U.S. patent number 3,907,695 [Application Number 05/099,646] was granted by the patent office on 1975-09-23 for liquid developer.
Invention is credited to Alan B. Amidon, Robert M. Ferguson, Joseph Mammino.
United States Patent |
3,907,695 |
Amidon , et al. |
September 23, 1975 |
Liquid developer
Abstract
Development of an electrostatic latent image is obtained with a
chemically stable, nonaqueous, ambipolar, liquid developer
comprising an oleaginous vehicle, solid colorant particles, a
dispersant soluble in the liquid developer which is capable of
substantially supressing background deposits, and a fixing agent
miscible with the liquid which penetrates the copy paper.
Inventors: |
Amidon; Alan B. (Penfield,
NY), Mammino; Joseph (Penfield, NY), Ferguson; Robert
M. (Penfield, NY) |
Family
ID: |
26796320 |
Appl.
No.: |
05/099,646 |
Filed: |
December 18, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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839801 |
Jul 1, 1969 |
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Current U.S.
Class: |
430/115;
430/112 |
Current CPC
Class: |
G03G
9/18 (20130101); G03G 13/10 (20130101); G03G
15/102 (20130101) |
Current International
Class: |
G03G
15/10 (20060101); G03G 13/06 (20060101); G03G
13/10 (20060101); G03G 9/00 (20060101); G03G
9/18 (20060101); G03G 009/04 () |
Field of
Search: |
;252/62.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Torchin; Norman G.
Assistant Examiner: Brammer; J. P.
Parent Case Text
BACKGROUND OF THE INVENTION
This application is a continuation-in-part of our copending
application Ser. No. 839,801 filed July 1, 1969, now abandoned.
Claims
What is claimed is:
1. A chemically stable, nonaqueous, ambipolar, absorptive drying
electrostatographic liquid developer of low volatility having a
resistivity of from about 10.sup.8 to 10.sup.15 ohm-cm comprising
from about 30 weight percent to about 85 weight percent of an
oleaginous liquid vehical having a bulk resistivity of from about
10.sup.8 ohm-cm to about 10.sup.15 ohm-cm, from about 5 weight
percent to about 60 weight percent of a particulate colorant which
is insoluble in at least one liquid present in the liquid
developer; from about 1 weight percent to about 35 weight percent
of a dispersant of alkylated polyvinyl pyrrolidones where the alkyl
substituent has a chain length of from 10 to 20 carbon atoms which
is soluble in the oleaginous vehicle and which is capable of
substantially suppressing background deposits, and from about 5
weight percent to about 45 weight percent of a fixing agent
comprising the ester of an acid selected from the group consisting
of mono and polybasic carboxylic acids wherein said acids have from
six to 20 carbon atoms and an alcohol selected from the group
consisting of saturated and unsaturated mono and polyhydric
aliphatic alcohols having from two to 20 carbon atoms.
2. The liquid developer of claim 1 wherein said colorant comprises
a pigment predispersed in a resin matrix.
3. The liquid developer of claim 2 wherein said resin matrix
comprises an ester gum.
4. The liquid developer according to claim 1 wherein said developer
has a volatility less than about .0050 grams per square centimeter
at 60.degree.C. after about 28 days exposure.
5. The liquid developer according to claim 1 wherein said developer
has a viscosity of from about 100 to about 3,000 centipoises at
25.degree.C.
6. The liquid developer according to claim 1 wherein said
particulate colorant has a particle size of from about .01 to about
10 micron.
7. The liquid developer according to claim 1 wherein said bulk
resistivity is from about 10.sup.10 to about 10.sup.14 ohm-cm.
8. The liquid developer according to claim 1 wherein said
oleaginous liquid vehicle comprises mineral oil.
9. The liquid developer according to claim 1 wherein said fixing
agent comprises triethylene glycol dicaprylate.
10. The liquid developer according to claim 1 wherein said
oleaginous vehicle is present in an amount of from about 35 to
about 75 weight percent, said colorant is present in an amount of
from about 10 to about 35 weight percent, said dispersant is
present in an amount of from about 2 to about 25 weight percent,
and said fixing agent is present in an amount of from about 10 to
about 35 weight percent.
Description
This invention relates to imaging systems, and more particularly,
to improved developer materials and development techniques.
The formation and development of images on the surface of
photoconductive materials by electrostatic means is well known. The
basic electrostatographic process, as taught by C. F. Carlson in
U.S. Pat. No. 2,297,691 involves placing a uniform electrostatic
charge on a photoconductive insulating layer, exposing the layer to
a light and shadow image to dissipate the charge on the areas of
the layer exposed to the light and developing the resulting
electrostatic latent image by depositing on the image a finely
divided electroscopic material referred to in the art as "toner."
The toner will normally be attracted to those areas of the layer
which retain a charge, thereby forming a toner image corresponding
to the electrostatic latent image. This powder image may then be
transferred to a support surface such as paper. The transferred
image may subsequently be permanently affixed to a support surface
as by heat. Instead of latent image formation by uniformly charging
the photoconductive layer and then exposing the layer to a light
and shadow image, one may form the latent image directly by
charging the layer in image configuration. The powder image may be
fixed to the photoconductive layer if elimination of the powder
image transfer step is desired. Other suitable fixing means such as
solvent or overcoating treatment may be substituted.
Similar methods are known for applying the electroscopic particles
to the electrostatic latent image to be developed. Included within
this group are the "cascade" development technique disclosed by E.
N. Wise in U. S. Pat. No. 2,618,552;the "powder cloud" technique
disclosed by C. F. Carlson in U.S. Pat. No. 2,221,776 and the
"magnetic brush" process disclosed, for example, in U.S. Pat. No.
2,874,063.
Development of an electrostatic latent image may also be achieved
with liquid rather than dry developer materials. In conventional
liquid development, more commonly referred to as electrophoretic
development, an insulating liquid vehicle having finely divided
solid material dispersed therein contacts the imaging surface in
both charged and uncharged areas. Under the influence of the
electric field associated with the charged image pattern, the
suspended particles migrate toward the charged portions of the
imaging surface separating out of the insulating liquid. This
electrophoretic migration of charged particles results in the
deposition of the charged particles on the imaging surface in image
configuration. Electrophoretic development of an electrostatic
latent image may, for example, be obtained by flowing the liquid
developer over the image bearing surface, by immersing the imaging
surface in a pool of the developer or by presenting the liquid
developer on a smooth surfaced roller and moving the roller against
the imaging surface.
A further technique for developing electrostatic latent images is
the liquid development process disclosed by R. W. Gundlach in U.S.
Pat. No. 3,084,043, hereinafter referred to as polar liquid
development. In this method, an electrostatic latent image is
developed or made visible by presenting to the imaging surface a
liquid developer on the surface of a developer dispensing member
having a plurality of raised portions or "lands" defining a
substantially regular patterned surface and a plurality of portions
depressed below the raised portions or "valleys." The depressed
portions of the developer dispensing member contain a layer of
conductive liquid developer which is maintained out of contact with
the electrostatographic imaging surface. Development is achieved by
moving the developer dispensing member loaded with liquid developer
in the depressed portions into developing configuration with the
imaging surface. The liquid developer is believed to be attracted
from the depressed portions of the applicator surface in the
charged or image areas only. The developer liquid may be pigmented
or dyed. The development system disclosed in U.S. Pat. No.
3,084,043, differs from electrophoretic development systems where
substantial contact between the liquid developer and both the
charged and uncharged areas of an electrostatic latent imaging
surface occurs. Unlike electrophoretic development systems,
substantial contact between the polar liquid and the areas of the
electrostatic latent image bearing surface not to be developed is
prevented in the polar liquid development technique. Reduced
contact between a liquid developer and the nonimage areas of the
surface to be developed is desirable because the formation of
background deposits is thereby inhibited. Another characteristic
which distinguishes the polar liquid development technique from
electrophoretic development is the fact that the liquid phase of a
polar developer actually takes part in the development of a
surface. The liquid phase in electrophoretic developers functions
only as a carrier medium for developer particles.
While capable of producing satisfactory images, these liquid
development systems can be improved upon in certain areas.
Troublesome difficulties are, for example, encountered in liquid
development systems employing a reusable or cycling
electrostatographic imaging surface. In these systems, for example,
an imaging surface such as a selenium or selenium alloy drum type
photoconductor is charged, exposed to a light and shadow image and
developed by bringing the image bearing surface into developing
configuration with an applicator containing developing quantities
of liquid developer thereon. The liquid developer is transferred
according to the appropriate technique from the developer
applicator onto the image bearing surface in image configuration.
Thereafter, the developer pattern is transferred from the imaging
surface to a receiving surface such as paper. During the transfer
step, not all the liquid developer is transferred and therefore a
subsequent cleaning step is required.
In an electrophoretic development system, the entire imaging
surface is contacted with the liquid developer with the charged
particles separating from the carrier liquid and migrating to the
charged field or image portions. The particles strongly adhere to
the imaging surface by means of van der Waals forces since the
particles frequently come within about five hundred angstroms of
the imaging surface. The van der Waals forces are so strong that in
the subsequent transfer step, a considerable portion of the
particles remain on the imaging surface thus, producing prints of
relatively low density. In addition to poor density with transfer,
the adhering particles on the imaging surface drastically increase
the effort necessary to clean the residual developer from the
imaging surface and frequently require sufficient cleaning to
result in degradation of the photoconductor. In general,
electrophoretic development in systems employing recycling
electrostatographic imaging surfaces provides low efficiency in
both transfer of the developer to a receiving surface and in the
cleaning step.
In the polar ink development systems disclosed in U.S. Pat. No.
3,084,043, the developing liquid is relatively conductive having a
resistivity less than 10.sup.10 ohm-cm. After transfer of the
developer in image configuration from the electrostatographic
imaging surface to a receiving surface and even relatively vigorous
cleaning, a portion of this type of developer is also observed to
remain on the imaging surface. This developer residue is damaging
to cyclical use of the imaging surface. Subsequent recharging of a
photoconductor, for example, may be inadequate since the conductive
liquid may dissipate the charge. Furthermore, lateral conductivity
of the liquid developer on the photoconductor may become excessive
and the resolution of the resulting image will be poor.
An electrostatographic imaging system and the general class of
developer materials useful therein which overcomes the above noted
deficiencies is the subject of copending parent application Ser.
No. 839,801. This basic technique involves the use of a relatively
electrically nonconductive liquid developer which is substantially
uniformly distributed in the depressed portions or valleys of a
developer dispensing member. Development is obtained by placing the
applicator surface sufficiently close to the electrostatographic
imaging surface such that the relatively nonconductive liquid
developer is pulled from the recessed portions of the applicator
surface to the imaging surface in image configuration. Generally,
to provide maximum image density, it is preferred to place the
raised portions of the applicator surface in slight or gentle
contact with the imaging surface provided that the raised portions
are substantially free of liquid developer.
This principal novel development technique enables the recycling of
reusable imaging surfaces in a type of development system employing
a liquid developer. In addition, this basic technique is capable of
producing prints of improved resolution and density and reduced
background.
The liquid developers presently available, however, are not suited
to use in this type of development technique. Those liquid
developers capable of use in the development technique disclosed in
U.S. Pat. No. 3,084,043 are generally aqueous or water compatible
and thus, generally too electrically conductive. Conventional
electrophoretic liquid developers generally are relatively unstable
in that they are somewhat volatile and therefore, evaporate on
standing. The composition of electrophoretic developers may be
altered by the settling of the toner particles and there may be a
gradual toner depletion since the toner particles separate from the
carried liquid during development. In addition, electrophoretic
developers are polarity sensitive in that the material must be
specially selected to develop charge patterns of either positive or
negative charge. To insure this sensitivity to but a single
polarity, most electrophoretic developers require the presence of a
material or agent to control the polarity of charge. In addition,
since conventional electrophoretic developers contact the entire
imaging surface during development they should not contain highly
penetrating liquids since the toner particles are separated from
the liquid and the liquid must be evaporated. Penetration of the
liquid would tend to increase background deposits. This
electrophoretic separation of charged particles from the carrier
liquid results in the deposition of the toner particles on the
surface of the receiving sheet rather than within the fibrous
matrix and images so produced are poorly fixed and subject to
considerable smearing or smudging of the toner pattern. The high
volatility required in electrophoretic developers to enable removal
from background areas requires some heating means capable of
vaporizing the liquid which presents an undesired fire hazard.
Electrophoretic liquid developers require low concentrations of
toner particles in order to maintain the viscosity sufficiently low
to enable rapid development without considerable background
deposition. Such developers when employed in the development
technique described in copending application Ser. No. 839,801,
produce images of low density.
It is, therefore, clear that there is a continuing need for a
better liquid development technique and a better liquid
developer.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a
development system and developer materials which overcome the above
noted deficiencies.
It is another object of this invention to provide a liquid
developer which is chemically stable.
It is another object of this invention to provide a liquid
developer which is of low volatility.
It is another object of this invention to provide a liquid
developer which does not require the use of a charge control
agent.
It is another object of this invention to provide a liquid
developer which is capable of developing charge patterns of both
positive and negative polarity with equal ability.
It is another object of this invention to provide a liquid
developer capable of producing images of increased smudge
resistance.
It is another object of this invention to provide a liquid
developer which is fast drying and fixes by absorption.
It is another object of this invention to provide liquid developers
which are not polarity sensitive and which are stable suspensions
independent of particle surface potential or concentration.
It is another object of this invention to provide liquid developers
having high pigment contents.
It is another object of this invention to provide a liquid
development system producing prints of improved resolution and
density.
It is another object of this invention to provide an
electrostatographic imaging system employing a nonvolatile liquid
developer which produces dry prints without subjecting the print to
vaporization of liquid in the background areas.
It is another object of this invention to provide an
electrostatographic imaging system of the liquid development type
which produces dry prints with reduced background deposits.
It is another object of this invention to provide liquid
development systems and liquid developers superior to known systems
and materials.
The above objects and others are accomplished, generally speaking,
by providing an electrostatographic imaging system wherein an
electrostatic latent image is developed with a relatively
nonconductive, nonaqueous, chemically stable, ambipolar liquid
developer of low volatility which is substantially uniformly
distributed in the depressed portions or "valleys" of a developer
dispensing member which member is positioned adjacent the image
bearing surface during development.
More specifically, an electrostatic charge pattern present on an
imaging surface is developed according to the technique described
in copending parent application Ser. No. 839,801 with a chemically
stable, absorptive drying liquid developer comprising an oleaginous
liquid vehicle, solid colorant particles, a dispersant which is
soluble in the liquid developer and which is capable of
substantially completely supressing background depositions, and a
fixing agent miscible with the vehicle and which is capable of
penetrating copy paper to enable the liquid developer to dry by
absorption.
The presence of the above recited four constituents each in
specified quantities when employed as a liquid developer in
electrostatographic imaging techniques provides developed images on
ordinary paper which are highly resistant to smudging and smearing,
which have superior image density and a marked absence of
background deposits. In addition, these liquid developers are
capable of developing charge patterns of both positive and negative
polarity with substantially equal ability. These liquid developers
provide dry images which are rapidly fixed on ordinary paper in the
absence of vaporization of excess liquid or chemical reaction. In
addition to the recited four constituents, the presence of an
additional material to act as a suspending agent for the solid
colorant particles is particularly advantageous in providing
maximum uniformity of suspension of the pigment particles in the
vehicle while maintaining the desired viscosity and in maintaining
the liquid developer substantially free of agglomerates.
The liquid developers according to this invention are ambipolar.
That is, when the liquid developer is placed adjacent to an imaging
surface bearing an electrostatic charge pattern, a charge of
opposite polarity is induced in the liquid developer and this
inducement of charge in the liquid developer may be accomplished in
any particular developer with respect to either a positive or a
negative charge on the imaging surface. In other words, unlike
classical electrophoretic developers, the ambipolar developers are
equally effective in developing positive as well as negative charge
patterns on imaging surfaces, the difference being only in the
polarity of charge which is induced in the developer. Further,
unlike electrophoretic developers, migration of the charged
particles from the insulating carrier liquid plays no significant
roll. Instead, charge is induced in the entire developer which
migrates substantially intact, both liquid portion and colorant
particles, from the developer applicator to the imaging surface. To
insure this ambipolar quality, the individual constituents of the
liquid developer must possess compatible electrical properties.
Typically, the liquid developers have bulk resistivities greater
than about 10.sup.8 ohm-cm and less than about 10.sup.15 ohm-cm. In
recycling systems, the more electrically conductive the developer,
the greater the opportunity for decreased charge retention and
increased lateral conductivity on the imaging surface and therefore
poor resolution. In these systems, experience has indicated that
the bulk resistivity should generally be greater than about
10.sup.10 ohm-cm. As described in application Ser. No. 839,801, the
more electrically resistive the developer, the greater the time
constant for lateral discharge of the image. This lateral discharge
is of significance in the recycling system since for each cycle a
small residue of the developer may remain on the imaging surface
from the preceding cycle and an additional charge is placed on the
imaging surface with this residual developer still on it. Since
practical electrostatic imaging rates require a latent image life
of at least about 1 second and preferably 2 to 5 seconds, liquid
developers possessing adequate time constants for lateral
discharge, generally have resistivities of at least about 10.sup.10
ohm-cm. In addition, since the rate of development involves the
rate of charge induction through the liquid developer which is
dependent upon the resistivity of the vehicle and practical
development speeds are generally greater than about 3 inches per
second, the resistivity of a practical operating range providing
balance between conductivity, time constant in development 28 is
from about 10.sup.10 to about 10.sup.14 ohm-cm.
Contrary to the relatively high volatility of the electrophoretic
liquid developers, the liquid developer according to this invention
in general, have very low evaporation rates which permits increased
shelf life and performance life in an automatic machine while
maintaining the concentration of all constituents substantially the
same throughout their entire life span. Typically, the liquid
developers of this invention have evaporation rates such that after
about 28 days exposure at a temperature of 60.degree.C. there is a
weight loss of less than about .0050 grams per square centimeter of
surface area exposed. In minimizing fluctuation in concentrations
of materials and in extending useful life of the developer, it is
preferred that this weight loss be less than about .004 grams per
square centimeter.
The liquid developers according to this invention are nonaqueous.
That is, they are not water or water compatible materials since
such materials generally have relatively high evaporation rates and
are relatively conductive. The liquid developer has low shear
viscosity ranges of up to about 3,000 centipoises measured at
25.degree.C. Such viscosities are practical for development systems
employing development speeds generally of the order of from about 5
to about 20 inches per second. Increased development speeds of the
order of 200 inches per second requires a lower viscosity,
typically of the order of about 100 centipoises. The viscosity is
in part dependent on the colorant loading of the vehicle and as the
concentration of colorant is increased, the viscosity of the liquid
developer increases and the operable development speed is
accordingly lowered. Control of the balance between colorant
loading and concentration of other constituents to obtain the
desired image density and development speed may be readily
determined by one skilled in the art within the proportional limits
hereinafter set forth.
The liquid developers of the present invention are fixed by
absorption. That is, the developer is absorbed by the copy paper
after transfer or during imaging. Image fixing does not rely on
evaporation, oxidation or precipitation of any component of the
liquid developer. Typically, the liquid developers of this
invention require only about 1 to 2 seconds to dry with the solid
colorant and the developer liquid penetrating into the paper and
substantially no colorant particles being held in relief on the top
surface of the paper. Thus, the liquid developers of this invention
provide a substantially instantaneous dry copy on ordinary paper
and since the colorant particles are held within the matrix of the
paper, provide excellent resistance to smudging.
Any suitable oleaginous vehicle contributing to the above
properties may be employed. By oleaginous vehicles, it is intended
to include oils, oil like vehicles or vehicles resembling the
properties of oils. Typically, the oleaginous vehicles have bulk
resistivities of from about 10.sup.8 ohm-cm to about 10.sup.15
ohm-cm. Typical materials within this group which may be employed
alone or in combination include among others mineral oil, the
vegetable oils such as castor oil and its oxidized derivatives,
peanut oil, coconut oil, sunflower seed oil, corn oil, rapeseed oil
and sesame oil. In addition, fluorocarbon oil such as DuPont's
Freon solvents, Krytox oils, silicon oils, kerosene, oleic acid and
mineral spirits may be employed. Mineral oils are especially
preferred as vehicles for liquid developers because they are
readily available in numerous viscosity grades and are colorless,
odorless, nontoxic and of low volatility.
Any suitable solid colorant material may be employed in the liquid
developer. To obtain image permanence, it is preferred that the
colorant be fast to light. The solid colorant may be of any
suitable size. Typically, the colored marking particles are from
about 0.01 to about 10 microns in size. For superior image
resolution, it is preferred that the colored marking particles be
from about 0.1 microns to about 1 micron. Typical solid colorants
include solid finely divided colored materials such as pigments,
xerographic toners and other marking particles. Typical pigments
include carbon black, charcoal and other forms of finely divided
carbon, quinacridones, phthalocyanine blues, iron oxide,
ultramarine blues, zinc oxide, titanium dioxide and benzidine
yellow. Typical xerographic toners include finely divided
thermoplastic resins or blends of thermoplastic resins in which
pigments such as carbon black are dispersed.
The dispersants are incorporated to provide substantially uniform
wetting of the colorant in the oleaginous liquid and dispersion of
the colorant material in the liquid developer. The dispersants
further function to reduce colorant agglomerates and sedimentation
and serve to maintain the colorant material in stable suspension
without flocculation. A principal function of the dispersant is to
suppress the deposition of deposits in the background and nonimage
areas of the imaging surface. The dispersant is miscible with the
liquid developer in order to provide an integral developer wherein
during development, there is no phase separation. The precise
mechanism by which the dispersant inhibits the deposition of
background deposits is not fully understsood. It is clear, however,
that in the absence of the presence of a dispersant, considerable
background is present. Any suitable dispersant may be employed that
is miscible with the developer vehicle. Typical dispersants
providing the dual function of dispersing the solid colorant
particles and suppressing background include alkylated polyvinyl
pyrrolidones and copolymers of alkyl vinyl ethers and maleic
anhydride which are miscible with the oleaginous vehicle of the
liquid developer. Typical alkylated polyvinyl pyrrolidones include
those wherein there is at least about one alkyl substitution for
each monomer unit the substitution generally being in the
pyrrolidone moiety and wherein the alkyl substituent has a carbon
chain length of from about 10 to about 20 carbon atoms. Also
included are polymers containing both nonalkylated and alkylated
polyvinyl pyrrolidones, which may, for example, be prepared by
copolymerizing mixtures of the alkylated and nonalkylated monomeric
vinyl pyrrolidones. In these polymers the nonalkylated vinyl
pyrrolidone units may be present in amounts up to about 80% of the
total number of vinyl pyrrolidone units. Generally, these alkylated
polyvinyl pyrrolidones have molecular weights of from about 5,000
to about 300,000. Typical specific materials include decalated
polyvinyl pyrrolidone, dodecalated polyvinyl pyrrolidone,
tridecalated polyvinyl pyrrolidone, tetradecalated polyvinyl
pyrrolidone, pentadecalated polyvinyl pyrrolidone, hexadecalated
polyvinyl pyrrolidone and octodecylated polyvinyl pyrrolidone.
Typical copolymers of alkyl substituted vinyl ethers and maleic
anhydride include those wherein the alkyl substitution of the vinyl
ether has a carbon chain of from about 14 to 20 carbon atoms.
Typical linear polymers may be manufactured by copolymerizing the
alkyl vinyl ethers and the maleic anhydride in from about one to
one to about a three to one mole ratio of ether to anhydride
respectively. A wide range of molecular weights for these
copolymers may be employed. Generally, the most suitable materials
have molecular weights of from about 5,000 to about 15,000. In
addition, it is to be understood that derivatives such as esters
and amides of these polymers may be employed particularly where
increased surface activity is desired. Specific suitable materials
with which the maleic anhydride may be copolymerized include
tetradecyl vinyl ether, hexadecyl vinyl ether, and octadecyl vinyl
ether. In each of these two classes of materials, the length of the
alkyl chain is controlled to provide the necessary miscibility and
solubility in the oleaginous vehicle of the liquid developer.
The liquid developer may contain any suitable fixing agent.
Typically, the fixing agent provides in addition to accelerating
the penetration of the liquid developer in the copy paper and the
absorption of the developer by the copy paper, a reduction in
viscosity of the liquid developer which may have been increased by
the presence of colorant particles. In this regard, the fixing
agent may in part, provide a secondary or auxiliary vehicle for the
liquid developer. The fixing agents employed in the practice of
this invention are alkyl and alkylene esters of saturated and
unsaturated mono and poly basic carboxylic acids. Any suitable
ester of this class may be employed. Typically, the ester has a
long chain acid portion which is soluble in the vehicle while the
alcohol moiety seeks to wet and penetrate the paper. Typically, the
fixing agents are prepared from the esterification of mono and
polybasic carboxylic acids having from about six to about 20 carbon
atoms. Typical monocarboxylic acids include phthalic, caprylic,
pelargonic, capric, stearic, palmitic and oleic acid. Typical
dicarboxylic acids include adipic acid and sebacic acid. Typical
tricarboxylic acids include trimellitic acid, trimesic acid,
hemimellitic acid. The fixing agents employed in the practice in
this invention are typically prepared from mono and polyhydric
alcohols derived from saturated and unsaturated aliphatic
hydrocarbons having from about two to about 20 carbon atoms.
Typical materials include ethyl alcohol, propyl alcohol, butyl
alcohol, amyl alcohol, hexyl alcohol, octyl alcohol, decyl alcohol,
and tridecyl alcohol. Typical alkylene glycols include ethylene
glycol, diethylene glycol, triethylene glycol, propylene glycol and
dipropylene glycol. Typical specific esters include dibutyl
phthalate, butyl isodecyl phthalate, butyl octyl phthalate, butyl
benzyl phthalate, diisooctyl phthalate, di(2-ethyl hexyl)
phthalate, isooctyl isodecyl phthalate, normal octyl decyl
phthalate, diisodecyl phthalate, ditridecyl phthalate isodecyl
tridecyl phthalate, diisooctyl adipate, di(2-ethyl hexyl) adipate,
isooctyl isodecyl adipate, normal octyl decyl adipate, diisodecyl
adipate, diisooctyl sebacate, di 2-ethyl hexyl sebacate, isooctyl
palmitate, butyl stearate, butyl oleate, triethylene glycol
dicaprylate, triethylene glycol caprylate-caprate, triethylene
glycol dipelargonate, diethylene glycol dipelargonate, butanedial
dicaprylate, triisooctyl trimellitate, tri 2-ethyl hexyl
trimellitate, and mixed normal trialkyl trimellitates.
The proportions of the several constituents of the developer may be
varied over a wide range depending upon the individual properties
of each of the constituents and the operational considerations
required by the specific development system. A significant fact in
determining these proportions is the speed of development, since
with higher speeds, lower viscosity developers must be used than at
lower speeds. From the enumerated ranges given below, one skilled
in the art may readily determine the appropriate proportions for
any given development speed.
The several constituents may generally be present in a liquid
developer in amounts according to the following weight
percentages:
Oleaginous vehicle from about 30 to about 85 wt.% Colorant from
about 5 to about 60 wt.% Dispersant from about 1 to about 35 wt.%
Fixing agent from about 5 to about 45 wt.%
Within this broad range of proportions, particularly improved
results with regard to reduced background deposits and increased
smudge and smear resistance are provided with a liquid developer
having the following compositions by weight:
Oleaginous vehicle from about 35 to about 75 wt.% Colorant from
about 10 to about 35 wt.% Dispersant from about 2 to about 25 wt.%
Fixing agent from about 10 to about 35 wt.%
The formulations providing optimum image density in resolution
while maintaining background deposits at a very low level are
obtained with colorant loadings of between about 15% to about 30%
by weight.
Developers of this invention may be prepared by any suitable
technique. The liquid developers may, for example, be prepared
simply by mixing the several constituents together. To provide
homogenity, however, it is generally preferred to premix the liquid
constituents of the developer while heating and then add the solid
constituents which may include the dispersant and solid colorant.
Alternatively, the solid colorant may be comminuted separately or
together with the vehicle.
Exceptional dispersion of the pigment particles in the liquid
developer accompanied by substantially no background deposition is
obtained when the colorant particles have been previously dispersed
in a resin matrix. This predispersion of the colorant particles
enables the liquid developer to be rapidly formed and facilitates
the maintenance of the substantially uniform dispersion of the
colorant particles in the liquid vehicle without the formation of
agglomerates. The colorant particles may be predispersed in any
suitable resinous material. Generally, the resin matrix in which
the colorant particles are predispersed remains coated on the
colorant particles throughout the useful life of the liquid
developer. Typical resinous materials include phenolic resins such
as Amberol ST-137X available from Rohm & Haas Company and
terpene phenolic resins such as LTP-100 available from Pennsylvania
Industrial Chemical Corporation, polychlorinated polyphenyl resins
such as Aroclor 5460 available from Monsanto Company, betapinene
polymers, such as Gammaprene A-115 or A-125, available from
Reichhold Chemicals, Incorporated, coumarone-indene resins such as
Piccovar-75 and Piccoumaron 450-L, styrene copolymers such as
Piccolastic-75, all available from Pennsylvania Industrial Chemical
Corporation and Gilsonite hydrocarbon resins available from
American Gilsonite Company. Particularly effective dispersion of
the colorant particles is obtained when they are dispersed in an
ester gum such as those produced from the esterification of natural
resins with polyhydric alcohols. Typical of this group of ester
gums are the glycerol and pentaerythritol esters of rosin. These
resins are made by the esterification of three separate acid
molecules in the rosin in which approximately 87% of the acid
mixture is dihydroabietic acid which in turn is comprised of
approximately 50% of the hydrogenated derivative of abietic acid.
The remainder of the acid constituents includes a small percentage
of abietic acid. Typically, these ester gums include the glycerol
ester of dihydroabietic acid, the glycerol triester of abietic
acid, the triethylene glycol diester of dihydroabietic acid, and
diethylene glycol diester of dihydroabietic acid, the diethylene
glycol diester of abietic acid, the ethylene glycol ester of
dihydroabietic acid, and the ethylene glycol ester of abietic acid.
The predispersed colorant particles may be made in any suitable
manner. Typically, the colorant particle and resin are mixed
together while suspended in a liquid and the mixture is dried to
provide solid colorant particles with a resinous coating. The
predispersed colorant particles may be employed in a liquid
developer in any suitable amount. Typically, the predispersed
colorant particles contain from about 20 wt.% to about 50 wt.% of
the colorant particle and from about 50 wt.% to about 80 wt.% resin
matrix all be weight of the predispersed colorant particle.
Superior dispersion of the colorant particles in the liquid
developer over an extended period of time is obtained when the
proportion of resin matrixes is from about 55 wt. % to about 70 wt.
% by weight of the predispersed colorant particle and the amount of
the predispersed colorant present in the liquid developer is from
about 25% to about 50% by weight of the liquid developer.
The liquid developer of the instant invention may be employed to
develop an electrostatic latent image present on any suitable
electrostatographic imaging surface. Basically, any surface upon
which an electrostatic charge pattern may be formed or developed
may be employed. Typical electrostatic imaging surfaces include
dielectrics such as plastic coated papers, xeroprinting masters,
and photoconductors. Typical photoconductors that may be employed
include selenium and selenium alloys, cadmium sulfide, cadmium
sulfo selenide, phthalocyanine binder coatings and polyvinyl
carbazole sensitized with 2,4,7-trinitrofluorenone. The
electrostatographic imaging surface may be employed in any suitable
structure including plates, belts or drums and may be employed in
the form of a binder layer coated on a substrate. The imaging
surfaces may be overcoated with suitable dielectric materials in
conventional manner. Development of electrostatic latent image may
be obtained by positioning an applicator surface with liquid
developer thereon adjacent to the electrostatographic imaging
surface. Any suitable applicator surface may be employed which has
a substantially uniform pattern of raised portions and depressed
portion provided that the depressed portions are sufficiently large
to hold developing quantities of liquid developer therein. To
minimize wear on the imaging surface, it is preferred to provide
raised portions which are uniformly curved or substantially flat on
the surfaces which contact the imaging surface.
Typical applicator surfaces include, among others, porous ceramics,
metallic sponge, patterned webs or belts, capillary combs, and
cylindrical rolls having surface patterns such as single screw cuts
or trihelicoid, pyramidal or quadragravure indentations.
The applicator surface may be loaded with developer in any suitable
manner. Typical developer loading techniques include applying
developer from a roll or sponge roll or immersing the applicator in
a bath. Prior to contacting the imaging surface, the applicator
surface should be wiped or "doctored" clean to remove substantially
all liquid developer from the raised portions of the applicator
surface. Any suitable means may be provided as the doctoring
device. Typical doctoring devices include scraper blades and
squeegee rolls. The doctoring in addition to removing liquid
developer from the raised portions of the applicator surface
preferably provides a slight wiping action of the liquid developer
in the recessed portions of the applicator surface to thereby
maintain the level of the liquid developer in the recessed portions
slightly below the level of the raised portions. Such a loading of
developer on the applicator surface minimizes deposits in the
nonimage areas.
In the cycling electrostatographic imaging systems of the present
invention, it is generally necessary to cyclically clean the
imaging surface. Any suitable cleaning system may be employed. A
typical cleaning system scrubs the ink film on the photoconductor
surface obliterating the image pattern by smearing the developer
over the surface. The residual developer is subsequently picked up
by an absorbent web which may absorb the developer. For example, a
squeegee roller may be used as the scrubbing or obliterating device
and an absorbent web wrapped around a portion of the photoconductor
drum and moving slowly counter to the direction of rotation of the
drum may be used.
The mechanism of development according to this invention is
presently believed to be substantially the same as that in the
polar liquid development technique described by R. W. Gundlach in
U.S. Pat. No. 3,084,043. The liquid developer is applied to the
patterned applicator such that the raised portions of the
applicator surface are substantially free of developer and the
level of liquid in the recessed portions of the applicator is
slightly below the level of the lands. Surface tension retains the
developer in cohesive configuration in the depressed portion of the
applicator surface and as the raised portions of the applicator
surface are placed in light or gentle contact with the
electrostatographic imaging surface, the liquid developer in
response to the electrostatic field of force on the imaging surface
creeps up the sides of the depressed portions of the applicator
surface and deposits on the imaging surface substantially only in
accordance with the pattern of electric charge. The developer
remains in the depressed portions of the applicator surface except
in those portions which are under the influence of the attracting
electrostatic force.
The developer applicator is generally biased or directly connected
to ground through connection to a variable D.C. potential source so
that the liquid developer will be electrostatically attracted from
the applicator to the imaging surface in image configuration. When
so biased, the charges on the imaging surface induce equal and
opposite charges in the liquid developer. For example, when the
applicator is grounded and the image surface carries a positive
charge, negative charge is induced in the liquid developer adjacent
the positive charges and the developer moves toward the imaging
surface in response to the electrostatic field generated between
these charges. Portions of the imaging surface carrying no charge,
induce no charge in the developer and thus, the developer is not
pulled out of the recessed portions of the applicator surface to
nonfield areas of the image surface.
Reversal development may be obtained by applying to the developer
applicator a potential of the same polarity and of the same amount
as the charged areas on the imaging surface to cancel out the field
at charged areas and provide an electrostatic field between the
uncharged areas of the imaging surface and the developer on the
applicator surface. Again, a charge is induced in the developer in
response to the electrostatic field and the developer creeps up the
recessed portions of the applicator surface adjacent areas of the
imaging surface which are uncharged.
As discussed above, unlike classical electrophoretic developers,
liquid developers of this invention are capable of developing
positively as well as negatively charged patterns by having induced
in the liquid developer in response to the charge pattern a
polarity of charge opposite that of the charge pattern. In
addition, unlike electrophoretic development, migration of charge
particles from the carrier liquid plays no significant role. While
this particle migration may not be totally inhibited, if present,
it is present to an extent which is insignificant as far as
formation of visible images is concerned. This mechanism is
generally substantiated by the fact that in development, according
to the disclosed technique, the liquid developer is readily
transferred and cleaned from the imaging surface and there is no
evidence of the deposition of pigment particles out of the
developer on the imaging surface. The additional observation that
the developed image obtained according to the instant technique
comprises both pigment particles and carrier liquid in
substantially the same relative proportions as present in the
original developer supply whereas the developed image obtained
through electrophoretic development comprises substantially only
the solid particles which have separated from the carrier liquid is
further evidence of the differences between conventional liquid
developers and the described liquid developer.
DESCRIPTION OF PREFERRED EMBODIMENTS
The following preferred nonlimiting examples further define,
describe and compare preferred materials and techniques of the
present invention. Examples II and III are included for comparitive
purposes to show the surprisingly superior and unexpected results
obtained in the practice of this invention. In the examples, all
parts and percentages are by weight unless otherwise specified.
EXAMPLE I
A commercially available paperbacked zinc oxide binder layer
photoconductor is charged and exposed in conventional manner. The
electrostatic latent image is developed with a developer having the
following composition by weight:
Mineral Oil (Drakeol 9) 35 parts by weight Carbon Black (Elftex 8)
20 parts by weight Alkylated Polyvinyl Pyrrolidone (Ganex V216) 12
parts by weight Triethylene Glycol Dicaprylate (Rucoflex TG-8) 33
parts by weight
Drakeol 9 is a mineral oil manufactured by Pennsylvania Oil and
Refining Company having a kinematic viscosity of about 17
centistokes at 25.degree.C. and a specific gravity of about .84.
Elftex 8 is a fine particle size carbon black available from Cabot
Corporation. Rucoflex TG-8 is triethylene glycol dicaprylate
available from Hooker Chemical Company. Ganex V216 is an alkylated
polyvinyl pyrrolidone compound with about 20% of the monomeric
vinyl pyrrolidone units nonalkylated and 80% alkylated with an
alkyl group of about 16 carbon atoms and an average molecular
weight of about 7,300 manufactured by GAF. The developer is
prepared by combining the mineral oil triethylene glycol
dicaprylate and the alkylated polyvinyl pyrrolidone in a suitable
vessel while stirring, and then adding the carbon black and ball
milling the mixture in a ball mill for about 48 hours. This liquid
developer has an electrical resistivity of about 10.sup.10 ohm-cm
and is applied to a cylindrical applicator roll having a
trihelicoid pattern on the surface such that the liquid developer
fills the grooves to a level slightly below the level of the ridges
and is doctored to provide substantially dry ridges. The image on
the zinc oxide binder layer is developed by moving this applicator
roller loaded with the liquid developer over the binder layer at a
speed of about 10 inches per second such that the edges of the
roller are just in contact with the surface of the binder layer.
The developer on the zinc oxide binder layer in image configuration
is transferred to Xerox 4024 bond paper where after about 2
seconds, a dry print with a resolution of about 8 line pairs per
millimeter is observed. In addition, the print has excellent image
density of about .93 and substantially no background, the
background density being less than about .01 and is highly
resistant to smudging when a pencil eraser is firmly pulled across
the image.
EXAMPLE II
The procedure of Example I is repeated except that the liquid
developer employed does not contain the alkylated polyvinyl
pyrrolidone. Imaging and development are accomplished in the same
manner as described in Example I. The paper is relatively dry after
about 4 seconds and the print obtained on the bond copy paper has a
resolution of about 6 line pairs per millimeter. Fair image density
of about .75 and high background density of about .2 makes this
developer unsuitable.
EXAMPLE III
The procedure of Example I is repeated except that the triethylene
glycol dicaprylate is omitted from the liquid developer. Imaging
and development are obtained in the same manner as Example I.
Transfer of the liquid developer to Xerox 4024 bond paper in image
configuration produces a final print which after about 30 seconds
is still wet and oily. After 45 seconds, a final print of
substantially the same quality as that obtained in Example I is
obtained. The extended period during which the print is moist is
highly undesirable from an automatic machine standpoint.
EXAMPLE IV
The liquid developer employed in this example is of the following
composition by weight and has a bulk resistivity of about 10.sup.10
ohm-cm and a dielectric constant of about 3.36.
______________________________________ Mineral Oil (Drakeol 9) 75
parts by weight Carbon Black (Statex B-12) 15 parts by weight
Copolymer of Octadecyl Vinyl Ether and Maleic Anhydride (Gantrez
AN-8194) 5 parts by weight Isoctyl Isodecyl Phthalate 5 parts by
weight ______________________________________
Statex B-12 is a carbon black available from Columbia Carbon
Company. Gantrez AN-8194 is a linear polymer formed from equal
molar quantities of octadecyl vinyl ether and maleic anhydride and
having a molecular weight of about 10,000 available from GAF
Corporation. The developer is prepared by combining the mineral oil
and the dispersant in a vessel while stirring and heating.
Subsequently, the pigment and the ester are added while continuing
the stirring. The mixture is cooled and then ball milled as in
Example I. An electrostatic latent image is formed on a clean
selenium xerographic plate comprising a surface layer of selenium
about 50 microns in thickness on a conductive aluminum plate. The
selenium plate is charged and exposed in conventional manner and
the image is developed by moving the applicator roller bearing
liquid developer in the manner described in Example I over the
selenium plate at a speed of about 10 inches per second such that
the edges are just in contact with the surface of the plate. The
developer is transferred from the selenium plate to bond paper in
image configuration. A dry image on the bond paper having a
resolution of about 10 line pairs per millimeter, an image density
of about .95 and substantially no background is obtained. The
selenium plate is manually cleaned with a cotton cloth to remove
substantially all the liquid developer. The selenium plate is again
charged, exposed, developed, the image transferred and cleaned as
above for a plurality of cycles. Satisfactory prints are obtained
for 5 cycles.
EXAMPLE V
The procedure of Example IV is repeated with a liquid developer of
the following composition by weight, a bulk resistivity of about
10.sup.11 ohm-cm and a dielectric constant of about 3.44.
______________________________________ Oleic acid 40 parts by
weight Benzidine Yellow OT 15 parts by weight Tetradecylated
Polyvinyl Pyrrolidone 5 parts by weight Butyl Benzl Phthalate 40
parts by weight ______________________________________
Benzidene Yellow OT is a pigment available from E. I. duPont
deNemours and Company. Results substantially the same as those
described in Example IV are observed.
EXAMPLE VI
The procedure of Example IV is repeated with a liquid developer
having the following composition by weight, a bulk resistivity of
about 10.sup.10 ohm-cm and a dielectric constant of about 3.0.
______________________________________ Peanut Oil 30 parts by
weight Hostaperm Pink E 20 parts by weight Alkylated polyvinyl
pyrrolidone (Ganex V-220) 25 parts by weight Tri-n-hexyl
trimeltitate 25 parts by weight
______________________________________
Hostaperm Pink E is a quinacridone pigment available from American
Hoechst Corporation. Ganex V-220 is an alkylated polyvinyl
pyrrolidone available from GAF Corporation with about 20% of the
monomeric vinyl pyrrolidone units nonalkylated and 80% alkylated
with an alkyl chain of about 20 carbon atoms. The resolution and
background of the print obtained on bond paper is substantially the
same as that obtained in Example IV. Image density and contrast,
however, are slightly superior to that in Example IV.
EXAMPLE VII
The procedure of Example IV is repeated except that the liquid
developer employed in this example is of the following composition
by weight and has a bulk resistivity of about 10.sup.12 ohm-cm.
______________________________________ Castor oil 55 parts by
weight Phthalocyanine (Monolite Fast Blue GS) 30 parts by weight
Alkylated polyvinyl pyrrolidone (Ganex V-516) 5 parts by weight
Butyl Stearate 10 parts by weight
______________________________________
Monolite Fast Blue GS is a phthalocyanine pigment available from
Imperial Chemicals, Ltd. Ganex V-516 is an alkylated polyvinyl
pyrrolidone with about 50% of the monomeric vinyl pyrrolidone units
nonalkylated and 50% alkylated with an alkyl chain of about 16
carbon atoms and available from GAF. Upon transfer of the developer
from the selenium plate to bond paper, print quality is observed to
be substantially the same as that in Example VI.
EXAMPLE VIII
The procedure of Example IV is repeated with the developer having
the following composition by weight and a bulk resistivity of about
10.sup.11 ohm-cm and a dielectric constant of about 3.2.
______________________________________ Mineral Oil (Drakeol 9) 38
parts by weight Predispersed Pigment (Microlith CT Black) 38 parts
by weight Alkylated Polyvinyl Pyrrolidone (Ganex V216) 15 parts by
weight Triethylene glycol dicaprylate (Rucoflex TG-8) 9 parts by
weight ______________________________________
Microlith CT Black is a resinated predispersed carbon black pigment
composed of about 33% by weight carbon black pigment and 66% by
weight ester gum resin available from CIBA. The mineral oil,
alkylated polyvinyl pyrrolidone and triethylene glycol dicaprylate
were mixed together in a suitable vessel and stirred to disperse
the several constituents. The mixture is thereafter added to the
tank of a Kady mill to which the predispersed carbon black is
charged sequentially in small amounts over a period of 10 minutes.
The developer is milled in the Kady mill for about 10 minutes.
Imaging and development are obtained in the same manner as that
described in Example IV. The final copy on bond paper is dry,
substantially free of background deposits, and has a resolution of
about 10 line pairs per millimeter. Immediately after transfer of
the developer from the selenium plate to the bond paper, the image
is not smeared when a finger is lightly drawn across it.
EXAMPLE IX
The procedure of Example VIII is repeated with a liquid developer
prepared according to the technique of Example VII and having the
following composition by weight, a bulk resistivity of about 10
ohm-cm and a dielectric constant of about 3.3.
______________________________________ Mineral Oil 40 parts by
weight Predispersed pigment (Microlith Green GT) 25 parts by weight
Copolymer of octadecyl vinyl ether and maleic anhydride (Gantrez
AN-8194) 5 parts by weight Butyl stearate 30 parts by weight
______________________________________
Microlith Green GT is a predispersed chlorinated phthalocyanine
pigment similar to Microlith CT Black available from CIBA. Prints
of substantially the same quality described in Example VIII are
obtained.
EXAMPLE X
A xeroprinting master is prepared by placing a thin insulating
coating of epoxy resin about .0005 inches thick in image
configuration on a conductive aluminum plate. The plate is
positively charged to 450 volts by passing it under a corona
charging unit. The image is developed in the manner described in
Example I with a liquid developer having the following composition
and a bulk resistivity of about 10.sup.10 ohm-cm.
______________________________________ Oleic acid 40 parts by
weight Carbon Black (Statex) 10 parts by weight Copolymer of
tetradecyl vinyl ether and maleic anhydride 15 parts by weight
n-octyl decyl adipate 35 parts by weight
______________________________________
The dispersant is formed from about equal molar quantities of
tetradecyl vinyl ether and maleic anhydride. The developer is
transferred to bond paper and the resulting print has image density
of about .8, background density of about .02 and a resolution of
about 7 line pairs per millimeter. Substantially no background
deposits are observed.
EXAMPLE XI
The procedure of Example I is repeated with a liquid developer
prepared in the manner described in Example VIII having the
following composition by weight and a resistivity of about
10.sup.11 ohm-cm.
______________________________________ Oil (Cottonseed Oil) 45
parts by weight Predispersed pigment (Microlith Bordeaux RT) 20
parts by weight Copolymer of nonadecyl vinyl ether and maleic
anhydride 10 parts by weight Diisooctyl sebacate 25 parts by weight
______________________________________
Microlith Bordeaux RT is a predispersed pigment similar to
Microlith Black CT available from CIBA. The dispersant is formed
from about equal molar quantities of nonadecyl vinyl ether and
maleic anhydride. Prints of substantially the same quality
described in Example VIII are obtained.
Examples I and IV through XI demonstrate the superior imaging
characteristics obtainable with the use of the liquid developers of
this invention. These developers provide a final copy or print
which is substantially completely free of background deposits which
is highly resistant to smearing and smudging and which is dry
rather than oily. In addition, the image density and contrast are
vastly superior to that obtained with prior liquid developers.
Comparison with Examples II and III readily demonstrates the
superiority with regard to background deposition drying and smudge
resistance. In Example II, the same developer as in Example I is
employed but without the presence of one of the selected
dispersants. This developer provides a final copy which has
considerable deposition in the background areas. Example III
provides final copy of quality similar to that in Example I after a
period of a time during which the liquid developer penetrates the
copy sheet. However, immediately following transfer to the copy
paper, the receiving sheet is wet and highly smudgable. Examples
VIII, IX and XI demonstrate the added advantage to preparation with
a predispersed pigment since ball milling of the mixture is not
required.
The liquid developers of the present invention have several
additional advantages over known liquid developers. They may, for
example, be employed in imaging systems which use both reusable
imaging surfaces and single use imaging surfaces. In addition, they
may be employed with imaging techniques that do not require a
drying or heat fixing step since they provide dry, nongreasy copy
prints without a separate fusing or fixing step. In addition, as
discussed above, the liquid developers of this invention provide
nongreasy background free copies substantially immediately after
development or transfer. Since there is substantially no particle
migration, the composition of the developer in the developer supply
does not have to be frequently monitored and adjusted. Further,
since the developer penetrates the copy paper, the final image on
the copy print is much more resistant to smearing and smudging.
Although specific materials and operational techniques are set
forth in the above exemplary embodiments using the developer
composition and techniques of this invention, these are merely
intended as illustrations of the present invention. There are other
developer materials and techniques such as those listed above which
may be substituted for those in the examples with similar results.
Other modifications of the present invention will occur to those
skilled in the art upon a reading of the present disclosure which
modifications are intended to be included within the scope of this
invention.
* * * * *