Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02387333 2005-02-25
IMPROVED LATENT IMAGE DEVELOPMENT APPARATUS
FIELD OF THE INVENTION
The present invention relates to development apparatus
in general and, more particularly, to latent image
development apparatus in electrophotographic imaging
systems.
BACKGROUND OF THE INVENTION
The method of developing a latent image formed on a
photoconductive surface by means of electrophoretic
transfer of liquid toner is well known in the art. In this
method, charged particles suspended in a non-polar
insulating carrier liquid migrate under the influence of
an electrostatic field and concentrate in an image forming
configuration upon relatively charged or discharged areas
of a photoconductive surface. The developed image is then
transferred to a substrate, such as paper, either directly
or by means of one or more intermediate transfer members.
In US Patent 4,504,138 a different method for the
developing of a latent image is described. This patent
describes applying a thin viscous high density layer of
toner particles on the circumferential surface of a roller
and bringing the layer so formed to the photoconductive
surface. Transfer of selected portions of the toner layer
onto the photoconductive surface then occurs due to the
electric field induced by the latent image.
In Canadian Patent 990589, a method of developing
electrostatic images is described which involves producing
a film of liquid toner on a first applicator and bringing
the applicator in contact with the final substrate which
carries a latent image, thereby to develop the image. A
second applicator bearing a layer of carrier liquid is then
brought into contact with the substrate to remove
background deposits and to squeegee out excess liquid. The
film of liquid toner described in Canadian Patent 990589
has between 2 - 4 per cent of toner concentrate dispersed
within the carrier liquid.
A latent image development apparatus described in U . S .
Patent No. 4,327,664 includes a porous, resilient sponge,
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development roller which is circumferentially surrounded by
a net of fine mesh size. The developer roller is urged
against the latent image carrying surface of a drum and
liquid toner, which is carried in the roller is squeezed
out of the compressed sponge through the fine net. Toner
particles which are contained in the liquid toner are
selectively deposited, by electrophoresis, onto the surface
of the drum to form an image.
U.S. Patent 4,400,079 describes a liquid toner
development system for developing a latent image on a
photoreceptor that uses a non-contacting developer roller.
The development roller surface may move in the same
direction as the photoreceptor surface or in the opposite
direction.
Most of the above mentioned apparatus, as well as many
other techniques which are known in the art, are concerned
with producing a layer of toner on the surface of a
developing roller and transferring the entire thickness of
the layer to image of a latent image on an image bearing
substrate. For such systems, the uniformity of the layer
thickness is important, since this thickness determines the
density of the image. Normally, it is very difficult to
control the uniformity of the developing layer even by
expensive and complicated means, especially when the layer
thickness is generally a function of the previous imaging
history of the apparatus.
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SUMMARY OF THE INVENTION
It is an object of the present invention to provide
simplified apparatus for the development of latent images
in electrophotographic imaging systems by transfer of
concentrated liquid toner, wherein the optical density of
toner in the toned regions of the final image is
substantially uniform.
In preferred embodiments of the present invention a
developer roller, preferably made of resilient material, is
urged against an image forming surface, such as a
photoreceptor, that has an electrostatic latent image
comprising image areas at a first voltage and background
areas at a second voltage formed thereon. The developer
roller is coated with a relatively thin film of
concentrated liquid toner material having a given layer
thickness. At least a portion of this layer thickness is
selectively transferred to the image-forming surface in
accordance with the latent image formed thereon.
According to one aspect of the invention, the
developer is electrified to a voltage which is intermediate
the first and second voltages . In a preferred embodiment of
the invention, the developer voltage is selected to cause
only a portion of the layer thickness to transfer to the
image areas of the latent image . The present inventors have
found that when the developer voltage is properly chosen,
the density of toner particles per unit area (DMA) is less
strongly dependent on the thickness of the toner
concentrate layer on the developer roller or on the layer' s
solids concentration. Thus, even if the thickness of the
layer on the developer roller varies by an unacceptable
amount, the non-uniformity of the layer transferred to the
image forming surface is improved at least by a factor of
two.
In a second aspect of the invention, the thickness
uniformity of the toner concentrate layer on the developer
is improved by supplying the toner concentrate preferably
from a sponge roller which is urged against the developer
roller and which travels at a different speed from that of
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the developer roller at the point of contact between the
two rollers . Increased uniformity results even if the toner
concentrate remaining on the developer roller is not
removed from the roller before application of a new layer
of toner concentrate. When the applicator roller and
developer rollers move at the same speed at the point of
contact, there is a substantial "memory" of the prior image
which non-uniformly effects the developed toner particle
mass per unit area (DMA) in the layer on the developer
roller.
In a preferred embodiment of the invention, the
concentration of toner particles on the layer is increased
by application of an electrified squeegee roller to the
layer before the transfer to the imaging surface.
In a preferred embodiment of the invention, the
applicator roller moves in a direction opposite to that of
the developer roller at the point of contact between them.
In one preferred embodiment of the invention, the
developer roller is coated by developing thereon a layer of
toner particles by electrophoresis from liquid toner using
a stationary plate type developer.
Preferably, the coating step is followed by
squeegeeing the layer on the developer roller with a
squeegee roller at a high voltage and with high pressure in
order to remove a large portion of the liquid therein,
before transfer of all or a portion of the resultant
thickness of the layer to the image forming surface.
Further, material remaining on the developer roller
after development of the latent image is preferably removed
in a cleaning step before the recoating of the developer
roller.
In a preferred embodiment of the invention, the
developer roller may be cleaned by a tandem roller system
in which a first, biased squeegee, roller removes the toner
particles from the developer roller by electrostatic
transfer. A second, sponge cleaning, roller removes the
toner particles from the biased squeegee roller by
abrasion, preferably aided by an electrostatic field. The
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toner is removed from the sponge roller by a blade which
indents the surface of the sponge and scrapes the material
which is extruded away. Preferably, one or both of the
squeegee-developer or squeegee-sponge surfaces is wetted by
a cleaning liquid or dilute toner to aid in transfer and
removal of the toner particles. The toner so removed is
preferably recycled and used for recoating the developer
roller.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood and
appreciated more fully from the following detailed
description, taken in conjunction with the drawings in
which:
Fig. 1 is a schematic diagram of imaging apparatus
constructed and operated in accordance with a preferred
embodiment of the present invention; and
Fig. 2 is a more detailed schematic diagram of a
developer assembly constructed and operated in accordance
with a preferred embodiment of the present invention.
Fig. 3 is a schematic diagram of a developer assembly
illustrating an alternative cleaning system in accordance
with a preferred embodiment of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Reference is made to Figs. 1 and 2 which illustrate
imaging apparatus constructed and operative in accordance
with a preferred embodiment of the present invention.
The apparatus includes a drum 10 preferably having a
cylindrical photoreceptor surface 16 made of selenium, a
selenium compound, an organic photoconductor or any other
suitable photoconductor known in the art.
During operation, drum 10 rotates in the direction
indicated by arrow 13 and photoreceptor surface 16 is
charged by a charger 18 to a generally uniformly
predetermined voltage, typically on the order of 1000
volts. Charger 18 may be any type of charger known in the
art, such as a corotron, a scorotron or a roller.
Continued rotation of drum 10 brings charged
photoreceptor surface 16 into image receiving relationship
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with an exposure device such as a light source 19, which
may be a laser scanner (in the case of a printer) or the
projection of an original (in the case of a photocopier).
Light source 19 forms a desired latent image on charged
photoreceptor surface 16 by selectively discharging a
portion of the photoreceptor surface, the image portions
being at a first voltage and the background portions at a
second voltage. The discharged portions preferably have a
voltage of less than about 100 volts.
Continued rotation of drum 10 brings the selectively
charged photoreceptor surface 16 into operative contact
engagement with a surface 21 of a developer roller 22.
Developer roller 22 preferably rotates in a sense opposite
that of drum 10, as shown by arrow 13, such that there is
substantially zero relative motion between their respective
surfaces at the point of contact. Developer roller 22 is
most preferably urged against drum 10.
In one embodiment of the invention, developer roller
22 is formed with a metal core coated with, preferably, 1-2
mm of a soft elastomer material having a Shore A hardness
of preferably 20-40. In one embodiment of the invention,
this coating is made conductive, preferably, to a
resistivity between 105 and 10' ohm-cm. In this embodiment,
the conductive layer is either covered with a smooth
elastomer layer or is formed by casting or other process to
have a smooth surface, preferably better than N3.
In a second embodiment of the invention, the soft
elastomer material, which may be non-conductive, is coated
with a very thin electroconductive layer, such as for
example a metal or conducting lacquer layer, which is
electrically attached to the metal core. This conductive
layer is preferably covered by a thin (preferably 15 to 60
micrometer) layer of conducting polymer having a
resistivity, preferably, between 10' to 109 ohm-cm.
Alternatively, drum 10 may be formed of a relatively
resilient material, and surface 21 may be composed of
either a rigid or compliant material.
As described below, surface 21 is coated with a thin
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layer of liquid toner, which is preferably very highly
concentrated liquid toner. Developer roller 22 itself is
charged to a voltage which is intermediate the voltage of
the charged and discharged areas on photoreceptor surface
16.
When surface 21 bearing the layer of liquid toner
concentrate is engaged with photoreceptor surface 16 of
drum 10, the difference in potential between developer
roller 22 and surface 16 causes selective transfer of the
layer of toner particles to surface 16, thereby developing
the latent image. Depending on the choice of toner charge
polarity and the use of a "write-white" or "write-black"
system as known in the art, the layer of toner particles
will be selectively attracted to either the charged or
discharged areas of surface 16, and the remaining portions
of the toner layer will continue to adhere to surface 21.
When liquid toner having a very high concentration of
solids at development is used, as in the preferred
embodiments of the present invention, there is little if
any electrophoresis and the entire thickness of the layer
or a controllable portion of the thickness is transferred
to the image areas of the latent image at substantially the
same toner concentration as the layer on the developer
surface.
In an alternative, especially preferred, embodiment of
the invention, the voltage difference between the image
portions of the latent image and the developer roller is
reduced to a value at which only part of the thickness of
the toner concentrate layer is transferred from the
developer roller to the image portions of the latent image .
The thickness of the layer that is transferred depends
mainly on the charge per unit volume in the layer and
depends only slightly on the local thickness or solids
concentration of the layer. Thus, even if the layer on the
developer roller is not uniform, the layer transferred to
the image areas has a uniform DMA and thus a uniform
optical density.
This phenomenon is probably due to the following
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effect: When a voltage is applied across the toner
concentrate layer between the development roller and the
image areas on the image forming surface, an electric field
between the two surfaces is generated. This field is
strongest at the image-forming surface and is reduced by
the charge in the layer, at points within the layer itself.
When a high voltage is applied to the toner concentrate
layer, the electric field within the layer is
unidirectional, and acts to urge the entire toner layer
toward the imaging surface at image regions. When the
impressed voltage is low, the electric field may reverse at
some point in the layer. For those portions of the layer
between this point and the developer roller the electric
field actually acts to force the toner particles toward the
developer roller.
If the cohesiveness of the layer is not too high, the
layer will split at or near this point, with part of the
toner layer being transferred to the image-forming surface
and part remaining on the developer roller. The amount of
solids which is transferred is dependent only on the charge
per unit mass in the layer and is not a strong function of
the layer thickness or the exact concentration of toner
particles in the layer. Thus, development system of the
present invention is seen to be substantially less
sensitive to variations in application parameters which are
difficult to control.
Furthermore, since the DMA is basically directly
proportional to the voltage difference applied, the DMA can
be easily controlled by changing this voltage. In
particular, in a preferred embodiment of the invention, a
sensor 100, as known in the art, is placed on the image
forming surface downstream of the development region to
measure the optical density of the image (and hence the
DMA).
The measured value of optical density is then supplied
to control electronics 102 which is operative to control a
power supply 104 which supplies voltage to developer roller
22.
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If the preferred liquid toner of the invention is
utilized at a concentration of 25-30% toner particles on
the developer layer at a DMA of 0.2 mgm/cm2 (with
variations of between about 0.17 and 0.25 mgm/cmz), the
transferred layer will preferably be about 0.15 mgm/cm2
with worst case variations of less than ~10%.
In this situation a voltage difference between the
image portion and the developer roller of 500-600 volts
will result in complete transfer of the layer, while a
voltage difference of between 300 and 500 volts will result
in the above-described more uniform partial transfer at a
process speed of 50 mm/sec.
The use of such partial development dramatically
reduces the effect of possible non-uniformities in the
toner layer on surface 21. Specifically, the present
inventors have found that a layer non-uniformity of
approximately ~20 (i.e, a difference of up to ~20% in toner
layer density between different areas) on developer surface
21 may be reduced, by using partial development, to a
non-uniformity of substantially less than ~10% on the
image portions of the latent image on photoreceptor surface
16. For lower initial non-uniformities, for example ~5%,
the non-uniformities are reduced to the 1-2% range.
This process results in an image of more uniform
density and is especially useful for half-tone imaging in
which the image density is to be controlled by the
percentage of area to be printed.
Other liquid toner concentrations, as high as 40-50%,
with the preferred or other toner materials, can also be
used in the practice of the invention for the layer on the
developer. For these other toners, other concentrations or
for different process speeds, the exact required voltage is
determined by experimentation.
For multicolor systems, a plurality of developer
rollers may be provided, one for each color, spaced
circumferentially around the photoreceptor which are
sequentially engaged with photoreceptor surface 16 to
develop sequentially-produced latent images.
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In a preferred embodiment of the invention, roller 22
is coated by an applicator assembly generally indicated by
reference numeral 23.
Applicator assembly 23 includes a toner dispenser 62
which can be visualized as having the shape of a flute,
i.e. a cylindrical tube having a plurality of holes at
different locations along its longitudinal dimension,
through which liquid toner is dispensed onto the surface 64
of an applicator roller 65. Applicator 65 is preferably
formed of a metal core 66 covered with a relatively thick
layer 68 of a resilient open-cell foam (sponge), such as
foamed polyurethane, which preferably contains conductive
additives. Preferably, the bulk resistivity of the
polyurethane (without the holes) is between 10' and 10g
ohm-cm. In a preferred embodiment, surface 64 of applicator
roller 65 is resiliently urged against surface 21 of
developer 22, for example, by virtue of a spring 72 which
acts upon the ends of core 66.
As can be seen in Fig. 2, dispenser 62 is preferably
forced into applicator roller 65 such that a depression is
formed in the outer portion of applicator roller 65,
thereby deforming surface 64. The continuous deformation of
surface 64 and compression of layer 68 is operative to open
cells of layer 68 which may occasionally clog during the
operation of developer assembly 23 and the successive
release of the deformation is operative to fill the cells.
Most of the toner dispensed from dispenser 62 is rapidly
absorbed by layer 68 of applicator roller 65, and is
homogeneously distributed within layer 68 due to the spongy
open-cell structure of the layer and the deformation of the
roller. The necessary pressure for dispensing the toner is
preferably supplied by a small pump (not shown) which pumps
the toner from a toner container (not shown) at a preset
pressure. Any suitable pump and any suitable container
known in the art may be used for this purpose, as well as
any other suitable means for providing the desired toner
pressure (such as a pressured tank containing the desired
liquid toner). Preferably, surplus toner unabsorbed by
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layer 68 returns to the container for reuse.
In a preferred embodiment of the present invention,
developer roller 22 and applicator roller 65 rotate in the
same rotational direction (indicated by arrows 13 and 70 in
Fig. 2, respectively), such that their surfaces move in
opposite directions. In this embodiment, applicator roller
65 is operative to scrub surface 21 and to remove the
residual toner (which normally remains after the selective
transfer of toner to surface 16) on surface 21 while
applying a new, homogeneous, toner layer to the surface
electrophoretically. More specifically, in a preferred
embodiment, the absolute velocity of surface 64 is
preferably approximately 2 - 3 times greater than that of
surface 21.
In the absence of this scrubbing action and if toner
remaining on the developer roller after development of the
image is not removed, the DMA on the development roller
will be uneven, with up to 30~ variations . Furthermore, the
toner which remains on the developer roller after
development of the image is highly concentrated, and not
easily removed, especially if a sponge roller is used for
cleaning, so as not to damage surface 21.
For the preferred scrubbing type application, as
surfaces 21 and 64 merge into contact at surface merge line
74, the residual toner is scraped off surface 21 by the
open cells of surface 64, due to the substantial relative
motion between the surfaces and the pressure applied by
spring 72. During the relatively long period of surface
engagement, the scraped toner is indistinguishably mixed
with the new toner carried by surface 64, and a homogeneous
layer of toner remains on surface 21 as the surfaces
disengage at divergence line 76.
Roller 65 is preferably electrified by a D.C. source,
to a different voltage than that of surface 21, in order to
induce electrophoretic transfer of toner particles from
roller 65 to surface 21. The physical contact between the
surfaces is operative more to squeegee and homogenize the
applied layer of toner, rather than to apply the layer of
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toner, which is applied, as aforesaid, by electrophoresis.
In general, the solids concentration of the toner rises
considerably during the electrostatic application of the
toner to surface 21.
In a preferred embodiment of the invention, a liquid
toner of 5°s - 10°s solids concentration is supplied by
dispenser 62 to roller 65. After application onto the
developer roller, the layer has a solids concentration of
between 15 and 20 percent.
When a more concentrated toner is supplied by
dispenser 62, applicator 65 may further or alternatively
be connected to an a.c voltage source, which is operative
to somewhat reduce the viscosity of the toner and
generally to cause the deposition of a smoother layer
on surface 21 of developer roller 22.
In general it is desirable that the liquid toner layer
which develops the latent image have as high a solids
concentration as possible, preferably 30-50~.
In a preferred embodiment of the invention, developer
assembly 23 further includes a squeegee roller 78 in
operative contact with roller 22 downstream of dispenser
roller 65 and before roller 22 contacts drum 10.
Preferably squeegee roller 78 is electrified with a voltage
comparable with that of applicator 65, such that the outer
surface of the squeegee repels the charged particles of the
toner layer on surface 21. Squeegee roller 78 is also
preferably resiliently urged against roller 22 such that
liquid carrier is removed from the layer as it passes the
squeegee roller. The mechanical pressure and the electric
repulsion of roller 78 are operative to squeegee the layer
of toner, so that the layer is more condensed and uniform
as the layer reaches image carrying surface 16. By
adjusting the mechanical pressure and by biasing the roller
to an appropriate voltage, the concentration of the toner
layer can be adjusted to a desirable level.
Thus, in a preferred embodiment, the liquid toner is
supplied to roller 78 at a concentration less than that
required for optimal development of the latent image . When
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roller 78 is urged against surface 21 of developer roller
22, it mechanically removes excess toner fluid from the
layer impressed on surface 21, and when charged with a
suitable electric potential, it repels the charged toner
particles and causes them to more closely adhere to surface
21. The excess fluid which has been removed is recovered
for reuse. The solids content of the layer is mainly a
function of the mechanical properties of the rollers and of
the applied voltages and pressures and is only slightly
influenced by the initial concentration for a considerable
range of initial toner concentrations.
In a preferred embodiment of the invention, squeegee
roller 78 comprises an aluminum core which is anodized and
coated with a thin layer (approximately 50 micrometers) of
polyurethane.
In principle, the system described above does not
require that the portions of the toner layer that have not
been transferred to drum 10 in the development of the
latent image be removed from developer roller 22 between
cycles. However, the inventors have found, that the toner
uniformity can be further improved if residual toner on the
developer roller is removed between coating cycles. For
this purpose a cleaning station 82 may be provided, which
may comprise a sponge or a brush or similar apparatus, to
remove the excess toner concentrate from surface 21 of
developer roller 22. The toner so removed may then be
pumped back for reuse, after mixture with fresh toner,
through dispenser 62 into the sponge of applicator 65.
Cleaning station 82 preferably comprises a sponge
roller 84, which is preferably formed of a resilient open
cell material similar to that of layer 68 of roller 65.
Roller 84 is situated such that it resiliently engages a
portion of surface 21 between the transfer area (i.e. the
area of surface 21 engaged by surface 16) and the
application area (i.e. the area of surface 21 engaged by
surface 64), thereby removing residual toner from surface
21 before the application of new toner. In a preferred
embodiment of the invention, sponge 84 may be supplied with
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toner carrier liquid which may assist in cleaning surface
21 by loosening and carrying away the residual toner
particles scraped off the surface.
An alternative preferred embodiment of a cleaning
system 110, especially suitable for removing residual toner
from the developer roller, is shown in Fig. 3. Cleaning 110
comprises a tandem roller arrangement in which a first,
biased squeegee, roller 112 removes residual toner
particles from developer roller 22 by electrostatic
transfer. To this end roller 112 is biased to a voltage
that, in conjunction with the developer roller voltage,
causes the charged toner particles to be attracted to
roller 112. The general construction of roller 112 is
preferably, similar to that described above for roller 78.
A second, sponge cleaning, roller 114, removes the
toner particles from the biased squeegee roller 112 by
abrasion, preferably aided by an electrostatic field. The
toner is removed from the sponge roller by a blade 116
which indents the surface of the sponge and scrapes the
material which is extruded away. In certain circumstances,
depending on the toner material used, one or both of the
squeegee-developer or squeegee-sponge surfaces is wetted by
a cleaning liquid or dilute toner to aid in transfer and
removal of the toner particles.
The toner removed by any of the methods is preferably
recycled and used for recoating the developer roller.
It has been found that such cleaning, even if it is
not perfect, tends to reduce or eliminate any "memory"
effects on the development roller. Cleaning station 82 may
be especially useful in the event the toner is of a type
which becomes discharged by the electric fields in the
interface between the surfaces of developer roller 22 and
drum 10.
The latent image developed by means of the process
described above may be directly transferred to a desired
substrate from the image forming surface in a manner well
known in the art. Alternatively, as shown in Fig. 1, there
may be provided an intermediate transfer member 40, which
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may be a drum or belt and which is in operative engagement
with photoreceptor surface 16 of drum 10 bearing the
developed image. Intermediate transfer member 40 rotates
in a direction opposite to that of photoreceptor surface
16, as shown by arrow 43, providing substantially zero
relative motion between their respective surfaces at the
point of image transfer.
Intermediate transfer member 40 is operative for
receiving the toner image from photoreceptor surface 16 and
for transferring the toner image to a final substrate 42,
such as paper, Disposed internally of intermediate
transfer member 40 there may be provided a heater 45, to
heat intermediate transfer member 40 as is known in the
art. Transfer of the image to intermediate transfer member
40 is preferably aided by providing electrification of
intermediate transfer member 40 to provide an electric
field between intermediate transfer member 40 and the image
areas of photoreceptor surface 16. Intermediate transfer
member 40 preferably has a conducting layer 44 underlying
an elastomer layer 46, which is preferably a slightly
conductive resilient polymeric layer.
Various types of intermediate transfer members are
known and are described, for example in U.S. Patent
4,684,238, PCT Publication WO 90/04216 and U.S. Patent
4, 974, 027 .
Following the transfer of the toner image to substrate
42 or to intermediate transfer member 40, photoreceptor
surface 16 engages a cleaning station 49, which may be any
conventional cleaning station. A scraper 56 completes the
removal of any residual toner which may not have been
removed by cleaning station 49. A lamp 58 then completes
the cycle by removing any residual charge, characteristic
of the previous image, from photoreceptor surface 16.
The cleaning system shown in Fig. 3 is also used, in
a preferred embodiment of the invention, in place of
cleaning station 49. In such case, a somewhat softer and
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more conformal roller is used so as to insure good contact
between the squeegee roller 112 and the image forming
surface.
In an alternative embodiment of the invention,
reversal transfer is used. In this embodiment, the desired
image is formed by the areas of toner concentrate which
remain on surface 21 of developer roller 22 after the
development of photoreceptor surface 16, and developer
roller 22 and not drum 10 which is then brought into
operative association with an intermediate transfer member
or a final substrate so as to obtain a print of the desired
image. Any preferred embodiment of the developer assembly
described above may also be used in the context of this
embodiment.
In a further preferred embodiment of the invention,
applicator assembly 65 may be replaced by a curved,
electrified plate developer situated parallel to the
surface of developer roller at about 6 o'clock on the
developer roller. Liquid toner at about 1-10% solids
concentration preferably, between 5-10~ concentration is
fed into the region between the plate and the developer
roller and plates the developer roller with a layer having
approximately 5-20~ toner solids, preferably, 15-20o toner
solids. The squeegee roller is then operative to further
concentrate the layer to the desired concentration for
developing the latent image. In this embodiment, if
cleaning station 49 is provided, a toner layer having a ~5°s
uniformity is presented to the image forming surface.
A preferred, but by no means limiting, liquid toner
material for use in the present invention is prepared in
the following manner:
Compounding
865.4 g of SurlynTM 1605 Ionomer (DuPont), 288.5
g Mogul-L carbon black (Cabot), 28.8 g Endurophtal blue
BT583DTM (Cookson) and 17.3 g aluminum stearate (Merck) are
blended for 20 minutes on a two roll mill heated to 150°C
until the blend is homogeneous. The blended material is
removed from the mill and shredded in preparation for the
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next step.
Plasticizing
2 Kg of the blended material and 2 Kg of MarcolTM 82
(EXXON) are heated for one hour in a double planetary
mixer, without mixing. The material is then mixed for 45
minutes at low speed and for 30 minutes at high speed. The
material is discharged, while still warm, from the mixer,
shredded and ground in a cooled meat grinder in preparation
for grinding.
Grinding-Size Reduction
690 g of plasticized material is ground together with
1610 g of MarcolTM 82 in an attritor charged with 3/16"
carbon steel balls. The material is ground at 250 RPM for
30 hours at 55°C ~ 3°C. The resulting material is diluted
to 10o non-volatile solids (NVS) content and screened
through a 300 micrometer screen to remove unground
particles. Any metallic contaminating material in the toner
is removed by magnetic treatment and the resulting material
is charged with charge director to form a 10o NVS liquid
developer, suitable for the present invention.
It will be appreciated by persons skilled in the art
that the present invention is not limited to what has been
particularly shown and described hereinabove. Rather, the
scope of the present invention is defined only by the
claims that follow:
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