JPH0692024A - Thermal recording - Google Patents

Abstract

(57) [Summary] [Purpose] The recording sensitivity of a recording layer containing a colorless or light-colored basic dye and a coloring agent on a support or a thermal recording medium having a protective layer formed on the recording layer. An excellent colored thermosensitive recording medium is provided. The present invention provides a recording layer containing a colorless or light-colored basic dye and a coloring agent on a support, or a thermosensitive recording medium provided with a protective layer on the recording layer.
Alternatively, as a colorant in the protective layer, 1- (4'-sulfo-
1'-naphthylazo) -2-naphthol-3,6-disulfonic acid, 1- (4'-sulfo-1'-naphthylazo)
-2-Naphthol-3,6-disulfonic acid, 1- (p-
Sulfophenylazo) -2-naphthol-6,8-disulfonic acid, 3-carboxy-5-hydroxy-1- (p
-Sulfophenyl) -4- (p-sulfophenylazo)
A thermosensitive recording medium containing at least one of pyrazole and a sodium salt, potassium salt, or ammonium salt of 5,5'-indigotin disulfonic acid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material colored with a coloring agent.

[0002]

2. Description of the Related Art A thermosensitive recording medium is known, in which a reaction between a colorless or light-colored basic dye and a color-forming agent is utilized to bring both color-forming substances into contact with each other by heat to obtain a recorded image. Such a thermosensitive recording medium is relatively inexpensive, and the recording device is compact and maintenance-free, so that it is used in a wide range of fields. For example, as one of its fields of use, colored thermal recording materials for labels and posters are used. Conventionally, as a method for obtaining a colored heat-sensitive recording material, a method of adding a coloring agent such as an organic or inorganic colored pigment, a water-soluble acidic dye, a basic dye or a direct dye into a recording layer or a protective layer has been disclosed. 61-134292, JP-A-1-105778, JP-A 1-114.
No. 480, gazette. However, since the coating liquid for forming the recording layer and the protective layer contains a thermally unstable heat-soluble substance, the mechanical stability of the coating liquid (when the coating liquid is added by a stirrer, etc. Stability) is low, especially
A coating liquid for forming a recording layer and a protective layer of a heat-sensitive recording material using a dye-based coloring agent excellent in coloring ability has an agglomerate generated in the coating due to a decrease in its thermal stability, resulting in a decrease in recording sensitivity. Invited. Therefore, there has been a demand for a colored thermosensitive recording medium that causes little reduction in recording sensitivity.

[0003]

A recording layer containing a colorless or light-colored basic dye and a coloring agent on a support, or a thermosensitive recording medium provided with a protective layer on the recording layer, has a high recording sensitivity. An object is to provide an excellent colored thermosensitive recording medium.

[0004]

In view of the present situation, the present inventors have aimed to obtain a colored thermosensitive recording medium having excellent recording sensitivity.
As a result of extensive studies, a recording layer containing a colorless or light-colored basic dye and a coloring agent on a support, or a thermosensitive recording medium having a protective layer formed on the recording layer, was used in the recording layer and / or Alternatively, 1- (4'-sulfo-1'-naphthylazo) -2-naphthol-3,6 as a colorant in the protective layer
-Disulfonic acid, 1- (4'-sulfo-1'-naphthylazo) -2-naphthol-3,6-disulfonic acid, 1-
(P-Sulfophenylazo) -2-naphthol-6,8
-Disulfonic acid, 3-carboxy-5-hydroxy-1
-(P-sulfophenyl) -4- (p-sulfophenylazo) pyrazole and 5,5'-indigotin disulfonic acid by incorporating at least one compound consisting of sodium salt, potassium salt, or ammonium salt, The inventors have found that the above problems can be solved and have completed the present invention.

[0005]

The present invention provides a recording layer containing a colorless or light-colored basic dye and a coloring agent on a support, or a thermosensitive recording medium having a protective layer formed on the recording layer, and / or in the recording layer. By adding the above-mentioned specific colorant to the protective layer, a recording layer coating material and a protective layer coating material having excellent thermal stability can be obtained. The reason why the specific colorant is different from the conventional colorant and improves the thermal stability of the recording layer coating material and the protective layer coating material is not necessarily clear, but the specific colorant has a hydrophobic structure in the molecular structure. Since it has phenyl as a group and has two or more sulfone groups as a hydrophilic group, it is considered to promote electrical stabilization especially to the heat-soluble organic finely ground product in the coating material. The amount of the specific colorant used is not particularly limited, but it is desirable to adjust the maximum optical density in the visible light region on the recording surface side within a range of 0.2 to 1.2.

As the colorless or light-colored basic dye constituting the heat-sensitive recording layer, various known dyes can be used, and specific examples thereof include the following. 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 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, 3,3-bis (1,2-dimethylindol-3-yl) -5-dimethylaminophthalide, 3,3-bis (1,2-dimethylindol-3-yl) ) -6-Dimethylaminophthalide, 3,3-bis (9-ethylcarbazol-3-yl) -6-dimethylaminophthalide, 3,3-bis (2
-Phenylindol-3-yl) -6-dimethylaminophthalide, 3-p-dimethylaminophenyl-3-
(1-Methylpyrrol-3-yl) -6-dimethylaminophthalide, 3,3-bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl) ethylene-
2-yl] -4,5,6,7-tetrachlorophthalide,
Triallylmethane dyes such as 3,3-bis [1,1-bis (4-hydridinophenyl) ethylene-2-yl] -4,5,6,7-tetrabromophthalide, 4,4′-
Bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leuco auramine, N-2,
Diphenylmethane dyes such as 4,5-trichlorophenylleuco auramine, benzoyl leuco methylene blue, thiazine dyes such as p-nitrobenzoyl leuco methylene blue, 3-methyl-spiro-dinaphthopyran,
3-ethyl-spiro-dinaphthopyran, 3-phenyl-
Spiro dyes such as spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho (6'-methoxybenzo) spiropyran, 3-propyl-spiro-dibenzopyran, rhodamine-B-anilinolactam, rhodamine ( Lactam dyes such as p-nitroanilino) lactam and rhodamine (o-chloroanilino) lactam, 3-dimethylamino-7-methoxyfluorane, 3-diethylamino-6-methoxyfluorane, 3
-Diethylamino-7-methoxyfluorane, 3-diethylamino-7-chlorofluorane, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6. 7-Dimethylfluorane, 3- (N-ethyl-p-toluidino) -7-methylfluorane, 3-diethylamino-7-N-acetyl-N-methylaminofluorane, 3-diethylamino-7-N-methyl Aminofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-N-methyl-N
-Benzylaminofluorane, 3-diethylamino-7
-N-chloroethyl-N-methylaminofluorane, 3
-Diethylamino-7-N-diethylaminofluorane, 3- (N-ethyl-p-toluidino) -6-methyl-7-phenylaminofluorane, 3- (N-ethyl-)
p-toluidino) -6-methyl-7- (p-toluidino) fluorane, 3-dimethylamino-6-methyl-7
-Phenylaminofluorane, 3-diethylamino-6
-Methyl-7-phenylaminofluorane, 3-di (n
-Butyl) amino-6-methyl-7-phenylaminofluorane, 3-di (n-pentyl) amino-6-methyl-7-phenylaminofluorane, 3-diethylamino-7- (2-carbomethoxy-phenyl Amino) fluorane, 3- (N-cyclohexyl-N-methylamino)
-6-Methyl-7-phenylaminofluorane, 3-pyrrolidino-6-methyl-7-phenylaminofluorane, 3-piperidino-6-methyl-7-phenylaminofluorane, 3-diethylamino-6-methyl- 7-Xylidinofluorane, 3-diethylamino-7- (o-
Chlorophenylamino) fluorane, 3-di (n-butyl) amino-7- (o-chlorophenylamino) fluorane, 3-pyrrolidino-6-methyl-7-p-butylphenylaminofluorane, 3- (N-methyl-). N-n-
Amyl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-Nn-amyl) amino-
6-methyl-7-phenylaminofluorane, 3- (N
-Ethyl-N-isoamyl) amino-6-methyl-7-
Phenylaminofluorane, 3- (N-methyl-Nn)
-Hexyl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-Nn-hexyl) amino-6-methyl-7-phenylaminofluorane, 3
-(N-ethyl-N-β-ethylhexyl) amino-6
-Methyl-7-phenylaminofluorane, 3- (N-
Ethyl-N-tetrahydrofurfuryl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-N-cyclopentyl) amino-6-methyl-7-phenylaminofluorane, 2,2-bis {4- [6'-
(N-Cyclohexyl-N-methylamino) -3'-methylspiro (phthalide-3,9'-xanthene) -2 '
Fluorane dyes such as -ylamino] phenyl} propane. Of course, it is not limited to these dyes,
A combination of two or more dyes is also possible.

Various known compounds can be used as the color-forming agent constituting the heat-sensitive recording layer, and specific examples are given below. 4-tert-butylphenol, α-naphthol, β
-Naphthol, 4-acetylphenol, 4-tert-octylphenol, 4,4'-sec-butylidene diphenol, 4-phenylphenol, 4,4'-dihydroxy-diphenylmethane, 4,4'-isopropylidenediphenol, hydroquinone , 4,4'-cyclohexylidene diphenol, 4,4 '-(1,3-dimethylbutylidene) bisphenol, 4,4'-dihydroxydiphenyl sulfide, 4,4'-thiobis (6-te
rt-butyl-3-methylphenol), 4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-
Methyldiphenyl sulfone, 4-hydroxy-4'-methoxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-
3 ', 4'-trimethylene diphenyl sulfone, 4-hydroxy-3', 4'-tetramethylene diphenyl sulfone, 3,4-dihydroxy-4'-methyldiphenyl sulfone, bis (3-allyl-4-hydroxyphenyl) Sulfone, 1,3-di [2- (4-hydroxyphenyl) -2-propyl] benzene, 1- [α-methyl-
α- (4′-hydroxyphenyl) ethyl] -4-
[Α ', α'-bis (4'-hydroxyphenyl) ethyl] benzene, hydroquinone monobenzyl ether, bis (4-hydroxyphenyl) acetic acid butyl ester, 4
-Hydroxybenzophenone, 2,4-dihydroxybenzophenone, 2,4,4'-trihydroxybenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, Ethyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, sec-butyl 4-hydroxybenzoate, pentyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, 4-hydroxybenzoic acid. Trill,
Chlorophenyl 4-hydroxybenzoate, phenylpropyl 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, p-chlorobenzyl 4-hydroxybenzoate, p-methoxybenzyl 4-hydroxybenzoate, novolac phenolic resin, phenol Phenolic compounds such as polymers, benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-sec
-Butyl-4-hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-
Hydroxybenzoic acid, salicylic acid, 3-isopropylsalicylic acid, 3-tert-butylsalicylic acid, 3,5-di-
tert-butylsalicylic acid, 3-benzylsalicylic acid, 3
-(Α-Methylbenzyl) salicylic acid, 3-chloro-5
-(Α-methylbenzyl) salicylic acid, 3-phenyl-
5- (α, α-dimethylbenzyl) salicylic acid, 3,5
-Aromatic carboxylic acids such as di-α-methylbenzyl salicylic acid, and salts of these phenolic compounds and aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin and nickel Organic acidic substances such as. In addition, the above color developing agent also
Of course, two or more kinds can be used in combination as required.

The use ratio of the basic dye and the color developing agent should be appropriately selected according to the type of the basic dye or the color developing agent to be used and is not particularly limited, but the basic dye 1 is generally used.
About 100 to 700 parts by weight, preferably about 150 to 400 parts by weight, of the coloring agent is used with respect to 00 parts by weight.

The thermosensitive recording medium of the present invention may use a heat-fusible substance in the recording layer in order to adjust the recording sensitivity. Specific examples thereof include fatty acid amides such as stearic acid amide, stearic acid methylene bisamide, stearic acid ethylene bisamide, oleic acid amide, palmitic acid amide and coconut fatty acid amide, 4,4′-
Butylidene bis (6-tert-butyl-3-methylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-tertbutylphenyl) butane, 1,13
-Hindered phenols such as tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane,
p-benzylbiphenyl, p- (4-trioxy) biphenyl, 1,5-bis (4-methoxyphenoxy) -3
-Oxa-pentane, 1,2-bis (phenoxy) ethane, 1,2-bis (4-methylphenoxy) ethane,
1,2-bis (3-methylphenoxy) ethane, 1-
Ethers such as (2-methylphenoxy) -2- (4-methoxyphenoxy) ethane and 2-naphtholbenzyl ether, dibenzyl terephthalate, 1-hydroxy-2-naphthoic acid-phenyl ester, oxalic acid dibenzyl ester, shu Esters such as acid di (4-methylbenzyl) ester, oxalic acid di (4-chlorobenzyl) ester, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2-hydroxy-4-benzyloxy An ultraviolet absorber such as benzophenone, and various other heat-fusible substances can be appropriately used together as a sensitizer.

Among the various heat-fusible substances as mentioned above, 1,2-bis (phenoxy) ethane and 1,2-bis (phenoxy) ethane are particularly preferable.
Since bis (3-methylphenoxy) ethane has a low melt viscosity, it is possible to obtain a high-sensitivity heat-sensitive recording material having excellent device characteristics when used in combination. The amount of the heat-fusible substance contained in the recording layer is not necessarily limited, and is generally 50% with respect to 100 parts by weight of the basic dye.
To 500 parts by weight, preferably about 100 to 300 parts by weight.

A coating liquid for forming a recording layer containing these is generally prepared using water as a dispersion medium and a dye, a coloring agent, the above-mentioned specific colorant and the like by a stirring and crushing machine such as a ball mill, an attritor or a sand mill. Dispersed together or separately,
It is prepared by mixing and stirring them.

In such coating liquid, starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, carboxy group-modified polyvinyl alcohol, sulfo group-modified polyvinyl alcohol, acetoacetyl group-modified are usually used as binders. Polyvinyl alcohol, various modified polyvinyl alcohol such as silicone modified polyvinyl alcohol, styrene / maleic anhydride copolymer salt, styrene / acrylic acid copolymer salt, styrene / butadiene copolymer emulsion, etc.
-40% by weight, preferably about 5-25% by weight. Of course, two or more kinds of these binders can be used together.

Further, various auxiliaries can be added to the coating liquid, for example, dioctylsulfosuccinic acid sodium salt, dodecylbenzenesulfonic acid sodium salt,
Examples thereof include dispersants such as lauryl alcohol sulfate / sodium salt and fatty acid metal salt, and other defoaming agents.

In order to improve the adhesion of dust to the recording head, inorganic pigments such as kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, fine anhydrous silica and activated clay, styrene microballs are used. , Nylon powder, polyethylene powder, urea
Organic pigments such as formalin resin fillers and starch particles can also be added. Further, it is possible to add, for example, a dispersion liquid or emulsion of stearic acid, polyethylene, carnauba wax, paraffin wax, zinc stearate, calcium stearate, ester wax or the like so that sticking does not occur due to contact with a recording device or a recording head. it can.

Examples of the water-soluble or water-dispersible polymer used for forming the protective layer provided on the recording layer of the present invention include various binders used in the recording layer as described above. The group-modified polyvinyl alcohol and the carboxyl group-modified polyvinyl alcohol are particularly preferably used for forming a strong resin film.

In the protective layer, a pigment may be added as necessary in order to further improve printability and sticking, and specific examples thereof include kaolin, clay, talc, calcium carbonate, calcined clay, Examples thereof include inorganic pigments such as titanium oxide, diatomaceous earth, fine particulate anhydrous silica, and activated clay, and organic pigments such as styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, and starch particles. It is generally desirable to adjust the amount used in the range of about 5 to 500% by weight based on the resin component.

In the coating solution for forming the protective layer, if necessary, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, and ester wax, surfactants such as sodium dioctylsulfosuccinate, and a detergent are used. Various auxiliaries such as foaming agents can also be added as appropriate. Furthermore, in order to further improve the water resistance, a water resistant agent such as glyoxal, boric acid, borax, dialdehyde starch, or an epoxy compound can be added. The protective layer coating liquid is prepared by stirring and dispersing an aqueous dispersion solution containing the above binder, an auxiliary agent and the like.

In the heat-sensitive recording material of the present invention, the method of forming the recording layer and the protective layer is not particularly limited, and various known methods can be appropriately used. For example, it is formed by coating and drying a coating liquid for forming a recording layer on a support with an appropriate coating device such as an air knife coater, a blade coater, a bar coater, a gravure coater and a curtain coater.

The coating amount of the coating liquid is not particularly limited, but the dry weight of the recording layer is adjusted in the range of 1.0 to 12 g / m ² , preferably 1.5 to 7 g / m ² . The dry weight of the protective layer is 0.1 to 15 g / m.
² , preferably in the range of 0.5 to 7 g / m ² . As the support, paper, plastic film,
Synthetic paper or the like is used, but paper is most preferably used in terms of cost and coating suitability.

If necessary, a protective layer may be provided on the back side of the thermosensitive recording medium to further improve the storability. Furthermore, providing an undercoat layer between the support and the recording layer,
If necessary, various known techniques in the field of heat-sensitive recording material production, such as forming an adhesive layer on the back surface of the heat-sensitive recording material and processing it into an adhesive label, can be added.

[0021]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In addition, unless otherwise indicated, the part and% in an example show a weight part and weight%, respectively.

Examples 1 to 5 and Comparative Examples 1 to 5 Formation of undercoat layer Baked clay (trade name: Ansilex, manufactured by EMC) 100 parts Styrene-butadiene copolymer latex (solid content: 50%) 15 parts 10 % Polyvinyl alcohol aqueous solution 30 parts water 200 parts An undercoat layer coating solution prepared by mixing and stirring the above composition is applied to a high-quality paper of 50 g / m ² at a coating amount of 10 g after drying.
/ M ² and comprising as coating and dried to form an undercoat layer.

Preparation of solution A 3-di (n-butyl) amino-6-methyl-7-phenylaminofluorane 10 parts 1,2-bis (3-methylphenoxy) ethane 25 parts 5% aqueous methylcellulose solution 30 parts water 20 parts This composition was ground with a sand mill until the average particle size was 0.8 μm.

Preparation of Solution B 4,4′-isopropylidenediphenol 30 parts 5% aqueous solution of methylcellulose 30 parts water 70 parts This composition was ground with a sand mill until the average particle size became 1.4 μm.

Formation of Recording Layer 85 parts of liquid A, 130 parts of liquid B, silicon oxide pigment (oil absorption 18
0 ml / 100g) 7 parts, light calcium carbonate (oil absorption 90 ml / 100g) 8 parts, polyvinyl alcohol 2
50 parts of 0% aqueous solution, 15 parts of 30% aqueous zinc stearate dispersion, 10 parts of water, and column A of Table 1 (Examples 1 to 1).
8) and the colorants shown in columns B (Comparative Examples 1 to 6) were measured with a Macbeth densitometer (RD 914 type), the optical density corresponding to the colorant in the unrecorded portion of the thermosensitive recording medium was about 0.5. Were added and stirred to obtain coating materials for each recording layer. The obtained coating material for each recording layer was applied on the undercoat layer in a dry coating amount of 4.5 g.
A thermal recording material was obtained by coating and drying so as to be / m ² .

Examples 6 to 10, Comparative Examples 6 to 10 Preparation of C liquid 3-di (n-butyl) amino-6-methyl-7-phenylaminofluorane 10 parts 2-naphthylbenzyl ether 25 parts 5% methylcellulose Aqueous solution 30 parts Water 20 parts This composition was ground by a sand mill until the average particle size became 0.8 μm.

Preparation of Solution D 4-Hydroxy-4′-isopropoxydiphenyl sulfone 30 parts 5% aqueous solution of methylcellulose 30 parts water 70 parts This composition was ground by a sand mill until the average particle size became 1.4 μm.

Formation of Recording Layer 85 parts of C liquid, 130 parts of D liquid, light calcium carbonate 35
Parts, 80 parts of a 20% aqueous solution of polyvinyl alcohol, and 80 parts of water were mixed and stirred to obtain a coating liquid for recording layer. The resulting coating liquid was applied onto the undercoat layer so that the dry coating amount was 6 g / m ^2, and dried to form a recording layer.

Formation of Protective Layer Acetoacetyl group-modified polyvinyl alcohol [trade name:
Gocefimer Z-200, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.]
200 parts of 0% aqueous solution, 20 parts of 30% aqueous dispersion of zinc stearate, kaolin [trade name: UW-90, manufactured by EMC] 60 parts, water 140 parts, and column A of Table 2 (Example 9). .About.16) and the colorants shown in columns B (Comparative Examples 7 to 12) were measured with a Macbeth densitometer [RD 914 type, manufactured by Macbeth Co.], the optical density corresponding to the colorant in the unrecorded portion of the thermosensitive recording medium was measured. Was added and stirred to obtain each protective layer coating material. The resulting protective layer coating material was applied onto the recording layer so that the coating amount after drying was 6 g / m ^2, and dried to obtain a thermosensitive recording medium having a protective layer.

With respect to the 20 kinds of heat-sensitive recording materials thus obtained, the color density of the unrecorded area and the heat-sensitive recording evaluation machine [TH-P
MD, manufactured by Okura Electric Co., Ltd., and applied energy 0.26
The recording density of the recorded image obtained by recording at mJ / dot was measured with a Macbeth densitometer, and the results are shown in [Table 1] and [Table 2].

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

As is apparent from the results of [Table 1] and [Table 2], the thermosensitive recording materials obtained in the respective examples of the present invention were colored thermosensitive recording materials having excellent recording sensitivity.

Claims (1)

[Claims] 1. A thermosensitive recording medium comprising a support containing a colorless or light-colored basic dye and a coloring agent on a support, or a protective layer provided on the recording layer. As a colorant in the layer, 1- (4'-sulfo-1'-
Naphthylazo) -2-naphthol-3,6-disulfonic acid, 1- (4'-sulfo-1'-naphthylazo) -2-
Naphthol-3,6-disulfonic acid, 1- (p-sulfophenylazo) -2-naphthol-6,8-disulfonic acid, 3-carboxy-5-hydroxy-1- (p-sulfophenyl) -4- ( A heat-sensitive recording material comprising at least one compound comprising p-sulfophenylazo) pyrazole and 5,5'-indigotindisulfonic acid sodium salt, potassium salt, or ammonium salt.