Process for the chain-lengthening of gelatine by partial hardening

Claim 1

In a process for chain-lengthening gelatin for a photographic material by an agent or agents to provide increased molecular weight, the steps comprising preparing a gelatin solution containing from 5 to 35% by weight of gelatin, contacting said gelatin solution for a period of 0.01 seconds to 10 minutes at 30° to 90° C. with 0.001 to 0.01 mole of an agent per 100 g of dry gelatin, said agent being capable of activating the carboxyl groups of the gelatin with the formation of reactive products causing cross-linking, and thereby providing chain-lengthening of the molecules of the gelatin resulting in a change of the distribution of the molecular weight within said gelatin solution by producing intercaternary bonds and linear chain-lengthening to increase the molecular weight of the gelatin derivative and in the absence of decreasing triple helix formation, said chain-lengthened gelatin solution being coatable into a layer on a support, said chain-lengthening agent being capable of converting a photographic gelatin layer resistant to boiling after treatment of a 20μ thick dry gelatin layer with an aqueous solution of the agent at a concentration of 0.01 to 0.03 mole chain-lengthening agent per 100 g dry gelatin at a pH value of the moist gelatin layer of 5 to 7 at a temperature of 20° C.