JP2000043424A - Thermal recording body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance recording sensitivity and the vividness of a recording part, and make two-color recording feasible at least by allowing a microcapsule including at least one kind of solid leuco dye and developer to be included in a thermal recording layer containing a plurality of leuco dyes being different in a coloring tone and developer. SOLUTION: A mixture of a solid leuco dye and developer obtained by heating and melting and then cooling a solid leuco dye and developer together is subjected to wet crushing by employing anion polymer, e.g. as a dispersant, and the wet-crushed dispersion liquid is contained in a microcapsule. For the film material of such a microcapsule, there is used, e.g. gelatin in a coacervation method, and melamine-formaldehyde resin is used in an in-situ method. If an intensifier is included in the microcapsule, coloring sensitivity can be enhanced, and also a coloring temperature in the microcapsule and a coloring temperature of the thermal recording layer can be controlled arbitrarily.

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 capable of recording at least two colors by utilizing a color-forming reaction between a leuco dye and a color former.

[0002]

2. Description of the Related Art A thermosensitive recording medium, which utilizes a color development reaction between a leuco dye and a color former to obtain a recorded image by heat, is well known. Such a thermosensitive recording medium is relatively inexpensive, and since the recording device is compact and easy to maintain,
It is widely used as output for facsimile and various computers, and as recording media for printers of scientific measuring instruments. In addition, multi-color heat-sensitive recording materials have been developed,
There have been proposed a color-added type in which two or more layers with different colors are provided, and a color-depleted type in which a layer for erasing the layer with initial color is provided between layers with different colors. However, there is a drawback that the cost increases.

In recent years, as a multicolor heat-sensitive recording material, for example, JP-A-59-99490 and JP-A-59-9143.
No. 8 discloses a heat-sensitive recording material in which a leuco dye dissolved in an organic solvent is placed in a microcapsule, and a developer around it passes through the capsule wall softened by heating and develops a color with the leuco dye in the microcapsule. Applications have been proposed. In this system, the storage stability of the recorded image is improved because the formed leuco dye is completely isolated on the capsule wall, but the heat response is slow, the color formation sensitivity is low, and the leuco dye is not used. There is a disadvantage that it is easily discolored by light because it is dissolved in an organic solvent.

A single-color heat-sensitive recording material in which microcapsules containing a leuco dye and a colorant are contained in a heat-sensitive recording layer in order to enhance the storage stability of the recording portion is disclosed in
No. 19193, a thermosensitive recording medium further containing a microcapsule encapsulating a leuco dye, a koico dye having a color tone different from that of the leuco dye in the microcapsule, and a coloring agent in a thermosensitive recording layer is disclosed in US Pat. Kaihei 8-282
Although described in Japanese Patent Publication No. 115, there is a problem in recording sensitivity and sharpness of a recording portion.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermosensitive recording medium which is excellent in recording sensitivity and sharpness of a recording portion and can record at least two colors.

[0006]

Means for Solving the Problems In a heat-sensitive recording medium having a heat-sensitive recording layer containing a plurality of leuco dyes having different color tones and a color former on a support, one of the above-mentioned objects can be attained. As one means, the present invention includes microcapsules containing at least one solid leuco dye and a color former in the same heat-sensitive recording layer.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A microcapsule enclosing a solid leuco dye and a coloring agent is prepared by, for example, using water as a dispersing medium and separately or together with a leuco dye and a coloring agent having an average particle size of 0.2. When wet pulverization to about 3 μm or after pulverization, an anionic polymer such as arabic gum, sodium alginate, carboxymethylcellulose and the like are added, and then microencapsulation is performed by a coacervation method or an in-situ method.

A solid leuco dye and a color former are heated and melted together to form a color, and then cooled. A mixture of the solid leuco dye and the color former is cooled, for example, as an anion as a dispersant. By wet-grinding with a hydrophilic polymer and enclosing the wet-ground dispersion in microcapsules, an effect particularly excellent in recording sensitivity and recording density can be obtained.
In addition, by treating the dispersion or microcapsule dispersion that has been wet-pulverized at 40 to 70 ° C. for at least 15 hours or more, a microcapsule liquid with less color fog can be obtained. When the dispersion containing the wet-ground pulverized leuco dye and the colorant is microencapsulated by a coacervation method or an in-situ method, the leuco dye and the colorant are encapsulated in the same microcapsule when the microcapsules are formed. As a result, an extremely excellent effect on recording sensitivity and recording density can be obtained.

As the film material of the microcapsules, for example, gelatin is used in the coacervation method, and, for example, melamine-formaldehyde resin is used in the in-situ method. The wall film material is about 1 to 30% by weight based on the total solid content of the microcapsules. The average particle size of the microcapsules is 0.5 to 10 μm
m.

[0010] The leuco dye contained in the heat-sensitive recording layer only needs to include at least one kind of carp dye in microcapsules. For example, it is of course possible to separately encapsulate two types of leuco dyes having different color tones in microcapsules.

Various known leuco dyes can be used. For example, as a black coloring leuco dye, 3- (N
-Ethyl-N-isoamylamino) -6-methyl-7-
Anilinofluoran, 3-dimethylamino-7- (m-
(Trifluoromethyl) anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-diethylamino-7- (m-trifluoromethyl) anilinofluoran, 3-diethylamino-6-methyl- 7-anilinofluoran, 3- (N-ethyl-Nn-hexyamino) -6-methyl-7-anilinofluoran, 3
-(N-ethyl-NN-isoamylamino) -7-
(O-chloroanilino) fluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-di (n
-Butyl) amino-6-methyl-7-anilinofluoran, 3-di (n-pentyl) amino-6-methyl-7-
Anilinofluoran, 3- [N- (3-ethoxypropyl) -N-ethylamino] -6-methyl-7-anilinofluoran, 3- [N- (3-ethoxypropyl) -N
-Methylamino] -6-methyl-7-anilinofluoran, 3-di (n-butyl) amino-6-methoxy-7-
Anilinofluoran, 3- (N-ethyl-p-toluidino) -6-methyl-7-anilinofluoran, 3-di (n-pentyl) amino-7- (m-trifluoromethylanilino) fluoran , 3-N-ethylanilino-6
-Methyl-7-o-toluidinofluoran 3-di (n-
Butyl) amino-6-methyl-7- (2,4-xylidino) fluoran, 3-di (n-butyl) amino-6-methyl-7-m-toluidinofluoran, 3-diethylamino-6-methyl -7 m-toluidinofluoran, 3-
Diethylamino-7- (o-chloroanilino) fluoran, 3-di (n-butyl) amino-7- (o-chloroanilino) fluoran, 3- (N-ethyl-N-2-tetrahydrofurfurylamino) -6-methyl -7-anilinofluoran, 3-diethylamino-7- (o-fluoroanilino) fluoran, 3-di (n-butyl) amino-7- (o-fluoroanilino) fluoran, 3-di (n- (Butyl) amino-6-methyl- (p-fluoroanilino) fluoran, 3- (N-ethyl-N-cyclopentylamino) -6-methyl-7-anilinofluoran, 3-diethylamino-6-chloro-7 -Anilinofluoran, 2,2-bis {4- [6 '-(N-cyclohexyl-N-methylamino) -3'-methylspiro (phthalide-3,9'-xan Down) 2'-ylamino]
Phenyl｝ propane etc.

As the red-forming leuco dye, 3,6-bis (diethylamino) fluoran-γ-anilinolactam, 3-piperidino-6-chlorofluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-
Diethylamino-7-chlorofluoran, 3-diethylamino-7,8-benzofluoran, 3-diethylamino-6-diethylamino- (N-2-chlorophenyl)
Rhodamine B lactam, 3-diethylamino-6,7-
Dimethylfluoran, 3-di (n-butyl) amino-6
-Methyl-7-bromofluoran, 3-diethylamino-benzo [a] fluoran, 3- (N-ethyl-p-toluidino) -7-methylfluoran, 3- (N-ethyl-N-isoamylamino)- 7,8-benzofluoran, 3,3'-bis (1-n-amyl-2-methylindol-3-yl) phthalide, 3-diethylamino-7
-Phenoxyfluoran, 3- (N-ethyl-N-isoamylamino) -7-phenoxyfluoran, 3,3 '
-Bis (1-n-butyl-2-methylindole-3-
Yl) phthalide, 3,3′-bis (1-ethyl-2-methylindol-3-yl) phthalide and the like,

As green-forming leuco dyes, 3,3-bis (p-dimethylaminophenyl) phthalide, 3- (N-
Ethyl-Np-tolylamino) -7- (N-phenyl-N-methylamino) fluoran, 3-diethylamino-7-anilinofluoran, 3-diethylamino-7-
Dibenzylaminofluoran, 3-diethylamino-7
-(O-chloroanilino) fluoran, 3- (N-ethyl-Nn-hexylamino) -7-anilinofluoran, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamini-6-methoxy- 7-aminofluoran, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-5-methyl-7-
Dibenzylaminofluoran, 3-pyrrolidino-7-dibenzylaminofluoran and the like,

As blue-forming leuco dyes, tris (4-
Dimethylaminophenyl) methane, 3,3-bis (p-
Dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-methylphenyl)
-3- (4-Dimethylaminophenyl) -6-dimethylaminophthalide, 3-diethylamino-7-aminobenzo [a] fluoran, 3-diethylamino-7-dibenzylaminobenzo [a] fluoran, 3-diphenylamino- 6-diphenylaminofluoran, 3,7-bis (dimethylamino) -10-benzoylphenothiazine, 3′-phenyl-7-N-diethylamino-2,
2′-spirodi- (2H-1-benzopyran), 3-
(4-diethylamino-2-ethoxyphenyl) -3-
(1-ethyl-2-methylindol-3-yl) -4
-Azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (4-diethylamino-2-n
-Hexyloxyphenyl) -4-azaphthalide and the like

As the yellow-coloring leuco dye, 3,6-dimethoxyfluoran, 1- (4-n-dodecyloxy-3)
-Methoxyphenyl) -2- (2-quinolyl) ethylene, 1,3,3-trimethylindoline-2,2'-spiro-6'-nitro-8'-methoxybenzopyran and the like.

Of course, it is not limited to these,
If necessary, two or more kinds can be used in combination. Further, on the heat-sensitive recording layer or between the support and the heat-sensitive recording layer,
The heat-sensitive recording layer may be a heat-sensitive recording layer containing a leuco dye having a different color tone and a coloring agent, or a heat-sensitive recording layer containing a diazonium compound and a coupler.

Various known colorants can be used together with the leuco dye. Specific examples of such a coloring agent include, for example, 4-hydroxyacetophenol,
2,2′-dihydroxydiphenol, 4,4′-isopropylidenediphenol, 4,4′-isopropylidenebis (2-tert-butylphenol), 4,4′-s
ec-butylidene diphenol, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 4,4'-
Cyclohexylidenediphenol, 2,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, 4-hydroxy-4'-methyldiphenylsulfone, 2,4- Bis (phenylsulfonyl) phenol, 4-hydroxy-4'-benzyloxydiphenylsulfone, 3,4'-dihydroxy-4 '
-Methyldiphenyl sulfone, hydroquinone monobenzyl ether, 4-hydroxybenzophenone, benzyl 4-hydroxybenzoate, 4-hydroxybenzoic acid-p
-Methoxybenzyl, novolak type phenolic resin, p
-Zinc tert-butylbenzoate, 3-cyclohexyl-4
-Zinc hydroxyhydroxybenzoate, 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.

The ratio of the leuco dye to the coloring agent contained in the microcapsules and in the heat-sensitive recording layer excluding the microcapsules is appropriately selected according to the type of the leuco dye used, and is not particularly limited. However, the specific colorant is generally 0.5 to 1 part by weight of the leuco dye.
It is about 10 parts by weight, preferably about 1 to 5 parts by weight.

Further, in the microcapsule or in the heat-sensitive recording layer excluding the microcapsule, a sensitizer, particularly, having a melting point of 7
The coloring sensitivity can be increased by adding a sensitizer composed of an aromatic compound at about 0 to 150 ° C., or the coloring temperature in the microcapsules and the coloring temperature of the heat-sensitive recording layer excluding the microcapsules can be appropriately adjusted. .

Specific examples of the sensitizer include dibenzyl oxalate, di-p-methylbenzyl oxalate, di-p-chlorobenzyl oxalate,
Terephthalic acid dimethyl ester, terephthalic acid dibenzyl ester, 1,2-di (3-methylphenoxy) ethane, 1,2-diphenoxyethane, 1-phenoxy-2
-Naphthoxyethane, 1-phenoxy-2- (4-methylphenoxy) ethane, 1- (4-methylphenoxy)
-2-naphthoxyethane, 1,3-naphthoxypropane, 1,4-naphthoxybutane, p-benzylbiphenyl, m-terphenyl, benzyl-2-naphthyl ether, 1,2-bis (3,4-dimethylphenyl) ethane , 1,4-bis (p-tolyloxy) benzene, diphenylsulfone, diphenyl carbonate, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole and the like.

The ratio of the leuco dye to the sensitizer used is appropriately selected depending on the type of the leuco dye and the developer used, and is not particularly limited. The sensitizer is used in an amount of 0.2 to 10 parts by weight, preferably about 0.3 to 5 parts by weight.

In the present invention, in order to further enhance the environmental preservation properties such as heat resistance and humidity resistance of the recording portion and the chemical preservability against oils and plasticizers, various known preservability improvers used for heat-sensitive recording media are used in microcapsules. It may be contained in the heat-sensitive recording layer except for the middle or microcapsules.

Specific examples of the preservability improver include, for example,
2,2'-methylenebis (4-methyl-6-tert-butylfeil), 2,2'-ethylenebis (4-methyl-
6-tert-butylfeil), 2,2'-ethylidenebis (4,6-di-tert-butylfeil), 2,2'-
Ethylidenebis (4-ethyl-6-tert-butylfeil), 1- [α-methyl-α- (4′-hydroxyphenyl) ethyl] -4- [α ′, α′-bis (4 ″ -hydroxy Phenyl) ethyl] benzene, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butyl Hindered phenolic antioxidants such as phenyl) butane, N, N'-di-2-naphthyl-p-phenylresinamine, 4,4 '
Amine-based antioxidants such as bis (ethyleneiminecarbonylamino) diphenylmethane, 4-benzyloxy-
Epoxy compounds such as 4 '-(2-mail-2,3-epoxypropyloxy) diphenylsulfone, terephthalic acid diglycidyl ether, and 4,4'-glycidyloxyphenylsulfone; 2- (2'-hydroxy-5'-
Methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl)-
5-chloro-benzotriazole, 2- (2'-hydroxy-3'-tert-5'-methylphenyl) -5-chloro-benzotriazole, 2- (2'-hydroxy-
Benzotriazole ultraviolet absorbers such as 3 ′, 5′-di-tert-butylphenyl) benzotriazole and 2- (2′-hydroxy-5′-tert-butylphenyl) benzotriazole are exemplified.

The heat-sensitive recording layer comprises water as a dispersion medium, for example, microcapsules containing a solid leuco dye and a coloring agent, a leuco dye finely pulverized to an average particle diameter of 2 μm or less, a coloring agent, and an adhesive. Coating solution for heat-sensitive recording layer prepared by mixing and stirring a sensitizer and, if necessary, a sensitizer and storage stability improvement, on a support such as acidic or neutral high-quality paper, film, synthetic paper, etc. after drying It is formed by coating and drying so that the amount is about ² to 15 g / m ² .

Examples of the adhesive used in the heat-sensitive recording coating solution include completely (partially) saponified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, and carboxy. Modified polyvinyl alcohol, starch, oxidized starch and other modified starches, gum arabic, gelatin, casein,
Chitosan, methylcellulose, hydroxyethylcellulose, hydroxymethylcellulose, carboxymethylcellulose, styrene-acrylic acid copolymer salt, styrene-maleic anhydride copolymer salt, methylvinyl ether-maleic anhydride copolymer salt, isopropylene-maleic anhydride Water-soluble resins such as salts of acid copolymers, and vinyl acetate latex, acrylate copolymer latex, methacrylate copolymer latex,
Water-dispersible resins such as vinyl acetate- (meth) acrylate copolymer latex, polyurethane latex, polyvinyl chloride latex, polyvinylidene chloride latex, and styrene-butadiene latex are exemplified. The amount of the adhesive used is preferably about 5 to 40% by weight based on the total solid content of the heat-sensitive recording layer.

The coating solution for the heat-sensitive recording layer further contains pigments such as amorphous silica, calcium carbonate, aluminum hydroxide, and kaolin, acetylene glycol, polyoxyethylene alkylphenyl ether, dialkyl sulfosuccinate, and alkylbenzene sulfonate. Surfactants such as zinc stearate and calcium stearate, waxes such as polyethylene wax, carnauba wax, paraffin wax and ester wax, and various assistants such as coloring dyes and fluorescent dyes can also be added.

The coating solution for the heat-sensitive recording layer is applied to the support by various known methods such as an air knife method, a pure blade method, a rod method, a roll method, a gravure method, a slot die method, and a curtain method.

On the heat-sensitive recording layer, a protective layer mainly composed of an adhesive and a pigment can be provided on the heat-sensitive recording layer in order to improve the chemical resistance of the recording portion and the running property of the printer. Examples of the adhesive include those contained in the heat-sensitive recording layer. Further, an uppermost layer obtained by irradiating an ultraviolet ray or an electron beam curable resin with an ultraviolet ray or an electron beam and curing the resin may be provided on the protective layer.

If necessary, an undercoat intermediate layer containing an oil-absorbing pigment or organic hollow particles as a main component may be provided between the support paper and the heat-sensitive recording layer, or a smoothing treatment such as super calendering may be applied after each layer is coated. It is also possible to add various known techniques in the field of thermal recording medium production as needed.

[0030]

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to these examples. In each of Examples and Comparative Examples, “parts” and “%” indicate “parts by weight” and “% by weight”, respectively.

Example 1 Preparation of Black Coloring Dispersion Black Coloring Leuco Dye 3-Di (n-butyl) amino-6
20 parts of methyl-7-anilinofluorane and 4-hydroxy-4'-isopropoxydiphenyl sulfone 20
40 parts of which were heated and melted together, 1 part of Arabic rubber
A composition comprising 40 parts of a 0% aqueous solution and 160 parts of water is pulverized by a sand mill until the average particle diameter becomes 1.5 μm, and then subjected to a decoloring treatment by leaving the composition at 60 ° C. for 24 hours.
Water was added to obtain a black color-forming dispersion having a solid concentration of 18%.

Preparation of Microcapsule Dispersion 100 parts of the above-described black coloring dispersion heated to 60 ° C.
30 parts of a 10% aqueous solution (solution temperature: 60 ° C.) of gelatin (Nippi Gelatin Co., S-1286, isoelectric point: 8.46) was added, and the pH was adjusted to 7.0 with ammonia. 20 parts of the aqueous solution was added and stirred. While stirring, a 10% aqueous solution of acetic acid was added dropwise to adjust the pH to 4.0. The temperature was gradually lowered to 10 ° C. to gelatinize the gelatin and form a capsule film on the surface of the dispersion. In this state, 6 parts of a 5% aqueous solution of glutaraldehyde is added to insolubilize the gelatin, enclose the color-forming component, and add water to give a solid concentration of 1%.
A 0% microcapsule dispersion was obtained.

Solution A A composition comprising 40 parts of the red-coloring leuco dye 3-diethylamino-7-chlorofluorane, 5 parts of a 5% aqueous solution of methylcellulose and 55 parts of water was adjusted to an average particle size of 1.5 μm by a sand mill. The solution A was obtained by pulverizing the solution until it was no longer necessary.

Solution B Preparation A composition comprising 40 parts of 4-hydroxy-4'-isopropoxydiphenylsulfone, 5 parts of a 5% aqueous solution of methylcellulose and 55 parts of water is pulverized by a sand mill until the average particle size becomes 1.5 μm. A solution was obtained.

Solution C Preparation A composition comprising 40 parts of 1,2-di (3-methylphenoxy) ethane, 5 parts of a 5% aqueous solution of methylcellulose and 55 parts of water is pulverized by a sand mill until the average particle diameter becomes 1.5 μm. Thus, solution C was obtained.

Preparation of Coating Liquid for Thermosensitive Recording Layer 10 parts of liquid A, 30 parts of liquid B, 20 parts of liquid C, 50 parts of microcapsule dispersion liquid, 1 part of completely saponified polyvinyl alcohol
80 parts of a 0% aqueous solution, 10 parts of a 30% aqueous dispersion of zinc stearate, and aluminum hydroxide 3 having an average particle diameter of 1 μm
A composition comprising 5 parts of a 5% aqueous solution of 5% sodium di (2-ethylhexyl) sulfosuccinate was mixed and stirred to obtain a coating solution for a heat-sensitive recording layer.

Preparation of Coating Solution for Undercoat Layer 100 parts of a 50% dispersion of calcined kaolin, 120 parts of a 40% dispersion of hollow particles (average particle diameter 1 μm, average thickness 0.1 μm) of polystyrene having a wall film, part 100 parts of a 10% aqueous solution of saponified polyvinyl alcohol was mixed and stirred to obtain a coating liquid for an undercoat layer.

Preparation of heat-sensitive recording medium On one side of neutral high-quality paper having a basis weight of 64 g / m ² , the coating amount after drying the coating solution for the undercoat layer and the coating solution for the heat-sensitive recording layer was 8 g / m2.
An undercoat layer and a heat-sensitive recording layer were sequentially formed by coating and drying to obtain a heat-sensitive recording medium having a m ² of 6 g / m ² . After the formation of each layer, a smoothing treatment was performed using a super calender.

Example 2 In the preparation of the black color-forming dispersion of Example 1, 20 parts of 3-di (n-butyl) amino-6-methyl-7-anilinofluoran and 4-hydroxy-4 ' -Instead of isopropoxydiphenylsulfone 20, 3-di (n-butyl) amino-6-methyl-7
-Anilinofluoran 15 parts, 4-hydroxy-4'-
15 parts of isopropoxydiphenyl sulfone and 2-
A heat-sensitive recording material was obtained in the same manner as in Example 1, except that 10 parts of (2'hydroxy-5'-methylphenyl) benzotriazole was used.

Example 3 In the preparation of the solution A of Example 1, the blue-coloring leuco dye 3,3-bis (p-dimethylamino) was used instead of the red-coloring leuco dye 3-diethylamino-7-chlorofluoran. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that phenyl) -6-dimethylaminophthalide was used.

Example 4 Example 1 was repeated except that 50 parts of the following microcapsule dispersion was used instead of 150 parts of the microcapsule dispersion used in the preparation of the coating solution for the heat-sensitive recording layer of Example 1. In the same manner as in the above, a thermosensitive recording medium was obtained. ★ Preparation of Microcapsule Dispersion To 100 parts of the black color dispersion of Example 1, 80 parts of a 30% aqueous solution of melamine-formaldehyde prepolymer was added dropwise, and 0.1N hydrochloric acid was added dropwise to adjust the pH to 5. After adjusting to 0.3, the mixture was kept at 60 ° C. for 1 hour, adjusted to pH 3.5 with 0.2N hydrochloric acid, kept at 65 ° C. for 4 hours, and cooled.
The mixture was diluted with water so as to have a solid concentration of 10% to obtain a microcapsule dispersion.

Example 5 In the preparation of solution B in Example 1, 4,4'-bis (p-tolylsulfonylaminocarbonylamino) diphenylmethane was used instead of 4-hydroxy-4'-isopropoxydiphenylsulfone. Except for the above, a thermosensitive recording medium was obtained in the same manner as in Example 1.

Example 6 In place of 100 parts of the black coloring dispersion used in the preparation of the microcapsule dispersion of Example 1, 100 parts of the following black coloring dispersion was used, and a coating solution for a heat-sensitive recording layer was used. A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 50 parts of the following microcapsule dispersion liquid was used in place of 10 parts of the liquid A, 30 parts of the liquid B, and 20 parts of the liquid C in the preparation of ★ Preparation of Black Coloring Dispersion 20 parts of 3-di (n-butyl) amino-6-methyl-7-anilinofluoran and 20 parts of 4,4′-bis (p-tolylsulfonylaminocarbonylamino) diphenylmethane And 40 parts of a 10% aqueous solution of arabic gum and 160 parts of water were pulverized with a sand mill until the average particle size became 1.5 μm, and then left at 60 ° C. for 24 hours. , And water was added to obtain a black-color-forming dispersion having a solid concentration of 18%. ★ Preparation of microcapsule dispersion liquid 15 parts of red-coloring leuco dye 3-diethylamino-7-chlorofluorane, 15 parts of 4-hydroxy-4′-isopropoxydiphenylsulfone and 1,2-di (3-methylphenoxy) ethane A composition comprising 40 parts obtained by heating and melting 10 parts together, 40 parts of a 10% aqueous solution of arabic gum and 160 parts of water was pulverized by a sand mill until the average particle diameter became 1.5 μm, and then the mixture was heated at 60 ° C. 2
After decolorizing by leaving for 4 hours, 100 parts of a red-forming leuco dye-based dispersion having a solid concentration of 18% obtained by adding water was heated to 60 ° C, and gelatin (Nippi Gelatin Co., S-1286). , Isoelectric point 8.46), 30 parts of a 10% aqueous solution (liquid temperature 60 ° C.), and the pH was adjusted to 7.0 with ammonia.
0 parts were stirred. While stirring, a 10% aqueous solution of acetic acid was added dropwise to adjust the pH to 4.0. The temperature was gradually lowered to 10 ° C. to gelatinize the gelatin and form a capsule film on the surface of the dispersion. In this state, 6 parts of a 5% aqueous solution of glutaraldehyde was added to insolubilize the gelatin and encapsulate the color-forming component, and water was added to obtain a microcapsule dispersion having a solid concentration of 10%.

Comparative Example 1 The procedure of Example 1 was repeated except that 50 parts of the microcapsule dispersion used in the preparation of the coating solution for the heat-sensitive recording layer was replaced by 13 parts of the black color-forming leuco dye dispersion of Example 1. Was obtained in the same manner as in Example 1.

Comparative Example 2 In the preparation of the black-color-forming leuco dye dispersion of Example 1, 3-di (n-butyl) amino-6 was used instead of 20 parts of 4-hydroxy-4'-isopropoxydiphenylsulfone. Example 1 except that 20 parts of -methyl-7- (o-chloroanilino) fluoran were used.
A thermosensitive recording medium was obtained in the same manner as in the above.

The heat-sensitive recording medium thus obtained was evaluated as follows, and the results are shown in Table 1. [Coloring property] Thermal recording medium evaluation machine (trade name: TH-PMD,
Okura Electric Co., Ltd.), applied voltage 24 V, pulse width 1.
Each thermosensitive recording medium is colored at 5 ms and 3.0 ms,
The density of the recording portion was measured with a Macbeth densitometer (trade name: Model 914, manufactured by Macbeth) using filters corresponding to each color tone. The sharpness of the color tone of the recording portion was visually evaluated as follows. ◎: Clear ○: Slightly clear ×: Unclear

[0047]

[Table 1]

As shown in Table 1, the heat-sensitive recording material of the present invention is excellent in recording sensitivity and has an effect of forming a clear recording portion having a different color tone.

Claims (3)

[Claims] 1. A thermosensitive recording medium having a thermosensitive recording layer containing a plurality of leuco dyes having different color tone and a color former on a support, wherein at least a solid leuco dye is contained in the same thermosensitive recording layer. A heat-sensitive recording material comprising microcapsules containing one type of dye and a color former. 2. The thermosensitive recording medium according to claim 1, wherein a sensitizer is further included in the microcapsules. 3. The thermosensitive recording medium according to claim 1, wherein the microcapsules are obtained by a coacervation method or an in-situ method.