CA1054838A - Non-filming dual additive developer - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An imaging technique and composition for developing electrostatographic latent images is given whereby a developer composition is employed comprising toner, a substantially smearless polymeric additive, and an abrasive material.

Description

~OS~38 B~CK~ROUND OF T}IE IN~TION
This invention relates to imaging systems, and more particularly, to improved electrostatographic developing materi~ls, their manufacture and use.
The formation and development of images on the surface of photoconductive materials by electrostatic means is well known.
- ~he 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 to a light and shadow image to dissipate the charge on the areas of 3 the layers exposed to the light and developing the resultin$ electro-static latent image by depositing on the image a finely divided ~lectroscopic 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 electro-static latent image. This powder image may then he transferred to a support surface such as paper, The transferred image may sub-stantially be permanently affixed to the support surface as by heat.
Instead of latent image formation by uniformly charging the photo-conductive layer and then exposing the layer to a light and shadow 3 image, one may form the latent imagc by directly charging tl)e layer in image configuration, The powder image may be fixed to ~he photoconductive layer if the powder image transfer step is ~ot desired. Other suitable fixing means such as solvent or overcoati~O
treatment may be substituted for the ~oregoing heat fixing step Several methods are known for applying the electroscopie particles to the electrostat;c latent image to be developed. One dcvelopmcnt metl;od~ as disclosed by ~. N. '~ise irl U. S. Patent

2,618,552 is ~no~n as "cascade" dcvelo~ment. In this mctho~l, a devcloper matcrial comprisin~ relatively largc carri~r particles -l ~

l(~S~;~3 having finely divided toner particles electrost~tically eoated thereon is conveyed to and rol]cd or cascaded across the electro-stati~ image bearing surface. The composition of the carrier particles ~s so selected as to triboelectrically charge the toner particles to their desired polarity. As the mixture cascades or rolls across the latent image bearing surface, the toner particles are electrostati-cally deposited and secured in positive develo~ment processes to the charged portion of the latent image and are not deposited on the uncharged or background portions of the image. Most of the toner particles accidentally deposited in the background areas are removed by the rolling carrier, due apparently, to the greater electrostatic ~traction between the toner and the carrier than be~een the toner , and the discharged background. The carrier and excess toner are ~hen recycled. This technique enhances development of line copy ~5 images.
Another method for developing eLectrostatic images is the "magnetic brush" process as disclosed, for example, in U. S. Patent 2,874,063. In this method, a developer material containing toner particles and magnetically attractabLe carrier particles are carried ~ by a magnet. The magnetic field of the magnet causes alignment of the magnetically attractable carrier particles into a brushlike configuration. This,'magnetic brush" is engaged with the electrostatic ima~e bearing surace and the toner particles are drawn from the brush to the latent image by electrostatic attraction, Still another,technique for developing electrostatic latent images is the "powder cloud" process as disclosed, for example, by C. F. Carlson in U. S. Patent 2,221,776.
Other development methods such as "touchdown" develop~ent as disclosed by R. W. ~.~mdlach in U. S. Patellt 3,166,432 may be usecl where suitable.

lOS~83t~

Generally, commercial electrostatographic development systems utilize automatic machines. Since automatic electrostato-gr~phic imaging machines should operate with a minimum of maintenance, the developer employed in the machines should ~e capabl~ of being recycled through many thousands of cycles. In automatic xero~raphic equipm~nt, it is conventional to employ an electrostatographic plate which is charged, exposed and then developed by contact with a developer mixture. In some automatic machines, the toner image formed on the electrostatographic plate is transferred to a receiving surface and the electrostatographic plate is then cleaned for reuse. Transfer is effected by a corona generating device ~hich imparts an electrosta.ic charge to attract the powder from the electrostatographic plate to the recording surface, The polarity of charge required to effect image transfer is dependent upon the visual form of the original copy relative to the reproduction and to the electroscopic characteristics of the develoning material employed to effect development. For examp]e, where a positive reproduction is to be made of the positive original, it is conventional to employ a positive corona to effect transfer of a negatively charged toner image to the recording surface. When a positive reproduction from a negative original is desired, it is conventional to employ positively charged toner ~hich is repelled by the charged areas on the plate to the discharged areas thereon to form a positive image which may be transferred by negative polarity corona_ In either case, a residual powder image usually remains on the image !5 a~ter transfer. Because the plate may be reused for a subsequent ~ycle, it is necessary that the residual image be removed to prevent further charging and redevelopment of the same image In a positive to positive reproduction process described above, the residual po~der is ~i~htly retained on the plate surfzce by a phenomenon not fully i understood which prevents complete transfer of the powder to the 105483l~

support surface, particularly in the image area. Incomplete transfcr of toner particles is undesirable because ima~e density of th~ ~ltimate copy is reduced and highly abrasive photoreceptor cleaning techniques are required to remove the residual toner from S the photoreceptor surfacc. This imaging process is ordinarily repeated from each copy reproduced by thc machine any time during the reusable life of the developer and the electrophotographic plate surface.
Various electrostatographic plate cleaning devices such as 0 the "brush" and the "web" cleaning apparatus are known in the prior ar~. A typical brush cleaning apparatus is disclosed by L. E. Walkup et al in U. S, Patent 2,832,977. The brush type cleaning means usually comprises one or more rotating brushes, which remove resid~1al powder from the plate into a stream of air which is exhausted through !5 a fi]tering system. A typical web cleaning device is disclosed by W. E. Graff, Jr, et al in U. S. Patent 3,186,838. As disclosed by Graff, Jr, et al, removal of the residual powder on the plate is effected by passing a web of fibrous materials over the plate surface.
Another useful system for removing residual toner particles from ~0 the surface of a photoreceptor comprises a flexible cleaning bladewhich wipes, scrapes, or otherwise removes the residual toner from the photoreceptor surface as the surface moves past the blade.
The foregoing cleaning systems do not, however, remove all types of toner particles from all types of reusable photoreceptGrs ~5 This is not a shortcomin~ of the cleaning system by itselE. If a particular toner would not tend to form an adherent residual film on a particular photoreceptor, the cleaning systems described would effectively remove all residual toner. }lo~ever, many commerical toners of their very nature do tend to form a residual film on reusable photoreceptors and such films are undesirable 105~38 because their pres~nce adversely affects the quality of the un-developed and developed images. The toner film problem is particularly acute in high speed copying and duplicating machines where contact between the developer and the imaging surface occurs a great many more times and at a higher velocity than in conventional electrostatographic systems. Ultimately, the toner buildup becomes so great that effective copying or duplicating is impaired.
In such systems there is a continuing need to have developers which exhibit high, long term triboelectric stability, while at the same time assisting in the elimination of buildup of toner film.
SUMMARY OF THE INVENTION
In accordance with one aspect of this invention there is provided an electrostatographic developing composition com-prising particles; said particles including (1) finely divided electroscopic toner material, (2) from about 0.1% to about 15%, based upon the weight of said toner material of a stable, tough, substantially smearless, polymeric additive having an average particle size less than about the average particle size of said finely divided toner material, and t3) from about 0.01% to about 5%, based on the weight of said toner material, of a finely divided nonsmearable abrasive material of a hardness greater than said polymeric additive and said toner material.
In accordance with another aspect of this invention there is provided an imaging process compr:ising the steps of:
(a) forming an electrostatic latent image on an imaging surface;
(b) developing said latent image by bringing an electrostato-graphic developing mixture within the influence of said latent image, said developing mixture comprising particles, said particles including (1) finely divided electroscopic toner .1 ` `

105483~

mat:erial, (2) from about 0.1% to about 15%, based upon the weight of said toner material of a stable, tough, substantially smearless, polymeric additive having an average particle size less than about the average particle size of said finely divided toner material, and (3) from about 0.01% to about 5% based on the weight of said toner material of a finely divided, non-smearable, abrasive material of a hardness greater than said polymeric additive and toner materials; (c) removing at least a portion of at least any residual developed image from said imag-ing surface by a force which causes the toner, polymericadditive and abrasive materials of said developing mixture to be wiped across at least a portion of said imaging surface; and (d) repeating the process sequence at least one additional time.
The toner material of the present invention may be any electroscopic toner material which preferably is pigmented or dyed. Typical toner materials include polystyrene resin, acrylic resin, polyethylene resin, polyvinyl chloride resin, polyacrylamide resin, methacrylate resin, polyethylene tere-phthalate resin, polyamide resin, and copolymers, polyblends,and mixtures thereof. Vinyl resins having a melting point or melting range starting at least about 110F are especially suitable for use in the toner of this invention. These vinyl resins may be a homopolymer or a copolymer of two or more vinyl monomers. Typical monomeric units which may r,, ~

11~159~838 be ~mployed to fornl ~;nyl polymers include: styrerle, vin~/l naphthalene, mono-olefins, such as, ethylene, propylene, butylene, isobutylene and the lil<e, vinyl esters, such as vinyl acetate, vinyl propionate, vinyl benzoate~ vinyl butryrate and the iike, esters of alphamethylene aliphatic monocarboxylic acids such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate,dodecyl acrylate, n-octyl acrylate, metllyl methacrylate, ethyl methacrylate, butyl methacrylate and the like, vinyl ethers such as vi.nyl methyl ether, vinyl isobutyl ether, vinyl ethyl ether, and the like, vinyl ketones such as vinyl methyl Icetone, vinyl hexyl ketone, methyl isopropyl ketone and the like; and mixtures thereof.
Suitable materials employed as the toner will usually have an avera~e molecular weight between about 3,000 to about 500,000, Any suitable pi~ment or dye may be employed as the colorant ~or the toner particles. Toner colorants are well known and inc~ude, fo~ example, carbon black, nigrosine dye, aniline blue, Calco Oil Blue, chrome yellow, ultramarine blue, duPont Oil Red, ~uinoline yellow, methylene blue chloride, phthalocyar.ine blue, Malachite ~reen Oxalate, lamp black, Rose Bengal and mixtures thereof. The pigment or dyes should be present in the toner in a sufficient quantit~ to render it highly colored so that it will form a clearly visib].e image on a recording member. Thus, for example, where conventional xerographic copies of typed documents are desired, the toner may comprise a black pigment such as carbon black or a black dye such as Amaplast Black r)ye available from the National Aniline Products, Incorporated. PreferabLy, the pigment i5 employed in an amount of from abou-t 1 percent to about 30 percent, by wei~ht, based on the total weight of the cnlored toner If the toner colorant employed is a dye, substantially srnaller quall-tities of the col.orant may be used.

The additives m;7y be inl-rodllcc~d into the ultir7ate developer material in any suita7~1e manner to forrn a physical mix of additive particles with developing material particles. Thus, ~or example, the additive particles rnay be initially mixed with carrier particles or tonCr particles and thereafter introduced into the developer mix.
Generally, when the additives are physically mixed with toner or ~-1 carrier particles, sacisfactory result-s are achieved when about ~.11 to about 15 percent additives based on the weight of the toner particles is employed. Greater cleaning efficiency at reduced cleaning pressures is achieved when the additives are present in an amount from about 0.1 percent to ahout 5 percent based on the weight of the toner in the final developer mixture, Any suitable stable, tough, smearless, solid, polymeric addi-tive having a Rockwell hardness (~STM Test D/785) of at least about lS R-10 may ~e employed in the developer of this invention, Undesirable filmingr of the additive is inhibited by employment of toug7n additiv particles having a Rockwell hardness of about R-10, If desired, addi-tive ma7erials having a Rockwell hardness as high as about R~20 may be utilized to form the developer of this invention. Generally, the additive particles have an average partic~e size less than about the particle size of i-he toner yarticles, An average particle size from about 0.05 to about 30 microns is preferred because more copies of higher quality images may be obtained, Particularly good results are obtained with an average particle size range from about 0.20 micron to about 8 microns because e~ficient cleaning is achievcd without adversely affecting image density as a result of additive particles present in transferred toner images. The additives o~ this invention may be of any suitable shape. Tvpical shapes include flake, cylindrical, spherical, granuiar and irreguiar particles, Op~ir"um 3n re~ults are obtained w;th additive particles having a spheric.71 , r~ Y.~ ~.~r);",~r~r,~--~3~3~
shape becausc more ef:rective removal of rcsidual toner particles at lower cleaning pressures is achieved, particularly with a blade cleaning systeM.
Generally, polymeric additive materials more electrone~ative S than sulfur are preferred because a greal-er number of higher quality images can be obtained on reusable photoreceptors with scraping devices such as doctor blades. Whether a material is more electro-negative than sulfur may be determined by known techniques such as by determining the position of the additive material relative to sulfur in a triboelectric series. The materials in a triboelectric series are arranged in such a way that each material is charged with positive electricity when contacted with any material below it in the series and with negative electricity when contacted with any material above it in the series, Thus any material which acquires a negative charge when contacted with sulfur may be considered more electronegative than sulfur and obviously would be below sulfur in the triboelectric series, Typical stable, solid, polymeric additive materials below sulfur in the triboelectric series include: polyvinylidene fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylchloride, polyviny].idine cllloride, polyethylene, polypropyl.ene, chlorinated polyethylene, chlorinated polyether, copolymers of tetrafluoroethylene and chlorotrifluoroethylene, copolyrners of tetrafluoroethylene and hexafluoropropylene, copolymers of tetra-fluoroethylene and vinylidine fluoride, copolymers of chlorotri~luoro~
ethylene and vinylidine fluoride, copolymers of vinyl chloride and vinyl fluoride, copolymers of vinyl chloride and polyethylene, copolymers of vinyl chloride and polypropylene and mixtures of any of the above homopolymers or copolymers. Ilornopolymers or copolymers o~ fl-loro-ole~ins detailed above are preferred because a ~(rreater nlln~)er o:L hi~ uali-ty lOS~38 copies can be obtained on a reusable photorecept~r surface.
The comhination of the resin comyonent, colorant, polymeric additive and abrasive additive, whether the resin component is a h~mopolymer, copo]ymer or blend, should have a blocking temperature of at least about 110 F. When the toner is characterized by a blocking temperature less than about 110F. ~he toner particles tend to agglomerate during storage and machine operation ancl also from undesirable films on the surface of reusable photoreceptcrs which adversely affect image quality.
The toner compositions of the present invention may ~e prepared by any well-known toner mixing and comrninution technique.
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 or forming lS toner particles is to spray-dry a ball-milled toner composition comprising a colorant, a resin and a solvent. When the toner mixtures of this invention are to be employed in a cascade development process, the toner should have an average particle size by weight percent less than about 30 microns and preferably between about 4 and about 20 microlls - 20 for optimum results.
Preferably, the additives of this invention are selected from materials having a lower critical surface tension than the critical surface tension of the toner employed therewith. Normally, a difference in critical tension value of at least about two dynes per centimeter between the toner and the additive is preferred for optimum cleaning and image quality. Good results are obtained with developer material comprising colored toner particles having a critical surface tension value greater .han about 24 dynes per centimeter in combi-nation with additives having a critical surfc3ce tension value less than about ~ dynes per centimeter Typical polymeric materi.31s - ].n -105~315 having a critical surface tension value less than about 33 dynes per centimeter include: polyvinylidine fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, copolymers of tetrafluoroethylene and chlorotrifluoroethylerle, copolymers of tetra~
~luoroet]lylene and hexafluoropropylene, copolymers of chlorotri~
fluoroethylene and vinylidelle fluoride, and mixtures thereo-E.
Excellent results are obtained with polyvinylidine fluoride. Developers containing polyvinylidine fluoride additives form the ~reatest number of dense background free images on reusable imaging surfaces.
A number of pigmented or dyed electroscopic toner material having a critical surface tension value greater than about 24 dynes per centimeter are described in the patent literature. Typical toner materials having a critical surface tension value greater than about 2l~ dynes per centimeter include polystyrene resin, acrylic lS resin, polyethylene resin, polyvinyl chloride resin, polyacrylamide resin, methacrylate resin, polyethylene terephthalate resin, polyamide resin, polyamide epichlorohydrin resin, resinous condensation product of 2,2, bis (4~hydroxy-isopropoxy-phenyl) - propane and fumaric acid, and copolymers, polyblends and mixtures thereof.
The critical surface tension values of many solid surfaces are well known. For further details as to the determination of the critical surface tension of a solid surface, reference is madc to the discussion in the Journal of Colloid Science, Vol. 7, 1952 beginning at page 109. The critical surface rension values employed herein are based on measurements made be~ween about 20C and about 25 C.
With no intention of being bound by any theory of action, it is believed that the use o~ a tough, stable, substantially smearless polymeric additive material with a nonsmearing abrasive reduces toner impaction and assists in enhancing the lon~ term i~)5~t~38 triboelcctric i~roperties of the developer. It is this which ls believed to help in forming and maintaining good high density ima~e quality while reducing background.
Contemplatcd abrasive mate~rials include colloidal silica, surface modi~ied organophilic silica, aluminum silicate, surface treated aluminum silicate, titanium dioxi~e, alumina, calcium carbonate, antimony trioxide, barium titanate, calcium titanate or strontium titanate, CaSiO3, MgO, ZnO, ZrO2 etc. and mixtures thereof.
The particularly preferred materials are these which have been surface modified to impart hydrophobic eharacteristics thereto. ~or example, hydrophobic silicas are prepared by reacting freshly prepared colloidal silica with at least one organo~ilicon compound having hydrocarbon ~roups as well as hydrolyzable groups lS attached to its silicon atom. In one technique, tne reactants and steam are pneumatically introduced in parallel flow into a fluidized bed reactor heated to about 400 C. The organosilicon compound reacts with silanol groups on the surface of the SiO2 particles and chemical attachment between the silicon atom in the organosilicon compound and the silicon atom in the SiO2 occurs through an o~ygen atom. Any suitable hydrocarbon or substituted hydrocarbon organic group directly attached to a silicon atom in the organosilicorl com-pound may be employed in preparing the modified silica. The org;lnic group is pre~erably one which imparts hydrophobic characterist cs to the abrasive material to improve the stability of developer materials under varying humidity conditions. The organic groups may comprise saturated or unsaturated hydrocarbon groups or derivatives thereo~.
Saturated organic groups include methyl, ethyl~ propyl, ~utyl, chloropropyl and chloromethyl groups. Examples of typ;cal orgal-lo-silicon compoullds include: dimethyl dichlorosilal~e, trimcthyl l~S~8 chlorosilane, methyl trich]orosilane, vinyl triethoxy silane.
The type oE organo groups can influence the triboelectric charac-teristics of the developcr For example, aminopropylsilane treated with silica can be used in a reversal type developer.
The particle size of the abrasive additive should a fall within the submicron range of from about l to about 500 milli-microns and preferably, between about lO to about lO0 millimicrons.
Concerning the comparative hardness of the abrasive type material, this material must be harder than both the toner material and the polymeric additive material While most of the materials disclosed can be considered to be very hard materials falling within Mohs' hardness scale, it is to be understood that any material of less hardness than talc of Mohs' hardness scale can also be employed so long as it is harder than the toner material and polymeric additive material. Materials softer than talc are conveniently classified according to the Shore durometer penetration technique and placed within either scale A, B, C and D of this test procedure The chemical composition of the abrasive additive is not critical so long as it does not introduce deleterious contaminents or adversely affect the imaging and developrncnt aspects of an electrostatographic system. In addition, there is no particular criticality surrounding the shape of each abrasive particle since both spherical and irregularly shaped additives function effectively, ~, ~
` Preferred materials are Aerosil R972, a hydrophobic silica available from DeGussa Incorporated, New York, New York and Kaophile-2, a hydrophobic aluminum silicate, available from Georgia Kaolin Company Elizabeth, New Jersey.
The compositîon oE the present invention finds utility in all known electrostatographic developmerlt systems, ~his includes ~ t~de m~r~s -- 1?~

~OS~ 8 systems which employ a carrier material such as magnetic brush deveJlopment and cascade development as well as systems ~hich do not necessarily employ a carrier material such as powder cloud develop-ment, fiber brush development and touchdo~ development.
Suitable coated and uncoate~ carrier materials and consumable carrier materials which are kno~Yn, are useful with this invention.
Many typical carriers are described in U. S. Pat~nt 2,618,552. An ultimate coated particle diameter between about 50 0 microns to about 2000 microns is preferred because the carrier particles then possess sufficient density and inertia to avoid adherence to the électrostatic images during the cascade development process. Adherence of carrier beads to electrostatic drums is undesirable because of the formation of deep scratches on the surface during the image transfer and drum cleaning steps. ALso, print deletion occurs when large carrier bcads adhere to xerographic imaging surfaces. For magnetic brush development, carricr particles having an average particle size less than about 8000 microns are satisfactory. Generally speaking, satisfactory results are obtained when about 1 part toner is used with about 10 to about 1000 partsby weight of carrier in the cascade and mag~netic brush developers.
Concerning the broad relative proportions of the toncr material versus the additive materials, the polymeric additive material should be present in an amount of about 0.1 percent to about 10 percent by weight based upon the toner. ~ particularly preferred ratio is from about 0.1 percent to about 5 percent by weight o polymeric additive material based on the IYei~ht of toner.
Generally, it has been found that from about 0.01 percent to about 5 percent by weight of ~brasive material base~ on the wei~ht of the toner material will achicve the desircd results _ lL~ --1~54~38 A particularly preferred range is from about 0.1 to about 1 percent by weight.
The toner compositions of the instant invention may be employed to develop electrostatic latent images on any suitable electrostatic latent image bearing surface includ-ing conventional photoconductive surfaces. Well known photoconductive materials include: vitreous selenium, organic or inorganic photoconductors embedded in a nonphoto-conductive matrix, organic or inorganic photoconductors em-bedded in a photoconductive matrix or the like. Representat-ive patents in which photoconductive materials are disclosed include: U.S. Patent 2,803,542 to Ullrich, U.S. Patent 2,970,906 to Bixby, U.S. Patent 3,121,006 to Middleton, U.S.
Patent 3,121,007 to Middleton and U.S. Patent 3,151,982 to Corrsin In ~.S. 2,986,521, Wielicki, there is taught a reversal type developer powder for electrostatic printing comprising electroscopic material, i.e. toner, coated with a finely divided colloidal silica. The toner material must have (1) a positive triboelectric relationship with respect to the silica and (2) the silica coated toner must be repelled from negatively charged areas of an imaging surface.
The only positively stated purpose or utility for the silica is to reduce tackiness and improve the free flowing character-istics of the developer powder.
In copending Canadian Serial No. 086,505, filed on June 25, 1970 in the name of Chatterji, it is taught that the inclusion at a minor proportion of similar polymeric additives in an electrostatic developer overcomes certain problems associated with the use of prior art toner materials.

In U,S. 3,522,850 issued to Stephen F. Royka et al, ~ - 15 -lOS4~38 it is taught to employ a dry lubricant when employing a blade cleaner in an electrostatographic imaging system.
This patent, however, - 15a ~054~38 does not t-each the use of a combination of additives to control tribo and improve print density.
In U, S, ~,7~0,617 issued to Chatterji et al, it is taught to employ silica as an additive in an eleetrostatographic imaging system. This patent does not teach or reeognize the enhance properties possible with the use of the additional polymeric additive of this invention.
an 13~ 77~ ~arrh /0~ /9~
~, In~ Serial No. 18~,570 filed Octobcr 1~, 1971, in the name of Jugle et al, it is taught to use a smearable additive and an abrasive to control the eoating of the smearable additive on the photoreceptor during repeated cyclic imaging, This patent does not teach or reeognize the enhance properties by using a nonsmearable additive in conjunetion with an abrasive additive, nor does it recognize that toner impaetion ean be reduced by the unique technique given in this speeification, The following examples further define, describe and eompare exemplary methods of preparing the development system components of the present invention and of utilizing them in a development and eleaning process. Parts and percentages are by weight unless other-wise indicated.

EXAMPLE I
The vitreous selenium drum of an automatic copying maehine is eorona eharged to a positive voltage of about 800 volts and exposed to a light-and-shadow image to form an electrostatie latent image, The selenium drum is then rotated through a easeade development station, ~ control developer comprising 1 part toner having a critical surface tension value of about 30 dynes per eentimeter and containing a styrene-butyl methacrylate copolymer - 16 _ -lOS4838 and about lO percent by weight carbon black is prepared hy the method disclosed in Example I of U. S. Patent 3,079,342 and about lO0 parts steel core carrier beads prepared by the process disclosed in U. S, Patent 2,618,551 is employed in the developer station.
S The toner particles have an average particle size of about lO microns and the carrier beads have an average particle size of about 450 microns. After the electrostatic latent image is developed in the developing station, the resulting toner image is transferred to a sheet of paper at a transfer st-ation. The residual toner particles remaining on the selenium drum after passage through the transfer station is removed by means of a cleaning blade comprising a rectangular strip of about 3/32 inch thick polyurethane elastomer having an edge spring biased against the photoreceptor surface. The trailing face of the cleaning blade is positioned to form an acute angle of about 2~ with the line of tangency extending through the line of blade contact, Sufficient pressure is applied to the blade to obtain maximum removal of the toner particles from the drum surface. The drum surface is rotated at a surface speed of about lO inches per second past the cleaning blade and 500 copies are made. After only a few copies are made, the copies and drum surface are examined for quality and condition, respectivcly, The copies made at the start and near the termination of the test are charac-terized by high background, streak marks, and irregular image density, Large portions of the drum are covered by a continuous toner film and occasional streaks and scratch marks. The electrical properties of the drum are measured and found to be erratic along the surface due to the toner deposits and scratches.
EXAMPLE II
The procedure of Example I is repeated under substantially the same conditions except that about l part of polyvinylidene ~OS48~

fluoride particles and 0.25 part of hydrophobic silica are added to about 100 parts toner particles. The polyvinylidene fluoride A~l (Kynar 201-Pennwalt Chemical Corporation) particles have a spherical shape, a particle size range from about 0.3 micron to about 0.4 micron, Shore D hardness (ASTM Test D676) of about 70-80 ~ockwell hardness 80-95). The silica is Aerosil R972. A fresh vitreous selenium drum is also substituted for the drum employed in Example I. After about 5,000 cycles, the copies, the drum surface, and the carrier particles are examined for quality and conditions, respectively. The copies formed throughout the test are characterized by high density print quality and substantially no background toner deposits. The electrical properties of the drum are measured and are found to exhibit sub-stantially the same resporlses before and after the test. The drum surface shows no signs of toner-filming, streaks, or scratches.
After long term use, the carrier triboelectric properties are xerographically enhanced over a sample without silica.
The expression "developer material" as employed herein is intended to include electroscopic toner material or combinations of toner material and carrier material.
Although specific materials and conditions are set forth in the foregoing examples, these are merely intended as illustrations of the present invention. Various other suitable toner components, additives, colorants and development techniques such as those listed above may be substituted for those in the examples with similar results Other materials may also be added to the toner or carrier to sensitize, synergize or other~Jise improve the imaging properties or other desirable of the system 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 in~ention, tr~de ~rks - 18 _

Claims (15)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An electrostatographic developing composition com-prising particles; said particles including (1) finely divided electroscopic toner material, (2) from about 0.1% to about 15%, based upon the weight of said toner material of a stable, tough, substantially smearless, polymeric additive having an average particle size less than about the average particle size of said finely divided toner material, and (3) from about 0.01% to about 5%, based on the weight of said toner material, of a finely divided nonsmearable abrasive material of a hardness greater than said polymeric additive and said toner material.

2. The developing composition of Claim 1 wherein the toner material has an average particle size of less than about 30 microns.

3. The developing composition of Claim 1 wherein the abrasive material has an average particle size between about 1 millimicron and about 500 millimicrons.

4. The developing composition of Claim 1 wherein said composition comprises from about 0.1% to about 10% by weight of said polymeric additive based upon the weight of said toner material.

5. The developing composition of Claim 1 wherein said polymeric additive is more electronegative than sulfur in the triboelectric series.

6. The developing composition of Claim 1 wherein said polymeric additive is polyvinylidene fluoride.

7. The developing composition of Claim 1 wherein said polymeric additive comprises spherical particles.

8. The developing composition of Claim 1 wherein said abrasive material comprises submicron size colloidal silica.

9. The developing composition of Claim 8 wherein said silica is silicon dioxide particles having surface silicon atoms chemically attached through silicon-oxygen-silicon bonding to silicon atoms having one to three organic groups directly attached thereto by silicon-carbon bonding.

10. The developing composition of Claim 1 including from 10 to 1000 parts by weight of carrier particles per part of toner material, said carrier particles being grossly larger than said finely divided toner material.

11. An imaging process comprising the steps of:
(a) forming an electrostatic latent image on an imag-ing surface;
(b) developing said latent image by bringing an electrostatographic developing mixture within the influence of said latent image, said developing mixture comprising particles, said particles including (1) finely divided electroscopic toner material, (2) from about 0.1% to about 15%, based upon the weight of said toner material of a stable, tough, substantially smearless, polymeric additive having an average particle size less than about the average particle size of said finely divided toner material, and (3) from about 0.01% to about 5% based on the weight of said toner material of a finely divided, non-smearable, abrasive material of a hardness greater than said polymeric additive and toner materials;

(c) removing at least a portion of at least any residual developed image from said imaging surface by a force which causes the toner, polymeric additive and abrasive materials of said developing mixture to be wiped across at least a portion of said imaging surface; and (d) repeating the process sequence at least one additional time.

12. The imaging process of Claim 11 wherein said particles include carrier particles which are grossly larger than said finely divided toner material.

13. The imaging process of Claim 11 wherein said force is applied via a cleaning blade.

14. The imaging process of Claim 11 wherein said force is applied via a cleaning web.

15. The imaging process of Claim 11 wherein said force is applied via a cleaning brush.