JPH0890930A - Thermal recording material - Google Patents

Abstract

PURPOSE: To enhance optical reading aptitude by adding at least one kind of a black developing fluorane derivative being a basic dye and at least one kind of a specific phenothiazine derivative to a recording layer and further adding a specific diphenylsulfone derivative thereto as a coupler. CONSTITUTION: In a thermal recording material wherein a recording layer containing a basic dye and a coupler is provided on a support, at least one kind of a black developing fluorane derivative being a basic dye and at least one kind of a phenothiazine derivative are added to the recording layer so that the phenothiazine derivative becomes 5-100wt.% of the fluorane derivative and a diphenylsulfone derivative represented by formula II is added thereto as a coupler. In the formulae I, II, R1 -R4 are an alkyl group, R5 is a hydrogen atom, a halogen atom or an alkyl group, R6 and R7 are an alkyl group or an alkenyl group, m is an integer of 1-3 and p and q are an integer of 0-2.

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 a color reaction of a colorless or light-colored basic dye and a color developing agent, and particularly, it is suitable for optical character reading (OCR) in a 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 thermal 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. As one of them, there is a demand for a thermal recording material for OCR or OMR which has a black color tone and is readable in the wavelength region of 650 to 700 nm. As a method for obtaining such a heat-sensitive recording material, the coating amount of the black-coloring fluoran dye which has been conventionally used is simply increased, or 65 is applied at the time of coloring.
Examples of the dye having a strong absorption at 0 to 700 nm include 3,3-bis (4-diethylamino-2-ethoxyphenyl) -4-azaphthalide or 3-di-n-butylamino-6,8,8-trimethyl-8. , 9-dihydro-
A method is used in which (3,2, e) pyridofluorane or the like is used in combination with a black coloring fluorane dye. However, although these methods have OCR suitability immediately after color development, OCR suitability disappears when exposed to high temperature and high humidity or exposed to light, and white paper parts develop color during long-term storage (background fog).
Therefore, the improvement is strongly demanded.

[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 proposed a thermosensitive recording medium comprising a support and a recording layer containing a colorless or light-colored basic dye and a color developing agent. As a dye, at least one black coloring fluoran derivative and at least one phenothiazine derivative represented by the following general formula (1) are contained so that the phenothiazine derivative is 5 to 100% by weight of the fluoran derivative,
Moreover, they have found that the above-mentioned problems can be solved by incorporating a diphenyl sulfone derivative represented by the following general formula (2) as a coloring agent, and have completed the present invention.

[0006]

[Chemical 5]

[In the formula, R _{1 to} R ₄ are respectively C _{1 to} C ₄
Represents an alkyl group of R ₅ is a hydrogen atom, a halogen atom,
An alkyl group or C ₁ -C ₄ alkoxyl group C ₁ -C _4. ]

[0008]

[Chemical 6]

[In the formula, R ₆ and R ₇ 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 and q each represent an integer of 0 to 2. ]

That is, in the present invention, as a colorless or light-colored basic dye, a black coloring fluorane derivative and a specific phenothiazine derivative are used in combination at a specific ratio, and a specific diphenylsulfone derivative is used as a coloring agent. Therefore, even if exposed to high temperature and high humidity or light for a long time,
Optical character reading in the wavelength region of 700 nm (O
(CR) aptitude is not deteriorated, and a black color type heat-sensitive recording material with less background fog can be obtained.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the heat-sensitive recording material of the present invention, a specific phenothiazine derivative is used in combination in an amount of 5 to 100% by weight, preferably 10 to 50% by weight, based on the black coloring fluoran derivative. By using a specific diphenyl sulfone derivative as an agent, the suitability for optical character reading (OCR) in the wavelength range of 650 to 700 nm does not deteriorate even when exposed to high temperature and high humidity or to light for a long time. It is possible to obtain a little black color type thermosensitive recording material.

When the amount of the basic dye in the recording layer is increased, the readability of optical characters is naturally improved, but the basic dye is taken into consideration in view of recording sensitivity, yellowing of unrecorded paper upon light exposure, and economy. As the amount of 0.2-1.0g
It is preferable to adjust in the range of / m ² . When the amount of the phenothiazine derivative in the recording layer is less than 5% by weight,
Especially, OCR suitability after being exposed to light for a long time is lost, and 1
If it exceeds 100% by weight, the suitability for OCR immediately after color development is deteriorated, and background fogging occurs due to the effects of temperature, humidity, light and the like.

As the black color-developing fluoran derivative used in the present invention, a compound represented by the following general formula (3) is preferable.

[0014]

[Chemical 7]

[Wherein R ₈ and R ₉ are each a C _{1 to} C ₆ alkyl group, an ethoxypropyl group or a p-toluidino group, R ₁₀ is a hydrogen atom or a methyl group, and R ₁₁ is a methyl group or a chlorine atom. Alternatively, it represents a trifluoromethyl group. k represents an integer of 0 to 2. ] Specific examples thereof include, for example, 3-diethylamino-6-
Methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (m-toluidino) fluorane, 3
-Diethylamino-6-methyl-7- (2,4-xylidino) fluorane, 3-diethylamino-6-methyl-
7- (2,6-xylidino) fluorane, 3-dimethylamino-6-methyl-7-anilinofluorane, 3-di-n-propylamino-6-methyl-7-anilinofluorane, 3- ( N-methyl-N-cyclohexylamino) -6-methyl-7-anilinofluorane, 3- (N
-Ethyl-N-cyclohexylamino) -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-butylamino-6-methyl-7-anilinofluorane, 3-di-
n-Pentylamino-6-methyl-7-anilinofluorane, 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-N-n-hexylamino) -7- (o-chloroanilino) fluorane, 3- (N-ethyl-N-isopentylamino) -7- (o-chloroanilino) fluorane, 3-di-n-butyl Amino-7- (o-fluoroanilino) fluorane, 3-di-n-butylamino-6
-Methyl-7- (p-chloroanilino) fluorane, 3
-Diethylamino-7- (m-trifluoromethylanilino) fluorane, 3-di-n-butylamino-7-
(P-trifluoromethylanilino) fluorane, 3-
Diethylamino-5-methyl-7- (p-trifluoromethylanilino) fluorane, 3- (N-ethyl-N-
Cyclopentylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-ethoxypropyl)
Amino-6-methyl-7-anilinofluorane, 3-
(N-methyl-N-ethoxypropyl) amino-6-methyl-7-anilinofluorane, di-n-butylamino-6-methyl-7- (m-toluidino) fluorane, di-n-butylamino- 6-methyl-7- (2,6-xylidino) fluorane and the like can be mentioned. Among them, the use of 3-di-n-butylamino-6-methyl-7-anilinofluorane is particularly preferable because it is excellent in color developability and background fog.

In the present invention, the phenothiazine derivative represented by the general formula (1) used in combination with the fluorane derivative as described above is a dye which produces a blue color tone when used alone, Examples of such compounds include 3,7-bis (dimethylamino) -10-benzoylphenothiazine and 3,7-bis (diethylamino)-
10-benzoylphenothiazine, 3,7-bis (di-
n-butylamino) -10-benzoylphenothiazine, 3,7-bis (dimethylamino) -10- (4-methylbenzoyl) phenothiazine, 3,7-bis (diethylamino) -10- (4-methylbenzoyl) phenothiazine, 3,7-bis (di-n-butylamino) -1
0- (4-methylbenzoyl) phenothiazine, 3,7
-Bis (dimethylamino) -10- (4-methoxybenzoyl) phenothiazine, 3,7-bis (dimethylamino) -10- (4-ethoxybenzoyl) phenothiazine, 3,7-bis (dimethylamino) -10- ( 4-chlorobenzoyl) phenothiazine, 3,7-bis (dimethylamino) -10- (2-methylbenzoyl) phenothiazine, 3,7-bis (dimethylamino) -10-
(2-Methoxybenzoyl) phenothiazine, 3,7-
Bis (dimethylamino) -10- (2-chlorobenzoyl) phenothiazine, 3,7-bis (di-n-butylamino) -10- (4-chlorobenzoyl) phenothiazine, 3-diethylamino-7-dimethylamino-10 −
Examples thereof include benzoylphenothiazine. Among these, the compounds represented by the following general formula (4) are particularly preferable because the raw materials are easily available, the cost is low, and the image storability, particularly, the light resistance is excellent. Of course, it is not limited to these, and two or more kinds may be used in combination as required.

[0017]

Embedded image

[In the formula, R ₅ is a hydrogen atom, a halogen atom,
An alkyl group or C ₁ -C ₄ alkoxyl group C ₁ -C _4. ]

In the heat-sensitive recording material of the present invention, the specific fluoran derivative and the specific phenothiazine derivative as described above are used in combination at a specific ratio, and the colorant is represented by the general formula (2). By selectively combining the diphenylsulfone derivatives, excellent effects can be obtained with respect to the storability of recorded images and background fog. Specific examples of such diphenylsulfone derivatives include the following.

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-4'-methoxydiphenyl sulfone, 4-hydroxy-4'-ethoxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl 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-trihydroxydiphenyl sulfone etc. Of course, it is not limited to these, and two or more kinds may be used in combination as required.

Among these diphenyl sulfone derivatives, 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone and 4-hydroxy-4'-isopropoxydiphenyl sulfone are In addition to the background fog, a heat-sensitive recording material excellent in recording sensitivity and OCR readability under high temperature and high humidity can be obtained, so that it is more preferably used.

In the present invention, the specific diphenyl sulfone derivative as described above is selectively used as a color-developing agent, but other known color-developing agents may be used as long as the desired effects of the present invention are not impaired. It is also possible to use agents together.

The ratio of the basic dye to the coloring agent used in the recording layer is not particularly limited, but is generally 100 to 1000 parts by weight, preferably 200 to 100 parts by weight with respect to 100 parts by weight of the dye.
500 parts by weight of color former are used.

Further, in the heat-sensitive recording material of the present invention,
As a recording sensitivity improver in the recording layer, for example, caproic acid amide, capric acid amide, palmitic acid amide, stearic acid amide, oleic acid amide, erucic acid amide,
Linoleic acid amide, linolenic acid amide, N-methylstearic 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- - (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-
Compounds such as (2'-hydroxy-5'-methylphenyl) benzotriazole and 2-hydroxy-4-benzyloxybenzophenone can also be contained.

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. In addition, inorganic pigments such as kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, fine anhydrous silica and activated clay can be added in order to improve adhesion of dust to the recording head. The recording layer may contain various known storability improvers in order to further improve the storability. Specific examples of the storage stability improver include 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,1.
3-tris (2-methyl-4-hydroxy-5-ter
t-Butylphenyl) butane, 4,4′-thiobis (3
-Methyl-5-tert-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'-diphenylacrylate, tetra (2,2,6,6-tetramethyl-4-piperidyl) -1, 2,3,4-butane tetracarboate, 4-benzyloxyphenyl-4'-
(2-Methyl-2,3-epoxypropyloxy) phenyl sulfone, 2,2'-methylenebis (4,6-di-
Examples thereof include sodium salt or magnesium salt of tert-butylphenyl) phosphoric acid.

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, attritor or sand mill, or separately, using water as a dispersion medium. To be done. Of course, the fluoran derivative and the phenothiazine derivative represented by the general formula [Chemical Formula 1] can be dispersed together or separately.

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 auxiliary agents 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. Also, in order to prevent sticking of the thermal recording material due to contact with recording equipment or recording heads, 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.

The support may be 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, synthetic paper manufactured by the film method or fiber method is used. In the film method, the synthetic resin, the filler and the additive are melt-kneaded and then extruded to form a film. method,
There are a surface coating method and a surface treatment method in which a pigment coating layer is provided, and synthetic fiber papers such as synthetic pulp paper and spunbond paper are available as the fiber method synthetic papers.

The method of 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 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, by providing a protective layer composed of an adhesive, a lubricant, a pigment or the like on the thermosensitive recording layer, a thermosensitive recording material having excellent chemical resistance against plasticizer, oil 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 and the like. It is of course possible to provide a protective layer on the back surface of the recording medium 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.

[0033]

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 the examples represent parts by weight and% by weight, respectively.

Example 1 [Preparation of solution A] 3-di-n-butylamino-6-methyl-
7-anilinofluorane 10 parts, 5 of methylcellulose
% Aqueous solution 3 parts and water 27 parts were pulverized with a sand mill until the average particle size was 0.8 μm, to obtain a liquid A.

[Preparation of solution B] 3,7-bis (dimethylaminophenyl) -10-benzoylphenothiazine 10
Parts, 3 parts of a 5% aqueous solution of methylcellulose, and 27 parts of water
Of the composition consisting of 1 part by a sand mill has an average particle diameter of 0.8 μm.
It was pulverized until it became, and a liquid B was obtained.

[Preparation of liquid C] 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 with a sand mill until the average particle size was 1.2 μm, to obtain a C liquid.

[Preparation of Solution D] 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 size of 1.2 μm. Was pulverized to obtain a liquid D.

[Formation of Recording Layer] Liquid A 32 parts, liquid B 8 parts,
Liquid C 80 parts, liquid D 80 parts, light calcium carbonate 10 parts,
50 g / m ^{2 of} a coating liquid obtained by mixing and stirring 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. 4g dry weight on high quality paper
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 to 7 Thermal recording materials were prepared in the same manner as in Example 1 except that the following compounds were used in place of 3,7-bis (dimethylaminophenyl) -10-benzoylphenothiazine in the preparation of solution B. Got Example 2: 3,7-bis (dimethylaminophenyl)
-10- (4-Methylbenzoyl) phenothiazine Example 3: 3,7-bis (dimethylaminophenyl)
-10- (4-Methoxybenzoyl) phenothiazine Example 4: 3,7-Bis (dimethylaminophenyl)
-10- (2-Methoxybenzoyl) phenothiazine Example 5: 3,7-bis (dimethylaminophenyl)
-10- (4-Isopropoxybenzoyl) phenothiazine Example 6: 3,7-Bis (diethylaminophenyl)
-10-Benzoylphenothiazine Example 7: 3,7-Bis (di-n-butylaminophenyl) -10- (4-chlorobenzoyl) phenothiazine

Examples 8 to 9 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that the following compounds were used in place of 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone in the preparation of the liquid C. Got Example 8: 2,4'-Dihydroxydiphenyl sulfone Example 9: 4-Hydroxy-4'-isopropoxydiphenyl sulfone

Example 10 In preparation of solution A, 3-di-n-butylamino-6-methyl-7-anilinofluorane was replaced with 3-diethylamino-7- (m-trifluoromethylanilino) fluorane. A thermal recording material was obtained in the same manner as in Example 1 except that the thermal recording material was used.

Examples 11 to 14 Thermal recording was carried out in the same manner as in Example 1 except that in the formation of the recording layer, A solution and B solution were used in the following ratios instead of 32 parts of A solution and 8 parts of B solution. Got the body Example 11: A solution 24 parts, B solution 16 parts Example 12: A solution 28 parts, B solution 12 parts Example 13: A solution 36 parts, B solution 4 parts Example 14: A solution 38 parts, B solution 2 copies

Comparative Examples 1 to 3 Thermal recording was carried out in the same manner as in Example 1 except that the liquid A and liquid B were used in the following ratios instead of liquid A 32 parts and liquid B 8 parts in the formation of the recording layer. Got the body Comparative Example 1: Liquid A 40 parts, Liquid B 0 part Comparative Example 2: Liquid A 39 parts, Liquid B 1 part Comparative Example 3: Liquid A 16 parts, Liquid B 24 parts

Comparative Examples 4 to 5 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that the following compounds were used in place of 3,7-bis (dimethylaminophenyl) -10-benzoylphenothiazine in the preparation of solution B. Got Comparative Example 4: 3,3-bis (4-diethylamino-2-)
Ethoxyphenyl) -4-azaphthalide Comparative Example 5: 3-di-n-butylamino-6,8,8-
Trimethyl-8,9-dihydro- (3,2, e) pyridfluorane

Comparative Example 6 Example 1 was repeated except that 4,4'-isopropylidenediphenol was used in place of 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone in the preparation of the liquid C.
A thermosensitive recording medium was obtained in the same manner as described above.

The heat-sensitive recording material thus obtained was 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.

The _{PCS = (R W -R P)} / R W R W represents the reflectivity of the unrecorded portion, R _P represents the reflectivity of the recording unit. Therefore, the higher the PCS value, the clearer the discrimination between the recorded portion and the unrecorded portion, and the higher the readability. Generally, the PCS value is 0.7 or more, preferably 0.8.
The above is required.

[Measurement of PCS value at 670 nm] Recording was carried out with a thermal recording evaluation device [TH-PMD type, manufactured by Okura Electric Co., Ltd., applied voltage 16 V, pulse cycle 0.51 ms, applied pulse width 0.3 ms]. The reflectance of the unrecorded area at a wavelength of 670 nm was measured with a spectrophotometer [U-3300, manufactured by Hitachi, Ltd.], and the PCS value was calculated from the value. The color tones of the obtained recorded images were all black.

[Background Fogging] The unrecorded area was measured with a Macbeth densitometer [Macbeth RD-914 model, visual filter].

[Moisture and heat resistance] After recording, 50 ° C., 90% RH
After being left for 72 hours under the above condition, the PCS value and the background fog were measured.

[Light resistance] After recording, after exposure to direct sunlight for 24 hours, the PCS value and the background fog were measured.

[0052]

[Table 1]

[0053]

As is clear from the results shown in Table 1, the thermosensitive recording medium of the present invention has a sufficiently high PCS value at 670 nm even when exposed to high temperature and high humidity or light for a long time, and has little background fog. Met.

Claims (5)

[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 at least a black coloring fluoran derivative is used as the basic dye in the recording layer. One and at least one phenothiazine derivative represented by the following general formula (1) are contained so that the phenothiazine derivative is 5 to 100% by weight of the fluoran derivative, and the following general formula (2) is used as a coloring agent. A heat-sensitive recording material containing a diphenyl sulfone derivative represented by: [Chemical 1] [In the formula, R _{1 to} R ₄ each represent a C _{1 to} C ₄ alkyl group, and R ₅ represents a hydrogen atom, a halogen atom, a C _{1 to} C ₄ alkyl group, or a C _{1 to} C ₄ alkoxyl group. . ] [Chemical 2] [In the formula, R ₆ and R ₇ 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 heat-sensitive recording material according to claim 1, wherein the black color-forming fluoran derivative is a compound represented by the following general formula (3). [Chemical 3] [Wherein R ₈ and R ₉ represent a C _{1 to} C ₆ alkyl group, an ethoxypropyl group or p-tolyl, R ₁₀ represents a hydrogen atom or a methyl group, R ₁₁ represents a methyl group, a chlorine atom or a trifluoromethyl group. Show. k represents an integer of 0 to 2. ] 3. A phenothiazine derivative represented by the following general formula (4):
The heat-sensitive recording material according to claim 1, which is a compound represented by: [Chemical 4] Wherein, R ₅ represents a hydrogen atom, a halogen atom, an alkyl group or an alkoxyl group of C ₁ -C ₄ a C ₁ -C _4. ] 4. The heat-sensitive recording material according to claim 1, wherein the phenothiazine derivative is 10 to 50% by weight of the fluoran derivative. 5. A diphenylsulfone derivative is 3,3′-
The heat-sensitive recording material according to any one of claims 1 to 4, which is diallyl-4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, or 4-hydroxy-4'-isopropoxydiphenyl sulfone. .