US3672928A - Electrostatographic developers having carriers comprising polyester coated cores - Google Patents

Abstract

A CARRIER FOR ELECTROSTATOGRAPHIC DEVELOPER MIXTURES IS PROVIDED COMPRISING A CORE COATED WITH A POLYESTER PREPARED FROM DIALLYL PHTHALATE, DIALLYL ISOPHTHALATE OR DIALLYL CHLORENDATE OR PREPOLYMERS THEREOF.

Description

United States Patent US. Cl. 117-175 Claims ABSTRACT OF THE DISCLOSURE A carrier for electrostatographic developer mixtures is provided comprising a core coated with a polyester prepared from diallyl phthalate, diallyl isophthalate or diallyl chlorendate or prepolymers thereof.

This invention relates in general to imaging systems and more particularly, to improved developing materials, their manufacture and use.

The formation and development of electrostatic latent images is Well known. The basic electrostatographic process, as taught by C. F. Carlson in US. Pat. 2,297,691, involves placing a uniform electrostatic charge on a photoconductive insulating layer, exposing the layer to a light and shadow image to dissipate the charge on the areas of the layer exposed to the light and developing the resulting latent electrostatic image by depositing on the image a finely-divided electroscopic material referred to in the art as toner. The toner will normally be attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the latent electrostatic image. This powder image may then be transferred to a support surface such as paper. The transferred image may subsequently be permanently afiixed to the support surface as by heat. Instead of latent image formation by uniformly charging the photoconductive layer and then exposing the layer to a light and shadow image, one may form the latent image by directly charging the layer in image configuration. The powder image may be fixed to the photoconductive layer if elimination of the powder image transfer step is desired. Other suitable fixing means such as solvent or overcoating treatment may be substituted for the foregoing heat fixing step.

Many methods are known for applying the electroscopic particles to the latent electrostatic image to be developed. One development method, as disclosed by E. N. Wise in US. Pat. 2,618,552 is known as cascade development. In this method, a developer material comprising relatively large carrier particles having finelydivided toner particles electrosatically clinging to the surface of the carrier particles is conveyed to and rolled or cascaded across the latent electrostatic imagebearing surface. The composition of the toner particles is so chosen as to have a triboelectric polarity opposite that of carrier particles. As the mixture cascades or rolls across the image-bearing surface, the toner particles are electrostatically deposited and secured to the charged portion of the latent image and not deposited on the uncharged background portions of the image. Most of the toner particles accidentally deposited in the background are removed by the rolling carrier, due apparent 1y, to the greater electrostatic attraction between the toner and the carrier than between the toner and the discharged background. The carrier particles and unused toner particles are then recycled. This technique is exice tremely useful for the development of line copy images. The cascade development process is the most widely used commercial electrostatographic development technique. A general purpose oflice copying machine incorporating this technique is dbscribed in US. Pat. 3,099,943.

Another technique for developing electrostatic images is the magnetic brush process as disclosed, for example, in US. Pat. 2,874,063. In this method, a developer material containing toner and magnetic carrier particles is carried by a magnet. The magnetic field of the magnet causes alignment of the magnetic carriers in a brushlike configuration. This magnetic brush is engaged with an electrostatic-image bearing surface and the toner particles are drawn from the brush to the electrostatic image by the electrostatic attraction. Many other methods such as touchdown development as disclosed by C. R. Mayo in US. Pat. 2,895,847 are known for applying electroscopic particles to the latent electrostatic image to be developed. The development processes as mentioned above together with numerous variations are well known to the art through various patents and publications and through the widespread availability and utilization of electrostatographic imaging equipment.

In automatic electrostatographic equipment, it is conventional to employ an electrostatographic plate in the form of a cylindrical drum which is continuously rotated through a cycle of sequential operations including charging, exposure, developing, transfer and cleaning. The plate is usually charged with corona with positive polarity by means of a corona generating device of the type disclosed by L. E. Walkup in U.S. Pat. 2,777,957 which is connected to a suitable source of high potential. After forming a powder image on the electrostatic image during the development step, the powder image is electrostatically transferred to a support surface by means of a corona generating device such as the corona device mentioned above. In automatic equipment employing a rotating drum, a support surface to which a powdered image is to be transferred from the drum is moved through the equipment at the same rate as the periphery of the drum and contacts the drum in the transfer position interposed between the drum surface and the corona generating device. Transfer is effective by the corona generating device which imparts an elec trostatic charge to attract the powder image from the drum to the support surface. The polarity of charge required to elfect image transfer is dependent upon the visual form of the original copy relative to the reproduction and the electroscopic characteristics of a de veloping material employed to effect development. For example, where a positive reproduction is to be made of a positive original, it is conventional to employ a positive polarity corona to effect transfer of a negatively charged toner image to the support surface. When a positive reproduction from a negative original is desired, it is conventional to employ a positively charged toner which is repelled by the charged areas on the plate to the discharged areas thereon to form a positive image which may be transferred to a negatively charged surface. In either case, a residual powder image and occasionally carrier particles remain on the plate after transfer. Before the plate may be reused for a subsequent cycle, it is necessary that the residual image and carrier particles, if any, be removed to prevent ghost images from forming on subsequent copies. In the posi- -tive-to-positive reproduction process described above, the

residual developer powder as well as any carrier particles present are tightly retained on the plate surface by a phenomenon that is not fully understood but believed caused by an electric charge. The charge is substantially neutralized by means of a corona generating device are advanced into pressure and rubbing or wiping contact with the imaging surface and are gradually advanced to present a clean surface to the plate whereby substantially complete removal of the residual powder and carrier particles from the plate is effected.

While ordinarily capable of producing good quality image, conventional developing systems suffer serious deficiencies 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 the distance between their relative positions in thetriboelectric 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 resulting images are very faint because the attractive forces between the carrier and toner particles compete with the attractive forces between the latent electrostatic image and the toner particles. Although the image density described in the immediately preceding sentence may be improved by increasing the toner concentration in the developer mixture, undesirably high background toner deposition as well as increased toner impaction and agglomeration is encountered when the toner concentration in the developer mixture is excessive. It has been proposed to increase the initial elec trostatographic plate charge to improve the density of the deposited powder image, but this would necessitate an electrostatographic imaging surfaces undesirable print deletion and massive carry-over of carrier particles often occur. Massive carrier carry-over problems are particularlyacute. 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 toner particles. Further, adherence of carrier particles to the re usable electrostatographic imaging surface promotes scratching of the surface during image transfer and surface cleaning operations.

CARRIER MATERIAL CRITERIA The criteria for selection of suitable carrier material are extremely rigid in that these materials must exhibit a unique balance of electrostatic properties. The carrier must be capable of introducing a triboelectric charge on the toner particles opposite in polarity to that Olf the image being developed in order to effect deposition of the toner particles on the latent image. However, the carrier must 4 carrier is probably a combination of coulomb attraction between the toner and carrier, along with short-range contact forces. These retention forces account for the high range contrast characteristic of all carrier developers as is desirable for line copy reproduction. It contributes to relatively clean dust-free background or nonimage areas, yet permits dense image development. I

Residual charge is almost inveriably present in the nominally discharged or background areas of the latent image. Relatively low as this charge density is, it may nevertheless be nonuniform, and such irregularities will be a source of small fields capable of trapping toner particles. This electrostatic noise in the background areas of the latent image is one of the primary sources of unwanted background toner.

Carrier particles are made from or coated with materials having appropriate triboelectrie properties as well as certain other physical characteristics. Thus, the materials employed as the carrier particles or the coatings thereon should have a triboelectric value commensurate with the triboelectric value of the toner to enable electrostatic adhesion of the toner to the carrier particles and subsequent transfer of the toner from the carrier particles to the image on the plate without excessive power requirements. Furthermore, the triboelectric properties of all the carrier particles should be relatively uniform to permit uniform pick-up and subsequent deposition of toner. The materials employed in the carrier particles should have an intermediate hardness so as not to scratch the plate or drum surface upon which the electrostatic image is initially placed while being suficiently hard to withstand the forces to which they are subjected during recycle. The carr'ier particles as well as the surface thereof also should not be comprised of materials which are so brittle as to cause either flaking of the surface or particle break-up under the forces exerted on the particles during recycle. The flaking causes undesirable effects in that the relatively small flaked particles will eventually be transferred to the copy surface thereby interfering with the deposited toner and causing imperfections in the copy image'lFurthermore, flaking of the carrier particle surface will cause the resultant carrier particles to halve non-uniform triboelectric properties when the carrier particle is composed of a core material different than the surface coating thereon. This results in undesirable non-uniform pick-up of toner by the carrier particles and non-uniform deposition of toner on the image. In addition when the carrier particle size is reduced, the removal of the resultant small particles from the plate becomes increasingly difficult. Thus, the type of materials useful for making carrier particles or for coating carrier particles, although having the appropriate triboelectric properties, are limited because other physical properties which they possess may cause the undesirable results discussed above.

While ordinarily capable of producing good quality images, conventional developing materials suffer serious faces during image transfer and surface cleaning steps.

The tendency of carrier particles to adhere t'o'imaging surfaces is aggravated when the carrier surfaces are rough and irregular. Furthermore, carriers having coatings which tend to chip and otherwise separate from the carrier core must be frequently replaced thereby increasing expense and consuming time. Fines and grit formed from carrier disintegration tend to drift and form unwanted deposits on critical machine parts. Many carrier coatings having high compressive and tensile strength either do not adhere well to the carrier core or do not possess the desired triboelectric characteristics. The triboelectric and flow characteristics of many carriers are adversely affected when relative humidity is high. For example, the triboelectric values of some carrier coatings fluctuate with changes in relative humidity and are not desirable for employment in electrostatographic systems, particularly in automatic machines which require carriers having stable and predictable triboelectric values. Another factor affecting the stability of carrier triboelectric properties is the susceptibility of carrier coatings to toner impaction. When carrier particles are employed in automatic machines and recycled through many cycles, the many collisions which occur between the carrier particles and other surfaces in the machine cause the toner particles carried on the surface of the carrier particles to be Welded or otherwise forced into the carrier coatings. The gradual accumulation of permanently attached toner material on the surface of the carrier particles causes a change in the triboelectric value of the carrier particles and directly contributes to the degradation of copy quality by eventual destruction of the toner carrying capacity of the carrier. Thus, there is a continuing need for a better system for developing latent electrostatic images.

It is highly desirable to alter triboelectric properties of the carrier cores to accommodate the use of desirable toner compositions while retaining the other desirable physical characteristics of the carrier particle. The alteration of the triboelectric properties of carrier particles by applying a surface coating thereon is a particularly desirable technique. With this technique, not only is it possible to alter the triboelectric properties of carrier particles made from materials having desirable physical characteristics, it is also possible to employ materials previously not suitable as carrier particles. Thus, for example, carrier particles having desirable physical properties with the exception of hardness, can be coated with a material hav ing desirable hardness as well as other physical properties, rendering the resultant product useful as carrier particles. 'Coating the carrier particles With the additive to alter the triboelectric properties thereof rather than blending the additive into the carrier material during initial formation of the carrier particles is preferred since less additive need be employed to effect the desired change in the triboelectric value. Furthermore, the addition of high concentrations of additive to the original carrier material to alter the triboelectric value thereof requires a major manufacturing operation and often undesirably alters the original physical characteristics of the carrier material. Thus, there is a present need for providing improved electrostatographic carrier particles which can have their triboelectric value varied over a wide range while retaining desirable physical characteristics of hardness, durability and the like. This is especially true in view of the constant development of new and improved toner compositions.

It is, therefore, an object of this invention to provide developers which overcome the above-noted deficiencies and are suitable for use in electrostatographic reproduction processes.

More particularly, it is an object of this invention to provide new carrier particles which possess electrostatic and physical properties needed for efficient and prolonged use in electrostatographic reproduction processes.

It is a further object of this invention to provide carrier beads having a hard and tough coating which tenaciously adheres to the carrier core whereby the carrier beads are highly resistant to toner impaction, chipping and flaking while having stable triboelectric values.

SUMMARY OF THE INVENTION These, as well as other objects, are accomplished by the present invention which provides a carrier for electrostatographic developer mixtures, said carrier comprising 6 a core coated with a polyester resin, prepared from diallyl phthalate, diallyl isophthalate or diallyl chlorendate or prepolymers and combinations thereof.

In general, the carriers of the present invention are prepared by coating the carrier core with the unsaturated monomeric ester or polyester prepolymer and curing the coated core to form a tough polyester coating on the core.

DESCRIPTION OF THE INVENTION Core materials Any suitable well known carrier material can be ernployed as the core of the carriers of this invention. Typical carrier materials include sodium chloride, ammonium chloride, aluminum potassium chloride, Rochelle salt, sodium nitrate, potassium chlorate, granular zircon, granular silicon, methyl methacrylate, glass, silicon dioxide, flintshot, iron, steel, ferrite, nickel, carborundum and mixtures thereof. Many of the foregoing and other typical carriers are described by L. E. Walkup in US. Pat. 2,- 618,551; L. E. Walkup et al. in 11.8. Pat. 2,638,416 and E. N. Wise in US. Pat. 2,618,552. An ultimate coated carrier particle diameter of between about 30 microns to about 1000 microns, preferably between about 50 microns to about 600 microns is employed 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 an electrostatographic drum is undesirable because of the formation of deep scratches on the drum surface during the image transfer and drum cleaning steps, particularly where cleaning is accomplished by a web cleaner such as the web disclosed by W. P. Graff, Jr., et al., in US. Pat. 3,186,838.

Coating layer Coating of the core materials is accomplished with monomer or prepolymer solutions which upon curing give rise to cross-linked polyesters. The polyesters useful as coating materials in the present invention are those polyesters derived from the diallyl esters of phthalic and isophthalic anhydrides or acids or chlorendic anhydride or the prepolymers thereof. These materials can be readily prepared by esterification of phthalic or isophthalic anhydride or acid or chlorendic anhydride with allyl alcohol. Chlorendic anhydride is the Diels-Alder adduct, 1,4,5,6, 7,7-hexachlorobicyclo-(2.2.1)-5 heptene 2,3 dicarboxylic anhydride prepared from hexachlorocyclopentadiene and maleic anhydride.

The carrier coatings employed in the present invention are non-tacky and have sufficient hardness at normal operating temperatures to prevent impaction; form strong adhesive coatings which do not fla ke under normal operating conditions; have triboelectric values such that they can be used with a wide variety of presently available toners in present electrostatographic processes and are hydrophobic so that they retain a constant triboelectric value. Thus, the coated carrier particles of this invention have desirable properties which permit their wide use in presently available electrostatographic processes.

While the diallyl phthalate and isophthalate are useful primarily as positive carrier coatings, diallyl chlorendate has been found to be especially useful as a reversal carrier coating because of its very low triboelectric value of about +1.5 ,uC/ gm. Because of its relatively low triboelectricity, it can easily be made into a reversal coating by incorporating therein relatively small amounts of a conventional reversal dye such as Luxol Fast Blue Dye or the like. Carrier coatings exhibiting highly positive triboelectric values are extremely difficult to convert to reversal carrier coatings since they would require large amounts of a reversal dye incorporated therein. Increasing the reversal dye content would adversely affect many important physical properties such as adhesion and moisture resistivity.

The prepolymers of diallyl phthalate and diallyl isoph-thalate are free flowing powders. Use of free flowing powders is quite advantageous in electrostatographic processes. Liquid monomers or prepolymers, if partially crosslinked, would coat the photoreceptor thereby adversely affecting the electrical properties thereof. The prepolymers of diallyl phthalate and isophthalate useful in the present invention have no adverse eflfects on the photoreceptor and additionally enable the triboelectric properties of the developer to be tailored internally for any electrostatographic process while simultaneously retaining the adhesion and toughness of the basic polymer.

The prepolymers useful in the present invention can be prepared by any means known in the art. Generally the prepolymers are prepared by arresting polymerization of the monomer before cross-linking and gelation occur by employing a polymerization inhibitor. The prepolymers are low molecular weight materials having internally cyclized structures containing unreacted allylic groups in the polymer chain. Final curing of the prepolymer is effected by mixing with additional monomer under polymerization conditions.

These esters can be polymerized alone under mild conditions using only one of the allyl groups to form linear polyesters which can undergo further polymerization to yield thermosetting, highly cross-linked polymers. It is, therefore, unnecessary to add any other polymerizing monomer such as a glycol although additional monomers can be added if desired.

The allyl esters and prepolymers of the present invention undergo thermal polymerization in the presence of a free radical initiator. Since the materials easily undergo a vinyl type polymerization, free radical initiators, such as peroxides and azo compounds, can be employed. The action of the initiator can be modified by use of activators and promoters. Peroxide type initiators which will initiate polymerization at relatively low temperatures (30 C. to 60 C.) are those such as acetyl benzoyl peroxide, peracetic acid, methyl ethyl ketone peroxide, cumene hydroperoxide and the like. For polymerization at intermediate temperatures (60 C.-l C.), peroxides such as tert.- butyl hydroperoxide, methyl amyl ketone peroxide, tert.- butyl perbenzoate and the like can be employed. At still higher temperatures (about 100 C.), peroxides such as p-chlorobenzoyl peroxide, di-tert.-butyl peroxide, dibenzal diperoxide are suitably employed. Azo compounds such as azobisisobutyronitrile, dimethylazodiisobutyrate, azobisl-phenylethane, alkali metal azodisulfonates and the like have been found useful. Catalytic activity is obtained when these free radical initiators are employed in an amount from about 0.0001 to about 5.0% based on the combined weight of the polymerizable ingredients.

The rate of cure can be increased if desired through use of an activator. Cobalt, in the form of its ethyl hexanoate or naphthenate salt, is a good general purpose activator for use with ketone peroxides. Activators cause rapid curing at room temperature and tend to reduce surface tackiness. Concentrations as low as about 30 p.p.m. of cobalt have been found efiective.

A promoter can also be added to the curing system if desired to reduce the time usually required for gelling the resin. Pre-gelled structures have sutficient rigidity to be handled, and thus can be transferred to ovens to obtain final cure. Promoters used with acyl peroxides include tertiary dialkyl aryl amines such as diethyl aniline and aliphatic thiols as, for example, lauryl mercaptan. Concentrations in the range of about 0.05 to about 0.5% by weight of promoter have been found suitable.

In addition, inhibitors or antioxidants can be added to the polyester to improve environmental stability. Inhibitors found useful for this purpose are for example -butyl catechol, 2,6-tert.-butyl-p-cresol, hydroquinone, p-benzoquinone and similar sterically hindered phenols.

The polyester coating can be applied to the carrier cores either as a monomeric solution or a prepolymer solution together with initiator, activator, promoter and/ or inhibitor. The coating solution can be applied by mixing, dipping, spraying and other similar liquid application methods. The coating solution is generally applied hot, i.e., at about C. to about C. to promote rapid curing. Upon application of a continuous thin film of solution to the core particles, the temperature is dropped below the softening point of the polyester and the curing is continued until integrally coated core particles having sufficient rigidity to be easily handled are obtained. Thereupon, the coated core particles are finally cured, generally in a vacuum oven at temperatures below the softening point of the polyester.

Any suitable coating thickness can be employed. A coating having a thickness at least sufiicient to form a continuous film is preferred, however, because the composite carrier coating will then possess sufficient thickness to resist abrasion and prevent pinholes which adversely affect the triboelectric properties of the coated carrier particles.

To achieve further variation in the properties of the final resinous product, well known additives such as plasticizers, reactive or non-reactive resins, dyes, pigments, wetting agents and mixtures thereof can be admixed with the coating solution.

Toner particles The electrostatographic developer mixtures of the present invention comprise finely-divided toner particles electrostatically clinging to the surface of carrier particles prepared in the manner hereinabove described. Generally, toner particles consist of carbon black dispersed in a resin; however, other pigments or dyes can also be employed, including fluorescent materials. Toner can be given special adhesive (or in some cases, non-adhesive) properties to control transfer of still other material in an image pattern; it can also be madeinert to acids or solvents in order to serve as a resist for selective etching applications. Toner particles, however, must be of sufiicient electric charge so that forces exerted by the electrostatic image fields are sufiicient to capture the particles from the developer mass.

Employing the coating materials and procedures described herein, a carrier is obtained which is composed of a tough, internally cross-linked coating on the carrier core. These carriers have been found extremely durable and resistant to impaction without the need to employ a pre-coating material to chemically couple the polyester coating through the precoat to the carrier core. The unsaturated polyester coatings of this invention exhibit a smooth, hard outer surface which is highly resistant to chipping and flaking. The smooth tough surface enhances the rolling action of the carrier particles across the electrostatogr-aphic surfaces and reduces the tendency of the carrier particles to adhere to the surfaces. Employment of the present carrier coatings unexpectedly extends carrier life, particularly in respect to toner impaction resistance. Additionally, the hydrophobic properties of the resins of this invention especially those derived from diallyl chlorendate appear to contribute in some unknown manner to the stability of the triboelectric properties of the coated carrier over a wide relative humidity range.

Coating additives When it is desirable, particulate or non-particulate conductive materials can be added to alter the triboelectric value of the coated carrier. Any suitable organic or inorganic finely-divided particulate material having a volume resistivity of less than about 10 ohm centimeters at 23 C. may be employed. Optimum results are achieved with particulate materials having a volume resistivity of less than about 1 ohm centimeter at 23 C. because maximum reduction of triboelectric value occurs with a minimum amount of alteration of the original carrier material characteristics. Preferably, the conductivity of the particulate additives should be independent of ambient relative humidity conditions. The particulate material should be of a maximum particle size of less than about 15 microns. Typical materials having volume resistivity of at least about ohm centimeters at 23 C. include: carbon, boron, aluminum bronz, antimony, arsenic, bismuth, bronze, beryllium, lithium, manganese, cadmium, isium, thallium, cesium, molybdenum, rhodium, titanium, tungsten, chromium, tantalum, steel, cobalt, calcium, rubidium, thorium, calcium chloride, potassium bromide, silver nitrate, sodium chloride, lithium chloride, silver iodide, lithium bromide, cesium bromide, sodium iodide, nickel oxide, ferric oxide, aurin tricarboxylic acid ammonium salts, isoviolanthrone, indanethrone black, cyananthrone, perylene-iodine complexes, tetracyanoquinodimethane complexes, isoviolanthrone,-iodine chloride complex, isoviolanthrene-aluminum chloride complex, isoviolanthrene-titanium chloride complex, isoviolanthreneiodine complex, isoviolanthrene-potassium complex, isoviolanthrene-sodium complex, sodium-anthracene complex, chloranil N,N,N',N tetramethyl p phenylene diamine complex, bromanil N,N,N,N' tetramethyl-pphenylene diamine complex, iodanil-N,N,N',N'-tetramethyl-p-phenylene diamine complex, chlorinal-3,8-diaminopyrene complex, chlorinal-3,IO-diaminopyrene complex, bromanil-3,8-diaminopyrene complex, iodanil3,8-diaminopyrene complex, tetracyanoquinodimethane-N,N- dimethyl-p-phenylenediamine complex, tetracyanoquinodimethane-Z-methyl-p-phenylenediamine complex, tetracyanoquinodimethane N,N,N'-N'-tetramethyl-p-phenylenediamine complex, lithium-tetracyanoquinodimethane complex salt, cesium-tetracyanoquinodimethane complex salt, sodium-tetracyanoquinodimethane complex salt, potassium-tetracyanoquinodimethane complex salt, coppertetracyanoquinodimethane complex salt, barium-tetracyanoquinodimethane complex salt, silver-tetracyanoquinodimethane complex salt, ammonium-tetracyanoquinodimethane complex salt, N-methylquinoliumtetracyanoquinodimethane complex salt, 4-hydroxy-N-benzylanilinium complex salt, 4-amino-N,N-diethylanilinium, 4- amino-2,3,5,6-tetramethylanilinium pyridium complex salt, quinolinium complex salt, N-(N-propyl)quinolium complex salt, 2,2'-bipyridinium complex salt, aluminum phthalocyanine, aluminum polychlorophthalocyanine, antimony phthalocyanine, barium phthalocyanine, beryllium phthalocyanine, cadmium hexadecachlorophthalocyanine, cadmium phthalocyanine, calcium phthalocyanine, chromium phthalocyanine, cobalt phthalocyanine, copper 4 amino-phthalocyanine, copper bromochlorophthalocyanine, copper-4-chlorophthalocyanine, copper-4- nitro-phthalocyanine, copper phthalocyanine, copper phthalcyanine sulfonate, copper polychlorophthalocyanine, deuteriophthalocyanine, dysprosium phthalocyanine, erbium phthalocyanine, europium phthalocyanine, gadolinium phthalocyanine, gallium phthalocyanine, germanium phthalocyanine, hafnium phthalocyanine, halogen substituted phthalocyanine, holmium phthalocyanine, indium phthalocyanine, iron phthalocyanine, iron polyhalophthalocyanine, lanthanum phthalocyanine, lead phthalocyanine, lead polychlorophthalocyanine, cobalt hexaphenylphthalocyanine, copper pentaphenylphthalocyanine, lithium phthalocyanine, lutecium phthalocyanine, magnesium phthalocyanine, manganese phthalocyanine, mercury phthalocyanine, molybdenum phthalocyanine, naphthlocyanine, neodymium phthalocyanine, nickel phthalocyanine, nickel polyhalophthalocyanine, osmium phthalocyanine, palladium phthalocyanine, palladium chlorophthalocyanine, alkoxyphthalocyanine, alkylaminophthalocyanine, alkylmercaptophthalocyanine, aralkylaminophthalocyanine, aryloxyphthalocyanine, arylmercaptophthalocyanine, copper phthalocyanine piperidine, cycloalkylaminophthalocyanine, dialkylaminophthalocyanine, diarralkylaminophthalocyanine, dicycloalkylaminophthalocyanine, hexadecahydrophthalocyanine, imidomethylphthalocyanine, 1,2-napthalocyanine, 2,3-naphthalocyanine, octaazaphthalocyanine, sulfur phthalocyanine, tetraazaphthalocyanine, tetra-4-acetylaminophthalocyanine, tetra-4- aminobenzoylphthalocyanine, tetra-4-aminophthalocyanine, tetrachloromethylphthalocyanine, tetradiazophthalocyanine, tetra-4,4-dimethyloctaazaphthalocyanine, tetra- 4,5-diphenylenediaxide phthalocyanine, tetra-4,5-diphenyloctaazaphthalocyanine, tetra-(G-methyl-benzothiazoyl) phthalocyanine, tetra-p-methyl-phenyl-aminophthalocyanine, tetramethylphthalocyanine, tetra-naiphthotriazolylphthalocyanine, tetra-4-naphthylphthalocyanine, tetra-4- nitrophthalocyanine, tetra-peri-naphthylene-4,S-octaazaphthalocyanine, tetra-2,3-phenyleneoxide phthalocyanine, tetra-4-phenyloctaazaphthalocyanine, tetraphenylphthalocyanine, tetraphenylphtlialocyanine tetracarboxylic acid, tetraphenylphthalocyanine tetrabarium carboxyalte, tetraphenylphthalocyanine tetra-calcium carboxylate, tertapyridylphthalocyanine, tetra 4 trifluoro-methylmercaptophthalocyanine, tetra 4 trifiuoromethylphthalocyanine, 4,5 thionaphthene octaazaphthalocyanine, platinum phthalocyanine, potassium phthalocyanine, rhodium phthalocyanine, samarium phthalocyanine, silver phthalocyanine and mixtures thereof.

When employing an additive, factors aifecting the quantity to be incorporated in the carrier particles include: the the separation in the triboelectric series between the electroscopic marking particles and the polyester coating; the average particle size of the conductive particulate additive, the concentration of the particular conductive material at the surface of the coating carrier particle; the average diameter of the carrier particle; and the conductivity of the particulate additive.

In a preferred embodiment, the finely-divided conductive material is incorporated into the outer surface of the coated carrier beads by bringing the finely-divided conductive particles into contact with the soft hardenable external surface of the coated beads and impacting the particulate additives therein by causing other beads to collide and roll across the soft surface thereof. In this manner each carrier head is subjected to thousands of collisions and rolling contacts with other beads during the impaction treatment. This impaction treatment is effected by suitable techniques such as tumbling a mixture of finely-divided conductive particles and carrier beads having a soft surface in hollow rotating cylinders; vibrating a mixture of finely-divided conductive particles and carrier beads having a soft surface linearly in high frequency reciprocating chambers; and contacting finely-divided particles with the soft external surfaces of carrier beads in an arcuate chamber vibrating in an oscillatory direction.

Where the finely-divided conductive additive is impacted into the softened carrier bead coating, the coating is softened by heat or a solvent. The quantity of heat energy or solvent employed to soften the coating should not exceed that quantity necessary to effect softening to a tacky or highly viscous state. When excessive heat energy or solvent is applied to the carrier coating, the coating material tends to flow and collect on the treatment chamber Walls, and in some cases, cause agglomeration of the carrier particles. Thus, it is preferred that flow of the coating is avoided during the impaction process. The coated carrier beads may be heated or treated with solvent prior to, during and/or subsequent to placement in the treatment chamber. Heating of the coated carrier beads may be effected by convection, conduction and/ or radiation. Generally, heating by convection or radiation is preferred for softening carrier coatings because the danger of coating removal by hot heat transfer surfaces is eliminated. Conventional hot air blower systems and/or infrared heater banks may be employed to heat the carrier particles. Solvents or partial solvents may be used to soften the external surface of the bead or the carrier coating on the bead. Generally, greater control of the softening process is achieved when solvent vapors or partial solvents for the coating material are employed. The use of solvents which rapidly dissolve the polyester coating is 1 1 less desirable because uniform surface softening of all the beads is difiicult to attain, particularly at temperatures at which the solvents are most effective.

Alternatively, the polyester and the finely-divided conductive additive may be applied simultaneously to a carrier surface. This can be effected by any conventional method such as spraying, dipping, fluidized bead coating, tumbling, brushing and the like. The coating compositions may be applied as a powder, dispersion, solution, emulsion or hot melt. When applied as a solution, any suitable solvent may be employed. Solvents having relatively low boiling points are preferred because less energy and time is required to remove the solvent subsequent to application of the coating to the carrier core.

Generally, an average conductive particle diameter of less than about 15 microns is preferred because the smooth surface of the ultimate treated head is substantially uninterrupted by portions of relatively large diameter conductive particles extending above the external bead surface. Optimum surface characteristics and maximum reduction of triboelectric value are achieved with conductive particles having an average particle size of less than about 100 millimicrons.

I The following examples further define, describe and compare the developer compositions of the present invention and of utilizing them to develop electrostatic latent images. Parts and percentages are by Weight unless otherwise indicated.

EXAMPLE 1 A coating solution containing the following composition was admixed with five pounds of 600 micron glass carrier cores (preheated to 110 C.) until said glass cores were uniformly coated.

20 parts (20 grams) diallyl phthalate polyester prepolymer (Dapon 35, manufactured by FMC Corporation) 180 parts 1,4-dioxane (solvent) 1.2 parts benzoyl peroxide 0.6 part cobalt naphthenate The blending is effected in a mixing apparatus that imparts a circular flow pattern to the material being blended by vibrating the chamber.

The temperature was then dropepd below the initial softening point of the prepolymer and held at such temperature 76 C. for about one-half hour. The coated cores were then transferred to a vacuum oven and post heated for seventy hours at 30 mm. Hg and at a temperature of about C. below the initial softening point of the prepolymer.

EXAMPLE 2 A coating solution containing the following composition was admixed with nine pounds of 450 micron high density glass carrier cores (preheated to 110 C.) until said glass cores were uniformly coated.

20 parts (20 grams) diallyl isophthalate polyester prepolymer (Dapon M manufactured by FMC Corporation) 180 parts methyl ethyl ketone 1.0 part t-butyl perbenzoate 1.2 parts methyl ethyl ketone peroxide The blending was effected in a barrel blender. The material was cascaded continuously by rotation of the mixing chamber. A vacuum was used to remove solvent.

The temperature was then dropped below the initial softening point of the prepolymer and held at such term perature 48 C. for about one-half hour. The coated cores were then transferred to a vacuum oven and post heated for seventy hours at 30 mm. Hg at a temperature of about 5 C. below the initial softening point of the prepolymer.

EXAMPLE 3 A coating solution containing the following composition was admixed with fifty pounds of 450 micron steel 12 shot carrier core (preheated to 120 C.) until said steel cores were uniformly coated.

64 parts (64 grams) diallyl chlorendate 600 parts 1,4-dioxane (solvent) 2 parts 2,5-dimethyl-2,5-di (peroxybenzoate) 0:5 part 2,6-ditert.-'butyl p-creso1 The blending was effected in a rotating mixing chamber containing stationary wiper blades. The material can be added as a solution or it can be sprayed into the chamber. In this instance, it was added as a solution.

The coating temperature was held at 120 C. for one hour. Thereafter, the coated cores were post cured in a vacuum oven for forty-eight hours at 120 C.

EXAMPLE 4 This example illustrates the extreme resistance to moisture alforded by the polyester coatings of the present invention.

Employing the coating procedures described in Examples 1 and 2, respectively, 600 micron soda lime glass, a normally hydrophilic carrier core, is coated with a polyester coating derived from diallyl phthalate and an additional sample of said carrier core is coated with the polyester derived from diallyl isophthalate.

The coated carrier cores are placed in an oven at about 92 C. and at -90% relative humidity. After 48 hours, an average of only 0.10 percent increase in moisture content is noted.

EXAMPLE 5 This example illustrates the extreme resistance to moisture afforded the reversal carrier coatings through use of diallyl chlorendate as compared to a typical reversal coating such as a vinyl chloride-vinyl acetate copolymer reversal coating.

A sample of coated carrier particles as prepared in Example 3 additionally containing 20% of the reversal dye, Luxol fast blue, is compared to a similar carrier coated with a vinyl chloride-vinyl acetate copolymer also containing 20% Luxol fast blue by placing both samples in an oven maintained at about 92 C. and a relative humidity of about 80-90%. After 48 hours, it is noted that the diallyl chlorendate coated carriers exhibit a 0.12% increase in moisture content Whereas the vinyl chloride-vinyl acetate copolymer coated carriers exhibit a 0.40 percent increase in moisture content.

EXAMPLE 6 This example compares the relative generation of grit in developers of the prior art with those of the present invention.

Employing the procedure described in Example 2, 600 micron flintshot was coated with diallyl isophthalate polyester prepolymer. A developer composition was prepared therefrom by adding a toner comprising a styrene-n-butyl methacrylate copolymer, polyvinyl butyral and carbon black prepared by the method disclosed in Example I of US. Pat. 3,079,342 to a 1% concentration. This developer was evaluated in a 2400 Xerox Copier to 25,000 prints and compared to a 2400 Xerox carrier comprising 600 micron coated particles toned to a 1% concentration with the toner composition described hereinabove.

After 25,000 prints, each developer was analyzed for grit content. The polyester coated carrier of the present invention was found to contain a grit level of 0.12% of carrier weight compared to 0.64% for the 2400 Xerox carrier. The prints obtained with the developer composition of the present invention were noticeably cleaner than those obtained with the 2400 Xerox developer.

EXAMPLE 7 In the following example, the relative triboelectroc values generated by contact of carrier beads with toner par ticles was measured by means of a Faraday Cage. The device comprises a brass cylinder having a diameter of one inch and a length of one inch. A -mesh screen is positioned at each end of the cylinder. The cylinder is weighed, charged with 2.0 grams of a mixture of carrier and toner particles and connected to ground through a capacitor and an electrometer connected in parallel. Dry compressed air is then blown through the brass cylinder to drive all the toner from the carrier. The charge on the capacitor is then read on the electrometer. Next, the chamber is reweighed to determine the weight loss. The resulting data is used to calculate the toner concentration and the charge in microcoulombs per gram of toner.

Employing the procedure described in Example 1, 450 micron glass beads were coated with diallyl phthalate polyester prepolymers. A developer composition was prepared therefrom by adding the toner composition described in Example 6 to a 1% concentration.

This developer was evaluated in a 914 Xerox Copier to 25,000 prints and compared to a conventional 914 Xerox carrier comprising coated 450 micron glass spheres with 1% of the toner composition described in Example 6.

The polyester coating of the present invention exhibited a triboelectric charge of 20 micro-coulombs per gram of toner as compared to 12-15 micro-coulombs per gram of toner for the conventional 914 Xerox coated carrier.

After 25,000 prints, it was found that the grit level in the developer sump (primarily attributable to free toner) was substantially higher when the conventional carrier was employed as compared to use of the developer composition of the present invention.

EXAMPLE 8 This example compares the degree of impaction which arises through use of conventional developers as compared to developers of the present invention. Impaction is basically the impingement of toner particles into a solid layer on the carrier surface. This layer drastically alters the triboelectric properties of the developer and also contributes to the accumulation of grit in the developer system by slufiing off as large fragments of toner-carrier coatings.

To determine the degree of impaction, a developer system toned to 1% toner concentration is milled on an .Abbe jar mill in an 8 oz. glass jar until completely impacted. During the cycle, small smaples are removed from the jar and examined With a stereo microscope for impacted material.

After 100 hours, a conventional 914 Xerox developer composition comprising 450 micron coated spheres toned to 1% with the toner composition of Example 6 contained about 90% of the surface of the carrier impacted with toner whereas the polyester coated carrier described in Example 7 showed only moderate impaction, i.e., less than about 20% of the surface of the carrier was impacted with toner.

Although specific materials and conditions were set forth in the above exemplary processes in making and using the carriers and developer compositions of the invention, these are merely intended as illustrations of the present invention. Various other toners, carrier cores, substituents and processes than those listed above may be substituted in the examples with similar results.

Other modifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. An electrostatographic developer mixture comprising finely-divided toner particles electrostatically clinging to 14 the surface of carrier beads, each of said carrier beads comprising a core having a thin coating thereon comprising a polyester prepared from an ester or prepolymer selected from the group consisting of diallyl isophthalate, diallyl phthalate, diallyl chlorendate and mixtures thereof.

2. An electrostatographic developer mixture according to claim 1 wherein the polyester is prepared from diallyl isophthalate or a prepolymer thereof.

3. An electrostatographic developer mixture according to claim 1 wherein the polyester is prepared from diallyl phthalate or a prepolymer thereof.

4. An electrostatographic developer mixture according to claim 1 wherein the polyester is prepared from diallyl chlorendate or a prepolymer thereof.

5. An electrostatographic developer mixture according to claim 1 wherein the carrier bead coating contains finelydivided conductive material having a volume resistivity of less than about 10 ohm centimeters at 23 C.

6. An electrostatographic developer mixture according to claim 2 wherein the carrier bead coating contains finelydivided conductive material having a volume resistivity of less than about 10 ohm centimeters at 23 C.

7. An electrostatographic imaging process comprising the steps of forming an electrostatic latent image on a surface and developing said laent electrostatic image with the developer mixture of claim 1 whereby at least a portion of said finely-divided toner particles are attracted to and held on said surface in conformance with said electrostatic latent image.

8. An electrostatographic imaging process comprising the steps of forming an electrostatic latent image on a surface and developing said latent electrostatic image with the developer mixture of claim 2 whereby at least a portion of said finely-divided toner particles are attracted to and held on said surface in conformance with said electrostatic latent image.

9. An electrostatigraphic imaging process comprising the steps of forming an electrostatic latent image on a surface and developing said latent electrostatic image with the developer mixture of claim 3 whereby at least a portion of said finely-divided toner particles are attracted to and held on said surface in conformance with said electrostatic latent image.

10. An electrostatographic imaging proces comprising the steps of forming an electrostatic latent image on a surface and developing said latent electrostatic image with the developer mixture of claim 4 whereby at least a portion of said finely-divided toner particles are attracted to and held on said surface in conformance with said electrostatic latent image.

References Cited UNITED STATES PATENTS 3,533,835 10/1970 Hagenbach et al. 117- -l00 M 2,728,740 12/1955 Iler 117-100 X 3,099,574 7/1963 Bernier l 17100 3,151,027 9/1964 Cooley et al l17-l00 X 3,259,482 7/1966 Hansen 117100 X 3,507,686 4/ 1970 Hagenbach 252-62.l X

CHARLES E. VAN HORN, Primary Examiner R. E. MARTIN, Assistant Examiner US. Cl. XJR.

1l7100 A, B, 100 M, 100 :R, 100 S; 25262.1