1. Field of the invention.
[0001] This invention relates to an apparatus used in the process of electrostatic printing
and more particularly in Direct Electrostatic Printing (DEP). In DEP, electrostatic
printing is performed directly from a toner delivery means on a receiving member substrate
by means of an electronically addressable printhead structure.
2. Background of the Invention.
[0002] In DEP (Direct Electrostatic Printing) the toner or developing material is deposited
directly in an imagewise way on a receiving substrate, the latter not bearing any
imagewise latent electrostatic image. The substrate can be an intermediate endless
flexible belt (e.g. aluminium, polyimide etc.). In that case the imagewise deposited
toner must be transferred onto another final substrate. Preferentially the toner is
deposited directly on the final receiving substrate, thus offering a possibility to
create directly the image on the final receiving substrate, e.g. plain paper, transparency,
etc. This deposition step is followed by a final fusing step.
[0003] This makes the method different from classical electrography, in which a latent electrostatic
image on a charge retentive surface is developed by a suitable material to make the
latent image visible. Further on, either the powder image is fused directly to said
charge retentive surface, which then results in a direct electrographic print, or
the powder image is subsequently transferred to the final substrate and then fused
to that medium. The latter process results in an indirect electrographic print. The
final substrate may be a transparent medium, opaque polymeric film, paper, etc.
[0004] DEP is also markedly different from electrophotography in which an additional step
and additional member is introduced to create the latent electrostatic image. More
specifically, a photoconductor is used and a charging/exposure cycle is necessary.
[0005] A DEP device is disclosed in e.g. US-P 3,689,935. This document discloses an electrostatic
line printer having a multi-layered particle modulator or printhead structure comprising
:
- a layer of insulating material, called isolation layer ;
- a shield electrode consisting of a continuous layer of conductive material on one
side of the isolation layer ;
- a plurality of control electrodes formed by a segmented layer of conductive material
on the other side of the isolation layer ; and
- at least one row of apertures.
Each control electrode is formed around one aperture and is isolated from each other
control electrode.
[0006] Selected potentials are applied to each of the control electrodes while a fixed potential
is applied to the shield electrode. An overall applied propulsion field between a
toner delivery means and a receiving member support projects charged toner particles
through a row of apertures of the printhead structure. The intensity of the particle
stream is modulated according to the pattern of potentials applied to the control
electrodes. The modulated stream of charged particles impinges upon a receiving member
substrate, interposed in the modulated particle stream. The receiving member substrate
is transported in a direction orthogonal to the printhead structure, to provide a
line-by-line scan printing. The shield electrode may face the toner delivery means
and the control electrode may face the receiving member substrate. A DC field is applied
between the printhead structure and a single back electrode on the receiving member
support. This propulsion field is responsible for the attraction of toner to the receiving
member substrate that is placed between the printhead structure and the back electrode.
[0007] A DEP device is well suited to print half-tone images. The densities variations present
in a half-tone image can be obtained by modulation of the voltage applied to the individual
control electrodes. In most DEP systems large apertures are used for obtaining a high
degree of density resolution (i.e. for producing an image comprising a high amount
of differentiated density levels).
[0008] For text quality, however, a high spatial resolution is required. This means that
small apertures must have to be made through said plastic material, said control electrodes
and said shield electrode.
[0009] If small apertures are used in the printhead structure in order to obtain a high
spatial resolution, then the overall printing density is rather low. This means that
either the printing speed too is rather low, or that multiple overlapping rows of
addressable apertures have to be implemented, yielding a complex printhead structure
and printing device.
[0010] By using apertures with a large aperture diameter, it is also necessary to provide
multiple rows of apertures in order to obtain an homogeneous grey density for the
whole image.
[0011] Printhead structures with enhanced density and/or spatial control have been described
in the literature. In US-P 4,860,036 e.g. a printhead structure has been described
consisting of at least 3 (preferentially 4 or more) rows of apertures which makes
it possible to print images with a smooth page-wide density scale without white banding.
The main drawback of this kind of printhead structure deals with the toner particle
application module, which has to be able to provide charged toner particles in the
vicinity of all printing apertures with a nearly equal flux. The problem of equal
toner flux has been addressed in several ways (see e.g. US-P 5,040,004, US-P 5,214,451,
US-P 5,136,311, EP-A 731 394.
[0012] The printing speed achievable with DEP devices does not only depend on the possibility
of using a printhead structure with multiple rows of printing apertures, nor does
the printing quality only depend on providing charged toner particles in the vicinity
of all printing apertures with a nearly equal flux, but both printing speed and printing
quality depend also on the amount of charged toner particles that is presented per
unity of time in the vicinity of the printing apertures.
[0013] There is thus a need for a DEP device wherein it is possible to provide in a simple
and reliable way a large amount of toner particles in the vicinity of the printing
apertures.
3. Objects and Summary of the Invention
[0014] It is an object of the invention to provide an improved Direct Electrostatic Printing
(DEP) device, printing with high maximum density and high spatial resolution at a
high printing speed.
[0015] It is a further object of the invention to provide a DEP device combining high spatial
resolution, high density resolution and high maximum density with good long term stability
and reliability.
[0016] It is still a further object of the invention to provide a printhead structure for
a DEP device, wherein said printhead structure combines a compact design with good
long term stability and reliability.
[0017] It is another object of the invention to provide a charged toner application module
which combines a compact design with high printing speed and good long term stability.
[0018] Further objects and advantages of the invention will become clear from the description
hereinafter.
[0019] The above objects are realized by providing a DEP device that comprises :
(i) a back electrode (105),
(ii) a printhead structure (106),
(iii) an array of printing apertures (107) in said printhead structure (106) through
which a particle flow can be electrically modulated by a control electrode (106a)
and having an extension C (in mm) (107) in the direction of the movement of a receiving
substrate (109),
(iv) delivery means for charged toner particles (101),
comprising a charged toner conveyer (103), the reference surface of said charged toner
conveyer being placed at a distance B (in mm) from the front of said printhead structure
(106), facing said charged toner conveyer,
said charged toner conveyer (CTC) passing in the vicinity of said printhead structure
at a linear surface speed LSC in mm/s, said charged toner particles being applied
to said CTC by a magnetic brush with a sleeve rotating at a linear surface speed LSM
in mm/s and said image receiving substrate traveling at a linear speed LSS in mm/s
between said back electrode (105) and said printhead structure (106), characterised
in that said surface speed LSM of said sleeve and said speed LSS of the image receiving
substrate relate to each other in a ratio LSM/LSS ≥ 0.50, and said surface speed LSC
of said CTC and said speed LSS of the image receiving substrate relate to each other
in a ratio LSC/LSS ≥ 0.50.
[0020] In a further preferred embodiment LSM/LSS ≥ 0.5 and LSC/LSS ≥ 0.5 and the ratio of
said surface speed of said sleeve LSM to said surface speed of said CTC (LSC) is equal
to or larger than 0.50.
4. Brief Description of the Drawings
[0021] Fig. 1 is a schematic illustration of a possible embodiment of a DEP device according
to the present invention.
[0022] Fig. 2 is a schematic illustration of the development zone.
[0023] Fig. 3 is a cross-section of fig 2 along the plane A-A'-A''.
5. Definitions
[0024] Throughout this disclosure following definitions are used :
- "charged toner conveyer (CTC)" is a conveyer for charged toner with a cylindrical
shape, rotated in one direction, said charged toner being applied to it by means of
a magnetic brush or a non-magnetic monocomponent toner charging member.
- "curvature of the CTC" is the curvature of the surface of said cylindrical CTC in
the development zone and is expressed as the radius of said cylinder.
- "reference surface of the CTC" is the surface of the CTC when NO toner is present
on said CTC.
- "development zone" is the volume between the printhead structure (106) and the toner
delivery means (101), wherein the toner cloud (104) is formed. In Fig. 2, a non-limitative
example of a development zone is given. It is the zone (volume) (111) between the
printhead structure (106) and the reference surface of the CTC (103), determined by
the surface of said printhead structure (106) facing said CTC, the perpendicular planes
dropping from the edges of the array of printing apertures (107) to said reference
surface of the sleeve of said cylindrical CTC and said reference surface itself (112)
within the volume determined by said perpendicular planes.
6. Detailed Description of the Invention
[0025] It has been found that printing speed and printing quality in DEP devices depend
on the amount of charged toner particles that is presented per unity of time in the
vicinity of the printing apertures. It was found that an easy and simple way to provide
the possibility to control the amount of charged toner particles that is presented
per unity of time in the vicinity of the printing apertures, was using, in a DEP device,
a CTC whereon the toner particles are provided from a rotating magnetic brush. It
was found that it is important to control the ratio of the linear surface speed in
mm/s of the sleeve of said magnetic brush (LSM) and of the image receiving substrate
(LSS), in order to provide good printing quality and good maximum density.
[0026] It was found that a DEP device, wherein the toner particles are provided in the vicinity
of a printhead structure (106) by a charged toner conveyer (CTC), having a linear
surface speed LSC in mm/s; wherein the charged toner particles are applied to said
CTC by a magnetic brush with a sleeve rotating at a linear surface speed LSM in mm/s
and wherein the toner image receiving substrate (109) travels at a speed LSS in mm/s,
could provide good printing quality and high maximum density when the ratio of said
surface speed of said sleeve (LSM) to said speed of said image receiving substrate
(LSS) is equal to or larger than 0.50.
[0027] It was found, that the achievable maximum density for a given speed of said image
receiving substrate (LSS) and for a given ratio of LSM/LSS could be further enhanced
by using a DEP device wherein the ratio the linear surface speed of the CTC (LSC)
to the linear speed of said image receiving substrate (LSS) was also equal to or larger
than 0.5.
[0028] The maximum density and the image quality, especially from the point of view of "banding"
(i.e. the formation of bands of different density perpendicular on the travelling
direction of said image receiving substrate 109), can be enhanced when the linear
surface speed of the sleeve of the magnetic brush (LSM) is adapted to the linear surface
speed (LSC) of the CTC. The image quality, both from the viewpoint of maximum density
and banding is largely enhanced when also LSM/LSC ≥ 0.5. The banding was found to
be almost absent in the image when LSM/LSC ≥ 1.00.
[0029] In the most preferred embodiment of the present invention, LSM/LSS ≥ 1.50, LSC/LSS
≥ 1.00, LSM/LSC ≥ 1.00.
[0030] The quality of the image can further be enhanced, when the surface roughness of the
CTC is higher than 0.5 µm when measured as a Ra-roughness according to ANSI/ASME B46.1-1985,
preferably higher than 1.0 µm. It was found that the surface roughness of the CTC
influences favourably the "cloudiness" of the image. By "cloudiness" is meant an unevenness
in the image, especially visible when the image is inspected D
max in a direction perpendicular to the travelling direction of the image receiving substrate.
[0031] The CTC used in a DEP device according to the present invention can have any shape,
e.g. a belt supported by one ore more wheels, a belt sliding of a shoe, a cylinder,
etc. The material to build said CTC can vary widely, it can be a metal belt, a metallized
polymeric belt, a polymeric belt, a metal or polymeric cylinder, etc.
[0032] In order to be able to print at higher speed, it is necessary that a DEP device comprises
a printhead structure with multiple rows of printing apertures.
[0033] Therefore, a DEP device according to the present invention, preferably comprises
a printhead structure (106) with several rows of printing apertures (107).
[0034] Since printing devices are preferably kept as small as possible, it is interesting
to use, in any printing device, the smallest components possible. For that reason
a cylindrical CTC with small diameter is preferably used in any electrographic device,
and thus also in a DEP device according to the present invention, but then the problem
of providing charged toner particles in the vicinity of all printing apertures with
a nearly equal flux, rises again. We have experimentally found that there is a maximum
curvature (i.e. minimum radius) of the CTC in said development zone that can give
good print quality with a printhead comprising a given number of rows of printing
apertures. Said given number of rows of printing apertures is in fact the extension
of the array of printing apertures in the direction of the movement of the receiving
substrate, measured from the middle of the apertures in the first row to the middle
of the apertures in the last row. As a result of experimentation it has been found
that good printing quality can be obtained with a cylindrically shaped CTC that is
not fully parallel to said printhead structure, provided that said CTC has a maximum
curvature (minimum radius) given by equation I :
![](https://data.epo.org/publication-server/image?imagePath=1998/28/DOC/EPNWB1/EP96200890NWB1/imgb0001)
wherein R is the radius of the sleeve of said cylindrical CTC, B is the distance
in mm between the reference surface of the CTC (103) and the printhead structure (106)
and C is the extension in mm of the array of printing apertures (107) measured in
the direction of arrow A, as described above.
[0035] Preferably R fulfils the equation II :
![](https://data.epo.org/publication-server/image?imagePath=1998/28/DOC/EPNWB1/EP96200890NWB1/imgb0002)
Most preferably R fulfils the equation III :
![](https://data.epo.org/publication-server/image?imagePath=1998/28/DOC/EPNWB1/EP96200890NWB1/imgb0003)
[0036] This relation between curvature of said CTC and total extension of the array of printing
apertures in said printhead structure is also dependent upon the actual distance of
said CTC from said printhead structure.
[0037] Preferably, a cylindrical CTC used in a DEP device according to the present invention
and fulfilling the equations above, has a radius R ≥ 10 mm.
[0038] Said cylindrical CTC can be made movable without friction or with reduced friction
in any way known in the art. It can e.g. comprise a inner shoe over which a sleeve
is rotated without friction, or it can be a hollow cylinder mounted on an axle and
being rotated in bearings, etc.
[0039] Depending upon the application for which the printing engine according to the DEP-technique
as described above has to be used, the printhead structure is fabricated in such a
way as to impose the smallest possible implication upon the size and cost of the charged
toner conveyer used in the toner application module. In e.g. a printing device with
high printing speed of full colour images at medium spatial resolution (i.e. medium
sharpness) but high density resolution (i.e. a high number of differentiated density
levels), it is advisable to use a CTC with small curvature in the development zone
combined with a printhead structure with many rows of apertures, each of said apertures
having a rather large diameter. In a printing device with a high spatial resolution
but a low density resolution it is advisable to use a low-cost CTC with a small diameter,
combined with a printhead structure comprising only a small amount of rows of apertures,
each of said apertures having a small diameter.
[0040] The printhead structure used in a preferred embodiment of the present invention is
made in such a way that reproducible printing is possible without clogging and with
accurate control of printing density. Such a printhead structure has been described
in EP-A 719 648.
[0041] The printing apertures in a printhead structure used in a DEP device according to
the present invention can have any shape, e.g. circular, elliptical, etc. In a preferred
embodiment of the present invention, the printing apertures 107 are square.
Description of the DEP device
[0042] A non limitative example of a device for implementing a DEP method using toner particles
according to the present invention comprises (fig 1):
(i) a toner delivery means (101), comprising a container for developer (102), a charged
toner conveyer (103) and a magnetic brush (104) , this magnetic brush forming a layer
of charged toner particles upon said charged toner conveyer
(ii) a back electrode (105)
(iii) a printhead structure (106), made from a plastic insulating film, coated on
both sides with a metallic film. The printhead structure (106) comprises one continuous
electrode surface, hereinafter called "shield electrode" (106b) facing in the shown
embodiment the toner delivering means and a complex addressable electrode structure,
hereinafter called "control electrode" (106a) around printing apertures (107), facing,
in the shown embodiment, the toner-receiving member in said DEP device. Said printing
apertures are arranged in an array structure for which the total number of rows can
be chosen according to the field of application. The location and/or form of the shield
electrode (106b) and the control electrode (106a) can, in other embodiments of a device
for a DEP method using toner particles according to the present invention, be different
from the location shown in fig. 1.
(iv) conveyer means (108) to convey an image receptive member (109) for said toner
between said printhead structure and said back electrode in the direction indicated
by arrow A.
(v) means for fixing (110) said toner onto said image receptive member.
[0043] Although in fig. 1 an embodiment of a device for a DEP method using two electrodes
(106a and 106b) on printhead 106 is shown, it is possible to implement a DEP method
using devices with different constructions of the printhead (106). It is, e.g. possible
to implement a DEP method with a device having a printhead comprising only one electrode
structure as well as with a device having a printhead comprising more than two electrode
structures. The apertures in these printhead structures can have a constant diameter,
or can have a broader entrance or exit diameter. The printhead structure used in a
DEP device according to the present invention can also be a mesh of wire electrode
as described in, e.g., EP-A 390 847.
The back electrode (105) of this DEP device can also be made to cooperate with the
printhead structure, said back electrode being constructed from different styli or
wires that are galvanically isolated and connected to a voltage source as disclosed
in e.g. US-P 4,568,955 and US-P 4,733,256. The back electrode, cooperating with the
printhead structure, can also comprise one or more flexible PCB's (Printed Circuit
Board).
[0044] Between said printhead structure (106) and the charged toner conveyer (103) as well
as between the control electrode around the apertures (107) and the back electrode
(105) behind the toner receiving member (109) as well as on the single electrode surface
or between the plural electrode surfaces of said printhead structure (106) different
electrical fields are applied. In the specific embodiment of a device, useful for
a DEP method, shown in fig 1. voltage V1 is applied to the sleeve of the charged toner
conveyer 103, voltage V2 to the shield electrode 106b, voltages V3
0 up to V3
n for the control electrode (106a). The value of V3 is selected, according to the modulation
of the image forming signals, between the values V3
0 and V3
n, on a timebasis or grey-level basis. Voltage V4 is applied to the back electrode
behind the toner receiving member. In other embodiments of the present invention multiple
voltages V2
0 to V2
n and/or V4
0 to V4
n can be used. Voltage V5 is applied to the surface of the sleeve of the magnetic brush.
[0045] A DEP device according to the present invention can be operated successfully when
a single magnetic brush with multi-component developer, comprising magnetic carrier
particles and non-magnetic toner particles is used in contact with the CTC to provide
a layer of charged toner on said CTC.
[0046] In a DEP device according to a preferred embodiment of the present invention, said
toner delivery means 101 creates a layer of toner particles upon said charged toner
conveyer using two magnetic brushes with multi-component developer (e.g. a two-component
developer, comprising carrier and toner particles wherein the toner particles are
triboelectrically charged by the contact with carrier particles or 1.5 component developers,
wherein the toner particles get tribo-electrically charged not only by contact with
carrier particles, but also by contact between the toner particles themselves). The
first of said two magnetic brushes is a pushing magnetic brush, used to jump charged
toner particles to said CTC and being connected to a DC-source with the same polarity
as the toner particles. The second of said two magnetic brushes is a pulling magnetic
brush, used to remove toner particles from said CTC and connected to a DC-source with
a polarity opposite to the polarity of the toner particles. By adapting the respective
voltages applied to the surface of the respective sleeves the resulting push/pull
mechanism provides a way of applying a highly homogeneous layer of well behaved charged
toner particles upon said charged toner conveyer. The first of said magnetic brushes
was located at the side of said CTC where the jumped toner particles were carried
in the direction of the movement of said CTC towards the printing apertures in said
printhead structure. The second of said magnetic brushes was located at the other
side of the CTC, namely at the side where unused toner particles that have passed
under the printing apertures of said printhead structure are removed.
[0047] In a DEP device according to the present invention where a "jumping" magnetic brush
and a "pulling" magnetic brush are used, it is the linear surface speed of the "jumping"
magnetic brush that is meant when the abbreviation LSM is used. It is important to
control the relationships of said surface speed LSM of said "jumping" magnetic brush
with both the linear speed of the image receiving member (LSS) and the linear speed
of the CTC (LSC). The relationship of the linear speed of the "pulling" magnetic brush
to both other speeds cited immediately above does not require such a strict control.
[0048] In a DEP device according to the present invention an additional AC-source can beneficially
be connected to the sleeve of a single magnetic brush or to any of the sleeves of
a device using multiple magnetic brushes.
[0049] The magnetic brush 104 (or plural magnetic brushes) preferentially used in a DEP
device according to the present invention is of the type with stationary core and
rotating sleeve.
[0050] In a DEP device, according to a preferred embodiment of the present invention, any
type of known carrier particles and toner particles can successfully be used. It is
however preferred to use "soft" magnetic carrier particles. "Soft" magnetic carrier
particles useful in a DEP device according to a preferred embodiment of the present
invention are soft ferrite carrier particles. Such soft ferrite particles exhibit
only a small amount of remanent behaviour, characterised in coercivity values ranging
from about 4 kA/m up to 20 (50 up to 250 Oe). Further very useful soft magnetic carrier
particles, for use in a DEP device according to a preferred embodiment of the present
invention, are composite carrier particles, comprising a resin binder and a mixture
of two magnetites having a different particle size as described in EP-B 289 663. The
particle size of both magnetites will vary between 0.05 and 3 µm. The carrier particles
have preferably an average volume diameter (d
v50) between 10 and 300 µm, preferably between 20 and 100 µm. More detailed descriptions
of carrier particles, as mentioned above, can be found in EP-A 675 417, titled "A
method and device for direct electrostatic printing (DEP)".
[0051] It is preferred to use in a DEP device according to the present invention, toner
particles with an absolute average charge (|q|) corresponding to 1 fC ≤ |q| ≤ 20 fC,
preferably to 1 fC ≤ |q| ≤ 10 fC. The absolute average charge of the toner particles
is measured by an apparatus sold by Dr. R. Epping PES-Laboratorium D-8056 Neufahrn,
Germany under the name "q-meter". The q-meter is used to measure the distribution
of the toner particle charge (q in fC) with respect to a measured toner diameter (d
in 10 µm). From the absolute average charge per 10 µm (|q|/10µm) the absolute average
charge |q| is calculated. Moreover it is preferred that the charge distribution is
narrow, i.e. shows a distribution wherein the coefficient of variability (ν), i.e.
the ratio of the standard deviation to the average value, is equal to or lower than
0.33. Preferably the toner particles used in a device according to the present invention
have an average volume diameter (d
v50) between 1 and 20 µm, more preferably between 3 and 15 µm. More detailed descriptions
of toner particles, as mentioned above, can be found in EP-A 675 417, titled "A method
and device for direct electrostatic printing (DEP)".
[0052] A DEP device making use of the above mentioned marking toner particles can be addressed
in a way that enables it to give black and white. It can thus be operated in a "binary
way", useful for black and white text and graphics and useful for classical bilevel
halftoning to render continuous tone images.
[0053] A DEP device according to the present invention is especially suited for rendering
an image with a plurality of grey levels. Grey level printing can be controlled by
either an amplitude modulation of the voltage V3 applied on the control electrode
106a or by a time modulation of V3. By changing the duty cycle of the time modulation
at a specific frequency, it is possible to print accurately fine differences in grey
levels. It is also possible to control the grey level printing by a combination of
an amplitude modulation and a time modulation of the voltage V3, applied on the control
electrode.
[0054] The combination of a high spatial resolution and of the multiple grey level capabilities
typical for DEP, opens the way for multilevel halftoning techniques, such as e.g.
described in the EP-A 634 862 with title "Screening method for a rendering device
having restricted density resolution". This enables the DEP device, according to the
present invention, to render high quality images.
EXAMPLES
[0055] Throughout the printing examples, the same developer, comprising toner and carrier
particles was used.
The carrier particles
[0056] A macroscopic "soft" ferrite carrier consisting of a MgZn-ferrite with average particle
size 50 µm, a magnetisation at saturation of 36 µTm
3/Kg (29 emu/g) was provided with a 1 µm thick acrylic coating. The material showed
virtually no remanence.
The toner particles
[0057] The toner used for the experiment had the following composition : 97 parts of a co-polyester
resin of fumaric acid and bispropoxylated bisphenol A, having an acid value of 18
and volume resistivity of 5.1 x 10
16 ohm.cm was melt-blended for 30 minutes at 110° C in a laboratory kneader with 3 parts
of Cu-phthalocyanine pigment (Colour Index PB 15:3). A resistivity decreasing substance
- having the following formula : (CH
3)
3N
+C
16H
33 Br
- was added in a quantity of 0.5 % with respect to the binder, as described in WO 94/027192.
It was found that - by mixing with 5 % of said ammonium salt - the volume resistivity
of the applied binder resin was lowered to 5x10
14 Ω.cm. This proves a high resistivity decreasing capacity (reduction factor : 100).
[0058] After cooling, the solidified mass was pulverized and milled using an ALPINE Fliessbettgegenstrahlmühle
type 100AFG (tradename) and further classified using an ALPINE multiplex zig-zag classifier
type 100MZR (tradename). The average particle size was measured by Coulter Counter
model Multisizer (tradename), was found to be 6.3 µm by number and 8.2 µm by volume.
In order to improve the flowability of the toner mass, the toner particles were mixed
with 0.5 % of hydrophobic colloidal silica particles (BET-value 130 m
2/g).
The developer
[0059] An electrostatographic developer was prepared by mixing said mixture of toner particles
and colloidal silica in a 4 % ratio (w/w) with carrier particles. The triboelectric
charging of the toner-carrier mixture was performed by mixing said mixture in a standard
tumbling set-up for 10 min. The developer mixture was run in the magnetic brush for
5 minutes, after which the toner was sampled and the tribo-electric properties were
measured, according to a method as described in the above mentioned EP-A 675 417.
The average charge, q, of the toner particles was -7.1 fC.
The printhead structure (106).
[0060] Throughout all examples the same printhead structure was used. A printhead structure
106 was made from a polyimide film of 50 µm thickness, double sided coated with a
17 µm thick copper film. On the back side of the printhead structure, facing the receiving
member substrate, a ring shaped control electrode 106a was arranged around each aperture.
Each of said control electrodes was individually addressable from a high voltage power
supply. On the front side of the printhead structure, facing the toner delivery means,
a common shield electrode (106b) was present. The printhead structure 106 comprised
a four-rowed-array of printing apertures. The extension of said array of printing
apertures (C in mm) as defined above was 1.95 mm. The apertures had an aperture diameter
of 200 µm. The width of the copper ring electrodes was 175 µm The rows of apertures
were staggered to obtain an overall resolution of 200 dpi.
[0061] For the fabrication process of the printhead structure, conventional methods of copper
etching and mechanical drilling were used, as known to those skilled in the art.
The toner delivery means (101)
[0062] In all examples, the toner delivery means 101 comprised a cylindrical charged toner
conveyer (103). The charged toner conveyer 103 was connected to an AC power supply
with a square wave oscillating field of 600 V at a frequency of 3.0 kHz with + 20
V DC-offset. The CTC was a cylinder with a sleeve made of aluminum, coated with TEFLON
(trade name of Du Pont, Wilmington, USA) with a surface roughness of 2.2 µm (Ra-value)
and a diameter of 30 mm
[0063] In the different examples, the linear surface speed (LSC in mm/s) of the charged
toner conveying means (CTC) was changed. And in two more examples, the surface roughness
of said CTC was changed at constant linear surface speed.
[0064] Charged toner was propelled to this conveyer from a stationary core/rotating sleeve
type magnetic brush (104) comprising two mixing rods and one metering roller. One
rod was used to transport the developer through the unit, the other one to mix toner
with developer.
[0065] The magnetic brush 104 was constituted of the so called magnetic roller, which in
this case contained inside the roller assembly a stationary magnetic core, having
three magnetic poles with an open position (no magnetic poles present) to enable used
developer to fall off from the magnetic roller (open position was one quarter of the
perimeter and located at the position opposite to said CTC (103).
The sleeve of said magnetic brush had a diameter of 20 mm and was made of stainless
steel roughened with a fine grain to assist in transport (Ra=3 µm) and showed an external
magnetic field strength in the zone between said magnetic brush and said CTC of 0.045
T, measured at the outer surface of the sleeve of the magnetic brush.
[0066] A scraper blade was used to force developer to leave the magnetic roller. On the
other side a doctoring blade was used to meter a small amount of developer onto the
surface of said magnetic brush. Depending on the example, the sleeve was rotating
at different linear surface speeds (LSM in mm/sec), the internal elements rotating
at such a speed as to conform to a good internal transport within the development
unit. The magnetic brush 104 was connected to a DC power supply of - 120 V.
The reference surface of said CTC was placed at a distance of 600 µm from the reference
surface of said magnetic brush.
The printing engine
[0067] The distance B between the front side of the printhead structure 106 and the sleeve
(reference surface) of the charged toner conveyer 103, was set at 400 µm. The distance
between the back electrode 105 and the back side of the printhead structure 106 (i.e.
control electrodes 106a) was set to 150 µm and the paper travelled at 50 mm/sec. The
shield electrode 106b was grounded : V2 = 0 V. To the individual control electrodes
an (imagewise) voltage V3 between 0 V and -300 V was applied. The back electrode 105
was connected to a high voltage power supply of +600 V. To the sleeve of the CTC an
AC voltage of 600 V at 3.0 kHz was applied, with + 20 V DC offset.
The linear surface speed of the CTC (LSC), of the sleeve of the magnetic brush (LSM),
the paper speed (LSS) and the ratios LSM/LSS, LSC/LSS and LSM/LSC for each example
and comparative example are reported in table 1.
Measurement of printing quality
[0068] A printout made on paper with a DEP device and developer described above, was judged
for homogeneity of the image density and the maximal achieved density, measured in
reflection mode with a Macbeth Desitometer (Type TR1224).
The results are given in table 2. In this table the data on banding are summarized
according to the following ranking :
- 1:
- unacceptable : severe banding.
- 2:
- poor : banding still clearly visible.
- 3:
- acceptable : very little banding visible.
- 4:
- good : banding barely visible.
- 5:
- very good : an homogeneous image density is obtained, with almost no banding visible.
[0069] The results on cloudiness, together with the results on D
max and banding, are, were appropriate, given in table 3. In this table the data on cloudiness
are summarized according to the following ranking :
- 1:
- unacceptable : severe cloudiness.
- 2:
- poor : cloudiness still clearly visible.
- 3:
- acceptable : very little cloudiness visible.
- 4:
- good : cloudiness barely visible.
- 5:
- very good : an homogeneous image density is obtained, with almost no cloudiness visible.
[0070] In examples 1 to 10 and comparative examples 1 to 6, a CTC with diameter 30 mm was
used, i.e. R
real = 15 mm. The distance B between the surface of the CTC and the printhead structure
was 0.4 mm and the extension of the array of four rows of printing apertures (C in
mm) as defined above was 1.95 mm. When calculating the minimal R, according to formulas
I, II and III, it is found that R
min is 1.95, 4.37 and 10.27 mm respectively. This means that in the printing situation
in these examples R
real is even greater than the R
min calculated with formula III.
EXAMPLE 1 (E1)
[0071] The charged toner conveyer (the toner delivery means) was rotated at a linear surface
speed LSC of 50 mm/s. The charged toner conveyer 103 was connected to an AC power
supply with a square wave oscillating field of 600 V at a frequency of 3.0 kHz with
0 V DC-offset.
[0072] Charged toner was propelled to this conveyer from a stationary core/rotating sleeve
type magnetic brush (104). The sleeve of said magnetic brush rotated at a linear speed
LSM of 50 mm/s.
[0073] The paper (the image receiving substrate 109) travelled at a linear speed of 50 mm/s.
[0074] The results of the printing, with respect to maximum density (D
max) and banding are reported in table 2.
EXAMPLE 2 (E2)
[0075] In example 2 a print was made with the same printhead structure, CTC and magnetic
brush as described in example 1, except for the fact that said CTC was rotated at
a linear speed of 50 mm/s, the sleeve of the magnetic brush rotated again at a linear
speed LSM of 75 mm/s.
[0076] The paper (the image receiving substrate 109) travelled at a linear speed of 50 mm/s.
[0077] The results of the printing, with respect to maximum density (D
max) and banding are reported in table 2.
EXAMPLE 3 (E3)
[0078] In example 3 a print was made with the same printhead structure, CTC and magnetic
brush as described in example 1. Except for the fact that said CTC was rotated at
a linear speed of 50 mm/s, the sleeve of the magnetic brush rotated again at a linear
speed LSM of 150 mm/s.
[0079] The paper (the image receiving substrate 109) travelled at a linear speed of 50 mm/s.
[0080] The results of the printing, with respect to maximum density (D
max) and banding are reported in table 2.
EXAMPLE 4 (E4)
[0081] In example 4 a print was made with the same printhead structure, CTC and magnetic
brush as described in example 1. Except for the fact that said CTC was rotated at
a linear speed of 50 mm/s, the sleeve of the magnetic brush rotated again at a linear
speed LSM of 300 mm/s.
[0082] The paper (the image receiving substrate 109) travelled at a linear speed of 50 mm/s.
[0083] The results of the printing, with respect to maximum density (D
max) and banding are reported in table 2.
EXAMPLE 5 (E5)
[0084] Example 4 was repeated except for the fact that a "jumping" and a "pulling" magnetic
brush were used. A first magnetic brush was used to feed the charged toner particles
to said CTC and a second magnetic brush was used to remove most of said charged toner
particles from said CTC. Both magnetic brushes were from the same construction as
described above. The first of said brushes was located at the side of said CTC where
the jumped toner particles were carried in the direction of the movement of said CTC
towards the printing apertures in said printhead structure. The second of said brushes
was located at the other side of the CTC, namely at the side were unused toner particles
that have passed under the printing apertures of said printhead structure are removed.
The sleeve of the first of said magnetic brushes was connected to a DC power supply
of -200 V, the sleeve of the second of said magnetic brushes was connected to a DC
power supply of +200 V. The sleeve of said CTC was connected to an AC power supply
with a square wave oscillating field of 600 V at a frequency of 3.0 kHz with 20 V
DC-offset.
The first of said magnetic brushes (the "jumping" magnetic brush) was rotated at a
linear speed LSC of 300 mm/s, the second at a linear speed of 250 mm/s. The distance
of both of said magnetic brushes towards said CTC was set to 500 µm and the distance
of said CTC to said printhead structure was set to 400 µm. The CTC was rotated at
a linear speed of 50 mm/s.
[0085] The paper (the image receiving substrate 109) travelled at a linear speed of 50 mm/s.
[0086] The results of the printing, with respect to maximum density (D
max) and banding are reported in table 2.
EXAMPLE 6 (E6)
[0087] In example 6 a print was made with the same printhead structure, CTC and magnetic
brush as described in example 1. Except for the fact that said CTC was rotated at
a linear speed of 75 mm/s and that the sleeve of the magnetic brush rotated again
at a linear speed LSM of 75 mm/s.
[0088] The paper (the image receiving substrate 109) travelled at a linear speed of 50 mm/s.
[0089] The results of the printing, with respect to maximum density (D
max) and banding are reported in table 2, in table 3 these measurements are reported
again together with the measurement of cloudiness.
EXAMPLE 7 (E7)
[0090] In example 7 a print was made with the same printhead structure, CTC and magnetic
brush as described in example 1. Except for the fact that said CTC was rotated at
a linear speed of 150 mm/s and that the sleeve of the magnetic brush rotated again
at a linear speed LSM of 150 mm/s.
[0091] The paper (the image receiving substrate 109) travelled at a linear speed of 50 mm/s.
[0092] The results of the printing, with respect to maximum density (D
max) and banding are reported in table 2.
EXAMPLE 8 (E8)
[0093] In example 8 a print was made with the same printhead structure, CTC and magnetic
brush as described in example 1. Except for the fact that said CTC was rotated at
a linear speed of 300 mm/s and that the sleeve of the magnetic brush rotated at a
linear speed LSM of 400 mm/s.
[0094] The paper (the image receiving substrate 109) travelled at a linear speed of 50 mm/s.
[0095] The results of the printing, with respect to maximum density (D
max) and banding are reported in table 2.
COMPARATIVE EXAMPLE 1 (C1)
[0096] In comparative example 1 a print was made with the same printhead structure, CTC
and magnetic brush as described in example 1. Except for the fact that said CTC was
rotated at a linear speed of 50 mm/s and that the sleeve of the magnetic brush rotated
at a linear speed LSM of 22.5 mm/s.
[0097] The paper (the image receiving substrate 109) travelled at a linear speed of 50 mm/s.
[0098] The results of the printing, with respect to maximum density (D
max) and banding are reported in table 2.
COMPARATIVE EXAMPLE 2 (C2)
[0099] In comparative example 2 a print was made with the same printhead structure, CTC
and magnetic brush as described in example 1. Except for the fact that said CTC was
rotated at a linear speed of 150 mm/s and that the sleeve of the magnetic brush rotated
at a linear speed LSM of 22.5 mm/s.
[0100] The paper (the image receiving substrate 109) travelled at a linear speed of 50 mm/s.
[0101] The results of the printing, with respect to maximum density (D
max) and banding are reported in table 2.
COMPARATIVE EXAMPLE 3 (C3)
[0102] In comparative example 3 a print was made with the same printhead structure, CTC
and magnetic brush as described in example 1. Except for the fact that said CTC was
rotated at a linear speed of 22.5 mm/s and that the sleeve of the magnetic brush rotated
at a linear speed LSM of 50 mm/s.
[0103] The paper (the image receiving substrate 109) travelled at a linear speed of 50 mm/s.
[0104] The results of the printing, with respect to maximum density (D
max) and banding are reported in table 2.
COMPARATIVE EXAMPLE 4 (C4)
[0105] In comparative example 4 a print was made with the same printhead structure, CTC
and magnetic brush as described in example 1. Except for the fact that said CTC was
rotated at a linear speed of 22.5 mm/s and that the sleeve of the magnetic brush rotated
at a linear speed LSM of 150 mm/s.
[0106] The paper (the image receiving substrate 109) travelled at a linear speed of 50 mm/s.
[0107] The results of the printing, with respect to maximum density (D
max) and banding are reported in table 2.
COMPARATIVE EXAMPLE 5 (C5)
[0108] In comparative example 5 a print was made with the same printhead structure, CTC
and magnetic brush as described in example 1. Except for the fact that said CTC was
rotated at a linear speed of 75 mm/s and that the sleeve of the magnetic brush rotated
at a linear speed LSM of 50 mm/s.
[0109] The paper (the image receiving substrate 109) travelled at a linear speed of 50 mm/s.
[0110] The results of the printing, with respect to maximum density (D
max) and banding are reported in table 2.
COMPARATIVE EXAMPLE 6 (C6)
[0111] In comparative example 6 a print was made with the same printhead structure, CTC
and magnetic brush as described in example 1. Except for the fact that said CTC was
rotated at a linear speed of 300 mm/s and that the sleeve of the magnetic brush rotated
at a linear speed LSM of 50 mm/s.
[0112] The paper (the image receiving substrate 109) travelled at a linear speed of 50 mm/s.
[0113] The results of the printing, with respect to maximum density (D
max) and banding are reported in table 2.
EXAMPLE 9 (E9)
[0114] In example 9, example 6 was repeated but the surface roughness of the CTC was 0.38
µm instead of 2.2 µm. The CTC was rotated at a linear speed of 75 mm/s and that the
sleeve of the magnetic brush rotated at a linear speed LSM of 75 mm/s.
[0115] The paper (the image receiving substrate 109) travelled at a linear speed of 50 mm/s.
[0116] The results of the printing, with respect to maximum density (D
max) and banding and cloudiness are reported in table 2.
EXAMPLE 10 (E10)
[0117] In example 10, example 9 was repeated but the surface roughness of the CTC was 3.6
µm instead of 0.38 µm.
TABLE 1
No |
LSC* |
LSM** |
LSS† |
LSM/LSS |
LSC/LSS |
LSM/LSC |
E1 |
50 |
50 |
50 |
1.00 |
1.00 |
1.00 |
E2 |
50 |
75 |
50 |
1.50 |
1.00 |
1.50 |
E3 |
50 |
150 |
50 |
3.00 |
1.00 |
3.00 |
E4 |
50 |
300 |
50 |
6.00 |
1.00 |
6.00 |
E5 |
50 |
300 |
50 |
6.00 |
1.00 |
6.00 |
E6 |
75 |
75 |
50 |
1.50 |
1.50 |
1.00 |
E7 |
150 |
150 |
50 |
3.00 |
3.00 |
1.00 |
E8 |
300 |
400 |
50 |
8.00 |
6.00 |
1.33 |
C1 |
50 |
22.5 |
50 |
0.45 |
1.00 |
0.45 |
C2 |
150 |
22.5 |
50 |
0.45 |
3.00 |
0.15 |
C3 |
22.5 |
50 |
50 |
1.00 |
0.45 |
2.22 |
C4 |
22.5 |
150 |
50 |
3.00 |
0.45 |
6.67 |
C5 |
75 |
50 |
50 |
1.00 |
1.50 |
0.67 |
C6 |
300 |
50 |
50 |
1.00 |
6.00 |
0.17 |
* linear surface speed of the charged toner conveyer in mm/s |
** linear surface speed of the magnetic brush in mm/s |
† linear surface speed of the image receiving substrate in mm/s |
TABLE 2
No |
LSM/LSS |
LSC/LSS |
LSM/LSC |
Dmax |
Banding |
E1 |
1.00 |
1.00 |
1.00 |
0.45 |
3 |
E2 |
1.50 |
1.00 |
1.50 |
0.68 |
4 |
E3 |
3.00 |
1.00 |
3.00 |
0.73 |
4 |
E4 |
6.00 |
1.00 |
6.00 |
0.75 |
5 |
E5 |
6.00 |
1.00 |
6.00 |
0.87 |
5 |
E6 |
1.50 |
1.50 |
1.00 |
0.65 |
4 |
E7 |
3.00 |
3.00 |
1.00 |
0.75 |
4 |
E8 |
8.00 |
6.00 |
1.33 |
0.90 |
5 |
C1 |
0.45 |
1.00 |
0.45 |
0.12 |
|
C2 |
0.45 |
3.00 |
0.15 |
0.02 |
|
C3 |
1.00 |
0.45 |
2.22 |
0.23 |
|
C4 |
3.00 |
0.45 |
6.67 |
0.17 |
|
C5 |
1.00 |
1.50 |
0.67 |
0.43 |
2 |
C6 |
1.00 |
6.00 |
0.17 |
0.37 |
1 |
TABLE 3
No |
Roughness Ra in µm |
Dmax |
Banding |
Cloudiness |
E6 |
2.2 |
0.65 |
4 |
4 |
E9 |
0.38 |
0.67 |
4 |
1 |
E10 |
3.6 |
0.64 |
4 |
5 |
[0118] In examples 11 to 20 and comparative examples 7 and 8 the printing quality with DEP
devices having different CTC's having different diameters, different head structures,
and varying distances between the surface of the CTC and the printhead structure was
investigated.
[0119] In examples 11 to 14 and comparative example 3, LSM/LSS was 10, LSC/LSS was 5 and
LSM/LSC was 2. In examples 15 and 16 and comparative example 2, LSM/LSS was 8.4, LSC/LSS
was 5 and LSM/LSC was 1.68. In examples 17 to 20, LSM/LSS was 7.8, LSC/LSS was 5 and
LSM/LSC was 1.57.
[0120] The particulars of the examples 11 to 20 and comparative example 7 and 8 are summarized
hereinafter.
[0121] The toner, carrier particles, developer mixture and magnetic brush were the same
as the ones used for examples 1 to 10 and comparative examples 1 to 6. The printhead
structure had basically the same structure as the one used in the examples and comparative
examples hereinbefore, except for the number of rows of printing apertures. Also the
toner delivery means was in principle the same except for the variation in radius
(curvature). All voltages and magnetic strengths were also equal to the ones used
in the examples and comparative examples hereinbefore.
[0122] The variables in the following examples 11 to 20 and comparative examples 7 and 8
are given hereinbelow and are summarized in table 4.
Measurement of printing quality
[0123] A printout made with a DEP device and developer described above, was judged for homogeneity
of the image density. The results are given in table 5. In this table the data are
summarized according to the following ranking :
1: unacceptable: different rows of apertures are not giving any density at all.
2: poor: toner particles are passing through all printing apertures but some of said
rows of apertures have such a small density value that correction of said low-density
printing apertures by applying a different voltage to said ccntrol electrodes in said
rows of apertures does not yield an homogeneous image density.
3: acceptable: the overall image density can be tuned to be homogeneous by changing
the voltage applied to some control electrodes of some printing apertures, but the
overall printing speed is lowered considerably.
4: good: only small corrections have to be performed for some of the control electrodes
in order to become a homogeneous image density. 5: excellent: an homogeneous image
density is obtained without any minor changes to the control electrodes of any printing
aperture.
[0124] The relevant parameters of the printing engines, the radius of the CTC (R), the distance
between the reference surface of the CTC and the printhead structure (B) and the extension
of the array of rows of printing apertures (C), used in each of the examples, are
summarized in table 4.
[0125] In table 5, the printing quality of each of the examples is shown together with the
figures, showing how well R fulfils the equations I,II and III.
EXAMPLE 11 (E11)
[0126] A printhead structure with 6 rows of apertures and an extension (C) in the direction
of the printing of 3.25 mm was placed at a distance (B) from a CTC of 0.35 mm, the
radius of the CTC was 10 mm. The paper travelled at 10 mm/sec.
EXAMPLE 12 (E12)
[0127] In example 12 a print was made with the same printhead configuration and CTC as described
in example 11, but the distance of said CTC towards said printhead structure was set
to 500 µm.
COMPARATIVE EXAMPLE 7 (CE7)
[0128] In comparative example 7 the same CTC as described in example 11 was used, but for
the printhead structure, an eight-rowed-array of printing apertures was used (same
aperture diameter, copper-ring diameter and staggering). The extension of said array
of printing apertures as defined above was 4.55 mm. The distance of said CTC towards
said printhead structure was set to 350 µm.
EXAMPLE 13 (E13)
[0129] In example 13 the same CTC as described in example 11 was used, but for the printhead
structure, a four-rowed-array of printing apertures was used (same aperture diameter,
copper-ring diameter and staggering). The extension of said array of printing apertures
as defined above was 1.95 mm. The distance of said CTC towards said printhead structure
was set to 500 µm.
EXAMPLE 14 (E14)
[0130] In example 14 the same CTC as described in example 11 was used, but for the printhead
structure, a compact design was chosen. The printhead structure was formed of 2 rows
of apertures, said apertures having a square form of 200 by 200 µm, a square copper
electrode of 50 µm around each aperture, said 2 rows of apertures isolated from each
other by a 100 µm broad isolation zone. This printhead structure had a resolution
of 127 dpi and was fabricated using the technique of plasma etching. The extension
of said array of printing apertures in said printhead structure was only 0.4 mm. The
distance of said CTC towards said printhead structure was set to 350 µm.
EXAMPLE 15 (E15)
[0131] In example 15 a printhead structure having an eight-rowed-array of printing apertures
was used (200 µm aperture diameter, copper-ring diameter of 550 µm and staggered to
obtain an overall resolution of 127 dpi). The extension of said array of printing
apertures as defined above was 4.55 mm.
The CTC had a sleeve with outer diameter of 40 mm and a surface roughness of 3.0 µm
(Ra), and was fed from the same magnetic brush as described in example 11. The CTC
was rotated at a speed of 40 rpm. The distance of said magnetic brush towards said
CTC was set to 500 µm and the distance of said CTC to said printhead structure was
set to 500 µm.
EXAMPLE 16 (E16)
[0132] In example 16 a printhead structure was used, having 8 rows of printing apertures,
each aperture having a diameter of 300 µm, and a copper electrode ring with a width
of 200 µm. Each row of apertures was further separated from each other by an additional
isolating zone of 200 µm. As printhead substrate a 125 µm thick PI-foil was used.
The 8 rows of printing apertures were staggered to obtain an overall printing resolution
of 100 dpi. The extension of said array of printing apertures in said printhead structure
was 6.30 mm. The CTC as described in example 15 was used. The CTC was placed at 500
µm from said printhead structure.
COMPARATIVE EXAMPLE 8 (CE8)
[0133] In comparative example 8 a print was made with the same printhead structure and CTC
as described in example 16, but the distance of said CTC towards said printhead structure
was set to 400 µm
EXAMPLE 17 (E17)
[0134] In example 17 the same printhead structure as described in example 16 was used.
The CTC had an aluminium sleeve with outer diameter of 60 mm and a TEFLON (trade name)
coating and a surface roughness of 3.2 µm (Ra ), and was fed from the same magnetic
brush as described in example 11. The CTC was rotated at a speed of 25 rpm. The distance
of said magnetic brush towards said CTC was set to 500 µm and the distance of said
CTC to said printhead structure was set to 700 µm.
EXAMPLE 18 (E18)
[0135] In example 18 a print was made with the same printhead structure and CTC as described
in example 17, but the CTC was placed at a distance of 400 µm from said printhead
structure.
EXAMPLE 19 (E19)
[0136] In example 19 a print was made with the same printhead structure as described in
example 15 and the same CTC as described in example 17, and the CTC was placed at
a distance of 400 µm from said printhead structure.
EXAMPLE 20 (E20)
[0137] In example 20 a print was made with the same printhead structure as described in
example 13 and the same CTC as described in example 17, and the CTC was placed at
a distance of 400 µm from said printhead structure.
TABLE 4
Example |
R* |
B** |
C*** |
E11 |
10.0 |
0.35 |
3.25 |
E12 |
10.0 |
0.50 |
3.25 |
CE7 |
10.0 |
0.35 |
4.55 |
E13 |
10.0 |
0.50 |
1.95 |
E14 |
10.0 |
0.35 |
0.40 |
E15 |
20.0 |
0.50 |
4.55 |
E16 |
20.0 |
0.50 |
6.30 |
CE8 |
20.0 |
0.40 |
6.30 |
E17 |
30.0 |
0.70 |
6.30 |
E18 |
30.0 |
0.40 |
6.30 |
E19 |
30.0 |
0.40 |
4.55 |
E20 |
30.0 |
0.40 |
1.95 |
* R is the radius (expressed in mm) of the cylindrically shaped CTC (103). |
** B is the distance in mm, between the reference surface of the CTC and the printhead
structure. |
*** C is the extension in mm of said array of printing apertures (107) in the direction
of the movement of said receiving substrate (109). |
TABLE 5
Example |
Rmin Equa. I |
Rmin Equa. II |
Rmin Equa. III |
Rreal |
Quality |
E11 |
6.08 |
13.13 |
29.75 |
10.0 |
3 |
E12 |
4.45 |
10.30 |
26.47 |
10.0 |
4 |
CE7 |
11.92 |
26.12 |
58.32 |
10.0 |
1 |
E13 |
1.60 |
3.71 |
9.51 |
10.0 |
5 |
E14 |
0.09 |
0.20 |
0.45 |
10.0 |
5 |
E15 |
8.72 |
20.20 |
51.76 |
20.0 |
4 |
E16 |
16.71 |
38.72 |
99.23 |
20.0 |
3 |
CE8 |
20.35 |
45.62 |
107.27 |
20.0 |
1 |
E17 |
12.31 |
29.73 |
86.28 |
30.0 |
4 |
E18 |
20.35 |
45.62 |
107.27 |
30.0 |
3 |
E19 |
10.62 |
23.80 |
55.95 |
30.0 |
4 |
E20 |
1.95 |
4.37 |
10.28 |
30.0 |
5 |
[0138] In table 5, columns 1 to 3 the minimal radius, R, necessary for good printing, calculated
according to equation I, II and III respectively, using the values of B and C from
table 4, is reported. Column 4 gives the real R corresponding with the CTC that was
used. The values reported in this column are taken from the second column of table
4. In column 5, the printing quality is given in values from 1 to 5, 5 being the highest
quality.
[0139] From table 5 it is clear that the best results are obtained when the radius, R, fulfils
even equation III. When R fulfils no equation at all, the printing quality is very
bad, see CE7 and CE8.