Silver Dye Bleach Processes

The silver dye-bleach process depends on destruction of a dye in a photographic layer in an amount proportional to the quantity of image silver present.94 95 The dye is normally an azo dye in which the azo bond is cleaved. Over the years a variety of metal-complexed azo dyes have been described for use in this process. These dyes must be immobile they must not wander from layer to layer, or color contamination of the final image will result. However, they must be reactive enough in an aqueous environment for the azo bond to break. 

A black-and-white system based on the silver dye-bleach process contains the single azoxy copper-complexed dye (36).10P During bleaching, low pH solutions are used and the dye is partially demetallized. This necessitates an after-bath treatment with a copper-containing solution. Dyes other than those containing the azo group can also be bleached, and derivatives of sulfonated copper phthalocyanine have been used to form cyan images.101... 

The archivally stable Cibachrome printing process is based on the use of developed silver metal in the negative image for the imagewise reduction of azo chro-mophores 39-41 to colorless anilines under highly acidic conditions. The anilines are then dissolved away to leave a positive image in dye. This process is also known as the silver dye bleach process [56,57],... 

Benzo[/]quinoxalines have been patented for use as catalysts for the silver dye bleaching process and as dyestuff intermediates. The latter compounds have been derived by nitration, sulfonation, or chlorosulfona-tion of either 2,3-dioxo- or 2,3-dichlorobenzo[/]quinoxaline. 

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