CA1077324A - Carrier/developer composition containing styrene alkyl acrylate or methacrylate polymer with acylated, pendant hydroxyl or amino groups - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Electrostatographic developer compositions for use in developing electrostatic latent images wherein the triboelectric charging potential of functional polymers employed in the toner materials are controlled through chemical alteration by acylation of hydroxyl and amino functions. The controlled variation of the triboelectric behavior of functional polymers by acylation provides a means of attaining optimum triboelectric responses in development systems.

Description

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~ACX~I~OUN~ ol~ INV~N'rlON
This inven-tion relates in general to imaging systems and more particularly to improved electrostatographic developer mixtures for use in such systems.
The formation and development of images on the surface of photoconductive materials by electrostatographic means is known. The basic electrostatographic process as taught by C. F. Carlson in U. S. Patent 2,297,691 involves placing a uniform electrostatic charge on a photoconductive insulating layer, exposing the layer tc a light and shadow image to dissipate the charge on the areas of the layer e~posed to the light, and developing the resultant electro-static latent images by depositing on the image, a finely-divided electroscopic material referred to in the art as "toneri'. The toner is attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This "powder" image may then be transferred, usually electro-statically, to a support surface such as paper. The trans-ferred image may subsequently be permanently affixed to the support surface by heat or other suitable affixing means such as solvent or overcoating treatment may be usea instead.
Many methods are known for applying the electro-scopic particles to the latent image to be developed. One development method as disclosed by E. N. Wise in U. S. Patent

2,618,582 is kno~n as "cascade" development. In this method, developer material, comprising relatively large carrier particles, having finely-divided toner particles electrostati-cally clinging to the surface of the carrier particles, is conveyed to, and rolled or cascaded across the surface bearing , .

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the elc~ctrosta~ic latent imacJc. 'l'he char~cd por~ions of the surface have a charge of the same polari-ty as, but stronger than, the carrier par~icles. Toner and c~-rrier particles having opposite polarities are selected so that -the toner particles cling to the carrier particles. In order to develop a negatively charged electrostatic latent image, a toner and carrier combination are selected in which the toner is triboelectrically positive in relation to the carrier. Conversely, to develop a positively charged electrostatic latent image, a toner and carrier combination wherein the toner is triboelectrically negative in xelation to the carrier is used. The triboelectric relationship between the toner and carrier depends on the relative posi-tions of the materials in the "triboelectric series". In this series, materials are arranged in ascending order of their ability to take on a positive charge. Each material is positive with respect to any material classified below it in the series; and, negative with respect to any material above it in the series. As the developer mixture cascades or rolls across the image-bearing surface, the toner particles are electrostatically attracted from the carrier to the charged portions of the image-bearing surface, whereas they are not electrostatically attracted to the uncharged or background portions of the image which they contact. The carrier particles and unused toner particles are then recycled. The cascade development process is extremely good for the development of line copy images, and is the most widely used commercial electrostatographic development technique. ~ general purpose office copying machine incor-porating this technique is described in U. S. Pat:ent 3,099,943.

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Ano~ller ~ecllni~luc for d~velouln~J electrostatic latent images is the "n)agnctic brush" process as discloscd, for example, in U. S. Patent 2,87~,063. In this process, a developer material containing toner and magnetic carrie~
particles is attracted to and is carried by a m'-gnet. The magnetic field causes alignment of the magnetic particles in a brush-like configuration. When this magnetic brush is brought into contact with an electrostatic latent image-bearing surface, the toner particles are attracted from the carrier particles of the brush to the charged areas of the image-bearing surface but not to the uncharged areas. Since the charged areas have an imagewise configuration, the toner material clings to the surface in imagewise configuration, thus developing the latent image.
Another method for developing electrostatic latent images is disclosed in U. S. Patent 3,503,776 issued to R. W.
Gundlach. I~ this method, images are formed by transporting an electrostatic latent image-bearing surface ir a generally ascending arcuate path, and contacting only the image in a contact zone with a bath of developer material transported in a concave chamber adjacent to the lower path of the imaging surface. The contact zone extends from about the lower-most point of the arcuate path to the uppermost point of the arcuate path. As the imaging surface is transported along its arcuate path, frictional contact between the developer and the imaging surface in the contact zone circulates the developer in the bath and brings developer material into developing configuration with the imaged surface.
Many other methods, such as the "touchdown" develop-ment method clisclosed by C. R. Mayo in U. S. Patent 2,895,847, ~3'773Z'~

are known for applyincJ clectroscopic particl~s to th~ electro-static latent image to be developed. The developmcnt process, as described above, together with numerous modifications, are well-known to the art through various patents and publications and through the widespread availability and utilization of electrostatographic imaging equipment~
In automatic reproduction equipment, it is conven-tional to employ as the imaging plate, a photoconductor on a conductive substrate in the form of a cylindrical drum or a flexible belt which is continuously rotated through a cycle of sequential opexations including charging, exposing, develop-ing, transferring and cleaning. The developer chamber is charged with a developer mixture comprising carrier particles and enough toner particles for hundred~ of reproduction cycles Generally, the freshly charged developer mixtures contain between about 1.5 and about 5% toner particles based upon the weight of the developer. This initial concentration provides sufficient toner for many reproduction cycles without causing undesirably high background toner deposition.
While ordinarily capable of producing good quality images, conventional developing systems s~ffer serious defi-ciencies in certain areas. In the reproduction of high contrast copies such as letters, tracings, and the like, it is desirable to select the electroscopic powder and carrier materials so that their mutual electrification is relatively large; the degree of such electrification being governed in most cases by their relative positions in the triboelectric series. However, when otherwise compatible electroscopic powder and carrier materials are removed from each other in the triboelectric series by too great a distance, the .
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rcs~ltincJ imagcr. arc vcry Fain~ becausc ~hc attrac~:ive forccs between the carrier an~ toner particles compete with the attractive forces between the electrostatic latent image and the carrier particles. Although the ima~e density described in the immediately preceding sentence may be improved by increasing the toner concentration in the developer mixture, undesirabl~ h~gh background toner deposition as well as increased toner impaction and agglomeration is encountered when the developer mixture is overtoned. The initial electrostatographic plate charge may be increased to improve the density of the deposited powder image, but the plate charge would ordinarily have to be excessively high in o.rder to attract the electroscopic powder away from the carrier particle. Excessively high electrostatographic plate charges are not only undesirable because of the high power consumption necessary to maintain the electrostatographic plate at high potentials, but also because the high potential causes the carrier particles to adhere to the electrostatographic plate surfaces rather than merely roll across and off the electro-statographic plate surface. Print deletion and massive carry-over of carrier particles often occur when carrier particles adhere to reusable electrostatographic imaging surfaces. Massive carrier carry-over problems are particularly acute when the developer is employed in solid area coverage machines where excessive quantities of toner particles are removed from carrier particles thereby leaving many carrier particles substantially bare of tonsr particles. Further, adherence of carrier particles to reusable electrostatographic imaging surfaces promotes the formation of undesirable scratches on the surface during image transfer and surface 7~2~

cleaning operations.
Thus, it is apparent from the description prescnted above as we~l as in other development techniques, that the tc,ner is subjected to severe mechanical attrition which tends to break down the particles into undesirable dust fines. The formation of fines is retarded when the toner contains a tough, high molecular weight resin which is capable of with-standing the shear and impact forces imparted to the toner in the machine. Unfortunately, many high molecular weight materials cannot be employed in high speed automatic machines because they cannot be rapidly fused during a powder image heat fixing step. On the other hand, low molecular weight resins which are easily heat fused at relatively low temper-atures are usually undesirable because these materials tend to form thick ~ilms on reusable photoconductor surfaces.
These films tend to cause image degradation and contribute to machine maintenance down time. Many low molecular weight resins decompose when subjected to fusing conditions in high s~eed copying and duplicating machines. In addition, low molecular weight resins tend to form tacky images on the copy sheet which are easily smudged and often offset to other adjacent sheets. Additionally, low molecular weight resins are often extremely difficult or even impossible to comminute in conventional grinding apparatus. Also, the tonex materials must be capable of accepting a charge of the correct polarity when brought into rubbing contact with the surface of carrier materials in cascade or touchdown development systems. Additionally, many toner materials cannot satisfactorily be transferred by conventional electrostatographic devclopment systems from reusable imaging .

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surfaces in a~ltomatic copyincJ and ~uplicatincJ machines. Since most polymeric toner m~t~rials are defic_ent in one or more of the above areas, there is a continuing need for improved toners and developers.
It is also apparent t:hat many materials which other-wise have suitable properties for employment as earrier particles are unsuitable because they possess too high a triboelectrie value. In addition, uniform triboelectric surface eharacteristics of many carrier surfaces are difficult to aehieve with mass production techniques. Quality images are, in some instances, almost impossible to obtain in high speed automatic machines when carriers having non-uniform trlboe-lectric properties are employed. Although it may be possible to alter the t~iboelectric value of an insulating earrier material by blending the carrier material with another insu~ating material having a triboelectric value from the triboelectrie value of the original carrier material, relatively larger quantities of additional material are necessary to alter the triboelectric value of the original carrier material. The addition of large quantities of material to the original earrier material to change the triboelectric properties thereof requires a major manufacturing operation and often undesirably alters the original physical characteristics of the earrier material. Further, it is hig.hly desirable to control the triboeleetrie properties of earrier surfaees to aeeommodate the use of desirable toner eompositions while retaining the other desirable physieal charaeteristics of the carrier. The alteration of the triboeleetric properties of a earrier by applying a surface coating thereon is a partieularly desirable teehnique. With this technique, not only is it possible to ~'773Z'~

control the triboelectric properties of a carrier made from materials having desirable physical characteristics, it is also possible to employ materials previously not suitable as a carrier. Thus, for example, a carrier having desirable physical properties with the exception of hardness, can be coated with a material having desirable hardness as well as other physical properties, rendering the resultant product more useful as a carrier. However, since most carrier coating materials are deficient in one or more of the above areas, there is a continuing need from improved electrostatographic carrier and developer compositions and methods for forming the same.
In accordance with one aspect of this invention there is provided an electrostatographic composition for use in developing electrostatic latent images on a recording surface, characterized in finely-divided particles comprising a polymer selected from the group consisting of styrene-alkylmethacrylate a~d styrene-alkylacrylate containing pendant hydroxyl or amino groups in the pendant ester functions, said polymer having been exposed to systematic chemical alteration of said pendant ester functions by acylation with an acylating agent to provide particles characterized as having controlled triboelectric charging properties.
In accordance with another aspect of this invention there is provided an electrostatographic carrier composition for use in developing electrostatic latent images on a record-ing surface, said carrier composition comprising carrier particles having an average particle diameter between about 50 microns and about 1,000 microns, each of sai~ carrier particles comprising a core surrounded by from about 0.1 percent to about 10.0 percent by weight based on the weight of said carrier particles of an outer coating of a polymer selected from the group consisting of styrene-alkylmethacrylate an~ styrene-~0'773~'~

alkylacrylate containing pendant hydrox~l and amuno moieties,said polymer having been exposed to systematic che~ical modifica-~i tion of the pendant hyd~o~ 1 and amino moieties of said polymercy /c~ g e ~ ~
I by acylation~to provide carrier particles characterized as having controlled triboelectric charging properties.
In accordance with another aspect of this invention there is provided an electrostatographic developer composition comprising finely-divided toner particles electrostatically cling-ing to the surface of carrier particles, said toner particles having an average particle diameter of between about 4 and 20 microns, said toner particles comprising a colorant and a polymer selected from the group consisting of styrene-alkylmetha-crylate and styrene-alkylacrylate containing pendant hydroxyl or amino groups in the pendant ester functions, said polymer having been exposed to systematic chemical alteration of said pendant ester functions by acylation with an acylating agent to convert said hydroxyl groups to esters and said amino groups to amides thereby providing toner particles characterized as having controlled triboelectric charging properties.
In accordance with another aspect of this invention there is provided an electrostatographic imaging process com-prising the steps of providing an electrostatographic imaging member having a recording surface, forming an electrostatic latent image on said recording surface, and contacting said electrostatic latent image with a developer composition com-prising finely-divided toner particles electrostatically clinging to the surface of carrier particles, said toner particles having an average particle diameter of between about 4 and about 20 microns, said toner particles comprising a colorant and a polymer selected from the group consisting of styrene-al~ylmethacrylate and styrene-alkylacrylate contain-ing hydroxyl or amino groups in the pendant ester functions, -9a-: : .
: - .

~(37'73~4 said polymer having been exposed to systematic chemical altera-tion of said pendant ester functions by acylation with an acylat-ing agent to convert said hydroxyl groups to esters and said amino groups to amides thereby providing toner particles charac-terized as having controlled triboelectric charging proper-ties, whereby at least a portion of said finely-divided toner particles are attracted to and deposited on said recording surface in conformance with said electrostatic latent image.
By way of added e.~planation, in accordance with an aspect of this invention chemical alteration of the triboelectric charging potential of functional polymers employed as developer materials is controlled. The controlled variations of the tri-boelectric behavior of functional polymers provides a means of attaining optimum triboelectric responses of electrostatographic developer materials for specifically defined applications.
Thus, in accordance with this invention, monomeric and/or polymeric materials are systematically chemically modified to provide structural effects which yield structure triboelectric property relationship among amines, amides, alcohols, esters, and urethanes. These relationships have been found to be extremely helpful in designing new toners and carriers. By this invention, the triboelectric charging properties of toner-carrier pairs are controlled to enable optimum triboelectric relationships in developer compositions.
It is to be noted that, by itself, no material has a triboelectric charge. The magnitude of a triboelectric :) .
.. . . . .
. .
.
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charg~ d~p~ncls u~on boLi~ the t~ncr and tlle c~lrrier n,aterial.
Thus, replacemcnt of one o~ the components to optimize tri-boelectric charging properties is generally necessary to provide the desired triboelectric response. Py so doing, greater latitude is available for speeific eleetrostatographie applieations. In aecordanee with this invention, it has been found that by varying the degree of ehemical modifica-tion of polymerie materials for use as toner partieles, either stoiehiometrieally or kinetically, the triboelectric properties of developçr materials ean be eontrolled in a continuous manner.
In eleetrostatographie development of selenium photoconduetor latent images, polymers which tend to take on a ~elatively high negative eharge are generally satisfaetory ~or use as toner materia~ and those that take on a high positive ch~r~e are generally satisfaetory for use as earrier or carrier ~oating materials, In eleetrostatographic development of other photQeonduGtor la~ent imageS~ for example, zine oxide, ~hthaloeya~ine, eadmium sulfide, polyvinylearbazole-trinitro-~l~re~one, polymexs generally, exaetly the opposite is true.
In aecordanee with ~his invention, the triboe'ectrie properties of developer matexials are eorrelated with their structural composition and ther@by predictably eontrolled. Sinee the distance b~tween a ~iven toner-earrier pair on a triboeleetrie char~in~ scale determines the triboelectric eharge between ~hem, their relative positions determine the sign of the triboeleetrie ehaxge. Those materials low on the scale prefer to adopt a positive charge and those materials high on the scale prefer to adopt a negative charge. ~ppropriate toner-carrier pairs ean be selected based on their triboel~ctric charging or triboelectric series relationship to satisfy a ~7~32~
particular accc~able tri~oele~ctric cllarging range requirement for a given electrostatographic machine developer housing.
It has been found that triboelectric behavior is a function of molecular structure which now allows the controlled and progressive modification of the triboelectric charging properties of developer compositions so as to obtain optimum triboelectric charging properties between toner and carrier ' pairs. Thus, by this invention, adjustment of the triboelectric charging properties of electrostatographic developer materials need not be done in stepwise fashion but may be accomplished in a continuous manner providing a high degree of "fine tuning"
of triboelectric properties for developer materials.
In accordance with this invention, the triboelectric charging properties of monomeric and polymeric compounds may be modified by systematic chemical modificàtion by means of acylation of hydroxy - or amino - containing monomers and polymers. Cascade development triboelectric charging evalu-ations of such acylated monomers and polymers have demonstrated that these materials charge more negatively than the starting materials.
It has been found that reaction of the pendant hydroxyl or amino moieties of monomers, polymers, or copolymers with an acylating agent provides a means of continuous control of the triboelectric properties of such materials. More specifically, as the degree of acylation increases, the capacity for negative triboelectric charging of such monomers, polymers, and copolymers increases~ The degree of acylation may be controlled, either kinetically or stoichiometrically enabling the desired con~ersion. Furthermore, various types ., ~ .. . .

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of ac~ tirl~J ~ ell~s ~Jhicll are reac~ive ~oward h~droxyl and amino functions may be employed.
Thus, in accordance with this invention, the triboelectrlc properties of monomers, polymers, and copolymers are continuously controllably variable by means of controlling the amount and type of acylating agent. It has also been found that the crosslinking of hydroxy or amino functionalized polymers via reaction of the pendant hydroxyl or amino moietles with a crosslinking agent such as a diisocyanate provides a further means of continuous control of the triboelectric properties of the polymer. Various types of crosslinking agents which are reactive toward hydroxyl or amino functions may be employed. However, the use of monofunctional tri-boelectric charging modifiers is generally preferred for toner materials. In addition, it is not necessary for the polymer material to be crosslinked to cbserve a change in its triboelectric charging properties since the change in tribo-electric charging is not due to molecular weight change.
Thus where polymer materials have satisfactory properties for electrostatographic use it is highly desirable to be able to alter and control their triboelectric properties as toner and carrier materials. For example, hydroxy or amino functionalized polymers such as styrene-alkyl methacrylate copolymers derived by aminolysis may be prepared to possess the desired triboelectric response when mixed with any given conventional carrier material thus enabling the "fine-tuning"
of the triboelectric properties of the developer comhination.
In addition to these transformations, functionalized polymers may be further derivatized. For example, an aminolyzed polymer having the general structure ~7732'~

~HC}12 I CI12 CONH ( CH2 ) 6X

where X may be N~12, OH, NHCOC6H4R, OCOC6H4R or H provides polymer compositions of varying triboelectric charging potential. More specifically, conversion of the ~H2 group to be a benzamide (X=NHCOC6H4R) causes the polymer to accept more negative charge. The nitro substituent (R) causes more negative charging than does methoxy (R). Likewise, conversion of the OH group to OCOC6H4R also allows the polymer to accept more negative charge. The effect of masking hydroxyl functions may also be obtained by providing polymers containing blocked diisocyanates~ Upon conversion from free hydroxyl to the urethance, upon blocking (thermal liberation of) the diisocyanate, the triboelectric charge on the polymeric material is more negative. Further, ethyl cellulose, treated with phenyl isocyanate to effect conversion of hydroxyl moieties to urethane functions is found to decrease its capaeity for positive charging.
It is also noted that the triboelectric charging capaeity is controlled by the substituent R of the benzamides (X=NHCOC6H4R~ and benzoates (X=OCOC6H4R). The propensity for negative eharging increases with increasing electron withdrawing power of R as measured by substituent constants in each case.
The chemical modification of such materials enables the alteration of materials having optimum physical properties iil such a ~ay as to improve their triboelectric properties for eleetrostatographic use. This invention may serve as a guide for the preparation of toner and carrier compositions having "finely-tuned triboelectric charging properties, and the ~ot7~732~

capdcity for con~inuous c~nLro1 of 5UCil ~ro~erti~s throu~h variation in the exte~t of reaction may be employed for such purpose.
Any suitable vinyl resin having a melting point of at least akout 110F may be emp]oyed in the toners of this invention. Generally, suitable vinyl resins employed in the toner have a weight average molecular weight between about

3,000 to about 500,000. The resins may be formed by the polymerization of mixtures of two or more of these unsa-turated monomers. The expression "addition polymerization" is intended to include known polymerization techniques such as free radical, anionic and cationic polymerization processes.
m e combination of the resin component and colorant whether the resin component is a homopolymer, copolymer, or blend should have a blocking temperature of at least about 110F and a melt viscosity of less than about 2.5 x 10 poise at temperatures up to about 450F. When the toner is characterized by a blocking temperature less than about 110F, the toner particles tend to agglomerate during storage and machine operation and also form undesirable films on the surface of reusable photoreceptors which adversely affect image quality.
Any suitable pigment or dye may be employed as the colorant for the toner particles. Toner colorants are well-known and include, for example, carbon black, nigrosine dye, aniline blue, Calco Oil Blue, chrome yellow, ultra marine blue, duPont Oil Red, Quinoline Yellow, methylene blue chloride, phthalocyanine blue, Malachite Green Oxalate, lamp black, Rose Bengal and mixtures thereof. The pigment or dye should be present in the toner in a sufficient quantity to .. . ...

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r~n~er i~ hicJhly colore~ so ~hat i~ wlll fo~n a clearly visible image on a recordincJ member. Thus, for cxample, ~here conventional electrostatographic copies of typed docu-ments are desired, the toner may comprise a black pigment such as carbon black pigment such as carbon black or a black dye such as Amaplast Blac~ dye, available from the National Aniline Products, Inc. General:Ly, the pigment is employed in an amount from about 1 percent to about 20 percent by weight based on the total weight of the colored toner. If the toner colorant employed is a dye, substantially smaller quantities of colorant may be used. ~Iowever, since a number of the above pigments used in electrostatographic toner compositions may affect both the glass transition and fusion temperatures of the toner compositions of this invention, their concentra-tion preferably should not exceed about 10 percent by weight of the colored toner.
The toner compositions of the present invention may be prepared by any well-known toner mixing and comminution techniques. For example, the ingredients may be thoroughly mixed by blending, mixing and milling the components and thereafter micropulverizing the resulting mixture. Another well-known technique for forming toner particles is to spray-dry a ball-milled toner composition comprising a colorant, a resin, and a solvent. In addition, there are various approaches to obtaining dyed polymers including, but not limited to, direct polymerization with the dye in the polymer backbone, direct polymerization with the dye pendant, or post polymer-ization attachment. The preferred method of preparing the toner materials of this invention is by direct polymerization of copolymerization to a reactive polymer. In this way, a -~773;~
small an~ con~lollcd amount, for ~xample, about 5 to abou~ 15 mole percent, o~ rcactive ~unctionali-ty may be introduced.
A dye may then bc attached to the reactive functionality to the extent desired. The remainin~ reactive groups may be reacted with another reagent -to enhance the triboelectric properties of the toner materials. With respect to dye attachment, many of the reactions in solid phase peptide synthesis using reactive resins are applicable. For example, polystyrene may be acylated under Friedel-Crafts conditions enabling the preparation of p-benzoyl derivatives which may be reduced to the benzhydrols and these may be converted to benzhydrol chlorides and bromides, all being in resin form.
m e halides are very reactive and may be used for attachment of the dye. The reactions of functional groups attached to polymers are frequently subject to steric influences such as hindrance caused by the proximity of reactive groups to th~
main polymer chainO Thus, polymers carrying 2-hydroxyethylamide side chains are found to be difficult to dye, while polymers carrying 6-hydroxy hexylamide moieties accept covalent dyes very readily. Likewise, 2-aminoethylamide side chains resist dye attachment, while 6-amino hexylamide side chains are dyes readily and to completion. There is no definite cut-off chain length for the "leash", but maximum conversion can usually not be reached unless at least about 3 methylene or other linking groups separate the polymer attachment group from the dye attachment group.
When the toner materials of this invention are to be employed in a cascade development process, the toner should have an average particle size less than about 30 microns and preferably between about 4 and about 20 microns for optimum ..

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results. l`or use in ~ OWCIeI cloud development me~hods, particlc diameters of slightl~ less than 1 micron are preferred.
Any suitable coated or uncoated carrier material including those prepared in accordance with this invention, as well as those well-known in the art may be used in conjunction with the toner of t:his invention. The carrier particles comprise any suitable solid materials, provided that the carrier particles acquire a charge having an oppGsite polarity to that of the toner particles when brought in close contact with the toner particles so that the toner particles adhere to and surround the carrier particles. When a positive reproduction of the electrostatic image is desired, the carrier particle is selected so that the toner particles acquire a charge having a polarity opposite to that of the electro-static image. Alternatively, if a reversal reproduction of the electrostatic image is desired, the carrier is selected so that the toner particles acquire a charge having the same polarity as that of the electrostatic image. Thus the material for the carrier particles are selected in accordance with their triboelectric properties in respect to the electroscopic toner so that when mixed or brought into mutual contact, one component of the developer is char~ed positively if the other component is below the first component in the triboelectric series and negatively if the other componert is above the first component in a triboelectric series. By proper selec-tion of carrier materials in accordance with their tribo-electric effects, the polarities of their charge, when mixed, are such that the electroscopic toner particles adhere to and are coated on the surfaces of carrier particles and also adhere to that portion of the electrostatic image-bearing :~ , ' ' ' : . ,' i63'77;~
surr~e llavill~J a gre.l~r a~Lr.lcLioll ~ur l~c ~ollc~r Lllan the carrier particles. 'rypical carriers include sodium chloride, ammonium chloride, aluminum potassium chloride, Rochelle salt, sodium nitrate, aluminum nitrate, potassium chlorate, granular zircon, ~ranular silicon, methyl methacrylate, glass, silicon dioxide, nickel, steel, iron, ferrites, and the like. The carriers may be employed with or without a coating. Many of the foregoing and other typical carriers are described by L. E. Walkup et al in U. S. Patent 2,368,~16 and ~. N. Wise in U. S. P~tent 2,618,552. An ultimate coated carrier particle diameter between about 50 microns to about 1,000 microns is preferred because the carrier particles then possess sufficient density and inertia to avoid adherence to the electrostatic images during the cascade development process. Adherence of carrier beads to electrostatographic drums is undesirable because of the formation of deep scratches on the surface during the imaging transfer and drum cleaning steps, particularly where cleaning is accomplished by a web c eaner such as the web disclosed by W~ P. Graff, Jr., et al in U. S. Patent 3,186,838. Also print deletion occurs when carrier beads adhere to electrostatographic imaging surface.
Generally speaking, satisfactory results are obtained when about 1 part toner is used with about 10 to 200 parts by weight of carrier.
With regard to carrier materials in accordance with this invention, it is to be noted that materials such as those derived by aminolysis of styrene-methacrylate copolymers provide excellent carriers and carrier coatings, especially in view of their crosslin~ability. By the use of such materials, toners that previously provided unacceptable triboelectric ~, .. . .

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r~sI~c)nse with conventior)al carricrs now funct:ion properly.
~hus, the coatincl of carrier corcs, for e~ample, metallic beads, with ~unctionalized polyrners eontaining ~ crosslinking agent provides a carrier material which in addition to improved toughness, the triboelectric prcperties thereof may be eontinuously varied by means of eontrolling the amount of the crosslinking agent in the eomposition.
The eoating of metallie carriers with hydroxy or amino funetionalized polymers and erosslinking these materials via reaetion of the pendant hydroxyl or amino moieties with a crosslinking agent sueh as diisoeyanate provides a means of continuous control of the triboelectric properties of the coated carriers. It has been found that as the degree of conversion increases, the eapaeity for positive triboelectric eharging decreases. In addition, the degree of conversion ean be controlled stoichiometrieally. Further, various types of crosslinking agents which are reaetive toward hydroxyl or amino funetions may be employed. In addition, various hydroxyl or amino containing polymers exhibit similar efects.
It is to be noted that it is not neeessary for the polymer material to be erosslinked to observe a ehange in the tribo-~leetrie eharging properties sinee the ehange in triboelectric eharging is not due to molecular weight ehange. Monofunetional reagents have been found to bring about similar ehanges.
Any suitable earrier material may be chemieally modified in accordance with this invention to eontrol the triboelectric properties of the carrier. Typieal materials inel~]de styrene-aerylate-organosilieon terpolymers, polyvinyls sueh as polyvinyl alcohol and polyvinyl butyral, thermoscttinc3 resins ineluding phenolic resins such as phenol-formaldehyde, . . .

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pherlol-fur~ ral ancl resorclrlol rorlnal~ehyde; amino resins such as urea-formaldehyde and melamineformaldehyde; epoxy resins; and the like. Many of the foregoiny and other typical carrier materials are described by L. E. Walkup in ~. S. Patent 2,618,551; ~. B. Jacknow et al in U. S. Pa-tent 3,526,533;
and R. J. Hagenbach et al in U. S. Patents 3,533,835 and 3,658,500.
Where a coated carrier is employed, any suitable electrostatographic coating thickness may be employed. However, a carrier coating having a thickness at least su~ficient to form a thin continuous film on the carrier particle is preferred because the carrier coating wi~l then possess sufficient thickness to resist abrasion and prevent pinholes which adversely affect the triboelectric properties of the coated carrier particles. Generally, for cascaae ana magnetic brush development, the carrier Coati~g may ~omprise from about 0.1 percent to about 10.0 percéht by weight based on the weight of the coated carrier parti~ie$. P~e~erably, the carrier coating should comprise from aboùt b.1 pe~cént to about 1.0 percent by weight based on the wéi~ht ~f ~hé
coated carrier particles because maximu~ du~a~ y, toner impaction resistance, and copy quality are a~h-ieved; ~o achieve further variation in the properties of the coated carrier particles, well-known additives such as plasticizers, reactive and non-reactive polymers, dyes, pigments, wetting agents and mixtures thereof may be mixed with the coating materials. An ultimate coated carrier particle having an average diameter between about 50 microns and about 1,000 microns is preferred in cascade systems because the carrier particle then possesses sufficient density and inertia to avoid ~ ; `

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~ crc~ o L]~ r~iL.I~ic i~ (J~ d~lrin(J L~ c~cad~
development process. ~dhc~rence of carrier particles to an electrostatographic drum is undesirahle because of the formation of deep scratches on the drum surface during the image transfer and drum cleaninq steps, particularly where cleaning is accomplished by a web cleaner such as the web disclosed by W. P. Graff, Jr., et al in U. S. Patent 3,186,838.
For coated carrier materials, any suitable uncoated electrostatographic carrier bead material may be employed such as for example, sodium chloride, ammonium chloride, aluminum potassium chloride~ Rochélle salt, sodium nitrate, potassium chlorate, granular zircon, granular silicon, glass, silicon dioxide, flintshot, iron, steel, ferrite, nickel, Carborundum, and mixtures thereof.
In addition to ~he toner materials prepared in accordance with this invention, an~ suitable well-known toner material may be employed with ~he carriers o ~his invention. Typical toner materi~ls include gum copal, gum sandarac, rosin, cumaroneindene re~in, asphal~um, gilsoni~e, phenolformaldehyde resins, rosin modified phenolformaldehyde resins, methacryli~ re~in~, polystyrene resins, polystyrene resins, epoxy resins, polyethylene resin~, polyester resins, and mixtures thereo. The particular toner mat~rial to b~
e~ployed obviously depends upon the ~paration o~ the toner parti~les ~rom the coated carrier in the triboelectric series and should be sufficient to cause the toner parti~les to electrostaticall~ ~ling to the carrier surface. Among the patents describin~ electroscopic toner compositions are U.S. Patent 2,659,670 to Copley; U. S. Patent 2,753,308 to ~andri~an;
U. S. Patent 3,079,342 to Insalaco; U. S. Patent Reissue 25,136 to Carlson and U.S. Patent 2,788,288 to -~3'7';~3'~
L r ~ rl k ~ cJ ~ t l ~ r l l l y ~ v ~ ~ n a v ~ r ~ ~ c particle diameter between about 1 and 30 microns.
The compositions of thc instant invention may be employed to develop electrostcltic latent images on any suitable electrostatic latent imaye-bearing surface including conventional photoconductive surfaces. Well-known photoconductive materials include vitreous selenium, organic or inorganic photoconductors embedded in a non~photoconductive matrix, organic or inorganic photoconductors embedded in a photoconductive matrix, or the like. Representative patents in which photoconductive materials are diselosed include U. S. Patent 2,903,542 to Ullrich, U. S. Patent " 970,906 to Bixby, U. S. Patent 3,121,006 to Middleton, U. S. Patent 3,121,007 to Middleton, and V. S. Patent 3,151,982 to Corrsin.
DESCR~PTION OE` PREF~RR~D EMBODIMENTS
The fol~owing examples further define, describe and compare me~hods of preparing the toner materials of the present inventi~n and of utilizing them to develop elect~o-sta~ic latent images. Parts and pereentages are by weight unlé~s o~her~ise indicated.
~ n the following, the relative triboeleetrie values ~ner~t~d by ~ontact of carrier beads with toner particles is ~eag~ed by means of a cascade device~ The deviee compxises a grounded metal plate set at an arbitrary but constant angle of elevation to horizontal, for example, 30 degrees, and a eup at the bottom of the ineline. The cup is not attached to the inc~line and is thus not grounded; it is attached to an electrometer. The material to be tested is coated onto a metallic sheet, SUCil as aluminur,l, and this is attached to the incline. Then ~eads of the desired carrier material are ,~ , 107~3,'~

ccl~ccl(l~d dowll Lll~ film ~lld illLo Llle eLccLrollleLcr cuL~, wll(!re the charge acqui~ed by the beads is m~asur~d. From this quantity and the weight of the beads the charge to mass ratio is calculated. This quantity is a direct measure of the triboelectric charging cap~c-ty of the polymeric film. The measurement is done at constant relative humidity and temper-ature. Since triboelectric measurementcs are relative, the measurements should for comparative purposes, be conducted under substantially identical conditions.
EXAMPLE I
A polymer was prepared by ester group aminolysis of a styrene-n-butyl methacrylate copolymer (2,54~1.00 mole ratio) with an aminoalcohol resulting in formation of hydroxyalkylamide functions. Thus, a mixture of about 117.5 grams (0.289 mole of ester functions based on elemental analysis) of the styrene-n-butyl methacrylate, about 41.0 grams (0.350 mole) of 6-aminohexanol, and about 39.3 grams (0.350 mole) of 1,4-diazabicyclo (2,2,2) octane was stirred under dry nitrogen at about 180C (oil bath temperature 205C) using an ambient air-cooled eondenser to allow escape of the n-butanol produeed. The polymer was aminolyzed to the extent of about 25 mole pereent. The polymer was puri-fied by dissolving in tetrahydrofuran and then 10% HCl was added. Tl-e liquid phase was deeanted from the gummy polymer.
This proeedure was repeated twiee, followed by a fourth and fifth wash using 5% methanolie HCl. The polymer was taken up in tetrahydrofuran and preeipitated by dropwise addition with rapid stirring to lO~s ~ICl. After homogenization in a blender and filtration, the process was repeated. Tllc polym~r in tetrahydrofuran solution was then precipitated in like '7~

manner from ~leionized w~ter, and this process repeated.
~fter a final precipitation from methanol, the polymer was dried in vacuo. Gencrally, the polymer sample was dissolved in about five times its weight of tetrahydrofuran. Volumes or the precipitating solutions were 6-10 times those of the polymertetrahydrofuran solution.
F~lms were cast from solutions onto aluminum plates and thoroughly dried. The cascade txiboelectric charging properties obtained using these films when using 250 micron nickel beads as carrier are given in Table I.
EXAMPLE_II
To a stirred solution of about 10.0 grams of the hydroxy polymer of Example I in ~kout ~Q ml, o~ ~y pyridine was added a solution of about 5.0 ~rams ~f substituted benzoyl chloride in dry pyridine. The ~olu~ion was refluxed about 18 hours and then pourçdintoabout ~pp,p ,ml Q~ lP~

by volume HCl. Afte~ homoge~iza~ign in ~ ~le~der with ip~
by volume HCl, then saturated ~lum bic~bo~tç ~ tion~
and then water, the polymer w~s ~ o~v@~ ln te~r~hy~rQ~uE~an and precipitated into 10~ by v~lume H~ like ~anneE, the polymer wa5 succes~ively px~ei~it~e~ ~rsm ~u~ated sodium bicarbonate twice, meth~n~l and wa~r ~hri~ç, In this way, the following p-subs~itu~ed bç~Qate esters we,re prepared: NO2 (60%), O~El3 (85%), ~1 (100%), ~ (90%), T,he degree of con~ersions was de~ermined by elemental analysis.
Films were cast fro~ ~olu~ion onto alumi~m plates and thoroughly dried. The cascade triboelectric charging properties obtained using these films when using 250 micron nic~el beads as carri~r are given in Tahle I.

-2~-' '73~'~

]X~MI~ r Functionali~ed polymers were prepared by es~er group aminolysis of a styrene-n-butyl methacrylate copolymer (2.54:1.00 mole ratio). A mixture of about 117.5 grams (0.289 mole of ester functions based on elemental analysis) of the styrene-n-butyl methacrylate, about 41.0 grams of 1,6 hexanediamine and about 39.3 grams (0.350 mole) of 1,4-diazabicyclo(2,2,2)octane was stirred under dry nitrogen at about 180C (oil bath temperature 205C) using an ambient air-cooled condenser to allow escape of the butanol produced.
Samples were removed periodically, quenched in 10% HCl by weight, and purified as in Example I.
Films were cast from solution onto aluminum plates and thoroughly dried. The cascade triboelectric charging properties obtained using these films when using 250 micron nic~el beads as carrier are given in Table I.
EXAMPLE IV
-To a stirred solution of about 10.0 grams of the amino polymer of Example III in about 30 ml. of dry pyridine was added a solution of about 5.0 grams of substituted benzoyl chloride in dry pyridine. The solution was reflu~ed about 18 hours and then poured into about ~00.0 ml of 10% by volume HCl. After homogenization in a blender with 10%
by volume HCl, then saturated sodium bicarbonate solution, and then water, the polymer was dissolved in tetrahydrofuran and precipitated into 10% by volume EICl. In like manner, the polymer was successively precipitated from saturated sodium bicarbonate 'cwice, methanol and water thrice. In this way, the following p-substituted benzamides were prepared:
N02 (100%), OCH3 (100%). The degree of conversions was determined by elemental analysis.

IL~'7'73~'~

l~'ilms were cast from solution on~o aluminum ~lates and thorou~hly dried. I~e cas~ade triboelectric charging properties obtained using thesc films when using 250 micron nickel beads as carrier are given in Table I.
TABLE I
Effect of polymer structure on triboelectric charging at ahout 30% relative humidity.

Example Polymer 250 micron nickel carrier charge (nanocoulorr~bs/gram) 1 a ~2.5 2 R=NO2 -1.4 2 R=ClC -1.9 2 R=~d -1.5 2 R=OCH3 -1.9 3 ~ -1.6

4 R=NO2 +1.2 4 R=OCH3 0-7 a) 28 mole % of ester groups of copolymer of styrene-n-butyl methacrylate aminolyzed b) 60 mole % of available OH groups esterified c) 100 mole % of available OH groups esterified d) 90 mole % of available OH groups esterified e) ~5 mole % of available OH groups esterified f) 2.3 mole % of ester groups aminolyzed, some crosslinking EXAMPLE V
A sample Or about 100 grams of 250 micron steel beads was continuously extracted with tetrahydrofuran for about 24 hours to remove soluble organics from their surface.

: .

:~07'73;~

~le be~ ; wcre ~]~cn vicJo~ously s~irred rnecllarlica]ly in tetra-hydrofuran for ~bout 20 hours. ~le solvent and suspended rust particles were decanted. Fresh tetra~lydrofuran was shaken with the beads and decanted. This was repeated until no further rust was evident in the decantate. The beads were dried in vacuo.
A solution of about 0.14 grams of polymer of Example I in about 125 ml. tetrahydrofuran was added to about 50.0 grams of the cleaned beads. The solvent was removed on a rotary evaporator at room temperature under vacuum.
m e eoated carrier beads which did not pass through a 177 micron sieve were then used in a cascade triboelectric eharging test. The triboelectric value obtained by cascading the coated carrier beads against a film of the untreated styrene-n-butyl methacrylate copolymer was found to be about +1.2 nanocoulombs per gram after correction for background eharge of the beads. Uncoated carrier beads developed a triboelectric eharge of about -0.30 nanocoulombs per gram against the same film under the same test eonditions. Thus, the triboelectric eharge on the carrier beads developed against the film changed sign from positive to negative by eoating the beads as described.
EXAMPLE VI
A hydroxy functionalized styrene-n-butyl methacrylate eopolymer containing about 0.5 p~rcent by weight of tolylene -2,4-diisocyanate which had been blocked with acetone oxime was coated onto steel carrier beads at a coating weight of about 0.22 percent by weight based on the weight of the beads. A portion of the beads were heated at 190C for 0.5 hour to release the diisocyanate and cause crosslinking. In .

3;~

Lril~o-l~cl:ric r~ o~ n~lc;urolnc~ Ls acJ.Iin~ a film Or ~llc non-functionall~cl styr~ne-methacrylate copolymer, the beads coated with the crosslink~cl polymer acquired a triboelectric charge of about ~-0.15 nanocoulombs per gram. By comparison, beads coated with the uncrosslinked copolymer and measured against the film of untreated styrene-methacrylate copolymer acquired a triboelectric charge of about ~1.2 nanocoulombs per gram. Versus a film of the hydroxy functionalized styrene-methacrylate copolymer, the trihoelectric charge acquired by the uncrosslinked coated beads and the crosslinked coated beads was about ~0.76 and -0.52 nanocoulombs per gram respectively. Thus a relatively large change in triboelectric charging properties was observed against both films; in both cases the beads with crosslinked coated accepted less positive charge.
EXAMPLE VII
Films of commercially available poly(vinyl alcohol), poly~vinyl hydrogen phthalate), and poly(vinyl acetate) were cast from solution onto aluminum plates and thoroughly dried.
The poly(vinyl alcohol) film caused 250 micron steel beads to acquire a charge of about -0.28 nanocoulombs per gram.
The poly(vinyl hydrogen phthalate~ film led to about ~3.7 nanocoulombs per gram charge on the 250 micron steel beads.
The poly(vinyl acetate) film led to the acauisition of about -0.18 nanocoulombs per gram charge on the 250 micron steel beads. The acylation of the hydroxyl functions of the alcohol caused a substantial decrease in positive charging propensity, an increase in negative charging capacity.
E~A~IPLE VIII
A mixture of a-bout 4.45 grams of ethyl cellulose .

3~773~
t0.52 hy~roxyl Ulli.~S pcr anl~ydrocJ~ucos~ Ullit), a~out 1.25 grams of phenyl isocyanate and about ~0 ml benzene was reflexed for about 1 hr. The solvent was removed in vacuo.
The residue was thrice pxecipitated from tetrahy~rofuran solution into water and dried in vacuo. Elemental analysis showed that about 55% of the available hydroxyls had been converted to urethane units. Films of the starting material and product were cast ~rom solu-tion onto aluminum plates and thoroughly dried. The starting hydroxy material caused 250 micron nickel shot to acquire a charge of about +0.43 nanocoulombs per gram, while the product urethane gave the beads a charge of about +1.0 nanocoulombs per gram. Conversion of the hydroxyl moieties to urethane function led to a significant increase in the negative charging capacity of the cellulose.
Although specific components, proportions and procedures have been stated in the above description of the preferred embodiments of the novel toner compositions, other suitable components, proportions and procedures as listed above may be used with similar results. Further, other materials and procedures may be employed to synexgize, enhance or otherwise modify the novel system.
OtheL modifications and ramifications of the present invention will appear to those skilled in the art upon a reading of this disclosure. These are intended to be included within the scope of this invention.

. ~ . .

Claims (26)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An electrostatographic carrier composition for use in developing electrostatic latent images on a recording surface, said carrier composition comprising carrier particles having an average particle diameter between about 50 microns and about 1,000 microns, each of said carrier particles comprising a core surrounded by from about 0.1 percent to about 10.0 percent by weight based on the weight of said carrier particles of an outer coating of a polymer selected from the group consisting of styrene-alkylmethacrylate and styrene-alkylacrylate contain-ing pendant hydroxyl and amino moieties, said polymer having been exposed to systematic chemical modification of the pendant hydroxyl and amino moieties of said polymer by acyla-tion with an acylating agent to provide carrier particles characterized as having controlled triboelectric charging properties.

2. An electrostatographic carrier composition in accord-ance with claim 1 wherein said coating comprises from about 0.1 percent to about 1.0 percent by weight based on the weight of said carrier particles.

3. An electrostatographic carrier composition in accord-ance with claim 1 wherein said systematic chemical modification of said polymer has been controlled stoichiometrically so as to provide said controlled triboelectric charging properties to said carrier particles.

4. An electrostatographic carrier composition in accord-ance with claim 1 wherein said systematic chemical modification of said polymer has been controlled kinetically so as to provide said controlled triboelectric charging properties to said carrier particles.

5. An electrostatographic carrier composition in accord-ance with claim 1 wherein said triboelectric charging properties of said carrier particles have been controlled by the amount and type of acylating agent employed in said acylation.

6. An electrostatographic carrier composition in accord-ance with claim 1 wherein said polymer has been crosslinked by reaction of said pendant hydroxyl and amino moieties with a crosslinking agent.

7. An electrostatographic developer composition comprising finely-divided toner particles electrostatically clinging to the surface of carrier particles, said toner particles having an average particle diameter of between about 4 and 20 microns, said toner particles comprising a colorant and a polymer select-ed from the group consisting of styrene-alkylmethacrylate and styrene-alkylacrylate containing pendant hydroxyl or amino groups in the pendant ester functions, said polymer having been exposed to systematic chemical alteration of said pendant ester functions by acylation with an acylating agent to convert said hydroxyl groups to esters and said amino groups to amides there-by providing toner particles characterized as having controlled triboelectric charging properties.

8. An electrostatographic developer composition in accord-ance with claim 7 wherein said polymer has a melting point of at least about 110°F.

9. An electrostatographic developer composition in accord-ance with claim 8 wherein said polymer has a weight average molecular weight between about 3,000 to about 500,000.

10. An electrostatographic developer composition in accord-ance with claim 7 wherein said toner particles have a blocking temperature of at least about 110°F and a melt viscosity of less than about 2.5 x 10-4 poise at temperatures of up to about 450°F.

11. An electrostatographic developer composition in accord-ance with claim 7 wherein said colorant is selected from the group consisting of pigments and dyes.

12. An electrostatographic developer composition in accord-ance with claim 7 wherein said colorant is present in said toner particles in an amount of from about 1 percent to about 20 percent by weight based on the weight of said toner particles.

13. An electrostatographic developer composition in accord-ance with claim 7 wherein said systematic chemical alteration of said polymer has been controlled stoichiometrically so as to provide said controlled triboelectric charging properties to said toner particles.

14. An electrostatographic developer composition in accord-ance with claim 7 wherein said systematic chemical alteration of said polymer has been controlled kinetically so as to provide said controlled triboelectric charging properties to said toner particles.

15. An electrostatographic developer composition in accord-ance with claim 7 wherein said triboelectric charging properties of said toner particles have been controlled by the amount and type of acylating agent employed in said acylation.

16. An electrostatographic developer composition in accord-ance with claim 7 wherein said polymer has been crosslinked by reaction of said hydroxyl and amino groups with a crosslinking agent.

17. An electrostatographic imaging process comprising the steps of providing an electrostatographic imaging member having a recording surface, forming an electrostatic latent image on said recording surface, and contacting said electrostatic latent image with a developer composition comprising finely-divided toner particles electrostatically clinging to the surface of carrier particles, said toner particles having an average particle diameter of between about 4 and about 20 microns, said toner particles comprising a colorant and a polymer selected from the group consisting of styrene-alkyl-methacrylate and styrene-alkylacrylate containing hydroxyl or amino groups in the pendant ester functions, said polymer having been exposed to systematic chemical alteration of said pendant ester functions by acylation with an acylating agent to convert said hydroxyl groups to esters and said amino groups to amides thereby providing toner particles characterized as having controlled triboelectric charging properties, whereby at least a portion of said finely-divided toner particles are attracted to and deposited on said recording surface in con-formance with said electrostatic latent image.

18. An electrostatographic imaging process in accordance with claim 17 wherein said polymer has a melting point of at least about 110°F.

19. An electrostatographic imaging process in accordance with claim 18 wherein said polymer has a weight average molecular weight between about 3,000 to about 500,000.

20. An electrostatographic imaging process in accordance with claim 17 wherein said toner particles have a blocking temperature of at least about 110°F and a melt viscosity of less than about 2.5 x 10-4 poise at temperatures of up to about 450°F.

21. An electrostatographic imaging process in accordance with claim 17 wherein said colorant is selected from the group consisting of pigments and dyes.

22. An electrostatographic imaging process in accordance with claim 17 wherein said colorant is present in said toner particles in an amount of from about 1 percent to about 20 percent by weight based on the weight of said toner particles.

23. An electrostatographic imaging process in accordance with claim 17 wherein said systematic chemical alteration of said polymer has been controlled stoichiometrically so as to provide said controlled triboelectric charging properties to said toner particles.

24. An electrostatographic imaging process in accordance with claim 17 wherein said systematic chemical alteration of said polymer has been controlled kinetically so as to provide said controlled triboelectric charging properties to said toner particles.

25. An electrostatographic imaging process in accordance with claim 17 wherein said triboelectric charging properties of said toner particles have been controlled by the amount and type of acylating agent employed in said acylation.

26. An electrostatographic imaging process in accordance with claim 17 wherein said polymer has been crosslinked by reaction of said hydroxyl and amino groups with a crosslinking agent.