Patent GB-978744-A (GB)
Title: Photolithographic printing and plate therefor and light sensitive material for producing it
IPC: G03F7/06
Filed: 1960-12-21
Abstract: 978, 744. Photolithographic printing and light sensitive materials therefor. KODAK Ltd. Dec. 21, 1960 [Dec. 21, 1959], No. 43994/60. Headings G2C and G2M. A method of photolithographic printing comprises imagewise exposing a light-sensitive photographic material comprising a support; a surface layer of a silver halide emulsion, which may be fogged or light sensitive, in a tannable hydrophilic organic colloid; and contained in the surface layer, or in a layer or layers between it and the support, a silver halide developing agent capable of oxidation in the presence of the tannable colloid to form a hydrophobic oleophilic image receptive to greasy inks and repellent of water; and, if the surface layer is not light sensitive, a light sensitive silver halide emulsion layer between the surface layer and the support: initiating the development of the exposed light sensitive emulsion layer with an alkaline solution, thereby causing an image to be developed therein and a hydrophobic oleophilic image to form on the surface: and, while the material remains moist, inking the surface image with greasy ink and printing therefrom. If the surface emulsion layer is an ordinary light sensitive silver halide emulsion in a tannable colloid, the process yields a negative print. To produce positive prints, if the surface layer is light sensitive it must be either a direct positive emulsion, e.g. as disclosed in Specifications 524,087, 635,841, 645,877, 667,206 or 702,162, or the process must be modified so that the exposed material is reversal processed, i.e. developed first with a solution to form a silver image without tanning the colloid or activating the tanning developer in the material, exposing the material after removal of the developing solution to render all the remaining silver halide developable, and then treating it with an alkaline solution to initiate the tanning development step. The tanning developers included in the material are substituted polyhydroxybenzene compounds e.g. chloro- or bromo-hydroquinone, pyrogallol or its formic or acetic esters, 4-nbutylpyrogallol, 4-phenylcatechol, 4-tert-butylcatechol, 4: 5-dibromocatechol, 3: 5: 6-tribromo- 4-phenylcatechol, nordihydroguairetic acid, 1- phenyl-3-(N-n-hexylcarboxamide)-4-[(#-hydroquinoylethyl)-phenylazo]-5 pyrazolone, and pyrogallol together with a non-tanning developer such as metol or a 3-pyrazolidone. The tannable colloid may be gelatin, preferably having a hardness equivalent to a pure gelatin layer containing at least 2 grams of dry formaldehyde per pound of gelatin, or soy bean protein, casein, polyvinyl alcohol, or hydrolyzed cellulose esters. Typical materials are (Example 1) film base of paper coated with a light sensitive gelatino-silver chloride emulsion, containing the tanning developer (4- phenylcatechol) and a paraffin wax dispersion, which yields a negative print;paper coated first with a colloidal silver antihalation layer containing the tanning developer and then with either (Example 2) a light sensitive green-sensitized gelatino-silver chloride emulsion, yielding a negative print, or (Example 10) a direct-positive emulsion yielding a positive print; (Examples 3 and 4) paper coated successively with the tanning developer layer, a light sensitive gelatino-silver chloride emulsion which may be green sensitized, and afogged gelatino-silver chloride emulsion, yielding positive prints. If desired the light sensitive and fogged emulsions may have different development induction periods. If a direct-positive light-sensitive emulsion is used with an outer fogged emulsion, negative prints are obtained. By including zinc oxide, aluminium oxide, carboxymethyl- or carboxyethyl-hydroxyethyl-cellulose, or polyacrylamide in the tannable outer layer and using phosphoric acid fountain solution before inking, increased contrast is obtained by decreasing background "scum". Instead of ordinary paper or film supports of aluminium or of paper water-proofed with coatings of cellulose esters or polythene may be used. The alkaline developer activating solutions may contain alkali metal carbonates, caustic alkali, quaternary ammonium hydroxides, or amines, while if direct positive emulsions of the internal latent image type, the alkaline solution preferably includes a fogging agent such as a hydrazine as disclosed in Specification 702,162. The Specification also describes other methods of photolithographic printing. In Example 6 paper coated successively with a contact printing speed gelatino-silver chloride emulsion containing a dispersion of 4-phenylcatechol and a silver chloride emulsion of higher speed in a binder vehicle of alkali-soluble acid-insoluble cellulose ether phthalate as described in Specification 868,241 is exposed to form an image in the outer layer only and developed with a metol-hydroquinone solution, flashed through the resulting negative image and then treated with sodium carbonate solution to develop a positive hydrophobic oleophilic image in the lower layer whereafter washing removes the upper alkali soluble layer so that the resulting positive image may be inked and used for printing. As an alternative the slow and higher speed emulsions may both be gelatin emulsions and separated by a stripping layer of an alkali metal salt of cellulose ether phthalate. Examples 7 and 8 employ supports-film or water-resistant paper-coated successively with a developer layer and a light-sensitive emulsion which after exposure is brought into contact in an alkaline solution with a reception sheet comprising a supportpaper or cellulose acetate-coated with either a fogged silver halide emulsion or gelatin containing manganese dioxide, the developer not used to develop the silver image in the light sensitive emulsion transferring to the reception sheet where it is oxidized and tans the gelatin to form a positive printing image. Reference is also made to transferring unused developer to a sheet bearing a tannable colloid which is then swabbed with a solution of an oxidizing agent such as a ferric chloride or ferric sulphate ethylene-diaminetetraacetic acid complex or to rehalogenating silver images and then redeveloping with tanning developers as set out above.