Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2001-08-22
2004-09-21
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S617000, C430S620000
Reexamination Certificate
active
06794123
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an aqueous dispersion comprising photosensitive silver halide and a substantially light-insensitive silver salt of an organic carboxylic acid and the preparation and use thereof.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,210,717 states that preparation processes for dispersions containing photosensitive silver halide and organic silver salts which allow the pH of the dispersion to rise above 9.0 using alkali salts of alkali or ammonium salts of organic acids such as disclosed in U.S. Pat. No. 3,761,273 and DOS 28 24 556 (=U.S. patent application Ser. No. 803,549, filed Jun. 6, 1977) give rise to silver hydroxide during the processes and to a loss of silver due to precipitation of silver hydroxide. U.S. Pat. No. 4,210,717 discloses a preparation process for dispersions of photosensitive silver halide and half soaps of organic acids and silver salts of organic acids in which a pH of less than 9.0 is maintained to improve the conversion percentage and improve the general quality thereof. It is well known that hydrolysis of silver halides to silver hydroxide and silver oxide give rise to increased background densities in conventional silver halide emulsions, see e.g. The Theory of the Photographic Process Fourth Edition, Ed. T. H. James, Eastman Kodak (1977), page 395, and hence the silver oxide formed at high pH's would also be expected to give rise to increased background and in general reduced stability in the background density in photothermographic materials.
WO 97/04355 discloses a photothermographic recording material, comprising a support and a photo-addressable thermally developable element comprising photosensitive silver halide in catalytic association with a substantially light-insensitive silver salt of an organic carboxylic acid, an organic reducing agent for said substantially light-insensitive silver salt of an organic carboxylic acid in thermal working relationship therewith and a binder, characterized in that said binder comprises a non-proteinaceous water-soluble binder, a non-proteinaceous water-dispersible binder or a mixture of a non-proteinaceous water-soluble binder and a non-proteinaceous water-dispersible binder. The emulsion used for coating the photographic silver behenate emulsion layer of invention example number 40 has a pH well below 8 as can be adduced from the pH's disclosed for the ingredients used.
In photothermographic materials in which both partners of the oxidation-reduction reaction forming the elemental silver particles which make up the image are still present after image development, there is a constant demand for ways of stabilizing these materials both before and after image formation without the necessity for lengthy conditioning at elevated temperatures and high relative humidities.
OBJECTS OF THE INVENTION
It is an object of the instant invention to provide an aqueous dispersion comprising photosensitive silver halide and substantially light-insensitive silver salt of an organic carboxylic acids capable of being used in the preparation of photothermographic materials with improved stability of the background density without the necessity for lengthy conditioning at elevated temperatures and high relative humidities.
It is a further object of the invention to provide a process for preparing an aqueous dispersion comprising photosensitive silver halide and substantially light-insensitive silver salt of an organic carboxylic acids capable of being used in the preparation of photothermographic materials with improved stability of the background density without the necessity for lengthy conditioning at elevated temperatures and high relative humidities.
It is a still further object of the invention to provide a photothermographic recording material with improved stability of the background density without the necessity for lengthy conditioning at elevated temperatures and high relative humidities.
Further objects and advantages of the invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
Surprisingly it has been found that by increasing the pH of aqueous dispersions comprising photosensitive silver halide and substantially light-insensitive silver salt of an organic carboxylic acids temporarily to a pH at or above 8.0, that photothermographic recording materials coated with such dispersions exhibit a substantial reduction in background density and an improvement in the stability of the background density without the necessity for lengthy conditioning at elevated temperatures and high relative humidities.
The above-mentioned objects are realized by a preparation process for a first aqueous dispersion comprising an ex-situ photosensitive silver halide and a substantially light-insensitive silver salt of an organic carboxylic acid, comprising the steps of: separately preparing a second aqueous dispersion comprising the ex-situ photosensitive silver halide and a third aqueous dispersion comprising the substantially light-insensitive silver salt of an organic carboxylic acid; and mixing the second aqueous dispersion with the third aqueous dispersion to produce a mixture thereof, characterized in that the first aqueous dispersion thereby produced is substantially free of a water-soluble metal or ammonium salt of an aliphatic carboxylic acid with greater than 12 carbon atoms and the process further comprises a step selected from the group consisting of: increasing the pH of the second aqueous dispersion to a value of at least 8.0 prior to mixing with the third aqueous dispersion; increasing the pH of the third aqueous dispersion to a value of at least 8.0 prior to mixing with the second aqueous dispersion; and increasing the pH of the mixture to a value of at least 8.0.
The above-mentioned objects are further realized by a first aqueous dispersion comprising an ex-situ photosensitive silver halide and a substantially light-insensitive silver salt of an organic carboxylic acid obtainable by the above-mentioned preparation process.
The above-mentioned objects are also realized by the use of the above-mentioned first aqueous dispersion in preparing a photo-addressable thermally developable element of a photothermographic recording material, the photo-addressable thermally developable element comprising the photosensitive silver halide, the substantially light-insensitive silver salt of an organic carboxylic acid, a reducing agent therefor in thermal working relationship therewith and a binder.
The above-mentioned objects are also realized by a preparation process for a fourth aqueous dispersion comprising a second in-situ photosensitive silver halide and a substantially light-insensitive silver salt of an organic carboxylic acid, comprising the steps of: (I) providing the above-described third aqueous dispersion and (II) partially converting the substantially light-insensitive silver salt of an organic carboxylic acid in the third aqueous dispersion with a non-fluoro halide ion source into the second in-situ photosensitive silver halide thereby producing the fourth aqueous dispersion; characterized in that the fourth aqueous dispersion thereby produced is substantially free of a water-soluble metal or ammonium salt of an aliphatic carboxylic acid with greater than 12 carbon atoms and the process further comprises a step selected from the group consisting of: increasing the pH of the third aqueous dispersion to a value of at least 8.0 prior to step (II); increasing the pH of the third aqueous dispersion to a value of at least 8.0 during step (II); and increasing the pH of the aqueous dispersion resulting from step (II) to a value of at least 8.0.
The above-mentioned objects are also realized by a fourth aqueous dispersion comprising a second in-situ photosensitive silver halide and a substantially light-insensitive silver salt of an organic carboxylic acid obtainable by the above-mentioned preparation process.
The above-mentioned objects are also realized by, the use of the above-mentioned fourth aqueous dispersion in preparing a photo-ad
Uytterhoeven Herman
Vissers Luc
AGFA-Gevaert
Chea Thorl
Leydig , Voit & Mayer, Ltd.
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