Offset Master For Imaging By Diffusion Transfer With Nucleating Agent, Cadium Salt And A Salt Of Zirconium, Thorium Or Titanium

Abstract

The preparation of an offset master for imaging to provide an oleophilic ink receptive image by diffusion transfer from an exposed silver halide negative in which the offset master has a surface which is water insoluble, water receptive, hydrophilic and lithographic and in which the lithographic surface is provided with one or more coatings providing the combination of a nucleating agent, a water soluble salt of cadmium and a water soluble salt of a metal selected from the group consisting of zirconium, thorium and titanium and in which the cadmium salt may be placed in whole or in part with an antioxidant.

Description

This invention relates to the art of offset or lithographic duplication and more particularly to a new and improved offset master and method for the preparation of same.

Offset masters for offset copy work are generally of the direct image type wherein the hydrophilic lithographic surface of the master is imaged directly by the application of an oleophilic ink receptive imaging material, as by inscribing with a crayon or ink, or by transfer from a carbon sheet in response to compression or impact by stylus, typewriter key, die impression or the like. When mounted on a lithographic press and wet with an oleophilic ink composition and an aqueous repellent, the nonimaged portions of the master accept the aqueous repellent while the ink composition is taken up by the oleophilic ink receptive imaged portions of the master for subsequent transfer either directly to copy sheets brought into surface contact with the inked master or indirectly to an offset blanket from which the image is transferred to copy sheets.

When it is desirable to prepare an offset master imaged from an original, it has been necessary to make use of an indirect offset master, more often referred to as a photolithographic master. A master of the type described has been produced wherein the hydrophilic lithographic surface is overcoated with a water soluble, resin forming, light sensitive diazo compound in which a negative transparency is first formed of the original and then the diazo light sensitive coating is exposed to the developed negative transparency to resinify the diazo compound in the exposed areas while the portions of the light sensitive diazo coating in the unexposed areas are removed by washing to produce an imaged photolithographic plate. Others of the photolithographic masters are somewhat similar in construction in that the master sheet is presensitized with a light sensitive material that is convertible to an ink receptive imaging material upon exposure to light. Such presensitized photolithographic masters are subject to a number of deficiencies including high cost, short shelf life, the need to make use of specialized equipment and materials, and the need to prepare a negative transparency by conventional photographic technique.

More recently lithographic or offset masters capable of being imaged by diffusion transfer technique from an exposed but underdeveloped silver halide negative have been produced in which the hydrophilic, lithographic surface is provided with a nucleating or fogging agent for reducing silver halide to an ink receptive, water repellent silver image whereby, when the master sheet is brought into contact with the exposed silver halide negative wet with a silver halide solvent and developer, the silver halide in the unexposed portions of the negative transfer by diffusion to the surface of the master where the silver halide or complex formed thereof is reduced to a silver, ink receptive, water repellent imaging material on the hydrophilic, water receptive lithographic surface to produce the master having an image corresponding to the original.

The diffusion transfer reversal technique makes use of equipment and materials which are of low cost and which have heretofore found widespread use in single copy diffusion transfer reversal processes commonly employed in the field. The diffusion transfer process also eliminates the need for the preparation of a negative transparency and the exposure of the negative transparency to a presensitized master is also completely eliminated.

To the present, the diffusion transfer reversal process for preparation of an imaged lithographic master from an original has been limited to use of a master sheet formed of a metal base such as aluminum, having its surface treated as by silicating, brushing, anodizing, or the like, to render the surface water receptive, hydrophilic and lithographic. It is desirable to expand the lithographic process to enable use of lower cost coated paper lithographic masters which can be imaged by diffusion transfer technique and it is also desirable to provide means for improving the definition of the image formed on the lithographic surface as by providing a desired differential between the hydrophilic, water receptivity of the lithographic surface and the ink receptivity and water repellency of the image that is formed thereon by the deposited silver and it is a related object of the invention to provide a lithographic master embodying such improvements and to provide a method for producing same.

Another object of this invention is to produce and to provide a method for producing an offset or lithographic master which can be fabricated of a paper or film base as well as of an amphoteric metal such as aluminum, which can be imaged directly or indirectly by diffusion transfer from an exposed silver halide negative or by direct application of silver halide to form the image on the lithographic surface, which provides a desirable balance between the hydrophilic nonimaged portion and the oleophilic imaged portion of the master, which need not be presensitized and therefore is not sensitive to light, and which is capable of use to produce a large number of copies of good quality by conventional lithographic duplicating technique.

These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, embodiments of the invention are shown in the accompanying drawings, in which:

FIG. 1 is a perspective view partially in section of a lithographic master prepared in accordance with the practice of this invention;

FIG. 2 is a sectional elevational view of a modification in a lithographic master prepared in accordance with the practice of this invention;

FIG. 3 is a sectional elevational view showing the arrangement of elements including the master shown in FIG. 1 and an exposed silver halide negative in position to form the image by diffusion transfer on the lithographic surface;

FIG. 4 is a perspective view partially in section of the imaged master produced with the master of FIG. 1; and

FIG. 5 is a perspective view partially in section of the master of FIG. 1 having a protective plastic film.

The offset or lithographic master embodying the features of this invention comprises a flexible base sheet 10 having a water insoluble, water receptive, ink repellent, lithographic surface 12 which is overcoated with one or more coatings 14 containing a silver halide fogging or nucleating agent, a zirconium salt and a cadmium salt as the essential components, and desirably though not essentially, a removable protective film 16 of plastic material covering the coated surface.

As the base sheet 10, use can be made of a foil of an amphoteric metal, such as aluminum, zinc or copper, in which the surface of the metal such as aluminum is rendered hydrophilic and lithographic by treatment such as brushing, anodizing, or preferably by silicating with a soluble silicate solution. Instead, use can be made of a paper base sheet 10 which is resinous impregnated or treated with a resinous material for high wet strength and which is provided with a continuous water insolubilized, water receptive, ink repellent, hydrophilic lithographic coating 12 formulated of a hydrophilic colloid of resin as a binder and a filler such as zinc oxide, satin white, clay and the like. Suitable binders comprise casein, starch, carboxymethylcellulose, polyacrylic acid, polyvinyl acetate, alginates, polyvinylpyrrolidone, and polyvinyl alcohol, reference being made to the following patents for illustrations of coated paper lithographic plates formulated of the above materials, namely: Worthem U.S. Pat. No. 2,534,650 (casein); Van Dusen U.S. Pat. No. 2,542,784 (carboxymethylcellulose); Ensink U.S. Pat. No. 2,806,424 (alignates); Beatty et al. U.S. Pat. No. 2,760,431 (zinc polyacrylate); Toland U.S. Pat. No. 2,230,982 (polyvinyl alcohol).

The base sheet is formed with openings 18 at one end for use in mounting the master onto the plate cylinder of a conventional planographic printing press for use in the production of multiple copies. Instead of openings for mounting on the press, other means on the end portion of the master may be provided for clamping the master onto the plate cylinder.

As the nucleating agent, it is preferred to make use of a stannous halide, such as stannous chloride, stannous bromide, stannous fluoride and the like. Though less desirable in the combination described, use can be made of other silver halide nucleating agents, sometimes referred to as fogging agents, as described in U.S. Pat. No. 2,352,014 and including colloidal silver and the like.

The zirconium salt comprises a water soluble salt of zirconium such as zirconyl methylate, zirconyl acetate, zirconyl propionate, zirconyl chloride, zirconyl nitrate, and other zirconyl halides and the like. While less desirable than the zirconyl salts and while not equivalent thereto in the described system, the zirconium salts can be replaced in whole or in part by the corresponding water soluble salts of thorium or titanium.

As the cadmium salt, use can be made of a water soluble salt of cadmium such as an organo cadmium salt represented by cadmium acetate or an inorganic salt such as cadmium chloride, cadmium bromide, cadmium nitrate, or other cadmium halide and the like. The cadmium salt can be replaced by an antioxidant but when use is made of an antioxidant it is preferred to make use of such antioxidant in combination with the cadmium salt. Representative of the antioxidants which may be employed are: ##SPC1##

The materials are formulated into a coating composition in the ratio of 1 part by weight stannous salt per 1.0 to 8 parts by weight of the zirconium salt and 0.01 to 0.5 parts by weight of the cadmium salt, and preferably in an amount within the range of 1 part by weight of the stannous salt to 1.7 to 3.5 parts by weight of the zirconium salt and 0.02 to 0.2 parts by weight of the cadmium salt. The materials can be formulated into a coating composition in which the materials are present in an amount to provide a solids content of 1 to 15 percent by weight and preferably 2 to 8 percent by weight. The composition is applied in coating weights within the range of 0.1 to 4 grams per square meter, and preferably in an amount within the range of 0.5 to 3 grams solids per square meter.

Instead of applying the materials from a single coating composition, the three essential components can be applied in corresponding amounts in separate coatings to provide one coating 20 containing the cadmium salt, with or without an antioxidant additive, and the other coating 22 containing the zirconium, thorium or titanium salt, and a third coating containing the fogging or nucleating agent, or the materials may be formulated into two coating compositions in which the components are present in the various combinations.

Application onto the lithographic surface can be made by conventional coating processes, such as by spray coating, roller coating, flow coating and the like, followed by air drying or drying at elevated temperature, such as up to 200.degree. F.

The following are examples of compositions which may be applied as coatings onto the lithographic surface in the preparation of diffusion transfer offset masters embodying the features of this invention: ##SPC2## ##SPC3##

An aluminum base sheet 10 having a silicated water receptive, lithograph surface 12, prepared in accordance with the teachings of the Jewett et al. U.S. Pat. No. 2,714,066, is roller coated with the composition of example 1 to provide a coating weight of about 0.75 grams per square meter. The applied coating 14 is either air dried or drying can be accelerated by heating to an elevated temperature of about 200.degree. F. to produce the finished master.

In the preparation of a coated paper lithographic plate embodying the features of this invention, use is made of a coated paper direct image plate formed of high wet strength paper base sheet 10 having a lithographic coating 12 provided thereon as described in the Worthem U.S. Pat. No. 2,534,650, or the Van Dusen U.S. Pat. No. 2,542,784, or the Ensink U.S. Pat. No. 2,806,424, or the Beatty et al. U.S. Pat. No. 2,760,431. The lithographic surface of the coated paper base sheet is over coated with a composition of one of the examples 1 to 5 applied to provide an overall coating having a coating weight of 0.5 to 3.0 grams per square meter. The applied coating is dried at elevated temperature within the range of 100.degree.--200.degree. F.

In the use of a plural coating process of example 6, part A is applied first onto the lithographic surface and then dried, after which part B is applied and dried to provide the plural coatings 20 and 22.

The shelf life of the masters prepared in accordance with the practice of this invention can be greatly extended and improved when the coating or coatings, applied in accordance with the practice of this invention, is covered with a removable film 16 of plastic material, such as a film of polystyrene, Teflon, polyvinylidene chloride, polyvinyl chloride, chlorinated rubber and the like.

More than one coating of the composition embodying the features of this invention can be applied onto the lithographic surface. Such plural coatings will enhance the protective features of one coating for another to resist oxidation and deterioration. In such event, the need for a protective film 16 is greatly minimized.

In use of an offset master prepared in accordance with the practice of this invention, use is made of a negative 30 in the form of a base sheet 32 having a light sensitive, silver halide gelatin coating 34. Representative of suitable negatives are Gevaert GS negative (Gevaert Photo Production of Antwerp, Belgium); Oricopy (Oriental Photocopy Company, Tokyo, Japan), or Anken Photo Rapid negative, of the Anken Chemical Company of the United States.

The negative 30 is exposed to the original in a conventional photographic exposure apparatus. The exposed negative is then brought into pressure contact with the coated surface of the master sheet after one or both of the surfaces have been wet with a monobath developer, as represented by the following example: ##SPC4##

The sheets can be processed through an A, B. Dick 110 Photocopier filled with the monobath solution. In operation, the monobath operates to form a soluble complex of the silver halide in the unexposed portions of the negative for transfer of the complex of silver halide by diffusion to the coated surface of the master where the silver halide is nucleated to deposit dense masses of silver 36 concentrated at the surface of the master to form an ink receptive, highly hydrophobic image 38 on the lithographic hydrophilic surface.

The formed silver image remains strongly bonded to the lithographic surface. The imaged plate is wet with a conventional fixer or conditioner, such as the CT offset fixer of Eastman Kodak or - 84-4966 A. B. Dick Photoplax Conditioner, which operates to make the nonimaged areas hydrophilic and fix the image onto the master. Thereafter the imaged master can be mounted on the plate cylinder of a conventional lithographic press and sequentially wet with aqueous repellent and oleophilic ink whereby the repellent wets out the nonimaged portions of the plate while the ink wets out the imaged portions of the plate thereby to enable production of thousands of copies of good quality.

It will be understood that changes may be made in the details of formulation, method of application and use without departing from the spirit of the invention, especially as defined in the following claims.

Claims

I claim:

1. An offset master for imaging to provide an oleophilic ink receptive image by diffusion transfer from an exposed silver halide negative comprising a base sheet having a water insoluble, water receptive, hydrophilic, lithographic surface, said master having on the lithographic surface the combination of a nucleating agent for silver halide a water soluble salt of cadmium as a component separate and apart from the nucleating agent and present in an amount within the range of 0.01 to 0.5 parts by weight of the cadmium salt to 1 part by weight of the nucleating agent, and a water soluble salt of a metal selected from the group consisting of zirconium, thorium and titanium as a component separate and apart from the nucleating agent and present in an amount within the range of 1 to 8 parts by weight of the metal salt to 1 part by weight of the nucleating agent.

2. An offset master as claimed in claim 1 in which the nucleating agent comprises a stannous halide.

3. An offset master as claimed in claim 2 in which the stannous halide, the zirconium salt and the cadmium salt are present in the same coating.

4. An offset master as claimed in claim 2 in which the stannous halide, zirconium salt and cadmium salt are present in separate coatings.

5. An offset master as claimed in claim 2 in which the salts are present in the ratio of 1 part by weight of the stannous salt to 1.7 to 3.5 parts by weight of zirconium salt and 0.02 to 0.2 parts by weight of cadmium salt.

6. An offset master as claimed in claim 2 in which the salts are present on the lithographic surface in a coating weight within the range of 0.1 to 4 grams per square meter.

7. An offset master as claimed in claim 2 in which the salts are present on the lithographic surface in a coating weight of 0.5 to 3 grams per square meter.

8. An offset master as claimed in claim 1 which includes a film of plastic material as a cover over the coated lithographic surface.