, a contaminated image tends to result. If the load is greater than
30 g/cm, friction on the image bearing member surface will increase. When the image
bearing member is used for a long time, the image tends to be scratchy or blurred.
The load can be measured by applying the tip edge of the cleaning blade 81 in contact
with the scale. Alternatively, it can be measured electrically by installing a sensor
(e.g. a load cell) at the contact portion between the image bearing member and tip
edge of the cleaning blade 8.
[0029] The contact angle of the cleaning blade 81 to the photoconductor 1 is preferred to
be within the range from 0 to 40 degrees particularly within the range from 0 to 25
degrees. If this angle is greater than 40 deg., so called blade separation tends to
occur; namely, the tip edge of the cleaning blade 81 tends to rotate in a reverse
direction in conformity to the movement of the image bearing member. If this angle
is smaller than 0 deg., cleaning force is reduced, with the result that image contamination
tends to occur. The contact angle is an acute angle formed by intersection between
the cleaning blade 81 and the contact surface of photoconductor 1 at the position
where the tip edge of the cleaning blade 81 and photoconductor 1 are in contact with
each other. As shown in Fig. 1, it is an angle θ as viewed on the downstream side
in the rotational direction of photoconductor 1 from the cleaning position.
[0030] An elastic body such as urethane rubber is used as a cleaning blade 81. It is preferred
to have a hardness (A, JIS) within the range from 20 to 90 as measured according to
JIS K-6253.
[0031] If the angle is smaller than 20 deg., hardness is too small. This tends to cause
blade separation. If it is 90 deg. or higher, the capacity will be too small to conform
to slight irregularities of the image bearing member or foreign substances. This is
likely to cause escape of toner particles.
[0032] The thickness of the cleaning blade 81 is preferred to be within the range from 1mm
to 3mm, particularly within the range from 1.5mm to 2.5mm. The length of the portion
not restricted by the blade holder 83, namely, the free length of the blade is preferred
to be within the range from 2mm to 20mm, particularly within the range from 3mm to
15mm.
[0033] Numeral 82 denotes a conductive or semiconductive elastic cleaning roller.
[0034] Voltage having the polarity reverse to that of the toner used for development is
applied to the cleaning roller 82 by means of the power supply 84. In other words,
development is carried out by negatively charged toner. When a toner image is formed
by the negatively charged toner, positive bias voltage is applied to the cleaning
roller 82 from the power supply 84.
[0035] A constant current power supply (a constant current source) is preferred to as power
supply 84. When bias voltage is applied to the cleaning roller 82 from the constant
current power supply, toner is electrostatically attracted to the cleaning roller
82 to provide an excellent cleaning effect. Current value applied from power supply
84 is changed under the control of a control means 85, as will be described later.
What is called constant current power supply hereunder is a power supply designed
to ensure that the output voltage is controlled in conformity to the resistance between
the cleaning roller and image former so that a constant current is issued at a1 times.
[0036] The following describes the excellent cleaning effect in the present embodiment in
comparison with the conventional method where constant voltage is applied.
[0037] An image portion, non-image portion and untransferred portion are present on the
surface of the image bearing member after transfer. The surface potential varies according
to the position. When constant voltage is applied to the cleaning roller, potential
difference between the cleaning roller and image bearing member varies according to
the potential distribution on the image bearing member, as described above. Different
values are shown according to an image portion, non-image portion and untransferred
portion.
[0038] Assume, for example, that V1 and V2 (where V1 > V2) is present on the image bearing
member. Where a constant potential V0 is applied to the cleaning roller, the potential
difference between the surface of the image bearing member and cleaning roller will
be V0 - V1 and V0 - V2, and electrostatic attraction acting on the charged toner on
the image bearing member will become uneven, with the result that difference in cleaning
effects appears depending on the site of the image bearing member. This leads to cleaning
failure.
[0039] Compared to said constant voltage application, when the bias voltage of constant
current is applied to the cleaning roller, electric field between the surfaces of
the image bearing member and the cleaning roller affecting the force to separate the
charged tone on the image bearing member from the image bearing member basically varies
according to the impedance of the image bearing member viewed from the cleaning roller,
independently of the potential on the image bearing member surface. The impedance
of the image bearing member is basically constant independently of the position on
the image bearing member.
[0040] Accordingly, uniform cleaning effect is obtained by application of constant current
to the cleaning roller. Namely, independently of the surface potential of the image
bearing member, roughly constant electrostatic attraction acts on the charged tone
on the image bearing member. This allows uniform cleaning effect to be obtained without
cleaning failure.
[0041] The applied current value is preferred to be within the range from 1 to 50 microamperes
in terms of absolute value.
[0042] If the value is smaller than one microampere, a sufficient cleaning effect may not
be obtained. If it is greater than 50 microamperes, electric discharge tends to occur.
Said current value varies according to the type of the image bearing member and resistance
of the cleaning roller. It is preferred to be within the range from 5 to 40 microamperes
when using the organic photoconductor formed into a photosensitive layer having a
thickness of 10 to 30 microns by dispersing in resin and a cleaning roller with a
surface resistivity of 10
2Ω/□ to 10
10Ω/□.
[0043] A rubber elastic body is used as a cleaning roller. Such an elastic body is preferred
to be made of rubbers such as silicone rubber and urethane rubber as is known in the
art heretofore, foams or foams coated with resin film.
[0044] To get excellent performances, the hardness of the cleaning roller is desired to
be within the range from 5 to 50 deg., or preferably from 10 to 50 deg. If it is below
5, durability will be insufficient. When it is greater than 60, the width of contact
with image former required for cleaning cannot be obtained. Furthermore, damages may
occur on the surface of the image former. Hardness is obtained by measuring the elastic
body having been formed into a roller with an Ascar C hardness meter (load: 300fg).
[0045] To ensure excellent performances, the width of the nip in constant with the image
former is desired to be within the range from 0.2 to 5 mm or more preferably from
0.5 to 3 mm, although it varies with the roller diameter. If it is below 0.2 mm, cleaning
capacity will be insufficient. If it is above 5 mm, the image former is likely to
be damaged at the time of rubbing.
[0046] The cleaning roller is preferred to be conductive or semiconductive, and to have
a surface resistivity within the range from 10
2Ω/□ to 10
10Ω/□. If the resistance is lower than 10
2Ω/□, banding tends to occur due to electrical discharge. If it is greater than 10
10Ω/□, the potential difference with the photoconductor will be reduced, and cleaning
failure tends to occur.
[0047] The surface resistivity Ω/□ of the cleaning roller was measured at the normal temperature
and relative humidity (26°C, 50% RH) at the applied voltage of 10 volts for the measuring
time of 10 sec., using Hirester IP (MCP-HT250) and HA Probe by Mitsubishi Petrochemical
Co., Ltd.
[0048] To ensure adequate resistance and nip width, the thickness of the conductive and
semiconductive elastic layer is preferred to be set approximately in the range between
0.5 to 50 mm although it varies with the surface resistivity and hardness of the material.
[0049] The contact portion of the cleaning roller is desired to move in the same direction
as the surface of the image bearing member. If said contact portion moves in the reverse
direction, toner removed by the cleaning roller may spill and contaminate the recording
paper or the system when excessive toner is present on the surface of the image bearing
member.
[0050] When the image bearing member and cleaning roller move in the same direction as described
above, the ratio of their surface speed is desired to be within the range from 0.5:1
to 2:1. Outside this range, the image bearing member may be damaged if the difference
of their speeds increases, and recording paper or other foreign substance is sandwiched
between the image bearing member and cleaning roller.
[0051] Toner or other unwanted substance transferred from the image bearing member to the
cleaning roller is desired to be removed by bringing the scraper in contact with the
cleaning roller. Fig. 2 shows an example of installing a scraper 89 on the cleaning
roller 82.
[0052] The scraper 89 uses such an elastic sheet as phosphor bronze sheet, polyethylene
terephthalate sheet or polycarbonate sheet. It may contact the cleaning roller 82
in either the trail method where a tip forms an acute angle on the non-cleaning side
of the cleaning roller 82 or the counter method where a tip forms an acute angle on
the cleaning side of the cleaning roller 82.
[0053] To remove toner and other unwanted object transferred to the cleaning roller 82,
a roller or brush may be used in addition to said scraper.
[0054] The cleaning system used in the image forming system related to the present embodiment
is particularly effective when a photoconductor as an image bearing member as is described
below and toner are used.
[0055] From the view point of environmental conservation and cost reduction, an organic
photoconductor is considered as providing a good image bearing member. The organic
photoconductor is represented by the photoconductor obtained by dispersing organic
photoconductor in resin. This photoconductor consists of an organic compound provided
with either electrical charge generation function or electrical charge feed function.
The surface of the organic photoconductor has less strength, and cannot be subjected
to powerful cleaning. If the contact pressure of the cleaning blade widely employed
in the cleaning system is made too high, the surface of the organic photoconductor
will be worn. To prevent this, the contact pressure is set at a lower value. This
makes it difficult to ensure stable cleaning performance for a long time.
[0056] Use of said cleaning system ensures the good cleaning effect without having to increase
the contact pressure of the cleaning blade. So even when the organic photoconductor
is used as an image bearing member, said cleaning problems in the conventional systems
have been solved.
[0057] In order to ensure high image quality, toner used in development is desired to have
a volume mean particle size within the range from 3.0 to 8.5 microns, particularly
from 3.0 to 6.5 microns. The volume mean particle size according to the present invention
has been measured by Coulter Counter TA-II or Coulter Multitizer (by Coulter). In
the present invention, the Coulter Multitizer was used wherein an interface (by Nikkaki)
to output the particle size distribution was connected with a personal computer. A
100-micron aperture was used in said Coulter Multitizer. The volume average particle
size was calculated by measuring the volume and quantity of the toner particles each
having a diameter of 2 microns or more.
[0058] The toner having such a small particle size is particularly preferred to be the one
where particles are formed by polymerization method including emulsion polymerization
method, suspension polymerization method or dispersion polymerization method. Namely,
the toner with its particles formed by polymerization method has a narrow distribution
of particle size. Its form is not restricted to a spherical form; particles of a desired
shape can be obtained. These advantages are effective in ensuring high image quality.
[0059] Toner whose particles are formed by polymerization includes the following two types.
In one type, particles formed by polymerization are directly used as toner particles.
In the other type, particles formed by polymerization are combined to form toner particles.
[0060] However, the toner of small particle size has a problem of difficult cleaning. Particularly
the toner whose particles have been formed by this polymerization method has spherical
toner particles in many cases. It has a conspicuous defect of difficult cleaning.
[0061] The embodiment of the present invention provides an excellent cleaning effect when
images are formed using the toner of greater particle size produced by pulverization
method where toner particles are formed by crushing the resin. Not only that, it provides
an excellent cleaning effect for said toner of small particle size, particularly,
the tone whose particles are produced by polymerization method.
[0062] In the cleaning work of removing toner from the image bearing member using the cleaning
blade and cleaning roller to which bias voltage is applied, charged toner is electrostatically
removed by the cleaning roller installed on the upstream side of the cleaning blade.
Non-charged or reverse-charged toner or fine particles not removed by the cleaning
roller are removed by the cleaning blade on the downstream side.
[0063] An effective way of improving cleaning performances is to increase the current value
of the bias voltage applied to the cleaning roller. When the cleaning effect by cleaning
roller is improved, however, such problems as separation of the cleaning blade and
vibration of the tip of the cleaning blade tend to occur in the initial phase of image
formation. This is considered to be due to the following reason: Toner working as
a lubricant between the image bearing member and cleaning blade is removed by the
cleaning roller; hence the amount of toner located at the tip of the cleaning blade
is less than that in the conventional cleaning method depending on the cleaning blade
alone. This phenomenon occurs particularly in the initial phase of image formation
when the contact edge of the cleaning blade is sharp.
[0064] To solve such a problem in the present embodiment, a smaller current is applied to
the cleaning roller in the initial phase of image formation, and, in response to increase
in the amount of images to be formed, the current value is increased by a control
means 85. This step ensures excellent cleaning effects throughout the entire image
formation process in the present embodiment. The amount of images to be formed is
preferred to be such that the time assigned for image formation and the number of
sheets for formed image can be used.
[0065] In the initial phase of image formation when a new cleaning blade has been installed,
the cleaning blade has excellent cleaning performances. Required cleaning performances
can be obtained for an entire cleaning system without having to increase cleaning
performances of the cleaning roller.
[0066] Fig. 3 shows an example of the relation between the number of sheets for formed image
and the current value of bias voltage applied to the cleaning roller. As shown, in
response to the increase in the number of sheets for formed image from N1 to N3, current
is increased stepwise from A1 to A3, for example. The current value is set back to
the initial value at every replacement of the cleaning blade, and is increased in
conformity to the number of sheets for formed image. This cycle is repeated.
[0067] The toner used in the present embodiment according to the present invention can be
used for both one-component and two-component developers. Furthermore, it can be used
as any one of magnetic toner and non-magnetic toner.
[0068] (1) In the present embodiment according to the present invention, an image formation
test was conducted using the image forming system shown in Figs. 1 and 3 under the
following conditions with regard to the photoconductor as an image bearing member,
exposure device, development device, toner, cleaning roller and cleaning blade:
[EXAMPLE 1-1]
[0069]
* Photoconductor:
A photoconductor consisting of a photoconductive layer with a thickness of 25 microns
formed by said organic photoconductor dispersed in the polycarbonate resin being coated
on the conductive drum made of aluminum (Al), using phthalocyanine pigment as an organic
photoconductor
* Exposure device:
An exposure device to provide scanning exposure using a laser diode as a light source
wherein a scanning optical system installed on said exposure device consists of a
polygon mirror, lens and mirror.
* Development device:
A development device, equipped with a development sleeve rotating at a linear velocity
of 370 mm, to carry out reversal development using the two-component developer by
applying bias voltage of the same polarity as that of the potential of the photoconductor
to said development sleeve
* Toner:
Toner having a volume mean particle size of 6.5 microns the particles of which are
formed by emulsion polymerization method
* Cleaning roller:
A conductive roller made up of foamed urethane having a surface resistivity of 5.0
× 104Ω/□. The hardness is 32 deg. Said roller is installed so that the nip portion in contact
with image former is 2mm wide. The roller is formed by winding an urethane layer on
a 6mm-diameter metallic shaft to a thickness of 4.5mm. (roller: 15mm in diameter)
To ensure movement in the same direction as the photoconductor at the position in
contact with the photoconductor, drive and rotation were given by the drive system
branched off from the photoconductor drive system. A scraper was provided to remove
the toner from the roller surface. The traveling speed ratio between the image former
and the contact portion was 1 to 1.
* Current value of the bias voltage applied to the cleaning roller
- +20 microamperes up to 150,000 sheets
Two cycles of this operation was performed to form up to 300,000 sheets of image.
Constant current control power supply was used. Current flowing from the cleaning
roller to the photoconductor was positive.
* Cleaning blade:
The cleaning blade was made of urethane rubber. It had a hardness of 70 deg. with
a thickness of 2.00mm and a free length of 10mm. The tip edge of this cleaning blade
was brought in contact with the photoconductor at a contact angle of 10 deg. with
a contact load of 5g/cm.
* Environment
- Normal temperature and normal relative humidity (20°C, 50% RH) up to 50,000 sheets
- High temperature and high relative humidity (30°C, 80% RH) from 50,001 to 150,000
sheets.
The cleaning blades used has a durability to withstand 150,000 sheets.
[0070] In the experiment, cleaning blade was replaced when 150,000 sheets of image had been
formed, and the succeeding 150,000 sheets were formed under said environment. Thus,
a total of 300,000 sheets were formed.
[EXAMPLE 1-2]
[0071] Image formation was carried out under the same conditions as Example 1-1 except that
the current value of bias voltage applied to the cleaning roller was changed as follows:
- +5 microamperes up to 50,000 sheets
- +15 microamperes from 50,001 to 100,000 sheets
- +30 microamperes from 100,001 to 150,000 sheets
[0072] (2) In a reference example, image formation test was conducted under the following
conditions:
<Reference Example 1>
[0073] Same as EXAMPLE 1-1 except that no current is applied to the cleaning roller (0 microampere).
<Reference Example 2>
[0074] Same as EXAMPLE 1-1 except that a +500-volt constant voltage power supply was used
as a power supply of voltage to be applied to the cleaning roller.
<Reference Example 3>
[0075] Same as Example 1-1 except that the traveling speed ratio on the contact surfaces
between the cleaning roller and image former is 0.3 to 1.0.
<Reference Example 4>
[0076] Same as Example 1-1 except that the traveling speed ratio on the contact surfaces
between the cleaning roller and image former is 2.5 to 1.
<Reference Example 5>
[0077] Same as Example 1-1 except that the contact load of the cleaning blade is 0.5 g/cm.
<Reference Example 6>
[0078] Same as Example 1-1 except that the contact load of the cleaning blade is 35 g/cm.
<Reference Example 7>
[0079] Same as Example 1-1 except that the hardness of the cleaning blade is 10 deg.
<Reference Example 8>
[0080] Same as Example 1-1 except that the hardness of the cleaning blade is 95 deg.
[0081] As a result of said experiment of image formation in Examples 1-1 and 1-2 according
to the present invention, present inventors have obtained excellent images free from
contamination or fogging. Especially in Example 1-2, stable cleaning performances
without any blade vibration were obtained.
[0082] In Reference Example 1, images were contaminated by cleaning failure resulting from
insufficient cleaning capacity of the cleaning blade after 40,000 sheets of image
were formed.
[0083] In Reference Example 2, images were contaminated by local cleaning failure resulting
from potential irregularity on the image former after 110,000 sheets of image were
formed.
[0084] In Reference Example 3, scratches were produced on the image former due to rubbing,
and black streaks appeared on the image after 60,000 sheets of image were formed.
[0085] In Reference Example 4, scratches were also produced on the image former due to rubbing,
and black streaks appeared on the image after 60,000 sheets of image were formed.
[0086] In Reference Example 5, images were contaminated by cleaning failure resulting from
insufficient cleaning capacity of the cleaning blade after 30,000 sheets of image
were formed.
[0087] In Reference Example 6, local streaks were produced on the image former due to excessive
wear of the image former film, fogging or scratching occurred on the image after 200,000
sheets of image were formed.
[0088] In Reference Example 7, the cleaning blade was curled up in the initial phase of
image formation due to excessive faithfulness of the cleaning blade in following the
movement on the image former.
[0089] In Reference Example 8, images were contaminated by cleaning failure resulting from
poor response of the cleaning blade after 40,000 sheets of image were formed.
[0090] The above Embodiment 1 provides the following effects: Uniform excellent cleaning
is ensured even if the image bearing member surface potential is not uniform. This
makes it possible to configure a highly durable image forming system capable of providing
formation of a sharp image free from contamination or fogging.
[0091] Sufficient cleaning performances are provided. Cleaning performances are excellent
without damaging the image bearing member even if foreign substances are sandwiched
between the image bearing member and cleaning roller.
[0092] Excellent cleaning performances are ensured for a long time.
[0093] It is possible to produce a highly durable image forming system characterized by
excellent cleaning performances and prolonged service life of the image bearing member.
[0094] Excellent cleaning performances without curling of the blade can be ensured.
[0095] It is possible to prevent curling of the blade which often occurs if cleaning performance
are improved. Excellent cleaning performances are ensured for a long time.
[0096] It is possible to configure a highly durable image forming system capable of providing
formation of a sharp image free from contamination or fogging.
[0097] It is possible to produce an image forming system characterized by low cost and high
image quality.
[0098] It is possible to provide an image forming system characterized by high image quality
with respect to resolution and others.
[EMBODIMENT 2]
[0099] The following describes the Embodiment 2 without duplicated explanation:
Voltage with polarity reverse to that of toner is applied to the cleaning roller 82
by the power supply 84. In the present embodiment according to the present invention,
negatively charged photoconductor 1 is reversely developed by negatively charged toner
to form an image. Said power supply 84 applies to the cleaning roller 82 the voltage
with positive polarity reverse to that of the negatively charged toner (hereinafter
referred to as "toner-collecting voltage"). Thus, the toner remaining on the photoconductor
1 after transfer is recovered and collected in the cleaning roller 82. The toner-collecting
voltage is used to transfer toner on the photoconductor 1 to the cleaning roller 82
electrostatically. Its polarity is reverse to that of the toner having been involved
in development to form images.
[0100] As will be described later, the power supply 84 applies toner-collecting voltage
which is controlled by the control means 85 and is increased with the amount of image
formed.
[0101] The following describes the cleaning action in the present embodiment according to
the present invention:
On the photoconductor 1, there is toner charged in reverse polarity and powder transferred
from the recording paper P, in addition to the toner charged in the same polarity
as charged potential of the photoconductor 1 in the development device 4. Particles
of toner changed in the same polarity as that of the toner involved in the development
device 4 in such a great variety of deposits are removed electrostatically by the
cleaning roller 82. The non-charged toner, reversely charged toner and other particles
which can not be removed by the cleaning roller 82 are removed mechanically by the
cleaning blade 81.
[0102] In the present embodiment according to the present invention, the power supply 84
is controlled by the control means 85, as shown in Figs. 1 and 4. As a result, voltage
increasing with the amount of image formed is applied to the cleaning roller 82.
[0103] As the cleaning blade 81 is used, the cleaning performance thereof is gradually reduced
due to the wear of the edge which scrapes off toner from the photoconductor 1. In
the present embodiment according to the present invention, the cleaning performance
of cleaning roller 82 is increased in response to the increasing amount of image formed,
as shown in Fig. 2. Then the load applied to the cleaning blade 81 is reduced in response
to the increasing amount of image formed. This ensures the cleaning performance of
the entire cleaning system 8 to be maintained throughout the entire image formation
process.
[0104] Toner is present between the photoconductor 1 and cleaning blade 81 and is known
to work as lubricant. This function of toner allows smooth cleaning to be provided
by cleaning blade 81. However, if there is little or no intervention of toner after
it has been removed by the cleaning roller 82, a big frictional drag between the photoconductor
1 and cleaning blade 81 will occur. This will result in chattering where the cleaning
blade vibrates or curling where the tip portion of the cleaning blade 81 is reversed
in response to the photoconductor 1. If the cleaning performance by the cleaning roller
82 is excessive, the amount of said toner as lubricant will be reduced, with the result
that chattering or curling tends to occur.
[0105] In the present embodiment according to the present invention, the voltage applied
to the cleaning roller 82 is set at a relatively low value in the initial phase of
image formation where the tip edge of the cleaning blade is sharp and curling tends
to occur. Said voltage is increased in response to the increasing amount in image
formation, thereby ensuring excellent cleaning performance throughout the entire image
formation process.
[0106] The bias voltage is controlled as follows; When the number of sheets for formed image
has increased from N1 to N3 as shown in Fig. 4, there is a gradual increase of bias
voltage from V1 to V3, and the voltage is set back to the initial value V1 by exchange
of the cleaning blade.
[0107] Toner-collecting voltage within the range from 0 or floating value to about one third
of the maximum value V3 is preferred to be applied as initial value V1.
[0108] An elastic body is used as the cleaning roller 82. Rubber including well-known silicone
rubber and urethane rubber, foam or foam coated with resin film is desired as a material
of such an elastic body. The hardness of the cleaning roller within the range from
5 to 60 deg., preferably, 10 to 50 deg. is adequate to get the excellent performance.
If the hardness is 5 deg., it is difficult to ensure high durability. If it is higher
than 60 deg., it is difficult to secure the width of contact with the image former
required for cleaning. In addition, damages tend to occur on the image former surface.
The hardness is obtained by measuring the elastic body shaped into a roller with an
Ascar C hardness meter (load: 300fg).
[0109] To ensure excellent performances, the width of the nip when in contact with the image
former is desired to be in the range from 0.2mm to 5mm, or preferably 0.5mm to 3mm,
although this varies with the roller diameter. If the width is below 0.2mm, cleaning
force is insufficient. If it is over 5mm, the image former tends to be damaged at
the time of rubbing.
[0110] The cleaning roller 82 is conductive or semiconductive, and is desired to have the
surface resistivity ranging from 10
2Ω/□ to 10
10Ω/□. If the resistivity is below 10
2Ω/□, banding due to discharge tends to occur. Furthermore, it is higher than 10
10Ω/□, potential difference is reduced, and cleaning failure tends to occur.
[0111] The surface resistivity Ω/□ of the cleaning roller was measured at the normal temperature
and relative humidity (26°C, 50% RH) at the applied voltage of 10 volts for the measuring
time of 10 sec., using Hirester IP (MCP-HT250) and HA Probe by Mitsubishi Petrochemical
Co., Ltd.
[0112] To ensure adequate resistance and nip width, the thickness of the conductive and
semiconductive elastic layer is preferred to be set approximately in the range between
0.5 to 50 mm although it varies with the surface resistivity and hardness of the material.
[0113] The cleaning roller 82 is desired to rotate so that the contact portion moves in
the same direction as the surface of the photoconductor 1. If said contact portion
moves in the reverse direction, the toner removed by the cleaning roller 82 may spill
to contaminate the recording paper or the system, when excessive toner is present
on the surface of the photoconductor 1.
[0114] When the photoconductor 1 and cleaning roller 82 move in the same direction as shown
above, the surface speed ratio between the two is desired to be within the range from
0.5:1 to 2:1. Outside this range, the photoconductor may be damaged if the difference
of their speeds increases, and recording paper or other foreign substance is sandwiched
between the photoconductor 1 and cleaning roller 82.
[0115] It is desired to remove the toner and other foreign substances transferred from the
photoconductor 1 to the cleaning roller 82 by bringing the scraper in contact with
the cleaning roller 82. Fig. 2 shows an example of the scraper 89 installed on the
cleaning roller 82.
[0116] The elastic plate such as phosphor bronze plate, polyethylene terephthalate plate
or polycarbonate plate is used as the scraper 89. It may contact the cleaning roller
82 using either the trail system where the tip edge forms an acute angle on the uncleaned
side of the cleaning roller 82 or the counter system where the tip forms an acute
angle on on the cleaned side of the cleaning roller 82.
[0117] Furthermore, a roller and brush in addition to said scraper can be used to remove
the toner and foreign substances transferred from the cleaning roller 82 to the cleaning
roller 82.
[0118] The cleaning system used in the image forming system according to the present embodiment
is especially effective when the image bearing member and toner to be described below
is used.
[0119] From the view point of environmental conservation and cost reduction, organic photoconductor
is useful as the image bearing member. The organic photoconductor is represented by
the photoconductor produced by an organic photoconductor dispersed in resin, where
the organic compound is provided with either electrical charge generation function
or electrical charge feed function. The surface of the organic photoconductor has
a low strength, which makes it difficult to use powerful cleaning capacity. If the
contact pressure of the cleaning blade extensively used as a cleaning system is excessive,
contact pressure is kept low by the wear of the organic photoconductor surface. This
makes it difficult to ensure stable cleaning performance for a long time.
[0120] Use of said cleaning system allows the excellent cleaning effect to be obtained without
having to increase the contact pressure of the cleaning blade. Even when the organic
photoconductor is used as an image bearing member, it is possible to ensure stable
excellent cleaning performance for a long time, and to solve said cleaning problem
encountered in the conventional technology.
[0121] To ensure high image quality, the preferred toner used for development has a volume
mean particle size ranging from 3.0 to 8.5 microns, more preferably from 3.0 to 6.5
microns. The volume mean particle size of the toner according to the present invention
is measured by the Coulter Counter TA-II or Coulter Multitizer (by Coulter). In the
present invention, the Coulter Multitizer was used for measurement, and the interface
(by Nikkaki) to output the data on particle size distribution was connected with a
personal computer. A 100-micron aperture was used in said Coulter Multitizer to measure
the volume and number of the tone particles of 2 microns or more, thereby calculating
the volume mean particle size.
[0122] The toner having such a small particle size is particularly preferred to be the one
where particles are formed by polymerization method including emulsion polymerization
method, suspension polymerization method or dispersion polymerization method. Namely,
the toner with its particles formed by polymerization method has a narrow distribution
of particle size. Its form is not restricted to a spherical form; particles of a desired
shape can be obtained. These advantages are effective in ensuring high image quality.
[0123] However, the toner of small particle size has a problem of difficult cleaning. Particularly
the toner whose particles have been formed by this polymerization method has spherical
toner particles in many cases. It has a conspicuous defect of difficult cleaning.
[0124] The embodiment of the present invention provides an excellent cleaning effect when
images are formed using the toner of greater particle size produced by pulverization
method where toner particles are formed by crushing the resin. Not only that, it provides
an excellent cleaning effect for said toner of small particle size, particularly,
the tone whose particles are produced by polymerization method.
[0125] (Toner whose particles are formed by polymerization includes the following two types.
In one type, particles formed by polymerization are directly used as toner particles.
In the other type, particles formed by polymerization are combined to form toner particles.
[0126] The toner used in the present embodiment according to the present invention can be
used for both one-component and two-component developers. Furthermore, it can be used
as any one of magnetic toner and non-magnetic toner.
[EMBODIMENT 3]
[0127] The following describes the Embodiment 3 where excellent cleaning performances without
chattering and curling of the cleaning blade can be ensured.
[0128] Fig. 5 shows the image forming system according to the Embodiment 3. In the Embodiment
3, power supplies 84 and 86 each having a reverse polarity with the other are connected
to the cleaning roller 82 through temporal selection. Namely, the power supply 84
applies to the cleaning roller 82 the toner-collecting voltage which transfers the
charged toner on the photoconductor electrostatically to the cleaning roller 82. The
power supply 86 applies the voltage which transfers the charged tone on the cleaning
roller 82 to the photoconductor 1. Namely, the power supply 86 applies the toner-releasing
voltage. The polarity of the toner-releasing voltage is reverse to that of the toner-collecting
voltage.
[0129] As described above, a proper amount of toner is present at all times on the photoconductor
1 by application of bias voltages reverse to each other and by discharging of the
toner on the cleaning roller 82 onto the photoconductor 1. This avoids said chattering
and curling.
[0130] Such a toner-releasing voltage is applied when cleaning by the cleaning roller 82
is not interfered. For example, it is preferred that toner-releasing voltage be applied
at periodic intervals so that toner-releasing voltage is applied at every formation
of 10 to 1000 sheets of image as to the number of sheets for formed image. Further,
the periodic intervals of application of toner-releasing voltage can be changed in
response to the volume of image to be formed. For example, excellent cleaning effect
can be obtained by application of toner-releasing voltage at every formation of 1000
sheets of image in the initial phase, and at every formation of 500 sheets after formation
of 100,000 sheets of image. As described in the embodimemts described later, images
can be formed while toner-releasing voltage is applied. It is also possible to apply
toner-releasing voltage while rotating the photoconductor 1 without image formation,
and to allow toner to be deposited on the photoconductor 1. Switching between toner-collecting
voltage and toner-releasing voltage is performed by controlling the switch 88 using
the control means 85.
[0131] In the image formation process based on reversal development, toner-releasing voltage
is desired to be 1.2 times the white background potential. For example, when the white
background voltage is -750 volts, voltage of -750 to-2250 volts is preferred. The
voltage equivalent to 1/10 to 5 times the white background voltage is preferred in
the image formation process based on normal development. When lower voltage, namely,
reversal development is used to prevent discharge in the image formation system where
discharge is likely to occur, 1 to 1.5 times the white background potential is preferred.
When normal development is used, 1/3 to 2/3 times the black background potential is
preferred in particular.
[0132] As toner-releasing voltage, it is also possible to apply the bias voltage obtained
from a.c. voltage from the power supply 87 superimposed on the d.c. voltage from the
power supply 86. Application of a.c. voltage provides an effective means for discharging
toner from the cleaning roller 82 to the photoconductor 1. It is particularly desirable
to use a.c. voltage within the frequency range from 0.5 kHz to 20 kHz. Further, as
amplitude of the a.c. voltage, 1/3 to 2 times the white background potential is desirable
in terms of peak-to-peak voltage in the image formation system based on reversal development.
In the image formation system based on normal development, 1/3 to 2 times the black
background potential is desirable.
[0133] A combined use of Embodiments 2 and 3 is also effective in improving the cleaning
performances. Namely, the power supply 84 and switch 88 is controlled by the control
means 85 in such a way that the toner-collecting voltage is increased in response
to the increasing number of sheets for formed image, and toner-releasing voltage is
applied to the cleaning roller 82 at periodic intervals, thereby ensuring an excellent
cleaning effect. In such an embodiment, periodic intervals for application of toner-releasing
voltage can be changed in response to the amount of formed image.
(1) Using the image forming system shown in Figs. 1 and 2 as Examples 2-1 according
to the present invention, image formation experiment was conducted with regards to
the photoconductor as image bearing member, exposure device, development device, toner,
cleaning roller and cleaning blade under the following conditions:
* Photoconductor:
A photoconductor consisting of a photoconductive layer with a thickness of 25 microns
formed by said organic photoconductor dispersed in the polycarbonate resin being coated
on the conductive drum made of aluminum (Al), using phthalocyanine pigment as an organic
photoconductor. Image formation is made by negative charging of the photoconductor.
The white background potential of -750 volts was used.
* Exposure device:
An exposure device to provide scanning exposure using a laser diode as a light source
wherein a scanning optical system installed on said exposure device consists of a
polygon mirror, lens and mirror.
* Development device:
A development device, equipped with a development sleeve rotating at a linear velocity
of 370mm, to carry out reversal development using the two-component developer by applying
bias voltage of the same polarity as that of the potential of the photoconductor to
said development during image formation sleeve
* Toner:
Negatively charged toner having a volume mean particle size of 6.5 microns the particles
of which are formed by emulsion polymerization method
* Cleaning roller:
A conductive roller made up of foamed urethane having a surface resistivity of 4.5
x 104Ω/□ and a hardness of 30 deg. Said roller is installed so that the nip portion in
contact with image former is 2mm wide. The roller is formed by winding an urethane
layer on a 6mm-diameter metallic shaft to a thickness of 4.5mm. (roller: 15mm in diameter)
This roller was designed to turn in the same direction as the photoconductor (to move
in the same direction at the nip portion). A scraper was provided to remove the toner
from the roller surface. The peripheral speed ratio with the image former was 1 to
1.
* Current value of the bias voltage applied to the cleaning roller
- +100 volts up to 50,000 sheets
- +300 volts from 50,001 to 100,000 sheets
- +600 volts from 100,001 to 150,000 sheets
* Cleaning blade:
This cycle was repeated twice to form 300,000 images. The cleaning blade was made
of urethane rubber. It had a hardness of 70 deg. with a thickness of 2.00mm and a
free length of 10mm. The tip edge of this cleaning blade was brought in contact with
the photoconductor at a contact angle of 10 deg. with a contact load of 5g/cm.
* Environment
- Normal temperature and normal relative humidity (20°C, 50% RH) up to 50,000 sheets
- High temperature and high relative humidity (30°C, 80% RH) from 50,001 to 150,000
sheets.
The cleaning blades used has a durability to withstand 150,000 sheets.
[0134] In the experiment, cleaning blade was replaced when 150,000 sheets of image had been
formed, and the succeeding 150,000 sheets were formed under said environment. Thus,
a total of 300,000 sheets were formed.
[0135] (2) In the Example 2-2, +600-volt toner-collecting voltage was applied to the cleaning
roller throughout the entire image formation process, and 500-volt peak-to-peak voltage
and 2kHz-frequency a.c. voltage superimposed on - 1000-volts d.c. voltage were applied
as toner-releasing voltage in the following manner at periodic intervals:
[0136] Said toner-releasing voltage was applied in the formation of one sheet of image for
every 1000 sheets in the range from 0 to 50,000 sheets, said toner-releasing voltage
in the formation of one sheet of image for every 500 sheets in the range from 50,001
to 100,000 sheets, and said toner-releasing voltage in the formation of one sheet
of image for every 100 sheets in the range from 100,001 to 150,000 sheets. Two cycles
of said toner-releasing voltage application were repeated twice to form 300,000 sheets
of image.
In Example 2-3, the following toner voltages were applied:
+100 volts up to 50,000 sheets
+300 volts from 50,001 to 100,000 sheets
+600 volts from 100,001 to 150,000 sheets
[0137] The same toner discharge electric field as in the case of Example 2-2 was applied
at the same timing as the Example. A total of 300,000 sheets of image were formed
by two cycles of said step. The test environment was the same as those in Examples
2-1 and 2-2; normal temperature and humidity (20°C, 50% RH) up to 50,000 sheets and
high temperature and humidity (30°C, 80% RH) from 50,001 to 150,000 sheets. A total
of 300,000 sheets of image were formed by two cycles of said step.
[0138] The test environment was the same as that in Example 1; normal temperature and humidity
(20°C, 50% RH) up to 50,000 sheets and high temperature and humidity (30°C, 80% RH)
from 50,001 to 150,000 sheets.
[0139] (3) In the Reference Example, image formation test was conducted under the following
conditions.
* Reference Example 1
[0140] Image formation was conducted under the same conditions as the Example except that
+ 600-volt toner-collecting voltage was applied to the cleaning roller throughout
the entire image formation process. In the Reference Example, toner-releasing voltage
is not applied.
[0141] In Examples 2-1 and 2-2, stable excellent cleaning performances were ensured without
image failure caused by curling and chattering of the cleaning blade or wear of the
photoconductor, until formation of 300,000 sheets of image was completed.
[0142] In the Example 2-3, stable excellent cleaning performances were ensured without image
failure caused by curling of the cleaning blade or wear of the photoconductor, particularly
without any chattering of the blade under the conditions of high temperature and humidity,
until formation of 300,000 sheets of image was completed.
[0143] In the Reference Example by contrast, curling of the cleaning blade occurred at the
formation of 60,000th sheet after image formation started at a high temperature and
humidity. Then the cleaning blade was replaced to continue image formation. Cleaning
failure due to chattering occurred at a 240,000th sheet was formed. Stable cleaning
performance could not be obtained.
[0144] The following effects are provided according to Embodiments 2 and 3:
[0145] Excellent cleaning effects are ensured for a long time without chattering or curling
of the cleaning blade.
[0146] Chattering or curling of the cleaning blade was successfully avoided, and excellent
cleaning effects were ensured for a long time.
[0147] Sufficient cleaning performances are provided.
Cleaning performances are excellent without damaging the image bearing member even
if foreign substances are sandwiched between the image bearing member and cleaning
roller.
[0148] Excellent cleaning performances are ensured for a long time.
[0149] It is possible to produce a highly durable image forming system characterized by
excellent cleaning performances and prolonged service life of the image bearing member.
[0150] Excellent cleaning performances without curling of the blade can be ensured.
[0151] It is possible to configure an image forming system capable of providing formation
of high quality images free from contamination or fogging for a long time, without
chattering or curling of the cleaning blade.
[0152] It is possible to produce an image forming system characterized by low cost and high
image quality.
[0153] It is possible to produce an image forming system characterized by high image quality
due to excellent resolution.
[EMBODIMENT 4]
[0154] The following describes the Embodiment 4 without duplicated explanation:
[0155] Voltage having a polarity reverse to that of the toner is applied to the cleaning
roller 82 by the power supply 84. Said power supply 84 applies to the cleaning roller
82 the voltage with positive polarity reverse to that of the negatively charged toner
(hereinafter referred to as "toner-collecting voltage"). Thus, the toner remaining
on the photoconductor 1 after transfer is recovered and collected in the cleaning
roller 82. The toner-collecting voltage is used to transfer toner on the photoconductor
1 to the cleaning roller 82 electrostatically. Its polarity is reverse to that of
the toner having been involved in development to form images.
[0156] As will be described later, the power supply 84 applies toner-collecting voltage
which is controlled by the control means 85 and is increased with the amount of image
formed.
[0157] The following describes the cleaning action in the present embodiment according to
the present invention:
On the photoconductor 1, there is toner charged in reverse polarity and powder transferred
from the recording paper P, in addition to the toner charged in the same polarity
as charged potential of the photoconductor 1 in the development device 4.
[0158] Particles of toner charged in the same polarity as that of the toner involved in
the development device 4 in such a great variety of deposits are removed electrostatically
by the cleaning roller 82. The non-charged toner, reversely charged toner and other
particles which can not be removed by the cleaning roller 82 are removed mechanically
by the cleaning blade 81.
[0159] The invention shown in Embodiment 4 is intended to carry out electric cleaning (by
a roller) to remove the greater part of the remaining toner. A means of mechanical
cleaning (by a blade) is used to eliminate a very small amount of toner which cannot
be removed electrostatically due to charging failure or charging in reverse polarity
resulting from transfer.
[0160] Application of bias to the cleaning roller at this time is started later than start
of image former traveling or application of bias to the development device. It terminates
later than termination of application of bias to said development device and earlier
than termination of said image former traveling.
[0161] If bias is applied when image formation stops, bias is applied to the same position
of the image former for a long time. As a result, discharge tends to occur between
that position and the roller, damaging both the image former and roller. Mechanical
damage also tends to occur. To avoid overshooting of bias application, bias is preferred
to be applied to the cleaning roller after start of image former movement or during
its movement.
[0162] Further, the instant when bias is applied to the development device, the excessive
voltage is applied to the development device due to overshoot as shown in Fig. 7.
As a result, the carrier in the developer, magnetic substance or mixed metallic chip
will be deposited on the image former to induce discharge from the cleaning roller.
To avoid discharge to foreign substances by said overshoot width, it is preferred
that the time of apply bias to the cleaning roller be delayed by application of bias
to the development device, and bias be applied to the roller after the image former
area to which foreign substances are deposited has passed through the roller section.
Then foreign substances are mechanically scraped off by the downstream cleaning blade.
[0163] When application is stopped, the cleaning roller is located on the downstream side
of the development device. Accordingly, in order to remove the developer on the image
former between the development device and cleaning device from the time of stopping
application of bias to the development device, it is basically necessary to stop application
of bias to the cleaning roller after the lapse of time for the image former to travel
between the development device and cleaning device.
[0164] From the viewpoint of preventing discharge, image former traveling is desired to
be stopped after termination of the bias application, with consideration given to
the falling time of bias applied to the cleaning roller.
[0165] The above can be summarized as follows:
As shown in Fig. 8, the timing for the start and stop of application of bias to the
cleaning roller is given below: Time of starting image formation: Start of image former
traveling -> Application of bias to development device -> Application of bias to cleaning
roller.
Time of stopping image formation: Start of application bias to development device
-> Start of application bias to cleaning roller -> Stop of image former traveling.
[0166] The following describes the details of the components:
1-b) Cleaning blade
[0167] The actual blade load is 1 to 30 grams/cm, or preferably, 10 to 25 grams/cm. When
it is below 1 grams/cm, cleaning force is insufficient, and a small amount of toner
which cannot be removed by the roller may not be completely removed. When it is 30
grams/cm or more, the wear of the image former surface will increase, and fogging
or blurring of image may occur after a long-term use.
[0168] For the measurement of loads, it is possible to use the numeral when the blade is
pressed against a scale by the same amount as that of the setting condition, or the
value obtained by electrical measurement by a sensor such as a load cell installed
on the contact point with the image former.
[0169] The angle θ between the surface of said cleaning blade facing the image former, and
the surface of said image former including said contact point between the cleaning
blade and image former where said blade has passed is desired to be in the range from
0 to 40°C, more preferably from 0 to 25°C. When it is smaller than 0 deg., cleaning
force is reduced. If it is greater than 40 deg., blade curling tends to occur, where
the blade tip follows the travel of the image former and the blade is curled (See
Fig. 1).
[0170] The blade can be supported by either stationary or rotary method if the angle between
the load and blade is within the above range.
[0171] The rubber hardness of said cleaning blade is desired to be 20 to 90 deg., more particularly,
60 to 80 deg. If it is below 20 deg., the blade is too soft, and curling and cleaning
failure tend to occur. If it is over 90 deg., the blade is too hard, and the blade
cannot respond to a slight amount of foreign substances deposited on the image former.
As a result, escape of toner particles tends to occur. The hardness of the blade is
measured according to JIS K 6253.
[0172] Polyurethane and other materials known in the conventional technology can be used
as a material for the blade. There is no resctriction if blade thickness, free length,
load and angle are within said range. To ensure good load controllability and to avoid
curling, the thickness is desired to be within the range from 1 to 3mm, or preferably
from 1.5 to 2.5mm. The desirable free length is from 2 to 20mm, or preferably from
3mm to 15mm.
1-c) Cleaning roller
[0173] To perform electric cleaning, bias is applied to the cleaning roller by power supply
84 (numeral 85 denotes its control means). Said power supply is preferred to be a
constant current power supply. What is called constant current power supply hereunder
is a power supply which is controlled to ensure that a constant current is issued
at a1 times in the stable output range.
[0174] The polarity of the bias applied for cleaning is reverse to that of the tone used
to create visible images. Namely, when toner is negatively charged, positive bias
is applied to the cleaning roller. If bias is applied by the constant current power
supply in this case, potential difference to feed a constant current at all times
necessarily occurs to the roller surface and image former surface. This potential
difference occurs constant at all times in response to the potential on the image
former. Accordingly, compared to the case when the constant voltage power supply is
used, irregularity due to the potential level of the image former and polarity or
cleaning failure occur very infrequently.
[0175] As described above, application of bias to this cleaning roller starts later than
the start of image former traveling or application of bias potential to said development
device, and terminates later than termination of application of bias to said development
device, and earlier than suspension of said image former movement.
[0176] For example, when the development device and cleaning roller section are 80mm away
from each other along the direction of image former traveling, and the traveling rate
of this image former is 400mm/sec and image formation (start of development on the
image former to the latent image) is carried out 1000ms after application of bias
to the development device in an image forming system, application of bias to the cleaning
roller can be started 200 to 1200ms after application of bias to the development device.
[0177] More preferably, to avoid said overshooting of development bias in the initial phase,
bias is preferred to be applied after the rising time of development bias power supply
(200 ms in this case). A delay of approximately 10 to 200 ms (210 to 400 ms in this
case) is preferred in this case although it varies with the power supply.
[0178] When application is stopped, the cleaning roller is located on the downstream side
of the development device. Accordingly, in order to remove the developer on the image
former between the development device and cleaning device from the time of stopping
application of bias to the development device, it is basically necessary to stop application
of bias to the cleaning roller after the lapse of time for the image former to travel
between the development device and cleaning device (200ms in this case).
[0179] In this case, consideration is given to the falling time of development bias power
supply, and bias application to the cleaning roller is stopped after rising time (approximately
10 to 200ms) added to the arrival time of the image former corresponding to stop of
development bias (200 ms in this case). (210 to 400 ms later in this case) (See Fig.
8).
[0180] From the viewpoint of preventing discharge, image former traveling is desired to
be stopped 10 to 1000 ms after termination of the bias application, with consideration
given to the falling time of bias applied to the cleaning roller.
[0181] Based on the discussion given above, timing to apply bias to the cleaning roller
is preferred to be determined in conformity to development bias timing in the case
of an image forming system of other linear velocity.
[0182] A preferred current value to be applied is 1 to 50 microamperes in terms of absolute
value. If it is below 1 microampere, cleaning will be insufficient. If it is over
50 microamperes, discharge will tend to occur. Although it varies with the thickness
of the image former film and resistance of the cleaning roller, this value is 15 to
30 microns -- equivalent to the film thickness of the organic photoconductor dispersed
in isolating resin as an image former. When the roller surface resistivity of 10
2Ω/□ to 10
10Ω/□ is used, it is preferred to apply 5 to 40 microamperes in terms of absolute value.
[0183] The roller is made of an elastic body to ensure good contact with the image former.
Such an elastic body can be made of rubbers such as silicone rubber and urethane rubber
as is known in the art heretofore, foams or foams coated with resin film.
[0184] The surface resistivity of the roller is desired to be 10
2Ω to 10
10Ω/□, as described above. If the value is greater than 10
10Ω/□, potential difference required to eliminate the toner cannot be obtained. If it
is smaller than 10
2Ω/□, discharge due to banding or others will tend to occur. The surface resistivity
(Ω/□) of the cleaning roller was measured at the normal temperature and relative humidity
(26°C, 50% RH) at the applied voltage of 10 volts for the measuring time of 10 sec.,
using Hirester IP (MCP-HT250) and HA Probe by Mitsubishi Petrochemical Co., Ltd.
To ensure adequate resistance and nip width, the thickness of the conductive and semiconductive
elastic layer is preferred to be set approximately in the range between 0.5 to 50
mm although it varies with the surface resistivity and hardness of the material.
[0185] To ensure excellent performances, the hardness of said cleaning roller is desired
to be 5 to 60 deg., more particularly, 10 to 50 deg. If it is below 5 deg., durability
will be poor. If it is over 60 deg., the width for contact with the image former required
for cleaning will be difficult and the image former surface tends to be damaged. The
hardness is obtained by measuring the elastic body shaped into a roller with an Ascar
C hardness meter (load: 300fg).
[0186] To ensure excellent performances, the width of the nip when in contact with the image
former is desired to be in the range from 0.2mm to 5mm, or preferably 0.5mm to 3mm,
although this varies with the roller diameter. If the width is below 0.2mm, cleaning
force is insufficient. If it is over 5mm, the image former tends to be damaged at
the time of rubbing.
[0187] To prevent toner from spilling, the contact portion of the cleaning roller is desired
to move in the same direction as the image former. If it moves in the reverse direction,
the recovered toner may spill on the transfer unit when excessive toner is present
on the surface of the image bearing member (transfer failure or occurrence of jam).
[0188] The peripheral speed ratio with the image former and the roller (roller: image former)
is desired to be within the range from 0.5:1 to 2:1. If it is below 0.5, cleaning
capacity tends to reduce. If it is over 2, the image former tends to be damaged when
foreign substances are sandwiched in-between.
[0189] The toner removed by the cleaning roller electrostatically is scraped off by a scraper
89 in contact with the roller. The scraper can be located in either the counter or
trail direction with respect to the roller. A phosphor bronze plate, polyethylene
terephthalate plate, polycarbonate plate or their combination known in the conventional
technology can be used as the material for the scraper. This is not restricted to
the scraper; a bias roller and fur brush can be used (see Figs. 9(a), 9(b) and 9(c)).
The toner collected by these cleaning system can be reused after being fed back to
the development device.
1-d) Toner
[0190] To ensure high image quality and easy production, it is preferred to use the toner
with a volume mean particle size of 8.5 microns or less, more preferably, 6.5 microns
or less which has been manufactured by so called polymerization method wherein tone
particles of a desired diameter can be obtained during the production of binding resin,
without using the kneading and pulverizing process. Further, to ensure good toner
charging stability at the time of development, use of toner with a particle size of
3 microns or more is desired.
[0191] Tone particles can be made by any one of emulsion polymerization method, suspension
polymerization method or dispersion polymerization method known in the conventional
technology. Even if toner particles are almost spherical, cleaning failure does not
occur according to the present invention. If only the desired particle size is secured,
there is no need of making toner particles indefinite.
[0192] The toner produced according to the conventional pulverization method can be used
for the present invention. To make full use of excellent performance of the present
invention, it is preferred to use the toner manufactured by the polymerization method.
[0193] The volume mean particle size of the toner according to the present invention is
measured by the Coulter Counter TA-II or Coulter Multitizer (by Coulter). In the present
invention, the Coulter Multitizer was used for measurement, and the interface (by
Nikkaki) to output the data on particle size distribution was connected with a personal
computer. A 100-micron aperture was used in said Coulter Multitizer to measure the
volume and number of the tone particles of 2 microns or more, thereby calculating
the volume mean particle size.
1-e) Others
[0194] If only the above configuration requirements are met in the present invention, there
is no restriction in the development method. It is applicable to either one-component
or two-component development, and either magnetic toner or non-magnetic development.
2-a) Overall configuration (See Figs. 1 and 6)
[0195] The invention shown in Embodiment 5 is the same as that of Embodiment 4 in that electric
cleaning is carried out (by a roller) to remove the greater part of the remaining
toner, and a means of mechanical cleaning (by a blade) is used to eliminate a very
small amount of toner which cannot be removed electrostatically due to charging failure
or charging in reverse polarity resulting from transfer.
[0196] However, said invention shown in Embodiment 5 is further characterized by:
W2 < W1 < W3 (See Fig. 10)
where;
W1: width of said cleaning roller in the longitudinal direction (mm),
W2: width of developer feed in the longitudinal direction in said development device
(mm), and
W3: width of the photosensitive layer on said image developer in the longitudinal
direction (mm).
[0197] If W1 > W3, on the substrate of the image former electric discharge will occur from
the cleaning roller with the result that the cleaning performance is seriously deteriorated.
If W1 < W2, toner will scatter from the development device, and toner deposited outside
the range of the cleaning roller cannot be removed. Hence, W2 < W1 < W3 is preferred.
[0198] To recover the scattered toner, W1 is preferred to be at least 3 mm or preferably
at least 7 mm greater than W2 on both sides (see Fig. 10). If there are much toner
on the image former which cannot be recovered, the charged electrode and optical system
will be contaminated, and such image failure as fogging or white streak will be observed.
[0199] To prevent electric discharge to conductive substrate of the image former, W1 is
preferred to be at least 2 mm or preferably at least 6 mm smaller than W3 on both
sides (see Fig. 10). If there is electric discharge to conductive substrate of the
image former, current will flow in that portion and the potential difference required
for cleaning does not occur on the cleaning surface. As a result, cleaning failure
tends to be observed.
[0200] For example, if W2 is 300mm, W1 is at least 306 mm, at least 3mm greater than W2
on both sides. The width of photosensitive layer W3 is set to at least 310 mm, at
least 2 mm greater than W1 on both sides. (See Fig. 11).
[0201] The width of the cleaning blade is preferred to be the same as that of the cleaning
roller. No problem arises if there is a difference of about 5mm on both sides for
mechanical designing requirements.
[0202] The following describes the details of the components:
2-b) Cleaning blade
[0203] The cleaning blade load and its components are the same those in Embodiment 4.
2-c) Cleaning roller
[0204] The components, application potential level and polarity are the same those in Embodiment
4.
2-d) Image former
[0205] It is possible to use the image former of the conductive substrate provided with
coating where the organic photoconductor is used as a photosensitive layer.
[0206] For example, the image former disclosed in Japanese Patent Laid-Open NO.216172/1989
can be used as material.
2-e) Toner
[0207] The same toner as used in the Embodiment 4 can be used.
2-f) Others
[0208] The development method can be used without any restriction as in the case of Embodiment
4.
[0209] The following Example gives more specific description of the present invention. It
goes without saying that the present invention is restricted thereto.
[EXAMPLE 4-1]
[0210] The following describes the details of Embodiment 4 according to the present invention:
* Evaluation device
[0211] The evaluation device used in the experiment has the same configuration as that of
the image forming system shown in Fig. 1, and is based on the reversal development
method where a latent image is formed by erasing the potential of the image section
on the image former through laser exposure.
[0212] Image former lineal velocity during image formation is 240mm/sec.
* Developer
[0213] Negatively charged toner having a mean volume particle size of 6.5 microns obtained
by emulsion polymerization method was used for two-component developer toner.
* Image former:
[0214] An aluminum tube coated with phthalocyanine pigment as an organic photo semiconductor
layer dispersed to polycarbonate was used.
[0215] The photoconductor layer including the electrical charge feed layer is 25 microns
thick, with a charged potential of - 750 volts on the non-image section and a potential
of -100V on the darkest image portion.
* Cleaning roller:
[0216] A roller made up of conductive foamed urethane having a surface resistivity of 4.5
× 10
4Ω/□ and a hardness of 30 deg. The peripheral speed ratio at the contact portion of
the image former was approximately 1 to 1. It is rotated synchronously with the image
former by a gear couple. Further, the roller is installed so that the nip width in
contact with the image former is 2mm, and is formed by winding an urethane layer on
a 6mm-diameter metallic shaft to a thickness of 4.5mm. (roller: 15mm in diameter)
[0217] This roller was designed to turn in the same direction as the image former at the
nip section. A scraper was provided to remove the recovered toner.
* Applied bias current:
[0218] The current of +20 microamperes was applied from the constant current power supply.
[0219] Fig. 12 shows the bias application timing. The bias rise time (including overshoot)
and fall time each were 10 ms.
* Cleaning blade:
[0220] The cleaning blade was made of urethane rubber. It had a hardness of 70 deg. with
a thickness of 2.00mm and a free length of 10mm. This blade was installed to be in
contact with the image former at an angle of 10 deg. with a contact load of 120 mN/cm.
* Copying test:
[0221] Copying test of 200,000 sheets was conducted under the above conditions.
[0222] In the test, 0 to 100,000 sheets were copied at normal temperature and normal relative
humidity (20°C, 50% RH), and 100,000 to 200,000 sheets were copies at high temperature
and high relative humidity (30°C, 80% RH).
[0223] Up to 200,000 sheets, stable high cleaning performances were ensured without cleaning
failure (escape of toner particles) or image failure such as electric discharge mark
due to the cleaning roller.
[EXAMPLE 5-1]
[0224] The following describes the details of Embodiment 5 according to the present invention:
* Evaluation device
[0225] The evaluation device is designed based on the reversal development method where
a latent image is formed by erasing the potential of the image section on the image
former through laser exposure.
[0226] The width of developer feed (mm) is W2, cleaning roller width is W1, width of photosensitive
layer on the image former is W3, and width of cleaning blade is the same as W1, as
shown in Fig. 13.
* Developer
[0227] Negatively charged toner having a mean volume particle size of 6.5 microns obtained
by emulsion polymerization method was used for two-component developer toner.
* Image former:
[0228] An aluminum tube coated with phthalocyanine pigment as an organic photo semiconductor
layer dispersed to polycarbonate was used.
[0229] The photoconductor layer including the electrical charge feed layer is 25 microns
thick, with a charged potential of -750 volts on the non-image section and a potential
of -100V on the darkest image portion.
* Cleaning roller:
[0230] A roller made up of conductive foamed urethane having a surface resistivity of 4.0
× 10
4Ω and a hardness of 30 deg. The peripheral speed ratio at the contact portion of the
image former was approximately 1 to 1. This roller was designed to move in the same
direction as the image former at the nip portion. A scraper was provided to remove
the toner. It was designed that the nip portion in contact with image former was 2mm
wide, and was formed by winding an urethane layer on a 6mm-diameter metallic shaft
to a thickness of 4.5mm. (roller: 15mm in diameter)
* Current value of applied bias:
[0231] A current of +20 microamperes was applied from the constant current power supply.
Cleaning blade:
[0232] The cleaning blade was made of urethane rubber. It had a hardness of 70 deg. with
a thickness of 2.00mm and a free length of 10mm. This cleaning blade was brought in
contact with the image former at a contact angle of 10 deg. with a contact load of
120mN/cm.
* Copying test:
[0233] Copying test of 200,000 sheets was conducted under the above conditions.
[0234] In the test, 0 to 100,000 sheets were copied at normal temperature and normal relative
humidity (20°C, 50% RH), and 100,000 to 200,000 sheets were copies at high temperature
and high relative humidity (30°C, 80% RH).
[0235] Up to 200,000 sheets, stable high cleaning performances were ensured without cleaning
failure, image contamination or image failure.
[0236] The Embodiment 4 of the present invention provides an image forming system which
ensures stable high quality images for a long time free from damage by electric discharge.
[0237] The Embodiment 5 of the present invention provides an image forming system provided
with a cleaning system which ensures stable cleaning performances for a long time,
while recovering the toner extensively scattered from the development device.
[EMBODIMENT 6]
[0238] The following describes the Embodiment 6 according to the present invention:
[0239] This description, however, is not intended to restrict the scope of the technologies
or terminologies disclosed in the Claims. The conclusive description of the embodiment
given below shows the best mode, without restricting the meaning of the terminologies
or technological range in the present invention.
[0240] The following describes the configuration and function of the image forming system
represented by the embodiment according to the present invention with reference to
Fig. 14:
[0241] In Fig. 14, numeral 110 denotes a photoconductor drum as an electrostatic latent
image bearing member, For example, it is composed of a conductive drum coated with
an OPC photoconductor comprising an organic photoconductive layer. It is grounded,
and is driven and rotated in the clockwise direction. Numeral 111 denotes a charging
device which provides uniform negative electric charging, for example, on the circumferential
surface of the photoconductor drum 110 by corona discharge, thereby providing potential
V
H. Prior to electric charging by said charging device 111, exposure is carried out
by PCL 11a using a light emitting diode or the like in order to remove the history
of the photoconductor up to the previous printing. Thus, electric charge is eliminated
from the surface on around the photoconductor.
[0242] After uniform electric charging to the photoconductor drum 110, the image is exposed
by the laser writer 112 based on image signal. After image signals entered from a
computer or image reader have been processed by the image signal processor, data on
this image exposure is entered into the laser writer 112, and an electrostatic latent
image is formed on the photoconductor drum 110.
[0243] The optical path is bent by multiple reflecting mirror M 112d through a fθ lens 112c
and a rotating polygon mirror 112b which is rotated using a laser diode (not illustrated)
as a light emitting light source, and horizontal scanning of the laser writer 112
is performed. An electrostatic latent image is formed by said horizontal scanning
and vertical scanning due to rotation of the photoconductor drum 110. In the present
Embodiment, image section is subjected to exposure based on said image signals. Then
a reversal latent image is formed and the potential of the exposure unit becomes V
L, where the absolute value of the potential is low.
[0244] A development device 113 is installed on the periphery of the photoconductor drum
110, wherein said development device contains negatively charged conductive toner
and a built-in two-component developer composed of a magnetic carrier. Reversal development
is carried out by a rotating development sleeve 113a which contains a built-in magnet
and holds the developer.
[0245] The developer is produced in such a way that electric charge controlling agent, silica,
titanium oxide or the like is added to a carrier using Ferrite as a core around which
insulating resin is coated and the toner provided with such a coloring agent as pigment
or carbon black, and they are mixed so that toner concentration will be from 5 to
10 wt. %, wherein said toner having a weight mean particle size (discussed later)
of 3 to 10 microns. The developer is controlled to the layer thickness of 0.1 to 0.6mm
on the development sleeve 113a, and is fed to the development area.
[0246] The space between the development sleeve 113a and photoconductor drum 110 in the
development area is 0.2 to 1.0 microns -- a value greater than the thickness of the
developer layer. The a.c. bias voltage obtained by superimposing the a.c. voltage
VAC onto the d.c. voltage V
DC is applied between the development sleeve 13a and photoconductor drum 110. Toner
is negatively charged in the same polarity as the d.c. voltage V
DC. Accordingly, the toner provided with the chance of getting separated from the carrier
by the a.c. voltage V
AC does not deposit on the portion V
H where the absolute value of the potential is higher than the d.c. voltage V
DC. The amount of toner in conformity to the potential difference is deposited on the
portion V
L where the absolute value of the potential is lower, thereby resulting in reversal
development. Further, only the d.c. voltage V
DC can be applied between the development sleeve 113a and photoconductor drum 110. Contact
development can be performed as development. The photoconductor drum 110 holding the
toner image performs transfer operations in the next transfer step.
[0247] The recording paper is fed to a timing roller 15d by a paper feed cassette 115 through
a semi-circular roller 115a and feed rollers 115b and 115c, and is stopped there once.
Then when the system is ready for transfer, said paper is fed to a transfer area 4b
by the rotation of a timing roller 115d. Synchronously with transfer, a transfer roller
114a to which a high voltage charged in the polarity reverse to that of toner is applied
by a high pressure power supply 134 is brought in contact with the circumferential
surface of the photoconductor drum 110 at a transfer area 114b. With the fed recording
paper P in-between, the toner image on the circumferential surface of the photoconductor
drum 110 is transferred to the recording paper P.
[0248] Electric charge is eliminated by peak electrodes 114c laid out with a slight gap
from the recording paper P where a toner image is transferred. Said paper is separated
from the circumferential surface by means of a photoconductor drum 110, and is fed
to a fusing device 117 by a feed belt 116. The transfer toner image is molten by heating
and pressure of the fusing roller 117a as a heating roller and pressure roller and
fusing roller 117b. After the image is fixed on the recording paper P, the paper is
ejected to the tray unit 50 by the ejecting rollers 18a and 18b.
[0249] After the recording paper P has passed by, said transfer roller 14a is kept separated
from the circumferential surface of the photoconductor drum 110 until the next image
image transfer.
[0250] After having transferred the toner image to the recording paper P, the photoconductor
drum 110 reaches the cleaning system 119. The greater part of toner remaining on the
surface is removed by being sucked to tone recovery roller 19b as a toner recovery
means consisting of e.g. the conductive elastic roller to which constant current bias
voltage to be discussed later is applied from the constant current high voltage power
supply 35. The deposited amount of toner per unit area on the photoconductor drum
10 is reduced to 0.25 mg/cm
2 or less. After that, the toner remaining on the circumferential surface is scraped
off into the cleaning system 119 by the cleaning blade 119a consisting of a urethane
rubber material in contact with the photoconductor drum 110. The toner moved to said
toner recovery roller 119b by the blade 119e is also scraped off into the cleaning
system 19 and is ejected or stored by the screw or the like.
[0251] The photoconductor drum 110 from which the remaining toner has been removed by the
cleaning system 119 is exposed by the PC L 111a. Then it is uniformly charged by a
charging device 111, and the next image formation cycle.
[0252] Toner of the developer used in the image forming system of said the present invention,
for example, is polymerized toner produced by emulsion polymerization association
method, and has an approximately circular form with a mean circularity of 0.96 to
0.99.
[0253] The mean circularity hereunder can be defined by a means value of m/M where M represents
the circumferential length of the projected image of the toner particle, and m denotes
the circumferential length of the equivalent circle having the same area as that of
the projected image of the toner particle. Circularity is 1 when the particle image
is truly circular, and the value is smaller as the particle image is more slender
or more irregular in shape.
[0254] Polymerized toner is produced by emulsion polymerization association method as follows:
The surfactant is used to to disperse coloring agent in water. In the meantime, surfactant,
emulsion polymerization initiator, styrene monomer and acryl monomer are placed in
water to produce resin emulsion by emulsion polymerization. Then said coloring agent
dispersant and resin emulsion are mixed. While keeping balance between the repulsive
force of the particles surface generated by PH regulation and coagulation force by
addition of electrolyte, gradual coagulation is carried out. Association is allowed
to take place while controlling particle size and particle size distribution, and
heating and agitation are implemented at the same time. In this manner, inter-particle
fusing and shape control are performed.
[0255] In this case, inter-particle fusing and shape control is implemented using an agitation
tank designed to ensure that agitation is carried out in a laminar flow free from
turbulent flow. For example, in this case, a flow type particle image analyzer FPIA-2000
(by Toa Medical Electronics) is used to measure the mean circularity. This analyzer
allows the shape of the particle to be monitored during generation of toner particles.
So reaction can be stopped when a desired mean circularity and weight mean particle
size has been obtained. Obtained particles are filtered, cleaned and dried, thereby
getting toner particles having a mean circularity of 0,96 to 0.99 and a weight mean
particle size (D50) of 3 to 10 microns.
[0256] In the present Embodiment, the weight mean particle size (D50) was measured by the
Coulter Counter TA-II (by Coulter).
[0257] Toner obtained in said manner according to emulsion polymerization association method
is characterized by a sharp distribution of particle size and a small amount of fine
particles, very small contamination of the carrier by toner ("Toner spent"), excellent
developer durability and uniform distribution of charged amount. Images of high quality
are ensured as compared to those obtained from the conventional pulverization system.
[0258] Fig. 15 is a cross sectional view representing an example of the cleaning system
of the image forming system shown in Fig. 14 according to the present invention;
[0259] In Fig. 15, numeral 110 denotes a photoconductor drum, and 119 indicates a cleaning
system. Numeral 119a represents a cleaning blade comprising a urethane rubber having
a rubber hardness of JISA 69 deg., a free length of 9mm and a thickness of 2mm, and
119b denotes a 15mm-diameter conductive and elastic toner recovery means which is
a toner recovery roller made of conductive urethane comprising a RUBISEL roller having
a hardness Ascar C 32 deg. (by Toyo Polymer), for example. Numeral 119c indicates
an energizing member such as a spring, and 119e denotes a blade to scrape off the
toner having moved onto the toner recovery roller 119b.
[0260] Cleaning blade 119a is an elastic blade installed in a counter form. It is brought
in contact with the surface of the photoconductor drum 110 by means of an energizing
member 119c so that normal load is 20 to 22mN/cm. The toner recovery roller 119b is
brought in light contact with the surface of the photoconductor drum 110, and follows
the rotation of the photoconductor drum 110. Voltage of the reverse polarity to toner
is applied to the recovery roller 119b from thee constant current high voltage power
supply 135 of the constant current control. Constant current bias voltage is applied
to ensure that the remaining toner passing through without being recovered by the
toner recovery roller 119b will not exceed 0.25mg/cm
2.
[0261] Fig. 16 is a chart representing the relation of the amount of deposited toner passing
through without being recovered by the toner recovery roller 119b when the amount
of deposited toner of 0.75 mg/cm
2 per area corresponding to untransferred solid black where the amount of toner deposited
on the surface of the photoconductor drum 110 is the maximum is fixed unchanged, and
the current value of the constant current bias voltage to be applied to the toner
recovery roller 119b is changed. Fig. 16 shows that constant current bias voltage
of 15 microamperes or more must be applied in order to ensure that the amount of toner
deposited after passing through the toner recovery roller 119b does not exceed 0.25
mg/cm
2. In the present Embodiment, constant current bias voltage of 15 microamperes or more
is applied, thereby ensuring that the amount of deposited toner on the photoconductor
drum 110 passing through the recovery roller 119b and reaching the cleaning blade
119a does not exceed 0.25 mg/cm
2.
(Test 1)
[0262] Using the polymerized toner having a mean circularity of 0.97 and a weight mean particle
size (D50) of 6 microns, the amount of deposited toner on the photoconductor drum
110 passing through the recovery roller 119b and reaching the cleaning blade 119a
was changed in the following order; 0.60, 0.53, ..., 0.20, 0.10 mg/cm
2 or less. In this case, a test was made to check if cleaning by the cleaning blade
119a was satisfactory or not. The result of this test is given in Table 1.

[0263] Cleaning failure occurs if toner passes through the edge of the cleaning blade 119a
(escape of toner particles) at the time of cleaning. To check if this phenomenon occurred
or not, the photoconductor portion having passed through the blade was transferred
to the white paper (A4-sized transfer paper), and contamination on the white paper
having transferred was checked. If it was contaminated, the contamination was considered
to be caused by the toner which had passed through the blade to be deposited on the
photoconductor. This is indicated by "X". By contrast, if there was no contamination
on the white paper having been transferred, "A" is used to represent this state. The
test was carried out, for example, by transferring to three sheets of white paper
for each 10 kP (10,000 prints) and 20 kP. The result is clear from Table 1. If the
remaining toner reaching the cleaning blade 119a does not exceed 0.25 mg/cm
2, escape of toner particles did not occur until 110 kP was reached, and excellent
cleaning continued, as is clear from Table 1.
(Test 2)
[0264] The inventors of the present invention prepared 15 types of toner as combinations
of five types of mean circularity; 0.95, 0.96, 0.97, 0.99, and 1.00 and three weight
mean particle sizes; 3, 6 and 10 microns. The amount of deposited toner on the photoconductor
drum 110 having passed through the recovery roller 119b and reached the cleaning blade
119a was adjusted not to exceed 0.20, 0.25, ..., 0.27 microns per unit area. 110 kP
printing test was conducted using image forming system shown in Fig. 1. Table 2 shows
the result of this test.
Table 2
Amount of toner deposited before blade |
Toner |
Cleaning performance |
Image quality |
Remarks |
|
Average circularity |
Weight mean particle size |
|
|
|
0.20 |
0.95 |
3 |
good |
passable |
(1) Not the present invention |
6 |
good |
passable |
10 |
good |
passable |
0.96 |
3 |
good |
good |
(2) Not the present invention |
6 |
good |
good |
10 |
good |
good |
0.97 |
3 |
good |
good |
(3) Not the present invention |
6 |
good |
good |
10 |
good |
good |
0.99 |
3 |
good |
good |
(4) Not the present invention |
6 |
good |
good |
10 |
good |
good |
1.00 |
3 |
bad |
bad |
(5) Not the present invention |
6 |
passable |
passable |
10 |
good |
good |
0.25 |
0.97 |
3 |
good |
good |
(6) Not the present invention |
6 |
good |
good |
10 |
good |
good |
0.27 |
0.97 |
3 |
bad |
bad |
(7) Not the present invention |
6 |
passable |
passable |
10 |
good |
good |
Amounts of toner deposited are given in terms of mg/cm2. |
[0265] Weight mean particle sizes are given in microns.
[0266] In each test, where 110kP printing had passed, 10 sheets of A4-sized print transfer
paper were picked up at random and evaluation was made from the view point of both
cleaning performance and image quality. A term of "good" is used to show that there
was no defect, while a term of "bad" was used to indicate that such a defect as fogging
or toner contamination was found out by visual observation. A defect found out by
using a loupe is marked with "passable". Cleaning performance is directly related
to image quality. When cleaning performance was found unsatisfactory, image quality
failure was also observed.
[0267] Adjustment was made so that the amount of deposited toner immediately before the
cleaning blade 119a did not exceed 0.20 mg/cm
2, and tests <2>, <3> and <4> were conducted using three types of mean circularity;
0.96, 0.97, and 0.99. These tests revealed that both cleaning performance and image
quality were satisfactory.
[0268] Adjustment was made so that the amount of deposited toner immediately before the
cleaning blade 119a did not exceed 0.25mg/cm
2, and test <6> was conducted using the mean circularity of 0.97. This test revealed
that both cleaning performance and image quality were satisfactory. The results of
tests <2>, <3> <4> and <6> in the present invention were satisfactory in both cleaning
performance and image quality.
[0269] Further, adjustment was made to ensure that the amount of deposited toner immediately
before the cleaning blade 119a did not exceed 0.20mg/cm
2, and test <1> was conducted using the mean circularity of 0.95. The test revealed
that cleaning performance was satisfactory without any problem, but irregularities
on image surface probably caused by development were found out.
[0270] Adjustment was made so that the amount of deposited toner immediately before the
cleaning blade 119a did not exceed 0.20mg/cm
2, and test <5> was conducted using the mean circularity of 1.00. In this test cleaning
failure was detected, and fogging phenomenon was observed. This phenomenon occurred
especially when small-diameter toner particles having a weight mean particle size
of 3 microns were used. Probably some of them passed through the blade, resulting
in this phenomenon.
[0271] In the test <1> using the toner with a mean circularity of 0.95 outside the scope
of the present invention, failure was observed in image quality.
In the test <5> using the toner with a mean circularity of 1.00, cleaning failure
was found out.
[0272] Adjustment was made to ensure that the amount of deposited toner immediately before
the cleaning blade 119a did not exceed 0.27mg/cm
2, and test <7> was conducted using the mean circularity of 0.97. In this test, cleaning
failure was observed. Fogging phenomenon and toner contamination were observed especially
when small-diameter toner particles having a weight mean particle size of 3 microns
were used.
[0273] Cleaning failure was detected in the test <7> outside the scope of the present invention
where the amount of deposited toner immediately before the cleaning blade 119a did
not exceed 0.27mg/cm
2.
[0274] In said Tests 1 and 2 have made it clear that cleaning is performed in an image forming
system illustrated in Fig. 14 using the toner with a mean circularity of 0.96 to 0.99,
wherein toner deposited on the photoconductor drum 110 having passed through the toner
recovery roller 119b and having reached the cleaning blade 119a was adjusted not to
exceed 0.25 mg/cm
2. Said Tests 1 and 2 have made it clear that high quality image without cleaning failure
can be obtained even if printing is performed up to 110 kP. It has also been made
clear that high quality image is provided by toner having a weight mean particle diameter
of 3 to 10 microns.
[0275] Thus, an image forming system is equipped with a cleaning system 119 wherein constant
current bias voltage having a current of 15 microamperes or more is applied to the
toner recovery roller 119b by the constant current high voltage power supply 135.
In this system, the surface of the photoconductor drum 110 reaches the cleaning system
119 after a formed toner image is transferred onto the recording paper P, and toner
image remaining untransferred due to jamming or other reasons reaches the cleaning
system 119. In this case, the remaining toner is fed to the toner recovery roller
19b by bias voltage applied to the remaining toner recovery roller 119b, and is reduced
so that the amount of deposited toner does not exceed 0.25 mg/cm
2. Then the remaining toner is scraped off by the cleaning blade 119a, and is completely
cleaned. The toner having moved to said toner recovery roller 119d is scraped off
by the blade 119e, and ejected or stored into a toner waste storage tank (not illustrated)
by the screw or the like together with the toner having been scraped off by said cleaning
blade 119a.
[0276] Fig. 17 is a cross sectional view representing the configuration of another example
of a cleaning system 119A in the image forming system according to the present invention.
[0277] In Fig. 17, the portions having the same numeric codes as those of the cleaning system
19 of Fig. 15 have the same functions; so they are not included in the following detailed
description. Numeral 119d denotes a toner recovery fur brush as an toner recovery
means. It is a toner recovery fur brush for toner collection, for example, consisting
of the conductive viscose rayon REC, SH (300/100, D/F, 224kF/inch
2) by Toa Sangyo, having a shaft diameter of 11 mm and brush diameter of 20mm with
4.5 mm-long hair around the shaft.
[0278] The hair tip of the toner recovery fur brush 119d lightly contacts the surface of
the photoconductor drum 110, and the contact portion is rotated by electric power
(not illustrated) in the same direction as the photoconductor drum 110. Bias voltage
of constant current having a current value of 15 microamperes or more, for example,
is applied to the toner recovery fur brush 119d by means of a constant current high
voltage power supply 135, as in the case of said toner recovery roller 19b illustrated
in Fig. 15.
[0279] In the image forming system equipped with said cleaning system 119 the surface of
the photoconductor drum 110 reaches the cleaning system 119 after a formed toner image
is transferred onto the recording paper P, and toner image remaining untransferred
due to jamming or other reasons reaches the cleaning system 119. In this case, the
remaining toner is reduced so that the amount of deposited toner does not exceed 0.25
mg/cm
2. So the remaining toner is scraped off by the cleaning blade 119a without escape
of toner particles, thereby ensuring perfect cleaning. The toner having moved to said
toner recovery fur brush 119b is scraped off by the blade 119e, and is ejected or
stored into a toner waste storage tank (not illustrated) by the screw or the like
together with the toner having been scraped off by said cleaning blade 119a.
[0280] The present invention according to Embodiment 6 provides an image forming method
and image forming system which ensure excellent images for a long time without toner
passing through the cleaning blade despite the use of approximately circular toner
of small particle size, or without deterioration of cleaning performance. This makes
it possible to provide an image forming system characterized by high quality printing
without particles being noticeable.
[EMBODIMENT 7]
[0281] The following describes the Embodiment 7 according to the present invention with
reference to drawings, without being restricted thereto:
[0282] Fig. 18 is a schematic drawing representing the relation between the cleaning system
and image bearing member according to the present invention. Numeral 202 denotes a
photoconductor drum as an image bearing member, and 204 indicates a cleaning system.
Numeral 241 shows a cleaning blade which performs cleaning by the pressure through
contact with the end to a photoconductor drum 202, and 242 denotes a spring to energize
the cleaning blade 241 to contact the photoconductor drum 202. Numeral 243 represents
a cleaning roller which is subjected to bias application and gets in contact with
said photoconductor drum 202 through rotation, thereby removing toner and cleaning
the photoconductor drum 202 electrostatically. Numeral 244 indicates a blade to scrape
off the toner from the cleaning roller 443, and 245 shows a toner recover roller which
collects the toner removed from the cleaning roller 243 by the blade 244 and feeds
it to a recycling pipe (not illustrated) connected to the development device. Numeral
246 denotes a housing of the cleaning system 4, 247 a power supply as an bias voltage
application means for application of bias voltage to the cleaning roller 243, and
248 a power supply controller as a control means for constant current control the
power supply 247.
[0283] Said cleaning roller 243 gets in contact with the photoconductor drum 202 to suck
and remove the toner electrostatically. Bias voltage applied to the cleaning roller
243 is required to have the polarity reverse to that of the toner on the photoconductor
drum 202 at the position in contact with the cleaning roller 243. In other words,
the power supply 247 applies positive bias voltage to the cleaning roller 243 when
toner is negatively charged, and applies negative bias voltage when toner is positively
charged. For example, when the photoconductor drum 202 is an OPC photoconductor (organic
photoconductor), toner is negatively charged, so positive bias voltage is applied.
In this case, applied bias voltage is subjected to constant current control by a power
supply controller 248. Constant current control allows a constant voltage to be applied
to the toner per unit amount, independently of the amount of remaining toner deposited
onto the photoconductor drum 202. Uniform suction and removal of toner is ensured
despite difference in the amount of deposit according to different positions. This
is a great advantage. A preferable constant current value under constant current control
is approximately 5 to 30 microamperes although it varies with the performances and
properties of the image bearing member or cleaning system.
[0284] If the photoconductor drum 202 turns in the arrow marked direction, the cleaning
roller 243 located on the upstream side of the cleaning system 204 with bias voltage
applied thereto is brought in contact with the photoconductor drum 202. The cleaning
roller 243 rotates in the arrow marked direction without opposing the rotation of
the photoconductor drum 202, and electrostatically attracts on its surface the remaining
toner deposited on the photoconductor drum 202 and foreign substances such as paper
powder. The toner sucked and deposited on the cleaning roller 243 reaches the blade
244 through further rotation. Then it is escaped off by the blade 244, and said scraped
toner is led into the recycling pipe (not illustrated) by the rotation of the toner
recovery roller 245 to be reused as development toner. The photoconductor drum 202
makes further rotation until the tip of the cleaning blade 41 reaches the contract
position. Then remaining toner and others are scraped off, and removed toner and others
are led into the recycling pipe by the toner recovery roller 45, as in the case of
said cleaning roller 243. As the cleaning blade 241 wears and deteriorates, a gap
may be formed between the blade and photoconductor drum 202, from which toner may
escape. However, such toner is again sucked and removed by the cleaning roller 243
located on the upstream side of the cleaning blade 241. Thus, the cleaning capacity
of the cleaning system 204 is not reduced by the lapse of time. This ensures continued
cleaning of the image bearing member sufficiently.
[0285] The cleaning roller 243 is preferred to be a conductive elastic roller. In order
that bias voltage is applied to the cleaning roller 243 and effective electrostatic
suction of toner from the photoconductor drum 202 is provided, the surface resistivity
of the cleaning roller 243 is preferred to be such that electric conductivity is within
the range from 10
5Ω to 10
8Ω.
[0286] Further, even if foreign substances are caught between the roller and photoconductor
drum 202, for example, toner can be brought into the cleaning system 204 without the
surface of the photoconductor drum 202 being damaged, when the cleaning roller 243
is elastic. Also if the cleaning roller 243 is elastic, the contact with photoconductor
drum 202 is increased. Thus, electrostatic suction not only allows toner to be removed
from the photoconductor drum 202, but also provides a wiping effect, thereby further
improving cleaning capacity. When the cleaning roller 243 is elastic, preferred surface
hardness is Ascar C 20 to 40 deg.
[0287] To put it more specifically, a RUBISEL roller (with a hardness of Ascar C 32 dg.)
by Toyo Polymer can be given as a preferred conductive elastic roller.
[0288] Fig. 19 is a schematic drawing representing a laser printer as an example of the
image forming system equipped with the cleaning system according to the present invention.
[0289] In Fig. 19, numeral 101 denotes a charging device, 202 a photoconductor drum as a
first image bearing member, and 203 a development drum with four development devices
(development means). Numeral 204a indicates a photoconductor cleaning system for cleaning
of the photoconductor drum 202, and 404b shows an intermediate transfer belt cleaning
system for cleaning of the intermediate transfer belt. Numeral 206 represents a primary
transfer roller, 207 a secondary transfer roller, and 208 a back up roller. Numerals
209, 210, 211 and 212 denotes support rollers, 214 a laser exposure device, 215 an
intermediate transfer belt as a second image bearing member, 230 a paper feed cassette
to store transfer paper P, and 231 a pick up roller 232 to feed out transfer paper
P. Numeral 232 indicates a resist roller, 233 a fusing device to heat and fuse the
toner image on the transfer paper P having been subjected to secondary transfer, and
234 an eject tray to eject the transfer paper P having been subjected to image formation.
Here the photoconductor cleaning system 404a and intermediate transfer belt cleaning
system 204b constitute a cleaning system 4 according to the present invention described
with reference to Fig. 18.
[0290] The following items are arranged in that order around the photoconductor drum 202;
(1) a charging device 201 which provides the surface of the photoconductor drum 202
with a uniform electrical charging of a specified polarity, (2) a laser exposure device
214 for uniform writing of an electrostatic latent image on the photoconductor drum
202, (3) a development drum 203 to deposit toner to said electrostatic latent image
to form a toner image, (4) a primary transfer roller 206 (conductive) to transfer
a toner image on said photoconductor drum 202 to the intermediate transfer belt 215.
[0291] The photoconductor drum 202 is rotated by a drum drive motor (not illustrated) in
the arrow marked direction shown in the drawing. A charger 201 is a charged electrode
such as Control, and is designed to allow the photoconductor drum 2 to be uniformly
charged. When the photoconductor drum 202 is an OPC photoconductor (organic photoconductor),
the photoconductor drum 202 is negatively charged uniformly.
[0292] Image signals transmitted from an image reading unit for a scanner (not illustrated)
and the like or personal computer are subjected to a specified processing at an image
processor (not illustrated), and are sent to a laser exposure device 214. Said laser
exposure device 214 scans and exposes the laser beam in conformity to said image signals
on the photoconductor drum 202. As a result, the negatively charged potential of the
photoconductor drum 202 are subjected to uniform damping to form an electrostatic
latent image.
[0293] Said electrostatic latent image formed on the photoconductor drum 202 is developed
by the toner in the first color development device out of development drum 203 equipped
with four developers, and the first color toner image is formed. In this case, toner
is negatively charged in said development device, and said toner is deposited on the
portion where charged potential on photoconductor drum 202 is damped. Thus, the image
is made visible. Said toner image carried by the photoconductor drum 202 is fed by
further rotation of the photoconductor drum 202 to the primary transfer position where
a primary transfer roller 206 is arranged. The toner image is primarily transferred
on the intermediate transfer belt 215. The intermediate transfer belt 215 moves in
the arrow marked direction shown in the drawing at almost the same speed with the
photoconductor drum 202. At said primary transfer position, the image is primarily
transferred to the intermediate transfer belt 15 by transfer electric field having
the characteristic reverse to that of said toner applied to the primary transfer roller
(positive polarity in this case).
[0294] Then the step from said latent image formation to primary toner transfer is repeated
for each of the second, third and fourth colors. Color toner image with multiple colors
superimposed thereon is formed on the intermediate transfer belt 215. Normally, there
are four toner colors; black, yellow, magenta and cyan. They are contained to four
development devices in the development drum 203. Until said color toner image is completed,
the secondary transfer roller 7 and intermediate transfer belt cleaning system 4b
are retracted from the intermediate transfer belt 15, and remain in the state of non-contact.
In the present Embodiment, a development drum incorporating multiple development means
was used in the formation of a color toner image.
However, it is also possible to use so-called tandem method, wherein the photoconductor
drum, development device and other image formation units are arranged for each color,
and multiple image formation units are arranged in one row on the intermediate transfer
belt 215, with each of them providing a primary transfer of the toner image to the
intermediate transfer belt 15.
[0295] The remaining toner is scraped off by the photoconductor cleaning system 4a from
the photoconductor drum 202 having transferred the toner image to the intermediate
transfer belt 215 at the primary transfer position in said manner. Potential on the
photoconductor drum 2 is canceled by an electric charge eliminator (not illustrated),
and preparation is thus made for the next image formation.
[0296] In the meantime, primary transfer of a color toner image to the intermediate transfer
belt 215 is completed and said color toner image is fed to the secondary transfer
position where a secondary transfer roller 207 is installed. At this time, transfer
paper P as a recording material is picked up by a pick up roller 231 from a paper
feed cassette 230. The picked up transfer paper P is fed out by the resist roller
232 at a specified timing, and is fed to the secondary transfer position by the intermediate
transfer belt 215 supported by a back up roller 208 and a secondary transfer roller
207 (left in the drawing). Bias potential with the polarity reverse to that of the
toner on the intermediate transfer belt 15 is applied to the secondary transfer roller
207 (not illustrated). The back up roller 208 is grounded (not illustrated). So when
the transfer paper P has passed between the secondary transfer roller 207 and intermediate
transfer belt 215, by the transfer electric field formed at a transfer voltage with
polarity reverse to the charged polarity of said toner image. Toner image carried
on the intermediate transfer belt 215 is transferred to the transfer paper P. In this
case, it goes without saying that the relation between the bias application of the
secondary transfer roller 207 and back up roller 208 and the ground may be opposite.
The transfer paper P to which the toner image is transferred secondarily is further
fed to a fusing device 233 comprising a pair of heating rollers, where it is heated,
pressed and fused, and is discharged into the paper eject tray 234.
[0297] In the meantime, the remaining toner or paper powder is removed from the intermediate
transfer belt 125 after secondary transfer by an intermediate transfer belt cleaning
system 204b, and preparation is thus made for the next image formation.
[0298] Each of the operations and sequence controls for said image formation is performed
by a control unit (not illustrated).
[0299] The following describes the toner having a mean circularity of 0.96 or more which
is to be removed by the cleaning system according to the present invention:
[0300] The known type of the toner having a mean circularity of 0.96 or more is the one
formed by polymerization method. A particularly excellent production art is the polymerization
method for producing polymerized toner through association between resin particles
and coloring agent particles disclosed in the Official Gazette of Japanese Patent
Laid-open NO. 186253/1.
[0301] Many other toner production arts based on association (fusing) of resin particles
have been disclosed. Measurement of polymerized toner circularity is not restricted.
However, use of a particle image analyzer FPIA-2000 (by Toa Medical Electronics) is
preferable. This device is suited for monitoring of a shape by real-time image processing
while allowing the liquid sample to pass by.
[0302] Fig. 20 is a drawing representing the shape of toner particles and major portions
of a shape distribution measuring instrument. Fig. 21 is a perspective view illustrating
the photographing unit in Fig. 21 and the flow of liquid sample. Further, Fig. 22
is a drawing representing how to obtain circularity.
[0303] In Figs. 20 and 21, the arrow mark shows the flow of the liquid sample 301 or sheath
solution, and 302 indicates sheath solution (coating solution). This allows the particles
to go to the photographing unit 303 without being overlapped with one another. In
conformity to the flashing of a stroboscope 304, a liquid sample 301 is photographed
by a high speed video camera 305. Numeral 306 denotes particles in the liquid sample,
and Y, Y and Z indicate longitudinal and lateral length and thickness of the photographing
unit 303. Fig. 22 shows how to obtain the "circumstantial length of a circle obtained
from circle-equivalent diameter of the particles photographed in this way" 307 and
"circumferential length of the particle projection" 308.
[0304] Circularity can be defined as follows:

In the present invention, the mean value of toner circularity (mean circularity)
is preferred to be within the range from 0.96 to 0.99.
[0305] If circularity is too small, attrition may be caused by stress due to agitation in
the development device, and deposition on the carrier and development device may occur,
resulting in reduced durability. If circularity is too high, a spherical shape may
be produced to deteriorate cleaning performances.
[0306] Further, the standard deviation for numeral level is preferred not be exceed 0.05.
If it exceeds 0.05, distribution will occur to development performance due to expanded
shape distribution, and selective development will take place with the result that
long-term stable development cannot be ensured. So-called fogging and changes in image
concentration may be observed.
[0307] The particle size of toner is measured in terms of volume. It can be obtained by
the method for measuring the frequency distribution based on the logarithm-converted
scale using the circle-equivalent diameter. The volume mean particle size is preferred
to be within the range from 3 to 9 microns. Particle size distribution can also be
measured by said measuring instrument simultaneously.
[0308] The method for producing toner having a circularity of 0.96 or more is not restricted
to said method. A preferred way is to form particles in conformity to the method disclosed
in the Official Gazette of Japanese Patent Laid-Open NO. 265252/1993, Official Gazette
of Japanese Patent Laid-Open NO. 329947/1994 and Official Gazette of Japanese Patent
Laid-Open NO. 15904/1997. After that, formed particles is subjected to heat treatment.
[Example 7-1]
[0309] An image formation test was conducted on the polymerized toner having a mean circularity
of 0.973, using an image forming system according to the present invention wherein
a cleaning system 204 shown in Fig. 18 is arranged as a photoconductor cleaning system
204a for the laser printer shown in Fig. 19. Similarly, another image formation test
was conducted on the polymerized toner with a mean circularity of 0.973, using an
image forming system for comparison wherein a cleaning system according to the conventional
technology equipped with only a cleaning blade without cleaning roller was arranged
as a photoconductor cleaning system 204a of laser printer shown in Fig. 19. The printing
count was set to zero when each of the new cleaning systems was installed, and a running
printing test was conducted. Then evaluation was made to check if the cleaning performance
was deteriorated with the lapse of time.
[0310] The cleaning system of the image forming system used for comparison is the same as
the cleaning system 204 of Embodiment 7 shown in Fig. 18 except that a cleaning roller
243, blade 244, power supply 247 or power supply controller 248 is not provided.
[0311] In the image forming system according to the present invention, a RUBISEL roller
(with a hardness of Ascar C 32 dg.) by Toyo Polymer was used as a cleaning roller
243 of the cleaning system. Bias voltage fed from the power supply 247 was placed
under constant current control at a constant current value of 20 microamperes by power
supply controller 248.
[0312] In said image forming system of the present invention and image forming system for
comparison, the cleaning performance of the photoconductor drum 202 by a photoconductor
cleaning system was evaluated as follows:
Untransferred toner image (without primary transfer onto the intermediate transfer
belt) on the full page of the A4-sized paper (solid filled) formed on each photoconductor
drum 202 is cleaned by each cleaning system. This cleaning operation was repeated
10 times (one cycle). After that, visual observation was made to check whether or
not there is any toner remaining on the photoconductor drum 202. A symbol of "X" is
used to show that toner remained, while a symbol of "A" (o) is used to indicate that
cleaning was satisfactory without toner remaining.
[0313] A total printing count is assumed to be the number of sheets for image formation
from the printing count of zero in installation of a new cleaning system to the secondary
transfer to the transfer paper. After the total print count shown in Tables 3 and
4 has been reached, according to the above-mentioned evaluation procedure, two cycles
of formation and cleaning of untransferred toner image on the A4-sized full page each
were carried out, wherein the amount of deposited toner is changed as given in Tables
3 and 4. All the results are given in Tables 3 and 4. Table 3 shows the image forming
system for comparison, while Table 4 shows the result of evaluating the image forming
system according to the present invention.

[0314] The above Tables have made it clear that, in an image formation using the toner having
a mean circularity of 0.96 or more, continued stable cleaning performances are provided
by the cleaning system equipped with a cleaning roller according to the present invention,
wherein bias voltage is applied said cleaning roller used in combination with a cleaning
blade and located on the upstream side.
[0315] The invention according to Embodiment 7 provides a cleaning system ensuring a continued
sufficient cleaning of an image bearing member despite the use of toner of higher
mean circularity, an image forming system equipped with said cleaning device and image
forming method.