Record receiver having plural interactive leaves or a colorless – Having a colorless color-former – developer therefor – or... – Heavy metal reactant
Reexamination Certificate
1999-06-01
2001-04-03
Hess, Bruce H. (Department: 1774)
Record receiver having plural interactive leaves or a colorless
Having a colorless color-former, developer therefor, or...
Heavy metal reactant
C503S202000
Reexamination Certificate
active
06211116
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to thermographic recording materials whose prints have improved image tone.
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.
Research Disclosure number 17029, published in June 1978, gives a survey of different methods of preparing organic heavy metal salts in section II. The invention examples of U.S. Pat. No. 5,380,635 and U.S. Pat. No. 5,434,043 describe the production of organic silver salts using fatty acids of the type HUMKO Type 9718 & Type 9022 from WITCO Co., which contain according to the manufacturer's catalogue a mixture of different fatty acids, in connection with their use in photothermographic recording materials. DE-OS 27 21 828 discloses a thermally developable light-sensitive material, consisting of a support, which contains thereon or in one or more layers at least (a) an organic silver salt, (b) a photocatalyst and (c) a reducing agent, wherein the organic silver salt (a) contains at least a silver salt with an uneven number of 21 or more carbon atoms; and examples with mixtures of two and three organic silver salts of monocarboxylic acids precipitated together, but all with 20 are more carbon atoms.
U.S. Pat. No. 5,677,121 discloses a heat-developable silver halide infrared ray-sensitive material comprising a support having on one side of the support an emulsion layer containing a binder, a nonsensitive silver salt, a reducing agent for silver ion and silver halide grains spectrally sensitized at a wavelength within the region of from 750 to 1400 nm, wherein the nonsensitive silver salt comprises a mixture of silver salts of at least three organic carboxylic acids, one of the acids is behenic acid, and the content of the behenic acid in the acids is from not less than 35 to less than 90 mol %.
However, technology from photothermographic materials on the basis of an organic silver salt, silver halide and a reducing agent is not readily extrapolatable to substantially light-insensitive thermographic recording materials on the basis of an organic silver salt and a reducing agent, since thermographic recording materials are subjected to image-wise heating whereas photothermographic materials are subjected to image-wise exposure and overall heating and much stronger reducing agents are used in thermographic recording materials than in photothermographic recording materials. Furthermore, thermographic recording materials are heated for much shorter times, typically 10 to 20 ms, during thermal development in thermographic printing than photothermographic recording materials, for which 10 s is an average heating time. Such shorter heating times make it difficult to obtain neutral image tones.
EP-A 730 196 discloses a heat-sensitive recording material suited for use in direct thermal imaging and having image-stabilization properties which material contains in a binder on a support (i) a substantially light-insensitive organic silver salt capable of thermally activated reduction to silver in thermal working relationship with (ii) at least one reducing agent capable of reducing the substantially light-insensitive organic silver salt when thermally activated, characterized in that the recording material contains in admixture with the reducing agent(s) at least one colourless photo-oxidizing substance that on exposure to ultraviolet radiation yields free radicals capable of inactivating the reducing agent(s) by oxidation, thereby rendering the reducing agent(s) incapable of reducing the organic silver salt to silver. Furthermore, in sub-claims the organic silver salt is silver palmitate, silver stearate or silver behenate or mixtures thereof. However, the efficacy of such physical mixtures is not exemplified. Physical mixtures in which each component forms a separate phase cannot be equated with mixed crystals in which the components together form a single phase.
Prior art substantially light-insensitive black and white thermographic recording materials exhibit an insufficiently neutral image colour. This is particularly important for thermographic recording materials for medical diagnostic applications for which image tone requirements are particularly severe, particularly at low optical densities. Prior art thermographic recording materials coated from solvent exhibit image tone closer to these requirements than those coated from aqueous media, although the latter are producible using much more environmentally friendly coating processes.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide substantially light-insensitive black and white thermographic recording materials coated from solvent media whose prints exhibit a more neutral image tone.
It is therefore another object of the present invention to provide substantially light-insensitive black and white thermographic recording materials coated from aqueous media whose prints exhibit a more neutral image tone.
Further objects and advantages of the invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
Surprisingly it has been found that substantially light-insensitive black and white thermographic recording materials coated from solvent or aqueous media and comprising mixed crystals of substantially light insensitive organic silver salts exhibit a more neutral image tone than physical mixtures thereof.
The above mentioned objects are realized by a substantially light-insensitive black and white thermographic recording material having a support and a thermosensitive element containing a substantially light-insensitive organic silver salt, an organic reducing agent therefor in thermal working relationship therewith and a binder, characterized in that the thermosensitive element contains substantially light-insensitive mixed crystals of two or more silver salts of organic carboxylic acids with one or more carboxylic acid groups.
A recording process is further provided according to the present invention comprising the steps of: (i) bringing an outermost layer of the above-mentioned thermographic recording material in proximity with a heat source; and (ii) applying heat from the heat source imagewise to the recording material while maintaining proximity to the heat source to produce an image; and (iii) removing the recording material from the heat source.
Preferred embodiments of the invention are disclosed in the dependent claims.
DETAILED DESCRIPTION OF THE INVENTION
In a preferred embodiment of the recording process, according to the present invention, the heat source is a thermal head with a thin film thermal head being particularly preferred.
SUBSTANTIALLY
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.
Substantially Light-Insensitive Mixed Crystals of Two or More Organic Silver Salts
The substantially light-insensitive mixed crystals of two or more silver salts of organic carboxylic acids with one or more carboxylic acid groups of the present invention are produced by slow addition, preferably metered, of a soluble silver salt to a solution or dispersion of a mixture of acids, or their salts, whose silver salts are capable of forming mixed crystals.
Mixed crystals of the present invention have the X-ray diffraction pattern of the organic silver salt which is present in the greatest quantity, although the peaks may be slightly shifted compared with the X-ray diffraction s
Defieuw Geert
Geuens Ingrid
Hoogmartens Yvan
Loccufier Johan
AGFA-GEVAERT
Baker & Botts L.L.P.
Hess Bruce H.
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