JPH08175020A - Thermal color former and thermal recording paper - Google Patents

Abstract

PURPOSE: To impart excellent image preservability, to show a developable hue from orange to red and to enable multi-coloration by using a thermal agent based on a specific imino compd. and a specific aromatic isocyanate compd. CONSTITUTION: The thermal agent contained in the color forming layer provided on the support of a thermal recording sheet is based on an imino compd. represented by formula I(A is C=O or C=NH, X is a substituent of which the σ-value of Hammet is +0.2 or less and n is an integer of 1-4) and an aromatic isocyanate compd. represented by formula II (Z is -CH2 -, -CHR-, -C- or -NH-, X1 and X2 are halogen, an alkyl group, an aryl group an alkoxyl group, hydroxyl group, etc., and a1 -c3 are an integer and satisfy specific relation). By using this imino compd., excellent image preservability is imparted and it is possible to express a hue from orange to red and multi-coloration can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive agent and a heat-sensitive recording sheet having excellent image storability. For more information,
The present invention relates to a heat-sensitive agent composed of an imino compound and an aromatic isocyanate compound, and a heat-sensitive recording sheet provided with a color forming layer containing these.

[0002]

2. Description of the Related Art In recent years, for example, in a variety of information devices such as facsimiles, printers, recorders, etc., a heat-sensitive recording system for recording by heat energy has been widely adopted. The mainstream of these recording methods is to use a recording sheet in which a color-forming layer containing a two-component chemical color-forming agent is provided on a support, and heat is applied as recording energy to this to form a color-forming agent component on the recording sheet. It is a method of recording colors by contacting each other. Among them, as a color former,
Many use leuco dyes and acidic substances.

Recording sheets using these conventionally known leuco dyes have a high whiteness, an appearance and a feeling close to those of plain paper.
It has many excellent characteristics such as good recording suitability such as color development sensitivity, and the thermal recording sheet has advantages such as small device size, maintenance-free and no noise generation. Applications have expanded to a wide range of fields such as facsimiles, printers, computer terminals, labels, ticket vending machines, and other vending machines. On the other hand, recording sheets using these leuco dyes are represented by, for example, a thermal paper (see US Pat. No. 3,539,375) having crystal violet lactone and 4,4′-isopropylidenediphenol (bisphenol A) as a coloring agent. As described above, since the recorded portion obtained by coloring has poor chemical resistance, the recording material is easily erased by contact with a plasticizer contained in a plastic sheet or an eraser or a chemical contained in food or cosmetics, In addition, since the light resistance of the recording portion is poor, the recording has a drawback that it is inferior in the storage stability of the record, such as fading or even disappearing of the recording by exposure to sunlight for a relatively short period of time. At present, the application is subject to certain restrictions, and its improvement is strongly desired.

As a heat-sensitive recording material capable of obtaining a recorded image having a good storability in response to such a demand, for example, Japanese Patent Laid-Open Publication No.
8-38733, JP-A-58-54085, JP-A-58-104959, JP-A-58-149388,
JP-A-59-115887, JP-A-59-11588
No. 8 and U.S. Pat. No. 4,521,793 disclose a recording sheet comprising a combination of a heat sensitive agent mainly containing an aromatic isocyanate and a heat sensitive agent mainly containing an imino compound. This heat-sensitive agent produces a colored product by a two-component contact reaction, and this colored product has excellent chemical resistance and light resistance. However, so far, JP-A-61-205
Many heat-sensitive agents having a purple hue such as those disclosed in Japanese Patent No. 183 and those having brown to purple hues close to this are known, but those showing red, orange, and yellow capable of multicolor recording. Is few.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a heat-sensitive agent which is excellent in image storability and has a hue capable of forming a color of orange to red, which enables multi-coloring in addition to a conventionally known coloring system. A heat-sensitive recording sheet using the heat-sensitive agent is provided.

[0006]

That is, the imino compound represented by the general formula (I) of the present invention (in the formula (I), A is C
═O or C═NH, and X represents a substituent having a Hammett σ value (para) of +0.2 or less. Also, n is 1
It represents an integer of 4 or more and 4 or less. When n is 2 or more, X may be different from each other. ) And an aromatic isocyanate compound represented by the general formula (II), and a heat-sensitive recording sheet in which the heat-sensitive agent is provided as a color-forming layer on a support.

[0007]

Embedded image

[0008]

[Chemical 4]

In formula (II), Z is --CH-- or --CR--.
(R is an alkyl group or an aryl group), -N-, -P-
Represents either X _{1 to} X ₃ are halogen, an alkyl group,
Aryl group, alkoxyl group, hydroxyl group, N, N
-Represents a dialkylamino group. a _{1 to} c ₃ are integers and satisfy the following relationships. 0 ≦ a ₁ , b ₁ , c ₁ ≦ 5, a ₁ + b ₁ + c ₁ = 50 0 ≦ a ₂ , b ₂ , c ₂ ≦ 5, a ₂ + b ₂ + c ₂ = 50 0 ≦ a ₃ , b ₃ , c ₃ ≦ 5, a ₃ + b ₃ + c ₃ = 5, where a ₁ + a ₂ + a ₃ ≠ 0 where 2 ≦ b ₁ , 2 ≦ b ₂ , and 2 ≦ b ₃ , X _{1 to} X ₃ are respectively They may be different from each other. A in formula (I)
Is preferably C = NH and X is a methyl group or a methoxy group.

The imino compound used in the present invention is 25
It is a colorless or pale compound that is solid at ℃. Examples of the substituent include an amino group, N-alkylamino group, N, N-dialkylamino group, N-arylamino group, N, N-diarylamino group, hydroxyl group, alkoxyl group,
Examples include a phenoxy group, an alkyl group, an aryl group, and a trialkylsilyl group. It is also possible to use two or more types of imino compounds in combination depending on the purpose. As a specific example, 1,
3-diimino-5-methylisoindolenin, 1,3-
Diimino-5-methoxyisoindolenine, 1,3-Diimino-5-phenoxyisoindolenine, 1,3-Diimino-5- (N, N-diethylamino) isoindolenine, 1,3-Diimino-5,6 -Dimethylisoindolenine, 1,3-diimino-5,6-dimethoxyisoindolenine, 1,3-diimino-5,6-di- (N, N
-Diethylamino) isoindolenine, 3-imino-5
-Methylisoindolenin-1-one, 3-imino-5
-Methoxyisoindolenin-1-one, 3-imino-
5- (N, N-diethylamino) isoindolenin-1
-One, 3-imino-5,6-dimethylisoindolenin-1-one, 3-imino-5,6-dimethoxyisoindolenin-1-one, 3-imino-5,6-di-
(N, N-diethylamino) isoindolenin-1-one and the like.

The aromatic isocyanate compound used in the present invention refers to a colorless or light-colored aromatic isocyanate compound which is solid at 25 ° C., and for example, one or more of the following isocyanate compounds are used. 4, 4 ',
4 ''-triisocyanatotriphenylamine, 4,
4 ', 4 "-triisocyanato-2-methoxytriphenylamine, 4,4', 4" -triisocyanato-
2,5-dimethoxytriphenylamine, 4,4 ′,
4 ″ -triisocyanato-2,2 ′, 5,5′-tetramethoxytriphenylamine and the like. These isocyanates may be used in the form of so-called block isocyanates, which are addition compounds with phenols, lantams, oximes, etc., if necessary, and uretdione which is a dimer of diisocyanate. , And isocyanurate which is a trimer, and may be used as a polyisocyanate adducted with various polyols.

The heat-sensitive recording sheet according to the present invention may contain a heat-fusible substance in order to improve its sensitivity. The melting point of the heat fusible substance is preferably 60 ° C to 180 ° C, particularly preferably 80 ° C to 140 ° C. As a specific example,
Benzyl p-benzyloxybenzoate, stearic acid amide, palmitic acid amide, N-methylol stearic acid amide, β-naphthylbenzyl ether, N-stearyl urea, N, N′-distearyl urea, β-naphthoic acid phenyl ester, 1-hydroxy-2-naphthoic acid phenyl ester, β-naphthol (p-methylbenzyl) ether, 1,4-dimethoxynaphthalene, 1
-Methoxy-4-benzyloxynaphthalene, N-stearoylurea, 4-benzylbiphenyl, 1,2-di (m-methylphenoxy) ethane, 1-phenoxy-2
Examples include-(4-chlorophenoxy) ethane, 1,4-butanediol phenyl ether, dimethyl terephthalate, metaterphenyl, dibenzyl oxalate, and oxalic acid (Pchlorobenzyl) ester.

The above-mentioned heat-fusible substances may be used alone or as a mixture, and in order to obtain a sufficient heat response, it is used in an amount of 10 to 300% by weight based on the aromatic isocyanate compound. It is more preferable to use 20 to 250% by weight. Further, the heat-sensitive recording sheet according to the present invention can contain an aniline derivative having at least one amino group, which is more effective in preventing background fog.

These compounds include methyl p-aminobenzoate, ethyl p-aminobenzoate, -n-propyl p-aminobenzoate and p-aminobenzoic acid-iso-.
Propyl, butyl p-aminobenzoate, dodecyl P-aminobenzoate, benzyl p-aminobenzoate, o-aminobenzophenone, m-aminoacetophenone, p-aminoacetophenone, m-aminobenzamide, o-aminobenzamide, p- Aminobenzamide, p-amino-N-methylbenzamide, 3-amino-4-methylbenzamide, 3-amino-4-methoxybenzamide, 3-amino-4-chlorobenzamide, p- (N-
Phenylcarbamoyl) aniline, p- [N- (4-chlorophenyl) carbamoyl] aniline, p- [N-
(4-Aminophenyl) carbamoyl] aniline, 2-
Methoxy-5- (N-phenylcarbamoyl) aniline, 2-methoxy-5- [N- (2'-methyl-3'-
Chlorophenyl) carbamoyl] aniline, 2-methoxy-5- [N- (2'-chlorophenyl) carbamoyl] aniline, 5-acetylamino-2-methoxyaniline, 4-acetylaminoaniline, 4- (N-methyl-N-). Acetylamino) aniline, 2,5-diethoxy-4- (N-benzoylamino) aniline, 2,5-dimethoxy-4- (N-benzoylamino) aniline, 2
-Methoxy-4- (N-benzoylamino) -5-methylaniline, 4-sulfamoylaniline, 3-sulfamoylaniline, 2- (N-ethyl-N-phenylaminosulfonyl) aniline, 4-dimethylamino Sulfonylaniline, 4-diethylaminosulfonylaniline, sulfathiazole, 4-aminodiphenylsulfone, 2-chloro-5-N-phenylsulfamoylaniline, 2-methoxy-5-N, N-diethylsulfamoylaniline, 2 , 5-Dimethoxy-4-N-phenylsulfamoylaniline, 2-methoxy-5-benzylsulfonylaniline, 2-phenoxysulfonylaniline, 2- (2'-chlorophenoxy) sulfonylaniline, 3-anilinosulfonyl-4. -Methylaniline, bis [4- (m-amido Phenoxy) phenyl] sulfone, bis [4-(p-aminophenoxy) phenyl] sulfone, bis [3-methyl-4-(p-aminophenoxy) phenyl] sulfone, 3,3'-dimethoxy-4,
4'-diaminobiphenyl, 3,3'-dimethyl-4,
4'-diaminobiphenyl, 2,2'-dichloro-4,
4'-diamino-5,5'-dimethoxybiphenyl,
2,2 ', 5,5'-tetrachloro-4,4'-diaminobiphenyl, ortho-tolidine sulfone, 2,4'-
Diaminobiphenyl, 2,2'-diaminobiphenyl,
4,4'-diaminobiphenyl, 2,2'-dichloro-
4,4'-diaminobiphenyl, 3,3'-dichloro-
4,4'-diaminobiphenyl, 2,2'-dimethyl-
4,4'-diaminobiphenyl, 4,4'-thiodianiline, 2,2 'dithiodianiline, 4,4'-dithiodianiline, 4,4'-diaminodiphenyl ether, 3,
3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, bis (3-amino-4-chlorophenyl) sulfone, bis (3,4-diaminophenyl) ) Sulfone, bis (4-aminophenyl) sulfone, bis (3-aminophenyl)
Sulfone, 3,4'-diaminodiphenyl sulfone,
3,3'-diaminodiphenylmethane, 4,4'-ethylenedianiline, 4,4'diamino-2,2'-dimethyldibenzyl, 4,4'-diamino-3,3'-dichlorodiphenylmethane, 3,3 ′ -Diaminobenzophenone, 4,4′-diaminobenzophenone, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4
-Aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 9,9-bis (4-aminophenyl) fluorene, 2,2-bis (4-aminophenoxyphenyl) propane, 4,4 ' -Bis (4-aminophenoxy) diphenyl, 3,3 ', 4,4'-tetraaminodiphenyl ether, 3,3', 4,4'-tetraaminodiphenyl sulfone, 3,3'4,4'-tetraamino Examples thereof include benzophenone.

Further, from the viewpoints of background fog and thermal responsiveness, N-stearyl-N '-(2-hydroxyphenyl) urea, N-stearyl-N'-(3-hydrococyphenyl) urea, N-stearyl. -N '-(4-hydroxyphenyl) urea, p-stearoylaminophenol, o-stearoylaminophenol, p-lauroylaminophenol, p-butyrylaminophenol, m-acetylaminophenol, o-acetylaminophenol, p -Acetylaminophenol, o-butylaminocarbonylphenol, o-stearylaminocarbonylphenol, p-stearylaminocarbonylphenol, 1,1,3-tris (3-tert.
-Butyl-4-hydroxy-6-methylphenyl) butane, 1,1,3-tris (3-tert.-butyl-4)
-Hydroxy-6-ethylphenyl) butane, 1,1,
3-tris (3,5-di-tert.-butyl-4-hydroxyphenyl) butane, 1,1,3-tris (3-
tert. -Butyl-4-hydroxy-6-methylphenyl) propane, 1,2,3-tris (3-tert.
-Butyl-4-hydroxy-6-methylphenyl) butane, 1,1,3-tris (3-phenyl-4-hydroxyphenyl) butane, 1,1,3-tris (3-cyclohexyl-4-hydroxy-5) -Methylphenyl) butane, 1,1,3-tris (3-cyclohexyl-4-hydroxy-6-methylphenyl) butane, 1,1,3-
Tetra (3-phenyl-4-hydroxyphenyl) propane, 1,1,3,3-tetra (3-cyclohexyl-)
4-hydroxy-6-methylphenyl) propane, 1,
1-bis (3-tert.-butyl-4-hydroxy-
It is also possible to add phenol compounds such as 6-methylphenyl) butane and 1,1-bis (3-cyclohexyl-4-hydroxy-6-methylphenyl) butane.

For the purpose of toning the image and improving the image density, a colorless or pale basic dye is used as the color developer and an inorganic or organic acid is used as the color developer, to the extent that the image storability is not impaired. A substance can also be used as a color-forming component. In this case, the color former and / or the developer can be contained in the layer containing the aromatic isocyanate compound and the aromatic imino compound, or can be provided as a separate layer.

Specific examples of the color former are shown below. (1) As a triarylmethane compound, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3,
3-bis (p-dimethylaminophenyl) phthalide, 3
-(P-Dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-methylindol-3-yl) phthalide, 3 -(P-Dimethylaminophenyl) -3- (2-phenylindol-3-yl) phthalide, 3,3-bis (1,2-dimethylindole-
3-yl) -5-dimethylaminophthalide, 3,3-bis (1,2-dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis (9-ethylcarbazole-3-) Yl) -5-dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl) -5-dimethylaminophthalide, 3-p-dimethylaminophenyl-3- (1-methylpyrrole-2) -Yl) -6-dimethylaminophthalide and the like.

(2) As a diphenylmethane compound,
4,4-bis-dimethylaminophenyl benzhydryl benzyl ether, N-halophenyl leuco auramine, N-2,4,5-trichlorophenyl leuco auramine and the like can be mentioned. (3) Rhodamine B anilinolactam, rhodamine B-p-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-octylaminofluorane, 3-diethylamino as xanthene compounds -7-phenylfluorane,
3-diethylamino-7-chlorofluorane, 3-diethylamino-6-chloro-7-methylfluorane, 3-
Diethylamino-7- (3,4-dichloroanilino) fluorane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3-diethylamino-6-methyl-
7-anilinofluorane, 3- (N-ethyl-N-tolyl) amino-6-methyl-7-anilinofluorane, 3
-Piperidino-6-methyl-7-anilinofluoran,
3- (N-ethyl-N-tolyl) amino-6-methyl-
7-phenethylfluorane, 3-diethylamino-7-
(4-nitroanilino) fluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3- (N-
Methyl-N-propyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamyl)
Amino-6-methyl-7-anilinofluorane, 3-
(N-Methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-
And tetrahydrofuryl) amino-6-methyl-7-anilinofluorane.

(4) Examples of thiazine compounds include benzoyl leuco methylene blue and p-nitrobenzoyl leuco methylene blue. (5) As a spiro compound, 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3,3-
Examples thereof include dichlorospirodinaphthopyran, 3-benzylspirodinaphthopyran, 3-methylnaphtho- (3-methoxybenzo) spiropyran, and 3-propylspirobenzopyran.

These color formers can be used alone or in combination of two or more kinds. As the developer, an electron-accepting substance generally used in thermal paper is used, and a phenol derivative, an aromatic carboxylic acid derivative or a metal compound thereof, an N, N-diarylthiourea derivative and the like are particularly preferable.
Particularly preferred are phenol derivatives. As a specific example, 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis (4-hydroxyphenyl) butane,
2,2-bis (4-hydroxyphenyl) pentane,
2,2-bis (4-hydroxyphenyl) heptane,
1,1-bis (4-hydroxyphenyl) cyclohexane, bis (4-hydroxyphenyl) butyl acetate, benzyl bis (4-hydroxyphenyl) acetate, bis (4-
Hydroxyphenyl) sulfone, bis (3-methyl-4)
-Hydroxyphenyl) sulfone, 4-hydroxyphenyl-4'-methylphenyl sulfone, 3-chloro-4
-Hydroxyphenyl-4'-methylphenyl sulfone, 3,4-dihydroxyphenyl-4'-methylphenyl sulfone, 4-isopropylphenyl-4'-hydroxyphenyl sulfone, 4-isopropyloxyphenyl-4'-hydroxyphenyl sulfone, Screw (2-
Allyl-4-hydroxyphenyl) sulfone, 4-hydroxyphenyl-4′-benzyloxyphenyl sulfone, 4-isopropylphenyl-4′-hydroxyphenyl sulfone, bis (2-methyl-3-tert.-butyl-4-hydroxy) Phenyl) sulfide, ethyl 4-hydroxybenzoate. Benzyl 4-hydroxybenzoate. 4-Hydroxybenzoic acid (4'-chlorobenzyl), 1,2-bis (4'-hydroxybenzoic acid) ethyl, 1,5-bis (4'-hydroxybenzoic acid) benzyl, 1,6 bis (4 ') Hexyl (hydroxybenzoic acid), dimethyl 3-hydroxyphthalate, stearyl gallate, lauryl gallate and the like.

In addition, diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, urea-formalin resin, etc. are contained in the heat-sensitive recording layer as pigments. You can also Also, for the purpose of preventing head wear and sticking, higher fatty acid metal salts such as zinc stearate and calcium stearate, paraffin,
Waxes such as paraffin oxide, polyethylene, polyethylene oxide, stearic acid amide, castor wax, dispersants such as sodium dioctyl sulfosuccinate, UV absorbers such as benzophenone and benzotriazole, surfactants, fluorescent dyes. Etc. can be contained as needed.

As the binder used in the heat-sensitive recording layer, various binders that are commonly used can be used. Examples of the binder include starches, hydroxyethyl cellulose, methyl cellulose,
Carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, acrylamide / acrylic acid ester copolymer, acrylamide / acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer Water-soluble binders such as alkali salts of ethylene, alkali salts of ethylene / maleic anhydride copolymers, etc., and water-insoluble latex systems such as styrene / butadiene copolymers, acrylonitrile / butadiene copolymers, methyl acrylate / butadiene copolymers Examples thereof include binders.

The heat-sensitive recording sheet according to the present invention comprises a support having thereon a heat-sensitive recording layer for color development by heating. Paper is mainly used as the support, but various woven fabrics, non-woven fabrics, synthetic resin films, laminated papers, synthetic papers, metal foils, or composite sheets in which these are combined are arbitrarily used in addition to the paper. be able to. The thermal recording layer may be composed of a single layer or plural layers. For example, each color-forming component may be contained in each layer to form a multi-layer structure. A protective layer composed of one or more layers may be provided on the thermosensitive recording layer, or an intermediate layer composed of one or more layers may be provided between the support and the thermosensitive recording layer. Good. This heat-sensitive recording layer can be obtained by mixing each aqueous dispersion obtained by finely pulverizing each color forming component or other component with a binder, coating on a support and drying.

[0024]

Example 1 2 g of 1,3-diimino-5-methylisoindolenin was dispersed and pulverized for 4 hours with a paint shaker together with 8 g of a 2.5 wt% polyvinyl alcohol aqueous solution,
Further, 2.5 g of a 15 wt% polyvinyl alcohol aqueous solution was added and dispersed for 15 minutes to obtain an aqueous dispersion. Separately 4,
4 ', 4''-triisocyanato-2,5-dimethoxytriphenylamine 2g 2.5g% polyvinyl alcohol aqueous solution 4g and 31% ethanol aqueous solution 4
g was dispersed and pulverized for 4 hours with a paint shaker, and 2.5 g of a 15% by weight polyvinyl alcohol aqueous solution was further added and dispersed for 15 minutes to obtain an aqueous dispersion. In addition, 2 g of 2-benzyloxynaphthalene was dispersed and pulverized with a paint shaker for 4 hours together with 8 g of a 2.5 wt% polyvinyl alcohol aqueous solution, and 2.5 g of a 15% wt polyvinyl alcohol aqueous solution was further added and dispersed for 15 minutes to obtain an aqueous dispersion. Got Further, 2-methoxy-3-N, N-diethylsulfamoylaniline (2 g) was dispersed and pulverized with a paint shaker for 4 hours together with a 2.5% by weight polyvinyl alcohol aqueous solution (8 g). In addition, the mixture was dispersed for 15 minutes to obtain an aqueous dispersion.

2.5 g of calcium carbonate 2 g by weight
An aqueous polyvinyl alcohol solution (8 g) was dispersed and pulverized with a paint shaker for 4 hours, and 15% by weight aqueous polyvinyl alcohol solution (2.5 g) was added and dispersed for 15 minutes to obtain an aqueous dispersion. These dispersions were mixed with 1,3-diimino-5
-Methyl isoindolenin dispersion 0.75 g, 4,
0.5 g of 4 ′, 4 ″ -triisocyanato-2,5-dimethoxytriphenylamine dispersion, 1 g of 2-benzyloxynaphthalene dispersion, 2-methoxy-3-N, N-
A coating liquid was obtained by mixing 1 g of diethylsulfamoylaniline dispersion liquid, 2.5 g of calcium carbonate dispersion liquid, and 0.75 g of zinc stearate dispersion liquid having a solid content concentration of 16% by weight with stirring. This solution was coated on a base paper having a weight of 50 g / m ² with a bar coater with a rod number of 16 and dried and then processed with a super calendar to obtain a heat sensitive recording sheet. The sensitivity was evaluated using a printing tester manufactured by Okura Electric Co., Ltd., and a thermal head was printed using KJT-256-8MGF1 manufactured by Kyocera with an applied voltage of 24 V and a pulse width of 1.3 ms.
The print density was measured with a Macbeth densitometer RS917. The print density was 0.45 and the color tone was reddish orange.

[0026]

Example 2 A heat-sensitive recording sheet as in Example 1 except that 1,3-diimino-5-methylisoindolenin was replaced by 1,3-diimino-5-methoxyisoindolenine. It was created. When the sensitivity was measured under the same conditions as in Example 1, the print density was 0.45 and the color tone was reddish orange.

[0027]

Example 3 In place of 4,4 ′, 4 ″ -triisocyanato-2,5-dimethoxytriphenylamine of Example 1, 4,4 ′, 4 ″ -triisocyanatotriphenylamine was used. A heat-sensitive recording sheet was prepared in the same manner as in Example 1 except that it was used. When the sensitivity was measured under the same conditions as in Example 1, the print density was 0.4 and the color tone was reddish orange.

[0028]

Example 4 In place of 4,4 ′, 4 ″ -triisocyanato-2,5-dimethoxytriphenylamine of Example 2, 4,4 ′, 4 ″ -triisocyanatotriphenylamine was used. A thermosensitive recording sheet was prepared in the same manner as in Example 2 except that it was not used. When the sensitivity was measured under the same conditions as in Example 2, the print density was 0.4 and the color tone was reddish orange.

[0029]

[Comparative Example 1] Example 1 was repeated except that 4,5,6,7-tetrachloro-1,3-diiminoisoindolenine was used in place of 1,3-diimino-5-methylisoindolenine of Example 1. A thermal recording sheet was prepared in the same manner as in Example 1. Example 1
When the sensitivity was measured under the same conditions as above, the print density was 1.2 and the color tone was magenta. The results of these Examples and Comparative Examples are summarized in Table 1.

[0030]

[Table 1]

[0031]

EFFECTS OF THE INVENTION Hammett σ value (para) is +0.2
By using the imino compound having the following substitution machine, compared with the conventional heat-sensitive agent and heat-sensitive recording material comprising an imino compound and an isocyanate compound, storage stability can be obtained, and an orange to red coloring hue can be obtained. .

Claims (3)

[Claims] 1. An imino compound represented by the general formula (I) (in the formula (I), A represents C═O or C═NH, and X is a substitution having a Hammett σ value (para) of +0.2 or less. Represents a group, and n represents an integer of 1 or more and 4 or less, and when n is 2 or more, X may be different from each other) and the general formula (I
A heat-sensitive agent which is mainly composed of an aromatic isocyanate compound represented by I). Embedded image Embedded image In formula (II), Z represents any one of -CH-, -CR- (R is an alkyl group or an aryl group), -N-, and -P-. X _{1 to} X ₃ represent a halogen, an alkyl group, an aryl group, an alkoxyl group, a hydroxyl group or an N, N-dialkylamino group. a _{1 to} c ₃ are integers and satisfy the following relationships. 0 ≦ a ₁ , b ₁ , c ₁ ≦ 5, a ₁ + b ₁ + c ₁ = 50 0 ≦ a ₂ , b ₂ , c ₂ ≦ 5, a ₂ + b ₂ + c ₂ = 50 0 ≦ a ₃ , b ₃ , c ₃ ≦ 5, a ₃ + b ₃ + c ₃ = 5, where a ₁ + a ₂ + a ₃ ≠ 0 where 2 ≦ b ₁ , 2 ≦ b ₂ , and 2 ≦ b ₃ , X _{1 to} X ₃ are respectively They may be different from each other. 2. A heat-sensitive recording sheet having a heat-sensitive agent containing the imino compound according to claim 1 and an aromatic isocyanate compound as a color-forming layer on a support. 3. The heat-sensitive agent according to claim 1, wherein A in the formula (I) is C═NH and X is a methyl group or a methoxy group.