Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C1/00—Photosensitive materials
  • G03C1/494—Silver salt compositions other than silver halide emulsions; Photothermographic systems ; Thermographic systems using noble metal compounds
  • G03C1/498—Photothermographic systems, e.g. dry silver
  • G03C1/4989—Photothermographic systems, e.g. dry silver characterised by a thermal imaging step, with or without exposure to light, e.g. with a thermal head, using a laser
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C1/00—Photosensitive materials
  • G03C1/494—Silver salt compositions other than silver halide emulsions; Photothermographic systems ; Thermographic systems using noble metal compounds
  • G03C1/498—Photothermographic systems, e.g. dry silver
  • G03C1/49872—Aspects relating to non-photosensitive layers, e.g. intermediate protective layers
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C1/00—Photosensitive materials
  • G03C1/494—Silver salt compositions other than silver halide emulsions; Photothermographic systems ; Thermographic systems using noble metal compounds
  • G03C1/498—Photothermographic systems, e.g. dry silver
  • G03C1/49827—Reducing agents
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C1/00—Photosensitive materials
  • G03C1/76—Photosensitive materials characterised by the base or auxiliary layers
  • G03C1/7614—Cover layers; Backing layers; Base or auxiliary layers characterised by means for lubricating, for rendering anti-abrasive or for preventing adhesion
  • G03C2001/7635—Protective layer
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C2200/00—Details
  • G03C2200/35—Intermediate layer
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C2200/00—Details
  • G03C2200/47—Polymer

Definitions

• the present invention concerns barrier layers for use in substantially light-insensitive thermographic recording materials.
• Thermography is an image-forming process including a heating step and hence includes photothermography in which the image-forming process includes image-wise exposure and direct thermal processes in which the image-forming process includes an image-wise heating step.
• direct thermal printing a visible image pattern is produced by image-wise heating of a recording material.
• US 3,933,508 discloses a heat developable light-sensitive material comprising, on a support, (1) an organic silver salt, (2) a light-sensitive silver halide or silver-halide prepared by reacting the organic silver salt with a halide, (3) a reducing agent, (4) a binder, and (5) an overcoat layer overlying components (1)-(4); said components (1)-(4) occurring in a single coated layer consisting essentially of a polymer having a refractive index greater than about 1.45 at 20°C, having heat resistance to temperatures greater than about 46°C, being colorless and soluble in organic solvents, and providing increased transparency for said overcoat layer.
• polymers used for the overcoat layer according to US 3,933,508, which are preferably heat-resistant, colorless and soluble in solvents are polyvinyl chloride, polyvinyl acetate, copolymers of vinyl chloride and vinyl acetate containing more than 50 mol% vinyl chloride but insufficient vinyl chloride to lower the heat resistance, polyvinyl butyral, polystyrene, polymethyl methacrylate, benzyl cellulose, ethyl cellulose, cellulose acetate butyrate, cellulose acetate, polyvinylidene chloride, polyvinyl pyrrolidone, cellulose propionate, polyvinyl formal, cellulose acetate phthalate, polycarbonates and cellulose acetate propionate.
• gelatin gelatin derivatives such as phthalated gelatin, acrylamide polymers, polyisobutylene, butadiene-styrene copolymers (no limitation on monomer proportions) and polyvinyl alcohol are preferred.
• EXAMPLES 5, 10, 12 and 18 exemplify an overcoat comprising a vinyl chloride-vinyl acetate copolymer (95 wt% vinyl chloride, 5wt% vinyl acetate).
• GB-A 1,422,057 discloses a heat-developable photosensitive material comprising, coated on a support, a layer of (1) an organic silver salt, (2) a light-sensitive silver halide as grains of which at least 30 mole % is silver iodide, (3) a reducing agent and (4) a spectrally sensitising dye adsorbed on the surface of the silver halide grains, which sensitizing dye has an oxidation potential not exceeding 1.00 volt and difference in values between its oxidation potential and its reduction potential of at least 2.00 volts.
• EXAMPLE 4 discloses a silver benzotriazolate-containing heat-developable photosensitive layer with a top-coat of a vinyl chloride-vinyl acetate copolymer (85:15 by weight).
• DE-A 24 39 460 discloses a thermally developable photosensitive material, comprising coated on a support, (a) an organic silver salt, (b) a catalytic quantity of a silver halide or photosensitive silver-halide prepared by reacting the organic silver salt with a halide, (c) a reducing agent and (d) a binder, and an overcoat, which comprises a polymer layer with kaolin dispersed therein.
• DE-A 24 39 460 discloses the following overcoat polymers: (a) copolyesters; (b) nylon compounds; (c) vinylidene dichloride copolymers; (d) ethylene-vinyl acetate-copolymers; (e) cellulose ethers; (f) polyethylene; (g) synthetic rubbers; (h) cellulose esters; (i) polyvinylesters; (j) polyacrylates and ⁇ -alkyl-polyacrylate esters; (k) high molecular weight polyethylene oxides of polyglycols with an average molecular weight of about 4000 to 1,000,000; (1) polyvinyl chloride and copolymers; (m) polyvinyl acetals; (n) polyformaldehydes; (o) polyurethanes; (p) polycarbonates; (q) polystyrenes; (r) gelatins and their derivatives; (s) polyvinyl alcohol; (t) naturally occurring colloids.
• EXAMPLE 4
• US 4,197,131 discloses a light-sensitive composition
• a light-sensitive composition comprising an intimate mixture of a substantially light-sensitive silver compound which upon reduction gives a visible change and sufficient of a silver halide to catalyse said reduction to give a visible change in those areas where the silver halide has been exposed to light and when the mixture is heated in the presence of a reducing agent, and as a yellow acutance dye a 1-alkyl-4-nitromethylene-quinolane, the alkyl substituent containing 1 to 4 carbon atoms.
• the EXAMPLES disclose overcoating of the light-sensitive dispersion with a layer comprising a vinyl chloride-vinyl acetate copolymer available from Union Carbide under the name VYNS.
• US 4,558,003 discloses an unexposed photothermographic article comprising a support, a silver containing layer comprising a binder, a silver compound having reducible silver ions, silver halide in catalytic proximity to said silver compound, and a reducing agent for silver ion, said binder comprising at least 25 percent by weight of a poly(vinyl acetal), said article being characterized by the presence of an amount of borate ion, a boric acid salt, or a boric acid, alone, or in combination with an isocyanate, sufficient to harden said binder.
• EXAMPLE 1 exemplifies a top coat of a poly(vinyl acetate)/poly(vinyl chloride)copolymer (80/20).
• US 4,460,681 discloses a color photothermographic imageable article comprising a substrate, a photothermographic emulsion layer, and organic solvent soluble barrier layer, a second photothermographic emulsion layer on a polymeric cover layer, wherein each of the photothermographic layers comprise a reducible silver source, photosensitive silver halide, a reducing agent for silver ion and solvent soluble binder, and further wherein each photothermographic layer is sensitized to a portion of the spectrum at least 60 nm different from the other photothermographic layer and each photothermographic layer contains a leuco dye which when oxidized forms a feasible dye having a maximum absorbance at least 60 nm different from that of the dye formed in the at least one other photosensitive layer, and the barrier layer is between said photothermographic layers and is impermeable to the solvent contained in the second photothermographic layer.
• Second layer “barrier” polymers may, according to US 4,460,681, be maleic anhydride/vinyl methyl ether copolymers, polyvinylidene chloride (SARANTM), or polyvinylpyrrolidone, with maleic acid copolymers such as alkyl monoesters of poly(methyl vinyl ether/maleic acid) being preferred.
• the "barrier” polymer, which is the fourth layer and preferably contains the color reactants is normally a methyl methacrylate polymer (preferably a hard polymer with a Tukon hardness of 20 or more), copolymer, or blend with other polymers or copolymers (e.g.
• a yellow/magenta barrier coating is disclosed of a butadiene/styrene copolymer and a polyvinyl chloride/acetate/alcohol) polymer (VAGH).
• EP-A 0 536 955 discloses a heat developable photothermographic article comprising: (a) an image-receiving element comprising a polymeric image-receiving layer; and (b) strippably adhered to said image-receiving element, an imageable photothermographic element comprising a plurality of emulsion layers, each of which emulsion layers comprises a binder, a silver source material, and a leuco dye, and interposed between each pair of said emulsion layers a dye-permeable interlayer.
• EP-A 0 536 955 further discloses that the first interlayer must be impermeable to solvents to be used for applying the subsequent coating; however, the polymer for forming the first interlayer can be applied from any organic solvent.
• the polymer of the first interlayer is preferably a thermoplastic polymer. Homopolymers of vinyl chloride or copolymers of vinyl chloride, preferably having a glass transition temperature greater than 80°C, for example, a copolymer of vinyl chloride (96%) and vinyl acetate (4%), a blend of poly(vinyl chloride)(90%) and poly(vinyl acetate)(10%), can be used to form the first interlayer.
• EXAMPLE 1 exemplifies an interlayer comprising a terpolymer of vinyl chloride(83%), vinyl acetate(16%) and maleic acid(1%).
• US 4,942,115 discloses a thermally processable imaging element comprising a support bearing a thermally processable hydrophobic imaging layer and, on the side of the imaging layer away from the support, an overcoat layer comprising poly(silicic acid) and a hydrophilic monomer or polymer, wherein the element comprises a polymeric adhesion promoting layer between the overcoat and the imaging layer.
• polymers that are useful in the polymeric adhesion promoting layer are: (1) terpolymers of 2-propenenitrile, 1,1-dichloroethene, and propenoic acid, such as disclosed in US 3,271,345; and (2) terpolymers of 2-propenoic acid, methyl ester, 1,1-dichloroethene and itaconic acid as disclosed in, for example, US 3,437,484, with a polymeric adhesion layer comprising poly(2-propenenitrile co-1,1-dichloroethene-co-2-propenoic acid) or poly(2-propenoic acid, methyl-ester-co-1,1dichloroethene-co-itaconic acid) being preferred and poly(2-propenenitrile co-1,1-dichloroethene-co-2-propenoic acid) being exemplified.
• US 6,352,819 discloses a high contrast black-and-white photothermographic material comprising a support having thereon: (a) a thermally developable, high contrast imaging layer(s) comprising a binder and in reactive association, photosensitive silver halide, a non-photosensitive source of reducible silver ions, a reducing composition for said non-photosensitive source reducible silver ions, and a high contrast agent, and (b) a barrier layer that is on the same side but farther from said support than said high contrast imaging layer(s), said barrier layer comprising a film-forming polymer and being impermeable to or reactive with any components that are diffusible from said image-forming layer(s) at a temperature greater than 80°C.
• US 6,352,819 further discloses but does not claim a high contrast black-and-white thermographic material comprising a support having thereon: (a) a thermally developable and non-photosensitive, high contrast imaging layer(s) comprising a binder and in reactive association, a non-photosensitive source of reducible silver ions, a reducing composition for said non-photosensitive source reducible silver ions, and a high contrast agent, and (b) a barrier layer that is farther from the support than the high contrast imaging layer(s), the barrier layer comprising a film-forming polymer and being impermeable to or reactive with any components that are diffusible from said image-forming layer(s) at a temperature greater than 80°C.
• thermographic material is a generic term which includes photothermographic materials and the recitation of the high contrast thermographic material does not exclude the presence of photosensitive species such as photosensitive silver halide. There is therefore no specific disclosure in US 6,352,819 concerning substantially light-insensitive thermographic materials and moreover US 6,352,819 contains no examples devoted to substantially light-insensitive thermographic materials.
• Some particularly useful barrier materials include polyvinyl alcohol, a styrene polymer (including polymers of styrene derivatives), a vinyl halide polymer, a vinyl acetate polymer [such as polyvinyl acetate, poly(ethylene-co-vinyl acetate) or a copolymer of a vinyl halide and vinyl acetate], a polyvinyl pyrrolidone, a water-soluble or water-dispersible polyester, and gelatin (including deionised and acid processed gelatin) or a gelatin derivative (such as phthalated gelatin and carbamoylated gelatin, with the styrene polymers, vinyl acetate polymers and polyvinyl alcohol being preferred.
• a styrene polymer including polymers of styrene derivatives
• a vinyl halide polymer such as polyvinyl acetate, poly(ethylene-co-vinyl acetate) or a copolymer of
• EXAMPLE 12 discloses a barrier layer comprising poly(vinyl chloride-co-vinyl acetate)
• EXAMPLE 32 discloses a barrier layer comprising poly(styrene-co-acrylonitrile) (75:25 weight)
• EXAMPLE 33 discloses a barrier layer comprising U CAR VYNS poly(vinyl chloride-co-vinyl acetate) from Union Carbide
• EXAMPLE 34 discloses a barrier layer comprising U CAR VAGH poly(vinyl chloride-co-acetate-co-vinyl alcohol) from Union Carbide.
• substantially light-insensitive black and white monosheet thermographic materials reducing agents and toning agents are required which diffuse to the surface of the material despite the presence of an outermost protective layer both during storage before printing and after printing and results, in extreme cases, in the user visually observing deposits of reducing agents, toning agents and reaction products of the imaging-forming process on the surface of the materials.
• Substantially light-insensitive black and white monosheet thermographic materials are therefore required which exhibit an acceptably neutral image tone, but do not exhibit the formation of such deposits of reducing agents, toning agents and reaction products of the imaging-forming process.
• thermographic material which exhibits acceptably neutral image tone, but do not exhibit the formation of surface deposits comprising, for example, reducing agent, toning agent and carboxylic acid.
• the barrier layer comprises a film-forming polymer(s) that reacts with or acts as a physical barrier to diffusible by-products resulting from the presence of high contrast agents such as acrylonitrile co-developers, hydrazide co-developers and isoxazole codevelopers.
• thermosensitive elements not containing a high contrast agent and containing at least one substantially light-insensitive silver salt of a carboxylic acid, ortho-dihydroxy-benzene derivatives as reducing agents in combination with a barrier layer comprising a copolymer comprising vinyl chloride units and vinyl acetate units and/or vinyl alcohol units and/or a copolymer comprising styrene units and acrylonitrile units inserted between the outermost protective layer and the thermosensitive element exhibit acceptably neutral image tones, as characterized by CIELAB a* and b* values, and that surface deposits are neither formed prior to printing nor after printing.
• the L*, a* and b* CIELAB-values were determined by spectrophotometric measurements according to ASTM Norm E179-90 in a R(45/0) geometry with evaluation according to ASTM Norm E308-90.
• thermosensitive element being exclusive of a high contrast agent and containing comprising a substantially light-insensitive silver salt of a carboxylic acid, at least one reducing agent therefor in thermal working relationship therewith, at least one toning agent and a binder, characterized in that the at least one reducing agent is an ortho-dihydroxy-benzene derivative and the barrier layer comprises a copolymer comprising vinyl chloride units and vinyl acetate units and/or vinyl alcohol, a copolymer comprising styrene units and acrylonitrile units, a copolymer comprising cationic units and/or a copolymer comprising styrene units and maleic acid units.
• alkyl means all variants possible for each number of carbon atoms in the alkyl group i.e. for three carbon atoms: n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl and tertiary-butyl; for five carbon atoms: n-pentyl, 1,1-dimethylpropyl, 2,2-dimethylpropyl and 2-methyl-butyl etc.
• the L*, a* and b* CIELAB-values are defined in ASTM Norm E179-90 in a R(45/0) geometry with evaluation according to ASTM Norm E308-90.
• Substantially light-insensitive means not intentionally light sensitive.
• high contrast agent which are sometimes identified as “co-developers” or “auxiliary developers”, have as their main function an increase in the contrast of the material by reducing most or all of the reducible silver ions in the substantially light-insensitive silver salt of a carboxylic acid in the radiation-exposed areas e.g. acrylonitrile co-developers, hydrazide co-developers and isoxazole co-developers as disclosed in US 6,352,819 herein incorporated by reference.
• substantially water-free condition means heating at a temperature of 80 to 250°C.
• 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.
• thermosensitive element as used herein is that element which contains all the ingredients, which contribute to image formation.
• the thermosensitive element contains at least a substantially light-insensitive silver salt of a carboxylic acid, an ortho-dihydroxy-benzene derivative reducing agent therefor in thermal working relationship therewith, a toning agent and a binder.
• the thermosensitive element may comprise a layer system in which the above-mentioned ingredients may be dispersed in different layers, with the proviso that the substantially light-insensitive silver salt of a carboxylic acid is in reactive association with the ortho-dihydroxy-benzene derivative reducing agent i.e.
• the reducing agent must be present in such a way that it is able to diffuse to the particles of the substantially light-insensitive silver salt of a carboxylic acid, so that reduction to silver can occur.
• Such materials include the possibility of the substantially light-insensitive silver salt of a carboxylic acid and/or the ortho-dihydroxy-benzene derivative reducing agent therefor being encapsulated in heat-responsive microcapsules, such as disclosed in EP-A 0 736 799 herein incorporated by reference.
• the substantially light-insensitive silver salt of a carboxylic acid is not a double organic salt containing a silver cation associated with a second cation e.g. magnesium or iron ions.
• said substantially light-insensitive silver salt of an carboxylic acid is a substantially light-insensitive silver salt of an aliphatic carboxylic acids known as a fatty acid, wherein the aliphatic carbon chain has preferably at least 12 C-atoms, e.g. silver laurate, silver palmitate, silver stearate, silver hydroxystearate, silver oleate and silver behenate, which silver salts are also called "silver soaps".
• Other silver salts of an organic carboxylic acid as described in GB-P 1,439,478, e.g. silver benzoate may likewise be used to produce a thermally developable silver image.
• Combinations of different silver salts of an organic carboxylic acids may also be used in the present invention, as disclosed in EP-A 964 300 herein incorporated by reference.
• the ortho-dihydroxy-benzene derivative is selected from the group consisting of catechol, 3-(3,4-dihydroxyphenyl) propionic acid, 3,4-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid esters, gallic acid, gallic acid esters, e.g.
• Combinations of reducing agents may also be used that on heating become reactive partners in the reduction of the one or more substantially light-insensitive organic silver salt.
• combinations of sterically hindered phenols with sulfonyl hydrazide reducing agents such as disclosed in US 5,464,738; trityl hydrazides and formyl-phenyl-hydrazides such as disclosed in US 5,496,695; trityl hydrazides and formyl-phenyl-hydrazides with diverse auxiliary reducing agents as disclosed in US 5,545,505, US 5,545,507 and US 5,558,983; acrylonitrile compounds as disclosed in US 5,545,515 and US 5,635,339; and 2-substituted malonodialdehyde compounds as disclosed in US 5,654,130.
• the at least one toning agent is selected from the group consisting of phthalazinone, phthalazinone derivatives, benzoxazine dione, benzoxazine dione derivatives, naphthoxazine dione and naphthoxazine derivatives, pyridazone, pyridazone derivatives, compounds represented by formula (I) : wherein R 1 is an alkyl group optionally substituted with a hydroxy, carboxy, carboxy ester, acyl or carbonate group; X is S, O or N-R 6 ; R 6 is an optionally substituted alkyl group; R 2 , R 3 , R 4 and R 5 independently represent a hydrogen atom, a halogen atom or an alkyl, an alkoxy, a thio-alkoxy, a nitro, a cyano, a carboxy, a
• Suitable optional substituents for the alkyl groups of R 1 , R 6 , R 7 and R 10 are independently include carboxy and carboxy ester groups.
• Suitable substituted alkyl groups include: -CH 2 COOH, -C 2 H 4 COOH and -C 2 H 4 COOC 2 H 5 .
• thermographic material Suitable benzoxazine dione toning agents for use in the thermographic material, according to the present invention, are disclosed in GB 1,439,478, US 3,951,660 and US 5,599,647, herein incorporated by reference.
• thermosensitive element Binder of the thermosensitive element
• the film-forming binder of the thermosensitive element may be all kinds of natural, modified natural or synthetic resins or mixtures of such resins, in which the at least one organic silver salt can be dispersed homogeneously either in aqueous or solvent media: e.g.
• cellulose derivatives starch ethers, galactomannan, polymers derived from ⁇ , ⁇ -ethylenically unsaturated compounds such as polyvinyl chloride, after-chlorinated polyvinyl chloride, copolymers of vinyl chloride and vinylidene chloride, copolymers of vinyl chloride and vinyl acetate, polyvinyl acetate and partially hydrolyzed polyvinyl acetate, polyvinyl alcohol, polyvinyl acetals that are made from polyvinyl alcohol as starting material in which only a part of the repeating vinyl alcohol units may have reacted with an aldehyde, preferably polyvinyl butyral, copolymers of acrylonitrile and acrylamide, polyacrylates, polymethacrylates, polystyrene and polyethylene or mixtures thereof.
• aldehyde preferably polyvinyl butyral
• copolymers of acrylonitrile and acrylamide copolymers of acrylonitrile and
• thermographic recording materials are: polyvinyl alcohol, polyacrylamide, polymethacrylamide, polyacrylic acid, polymethacrylic acid, polyvinylpyrrolidone, polyethyleneglycol, proteinaceous binders, polysaccharides and water-soluble cellulose derivatives.
• a preferred water-soluble binder for use in the thermographic recording materials of the present invention is gelatine.
• the binder to organic silver salt weight ratio is preferably in the range of 0.2 to 7, and the thickness of the thermosensitive element is preferably in the range of 5 to 50 ⁇ m. Binders are preferred which do not contain additives, such as certain antioxidants (e.g. 2,6-di-tert-butyl-4-methylphenol), or impurities which adversely affect the thermographic properties of the thermographic recording materials in which they are used.
• additives such as certain antioxidants (e.g. 2,6-di-tert-butyl-4-methylphenol), or impurities which adversely affect the thermographic properties of the thermographic recording materials in which they are used.
• thermosensitive element being exclusive of a high contrast agent and containing at least one substantially light-insensitive silver salt of a carboxylic acid, at least one reducing agent therefor in thermal working relationship therewith, at least one toning agent and a binder, characterized in that the at least one reducing agent is an ortho-dihydroxy-benzene derivative and the barrier layer comprises a copolymer comprising vinyl chloride units and vinyl acetate and/or vinyl alcohol units, a copolymer comprising styrene units and acrylonitrile units, a copolymer comprising cationic units and/or a copolymer comprising styrene units and maleic acid units.
• the barrier layer is interposed between the thermosensitive element and the outermost protective layer.
• the mechanism of the restraining influence of the barriers layers, according to the present invention, upon the diffusion of ingredients and reaction products of the imaging forming process to the surface of the protective layer is unknown, but it is believed that these layers may perform a dual role in providing an impervious barrier for certain of the ingredients and reacting with others of the diffusing species.
• the copolymers used in the barrier layer of the thermographic material, according to the present invention all have a more polar species, e.g. vinyl chloride, acrylonitrile, maleic acid and cationic units, and less polar species, e.g. styrene and vinyl acetate. Such polar species could represent a barrier to the diffusion of non-polar species.
• the copolymer comprising vinyl chloride units and vinyl acetate units contains up to 95% by weight of vinyl chloride.
• the weight ratio of vinyl chloride to vinyl acetate has not been found to be critical. Further comonomers may be present, but have not been found to be critical to the performance of the copolymer as a barrier to diffusion of ingredients or reaction products from the image-forming process.
• the copolymer comprising styrene units and acrylonitrile units contains between 20 and 60% by weight of acrylonitrile.
• the copolymer containing cationic units contains quaternary ammonium, quaternary phosphonium or ternary sulphonium units.
• the copolymer containing cationic units contains methacrylamidopropyltrimethylammonium chloride or dimethyl-diallylammonium chloride units.
• the barrier layers exhibit an optimal restraining influence upon the diffusion of ingredients and reaction products of the imaging forming process when coated from coating solutions containing 5 to 20% by weight of the copolymer and/or with wet layer thicknesses of 5 to 20 ⁇ m.
• Suitable copolymers for use in the substantially light-insensitive black and white monosheet thermographic recording material include: Copolymer nr. Copolymer composition 1 VINNOLTM E15 45, a vinyl chloride-vinyl acetate-copolymer (85:15 by weight) from Wacker Chemie 2 VINNOLTM E15 45M, a vinyl chloride-vinyl acetate-maleic acid anhydride-copolymer (80.9:18.5:0.6 by weight) from Wacker Chemie 3 VINNOLTM E15 45A, a vinyl chloride-vinyl alcohol-copolymer (83.5:16.5 by weight) from Wacker Chemie 4 VINNOLTM H40 60, a vinyl chloride-vinyl acetate-copolymer (60:40 by weight) from Wacker Chemie 5 VINYLITETM VAGD, a vinyl chloride-vinyl acetate-vinyl alcohol-copolymer (91:3:6 by weight) from Rohm and Haa
• the outermost protective layer protects the thermosensitive element from atmospheric humidity and from surface damage by scratching etc. and prevents direct contact of printheads or heat sources with the recording layers.
• Protective layers for thermosensitive elements which come into contact with and have to be transported past a heat source under pressure, have to exhibit resistance to local deformation and good slipping characteristics during transport past the heat source during heating.
• a slipping layer being the outermost layer, may comprise a dissolved lubricating material and/or particulate material, e.g. talc particles, optionally protruding from the outermost layer.
• suitable lubricating materials are a surface-active agent, a liquid lubricant, a solid lubricant or mixtures thereof, with or without a polymeric binder.
• the outermost protective layer comprises the reaction product of at least one hydrolyzed polyalkoxysilane and a hydroxy-group containing polymer.
• the outermost protective layer comprises the reaction product of a hydrolyzed tetra-alkoxysilane, e.g. tetramethoxysilane or tetra-ethoxysilane, and polyvinyl alcohol.
• thermosensitive element further contains a stabilizer.
• the thermosensitive element further contains a stabilizer selected from the group consisting of benzotriazole; substituted benzotriazoles; aromatic polycarboxylic acid, such as ortho-phthalic acid, 3-nitro-phthalic acid, tetrachlorophthalic acid, mellitic acid, pyromellitic acid and trimellitic acid and anhydrides thereof; 1-phenyl-5-mercapto-tetrazole compounds in which the phenyl group is substituted with a substituent containing an optionally substituted aryl group, 1-(5-mercapto-1-tetrazolyl)-acetyl compounds represented by formula (IV): wherein R 15 is -NR 16 R 17 , -OR 18 or an optionally substituted aryl or heteroaryl group; R 16 is hydrogen or an optionally substituted alkyl, aryl or heteroaryl group; R 17 is an optionally substituted
• the thermosensitive element further contains at least one optionally substituted aliphatic or carbocyclic polycarboxylic acid and/or anhydride thereof in a molar percentage of at least 15 with respect to all the organic silver salt(s) present and in thermal working relationship therewith.
• the polycarboxylic acid may be used in anhydride form or partially esterified on the condition that at least two free carboxylic acids remain or are available during the heat recording step.
• the substantially light-insensitive thermographic material used in the present invention may contain one or more surfactants, which may be anionic, non-ionic or cationic surfactants and/or one or more dispersants.
• Suitable dispersants are natural polymeric substances, synthetic polymeric substances and finely divided powders, e.g. finely divided non-metallic inorganic powders such as silica. It has been found that the addition of a silicone oil to the coating solution of the Copolymer endowed the barrier coating solution with improved wetting properties.
• the barrier layer contains a silicone oil.
• the support is transparent or translucent. It is preferably a thin flexible carrier made transparent resin film, e.g. made of a cellulose ester, e.g. cellulose triacetate, polypropylene, polycarbonate or polyester, e.g. polyethylene terephthalate.
• the support may be in sheet, ribbon or web form and subbed if needs be to improve the adherence to the thereon coated thermosensitive element.
• the support may be dyed or pigmented to provide a transparent coloured background for the image.
• any layer of the substantially light-insensitive thermographic material used in the present invention may proceed by any coating technique e.g. such as described in Modern Coating and Drying Technology, edited by Edward D. Cohen and Edgar B. Gutoff, (1992) VCH Publishers Inc., 220 East 23rd Street, Suite 909 New York, NY 10010, USA. Coating may proceed from aqueous or solvent media with overcoating of dried, partially dried or undried layers.
• Thermographic imaging is carried out by the image-wise application of heat either in analogue fashion by direct exposure through an image or by reflection from an image, or in digital fashion pixel by pixel either by using an infra-red heat source, for example with a Nd-YAG laser or other infra-red laser, with a substantially light-insensitive thermographic material preferably containing an infra-red absorbing compound, or by direct thermal imaging with a thermal head.
• thermal printing image signals are converted into electric pulses and then through a driver circuit selectively transferred to a thermal printhead.
• the thermal printhead consists of microscopic heat resistor elements, which convert the electrical energy into heat via Joule effect.
• the operating temperature of common thermal printheads is in the range of 300 to 400°C and the heating time per picture element (pixel) may be less than 1.0ms, the pressure contact of the thermal printhead with the recording material being e.g. 200-1000g/linear cm, i.e. with a contact zone (nip) of 200 to 300 ⁇ m a pressure of 5000 to 50,000 g/cm 2 , to ensure a good transfer of heat.
• the image-wise heating of the recording material with the thermal printing heads may proceed through a contacting but removable resin sheet or web wherefrom during the heating no transfer of recording material can take place.
• Activation of the heating elements can be power-modulated or pulse-length modulated at constant power.
• EP-A 654 355 discloses a method for making an image by image-wise heating by means of a thermal head having energizable heating elements, wherein the activation of the heating elements is executed duty cycled pulsewise.
• EP-A 622 217 discloses a method for making an image using a direct thermal imaging element producing improvements in continuous tone reproduction.
• Image-wise heating of the recording material can also be carried out using an electrically resistive ribbon incorporated into the material.
• Image- or pattern-wise heating of the recording material may also proceed by means of pixel-wise modulated ultrasound.
• Thermographic imaging can be used for the production of reflection type prints and transparencies, in particular for use in the medical diagnostic field in which black-imaged transparencies are widely used in inspection techniques operating with a light box.
• Subbing layer Nr. 01 on the emulsion side of the support has the composition: copolymer of 88% vinylidene chloride, 10% methyl acrylate and 2% itaconic acid 79.1 mg/m 2 Kieselsol® 100F, a colloidal silica from BAYER 18.6 mg/m 2 Mersolat® H, a surfactant from BAYER 0.4 mg/m 2 Ultravon® W, a surfactant from CIBA-GEIGY 1.9 mg/m 2
• thermosensitive elements used: Thermosensitive element types 1 2 3 4 5 AgBeh [g/m 2 ] 3.94 4.150 3.960 4.15 4.42 BL5HP [g/m 2 ] 15.32 16.601 15.841 16.60 16.796 R01 [g/m 2 ] 0.595 0.439 - - 0.618 R02 [g/m 2 ] 0.566 0.894 - - - R03 [g/m 2 ] - - 0.940 0.845 0.515 BOD01 [g/m 2 ] - - 0.216 - - BOD02 [g/m 2 ] 0.111 - 0.111 0.116 0.226 BOD03 [g/m 2 ] 0.156 0.246 - - - BOD04 [g/m 2 ] - - - 0.269 - S01 [g/m 2 ]
• thermosensitive element type 1 in 2-butanone was prepared by coating a dispersion with the following ingredients of thermosensitive element type 1 in 2-butanone onto a 175 ⁇ m thick blue-pigmented polyethylene terephthalate support with CIELAB a*-and b*-values of -9.5 and -17.9 respectively subbed on the emulsion-coated side with subbing layer 01 giving type 1 thermosensitive elements after drying at 50°C for 1h in a drying cupboard, for composition see above.
• the type 1 thermosensitive elements were then coated with a barrier layer from a 2-butanone solution, for type of copolymer used and coating weight see Tables 1A and 1B.
• the barrier layers were then further coated with an aqueous composition with the following ingredients, which was adjusted to a pH of 3.8 with 1N nitric acid, to a wet layer thickness of 85 ⁇ m and then dried at 50°C for 15 minutes to produce a protective layer PRO-L with the composition: ERCOLTM 48 20 2.1g/m 2 LEVASILTM VP AC 4055 1.05g/m 2 ULTRAVONTM W 0.075g/m 2 SYLOIDTM 72 0.09 g/m 2 SERVOXYLTM VPDZ 3/100 0.075g/m 2 SERVOXYLTM VPAZ 100 0.075g/m 2 MICROACE TALC P3 0.045g/m 2 RILANITTM GMS 0.15g/m 2 TMOS 0.87g/m 2 (assuming that the TMOS was completely converted to SiO 2 ) After coating the protective layer was hardened by heating the substantially light-insensitive thermographic material at 45°C for 7 days at a relative humidity of 70%.
• thermographic recording materials of COMPARATIVE EXAMPLES 1 to 24 and INVENTION EXAMPLES 1 to 31 were printed using a DRYSTARTM 4500 printer from AGFA-GEVAERT with a resolution of 508 dpi which had been modified to operate at a printing speed of 14 mm/s and a line-time of 3.5 ms instead of 7.1 ms and in which the 75 ⁇ m long (in the transport direction) and 50 ⁇ m wide thermal head resistors were power-modulated to produce different image densities.
• the maximum densities of the images (D max ) measured through a visible filter with a MACBETHTM TR924 densitometer were all greater than 2.0.
• COMPARATIVE EXAMPLE 1 show that there is very considerable diffusion of ingredients and reaction products of the imaging forming process to the surface even prior to printing.
• the results for COMPARATIVE EXAMPLE 2 show that the protective layer used based on the reaction product of polyvinyl alcohol with hydrolyzed tetramethoxysilane was able to prevent further transport to the surface of the protective layer prior to printing, but after printing considerable diffusion of ingredients and reaction products of the imaging forming process could be detected after 20 days.
• copolymers nr. 1 to 3 copolymers comprising vinyl chloride and vinyl acetate units
• copolymers nr. 6 to 8 copolymers comprising styrene-acrylonitrile
• copolymers with cationic units Copolymers nr. 11 to 13
• styrene-maleic acid copolymers Copolymer nr. 14
• thermographic materials of COMPARATIVE EXAMPLES 25 to 29 and INVENTION EXAMPLES 32 to 38 were prepared as described for COMPARATIVE EXAMPLES 1 to 24 and INVENTION EXAMPLES 1 to 31 except for the barrier layers, which are given in Tables 2A and 2B for COMPARATIVE EXAMPLES 25 to 29 and INVENTION EXAMPLES 32 to 38 respectively.
• Copolymer nr coverage [g/m 2 ] 32 1 2 0 0 0 0 0 0 0 0 0 33 1 2 0 0 0 0 0 0 0 0 34 2 2 0 0 0 0 0 0 0 0 35 3 2 0 0 0 0 0 0 0 0 36 6 2 0 0 0 0 0 0 0 0 37 7 2 0 0 0 0 0 0 0 0 0 38 8 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
• a barrier layer to be usable in substantially light-insensitive thermographic materials, it is important that it is not only able to restrain the diffusion of ingredients and reaction products of the imaging forming process to the surface of the protective layer but also has no adverse effect on the image tone of the prints.
• Copolymer nr coverage [g/m 2 ] 32 1 2 -4.72 -6.29 -3.12 -5.65 33 1 2 -4.56 -5.74 -2.95 -5.86 34 2 2 -4.61 -6.76 -3.01 -6.24 35 3 2 -4.65 -6.24 -3.15 -5.99 36 6 2 -4.68 -6.97 -3.06 -6.36 37 7 2 -4.73 -6.94 -3.08 -6.19 38 8 2 -4.74 -6.90 -3.01 -6.21
• the substantially light-insensitive thermographic materials of COMPARATIVE EXAMPLE 30 and INVENTION EXAMPLES 39 to 50 were prepared by coating a dispersion with the ingredients of thermosensitive element type 2 in 2-butanone onto a 175 ⁇ m thick blue-pigmented polyethylene terephthalate support with CIELAB a*-and b*- values of -9.5 and -17.9 respectively subbed on the emulsion-coated side with subbing layer 01 giving type 2 thermosensitive elements after drying at 85°C for 3 minutes in a drying cupboard, for composition of the type 2 thermosensitive element see above.
• the type 2 thermosensitive elements were then coated with a barrier layer from a 2-butanone solution, for copolymer type used and coating weight see Table 4.
• the barrier layers were then provided with the same protective layer as for the substantially light-insensitive thermographic materials of COMPARATIVE EXAMPLES 1 to 24 and INVENTION EXAMPLES 1 to 31.
• a barrier layer to be usable in substantially light-insensitive thermographic materials, it is important that it is not only able to restrain the diffusion of ingredients and reaction products of the imaging forming process to the surface of the protective layer but also has no adverse effect on the image tone of the prints.
• thermographic materials of COMPARATIVE EXAMPLE 31 and INVENTION EXAMPLES 51 to 62 were prepared as described for COMPARATIVE EXAMPLE 30 and INVENTION EXAMPLES 39 to 50 except that type 2 thermosensitive elements were used and for the barrier layers, which are given in Table 6.
• Comparative Example nr. Polymer assessment of diffusion for prints subjected to 57°C/34%RH for 3d nr coverage [g/m 2 ] 31 - - 5 Invention Example nr.
• Copolymer nr coverage [g/m 2 ] 51 2 1 0 52 3 1 0 53 4 1 0 54 5 1 0 55 5 1 0 56 6 1 0 57 7 1 0 58 9 1 0 59 10 1 0 60 11 1 0 61 12 1 0 62 14 1 0
• barrier layers of Copolymers nr. 2 to 7, 9 to 12 and 14 with a coverage of 1g/m 2 Most of these barrier layers were applied from 2-butanone solutions, but barrier layers of Copolymer nr. 11, 12 and 14 were applied from aqueous solutions.
• These copolymers can mainly be grouped into copolymers comprising vinyl chloride and vinyl acetate units (Copolymers nr. 1 to 5), copolymers comprising styrene-acrylonitrile (Copolymers nr. 6 to 10) and copolymers with cationic units (Copolymers nr. 11 and 12).
• Copolymer nr coverage [g/m 2 ] 51 2 1 -2.58 -11.15 -0.82 -10.6 52 3 1 -2.68 -11.14 -0.63 -10.5 53 4 1 -3.04 -10.39 -0.8 -9.41 54 5 1 -3.05 -11.27 -1.32 -10.86 55 5 1 -2.17 -10.15 +0.54 -9.7 56 6 1 -2.34 -10.63 -0.03 -10.1 57 7 1 -2.4 -10.41 +0.16 -9.81 58 9 1 -2.54 -10.58 +0.12 -10.04 59 10 1 -2.53 -10.2 -0.15 -9.68 60 11 1 -2.32 -8.3 +0.33 -7.15 61 12 1 -2.14 -8.85 +0.77 -8.35 62 14 1 -2.73 -8.87 -0.14 -8.76
• composition of barrier layers of copolymers containing styrene and acrylonitrile with various weight percentages of styrene and acrylonitrile did not have a significant influence upon image tone i.e. for weight percentages of styrene units between 54 and 75 and for weight percentages of acrylonitrile between 25 and 46.
• thermosensitive thermographic materials of COMPARATIVE EXAMPLES 32 to 39 and INVENTION EXAMPLES 63 to 74 were prepared by coating dispersions containing the ingredients for the appropriate thermosensitive element type (see Table 8 for the thermosensitive element type used for the particular COMPARATIVE or INVENTION EXAMPLE) in 2-butanone onto the support described for COMPARATIVE EXAMPLES 1 to 24 and INVENTION EXAMPLES 1 to 31 giving the particular type of thermosensitive element for the particular COMPARATIVE or INVENTION EXAMPLE after drying at 85°C for 3 minutes in a drying cupboard with the compositions given above.
• thermosensitive elements were then optionally coated with a barrier copolymer from a 2-butanone solution, see Table 8 for copolymer type and coating weight.
• barrier layers were then provided with the same protective layer as for the substantially light-insensitive thermographic materials of COMPARATIVE EXAMPLES 1 to 24 and INVENTION EXAMPLES 1 to 31.
• the present invention may include any feature or combination of features disclosed herein either implicitly or explicitly or any generalisation thereof irrespective of whether it relates to the presently claimed invention.

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