CA1062069A - Liquid electrographic developer composition and process - Google Patents

Abstract

LIQUID ELECTROGRAPHIC DEVELOPER COMPOSITION AND PROCESS

Abstract of the Disclosure A liquid developer containing redispersible, readily heat-fixable toner particles and a process for using the same.
The developer is characterized by toner particles containing certain linear polyesters which are physically inert to the liquid carrier vehicle of the liquid developer and which, advantageously, have a melting point below about 100°C.

Description

iO~;~069 , Field of the Invention This invention relates to electrography and more particularly to novel liquid developer compositions and their use in the development of electrostatic charge patterns.
Background of the Invention Electrographic imaging and development processes, e.g., electrophotographic imaging processes and techniques, have been extensively described in both the patent and other literature, for example, U.-S. Patent Nos. 2,221,776, issued November 19, 1940, 2,277,013, issued March 17, 1942 , 2,297,691, issued October 6, 1942, 2,357,809, issued September 12, 1944;

2,551,582, issued May 8, 1951; 2,825,814, issued March 4, 1958;
2,833,648, issued May 6, 1958; 3,220,324, issued November 30, ;
1965, 3,220,831, issued November 30, 1965, 3,220,833, issued November 30, 1965, and many others. Generally, these processes have in common the steps of formin~ a latent electrostatic charge image on an insulating electrographic element, such as a photo- ~ -conductive insulating layer coated on a conductive sup~ort. The electrostatic latent image is then rendered visible by a develop-20 ment step in which the charge image-bearin~ surface of the electro-graphic element is brought into contact with a suitable developer composition.

Many types of developer compositions, including both dry developer compositions and liquid developer compositions, have been proposed heretofore for use in the development of latent electrostatic charge images. Dry developer compositions typically suffer from the disadvantagethat distribution of the dry toner powder contained therein on the surface of the electrographic element bearing the electrostatic latent image is difficult to control.
These dry developers have the further disadvantage that the use thereof may create excessive amounts of dust and that high 106;~:)69 resolution is often difficult to obtain due to the generally relatively large size of the dry developer powder particles.
, ; Many of the disadvantages accompanying the use of dry developer compositions have been avoided in the past by the use of a liquid developer of the type described, for ;
example, in Metcalfe et al, U.S. Patent 2,907,674 issued August 6, 1959. Such developers usually comprise an electrically -~
insulating liquid which serves as a carrier and which contains -a stable dispersion of charged particles known as toner particles comprising a pigment such as carbon black, generally associated with a resinous binder, such as, for example, an alkyd resin.
A charge control agent is often included to stabilize the magnitude and polarity of the charge on the toner particles. In some cases, the binder itself serves as a charge control agent.
To achieve suitable physical stability of the toner particles dispersed in conventional liquid electrographic developers, any of several types of various "stabilization"
additives are incorporated in such a liquid developer to prevent the toner particles from settling out of the carrier liquid.
Typical of such additives are those described in York, U.S.
Patent 2,899,335 issued August 11, 1955 and various types of dispersants as described, for example, in British Patent 1,065,796.
One problem which has continued to persist with conventional "stabilized" liquid electrographic developer compo-sitions as described above is that even these "stabilized"
compositions,which contain various kinds of stabilization additives, tend to become "deactivated" within a few weeks and the toner particles tend to agglomerate or settle out of the developer. As a - 106;~69 consequence, the resultant liquid developer composition containing conventional liquid developer toner particles tends to become incapable of producing electrostatic prints of good quality and density (See British Patent 1,065,796 noted above).
This deactivation of conventional stabilized liquid developers is particularly troublesome because once the toner particles settle out of the developer suspension, it is often difficult to redisperse them. And, even if redispersed, it is often found that the redispersed liquid developer does not possess the same developer characteristics as the original developer.
Developer stability, even in conventional so-called "stabilized" liquid developers has been and is still a difficult problem to overcome~ This is one reason, in addition to convenience, that liquid developers are o~ten prepared in the form o~ so~called "concentrates" i.e., mixtures of resins, pigments and/or dyes with a low liquid content. These concentrates are stable and exhibit a relativély long shelf life. The loss of "stability" which occurs in conventional liquid electrographic developers,as noted hereinabove, occurs primarily in the diluted form of the concentrate which is the "working" form of the developer, i.e., the form of developer composition actually used in most electrographic developing processes.
Stability in "working" liquid developer compositions may be improved to some extent, as noted above in the afore-mentioned York patent, by the use of various stabilization agents.
These additives are most effective in a developer when used in conjunction with toner particles having a very small particle size. However, even in these situations where stability is achieved in working developers, this stability is often accom-panied by too high a developer sensitivity which tends to resultin a high degree of background density in the resultant liquid developed electrographic images.

~ . . . . . .. . .... . ....... ..

10tj;~065 A further problem associated with conventional "stabil- -ized" liquid developers has been the problem of replenishment.
That is, once the developer is used to produce a num~er of developed images, the developer becomes depleted of toner particles and must be replenished. However, as might be expected in any dispersed system wherein a delicate equilibrium must necessarily be maintained to avoid settling out or precipitation of the dis-persed particles, replenishment by in~ecting new particles into the suspension is a particularly complex problem.
In addition to the "stabilized" liquid developers described above, various "redispersible" liquid developers have been formulated. These "redispersible" developers are characterized by toner particles which, upon settling out of suspension with ~he liquid carrier ~ehicle of the developer, are readily redispersed in the liquid carrier and, when so redispereed, exhibit developer characteristics similar to the original developer However, various problems still exist with many of these "redispersible" developers. For example, the toner particles of many of these developers do not adhere well, i.e., they cannot read~ly be fixed, except to rough-surfaced toner-image receiving sheets such as conventional zinc oxide coated papers, using preferred fixing temperatures of about 100C. or less.
These developers, therefore, cannot be employed, except with further binder addenda, in various transfer processes such as many of the so-called TESI processes (as described in "Electrophotogra-phy" by R.M Schaffert, p. 67-p. 85, The Focal Press, 1965), because these processes use smooth-surfaced toner-image receiving elements, such as dielectric resin-coated papers, i.e., papers coated with a film-forming dielectric resin Still other avail-able redispersible developers, although redispersible at ordinaryroom temperatures, exhibit pronounced caking or agglomeration ~of the toner particles when subjected to extended periods of storage (e.g., 24 hours) at temperatures above room temperature, i.e ~ at about 55-60C., and cannot be readily redispersed.

.... . .- . . ............. . . . . .
.. .. .

iO6;~0~9 Summary of the. I~ye~ti:on :
rn accord with the presen.t inyenti`on there is `-~
provided an ïmproYed li.quïd developer composlt~on comprising a .
suitable liqui:d carrier vehicle. in whlch are diæpersed heat-fixable electrostati`cally-attractable toner parti`cles comprising as a binder component thereof certain linear polyesters, as described hereinafter, which.are physically inert in the carrier liquid. ..
The toner particles contained in llquia developers of the present invention are characterized by their ready heat-fixability to a .
lQ smooth-surfaced receiving element and by their ease, upon settling out of the liquid carrier vehicle, of bei.ng redispersed in the ..
liquid carrier. The aforementioned linear polyesters are present -~
in the liquid developer of the invention in an amount greater than ~
0.05 wei.ght percent based on the total weight of the developer composition and, as indicated above, serve as a binder component ;.
of the developer, L.e., a component of the developer used to fix the toner particle~ to the toner-image receiving element. .
In accordance with the present teachings, an electrographic liquid developer composition is provided which ;
2Q. comprises a mixture of electrostatically-attractable, heat-fixable toner particles in an electrically insulating liquid carrier which has a volume resistiveity greater than 101 ohm-cms. and a diel- ~
ectric constant less than about 3Ø The toner particles are present in an amount of from about 0.05 to about 15 weight per-cent of the developer composition and comprise in an amount ~
greater than about 0.05 weight percent of the developer composi-ti.on, a linear polyester physically inert with respect to the carrier liquid of the formula o a o o Rl ll 2 " 3 "
tlQa x~- R O C R C~x . .
.~ ~

., . , . , . . . "
.

-' 106'~0~;9 wherein X repres.ents a mole ~ercentage value ~ithin the range of ~ -O to lOQ mole.perce~t; R and R2, which.may be. the same or differ-ent, represen.t a ~ember of the group selected from. the divalent res:i`due. of an aliphati`.c, ali.cyclic, or aromatic diol upon removal :
of the tw.o hydroxy groups fr~m the diol; Rl is a member selected from the group consisti~g of the. divalent resi`due of a sulfonamido -free aliphatic, ali`cycli.c or aromati`.c di`carboxylic acid upon the removal of the tw.o carboxyl groups from the acid; and R3 repres-ents a member selected fr~m the same group as Rl and may be the same as or different from Rl or represents the divalent residue of a disulfonamido group containing aromatic dicarboxylic acid upon removal of the two carboxyl groups from the acid with the disulfonamido group having a monovalent cation on the amido nitrogen atom thereof.
In accordance with a further embodiment a process is provided wherein an electrostatic charge pattern which is carried on a dielectric substrate is developed into a visible image by applying the electrographic liquid developer composition outined above to the charge pattern.
2a Certain insoluble polymeric materials have been used heretofore as the binder component of the toner particles of liquid developer compositions, for example, certain of the poly-amides described in Straughan, U.S. 2,899,335, August 11, 1959.
In addition, certain types of polymers containing ester groups have been proposed for use in various kinds of liquid developers.
For example, liquid developers containing an insulating organic solvent and an oil-soluble, surface-active copolymer which may contain ester groups derived from unsaturated acids (e.g., fumari.c acid). are described in British.Patent 1,266,545 dated 3Q March.8, 1972. In addition, U.S. Patent 3,668,127 issued June 6, 1972 descri.bes- li.qui.d developers: contai`ning an insulating carrïer li.qui.d and pi.gment-containing toner partïcles bearing ~ -6a-.~

lU6;~069 at least t~o ~oly~er coati`ngs, namely~ an ~nner polymer coating insolub.le. in t~e. carri`er liquîd ..
~:`

: -~; .
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~.:'...
lQ ~::

:

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,,:

-6b-.,~,. ~
t ~ -''~` ' ' ' ''', : .

106~0~;9 (e.g., a styrene-butylmethacrylate copolymer) and an outer polymer coating partially soluble in the carrier liquid.
Perhaps the closest the art has come to the improved, liquid developers of the invention is in the formulation of certain commercially available, redispersible liquid developers which, upon analysis, have been found to contain as the binder component thereof various drying oils which are soluble in the carrier vehicle of the developer. These prior art liquid developers also appear to contain a very small amount of a polymer consisting of a mixed isophthalate-terephthalate ester (i.e., an amount equal to about 0.001 weight percent based on the total weight of the working strength developer in association with the colorant material - -of the developer. The precise reason(s) this small amount of the aforementioned mixed-ester polymer is present in such redispersible developers is not known although it may be present simply as a polymeric component used to modify or en-hance certain properties of the pigments used in these developers.
The aforementioned mixed-ester polymer appears to be similar and may be identical to certain of the non-crystalline members of the class of linear polyesters described herein-after for use as the binder component of the liquid developers -of the present invention. Of course, the function of these polyesters as the binder component in the developers of the -; ;
present invention appears to be quite different from the unknown function of the apparently similar or identical materials used in the prior art. Indicative of this fact is that the working strength developers of the present invention contain, at a minimum, 50 times more of these mixed ester polymers then is used by the prior art developers, i.e., 0.05 weight percent compared to about 0.001 weight percent; and further that the liquid developers of the present invention 1(~6;~C~69 ., .
exhibit good fixing properties, even to smooth-surfaced receiver elements, without the need for a separate fixing component soluble in the liquid carrier vehicle of the developer, such as i a drying oil, whereas the aforementioned prior art developers do employ, as an essential component, a separate soluble, fixing component to achieve fixing of the toner images formed by these prior art developers. Thus, it does not appear that the ~ -linear polyesters having the properties described more specific-ally hereinafter have been used as the binder component of liquid developers. And, accordingly, the art does not appear to have recognized the combination of advantageous properties, such as redispersibility and fusibility, which the liquid developers of the invention are capable of providing.

Certain polyester materials or modified polyesters similar to or like those used in the present invention have been proposed for use in dry electrographic developers or in dry printing ink compositions, as in U.S. Patent 3,557,691 issued January 26, 1971; U.S. Patent 3,590,000, issued June 29, 1971;
and Belgian Patent No. 793,247 dated June 22, 1973.
However, these patents do not disclose or recognize the useful and unexpected advantages obtained by the present invention wherein certain linear polyesters are used as the binder component of liquid developer compositions.
Description of the Preferred Embodiments One of the particularly noteworthy aspects of the liquid developer of the present invention is the ease with which the toner particles can be redispersed in the carrier liquid. In accord with the present invention there is provided a "redispers-ible" liquid developer which is highly practical and substantially 106'~069 avoids the difficult problems of developer stabilization and replenishment which must be faced with conventional "stabilized"
liquid developers. That is, one need not worry about the toner particles settling out of the developer of the present invention during periods of little or no usage or during the replenishment thereof. With only a minimal amount of agitation, the toner particles of the present developer composition are readily redispersed within the carrier liquid and exhibit substantially the same developer properties as when first dispersed therein so that no noticeable loss in image quality results. This is true even though the toner particles contained in the liquid developer of the invention may have settled out and been redlspersed a countless number of times between the first and last electrostatic charge pattern developed by the liquid developer of the present in~ention.
Another especially advantageous feature of the llquid developers of the present invention is that the polyester- `
containing toner particles thereof are physically inert with ;
respect to the liquid carrier vehicle of the developers. That is, the toner particles, when dispersed in the liquid carrier vehicle of the developer, are hard and non-tacky and are not solubilized, softened,or swelled by the liquid carrier vehicle at ordinary room temperatures or at usual storage and operating liquid development temperatures. Therefore, one need not worry about "caking" or agglomeration of these toner particles when the developer is stored or subjected to periods of non-use, even under temperatures somewhat higher than ordinary room temperatures, i.e., up to about 55-60C., for extended periods up to 24 hours.
In addition, in accord with a further feature of the developers of the invention, the toner particles contained therein are characterized by relatively low m~ting points,preferably ~thin the _9_ `:

-lO~;Z~)69 range of from 60 to about 100C., and therefore the developers of -the invention require low energy levels for heat-fixing an image deve:Loped therewith to an image-bearing support. Moreover, in accord with this embodiment of the invention, the polyester toner materials contained in the liquid developer fuse at an extremely rapid rate so that an image which is liquid developed ~;
using the developer of the present invention can be fixed very quickly.
In accord with a further especially useful embodiment of the present invention the polyester-containing toner particles of the developer not only possess a relatively low melting point, but in addition exhibit a relatively sharp melting range on the order of less than about 10C. Such a sharp melting point range further en.~ances the heat-fixability of these toner particles to an image-bearing receiving sheet or support.
Still another advantage of the preferred liquid developOE of the present invention is that they are readily fixed to even extremely smooth toner-image receiving elements, such as dielectric resin-coated papers, when heated to a temperature of about 100C.
A "redispersable" liquid developer is defined in the present specification in terms of the following test: A first 25 ml. portion of a freshly prepared, working strength liquid developer containing about 99.85 weight percent of liquid carrier vehicle and about 0.15 weight percent of toner particles ~(the toner particles containing carbon as a colorant in an amount equal to about 0.5 g. of carbon per liter of developer)is used to develop a latent electrostatic charge pattern in a conven-tional liquid development electrophotographic process such as described in Metcalfe et al., U.S. 2,907,674. The resultant visible, liquid developed images are retained. A second 25 ml.
portion of this freshly prepared developer is poured into a clear glass bottle which is capped with a clear glass stopper.

106Z~69 , .
This second portion of the developer is then allowed to stand at room temperature (i.e. 22C.) at 50 percent relative humidity for a period of four weeks. At the end of this four week period, at least some of the toner particles dispersed in the developer will have settled out of the developer and be visible in the glass bottle in which the developer is stored. The bottle in which the developer is stored is then turned upside down and righted (i.e. inverted) two times over a 3 second time span, and the "settled-out" toner particles are redispersed in the developer. This redispersed developer is then used to develop a latent electrostatic charge pattern identical to that developed by the original, freshly prepared developer using a liquid development process identical to that in which the freshly pre-pared developer was employed. The resultant visible, liquid developed images possess an image quality substantially similar to that of the images produced from the freshly prepared developers as evaluated in terms of: optical density in the image areas;
optical density in background, non-image areas; fine-line and solid-area image reproduction; and resolution capabilities.
The polyester materials contained in the toner particles of the liquid developers of the present invention and which are responsible for many of the advantageous properties of the present invention are thermoplastic, linear polymeric materials. In accord with a preferred embodiment of the invention these polyester materials are crystalline polymers. The polyesters used in the toner particles of the present invention have structural formula I:
O O O O
I. ~0 - R - 0 - C - R -C~ ~0 - R -0- C -R3-C~

106'~069 ~
wherein X represents a mole percentage value within the range .
of O to 100 mole percent; R and R2, which may be the same or ~ :
different, represent the divalent residue of an aliphatic, alicyclic, or aromatic diol upon removal of the two hydroxy groups from said diol; Rl represents the divalent residue of a sulfonamido-free aliphatic, alicyclic, or aromatic dicarboxylic : :
acid upon removal of the two carboxyl groups from said acid; and R3 represents a member selected from the same group as Rl and may be the same as or different from Rl,or R3 represents the divalent residue of a disulfonamido group-containing aromatic dicarboxylic acid upon removal of the two carboxyl groups from said acid, said disulfonamido group having a monovalent cation on :
the amido nitrogen atom. In an especially useful embodiment of the invention, R3 in formula I abo~e represents a member selected ~rom the same group as Rl The diols, including aliphatic, alicyclic, and aromatic diols, which may be used in the preparation of the crystalline polyester contained in the toner particles of the liquid developers -of the present invention may be selected from a variety of known such diols Useful diols which may be used to provide R and R2 of Formula I include bisphenols, alkylene glycols, and monocyclic and polycyclic diols. Representative bisphenols which may be employed are generally of the structure of formula II: -HO ~ - C - ~ - OH

wherein each R4 and R5, which can be the same or different, are selected from the group consisting of hydrogen atoms, aryl radicals, such as phenyl, including substituted phenyl, halogen 3o atoms, nitro radicals, cyano radicals, alkoxy radicals and the ~, .. . . . .

lU6;~V69 like, and wherein the substituents on the phenyl radical may be a halogen atom, nitro radical, cyano radical, or alkoxy radical. R and R7 represent aliphatic, monocyclic or bicyclic radicals and can each be hydrogen atoms; alkyl radicals of from 1 to 6 carbon atoms, including substituted alkyl radicals, such as fluoromethyl, difluoromethyl, trifluoromethyl, dichloro~ `'. '.r-fluoromethyl, 2-[2,3,4,5-tetrahydro-2,2-dimethyl-4-oxofur-3-yl] --ethyl and the likej cycloalkyl radicals of from 4 to 6 carbon atoms, such as cyclohexyl; and aromatic radicals having from 6 to 20 carbon atoms, such as phenyl, 3,4-dichlorophenyl, 2,4-dichlorophenyl. R6 and R taken together with the carbon atoms to which they are attached can represent a monocyclic, bicyclic, or he~erocyclic moiety having from 4 to 7 atoms in the ring.
Tgpical useful bisphenols include: Bispheno~ A, 2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane[tetrachlorobisphenol A];
l-phenyl-l,l-bis(4-hydroxyphenyl)ethane; 1-(3,4-dichlorophenyl)-1,1-bis(4-hydroxyphenyl)ethane; 2,?-bis(4-hydroxyphenyl)-4-.
(2,3,4,5-tetrahydro-2,2-dimethyl-5-oxofur-3-yl)butane; bis~4-hydroxyphenyl)methane; 2,4-dichlorophenylbis ~4-hydroxyphenyl) methane; 1,1-bis(4-hydroxyphenyl)cyclohexane; 1,1,1,3,3,3-hexa-fluoro-2,2-bis(4-hydroxyphenyl)propane; diphenyl-bis(4-hydroxy-phenyl)methane.
Other useful bisphenols include 1,4-naphthalene diol, 2,5-naphthalene diol, bis(4-hydroxy-2-methyl-3-propylphenyl)methane, 1,1-bis(2-ethyl-4-hydroxy-5-sec.-butylphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxy-2-methyl-5-tert.-butylphenyl)propane, l,l-bis(4-hydroxy-2-methyl-5-isooctylphenyl) isobutane, bis-(2-ethyl-4-hydroxyphenyl)-4,4-di-p-tolylmethane.
Still other useful bisphenols are disclosed in U.S Patçnt

3,030,335 and Canadian Patent 576,491.

., `: .
Typical monocyclic diols include hydroquinone and hydroquinones substituted with alkyl groups of 1 to 15 carbon atoms, or halogen atoms, resorcinol, unsubstituted or substituted ~-with lower alkyl groups or halogen atoms, and the like, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanedi-ethanol, 1,4-bis(2-hydroxyethoxy)cyclohexane, 1,4-benzenedi-methanol, 1,4-benzenediethanol and the like.
Illustrative examples of polyalicyclic diols include -norbornylene glycol, decahydro-2,6-naphthalenedimethanol and the compounds listed in Table I of U.S. Pat. 3,317,466 under the heading of "Bisphenols".
Exemplary alkylene glycols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol~
1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, ;;
1,10-decanediol, 1,12-dodecanediol, neopentyl glycol, 2,2,4-trimethyl-1,6-hexanediol and 4-oxa-2,6-heptanediol.
It will be appreciated, of course, that a variety of other diols may also be used in addition to those specified above in the preparation of the linear polyester materials used in the present invention. In general, it has been found that, to date, polyester materials of the present invention which are especially preferred due to their composite properties of redispersibility, crystallinity, low melting point and sharp melting point range are those polyesters which are prepared from aliphatic diols. --Uséful dicarboxylic acids which may be used to provide the sulfonamido-free dicarboxylic acid residue R in formula I may be selected from any of a variety of aliphatic, alicyclic, and aromatic dicarboxylic acids. Useful dicarboxylic acids as defined , ~06Z069 -; ~
herein include the free acid form of these materials as well as the corresponding bifunctional equivalents of these acids including the equivalent corresponding acid anhydrides, where available.
Other useful corresponding bifunctional equivalents of the free acid form of the dicarboxylic acids are the lower monohydric alcohol or phenyl esters of dicarboxylic acids and the dicarboxylic acid halides, e.g., the chlorides or bromides.
A partial list of representative sulfonamido-free dicar-boxylic acids which may be employed to prepare Rlin formula I in-clude succinic acid, sebacic acid, 2-methyladipic acid, diglycolic acid, thiodiglycolic acid, fumaric acid~ cyclohexane-1,3-dicar-boxylic acid, cyclohexane-1,4-dicarboxylic acid, cyclopentane-l, 3-dicarboxylic acid, 2,5-norbornanedicarboxylic acid (the above-described acids being useful either as the cis or trans form~, phthalic acid, isophthalic acid, terephthalic acid, t-butyliso-phthalic acid, phenylenediacetic acid, phenylenedipropionic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1,7-naphthalenedicarboxylic acid, 4,4'-diphenic acid, 4,4~-sulfonyldibenzoic acid, 4,4~-oxydibenzoic acid, binaphthyldicarboxylic acid, 4,4'-stilbenedicar-boxylic acid, and 9,10-triptycenedicarboxylic acid.

In accord with one especially useful embodiment of the present invention wherein crystalline polyesters having low, sharp melting points are provided, it has been found particularly advantageous to use as the sulfonamido-free dicarboxylic acid precursor material(from which R1 in formula I is obtained)an aliphatic dicarboxylic acid such that Rl in formula I has the formula ~CH2~n wherein n is an integer of from 4 to about 12.

. . ~ .

106;~069 .. '~'' . .
Useful dicarboxylic acids which may be employed as precursors to prepare the residue R3 of formula I illustrated above (when R3 is not selected from the same group as Rl) are ; dicarboxylic acids containing a disulfonamido group. Such acids typically have the structure of formula III: -O O '''' III. R8 C Y Qm - C - R8 Q'n wherein R can be, for instance, an hydroxyl group where the 10 material is a free acid, an oxy atom linkag~ where the compound is an acld anhydride, a halogen atom where the compound is in *
the form of an acid halide or an alkoxy group where the compound i8 in the form of an ester m and n are integers whose sum equals 1;
Q is defined by the structure of formula IV:
0 M o IV. - S - N - S - Y -., .~
O O ' . -Q' is defined by the structure of formula V:
o M o " , " .
V. - S - N - S - Y' ~ 11 ..
O O
Y is an aromatic group, such as an arylene group (e.g. phenylene, naphthylene, etc.) or arylidyne group (e.g.
phenyl, naphthylidyne; etc.), .
Y' is an alkyl or aromatic group, such as an aryl, alkaryl or aralkyl group, in which each of the alkyl moietles includes from 1 through 12 carbon atoms and, preferably, from 1 through 6 carbon atoms; and A~ ; -16-106~069 M is a monovalent cation such as an alkali metal or ammonium cation.
A partial listing of representative compounds for use in forming R3 of formula I (when R3 is not selected from the same group as Rl) are: 3,3~-~(sodio-imino)disulfonyl~di-benzoic acid; 3,3'-~(potassium-imino)disulfonyl]dibenzolc acid;
3,3'-[(lithium-imino)disulfonyl]dibenzoic acid; 4,4'-~(lithium-imino)disulfonyl]dibenzoic acid; 4,4~-[(sodio-imino)disulfonyl]-dibenzoic acid; 4,4'-[(potassium-imino)disulfonyl]dibenzoic acid; 3,4'-[(lithium-imino)disulfonyl]dibenzoic acid; 3,4'-[(sodio-imino)disulfonyl]dibenzoic acid; 5-[4-chloronaphth-1-ylsulfonyl-(sodio-imino)-sulfonyl]isophthalic acid; 4,4'-[(potassium-imino)-disulfonyl]dinaphthoic acid; 5-[p-tolyl-sulfonyl-((potassium-imino)-sulfonyl]isophthalic acid; 4-~p-tolyl~sulfon~l-(sodio-imino)-sulfonyl]-1,5-naphthalene-dicarboxylic acid; 5-[n-hexylsulfonyl-(lithium imlno)-sulfonylj-isophthalic acid; 2-[phenylsulfonyl-(potassium-imino)-sulfonyl]-isophthalic acid; 2-~phenylsulfonyl-(potassium-imino)-sulfonyl]-terephthalic acid and functional derivatives thereof.
These and other dicarboxylic acids useful in forming repeatingunits R of the crystalline polymeric polyesters used in this invention are disclosed in Caldwell and Jones U.S. Patent 3,546,180, issued December 8 1970.
The linear polyester materials used in the present invention as suggested above may be selected from a variety of well known such materials. Accordingly, extended description of the preparation thereof is unnecessary herein.
In general, these linear polymers are prepared by well known condensation reaction procedures between the diol precursor .
materials and the dicarboxylic acid precursor materials, thereby ~17-A~
. .
,, : . , . .. ~ - . . , . . ~ . . .

5' ~06'~(~69 obtaining the resultant linear polymeric esters used in the present invention.
The molecular weight of the linear polyester materials used in the present invention may vary over a considerable range.
Rather than specifying a particular molecular weight range for the various polyester materials useful in the invention, it has been fol~nd more convenient in practice to identify suitable polyesters by their melting point. That is, if a particular polymer has too low a melting point, it is generally unsuitable for use because it will become tacky which leads to agglomera-tion or sticking together of individual toner particles at ordinary room operating temperatures. In general, useful polyester materials for the present invention should have a melting polnt of at least about 60C, preferably within the range of from about 60C to about 100C. Polyester materials -having a melting point in the aforementioned preferred range can be heat fixed to smooth-surfaced dielectric coated receiving elements as well as ordinary support surfaces, such as paper, etc., without difficulty. Higher melt point polyester materials may also be used, i e., materials having a melting point above about 100C; however, in this latter case one may have to be more selective as to the choice of the support to which the toner image is to be fused so that the fusing temperature employed does not damage or char the support. In addition, as described earlier herein, it is especially useful to employ a linear polyester in the present invention which has a relatively sharp melting point range, i.e., the polymeric material is completely melted over a temperature range of less than about 10C.

r _~

. 106;~069 ~
The melting point of useful polymers as described herein ~
is determined by conventional melt point techniques. The melt -point of crystalline polymers is determined by placing a small amount of the polymer in a capillary tube and heating the tube in a silicone oil bath The melting point of the crystalline polymer is the point at which the crystalline polymer becomes fluid and undergoes a visual change from an opaque crystalline polymeric material to a transparent amorphous polymeric material.
The melting point of useful noncrystalline polyesters is defined herein as a point 25C. above the glass transition temperature, Tg, of the polymer as measured by differential scanning calorimetry using an E I. duPont de Nemours Co. Differential Scanning Calorimeter at a 10C./minute temperature rise As indicated previously, a particularly useful feature of the preferred liquid developers of the invention is their ready heat-fixability. More specifically, it has been determined that the liquid developers of the invention, without the addition of a separate fixing component, such as a drying oil, soluble in the liquid carrier vehicle of the developer, are capable of providing liquid-developed images exhibiting good adherence to a smooth-surfaced receiving element, for example, a paper receiving element composed of an electrically conducting paper base over-coated with a smooth, dielectric resin film, such as a Butvar-coated paper (Butvar is the trademark for poly(vinyl butyral) resin sold by Shawinigan Products Corporation These smooth-~urfaced,dielectric resin-coated papers typically have a Sheffield Smoothness value of about 90 or less In accord with the present invention, it has been found that an electrostatic charge image formed on such a dielectric-coated paper may be developed using the preferred developers of the present invention by air drying the liquid-developed toner image -1~6~069 :

to remove the liquid carrier vehicle from the image areas, and moving the resultant air-dried toner image carried on the dielectric-coated paper past an infra-red heating lamp at a rate of about 5 cm /sec to heat the toner particle image to a temperature of about 100C. In contrast, most, if not all, prior art redis-persable liquid developers either are not capable of providing ~;
images which are well fixed, i.e., tightly adhered, to a smooth-coated dielectric-coated paper (although these prior art redis-persable developers may exhibit good adherence to a rough-surfaced 10 paper, such as zinc oxide-coated paper), or they are able to `~
achieve good fixing to a smooth-surfaced dielectric-coated paper but only because a separate, fixing component, such as a drying -oil, is present solubilized in the carrier liquid of the prior art developer As indicated above, a molecular weight range for poly-esters useful in the present invention is difficult to specify because the molecular weight of useful materials can vary considerably depending on the particular polyester being con-sidered However, it can be said that the polymers used in the invention advantageously contain more than three repeating units having formula I noted above and typically contain more than about 10 such units.
The following Table represents a partial listing of useful linear polyester materials which can be employed in the present invention TABLE

1. crystalline poly(decamethylene sebacate) having a m.p.
of about 72C.

2. crystalline poly~nonamethylene terephthalate) having a 3o m p. of about o5C.

3 non-crystalline poly(ethylene terephthalate:
isophthalate) having a m.p. of about 60C.

4. crystalline poly(tetramethylene succinate:sebacate) having a variable melting point within the range of from about 65C. to 100C depending on the ratio of succinate to sebacate units in this copolymer . _ . . ., . _ _ ... . .. . . _ . . _ .
.

106Z069 ``
,

5. crystalline poly(ethylene sebacate) having an m.p. :
of about 75C.

6 crystalline poly(~-xylylene sebacate) having an m.p.
of about 84C.

7 crystalline poly(decamethylene adipate) having an m.p.
of about 75C.

8. crystalline poly(ethylene suberate) having an m.p. of about 80C.

9. crystalline poly ~decamethylene sebacate:3,3~-[(sodio-imino)disulfonyl]dibenzoate~ having a m.p. of about As described herein an especially desirable character-istic of the polyesters used in accord with a preferred embodi-ment of the present invention is their crystallinity. Such crystallinity is believed to contribute to the desirable proper-tie~ of toner hardne~s, nontackiness at room temperature (i e., 22~C), and sharp melting point The crystallinlty of the preferred polyesters used in the invention can be readily recognized using standard crystallographic identification techniques to detect the characteristic ordered structure of crystalline materials; for example, X-ray diffraction measure-ments. For purposes of the present invention, a polymer which does not exhibit crystallinity when examined by X-ray diffraction is considered to be non-crystalline. A convenient X-ray dif~raction technique which may be used to detect crystallinity of polymeric particles consists of taking a flat plate powder X-ray photograph of the specific polymeric particles to be measured such as described, for example, in the book entitled Polymer Single Crystal, by P. H. Geil, published by Interscience Publishing Co., New York, 1963.
Many of the linear polyesters useful in the invention undergo spontaneous crystallization after polymerization -21- ;
, 106;~069 thereof. However, if necessary or desirable, crystallization can be induced in many polyesters which do not undergo spontaneous -crystallization after the preparation thereof to render these otherwise noncrystalline polyesters more useful in the invention.
Several different polymer crystallization techniques are known and any of these techniques may be employed. Further details concerning such polymer crystallization methods may be found, for example, in the book entitled Principles of Polymer Systems !` -.

published by l~cGraw-Hill (1970) and authored by F. Rodrequez.
.
The liquid developers of the present invention, as indicated above, typically comprise a dispersion of the linear polyester toner particles in a suitable carrier liquid. A common method of preparing such a liquid developer is to first prepare a so-called "concentrate". One method of preparing such a concentrate is by solvent milling A quantity of the polyester material, as described above, is dissolved in a suitable solvent, such as dichloromethane, and the solution placed in a ball mill. Pigments and other additives which may be desirable -or necessary depending on the particular end use of a given developer composition may be added to the mix and the whole mix milled using stainless steel milling beads about 0.3 cm in diameter for a suitable time, typically on the order of about 1 or 2 days. The polymer-solvent mixture is then separated from the milling beads and the solvent, such as dichloroethane, removed.
The resultant dry polymer-containing material may then be ground and ball milled in a small amount of a suitable liquid carrier vehicle in which the polyester is insoluble to reduce the particle size of the polymeric toner material to a size of less than about 5 microns, typically within 3 the range of from about 0.01 to about 1.0 micron. The resultant composition represents a so-called developer "concentrate."

, , ... .. .... , ~ .. . . ,. ... _ ... .. , . _ , . .. . .

106;~069 ~ working strength liquid developer is typically prepared from the above-described concentrate by mixing an amount of concentrate together with an amount of suitable liquid carrier vehicle to provide a developer containing the desired amount of toner particles dispersed in the liquid carrier vehicle.
In general, useful working strength developers of the present inventlon contain from about 0.05 to about 15% by weight of polymeric toner particles and from about 99.95 to about 85% by weight of liquid carrier vehicle. Best results are generally obtained wherein the toner particles are present in the range of from about 0 1 to about 3~ by weight and the liquid carrier vehicle is present in the range of from about 99 9 to about 97 by weight of the resultant developer composition As indicated above, suitable liquid carrier vehicles useful in the developer compositions of the present invention may be selected from a variety of liquid materials. These materials should be electrically insulating and have a fairly low dielectric constant. In addition, the carrier vehicle should be selected as a liquid with respect to which the particular linear polyester contained in the toner particles is physically inert. The term "physically inert", as used herein, as suggested above, is defined to mean that the toner particles contained in ' the liquid developers of the invention are not soluble in or swellable or softenable by the liquid carrier vehicle of the developer In general, useful carrier liquids should have a di-electric constant of less than about 3, and a volume resistivity greater than about 101 ohm/cm. Suitable carrier liquids include halogenated hydrocarbon solvents, for example, fluorinated lower alkanes, such as trichloromonofluoromethane, trichloro-3o trifluoroethane, etc., having a boiling range typically from . _ _ 106;~069 ``

about 2C to about 55C. Other hydrocarbon solvents are useful such as isoparaffinic hydrocarbons having a boiling range of from about 145C to about 185C such as Isopar G (A
trademark of the Exxon Corp.) or cyclohydrocarbons such as cyclohexane. Additional carrier liquids which may be useful in certain situations include polysiloxanes, odorless mineral spirits, octane, and the like. As noted above, to insure the proper solvent properties exist between the carrier vehicle and the polyester used in the toner particles contained in the developer of the present invention, it will ; be appreciated that the particular liquid carrier vehicle selected must depend in large part on the solvent properties of the particular polyester material used in thé toner particle.
Although it is possible to use the liquid developers of the present invention without further addenda such as charge control agents or colorants, it is often desirable to incorporate such materials For example, it is usually desirable to incorporate a colorant such as a dye or pigment in the developer to provide suitable image density. Of course, if a colorless image is desired as may be the case in certain situations;
for example, the developer of the invention may be used to form a colorless hydrophobic image in a lithographic printing process, it may be unnecessary to add any colorant or other additives. In such case the resultant developer composition consists essentially of the liquid carrier vehicle and the above-described polyester toner particle. Generally, however, suitable colorants are desirable for use in the liquid developers of the present invention and such colorants may be selected from a variety of known dyes or pigments. Although useful results may be obtained from virtually any of a wide variety of known dyes or 1~6;~i9 , pigment materials. Particularly good results are obtained, for example, by using various kinds of carbon black pigments.
However a variety of other dyes and pigments may also be used, a partial representatlve list thereof may be found, for example, in Research Disclosure, Vol. No. 109, May, 1973, in an article entitled "Electrophotographic Elements, Materials and Processes" appearing at page 61, in paragraph IX (C)(2) thereof.
As suggested hereinabove, the colorant when employed in the liquid developer of the present invention typically may be incorporated in the developer by admixture of the colorant together with the linear polyester during the initial preparative stages of the developer, for example, when the developer concentrate is prepared Typically, when the developers of the present lnvention are prepared using the so- -called concentrate technique as described hereinabove, the amount of colorant which may be employed may vary widely depending upon the desired optical density of the developed image, the particular colorant or colorants employed, and the like. Typically, one generally employs in the preparation of a concentrate an amount of colorant within the range of from about 0 to about 200 ~-weight percent based on the weight of the linear polyester used in preparing the concentrate. A final working strength developer of the present invention which, as described herein- ;
above, typically contains from about 85 to about 99.95% liquid carrier vehicle and from about 0.05 to about 15 weight percent of toner particles will generally contain an amount of colorant, if a colorant is used in the developer, within the range of from about 0.01 to about 5 weight percent based on the total weight 3o of the working strength developer including carrier liquid, .-y ..

106;~069 toner particles, and any other additives which may be present.
In general, it is believed that most colorants incorporated in the developers of the present invention are contained dispersed or encapsulated within the linear polyester which forms the insoluble toner particles used in the liquid developers of the present invention.
In addition to colorants, the developers of the present invention may contain, if desired, various charge control agents to enhance the charge polarity uniformity of the toner particles dispersed therein, i.e., to provide a developer containing either predominantly positively charged or predominantly negatively charged toner particles. Such charge control agents are not necessary but are often useful to eliminate or at least -substantially reduce possible bicharging of the toner particles within the developer composition, i.e., to prevent or at least substantially reduce the presence of positively charged particles when negatively charged particles are desired or, in the alterna-tive, to reduce or prevent the occurrence of a large number of negatively charged toner particles in the situation where it is desired to obtain a developer containing essentially positively charged particles.
Various such charge control agents have been described heretofore in the liquid developer art. An extensive discussion thereof is deemed unnecessary herein Examples of such charge control agents may be found, for example, in U S
Patent 3,788,995, issued January 29, 1974 which describes various polymeric charge control agents such as terpolymers, for example, a styrene-lauryl methacrylate-sulfoethyl methacrylate terpolymer These polymeric charge control agents are typically substantially soluble in the liquid carrier vehicle or at least readily dis-

10~;~0~ ~

i~ ~
persible therein so that there is no problem of these materials settling out of the developer. Various non-polymeric charge control agents may also be employed such as for example the - various metal salts described, for example, in Beyer U.S
; Patent 3,417,019, issued December 17, 1968. Other charge control agents known in the liquid developer art may also be employed.
Although the amount of such charge control agents, if they are used, will vary depending upon the particular charge control agent and its particular relationship to a given toner particle and liquid carrier vehicle, it is usually desirable to employ an amount of charge control agent within the range of from about 0.1 to about 2.0 weight percent based on the total weight of a working strength liquid developer composition.
Al~hough a charge control agent, if it i~ used, may be incorpor- -ated in the liquid developer durlng the preparation of a so-called developer concentrate, it is more frequently the case that the charge control agent is incorporated in the final work- -~
ing strength developer simply by dissolving or dispersing the -charge control agent in the liquid carrier vehicle at the time the developer concentrate is combined with the liquid carrier vehicle to form a working strength developer.
The following examples are included for a further understanding of the invention:
Example 1 .
A particulate composition was prepared by dissolving 18 parts (by weight) of the linear crystalline polyester poly(deca-methylene sebacate) having a melting point of 72C. in 73 parts (by weight) of dichloromethane and then adding with agitation 9 parts (by weight) of carbon black (purchased from Columbian Carbon Co. under the trademark Peerless 155) followed by ball milling of the composition for twenty-four hours using 1/8 inch ~; ..... :. . . . . . , . , ..... j , . . .

steel balls. The carbon-polymer mixture is then separated from the milling beads and the dichloromethane removed. The resultant dry, particulate composition was then ground and ball~milled in a small amount of Isopar G ~ to reduce the particle size to 2 microns or less, The~ esultant reduced particle size compo-sition containing Isopar constituted a liquid developer concentrate and contained about 90 percent (by weight) Isopar A working strength liquid developer was then prepared by mixing enough of the above-described concentrate in Isopar G
to yield a carbon content of 0.5g/liter. The Isopar G ~ also contained .5g/liter of a styrene-lauryl methacrylate-sulfoethyl-methacrylate terpolymer as charge control agent. When used to develop a negative electrostatic charge pattern formed on an organic photoconductive composition coated on a fle~ible con- ;
ductive film support in à conventional liquid development electrophotographic process such as described in Metcalfe et. al.
U,S. Patent 2,907,674 this developer containing positively-charged toner particles provided good quality images. After standing a few weeks, the toner particles that had settled out of the developer suspension were readily redispersed using a minimal amount of agitation by merely inverting the bottle in which the developer was stored. The resultant redispersed developer, when used in an electrophotographic process identical ~-to that in which the original developer was used, produced the same developed image quality as the original developer.
Example 2 ~ particulate composition was prepared as described in Example 1 and then jet pulverized to a 10-20 micron particle size. This material was then ball-milled in a small amount of Isopar G ~ (also containing .6g/liter of styrene-lauryl . .

106~069 .
methacrylatesulfoethylmethacryl terpolymer charge control agent) to reduce the particle size to 2 microns or less. Additional ~sopar G ~ was then added and the resultant positively-charged liqu:Ld developer contained about 0.15 weight percent toner particles and about 99.85 percent Isopar G ~. This developer was used in an electrophotographic process as described in Example 1 to develop negatively-charged electrostatic image ;
patterns, it produced images of excellent quality. Toner particles which settled out of the developer when the developer was allowed to stand during a period of little or no usage could be easily redispersed by agitation without affecting the image quality.
Example 3 -.
The li~uid developer of this example was prepared in a manner similar to Example 1 except that Monastral Blue pig-ment was utilized in place of the carbon black pigment.
Excellent quality electrophotographic images were obtained when the developer of this example was used in a conventional electrophotographic imaging process as described in Example 1.

,:0 Example 4 The liquid developer prepared in this example was --prepared in a manner similar to Example 2 except that a wetting agent, Aerosol TR (a trademark of American Cyanamid Co. for tridecyl sodium sulfosuccinate), was used in place of the ter-polymer charge control agent. The resultant liquid developer contained negatively charged toner particles and was utilized in an electrophotographic process to develop positively-charged electrostatic image patterns.

Example 5 A liquid developer toner mixture was prepared by -?9-106;~0~;9 dissolving 20 parts (by weight) of the linear crystalline` -polyester poly(nonamethylene terephthalate) having a m.p. of about 85C. in 70 parts (by weight) of dichloromethane and adding -thereto 10 parts (by weight) of carbon black pigment (purchased from Cabot Carbon Co. under the trademark of Regal~ 300R). The mixture was then ball-milled for 24 hours, precipitated in -cyclohexane, filtered and then dried. The dry particles were then milled in a small amount of Isopar G~ to disperse the particles. The resulting concentrate was then diluted to form a working strength developer by adding about~l3.5 gms.~of the above-described mixture to about one liter of Isopar G . The resulting liquid developer contained about 0.15 weight percent of toner particles dispersed in about 99.85 weight percent Isopar ~ No charge control agent was used in the developer of this example. The developer of this example provided excellent quality images when used in a conventional electrophotographic -process as described in Example 1. The toner was easily redlspersible as in Example 1.
Example 6 A liquid developer was prepared as described in Example 5 except that a noncrystalline, linear polymer of poly(ethylene terephthalate:isophthalate) having a melting point of about 60C. was used as the linear polyester. When used as a developer in a conventional electrophotographic process as described ln Example 1, high-density, good quality images were obtained.

Example 7 A liquid developer was prepared as described in Example 5 except that poly(ethylene sebacate) was used as the 3o linear crystalline polyester. Excellent quality images were

11)6;~0~9 l:
also obtained with this developer when employed in a con~
ventional electrophotographic process as described in Example 1. ~ ;
,.~ .
Example 8 ~ .
A dry particulate composition was prepared by ~.
dissolving 10 g of the linear, crystalline polyester poly~decamethylene sebacate:3,3'-~(sodio-imino)disulfonyl]- .
dibenzoate} in methylene chloride and adding thereto 5.0 g ~`~
Regal ~ 300R carbon black pigment and 0.75 g Monastral blue pigment; the mixture was then ball-milled for 24 hours and .
then precipitated in methanol, filtered and dried.
4.5g.of the above-noted dry, particulate composition was then gro~nd further in about 45 ml of Isopar G ~ containing about 0.6 g/l of the terpolymer poly(styrene-co-lauryl .
methacrylate-co-sulfethylmethacrylate) to form a liquid developer concentrate The working developer was then prepared by adding about 7.6 g of the above-noted concentrate to about 600 ml Isopar G ~. The developer of this example provided good quality liquid developed images when used in a conventional electro-photographic process as described in Example 1. The toner particles contained in this liquid developer were easily ...
redispersible as in Example 1.
The invention has been described in detail withparticular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

... , ,.. ~,~ .. .
. . ~
- , . .

Claims (10)

I claim:

1. An electrographic liquid developer composition comprising a mixture of electrostatically-attractable, heat-fixable toner particles in an electrically insulating liquid carrier having a volume resistivity greater than 1010 ohm-cms.
and a dielectric constant less than about 3.0, said toner particles (a) present in an amount of from about 0.05 to about 15 weight percent of said developer composition and (b) com-prising, in an amount greater than about 0.05 weight percent of said developer composition, a linear polyester physically inert with respect to said carrier liquid, said polyester having the formula wherein X represents a mole percentage value within the range of 0 to 100 mole percent; R and R2, which may be the same or different, represent a member of the group selected from the divalent residue of an aliphatic, alicyclic, or aromatic diol upon removal of the two hydroxy groups from said diol; R1 is a member selected from the group consisting of the divalent residue of a sulfonamido-free aliphatic, alicyclic or aromatic dicarboxylic acid upon removal of the two carboxyl groups from said acid; and R3 represents (i) a member selected from the same group as R1 and may be the same as or different from R1 or (ii) the divalent residue of a disulfonamido group-containing aromatic dicarboxylic acid upon removal of the two carboxyl groups from said acid, said disulfonamido group having a monovalent cation on the amido nitrogen atom thereof.

2 An electrographic liquid developer composition as defined in claim 1 wherein R3 is a member selected from the same group as R1.

3. An electrographic liquid developer composition comprising a mixture of electrostatically-attractable, heat-fixable toner particles in an electrically insulating liquid car-rier having a volume resistivity greater than 1010 ohm-cms. and a dielectric constant less than about 3.0, said toner particles (a) present in an amount of from about 0.05 to about 15 weight percent of said developer composition and (b) comprising, in an amount greater than about 0.05 weight percent of said developer composition, a linear crystalline polyester inert with respect to said carrier liquid, said polyester having the formula wherein X represents a mole percentage value within the range of 0 to 100 mole percent, R and R2, which may be the same or different, represent a member of the group selected from the divalent residue of an aliphatic, alicyclic, or aromatic diol upon removal of the two hydroxy groups from said diol; and R1 and R3, which may be the same or different, represent a member selected from the group consisting of the divalent residue of a sulfonamido-free aliphatic, alicyclic or aromatic dicarboxylic acid upon removal of the two carboxyl groups from said acid.

4. An electrographic liquid developer composition as defined in Claim 3 wherein said toner particles have a melting point within the range of from about 60° to about 100°C.

5. An electrographic liquid developer composition as defined in Claim 3 wherein said crystalline polyester is selected from the group consisting of poly(decamethylene sebacate), poly(nonamethylene terephthalate), poly(tetra-methylene succinate:sebacate), poly(ethylene sebacate), poly(p-xylylene sebacate), poly(decamethylene adipate) and poly(ethylene suberate).

6 An electrographic liquid developer composition comprising a mixture of electrostatically attractable toner particle in an electrically insulating liquid carrier having a volume resistivity greater than 1010 ohm-cms. and a dielectric constant less than about 3.0, said toner particles (a) present in an amount of from about 0.1 to about 3 weight percent of said developer composition and (b) comprising, in an amount greater than about 0.05 weight percent of said developer composition, a linear polyester physically inert with respect to said carrier liquid, said polyester having the formula wherein X represents a mole percentage value within the range of 0 to 100 mole percent; and R and R2, which may be the same or different, represent a member of the group selected from the divalent residue of an aliphatic, alicyclic, or aromatic diol upon removal of the two hydroxy groups from said diol; and R1 and R3, which may be the same or different, represent a member selected from the group consisting of the divalent residue of a sulfonamido-free aliphatic, alicyclic or aromatic dicarboxylic acid upon removal of the two carboxyl groups from said acid, said toner particles contained in said developer composition having an average particle size within the range of from about 0.1 to about 10 microns and having a melting point within the range of from about 60° to about 100°C., and comprising from about 0.1 to about 33 percent by weight of a colorant.

7. An electrographic liquid developer composition as defined in Claim 6 wherein said linear polyester is selected from the group consisting of poly(decamethylene sebacate), poly(nonamethylene terephthalate), poly(ethylene terephthalate:
isophthalate), poly(tetramethylene succinate:sebacate), poly(ethyl-ene sebacate), poly(p-xylylene sebacate), poly(decamethylene adipate) and poly(ethylene suberate).

8. An electrographic liquid developer composition comprising a mixture of electrostatically attractable toner particle in an electrically insulating liquid carrier having a volume resistivity greater than 1010 ohm-cms. and a dielectric constant less than about 3.0, said toner particles (i) present in an amount of from about 0.1 to about 3 weight percent of said developer composition, (ii) having a melting point within the range of from about 60° to about 100°C., and (iii) com-prising, in an amount greater than about 0.05 weight percent of said developer composition, a linear crystalline polyester physically inert with respect to said carrier liquid, said polyester having the formula wherein X represents a mole percentage value within the range of 0 to 100 mole percent; R and R2, which may be the same or different, represent a divalent residue of an aromatic diol;
and R1 and R3, which may be the same or different, represent a divalent residue of a sulfonamido-free aliphatic dicarboxylic acid.

9. An electrographic liquid developer composition comprising a mixture of electrostatically attractable toner particle in an electrically insulating liquid carrier having a volume resistivity greater than 1010 ohm-cms. and a dielectric constant less than about 3.0, said toner particles (i) present in an amount of from about 0.1 to about 3 weight percent of said developer composition, (ii) having a melting point within the range of from about 60° to about 100°C, and (iii) com-prising, in an amount greater than about 0.05 weight percent of said developer composition, a linear polyester physically inert with respect to said carrier liquid, said polyester having the formula wherein X represents a mole percentage value within the range of 0 to 100 mole percent; R and R2, which may be the same or different, represent a divalent residue of an alkylene glycol upon removal of the two hydroxy groups from said glycol and R1 and R3, which may be the same or different, represent the divalent residue of a sulfonamido-free aliphatic dicarboxylic acid.

10. In an electrographic development process wherein an electrostatic charge pattern carried on a dielectric sub-strate is developed into a visible image by applying an electrographic liquid developer composition to said charge pattern, the improvement which comprises applying, as said liquid developer composition to said charge pattern, a composition comprising a mixture of electrostatically-attractable, heat-fixable toner particles in an electrically insulating liquid carrier having a volume resistivity greater than 1010 ohm-cms. and a dielectric constant less than about 3.0, said toner particles (a) present in an amount of from about 0.05 to about 15 weight percent of said developer composition and (b) comprising, in an amount greater than about 0.05 weight percent of said developer composition, a linear polyester physically inert with respect to said carrier liquid, said polyester having the formula wherein X represents a mole percentage value within the range of 0 to 100 mole percent; R and R2, which may be the same or different, represent a member of the group selected from the divalent residue of an aliphatic, alicyclic, or aromatic diol upon removal of the two hydroxy groups from said diol; R1 is a member selected from the group consisting of the divalent residue of a sulfonamido-free aliphatic, alicyclic or aromatic dicarboxylic acid upon removal of the two carboxyl groups from said acid; and R3 represents (i) a member selected from the same group as R1 and may be the same as or different from R1 or (ii) the divalent residue of a disulfonamido group-containing aromatic dicarboxylic acid upon removal of the two carboxyl groups from said acid, said disulfonamido group having a monovalent cation on the amido nitrogen atom thereof.