Record receiver having plural interactive leaves or a colorless – Having a colorless color-former – developer therefor – or... – Color developed by mere decomposition of color-former
Reexamination Certificate
1999-05-06
2001-02-06
Hess, Bruce H. (Department: 1774)
Record receiver having plural interactive leaves or a colorless
Having a colorless color-former, developer therefor, or...
Color developed by mere decomposition of color-former
C427S150000, C430S617000, C430S620000, C503S210000, C503S214000
Reexamination Certificate
active
06184179
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to thermographic recording materials with improved stability to incident light and improved archivability.
BACKGROUND OF THE INVENTION
Thermal imaging or thermography is a recording process wherein images are generated by the use of thermal energy. In direct thermal thermography a visible image pattern is formed by image-wise heating of a recording material containing matter that by chemical or physical process changes colour or optical density. Such recording materials become photothermographic upon incorporating a photosensitive agent which after exposure to UV, visible or IR light is capable of catalyzing or participating in a thermographic process bringing about changes in colour or optical density.
Examples of photothermographic materials are the so called “Dry Silver” photographic materials of the 3M Company, which are reviewed by D. A. Morgan in “Handbook of Imaging Science”, edited by A. R. Diamond, page 43, published by Marcel Dekker in 1991.
In U.S. Pat. No. 2,910,377 the following statement is made in the description in column 7, lines 23-27: “Stability towards exposure to light is improved by selecting highly purified materials; freedom from halides and sulphides is particularly important in the case of compositions involving silver salts”. The disclosure in U.S. Pat. No. 2,910,377 concerned thermographic recording materials coated from solvent media.
WO 94/16361 discloses a multilayer heat-sensitive material which comprises: a colour-forming layer comprising: a colour-forming amount of finely divided, solid colourless noble metal or iron salt of an organic acid distributed in a carrier composition; a colour developing amount of a cyclic or aromatic organic reducing agent, which at thermal copy and printing temperatures is capable of a colour-forming reaction with the noble metal or iron salt; and an image-toning agent; characterized in that (a) the carrier composition comprises a substantially water-soluble polymeric carrier and a dispersing agent for the noble metal or iron salt and (b) the material comprises a protective overcoating layer for the colour-forming layer. WO 94/16361 concerns thermographic materials coated from aqueous media.
Ever tighter solvent emission regulations and measures to avoid solvent explosions, make the avoidance of solvent coating desirable. However, thermographic materials of the type disclosed in WO 94/16361 while being coatable from aqueous media exhibit an inadequate archivability for many applications. Furthermore, the presence of chloride ions in the ingredients has been found to cause poor light stability. There is therefore a need for thermographic recording materials coatable from aqueous media based on substantially light-insensitive organic silver salts with improved shelf-life and stability to light, whose prints exhibit improved archivability and stability to incident light.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide thermographic recording materials coated from aqueous media with improved stability to incident light.
It is therefore another object of the present invention to provide thermographic recording materials which are capable of producing thermographic prints with improved archivability and stability to incident light.
Further objects and advantages of the invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
It is known that conversion of organic silver salts into silver non-fluoro-halides renders thermographic materials photosensitive, since this is the basis of photothermographic materials. This conversion would be expected to occur more readily in aqueous media due to the non-fluoro-halide ions being more mobile in a highly polar medium such as water. The statement made in U.S. Pat. No. 2,910,377 to the effect that the use of highly purified materials improves the light-stability of thermographic materials and in particular freedom from halides and sulphides, concerns thermographic materials coated in solvent media in which the mobility of non-fluoro-halide ions is much lower than in water.
It is therefore surprising that in the presence of gelatin and despite the greater potential for silver halide formation in aqueous media, the expected light instability due to non-fluoro-halide ions only becomes significant, relative to the general stability of the material concerned (dependent upon choice of reducing agent and other ingredients), at non-fluoro-halide ion concentrations above 700 ppm with respect to the gelatin present. This invention enables the use of ingredients in thermographic materials without the exhaustive removal of non-fluoro-halides.
The above objects of the present invention are realized by providing a thermographic recording material comprising a support and a thermosensitive element containing a substantially light-insensitive silver salt of an organic carboxylic acid, a reducing agent therefor in thermal working relationship therewith and at least one proteinaceous binder, wherein the thermosensitive element contains between 700 ppm and 5 ppm of a non-fluoro-halide ion with respect to the proteinaceous binders in the thermosensitive element and the thermographic recording material is thermally developable under substantially water-free conditions.
A process for producing a thermographic recording material as described above is further provided by the present invention comprising the steps of: producing an aqueous dispersion of the substantially light-insensitive silver salt of an organic carboxylic acid; producing one or more aqueous coating compositions containing together the aqueous dispersion of the substantially light-insensitive silver salt of an organic carboxylic acid, the reducing agent and the proteinaceous binder(s); and applying the one or more aqueous coating compositions to the support thereby forming after drying the thermosensitive element.
Preferred embodiments of the present invention are disclosed in the detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
In a preferred embodiment the substantially light-insensitive thermographic recording materials of the present invention are black and white thermographic recording materials.
Definitions
The term aqueous for the purposes of the present invention includes mixtures of water with water-miscible organic solvents such as alcohols e.g. methanol, ethanol, 2-propanol, butanol, iso-amyl alcohol etc.; glycols e.g. ethylene glycol; glycerine; N-methyl pyrrolidone; methoxypropanol; and ketones e.g. 2-propanone and 2-butanone etc.
By substantially light-insensitive is meant not intentionally light sensitive. By substantially solvent-free aqueous medium is meant that solvent, if present, is present in amounts below 10% by volume of the aqueous medium.
Heating in a substantially water-free condition as used herein, means heating at a temperature of 80 to 250° C. The term “substantially water-free condition” means that 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 to the element. Such a condition is described in T. H. James, “The Theory of the Photographic Process”, Fourth Edition, Macmillan 1977, page 374.
Non-fluoro-halide Ion Concentration in the Thermosensitive Element
According to the present invention a thermographic recording material is provided comprising a support and a thermosensitive element containing a substantially light-insensitive silver salt of an organic carboxylic acid, a reducing agent therefor in thermal working relationship therewith and at least one proteinaceous binder, characterized in that the thermosensitive element contains between 700 ppm and 5 ppm of a non-fluoro-halide ion with respect to the proteinaceous binders in the thermosensitive element. In a preferred embodiment the non-fluoro-halide ion concentration in the thermosensitive element is between 500 ppm and 5 ppm of a non-fluoro-halide with respect to the
Geuens Ingrid
Gilliams Yvan
Hoogmartens Yvan
Uyttendaele Carlo
AGFA-GEVAERT
Baker & Botts L.L.P.
Hess Bruce H.
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