JPH03193387A - Thermal recording body - Google Patents

Abstract

PURPOSE:To improve imprinting aptitude and various writing aptitude, and to prevent the whitening phenomenon of a printing section by containing a pigment having the primary particles of mean particle size of 0.2mum or less in an overcoating layer. CONSTITUTION:A thermal recording body is manufactured by including a pigment having the primary particles of mean particle size of 0.2mum or less in an overcoat layer formed onto a thermal recording layer containing a coloring agent capable of being colored by contacts with a colorless or light-colored basic dye and the basic dye. When the pigment having the primary particles of mean particle size exceeding 0.2mum is used, the tendency of the scattering of light is increased, and the whitening phenomenon of a printing section is brought, thus remarkably lowering picture density. Clay, urea-formalin resin fine particles, etc. are cited as the pigment. The pigments having the primary particles of mean particle size of 0.15mum or less in these pigments are favorable because the whitening phenomenon is improved particularly and the thermal recording body having high picture density is acquired.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention relates to a heat-sensitive recording material having an overcoat layer,
In particular, it relates to a heat-sensitive recording medium that is excellent in imprintability, writing ability, etc.

``Prior art'' Conventionally, a coloring reaction between a colorless or light-colored basic dye and a coloring agent that develops color when it comes into contact with the basic dye is used to create a colored image by bringing both photochromic substances into contact with each other using heat. Thermosensitive recording materials designed to obtain the following are well known.

Such thermal recording media are relatively inexpensive, the recording device is compact, and maintenance is relatively easy, so they are used not only as recording media for facsimiles and various computers, but also in a wide range of fields.

In recent years, facsimiles that use uncoated high-quality paper, so-called plain paper, have appeared as recording media, and the texture of the paper,
Since it is superior to conventional heat-sensitive recording materials in its suitability for stamping and various types of writing, there is a demand for heat-sensitive recording materials having such properties.

However, conventional heat-sensitive recording materials without an overcoat layer
Organic coloring substances and lubricants are exposed directly to the surface, so
It also has the drawbacks of producing stains (scratch stains) when lightly scratched with a fingernail, and having insufficient aptitude for printing and poor aptitude for writing with a pencil.

On the other hand, in the case of a thermal recording material having an overcoat layer, the main purpose of providing the overcoat layer is to provide barrier properties, so although scratch stains are improved, pencil writing suitability and stamping suitability are not improved; Since the drying properties of the ink are reduced, the suitability for printing further deteriorates, and the paper is far from being suitable for plain paper.

For the purpose of improving these drawbacks, for example, Japanese Patent Application Laid-Open No. 61-2
Japanese Patent No. 49789 proposes a heat-sensitive recording material in which the overcoat layer contains an amino acid compound such as N-acyl amino acid ester to improve ink receptivity.

However, such heat-sensitive recording materials are inferior in pencil writability and do not necessarily provide satisfactory characteristics.
Publication No. 5189 states that the oil absorption amount is 50mj! A method has been proposed to improve the bleeding of water-based ink by incorporating an inorganic pigment with a particle size of 1 μm to 5 μm in the overcoat layer in an amount of /100 g or less. If these pigment particles are included in the pigment particles, the print will appear to be blocked by these pigment particles (hereinafter referred to as a whitening phenomenon), resulting in a disadvantage that the image density will be significantly reduced.

"Problems to be Solved by the Invention" In view of the current situation, the inventors of the present invention have conducted intensive research to obtain a thermal recording medium that has excellent sealability and various writing aptitudes, and is free from whitening of the printed portion. The present inventors have discovered that the desired heat-sensitive recording material can be obtained by incorporating a pigment having an average particle size of 0.2 μm or less into the overcoat layer, and have completed the present invention.

"Means for Solving the Problems" The present invention provides an overcoat layer on a heat-sensitive recording layer containing a colorless or light-colored basic dye and a coloring agent capable of coloring when in contact with the basic dye. In the heat-sensitive recording material, the average particle diameter of primary particles in the overcoat layer is 0.2 μm.
This is a heat-sensitive recording material characterized by containing the following pigments.

"Function" The heat-sensitive recording material of the present invention has an important feature in that the overcoat layer contains a pigment whose primary particle average particle diameter is 0.2 μm or less. Incidentally, if a pigment with an average particle size of secondary particles exceeding 0.2 μm is used, the tendency of light scattering becomes strong, leading to a whitening phenomenon in the printed area, and as a result, the image density is significantly reduced.
In addition, when the average particle diameter of the secondary particles becomes around 4 μm or more, the tendency of light scattering becomes weaker and the whitening phenomenon is improved, but the voids between the pigment particles decrease and the vermilion attached to the surface of the coarse pigment decreases. Since it will not be absorbed forever, if you touch the place where the seal was stamped with your finger, the impression will become illegible.

For this reason, in the present invention, by selectively using extremely fine pigments with an average particle diameter of 0.2 μm or less as pigments to be blended into the overcoat layer, the tendency of light scattering can be greatly reduced. The present invention provides a heat-sensitive recording material which maintains a high porosity while suppressing the amount of porosity, and has excellent printing suitability and various writing passability without causing any whitening phenomenon in the printed portion.

The pigment to be added to the overcoat layer is not particularly limited as long as the average particle size of the secondary particles is 0.2 μm or less, and examples include clay calcium carbonate, magnesium carbonate, aluminum hydroxide, talc, Examples include titanium oxide, silicon oxide, zinc oxide, urea-formalin resin fine powder, and the like. Of course, it is also possible to use two or more pigments in combination, if necessary.

Among these pigments, pigments whose primary particles have an average particle diameter of 0.15 μm or less are particularly preferable because the whitening phenomenon is improved and a heat-sensitive recording medium with high image density can be obtained.

Furthermore, when reducing the coating amount of the overcoat layer in order to obtain a highly sensitive heat-sensitive recording medium, the color-forming substance in the heat-sensitive layer oozes onto the overcoat layer, which tends to cause sticking with the thermal head. In order to prevent this, it is desirable to use a pigment whose primary particles have an average particle diameter of 1.0 μm or more. The average particle diameter of such -order particles is 1
．． The type of pigment having a diameter of 0 μm or more is not particularly limited, and can be appropriately selected from the pigments listed above.

In addition, when using a pigment with an average particle diameter of primary particles of 1.0 μm or more, it is necessary to keep it within a range that does not inhibit the desired effect of the present application, and the amount used is such that the average particle diameter of primary particles is 0 μm or more. It is desirable that the amount of the pigment be 50% by weight or less, preferably 30% by weight or less of the pigment having a diameter of .2 μm or less.

Incidentally, the average particle diameter of the primary particles mentioned in the present invention is determined by measuring the pigment powder with a scanning electron microscope (JSM-T-300).
The particle size was determined under 5000x magnification.

The binder constituting the overcoat layer together with the above pigments includes water-soluble polymers, such as starches such as oxidized starch, enzyme-modified starch, cationic starch, esterified starch, and etherified starch. , cellulose derivatives such as methylcellulose, ethylcellulose, carboxymethylcellulose, methoxycellulose, hydroxyethylcellulose, polyvinyl alcohols such as completely (or incompletely) saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, polyac 'J/L' Acid soda, polyacrylamide, polyvinylpyrrolidone, acrylic amide/acrylic ester copolymer, acrylic amide/acrylic ester/methacrylic acid copolymer, styrene/maleic anhydride copolymer alkali salt, isobutylene/maleic anhydride Examples include copolymer alkali salts, water-soluble polymers such as sodium alginate, gelatin, and casein. Of course, it is not limited to these, and two or more types can be used in combination if necessary.

The amount of these binders used is desirably adjusted within the range of 20 to 50% by weight based on the total solid content of the overcoat opening paint.

In addition, this overcoat layer may contain various release agents, dispersants,
Various auxiliary agents used in preparing coatings for heat-sensitive recording layers, such as fluorescent dyes and antifoaming agents, can be used in combination.

Overcoat opening paints are prepared by dispersing specific pigments, binders, etc. using water as a dispersion medium, and are applied onto the heat-sensitive recording layer, but there are no particular limitations on the coating method. (It can be formed according to conventionally well-known and commonly used techniques, such as an air knife coater, a blade coater,
A suitable coating device such as a bar coater, gravure coater, curtain coater, etc. is used. The coating amount of the coating liquid is also not particularly limited, but in order to more effectively transfer the Joule heat from the thermal head to the heat-sensitive recording layer, the coating amount is preferably 5 g/n (hereinafter, preferably 3 g/% or less). On the other hand, in order to achieve the effect of improving scratch aptitude, imprint aptitude, and writing aptitude, a coating amount of 0.8 g/rrf or more is good, so the appropriate coating amount is in the range of 0.8 to 3 g/rrf. is desirable.

In the heat-sensitive recording material of the present invention, known colorless or light-colored basic dyes can be used as basic dyes constituting the recording layer, and specific examples include the following.

3.3-bis(p-dimethylaminophenyl)6-dimethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)phthalide, 3-(p-dimethylaminophenyl)-3-(1,2 -dimethylindol-3-yl)phthalide, 3-(P-dimethylaminophenyl)-3
-(2-methylindole-3-ylphthalide, 3,3
-bis(l,2-dimethylindol-3-yl)-5
=dimethylaminophthalide, 3.3-bis(1゜2-dimethylindol-3-yl)-6-dimethylaminophthalide, 3.3-bis(9-ethylcarbazol-3-
yl)-6-dimethylaminophthalide, 3,3-bis(
2-phenylindol-3-yl)-6-dimethylaminophthalide, 3-p-dimethylaminophenyl-3-
Triallylmethane dyes such as (1-methylpyrrol-3-yl)-6-dimethylaminophthalide, 4,4'-bis-dimethylaminobenzhydryl benzyl ether,
N-halophenyl-leukoolamine, N-2,4,5
-)+7 Diphenylmethane dyes such as chlorophenyl-coalamine, benzoylleucomethylene blue, p
- Thiazine dyes such as nitrobenzoylleucomethylene blue, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho(6 '-Methoxybenzo) spiropyran, 3-probilous virodihenzopyran and other spiro dyes, rhodamine B-anilinolactam, rhodamine (p-nitroanilino)lactam, rhodamine (
Lactam dyes such as 0-chloroanilino)lactam, 3
-dimethylamino-7-medoxyfluoran, 3-diethylamino-6-medoxyfluoran, 3-diethylamino-7-medoxyfluoran, 3-diethylamino-
7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6,
7-dimethylfluorane, 3-(N-ethyl-p-)luidino)-7=methylfluorane, 3-diethylamino-7-N~acetyl N-methylaminofluorane, 3
diethylamino-7-N-methylaminofluorane, 3
-diethylamino-7-dibenzylaminofluorane,
3-diethylamino-7-N-methyl-N-benzylaminofluorane, 3-diethylamino-7-N-chloroethyl-N-methylaminofluorane, 3-diethylamino-7-diethylaminofluorane, 3-(N-ethyl -p-toluidino)-6-methyl-7-phenylaminofluorane, 3-(N-ethyl-p-)luidino)-6
-Methyl-7-(p-toluidino)fluorane, 3-diethylamino-6-methyl-7-phenylaminofluorane, 3-dibutylamino-6-methyl-7-phenylaminofluorane, 3-diethylamino-7-(2 -carbomethoxy-phenylamino)fluorane, 3-(N-
cyclohexyl-N-methylamino)-6-methyl-7
Phenylaminofluorane, 3-pyrrolidino-6=methyl-7-phenylaminofluorane, 3-piperidino-
6-methyl-7-phenylaminofluorane, 3-diethylamino-6-methyl-7=xylidinofluorane,
3-diethylamino 7-(o-chlorophenylamino)
Fluoran, 3-dibutylamino-7-(o-chlorophenylamino)fluoran, 3-pyrrolidino-6-methyl-7-P-7'tylphenylaminofluoran, 3-
(N-methyl-N-n-amyl)amino-6methyl-7
-phenylaminofluorane, 3-(N-ethyl-N-
n-amyl)amino-6-methyl-7-phenylaminofluorane, 3-(N-ethyl-N-isoamyl)amino-6-methyltwophenylaminofluorane, 3-(N
-Methyl-N-n-hexyl)amino-6-methyl=7
-phenylaminofluorane, 3-(N-ethyl-N-
Fluoran dyes such as n-hexyl)amino-6-methyl-7=phenylaminofluorane, 3-(N-ethylN-β-ethylhexyl)amino-6-methyltwophenylaminofluorane, and the like. Of course, the dyes are not limited to these dyes, and two or more types of dyes can be used in combination.

Furthermore, various compounds are known as coloring agents to be used in combination with the above basic dyes, for example, the following are exemplified.

4-tert-butylphenol, α-naphthol, β
-naphthol, 4-acetylphenol, 4-tert
-octylphenol, 4.4'-5ec-butylidene diphenol, 4-phenylphenol, hydroquinone, 4.4'-dihydroxy-diphenylmethane, 4,
4'-isopropylidenediphenol, 2,2-bis(
4-hydroxyphenyl)-4-methylpentane, 4.
4'-cyclohexylidene diphenol, 4.4'-
Dihydroxydiphenyl sulfide, 4,4'-thiobis(6-tert-butyl-3-methylphenol)
, 4.4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxy-4'-methoxydiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, hydroquinone monobenzyl ether, 4- Hydroxybenzophenone, 2,4-dihydroxybenzophenone, 2,
4.4'trihydroxybenzophenone, 2.2',4
゜4'-tetrahydroxybenzophenone, 2.2'methylenebis(4-chlorophenol), 1゜3-di(2
-(4-hydroxyphenyl)-2=propyl]benzene, bis(3-allyl-4-hydroxyphenyl)sulfone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, 4
-propyl hydroxybenzoate, 5ec-butyl 4-hydroxybenzoate, pentyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, 4-
Chlorophenyl hydroxybenzoate, phenylpropyl 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, M-p-chlorobenzyl 4-hydroxybenzoate, p-methoxybenzyl 4-hydroxybenzoate, novolac type phenolic resin, phenol polymer Phenolic compounds such as benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-5e
c -Butyl-4-hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, 3,5-dimethyl-
4-hydroxybenzoic acid, salicylic acid, 3-isopropylsalicylic acid, 3-tert-butylsalicylic acid, 3,5
-di-tert-butylsalicylic acid, 3-benzylsalicyl M, 3-(α-methylbenzyl)salicylic acid, 3-
Chlor-5-(α-methylbenzyl)salicylic acid, 3-
Phenyl-5-(α,α-dimethylbenzyl)salicylic acid, 3,5-di-α-methylbenzylsalicylic acid, 4-
Aromatic carboxylic acids such as the zinc salt of (3-p-tolylsulfonylpropyloxy)salicylic acid, and these phenolic compounds, aromatic carboxylic acids such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel, etc. Salts with polyvalent metals, and organic complexes such as antipyrine complexes of zinc thiocyanate. Note that two or more of these coloring agents can be used in combination as necessary.

Among these coloring agents, it is particularly preferable to use zinc salt of 4-(3-p-)lylsulfonylpropyloxy)salicylic acid and 4-hydroxy-4'-isopropoxydiphenylsulfone in combination because the stability of recorded images is excellent.

The ratio of the basic dye and coloring agent to be used is appropriately selected depending on the type of basic dye and coloring agent used, and is not particularly limited. 100 to 700 parts by weight, preferably 150 to 4 parts by weight
About 0.00 parts by weight of coloring agent is used.

The coating liquid for the heat-sensitive recording layer containing these is generally prepared by using water as a dispersion medium and dispersing the dye and coloring agent together or separately using a stirring/pulverizing machine such as a ball mill or attritor sand mill. prepared.

Such coating liquids usually contain starches and binders as binders.
Hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, various modified polyvinyl alcohols such as carboxyl group-modified, sulfone group-modified, acetoacetyl group-modified, and silicone-modified polyvinyl alcohols, styrene/maleic anhydride copolymer salts, Styrene/acrylic acid copolymer salt,
Styrene-butadiene copolymer emulsion etc. is 2 to 40% by weight of the total solids, preferably 5 to 25% by weight.
It is set up. Of course, two or more of these binders can also be used in combination.

Further, fatty acid amides such as stearic acid amide, stearic acid methylene bisamide, oleic acid amide, palmitic acid amide, coconut fatty acid amide, 2゜2'-methylene bis(4
-methyl-6tert-butylphenol), 4.4'
-Butylidenebis(6tert-butyl-3-methylphenol), ■.

1, 3-1-lis(2-methyl-4-hydroxy5
Hindered phenols such as tert-butylphenyl)butane, p-benzylbiphenyl, 1゜2-bis(
phenoxy)ethane, 1.2-bis(4-methylphenoxy)ethane, 1.2-bis(3-methylphenoxy)
Ethers such as ethane, 1-(2-methylphenoxy)-2-(4-methoxyphenoxy)ethane, 2-naphtholbenzyl ether, hensyl-4-methylthiophenyl ether, dibenzyl terephthalate, l-hydroxy-2-naphthoic acid Esters such as phenyl ester,
Ultraviolet absorbers such as 2-(2'-hydroxy-5'-methylphenyl)benzotriazole and 2-hydroxy4-benzyloxybenzophenone, and various known thermofusible substances can also be added as sensitizers. .

Among such sensitizers, 1-(2-methylphenoxy) ~
2-(4-methoxyphenoxy)ethane is particularly preferred since it has an excellent sensitizing effect.

In addition, inorganic pigments such as kaolin, clay talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, fine particulate anhydrous silica, and activated clay are added to the heat-sensitive recording layer in order to help improve the adhesion of residue in the overcoat layer. be able to.

In the present invention, the method for forming the heat-sensitive recording layer is not particularly limited, and it can be formed using conventionally well-known and commonly used techniques, such as an air knife coater, blade coater, bar coater, gravure coater, curtain coater, etc. Appropriate coating equipment is used.

Furthermore, the amount of coating liquid to be applied is not particularly limited, and is generally 2 to 12 g/rr in terms of dry weight. , preferably within the range of 3 to 10 g/rrf.

As the support, paper, synthetic fiber paper, transparent or opaque plastic film, etc. are used.

It is also possible to provide an undercoat layer between the support and the heat-sensitive recording layer, and various known techniques in the field of heat-sensitive recording material manufacturing may be used, such as providing a protective layer on the back side of the support or applying adhesive processing. can be added.

"Example" The present invention will be described in more detail with reference to Examples below, but the present invention is of course not limited to these.

Further, unless otherwise specified, parts and % in the examples indicate parts by weight and % by weight, respectively.

Example 1 [Preparation of undercoat coating liquid] Amorphous silica (trade name:
Mizuriki Seal P-527. (manufactured by Mizusawa Chemical Co., Ltd.) 100 parts Styrene-butadiene copolymer latex (Tg point Kony-35C) (in terms of solid content) 15 parts Hydroxypropylated starch (in terms of solid content) 5 parts Dispersant (in terms of solid content) 0.5 parts The composition was mixed uniformly to obtain an undercoat shoe coating liquid with a solid content concentration of 30%.

[Formation of undercoat layer]

The above-mentioned undercoat coating solution was applied to a 45 g/r+f high-quality paper using a bar coater so that the coated amount after drying was 15 g/rrr and dried to obtain an undercoat coated paper.

[Preparation of coating liquid for recording layer]

3-Dibutylamino-6-methyl-7-phenylaminofluorane 10 parts Benzyl-4-methylthiophenyl ether 20 parts Methyl cellulose 5% aqueous solution 15 parts water
80 parts of this composition was ground in a sand mill until the average particle size was 1 μm.

4-Hydroxy-4'-isopropoxydiphenylsulfone 30 parts Methyl cellulose 5%
Aqueous solution 30 parts water
70 parts of this composition was ground in a sand mill until the average particle size was 2 μm.

125 parts of liquid A, 130 parts of liquid B, amorphous silica (oil absorption 1
80cc/100g) 30 parts, 20% oxidized starch aqueous solution 1
A recording layer coating liquid was prepared by stirring and mixing 50 parts and 55 parts of water.

[Formation of recording layer]

The obtained recording layer coating liquid was applied onto the undercoat coated paper using a Mayer bar so that the coating amount after drying was 5 g/m.
A thermosensitive recording paper was obtained by drying.

[Preparation of coating liquid for overcoat]

An overcoat shoe coating liquid having a paint concentration of 7% was prepared by blending the following composition at the solid content ratio shown below.

Ultrafine light calcium carbonate (trade name: PX, manufactured by Shiraishi Calcium Co., Ltd., average particle size of secondary particles 0.1 μm)
35 parts heavy calcium carbonate (trade name: Softon 1500, manufactured by Bihoku Funka Kogyo Co., Ltd., average particle size of secondary particles 1.5 μm) lo part exogenous polyvinyl alcohol trade name: Goseheimer Z
-200, manufactured by Nippon Gosei Kagaku Co., Ltd.) 30 parts zinc stearate emulsion (product name: Hydrin Z)
-7. (manufactured by Chukyo Yushi Co., Ltd.) 0.3 parts of 5-part dispersant (trade name: Nearon A-9. Manufactured by Toagosei Kagaku Co., Ltd.) [Formation of overcoat layer] The above-mentioned overcoat coating liquid was applied on the previously formed heat-sensitive recording layer. It was coated and dried with a Mayer bar so that the dry coating amount was 2.0 g/bore, and smoothed with a super calendar to obtain a heat-sensitive recording paper.

Example 2 In the preparation of the overcoat shoe coating liquid of Example 1, ultrafine zinc oxide (trade name: FINEX-25, manufactured by Sakai Kagaku Co., Ltd., average particle diameter of 0) was used instead of ultrafine light calcium carbonate. A thermosensitive recording paper was obtained in the same manner as in Example 1, except that .06 μm) was used.

Example 3 In the preparation of the overcoat shoe coating liquid of Example 1, ultrafine silicon oxide (trade name: Rheolo Seal 102, manufactured by Tokuyama Soda Co., Ltd., average particle diameter of 0.000000 particles) was used instead of ultrafine light calcium carbonate. A thermosensitive recording paper was obtained in the same manner as in Example 1 except that 015 μm) was used.

Example 4 All examples were the same as in Example 1 except that ultrafine light calcium carbonate (trade name: PX) was used instead of heavy calcium carbonate (trade name: Softon 1500) in the preparation of the overcoat shoe coating liquid. A thermosensitive recording paper was obtained in the same manner as in 1.

Example 5 3-dibutylamino-6-methyl-7-phenylaminofluorane manufactured by Dankyu Sara 10 parts 1-(2-methylphenoxy)-2-(4-methoxyphenoxy)ethane
20 parts methylcellulose 5% aqueous solution 15
Department water 8
0 parts This composition was ground in a sand mill until the average particle size was 1 μm.

■4-Hydroxy-4'-isopropoxydiphenylsulfone manufactured by Oka R 30 parts Zinc salt of 4-(3-p-tolylsulfonylpropyloxy)salicylic acid
25 parts 5% methylcellulose aqueous solution 30 parts water 70
This composition was ground in a sand mill until the average particle size was 2 μm.

A thermosensitive recording paper was obtained in the same manner as in Example 3 except that 125 parts of Liquid A and 130 parts of Liquid B in Example 3 were replaced with 125 parts of Liquid C and 155 parts of Liquid D, respectively.

Comparative Example 1 In the preparation of the overcoat shoe coating liquid of Example 1, light calcium carbonate (trade name: PZ, manufactured by Shiraishi Calcium Co., Ltd., average particle size of secondary particles 0.25 μm) was used instead of ultrafine light calcium carbonate. A thermosensitive recording paper was obtained in the same manner as in the example except that .

Comparative Example 2 In the preparation of the overcoat shoe coating liquid of Example I, zinc oxide and zinc white 1 were used instead of ultrafine light calcium carbonate.
A thermosensitive recording paper was obtained in the same manner as in Example 1, except that No. (manufactured by Sakai Chemical Co., Ltd., average particle size of secondary particles 0.6 μm) was used.

Comparative Example 3 In the preparation of the overcoat shoe coating liquid of Example 1, silicon oxide (trade name:
5P-11, manufactured by Tokuyama Soda Co., Ltd., average particle size of primary particles 0
．． A thermosensitive recording paper was obtained in the same manner as in Example 1, except that 30 μm) was used.

Comparative Example 4 In the preparation of the coating solution for overcoating in Example 1, light calcium carbonate (trade name: Albagros, manufactured by Pfizer Inc., average particle size of secondary particles 0.6 μm) was used instead of ultrafine light calcium carbonate. A thermosensitive recording paper was obtained in the same manner as in Example 1 except that .

Comparative Example 5 In the preparation of the coating solution for overcoating in Example 1, heavy calcium carbonate (trade name: BF-100, manufactured by Bihoku Funka Kogyo Co., Ltd., average particle size of -2) was used instead of ultrafine light calcium carbonate. A thermosensitive recording paper was obtained in the same manner as in Example 1 except that a paper sheet (diameter: 3.6 μm) was used.

Comparative Example 6 Same as Comparative Example 1 except that light calcium carbonate (trade name: PZ) was used instead of heavy calcium carbonate (trade name: Softon 1500) in the preparation of the coating solution that required overcoat in Comparative Example 1. A thermosensitive recording paper was obtained.

The 10 types of thermal recording papers obtained in this way were heated using a Kyocera thermal simulator (voltage: 16cm, pulse cycle: 5m5).
ec) was used to record printing pulse times of 0.35 m5 ec and 0.45 m5 ec, and each color density was measured using a Macbeth densitometer (RD-100R model, using an amber filter).
The results are listed in the table. In addition, the degree of whitening of each recorded image was visually evaluated, and those where whitening was observed were marked as x, and those where no whitening was observed were marked as ○, and the results were added to the table.

Note that the color density is low because of the whitening phenomenon.

Next, a seal was placed on the non-printed area, and after 1 minute, the vermilion area was rubbed with a finger to evaluate the dyeability. In this case, high-quality paper (Reference Example 1) was used as the evaluation standard, and those with the same dyeability were marked as ○, those with poor dyeability were marked as ×, and those with very good dyeability were marked as @.

In addition, the ease of writing was evaluated by writing on the non-printing area with a pencil (HB). In this case, high-quality paper was also used as the evaluation standard, and those equivalent to this paper were rated as ○, those with poor writing properties were rated as ×, and those with extremely good writing properties were rated as ◎.

Further, ballpoint pens were also evaluated in the same manner.

Next, the paper was lightly scratched with a fingernail and the degree of color development was compared with that of non-overcoated thermal paper (Reference Example 2), and the results are added to the table. O that has good scratch resistance in practical use
The non-overcoated thermal paper was rated as ×.

Furthermore, printing was performed using a thermal facsimile (NEFAX-27) to evaluate the level of sticking.

Good sticking was evaluated as ○, and cases with slight sticking were evaluated as Δ.

"Effects" As is clear from the table, the heat-sensitive recording material obtained by the present invention has
It was an excellent heat-sensitive recording material with no whitening phenomenon or accompanying decrease in image density, very good ink dye adhesion, good writability, improved sticking, and properties very close to those of plain paper.

Claims (3)

[Claims] (1) In a heat-sensitive recording material in which an overcoat layer is provided on a heat-sensitive recording layer containing a colorless or light-colored basic dye and a coloring agent that can change color when it comes into contact with the basic dye, the overcoat layer contains a colorless or light-colored basic dye. 1. A heat-sensitive recording material comprising a pigment having an average primary particle diameter of 0.2 μm or less. (2) The heat-sensitive recording material according to claim (1), further comprising a pigment whose primary particles have an average particle diameter of 1.0 μm or more. (3) 1-(2-methylphenoxy)- in the heat-sensitive recording layer
The heat-sensitive recording material according to claims (1) and (2), which contains 2-(4-methoxyphenoxy)ethane.