IL31542A - Xerographic plate - Google Patents

Description

XBROX LIMITED This invention relates to xerography and in particular to novel xerographic their fabrication and their use in In the process of for example as disclosed in a xerographic plate comprising a layer of photoconductive insulating material on an electrically conductive backing is given a uniform electric charge over its surface and is then exposed to a light and shadow image of the subject matter to be usually by conventional projection This exposure discharges the plate areas in accordance with the radiation intensity that reaches them and thereby creates an electrostatic latent image on or in the photoconductive layer corresponding to the light and shadow image Development of latent image is effected with an electrostatically finely divided such as an electroscopic that is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a pattern corresponding to the electrostatic latent The xerographic marking material image may be fixed or made permanent on the xerographic plate if it is desire to apply the developed xerographic powder image to metal plastic film or other transfer the developed image may be transferred from the xerographic plate to such a support surface to which it may be affixed by any suitable Fixing of the develpped image onto the xerograp plate itself becomes attractive for relatively inexpensive plates such as those comprising photoconductive material impregnated into paper may by melting or from with organic or inorganic photoconductive of layer of the oxide of the metal substrate of the graphic for These insulating interfaces are often found to be fragile and subject to local due to thin or chemical impurities which give rise to deficient and other print This tendency to degrade is of course vated by prolonged cycling conditions which modern day xerographic copiers are being increasingly subjected The requirement of avoiding these localized failures makes it difficult to use such well known blocking layers as aluminum oxide over aluminum because of their fragility under belt flexing This is unfortunate because belts made of metals such as brass and otherwise possess the desired mechanical properties required in flexible xerographic belt In such thin insulating barrier layers are found to be unsatisfactory over highly substrates such as brass and similar alloys which mechanically and otherwise are highly desirable substrates especially for continuous flexible web xerographic because of the significant decrease in charge acceptance of the member in prolonged cycling found when these substrates are used with such important photoconductors as those comprising amorphous selenium or phthalocyanine enamels as further described in British specification and since the known dielectric barrier used on brass had to be extremely thin in order to minimize residual potential they could not serve as effective chemical barrier layers between selenium and the brass substrate and specialized barriers such as chromate for example see British patent specification Number amorphous selenium by the This contamination was 2 to substantially degrade the electrical properties of the plate 3 if the plate was aged a few Especially drastic was the decrease in charge acceptance brought about by this in xerographic plate preferred photoconductive insulating for those comprising amorphous have been deposited upon rigid backing materials such as flat plates or rigid cylindrical drums and it is found that using ordinary cleaning procedures for the the physical bond existing between the supporting base or substrate and the deposited photoconductor is suff cient to ensure an adequate commercial life for the xerographic in order to increase the speed of commercial xerographic interest has recently been shown in going from a rigidly backed plate to a xerographic plate wherein the backing takes the form of a flexible for similar US to the one shown in Clark et Patent Such a plate configuration and variations thereof offer an increased reproduction surface thereby permitting an increased rate of reproduction of copies from an the use of such a flexible belt system has a number of attendant A major problem is one of obtaining sufficient adhesion of photoconductor to the belt base since it is found that the continuous flexing of the photoconductive layer as it is passed for example entraining pulleys or often leads to cracks and separation of the photoconductor from the In such relatively frangible but preferred photoconductors such as amorphous selenium optionally doped various additives or mixed with various other materials such as arsenic and tellurium suffer even more from cracking and spalling or f aking problems due to flexing and other strains conductive substrate in order to ensure the rapid dissipation of charge from light struck areas of the This means that a belt like support layer which is not electrically conductive must first fee layered with an electrically conductive layer which can he a costly and difficult to control Such a process also generally leaves the seam in the underlying belt substrate as a discontinuity even after deposition of the electrically conductive this interfacial layer is electrically insulated and may suffer from the inherent disadvantages of such insulating as pointed out Also in British it is suggested that an adhesive coating of about to about 5 microns of a pho phthalocyanine pigment in an insulating resin binder be coated on the electrically conductive substrate and this interfacial binder then be overcoated with the amorphous In this approach also the substrate must be electrically an interface of a particular photoconductive insulating material with a particular overlayer specifications are in the British patent just referred to the maximum thickness of the facial layer is quite thin necessitating carefully controlled layering unless the interfacial layer also serves as an effective barrier then the fabrication of a flexible belt type xerographic plate is further complicated by the requirement of depositing such a barrier layer over the interfacial layer during plate it is seen there is a continuing need for an simple and workable system provide a xerographic plate and especially a flexible belt type xerographic plate with acceptable and eleetrloal According to the present invention there is provided a xerographic plate comprising a support overlying said support base an comprising electrically conductive pigment dispersed in an electrically insulating organic and a photoconductive insulating layer comprising amorphous selenium overlying a better understanding of the invention as well as further features reference is to the following detailed disolosure of this invention taken in conjunction with the accompanying drawing the single figure is partially partially sectional view of an embodiment of an automatic xerographic copying apparatus employing xerographic plate according to the The xerographic plates of the present inventio are preferably prepared by applying the conductive insulating organic binder composition to a graphic plate base and applying thereover a layer of the photoconductive insulating in a to be to optimize the adhesive and the other mechanical properties of the inventive interlayer and op imize aa well the electrical properties including the conductive yet effective barrier layer characteristics the It was by means expected or obvious that a carbon or other electrically conductive pigment loaded enamel or oast film should act as its own effective blocking no added dielectric layer to prevent substantial dark of carriers the electrode into the photoconductive once it is coated the conductive the support may he selected without concern for its electrical the latter may be either a such as a brass or a plastics such as While this invention is particularly applicable and advantageous in fabricating flexible belt type xerographic plates it should be noted that the invention is entirely applicable to rigid substrates even though the problem of constant flexing is not present and the adhesive advantages of the invention may not be completely Referring now to there is shown automatic xerographic copying apparatus The apparatus is seen to include a pair of rollers 10 and 11 about which is supported a xerographic plate 12 in the form of an endless flexible belt according to the basically three an overlying layer of photoeonductive insulating material an interfaclal layer according to the invention 8 and flexible belt support layer Layer thicknesses are exaggerated for purposes of Because of the invention herein belt base 9 need not be electrically conductive as was required in the prior Any suitable electrically conductive or insulating material may be Electrically insulating plate bases are found to be preferred herein because of the excellent mechanical and electrical characteristics of plates made according to the invention on such preferred electrically insulating bases are plain polyethylene terephthalate polyester film available under the trademark Mylar from other polvester glass polycarbonates such as Plestar film of General Aniline ft Film cellulose cellulose such as Kapton from DuPont and mixtures Any suitable electrically insulating plate base material may be Typical electrical insulating base materials include other film formable polymeric for see a partial list in Patent Specification woven or fibrous cloth belts which combine great tensile strength and for of silk or fibrous resin for example acetate and other than polyethylene and polypropylene which belts may optionally be impregnated with a resin or polymeric type Electrically conductive belt bases may also be used Typical such bases include strips of cold rolled brass or for in the order of from 2 to 10 mils plastic webs such as aluminized Mylar polyester film and so Amorphous selenium alone or alloyed with or amorphous selenium or its alloys doped with for is found to be a preferred photeconduetive insulating material for herein because of its extremely high quality image making high light capability to receive and retain charge of different potentials and different its ability to be xerographically processed many times in succession and its excellent xerographic performance when employed on interlayers of this A more disclosure of selenium alloys may be found in Ullrich latent Mayer et Patent Patent Paris Patent the thickness of the photoconduetor will depend on the desired xerographic properties the resultant for thicker photoconduetor layers for example much greater than 40 microns it is for amorphous that the layer thickness determined by the beam like flexing forces induced in the photocondactive layer itself as a result of extreme bending which tend to fracture the photoconduetor regardless of the type of substrate or interface found herein that amorphous selenium layers up to 35 microns in thickness deposited onto the interfacial layers of this invention show superb If deposited on a rigid substrate according to the the preferred thickness range of a photoconduetor comprising amorphous selenium is between about 20 and 80 The inventive interlayer 8 may comprise any suitable conductive pigment dispersed in a suitable insulating organic binder preferably so that layer 8 has an electrical resistivity less than about 10 10 and preferably than about 10 in order to rapidly dissipate charge from the photoconduetor in illuminated Generally the electrically conductive pigments used herein will have a bulk electrical resistivity less than about and the electrically insulating organic binder a bulk electrical resistivity greater than about and generally 10 greater than about 10 and less than about 1019 According to the invention the conductive pigment is dispersed in an insulating organic Any suitable insulating organic binder material capable of having conductive pigments dispersed for in a dispersion or in a melt and which are capable of being coated or layered on a belt base to form an adhesive coating for an overcoating of a photoconduotive insulating material and which is capable of forming a continuous film at the pigment concentrations necessary to provide electrical and xerographic properties may be aery vinyl vinyl polymers and copolymers and mixtures thereof and rubber are found to be preferred resinous insulating organic binder materials herein because of their superior adhesive properties and xerographic and electrical properties when pigmented with electrically conductive particles as taught any suitable insulating organic binder material may be Typical such organic binders are resinous materials which include modified bitumen solutions or such as cellulose phenol polyvinyl urea and aldehyde polyesters for example amino polyvinyl chlorinated rubber and Of such resins and rubbers may be mixed with each other or with and additives to improve their adhesive or xerographic rezyl 869 a linseed alkyd available American Cyanamide may be added to chlorinated rubber to improve its adhesion and Typical insulating organic materials for use herein include and fatty acids plus a metal to form an organic aluminum It will he understood that binders must be selected in each case to wet and adhere to the film base as well as to provide adequate flexibility and pigment Carbon black and silver particles are to be preferred conductive pigments herein because of the excellent imaging results from plates constructed any suitable conductive pigment may be used in the inventive layer Typical such pigments the powdered or particulate form of most for conductive metal oxides such as tin the hexagonal form of selenium and electrically conductive organic materials such as carbon other electrically conductive forms of carbon other than carbon black including and similar conductive The conductive pigment may be dispersed in finely flaked or other particulate in the organic binder with the powder in a suitable vehicle such as an organic as in any suitable proportion of On a conductive binder dry weight the useful range of pigmentation appears to extend from about the lower preferred level for carbon black to about the upper preferred level for silver Optimum results are obtained when ratios from about to about are used and accordingly this range especially The conductive pigment may be incorporated in the dissolved or melted organic binder by any suitable means such as stron shear aitation referab w t u These means Include hall roll sand ultrasonic high speed and any desirable combination of these pigmented resins or elastomers may be impregnated in woven or cloth A typical example would be polyester cloth overcoated with conductive ed synthetic The layer of this invention may have any suitable thickness but in order to achieve the dual properties preferred of electrical conductivity and barrier layer istics to prevent excessive dark decay when conductive support bases are and to provide the other electrical and mechanical advantages noted the interfaeial layer should have a thickness substantially uniform over the effective surface of the xerographic plate to assure uniform xerographic in the preferred range of from about 1 to about The slurry or the binder melt may be applied to the belt base by any of the well known painting or coating methods including flow knife eleetrostatio dip reverse roll coating and so After or during the curing of this interfaeial layer the photoconductor may be applied thereover by any suitable method such as vacuum Referring again to xerographic plate 12 in the form of a flexible endless belt is advanced in a clockwise direction by drive roller 10 powered by motor 13 around guide and tension roller the belt advanced sequentially past corona charging device exposure station developing station 19 to a developed image transfer station in rotating 27 which cleans and readies surface of the xerographic plate for a new cycle of The corona discharge device 15 is a preferred for sensitizing the xerographic plate before exposure which sensitization consists of imparting a uniform electric charge to the surface of the examples of preferred corona discharge devices are disclosed in Vyverberg Patent and Patent plate 12 is preferably charged when it is at its highest insulating in the absence of actinic radiation or in the After the plate advances to exposure station 17 where light rays 21 from an preferably synchronized to the movement of the xerographic plate by conventional apparatus not selectively discharges the xerographic plate in accordance with the intensity of the actinic radiation reaching the thereby leaving on the plate as it advances towards roller 10 a latent electrostatic image corresponding to the image of the Other methods of forming a latent image are available in the art and include latent image transfer techniques for example see Carlson Patents and and by the use of shaped electrodes pin for example see Schwertz Patents and and by electron beam for example see Glenn Patent The latent electrostatic images may be rendered visible by any suitable developin means known to those skilled in the art and illustratively by the form of cascade developmen developer material 33 consisting of a two component material of the type for in et Patent the xerographic plate hearing the latent two components consist of an eleotroacopic powder termed toner and a granular material called carrier and which by mixing acquire trlboeleetrie charges of opposite In development the toner usually oppositely charged to the latent image is deposited on the latent electrostatic image to render that image In operation developer material 33 is carried by a conveyor 34 to chute with gate 30 to regulate the flow of developer down the chute to cascade in contact with the latent electrostatic The developer after passing over the latent electrostatic image passes into developer reservoir 36 where it may be used over again with allowance made to replenish amount of toner left behind on the xerographic The xerographic powder image 37 formed on the surface of plate 12 during development is then advanced contiguous to transfer web 25 where the powder image is transferred to the web and affixed thereto by any suitable means such as solvent vapor or heat The fixed image is then rolled onto roll 35 where it is stored until ready for The following further specifically define the inventive interfacial layer and the novel xerographic plate of this one embodiment of which is shown in 1 as plate The parts and percentages are by weight unless otherwise The Examples below are intended to illustrate various preferred embodiments of the inventive interfacial layer and xerographic plate and process of making and using same of In each Bxample a qualitative tape test is performed by applying pressure sensitive adhesive tape such as Scotch brand pressure sensitive Transparent Tape 810 to the bonded photoconductor surface for testing the adherence the photoconductive insulator to the underlying The strip of tape is snapped off the photoconductor by a quick movement of the hand to give a quick but rather severe of since insufficiently bonded material will be pulled off either in part or in in each Example a qualitative flex test is performed by bending the specimen once over a 3 inch diameter steel bar ana carefully observing for any aicrocracks in the photoconductor Xerographic prints are made using the sample specimens in the Examples by taping the test specimens on a rigid xerographic drum and performing the sequential xerographic operations generally described where otherwise the test specimen is xerographically processed with positive the exposure being from a tungsten ilament lamp operating at a filament temperature of about at an exposure level at the conductor surface in illuminated areas of about to form a latent eleotrostatic image which is then cascade e sharp image thus produced is transferred to a sheet and fused to produce a high quality xerographic Each test specimen holds up under the tape and flex tests better than a control plate constructed according to the Example bu without the inventive Also the control plate exhibits inferior xerographic especially lacking the ability to effectively dissipate charge in illuminated areas About a 1 jail thick sheet of Mylar film is dip coated into a conductive pigmented insulating organic resin hinder composition of about 40 parts of an alcoholic dispersion of carbon available under the trademark from Columbian Carbon about 2 parts of dry orange shellac powder and about parts iaopropyl Mylar is removed and dried to form about a 5 micron thick coating on the The surface resistivity of the coated Mylar film measured laterally is found to be about x 10 About a 20 layer of amorphous selenium is then vacuum evaporated over the layer on the Mylar A dispersion of finely divided carbon black in an acrylic resin sold under trademark Lucite 2045 by is prepared by ball for about 3 about 17 per cent of a of predispersed carbon black available under the designation from Columbian Carbon containing total solids of about 60 per about 45 per cent carbon a dispersing agent and mineral about per cent Lucite 2045 and the remainder The dispersion is spray coated on about 8 mil brass of about per cent copper and about per cent zinc and dried for about an hour at about to produce a dried film about microns About a 45 micron layer of amorphous selenium is vacuum evaporated onto the A control plate without the pigmented interlayer prepared and both plates are cycled on a drum revolving at about Exposures are at about 30 from a white fluorescent Both plates are charged positively to an initial value of about 800 Both plates are sequentially charged and discharged for 150 cycles and then the percentage dark discharge of both plates is measured 30 seconds after charging and no The control plate has a fatigued dark discharge 30 seconds after after 150 rapid cycles of charge and discharge of about per cent and the Inventive although not as low as the compares favorably with a dark discharge of about 26 per cent which is certainly not a tremendous advantage in lower residual buildup is found for the inventive The control plate after about 60 built up and maintained for further cycles a residual potential of about 120 volts while the inventive plate more slowly built up and maintained for further cycles a residual potential of about only 30 This marked advantage of lower residual potential for the inventive plate manifested itself in lower higher contrast copies than those produced on the control Also as the control plate the electrical current required to charge the plate to a given increases with the maximum potential to which the control selenium plate can be charged by conventional corona discharge reaching a lowered limiting value of about 600 volts for a year old where the same could be charged 1300 volts under the same while no such degradation is observed in the The and flexing properties of the plates are tested as follows the adhesion test is by scoring yertical and horizontal lines on the plate surface to yield a checkered pattern various sized squares about 1 square inch to about 1 and determining how much selenium could be removed with 600 High Per ormance Transparent Scotch Tape from Determination of the smallest diameter rod about which the could be wrapped before visible cracking occurred used as a measure of flexing Selenium adhesion to the interlayer of the above plate is no selenium is removed by the The plate is successfully flexed around a three inch diameter roll without any evidence of cracking spalling in the selenium The adhesion of selenium coated directly on brass is particularly under flexing Considerable cracking and spalling occurs when the control selenium plate is flexed around a three inch diameter the of this invention confers unexpectedly excellent and physical blooking conditions to the interface with a dramatically lower residual insufficientOCRQuality

Claims (1)

1. CLAIMS 1. A xerographic plate comprising: (a) a support base; (b) overlying said support base an interface comprising an electrically conductive pigment dispersed in an electrically insulating organic blndert and (c) a photoconductive insulating layer comprising amorphous selenium overlying said interface. 2# A xerographic plate according to Claim 1 wherein the photoconductive layer comprises an alloy of amorphous selenium 3· A xerographic plate according to any of the preceding claims wherein said support base is flexible* 4· A xerographic plate according to Claim 1 or 2 wherein said support base is flexible and the thickness of the photoconductive layer is from 20 to 35 microns. 5· A xerographic plate according to any of claims 1 to 4 wherein said interface is between 1 and 25 microns thick. 6· A xerographic¾>late according to any of Claims 1 to 5 wherein the electrical resistivity of said interface is less than 10^ ohm-cm, the electrical resistivity of saidjelectrically conductive pigment is less than 10 ohm-cm and the electrical resistivity of said electrically insulating organic binder is between 10^" and 10^ ohm-em. 7· A xerographic plate according to any of the preceding claims wherein the ratio, on a dry weight basis, of conductive pigment/organic binder is from 1/5 to 4Α· 8# A xerographic plate according to Claim 7 wherein the ratio, on a dry weight basis, of conductive pigment/organic binder 31542/2 · is from 1/4 to 1/2, 9, A xerographic plate according to any of the preceding claims wherein said electrically conductive pigment comprises carbon black. 10· A xerographic plate according to any of Claims 1 to 8 wherein said electrically conductive pigment comprises silver particles. 11* A xerographic plate according to any of the preceding claims wherein said electrically insulating organic binder comprises epoxy, phenolic, acrylic or acrylate resin, shellac, vinyl toluene-butadiene copolymer, a polycarbonate, or a vinyl polymer or copolymer. 12. A xerographic plate according to any of the preceding claims wherein said support base is electrically insulating. 13. A xerographic plate according to the preceding claim wherein said support base comprises a polyester film or cloth, glass cloth, polypropylene, polyethylene, a polyolefin, a poly-olefin, a poly-carbonate polystyrene, cellulose acetate, cellulose triacetate or a polyamide. 14· A xerographic plate according to any of Claims 1 to 11 wherein said support base is electrically conductive. 15· A xerographic plate according to claim 14 wherein said support base is aluminium, brass or steel from 2 to 10 mils thick or an aluminized polyester film. 16. A xerographic plate according to claim 14 or 15 wherein said substrate is brass, with between 60# and 95$ copper and the remainder zinc, and said photoconductive insulating layer comprises X-form metal-free phthalocyanine in an electrically ineulating organic binder* For the Applicants DR. R HOLD GOHK AND PARTNERS 2