JPH10278431A - Heat-sensitive recording body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a recording part in black from a low density to a high density, by adding into a heat-sensitive recording layer containing a leuco dye and a colorant at least a specific leuco dye B to a specific leuco dye A by a specific ratio, and using the leuco dyes A and B of a specific absolute value of a difference of melting points. SOLUTION: At least a leuco dye B generating a red color which is expressed by a formula II (wherein R3 , R4 is one of a hydrogen atom, a chlorine atom or a bromine atom, and R3 and R4 bond to form a benzo ring) is added by 5-20 wt.% to a leuco dye A generating a black color which is expressed by a formula I (wherein R1 , R2 is one of a 1-5C alkyl group, a phenyl group, etc., R1 and R2 bond to a pyrrolidino group forming N and a ring, etc., R3 is a hydrogen atom, etc., R4 , R5 is one of a hydrogen atom, a methyl group, etc.) in a heat-sensitive recording layer. At the same time, the leuco dyes A and B have an absolute value of a difference of melting points within 15 deg.C. Accordingly a color tone is black when a recording part is seen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosensitive recording medium utilizing a color-forming reaction between a leuco dye and a color former, and more particularly to a black thermosensitive recording medium in which the apparent color tone of a recording portion ranges from a low density to a high density. It is about.

[0002]

2. Description of the Related Art Thermal recording media utilizing a color development reaction between a leuco dye and a developer are well known. Such a thermosensitive recording medium is relatively inexpensive, and since the recording apparatus is compact and easy to maintain, it can be used not only as a recording medium for a facsimile, a scientific measuring instrument and the like, but also as a POS label, an AT.
It is used in a wide range of fields, such as recording media for various printers such as M, CAD, ultrasonic diagnostics, X-ray images, and CRT medical images. Above all, the thermal recording medium for ultrasonic diagnosis, X-ray image, and CRT medical image places importance on the image quality and color tone of the halftone.

The color tone of the recording portion of such a thermosensitive recording medium is often black due to the stability of the recorded image. Generally, a fluoran leuco dye which develops black is used as a leuco dye which develops black. However, a fluoran leuco dye which develops black has a drawback that it appears green when the color density is low.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a black thermosensitive recording medium in which the apparent color tone of a recording section ranges from low density to high density.

[0005]

Means for Solving the Problems In a heat-sensitive recording medium in which a heat-sensitive recording layer containing a leuco dye and a coloring agent is provided on a support, as one means for solving the above-mentioned problems,
The present invention provides a thermosensitive recording layer containing at least 5 to 20% by weight of leuco dye B represented by the general formula (2) with respect to leuco dye A represented by the general formula (1), and The one whose absolute value of the difference between the melting point and the leuco dye B is within 15 ° C. is used.

[0006]

Embedded image

(In the general formula (1), R ₁ and R ₂ each represent an alkyl group having 1 to 5 carbon atoms, a phenyl group, a tolyl group,
It represents at least one selected from a cyclohexyl group and an ethoxypropyl group. R ₁ and R ₂ represent a pyrrolidino group or a piperidino group which forms a ring with N. R
₃ represents a hydrogen atom or a methyl group. R ₄ and R ₅ each represent at least one selected from a hydrogen atom, a methyl group, a trifluoromethyl group, a fluorine atom or a chlorine atom. )

[0008]

Embedded image

(In the general formula (2), R ₁ and R ₂ each represent an alkyl group having 1 to 5 carbon atoms, a phenyl group, a tolyl group,
It represents at least one selected from a cyclohexyl group and an ethoxypropyl group. R ₁ and R ₂ represent a pyrrolidino group or a piperidino group which forms a ring with N. R
₃ and R ₄ represent at least one selected from a hydrogen atom, a chlorine atom and a bromine atom. Further, it represents a benzo ring in which R ₃ and R ₄ are bonded. )

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a black coloring leuco dye A represented by formula (1) in a heat-sensitive recording layer.
To 5 to 20% by weight of the red-coloring leuco dye B represented by the general formula (2), and the absolute value of the difference between the melting points of the leuco dye A and the leuco dye B is within 15 ° C. When the amount of leuco dye B is less than 5% by weight, the apparent color tone may be green when the optical density of the recording portion is 0.2 to 0.6, and when the amount exceeds 20% by weight, the apparent color tone may be increased. May be red.

The melting point of the leuco dye A and the leuco dye B
When the difference between the melting point of Leuco Dye A and the melting point of Leuco Dye B exceeds + 15 ° C. in the absolute value of the difference in melting point, the apparent color tone is green when the optical density of the recording portion is 0.2 to 0.6. And the melting point of leuco dye A and leuco dye B
If the difference between the melting points of the two is less than −15 ° C., the apparent color tone may become red.

Specific examples of the leuco dye A represented by the general formula (1) contained in the heat-sensitive recording layer include, for example, 3-diethylamino-6-methyl-7-anilinofluoran (melting point: 201 ° C.), Di (n-butyl) amino-6-methyl-7-anilinofluoran (melting point 180 ° C.), 3-di (n-pentyl) amino-6-methyl-7-anilinofluoran (melting point 182 ° C.), 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluoran (melting point 166 ° C.), 3- (N-methyl-NNpropylamino) -6-methyl-7-ani Linofluoran (melting point 173 ° C), 3-diethylamino-7- (m-trifluoromethyl) anilinofluoran (melting point 181 ° C),
3-di (n-butyl) amino-7- (o-chloroanilino) fluoran (melting point 187 ° C), 3-diethylamino-6-methyl-7- (2,4-xyridino) fluoran (melting point 167 ° C), 3- Di (n-butyl) amino-7-
(O-fluoroanilino) fluoran (melting point 165)
C), 3-diethylamino-6-chloro-7-anilinofluoran (melting point 180C), 3- (N-ethyl-N-
p-tolylamino) -6-methyl-7-anilinofluoran (melting point 207 ° C.), 3- (N-cyclohexyl-N
-Methylamino) -6-methyl-7-anilinofluoran (melting point 202 ° C.), 3-pyrrolidino-6-methyl-7
-Anilinofluoran (melting point 227 ° C), 3-piperidino-6-methyl-7-anilinofluoran (melting point 226)
° C), 3- [N- (3-ethoxypropyl) -N-ethylamino] -6-methyl-7-anilinofluoran (melting point 150 ° C) and the like. Of course, the present invention is not limited to these, and two or more of them can be used as needed.

Specific examples of the leuco dye B represented by the general formula (2) include, for example, 3-piperidino-6-chlorofluorolan (melting point 180 ° C.), 3-diethylamino-7-chlorofluorolan (melting point 235 ° C.) , 3-diethylamino-6,7-dimethylfluoran (melting point 169 ° C),
Di (n-butyl) amino-6-methyl-7-bromofluoran (mp 177 ° C), 3-diethylamino-7,8
-Benzophthalol (melting point 217 ° C) phthalide and the like. The total amount of leuco dye A and leuco dye B is not particularly limited, but is preferably about 5 to 40% by weight based on the heat-sensitive recording layer.

Various known colorants can be used together with the leuco dye A and the leuco dye B. Specific examples of such a coloring agent include, for example, hydroquinone monobenzyl ether, 4,4′-isopropylidene diphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, and 4,4′-dihydroxydiphenyl-2,2. -Butane, 4,4'-dihydroxydiphenylmethane, 2,2-bis (4-hydroxyphenyl)-
4-methylpentane, 2,2-bis (hydroxyphenyl) heptane, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio) -3-oxapentane, 1,1-bis (4-hydroxyphenyl) -1-phenylethane 1,4-bis [α
-Methyl-α- (4′-hydroxyphenyl) ethyl]
Benzene, 1,3-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, 4,4′-dihydroxydiphenyl sulfide, di (4-hydroxy-
3-methylphenyl) sulfin, 4,4'-dihydroxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, 4- Hydroxyphenyl-4'-
Benzyloxydiphenylsulfone, 4-hydroxy-
3 ′, 4′-tetramethylenebiphenyl sulfone, 3,
4-dihydroxyphenyl-p-tolylsulfone, 4-
Benzyl hydroxy-benzoate, N, N-di-m-chlorophenylthiourea, zinc 4- [2- (p-methoxyphenoxy) ethyloxy] salicylate, 4- [3- (p
-Tolylsulfonyl) propyloxy] zinc salicylate, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] zinc salicylate, 4,4′-bis (p-tolylsulfonylaminocarbonylamino) diphenylmethane, Np- Tolylsulfonyl-N'-phenylurea and the like.

In the combination of leuco dye A and leuco dye B, 3-di (n-butyl) amino-6-methyl-7-anilinofluoran (melting point: 18
0 ° C.) and 3-di (n-butyl) amino-6-methyl-7-bromofluoran (melting point: 177 ° C.) as the leuco dye B, so that the apparent color tone of the recording portion can be reduced from low density. An extremely black thermosensitive recording medium can be obtained up to a high density. As the colorant, bis (3-allyl-4-hydroxyphenyl) sulfone or 4-hydroxy-4′-isopropoxydiphenylsulfone is preferable because of excellent storage stability of the recording portion.

The ratio of the total amount of the leuco dye A and leuco dye B and the amount of the color former is not particularly limited, but is 0.5 to 8 parts by weight, preferably 2 parts by weight, per 1 part by weight of the total leuco dye.
About 5 parts by weight of a color former.

Further, the heat-sensitive recording layer may contain a sensitizer for improving the recording sensitivity and a storability improving agent for further improving the storage stability of the recording portion over time. Specific examples of such a sensitizer include, for example, stearic acid amide,
Ethylene bisamide stearate, 2-naphthyl benzyl ether, dibenzyl oxalate, di-p-methylbenzyl oxalate, di-p-chlorobenzyl oxalate, dibenzyl terephthalate, dibenzyl terephthalate, 1- Hydroxynaphthoic acid phenyl ester, 1,2-di (3-methylphenoxy) ethane, 1,2-diphenoxyethane, 1-phenoxy-2- (4-methylphenoxy) ethane, p-acetotoluizide, p-acetophenethene Zide, N-acetoacetyl-p-toluidine, p-benzylbiphenyl and the like.

Specific examples of the preservability improver include, for example, 2,2'-methylenebis (4-methyl-6-tert-
Butylphenol), 2,2′-ethylenebis (4-methyl-6-tert-butylphenol), 2,2′-ethylidenebis (4,6-di-tert-butylphenol),
2,2′-ethylidenebis (4-methyl-6-tert-butylphenol), 2,2′-ethylidenebis (4-ethyl-6-tert-butylphenol), 1- [α-methyl-α- (4 ′ -Hydroxyphenyl) ethyl] -4-
[Α ′, α′-bis (4 ″ -hydroxyphenyl) ethyl] benzene, 1,1,3-tris (2-methyl-4-
(Hydroxy-5-cyclohexylphenyl) butane,
1,1,3-tris (2-methyl-4-hydroxy-5
-Tert-butylphenyl) butane, N, N'-di-2-
Naphthyl-p-phenylenediamine, sodium 2,2'-methylenebis (4,6-di-tert-butylphenyl) phosphate, 4-benzyloxy-4 '-(2-methyl-2,
3-epoxypropyloxy) diphenyl sulfone, novolak type resin and the like.

These sensitizers and storage stability improvers are used in an amount of about 0.1 to 2 parts by weight per 1 part by weight of the color former.

The heat-sensitive recording layer generally uses water as a dispersion medium,
The average particle size of a leuco dye A, a leuco dye B, a color former and, if necessary, a sensitizer and a preservative improver together or separately with a dispersing agent together with a ball mill, an attritor, a sand mill, etc. After finely dispersing so as to have a diameter of about 0.3 to 3 μm, an adhesive is added, and a thermosensitive recording layer coating liquid prepared by mixing and stirring is coated on a support and dried.

As the adhesive to be added to the coating solution for the heat-sensitive recording layer, for example, completely (partially) saponified polyvinyl alcohol,
Acetoacetyl group-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, starch, oxidized starch, gum arabic, casein,
Methylcellulose, hydroxyethylcellulose, hydroxymethylcellulose, styrene-acrylic acid copolymer salt, styrene-maleic anhydride copolymer salt, methylvinyl ether-maleic anhydride copolymer salt, isopropylene-maleic anhydride copolymer Salt, vinyl acetate latex, polyurethane latex, acrylic resin latex, polyvinyl chloride latex, polyvinylidene chloride latex, styrene-butadiene latex, and the like.

Further, various auxiliaries can be added to the coating solution for the heat-sensitive recording layer. Such auxiliaries include, for example, glyoxal, polyamide epichlorohydrin resin, melamine resin, dimethylol urea compound, aziridine compound, ammonium persulfate, zirconium ammonium carbonate, boric acid, borax, and other water-resistant agents, calcium carbonate, magnesium carbonate, oxide Magnesium, kaolin, clay,
Talc, calcined clay, amorphous silica, synthetic aluminum silicate, zinc oxide, titanium oxide, aluminum hydroxide,
Pigments such as barium sulfate, urea-formalin resin fillers, surfactants such as sodium dodecylbenzenesulfonate, acetylene glycol, sodium dioctylsulfosuccinate, zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, etc. Lubricants, antifoaming agents, coloring dyes, fluorescent dyes and the like can be mentioned.

The heat-sensitive recording layer is formed by an air knife method, a Meyer bar method, a pure blade method, a rod blade method, a reverse roll method, a slit die method, a gravure method, a microgravure method, and a curtain method conventionally used by those skilled in the art. The coating solution for the heat-sensitive recording layer is dried on one side of a support such as high-quality paper (acid paper, neutral paper), coated paper, synthetic paper, plastic film, non-woven fabric, metal deposit, etc. The subsequent coating amount is 2 to 20 g /
It is formed by coating and drying so as to have a thickness of about m ² .

In the present invention, a protective layer containing an aqueous adhesive having a film-forming property can be provided on the heat-sensitive recording layer in order to enhance the preservability of the recorded image and the recording running property. Examples of such an aqueous adhesive include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, diisobutylene. Examples thereof include a maleic anhydride copolymer salt, a styrene-maleic anhydride copolymer salt, an ethylene-acrylic acid copolymer salt, a urea resin, an amide resin, and a polyester polyurethane resin.

In the protective layer, inorganic pigments such as calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, aluminum hydroxide, amorphous silica, styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, raw urea Organic pigments such as starch particles, zinc stearate, calcium stearate, polyethylene wax, carnauba wax, puffin wax,
Various auxiliaries such as a lubricant such as ester wax and a surfactant such as sodium dioctylsulfosuccinate and sodium dodecylbenzenesulfonate can also be appropriately added.

A back layer may be provided on the back side of the support for the purpose of imparting conductivity or improving writability, if necessary. The coating solution for the back layer for forming the back layer is prepared by adding an adhesive, and if necessary, a conductive agent and a pigment using water or an organic solvent as a medium. For example, when water is used for the medium, the adhesive contained in the heat-sensitive recording layer or the protective layer is used.

Examples of the conductive agent to be added to the coating liquid for the back layer include polystyrene sulfonic acid salt, polyacryl sulfonic acid salt, alkylbenzene sulfonic acid salt, dioctyl sulfosuccinic acid hydrochloride, and polymer cationic conductive agent. Agents, conductive zinc oxide, conductive titanium oxide, synthetic hectorite clay, and the like.

Further, a dispersant, an antifoaming agent, a fluorescent dye, a curing agent, an ultraviolet absorber, a lubricant, and the like are added to the back layer coating liquid as required.

The protective layer and the back layer are formed by the same method as the coating method for forming the heat-sensitive recording layer. The coating amount after drying, the protective layer is about 0.5~6g / m ^2, the backside layer is about 0.1-4 g / m ^2. The order of forming the back layer, the heat-sensitive recording layer, and the protective layer is not particularly limited. However, considering background fog, it is preferable to form the back layer first.

In addition, as long as the effects of the present invention are not impaired,
Various kinds of heat-sensitive recording material manufacturing fields such as providing a gloss layer containing a resin cured by electron beam or ultraviolet irradiation on the protective layer, or performing a super calender treatment, and further performing an adhesive process on the back surface Known techniques can be added as appropriate.

[0031]

The present invention will be described in more detail with reference to the following Examples, but it should be understood that the present invention is by no means restricted thereto. Unless otherwise specified, parts and% in the examples indicate parts by weight and% by weight, respectively.

Example 1 Preparation of solution A (dispersion of black-coloring leuco dye A) 10 parts of 3-di (n-butyl) amino-6-methyl-7-anilinofluoran (melting point: 180 ° C.) Sulfone group-modified polyvinyl alcohol (trade name: Goselan L-32)
66, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), and a composition composed of 3 parts of a 20% aqueous solution and 22 parts of water was pulverized with an Ultra Viscomill until the average particle diameter became 0.8 μm to obtain a liquid A.

Preparation of Solution B (Dispersion of Leuco Dye B Having Red Color) 10 parts of 3-di (n-butyl) amino-6-methyl-7-bromofluoran (melting point: 177 ° C.), sulfone group-modified polyvinyl Alcohol (trade name: Gohselan L-326)
6, a product consisting of 3 parts of a 20% aqueous solution of Nippon Synthetic Chemical Industry Co., Ltd.) and 22 parts of water were pulverized with an Ultra Viscomill until the average particle diameter became 0.8 μm to obtain a liquid B.

Liquid C Preparation (Dispersion of Coloring Agent) Bis (3-allyl-4-hydroxyphenyl) sulfone 20 parts, sulfone group-modified polyvinyl alcohol (trade name: Goselan L-3266, manufactured by Nippon Synthetic Chemical Industry) A composition comprising 2 parts of a 20% aqueous solution and 29 parts of water was pulverized with an Ultraviscomiler until the average particle diameter became 0.8 μm to obtain a liquid C.

Preparation of Thermal Recording Coating Solution 25 parts of solution A, 3.0 parts of solution B, 84 parts of solution C, 45 parts of 60% slurry of light calcium carbonate, average particle size 0.8 μm
20 parts of a 30% dispersion of stearic acid amide, 40 parts of a 10% aqueous solution of polyvinyl alcohol, and a solid concentration of 48%
Of a styrene-butadiene-based latex and 70 parts of water were mixed and stirred to obtain a coating solution for a heat-sensitive recording layer.

Preparation of Coating Solution for Protective Layer 100 parts of a 60% slurry of kaolin (trade name: UW-90, manufactured by EC Company), acetoacetyl group-modified polyvinyl alcohol (trade name: Gosefimer Z-200, Nippon Synthetic Chemical Co., Ltd.) Coating for a protective layer obtained by mixing and stirring a composition comprising 300 parts of a 10% aqueous solution (manufactured by Kogyo Co., Ltd.), 25 parts of a 30% dispersion of zinc stearate, 4 parts of a 10% aqueous solution of glyoxal, and 230 parts of water. A liquid was obtained.

Preparation of Thermosensitive Recording Material A transparent PET film (thickness: 125 μm) anchor-coated on both surfaces was coated with a coating solution for a thermosensitive recording layer and a coating solution for a protective layer on one side at a coating amount of 12 g / m 2 after drying. ² , 3g / m
To obtain a heat-sensitive recording material was sequentially formed thermosensitive recording layer and the protective layer by coating and drying by using a micro gravure coater such that the ^2.

Example 2 In the preparation of solution B of Example 1, 3 was used instead of 3-di (n-butyl) amino-6-methyl-7-bromofluoran.
-Diethylamino-7-chlorofluoran (melting point: 17
3 ° C.) to obtain a thermosensitive recording medium in the same manner as in Example 1.

Example 3 In the preparation of Solution A of Example 1, 3-di (n-butyl) amino-6-methyl-7-anilinofluoran (melting point: 1)
80 ° C.) instead of 3-di (n-butyl) amino-7-
A heat-sensitive recording material was obtained in the same manner as in Example 1, except that (o-chloroanilino) fluoran (melting point: 187 ° C) was used.

Example 4 In the preparation of solution A of Example 1, 3-di (n-butyl) amino-6-methyl-7-anilinofluoran (melting point: 1)
Thermal recording was performed in the same manner as in Example 1 except that 3- (N-methyl-NNpropylamino) -6-methyl-7-anilinofluoran (melting point: 173 ° C) was used instead of (80 ° C). I got a body.

Example 5 In the preparation of solution C of Example 1, bis (3-allyl-4-
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 4-hydroxy-4′-isopropoxydiphenyl sulfone was used instead of (hydroxyphenyl) sulfone.

Example 6 In the preparation of Solution C of Example 1, bis (3-allyl-4-
Example 1 except that 4,4'-isopropylidene diphenol was used in place of (hydroxyphenyl) sulfone.
In the same manner as in the above, a thermosensitive recording medium was obtained.

Example 7 In the preparation of the coating solution for the heat-sensitive recording layer of Example 1,
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 0 parts was changed to 1.5 parts.

Example 8 In the preparation of the coating solution for the heat-sensitive recording layer of Example 1,
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 4.5 parts was used instead of 0 parts.

Comparative Example 1 In the preparation of solution B of Example 1, 3-di (n-butyl) amino-6-methyl-7-bromofluoran (melting point: 177)
° C) instead of 3-diethylamino-6-methyl-7-
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that chlorofluorane (melting point: 235 ° C.) was used.

Comparative Example 2 In the preparation of Solution B of Example 1, 3-di (n-butyl) amino-6-methyl-7-bromofluoran (melting point: 177)
Example 1 except that 3-diethylamino-7,8-benzofluoran (melting point: 217 ° C) was used instead of (° C).
In the same manner as in the above, a thermosensitive recording medium was obtained.

Comparative Example 3 In the preparation of Solution B of Example 1, 3,3′-bis (1-n-butyl-butyl) was used instead of 3-di (n-butyl) amino-6-methyl-7-bromofluoran. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 2-methylindol-3-yl) phthalide (melting point: 162 ° C) was used.

Comparative Example 4 In the preparation of the coating solution for the heat-sensitive recording layer of Example 1,
A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 0 part was changed to 1.0 part.

Comparative Example 5 In the preparation of the coating solution for the heat-sensitive recording layer of Example 1,
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 6.0 parts was used instead of 0 parts.

The thus obtained heat-sensitive recording medium was recorded at 17 gradations using a built-in pattern of a multi-scan video printer: UP-930 manufactured by Sony Corporation, and the color tone and recording density in the halftone density range were evaluated. The results are shown in Table 1. [Color tone of halftone density range] The color tone of 5 to 10 gradations (halftone) was visually evaluated. [Recording Density] The 17th gradation was measured with a transmission densitometer TD904 manufactured by Macbeth.

[0051]

[Table 1]

[0052]

As can be seen from the results shown in Table 1, the thermosensitive recording medium of the present invention is black from a low density to a high density in the apparent color tone of the recording portion.

Claims (3)

[Claims] 1. A heat-sensitive recording medium having a heat-sensitive recording layer containing a leuco dye and a color former on a support, wherein at least the leuco dye A represented by the general formula (1) is contained in the heat-sensitive recording layer.
To leuco dye B represented by the general formula (2)
A thermosensitive recording medium containing 0% by weight, and the absolute value of the difference between the melting points of leuco dye A and leuco dye B is within 15 ° C. Embedded image (In the general formula (1), R ₁ and R ₂ each have 1 to 1 carbon atoms.
5 represents at least one selected from an alkyl group, a phenyl group, a tolyl group, a cyclohexyl group and an ethoxypropyl group. Further, R ₁ and R ₂ represent a pyrrolidino group or a piperidino group in which a ring is formed with N. R ₃ represents a hydrogen atom or a methyl group. R ₄ and R ₅ each represent at least one selected from a hydrogen atom, a methyl group, a trifluoromethyl group, a fluorine atom or a chlorine atom. ) (In the general formula (2), R ₁ and R ₂ each have 1 to 1 carbon atoms.
5 represents at least one selected from an alkyl group, a phenyl group, a tolyl group, a cyclohexyl group and an ethoxypropyl group. Further, R ₁ and R ₂ represent a pyrrolidino group or a piperidino group in which a ring is formed with N. R ₃ , R
₄ represents at least one selected from a hydrogen atom, a chlorine atom and a bromine atom. Further, it represents a benzo ring in which R ₃ and R ₄ are bonded. ) 2. The leuco dye A is 3-di (n-butyl) amino-6-methyl-7-anilinofluoran (melting point 180).
C.) and the leuco dye B is 3-di (n-butyl) amino-6-methyl-7-bromofluoran (mp 177).
C.). 3. The heat-sensitive recording material according to claim 1, wherein the color former is bis (3-allyl-4-hydroxyphenyl) sulfone or 4-hydroxy-4′-isopropoxydiphenylsulfone.