JPH10147070A - Thermal recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve optical character reading suitability in a specific wavelength range by using one type of indolylazaphthalide derivatives of a specific structure as a basic bye in a recording layer, and incorporating 1,1-bis(4- hydroxyphenyl)-1-phenylethane as a colorant. SOLUTION: In the thermal recording medium comprising a recording layer containing a colorless or pale basic dye and a colorant on a support with excellent optical character reading(OCR) suitability in a wavelength range of 650 to 700nm, at least one type of indolylazaphthalide derivatives rephresented by the formula is used as the basic bye and 1,1-bis(4-hydroxypenyl)-1- phenylethane is contained as a colorant in the recording layer. In the formula, R1 indicates a 1-8C alkyl group, R2 indicates a 1-6 alkyl group, and R3 , R4 indicate 1-6C alkyl groups. The R3 , R4 may form a heatero ring together with adjacent nitrogen atom.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosensitive recording material utilizing a color-forming reaction between a colorless or pale-colored basic dye and a color former, and more particularly, to the suitability for optical character reading (OCR) in the wavelength region of 650 to 700 nm. The present invention relates to a thermosensitive recording medium having excellent heat resistance.

[0002]

2. Description of the Related Art A thermosensitive recording material is known which utilizes a color reaction between a colorless or light-colored basic dye and an organic or inorganic colorant to contact a color-forming substance with heat to obtain a recorded image. Have been. Such a thermosensitive recording medium is relatively inexpensive, and its recording equipment is compact and its repair is relatively easy. Therefore, it is used not only as a recording medium for facsimile machines and various computers but also in a wide range of fields.

[0003] With the recent diversification of needs, various performances are also required for heat-sensitive recording media. One of them is an OCR or OMR that can read in a wavelength range of 650 to 700 nm. There is a need for a thermal recording medium. As a method for obtaining such a thermosensitive recording material, as a dye having a strong absorption at 650 to 700 nm at the time of coloring, for example, 3,3-bis (4-diethylamino-2-ethoxyphenyl) -4-azaphthalide or 3-di-n-butyl For example, amino-6,8,8-trimethyl-8,9-dihydro-9-ethyl- (3,2, e) pyridfluoran or the like is used alone or in combination with a black-coloring fluoran dye. However, although these methods have the OCR suitability immediately after color development, the OCR suitability is deteriorated when stored in a high-temperature environment or high humidity or exposed to light.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a thermosensitive recording material having excellent suitability for optical character reading (OCR) in a wavelength range of 650 to 700 nm.

[0005]

Means for Solving the Problems The present inventors have proposed a thermosensitive recording medium in which a recording layer containing a colorless or light-colored basic dye and a color former is provided on a support. At least one of the indolyldiazaphthalide derivatives represented by the following general formula (1) is used as the dye, and 1,1-bis (4-hydroxyphenyl) -1 is used as a colorant.
It has been found that the above problems can be solved by including phenylethane, and the present invention has been completed.

[0006]

Embedded image

(Wherein, R ₁ represents a C ₁ -C ₈ alkyl group, R ₂ represents a C ₁ -C ₆ alkyl group, and R ₃ and R ₄ each represent a C ₁ -C ₆ alkyl group. Note that R ₃ and R
₄ may form a heterocyclic ring with an adjacent nitrogen atom. )

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The heat-sensitive recording material of the present invention uses a specific indolyldiazaphthalide derivative as a colorless or light-colored basic dye, and furthermore uses 1,1-bis (4-hydroxyphenyl) as a color former. ) By using 1-phenylethane, a thermosensitive recording material having excellent suitability for optical character reading (OCR) in a wavelength range of 650 to 700 nm can be obtained even in a high-temperature environment, high humidity, or long-term exposure to light. It is something that can be done.

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-methyl-4-diethylaminophenyl) -4,7-diazaphthalide, 3-
(1-methyl-2-phenylindol-3-yl)-
3- (2-methyl-4-di-n-propylaminophenyl) -4,7-diazaphthalide, 3- (1-methyl-2
-Phenylindol-3-yl) -3- (2-methyl-4-di-n-butylaminophenyl) -4,7-diazaphthalide, 3- (1-methyl-2-phenylindol-3-yl)- 3- (2-methyl-4-dimethylaminophenyl) -4,7-diazaphthalide, 3- (1-methyl-2-phenylindol-3-yl) -3- (2
-Methyl-4-pyrrolidinophenyl) -4,7-diazaphthalide, 3- (1-ethyl-2-phenylindol-3-yl) -3- (2-methyl-4-pyrrolidinophenyl) -4,7 -Diazaphthalide, 3- (1-n-butyl-2-phenylindol-3-yl) -3- (2-
Methyl-4-pyrrolidinophenyl) -4,7-diazaphthalide, 3- (1-ethyl-2-phenylindole-
3-yl) -3- (2-methyl-4-diethylaminophenyl) -4,7-diazaphthalide, 3- (1-ethyl-2-phenylindol-3-yl) -3- (2-methyl-4- Di-n-butylaminophenyl) -4,7-
Diazaphthalide, 3- (1-n-butyl-2-phenylindol-3-yl) -3- (2-methyl-4-diethylaminophenyl) -4,7-diazaphthalide, 3-
(1-n-butyl-2-phenylindol-3-yl) -3- (2-methyl-4-di-n-butylaminophenyl) -4,7-diazaphthalide, 3- (1-methyl-2- Phenylindol-3-yl) -3- (2-ethyl-4-diethylaminophenyl) -4,7-diazaphthalide, 3- (1-methyl-2-phenylindol-3-yl) -3- (2-ethyl -4-di-n-butylaminophenyl) -4,7-diazaphthalide, 3- (1
-Ethyl-2-phenylindol-3-yl) -3-
(2-ethyl-4-diethylaminophenyl) -4,7
-Diazaphthalide, 3- (1-n-butyl-2-phenylindol-3-yl) -3- (2-ethyl-4-diethylaminophenyl) -4,7-diazaphthalide,
-(1-n-octyl-2-phenylindole-3-
Yl) -3- (2-methyl-4-diethylaminophenyl) -4,7-diazaphthalide, 3- (1-methyl-2
-Phenylindol-3-yl) -3- (2-methyl-4-N-ethyl-N-isopentylaminophenyl)
-4,7-diazaphthalide, 3- (1-methyl-2-phenylindol-3-yl) -3- (2-methyl-4
-N-methyl-NN-propylaminophenyl)-
4,7-diazaphthalide and the like.

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

In the heat-sensitive recording material of the present invention, a specific indolyldiazaphthalide derivative is used as the basic dye as described above, but 1,1-bis (4-hydroxyphenyl) is used as a color former. By selectively combining -1-phenylethane, an excellent effect on OCR readability is exhibited. The amount of these colorants used is not particularly limited, but is generally adjusted in the range of 50 to 700 parts by weight, preferably about 100 to 500 parts by weight, per 100 parts by weight of the basic dye.

In the present invention, a specific indolylazaphthalide derivative and another basic dye can be used in combination within a range that does not impair the desired effects of the present invention. Examples of other basic dyes include known triarylmethane derivatives, diarylmethane derivatives, fluoran derivatives, phenothiazine derivatives, rhodamine lactam derivatives, spiropyran derivatives, leuco auramine derivatives, and the like.

By using at least one of the fluoran compounds represented by the general formula (2) among these basic dyes, the fluoran compound can be stored in a black color system and under a high temperature environment or high humidity, or can be exposed to light. , It is possible to obtain a thermosensitive recording medium having particularly excellent OCR readability.

[0014]

Embedded image

(Wherein R ₅ and R ₆ each represent C ₁ -C
₆ , an alkyl group, an ethoxypropyl group or a p-tolyl group, R ₇ represents a hydrogen atom or a methyl group, and R ₈ represents a methyl group, a chlorine atom or a trifluoromethyl group. k shows the integer of 0-2. )

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

Of these, 3-di-n-butylamino-6-methyl-7-anilinofluoran exhibits excellent performance especially in terms of color development and background fog.
Particularly preferably used. In the present invention, other known dyes can of course be used in combination as long as the desired effect is 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. Such heat-fusible substances include, for example, caproic amide, capric amide, palmitic amide, stearic amide, oleic amide, erucic amide, linoleic amide, linolenic amide, N-
Methyl stearamide, stearic anilide, N
-Methyloleic amide, benzanilide, linoleic anilide, N-ethylcapramide, N-butyllauric amide, N-octadecylacetamide, N
-Olein acetamide, N-oleyl benzamide,
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, 1- (2-naphthoxy) -2-phenoxyethane, 1,3-bis (2-naphthoxy) propane, dibenzyl terephthalate, dibenzyl oxalate, di (oxalate) -Methylbenzyl) ester, oxalic acid di (4-chlorobenzyl) 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, benzyl (4-methylphenyl) ketone and the like.

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

The recording layer may contain various known storage improvers for further improving the storage stability. Specific examples of the preservability improver include, for example, 1,
1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4 ′ -Thiobis (3-methyl-
6-tert-butylphenol), 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-
Butyl-4-hydroxybenzyl) benzene, 2- (2
-Hydroxy-5-methylphenyl) benzotriazole, tetrakis (1,2,2,6,6-pentamethyl-
4-piperidyl) -1,2,3,4-butanetetracarboxylate, 4-benzyloxyphenyl-4′-
(2-methyl-2,3-epoxypropyloxy) phenyl sulfone, 1,3,5-tris (4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanuric acid, 1- [α-methyl -Α- (4-hydroxyphenyl) ethyl] -4- [α ′, α′-bis (4-
(Hydroxyphenyl) ethyl] benzene, 4,4′-butylidenebis (6-tert-butyl-m-cresol), bis [2-hydroxy-3- (2′H-benzotriazol-2′-yl) -5-octyl Phenyl] methane, 2,2'-methylenebis (4,6-di-tert
And sodium salts and magnesium salts of (-butylphenyl) phosphoric acid.

The preparation of a coating liquid containing these is generally performed by using water as a dispersion medium, a ball mill, an attritor, a sand mill,
It is prepared by dispersing a dye, a color former, a heat-fusible substance and the like together or separately using a stirring / pulverizer such as a colloid mill.

The heat-sensitive recording material of the present invention generally comprises an indolyl diazaphthalide derivative represented by the general formula (1) as a basic dye and a coloring agent in a medium in which a binder is dissolved or dispersed. It is produced by applying a coating liquid obtained by dispersing fine particles of 1,1-bis (4-hydroxyphenyl) -1-phenylethane on a suitable support.

In such a coating solution, starch, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, gum arabic, polyvinyl alcohol, styrene / maleic anhydride copolymer salt, styrene / acrylic acid copolymer are usually used as binders. The combined salt, styrene / butadiene copolymer emulsion or the like is 10 to 40% by weight of the total solids, preferably 15 to 3% by weight.
About 5% by weight is used.

Further, various auxiliaries can be added to the coating liquid, for example, dispersants such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium salt of lauryl alcohol sulfate, fatty acid metal salt, and triazole. UV absorbers, other defoamers, fluorescent dyes, coloring dyes, antioxidants and the like. In addition, a dispersion or emulsion of stearic acid, polyethylene, carnauba wax, paraffin wax, zinc stearate, calcium stearate, ester wax, etc. is used in the coating so that the thermal recording medium does not stick due to contact with a recording device or a recording head. It can also be added.

In addition, kaolin, clay, talc, calcium carbonate,
Inorganic pigments such as calcined clay, titanium oxide, diatomaceous earth, fine anhydrous silica and activated clay can also be added.

As the support, paper (including neutral paper), plastic film, synthetic paper, or plastic film or synthetic paper bonded to coated paper or woodfree paper with an adhesive, or to paper Plastic laminates are used. Examples of such a plastic film include films of polyethylene, polyester, polypropylene, polyvinyl chloride, polystyrene, nylon and the like. As the synthetic paper, for example, a synthetic paper manufactured by a film method or a fiber method is used, but in the film method, a synthetic resin, a filler and an additive are melt-kneaded, and then extruded to form a film. There are a system, a surface coating system in which a pigment coating layer is provided, a surface treatment system, and the like. Examples of the fiber synthetic paper include synthetic pulp paper and spunbond paper.

The method for applying the recording layer is not particularly limited, and the recording layer can be formed according to a conventionally 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 a coating liquid by the method described above. When a plastic film is used as the support, the coating efficiency can be increased by subjecting the surface to a treatment such as corona discharge or electron beam irradiation. The amount of the coating solution is not particularly limited, but is usually ^{2 to} 10 g / m ² , preferably 3 to 7 g in terms of dry weight.
/ M ² .

Furthermore, an adhesive, a lubricant,
By providing a protective layer composed of a pigment or the like, a thermosensitive recording medium having excellent chemical resistance such as a plasticizer and oil can be obtained. Specific examples of the adhesive used for the protective layer include, for example, polyvinyl alcohol having various degrees of saponification, acetoacetyl group-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, acrylic resin, and polyurethane resin. It is desirable that these adhesives are adjusted in a range of 10 to 95% by weight, preferably 30 to 90% by weight, based on the total solid amount. 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, it is also possible to provide a layer containing a water-soluble, water-dispersible, electron beam-curable or ultraviolet-curable resin on the protective layer for the purpose of imparting high gloss. Of course, it is also possible to provide a protective layer on the back surface or an undercoat layer on the support, and various known techniques in the field of heat-sensitive recording material production can be added.

[0030]

The present invention will be described in more detail with reference to the following Examples, but it should be understood that the present invention is by no means restricted thereto. Unless otherwise specified, parts and% in examples are parts by weight and% by weight, respectively.

Example 1 [Formation of Intermediate Layer] Fired clay (trade name: Ansilex, apparent specific gravity: 0.22, manufactured by Engelhard Co.) 10
A composition comprising 0 parts, 15 parts of a styrene-butadiene copolymer latex (solid content: 50%), 30 parts of a 10% aqueous solution of polyvinyl alcohol, and 200 parts of water was mixed to prepare a coating liquid for an intermediate layer. 50 g / m ^{2 of the} obtained coating liquid
Was applied so that the coated amount after drying was 10 g / m ^2, and dried to form an intermediate layer.

[Preparation of solution A] 3- (1-Methyl-2-phenylindol-3-yl) -3- (2-methyl-4-
Diethylaminophenyl) -4,7-diazaphthalide 1
0 parts, 3 parts of a 5% aqueous solution of methylcellulose, and 2 parts of water
The composition comprising 7 parts was sand-milled to have an average particle size of 0.8 μm.
It grind | pulverized until it became m, and obtained liquid A.

[Preparation of Solution B] A composition comprising 20 parts of 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 5 parts of a 5% aqueous solution of methylcellulose and 55 parts of water was subjected to sand milling to obtain an average particle diameter of 1 part. The mixture was pulverized to a thickness of 0.2 μm to obtain a liquid B.

[Preparation of Solution 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 is sand-milled to have an average particle diameter of 1.2 μm. To obtain a liquid C.

[Formation of Recording Layer] 40 parts of solution A, 80 parts of solution B
Parts, 80 parts of liquid C, 10 parts of light calcium carbonate, 20 parts of fine particle silicon oxide pigment (oil absorption: 180 ml / 100 g), 15 parts of a 30% dispersion of zinc stearate, and 100 parts of a 15% aqueous solution of polyvinyl alcohol. The coating liquid obtained by stirring was applied onto the undercoat layer at a dry weight of 4 g / m.
^The coating was dried so as to obtain a composition No. ^2, and subjected to a super calender treatment to obtain a thermosensitive recording medium.

Examples 2 to 7 In the preparation of solution A, 10 parts of 3- (1-methyl-2-phenylindol-3-yl) -3- (2-methyl-4-diethylaminophenyl) -4,7-diazaphthalide Was obtained in the same manner as in Example 1 except that the following compound was used instead of

Example 2: 10 parts of 3- (1-methyl-2-phenylindol-3-yl) -3- (2-methyl-4-di-n-butylaminophenyl) -4,7-diazaphthalide Example 3: 3- (1-methyl-2-phenylindol-3-yl) -3- (2-methyl-4-diethylaminophenyl) -4,7-diazaphthalide and 3 parts of 3-di-n
-Butylamino-6-methyl-7-anilinofluoran 7 parts Example 4: 3- (1-methyl-2-phenylindol-3-yl) -3- (2-methyl-4-di-n- Butylaminophenyl) -4,7-diazaphthalide 3 parts and 3-
7 parts of di-n-butylamino-6-methyl-7-anilinofluoran Example 5: 3- (1-Ethyl-2-phenylindol-3-yl) -3- (2-methyl-4-diethylamino Phenyl) -4,7-diazaphthalide (3 parts) and 3-di-n
-Butylamino-6-methyl-7-anilinofluorane 7 parts Example 6: 3- (1-n-butyl-2-phenylindol-3-yl) -3- (2-methyl-4-diethylaminophenyl ) -3 parts of -4,7-diazaphthalide and 3-
7 parts of di-n-butylamino-6-methyl-7-anilinofluoran Example 7: 3- (1-Methyl-2-phenylindol-3-yl) -3- (2-methyl-4-pyrroli (Dinophenyl) -4,7-diazaphthalide (3 parts) and 3-di-n-butylamino-6-methyl-7-anilinofluoran (7 parts)

Comparative Examples 1 to 3 In the preparation of Solution A, 10 parts of 3- (1-methyl-2-phenylindol-3-yl) -3- (2-methyl-4-diethylaminophenyl) -4,7-diazaphthalide Was obtained in the same manner as in Example 1 except that the following compound was used instead of

Comparative Example 1: 3,3-bis (2-ethoxy-
4-diethylaminophenyl) -4-azaphthalide 3
Part and 7 parts of 3-di-n-butylamino-6-methyl-7-anilinofluoran Comparative Example 2: 3-di-n-butylamino-6,8,8-trimethyl-8,9-dihydro -9-ethyl- (3,
2, e) pyridofluorane 3 parts 3-di-n-butylamino-6-methyl-7-anilinofluoran 7 parts Comparative Example 3: 3-di-n-butylamino-6-methyl-7
-Anilino fluoran, 10 parts

Comparative Examples 4 to 5 Heat-sensitive recording materials were obtained in the same manner as in Example 3 except that the following compounds were used instead of 1,1-bis (4-hydroxyphenyl) -1-phenylethane. Comparative Example 4: 1- [α-methyl-α- (4-hydroxyphenyl) ethyl] -4- [α ′, α′-bis (4-hydroxyphenyl) ethyl] benzene Comparative Example 5: 4,4′- Isopropylidene diphenol

The twelve kinds of heat-sensitive 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 the OCR. The PCS value represents a relative density difference between a recorded portion and an unrecorded portion, and is obtained 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 distinction between a recorded portion and an unrecorded portion, and the readability is improved. 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 evaluator [manufactured by Okura Electric Co., Ltd., TH-PMD type, applied voltage 18 V, pulse cycle 3.0 ms, applied pulse width 2.0 ms]. And unrecorded wavelength 6
The reflectance at 70 nm was measured using a spectrophotometer [manufactured by Hitachi, Ltd.
U-3300], and the PCS value was calculated from the measured value.

[Background fog] The unrecorded area was measured with a Macbeth densitometer (RD-914, Macbeth, visual filter).

[Moisture resistance] After recording, the recording paper was left standing at 40 ° C. and 90% RH for 72 hours, and then the PCS value and the background fog were measured.

[Heat resistance] After recording, the substrate was allowed to stand in a hot air drier at 80 ° C for 3 hours, and then the PCS value and the background fog were measured.

[Light Resistance] After recording, the film was exposed to a Sunshine Super Long Life Xenon Weather Meter (WM) manufactured by Suga Test Instruments Co., Ltd. for 18 hours, and then the PCS value and the background fog were measured.

[0048]

[Table 1]

[0049]

As is evident from the results in Table 1, the thermal recording medium of the present invention has a high initial PCS value and can be stored in a high-temperature environment or high humidity, or exposed to light for a long time.
The PCS value at 0 nm was sufficiently high and the background fog was small.

Claims (2)

[Claims] 1. A thermosensitive recording medium having a recording layer containing a colorless or light-colored basic dye and a colorant on a support, wherein the basic dye is represented by the following general formula (1): A heat-sensitive recording material comprising at least one of the indicated indolyldiazaphthalide derivatives and containing 1,1-bis (4-hydroxyphenyl) -1-phenylethane as a coloring agent. Embedded image Wherein R ₁ is a C ₁ -C ₈ alkyl group, and R ₂ is a C ₁
And R ₃ and R ₄ are each a C ₁ -C ₆ alkyl group.
_{6 represents} an alkyl group. Note that R ₃ and R ₄ may form a hetero ring with an adjacent nitrogen atom. ) 2. The heat-sensitive recording material according to claim 1, wherein at least one fluoran compound represented by the following general formula (2) is used in combination as the basic dye. Embedded image (Wherein R ₅ and R ₆ are each a C ₁ -C ₆ alkyl group, ethoxypropyl group or p-tolyl group, R ₇ is a hydrogen atom or a methyl group, R ₈ is a methyl group, a chlorine atom or a trifluoro group. Represents a methyl group, and k represents an integer of 0 to 2.)