JP2006192662A - Thermal recording material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording material which has a desirable image hue after printing and can inhibit a hue change with time effectively. <P>SOLUTION: This thermal recording material has a thermal recording layer containing a microcapsule encapsulating a colorless or pale-color electron-donative dye precursor and an electron-receptive compound, formed on a support. The electron-donative dye precursor contains at least a chemical compound represented by formula (I) and a chemical compound represented by formula (II). In these formulae (I) and (II), R<SP>1</SP>, R<SP>2</SP>, R<SP>7</SP>and R<SP>8</SP>are each an alkyl group; R<SP>3</SP>to R<SP>6</SP>and R<SP>9</SP>are each a hydrogen atom or an alkyl group. In addition, the total number of carbon atoms of the substituting groups represented by R<SP>1</SP>to R<SP>6</SP>, is not less than 8. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat-sensitive recording material using a color development reaction between an electron-donating dye precursor and an electron-accepting compound, and more specifically, the hue of an image after printing is preferable, and the hue change with time is effective. The present invention relates to a heat-sensitive recording material suitable for a medical recording material and the like that can be suppressed.

In the thermal recording method, (1) development is unnecessary, (2) when the support is paper, the material is close to general paper, (3) easy to handle, (4) high color density, (5 ) The recording device has advantages such as simple, reliable and inexpensive, (6) low noise during recording, (7) no maintenance, etc. In recent years, the application has been expanded to a wide range of fields. We also provide transparent thermal recording materials that are suitable for applications such as multi-coloring, for example, projecting images etc. with an overhead projector, or directly observing on a light table, such as medical recording materials. Has been.
As a heat-sensitive recording material used for such heat-sensitive recording, a material using a reaction between an electron-donating dye precursor and an electron-accepting compound is well known (see, for example, Patent Document 1). ).

  In particular, when a heat-sensitive recording material is used as a medical recording material or the like, it is required that the color of the image portion is close to pure black. However, it is difficult to produce a pure black color with a single electron-donating dye precursor. For this reason, a plurality of types of electron-donating dye precursors are used and the absorption region is complemented to obtain a pure black color. ing. As a means for obtaining a pure black color by using a plurality of electron donating dye precursors, for example, a method using a specific electron donating dye precursor in a specific ratio has been proposed (for example, Patent Documents). 2).

  However, in the heat-sensitive recording material as described above, a part of the electron-donating dye precursor that remains uncolored as a closed ring after printing may leak from the microcapsule and develop color. There was a problem in that the balance of the electron-donating dye precursor that develops color after storage is lost, and the color of the obtained image changes (red).

Further, it is still insufficient from the viewpoint of obtaining a pure black image, and there is a problem that a change in a ^* value from a medium density to a high density is particularly large, and further improvement has been desired.
JP 2003-2111845 A Japanese Patent Laid-Open No. 10-278431

An object of the present invention is to solve the conventional problems and achieve the following objects.
That is, an object of the present invention is to provide a heat-sensitive recording material in which the hue of an image after printing is preferable and the hue change with time can be effectively suppressed.

Means of the present invention for solving the above-mentioned problems are as follows.
<1> A heat-sensitive recording material having a heat-sensitive recording layer containing a microcapsule encapsulating a colorless or light-colored electron-donating dye precursor and an electron-accepting compound on a support, the electron-donating dye A thermosensitive recording material comprising at least a compound represented by the following general formula (I) and a compound represented by the general formula (II) as a precursor.

[In general formula (I) and general formula (II), R < ¹ >, R < ² > and R < ⁷ >, R < ⁸ > represents an alkyl group. R ^{3 to} R ⁶ and R ⁹ represent a hydrogen atom or an alkyl group. In addition, the total carbon number of the substituent represented by R < ¹ > -R < ⁶ > is 8 or more. ]

  <2> The thermosensitive recording material according to <1>, wherein the electron-accepting compound includes at least a metal salt of a salicylic acid derivative and a phenol derivative.

  <3> The thermosensitive recording material according to <1> or <2>, wherein the capsule wall of the microcapsule is made of polyurethane and / or polyurea resin.

  <4> The above-mentioned <1>, wherein the thermosensitive recording layer added with polyvinyl alcohol on the support, the intermediate layer added with a water-soluble binder, and the protective layer added with polyvinyl alcohol in this order. >-<3> The heat-sensitive recording material according to any one of the above.

  <5> The heat-sensitive recording material according to any one of <1> to <4>, wherein the support is a polyethylene terephthalate film having a thickness of 100 μm or more.

  According to the present invention, it is possible to provide a heat-sensitive recording material in which the hue of an image after printing is preferable and the hue change with time can be effectively suppressed.

  The heat-sensitive recording material of the present invention is a heat-sensitive recording material having a heat-sensitive recording layer containing a microcapsule encapsulating a colorless or light-colored electron-donating dye precursor and an electron-accepting compound on a support, The electron-donating dye precursor includes at least a compound represented by the following general formula (I) and a compound represented by the general formula (II). According to the heat-sensitive recording material of the present invention using a microcapsule encapsulating a specific electron donating dye precursor, the hue of an image after printing is preferable, and the change in hue over time can be effectively suppressed.

[In general formula (I) and general formula (II), R < ¹ >, R < ² > and R < ⁷ >, R < ⁸ > represents an alkyl group. R ^{3 to} R ⁶ and R ⁹ represent a hydrogen atom or an alkyl group. In addition, the total carbon number of the substituent represented by R < ¹ > -R < ⁶ > is 8 or more. ]
Hereinafter, the main components of the heat-sensitive recording material of the present invention will be described in detail.

<Thermal recording layer>
In the present invention, the thermosensitive recording layer provided on the support is composed of an electron donating dye precursor represented by the general formula (I) and an electron donating dye precursor represented by the general formula (II) (in the following, When referring to both, the microcapsules containing at least the “electron-donating dye precursor essential to the present invention”) and the electron-accepting compound are essential components, and other components as necessary. Can be contained. First, an electron donating dye precursor and an electron accepting compound, which are important requirements of the present invention, will be described.

(Electron-donating dye precursor)
In the heat-sensitive recording material of the present invention, a substantially colorless or light-colored electron-donating dye precursor essential to the present invention is used as the electron-donating dye precursor. The compound has a property of coloring by donating electrons or accepting protons such as acid, and in particular, has a partial skeleton such as lactone, lactam, sultone, spiropyran, ester, amide, A compound in which these partial skeletons are ring-opened or cleaved when contacted with an electron-accepting compound is preferable.
The compound represented by the general formula (I) is characterized in that the total number of carbon atoms of the substituents represented by R ^{1 to} R ⁶ in the formula is 8 or more. When the total number of carbon atoms is 7 or less, the molecular weight is small, so that the electron-donating dye precursor and the color former are oozed out from the microcapsule during storage of the recording material after printing, and the hue of the image area over time The change becomes noticeable.

Here, the electron donating dye precursor essential to the present invention will be described.
In general formula (I) and general formula (II), the alkyl group represented by R ^{1 to} R ⁹ may be linear, branched or cyclic, and may be a double bond or triple bond. You may have a bond. Furthermore, it may be substituted with an alkoxy group, an alkylamino group, a cyclic substituent or the like.
Specific examples of the alkyl group include, for example, methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, t-butyl group, n-amyl group, t-amyl group. Group, n-hexyl group, n-octyl group, t-octyl group, n-decyl group, n-dodecyl group, allyl group, propenyl group, cyclopentyl group, cyclohexyl group, p-propylcyclohexyl group, benzyl group, methoxymethyl Group, methoxyethyl group, ethoxyethyl group, phenoxymethyl group, dimethylaminomethyl group, diethylaminomethyl group and the like.

Specific examples of the electron donating dye precursor essential to the present invention are listed below, but the present invention is not limited thereto.
Specific examples of the compound represented by the general formula (I) include, for example, 3-di (n-propyl) amino-6,8-dimethylfluorane, 3-di (n-butyl) amino-6,8- Dimethylfluorane, 3-di (n-amyl) amino-6,8-dimethylfluorane, 3-di (n-hexyl) amino-6,8-dimethylfluorane, 3-di (n-octyl) amino- 6,8-dimethylfluorane, 3-di (n-decyl) amino-6,8-dimethylfluorane, 3-di (n-dodecyl) amino-6,8-dimethylfluorane, 3-diethylamino-6, 8-diethylfluorane, 3-diethylamino-7- (n-butyl) fluorane, 3-diethylamino-7- (i-butyl) fluorane, 3-diethylamino-7- (t-butyl) fluorane, 3-diethyla No-7- (n-amyl) fluorane, 3-diethylamino-7- (t-amyl) fluorane, 3-diethylamino-7- (n-hexyl) fluorane, 3-diethylamino-7- (n-octyl) fluorane, 3-diethylamino-7- (t-octyl) fluorane, 3-diethylamino-7- (pn-propylhexyl) fluorane, 3-di (n-butyl) amino-7- (t-butyl) fluorane, 3- Examples include di (n-butyl) amino-7- (t-octyl) fluorane and 3-di (n-butyl) amino-7- (n-dodecyl) fluorane.

  Specific examples of the compound represented by the general formula (II) include, for example, 2-anilino-3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-di (n-propyl). Aminofluorane, 2-anilino-3-methyl-6-di (n-butyl) aminofluorane, 2-anilino-3-methyl-6-di (n-amyl) aminofluorane, 2-anilino-3- Methyl-6-di (n-hexyl) aminofluorane, 2-anilino-3-methyl-6-di (n-octyl) aminofluorane, 2-anilino-3-methyl-6-di (n-decyl) Aminofluorane, 2-anilino-3-methyl-6-di (n-dodecyl) aminofluorane, 2-anilino-3-methyl-6-N-ethyl-N- (i-butyl) aminofluorane, 2 -Anilino-3 Methyl-6-N-ethyl-N-dodecylaminofluorane, 2-anilino-3-methyl-6-N-ethyl-N-cyclohexylaminofluorane, 2-anilino-3-methyl-6- (dimethoxy) Methyl) aminofluorane, 2-anilino-3-methyl-6- (diethoxyethyl) aminofluorane, 2-anilino-3-methyl-6- (dimethylaminomethyl) aminofluorane, 2-anilino-3- Methyl-6-dibenzylaminofluorane, 2-anilino-3-methyl-6- (dibenzyloxymethyl) aminofluorane, 2-anilino-6-diethylaminofluorane, 2-anilino-6-N-ethyl- N- (i-butyl) aminofluorane and the like can be mentioned.

In addition, it is preferable that it is 0.1-0.2 g / m < ² >, and, as for content of the compound represented by general formula (I), it is more preferable that it is 0.2-1.0 g / m < ² >. Moreover, it is preferable that it is 0.3-4.5 g / m < ² >, and, as for content of the compound represented by general formula (II), it is more preferable that it is 0.8-3.0 g / m < ² >.
Moreover, as content rate of the compound represented by general formula (I) with respect to the compound represented by the said general formula (II), 5-70 mass% is preferable, 10-60 mass% is more preferable, 20-50 Mass% is particularly preferred.

  In addition, when the thermosensitive recording material of the present invention is used as a medical recording material or the like, other known electron donating dye precursors can be used in combination as necessary. By using other known electron-donating dye precursors in addition to the electron-donating dye precursors essential to the present invention, it is possible to complement each other's absorption region and obtain an image portion close to pure black.

  Examples of the other known electron-donating dye precursors include, for example, triphenylmethane phthalide compounds, fluoran compounds, phenothiazine compounds, indolyl phthalide compounds, leucooramine compounds, rhodamine lactam compounds, Examples include triphenylmethane compounds, triazene compounds, spiropyran compounds, pyridine compounds, pyrazine compounds, and the like.

Specific examples of the phthalides include compounds described in U.S. Reissue Patent No. 23024, U.S. Pat. Nos. 3,491,111, 3,491,112, 3,491,116, and 3,509,174. .
Specific examples of the spiropyrans 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 and 4,246,318.
Specific examples of the fluorane compound include U.S. Pat. Nos. 3,624,107, 3,627,787, 3,410,411, 3,462,828, 3,681,390, 3,920,510, 3,959,571, and Japanese Patent Application No. 3959571. Examples thereof include compounds described in JP-A-61-240989.

As the content of the electron donating dye precursor, the total content of all the electron donating dye precursors is preferably 0.1 to 5.0 g / m ² , and 1.0 to 4.0 g. / M ² is more preferable. When the content is within the above range, a sufficient color density can be obtained, and the transparency of the heat-sensitive recording layer can be maintained particularly when the content is within 5.0 g / m ² .

(Electron-accepting compound)
Examples of the electron-accepting compound that reacts with the electron-donating dye precursor include acidic substances such as organic acid derivatives and metal salts thereof, phenol derivatives, and oxybenzoic acid esters. These electron-accepting compounds may be used alone or in combination of two or more. In particular, from the viewpoint of lowering the haze value and improving the transparency of the thermosensitive recording layer, at least a metal salt of a salicylic acid derivative. And phenol derivatives are preferably used.

  Examples of the electron-accepting compound include compounds described in JP-A No. 61-291183, and more specifically, 3,5-di-α-methylbenzylsalicylic acid, 3,5 -Salicylic acid derivatives such as di-tertiary butylsalicylic acid, 3-α-α-dimethylbenzylsalicylic acid, 4- (β-p-methoxyphenoxyethoxy) salicylic acid; and polyvalent metal salts thereof (especially zinc and aluminum are preferred) Phenol derivatives such as p-phenylphenol, 3,5-diphenylphenol, cumylphenol, 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy-4′-phenoxydiphenylsulfone;

  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′-hydroxy) Phenyl) heptane, 1,1-bis (4′-hydroxyphenyl) octane, 1,1-bis (4′-hydroxyphenyl) -2-methylpentane, , 1-bis (4′-hydroxyphenyl) -2-ethylhexane, 1,1-bis (4′-hydroxyphenyl) dodecane, 1,4-bis (p-hydroxyphenylcumyl) benzene, 1,3- Bisphenols such as bis (p-hydroxyphenylcumyl) benzene, bis (p-hydroxyphenyl) sulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, bis (p-hydroxyphenyl) acetic acid benzyl ester; p- Examples thereof include oxybenzoic acid esters such as hydroxybenzoic acid benzyl ester, p-hydroxybenzoic acid-2-ethylhexyl ester, and β-resorcinic acid- (2-phenoxyethyl) ester.

  In this invention, 0.5-30 mass parts is preferable with respect to 1 mass part of all the electron-donating dye precursors, and, as for content of the said electron-accepting compound, 1.0-10 mass parts is more preferable.

(Micro capsule)
A method for producing a microcapsule encapsulating the above electron donating dye precursor will be described.
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. Among them, 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, and stirred by a homogenizer or the like. It is preferable to employ an interfacial polymerization method in which after the emulsification and dispersion by means, a polymer forming reaction is caused at the oil droplet interface by heating to form a microcapsule wall made of a polymer substance.

  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.

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

As the polyisocyanate, a compound having a trifunctional or higher functional isocyanate group is preferable, but a bifunctional isocyanate compound may be used in combination, or a bifunctional isocyanate compound may be used alone.
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. Alternatively, 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.
Further, compounds described in JP-A-62-212190, JP-A-4-26189, JP-A-5-317694, JP-A-10-114153 and the like are also 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 aqueous phase and / or oil phase as components constituting the microcapsule wall by reacting with polyisocyanate include propylene glycol, glycerin, trimethylolpropane, and triethanolamine. Sorbitol, hexamethylenediamine, tetraethylenepentamine, diethylenetriamine and the like. 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.
These polyisocyanates, polyols, reaction catalysts, and polyamines for forming a part of the walling agent are described in detail in “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 contained in the capsule wall at the time of forming the capsule wall 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, a plasticizer suitable for the polymer used as the wall material can be used to make the wall of the microcapsule excellent in material permeability even under low temperature conditions and rich in color development sensitivity. 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 suitably used as the plasticizer.

In the preparation of the oil phase, a hydrophobic organic solvent may be used to dissolve the electron donating dye precursor and form the core of the microcapsule, and an organic solvent having a boiling point of 300 ° C. or lower is preferable.
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 dispersion.

  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, phthalate Phthalic acid esters such as octyl acid and butyl benzyl phthalate; Dioctyl tetrahydrophthalate; Benzoic acid esters such as ethyl benzoate, propyl benzoate, butyl benzoate, isopentyl benzoate, and benzyl benzoate; Dioctyl adipate; isodecyl succinate; dioctyl azelate; oxalate esters such as dibutyl oxalate and dipentyl oxalate; diethyl malonate; dimethyl maleate, diethyl maleate, dibutyl maleate Maleic acid esters such as 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; Examples thereof include 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. The above organic solvents can be used together or in combination with other organic solvents.

  When the electron-donating dye precursor to be encapsulated has poor solubility in the hydrophobic organic solvent, a low-boiling solvent having high solubility can be used. Preferred examples of such a low boiling point solvent include ethyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, and methylene chloride. In order to further improve the storability of the image, it is more preferable that there is no core oil.

  On the other hand, an aqueous solution in which a water-soluble polymer is dissolved as a protective colloid is used for the aqueous phase to be used, and after the oil phase is added thereto, the mixture is emulsified and dispersed by a stirring means such as a homogenizer. The water-soluble polymer acts as a dispersion medium that makes the dispersion uniform and easy and stabilizes the emulsified and dispersed aqueous solution. 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 well-known emulsifying surfactant can be used. 0.1-5% is preferable with respect to the mass of an oil phase, and, as for the addition amount of this surfactant, 0.5-2% is more preferable.

As the surfactant to be contained in the aqueous phase, an anionic or nonionic surfactant that does not act on the protective colloid to cause precipitation or aggregation can be appropriately selected and used. .
Preferable surfactants include, for example, sodium alkylbenzene sulfonate, sodium alkyl sulfate, dioctyl sulfosuccinate sodium salt, polyalkylene glycol (for example, polyoxyethylene nonyl phenyl ether), acetylene glycol and the like.

  Emulsification dispersion is a means used for normal fine particle emulsification, such as a high-speed stirrer, an ultrasonic dispersion device, etc., for example, an oil phase containing the above-mentioned components and an aqueous phase containing a protective colloid and optionally a surfactant. It can be easily carried out using a known emulsifying and dispersing apparatus such as a homogenizer, a menton gorey, an ultrasonic disperser, a dissolver, a teddy mill or the like. After emulsification and dispersion, 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 to perform sufficient stirring.

  Further, a dispersing agent for preventing aggregation may be added again during the capsule formation 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 formation reaction. Usually, the target microcapsule can be obtained by reacting for several hours.

(Contained in polymer)
In addition, as in the heat-sensitive recording material of the present invention, an embodiment in which the electron donating dye precursor is contained in a polymer rather than encapsulated in a microcapsule is also mentioned as a preferred embodiment. As a method of including an electron donating dye precursor in a polymer, a polyisocyanate compound as a polymerization component is used as a solvent without using an organic solvent, and the electron donating dye precursor is dissolved therein. Except for this, composite fine particles to be a polymer containing an electron-donating dye precursor can be produced (composite fine particles) by a method similar to the method for producing the microcapsules.

  For the composite fine particles, for example, details described in JP-A-9-263057 can be referred to. This aspect of the composite fine particles limits the solubility of the solute, increases the amount of the composite fine particles applied more than necessary, and completely separates the electron donating dye precursor from the electron accepting compound (developer). In this case, the microcapsule is more preferable because it is difficult to carry out the treatment and is likely to be accompanied by background coloration and deterioration of image storage stability.

(Emulsified dispersion)
In the present invention, the electron-accepting compound can be used as a solid dispersion by a mixing means such as a sand mill together with, for example, a water-soluble polymer and an organic base, and other coloring aids. After being dissolved in an organic solvent having a high boiling point, it is mixed with a polymer aqueous solution (aqueous phase) containing a surfactant and / or a water-soluble polymer as a protective colloid and used as an emulsion emulsified and dispersed with a homogenizer or the like. Is more preferable. In this case, a low boiling point solvent can be used as a dissolution aid, if necessary.

  The high boiling point organic solvent used in this case can be appropriately selected from, for example, high boiling point oils described in JP-A-2-141279. Among them, it is preferable to use esters from the viewpoint of the emulsion stability of the emulsion dispersion, and among them, tricresyl phosphate and diethyl malonate are particularly preferable. A combination of a plurality of the above oils or a combination of other oils is also possible.

The water-soluble polymer that can be contained as the protective colloid can be appropriately selected from known anionic polymers, nonionic polymers, and amphoteric polymers, and is suitable for water at the temperature to be emulsified. A water-soluble polymer having a solubility of 5% or more is preferred. Specific examples thereof 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, isobutylene-anhydride. Maleic acid copolymer, polyvinylpyrrolidone, ethylene-acrylic acid copolymer, vinyl acetate-acrylic acid copolymer, cellulose derivatives such as carboxymethylcellulose and methylcellulose, casein, gelatin, starch derivatives, arabic gum, sodium alginate, etc. . Among these, polyvinyl alcohol, gelatin, and cellulose derivatives are particularly preferable.
Suitable examples of the polyvinyl alcohol include fully saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, silica-modified polyvinyl alcohol, and terminal hydrophobic group-modified polyvinyl alcohol.

  Moreover, 0.1-2.0 are preferable and, as for the mixing ratio (oil phase mass / water phase mass) with respect to the water phase of an oil phase, 0.5-1.5 are more preferable. When the mixing ratio is in the range of 0.1 to 2.0, an appropriate viscosity can be maintained, the production suitability is excellent, and the stability of the coating solution over time is excellent.

(Other ingredients)
Next, in addition to the components described above, other components that can be used in the heat-sensitive recording layer will be described.
There is no restriction | limiting in particular as said other component, Although it can select suitably according to the objective or necessity, For example, a well-known thermofusible substance, a ultraviolet absorber, antioxidant, etc. are mentioned.
As the coated 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.

  The heat-fusible substance can be contained in the heat-sensitive recording layer for the purpose of improving thermal response. Examples of such heat-fusible substances include aromatic ethers, thioethers, esters, aliphatic amides, ureidos, and the like. 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, 50-10726, U.S. Pat. 3707375, 3754919, and 4220711.

  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 heat-sensitive recording layer in the present invention is used for obtaining a saturated transmission density (D _T-max ) in order to obtain a high-quality image by suppressing density unevenness caused by a slight difference in thermal conductivity of the thermal head. A thermal recording layer having a wide required energy amount, that is, a wide dynamic range is preferable. The heat-sensitive recording material of the present invention has the above-mentioned heat-sensitive recording layer, and has a characteristic that a transmission density (D _T-max ) of 3.0 can be obtained with a heat energy amount in the range of 70 to 130 mJ / mm ^2. A heat-sensitive recording layer is preferable.

The heat-sensitive recording layer in the present invention is applied so that the solid content after coating and drying is 1 to 25 g / m ² , and the thickness of the recording layer is 1 to 25 μm. It is preferable. In addition, two or more heat-sensitive recording layers can be laminated and used. In this case, the solid coating amount after application and drying of the entire thermosensitive recording layer is preferably 1 to 25 g / m ² .

(Formation of thermal recording layer)
The coating solution used for forming the heat-sensitive recording layer in the present invention (heat-sensitive recording layer coating solution) can be prepared, for example, by mixing the microcapsule solution prepared as described above and an emulsified dispersion. Here, a water-soluble polymer that can be used as a protective colloid in the preparation of the microcapsule liquid, and a water-soluble polymer that can be used as a protective colloid in the preparation of the emulsified dispersion include a thermosensitive recording layer. Functions as a binder. In addition to these protective colloids, a binder may be added and mixed to prepare a thermal recording layer coating solution.

The binder to be added is generally a water-soluble binder, such as polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, epichlorohydrin modified polyamide, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer. Examples of the polymer include isobutylene-maleic salicylic acid copolymer, polyacrylic acid, polyacrylic acid amide, methylol-modified polyacrylamide, starch derivative, casein, and gelatin.
In addition, a water resistance improver may be added for the purpose of imparting water resistance to these binders, or an emulsion of a hydrophobic polymer, specifically, a styrene-butadiene rubber latex, an acrylic resin emulsion, or the like may be added.

In order to apply the thermal recording layer coating liquid onto the support, known coating means used for aqueous or organic solvent based coating liquids are used. In this case, the thermal recording layer coating liquid is applied safely and uniformly. In addition, in order to ensure the strength of the coating film, in the coating solution for the heat sensitive recording layer in the present invention, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, 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, polyurethane resin, polyamide resin, polyvinyl butyral It is possible to use resin etc. Kill.
Here, examples of the known coating means include a method using a bar coater, an air knife coater, a blade coater, a curtain coater, slide coating with an extrusion die, and the like.

  In addition, by configuring the heat-sensitive recording layer in the present invention so as to reduce the haze value calculated from (diffuse transmittance / total light transmittance) × 100 (%), an image having excellent transparency can be obtained. A heat-sensitive recording material can be obtained. The haze value is an index representing the transparency of the material, and is generally calculated from the total transmitted light amount, diffuse transmitted light amount, and parallel transmitted light amount using a haze meter.

As a method for lowering the haze value, for example, (1) the 50% volume average particle size of both the electron donating dye precursor and the electron accepting compound contained in the thermosensitive recording layer is 1.0 μm or less, preferably A method of containing 0.6 to [mu] m or less and a binder in the range of 30 to 60% by mass of the total solid content of the heat-sensitive recording layer, or (2) electron accepting to the electron donating dye precursor encapsulated in the microcapsule And a method of using the active compound as a material that substantially constitutes a continuous layer after coating and drying (for example, an emulsified dispersion). It is also effective to make the refractive index of the component used for the thermosensitive recording layer as close as possible to a constant value.
Here, in the present invention, the 50% volume average particle diameter is, for example, a pigment corresponding to 50% volume in the pigment measured by a laser diffraction particle size distribution measuring apparatus “LA700” manufactured by Horiba, Ltd. It means the average particle size of the particles (hereinafter sometimes simply referred to as “average particle size”).

<Intermediate layer>
In the heat-sensitive recording material of the present invention, in order to prevent mixing of each layer and to block gases (oxygen, ozone, etc.) harmful to image storability, the support is provided on the color-forming surface side having a heat-sensitive recording layer and a protective layer. It is preferable to provide an intermediate layer. Further, particularly in the present invention, from the viewpoint of preventing the mixing of each layer, as the layer structure, the thermosensitive recording layer added with polyvinyl alcohol on the support, the intermediate layer added with a water-soluble binder, and polyvinyl alcohol were added. It is preferable to have a protective layer in this order.
The intermediate layer may contain a crosslinking agent, a lubricant, a surfactant, other additives, etc., depending on the purpose and necessity.

As the binder, gelatin, polyvinyl alcohol, polyvinyl pyrrolidone, cellulose derivatives and the like can be preferably used depending on the system, and among them, gelatin is particularly preferable.
Gelatin has fluidity at high temperatures, but it loses fluidity at low temperatures (for example, 35 ° C or less) and has excellent gelation properties (setability), so multiple layers are formed on the support. In this case, for example, even in a method in which a plurality of layers are sequentially applied and dried or a method in which a plurality of layers are applied and dried at once by an extrusion die method or the like, it is effectively prevented that two adjacent layers are mixed 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. Therefore, it is suitable for medical recording materials that need to form clear images in detail. It is. Further, even when dried at a high wind speed, the surface condition is not deteriorated, so that the production efficiency is improved.

  As the gelatin, any 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. Of these, alkali-processed gelatin having a low isoelectric point (for example, lime-processed gelatin) and derivative gelatin (for example, phthalated gelatin) in which an amino group is reacted are preferable.

  Specific examples of binders other than gelatin such as polyvinyl alcohol, polyvinyl pyrrolidone, cellulose derivatives and the like include vinyl acetate-acrylamide copolymer, silicon-modified polyvinyl alcohol, starch, modified starch, methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, Arabic Rubber, casein, styrene-maleic acid copolymer hydrolyzate, styrene-maleic acid copolymer, half ester hydrolyzate, isobutylene-maleic anhydride copolymer hydrolyzate, polyacrylamide derivative, polyvinylpyrrolidone, polystyrene sulfone Water-soluble polymers such as acid soda and sodium alginate, and styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene Arm latex, water-insoluble polymers such as vinyl acetate emulsion.

In the intermediate layer of the present invention, the coating amount of the binder is preferably in the range of 0.2 to 10 g / m ² . By setting it within this range, it becomes easy to prevent mixing of coloring components and adjust sensitivity between recording layers.

  For the purpose of further improving the water resistance, it is effective to use a crosslinking agent and a catalyst for promoting the reaction in combination. Examples of the crosslinking agent include epoxy compounds, blocked isocyanates, vinyl sulfone compounds, and aldehyde compounds. , Methylol compounds, boric acid, carboxylic acid anhydrides, silane compounds, chelate compounds, halides, etc., and the pH of the coating solution used for forming the intermediate layer (intermediate layer coating solution) is 6.0 to 7.5. What can be adjusted is preferable. Moreover, as said catalyst, a well-known acid, a metal salt, etc. are mentioned, The thing which can adjust the pH of a coating liquid to 6.0-7.5 similarly to the above is preferable.

Examples of the lubricant preferably include zinc stearate, calcium stearate, paraffin wax, and polyethylene wax.
Examples of the surfactant preferably include sulfosuccinic acid salts and fluorine-containing surfactants so that an intermediate layer can be uniformly formed on the thermosensitive recording layer. Examples thereof include sodium salts such as (2-ethylhexyl) sulfosuccinic acid and di- (n-hexyl) sulfosuccinic acid, and ammonium salts.

The coating solution for forming the intermediate layer is obtained by mixing the above components. Furthermore, you may add a mold release agent, a wax, a water repellent, etc. as needed.
The heat-sensitive recording material of the present invention can be formed, for example, by applying an intermediate layer coating solution on a heat-sensitive recording layer formed on a support by a known coating method. Examples of the known coating method include the same ones as mentioned in the above section (Formation of thermosensitive recording layer).
Dry coating amount of the intermediate layer is preferably ^{0.2~4.0g / m 2, 0.5~3.0g / m} 2 is more preferable.

<Protective layer>
In the present invention, a protective layer can be formed on the color development surface as an upper layer of the heat-sensitive recording layer and the intermediate layer. The protective layer is usually prepared and applied as a protective layer coating solution, and the protective layer coating solution is a water-soluble binder in order to maintain a good head matching property over a wide recording energy range. A form containing at least polyvinyl alcohol and further containing a pigment and a liquid or solid lubricant is preferred. Further, as described above, particularly from the viewpoint of preventing mixing of each layer, the thermosensitive recording layer added with polyvinyl alcohol on the support, the intermediate layer added with a water-soluble binder, and the protective layer added with polyvinyl alcohol, It is preferable to have a layer structure in this order.

(Pigment)
The pigment used in the protective layer of the heat-sensitive recording material of the present invention is usually used for the purpose of making thermal recording with a thermal head suitable, that is, for the purpose of suppressing the occurrence of sticking, abnormal noise, etc. Both pigments and inorganic pigments can be used.

  The pigment used in the protective layer of the present invention preferably has an average particle size, specifically, a 50% volume average particle size measured by the laser diffraction method described above of 0.10 to 5.0 μm, particularly When performing thermal recording with a thermal head, the 50% volume average particle size is 0.20 to 0.50 μm from the viewpoint of more effectively suppressing the occurrence of sticking or abnormal noise between the thermal head and the thermal recording material. More preferably, it is in the range. When the 50% volume average particle size is in the range of 0.10 to 5.0 μm, the effect of reducing friction against the thermal head is great, and as a result, the thermal head and the protective layer of the heat-sensitive recording material adhere to each other during printing. In other words, the so-called sticking phenomenon can be prevented.

  The type of pigment that can be used in the protective layer of the present invention is not particularly limited, and can be appropriately selected from known organic and inorganic pigments. Inorganic pigments such as titanium, kaolin, aluminum hydroxide, amorphous silica, and zinc oxide, and organic pigments such as urea formalin resin and epoxy resin are preferable. Of these, kaolin, aluminum hydroxide, and amorphous silica are particularly preferable. These pigments may be used alone or in combination of two or more. Among the above pigments, a pigment whose surface is coated with at least one selected from the group consisting of higher fatty acids, higher fatty acid metal salts, and higher alcohols can be suitably used. Examples of the higher fatty acid used for the surface treatment include stearic acid, palmitic acid, myristic acid, lauric acid, and the like.

  The above pigments include, for example, sodium metametaphosphate, 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 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 finely dispersed until the 50% volume average particle size of the pigment is in the range of 0.1 to 5.0 μm.

(lubricant)
The lubricant used in the protective layer in the present invention is usually a liquid having a liquid or a melting point of less than 40 ° C. at a normal temperature and a melting point of 40 ° C. in order to reduce printing torque and make thermal recording with a thermal head suitable. A form containing the above lubricant is preferred.
Examples of the lubricant that is liquid at room temperature include silicone oil, liquid paraffin, and lanolin, and silicone oil is particularly preferable. The silicone oil may have a substituent such as a carboxyl group or a polyoxyethylene group, and the viscosity of the silicone oil is preferably 100 to 100,000 mPa · s.

  Examples of the lubricant having a melting point of less than 40 ° C. include polyoxyethylene alkyl ether, polyoxyethylene alkyl ether acetate, polyoxyethylene alkyl ether sulfate, polyoxyethylene alkyl ether phosphate, etc. A polyoxyethylene alkyl ether phosphate represented by the following structural formula [001] is preferred.

In the above formula [001], R represents an alkyl group, and the alkyl group may have a substituent. n represents an integer of 2 to 30.
The above-mentioned lubricant that is liquid at normal temperature and the lubricant having a melting point of 40 ° C. or less may be used alone or in combination of two or more.

  As the lubricant having a melting point of 40 ° C. or higher, a melting point of 160 ° C. or lower, preferably 140 ° C. or lower is desirable, stearic acid amide (melting point 100 ° C.), methylol stearic acid amide (melting point 101 ° C.), Polyethylene wax (melting point 110 ° C. or lower), paraffin wax with melting point 50-90 ° C., glycerin tri-12-hydroxystearate (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), PAL Chinsan magnesium (melting point 122 ° C.), and the like magnesium myristate (melting point 131 ° C.). These lubricants having a melting point of 40 ° C. or higher may be used alone or in combination of two or more.

  When the lubricant used in the present invention is insoluble in water, it is preferably added to the protective layer in the form of dispersion or emulsion. In the case of a solid, (1) an aqueous dispersion dispersed with a known disperser such as a homogenizer, dissolver or sand mill in the presence of a water-soluble polymer such as polyvinyl alcohol or a dispersant such as various surfactants. (2) Emulsified after being dissolved in a solvent and then emulsified and dispersed with a known emulsifying device such as a homogenizer, dissolver or colloid mill in the presence of a dispersing agent such as a water-soluble polymer or various surfactants Used in the form of In the case of a liquid, it is used in the form of an emulsion as described above. The preferred average particle size of the dispersion or emulsion is 0.1 to 5.0 μm, more preferably 0.1 to 2.0 μm. Here, the average particle diameter refers to a 50% volume average particle diameter measured by the laser diffraction method described above.

(Binder etc.)
In the protective layer of the present invention, polyvinyl alcohol is preferably used as the binder from the viewpoint of improving transparency, and modified polyvinyl alcohol such as carboxy-modified polyvinyl alcohol and silica-modified polyvinyl alcohol can also be used.

  The protective layer of the present invention may contain a known hardener or the like. Examples of the hardener include inorganic compounds such as boric acid, borax, colloidal silica, and dialdehyde derivatives represented by the following structural formula [002].

  In the present invention, it is preferable to add a surfactant to the coating solution for the protective layer in order to uniformly form the protective layer on the heat-sensitive recording layer or the intermediate layer. As the surfactant, sulfosuccinic acid-based alkali metal salts, fluorine-containing surfactants, and the like are preferable. Specific examples include di- (2-ethylhexyl) sulfosuccinic acid and di- (n-hexyl) sulfosuccinic acid. Examples thereof include sodium salt, potassium salt, or ammonium salt; acetylene glycol derivative; sodium perfluoroalkyl sulfate, potassium salt, or ammonium salt; perfluoroalkyl betaine compound.

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.
Dry coating amount of the protective layer is preferably ^{0.2~7g / m 2, 1~4g / m} 2 is more preferable.

<Back layer>
In the heat-sensitive recording material of the present invention, in order to improve the curl balance, a back layer may be provided on the opposite side (back surface) of the support to the color-forming surface having the heat-sensitive recording layer, intermediate layer and protective layer. it can. The back layer preferably contains a water-soluble binder, in particular gelatin, gelatin coating amount, from the viewpoint of further improving the curl balance, is preferably 1 to 5 g / m ^2, in particular 2 to 4 g / m ² Most preferably.

  The back layer in the present invention may be composed of one layer or may be composed of two or more layers. In particular, it is preferably composed of two or more layers from the viewpoint that a coating film can be formed satisfactorily while increasing the coating amount of a water-soluble binder containing gelatin without causing any other problems. Moreover, you may contain other components, such as a hardening agent, a mat agent, a ultraviolet absorber, dye, a pH adjuster, antiseptic | preservative, and surfactant, as needed or the objective.

  Examples of the water-soluble binder used in the back layer in the present invention include gelatins such as alkali-treated gelatin and phthalated gelatin, vinyl acetate-acrylamide copolymer, silicon-modified polyvinyl alcohol, acetyl-modified polyvinyl alcohol, and acetyl fluoride-modified. Polyvinyl alcohols such as polyvinyl alcohol, starch, modified starch, methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, gum arabic, casein, styrene-maleic acid copolymer hydrolyzate, styrene-maleic acid copolymer half ester hydrolysate, Water-soluble polymers such as hydrolysates of isobutylene-maleic anhydride copolymer, polyacrylamide derivatives, polyvinyl pyrrolidone, polystyrene sulfonate sodium, sodium alginate, etc. It is. Further, in combination with the water-soluble binder, the following water-insoluble binder can also be used. Specific examples thereof include styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex, Examples thereof include water-insoluble polymers such as vinyl acetate emulsion.

<Support>
The support used in the heat-sensitive recording material of the present invention has a heat shrinkage rate of less than 1%, preferably 0.5% or less in the longitudinal and transverse directions in order to effectively prevent deformation such as curling. Is preferred. By selecting a support having a low thermal shrinkage rate, the thermal contraction of the support itself can be suppressed even when used in applications where high thermal energy is applied, such as when used for medical recording, and curling after recording is possible. It is possible to prevent problems such as deformation.

  The support of the present invention can be used without particular limitation as long as it has a low thermal shrinkage as described above, and can be appropriately selected from known supports. Among them, a transparent support is preferable, and as the transparent support, a synthetic polymer film such as a polyester film such as polyethylene terephthalate, polybutylene terephthalate, or polyethylene naphthalate, a cellulose triacetate film, or a polyolefin film such as polypropylene or polyethylene is used. In particular, a support of polyethylene terephthalate (PET) is preferable. These can be used alone or in combination. The thickness of the synthetic polymer film is preferably 100 μm or more, more preferably 120 to 200 μm, and particularly preferably 150 to 190 μm from the viewpoints of curling reduction of the film after printing and improvement in ease of handling of the film.

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

  In particular, when the transmission is observed on the Schaukasten, the Schaukasten light transmitted through the transparent non-image portion may cause illusion and make the image difficult to see. In such a case, in order to avoid the above-mentioned illusion, A (x = 0.2055, y = 0.3005), B on the chromaticity coordinates defined by the method described in JIS-Z8701 (1999). (X = 0.2820, y = 0.2970), C (x = 0.2885, y = 0.015), and D (x = 0.2870, y = 0.040). It is particularly preferable to use a synthetic polymer film colored blue in a rectangular region.

<Other layers>
In the present invention, an ultraviolet filter layer may be provided at any position on the support for the purpose of preventing image fading. The ultraviolet filter layer contains an ultraviolet absorber such as benzotriazole, benzophenone, or hindered amine.
Moreover, you may have further a light reflection prevention layer. The light reflection preventing layer can be constituted by containing fine particles suitable for a matting agent usable for the back layer.

  In order to prevent the heat-sensitive recording layer from peeling off from the support, an undercoat layer may be formed on the support in advance before applying the heat-sensitive recording layer, the protective layer or the like. The undercoat layer is made of an acrylate copolymer, polyvinylidene chloride, SBR, aqueous polyester, or the like, and the thickness of the layer is preferably 0.05 to 0.5 μm.

  When applying the heat-sensitive recording layer on the undercoat layer, the undercoat layer may swell due to moisture contained in the heat-sensitive recording layer coating solution, and the image recorded on the heat-sensitive recording layer may deteriorate. It is preferable to harden using dialdehydes such as glutaraldehyde, 2,3-dihydroxy-1,4-dioxane, or a hardener such as boric acid. The addition amount of the hardener is preferably in the range of 0.2 to 3.0% by mass with respect to the dry mass of the undercoat layer, and can be appropriately added according to the desired degree of curing.

The heat-sensitive recording material of the present invention forms a heat-sensitive recording layer by applying a heat-sensitive recording layer coating solution on one side of a support, and, if necessary, an intermediate layer coating solution on the heat-sensitive recording layer. And coating the protective layer coating liquid, and forming the back layer consisting of a single layer or a plurality of layers on the opposite side of the side by applying the back layer coating liquid, as described above, Furthermore, it is obtained by forming another layer on the one and the other. The heat-sensitive recording material of the present invention may be applied by any method. Specifically, various coating operations are used, 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. F. Kistler, Petert M. Extrusion coating or slide coating described in “LIQUID FILM COATING” by Schwaizer (CHAPMAN & HALL 1997) pages 399 to 536 is preferably used, and slide coating is particularly preferably used. As the shape of the slide coater used for the slide coating, page 11 of page 427, Figure 11b. 1 If desired, two or more layers can be simultaneously coated by the method described on pages 399 to 536 of the same document, the method described in US Pat. No. 2,761791 and British Patent No. 837095. Drying is performed with a 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.
Here, the heat-sensitive recording layer, the intermediate layer and the protective layer may be formed at the same time. In this case, the heat-sensitive recording layer coating solution, the intermediate layer and the protective layer coating solution are simultaneously coated on the support. Can be formed.

  The heat-sensitive recording material of the present invention can preferably record an image with a heating element such as a thermal head. The thermal head is protected by a heating element having a heating resistor and an electrode on the glaze layer using a known film forming apparatus so that the carbon ratio of the uppermost layer in contact with the thermal recording material is 90% or more. What provided the layer is used suitably. The head protective layer may be two or more layers, but at least the uppermost layer preferably has a carbon ratio of 90% or more.

  Examples of the present invention are shown below, but the present invention is not limited to these examples. In the following, “%” means “mass%”.

Example 1
(Preparation of coating solution for first back layer)
Water was added to the following composition to prepare a total amount of 21.03 liters to obtain a first back layer coating solution (hereinafter referred to as “BC layer coating solution”). Here, the gelatin content in the present back layer is the total amount of “lime-processed gelatin” in the following composition and gelatin in “gelatin dispersion containing 12% spherical PMMA matting agent”. The polymer content of the latex is the solid content in the “polyethyl acrylate latex (20% liquid)” in the following composition.

<Composition of coating solution for BC layer>
・ Lime-treated gelatin (water-soluble binder): 1000g
Gelatin dispersion containing 12% spherical PMMA matting agent (average particle size: 5.7 μm)
………… 180g
-Compounds represented by the following structural formulas [1] to [5]
Emulsions of UV absorbers with the following content:… 1028g
[The content of the ultraviolet absorber per kg of the emulsion is 14.9 g of the compound represented by the structural formula [1], 12.7 g of the compound represented by the structural formula [2], and represented by the structural formula [3]. 14.9 g of the compound, 21.1 g of the compound represented by the structural formula [4], and 44.5 g of the compound represented by the structural formula [5]. ]
・ 1,2-Benzisothiazolin-3-one… 0.98g
・ Sodium poly-p-vinylbenzenesulfonate (molecular weight: about 400,000)
... 16.4g
-Compound represented by the following structural formula [6] ... 3.79 g
・ Polyethyl acrylate latex (20% solution) …… 1448 ml
・ N, N-ethylene-bis (vinylsulfonylacetamide) ... 52.2g
・ 1,3-Bis (vinylsulfonylacetamide) propane ………… 17.4g

(Preparation of coating solution for second back layer)
Water was added to the following composition to prepare a total amount of 26.59 liters to obtain a second back layer coating solution (hereinafter referred to as “BPC layer coating solution”). Here, the gelatin content in the present back layer is the total amount of “lime-processed gelatin” in the following composition and gelatin in “gelatin dispersion containing 15% spherical PMMA matting agent”.

<Composition of coating solution for BPC layer>
・ Lime-treated gelatin (water-soluble binder): 1000g
Gelatin dispersion containing 15% spherical PMMA matting agent (average particle size: 0.7 μm)
……… 1015g
・ 1,2-Benzisothiazolin-3-one ……… 2.09g
・ Pt-octylphenoxy sodium polyoxyethylene ethylsulfonate
......... 9.53g
・ Sodium polyacrylate (Molecular weight: approx. 100,000) ... 57.9g
・ Sodium poly-p-vinylbenzenesulfonate (molecular weight: about 400,000)
......... 22.9g
・ N-propyl-N-polyoxyethylene-perfluoro octanesulfonic acid amidobutylsulfonic acid sodium salt ............ 0.37 g
・ Hexadecyloxy-nonyl (ethyleneoxy) -ethanol
......... 8.97 g
・ 1N sodium hydroxide aqueous solution …… 28.1g
・ Polyethyl acrylate latex (20% solution) ...... 2087 ml
・ N, N-ethylene-bis (vinylsulfonylacetamide) ............ 18.0g
・ 1,3-Bis (vinylsulfonylacetamide) propane …… 6.0g

(Preparation of support with back layer)
A transparent PET support (thickness: 175 μm) dyed blue with x = 0.2850 and y = 0.2995 with chromaticity coordinates defined by the method described in JIS-Z8701 (1999) was obtained from the above. The BC layer coating solution and the BPC layer coating solution were applied on the transparent PET support in the order of the BC layer coating solution and the BPC layer coating solution in the order of 51.37 ml / The layers were applied simultaneously by a slide bead method so as to be m ² and 14.70 ml / m ² and dried. Here, the coating and drying conditions are as follows.

The coating speed was 160 m / min, the gap between the coating die tip and the support was 0.10 to 0.30 mm, and the pressure in the decompression chamber was set lower by 196 to 882 Pa than the atmospheric pressure. The support was previously charged with ion wind before application. Subsequently, in the chilling zone, the coating solution is cooled with wind at a dry bulb temperature of 10 to 20 ° C., then conveyed in a non-contact manner, and a dry bulb temperature of 23 to 45 ° C. and a wet bulb with a helical contactless dryer. It dried with the drying wind of temperature 15-21 degreeC.
As described above, a back layer composed of two layers was formed on one side of the transparent PET support. The total coating amount of gelatin contained in the backing layer of the two layers is 3.05 g / m ^2, the coating amount of the latex is 0.94 g / m ^2.

(Preparation of coating solution for protective layer)
(1) Preparation of pigment dispersion After adding 280 g of aluminum hydroxide (trade name “Hijilite H42S” manufactured by Showa Denko KK) surface-treated with stearic acid as a pigment to 900 g of water, the mixture was stirred for 3 hours. The dispersion aid (trade name “Poise 532A” manufactured by Kao Corporation) 8.5 g, 10% polyvinyl alcohol aqueous solution (trade name “PVA105” manufactured by Kuraray Co., Ltd.) 300 g, 2% adjusted to the following 75 g of an aqueous solution of the compound represented by the structural formula [100] was added and dispersed with a sand mill to an average particle size of 0.33 μm, and water was added to adjust the concentration to 18% to obtain a pigment dispersion for protective layer. .

  Here, the average particle size is obtained by dispersing the test solution in which the pigment to be used is dispersed in the presence of a dispersant and diluted to 0.5% by adding water to the pigment dispersion immediately after the dispersion. The sample was poured into warm water and adjusted so that the light transmittance was 72 ± 1%, and then subjected to ultrasonic treatment for 30 seconds, and a laser diffraction particle size distribution measuring apparatus (trade name “ The average particle diameter of pigment particles corresponding to 50% volume of all pigments measured by LA700 "), and the average particle diameters described below all represent average particle diameters measured by the same method.

(2) Preparation of Lubricant Dispersion To 280 g of water, 110 g of glycerin tri-12-hydroxystearate (trade name “K3 Wax 500” manufactured by Kawaken Fine Chemical Co., Ltd.) as a lubricant was added and stirred for 3 hours. Dispersion aid (trade name “Poise 532A” manufactured by Kao Corporation) 3 g, 10% polyvinyl alcohol aqueous solution (trade name “MP103” manufactured by Kuraray Co., Ltd.) 340 g, and the above structural formula adjusted to 2% [ 100] of an aqueous solution of a compound represented by [100] was added and dispersed with a sand mill to an average particle size of 0.26 μm, and water was added thereto to adjust to 18% to obtain a lubricant dispersion for protective layer. Here, the concentration of glycerin tri-12-hydroxystearate, which is a lubricant, is 13.6%.

(3) Preparation of coating solution for protective layer 430 g of 5% polyvinyl alcohol (trade name “PVA124C” manufactured by Kuraray Co., Ltd.), 5 g of 72% aqueous sodium dodecylbenzenesulfonate, acetylene glycol surfactant (Nisshin Chemical ( Co., Ltd. product name “Surfinol 104”) 50% liquid 5.5 g, “Surflon S131S” (Asahi Glass Co., Ltd.) 10 g, melting point 35 ° C. polyoxyethylene alkyl ether phosphate (Daiichi Kogyo Seiyaku) "Plysurf A217E" manufactured by KK) 2 g, 245 g of the 18% pigment dispersion obtained above, 10 g of the 18% lubricant dispersion obtained above, 20.5% zinc stearate dispersion (Chukyo Yushi) 21 g, 18% stearic acid dispersion (trade name “Cerosol 920” manufactured by Chukyo Yushi Co., Ltd.) 3 1 g, 35% silicone oil aqueous dispersion (trade name “BY22-840” manufactured by Toray Dow Corning Co., Ltd.) 41.5 g, 5% styrene maleic acid copolymer ammonium salt aqueous solution (manufactured by Arakawa Chemical Co., Ltd.) 110 g of trade name “Polymalon 385”), 53 g of 20% colloidal silica (trade name “Snowtex” manufactured by Nissan Chemical Co., Ltd.), 70 g of 4% boric acid aqueous solution, 30 g of 2% acetic acid aqueous solution, represented by the above structural formula [002] 22 g of a 50% aqueous solution of the above compound was mixed. Water was added to this to adjust the concentration to 12% to obtain the intended protective layer coating solution.

(Preparation of coating solution for thermosensitive recording layer)
According to the following procedure, a microcapsule liquid and an electron-accepting compound emulsified dispersion each containing an electron-donating dye precursor as a core substance were prepared.
(1) Preparation of microcapsule A solution As an electron-donating dye precursor, 63.7 g of a compound represented by the following structural formula [201], 21 g of a compound represented by the following structural formula [208], and the following structural formula [203 10.8 g of the compound represented by the following structural formula [204], 5.8 g of the compound represented by the following structural formula [205], represented by the following structural formula [206] 2.7 g of the compound and 2.6 g of a compound represented by the following structural formula [207] as a UV absorber were added to 110 g of ethyl acetate, heated to 70 ° C. and dissolved, and then cooled to 45 ° C. To this, 70 g of capsule wall material (trade name “Takenate D140N” manufactured by Mitsui Takeda Chemical Co., Ltd.) was added and mixed.
This solution was added to an aqueous phase of 300 g of a 5.9% aqueous polyvinyl alcohol solution (trade name “MP-103” manufactured by Kuraray Co., Ltd.), and then rotated using an ace homogenizer (manufactured by Nippon Seiki Co., Ltd.). Emulsification and dispersion were performed at 15000 rpm. After adding 275 g of water and 6.5 g of tetraethylenepentamine to the obtained emulsion, an encapsulation reaction was performed at a temperature of 60 ° C. for 4 hours, and finally the concentration was adjusted to 25% with water to obtain an average particle size. A microcapsule A solution having a diameter of 0.8 μm was obtained.

(2) Preparation of microcapsule B solution As an electron-donating dye precursor, 54.5 g of a compound represented by the following structural formula [201], 14.8 g of a compound represented by the following structural formula [208], and the following structural formula 10.5 g of a compound represented by [203], 6.4 g of a compound represented by the following structural formula [204], 3.4 g of a compound represented by the following structural formula [205], and represented by the following structural formula [206] 0.5 g of the compound obtained and 2.1 g of the compound represented by the following structural formula [207] as a UV absorber were added to 110 g of ethyl acetate, heated to 70 ° C. and dissolved, and then cooled to 45 ° C. did. To this, 65.5 g of capsule wall material (trade name “Takenate D127N” manufactured by Mitsui Takeda Chemical Co., Ltd.) was added and mixed.
This solution was added to an aqueous phase of 273 g of a 5.9% aqueous polyvinyl alcohol solution (trade name “MP-103” manufactured by Kuraray Co., Ltd.), and then rotated using an ace homogenizer (manufactured by Nippon Seiki Co., Ltd.). Emulsification and dispersion were performed at 15000 rpm. After adding 275 g of water and 5.70 g of tetraethylenepentamine to the obtained emulsified liquid, an encapsulation reaction was performed at a temperature of 60 ° C. for 4 hours, and finally the concentration was adjusted to 28% with water. A microcapsule B solution having a diameter of 0.3 μm was obtained.

(3) Preparation of an electron-accepting compound emulsion dispersion As an electron-accepting compound, 220 g of a compound represented by the following structural formula [301], 80 g of a compound represented by the following structural formula [302], and the following structural formula [303] A compound 26g represented by the following structural formula [304], a compound 4.8g represented by the following structural formula [305], and a compound 41g represented by the following structural formula [306]. It was added to 160 g of ethyl acetate together with 10 g of cresyl phosphate and 5 g of diethyl maleate and dissolved by heating to 70 ° C. This solution is represented by 1340 g of water, 43.5 g of polyvinyl alcohol (trade name “PVA217C” manufactured by Kuraray Co., Ltd.), 29 g of polyvinyl alcohol (trade name “PVA205C” manufactured by Kuraray Co., Ltd.), represented by the following structural formula [401]. 110 g of a 2% aqueous solution of the compound and 110 g of a 2% aqueous solution of the compound represented by the following structural formula [402] are added to the mixed aqueous phase, and then rotated using an ace homogenizer (manufactured by Nippon Seiki Co., Ltd.). The mixture was emulsified and dispersed so that the average particle size became 0.7 μm at several 10000 rpm, and adjusted with water so that the concentration became 22%, and an electron-accepting compound emulsified dispersion was obtained.

(4) Preparation of thermosensitive recording layer coating solution (A) 160 g of the above microcapsule A solution (solid content concentration 25%), 30 g of the above microcapsule B solution (solid content concentration 28%), and the above-mentioned electron-accepting compound emulsion dispersion (Solid content 22%) 710 g, 7.2 g of 50% aqueous solution of the compound represented by the structural formula [002], and colloidal silica (trade name “Snowtex O” manufactured by Nissan Chemical Co., Ltd.) 25.5 g Were mixed and adjusted to a concentration of 21.5% with water to prepare the desired thermal recording layer coating solution (A).

(5) Preparation of thermosensitive recording layer coating liquid (B) 60 g of the above microcapsule A liquid (solid content concentration 25%), 110 g of the above microcapsule B liquid (solid content concentration 28%), and the above-mentioned electron-accepting compound emulsion dispersion (Solid content 22%) 725 g, a 50% aqueous solution of the compound represented by the structural formula [002] 6.5 g, and colloidal silica (trade name “Snowtex O” manufactured by Nissan Chemical Co., Ltd.) 23.5 g Were mixed and adjusted to a concentration of 21.5% with water to prepare the desired thermal recording layer coating solution (B).

(Preparation of coating solution for intermediate layer)
After 14500 g of water was added to 1000 g of lime-processed gelatin and dissolved, a 5% solution of di-2-ethylhexylsulfosuccinate Na salt (“Nissan Rapizol B90” manufactured by NOF Corporation) (water / methanol = 1 / 1 volume mixed solvent) 137 g, 3.5% 1,2-benzisothiazolin-3-one aqueous solution 25 g, 3.0% sodium poly (p-vinylbenzenesulfonate) (molecular weight: about 400,000) 1080 g were added. A target intermediate layer coating solution was prepared.

(Preparation of thermal recording material)
The coating liquid for thermal recording layer (A), the coating liquid for thermal recording layer (B), and the coating liquid for intermediate layer are formed on the surface opposite to the back layer of the support with back layer from the side close to the support. In the order of the coating solution for the protective layer, simultaneous overlaying is performed by the slide bead method so that the coating amount becomes 41.3 mL / m ² , 22.5 mL / m ² , 24.7 mL / m ² , 27.5 mL / m ² , respectively. It was applied and dried to obtain a transparent thermosensitive recording material of the present invention having a thermosensitive recording layer (A), a thermosensitive recording layer (B), an intermediate layer and a protective layer on a support.
The above coating and drying conditions are as follows. The coating solution for each layer was adjusted to a temperature range of 33 ° C to 37 ° C. The coating speed was set to 160 m / min, the distance between the coating die tip and the support was set to 0.10 to 0.30 mm, and the pressure in the decompression chamber was set to 200 to 1000 Pa lower than the atmospheric pressure. The support was neutralized with an ion wind before coating. In the subsequent initial drying zone, after drying with wind at a temperature of 45 ° C. to 55 ° C. and a dew point of 0 to 5 ° C., it is transported in a non-contact manner, and the dry bulb temperature is 30 to 45 ° C. It dried with the dry wind of wet-bulb temperature 17-23 degreeC, and humidity was adjusted at 40 to 60% of humidity at 25 degreeC after drying.
Here, the gelatin coating amount of the intermediate layer on the heat-sensitive recording layer side (coloring surface) is 1.50 g / m ² .

(Example 2)
Example 1 except that the compound represented by the structural formula [208] used in the preparation of the microcapsule A liquid and the B liquid in Example 1 was changed to the compound represented by the following structural formula [209]. The thermosensitive recording material of the present invention was produced in the same manner as described above.

(Example 3)
Example 1 except that the compound represented by the structural formula [208] used in the preparation of the microcapsule A liquid and the B liquid in Example 1 was changed to the compound represented by the following structural formula [210]. The thermosensitive recording material of the present invention was produced in the same manner as described above.

(Comparative Example 1)
Example 1 except that the compound represented by the structural formula [208] used in the preparation of the microcapsule A liquid and the B liquid in Example 1 was changed to the compound represented by the following structural formula [202]. The thermosensitive recording material of the present invention was produced in the same manner as described above.

(Measurement of chromaticity and image storage stability test)
Each thermal recording material obtained as described above was subjected to OD = 0.5 for chromaticity measurement using a thermal head (trade name: KGT, 260-MPH8, manufactured by Kyocera Corporation) with a head pressure of 10 kg / cm ^2. Samples were prepared by solid printing with OD = 1.0. The chromaticity at each print density of the sample was measured using a spectroscan transmission manufactured by Gretag Macbeth under the conditions of a tungsten lamp F5 light source, a visual field of 2 °, and a colorimetric CIE-L ^* a ^* b ^* .
The prepared sample was stored in an oven at 45 ° C. and 60% RH for 7 days, and the chromaticity at each printing density of the sample after storage was measured in the same manner as described above.
The results of obtaining the a ^* and b ^* values and the distance between two points of chromaticity before and after storage on the a ^* and b ^* planes in each measurement, and the result of visual color change are shown.

  From the results in Table 1 above, it can be seen that all of the heat-sensitive recording materials of the examples have excellent storage stability and a small change in hue before and after storage, while maintaining a favorable hue as compared with the comparative example.

Claims (5)

A heat-sensitive recording material having a heat-sensitive recording layer comprising a microcapsule encapsulating a colorless or light-colored electron-donating dye precursor and an electron-accepting compound on a support, wherein the electron-donating dye precursor is A heat-sensitive recording material comprising at least a compound represented by the following general formula (I) and a compound represented by the general formula (II).

[In general formula (I) and general formula (II), R < ¹ >, R < ² > and R < ⁷ >, R < ⁸ > represents an alkyl group. R ^{3 to} R ⁶ and R ⁹ represent a hydrogen atom or an alkyl group. In addition, the total carbon number of the substituent represented by R < ¹ > -R < ⁶ > is 8 or more. ]   2. The heat-sensitive recording material according to claim 1, wherein the electron-accepting compound includes at least a metal salt of a salicylic acid derivative and a phenol derivative.   The thermosensitive recording material according to claim 1 or 2, wherein the capsule wall of the microcapsule is made of polyurethane and / or polyurea resin. The thermosensitive recording layer added with polyvinyl alcohol on the support, the intermediate layer added with a water-soluble binder, and the protective layer added with polyvinyl alcohol in this order. The heat-sensitive recording material according to any one of the above.   The heat-sensitive recording material according to claim 1, wherein the support is a polyethylene terephthalate film having a thickness of 100 μm or more.