Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2001-05-14
2003-06-17
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S631000, C554S074000
Reexamination Certificate
active
06579671
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to recording materials suitable for thermographic or photothermographic development. In particular, it concerns materials with improved shelf-life and prints with improved archivability produced with such materials.
BACKGROUND OF THE INVENTION
Thermal imaging or thermography is a recording process wherein images are generated by the use of thermal energy.
In direct thermography a visible image pattern is formed by image-wise heating of a recording material containing matter that by chemical or physical process changes color 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 color or optical density.
Most of the “direct” thermographic recording materials are of the chemical type. On heating to a certain conversion temperature, an irreversible chemical reaction takes place and a colored image is produced.
According to U.S. Pat. No. 3,080,254 a typical heat-sensitive (thermographic) copy paper includes in the heat-sensitive layer a thermoplastic binder, a water-insoluble silver salt and an appropriate organic reducing agent. Thermosensitive copying paper is used in “front-printing” or “back-printing” using infra-red radiation absorbed and transformed into heat in contacting infra-red light absorbing image areas of an original as illustrated in FIGS. 1 and 2 of U.S. Pat. No. 3,074,809.
GB-A 1,542,327 discloses a thermally developable light-sensitive sheet material, comprising a support and (a) a silver salt of an organic acid, (b) a catalyst in an amount capable of catalyzing the reaction in exposed areas of the material of components (a) and (c) after imagewise exposure and heating of the material, (c) a reducing agent for the silver salt, (a), and (d) sulphur in an amount to reduce the color change after processing and to reduce thermal fogging, the components (a) to (d) are contained, separately or together, in one or more layers coated on the support or being all present in the support or one or more of the components being present in the support and the remainder being in one or more layers coated thereon. The description of GB 1,542,327 includes an exhaustive list of silver salts of organic acids including silver palmitate. Furthermore, D. S. Avose, V. V. Tsvetkov and V. D. Yagodovskii in Sci. Appl. Photo. volume 35, pages 587-594 published in 1994 by Gordon and Breach Science Publishers S.A. describe photothermographic materials based on silver bromide and silver palmitate.
U.S. Pat. No. 4,273,723 discloses a process for preparing a silver salt of a fatty acid with 12 to 24 carbon atoms consisting essentially of reacting an alkali metal salt of the fatty acid with a water-soluble silver salt. The reaction is effected in a reaction system consisting essentially of (I) the alkali metal salt of the fatty acid, (II) the water-soluble silver salt, (IR) at least one water-soluble or partially water-soluble C
3
-C
8
alcohol and (IV) water, the volume ratio of the component (III) to the component (IV) being from 1/5 to 5/1.
EP-A 754,969 discloses a process for producing a suspension of particles containing a substantially light-insensitive silver salt of an organic carboxylic acid. The process comprises simultaneous metered addition of an aqueous solution or suspension of an organic carboxylic acid or its salt and an aqueous solution of a silver salt to an aqueous liquid. The metered addition of the aqueous solution or suspension of the organic carboxylic acid or its salt and/or the aqueous solution of the silver salt is regulated by the concentration of silver ions or the concentration of anions of the silver salt in the aqueous liquid.
Research Disclosure number 17029, published in June 1978, in section II gives a survey of different methods of preparing organic heavy metal salts. Method 5, for example, describes the preparation of silver behenate by (a) heating behenic acid in water to a temperature above the melting point of the acid, but below the boiling point of the dispersion, (b) adding an aqueous solution of alkali metal or ammonium hydroxide, and (c) adding an aqueous solution of silver nitrate. However, in order to obtain a fine emulsion of an organic heavy metal salt, either the synthesis has to be carried out in an organic solvent medium as disclosed, for example, in U.S. Pat. No. 3,700,458 or in a mixture of water and a substantially water insoluble organic solvent as disclosed, for example, in U.S. Pat. No. 3,960,908 for silver carboxylates.
GB-A 1,378,734 discloses a process of producing a silver salt of an organic carboxylic acid, which comprises mixing (a) an aqueous solution of silver nitrate or a silver complex with (b) a solution of an organic carboxylic acid in a solvent in which the organic carboxylic acid is soluble. The solvent is chosen so that both the silver salt of an organic carboxylic acid and the silver nitrate are almost insoluble in the solvent and water is sparingly miscible in the solvent. In the mixture, the organic carboxylic acid reacts with silver ions. The reaction is conducted in the presence of a soluble mercury compound and/or a soluble lead compound.
The association of silver behenate, silver palmitate, or silver stearate with mercury or lead ions, particularly mercury ions, as disclosed in GB 1,378,734 is environmentally undesirable and infringes governmental regulations. Direct thermal recording materials with silver behenates produced using the processes described in RD 17029 exhibit a brown image color upon image-wise heating which is undesirable for medical images viewed in transmission with a viewing box. This lack of image color neutrality can be quantified by spectrophotometric measurements according to ASTM Norm E179-90 in a R(45/0) geometry with evaluation according to ASTM Norm E308-90 to produce the CIELAB a* and b* co-ordinates. Color neutrality on the basis of CIELAB-values corresponds to a* and b* values of zero, with a negative a*-value indicating a greenish image-tone becoming greener as a* becomes more negative, a positive a*-value indicating a reddish image-tone becoming redder as a* becomes more positive, a negative b*-value indicating a bluish image-tone becoming bluer as b* becomes more negative and a positive b*-value indicating a yellowish image-tone becoming yellower as b* becomes more positive.
Additionally, recording materials prepared using prior art silver palmitate processes and compounds exhibit poor shelf-life. Recording materials prepared using prior art silver stearate processes and compounds also exhibit poor shelf-life and prints produced with these materials exhibit poor archivability, particularly as regards increase in D
max
.
SUMMARY OF THE INVENTION
Objects of the Invention
It is therefore an object of the invention to provide recording materials with improved shelf-life.
It is a further object of the present invention to provide thermographic and photothermographic recording materials whose prints exhibit improved archivability and light stability.
It is a still further object of the present invention to provide a production process for substantially light-insensitive organic silver salts comprising silver behenate, palmitate, and/or stearate.
Further objects and advantages of the invention will become apparent from the description below.
Surprisingly, it has been found that recording materials comprising a support and a thermosensitive element comprising silver behenate, silver palmitate or silver stearate with a higher crystallinity than respective prior art organic silver salts, an organic reducing agent therefor in thermal working relationship therewith and a binder exhibit a marked improvement in shelf-life and/or archivability of prints produced with the recording materials relative to recording materials of the prior art.
The above mentioned objects of the invention are realized with a recording material comprising a support and a
Bellens Andre
Bollen Dirk
Emmers Sabine
Geuens Ingrid
Gilliams Yvan
AGFA-Gevaert
Chea Thorl
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