JP2003025734A - Heat sensitive recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat sensitive recording material having a high color developing density at a high sensitivity and excellent storage stability (heat resistance, moisture resistance and plasticizer resistance (solvent resistance)) of an image part and a non-image part (skin part). SOLUTION: The heat sensitive recording material comprises a heat sensitive color developing layer containing an electron donative colorless dye and an electron acceptive compound on a support. In this material, the electron acceptive compound is a 2,4-bis(phenylsulfonyl) phenol, and is contained by dispersing in a volumetric mean particle size of 0.4 to 1.0 μm in a sulfonate modified polyvinyl alcohol.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material having high color density and excellent storage stability.

[0002]

2. Description of the Related Art Thermal recording materials for recording images by applying heat with a thermal head or the like are relatively inexpensive, their recording devices are simple and highly reliable, and maintenance is unnecessary. Widely used. Under such circumstances, in recent years, there has been a particularly strong demand for higher performance such as higher image quality and improved storage stability, and research on the color density, image quality, storability, etc. of thermosensitive recording materials has been earnestly conducted. .

As a heat-sensitive recording material having high sensitivity, for example, in JP-A No. 11-342676, 2,4-bis (phenylsulfonyl) phenol is used as an electron-accepting compound, and the volume average particle diameter is measured by a sand grinder. An example in which they are dispersed to about 1.5 μm is shown. In addition, JP 2001-39037A and JP 2001-632A.
27 shows an example in which 2,4-bis (phenylsulfonyl) phenol is also used as an electron-accepting compound and is dispersed by a sand grinder, but it is described that the volume average particle diameter is 2 μm or less. Only. Although the above-mentioned heat-sensitive recording materials have higher sensitivity than conventional ones, they cannot be said to satisfy the market demands such as higher sensitivity in recent years.

[0004]

Therefore, the present inventors have found that the particle size of the electron-accepting compound is heat-sensitive in a region where the volume-average particle size of the electron-accepting compound is 2 μm or less (hereinafter referred to as a fine region). As a result of diligent examination of the effect on the performance (sensitivity, etc.) of the recording material, it was found that the performance of the heat-sensitive recording material is improved particularly when the volume average particle diameter of the electron-accepting compound is in a specific range of the fine region, The present invention has been completed. Therefore, it is an object of the present invention to provide a heat-sensitive recording material having high sensitivity and high color density by using an electron-accepting compound having a controlled volume average particle size. Further, the present invention is
Storage stability of the image area and non-image area (background area) (heat resistance,
It is an object of the present invention to provide a heat-sensitive recording material excellent in moisture resistance and plasticizer resistance (solvent resistance).

[0005]

Means for solving the problems Means for solving the above problems are as follows. <1> A thermal recording material having a thermosensitive coloring layer containing an electron-donating colorless dye and an electron-accepting compound on a support, wherein the electron-accepting compound is 2,4-bis (phenylsulfonyl). Phenol and volume average particle size of 0.4-
It is a heat-sensitive recording material characterized by being dispersed and contained in 1.0 μm. <2> 2, in sulfonic acid modified polyvinyl alcohol
The heat-sensitive recording material according to <1>, in which 4-bis (phenylsulfonyl) phenol is dispersed using a sand grinder.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The heat-sensitive recording material of the present invention has a heat-sensitive color forming layer containing an electron-donating colorless dye and an electron-accepting compound on a support, and the electron-accepting compound is 2,4
-Bis (phenylsulfonyl) phenol and the electron-accepting compound has a volume average particle diameter of 0.4 to 0.4 in sulfonic acid-modified polyvinyl alcohol as a binder.
It is dispersed and contained in 1.0 μm.

The thermal recording material of the present invention will be described in detail below. The heat-sensitive recording material of the present invention has at least one heat-sensitive color-developing layer on a support, and may have a plurality of laminated layers. If necessary, another layer such as an undercoat layer or a protective layer is provided. It may be.

<Thermosensitive Coloring Layer> The thermosensitive coloring layer contains an electron-donating colorless dye and an electron-accepting compound, and if necessary, other components such as a heat-fusible substance and an image stabilizer. contains.

—Electron-Accepting Compound— In the heat-sensitive recording material of the present invention, 2,4-bis (phenylsulfonyl) phenol is used as an electron-accepting compound that acts on an electron-donating colorless dye described below to cause color development. By using 2,4-bis (phenylsulfonyl) phenol as the electron-accepting compound, the heat-sensitive recording material has excellent storage stability. Also, this 2,
It is necessary that 4-bis (phenylsulfonyl) phenol is dispersed in a sulfonic acid-modified polyvinyl alcohol, which is a binder of the thermosensitive coloring layer, to have a volume average particle diameter of 0.4 to 1.0 μm, and 0.4 to 0. It is preferably contained in a dispersed state of 0.8 μm. The volume average particle size is 0.
If it is less than 4, the fog density in the background may increase during storage, and if it exceeds 1.0, the thermal sensitivity may decrease. Further, if the volume average particle size is less than 0.3, it is difficult to manufacture.

In the present invention, since 2,4-bis (phenylsulfonyl) phenol is used as the electron-accepting compound and the volume average particle diameter is within the above range, the sensitivity is improved and a high color density can be obtained. . The volume average particle size is measured by a laser diffraction particle size distribution measuring device (for example, L
It can be easily measured with A500 (manufactured by Horiba Ltd.) or the like.

The above 2,4-bis (phenylsulfonyl)
Examples of the method for dispersing phenol include a method using a ball mill, a method using a rod mill, a method using an attritor, and a method using a sand grinder, but in view of the increasing demand for heat-sensitive recording materials in recent years,
It is preferable to use a sand grinder from the viewpoint of practical production efficiency. In the dispersion by the sand grinder, it is preferable to use glass beads, ceramic beads or steel beads having a diameter of 0.2 to 10 mm as dispersion beads.

In the present invention, other known electron-accepting compounds may be used in combination with the 2,4-bis (phenylsulfonyl) phenol as long as the effects of the present invention are not impaired.

The known electron-accepting compound can be appropriately selected according to the purpose and the like, but from the viewpoint of suppressing background fog, a phenolic compound, a salicylic acid derivative and a polyvalent metal salt thereof are preferable.

Examples of the phenolic compound include 2,2'-bis (4-hydroxyphenol) propane (bisphenol A), 2,4-bis (2,5-dimethylphenylsulfonyl) phenol, 4-t- Butylphenol, 4-phenylphenol, 4-hydroxydiphenoxide, 1,1′-bis (4-hydroxyphenyl) cyclohexane, 1,1′-bis (3-chloro-4-hydroxyphenyl) cyclohexane, 1,1 ′
-Bis (3-chloro-4-hydroxyphenyl) -2-
Ethyl butane, 4,4'-sec-isooctylidene diphenol, 4,4'-sec-butylylene diphenol, 4-tert-octyl phenol, 4-p-methylphenylphenol, 4,4'-methylcyclohexylidenephenol , 4,4′-isopentylidenephenol, benzyl p-hydroxybenzoate, 4-hydroxy-4′-isopropyloxydiphenyl sulfone and the like.

As the salicylic acid derivative, for example,
4-pentadecylsalicylic acid, 3-5-di (α-methylbenzyl) salicylic acid, 3,5-di (tert-octyl) salicylic acid, 5-octadecylsalicylic acid, 5-α
-(P-α-methylbenzylphenyl) ethylsalicylic acid, 3-α-methylbenzyl-5-tert-octylsalicylic acid, 5-tetradecylsalicylic acid, 4-hexyloxysalicylic acid, 4-cyclohexyloxysalicylic acid, 4-decyloxysalicylic acid, 4-dodecyloxysalicylic acid, 4-pentadecyloxysalicylic acid, 4
-Octadecyloxysalicylic acid and the like, and zinc, aluminum, calcium, copper and lead salts thereof.

The electron-accepting compounds may be used alone or in combination of two or more. Among the above, from the viewpoint of obtaining a particularly high color density, 2,4
-Bis (2,5-dimethylphenylsulfonyl) phenol and the like are preferable.

The content of the electron-accepting compound (2,4-bis (phenylsulfonyl) phenol) is 50 to 500, which is the content (mass) of the electron-donating colorless dye described later.
Mass% is preferable, and 100-300 mass% is more preferable. In the present invention, 2,4 which is an electron-accepting compound
Since the volume average particle diameter of -bis (phenylsulfonyl) phenol is within the above range, the sensitivity can be improved and the content of the electron-accepting compound can be reduced.

-Electron-donating colorless dye- The electron-donating colorless dye is not particularly limited and can be appropriately selected from known ones, and examples thereof include the compounds shown below. However, the present invention is not limited to these. Examples of the electron-donating colorless dye that develops black color include 3-di (n-butylamino)
-6-Methyl-7-anilinofluorane, 2-anilino-3-methyl-6-N-ethyl-N-sec-butylaminofluorane, 3-di (n-pentylamino) -6-
Methyl-7-anilinofluorane, 3- (N-isoamyl-N-ethylamino) -6-methyl-7-anilinofluorane, 3- (Nn-hexyl-N-ethylamino) -6- Methyl-7-anilinofluorane, 3- [N
-(3-Ethoxypropyl) -N-ethylamino) -6
-Methyl-7-anilinofluorane, 3-di (n-butylamino) -7- (2-chloroanilino) fluorane,
3-diethylamino-7- (2-chloroanilino) fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3- (N-cyclohexyl-N-methylamino) -6-methyl-7-anilinoflu Oran etc. are mentioned.

Among them, 3-di (n-butylamino) -6-methyl-7-anilinofluorane and 2-anilino-3-methyl-6-N are preferable in terms of good background fog in the non-image area.
-Ethyl-N-sec-butylaminofluorane is preferred.

In addition, red or magenta, orange,
The electron-donating colorless dyes that develop blue, green and yellow can also be appropriately selected from known compounds and used. These electron-donating colorless dyes may be used alone or in combination of two or more for color tone correction and the like. The electron-donating colorless dye is contained in a coating liquid for forming a thermosensitive coloring layer (hereinafter, may be referred to as "thermosensitive coloring layer coating liquid").
It may be used as a solid dispersion dispersed in a solvent, or may be used by being encapsulated in a thermo-responsive and / or pressure-responsive macrocapsule.

A plurality of types of the above-mentioned electron-donating colorless dyes may be appropriately selected to prepare a multicolor coloring type heat-sensitive recording material.
Specifically, a thermosensitive coloring layer is formed by incorporating electron-donating colorless dyes that develop different hues into different layers.
It can be produced by, for example, forming a thermosensitive coloring layer by encapsulating two or more types of electron-donating colorless dyes in different types of microcapsules, each having a laminated structure of layers or more.

The thermosensitive coloring layer containing the electron-donating colorless dye is applied, for example, by coating a support with a coating liquid for forming the thermosensitive coloring layer. The electron-donating layer in the thermosensitive coloring layer is applied. The content of the water-soluble colorless dye is 0.1 to 1.0
g / m ² is preferable, and 0.2 to 0.5 g / m ² is more preferable in terms of color density and fog density in the background.

As a method of microencapsulating the color-forming component, a conventionally known method can be appropriately selected and used. For example, an oil phase prepared by dissolving or dispersing one color-forming component (for example, an electron-donating dye precursor) in a hydrophobic organic solvent serving as a core of a capsule is mixed with an aqueous phase in which a water-soluble polymer is dissolved, A suitable method is, for example, an interfacial polymerization method of emulsifying and dispersing by a means such as a homogenizer and then heating to cause a polymer forming reaction at the oil droplet interface to form a microcapsule wall of a polymer substance. The interfacial polymerization method is useful in that a capsule having a uniform particle size can be formed within a short period of time, and a heat-sensitive recording material excellent in raw preservability can be obtained.

-Other Components- The thermosensitive coloring layer may further contain other components such as a heat-fusible substance, a sensitizer and an image stabilizer.

(Heat-fusible substance) As the heat-fusible substance,
2-naphthylbenzyl ether and amide compounds are preferable. By containing the heat-fusible compound in the thermosensitive coloring layer, the storage stability of the image part (coloring part) and the non-image part (background part) is improved. The amide compound can be appropriately selected from known compounds, for example, palmitic acid amide, stearic acid amide, behenic acid amide, hydroxystearic acid amide, methylol stearic acid amide, methylol behenic acid amide, methylene. Examples thereof include bisstearic acid amide, ethylenebisstearic acid amide, ethylenebisstearic acid amide, and ethylenebisbehenic acid amide. Of these, stearic acid amide, ethylenebisstearic acid amide, and methylolstearic acid amide are particularly preferable.

When the 2-naphthylbenzyl ether and the amide compound are used, the usage ratio is 2
-The content of the amide compound is preferably 2 to 100 parts by mass with respect to 100 parts by mass of naphthylbenzyl ether,
It is more preferably 10 to 50 parts by mass. If the content of the amide-based compound is less than 2 parts by mass, high concentration may not be obtained, and if it exceeds 100 parts by mass, fog of the background part when kept in a high temperature and high humidity environment. The concentration may increase (the storage stability of the background part may decrease).

Further, other known heat-fusible substances may be used in combination. Examples of the known heat-fusible substance include stearyl urea, p-benzyl biphenyl, di (2-methylphenoxy) ethane, di (2-methoxyphenoxy) ethane, β-naphthol- (p-methylbenzyl).
Ether, α-naphthylbenzyl ether, 1,4-butanediol-p-methylphenyl ether, 1,4-
Butanediol-p-isopropylphenyl ether,
1,4-butanediol-p-tert-octylphenyl ether, 1-phenoxy-2- (4-ethylphenoxy) ethane, 1-phenoxy-2- (chlorophenoxy) ethane, 1,4-butanediol phenyl ether, Diethylene glycol bis (4-methoxyphenyl) ether, m-terphenyl oxalic acid methylbenzyl ether, 1,2-diphenoxymethylbenzene,
1,2-bis (3-methylphenoxy) ethane, 1,4
-Bis (phenoxymethyl) benzene and the like.

The total content of the heat-fusible substance in the thermosensitive coloring layer is preferably 75 to 200 parts by mass, and 100 to 15 parts by mass based on 100 parts by mass of the electron-accepting compound.
0 mass% is more preferable. When the known heat-fusible substance is used in combination with the 2-naphthylbenzyl ether or amide compound, the sum of the contents of the 2-naphthylbenzyl ether and the amide compound is the total content of the heat-fusible substance. The amount is preferably 50% by mass or more, and 70% by mass
The above is particularly preferable.

(Image Stabilizer) As the image stabilizer,
It can be appropriately selected from known compounds, and a phenol compound, particularly a hindered phenol compound is effective. For example, 1,1,3-tris (2-methyl-4-hydroxy-tert-butylphenyl) butane, 1,1,3-
Tris (2-ethyl-4-hydroxy-5-tert-
Butylphenyl) butane, 1,1,3-tris (3,5
-Di-tert-butyl-4-hydroxyphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) propane, 2,
2'-methylene-bis (6-tert-butyl-4-methylphenol), 2,2'-methylene-bis (6-t
ert-butyl-4-ethylphenol) 4,4′-butylidene-bis (6-tert-butyl-3-methylphenol), 4,4′-thio-bis- (3-methyl-6)
-Tert-butylphenol) and the like.

The content of the image stabilizer is preferably 10 to 100 parts by mass, and more preferably 30 to 60 parts by mass with respect to 100 parts by mass of the electron-donating colorless dye. When the content is less than 10 parts by mass, the desired effect may not be exhibited in terms of background fog and image storability.
If it exceeds 100 parts by mass, a sufficient effect may not be obtained.

-Binder- In the heat-sensitive recording material of the present invention, as a binder,
Sulfonic acid-modified polyvinyl alcohol is used. In the heat-sensitive recording material of the present invention, since the sulfonic acid-modified polyvinyl alcohol is used as the binder, the dispersion stability of 2,4-bis (phenylsulfonyl) phenol is improved, and 2,4-bis (phenylsulfonyl) phenol is improved. The volume average particle diameter is in the above range (0.4 to 1.0 μm,
It is preferably 0.4 to 0.8 μm).

Other known water-soluble binders may be used in combination with the sulfonic acid-modified polyvinyl alcohol as long as the effects of the present invention are not impaired. The other known water-soluble binder is preferably a compound that dissolves in water at 25 ° C. in an amount of 5% by mass or more, and examples thereof include polyvinyl alcohol (including modified polyvinyl alcohol), methyl cellulose, carboxymethyl cellulose, starches (modified starch). ), Gelatin, gum arabic, casein, and a saponified product of a styrene-maleic anhydride copolymer.

The binder is used not only for the purpose of dispersion but also for the purpose of improving the film strength of the formed thermosensitive coloring layer. In order to further improve the film strength, a styrene-butadiene copolymer, a vinyl acetate copolymer, an acrylonitrile-butadiene copolymer, a methyl acrylate-butadiene copolymer, a synthetic polymer latex system such as polyvinylidene chloride is used. A binder can also be used together.

The other components such as the electron-donating colorless dye, the electron-accepting compound and the sensitizer are dispersed by stirring with a ball mill, rod mill, attritor, sand grinder or the like.
It is dispersed simultaneously or individually by a pulverizer and finally prepared as a coating liquid. When dispersed individually,
When the electron-accepting compound is dispersed, the sulfonic acid-modified polyvinyl alcohol is used for dispersion (when other substances are dispersed, the sulfonic acid-modified polyvinyl alcohol is not necessarily used). If necessary, various pigments, metal soaps, waxes, surfactants, antistatic agents, ultraviolet absorbers, defoamers, fluorescent dyes, etc. may be added to the coating liquid.

Examples of the pigment include calcium carbonate, barium sulfate, lithopone, wax, kaolin, calcined kaolin, amorphous silica and aluminum hydroxide. Examples of the metal soap include higher fatty acid metal salts, and specific examples thereof include zinc stearate, calcium stearate, and aluminum stearate. Examples of the wax include paraffin wax, microcrystalline wax, carnauba wax, methylol stearamide, polyethylene wax, polystyrene wax, and fatty acid amide wax, and they may be used alone or in combination of two or more. To be As the surfactant, for example,
Examples thereof include sulfosuccinic acid-based alkali metal salts and fluorine-containing surfactants.

After being dispersed as described above and prepared as a coating solution, it is coated on a support by a known coating method. After coating and drying, it is smoothed with a calender and used. When forming the thermosensitive coloring layer,
The coating amount for forming the thermosensitive coloring layer is not particularly limited,
Usually, the dry weight is preferably about ² to 7 g / m ² . The known coating method is not particularly limited, and examples thereof include a coating method using an air knife coater, a roll coater, a blade coater, a curtain coater, and the like. Among them, the method using a curtain coater is particularly preferable.

<Support> As the support, a conventionally known support can be used. Specifically, a paper support such as high-quality paper, coated paper obtained by coating resin or pigment on paper, resin-laminated paper, high-quality paper having an undercoat layer, recycled paper having an undercoat layer, synthetic paper, or plastic film, etc. A support is mentioned. As the support, JI
From the viewpoint of dot reproducibility, a smooth support having a smoothness defined by S-8119 of 300 seconds or more is preferable.

When an undercoat layer is provided on the support as described above, it is preferable to provide an undercoat layer containing a pigment as a main component. As the pigment, all of general inorganic and organic pigments can be used, but those having an oil absorption of 40 ml / 100 g (cc / 100 g) or more specified by JIS-K5101 are particularly preferable. Specific examples thereof include calcium carbonate, barium sulfate, aluminum hydroxide, kaolin, calcined kaolin, amorphous silica, and urea formalin resin powder. Among them, the oil absorption is 70 ml / 100 g
The above is particularly preferable. As the coated amount of the pigment is preferably 2 g / m ² or more, 4g / m ² or more preferably, 7~12g / m ² is most preferred.

Examples of the binder used in the undercoat layer include water-soluble polymers and water-soluble binders. These may be used alone or in combination of two or more. Examples of the water-soluble polymer include starch, polyvinyl alcohol, polyacrylamide, carboxymethyl alcohol, methyl cellulose, casein and the like. As the water-soluble binder, for example, synthetic rubber latex and synthetic resin emulsion are generally used, and specifically, styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex, vinyl acetate emulsion. Etc. In addition, wax, a decoloring inhibitor, a surfactant and the like may be added to the undercoat layer.

The content of the binder is preferably 3 to 100% by mass, more preferably 5 to 50% by mass, and 8 to 15% by mass with respect to the pigment added to the undercoat layer.
Is most preferred.

A known coating method can be used for forming the undercoat layer. For example, a coating method using an air knife coater, a roll coater, a blade coater, a gravure coater, a curtain coater or the like can be used, and among them, a method using a blade coater is preferable. Furthermore,
If necessary, a smoothing process such as calendering may be performed.

<Protective Layer> A protective layer may be provided on the thermosensitive coloring layer, if desired. The protective layer contains organic or inorganic fine powder, a binder, a surfactant, a heat-fusible substance and the like. Examples of the fine powder include calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, inorganic fine powder of surface-treated calcium and silica, urea- Formalin resin, styrene / methacrylic acid copolymer, organic fine powder such as polystyrene, and the like can be mentioned.

Examples of the binder used in the protective layer include polyvinyl alcohol, carboxy-modified polyvinyl alcohol, vinyl acetate-acrylamide copolymer, silicon-modified polyvinyl alcohol, starch, modified starch, methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, gelatins, Arabica rubber, casein, styrene-maleic acid copolymer hydrolyzate, polyacrylamide derivative, polyvinylpyrrolidone, styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex, latexes such as vinyl acetate emulsion, etc. Is mentioned.

A water-proofing agent may be added for the purpose of cross-linking the binder and further improving the storage stability of the heat-sensitive recording material. Examples of the waterproofing agent include:
N-methylol urea, N-methylol melamine, urea-
Examples thereof include water-soluble initial condensates such as formalin, dialdehyde compounds such as glyoxal and glutaraldehyde, inorganic cross-linking agents such as boric acid, borax and colloidal silica, and polyamide epichlorohydrin.

[0045]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Hereinafter, "parts" and "%" in the examples mean "parts by mass" and "mass%", respectively. The volume average particle diameter is measured by a laser diffraction type particle size distribution measuring instrument LA500 (Horiba Ltd.).
Manufactured).

(Example 1) <Formation of thermosensitive recording material> -Preparation of coating liquid for thermosensitive coloring layer- <Preparation of dispersion A> The following components were dispersed using a sand grinder to give a volume average particle diameter of 1.0 μm dispersion A
Got [Composition of Dispersion A] 3-dibutylamino-6-methyl-7-anilinofluorane 10 parts (electron-donating colorless dye) 10% aqueous solution of polyvinyl alcohol 15 parts (PVA-105, (stock ) Made by Kuraray) ・ Water… 25 parts

<< Preparation of Dispersion Liquid B >> The following components were dispersed using a sand grinder to give a volume average particle size of 0.7 μm.
A dispersion B of m was obtained. [Composition of Dispersion B] 2,4-bis (phenylsulfonyl) phenol: 20 parts (electron-accepting compound) 2-naphthylbenzyl ether: 20 parts 10% aqueous solution of sulfonic acid-modified polyvinyl alcohol: 60 parts ( Gocelan L3266; manufactured by Nippon Gosei Kagaku) ・ Water: 100 parts

<Preparation of Dispersion C> The following components were dispersed using a sand mill to obtain Dispersion C having a volume average particle size of 1.5 μm. [Composition of Dispersion C] Light calcium carbonate 25 parts 40% aqueous sodium polyacrylate solution 0.25 parts Sodium hexametaphosphate 0.25 parts Water 34 parts

A compound having the following composition was mixed to obtain a coating solution for a thermosensitive color developing layer. [Coating liquid composition for thermosensitive color developing layer] -Dispersion liquid A--50 parts-Dispersion liquid B-200 parts-Dispersion liquid C--60 parts-Zinc stearate 30% dispersion liquid--10 parts Paraffin wax-30 % Dispersion: 20 parts 20% dispersion of stearic acid amide: 2 parts 50% aqueous solution of optical brightener: 1 part 10% aqueous solution of polyvinyl alcohol: 40 parts (PVA-117, manufactured by Kuraray Co., Ltd.) )

-Formation of heat-sensitive recording material-A pigment having a basis weight of 70 g / m ² was applied with a blade coater so that the coating amount after drying was 10 g / m ² .
An undercoat layer composed mainly of a binder was applied to form an undercoat base paper. Next, the undercoat layer of the base paper was coated with the coating liquid for the thermosensitive color forming layer obtained above from a curtain coater so that the coating amount after drying was 4 g / m ^2, and dried. The surface of the formed thermosensitive coloring layer was subjected to a calendar treatment to obtain a thermosensitive recording material of the present invention.

(Example 2) In Example 1, the dispersion B was prepared.
A heat-sensitive recording material of the present invention was produced in the same manner as in Example 1 except that the volume average particle size in Example 1 was 0.4 μm.

(Example 3) In Example 1, the dispersion B was prepared.
A heat-sensitive recording material of the present invention was produced in the same manner as in Example 1 except that the volume average particle diameter in Example 1 was 1.0 μm.

Comparative Example 1 Dispersion B in Example 1
A heat-sensitive recording material of Comparative Example was prepared in the same manner as in Example 1 except that bisphenol A was used instead of using 2,4-bis (phenylsulfonyl) phenol in the preparation of.

COMPARATIVE EXAMPLE 2 Dispersion B in Example 1
A heat-sensitive recording material of Comparative Example was produced in the same manner as in Example 1 except that the volume average particle size in Example 1 was set to 0.3 μm. (Comparative Example 3) A thermosensitive recording material of Comparative Example was produced in the same manner as in Example 1 except that the volume average particle diameter of the dispersion B was changed to 1.5 µm. (Comparative Example 4) A thermosensitive recording material of Comparative Example was prepared in the same manner as in Example 1 except that the volume average particle diameter of the dispersion B was 1.2 μm. (Comparative Example 5) In Example 1, except that polyvinyl alcohol (PVA-105; manufactured by Kuraray Co., Ltd.) was used in place of the sulfonic acid-modified polyvinyl alcohol in the preparation of the dispersion liquid B in Example 1. Dispersion was carried out in the same manner as above, but when the volume average particle size was less than 0.9 μm, the liquid thickened and solidified, so that the dispersion liquid could not be obtained,
A thermal recording material could not be prepared.

<Evaluation> With respect to the heat-sensitive recording materials of Examples 1 to 3 and the heat-sensitive recording materials of Comparative Examples 1 to 4 obtained as described above, color density, storage stability (heat resistance, moisture resistance, The plasticizer resistance) was evaluated.

(1) Printing density Kyocera Corp. thermal head (KJT-216-8M)
PD1) and a thermal printer having a pressure roll of 100 kg / cm ² immediately before the head, and the head voltage is set to 2
Printing was performed with a pulse width of 2.1 ms while using a pressure roll under the conditions of 4 V and a pulse cycle of 10 ms. The print density of the print portion was measured with a Macbeth reflection densitometer (RD-918, manufactured by Macbeth Co.). Further, this print density was used as a reference density of print density in the following evaluation of storage stability. As the standard fog value of the density of the non-image area (background fog), the density of unprinted (background area) of each thermal recording material was measured with a Macbeth reflection densitometer (RD-918, manufactured by Macbeth Co.).

(2) Storage stability-Heat resistance-After leaving each printed thermal recording material for 24 hours under the environmental conditions of 60 ° C and 30% RH, the print density of each print area and the density of the background area Macbeth reflection densitometer RD-91
8 was used as an index showing heat resistance. It should be noted that the larger the numerical value of the density of the printed portion, the smaller the fluctuation from the reference density and the better, and the smaller the numerical value of the density of the background portion, the smaller the fluctuation from the standard fog value and the better.

-Moisture resistance-After leaving each printed thermal recording material for 24 hours under the environmental conditions of 40 ° C and 90% RH, the print density and the background density of each printed portion were measured by Macbeth reflection densitometer RD. -91
8 was used as an index showing moisture resistance. Similar to the above evaluation, the larger the numerical value of the density of the printed portion and the smaller the numerical value of the background portion, the smaller the fluctuation of the density and the better.

-Plasticizer resistance-After leaving each printed thermal recording material in contact with a commercially available vinyl chloride sheet (Polymer wrap, manufactured by Shin-Etsu Polymer Co., Ltd.) under an environmental condition of 25 ° C for 24 hours The print density and the background density of each print area were measured with a Macbeth reflection densitometer RD-918, and used as an index showing the plasticizer resistance. Similar to the above evaluation, the larger the numerical value of the density of the printed portion and the smaller the numerical value of the background portion, the smaller the fluctuation of the density and the better.

The measurement results were judged as follows in consideration of the practical level. Regarding the print density, 1.35 or more is excellent (very good), and 1.30 or more and less than 1.35 is good.
(Good) and less than 1.30 were judged as x (bad).
Regarding the background density, less than 0.10 is ◎ (very good), 0.10 or more and less than 0.15 is ◯ (good), 0.1
5 or more was judged as x (bad). Regarding the plasticizer resistance, the residual rate of the printed portion is 95% or more ◎ (very good),
90% or more and less than 95% ○ (good), less than 90% ×
It was judged as (defective). Table 1 below shows the results of measurement and judgment.
Shown in.

[0061]

[Table 1]

As is apparent from Table 1 above, Examples 1 to 1
In the heat-sensitive recording material of 3, high color density is obtained, and storage stability (heat resistance, moisture resistance, plasticizer resistance (solvent resistance)) in the printed portion and non-printed portion (background portion) is excellent, All the evaluations were good. On the other hand, in Comparative Example 1 in which bisphenol A was used as the electron-accepting compound instead of 2,4-bis (phenylsulfonyl) phenol, the heat resistance and the plasticizer resistance were obviously low, and this was not at a practical level. It was Further, in Comparative Example 2 in which the volume average particle diameter of the electron-accepting compound was 0.3 μm, the heat resistance of the background portion was low, and this was not at a practical level. In Comparative Example 3 in which the volume average particle diameter of the electron-accepting compound was 1.5 μm and Comparative Example 4 in which the volume average particle diameter of the electron-accepting compound was 1.2 μm, the color density was low and not at a practical level. Comparative Example 5 in which sulfonic acid-modified polyvinyl alcohol was not used as a binder
However, when the volume average particle diameter was made small, thickening and solidification started, and a dispersion liquid could not be obtained, and a heat-sensitive recording material could not be obtained.

[0063]

According to the present invention, the sensitivity is high and the color density is high, and the storage stability (heat resistance, moisture resistance, plasticizer resistance (solvent resistance) of image areas and non-image areas (background areas) is high. It is possible to provide a heat-sensitive recording material excellent in)).

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hirofumi Mitsuo             200, Onakazato, Fujinomiya City, Shizuoka Prefecture Fuji Photo             Within Film Co., Ltd. F term (reference) 2H026 AA07 AA28 BB02 BB25 CC05                       EE03 FF01 FF15

Claims (2)

[Claims] 1. A thermosensitive recording material having a thermosensitive coloring layer containing an electron-donating colorless dye and an electron-accepting compound on a support, wherein the electron-accepting compound is 2,4-bis (phenyl). (Sulfonyl) phenol and volume average particle diameter of 0.4 to 1.0 μm in sulfonic acid-modified polyvinyl alcohol
A heat-sensitive recording material characterized by being dispersed in and contained in. 2. The heat-sensitive recording material according to claim 1, wherein 2,4-bis (phenylsulfonyl) phenol is dispersed in sulfonic acid-modified polyvinyl alcohol using a sand grinder.