Photothermographic recording material with tabular silver halide grains and a hydrazine compound

Abstract

 A photothermographic recording material comprising a support and a photo-addressable thermally developable element containing a substantially light-insensitive organic silver salt, an organic reducing agent therefor in thermal working relationship therewith, photosensitive tabular silver halide grains in catalytic association with the substantially light-insensitive organic silver salt and a binder, characterized in that the photo-addressable thermally developable element further contains a hydrazine compound; and a recording process therefor.

Description

1. Field of the invention.

[0001] The present invention relates to a photothermographic recording material with increased sensitivity containing photosensitive tabular silver halide grains and a hydrazine compound.

2. Background of the invention

[0002] Thermal imaging or thermography is a recording process wherein images are generated by the use of imagewise modulated thermal energy. Thermographic materials become photothermographic when a photosensitive agent is present which after exposure to UV, visible or IR light is capable of catalysing or participating in a thermographic process bringing about changes in colour or optical density. Examples of photothermographic materials are the so called "Dry Silver" photographic materials of the 3M Company, which are reviewed by D.A. Morgan in "Handbook of Imaging Science", edited by A.R. Diamond, page 43, published by Marcel Dekker in 1991.

[0003] US-A 4,435,499 describes a photothermographic material wherein the material comprises a support bearing in reactive association photosensitive thin tabular exemplified silver bromoiodide grains having an average grain thickness of less than 0.3 µm and a photosensitive silver halide processing agent.

[0004] The inventors have found that photothermographic materials on the basis of organic silver salts, organic reducing agent and photosensitive silver halide tabular grains exhibit low optical densities. This is a not unexpected result on the basis of the generally accepted model developed by Klosterboer and Rutledge [Paper Summaries, SPSE 33rd Annual Conference, Minneapolis, MN, N-7 (1980)] and described by Donald H. Klosterboer in Chapter 9 of "Imaging Processes and Materials Neblette's 8th Edition", Ed. J. Surge, V. Walworth and A. Shepp, published by Van Nostrand, New York (1989). Klosterboer states on page 287 second column in paragraph 1 that: "The number of silver halide grain must be such that the average distance between them is approximately 1µm. This spacing allows the silver ion from the silver soap to diffuse to the latent image on the silver halide grain during the heat development process and to produce maximum image density D_max. If one increases silver halide grain size from L = 0.1µm to L = 1.0µm at constant silver halide weight, the grain number decreases by 1000 and the average distance between silver halide grains becomes 1000µm."

[0005] However, it is desirable to use tabular silver halide grains in photothermographic materials because tabular grains have a higher light absorption and higher surface area available for spectral sensitization for a given coating weight of silver halide, despite the expected disadvantage of lower sensitivity according to the widely accepted Rutledge-Klosterboer model and the empirical evidence on which it is based.

2. Objects of the invention.

[0006] It is an object of the present invention to provide a photothermographic recording material with enhanced photosensitivity incorporating tabular silver halide grains.

[0007] It is a further object of the present invention to provide a recording process for use with a photothermographic recording material with enhanced photosensitivity incorporating tabular silver halide grains.

[0008] Further objects and advantages of the invention will become apparent from the description hereinafter.

3. Summary of the invention

[0009] Surprisingly and contrary to the teaching of Donald H. Klosterboer in chapter 9 of "Imaging Processes and Materials Neblette's 8th Edition", Ed. J. Surge, V. Walworth and A. Shepp, published by Van Nostrand (1989) mentioned above, it has been found by the inventors that in the presence of hydrazide compounds photothermographic materials on the basis of organic silver salts, organic reducing agents and photosensitive tabular silver halide grains exhibit very high maximum image densities D_max and enhanced sensitivity over materials with a comparable configuration and comparable ingredient coating weights with photosensitive cubic silver halide grains.

[0010] According to the present invention, a photothermographic recording material is provided comprising a support and a photo-addressable thermally developable element containing a substantially light-insensitive organic silver salt, an organic reducing agent therefor in thermal working relationship therewith, photosensitive tabular silver halide grains in catalytic association with the substantially light-insensitive organic silver salt and a binder, characterized in that the photo-addressable thermally developable element further contains a hydrazine compound.

[0011] A recording process is further provided comprising the steps of bringing the above-described photothermographic recording material into the proximity of a source of actinic radiation; image-wise exposing the photothermographic recording material with the source of actinic radiation; bringing the image-wise exposed photothermographic recording material into the proximity of a heat source; uniformly heating the image-wise exposed photothermographic recording material; and removing the photothermographic recording material from the heat source.

4. Detailed description of the invention.

photo-addressable thermally developable element

[0012] The photo-addressable thermally developable element contains a substantially light-insensitive organic silver salt, an organic reducing agent therefor in thermal working relationship therewith, photosensitive tabular silver halide grains in catalytic association with the substantially light-insensitive organic silver salt, a binder and a hydrazine compound. The element may comprise a layer system with the silver halide in catalytic association with the substantially light-insensitive organic silver salt ingredients, spectral sensitizer optionally together with a supersensitizer in intimate sensitizing association with the tabular silver halide particles and the other ingredients active in the thermal development process or pre- or post-development stabilization of the element being in the same layer or in other layers with the proviso that the organic reducing agent and the toning agent, if present, are in thermal working relationship with the substantially light-insensitive organic silver salt i.e. during the thermal development process the reducing agent and the toning agent, if present, are able to diffuse to the substantially light-insensitive organic silver salt, e.g. a silver salt of a fatty acid.

[0013] In a preferred embodiment the photothermographic recording material according to the present invention further comprises a second photo-addressable thermally developable element on the opposite side of the support to the first photo-addressable thermally addressable element.

hydrazine compounds

[0014] The term hydrazine compound for the purposes of this invention means hydrazine, substituted hydrazine compounds together with salts and complexes thereof. Preferred hydrazine compounds are represented by fomula (I):

        R¹-NR²-NR³-R⁴     (I)

where R¹ and R⁴ independently represent hydrogen, an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, a formyl group, an oxo-alkyl group, an oxo-substituted alkyl group, an oxo-aryl group, an oxo-substituted aryl group, a sulfo-alkyl group, a sulfo-substituted alkyl group, a sulfo-aryl group, a sulfo-substituted aryl group, a phosphoryl-alkyl group, a phosphoryl-substituted alkyl group, a phosphoryl-aryl group or a phosphoryl-substituted aryl group; and R³ and R⁴ independently represent hydrogen, an oxo-alkyl group, an oxo-substituted alkyl group, an oxo-aryl group, an oxo-substituted aryl group, a sulfo-alkyl group, a sulfo-substituted alkyl group, a sulfo-aryl group, a sulfo-substituted aryl group, a phosphoryl-alkyl group, a phosphoryl-substituted alkyl group, a phosphoryl-aryl group or a phosphoryl-substituted aryl group. A particularly preferred hydrazine compound for use in the photothermographic recording materials of the present invention is 1-formyl-2-phenylhydrazine.

photosensitive silver halide

[0015] According to the present invention the photo-addressable thermally developable element contains photosensitive tabular silver halide grains. The concentration of photosensitive tabular silver halide grains that may be used is usually in the range of 0.1 to 90 mole percent of the substantially light-insensitive organic silver salt, with the range from 0.2 to 50 mole % being preferred and the range from 0.5 to 35 mole percent being particularly preferred and the range from 1 to 12 mole percent of the substantially light-insensitive organic silver salt being especially preferred.

[0016] The photosensitive tabular silver halide grains in the in the photo-addressable thermally developable element of the photothermographic recording material of the present invention preferably have an average thickness of less than 0.3µm and in particular an average thickness less than 0.15µm. The diameter of the photosensitive tabular silver halide grains is preferably greater than 0.3µm and the aspect ratio of the photosensitive tabular silver halide grains is preferably in the range of 5:1 to 15:1.

[0017] The photosensitive tabular silver halide grains may be any photosensitive silver halide such as silver bromide, silver iodide, silver chloride, silver bromoiodide, silver chlorobromoiodide, silver chlorobromide etc.

[0018] Non-tabular photosensitive silver halide grains may be present in the photo-addressable thermally developable element in addition to the photosensitive tabular silver halide grains. These non-tabular photosensitive silver halide grains may be in any non-tabular form which is photosensitive including, but not limited to, cubic, orthorhombic, tetrahedral, octagonal etc. and may have epitaxial growth of crystals thereon and may also be chemically sensitized.

[0019] Photosensitive tabular silver halide grains preferably account for at least 50% of the projected area of the photosensitive silver halide grains in the photo-addressable thermally developable element of the photothermographic recording materials of the present invention and in a particularly preferred embodiment 70% of the projected area of the photosensitive silver halide grains.

[0020] Mixtures of emulsions having the same or different halide composition, crystal habit, crystal size, crystal size distribution and/or dopant(s) may be used in order to obtain improved sensitometry and image quality.

[0021] The silver halide used in the present invention may be employed without modification. However, it may be chemically sensitised with a chemical sensitising agent such as a compound containing sulphur, selenium, tellurium etc., or a compound containing gold, platinum, palladium, iron, ruthenium, rhodium or iridium etc., a reducing agent such as a tin halide etc., or a combination thereof. Details of these procedures are described in T.H. James, "The Theory of the Photographic Process", Fourth Edition, Macmillan Publishing Co. Inc., New York (1977), Chapter 5, pages 149 to 169. If mixtures of silver halide emulsion crystals are used chemical sensitisation is preferably performed before mixing them in order to preserve an optimised chemical sensitisation.

spectral sensitization

[0022] The photosensitive silver halide in the photo-addressable thermally developable element of the photothermographic recording material, according to the present invention, may be spectrally sensitized with a spectral sensitizer, optionally together with a supersensitizer. Various known dyes are suitable spectral sensitizers including cyanine, merocyanine, styryl, hemicyanine, oxonol, hemioxonol and xanthene dyes optionally. Preferred cyanine dyes include those having a basic nucleus, such as a thiazoline nucleus, an oxazoline nucleus, a pyrroline nucleus, a pyridine nucleus, an oxazole nucleus, a thiazole nucleus, a selenazole nucleus and an imidazole nucleus. Preferred merocyanine dyes include those having not only the above described basic nuclei but also acid nuclei, such as a thiohydantoin nucleus, a rhodanine nucleus, an oxazolidinedione nucleus, a thiazolidinedione nucleus, a barbituric acid nucleus, a thiazolinone nucleus, a malononitrile nucleus and a pyrazolone nucleus. Of the above described cyanine and merocyanine dyes, those having imino groups or carboxyl groups are particularly preferred. Suitable sensitizers of silver halide to infra-red radiation include those disclosed in EP-A's 465 078, 559 101, 616 014 and 635 756, JN's 03-080251, 03-163440, 05-019432, 05-072662 and 06-003763 and US-P's 4,515,888, 4,639,414, 4,713,316, 5,258,282 and 5,441,866. Suitable supersensitizers for use with infra-red spectral sensitizers are disclosed in EP-A's 559 228 and 587 338 and in US-P's 3,877,943 and 4,873,184.

substantially light-insensitive organic silver salts

[0023] By substantially light-insensitive is meant not intentionally light sensitive. Preferred substantially light-insensitive organic silver salts are silver salts of organic carboxylic acids in particular aliphatic carboxylic acids known as fatty acids, 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"; silver dodecyl sulphonate described in US-A 4,504,575; and silver di-(2-ethylhexyl)-sulfosuccinate described in EP-A 0 227 141. Modified aliphatic carboxylic acids with thioether group as described e.g. in GB-P 1,111,492 and other organic silver salts as described in GB-P 1,439,478, e.g. silver benzoate and silver phthalazinone, may be used likewise to produce a thermally developable silver image. Further are mentioned silver imidazolates and the substantially light-insensitive inorganic or organic silver salt complexes described in US-A 4,260,677. Combinations of different organic silver salts may also be used in the photo-addressable thermally developable element of the photothermographic materials of the present invention.

emulsion of organic silver salt and photosensitive silver halide

[0024] A suspension of particles containing a substantially light-insensitive organic silver salt may be obtained by using a process, comprising simultaneous metered addition of an aqueous solution or suspension of an organic carboxylic acid or its salt; and an aqueous solution of a silver salt to an aqueous liquid, as described in EP-A 0 754 969.

[0025] The silver halide emulsion grains described above may be added to the photo-addressable thermally developable element in any fashion which places it in catalytic proximity to the substantially light-insensitive organic silver salt. Silver halide and the substantially light-insensitive organic silver salt which are separately formed, i.e. ex-situ or "preformed", in a binder can be mixed prior to use to prepare a coating solution, but it is also possible to obtain the required intimate contact with the large specific surface area of the tabular grains by blending them for a long period of time in order. It is also possibleto add a halogen-containing compound to the organic silver salt to partially convert the substantially light-insensitive organic silver salt to silver halide as disclosed in US-A 3,457,075.

[0026] A particularly preferred mode of preparing the emulsion of organic silver salt and photosensitive silver halide for coating of the photo-addressable thermally developable element from solvent media, according to the present invention is that disclosed in US-A 3,839,049, but other methods such as those described in Research Disclosure, June 1978, item 17029 and US-A 3,700,458 may also be used.

[0027] A particularly preferred mode of preparing the emulsion of organic silver salt and photosensitive silver halide for coating of the photo-addressable thermally developable element from aqueous media, according to the present invention is that disclosed in unpublished Application PCT/EP 96/02579, filed June 13, 1996, which discloses a production method for a photothermographic recording material comprising the steps of: (i) providing a support; (ii) coating the support with a photo-addressable thermally developable element comprising a substantially light-insensitive organic silver salt, photosensitive silver halide in catalytic association with the substantially light-insensitive organic silver salt, a reducing agent in thermal working relationship with the substantially light-insensitive organic silver salt and a binder, characterised in that the photosensitive silver halide is formed by reacting an aqueous emulsion of particles of the substantially light-insensitive organic silver salt with at least one onium salt with halide or polyhalide anion(s) and that the photo-addressable thermally developable element is coated from an aqueous dispersion medium.

organic reducing agent for photo-addressable thermally developable elements

[0028] Suitable organic reducing agents for the reduction of the substantially light-insensitive organic silver salts in photo-addressable thermally developable element are organic compounds containing at least one active hydrogen atom linked to O, N or C, such as is the case with, mono-, bis-, tris- or tetrakis-phenols; mono- or bis-naphthols; di- or polyhydroxy-naphthalenes; di- or polyhydroxybenzenes; hydroxymonoethers such as alkoxynaphthols, e.g. 4-methoxy-1-naphthol described in US-A 3,094,41; pyrazolidin-3-one type reducing agents, e.g. PHENIDONE (tradename); pyrazolin-5-ones; indan-1,3-dione derivatives; hydroxytetrone acids; hydroxytetronimides; 3-pyrazolines; pyrazolones; reducing saccharides; aminophenols e.g. METOL (tradename); p-phenylenediamines, hydroxylamine derivatives such as for example described in US-A 4,082,901; reductones e.g. ascorbic acids; hydroxamic acids; hydrazine derivatives; amidoximes; n-hydroxyureas; and the like, see also US-A 3,074,809, 3,080,254, 3,094,417 and 3,887,378.

[0029] Polyphenols such as the bisphenols used in the 3M DRY SILVER™ materials, sulfonamide phenols such as used in the Kodak DACOMATIC™ materials, and naphthols are particularly preferred for photothermographic recording materials with photo-addressable thermally developable elements on the basis of photosensitive silver halide/organic silver salt/reducing agent.

binder

[0030] The film-forming binder for the photo-addressable thermally developable element according to the present invention may be coatable from a solvent or aqueous dispersion medium.

[0031] The film-forming binder for the photo-addressable thermally developable element coatable from a solvent dispersion medium may be all kinds of natural, modified natural or synthetic resins or mixtures of such resins, wherein the organic silver salt can be dispersed homogeneously: e.g. polymers derived from α,β-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 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. A particularly suitable polyvinyl butyral containing a minor amount of vinyl alcohol units is marketed by MONSANTO USA under the trade names BUTVAR™ B76 and BUTVAR™ B79 and provides a good adhesion to paper and properly subbed polyester supports.

[0032] The film-forming binder for the photo-addressable thermally developable developable element coatable from an aqueous dispersion medium may be all kinds of transparent or translucent water-dispersible or water soluble natural, modified natural or synthetic resins or mixtures of such resins, wherein the organic silver salt can be dispersed homogeneously for example proteins, such as gelatine and gelatine derivatives (e.g. phthaloyl gelatine), cellulose derivatives, such as carboxymethylcellulose, poly-saccharides, such as dextran, starch ethers, galactomannan, polyvinyl alcohol, polyvinylpyrrolidone, acrylamide polymers, homo-or co-polymerized acrylic or methacrylic acid, latex's of water dispersible polymers, with or without hydrophilic groups, or mixtures thereof. Polymers with hydrophilic functionality for forming an aqueous polymer dispersion (latex) are described in US-A 5,006,451, but serve therein for forming a barrier layer preventing unwanted diffusion of vanadium pentoxide present as an antistatic agent.

weight ratio of binder to organic silver salt

[0033] The binder to organic silver salt weight ratio is preferably in the range of 0.2 to 6, whereas the thickness of the photo-addressable thermally developable element is preferably in the range of 5 to 50 µm.

thermal solvents

[0034] The above mentioned binders or mixtures thereof may be used in conjunction with waxes or "heat solvents" also called "thermal solvents" or "thermosolvents" improving the reaction speed of the redox-reaction at elevated temperature.

[0035] By the term "heat solvent" in this invention is meant a non-hydrolyzable organic material which is in solid state in the recording layer at temperatures below 50°C but becomes a plasticizer for the recording layer in the heated region and/or liquid solvent for at least one of the redox-reactants, e.g. the reducing agent for the organic silver salt, at a temperature above 60°C.

toning agent

[0036] In order to obtain a neutral black image tone in the higher densities and neutral grey in the lower densities the photo-addressable thermally developable element may contain a so-called toning agent known from thermography or photothermography.

[0037] Suitable toning agents are succinimide and the phthalimides and phthalazinones within the scope of the general formulae described in US-A 4,082,901. Further reference is made to the toning agents described in US-A 3,074,809, 3,446,648 and 3,844,797. Other particularly useful toning agents are the heterocyclic toner compounds of the benzoxazine dione or naphthoxazine dione type as described in GB-P 1,439,478, US-A 3,951,660 and US-A 5,599,647.

[0038] Alternatively in a transparent photothermographic recording material comprising tabular silver halide grains according to the present invention use in photosensitive silver halide emulsion layers comprising the tabular grains of blue coloured polymeric matting particles as disclosed in EP-Application 96203262, filed November 21, 1996, is recommended in favour of image tone.

stabilisers and antifoggants

[0039] In order to obtain improved shelf-life and reduced fogging, stabilizers and antifoggants may be incorporated into the photothermographic materials of the present invention. Examples of suitable stabilizers and antifoggants and their precursors, which can be used alone or in combination, include the thiazolium salts described in US-P 2,131,038 and 2,694,716; the azaindenes described in US-P 2,886,437 and 2,444,605; the urazoles described in US-P 3,287,135; the sulfocatechols described in US-P 3,235,652; the oximes described in GB-P 623,448; the thiuronium salts described in US-P 3,220,839; the palladium, platinum and gold salts described in US-P 2,566,263 and 2,597,915; the tetrazolyl-thio-compounds described in US-P 3,700,457; the mesoionic 1,2,4-triazolium-3-thiolate stablizer precursors described in US-P 4,404,390 and 4,351,896; the tribromomethyl ketone compounds described in EP-A 600 587; the combination of isocyanate and halogenated compounds described in EP-A 600 586; the vinyl sulfone and β-halo sulfone compounds described in EP-A 600 589; and those compounds mentioned in this context in Chapter 9 of "Imaging Processes and Materials, Neblette's 8th edition", by D. Klosterboer, edited by J. Sturge, V. Walworth and A. Shepp, page 279, Van Nostrand (1989); in Research Disclosure 17029 published in June 1978; and in the references cited in all these documents.

surfactants for photo-addressable thermally developable elements coated from aqueous media

[0040] Non-ionic, cationic or anionic surfactants may be used separately or as mixtures, according to the present invention, to produce dispersions of particles of the substantially light-insensitive organic silver salt in aqueous media and to disperse water-dispersible binders, such as polymer latex's, in aqueous media.

other additives

[0041] In addition to the ingredients the photo-addressable thermally developable element may contain other additives such as free fatty acids, surface-active agents, antistatic agents, e.g. non-ionic antistatic agents including a fluorocarbon group as e.g. in F₃C(CF₂)₆CONH(CH₂CH₂O)-H, silicone oil, e.g. BAYSILONE Öl A (tradename of BAYER AG - GERMANY), ultraviolet light absorbing compounds, white light reflecting and/or ultraviolet radiation reflecting pigments, silica, colloidal silica, fine polymeric particles [e.g. of poly(methyl methacrylate)] and/or optical brightening agents.

antihalation dyes

[0042] In addition to the ingredients, the photothermographic recording materials used in the present invention may also contain antihalation or acutance dyes which absorb light which has passed through the photosensitive thermally developable photographic material, thereby preventing its reflection. Such dyes may be incorporated into the photo-addressable thermally developable element or in any other layer of the photographic material of the present invention.

support

[0043] The support for the photothermographic recording material according to the present invention is a transparent resin film, e.g. made of a cellulose ester, e.g. cellulose triacetate, corona and flame treated polypropylene, polystyrene, polymethacrylic acid ester, polycarbonate or polyester, e.g. polyethylene terephthalate or polyethylene naphthalate as disclosed in GB 1,293,676, GB 1,441,304 and GB 1,454,956.

[0044] The support may be in sheet, ribbon or web form and subbed if need be to improve the adherence to the thereon coated thermally developable recording layer. The support may be made of an opacified resin composition, e.g. polyethylene terephthalate opacified by means of pigments and/or micro-voids and/or coated with an opaque pigment-binder layer, and may be called synthetic paper, or paperlike film; information about such supports can be found in EP-A's 0 194 106 and 0 234 563 and US-A's 3,944,699, 4,187,113, 4,780,402 and 5,059,579. Should a transparent base be used, the base may be substantially colourless or coloured, e.g. having a blue colour. One or more backing layers may be provided to control physical properties such as curl or static.

Outermost layer

[0045] The outermost layer of the photothermographic recording material may in different embodiments of the present invention be the outermost layer of the photo-addressable thermally developable element, a protective layer applied to the photo-addressable thermally developable element or a layer on the opposite side of the support to the photo-addressable thermally developable element.

Protective layer

[0046] According to a preferred embodiment of the photothermographic recording material, according to the present invention, the photo-addressable thermally developable element is coated with a protective layer to avoid local deformation of the photo-addressable thermally developable element and to improve resistance against abrasion.

[0047] The protective layer preferably comprises a binder, which may be solvent-soluble, solvent-dispersible, water-soluble or water-dispersible. Among the solvent-soluble binders polycarbonates as described in EP-A 614 769 are particularly preferred. However, water-soluble or water-dispersible binders are preferred for the protective layer, 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.

[0048] A protective layer according to the present invention may comprise in addition a thermomeltable particle optionally with a lubricant present on top of the protective layer as described in WO 94/11199. In a preferred embodiment at least one solid lubricant having a melting point below 150°C and at least one liquid lubricant in a binder is present, wherein at least one of the lubricants is a phosphoric acid derivative.

Crosslinking agents for outermost layer

[0049] The outermost layer according to the present invention may be crosslinked. Crosslinking can be achieved by using crosslinking agents such as described in WO 95/12495 for protective layers, e.g. tetra-alkoxysilanes, polyisocyanates, zirconates, titanates, melamine resins etc., with tetraalkoxysilanes such as tetramethylorthosilicate and tetraethylorthosilicate being preferred.

Matting agents for outermost layer

[0050] The outermost layer of the thermographic recording material according to the present invention may comprise a matting agent. Suitable matting agents are described in WO 94/11198 and include e.g. talc particles and optionally protrude from the outermost layer.

Lubricants for outermost layer

[0051] Solid or liquid lubricants or combinations thereof are suitable for improving the slip characteristics of the thermographic recording materials according to the present invention.

[0052] Solid lubricants which can be used according to the present invention are polyolefin waxes, ester waxes, polyolefin-polyether block copolymers, amide waxes, polyglycols, fatty acids, fatty alcohols, natural waxes and solid phosphoric acid derivatives. Preferred solid lubricants are thermomeltable particles such as those described in WO 94/11199.

[0053] Liquid lubricants which can be used according to the present invention according to the present invention are fatty acid esters such as glycerine trioleate, sorbitan monooleate and sorbitan trioleate, silicone oil derivatives and phosphoric acid derivatives.

antistatic layer

[0054] In a preferred embodiment the recording material of the present invention an antistatic layer is applied to the outermost layer on the side of the support not coated with the photo-addressable thermally developable element.

[0055] Suitable antistatic layers therefore are described in EP-A's 0 444 326, 0 534 006 and 0 644 456, US-A's 5,364,752 and 5,472,832 and DE-OS 4 125 758.

coating

[0056] The coating of any layer of the photothermographic 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.

[0057] According to the present invention a method of preparing a photothermographic material is further disclosed, wherein the method comprises the steps of coating on a support a photo-addressable thermally developable element and optionally overcoating with a protective layer.

photothermographic recording process

[0058] Photothermographic materials, according to the present invention, may be exposed with radiation of wavelength between an X-ray wavelength and a 5 microns wavelength with the image either being obtained by pixel-wise exposure with a finely focused light source, such as a CRT light source; a UV, visible or IR wavelength laser, such as a He/Ne-laser or an IR-laser diode, e.g. emitting at 780nm, 830nm or 850nm; or a light emitting diode, for example one emitting at 659nm; or by direct exposure to the object itself or an image therefrom with appropriate illumination e.g. with UV, visible or IR light. For the thermal development of image-wise exposed photothermographic recording materials, according to the present invention, any sort of heat source can be used that enables the recording materials to be uniformly heated to the development temperature in a time acceptable for the application concerned e.g. contact heating, radiative heating, microwave heating etc.

applications

[0059] The photothermographic recording materials of the present invention can be used for the production of transparencies, which are widely used in graphics applications, e.g. in masks or for display purposes, and in the medical diagnostic field in which black-imaged transparencies are widely used in inspection techniques operating with a light box.

[0060] Application of the present invention is envisaged in the fields of both graphics images requiring high contrast images with a very steep dependence of print density upon applied dot energy and continuous tone images requiring a weaker dependence of print density upon applied dot energy, such as required in the medical diagnostic field.

[0061] The following ingredients were used in the invention and comparative examples of the present invention: preparation of silver halide emulsions:

• R6875: type 16875, a phthaloyl gelatine from ROUSSELOT;
• K17329: type 17329, an oxidized gelatine from AGFA-GEVAERT GELATINEFABRIEK.

photo-addressable thermally developable element:

[0062] 

i) silver behenate/silver halide emulsion layer:

B76:

BUTVAR™ B76, a polyvinylbutyral from MONSANTO;

TMABP:

tetramethylammonium bromide perbromide;

LOWINOX™ 22IB46:

2-propyl-bis (2-hydroxy-3,5-dimethylphenyl)methane from CHEM. WERKE LOWI;

TMPS:

tribromomethyl benzenesulfinate;

Dye S-1:

ii) overcoat layer:

CAB:

cellulose acetate butyrate, CAB-171-15S from EASTMAN;

PMMA:

poly(methyl methacrylate), Acryloid^TM K120N from ROHM & HAAS.

LOWINOX™ 22IB46:

2-propyl-bis (2-hydroxy-3,5-dimethylphenyl)methane from CHEM. WERKE LOWI;

Hydrazide H-1 :

[0063] The following examples illustrate the present invention without however limiting it thereto. All percentages, parts and ratios are by weight unless otherwise mentioned.

INVENTION EXAMPLE 1 and COMPARATIVE EXAMPLES 1 & 2

preparation of silver halide emulsion A (cubic grain)

[0064] A silver halide emulsion consisting of 3.11% by weight of silver halide particles consisting of 97mol% silver bromide and 3 mol% silver iodide with an weight average particle size of 50nm, 0.47% by weight of R16875 as dispersing agent in deionized water was prepared using conventional silver halide preparation techniques such as described, for example, in T.H. James, "The Theory of the Photographic Process", Fourth Edition, Macmillan Publishing Co. Inc., New York (1977), Chapter 3, pages 88-104.

preparation of silver halide emulsion B (tabular grain)

[0065] The solutions used in the preparation of 3.5 moles of emulsion B were prepared as follows:

• solution C was prepared by dissolving 1.3g of potassium bromide and 6.45g of K17329 in 2.91L of deionized water at 45°C and adjusting the pH to 6.0;
• solution A1 was prepared by dissolving 595g of silver nitrate in 1.675L of deionized water at 20°C;
• solution B1 was prepared by dissolving 228g 0f potassium bromide in 0.9L of deionized water at 20°C;
• solution B2 was prepared by dissolving 311g of potassium bromide and 7g of potassium iodide in 1,247L of deionized water at 20°C;
• solution G was prepared by dissolving 43g of R16875 in 0.43L of deionized water at 20°C.

[0066] Emulsion B was prepared by jetting solutions A1, B1, B2 and G into the solution C as described by the following precipitation scheme :

Step	Duration (s)	Temperature (°C)	A1 (ml/min)	B1 (ml/min)	B2 (ml/min)	G (ml/min)
1	36	45	68.8	68.8

Adjustment of temperature to 70°C
2	120	70				230

Adjustment of pH to 6
3	180			4.3
4	100		4.3	pAg = 8.6
5	2152		Start: 4.3	pAg = 8.6
			End: 18.2
6	180		6.4
7	60		6.4		pAg = 8.6
8			Start:6.4		pAg = 8.6
			End: 32.4

[0067] This resulted in tabular silver halide particles consisting of 99 mol% silver bromide and 1 mol% silver iodide with an weight average particle size of 325nm and an average thickness of 100nm. The emulsion was washed with water and desalted.

preparation of emulsion of silver behenate and silver halide emulsion A

[0068] The emulsion of silver behenate and silver halide emulsion A was prepared by adding a solution of 6.8 kg of behenic acid in 67L of 2-propanol at 65°C to a 400L vessel heated to maintain the temperature of the contents at 65°C, converting 96% of the behenic acid to sodium behenate by adding with stirring 76.8L of 0.25M sodium hydroxide in deionized water, then adding with stirring 10.5kg of the above described silver halide emulsion A at 40°C and finally adding with stirring 48L of a 0.4M solution of silver nitrate in deionized water. Upon completion of the addition of silver nitrate the contents of the vessel were allowed to cool and the precipitate filtered off, washed, slurried with water, filtered again and finally dried at 40°C for 27 hours.

[0069] 7 kg of the dried powder containing 9 mol% silver halide and 4 mol% behenic acid with respect to silver behenate were then dispersed in a solution of 700 g of B76 in 15.6 kg of 2-butanone using conventional dispersion techniques yielding a 33% by weight dispersion. 7.4 kg of 2-butanone were then added and the resulting dispersion homogenized in a MICROFLUIDICS™ M-110Y high pressure microfluidizer. Finally 2.8kg of B76 were added with stirring to produce a dispersion with 31% by weight of solids.

preparation of emulsion of silver behenate and silver halide emulsion B

[0070] The same procedure was followed as for the preparation of the emulsion of silver behenate and silver halide emulsion A, except that silver halide emulsion B was used to obtain a dispersion with 31% by weight of solids containing 9 mol% of tabular silver halide grains with respect to silver behenate.

preparation of the silver behenate/silver halide emulsion layers of the photothermographic elements

[0071] The emulsion layer coating compositions for the photothermographic recording materials of COMPARATIVE EXAMPLES 1 & 2 and INVENTION EXAMPLE 1 were prepared by adding the following solutions of liquids to 40.86g of the above-mentioned silver behenate/silver halide emulsion in the following sequence with stirring: 10.87g of 2-butanone, 0.75g of a 9% solution of TMABP in methanol followed by 2 hours stirring, 1.3g of 2-butanone, 0.2g of a 11% solution of calcium bromide in methanol and 1.3 g of 2-butanone followed by 30 minutes stirring, a solution consisting of 0.21g of LOWINOX™ 22IB46, 0.5g of TMPS and 9.24g of 2-butanone followed by 10 minutes stirring and finally 4.35g of B76 were added followed by 45 minutes of stirring and then 6.42 g of 2-butanone.

[0072] The PET-support subbed and coated with a backside layer as described above was then doctor blade-coated at a blade setting of 150µm on the side of the support not coated with a backside layer with the coating composition to a wet layer thickness of 80µm followed by drying for 5 minutes at 80°C on an aluminium plate in a drying cupboard.

preparation of the overcoat layers

[0073] An overcoat layer coating composition for the photothermographic recording materials of COMPARATIVE EXAMPLES 1 & 2 and INVENTION EXAMPLE 1 was prepared by dissolving 4.08g of CAB and 0.16g of PMMA in 36.3g of 2-butanone and 4.16g of methanol adding the following solids or solution with stirring in the following sequence: 0.5g of phthalazine, 0.2g of 4-methylphthalic acid, 0.1g of tetrachlorophthalic acid, 0.2g of tetrachlorophthalic anhydride and a solution of 2.55g of LOWINOX™ 22IB46 in 5.95g 2-butanone.

[0074] The emulsion layer was then doctor blade-coated at a blade setting of 100µm with the protective layer coating composition to a wet layer thickness of 57µm, which after drying for 8 minutes at 80°C on an aluminium plate in a drying cupboard produced a layer with the following composition:

CAB	4.08g/m2
PMMA	0.16g/m2
Phthalazine	0.50g/m2
4-methylphthalic acid	0.20g/m2
tetrachlorophthalic acid	0.10g/m2
tetrachlorophthalic acid anhydride	0.20g/m2
LOWINOX™ 22IB46	2.55g/m2

[0075] For the overcoat layer of INVENTION EXAMPLE 1, sufficient of the hydrazide H-1 was added to the coating composition to obtain a concentration in the overcoat layer of 9 mg/m². The resulting layer configurations of the photothermographic recording materials of COMPARATIVE EXAMPLES 1 & 2 and INVENTION EXAMPLE 1 are given in table 1 below :

Table 1

Example	Emulsion layer	Overcoat layer
Comparative nr 1	with silver halide emulsion A (cubic grains)	without hydrazide H-1
Comparative nr 2	with silver halide emulsion B (tabular grains)	without hydrazide H-1
Invention nr 1	with silver halide emulsion B (tabular grains)	with hydrazide H-1

Image-wise exposure and thermal processing

[0076] The photothermographic recording materials of COMPARATIVE EXAMPLES 1 & 2 and INVENTION EXAMPLE 1 were exposed for 1 s to a 750W lamp through a wedge filter varying between 0 and 3.0 in steps of 0.15.

[0077] Thermal processing was carried out with the side of the support provided with a silver behenate/silver halide emulsion layer in contact with a heated drum for 10s at different drum temperatures.

[0078] The optical densities of the resulting images were measured in transmission with a MACBETH™ TR924 densitometer through a visible filter to produce a sensitometric curve for the photothermographic recording materials from which the maximum and minimum optical densities, D_max and D_min, and the relative sensitivities for D_min + 1.0 determined.

[0079] The D_max- and D_min-values and the relative sensitivity values to obtain an optical density of D_min + 1.0 obtained upon image-wise exposure and thermal processing of the photothermographic recording materials of COMPARATIVE EXAMPLES 1 and 2 and INVENTION EXAMPLE 1 together with the thermal processing conditions used are summarized in table 2.

Table 2

Comparative example number	Thermal processing conditions		Dmax	Dmin	Relative sensitivity at Dmin + 1.0
	temperature[°C]	time [s]
1	121	10	4.4	0.18	2.5
2	121	10	0.4	0.25	-

Invention example number
3	121	10	>6.0	>6.0	-
	118	10	>6.0	0.17	1.0

[0080] The results in the table 2 show that the tabular grains of comparative example 2 were not capable of producing a high D_max. In combination with the hydrazide H-1 (INVENTION EXAMPLE 1) a higher D_max and speed are obtained at a lower processing temperature compared with COMPARATIVE EXAMPLE 1.

COMPARATIVE EXAMPLES 3 to 5 and INVENTION EXAMPLES 2 & 3

[0081] The photothermographic recording materials of COMPARATIVE EXAMPLES 3 to 5 and INVENTION EXAMPLE 2 & 3 demonstrate that the increase in speed and D_max can also be realised with spectrally sensitized silver halide emulsions. The silver halide emulsions of COMPARATIVE EXAMPLES 1 & 2 and INVENTION EXAMPLE 1 were optimally spectrally sensitized for green light using Dye S-1.

[0082] The layer configurations of the photothermographic recording materials of COMPARATIVE EXAMPLES 3 to 5 and INVENTION EXAMPLES 2 & 3 coated on a polyethylene terephthalate (PET) foil of 175 µm pigmented with a blue pigment are given in table 3.

Table 3

Example	Silver halide emulsion	Dye S-1/mole silver halide	Hydrazide H-1 [mg/m2]
Comparative nr 3	A	5.10-3 mole	-
Comparative nr 4	A	5.10-3 mole	9
Comparative nr 5	B	5.10-3 mole	-
Invention nr 2	B	5.10-3 mole	9
Invention nr 3	B	1.10-2 mole	9

[0083] The photothermographic recording materials of COMPARATIVE EXAMPLES 3 to 5 and INVENTION EXAMPLES 2 & 3 were exposed for 1 s to a 750W lamp through a L519-filter and a wedge filter varying between densities of 0 and 3.0 in steps of 0.15. Thermal processing was carried out with the side of the support provided with a silver behenate/silver halide emulsion layer in contact with a heated drum.

[0084] The D_max- and D_min-values and the relative sensitivity values to obtain an optical density of D_min + 1.0 obtained upon image-wise exposure and thermal processing of the photothermographic recording materials of COMPARATIVE EXAMPLES 3 to 5 and INVENTION EXAMPLES 2 & 3 together with the thermal processing conditions used are summarized in table 4.

Table 4

Comparative example number	Thermal processing conditions		Dmax	Dmin	Relative sensitivity at Dmin + 1.0
	temperature [°C]	time [s]
3	117	10	1.8	0 28	3.4
	118	10	4.1	0.40	2.4
4	115	10	5.6	0.29	2.6
5	121	10	0.6	0.37	-

Invention example number
2	116	10	3.5	0.35	2.6
3	118	10	3.4	0.26	2.3
	119	10	3.5	0.30	1.9

[0085] As seen from the table 4, the photothermographic recording materials according to the present invention combining the present of silver halide tabular grains with hydrazides provided higher sensitivities and high Dmax.

[0086] Having described in detail preferred embodiments of the current invention, it will now be apparent to those skilled in the art that numerous modifications can be made therein without departing from the scope of the invention as defined in the following claims.

Claims

1. A photothermographic recording material comprising a support and a photo-addressable thermally developable element containing a substantially light-insensitive organic silver salt, an organic reducing agent therefor in thermal working relationship therewith, photosensitive tabular silver halide grains in catalytic association with said substantially light-insensitive organic silver salt and a binder, characterized in that said photo-addressable thermally developable element further contains a hydrazine compound.

2. Photothermographic recording material according to claim 1, wherein said hydrazine compound is represented by formula (I):

        R¹-NR²-NR³-R⁴     (I)

where R¹ and R⁴ independently represent hydrogen, an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, a formyl group, an oxo-alkyl group, an oxo-substituted alkyl group, an oxo-aryl group, an oxo-substituted aryl group, a sulfo-alkyl group, a sulfo-substituted alkyl group, a sulfo-aryl group, a sulfo-substituted aryl group, a phosphoryl-alkyl group, a phosphoryl-substituted alkyl group, a phosphoryl-aryl group or a phosphoryl-substituted aryl group; and R³ and R⁴ independently represent hydrogen, an oxo-alkyl group, an oxo-substituted alkyl group, an oxo-aryl group, an oxo-substituted aryl group, a sulfo-alkyl group, a sulfo-substituted alkyl group, a sulfo-aryl group, a sulfo-substituted aryl group, a phosphoryl-alkyl group, a phosphoryl-substituted alkyl group, a phosphoryl-aryl group or a phosphoryl-substituted aryl group.

3. Photothermographic recording material according to claim 1 or 2, wherein said hydrazine compound is 1-formyl-2-phenylhydrazine.

4. Photothermographic recording material according to any of the preceding claims, wherein the average thickness of said photosensitive tabular silver halide grains is less than 0.3µm.

5. Photothermographic recording material according to claim 4, wherein said photosensitive tabular silver halide grains have an average layer thickness of less than 0.15µm.

6. Photothermographic recording material according to any of the preceding claims, wherein the average diameter of said photosensitive tabular silver halide grains is greater than 0.3µm.

7. Photothermographic recording material according to any of the preceding claims, wherein said photosensitive tabular silver halide grains have an aspect ratio in the range 5:1 to 15:1.

8. Photothermographic recording material according to any of the preceding claims, wherein said photosensitive tabular silver halide grains account for at least 50% of the projected area of the photosensitive silver halide grains in said photo-addressable thermally developable element.

9. Photothermographic recording material according to any of the preceding claims, wherein said photosensitive tabular silver halide grains are spectrally sensitized.

10. Photothermographic recording material according to any of the preceding claims, wherein said phothermographic recording material further comprises a second photo-addressable thermally developable element on the opposite side of said support to said first photo-addressable thermally addressable element.

11. A photothermographic recording process comprising the steps of: bringing a photothermographic recording material according to any of claims 1 to 10 into the proximity of a source of actinic radiation; image-wise exposing said photothermographic recording material with said source of actinic radiation; bringing said image-wise exposed photothermographic recording material into the proximity of a heat source; uniformly heating said image-wise exposed photothermographic recording material; and removing said photothermographic recording material from said heat source.