US 3559570 A
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United States Patent  METHOD OF PREPARING AND USING A GRAVURE PRINTING PLATE 14 Claims, 5 Drawing Figs.
 US. CL. 101/170, 96/1, 96]].4,117/37,]18/637,101/395,101/401, 101/401.1, 101/426 51 lnt.(l .....B4lml/l0, G03g 13/10, 003 13/14 50 Fieldoisearchwt 96/l,l.4;
 References Cited UNITED STATES PATENTS 3,084,043 4/1963 Gundlach 96/ 1 Primary ExaminerCharles E. Van Horn Attorneys-Stanley 2. Cole and James J. Ralabate ABSTRACT: A method of producing a reusable gravure printing plate and copies from same is disclosed which allows the use of aqueous developers in connection with a gravure plate molded out of or coated with hydrophobic composition. It has been found that when electrostatic charges are placed on the surface of a charge carrier having hydrophobic properties aqueous liquids formerly incapable of wetting the surface now are retained by reason of the presence of the electrostatic charge pattern. This discovery is employed in conjunction with the gravure imaging process of the present invention. For, example, a gravure dispensing member is coated with a layer of hydrophobic photoconductive composition. The resulting photoconductive gravure member is electrostatically charged in the dark selectively exposed and developed using an aqueous base developer employing well-known xerographic techniques. The developed surface of the plate may then be contacted to a copy sheet to produce a reproduction of the original.
PATENTEU FEBZ 197i INVENTORS.
ATTORNEY METHOD OF PREPARING AND USING A GRAVURE PRINTING PLATE This invention relates to an imaging system, and more specifically to a gravure imaging system.
Gravure printing is a reproduction process wherein the printing is done from an engraved image which has been etched below the surface of the nonprinting areas of a cylinder or plate. In the preparation of a conventional gravure printing master, a continuous tone photograph is copied to obtain a continuous tone positive transparency otherwise known as a diapositive, and this transparency and a gravure screen are then used in successive exposures to harden to varying degrees a light-sensitive acid-resist material which has been coated on the surface of a cylinder or plate. An etchant solution, such as ferric chloride. permeates the resist material and etches the copper plate so as to produce recessed areas or tiny cells, a typical plate representing about 22,500 cells per square inch. The engraved cylinder rotates in an ink reservoir and a doctor blade wipes the surface of the cylinder clean of ink while each cell retains its capacity of ink. When an impression cylinder presses a fed-in paper against the engraved plate, the ink from the cells is transferred to the paper. The tonal range of the print is obtained by varying the depth of the cells. Although the surface dimensions of each cell are theoretically identical with all other cells the depth may vary. Since shallow cells hold less ink than the deep cells, the amount of ink that is available to be transferred to the paper is more or less depending upon the depth of the cell. Therefore, a shallow cell prints a light tone on the paper and a deeper cell a more intense tone. Each cell corresponds to the tonal variation of the original photograph. The gravure process may also be used to reproduce line copy prints in which instance the tone variations generally no longer play an important role in the procedure and the cell depth substantially is maintained constant. Again, the gravure screen or halftone negative is used to form a line pattern which acts as a support for the doctor blade on the gravure presses thereby preventing the blade from wiping the fluid ink out of the etched depressions during the process of printing.
While this technique has generally been found useful as an imaging system, there are inherent disadvantages to its use.
For example, in preparing the gravure printing plate it is generally necessary to subject the expected printing surface to long exposure times in order to produce the surface effect desired. A second disadvantage to this process is that it is generally necessary to subject the printing surface of the plate to various chemical treatments in order to produce the desired end result. A further disadvantage is that once the image is etched into the surface of the printing plate it is permanently affixed therein to become a permanent impression of the image to be reproduced and the plate is no longer reusable. Yet, still a further disadvantage to this system is that the entire procedure requires considerable technical know-how and skill in order to produce a satisfactory result.
It is, therefore, an object of this invention to provide a gravure imaging system which will overcome the above-noted disadvantages.
' ductive plate.
Still a further object of this invention is to provide a process of using a novel printing plate.
Yet, still a further object of this invention is to provide an imaging system wherein the novel gravure printing plate may be reused.
The foregoing objects and others are accomplished in accordance with this invention, generally speaking, by providing a gravure plate the surface of which or gravure pattern of which has been molded out of or coated with a hydrophobic composition containing a photoconductive material therein. The surface of the photoconductive gravure plate may then be electrostatically charged and imaged in accordance with conventional xerographic techniques as more fully described in US. Pat. No. 2,297,691. The electrostatic latent image is then developed with an aqueous-based developer or ink the electrostatic charges on the surface of the gravure plate having such an effect upon the properties of the hydrophobic photoconductive composition that the aqueous medium adheres to and is trapped within the cells of the gravure plate at the location of the electrostatic charges thereby selectively wetting the plate in an imagewise configuration. Following development of the electrostatic latent image, the plate is contacted with a copy sheet an d the ink is deposited on the surface of the copy sheet in accordance with the charge pattern. The process may be repeated until the desired copies are produced at which time the gravure plate may be cleaned and prepared for reimaging and reuse as a gravure printing master.
It has been discovered that electrostatic charges on the surface of a charge carrier having hydrophobic properties are capable of influencing the interfacial tension between the hydrophobic surface and a liquid medium such that due to the presence of the charge the surface may be wetted by a liquid by which the surface is normally substantially unwettable. For example, water-based inks, such as glycol inks, wet charged areas of normally hydrophobic photoconductive surfaces. When used in the course of the present invention in relation to a charge carrier surface, the term hydrophobic means that water forms on such a surface, in the absence of an electrostatic charge, a contact angle of at least The contact angle is generally considered a measure of the wettability of a particular liquid on a solid surface. As herein used, it is defined as being the angle through the liquid which is measured between the horizontal solid surface and the tangent to the drop of the developer t the point at which the surface of the drop intersects the horizontal surface. The tangent will be in a plane perpendicular to the horizontal surface which also passes through the center of the drop. In the case of the present invention, those areas retaining an electrostatic charge are affected in such a manner so as to become water receptive as a result of a reduction in contact angle between the charged surface and the water droplets. This difference in wettability of the latent image and the remaining uncharged areas forms the basis for the development and imaging techniques of the present invention.
In accordance with the present invention a gravure dispensing member comprising a support base such as a conductive rubber core, having disposed on its surface a raised pattern, similar to that disclosed in US. Pat. No. 3,084,043, presenting a uniform porous surface for dispensing a liquid developer, is coated with a layer of a hydrophobic photoconductive composition to a thickness of from about 5 to about 200 microns. It is preferred in ,order to achieve optimum results that the layer be from abdut 10 to about microns thick. The support base may present a flat surface or it may be in the form of a cylindrical roller, the latter being more suitable for a continuous rotogravure system The hydrophobic pattern may be prepared from a composition comprising either an organic or inorganic photoconductive material dispersed in a hydrophobic resinous binder, suleh as a zinc oxide photoconductive pigment dispersed in an epoxy resinous material, or from a homogeneous, hydrophobic photoconductive composition such as a polycarbonate oi phenolic resinous charge transfer complex. The photoconductive hydrophobic composition may be applied to the entire gravure surface or it may be restricted so as to form or coat only the raised areas or ridges on the support substrate. In another configuration the photoconductive hydrophobic co position may coat only the recessed areas or valleys of the gravure pattern with the ridges consisting of a semidielectric material such as regenerated celstatic latent image, an aqueous-base developer is contacted with the surface of the hydrophobic gravure plate, the
developer being held in imagewise configuration to the charged portion of the plate thereby filling the gravure cells or recesses in the image areas represented by the electrostatic charge. The imaged or developed surface of the plate is then contacted with a copy sheet and the liquid developer transferred thereto in an image pattern to produce a reproduction of the original. The process may be continually repeated until the desired number of copies are reproduced.
Any suitable photoconductive layer with hydrophobic propenies may be used as the charge carrier for the electrostatic charge pattern of the present invention. The photoconductive layer may comprise a photoconductor dispersed in an insulating binding composition, a solution of photoconductor and binder or it may consist of a homogeneous hydrophobic photoconductive composition. When used in the dispersed phase the photoconductive layer generally may consist of an organic or inorganic photoconductive material dispersed in an organic hydrophobic binder composition. Typical binder materials are similar to those disclosed in U.S. Pats. Nos. 3, l 21 .006 and 3, l 2 l ,007. The specific binder material chosen will depend upon the nature of the photoconductor pigment utilized to prepare the xerographic plate used in conjunction with the present invention. When necessary, the binder material employed with the photoconductive compound is such that it is an insulator to the extent that an electrostatic charge placed on the photoconductive layer is not conducted by the binder, at least in the absence of illumination, at a rate to prevent the fonnation and retention of an electrostatic latent image thereon. The binder material is adhered tightly to the base of the plate and provides an efficient dispersing medium for the photoconductive pigment. Further, a binder material should be selected so as to be relatively inert when in the presence of the photoconductive compound. Typical organic binders and polystyrene, epoxy resins such as Epon Resins commercially available from the Shell Chemical Co., silicone resins such as DC-80l. DC-804, and DC-996 commercially available from the Dow Corning Corp. acrylic and methacrylic polyesters such as Acryloid A-l and Acryloid B- 72, polymerized ester derivatives of acrylic and alpha-acrylic acids all commercially available from Rohm and Haas Co. Lucite, polymerized butylmethacrylate commercially available from El. duPont de Nemours & Co., and vinyl polymers and copolymers such as polyvinyl chloride and polyvinyl acetate.
As mentioned above, when the binder material itself is photoconductive then a homogeneous layer of the binder may be used to coat the surface of the gravure printing master. When the binder material is photoconductive it is preferred that the specific resistivity of the binder be at least about ohms centimeters to satisfactorily fulfill the requirements of the resulting photoconductive insulating plate. Typical photoconductive binders are selenium, sensitized polyvinyl carbazole, anthracene, sulfur, .and resinous charge transfer complexes, such as those disclosed in U.S. Pats. Nos. 3,408,183; 3,408,186; 3,408,184; 3,408,182; 3,408,185 filed Jan. 18, 1965, as well as mixtures thereof.
When the dispersed phase of the photoconductive composition is used as the hydrophobic coating, any suitable photoconductive material may be applicable to the present invention. Typical inorganic photoconductor materials are: sulfur, selenium, zinc sulfide, zinc oxide, zine cadmium sulfide, zinc magnesium oxide, cadmium selenide, zinc silicate, calcium-strontium sulfide, cadmium sulfide, mercuric iodide, mercuric oxide, mercuric sulfide, indium trisulfide, gallium triselenide, arsenic disulfide, arsenic trisulfide, arsenic triselenide, antimony trisulfide, cadmium sulfo-selenide and mixtures thereof. Typical organic photoconductors are triphenylamine, 2,4-bis (4,4 '-diethyl-amino-phenyl)-1,3 ,4-oxadiazol, N- isopropylcarbazole, triphenylpyrrol, 4,5-diphenylimidazolidinone, 4,5diphenylimidazolidinethione, 4,5-bis-(4- amino-pheny] )-imidazolidinone, l,5-dicyanonaphthalene, l ,4-dicyanonaphthalene, aminophthalodinitrile, nitrophthalodinitrile, l ,2,5,-tetraazacyclooctatetraene- (2,4,6,8), Z-mercapto-benzthiazol 2-phenyl-4-diphenylideneoxazolone. 6-hydroxy-2,3-di(p-methoxy-phenyl )-benzofurane; 4-dimethylamino-benzylidene-benzhydrazide; 3-benzylidene-amino-carbazole. polyvinyl carbazole; (2-nitro-benzylidene)-p-bromo-aniline; 2.4-diphenyl-quinazoline; 1,2.4- trizine; l.S-diphenyl-3-methyl-pyrazoline; 2-(4 dimethylamino phenyl)-benzoxazole; 3-amino-carbazole; phthalocyanines and mixtures thereof.
Any suitable material may be used to prcpare the support base for the gravure master of the present invention. Generally, the preferred support material should have an electrical resistance less than the photoconductive layer so that it will act as a ground when the electrostatically charged coating is exposed to light. Typical materials are aluminum, brass, steel, copper, nickel, zinc, conductive rubber and conductive or otherwise tin oxide coated glass. In addition, glass binderphotoconductive plates as disclosed in U.S. Pat. No. 3.151982 may also serve as the support substrate. The selection of the particular support base material used may depend upon the desired use of the gravure printing master. For example. if the master is to take the shape of a flat printing plate then it may be more desirable to select a support substrate which will add additional strength to the system. However, if the gravure printing master is to be prepared in the form of a roller or cylinder then it would be generally more desirable to select a material which will provide the necessary flexibility properties. When a rotogravure type of printing master is fabricated the support surface may be cylindrical in nature or it may n consist of a solid core such as a solid conductive rubber roller.
The raised patter on the surface of the support base may be formed by any suitable method so as to produce a spacing ranging from about 50 to about 300 cells per inch. in order to obtain maximum resolution it is preferred that the number of cells per inch approach the upper limit of the specified operable range. The method of preparing the gravure roller or plate may be, as mentioned above, similar to the approach followed in U.S. Pat. No. 3,084,043 with the exception that the resin pattern in halftone dots would generally consists of one of the above-mentioned photoconductive compositions suitable for use herein. Alternatively, the gravure pattern of the photoconductive material may be formed on the support base by direct contact with a knurled roller applicator or the gravure pattern may consist of patterned cloth belts of photoconductive fibers. Additional methods of forming the gravure pattern on the surface of the support base would entail etching gravure pockets in the surface of the cylinder or core in which case the hydrophobic photoconductive composition would then applied to the surface thereof following the etching process, or molding the support base in such a manner so as to initially present a gravure or porous surface thereby eliminating intermediate chemical treatments and simplifying the process while directly providing the necessary recessed areas in the surface. For expediency and to eliminate time-consuming steps it is generally considered more desirable to coat the hydrophobic photoconductive composition of the present invention on the surface of a roller or plate which has been provided with the necessary gravure pattern.
Any suitable aqueous-based developer may be used in the process of this invention, said developers having viscosities ranging from 1 to 100,000 centipoises, preferably 5,000 to 20,000 centipoises in order to obtain optimum results. By the expression aqueous-based developer is meant a liquid developer which will wet a hydrophobic surface under the influence of electrostatic attractive charges so as to record the electrostatic charge pattern in terms of surface wetting. The presence of the electrostatic charge reduces the contact angle between the liquid and the hydrophobic surface to such an extent that substantially complete wetting occurs. The developer may comprise water alone or a mixture of liquids comprising a major proportion of water and a minor proportion of another solvent, such as alcohol. It may be a polar liquid such as ethylene glycol, propylene glycol or glycerol; when the situation so warrants, such as when the charge carrier surface comprises a composition such as polytetrafluoroethylene or polyhexafluoropropylene with a low surface free energy, the developer may take the form of a petroleum hydrocarbon as, for example, benzene, kerosene. hexane, heptane, n-decane and ntetradecane. Furthermore. when desirable the surface free energy of the charge receptive surface may be decreased by the application of a monolayer of a fluoronated long chain acid such as dodecanoic acid. Typical developer components or additives are vinyl resins such as carboxy vinyl polymers, polyvinylpyrrolidones, methylvinylether-maleic anhydride interpolymers, polyvinyl alcohols, cellulosics such as sodium carboxy-methyl cellulose, hydroxypropylmethyl cellulose, hydroxyethyl cellulose, methyl cellulose, cellulose derivatives such as esters and ethers thereof, water, starch, alkali soluble proteins, casein, gelatin, acrylate salts, such as ammonium polyacrylate, and sodium polyacrylate, polyacrylic acid, polymethylacrylic acid, and copolymers thereof and the alkali and ammonia salts of alginic acid and mixtures thereof. For purposes of this invention, optimum results are obtained when a vinyl resin is added to the liquid selective wetting developer inasmuch as the preferred viscosity level could be readily reached at a low concentration.
Any suitable aqueous-based ink may be used in the process of the present invention as the selective wetting agent, either alone or in conjunction with the above developer composition particularly when the developer is colorless. This includes both the inks containing a water soluble dye substance and the pigmented inks, Typical dye substances are Methylene Blue, commercially available from Eastman Kodak Co., Brilliant Yellow, commercially available from the Harlaco Chemical Co., potassium pennanganate, ferric chloride, cobaltous chloride, commercially available from Dayco Laboratories and Methylene Violet, Rose Bengal and Quinoline Yellow, the latter three commercially available from the Allied Chemical Co. Typical pigments are carbon black, graphite, lamp black, bone black, charcoal, titanium dioxide, white led, zinc oxide, zinc sulfide, iron oxide, chromium oxide, lead chromate, zinc chromate, cadmium yellow, cadmium red, red lead, antimony dioxide, magnesium silicate, calcium carbonate, calcium silicate, phthalocyanines, benzidines, naphthols and toluidines. The pigmented inks are preferred inasmuch as the final reproduced prints are longer lasting and possess optimum optical density characteristics. Specifically preferred among the pigments is carbon black because it is more suitable for most printing operations.
It is also possible to use simple compounds to colored water soluble complexes such as those which are formed by certain number of transition elements. Typical examples are the known cuprous tetrammine complex, chromium salts, such as chromium sulfate potassium chrome alum, potassium chromate, the aquo and acid-complexes of trivalent chromium, certain ferric compounds such as ferrid. thiocyanate and the thiocyanato ferrates, the acetate complexes of ferric salts, iron-ammonium citrate, the thiocyanate and the thiocyanocobaltates of bivalent cobalt, cobaltous sulfate and chloride, the chlorides and sulfates of bivalent nickel. The copper tartrate complex, copper-glycine, the soluble compounds of iron and gallic acid, the complexes of ferrous salts with alpha-picoliriic acid, iron or bivalent cobalt complexes with the alpha-picolinic acid, iron or bivalent cobalt complexes with the aIpha-dioximes, such as dimethyl-glyoxime, the ferric complexes with salicylic acid, compounds formed between titanium or iron salts and pyrocatechol or chromotropic acid. Coupling reactions which use diazonium compounds and which lead to the formation of colored products are especially suitable.
The invention is illustrated in the accompanying drawings in which:
FIG. 1 represents a magnified cross section through a gravure dispensing member of the present invention with an electrostatic charge developed thereon;
FIG. 2 illustrates the gravure plate of FIG. 1 under exposure;
FIG. 3 further illustrates the exposed plate of FIG. 2 during the liquid development stage;
FIG. 4 represents a magnified cross section through a rotogravure printing master according to an alternate embodiment of the present invention;
FIG. 5 illustrates a side sectional view of an exemplary continuous imaging apparatus of the present invention.
Referring now to FIG. 1. there is seen a gravure dispensing member generally designated 1 comprising a support base 2, in this instance comprising a glass binder-photoconductive plate, having disposed on its surface a raised pattern 3 comprising a homogeneous photoconductive composition of the present invention. This member is characterized by being wettable by an applied liquid developer in the depressions or valleys formed by the raised areas 3 when an electrostatic charge 4 is formed on the surface of the hydrophobic photoconductive material making up the raised areas of the gravure plate. Upon selective exposure of the charged gravure plate, as illustrated in FIG. 2, to radiant energy designated for illustrative purposes by lines 5, the charge in the exposed areas is dissipated thereby leaving an electrostatic latent image4a on the surface of the plate. FIG. 3 illustrates the development phase of the process whereby an aqueous based developer 7 from source 8 is applied by means of roller 9 to the imaged surface of the photoconductive gravure plate 1. The developer 7 is attracted and held in imagewise configuration 7a within the gravure recesses formed by the hydrophobic photoconductive raised areas 3 retaining electrostatic charge 4a.
FIG. 4 represents a cylindrically-shaped image support member generally designated 10, made up of a support base 12 having coated on the surface thereof photoconductive composition 13 comprising a photoconductive material 14 dispersed in a hydrophobic insulating binder composition 15. The means of applying the photoconductive coating to the surface of the support base will generally be governed by the particular photoconductor that is utilized. For example, if the photoconductive layer is to consist of a dispersed phase of, for example, a phthalocyanine photoconductor in a hydrophobic insulating binder then the coating may be applied by either flow coating, dipping, spraying or by any other suitable technique. However, if the surface of the support base 12 is to be coated by a layer of selenium, for example, then the coating would generally be vacuum deposited on the surface of the gravure roller.
FIG. 5 represents a simple exemplary apparatus for carrying out the imaging technique of the present invention. In this apparatus, there is seen a rotary gravure roller 20 made up of a conductive rubber core 16 with a coating of a hydrophobic photoconductive composition 17 thereon. The roller, when in operation, is generally rotated at a uniform velocity in the direction indicated by the arrow so that the surface of the roller passes beneath a charging unit 18, such as a high voltage corona discharge electrode adapted to supply ions or electric charges to the surface of the roller, and after having been uniformly charged passes beneath a scanning image mechanism 19 or other means for exposing the charged plate to the image to be reproduced. Following exposure, the imaged surface of the roller or drum moves past the developing unit generally designated 30 consisting of a gravure applicator 21, doctor blade 22 and dispenser 23 containing an aqueous developer 24. Upon contact with the gravure applicator, the aqueous developer is deposited upon the surface of the exposed hydrophobic rotogravure roller in an imagewise configuration, corresponding to the charged areas on the roller. As a result of the retained charge ink is deposited within the recessed areas on the surface of the drum and retained therein due to the attraction of the developer by the charge as discussed above. After passing the developing unit 30 the photoconductive drum bearing the developed image 40 continues around so as to contact copy web 25 which is fed from supply roll 26 and passed up against the drum surface by transfer roller 27 and which travels at the same speed as the periphery of the drum. The developed image 40 is transferred upon contact by capillary action to the surface of the copy web. The transferred image 400 is then wound on takeup roller 31 after allowing adequate time for the transferred image to dry. Following transfer of the developed image to the copy web 25 the surface of the drum continues around and is passed up against a cleaning sponge 28 which is so arranged to remove the residue of the developer from the recessed areas of the gravure roller thereby preparing it for a new cycle of operation. It is possible to introduce a new document at the beginning of each new cycle.
Although the invention has been described in connection with corona charging, it is to be understood that this is exemplary only, and that any suitable charging technique may be utilized. Other charging methods include friction charging and induction charging as described in U.S. Pats. Nos. 2,934,649 and 2,833,930 and roller charging as described in US. Pat. No. 2,934,650.
To further define the specifics of the present invention, the following examples are intended to illustrate and not limit the particulars of the present invention. Parts and percentages are by weight unless otherwise indicated. The examples are also intended to illustrate various preferred embodiments of the present invention.
EXAMPLE I A zinc oxide photoconductive composition commercially available from the New Jersey Zinc Co. is mixed with a hydrophobic silicone resin binder commercially available under the name DC-996, from the Dow Corning Corp. The photoconductive composition and the binder material are mixed together in equal parts by weight with a toluene solvent in an amount equal to the volume of the binder material. The resulting mixture was spray coated on the surface of a conductive rubber gravure roller to a thickness of about microns and allowed to dry. Following drying of the roller, the photoconductive coating is charged in the dark to a potential of about 400 volts by means of a laboratory corotron unit powered by a high voltage power supply. The charged surface of the plate is exposed to a light pattern through a transparent positive image with a 75 watt photoflood lamp to selectively dissipate the electric charge thereby producing an electrostatic latent image on the imaging surface of the hydrophobic gravure roller. An exposure ofabout 2O foot-candle-seconds is required. A water-based ink comprising:
Water cc.s-- 100 Methylene blue grams 2 Glycerol do 2 is contacted with the imaged surface of the gravure roller and the final print made by contacting the resulting developed plate with a copy sheet. Blue images of good density and resolution are obtained.
EXAMPLE I] The process of example l is repeated except that an epoxy resin, Epon lOOl, commercially available from the Shell Chemical Co., is substituted for the silicone resin used in example l. The electrostatic latent image developed on the surface of the hydrophobic gravure roller is capable o of producing photographic reproductions similar to those obtained in example 1.
EXAMPLE Ill A flat gravure printing plate is prepared by mixing in a l to 1 ratio by volume a zinc oxide photoconductive composition with silicone resin DC-996. The mixture is applied by means of knurled applicator to the surface ofa 4 by 5 inch aluminum plate thereby producing a gravure dispensing member. The plate is dried and the surface charged in the dark to a potential of about -400 volts by means of a laboratory corotron unit powered by high voltage power supply. The charged surface of the plate is exposed to a light pattern through a transparent positive image with a 75 watt photoflood lamp, selectively dissipating the electric charge in the exposed areas and producing an electrostatic latent image on the surface of the hydrophobic gravure plate. The electrostatic latent image is developed with a liquid of the following composition:
Water cc.s Methylene Blue grams 2 Carboxy methyl cellulose do- 2 The imaged surface of the gravure plate is then contacted with a copy sheet thereby producing images of good uniformity. density and resolution.
EXAMPLE 1V About a S-gram sample of a diphenyloxide modified Novalac resin No. ET-395-l300 commercially available from the Dow Chemical Co. is put into a 100-milliliter beaker con taining about 45 grams of a solvent mixture consisting of about 25 grams acetone and about 20 grams toluene. The mixture is agitated by means of a stirrer until the resin is fully dissolved in the solvent. About 250 milligrams of 2,4,7- trinitrofluorenone are added to about a lO-gram portion of the diphenyloxide modified Novalak resin solution prepared above. The mixture is stirred as before until solution of the 2,4,7-trinitrofluorenone is obtained. The solution is applied by dip coating onto the surface of a conductive rubber gravure roller to a thickness of about 10 microns and allowed to dry. Following drying of the roller, the photoconductive coating is charged in the dark to a potential of about 300 volts by means of a corona discharge, selectively exposed for about 15 seconds by projection using a Simmons Omega D3 enlarger equipped with an f/4.5 lens at a color temperature of2,950 K. The illumination level at the exposure plane is 4 foot-candles as measured with a Weston Illumination Meter Model No. 756. A water-based ink comprising:
Water c cc.s 100 Crystal Violet- A s grams- 2 Glycerol a do 2 EXAMPLE V Glass frit formulation:
PE RCENT B Y WEI GllT Constituent Percent N0.
About 200 grams glass frit of the formulation above is blended with about 32 grams of a cadmium sulfoselenide photoconductive material in about 200 grams of water. The resulting composition is mixed in a ball mill for approximately 18 hours. The resulting blend is then thoroughly dried. Approximately 200 milliliters ofisopropyl alcohol is added to the dried composition and the milling process repeated for approximately 2 hours. The resulting glass binder-photoconductive composition is cylindrically-shaped, dried and fired to a temperature of about 1 F. for approximately 10 minutes and then cooled. A photoconductive composition consisting of a l to 1 ratio by volume of zinc oxide photoconductive composition with silicone resin DC-996 is prepared as described in example I and the composition applied by means of a knurled applicator to the surface of the photoconductive glass binder cylinder thereby producing a gravure dispensing member. The cylinder is dried and the surface charged in the dark by a laboratory corotron unit at 6000 volts, The charged surface of the cylinder is exposed to a light pattern through a transparent positive image with a 75 watt photoflood lamp, selectively dissipating the electric charge in the exposed areas and producing an electrostatic latent image on the surface of the gravure cylinder. The electrostatic latent image is developed with a liquid of the following compositions:
Water cc.s 100 Crystal violetgrams- 2 Glycerol -do- 2 The imaged surface of the gravure cylinder is then contacted with a copy sheet thereby producing images of good uniformity, density and resolution.
EXAMPLE VI A flat gravure printing plate is prepared by initially mixing 6 grams of Oxiron 2002, an epoxidized polyolefin, and 1 gram of x-form metal-free phthalocyanine prepared according to the process described in US. Patent application Ser. No. 375, l 91. This mixture is formulated together with about 3.5 grams phthalic anhydride, 9 grams n-butanol and grams of acetone. The above mixture is milled for about 8 hours with porcelain pebbles in a 6-ounce mixing vessel. The resulting mixture is applied by means of a knurled applicator to the surface of a conductive rubber plate thereby producing a gravure dispensing member. The coating is cured for about 60 minutes at about 175 C. The plate is charged in the dark by a laboratory corotron unit at about 6,000 volts. The charged plates is then selectively exposed to 3 foot-candle-seconds seconds of photoflood illumination thereby producing an electrostatic latent image on the surface of the gravure plate. The latent image is developed with a liquid having a composition similar to that of example V and the resulting developed image transferred upon contact to the surface of a copy sheet thereby producing images of high density and resolution.
EXAMPLE VII A conductive rubber gravure roller is vacuum coated with a layer about microns thick of vitreous selenium. The surface of the roller is charged to about +400 volts by means of a laboratory corotron unit powered by a high voltage power supply. The charging current is about 0.1 of a milliamp at about 7,000 volts. The surface of the selenium coated roller is selectively exposed through a transparent positive image to a light source consisting of a tungsten filament at about 2,800 K. for an exposure of about 2 foot-candle-seconds. The electrostatic latent image produced is developed with a liquid developer similar to that disclosed in example V. The imaged surface of the roller is then contacted with a copy sheet thereby producing images of high quality, good density and resolution.
Although the present examples were specific in terms of conditions and materials used, any of the above-listed typical materials may be substituted when suitable in the above examples with similar results being obtained. In addition to the steps used to prepare the gravure printing master of the present invention, other steps or modifications may be used, if desirable. For example, the gravure pattern of the hydrophobic photoconductive coating may be applied through the apertures of a silk screen. In addition, other materials may be incorporated in the developer, the layer for increasing the hydrophobic properties, the photoconductive layer, and the support plate, which will enhance, synergize or otherwise desirably affect the properties s of these materials for their present use. For example, the photoconductive layer may contain known additives such as plasticizers, dispersing agents, substances counteracting oxidation and aging, and sensitizing dyes which will modify the spectral sensitivity of the photoconductive plates.
Anyone skilled in the art will have other modifications occur to him based on the teaching of the present invention. These modifications are intended to be encompassed within the scope of this invention.
1. A process for preparing a reusable gravure printing plate which comprises:
a. forming an electrostatic latent image It on the surface of a photoconductive plate, said plate comprising a support base having affixed substantially completely to the surface thereof in a gravure pattern a hydrophobic photoconductive insulating composition said pattern having a cell spacing ranging from about 50 to about 300 cells per inch; and
b. developing said latent image with an aqueous-base developer in such a manner that said developer is distributed thereon conforming to said latent image in an imagewise configuration.
2. The process as described in claim 1 wherein said photoconductive composition comprises a hydrophobic resinous charge transfer complex.
3. The process as described in claim 1 wherein said photoconductive composition comprises selenium.
4. The process as described in claim 1 wherein said photoconductive composition comprises a hydrophobic binder insulating material having dispersed therein a member selected from the group consisting of organic and inorganic photoconductive materials.
5. The process as described in claim 4 wherein said dispersed member is an organic photoconductive material comprising phthalocyanine.
6. The process as described in claim 4 wherein said dispersed member is an inorganic photoconductive material comprising zinc oxide.
7. A method of preparing a reusable gravure printing plate which comprises forming a gravure pattern substantially completely on the surface of a support substrate, said pattern comprising a hydrophobic photoconductive composition and having a cell spacing ranging from about 50 to about 300 cells per inch, forming an electrostatic charge on the surface of said gravure pattern, selectively exposing said charged surface so as to produce an electrostatic latent image, applying to the surface of said exposed surface an aqueous-base developer in such a manner that the developer is distributed thereon conforming to said latent image in an imagewise configuration to form said gravure printing plate.
8. The process as defined in claim 7 wherein said support substrate comprises a rotagravure cylinder and said photoconductive composition is selected from at least one member of the group consisting of a hydrophobic resinous charge transfer complex, selenium and zinc oxide.
9. The process as described in claim 7 wherein said photoconductive composition comprises a hydrophobic resinous binder with an organic photoconductive material comprising phthalocyanine.
10. A method of preparing multiple copies from a gravure printing plate which comprises:
a. forming an electrostatic latent image on the surface of a photoconductive member, said member comprising a substrate having fixed substantially completely to the surface thereof in a gravure pattern a hydrophobic photoconductive insulating composition said pattern having a cell spacing ranging from about 50 to about 300 cells per inch;
b. developing said latent image with an aqueous-base developer in such a manner that said developer is distributed thereon conforming to said latent image in an imagewise configuration;
c. contacting said developed image with a copy sheet thereby transferring said aqueous developer held in the recessed areas of the gravure pattern to the surface of said copy sheet in an imagewise configuration; and
d. repeating the above steps in their given sequence to form a multiplicity of reproductions.
11. The process as described in claim wherein said photoconductive member comprises a rotagravure cylinder and said photoconductive composition is selected from at least one member of the group consisting of a hydrophobic resinous charge transfer complex, selenium and zinc oxide.
12. The process as described in claim 10 wherein said photoconductive member comprises a hydrophobic resinous binder having dispersed therein an organic photoconductive material comprising phthalocyanine.
13. A method of making multiple copies from a xerographic image which comprises:
a. forming a gravure pattern substantially completely on the surface of a support substrate, said pattern comprising a hydrophobic photoconductive composition, and having a cell spacing ranging from about 50 to about 300 cells per inch;
b. developing an electrostatic charge on the surface of said gravure pattern;
c. selectively exposing said charged surface so as to produce an electrostatic latent image;
d applying to said exposed surface an aqueous-based developer in such a manner that said developer is distributed thereon conforming to said latent image in an imagewisc configuration;
e. contacting said developed image with a copy sheet thereby transferring said aqueous developer held in the recessed areas of the gravure pattern to the surface of said copy sheet in an imagewise configuration; and
f. repeating steps b through e in their given sequence to form a multiplicity of reproductions.
14. The process as described in claim 13 wherein said support substrate comprises a rotagravure cylinder and said photoconductive composition is selected from at least one member of the group consisting of a hydrophobic resinous charge transfer complex, selenium, zinc oxide, and phthalocyanine dispersed in a hydrophobic resinous binder.