Ilford Limited

Pierre A Brugger

Rolf Steiger

There is described a process for the spectral sensitization of photographic silver halide emulsions which comprises forming and chemically sensitizing silver halide crystals in a colloid dispersion medium, the process being characterized in that it comprises forming a shell of silver halide on the chemically sensitized crystals by simultaneously adding to the dispersion an aqueous solution of a water soluble halide or pseudo-halide, an aqueous solution of silver nitrate and a J-band aggregating spectral sensitizing dye in an aqueous medium, the said simultaneous additions being continued for sufficient time to form a shell of silver halide or pseudo-halide on the said chemically sensitized silver halide crystals which is up to 15 mole percent of the total silver halide or pseudo-halide of the fully grown crystals. It is thought that in the process of the present invention there is formed on the surface of the chemically sensitized silver halide crystal terraces of the halide or pseudo-halide being added, these terraces being separated from each other by steps of high surface energy. The J-band aggregating dye nucleates on these steps and is deterred from recombining. At the end of the process frequently the whole surface of the silver halide crystals is coverd with such terraces and steps on which the J-band dyes have nucleated. When such crystals are photo exposed, electron hole recombination is decreased leading to higher photographic speed and low LIRF.

Growing community of inventors

Village Amont Fribourg, Switzerland

Pierre A Brugger