GB711702A - Improvements in photographic methods of preparing relief matrices and diazo containing light sensitive materials therefor - Google Patents

Abstract

711,702. Photographic diazotype layers for relief and photomechanical procedure. KODAK, Ltd. April 15, 1952 [April 16, 1951]. No. 8864/51. Class 98(2) A support having a layer of gelatin containing a diazo compound of such nature that, after exposure of the layer to light exposed portions of the layer can be removed by washing in water at pH below 2.5, such as diazotized wherein R and R<SP>1</SP> represent hydrogen, alkyl or aryl groups, D and D' represent paraphenylene radicals which may contain alkyl groups, and n has a value of 0 or 1, is exposed imagewise and washed at a pH of less than 2.5 to remove exposed parts of the layer. Either the washing water or the layer itself may contain acid to give. the required pH. Preferably the gelatin contains a hardening agent, and in this case the layers are included within the terms of the invention. The support may be glass, metal, film or paper with a hydrophobic subbing layer, whereby, with the gelatin layer being hydrophilic, the product constitutes a lithographic printing plate. The diazo compounds may be derivatives of p-phenylenediamine, N-alkyl-pphenylenediamine, N : N-dialkyl-p-phenylenediamine, N-aryl-p-phenylenediamine, 4 4-diaminodiphenylmethane or N-alkyl- or N : N-dialkylderivatives of the latter. A hardener such as chrome alum or formaldehyde may be included in the layer and a comminuted solid such as baryta, in amount up to 10 times the weight of the gelatin, may be included as well. Hydrochloric, citric, acetic or oxalic acid may be used to produce the desired pH. In Example 1 a glass plate is coated with a solution of gelatin and chrome alum, dried, bathed in a diazo solution of 3-methyl-4-aminodiethylaniline, hydrochloric acid and sodium nitrate, dried, exposed under a line negative and washed in running water to leave unexposed portions as a relief image on the glass plate. In Example 2 a cellulose nitrate subbed paper base is provided with a gelatin-baryta-chrome alum layer, sensitized as in example 1 and exposed and developed similarly to produce a lithographic plate. In Example 3 tetrazotized 4:4'-diamine-diphenylmethane at pH 0.6 is used as sensitizer, or may be used at pH 7, in which case acidified hydrogen peroxide is used as washing water. Example 4 indicates the use of formaldehyde as hardener; and Example 5 the production of a negative relief image from a negative silver half-tone by diazotization, exposure and acid treatment, the silver half-tone portions preventing exposure of underlying gelatin. Silk screen stencils are referred to.