Patent GB-697521-A (GB)
Title: Improvements relating to the manufacture of diazo sensitised paper printing foils for photo-lithographic purposes
IPC: G03F7/016
Filed: 1949-10-06
Abstract: 697,521. Diazo sensitized paper foils for lithographic printing. KALLE & CO. AKT.- GES. Oct. 6, 1949 [Oct. 8, 1948], No. 25722/49. Class 98 (ii). A layer, free from coupling components and free from colloidal substances tannable by diazo compounds under the action of light, containing a diazonium salt corresponding to the formula wherein X stands for an equivalent of an anion of an acid, Ar for a phenylene residue which may be substituted by alkyl, alkoxy, aroxy, arylsulphonamide or halogen; R for an aryl residue which may be substituted by alkyl, alkoxy, halogen or carboxyl; and R 1  for H or alkyl; the condensates of any of these with aldehydes, or the diazosulphonates obtained by reaction of sulphite on the diazonium salts or their aldehyde condensates, is formed from aqueous solution or dispersion on a paper base, dried, exposed under an original, washed to remove unexposed parts or else treated with a water-soluble coupling component which forms a hydrophilic azo dye with the residual undecomposed diazonium compound, and then treated with greasy ink and aqueous liquid, to result in a printing foil yielding a positive print from a negative original. The invention includes the light-sensitive material itself when the specified diazo sulphonates are used in the light-sensitive layer. Suitable diazo compounds are those of 4-amino- 2 : 5 : 4<SP>1</SP> - tribromo - diphenylamine, 4 - amino - 2<SP>1</SP>: 4<SP>1</SP>: 61 - trichloro - diphenylamine, 4 - amino - 2 - [N - (2 : 5 - diethoxy - phenyl) - sulphamido] - diphenylamine, 4 - amino - 3: 6 - dimethoxy - diphenylamine - 2<SP>1</SP> - carboxylic acid. The paper foils to be used may be laminated with plastic material, metal or other paper foils, may be coated on the back with water-insoluble lacquers, may be pre-treated with condensation products of formaldehyde with phenol, urea or melamine or coated with casein or clay. To give better stability during storage the diazo sensitizing solution can include substances which render the diazo compounds difficultly soluble, such as inorganic salts and salts of sulphonic acids of the aliphatic or aromatic series, of which nineteen are specified. In example 1 the diazo sulphonate of 2<SP>1</SP>: 41: 61-trichlorodiphenylamine in aqueous solution is brushed on parchment paper which is laminated to aluminium foil, the coating is dried, exposed to an arc lamp under a negative, clamped in a printing-machine, washed with water by means of a sponge and then printing ink and water are applied as usual to produce positive prints. Examples 2 and 4 describe, somewhat similarly, use of the condensation product of diazotized amino-diphenylamine with formaldehyde as light-sensitive material; and example 3 the sulphonate of diazotized amino-diphenylamine. In example 5 the exposed foil of examples 2 and 4 is desensitized by coupling with sodium phenyl-methyl-pyrazolone sulphonate instead of sponging with water. Example 6 specifies a melamine-formaldehyde resin-coated paper base sensitized with a coating comprising the sulphonate of the condensation product of 4- amino-diphenylamine with paraformaldehyde, which is adapted for further treatment as in example 3. The Specification as open to inspection under Sect. 91, comprises also, in examples, use of the diazo compounds obtained from 1-amino-2: 5- di-n-propyl-41-methyl-diphenylsulphide, 4-(N- benzoyl) - amino - 2: 5 . diethoxyaniline and 4-amino-1: 3-dimethoxybenzene for similar purposes; further diazo compounds are listed. This subject-matter does not appear in the Specification as accepted.