JPH0939409A - Thermal recording - Google Patents

Abstract

A thermosensitive recording medium having a recording layer containing a colorless or light-colored basic dye and a coloring agent on a support is used as a basic dye represented by the following general formula ( Using at least one indolyldiazaphthalide derivative represented by 1),
A heat-sensitive recording material containing at least one diphenylsulfone derivative represented by the following general formula (2) as a coloring agent. Embedded image (In the formula, R ₁ is a C ₁ -C ₈ alkyl group, and R ₂ is C ₁
To C ₆ alkyl groups, R ₃ and R ₄ are C _{1 to} C, respectively.
₆ alkyl group, C ₃ -C ₆ alkoxyalkyl group or p-tolyl group. ) (In the formula, R ₅ and R ₆ each represent a C _{1 to} C ₄ alkyl group, a C _{2 to} C ₄ alkenyl group, a C _{1 to} C ₄ alkoxyl group, a benzyloxy group or a halogen atom.
m is an integer of 0 to 2, n is an integer of 1 to 3, and p and q are integers of 0 to 2, respectively. )

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 utilizing the color reaction of a colorless or light-colored basic dye and a coloring agent, and particularly to suitability for optical character reading (OCR) in the wavelength region of 650 to 700 nm. The present invention relates to an excellent thermal recording material.

[0002]

2. Description of the Related Art A thermosensitive recording medium is known in which a color or color reaction between a colorless or pale basic dye and an organic or inorganic coloring agent is used to bring a color image into contact with each other to obtain a recorded image. Has been. Since such a heat-sensitive recording material is relatively inexpensive and the recording device is compact and its repair is relatively easy, it is used not only as a recording medium for facsimiles and various computers but also in a wide range of fields.

With the recent diversification of needs, various performances are required for the thermal recording material. One of them is for OCR or OMR which can read in the wavelength region of 650 to 700 nm. A thermal recording material has been demanded. As a method for obtaining such a heat-sensitive recording material, for example, 3,3-bis (4-diethylamino-2-ethoxyphenyl) -4-azaphthalide or 3-di-n-butyl is used as a dye having a strong absorption at 650 to 700 nm at the time of color development. Amino-6,8,8-trimethyl-8,9-dihydro- (3,2, e) pyridofluorane or the like is used alone or in combination with a black coloring fluorane dye. However, with these methods, OCR immediately after color development
Although it has aptitude, its OCR aptitude decreases when it is stored under high temperature and high humidity or exposed to light, and its improvement is strongly desired.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a thermal recording material having excellent suitability for optical character reading (OCR) in the wavelength region of 650 to 700 nm.

[0005]

DISCLOSURE OF THE INVENTION The present inventors have prepared a thermosensitive recording medium in which a recording layer containing a colorless or light-colored basic dye and a coloring agent is provided on a support as the basic dye By using at least one of the indolyldiazaphthalide derivatives represented by the formula (1) and containing at least one diphenylsulfone derivative represented by the following general formula (2) as a color developing agent, The inventors have found that the above problems can be solved and completed the present invention.

[0006]

Embedded image

(Wherein R ₁ is a C ₁ -C ₈ alkyl group, R ₂ is a C ₁ -C ₆ alkyl group, R ₃ and R ₄ are each a C ₁ -C ₆ alkyl group, C 1 _{3 to} C ₆ alkoxyalkyl group or p-tolyl group is shown.)

[0008]

Embedded image

(In the formula, R ₅ and R ₆ are each C _{1 to} C ₄
Alkyl group, an alkenyl group of C ₂ -C ₄ of, C ₁ -C ₄
Represents an alkoxyl group, a benzyloxy group or a halogen atom. m is an integer of 0 to 2, n is an integer of 1 to 3, p,
q shows the integer of 0-2, respectively. )

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The heat-sensitive recording material of the present invention is obtained by using a specific indolyldiazaphthalide derivative as a colorless or light-colored basic dye and further using a specific diphenylsulfone derivative as a color developing agent. , 650-700nm even under high temperature and high humidity or exposed to light for a long time
It is possible to obtain a heat-sensitive recording material having excellent suitability for optical character reading (OCR) in the wavelength region of.

Specific examples of the indolylazaphthalide derivative represented by the general formula (1) used in the present invention include, for example, 3- (1-methyl-2-phenylindol-3-yl) -3-. (2-Ethoxy-4-diethylaminophenyl) -4,7-diazaphthalide, 3-
(1-Methyl-2-phenylindol-3-yl)-
3- (2-ethoxy-4-di-n-propylaminophenyl) -4,7-diazaphthalide, 3- (1-methyl-
2-Phenylindol-3-yl) -3- (2-ethoxy-4-di-n-butylaminophenyl) -4,7-
Diazaphthalide, 3- (1-methyl-2-phenylindol-3-yl) -3- (2-ethoxy-4-di-n
-Pentylaminophenyl) -4,7-diazaphthalide, 3- (1-methyl-2-phenylindole-3-
Yl) -3- (2-ethoxy-4-dimethylaminophenyl) -4,7-diazaphthalide, 3- (1-methyl-
2-Phenylindol-3-yl) -3- (2-ethoxy-4-N-ethyl-N-isopentylaminophenyl) -4,7-diazaphthalide, 3- (1-methyl-2)
-Phenylindol-3-yl) -3- (2-ethoxy-4-N-ethyl-Nn-hexylaminophenyl) -4,7-diazaphthalide, 3- (1-methyl-2)
-Phenylindol-3-yl) -3- (2-ethoxy-4-N-ethyl-Np-toluidinophenyl)-
4,7-diazaphthalide, 3- (1-methyl-2-phenylindol-3-yl) -3- (2-methoxy-4)
-Diethylaminophenyl) -4,7-diazaphthalide, 3- (1-methyl-2-phenylindole-3-
Yl) -3- (2-Methoxy-4-di-n-butylaminophenyl) -4,7-diazaphthalide, 3- (1-methyl-2-phenylindol-3-yl) -3- (2
-N-n-hexyloxy-4-diethylaminophenyl) -4,7-diazaphthalide, 3- (1-ethyl-2)
-Phenylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4,7-diazaphthalide, 3- (1-n-butyl-2-phenylindol-3-yl) -3- ( 2-ethoxy-4-diethylaminophenyl) -4,7-diazaphthalide, 3- (1-
n-octyl-2-phenylindol-3-yl)-
3- (2-ethoxy-4-diethylaminophenyl)-
4,7-diazaphthalide, 3- (1-n-butyl-2-
Phenylindol-3-yl) -3- (2-ethoxy-4-N-ethyl-Np-toluidinophenyl)-
4,7-diazaphthalide, 3- (1-methyl-2-phenylindol-3-yl) -3- (2-ethoxy-4)
-N-methyl-N-ethoxypropylaminophenyl)
-4,7-diazaphthalide and the like can be mentioned.

Of course, the indolyl diazaphthalide as described above is not limited to these, and two or more kinds can be used in combination as required.

In the heat-sensitive recording material of the present invention, a specific indolyldiazaphthalide derivative is used as the basic dye as described above, and the diphenyl represented by the general formula (2) is used as the color developing agent. By selectively combining the sulfone derivatives, an excellent effect on OCR readability is exhibited. Specific examples of such diphenyl sulfone derivative include, for example, 4,4′-dihydroxydiphenyl sulfone, 2,4′-dihydroxydiphenyl sulfone, 3,3′-diallyl-4,4′-dihydroxydiphenyl sulfone, 3,3 ′, 5,5'-tetrabromo-4,4'-dihydroxydiphenyl sulfone, 3,3 ', 5,5'-tetrachloro-4,4'-dihydroxydiphenyl sulfone, 4-hydroxydiphenyl sulfone, 4-hydroxy-4' -Methyldiphenyl sulfone, 4-hydroxy-3 ', 4'-tetramethylene diphenyl sulfone, 4-hydroxy-4'-methoxydiphenyl sulfone, 4-hydroxy-4'-ethoxydiphenyl sulfone, 4-hydroxy-4'-iso Propoxydiphenyl sulfone, 4-hydroxy-4 '
-N-butoxydiphenyl sulfone, 4-hydroxy-
4'-benzyloxydiphenyl sulfone, 3,4-dihydroxydiphenyl sulfone, 3,4-dihydroxy-4'-methyldiphenyl sulfone, 3,4,4'-trihydroxydiphenyl sulfone, 3,4,3 ', 4'
-Tetrahydroxydiphenyl sulfone, 2,3,4-
Examples thereof include trihydroxydiphenyl sulfone.

Of course, the above-mentioned diphenyl sulfone derivative is not limited to these, and if necessary, two or more kinds may be used in combination. Among these, 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone is particularly preferably used because a heat-sensitive recording material excellent in OCR reading can be obtained.

The amount of these colorants used is not particularly limited, but is generally 50 to 700 parts by weight, preferably 100 to 500 parts by weight with respect to 100 parts by weight of the basic dye.
It is adjusted within the range of about parts by weight.

In the present invention, known basic dyes such as triarylmethane derivative, diarylmethane derivative, fluorane derivative, phenothiazine derivative, rhodamine lactam derivative, spiropyran derivative are used within a range that does not impair the desired effect. It is also possible to use a derivative, a leuco auramine-based derivative or the like together.

Among these basic dyes, by using at least one of the fluorane compounds represented by the general formula (3) in combination, they are stored in a black color system and stored under high temperature and high humidity, or are long-lived to light. Even if it is exposed to time, a thermal recording material excellent in OCR readability can be obtained.

[0018]

[Chemical 6]

(Wherein R ₇ and R ₈ are C _{1 to} C, respectively)
_{6 represents} an alkyl group, an ethoxypropyl group or a p-tolyl group, R ₉ represents a hydrogen atom or a methyl group, and R ₁₀ represents a methyl group, a chlorine atom or a trifluoromethyl group. k represents an integer of 0 to 2. )

In the present invention, specific examples of the black color-developing fluorane compound represented by the general formula (3) include, for example, 3-diethylamino-6-methyl-7-anilinofluorane and 3-di-n-butyl. Amino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-
7- (m-toluidino) fluorane, 3-di-n-butylamino-6-methyl-7- (m-toluidino) fluorane, 3-diethylamino-6-methyl-7- (2,4
-Xylidino) fluorane, 3-diethylamino-6-
Methyl-7- (3,5-xylidino) fluorane, 3-
Diethylamino-6-methyl-7- (2,6-xylidino) fluorane, 3-di-n-butylamino-6-methyl-7- (2,4-xylidino) fluorane, 3-di-
n-Butylamino-6-methyl-7- (3,5-xylidino) fluorane, 3-di-n-butylamino-6-methyl-7- (2,6-xylidino) fluorane, 3-dimethylamino-6 -Methyl-7-anilinofluorane,
3-di-n-propylamino-6-methyl-7-anilinofluorane, 3- (N-ethyl-p-toluidino)-
6-methyl-7-anilinofluorane, 3- (N-ethyl-p-toluidino) -6-methyl-7- (p-toluidino) fluorane, 3-di-n-pentylamino-6-
Methyl-7-anilinofluoran, 3- (N-methyl-
N-propylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isopentylamino)
-6-Methyl-7-anilinofluorane, 3- (N-ethyl-Nn-hexylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isobutylamino) -6-Methyl-7-anilinofluorane, 3-
Diethylamino-7- (o-chloroanilino) fluorane, 3-di-n-butylamino-7- (o-chloroanilino) fluorane, 3- (N-ethyl-Nn-hexylamino) -7- (o-chloroanilino ) Fluoran,
3- (N-ethyl-N-isopentylamino) -7-
(O-chloroanilino) fluorane, 3-di-n-butylamino-7- (o-fluoroanilino) fluorane,
3-di-n-butylamino-6-methyl-7- (p-chloroanilino) fluorane, 3-diethylamino-7-
(M-trifluoromethylanilino) fluoran, 3-
Di-n-butylamino-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7- (p-trifluoromethylanilino) fluorane, 3- (N-ethyl-N- Ethoxypropyl) amino-6-methyl-7-anilinofluorane, 3- (N-methyl-N-ethoxypropyl) amino-6-methyl-7
-Anilino fluoran and the like.

Of these, 3-di-n-butylamino-6-methyl-7-anilinofluorane exhibits excellent properties especially in terms of color developability and background fog.
Particularly preferably used. In the present invention, it is of course possible to use other known dyes in combination as long as the desired effects are not impaired.

In the heat-sensitive recording material of the present invention, various heat-fusible substances can be used as a recording sensitivity improver in the recording layer. Examples of such a heat-fusible substance include caproic acid amide, capric acid amide, palmitic acid amide, stearic acid amide, oleic acid amide, erucic acid amide, linoleic acid amide, linolenic acid amide, and N-
Methyl stearic acid amide, stearic acid anilide, N
-Methyloleic acid amide, benzanilide, linoleic acid anilide, N-ethylcapric acid amide, N-butyllauric acid amide, N-octadecylacetamide, N
-Oleinacetamide, N-oleylbenzamide,
N-stearylcyclohexylamide, polyethylene glycol, 1-benzyloxynaphthalene, 2-benzyloxynaphthalene, 1-hydroxynaphthoic acid phenyl ester, 1,2-diphenoxyethane, 1,4-diphenoxybutane, 1,2-bis (3-methylphenoxy) ethane, 1,2-bis (4-methoxyphenoxy)
Ethane, 1-phenoxy-2- (4-chlorophenoxy) ethane, 1-phenoxy-2- (4-methoxyphenoxy) ethane, 1- (2-methylphenoxy) -2
(4-Methoxyphenoxy) ethane, terephthalic acid dibenzyl ester, oxalic acid dibenzyl ester, oxalic acid di (4-methylbenzyl) ester, p-benzyloxybenzoic acid benzyl ester, p-benzylbiphenyl, 1,5-bis (P-Methoxyphenoxy) -3-oxa-pentane, 1,4-bis (2-vinyloxyethoxy) benzene, p-biphenyl-p-tolyl ether, benzyl-p-methylthiophenyl ether, 2-
(2'-hydroxy-5'-methylphenyl) benzotriazole, 2-hydroxy-4-benzyloxybenzophenone and the like can be mentioned.

The amount of the recording sensitivity improver used is not particularly limited, but is generally 50 to 1000 parts by weight, preferably 10 parts by weight with respect to 100 parts by weight of the basic dye.
It is preferably used in the range of 0 to 500 parts by weight.

The recording layer may contain various known storability improvers in order to further improve the storability. Specific examples of the storage stability improving agent include 1,1,3-tris (3′-cyclylhexyl-4′-hydroxyphenyl) butane and 1,1,3-tris (2-
Methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4′-thiobis (3-methyl-ter
t-butylphenol), 1,3,5-trimethyl-
2,4,6-Tris (4,5-di-tert-butyl-
4-hydroxybenzyl) benzene, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, p-octylphenyl salicylate, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, ethyl-2-cyano -3,3'-diphenyl acrylate, tetra (2,2,6,6-tetramethyl-4-piperidyl) -1,2,3,4-butane tetracarboate,
Examples thereof include sodium salt or magnesium salt of 2,2′-methylenebis (4,6-di-tert-butylphenyl) phosphoric acid.

A coating solution containing these is generally prepared by using water as a dispersion medium and using a ball mill, an attritor, a sand mill,
It is prepared by dispersing a dye, a coloring agent, a heat-fusible substance, etc. together or separately by a stirring / crushing machine such as a colloid mill.

The heat-sensitive recording material of the present invention is generally a medium in which a binder is dissolved or dispersed, and a basic dye, an indolyldiazaphthalide derivative represented by the general formula (1), and a coloring agent. It is produced by applying a coating liquid obtained by dispersing fine particles of the diphenylsulfone derivative represented by the general formula (2) onto a suitable support.

The coating liquid containing these is generally prepared by dispersing water and a dye together with a stirrer or grinder such as a ball mill, an attritor or a sand mill, or separately, using water as a dispersion medium. To be done.

In such a coating liquid, starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, styrene / maleic anhydride copolymer salt, styrene / acrylic acid copolymer are usually used as binders. Combined salt, styrene-butadiene copolymer emulsion, etc. are 10 to 40% by weight of the total solid content, preferably 15 to 3%.
About 5% by weight is used.

Further, various auxiliaries can be added to the coating liquid, for example, dispersion of sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate / sodium salt, fatty acid metal salt and the like. Agent, UV absorbers such as triazoles,
Other examples include defoaming agents, fluorescent dyes, coloring dyes and antioxidants. In order to prevent sticking of the thermosensitive recording medium due to contact with recording equipment or recording head, use a dispersion or emulsion of stearic acid, polyethylene, carnauba wax, paraffin wax, zinc stearate, calcium stearate, ester wax, etc. in the paint. It can also be added.

In addition, kaolin, clay, talc, calcium carbonate,
It is also possible to add an inorganic pigment such as calcined clay, titanium oxide, diatomaceous earth, particulate anhydrous silica, activated clay.

As the support, paper (including neutral paper), plastic film, synthetic paper, or plastic film or synthetic paper laminated with coated paper or high-quality paper via an adhesive, or paper A laminate of plastic is used. Examples of such plastic film include films of polyethylene, polyester, polypropylene, polyvinyl chloride, polystyrene, nylon and the like. As the synthetic paper, for example, a synthetic paper produced by a film method or a fiber method is used. In the film method, an internal paper is formed by melt-kneading a synthetic resin, a filler and an additive and then extruding to form a film. System, a surface coating system in which a pigment coating layer is provided, a surface treatment system, and the like, and synthetic fiber papers such as synthetic pulp paper and spunbond paper.

The coating method of the recording layer is not particularly limited, and it can be formed according to a conventionally well-known and commonly used technique. For example, bar coating, air knife coating, rod blade coating, pure blade coating, short dwell coating. It is formed by a method of applying and drying the coating liquid by the above method. When a plastic film is used as the support, the coating efficiency can be increased by subjecting the surface to treatments such as corona discharge and electron beam irradiation. The coating amount of the coating liquid is also not particularly limited, but it is usually ^{2 to} 10 g / m ² , preferably 3 to 7 g in dry weight.
It is adjusted in the range of about / m ² .

Further, on the heat-sensitive recording layer, an adhesive, a lubricant,
By providing a protective layer composed of a pigment or the like, a thermosensitive recording material having excellent chemical resistance to plasticizers, oils and the like can be obtained. Specific examples of the adhesive used in the protective layer include polyvinyl alcohols having various degrees of saponification, acetoacetyl group-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, acrylic resin, and polyurethane resin. Further, it is desirable that these adhesives are adjusted in the range of 10 to 95% by weight, preferably 30 to 90% by weight, based on the total solid content. The coating amount of the protective layer is 0.5 to 10 by dry weight.
g / m ^2, it is adjusted preferably, 1 to 7 g / m ² range of about.

In addition, a layer containing a water-soluble, water-dispersible, electron beam curable or ultraviolet curable resin may be provided on the protective layer for the purpose of imparting high gloss, etc. It is of course possible to provide a protective layer on the back surface of the sheet or to provide an undercoat layer on the support, and various known techniques in the field of producing a thermosensitive recording medium can be added.

[0035]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Unless otherwise specified, parts and% in examples are parts by weight and% by weight, respectively.

Example 1 [Formation of Intermediate Layer] 100 parts of calcined clay (trade name: Ansilex, apparent specific gravity: 0.22 g / cm ³ , manufactured by Engelhard), styrene-butadiene copolymer latex (solid content: 50%), 30 parts of a 10% aqueous solution of polyvinyl alcohol, and 200 parts of water were mixed to prepare a coating liquid for the intermediate layer. The obtained coating liquid is 5
An intermediate layer was formed by coating onto a high-quality paper of 0 g / m ^{2 so} that the coating amount after drying was 10 g / m ² and drying.

[Preparation of Solution A] 3- (1-Methyl-2-phenylindol-3-yl) -3- (2-ethoxy-4)
-Diethylaminophenyl) -4,7-diazaphthalide, 10 parts, 3 parts of a 5% aqueous solution of methylcellulose, and 27 parts of water were used to sand-mill a composition having an average particle size of 0.8.
The solution was pulverized to a size of μm to obtain solution A.

[Preparation of solution B] 3,3′-diallyl-4,
A composition consisting of 20 parts of 4′-dihydroxydiphenyl sulfone, 5 parts of a 5% aqueous solution of methylcellulose, and 55 parts of water was pulverized by a sand mill until the average particle size was 1.2 μm to obtain a liquid B.

[Preparation of Liquid C] A composition comprising 25 parts of 1,2-bis (3-methylphenoxy) ethane, 7 parts of a 5% aqueous solution of methylcellulose, and 48 parts of water was sand-milled to an average particle diameter of 1.2 μm. Was pulverized to obtain a C liquid.

[Formation of Recording Layer] Liquid A 40 parts, liquid B 80
Part, liquid C 80 parts, light calcium carbonate 10 parts, fine particle silicon oxide pigment (oil absorption 180 ml / 100 g) 20 parts, zinc stearate 30% dispersion 15 parts, and polyvinyl alcohol 15% aqueous solution 100 parts The coating liquid obtained by stirring is applied to a high-quality paper of 50 g / m ² and the dry weight is 4 g.
It was coated and dried so as to be / m ^2, and subjected to a super calender treatment to obtain a heat-sensitive recording material.

Examples 2-6 In the preparation of solution A, 10 parts of 3- (1-methyl-2-phenylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4,7-diazaphthalide were prepared. A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the following compounds were used instead of.

Example 2: 3- (1-Methyl-2-phenylindol-3-yl) -3- (2-ethoxy-4-)
Di-n-butylaminophenyl) -4,7-diazaphthalide 10 parts Example 3: 3- (1-Methyl-2-phenylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl)- 4,7-diazaphthalide 3 parts and 3-di-
n-Butylamino-6-methyl-7-anilinofluorane 7 parts Example 4: 3- (1-Methyl-2-phenylindol-3-yl) -3- (2-ethoxy-4-di-n -Butylaminophenyl) -4,7-diazaphthalide 3 parts and 3
-Di-n-butylamino-6-methyl-7-anilinofluorane 7 parts Example 5: 3- (1-Methyl-2-phenylindol-3-yl) -3- (2-ethoxy-4-). N-ethyl-
N-p-toluidinophenyl) -4,7-diazaphthalide 3 parts and 3-di-n-butylamino-6-methyl-7-
7 parts of anilinofluorane Example 6: 3- (1-Butyl-2-phenylindol-3-yl) -3- (2-ethoxy-4-N-ethyl-
N-p-toluidinophenyl) -4,7-diazaphthalide 3 parts and 3-di-n-butylamino-6-methyl-7-
7 parts of Anilino Fluoran

Examples 7 to 8 A thermosensitive recording medium was prepared in the same manner as in Example 3 except that the following compounds were used in place of 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone in the preparation of solution B. Got Example 7: 4-Hydroxy-4'-isopropoxydiphenyl sulfone Example 8: 2,4'-Dihydroxydiphenyl sulfone

Comparative Examples 1 to 3 Instead of 3- (1-methyl-2-phenylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4,7-diazaphthalide in the preparation of solution A A thermal recording material was obtained in the same manner as in Example 1 except that the following compounds were used.

Comparative Example 1: 3,3-bis (2-ethoxy-
4-diethylaminophenyl) -4-azaphthalide 3 parts and 3-di-n-butylamino-6-methyl-7-anilinofluorane 7 parts Comparative Example 2: 3-di-n-butylamino-6,8, 3-Trimethyl-8,9-dihydro- (3,2, e) pyridfluorane 3 parts and 3-di-n-butylamino-6-methyl-7-anilinofluorane 7 parts Comparative Example 3: 3-di- n-butylamino-6-methyl-7
-10 parts of Anilino Fluoran

Comparative Example 4 A thermosensitive recording medium was prepared in the same manner as in Example 3 except that 4,4'-isopropylidenediphenol was used instead of 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone. Obtained.

The 12 types of thermal recording materials thus obtained were evaluated by the following methods, and the results are shown in Table 1. [PCS value] The PCS value is an index indicating the degree of readability of OCR. The PCS value represents the relative density difference between the recorded portion and the unrecorded portion, and is calculated by the following equation.

PCS = (RW-RP) / RW RW represents the reflectance of the unrecorded portion, and RP represents the reflectance of the recorded portion. Therefore, the higher the PCS value, the clearer the discrimination between the recorded portion and the unrecorded portion, and the higher the readability. Generally, a PCS value of 0.7 or more is required.

[Measurement of PCS value at 670 nm] Recording was performed using a thermal recording evaluation device [THK-PMD type, manufactured by Okura Electric Co., Ltd., applied voltage 18 V, pulse cycle 3.0 ms, applied pulse width 1.6 ms]. And wavelength 6 of unrecorded area
The spectrophotometer [Hitachi,
U-3300] and the PCS value was calculated from the measured value.

[Moisture and heat resistance] After recording, 40 ° C., 90% RH
After being left for 72 hours under the above condition, the PCS value was measured.

[Light resistance] After recording, after exposure to a Sunshine Super Long Life Xenon Weather Meter (WM) manufactured by Suga Test Instruments Co., Ltd. for 15 hours, the PCS value was measured.

[Plasticizer resistance] After recording, a vinyl chloride film containing a plasticizer was overlaid on the recording surface and left at room temperature for 8 hours.
The PCS value was measured.

[0053]

[Table 1]

[0054]

As is clear from the results shown in Table 1, the thermal recording material of the present invention has a high initial PCS value and is 670 nm even if it is stored under high temperature and high humidity or is exposed to light for a long time.
The PCS value in Table 2 was sufficiently high.

Claims (2)

[Claims] 1. A thermosensitive recording medium comprising a support and a recording layer containing a colorless or light-colored basic dye and a coloring agent, wherein the basic dye is an indolyldia represented by the following general formula (1). Using at least one kind of zaphthalide derivative,
A heat-sensitive recording material containing at least one diphenylsulfone derivative represented by the following general formula (2) as a coloring agent. Embedded image (In the formula, R ₁ is a C ₁ -C ₈ alkyl group, and R ₂ is C ₁
To C ₆ alkyl groups, R ₃ and R ₄ are C _{1 to} C, respectively.
₆ alkyl group, C ₃ -C ₆ alkoxyalkyl group or p-tolyl group. ) (In the formula, R ₅ and R ₆ each represent a C _{1 to} C ₄ alkyl group, a C _{2 to} C ₄ alkenyl group, a C _{1 to} C ₄ alkoxyl group, a benzyloxy group or a halogen atom.
m is an integer of 0 to 2, n is an integer of 1 to 3, and p and q are integers of 0 to 2, respectively. ) 2. The thermosensitive recording medium according to claim 1, wherein at least one fluorane compound represented by the following general formula (3) is used in combination as the basic dye. Embedded image (Wherein R ₇ and R ₈ are each a C ₁ -C ₆ alkyl group, ethoxypropyl group or p-tolyl group, R ₉ is a hydrogen atom or a methyl group, and R ₁₀ is a methyl group, a chlorine atom or trifluoro group. Represents a methyl group, and k represents an integer of 0 to 2.)