1. Field of the Invention
This invention relates to certain azo spectral sensitizing dyes for photographic and photothermographic silver halide materials. In one of its aspects, it relates to photographic silver halide compositions and elements containing certain azo sensitizing dyes. In another of its aspects, this invention relates to a photothermographic element suitable for processing with heat containing photographic silver halide in reactive association with a reducing agent, a silver salt oxidizing agent, and certain azo spectral sensitizing dyes. It further relates to a photothermographic composition having the described components and a method for developing an image in such material in the absence of processing solutions.
2. Description of the State of the Art
Various classes of dyes, such as cyanines, merocyanines, phthaleins, acridines, diphenylmethanes, triphenylmethanes, anthraquinones and styryls are well known as spectral sensitizers for conventional silver halide photographic materials.
It is also known to develop a latent image in a photothermographic element using thermal processing. After imagewise exposure, the resulting latent image in the photothermographic element is developed and, in some cases, stabilized, merely by uniformly heating the photothermographic element. Certain photothermographic materials for producing an image in color are also known. After imagewise exposure of these photothermographic materials, images can be developed by merely heating the elements to moderately elevated temperatures for a few seconds.
It is further known to use non-azo spectral sensitizers in photothermographic materials. These are described, for instance, in U.S. Pat. No. 3,801,321 of Evans et al, issued Apr. 2, 1974. A continuing need has existed for new classes of spectral sensitizers for photothermographic materials, especially silver halide photothermographic materials.
Azo dyes have been useful as dyestuffs for fibers, paints, varnishes and printing inks for many years. The use of certain azo dyes in electrophotographic materials is also known.
British Pat. No. 1,253,933 published Nov. 17, 1971 relates to certain azo dyes having pyrazolotriazole moieties which are useful as spectral sensitizers in conventional photographic silver halide emulsions. No use of such dyes in photothermographic materials is taught or suggested.
U.S. Pat. No. 3,870,523 of Ikenone et al, issued Mar. 11, 1975 relates to heat developable photographic materials comprising azo dye sensitizers which have the general formulae Ar.sub.1 --N.dbd.N--Ar.sub.2 or A.sub.3 --N.dbd.N--Ar.sub.4 --N.dbd.N--Ar.sub.5 wherein Ar.sub.1, Ar.sub.2, Ar.sub.3 and Ar.sub.5 are substituted or unsubstituted aryl groups and Ar.sub.4 is arylene. This reference fails to teach or suggest the azo sensitizers useful in the photographic and photothermographic elements of the present invention.
Azo dyes as a class are generally poor spectral sensitizers for silver halide photographic and photothermographic materials. However, they are sometimes used in photothermographic materials when conventional sensitizing dyes are unsuitable or inadequate.
Therefore, it has been desirable to provide improved photographic and photothermographic materials comprising azo spectral sensitizing dyes, particularly when non-azo spectral sensitizers do not provide satisfactory results in such materials. It has been further desirable to use sensitizing dyes which absorb readily to the silver halide grains and which cannot be readily displaced from the grains by chemicals commonly incorporated into photographic and photothermographic materials.