Photographic products and processes employing pH sensitive filte

Details Photographic products and processes employing pH sensitive filte Photographic products and processes employing pH sensitive filte

1977-09-23

1979-02-13

Schilling, Richard L.

Gas separation: apparatus

Magnetic separating means

And electric field separation apparatus

96 29R, 96 63, 96 66R, 96 73, 96 74, 96 76R, 96 76C, 96 77, 96 84R, 96112, G03C 700, G03C 140, G03C 184, G03C 554

Patent

active

041393813

ABSTRACT:
This invention is concerned with photographic products, particularly diffusion transfer photographic film units, useful in photographic processes conducted outside of a camera wherein post-exposure fogging by ambient light is prevented by a compound initially present as a substantially colorless compound which is activated by base to provide a light-absorbing reagent or colored optical filter agent which is capable of being irreversibly discharged without a change in pH. The colorless compound or filter agent precursor is initially disposed in a layer of the film unit, for example, in a layer coated over the photosensitive element. Subsequent to imagewise exposure of the photosensitive element, the colored optical filter agent is generated by contacting the colorless precursor with a basic processing composition. After remaining in contact with said basic composition for a given time, the colored optical filter agent is discharged by forming a new compound which is substantially colorless and which is different from and non-reversible to said precursor and different from and non-reversible to said optical filter agent.

REFERENCES:
patent: 3498789 (1970-03-01), Sutherns
patent: 3647437 (1972-03-01), Land
patent: 3702244 (1972-11-01), Bloom et al.
patent: 3702245 (1972-11-01), Simon et al.
patent: 3726675 (1973-04-01), Borror
patent: 3976659 (1976-08-01), Borror

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