US3402045A - Lithogaphic printing plate - Google Patents

Description

p 1963 R. N. WOODWARD 3,402,045

LITHOGRAPHI C PR INTING PLATE Filed July 27, 1964 I4 I4 11 g EMULSION 1o r-SUPPORT F G I 14 I4 J I! EMULSION l0 SUPPORT UNTANNED COLLOID IO WASHED OFF SUPPORT ROBERT N WOODWARD INVENTOR.

BY fim/m AT TORNEY$ United States Patent 3,402,045 LITHOGRAPHIC PRINTING PLATE Robert N. Woodward, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, J. .Y., a corporation of New Jersey Filed July 27, 1964, Ser. No. 385,364 19 Claims. (CI. 9633) ABSTRACT OF THE DISCLOSURE A lithographic printing plate comprises a support having a hydrophobic surface which may be a polymeric material such as polyethylene, polypropylene, cellulose acetate, polyester, etc., and having thereon an unhardened light sensitive silver halide emulsion containing a water soluble substituted hydroquinone silver halide developing agent such as bromohydroquinone, chlorohydroquinone, toluhydroquinone, morpholinemethyl hydroquinone, etc., which forms hydrophilic areas upon development.

This invention is concerned with lithographic plates, more articularly lithographic plates utilizing a hydrophobic surface having thereon hyd'rophilic image areas.

Various methods of making lithographic plates are known in which the support has a hydrophilic surface, wherein the image areas are hydrophobic. For instance, in the colloid transfer system, a soft gelatin image is transferred from a moist developed silver halide emulsion to a hydrophilic support. In other systems, light sensitive compounds such as diazo resins are employed which become hardened on exposure to light, so that the unexposed areas can be removed by washing. In these systems the support is hydrophilic whereas the image is either hydrophobic or is rendered hydrophobic by lacquering or some other treatment.

It has also been desirable to have a projection speed emulsion for use in the preparation of lithographic plates which could be used for printing a positive image. The customary direct positive emulsions employing the Herschel effect to obtain a positive image from direct exposure are relatively slow, so that when higher speed is required, a negative is often made and the positive printing plate prepared from this negative.

An alternative method of preparing a plate for making a positive impression has been to employ a more complex photographic element as described in US. application Ser. No. 861,125, filed Dec. 21, 1959.

It has been desirable to prepare a plate which could employ a relatively high speed emulsion and which would result in a simple high speed direct positive printing plate.

I have found a method of using a silver halide emulsion on a hydrophobic support to provide a lithographic plate having a hydrophilic image thereon, which can be used for making right reading positive impressions.

One object of this invention is to provide a lithographic reproduction system utilizing plates with hydrophobic surfaces. An additional object is to provide a plate capable of producing right reading negative images instead of the normal positive right reading images. A further object is to provide a silver halide emulsion which, when developed, produces a hydrophilic image with respect to a hydrophobic base. A still further object is to provide a method of making a lithographic plate having a hydrophobic base and hydrophilic image areas. Additional objects will be apparent from the following disclosure.

The above objects are attained by employing a hydrophobic support which is receptive to greasy printing inks. Suitable organic polymeric material may be coated on a base such as paper, and the like. Of course, the support can be composed solely of the polymeric material, or a 3,402,045 Patented Sept. 17, 1968 suitable laminate, as long as the surface is oleophilic. The support may be pigmented or may be transparent to provide for exposure through the support.

The hydrophobic surface is treated to obtain adhesion to a silver halide emulsion by methods known for improving the adhesion of hyydrophobic materials such as electron bombardment, flame treating, oxidation with sulfuric acid-dichromate solution, treatment with chlorine gas, hydrogen peroxide, nitric acid, etc.

Over the polymeric hydrophobic surface is coated a silver halide emulsion. The light sensitive silver halide emulsion is preferably silver chloride or silver chlorobromide but may be any of those known in the art, such as silver bromide, silver iodide, silver bromoiodide and silver chlorobromoiodide. The emulsion may contain the water soluble substituted hydroquinone tanning developing agent in an amount of 2050 g./Ag mole which resuits in forming a hydrophilic image upon development, such as bromohydroquinone, chlorohydroquinone, toluhydroquinone, morpholinomethyl, hydroquinone, etc. however, if the emulsion does not contain the developing agent, it may be developed in a bath containing as the developing agent, a water soluble substituted hydroquinone such as bromohydroquinone, chlorohydroquinone, toluhydroquinone, morpholinomethyl hydroquinone, etc.

To increase sharpness it may be desirable to include an antihalation pigment or dye in the emulsion. Typical dyes and pigments used in antihalation layers may be used provided they are inert to the emulsion and do not affect the tannning of the emulsion. In a preferred embodiment, a carbon pigment is used. A useful amount of antihalation dye or pigment is 20-50 g./ silver mole.

It will be understood that the emulsion can be sensitized chemically, spectrally, etc., as is well known. It can be coated using methods known in the art, but must be substantially unhardened so that the unexposed and untanned areas can be washed off after development with the tanning type silver halide emulsion.

Although gelatin is the preferred embodiment for the colloid in which the silver halide is dispersed, it will be appreciated that other colloid materials may be used providing the silver halide carrying colloid is alkali permeable and can be hardened with a silver halide hardening type developer. The coverage of the silver halide emulsion is not critical and can be varied depending upon the use intended. A useful range is about to 800 milligrams per square foot of gelatin preferably 100 to 400 and about 50 to 200 milligrams per square foot of silver as silver halide, preferably 50 to 125.

Unhardened direct positive emulsions of the type described by P. J. Hillson in US. Patent 3,062,651 may be utilized to obtain direct positive images.

If the developing agent is incorporated in the silver halide emulsion or in a contiguous layer, the development is attained by using an alkaline developer.

Typical activator baths for the photographic emulsion containing the developing agent comprise, for example, an equeous solution of an alkaline solution, such as, sodium carbonate, sodium hydroxide, potassium carbonate, potassium hydroxide, etc. Suitable baths can comprise, for example, an aqueous solution containing about 1% sodium hydroxide.

Typical of the activator solutions which can be used in my process are those disclosed in U.S. Patents 2,596,754, 2,596,756, 2,725,298, 2,739,890, 2,763,553, 2,835,575, 2,852,371 and 2,865,745.

It will be appreciated that any of the known hydroquinone compounds which have alkali splittable groups thereon to stabilize the hydroquinone during storage, but which cleave to form a water soluble substituted hydroquinone such as bromohydroquinone, chlorohydroquinone, toluhydroquinone, morpholinomethyl hydroquinone, etc. may be incorporated in the emulsion. These compounds may be used in whole or in part to replace the water soluble substituted hydroquinone incorporated in the silver halide emulsion or in a contiguous layer.

It will also be appreciated than an auxiliary developing agent can be used in an amount of -20% of the substituted hydroquinone along with the substituted hydroquinone developing agent in order to improve the speed without affecting the operation of my invention.

Typical auxiliary agents include 3-pyrazolidone developing agents known in the art as well as Elon (N-methylp-aminophenol sulfate), and the like. Useful axuiliary agents are lphenyl-3-pyrazolidone and 1-phenyl-4,4-dimethyl-3- pyrazolidone.

Suitable hydrophobic surfaces comprise such materials as polyethylene, polystryrene, cellulose esters, such as cellulose acetate, polyesters, polytetrafluoroethylene, polystyrene-butadiene, etc.

Photographic developing out silver halide emulsions in this invention can also contain such addenda as chemical sensitizers, speed increasing compounds, reducing agents, sensitizing dyes, etc., which are known to those skilled in the art. They may be blue sensitive, orthochromatic, panchromatic, infrared sensitive, etc.

By substantially unhardened colloi is meant colloid which is not harder than would be the case of gelatin containing 0.25 ounce of formaldehyde (40% diluted 1:3 with water); or 0.7 gram dry formaldehyde per pound when freshly coated; or 0.1 ounce of the solution per pound for a sample aged three to six months. It will also be appreciated that the resistant image can be treated with hardeners or other known materials in order to make the image more resistant to abrasion or the like when used for printing.

The drawing shows a preferred embodiment of my invention.

FIG. 1 discloses a support having thereon an exposed silver halide photographic emulsion 11 showing a latent image 14.

FIG. 2 shows the same photographic element of FIG. 1 after the development with a tanning silver halide developer which renders the exposed areas water insoluble and hydrophilic.

FIG. 3 shows the image areas 14 in tanned colloid remaining after the untanned colloid in the non-image areas has been washed off.

The following examples are intended to illustrate my invention but not to limit it in any way.

Example 1 A support is prepared having a formaldehyde free paper base coated with clear polyethylene on one side and colored or pigmented polyethylene on the other. The colored polyethylene contains a coloring agent such as titanium dioxide, baryta, carbon black, red dye, etc. The surface of the colored polyethylene is electron bombarded to obtain adhesion to a silver halide emulsion. Over the colored polyethylene layer is coated a projection speed silver chlorobromide gelatino-emulsion containing bromohydroquinone having a silver coverage of 80 milligrams per square'foot, gelatin coverage of 139 milligrams per square foot and a bromohydroquinone coverage of milligrams per square foot.

The silver halide emulsion is exposed in the prismtype process camera and activated in an alkaline activator whereby the gelatin is tanned by the oxidation products of the bromohydroquinone to produce areas of tanned and untanned gelatin resulting in a right reading negative of the original. The unexposed soft gelatin is removed with warm water at a temperature of 90 F. The lithographic plate is then put on a lithographic press using 1% phosphoric acid fountain solution, inked with a greasy printing ink and printed with the water adhering to the image and the ink adhering to the hydrophobic base in the nonimage areas.

Example 2 Polystyrene, polypropylene, polyesters, styrenebutadiene copolymers and cellulose acetate are substituted for polyethylene with similar results as in Example 1.

EXAMPLE 3 A product according to Example 1 is made in which additives to the gelatin are incorporated to make the gelatin image more receptive. For example, compounds which are used are silica, sugars, and salts of heavy metals (e.g., lead acetate and zinc nitrate). These are used in amounts up to 20 milligrams per square foot in the silver halide emulsion.

EXAMPLE 4 A structure is prepared according to Example 1 except that a carbon dispersion is incorporated in the silver halide emulsion and the emulsion coated over a clear cellulose triacetate support. The carbon acts as an antihalation agent during the exposure step. Instead of washing the soft untanned gelatin from the developed emulsion, the silver halide emulsion is contacted while still moist against a paper receiving sheet so that the untanned areas adhere to the receiving sheets leaving the image areas adhering to the cellulose triacetate surface. The resulting product provides a hydrophobic support which is oleophilic having thereon hydrophilic image areas.

EXAMPLE 5 A plate according to Example 1 is prepared except that unsubstituted hydroquinone itself is used, it is found to be unsatisfactory due to its poor ability to render the image hydrophilic with respect to the base. Moreover, unsubstiuted hydroquinone readily oxidizes, particularly when used alone. When unsubstituted hydroquinone is incorporated in a silver halide emulsion, it has a tendency to sublime and to leach out before development occurs. For these reasons, unsubstituted hydroquinone cannot be used in carrying out the invention.

EXAMPLE 6 A paper support was prepared having a water resistant coating as described in Murphy and Wood U.S. Patent 3,021,214, issued Feb. 13, 1962. Over the latex coating was coated a projection speed silver chlorobromide gelaino emulsion containing bromohydroquinone having silver coverage of mg. per square foot, gelatin coverage of 1.39 mg. per square foot and a bromohydroquinone coverage of 20 mg. per square foot.

When the silver halide emulsion was exposed and processed as in Example 1, the image areas were found to be 'hydrophilic with respect to greasy printing ink, whereas the greasy printing ink adhered to the latex coating in the non-image areas. When used on a lithographic press, right-reading positive prints were obtained.

Murphy and Wood U.S. Patent 3,021,214 is incorporated herein by reference. The coatings described therein are particularly useful in forming a support which is receptive to greasy printing inks when used with a hardening developer which forms hydrophilic image areas.

For some purposes it may be desirable to have a negative image printed with respect to the image to which the sensitized lithographic plate is exposed. A suitable element may be prepared having a first layer on the hydrophobic surface comprising a fogged silver halide light sensitive emulsion. Over this fogged emulsion is coated a light sensitive silver halide emulsion. Both emulsions must be substantially unhardened and must be developed using a water soluble substituted hydroquinone silver halide developing agent of this invention. A particularly useful embodiment has the water soluble substituted hydroquinone developer incorporated in the top emulsion layer so that the exposed element can be developed by immersing in an alkaline activator. The exposed areas in the top emulsion layer became developed and hardened permitting the unused developer to develop and harden the fogged emulsion layer imagewise in those areas directly underneath the unexposed areas of the top emulsion layer. Upon washing in warm water, the top layer, as well as the unhardened areas of the fogged emulsion layer, are removed to provide a lithographic plate having hydrophilic image areas and an oleophilic surface. When this lithographic plate is used for printing on a lithographic printing press, the printed impressions will be negative with respect to the image to which the element was exposed initially.

The inks, which are useful in making lithographic prints on a lithographic press with the plates of this invention, are not critical provided they are greasy inks. Typical inks which are operative include Van Son ink, Multigraph ink ML 36, A. B. Dick 21010 ink, etc.

Fountain solutions known in the art may also be used. For instance, fountain solutions disclosed in Van Dusen US. Patent 2,393,875, issued Jan. 29, 1946, are useful solutions.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention .as described hereinabove and as defined in the appended claims.

I claim:

1. A photographic element comprising a support having a hydrophobic surface having thereon an unhardened light sensitive silver halide emulsion and integral therewith a water soluble substituted hydroquinone silver ha lide developing agent which forms hydrophilic areas upon development selected from the class consisting of bromohydroquinone, chlorohydroquinone, and morpholinomethyl hydroquinone.

2. An element of claim 1 in which said emulsion is a direct positive emulsion.

3. An element of claim 1 in which the developing agent is bromohydroquinone.

4. An element of claim 1 in which the developing agent is chlorohydroquinone.

5. An element of claim 1 in which the developing agent is morpholinomethyl hydroquinone.

6. An element comprising a ployethylene surface having thereon an unhardened light sensitive silver halide emulsion and integral therewith a water soluble substituted hydroquinone silver halide tanning developing agent selected from the class consisting of bromohydroquinone., chlorohydroquinone, and morpholinomethyl hydroquinone.

7. An element comprising a polyethylene surface having thereon an unhardened light sensitive silver halide emulsion containing bromohydroquinone.

8. An element comprising a polyethylene surface having thereon an unhardened light sensitive silver halide emulsion containing chlorohydroquinone.

9. An element comprising a cellulose triacetate surface having thereon an unhardened light sensitive silver halide emulsion and integral therewith a water soluble substituted hydroquinone silver halide tanning developing agent selected from the class consisting of bromohydroquinone, chlorohydroquinone, and morpholinomethyl hydroquinone.

10. An element comprising a polyester surface having thereon an unhardened light sensitive silver halide emulsion and integral therewith a water soluble substituted hydroquinone silver halide tanning developing agent selected from the class consisting of bromohydroquinone, chlorohydroquinone, and morpholinomethyl hydroquinone.

11. An element comprising a support having thereon a coating containing sty-rene-butadiene copolymer, polystyrene and casein, and having thereon an unhardened light sensitive silver halide emulsion having integral therewith a water soluble substituted hydroquinone silver halide tanning developing agent selected from the class consisting of bromohydroquinone, chlorohydroquinone, and morpholinomethyl hydroquinone.

12. A process of forming a lithographic printing plate having a hydrophobic surface and hydrophilic image areas, comprising activatin an exposed unhardened light sensitive silver halide emulsion on said hydrophobic surface, said emulsion having integral therewith a water soluble substituted hydroquinone silver halide tanning developing agent selected from the class consisting of bromohydroquinone, chlorohydroquinone, and morpholinomethyl hydroquinone to form hardened hydrophilic areas and removing unhardened emulsion areas.

13. A process of forming a lithographic printing plate having a hydrophobic surface and hydrophilic image areas, comprising activating an exposed unhardened light sensitive silver halide emulsion on said hydrophobic surface, said emulsion having integral therewith bromohydroquinonc, to form hardened hydrophilic areas and removing the unhardened emulsion areas.

14. A process of forming a lithographic printing plate having a hydrophobic surface and hydrophilic image areas, comprising activating an exposed unhardened light sensitive silver halide emulsion on said hydrophobic surface, said emulsion having inte ral therewith chlorohydroquinone, to form hardened hydrophilic areas and removing the unhardened emulsion areas.

15. A process of forming a lithographic printing plate having a hydrophobic surface and hydrophilic image areas comprising activating an exposed unhardened light sensitive silver halide emulsion on said hydrophobic surface, said emulsion having integral therewith morpholinomethyl hydroquinone, to form hardened hydrophilic areas and removing the unhardened emulsion areas.

16. A process for providing a lithographic printing plate having a hydrophobic surface and hydrophilic image areas, comprising developing the exposed unhardened light sensitive silver halide emulsion on said hydrophobic surface with a water soluble substituted hydroquinone silver halide tanning developing agent selected from the class consisting of b-romohydroquinone, chlorohydroquinone, and morpholinomethyl hydroquinone to form hardened hydrophilic areas and removing the untanned emulsion areas.

17. A process for providing a lithographic printing plate having a hydrophobic surface and hydrophilic image areas, comprising developing the exposed unhardened light sensitive silver halide emulsion on said hydrophobic surface With a bromohydroquinone silver halide tanning developing agent to form hardened hydrophilic areas and removing the untanned emulsion areas.

18. A process for providing a lithographic printing plate having a hydrophobic surface and hydrophilic image areas, comprising developing the exposed unhardened light sensitive silver halide emulsion on said hydrophobic surface with a chlorohydroquinone silver halide tanning developing agent to form hardened hydrophilic areas and removing the untanned emulsion areas.

19. A process for providing a lithographic printing plate having a hydrophobic surface and hydrophilic image areas, comprising developing the exposed unhardened light sensitive silver halide emulsion on said hydrophobic surface with a morpholinomethyl hydroquinone silver halide tanning developing agent to form hardened hydrophilic areas and removing the untanned emulsion areas.

References Cited UNITED STATES PATENTS 3,053,658 9/1962 Spencer 9633 3,146,104 8/1964 Yackel et al. 96-33 NORMAN G. TORCHlN, Primary Examiner.

R. E. MARTIN, Assistant Examiner.

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