Dry Planographic Plates And Methods, Production And Use

Abstract

A new "dry planographic" plate comprised of a flexible substrate having coated thereon a cured solid but elastic silicone rubber film which will not remove conventional lithographic ink from an ink roller on a printing press, a method of producing this plate and a new "dry planographic" process wherein the new planographic plate of the present invention is not wet with a fountain solution.

Parent Case Text

RELATIONSHIP TO OTHER APPLICATION

The present application is a continuation-in-part of my co-pending application entitled "Method for Preparing Dry Lithographic Plates," Ser. No. 494,768, filed Oct. 11, 1965 and now abandoned.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a new form of planography or planographic printing which may be called "dry planography." Planography, as the name implies, is printing from a printing plate or equivalent surface which is substantially level or plane.

The most important branch of conventional planography is lithography, which is based on the mutual repellency of oil and water. In practice, a lithographic plate, which may be made of stone, coated or roughened metal, coated paper, or coated plastic film, has affixed thereto an image that is repellent to water but that readily accepts greasy printing ink. The methods of producing the images are well known to those skilled in the art. After the plate has been imaged, an aqueous lithographic solution which usually contains an acid phosphate salt is applied to the plate. The aqueous lithographic solution may also contain glycerine or other humectant and gum arabic. The water repellent image is not wet by the lithographic solution, but the unimaged background areas are all wet by the solution. Following the wetting of the unimaged areas, a roller covered with greasy lithographic printing ink is rolled across the surface leaving a film of ink on the image but not on the wet background areas. This ink film can then be transferred to another surface brought into contact therewith, such as the paper sheet in direct lithography or the offset blanket in offset lithography. Before another print is made from the plate, a fountain roller applies more aqueous lithographic solution to the plate and an inking roller applies more ink to the image. Then another print is made. The process can be repeated for as many prints as are desired.

In the history of commercial offset lithography, the fact that water must be used to prevent ink from sticking to the background has been one of the major technical problems which has slowed the growth of commercial offset lithography. Special inks had to be developed which would not mix with the water. Special rollers had to be developed that would continue to carry ink in the presence of water and not "strip" . Special papers had to be developed in which the adhesives were insolubilized so that the water would not penetrate and in turn allow the printing stresses to pull the paper and/or coatings thereon apart. All these developments either made the plates, inks and rollers more costly to make or led to compromises which resulted in the loss of other desirable characteristics. The present invention is directed to a dry planographic process which eliminates the use of a water fountain and the attendant difficulties arising from the use thereof.

Furthermore, in offset lithography a careful balance must be maintained between the amount of ink fed to the printing plate and the amount of water applied to the surface of the plate. Too much water causes weak prints and insufficient water allows the non-image areas to pick up ink and to print. With the new plate and new dry planographic process of the present invention, only the ink feed needs to be controlled.

The new planographic plate and new dry planographic method of the present invention do not require the use of a fountain solution of any type. The new planographic plate can be completely dry when mounted on the printing press and is run without having hydrocarbon fountain solutions as described by Greubel in U.S. Pat. Nos. 3,209,683; 3,241,486 and 3,356,030 or water applied to its surface before or during the run. When imaged with an oleophilic image and rolled over the greasy printing ink, the oleophilic image takes up the ink, but the silicone rubber background of the plate rejects the ink. Therefore, only the oleophilic image areas print and the background or non-imaged areas remain clean. In another adaptation, when the plate is imaged with a hydrophilic image, it can be rolled over with water-base or glycol-base ink which will adhere to the hydrophilic image but be rejected by the background areas. Thus, the present invention provides an additional advantage over prior art lithographic plates and processes in that the plate of the present invention can be imaged with either a hydrophilic or oleophilic image which allows the use of wither water-base or oil base inks.

This novel plate also permits much simpler press design than either offset lithography or letterpress. Letterpress requires very precise positioning of the plate for both inking and impression. Massive, costly presses are required to achieve the desired precision. Such presses would not be necessary for the use of the plate of the present invention. Furthermore, in offset lithography the water applying systems have never been satisfactory. Improvements in molleton covering materials and fairly complex metering systems have decreased the problem somewhat, but the water application systems still need further refinement. "Dry planography" employing the new plates and method of the present invention permits the building of a much simpler press without a water or hydrocarbon application system. Along with this simplification less precautions need to be taken to prevent the corrosion which is caused by the acidic fountain solutions used in lithography.

In printing metal foils and plastic films by offset lithography, the water used to wet the plate is very troublesome as it is not absorbed by the films being printed as it would when paper is being printed. This causes additional problems in ink emulsification, press balance, and unwanted wetting of the product. "Dry planography" is, therefore, more satisfactory for the printing of materials that do not absorb water.

Another unusual and advantageous application of this novel plate is on letterpress machines where the dry plates may be mounted type high on either a flat bed or rotary press and clean copy may be produced from this planar surface since the ink will only be transferred to the plate in the image areas. The non-image areas of the plate will not accept ink because there is insufficient adhesion between the ink and plate surface.

Various silicon containing materials have been employed in the production of lithographic plates, e.g., soluble silicates, U.S. Pat. No. 3,085,008; colloidal hydrated silica and polymerized silicic acid, U.S. Pat. No. 2,714,066; and ink receptive organosilicones, U.S. Pat. No. 2,804,388. In all of these cases, a conventional aqueous fountain solution is employed to prevent the ink from sticking to the hydrophilic surfaces. The Greubel et al patents, U.S. Pat. Nos. 3,209,683; 3,241,486 and 3,356,030, employ thermo-setting alkyl and aryl substituted polysiloxanes in the production of a planographic plate which must be wet with a hydrocarbon fountain solution to prevent the ink from adhering to the silicone surface.

SUMMARY OF THE INVENTION

The present invention is directed to a new planographic plate, a method of producing the new planographic plate and a new dry planographic printing method employing the new plates herein described.

The new planographic plate of the present invention comprises a sheet of flexible substrate sufficiently strong to withstand the stresses normally employed in a lithographic printing process; said substrate having coated on at least one surface thereof a layer of silicone rubber that will not remove conventional lithographic printing ink from an inking roller of a printing press.

The term silicone rubber as employed in the present specification and claims represents a diorganopolysiloxane composition which upon curing to a solid elastic state provides a surface will not remove conventional lithographic printing ink from an inking roller. Representative silicone rubbers to be employed in the present invention result from the curing of a diorganopolysiloxane selected from the group consisting of

a. linear diorganopolysiloxanes having terminal silicon-bonded acyloxy groups;

b. linear diorganopolysiloxanes having terminal reactive end-blocking groups and a metal salt of carboxylic acid; and

c. linear fluid diorganopolysiloxanes having terminal silicon-bonded hydroxy groups, a metal salt of an organic carboxylic acid and a member of the group consisting of an alkyl silicate or methyl hydrogen polysiloxanes. The term diorganopolysiloxane as employed herein represents disubstituted polysiloxanes wherein the substituents are monovalent aliphatic or cyanoalkyl groups having from one to four carbon atoms, inclusive. Representative aliphatic and cyanoalkyl groups include methyl, ethyl, propyl, butyl, vinyl, allyl, beta-cyanoethyl, beta-cyanopropyl and halo alkyl groups such as 3,3,3-trifluoropropyl and chloromethyl. Representative metal salts of organic carboxylic acids include tin naphthenate, tin octoate, lead octoate, tin oleate, iron stearate, tin butyrate, dibutyl tin dilaurate, dibutyl tin diacetate, zinc naphthenate, lead 2-ethylhexoate and the like with the tin and zinc salts generally being preferred. The term reactive end groups as employed in the present invention designates acetoxy, hydroxy and oxime groups.

The diorganopolysiloxane compositions employed to produce the solid but elastic silicone rubber films of the present invention are conveniently applied to at least one surface of the flexible substrate in the form of an aqueous emulsion or aqueous or solvent dispersion. The diorganopolysiloxane compositions are applied to the substrate by means of a blade coater, Mayer bar, reverse roll coater, knife or by other commonly employed coating techniques. The surface to be coated should be clean and preferably dry when the diorganopolysiloxane composition is applied. The silicone rubber film can be of any desired thickness as long as the film is coherent, continuous and securely bonded to the substrate. It has been found convenient to apply the diorganopolysiloxane composition in an amount sufficient to provide a coating of silicone rubber having a thickness of from 0.02 to 0.2 mils. Films thicker than 0.2 mils can be employed; however, they are generally not deemed to be necessary.

Following the application of the diorganopolysiloxane composition to the surface of the substrate, the diorganopolysiloxane composition must be allowed to cure to produce the solid but elastic silicone rubber. Most of the diorganopolysiloxane compositions of the present invention cure at room temperature. The curing generally takes place within minutes to 24 hours. However, the curing time will vary according to thickness of the film, humidity and temperature. While most of the diorganopolysiloxanes cure at room temperatures and, therefore, do not require additional heating, the coated plate can be heated to decrease the cure time if desired. When employing a diorganopolysiloxane composition comprising a fluid diorganopolysiloxane having terminal silicon bonded hydroxy groups, a metal salt of a carboxylic acid and a methylhydrogen polysiloxane, heat curing is recommended, temperatures of from 90.degree. to 500.degree. F are operable and temperatures between 90.degree. and 160.degree. F are preferred. Curing is obtained by heating the film to be cured for a period of from about 10 seconds to about 3 minutes or more.

The flexible substrate employed in the present invention should be sufficiently flexible that it can be mounted on a lithographic press and strong enough that it can withstand the stresses normally produced by the lithographic process. Representative substrates include coated papers, metals or plastics such as polyethylene terephthalate). While aluminum appears to be the preferred metal substrate on the basis of cost, handling properties, and the like, sheets of lithographic zinc, foils of copper, steel and copper surfaces all can be employed as the flexible substrate in the present invention.

Any grade of paper can be employed as the substrate in the present invention provided that it has the strength to withstand the stresses normally employed in the lithographic process. Such papers are well known in the art and generally range from 70 to 250 pounds per ream. The diorganopolysiloxane compositions employed to produce the solid but elastic silicone rubber coating can be applied directly to the surface of the paper. However, such application often requires the use of relatively large amounts of diorganopolysiloxane compositions and the use of such large amounts is generally not economically desirable. Therefore, in a convenient procedure, the surface of the paper plate is precoated prior to the application of the diorganopolysiloxane composition. The precoat serves to "hold out" the aqueous emulsion or organic solvent carrier employed in the application of the diorganopolysiloxane composition. Coatings which provide the desired carrier "hold out" and are useful in the present invention include polyvinyl alcohol, casein, starch, carboxylated starch, hydroxyethylated starch, alpha protein, styrene butadiene based coatings, acrylic copolymer coatings, vinyl acetates, fluorocarbons and the like. Such coatings may contain fillers, pigments, antifoam agents, spreading agents and other additives commonly employed in paper coating compositions. A coated paper substrate designed to give 15,000 or more copies is easily provided by a paper base made from moderately beaten chemical wood pulp fibers and weighing from 80-90 pounds per ream of 500 sheets (25 .times. 38 inches in size). A specific example of a suitable paper is one weighing 87 pounds per ream made from a furnish containing beaten wood pulp fibers of coniferous and deciduous trees, a small portion of clay filler, rosin size and alum. The paper is then coated on one or both sides with about 10 pounds per ream dry weight of clay and casein in a 5:1 ratio. The sheet is then dried and calendered.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2, 3, 4, 5(a) and 5( b) are enlarged cross-sections of plates having an ink-repellent silicone rubber background.

DETAILED DESCRIPTION

The new planographic plate of the present invention as depicted by FIG. 1 is comprised of a flexible substrate 5 having at least one surface thereof continuously coated with a film 6 of solid but elastic ink-repellent silicone rubber. Following the curing of the diorganopolysiloxane to obtain the solid but elastic silicone rubber layer, the plate is ready to be imaged. A short run imaged plate is produced by passing the plate through a xerographic electrophotographic copier. In this process, a powder image previously electrostatically formed on a selenium-plated drum is transferred by contact to the plate. The plate and image are then heated to cause the powder particles to fuse to each other and to the surface of the plate. The imaged plate produced in this manner is mounted on a printing press, inked and used to produce clean copies having no ink in the background areas. This method of imaging the plate is useful for producing copies of line copy and the like.

A pre-sensitized plate as illustrated by FIG. 2 is prepared by applying to the cured solid but elastic surface of the silicone rubber film 6 one of the water soluble photo-responsive diazo compounds employed in conventional diazo-sensitized lithographic plates. The dried powdered photo-responsive diazo compound is rubbed over and onto the surface of the silicone rubber to produce a photo-responsive diazo layer 13 which adheres to the surface of the silicone rubber. The excess diazo not adhering to the surface is removed by light brushing, air knife or the like. The sensitized plate thus prepared is exposed through a negative transparency 14 to radiation having a wave length of the proper magnitude to initiate the photo-response of the diazo layer. Generally, actinic radiation will be sufficient to initiate the photo-responsive reaction. However, radiation having a wave length outside of the range of actinic radiation may be employed when necessary. During the radiation procedure, those areas of the plate exposed to radiation become insoluble and oleophilic forming an image area 15 which adheres to the silicone rubber layer 6. Following the radiation or exposure procedure, the surface of the plate is washed with water to remove the unexposed water soluble diazo compound leaving bared surfaces 16 of ink repelling silicone rubber as the background. The washed plate is then dried and mounted on a printing press. The rotating ink rollers of the press are applied to the surface of the plate inking the oleophilic image areas but leaving the unimaged silicone rubber background areas clear.

In another embodiment of the present invention is illustrated by FIG. 3, the ink repellent silicone rubber is applied to the surface of a conventional pre-sensitized lithographic plate to provide in the non-imaged areas a silicone rubber surface which will not remove ink from ink rollers and, therefore, does not require wetting with a fountain solution. This embodiment results in the formation of a long run pre-sensitized plate that can be imaged by exposure through a positive transparency and can be made as follows. A flexible substrate such as an aluminum-base diazo-sensitized plate as disclosed in the Case and Jewett U.S. Pat. No. 2,714,066 or a paper-base sensitized plate as disclosed in the Brinnick et al U.S. Pat. No. 2,778,735 is prepared. The diazo-sensitized plate comprised of a substrate 20 and a diazo coating 21 is then coated with a layer 22 of silicone rubber as herein defined. The silicone rubber is applied by conventional coating methods, and if desired, can be further squeegeed or wiped down with a soft cloth to leave a film which after hardening may be as thin as 0.05 mils or even 0.02 mils. A thicker film, for example from 0.05 to 0.02 mils, can be left if desired. A very thin film may harden sufficiently in about half an hour, especially if the atmosphere is rather humid. But ordinarily, especially for thicker films, it is preferred to let the film age for about 24 hours before developing an image formed thereon. A latent image itself can be formed in the film any time after the film has become reasonably firm by exposure of the plate through a positive transparency 23. This exposure insolubilizes the underlying diazo compound in the exposed areas 24, that is the background or non-image area, but leaves the diazo compound unchanged and still soluble in the image area 26. The latent image so formed can then be developed at once, or if desired the development can be postponed for 24 hours or longer. Development is readily accomplished merely by swabbing the surface with a cotton pad wet with water containing a small amount of a wetting agent such as sodium lauryl sulfonate, alkyl phenyl ethers, polyethylene glycol, trimethyl nonyl ether of propylene glycol, polyalkylene glycol ethers and the like. The swabbing does not affect the background area 24 where the exposed diazo compound apparently acts to bond the silicone rubber to the underlying base; but in the imaged areas 26 the silicone rubber and the underlying still soluble diazo compound are removed by the swabbing, laying bare the surface of the original substrate. In those cases where the silicone rubber layer is unusually thick or has been aged for a considerable period, the swabbing liquid may be a mixture of equal parts of trichloroethane (sold as P & J cleaner) and xylene and about one-fourth part of ethylene glycol. The bared surface of the substrate in the image area 26 accepts ink from the rotating inking rollers and prints it either directly upon paper or upon an offset blanket which will transfer the print to paper. Normally the substrate image, when dry, will accept either oil-base ink or aqueous-base ink, depending upon which is applied first. In most cases, the layer of silicone rubber will be thin enough that the recesses left by its removal in the image area are so shallow that the plate can be considered to be a planographic plate. Of course, thicker layers of silicone rubber can be used, and in such cases the image areas 26 may be too deep to be inked by the usual inking roller. Deep image recesses may be filled with ink-receptive matter to make the image flush with the plate surface. For use when printing with greasy lithographic ink is contemplated the recess filler used should be oleophilic, e.g., a viscous polyvinyl acetate emulsion, asphaltum, lacquers or the like. When use of aqueous ink is contemplated, the recess filler should be hydrophilic, for example, a mixture of zinc-carboxymethylcellulose and clay, or the like.

In a still further embodiment of the present invention, as illustrated by FIG. 4, a long lasting plate that can be given a latent image by exposure through a negative transparency is made as follows. A flexible metal substrate 30 such as aluminum or zinc is coated with from 1 to 50 grams per square meter of diorganopolysiloxane composition to form silicone layer 31. Immediately after applying the diorganopolysiloxane layer 31 and while the layer is still tacky, a sheet of soft chemically etchable metallic foil 33 is pressed into intimate contact with the liquid layer. Representative chemically etchable metallic foils include zinc, copper and aluminum. The sandwich so formed is allowed to age for from 12 to 96 hours to permit the silicone rubber to cure or become solid, and to form an adhesive bond with the metallic foil 33. Thereafter, the exposed surface of the foil 33 is cleaned by brief immersion in a standard etching solution, washed and dried. Next the clean and dry surface is given a photopolymerizable photo-resist layer 34 and exposed through a negative transparency 36. The exposure hardens and insolubilizes the photopolymerizable material in the exposed areas 38 to form a latent image. Thereafter, the surface is swabbed with a photo-resist developer which removes all the unexposed photopolymerizable material in area 40 and leaves the underlying foil 33 bare, but does not remove the photopolymerized layer in the image area 38. Then the surface is again immersed in the same etching solution in which the foil 33 had previously been cleaned and allowed to remain there until all of the foil 33, except that covered by the photopolymer image, has been dissolved down to the underlying silicone rubber background 31. The plate is then thoroughly washed and dried. This plate, after the background had been etched away, has an image area of metal, still covered by the photopolymer resist, raised slightly above the silicone background, and so is not, strictly speaking, a planographic plate. However, the plate can be used in the same way, and on the same printing press, as the other plates having silicone rubber background areas as described above. In such use the rotating inking rollers and offset blanket will come in contact with the silicone rubber background. The silicone rubber background remains free of ink as in the previously discussed cases, and does not print on the offset blanket or paper.

Another embodiment of the present invention as illustrated by FIG. 5 is prepared as follows: a silicated aluminum plate 50 is sensitized with a conventional diazo compound, exposed and developed by swabbing with an aqueous emulsion of lacquer which removes unreacted diazo and leaves a layer of lacquer 51 on the exposed image areas 52. After washing, the entire surface of the plate is again swabbed with aqueous solution of a photo-responsive diazo compound such as the formaldehyde condensate of a paradiazodiphenyl amine salt or the like to form the layer 53. The plate is then allowed to dry, and thereafter coated with a layer of silicone rubber 54. The silicone layer is cured and the entire plate exposed to radiation of sufficient wave length to initiate the photo-responsive reaction of the diazo compound. By this treatment the diazo compound is insolubilized and its adherence to the silicone rubber layer is improved, and likewise the silicone rubber layer itself is further cured. Next, the plate is swabbed vigorously with a mixture of equal parts of 1,1,1-trichloroethane and xylene and one-fourth part of ethylene glycol which penetrates through the silicone layer 54 and loosens the lacquer layer 51 covering the image area 52. The lacquer and overlying silicone rubber come away from the image leaving the imaged area 52 slightly recessed. The plate thus prepared can be used in this condition or the recessed areas can be filled with oleophilic material such as viscous polyvinyl acetate emulsion. In the latter case the resulting plate has a level surface, with image areas of oleophilic polyvinyl acetate and ink-repellent background areas of a silicone rubber.

Other plates can be made by coating a metal or paper plate with a layer of silicone rubber, curing the silicone rubber at room temperature for several hours, and then using an engraver's tool to cut a pattern through the silicone to the underlying base. The pattern is then ink-receptive, but the silicone layer is not. This plate thus prepared can then be employed on a press or the pattern can be filled with an oleophilic substance before the plate is so employed.

EXAMPLE 1

A paper is prepared from paper stock which is composed of about equal amounts of long fibers and short fibers and contains from 6 to 8 percent mineral filler. The paper sized with rosin and alum and weighs about 52 pounds per ream (500 sheets - 25" .times. 38"). One side of the paper is base-coated with 10 pounds per ream dry weight of a coating comprised of clay (100 parts), casein (20 parts) and dimethylol urea (2 parts) and is then dried and calendered. The paper plate is then reverse-roll coated with 2 pounds dry weight per ream of a xylene dispersion of a diorganopolysiloxane composition comprised of a dimethylpolysiloxane, methylhydrogensiloxane and zinc octoate, and the resulting layer of diorganopolysiloxane is dried and cured for 40 seconds at 500.degree. F. The silicone rubber coated plate is then fed through a Xerox 914 copy machine. As a result of this procedure, a powder image previously electrostatically formed on a selenium-plated drum is transferred to the plate. This image is then heated to cause the powder particles to fuse to each other and to the surface of the plate. The plate thus prepared is then mounted on a rotary offset duplicator Addressograph Multigraph Corporation, Multilith No. 1,250) from which the molleton rollers (water fountain rollers) have been removed. The plate is merely clamped to the plate cylinder and while dry is inked with regular lithographic ink (Addressograph-Multigraph ink No. ML 36) by the inking roller and the image is printed on the offset blanket from which it was transferred to a paper sheet. Fifty copies having clean un-inked background areas are produced from this plate.

EXAMPLE 2

A paper substrate as prepared in Example 1 is air knife coated with 3 pounds per ream dry weight of a diorganopolysiloxane composition composed of dimethylpolysiloxane having silicon-bonded hydroxy groups, methylhydrogen polysiloxanes and dibutyl tin laurate. The diorganopolysiloxane composition is dispersed in toluene in an amount sufficient to provide a dispersion having about 10 percent by weight of solids. The coating layer is cured at 300.degree. F for about 5 minutes. This plate is then sensitized by rubbing the silicone rubber surface with a cotton pledget filled with powdered double chloride of zinc and the para-formaldehyde condensate of diazotized para-aminodiphenyl amine. Excess diazo powder is then carefully wiped off. The sensitized plate thus prepared is then exposed through a negative transparency to a 35 amp. double carbon arc at a distance of 36 inches for one minute. The partially exposed plate is then washed or developed with water to remove the diazo compound from the unexposed areas. The plate thus prepared was completely dried and clamped to the plate cylinder of a rotary offset duplicator as described in Example 1 and the plate inked and employed to produce over 50 copies. The copies thus produced were clean with no toning or inking in the background areas.

EXAMPLE 3

An aluminum based diazo sensitized plate is prepared by coating an aluminum plate with an aqueous solution of sodium silicate and thereafter coating the silicated surface with an aqueous 1 percent solution of the double salt of zinc and condensate of para-formaldehyde and para-diazo-diphenyl amine as described in U.S. Pat. No. 2,714,066. After the diazo coating has dried, a layer of the diorganopolysiloxane composition is applied by Mayer bar coater. The diorganopolysiloxane composition comprises dimethylpolysiloxane gums, silane oxime and titanium dioxide. The surface bearing the diorganopolysiloxane coating is wiped down with a soft cloth to leave a film which has a thickness of 0.05 mils after curing for about 12 hours at room temperature. The plate thus prepared is exposed through a positive transparency for 60 seconds to a 35 ampere double arc at a distance of 36 inches. Following the exposure, the surface of the exposed plate is swabbed with a water solution containing a small amount of Eastman Kodak's FOTOFLO, a wetting agent. This water removes the silicone layer and soluble diazo compound from the unexposed areas, laying bare the surface of the original substrate in these areas. Thereafter, the plate is dried, mounted on a rotary press as described in Example 1, inked and employed to produce 1,000 clean copies.

EXAMPLE 4

A 5 mil sheet of aluminum foil having a surface roughened by sand blasting is coated with a 0.2 mil layer of a diorganopolysiloxane comprised of hydroxyl end-blocked dimethylpolysiloxane and vinyltriacetoxy silane, said composition on curing forming an acetoxy end-block vinyl substituted dimethylpolysiloxane silicone rubber. Immediately thereafter while the diorganopolysiloxane layer is still liquid, a 3 mil sheet of soft copper foil is pressed into intimate contact with the aforesaid layer. The sandwich so formed is allowed to age for 72 hours. Following the aging period, the exposed surface of the copper is cleaned by immersing for two minutes in a standard etching solution consisting of the following:

100 milliliters of calcium chloride solution of 40.degree. - 41.degree. F Baume,

380 grams of zinc chloride,

285 milliliters of ferric chloride solution of 50.degree. -51.degree. F Baume, and

14 milliliters of 38 percent hydrochloric acid. Following the etching procedure, the copper surface is immediately washed and dried. The dry copper surface is then given a photo-resist layer of a photopolymerizable material containing polyvinyl einnamate polymers. The photo-resist layer is dried and the surface exposed through a negative transparency to the light from a 35 ampere double arc at a distance of 36 inches for 3 minutes. Following the exposure period, the surface of the plate is swabbed with developer which removes all of the unexposed photopolymerizable material and leaves the underlying copper bare but does not remove the photopolymerized layer in the image area. The surface of the plate is then immersed in the same etching solution in which the copper was previously cleaned and allowed to remain there until all the copper except that covered by the photopolymer image has been dissolved. The plate is then washed and dried. The plate thus prepared is then mounted on a rotary press as described in Example 1, coated with ink and used to print 10,000 copies.

EXAMPLE 5

A sand blasted aluminum plate is treated with sodium silicate, washed and dried, and thereafter sensitized by swabbing with an aqueous 2 percent solution of a zinc salt of the condensate of para-formaldehyde and para-diazodiphenyl amine. Following the coating procedure the plate is dried and the dried plate exposed through a negative transparency for 60 seconds to a 35 ampere double arc at a distance of 36 inches. The image so formed is developed by swabbing the surface of the plate with an emulsified colored nitrocellulose lacquer in an aqueous solution of gum arabic. This procedure removes the diazo compound from the unexposed or background area but does not remove the exposed image. In addition, the emulsion breaks sufficiently to permit the lacquer to adhere to and coat the surface of the image. The plate is then washed with water to remove all traces of the gum arabic from the surface of the plate without removing the lacquer from the image area. Following the removal of the gum arabic, the plate is again swabbed all over with an aqueous solution of the formaldehyde condensate of a para-diazodiphenyl amine salt and then allowed to dry. The dried plate is then roller coated with a diorganopolysiloxane composition comprised of an acetoxy end-blocked dimethylpolysiloxane and dibutyl tin diacetate in an amount sufficient to provide about 35 grams per square meter of the diorganopolysiloxane composition. This layer is allowed to air-cure for 30 minutes and then it is exposed over its entire surface to radiation from a 35 ampere double arc lamp at a distance of 24 inches for 3 minutes. By this treatment the diazo compound is insolubilized and its adherence to the silicone layer improved, and likewise the silicone layer itself is further cured. Next, the plate is rubbed with a mixture of equal parts of 1,1,1-trichloroethane and xylene and one-fourth part of ethylene glycol. This liquid penetrates through the silicone layer and loosens the lacquer layer covering the image and the rubbing removes the loosened silicone rubber leaving the image area slightly recessed. The depressions thus formed are filled with polyvinyl acetate emulsion and allowed to dry. The resulting plate has a level surface, with image areas of oleophilic polyvinyl acetate and ink repellent background areas of silicone rubber. The plate thus prepared is mounted on a lithographic press as described in Example 1 and used to print 1,500 copies.

The various diorganopolysiloxane compositions employed in the present invention are known in the art and are prepared in accordance with known methods. Representative acetoxy end-blocked diorganopolysiloxanes to be employed in the present invention, such as the dimethylpolysiloxanes, vinyl substituted dimethylpolysiloxanes, alkyl substituted dimethylpolysiloxanes, cyanoalkyl substituted dimethlypolysiloxanes and 3,3,3-trifluoropropyl and other haloalkyl substituted dimethylpolysiloxanes, are prepared in accordance with methods known to the skilled in the art as illustrated by the teachings of U.S. Pat. Nos. 3,035,016 and 3,077,465. Representative diorganopolysiloxane compositions comprised of dimethylpolysiloxanes having terminal silicon-bonded hydroxy groups, methyl hydrogen polysiloxane and dibutyl tin dilaurate or dibutyl tin diacetate are also well known in the art and are produced in accordance with known methods. A representative method of production is taught in U.S. Pat. No. 2,985,545. Similarly, the diorganopolysiloxane compositions comprised of diorganopolysiloxanes having terminal silicon-bonded hydroxy groups, an alkyl silicate and a metallic salt of an organic carboxylic acid are known in the art and are produced by known methods such as the procedures taught by U.S. Pat. No. 2,843,555.

The photo-responsive diazo compounds to be employed in the present invention are well known in the art. Representative diazo compounds are described in U.S. Pat. Nos. 2,714,066 and 2,778,735, and include 4-N-benzyl-N-ethyl)-amino-aniline, 4-(N-2,6-dichloro-benzyl)-amino-aniline, 4-(N-cyclohexyl)-amino-aniline, 4-amino-2,5,4'-tribromo-diphenylamine, 4-amino-2' , 4' , 6' -trichloro-diphenylamine, 4-amino-2-[N-(2,5-diethoxy-phenyl)-sulfamido] -diphenylamine, 4amino-3,6 -dimethoxy-diphenylamine-2' -carboxylic acid, 1-amino-2,5-di-n-propoxy-4' -methyl-diphenylsulfide, N-(2,6-dichlorobenzyl)-3-amino-carbazol, 4-(N-2,3,4,6-tetrachlorobenzyl)-amino-aniline, 4-(N-2,6-dichloro-benzyl-N-ethyl)-amino-2,5 -diethoxy-aniline and 4-amino-2,5,4' -triethoxy-diphenylether and their aldehyde condensates and the sulfonates of both.

The term conventional lithographic ink as employed in the present invention refers to the inks commonly employed by those skilled in the art and may be generally defined as being highly pigmented varnished of heat-bodied linseed oil or the equivalent and giving inkometer values from about 12-20 when measured at 90.degree. F and 400 r.p.m. The inkometer values are standard test values and the test is fully set forth in U.S. Pat. No. 2,101,322.

Claims

I claim:

1. A dry planographic printing plate comprising a base layer sufficiently strong to withstand the stresses normally encountered in a printing process, and at least two additional layers disposed in superimposed relation to each other and both overlying said base layer, one of said additional layers being a layer of silicone rubber material and another of said additional layers being capable of being removed in selected areas so as to define the boundaries of an image to be printed from said plate, said silicone rubber material being adapted in the absence of dampening to provide an ink repellent background for said image.

2. A dry printing plate comprising a base layer having sufficient strength to withstand the stresses normally produced by a printing process, a layer of silicone rubber material overlying said base layer, and a continuous chemically etchable metallic layer mounted on the outside surface of the silicone rubber layer and capable of being etched away in selected areas so as to define the boundaries of an image to be printed from said plate, said silicone rubber material being adapted in the absence of dampening to provide an ink repellent background for said image.

3. The printing plate of claim 1 wherein said second layer overlies said layer of silicone rubber material.

4. The printing plate of claim 1 wherein said second layer is between said layer of silicone rubber material and said base layer.

5. A dry planographic printing plate comprising a base layer and at least two additional layers disposed in superimposed relation to each other and both overlying said base layer, one of said additional layers being a layer of silicone rubber material, and another of said additional layers being light sensitive and capable of being removed in selected areas so as to define the boundaries of an image to be printed from said plate, said silicone rubber material being adapted in the absence of dampening to provide an ink repellent background for said image.

6. The printing plate of claim 5 wherein said light sensitive layer overlies said layer of silicone rubber material.

7. The printing plate of claim 5 wherein said light sensitive layer is between said layer of silicone rubber material and said base layer.

8. An imaged dry planographic printing plate, which accepts ink in the image area and prints therefrom, and repels ink in the non-image area, comprising a base layer, an ink-receptive image area, and a silicone rubber material overlying said base layer and providing the ink repellent non-image area.

9. A process for printing planographically in the absence of dampening with an imaged dry planographic printing plate which accepts ink in the image area and prints therefrom and which repels ink in the non-image area, which process comprises rolling the surface of the imaged dry planographic printing plate with ink in the absence of dampening whereby the ink is contacted with the image and the non-image areas of the plate, the ink being repelled in the non-image area by a silicone rubber material and the ink being accepted in the image area, and thereafter transferring ink accepted in the image area to an ink-receptive surface.