U.S. patent number RE37,859 [Application Number 09/544,820] was granted by the patent office on 2002-09-24 for development control system.
This patent grant is currently assigned to Indigo N.V.. Invention is credited to Ehud Chatow, Amiran Lavon, Ishaiu Lior.
United States Patent |
RE37,859 |
Lior , et al. |
September 24, 2002 |
Development control system
Abstract
Toning apparatus for toning an electrostatic latent image,
having image and background portions at different potentials on an
imaging surface. The apparatus comprises an endless toning surface
coated with a layer of concentrated toner and engaging the imaging
surface at a toning region. The apparatus additionally comprises a
source: of voltage connected to the toning surface and electrifying
the toning surface to a voltage operative to selectively transfer
at feast a portion of the layer to image: portions on the imaging
surface. A developed mass per unit area (DMA) controller having an
input indicative of the DMA on the imaging surface is operative to
adjust the DMA on the toning surface in response to the input.
Inventors: |
Lior; Ishaiu (Rehovot,
IL), Chatow; Ehud (Raanana, IL), Lavon;
Amiran (Bat Yam, IL) |
Assignee: |
Indigo N.V. (Maastright,
NL)
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Family
ID: |
27517659 |
Appl.
No.: |
09/544,820 |
Filed: |
April 6, 2000 |
PCT
Filed: |
February 03, 1994 |
PCT No.: |
PCT/NL94/00027 |
371(c)(1),(2),(4) Date: |
April 04, 1996 |
PCT
Pub. No.: |
WO95/10801 |
PCT
Pub. Date: |
April 20, 1995 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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464851 |
Aug 17, 1995 |
5610694 |
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615187 |
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434236 |
May 4, 1995 |
5596396 |
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170347 |
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5436706 |
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727599 |
Jul 9, 1991 |
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Reissue of: |
615187 |
Apr 4, 1996 |
05737666 |
Apr 7, 1998 |
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Foreign Application Priority Data
Current U.S.
Class: |
399/57;
399/240 |
Current CPC
Class: |
G03G
15/101 (20130101); G03G 15/104 (20130101); G03G
15/105 (20130101); G03G 15/5041 (20130101); G03G
2215/00042 (20130101) |
Current International
Class: |
G03G
15/00 (20060101); G03G 15/10 (20060101); G03G
015/10 () |
Field of
Search: |
;399/57,237,239,240,241,249 ;430/117 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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990589 |
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Jun 1976 |
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CA |
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0226750 |
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Jul 1987 |
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EP |
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0306217 |
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Mar 1989 |
|
EP |
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0481516 |
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Apr 1992 |
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EP |
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1155610 |
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Jun 1969 |
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GB |
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3-279986 |
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Dec 1991 |
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JP |
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4-247472 |
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Sep 1992 |
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JP |
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WO 90/04216 |
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Apr 1990 |
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WO |
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9004216 |
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Apr 1990 |
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WO |
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9010896 |
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Sep 1990 |
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WO |
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9203765 |
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Mar 1992 |
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WO |
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9301531 |
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Jan 1993 |
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WO |
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Other References
US 5,083,165, 01/1999, Landa (withdrawn) .
Patent Abstracts of Japan, vol. 011, No. 002(P-532), Jan. 6, 1987.
(61-179480). .
Patent Abstracts of Japan, vol. 011, No. 373(P-643), Dec. 5, 1987.
(62-144184). .
Patent Abstracts of Japan, vol. 008, No. 105(P-274), May 17, 1984.
(54-15956). .
Patent Abstracts of Japan. vo. 010, No. 149(P-461), May 30, 1986.
(61-3160). .
Patent Abstract of Japan. vol. 007, No. 180(P-215), Aug. 9, 1983.
(58-82277). .
Patent Abstract of Japan. vol. 017, No. 277(P-1546), May 27, 1993.
(5-11584). .
Patent Abstracts of Japan. vol. 005, No. 150(P-081), Sep. 22, 1981,
(56-81870). .
International Search Report and Annex. .
Xerox Disclosure Journal, vol. No. 6, Nov./Dec. 1986, "Leak Free
Developer Module", Monkelbaan, E. et al., pp. 305-306..
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Primary Examiner: Pendegrass; Joan
Attorney, Agent or Firm: Fenster & Company Patent
Attorneys, Ltd.
Parent Case Text
.Iadd.RELATED APPLICATIONS
This application is a U.S. National stage application of PCT
application PCT/NL94/00027, filed Feb. 3,1994. This application is
also a continuation-in-part of U.S. patent application Ser. No.
08/434,236, filed May 4, 1995, now U.S. Pat. No. 5,596,396, which
is a continuation of U.S. patent application Ser. No. 08/170,347,
filed Feb. 3, 1994, now U.S. Pat. No. 5,436,706, which is the
national stage application of PCT application PCT/NL91/00243, filed
Nov. 291991, and is also a continuation-in-part of U.S. patent
application Ser. No. 07/727,599, filed Jul. 9, 1991, now abandoned.
This application is also a continuation-in-part of U.S. patent
application Ser. No. 08/464,851 filed Aug. 17,1995, now U.S. Pat.
No. 5,610,694, which is the U.S. national stage application of
PCT/NL93/00010, filed Jan. 11, 1993..Iaddend.
Claims
We claim:
1. Toning apparatus for toning an electrostatic latent image,
having image and background portions at different potentials, on an
imaging surface comprising: a source of liquid develops having a
given concentration of toner material; an toning surface, coated
wilt a layer of concentrated liquid developer having a higher toner
concentration than the given concentration and derived from the
source of liquid develops and engaging the imaging surface at a
toning region; a source of voltage connected to the toning surface
and electrifying the toning surface to a voltage operative to
selectively transfer at least a portion of the layer to image
portions on the imaging surface; and a developed mass per unit area
controller having an input indicative of the mass of tone material
per unit area (DMA) on the imaging surface and operative to adjust
the DMA on the toning surface, without changing the given
concentration, in response to the input.
2. Apparatus according to claim 1 further comprising: an applicator
which receives liquid developer from the source and coats a layer
of said concentrated liquid developer having a toner concentration
greater than said given concentration onto the toning surface.
3. Apparatus according to claim 2 wherein the applicator includes
an applicator electrode charged to an applicator cottage which
affects the DMA of the coating said applicator voltage being
controlled by the controller, whereby the controller is operative
to control the DMA on the imaging surface.
4. Apparatus according to claim 2 and also comprising: a squeegee
roller associated with the toning surface and charged to a squeegee
voltage different from that of the toning surface, said squeegee
voltage being controlled by the controller, whereby the controller
is operative to control the DMA on the imaging surface.
5. Apparatus according to claim 4 and further comprising a leaf
spring fixedly mounted on a first end portion thereof and having a
resilient pad mounted on a second end portion thereof, said
resilient pad being urged against said squeegee roller by said leaf
spring thereby urging the squeegee roller against said toning
surface.
6. Apparatus according to claim 1 and further comprising a DMA
sensor which provides to the controller input a signal responsive
to the DMA of the coating on the toning surface.
7. Apparatus according to claim 1 and further comprising a DMA
censor which provides a signal to the controller input responsive
to the DMA of an image area on the imaging surface.
8. Apparatus according to claim 6 wherein the DMA sensor comprises
an optical sensor associated with the toning surface for measuring
the optical density on a pre-selected portion of the toning
surface.
9. Apparatus according to claim 1 and further comprising a solids
concentration sensor which provides a signal to the controller
input responsive to the solids concentration of the liquid
developer in the source.
10. Apparatus according to claim 2 and further comprising a
temperature sensor, operative for providing an output signal to the
controller input responsive to the temperature of the liquid
developer in the source.
11. Apparatus according to claim 9 wherein the solids concentration
sensor comprises a viscosity sensor.
12. Imaging apparatus comprising: an imaging surface having a
latent electrostatic image thereon; and toning apparatus according
to any of the preceding claims operative for toning the image
portions of the late image with a layer of liquid developer.
13. Imaging apparatus according to claim 12 wherein the imaging
surface is a photoconductive surface and further comprising: a
charging station operative for charging the photoconductive surface
to a first voltage; and an exposure station operative for
selectively discharging portions of the charged photoconductive,
thereby creating a latent image comprising image portions at a
first voltage and background portions at a second voltage.
14. A replaceable toning cartridge comprising: a housing adapted
for mounting on a toner station of as imaging apparatus in
operative association with an imaging surface thereof; and toning
apparatus according to claim 1 contained in said housing.
15. Apparatus according to claim 3 and comprising: a squeegee
roller associated with the toning surface and charged to a squeegee
voltage different from that of the toning surface, said squeegee
voltage being controlled by the controller, whereby the controller
is operative to control the DMA on the imaging surface.
16. Apparatus according to claim 15 and comprising a DMA sensor
which provides to the controller input a signal responsive to the
DMA of the coating on the toning surface.
17. Apparatus according to claim 15 and comprising a DMA sensor
which provides a signal to the controller input responsive to the
DMA of an image area on the imaging surface.
18. Apparatus according to claim 3 and comprising a DMA sensor
which provides to the controller input a signal responsive to the
DMA of the coating on the toning surface.
19. Apparatus according to claim 3 and comprising a DMA sensor
which provides a signal to the controller input responsive to the
DMA of to image area on the imaging surface.
20. Apparatus according to claim 2 and comprising a DMA sensor
which provides to the controller input or signal responsive to the
DMA of the coating on the toning surface.
21. Apparatus according to claim 4 and comprising a DMA sensor
which provides to the controller input a signal responsive to the
DMA of the coating on the toning surface.
22. Apparatus according to claim 2 and comprising a DMA sensor
which provides a signal to the controller input responsive to the
DMA of an image area on the imaging surface.
23. Apparatus according to claim 4 and comprising a DMA sensor
which provides a signal to the controller input responsive to the
DMA of en image area on the imaging surface.
24. Imaging apparatus comprising: an imaging surface having a
latent electrostatic image thereon; toning apparatus according to
claim 6 operative for toning the image portions of the latent image
with a layer of liquid developer; and an intermediate transfer
member which receives the toned image from the: imaging surface and
transfers it to a further surface, wherein the DMA sensor comprises
an optical sensor associated with the toning surface for measuring
the optical density on a preselected portion of the toning
surface.
25. Squeegeeing apparatus for use in liquid imaging to squeegee an
endless moving surface, comprising: a squeegee roller having a
squeegee surface associated with said endless moving surface, and a
source of pressure applied to a central portion of the squeegee
surface and arranged such that the pressure urges the squeegee
surface against said endless surface.
26. Apparatus according to claim 25 wherein the source of pressure
is a leaf spring mounted on a first end thereof and having a second
end thereof urged toward the squeegee roller.
27. Apparatus according to claim 26 and including a resilient pad
mounted on said second end thereof, said resilient pad being urged
against the squeegee surface by said leaf spring..Iadd.
28. Toning apparatus for toning an electrostatic latent image,
having image and background portions at different potentials, on an
imaging surface comprising: a toning surface, coated with a layer
of concentrated liquid developer having a toner layer thickness,
engaging the imaging surface at a toning region; a source of
voltage connected to the toning surface and electrifying the toning
surface to a voltage operative to selectively transfer a portion,
but not all, of the thickness to image portions on the imaging
surface..Iaddend..Iadd.
29. Apparatus according to claim 28 wherein the voltage is such
that substantially none of the layer is transferred to background
portions on the imaging surface..Iaddend..Iadd.
30. Apparatus according to claim 28 and including: a source of
liquid developer having a concentration of toner particles; and an
applicator that receives liquid developer from the source and coats
said layer of concentrated developer on the toner surface, said
layer having a greater concentration of toner particles than the
liquid developer received from the source..Iaddend..Iadd.
31. Apparatus according to claim 30 wherein the applicator includes
an applicator electrode charged to an applicator voltage which
affects the mass of toner material per unit area (DMA) of the
coating..Iaddend..Iadd.
32. Apparatus according to claim 31 and including a controller that
controls the applicator voltage, thereby to control the toner layer
thickness..Iaddend..Iadd.
33. Apparatus according to claim 32 and comprising: a squeegee
roller associated with the toning surface and charged to a squeegee
voltage different from that of the toning surface, said squeegee
voltage being controlled by the controller, whereby the controller
is operative to control the DMA on the toning
surface..Iaddend..Iadd.
34. Imaging apparatus comprising: an imaging surface having a
latent electrostatic image formed thereon; and toning apparatus
according to any of claims 28-33 operative for toning the image
portions of the latent image with said concentrated liquid
developer..Iaddend.
Description
FIELD OF THE INVENTION
The present invention relates to development control in
elecrorostatographic imaging and, more particularly, to liquid
toner development control.
BACKGROUND OF THE INVENTION
Generally, there are two types of development systems employed by
electrostatographic imaging apparatus, namely, powder toner
development systems and liquid toner development systems. Although
powder toner is more conventional, liquid toner is often preferred
for its higher intrinsic resolution. Considerable efforts have been
made in the past to design more efficient and more convenient
liquid toner development systems.
Liquid toner systems are sensitive to physical changes in the
toner, such as changes in temperature, charge level, viscosity and
liquid concentration, most of which are not relevant in powder
toner systems. It is appreciated that these toner changes may
affect the development level, thereby resulting in inconsistent
imaging. Therefore, control of the liquid toner properties is
generally considered to be crucial for maintaining a constant level
of developed mass per unit area (DMA) on a photoreceptor of the
imaging apparatus.
One current approach to maintaining image quality measures the
optical density, volume and conductivity of the liquid toner used
in the process. Based on these measurements, toner concentrate,
carrier liquid a charge directs, respectively are added to the
liquid toner. Such an approach is described in U.S. Pat. No.
4,860,924, the disclosure of which is incorporated herein by
reference.
It is appreciated that construction and maintenance of a closed
loop development system as described above is both complex and
expensive. Therefore, liquid toner development systems have never
been embodied in low-cost disposable cartridges, as normally is the
case in powder toner systems.
In U.S. Pat. No. 4,341,461, the bias voltage of a development rolls
in a powder development system la adjusted in accordance with a
measurement of toner density on a developed patch on a
photoreceptor. The toner density is measured by an infrared
densitometer which apparently measures the optical density of the
layer of toner developed on the photoreceptor.
U.S. Pat No. 4,678,317 describes a liquid toner system in which a
sensor electrode is used to sense the potential of a charged
photoreceptor and to adjust a development electrode voltage to
compensate for variations in the sensed potential
WO 93/01531, the disclosure of which is incorporated herein by
reference, describes a direct-transfer liquid toner development
system. A layer of concentrated liquid toner coating a toning
roller is brought into virtual contact with a photoreceptor, and
portions of substantially even thickness are transferred from the
toning roller onto attractive portions the photoreceptor. .[.Either
the full thickness of the portions is transferred, is a binary mode
of operation or, in a quasi-binary mode of operation, a partial yet
even thickness is transferred. The voltage between the toning
roller and the photoreceptor determines the thickness of the layer
which is transferred. In the binary mode, the DMA on the
photoreceptor is substantially equal to the DMA on the toning
roller and, in the quasi-binary mode, the photoreceptor DMA is
dependent in a well defined manner upon the toning roller DMA. For
quasi-binary transfer the photoreceptor DMA is generally more
uniform than the toning roller DMA..].
The direct-transfer system described above normally employs a toner
applicator and a squeegee associated with the toning roller.
SUMMARY OF THE INVENTION
It is so object of the present invention to provide an improved
liquid toning system. In accordance with a preferred embodiment of
the present invention, consistent toning of latent electrostatic
images is maintained throughout numerous toning cycles without
adding liquid toner or liquid toner components to the system and/or
adjusting the material composition of the liquid toner, i.e. the
ratio between toner particles and carrier liquid.
In general, liquid toner including charged toner particles and
carrier liquid is contained in a sump of the toning system. The
toner particles are selectively removed from the liquid toner
during the toning process as they are transferred to a latent image
bearing surface such as a photoreceptor. The carrier liquid is
generally removed at a different rate, usually a lower rate. Thus,
the percentage of toner particles in the liquid toner, hereinafter
referred to as the solids concentration, rises or falls as a
function of the total area toned by the toning system. For some
colors, for which the proportion of printed surface to unprinted
surface is small, the solids concentration may rise with time.
When either the solids concentration or the total quantity of
liquid toner in the system is reduced below a pre-set value, either
the sump or the entire toning system is replaced or refilled.
In accordance with a preferred embodiment of the present invention,
there is thus provided a direct transfer toning system inducting an
endless toning surface, preferably the surface of a toning roller
charged to a predetermined voltage, coated with a lays of tone
concentrate, a developed mass pet unit area (DMA) controller having
an input for receiving an indication of the DMA on an imaging
outface such as a photoreceptor, and adjusting the DMA on the
toning surface in response to the received input, whereby the DMA
on the toning roller is maintained substantially constant.
Preferably, the DMA controller controls at least one voltage which
affects the DMA on the toning roller.
According to one aspect of the present invention, the input to the
DMA controller is supplied by a DMA sensor which monitors the DMA
on the imaging surface. Since, in direct-transfer toning systems,
the DMA on the imaging surface is dependent upon the DMA on the
toning rolls, by controlling the DMA on the toning roller, a
consistent toning level is readily maintained.
In one embodiment of this aspect of the invention, the DMA sense
includes an optical sensor which monitors the optical density (OD)
on the surface of the photoreceptor or, alternatively, on the
surface of the toning roller and supplies an indication of the OD
to the input. In this case, the DMA controller includes a
comparator which compares the signal to a value representative of a
desired DMA and adjusts at least one voltage to product the desired
DMA.
In accordance with another aspect of the present invention, the
input to the DMA controller is generated by a solids concentration
indicator responsive to the solids concentration of the liquid
toner. In this aspect of the invention the development system
preferably further includes apparatus for measuring the temperature
of the toner. Based on the solids concentration indication and the
measured toner temperature, the at least one voltage is adjusted
according to a look-up table to provide the desired DMA.
According to one, preferred, embodiment of this aspect of the
invention, the solids concentration indicator includes a
concentration detector which measures the concentration of solids
in the toner. The concentration detector may include a viscosity
sensor an optical sensor, a permitivity sensor or a sensor of any
other property of the tone which is related to the solids
concentration.
According to another, preferred, embodiment of this aspect of the
invention, the solids concentration indicator includes a
concentration calculator which generates an output responsive to
the total area toned by the toning system since the last
refill/replacement of the toning system. Since the total toned area
can be approximated by the number of toning cycles performed by the
system, the concentration calculator may include a counter of the
number of toning cycles performed since the last refill/replacement
of the system it is appreciated that the concentration of solids is
the liquid toner is substantially a function of the total area
towed and, thus, only approximately, a function of the number of
toning cycles performed by the system
Alternatively or additionally, the proportion of printed to
none-printed area on each of the cycles is calculated and the
amount of carrier liquid and toner particles per page is
determined. In this embodiment the concentration calculation would
be improved over the concentration calculation of the previous
embodiment.
In a preferred embodiment of the invention, the concentration
calculator is at least partially comprised in a "smart chip" which
is part of the cartridge. In this case, the smart chip stores
specific concentration information for the cartridge. This allows
replacement of cartridges without having to reset any counts on the
computer. For example, it is sometimes useful to print with inks
having special properties, such as fluorescent inks or non-process
color inks. Since these cartridges are used only intermittently and
must be removed when another special color is to be printed, it is
very useful to have the concentration information attached to the
cartridge itself.
The accuracy of the calculation of toner particle usage may be
improved by using the DMA measurement to determine more accurately
the amount of toner particles per unit printed area. A level
detector in the sump may be used to determine the amount of liquid
toner which has been removed from the sump. This determination,
together with the determination of the amount of toner particles
used in printing, can be used to give a very accurate determination
of the concentration.
For improved development control, the liquid toner in the
development system preferably includes a toner charge stabilizer
operative for maintaining a substantially constant level of
electric charge per unit mass (hereinafter Q/M) in the liquid
toner. In a preferred embodiment, the toner charge stabilizer
includes a charge director.
Further, in accordance with a preferred embodiment of the
invention, the development system includes an applicator manifold
for supplying liquid tone and coating the toning surface with a
layer of concentrated liquid toner. A portion of the applicator
manifold juxtaposed with the toning surface, hereinafter referred
to as the coating electrode, is preferably charged to a relatively
high voltage which aids the coating process. Preferably, the DMA
controller includes apparatus for adjusting the voltage on the
applicator manifold.
Preferably, the toning system includes a squeegee roller associated
with the toning surface and electrified to a voltage different from
that of the toning surface. Preferably, the DMA controller controls
the squeegee voltage on the squeegee roller is response to the
input received from the DMA monitor or the concentration indicator
and the temperature sensor, in accordance with the alternative
aspects of the present invention described above.
For the preferred embodiment described herein, the DMA on the
toning surface is a function, inter alia of the voltages on the
applicator manifold and the squeegee rolls.
In a preferred embodiment of the invention, the squeegee roller is
urged against the surface of the toning roller by the action of a
leaf spring. The portion of the leaf spring in contact with the
squeegee roller is preferably coated with a compressible pad which
is, more preferably, formed of a closed cell foam or elastomer.
In a preferred embodiment of the present invention, the toning
system is embodied in a replaceable cartridge.
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
operative in accordance with a preferred embodiment of the present
invention;
FIGS. 2A and 2B are schematic diagrams of multi-color imaging
apparatus in accordance with preferred embodiments of the present
invention;
FIGS. 3A and 3B are schematic, cross-sectioned illustrations of a
toning assembly in accordance with a preferred embodiment of the
invention;
FIG. 4A is a schematic, cross-sectional view of the toning assembly
of FIGS. 3A and 3B along line IV A;
FIG. 4B is a schematic, cross-sectional view of the toning assembly
of FIGS. 3A and 3B along line IV B;
FIG. 5A is a simplified block diagram of toning control apparatus,
in accordance with one aspect of the present invention;
FIG. 5B is a simplified block diagram of toning control apparatus,
in accordance with another aspect of the present invention;
FIG. 6 is a more detailed schematic illustration of a portion of
the assembly of FIGS. 3A-4B, is accordance with a preferred
embodiment of the present invention;
FIGS. 7 and 8 are graphs showing the dependence of liquid toner
viscosity and toner charge density, respectively, on toner
temperature; and
FIG. 9 is an experiment-based graph showing the dependents of DMA
on toner concentration.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Reference is now made to FIG. 1 which illustrates imaging apparatus
constructed and operative in accordance with a preferred embodiment
of the present invention.
The apparatus of FIG. 1 includes a drum 10 arranged for rotation in
a direction generally indicated by arrow 14. Drum 10 is covered by
as imaging surface 16 such as a cylindrical photoconductive surface
made of selenium, a selenium compound, an organic photoconductor or
say other suitable photoconductor known in the art.
In operation, drum 10 rotates and surface 16 is charged by a
charger 18 to a generally uniform, predetermined, voltage typically
on the order of -900 to -1000 volts. Charger 18 may be any type of
charges known in the art, such as a corotron, scorotron or charging
roller.
Continued rotation of drum 10 brings charged surface 16 into image
receiving relationship with an exposure means such as a light
source 19, which may be a laser or LED 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 electrostatic latent
image on charged photoconductive surface 16 by selectively
discharging portions of the photoconductive surface, image portions
being at a first voltage and background portions at a second
voltage. The discharged portions preferably have a voltage of
between zero and about (-200) volts.
Other methods of providing an electrostatic latent image on the
imaging surface (and other types of imaging surfaces) are also
useful in the practice of the invention. For example the imaging
surface may be an electrostatic master in which case the light
source is omitted, or an ionographic or other system as is known in
the art may be substituted for the photoreceptor, charger and light
source.
Continued rotation of drum 10 brings charged photoconductive
surface 16, bearing the electrostatic latent image, into operative
engagement with the surface 21 of a toning roller 22 which is part
of a toning assembly 23, more fully described blow with reference
to FIGS. 3A, 3B, 4A and 4B. In a preferred embodiment of the
present invention, assembly 23 is contained is a disposable
cartridge which may be replaced after a preselected number of
imaging cycles or after the liquid toner contained therein is
effectively depleted.
Toning roller 22 rotates is a direction 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. Surface 21 of toning roller 22 is preferably composed of a
soft polyurethane material, preferably made more electrically
conductive by the inclusion of conductive additives, while the bulk
of toning roller 22 may be composed of any suitable electrically
conductive material and preferably includes a metal core.
Alternatively, drum 10 may be formed of a relatively resilient
material, and in such a case surface 21 may be composed of either a
rigid or compliant material.
As described below, surface 21 is coated with a thin layer of
liquid toner, preferably having a high concentration of charged
toner particles. In the present example the charges art assumed to
be charged negatively. Developer roller 22 is charged to a voltage
which is intermediate the voltage of the charged and discharged
areas on photoconductive surface 16, preferably in the order of
-500 to -600 volts.
When surface 21 bearing the layer of liquid toner is engaged with
photoconductive surface if of drum 10, the difference in potential
between toning roller 22 and surface 16 causes selective transfer
of the layer of concentrated liquid toner to surface 16, thereby
toning the latent image. Depending on the choice of toner charge
polarity and the use of a "write-white" or "write-black" system,
the layer 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. In a preferred
embodiment of the invention, the concentration of toner on surface
if is between 20 and 40 percent solids, more preferably between 25
and 30 percent solids.
For multicolor systems, as shown in FIG. 2A, a plurality of toning
rollers, one for each color, are provided. The toning rollers are
sequentially engaged with surface 16 to develop sequentially
produced latent images. The plurality of toning rollers 22 are part
of a respective plurality of toning assemblies 23, wherein each
assembly includes liquid toner of a different color.
Alternatively, as shown in FIG. 2B, the plurality of toning
assemblies 23 may be positioned side by side as for example on a
chassis (not shown). The toning assembly containing the desired
color for printing is brought into alignment by moving the chassis
sideways as indicated in the drawing. The toning assembly to be
used is then urged against drum 16 by a spring or other means (not
shown).
In one preferred mode of operation, hereinafter referred to as the
binary mode, attracted portions of the toner layer are completely
transferred to the photoreceptor surface. Alternatively, in another
preferred mode of operation, hereinafter referred to as the
quasi-binary mode, the selective transfer of toner from surface 21
to surface 16 is only partial. The quasi-binary mode is achieved
when the voltage difference between the image portions and the
voltage of surface 21 is relatively low and/or the developed mass
per unit area (DMA) on surface 21 is relatively large (typically
0.2 milligram per square centimeter). However even in the
quasi-binary mode, the resultant DMA on surface 16 is strongly
dependent upon the DMA on surface 21 of toning roller 22.
For the quasi-binary system, the difference in potential (i.e. the
voltage) between the image areas on surface 16 and surface 21 is
chosen so that only the desired amount of charged toner particles
are transferred to charged portions of surface 16. In this system
the voltage and the total charge on the particles in the toner
layer are chosen such that the direction of the electric field
reverses itself within the layer. That portion of the layer which
is between the reversal plane and surface 16 will be attracted to
surface 16 and the rest of the layer will be attracted to surface
21 If the viscosity and cohesiveness of the layer art not too high,
the layer will split along the reversal plane. Providing the charge
per unit mass is kept constant, the DMA which is transferred to
surface 16 will be more uniform then that on surface 21. However,
the DMA on imaging surface 16 is dependent on the thickness and DMA
of the layer on surface 21.
The latent image toned by means of the processes described above
may then be directly transferred to a desired substrate in a manner
well known in the art. Alternatively as shown in FIG. 1, there may
be provided an intermediate transfer member 40, which may be a drum
or belt and which is in operative engagement with photoconductive
surface 16 of drum 10 bearing the developed image. Intermediate
transfer member or rotates in a direction opposite to that of
photoconductive 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 receives the toner image from
photoconductive surface 16 and transfers it to a final substrate
42, such as paper. A heater 45 may be disposed internally of
intermediate transfer member 40, 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 imaging 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. Pat. No. 4,684,238, PCT Publication
WO 90/04216 and U.S. Pat. No. 4,974,027, the disclosures of all of
which are incorporated herein by reference.
In a preferred embodiment of the invention the various layers of
intermediate transfer member 40 are formed by the following
method:
FORMULATION
Blend A is prepared by diluting 100 grams of adhesive (preferably
Chemlok 218 distributed by Lord Chemical) with 100 grams of MEK
solvent. 5.2 grams of conductive carbon black (preferably Printer
XE2, distributed by Degussa). The mixture is charged into an 01
attritor (Union Process) and ground for 5 hours at 10.degree.
C.
Blend B is prepared by mixing 30 grams of SylOff 7600 (Dow Corning
with 3 grains of SylOff 7601 (Dow Corning) and 450 grams of
n-Hexene and shaking the mixture well.
Blend C is prepared by blending 90 grams of Polyurethane resin
(Monotane A20) with 90 grams of Monotone A30 (C.I.L., England) and
heating and stirring the blend undo vacuum at 80.degree. C., for 16
hours and at 120.degree. C., for an additional hour.
MANUFACTURING PROCESS
A metal core for the intermediate transfer member is coated with
the required layers by the following process:
The metal core is painted with a thin layer of Blend A and dried
for one hour at 110.degree. C.,
The inner side of a mold having a diameter approximately 4
millimeters larger than the: core is dip coated with Blend B. The
coated mend is cured for one hour at 110.degree. C.
The coated mold and the coated core are preheated to 80.degree. C.
before casting. The hot mold is filled with hot (120.degree. C.)
Blend C. The core is carefully inserted into the mold and the
system is cured for 8 hours at 135.degree. C. Removal of the cured
intermediate transfer member is aided by dripping Isopar I. (Exxon)
or the inner side (edge) of the mold.
A 3 micrometer thick release layer is added to the intermediate
transfer member by dip coating the member in RTV 236 dispersion
(Dow Corning) and curing the layer.
The resulting layer has a thickness of approximately 2 millimeters
and the resistivity of the Blend C material at 50.degree. C. is
about 10.sup.9 ohm-cm.
Following the transfer of the toner image in substrate 42 or to
intermediate transfer member 40, photoconductive surface 16 engages
a cleaning station 49, which may be any conventional cloning
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 photoconductive surface
16.
In a preferred embodiment of the invention a pre-transfer discharge
lamp (not shown) is used to reduce charge on the portion of the
photoreceptor behind the toner (i.e., on the image portions), it
being noted that the background portions are discharged during the
formation of the latent image. This reduces the amount of arcing
which occurs during transfer of the image to the intermediate
transfer member. A preferred embodiment of a pre-transfer discharge
lamp is disclosed in US. Pat. No. 5,166,734, the disclosure of
which is incorporated herein by reference.
The present inventors have found that, if such a pre-transfer lamp
is used and a roller charger is used for charger 18, then lamp 58
may be omitted.
Reference is now made to FIGS. 3A and 4A, which illustrate in more
detail developer assembly 23 in accordance with a preferred
embodiment of the present invention. In addition to toning roller
22, which has been described above, toning assembly 23 preferably
includes a squeegee roller 78, a cleaning roller 84, an applicator
64 and an agitator 66, all contained within a preferably
replaceable housing 75. The lower part 77 of housing 75,
hereinafter referred to as a sump 77, is at least partially filled
with liquid toner. All of the above mentioned elements contained in
75 are described below is greater detail.
In operation, agitator 66 rotates in a preselected direction
constantly agitating the toner in sump 77, thereby ensuring the
homogeneity of the toner throughout the toning process. Agitator 66
is preferably powered through an input shaft 68, as seen
particularly in FIG. 3A. Input shaft 68 is preferably also
associated with toner pumping apparatus which will be described in
detail below.
Reference is now also made to FIGS. 3B and 4B which illustrate
additional portions of developer assembly 23 not seen in FIGS. 3A
and 4A. Assembly 23 preferably includes a gear pump 100 having a
pair of interlaced clogged gears 102 which rotate in opposite
directions, as indicated generally by arrows 103. This rotation of
gears 102 provides upward pumping action which pumps tone from an
intake pipe 104, associated with sump 77, to an output pipe 106
associated with a toner application manifold 108 having a lower
level 107 and an upper level 109. In a preferred embodiment of the
invention, application manifold 108 is formed within applicator 64,
which is preferably made of a rigid, non-conductive, preferably
plastic, material. The upper surface 112 of applicator 64, i.e. the
surface juxtaposed with surface 21 of toning roller 22, is
preferably coated with a conductive layer. The conductive layer is
preferably charged to a high voltage, preferably in the order of
-1100 to -1200 volts. Surface 112 is hereinafter referred to as
applicator electrode 112.
During operation of assembly 23, toner is pumped by pump 100 out of
sump 77 and into application manifold 108. As seen in FIG. 3B pipe
106 connects pump 100 to lower level 107 of manifold 108, while
FIG. 4A shows a toner passage 111 between lower level 107 and upper
level 109. By virtue of the pressure produced at pump 100, the
toner in upper level manifold 109 is released via a plurality of
application tunnels 114, through applicator electrode 112 of
applicator 64, into on application region 116 formed in the narrow
space between roller 22 and electrode 112.
The voltage difference between electrode 112 and toning roller 22
causes repulsion of the charged toner particles in application
region 116 from electrode 112 and attraction of the particles to
toning roller 22, thereby coating toning roller 22 with a layer of
concentrated liquid toner.
As shown in FIGS. 4A and 4B, squeegee roller 78 is situated near
surface 21 of toning roller 22 and is preferably urged by a leaf
spring 80 against surface 21. Squeegee roller 78 is preferably
constructed of a rigid conductive material, optionally coated with
a thin layer of polymer material, and is preferably biased by a
voltage in the order of -1000 V. such that the outer surfer of
squeegee 78 repels the charged particles of the toner layer on
surface 21. The mechanical pressures and the electric repulsion of
roller 78 are operative to squeegee the layer of toner, so that the
layer of toner will be mere condensed and uniform as surfaces 21 of
roller 22 comes into contact with image carrying surface 16.
Since coating region 116 preferably extends to the vicinity of
squeegee roller 78, as can be seen in FIG. 4A, additional toner
particles may be coated onto surface 22, in accordance with the
voltage on squeegee roller 78. Thus, squeegee roller may also set
as a coating electrodes. By adjusting the pressure applied by leaf
spring 80 and by biasing the roller to an appropriate voltage, the
thickness and density of the toner layer can be adjusted to a
desirable level.
Squeegee roller 78 preferably rotates in a direction opposite that
of toning roller 22, such that there is substantially zero relative
motion between their respective surfaces at the region of contact.
To one embodiment of the invention, the common surface spend of
rollers 22 and 78 is approximately 2 inches per second, which
preferably matches the speed of imaging surface 16.
The excess fluid which is removal by squeegee roller 78 is returned
by gravity to sump 77 for reuse.
The solids content of the layer is mainly a function of the
mechanical properties of the rollers and of the voltages applied
and pressures and is only slightly influenced by the initial toner
concentration for a considerable range of initial toner
concentrations.
Reference is now made to FIG. 6, which illustrates in more detail
squeegee roller 78 urged by leaf spring 50. Leaf spring 50
preferably includes a relatively rigid metal spring body 90 and a
relatively soft, preferably compressible, pad 92. Pad 92 is
attached to spring body 90 at the portion of leaf spring 80 which
urges roller 78, such that direct contact between spring body 90
and roller 78 is avoided. It should be appreciated that pad 92
protects squeegee 78 from being scratched or otherwise damaged and,
thus, extends the useful lifetime of squeegee 78. Pad 92 is
preferably farmed of a resilient material, preferably a closed-cell
foam or elastomer, such as Hydrine, Neoprene to Nitrile. A
preferred material is a soft closed cell and hydrocarbon resistant
material such as Epichlorohydrin elastomer available from Regumi,
Petach Tikva, Israel.
It is a feature of a preferred embodiment of the present invention
that scratching of squeegee roller 78 is prevented by virtue of pad
92. It should be noted that other techniques and/or apparatus
tested in rise past have failed to prevent such wear of the
squeegee. Even Teflon coating of the leaf spring has failed to
provide adequate protection.
As described above, the layer of liquid toner which is deposited on
surface 21 of roller 22 is selectively transferred to
photoconductive surface 16 in the process of toning the latent
image. In principle, the portions of the toner layer that have not
been used in the development of the latent image need not be manual
from toning roller 22. However, a cleaning station 84, comprising a
sponge or a brush or similar apparatus, is preferably provided to
remove the remaining toner concentrate from surface 21 of toning
roller 22, especially if the toner is of a type which is discharged
by the electric fields in the interface between the surfaces of
toning roller 22 and surface 16. The toner so removed returns by
gravity to sump for reuse after being remixed with the remaining
liquid toner by agitator 66.
Cleaning station 82 (shown in FIGS. 4A and 4B) preferably comprises
a sponge collar 84, which is preferably formed of a resilient open
cell material, such as foamed polyurethane, 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, thereby removing residual toner from
surface 21 before the application of new toner. In a preferred
embodiment of the invention, sponge roller 84 rotates in the same
direction as toning roller 22, as indicated generally by arrow 85,
but at a surface velocity approximately 10 times higher than that
of roller 22. For example, if surface 21 of toning roller 22 moves
at a spend of 2 inches per second, the surface of roller 84 moves
at approximately 20 inches per second. The relative motion between
the two surface assists in soaping toner off surface 21.
It should be appreciated that the different parts of toning
assembly 23, as described to detail above, may be constructed of
inexpensive materials and contained in a plastic housing 75, such
that the entire toning assembly can be replaced when the liquid
toner is at the end of its useful lifetime. Thus, it is a feature
of the present invention that the toning assembly may be
disposable, in contrast to prior art liquid toner systems which are
not generally suitable for being disposable apparatus.
Reference is now made to FIGS. 5A and 5B which are simplified block
diagrams of two preferred embodiments of toner control apparatus in
accordance with the present invention. FIG. 5A shows apparatus for
controlling the DMA on the toning roller, based on measurement of
the DMA on the toning roller or on the imaging surface. FIG. 5B
shows apparatus for controlling the DMA based on measurements of
physical properties of the toner which have been found to affect
the DMA and/or calculation of toner properties based on usage of
the cartridge.
In both embodiments, the toning control apparatus preferably
includes a voltage control unit 120 operative for adjusting the
voltage of one or both of application electrode 112 or squeegee
roller 78. In the apparatus of FIG. 5A, the voltages are adjusted
is accordance with signals received from a DMA monitor 122. DMA
monitor 122 receives an input from a DMA sensor, which is
preferably an optical sensor 124 such as infrared densitometer
which views surface 21 of toning roller 22, imaging surface 16 or
Intermediate transfer member 40. Optical sensor 124 is operative
for generating an output, responsive to the optical density (OD) of
the respective surface which is received by DMA monitor 122.
In a preferred embodiment of the invention, the DMA is optically
measured on the intermediate transfer member. This measurement has
been found to be more accurate than measuring the DMA in other
places.
DMA monitor 122 preferably compares the output of optical sensor
124 to a pre-determined value which is indicative of the desired
DMA required. While the optical density may be measured on either
roller 21 or surface 16, either measurement may be rotated to a
desired DMA and optical density on the imaging surface. If the
optical density is measured on the imaging surface, a patch is
generally toned on the imaging surface to act as a reference.
In the apparatus of FIG. 5B the voltages of squeegee roller 78 and
electrode 112 are adjusted based on command signals received from a
DMA calculate 126. In one preferred embodiment of the present
invention, the DMA calculator includes a developer usage indicator
127 operative for providing calculate 126 with an indication
responsive to the total area developed by development assembly 23,
or to the number of copies/prints developed. The DMA calculator
than determines, preferably by reference to an electronic "look-up
table", the appropriate voltages of surface 112 and roller 78 to
give the desired DMA.
Alternatively, the proportion of printed to non-printed area on
each of the cycles is calculated and the amount of carrier liquid
and toner particles per page is determined. In this embodiment the
concentration calculation would be improved over that of the
previous embodiment.
In a preferred embodiment of the invention, the usage indicator
and/or DMA calculator are at least partially comprised in a "smart
chip" which is part of the cartridge. In this case the smart chip
stores specific concentration information for the cartridge. This
allows replacement of cartridges without having to reset any counts
on the computer. For example, it is sometime useful to print with
inks having special properties, such as fluorescent inks or non
process color inks. Since these cartridges are used only
intermittently and must be removed when another special color is to
be printed, it is very useful to have the concentration information
attached to the cartridge itself.
The accuracy of the calculation of toner particle usage may be
improved by using the DMA measurement to more accurately determine
the amount of toner particles per unit printed area. A level
detector in the sump may be used to determine the amount of liquid
toner which has been removed from the sump. This determination,
together with the determination of the amount of toner particles
used is printing can be used to give a very accurate determination
of the concentration.
The DMA is a function of the charge per unit mass of the toner, the
solids concentration and the temperature. Therefore, in an
alternative embodiment of the invention, the develops usage
indicator is replaced by a toner concentration sensor 128 which
provides an electric output responsive to the solids concentration
in the liquid toner. Toner concentration sensor 128 may include a
toner viscosity senses 129 which may be a differential pressure
sensor. Alternatively, the concentration sensor may include an
optical sensor for measuring the optical density of the tone in the
sump, as ultrasonic sensor or a permitivity sensor for measuring
properties of the toner concentrate which are related to the solids
concentration in the sump.
The toner temperature affects both the viscosity and charge density
(Q/M) of the toner and, thus, the DMA. Therefore, in a preferred
embodiment of the invention, the development control system
includes a toner temperature sensor 130, preferably located ice the
tone sump. Temperature sensor 130 provides DMA calculator 126, in
the embodiment of FIG. 5B with an electric input responsive to the
temperature of the liquid toner. The temperature input is used by
calculator 126, using stored DMA vs. temperature data, in
determining the control signals generated to voltage control unit
126.
FIGS. 7 and 8 illustrate the temperature dependence of the toner
viscosity (in centipoise) and toner charge density (in microcoulomb
per gram), respectively for the preferred toner. The curve marked
"Marcol-82" in FIG. 7 is the temperature vs. viscosity curve for
the carrier liquid used in the preferred tone. By using took up
tables based on experimental graphs such as FIGS. 7 and 8, DMA
monitor 122 (or calculator 126 performs the required temperature
compensation.
FIG. 9 is a graph of experimental data showing the relationship
between the DMA (on toning roller 22) and the solids concentration
in the toner for the preferred toner for various squeegee 78 to
roller 22 voltage differences. As can be seen in FIG. 9, the DMA on
roller 22 remains fairly stable over a wide range of toner
concentrations but drops rapidly under a predetermined level of
toner concentration. Thus, by including experiment-based look-up
tables in the circuitry of DMA calculator 126, toner concentration
data can be properly interpreted to corresponding DMA data.
Additionally, the charged and discharged voltage on the
photoreceptor may be measure or calculated (based on usage of the
photoreceptor) using methods which are well known in the art. The
charging voltage may then be adjusted as may be the voltage of
roller 22. This generally requires the adjustment of the applicator
and squeegee voltages as well. It is also possible to use the
applicator and squeegee voltage to compensate for aging effects is
the photoreceptor.
It is a feature of a preferred embodiment d the present invention
that liquid toner can be used ova a wide range of concentrations.
By proper compensation of the voltages of squeegee roller 78 and
electrode 112, the DMA on toning roller 22 (and hence of imaging
surface 16) can be maintained substantially constant. This can be
appreciated from FIG. 9, where it is seen that differences in the
voltage between squeegee roller 78 and toning roller 22 result in
corresponding difference in the DMA on roller 22.
A preferred toner for use in the invention is prepared as
follows:
COMPOUNDING
865.4 grams of Surlyn 1605 ionomer (DuPont), 288.5 grams of Mogul-L
(Cabot), 28.8 grams of copper Phtalocynin (Cookson Pigments) and
17.3 grams of Aluminum tristearate (Merck) are compounded on an
Idon two roll mill at 150.degree. C., for 40 minutes.
SOLUBILIZATION
1000 grams of the result of the compounding step and 1500 grams of
Marcol 82 mineral oil (EXXON) are charged into a Ross double
planetary mixer (two gallon size), preheated to 200.degree. C.,
(hot oil heating). The material is heated without mixing for one
hour. Mixing is then started as low speed (speed control setting 2)
for 50 minutes, then raised to a higher speed (SCD 4) for an
additional 50 minutes. By this time the material is completely
solubilized and homogeneous. The material is discharged from the
mixer while still warm After cooling the material is passed though
a cooled meat grinder three times.
SIZE REDUCTION
862.5 grams of ground material from the previous step (at 40%
non-volatile solids concentration) and 1437.5 grams of Marcol 82
are loaded into a 1S attritor (Union Process) equipped with 3/16 "
carbon steel balls. The mixture is ground at 250 RPM for 30 hours
at 55.degree. C. The material is manually recycled through the
system three times. The material is then diluted to the required
concentration (normally 8-12% non-volatile solids) with Marcol 82
and screened through a 300 micrometer screen. The material is
magnetically treated to remove metal contamination as is known in
the art.
CHARGING
The resulting concentrated toner is charged with the following
combination of materials.
1-Lubrizol 890 (Lubrizol Corporation) is added at a level of 80
milligrams per gram solids and 1 milligram per gram of Marcol 82;
and
2-Petronate L (Witco) is added at a level of 20 milligrams per gram
solid. The system is left to equilibrate overnight before use.
Other color liquid toners are produced by a similar process.
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 following claims:
* * * * *