Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2001-08-23
2003-06-10
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C601S018000, C601S018000, C601S018000, C601S018000, C601S018000
Reexamination Certificate
active
06576413
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an aqueous dispersion of a substantially light-insensitive organic silver salt and a photosensitive silver halide and a photothermographic recording material prepared therefrom.
BACKGROUND OF THE INVENTION
The SPSE Handbook of Photographic Science and Engineering, edited by Woodlief Thomas, Wiley-Interscience, New York (1973), page 422 states that compounds such as stannous salts, sodium hydrosulfite and silanes are capable of seducing silver halide in a grain.
The Theory of the Photographic Process Fourth Edition, edited by T. H. James, Eastman Kodak (1977), pages 151-152 discusses the reduction sensitization of silver halide emulsions. The chemicals studied therefor, according to James, include stannous chloride, hydrazine, ethanolamine and aminoiminomethane sulfinic acid. Furthermore, low pAg sensitization, also called silver digestion, with inert gelatin produces a form of reduction sensitization.
EP-A 911 692 discloses the possibility of reduction sensitization of silver halide for use in photothermographic recording materials and discloses therefor: ascorbic acid, thiourea dioxide, stannous chloride, aminoiminomethane sulfinic acid, hydrazine derivatives, boran compounds, silane compounds, and polyamine compounds. Furthermore, it discloses that reduction sensitization can be performed by ripening the emulsions while maintaining the pH of the emulsions at 7 or higher, or at pAg 8.3 or lower and also that reduction sensitization can be conducted by introducing a single addition portion of silver ions during grain formation.
EP-A 962 812 discloses the possibility of reduction sensitization of silver halide for use in photothermographic recording materials and discloses therefor: stannous chloride, aminoiminomethane sulfonic acid, hydrazine derivatives, borane compounds, silane compounds, polyamines, ascorbic acid and thiourea dioxide. Furthermore, it discloses that reduction sensitization can be performed by ripening the emulsions while maintaining the pH of the emulsions at 7 or more, or the pAg thereof at 8.3 or less and also that reduction sensitization can be conducted by introducing single addition portions of silver ions during grain formation.
U.S. Pat. No. 5,965,346 discloses the possibility of reduction sensitization of silver halide for use in photothermographic recording materials and discloses therefor: ascorbic acid, thiourea dioxide, stannous chloride, aminoiminomethane sulfinic acid, a hydrazine derivative, a borane compound, a silane compound and a polyamine compound. Furthermore, it discloses that reduction sensitization may be performed by ripening the grains while keeping the emulsion at a pH of 7 or more, or at a pAg of 8.3 or less and also that reduction sensitization may also be performed by introducing single addition part of silver ion during the formation of grains.
U.S. Pat. No. 6,083,680 discloses the possibility of reduction sensitization of silver halide for use in photothermographic recording materials and discloses therefor: stannous chloride, aminoiminomethane sulfonic acid, hydrazine derivatives, borane compounds, silane compounds, polyamines, ascorbic acid and thiourea dioxide. Furthermore, it discloses that reduction sensitization can be performed by ripening the emulsions while maintaining the pH of the emulsions at 7 or more, or the pAg thereof at 8.3 or less and also that reduction sensitization can be conducted by introducing single addition portions of silver ions during grain formation.
A principal problem in developing photothermographic recording materials is their lower photosensitivities than silver halide emulsions. The environmental benefits of dispensing with the wet development necessary for silver halide emulsions by switching to photothermographic recording materials are self-evident. Furthermore, there are significant environmental and economic benefits in coating photothermographic recording materials from aqueous media over solvent media e.g. strongly reduced solvent emissions, no danger of solvent vapour explosions, availability of plant etc. A means of boosting the photosensitivity of photo-addressable thermally developable elements coated from aqueous media is therefore desirable.
Aspects of the Invention
It is therefore an aspect of the invention to provide a means of increasing the photosensitivity of photothermographic recording materials coated from aqueous media.
It is therefore a further aspect of the invention to provide a photothermographic recording material with increased photosensitivity whose photo-addressable thermally developable element is coated from aqueous media.
It is therefore another aspect of the invention to provide an aqueous dispersion for use in providing a photothermographic recording material with increased photosensitivity whose photo-addressable thermally developable element is coated from aqueous media.
Further aspects and advantages of the invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
Reduction sensitization of silver halide is a well-known technique for increasing the sensitivity of silver halide emulsions and hence it would be expected by one skilled in the art, that reducing agents known from such techniques could be used for reduction sensitization of photothermographic emulsions in which silver halide is used as the photosensitive agent. However, it has been found that many of the well-known reduction sensitizers from silver halide emulsion technology give rise to prohibitive fogging and a prohibitive increase in the exposure S required to achieve an optical density of 1.0 above the fogging level, i.e. a prohibitive decrease in photosensitivity, when used in aqueous dispersions of substantially light-insensitive silver salt and a photosensitive silver halide. However, a limited group of reduction agents have been identified which do effect sensitization in such aqueous dispersions.
The above mentioned aspects are realized by an aqueous dispersion comprising a binder or a surfactant, a substantially light-insensitive and substantially water-insoluble organic silver salt and a photosensitive silver halide, wherein the aqueous emulsion further comprises a sensitization agent selected from the group consisting of: tin(II) bromide, aminoiminomethane sulfinic acid, water-soluble salts of H
3
PO
3
, water-soluble salts of H
3
PO
2
, water-soluble SO
3
2−
salts and water-soluble HSO
3
−
salts.
The above mentioned aspects are also realized by a process for producing an aqueous dispersion comprising the steps of: (i) preparing a dispersion of photosensitive silver halide in an aqueous medium; (ii) adding at least one sensitization agent selected from the group consisting of: tin(II) bromide, aminoiminomethane sulfinic acid, water-soluble salts of H
3
PO
3
, water-soluble salts of H
3
PO
2
, water-soluble SO
3
2−
salts and water-soluble HSO
3
−
salts to the dispersion prepared in step (i); and (iii) adding a substantially light-insensitive and substantially water-insoluble organic silver salt.
The above-mentioned aspects are also further realized by a photothermographic recording material comprising a support and a photo-addressable thermally developable element, the photo-addressable thermally developable element fulfilling two requirements: (i) the photo-addressable thermally developable element contains a substantially light-insensitive and substantially water-insoluble organic silver salt, a reducing agent for the substantially light-insensitive and substantially water-insoluble organic silver salt and in thermal working relationship therewith, a photosensitive silver halide and a binder; and (ii) the photo-addressable thermally developable element comprises a layer obtainable by coating the above-mentioned aqueous dispersion onto the support.
The above-mentioned aspects are also realized by a process for preparing a photothermographic recording material having a photo-addressable thermally developable element, the photo-addressable thermally developable element
Gilliams Yvan
Loccufier Johan
Uytterhoeven Herman
Agfa-Gevaert
Chea Thorl
Leydig , Voit & Mayer, Ltd.
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