Background of the Invention
(1) Field of the Invention
[0001] The present invention relates to an electrophotographic toner for negative charging.
More particularly, the present invention relates to an electrophotographic toner for
negative charging, which is capable of forming a high-density image without scattering
of the toner.
(2) Description of the Related Art
[0002] In commercial electrophotographic reproduction or electrophotographic printing, in
order to reduce the amount of ozone generated at the charging step, there is ordinarily
adopted a process in which an electrostatic image positively charged is formed, and
therefore, a toner for negative charging is widely used as the developing toner for
developing this electrostatic image.
[0003] Recently, development of a laser beam printer or a digital copying machine has advanced,
and in this image-forming apparatus, there is adopted an operation of writing a latent
image into an organic photosensitive material of the negative charging type by a laser
and performing reversal development by a toner for negative charging, and a high quality
is also required for the toner negative charging.
[0004] The developing toner is generally formed by pulverizing a resin composition comprising
a fixing resin, a colorant and a charge-controlling agent as indispensable components
into an average particle size of 5 to 15 µm. Naturally, a charge-controlling agent
exerting a negative charge-controlling action at the frictional charging is used in
case of a toner for negative charging.
[0005] In the conventional toner charge-controlling process, the average value of the charge
quantity as the entire toner is controlled according to the kind of the charge-controlling
agent or the amount added of the charge-controlling agent. However, even if the average
value of the charge quantity as the entire toner can be controlled, it is very difficult
to strictly control the distribution of the charge quantity in toner particles.
[0006] It is known that a plurality of charge-controlling agents having charging performances
reverse to each other are incorporated in toner particles. For example, Japanese Unexamined
Patent Publication No. 54-34243 discloses a developer for developing an electrostatically
charged image, comprising a toner and a carrier, in which the toner is a toner for
negative charging, which comprises a dye positively charged by friction with the carrier.
[0007] JP-A-2,264,970 discloses a negatively charged color toner comprising, as positive
charge controller, quaternary ammonium salt.
[0008] Furthermore, Japanese Unexamined Patent Publication No. 57-196264 discloses an electrically
insulating magnetic one-component developer comprising an electrically insulating
fixing medium and, dispersed in the fixing medium, a magnetic material powder and
a charge-controlling agent, in which the charge-controlling agent comprises a negative
or positive charge-controlling agent and a charge-controlling agent having a reverse
polarity at a weight ratio of from 1/0.05 to 1/1.5.
[0009] In the conventional toner for negative charging, even though the average value of
the charge quantity can be maintained at a satisfactory level by adjusting the kind
or amount added of the charge-controlling agent, a disadvantage of considerable broadening
of the distribution of the charge quantity cannot be eliminated. Namely, a highly
charged toner having a much larger charge quantity than the average value, which is
not consumed for the development, is inevitably generated at a certain frequency (distribution
quantity). Furthermore, a lowly charged toner having a much smaller charge quantity
than the average value and causing scattering of the toner is generated at a certain
frequency.
[0010] Particles of the former highly charged toner are electrically strongly attracted
to surfaces of the carrier particles and are present in a hardly separable state,
and they extraordinarily inhibit frictional chargeability performances of the carrier
particles. Accordingly, even in case of a toner causing no particular problem at the
initial stage of the development, with the lapse of the developing time, the proportion
of the uncharged or lowly charged toner increases, and such troubles as scattering
of the toner, fogging and reduction of the image density are caused.
[0011] In the above-mentioned prior art process in which a charge-controlling agent for
negative charging is combined with a positively chargeable dye (charge-controlling
agent), there can be attained an advantage that the distribution of the charge quantity
can be considerably freely shifted to the high charge quantity side or the low charge
quantity side, but this process is still insufficient for sharpening the distribution
of the charge quantity of the toner and controlling formation of a highly charged
toner or a lowly charged toner completely or to a level that can be neglected.
Summery of the Invention
[0012] It is a primary object of the present invention to overcome the above-mentioned defects
of the conventional toner for negative charging and provide a toner for negative charging,
in which the charge quantity of the toner can be preferably adjusted, the average
value of the charge quantity of the toner is arranged within a range optimum for prevention
of scattering of the toner and reduction of the image density, the distribution of
the charge quantity of the toner is sharp, and there are hardly present a highly charged
toner not used for the development and a lowly charged toner causing scattering of
the toner.
[0013] Another object of the present invention is to provide a toner for negative charging,
in which the distribution of the charge quantity of the toner is sharp, rise of the
charge is quick at the time of charging, and at the long-time operation the charging
characteristics are hardly degraded.
[0014] In accordance with the present invention, there is provided an electrophotographic
toner for negative charging, comprising a fixing resin, a colorant, a charge-controlling
agent for negative charging, which is a metal compound of an aromatic hydroxycarboxylic
acid and a charge-controlling assistant which is a positive charge-controlling substance
which is incompatible with the fixing resin and is dispersed therein, and which charge-controlling
assistant is a compound of formula (I)

wherein one or two of the groups R are alkyl or alkenyl having at least 8 carbon
atoms and the other groups R are alkyl of up to 4 carbon atoms or benzyl and A
- is an oxyacid anion.
[0015] It is preferred that the charge-controlling agent (A) and the charge-controlling
assistant (B) be present at an (A)/(B)/ weight ratio of from 1/0.05 to 1/1, especially
from 1/0.1 to 1/0.7, and it also is preferred that the charge-controlling agent and
charge-controlling assistant be used in a total amount of 0.5 to 5 parts by weight,
especially 2 to 4 parts by weight, per 100 parts by weight of the fixing resin.
Brief Description of the Drawings
[0016] Fig. 1 is a diagram illustrating the distribution of the charge quantity of the toner
of the present invention (Example 1).
[0017] Fig. 2 is a diagram illustrating the distribution of the charge quantity of the toner
for negative charging (Comparative Example 1), in which the positive charge-controlling
substance is not incorporated.
[0018] Fig. 3 is a diagram illustrating the distribution of the charge quantity of a toner
in which a charge-controlling agent for negative charging and a positively chargeable
dye compatible with a fixing resin are incorporated in combination.
[0019] Fig. 4 is a diagram illustrating an apparatus for measuring the charge quantity of
the toner.
[0020] Fig. 5 is a diagram illustrating the distribution of the charge quantity after formation
of 5,000 copies, observed with respect to the toner of Example 1.
[0021] Fig. 6 is a diagram illustrating the distribution (curve A) of the initial charge
quantity and the distribution (curve B) of the charge quantity after formation of
50,000 copies, observed with respect to the toner of Example 3.
[0022] Fig. 7 is a diagram illustrating the distribution (curve A) of the initial charge
quantity and the distribution (curve B) of the charge quantity after formation of
50,000 copies, observed with respect to the toner of Example 5.
[0023] Fig. 8 is a diagram illustrating the distribution (curve A) of the initial charge
quantity and the distribution (curve B) of the charge quantity after formation of
50,000 copies, observed with respect to the toner of Example 7.
Detailed Description of the Invention
[0024] The present invention is based on the finding that if a positive charge-controlling
substance incompatible with a fixing resin but dispersible therein is combined as
the charge-controlling assistant with a charge-controlling agent for negative charging,
instead of a positively chargeable dye compatible with the fixing resin, conventionally
used, the distribution of the charge quantity can be made conspicuously sharper than
in the conventional toner, with the result that generation of a highly charged toner
not used for the development or a lowly charged toner causing scattering of the toner
can be effectively controlled.
[0025] These effects of the present invention can be readily understood from Figs. 1 through
3 showing the distributions of charge quantities of toners.
[0026] The distributions of charge quantities shown in Figs. 1 through 3 are determined
by using a charge quantity-measuring apparatus shown in Fig. 4 according to the following
method.
Measurement of Distribution of Charge Quantity
[0027] The charge quantity-measuring apparatus shown in Fig. 4 comprises a separating portion
2 arranged in a cylindrical housing 1 to separate a toner from a developer, a measuring
portion 3 for measuring the distribution of the charge quantity of the separated toner,
and a sucking device 11 such as an air pump.
[0028] The separating portion 2 is separated from the measuring portion 3 by a partition
plate 7. A circulating hole 1a for introducing air into the housing 1 is formed on
the side wall of the housing 1 slightly below the partition plate 7. An air-rectifying
filter 8 is arranged slightly below the circulating hole 1a.
[0029] In the separating portion 2, compressed air is blown by an air needle 5 to a developer
maintained on a magnet 4, whereby only the light toner is blown up and scattered while
leaving a carrier attracted magnetically to the magnet 4.
[0030] A funnel 6 supported by the partition plate 7 is arranged between the separating
portion 2 and the measuring portion 3. A receiving opening 6d on the top end of the
funnel 6 projects above the partition plate 7, and a dent 6a on the lower end pierces
through the filter 8 and is exposed to the side of the measuring portion 3.
[0031] In the measuring portion 3, by applying a direct current power R to a pair of electrode
rods 9a and 9b embedded in the side wall of the housing 1, a horizontal parallel electric
field is formed between the electrode rods 9a and 9b. Reference numeral 10 represents
a filter.
[0032] The sucking device 11 forms a main air current flowing from the outside of the housing
1 to the measuring portion 3 through the circulating hole 1a and the rectifying filter
8 and also forms an air current for sucking the toner into the funnel 6 above the
funnel 6.
[0033] In the above-mentioned charge quantity-measuring apparatus, the toner particles separated
by the separating portion 2, collected by the funnel 6 and introduced into the measuring
portion are vertically dropped while being carried by the air current formed by the
sucking device 11 and are allowed to fall on the filter 10 through between the electrode
rods 9a and 9b. Since the toner particles fall down in the horizontal parallel electric
field between the electrode rods 9a and 9b under Coulomb force H corresponding to
the charge quantity in the horizontal direction and gravity V in the vertical direction.
Accordingly, the toner particles are dispersed on the filter 10 at a position corresponding
to the mass or charge quantity thereof. Then, from the distribution of falling positions
of the toner particles, the distribution of the charge quantity of the toner is calculated
by an image treatment.
[0034] The charge quantity distributions curves shown in Figs. 1, 2 and 3 are those determined
according to the above-mentioned method.
[0035] In case of toner A where a controlling agent for negative charging alone is used
(toner of Comparative Example 1), as shown in Fig. 2, a highly charged toner in area
a is present in a large quantity, and a reversely charged toner or an uncharged toner
in zone
d is contained in a considerable proportion. In case of toner B of the prior art where
a positively chargeable dye is combined with a controlling agent for negative charging
(toner of Comparative Example 2), as shown in Fig. 3, the average value of the charge
quantity can be shifted to a low charge quantity side but the distribution width is
not substantially changed from that of toner A, the amount of the highly charged toner
is reduced but the highly charged toner is still present, and the proportion of the
reversely charged toner or uncharged toner in area
d increases. In contrast, in case of toner C of the present invention where a controlling
agent for negative charging is combined with a positive charge-controlling assistant
in compatible with a fixing resin (toner of Example 1), the quantity of the toner
present in appropriate charging areas
b and
c increases and the width of the distribution of the charge quantity is drastically
narrowed, and the quantity of the highly charged toner in area
a or the reversely charged or uncharged toner in area
d is reduced (is not present in this case).
[0036] By using the foregoing toners A, B and C, copying for obtaining 5,000 prints is continuously
carried out in a remodelled machine (the developing process is changed to the reversal
developing process) of Laser Beam Printer LPX-1 (Registered Trade Mark in one or more
designated States) (supplied by Mita Industrial Co.), and the image density (ID),
the fog density (FD) of the image and scattering of the toner in the periphery of
the developing device are examined. The obtained results are shown in Table 1.
[0037]
Table 1
Toner |
Image Density (ID) |
Fog Density (FD) of Image |
Toner Scattering (FD) |
A |
1.20 - 1.41 |
0.001 - 0.009 |
conspicuous |
B |
1.21 - 1.50 |
0.005 - 0.010 |
very conspicuous |
C |
1.30 - 1.32 |
below 0.001 |
not observed |
[0038] From Figs. 1 through 3 and Table 1, it is understood that the toner of the present
invention has such preferred charging characteristics that variation of the image
density, formation of fogging of the image and scattering of the toner can be controlled.
[0039] In the toner of the present invention, not only at the initial stage of the development,
but also when the development is continued for a long time, variation of the image
density, occurrence of fogging and scattering of the toner are not caused and a high
effect of preventing the deterioration can be attained.
[0040] The fact that by using a charge-controlling assistant for positive charging, which
is in compatible with the fixing resin, in the toner of the present invention, the
distribution of the charge quantity can be sharpened was found as a phenomenon as
the result of many experiments. The reason has not been elucidated, but since a positively
chargeable dye compatible with the fixing resin has no effect of sharpening the distribution,
it is estimated that the dispersion structure in which in a matrix having the controlling
agent for negative charging dissolved or dispersed therein, the positively chargeable
substance is dispersed in a larger macro particle size will exert a function of reducing
numbers of the highly charged toner and the negatively charged toner. In general,
one of serious defects of the combination of the positive charge-controlling substance
as the assistant with the negative charge-controlling agent is that when a developer
comprising this toner and a carrier is stirred in the developing device, rising of
the charge is delayed, even though the charge of the toner particles is finally controlled
to a negative value. In contrast, in the toner having the composition and dispersion
structure specified in the present invention, when the developer is stirred to initiate
stirring, rising of the charge is as quick as in case of the negatively chargeable
toner comprising a negative charge-controlling agent alone. This is another advantage
attained by the present invention.
[0041] In the present invention, it is also important to use an aromatic oxycarboxylic acid
metal compound as a negative charging controlling agent. By using such a metal compound,
the toner can be effectively charged negatively, and the electric properties of the
toner such as the charging characteristics can be stably maintained.
[0042] The negatively chargeable toner of the present invention can be effectively used
not only as a toner for forming an ordinary single-color image but also as a toner
for forming a so-called full-color image. For example, a full-color image can be formed
by lapping a cyan toner, a yellow toner and a magenta toner, but it sometimes happens
that the charging characteristics of the respective color toners are changed by a
mechanical impact force or heat generated by the stirring operation in the developing
device. More specifically, even if the distribution of the charge quantity of each
color toner is sharp, it is difficult to maintain this state while continuing the
copying operation. Furthermore, if the charging characteristics of each color toner
are changed, development of the color toner is not effectively attained, and a desired
full-color image can hardly be reproduced. According to the present invention, a sharp
distribution of the charge quantity can be effectively maintained over a long period,
and the above problem in formation of a full-color image can be effectively eliminated.
Charge-Controlling Assistant
[0043] The positive charge-controlling substance used as the charge-controlling assistant
in the present invention is a quaternary ammonium salt incompatible with the fixing
resin but dispersible therein and has a charge-controlling action of a polarity reverse
to that of the charge-controlling agent for negative charging.
[0044] As the quaternary ammonium salt, there is preferably used a compound represented
by the following formula:

wherein at least one of groups R represents a long-chain alkyl or long-chain alkenyl
group having at least 8 carbqn toms, especially 8 to 22 carbon atoms, other groups
R represent a lower alkyl group, a benzyl group, a long chain alkyl group of a long-chain
alkyl group, with the proviso that at least 2 of these groups R represent a lower
alkyl group having up to 4 carbon atoms or a benzyl group, and A represents an oxyacid
anion.
[0045] As the oxyacid anion, there can be mentioned anions of oxyacids such as orthophosphoric
acid and pyrophosphoric acid, molybdic acid, tungstic acid, antimonic acid and bismuthic
acid. These quaternary ammonium salts are especially suitable for sharpening the distribution
of the charge quantity without delaying rising of charging of the toner.
Charge-Controlling Agent
[0046] In the present invention, examples of metal compounds of an aromatic oxycarboxylic
acid used as a charge-control agent are metal salts or metal complex compounds of
oxybenzoic acid such as salicylic acid, para-oxy-benzoic acid, and metaoxybenzoic
acid and metal salts and metal complex compounds such as oxy-1-naphthoic acid, 3-oxy-2-naphthoic
acid and 3-oxy-2-naphthoic acid. Of these, metal salts and metal complexes of salicylic
acid, especially, salicylate and a complex compound of salicylic acid and zinc are
preferred.
[0047] In the present invention, the charge-controlling agent and the charge-controlling
assistant are preferably used at a weight ratio of from 1/0.005 to 1/1, especially
from 1/0.1 to 1/0.7. It is preferred that the combination of the charge-controlling
agent and charge-controlling assistant be present in an amount of 1 to 5 parts by
weight, especially 2 to 4 parts by weight, per 100 parts by weight of the fixing resin.
Fixing Resin
[0048] A known resin which is not compatible with the charge-controlling assistant but is
capable of dispersing the charge-controlling assistant therein is used as the fixing
resin. Since the fixing resin negatively charges the toner, it is preferred that the
fixing resin should have a tendency to be negatively charged. For example, a styrene
resin, an acrylic resin, a styrene-acrylic resin and a polyester resin are generally
used.
[0049] As the styrene monomer constituting the fixing resin, there can be mentioned monomers
represented by the following formula:

wherein R
1 represents a hydrogen atoms, a lower alkyl group (having up to 4 carbon atoms) or
a halogen atom, R
2 represents a hydrogen atom or a substituent such as a lower alkyl group or a halogen
atom,
such as styrene, vinyltoluene, α-methylstyrene, α-chlorostyrene and vinylxylene, and
vinylnaphthalene. Of these monomers, styrene is preferably used.
[0050] As the acrylic monomer, there can be mentioned monomers represented by the following
formula:

wherein R
3 represents a hydrogen atom or a lower alkyl group, and R
4 represents a hydrogen atom or a substituted or unsubstituted alkyl group having up
to 18 carbon atoms,
such as ethyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl
acrylate, 2-ethylhexyl methacrylate, acrylic acid and methacrylic acid. As the acrylic
monomer, there can be used other ethylenically unsaturated carboxylic acids and anhydrides
thereof, such as maleic anhydride, crotonic acid and itaconic acid.
[0051] A styrene acrylic copolymer resin is one of preferred fixing resins, and the weight
ratio A/B of the styrene monomer (A) to the acrylic monomer (B) is preferably from
50/50 to 90/10, especially preferably from 60/40 to 85/15. Preferably, the acid value
of the resin used is 0 to 25. From the viewpoint of the fixing property, it is preferred
that the resin should have a class transition temperature (Tg) of 50 to 75°C.
[0052] Generally, it may be obtained preferably as a polyester resin obtained by polycondensing
a diol component

wherein R is an ethylene group or propylene group, and m or n is a positive integer,
with a polycarboxylic acid or acid anhydride as an acid component or its derivative.
[0053] Examples of the diol component include polyoxypropylene-2,2-bis(4-hydroxyphenyl)
propane, polyoxyethylene-2,2-bis(4-hydroxyphenyl) propane, and polyoxypropylene-polyoxyethylene-2,2-bis(4-hydroxyphenyl)propane.
[0054] Examples of the carboxylic acid are maleic acid, fumaric acid, mesaconic acid, citraconic
acid, taconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic
acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacid acid, malonic
acid, 1,2,4-benzenetricarboxylc acid, 1,2,5-benzenetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic
acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,5-hexanetricarboxylic
acid, 1,2,4-butanetricarboxylic acid, 1,3-dicarboxy-2-methylcarboxypropen, 1,3-dicarboxylic-2-methyl-2-methylcarboxy
propane tetra(methylene carboxy)methane, 1,2,7,8-octanetetracarboxylic acid, enball
trimer and anhydrides of these.
[0055] This polyester resin may be produced by polycondensing the diol component with the
polycarboxylic acid component. In the reaction, other diol components such as ethylene
glycol and bisphenol A in addition to 10 mole% of may be concurrently used etherified
bisphenols A of the above formula.
Cororant
[0056] As the colorant to be incorporated into the binder resin, there can be used at least
one member selected from the group consisting of inorganic and organic pigments and
dyes, for example, carbon blacks such as furnace black and channel black, iron blacks
such as triiron tetroxide, rutile titanium dioxide, anatase titanium dioxide, Phthalocyanine
Blue, Phthalocyanine Green, cadmium yellow, molybdenum orange, Pyrazolone Red and
Fast Violet B.
[0057] In the case where the toner of the present invention is used as the yellow toner
for full-color development, for example, there are preferably used benzidine pigments
such as C.I. Pigment Yellow 13 (Benzidine Yellow GR) (Registered Trade Mark in one
or more designated states), C.I. Pigment Yellow 14 (Vulcan Fast Yellow G) (Registered
Trade Mark in one or more designated states), C.I. Pigment Yellow 17 (Registered Trade
Mark in one or more designated states), C.I. Pigment Yellow 55 (Registered Trade Mark
in one or more designated states), C.I. Pigment Yellow 12 (Registered Trade Mark in
one or more designated states) and C.I. Pigment Yellow 83 (Registered Trade Mark in
one or more designated states). In this case, a yellow colorant such as chrome yellow,
titanium yellow or quinoline yellow lake can be used in addition to the benzidine
pigment according to need.
[0058] In the case where the toner of the present invention is used as the magenta toner
full-color development, quinacridone pigments such as C.I. Pigment Red 122 (Quinacridone
Magneta) (Registered Trade Mark in one or more designated states), C.I. Pigment Red
192 (Registered Trade Mark in one or more designated states), C.I. Pigment Red 209
(Registered Trade Mark in one ore more designated states) and C.I. Pigment Violet
19 (Quinacridone Violet) (Registered Trade Mark in one or more designated states)
are preferably used.
[0059] In the case where the toner of the present invention is used as the cyan toner for
full-color development, copper phthalocyanine pigments such as C.I. Pigment Blue 15
(Phthalocyanine Blue) (Registered Trade Mark in one or more designated states), C.I.
Pigment 16 (Heliogen Blue G) (Registered Trade Mark in one or more designated states)
and C.I. Pigment Blue 17 (Fast Sky Blue) (Registered Trade Mark in one or more designated
states) are preferably used.
[0060] the colorant is generally used in an amount of 2 to 15 parts by weight, preferably
3 to 10 parts by weight, per 100 parts by weight of the resin.
Toner
[0061] The particle size of toner particles is such that the volume-based median diameter
measured by a Coulter Counter is 5 to 15 µm, especially 7 to 12 µm. The particles
can have an indeterminate shape formed by melt-mixing and pulverization or a spherical
shape formed by dispersion or suspension polymerization.
[0062] The toner of the present invention is combined with a known magnetic carrier and
used as a two-component magnetic developer to exert excellent charging characteristics.
[0063] As the magnetic carrier, there can be used a ferrite carrier and an iron powder carrier.
The carrier can be used in an uncoated stated or resin-coated stated. In general,
a ferrite carrier is preferably used.
[0064] As the ferrite, there have been used sintered ferrite particles composed of at least
one member selected from the group consisting of zinc iron oxide (ZnFe
2O
4), Yttrium iron oxide (Y
3Fe
5O
12), cadmium iron oxide (CdFe
2O
4), gadolinium iron oxyde (Gd
3Fe
5O
12), copper iron oxide (CuFe
2O
4), lead iron oxide (PbFe
12O
19), nickel iron oxide (NiFe
2O
4), neodium iron oxide (NdFeO
3), barium iron oxide (BaFe
12O
19), magnesium iron oxide (MgFe
2O
4), manganes iron oxide (MnFe
2O
4) and lanthanum iron oxide (LaFeO
3). Especially, soft ferrites containing at least one member, preferably at least two
members, selected from the group consisting of Cu, Zn, Mg, Mn and Ni, for example,
a copper/zinc/magnesium ferrite, can be used.
[0065] As the coating resin for magnetic carriers, there are known an acrylic resin, a styrene
resin, a silicone resin, a fluorine resin and an amino-modified resin. A resin that
controls indirectly the toner charge to a negative level by controlling the charge
of the resin-coated magnetic carrier to a positive level is preferably used. Of course,
in the present invention, even if this carrier-coating resin is not present, control
of the charge can be accomplished effectively and assuredly.
[0066] It is preferred that the saturation magnetization of the carrier be 40 to 75 emu/g,
especially 45 to 70 emug. A ferrite carrier satisfying the above requirement, especially
a ferrite carrier having a spherical shape, is preferably used. It is preferred that
the particle size of the ferrite carrier be 20 to 140 µm, especially 50 to 100 µm.
[0067] The mixing ratio of the toner and the magnetic carrier depends on the physical properties
of the toner and the magnetic carrier, but it is preferred that the mixing weight
ratio be in the range of from 1/99 to 10/90, especially from 2/98 to 5/95.
[0068] It also is preferred that the resistivity of the developer as a whole be 5 x 10
9 to 5 x 10
12Ω-cm, especially 5 x 10
9 to 5 x 10
11Ω-cm.
[0069] At the development of an electrostatic image, the above-mentioned toner and magnetic
carrier are mixed, a magnetic brush having a predetermined length is formed on a developing
sleeve having a magnet roll arranged therein, and the magnetic brush is brought into
sliding contact with a photosensitive material having the electrostatic image, or
the magnetic brush is brought into close proximity to the electrostatic image-holding
photosensitive material in a field to which a vibrating electric field is applied.
Examples
[0070] The present invention will now be described in detail with reference to the following
examples that by no means limit the scope of the invention.
Example 1
[0071] By a twin-screw kneader, 100 parts by weight of a styrene/acrylic copolymer as the
fixing resin, 8 parts by weight of carbon black as the colorant, 1.5 parts by weight
of low-molecular-weight polypropylene as the offset-preventing agent, 2 parts by weight
of a zinc salicylate as the charge-controlling agent for negative charging and 0.5
part by weight of a quaternary ammonium salt represented by the following formula:

as the charge-controlling assistant incompatible with the styrene/acrylic copolymer
were melt-kneaded, and the melt-kneaded mixture was cooled, pulverized and sieved
to obtain a toner having an average particle size of 11 µm. The toner was mixed and
stirred with a resin-coated ferrite carrier having an average particle size of 85
µm at a toner concentration of 4.5% to form a developer. The distribution of the charge
quantity was measured by the toner charge quantity-measuring apparatus shown in Fig.
4. The obtained results are shown in Fig. 1.
[0072] By using a remodelled machine (the developing process was changed to the reversal
developing process) of Laser Beam Printer LPX-1 (supplied by Mita Industrial Co.)
having an organic photosensitive material for negative charging mounted thereon (surface
potential of photosensitive material: -700 V, developing bias voltage: - 500 V), the
above-mentioned developer was subjected to the continuous copying test for forming
5,000 prints. Reduction of the image density or occurrence of fogging of the image
was not observed, and scattering of the toner was not caused. Furthermore, the distribution
of the charge quantity after formation of 5,000 copies is showed in Fig. 5.
[0073] The obtained results are shown in Table 1.
Example 2
[0074] A toner having an average particle size of 11 µm was prepared in the same manner
as described in Example 1 except that 0.5 part by weight of a quaternary ammonium
salt represented by the following formula:

was used as the charge-controlling assistant.
[0075] Then, in the same manner as described in Example 1, a developer was formed and 5,000
prints were continuously formed. As in Example 1, a good image was obtained, and scattering
of the toner in the machine was not caused. Furthermore, the distribution of the charge
quantity of the toner was as sharp as in Example 1.
Comparative Example 1
[0076] A toner was prepared in the same manner as described in Example 1 except that the
charge-controlling assistant was not used. The distribution of the charge quantity
of the toner was measured in the same manner as described in Example 1. The obtained
results are shown in Fig. 2. Furthermore, 5,000 prints were continuously formed in
the same manner as described in Example 1. The image density was unstable and dropping
of the image density often occurred. Fogging of the image or scattering of the toner
was sometimes caused.
Comparative Example 2
[0077] A toner was prepared in the same manner as described in Example 1 except that 2 parts
by weight of Solvent Yellow 56, compatible with the fixing resin, was used instead
of the charge-controlling assistant used in Example 1. The distribution of the charge
quantity of the toner was measured in the same manner as described in Example 1. The
obtained results are shown in Fig. 3. Furthermore, 5,000 prints were continuously
formed in the same manner as described in Example 1. Fogging of the image and scattering
of the toner were conspicuous. The image density was satisfactory to some extent,
but the density often became uneven.
Comparative Example 3
[0078] A toner was prepared in the same manner as described in Example 1 except that 2 parts
by weight of Basic Blue 26, compatible with the fixing resin, was used instead of
the charge-controlling assistant used in Example 1. The distribution of the charge
quantity of the toner was measured in the same manner as described in Example 1. The
obtained results similar to those shown in Fig. 3 were obtained. Furthermore, 5,000
prints were continuously formed in the same manner as described in Example 1. Fogging
of the image and scattering of the toner were conspicuous. The image density was satisfactory
to some extent, but the density often became uneven.
Example 3
[0079] A toner (yellow toner) having an average particle size of 11 µm was prepared in the
same manner as described in Example 1 by using 100 parts by a styrene/acrylic copolymer
as the fixing resin, 5 parts by weight of C.I. Pigment Yellow 17 as the colorant,
1.5 parts by weight of low-molecular-weight polypropylene as the offset-preventing
agent, 2 parts by weight of a zinc salicylate as the charge-controlling agent for
negative charging and 0.5 part by weight of the quaternary ammonium salt used in Example
1.
[0080] Then, a developer was prepared in the same manner as described in Example 1, and
the distribution of the charge quantity was measured by using the apparatus shown
in Fig. 4. A sharp distribution shown in curve A in Fig. 6 was observed.
[0081] Still further, 50,000 prints were continuously formed and the distribution of the
charge quantity of the toner was measured. The obtained distribution curve (curve
B in Fig. 6) was as sharp as the curve A of the initial distribution of the charge
quantity.
Example 4
[0082] A toner (yellow toner) was prepared in the same manner as described in Example 3
except that 5 parts by weight of C.I. Pigment Yellow 13 was used as the colorant and
0.5 part by weight of the quaternary ammonium salt used in Example 2 was used as the
charge-controlling assistant.
[0083] The distribution of the charge quantity was measured in the same manner as described
in Example 1. The obtained distribution curve was sharp and similar to the curve A
in Fig. 6.
[0084] Furthermore, in the same manner as described in Example 3, the distribution of the
charge quantity was measured after 50,000 prints were continuously formed. Scattering
of the toner was not caused and a good image was obtained, and the distribution of
the charge quantity was substantially as sharp as in the initial stage.
Comparative Example 4
[0085] A toner was prepared in the same manner as described in Example 3 except that 0.5
part by weight of C.I. Solvent Yellow 56 compatible with the fixing resin was used
instead of the charge-controlling assistant used in Example 3. The distribution of
the charge quantity of the toner was measured in the same manner as described in Example
1. A board distribution similar to that shown in Fig. 3 was observed.
[0086] When 5,000 prints were continuously formed, fogging of the image and scattering of
the toner were conspicuous. The image density was satisfactory to some extent, but
density unevenness was sometimes caused.
Example 5
[0087] A toner (magenta toner) was prepared in the same manner as described in Example 3
except that 5 parts by weight of C.I. Pigment Red 122 was used as the colorant. A
sharp distribution similar to that shown in the curve A in Fig. 7 was obtained.
[0088] In the same manner as described in Example 3, 50,000 prints were continuously formed
and the image characteristics were observed. A good image was obtained without scattering
of the toner. Then, the distribution of the charge quantity was measured. As shown
by the curve B in Fig. 7, the obtained distribution was sharp and was not substantially
different from the initial distribution of the charge quantity.
Example 6
[0089] A toner (magenta toner) was prepared in the same manner as described in Example 4
except that 5 parts by weight of C.I. Pigment Red 122 was used as the colorant. A
sharp distribution similar to that shown in the curve A in Fig. 7 was obtained.
[0090] In the same manner as described in Example 4, 50,000 prints were continuously formed
and the distribution of the charge quantity was measured. The obtained distribution
was sharp and was not substantially different from the initial distribution of the
charge quantity.
Example 7
[0091] A toner (cyan toner) was prepared in the same manner as described in Example 3 except
that 5 parts by weight of C.I. Pigment Blue 15 was used as the colorant. A sharp distribution
similar to that shown in the curve A in Fig. 8 was obtained.
[0092] In the same manner as described in Example 3, 50,000 prints were continuously formed
and the image characteristics were observed. A good image was obtained without scattering
of the toner. Then, the distribution of the charge quantity was measured. As shown
by the curve B in Fig. 8, the obtained distribution was sharp and was not substantially
different from the initial distribution (curve A) of the charge quantity.
Example 8
[0093] A toner (cyan toner) was prepared in the same manner as described in Example 4 except
that 5 parts by weight of C.I. Pigment Blue 15 was used as the colorant. A sharp distribution
similar to that shown in the curve A in Fig. 8 was obtained.
[0094] In the same manner as described in Example 4, 50,000 prints were continuously formed
and the distribution of the charge quantity was measured. The obtained distribution
was sharp and was not substantially different from the initial distribution of the
charge quantity.
1. Elektrophotographischer Toner zum negativen Aufladen, dadurch gekennzeichnet, daß
er ein Fixierharz, ein Farbmittel, ein Ladungskontrollmittel für negative Aufladung,
das eine Metallverbindung einer aromatischen Hydroxycarbonsäure ist, und ein Ladungskontroll-Hilfsmittel,
das ein eine positive Ladung kontrollierender Stoff ist, der mit dem Fixierharz inkompatibel
und darin dispergiert ist, umfaßt, und worin das Ladungskontroll-Hilfsmittel eine
Verbindung der Formel (I) ist

worin ein oder zwei der Reste R Alkyl oder Alkenyl mit mindestens 8 Kohlenstoffatomen
bedeuten, und die anderen Reste R Alkyl mit bis zu 4 Kohlenstoffatomen oder Benzyl
sind, und A
- ein Anion einer Sauerstoffsäure ist.
2. Toner nach Anspruch 1, dadurch gekennzeichnet, daß mindestens einer der Reste R Alkyl
oder Alkenyl mit 8 bis 22 Kohlenstoffatomen ist.
3. Toner nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß das Ladungskontroll-Hilfsmittel
ein quaternäres Ammoniumsalz einer Orthophosphorsäure, Molybdänsäure, Wolframsäure,
Antimonsäure oder Bismutsäure ist.
4. Toner nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß das Ladungskontrollmittel
und das Ladungskontroll-Hilfsmittel in einem Gewichtsverhältnis von 1:0.05 bis 1:1
vorhanden sind, und in einer Gesamtmenge von 0.5 bis 5 Gewichtsteilen pro 100 Gewichtsteile
des Fixierharzes verwendet werden.
5. Gelbtoner nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß die Metallverbindung
ein Salz oder Komplex von Salicylsäure und Zink ist.
6. Gelbtoner nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß das Farbmittel
ein Benzidinpigment ist.
7. Magentatoner nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß das Farbmittel
ein Chinacridonpigment ist.
8. Cyantoner nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß das Farbmittel
ein Kupferphthalocyaninpigment ist.
9. Verwendung eines Toners nach einem der Ansprüche 1 bis 8 in elektrophotographischen
Druckverfahren und elektrophotographischen Reproduktionsverfahren von Bildern.
10. Magnetischer Zweikomponenten-Entwickler, dadurch gekennzeichnet, daß er einen Toner
nach einem der Ansprüche 1 bis 8 und einen Magnetträger enthält.
11. Verfahren zur Herstellung eines elektrophotographischen Toners zum negativen Aufladen,
dadurch gekennzeichnet, daß das Verfahren umfaßt: Schmelzkneten einer Mischung umfassend
ein Fixierharz, ein Farbmittel, ein Ladungskontrollmittel zum negativen Aufladen,
das eine Metallverbindung einer aromatischen Hydroxycarbonsäure ist, und ein Ladungskontroll-Hilfsmittel,
das ein eine positive Ladung kontrollierender Stoff ist, der mit dem Fixierharz inkompatibel
und darin dispergiert ist, und worin das Ladungskontroll-Hilfsmittel eine Verbindung
der Formel (I) ist

worin ein oder zwei der Reste R Alkyl oder Alkenyl mit mindestens 8 Kohlenstoffatomen
bedeuten und die anderen Reste R Alkyl mit bis zu 4 Kohlenstoffatomen oder Benzyl
sind, und A
- ein Anion einer Sauerstoffsäure ist.
12. Verfahren nach Anspruch 11 zur Herstellung eines Toners gemäß einem der Ansprüche
2 bis 8.
13. Verfahren zur Herstellung eines magnetischen Zweikomponenten-Entwicklers, dadurch
gekennzeichnet, daß das Verfahren umfaßt: Mischen eines Magnetträgers mit einem elektrophotographischen
Toner zum negativen Aufladen, der ein Fixierharz, ein Farbmittel, ein Ladungskontrollmittel
zum negativen Aufladen, das eine Metallverbindung einer aromatischen Hydroxycarbonsäure
ist, und ein Ladungskontroll-Hilfsmittel, das ein eine positive Ladung kontrollierender
Stoff ist, der mit dem Fixierharz imkompatibel und darin dispergiert ist, umfaßt,
und worin das Ladungskontroll-Hilfsmittel eine Verbindung der Formel (I) ist,

worin ein oder zwei der Reste R Alkyl oder Alkenyl mit mindestens 8 Kohlenstoffatomen
bedeuten und die anderen Reste R Alkyl mit bis zu 4 Kohlenstoffatomen oder Benzyl
sind, und A
- ein Anion einer Sauerstoffsäure ist.
14. Verfahren nach Anspruch 13, dadurch gekennzeichnet, daß der Toner ein solcher gemäß
einem der Ansprüche 2 bis 8 ist.