JPH0585054A - Thermal recording material - Google Patents

Abstract

PURPOSE:To extremely enhance color forming sensitivity and to improve color re-development properties by forming a thermal recording material by providing a thermal color forming layer containing a color forming substance, an acidic substance, a color developability enhancer and extender pigment on a base material. CONSTITUTION:A color forming substance, an acidic substance, a color developability enhancer composed of oxalic ester and extender pigment wherein the pH of a 5wt.% suspension is 4.0-8.5 are separately finely group in water or a solvent by predetermined quantities using a grinder such as a ball mill and mixed to prepare a coating solution which is, in turn, applied to a base material such as paper or a synthetic resin sheet using a coating apparatus such as air knife coater and dried to obtain a thermal recording material having a thermal recording layer. As pref. extender pigment, there is silica type and/or alumina-silica type extender pigment wherein the pH of a 5wt.% suspension is 5.5 to 7.5. As the color developability enhancer, benzyl oxalate or di-p- methylbenzyl oxalate is designated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material which has a remarkably improved recolorability (storability of heat-sensitive color-developing performance), high sensitivity, and excellent image stability.

[0002]

2. Description of the Related Art A heat-sensitive recording material is one in which an image of characters, figures, etc. is developed on the recording material by heat energy.
In recent years, due to its simplicity, it has come to be used in fields such as POS labels, various printer recorders, automatic ticket gates, and prepaid cards, as well as facsimile paper.

There are various types of thermal recording, but from the viewpoints of image sharpness, resolution, image color tone, etc., dye precursors such as crystal violet lactone (CVL) are used.
The method that uses a color-forming substance such as the above and an acidic substance that develops the color is the main force. In this method, a phenol compound such as bisphenol A, which is a solid at room temperature as an acidic substance and which melts and liquefies when heated to act as an acidic substance, has been conventionally used.

The thermosensitive recording medium is required to have high sensitivity, no background fog (high whiteness), and excellent image stability and recolorability. Above all, there is a strong demand for high sensitivity in response to speeding up and energy saving of facsimiles, and various improvement methods have been reported. For example, a method of adding stearic acid amide or the like as a color-forming performance improving agent (JP-A-54-139740).
JP-A No. 60-82382), a method of using benzyl p-hydroxybenzoate etc. as an acidic substance (JP-A-54-74762), and the like. However, although the methods described in these publications improve the coloring sensitivity,
It was still inadequate, and the image stability and recolorability were not satisfactory.

Previously, the inventors of the present invention have conducted extensive studies and found that when an oxalic acid ester and / or an aliphatic dibasic acid ester is used as a color-developing performance improving agent, the sensitivity and image stability are higher than those of conventional ones. Obtaining an excellent thermal recording material (Japanese Patent Laid-Open No. 64-1583, 63-183878)
JP-A-63-251286).

[0006]

However, storability, which is said to be the greatest disadvantage in thermal recording,
Among them, the re-coloring property of the thermosensitive recording material (preservation property of thermosensitive coloring performance) was still insufficient in view of the demand level which has been increased in recent years.

[0007]

Means for Solving the Problems The inventors of the present invention have made further studies in view of such circumstances, and as a result, as a result, a chromogenic substance, an acidic substance, and an oxalic acid ester and / or an aliphatic 2 base as a chromogenic performance improving agent. In a thermosensitive recording medium having a thermosensitive coloring layer containing an acid ester and an extender pigment, a 5% by weight suspension of PH (extendant pigment 2.5 g and water 4
7.5 g and a beaker were placed in a beaker, and the suspension was stirred for 10 minutes with a stirrer to obtain a pH value measured by a pH meter.
It was found that a heat-sensitive recording material having significantly improved storage stability (recolorability) of recording performance can be obtained by using a recording medium having the same characteristics (hereinafter, the same) of 4.0 to 8.5, thereby completing the present invention. It was

That is, according to the present invention, the chromogenic substance (A), the acidic substance (B), the oxalic acid ester and / or the aliphatic 2
A thermosensitive color developing layer containing a color-developing performance improving agent (C) composed of a basic acid ester and an extender pigment (D) having a pH of a 5 wt% suspension of 4.0 to 8.5. The present invention provides a thermosensitive recording medium.

The extender pigment (D) used in the present invention is
Any 5% suspension having a pH of 4.0 to 8.5 can be used. For example, a silica-based extender pigment; silica-
Alumina-based extender pigments; calcium oxide-based extender pigments such as calcium sulfate and calcium sulfite; calcium carbonate surface-treated with fatty acids, resin acids and the like; zeolite, sericite and the like. Above all, the pH of the 5% by weight suspension is 5.5 to 5.5% from the viewpoint that a thermosensitive recording medium having excellent color development sensitivity, whiteness and anti-sticking property and free of background fog can be obtained.
A silica-based extender pigment such as finely divided silicas, silica sand, diatomaceous earth, etc., which is 7.5; and a silica-alumina-based extender pigment such as kaolin and clay are preferred. In addition, p of 5 wt% suspension
With an extender pigment having an H of less than 4.0, background fog and color development of the heat-sensitive coating liquid are likely to occur, and the pH of a 5 wt% suspension is 8.5.
Larger extender pigments only give less recolorability.

Specific examples of these include Mizukas.
il P603 [fine silica powder manufactured by Mizusawa Chemical Industry Co., Ltd.,
5 wt% suspension pH = 7.1], Mizukasil
P527 (fine powder silica manufactured by the same company, pH of suspension of 5% by weight = 6.7), Mizukasil P707 (fine silica powder manufactured by same company, pH of suspension of 5% by weight = 7.3),
Optiwhite [Kaolin clay manufactured by Shiraishi Calcium Co., Ltd., pH of suspension of 5% by weight = 5.5], No. Two
0 (pH of a 5% by weight suspension of kaolin clay manufactured by the same company)
= 6.8), No. 5 Clay [Takehara Chemical Industry Co., Ltd.
Clay, 5 wt% suspension pH = 7.0], Glo
max LL (clay manufactured by the same company, p of 5% by weight suspension)
H = 6.0), Carplex CS-7 [fine silica powder manufactured by Shionogi Pharmaceutical Co., Ltd., 5% by weight suspension pH = 6.
5], Carplex CS-8 (fine silica powder manufactured by the same company, pH of suspension of 5% by weight = 6.5), Nipsil
E-200A [fine silica powder manufactured by Nippon Silica Industry Co., Ltd.,
5 wt% suspension pH = 6.5], Nipsil LP
(Powdered silica manufactured by the same company, pH of 5% by weight suspension =

6.0), Transpafill [De
gussa Corp. Made of silica-alumina, pH of suspension of 5% by weight = 7.0], FK 320DS (fine silica powder of the same company, pH of suspension of 5% by weight = 6.3), S
ipernat 22LS (the same company fine silica powder, 5
Wt% suspension pH = 6.3), Tokusil GU
-N [fine silica powder manufactured by Tokuyama Soda Co., Ltd., pH of suspension of 5% by weight = 6.5], Riodiolite F [diatomaceous earth manufactured by Showa Chemical Industry Co., Ltd., pH of suspension of 5% by weight =]
7.4], ASP # 600 [Engelhard C
orp. Kaolin, 5 wt% suspension pH = 4.
3], SCP-E # 2010 [fatty acid surface-treated calcium carbonate manufactured by Sankyo Seiko Co., Ltd., 5% by weight suspension pH =
8.4], Syloid 162 [fine powdered silica manufactured by Fuji Devison Chemical Co., Ltd., pH of suspension of 5% by weight = 7.
5], Syloid 244 (fine silica powder manufactured by the same company,
5 wt% suspension pH = 7.5) and the like.

Examples of the color-forming performance improver (C) used in the present invention include oxalate esters such as dibenzyl oxalate, di-o-chlorobenzyl oxalate and di-m oxalate.
-Chlorobenzyl, di-p-chlorobenzyl oxalate,
Di-o-ethoxyphenyl oxalate, Di-p-oxalate
Methylcyclohexyl, di-o-methylbenzyl oxalate, o-ethylbenzyl oxalate, di-m-oxalate
Methylbenzyl, di-m-ethylbenzyl oxalate, di-p-methylbenzyl oxalate, di-p-ethylbenzyl oxalate, di-1-naphthylmethyl oxalate, dicinnamyl oxalate, dibenzhydryl oxalate and the like can be mentioned. Of these, dibenzyl oxalate, di-p-chlorobenzyl oxalate and di-p-methylbenzyl oxalate are preferred.

Examples of the aliphatic dibasic acid ester include di-p-nitrobenzyl malonate and di-p succinate.
-Nitrobenzyl, di-o-chlorobenzyl succinate,
Di-p-chlorobenzyl succinate, diphenacyl succinate, diphenacyl glutarate, di-o-chlorobenzyl adipate, di-p-chlorobenzyl adipate, phenacyl adipate, di- (2-isopropyl-5-adipate. (Methylcyclohexyl), diphenacyl pimelate, di-p-nitrobenzyl suberate, di-p-nitrobenzyl sebacate, diphenacyl sebacate, di-p-bromophenacyl sebacate and the like, among which di-o-chloro adipate. Benzyl and diphenacyl glutarate are preferred. As the aliphatic dibasic acid ester, a sulfur-containing one can be used, and examples thereof include diphenacyl thiodipropionate, di-p-chlorobenzyl thiodipropionate, and diphenyl thiodipropionate. Diphenacyl pluropionate is preferred.

The color-forming substance (A) used in the present invention is not particularly limited, and examples thereof include fluoran-based, phthalide-based, phenoxazine-based, phenothiazine-based, rhodamine lactam-based, leucoauramine-based, triphenylmethane-based, spiropyran. Examples include various derivatives such as system compounds.

Specific examples thereof include 3- (N, N-diethylamino) -6-chloro-7-fluorane and 3-N-.
Cyclohexylamino-6-chlorofluorane, 3-
(N, N-diethylamino) -7-chlorofluorane,
3- (N, N-diethylamino) -7,8-benzfluorane, 3- (N, N-diethylamino) -6-methyl-7-chlorofluorane, 3-pyrrolidino-6-methyl-7-anilino Fluorane, 3- (N, N-diethylamino) -o-chloroanilinofluorane, 3- (N-methyl-N-cyclohexylamino) -6-methyl-7-
Anilinofluorane, 3- (N, N-diethylamino)
-5-Methyl-7- (N, N-dibenzylamino) fluorane, 3- (N-ethyl-N-propylamino) -6
-Methyl-7-anilinofluorane, 3- (N, N-diethylamino) -6-methyl-7- (2,4-dimethylanilino) fluorane, 3- (N, N-diethylamino) -7- ( o-fluoroanilino) fluorane, 3-
(N, N-dibutylamino) -7- (o-fluoroanilino) fluorane, 3-N-cycloheptylamino-7
-(N, N-dibenzylamino) fluorane, 3-
(N, N-diethylamino) -7- (N-ethylanilino) fluorane, 3- (N-ethyl-N-cyclohexylamino) -7-anilinofluorane, 3- (N, N-
Diethylamino) -7- (N, N-dibenzylamino)
Fluoran, 3- (N, N-diethylamino) -7-anilinofluorane, 3- (N, N-diethylamino)-
6-Methyl-7-anilinofluorane, 3- (N-ethyl-N-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane, 3- (ethyl-N-isobutylamino) -6- Methyl-7-anilinofluorane,
3- (N, N-diethylamino) -7-N-n-octylaminofluorane, 3- (N, N-diethylamino)
−

7-m-Trifluoromethylanilinofluorane, 3- (N, N-diethylamino) -6-chloro-
7-anilinofluorane, 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane, 3- (N, N-dibutylamino) -6-methyl-7
-Anilinofluorane, 3- (N, N-dibutylamino) -7-o-chloroanilinofluorane, 3- (N,
N-diethylamino) -6,8-dimethylfluorane,
3- (N-ethyl-N-isoamylamino) -7,8-
Benzofluorane, 3- (N-ethyl-p-toluidino) -6-methyl-7-anilinofluorane, 3- (N
-Ethyl-p-toluidino) -7-N-methylanilinofluorane, 3- (N-ethyl-p-toluidino) -7
-Methylfluorane, 3- (N, N-diethylamino)
-7-Methylfluorane, 3- (N, N-dimethylamino) -7-methylfluorane, 3- (N-methyl-N-
Butylamino) -6-methyl-7-anilinofluorane, 3- (N, N-diamylamino) -6-methyl-7
-Anilinofluorane, 3-methoxyamino-6-methoxyfluorane, 3- (N, N-diethylamino) -7
-T-butylfluorane, 3- (N, N-diethylamino) -6-methylfluorane, 3- (N-methyl-N-)
Amylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-amylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-p-
Toluidino) -6-methyl-7-p-toluidinofluorane, 3- (N, N-diethylamino) -7-o-carbomethoxyanilinofluorane, 3-piperidino-6-
Methyl-7-anilinofluorane, 3- (N-ethyl-
N-ethoxypropylamino) -6-methyl-7-anilinofluorane, 3,3-bis (p-

Dimethylaminophenyl) phthalide, 3,
3-bis (p-dimethylaminophenyl) -6-aminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-nitrophthalide, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthali Do three
-(4-Diethylaminophenyl) -3- (1-ethyl-2-methylindol-3-yl) phthalide, 3,3
-Bis (1-n-butyl-2-methylindole-3-
Yl) phthalide, 3,3-bis (1-ethyl-2-methylindol-3-yl) phthalide, 3,3-bis (1
-N-octyl-2-methylindol-3-yl) phthalide, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindole-3
-Yl) -4-azaphthalide, 3- (4-N-cyclohexyl-N-methylamino-2-methoxyphenyl)-
3- (1-ethyl-2-methylindol-3-yl)
-4-azaphthalide, 3,6-bis (diethylamino)
Fluoran-γ-anilinolactam, 3,6-bis (diethylamino) fluorane-γ- (p-nitro) anilinolactam, 3,6-bis (diethylamino) fluorane-γ- (o-chloro)

Anilinolactam, 3,7-bis (dimethylamino) -10-benzoylphenothiazine, tris (4-dimethylaminophenyl) methane, N-butyl-
3- [bis [4- (N-methylanilino) phenyl] methyl] carbazole, 1,3,3-trimethylindoline-2,2'-spiro-6'-nitro-8'-methoxybenzopyran, 3-methyl- Spiro-dinaphthopyran,
3-ethyl-spiro-dinaphthopyran, 3-benzyl-
Spiro-dinaphthopyran, 3,6,5'-tris (dimethylamino) fluorene-9-spiro-1 '-(3'-
Isobenzofuran), 2,2-bis [4- [6 '-(N
-Cyclohexyl-n-methylamino) -3'-methylspiro (phthalide-3,9'-xanthene) -2'-ylamino] phenyl] propane and the like.

Among them, 3- (N, N-diethylamino)
-6-Methyl-7-anilinofluorane, 3- (N, N
-Dibutylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamylamino) -6
-Methyl-7-anilinofluorane, 3- (N-methyl-N-cyclohexylamino) -6-methyl-7-anilinofluorane, 3- (N, N-diamylamino) -6
-Methyl-7-anilinofluorane is preferred.

Furthermore, the acidic substance (B) used in the present invention is a solid at room temperature, and when heated to about 60 to 180 ° C.,
Any compound may be used as long as it can be melted and liquefied to open the lactone ring of the color-forming substance to form a color, and all of them function well in the presence of the color-forming performance improver (C), for example, 1,1.
-Bis (4-hydroxyphenyl) ethane, 1,1-bis (4-hydroxyphenyl) propane, 1,1-bis (4-hydroxyphenyl) butane, 1,1-bis (4
-Hydroxyphenyl) -2-methylpropane, 2,2
-Bis (4-hydroxyphenyl) propane, 2,2-
Bis (2-chloro-4-hydroxyphenyl) propane, 2,2-bis (3-methyl-4-hydroxyphenyl) propane, 2,2-bis (4-hydroxyphenyl) heptane, 2,2-bis (4 -Hydroxyphenyl) hexane, 2-methyl-3,3-bis (4-hydroxyphenyl) butane, 2-methyl-4,4-bis (4
-Hydroxyphenyl) pentane, 2-methyl-5,5
-Bis (4-hydroxyphenyl) hexane, α, α-
Bis (4-hydroxyphenyl) ethylbenzene, 2,
2-bis (4-hydroxy-3,5-dimethylphenyl) propane, 2,2-bis (4-hydroxy-2-methylphenyl) propane, 2,2 '-(3-hydroxy

Phenyl-4'-hydroxyphenyl) propane, 2,2-bis (3,5-dichloro-4-hydroxyphenyl) propane, 2,2-bis (4-hydroxyphenyl) pentane, 2,2-bis (4-hydroxyphenyl) butane, 2,2-bis (4-hydroxyphenyl) octane, 2,2-bis (4-hydroxyphenyl) hexafluoropropane, 1,1-bis (4-hydroxyphenyl) methane, 1 , 1-bis (4-hydroxyphenyl) cyclohexane, 1,1-bis (2,6-
Dimethyl-4-hydroxyphenyl) methane, 1,1-
Bis (2-hydroxy-4-chlorophenyl) methane,
1,1-bis (2-hydroxy-4-methyl-6-te
rt-butylphenyl) methane, 1,1-bis (2-hydroxy-4-methylphenyl) methane, 1,2-bis (4-hydroxy-2-methylphenyl) ethane, 1,
1-bis (4-hydroxy-2-isopropylphenyl) cyclohexane, 1,1,1-tris (4-hydroxyphenyl) methane, 1- (4-hydroxyphenyl) -1,1-bis (4-hydroxy-3) -Methylphenyl) methane, 1- (4-hydroxyphenyl) -1,
1-bis (4-hydroxy-3,5-dimethylphenyl) methane, 1,1,1-tris (4-hydroxyphenyl) ethane, 4- [4- {1,1-bis (4-hydroxyphenyl)} Ethyl] -α, α-dimethylbenzylphenol, bis (4-hydroxyphenyl)

Acetic acid, methyl bis (4-hydroxyphenyl) acetate, butyl bis (4-hydroxyphenyl) acetate, benzyl bis (4-hydroxyphenyl) acetate,
2,2-bis (4-hydroxyphenyl) propionic acid, methyl 2,2-bis (4-hydroxyphenyl) propionate, 2,2-bis (4-hydroxyphenyl)
Ethyl propionate, 3,3-bis (4-hydroxyphenyl) butanoic acid, 4,4-bis (4-hydroxyphenyl) pentanoic acid, α, α-bis (4-hydroxyphenyl) -1,4-dimethylbenzene , Α, α-bis (4
-Hydroxyphenyl) -1,4-diisopropylbenzene, α, α-bis (3,4-dihydroxyphenyl)
-1,3-diisopropylbenzene, α, α-bis (4
-Hydroxyphenyl) -1,3-diisopropylbenzene, bis (4-hydroxyphenyl) sulfide, bis (4-hydroxy-3-methylphenyl) sulfide, bis (3-methyl-4-hydroxy-6-tert)
-Butylphenyl) sulfide, bis (3,6-dimethyl-4-hydroxyphenyl) sulfide, bis (4-
Hydroxyphenyl) sulfone, (4-hydroxyphenyl-4′-isopropyloxyphenyl) sulfone,
(3,4-dihydroxyphenyl-4′-methylphenyl) sulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, bis (4-hydroxyphenylthioethoxy) methane, 1,2-bis (4-hydroxyphenyl) Thioethoxy) ethane, 1,5-bis (4-hydroxyphenylthio) -3-oxapentane, bis (4-hydroxyphenyl) ether, 4,4'-

Dihydroxybenzophenone, 4,4'-
Dihydroxydiphenyl, 2,2'-dihydroxydiphenyl, p-phenylphenol, α-naphthol, β
-Naphthol, 2,5-di-tert-butyl-p-cresol, 2-tert-butyl-p-cresol,
2,6-di-tert-butylphenol, p-methylphenol, phloroglysin, pyrogallol, 4-te
rt-octylcatechol, hydroquinone, resorcin, catechol, 4-hydroxyacetophenone, p-
tert-Butylphenol, thymol, 3,5-xylenol, gallic acid, lauryl gallate, stearyl gallate, salicylic acid, anilide salicylate, m-hydroxybenzoic acid, p-hydroxybenzoic acid, methyl p-hydroxybenzoate, p-hydroxy. Benzyl benzoate,
Ethyl p-hydroxybenzoate, butyl p-hydroxybenzoate, tolylmethyl p-hydroxybenzoate, p-
Phenethyl hydroxybenzoate, phenyl p-hydroxybenzoate, 2-hydroxy-p-toluic acid, 1-hydroxy-2-naphthoic acid, dimethyl 3-hydroxy-o-phthalate, 3-phenylsalicylic acid, 3,5-di −
Methyl tert-butyl salicylate and the like can be mentioned.

Among them, 2,2-bis (4-hydroxyphenyl) propane, 2-methyl-4,4-bis (4-hydroxyphenyl) pentane, 4-hydroxyphenyl-4'-isopropyloxyphenyl) sulfone, bis (3-allyl-4-hydroxyphenyl) sulfone and bis (4-hydroxyphenyl) butyl acetate are preferred.

These acidic substances (B) are chromogenic substances 1
Usually 10 to 100 parts by weight (hereinafter simply referred to as "part")
1,000 parts, preferably 100 to 500 parts are used.
In addition, the color-forming performance improver (C) and the extender pigment (D) are each usually 1 to 1, relative to 100 parts of the acidic substance (B).
000 parts, preferably 30 to 1,000 parts are used.

The color-forming substance (A), the acidic substance (B) and the color-forming performance improving agent (C) are all used in the form of fine particles, preferably fine particles having a particle diameter of several microns or less. In order to produce the heat-sensitive recording material of the present invention, various commonly known methods can be used, but usually, the color-forming substance (A), the acidic substance (B), the color-forming performance improver (C) and the constitution Pigment (D)
Each separately, or at least one of the color-forming substance (A) contains a color-forming performance improver (C) and / or an extender pigment (D), and each separately in water or a solvent,
Using a crusher such as a ball mill or sand grinder,
A method of finely dispersing and coating the prepared coating liquid on a substrate using a coating machine such as an air knife coater, a blade coater, a reverse roll coater, etc. is used.

Of course, as a binder for the above coating liquid,
For example, polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methoxy cellulose, ethyl cellulose, casein, starch, gelatin, polystyrene-maleic acid,
Polyacrylic acid, polyvinylpyrrolidone, polyisobutylene-maleic acid, polyvinyl acetate, ethylene-vinyl acetate copolymer, styrene-butadiene copolymer, styrene-butadiene-acrylonitrile copolymer, vinyl chloride-vinyl acetate copolymer, Polyacryl, polyacrylamide, polyester, polyurethane, polyolefin, alkyds and the like are used.

In addition, stabilizers such as hindered phenols may be added to the coating solution, if necessary, to improve performance.
UV absorbers such as benzophenone type and triazole type,
Lubricants such as polyethylene wax and paraffin wax,
A water resistant agent and various other chemicals can be added. Furthermore, various dispersants for dispersing various chemicals in water or a solvent can be added to the coating liquid.

The heat-sensitive recording material of the present invention is applied, for example, to a base material so that the dry weight thereof is generally ² to 12 g per 1 m ^{2 of the} base material, and then dried at room temperature to about 50 ° C. It can be obtained by forming a coating film. Paper is generally used as the base material, but synthetic resin sheets, non-woven fabric sheets, and the like can also be used as appropriate.

[0030]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. All parts and% in the examples are based on weight.

Example 1 Liquid A (color-forming substance liquid) 3- (N-methyl-N-isoamyl) -6-methyl-7-anilinofluorane 1.0 part Dibenzyl oxalate 2.0 parts 10% polyvinyl Aqueous alcohol solution 3.0 parts Water 5.0 parts ───────────────────────────────── Total 11.0 parts B Liquid (acidic substance liquid) 2,2-bis (4-hydroxyphenyl) propane 3.0 parts Mizukasil P603 [fine silica powder manufactured by Mizusawa Chemical Industry Co., Ltd., pH of 5% suspension = 7.1] 3. 0 part Zinc stearate 0.5 part 10% polyvinyl alcohol aqueous solution 7.0 parts water 10.0 parts ──────────────────────────── ────── Total 23.5 parts The above liquids A and B are blended separately, and paint Milled dispersion was to obtain a coating stock solution in conditioners.

Next, 11.0 parts of solution A and 23.5 parts of solution B were mixed to obtain a heat-sensitive coating solution, which was applied onto a high quality paper of 64.5 g / m ² to give a coating amount of 8 g / m ² after drying. It was coated in the above manner and dried to obtain the thermosensitive recording medium of the present invention.

The thermosensitive recording material thus obtained was tested for color development sensitivity and recolorability in the following manner. The recording material was excellent not only in color development sensitivity but also in recolorability.
The results are shown in Table 1.

[Evaluation of color development sensitivity] MS manufactured by Okura Electric Co., Ltd.
Using an I-type thermal head printer, pulse width 0.1 to
Printing and color development on the test recording medium under the condition of 1.0 millisecond, and the color density is Macbeth densitometer RD- manufactured by Macbeth Co.
918, the pulse width when the color density value becomes 1.0 was obtained from the color density / pulse width curve, and the color development sensitivity was evaluated by the magnitude of this pulse width value (small pulse width value). The higher the color development sensitivity).

[Evaluation of Color Reappearance] A test recording material was subjected to Condition A.
(Temperature 40 ° C., Humidity 90% RH) and Condition B (Temperature 60
Left for 168 hours in an atmosphere of ℃, humidity 55% RH)
The color development sensitivities before and after storage were compared and evaluated by the retention rate (the higher the retention rate, the better the recolorability).

Examples 2 to 5 Instead of Mizukasil P603, Mizuk
asil P527 [fine silica powder made by Mizusawa Chemical Industry Co., Ltd., pH of 5% suspension = 6.7], Radiolite
F [diatomaceous earth manufactured by Showa Kagaku Co., Ltd., p of 5% suspension]
H = 7.4], ASP # 600 [Engelhard
Corp. Kaolin, 5% suspension pH = 4.
3] or SCP-E # 2010 [fatty acid-treated calcium carbonate manufactured by Sankyo Seiko Co., Ltd., pH of 5% suspension = 8.
4] was used to prepare the thermosensitive recording medium of the present invention in the same manner as in Example 1 except that the solution B was blended, and then the color developing sensitivity and recolorability were tested in the same manner as described below. All of the recording materials of No. 1 had excellent color reproducibility as well as color development sensitivity. However, ASP # 600
The heat-sensitive recording material obtained in Example 4 using No. 2 had some background fog. The results are shown in Table 1.

Examples 6 to 10 Instead of dibenzyl oxalate, di-p-methylbenzyl oxalate, di-p-chlorobenzyl oxalate, di-o-chlorobenzyl adipate, diphenacyl glutarate or thiodipropionic acid. A thermosensitive recording medium of the present invention was obtained in the same manner as in Example 1 except that the liquid A was blended using diphenacyl, and then the color developing sensitivity and recoloring properties were tested in the same manner as described below. All of the recording materials were excellent in color reproducibility as well as color development sensitivity. The results are shown in Table 1.

Examples 11-13 Instead of 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane, 3- (N, N).
-Diethylamino) -6-methyl-7-anilinofluorane, 3- (N, N-dibutylamino) -6-methyl-
The present invention was carried out in the same manner as in Example 1 except that the solution A was blended using 7-anilinofluorane or 3- (N-methyl-N-cyclohexylamino) -6-methyl-7-anilinofluorane. When a thermal recording material was obtained and then a test for color developing sensitivity and recoloring property was carried out in the same manner as described below, all of these recording materials were excellent not only in color developing sensitivity but also in recoloring property. The results are shown in Table 1.

Examples 12-17 Instead of 2,2-bis (4-hydroxyphenyl) propane, 2-methyl-4,4-bis (4-hydroxyphenyl) pentane, (4-hydroxyphenyl-4'-)
Isopropyloxyphenyl) sulfone, bis (3-allyl-4-hydroxyphenyl) suriphone or bis (4
-Hydroxyphenyl) butyl acetate was used, and a thermosensitive recording medium of the present invention was obtained in the same manner as in Example 1 except that the test for color developing sensitivity and recoloring property was conducted as follows. As a result, all of these recording materials were excellent not only in color development sensitivity but also in recolorability.
The results are shown in Table 1.

[0040]

[Table 1] Comparative Examples 1-5 Instead of Mizukasil P603 (silica),
Mizukasil P832 [fine silica powder made by Mizusawa Chemical Co., Ltd., pH of 5% suspension = 10.3], Fine
sil SP-10 [fine silica powder manufactured by Tokuyama Soda Co., Ltd.,
5% suspension pH = 10.5], Escalon # 2
000 [calcium carbonate manufactured by Sankyo Seiko Co., Ltd., pH of 5% suspension = 9.2], Calshitec brill
iant-15 [calcium carbonate manufactured by Shiraishi Industry Co., Ltd.,
5% suspension pH = 9.4] or PC [Shiraishi Industry Co., Ltd.]
Calcium carbonate, 5% suspension pH = 10.5] was used to prepare solution B, and a thermosensitive recording medium for comparison was obtained in the same manner as in Example 1, and color sensitivity was similarly obtained. ,
When a test for recoloring property was conducted as follows, all of these recording materials were remarkably inferior in recoloring property. The results are shown in Table 2.

Comparative Examples 6 to 7 A thermosensitive recording medium for comparison and control was prepared in the same manner as in Example 1 except that stearyl amide or p-benzylbiphenyl was used instead of dibenzyl oxalate to prepare the solution A.
Then, similarly, a test for color developing sensitivity and recoloring property was carried out as follows. As a result, not only the color developing sensitivity of each of these recording materials but recoloring property was remarkably poor. The results are shown in Table 2.

[0042]

[Table 2]

[0043]

The heat-sensitive recording material of the present invention has extremely high color-developing sensitivity and excellent recolorability.

Claims (6)

[Claims] 1. A chromogenic substance (A) and an acidic substance (B)
And a color-developing performance improving agent (C) composed of an oxalic acid ester and / or an aliphatic dibasic acid ester, and an extender pigment (D) having a pH of a 5 wt% suspension of 4.0 to 8.5. A heat-sensitive recording material having a heat-sensitive coloring layer contained therein. 2. The extender pigment (D) is a 5% by weight suspension of p
The heat-sensitive recording material according to claim 1, which is a silica-based and / or alumina-silica-based extender pigment having H of 5.5 to 7.5. 3. The heat-sensitive material according to claim 1, wherein the color-forming performance improving agent (C) is oxalic acid dibenzyl ester which may have a lower alkyl group, a lower alkyloxy group or a halogen atom as a nuclear substituent. Record body. 4. The color-forming performance improver (C) is dibenzyl oxalate, di-p-methylbenzyl oxalate, di-o-chlorobenzyl oxalate, di-p-chlorobenzyl oxalate, di-o oxalate. -Methoxybenzyl, oxalic acid di-
The thermosensitive recording medium according to claim 1 or 2, which is at least one dibenzyl oxalate ester selected from the group consisting of p-methoxybenzyl. 5. The coloring performance improver (C) is a dialkyl of malonic acid, succinic acid, adipic acid or glutaric acid, which may have a lower alkyl group, a lower alkoxy group, a nitro group or a halogen atom as a nuclear substituent. The thermosensitive recording medium according to claim 1 or 2, which is a benzyl ester or a diphenacyl ester. 6. The color-forming performance improver (C) is selected from the group consisting of di-o-chlorobenzyl adipate, diphenacyl glutarate, and diphenacyl thiodipropionate.
Or, two or more kinds of aliphatic dibasic acid dibenzyl or aliphatic 2
The thermosensitive recording medium according to claim 1, which is a diphenacyl basic acid.