Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
1998-08-21
2001-10-09
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S528000, C430S529000, C430S531000
Reexamination Certificate
active
06300052
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a substantially light-insensitive black and white thermographic material comprising a thermosensitive element including a binder having covalently bonded ionic groups.
BACKGROUND OF THE INVENTION
Thermal imaging or thermography is a recording process wherein images are generated by the use of thermal energy.
In thermography three approaches are known:
1. Direct thermal formation of a visible image pattern by image-wise heating of a recording material containing matter that by chemical or physical process changes colour or optical density.
2. Image-wise transfer of an ingredient necessary for the chemical or physical process bringing about changes in colour or optical density to a receptor element.
3. Thermal dye transfer printing wherein a visible image pattern is formed by transfer of a coloured species from an image-wise heated donor element onto a receptor element.
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 coloured image is produced. A wide variety of chemical systems has been suggested some examples of which have been given on page 138 of “Imaging Systems” by Kurt I. Jacobson-Ralph E. Jacobson, The Focal Press—London and New York (1976), describing the production of a silver metal image by means of a thermally induced oxidation-reduction reaction of a silver soap with a reducing agent.
DE 3635441 discloses a process for producing an image, characterized in that a thermally developable photosensitive material, comprising a support with at least a photosensitive silver halide and a high molecular weight compound containing a repeating unit derived from a vinyl monomer with a —COOM-group and/or a —SO
3
M-group, wherein M represents a hydrogen atom or an alkali metal atom, is heated, simultaneously or after image-wise exposure, in the presence of water and at least a base and/or a base-precursor.
JP 61-193142 discloses a heat development photosensitive material characterized in that in thermally developed photosensitive material which has a photosensitive layer containing at least silver halide particles on a support, the said photosensitive material has a layer which contains a water soluble or water dispersible block copolymer which has a polyvinyl alcohol system polymer as one component and a polymer which has an ionic group as the other component.
EP 678 776 discloses a thermally processable imaging element, said element comprising: (1) a support; and (2) a thermographic or photothermographic imaging layer on one side of said support; characterized in that said element additionally comprises (3) at least one electroconductive outermost layer comprised of electrically-conductive metal-containing particles dispersed in a polymeric binder in an amount sufficient to provide a surface resistivity of less than 5×10
11
ohms/square. However, there is no teaching in this document as regards thermographic materials based on organic silver salts and reducing agents.
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. In the description of WO 94/16361 are recited the following water-soluble polymeric carriers: polyvinyl alcohol, methyl cellulose, carboxy methyl cellulose, polysaccharide gums, gelatins, styrene butadiene copolymers, hydroxylated corn starch, acrylic latexes and blends and mixtures thereof. As dispersing agent the ammonium salt of styrene/acrylic acid is recited, with LUPASOL™ FF-3249 from BASF being used in the invention examples.
The inventors of the present invention found that thermographic materials containing conventional acrylic latexes coated from aqueous media exhibited poor archivability and poor light stability.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide thermographic materials coated from aqueous media which exhibit improved archivability and/or improved light stability, while maintaining high maximum density and low minimum density levels upon printing.
Further objects and advantages of the invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
It has been surprisingly found that black and white prints made with thermographic materials coated from an aqueous medium exhibit substantially improved archivability and increased light stability upon using water-dispersible film-forming polymers with covalently bonded ionic groups instead of the conventional acrylic latexes disclosed for this purpose in WO 94/16361.
The above-mentioned objects are realized by a substantially light-insensitive black and white thermographic material including a support and a thermosensitive element, containing a substantially light-insensitive organic silver salt, a reducing agent therefor in thermal working relationship therewith and a binder, wherein the binder is a water-dispersible film-forming polymer having covalently bonded ionic groups and the thermographic material is thermally developable under substantially water-free conditions.
A process is also provided, according to the present invention, for producing the substantially light-insensitive black and white thermographic material referred to above comprising the steps of: producing an aqueous dispersion of the substantially light-insensitive organic silver salt; producing one or more aqueous coating compositions containing together the aqueous dispersion of the substantially light-insensitive organic silver salt, the reducing agent and the binder; 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
Substantially
By substantially light-insensitive is meant not intentionally light sensitive.
By thermally developable under substantially water-free conditions as used herein, 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.
Aqueous
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, octanol, cetyl alcohol etc.; glycols e.g. ethylene glycol; glycerine; N-methyl pyrrolidone; methoxypropanol; and ketones e.g. 2-propanone and 2-butanone etc.
Water-dispersible Binder
The binder used according to the present invention is a water-dispersible film-forming polymer having covalently bonded ionic groups. The water-dispersible film-forming polymer having covalently bonded ionic groups used in the present invention is preferably a copolymer of an ionic monomer with covalently bonded anionic or cationic groups, for example:
Ionic monomer 1=potassium salt of N-[(4′-sulfobenzamido)-oxo-decyl]methacrylamide;
Ionic monomer 2=sodium salt of vinyl 2-sulfohexadecanoate;
Ionic monomer 3=ammonium N-(1′,1′-dimethyl
Aert Huub Van
Hoogmartens Ivan
Louwet Frank
Ruttens Frank
AGFA-GEVAERT
Chea Thorl
Leydig , Voit & Mayer, Ltd.
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