GB2181564A - Heat-sensitive recording material - Google Patents

Abstract

In a heat-sensitive recording material comprising a support and a heat-sensitive recording layer which is provided on the support and contains a diazo compound and a coupling component in a binder, the improvement wherein said heat-sensitive recording layer contains a diazo compound having the formula (I): <IMAGE> wherein R<1> is a hydrogen atom, a group having 1-30 carbon atoms selected from those consisting of alkyl, alkenyl, aralkyl, aryl, acyl, acyloxy and ester which may be substituted, or a group selected from the group consisting of amido, carbamoyl, urethane, ureido, sulfone, oxysulfonyl, sulfonyloxy, sulfonamido and sulfamoyl; each of R<2> and R<3> independently is a hydrogen atom or a group having 1 - 10 carbon atoms selected from those consisting of alkyl, alkenyl, aralkyl, alkyloxy and aryloxy which may be substituted; R<4> is a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group, a lower alkylester group or a lower alkyl carbamoyl group, R<4> being the same or different from each other when m is 2 or more; X<-> is an acid anion; n is an integer of 1 to 18; and m is an integer of 1 to 4.

Description

SPECIFICATION Heat-sensitive recording material Background of the invention Field of the invention The present invention relates to a heat-sensitive recording material belonging to a diazo color4orming type, which uses a new diazo compound.

Description ofpriorarts As a recording material for a heat-sensitive recording process, a heat-sensitive recording material of leuco color-forming type is generally utilized. A heat-sensitive recording material of this type gives an image on the recording material, utilizing such a system in which either one of a leuco dye and an acid component dispersed in the heat-sensitive recording layer is melted under application of thermal energy to form a color. A recording material belonging to this type has a drawback in that a recorded image is likely stained by unexpected color formation produced in an unexpected area when the recording material is handled with no care or heat is applied to the recording material afterthe image is recorded, because the recorded image is poorly fixed.

Recently, a heat-sensitive recording material of diazo color-forming type has been studied. For instance, Japanese Patent Provisional Publication No. 57(1982)-123086 and "Publication of Image Electronics (Gazo Denshi-Gakkaisi)", vol. 11,290(1982) describe a recording material having a recording layer which contains a color4orming composition comprising a diazo compound, a coupling component and a basic component (including a component which is convertible into a basic component). In the use ofthis recording material, an image is formed on the recording material by heating and the recording material is subsequently irradiated with light to decompose an unreacted diazo compound to terminate color formation (to perform fixing pro- cess).In the use of recording materials (utilizing the diazo compound, however, pre-coupling (i.e., colorforming reaction) takes place gradually in the storage of the recording material prior to the use forthermal recording and the pre-coupling often gives an unfavorable color formation (i.e., fog) to the resulting image.

Various improvements for reducing the unfavorable color formation (fog) have been proposed. Forinstance, Japanese Patent Provisional Publication 57(1982)-I 23086 proposes that one of the components participating in the color formation reaction be incorporated in the form of non-continuous particles (namely, dispersed solid) or one of the components participating inthecolorformation reaction be incorporated into a separate layer. These measures are based on the idea of preventing the progress of the pre-coupling by keeping the components separately. While these measures are favorable in the improvement of the storage stability (namely, pre-use stability), these likely cause reduction of heat response (i.e., easiness in melting under application ofthermal energy) which also is an important property.

Measures for simultaneously improving both the pre-use stability and the heat response are further prop osed. Japanese Patent Provisional Publications 57(1 982)-44141 and 57(1982)-i 42636 propose that one ofthe components participating in the color formation be encapsulated using a non-polarwax material forseparation from other components, and Japanest Patent Provisional Publication 57(1982)-192944 proposes that such one component be encapsulated using a hydrophobic polymer material forthe separation. The encapsulation of the above processes is performed by dissolving a wax material or polymer material in an appropriate solvent and then dissolving or dispersing the component to be separated in the resulting solution for encapsulation.Thus, the produced capsule is not an exact capsule which a core material should been closed within a shell. Accordingly, in the case that the component to be separated is dissolved in the solution, the incorporated component is not enclosed within a shell but is uniformly mixed with the shell material, and the pre-coupling takes place gradually on the surface of the capsule to reduce the pre-use stability. In the case that the component is dispersed in the solution, the thermal response is often reduced because quick release of the dispersed components is not expected.Further, these processes have another disadvantage in thatthe process is required to have an additional stage for removing the solvent employed for the preparation ofthe solution of the wax material orthe polymer material after the stage for encapsulation. For the above reasons, these processes are still not satisfactory.

As other measure, Japanese Patent Provisional Publications 59(1984)-190886 and 60(1985)-6493 propose that a shell be so formed by polymerization around at least one of the components participating in the color formation reaction as to prepare a micro-capsule enclosing the core material within the polymer shell.

The above measure utilizing the micro-capsule is of value. However, there is a drawback in that the diazo compounds employed conventionally in the art as the color-forming material are poorly soluble in a solvent and the dissolution of the conventional diazo compound requires use of a large amount of a solvent. Further disadvantageous is that the conventional diazo compound is not well dispersed in an ordinarily employed solvent. Accordingly, the preparation of the recording material using the proposed micro-capsule and the conventional diazo dye compound involves certain troubles such as requirement of removal of a large amount of a solvent. Moreover, the improvement of the characteristics ofthe recorded image is not sat- isfactorily accompolishod by the previously proposed recording material.In addition, the known diazo com pound is not sufficiently satisfactory in the resistance to heat or light (for instance, easiness in melting under application of heat or easiness in decomposition under application of light). These unfavorable properties also reduce various characteristics of the light-sensitive recording material.

Summary of the invention It is an object of the present invention to provide a heat-sensitive recording material which is satisfactory in the characteristics ofthe recorded image such as the density offormed color.

It is another object of the invention to provide a heat-sensitive recording material which is improved in the stability, particularly in the pre-use stability.

There is provided by the invention the improvement in a heat-sensitive recording material comprising a support and a heat-sensitive recording layer which is provided on the support and contains a diazo compound and a coupling component in a binder, wherein said heat-sensitive recording layer contains a diazo compound having the formula (I):

wherein R1 is a hydrogen atom, a group having 1 -30 carbon atoms selected from those consisting of alkyl, alkenyl, aralkyl, aryl, acyl, acyloxy and ester which may be substituted or a group selected from the group consisting of amido, carbamoyl, urethane, ureido, sulfone, oxysulfonyl, sulfonyloxy, sulfonamido and sulfamoyl; each of R2 and R3 independently is a hydrogen atom or a group having 1-10 carbon atoms selected from those consisting of alkyl, alkenyl, aralkyl, alkyloxy and aryloxywhich may be substituted; R4 is a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group, a lower alkylester group ora lower alkylcarbamoyl group, R4 being the same or different from each other when mis 2 or more; Xis an acid anion; n is an integerof 1 to 18 and m isan integer of 1 to4.

The diazo compound having the formula (I) which is employed in the present invention is a new compound.

The new diazo compound oftheformula (I) is highly soluble in various solvents, as compared with the conventional diazo compoundsforthe heat-sensitive recording material of diazo color4orming type, and is sparingly soluble in water. Therefore, the incorporation of the diazo compound oftheformula (I) into a micro-capsule as a core material advantageously requires a reduced amount of the solvent, and the diazo compound is well dispersed in the solvent. For this reason, the diazo compound of the formula (I) can be incorporated very densely into the micro-capsule.

Further,the diazo compound oftheformula (I) shows improved characteristics. In more detail, the diazo compound ofthe formula (I) responds very sensitivelyto heat of a temperature in the specific range (that is, temperature range of heat supplied from a thermal head or the like in the course of an image recording process), that is, the compound melts very easily.Then, the diazo compound of the formula (I) responds very quickly to irradiated light, that is, the compound is easily decomposed by light. These characteristics of the diazo compound make it possible to prominently enhance the reactivity to the coupling component in the recording layer and further to secure the fixation of the recorded image in the developing stage (namely, a stage for light irradiation subsequent to the image recording stage).

Therefore, the heat-sensitive recording material according to the invention which uses the diazo compound of the formula (I) makes it possible to form an image of high density on the recording layer. Further,the preuse stability of the recording material of the invention is prominently improved because the unreacted diazo compound can be easily and quickly removed.

Detailed description of the invention The heat-sensitive recording material of the present invention comprises a support and a heat-sensitive recording layer provided on the support.

The heat-sensitive recording layer contains a diazo compound and a coupling component in a binder.

The diazo compound which is the requisite of the invention is a diazonium salt having the following formula (I) which forms a color upon coupling with a coupling component;

wherein R1 is a hydrogen atom, a group having 1-30 carbon atoms selected from those consisting of alkyl, alkenyl,aralkly, aryl, acyl, acyloxy and ester which may be substituted, ora group selected from the group consisting of amido, carbamoyl, urethane, ureido, sulfone, oxysulfonyl, sulfonyloxy, sulfonamido and sul famoyl; each of R2 and R3 independently is a hydrogen atom or a group having 1-10 carbon atoms selected from those consisting of alkyl, alkenyl, aralkyl, alkyloxyand aryloxywhich may be substituted;R4isa hydrogen atom, a halogen atom, a loweralkyl group, a loweralkoxygroup, a loweralkylestergroup ora lower aikylcarbamoyl group, R4 being the same or different from each other when m is 2 or more; Xis an acid anion; n is an integer of 1 to 18; and m is an integer of 1 to 4.

In the above description, the term "lower" means "1-6 carbon atoms -containing ".

The diazo compound of the invention preferably has the total number of carbon atoms contained in R1, R2 and R3 oftheformula (I) inthe range of 5to 30.

Examples of the acid anions represented by X in the formula (I) include: isan integer of 3 to 9); (b)C#F2#+iSO3#(kisan integer of 2 to 8); (c) (CeF2e+1SO2)2CH. (t is an integer of 1 to 18);

(i)BF4 (j) PF6 (k) ZnC,'3 Among the above-given acid anions, the anions containing perfluoroalkyl group or perfluoroalkenyl group and PF6- are preferred, because these anions are extremely effective in the reduction of fog in the pre-use storage.

Examples of the diazo compounds (i.e., diazonium salts) of the formula (I) according to the invention include: (A) 4-(ss-(2,4-di-tert-amylphenoxy)butyloxy)benzenediazonium hexafluorophosphate (m.p. 145 C); (B) 4-(2-phenoxyethyloxy) benzenediazonium hexafluorophosphate (m.p. 1 28 C); (C) 4-oxtadecyloxybenzenediazonium hexafluorophosphate (m.p. 96 C); (D) 4-(2-ethylhexyloxy)benzenediazonium hexafluorophosphate (m.p. 82 C); (E) 4-(tert-octylamidomethyloxy)butyloxy)benzenediazonium hexafluorophosphate (m.p. 1 29 C); (F)4-(N,N-dibutylamidomethyloxy)benzenediazonium hexafluorophosphate (m.p. 139 C);; (G) 4-(N,N-di-2-ethylhexylamidomethyloxy)benzenediazonium hexafluorophosphate (m.p. 1 23 C); (H) 4-(2-ethylhexyloxycarbonylmethyloxy)benzenediazonium hexafluorophosphate (m.p. 71 C); (I) 4-(benzylamidomethyloxy)benzenediazonium hexafluorophosphate (m.p. 142 C); (J) 4-(2,4-di-tert-amylphenoxycarbonylmethyloxy)-benzenediazonium hexafluorophosphate (m.p. 11 0 C); and (K) 2-(n,N-di-tert-ethylhexylmethyloxy)benzenediazonium hexafluorophosphate (m.p. 97 C).

The diazo compound can be employed singly or in combination according to the purpose. The combination may comprise a combination with a known diazo compound.

The coupling component employable in the recording material ofthe invention is a compound which is reactive to the above-mentioned diazo compound under a basic condition to form a color. The coupling component is chosen according to the desired color hue.

Examples of the coupling components include resorcinol, fluoroglycine, sodium 2,3 dihydroxynaphthalene-6-sulfonate, sodium 2-hydroxy-3-naphthalenesulfonate, 2-hydroxy-3 naphthalenesulfonanilide, 2-hydroxy-3-naphthalenesulfonmorpholinoamide, 2-hydroxy-3- naphthalenesulfonmorpholinopropylamide,2-hydroxy-3-naphthalenesulfon-2-ethylheXyloxypropylamide, 2-hydroxy-3-naphthalenesulfon-2-ethylhexylamide, sodium 1-hydroxy-8-acetylaminonaphthalene-3,6- disulfonate, 1 -hydroxy-8-acetylaminonaphthalene-3, 6-disulfonanilide, 1 -hydroxy-2- naphthomorpholinopropylamide, 1 ,5-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,3-dihydroxy-6- sulfanylnaphthalene, 2-hydroxy-3-naphthomorpholinopropylamide, 2-hydroxy-3-naphthoanilide, 2- hydroxy-3-naphtho-2'-methylanilide, 2-hydroxy-3-naphthoethanolamide, 2-hydroxy-3-naphthooctylamide, 2-hydroxynaphthomorphorlinoethylamide, 2-hydroxynaphthopiperidinopropylamide, 2- hydroxynaphthopiperidinoethylamide, 2-hydrxoy-3-naphtho-N-dodecyloxypropylamide, 2-hydroxy-3- naphthotetradecylamide, acetanilide, benzoylacetoanilide, 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-phenylacetamido-5-pyrazolone.

The coupling component can be employed singly or in combination.

The diazo compound of the formula (I) is generally contained in the heat-sensitive layer in an amount ranging from 0.02 to 2 g/m2 on the support, preferably in an amount ranging from 0.1 to 1 g/m2.

The basic condition employed in the colorformation in the use of the recording material of the invention is formed using a basic compound which can be selected from various compounds such as organic base compounds and compounds capable of releasing an alkali under heating.

Examples of the basic compounds include ammonium acetate, tricyclohexylamine, tribenzylamine, octa- decylbenzylamine, stearylamine, 2-benzylimidazole, 4-phenylimidazole, 2-phenyl-4-methylimidazole, 2- undecylimidazoline, 2,4,5-trifu ryl-2-imidazol ine, 2,4,5-trifuryl-2-imidazoline, 1 ,2-diphenyl-4, 4- dimethylimidazoline, 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, Zaminobenzothiazol, and 2benzoylhydrazinobenzothiazol.

The basic compound can be employed singly or in combination according to the purpose.

Examples of the binder employable in the preparation of the heat-sensitive recording layer include polyvinyl alcohol, methyicellulose, carboxymethylcellulose, hydroxypropylcellulose, gum arabic, gelatin, polyvinyl pyrrolidone, casein, styrene-butadiene latex, acrylonitrile-butadiene latex, polyvinyl acetate, polyacrylic acid ester, and ethylene-vinyl acetate copolymer. The binder compound can be employed in the form of an emulsion.

The binder can be employed in an amount (amount of solid) ranging from 0.5 to 5 g/m2 on the support.

The heat-sensitive recording layer can be formed by mixing and dispersing the diazo compound, a coupling component, a basic compound and a binder in an appropriate solvent by means of a mixing device such as atraiter, sand mill to prepare a coating solution (or dispersion), coating the coating solution (or dispersion) on a support using a known coating metod such as bar-coating, blade-coating, air knife-coating, gravurecoating, roll-coating, spray-coating, or dip-coating, and drying the coated layer.

The recording layer can be formed from the diazo compound enclosed in micro-capsules.

The preparation of micro-capsules containing the diazo compound can be accomplished by a known process. A brief description on the encapsulation process is given below.

The diazonium compound is first dissolved or dispersed in an apprpriate organic solvent, and the resulting solution or dispersion (in the form of oily liquid) is emulsified or dispersed in an aqueous solvent.

The organic solvent employed preferably has a boiling point of not lower than 180 C, because an organic solvent having a lower boiling point evaporates in the storage ofthe solution or dispersion. Examples ofthe organic solvent include phosphoric acid esters, phthalic acid esters, other carboxylic acid esters, fatty acid amides, alkylated biphenyls, alkylated terphenyls, chlorinated paraffins, and diarylethanes.

Subsequently, around the oil droplet formed by the emulsifying or dispersing the oil liquid is formed a shell of a polymer material. The polymer shell is formed utilizing a reactant(s) which is added to the oily liquid and/orthe aqueous solvent.

The capsule shell of the polymer material prevents permeation of the materials participating in the colorforming reaction therethrough at environmental temperatures and allows permeation of these compounds therethough when it is heated. Preferred are polymers having glass transition temperature in the range of 60 to 2000C. Preferred examples of the polymers include polyurethane, polyurea, polyamide, polyester, ureaformaldehyde resin, melamine resin, polystyrene, styrene-methacrylate copolymer, styrene-acrylate copolymer, and mixtures of these polymers.

Details with respectto the process forthe capsule formation and the reactants are described in United States Patents No. 3,726,804 and No.3,796,669. For instance, a micro-capsule having a polyureapolyurethane shell can be prepared by mixing polyisocyanate and other material (referred to as "second material", e.g., polyol or polyamir,e) capable of reacting with the polyisocyanate for the formation ofthe capsule shell in an aqueoussolventorin an oily liquid (which isto be also encapsulated within the shell), emulsifying or dispersing the resulting mixture to form oily droplets, and then heating the resulting emulsion to form the desired micro-capsule shell by polymerization of the reactants on the surface of the oily droplets.

The oily liquid can contain an auxiliary solvent having a low boiling point and high dissolving power. The second material can be omitted from the reactants to form a polyurea which is a reaction product of polyisocyanate and water.

In the formation of the micro-capsules, a water-soluble polymer serving as a protective colloid can be employed. Examples of the water-soluble polymer include water-soluble anionic polymers, water-soluble nonionic polymers and water-soluble amphoteric polymers. The water-soluble polymer can be employed in the form of an aqueous solution in which the polymer is contained in an amount ranging from 0.01 to 10wt.%.

In the binder solution employed for the formation of the heat-sensitive recording layer can contain a compound which is capable of increasing the color density of the image recording. Such compound may have a melting point in the range of 50 to 1 500C, preferably 90' to 1 300C, and is miscible or compatible with the diazo compound, the coupling compound orthe basic compound. Examples of such compounds include fatty amides, ketones, ethers, ureas and esters. Such compound may be divided to give particles having size in the range of 1 to 10 iim and may be incorporated into the layerto show a solid content in the range of 0.2 to 7 g/m2 over the support.

The heat-sensitive recording layer can contain fine particles such as pigments, for instance, kaolin, talc, silica, barium sulfate, titanium dioxide, aluminum hydroxide, zinc oxide and calcium carbonate or polymer beads such as styrene beads and beads of urea-melamine resin to prevent sticking to a thermal head or improve the writing property (i.e., easiness for receiving a writing material such as pencil or ink on the surface of the layer). For the prevention of sticking, a metal soap can be employed. These additives may be incorpora ted in the layer to show a content in the range of 0.2 to 7 g/m2 over the support.

A stabilizer such as citric acid, tartaric acid, oxalic acid, boric acid or phosphoric acid can be further incor porated into the recording layer.

The recording layer is generally so formed as to show a solid content in the range of 2.5 to 25 g/m2 overthe support.

There is no specific limitation with respect to the support. Any known support of the conventional heat sensitive recording material such as coated paper, synthetic paper or a polymerfilm can be employed accord- ing to the purpose. As the paper support, preferred is a neutral paper having a heat-extraction pH 6-9 (dis- closed in Japanese Patent Provisional Publication 55(1980)-14281) which is sized using a neutral sizing agent such as alkylketene dimer, because the neutral paper is very stable in the storage. Also employable are papers disclosed in Japanese Patent Provisional Publications No.57(1982)-116687, No 58(1983)-136492, No.58(1 983)-69091.

Examples of the present invention are given below with no intention to restrict the present invention. The "part(s)" hereinafter means "part(s) by weight", unless otherwise indicated.

Example 1 (1) In a vessel were placed 30.6 parts of p-2, 4-di-tert-amylphenoxybutanol, 16.5 parts of p nitrochlorobenzene, 21 parts of anhydrous potassium carbonate and 0.5 part of copper powder, and the vessel was heated in an oil bath at 1 800C for 30 min, for peforming a reaction. After the reaction was complete, the product was poured into water. The solid content was collected by filtration and extracted with ethyl acetate. The extract was washed with water and subjected to evaporation for removing ethyl acetate. There were obtained 36 parts of an oily product of j3-(2A-di-tert-amylphenoxy)butyloxy-4-nitrnphenylether.

(2)34 parts of the product obtained in the (1) above were reduced in methanol using hydrazinehydrateto obtain 31 parts of (3-(2A-di4ert-amylphenoxy)butyloxy-4-aminophenylether.

(3) 31 parts of t3-(2,4-di-tert-amylphenoxy)butyloxy-4-aminophenylether obtained in the (2) above were dissolved in 160 parts of methanol. To the resulting solution was added 18 parts of hydrochloric acid, and the solution was chilledto to 0 C. To the chilled solution were added 5.5 parts of sodium nitrite in water, keeping the temperature of the resulting solution lower than 00C. There was obtained a diazonium salt. To the solution containing the diazonium salt were added 14.4 parts of potassium hexafluorophosphate, and then the resulting mixture was kept at O"C for 2 hrs. under stirring. Thus precipitated crystals were collected by filtration and dried to obtain 35.7 parts of 4-(ss-(2,4-di-tert-amylphenoxy)butyloxy)benzenediazonium hexafluorophosphate.Yield 83 %.

Thus, the diazonium compound identified by (A) hereinbefore was prepared.

Example2 (1 In 150 parts of acetonitrile was dissolved a mixture of 26 parts of 2-ethylhexyl alcohol and 20.2 parts of triethylamine. The resulting solution was chilled to Oto 5 C. To the chilled solution were added 45.3 parts of p-nitrophenoxyacetate hydrochloride in acetonitrile, keeping the temperature of the resulting solution lower than 5"C. The reaction product was poured into water, and the content was extracted with ethyl acetate. The extract was washed with water and subjected to evaporation for removing ethyl acetate. There were obtained 56 parts of 2-ethylhexylester of p-nitrophenoxyacetic acid.

(2) The product (56 parts) obtained in the (1) above was treated in the same manner as in Example 1-(2)to obtain 41.8 parts of 2-ethyihexylesterof p-aminophenoxyacetic acid. Yield 98%.

(3) The product (41.8 parts) obtained in the (2) above was treated in the same manner as in Example 1 -(3) to obtain 56.9 parts of4-(2-ethylhexyloxycarbonylmethyloxy)benzenediazonium hexafluorophosphate. Yield 87%.

Thus, the diazonium compound identified by (H) hereinbeforewas prepared.

Example 3 (1)The procedures of Example 2-( 1) were repeated except that a mixture of 46.8 parts of t3-2, 4-di-tert- amylphenol and 21.2 parts oftriethylamine was dissolved in 200 parts of acetonitrile and that 45.2 parts of p-nitrophenoxyacetate hydrochloride were used. There were obtained70.5 parts of ss-2,4-di-tert- amylphenylester of p-nitrophenoxyacetic acid. Yield 85 %.

(2) The product (45.5 parts) obtained in the (1) above was treated in the same manner as in Example 1 -(2) to obtain 40.8 parts of #-2, 4-di-tert-amylphenylester of of p-aminophenoxyacetic acid. Yield 97 %.

(3) The product (38.4 parts) obtained in the (2) above was treated in the same manner as in Example 1-(3)to obtain 40.8 parts of 4-(2,4-di-tert-amylphenoxywarbonyimethyloxy)benzenediazonium hexafluorophosphate. Yield 76 %.

Thus, the diazonium compound identified by (J) hereinbefore was prepared.

The diazonium compounds (A), (H) and (J) obtained above were examined with respect to their properties (melting point and solubility) according to the conventional methods.

The results are setforth in Table 1.

Table 1 Diazo Melting Solubility Compound Point (C) in TCP (%) in Water (A) 145 13 Sparingly soluble (H) 71 40 Sparingly soluble (J) 110 30 Sparinglysoluble The solubility in TCP (tricresyl phosphate) was determined at 50 C (temperature of liquid).

As is apparent from the results shown in Table 1 the diazo compounds according to the invention have a melting point in the range of 60 - 150 C. This temperature range covers temperatures given to a heat-sensitive recording material by heat in the conventional recording process. Also apparent is that these compounds are highly soluble in an organicsolvent (TCP),while are sparingly soluble in water.

Example4 (1)20 parts ofthe diazonium compound (A) obtained in Example 1 [ 4-(,S-(2,4-di-tert- amylphenoxy)butyloxy)-benzenediazonium hexafluorophosphate] were added to 100 parts of aqueous polyvinyl alcohol solution (5wt.%solution), and the mixture was dispersed using a Dinomyl (tradename)to prepare a dispersion containing the diazo compound in the form of particles (mean particle size: 2,sum).

(2) To 100 parts of aqueous polyvinyl alcohol solution (5wt.% solution) were added 20 parts oftriphenylguanidine, and the mixture was dispersed using a Dinomyl (tradename) to prepare a basic compoundcontaining dispersion inwhichtriphenylguanidinewasdispersed in the form of particles (mean particle size: 3 > m).

(3) To 100 parts of aqueous polyvinyl alcohol solution (5wt.%soiution)wereadded 20 parts of 2-hydroxy-3naphthoanilide, and the mixture was dispersed using a Dinomyl (tradename) to prepare a coupling component-containing dispersion in which 2-hydroxy-3-naphthoanilidewas dispersed in the form of particles (mean particle size: 3 wm).

(4)To 0.4 part of hexamethaphosphoric acid in 60 parts of water were added 40 parts of calcium carbonate, and the mixture was dispersed using a Dynomyl to prepare a calcium carbonate-containing dispersion.

10 parts of the diazonium compound-containing dispersion, 10 parts of the basic compound-containing dispersion, 15 parts of the coupling component-containing dispersion, and 15 parts of the calcium carbonatecontaining dispersion, all having been prepared above, were mixed to prepare a coating dispersion.

The coating dispersion was coated on a coated paper having a smooth surface in an amount of 50 parts/m2, and dried at 40 C for 30 min. to prepare a heat-sensitive recording laye#r of 5 g/m2 (dry basis).

Thus, a heat-sensitive recording sheet containing the diazonium compound (A) dispersed in the layerwas prepared.

Example 5 The procedures of Example 4 were repeated except that the diazonium compound (A) was replaced with the diazonium compound (H) [ 4-(2-ethylhexyloxylcarbonyl-methyloxy)benzenediazonium hexafluorophosphate] to prepare a heat-sensitive recording sheet containing the diazonium compound (H) dis persed in the layer.

Example 6 The procedure of Example 4 were repeated except that the diazonium compound (A) was replaced with the diazonium compound (J) [ 4-(2,4-di-tert-amylphenoxycarbonylmethyloxy)benzenediazonium hexa fluorophosphate] to prepare a heat-sensitive recording sheet containing the diazonium compound (J) dis persed in the layer.

Evaluation of heat-sensitive recording sheet The heat-sensitive recording sheets prepared in the above examples were respectively employed for thermal recording in the following manner.

The heat-sensitive recording sheet was placed on a facsimile (Melfax-6200, tradename of Mitsubishi Electric Co.,Ltd., Japan) and a heated thermal head of the facsimile was applied onto the recording sheetto perform thermal recording. Clear red image was observed on each of the tested heat-sensitive recording sheets.

The heat-sensitive recording sheets thus having a recorded imagethereonwerefurtherexamined on the color density according to the following color density test.

Color density test The density (magenta density) of the colored image provided on each heat-sensitive recording sheet was measured from the side ofthe recording layer using Macbeth reflection densitometer (RD-91 8, tradename).

The results are set forth in Table 2.

Table2 Recording Sheet Color Density Example4 0.95 Example 5 1.05 Example 6 1.02 The results set forth in Table 2 apparently indicate that the heat-sensitive sheets containing the diazo compound of the formula (I) dispersed in the recording layer (Examples 4 - 6) according to the present invention give a color image density of recording at almostthe same level which is generally required for an acceptable heat-sensitive recording material.

The respective heat-sensitive recording sheets were separately examined with respect to the pre-use stabilit (resistance to humid, resistance to heat and resistance to light) according to the following test conditions.

Test for resistance to humid The heat-sensitive recording sheet was allowed to stand at 400C and 90%RH for 24 hours. The recording sheet was subsequently measured with respect to the color density on the surface in the same manner as above.

Test for resistance to heat The heat-sensitive recording sheet was allowed to stand at 600C and 30 %RH for 24 hours. The recording sheet was subsequently measured with respect to the color density on the surface in the same manner as above.

Test for resistance to heat The heat-sensitive recording sheet was exposed on the surface on the side of the recording layer to light of a fluorescent lamp (28,000 Lux)for 16 hours. The recording sheet was subsequently measured with respectto the color density on the surface in the same manner as above.

The results are all set forth in Table 3. In Table 3, the color density determined prior to the test is also set forth.

Table 3 Recording Priorto Resistance Resistance Resistance Sheet Test to Humid to Heat to Light Example4 0.08 0.11 0.14 0.12 Examples 0.09 0.12 0.14 0.12 Example6 0.09 0.12 0.12 0.11 The results setforth in Table 3 apparently indicate that the heat-sensitive sheets containing the diazo compound ofthe formula (I) dispersed in the recording layer (Examples 4-6) according to the present invention show satisfactory pre-use stability.

Example 7 (1)5.1 parts of the diazonium compound (A) obtained in Example 1 [ 4-(ss-(2,4-di-tert-amylphenoxy)- butyloxy) benzenediazonium hexafluorophosphate ] , 6 parts of tricrecyl phosphate, 12 parts of methylene chloride, 18 parts oftrimethylolpropanetrimethacrylateand 24 parts of polyisocyanate adduct (Takenate D-1 1 0N,tradename of Takeda Chemical Industries, Ltd., Japan) were mixed to prepare a solution (core mat- erial).

The resulting solution was added to an aqueous solution of 63 parts of aqueous polyvinyl alcohol (8wt.% solution) in 100 parts of distilled water, and emulsified and dispersed in the solution at 200C to obtain an emulsion containing oily droplets (mean size: 2 #m). The emulsion was stirred at40 Cfor3 hours, and then cooled to 20"C. Thus, a solution containing microcapsulseswhich enclosed in the shell the diazo compound (A) as the core material was obtained.

(2) To 124 parts of aqueous polyvinyl alcohol (6.7 wt.% solution) were added 42 parts oftriphenylguanidine, and the mixture was dispersed using a Dinomyl (tradename) to prepare a basiccompound-containing disper- sion in which triphenylguanidine was dispersed in the form of particles (mean particle size: 3 #m).

(3) To 138 parts of aqueous polyvinyl alcohol (4wt.% solution) were added 28 parts of 2-hydroxy-3naphthoanilide, and the mixturewas dispersed using a Dinomyl (tradename) to prepare a coupling component-containing dispersion in which 2-hydroxy-3-naphtoanilide was dispersed in the form of particles (mean particle size: 3,am).

10 parts of the microcapsule-containing dispersion, 10 parts of the basic compound-containing dispersion, 10 parts of the coupling component-containing dispersion, and 30 parts of the calcium carbonate-containing aqueous dispersion (40 wt.% dispersion) to prepare a coating dispersion.

The coating dispersion was coated on a coated paper having a smooth surface in an amount of 50 parts/m2, and dried at40"C for 30 minutes to prepare a heat-sensitive recording layer of 15 g/m2 on the support (dry basis).

Thus, a heat-sensitive recording sheet containing the encapsulated diazonium compound (A) dispersed in the layer was prepared.

Example 8 The procedures of Example 8 were repeated except that the diazonium compound (A) was replaced with the diazonium compound (H) [ 4-(2-ethylhexyloxylcarbonylmethyloxy)benzenediazonium hexafluorophosphate ] to prepare a heat-sensitive recording sheet containing the encapsulated diazonium compound (H) dispersed in the layer.

Example 9 The procedures of Example 7 were repeated except that the diazonium compound (A) was replaced with the diazonium compound (J) [ 4-(2,4-di-tert-amylphenoxycarbonylmethyloxy)benzenediazonium hexafluorophosphate] to prepare a heat-sensitive recording sheet containing the encapsulated diazonium compound (J) dispersed in the layer.

Evaluation of heat-sensitive recording sheet The heat-sensitive recording sheets prepared in the above examples were respectively employed for thermal recording in the following manner.

The heat-sensitive recording sheet was placed on the same facsimile as described hereinbefore and a heated thermal head ofthefacsimile was applied to the recording sheet. Clear red image was observed on each of the tested heat-sensitive recording sheets.

The heat-sensitive recording sheets thus having a recorded image thereon were further examined on the color density according to the color density test described hereinafter. Almost the same results as those set forth in Table 2 were given.

Therefore, it was confirmed that the heat-sensitive recording sheets (Examples 7 - 9) containing the en capsulated diazonium compound of the formula (I) dispersed in the layer showed almostthe same color density of recording, respectively, as that shown by the heat-sensitive recording sheets (Examples 4 - 6) containing the same diazonium compound simply dispersed in the recording layer.

The respective heat-sensitive recording sheets were separately examined with respect to the pre-use stability (resistance to humid, resistance to heat and resistance to light) according to the test conditions descri bed hereinbefore.

The results are all setforth in Table 4. In Table 4, the color density determined prior to the test is also set forth.

Table4 Recording Priorto Resistance Resistance Resistance Sheet Test to Humid to Heat to Light Example7 0.06 0.07 0.07 0.07 Example 8 0.06 0.07 0.07 0.07 Example 9 0.04 0.06 0.06 0.06 The results setforth in Table 4 apparently indicate that the heat-sensitive sheets containing the encapsula ted diazo compound of the formula (I) dispersed in the recording layer (Examples 7 - 9) according to the present invention show satisfactory pre-use stability.

Example 10 (1) The procedures of Example 7-(1 ) were repeated except thatthe diazonium compound (A) was replaced with a known diazo compound, 2,5-dibutoxy-4-morpholinobenzene-diazonium hexafluorophosphate, to prepare a microcapsule-containing solution in which a diazonium compound different from the diazo compound oftheformula (I) of the invention was encapsulated.

(2) The procedures of Example 7-(2) were repeated except that 2-hydroxy-3-naphthoanilide was replaced with m-xylenediaminebispivaloylacetamide to prepare a coupling component-containing dispersion.

5 parts ofthe microcapsule-containing solution obtained in the (1) above, 5 parts of the microcapsule containing solution obtained in Example 7-(1 ), 20 parts of the basic compound-containing dispersion, 10 parts of the coupling component-containing dispersion obtained in the (2) above, 10 parts of the coupling component-containing dispersion obtained in Example7-(2), and 40 parts of calcium carbonate-containing dispersion were mixed to give a coating solution.

The procedures of Example 7 were repeated exceptfor using the above coating solution to form a heatsensitive recording layer of 20 gIm2 on the support (dry basis). Thus, there was prepared a heat-sensitive recording sheet containing an encapsulated diazonium compound (A) of the invention as well as an encapsulated known diazonium compound.

Evaluation of heat-sensitive recording sheet The heat-sensitive recording sheet prepared in the above Example 10 was employed forthermal recording in the following manner.

The heat-sensitive recording sheet was placed on the same facsimile as described hereinbefore and a heated thermal head of the facsimile was applied to the recording sheet. Sharp black image was observed on the tested heat-sensitive recording sheet.

Thus tested heat-sensitive recording sheet was then irradiated with light (wavelength: 400 nm) for 6 min- utes and a heated thermal head of the facsimile was again applied to the irradiated recording sheet. Clear red image was observed on the heat-sensitive recording sheet.

The heat-sensitive recording sheet thus having a recorded image thereon was further examined on the color density according to the color density test described hereinbefore. Almost the same result (magenta color density: 1.02) as those set forth in Table 2 was given.

Therefore, it was confirmed that the heat-sensitive recording sheet (Example 10) containing the encapsula ted diazonium compound of the formula (I) as well as the encapsulated known diazo compound dispersed in the layer showed almost the same color density of recording, as that shown by the heat-sensitive recording sheets (Examples 4-6) containing the same diazonium compound simply dispersed in the recording layer.

The heat-sensitive recording sheet was separately examined with respect to the pre-use stability (resistance to humid, resistance to heat and resistance to light) according to the test conditions described herein before.

The results are all setforth in Table 5. In Table 5, the color density determined priorto the test is also set forth.

Table 5 Recording Priorto Resistance Resistance Resistance Sheet Test to Humid to Heat to Light Example 10 0.07 0.08 0.08 0.07 The results setforth in TableS apparently indicate that the heat-sensitive sheet containing the encapsulated diazo compound of the formula (I) as well as the encapsulated other diazonium compound dispersed in the recording layer (Example 10) according to the present invention show satisfactory pre-use stability.

Claims (4)

1. In a heat-sensitive recording material comprising a support and a heat-sensitive recording layerwhich is provided on the support and contains a diazo compound and a coupling component in the binder, the improvement wherein said heat-sensitive recording layer contains a diazo compound having the formula (I)

wherein R1 is a hydrogen atom, a group having 1-30 carbon atoms selected from those consisting of alkyl, alkenyl, aralkyl, aryl, acyl, acyloxy and ester which may be substituted, or a group selected from the group consisting of amido, carbamoyl, urethane, ureido, sulfone, oxysulfonyl, sulfonyloxy, sulfonamido and sul famoyl; each of R2 and R3 independently is a hydrogen atom or a group having 1-10 carbon atoms selected from those consisting of alkyl, alkenyl, aralkyl, alkloxy and aryloxy which may be substituted;R4 is a hydrogen atom, a halogen atom, a loweralkyl group, a loweralkoxygroup, a loweralkylestergroup ora lower alkylcarbamoyl group, R4 being the same or different from each other when mis 2 or more; X- is an acid anion;n isan integer of 1 to 18; and mis an integer of 1 to4.

2. The heat-sensitive recording material as claimed in claim 1, wherein the total number of carbon atoms contained in R', R2 and R3 oftheformula (I) ranges from 5to30.

3. The heat-sensitive recording material as claimed in claim 1, wherein the diazo compound having the formula (I) is contained in the heat-sensitive recording layer in an amount ranging from 0.02 to 2 g/m2.

4. The heat-sensitive recording material as claimed in claim 1, wherein the diazo compound having ghe formula (I) is encapsulated.