JP2006021500A - Heat-sensitive recording material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-sensitive recording material with almost no change of color developing density due to preservation. <P>SOLUTION: The heat-sensitive recording material has a heat-sensitive recording layer, which at least includes color developing components and a binder, on a support. At least one of the color developing components is encapsuled in a microcapsule. The heat-sensitive recording layer includes at least one kind of sugar alcohol outside the microcapsule. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat-sensitive recording material, and more particularly, to a heat-sensitive recording material with little color density change due to storage.

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. ing.
As the 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, a material using a reaction between a diazonium salt compound and a coupler, etc. are often used. Are known.

  A diazonium salt compound is a compound having a very high chemical activity, reacts with a compound called a coupling component having a phenol derivative or an active methylene group, easily forms an azo dye, and also has photosensitivity. Decomposes by light irradiation and loses its activity. For this reason, diazonium salt compounds have been used for a long time as optical recording materials represented by diazocopy (see Non-Patent Document 1).

  Furthermore, by utilizing the property of decomposing by light and losing activity, diazonium salt compounds have recently been applied to recording materials that require image fixing. As representative examples, diazonium salt compounds and coupling components are used. There has been proposed a so-called photo-fixing type thermosensitive recording material in which a recording material provided with a recording layer is heated and reacted in accordance with an image signal to form an image and then irradiated with light to fix the image (for example, non-fixing type thermosensitive recording material). Patent Document 2).

  However, these recording materials using a diazonium salt compound as a color forming component have a very high chemical activity of the diazonium salt compound, and the diazonium salt compound gradually decomposes and loses its reactivity even in the dark. Therefore, there is a drawback that the shelf life as a recording material is short. Further, in the background portion which is a non-image portion, the residual diazonium salt compound is decomposed at the time of photofixing, and the non-image portion is colored due to the generation of the colored decomposition product (stain). Further, even in a completed image after fixing, the non-image portion has low light resistance, and there is a disadvantage that coloring is increased when left for a long time under sunlight or a fluorescent lamp.

  Various methods have been proposed as means for improving the instability of the diazonium salt compound. One of the most effective means is a method of encapsulating the diazonium salt compound in a microcapsule. By microencapsulating the diazonium salt compound in this way, the diazonium salt compound is isolated from those that promote decomposition such as water and base, so that the decomposition is remarkably suppressed, and the shelf life of the recording material using this is also reduced. Greatly improved (see Non-Patent Document 3).

  A general method for encapsulating a diazonium salt compound in a microcapsule is to dissolve the diazonium salt compound in a hydrophobic solvent (oil phase) and add it to an aqueous solution (water phase) in which a water-soluble polymer is dissolved. In addition, the monomer or prepolymer that becomes the microcapsule wall material is added to either or both of the oil phase and the water phase so that the polymerization reaction occurs at the interface between the oil phase and the water phase. Or by depositing a polymer to form a wall of a polymer compound to form microcapsules (see, for example, Non-Patent Documents 4 and 5).

However, even with a heat-sensitive recording material using such microcapsules, the color density may change upon storage.
Edited by the Japan Photographic Society, "Basics of Photographic Engineering-Non-Silver Salt Photo Edition", Corona (1982) P89-P117, P182-P201 Koji Sato et al. Journal of the Institute of Image Electronics Engineers of Japan, Vol. 11 No. 4 (1982) P290-296 Tomomasa Usami et al. Electrophotographic Society of Japan Vol. 26 No. 2 (1987) P115-125 Kondo Asashi, "Microcapsule" Nikkan Kogyo Shimbun (published in 1970) Kondo et al., "Microcapsule" Sankyo Publishing (published in 1977)

  Accordingly, an object of the present invention is to provide a heat-sensitive recording material in which the color density change due to storage is small.

In view of such circumstances, the present inventor has conducted extensive research and found that the above-mentioned problems can be solved by incorporating a sugar alcohol into the heat-sensitive recording layer, thereby completing the present invention.
That is, the present invention provides the following.

<1> A thermosensitive recording material having a thermosensitive recording layer containing at least a color forming component and a binder on a support, wherein at least one of the color developing components is encapsulated in a microcapsule, and the thermosensitive recording layer is the micro recording layer. A heat-sensitive recording material comprising at least one sugar alcohol outside the capsule.

<2> The heat-sensitive recording material according to <1>, wherein the binder is gelatin.
<3> The thermosensitive recording material according to <1> or <2>, wherein the thermosensitive recording layer contains a diazonium salt compound and a coupler as the color forming component.

  According to the present invention, it is possible to provide a heat-sensitive recording material with little change in color density due to storage.

Hereinafter, the heat-sensitive recording material of the present invention will be described in detail.
The thermosensitive recording material of the present invention is a thermosensitive recording material having a thermosensitive recording layer containing at least a color developing component and a binder on a support, wherein at least one of the color developing components is encapsulated in a microcapsule, and the thermosensitive recording material is provided. The recording layer contains at least one sugar alcohol outside the microcapsules.

(Coloring component)
As the color-forming component, any composition can be used as long as it has excellent transparency when not processed and has a property of rapidly coloring when heated. Examples of such a coloring component include a so-called two-component coloring component that contains a substantially colorless coloring component A and a substantially colorless coloring component B that reacts with the coloring component and develops color. However, from the viewpoint of storage stability and background fogging, the color developing component A or the color developing component B is preferably in the form of being encapsulated in a microcapsule. The following (a) to (m) are mentioned as the combination of the two components constituting the two-component thermosensitive recording layer.

(A) a combination of an electron-donating dye precursor and an electron-accepting compound (b) a combination of a diazonium salt compound and a coupler (c) an organometallic salt such as silver behenate or silver stearate, protocatechinic acid, spiroindane (D) A combination of a long-chain aliphatic salt such as ferric stearate or ferric myristate with a phenol such as gallic acid or ammonium salicylate (e) Acetic acid or stearin Combination of organic acid heavy metal salt such as acid, salt with nickel, cobalt, lead, copper, iron, mercury, silver etc. and alkaline earth metal sulfide such as calcium sulfide, strontium sulfide, potassium sulfide etc. Or a combination of the organic acid heavy metal salt and an organic chelating agent such as s-diphenylcarbazide or diphenylcarbazone. (F) Silver sulfide, lead sulfide, sulfide A combination of a (heavy) metal sulfate such as silver or sodium sulfide and a sulfur compound such as Na-tetrathionate, sodium thiosulfate or thiourea (g) an aliphatic ferric salt such as ferric stearate; A combination with an aromatic polyhydroxy compound such as 3,4-dihydroxytetraphenylmethane (h) an organic noble metal salt such as silver oxalate and mercury oxalate, and an organic polyhydroxy compound such as polyhydroxy alcohol, glycerin and glycol (I) Combination of an aliphatic ferric salt such as ferric pelargonate and ferric laurate and a thiocesylcarbamide or isothiocecilcarbamide derivative (j) Lead caproate, lead pelargonate, behen Combinations of organic acid lead salts such as lead acid and thiourea derivatives such as ethylenethiourea and N-dodecylthiourea (k) ferric stearate, steer A combination of a higher fatty acid heavy metal salt such as copper acid and a zinc dialkyldithiocarbamate (l) a compound that forms an oxazine dye such as a combination of resorcin and a nitroso compound (m) a formazan compound and a reducing agent and / or a metal salt Combination with

  Among the above, the thermosensitive recording layer in the present invention includes, as a color forming component, (a) a combination of an electron donating dye precursor and an electron accepting compound, or (b) a combination of a photodegradable diazo compound and a coupler. It is preferable to use (b) a combination of a photodegradable diazo compound and a coupler.

Next, (a) and (b), which are preferable combinations of coloring components, will be described in detail below.
(A) Combination of electron-donating dye precursor and electron-accepting compound The electron-donating dye precursor preferably used in the present invention is not particularly limited as long as it is substantially colorless. Or has a property of accepting a proton such as an acid to develop a color, in particular, having a partial skeleton such as lactone, lactam, sultone, spiropyran, ester, amide, Those which are colorless compounds in which these partial skeletons are opened or cleaved when contacted are preferred.

  Examples of the electron-donating dye precursor include triphenylmethane phthalide compounds, fluoran compounds, phenothiazine compounds, indolyl phthalide compounds, leucooramine compounds, rhodamine lactam compounds, triphenylmethane compounds. Examples thereof include compounds, triazene compounds, spiropyran compounds, fluorene compounds, pyridine compounds, pyrazine compounds.

Specific examples of the phthalides include compounds described in U.S. Reissue Patent No. 23024, U.S. Pat. Nos. 3491111, 3491112, 3491116, 3509174, and the like. .
Specific examples of the fluorans are described in 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 the like. Compounds.
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 U.S. Pat. Nos. 3,775,424, 3,853,869 and 4,246,318.
Specific examples of the fluorene compound include compounds described in Japanese Patent Application No. 61-240989.
Among these, black-colored 2-arylamino-3- [H, halogen, alkyl, or alkoxy-6-substituted aminofluorane] is particularly preferably used.

  Specifically, for example, 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-dioctylaminofluorane, 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-isoamylaminophen Oran, 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-ethoxypropylamino Fluorane, 2-anilino-3-methyl-6-N-ethyl-N-γ-ethoxypropylaminofluorane, 2-anilino 3-methyl -6-N-ethyl--N-.gamma. propoxypropyl aminofluoran like.

Examples of the electron-accepting compound that reacts with the electron-donating dye precursor include acidic compounds such as phenol compounds, organic acids or metal salts thereof, and oxybenzoic acid esters, and examples thereof include those disclosed in JP-A-61-291183. And compounds described in Japanese Patent Publication No.
Specifically, 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′-hydroxyphenyl) -2-methyl-pentane, 1, -Bis (4'-hydroxyphenyl) -2-ethyl-hexane, 1,1-bis (4'-hydroxyphenyl) dodecane, 1,4-bis (p-hydroxyphenylcumyl) benzene, 1,3-bis Bisphenols such as (p-hydroxyphenylcumyl) benzene, bis (p-hydroxyphenyl) sulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, bis (p-hydroxyphenyl) acetic acid benzyl ester;

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 preferred); 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. Moreover, these electron-accepting compounds may be used individually by 1 type, and may use 2 or more types together.
The amount of the electron-accepting compound used is based on 1 part by mass of the electron-donating dye precursor.
1-20 mass parts is preferable.

(B) Combination of diazonium salt compound and coupler As the diazonium salt compound, a photodegradable diazo compound or the like can be used.
This photodegradable diazo compound is a compound that causes a coupling reaction with a coupler, which will be described later, and develops a desired hue. It decomposes when receiving light in a specific wavelength region before the reaction, and is It is a diazonium salt compound that has no coloring ability even in the presence of a ring component.
The hue in this color developing system is determined by the diazo dye produced by the reaction of the photodegradable diazo compound and the coupler. Therefore, by changing the chemical structure of the photodegradable diazo compound or coupler compound, the color hue can be easily changed, and depending on the combination, any color hue can be obtained.

Examples of the photodegradable diazo compound preferably used in the present invention include aromatic diazo compounds, and specifically include aromatic diazonium salts, diazosulfonate compounds, diazoamino compounds and the like.
Preferred examples of the aromatic diazonium salt include, but are not limited to, compounds represented by the following structural formula. The aromatic diazonium salt is preferably used because it is excellent in photofixability, generates little colored stain after fixing, and has 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 recently, and each diazonium salt is obtained by treating 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, any coupler capable of coupling with the diazonium salt compound can be used as long as it forms a dye by coupling with the diazonium salt compound in a basic atmosphere and / or a neutral atmosphere. All so-called 4-equivalent couplers for silver halide photographic materials can be used as couplers. These can be selected according to the target hue. For example, there are so-called active methylene compounds having a methylene group next to a carbonyl group, phenol derivatives, naphthol derivatives, and the like. Specific examples include the following, which are used within the scope of the object of the present invention.

  Examples of the coupler include resorcin, phloroglucin, 2,3-dihydroxynaphthalene, sodium 2,3-dihydroxynaphthalene-6-sulfonate, 1-hydroxy-2-naphthoic acid morpholinopropylamide, 2-hydroxy-3-naphthalene. Sodium sulfonate, 2-hydroxy-3-naphthalenesulfonic acid anilide, 2-hydroxy-3-naphthalenesulfonic acid morpholinopropylamide, 2-hydroxy-3-naphthalenesulfonic acid-2-ethylhexyloxypropylamide, 2-hydroxy-3 -Naphthalenesulfonic acid-2-ethylhexylamide, 5-acetamido-1-naphthol, 1-hydroxy-8-acetamidonaphthalene-3,6-disulfonic acid sodium salt, 1-hydroxy-8-acetamido Talen-3,6-disulfonic acid dianilide, 1,5-dihydroxynaphthalene, 2-hydroxy-3-naphthoic acid morpholinopropylamide, 2-hydroxy-3-naphthoic acid octylamide, 2-hydroxy-3-naphthoic acid anilide, 5,5-dimethyl-1,3-cyclohexanedione, 1,3-cyclopentanedione, 5- (2-n-tetradecyloxyphenyl) -1,3-cyclohexanedione, 5-phenyl-4-methoxycarbonyl -1,3-cyclohexanedione, 5- (2,5-di-n-octyloxyphenyl) -1,3-cyclohexanedione,

N, N′-dicyclohexylbarbituric acid, N, N′-di-n-dodecylbarbituric acid, Nn-octyl-N′-n-octadecylbarbituric acid, N-phenyl-N ′-(2, 5-di-n-octyloxydiphenyl) barbituric acid, N, N′-bis (octadecyloxycarbonylmethyl) barbituric acid, 1-phenyl-3-methyl-5-pyrazolone, 1- (2,4,6 -Trichlorophenyl) -3-anilino-5-pyrazolone, 1- (2,4,6-trichlorophenyl) -3-benzamido-5-pyrazolone, 6-hydroxy-4-methyl-3-cyano-1- (2 -Ethylhexyl) -2-pyridone, 2,4-bis- (benzoylacetamido) toluene, 1,3-bis- (pivaloylacetamidomethyl) benzene, benzo L-acetonitrile, thenoylacetonitrile, acetoacetanilide, benzoylacetanilide, pivaloylacetanilide, 2-chloro-5- (Nn-butylsulfamoyl) -1-bivaloylacetamidobenzene, 1- (2-ethylhexyloxypropyl) ) -3-Cyano-4-methyl-6-hydroxy-1,2-dihydropyridin-2-one, 1- (dodecyloxypropyl) -3-acetyl-4-methyl-6-hydroxy-1,2-dihydropyridine- 2-one, 1- (4-n-octyloxyphenyl) -3-tert-butyl-5-aminopyrazole and the like can be mentioned.

  For details of the coupler, JP-A-4-201483, JP-A-7-223367, JP-A-7-223368, JP-A-7-323660, Japanese Patent Application No. 5-278608, Japanese Patent Application No. 5-297024, Japanese Patent Application No. 6-18669, Japanese Patent Application No. 6-18670, Japanese Patent Application No. 7-316280, Japanese Patent Application No. 8-027095, Japanese Patent Application No. 8-027096, Japanese Patent Application No. 8-030799, Japanese Patent Application No. 8-12610, Japanese Patent Application No. 8-132394, Japanese Patent Application No. 8-358755, Japanese Patent Application No. 8-358756, Japanese Patent Application No. 9-069990, and the like.

Of the couplers described above, a compound represented by the following general formula (1) or a tautomer thereof is preferable.
E ¹ —CH ₂ —E ² general formula (1)
Here, E ¹ and E ² each independently represent an electron-withdrawing group, and E ¹ and E ² may be bonded to each other to form a ring.

The electron-withdrawing group represented by E ¹ or E ² means a substituent having a positive Hammett σ _p value, which may be the same or different. For example, an acetyl group, Propionyl group, pivaloyl group, chloroacetyl group, trichloroacetyl group, trifluoroacetyl group, 1-methylcyclopropylcarbonyl group, 1-ethylcyclopropylcarbonyl group, 1-benzylcyclopropylcarbonyl group, benzoyl group, 4-methoxybenzoyl Group, acyl group such as thenoyl group; oxycarbonyl group such as methoxycarbonyl group, ethoxycarbonyl group, 2-methoxyethoxycarbonyl group, 4-methoxyphenoxycarbonyl group; carbamoyl group, N, N-dimethylcarbamoyl group, N, N -Diethylcarbamoyl group, N-phenylcarbamoyl Carbamoyl groups such as N- [2,4-bis (pentyloxy) phenyl] carbamoyl group, N- [2,4-bis (octyloxy) phenyl] carbamoyl group, morpholinocarbonyl group; methanesulfonyl group, benzenesulfonyl group Alkylsulfonyl group such as toluenesulfonyl group or arylsulfonyl group; phosphono group such as diethylphosphono group; benzoxazol-2-yl group, benzothiazol-2-yl group, 3,4-dihydroquinazolin-4-one- Preferred examples include a heterocyclic group such as a 2-yl group and a 3,4-dihydroquinazolin-4-sulfon-2-yl group; a heterocyclic group; a nitro group; an imino group; and a cyano group.

The electron-withdrawing group represented by E ¹ or E ² may be bonded to form a ring, and the ring formed is preferably a 5-membered to 6-membered carbocyclic or heterocyclic ring.
The amount of the coupler used is preferably 0.1 to 30 parts by mass with respect to 1 part by mass of the diazonium salt compound.

In the present invention, an organic base is preferably added as a basic substance for the purpose of promoting the coupling reaction between the diazonium salt compound and the coupler.
Examples of the organic base include tertiary amines, piperidines, piperazines, amidines, formamidines, pyridines, guanidines, morpholines, nitrogen-containing compounds, and the like. JP-A-46806, JP-A-62-20082, JP-A-57-169745, JP-A-60-94381, JP-A-57-123086, JP-A-60-49991, Preferred examples include those described in JP-B-2-24916, JP-B-2-28479, JP-A-60-165288, and JP-A-57-185430. These may be used alone or in combination of two or more.

  Among the above, specifically, N, N′-bis (3-phenoxy-2-hydroxypropyl) piperazine, N, N′-bis [3- (p-methylphenoxy) -2-hydroxypropyl] piperazine, N, N′-bis [3- (p-methoxyphenoxy) -2-hydroxypropyl] piperazine, N, N′-bis (3-phenylthio-2-hydroxypropyl) piperazine, N, N′-bis [3- (Β-naphthoxy) -2-hydroxypropyl] piperazine, N-3- (β-naphthoxy) -2-hydroxypropyl-N′-methylpiperazine, 1,4-bis {[3- (N-methylpiperazino) -2 Piperazines such as -hydroxy] propyloxy) benzene, N- [3- (β-naphthoxy) -2-hydroxy] propylmorpholine, 1,4-bis (3- Morpholines such as morpholino-2-hydroxy-propyloxy) benzene and 1,8-bis (3-morpholino-2-hydroxy-propyloxy) benzene, N- (3-phenoxy-2-hydroxypropyl) piperidine, N- Piperidines such as dodecylpiperidine and guanidines such as triphenylguanidine, tricyclohexylguanidine and dicyclohexylphenylguanidine are preferred.

  As the usage-amount of the said organic base, 0.1-30 mass parts is preferable with respect to 1 mass part of diazonium salt compounds. When the amount of the organic base used is 0.1 to 30 parts by mass, a sufficient color density is obtained and the decomposition of the diazonium salt compound is not accelerated.

(Micro capsule)
In the present invention, at least one of the coloring components is encapsulated in microcapsules. Further, when the color-forming component is a preferred embodiment (a) a combination of an electron-donating dye precursor and an electron-accepting compound, or (b) a combination of a diazonium salt compound and a coupler, The dye precursor or diazonium salt compound is preferably encapsulated in microcapsules.

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.
Hereinafter, a preferred embodiment in which a combination of a diazonium salt compound and a coupler is used as the color forming component and the diazonium salt compound is encapsulated in a microcapsule will be described.
In the production of the microcapsules according to the present invention, an oil phase prepared by dissolving or dispersing a diazonium salt compound serving as a capsule core in a hydrophobic organic solvent is introduced into an aqueous phase in which a water-soluble polymer is dissolved. , And emulsifying and dispersing by a stirring means such as a homogenizer, preparing an emulsion, and then heating to cause a polymer formation reaction at the oil droplet interface, thereby forming a microcapsule wall made of a polymer substance. It is preferable to adopt a legal method.

  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, polyisocyanate such as diisocyanate, triisocyanate, tetraisocyanate, polyisocyanate prepolymer, polyamine such as diamine, triamine, tetraamine, etc., prepolymer having two or more amino groups, A microcapsule wall can be easily formed by reacting piperazine or a derivative thereof, 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, for example, water-soluble polyisocyanate and a second substance that reacts therewith to form a capsule wall (for example, acid chloride, polyamine, or polyol). It can be prepared by mixing in an aqueous polymer solution (aqueous phase) or an oily medium (oil phase) to be encapsulated, emulsifying and dispersing them, and then heating. Details of the method for producing the composite wall comprising polyurea and polyamide are described in JP-A-58-66948.

As the polyisocyanate compound, a compound having a trifunctional or higher functional isocyanate group is preferable, but a bifunctional isocyanate compound may be used in combination.
Specifically, xylene diisocyanate and hydrogenated products thereof, hexamethylene diisocyanate, tolylene diisocyanate and hydrogenated products thereof, and diisocyanates such as isophorone diisocyanate are used as main raw materials, and these dimers or trimers (burette or isocyanate). Nurate), other polyfunctional adducts such as trimethylolpropane polyols and bifunctional isocyanates such as xylylene diisocyanate, adducts of trimethylolpropane polyols and xylylene diisocyanate and other bifunctional isocyanates Examples thereof include a compound in which a high molecular weight compound such as polyether having active hydrogen such as polyethylene oxide is introduced, and a formalin condensate of benzene isocyanate.
The compounds described in JP-A-62-212190, JP-A-4-26189, JP-A-5-317694, and Japanese Patent Application No. 8-268721 are also preferable.

  The polyisocyanate is preferably added so that the average particle diameter 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.

In preparing the oil phase in the production of microcapsules, the diazonium salt compound is usually used by dissolving in a hydrophobic organic solvent or dispersing in a solvent. The hydrophobic organic solvent used in this case 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 dispersion.

Examples of the esters include phosphate esters such as triphenyl phosphate, tricresyl phosphate, butyl phosphate, octyl phosphate, cresyl phenyl phosphate; dibutyl phthalate, 2-ethylhexyl phthalate, ethyl phthalate, Phthalate esters such as octyl phthalate, butyl benzyl phthalate or diphenyl phthalate; dioctyl tetrahydrophthalate; ethyl benzoate, propyl benzoate, butyl benzoate, isopentyl benzoate, benzyl benzoate or phenyl 2-benzoyloxybenzoate Benzoic acid esters such as ethyl abietate and benzyl abietic acid; dioctyl adipate; isodecyl succinate; dioctyl azelate; oxalic acid esters such as dibutyl oxalate and dipentyl oxalate; Ethyl; maleic acid esters such as dimethyl maleate, diethyl maleate and dibutyl maleate; tributyl citrate; sorbic acid esters such as methyl sorbate, ethyl sorbate and butyl sorbate; sebacins such as dibutyl sebacate and dioctyl sebacate Acid esters; ethylene glycol esters such as formic acid monoesters and diesters, butyric acid monoesters and diesters, lauric acid monoesters and diesters, palmitic acid monoesters and diesters, stearic acid monoesters and diesters, oleic acid monoesters and diesters; triacetin Diethyl carbonate; diphenyl carbonate; ethylene carbonate; propylene carbonate; boric acid esters such as tributyl borate and tripentyl borate; These may be used alone or in combination with other hydrophobic organic solvents.
Among these, when a phosphoric acid ester, a phthalic acid ester or a benzoic acid ester is used, the stability of the emulsion becomes the best and is preferable.

  When the solubility of the diazonium salt compound, which is the core substance to be encapsulated, in the hydrophobic organic solvent is poor, 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, methylene chloride, tetrahydrofuran, and acetone. In this case, the low boiling point solvent evaporates during the encapsulation reaction and does not remain in the finished capsule. Therefore, there is no restriction | limiting in particular about the usage-amount of this low boiling-point solvent.

  The diazonium salt compound is preferably contained in the oil phase in a mass ratio of 10 to 70%, particularly preferably 20 to 50%.

Specific examples of polyols and / or polyamines that react with polyisocyanate and are preferably added to the oil phase as one of the components of the microcapsule wall include propylene glycol, glycerin, trimethylolpropane, triethanolamine, and sorbitol. And hexamethylenediamine. 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.
The polyisocyanate, polyol, reaction catalyst, polyamine for forming a part of the wall agent, etc. are well-known in the book (Keiji Iwata, Polyurethane Handbook, Nikkan Kogyo Shimbun (1987)).

  In addition, a metal-containing dye, a charge control agent such as nigrosine, or any other additive 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 the present invention, when producing the aforementioned microcapsule dispersion, the solid content concentration of the emulsion is preferably 22% or more, and more preferably 23.5% or more.
Moreover, the mixing ratio (oil phase mass / water phase mass) of the water phase and the oil phase is preferably 0.25 to 0.75, and more preferably 0.45 to 0.65.
Here, in order to stabilize the dispersion of the emulsion, a surfactant may be added to at least one of the oil phase and the water phase. A known emulsifying surfactant can be used as the surfactant. The addition amount of the surfactant is preferably 0.1 to 5%, more preferably 0.2 to 2% with respect to the mass of the oil phase.

As the surfactant to be contained in the aqueous phase, an anionic or nonionic surfactant that does not cause precipitation or aggregation by acting on the protective colloid described later can be suitably 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) and the like.

  The water-soluble polymer to be contained as a protective colloid in the aqueous phase can be appropriately selected from known anionic polymers, nonionic polymers and amphoteric polymers. Among them, for example, polyvinyl alcohol Gelatin and cellulose derivatives are preferred.

  The emulsification is a means used for normal fine particle emulsification such as high-speed stirring and ultrasonic dispersion of the oil phase and the aqueous phase, for example, a known emulsifier such as a homogenizer, a manton gorey, an ultrasonic disperser, a dissolver, a teddy mill, etc. Can be easily performed.

  It is preferable to emulsify under the condition that the temperature of the emulsified liquid in the emulsification step is 20 to 35 ° C. during the production of the microcapsules. By emulsifying and dispersing under these conditions, the problem that aggregation occurs during microcapsule preparation does not occur.

In order to promote the capsule wall formation reaction after the emulsification step, the emulsion is preferably heated to 30 to 70 ° C. Especially preferably, it is 35-50 degreeC.
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.
When performing the stirring, a stirring blade may be used. In this case, the stirring speed is preferably 2 to 17 m / s, particularly preferably 2.5 to 14 m / s, and more preferably 3 to 11 m / s.
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.

  Various additives may be added to the water phase and the oil phase to the extent that the effects of the present invention are not impaired. Examples thereof include a dispersion for preventing aggregation during the encapsulation reaction.

The heat-sensitive recording layer in the heat-sensitive recording material of the present invention contains a binder.
Specific examples of the binder in the present invention include gelatin, casein, gum arabic, polyvinyl alcohol, modified polyvinyl alcohol, a copolymer having maleic anhydride as one of the constituent components, polyacrylamide, polystyrene sulfonic acid, polyvinyl pyrrolidone, ethylene- Acrylic acid copolymers, cellulose derivatives, starch derivatives and the like can be mentioned. Among these, gelatin is particularly preferred from the viewpoint of coating suitability when simultaneously coating multiple layers.

  In addition, a latex emulsion of a hydrophobic polymer can be added to the binder in the present invention. Regarding the latex emulsion of the hydrophobic polymer, a latex emulsion described in “Emulsion Latex Handbook” (Taisei Co., 1975) or the like can be used. The emulsion latex handbook includes styrene-butadiene copolymer, carboxy-modified styrene-butadiene copolymer, acrylonitrile-butadiene copolymer and the like as latex emulsion.

The gelatin is not particularly limited, and examples thereof include alkali-treated gelatin and acid-treated gelatin. As gelatin derivatives, modified gelatin (for example, phthalated gelatin) obtained by modifying a part of the functional group of gelatin. Also mentioned.
Examples of the gelatin commercially available include # 680 gelatin, # 681 gelatin, # 690 gelatin, # 700 gelatin, # 701 gelatin, # 721 gelatin, # 750 gelatin, and # 750 manufactured by Nitta Gelatin Co., Ltd. 760 gelatin, # 810 gelatin, # 860 gelatin, and # 950 gelatin.

The binder in the present invention is contained in the aqueous phase used for producing the microcapsules.
In this case, the content of the binder is preferably 3 to 15% by mass, and more preferably 5 to 10% by mass in the aqueous phase.

The heat-sensitive recording layer in the heat-sensitive recording material of the present invention contains at least one sugar alcohol in addition to the microcapsules.
The sugar alcohol in the present invention is a monosaccharide having an aldehyde-type carbonyl group or a monosaccharide having a hemiacetal structure (that is, a monosaccharide having a potential aldehyde-type carbonyl group) having a structure in which the carbonyl group is reduced. Specific examples thereof include erythritol, D-threitol, ribitol, D-xylitol, 4-O-methyl-D-xylitol, 2-O-methyl-D-xylitol, D-arabinitol, allitol, D- Alliitol, D-glucitol (D-sorbitol), L-glucitol (L-sorbitol), D, L-glucitol (D, L-sorbitol), D-mannitol, D-iditol, paratinitol, maltitol, lactitol, D- Galactitol, heptitol, octitol D- fucitol, L- fucitol, D- rhamnitol, L- rhamnitol, D-threo-L-galacto- but Okuchitoru like, but is not limited thereto.
The sugar alcohol is preferably a sugar alcohol having 5 to 6 carbon atoms, and more preferably D-glucitol (D-sorbitol), D-mannitol, or D-xylitol.

The sugar alcohol in the present invention is contained outside the microcapsules.
The content of the sugar alcohol is preferably 1 to 100 parts by mass, more preferably 5 to 50 parts by mass, and further preferably 10 to 30 parts by mass with respect to 100 parts by mass of the bainter. preferable. When the content of the sugar alcohol is 1 to 100 parts by mass with respect to 100 parts by mass of the bainter, an effect that a change in color density due to storage is small can be further exhibited.

  In the present invention, when an electron-accepting compound or coupler is used, the electron-accepting compound and coupler are used by being dispersed in a solid using a sand mill or the like together with, for example, a water-soluble polymer, an organic base, and other coloring assistants. However, it is particularly preferred that the polymer aqueous solution (aqueous phase) containing a surfactant and / or a water-soluble polymer as a protective colloid after previously dissolved in a water-insoluble or insoluble high-boiling organic solvent. And an emulsified dispersion emulsified with a homogenizer or the like. In this case, a low boiling point solvent can be used as a dissolution aid, if necessary. The sugar alcohol in the present invention is preferably used by being contained in this emulsified dispersion. Furthermore, the electron-accepting compound or coupler and the organic base can be emulsified and dispersed separately, or mixed and then dissolved in a high-boiling organic solvent to be emulsified and dispersed. A preferable emulsified and dispersed particle size is 1 μm or less.

  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 these, from the viewpoint of emulsion stability of the emulsified dispersion, esters are preferable, and tricresyl phosphate is particularly preferable. The above oils can be used together with other oils.

  A low-boiling auxiliary solvent can also be added to the organic solvent as a dissolution aid, and examples of the auxiliary solvent include ethyl acetate, isopropyl acetate, butyl acetate, and methylene chloride. Depending on the case, it is possible to use only a low-boiling point auxiliary solvent without containing a high-boiling point oil.

(Other ingredients)
In addition to the above-described components, a color developing aid can be added to the heat-sensitive recording layer for the purpose of accelerating the color developing reaction, that is, for rapid and complete thermal printing with low energy. Here, the color development aid is a substance that increases the color density during heat recording or controls the color development temperature, lowers the melting point of couplers, basic substances or diazonium salts, and softens the capsule wall. It is for making it the conditions which a diazonium salt, a basic substance, a coupler, etc. react easily by the effect | action which can reduce this.
Examples of the coloring aid include phenol derivatives, naphthol derivatives, alkoxy-substituted benzenes, alkoxy-substituted naphthalenes, aromatic ethers, thioethers, esters, amides, ureidos, urethanes, sulfonamide compounds, hydroxy compounds, and the like.

  The coloring aid includes a heat-melting substance. The heat-meltable substance is a substance that is solid at room temperature and has a melting point of 50 to 150 ° C. that is melted by heating, and can dissolve a diazonium salt, a coupler, or an organic base. Specific examples include carboxylic acid amides, N-substituted carboxylic acid amides, ketone compounds, urea compounds, and esters.

In the heat-sensitive recording material of the present invention, for the purpose of improving fastness to light and heat of a color image or reducing yellowing due to light of a non-printed part (non-image part) after fixing, the following publicly known It is also preferable to use an antioxidant or the like.
Examples of the antioxidant include, for example, European Patent Publication No. 223739, Publication No. 309401, Publication No. 309402, Publication No. 310551, Publication No. 310552, Publication No. 457416, and German Patent No. 3435443, JP-A-54-48535, JP-A-62-262047, JP-A-63-113536, JP-A-63-163351, JP-A-2-262654, JP-A-2-71262. JP-A-3-121449, JP-A-5-61166, JP-A-5-119449, US Pat. No. 4,814,262, US Pat. No. 4,980,275, and the like.

For the heat-sensitive recording material of the present invention, it is also effective to use various known additives already used in heat-sensitive or pressure-sensitive recording materials.
Examples of the various additives include, for example, JP-A-60-107384, JP-A-60-107383, JP-A-60-125470, JP-A-60-125471, JP-A-60-125472, and JP-A-60-287485. No. 60-287486, No. 60-287487, No. 60-287488, No. 61-160287, No. 61-185483, No. 61-2111079, No. 62-146678. Gazette, 62-146680 gazette, 62-146679 gazette, 62-282858 gazette, 63-051174 gazette, 63-898877 gazette, 63-88380 gazette, 63-088381 gazette. 63-203372, 63-224989, 63-25128 No. 63-267594, No. 63-182484, JP-A-1-239282, No. 4-29185, No. 4-291684, No. 5-188687, No. 5-188686. And JP-A-5-110490, JP-A-5-170361, JP-B-48-043294, JP-A-48-033212, and the like.

  Specifically, 6-ethoxy-1-phenyl-2,2,4-trimethyl-1,2-dihydroquinoline, 6-ethoxy-1-octyl-2,2,4-trimethyl-1,2-dihydroquinoline 6-ethoxy-1-phenyl-2,2.4-trimethyl-1,2,3,4-tetrahydroquinoline, 6-ethoxy-1-octyl-2,2,4-trimethyl-1,2,3 4-tetrahydroquinoline, nickel cyclohexaneate, 2,2-bis (4-hydroxyphenyl) propane, 1,1-bis (4-hydroxyphenyl) -2-ethylhexane, 2-methyl-4-methoxy-diphenylamine, 1 -Methyl-2-phenylindole and the like.

As addition amount of the said antioxidant or various additives, when using a diazonium salt compound as a color development component, 0.05-100 mass parts is preferable with respect to 1 mass part of diazonium salt compounds, 0.2-30 Part by mass is more preferable. Moreover, when using an electron-donating dye precursor as a color-forming component, 0.01-50 mass parts is preferable with respect to 1 mass part of electron-donating dye precursor, and 0.05-20 mass parts is more preferable.
The antioxidant and various additives may be contained in a microcapsule together with a coloring component such as a diazonium salt, or together with a coloring component such as a coupler, a basic substance, and other coloring aids as a solid dispersion. You may make it contain, you may make it an emulsion and make it contain with a suitable emulsification auxiliary | assistant, or you may make it contain in both the forms. Moreover, antioxidant or various additives may be used independently and can also be used together. Furthermore, it can also be contained in the protective layer.

The antioxidant and various additives are not necessarily added to the same layer.
When a plurality of the antioxidants and / or various additives are used in combination, they are structurally classified as anilines, alkoxybenzenes, binderd phenols, hindered amines, hydroquinone derivatives, phosphorus compounds, sulfur compounds. In addition, different structures may be combined with each other, or a plurality of the same structures may be combined.

For the purpose of reducing yellowing of the background after image recording, a free radical generator (compound that generates free radicals upon light irradiation) used in a photopolymerizable composition or the like can also be added.
Examples of the free radical generator include aromatic ketones, quinones, benzoin, benzoin ethers, azo compounds, organic disulfides, acyl oxime esters, and the like.
The addition amount of the free radical generator is preferably 0.01 to 5 parts by mass with respect to 1 part by mass of the diazonium salt compound when a diazonium salt compound is used as the color forming component.

Similarly, for the purpose of reducing yellow coloring, a polymerizable compound having an ethylenically unsaturated bond (hereinafter referred to as “vinyl monomer”) can also be used. A vinyl monomer is a compound having at least one ethylenically unsaturated bond (vinyl group, vinylidene group, etc.) in its chemical structure, and has a chemical form of monomer or prepolymer.
Examples of the vinyl monomer include unsaturated carboxylic acids and salts thereof, esters of unsaturated carboxylic acids and aliphatic polyhydric alcohols, amides of unsaturated carboxylic acids and aliphatic polyvalent amine compounds, and the like. The vinyl monomer is used in a proportion of 0.2 to 20 parts by mass with respect to 1 part by mass of the diazonium salt.
The free radical generator and the vinyl monomer can be used in a microcapsule together with a diazonium salt.
Furthermore, citric acid, tartaric acid, oxalic acid, boric acid, phosphoric acid, pyrophosphoric acid and the like can be added as an acid stabilizer.

The heat-sensitive recording layer is prepared by preparing a coating solution for forming a heat-sensitive recording layer containing a color forming component, a coupler, and if necessary, an organic base and other additives, and coating the coating solution on a support. It can be coated by drying.
The application of the coating liquid can be appropriately selected from known coating methods, and examples thereof include bar coating, blade coating, air knife coating, gravure coating, roll coating coating, spray coating, dip coating, and curtain coating. It is done. The dry coating amount of the heat sensitive recording layer is preferably 2.5 to 30 g / m ² .

  The configuration of the heat-sensitive recording layer in the heat-sensitive recording material of the present invention is not particularly limited. For example, the heat-sensitive recording layer is a single layer in which microcapsules, couplers, organic bases and the like are all contained in the same layer. Alternatively, it may be a multi-layer stacked type that is included in a separate layer. Alternatively, an intermediate layer described in Japanese Patent Application No. 59-177669 may be provided on the support, and then a heat-sensitive recording layer may be applied and formed.

  Further, as will be described later, a full-color color development mode in which a plurality of monochromatic and single thermosensitive recording layers having different hues are laminated may be used.

  In the heat-sensitive recording material of the present invention, in addition to the heat-sensitive recording layer, each layer such as an intermediate layer or a protective layer described later can contain a binder. Examples of the binder include known water-soluble polymer compounds and latexes. Can be selected as appropriate.

Examples of the water-soluble polymer compound used in each layer such as an intermediate layer or a protective layer described later include, for example, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, starch derivatives, casein, gum arabic, gelatin, and ethylene-anhydrous maleic acid. Acid copolymer, styrene-maleic anhydride copolymer, polyvinyl alcohol, silanol-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, epichlorohydrin-modified polyamide, isobutylene-maleic salicylic anhydride copolymer, polyacrylic acid, polyacrylic acid amide, etc. These modified products are exemplified.
Examples of the latex include styrene-butadiene rubber latex, methyl acrylate-butadiene rubber latex, and vinyl acetate emulsion.
Of these, hydroxyethyl cellulose, starch derivatives, gelatin, polyvinyl alcohol derivatives, polyacrylic acid amide derivatives and the like are preferable.

  Further, the heat-sensitive recording material of the present invention may contain a pigment, and examples of the pigment include organic and inorganic materials such as kaolin, calcined kaolin, talc, wax, and diatomaceous earth. , Calcium carbonate, aluminum hydroxide, magnesium hydroxide, zinc oxide, lithopone, amorphous silica, colloidal silica, calcined stone, silica, magnesium carbonate, titanium oxide, alumina, barium carbonate, barium sulfate, mica, microballoon, Examples include urea-formalin filler, polyester particles, and cellulose filler.

  In addition, various additives such as known waxes, antistatic agents, antifoaming agents, conductive agents, fluorescent dyes, surfactants, ultraviolet absorbers and their precursors can be used as necessary.

(Other layers)
A single protective layer or two or more protective layers may be provided on the thermosensitive recording layer.
Materials used for the protective layer include polyvinyl alcohol, carboxy-modified polyvinyl alcohol, vinyl acetate-acrylamide copolymer, silicon-modified polyvinyl alcohol, starch, modified starch, methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, gelatins, gum arabic, and casein , Styrene-maleic acid copolymer hydrolyzate, styrene-maleic acid copolymer half ester hydrolyzate, isobutylene-maleic anhydride copolymer hydrolyzate, polyacrylamide derivative, polyvinylpyrrolidone, polystyrene sulfonate soda, alginic acid Water-soluble polymer compounds such as soda, styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex , Latexes such as vinyl acetate emulsion.

  The water-soluble polymer compound used in the protective layer can be further improved in storage stability by crosslinking. The crosslinking agent can be appropriately selected from known crosslinking agents, and examples thereof include water-soluble initial condensates such as N-methylol urea, N-methylol melamine, and urea-formalin; dioxals such as glyoxal and glutaraldehyde. Aldehyde compounds; inorganic crosslinking agents such as boric acid and borax; polyamide epichlorohydrin and the like.

For the protective layer, known pigments, metal soaps, waxes, surfactants and the like can also be used. Moreover, you may contain a well-known ultraviolet absorber and its precursor.
The protective layer can be formed by applying a coating solution for forming a protective layer, and the coating amount is preferably 0.2 to 5 g / m ^{2 in} terms of dry coating amount, and 0.5 to ² g / m. ² is more preferable. The film thickness is preferably 0.2 to 5 μm, and more preferably 0.5 to 2 μm.
The protective layer can be provided by the above-described known coating method as in the case of forming the heat-sensitive recording layer on the support.

When the heat-sensitive recording material of the present invention is a multicolor heat-sensitive recording material having a light-fixing type heat-sensitive recording layer on a support, an intermediate layer is provided between the heat-sensitive recording layers for the purpose of preventing color mixing between the heat-sensitive recording layers. You can also
The intermediate layer is made of a water-soluble polymer compound such as gelatin, phthalated gelatin, polyvinyl alcohol, or polyvinylpyrrolidone, and may contain various additives as appropriate.

  In the case of a multicolor heat-sensitive recording material, it is desirable to further provide a light transmittance adjusting layer or protective layer, or a light transmittance adjusting layer and a protective layer as an upper layer, if necessary. The light transmittance adjusting layer is described in JP-A-9-39395, JP-A-9-39396, Japanese Patent Application No. 7-208386, and the like.

  When a component that functions as a precursor of an ultraviolet absorber is used in the light transmittance adjustment layer, it does not function as an ultraviolet absorber before irradiating light in a wavelength region necessary for fixing, so that a high light transmittance is obtained. Therefore, when fixing the light-fixing type thermosensitive recording layer, the wavelength of the region necessary for fixing can be sufficiently transmitted, and the visible light transmittance is also high, which may hinder the fixing of the thermosensitive recording layer. Absent.

  On the other hand, the precursor of the ultraviolet absorber is irradiated with light in a wavelength region necessary for photofixation (photodecomposition of diazonium salt by light irradiation) of the photofixing type thermosensitive recording layer, and then reacts with the light to absorb ultraviolet rays. To function as an agent. This ultraviolet absorber absorbs most of the light having a wavelength in the ultraviolet region and lowers its transmittance, thereby making it possible to improve the light resistance of the heat-sensitive recording material. However, since there is no visible light absorptivity, the visible light transmittance is not substantially changed.

  The light transmittance adjusting layer can be provided in at least one layer in the heat-sensitive recording material, and in particular, it is preferably formed between the heat-sensitive recording layer and the protective layer. Further, the protective layer may have the function of the light transmittance adjusting layer and may be used in combination.

(Support)
As the support usable for the heat-sensitive recording material of the present invention, any of the paper supports used for ordinary pressure-sensitive paper and heat-sensitive paper, dry or wet diazo copy paper, etc. can be used, acidic paper, Neutral paper, coated paper, plastic film laminated paper, synthetic paper, plastic films such as polyethylene terephthalate and polyethylene naphthalate can be used.

On the support, a back coat layer may be provided for the purpose of correcting the curl balance or improving the chemical resistance from the back surface. The back coat layer can be provided in the same manner as the protective layer.
Further, if necessary, an antihalation layer is provided between the support and the heat-sensitive recording layer or on the surface of the support on which the heat-sensitive recording layer is provided, and a slip layer or an antistatic layer is provided on the back surface. An adhesive layer or the like can also be provided.
Also, a label may be formed by combining release paper with an adhesive layer on the back surface of the support (the surface on which the thermosensitive recording layer is not provided).

-Image forming method-
Image formation using the heat-sensitive recording material of the present invention may be carried out by the following method when a diazonium salt compound and a scarf are contained as a color forming component. For example, the surface of the heat-sensitive recording material on which the heat-sensitive recording layer is provided is image-wise heated and printed by a heating device such as a thermal head, so that the polyurea and / or polyurethane in the layer is heated at the heating portion of the heat-sensitive recording layer. It is possible to use a method in which the capsule wall containing the material softens and becomes material permeable, and when a coupler or a basic substance (organic base) outside the capsule enters the microcapsule, the image is colored to form an image. . In this case, after color development, by further irradiating light corresponding to the absorption wavelength of the diazonium salt (photofixing), the diazonium salt undergoes a decomposition reaction and loses reactivity with the coupler, thereby fixing the image. . By performing photofixing as described above, the unreacted diazonium salt loses its activity by causing a decomposition reaction, so coloring due to density fluctuations in the formed image and the occurrence of stain in the non-image area (background area) That is, a decrease in whiteness and a decrease in image contrast accompanying the decrease can be suppressed.

Examples of the light source used for the light fixing include various fluorescent lamps, xenon lamps, mercury lamps, and the like, and it is highly efficient that the emission spectrum of these light sources substantially matches the absorption spectrum of the diazonium salt in the heat-sensitive recording material. It is preferable in that it can be fixed on the surface.
In particular, in the present invention, it is particularly preferable to use a light source having an emission center wavelength of 350 to 430 nm.

  Further, it can also be used as a light-writing heat-developable heat-sensitive recording material in which image-like writing is performed with light and heat development is performed to form an image. In this case, the printing process is performed by a light source such as a laser instead of the heating device as described above.

  Hereinafter, the heat-sensitive recording material of the present invention will be specifically described with reference to examples, but the present invention is not limited to the following examples. In the examples below, “part” means “part by mass” unless otherwise specified, and “%” means “% by mass” unless otherwise specified.

Example 1
<Preparation of aqueous solution of phthalated gelatin>
Phthalated gelatin (trade name; # 801 gelatin, Nitta Gelatin Co., Ltd.) 32 parts, 1,2-benzothiazolin-3-one (3.5% methanol solution, Daito Chemical Industry Co., Ltd.) 0 9143 parts and 367.1 parts ion-exchanged water were mixed and dissolved at 40 ° C. to obtain a phthalated gelatin aqueous solution.

<Preparation of alkali-treated gelatin aqueous solution>
25.5 parts of alkali-treated low ion gelatin (trade name; # 750 gelatin, manufactured by Nitta Gelatin Co., Ltd.), 1,2-benzothiazolin-3-one (3.5% methanol solution, Daito Chemical Industry Co., Ltd.) )) 0.73 parts, calcium hydroxide 0.15 parts, and ion-exchanged water 143.6 parts were mixed and dissolved at 50 ° C. to obtain an alkali-treated gelatin aqueous solution.

(1) Preparation of yellow color thermosensitive recording layer solution <Preparation of diazonium salt compound-encapsulated microcapsule solution (a)>
16.1 parts of ethyl acetate, 2.2 parts of the following diazonium salt compound A (maximum absorption wavelength 420 nm), 2.2 parts of the following diazonium salt compound B (maximum absorption wavelength 420 nm), 4.9 parts of monoisopropylbiphenyl, phthalic acid 4.9 parts of diphenyl and 0.4 part of diphenyl- (2,4,6-trimethylbenzoyl) phosphine oxide (trade name: Lucillin TPO, manufactured by BASF Japan Ltd.) were added and heated to 40 ° C. uniformly. Dissolved. Mixture of xylylene diisocyanate / trimethylolpropane adduct and xylylene diisocyanate / bisphenol A adduct as a capsule wall material in the above mixture (trade name: Takenate D119N (50% ethyl acetate solution), manufactured by Mitsui Takeda Chemical Co., Ltd.) 8.6 parts was added and stirred uniformly to obtain a mixture (I).

  Separately, 16.6 parts of ion-exchanged water and 0.35 part of Scratch AG-8 (50%) manufactured by Nippon Seika Co., Ltd.) were added to 59.7 parts of the phthalated gelatin aqueous solution, and the mixed solution [II] was added. Obtained. The mixed solution (I) was added to the mixed solution (II), and the mixture was emulsified and dispersed at 40 ° C. using a homogenizer (manufactured by Nippon Seiki Seisakusho). After adding 20 parts of water to the obtained emulsion and homogenizing it, the mixture was stirred at 40 ° C. to carry out an encapsulation reaction for 3 hours while removing ethyl acetate. Thereafter, 3.0 parts of ion exchange resin Amberlite SWA100-HG (manufactured by Organo Corp.) and 6.0 parts of Amberlite IRA67 (manufactured by ROHM AND HAAS (UK) LIMITED) were added and further stirred for 1.5 hours. . Thereafter, the ion exchange resin was removed by filtration, and the concentration was adjusted so that the solid content concentration of the capsule liquid was 20.0% to obtain a diazonium salt compound-encapsulating microcapsule liquid (a). The obtained microcapsules had a median diameter of 0.47 μm as a result of particle size measurement (LA-700, manufactured by Horiba, Ltd.).

<Preparation of coupler compound emulsion (a)>
33.0 parts of ethyl acetate, 9.9 parts of the following coupler compound C, 9.9 parts of triphenylguanidine (manufactured by Hodogaya Chemical Co., Ltd.), 4,4 ′-(m-phenylenediisopropylidene) diphenol (trade name) Bisphenol M (manufactured by Mitsui Petrochemical Co., Ltd.) 20.8 parts, 3,3,3 ′, 3′-tetramethyl-5,5 ′, 6,6′-tetra (1-propyloxy) -1, 3.3 parts of 1'-spirobisindane, 13.6 parts of 4- (2-ethylhexyloxy) benzenesulfonic acid amide (manac), 4-n-pentyloxybenzenesulfonic acid amide (manac) 6.8 parts of calcium dodecylbenzenesulfonate (trade name: Piionin A-41-C 70% methanol solution, manufactured by Takemoto Yushi Co., Ltd.) was dissolved to obtain a mixed liquid (III).

Separately, 142.4 parts of ion-exchanged water and 6.2 parts of D-sorbitol (sugar alcohol in the present invention) were added to and dissolved in 165.0 parts of the alkali-treated gelatin aqueous solution to obtain a mixed liquid (IV). Next, the mixed liquid (III) was added to the mixed liquid (IV), and the mixture was emulsified and dispersed at 40 ° C. using a homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd.). The obtained coupler compound emulsion was heated under reduced pressure to remove ethyl acetate, and then the concentration was adjusted so that the solid content concentration was 26.5%. The resulting coupler compound emulsion had a median diameter of 0.21 μm as a result of particle size measurement (LA-700, manufactured by Horiba, Ltd.).
Furthermore, 9 parts of SBR latex (trade name SN-307, 48% solution, manufactured by Sumika Aves Latex Co., Ltd.) with a concentration adjusted to 26.5% are added to 100 parts of the coupler compound emulsion. The mixture was stirred uniformly to obtain a coupler compound emulsion (a).

<Preparation of thermosensitive recording layer coating solution (a)>
The diazonium salt compound-encapsulated microcapsule liquid (a) and the coupler compound-emulsified liquid (a) are mixed so that the mass ratio of the encapsulated coupler compound / diazo compound is 2.2 / 1, and thermal recording is performed. A layer coating solution (a) was obtained.

(2) Preparation of coating solution for protective layer <Preparation of polyvinyl alcohol solution for protective layer>
150 parts of vinyl alcohol-alkyl vinyl ether copolymer (trade name: EP-130, manufactured by Denki Kagaku Kogyo Co., Ltd.), mixed solution of sodium alkyl sulfonate and polyoxyethylene alkyl ether phosphate (trade name: Neoscore CM-57 , (54% aqueous solution), manufactured by Toho Chemical Co., Ltd.) 7.5 parts, ethylene oxide adduct of acetylene diol (trade name: Dinol 604, manufactured by Air Products Japan Co., Ltd.), silicon-based interface 6.9 parts of an activator (trade name: SYLGARD309, manufactured by Toray Dow Corning Silicon Co., Ltd.) and 3682 parts of ion-exchanged water are mixed and dissolved at 90 ° C. for 1 hour to form a uniform polyvinyl alcohol for protective layer A solution was obtained.

<Preparation of protective layer pigment dispersion>
Barium sulfate (trade name: BF-21F, barium sulfate content 93% or more, manufactured by Sakai Chemical Industry Co., Ltd.) 8 parts anionic special polycarboxylic acid type polymer activator (trade name: Poise 532A (40% Aqueous solution), Kao Co., Ltd.) 0.2 part and ion-exchanged water 11.8 parts were mixed and dispersed in a dynomill to prepare a barium sulfate dispersion. As a result of particle size measurement (LA-910, manufactured by HORIBA, Ltd.), this dispersion was found to have a median diameter of 0.15 μm or less.
Furthermore, with respect to 1000 parts of the barium sulfate dispersion, 3.06 parts of an aqueous dispersion of 1-2 benzisothiazoline 3-one (trade name: PROXELB.D, manufactured by CI Co., Ltd.), wheat starch (trade name: 36.4 parts of wheat starch S, manufactured by Shinshin Food Industry Co., Ltd., colloidal silica (trade name: Snowtex O (20% aqueous dispersion), 181 parts manufactured by Nissan Chemical Co., Ltd.), acrylic / silicone modified resin emulsion (Product name: ARJ-2A, 44% dispersion, manufactured by Nippon Pure Chemical Co., Ltd.) 67.7 parts was mixed with stirring to prepare a pigment dispersion for protective layer.

<Preparation of coating solution for protective layer>
90.4 parts of ion-exchanged water, 1000 parts of the polyvinyl alcohol solution for the protective layer, 49.4 parts of sodium (4-nonylphenoxytrioxyethylene) butyl sulfonate (2.0% aqueous solution manufactured by Sankyo Chemical Co., Ltd.), 87.6 parts of the pigment dispersion for the protective layer, 48.2 parts of zinc stearate dispersion (trade name: Hymicron L111, 21% aqueous solution, manufactured by Chukyo Yushi Co., Ltd.), the following compound (J) (Wako Pure Chemical Industries, Ltd.) 153.9 parts of 4% aqueous solution (made by Co., Ltd.) and 51.3 parts of 4% aqueous solution of the following compound (J ′) (made by Wako Pure Chemical Industries, Ltd.) are uniformly mixed to obtain a coating blend solution for protective layer. It was.

(3) Application of each coating solution for heat-sensitive recording layer On the support with an undercoat layer, two layers of the heat-sensitive recording layer coating solution (a) and the protective layer coating solution were successively applied in the order of 30 ° C. Heat-sensitive recording materials were obtained by drying under conditions of 30% humidity and 30% humidity at 40 ° C.
At this time, the coating amount of the thermal recording layer coating solution (a) was applied such that the coating amount of the diazonium salt compound A contained in the solution was 0.08 g / m ^{2 in} terms of solid content coating amount.
The protective layer was applied so that the solid content was 1.39 g / m ² .

(Example 2)
In Example 1 <Preparation of coupler compound emulsion (a)>, except that 6.2 parts of D-sorbitol was changed to 6.2 parts of D-xylitol (sugar alcohol in the present invention), Example In the same manner as in Example 1, a thermosensitive recording material was obtained.

(Comparative Example 1)
In <Preparation of coupler compound emulsion (a)> in Example 1, 142.4 parts of ion-exchanged water and 6.2 parts of D-sorbitol were added to 165.0 parts of the alkali-treated gelatin aqueous solution. A thermosensitive recording material was obtained in the same manner as in Example 1, except that 107.3 parts of ion exchanged water was added to 206.3 parts to obtain a mixed liquid (IV).

Example 3
(1) Preparation of magenta color thermosensitive recording layer solution <Preparation of diazonium salt compound-encapsulated microcapsule solution (b)>
15.1 parts of ethyl acetate, 2.8 parts of the following diazonium salt compound D (maximum absorption wavelength 365 nm), 3.8 parts of diphenyl phthalate, 3.9 parts of phenyl 2-benzoyloxybenzoate, trimethylolpropane methacrylate (product) Name: 4.2 parts of light ester TMP, manufactured by Kyoei Yushi Chemical Co., Ltd.) and 0.1 parts of calcium dodecylbenzenesulfonate (trade name: Pionein A-41-C 70% methanol solution, manufactured by Takemoto Yushi Co., Ltd.) Added and heated to dissolve uniformly. Mixture of xylylene diisocyanate / trimethylolpropane adduct and xylylene diisocyanate / bisphenol A adduct as a capsule wall material in the above mixture (trade name: Takenate D119N (50% ethyl acetate solution), manufactured by Mitsui Takeda Chemical Co., Ltd.) 2.5 parts and 6.8 parts of xylylene diisocyanate / trimethylolpropane adduct (trade name: Takenate D110N (75% ethyl acetate solution), manufactured by Mitsui Takeda Chemical Co., Ltd.) are added, and the mixture is stirred uniformly. (V) was obtained.

Separately, 21.0 parts of ion-exchanged water was added to and mixed with 55.3 parts of the phthalated gelatin aqueous solution to obtain a mixed liquid (VI).
The mixed solution (V) was added to the mixed solution (VI), and the mixture was emulsified and dispersed at 40 ° C. using a homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd.). After 24 parts of water was added to the obtained emulsion and homogenized, the mixture was stirred at 40 ° C. to carry out an encapsulation reaction for 3 hours while removing ethyl acetate. Thereafter, 4.1 parts of ion exchange resin Amberlite SWA100-HG (manufactured by Organo Corporation) and 8.2 parts of Amberlite IRA67 (manufactured by ROHM AND HAAS (UK) LIMITED) were added, and the mixture was further stirred for 1 hour. Thereafter, the ion exchange resin was removed by filtration, and the concentration was adjusted so that the solid content of the capsule liquid was 20.0%, whereby a diazonium salt compound-encapsulating microcapsule liquid (b) was obtained. The obtained microcapsules had a median diameter of 0.43 μm as a result of particle size measurement (LA-700, carried out by Horiba, Ltd.).

<Preparation of coupler compound emulsion (b)>
36.9 parts of ethyl acetate, 11.9 parts of the following coupler compound F, 14.0 parts of triphenylguanidine (manufactured by Hodogaya Chemical Co., Ltd.), 4,4 ′-(m-phenylenediisopropylidene) diphenol (trade name) Bisphenol M (Mitsui Petrochemical Co., Ltd.)) 14.0 parts, 1,1- (p-hydroxyphenyl) -2-ethylhexane 14 parts, 3,3,3 ′, 3′-tetramethyl-5 , 5 ′, 6,6′-tetra (1-propyloxy) -1,1′-spirobisindane, 3.5 parts of the following compound G, 1.7 parts of tricresyl phosphate, diethyl maleate 8 parts, calcium dodecylbenzenesulfonate (trade name: Piionin A-41-C 70% methanol solution, manufactured by Takemoto Yushi Co., Ltd.) 4.5 parts were dissolved to obtain a mixture (VII).

Separately, 142.4 parts of ion-exchanged water and 6.2 parts of D-sorbitol (sugar alcohol in the present invention) were added to 165.0 parts of the alkali-treated gelatin aqueous solution and dissolved to obtain a mixed liquid (VIII).
The mixed solution (VII) was added to the mixed solution (VIII), and the mixture was emulsified and dispersed at 40 ° C. using a homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd.). The obtained coupler compound emulsion was heated under reduced pressure to remove ethyl acetate, and then the concentration was adjusted so that the solid content concentration was 24.5% to obtain a coupler compound emulsion (b). The resulting coupler compound emulsion had a median diameter of 0.22 μm as a result of particle size measurement (LA-700, manufactured by Horiba, Ltd.).

<Preparation of thermal recording layer coating liquid (b)>
The diazonium salt compound-encapsulated microcapsule liquid (b) and the coupler compound-emulsified liquid (b) were mixed so that the mass ratio of the encapsulated coupler compound / diazo compound was 3.5 / 1. Further, an aqueous solution (5%) of polystyrene sulfonic acid (partially potassium hydroxide neutralized) was mixed so that the amount of capsule liquid was 0.2 part with respect to 10 parts of the capsule liquid, and the thermal recording layer coating liquid (b) was prepared. Obtained.

(3) Application of each coating solution for heat-sensitive recording layer On the support with the undercoat layer, the coating solution for heat-sensitive recording layer (b), the coating solution for protective layer (the coating for protective layer prepared in Example 1). The two layers were successively applied in the order of (Liquid) and dried under the conditions of 30 ° C. humidity 30% and 40 ° C. humidity 30% to obtain a heat-sensitive recording material.
At this time, the coating amount of the thermal recording layer coating solution (b) was applied such that the coating amount of the diazonium salt compound D contained in the solution was 0.20 g / m ^{2 in} terms of solid content coating amount.
The protective layer was applied so that the solid content was 1.39 g / m ² .

Example 4
Thermosensitive recording was performed in the same manner as in Example 3 except that 6.2 parts of D-sorbitol was changed to 6.2 parts of D-xylitol in <Preparation of coupler compound emulsion (b)> in Example 3. Obtained material.

(Comparative Example 2)
In <Preparation of coupler compound emulsion (b)> in Example 3, 142.4 parts of ion-exchanged water and 6.2 parts of D-sorbitol were added to 165.0 parts of the alkali-treated gelatin aqueous solution. A thermosensitive recording material was obtained in the same manner as in Example 1 except that 107.3 parts of ion-exchanged water was added to 206.3 parts to obtain a mixed liquid (VIII).

(Example 5)
(1) Preparation of cyan color thermosensitive recording layer solution <Preparation of electron-donating dye precursor-encapsulated microcapsule solution (c)>
18.1 parts of ethyl acetate, 7.6 parts of the following electron donating dye precursor H, trimethylolpropane trimethacrylate (trade name; Light Ester TMP, manufactured by Kyoeisha Yushi Chemical Co., Ltd.), diisopropylnaphthalene (Trade name; KMC113, Kureha Chemical Co., Ltd.) 6.0 parts, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane (trade name; Adeka Cruz DH -37, manufactured by Asahi Denka Kogyo Co., Ltd.) was added and heated to dissolve uniformly. 7.1 parts of xylylene diisocyanate / trimethylolpropane adduct as a capsule wall material in the above mixture (trade name; Takenate D110N (75% ethyl acetate solution), manufactured by Mitsui Takeda Chemical Co., Ltd.), formalin condensate of phenyl isocyanate (Product name: Millionate MR-200, manufactured by Nippon Polyurethane Industry Co., Ltd.) 5.3 parts, xylylene diisocyanate / 3.1 parts of the following compound I adduct (50% ethyl acetate solution) was added and stirred uniformly. A liquid mixture (IX) was obtained.

Separately, 57.6 parts of the above phthalated gelatin aqueous solution, 9.5 parts of ion-exchanged water, 0.17 part of Scraph AG-8 (50%) manufactured by Nippon Seika Co., Ltd.) and sodium dodecylbenzenesulfonate (10% aqueous solution) ) 4.3 parts were added and mixed to obtain a mixed solution (X).
The mixed solution (XI) was added to the mixed solution (X), and the mixture was emulsified and dispersed at 40 ° C. using a homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd.). 21.2 parts of water and 0.12 part of tetraethylenepentamine are added to the resulting emulsion and homogenized. The mixture is stirred at 65 ° C. for 3 hours while removing ethyl acetate, and the solid content concentration of the capsule liquid The concentration was adjusted to 33% to obtain a microcapsule solution. The obtained microcapsules had a median diameter of 1.10 μm as a result of particle size measurement (LA-700, carried out by Horiba, Ltd.).
Further, with respect to 100 parts of the above microcapsule solution, 3.7 parts of sodium dodecylbenzenesulfonate 25% aqueous solution (trade name; Neoperex F-25, manufactured by Kao Corporation) and 4,4′-bistriazinylaminostilbene A -2,2'-disulfone derivative (trade name; Kaycall BXNL, manufactured by Nippon Soda Co., Ltd.) was added and stirred uniformly to obtain an electron donating dye precursor-encapsulated microcapsule liquid (c).

<Preparation of electron-accepting compound dispersion (c)>
8.5 parts of the phthalated gelatin aqueous solution and 11.3 parts of 6% aqueous solution of PGLE, ML10 (trade name) manufactured by Daicel Corporation 30.1 parts of ion-exchanged water, 4, 4 ′-(P-phenylenediisopropylidene) 7.5 parts of diphenol (trade name: bisphenol P, manufactured by Mitsui Chemicals) and 1,1-bis (4-hydroxyphenyl) -1-phenylethane (trade name: Bisp-Ap, manufactured by Honshu Chemical) 0.5 part, 3.8 parts of 2% -1 ethylhexyl sodium succinate aqueous solution and 1.0 part of 2% demole NL (manufactured by Kao Corporation) were added and dispersed overnight in a ball mill to obtain a dispersion. . The solid content concentration of this dispersion was 26.6%.
After adding 15.8 parts of the alkali-treated gelatin aqueous solution and 15.8 parts of 15% D-sorbitol aqueous solution to 100 parts of the above dispersion and stirring for 30 minutes, the solid content concentration of the dispersion is 23.5%. Ion-exchanged water was added to to obtain an electron-accepting compound dispersion (c).

<Preparation of thermal recording layer coating solution (c)>
The mass ratio of the electron-accepting compound / electron-donating dye encapsulating the electron-donating dye-encapsulating microcapsule liquid (c) and the electron-accepting compound dispersion liquid (c) is 10/1. The mixture was mixed to obtain a thermal recording layer coating solution (c).

(3) Application of each coating solution for heat-sensitive recording layer On the support with the undercoat layer, the coating solution for heat-sensitive recording layer (c), the coating solution for protective layer (the coating for protective layer prepared in Example 1). The two layers were successively applied in the order of (Liquid) and dried under the conditions of 30 ° C. humidity 30% and 40 ° C. humidity 30% to obtain a heat-sensitive recording material.
At this time, the coating amount of the thermal recording layer coating solution (c) was applied so that the coating amount of the electron donating dye precursor H contained in the solution was 0.355 g / m ^{2 in} terms of solid content coating amount. It was.
The protective layer was applied so that the solid content was 1.39 g / m ² .

(Comparative Example 3)
In <Preparation of Electron-Accepting Compound Dispersion (c)> in Example 5, 15.8 parts of an alkali-treated gelatin aqueous solution and 15.8 parts of a 15% D-sorbitol aqueous solution were added to 100 parts of the dispersion. A heat-sensitive recording material was obtained in the same manner as in Example 5 except that 31.6 parts of the alkali-treated gelatin aqueous solution was added to 100 parts.

(Evaluation of thermal recording materials)
For the heat-sensitive recording materials of Examples 1 to 5 and Comparative Examples 1 to 3 obtained as described above, the color density before and after the forced deterioration treatment of the recording material was measured, and the change in density was evaluated.

(1) Forced deterioration treatment The heat-sensitive recording materials of Examples 1 to 5 and Comparative Examples 1 to 3 were left in a constant temperature and humidity chamber adjusted to an environmental condition of 45 ° C.-60% RH for 14 days for forced deterioration treatment. gave.

(2) Measurement of color density The heat-sensitive recording materials of Examples 1 to 5 and Comparative Examples 1 to 3 stored for 14 days under an environmental condition of 23 ° C.-50% without forced deterioration treatment, and forcibly in (1) After the deterioration treatment, heat-sensitive recording materials of Examples 1 to 5 and Comparative Examples 1 to 3 which were conditioned for 24 hours under an environmental condition of 23 ° C.-50% were prepared.

For each of the above samples, using a thermal head KST type (manufactured by Kyocera Corporation), the printing energy per unit area is 50 mJ / mm ^{2 in} the case of a yellow color recording material,
80 mJ / mm ² in the case of magenta color recording material, so that 110 mJ / mm ² in the case of the cyan color-forming recording material, after adjusting the printing power, and the pulse width for the thermal head, and thermally printed on each thermosensitive recording material An image was recorded. Thereafter, in the case of yellow and magenta color thermosensitive recording materials, they were light-fixed by irradiation for 10 seconds using an ultraviolet lamp having an emission center wavelength of 420 nm or 365 nm and an output of 40 W. The optical reflection density (yellow or magenta or cyan density) of the color development portion of the obtained photofixed image was measured 10 minutes after photofixation with an X-rite densitometer. The results are shown in Table 1.

  As shown in Table 1, the heat-sensitive recording material to which sugar alcohol is added has little storage color change during storage and is excellent in storage stability.

Claims (3)

A thermosensitive recording material having a thermosensitive recording layer containing at least a color forming component and a binder on a support,
At least one of the coloring components is encapsulated in a microcapsule,
The thermosensitive recording material, wherein the thermosensitive recording layer contains at least one sugar alcohol outside the microcapsules.   The heat-sensitive recording material according to claim 1, wherein the binder is gelatin.   The heat-sensitive recording material according to claim 1 or 2, wherein the heat-sensitive recording layer contains a diazonium salt compound and a coupler as the color forming component.