Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
1998-08-17
2002-02-19
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S200000, C430S616000, C430S618000, C430S620000, C430S611000, C430S964000
Reexamination Certificate
active
06348308
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a substantially light-insensitive thermographic recording material suitable for thermal development. In particular, it concerns improvements in stabilization thereof.
BACKGROUND OF THE INVENTION
Thermal imaging or thermography is a recording process wherein images are generated by the use of imagewise modulated thermal energy. A survey of “direct thermal” imaging methods is given e.g. in the book “Imaging Systems” by Kurt I. Jacobson-Ralph E. Jacobson, The Focal Press—London and New York (1976), Chapter VII under the heading “7.1 Thermography”. Direct thermal thermography is concerned with materials which are substantially not photosensitive, but are sensitive to heat or thermosensitive. Imagewise applied heat is sufficient to bring about a visible change in a thermosensitive imaging material.
WO 94/16361 discloses a multilayer heat-sensitive material for direct thermal recording for which no intermediate drying of organic noble metal salts is necessary and which is coatable from aqueous dispersions. This material comprises: a colour-forming amount of finely divided, solid colourless noble metal or iron salt of an organic acid distributed in a carrier composition; a color-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. This patent application also discloses that suitable antifoggants for use in the invention are well-known photographic antifoggants such as 2-mercaptobenzo-triazole, chromate, oxalate, carbonate, benzotriazole (BZT), 5-methylbenzo-triazole, 5,6-dimethylbenzotriazole, 5-bromobenzotriazole, 5-chlorobenzo-triazole, 5-nitrobenzotriazole, 4-nitro-6-chlorobenzotriazole, 5-nitro-6-chlorobenzotriazole, 4-hydroxy-6-methyl-1,3,3a, 7-tetraazaindene, benzimidazole, 2-methylbenzimidazole, 5-nitrobenzimidazole, 1-phenyl-5-mercaptotetrazole (PMT), 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptothiazoline, 2-mercapto-4-methyl-6,6′-dimethylpyrimidine, 1-ethyl-2-mercapto-5-amino-1,3,4-triazole, 1-ethyl-5-mercapto-1,2,3,4-tetrazole, 2,5-dimercapto-1,3,4-thiodiazole, 2-mercapto-5-amino-1,3,4-thiodiazole, dimethyldithiocarbamate, and diethyldithiocarbamate.
EP-A 809 143 discloses a substantially non-photosensitive recording material comprising a thermosensitive element comprising a substantially light-insensitive organic silver salt, an organic reducing agent therefor in thermal working relationship therewith and a binder, on a support, characterized in that the thermosensitive element further comprises in reactive association with the substantially light-insensitive organic silver salt and the organic reducing agent a substituted or unsubstituted compound with an unsaturated 5-membered heterocyclic ring consisting of nitrogen and carbon atoms with at least one of the nitrogen atoms having a hydrogen atom and none of the carbon atoms being part of a thione-group, the ring not being annulated with an aromatic ring system and the compound being exclusive of 1,2,4-triazole and substituted 1,2,4-triazole compounds.
EP-A 809 144 discloses a substantially non-photosensitive recording material comprising a thermosensitive element comprising a substantially light-insensitive organic silver salt, an organic reducing agent therefor in thermal working relationship therewith and a binder, on a support, characterized in that the thermosensitive element further comprises in reactive association with the substantially light-insensitive organic silver salt and the organic reducing agent a substituted or unsubstituted 1,2,4-triazole compound with at least one of the nitrogen atoms having a hydrogen atom and none of the carbon atoms being part of a thione-group, the compound not being annulated with an aromatic ring system.
EP-A 809 142 discloses a recording material comprising a support, a thermosensitive element and a protective layer therefor, the thermosensitive element comprising a substantially light-insensitive organic silver salt, an organic reducing agent therefor in thermal working relationship therewith and a binder, wherein the thermosensitive element further comprises in reactive association with the substantially light-insensitive organic silver salt and the organic reducing agent a substituted, exclusive of groups having an exclusively electron withdrawing character, or unsubstituted compound with an unsaturated 5-membered heterocyclic ring annulated with an aromatic ring system, the ring consisting of nitrogen and carbon atoms with at least one of the nitrogen atoms having a hydrogen atom and none of the carbon atoms being directly linked to a sulfur atom or being part of a carbonyl-group.
Prior art stabilizers have been found by the inventors to be unsuitable for stabilizing thermographic materials for graphics applications during storage prior to use.
OBJECTIONS THE INVENTION
It is therefore an object of the invention to provide a means of stabilizing the image of thermographic recording materials during storage.
It is a further object of the invention to provide a process utilizing a substantially non-photosensitive recording material with improved light stabilization to obtain a direct thermal image.
Further objects and advantages of the invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
EP-A 809 142, EP-A 809 143 and EP-A 809 144 address the problem of background colour resulting from exposure to light, which is a particular problem in thermographic materials used for producing continuous tone transparencies for medical and other applications having numerical gradation values less than or equal to 2.3. The present invention addresses the problem of stabilization of the background density during storage prior to use of the intrinsically more thermosensitive thermographic materials based on substantially light-insensitive organic silver salts and reducing agents used for producing steep gradation, so-called graphics images, with numerical gradation values greater than 2.3 as transparencies or on a white support, for which the prior art stabilizers are unsuitable.
The above mentioned objects are realised by a substantially light-insensitive monosheet recording material comprising 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, wherein the thermosensitive element further contains an unsaturated carbocyclic or heterocyclic stabilizer compound substituted with a —SA group where A is hydrogen, a counterion to compensate the negative charge of the thiolate group or a group forming a symmetrical or an asymmetrical disulfide and the recording material is capable of producing prints with a numerical gradation value defined as the quotient of the fraction (2.5−0.1)/(E
2.5
−E
0.1
) greater than 2.3, where E
2.5
is the energy in Joule applied in a dot area of 87 &mgr;m×87 &mgr;m of the imaging layer that produces an optical density value of 2.5, and E
0.1
is the energy in Joule applied in a dot area of the imaging layer material that produces an optical density value of 0.1.
A thermal image recording process is also provided comprising the steps of: (i) providing a substantially light-insensitive recording material, as described above; (ii) bringing an outermost layer of the recording material into proximity with a heat source; (iii) applying heat from a heat source image-wise to the recording material while maintaining proximity to the heat source to produce an image; and (iv) separating the recording material from the heat source.
Preferred embodiments of the invention are d
Horsten Bartholomeus
Loccufier Johan
Terrell David
Uyttendaele Carlo
Agfa-Gevaert
Leydig Voit & Mayer Ltd
Schilling Richard L.
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