GB2183356A - Heat sensitive diazo recording material - Google Patents

Abstract

Heat sensitive recording material is of the type containing in a sensitive layer a diazonium salt and a coupler (e.g. resorcinol) and optionally a basic substance which react to form a dye; the layer also contains a hindered phenol of which five general formulae are shown and numerous examples. The phenols may have a variety of substituents and the phenolic ring can be fused or linked to one or more other rings. Preferably one of the color-forming components is enclosed in microcapsules which rupture or become permeable when heated; the making of polyurethane capsules is described. Capsule size is 20 microns or less. The phenol can be inside or outside capsules. Amount by weight of the phenol, per part of the diazonium salt, is 0.01-5 parts in microcapsules and 0.05-20 parts as separate particles. Other additives can be present to improve heat coloration of lower melting point in the layer. The hindered phenol improves the storage life before recording with a facsimile or computer printer and it reduces background yellow fog after recording. <IMAGE>

Description

SPECIFICATION Heat sensitive diazo recording materials The present invention relates to a heat sensitive recording material, especially to a diazo type heat sensitive recording material.

Hitherto the most used type of heat-sensitive recording material has been of the leuco coloring type. How ever, ifthistype of material after recording is handled roughly, exposed to heatorstained with solvents, undesired coloring occurs, which spoils the recorded images. In orderto solve such a problem, a heatsensitive recording material of a diazo coloring type has been proposed recently (e.g., Japanese PatentApplication (OPI) No. 123086182 (the term "OPI" as used herein means an unexamined published application), orGazo Denshi Gakkai Shi, 11, p.290,Japan(1982)).

In this case, thermal recording is carried out using a recording material comprising a diazo compound, a coupling component and a basic component (including also a substance which changes to become basic when it is heated) which is then irradiated with light to decompose remaining unreacted diazo compound in orderto stop the coloring. According to this method, it is possiblewith certainty to stop coloring (hereinafter this is referred to as "fixing") ofthe parts to which no recording is needed. However, this recording material has a disadvantage in that precoupling gradually proceeds during its storage so asto cause undesirable coloring (fogging).To solve such a problem, one ofthe coloring components is made to exist in a form of separated particles (solid dispersion) sothatthecomponents are prevented from contacting each otherand thereby the pre-cou pl i ng is prevented. Even in this case, storage life before use of the recording material is not satisfactory and its thermal coloring ability is lowered.

Another known method to solve the above-described problem isto prepared a diazo compound and coupling components in separate layers to minimize the contact between the components (e.g., as described in the afore-mentioned Japanese Patent Application (OPI) No. 123086/82). According to this method, the storage life is greatly improved while the thermal coloring is much reduced. Thus, the material is not practical since it cannot respond to a high-speed recording of which the pulse width is narrow.

In orderto attain satisfactory storage life and thermal coloring ability, it is proposed to enclose eitherthe coupling component or a basic substance in capsules of a non-polarwaxy substance (Japanese PatentApplication (OPI) No. 142636/82) or of a hydrophobic high molecular substance (Japanese PatentApplication (OPI) No. 192944/82) whereby the encapsulated component is isolated from the other components.However, this encapsulating method is different from the usual one wherein a core substance is covered with a kind of shell, because in the method, wax or a high polymer substance is dissolved in a solvent and a coloring component is dissolved or dispersed into the resulting solution forencapsulation. Therefore,thecoloring component does not become a core of a capsule but uniformly mixes with the encapsulating substance.

While the material thus prepared is being preserved, pre-coupling gradually proceeds around the wall ofthe capsules, which results in spoiling the material's preservability. Moreover, since a coloring reaction will not start unless the wall ofthe capsules is heat-fused,thethermal coloring ability inevitably lowers. Also, there is a manufacturing problem that solventwhich is used for dissolving wax or a macromolecule has to be removed after forming capsules.

As a method for solving the above problems, we have already proposed a heat sensitive recording material which has an improved storage life (Japanese Patent Application (OPI) No.190886/84). In this method, at least one component which relates to a coloring reaction is enclosed as a core substance and awall isformed around the core by a polymerization reaction to form a microcapsule.

The above-described heat sensitive recording material prepared by the microencapsulating method still has the drawbacks that the recorded image after fixing with light is notfastenough against light and heatand that unrecorded parts become more yellowish. Therefore, there has been a need forfurther improvement.

The first object ofthe present invention is to provide a heat sensitive recording material which makes it possible to properly fix the recorded image and to obtain highly white unrecorded parts.

The second object is to provide a heat sensitive recording material, the thermally colored image recorded onto said material having a favorable fastness against light and heat after its fixing.

The third object is to provide a heat sensitive recording material which has excellent storage life image quality and image preservability.

The fourth object of the invention is to provide a heat sensitive recording material which is easily produced.

The above objects of the present invention have been accomplished bya heat sensitive recording material which comprises on a support heat sensitive layer containing a diazonium salt and a coupler, wherein said heat sensitive layer includes at least one hindered phenol, which may carry various substituents.

The heat sensitive recording material of the present invention makes it possible to obtain a high image density, and at the same time, its storage life before use and image fastness after recording are excellent. The material is especially effective for preserving recorded imagesfora long period oftimesincethecoloring density of the ground afterfixing with light is low.

The storage life and recorded image fastness can be further improved by microencapsulating at least one ofthe compounds participating in coloring.

The heat sensitive recording material ofthis invention can be used as printing paper in a facsimile oran electronic computerwhich needs a high speed recording. When thermal printing is done, the print can be fixed by being exposed to the light to let the unreacted color former decompose. Moreover, the material can be used as copying paper of a thermal development type.

The hindered phenols and their derivatives used in this invention function to stabilize the azo dye image formed as well as to preventthe ground from yellowing. Preferred examples of these compounds are represented by the formulae (I) - (V) below: Formula (I)

Formula (II)

In the above formulae, R1, R2 and R3 can be the same ordifferentfrom each otherand represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group or a halogen atom. Among these substituents, an alkyl group, an aryl group and an alkoxygroup may have further substituents.

arid alkylene group or an arylene group, of which the latter two groups may have furthersubstituents.

Examples of the compounds represented by the formula (I) are 2,6-di-tert-butyl-p-cresol, 2,6-di-tert- butylphenol, 2,4-dimethyl-tert-butylphenol, and 3-tert-butyl-4-hydroxy-anisole (" List A" ).

Examples of the compounds represented by theformula (Il) are 2,2'-methylene-bis-(4-methyl-6-tert- butylphenol), 4,4'-butylidene-bis-(3-methyl-6-tert-butylphenol), 4,4'-methylene-bis.(2,6-di-tert.butylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)buta ne, n-octadecyl-3-(3',5'-di-tert-butyl-4'hydroxyphenyl)propionate, pentaerythrityl-tetrakis, (3,5-di-tert-4-hydroxyphenyl)propionate, bis-(2-(2hydroxy-5-methyl-3-tert-butyl benzyl )-4-methyl-6-tert-butylphenyl )-terephthalate, 4,4'-thiobis(3-methyl-6- tert-butylphenol), 4,4-thiobis(2-methyl-6-tert-butylphenol). ("List B").

Formula (III)

In the above formula, Rand R' can be the same or different from each other and each represents a hydrogen atom or an alkyl group, R3 1' R32, R#, and R34can bethesame ordifferentfrom each other and each represents a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, an alkylthio group, an acylamino group, a hydroxyl group ora halogen atom. At least one of OR and OR' may be bonded with any of R31 - R34at their ortho-position to form a 5 or 6 membered ring and at least one pair out of R31 - R34, which are in an ortho-position each other, may be bonded to form a 5 or 6 mom bored ring.

Preferred features of the compound represented by the formula (III) are as follows: R and R' are the same or different from each other and each represents a straight chain, a branched chain or a cyclic alkyl group having 1 to 20 carbon atoms (e.g., methyl, ethyl, propyl, n-butyl, i-butyl, n-octyl, n-dodecyl, n-hexadecyl and cyclohexyl groups, etc.), R31, R32, R33 and R34 can be the same or different from each other and each represents a hydrogen atom, a straight chain, a branched chain ora cyclic alkyl group having 1 to 20 carbon atoms (e.g., methyl, ethyl, t-butyl, t-hexyl, t-octyl, sec-dodecyl, n-hexadecyl and cyclohexyl groups, etc.), an aryl group having 6 to 20 carbon atoms (e.g., phenyl and naphthyl groups, etc.), an alkoxy group having 1 to 20 carbon atoms (e.g., methoxy, ethoxy, n-butoxy, i-butoxy, n-octyloxy and n-hexadecyloxy groups, etc.), an alkylthio group having 1 to 20 carbon atoms (e.g., methyl-thio, n-butylthio and n-octylthio groups, etc.), and acylamino group having 1 to 20 carbon atoms (e.g., acetylamino and propionylamino groups, etc.), a hydroxyl group, and a halogen atom (e.g., chlorine or bromine atom).

At least one of OR and OR' may be bonded with one of R3, - R34 which are in an ortho-position to each other to form a 5 o r 6 membered ring (e.g., a chroman, spirochroman and cumarane ring.Also, at least one pairout of R31 - R34, which are in an ortho position to each other, may be bonded to form a or 6 membered ring (e.g., aliphatic, hetero, aromatic and spiro rings, etc.).

Among R, R',R31, R32, R33 and R34 those which include an alkyl group or an aryl group can befurtherdispla- cod by substituents. Desirable substituents are alkyl, aryl, alkoxy, aryloxy, alkylthio, arylthio, acyl, acylamino, hydroxyl, cyano, alkoxycarbonyl, carbamoyl, sulfamoyl, acyloxy and nitro groups, and a halogen atom.

Also, among the compounds represented by the formula (Ill), those of which OR' is at an ortho orpara position in relation to OR are preferred; and those represented by the following formulae (Illa), (Illb),(lllc), (lIld) and (Ille) are most preferable.

Formula (Illa)

Formula (glib)

Formula (IIIc)

Formula (I I Id)

Formula (Ille)

R, R', R31, R33 and R34 in the compounds represented bythe formulae (Illa) - (Ille) are defined as forthose in the formula (III). R3#, R36, R37, R38, R39 and R40 can be the same or different from each other and each represents a hydrogen atom, an alkyl group (a straight chain, a branched chain ora cyclic alkyl group having 1 to 20 carbon atoms, e.g., methyl, ethyl, n-butyl, n-octyl and cyclohexyl groups, etc.), an aryl group (an aryl group having 6 to 20 carbon atoms, e.g., phenyl and naphtyl groups, etc.), an alkoxy group (an alkoxy group having 1 to 20 carbon atoms, e.g., methoxy, n-butoxy and n-octyloxy group, etc.), a heterocyclic group (e.g., a morpholinyl group), an alkyl-amino group (an alkylamino group having 1 to 20 carbon atoms, e.g., die- thylamino, dibutylamino and n-octylamino groups, etc.), and an alkoxycarbonyl group (an alkoxycarbonyl group having 1 to 20 carbon atoms; e.g., othoxycarbonyl and n-hexyloxy-carbonyl groups).

In the practice of the present invention, the above compounds can be used singly or as a combination of two or more, and also can be used with other known anti-fading agents. Examples of the known anti-fading agents are hydroquinones, phenols, chromanols, cumaranes, hindered amines and complexes. They are, for example, described in specifications ofJapanese Patent Applications (OPI) Nos. 83162/84,24141/83 and 152225/77, U.S. Patents Nos. 3,698,909 and 4,268,593 and British Patent Nos. 2,069,162 and 2,027,731, etc.

The compounds used in the present invention and represented by the formula (III) can be produced easily according to a method described in U.S. Patent Nos. 4,360,589 and 4,273,864, Japanese Patent Applications (OPI) Nos. 50244/80,20327/78, 77526/78 and 10539/84 and Japanese Patent Publication No.37856/82, cor responding to EP001 1051. Japanese PatentApplication No.50244/80 corrrospondsto U.S. Patent4266060.

Detailed examples of the compounds represented by the formula (III) are shown below.

Formula (IV)

In the above formula, R41 and R45 each represents a bydrogen atom, an alkyl group or a heterocyclic group.

R42, R43 and R44 may be the same or different from each other and each represents a hydrogen atom, any of alkyl, aryl, alkoxy, aryloxy, alkylthio, arylthio, acylamino, diacylamino, sulfonamide, alkylamino, alkoxycarbonyl and acyloxy groups or a halogen atom. However R41 and R45 can not be both hydrogen atoms at the same time.

The compounds represented by the formula (lV) are explained below in further details.

In the formula (IV), R41 and R45 each represents a hydrogen atom, an alkyl group (preferably an alkyl group having not more than 20 carbon atoms, e.g., a straight or branched chain alkyl group, aralkyl group, alkenyl group, cycloalkyl group or cycloalkenyl group; for example, methyl, ethyl, i-propyl, t-butyl, t-octyl, n-octyl, t-hexadecyl, benzyl, aryl, cyclopentyl and cyclohexenyl groups, etc.), an aryl group (preferably an aryl group having not more than 20 carbon atoms, e.g., phenyl,p-mothylphonyl,p-mothoxyphonyl, p- octanamidephenyl, o-chlorophenyl and a-naphthyl groups, etc.), an alkoxy group (preferably an alkoxy group having not more than 20 carbon atoms, e.g., methoxy, t-butoxy, cyclohexyloxy, n-dodecyloxy, n- octadocyloxy, benzyloxy and aryloxy groups, etc.), an aryloxy group (preferably an aryloxy group having not more than 20 carbon atoms, e.g., phenoxy,p-methyl-phenoxy,p-methoxyphenoxy, m-chlorophenoxyand #-naphthoxy groups, etc.), an alkylthio group (preferably an alkylthio group having not more than 20 carbon atoms, e.g., methylthio, i-butylthio, n-hexylthio, cyclohexylthio and n-octadecylthio groups, etc.). an arylthio group (preferably an arylthio group having not more than 20 carbon atom, e.g., phenylthio,pmethylphenylthio, o-carboxyphenoxy, m-methylphenylthio, o-methoxycarbonylphenylthio and mnitrophenylthio groups, etc.), an acyl amino group (preferably an acylamino group having not more than 20 carbon atoms,e.g., acetylamino, benzoylamino, and caproamino groups, etc.), a diacylamino group (preferably a diacylamino group having not more than 30 carbon atoms, e.g., succinic acidimide and 3-hydantoinyl groups, etc.), a sulfonamide group (preferably a sulfonamide group having not more than 20 carbon atoms, e.g., methanesulfonamide and benzenesulfonamide groups etc.), an alkylamino group (preferably an alkylamino group having not more than 30 carbon atoms, e.g., ethylamino, t-butylamino, dioctylamino and noctadecylamino groups, etc.), an acyl group (preferably an acyl group having not more than 20 carbon atoms, e.g., acotyl, capryl and p-methoxybenzoyl groups, etc.), an alkoxycarbonyl group (preferably an alkoxycar- bonyl group having not more than 20 carbon atoms, e.g., methoxycarbonyl, t-butoxycarbonyl and n octadecyloxycarbonyl groups, etc.), an acyloxy group (preferably an acyloxy group having not more than 20 carbon atoms, e.g., acetoxy, caproxy, lauroxyand benzoyloxy groups, etc.), ora halogen atom (e.g., chlorine or bromine atoms). R3 and R4 are preferred to be both hydrogen atoms at the same time.

Among the above-mentioned groups, those containing an alkyl oran aryl partmaybefurtherdisplaced by substituonts. Examples of such substituents are as partly described in the above definition oftho formula (IV) and include alkyl, cycloalkyl, alkenyl, aryl, benzyl, nitro, cyano, hydroxyl, alkyloxy, cycloalkyloxy, alkenyloxy, aryloxy, benzyloxy, alkylthio, arylthio, amino alkylamino, acylamino, sulfonamide, alkoxycarbonyl, silyl, acyl, acyloxy, sulfamoyl and sulfonyl groups, a halogen atom etc.

Among the compounds represented by the formula (IV), those represented by the following formula (IVa) arepreferablefortheireffectsinthepresentinvention.

Formula (IVa)

In the above formula, R46 and R47 each represents a hydrogen atom or an alkyl group, but they cannot be both hydrogen atoms at the same time.

Representative examples ofthe compounds represented by the formula (lV) are shown below.

The compounds represented bytheformula (IV) can be produced according to the method described in U.S. Patent No.4,264,720.

In the practice of the invention, they can be used singly or as a combination oftwo or more, and also together with the afore-mentioned known anti-fading agents.

Formula (V)

In the formula, R, is a substituted or unsubstituted 4-piperidyl group, preferably representing

In the formula, R51 is a substituted or unsubstituted alkyl group (e.g. methyl, propyl, methoxyethyl, hydroxyethyl etc.), a substituted or unsubstituted alkenyl group (e.g. vinyl, aryl etc.), a substituted or unsubstituted alkinyl group (e.g. ethynyl, propagyl etc.), a substituted or unsubstituted aralkyl group (e.g. benzyl, pmethoxybenzyl, phonethyl etc.) ora substituted or unsubstituted acyl group (e.g. acetyl, chloroacotyl,acry- loil, methacryloil, crotonoil etc.).

R52 is a hydrogen atom or or one or more alkyl group (e.g. methyl, ethyl, chloromethyl etc.) which is substituted on a piperidine ring. Said alkyl groups may be same or different from each other and may be further displaced by substituents.

R53 is a hydrogen atom or one or more alkyl group (e.g. methyl, isopropyl, t-butyl, t-amyl, chloromethyl etc.) which is substituted on a benzene ring. Said alkyl groups may be further displaced by substituents.

Y is a hydrogen atom or a substituted or unsubstituted alkyl group (e.g. butyl, dodecyl, ss- methoxycarbonyl,

wherein m is 1 or 2 and m+p=2.

Among the compounds represented by the formula (V), those represented by the following formula (Va) give better effects in the invention.

In the above formula, R5X, Y, m and p are the same as those in the formula (V).

Representative examples of the compounds represented by the formula (V) are shown below.

The compounds represented by the formula (V) are known ones described in, for example, German Patents (open to public inspection) Nos. 2,456,364,2,647,452, 2,654,058 & 2,656,769 and Japanese Patent Publication No.20617/82; and they can be produced by the methods explained in these patents and patent publication.

In the practice of the invention, the compounds can be used singly or as a combination oftwo or more, and also together with other known anti4ading agents.

Known anti-fading agents are hydroquinones, phenols, chromanols, cumaranes, hindered amines, complexes, etc, They are described in, for example, Japanese Patent Applications (OPI) Nos. 83162/84,24141/83 & 152225/77, U.S. Patents Nos. 3,698,909 & 4,268,593, British Patents Nos. 2,069,162(A) & 2,027,731, etc.

The hindered phenol compounds can be added to the form of fine particles. When diazonium salt ortho coupler is contained in microcapsules, they can be added either into the capsules orto both inside and outside of the capsules. Preferred amount of the compounds added in the form of fine particles is 0.05 - 20 weight parts, especially 0.2 - 5 weight parts, per 1 weight part of diazonium salt.

Diazo compounds are (as is well known) diazonium salts which can be represented by the general formula ArN2 X-.Whiletheyform X-. While they form color by undergoing a coupling reaction with a coupling component, they decompose by absorbing light In the formula, Ar represents an aromatic moiety N2+ represents a diazonium group and X- represents an acid anion. Any of these compounds can be suitably chosen for the use in the present invention.

As the aromatic moiety mentioned above, one having the following formula is desirable:

In the formula, 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, while R represents a hydrogen atom, an alkyl group, an alkoxy group, an aryloxy group, an arylamino group or a halogen atom (I, Br, ce, F).

As a substituted amino group represented byY, a monoalkylamino, dialkylamino, arylamino, morpholino, piperidino or pyrrolidino, etc. are desirable.

Diazonium compounds which form salts are 4-diazo-1-dimothylaminobenzone, 4-diazo-1 - diethylaminobonzene,4-diazo-1 -dipropylaminobonzono, 4-diazo-1 -methylbenzylaminobenzene,4-diazo-1 - dibonzylaminobonzone, 4-diazo-1 -ethyl hydroxyethyl-aminobenzene, 4-diazo-l -diethylamino-3 methoxybenzene,4-diazo-1 -dimethylam ino-2-methyl benzene, 4-diazo-1 -benzoyla m ino-2,5-diethoxybenzene,4-diazo-1 -morpholino-2,5-diethoxybenzeno, 4-diazo-1 morpholino-2,5-dibutoxybonzene, 4-diazo-1 -anilino-bonzono, 4-diazo-1 -toluylmercapto-2,5diethoxybenzene,4-diazo-1,4-methoxybenzoylamino-2,5-diethoxybenzene,4-diazo-1 -pyrrolidino-2 ethylbonzeno, etc.

Examples of an acid anion are CnF2n+1COO- (n is an integer of 3-9), CmF2m+1SO3- (m is an integer of2-8) and (ClF21+1SO2)2CH- (# is an integer of 1 - 18).

(n: an integer of 3 - 9) Especially as an acid anion,those having a perfluoroalkyl group ora perfluoroalkenyl group or PFB - are preferable because fogging occurs less during the storage prior to use ofthe material.

Detailed examples of diazonium compounds (diazonium salts) are as below:

The coupling components which react with the above diazonium salts to develop colors are compounds which form colors by coupling with diazonium salts. Examples of the coupling components used in this invention are resorcinol, phloroglucin, 2,3-dihydroxynaphthalono-6-sodium sulfonate, l-hydroxy-naphthoic acid morpholinopropylamido, 1 ,5-dihydroxynaphthaleno, 2,3-dihydroxynaphthaleno, 2,3-dihydroxy-6- sulfanylnaphthalene, 2-hydroxy-3-naphthoic acid morpholinopropylamido, 2-hydroxy-3-naphtoic acid-2' methyla n ilide, 2-hyd roxy3-naphth oic acid othanolamide, 2-hydroxy-3-naphthoic acid octylamide, 2- hydroxy-3-naphtoic acid-N-dodeciloxy-propylamide,2-hydroxy-3-naphthoic acid tetradecylamide, acotoanilide, acetoacotoanilide, benzoylacotoanilide, 1 -phenyl-3-methyl-5-pyrazolone,1 -(2',4',6'- trichlorophonyl)-3-benzamide-5-pyrazolone, 1 -(2',4',6',-tn'chlornphenyl)-3-anilino-5-pyrnzolone, 1 -phenyl-3- phenylacetamido-5-pyrazolone, etc.

By employing two or more ofthese coupling components, images of any color tones can be obtained. It is desirable to add a basic substance to the present invention's heat sensitive recording material in orderto accelerate coloring. Such a substance is one hardly soluble or insoluble in water or one which generates alkali when heated.

Examples of the basic substances used in the present invention are nitrogen-containing compounds such as organic ammonium salt, organic amine, amide, urea or thiouroa and its derivatives, thiazolos, pyrrolos, pyrimidines, piperazines, guanidines, indoles, imidazoles, imidazolines, triazoles, morpholines, piperidines, amidinos, formamidine, pyridines, etc.More particularly, they are ammonium acetate, tricyclohoxylamino, tribenzylamine, octadecyl-benzylamine, stearylamine, aryluroa, thiouroa, methylthiourea, arylthiourea, ethylenethiourea,2-benzylimidazole,4-phenylimidazole,2-phenyl-4-methyl-imidazole,2-undecyl- imidazoline, 2,4,5-trifuryl-imidazolino, 1 ,2-diphenyl-4,4-dimethyl-2-imidazolino, 2-phonyl-2-imidazolino, 1,2- ditolyl guanidine, 1 ,2-dicyclohexylguanidino, 1 ,2,3-tricyclohoxyl-guanidine, guanidine trichloroacetato, N,N'-dibonzyl-piperazino, 4,4'-dithiomorpholine, morpholiniumtrichoro-acetate, 2-amino-benzothiazole,2- benzoyihydrazino-benzothiazole, etc. These basic substances can be used in combination of two or more.

Microcapsules in this invention are not only of the type which have been used in usual recording materials and are ruptured by heat or pressure but also those having a wall through which reactive substances inside and outside the capsules can permeate to react when heated. For coloration by heating, the latter type of microcapsules are preferable. The use of those microcapsules is now explained in detail.

The following is a description of the preferred microcapsule used in the present invention. In this invention a reactive substance which is encased as a core substance in the microcapsule is dissolved or dispersed in water using an organic solvent insoluble in water and emulsified. Then a microcapsule wall is formed by polymerization. The organic solvent used in this case is preferred to be one having a boiling point of 1800Cor higher. They are, for example, a phosphate, phthalate, fatty acid amide, alkylated biphenyl, alkylated terphenyl, chlorinated paraffin, alkylatod naphthaleno, diarylothano, etc.

More particularly, they are tricresyl phosphate, diphonyicresyl phosphate, tricyclohexyl phosphate, dibutyl phthalate, dioctyl phthalate, dilauryl phthalate, dicyclohexyl phthalate, butyl oleate, diethylene glycol dibenzoate, dioctyl sebacinate, dibutyl sebacinate dioctyl adipate, trioctyl trimellitate, acetyltriethyl citrate, octyl maleate, dibutyl maleate, isopropyl biphenyl, isoamyl biphenyl, chlorinated paraffin, diisopropyl naph thalene, 1,1 -ditolylethane, 2,4-di-t-aminophenol, N,N-dibutyl-2-butoxy-5-t-octylaniline, etc.

Among these, ester solvents such as dibutyl phthalate, diphenylcresyl phosphate, tricresyl phosphate, diethyl phthalate, dibutyl maleate, etc. are more desirable. In the present invention, when a wall of a macromolecuiarsubstance is formed around the oil drop obtained by emulsifying a core substance containing a reactive substance such as a color former, etc. to produce a microcapsule, the reactant to form a macromolecularsubstance is added inside and/oroutsidethe oil drop. Examples of such a macromolecular substance are a polyurea, polyamide, polyester, polycarbonate, urea-formaldehyde resin, melamine resin, polystyrene, styrenemethacrylate copolymer, styrene-acrylate copolymer, gelatin, poly(vinylpyrrolidone), poly(vinylalcohol), etc. These macro molecular substances can be used as a combination of two or more in the present invention.

Also, among the above substances, a polyurethane, polyurea, polyamide, polyester or polycarbonate, is preferred in this invention. Especially, polyurethane and polyurea are preferable.

The method of preparing a wall of a microcapsule by polymerizing the reactant from the inside of an oil drop is desirable in the present invention since it is possible to form capsules of a uniform diameterwithin a short period of time, which is suitable for producing a recording material with an excellent storage life before recording.

The above method and examples of the compounds are, as briefly explained below, described in the specifications of U.S. Patents Nos. 3,726,804 and 3,796,669.

When the polyurethane is used as a material for a capsule wall, a polyisocyanate and the second substance (e.g., a polyol and a polyamine) which reacts with the polyisocyanatetoformthewall are mixed into an oily liquid to be capsuled. The mixture is dispersed and emulsified in water, and then the temperature ofthe resultant emulsion is raised to let the reaction to form a macromolecule proceed around the surface of the oil drops. In this case, it is possible to let the oily liquid include an auxiliary solvent which has a high dissolving ability and a low boiling point.

The polyisocyanate used for forming capsules and the polyol as well as the polyamine, etc. which react with the polyisocyanate are disclosed in U.S. Patent Nos. 3,281,383,3,773,695 and 3,793,268, Japanese Patent Publications Nos. 40,347/73 and 24,159/74, and Japanese Patent Applications (OPI) Nos. 80,191/73 and 84,086/73. The disclosed examples can be also used in the present invention.

A catalyst such as a tin salt can be used to accelerate the urethane-forming reaction.

Especially, when using the polyisocanateas a first substance and the polyol as a second substance to form the wall of the microcapsule, a heat sensitive material having excellent storage life before use is obtainable.

By selecting a combination of the first substance and the second substance, the heat permeability of the reactant can be controlled arbitrarily.

Examples of polyisocyanato which is the first substance for forming a wall membrane are diisocyanatos such as m-phenylene diisocyanate, p-phenylene diisocyanate, 2,6-trilene diisocyanate, 2,4-trilene diisocyanate, naphtalene-1,4-diisocyanate, diphenylmethane-4,4'-diisocyanate, 3,3'-dimothoxy-4,4'-biphonyl- diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, xylilene-1,4-diisocyanate,4,4'- diphenylpropane diisocyanate, trimothylene diisocyanate, hexamethylene diisocyanate, propylene ,2-diisocyanate, butylene-1 ,2-diisocyanate, cyclohexyiene-l ,2-diisocyanate, cyclohexylene-1,4diisocyanate, etc.; triisocyanates such as 4,4',4"-triphenylmethanetriisocyanate,toluene2,4,6-triisocyanate, etc.; tetraisocyanates such as 4,4'-dimothylphonylmethane-2,2',5,5'-tetraisocyanate, etc.; isocyanate pre- polymers such as an addition product of hexamethyleno diisocyanate and trimethylol propane; an addition product of 2,4-trilone diisocyanate and trimethylol propane; an addition product ofxylilene diisocyanate and trimethylol propane; and an addition product oftrilene diisocyanate and hexanetriol.

Examples of the second substances for forming a wall membrane, i.e., polyols, are aliphatic and aromatic polyhydric alcohols, hydroxypolyoster, and hydroxypolyalkylene other. Preferred polyols have the following group (1), (2), (3) or (4) between the two hydroxyl groups in their molecular structures. They are, for example polyhydroxy compounds having a molecularweight of not more than 5,000.

(1) aliphatic hydrocarbon groups having 2 - 8 carbon atoms

Ar in (2), (3) and (4) is a substituted or an unsubstituted aromatic moiety. An aliphatic hydrocarbon group of the above (1) has-CnH2n- as a basic structure and the hydrogen group here can be substituted with other elements.

Examples of the group (1) are ethyleneglycol, 1 ,3-prnpanediol, 1 ,4-butanodiol, 1 5-pentanediol, 1,6- hexanediol, 1 7-heptanediol, 1 ,8-actanediol, propyloneglycol, 2,3-dihydroxybutane, 1 2-dihydroxybutane, 1 ,3-dihydrnxybutane, 2,2-dimothyl-1 3-propanediol, 2,4-pentanodiol, 2,5-hexanediol, 3-methyl-1 ,5- pentanedioi, 1,4-cyclohexane dimethanol, dihydroxy-cyclohexane, diethyleneglycol, 1,2,6- trihydroxyhexane, phenylothyleneglycol, 1,1,1 -trimethylol propane, hexanetriol, pentaerythritol, glycerine.

Examples of the group (2) are condensation products of aromatic polyhydric alcohols such as 1,4-di(2hydroxyethoxy)-henzene, resorcinol dihydroxyethyl other, and an alkyleneoxide.

Those of the group (3) arep-xylileneglycol, m-xylileneglycol, a, a'-dihydrnxy-p-diisoprnpylbenzone.

The group (4) includes, for example, 4,4'-dihydroxy-diphonylmethane, 2-(p,p'-dihydroxy diph onylmethyl)benzyl-alcohol, an addition product of bisphenol A and othyleneoxide, an addition product of bisphenoi A and propyleneoxide. It is desirable to use polyol in such an amount as will make the proportion of hydroxyl group 0.02 - 2 mols per 1 mol of an isocyanate group.

In the present invention, it is possible to form macrocapsules by using a water-soluble micromolecule.This macromolecule can be anyofanionic, nonionic and amphotericwater-soluble macromolecules, and it can be either natural or synthetic. Example of such a macromolecule are those having a-COO- or-SO3 group, etc.

More specific examples of a natural anion macromolecule are gum arabic,an alginic acid, etc. and those of a semi-synthetic one are a carboxymethylcellulose, a phthalized gelatin, a sulfated starch, a sulfated cellulose, a lignin sulfonic acid, etc. Synthetic water soluble macromolecules are, for example, copolymers of maleic anhydride system (including hydrolyzed ones), polymers and copolymers of an acrylic acid system (including metacrylic acid ones), polymers and modified poly vinyl alcohol, etc. Amphoteric compounds are gelatin, etc.

Amongthesewater-soluble macromolecules, the most preferred one is polyvinyl alcohol of which degree of saponification is 75 % or more and that of polymerization is 300 - 2400. These macromolecules are used as an aqueous solution of 0.01 -20wt%.

The diameter of a microcapsule used in this invention is adjusted to be 20 microns or less. Generally if the diameter becomes largerthan 20 microns quality of imaging is reduced. Especially, when the heating with a thermal head is carried out on the side coated with microcapsules, it is preferable to adjust the diameter to 8 microns or less in orderto avoid the fog caused by pressure.

In the preparation of the present invention's heat sensitive recording material, one member of the components of the heat sensitive layer, i.e., a diazo compound, a coupling component and, if necessary, a basic substance, is enclosed in microcapsules. Also, two or three members of the components can be encapsulated. When two members are held in microcapsules, they can be enclosed either in the same microcapsule or in separate ones. In the case of microencapsulating three members ofthe components, although they can not be contained in the same microcapsule, various combinations out ofthe three can be arranged. The components which are notto be encapsulated are outside the microcapsules in the heat sensitive layer.

The hindered phenol compounds used in the present invention can be either microencapsulated or outside the microcapsules.

The microcapsules are prepared by using an emulsion containing 0.2 wt% or more of the component to be contained in them.

The desirable proportion of the three components used in this invention, i.e., a diazo compound, a coupling component, and if necessary, a basic substance, is 0.1 - 10 parts by weight of a coupling component and 0.1 - 20 parts by weight of a basic substance per 1 part by weight of a diazo compound. This proportion does notvarywhethorthe components are microencapsulated or not. Also, a diazo compound is preferably applied in an amount of 0.05 - 5.0 g/m2.

When the color former, developer and basic substance are not encased in a microcapsule, it is preferred thatthey are solid-dispersed using a sand mill, etc. togetherwith a water soluble macromoleculo. In this case, the preferable water soluble macromolecule is the one which is used for preparing the microcapsule. Its concentration is to be 2 -30 by weight, and the color former, developer and basic substance are used in an amount of 4-40 % by weight each based on the macromolecule solution.

A particle size ofthe components is desired to be 10 microns or smaller than that.

In orderto improve the heat coloring property of the heat sensitive recording material, a hydroxycompound, a carbamic acid ester compound, an aromatic methoxy compound or an organic sulfonamide can be added. These compounds are able to lowerthe melting point of a coupling component or a basicsubstance, orto improve heat permeability of microcapsule walls; thereby practical density at the time of thermal recording is increased.

Specific examples of hydroxy compounds are phenol compounds such asp-t-butylphenol,p-t octylphenol,p#a-cumyIphenol, p-t-pentylphenol, m-xylenol, 2,5-dimethylphenol, 2,4,S4rimethylphenol, 3.

methyl-4-isopropylphonol,p-bonzylphonol, o-cyclohoxylphonol,p-(diphenylmothyl)phenol, p-( a, a- diphenylethyl)phenol, o-phenylphenol,p-hydroxy ethyl benzoate,p-hydroxy butyl benzoate,p-hydroxy benzyl benzoate,p-methoxyphenol,p-butoxyphenol,p-heptyloxyphenol,p.benzyloxyphenol, 3- hydroxydimethyl phthalate, vanillin, 1,1 -bis(4-hydroxyphenyl)dodecane, 1,1 ,-bis(4-hydroxyphenyl)-2-ethyl- hexane, 1,1 -bis(4-hydroxyphenyl)-2-methyl-pentane, 2-t-butyl-4-methoxyphenol, 2,2'-dihydroxy-4-mothoxy- benzophenone, etc.

Special examples of alcoholic compounds are 2,5-dimethyl-2,5-hexanediol, resorcinol-di(2hydroxyethyl )ether, reso rcinol -m ono(2-hyd roxyethyl)ether, salicylic alcohol, 1,4- di(hydroxyethoxy)benzene, p-xylenediol,1-phenyl-1,2-ethanediol, diphenyl methanol,1,1-diphenyl ethanol, 2-methyl-2-phenyl-l ,3-propanediol, 2,6-dihydroxymethyl-p-cresolbenzyl ether, 3-(o-methoxyphenoxy)-1 2- propanediol, etc.

Specific examples of carbamate compounds are N-phenyl ethyl carbamate, N-phenyl benzly carbamate, N-phenyl phenethylcarbamate, benzyl carbamate, butyl carbamate, isopropyl carbamate, etc.

Aromatic methoxy compounds are, for exa mple, 2-methoxy benzoate, 3,5-dimethoxyphenyl acetate, 2methoxy naphthalene, 1 ,3,5-trimethoxybenzene,pdimethoxybenzene benzene, etc.

Specific examples of sulfonamides arep-toluene sulfonamide, o-toluene sulfonamide, benzene sulfonamide, N-(p-methoxyphenyl)-p-toluene sulfonamide, N-(p-chlorophonyl)-p-tolueno sulfonamide, N-(o chlorophenyl)-p-toluene sulfonamide, N-(p-tolyl)-p-toluene sulfonamide, N-(o-tolyl)-p-toluono sulfonamide, N-(o-hydroxyphonyl)-p-toluene sulfonamide, N-benzyl-p-toluene sulfonamide, N-(2-phenetyl)-p-toluene sulfonamide, N-(2-hydroxyethyl-p-toluene sulfonamide, N-(3-methoxypropyl)-p-toluene sulfonamide, N-(ptolyl)sulfonamide, N-(o-tolyl)sulfonamide, N-(p-methoxyphenyl)sulfonamide, N-(o-methoxy)sulfonamide, N-(p-chlorophenyl) sulfonamide, N-(o-chlorophenyl)sulfonamide, N-benzyl methane sulfonamide, N-(2 phonoxyothyl)methanesulfonamide, 1 ,3-bis(mothanesulfonylamino)benzene, 1 ,3-bis(p-toluene sul- fonylamino)propane, etc.

The above compounds can be enclosed in microcapsules together with the main components of the heat sensitive layer, or they can be added to a coating solution for the heat sensitive recording material outside the microcapsules. Of these two methods, the former is preferred. However, in both cases, the amount ofthe compound to be added in suitably chosen from the range of 0.01 - 10 parts by weight, preferably 0.1 - 5parts by weight, depending on the desired coloring density.

For the purpose of reducing the yellowing of the ground after fixing with light, a polymerizablo compound having an unsaturated ethylene bond (hereinafter referred to as a vinyl monomer) can be incorporated in the heat sensitive recording material of the present invention.

A vinyl monomer is a compound having at least one unsaturated ethylene bond (e.g., vinyl andvinylidene groups, etc.) in its chemical structure, and takes various chemical forms such as monomer or a prepolymer, i.e., dimer, trimer, other oligomers, their mixtures and copolymers, etc. Examples of vinyl monomers are unsaturated carboxylic acid and its salt, an ester of unsaturated carboxylic acid and an aliphatic polyhydric alcohol compound, an amide of unsaturated carboxylic acid and an aliphatic polyhydric aminecompound, etc.

The proportion of a vinyl monomer to be used is 0.2 - 20 parts by weight, preferably 1 - 10 parts byweight, per 1 part by weight of a diazo compound. The monomer is enclosed in microcapsules together with a diazo compound. In this case, it can replace a part or all of the organic solvent (or a dispersion medium) used for substances to be microencapsulated by vinyl monomer. However, it is not necessary to add the vinyl mon- omer as much as to harden said substances.

When a diazo compound is enclosed in microcapsules in the present heat sensitive recording material, a coupling reaction deactivator is added outside the microcapsules so that the diazo compound existing in liquid phase and that in imperfect capsules (i.e., a diazo compound which is not sufficiently held bythe microcapsule walls) react with the deactivatorto deprive the diazo compound of its coupling reaction (coloring reaction) ability, whereby fogging can be prevented.

Any substance which can reduce coloring of the solution in which a diazo compound has been dissolved can be a coupling reaction deactivator. It can be selected by dissolving a diazo compound in water or in an organic solvent, adding another compound dissolved in water or in an organic solventto the resulting solution and observing the color change ofthe diazo compound.

Examples of such substances are hydroquinone, sodium bisulfite, potassium nitrite, hypophosphorous acid, stannious chloride, formalin, etc. In addition, they can be chosen out ofthose described in the book "The Aromatic Diazo Compounds and theirTechnical Applications" by K. H. Sawnders (London), 1949, pp.

105-306.

Preferred coupling reaction deactivators are those which themselves are less colored, especially soluble in water and give loss side actions. They are employed in such an amount as will not inhibitthe heatcoloring reaction of a diazo compound. The preferred amount is usually 0.01 - 2 mols, especially 0.02 - 1 mol, per 1 mol ofthe diazo compound used.

The coupling reaction deactivator used in this invention is dissolved in a solvent, and added to a solution in which microcapsules containing a diazo compound have been dispersed, a solution in which a coupler or a basic substance has been dispersed ora mixture ofthesetwo solutions. Especially, it is preferable to use the deactivator in the form of its aqueous solution.

To the heat sensitive recording material ofthe present invention, pigments such as silica, barium sulfate, titamium oxide, aluminium hydroxide, zinc oxide, or calcium carbonate, orfinely powdered styrene beads, urea-melamine resin, etc. can be added for the purpose of preventing sticking of the heat sensitive recording material to a thermal head and improving the ability of the material to receive writing.

Also, such a sticking can be prevented by adding metal soaps. Their amounts to be used are 0.2 - 7 g/m2.

In the present invention, for the purpose of increasing the thermal recording density, a heat-fusing subst ance can be added to the heat sensitive recording material. Such a heat-fusing substance is solid at ordinary temperature and melts at 50 - 150 C by heating with a thermal head. It can meltthe diazo compound,coupl ing component or basic substance, and it is used in an amount of 0.2 - 7 g/m2 as a solid matter by being dispersed into particles of size 0.1 - 10 p. Examples of such a heatjusing substance are a fatty acid amide, N-substituted fatty acid amide, ketone compound, urea compounds or ester.

The heat sensitive material of the present invention can be coated using a suitable binder. As a binder, various emulsions of polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, gum arabic, gelatin, polyvinyl pyrrollidone, casein, styrenebutadiene latex, acrylonitrile-butadiene latex, polyvinyl acetate, polyacrylic ester, ethylene-vinyl acetate copolymer, etc. are used. The amount to be used is 0.5 - 5 g/m2 as solid matter.

In addition, as an acid stabilizer, citric acid, tartaric acid, oxalic acid, boric acid, phosphoric acid, pyro phosphoric acid, etc. can be added in this invention.

The heat sensitive recording material ofthe present invention is produced by preparing a coating solution which contains main components such as a color former, a developer, etc. and other additives, coating a support such as paper, synthetic resin films, etc. with the obtained solution by a bar coating, blade coating, air knife coating, gravure coating, roll coating, spray coating, dip coating, etc. and drying to form a heat sensitive layer at a solids coverage of 2.5 - 25 g/m2. In another method, it is possible to produce a layered coating type: main components such as a developer, a coloring reaction assistant or other additives are added as core substances of a microcapsule or solid-dispersed, or they are dissolved to make an aqueous solution, and then mixed to prepare a coating solution.The obtained solution is coated on a support and dried to form a precoated layer at a solids coverage of 2 - 10 g/m2. Further, a main component such as a color former and other additives are added as core substances of a microcapsule solution, and then mixed to prepare a coating solution which was coated over the previous precoated layer and dried to constitute a coated layer at a solids coverage of 1 - 15 g/m2. The heat sensitive recording material of this layered type can have a layered coating which is prepared by reversing the above procedures. In any cases, coating ofthe layers can be carried out either one by one or at the same time. Such a heat sensitive recording material of a layered coating type is desirable since it is especially excellent in its long-term storage life.

Also, the heat sensitive layer can be applied on an intermediate layer which is prepared on a support as is described in the specification of Japanese Patent Application No. 177669/84.

EXAMPLES Examples of the present invention are shown below. However, the invention is notto be restricted bythem.

The unit "part", used to express amounts to be added means "part by weight".

Example 1 100 g of Compound Awere added to 200 g of a 5 % aqueous solution of polyvinyl alcohol (PVA 205: Trade name, produced by KurareCo., Ltd.) and dispersed using a ball mill for 24 hours to obtain Solution A. 18 g of I Compound (B-l ), 2 g Compound (B-2), 20 g of Compound C and 60g of Compound (D-1) were added to 200 g of a 5% aqueous solution of polyvinyl-alcohol and dispersed using a ball mill for 24 hours to obtain Solution (B-D).

Then, 400 g of calcium carbonate were added to 600 g of water and dispersed using a dissolver to obtain a pigment solution.

Further, 30 g of Compound (E-1) were added to 170 g of a 5% aqueous solution of polyvinyl alcohol and dispersed using a ball mill for 24 hours to obtain Solution E.

2 parts of Solution A, 10 parts of Solution (B-D), 5 parts ofthe pigment solution and 3 parts of Solution E were mixed to prepared a coating solution which was bar-coated over paper of hight quality to have a coated amount of8 g/m2 on the dry base. The resulting paper was dried at room temperature to obtain a heat sensitive recording material (1) (Test Method) Thermal recording was performed on the heat sensitive recording material obtained in the above using a G III Mode Thermal Printer (U F-2: manufactured by Matsushita Denso Co., Ltd.). The recorded material was overall exposed so as to fix it using a Recopy Superdry 100 (manufactured by Ricoh Co., Ltd.).The density of the obtained recorded image was measured by a McBeath reflection densitometer. Also, the yellow density of the background was measured. The results are shown in Table 1. Although another thermal recording was tried upon the thus fixed part, no image was recorded, which confirmed that the fixing had been properly done.

Next, the storage life was examined. The density (fogging) of the heat sensitive recording material's ground and the fogging of the same material afteraforced deterioration test in which the material was preserved in a dark place at a temperature of 400C and a relative humidity of 90% RH for 24 hours were measured by a McBeath reflection densitometer to soothe change of fogging density. In order to examine stability ofthe color image and yellowing of the ground after fixing, the recorded image obtained byfixing was irradiated for 24 hours using a Xenon fade meter (FAL-25 AX-HC Type: manufactured by Suga Shikenki Co., Ltd.) and the densities ofthe resulting recorded image and ground were measured. The results are shown in Table 1.

The compounds used for preparing the samples wore as follows: Compound A: Diazonium salt

Compopund B-l: Coupler

Compound B-2: Coupler

Compound C: Organic basic compound

Compound D-1:Coloring improve

Compound E-l: Hindered phenol compound

Table 1 Test Results Heat sensitive recording Density Yellow Yellow density Density of the Yellow density material samples ofthe density ofthe ground image after 24 of the ground (No.) image ofthe aftertheforced hours of after 24 hours ground deterioration irradiation by of irradiation test a fade meter by a fade meter (1) 1.33 0.24 0.50 1.20 0.35 (2) 1.33 0.22 0.38 1.28 0.26 (3) 1.34 0.22 0.35 1.30 0.28 (4) 1.32 0.20 0.35 1.27 0.26 (Comparison-1) 1.33 0.30 1.15 1.10 0.37 Comparative 7 A sample for comparison (Comparison-1) was prepared according to the same manner as in Example 1 except using no Solution E. The same test as in Example 1 was carried out.The results are shown in Table 1.

It is apparent from Table 1 that the heat sensitive recording material of the present invention is improved in four points, i.e., density of the ground at the time of recording, deterioration of an image after recording, yellowing of the ground after recording and raw preservability before recording.

Examples 2-4 Heat sensitive recording materials (2), (3) and (4) were prepared according to the same manner as in Example 1, except using Compounds (E-2), (E-3) and (E-4) instead of Compound (E-1) used for Solution E. The same test as in Example 1 was performed, of which results are shown in Table 1. Compounds (E-2), (E-3) and (E-4) are shown below.

Compound E-2: Hindered phenol compound

Compound E-3 : Hindered phenol compound

Compound E-4: Hindered Phenol compound

Example 5 Heat sensitive recording material (5) was obtained according to the same manner as in Example 1 except using 30 g of Compound (111-29), which was exemplified as a color image stabilizer in this specification, instead of Compound (E-1) used for Solution E.

The same test as in Example 1 was performed. The results are as shown in Table 2.

Examples 6- 8 Heat sensitive recording materials (6), (7) and (8)were prepared according to the same manner as in Example 5, except using Compounds (111-2), (111-12) and (111-18) instead of Compound (111-29) usedforSolution E. The same test as in Example 1 was performed, of which results are shown in Table 2. Compounds (111-2), (111-12) and (111-18) are the ones exemplified in this specification.

Comparative Example 2 A sample for comparison (Comparison-2) was prepared according to the same manner as in Example 5 except using no Solution E. The same test as in Example 1 was carried out. The results are shown in Table 2.

As is apparentthe results in Table 2, it is proved that the heat sensitive recording material of the present invention is improved in four points, i.e., density of the ground at the time of recording, deterioration of an image after recording, yellowing of the ground after recording and storage life before recording.

Table 2 Test Results Heat sensitive recording Density Yellow Yellow density Density of the Yellow density material samples ofthe density ofthe ground image after 24 oftheground (No.) image ofthe aftertheforced hours of after 24 hours ground deterioration irradiation by of irradiation test a fade meter by a fade meter (5) 1.33 0.28 0.53 1.22 0.27 (6) 1.32 0.22 0.45 1.29 0.26 (7) 1.33 0.22 0.39 1.30 0.26 (8) 1.25 0.21 0.38 1.27 0.26 (Comparison-2) 1.33 0.30 1.15 1.10 0.37

Example 9 Heat sensitive recording material (9) was obtained according to the same manner as in Example 1 except using 30 g of Compound (IV-1 ), which was exemplified as a color image stabilizer in this specification, instead of Compound (E-1) used for solution E.

The same test as in Example 1 was performed. The results are shown in Table 3.

Example 10 Heat sensitive recording material (10) was obtained according to the same manner as in Example 9 except using Compound (IV-3), which was exemplified as a color image stabilizer in this specification, instead of Compound (IV-1 ) used for solution E.

The same test as in Example 1 was performed. The results are shown in Table 3.

Comparative Example 3 Asample for comparison (comparison-3) was prepared according to the same manner as in Example 9 except using no Solution E. The same test as in Example 1 was carried out. The results are shown in Table 3.

Table 3 Test Results Heat sensitive recording Density Yellow Yellow density Densityofthe Yellow density material samples ofthe density oftheground image after 24 oftheground (No.) image ofthe aftertheforced hours of after24hours ground deterioration irradiation by of irradiation test a fade meter by a fade meter (9) 1.31 0.24 0.40 1.25 0.25 (10) 1.31 0.23 0.39 1.28 0.25 (Comparison-3) 1.33 0.30 1.15 1.10 0.37 Example 71 Heat sensitive recording material (11 was obtained according to the same manner as in Example 1 except using 30 g of Compound (V-1), which was exemplified as a color image stabilizer in this specification, instead of Compound (E-1) usedforsolution E.

The same test as in Example 1 was performed. The results are shown in Table 4.

Example 12 Heat sensitive recording material (12) was obtained according to the same manner as in Example 11 except using Compound (V-3), which was exemplified as a color image stabilizer in this specification, instead of Compound (V-1) used for solution E.

The same test as in Example 1 was performed. The results are shown in TabIe4.

Comparative Example 4 Asamplo of comparison (comparison-4)was prepared according to the same manner as in Example 11 except using no Solution E. The same test as in Example 1 was carried out. The results are shown in Table 4.

Table 4 Test Results Heat sensitive recording Density Yellow Yellow density Density of the Yellow density material samples ofthe density oftheground image after 24 oftheground (No.) image ofthe aftertheforced hours of after 24 hours ground deterioration irradiation by of irradiation test a fade meter by a fade meter (11) 1.33 0.24 0.40 1.20 0.26 (12) 1.33 0.23 0.40 1.28 0.26 (Comparison-4) 1.33 0.30 1.15 1.10 0.37 Example 13 An example of microencapsulating Compound A is described below.

To 50 g of Compound Awere added 150 g of methylono chloride, 50 g oftricresylphosphate, 150 g of trimethylol propane trimethacrylate, 200 g of a 75 % ethylacetate solution of an addition product of m-xylene diisocyanate and trimethylol propane (3:1) (TAKENET DIION: trade name, manufactured byTakeda Yakuhin Kogyo Co., Ltd.) and uniformly mixed to prepare an oil phase solution.

On the other hand, 600 g of 7 % polyvinyl alcohol (PVA 217E, Degree of saponification: 88-89%, Degree of polymerization: 1700,trade name, manufactured by KU RARE Co., Ltd.) was made into an aqueous solution of a water soluble macromolecule.

An aqueous solution of protective colloid was added to a 5 liter stainless steel pot equipped with a hot bath and a dissolver. Then, the oil phase solution was added while stirring with the dissolver. The emulsification/ dispersion was continued until an average particle size became about 1.5 ij. When the dispersion was completed, stirring was eased, while warmed water at 42 "C was sent into the hot bath (inside temperature at 40 "C) to carry out an encapsulation reaction for 3 hours. The obtained solution (A-1 ) was used as below after removing with an ion exchange resin the diazonium saltwhich had not been encapsulated.

Acoating solution was prepared by mixing 5 parts of solution (A-1) and 7 parts of solution (B-D), 3.5 parts of a pigment solution, 2.1 parts of solution Ewhich were used in Example 1,then coated over paper of high quality to have a coated amount of 10 g/m2 on the dry base. Thus, the heat sensitive recording material (13) was obtained.

The same test as in Example 1 was carried out. The results are shown in Table 5.

Examples 14- 16 Heat sensitive recording materials (14), (15) and (16) were prepared according to the same manner as in Example 13, except using solutions E used in the Examples 2-4 instead of solution E of Example 13respectively.

The same test as in Example 1 was performed. The results are shown in Tables.

Example 17 An example of microencapsulating Compound A and Compound (E-1) is described below.

An (A-2) solution was obtained according to the same manner as in Example 13 except adding 5 g of Compound (E-1) into the oil phase solution to carry out a microencapuslation reaction.

Heat sensitive recording material (17) was obtained according to the same manner as in Example 13except using (A-2) solution instead of (A-1 ) solution.

The same test as in Example 1 was performed. The results are shown in Table 5.

Examples 18-20 Heat sensitive recording materials (18), (19) and (20)were prepared according to the same manner as in Example 17, except using Compounds (E-2), (E-3) and (E-4) instead of Compound (E-1) used for Solution E.

The same test as in Example 1 was performed, of which results are shown in Table 5.

Comparative Example 5 Asample ofcomparison (Comparison-5) was prepared according to the same manner as in Example 13 except using no Solution E. The same test as in Example 1 was carried out. The results are shown in Table 5.

From the results in Table 5, the effect of the hindered phenols is apparent and the usefulness of the present invention is proved by these results.

Table 5 Test Results Heat sensitive recording Density Yellow Yellow density Density of the Yellow density material samples ofthe density ofthe ground image after 24 of the ground (No.) image ofthe aftertheforced hours of after 24 hours ground deterioration irradiation by of irradiation test a fade meter by a fade meter (13) 1.27 0.09 0.12 1.15 0.12 (14) 1.26 0.08 0.10 1.24 0.10 (15) 1.26 0.08 0.10 1.24 0.10 (16) 1.26 0.08 0.11 1.24 0.10 (17) 1.28 0.09 0.13 1.20 0.12 (18) 1.28 0.08 0.11 1.24 0.11 (19) 1.28 0.08 0.11 1.24 0.11 (20) 1.28 0.08 0.11 1.24 0.11 (Comparison-5) 1.29 0.11 0.16 1.05 0.16 Example 2? Acoating solution was propard by mixing 5 parts of solution (A-1) prepared in Example 13 and 7 parts of solution (B-D), 3.5 parts of a pigment solution, 2.1 parts of Solution E which were used in Example 5, then coated over paper of high quality to have a coated amount of 10 g/m2 on the dry base. Thus, the heat sensitive recording material (21), in which the compound A was microencapsulated just same as the case of Example 13, was obtained.

thesametestas in Example 1 was carried out. The results are shown in Table 6.

Examples22-24 Heat sensitive recording materials (22), (23) and (24) were prepared according to the same manner as in Example 21, except using Solutions E which are used in Examples 6 - 8 respectively instead of Solution E used in Example 21.

The same test as in Example 1 was performed, of which results are shown in Table 6.

Example 25 An (A-3) solution was obtained accordingtothe same manner as in Example 13 except adding 5 g of Compound (Ill - 29), which was exemplified as a color image slabilizer in this specification, into the oil phase solution to carry out a microencapsulation reaction.

Heat sensitive recording material (25) was obtained according to the same manner as in Example 21 except using (A-3) solution instead of (A-1 ) solution.

The same test as in Example 1 was performed. The results are shown in Table 6.

Examples26-28 Heat sensitive recording materials (26), (27) and (28) were prepared according to the same manner as in Example 25, except using Compounds (111-2), (111-12) and (111-18) instead of Compound (111-29). The sametest as in Example 1 was performed, of which results are shown in Table 6.Compounds Table 6 Test Results Heat sensitive recording Density Yellow Yellow density Density ofthe Yellow density material samples ofthe density oftheground image after 24 oftheground (No.) image ofthe aftertheforced hours of after24hours ground deterioration irradiation by of irradiation test a fade meter by a fade meter (21) 1.27 0.09 0.12 1.15 0.12 (22) 1.26 0.09 0.10 1.24 0.10 (23) 1.27 0.08 0.10 1.24 0.10 (24) 1.27 0.08 0.13 1.24 0.12 (25) 1.30 0.09 0.11 1.20 0.12 (26) 1.30 0.08 0.11 1.24 0.11 (27) 1.30 0.09 0.11 1.25 0.11 (28) 1.31 0.09 0.14 1.25 0.11 (Comparison-6) 1.29 0.11 0.16 1.05 0.16 (111-2), (111-12) and (111-18) are the ones exemplified in this specification.

Comparative Example 6 Asampleforcomparison (Comparison-6)was prepared according to the same manner as in Example 21 except using no Solution E.

The same test as in Example 1 was carried out. The results are shown in Table 6, which show that a color image stabilizer is still effective even when a diazo compound is microencapsulatod. Effectiveness of the compound represented by the formula (Ill) was proved.

Example 29 A coating solution was prepared by mixing 5 parts of solution (A-1) prepared in Example 13 and 7 parts of Solution (B-D), 3.5 parts ofthe pigment solution, 2.1 parts ofthe Solution Ewhich were used in Example 9, then coated over a paper of high quality to have a coated amount of 10 g/m2 on the dry base. Thus, the heat sensitive rocoarding material (29), in which the compound Awas microencapsulated just same as the case of Example 13, was obtained.

The same test as in Example 1 was carried out. The results are shown in table7.

Example 30 Heat sensitive recording material (30) was obtained according to the same manner as in Example 29 except using the solution E which was used in Example 10 instead of Solution E of Example 29.

The same test as in Example 1 was performed. The results are shown in Table 7.

Example 3 1 An (A-4) solution was obtained according to the same manner as in Example 13 except adding 5g of Compound (lV-1 ), which was exemplified as a color image stabilizer in this specification, into the oil phase solution to carry out a microencapsulation reaction.

Table 7 Test Results Heat sensitive recording Density Yellow Yellow density Densityofthe Yellowdensity material samples ofthe density of the ground image after 24 of the ground (No.) image ofthe aftertheforced hours of after24hours ground deterioration irradiation by of irradiation test a fade meter by a fade meter (29) 1.25 0.08 0.11 1.22 0.12 (30) 1.26 0.09 0.11 1.22 0.12 (31) 1.26 0.08 0.12 1.22 0.11 (32) 1.26 0.09 0.12 1.22 0.11 (Comparison-7) 1.29 0.11 0.16 1.05 0.16 Heat sensitive recording material (31 ) was obtained according to the same manner as in Example 29 except using (A-4) solution instead of (A-1 ) solution.

The same test as in Example 1 was carried out. The results are shown in Table 7.

Example 32 Heat sensitive recording material (32) was obtained according to the same manner as in Example 31 except using Compound (IV-3), which was exemplified as a color image stabilizer in this specification, instead of Compound (lV-1).

The same test as in Example 1 was performed. The results are shown in Table 7.

Comparative Example 7 Asample of comparison (Comparison-7) was prepared according to the same manner as in Example 29 except using no Solution E.

The same test as in Example 1 was conducted. The results are shown in Table 7.

It is apparent from the table that the heat sensitive recording material of the present invention is improved in four points, i.e., density of the ground atthe time of recording, deterioration of an image after recording, yellowing ofthe ground after recording and storage life before recording. These effects are the same even when a diazo compound is microencapsulated. Effectiveness of the compound represented bytheformula (IV) was proved by these Examples.

Example 33 Acoating solution was prepared by mixing 5 parts of solution prepared in Example 13 and 7 parts of Solution (B-D), 3.5 parts of the pigment solution, 2.1 parts of the Solution E which were used in Example 11, then coated over a paper of high quality to have a coated amount of 10 g/m2 on the dry base. Thus, the heat sensitive recording material (33), in which the compound Awas microencapsulated just same as the case of Example 13, was obtained.

The same test as in Example 1 was carried out. The results are shown in Table 8.

Example 34 Heat sensitive recording material (34) was obtained according to the same manner as in Example 33 except using Solution E which was used in Example 12 instead of Solution E of Example 33.

The same test as in Example 1 was performed. The results are shown in Table 8.

Example 35 An (A-5) solution was obtained according to the same manner as in Example 13 except adding 5 g of Compound (V-1 ), which was exemplified as a color image stabilizer in this specification, into the oil phase solution to carry out a microencapsulation reaction.

Heat sensitive recording material (35) was obtained according to the same manner as in Example 33 except using (A-5) solution instead of (A-1) solution.

The same test asin Example 1 was performed. The results are shown in Table 8.

Example 36 Heat sensitive recording material (36) was obtained according to the same manner as in Example 35 except using Compound (V -3),which is exemplified as a color image stabilizer in this specification, instead of Compound (V -1).

The same test as in Example 1 was performed. The results are shown in Table 8.

Comparative Example 8 A sample for comparison (Comparson-8) was prepared according to the same manner as in Example 33 except using no Solution E.

The same test as in Example 1 was performed. The Table 8 Test Results Heat sensitive recording Density Yellow Yellow density Densityofthe Yellow density material samples ofthe density of the ground image after 24 ofthoground (No.) image ofthe aftertheforced hours of after24hours ground deterioration irradiation by of irradiation test a fade meter by a fade meter (33) 1.29 0.09 0.12 1.22 0.11 (34) 1.29 0.09 0.12 1.22 0.11 (35) 1.28 0.09 0.11 1.25 0.11 (36) 1.29 0.09 0.11 1.25 0.11 (Comparison-8) 1.29 0.11 0.16 1.05 0.16 results are in Table 8.

It is apparent from the table that the heat sensitive recording material ofthe present invention is improved in four points, i.e., density of the ground at the time of recording, deterioration of an image after recording, yellowing ofthe ground after recording and storage life before recording. The effect is obtained even when a diazo compound is microoncapsulatod. Effectiveness of the compound V was proved by these Examples.

Example 37 A (B-D)' solution was prepared according to the same manner as in Example 1 except using a compound (D-2) instead of the compound (D-1) as an agent to improved the heat coloring property. Next, a coating solution was prepared according to the same manner as in Example 5 using 5 parts of Solution (A-l), 7 parts of Solution (B-D)', 3.5 parts of a pigment solution and 2.1 parts of the Solution E of compound (E- 1 ),then coated over a paper of high quality to have a coated amount of 10 g/m2 on the dry base. Thus, the heat sensitive recording material (37) was obtained.

The same test as in Example 1 was carried out. The results are shown in Table 9.

Compound (D-2):

Example 38-40 Heat sensitive recording materials (38), (39) and (40) were prepared according to the same manner as in Example 37, except using Solution E used in the Example 2-4 instead of Solution E of Example 37 respectively. The same test as in Example 1 was performed, of which results are shown in Table 9.

Table 9 Test Results Heat sensitive recording Density Yellow Yellow density Densityofthe Yellow density materiaísamples ofthe density of the ground image after 24 ofthe ground (No.) image ofthe aftertheforced hours of after24hours ground deterioration irradiation by of irradiation test a fade meter by a fade meter (37) 1.29 0.10 0.14 1.20 0.13 (38) 1.30 0.09 0.12 1.28 0.11 (39) 1.30 0.09 0.13 1.28 0.11 (40) 1.30 0.09 0.13 1.28 0.11 (Comparison-9) 1.30 0.12 0.18 1.11 0.17 Comparative Example 9 A sample for comparison (Comparison-9) was prepared according to the same manner as in Example 37 except using no Solution E The same test as in Example 1 was performed.As apparent from the results which are shown in Ta ble 9, the heat sensitive recording material of the present invention is excellent in its performance. Effectiveness of the invention is the same even when a coloring improver is changed, which prove that the effect of this invention is obtained especially by adding a hindered phenol.

Example 41-45 The following is an example to study an effect of varied amounts of a hindered phenol compound using Compound (E-2), when Compound (A) is microencapsulated.

As in Example 13, coating solution were prepared by adding Solution E (containg Compound (E-2) in amount of 0.085,0.34, 1.7,5.1 and 10.2 parts respectively to mixtures each comprising 5 parts of Solution (A-i), 7 parts of Solution (B-D) and 3.5 parts of a pigment solution. The resulting solution were coated over a paper of high quality to have a coated amount of 10 g/ m2 each on the dry base. Thus, the heatsensitive recording materials (41), (42), (43), (44) and (45) were obtained.

The sametest as in Example 1 was carried out. The results are in Table 10.

Comparative Example 10 Asample ofcomparison (Comparison-lO) was prepared according to the same manner as in Examplo4i except using no Solution E.

The same test as in Example 1 was carried out. The results are shown in Table 10.

Table 10 Test Results Heat sensitive recording Density Yellow Yellow density Densityofthe Yellow density materials samples ofthe density of the ground image after 24 of the ground (No.) image ofthe aftertheforced hours of after24hours ground deterioration irradiation by of irradiation test a fade meter by a fade meter (41) 1.29 0.11 0.15 1.10 0.14 (42) 1.28 0.09 0.12 1.24 0.11 (43) 1.27 0.08 0.10 1.24 0.10 (44) 1.23 0.08 0.10 1.21 0.10 (45) 1.14 0.07 0.09 1.12 0.09 (Comparison-10) 1.29 0.11 0.16 1.06 0.16

Claims (22)

1. A heat sensitive recording material which comprises on a support a heat sensitive layer containing at least a diazonium saltand a couplerwhich is able to change the diazonium compound to a colored form, wherein said heat sensitive layer contains at least one compound selected from hindered phenols.

2. A heat sensitive recording material as claimed in Claim 1, wherein said hindered phenol is o-tert-butyl phenol or derivative thereof.

3. A heat sensitive recording material as claimed in Claim 2, wherein said o-tert-butyl phenol derivative is represented by the following formula (I):

in which R1, R2 and R3 each represents a hydrogen atom, an alkyl group, an alkoxy group or a halogen atom 40 and may be the same or differentfrom each other.

4. A heat sensitive recording material as claimed in Claim 2, wherein said o-tert-butyl phenol derivative is represented by the following formula (ill):

in which R1 and R2 each represents a hydrogen atom, an alkyl group, an aryl group, an alkoxy group ora halogen atom and may be the same or different from each other; and Y is

an alkyl group or an arylene group, ofwhich an alkyl group and an arylene group mayfurtherhavesubsti- tuents.

5. A heat sensitive recording material as claimed in claim 1,wherein said hindered phenol is represented bythe following formula (III):

in which Rand R' each represents a hydrogen atom or an alkyl group and may be the same or different from each other; and R31, R32, R33 and R34 each represents a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, an alkylthio group, an acylamino group, an hydroxyl group or a halogen atom, and also may be the same or different from each other.

6. A heat sensitive recording material as claimed in Claim 5, wherein said hindered phenol is represented bythe following formula (alia):

in which R, R', R31, R32, R33 and R34 are the same as those in Claim 5.

7. A heat sensitive recording material as claimed in Claim 5, wherein said hindered phenol is represented bythofollowingformula (Illb):

wherein R, R31, R33 and R34 are the same as those in Claim Sand R35-R40 each represents a hydrogen atom, an alkyl group, an aryl group, an alkoxygroup, a heterocyclicgroup, an alkylamino group oran alkoxycarbonyl group and may be the same or different from each other.

8. A heat sensitive recording material as claimed in Claim 5, wherein said hindered phenol is represented bythefollowingformula (Illc):

wherein R, R', R3r, R33 and R34 are the same as those in Claim 5.

9. A heat sensitive recording material as claimed in Claim 5, wherein said hindered phenol is represented bythefollowing formula (lid):

wherein R, R', R31, R32, R33 and R34 are the same as those in Claim 5 and R35 and R36 are the same as those in Claim 7.

10. A heat sensitive recording material as claimed in Claim 5, wherein said hindered phenol is represented by the following formula (Ille):

wherein R, R', R31, R32, R33 and R34 are the same as those in Claim 5 and R35, R36, R37 and R38 are the sameas those in Claim 7.

11. A heat sensitive recording material as claimed in Claim 1, wherein said hindered phenol is represented by the following formula (IV):

wherein R41 and R45 each represents a hydrogen atom, an alkyl group or a heterocyclic group; R42, R43 and R44 may be the same or different from each other and each represents a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, an acylamino group, a diacylamino group, an sulfonamide group, an alkylamino group, an alkoxycarbonyl group, an acyloxygroup ora halogen atom; while R41 and R45 are not both hydrogen atoms at the sametime.

12. A heat sensitive recording material as claimed in Claim 11,wherein said hindered phenols is that represented by the following formula (IVa):

wherein R46 and R47 each represents a hydrogen atom or an alkyl group, while R46 and R47 are not both hydrogen atoms at the same time.

13. A heat sensitive recording material as claimed in Claim 1, wherein said hindered phenols is that represented by the following formula (V):

wherein R represents a substituted or unsubstituted 4-pyperidine group; R53 represents hydrogen atom or a substituted or unsubstituted alkyl group which may be the same or different in each benzene ring; Y represents a hydrogen atom or a substituted or unsubstituted alkyl group; and m is 1 or 2 while m +p=2.

14. A heat sensitive recording material as claimed in Claim 13, wherein said R is represented bythe following formula:

wherein R51 represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aralkyl group, ora substituted or unsubstituted acyl group; and R52 represents one or more of a substituted or unsubstituted alkyl group which may be the same or differentfrom each other and substituted with a hydrogen atom ora piperidine ring.

15. A heat sensitive recording material as claimed in Claim 13, wherein said hindered phenol is that represented by the following formula (Va):

wherein Y, m and p the same as those in Claim 13 and R51 represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aralkyl group, or a substituted or unsu bstituted acyl group.

16. A heat sensitive recording material as claimed in one of Claims 1 - 15, wherein at least one component of diazonium salt and a coupler in said heat sensitive layer is contained in microcapsules.

17. A heat sensitive recording material as claimed in Claim 16, wherein said diazonium salt is contained in microcapsules.

18. A heat sensitive recording material, as claimed in any of Claims 1 to 17, wherein said hindered phenol is present in the layer as particles and in a proportion of 0.05-20 parts by weight per part by weight ofthe diazonium salt.

19. A heat sensitive recording material, as claimed in Claims 16 or 17, wherein said hindered phenol is present in microcapsules in a proportion of 0.01-5 parts by weight per part by weight of the diazonium salt.

20. A heat sensitive recording material as claimed in Claim 1, 16 or 17, wherein said hindered phenol or derivative thereof is any of the compounds named hereinbefore in List A or List B or shown by any offormulae (lli-1 ) to (11128), (IV-1 ) to (IV-27) or (V-1 ) to (V-10).

21. A heat sensitive recording material as claimed in Claim 1, substantially as hereinbefore described in any of Examples 1 to 45.

22. A recording method which comprises locally heating the sensitive layer of a material as claimed in any preceding claim.