Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2001-08-27
2003-05-06
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S935000, C430S964000
Reexamination Certificate
active
06558895
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for preparing photothermographic recording materials with an improved stability.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 3,152,904 discloses an image reproduction sheet which comprises a radiation-sensitive heavy metal salt which can be reduced to free metal by a radiation wave length between an X-ray wave length and a five microns wave length and being distributed substantially uniformly laterally over the sheet, and as the image forming component an oxidation-reduction reaction combination which is substantially latent under ambient conditions and which can be initiated into reaction by the free metal to produce a visible change in colour comprising an organic silver salt containing carbon atoms and different from the heavy metal salt as an oxidizing agent and in addition an organic reducing agent containing carbon atoms, the radiation-sensitive heavy metal salt being present in an amount between about 50 and about 1000 parts per million of the oxidation-reduction reaction combination.
EP-A 386 761 discloses a heat developable color photographic material comprising a support having thereon at least a photosensitive silver halide, a binder, and a dye providing compound capable of releasing or forming a diffusible dye in correspondence or counter correspondence to reduction of the silver halide to silver, said heat developable color photosensitive material further comprising a compound represented by formula (I): C
6n
(H
2
O)
5n+1
wherein n represents an integer of 1 or more.
There is a constant demand for new ways of stabilizing photothermographic recording materials.
ASPECTS OF THE INVENTION
It is an aspect of the instant invention to provide a photothermographic material with improved background density stability.
It is a further aspect of the instant invention to provide a photothermographic material with an improved stability of the photosensitivity.
Further aspects and advantages of the invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
Surprisingly, it has been found that by subjecting photothermographic recording materials with at least one layer of the one or more layers of the photo-addressable thermally developable element coated from an aqueous medium to temperatures at or above 35° C. in the dark for at least 3 days, there is little or no change in background density Dmin and moreover that the Dmin had been stabilized, as evidenced by the little or no additional change in Dmin upon storage in the dark under conditions such as 7 days at 45° C. and 70% relative humidity, which simulate prolonged shelf-life conditions, whether the photothermographic recording material was present as a roll of material or as individual sheets, whereas with conventional photothermographic recording materials with a photo-addressable thermally developable element coated from solvent a loss of image density is obtained under such conditions.
The above-mentioned aspects of the invention are realized by providing a process for preparing a monosheet black and white photothermographic recording material, the photothermographic recording material being exclusive of a dye-providing compound and comprising a support and a photo-addressable thermally developable element, the photo-addressable thermally developable element being thermally developable under substantially water-free conditions and consisting of one or more layers, the layers together comprising photosensitive silver halide, a substantially light-insensitive organic silver salt, a reducing agent therefor in thermal working relationship therewith and a binder, comprising the steps of: (i) coating at least one of the one or more layers of the photo-addressable thermally developable from an aqueous medium; (ii) drying the layer or layers coated in step (i); and (iii) heating the photothermographic recording material at a temperature of at least 35° C. in the dark for a period of at least 3 days.
A photothermographic recording material is also provided by the present invention obtainable by the above-mentioned process.
Further preferred embodiments of the present invention are disclosed in the dependent claims.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
The term aqueous for the purposes of the present invention means containing at least 60% by volume of water, preferably at least 80% by volume of water, and optionally containing water-miscible organic solvents such as alcohols e.g. methanol, ethanol, 2-propanol, butanol, iso-amyl alcohol, octanol, cetyl alcohol etc.; glycols e.g. ethylene glycol; glycerine; N-methyl pyrrolidone; methoxypropanol; and ketones e.g. 2-propanone and 2-butanone etc.
Substantially light-insensitive means not intentionally light sensitive and resistant to darkening upon exposure.
A monosheet photothermographic recording material is a photothermographic recording material in which all the ingredients for image formation are present in a single sheet and the image formation occurs in that sheet without the assistance of one or more additional sheets.
A black and white and white photothermographic recording material is a photothermographic recording material with which substantially neutral black images are produced.
Exclusive of a dye providing compound means that dyes providing compounds capable of releasing or forming a diffusible or non-diffusible dye are not present
The UAg of an aqueous liquid is defined in this specification as the potential difference between a silver electrode (of 99.99% purity) in the aqueous liquid and a reference electrode consisting of a Ag/AgCl-electrode in 3M KCl solution at room temperature connected with the liquid via a salt bridge consisting of a 10% KNO
3
salt solution.
S is defined as that exposure in mJ/m
2
at which the photothermographic recording material attained an optical density of 1.0 above Dmin. Thus the lower the value of S, the higher the photosensitivity of the photothermographic recording material.
By the term “heat solvent” in this specification is meant a non-hydrolyzable organic material which is in solid state in the recording layer at temperatures below 50° C. but becomes a plasticizer for the recording layer in the heated region and/or liquid solvent for at least one of the redox-reactants, e.g. the reducing agent for the first silver salt, at a temperature above 60° C.
By thermally developable under substantially water-free conditions as used is the present specification, means heating at a temperature of 80° to 250° C. under conditions in which the reaction system is approximately in equilibrium with water in the air, and water for inducing or promoting the reaction is not particularly or positively supplied from the exterior of the thermographic recording material. Such a condition is described in T. H. James, “The Theory of the Photographic Process, Fourth Edition, Macmillan 1977”, page 374.
Process for Preparing a Photothermographic Recording Material
A process for preparing a photothermographic recording material, the photothermographic recording material comprising a support and a photo-addressable thermally developable element, the photo-addressable thermally developable element consisting of one or more layers, the layers together comprising photosensitive silver halide, a substantially light-insensitive organic silver salt, a reducing agent therefor in thermal working relationship therewith and a binder, comprising the steps of: (i) coating at least one of the one or more layers of the photo-addressable thermally developable element from an aqueous medium; (ii) drying the layer or layers coated in step (i); and (iii) heating the photothermographic recording material at a temperature of at least 35° C. in the dark for a period of at least 3 days. The temperature is preferably at least 40° C. and particularly preferably at least 45° C. Furthermore, the temperature is preferably less than 50° C.
The period is preferably at least 1 week and the heating is preferably carried out at a relative humidity between 10 and 75% and particul
Uytterhoeven Herman
Vissers Luc
Agfa-Gevaert
Chea Thorl
Leydig , Voit & Mayer, Ltd.
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