GB2199959A - Heat-sensitive diazo recording material - Google Patents

Abstract

A paper support is coated with an aromatic diazo salt, a coupling component therefor, and a phenol derivative ortho - substituted with one or two hydroxymethyl groups and optionally with other substituents. The reactants may be microencapsulated, preferably with a polyurethane. A heat-fusible substance, a nitrogenous basic substance and a binder can be included in the layer. Imagewise heating e.g. in a facsimile, followed by overall exposure to light produces images of good density and stability.

Description

HEAT-SRNSiTIV# DIAZO RECORDING MATERIAL The present invention relates to a heatsensitive recording material and, more particularly, to a fixable diazo type heat-sensitive recording material.

t#re specifically, the present invention relates to a heat-sensitive recording material having excellent storage stability before heat-recording and high color density upon heat-recording, and which can be lightfixed after heat-recording.

A leuco color-forming type heat-sensitive recording material is generally used as a recording material for heat-sensitive recording systems. However, such a heat-sensitive recording material has certain drawbacks in that they may develop undesired color at unexpected areas (nonimage areas) due to rough handling after recording, heating or contact with solvents and the like, thereby spoiling the recorded images.

A diazo color-forming type heat-sensitive recording material, which does not have the above defects, has recently been studied very extensively.

For example, Japanese Patent Application (OPI) No. 123086/82 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), Journal of Electric Image Society, Ilr 290 (1982) and other publications disclose diazo color-forming type heat-sensitive recording materials that are used in such a way that a recording material containing a diazo compound, a coupling component and a basic component (including substances which can become basic by heating) is heat-recorded, and thereafter the recording material is exposed to light to decompose the unreacted diazo compounds, resulting in stopping the color development.

In fact, color development at the nonrecorded areas can be stopped (hereinafter referred to as "fixa tion") by this method. However, in the recording material of thi type, precoupling gradually occurs during storage before use and, therefore, undesired color formation (fog) occurs in many cases.

Precoupling can be prevented in diazo type heat-sensitive recording material by introducing any one of the color-forming components to the recording material in the form of discontinuous particles, so as to prevent it from coming in contact with other components. However, the storage stability (shelf life stability) of such recording materials before recording is still not suffi ciently satisfactory and there is the disadvantage that the color-forming property at heating is reduced.

Further, it is disclosed, for example, in Japanese Patent Application (OPI) No. 123086/82 that diazo compounds and a coupling component may be incorporated into separate layers in order to minimize the contact between the color-forming components. Storage stability before recording can be improved by the above method, but the color-forming property by heating decreases substantially. The recording material of this type cannot respond to high speed recording with a short pulse width and, thus, is not suitable for practical use.

Still further, in order to realize both satisfactory storage stability before recording and satisfactory color-firming property by heating, it is known that one of a coupling component and a basic substance can be encapsulated by a nonpolar wax-like substance (as disclosed in Japanese Patent Application (OPT) Nos.

44141/82 (corresponding to U.S. Patent 4,400,456) and 142636/82) or by a hydrophobic high molecular weight substance (as disclosed in Japanese Patent Application (OPI) No. 192944/82) in order to separate the coupling component and/or a basic substance from other components.

However, these encapsulation methods comprise dissolving a wax or a high molecular weight substance in compatible solvents and dissolving or dispersing a color-forming component into the thus-obtained solution to form capsules, whose function is different from the usual concept of capsules where a core substance is covered with a shell.

For the above reason, when a color-forming component is dissolved to form capsules, the colorforming component does not become a core substance for a capsule, but is mixed with dispersions in. the encapsulating substance homogeneously. Therefore, precoupling occurs at the wall interface of the capsule during storage, resulting in poor storage stability before recording. On the other hand, when a color-forming component is dispersed to form a capsule, it is necessary to heat and melt the wall of the capsule in order to cause the color-forming reaction. This results in poor color-forming properties by heating. Further, the abovedescribed methods have a manufacturing problem in that the solvents used for dissolving the wax or the high molecular weight substance should be removed after the formation of the capsules.Therefore, the above methods are not sufficiently satisfactory.

In order to solve the above problems, another encapsulation method has been studied and it was found that the problems could be solved by an excellent heatsensitive recording material prepared by incorporating at least one of the color-forming components in a core substance and forming a wall around the core substance by polymerization to obtain microcapsules.

However, in the heat-sensitive recording material prepared by the above-described microencapsulation method, heat responsivity during high speed recording is not complete and the optical density at the image recorded areas appears to decrease upon long term storage after heat-recording in many cases. Therefore, further improvement has been necessary.

A first object of the present invention is to provide a heat-sensitive recording material having excel lent storage stability before recording, quick heat response properties, high color-forming properties upon heating and a reduced loss of recorded image density after long term storage of the recorded image.

A second object of the present invention is to provide a heat-sensitive recording material which can decompose unreacted diazo compounds by exposure to light after heat-recording, resulting in fixation.

A third object of the present invention is to provide a heat-sensitive recording material having excellent manufacturing suitability.

As a result of extensive studies, the inventors of the present invention have found that the abovedescribed objects can be attained with a heat-sensitive recording material comprising a support having provided thereon a recording layer containing a diazo compound and a coupling component, wherein the recording layer contains at least one phenol derivative substituted with a hydroxymethyl group at one or two ortho positions.

It is preferred that one of the diazo compounds or coupling components is incorporated in a microcapsule, and it is particularly preferred that diazo compounds. are contained in a microcapsule.

The microcapsules generally used in a recording material are ruptured by heating or pressure so that the reactive substance contained in the core of the microcapsule makes contact with the reactive substance outside of the microcapsule, thereby causing a color-forming reaction, whereas in the present invention, reactive substances contained in the core and present outside of the microcapsule are allowed to pass through the wall of the microcapsule by heating so that those substances contact and react with each other.

The inventors of the present invention have studied the heat-sensitive recording material using the above-described microcapsules and have found that it is remarkably effective to incorporate at least one phenol derivative substituted with a hydroxymethyl group at at least one of two ortho positions into a recording layer in addition to the above-described diazo compounds and coupling components in order to obtain a heatsensitive recording material having excellent storage stability before recording, good color-forming properties upon heating and a reduced loss of recorded image density after long term storage of the recorded image.

Preferred examples of the above-described phenol derivatives of the present invention are those compounds represented by the formula (I):

In the formula, R1, R2 and R3 each represents a hydrogen atom, an alkyl group (preferably C1-C8), an aryl group, an alkoxy group, an aryloxy group, an arylalkyloxy group, an alkylthio group, an arylthio group, an acylthio group, a halogen atom, a carbamoyl group, a sulfamoyl group, a hydroxyalkyl group, an amino group, a substituted amino group, a cyano group, a nitro group, an acyl group, an acyloxy group or a sulfo group. Two of R1, R2 and R3 may combine to form a ring.

Among these compounds represented by the formula (I), those compounds having a melting point of from 50 to 250 CC are preferred and, particularly of m.pt, 65 to 2000C are more preferred. Further, compounds having a solubility in water(259C)#of 4 or less, particularly 0.5 or less, are preferred in view of durability of the recording material. Solubility is in g/100 g water.

Among the phenol derivatives represented by the above formula (I), those compounds having the formula (II) or (III) are particularly preferred.

In the formulae (II) and (III), X represents an oxygen atom or a sulfur atom; R4 represents an alkyl group (preferably C1-C8), or an aryl group; R5 and R6 and the substituents of R4 may represent a hydrogen atom, a halogen atom, an alkyl group (preferably C1-C8), an alkoxy group, a hydroxyalkyl group, an amino group, a substituted amino group (e.g., an amino group substituted with a substituent such as a mono- or di-C1-C4 alkyl group, a mono- or diaryl group or a mono- or diarylalkyl group), a cyano group, a nitro group, an acyl group, an acyloxy group, a sulfo group, a carbamoyl group, a sulfamoyl group, an alkylthio group, an aryl group, an arylthio group or an acylthio group.

R4 may be substituted with one or more of the substituents represented by R5 and R6.

Phenol derivatives wherein both ortho positions of phenolic hydroxyl groups are substituted with a hydroxymethyl group are also preferred.

Specific examples of the phenol derivatives include 2-hydroxymethyl-4-methylphenol, 2-hydroxymethyl4-ethylphenol, 2-hydroxymethyl-4-phenylphenol, 2-hydroxy methyl-4-benzylphenol, 2-hydroxymethyl-4-methoxyphenol, 2-hydroxymethyl-4-phenoxyphenol, 2-hydroxymethyl-4benzyloxyphenol, 2-hydroxymethyl-4-methoxycarbonylphenol, 2-hydroxymethyl-4-phenoxycarbonylphenol, 2-hydroxymethyl4-benzyloxycarbonylphenol, 2-hydroxymethyl-4-acetylphenol, 2-hydroxymethyl-4-benzoylphenol, 2-hydroxymethyl-4benzylcarbonylphenol, 2-hydroxymethyl-4-phenylthiophenol, 2-hydroxymethyl-4-benzylthiophenol, 2-hydroxymethyl-4 N-benzylaminophenol, 2-hydroxymethyl-4- (2-phenoxyethyl= thio) phenol, 2-hydroxymethyl-4- (2-phenylthioethylthio) - phenol, 2-hydroxymethyl-4-chlorophenol, 2-hydroxymethyl 4-bromophenol, 2,6-bis(hydroxymethyl)-4-methylphenol, 2,6-bis(hydroxymethyl)-4-ethylphenol, 2,6-bis(hydroxymethyl) -4-phenylphenol, .2 ,6-bis (hydroxymethyl) -4-benzyl- phenol, 2,6-bis(hydroxymethyl)-4-methoxyphenol, 2, 6-bis- (hydroxymethyl) -4-phenoxyphenol, 2 ,-6-bis (hydroxymethyl) 4-benzyloxyphenol, 2, 6-bis (hydroxymethyl) -4-methoxy- carbonylphenol, 2,6-bis(hydroxymethyl)-4-phenoxycarbonyl- phenol, 2,6-bis(hydroxymethyl)-4-benzyloxycarbonylphenol, 2, 6-bis (hydroxymethyl) -4-acetylphenol, 2, 6-bis (hydroxy- methyl) -4-benzoylphenol, 2,6-bis(hydroxymethyl)-4- benzoylcarbonylphenol, 2,6-bis(hydroxymethyl)-4-benzylthiophenol, 2,6-bis(hydroxymethyl)-4-N-benzylaminophenol, 2,6-bis(hydroxymethyl)-4-(2-phenoxyethylthio)phenol, 2,6-bis(hydroxymethyl)-4-(2-phenylthioethylthio)phenol, 2,6-bis(hydroxymethyl)-4-chlorophenol and 2, 6-bis- (hydroxymethyl) -4-bromophenol.

The diazo compounds used in the present invention can be diazonium salts represented by the formula + ArN2 X , wherein Ar represents an aromatic moiety, N2 represents a diazonium group and X represents an acidic anion. Further, the diazo compounds are those that can form a color by reaction with coupling components and can be decomposed by light.

The aromatic moiety preferably has the follow ing formula:

In the above formula, Y may represent a hydrogen atom, a substituted amino group, an alkoxy group, an aryloxy group, an arylthio group, an alkylthio group or an acylamino group; R may represent a hydrogen atom, an alkyl group, an alkoxy group, an aryloxy group, an arylamino group or a halogen atom (I, Br, CQ, F); and n represents 1 or 2.

The substituted amino groups represented by Y are preferably a monoalkylamino group, a dialkylamino group, an arylamino group, a morpholino group, a piperidino group or a pyrrolidino group.

Specific examples of diazoniums which form diazonium salts include 4-diazo-1-dimethylaminobenzene, 4-diazo-1 -diethylaminobenzene, 4-diazo-1 -dipropylamino- benzene, 4-diazo-1-methylbenzylaminobenzene, 4-diazo-1 - dibenzylaminobenzene, 4-aiazo-1-ethylhydroxyethylamino- benzene, 4-diazo-1-diethylamino-3-methoxybenzene, 4diazo-1-dimethylamino-2-methylbenzene, 4-diazo-1 -benzoyl- amino-2,5-diethoxybenzene, 4-diazo-1 -morpholinobenzene, 4-diazo-1-morpholino-2 ,5-diethoxybenzene, 4- iazo-1- morpholino-2,5-dibutoxybenzene, 4-diazo-1 -anilinobenzene 4-diazo-1-toluylmercapto-2,5-diethoxybenzene, 4-diazo1,4-methoxybenzoylamino-2,5-diethoxybenzene and 4-diazo 1-pyrrolidino-2-ethylben-zene.

Specific examples of an acidic anion include CpF2p+1COO (p is an integer of from 3 to 9), CqF2q+1SO3- (q is an integer of from 2 to 8)1 (CrF2r+1SO2)2CH (r is

Acidic anions containing a perfluoroalkyl group or a perfluoroalkenyl group or PF6 -are preferred because their use reduces the amount of fogging due to storage before recording.

Specific examples of diazo compounds (diazonium salts) for use in the present invention are illustrated below.

The coupling components used in the present invention are those which can form dye by a coupling reaction with diazo compounds (diazoniunt salts) in a basic environment. Specific examples thereof include resorcin, phloroglucin, sodium 2,3-dihydroxynaphthalene6-sulfonate, 1 -hydroxy-2-naphthoic acid morpholinopropylamide, 1 , 5-dihydroxynaphthalene, 2,3-dihydroxynaphthalenet 2, 3-dihydroxy-6-sulfanilnaphthalene, 2-hydroxy-3 naphthoic acid morpholinopropyi::amide, 2-hydroxy-3naphthoic acid anilide, 2-hydroxy-3-naphthoic acid-2' - methylanilide, 2-hydroxy-3-naphthoic acid ethanolamide, 2-hydroxy-3-naphthoic acid octylamide, 2-hydroxy-3- naphthoic acid-N-dodecyloxypropylamide, 2-hydroxy-3naphthoic acid tetradecylamide, acetanilide, acetoacetanilide, benzoylacetanilide, 1-phenyl-3-methyl-5- pyrazolone, 1-(2' ,4' ,61-trich1orophenyl)-3-benzamido-5- pyrazolone, 1-(2',4g,6'-trichlorophenyl)-3-anilino-5- pyrazolone, 1 -phenyl-3-phenylacetamide-5-pyrazolone, etc.

Images having a selected tone can be obtained by a combination of two or more of these coupling components.

It is preferable to add a basic substance to the heat-sensitive recording material of the present invention to facilitate color development. Such basic substances are those that are hardly soluble or insoluble in water or those that release an alkali by heating.

The useful basic substances include nitrogencontaining compounds such as organic and inorganic ammonium salts, organic amines, amides, ureas, thiouteas, and the derivatives thereof, thiazoles, pyrroles, pyrimidines, piperazines, guanidines, indoles, imidazoles, imidazolines, triazoles, morpholines, piperidines, amidines, formamidines or pyridines.Specific examples thereof include ammonium acetate, tricyclohexylamine, tribenzylamine, octadecylbenzylamine, stearylamine, allylurea, thiourea, methylthiourea, allylthiourea, ethylenethiourea, 2-benzylimidazole, 4-phenylimidazole, 2-phenyl-4-methylimidazole, 2-undecylimidazole, 2,4,5trifuryl-2-imidazoline, 1 ,2-diphenyl-4,4-dimethyl-2- imidazoline, 2-phenyl-2-imidazoline, 1 ,2,3-triphenyl- guanidine, 1 ,2-ditolylguanidine, 1 ,2-dicyclohexyl- guanidin#e, 1,2,3-tricyclohexylguanidine, guanidine trichloroacetate, N,N '-dibenzylpiperazine, 4,4 '-dithio- morpholine, morpholinium trichloroacetate, 2-aminobenzotriazole and 2-benzoylhydrazinobenzothiazole.Two or more of these basic substances can be used in combination.

In the present invention, reactive substances contained in the core substance of a microcapsule are dissolved or dispersed by a water-insoluble organic solvent to form an emulsion, and then the wall of the microcapsule is formed therearound by polymerization.

Organic solvents having a boiling point of 1800C or higher are preferred. Specific examples thereof are phosphates, phthalates, other carboxylic acid esters, fatty acid amides, alkylated biphenyls, alkylated terphenyls, chlorinated paraffins, alkylated naphthalenes, diaryl ethanes, and the like. More specific examples are tricresyl phosphate, trioctyl phosphate, octyldiphenyl phosphate, tricyclohexyl phosphate, dibutyl phthalate, dioctyl phthalate, dilauryl phthalate, dicyclohexyl phthalate, butyl oleate, diethylene glycol dibenzoate, dioctyl sebacate, dibutyl sebacate, dioctyl adipate, trioctyl trimellitate, acetyltriethyl citrate, octyl maleate, dibutyl maleate, isopropyl biphenyl, isoamyl biphenyl, chlorinated paraffin, diisopropyl naphthalene, 1 , 1 '-ditolylethane, 2,4-ditertiary aminophenol and N ,N-dibutyl-2-butoxy-5-tertiary octani#ine.

Among these solvents, ester solvents such as dibutyl phthalate, tricresyl phosphate, diethyl phthalate or dibutyl maleate are particularly preferred.

A microcapsule in the present invention is prepared by emulsifying the core substance containing reactive substances and thereafter forming a wall made of a high molecular weight substance around the oil drop.

A reactant which forms a high molecular weight substance is added inside and/or outside of the oil drop. Specific examples of the high molecular weight substances are polyurethane, polyurea, polyamide, polyester, polycarbonate, urea-formaldehyde resin, a melamine resin, polystyrene, styrene-methacrylate copolymer, styrene acrylate copolymer, gelatin, polyvinyl pyrrolidone and polyvinyl alcohol.

The high molecular weight substances can be used in combination. Preferred high molecular weight substances are polyurethane, polyurea, polyamide, polyester and polycarbonate, and the most preferred substances are polyurethane and polyurea.

For preparing the wall of a microcapsule of the present invention, the method of microencapsulation by polymerizing reactants from the inside of an oil drop is most effective. That is, in accordance with the above method, a capsule which is preferably used for a recording material having a good storage stability before recording and having a uniform particle size can be prepared in a short time.

The above method and specific examples of the compounds are disclosed in U.S. Patents 3,726,804 and 3,796,669.

When polyurethane is used as a material for the capsule wall, the microcapsule wall is prepared by mixing a polyhydric isocyanate and a second substance, for example, a polyol, which forms a capsule wall by the reaction with polyhydric isocyanate in the oily liquid to be encapsulated, emulsifying and dispersing the mixture in water and causing a reaction to form a high molecular weight wall on the surface of an oil drop by increasing the temperature. In this case, an auxiliary solvent having a low boiling point and having high dissolving power can be used in the oily liquid.

In this instance, polyisocyanate and the second substance to be reacted, for example, polyol, and polyamine are disclosed in U.S. Patents 3,281,383, 3,773,695, 3,793,268, Japanese Patent Publication Nos. 40347/73 (corresponding to British Patent 1,127,338A) and 24159/74 (corresponding to U.S. Patent 3,723,363) and Japanese Patent Application (OPI) Nos. 80191/73 (corresponding to U.S. Patent 3,838,108 and British Patent 1,423,302A) and 84086/73 (corresponding to British Patent 1,416,224A).

These can be used in the present invention.

A tin salt can be used in combination to access erate a urethanation reaction.

It is preferred that a polyhydric isocyanate be used as a first wall-forming substance and a polyol be used as a second wall-forming substance in order to increase storage stability before recording. Beat permeability of the reacted substance can be optionally varied by varying the combination of the first and second substances.

The polyhydric isocyanate to be used as a first wall-forming substance includes diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate, naphthalene-1,4-diisocyanate, diphenylmethane-4 , 4'- diisocyanate, 3,3 '-dimethoxy-4 ,4 '-biphenyl diisocyanate, 3,3 '-dimethyldiphenylmethane-4 '4 '-diisocyanate, xylyleneo 1 ,4-diisocyanate, 4,4'-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate propylene-1 ,2-diisocyanate, butylene-1 ,2-diisocyanate, cyclohexylene-1 ,2-diisocyanate or cyclohexylene-1,4diisocyanate; triisocyanates such as 4,4',4"triphenyl- methane trilsocyanate or toluene-2,4,6-triisocyanate; tetraisocyanates such as 4,4' -dimethyldiphenylmethane- 2,2',5,5'-tetraisocyanate; and isocyanate prepolymers such as an adduct product of hexamethylene diisocyanate and trimethylolpropane, an adduct product of 2,4-tolylene diisocyanate and trimethylolpropane, an adduct product of xylylene diisocyanate and trimethylolprop#ane, and an adduct product of tolylene diisocyanate and hexanetriol.

The polyol as a second wall-forming substance includes aliphatic and aromatic polyhydric alcohols, hydroxypolyesters and hydroxypolyalkylene ethers. The preferred polyol is a polyhydroxy compound having a molecular weight of 5,000 or less and having the follow ing groups (IV), (V) (VI) or (VII) between two hydroxy groups in the molecule: (IV) Aliphatic hydrocarbon groups having from 2 to 8 carbon atoms;

In the above groups, Ar in groups (V), (VI) and (VII) is a substituted or unsubstituted aromatic moiety. The aliphatic hydrocarbon group in group (IV) has a fundamental structure of -CnH2n- and may have a substituent such as a halogen atom, an alkyl group, a hydroxyl group or an alkoxy group in the side chains.

Specific examples of members of group (IV) are ethylene glycol, 1 , 3-propanediol, 1 ,4-butanediol 1 ,5- pentanediol, 1,6-hexanediol, 1 ,7-heptanediol, 1 ,8-octane- diol, propylene glycol, 2,3-dihydroxybutane, 1,2dihydroxybutane, 1,3-dihydroxybutane, 2,2-dimethyl-1,3propanediol, 2,4-pentanediol, 2,5-hexanediol, 3-methyl 1 , 5-pentanediol, 1,4-cyclohexanedimethanol, dihydroxycyclohexane, diethylene glycol, 1 ,2 ,6-trihydroxyhexane, phenylethylene glycol, 1,1,1-trimethylol propane, hexanetriol, pentaerythritol and glycerine.

Examples of members of group (V) are condensed products of alkylene oxide and aromatic polyhydric alcohols such as 1,4-di(2-hydroxyethoxy)benzene or resorcinol dihydroxyethyl ether.

Specific examples of members of group (VI) are p-xylylene glycol, m-xylylene glycol and c',#1-dihydroxy- p-diisopropylbenzene.

Specific examples of members of group (VII) are 4,4'-dihydroxydiphenylmethane, 2- (p ,p'-dihydroxydiphenyl- methyl)benzylalcohol, an adduct product of bisphenol A with ethylene oxide and an adduct product of bisphenol A with propylene oxide.

The polyol is preferably used in such an amount that the hydroxyl group is present in an amount of from 0.02 to 2 mols per mol of isocyanate group.

A water-soluble high molecular weight substance can be used to prepare the microcapsule and may be a water-soluble anionic, nonionic, or amphoteric high molecular weight substance.

The anionic high molecular weight substance may be a natural or synthetic substance and those having -COO , 503 and the like may be used. Natural anionic high molecular weight substances include gum arabic and alginic acid. Semisynthetic substances include carboxymethyl cellulose, phthalated gelatin, sulfated starch, sulfated cellulose and lignin sulfonic acid.

Synthetic anionic high molecular weight substances include maleic anhydride copolymer (including hydrolysis compounds), polymers and copolymers of acrylate (including methacrylate), polymers and copolymers of vinylbenzene sulfonate and carboxy-modified polyvinyl alcohol.

The nonionic high molecular weight substances include polyvinyl alcohol, hydroxyethyl cellulose and methyl cellulose.

The amphoteric compound includes gelatin and the like.

These water-soluble high molecular weight substances are used as a 0.01 to 10 wt% aqueous solution.

The particle size of the microcapsules is adjusted to be 20 um or less. When the particle size thereof exceeds 20 wm, the quality of the printed images generally becomes inferior in many cases.

Particularly, when-a thermal head is heated from the side of a coated layer, the particle size is preferably 8 pm or less in order to prevent fog caused by pressure from the thermal head.

In the present invention, diazo compounds and a coupling component, which are the main components, and a basic substance, which is used if necessary, may be used in the core substance of a microcapsule. And one, two or three of the above compounds can be employed as a core material in a microcapsule. When two of the substances are included in a core substance of a microcapsule, they may be included in separate microcapsules, respectively, or they may be included in the same microcapsule. When three of them are included in a core substance of a microcapsule, they cannot be included in one microcapsule simultaneously, but there are variable combinations of three components to be incorporated as a core material.

The other components which are not incorporated as a core material of a microcapsule are iricorporated into a heat-sensitive recording layer outside the microcapsule.

The arylalkanol compound in the present invention may be present inside or outside of the core of the microcapsules.

The microcapsules may be prepared from an emulsion containing 0.2 wt% or more of components to be encapsulated.

Whenever diazo compounds, a coupling component and, if necessary, a basic substance are present inside of microcapsules or in a heat-sensitive layer outside of microcapsules, it is preferred that the coupling component is used in an amount of 0.1 to 10 parts by weight, and the basic substance is used in an amount of 0.1 to 20 parts by weight, per part by weight of diazo compounds.

It is also preferred that the diazo compounds are coated in an amount of from 0.05 to 5.0 g/m2.

When diazo compounds, a coupling component and a basic substance are not microencapsulated, they are preferably used as a solid dispersion together with a water-soluble high molecular weight substance which are dispersed with a sand mill or the like. The preferable water-soluble high molecular weight substance used there in is that used for preparing a microcapsule. The concentration of the water-soluble high molecular weight substance is from 2 to 30 wt%, and the diazo compounds, a coupling component and a basic substance are introduced into the solution of the water-soluble high molecular weight substance in an amount of from 5 to 40 wt%, respectively.

The particle size of the dispersion is preferably 10 um or less.

Compounds, such as ethers, phenols, sulfonamides, benzamides, carboxylic acid amides, esters, ketones or the like may be-used together with the phenol derivatives of the present invention in order to improve the heat-sensitive color-forming property. Among these compounds, the benzamides are preferred.

Specific examples thereof include: (a) ethers and esters, such as 2-benzyloxy- naphthalene, 1-p-biphenyloxy-2-phenylethane, 2-benzoyloxynaphthalene, 2-phenoxyacetyloxynaphthalene, 2-p-chloro- benzyloxynaphthalene, 1-hydroxy-2-phenoxycarbonylnaphthalene, 1 ,4-bisphenoxybutane, 1,2-bis-m-tolyloxyethane, 1-phenoxy-2-p-ethylphenoxyethane, 1 ,2-diphenoxy- ethane, 1-phenoxy-2-p-chlorophenoxyethane, bis(?henoxy- ethyl)oxalate, 1-phenoxy-2-p-methoxyphenoxyethane, ss- chloroethdxynaphthalene, 1-phenoxy-2-p-tolyloxyethane, bis(phenoxyethyl)carbonate, biphenyl-i3-methoxyethyl ether, p-biphenyl-ss-cyclohexyloxyethyl ether, ss-cyanoethoxy- naphthalene, B-chloroethoxy-p-biphenyl, 2-phenoxyphenyloxycarbonylphenol, 2-p-biphenyloxycarbonyl phenol, 2-ss-naphthyloxycarbonyl phenol, bis(2-p-methoxyphenoxy- ethyl) ether, bis(2-p-ethoxyphenoxyethyl) ether, bis(2 p-inethoxyphenoxyethoxy)meth#l ether or 1,2-bis-4-methoxy- thiophenoxy ethane; (b) phenols, such as butyl phenol~, p-t-octylphenol, p-a-cumylphenol, p-t-pentylphenol, 2,5-dimethyl- phenol, 2,4,5-trimethylphenol, 3-methyl-4-isopropylphenol, p-benzylphenol, o-cyclohexylphenol, p-(diphenylmethyl)- phenol, p-(α,α;-diphenylethyl)phenol, o-phenylphenol, ethyl p-hydroxybenzoate, chloropyl p-hydroxybenzoate, butyl p-hydroxybenzoate, benzyl p-hy#roxybenzoate, p methoxyphenol, p-butoxyphenol, p-heptyloxyphenol, Un- benzyloxyphenol, 3-hydroxyphthalic acid, methyl vanillin, 2,5-diethylphenol, 1, 1-bis (4-hydroxyphenyl) - dodecane, 1,1-bis(4-hydroxyphenyl)-2-ethylhexane, 1,1 bis (4-hydroxyphenyl) -2-methylpentane, 2, 2-bis (4-hydroxy phenyl) heptane, vanillin, 2-t-butyl-4-methoxyphenol, 2,6 dimethoxyphenol, 2,2 ' -dihydroxy-4-methoxybenzophenone, ss-resorcinol acid phenoxyethyl ester, orsellinic acid a-methylbenzyl ester or methyl hydroxy cinnamate; (c) sulfonamides, such as ethylbenzenesulfonamide, toluenesulfonamide, methoxybenzenesulfonamide, ethyltoluenesulfonamide, chloroethoxybenzenesulfonamide, (iso) propylbenzenesulfonamide, ethoxytoluenesulfonamide, t-amylbenzenesulfonamide, diethylbenzenesulfonamide, allylbenzenesulfonamide, ethoxybenzenesulfonamide or cyclohexylbenzenesulfonamide, (d) carboxylic acid amides and benzamides, such as stearic acid amide, benzamide, m-methoxybenzamide, methylbenzamide, ethylbenzamide ,- isopropyl- benzamide, butylbenzamide, t-amylbenzamide, cyclohexylbenzamide, dimethylbenzamide, nicotinamide, picolinamide, naphthamide, phenylbenzamide, chlorobenzamide, o-chlorobenzamide, methoxychlorobenzamide, methoxytoluamide, ethoxybenzamide, butylbenzamide, dimethylnaphthamide, trimethylbenzamide, dimethylchlorobenzamide, dimethoxychlorobenzamide, dimethoxybenzamide, diethoxybenzamide, chiorophenoxyacetamide, pivaloylamide, 2ethylhexanoic acid amide, p-acetoxybenzamide, dimethyls aminobenzamide, phthalamide, methoxycarbonylbenzamide, methoxynaphthamide, benzylbenzami#e, chloroethylbenzamide, chloroethoxybenzamide, cyanobenzamide or benzyloxybenzamide; or (e) ketones, such as benzophenone or p-hydroxyacetophenone.

Among the above--mentioned compounds that may be used with the phenol derivatives of the present invention, preferred compounds are the amide compounds, such as o-toluamide, o-chlorobenzamide, p-ethylbenzamide, p isopropylbenzamide, p-phenylbenzamide, a-toluamide, 2,4dichlorobenzamide, 2,4-dimethylbenzamide, o-, m- or pmethoxybenzamide, o-, m- or p-ethoxybenzamide, 2,4diethoxybenzamide, 4-ethoxy-2-hydroxybenzamide, acetoxybenzamide or o-, m- or p-butoxybenzamide.

The above compounds may be used together with a core substance of a microcapsule to prepare a microcapsule or may be added to the coating solution of a heat-sensitive recording material to be present outside of the microcapsules. It is preferred that the above compounds are used with a core substance to prepare a microcapsule. In all cases, the additive amount thereof is from 0.01 to 10 parts by weight, preferably from 0 1 to 5 parts by weight, per part by weight of a coupling component. The additive amount can be optionally selected in order to adjust the desired color-forming density.

Radical generating agents (i.e., compounds which generate radicals by light irradiation) used for photopolymerization compositions can be added to the heat-sensitive recording material of the present inven tion to reduce yellow color formation in the background of the recording material after light fixation.

The radical generating agents include: (a) aromatic ketones, such as benzophenone, 4,4' -bis (dimethylamino) benzophenone, 4,4'-bis(diethyl amino)benzophenone, 4-methoxy-4 '- (dimethylamino) benzophenone, 4,41 -dimethoxybenzophenone, 4-dimethylaminobenzophenone, 4-methoxy-3 , 31 -dimethylbenzophenone, 1hydroxycyclohexylphenyl ketone, 4-dimethylaminoacetophenone, or 2-methyl-1- [ 4- (methylthio) phenyl ] -2- morpholinopropanone- 1 -acetophenone-benzyl; (b) cyclic aromatic ketones, such as fluorenone, anthrone, xanthone, thioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, acridone, N-ethylacridone or benzanthrone;; (c) qyiinones, such as benzoquinone, 2,3,5trimethyl-6-bromobenzoquinone, 2,6-di-n-decylbenzoquinone, 1f4-naphthoquinone, 2-isopropoxy-1 ,4-naphthoquinone, 1 , 2-naphthoquinone, anthraquinone, 2-chloroanthraquinone, 2-methylanthraquinone, 2-tert-butylanthraquinone or phenanthraquinone; (d) benzoins and benzoin ethers, such as benzoin methyl ether, benzoin ethyl ether, 2,2-dimethoxy2-phenylacetophenone or a-methylolbenzoin methyl ether; (e) aromatic polycyclic hydrocarbons, such as naphthalene, anthracene, phenanthrene or pyrene; (f) azo compounds, such as azobisisobutyronitrile, #-azo-1-cyclohexanecarbonitrile or azobisvaleronitrile; (g) organic disulfides, such as thiuram di sulfide;; and (h) acyloxime esters, such as benzyl(o-ethoxy carbonyl)- -monooxime.

The radical generating agents are preferably used in an amount of 0.01 to 5 parts by weight, more preferably from 0.1 to 1 part by weight, per part by weight of the diazonium compounds.

Yellow color formation in the background formed after light fixation can be reduced by including the radical generating agents together with diazonium salts as the core substance of the microcapsules.

Further, a polymerizable compound having ethylenically unsaturated bonds (hereinafter referred to as "vinyl monomer") may also be added to the heatsensitive recording material of the present invention to reduce yellow color formation in the background of the material after light fixation.

The vinyl monomer referred to herein is a compound having at least one ethylenically unsaturated bond (e.g.., a vinyl group, a vinylidene group and the like) in its chemical structure, and which has a chemical form such as a monomer, or a prepolymer, namely, a dimer, a trimer, an oligomer, a mixture thereof and a copolymer thereof. Specific examples thereof include unsaturated carboxylic acids and salts thereof, esters of unsaturated carboxylic acids and aliphatic polyhydric alcohol compounds, amides of unsaturated carboxylic acids and aliphatic polyhydric amine compounds and the like.

The vinyl monomer may be added in an amount of from 0.2 to 20 parts by weight, preferably -from 1 to 10 parts by weight, per part by weight of the diazo compounds.

When a vinyl monomer is present, it is included in the core substance of a microcapsule with the diazo compounds and a part of or all of the organic solvents used as a solvent (or dispersion medium) for the core substance can be substituted with vinyl monomers. The additive amounts of the monomer need not be sufficient to harden the core substance.

When diazo compounds are included as a core substance in the heat-sensitive recording material of the present invention, an agent which deactivates the coupling reaction may be added to the material outside of the microcapsules. The diazo compounds present in the water phase and present in incomplete capsules which are not completely blocked off by the microcapsule wall are reacted with the deactivating agent, whereby the diazo compounds lose their capacity to undergo a coupling reaction (color-forming reaction), thereby preventing fog.

The coupling reaction deactivating agents can be any substances so long as those substances can reduce color formation of a solution having diazo compounds dissolved therein. Whether or not a compound can be used as a coupling reaction deactivating agent can be determined by adding the compound dissolved in water or an organic solvent to a solution containing diazo compounds dissolved in water or an organic solvent to see the color change of the diazo compounds.

Specific examples include hydroquinone, sodium bisulfite, potassium nitrite, hypophosphorous acid, stannous chloride, formalin and the like and may be those selected from the examples disclosed in K.H.

Sawnders, The Aromatic Diazo-Comounds and Their Technical Applications, 1949, pp. 105-306.

The preferred coupling reaction deactivating agents are those which are less colored themselves and have less side effects, and the most preferred deactivating agents are those which are water-soluble.

The coupling reaction deactivating agents are used in such an amount that they#do not impede the heat color-forming reaction of the diazo compounds and generally are used in an amount of from 0.01 to 2 mols, preferably from 0.02 to 1 mol, per mol of diazo compounds.

The coupling reaction deactivating agents are used in such a manner that the deactivating agents are dissolved in a solvent and then added to the dispersion of microcapsules containing diazo compounds, or into the dispersion of the coupling agent, the basic substance or the mixture thereof. It is preferred that the activating agents are used as an aqueous solution thereof.

In the heat-sensitive recording material of the present invention, pigments such as silica, barium sulfate, titanium oxide, aluminum hydroxide, zinc oxide or calcium carbonate and fine particles such as styrene beads or urea-melamine resin can be used to prevent sticking to the thermal head or to improve the write-onproperty.

Metal soaps may also be used to prevent sticking and may be used in an amount of from 0.2 to 7 g/m2.

A heat-fusible substance may be used to increase the heat-recording density in the heat-sensitive recording material of the present invention. The heatfusible substance is a substance which is solid at normal temperatures, has a melting point of from 50 to 1500C under heating by a thermal head and dissolves the diazo compounds, the coupling component or the basic substance.

The heat-fusible substance may be used as a dispersion having a particle size of from 0.1 to 10 pm and in an amount of from 0.2 to 7 g/m2 (solid content).

Specific examples of the heat-fusible substance include fatty acid amides, N-substituted fatty acid amides, ketone compounds, urea compounds, esters and the like.

The recording layer can be coated by using suitable binders to prepare a heat-sensitive recording material of the present invention.

Binders include various emulsions of polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, gum arabic, gelatin, polyvinyl pyrrolidone, casein, styrene-butadiene latex, acrylo nitrile-butadiene latex, polyvinyl acetate, polyacrylate and a copolymer of ethylene-vinyl acetate. The additive amount may be from 0.5 to 5 g/m2 (solid content).

In addition to the materials described above, citric acid, tartaric acid, oxalic acid, boric acid, phosphoric acid and pyrophosphoric acid may be added as acid stabilizing agents.

The heat-sensitive recording material of the present invention can be prepared by a method which comprises-preparing a coating composition containing the main ingredients, such as diazo compounds or a coupling component, and a basic substance and other additives, coating the thus-obtained coating composition on a paper support or a synthetic resin film support by a bar coat ing method, a blade coating method, an air knife coating method, a gravure coating method, a roll coating method, a spray coating method, a dip coating method or the like and drying it to obtain a heat-sensitive layer having a solid content of from 2.5 to 25 g/m2.

Another method for preparing a heat-sensitive recording material comprises preparing two coating solutions (a first coating solution and a second coating solution), coating the first coating solution on a support and drying it to obtain a precoat layer having a solid content of from 2 to 10 g/m2 and then coating the second coating solution on the precoat layer and drying, it to obtain a layer having a solid content of 2 from 1 to 15 g/m , whereby a laminated layer can be obtained. The first coating solution is prepared by adding a coupling component as a main ingredient, a basic substance and other additives as the core substance of the microcapsules or dispersing or dissolving those substances in water to prepare an aqueous solution thereof.The second coating solution is prepared by adding diazo compounds as a main ingredient and other additives as the core substance of the microcapsules or dispersing or dissolving those substances in water to prepare an aqueous solution thereof. The first precoat layer and the second layer can be laminated in the reverse order.

Coating of two layers can be performed one after another simultaneously. Such a laminated layer type heat-sensitive recording material is excellent, particularly with regard to long term storage stability before recording.

The heat-sensitive layer may be coated after an intermediate layer disclosed in Japanese Patent Application (OPI) No. 54980/86 is provided on a support.

The paper used as a support is preferably a neutral paper having a heat extraction pH of from 6 to 9, which is sized by a neutral sizing agent such as an alkylketene dimer as disclosed in Japanese Patent Applies cation (OPI) No. 14281/80 (corresponding to U.S. Patent 4,255,491), because it provides good storage stability with the passage of time A paper having a Bekk smoothness of 90 seconds or more and meeting the following equation as disclosed in Japanese Patent Application (OPI) No. 116687/82 (corresponding to U.S. Patent 4,416,939) is preferred to prevent permeation of the coating solution into the paper support and to improve contact between the thermal head and the heat-sensitive recording layer.

Stockist sizing degree 2 3 X 10-3 (meter weighing capacity)2 A paper having an optical surface roughness of 8 um or less and having a thickness of from 40 to 75 pm (as disclosed in Japanese Patent Application (OPI) No.

136492/83), a paper having a density of 0.9 g/cm3 or less and having an optical contact degree of 15% or more (Japanese Patent Application (OPI) No. 69091/83), a paper made of pulp beat-treated at 400 cc or more of Canadian standard freeness (JIS P & 21) and treated to prevent permeation of the coating solution (Japanese Patent Applicat.on (OPI) No. 69097/83), a paper having improved color-forming density and resolving power, whose basic paper having a coated gloss surface is prepared by a Yankee machine (Japanese Patent Application (OPI) No.

65695/83 (corresponding to U.S. Patent 4,466,007)), and a paper whose basic paper is corona discharge-treated to improve the coating property as disclosed in Japanese Patent Application (OPI) No. 35985/84 may be used and provide good results in the present invention. Other supports generally used in the field of heat-sensitive recording papers may be also used in the present invent tion.

The heat-sensitive recording material of the present invention may be used as a printing paper for a facsimile machine or an electronic computer, for which high speed recording is required. After printing is done by heating, unreacted diazo compound is decomposed with light exposure, whereby fixation can be done. Additiorls ally, the heat-sensitive recording material of the present invention may be used as a heat-developing type copying paper.

The present invention will be illustrated in more detail by the following examples and comparative examples, but should not be construed as being limited thereto. Unless otherwise specified, all percentages, ratios and the like are by weight.

EXAMPLE 1 -3.45 parts of the following diazo compound and 18 parts of an adduct product (3:1) of xylylene diisocyanate and trimethylolpropane were added to a mixed solvent of 24 parts of tricresyl phosphate and 5 parts of ethyl acetate and dissolved.

Diazo Compound

The thus obt#'#ned solution of the diazo compound was mixed with an aqueous solution having 5.2 parts of polyvinyl alcohol dissolved in 58 parts of water, and was emulsified and dispersed at 200C to obtain an emulsion having an average particle size of 2.5 pm. To the thus-obtained emulsion was added 100 parts of water and the mixture was stirred and heated to 600C. In 2 hours, a solution of capsules containing diazo compounds as a core substance was obtained.

Subsequently, -10 parts of 2-hydroxy-3-naphthoic acid anilide and 10 parts of triphenyl guanidine were added to 100 parts of a 5% aqueous solution of polyvinyl alcohol and were dispersed by a sand mill for about 24 hours to obtain a dispersion of a coupling component and triphenyl guanidine having an average particle size of 3 urn.

To 20 parts of 2-hydroxymethyl-4-benzylthio phenol were added 100 parts of a 48 aqueous solution of polyvinyl alcohol and 100 parts of water, and they were dispersed by a paint shaker for 2 hours to obtain a solution containing a dispersion having an average particle size of 3 urn.

To 50 parts of the thus-obtained capsule solu tion of diazo compounds were added 24 parts of the dispersion of a coupling component and triphenyl guanidine and 28 parts of the dispersion of 2-hydroxymethyl-4-benzylthiophenol to prepare a coating solution.

The coating solution was coated on a smooth high quality paper (50 g/m2) using a coating bar so that the dry weight of the coating was 10 g/m' and dried at 250C for 30 minutes to obtain a heat-sensitive material.

E EMPLES 2 Z4D 3 The same procedure as in Example 1 was repeated to prepare a heat-sensitive recording material, except that 2 ,6-bis (hydroxymethyl) -4-benzylthiophenol and 2 hydroxymethyl-4-methylphenol were used instead of 2 hydroxymethyl-4-benzylthiochenol of Example 1.

COMPARATIVE EXE4PLZ 1 The same procedure as in Example 1 was repeated to prepare a heat-sensitive recording material, except that 4-benzyloxyphenol was used instead of 2-hydroxymethyl-4-benzylthiophenol of. Example 1.

Test Method Tests were done in the following manner: Heat-recording was conducted on the thusobtained heat-sensitive recording materials using a Gill Mode Thermal Printer ("Hi-Fax 700", a trade name, manufactured by Hitachi, Ltd.) and the entire surface area of each sample was exposed to light for fixation using a "Recopy Super Dry 100" exposure machine manufactured by Ricoh Ltd Blue densities of the thus-obtained recorded images were measured and yellow densities in the background were measured by a Macbeth reflective densitometer.

In order to evaluate the storage stability before recording under high temperature and high humidity conditions, the heat-sensitive recording materials were allowed to stand at 600C and 308 E (dry heat) and at 400C and 90% RE (wet heat) for 24 hours and thereafter the color formation in the background (i.e., fog formation) was evaluated.

Heat-recording was conducted on the fixed area again and it was observed that images were not recorded, thereby confirming that the area to be fixed had positively been fixed.

In order to evaluate the decrease of optical densities of color-formed areas after long storage of recorded images, the recorded images of the heatsensitive recording material were stored for 16 hours at 600C in darkness to carry out a deliberate deterioration test.

The results of these tests were as follows: Samples of Examples 1 through 3 had image densities greater than 1.2, yellow densities in the background less than 0.08, decreases in image densities of recorded images after deliberate deterioration less than 5%, dry heat color formation less than 0.15 and wet heat color formation less than 0.15, exhibiting better characteristics than those of Comparative Example 1 using 4-benzyloxyphenol.

Samples of Comparative Example 1 had image densities of 1.1 to 1.2, yellow densities in the background less than 0.08, decreases in image densities of recorded images after deliberate deterioration of 5 to 7%, dry heat color formation less than 0.15 and wet heat color formation of 0.15 to 0.20.

It is apparent from the results that the compounds of the present invention are effective in remarkably improving image densities, storage stability before recording and storage stability of recorded images.

Claims (14)

CLAIMS:

1. A heat-sensitive recording material comprising a support having provided thereon a recording layer containing a diazo compound and a coupling component, wherein said recording layer contains at least one phenol derivative substituted with a hydroxymethyl group at an ortho-position.

2. A heat-sensitive recording material of Claim 1, wherein the phenol derivative is a compound represented by the formula (I):

wherein R1 R2 and R3 each represents a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an arylalkyloxy group, an alkylthio group, an arylthio group, an acylthio group, a halogen atom, a carbamoyl group, a sulfamoyl group, a hydroxyalkyl group, an amino group, a substituted amino group, a cyano group, a nitro group, an acyl group, an acyloxy group or a sulfo group.

3. A heat-sensitive recording material of Claint 2, wherein the phenol derivative has a melting point of from 50 to 2500C and a water solubility of 4 or less.

4. A heat-sensitive recording material of Claim 3, wherein the phenol derivative has a melting point of from 65 to 2000C and a water solubility of 0.5 or less.

5. A heat-sensitive recording material of Claim 2, 3 or 4, wherein the phenol compound-is a compound of the formula (11) or (III):

wherein X represents an oxygen atom or a sulfur atom; R4 represents an alkyl group or an aryl group; and R5 and R6 represent a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, a hydroxyalkyl group, an amino group, a substituted amino group, a cyano group, a nitro group, an acyl group,#an acyloxy group, a sulfo group, a carbamoyl group, a sulfamoyl group, an alkylthio group, an aryl group, an arylthio group or an acylthio group; and R4 may be substituted with one or more of the substituents represented by R5 and R6.

6. A heat-sensitive recording material of any preceding claim, wherein the diazo compounds are diazonium salts that form color by reaction with the coupling component and are decomposed when exposed to light which are represented by the formula Ar X wherein Ar represents an aromatic moiety; + N2 represents a diazonium group; and X represents an acidic anion.

7. A heat-sensitive recording material of Claim 6, wherein the aromatic moiety has the formula:

wherein Y represents a hydrogen atom, a substituted amino group, an alkoxy group, an aryloxy group, an arylthio group, an alkylthio group or an acylamino group; R represents a hydrogen atom, an alkyl group, an alkoxy group, an aryloxy group, an arylamino group or a halogen atom; and n represents 1 or 2;

8. A heat-sensitive recording material of Claim 7, wherein the acidic anion is an anion represented by the.

formula CpF2p+1COO , wherein p is an integer of from 3 to p 2p~ 9, C F SO , wherein q is an integer of from 2 to 8, q 2q+I 3 (CrF2r+1SO2)2CH2-, wherein r is an integer of from

9. A heat-sensitive recording material of any preceding claim, which further contains a basic substance that is hardly soluble or insoluble in water or generates an alkaline condition upon exposure to heat.

10. A heat-sensitive recording material of any preceding claim, wherein the diazo compound or coupling component is present as the core substance of microcapsules.

11. h heat-sensitive recording r.:aterial OL Claim 10, wherein the walls of the microcapsules are formed from the reaction of a polyhydric isocyanate and a polyol.

12. A heat-sensitive recording material as claimed in any preceding claim, wherein said phenol derivative is any of those listed hereinbefore.

13. A heat-sensitive recording material as claimed in Claim 1, substantially as hereinbefore described with reference to any of the Examples 1 to 7.

14. A visible image formed by local heating and overall exposure to light, to decompose unreacted diazo compound, of a material as claimed in any preceding claim.