US3518081A - Image formation and development - Google Patents

Description

June 30, 1970 K ET AL 3,518,081

IMAGE FORMATIOI I AND DEVELOPMENT Filed Feb. 7. 1964 IMAGE WISE TRIBOELECTRIC MODIFICATION CHARGE BY FRICTiONAL CONTACT DEVELOP IN VEN TOR.

WILLIAM L. GOF'F'E JOHN KMORE BYJ%%BQ(QQQ ATTORNEY 6f 'electrostatography.

n te-d ees P ABSTRACT on THE DISCLOSURE 1 Graphic reproductions are achieved by the image-wise modification of the triboelectric charging capability of a surface followed by the triboelectric charging of the modified surface to produce a charge pattern corresponding to an image; The charge pattern may be developed with finely divided colored electroscopic particles and the resulting colored image either fixed on the surface of the insulating member or transferred to a receiving surface and fixed thereon. V

This invention relates in general to electrostatography "and moreparticularly to a new method for the reproduction of' images based on the imagewise modification of the-triboelectric charging capability of a surface.

"Electrostatography encompasses the entire field of forming and utilizing latent electrostatic charge patterns to record and reproduce images in visible form. The field of electrostatography was pioneered by Chester F. Carlson when he disclosed in US. Pat. 2,297,691 the basic technique of one major sector of the electrostatographic field referred to as xerography. In the most commonly practiced form of xerography, a photoconductive insulating layer is first given a uniform electrostatic charge over its entire surface and is thenexposed to an image of activating electromagnetic radiation such as light which selectively dissipat'es the charge in illuminated areas of the photoconductive insulator, while charges in the non- -il1uminated areas are retained, thus forming a latent electrostatic imaige. This latent image may then be developed or made' visible by the deposition of finely divided colored electroscopic marking particles on the surface of the' photoconductive insulating layer, as a result of which-the markiiig' particles adhere to the surface of the photoconductive insulating layer only in areas of retained charge. This developed image may then be utilized, in a number of diverse ways. For example, the imagefimay be viewed in sitii on the photoconductive insulator, fixed 'in placeon its surface or transferred to a second surface "suchas'a sheet of paper 'and'fixed thereon as desired, depending upon whether the' photoconductive insulating layer is reusable the process or not. Hundreds of additional patents have issued in the'field of xerography since the time of the original Carlsonpatents incorporating many improvements and modifications into the basic process and as a result of this development, xerography is 'today; by a greatmargin the largest commercial sector The other broad general branchof electrostatography .r. eiierally-referred to'as electrofgraphy and it is contloesi not employ a photoconductorand light exposure to control" the formation of its "latent electrostatic charge pattern; Electrography 3 as it is "generally known' today l rriay be'divided into two broad 'sectors which are, xeroa 12 Claims sidered"distinct'fromthexerographic'branch in that it 3,518,081 Patented June 30, 187i) ice stemming from thephrase Transfer of Electrostatic Images) the electrostatic charge.v patterns conforming to the desired reproduction are formed on a uniform insulating layer by means of an electrical discharge between two or more electrodes on opposite sides of the insulating medium. By controlling the shapes, combinationsand numbers of electrodes employed, charge patterns of almost any shape may be formed on the insulating material. In both xeroprinting and TESI recording, image development is by the same techniques employed in xerography.

The common feature of all of these electrostatographic systems is that they employ the lines of force from the electric field of a latent electrostatic image to control the deposition of the colored finely dlivided marking particles known as toner, thus forming a visible image corresponding to the charge pattern.

Now in accordance with the present invention there is provided a new method of forming a latent electrostatic image and an improved electrostatographic process in which reproduction is formed by the imagewise modification of the triboelectric charging capability of an insulating surface followed by triboelectric charging of the modified surface to produce a charge pattern corresponding to the image, and optionally development of the charge pattern with finely divided colored electroscopic particles and alternatively fixing the particles on the surface of the insulating member or transferring the particles to another copy surface and fixing thereon.

The above and still further features, objects, and advantages of the present invention will become apparent upon consideration of the following detailed disclosure of specific embodiments of the invention especially when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a flow sheet of the process steps of the invention.

FIG. L2 is a side-sectional view of an apparatus employing one of the process embodiments of the present invention.

Referring now to FIG. 1, it is seen that the first step of the process consists of modifying the surface of the layer upon which the image is to beforrned in imagewise configuration so that areas of this surface which correspond to the image to be reproduced differ significantly in their triboelectric charging capabilities from the remainder of this surface. By way of background, it should be noted at this point that many materials may be charged by triboelectrification, that is to say, by rubbing them together with another material. Various materials have been arranged into a sequence knownas the triboelectric series which-is so arranged that any one of the materials is positively electrified or charged by rubbing it with any other material below it in the sequence.

Conversely, any material in the triboelectric series may such electrification is governedlby the distance between the material positions in the triboelectric series, that is to say, the greater the distance they arefremoved'from one another in the series,' the greater the mutual electrification or charging and the closertogether they are in' the series, the less the mutual electrification o'r' charging. The

present invention thus contemplates modifying allthe imageareas' or all the non-image areas of a surface upon which the image is to be formed so as to change the'posi- -tion of these modified areas in the triboelectric series with respect tothe remainder of the imaging surface. "this sway, .whenihejmagingsurfaceis. rubbervw-ith amaterial a range -0f-visible alightthey generally still remain -most which is distant in the triboelectric series from either the image or non-image areas, from this surface a differential charge pattern" or latent electrostatic image is. formed von hi aains sgrfac'el v I if T is latent electrostatic image .rnay then be used ina number. 9f. ways. For example, it, maybe read-out .by ieleetrostatie chargesensing as with an electrometer for ,direct. use or radio transmission to a distant point or. it ,may be made visibleby any, one of a number of well ltnowntdeveloping te chniquesva s described hereinafter, .Ihe d erential -in .triboelectricalcharging susceptibility. of ge ornon-ijmag e. .areas j of vthe surface upon which the number of different techniques which are explained in greater detailiin the examples given below. These techniques, however, may generally be grouped into two categories which are (1) charing the triboelectric charg- .ing susceptibility of the imaging surface itself in imagewise configuration or (2) coating the imaging surface in imagewise configuration with a thin layer of a second material remote from it in the triboelectric series. With either technique the object is to end up with either image or non-image areas having a position in the triboelectric series which is remote from the position in the triboelectric series of the material which is rubbed against the surface to charge it while other areas of the surface have a sub- ,stantially different position in the triboelectric series with respect to this charging material.

In one of the exemplary techniques described below in the examples, the triboelectric charging susceptibility of the imaging surface is itself, modified by employing a polymerizable material as the image forming material and polymerizing or crosslinking the material in image configuration by photographic exposure where the material is .photopolymerizable or by imagewise selective heating where the monomer can be polymerized (or a polymeric material can be crosslinked) by heating. This technique achieves the desired results because the polymer or crosslinked polymer has a different triboelectric charging susceptibility than the monomer or non-crosslinked poly- .rner from which it is formed and the more highly polymerized the material is, the greater is this difference in triboelectric charging susceptibility. Since polymerization from a simple monomer and crosslinking of already formed polymeric units both serve to increase the molec- -ular weight of the material acted upon, the verb reproduction .is to be formed may be establishedby a 'polymerize and the noun polymer shall be used .generically to includeboth of these concepts. Because triboelectric charging is based on a surface phenomenon, it is only necessary to modify a very thin layer of the surface of the imaging surface in order to achieve the desired results and this rule applies equally to modification of the material itself or to imagewise coating of the material as described above. Accordingly, it is only necessary to polymerize or crosslink a very thin surface layer of the material to achieve the desired results and polymerizationor crosslinking throughout the bulkof the layer is unnecessary although it does not detract from the results. inany' way. =-Thisisqmost important since, with most photopolymerizablematerials, electromagnetic radi- {ation in;v the ultraviolet range is required to cause, photog-polymerizatipmandthe greatest part'of this radiation is -of' instant invention- -only requires surface polymaerizat-ion,it'imrnediately becomes apparent that this sys- .-tem has" a faster effectivephotographic speed thanother timaging-systems based on photopolymerizationwhich reiqlet whiehpenetr ates, into the layer. Since-the process iquire. polymerization throughout the bulk of their imaging layers. Eventhough many;photopolymerizable systems may be sensitized to electromagnetic radiation in the electroscopic, colored marking :particleg,

of this :type generally; range, in, size from ab microns with average particle sizes from,abou

-.electric ally insulating, the moplastieresins; hpwever, .of -the- -con;ventional deye oping ;-materia s.. .u sed ,in, v xerosensitive to UV light.

The fact that modification of only a thin surface layer of the image forming material is required in the process of the instant inyention 'i's falsiiadvantageous in thetechniqiie "where surface eoatin'gsare employed {detect this change in imagewise configuration,- sin:e' verjy=thin layers of these co'atingsranging tofmonorn c'u'lar '1n- 1c ness may be effectively employedf-ln' fact, t-h ese layers may be so thin that theyfma-y bethought of as almost surface ;coj nt a m inant layers. These contaminants;,may eithefibe inert to, or reactive with the imaging surface. In fact, the contaminant "may 'evea'tea catalyst or oxidizing agent for 'examplewhich serves to increase. the/molecular weight of the surface it contacts as.by-ordinaryiaddition or condensation polymerization of thepsurfac e orby oxy gen bridging polymerization of unsaturated molecules (this latter mechanism isbelieved to bethe .one respon sible for the hardening 'of the drying oils).

Once the modification .of .triboelectric echarging stlsceptibility of the image forming surface has.been accomplished in imagewise configuration, the surfaceyistribo: electrically charged by uniformfrictional c onta et with a charging member. This charging may be accomplished by rubbing with glass,-rubber,-fur, metals, wool, other fabric or any other material selected according-dons;position in the triboelectric series with. respect ,to the position in that series of image and. non-image ,areasoffl-the image forming layer so as to effect the desired chargingpattern. Friction charging can also be acliieyedby the-,flow, of a liquid or gas past thestlrfaceto,belcharged,,-In addition to rubbing the surface to. becharged. witht one' ofthe materials listed above, charging maybe accomplished by cascading small beads of the material over-the.,surfac e to be charged. This technique may employ. coated carrier beads of the type described in U.S. Pat. 2, 6-18,55'1 to Walkup, and depending upon the material employed for the surface coating of the heads, a positive or negative image may be formed. N a

In the following examples beads are referred to, as type A where the position of their coatings in the.triboelectric series is suchthat they will charge most materialswhich they rub against negatively and as type B where theywill charge these materials positively. Typical ,type A -bea ds are described in detail in Examples 4-7 of U.S;.Pa,t. 2,618,551 and typical type B beads are described in Examples 1-3 of that patent. Image and non-image areas of the imaging surface may be on opposite sides of the charging material in the triboelectric series so that the charging material charges one positively and the ,other'negatively, or, in the alternative both types of areasrnay-be on one side of the charging material in the triboelectric series but separated from each other so that, for, example, the

charging material may render image areasmqrepositive than non-image areas or more negative than non-image areas. Thus, image areas can becharged to6 00..vol,ts,positive while non-image areas are chargedto; 300yoltspositive by the triboelectric charging of thefrictioneharging material.

. cally charged by frictional contactyviththe.clnirgingrnates t image b i i t e i sl ee ftt rial, thus forming a latent electrostatic chargepattern, s. charge p nmar .e a z lee-bs ds s s or -r i e ed p si i a he o rof-finel m s ed, w xix-th electrostatographic artv as fitQn 10 microns and in most gcases, are ,ma de up of pigmented,

graphy may be employed to develop the latent electrostatic: image formed by the method described above. Reference is hereby made to U.S. patents, Re. No. 25,136 to Carlson; 2,891,001 to Insalaco; 3,079,342 to Insalaco; 21659 ;679' to C6pley'.and2',788,288' to Rheinfrank et al. for a more detailed disclosure of these toners. The develbring nr ess...('as.distingu hedtromt e evelop material or toner itself) may be accomplished using any one of a number of, Well .known xerographic developing techniques such as brush development as described in U.S. 2,975,578 to 'Byrd, powder cloud development as described "in-U.S. 2,918,900 to Carlson, skid development as described in U.S. Pat. 2,895,847 to Mayo or immersion development wherein the toner particles are suspended inan insulating liquid as describedin U.S. Pat. 3,010,842 to Ricker. Another development technique which may be employed. isrthe cascade development technique which is, today, perhaps the most widely commercially used xerographic development technique. This development technique which is more fully described in U.S. Pat. 2,618,552 and 2, 638,416 utilizesatwo element developing mixture including the finely divided toner particles and grossly larger carriergbeads of the same type as the coated beads described above for frictionally charging the imaging surface. These carrier beads serve bothto maintain the fine toner particles deagglomerated and to charge them by virtue; of the relativerpositionof the toner and carrier materials in'thetriboelectric series and the constant rubbing together of these materials as the developing mixture-is conveyed through the developing system. Since the carrier. beads and toner particles tend to charge each other. ,to opposite polarity the carrier .beads collect the toner particles on their surfaces and carry them through the developing apparatus. When this mixture is cascaded over the' surface bearing the .latent electrostatic image, theyelectrostatimfield from the charge pattern removes the toner particles from the carrier beadsbecause its electrostatic attraction for the toner particles is stronger than that of-the .carrier beads in charged areas, Once the developing-mixture ?has cascaded over the surface to be developed, the carrier beads along with any toner particles not employed in the development fall back into the bottom ,of an 'adjacent container for later recirculating in the developing process. Wherever this developer-is recirculated; as'described above,toner particles in the mixture arerrreplenished periodically; It isalso possible to combine charging and development withrthis and other types of v developers where the developer isin'frictional contact with the imaging surface during development, however, development usually takesa longer time with this. combined technique-because there is no charge on the irnaging surface when the developer first contacts it. Elhistechnique has been experimentally proven with good results.., I i 1 r Afterthe latentelectrostaticirnage hasbeen developed, it maybe either transferred to "another'surface as by bringing ithetoner'particle image'into contact with an adhesive web or it may b'etransferred to an insulating web-by electrostatic transfer as described in U.S. Pat". 2,576,047- to Sc-haired; In the event that the toner particle image is'not transferred to an' adhesive surface, it is gen wally-perma ently attached to either the surfac :npon which it was originally formed or the 's urface to which it"ist'ransferred-by fixing; This fixing may beaccomplished by: heating the toner particles to"'fuse them to their substrate when 'they are thermoplastic in nature or by s ulr them'iwitli an adhesive material. lrl-additiori td d'e velop i'r'lg 'the' lateiiit electi'ostatic image, as described "above, the image-"may "be fre'ad out' by a sfca'iining device capable of sensi g'the charge lever in sequential image areas or ;it

6 and then softening the surfaceuntilthe electrical ,field forces of the electrostatic image exceed the surface ten: sion forces of the surface. Transfer of electrostatic images from one surface to another is described in Walkup Pat,

may'bereridfered: visiblebyw techniques'such as charge indtieed plastic deformationf Thia latter technique inf volves forrriirigfth latent electrostatic image one surface ii capable' oflfornfiiiig' a plastic deformation image ortransferring: the electrostatic image to such a: surface No. 2,833,648. An exemplary process of plastic'deformai tion imaging is described in more detail in U.S. patent application, Ser. No. 193,277, filed May 8, 1962, now Pat. No. 3,196,011. I The process of the invention was carried out inanumber of experiments as described in the following examples: In all examples the same toner which is described in detail in U.S. Pat. 3,079,342 to. Insalacowas used both for a positively and a negatively charged developing material, only different types of carrier beads were used,

as described above, to charge the toner particles. tor' different polarities.

All exposures to ultraviolet light in the examples were one minute exposures with, a .Hanovia high pressure mercury arc lamp of watts.

EXAMPLE I A 1.5 mil biaxially oriented (1,4-bis methyl cyclohexarie polyterephthalate) and available from the Eastman Kodak Cc'un'p'anyof Rochester, New York under the traden'ame of ."Ko dai" was laid down on a support ,a'nda persons finger was brought into contact with the surface of .thelfilr'll j bl ali ently leaving behinda surface]lcontamination'of'body oils in the form-of a finger print. Thefilm was then friction charged by icascading'a number 'of type I B coated carrier beads across the surface of the Kodar and was developed wi'thpositively charged developer-according to the cascade development technique as described above; This developed the areas of the-Kodar to which body oils had been'trans ferred'while'the 'use of negatively charged developer produced development in background L I z AM EIL. 4 r r.

A 1.5 mil Kodar film was'coated'with' a thin layer of KPR (Kodak"'Photoresist availa'ble'fromdh e Eastman Kodak Company of Rochester, New-York). KPR may be describedchemic'ally as the cinnamate esters ofp'oly' vinyl alcohol and of celluloser'zThis "polymer contains unsaturated side groups which may be caused to cro'ss link upon exposure to form very large insoluble molecules and may be further sensitized by the presence of anthrones and their derivatives, polynuclear quinacridone derivatives and. certain ketones; such as;Michlersketoneas more .u y d s d: n las-11 70 285; $61 2 6 and 2 6 2 -i 1; 1 M a k t a The KPR fi m. s d ed n e o o a i h '1 .&t a -.-Qr' hd n Q theimage t0bereprodueed-With alight, source rich .in avi et sites lte n th e ssl nk ns annt r age t i ql b li neisfthe KPR.' PQ :araf ewr ing exposure the KPR was washed with a trichloro ethylene solvent to remove the KPR in unexposedar eas and allowed to dryrjThi s-r esulted-in.a-Kodar film coated with KPR in exposed areas. The film surface was then friction charged by cascading type B coated charging beads over 'its errate. This-"served to charge KPR): coated areas jmor 1 positive than the Koaar' bs rgrpuna 'areas: When a negatively charged developing material (cascade type) was applied to this "surface, KPR"coated areas w I 'e developed and when a positively charged developer was used, the uncoated Kodar areas were developed. Both types of development produced good images. This experiment was also successfully repeated using a polyethylene terephthalate substrate in place of the Kodar film.

EXAMPLE III A thin layer of KPR was coated on the surface of a supporting substrate and exposed in the same manner as described in Example II, except that unexposed surface areas of the KPR were not etched away with an organic solvent but instead the complete KPR surface including both exposed, crosslinked areas of the KPR and nonexposed areas were friction charged with type B coated charging beads which made unexposed areas more positive than exposed areas. Application of a negatively charged cascade developing material developed unexposed KPR areas.

EXAMPLE IV A 1.5 mil Kodar film was laid over a printed page from a book and then exposed to a strobe light flash through the Kodar of sufficient intensity to cause the more volatile components of the ink to volatilize and evaporate across to the Kodar surface in the configuration of the printed copy. This coated Kodar was then friction charged with coated charging beads and developed with a cascade developing material as described in Example I with the same results.

EXAMPLES V-VIII Four imaging surfaces were prepared exactly in accordance with the provisions of Examples I-IV except that instead of charging the surfaces which coated charging beads described in those examples, each of the surfaces was charged by rubbing it with a viscose rayon, long fibered, cotton-like material and was developed by cascade development as described above. Good quality positive and negative toner images of generally higher contrast were produced depending upon the polarity of the developer.

EXAMPLES lX-XII of polymethyl methacrylate and on a 1.5 mil thick sheet of polyethylene terephthalate available from E. I. du Pont and Company under the tradenarne Mylar. These materials produced images of about the same quality as the imagesformed with the Kodar film utilized in 'Examplesl a i f f Sa mplesof aIL S miljKodar film, a-Mylar brand polyethylene terephthalate film and a Lucite brandpolymethyl methacrylate film were exposed to images with UV light. When these films-were triboelectrically charged by rubbing with various materials there was a distinct difference in the charge on exposed and unexposed areas as indicated in the table below: 1

Good quality positive and negative (photographically) images were developed on all surfaces after rubbing,'with the type of image depending upon the polarity of'the toner employed in development.

Additional experiments were run on KPR films to deter mine how exposure changes the films charging ability with different amounts of rubbing with rayon. It was found that a straight line relationship exists between the voltage on exposed film areas and voltage on unexposed film areas with each point plotted for increasing amounts of rubbing. The line was found to start at (0, 0) with no rubbing and run through a point equal to 2000 volts for exposed areas and 3000 volts for unexposed areas.

It is to be noted that the examples given above are exemplary only and are in no way intended to be limiting upon the invention since many other alternative materials and techniques which now become obvious may be substituted for the specific materials employed in the exam ples. Thus, for example, instead of charging a polymethyl methacrylate layer by rubbing it with a viscose rayon it may be charged by rubbing with a material even more remote from it than rayon in the triboelectric series such as rubber or polyethylene. In addition, a surface contaminant may be transferred to the imaging sheet through a stencil or by pressing it against a printed or typed page with heat and/or pressure, by directly typing or printing the contaminant on the image forming surface, by electrostatic transfer or by other techniques with or without intermediate transfer. I

Referring now to FIG. 2 there is shown a copying apparatus embodying the concept of this invention in which the imaging surface 11 is fed up from a supply roll 12 around idle rollers 13 and 14 to a take-up roll 16, in the meantime passing the process stations of the apparatus. In this particular instance, the imaging surface 11 consists of a substrate layer coated with a thin coating of KPR as described above. As the imaging surface begins its movemeut through its path of travel in the apparatus, it passes a projector 17 which projects a light image of the original to be reproduced on the imaging surface with light which is rich in ultraviolet. This projector may either employ a flash exposure with light of sufiicient intensity to crosslink exposed portions of the KPR layer on the imaging surface 11 as it moves past the projector or in the alternative, a weaker light source may be employed providing that the imaging surface is stopped opposite the projector at intervals to allow for a longer exposure. Once the imaging surface 11 has been exposed, it continues on in its path of movement until it comes opposite a triboelectric charging roller 18 which serves to charge the imaging surface producing a differential charge pattern on it as described above in connection with the examples. This charging roller preferably rotates in a direction such that its periphery moves opposite the direction of movement of the imaging surface and at a speed sufficient to impart a significant charge to the imaging surface. Actually, the direction of rotation is not critical so long as the roller 18 may have a surface coating of any of the materials described above such as viscose rayon, nylon, wool or the like. This frictional rubbing serves to form a differential charge pattern on exposed and unexposedareas of the KPR layer as described in Example HI above. Once charging has been completed, the imaging web continues on, moving past a cascade developing unit generally desig-, nated 19. The cascade unit includes an outer container or cover 21 with a trough at its bottorn containing a supply ofthe two component developing material 22. Thisdeveloping material is picked up from thebottom of the trough and dumped or cascaded over the surface of the imaging web 11 by a number of buckets 23 on an endless driven conveyor belt 24 which rotates about two pulleys 26. As stated above, the cascade development technique is more fully described in U. S;j Pat 2,618,552 and utilizes amixture including finely" divided, colored toner particles, and grossly larger carrier beadsvvith'a surface coa'ting'of the type described above in connection with FIG. 1. The carrier beads serve both to maintain the fine toner particles deagglomerated and to charge them when the materials are tumbled together in the developing system by virtue of the relative positions of the toner and carrier materials in the triboelectric series. Since the carrier beads and toner particles acquire charge of opposite polarity, the toner particles tend to cling to the carrier beads after triboelectric charging has taken place. By changing either the coating on the carrier beads or the material from which the toner particles are fabricated so that the toner particles are moved from below, the carrier beadcoating material to above this material in the triboelectric series, the polarity of charge imparted. to the tonerparticles by this frictional charging may be reversed so that the positive toner particles may be employed to develop a negatively charged image on the imaging surface 11 or negatively charged toner particles may be employed to develop a positively charged image. Alternatively, the toner particles may be charged to the same polarity as the polarity of the image on the imaging surface 11 so that the toner particles will be repelled by these charged areas and will be deposited only upon uncharged areas thereby producing a photographic reversal image. At any event when toner particles and imaging surfaces are charged opposite in polarity, the charged image areas pull toner particles off the earner beads when the carrier bead-toner particles developing mixture is cascaded over this surface. The carrier beads along with any toner particles not used in developingthe image then fall back into the bottom trough of container 21 and the developed image continues around in itspath until it comes opposite a fixing unit 27 which serves to fuse or permanently fix the toner image to the imaging surface. In this case a resistance type radiant heating unit is illustrated as this type of unit has proved to be most effective in fixing toner particles including thermoplastic materials which may be heat fused to the imaging surface 11; however, other techniques known in the art may be utilized including the subjection of the toner image to a solvent vapor or the spraying of the toner image with an adhesive overcoating.

What is claimed is:

1. The method of forming a visible image comprising exposing an imaging sheet having at least a surface layer of an ultraviolet light photopolymerizable material to an imagewise exposure with ultraviolet light of sufficient intensity to cause polymerization of at least the surface of said photopolymerizable material, bringing said imagewise polymerized surface into frictional contact wlth a materal remote in the triboelectric series from at least one of the polymerized and the unpolymerized portions of said imaging sheet so that a differential charge pattern is set up between image and non-image areas on said sheet and developing said charge surface by depositing finely divided, colored, electroscopic marking particles thereon.

2. The method according to claim 1 in which said photopolymerizable material is polyethylene terep'hthalate.

3. A method according to claim 1 in which said photopolymerizable material includes the cinnamate esters of polyvinyl alcohol and of cellulose.

4. The method according to claim -1 in which said photopolymerizable material is 1,4-bis methyl cyclohexane polyterephthalate.

5. T he method of forming a latent electrostatic image on an imaging layer comprisingincreasing the molecular weight of atleast a surface of-said layer by subjecting it to, a polymerizing influencein imagewise configuration thereby modifying the triboelectric charging susceptibility of said surfacein imagewise configurationand bringing said surface into frictional contact with a ma terial remote ;-in the triboelectricv series from atleast one of the. modified and the unmodified portions of said surfaceso that (a differential charge pattern is*set.up between image and non-image areas on said surface. t .6. A method offorming a latent electrostatic image on an imaging layer comprising coating asurface of said layer with a contaminant comprising a material selected from the group consisting of an oil based ink and human body oils in imagewise configuration thereby modifying the triboelectric charging susceptibility of said surface in imagewise configuration and bringing said surface into frictional contact with a material remote in the triboelectric series from at least one of the modified and unmodified portitons of said surface so that a differential charge pattern is set up between image and non-image areas of said surface.

7. The method of reproducing a page of copy formed with an oil based ink comprising placing said page of copy in face to face relationship with an imaging surface, heating at least the inked portions of said page of copy until at least a portion transfers across to, said imaging surface in imagewise configuration by volatilization and condensation of at least one of the ink components which is capable of modifying the triboelectric charging susceptibility of said imageing surface, separating said imaging surface from said page of copy, bringin said imaging surface into frictional contact with a material remote in the triboelectric series from at least the ink coated portion of said imaging surface or the noncoated portion of said imaging surface so that a differential charge pattern is set up between image and nonimage areas on said imaging surface and developing said surface by depositing finely divided, colored, electroscopic marking particles thereon.

8. A method according to claim 7 in which said page of copy is right reading and said imaging surface is transparent whereby the mirror reversed image produced on said imaging surface may be easily read through its back.

9. The method of reproducing a page of copy formed with an oil based ink comprising placing said'page of copy in face to face relationship with a smooth surfaced impervious master sheet, heating said page of copy and said master sheet until at least a portion of the ink from said page of copy volatilizes and recondenses on said master sheet in imagewise configuration, separating said master sheet and said page of copy, placing said master sheet in face to face relationship with an imaging surface, heating said master sheet and said imaging surface until at least a portion of the ink on said master surface volatilizes and recondenses on said imaging surface in imagewise configuration, separating said master sheet from said imaging surface, bringing said imaging surface into frictional contact with a material remote in the triboelectric series from at least one of the ink coated and the uncoated portions of said imaging surface so that a differential charge pattern is set up between image and non-image areas on said imaging surface and developing said surface by depositing finely divided, colored, electroscopic marking particles thereon.

10. A method according to claim 9 in which said original page copy is right reading and said imaging surface is transparent whereby the mirror reversed image produced on said imaging surface may be easily read through its back.

11. The method of forming a reproduction of a page of copy formed with an oil based ink comprising placing said page of copy in face to face relationship with an imaging surface, pressing the two surfaces together with if s-ufficieht force to transfer at' least a portion of the ink fromi's'aid pagelofcopy-to said-imaging" 'su'rfaceg separat' ing 'saidpage of"'copy- -from said imaging l surface, "bringing saidimagin'g' surface into frictibnal'contact with a material-:re'mote-inthef-triboelectric series from at least one Ofathe inkLcQatedand the uncoated portions of said imaging surface so that a d'ifferential char'ge'pattern "is set up btweenimage' a'nd' non-image area-s on -sa'id i'mag ing surfaee and devloping' said' surface 'by depositing finelydivided, 1 'electroscopie marking 1 particles thereon; v r a 7% 1 21x12; The method 0f"-1 eproduc1ng an= image? on a" sheet of copy :foimed" awith an" oil" based: ink comprising placin said copy-sheet inface 'to face relation Witha -smo'oth surfaced-master sheet; applying sufiicient pressure'to'said sheets so that at least a portion of the ink is transferred to said master, separating said masterfrom said sheet ofcopy, bringing said master into face to face contact with an imaging surface, applying sufficient pressure to said master and said imaging surface so that at least a portion of said ink transferred to said master is retransferred to said imaging surface in imagewise configuration, separating said imaging surface from said master, bringing said imaging surface into frictional contactwith a material remote in the triboelectric series from at least one of the ink coated and' the non-coated portionsaof said imaging surface so that a differential charge pattern is set up between image and non-image 12 a'reas"on;said imaging Lsurfaceanii developing said surfabe' by depositing' finely Tdivided, colored; electroscopic marking-particles the'reon'.. I

v i I References Cited 'Q'UNITED STATES PATENTS Schwartz 96-1. 1

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