JP2005238794A - Thermal recording material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording material which is high in transparency, excellent in uniformity of a coated surface, has chemical resistance and can form an image with a high dignity free from density irregularity. <P>SOLUTION: The thermal recording material is a compound having an electron acceptive compound represented by formula (1) and contains compounds represented by formulae (2), (3). In the formula (1), R<SP>1</SP>and R<SP>2</SP>each independently represents hydrogen and an alkyl group. The formula (2) is represented by R<SP>3</SP>-SO<SB>3</SB>M (wherein R<SP>3</SP>represents an alkyl group, an alkyl aryl group or an alkyl phenoxy group and M represents an anion). The formula (3) is represents by R<SP>4</SP>-O-(CH<SB>2</SB>CH<SB>2</SB>0)<SB>n</SB>-H (wherein R<SP>4</SP>represents an alkyl group or an alkyl aryl group, and n represents an integer of 1-50). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heat-sensitive recording material, and more particularly to a transparent heat-sensitive recording material suitable for medical recording media and the like.

  In the thermal recording method, (1) no development is required, (2) when the support is paper, the paper quality is close to ordinary paper, (3) easy handling, (4) high color density, ( 5) Since the recording apparatus is simple and inexpensive, and (6) it has advantages such as no noise during recording, the application is expanding to the fields of facsimiles and printers, label fields such as POS, and the like.

  In recent years, a thermal recording layer has been provided on a transparent support for direct recording with a thermal head in order to project an image or the like with an overhead projector or to directly observe an image on a light table. There is a demand for the development of possible thermal recording materials. In particular, transparent thermosensitive recording materials have attracted attention as those for forming medical diagnostic images.

  However, a transparent heat-sensitive recording material has good transparency, but has a problem that sticking and noise are likely to occur when printing is performed with a heat-sensitive recording device such as a heat-sensitive printer. In particular, when a transparent thermosensitive recording material is used for medical purposes, a high transmission density is required. For this reason, large thermal energy is required when printing with the thermal head, and problems such as sticking, noise during recording, and thermal head wear become serious. On the other hand, for the purpose of improving noise during sticking and printing, a protective layer mainly composed of a pigment, a lubricant, and a binder is provided on the heat-sensitive recording layer.

  For example, as a heat-sensitive recording material for the purpose of improving transparency and thermal head suitability (sticking property, printing sound), a material provided with a protective layer containing a pigment surface-treated with a higher fatty acid salt is disclosed. (For example, refer to Patent Document 1). For the purpose of improving chemical resistance, sticking resistance and antistatic effect, a water-soluble resin layer containing a specific amount of alkylsulfosuccinate and a fluorosurfactant is provided as a protective layer. A recording material is disclosed (for example, see Patent Document 2).

  Furthermore, in addition to the protective layer, the heat-sensitive recording material can be appropriately provided with a gas blocking layer, an undercoat layer, an ultraviolet filter layer, an antireflection layer, and the like. In order to provide these layers on the support, in addition to a method of sequentially forming each layer on the support, a method of coating all layers in a uniform manner by an extrusion die method or the like is known (for example, Patent Documents). 3).

  However, a heat-sensitive recording material that is sufficiently satisfactory with respect to the uniformity of the coated surface has not yet been obtained. For example, there is a problem that the surface condition of the coating is deteriorated due to the organic solvent remaining in the applied heat-sensitive recording layer, and such a problem is remarkable when multi-layer coating is applied. It was. In particular, when a medical diagnostic image is produced using a transparent thermosensitive recording material, an accurate diagnosis cannot be made if there is density unevenness or a clear image is not formed in detail. Also from such a viewpoint, the above-described deterioration of the surface condition in the heat-sensitive recording material adversely affects image formation and becomes a problem. In addition, when the heat-sensitive recording material is used for medical purposes, it is particularly required to have resistance to chemicals.

  Furthermore, an electron-accepting compound having excellent transparency has been proposed as a developer used in a heat-sensitive recording material (see, for example, Patent Document 4 below). However, although such an electron-accepting compound is excellent in transparency, there is a problem that it is difficult to apply uniformly when a protective layer is applied thereon.

  Therefore, there is a demand for a heat-sensitive recording material that is highly transparent and suitable for medical recording media and the like, has a good coated surface shape, excellent chemical resistance, and is capable of forming a high-quality image without density unevenness. However, it has not been provided yet.

JP-A-6-340179 JP-A-6-328849 Japanese Patent Laid-Open No. 4-97886 JP-A-1-101188

  The present invention aims to solve the following problems in order to solve the above-mentioned problems. That is, an object of the present invention is to provide a heat-sensitive recording material having high transparency, excellent uniformity of the coated surface, chemical resistance, and capable of forming a high-quality image without density unevenness. To do.

The above-mentioned problem of the present invention is solved by the following means.
<1> A thermosensitive recording layer comprising an electron-donating dye precursor and an electron-accepting compound that develops the color of the electron-donating dye precursor on a support, and at least one layer provided on the thermosensitive recording layer The electron-accepting compound is a compound represented by the following general formula (1), and the protective layer is represented by the following general formula (2). A heat-sensitive recording material comprising a compound and a compound represented by the general formula (3).

（一般式（１）中、Ｒ¹およびＲ²は、それぞれ独立して、水素原子、炭素数１〜２０のアルキル基を表す。）
Ｒ³−ＳＯ₃Ｍ 一般式（２）
（一般式（２）中、Ｒ³は、炭素数４〜２０のアルキル基、炭素数６〜２０のアルキルアリール基、または炭素数６〜２０のアルキルフェノキシ基を表す。Ｍは、アニオンを表す。）
Ｒ⁴−Ｏ−（ＣＨ₂ＣＨ₂Ｏ）_n−Ｈ 一般式（３）
（一般式（３）中、Ｒ⁴は、炭素数４〜２０のアルキル基、または炭素数６〜２０のアルキルアリール基を表す。ｎは１〜５０までの整数を表す。）

(In General Formula (1), R ¹ and R ² each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.)
R ³ —SO ₃ M General formula (2)
(In General Formula (2), R ³ represents an alkyl group having 4 to 20 carbon atoms, an alkylaryl group having 6 to 20 carbon atoms, or an alkylphenoxy group having 6 to 20 carbon atoms. M represents an anion. .)
R ⁴ —O— (CH ₂ CH ₂ O) _n —H Formula (3)
(In General Formula (3), R ⁴ represents an alkyl group having 4 to 20 carbon atoms or an alkylaryl group having 6 to 20 carbon atoms. N represents an integer of 1 to 50.)

  <2> Further, the thermosensitive recording layer contains at least one selected from the compound represented by the general formula (2) and the compound represented by the general formula (3). <1> The heat-sensitive recording material.

  <3> The thermosensitive recording material according to <1> or <2>, wherein the compound represented by the general formula (2) is an alkylbenzene sulfonate.

  <4> The compound represented by the general formula (2) is at least one selected from an alkali metal salt of alkylbenzenesulfonic acid, a triethanolamine salt of alkylbenzenesulfonic acid, and an ammonium salt of alkylbenzenesulfonic acid. <1> or <2>, which is characterized by the above.

  <5> The heat-sensitive recording material according to <3> or <4>, wherein the alkyl group of the alkylbenzenesulfonic acid is a linear alkyl group.

  <6> The thermosensitive recording material according to <1> to <5>, wherein the electron donating dye precursor is encapsulated in a microcapsule.

  <7> A coating solution containing an emulsion in which the thermosensitive recording layer is obtained by dissolving and emulsifying the microcapsules encapsulating the electron-donating dye precursor and the electron-accepting compound in an organic solvent hardly soluble or insoluble in water. The heat-sensitive recording material according to <1> to <5> above, which is formed by coating the substrate on the support.

  According to the present invention, it is possible to provide a heat-sensitive recording material having high transparency, excellent uniformity of the coated surface, chemical resistance, and capable of forming a high-quality image without density unevenness.

《Thermal recording material》
The heat-sensitive recording material of the present invention is provided on a support with a heat-sensitive recording layer comprising an electron-donating dye precursor and an electron-accepting compound that develops color of the electron-donating dye precursor, and the heat-sensitive recording layer. The electron-accepting compound is a compound represented by the following general formula (1), and the protective layer is represented by the following general formula (2). It contains a compound and a compound represented by the general formula (3).

（一般式（１）中、Ｒ¹およびＲ²は、それぞれ独立して、水素原子、炭素数１〜２０のアルキル基を表す。）

(In General Formula (1), R ¹ and R ² each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.)

R ³ —SO ₃ M General formula (2)
(In General Formula (2), R ³ represents an alkyl group having 4 to 20 carbon atoms, an alkylaryl group having 6 to 20 carbon atoms, or an alkylphenoxy group having 6 to 20 carbon atoms. M represents an anion. .)

R ⁴ —O— (CH ₂ CH ₂ O) _n —H Formula (3)
(In General Formula (3), R ⁴ represents an alkyl group having 4 to 20 carbon atoms or an alkylaryl group having 6 to 20 carbon atoms. N represents an integer of 1 to 50.)

  According to the present invention, the electron-accepting compound represented by the general formula (1) having excellent transparency in the heat-sensitive recording layer and the interface represented by the general formulas (2) and (3) in the protective layer. By using in combination with the activator, coating unevenness of the protective layer can be suppressed, transparency can be improved, and chemical resistance can be further improved.

  The compound represented by the general formula (1) (hereinafter sometimes referred to as “electron-accepting compound in the present invention”) is an electron-accepting compound having excellent transparency, and a heat-sensitive recording layer using this compound. The surface of the protective layer formed on the surface of the protective film is deteriorated. Therefore, the compound represented by the general formula (2) and the compound represented by the general formula (3) (hereinafter, these may be collectively referred to as “surfactants in the present invention”) in the protective layer. By using together, it is possible to improve the coated surface state of the protective layer while maintaining the transparency of the thermosensitive recording layer, and to improve the chemical resistance.

  The surfactant in the present invention is only required to be contained in at least the protective layer, and the surfactant in the present invention can also be contained in a layer formed on the side of the support on which the heat-sensitive recording layer is provided. For example, the effect of the present invention can be sufficiently exerted by including only in the protective layer, but the surfactant in the present invention is incorporated in the heat-sensitive recording layer in order to further exhibit the effect of the present invention. You can also. Further, when the protective layer in the present invention comprises a plurality of layers, it is preferably contained in a protective layer adjacent to the thermosensitive recording layer. In the present invention, it is particularly preferred that the heat-sensitive recording layer and the protective layer adjacent thereto contain the surfactant in the present invention.

Hereinafter, the heat-sensitive recording material of the present invention will be described in detail.
The heat-sensitive recording material of the present invention has at least a heat-sensitive recording layer on a support, and further has at least one protective layer. The heat-sensitive recording material of the present invention may have an undercoat layer, an intermediate layer and other layers as necessary.

<Thermal recording layer>
The heat-sensitive recording layer according to the present invention contains at least the electron donating dye precursor and the electron accepting compound according to the present invention, and may further contain other components as necessary.

(Electron-accepting compound)
The heat-sensitive recording material of the present invention comprises a compound represented by the following general formula (1) (electron-accepting compound in the present invention) as an electron-accepting compound that acts on an electron-donating dye precursor described later on the heat-sensitive recording layer. contains.

In general formula (1), R ¹ and R ² each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

The alkyl group having 1 to 20 carbon atoms represented by R ¹ and R ² may have a substituent, may be a linear alkyl group, or is a branched alkyl group. Also good. Moreover, carbon number of the said alkyl group is 1-20, 1-10 are preferable and 1-6 are more preferable. If the alkyl group has more than 20 carbon atoms, the solubility in an organic solvent during preparation of the emulsion may be reduced, and transparency may be deteriorated.

  Examples of the alkyl group having 1 to 20 carbon atoms include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, t-butyl group, n-pentyl group, Examples thereof include 2-ethylhexyl group, and ethyl group, propyl group, n-butyl group and i-butyl group are preferable.

  The specific example of the electron-accepting compound in this invention is shown. However, the present invention is not limited to this.

Moreover, in this invention, the electron-accepting compound in this invention and another well-known electron-accepting compound can be used together.
Examples of the known electron-accepting compound include acidic substances such as phenol compounds, organic acids or metal salts thereof, and oxybenzoic acid esters, and are described in, for example, JP-A No. 61-291183. Compounds.
Specific examples of the known electron-accepting compound include 2,2-bis (4′-hydroxyphenyl) propane (generic name: bisphenol A), 2,2-bis (4′-hydroxyphenyl) pentane, 2, 2-bis (4′-hydroxy-3 ′, 5′-dichlorophenyl) propane, 1,1-bis (4′-hydroxyphenyl) cyclohexane, 2,2-bis (4′-hydroxyphenyl) hexane, 1,1 -Bis (4'-hydroxyphenyl) propane, 1,1-bis (4'-hydroxyphenyl) butane, 1,1-bis (4'-hydroxyphenyl) pentane, 1,1-bis (4'-hydroxyphenyl) ) Hexane, 1,1-bis (4′-hydroxyphenyl) heptane, 1,1-bis (4′-hydroxyphenyl) octane, 1,1-bis (4′-hydroxypheny) ) -2-methyl-pentane, 1,1-bis (4′-hydroxyphenyl) -2-ethyl-hexane, 1,1-bis (4′-hydroxyphenyl) dodecane, 1,4-bis (p-hydroxy) Phenylcumyl) benzene, 1,3-bis (p-hydroxyphenylcumyl) benzene, bis (p-hydroxyphenyl) sulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, bis (p-hydroxyphenyl) Bisphenols such as benzyl acetate;

Salicylic acid derivatives such as 3,5-di-α-methylbenzylsalicylic acid, 3,5-di-tertiarybutylsalicylic acid, 3-α-α-dimethylbenzylsalicylic acid, 4- (β-p-methoxyphenoxyethoxy) salicylic acid;

Or a polyvalent metal salt thereof (in particular, zinc or aluminum is preferable); p-hydroxybenzoic acid benzyl ester, p-hydroxybenzoic acid-2-ethylhexyl ester, β-resorcinic acid- (2-phenoxyethyl) ester, etc. Oxybenzoates; phenols such as p-phenylphenol, 3,5-diphenylphenol, cumylphenol, 4-hydroxy-4'-isopropoxy-diphenylsulfone, 4-hydroxy-4'-phenoxy-diphenylsulfone Is mentioned.
Among these, bisphenols are particularly preferable from the viewpoint of obtaining good color development characteristics.

The content of the electron-accepting compound contained in the heat-sensitive recording layer in the invention is preferably 0.5 to 30 parts by mass, and 1.0 to 10 parts per 1 part by mass of the electron donating dye precursor described later. Part by mass is more preferable.
Further, from the viewpoint of sufficiently exerting the effect of the present invention, when the electron accepting compound of the present invention is used in combination with another known electron accepting compound, the electron accepting compound of the present invention with respect to the total electron accepting compound The content is preferably 5% by mass or more, and more preferably 10% by mass.

(Electron-donating dye precursor)
The electron donating dye precursor used in the present invention is not particularly limited as long as it is substantially colorless, and has a property of coloring by donating electrons or accepting protons such as acids. What is necessary is just to have. The electron donating dye precursor has a partial skeleton such as lactone, lactam, sultone, spiropyran, ester, amide, etc., and these partial skeletons are opened or cleaved when contacted with an electron accepting compound. A colorless compound is preferred.

  Examples of the electron donating dye precursor include phthalide compounds such as triphenylmethane phthalide compounds or indolyl phthalide compounds, fluorane compounds, spiropyran compounds, pyridine compounds, pyrazine compounds, and fluorene compounds. Examples thereof include compounds, phenothiazine compounds, leucooramine compounds, rhodamine lactam compounds, triphenylmethane compounds and triazene compounds.

Specific examples of the phthalide compounds include U.S. Reissued Patent No. 23,024, U.S. Pat. Nos. 3,491,111, 3,491,112, and 3,491. , 116 specification, 3,509, 174 specification and the like.
Specific examples of the fluorane compound include U.S. Pat. Nos. 3,624,107, 3,627,787, 3,641,011, and 3,462. Examples thereof include the compounds described in 828, 3,681,390, 3,920,510, 3,959,571, and the like.

Specific examples of the spiropyran compounds include compounds described in US Pat. No. 3,971,808.
Examples of the pyridine-based and pyrazine-based compounds include compounds described in US Pat. Nos. 3,775,424, 3,853,869, 4,246,318, and the like. Is mentioned.
Specific examples of the fluorene compound include compounds described in JP-A No. 63-094878.
Among these, black coloring 2-arylamino-3- [H, halogen, alkyl or alkoxy-6-substituted aminofluorane] is particularly preferable.

  Specific examples of the electron donating dye precursor include 2-anilino-3-methyl-6-N-ethyl-N-sec-butylaminofluorane, 2-anilino-3-methyl-6-diethylaminofluorane. 2-anilino-3-methyl-6-N-cyclohexyl-N-methylaminofluorane, 2-p-chloroanilino-3-methyl-6-dibutylaminofluorane, 2-anilino-3-methyl-6-dioctyl Aminofluorane, 2-anilino-3-chloro-6-diethylaminofluorane, 2-anilino-3-methyl-6-N-ethyl-N-isoamylaminofluorane, 2-anilino-3-methyl-6-N -Ethyl-N-dodecylaminofluorane, 2-anilino-3-methoxy-6-dibutylaminofluorane, 2-o-chloroanilino-6 Dibutylaminofluorane, 2-p-chloroanilino-3-ethyl-6-N-ethyl-N-isoamylaminofluorane, 2-o-chloroanilino-6-p-butylanilinofluorane, 2-anilino-3- Pentadecyl-6-diethylaminofluorane, 2-anilino-3-ethyl-6-dibutylaminofluorane, 2-o-toluidino-3-methyl-6-diisopropylaminofluorane, 2-anilino-3-methyl-6- N-isobutyl-N-ethylaminofluorane, 2-anilino-3-methyl-6-N-ethyl-N-tetrahydrofurfurylaminofluorane, 2-anilino-3-chloro-6-N-ethyl-N- Isoamylaminofluorane, 2-anilino-3-methyl-6-N-methyl-N-γ-ethoxypropylaminofluorane Lan, 2-anilino-3-methyl-6-N-ethyl-N-γ-ethoxypropylaminofluorane, 2-anilino-3-methyl-6-N-ethyl-N-γ-propoxypropylaminofluorane, etc. Is mentioned.

The content of the electron-donating dye precursor in the heat-sensitive recording layer is preferably from ^{0.1~5.0g / m 2, 0.4~4.0g / m} 2 is more preferable. When the content of the electron donating dye precursor is in the above range, a sufficient color density can be obtained and the transparency of the thermosensitive recording layer can be maintained.

(Microcapsule)
The electron donating dye precursor is preferably encapsulated in microcapsules. Below, the manufacturing method of a microcapsule is explained in full detail.
There are an interfacial polymerization method, an internal polymerization method, an external polymerization method and the like in the production of microcapsules, and any method can be adopted.
As a method for producing the above microcapsules, an oil phase prepared by dissolving or dispersing an electron-donating dye precursor serving as a capsule core in a hydrophobic organic solvent is put into an aqueous phase in which a water-soluble polymer is dissolved. In addition, it is preferable to employ an interfacial polymerization method in which a microcapsule wall made of a polymer substance is formed by a polymer formation reaction that occurs at the oil droplet interface by heating after emulsification and dispersion by a stirring means such as a homogenizer. .

  The reactant that forms the polymer substance is added inside the oil droplet and / or outside the oil droplet. Specific examples of the polymer substance include polyurethane, polyurea, polyamide, polyester, polycarbonate, urea-formaldehyde resin, melamine resin, polystyrene, styrene methacrylate copolymer, styrene-acrylate copolymer, and the like. Among these, polyurethane, polyurea, polyamide, polyester, and polycarbonate are preferable, and polyurethane and polyurea are particularly preferable.

  For example, when polyurea is used as a capsule wall material, polyisocyanates such as diisocyanate, triisocyanate, tetraisocyanate, and polyisocyanate prepolymer, polyamines such as diamine, triamine, and tetraamine, two or more amino acids A microcapsule wall can be easily formed by reacting a prepolymer having a group, piperazine or a derivative thereof, a polyol or the like in the aqueous phase by an interfacial polymerization method.

  The microcapsule is, for example, a composite wall made of polyurea and polyamide, or a composite wall made of polyurethane and polyamide is, for example, a polyisocyanate and a second substance that forms a capsule wall by reacting with it (for example, , Acid chloride, polyamine, polyol) can be prepared by mixing water-soluble polymer aqueous solution (aqueous phase) or oily medium (oil phase) to be encapsulated, emulsifying and dispersing them, and then heating. . Details of the method for producing a composite wall composed of polyurea and polyamide are described in JP-A-58-66948.

The polyisocyanate is preferably a compound having a trifunctional or higher functional isocyanate group, but a bifunctional isocyanate compound may be used in combination.
Specifically, diisocyanates such as xylene diisocyanate and hydrogenated products thereof, hexamethylene diisocyanate, tolylene diisocyanate and hydrogenated products thereof, isophorone diisocyanate and the like, and dimers thereof. In addition to a trimer (burette or isocyanurate), a polyfunctional adduct of a polyol such as trimethylolpropane and a bifunctional isocyanate such as xylylene diisocyanate, a polyol such as trimethylolpropane and a xylylene Examples thereof include a compound in which a high molecular weight compound such as polyether having active hydrogen such as polyethylene oxide is introduced into an adduct with a bifunctional isocyanate such as range isocyanate, and a formalin condensate of benzene isocyanate.
As the polyisocyanate, compounds described in JP-A-62-212190, JP-A-4-26189, JP-A-5-317694, JP-A-10-114153 and the like are preferable.

  The polyisocyanate is preferably added so that the average particle size of the microcapsules is 0.3 to 12 μm and the thickness of the capsule wall is 0.01 to 0.3 μm. The dispersed particle size is generally about 0.2 to 10 μm.

Specific examples of polyols and / or polyamines that are added to the water phase and / or the oil phase as one of the components of the microcapsule wall by reacting with the polyisocyanate include propylene glycol, glycerin, trimethylolpropane, Examples include triethanolamine, sorbitol, hexamethylenediamine and the like. At this time, when a polyol is added, a polyurethane wall is formed. In the above reaction, it is preferable to keep the reaction temperature high or to add an appropriate polymerization catalyst from the viewpoint of increasing the reaction rate.
Polyisocyanates, polyols, reaction catalysts, polyamines for forming a part of the wall agent, etc. are well known in the book (Polyurethane Handbook, Nikkan Kogyo Shimbun (1987) edited by Keiji Iwata).

  Further, a metal-containing dye, a charge control agent such as nigrosine, or any other additive substance can be added to the microcapsule wall as necessary. These additives can be included in the wall of the capsule at the time of wall formation or at any time. Further, a monomer such as a vinyl monomer may be graft-polymerized in order to adjust the chargeability of the capsule wall surface as necessary.

Furthermore, it is preferable to use a plasticizer suitable for the polymer used as the wall material in order to make the wall of the microcapsule excellent in material permeability even under a lower temperature and rich in color development. The plasticizer preferably has a melting point of 50 ° C. or higher, and more preferably has a melting point of 120 ° C. or lower. Among these, those that are solid at room temperature can be suitably selected and used.
For example, when the wall material is made of polyurea or polyurethane, a hydroxy compound, a carbamic acid ester compound, an aromatic alkoxy compound, an organic sulfonamide compound, an aliphatic amide compound, an arylamide compound, or the like is preferably used.

In preparing the oil phase, the hydrophobic organic solvent used for dissolving the electron-donating dye precursor and forming the core of the microcapsule is preferably an organic solvent having a boiling point of 100 to 300 ° C.
Specifically, in addition to esters, dimethylnaphthalene, diethylnaphthalene, diisopropylnaphthalene, dimethylbiphenyl, diisopropylbiphenyl, diisobutylbiphenyl, 1-methyl-1-dimethylphenyl-2-phenylmethane, 1-ethyl-1-dimethylphenyl -1-phenylmethane, 1-propyl-1-dimethylphenyl-1-phenylmethane, triallylmethane (eg, tritoluylmethane, toluyldiphenylmethane), terphenyl compound (eg, terphenyl), alkyl compound, alkylated diphenyl ether (For example, propyl diphenyl ether), hydrogenated terphenyl (for example, hexahydroterphenyl), diphenyl ether, and the like. Among these, it is particularly preferable to use esters from the viewpoint of emulsion stability of the emulsion.

  Examples of the esters include phosphate esters such as triphenyl phosphate, tricresyl phosphate, butyl phosphate, octyl phosphate, and cresyl phenyl phosphate; dibutyl phthalate, 2-ethylhexyl phthalate, ethyl phthalate, Phthalic acid esters such as octyl phthalate and butyl benzyl phthalate; Dioctyl tetrahydrophthalate; Benzoic acid esters such as ethyl benzoate, propyl benzoate, butyl benzoate, isopentyl benzoate and benzyl benzoate; Ethyl abietic acid, abietic acid Abietic acid esters such as benzyl; dioctyl adipate; isodecyl succinate; dioctyl azelate; oxalic acid esters such as dibutyl oxalate and dipentyl oxalate; diethyl malonate; dimethyl maleate, diethyl maleate, di maleate Maleic acid esters such as chill; Tributyl citrate; Sorbic acid esters such as methyl sorbate, ethyl sorbate, and butyl sorbate; Sebacic acid esters such as dibutyl sebacate and dioctyl sebacate; Formic acid monoesters and diesters, butyric acid monoesters And ethylene glycol esters such as diester, lauric acid monoester and diester, palmitic acid monoester and diester, stearic acid monoester and diester, oleic acid monoester and diester; triacetin; diethyl carbonate; diphenyl carbonate; ethylene carbonate; propylene carbonate And boric acid esters such as tributyl borate and tripentyl borate.

  Among these, in particular, when tricresyl phosphate is used alone or in combination, the stability of the emulsion is most favorable, which is preferable. It is also possible to use the above oils in combination with other oils.

  When the electron-donating dye precursor to be encapsulated has poor solubility in a hydrophobic organic solvent, a low-boiling solvent having high solubility can be used in combination. Preferred examples of such a low boiling point solvent include ethyl acetate, isopropyl acetate, butyl acetate, and methylene chloride.

  On the other hand, an aqueous solution in which a water-soluble polymer is dissolved as a protective colloid can be used for the aqueous phase. After the oil phase is added to this aqueous solution, it is emulsified and dispersed by means such as a homogenizer. The water-soluble polymer serves as a dispersion medium that makes the dispersion uniformly and easy and stabilizes the emulsified and dispersed aqueous solution. Works. Here, in order to more uniformly emulsify and disperse and stabilize, a surfactant may be added to at least one of the oil phase and the aqueous phase. As the surfactant, a known surfactant for emulsification can be used. 0.1-5% is preferable with respect to the mass of an oil phase, and, as for the addition amount of surfactant, 0.5-2% is more preferable.

As the surfactant for emulsification contained in the aqueous phase, an anionic or nonionic surfactant that does not cause precipitation or aggregation by acting with the protective colloid should be used. Can do.
Preferable surfactant for emulsification includes, for example, sodium alkylbenzene sulfonate, sodium alkyl sulfate, dioctyl sulfosuccinate sodium salt, polyalkylene glycol (for example, polyoxyethylene nonylphenyl ether) and the like.

  The above emulsification is easy using means used for normal fine particle emulsification such as high-speed stirring and ultrasonic dispersion of the oil phase containing the above-described components and the aqueous phase containing a protective colloid and a surfactant for emulsification. Can be done. Examples of the means used for the fine particle emulsification include known emulsification apparatuses such as a homogenizer, a manton gorey, an ultrasonic disperser, a dissolver, and a teddy mill. After emulsification, the emulsion is preferably heated to 30 to 70 ° C. in order to promote the capsule wall formation reaction. Further, during the reaction, in order to prevent aggregation between the capsules, it is preferable to add water to reduce the collision probability between the capsules or perform sufficient stirring.

  Further, a dispersion for preventing aggregation may be added again during the reaction. Generation of carbon dioxide gas is observed as the polymerization reaction proceeds, and the end of the generation can be regarded as an approximate end point of the capsule wall formation reaction. Usually, the target microcapsule can be obtained by reacting for several hours.

(Emulsion)
When the electron-donating dye precursor is encapsulated as a core substance, the electron-accepting compound is solid-dispersed by means of a sand mill or the like together with, for example, a water-soluble polymer, an organic base, and other color forming aids. Can be used. In particular, the microcapsules encapsulating the above electron-donating dye precursor and the electron-accepting compound in the present invention are dissolved in an organic solvent (high boiling point organic solvent) that is hardly soluble or insoluble in water, and then the surface-active property is obtained. More preferably, it is used as an emulsion obtained by mixing an aqueous solution of polymer and / or water-soluble polymer as a protective colloid (aqueous phase) and emulsifying with a homogenizer or the like. In this case, a low boiling point solvent can be used as a dissolution aid, if necessary. At this time, the emulsified dispersion particle diameter is preferably 1 μm or less.
The above “water-insoluble or insoluble organic solvent” means a solvent having a solubility in 100 ml of water of 3% or less at 25 ° C. and 1 atm.
Such an organic solvent can be appropriately selected from, for example, high-boiling oils described in JP-A-2-141279. Specifically, tricresyl phosphate, dibutyl phthalate, dioctyl adipate , Dibutyl sebacate, diethyl succinate, diethyl maleate and the like. Among them, the use of esters is preferable from the viewpoint of the emulsion stability of the emulsified dispersion, and tricresyl phosphate and diethyl maleate are particularly preferable. . The organic solvent may be used in combination with other oils.

The water-soluble polymer contained as the protective colloid can be appropriately selected from known anionic polymers, nonionic polymers, and amphoteric polymers. In particular, the water-soluble polymer is preferably a water-soluble polymer having a water solubility of 5% or more at the temperature to be emulsified. Specific examples of the water-soluble polymer include polyvinyl alcohol or a modified product thereof, polyacrylic acid amide or a derivative thereof, ethylene-vinyl acetate copolymer, styrene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer. Polymer, isobutylene-maleic anhydride copolymer, polyvinylpyrrolidone, ethylene-acrylic acid copolymer, vinyl acetate-acrylic acid copolymer, carboxymethylcellulose, cellulose derivatives such as methylcellulose, casein, gelatin, starch derivatives, arabic gum, alginic acid Sodium etc. are mentioned.
Among these, polyvinyl alcohol, gelatin, and cellulose derivatives are particularly preferable.

  Moreover, 0.02-0.6 are preferable and, as for the mixing ratio (oil phase mass / aqueous phase mass) with respect to the water phase of an oil phase, 0.1-0.4 are more preferable. When the mixing ratio is in the range of 0.02 to 0.6, an appropriate viscosity can be maintained, the production suitability is excellent, and the coating solution stability is excellent.

(Other coloring components)
The heat-sensitive recording material of the present invention can be provided with two or more heat-sensitive recording layers. The heat-sensitive recording material of the present invention is substantially colorless as a heat-sensitive recording layer other than the heat-sensitive recording layer containing the electron-accepting compound and the electron-donating dye precursor (heat-sensitive recording layer of the present invention). A so-called two-component thermosensitive recording layer containing component A and a substantially colorless coloring component B that develops color by reacting with coloring component A can be provided. The coloring component A or the coloring component B is preferably encapsulated in a microcapsule. Examples of the combination of the two components constituting the two-component heat-sensitive recording layer include the following (a) to (m).
Examples of combinations of coloring components that can be applied to the heat-sensitive recording layer according to the present invention include the following combinations (a) to (m).

(A) A combination of an electron donating dye precursor and an electron accepting compound.
(B) A combination of a photodegradable diazo compound and a coupler.
(C) A combination of an organic metal salt such as silver behenate or silver stearate and a reducing agent such as protocatechinic acid, spiroindane or hydroquinone.
(D) A combination of a long-chain aliphatic salt such as ferric stearate or ferric myristate and a phenol such as gallic acid or ammonium salicylate.
(E) Organic acid heavy metal salts such as salts with nickel, cobalt, lead, copper, iron, mercury, silver, etc. such as acetic acid, stearic acid, palmitic acid, and alkaline earths such as calcium sulfide, strontium sulfide, potassium sulfide, etc. A combination of a metal sulfide or a combination of the organic acid heavy metal salt and an organic chelating agent such as s-diphenylcarbazide or diphenylcarbazone.
(F) A combination of a (heavy) metal sulfate such as silver sulfide, lead sulfide, mercury sulfide or sodium sulfide and a sulfur compound such as Na-tetrathionate, sodium thiosulfate or thiourea. (G) A combination of an aliphatic ferric salt such as ferric stearate and an aromatic polyhydroxy compound such as 3,4-dihydroxytetraphenylmethane.
(H) A combination of an organic noble metal salt such as silver oxalate or mercury oxalate and an organic polyhydroxy compound such as polyhydroxy alcohol, glycerin or glycol.
(I) A combination of an aliphatic ferric salt such as ferric pelargonate or ferric laurate, and a thiocesylcarbamide or isothiocecilcarbamide derivative.
(J) A combination of an organic acid lead salt such as lead caproate, lead pelargonate or lead behenate and a thiourea derivative such as ethylenethiourea or N-dodecylthiourea.
(K) A combination of a higher fatty acid heavy metal salt such as ferric stearate or copper stearate and zinc dialkyldithiocarbamate.
(L) A substance that forms an oxazine dye such as a combination of resorcin and a nitroso compound.
(M) A combination of a formazan compound and a reducing agent and / or a metal salt.

  Among these, in the heat-sensitive recording material of the present invention, (a) a combination of an electron donating dye precursor and an electron accepting compound, (b) a combination of a photodegradable diazo compound and a coupler, and (c) an organic It is preferable to use a combination of a metal salt and a reducing agent, and it is particularly preferable to use a combination of the above (a) and (b).

  Next, the combination (a, b, c) of the above composition that is preferably used for the thermosensitive recording layer will be described in detail below.

(A) Combination of an electron-donating dye precursor and an electron-accepting compound As a combination of an electron-donating dye precursor and an electron-accepting compound, the electron-accepting compound in the present invention and the electron-donating dye precursor In addition to the above-mentioned combinations, combinations of the above-mentioned other known electron-accepting compounds and the above-mentioned electron-donating dye precursors can be mentioned.

(B) Combination of a photodegradable diazo compound and a coupler The photodegradable diazo compound is a compound that undergoes a coupling reaction with a coupler, which will be described later, to develop a desired hue, and is specified before the reaction. It is a photodegradable diazo compound that decomposes when receiving light in the wavelength range and no longer has a coloring ability even in the presence of a coupling component.
The hue in this color developing system is determined by a diazo dye formed by the reaction of a diazo compound and a coupler. Accordingly, the color hue can be easily changed by changing the chemical structure of the diazo compound or coupler, and an arbitrary color hue can be obtained depending on the combination.

Examples of the photodegradable diazo compound include aromatic diazo compounds. Specific examples include aromatic diazonium salts, diazosulfonate compounds, diazoamino compounds, and the like.
Examples of the aromatic diazonium salt include compounds represented by the following formulas. The aromatic diazonium salt is preferably used since it has excellent photofixability, little generation of colored stain after fixing, and a stable color developing portion.
Ar-N ₂ ⁺ X ^-
In the above formula, Ar represents a substituted or unsubstituted aromatic hydrocarbon ring group, N ₂ ⁺ represents a diazonium group, and X ⁻ represents an acid anion.

  As the diazo sulfonate compound, a large number of diazo sulfonate compounds have been known in recent years. The diazo sulfonate compound is obtained by treating each diazonium salt with a sulfite and can be suitably used for the heat-sensitive recording material of the present invention.

The diazoamino compound can be obtained by coupling a diazo group with dicyandiamide, sarcosine, methyltaurine, N-ethylanthranic acid-5-sulfonic acid, monoethanolamine, diethanolamine, guanidine, etc. It can be suitably used for the heat-sensitive recording material of the invention.
Details of these diazo compounds are described in detail, for example, in JP-A-2-136286.

  On the other hand, examples of couplers that undergo a coupling reaction with the above-mentioned diazo compound include those described in JP-A-62-146678, including resorcin, in addition to 2-hydroxy-3-naphthoic acid anilide. It is done.

When using a combination of a diazo compound and a coupler in the thermosensitive recording layer, these coupling reactions can be further promoted by performing them in a basic atmosphere, and as a sensitizer, Basic substances may be added.
Examples of the basic substance include water-insoluble or hardly soluble basic substances and substances that generate alkali by heating, such as inorganic or organic ammonium salts, organic amines, amides, urea, thiourea or derivatives thereof, Nitrogenous compounds such as thiazoles, pyrroles, pyrimidines, piperazines, guanidines, indoles, imidazoles, imidazolines, triazoles, morpholines, piperidines, amidines, forimazines or pyridines .
Specific examples thereof include those described in JP-A No. 61-291183.

(C) Combination of organometallic salt and reducing agent Next, the combination of the organometallic salt and the reducing agent will be described.
Specific examples of the organic metal salts include silver salts of long chain aliphatic carboxylic acids such as silver laurate, silver myristate, silver palmitate, silver stearate, silver arachidate or silver behenate; benzotriazole silver Silver salts of organic compounds having an imino group such as salts, benzimidazole silver salts, carbazole silver salts or phthalazinone silver salts; silver salts of sulfur-containing compounds such as s-alkylthioglycolates; aromas such as silver benzoate and silver phthalate A silver salt of an aromatic carboxylic acid; a silver salt of a sulfonic acid such as silver ethanesulfonate; a silver salt of a sulfinic acid such as silver o-toluenesulfinate; a silver salt of a phosphoric acid such as silver silver phenylphosphate; a silver barbiturate; Examples include silver saccharinate, silver salt of salicyl asdoxime, or any mixture thereof.
Of these, long-chain aliphatic carboxylic acid silver salts are preferable, and silver behenate is more preferable. Further, behenic acid may be used together with silver behenate.

The above reducing agent can be used as appropriate based on the description in JP-A 53-1020, page 227, lower left column, line 14 to page 229, upper right column, line 11. Among them, mono, bis, tris or tetrakisphenols, mono or bisnaphthols, di or polyhydroxynaphthalenes, di or polyhydroxybenzenes, hydroxy monoethers, ascorbic acids, 3-pyrazolidones, pyrazolines, pyrazolones It is preferable to use reducing sugars, phenylenediamines, hydroxylamines, reductones, hydroxamic acids, hydrazides, amide oximes, N-hydroxyureas and the like.
Of the above, aromatic organic reducing agents such as polyphenols, sulfonamidophenols or naphthols are particularly preferred.

<Coating solution for thermal recording layer>
The heat-sensitive recording layer containing the electron-accepting compound in the present invention is prepared by preparing a coating solution for a heat-sensitive recording layer obtained by mixing the microcapsule liquid prepared as described above and an emulsion, and placing the coating solution on a support. It can be formed by coating. Here, the water-soluble polymer used as the protective colloid in the preparation of the microcapsule liquid and the water-soluble polymer used as the protective colloid in the preparation of the emulsion function as a binder in the thermosensitive recording layer. To do. In addition to these protective colloids, a binder may be added and mixed to prepare a thermal recording layer coating solution.

(Surfactant)
The surfactants used for emulsification listed above act to stabilize the emulsion, and the surfactant for emulsification alone does not show a sufficient effect for improving applicability. It is effective to add a compound represented by the following general formula (2) or (3) described later to the coating solution. As described above, at least one selected from the compound represented by the general formula (2) and the compound represented by the general formula (3) is added to the coating solution, and the electron-accepting compound according to the invention is used. The coating property can be improved by incorporating it in the heat-sensitive recording layer.
The compound represented by the general formula (2) may be used alone or in combination of two or more. The content of the compound represented by the general formula (2) in the thermal recording layer coating solution is preferably 0.1 to 5.0% by mass, and more preferably 0.2 to 1.0% by mass. .

  Moreover, the compound represented by the said General formula (3) may be used by 1 type, and may use 2 or more types together. The content of the nonionic surfactant in the coating solution for the thermosensitive recording layer is preferably 0.1 to 5.0% by mass, and more preferably 0.2 to 1.0% by mass.

  When the compound represented by the general formula (2) and the compound represented by the general formula (3) are contained in the thermal recording layer coating solution, the compound represented by the general formula (2) and the general formula The content ratio with the compound represented by (3) is preferably 1: 5 to 5: 1, more preferably 1: 2 to 2: 1.

-Binder-
A water-soluble binder can be used as the binder. Examples of the water-soluble binder include polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, epichlorohydrin-modified polyamide, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, and isobutylene-maleic salicylic acid copolymer. Examples include coalesced polyacrylic acid, polyacrylic amide, methylol-modified polyacrylamide, starch derivatives, casein, and gelatin.
Further, for the purpose of imparting water resistance to these binders, a water-proofing agent may be added, or a hydrophobic polymer emulsion, specifically, a styrene-butadiene rubber latex, an acrylic resin emulsion, or the like may be added.

  When the coating solution for the heat-sensitive recording layer is coated on the support, known coating means used for water-based or organic solvent-based coating solutions can be used. In the thermosensitive recording material of the present invention, the coating solution for the thermosensitive recording layer is applied safely and uniformly, and in order to maintain the strength of the coating film, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, starches, gelatin, polyvinyl alcohol, carboxy Modified polyvinyl alcohol, polyacrylamide, polystyrene or copolymer thereof, polyester or copolymer thereof, polyethylene or copolymer thereof, epoxy resin, acrylate resin or copolymer thereof, methacrylate resin or copolymer thereof, It is preferable to use a polyurethane resin, a polyamide resin, a polyvinyl butyral resin, or the like.

(Other ingredients)
Hereinafter, other components that can be used in the thermosensitive recording layer will be described.
Other components that can be suitable for the heat-sensitive recording layer are not particularly limited and may be appropriately selected depending on the purpose. For example, known heat-fusible substances, ultraviolet absorbers, antioxidants and the like can be mentioned.

The heat-fusible substance can be contained in the heat-sensitive recording layer for the purpose of improving thermal response.
Examples of the thermofusible substance include aromatic ethers, thioethers, esters, aliphatic amides, and ureidos. Examples of these are disclosed in JP-A Nos. 58-57989, 58-87094, 61-58789, 62-109682, 62-132673, 63-151478, and 63-235961. It is described in Japanese Laid-Open Patent Publication Nos. 2-184289 and 2-215585.

  Preferred examples of the UV absorber include benzophenone UV absorbers, benzotriazole UV absorbers, salicylic acid UV absorbers, cyanoacrylate UV absorbers, and oxalic acid anilide UV absorbers. Examples of these are disclosed in JP-A-47-10537, 58-111942, 58-21284, 59-19945, 59-46646, 59-109555, 63-53544, JP-A 36-10466, 42-26187, 48-30492, 48-31255, 48-41572, 48-54965, and 50-10726, U.S. Pat. No. 086, No. 3,707,375, No. 3,754,919, No. 4,220,711, and the like.

  Preferable examples of the antioxidant include hindered amine antioxidants, hindered phenol antioxidants, aniline antioxidants, and quinoline antioxidants. Examples of these are described in JP-A Nos. 59-155090, 60-107383, 60-107384, 61-137770, 61-139481, 61-160287, and the like. Yes.

The coating amount of the other ingredients, preferably about ^{0.05~1.0g / m 2, 0.1~0.4g / m} 2 is more preferable. The other components may be added inside the microcapsule or outside the microcapsule.

Further, the heat-sensitive recording material of the present invention is an image having excellent transparency by constituting the heat-sensitive recording layer so as to lower the haze value calculated from (diffuse transmittance / total light transmittance) × 100 (%). Can be obtained. The haze value is an index representing the transparency of the material, and is generally calculated from the total light transmission amount, diffuse transmission light amount, and parallel transmission light amount using a haze meter.
In the present invention, as a method for reducing the haze value, for example, the 50% volume average particle size of both the coloring components A and B contained in the heat-sensitive recording layer is 1.0 μm or less, preferably 0.6 μm or less. And a method of containing a binder in the range of 30 to 60% by mass of the total solid content of the heat-sensitive recording layer, either one of the coloring components A and B is microencapsulated, and the other is coated and dried to be a substantially continuous layer. For example, the method of using as what is like an emulsion etc. is mentioned. It is also effective to make the refractive index of the component used for the thermosensitive recording layer as close to a constant value as possible.

Furthermore, the heat-sensitive recording layer suppresses density unevenness caused by a slight difference in thermal conduction of the thermal head and the like, and an energy amount width necessary for obtaining a saturated transmission density (Dt-max) in order to obtain a high-quality image. That is, a heat-sensitive recording layer having a wide dynamic range is preferable. The heat-sensitive recording material of the present invention has the heat-sensitive recording layer as described above, and has the characteristic that a transmission density Dt-max = 3.0 can be obtained with a heat energy amount in the range of 90 to 150 mJ / mm ^2. A layer is preferred.

The heat-sensitive recording layer is preferably applied so that the dry application amount after application and drying is 1 to 25 g / m ² , and the thickness of the layer is 1 to 25 μm. . Two or more heat-sensitive recording layers can be laminated and used. In this case, it is preferable that the coating amount of the entire heat-sensitive recording layer and the dry coating amount after drying are 1 to 25 g / m ² .

<Protective layer>
In the heat-sensitive recording material of the present invention, at least one protective layer can be provided on the heat-sensitive recording layer. An intermediate layer may be provided between the thermosensitive recording layer and the protective layer.

(Surfactant)
The protective layer contains the surfactant (the compound represented by the general formula (2) and the compound represented by the general formula (3)) in the present invention.

-Compound represented by general formula (2) (anionic surfactant)-
R ³ —SO ₃ M General formula (2)

  The compound represented by the general formula (2) is an anionic surfactant and is used together with the compound represented by the general formula (3) which is a nonionic surfactant described later. The effect can be demonstrated.

In General Formula (2), R ³ represents an alkyl group having 4 to 20 carbon atoms, an alkylaryl group having 6 to 20 carbon atoms, or an alkylphenoxy group having 6 to 20 carbon atoms. M represents an anion. R ³ may further have a substituent.

The alkyl group having 4 to 20 carbon atoms represented by R ³ is more preferably an alkyl group having 8 to 16 carbon atoms. Specific examples of the alkyl group having 4 to 20 carbon atoms include octyl group, decyl group, dodecyl group, myristyl group, cetyl group, 2-ethylhexyl group, and the like.

As a C6-C20 alkylaryl group represented by said R < ³ >, a C14-C18 alkylaryl group is still more preferable. Specific examples of the alkylaryl group having 6 to 20 carbon atoms include octylphenyl group, decylphenyl group, dodecylphenyl group, and the like.

The alkylphenoxy group having 6 to 20 carbon atoms represented by R ³ is more preferably an alkylphenoxy group having 14 to 18 carbon atoms. Specific examples of the alkylphenoxy group having 6 to 20 carbon atoms include octylphenoxy group, decylphenoxy group, dodecylphenoxy group, and the like.

  Examples of the anion represented by M include alkali metal salts such as Na and K, triethanolamine salts, ammonium salts and the like.

  As the compound represented by the general formula (2), anionic surfactants such as alkylbenzene sulfonate, alkyl sulfate, alkyl sulfosuccinate, alkyl carboxylate, polyoxyethylene alkyl sulfate, and the like are preferable.

  In particular, the compound represented by the general formula (2) is preferably an alkylbenzene sulfonate. The alkylbenzene sulfonate is more preferably at least one selected from the group consisting of alkali metal alkylbenzene sulfonates, triethanolamine salts, and ammonium salts. Further, the alkyl group of the alkylbenzene sulfonate may be any of a linear, branched and cyclic alkyl group, but is preferably a linear alkyl group having 8 to 8 carbon atoms. More preferably, it is about 20 linear alkyl groups.

  Specific examples of the compound represented by the general formula (2) include, for example, sodium n-dodecylbenzenesulfonate, ammonium n-dodecylbenzenesulfonate, triethanolamine n-dodecylbenzenesulfonate, and n-decylbenzenesulfone. Acid sodium, sodium n-undecylbenzenesulfonate, sodium pentadecylbenzenesulfonate, potassium dodecylbenzenesulfonate, sodium 2-ethylhexylsulfonate, sodium decylsulfonate, sodium dodecylsulfonate, sodium octylsulfonate, lauryl sulfone Preferable examples include potassium acid, dodecyl benzene ether sulfonate, and octyl benzene ether sulfonate.

  Moreover, a commercial item can also be applied as a compound represented by the said General formula (2). In this case, for example, Neoperex G-15 (manufactured by Kao Corporation), Neogen T (manufactured by Daiichi Kogyo Co., Ltd.), Teica Power BN2060, Teica Power LN2050 (manufactured by Teika Corporation), Pionein A41C (Takemoto Yushi) Etc.) are preferably used.

The content of the compound represented by the general formula (2) in the protective layer is preferably from 0.01 to 1.0 g / m ^2, 0.02 to 0.5 g / m ² is more preferable.

-Compound represented by general formula (3) (nonionic surfactant)-
R ⁴ —O— (CH ₂ CH ₂ O) _n —H Formula (3)

  The compound represented by the general formula (3) is a nonionic surfactant and exhibits the effects of the present invention when used together with the above-described anionic surfactant (compound represented by the general formula (2)). can do.

In the general formula (3), R ⁴ represents an alkyl group having 4 to 20 carbon atoms or an alkylaryl group having 6 to 20 carbon atoms. n represents an integer of 1 to 50.

The alkyl group having 4 to 20 carbon atoms represented by R ^4, and more preferably an alkyl group having 8 to 16 carbon atoms. Specific examples of the alkyl group having 4 to 20 carbon atoms include octyl group, decyl group, dodecyl group, myristyl group, cetyl group, and 2-ethylhexyl group.

The alkylaryl group having 6 to 20 carbon atoms represented by R ⁴ is more preferably an alkylaryl group having 14 to 18 carbon atoms. Specific examples of the alkylaryl group having 6 to 20 carbon atoms include octylphenyl group, decylphenyl group, dodecylphenyl group, and the like.

  N represents an integer of 1 to 50, and more preferably 6 to 20.

  Specific examples of the nonionic surfactant applied to the present invention include, for example, polyoxyethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene dodecyl ether, polyoxyethylene (2-ethylhexyl) ether, polyoxyethylene Preferred examples include dodecyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, and the like.

  Moreover, a commercial item can also be applied as a nonionic surfactant. For example, Emulgen 109P (manufactured by Kao Corporation), Emulgen 903P (manufactured by Kao Corporation), Neugen EA-160 (manufactured by Daiichi Kogyo Co., Ltd.), Surfynol 104E (manufactured by Nissin Chemical Industry Co., Ltd.), Sintol PS (manufactured by Takamatsu Yushi Co., Ltd.), Emarex NP-10 (manufactured by Nippon Emulsion Co., Ltd.), and the like are preferably used.

  Moreover, in this invention, the compound represented with General formula (3) and other well-known nonionic surfactant can also be used together. Examples of the other known nonionic surfactants include nonionic surfactants such as sorbitan esters, glycerides, polyglycerin alkyl fatty acid esters, sucrose fatty acid esters, alkyl glyceryl ethers, alkyl polyglucosides, and lecithins. Can be mentioned.

The content of the compound represented by the general formula (3) in the protective layer is preferably from ^{0.01~1.0g / m 2, 0.02~0.5g / m} 2 is more preferable.

  The content ratio of the nonionic surfactant to the anionic surfactant in the protective layer is preferably 1: 5 to 5: 1, more preferably 1: 2 to 2: 1.

(Other ingredients)
Other components contained in the protective layer will be described.
The protective layer usually contains a binder, a pigment, a lubricant, a dispersant, a fluorescent brightening agent, a metal soap, a hardener, an ultraviolet absorber, a crosslinking agent, and the like.

-Binder-
The binder that can be used for the protective layer is preferably a water-soluble resin, and can be appropriately selected from known water-soluble resins. Examples of the water-soluble resin include polyvinyl alcohol, silicon-modified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, starch and derivatives thereof, casein, sodium alginate, polyvinyl pyrrolidone, sodium polyacrylate, polyacrylamide, and styrene maleic acid polymer. Examples include salts, polyurethane resins, urea resins, melamine resins, and the like.

-Pigment-
The above pigment is usually added for the purpose of suppressing the occurrence of sticking or abnormal noise during recording with a thermal head, and organic and / or inorganic pigments are used.
Although there is no particular limitation on the type of the pigment, publicly known organic and inorganic pigments can be mentioned, but in particular inorganic pigments such as calcium carbonate, titanium oxide, kaolin, aluminum hydroxide, amorphous silica, zinc oxide, Organic pigments such as urea formalin resin and epoxy resin are preferred. Of these, kaolin, aluminum hydroxide, and amorphous silica are more preferable. These pigments may be used alone or in combination of two or more. Of these, the surface may be coated with at least one or more selected from the group consisting of higher fatty acids, metal salts of higher fatty acids, and higher alcohols. Examples of the higher fatty acid include stearic acid, palmitic acid, myristic acid, lauric acid and the like.
These pigments include, for example, sodium hexametaphosphate, partially saponified or fully saponified polyvinyl alcohol, polyacrylic acid copolymer, various surfactants and other dispersing aids, preferably partially saponified or fully saponified polyvinyl alcohol, polyacrylic. In the presence of an acid copolymer ammonium salt, it is preferably used after being dispersed to the above-mentioned average particle size by a known disperser such as a dissolver, a sand mill, or a ball mill. That is, the pigment is preferably used after being dispersed until the 50% volume average particle size is in the range of 0.1 to 5.0 μm.

  The average particle diameter of the pigment, specifically, 50% volume average particle diameter measured by a laser diffraction method (corresponding to 50% volume in the pigment measured by a laser diffraction particle size distribution measuring device (trade name: LA700, manufactured by Horiba Seisakusho). The average particle diameter of the pigment particles (hereinafter sometimes simply referred to as “average particle diameter”) is preferably 0.10 to 5 μm, particularly between the thermal head and the thermal recording material when recording with a thermal head. From the viewpoint of preventing the occurrence of sticking, abnormal noise, and the like, and from the viewpoint of transparency, the 50% volume average particle diameter is more preferably in the range of 0.20 to 0.50 μm. When the 50% volume average particle size is in the range of 0.10 to 5.0 μm, the effect of reducing friction with respect to the thermal head is great, and as a result, the thermal head and the protective layer of the thermal recording material adhere to each other at the time of printing. Sticking can be effectively prevented.

-Lubricant-
Moreover, it is preferable to add a lubricant to the protective layer. Examples of the lubricant include stearamide (melting point: 100 ° C.), methylol stearamide (melting point: 101 ° C.), polyethylene wax (melting point: 110 ° C. or lower), paraffin wax having a melting point of 50 to 90 ° C., glycerin-12-hydroxy. Stearate (melting point 88 ° C), oleic acid amide (melting point 73 ° C), zinc oleate (melting point 75 ° C), lauric acid amide (melting point 84 ° C), aluminum stearate (melting point 102 ° C), manganese stearate (melting point 112) ° C), zinc stearate (melting point 125 ° C), calcium stearate (melting point 160 ° C), ethylene bisstearamide (melting point 140 ° C), magnesium stearate (melting point 132 ° C), magnesium palmitate (melting point 122 ° C), myristic Magnesium oxide (melting point 131 ° C), etc. It can gel. The above lubricants may be used alone or in combination of two or more.

When the lubricant is insoluble in water, it is added to the protective layer in the form of a dispersion or an emulsion. When the lubricant is solid, 1) In the form of an aqueous dispersion dispersed with a known disperser such as a homogenizer, dissolver, sand mill in the presence of a water-soluble polymer such as polyvinyl alcohol or a dispersant such as various surfactants. 2) Used in the form of an emulsion emulsified with a known emulsifier such as a homogenizer, dissolver or colloid mill in the presence of a dispersant such as a water-soluble polymer or various surfactants after being dissolved in a solvent. It is done. When the lubricant is a liquid, it is used in the form of an emulsion as described above. A preferable average particle size of the dispersion and the emulsion is 0.1 to 5.0 μm, and more preferably 0.1 to 2.0 μm. The average particle diameter here refers to a 50% average particle diameter measured at a transmittance of 71 ± 1% with a laser diffraction particle size distribution analyzer (trade name: LA-700, Horiba Seisakusho).
In the case of water-soluble lubricants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl ether acetate, polyoxyethylene alkyl ether sulfate, polyoxyethylene alkyl ether phosphate, etc. , Can be dissolved in any concentration and added to the protective layer.

  The protective layer may contain a known hardener or the like. Examples of the hardener include dialdehyde derivatives represented by the following structural formula (001) in addition to inorganic compounds such as boric acid, borax, and colloidal silica.

Moreover, the said protective layer may contain other surfactant other than the surfactant in this invention explained in full detail in the range which does not impair the effect of this invention.
Furthermore, metal oxide fine particles, inorganic electrolytes, polymer electrolytes, and the like may be added to the protective layer for the purpose of preventing charging of the thermosensitive recording material.

The protective layer may have a single layer structure or a laminated structure of two or more layers. The dry coating amount of the protective layer is preferably ^{0.2~7g / m 2, 1~4g / m} 2 is more preferable.

<Support>
In the present invention, both a transparent support and an opaque support such as paper can be used depending on the purpose or application. In the present invention, it is preferable to use a transparent support.
Examples of the transparent support include polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, cellulose triacetate films, and synthetic polymer films such as polyolefin films such as polypropylene and polyethylene. Can be used together.

  When the heat-sensitive recording material of the present invention is used for medical purposes, the transparent support may be colored with a blue dye (for example, dye-1 described in Examples of JP-A-8-240877) or uncolored. Good. The support is preferably subjected to an undercoat such as gelatin or water-soluble polyester. Regarding the undercoat layer, for example, those described in JP-A Nos. 51-11420, 51-123139 and 52-65422 can be used. The thickness of the support is preferably 25 to 250 μm, more preferably 50 to 210 μm.

  The synthetic polymer film may be colored in an arbitrary hue. As a method of coloring a polymer film, a method of forming a film by kneading a dye into a resin before forming a resin film, preparing a coating solution in which a dye is dissolved in an appropriate solvent, and preparing this as a colorless transparent resin Examples of the coating method include a known coating method on the film, for example, a gravure coating method, a roller coating method, a wire coating method, and the like. Among them, a polyester resin such as polyethylene terephthalate or polyethylene naphthalate kneaded with a blue dye is preferably formed into a film and subjected to heat treatment, stretching treatment, and antistatic treatment.

  In particular, when the heat-sensitive recording material of the present invention is observed from the support side on a shears ten, the image may be difficult to see due to illusion due to the shears ten light passing through the transparent non-image portion. Therefore, from the viewpoint of avoiding this, A (x = 0.2805, y = 0.3005), B (x = 0.2820, y) on the chromaticity coordinates defined by the method described in JIS-Z8701. = 0.2970), C (x = 0.2885, y = 0.015), and D (x = 0.2870, y = 0.04040) are colored blue in a rectangular region formed by four points. It is particularly preferable to use a synthetic polymer film.

<Other layers>
In the heat-sensitive recording material of the present invention, an intermediate layer, an undercoat layer, an ultraviolet filter layer, a back layer and the like can be provided as other layers on the support.

(Middle layer)
The intermediate layer is a layer provided for preventing gas mixing (oxygen or the like) harmful to layer mixing prevention and image storage stability. The intermediate layer is preferably formed on the thermosensitive recording layer.

In the present invention, it is a more preferable embodiment that the surfactant in the present invention is contained in the intermediate layer in addition to the protective layer and the heat-sensitive recording material described above. By including the surfactant of the present invention in the intermediate layer, the excellent effects of the present invention such as uniform coating surface and chemical resistance can be further exhibited.
As a total content in case the surfactant in this invention contains in the said intermediate | middle layer, 0.001-0.5 g / m < ² > is preferable and 0.01-0.1 g / m < ² > is more preferable. .

  The binder used for the intermediate layer is not particularly limited, and polyvinyl alcohol, gelatin, polyvinyl pyrrolidone, cellulose derivatives, and the like can be used depending on the system. Among them, gelatin has fluidity at high temperatures, but has a property (set property) that loses fluidity and gels at low temperatures (for example, 35 ° C. or lower), so that a plurality of layers are formed on a support. When the above-mentioned layer is provided by applying and drying a coating solution for forming, the two adjacent layers may be applied by a method in which a plurality of layers are sequentially applied and dried, or in a method in which multiple layers are applied and dried at once by an extrusion die method or the like. It is effectively prevented that the layers mix with each other. Therefore, the surface shape of the obtained heat-sensitive recording material is improved, and a heat-sensitive recording material capable of forming a high-quality image can be obtained, and particularly suitable for medical diagnosis in which a clear image must be formed in detail. It is. Furthermore, even if it is dried at a high wind speed, the surface condition does not deteriorate, so that the production efficiency is improved.

As such gelatin, unmodified (untreated) gelatin or modified (treated) gelatin can be used without any problem. Examples of modified gelatin include lime-processed gelatin, acid-processed gelatin, phthalated-processed gelatin, deionized-processed gelatin, and enzyme-processed low-molecular-weight gelatin. Further, various surfactants may be added for imparting coatability. In order to further improve the gas barrier properties, inorganic fine particles such as mica may be added to the binder in an amount of 2 to 20% by mass, more preferably 5 to 10% by mass. The binder concentration of the intermediate layer coating solution is 3 to 25% by mass, preferably about 5 to 15% by mass. The dry coating amount of the intermediate layer is 0.5 to 6 g / m ² , preferably 1 to 4 g / m ² .

(Undercoat layer)
In the heat-sensitive recording material of the present invention, for the purpose of preventing the heat-sensitive recording layer from peeling off from the support, an undercoat layer is formed on the support before applying a heat-sensitive recording layer containing microcapsules or the like and an antireflection layer. Can be provided. As the undercoat layer, an acrylate copolymer, polyvinylidene chloride, SBR, aqueous polyester or the like can be used, and the thickness of the layer is preferably 0.05 to 0.5 μm.
When a heat-sensitive recording layer is applied on the undercoat layer, the image recorded on the heat-sensitive recording layer may deteriorate due to the undercoat layer being swollen by water contained in the heat-sensitive recording layer coating solution. Is preferably hardened using a dialdehyde such as glutaraldehyde, 2,3-dihydroxy-1,4-dioxane, and a hardener such as boric acid. The amount of these hardeners can be appropriately added in accordance with the desired degree of curing in the range of 0.2 to 3.0% by mass depending on the mass of the undercoat material.
With respect to the undercoat layer, for example, those described in JP-A Nos. 51-11420, 51-123139, and 52-65422 can be used.

(UV filter layer)
In the heat-sensitive recording material of the present invention, an ultraviolet filter layer may be provided to prevent discoloration of the image and background fogging. The ultraviolet filter layer is obtained by uniformly dispersing an ultraviolet absorber in a binder, and the uniformly dispersed ultraviolet absorber effectively absorbs ultraviolet light, whereby the background is discolored by ultraviolet light, Prevents the image portion from being discolored or fading. As the method for preparing the ultraviolet filter layer and the compound to be used, those described in JP-A-4-197778 can be used in addition to ultraviolet absorbers such as benzotriazole, benzophenone, and hindered amine.

(Back layer)
The heat-sensitive recording material in the present invention is preferably a single-sided light-sensitive material having a heat-sensitive recording layer containing microcapsules on one side of the support and a back layer on the other side. A matting agent is preferably added to the back layer for the purpose of imparting transportability and preventing light reflection. By adding a matting agent, the glossiness measured at an incident light angle of 20 ° is preferably 50% or less, and more preferably 30% or less.
Examples of the matting agent include fine particles such as starch obtained from barley, wheat, corn, rice, beans, etc., cellulose fiber, polystyrene resin, epoxy resin, polyurethane resin, urea formalin resin, poly (meth) acrylate resin, polymethyl (Meth) acrylate resin, copolymer resin such as vinyl chloride or vinyl acetate, fine particles of synthetic polymer such as polyolefin, calcium carbonate, titanium oxide, kaolin, smectite viscosity, inorganic substances such as aluminum hydroxide, silica, zinc oxide Examples thereof include fine particles. The average particle size of the matting agent is 0.5 to 20 μm, preferably 0.5 to 10 μm. The mat materials may be used alone or in combination of two or more.
Further, from the viewpoint of improving the transparency of the heat-sensitive recording material, the refractive index is preferably in the range of 1.4 to 1.8. Various dyes (for example, CI Pigment Blue 60, CI Pigment Blue 64, CI Pigment Blue 15: 6) can be used for the back layer from the viewpoint of improving the hue. A hardener may be used for the back layer. Examples of the hardener include T.W. H. There are various methods described in “THE THEORY OF THE PHOTOGRAPHIC PROCESS 4th EDITION” by James (pages 77 to 87), and vinyl sulfone compounds are preferred.

<Production of thermal recording material>
Hereinafter, the method for producing the heat-sensitive recording material of the present invention will be described.
Each layer constituting the heat-sensitive recording material of the present invention is prepared by adjusting a coating solution for forming a plurality of layers including the above-described heat-sensitive recording layer, intermediate layer, protective layer, etc., and applying the coating solution on a support. It can be formed by applying multiple layers sequentially or simultaneously and drying.
The heat-sensitive recording material of the present invention provides a coated surface with excellent uniformity even when each layer is formed by multi-layer coating, and thus has excellent characteristics such as chemical resistance and high-quality image formability. Can be demonstrated. Therefore, multilayer coating can be suitably used in the method for producing the heat-sensitive recording material of the present invention.

  In the method for producing a heat-sensitive recording material of the present invention, a blade coating method, an air knife coating method, a gravure coating method, a roll are used to sequentially form an undercoat layer, a heat-sensitive recording layer, an intermediate layer, a protective layer, etc. on a support. Known coating methods such as a coating coating method, a spray coating method, a dip coating method, and a bar coating method are used. An example of a method for applying a plurality of layers simultaneously is an extrusion die method.

  Specific coating methods include various coating methods including extrusion coating, slide coating, curtain coating, knife coating, dip coating, flow coating or extrusion coating using a hopper of the type described in US Pat. No. 2,681,294. It is done. Among them, Stephen F.M. Kistler, Peter M. et al. The extrusion coating or slide coating described in “LIQUID FILM COATING” (CHAPMAN & HALL 1997, pages 399 to 536) by Schwaizer is preferably used, and slide coating is particularly preferably used.

An example of the shape of a slide coater used for slide coating is shown in “Fogure 11b. 1. If desired, a coating solution for a thermosensitive recording layer can be formed on the support using the method described on pages 399 to 536 of the same document, the method described in US Pat. No. 2,7617,91 and British Patent No. 837095. The above-mentioned heat-sensitive recording layer, protective layer, and other layers (intermediate layer, etc.) can be simultaneously formed by simultaneously applying the coating liquids.
Drying is performed with dry air having a dry bulb temperature of 20 to 65 ° C, preferably 25 to 55 ° C, and a wet bulb temperature of 10 to 30 ° C, preferably 15 to 25 ° C.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, “part” means “part by mass”, “%” means “mass%”, and “molecular weight” means “weight average molecular weight” unless otherwise specified.

[Example 1]
<Preparation of electron-donating dye precursor-encapsulated microcapsule solution>
14 g of 2-anilino-3-methyl-6-N-ethyl-N-sec-butylaminofluorane as an electron-donating dye precursor, 0.6 g of Tinuvin P (manufactured by Ciba-Gaigi) as an ultraviolet absorber, and a capsule wall agent 10 g of Takenate D-110N (manufactured by Takeda Pharmaceutical Co., Ltd.) and 10 g of Sumidur N3200 (manufactured by Sumitomo Chemical Co., Ltd.) were dissolved in 20 g of ethyl acetate. This solution was mixed with 112 g of a 5% aqueous solution of polyvinyl alcohol (trade name: PVA217C, manufactured by Kuraray Co., Ltd.) and emulsified at 8000 rpm for 5 minutes using an ace homogenizer (manufactured by Nippon Seiki Co., Ltd.). 142 g of water was further added and reacted at 55 ° C. for 3 hours to prepare a microcapsule solution containing an electron donating dye precursor having a capsule size of 0.7 μm.

<Preparation of electron-accepting compound emulsion A>
18 g of an electron-accepting compound (a) represented by the following structural formula (Exemplary compound 1 of the above general formula (1)), 18 g of an electron-accepting compound (b), 1.7 and g of tricresyl phosphate, malein 0.8 g of diethyl acid was dissolved in 38 g of ethyl acetate. The obtained electron-accepting compound solution was mixed with an aqueous solution containing 100 g of 8% polyvinyl alcohol (trade name: PVA205C: manufactured by Kuraray Co., Ltd.), 150 g of water, and 0.5 g of sodium dodecylbenzenesulfonate. Then, using an ace homogenizer (manufactured by Nippon Seiki Co., Ltd.), the mixture was emulsified at 10,000 rpm for 5 minutes to obtain an electron-accepting compound emulsion A having an average particle size of 1.0 μm.

<Preparation of thermal recording material>
(Formation of thermal recording layer)
5.0 g of the electron-donating dye precursor-encapsulated microcapsule solution, 10.0 g of the electron-accepting compound emulsion A, 5.0 g of water, 2% sodium n-dodecylbenzenesulfonate (represented by the general formula (2)) Compound, trade name: Neoperex G-15, manufactured by Kao Corporation 0.05 g, 2% polyethylene glycol dodecyl ether (compound represented by general formula (3), trade name: Emulgen 109P, Kao Corporation) 0.05 g) was stirred and mixed to prepare a thermal recording layer coating solution. Next, the thermosensitive recording layer coating solution is applied to one side of a 75 μm thick transparent polyethylene terephthalate support so that the solid content is 10 g / m ² and dried to form a thermosensitive recording layer on the support. did.

(Formation of protective layer)
-Preparation of coating solution for protective layer-
6 g of water, 10% polyvinyl alcohol (trade name: PVA-205, manufactured by Kuraray Co., Ltd.) 5 g, 2% sodium dodecylbenzenesulfonate (trade name: Neoperex G-15, manufactured by Kao Co., Ltd.) 2 g, pigment (Product name: Kao Gloss, manufactured by Shiroishi Kogyo Co., Ltd.) 15 g was added and dispersed until the average particle size became 0.8 μm to obtain a pigment dispersion. Subsequently, the following composition (solid content composition) was mixed, and the coating liquid for protective layers was obtained.

〔composition〕
・ 7 parts of polyvinyl alcohol (trade name: R2105, manufactured by Kuraray Co., Ltd.)
・ 7 parts of colloidal silica (Product name: Snowtex o, manufactured by Nissan Chemical Co., Ltd.)
-12 parts of the above pigment dispersion-0.2 parts of zinc stearate emulsion (trade name: Hymicron F115, manufactured by Kao Corporation)
-Sodium n-dodecylbenzenesulfonate 0.025 part (compound represented by the general formula (2), trade name: Neoperex G15, manufactured by Kao Corporation)
Polyoxyethylene dodecyl ether 0.025 parts (compound represented by general formula (3), trade name: Emulgen 109P, manufactured by Kao Corporation)

-Formation of protective layer-
The obtained coating liquid for protective layer was applied and dried on the heat-sensitive recording layer so that the mass after drying was 2.5 g / m ² , thereby producing the heat-sensitive recording material of the present invention.

[Example 2]
<Preparation of electron-accepting compound emulsion B>
7 g of the following electron-accepting compound (c) (exemplary compound 2 of the general formula (1)), 7 g of the electron-accepting compound (b), and 16 g of the electron-accepting compound (d) represented by the following structural formula Then, 11 g of the electron-accepting compound (e), 1.7 g of tricresyl phosphate, and 0.8 g of diethyl maleate were dissolved in 38 g of ethyl acetate. The obtained electron-accepting compound solution was mixed with an aqueous solution containing 100 g of 8% polyvinyl alcohol (trade name: PVA205C: manufactured by Kuraray Co., Ltd.), 150 g of water, and 0.5 g of sodium dodecylbenzenesulfonate. Then, using an ace homogenizer (manufactured by Nippon Seiki Co., Ltd.), the mixture was emulsified at 10,000 rpm for 5 minutes to obtain an electron-accepting compound emulsion B having an average particle size of 1.0 μm.

<Preparation of thermal recording material>
(Formation of thermal recording layer)
The electron-donating dye precursor-encapsulated microcapsule solution 5.0 g obtained in Example 1 and 10.0 g of the electron-accepting compound emulsion B were stirred and mixed to prepare a thermal recording layer coating solution. Next, the thermosensitive recording layer coating solution is applied to one side of a 75 μm thick transparent polyethylene terephthalate support so that the solid content is 10 g / m ² and dried to form a thermosensitive recording layer on the support. did.

(Formation of protective layer)
-Preparation of pigment dispersion-
Water 60 g, 10% polyvinyl alcohol (trade name: PVA205, manufactured by Kuraray Co., Ltd.) 5 g, 2% sodium dodecylbenzenesulfonate (trade name: Neoperex G-15, manufactured by Kao Corp.) 2 g, stearin 15 g of acid-treated aluminum hydroxide (trade name: Heidilite H42S, manufactured by Showa Denko KK) was added and dispersed so that the average particle size became 0.7 μm to obtain a pigment dispersion.

-Formation of protective layer-
A coating solution for the protective layer was prepared so as to have the following composition in solid content. The obtained coating liquid for protective layer was applied on the heat-sensitive recording layer so as to have a solid content of 2.5 g / m ² to form a protective layer, thereby producing the heat-sensitive recording material of the present invention.

[Composition of coating solution for protective layer]
・ 7 parts of polyvinyl alcohol (trade name: PVA124, manufactured by Kuraray Co., Ltd.)
-12 parts of the above pigment dispersion-0.9 part of an emulsion of paraffin wax (trade name: Cellosol 428, manufactured by Chukyo Yushi Co., Ltd.)
・ Zinc stearate emulsion 0.2 parts (trade name: Hi-micron F115, manufactured by Chukyo Yushi Co., Ltd.)
・ 0.05 parts of polyoxyethylene alkyl ether phosphate (trade name: Neoscore CM57, manufactured by Toho Chemical Co., Ltd.)
-Sodium n-dodecylbenzenesulfonate 0.05 parts (Compound represented by the general formula (2), trade name: Neoperex G-15, manufactured by Kao Corporation)
・ 0.05 parts of polyoxyethylene dodecyl ether (compound represented by general formula (3), trade name: Emulgen 109P, manufactured by Kao Corporation)

[Example 3]
In Example 1, instead of the protective layer coating solution prepared in Example 1, the protective layer coating solution prepared in Example 2 was applied so that the solid content was 2.5 g / m ^2. A heat-sensitive recording material of the present invention was produced in the same manner as in Example 1 except that was formed.

[Example 4]
In Example 1, the electron-accepting compound (a) used for the preparation of the electron-accepting compound emulsion was changed to the following electron-accepting compound (f) (exemplary compound 9 of the above general formula (1)), N-dodecylbenzenesulfonic acid triethanolamine salt (trade name: Neogen T, Daiichi Kogyo Co., Ltd.) was used for the preparation of the thermal recording layer coating solution and the protective layer coating solution. In the same manner as in Example 1 except that the polyoxyethylene dodecyl ether is changed to polyoxyethylene decyl ether (trade name: Nonion HS210, manufactured by NOF Corporation). A recording material was prepared.

[Example 5]
In Example 2, the sodium n-dodecylbenzenesulfonate used in “-Formation of the protective layer” was replaced with n-dodecylbenzenesulfonate triethanolamine salt (trade name: Neogen T, manufactured by Daiichi Kogyo Co., Ltd.). In addition, the heat-sensitive recording of the present invention was carried out in the same manner as in Example 2 except that polyoxyethylene dodecyl ether was changed to polyoxyethylene alkylphenyl ether (trade name: Neugen EA-160, manufactured by Daiichi Kogyo Co., Ltd.). The material was made.

[Example 6]
In Example 2, the sodium n-dodecylbenzenesulfonate used in “-Formation of the protective layer” was converted to ammonium n-dodecylbenzenesulfonate, and the polyoxyethylene dodecyl ether was converted to polyoxyethylene alkylphenyl ether ( A heat-sensitive recording material of the present invention was produced in the same manner as in Example 2 except that the product name was changed to “Emulgen 903, manufactured by Kao Corporation”.

[Example 7]
In Example 2, except that polyoxyethylene dodecyl ether used in “-Formation of protective layer” was changed to polyoxyethylene tridecyl ether (trade name: Neugen TDS-50, manufactured by Daiichi Kogyo Co., Ltd.). Produced a heat-sensitive recording material of the present invention in the same manner as in Example 2.

[Comparative Example 1]
In Example 1, except that the electron-accepting compound (a) used for the preparation of the coating solution for the heat-sensitive recording layer was changed to the electron-accepting compound (d), the same heat-sensitive recording for comparison as in Example 1. The material was made.

[Comparative Example 2]
In Example 1, instead of sodium n-dodecylbenzenesulfonate and polyoxyethylene dodecyl ether used in the preparation of the coating solution for the protective layer, sulfosuccinic acid 2-ethylhexyl ester sodium salt (trade name: Rapisol B-90, Japan) A comparative heat-sensitive recording material was produced in the same manner as in Example 1 except that the amount was changed to 0.05 part (Oil & Fats Co., Ltd.).

[Comparative Example 3]
Example 2 except that the amount of polyoxyethylene dodecyl ether added was changed to 0.05 parts without using sodium n-dodecylbenzenesulfonate used in “-Formation of protective layer” in Example 2. In the same manner, a heat-sensitive recording material for comparison was produced.

[Comparative Example 4]
Example 2 except that the amount of sodium n-dodecylbenzenesulfonate was changed to 0.05 parts without using the polyoxyethylene dodecyl ether used in “-Formation of protective layer” in Example 2. In the same manner, a heat-sensitive recording material for comparison was produced.

[Comparative Example 5]
Instead of sodium n-dodecylbenzenesulfonate and polyoxyethylene dodecyl ether used in “-Formation of protective layer” in Example 2, polyoxyethylene alkyl ether phosphate ester (trade name: Neoscore CM57, Toho A comparative heat-sensitive recording material was produced in the same manner as in Example 2 except that the amount was changed to 0.05 part (made by Chemical Co., Ltd.).

[Comparative Example 6]
Instead of sodium n-dodecylbenzenesulfonate and polyoxyethylene dodecyl ether used in “-Formation of protective layer” in Example 2, sodium butylnaphthalenesulfonate (trade name: Perex NB-L, Kao) A comparative heat-sensitive recording material was prepared in the same manner as in Example 2 except that the amount was changed to 0.05 part.

[Comparative Example 7]
Instead of sodium n-dodecylbenzenesulfonate and polyoxyethylene dodecyl ether used in “-Formation of protective layer” in Example 2, perfluoroalkylbetaine (trade name: Surflon S131, manufactured by Asahi Glass Co., Ltd.) A comparative heat-sensitive recording material was produced in the same manner as in Example 2 except that the amount was changed to 0.05 part.

<Evaluation>
Each thermosensitive recording material produced as described above was printed with a thermal imager FTI1000 (manufactured by Fuji Photo Film Co., Ltd.), and evaluated for haze value, image quality, and chemical resistance. Evaluation methods and evaluation criteria are as follows. The results are shown in Table 3.

<Haze value>
In each example and comparative example, when the heat-sensitive recording layer was applied, the haze value of the heat-sensitive recording layer was measured with a haze meter (manufactured by Suga Test Instruments Co., Ltd.).

<Evaluation of image quality>
Each sample after printing was visually observed, and the image quality was evaluated according to the following criteria.
[Standard]
A: Density unevenness was not observed at all.
A: Density unevenness was hardly observed.
Δ: Some density unevenness was observed.
X: Image missing due to repelling.

<Evaluation of chemical resistance>
After applying ethanol to the sample surface with a cotton swab soaked with ethanol, the discoloration of the background portion was visually observed and evaluated for chemical resistance according to the following criteria.
A: The background was not discolored and beautiful.
○: Almost no discoloration in the background.
Δ: Moyamura was observed on the background.
X: The fog had generate | occur | produced in the ground part.

As can be seen from Table 3, the heat-sensitive recording material of the present invention has a low haze value of the heat-sensitive recording layer, excellent transparency, excellent image quality in an actual machine, and excellent chemical resistance without causing discoloration by chemicals or the like. .
In contrast, the heat-sensitive recording material of Comparative Example 1 that did not use the electron-accepting compound in the present invention had a high haze value and was inferior in image quality and chemical resistance. In addition, although the heat-sensitive recording materials of Comparative Examples 2 to 7 that did not use the surfactant in the present invention had a low haze value, they could not achieve both image quality and chemical resistance.

Claims (7)

A heat-sensitive recording layer comprising an electron-donating dye precursor and an electron-accepting compound for coloring the electron-donating dye precursor on a support, and at least one protective layer provided on the heat-sensitive recording layer A thermal recording material having
The electron accepting compound is a compound represented by the following general formula (1):
The protective layer contains a compound represented by the following general formula (2) and a compound represented by the general formula (3).

(In General Formula (1), R ¹ and R ² each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.)
R ³ —SO ₃ M General formula (2)
(In General Formula (2), R ³ represents an alkyl group having 4 to 20 carbon atoms, an alkylaryl group having 6 to 20 carbon atoms, or an alkylphenoxy group having 6 to 20 carbon atoms. M represents an anion. .)
R ⁴ —O— (CH ₂ CH ₂ O) _n —H Formula (3)
(In General Formula (3), R ⁴ represents an alkyl group having 4 to 20 carbon atoms or an alkylaryl group having 6 to 20 carbon atoms. N represents an integer of 1 to 50.)   The heat-sensitive recording layer further comprises at least one selected from the compound represented by the general formula (2) and the compound represented by the general formula (3). The heat-sensitive recording material described.   The heat-sensitive recording material according to claim 1 or 2, wherein the compound represented by the general formula (2) is an alkylbenzene sulfonate.   The compound represented by the general formula (2) is at least one selected from an alkali metal salt of alkylbenzenesulfonic acid, a triethanolamine salt of alkylbenzenesulfonic acid, and an ammonium salt of alkylbenzenesulfonic acid. The heat-sensitive recording material according to claim 1 or 2.   The heat-sensitive recording material according to claim 3 or 4, wherein the alkyl group of the alkylbenzenesulfonic acid is a linear alkyl group.   6. The heat sensitive recording material according to claim 1, wherein the electron donating dye precursor is encapsulated in a microcapsule.   The thermosensitive recording layer includes a coating liquid containing an emulsion obtained by dissolving and emulsifying a microcapsule encapsulating the electron-donating dye precursor and the electron-accepting compound in an organic solvent hardly soluble or insoluble in water. The heat-sensitive recording material according to claim 1, wherein the heat-sensitive recording material is formed by coating on a body.