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
  • G03C1/005—Silver halide emulsions; Preparation thereof; Physical treatment thereof; Incorporation of additives therein
  • G03C1/04—Silver halide emulsions; Preparation thereof; Physical treatment thereof; Incorporation of additives therein with macromolecular additives; with layer-forming substances
• • 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
  • G03C1/49836—Additives
  • G03C1/49863—Inert additives, e.g. surfactants, binders
• • 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
  • G03C1/76—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

Definitions

• the present invention concerns binders for use in the thermosensitive elements of 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.
• EP-A 0 752 616 further discloses that the film-forming binder of the recording layer containing the substantially light-insensitive organic heavy metal salt may be all kinds of natural, modified natural or synthetic resins or mixtures of such resins, wherein the organic heavy metal salt can be dispersed homogeneously: e.g. cellulose derivatives such as ethylcellulose, cellulose esters, e.g.
• cellulose nitrate carboxymethylcellulose, 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, polyacrylic acid esters, polymethacrylic acid esters, polystyrene and polyethylene or mixtures thereof.
• EP-A 0 752 616 also alludes to binders suitable for use in the non-organic silver salt containing donor layers used in reductor transfer printing which include: cellulose derivatives, such as ethyl cellulose, methyl cellulose, cellulose nitrate, cellulose acetate formate, cellulose acetate hydrogen phthalate, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate pentanoate, cellulose acetate benzoate, cellulose triacetate; vinyl-type resins and derivatives, such as polyvinyl acetate, polyvinyl butyral, copolyvinyl butyral-vinyl acetal-vinyl alcohol, polyvinyl pyrrolidone, polyvinyl acetoacetal, polyacrylamide; polymers and copolymers derivated from acrylates and acrylate derivatives, such as polymethyl methacrylate and styrene-acrylate copolymers
• the binder for the donor layer of the present invention comprises poly(styrene-co-acrylonitrile) or a mixture of poly(styrene-co-acrylonitrile) and a toluenesulphonamide condensation product.
• EP-A 0 809 144 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 said thermosensitive element further comprises in reactive association with said substantially light-insensitive organic silver salt and said 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, said compound not being annulated with an aromatic ring system.
• thermosensitive element may be all kinds of natural, modified natural or synthetic resins or mixtures of such resins, wherein the organic heavy metal salt can be dispersed homogeneously: e.g. cellulose derivatives such as ethylcellulose, cellulose esters, e.g.
• cellulose nitrate carboxymethylcellulose, 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, polyacrylic acid esters, polymethacrylic acid esters, polystyrene and polyethylene or mixtures thereof.
• JP 2001-13618A discloses a heat developing sensitive material containing organic silver, a photosensitive silver halide, a developer, and a binder resin at least on a base material, said binder resin containing a polyvinyl aceto acetal resin in 70% by weight or more among [ all ] the binder resin, said polyvinyl aceto acetal resin being characterized by the degree of acetalization of more than 50mol%.
• EP-A 1 241 520 discloses a silver salt photothermographic dry imaging material comprising a support having thereon a photosensitive layer comprising silver aliphatic carboxylate grains and photosensitive silver halide grains, a reducing agent for silver ions, a binder and a cross-linking agent, wherein the photothermographic material has a silver coverage of 1.0 to 1.7 g/m 2 ; the photosensitive silver halide grains have a mean grain size of 0.03 to 0.05 ⁇ m and a degree of grain size dispersity of not more than 30%; after the dry imaging material has been subjected to photothermographic processing at a temperature of 100 to 200°C for 5 to 50 seconds, the photosensitive layer exhibits a thermal transition temperature of 46 to 200°C.
• binder incorporated in the photosensitive layer which includes such as silver aliphatic carboxylates, photosensitive silver halide grains and reducing agent on a support, can be employed high polymers well known in the art.
• the high polymers have a Tg of 70 to 105°C.
• the examples include: compounds comprised of polymers or copolymers containing ethylenically unsaturated monomers as constitutive units such as vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylate ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylate ester, styrene, butadiene, ethylene, vinyl butyral, vinyl aceto-acetal and vinyl ether; polyurethane resins and various kinds of rubber resin.
• EP-A 1 270 608 which corresponds to WO 01/053357A1 and JP 2002-201215, discloses a polyvinyl acetal resin for heat-developable photosensitive materials which is a polyvinyl acetal resin synthesized by the acetalization reaction between a polyvinyl alcohol and an aldehyde and which comprises having a degree of polymerization of 200 to 3,000, a residual acetyl group content of 0 to 25 mole percent and a residual hydroxyl content of 17 to 35 mole percent, as calculated while regarding one acetal group as two acetalized hydroxyl groups, a water content of not more than 2.5% by weight and a residual aldehyde content of not more than 10 ppm and is free of any antioxidant, preferably having a glass transition temperature of 55 to 110°C.
• Resins containing vinyl alcohol, vinyl acetal and vinyl butyral monomer units are disclosed in Examples 4, 5, 6 and 8 with glass transition temperatures of 80, 70, 76, 103 and 93°C respectively of EP-A 1 270 608 and had the compositions given in Table 2: Example No.
• EP-A 1 278 101 discloses a photothermographic imaging material comprising a support having thereon a photosensitive layer comprising a photosensitive silver halide, a light-insensitive organic silver salt, a binder, and a reducing agent for silver ions, wherein the reducing agent is represented by the following Formula (S): wherein Z is a group of atoms necessary to form a non aromatic ring of 3 to 10 members; Rx is a hydrogen or an alkyl group; each Ro' and Ro" is independently a hydrogen, an alkyl group, or a heterocyclic group; Qo is a substituent; and each n and m is independently an integer of 0 to 2; and plural Qo's may be the same or different.
• Formula (S) wherein Z is a group of atoms necessary to form a non aromatic ring of 3 to 10 members; Rx is a hydrogen or an alkyl group; each Ro' and Ro" is independently a hydrogen, an alkyl group, or a heterocyclic
• EP-A 1 278 101 further discloses the following polymers preferably employed in the invention: Polymer name Aceto-acetal [mol%] Butyral [mol%] acetal [mol%] acetyl [mol%] hydroxyl group [mol%] Tg value [°C] P-1 6 4 73.7 1.7 24.6 85 P-2 3 7 75.0 1.6 23.4 75 P-4 7 3 71.1 1.6 27.3 88 P-7 3 7 74.4 1.6 24.0 75 P-8 3 7 75.4 1.6 23.0 74
• EP-A 1 143 292 discloses a photothermographic material comprising a support having on one side of the support at least an image forming layer containing organic silver salt grains, light sensitive silver halide grains and a reducing agent and a surface protective layer, wherein the element composition on the surface of the image forming layer exhibits a ratio of the number of carbon elements to the number of oxygen elements of not more than 9, and wherein the element composition is obtained by X-ray photoelectron spectroscopy.
• binders disclosed for use in the image forming layer include polyvinyl acetals (e.g. polyvinyl formal, polyvinyl butyral).
• binders such as polyvinyl butyral and polyvinyl acetal, and cellulose esters such as cellulose acetate and cellulose acetate-butyrate are preferred, which may be used alone or in combination.
• mixed acetals obtained from two aldehydes, such as polyvinyl acetobutyral are also preferred according to EP-A 1 143 292. However, such mixed acetals are not exemplified therein.
• EP-A 1 136 877 discloses a photothermographic material comprising on a support light sensitive silver halide grains, an organic silver salt, a reducing agent and a binder, wherein the photothermographic material comprises a silane compound represented by formula (1) or (2) : formula (1) (R 1 O) m -Si-[(L 1 ) x R 2 ] n wherein R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 and R 8 represent each an alkyl group, an alkenyl group, an alkynyl group, an aryl group or a heterocyclic group; L 1 , L 2 , L 3 and L 4 represent each a bivalent linkage group; m and n are each an integer of t to 3, provided that m+n is 4; p1 and p2 are each an integer of 1 to 3 and q1 and q2 are each 0, 1 or 2, provided that p1+q1 and p2+q2 are each
• Binders usable on the organic solvent-based coating include cellulose derivatives, polyvinyl alcohol derivatives, acrylate polymer derivatives, polyimide derivatives, polyamide derivatives, phenol resin derivatives, urethane resin derivatives and polyester derivatives. Of these, polyvinyl alcohol derivatives and vinyl acetate derivatives are preferred, particularly with vinyl acetal monomer units.
• JP 2002-293825 which corresponds to WO 02/059167, discloses a polyvinyl acetal characterized by containing one or more functional groups in one molecule e.g. a carboxyl group, a silyl moiety, a halogen moiety, an amino group, a sulfhydryl group, a sulfonyl group, a thionyl group, an epoxy group, an oxazoline moiety, a maleimide moiety, a hydroxyl group etc.
• An ionic group such as an acidic group (e.g. a carboxyl group or a sulfonic group) or a basic group (e.g. containing a nitrogen atom) are preferred.
• the binder preferably has a glass transition point of 70 to 105°C and is preferably a polyvinyl acetal substantially having an acetoacetal structure or is a polymer compound represented by formula (V).
• Exemplary polymer compounds represented by formula (V) are disclosed with the composition given in Table 4 below: Polymer Tg [°C] vinyl acetal ⁇ mol%/wt%] vinyl butyral [mol%/wt%] vinyl alcohol [mol%/wt%] vinyl acetate [mol%/wt%] P-1 83 51.59/57.4 22.11/30.6 24.6/10.6 1.7/1.4 P-2 75 22.5/22.9 52.5/66.7 23.4/9.2 1.6/1.2 P-4 88 49.77/56.5 21.33/30.2 27.3/12.0 1.6/1.3 P-5 99 64.62/76.0 7.18/10.5 26.7/12.1 1.5/1.4 P-6 90 57.12/66.0 14.28/20.6 27.0/12.0 1.6/1.4 P-7 76 21.12/22.3 49.28/65.0 2
• Pioloform TM BL16 a copolymer consisting of 42% by weight of vinyl acetal, 40% by weight of vinyl butyral, 16% by weight of vinyl alcohol and 2% by weight of vinyl acetate having a Tg of 84°C, produced by Wacker Chemie, is used as the sole binder in the thermosensitive element of a substantially light-insensitive thermographic material produced by AGFA-GEVAERT N.V. and marketed by AGFA-GEVAERT N,V. as AGFA FREEWAY TM film and by AUTOLOGIC as Autotype Aspect TM HR.
• the weight ratio of substantially light-insensitive organic silver salt to Pioloform TM BL16 in this thermosensitive element is approximately 1.0.
• thermographic recording materials Differences between substantially light-insensitive thermographic recording materials and photothermographic recording materials
• thermographic materials in which image formation is based on the reduction of organic silver salts is significantly different from that of photothermographic recording materials, despite the fact that in both cases the image results from the reduction of organic silver salts.
• this a superficial similarity masking the fact that the realization of the species which catalyze this reduction is completely different, being image-wise exposure of photosensitive silver halide-containing photo-addressable thermally developable elements in the case of photothermographic recording materials and image-wise heating of thermosensitive elements which do not contain photosensitive silver halide in the case of thermographic recording 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 monosheet thermographic recording 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 recording material which does not exhibit the formation of surface deposits comprising, for example, reducing agent, toning agent and reaction products of the image-forming process.
• thermosensitive element of substantially light-insensitive monosheet thermographic recording materials strongly reduces the diffusion of ingredients present therein and reaction products thereof to the surface of the thermosensitive element and therefrom to the surface of the thermographic recording material, should the outermost surface of the thermosensitive element not be the outermost layer of the thermographic recording material itself.
• the image tone is rendered more neutral by the presence of vinyl butyral monomer units in the polymer consisting of vinyl aceto-acetal monomer units and optionally monomer units selected from the group consisting of vinyl butyral, vinyl alcohol and vinyl acetate monomer units, or by the additional presence of a polymer consisting of vinyl butyral monomer units and optionally vinyl alcohol and/or vinyl acetate monomer units.
• thermosensitive element comprising at least one substantially light-insensitive silver salt of a carboxylic acid, at least one reducing agent therefor in thermal working relationship therewith and at least one binder
• the at least one binder comprising at least one first polymer consisting of vinyl aceto-acetal monomer units, vinyl butyral monomer units and monomer units selected from the group consisting of vinyl alcohol, vinyl acetate and itaconic acid monomer units, characterized in that the weight ratio of the at least one binder to the light-insensitive silver salt(s) of a carboxylic acid in the thermosensitive element is greater than 1.5; and the at least one binder optionally contains less than 40% by weight of a second polymer consisting of vinyl butyral monomer units and optionally vinyl alcohol and/or vinyl acetate monomer 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.
• poly(vinyl acetals) refers to the condensation product of poly(vinyl alcohol) with one or more aldehydes.
• Vinyl acetal as used in disclosing the present invention, is the condensation product of vinyl alcohol and an aldehyde. To distinguish the condensation product of vinyl alcohol and an aldehyde from that of vinyl alcohol and unsubstituted aldehyde (ethanal), the latter condensation products have been referred to as vinyl aceto-acetal in disclosing the present invention.
• Vinyl butyral as used in disclosing the present invention, is the condensation product of vinyl alcohol and butyraldehyde (butanal), which is not further substituted.
• 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.
• thermographic recording material is a black and white thermographic recording material.
• thermosensitive element is exclusive of a high contrast agent.
• thermographic recording material is exclusive of a silane compound represented by formula (1) or (2): formula (1) (R 1 O) m -Si-[(L 1 ) x R 2 ] n wherein R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 and R 8 represent each an alkyl group, an alkenyl group, an alkynyl group, an aryl group or a heterocyclic group; L 1 , L 2 , L 3 and L 4 represent each a bivalent linkage group; m and n are each an integer of t to 3, provided that m+n is 4; p1 and p2 are each an integer of 1 to 3 and q1 and q2 are each 0, 1 or 2, provided that p1+q1 and p2+q2 are each 3; r1 and t are each 0 or an integer of 1 to 1000; and x is
• 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, a reducing agent therefor in thermal working relationship therewith, and at least one 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 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 reducing agent therefor being encapsulated in heat-responsive microcapsules, such as disclosed in EP-A 0 736 799 herein incorporated by reference.
• first polymer consisting of vinyl aceto-acetal and monomer units, vinyl butyral monomer units and monomer units selected from the group consisting of vinyl alcohol and vinyl acetate monomer units should not be taken as implying that the copolymer has to be produced by copolymerizing vinyl aceto-acetal, vinyl butyral, vinyl alcohol and optionally vinyl acetate, merely that the copolymer consists of such monomer units.
• second polymer consisting of vinyl butyral monomer units, vinyl alcohol monomer units and optionally vinyl acetate monomer units should not be taken as implying that the copolymer has to be produced by copolymerizing vinyl butyral, vinyl alcohol and optionally vinyl acetate, merely that the copolymer consists of such monomer units.
• a main source of polyvinyl alcohol is the hydrolysis of polyvinyl acetate and that this hydrolysis is usually not carried out to completion resulting in vinyl acetate monomer units still being present in the polyvinyl alcohol chains.
• poly(vinyl acetals) are usually produced in a condensation reaction upon treating poly(vinyl alcohol) with one or more aldehydes or directly from poly(vinyl acetate). Since the reaction between the aldehyde(s) and the hydroxyl groups of the poly(vinyl alcohol) occurs at random, some hydroxyl groups become isolated and are incapable of reaction. The product will thus contain: vinyl acetal units, residual vinyl alcohol units and residual vinyl acetate units.
• the weight ratio of the at least one binder to the light-insensitive silver salt(s) of a carboxylic acid in the thermosensitive element is greater than 1.75, with a ratio greater than 2.0 being particularly preferred and a ratio greater than 2.5 being especially preferred.
• the weight ratio of the at least one binder to the light-insensitive silver salt(s) of a carboxylic acid in the thermosensitive element is less than 6.0, with less than 5.2 being preferred and less than 4.5 being particularly preferred.
• thermosensitive element contains at least one further first polymer.
• the molecular ratio of vinyl aceto-acetal units (VA-A) to vinyl butyral units (VB) is between 0.5 and 2.5, being preferably between 0.75 and 2.1 and particularly preferably between 1.0 and 1.8.
• the molecular ratio of vinyl aceto-acetal units to vinyl butyral units can be accurately determined using 13 C NMR measurements. It has been found that whereas vinyl aceto-acetal units render the image tone more red, the vinyl butyral units render the image tone more blue.
• the first polymer contains between 20 and 70% by weight of vinyl butyral monomer units, with between 30 and 70% by weight of vinyl butyral monomer units being preferred.
• the first polymer has a weight averaged molecular weight greater than 80,000, with greater than 90,000 being preferred and greater than 100,000 being particularly preferred.
• the first polymer contains less than 20 wt% of vinyl alcohol monomer units, with less than 17 wt% of vinyl alcohol monomer units being preferred and less than 14 wt% of vinyl alcohol monomer units being particularly preferred.
• concentration of vinyl alcohol units can also be determined by 13 C NMR, but peak overlap requires careful calibration to avoid overestimating or underestimating the vinylalcohol concentration. Titration generally yields more reliable vinyl alcohol concentrations.
• Suitable first polymers for use in substantially light-insensitive thermographic recording materials in which AB represents polymers containing both vinyl aceto-acetal and vinyl butyral monomer units are given in table 5 below:
• Suitable second polymers for use in substantially light-insensitive thermographic recording materials in which B represents polymers containing vinyl butyral monomer units but no vinyl aceto-acetal monomer units are given in the Table 7 below:
• B represents polymers containing vinyl butyral monomer units but no vinyl aceto-acetal monomer units are given in the Table 7 below:
• Polymers 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.
• 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.
• the 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.
• thermographic recording material according to the present invention, the reducing agent is an ortho-dihydroxy-benzene derivative.
• 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.
• thermosensitive element further contains at least one toning agent.
• 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 bv formula (I): wherein R 1 is an alkyl group optionally substituted with a hydroxy, carboxy, carboxy ester, acyl or carbonato 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 carboxy ester, an
• 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 recording material Suitable benzoxazine dione toning agents for use in the thermographic recording 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, and include:
• thermographic recording material Suitable toning agents represented by formula (I) for use in the thermographic recording material, according to the present invention, include:
• Suitable toning agents represented by formula (II) according to the present invention include:
• Suitable 2-hydroxy-pyrimidine derivatives, according to the present invention include:
• 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 hydrolyzed tetramethoxysilane or tetraethoxysilane and a hydroxy-group containing polymer.
• the outermost protective layer comprises the reaction product of at least one hydrolyzed polyalkoxysilane and poly(vinyl 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 (III): wherein R 3 is -NR 4 R 5 , -OR 6 or an optionally substituted aryl or heteroaryl group; R 4 is hydrogen or an optionally substituted alkyl, aryl or heteroaryl group; R 5 is an optionally substituted ary
• 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 recording 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.
• Preferred anionic surfactants are surfactants represented by formula (3): or alkali salts thereof, where a is an integer between 1 and 15; and b is an integer between 1 and 5; and surfactants represented by formula (4): wherein M is hydrogen, an alkali atom or an ammonium group; R 1 is an alkyl, alkenyl-, alkynyl-, thioalkyl-, thioalkenyl- or thioalkynyl-group in which the alkyl-, alkenyl- or alkynyl- group has 6 to 25 carbon atoms; X is -O-, -S- or -N(R 2 )-; and R 2 is hydrogen, a -(CH 2 ) m SO 3 M group or a group; and m is an integer between 1 and 5.
• M is hydrogen, an alkali atom or an ammonium group
• R 1 is an alkyl, alkenyl-, alkynyl-,
• Suitable surfactants include:
• Suitable dispersants are natural polymeric substances, synthetic polymeric substances and finely divided powders, e.g. finely divided non-metallic inorganic powders such as silica.
• the support is transparent or translucent. It is preferably a thin flexible carrier made of 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 need 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 recording 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 recording material preferably containing an infra-red absorbing compound, or by direct thermal imaging with a thermal head.
• an infra-red heat source for example with a Nd-YAG laser or other infra-red laser
• a substantially light-insensitive thermographic recording material preferably containing an infra-red absorbing compound
• 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.
• thermosensitive element in addition to the above-mentioned ingredients:
• thermosensitive elements Compositions of thermosensitive elements used:
• thermographic recording materials of COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2 were prepared by coating a dispersion prepared as follows: a first solution containing 25.42 g methylethylketone, 12.375 g of binder and 33 mg Oil (Baysilon) was prepared. To this solution 36.8 g of a AgBehenate-dispersion, containing per 100g dispersion 10.7 g of AgBehenate and 9.35 g of binder, was added. Then 0.257 g of S01, 0.116 g of BOD2 and 0.164 g of BOD3 was added.
• thermosensitive elements The coverage of silver behenate and the quantities and types of polymers used in the thermosensitive elements are given in Table 9 below.
• thermosensitive element Assessment of diffusion of ingredients and reaction products of the imaging forming process to the surface of thermosensitive element
• thermosensitive element The diffusion of ingredients and reaction products of the imaging forming process to the surface of the thermosensitive element was assessed by:
• AB02 at a concentration of 21.75% by weight in the total binder present had no effect on the diffusion of ingredients and reaction products thereof in a mixture with B01 in the substantially light-insensitive thermographic recording material of the present invention.
• a concentration of 78.25% by weight in the total binder present AB02 had a significant effect on the diffusion of ingredients and reaction products thereof in the presence of B01 in the substantially light-insensitive thermographic recording material of the present invention.
• the threshold concentration of AB02 for having an effect on the diffusion of ingredients and reaction products thereof in the presence of B01 is between 21.75% by weight and 78.25% by weight of the binder present in the thermosensitive element of the substantially light-insensitive thermographic recording material of the present invention.
• AB02 itself had a strong effect on the diffusion of ingredients and reaction products thereof in the substantially light-insensitive thermographic recording material of the present invention.
• thermographic recording materials of COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2 were printed using the above-mentioned modified DRYSTAR TM 4500 printer from AGFA-GEVAERT to produce different image densities.
• the maximum densities of the images (D max ) measured through a visible filter with a MACBETH TM TR924 densitometer were all greater than 2.0.
• the CIELAB a*- and b*-values for densities of 1.0 and 2.0 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. The results are summarized in Table 10. Comparative example nr.
• thermographic recording material of INVENTION EXAMPLE 2 with the first polymer AB02 as both dispersion and added polymer exhibited a fairly neutral image tone together with a superior diffusion assessment compared with the thermographic recording material of INVENTION EXAMPLE 1, whereas the thermographic recording material of INVENTION EXAMPLE 1 with the second polymer B01 as dispersion polymer and first polymer AB02 as added polymer exhibited a slightly reddish tone.
• thermographic recording materials of COMPARATIVE EXAMPLES 8 to 10 and INVENTION EXAMPLES 3 to 7 were prepared by coating a dispersion prepared as follows: a first solution containing 37.44 g methylethylketone, 12.375 g of binder and 33 mg Oil (Baysilon) was prepared. To this solution 28.35g of a AgBehenate-dispersion, containing per 100g dispersion 14 g of AgBehenate and 12.1 g of binder, was added. Then 0.280 g of S01 and 0.246 g of BOD3 was added.
• thermosensitive elements The diffusion through the thermosensitive elements was assessed as described for the thermosensitive elements of COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2 and the results are summarized in Table 11. In the presence of 21.75% by weight of B01, AB01, AB05 and AB02 have a fair effect on the diffusion of ingredients and reaction products thereof.
• AB02 In the presence of 21.75% by weight of AB02, AB02 and A01 both had a strong effect on the diffusion of ingredients and reaction products thereof in the substantially light-insensitive thermographic recording material of the present invention.
• the AB02 has no effect at a concentration in the at least one binder of 21.75% by weight in a matrix of B01.
• thermosensitive elements of COMPARATIVE EXAMPLES 8 to 10 and INVENTION EXAMPLES 3 to 7 were further coated with a protective layer as described for the substantially light-insensitive thermographic recording materials of COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2 and the image tone of the fresh thermographic recording materials determined as described for COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2, the results being summarized in Table 12.
• thermosensitive element type 2 With thermosensitive element type 2, the most neutral image tone is exhibited by the thermographic recording material of INVENTION EXAMPLE 3 with second polymer B01 as the dispersion polymer and first polymer AB01 as the added polymer, the thermographic recording material of INVENTION EXAMPLE 8 with first polymer AB02 as both dispersion and added polymer exhibiting far superior diffusion assessments. Comparative example nr.
• thermographic recording materials of COMPARATIVE EXAMPLE 11 and INVENTION EXAMPLE 8 were prepared by coating a dispersion prepared as follows: a first solution containing 28.0 g methylethylketone, 13 g of binder and 33 mg Oil (Baysilon) was prepared. To this solution 36.3 g of a AgBehenate-dispersion, containing per 100g dispersion 11.4 g of AgBehenate and 9.9 g of binder, was added. Then 0.246 g BOD3 was added.
• the resulting dispersion was doctor blade-coated onto a subbed 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 3 thermosensitive elements with the composition given above, after drying at 50°C for 1h in a drying cupboard.
• thermosensitive elements The diffusion through the thermosensitive elements was assessed as described for the thermosensitive elements of COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2 and the results are summarized in Table 13.
• the AB06 has an effect at a concentration in the at least one binder of 78% by weight.
• thermosensitive elements of COMPARATIVE EXAMPLE 11 and INVENTION EXAMPLE 8 were further coated with a protective layer as described for the substantially light-insensitive thermographic recording materials of COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2 and the image tone of the fresh thermographic recording materials determined as described for COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2, the results being summarized in Table 14.
• thermographic recording materials of INVENTION EXAMPLE 8 with thermosensitive element type 3 with second polymer B01 as the dispersion polymer and AB06 as the added polymer an acceptable image tone neutrality was observed.
• thermographic recording materials of COMPARATIVE EXAMPLE 12 and INVENTION EXAMPLES 9 and 10 were prepared by coating a dispersion prepared as follows: a first solution containing 33.8 g methylethylketone, 11.28 g of binder, 0.138 g S04, 0.296 g BOD04 and 33 mg Oil (Baysilon) was prepared. To this solution 29.2 g of a AgBehenate-dispersion, containing per 100g dispersion 14.2 g of AgBehenate and 12.6 g of binder, was added.
• the resulting dispersion was doctor blade-coated onto a subbed 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 4 thermosensitive elements with the composition given above, after drying at 50°C for 1h in a drying cupboard.
• thermosensitive elements The diffusion through the thermosensitive elements was assessed as described for the thermosensitive elements of COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2 and the results are summarized in Table 15.
• the AB01 and AB05 have an effect at a concentration in the at least one binder of 76% by weight.
• thermosensitive elements of COMPARATIVE EXAMPLE 12 and INVENTION EXAMPLES 9 and 10 were further coated with a protective layer as described for the substantially light-insensitive thermographic recording materials of COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2 and the image tone of the fresh thermographic recording materials determined as described for COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2, the results being summarized in Table 16. Comparative example nr.
• thermographic recording material of INVENTION EXAMPLE 9 with a thermosensitive element containing second polymer B01 as dispersion polymer and first polymer AB01 as added polymer exhibited a marginally inferior image tone compared with the thermographic recording material of COMPARATIVE EXAMPLE 14 with a neutral image tone.
• thermographic recording materials of COMPARATIVE EXAMPLE 13 and INVENTION EXAMPLES 11 to 13 were prepared by coating a dispersion prepared as follows: a first solution containing 33.5 g methylethylketone, 11.28 g of binder, 0.028 g S03, 0.069 g S04, 0.296 g BOD04 and 33 mg Oil (Baysilon) was prepared. To this solution 29.2 g of a AgBehenate-dispersion, containing per 100g dispersion 14.2 g of AgBehenate and 12.6 g of binder, was added.
• the resulting dispersion was doctor blade-coated onto a subbed 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 5 thermosensitive elements with the composition given above, after drying at 50°C for 1h in a drying cupboard.
• the diffusion through the thermosensitive elements was assessed as described for the thermosensitive elements of COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2 and the results are summarized in Table 17.
• the AB01 has an effect at a concentration in the at least one binder of 76% by weight.
• the AB05 has an effect at a concentration in the at least one binder of ⁇ 76% by weight.
• the AB02 has an effect at a concentration in the at least one binder of ⁇ 76% by weight.
• thermosensitive elements of COMPARATIVE EXAMPLE 13 and INVENTION EXAMPLES 11 and 13 were further coated with a protective layer as described for the substantially light-insensitive thermographic recording materials of COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2 and the image tone of the fresh thermographic recording materials determined as described for COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2, the results being summarized in Table 18. Comparative example nr.
• thermographic recording materials of COMPARATIVE EXAMPLE 14 and INVENTION EXAMPLES 14 to 19 were prepared by coating a dispersion prepared as follows: a first solution containing 36.6 g methylethylketone, 12.50 g of binder and 33 mg Oil (Baysilon) was prepared. To this solution 32.8 g of a AgBehenate-dispersion, containing per 100g dispersion 12.7 g of AgBehenate and 11 g of binder, was added. Then 0.247 g BOD3 and 0.320 g S01 was added.
• the resulting dispersion was doctor blade-coated onto a subbed 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 6 thermosensitive elements with the composition given above, after drying at 50°C for 1h in a drying cupboard.
• thermosensitive elements The diffusion through the thermosensitive elements was assessed as described for the thermosensitive elements of COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2 and the results are summarized in Table 19.
• thermosensitive elements An improvement in diffusion through the thermosensitive elements over the situation with the at least one binder being 100% B01 was observed upon replacing 60% or more of the B01 with AB02, AB05 or A07.
• thermosensitive elements of COMPARATIVE EXAMPLE 14 and INVENTION EXAMPLES 14 to 19 were further coated with a protective layer as described for the substantially light-insensitive thermographic recording materials of COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2 and the image tone of the fresh thermographic recording materials determined as described for COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2, the results being summarized in Table 20. Comparative example nr.
• thermosensitive elements containing AB05 with or without B01 give slightly more neutral image tones than thermographic recording materials with thermosensitive elements containing AB02 with or without B01 with or without B01 for comparable B01-concentrations.
• thermographic recording materials of COMPARATIVE EXAMPLE 15 and INVENTION EXAMPLES 20 to 27 were prepared by coating a dispersion prepared as follows: a first solution containing 25.9 g methylethylketone, 9.86 g of binder, 0.044 g S03, 0.056 g BOD02 and 0.196 g B0D03 and 33 mg Oil (Baysilon) was prepared. To this solution 24.14 g of a AgBehenate-dispersion, containing per 100g dispersion 13.6 g of AgBehenate and 8.3 g of binder, was added.
• the resulting dispersion was doctor blade-coated onto a subbed 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 7 thermosensitive elements with the composition given above, after drying at 50°C for 1h in a drying cupboard.
• the coverage of silver behenate was kept constant at 3.298 g/m 2 .
• thermosensitive elements The quantities and types of polymers used in the thermosensitive elements are given in Table 21 below together with the M w values for the copolymers with both vinylaceto-acetate and vinylbutyral monomer units.
• thermosensitive elements The diffusion of behenic acid, a byproduct of the imaging forming process, and BOD03 to the surface of the thermosensitive elements of COMPARATIVE EXAMPLE 15 and INVENTION EXAMPLES 20 to 27 was assessed by:
• thermosensitive element A further diffusion test was the pinhole test in which the occurrence of pinholes due to the transport of volatile components through the thermosensitive element was monitored by observing under a microscope with an magnification of 100x the number of density steps without pinholes in a 64 step density wedge with a step of 0.05 giving 65 steps in all including zero density.
• the results are also given in Table 21.
• thermosensitive elements A substantial improvement in diffusion through the thermosensitive elements over the situation with the at least one binder being 100% B08 was observed upon replacing 83% of the B08 with AB07 to AB13.
• the results in Table 21 show that a very low diffusion of behenic acid and BOD03 can be realized with copolymers with a molar ratio of vinyl aceto-acetal to vinyl butyral of ca. 1.5 and that by increasing this ratio still further a further decrease in diffusion was observed.
• thermosensitive elements crosslinked with 0.185 g/m 2 of Desmodur TM VL be reduced by increasing the weight averaged molecular weight of the copolymers containing vinyl aceto-acetal and vinyl butyral units with thermosensitive elements containing copolymers with a molecular weight above 100,000 yielding 64 or 65 density steps without pinholes i.e. one or no density steps with pinholes.
• thermosensitive elements of COMPARATIVE EXAMPLE 15 and INVENTION EXAMPLES 20 to 27 were further coated with a protective layer as described for the substantially light-insensitive thermographic recording materials of COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2 and the image tone of the fresh thermographic recording materials determined as described for COMPARATIVE EXAMPLES 1 to 7 and INVENTION EXAMPLES 1 and 2, the results being summarized in Table 22. Comparative example nr.
• thermosensitive thermographic recording materials of INVENTION EXAMPLES 20 to 27, according to the present invention compared with the substantially light-insensitive thermographic recording material of COMPARATIVE EXAMPLE 17. Therefore, the substantial reduction in the diffusion of behenic acid and BOD03 through the thermosensitive element has surprisingly not resulted in a significant deterioration in image tone neutrality.
• 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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