In photography, an image is recorded onto film and the image on the film is then developed into a photographic reproduction of the image. Usually the film contains an emulsion on which the image is recorded. In the standard photodeveloping process, the exposed film is processed in a developer which contains primary developing agents which reduce silver in the film emulsion to produce an image thereon.
In high resolution microfilm, the film emulsion is loaded with a high level of accutance, antihalation and sensitization dyes.
When film is developed in a film processor, oily dye residues are released from the film emulsions. These oily dye residues build up over time. If these oily dye residues do not remain in solution, they will stain microfilm that is subsequently developed in the film processor or build up on the surfaces of the film processor, plugging orifices or otherwise adversely affecting the performance of the film processor.
One solution to the dye residue buildup problem is to change the developer solution in the film processor frequently. This, however, escalates the cost of photodevelopment and is not the preferred alternative. Furthermore, closed loop film processors are designed so that they will not have to be shut down prior to having developed a certain amount of film. Shutting down a closed loop process during a development cycle reduces the efficiency and economic advantages of the closed loop process.
Preferably, an emulsifier is used to solubilize the oily residues in the photodeveloper to prevent the oily dye residues from adhering to the film or the components of the film processor. Standard emulsifiers such as disodium mono- and didodecyl diphenyl oxide disulfide anionic emulsifier or sodium alpha olefin sulfonate foam are not suited for this purpose, especially when the photodeveloping solution is continuously circulated through the film processor. These standard emulsifiers foam excessively when subjected to the constant recirculation of the developing solution in this type of film processor. The very alkaline conditions of the photodeveloper solutions in this type of chemical environment also adversely affect the stability of many emulsifiers.
The foam generated by these standard emulsifiers in photodeveloping solutions is very undesirable. Conventional surfactants are therefore of limited usefulness for preventing the build up of oily dye residues in the chemical environment required by film development, especially in closed loop film processors.
Brightening agents have also been incorporated into photodeveloping solutions in order to control, reduce or eliminate the problem of dye stains on developed film. U.S. Pat. No. 4,264,716 to Vincent et al. incorporates brightening agents into photodeveloping compositions to reduce staining.
However, brightening agents merely cover up or correct dye stains on photographs. Brightening agents do not solubilize the oily dye residues in the developer solution to prevent them from staining the film or adhering to components of the film processing tanks.
Typical brightening agents include stilbene type brightening agents. Stilbene-containing compositions have been used to reduce or eliminate stains on film caused by the build up of oily dye residues in the developer solution.
A published disclosure, Cappel, C.R. and Purol, M.D., "Method for Reducing Spectral Sensitizing Dye Stain in Photographic Elements," Research Disclosures, No. 20733 (Kenneth Mason Publications, Ltd, Jul. 10, 1981) describes adding a water soluble stilbene, bis-4, 4'-s-triazyl amino stilbene sulfonic acid or mixtures of water-soluble stilbenes and nonionic surfactants, into a developing solution. The build up of dibenzooxazole carbocyanine sensitizing dyes in the gel matrix or within a coupler dispersion in the photographic emulsion layers was said to be avoided by the addition of the aqueous amino stilbene sulfonic acid solution. Dibenzooxazole carbocyanine sensitizing dyes extend the sensitivity of photographic emulsions to electromagnetic radiation which is beyond the wave lengths of visible light.
U.S. Pat. No. 4,587,195 to Ishikawa et al. discloses a method of processing a silver halide photographic light-sensitive film material. The method is said to be economical because the amount of photodeveloping solution used in the process is reduced.
In Ishikawa et al. the reduction in the amount of photodeveloping solution used is accomplished by not changing the photodeveloping solution in the film processor as often. Since the photodeveloping solution is not changed as often, the problems associated with the accumulation of oily dye residues on film processing equipment become more acute.
In Ishikawa et al., a combination of two different triazyl stilbene-type brightening agents must be added to the color developer to avoid the adverse effects caused by the build up of oily dye residues therein. The brightening agents are present in the photodeveloper in an amount of about 0.3 gram to about 10 grams per liter of color developer solution.
If the maximum fluorescent wavelengths of the fluorescent spectra of the two triazyl stilbenes used in Ishikawa et al. are less than 4 m.mu. apart, the triazyl stilbene solution will not remove the dye stains, however. If only one of the two types of stilbene brightening agents is used or if the difference in the maximum fluorescent wavelength of the two triazyl stilbenes is not at least 4 m.mu. , build up of oily dye residues in the developer solution remains a problem. If the amount of triazyl stilbene in solution exceeds 10 grams per liter, the film's development will be adversely effected and fluorescent quenching or an unfavorable photographic performance such as non-color may result.
From the foregoing it is apparent that the type of stilbene used to reduce dye stains on films is linked to the type of dye residue in the process. The type of dye residue in the process is linked to the emulsion on the film. The emulsion on the film is linked to the type of film and the process by which the film is developed.
Standard films have an emulsion thereon which is compatible with the developing process for standard films which requires bleaching steps to convert the negative image on the film to a positive photographic image. Other films, such as direct positive films, do not require bleaching steps because a positive image is recorded directly onto the film when the film is exposed to that image. Photographic emulsions are provided on direct positive films which are compatible with this type of developing process.
Thus, there continues to be a need for a composition which will solubilize the oily dye residues produced by the development of direct positive silver halide film without foaming. If the oily dye residues are sufficiently solubilized, they will remain in solution and not adhere to the film or build up on the components of the film processor.
In continuous, automatic developers where the photodeveloping solution is recirculated and not replenished until a predetermined amount of film is developed, it is important that the oily dye residues remain solubilized until the photodeveloping solution is spent. Otherwise the film processor has to be shut down more frequently to change the solution, and the economy of the continuous, nonreplenished process is adversely effected. The composition also must not adversely affect the direct positive silver halide film developing process.