EP1211092B1 - Matériau thermographique d'enregistrement avec ton de l'image amélioré - Google Patents

Matériau thermographique d'enregistrement avec ton de l'image amélioré Download PDF

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Publication number
EP1211092B1
EP1211092B1 EP20010000629 EP01000629A EP1211092B1 EP 1211092 B1 EP1211092 B1 EP 1211092B1 EP 20010000629 EP20010000629 EP 20010000629 EP 01000629 A EP01000629 A EP 01000629A EP 1211092 B1 EP1211092 B1 EP 1211092B1
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EP
European Patent Office
Prior art keywords
ion
recording material
thermographic recording
substantially light
insensitive
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German (de)
English (en)
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EP1211092A1 (fr
Inventor
Johan c/o Agfa-Gevaert Loccufier
Ivan c/o AGFA-GEVAERT Hoogmartens
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Agfa Gevaert NV
Agfa Gevaert AG
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Agfa Gevaert NV
Agfa Gevaert AG
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
    • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
    • B41M5/30—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using chemical colour formers
    • B41M5/337—Additives; Binders
    • B41M5/3375—Non-macromolecular compounds
    • 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
    • G03C1/49845—Active additives, e.g. toners, stabilisers, sensitisers
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
    • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
    • B41M5/30—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using chemical colour formers

Definitions

  • the present invention relates to thermographic recording materials whose prints have improved archival properties.
  • Thermal imaging or thermography is a recording process wherein images are generated by the use of thermal energy.
  • direct thermal thermography a visible image pattern is formed by image-wise heating of a recording material.
  • US 5,672,560 discloses a heat-sensitive imaging material comprising: a support and a heat-sensitive imaging layer formed thereon, the imaging layer comprising a color-forming amount of a substantially colorless, finely divided solid noble metal salt of an organic acid; an organic reducing agent that under conditions of heating is capable of a color-forming reaction with said noble metal salt, thereby producing a colored image; an image toning agent; and a stabilizer compound that mitigates the formation of non-imagewise background color in said imaging layer, said stabilizer compound having the formula: wherein Z 1 , Z 2 and Z 3 each independently represents hydrogen, an alkali metal ion, an alkyl group comprising 1 to about 8 carbon atoms, an aralkyl or cycloalkyl group comprising 5 to about 10 carbon atoms, or an alkyl group comprising 6 to about 15 carbon atoms; or Z 1 and Z 2 together represent a divalent alkaline earth metal ion, a divalent alkylene group comprising 2 to about 8 carbon
  • ingredients are required for substantially light-insensitive thermographic recording materials, which provide a balance of image tone stabilizing properties, enabling prints to be obtained with image tone which after pretempering is less dependent upon storage time prior to printing and to archival time after printing, while exhibiting image tone acceptable for radiologists viewing images in transmission on a light box.
  • thermographic recording materials with improved image tone stability not only capable of producing prints with image tone which is less dependent upon storage time prior to printing.
  • thermographic recording materials which is less dependent upon archival time after printing, while having an acceptable image tone for medical and graphics images.
  • thermographic recording materials comprising a thermosensitive element containing particular phosphonic acid derivatives are capable of providing prints whose image tone is less dependent upon storage time prior to printing and is less dependent upon archival time after printing, such a balance of properties combined with acceptable image tone not being provided by prior art thermographic recording materials.
  • a substantially light-insensitive black and white thermographic recording material comprising a thermosensitive element and a support, the thermosensitive element containing at least one substantially light-insensitive organic silver salt, an organic reducing agent therefor in thermal working relationship therewith, an image tone stabilizer and a binder, characterized in that the image tone stabilizer is a compound according to formula (I): wherein R 1 is hydrogen, an alkali metal ion, an ammonium ion, a phosphonium ion, a sulphonium ion, an alkaline earth ion or an optionally substituted alkyl, cycloalkyl, heterocyclic, alkaryl, aralkyl, heteroaryl or aryl group; R 2 is an optionally substituted alkyl, cycloalkyl, heterocyclic, alkaryl, aralkyl, heteroaryl or aryl group; or R 1 and R 2 together represent the atoms necessary to form a ring structure;
  • thermographic recording material as described above into proximity with a heat source; (ii) applying heat from the heat source imagewise to the thermographic recording material in a substantially water-free condition while maintaining proximity to the heat source to produce an image; and (iii) removing the thermographic recording material from the heat source.
  • R 1 is hydrogen, an alkali metal ion, an ammonium ion, a phosphonium ion, a sulphonium ion, an alkaline earth ion or an optionally substituted alkyl, cycloalkyl, heterocyclic, alkaryl, aralkyl, heteroaryl or aryl group
  • R 2 is an optionally substituted alkyl, cycloalkyl, heterocyclic, alkaryl, aralkyl, heteroaryl or aryl group; or R 1 and R 2 together represent the atoms necessary to form a ring structure
  • X is hydrogen, an alkali metal ion, an ammonium ion, a phosphonium ion, a sulphonium ion or an alkaline earth ion; in a substantially light-insensitive thermographic recording material as an image tone stabilizer is also provided by aspects of the present invention.
  • the heat source is a thermal head.
  • the heat source is a thin film thermal head.
  • 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.
  • substantially light-insensitive is meant not intentionally light sensitive.
  • a fatty acid is an organic monobasic acid of general formula C n H 2n + 1 COOH derived from the saturated series of aliphatic hydrocarbons, such as palmitic acid, stearic acid, behenic acid and arichidic acid.
  • Heating in a 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.
  • a substantially light-insensitive black and white thermographic recording material comprising a thermosensitive element containing at least one substantially light-insensitive organic silver salt, an organic reducing agent therefor in thermal working relationship therewith, an image tone stabilizer and a binder, characterized in that the image tone stabilizer is a compound according to formula (I): wherein R 1 is hydrogen, an alkali metal ion, an ammonium ion, a phosphonium ion, a sulphonium ion, an alkaline earth ion or an optionally substituted alkyl, cycloalkyl, heterocyclic, alkaryl, aralkyl, heteroaryl or aryl group; R 2 is an optionally substituted alkyl, cycloalkyl, heterocyclic, alkaryl, aralkyl, heteroaryl or aryl group; or R 1 and R 2 together represent the atoms necessary to form a ring structure; and X is hydrogen, an alkali metal ion, an ammoni
  • the substituents for the alkyl, cycloalkyl, heterocyclic, alkaryl, aralkyl, heteroaryl or aryl group representing R 1 in formula (I) are: carboxy, carboxyalkyl, alkyl, hydroxy, acyl, heteroaryl, mercapto, acyloxy, alkoxy, aryloxy and oxoamino groups.
  • the substituents for the alkyl, cycloalkyl, heterocyclic, alkaryl, aralkyl, heteroaryl or aryl group representing R 2 in formula (I) are: carboxy, carboxyalkyl, alkyl, hydroxy, acyl, heteroaryl, mercapto, acyloxy, alkoxy, aryloxy and oxoamino groups.
  • Suitable image tone stabilizing compounds according to the present invention are:
  • the image tone stabilizer is 2-phosphono-1,2,3-propanetricarboxylic acid (ITS-1) or the calcium salt of 4-ethylphosphomethyl-2,5-di-t-butylphenol (ITS-2).
  • thermosensitive element as used herein is that element which contains all the ingredients which contribute to image formation.
  • the thermosensitive element contains a substantially light-insensitive organic silver salt, an organic reducing agent therefor in thermal working relationship therewith, a image tone stabilizer and a binder.
  • the thermosensitive element comprises a layer system in which the above-mentioned ingredients may be dispersed in different layers, with the proviso that the substantially light-insensitive organic silver salt is in reactive association with the reducing agent i.e. during the thermal development process the reducing agent must be present in such a way that it is able to diffuse to the particles of substantially light-insensitive organic silver salt so that reduction to silver can occur.
  • the substantially light-insensitive organic silver salt is a substantially light-insensitive silver salt of an organic carboxylic acid.
  • the substantially light-insensitive silver salt is a silver salt of an aliphatic carboxylic acid.
  • the substantially light-insensitive silver salt is a silver salt of a fatty acid.
  • the substantially light-insensitive silver salt is a silver salt of an aliphatic carboxylic acid, wherein the aliphatic carbon chain has between 12 and 30 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".
  • the substantially light-insensitive silver salt is an organic carboxylic acid as described in GB-P 1,439,478, e.g. silver benzoate.
  • 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.
  • Organic silver salts may be dispersed by standard dispersion techniques e.g. using ball mills, bead mills, microfluidizers, ultrasonic apparatuses, rotor stator mixers etc. have been found to be useful in this regard. Mixtures of organic silver salt dispersions produced by different techniques may also be used to obtain the desired thermographic properties e.g. of coarser and a more finely ground dispersions of organic silver salts.
  • the organic reducing agent for the reduction of the substantially light-insensitive organic silver salt is an organic compound containing at least one active hydrogen atom linked to O, N or C, such as is the case with, aromatic di- and tri-hydroxy compounds.
  • the organic reducing agent is a 1,2-dihydroxybenzene derivative, such as catechol, 3-(3,4-dihydroxyphenyl) propionic acid, 1,2-dihydroxybenzoic acid, gallic acid and esters e.g. methyl gallate, ethyl gallate, propyl gallate, tannic acid, and 3,4-dihydroxy-benzoic acid ester.
  • 1,2-dihydroxybenzene derivative such as catechol, 3-(3,4-dihydroxyphenyl) propionic acid, 1,2-dihydroxybenzoic acid, gallic acid and esters e.g. methyl gallate, ethyl gallate, propyl gallate, tannic acid, and 3,4-dihydroxy-benzoic acid ester.
  • the organic reducing agent is an organic reducing agent disclosed in EP-B 692 733, e.g. ethyl 3,4-dihydroxybenzoate and n-butyl 3,4-dihydroxybenzoate,
  • thermographic recording material is an organic reducing agent disclosed in EP-A 903 625, e.g. 3,4-dihydroxybenzonitrile.
  • Combinations of reducing agents may also be used that on heating become reactive partners in the reduction of the substantially light-insensitive organic silver salt containing mixed crystals of two or more organic silver salts.
  • combinations of sterically hindered phenols with sulfonyl hydrazide reducing agents such as disclosed in US-P 5,464,738; trityl hydrazides and formyl-phenyl-hydrazides such as disclosed in US-P 5,496,695; trityl hydrazides and formyl-phenyl-hydrazides with diverse auxiliary reducing agents such as disclosed in US-P 5,545,505, US-P 5.545.507 and US-P 5,558,983; acrylonitrile compounds as disclosed in US-P 5,545,515 and US-P 5,635,339; and 2-substituted malonodialdehyde compounds as disclosed in US-P 5,654,130.
  • thermosensitive element Binder of the thermosensitive element
  • the binder is a natural, modified natural or synthetic resins or mixtures of such resins, in which the substantially light-insensitive organic silver salt can be homogeneously dispersed either in aqueous or solvent media: 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.
  • the binder is a water-soluble film-forming binder, for example: polyvinyl alcohol, polyacrylamide, polymethacrylamide, polyacrylic acid, polymethacrylic acid, polyvinylpyrrolidone, polyethyleneglycol, proteinaceous binders such as gelatine, modified gelatines such as phthaloyl gelatine, polysaccharides, such as starch, gum arabic and dextran and water-soluble cellulose derivatives.
  • a water-soluble film-forming binder for example: polyvinyl alcohol, polyacrylamide, polymethacrylamide, polyacrylic acid, polymethacrylic acid, polyvinylpyrrolidone, polyethyleneglycol, proteinaceous binders such as gelatine, modified gelatines such as phthaloyl gelatine, polysaccharides, such as starch, gum arabic and dextran and water-soluble cellulose derivatives.
  • the binder is gelatin.
  • the weight ratio of binder to substantially light-insensitive organic silver salt is in the range of 0.2 to 7.
  • the thickness of the thermosensitive element is in the range of 5 to 50 ⁇ m.
  • the binder does not contain additives or impurities which adversely affect the thermographic properties of the substantially thermographic recording material.
  • thermosensitive element further contains a toning agent in order to obtain a neutral black image tone in the higher densities and neutral grey in the lower densities.
  • the thermosensitive element further contains at least one toning agent selected from the group consisting of phthalimides and phthalazinones.
  • Suitable toning agents are the within the scope of the general formulae described in US 4,082,901. Further reference is made to the toning agents described in US 3,074,809, 3,446,648 and 3,844,797.
  • the thermosensitive element contains at least one heterocyclic toning compounds of the benzoxazine dione or naphthoxazine dione type as disclosed in GB 1,439,478, US 3,951,660, e.g. benzo[e][1,3]oxazine-2,4-dione and 7-methyl-benzo[e][1,3]oxazine-2,4-dione, and US 5,599,647, e.g. 7-(ethylcarbonato)-benzo[e][1,3]oxazine-2,4-dione.
  • the substantially light-insensitive thermographic recording material further contains an antifoggant to obtain improved shelf-life and reduced fogging.
  • the substantially light-insensitive thermographic recording material further contains at least one antifoggant selected from the group consisting of benzotriazole, substituted benzotriazoles, tetrazoles, mercaptotetrazoles such as 1-phenyl-5-mercapto-tetrazole, and aromatic polycarboxylic acids such as ortho-phthalic acid, 3-nitro-phthalic acid, tetrachlorophthalic acid, mellitic acid, pyromellitic acid and trimellitic acid, and anhydrides thereof.
  • at least one antifoggant selected from the group consisting of benzotriazole, substituted benzotriazoles, tetrazoles, mercaptotetrazoles such as 1-phenyl-5-mercapto-tetrazole, and aromatic polycarboxylic acids such as ortho-phthalic acid, 3-nitro-phthalic acid, tetrachlorophthalic acid, mellitic acid, pyromellitic acid and trimellitic
  • thermosensitive element further comprises at least one 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 thermosensitive element further comprises at least one aliphatic (saturated as well as unsaturated aliphatic and also cycloaliphatic) or aromatic polycarboxylic acid, optionally substituted and optionally used in anhydride form or partially esterified form on the condition that at least two free carboxylic acids remain or are available in the heat recording step.
  • at least one aliphatic (saturated as well as unsaturated aliphatic and also cycloaliphatic) or aromatic polycarboxylic acid optionally substituted and optionally used in anhydride form or partially esterified form on the condition that at least two free carboxylic acids remain or are available in the heat recording step.
  • Surfactants and dispersants aid the dispersion of ingredients or reactants which are insoluble in the particular dispersion medium.
  • the substantially light-insensitive thermographic recording material further comprises one or more surfactants, which may be anionic, non-ionic or cationic surfactants, and/or one or more dispersants.
  • one or more surfactants which may be anionic, non-ionic or cationic surfactants, and/or one or more dispersants.
  • the recording material may contain in addition to the ingredients mentioned above other additives such as antistatic agents, e.g. non-ionic antistatic agents including a fluorocarbon group as e.g. in F 3 C(CF 2 ) 6 CONH(CH 2 CH 2 O)-H, silicone oil, e.g. BAYSILONTM MA (from BAYER AG, GERMANY).
  • antistatic agents e.g. non-ionic antistatic agents including a fluorocarbon group as e.g. in F 3 C(CF 2 ) 6 CONH(CH 2 CH 2 O)-H
  • silicone oil e.g. BAYSILONTM MA (from BAYER AG, GERMANY).
  • the support for the thermosensitive element according to the present invention may be transparent, translucent or opaque and is a thin flexible carrier made of transparent resin film, e.g. made of a cellulose ester, cellulose triacetate, polypropylene, polycarbonate or polyester, e.g. polyethylene terephthalate.
  • transparent resin film e.g. made of a cellulose ester, 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. It may be pigmented with a blue pigment as so-called blue-base.
  • One or more backing layers may be provided to control physical properties such as curl and static.
  • thermosensitive element is provided with a protective layer to avoid local deformation of the thermosensitive element and to improve resistance against abrasion.
  • thermosensitive element is provided with a protective layer comprising a binder, which may be solvent-soluble, solvent-dispersible, water-soluble or water- dispersible.
  • a binder which may be solvent-soluble, solvent-dispersible, water-soluble or water- dispersible.
  • thermosensitive element is provided with a protective layer comprising a solvent-soluble polycarbonate binder as described in EP-A 614 769.
  • the thermosensitive element is provided with a protective layer comprising a water-soluble or water-dispersible binders, as coating can be performed from an aqueous composition and mixing of the protective layer with the immediate underlayer can be avoided by using a solvent-soluble or solvent-dispersible binder in the immediate underlayer.
  • thermosensitive element is provided with a crosslinked protective layer.
  • thermosensitive element is provided with a protective layer crosslinked with crosslinking agents such as described in WO 95/12495.
  • thermosensitive element is provided with a protective layer comprising solid or liquid lubricants or combinations thereof for improving the slip characteristics of the substantially light-insensitive thermographic recording material.
  • thermosensitive element is provided with a protective layer comprising thermomeltable particles as solid lubricants are thermomeltable particles, such as those described in WO 94/11199.
  • thermosensitive element is provided with a protective layer comprising a matting agent, such as described in WO 94/11198, e.g. talc particles, which optionally protrude from the protective layer.
  • a matting agent such as described in WO 94/11198, e.g. talc particles, which optionally protrude from the protective layer.
  • any layer of the recording material of 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, U.S.A.
  • 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. 200-500g/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.
  • thermographic materials according to US 5,672,560 Comparison of the image tone stability of prints of thermographic materials according to US 5,672,560 with that of thermographic materials according to present invention
  • the silver behenate dispersion was produced as follows: 25kg (73.5M) behenic acid was dispersed with stirring at 80°C in 100L of a 10% solution of Surfactant Nr. 1 per g behenic acid made up to 250L with deionized water at a temperature of 80°C; then 36.75L of a 2M aqueous solution of sodium hydroxide was added over a period of 10 to 20 minutes to give a clear solution substantially containing sodium behenate; then 25L of a 2.94M aqueous solution of silver nitrate was added with stirring at a rate of 0.163 moles/moles silver behenate ⁇ min to convert the sodium behenate completely into silver behenate; and finally ultrafiltration was carried out with a 500000 MW polysulfone cartridge filter at room temperature to concentrate the resulting silver behenate dispersion while adding ammonium nitrate to convert Surfactant Nr 1 into its ammonium salt, the final AgBeh-concentration was 20.4% with 0.062g
  • thermographic recording materials Preparation of thermographic recording materials
  • the coating dispersion for the thermosensitive element was produced by first allowing 3.44g of K17881 to swell in 16.33g of deionized water over a period of 30 minutes. 3.05g of a first aqueous toning agent dispersion containing 18.08% of T01 and 9.95% of K17881 and 0.8g of a second toning agent dispersion containing 20.12% of T02 and 8.88% of R16875 were then added and the resulting dispersion heated with stirring up to 50°C.
  • This coating dispersion at a temperature of 36°C was then doctor-blade coated onto the non-backing layer side of a subbed 168 ⁇ m thick blue-pigmented polyethylene terephthalate support with a backing layer (optical density upon measurement with a MACBETHTM TR924 densitometer through visible and blue filters in transmission of subbed support with backing layer was 0.19 and 0.05 respectively) to a wet coating weight of 72 g/m 2 and while undried was overcoated with 11g/m 2 of an aqueous solution with 1.8% by weight of 1,1-bis(vinylsulfono)methane and 0.9091% by weight of Surfactant Nr. 1.
  • thermosensitive elements of COMPARATIVE EXAMPLES 1 to 4 and INVENTION EXAMPLES 1 and 2 were obtained.
  • Table 1 Compar- ative example nr AgB g/m 2 Image tone stabilizer type mol% vs AgB Added as 1 4.847 - - - 2 4.768 RU01 10 Aqueous dispersion of 8.46% RU01; 7.45% K17881 & 0.6% Surfactant Nr.
  • thermographic printing of the substantially light-insensitive thermographic recording materials of COMPARATIVE EXAMPLES 1 to 4 and INVENTION EXAMPLES 1 and 2 the print head was separated from the imaging layer by a thin intermediate material contacted with a slipping layer of a separable 5 ⁇ m thick polyethylene terephthalate ribbon coated successively with a subbing layer, heat-resistant layer and the slipping layer (antifriction layer) giving a ribbon with a total thickness of 6 ⁇ m.
  • the DRYSTAR® 2000 printer from AGFA-GEVAERT was equipped with a thin film thermal head with a resolution of 300 dpi and was operated with a line time of 11.8ms (the line time being the time needed for printing one line). During this line time the print head received constant power. The printing power was 90mW and the thermal head resistors were time-modulated to produce different image densities.
  • the image tone of fresh prints made with the substantially light-insensitive thermographic recording materials of COMPARATIVE EXAMPLES 1 to 4 and INVENTION EXAMPLES 1 and 2 was assessed on the basis of the L*, a* and b* CIELAB-values.
  • 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.
  • the a* and b* CIELAB-values of fresh prints of the substantially light-insensitive thermographic recording materials of COMPARATIVE EXAMPLES 1 to 4 and INVENTION EXAMPLES 1 and 2 at optical densities, D, of 1.0 are also given in Table 2 and with the exception of the thermographic recording material of COMPARATIVE EXAMPLE 1 represent acceptable values.
  • the D min values are mainly due to the density of the support, which had a D vis value of 0.19.
  • a negative CIELAB a*-value indicates a greenish image-tone becoming greener as a* becomes more negative, a positive a*-value indicating a reddish image-tone becoming redder as a* becomes more positive.
  • a negative CIELAB b*-value indicates a bluish tone which becomes increasingly bluer as b* becomes more negative and a positive b*-value indicates a yellowish image-tone becoming more yellow as b* becomes more positive.
  • the image tone of elements of the image with a density of 1.0 have a stronger effect than the image tone of elements with lower or higher optical density and variation in a*-values has a greater impact than variation in b*-values.
  • thermographic recording material of COMPARATIVE EXAMPLE 3 incorporating a stabilizer according to US 5,672,560, which exhibited shelf-life behaviour broadly similar to that observed with the substantially light-insensitive thermographic recording materials of INVENTION EXAMPLES 1 and 2, exhibited very poor archival properties as indicated by the very high ⁇ a*- and ⁇ b*-values.
  • thermographic recording material of COMPARATIVE EXAMPLE 2 incorporating a stabilizer according to US 5,672,560, which exhibited archival behaviour broadly similar to that observed with the substantially light-insensitive thermographic recording materials of INVENTION EXAMPLES 1 and 2, exhibited very poor shelf-life properties as indicated by the very ⁇ a*-values.
  • thermographic recording material of COMPARATIVE EXAMPLES 1 and 4 not incorporating a stabilizer and incorporating a stabilizer according to US 5,672,560 respectively, exhibited both poor shelf-life behaviour as evidenced by the high ⁇ a*-values and poor archival properties as indicated by the high ⁇ a*- and ⁇ b*-values.
  • thermographic recording materials incorporating the image tone stabilizing compounds according to formula (I) exhibit both improved shelf-life image tone stability and improved archival image tone stability, which is not available if the stabilizer compounds taught by US 5,672,560 or other image tone stabilizers are used.
  • the stabilizer compounds taught by US 5,672,560 may produce one or other beneficial effect, but are unable to provide the mix of image tone stabilizing effects required by thermographic recording materials for medical imaging and graphics imaging purposes and provided by the compounds according to formula (I) of the present invention.

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  • Engineering & Computer Science (AREA)
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Claims (8)

  1. Matériau d'enregistrement thermographique en noir et blanc essentiellement non photosensible comprenant un élément thermosensible et un support, ledit élément thermosensible contenant au moins un sel d'argent organique essentiellement non photosensible, un agent de réduction organique pour ledit sel d'argent en relation de travail thermique avec lui, un stabilisateur du ton d'image et un liant, caractérisé en ce que ledit stabilisateur du ton d'image est un composé répondant à la formule (I) :
    Figure imgb0019
     dans laquelle R1 représente un atome d'hydrogène, un ion de métal alcalin, un ion ammonium, un ion phosphonium, un ion sulfonium, un ion de métal alcalino-terreux ou encore un groupe alkyle, un groupe cycloalkyle, un groupe hétérocyclique, un groupe alkaryle, un groupe aralkyle, un groupe hétéroaryle ou un groupe aryle chacun de ces groupes étant le cas échéant substitué ; R2 représente un groupe alkyle, un groupe cycloalkyle, un groupe hétérocyclique, un groupe alkaryle, un groupe aralkyle, un groupe hétéroaryle ou un groupe aryle, chacun de ces groupes étant le cas échéant substitué ; ou bien R1 et R2 représentent ensemble les atomes nécessaires pour former une structure cyclique ; et X représente un atome d'hydrogène, un ion de métal alcalin, un ion ammonium, un ion phosphonium, un ion sulfonium ou un ion de métal alcalino-terreux.
  2. Matériau d'enregistrement thermographique selon la revendication 1, dans lequel ledit élément thermosensible contient en outre un agent influençant le ton d'image.
  3. Matériau d'enregistrement thermographique selon la revendication 2, dans lequel ledit agent influençant le ton d'image est la phtalazinone, un dérivé de phtalazinone, la pyridazone, un dérivé de pyridazone, un dérivé de benzoxazine ou un dérivé de benzoxazine substitué.
  4. Matériau d'enregistrement thermographique selon la revendication 1, dans lequel ledit stabilisateur est un composé répondant à la formule (I) possédant la structure ci-après :
    Figure imgb0020
  5. Matériau d'enregistrement thermographique selon la revendication 1, dans lequel ledit stabilisateur est un composé répondant à la formule (I) possédant la structure ci-après :
    Figure imgb0021
  6. Procédé d'enregistrement comprenant les étapes consistant à : (i) amener une couche située le plus à l'extérieur, d'un matériau d'enregistrement thermographique selon la revendication 1, à proximité d'une source de chaleur ; (ii) appliquer de la chaleur à partir de ladite source de chaleur, en forme d'image, sur ledit matériau d'enregistrement thermographique dans des conditions essentiellement anhydres, tout en maintenant ledit matériau à proximité de ladite source de chaleur pour produire une image ; et (iii) éloigner ledit matériau d'enregistrement thermographique de ladite source de chaleur.
  7. Procédé d'enregistrement selon la revendication 6, dans lequel ladite source de chaleur est une tête thermique en film mince.
  8. Utilisation d'un composé répondant à la formule (I) :
    Figure imgb0022
     dans laquelle R1 représente un atome d'hydrogène, un ion de métal alcalin, un ion ammonium, un ion phosphonium, un ion sulfonium, un ion de métal alcalino-terreux ou encore un groupe alkyle, un groupe cycloalkyle, un groupe hétérocyclique, un groupe alkaryle, un groupe aralkyle, un groupe hétéroaryle ou un groupe aryle chacun de ces groupes étant le cas échéant substitué ; R2 représente un groupe alkyle, un groupe cycloalkyle, un groupe hétérocyclique, un groupe alkaryle, un groupe aralkyle, un groupe hétéroaryle ou un groupe aryle, chacun de ces groupes étant le cas échéant substitué ; ou bien R1 et R2 représentent ensemble les atomes nécessaires pour former une structure cyclique ; et X représente un atome d'hydrogène, un ion de métal alcalin, un ion ammonium, un ion phosphonium, un ion sulfonium ou un ion de métal alcalino-terreux, dans un matériau d'enregistrement thermographique essentiellement non photosensible, à titre de stabilisateur du ton d'image.
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