Radiation imagery chemistry: process – composition – or product th – Thermographic process – Heat applied after imaging
Reexamination Certificate
1998-12-14
2001-08-14
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Thermographic process
Heat applied after imaging
C430S619000
Reexamination Certificate
active
06274297
ABSTRACT:
DESCRIPTION
1. Field of the Invention
The present invention relates to a photothermographic recording material with improved sensitivity and contrast.
2. Background of the Invention
U.S. Pat. No. 3,457,075 discloses a sheet material useful in imaging by a process involving exposure to a light-image followed by uniform heating and including a stratum containing (a) photosensitive silver halide catalyst-forming means and (b) heat-sensitive reactant image-forming means including (1) a water-insoluble silver salt of a long chain fatty acid as an oxidizing agent, and (2) a reducing agent for silver ion, the oxidation-reduction reaction of which to produce a visible change is accelerated by the catalyst; the stratum being further characterized in that a sufficient quantity, of at least about one-fourth mol percent based on the fatty acid silver salt, of the photosensitive means is in catalytic proximity with a sufficient proportion of the heat-sensitive means to provide a gamma infinity value of at least about 0.5 when the stratum is exposed image-wise to the light-image and the image is then developed by uniform heating and wherein the manufacture method for the sheet material comprises mixing with the fatty acid silver salt a source of halide ions under conditions permitting reaction therebetween with formation of the silver halide catalyst-forming means. As sources of halide ions for the conversion of organic silver salts to silver halides GB 1,547,326 lists: inorganic halides, halogen-containing metal complexes, onium halides (for example quaternary ammonium halides, quaternary phosphonium halides and ternary sulfonium halides), halogenated hydrocarbons, N-halo compounds and other halogen-containing compounds.
WO 97/48014 discloses a production method for a photothermographic recording material comprising the steps of: (i) providing a support; (ii) coating the support with a photo-addressable thermally developable element comprising a substantially light-insensitive organic silver salt, photosensitive silver halide in catalytic association with the substantially light-insensitive organic silver salt, a reducing agent in thermal working relationship with the substantially light-insensitive organic silver salt and a binder, characterized in that the photosensitive silver halide is formed by reacting an aqueous emulsion of particles of the substantially light-insensitive organic silver salt with at least one onium salt with halide or polyhalide anion(s) and that the photo-addressable thermally developable element is coated from an aqueous dispersion medium.
WO 97/48015 discloses a photothermographic recording material comprising a photo-addressable thermally developable element coatable from aqueous media comprising a substantially light-insensitive organic silver salt, photosensitive silver halide in catalytic association with the substantially light-insensitive organic silver salt and a reducing agent in thermal working relationship with the substantially light-insensitive organic silver salt and a binder, characterized in that the binder comprises a water soluble polymer, a water-dispersible polymer or a mixture of a water soluble polymer and a water-dispersible polymer and particles of the photosensitive silver halide are non-aggregating in the photo-addressable thermally developable element and are uniformly distributed over and between particles of the substantially light-insensitive organic silver salt, at least 80% by number of the particles having a diameter, determined by transmission electron microscopy, of <40 nm.
U.S. Pat. No. 3,871,887 discloses a method of preparing a photothermographic composition comprising: A) preparing a dispersion of: a) an oxidation-reduction image-forming combination comprising: i) a silver salt oxidizing agent and ii) an organic reducing agent with: b) ex-situ synthetic polymer-peptized photosensitive silver halide, and c) a cyclic imide toner in d) a non-gelatin polymeric binder and B) mixing with the dispersion a sensitizing concentration of a non-silver iodide salt, the iodide salt having the property of increasing the photosensitvity of the photothermographic composition.
However, there is a need for photothermographic recording materials with still higher photosensitivities than those achievable using the teaching of WO 97/48014 and WO 97/48015 in particular for photothermographic recording materials coated from aqueous solutions and dispersions. Further desirable aims are improvement in contrast and a reduction in the amount of photosensitive silver halide necessary to achieve the required photosensitivity in photothermographic materials based on a substantially light-insensitive organic silver salt, photosensitive silver halide in catalytic association with the organic silver salt and a reducing agent for the organic silver salt. A reduction in the amount of silver halide would increase the intrinsic stability of such materials and hence their photosensitivity (or the amount of silver halide necessary to attain the same photosensitivity), since this reduces the amount of stabilizer necessary to achieve acceptable pre- and post-exposure stability and hence the degree of stabilizer-induced photosensitivity loss.
OBJECTION OF THE INVENTION
It is therefore a first object of the invention to provide a process for producing a photothermographic recording material comprising a photo-addressable thermally developable element based on a substantially light-insensitive organic silver salt, photosensitive silver halide in catalytic association with the organic silver salt and a reducing agent for the organic silver salt with increased photosensitivity by coating from an aqueous medium.
It is a second object of the invention to provide a photothermographic recording material comprising a photo-addressable thermally developable element based on a substantially light-insensitive organic silver salt, photosensitive silver halide in catalytic association with the organic silver salt and a reducing agent for the organic silver salt having an increased photosensitivity.
It is a still further object of the invention to provide a recording process for a thermographic recording material with the above improved characteristics.
Further objects and advantages of the invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
In variance to U.S. Pat. No. 3,871,887 in which the invention examples show that no significant change in photosensitivity was realized by varying the added iodide between 0.05 and 0.25 moles per mole ex-situ photosensitive silver bromide with photothermographic image-forming elements coated from solvent media, it has been surprisingly found by the inventors that with photothermographic image-forming elements coated from aqueous media the photosensitivity increased strongly with iodide concentration, the optimum iodide concentration being greater than 0.25 moles per mole ex-situ photosensitive silver halide.
The above-mentioned objects of the present invention, were realized by providing a production process for a photothermographic recording material thermally developable under substantially water-free conditions comprising the steps of: (i) providing a support; (ii) producing one or more aqueous dispersions or solutions containing together a substantially light-insensitive organic silver salt, photosensitive ex-situ silver halide in catalytic association with the substantially light-insensitive organic silver salt, a reducing agent in thermal working relationship with the substantially light-insensitive organic silver salt and a binder; (iii) coating the one or more aqueous dispersions or solutions onto the support to form layers which upon drying become a photo-addressable thermally developable element; and (iv) drying the layers, wherein the photo-addressable thermally developable element contains between 0.2 and 2.5 moles of in-situ photosensitive silver iodide per mole of ex-situ photosensitive silver halide produced by reacting particles of the substantially light-insensitive organic silver salt i
Bastiaens Luc
Gilliams Yvan
Uytterhoeven Herman
Van Roost Chris
Vissers Luc
AGFA-GEVAERT
Baker & Botts L.L.P.
Chea Thorl
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