JPH05278328A - Thermal recording material - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a heat-sensitive recording material having high whiteness, high density and high-contrast recording, and having a color tone similar to that of photographic paper. [Structure] 45 parts of a black-coloring leuco dye dispersion having a melting point of 164 ° C. (solid content 40%) and a melting point of 182 are formed on one side of a synthetic paper.
Blue-coloring leuco dye dispersion at 40 ° C (solid content 40%) 1.5
Parts, red coloring leuco dye dispersion having a melting point of 235 ° C. (solid content 40%) 0.5 parts, developer dispersion (solid content 40%) 10
Thermosensitive coloring formed by mixing 0 part, 60% calcium carbonate slurry 30 parts, 10% polyvinyl alcohol aqueous solution 60 parts, SBR latex (solid content 50%) 24 parts, 30% zinc stearate dispersion 17 parts, and water 55 parts The layer coating material was applied such that the coating amount after drying was 7.5 g / m ^2, and the protective layer coating material was applied. Further, after coating on the surface opposite to the protective layer, super calender treatment was carried out to obtain a heat-sensitive recording material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal recording material, and more particularly to a thermal recording material suitable for use in an image thermal printer which outputs a CRT image for medical measurement as a hard copy. It is a thing.

[0002]

2. Description of the Related Art A heat-sensitive recording material generally comprises a support made of paper, synthetic paper, plastic film or the like, and a colorless or light-colored coloring substance (leuco dye) such as an electron-donating leuco dye on at least one surface of the support. An organic acidic substance (developing agent) such as an electron-accepting phenolic compound and a thermosensitive coloring layer containing an adhesive as a main component are provided, and the leuco dye and the developing agent are heated. A recorded image can be obtained by reacting with energy to develop color. Such a thermal recording medium has advantages such as a compact recording apparatus, low cost, and easy maintenance, and is not only used as a recording medium for a facsimile, an automatic ticket vending machine, or a scientific measuring machine, It is widely used as an output medium for various printers and plotters for POS labels, CAD and CRT medical images.

Among them, an image printer for CRT medical measurement that requires uniformity of recorded images and high resolution and a CAD plotter that requires dimensional stability and fine line recording require synthetic paper having a multi-layered structure, and According to 2 containing inorganic pigment
An axially stretched thermoplastic resin film is used.

In particular, as an image printer sheet for CRT medical measurement, a recording sheet having high whiteness and high recording density is desired. Further, since a silver salt recording type photographic paper has been conventionally used for recording a CRT image, a bluish black color is desired as a color tone of a thermosensitive recording medium. However, whiteness and color tone tend to be largely determined by the combination of the leuco dye and the color developer. When a large amount of white pigment is used to increase the whiteness, there is a problem that the density is lowered. As for the color tone, the black leuco dye alone produces reddish black or greenish black color, and there is a problem that a desirable color tone cannot be obtained.

[0005]

DISCLOSURE OF THE INVENTION According to the present invention, when a thermosensitive recording medium is used for CRT image recording, the whiteness and recording density are low and the color tone is reddish black or greenish black. It is an object of the present invention to solve the problems and provide a heat-sensitive recording material having high whiteness, recording density, and color tone of coloring as high as those of a silver salt type printing paper.

[0006]

As a result of intensive investigations by the present inventors, a method for improving the whiteness, recording density and color tone of a thermal recording material to the same degree as a silver salt type photographic paper was obtained. The present invention has been completed.

That is, the present invention provides a thermosensitive coloring layer containing a colorless or light-colored electron-donating leuco dye on at least one side of a support, a color developer that develops the leuco dye by heating and an adhesive as main components. The leuco dye contains, in addition to the black-colored leuco dye, a blue-colored and / or red-colored leuco dye having a melting point higher than the melting point of the leuco dye, which is measured according to JIS P 8123. The whiteness of the white paper portion of the thermal recording medium is set to 80% or more, and solid printing is performed so that there are 10 steps of density difference from the white paper to the maximum density at almost equal intervals.
A representing the color tone of the printed part measured according to Z 8729
^* Value is -2.0 to +10.0, and b ^* value is -8.0.
By setting it in the range of to +2.0, it is possible to obtain a coloring color tone that does not give an unnatural feeling.

When the a ^* value is less than -2.0, the green-based coloring degree becomes strong, and when it exceeds +10.0, the red-based coloring becomes strong. When the b ^* value is less than -8.0, the bluish color is strong, and when it exceeds +2.0, the yellowish color is strong.

The coloring color tone is generally determined by a combination of a leuco dye which is a color developing agent and a color developing agent. When the coloring color tone is not preferable, another dye having a complementary color relation with the color tone is blended for toning. However, in the case of a heat-sensitive recording material, the melting point of the leuco dye is different, so that it is not possible to obtain the target color tone simply by mixing the leuco dyes having different coloring colors. It was

For example, it is desirable to use a red-coloring leuco dye in order to improve the color tone of the green-based black-coloring leuco dye, but a red-coloring leuco dye having a lower melting point than the green-based black-coloring leuco dye is used. When used, the red dye is strongly colored at a halftone density, which is not preferable. It is necessary to blend a red-coloring leuco dye having a melting point higher than that of the green-based black-coloring leuco dye, and further blending a blue-coloring dye having a melting point higher than that of the black-coloring leuco dye, if necessary.

The color tone is adjusted in this way, and the JIS Z
A * value measured according to 8729 is -2.0 to +1
A target color tone can be obtained by setting 0.0 and the b * value to −8.0 to +2.0.

The support used in the present invention is obtained by heat-kneading a polyolefin resin and a white inorganic pigment, extruding from a die, and stretching in the machine direction. ~ 2
Synthetic paper produced by laminating layers and further stretching in the transverse direction, and thermoplastic resin such as polyolefin resin and polyester resin, or those obtained by extruding biaxially a mixture of thermoplastic resins from the die, and the thermoplastic resin of white color In addition to those obtained by extruding a mixture of inorganic pigments heated and kneaded through a die and biaxially stretching, those prepared from pulp fibers such as high-quality paper, medium-quality paper, roll paper, recycled paper and coated paper can be used. In order to improve the uniformity of the image, it is preferable that the support made of pulp fibers is provided with a coating layer in advance and then coated with the thermosensitive coloring layer.

The thermosensitive coloring layer of the present invention is a colorless or light-colored electron-donating leuco dye having a blue and / or red coloring property in addition to black coloring, a developer and an adhesive agent for coloring the leuco dye by heating. In addition to containing a white pigment as a main component, it may contain a heat-fusible substance, an auxiliary additive component such as a dispersant, a defoaming agent, and a fluorescent dye, if necessary.

[0014] thermosensitive coloring layer of the present invention on at least one surface of the support, the coating amount after drying 2~12g / m ^2, preferably be obtained by coating such that 3 to 10 g / m ² it can. As a coating method, an air knife method, a Mayer bar method, a blade method, a reverse roll method, a slit die method, or the like conventionally used by those skilled in the art can be used.

By smoothing the surface of the thermosensitive coloring layer with a super calender, gloss calender, machine calender or the like, the color developing sensitivity and the image uniformity can be improved.

The color-forming dye used in the present invention is a colorless or light-colored electron-donating leuco dye capable of reacting with a color developer under heating to form a color.

Examples of black leuco dyes include 3
-Diethylamino-6-methyl-7-anilinofluorane, 3- (N-methyl-N-cyclohexyl) amino-
6-methyl-7-anilinofluorane, 3-dibutylamino-7-chloroanilinofluorane, 3- [N-ethyl-N- (p-methylphenyl)] amino-6-methyl-7-anilino Fluoran, 3-diethylamino-7-
(Metatrifluoromethyl) anilinofluorane, 3-
(N-ethyl-N-tetrahydrofurfuryl) amino-
6-Methyl-7-anilinofluorane, 3- (N-ethyl-N-isopentyl) amino-6-methyl-7-anilinofluorane, 3- (N, Ndibutyl) amino-6-
There are fluoran dyes such as methyl-7-anilinofluorane.

As a blue-coloring dye, there is crystal violet lactone. Examples of red-colored leuco dyes include 3-diethylamino-6-methyl-7-chlorofluorane, rhodamine-B orthochloroanilinolactam, 3,6-bis (diethylamino) fluorane-γ-.
There are (4'-nitro) anilinolactam, 6-diethylamino-benzo-fluorane.

The color developer used in the present invention comprises an electron-accepting organic acidic substance capable of reacting with a color-forming dye under heating to form a color.

Such a color developer liquefies or vaporizes at room temperature or higher, preferably 70 ° C. or higher, and reacts with the color forming dye to develop a color thereof.
4'-isopropylidene diphenol (bisphenol A), 4,4'-isopropylidene bis (2-chlorophenol), 4,4'-isopropylidene bis (2-methylphenol), 4,4'-isopropylidene bis (2,6-t-butylphenol), 4,4'-sec
-Butylidene diphenol, 4,4'-cyclohexylidene diphenol, 4-t-butylphenol, 4-phenylphenol, 4-hydroxydiphenoxide,
4,4'-dihydroxydiphenyl sulfone, 2,4 '
-Dihydroxydiphenyl sulfone, 3,3'-dihydroxydiphenyl sulfone, 3,3'-diamino-4,
4'-dihydroxy-diphenyl sulfone, 3,3'-
Diallyl-4,4'-dihydroxy-diphenyl sulfone, 3,3'-dichloro-4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-diphenyl sulfone, 4-hydroxy-4'-isopropyloxydiphenyl sulfone, 4-hydroxy -4'-benzyloxydiphenyl sulfone, 2,4-dihydroxy-diphenyl sulfone, 2,4-dihydroxy-4'-methyldiphenyl sulfone, and 3,4-dihydroxyphenyl-p-trisulfone.

Since the color developer usually has the highest color density,
It is mixed and used in a ratio of 1 to 5 parts by weight, preferably 1.5 to 3 parts by weight with respect to 1 part by weight of the color forming dye.

In the present invention, the adhesive contained in the thermosensitive coloring layer may be either a water-soluble resin or a water-dispersible resin. Examples thereof include polyvinyl alcohol, starch, modified starch, gum arabic, gelatin, casein, chitosan, and the like. Methyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, polyvinylpyrrolidone, polyacrylic acid salt, polyacrylic amide, styrene-maleic anhydride copolymer, methyl vinyl ether-maleic anhydride copolymer, isopropylene-maleic anhydride copolymer, etc. Water-soluble resin, vinyl acetate emulsion, acrylic ester copolymer emulsion such as vinyl acetate- (meth) acrylic ester copolymer emulsion, methacrylic ester copolymer emulsion, polyurethane emulsion, poly Vinyl emulsion, polyvinylidene chloride emulsion, SBR latex, minimum film forming temperature in emulsion, such as MBR latex can be used alone or in combination with 20 ° C. less film forming properties of good water-dispersible resin.

However, it is necessary that the mixed liquid does not develop color, aggregate, or have a high viscosity when mixed with the respective dispersion liquids of the color forming dye and the color developing agent,
Further, it is necessary that the formed heat-sensitive recording layer film be tough and have no desensitizing effect.

Further, in order to improve the water resistance of the thermosensitive coloring layer, a crosslinking agent for curing the resin can be used. For example, glyoxal, dialdehyde compounds such as polyaldehydes, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins,
Melamine resin, diglycidyl compounds such as glycerin diglycidyl ether, dimethylolurea compounds, aziridine compounds, blocked isocyanate compounds, and inorganic compounds such as ammonium persulfate, ferric chloride, and magnesium chloride at 1% of the resin. -10%
It can be used in the range of.

The white pigment used in the heat-sensitive layer of the present invention is
In order to increase the whiteness of the thermosensitive color developing layer and prevent the occurrence of sticks and debris, it is desirable that the oil absorption amount be 50 ml / 100 g or more, and it is blended in the range of 20 to 60% in the solid content of the thermosensitive color developing layer.

For example, calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcined clay, silica,
Diatomaceous earth, synthetic aluminum silicate, zinc oxide, titanium oxide, aluminum hydroxide, barium sulfate, surface-treated inorganic pigments such as calcium carbonate and silica, and urea-formalin resin powder, styrene / methacrylic acid copolymer resin powder Although organic pigments such as benzoguanamine resin powder and polystyrene resin powder can be used, fine particles having an average particle size of 5 μm or less are preferable.

Examples of the heat-fusible substance used in the thermosensitive coloring layer of the present invention include fatty acids such as stearic acid amide, stearic acid ethylenebisamide, oleic acid amide, palmitic acid amide, coconut fatty acid amide and behenic acid amide. Amides, waxes such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax and ester wax, oxalic acid di-p-methylbenzyl ester, oxalic acid di-p
-Chlorobenzyl ester, terephthalic acid dimethyl ester, terephthalic acid dibutyl ester, terephthalic acid dibenzyl ester, isophthalic acid dibutyl ester, 1
-Hydroxynaphthoic acid phenyl ester, 1,2-di (3-methylphenoxy) ethane, 1,2-diphenoxyethane, 1-phenoxy-2- (4-methylphenoxy) ethane, diphenyl carbonate, p-benzylbiphenyl, 2,2'-methylenebis (4-methyl-6-t-butylphenol), 4,4'-butylidenebis (6-t
-Butyl-3-methylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 2,2'-methylenebis (4-ethyl-)
6-t-butylphenol), 2,4-di-t-butyl-3-methylphenol, hindered phenols such as 4,4′-thiobis (3-methyl-6-t-butylphenol), 2- (2 '-Hydroxy-5'-methylphenyl) -benzotriazole, and 2-hydroxy-
There are sensitizers such as 4-benzyloxybenzophenone, antioxidants, and ultraviolet absorbers.

The heat-fusible substance is preferably contained in the heat-sensitive color forming layer in a proportion of 4 parts by weight or less with respect to 1 part by weight of the color developer.

Further, in order to improve the wetting of the heat-sensitive layer coating and eliminate repelling, a wetting improving agent such as acetylene glycol or dialkyl sulfosuccinate may be added.

It is possible to appropriately provide a protective layer on the thermosensitive color developing layer of the present invention to improve storage stability such as scratch resistance, water resistance and chemical resistance. In the protective layer, a water-soluble and / or water-dispersible resin and a crosslinking agent for improving water resistance and a white pigment for imparting writability and naturalness can be added. The water-soluble and / or water-dispersible resin, cross-linking agent, and white pigment used in the protective layer can be appropriately selected from those used in the thermosensitive color-developing layer.

The protective layer has a coating amount after drying of 1.0 to 5.0 g / m ² , preferably 2.0 to 4.0 on the thermosensitive coloring layer.
It can be obtained by applying g / m ² . The coating method can be appropriately selected and used from the methods used for the thermosensitive coloring layer. If the coating amount of the protective layer is less than 1.0 g / m ² , the coating film is not formed uniformly, so the storage stability decreases, and if the coating amount exceeds 5.0 g / m ² , the sensitivity decreases. However, there is a drawback that the recording density decreases.

A back layer may be applied to the opposite surface of the protective layer from the viewpoint of curl prevention and antistatic. The back layer coating material comprises a water-soluble resin and / or a water-dispersible resin, a crosslinking agent, a pigment, a conductive agent, and auxiliary agents such as a dispersant, a defoaming agent, and a lubricant. The resin, cross-linking agent, pigment, auxiliary agent and the like can be appropriately selected and used from those used in the thermosensitive color developing layer.

The conductive agent is preferably an anionic one such as polystyrene sulfonate sodium salt or ammonium salt, polyacrylic acid sodium salt or ammonium salt. The compounding amount of the conductive agent is 20 ° C. 65% RH
The surface electrical resistivity of the back surface measured under the above environmental conditions is 1 ×
It is desirable that the compounding amount be 10 ¹⁰ Ω or less.

After coating the heat-sensitive coloring layer, if necessary, a protective layer,
After coating the back layer, smoothing treatment can be performed with a super calender, gloss calender, machine calender, or the like to improve the uniformity of recording.

[0035]

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 example, “part” means “part by weight”.

Example 1 On one side of synthetic paper YUPO FPG-80, the following thermosensitive color developing layer coating material was applied so that the coating amount after drying was 7.5 g / m ^2, and the protective layer was applied thereon. The amount of coating after drying the paint is 3.0g
It was coated so as to be / m ² . Further, a back layer coating material was applied to the surface opposite to the protective layer so that the coating amount after drying was 3.5 g / m ^2, and then super calendar treatment was performed.

Preparation of coating material for thermosensitive coloring layer Liquid A (black coloring leuco dye dispersion liquid) 3- (N-ethyl-N-isopentyl) amino-6-methyl-7-anilinofluorane (mp = 164 ° C.) ) 20 parts 10% aqueous polyvinyl alcohol solution 20 parts water 10 parts solution B (blue coloring leuco dye dispersion) crystal violet lactone (mp = 182 ° C.) 10 parts 10% aqueous polyvinyl alcohol solution 10 parts water 5 parts solution C (red coloring) Leuco dye dispersion) 3-diethylamino-6-methyl-7-chlorofluorane (mp = 235 ° C.) 10 parts 10% polyvinyl alcohol aqueous solution 10 parts water 5 parts D liquid (developing agent dispersant) 4-hydroxy- 4'-isopropyloxydiphenyl sulfone 50 parts 10% aqueous polyvinyl alcohol solution 50 parts water 25 parts A solution, B solution, C solution, D The separately distributed Ultra Visco Mill, milled, average particle size was adjusted to 1μm or less.

Solution A 45 parts, solution B 1.5 parts, solution C 0.5
Part, D solution 100 parts, 60% calcium carbonate slurry (Brilliant-15 Shiraishi Industry Co., Ltd. product) 30 parts, 10% polyvinyl alcohol aqueous solution (NL-05, polymerization degree 50)
0, Nippon Synthetic Chemical Co., Ltd. product, 60 parts, SBR latex (OX-1060, Nippon Zeon Co., Ltd. product, solid content 50)
%) 24 parts, 30% zinc stearate dispersion liquid (Hydrin Z-7-30, Chukyo Yushi Co., Ltd. product) 17 parts, and water 55 parts were mixed to obtain a thermosensitive coloring layer coating material.

Protective layer paint 60% Kaolinite clay dispersion 33 parts 10% modified polyvinyl alcohol aqueous solution 300 parts (F-1842GH, Showa Denko KK) acrylic emulsion 195 parts (SC-297-1, solid content 18) %, Nippon Shokubai Co., Ltd. product dimethylol urea solution 50 parts (Papyrrole J-001, 30% solution, Showa Denko KK product) 255 parts water were mixed to form a protective layer paint.

-Back layer coating material Sodium polystyrene sulfonate 33 parts (Chemist 6120, solid content 30%, Sanyo Kasei Co., Ltd. product) Acrylic emulsion 113 parts (Dyulimer SEK-301, solid content 40%, Nippon Pure Chemical Co., Ltd.) ) Product) 10% aqueous solution of oxidized starch (Ace A, product of Oji Corn Starch Co., Ltd.) 100 parts 60% Kaolinite clay dispersion 150 parts Dimethylol urea solution (solid content 30%) 17 parts Water 87 parts are mixed to form a back layer. It was paint.

Example 2 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the thermosensitive coloring layer shown below was used instead of the thermosensitive coloring layer used in Example 1. Liquid E (black coloring leuco dye dispersion) 3- (N, N-dibutyl) amino-6-methyl-7-anilinofluorane (mp = 182 ° C.) 20 parts 10% aqueous polyvinyl alcohol solution 20 parts water 10 parts F Liquid (developing agent dispersant) 4,4'-dihydroxydiphenyl sulfone 50 parts 10% polyvinyl alcohol aqueous solution 50 parts water 25 parts G liquid (sensitizer dispersion) oxalic acid di-p-methylbenzyl ester 50 parts 10% Polyvinyl alcohol aqueous solution 50 parts Water 25 parts E liquid, F liquid, and G liquid were separately dispersed and pulverized with an Ultraviscomill, and adjusted so that the average particle diameter was 1 μm or less.

Solution E 50 parts, solution B (used in Example 1) 5
Part, C liquid (used in Example 1) 1 part, F liquid 50 parts, G liquid 5
0 part, 60% calcium carbonate slurry 8 parts, 10% polyvinyl alcohol aqueous solution 60 parts, SBR latex (solid content 50%) 24 parts, 30% zinc stearate dispersion 1
7 parts and 43 parts of water were mixed to obtain a thermosensitive coloring layer coating material.

Example 3 On one surface of synthetic paper YUPO FPG-80, the following thermosensitive coloring layer coating material was applied so that the coating amount after drying was 5.5 g / m ² and supercalendering was performed. It was・ Paint preparation of thermosensitive coloring layer H liquid (red coloring leuco dye dispersion liquid) Rhodamine-B-orthochloroanilinolactam (mp = 172 ° C) 10 parts 10% polyvinyl alcohol aqueous solution 10 parts water 5 parts H liquid is ultra It was dispersed and pulverized with a biscomill and adjusted so that the average particle diameter was 1 μm or less.

Solution A used in Example 1 45 parts, solution B 1.
25 parts, D solution 75 parts, G solution used in Example 2 25 parts,
0.5 part of H liquid, 25 parts of 60% calcium carbonate slurry,
10% Hydroxyethylated Starch Aqueous Solution (Aberex 2
530, Matsutani Chemical Co., Ltd. product (180 parts) and 30% zinc stearate dispersion liquid (17 parts) were mixed to obtain a thermosensitive coloring layer coating material.

Example 4 A thermosensitive recording medium was obtained in the same manner as in Example 3 except that the thermosensitive coloring layer shown below was used instead of the thermosensitive coloring layer used in Example 3. Solution A 45 parts used in Example 1, Solution B 1.5 parts, Solution D 75 parts and Solution H 0.7 parts used in Example 3, 60% calcium carbonate slurry 47 parts, 10
% Hydroxyethylated Starch Aqueous Solution (Abelex 253
0, Matsutani Chemical Co., Ltd. product (180 parts) and 30% zinc stearate dispersion liquid (17 parts) were mixed to obtain a thermosensitive coloring layer coating material.

Comparative Example 1 The same procedure as in Example 1 was repeated except that a red-coloring leuco dye having a melting point lower than that of the black-coloring leuco dye was used instead of the thermosensitive coloring layer used in Example 1, as shown below. A thermosensitive recording medium was obtained.

Preparation of paint for thermosensitive coloring layer Liquid I (black coloring leuco dye dispersion liquid) 3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluorane (mp = 205 ° C.) ) 10 parts 10% aqueous polyvinyl alcohol solution 10 parts water 5 parts Liquid I was dispersed and pulverized with an Ultraviscomill and adjusted to have an average particle size of 1 μm or less. Liquid J (red coloring leuco dye dispersion liquid) 3-diethylamino-7-chlorofluorane (mp = 172 ° C.) 10 parts 10% polyvinyl alcohol aqueous solution 10 parts water 5 parts J liquid is dispersed and pulverized with an Ultra Viscomill, The average particle size was adjusted to 1 μm or less.

45 parts of solution I, solution B used in Example 1
5 parts, J solution 1.5 parts, D solution 100 parts, 60% calcium carbonate slurry 30 parts, 10% polyvinyl alcohol aqueous solution 60 parts, SBR latex (solid content 50%) 24 parts,
17 parts of a 30% zinc stearate dispersion and 54 parts of water were mixed to obtain a thermosensitive coloring layer coating material.

Comparative Example 2 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the coating material for thermosensitive coloring layer shown below was used. 45 parts of E solution, 7.5 parts of B solution, and J used in Examples 1 and 2
Liquid 2.5 parts, liquid F 100 parts, 60% calcium carbonate slurry 25 parts, 10% polyvinyl alcohol aqueous solution 60
Part, SBR latex (solid content 50%) 24 parts, 30%
17 parts of zinc stearate dispersion and 52 parts of water were mixed to obtain a thermosensitive coloring layer coating material.

Comparative Example 3 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the coating material for thermosensitive coloring layer shown below was used. Liquid K (developing agent dispersant) 4,4'-isopropylidenediphenol 50 parts 10% polyvinyl alcohol aqueous solution 50 parts water 25 parts K liquid is dispersed and pulverized with an Ultra Viscomill to have an average particle diameter of 1 μm or less. Was adjusted.

45 parts of solution I and 10 parts of solution K used in Comparative Example 1
0 part, 60% calcium carbonate slurry 32 parts, 10% polyvinyl alcohol aqueous solution 60 parts, SBR latex (solid content 50%) 24 parts, 30% zinc stearate dispersion 17 parts, water 55 parts are mixed to form a thermosensitive coloring layer. It was paint.

While measuring the whiteness of the thermal recording materials obtained in Examples 1 to 4 and Comparative Examples 1 to 3,
A commercially available thermal printer (UP-930, manufactured by Sony) was used to record the gradation by changing the energy level in 10 steps, and a spectral reflectance measuring device (MCPD-1000, manufactured by Otsuka Electronics Co., Ltd.) was used to measure the color tone of the color-developed part and blank paper. It was used for measurement and a ^* value and b ^* value were determined.

The results are shown in Table 1.
In Example 4, the whiteness was 80% or more and the a ^* value was −.
The range of 2.0 to +10.0 and the b ^* value was in the range of -8.0 to +2.0, which was excellent in the bluish black color development, but Comparative Example 1,
In Comparative Example 2, red coloring was strong in a part of the halftone density portion, and it was unsuitable as the color tone of the thermal recording material for image recording.

[0054]

[Table 1] Whiteness: Measured according to JIS P8123. Recording density: Measured with a Mcbeth RD-914 densitometer. Color tone: Spectral reflectance measuring device (MCPD-1000,
Otsuka Electronics Co., Ltd.).

[0055]

The thermosensitive recording medium produced according to the present invention has a high whiteness, a high recording density after printing, a good contrast, and a color tone of bluish black which is good for image recording.

Claims (1)

[Claims] 1. A black leuco dye as a leuco dye in a thermosensitive coloring layer containing a colorless or light-colored electron-donating leuco dye, an organic acidic substance that develops the leuco dye by heating, and an adhesive as main components on at least one surface of a support. In a heat-sensitive recording material containing a blue-colored and / or red-colored leuco dye having a melting point higher than that of the color-forming leuco dye and the black-coloring leuco dye, the whiteness of the recording surface measured according to JIS P 8123 is 80. % Or more and JIS Z 8
The a ^* value of the color tone of the color-developing portion measured according to 729 is -2.
A thermosensitive recording medium characterized by having a range of 0 to +10.0 and ab ^* value of -8.0 to +2.0.