IL30117A - Xerographic developer material and imaging process in which it is used - Google Patents

Description

npnyn η» πηι »ma viD:> mn»© nam τπ torna o otwo na Xerographic developer material and imaging process in which it ie used RANK XEROX LIMITED Ci 28434 2 This invention relates to imaging systems, and more ·''·. . 1 3 particularly, to improved xerographic developing materials, their !"'"'. · 4 manufacture and use. . · The "formation and development of images on the surface β of photoconductive materials by electrostatic means is well known. The basic xerographic process, as. taught by C. F. Carlson • s in U.S. Patent 2,297,691, involves placing a uniform electro- ·. static charge on a photoconductive insulating layer, exposing . · '·. 10 the layer to a ight-and-shadow image to dissipate the charge + ". 11 •on the areas of the layer exposed to the light and developing ·* 12 .the resulting latent electrostatic image by depositing on the -'; 13 image a . finely-divided electroscopic material referred to in the •■: 14 art as "toner". The toner will normally be attracted to those •; 15 . areas of the layer which retain a charge, thereby forming a toner : -16 .image corresponding to the latent electrostatic image. This " 17 powder image may then be transferred to a support surface such S :; as paper. The transferred image may subsequently be permanently . is! •affixed to the support surface as by heat. Instead of latent image formation by uniformly charging the photoconductive layer 21 il and then exposing the layer to a light-and-shadow image, one may form the latent image by directly charging the layer in image 23 configuration. The powder image may be fixed to the photoconduc2 tive layer if elimination of the powder image transfer step is desired. . Other suitable fixing means such as solvent or over¬ 26 i! coating treatment may be substituted for the foregoing heat fixing I steps. .

Several methods are known for applying the electroscopic particles to the latent electrostatic image to be 0 !! developed. One development technique, as disclosed by E.N. Wise 31 I! in U.S. Patent 2,618,552, is known as "cascade" development.

Other development methods such as "touchdown" development as disclosed by R. W. Gundlach in U.S. Patent 3,166,432 may ;' , " be used where suitable. ■· •if.

Although some of the foregoing development techniques are employed commercially today, the most widely used commercial xerographic development technique is the process known as "cascade" development. A general purpose office copying machine 8 incorporating this development method is described in U.S. Patent ' 9 3,099,943. The cascade development technique is generally carried) 10 out in a commercial apparatus by cascading a developer mixture 11 over the upper surface of an electrostatic latent image-bearing •12 drum having a horizontal axis. The developer is transported from .IS a trough or sump to the upper portion of the drum by means of an 14 endless belt conveyor. After the developer is cascaded downward 1δ along the upper quadrant surface of the drum into the sump, it 16 is recycled through the developing system to develop additional 17 electrostatic latent images. Small quantities of toner are 13 periodically added to the developing mixture to compensate for IS the toner depleted by development.. The resulting'toner image is 20 usually transferred to a receiving sheet and thereafter fused by 21 suitable means such as an oven. The surface of the drum is 22 thereafter cleaned for reuse. This imaging process i¾ then 23 repeated for each copy produced by the machine and is ordinarily '24 repeated many thousands of times during the usable life of the 2δ developer. 23 Thus, it is apparent from the description presented «-1 · ! above as well as in other development techniques, that the toner 2S is su jected to severe mechanical attrition which tends to break 29 down the particles into undesirable dust fines. The formation SO of. fines is retarded when the toner contains a tough, high Si- molecular weight resin which is capable of withstanding the ■ 1 Unfortunately, many high molecular weight materials cannot be 2 employed in high speed automatic machines because they cannot, . 3 be rapidly fused during a powder image heat fixing step. ■Ί.'' '<■ , 4 Attempts to rapidly fuse a high melting point toner by means of ·" 5 oversized high capacity heating units have been confronted with 6 the problems of preventing the charring of paper receiving sheets ' 7 and of adequately dissipating the heat evolved from the fusing S unit or units. In some cases, the. receiving sheet has actually : 9 burst into flames after passage through the fusing unit. Thus, 10 in order to avoid charring or combustion, additional equipment II such as complex and expensive cooling units are necessary to ' . 12 properly dispose, of the large quantity of heat generated by the. 13 fuser. Incomplete removal of the heat evolved will result in the 14 operator discomfort and damage to/heat sensitive machine components. Further, the increased space occupied by and the 16 high operating costs of the heating and cooling units often 17 outweigh the advantages achieved by the increased machine speed. 18 On the other hand, low molecular weight resins which are easily 19 heat fused at relatively low temperatures are usually undesirable 20 because these materials tend to form thick films on reusable . 21 photoconductor surfaces. These films tend to cause image 22 degradation and contribute to machine maintenance down time. 23 Many low molecular weight resins decompose when subjected to 24 fusing conditions in high speed copying and duplicating machines. 25 In addition, low molecular weight resins tend to form tacky 2δ images on the copy sheet whi'ch are easily smudged and often 27 offset, to other adjacent sheets. Additionally, low molecular 23 weight resins are often extremely difficult or even impossible 20 to comminute in conventional grinding apparatus. Also, the toner 30 material must be capable of accepting a charge of the correct 31 polarity when brought into rubbing contact with the surface of 32 carrier materials in cascade or touchdown development systems.

The triboelectric and, flow characteristics of many toners are adversely affected by changes in the ambient humidity. For n O example, the triboelectric values of some toners fluctuate with-- '4 changes in relative humidity and are not desirable for employment δ in xerographic systems, particularly in precision automatic machines which require toners having stable and predictable triboelectric values. Another factor affecting the stability of carrier triboelectric properties' is the tendency of some toner 9 materials to "impact" on the surface of carrier particles. When 10 developers are employed in automatic cascade developing machines 11 and recycled through many cycles, the many collisions .which occur 12 between the carrier and toner particles in„.the machine cause the ,13 toner particles carried on the surface of 'the carrier particles of the 14 to be welded or otherwise forced into the surface ae carrier 15 particles. The gradual accumulation of permanently attached 15 toner material on the surface of carrier particles causes a 17 change in the triboelectric value of the carrier particles and S directly contributes to the degradation of copy quality by 19 eventual destruction of the toner carrying capacity of the carrier. Numerous known carriers and toners are abrasive in 21 nature. Abrasive contact between toner particles, carriers, and 22 xerographic imaging surfaces accelerates mutual deterioration of 23 these components. Replacement of carriers and electrostatic 24 image bearing surfaces is expensive and time consuming. Xero- 25 j graphic copies should possess good line image contrast as well 'as 26 j acceptable solid area coverage. However, when a process is 2< j; designed to improve either line image contrast or solid area 28 j: coverage, reduced quality of the other can be expected. . Attempts ^9 to increase image density by depositing greater quantities of . !i j! toner particles on the latent electrostatic image are usually i! ' · ■ Si |! rewarded with an undesirable increase in background deposits. (i) a colorant, and (ii) a resin which comprises a polymeric esteri- acyclic or carbocyclic fication product of arVdicarboxylic acid or anhydride thereof and a diol component which inoludea a diol containing a group f6rmed by removal of two phenolic hydrogen atoms from a diphenol, and (b) a carrier for said toner particles and/or from 0.02 to 20$ by weight, based on the weight of said toner particles, of at least one solid, hydrophobic metal salt of a substituted or unsubstituted, saturated or unsaturated fatty acid available at or immediately adjacent external surfaces of said toner particles and/or said carrier. Preferably, the diol is a diether of a diphenol. The diphenol is preferably of the formula:- x x wherein R represents methylene or a substituted and/or un3U.be ituted alkylene radical having from 2 to 12 carbon atoms, or an alkylidene radical having from 2 to 12 carbon atoms, or a cycloalkylidene radical having from 3 to 12 carbon atoms; R' and- R" represent substituted and unsubsti- tuted alkylene radicals having from 2 to 12 carbon atoms, alkylene arylene radicals having from 8 to 12 carbon atoms or arylene radicals; X and X' represent hydrogen or an alk l radical having from"! to 4 carbon atoms; and n^ and 2 are each at least 1 and the average sum of and ng is less than 21. Diphenols wherein R represents an alkylidene radical having from 2 to 4 carbon atoms and R' and R" represent an alkylene radical having 3 or 4 carbon atoms are preferred because greater blocking resistance (i.e. resistance of the toner to agglomeration during storage), increased definition of xerographic characters and more opmplete transfer of toner images are achieved. Optimum results are obtained with diols in which R is an isopropylidene radical and R' and R" are propylene or butylene radicals because the resins formed from these diols possess higher agglomeration resistance and penetrate extremely rapidly into paper receiving sheets under fusing conditions. Dicarboxylic acids having from 3 to 5 carbon atoms are preferrcjd because the resulting toner resins posseos greater resistance to film formation on reusable imaging surfaces and resist the formation of fines under machine operation conditions. Optimum results are obtained with alpha, unsaturated dicarboxylic acids including fumaric acid, maleic acid or maleic acid anhydride because maximum resistance to physical degradation of the toner as well as rapid melting properties are achieved* Although not entirely clear, it is .... i believed that the presence of the unsaturated bonds in the alpha unsaturated dicarboxylic acid reactants provides the resin molecules with a greater degree of toughness without adversely affecting the fusing and comminution characteristics. The developers of this invention preferably contain from 0.02 percent to 20 percent by weight, based on the weight of the toner in the final developer mixture, of the solid hydrophobic metal salt of a fatty acid. Preferably, the developers of this invention contain from 0.05 to 4 percent by weight of the metal salt because maximum reduction of background deposits and image density are achieved,. · Without the presence of a solid hydrophobic metal salt of a fatty acid in the developer? extremely rapid degradation of reusable imaging surfaces, untenably high background, reduced toner image density, poor toner image transfer, reduced carrier particle life, increased difficulty in removing residual toner material from reusable imaging Surfaces, and reduced electrical stability may occur. Although the initial electrostatic imaging surface potential may be reduced . and abrasion resistance improved when the proportion of metal ;' ' *■ salt present is increased above about 10 percent, undesirable may ' "·' .' background deposits/increase noticeably. If the charge voltage is reduced to co^ansate for the presence of metal salt in excess of about 10 percent, the images begin to acquire a "washed out" appearance. It is not essential that the entire surface of each toner particle be coated with the.metal salt, e.g., sufficient metal salt is present when about 10 to abovtte 16 percent of the toner particle surfaces are coated with a metal salt. When the ' metal salt is dispersed in rather than coated on a toner or r; carrier particle, proportionately more metal salt is necessary in order to maintain a sufficient quantity of the exposed sal at the surface of the toner or carrier particle. The additional i:- amount of metal salt necessary depends to a large extent on the r surface area of the developer particles, hence upon the particle diameter selected. Any suitable stable solid hydrophobic metal preferably one salt of a fatty acidshaving a melting point greater than about 57° C may be' employed. Optimum results are obtained when about 0.05 to about 4 percent by weight, based on the weight of. the toner, of zinc stearate is available at the outer surfaces of the particles in the developing material. The developers of this invention containing zinc stearate are preferred because the resulting mixture is characterized by outstanding fusing rates, high cleanability from electrostatic imaging surfaces, greater triboelectric stability, dense toner images and increased resistance to mechanical attrition. Unexpectedly, both the fire hazard and excessive power consumption problems encountered in prior art high speed xerographic development processes are obviated when toners containing the above described polymeric esterification product and metal salt are employed. Diphenolic v 1.1-bis('4-hydroxy isopropoxy-phenyl) heptane, 2,2-bls(3-methyl-4' bota-hydroxy ethoxy-phenyl) propane, l,l-bls(4-beta hydroxy ethoxy phenyl)-cydohexane, 2,2'-bis(4-beta hydroxy ethoxy phenyl)-norbornane, 2,2,-bis(4-beta hydroxy ethoxy phenyl) norbornane, the polyoxyethylene ether of isopropylidene diphenol in which both phenolic hydroxyl groups are oxyethylated and the average number of oxyethylene groups per mole is 2.6 , the polyoxypropylene ether of.2-butylidene diphenol in which both the phenolic hydroxyl groups are oxyalkylated and the average number of oxypropylene groups per mole is 2.5. An example of a sui able diphenol not having the formula given above is 2.2-bis(4-beta hydroxy styryl oxy henyl)pro ane.- Any suitable dicarboxylic acid may be reacted with the diols described above to form the toner resins of this invention. These acids may be substituted, unsubstit ted, saturated or unaaturated. These acids may have the general formula: H00G R' · ·η3 COOH wherein 1 ' · · represents a substituted or unsubstituted alkylene or alkenylene radical having from 2 to 12 carbon atoms, an arylene radical or an alkylene arylene radical having from 10 to 12 carbon atoms and nj is 0 or 1.

Typical dioarboxylic acids and anhydrides thereof include: oxalic acid, raalonic acid, succinio acid, glutaric acid, adipic acid, plmelic acid, suberic aoid, azelaic acid, sebacic acid, phthalic acid, mesoconic acid, homophthalic acid, isophthalic acid, terephthallc acid, o-phenyleneacetic-beta-propionic acid, itaconic acid, malelc acid, maleic acid anhydride, funaric acid, 2,2-dimethyl fumaric acid, phthalic acid anhydride, traumatic acid and citraconic aoid.

Any suitable conventional esterfioation process may be employed to form the linear resins of this invention.

Generally, the dihydric alcohols and dioarboxylic acids are est©rifled in approximately equimolar proportions. In preparing the linear toner polymer's, the esterifica ion reaction is continued until a cooled sample of the product forma a clear solid having a melting point of at least 110°F. Preferably, the resins of this invention are selected to have a melting point between 110°F. and 240°F. for maximum fusing efficiency in high speed copying and duplicating machines. The molecular weight of the toner resins of this invention at a given melting point temperature varies considerably depending upon the reactants employed. The melting point of the toner resins of this invention may be polymerization inhibitor such as hydroquinone or pyrogallol, may be added to the charge during the esterification where the possibility of cross-linking through the acid unsaturation groups may occur.

Minor proportions of a lower alkylene glycol may also be employed in the diol component with the diols derived from diphenols in preparing the linear toner polymers of this invention. The term "lower alkylene" means an alkylene having up to 12 carbon atoms. Typical lower alkylene glycols include* ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol and mixtures thereof. For satisfactory results, the proportions of lower alkylene glycol should remain below about 50 mole percent of the total diol employed in the esterification reaction. Resistance to film formation and physical degradation are greatly enhanced when the quantity of lower alkylene glycol is maintained below about 10 mole percent of the total reacting diol component.

The polymeric esterification product employed in the toners of this invention may be blended with one or more other thermoplastic resins if desired. When blended with another thermoplastic resin, the added resin is preferably an aromatic resin, aliphatic resin, or mixtures thereof because the resulting blend is characterized by especially uniform consistency and high predictability of physical properties from batch to batoh. Many thermoplastic resins may be blended with the resin of this invention. Typical thermoplastic resins include resin modified phenol formaldehyde resins, oil modified epoxy resins, polyurethane resins, cellulose ester resins, vinyl type resins and mixtures thereof. When the resin component of the toner contains an added resin, the added component should be present 1 or carrier particles or intimately dispersed in each toner or 2 carrier particle. However, the latter embodiment is less . 3 desirable than the tumbled or milled mixtures because..a greater " 4 quantity of metal salt is required to provide a sufficient . 5 . quantity of metal -salt, exposed at. the surface of the developer . 6 .particles. The metal salts are preferably mixed with toner . 7 material by tumbling preformed finely divided metal salt 3 particles with preformed finely divided toner particles. The 9 tumbling process is continued until the preformed metal salt particles are uniformly distributed throughout the mass of toner particles. Excellent toner mixtures are obtained when the pre-'4 formed toner particles are tumbled with preformed metal salt . i! particles having a size range' between -about 0.5 to about 50 microns. The tumbled mixtures are preferred because the re- suiting treated toner exhibits extremely stable imaging charac teristics under widely fluctuating humidity conditions.

Typical fatty acids from which stable solid hydrophobic : 18 metal salts may be derived include: caproic acid, enanthylic ;, 19 acid, caprylic acid, pelargonic acid, capric .acid, undecylic acid : '. 20 ! lauric acid, tridecoic acid, myristic acid, pentadecanoic acid, 21 palmitic acid, margaric acid, stearic acid, nondecylic acid, •22 arachidic acid, behenic acid,, stillingic acid, palmitoleic acid, 23 oleic acid, ricinoleic acid, petroselinic acid, vaccenic acid, 24 I linoleic acid, linolenic acid, eleostearic acid, licanic acid, parinaric acid, gadoleic acid, arachidonic acid, cetoleic acid- and. mixtures thereof. Typical stable solid metal salts, of fatty include: zinc stearate, cadmium stearate, barium stearate, 28 lead stearate, iron stearate, nickel stearate, cobalt stearate, :'i copper stearate, strontium stearate, calcium stearate, cadmium O jj stearate, magnesium stearate, zinc oleate, manganese oleate, iron . ;i . · 31 ;j oleate, cobalt oleate, copper oleate, lead oleate, magnesium !' ■ ' · · 32 I; oleate, zinc palmitajte, cobalt palmitate, copper palmitate, magnesium palmitate, aluminum palmitate, calcium palmita d, lead caprylate, lead caproate, zinc linoleate, oobalt linoleate, calcium linoleate, zinc ricinoleate, cadAium ricinoleate and mixtures thereof.

When the solid hydrophobic metal salt of a higher fatty acid is physically mixed with or applied as a coating on toner or carrier particles, rather than dispersed throughout the toner matrix, the metal salt is preferably present in an amount from 0.02?o to XQ% based on the weight of the toner in the final developer mixture. Optimum results are obtained with 0.05 to 4% of the metal salt.

The use of small quantities of calcium stearate as a pigment wetting agent in zinc oxide developing powders is known as disclosed by Greig in U.S. Patent 3 ,053 » 688 at column 5 » line 41 and Greig et al in Canadian Patent 633 * 458 at column 9 t line 8. However, the quantity of calcium stearate used by Greig and Greig et al to facilitate the wetting of pigments dispersed in zinc ' 1 treated with zinc stearate, particularly in the range of a¼eu½ 2 0.05 to about 4 percent by weight, ' based on the total weight of 3 toner, better flow, less background, higher density .images at ·ι;·· '·' '4 lower initial charging voltages, and higher machine speeds with 5 less power are 'achieved. Drum wear is markedly reduced. 6 It is to be understood that the specific formulas given used ifa " 7 for the units contained in the resins/-of this invention represent S the vast majority of the units pre&ent, but do not exclude the · , 9 presence of other ' monomeric units or reactants than those which, have been shown. For example, some commercial materials such as t •11 the polyoxyethylene ether of isopropylidene diphenol may contain thereof 12 trace amounts of homologues/or unreaoted ethylene oxide. Any con ··. 13 minor amount of such .rubstituents may be -'present in the materials. / Xf of this invention.

Any suitable pigment or dye may be employed as the 16 colorant for the toner particles.' Toner colorants are well P known and include, for example, carbon black/ nigrosine dye, 18 aniline blue, Calco Oil Blue, chrome yellow, ultra marine blue, 19 •Quinoline Yellow, methylene blue chloride, Monas'tral Blue, Malachite Green Oxalate, lampblack,' Rose Bengal, Mona'stral Red,. 21 Sudan Black BN, and mixtures thereof. The' pigment or dyes should 22 be present in the toner in a sufficient quantity to render it 23 h Vighly colored so that it will form a clearly visible image on a 24 recording member. Thus, for example, where conventional xero25 graphic copies of typed documents are desired, the toner may 23 comprise a black pigment such as carbon black or a black dye such 27 as Sudan Black 3N dye available from General Aniline and Film 23 Corporation. Preferably, for sufficient color density, the 29 I pigment is employed in an amount from about- 1% to -about 20% by : weight, based on the total weight of the colored toner. If the 31 i toner colorant employed is a dye, substantially smaller quantities' used in have a surprisingly high affinity for dyes and are more easily and uniformly dyed than most conventional toner resins. Although 3 it is not entirely clear, it is postulated' that the unusually .· 4 large spacing between the linear polymer molecules of "the toners 5 of this invention- allow large dye molecules to uniformly penetrate 6 and intimately mix with the resin molecules. . The colorants may 7 be mixed with the resin component- rior to, during or after the S resin component is polymerized. Obviously, any colorant hich 9 inhibits polymerization should be blended with the resin after !; the resin is formed'.

The toner compositions of the present invention may- be 12 prepared by any well know, toner mixing and comminution technique,] 13 For example, the ingredients may be thoroughly mixed by blending ■. 14 and milling the components and thereafter micropulverizing the 15 ! resulting mixture. Another well known technique for forming 16 toner particles is to spray-dry a (Suspension, a hot melt, or a 17 solution of the toner composition.

IS When the toner mixtures of this invention are to be 19 )i .employed in cascade development processes, the toner should j! j1 have an average particle diameter less-, than about 30 microns and j 21j preferably between about 5 and about 17 microns for optimum 22 !| results. For use in powder cloud development methods, particle V 23p diameters of slightly less than 1 micron are preferred. 24 Suitable coated and uncoated carrier materials for i! cascade and magnetic brush development, are well known in the art. The carrier particles may be electrically conductive, insulating, •27 !! magnetic or non-magnetic, provided that the carrier particles 23 acquire a charge having an opposite polarity to that of the toner 29 particles when brought in close contact with the toner par-cicles '30 so that the toner particles adhere to and surround the. carrier 01 particles. When a positive reproduction of an electrostatic 32 image is desired, the carrier particle is selected so that the black in the thermoplastic resin body. The resulting mixed composition is cooled and then finely subdivided in a jet pulverizer to size of ebeat of the pulverized toner particles are mixed with about 0.0040 parts by weight of zinc stearate particles having a particle size j between abettfe 5 to about- 40 microns, and about 99 parts by weight of Xerox 813- carrier beads and substituted for the 813 developer in the testing machine described in Example I. Under substantially identical test conditions, it is found that the original standard Xerox 813 drive motor can be used and that the minimum fuser . temperature at which legible copies obtained after an abrasion run of 5 revolutions of the abrading cylinder is about 505° F.

This is a reduction of about 95° F. from the fuser temperature required for the- control sample of Example I. No glowing embers are observed'on the copy samples as they emerge from the fuser. surface Micrograph studies of the reusable imaging/after 10,000 cycles reveals less wear and degradation of the imaging surface than the imaging surface of Example I. Microscopic examination of the fused toner image reveals substantial wetting of the paper fibers by the resin. with most of the resin material embedded below the outer surface of the paper copy sheet.

' , EXAMPLE IV A toner mixture is prepared comprising about 7 parts by weight of carbon black (Super Carbobar) and about 93 parts .. by weight of a polymeric condensation product of 2 2-bis (4- beta hydroxy e'thoxy phenyl) -propane and fumaric acid having a ! molecular weight of about 5,000. After melting and preliminary mixing, the composition is fed into a rubber mill and thoroughly milled to yield a uniformly dispersed composition of. the carbon* black in the thermoplastic resin body. The resulting mixed inel subdivided in a et 1" J and about 99 parts. by weight of 813 Xerox carrier beads and 2 substituted for the 813 developer in the testing machine ύ described in Example I. Under substantially identical test conditions, it is found that the original standard Xerox 813 drive motor can be employed and that the minimum fuser temperature at which legible copies are obtained after an abrasion run of 5 revolutions of the abrading cylinder is about 570° F. This is a 8 reduction of 30° F. from the fuser temperature required for the 9 control sample of Example I. No glowing embers are observed on 10 the copy sheet samples as they emerge from the fuser. Micro- IX I graph studies of the imaging surface after 10, 000 cycles reveals.- 12 less wear and degradation of the surface than the imaging surface *3 of Example I. Microscopic examination of;l>the fused toner image 14 ' reveals very good wetting' of the paper by the toner with a Ίδ substantial portion of the resin material embedded below the • 16 outer surface of the paper copy sheet. 17 EXAMPLE VII 18 A toner mixture is prepared comprising about 3 parts 19 by weight of Sudan Black-BN dye, 2 parts by weight carbon black 20 (Neo Spectra Mark II)·, and about 95 parts by weight of a polymeric! 21 condensation product of 2,2-bis (4-hydroxy isopropoxy phenyl)- . 22 propane, ethylene glycol and itaconic acid having a- molecular 23 weight of about 1,500. After melting and preliminary mixing, the 24 composition is fed into a rubber mill and thoroughly milled to ; yieid a uniformly dispersed composition of the dye in the thermo¬ 26 ί plastic resin body. The resulting mixed composition is cooled 27 and then finely subdivided in a jet pulverizer to yield toner 23 particles having an average particle size of about ό to about 9 microns. About 2 parts by weight of the pulverized tonsr particles are mixed with about 0.1 parts by weight or zinc oleate 31 j! having a particle size from about 0.75 to a out 30. microns, and 1 :l - about 99 parts by weight of 813 Xerox carrier beads and

Claims (9)

1. WHAT WE CLAIM IS: 1. A xerographic developer material comprising particles, said particles including (a) finely divided toner . articles comprising (i) a colorant and (ii) a resin which comprises a . , acyclic or qarbpcyclJLc polymeric esterificat ion product of a/dicarboxylic acid or anhydride thereof and a diol component which includes a diol containing a group formed by remoyal of two phenolic hydrogen atoms from a diphenol and (b) a carrier for said toner, particles and/or from 0.02 per cent to 20 per cent by weight, based on the weight of said toner particles, of at least one solid, hydrophobic metal salt of a substituted or unsubstituted, saturated or unsaturated fatty acid at or immediately adjacent, external surfaces^of said toner particles and/or said carrier.

2. Ά xerographic developer material according to claim 1 wherein R is methylene or a substituted or unsubstituted alkylene radical having from 2 to 12 carbon atoms, or an alkylidene radical having from 2 to 12 carbon atoms or a cycloaklylidene radical having from 3 to 12 carbon atoms; R' and R" are substituted or unsubstituted alkylene radicals having from 2 to 12 carbon atoms, alkylene arylene radicals having from 8 to 12 carbon atoms or arylene radicals; X and X' are hydrogen or alkyl radicals having from 1 to 4 carbon atoms; and n^ and are each at least 1 and the average sum of n, and n. is less than 21.

3. A xerographic developer material according to claim 1 -or 2 wherein said dicarboxylic acid or anhydride thereof is selected from dicarboxylic acids of the general formula "· ': H OOCR' ' ' COOH and anhydrides thereof wherein R1 1 ' is an alkylene radical having from 1 to 12 carbon atoms, an alkenylene radical having from 2. to 12 carbon atoms, an arylene radical or an alkylene arylene radical having from 10 to 12 carbon atoms and n is .*.. 0 or 1; ' '

4. Λ xerographic developer material according to any of claims Γ to 3 wherein' said toner particles have an average particle diameter less than 30 microns and said resin has a melting, point of ,at least 110°F.

5. A xerographic developer^material according to any of claims l 'to 4 wherein said polymeric esterification product is a condensation product of 2,2 bis (4-hydroxy-' isopropoxy-phenyl) -propane and fumaric acid.

6. A xerographic developer material according' to any of claims 1 to 4 wherein said polymeric esterificat on product is a condensation product of 2,2 bis (4-hydroxy-. isopropoxy-phenyl) -propane and 2,2 dimethyl fumaric acid.

7. A xerographic developer material according to any of claims 1 to 4 wherein said. polymeric esterification product is a condensation reaction product of 2,2 bis (4-hydroxy-butoxy-phenyl) -propane and fumaric acid.

8. A xerographic developer material according to . any of claims 1 to 4 wherein said polymeric esterification product is a condensation product of 2,2 bis (4-hydroxy-butoxy-phenyl) -propane and 2,2-dimethyl fumaric acid. acid has a melting point greater t an C. 17. A xerographic developer material according to any of claims .1 to 16 wherein said toner particles have an average particle diameter less than 30 microns. 18. ' A xerographic developer material according to any of claims- 1 to 17 wherein said developer material includes carrier particles larger than said toner particles 1

9. ' A xerograp ic developer material according to claim 18. herein said carrier particles have an average particle diameter between 50 to 1000 microns. 20. A xerographic developer material according to · claim- 17 or 18 comprising 1 part by weight of said toner particles and from 10 to 200 jparts of said carrier particle 21. A xerographic developer..material according to ■ any' of claims 1 to 17 which is free from carrier particles. 22. A process for the preparation of said xerographic developer of claim 1 comprising forming said finely-divided toner particles as particles having an average particle diameter less than 30 microns and thereafter tumbling said finely-divided toner material with said solid, stable hydrophobic metal salt of a fatty acid until said metal salt is uniformly mixed with said finely-divided toner material. 23. An imaging process comprising the steps .'of forming an electrostatic latent image on a surface and contacting said surface with a xerographic developer material according to any of claims 1 to 21 whereby at least a portion of said finely-divided toner material is attracted to and held on said surface in conformance to said electrostatic latent image. 24. An imaging process according to claim 23 further including the steps of transferring said toner image to a receiving surface and fusing said toner image on said receiving surface. 25. A xerographic developer material according to claim 1 substantially as herein described. Fey the Applicants i!iJ&lNKOLi) O!IH 'AND MBT1¾3$