US3279366A - Aluminum photolithographic plate and method of imaging same - Google Patents

Description

Oct. 18, 1966 F. A. REGAN, J-R., ETAL 3,279,366

ALUMINUM PHOTOLITHOGRAPHIC PLATE AND METHOD OF IMAGING SAME Original Filed March 31, 1955 Fire. 1

LITH06RAPHIC PzArE GELAT/N COA TING WITH SILVER HAL/DE gas-5511557 0F flCETATE l0 ALUMINUM 5HEET H EXPOSED GEMT/N W LAYER CON THIN/N6 LEADACETATE LATENT IMAGE 0F SOD/UMSULF/DE SILVER HAL/DE ALUM- SHEET DEVELOPING AND FIXING BATH LATENT/MAGf 0F S/L v52 HAL/DE GELAT/AI COATING w/m EXPOSED SILVER HAl/DE 11v VEA/TORS BASES/1E Francis APgganyn Seaman A. Lmcoln EXPOSED PHOTO. NEG.

51 Donald E, ansorz %Q7z// M YM Clifys' United States Patent 8 Claims. c1. 101-149.2

This is a division of our copending application Ser. No. 498,192, filed March 31, 1955, and entitled Method of Imaging a Photolithographic Plate and Elements for use in the Preparation of Same.

This invention relates to the production of multiple copies by a lithographic duplicating process and it relates more particularly to the manufacture of a new and improved lithographic plate and to a new and improved process for producing the ink receptive, water repellent image on the lithographic surface of the plate.

Various methods are employed in the lithographic art for the formation of the ink receptive, water repellent image on a water receptive, ink repellent surface of a lithographic duplicating plate. To the present, these processes may be divided into two principal groups generally referred to as the direct image process and the indirect or photolithographic processes. In the direct process, an ink receptive, water repellent imaging material is applied directly onto the lithographic surface of the lithographic plate. For such purposes, the lithographic plate may be imaged by the use of a writing instrument for applying the oleophilic, water repellent imaging material onto the surface of the plate. Instead, the image may be formed on the plate by means of a typewriter or by a die, using a ribbon or a transfer sheet coated with an ink receptive, water repellent imaging material which is transferred by the impressions from the transfer sheet to the lithographic surface to form the image thereon.

The indirect or photolithographic p ocess is used for the reproduction of copies from an original. In general, a photographic negative is first produced of the original and then the negative is exposed in combination with a lithographic plate in which the lithographic surface has been presensitized with a material such as a resin-forming diazo compound or with a bichromate capable of tanning the colloid in combination therewith in the exposed areas whereby the exposed areas are converted to an ink receptive, water repellent surface upon exposure to light to form the image thereon. The light sensitve materials remaining in the unexposed portions of the plate, or the non-imaged portions must be removed, as by washing, before use can be made of the plate to produce copies.

The concepts described and claimed herein have application chiefly to the indirect process for the production of .an imaged lithographic plate and the invention will hereinafter be described with reference to the manufacture and use of such a photolithographic plate.

Photolithographic plates of the type heretofore produced have been constructed chiefly with a surface sensitized with a light sensitive material, such for example as a resin-forming diazo compound which is converted to an ink receptive, water repellent resinous material upon exposure to light. Such photolithographic plates formed with [light sensitive diazo compounds are subject to dark or thermal decomposition reactions which results in overall ink receptivity or scumming. As a result they have limited shelf life and it is necessary to prescribe an expiration period of relatively short time in which the plate must be used.

Aside from the limited shelf life inherent in plates of the type heretofore produced, the labor and equipment required for the preparation of a photolithographic plate to produce the image thereon from an original are excessive and relatively expensive.

The more recently developed xerographic process for producing an imaged lithographic plate from an original embodies fewer limitations than the diazo-sensitized photolithographic plates, especially from the standpoint of plate life and the character of the original, but the initial investment in equipment required is excessive and the methods for preparing the masters are tedious and involved.

It is an object of this invention to produce a new and improved lithographic plate and method for imaging same which is not subject to any of the deficiencies and disadvantages of the processes and products heretofore employed.

More specifically, it is an object of this invention to produce a new and improved lithographic plate and process for imaging same and it is a related object to produce a lithographic plate of the type described which can be fabricated in a simple and eflicient manner; which is produced of low cost and readily available materials; which is not light-sensitive and therefore is not limited in time of use after preparation; in which the process enjoys the desired degree of exposure latitude; in which the process has a broad range of spectral sensitivity; which does not require an initial investment of expensive equipment for use in imaging the plate; which can be imaged in a simple and eflicient manner from the original without an additional expenditure of time and labor; which has application chiefly as a postive working photolith-ographic plate; which may be used as a direct image plate, and which can be used to produce a large number of copies of good quality.

It is a further object of this invention to produce a lithographic plate and to provide a one-step photographic process for imaging same, and it is a related object to produce an imaged lithographic plate by a photo-reflex process.

These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawing in which:

FIGURE 1 is a perspective view, partially in section, of a photolithographic plate embodying features of this invention;

FIGURE 2 is a schematic elevational view illustrating the arrangement of parts in an initial step of the process;

FIGURE 3 is a perspective View, partially in section, of the element prepared by the step of FIGURE 2; and

FIGURE 4 is a schematic sectional elevational view illustrating a final step in the manufacture of the imaged lithographic plate.

In the Rott Patent No. 2,352,014, description is made of a single copy process wherein a photographic image of an original produced in a silver halide layer is caused to produce a reverse image on a copy sheet, provided the silver halide layer, after being exposed to light for the production of a master image and then vbeing impregnated with a developer to' develop the image, is pressed or squeezed in the presence of a fogging agent and a silver halide solvent onto the copy sheet while the layer is still imbibed with the developing liquid. That part of the silver halide in the layer which was not reduced during development after exposure to light and which in the ordinary photographic process would be fixed out of the fixing bath, will adhere to and enter the copy sheet surface by diffusion and will thus produce thereon a reversed image. In order .to render this image freely visible, the light sensitive layer containing the master image will nor mally be removed from the copy sheet.

In the Rott process, use may be made of the silver halide solvents contained in the usual photographic developers, such as sodium sulfite, sodium thiosulfate and the like. As fogging agents, use is made of substances capable of promoting the reduction of silver halides without requiring the action of light, such for example as colloidal silver, colloidal forms of sulphur, silver sulfides, hypophosphites, stannous chloride, and organic compounds which are capable of splitting off silver in the form of bivalent ions, such as thiosinamine. Such fogging agents or nucleating agents are preferably embodied in the copy sheet during manufacture thereof by subsequent impregnation.

It has now been found that when use is made of a nucleating agent for reduction of the silver halide, somewhat similar to the fogging agents of Rott, instead of producing a reversed image as a single copy on a receptive material or copy sheet, a reversed image of an oleophilic or water repellent image is formed which, when produced on a hydrophilic, water receptive lithographic surface, can be used to produce a large number of inked copies by conventional lithographic printing methods.

The reversed image of the oleophilic, water repellent or ink receptive imaging material is formed by diffusion on the lithographic surface as a reaction product when an alkali metal thiocyanate is present as an ingredient dissolved in the development solution.

It is desirable to make use of a plate having a nonporous, non-absorbent surface because the amount of complexed silver halide available for transfer from the photographic image on the exposed negative or the like is usually insuflicient to develop the desired image intensity on the surface of the lithographic plate when portions thereof are capable of being diffused inwardly into the interior of the plate.

Thus it is important to make use of a plate formed of metal such as zinc or aluminum in the form of a rigid plate, sheet stock or foil which has been treated on the printing surface for rendering the surface hydrophilic, as by brushing, silicating, anodizing, etching, and the like.

It has been found that the ink receptivity of the reversed image formed on the aluminum lithographic surface is markedly improved to produce inked copies of better quality when a soluble sulfide, such as sodium sulfide, potassium sulfide or ammonium sulfide is present as a coating on the surface of the lithographic plate.

Instead of sodium sulfide, use can be made of other soluble sulfides such as potassium sulfide and ammonium sulfide, as previously described, or water soluble compounds capable of releasing sulfide ions for reaction upon solution in the transfer medium.

By way of still further improvement, it has been found that the ink receptivity of the reversed image and the anchorage of the oleophilic water-insoluble image produced on the plate surface is increased by the presence of lead ions on the lithographic surface, preferably in the form of a soluble lead salt, such as lead acetate, or other soluble bivalent metal salts such as lead chloride, lead propionate, lead nitrate and similar salts of zinc, nickel, copper, cobalt and the like. Since the lead salts form insoluble compounds with the sulfides, it is preferred, when used, to apply the lead as a coating onto the lithographic plate separate and apart from the sulfide. The concentration of metal salts is not critical as long as sufficient lead ions are present in the coating to cause development of the desired oleophilic material upon diffusion of the complexed silver halide from the photographic image.

The following is a description of the preferred practice of this invention:

Example I.Manufacture of the lithographic plate For use in the practice of this invention, an aluminum sheet 10, the surface of which has been treated by brushing, silicating, anodizing, etching or the like to render the surface lithographic, is coated with a solution containing 30 parts by weight sodium sulfide in parts by weight of water. Application of the coating is made by any conventional process, such as by spray coating, roller coating, brush coating and the like but it is preferred to coat the treated aluminum surfaces by means of a pair of squeegee rolls mounted to engage the opposite sides of continuous strips of aluminum advanced in face to face relation from a pair of feed rolls.

The coating composition is applied in quantities sufficient to completely coat the surface of the aluminum to provide at least a monomolecular layer 11. The amount applied to the surface of the plate is such that the coating air dries within a very short time, such for example as in about 10-30 seconds, without the necessity for using elevated temperatures,

Following the first coating, the aluminum surface is subsequently coated with a 10 percent solution of lead acetate in water. Application is made in substantially the same manner as the first coating to provide a thin layer 12 following which the sheet is dried, as by air drying, in a relatively short time such as from 10-30 seconds.

An aluminum sheet treated in the manner described is not sensitive to light and thus may be manufactured in mass production processes in unlimited amounts and may be sheeted and packaged for subsequent use in the manufacture of imaged photolithographic plates without limi- .tations as to the conditions of storage or the length of time intervening between manufacture and use.

Example lI.--Preparati0n of the imaged master Description will now be made of the use of the lithographic plate of Example I in the preparation of an imaged master by print-through contact exposure from an original 14. First a photo-negative 15 containing a light sensitive silver halide in a gelatin emulsion or the like hydrophilic colloid coating 16 on a suitable base sheet such as paper or plastic film stock is exposed to an original by reflex or by print-through contact or by projection printing to form a latent image in the silver halide gelatin emulsion. It is preferred in this process to make use of a photographic negative which is transparent or translucent in order to give maximum latitude of the original. The photographic negative does not have to be flexible and the thickness and dimension of the negative do not con stitute important factors in the process. By way of example, a suitable photographic negative is marketed by AGFA under the trade name Copyrapid.

The exposed photographic negative is developed in a solution containing the normal developing components plus a material which is a solvent for the silver halide such as in a typical monobath developer including a developer and fixer such as are ordinarily employed in photographic practice, a typical composition of which may be formulated of 30 grams hydroquinone, 30 grams sodium hydroxide, 40 grams sodium sulfite, 10 grams sodium thiosulfate, 1.5 grams benzotriazole, with water sufficient to make up one liter. This development is carried out under such conditions that the photographic negative wet with the solution and the photolithographic surface wet with the solution are brought into surface contact with each other, as illustrated in FIGURE 4, so that the soluble silver complex that is formed of the silver halide in the photographic image is caused to diffuse to the corresponding areas of the lithographic surface. Usually; contact under the conditions described for from /22 minutes is suflicient to effect the desired transfer for the development of the reversed, oleophilic, water-insolw ble image on the lithographic plate.

The. lithographic surface containing the nucleating agent in combination with sodium sulfide and/ or lead acetate promotes the reduction of the silver halide complex without the action of light to produce an oleophilic, water-insoluble reaction product which is transferred or forms on the surface of the lithographic plate. The oleophilic reaction product formed in the areas corresponding to the original becomes strongly anchored to the lithographic surface to form the image which can now be used to produce a large number of copies by lithographic duplicating technique. The printing plate may be lacquered by known techniques or printed without lacquer, as preferred, on an offset lithographic press to produce exact and clear copies of the original.

In the presence of lead acetate or other soluble bivalent metal salts of the type described, with or without a soluble sulfide, almost any of the fogging agents of the type described in the Rott patent which will precipitate soluble silver may be used to produce an ink receptive, water, repellent, reversed image on the aluminum lithographic surface for use in the production of multiple copies.

The following compositions may be employed in lieu of the lead acetate solution applied as a second coating on the surface of the lithographic plate:

Example lII.5-15 percent by weight barium chloride in water Example lV.-520 percent by weight copper in water Instead of making use of a photo-negative, it has been found that the gelatin coating sensitized with the silver halide may be applied as a coating directly onto the surface of the aluminum lithographic plate which has previously been coated with the desired materials for reaction to produce a desirable silver compound with the silver salide. After exposure, the silver halide in the unexposed areas corresponding to the image in the original is caused to diffuse to the coated surface of the lithographic plate during immersion in the developer for the exposed silver halide in which a suitable solvent for the unexposed silver halide complex is present to enable diffusion.

Transfer of the silver halide in the processes described has been found to cause adhesion of the lead salts and the formed reaction product with the silver salts to the aluminum or other base of the lithographic plate. Upon formation of the water-insoluble, oleophilic image as a reaction product, the gelatin is removed from the surface with warm water.

By way of further modification, film forming agents such as water soluble, hydrophilic colloids including gelatin, casein, polyvinyl alcohol, the alginates and the like, may be formulated in small amounts in the initial coating composition for use as a film former adhesive to anchor the materials to the lithographic surface.

As previously indicated, the lithographic plate formed in accordance with the practice of this invention can, if desired, be used as a direct image plate wherein the imaging material applied to the surface of the plate as a writing fluid or as a composition transferred by impact of a typewriter or die, contains a silver halide in solution capable of reaction with thiocyanate or other reactive materials described on the plate surface to form the described water-insoluble, oleophilic, reaction product.

In sheeting, the plate may be formed to size with suitable openings in the leading edges for attachment to the hooks provided on the plate cylinder of a lithographic press, and the plates may also be formed with serrated trailing edges for engagement by the clamping means on the plate cylinder.

It will be understood that the concepts of this invention are not dependent on the concentrations of the various materials in the coating composition so long as a uniform coating can be applied to the surface of the plate for deposition of a thin layer of the essential ingredients thereon. It would be undesirable to make use of coating compositions having high concentrations of the salts or other materials such as in excess of 30 percent by weight, since such large amounts are unnecessary and such coating compositions might render the product and process uneconomical.

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

We claim:

'1. A lithographic duplicating master consisting of an aluminum base sheet having a water receptive, ink repellent, hydrophilic lithographic surface containing nuclei for precipitation of silver from a soluble silver complex and separate coatings on the aluminum lithographic surface in which one of the coatings contains a water soluble salt of a bivalent metal and the other coating contains a water soluble sulfide.

2. A lithographic duplicating master consisting of an aluminum base sheet having a water receptive, ink repellent, hydrophilic lithographic surface containing nuclei for precipitation of silver from a soluble silver complex and a coat-ing on the hydrophilic lithographic surface containing a water soluble sulfide and a second coating over the sulfide containing a salt of a bivalent met-a1.

3. A lithographic duplicating master consisting of an aluminum base sheet having a water receptive, ink repellent, hydrophilic lithographic surface containing nuclei for precipitation of silver from a soluble silver complex and a coating on the hydrophilic lithographic surface containing a water soluble sulfide and a second coating over the sulfide containing a salt of a bivalent metal selected from the group consisting of lead, zinc, nickel, copper and cobalt.

4. A lithographic duplicating master consisting of an aluminum base sheet having a water receptive, ink repellen-t, hydrophilic lithographic surface containing nuclei for precipitation of silver from a soluble silver complex, a first coating on the hydrophilic lithographic surface containing a salt of a bivalent metal selected from the group consist-ing of lead, zinc, nickel, copper and cobalt, and a second coating containing a water soluble sulfide.

5. A multiple copy process comprising the steps of applying an aqueous alkaline solution of a silver halide developer and a silver halide solvent to a photo-exposed silver halide stratum and a superposed aluminum base sheet having a water receptive, ink repellent, hydrophilic lithographic surface containing nuclei for precipitation of silver from a water soluble silver complex, reducing the exposed silver halide in the silver halide stratum to silver, forming from unreduced silver in the silver halide stratum a water soluble silver complex, diffusing the complex to the lithographic surface of the aluminum base sheet, producing from the complex in conjunction with the nuclei a silver image which is ink receptive and water repellent, stripping the silver halide stratum from the aluminum base sheet, wetting the aluminum base sheet with an aqueous medium to wet out the water receptive, ink repellent, hydrophilic non-imaged portions of the aluminum base sheet, coating the aluminum base sheet with an ink which preferably wets out the silver imaged portions, and pressing the ink surface onto .a copy member for the transfer of the ink image thereto.

6. The process as claimed in claim 5 in which the water receptive, ink repellent, hydrophilic, lithographic surface of the aluminum base sheet has separate coatings one of which contains a water soluble sulfide and the other of which contains a water soluble salt of a polyvalent metal.

7. The process as claimed in claim 6 in which the water soluble sulfide constitutes a first coat on the surface of the aluminum base sheet and the water soluble salt of a polyvalent metal comprises the second coat.

8. The process as claimed in claim '6 in which the water soluble salt of a polyvalen-t metal constitutes a first coat on the surface of the aluminum base sheet and the water soluble sulfide comprises 'the second coat.

References Cited by the Examiner UNITED STATES PATENTS 5 OTHER REFERENCES 9/1896 Strecker 101-4492 Tritt'on: Pen-rose Annual, 1939, pp. 107-111. 5/1939 Webb 101-1493 10/1942 Carlson 961 6/1944 Rim m 96 29 NORMAN G. TORCHIN, Primary Exammer. 12/1954 Land 9629 10 D. LEVY, Assistant Examiner.

8 FOREIGN PATENTS 731,997 12/ 1931 France. 3,186,842 6/1965 Great Britain.

Claims (1)

1. A LITHOGRAPHIC DUPLICATING MASTER CONSISTING OF AN ALUMINUM BASE SHEET HAVING A WATER RECEPTIVE, INK REPELLENT, HYDROPHILIC LITHOGRAPHIC SURFACE CONTAINING NUCLEI FOR PRECIPITATION OF SILVER FROM A SOLUBLE SILVER COMPLEX AND SEPARATE COATINGS ON THE ALUMINUM LITHOGRAPHIC SURFACE IN WHICH ONE OF THE COATINGS CONTAINS A WATER SOLUBLE SALT OF A BIVALENT METAL AND THE OTHER COATING CONTAINS A WATER SOLUBLE SULFIDE.

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