GB550775A - Improvements in sensitive photographic materials - Google Patents

Abstract

550,775. Photographic printing paper and developing solutions. KODAK, Ltd., and BATLEY, A. March 21, 1941, No. 3841. [Class 98 (ii)] Photographic printing paper for printing from wet negatives comprises a paper support carrying a lieht sensitive silver salt emulsion laver having a layer of a binder which is insoluble in plain water but soluble in alkali solutions, such as a colourless overcoating of less than 25 thickness of a polyvinyl acid ester resin or a resin ester of a polybasic acid. Preferably the dried coating should not be more than 10 Á or even more than 5Á thick, and coatings as thin as 2 Á or lower can be used in some cases, a resin or low acid value being applied more thinly than one of high acid value. Thicker coatings can be used if longer development times are permissible. The coatings may be formed from a solution of polyvinyl phthalate in a mixture of ethylene glycol monomethylether, acetone, and methol alcohol, or from a resin formed by condensing a terpene, e.g. rosin, with an x: #-unsaturated poly-carboxylic acid or acid anhydride, e.g. maleic acid anhydride, or from an alkyd resin formed by condensing a polyhydric alcohol, e.g. glycols, glycerol, sugars, and simple derivatives thereof, with polycarboxylic acids, e.g. citric, maleic, phthalic, succinic, or tartaric acid, or from a hydrolysed natural resin of the kind described in Specification 511,180. In example 1, a solution of polyvinyl acetate phthalate of acid value 270 in acetone and ethylene glycol monomethyl ether is coated on the silver bromide emulsion layer of photographic paper and dried to give a layer 7Á thick. In example 2, a dried layer 15 # thick is formed from a solution of a rosin maleic anhydride adduct of acid value 250-275 in acetone and ethylene glycol monomethyl ether. In example 3, a dried layer 7 Á thick is formed from a solution of Abralac PK (Registered Trade Mark) in acetone and ethylene glycol monomethyl ether. In example 4, a dried layer 2-3 Á thick is formed from a solution of hydrolysed soft lac in industrial spirits. In example 5, a layer 15 Á thick is formed from a solution of rosin maleic anhydride adduct of acid value 250- 275 and Abralac BG in acetone. The wet negative may contain sodium thiosulphate, but not free alkali. Specifications 355,281, [Group IV], 450,220, 524,378 and 529,035 also are referred to. The Provisional Specification describes also a developer containing catechol, sodium sulphite, sodium hydroxide, and potassium bromide, and refers also to an acid value of at least 100 to 150.