GB2182157A - Heat-sensitive recording materials - Google Patents

Abstract

A heat-sensitive recording material comprises a support having provided thereon a recording layer which comprises a diazo compound, a coupling component and at least one arylsulfonamide compound of formula (I): <IMAGE> wherein R1 represents substituted or unsubstituted C2-12alkyl, C1-12alkoxy or C6-9aryloxy, Cl or F; and R2 represents substituted or unsubstituted C1-12alkyl, C1-12alkoxy, C6-9aryloxy or H, at least one of the diazo compound and the coupling component being contained in microcapsules.

Description

SPECIFICATION Heat-sensitive recording materials This invention relates to diazo-containing heat-sensitive recording materials capable of being fixed, and which have excellent shelf life before heat recording (hereinafter referred to as "keeping quality") and high coloring density when heat recording is carried out; and which can furthermore be fixed by lightafterheat recording has been carried out.

As a recording material for use in heat-sensitive recording methods, usually a leuco coloring type heat-sensitive recording material has been used. This type of heat-sensitive recording material, however, has the defects that coupling is caused in unexposed portions and recorded images are solid by severe handling, heating, or solvents adhering to the material after recording. Extensive research on a diazo coloring type heat-sensitive recording material has been conducted to try to find a material having no such defects.

For example, there are heat-sensitive recording materials as disclosed in Japanese Patent Application (OPI) No. 123086/82 (The term "OPl"-used herein means a published unexamined Japanese patent application), "Gazoudenshigakkaishi (Journal of Image Electron Society)", 11290(1982), and the like. In these recording materials, heat recording is carried out with a recording material comprising a diazo compound, a coupling component and a basic component (including a substance which can provide a base by heating) and, after that, the recording material is irradiated with light to decompose the unreacted diazo compound and to stop the coupling. Certainly, by the method, coupling in the portions on which no recording is required can be stopped (which is termed "fixing" hereinafter).However, precoupling (coupling during the preservation) often progresses slowly while the recording material is preserved causing undesired coloring (fog).

Therefore, a method to prevent the precoupling by transforming either of the coloring components into the form of discontinuous particles (the form of solid dispersion) to prevent contact between the components is in use. But, the method has defects that the keeping quality is still insufficient and the heat coupling properties are reduced.

As another countermeasure, there is a method comprising placing the diazo compound and the coupling component in sep#arate layers to minimize contact between the two components (as disclosed, forexample, in Japanese Patent Application (OPI) No. 123086/82). The keeping quality is improved markably by this method, but the heat coloring properties are reduced remarkably so that materials produced according to this method cannot respond to high-speed recording of short pulse width and, thus, this is not a practical method.

As a method for satisfying both the keeping quality and the heat coloring properties, a method is known for encapsulating either the coupling component or basic substance with a non-polar waxy substance (disclosed, for example, in Japanese Patent Application (OPI) Nos. 44141/82 and 142636/82) or a hydrophobic high molecularsubstance(disclosed,forexample, inJapanese PatentApplication (OPI) No. 192944/82)to isolate one component from othercomponents. However, in the encapsulating method, a waxora high molecularweight substance is dissolved in a solvent and a coloring component is dissolved or dispersed in the resulting solution to form capsules, so that these capsules are different from the usual capsules in which a core substance is covered with a shell. Therefore, in the case where a coloring component is dissolved in a solvent to form capsules as mentioned above, the coloring substance does not form the core substance of capsules but is mixed uniformly with the encapsulating substance, so that precoupling progresses slowly at the intereface of the capsule walls while the recorrding material is preserved and the keeping quality ofthe material is not sufficiently satisfied.In the case where a coloring component is dispersed in a solvent to form capsules as mentioned above, the coloring reaction does not take place until the wall of capsules is melted by heat, so that the heat coloring properties of the recording material is reduced. In addition, in the production process, there is a problem that a solvent used for dissolving the wax or high molecularweightsubstance must be removed after the capsules are formed, so that this method is not a satisfactory one.

An excellent heat-sensitive recording material can be produced by the method described in Japanese Patent Application (OPI) No. 190886/84 for solving the above problems. This method is characterized in that at least one of components involved in the coloring reaction is contained in a core substance and a wall is formed around the core substance by polymerization to encapsulate the core substance. However, when a heat-sensitive recording material produced by the above encapsulation method is preserved for a long period after heat recording is carried out, the optical density of image recorded portions is often lowered, so that further improvement of the heat-sensitive recording material has been demanded.

Afirst object of the present invention is to provide a heat-sensitive recording material having both excellent keeping quality and heat coloring properties and wherein the density of the recorded image formed is hardly reduced upon preservation for a long period after heat recording is carried out.

A second object of the present invention is to provide a heat-sensitive recording material capable of being fixed by decomposing the unreacted diazo compound by light after heat recording has been carried out.

Athird object of the present invention is to provide a heat-sensitive recording material having excellent producibility.

The present inventors have devoted themselves to conducting research to solve the forementioned problems of heat-sensitive recording materials and, as a result, have found that the problems can be overcome and the above and other objects can be achieved by a heat-sensitive recording material comprising a support having provided thereon a recording layer comprising a diazo compound and a coupling component wherein said recording layerfurther comprises at least one arylsulfonamide compound represented by the following general formula (I)::

where R1 represents a substjacted or unsubstituted alkyl group having from 2 to 12 carbon atoms, an alkoxy group having from 1 to 12 carton atoms oran aryloxy group having from 6to 9 carbon atoms, ora chlorine or fluorine atom, and R2 represents a substituted or unsubstituted alkyl group having from 1 to 12 carbon atoms, an alkoxygroup having from 1 to 12 carbon atoms oran aryloxy group having from 6to 9carbon atoms of a hydrogen atom.

At least one of the above-mentioned diazo compound and coupling component is contained in microcapsules. The microcapsules that can be used in the present invention are not ones which are ruptured by heat or pressure to allow a reactive substance contained in the core of microcapsules and another reactive substance outside the microcapsules to be brought into contact with each other, and the coupling reaction to take place, but ones which allow a reactive substance and another reactive substance existing within and outside the capsules, respectively, to permeate through the wall ofthe microcapsules upon heat the substances, thus allowing both substances to react with each other.

Preferably, Rt in formula (I) represents a substituted or unsubstituted alkyl group having from 2 to 4 carbon atoms ora substituted or unsubstituted alkoxy group having from 1 to 5 carbon atoms. The alkyl and alkoxy groups may have linear, branched, or cyclic structure and substituent groups. Exaniples ofthe substituent groupsforthe alkyl, alkoxy, and aryloxygroup include an alkyl group, a halogen atom, a cyano,hydroxy, acyloxy, aryloxy or acyl group. Preferred substituents are a hydrogen atom and an aryloxy group.

Specific examples of R1 and R2 in formula (I) includes a hydrogen atom, a methyl group, an ethyl group, a propyl group, an isopropyl group, an allyl group, a dimethylbutyl group, a t-amyl group, a hexyl group, an isoamyl group, a cyclohexyi group, a cyclohexylmethyl group, a chlorine atom, a methylcyclohexyl group, a chloroethyl group, ss-acetyxyethyl group, 3-ketobutyl group, a benzyl group, an a- or t3-phenethyl group, a vinyl group, a methoxy group, a thiomethoxy group, an ethoxy group, a propoxy group, a butoxy group, a hydroxy group, a diethylamino group, a butylamino group, a butoxycarbonyl group, an ethylhexyloxycarbonyl group, a N-hexylcarbamoyl group, a ss-acetoxyethoxy group, a hydroxyethoxy group, a phenoxyethyl group, a 2-chlorophenoxy-2-methylethoxy group, a dichlorophenoxy group, a dichlorophenyl group, a trimethylphenyl group, an amino group and a nitro group.

Preferable examples ofthe arylsulfonamide compound ofthe present invention include ethylbenzenesulfonamide, ethyltoluenesulfonamide, chloroethoxybenzenesulfonamide, isopropylbenzenesulfonamide, methoxybenzenesulfonamide, ethoxytoluenesulfonamide, t-amylbenzenesulfonamide, diethylbenzenesulfonamide, allylbenzenesulfonamide, ethoxybenzenesulfonamide and cyclohexylbenzenesulfonamide.

The more preferred examples ofthe arylsulfonamide compound include p-ethylenebenzensulfonamide, p-methoxybenzenesulfonamide, p-ethoxybenzenesulfonamide, p-isopropylbenzenesulfonamide and m-ethylbenzenesuifonamide.

The arylsulfonamide compound of the present invention is preferably used in an amount of from 1 to 5 g/m2.

The diazo compound used in the present invention preferably is a diazonium salt represented byformula (it) : ArN2+X- (II) wherein Ar represents an aromatic group, N+ represents a diazonium group, and X- represents an acid anion. The diazo compound can be coupled with the coupling component to develop a color and can also be decomposed by light.

Specific examples of the aromatic group Ar of the diazo compound represented byformula (11) include a group represented byformula (III):

wherein Y represents a hydrogen atom, a substituted amino group, a substituted or unsubstituted alkoxy group, aryloxy group, arylthio group, alkylthio group oracylamino group, and R represents a hydrogen atom, a substituted or unsubstituted alkyl group, alkoxy group, aryloxygroup orarylamino group, ora halogen atom (such as I, Br, Cl, or F).

As the substituted amino group represented byY in formula (III), a monoalkylamino group, a dialkylamino group, an arylamino group, or a morpholino group, a piperidino group, a pyrrolidino group, and the like are preferred.

Preferred examples of R in formula (III) include a substituted or unsubstituted alkoxy group.

Specific examples of diazonium which forms a salt include 4-diazo-1 -dimethylaminobenzene, 4-diazo-1 -diethylaminobenzene, 4-diazo-1 -dipropylaminobenzene, 4-diazo-1 -methylbenzylaminobenzene, 4-diazo-1-benzylaminobenzene, 4-diazo-1-ethylhydroxyethylaminobenzene, 4-diazo-1 -diethylamino-3-methoxybenzene, 4-diazo-1 -dimethylamino-2-methylbenzene, 4-diazo-1 -benzoylamino-2,5-diethoxybenzene, 4-diazo-1-morpholinobenzene, 4-diazo-1 -morpholino-2,5-diethoxybenzene, 4-diazo-1 -morpholino-2,5-dibutoxy-benzene, 4-diazo-1 -anilinobenzene, 4-diazo-1 -tolyl-mercapto-2,5-diethoxybenzene, 4-diazo- 1 ,4-methoxybenzoyl-amino-2,5-diethoxybenzene and 4-d iazo- 1 -pyrrolidino-2-ethylbenzene.

Specific examples of the acid anion includeCnF2n+COO- (n is an integer of from 3to 9), CmF2m+1SO3- (m is an integer of from 2 to 8), (C6F2#+1SO2)2CH- ce is an integeroffrom 1 to 18),

(n is an integer of from 3 to 9) BF4-, PF6-, and the like.

As the acid anion, in particular, those containing a perfluoroalkyl group or a perfluoroalkenyl group, and PF6- are preferred because the acid ion reduces fog during preservation of the heat-sensitive recording material before heat recording is carried out.

Specific examples ofthe diazo compound (diazonium salt) represented byformula (II) are shown below.

The diazo compound ofthe present invention is preferably used in an amount offrom 0.1 to 2 g/m2.

The coupling component used in the present invention is a compound which is coupled with the diazo compound (diazonium salt) in a basic atmosphere to provide dyes. Specific examples thereof include resorcinol, phloroglucinol, sodium 2,3-dihydroxynaphthalene-6-sulfonate, 1 -hydroxy-2-naphthoic acid morpholinopropylamide, 1 ,5-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,3-dihydroxy-6-sulfanilyl naphthalene, 2-hydroxy-3-naphthoic acid morpholinopropylamide, 2-hydroxy-3-naphthoic 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-dodecyloxy-propylamide, 2-hydroxy-3-naphthoic acid tetradecylamide, acetanilide, acetoacetanilide, benzoylacetanilide, 1 -phenyl-3-methyl-5-pyrazolone 1 -(2', 4', 6'4richlorophenyl)-3-benzamide-5-pyrazolone, 1-(2',4',6'-trichlorophenyl)-3-anilino-5-pyrazoione and 1-phenyi-3-phenylacetamide-5-pyrazolone.

Further, an image ofarbitrarycolortone can be obtained by using the combination oftwo or more compounds of these coupling components.

The coupling component ofthe present invention is preferably used in an amount offrom 0.2 to 8 g/m2.

it is preferred to incorporate a basic substance in the heat-sensitive recording material of the present invention to accelerate the color formation in the recording material. As the basic substance, awater-slightly soluble of water-insoluble basic substance or a substance which produces an alkali upon heating is used.

The basic substance includes nitrogen-containing compounds such as inorganic and organic ammonium salts, organic amines, amides, ureas and derivatives thereof, thioureas and derivatives thereof, thiazoles, pyrroles, perimidines, piperazines, guanidines, indoles, imidazoles, imidazolines, triazoles, morpholines, piperidines, amidines, formazines and pyridines.Specific examples of these compounds include ammonium acetate, tricyclohexylamine, tribenzylamine, octadecylbenzylamine, stearylamine, allylurea, thiourea, methylthiourea, allylthiourea, ethylene thiourea, 2-benzylimidazole, 4-phenylimidazole, 2-phenyl-4-methylimidazole, ndecylim idazol 2,4,5-trifuryl-2-imidazoline, 1 ,2-diphenyl-4,4-dimethyl-2-imidazoline, 2-phenyl-2-imidazoline, 1 ,2,3-triphenylguanidine, 1 2-ditolylguanidine, 1 ,2-dicyclohexylguanidine, 1 ,2,3-tricyclohexylguanidine, guanidinetrichloroacetate, N,N'-dibenzylpiperazine, 4,4-dithiomorpholine, morpholinium trichloroacetate, 2-amino-benzothiazole, and 2-benzoylhydrazino-benzothiazole. Two or more of these basic substances can be used in combination.

In the present invention, it is preferred that the reactive substance to be contained in the core substance of the microcapsules is dissolved or dispersed in a water-insoluble organic solvent, then the resulting solution or dispersion is emulsified in water, and after that, the wall of microcapsules is formed by polymerization around emulsified droplets ofthe solution or dispersion. The organic solvent preferably has a boiling point of 1800C or higher (e.g., a phosphate, a phthalate, an ester of a carboxylic acid, afatty acid amide, an alkylated biphenyl, an alkylated terphenyl, a chlorinated paraffin, an alkylated naphthalene, a diarylethane, or the like) is used.Specific examples of these solvents include tricresyl phosphate, trioctyl phosphate, octyl diphenyl phosphate, tricyclohexyl phosphate, dibutyl phthalate, dioctyl phthalate, dilauryl phthalate, dicyclohexyl phthalate, butyl oleate, diethylene glycol dibenzoate, dioctyl sebacate, dibutyl sebacate, dioctyl adipate, trioctyl trimellitate, acetyl triethyl citrate, octyl maleate, dibutyl maleate, isopropylbiphenyl, isoamylbiphenyl, chlorinated paraffin, diisopropylnaphthalene, 1,1 '-ditolylethane, 2,4-ditertiarybutylamino phenol and N,N-dibutyl-2-butoxy-5-tert-octylaniline.

Of these, ester solvents such as dibutyl phthalate, tricresyl phosphate, diethyl phthalate, dibutyl maleate, and the like are specially preferred.

The microcapsules of the present invention are produced by emulsifying a core substance containing the reactive substance, and afterthat,forming thewall of a high molecularsubstance around the emulsified oil droplets. Reactantforforming the high molecular substance is added to the inside and/or outside ofthe oil droplets. The specific examples of the high molecular substance include polyurethane, poiyurea, polyamide, polyester, polycarbonate, a urea-formaldehyde resin, a melamine resin, polystyrene, a styrene-methacrylate copolymer, a styrene-acrylate copolymer, gelatin, polyvinyl pyrrolidone and polyvinyl alcohol.

Two or more kinds ofthese high molecular substances can be combined for use. The preferred high molecular substances are polyurethane, polyurea, polyamide, polyester and polycarbonate, and the most preferred high molecular weight substances are polyurethane and polyurea.

If the encapsulation method comprising polymerization of a reactant existing inside the oil droplets is used, the method for producing the wall of microcapsules of the invention has a great effect. That is, capsules having a uniform particle diameter and excellent keeping quality which are suitable for a recording material can be obtained in a shorttime.

Specific examples ofthe method and compounds which can be used in this method are mentioned in U.S.

Patents 3,726,804 and 3,796,669.

For example, if polyurethane is used asthewall material ofthe capsules, a polyvalentisocyanate and a second substance (e.g., a polyol) which reacts with the isocyanateto form the wall material of capsules are mixed in an oily liquid to be encapsulated, the oily liquid is emulsified and dispersed in water, and then the emulsion is heated to cause a reaction which results in formulation of a high molecularweight substance at the interface of oil droplets and water, thus forming the wall of microcapsules. In this process, a low-boiling point assistant solvent having strong dissolving power can be co-used in the oily liquid.

Polyisocyanates usable in this process and polyols or polyaminesto react with the polyisocyanate are disclosed in U.S. Patents 3,281,383,3,773,695, and 3,793,268, Japanese Patent Publication Nos. 40347/73 and 24159/74, and Japanese Patent Application (OPI) Nos. 80191/73 and 84086/73.

Further, a tin salt orthe like can be used in combination with these compounds in orderto accelerate the polyurethane forming reaction.

In particular, it is preferred to use a polyvalent isocyanate as the first substance to form the wall ofcapsules and a polyol asthesecond substance to form the wall of capsules, in respectofthe keeping quality of the heat-sensitive recording material using the capsules. Further, it is also possible to control the heattransfer coefficient of the reactive substance by varying the combination of both compounds.

Examples of the polyvalent isocyanate which is the first substance to form the walls ofthe capsule include diisocyanates such as m-phenylenediisocyanate, p-phenylenediisocyante, 2,6-tolylenediisocyanate, 2,4-tolyl enediisocyanate, naphthalene-1 nte, diphenyl metha diphenylmethane-4,4'-diisocyanate, 3,3'-dimethoxy-4,4'-biphenyl-diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, xylylene-1 ,4-diisocyanate, diphenyl propane-4,4'-diisocyante, tri methylenediisocyanate, hexamethylenediisocyanate, propylene-1,2-diisocyanate, butylene-1 ,2-diisocyanate, cyclohexylene-1 ,2-diisocyanate, cyclohexylene-1 ,4-diisocyanate;; triisocyanates such as 4,4',4" -tri phe nyl m eth a ne triisocyanate, toluene-2,4,6-triisocyanate; tetraisocyanates such as 4,4'-dimethyldiphenylmethane-2,2',5,5'-tetraisocyanate; and isocyanate prepolymers such as an adduct of hexamethylenediisocyanate with trimethylolpropane, an adduct oftolylenediisocyanate with trimethylolpropane, an adduct of xylylenediisocyanate with trimethylolpropane, and an adduct of tolylenediisocyanate with hexanetriol.

Examples of the polyol which is the second substance to form the wall of capsules include liphaticand aromatic polyhydric alcohols, hydroxy polyesters, and hydroxy polyalkylene ethers. Preferred examples of the polyol include polyhydroxy compounds which have a group represented by (a), (b), (c) or (d) as setforth below between two hydroxy groups and have a molecular weight of 5,000 or less.

(a) An aliphatic hydrocarbon group having from 2 to 8 carbon atoms;

Ar in group (b), (c), and (d) represents a substituted or unsubstituted aromatic group, and the aliphatic hydrocarbon group in (a) represents a group having -CnH2n- as the basic skeleton wherein the carbon atoms may contain substituents other than M.

Examples ofthe polyhydroxy compound having a group represented by (a) include ethylene glycol, 1 ,3-propanediol, 1 4-butanediol, 1 5-pentanediol, 1 6-hexanediol, 1 7-heptanediol, 1 ,8-octanediol, propylene glycol, 2,3-dihydroxybutane, 1 ,2-dihydroxybutane, 1 3-dihydroxybutane, 2,2-dimethyl-1 3-propanediol, 2,4-pentanediol, 2,5-hexanediol, 3-methyl-i ,5-pentanediol, 1 ,4-cyclohexanedimethanol, dihydroxycyclohexane, diethylene glycol, 1 2,6-trihydroxyhexane, phenyl ethylene glycol, 1,1,1 -trimethylolpropane, hexanetriol, pentaerythritol and glycerine.

Examples ofthe polyhydroxy compound having a group represented by (b) include a condensation product of an aromatic polyhyric alcohol such as 1 ,4-di(2-hydroxyethoxy)benzene, resorcinol dihydroxyethyl ether with an alkylene oxide.

Examples of the polyhydroxy compound having a group represented by (c) include p-xylylene glycol, m-xylylene glycol and a,a'-dihydroxy-p-diisopropylbenzene.

Examples ofthe polyhydroxy compound having a group represented by (d) include an adduct ofethylene oxide with 4,4'-dihydroxy-diphenyl methane, 2-(p,p'-dihydroxydiphenylmethyl)benzyl alcohol, or bisphenol A and an adduct of propylene oxide with bisphenol.

The polyhydroxy compound is preferably used in an amount of from 0.02 to 2 mols of its hydroxyl groups based on 1 mol of the isocyanate groups.

Awater soluble high molecularweight substance can be used to produce the microcapsules. The water soluble high molecularweightsubstance may be an anionic one, a nonionicone, oran amphoteric one. As the anionic water soluble high molecularweightsubstance, a natural one ora synthetic one can be used. For example, anionic high molecular substances having -COO- or -S03- group can be used. Specific examples of natural anionic high molecularweightsubstance include gum arabic and alginicacid. Specific examples of semi-synthetic anionic high molecularweight substances include carboxymethylcellulose, phthalic acid-modified gelatin, sulfated starch, sulfated cellulose and lignum sulfonic acid.Examples of synthetic anionic high molecular weight substance include maleic anhydride-containing copolymers including hydrolyzed ones, (meth)acrylic acid-containing polymers and copolymers and carboxy-modified polyvinyl alcohol.

Examples of nonionic high molecularweight substance include polyvinyl alcohol, hydroxyethyl cellulose and methyl cellulose.

Examples ofamphoteric high molecularweightsubstance include gelatin.

An aqueous solution of such a water soluble high molecular weight substance is preferably used in a concentration offrom 0.01 to 10 wt%. The particle diameter of microcapsules is preferably controlled to 20 ym or less. When the particle diameter exceeds 20 ym, in general, the printed image quality is apt to be impaired.

In particular, if heating with a thermal head is carried out from the side ofthe coated layer, it is preferred that the particle diameter of the microcapsules is 8 am or less so that pressure smudge is avoided.

The diazo compound and the coupling component are used as the main components in the heat-sensitive recording material of the present invention, and the basic substance is also used in the invention if required.

One of these components can be used as a microcapsule core substance, or two orthree of these components can be used as the core substance. If two components ofthese components are contained in the core substance, the two components may be housed in the same microcapsule or may be separately housed in different microcapsules. If three components ofthese components are contained in the core substance, the three components cannot be contained in the same microcapsule at the same time, however, various combinations of two components can be contained in the same microcapsule. Further, the three components may each be separately contained in different microcapsules. Components that are not contained in microcapsules are used in the heat-sensitive layer.

The arylsulfonamide compound ofthe present invention may be contained in the core substance of microcapsules or may exist outside the microcapsule.

The microcapsules can be produced from an emulsion containing 0.2wt% or more ofthe components that are to be transformed into microcapsules.

It is preferred that from 0.1 to 10 parts by weight of the coupling component and from 0.1 to 20 parts by weight of the basic substance, based on 1 part by weight of the diazo compound, are used in the recording layer of the heat-senstive recording material, whether each of the three components are contained outside of microcapsules. Further, it is preferred that the coating amount ofthe diazo compound is from 0.05 to 5.0 g/m2.

If the diazo compound, the coupling component, and the basic substance used in the present invention are not encapsulated, it is preferred that they are dispersed as solids together with a water soluble high molecular weight substance bythe useofa sand mill orthe like. As the preferred water soluble high molecularweight substance, those used in producing microcapsules can be employed. The solution of the water soluble high molecular weight substance used in this process has a concentration of from 2 to 30 wt%, and the diazo compound, the coupling compound, and the basic substance are used in the solution so thatthe concentration of each of them in the solution becomes from 5 to 40%. The preferred size of the thus dispersed particles is 1 0#m or less.

In orderto improve the heat coloring properties of the heat-sensitive recording material of the present invention, a hydroxy compound, a carbamicacid ester compound, an aromatic methoxy compound, oran organic sulfonamide compound can be added to the heat-sensitive recording material. It is considered that these compounds lower the melting point of the coupling component or the basic substance, or increase the heat transfer coefficient of the wall of microcapsules, thereby increasing the density ofthe colored image.

Specific examples ofthe hydroxy compound include phenol compounds such as p-t-butylphenol, p-t-octylphenol, p-a-cumylphenol, p-t-pentylphenol, m-xylenol, 2,5-dimethylphenol, 2,4,5-trimethylphenol, 3-methyl-4-isopropylphenol, p-benzylphenol, o-cyclohexylphenol, p-(diphenylmethyl)phenol, p-(a,a'-diphenylethyl)phenol, o-phenylphenol, ethyl p-hydroxybenzoate, propyl p-hydroxybenzoate, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate, p-methoxyphenol, p-butoxyphenol, p-heptyloxyphenol, p-benzyloxyphenol, dimethylvanillin 3-hydroxyphthalate, 1,1 -bis(4-hydroxyphenyl)dodecane, 1,1 -bis(4-hydroxyphenyl)-2-ethylhexane, 1,1 -bis(4-hydroxyphenyl)-1 -methylpentane, 2,2-bis(4-hydroxyphenyl)heptyl-vanillin, 2-t-butyl-4-methoxyphenol, 2,6-dimethoxyphenol, 2,2'-dihydroxy-4-methoxybenzophenone; and alcohol compounds such as 2,5-dimethyl-2,5-hexanediol, resorcinol di(2-hydroxyethyl)ether, resorcinol mono(2-hydroxyethyl)ether, salicyl alcohol, 1,4-di(hydroxyethoxy)benzene, p-xylylenediol, 1-phenyl-1,2-ethanediol,diphenyl methanol, 1,1-diphenyl ethanol, 2-methyl-2-phenyl-1 3-propanediol, 2,6-dihydroxyethyl-p-cresol benzyl ether, 2,6-dihydroxymethyl-p-cresol benzyl ether, 3-(o-methoxyphenoxy)-1 2-propanediol. Specific examples of the carbamic acid ester compounds include ethyl N-phenylcarbamate, benzyl N-phenylcarbamate, benzyl carbamate, butyl carbamate, isopropyl carbamate. Specific examples of the aromatic methoxy compounds include 2-methoxybenzoic acid, 3,5-dimethoxyphenyl acetic acid, 2-methoxynaphthalene, 1,3,5-trimethoxybenzene, p-dimethoxybenzene, p-benzyloxymethoxybenzene.

These compounds can be encapsulated together with the core substance of microcapsules, or can be added to a coating solution for a heat-sensitive recording material outside microcapsules. However, it is preferred to encapsulate these compounds together with the core substance of microcapsules. The amount of these compounds used is preferably from 0.01 to 10 parts by weight, more preferably from 0.1 to 5 parts by weight based on 1 part by weight of the coupling component, but it may be selected appropriately to control the coloring density to a desired level.

Afree radical generatorwhich is used in a photopolymerizable composition orthe like (a compound generating a free radical when irradiated with light) can be added to the heat-sensitive recording material of the present invention in orderto alleviate yellow stain on the uncolored part ofthe recording material after being fixed with light.Examples of the free radical generator include aromatic ketones (e.g., benzophenone, 4,4'-bis(dimethylamino)benzophenone, 4,4'-bis(diethylamino)benzophenone, 4-methoxy-4'-(dimethylamino)benzophenone, 4,4'-dimethoxybenzophenone, 4-dimethylaminobenzophenone, 4-methoxy-3,3'-dimethylbenzophenone, 1 -hydroxycyclohexylphenylketone, 4-dimethylaminoacetophenone, 2methyl1 - [ 4-(methylthio)phenylj-2-morpholinopropane-1 -acetophenone, and benzil), cyclic aromatic ketones (e.g., fluorenone, anthrone, xanthone, thioxanthone,2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, acridone, N-ethylacridone, and benzanthrone), quinones (e.g., benzoquinone, 2,3,5-trimethyl-6-bromobenzoquinone, 2,6-di-n-decylbenzoquinone, 1,4-naphthoquinone, anthraquinone, 2-chioroanthraquinone, 2-methylanthraquinone, 2-isopropoxy-1 ,4-naphthoquinone, 2-tert-butylanthraquinone, and phenanthraquinone), benzoins and benzoin ethers (e.g., benzoin methyl ether, benzoin ethyl ether, 2,2-dimethoxy-2-phenylacetophenone, and a-methylolbenzoin methyl ether), aromatic polycyclic hydrocarbons (such as naphthalene, anthrathene, phenanthrene, and pyrene), azo compounds (e.g., azobisisobutyronitrile, a-azo-1 -cyclohexanecarbonitrile, and azobisvaleronitrile), organic disulfides (e.g., thiuram disulfide), and acyloxim esters (e.g., benzyl (o-ethoxycarbonyl )-a-monooxim).

The preferred amount of the free radical generator added is from 0.01 to 5 parts by weight based on 1 part by weight ofthe diazonium compound, and the more preferred amount ofthefree radical generator isfrom 0.1 to 1 part by weight based on the same basis.

Use of the above-mentioned free radical generator together with the diazonium salt as the core substance of microcapsules enables the alleviation of yellow stain on the uncolored part ofthe heat-sensitive recording material after being fixed with light.

A polymerizable compound having an ethylenically unsaturated bond (hereinafter "vinyl monomer") can be used in the heat-sensitive recording material of the present invention in order to alleviate yellow stain on the uncolored part of the recording material after being fixed with light. "Vinyl monomer" refers to a compound containing at least one ethylenically unsaturated bond (such as a vinyl orvinylidene group) inthe chemical structure thereof which is in the form of monomer or prepolymer, that is, a dimer, a trimer, or other oligomers, and a mixture orcopolymerthereof. Examples ofthevinyl monomer include an unsaturated carboxylic acid and a saltthereof, an ester of an unsaturated carboxylic acid with an aliphatic polyhydric alcohol compound, and an amide of an unsaturated carboxylic acid with an aliphatic polyvalent amine compound.

The amount of the vinyl monomer used is preferably from 0.2 to 20 parts by weight, more preferably from 1 to 10 parts byweight, based on 1 part byweightofthe diazo compound.

The vinyl monomer is contained and used in the core substance of microcapsules together with thediazo compound, and an organic solvent used as a solvent (or a dispersing medium) for the core substance can be replaced partially or wholly by the vinyl monomer, but the amount ofthe vinyl monomer added need not be large enough to harden the core substance.

In the case where the diazo compound is contained as the core substance of the microcapsules in the heat-sensitive recording material of the present invention, a coupling reaction deactivator can be contained outside microcapsules in the recording layer of the heat-sensitive recording material. Thereby the coupling reaction deactivator reacts with the diazo compound existing in the aqueous phase and with the diazo compound within incomplete capsules (that is,the diazo compound which is not completely blocked by the wall of capsules) to prevent the diazo compound from undergoing a coupling reaction (coloring reaction) and to preventfogging ofthe recording material.

The coupling reaction deactivator is selected from substances which can reduce coloring of a solution of the diazo compound.The deactivator can be chosen by inspecting a change in colorofthe diazo compound solution in water or an organic solvent when thetest compound solution in water oran organic solvent is added to the solution of the diazo compound.

Specific examples ofthe coupling reaction deactivator include hydroquinone, sodium hydrosulfite, potassium nitrite, hypophosphorous acid, stanous chloride and formal in. Beside these, the deactivator can also be selected from the compounds mentioned in K.M. Sawnders, TheAromatic Diazo-Compoundsand Their TechnicalApplications pp. 105-306 (London 1949).

Preferably the coupling reaction deactivator is hardly colored and has few side effects by itself and, more preferably, it is soluble in water.

The coupling reaction deactivator is used in such an amount as not to obstruct the heat coupling reaction of the diazo compound. The amountofthe deactivator used is preferably from 0.01 to 2 mols and, more preferably, from 0.01 tol mol,permolofthediazocompound.

After the coupling reaction deactivator is dissolved in a solvent, the solution obtained is added to the dispersion ofthe microcapsules containing the diazo compound, the dispersion ofthe coupling component and/orthe basic substance, or the mixture of these dispersions. It is preferred to use the deactivator in the form of an aqueous solution.

In orderto prevent the heat-sensitive recording material ofthe present invention from sticking to a thermal head orto improve the handwriting properties ofthe recording material, pigments such as silica, barium sulfate, titanium oxide, aluminium sulfate, zinc oxide, or calcium carbonate, or a fine powder of styrene beads or urea-melamine resin can be used in the recording material. Similarly, metal soaps can be used to prevent the recording material from sticking to a thermal head. The preferred amount of these substances used is from 0.2 to 7 g/m2.

A heatfusible substance can be used in the heat-sensitive recording material of the present invention to improve the heat recorded density of the recording material. The heat fusible substance is a substance having a melting point offrom 50 to 150 C which is solid ata normal temperature and is fused by heating with a thermal head. It also can dissolve the diazo compound, coupling component, or basic substance in the fused state. The heatfusible substance is used as a dispersion having a particle diameter of from 0.1 to 10 microns and in a solid amount of from 0.2 to 7 g/m2.Specific examples of the heat fusible substance include a fatty acid amide, an N-substituted fatty acid amide, a ketone compound, a urea compound and an ester.

An appropriate binder can be used in the heat-sensitive recording material of the present invention for coating the recording layer.

As the binder, an emulsion of polyvinyl alcohol, methylcellulose, carboxymethylcellulose, hydroxypropylcellulose, gum arabic, gelatin, polyvinyl pyrrolidone, casein, a styrene-butadiene latex, an acrylonitrilebutadiene latex, polyvinyl acetate, polyacrylate, or an ethylene-vinyl acetate copolymer can be used. The solid amount of the emulsion used is preferably from 0.5 to 5 g/m2.

In addition to the above-mentioned substances, an acid stabilizer such as citric acid, tartaric acid, oxalic acid, boric acid, phosphoric acid, or picric acid can be added to the heat-sensitive recording material ofthe present invention.

In a process for producing the heat-sensitive recording material ofthe present invention, a coating solution containing the main components (that is, the diazo compound and the coupling component),the basic substance, and other additives is prepared and, then, the coating solution is coated on a support such as a paper, a synthetic resin film, orthe like by a coating method such as bar coating, blade coating, air knife coating, dip coating, or the like, and dried to dispose a heat-sensitive layer (recording layer) in a coated amount of from 2.5 to 25 g/m2 as the solid content.

In another process for producing the heat-sensitive recording material of the present invention,the coupling component, the basic substance, and other additives are added as the core substance of microcapsules, solid-dispersed, or dissolved in water. After that, the solutions and/or dispersions obtained are mixed to prepare a coating solution and the coating solution is coated on a support and dried to provide a precoated layer having a solid coated amount of from 2 to 10 g/m2. Next, the diazo compound and other additives are added as the core substance of microcapsules, solid-dispersed, or dissolved in water.After that, the thus obtained solutions and/or dispersions are mixed to prepare a coating solution and the coating solution is coated on the precoated layer and dried to provide a coated layer having a solid coated amount of from 1 to 15 g/m2, thus producing a lamination type heat-sensitive recording material. In the lamination type heat-sensitive recording material, the order of lamination may be reversed, and as the coating method, successive or simultaneous coating can be carried out. The lamination type heat-sensitive recording material is particularly excellent in keeping quality for an especially long period oftime.

After an intermediate layer as mentioned in Japanese Patent Application (OPI) No. 54980/86 is provided on a substrate, a heat-sensitive layer (recording layer) can be coated on the intermediate layer.

As the support, neutral paper sized with a neutral sizing agent such as alkyl ketenedimerorthe like and having a heat extract pH offrom 6 to 9 (as mentioned in Japanese Patent Application (OPI) No. 14281/80) is advantageous in view of the keeping quality of the heat-sensitive recording material of the present invention.

In orderto prevent the permeation of the coating solution into the support paper and to improve the contact of a recording thermal head with the heat-sensitive recording layer, it is advantageous to use paper meeting to the requirementoftheformula, Stuckigtsizing degree (meter basis weight)2 and having a Beck smoothness of 90 seconds or more, as mentioned in U.S. Patent 4,416,939. Stuckigtsizing degree conforms to JIS 8122 and is disclosed in more detail in U.S. Patent4,416,939.

Further, paper having an optical surface roughness of 8 microns or less and thickness of from 40to75 microns which is mentioned in Japanese Patent Application (OPI) No. 136492/83; paper having a density of 0.9 g/cm3 or less and an optical contact ratio of 15% or more which is mentioned in Japanese Patent Application (OPI) No.69091/83; paper produced from pulp beating-treated to Canadian standard freeness (JIS P8121) of 400ce or more and furthertreated so asto prevent permeation of the coating solution as mentioned in Japanese Patent Application (OPI) No.69091/83 and British Patent Application No.2,1 12,155A; base paper produced by a Yankee paper machine wherein the glossy surface thereof is provided a heat-sensitive recording layer, so asto improve the coloring density and resolving power ofthe heat-sensitive recording material as mentioned in Japanese Patent Application (OPI) No.65695/83; and paper corona discharge4reated the surface thereof so as to improve the coating adaptability thereof as mentioned in Japanese Patent Application (OPI) No.35985/84 are usable in the present invention as the support ofthe heat-sensitive recording material with a good result. Besides the above-mentioned paper, any support used in the usual heat-sensitive recording material is usable as a support of the present invention.

The heat-sensitive recording material ofthe present invention can be used as a recording paperfor facsimiles and printers of computers which requires high-speed recording, and also, after printing, it can be fixed by exposing with light to decompose the unreacted diazo compound. It can also be used as a heat development type copying paper.

Examples ofthe present invention will be described hereinafter but the invention should not be construed as being limited to these examples. All parts, raitos, etc. referred in the Examples represent those byweight.

Example 1 3.45 parts ofthe diazo compound set forth below and 18 parts of an adduct of xylylenediisocyanate with trimethylolpropane (in a mol ratio of 3:1)were added to a mixed solvent consisting of 24 parts oftricresyl phosphate and 5 parts of ethyl acetate to dissolve them in the solvent. This diazo compound solution was mixed with an aqueous solution prepared by dissolving 5.2 parts of polyvinyl alcohol in 58 parts of water, and was emulsified and dispersed at 20"C to obtain an emulsion having an average oil droplet diameter of 2.5 m.

100 parts of water was added to the resulting emulsion, the emulsion with water added was heated to 60 C under stirring, and after 2 hours under stirring, a dispersion of capsules having the diazo compound contained in the core substance was obtained.

Diazo compound

Next, 10 parts of 2-hydroxy-3-naphthoic acid anilide and 10 parts oftriphenylguanidine were added to 100 parts of 5% aqueous solution of polyvinyl alcohol and the mixture was dispersed with a sand mill forabout24 hours to obtain a dispersion of the coupling componentandtriphenylguanidine having an average particle diameter of 3 #m.

Further, 20 parts of p-ethylbenzene sulfonamide was added to a mixture of 100 parts of a 4% aqueous solution of polyvinyl alcohol and 100 parts of water and they were dispersed by using a paint shakerfor2 hours to obtain a dispersion of p-ethylbenzene sulfonamide having an average particle diameter of3 jim.

24 parts of the dispersion of the coupling component and triphenylguanidine and 28 parts of the dispersion of p-ethylbenzene sulfonamide were added to 50 parts ofthe dispersion of the encapsulated diazo compound to produce a coating solution. The coating solution was coated on a high quality paper having an even surface (50 g/m2) with a coating barto a dry coating weight of 10 g/m2) and dried at 250C for 30 minutes to produce a heat-sensitive recording material.

Example2 A heat-sensitive recording material was produced by the same process as in Example 1 exceptthat p-methoxybenzene sulfonamide was used instead of p-ethylbenzene sulfonamide which was used in Example 1.

Example 3 A heat-sensitive recording material was produced by the same process as in Example 1 exceptthat p-(2-chloroethoxy)benzene sulfonamide was used instead of p-ethylbenzene sulfonamide which was used in Example 1.

Example 4 A heat-sensitive recording material was produced by the same process as in Example 1 exceptthat p-octylbenzene sulfonamide was used instead of p-ethylbenzene sulfonamide which was used in Example 1.

Comparative Example 1 A heat-sensitive recording material was produced by the same process as in Example 1 exceptthat p-toluene sulfonamide was used instead of p-ethylbenzene sulfonamide which was used in Example 1.

Heat recording was carried out with the thus obtained heat-sensitive recording materials of Examples 1 to 4 and Comparative Example 1 bythe use of a G lil mode thermal printer(HlFACS 700: a productof Hitachi, Ltd.), and subsequently the entire surface of the materials was exposed by using Recopy Superdry 100 (a product of Ricoh Company Ltd.) to fix the image. The resulting recorded images were measured for blue density by the use of a Macbeth reflection densitometer. Similarly, the yellow density in the uncolored part of the recorded material was measured. Subsequently, heat recording was carried out again on the unloaded fixed parts and as a result, an image was not recorded on any place of the fixed parts, so that it was confirmed that complete fixing had been achieved.

Next, in orderto evaluate the keeping quality of the heat-sensitive recording materials, the texture density (fog) ofthe heat-sensitive recording material and the fog of the recording material after being preserved in a dark place for 24 hours underthe condition of relative humidity (RH) of 90% for a forced deterioration test were measured by a Macbeth reflection meter and the change in the fog of the recording material was determined.

Next, in orderto investigate the lowering in the optical density of colored portions which occured long-term preservation of heat-sensitive recording material after heat recording, the recorded image of the heat-sensitive recording material was preserved in a dark place at 60'for 16 hours for a forced deterioration test and the degree of lowering in the density of the recorded image was evaluated.

The results are shown in Table 1 below.

TABLE 1 Heat- Yellow density in Lowering in recorded sensitive Yellow density texturepartafter image densityafter recording in uncolored forced deterioration forced deterioration material Image density part test test Example 1 1.23 0.09 0.10 A Example 2 1.23 0.09 0.10 A Example3 1.17 0.09 0.10 A Example4 1.15 0.09 0.10 B Comparative 1.21 0.09 0.10 C example 1 Evaluation of the lowering in recorded image density after forced deterioration test: A Lowering in recorded image density afterthe forced deterioration test was less than 5% based on the initial recorded image density.

B Lowering in recorded image density was from 5 to 10% based on the initial recorded density.

C Lowering in recorded density was from 10 to 20% based on the initial recorded image density.

From the results shown in Table 1, it can be seen that the heat-sensitive recording materials according to the present invention are excellent in both keeping quality and heat coloring properties, and that the density of the recorded image formed thereon hardly lowers upon preservation for a long period of time after heat recording is carried out.

Claims (18)

1. A heat-sensitive recording material comprising a support having provided thereon a recording layer which comprises a diazo compound, a coupling component and at leastone arylsulfonamidecompound represented bythefollowing general formula (I):

wherein R1 represents a substituted or unsubstituted alkyl group having from 2 to 12 carbon atoms, an alkoxy group having from 1 to 12 carbon atoms oran aryloxy group having from 6to 9carbon atoms, or a chlorineor fluorine atom, and R2 represents a substituted or unsubstituted alkyl group having from 1 to 12 carbon atoms, an alkoxygroup having from 1 to 12 carbon atoms oran aryloxy group having from 6to 9carbon atoms, ora hydrogen atom, at least one of said diazo compound and said coupling component being contained in microcapsules.

2. A material as claimed in claim 1 wherein R1 represents a substituted or unsubstituted alkyl group having from 2 to 4 carbon atoms or alkoxy group having from 1 to 5 carbon atoms.

3. A material as claimed in claim 1, wherein said arylsulfonamide compound is selected from ethylbenzenesulfonamide, ethyltoluenesulfonamide, chloroethoxybenzenesulfonamide, isopropylbenzenesulfonamide, methoxybenzenesulfonamide, ethoxytoluenesulfonamide, t-amylbenzenesulfonamide, diethylbenzenesulfonamide, allylbenzenesulfonamide, ethoxybenzenesulfonamide and cyclohexylbenzenesulfonamide.

4. A material as claimed in claim 3, wherein said arylsulfonamide compound is selected from the group consisting of p-ethylbenzenesulfonamide, p-methoxybenzenesulfonamide, p-ethoxybenzenesulfonamide, p-isopropylbenzenesulfonamide and m-ethylbenzenesulfonamide.

5. A material as claimed in any preceding claim, wherein said diazo compound is a diazonium salt represented bythefollowing general formula (ill): ArN2+X- (II) wherein Ar represents an aromatic group, Na+ represents a diazonium group, and X- represents an acid anion.

6. A material as claimed in claim 5, wherein Ar in formula (II) represents a group represented bythe following general formula (III):

wherein Y represents a hydrogen atom, a substituted amino group, a substituted or unsubstituted alkoxy group, aryloxy group, arylthio group, alkylthio group or acylamino group; and R represents a hydrogen atom, a substituted or unsubstituted alkyl group, alkoxy group, aryloxy group or arylamino group, ora halogen atom.

7. A material as claimed in claim 6, wherein Y represents a substituted amino group selected from monoalkylamino groups, dialkylamino groups, arylamino groups, morpholino groups, piperidino groups and pyrrolidino groups.

8. A material asclaimed in claim 5,6 or7,wherein X in formula (II) represents an acid anion containing a perfluoroalkyl group, a perfluornalkenyl group or PF6-.

9. Amaterial as claimed in any preceding claim,wherein said coupling component is selected from resorcinol, phloroglucinol, sodium 2,3-dihydroxynaphthalene-6-sulfonate, -hydroxy-2-naphthoic acid morpholinopropylamide, 1 ,5-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,3-dihydroxy-6-sulfanilyl naphthalene, 2-hydroxy-3-naphthoic acid morpholinopropylamide, 2-hydroxy-3-naphthoic acid anilide, 2-hydroxy-3-naphthoic acid-2'-methylanilide, 2-hydroxy-3-naphthoic acid ethanolamide, 2-hydroxy-3-naphthoic acid acetylamide, 2-hydroxy-3-naphthoic acid-N-dodecyloxypropylamide, 2-hydroxy-3-naphthoic acid tetradecylamide, acetanilide, acetoacetanilide, benzoylacetanilide, 1-phenyl-3-methyl-5-pyrazolone 1-(2',4',6'-trichlorophenyl)-3-benzamide-5-pyrazolone, 1-(2',4',6'-trichlorophenyl)-3-anilino-5-pyrazolone and 1 -phenyl-3-phenylacetamide-5-pyrazolone.

10. A material as claimed in any preceding claim, wherein said coupling component comprises two or more compounds in combination.

11. A material as claimed in any preceding claim,wherein said heat-sensitive recording material further comprises a basic substance.

12. A material as claimed in any preceding claim,wherein said arylsulfonamide compound is used in an amountoffrom 1 to 5 g/m2.

13. A material as claimed in any preceding claim, wherein said diazo compound is used in an amountof from 0.1 to 2 g/m2.

14. A material as claimed in any preceding claim, wherein said coupling component is used in an amount offrom 0.2 to 8 g/m2.

15. A material as claimed in claim 1 and substantially as herein described.

16. A heat-sensitive recording material substantially as herein described with reference to any one ofthe foregoing Examples 1 to 4.

17. A sheet as claimed in any preceding claim and bearing a record formed by local exposure to heat.

18. The features as herein disclosed, ortheir equivalents, in any novel patentable selection.