JP2006240102A - Thermal recording material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording material having the sensitivity and transparency of an excellent color former. <P>SOLUTION: This thermal recording material comprises a thermal recording layer containing a microcapsule encapsulating a colorless or pale-color electron-donative dye precursor and at least two different kinds of solid dispersion-type developers. As the two different kinds of the solid dispersion-type developers, a chemical compound represented by formula (1) and a chemical compound with amorphous property, are added. In formula (1), R<SP>1</SP>and R<SP>2</SP>are each independently an alkyl group, an alkenyl group, an alkinyl group, an aryl group, an aralkyl group, an alkoxy group or a halogen atom. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  The heat-sensitive recording material is (1) no development is required, (2) when the support is paper, the material is close to plain paper, (3) easy to handle, (4) high color density, (5 Since the recording apparatus has advantages such as simple, reliable and inexpensive, (6) low noise during recording, and (7) no maintenance required, it has been used in various fields in recent years. For example, applications are expanding in the fields of facsimiles and printers, labels such as POS, and medical images.

  In the field of medical images, basic performances required for heat-sensitive recording materials include high translucency, fastness, sensitivity, dark heat storage property, etc. of the uncolored portion.

  Among these, with respect to the translucency of the uncolored portion, in the conventional solid dispersion type heat-sensitive recording material, high translucency was not obtained mainly due to voids in the film, but an emulsified dispersion such as a developer. By applying, a layer in which the components were closely packed was obtained, and certain results were achieved. (For example, refer to Patent Document 1).

  However, since the emulsified dispersion is amorphous, it has high diffusibility at low temperatures, and there are problems with fog and dark heat storage. On the other hand, it was considered to encapsulate the dye precursor in a microcapsule, but this was not always sufficient (for example, see Patent Documents 2 and 3).

On the other hand, in order to suppress changes in print density with respect to changes in the environment and print conditions (humidity, head offset position, etc.), it is conceivable to soften the sensitivity characteristics. Printing energy increases, the burden on the uppermost protective layer of the thermal recording material that comes into contact with the thermal head increases, and problems such as surface roughness occur.
In order to reduce the printing energy, it is necessary to make the color development start energy as small as possible, that is, to make the color former highly sensitive, but satisfactory results are not always obtained.
JP-A-1-108086 JP 63-45084 A JP-A 63-265682

  An object of the present invention is to solve the above conventional problems and achieve the following objects. That is, an object of the present invention is to provide a heat-sensitive recording material having excellent color former sensitivity and transparency.

The above object is achieved by the following thermal recording material.
That is, the present invention
<1> 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 at least two solid-dispersed color developers on a support. A heat-sensitive recording material comprising a compound represented by the following general formula (1) and a compound having an amorphous property as the two kinds of solid dispersion developers.

[In General Formula (1), R ¹ and R ² each independently represents an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an aralkyl group, an alkoxy group, or a halogen atom. ]

<2> The heat-sensitive recording material according to <1>, wherein the wall material of the microcapsule is made of polyurethane, polyurea, or a composite of both.
<3> The heat-sensitive recording material according to <1> or <2>, wherein the support is a polymer film, and the haze value of the heat-sensitive recording material is 55% or less.

<4> The heat-sensitive recording material according to any one of <1> to <3>, wherein the support is a polyethylene terephthalate film having a thickness of 100 μm or more.
<5> The developer contained in the solid dispersion is solid-dispersed with one or more water-soluble polymers selected from partially saponified polyvinyl alcohol and gelatin. <1> to <4 The thermal recording material according to any one of the above.

  According to the present invention, a heat-sensitive recording material having excellent color former sensitivity and transparency can be provided.

Hereinafter, the heat-sensitive recording material of the present invention will be described in detail.
The heat-sensitive recording material of the present invention has a heat-sensitive recording layer comprising a microcapsule encapsulating a colorless or light-colored electron-donating dye precursor and at least two solid-dispersed color developers on a support. A recording material comprising the compound represented by the following general formula (1) and a compound having an amorphous property as the two types of solid dispersion developers.
The developer represents an electron-accepting compound that develops color by reacting with a colorless or light-colored electron-donating dye precursor.

[In General Formula (1), R ¹ and R ² each independently represents an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an aralkyl group, an alkoxy group, or a halogen atom. ]

In the present invention, the solid dispersion developer means that the developer is present as solid particles.
The average particle size of the solid particles is preferably 0.15 to 1.0 μm, and more preferably 0.2 to 0.7 μm. When the average particle diameter of the solid particles is 0.15 to 0.7 μm, the background fog does not occur and the transparency is further improved. In addition, the average particle diameter in this invention means a median average particle diameter.

[Thermosensitive recording layer]
(Developer)
In the present invention, the compound represented by the general formula (1) is contained as one type of the solid dispersion developer. Hereinafter, the compound represented by the general formula (1) will be described.
In the general formula (1), the alkyl group represented by R ¹ and R ² is preferably an alkyl group having 1 to 12 carbon atoms, and more preferably an alkyl group having 1 to 8 carbon atoms. Specifically, methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, t-butyl group, s-butyl group, n-pentyl group, t-pentyl group , Cyclopentyl group, n-hexyl group, cyclohexyl group, n-heptyl group, n-octyl group, t-octyl group, 2-ethylhexyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group A methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, and a t-butyl group are particularly preferable.

In the general formula (1), the alkenyl group represented by R ¹ and R ² is preferably an alkenyl group having 2 to 12 carbon atoms, and more preferably an alkenyl group having 2 to 8 carbon atoms. Specific examples include a vinyl group, a propenyl group, a butenyl group, a pentenyl group, a hexenyl group, an octenyl group, a decenyl group, a dodecenyl group, and a butadienyl group, and among them, a vinyl group, a propenyl group, a butenyl group, and a butadienyl group are particularly preferable. .

In the general formula (1), the alkynyl group represented by R ¹ and R ² is preferably an alkynyl group having 2 to 12 carbon atoms, and more preferably an alkynyl group having 2 to 8 carbon atoms. Specific examples include an ethynyl group, a propynyl group, a butynyl group, an octynyl group, and a dodecynyl group, and among them, an ethynyl group and a propynyl group are particularly preferable.

In the general formula (1), the aryl group represented by R ¹ and R ² is preferably an aryl group having 6 to 20 carbon atoms, and more preferably an aryl group having 6 to 15 carbon atoms. Specifically, phenyl group, 2-methylphenyl group, 3-methylphenyl group, 4-methylphenyl group, 2-chlorophenyl group, 3-chlorophenyl group, 4-chlorophenyl group, 2-methoxyphenyl group, 4-methoxy Examples thereof include a phenyl group and a 4-benzylphenyl group, and among them, a phenyl group, a 2-methylphenyl group, and a 4-methylphenyl group are particularly preferable.

In the general formula (1), the aralkyl group represented by R ¹ and R ² is preferably an aralkyl group having 7 to 9 carbon atoms, and more preferably an aralkyl group having 7 to 8 carbon atoms. Specific examples include a benzyl group, an α-methylbenzyl group, a phenethyl group, and a cinnamyl group, and among them, a benzyl group, an α-methylbenzyl group, and a phenethyl group are particularly preferable.

In the general formula (1), the alkoxy group represented by R ¹ and R ^2, preferably an alkoxy group having 1 to 12 carbon atoms, more preferably an alkoxy group having 1 to 8 carbon atoms. Specifically, methoxy group, ethoxy group, n-propyloxy group, i-propyloxy group, n-butoxy group, t-butoxy group, n-pentyloxy group, t-pentyloxy group, 2-ethylhexyloxy group , N-hexyloxy group, n-heptyloxy group, n-octyloxy group, t-octyloxy group, n-nonyloxy group, n-decyloxy group, n-dodecyloxy group, among them methoxy group, ethoxy group N-propyloxy group, i-propyloxy group, n-butoxy group, t-butoxy group, n-pentyloxy group, t-pentyloxy group, n-hexyloxy group, n-octyloxy group, t-octyl An oxy group is particularly preferred.

In the general formula (1), examples of the halogen atom represented by R ¹ and R ² include a chlorine atom, a bromine atom, and an iodine atom, and a chlorine atom is particularly preferable.

The content of the heat-sensitive recording layer of the compound represented by the general formula (1) is preferably 0.2~8g / m ^2, more preferably 0.5-4 g / m ^2.

  Specific examples (exemplary compounds (A) to (F)) of the general formula (1) are shown below, but the present invention is not limited thereto.

  In the present invention, as another type of the solid dispersion developer, a compound having an amorphous property is contained. Transparency of the heat-sensitive recording material is an important performance for use in medical applications. As a cause of impairing the transparency, there are crystal precipitation of the developer dispersion and voids between coating layer components, and by using the developer having an amorphous property and the compound represented by the general formula (1) in combination. It can be effectively prevented. As the developer according to the present invention, by using together with the amorphous developer co-dissolved with the compound represented by the general formula (1), the coating layer tends to be a continuous layer, and in particular, the coating of a solid dispersion. It is possible to prevent the opacity caused by the voids that are likely to occur. Here, the amorphous property refers to those in which no clear melting point is observed in DSC measurement or the like. The usage ratio of the developer exhibiting amorphous properties is preferably 20 to 80%, more preferably 30 to 60% of the solid amount of the developer dispersion. Examples of the compound having such an amorphous property include zinc 3,5-di (α-methylbenzyl) salicylate, zinc 3- (α-methylbenzyl) salicylate, zinc 5- (α-methylbenzyl) salicylate, 3,5 -Zinc di-t-butylsalicylate, zinc 3-t-butylsalicylate and zinc 5-t-butylsalicylate are mentioned, and 3,5-di (α-methylbenzyl) salicylate zinc is particularly preferable.

  The above-mentioned developer is used, for example, by solid dispersion by means of a sand mill or the like together with a water-soluble polymer, an organic base, and other color forming aids. When the developer is prepared by solid dispersion, a developer powder is added to a known method, that is, a surfactant, a water phase containing a water-soluble polymer as a protective colloid, a ball mill, an attritor, It is carried out by stirring using a sand mill or the like and dispersing using a pulverizer.

In the present invention, the protective colloid used in the production of the solid dispersion developer is preferably at least one selected from partially saponified polyvinyl alcohol and gelatin.
The partially saponified polyvinyl alcohol is preferably polyvinyl alcohol having a saponification degree of 75 to 95 mol% and a polymerization degree of 200 to 2500, and more preferably polyvinyl alcohol having a saponification degree of 85 to 90 mol% and a polymerization degree of 300 to 2000.
The gelatin is preferably alkali-processed gelatin having a low isoelectric point, or a derivative gelatin (for example, phthalated gelatin) reacted with an amino group, and phthalated gelatin is particularly preferable.
By using these protective colloids, the transparency of the coating film is improved.

  Further, a water-proofing agent may be added for the purpose of imparting water resistance to these binders, or a hydrophobic polymer emulsion, specifically, a styrene-butadiene rubber (SBR) latex, an acrylic resin emulsion, or the like may be added. .

(Electron-donating dye precursor)
The electron-donating dye precursor preferably used in the present invention is not particularly limited as long as it is colorless or light-colored. However, the electron-donating dye precursor is colored by donating electrons or accepting protons such as acids. In particular, it has a partial skeleton such as lactone, lactam, sultone, spiropyran, ester, amide, etc., and when contacted with a developer, these partial skeletons are ring-opening or cleaving. What is a compound of these is preferable.

  Examples of the electron-donating dye precursor include triphenylmethane phthalide compounds, fluoran compounds, phenothiazine compounds, indolyl phthalide compounds, leucooramine compounds, rhodamine lactam compounds, and 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. 3,491,111, 3,491,112, 3,491,116, and 3,509,174. .
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 piperazine-based compounds include compounds described in US Pat. Nos. 3,775,424, 3,853,869 and 4,246,318.
Specific examples of the fluorene compound include compounds described in JP-A-63-94878.
Among these, black-colored 2-arylamino-3- [H, halogen, alkyl, or alkoxy-6-substituted aminofluorane] is particularly preferable.

  Specifically, for example, 2-anilino-3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-Ncyclohexyl-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-isoamylaminofluor Lan, 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- -Methyl-6-N-ethyl-N-γ-propoxypropylaminofluorane, 3 ', 6'-bis (hexyloxy) -2- (2-thienyl) -spiro [4H-3,1-benzoxazine- 4,9 ′-[9H] xanthrene], 3 ′, 6′-bis (hexyloxy) -2- (2-phenyl) -spiro [4H-3,1-benzoxazine-4,9 ′-[9H] Xanthrene], and the like.

(Micro capsule)
In the present invention, the electron donating dye precursor is encapsulated in microcapsules. In the present invention, the microcapsule wall material is preferably polyurethane, polyurea, or a composite of both. Hereinafter, the microcapsule will be described in detail.
There are an interfacial polymerization method, an internal polymerization method, an external polymerization method and the like in the production of microcapsules, and any method can be adopted.
When encapsulating an electron-donating dye precursor in a microcapsule, an oil phase prepared by dissolving or dispersing an electron-donating dye precursor serving as the core of the capsule in a hydrophobic organic solvent is used. It is put into a dissolved aqueous phase, emulsified and dispersed by stirring means such as a homogenizer, and then heated 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, 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, or a polyol with the interfacial polymerization method in the aqueous phase.

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

The polyisocyanate compound is preferably a compound having a trifunctional or higher functional isocyanate group, but a bifunctional isocyanate compound may be used in combination. Specifically, diisocyanates such as xylene diisocyanate and hydrogenated products thereof, hexamethylene diisocyanate, tolylene diisocyanate and hydrogenated products thereof, isophorone diisocyanate and the like, and dimers thereof. 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.
The compounds described in JP-A-62-212190, JP-A-4-26189, JP-A-5-317694, JP-A-10-114153 and the like are preferable.

  The polyisocyanate is preferably added so that the average particle size of the microcapsules is 0.1 to 10 μm and the thickness of the capsule wall is 0.01 to 0.3 μm. The dispersed particle size is generally about 0.1 to 10 μm.

Specific examples of polyols and / or polyamines that react with the polyisocyanate and are added to the water phase and / or the oil phase as one of the components of the microcapsule wall include propylene glycol, glycerin, trimethylolpropane, Examples include ethanolamine, sorbitol, hexamethylenediamine, tetraethylenepentamine, triethylenetetramine, and diethylenetriamine. 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, and the like are detailed in, for example, “Polyurethane Handbook” (Nikkan Kogyo Shimbun, 1987) edited by Keiji Iwata.

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

Furthermore, it is preferable to use a plasticizer suitable for the polymer used as the wall material, in order to make the wall of the microcapsule excellent in material permeability even under lower temperature conditions 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. Of these, those that are solid at room temperature can be suitably selected and used.
For example, when the wall material is made of polyurea or polyurethane, a hydroxy compound, a carbamic acid ester compound, an aromatic alkoxy compound, an organic sulfonamide compound, an aliphatic amide compound, an arylamide compound, or the like is preferably used.

In preparing the oil phase, the hydrophobic organic solvent used for dissolving the electron-donating dye precursor and forming the core of the microcapsule is preferably an organic solvent having a boiling point of 100 to 300 ° C.
Specifically, in addition to esters, dimethylnaphthalene, diethylnaphthalene, diisopropylnaphthalene, dimethylbiphenyl, diisopropylbiphenyl, diisobutylbiphenyl, 1-methyl-1-dimethylphenyl-2-phenylmethane, 1-ethyl-1-dimethylphenyl -1-phenylmethane, 1-propyl-1-dimethylphenyl-1-phenylmethane, triallylmethane (eg, tritoluylmethane, toluyldiphenylmethane), terphenyl compound (eg, terphenyl), alkyl compound, alkylated diphenyl ether (For example, propyl diphenyl ether), hydrogenated terphenyl (for example, hexahydroterphenyl), diphenyl ether, and the like. Among these, it is particularly preferable to use esters from the viewpoint of emulsion stability of the emulsion 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, Phthalic acid esters such as octyl phthalate and butyl benzyl phthalate; Dioctyl tetrahydrophthalate; Benzoic acid esters such as ethyl benzoate, propyl benzoate, butyl benzoate, isopentyl benzoate and benzyl benzoate; Ethyl abietic acid, abietic acid Abietic acid esters such as benzyl; dioctyl adipate; isodecyl succinate; dioctyl azelate; oxalic acid esters such as dibutyl oxalate and dipentyl oxalate; diethyl malonate; dimethyl maleate, diethyl maleate, di maleate Maleic acid esters such as til; Tributyl citrate; Sorbic acid esters such as methyl sorbate, ethyl sorbate and butyl sorbate; Sebacic acid esters such as dibutyl sebacate and dioctyl sebacate; Ethylene glycol and formic acid, butyric acid, lauric acid And monoesters and diesters with palmitic acid, stearic acid and oleic acid; triacetin; diethyl carbonate; diphenyl carbonate; ethylene carbonate; propylene carbonate; boric acid esters such as tributyl borate and tripentyl borate.

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

  In the preparation of the oil phase, the organic solvent used when dissolving the electron-donating dye precursor to form the core of the microcapsule has a boiling point of 50 to 150 ° C., which has high solubility and does not remain in the capsule after the encapsulation reaction. These low boiling solvents are preferred. Preferred examples of such a low boiling point solvent include ester organic solvents such as ethyl acetate, isopropyl acetate, and butyl acetate, and methylene chloride, with ethyl acetate being most preferred.

  When the solubility of the electron donating dye precursor as a solute is poor, or when the electron donating dye precursor is highly polar and cannot be separated preferably from the microcapsule wall, a hydrophobic oil having a relatively high boiling point may be used in combination. it can. Since the hydrophobic oil remains in the capsule even after the encapsulation reaction, it may cause adverse effects such as deterioration in image storage stability. However, phosphate esters such as tricresyl phosphate, benzoate esters such as isopentyl benzoate, etc. , Maleic acid esters such as dibutyl maleate, and boric acid esters such as tributyl borate can be preferably used. In particular, tricresyl phosphate is preferable because of good emulsion stability and image storage stability.

In this invention, 0.1-5.0 g / m < ² > is preferable and, as for content of the said electron-donating dye precursor, 1.0-4.0 g / m < ² > is more preferable.
When the content of the electron donating dye precursor is in the range of 0.1 to 5.0 g / m ² , a sufficient color density can be obtained.

  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, emulsification and dispersion are performed by means of a homogenizer or the like. And a dispersion medium that 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 known surfactant for emulsification can be used. 0.1-5% is preferable with respect to the mass of an oil phase, and, as for the addition amount of 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 cause precipitation or aggregation by acting with the protective colloid 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), acetylene glycol and the like.
A preferred protective colloid is polyvinyl alcohol (PVA). Particularly, modified PVA hydrophobized at the end can control aggregation and sedimentation during emulsification and encapsulation reaction.

Next, an embodiment in which the electron donating dye precursor is included in the polymer will be described.
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 the above, composite fine particles to be a polymer containing an electron donating dye precursor can be produced by a method similar to the method for producing the microcapsule. The composite fine particles are described in detail, for example, in JP-A-9-263057. In addition, the aspect of this composite fine particle has limited solubility of the solute, and the coating amount of the composite fine particle is increased more than necessary, or the electron donating dye precursor and the electron accepting compound (developer) are completely separated. It is difficult to do this, and background coloration and deterioration of image storage stability may occur. Therefore, an embodiment in which the microcapsules are included is preferable.

  For emulsification, the oil phase containing the above components and the aqueous phase containing the protective colloid and the surfactant are stirred by means of normal fine particle emulsification such as high-speed stirring and ultrasonic dispersion, such as a homogenizer, Manton Gorey, It can be easily carried out using a known emulsifying device such as an ultrasonic disperser, a dissolver, a teddy mill or the like. After the emulsification, the emulsion is preferably heated to 30 to 70 ° C. in order to promote the capsule wall formation reaction. Further, during the reaction, in order to prevent aggregation between the capsules, it is preferable to add water to reduce the collision probability between the capsules or perform sufficient stirring.

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

(Coating solution for thermal recording layer)
The thermosensitive recording layer coating liquid can be prepared, for example, by mixing the microcapsule liquid prepared as described above and a solid dispersion of the developer. Here, the water-soluble polymer used as a protective colloid in the preparation of the microcapsule liquid, and the water-soluble polymer used as a protective colloid in the preparation of the solid dispersion developer are used in the thermal 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.

  As a binder used as a protective colloid in the preparation of the microcapsule liquid, polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, epichlorohydrin-modified polyamide, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, isobutylene -Maleic salicylic anhydride copolymer, polyacrylic acid, polyacrylic acid amide, methylol-modified polyacrylamide, starch derivative, casein, gelatin and the like.

  When applying the above-mentioned heat-sensitive recording layer coating solution on the support, known coating means used for aqueous or organic solvent-based coating solutions are used. In this case, the heat-sensitive recording layer coating solution is applied safely and uniformly. In addition, in order to maintain the strength of the coating film, in the heat-sensitive recording material of the present invention, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, starches, gelatin, polyvinyl alcohol, carboxy-modified polyvinyl alcohol, polyacrylamide, polystyrene or a co-polymer thereof. Polymer, 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 resin, etc. are used. can do.

Next, other components that can be used in the heat-sensitive recording layer will be described.
The other components are not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include known heat-fusible substances, ultraviolet absorbers and antioxidants.

The heat-fusible substance can be contained in the heat-sensitive recording layer for the purpose of improving thermal response. Examples of the heat-fusible substance 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, and 50-10726, U.S. Pat. No. 086, No. 3,707,375, No. 3,754,919, No. 4,220,711, and the like.

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

The coating amount of the other components, 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-sensitive recording layer of the present invention has an energy amount necessary for obtaining a saturated transmission density (D _t-max ) in order to obtain a high-quality image while suppressing density unevenness caused by a slight difference in thermal conductivity of the thermal head. A thermal recording layer having a wide width, that is, a wide dynamic range is preferred. The heat-sensitive recording material of the present invention has the heat-sensitive recording layer as described above, and can obtain a transmission density (D _t-max ) = 3.0 with a heat energy amount in the range of 70 to 130 mJ / mm ^2. It is preferable that the recording layer has a heat sensitive recording layer.

The heat-sensitive recording layer according to 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 layer is 1 to 25 μm. It is preferable. Further, two or more thermosensitive recording layers can be laminated and used. In this case, it is preferable that the solid coating amount after application and drying of the entire heat-sensitive recording layer is 1 to 25 g / m ² .

(Support)
In the heat-sensitive recording material of the present invention, a polymer film is used as the support, and the haze value of the heat-sensitive recording material is preferably 55% or less, more preferably 50% or less, and 45% or less. Is more preferable. The haze value is an index representing the transparency of the material, and is a value calculated from (diffuse transmittance / total light transmittance) × 100 (%). Generally, the total light transmission amount using a haze meter. , The diffuse transmitted light amount, and the parallel transmitted light amount. If the haze value is set to be lowered, an image having excellent transparency can be obtained.

In the heat-sensitive recording material of the present invention, it is preferable to use a transparent support in order to obtain a transparent heat-sensitive recording material. Examples of the transparent support include polyester films such as polyethylene terephthalate (PET) and polybutylene terephthalate, cellulose triacetate films, and synthetic polymer films such as polyolefin films such as polypropylene and polyethylene. These may be used alone or bonded together. Can be used.
In the case of medical use, the transparent support may be colored with a blue dye (for example, dye-1 described in Examples of JP-A-8-240877) or may be uncolored. The support is preferably primed with gelatin or water-soluble polyester. Regarding the undercoat layer, for example, those described in JP-A Nos. 51-11420, 51-123139 and 52-65422 can be used. The thickness of the support is preferably 25 to 250 μm, and more preferably 50 to 210 μm.
In the present invention, a PET film having a thickness of 100 μm or more (preferably 150 to 200 μm) is preferably used as the support from the viewpoint of curling reduction after film printing and ease of handling of the film.

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

In particular, when the transparent heat-sensitive recording material of the present invention is observed from the support side on a schacus ten, illusion may occur due to scherkasten light that passes through a transparent non-image portion, resulting in an unsightly image.
In order to avoid this, as the transparent support, A (x = 0.8055, y = 0.3005), B (x = 0.820, on the chromaticity coordinates defined by the method described in JIS-Z8701. y = 0.2970), C (x = 0.2885, y = 0.015), D (x = 0.2870, y = 0.04040) is colored blue in a rectangular region formed by four points It is particularly preferable to use a synthetic polymer film prepared.

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

(Protective layer)
The protective layer is formed on the heat-sensitive recording layer or when the intermediate layer is provided on the heat-sensitive recording layer as another layer. This protective layer is usually formed by applying a protective layer coating solution, and the protective layer coating solution covers a wide recording energy region and contains a pigment and a lubricant in order to provide good head matching properties. Those are preferred. The lubricant preferably contains (A) a liquid or a lubricant having a melting point of less than 40 ° C. and (B) a lubricant having a melting point of 40 ° C. or higher.

  Examples of the lubricant that is liquid at room temperature include silicone oil, liquid paraffin, and lanolin, and silicone oil is particularly preferable. These silicone oils 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 cps.

  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 be substituted with a substituent. n represents an integer of 2 to 50.
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.

The lubricant having a melting point of 40 ° C. or higher is preferably a lubricant having a melting point of 160 ° C. or lower, preferably 140 ° C. or lower, stearic acid amide (melting point 100 ° C.), methylol stearic acid amide (101 ° C.), polyethylene Wax (melting point 110 ° C. or less), paraffin wax with melting point 50 to 90 ° C., glycerin tri-12-hydroxystearate (melting point 88 ° C.), oleic acid amide (melting point 73 ° C.), zinc oleate (melting point 75 ° C.), laurin 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), Palmiti Magnesium acid (melting point 122 ° C.), magnesium myristate (melting point 131 ° C.), and the like.
The above-mentioned lubricant having a melting point of 40 ° C. or higher may be used alone or in combination of two or more.

The protective layer contains (A) a liquid or a lubricant having a melting point of less than 40 ° C. and (B) a lubricant having a melting point of 40 ° C. or more in a mass ratio of (A) :( B) = 65: 35 to 55:45. It is preferable to do. When the mass ratio (A) :( B) of the lubricant exceeds 65:35 and the component (A) is increased, the coating strength of the protective layer is reduced, and the coating is peeled off during handling. In this case, the surface is easily scratched, which is not preferable. When the mass ratio (A) :( B) of the lubricant exceeds 55:45 and the component (B) is increased, the melted lubricant is cooled after recording and crystallized on the surface of the recording material. It is not preferable because it is transferred to a transport roll or guide plate in the apparatus and causes contamination.
In addition, as mass ratio (A) :( B) of said lubricant, the mass of 64: 36-56: 44 is further considered from the viewpoint of further improving the coating film strength and further suppressing crystallization of the melted lubricant. A ratio is more preferable, and a mass ratio of 63:37 to 57:43 is most preferable.

  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 average particle diameter of the dispersion or emulsion is preferably 0.1 to 5.0 μm, more preferably 0.1 to 2.0 μm. Here, the average particle diameter refers to, for example, a 50% volume average particle diameter measured at a transmittance of 71 ± 1% using a laser diffraction particle size distribution measuring device “LA-700” manufactured by Horiba, Ltd. .

  On the other hand, water-soluble lubricants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl ether acetate, polyoxyethylene alkyl ether sulfate, polyoxyethylene alkyl ether phosphate, etc. are optional in consideration of solubility. And can be added to the protective layer.

  Further, the protective layer of the heat-sensitive recording material of the present invention has a surface scratch resistance of 40 g or more as defined in JIS K6718 on the surface thereof in order to prevent coating film peeling during cutting and damage during handling. Preferably. In the present invention, as a test method for the above-mentioned surface scratch hardness, a continuous load type scratch strength tester is used, and a sapphire cone-shaped scratching needle (tip R: 0.1 mm) is used for a movement distance of 100 mm. Scratching the surface of the protective layer by changing the weight continuously in the range of 0 to 200 g, and observing the color developed to a transmission density of 1.2 under transmitted light. The scratch hardness was sought from.

(Pigment)
The protective layer of the heat-sensitive recording material of the present invention contains a pigment. The pigment is usually an organic and / or inorganic pigment that is suitable for recording by a thermal head, that is, for the purpose of suppressing the occurrence of sticking or abnormal noise.

  The pigment used for the protective layer has an average particle size, specifically 50% volume average particle size measured by laser diffraction method (measured with a laser diffraction particle size distribution measuring device “LA700” manufactured by Horiba, Ltd.) The average particle diameter of the pigment particles corresponding to 50% of the volume (hereinafter sometimes referred to simply as “average particle diameter”) is preferably 0.10 to 5 μm, particularly when recording with a thermal head. From the viewpoint of preventing sticking or abnormal noise between the thermal head and the heat-sensitive recording material, the 50% volume average particle size is more preferably in the range of 0.20 to 0.50 μm. When this 50% volume average particle size is in the range of 0.10 to 5.0 μm, the effect of reducing friction with respect to the thermal head is large, and as a result, the thermal head and the protective layer of the thermal recording material adhere to each other at the time of printing. The so-called sticking phenomenon can be effectively prevented.

  The pigment that can be used for the protective layer is not particularly limited, and examples thereof include known organic and inorganic pigments, and in particular, calcium carbonate, titanium oxide, kaolin, aluminum hydroxide, amorphous silica. Inorganic pigments such as zinc oxide and organic pigments such as urea formalin resin and epoxy resin are preferred. Of these, kaolin, aluminum hydroxide, and amorphous silica are more preferable. These pigments may be used alone or in combination of two or more. Among the above-mentioned pigments, a pigment whose surface is coated with at least one or more 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 include stearic acid, palmitic acid, myristic acid, lauric acid and the like.

  These 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 above average particle diameter by a known disperser such as a dissolver, a sand mill, or a ball mill. That is, the pigment is preferably used after being dispersed until the 50% volume average particle size is in the range of 0.1 to 5.0 μm.

(binder)
From the viewpoint of improving the transparency of the protective layer, it is preferable to use polyvinyl alcohol, carboxy-modified polyvinyl alcohol, silica-modified polyvinyl alcohol or the like as a binder.

(Other ingredients)
The protective layer 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, in order to form a protective layer uniformly on the heat-sensitive recording layer or the intermediate layer, it is preferable to add a surfactant to the protective layer forming coating solution. 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 include sodium salts, potassium salts, or ammonium salts, acetylene glycol derivatives, sodium perfluoroalkyl sulfate, potassium salts, ammonium salts, perfluoroalkyl betaine compounds, and the like.

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.

(Middle layer)
The intermediate layer is preferably formed on the thermosensitive recording layer. The intermediate layer is provided to prevent mixing of layers and to block gases (oxygen and the like) harmful to image storage stability. The binder to be used is not particularly limited, and polyvinyl alcohol, gelatin, polyvinyl pyrrolidone, cellulose derivatives and the like can be used depending on the system. Among them, gelatin has fluidity at high temperatures, but has a property (set property) that loses fluidity and gels at low temperatures (for example, 35 ° C. or lower), so that a plurality of layers are formed on a support. In the case of providing the layer by applying and drying a coating solution for forming, the two adjacent layers may be applied by a method in which a plurality of layers are sequentially applied and dried, or in a method in which multiple layers are applied and dried at once by an extrusion die method or the like. The layers can be effectively prevented from mixing with each other, the surface shape of the resulting heat-sensitive recording material is improved, and a heat-sensitive recording material capable of high-quality image formation can be obtained. It is suitable for a medical diagnostic recording material that needs to be formed. Further, even when dried at a high wind speed, the surface condition is not deteriorated, so that the production efficiency is improved.

As such gelatin, unmodified (untreated) gelatin or modified (treated) gelatin can be used without any problem. Examples of modified gelatin include lime-processed gelatin, acid-processed gelatin, phthalated-processed gelatin, deionized-processed gelatin, and enzyme-processed low-molecular-weight gelatin. Further, various surfactants may be added for imparting coatability. In order to further improve the gas barrier properties, inorganic fine particles such as mica may be added to the binder in an amount of 2 to 20% by mass, more preferably 5 to 10% by mass. The binder concentration of the intermediate layer coating solution is 3 to 25% by mass, preferably about 5 to 15% by mass. The dry coating amount of the intermediate layer is 0.5 to 6 g / m ² , preferably 0.8 to 4 g / m ² .

(Undercoat layer)
In the heat-sensitive recording material of the present invention, for the purpose of preventing the heat-sensitive recording layer from being peeled off from the support, before coating the heat-sensitive recording layer containing the microcapsules or the like, the antireflection layer, etc., an undercoat is applied on the support. A layer can be provided.
As the undercoat layer, an acrylate copolymer, polyvinylidene chloride, SBR, aqueous polyester, or the like can be used, and the thickness of the layer is preferably 0.05 to 0.5 μm.

  When 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. Is preferably cured using dialdehydes such as glutaraldehyde, 2,3-dihydroxy-1,4-dioxane, and hardeners such as boric acid. The amount of these hardeners can be appropriately added according to the desired degree of curing in the range of 0.2 to 3.0% by mass depending on the mass of the undercoat material.

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

(Back layer)
The heat-sensitive recording material in the present invention is preferably a single-sided light-sensitive material having a heat-sensitive recording layer containing microcapsules on one side of the support and a back layer (light reflection preventing layer) on the other side. It is preferable to add a matting agent to the back layer (light reflection preventing layer) for the purpose of imparting transportability and preventing light reflection. By adding a matting agent, the glossiness measured at an incident light angle of 20 ° is preferably 50% or less, and more preferably 30% or less.
Examples of the matting agent include fine particles such as starch obtained from barley, wheat, corn, rice, beans, etc., cellulose fiber, polystyrene resin, epoxy resin, polyurethane resin, urea formalin resin, poly (meth) acrylate resin, polymethyl (Meth) acrylate resin, copolymer resin such as vinyl chloride or vinyl acetate, fine particles of synthetic polymer such as polyolefin, calcium carbonate, titanium oxide, kaolin, smectite viscosity, inorganic substances such as aluminum hydroxide, silica, zinc oxide Examples thereof include fine particles. The average particle size of the matting agent is 0.5 to 20 μm, preferably 0.5 to 10 μm. The mat materials may be used alone or in combination of two or more.

  Further, from the viewpoint of improving the transparency of the heat-sensitive recording material, the refractive index is preferably in the range of 1.4 to 1.8. Various dyes (for example, CI Pigment Blue 60, CI Pigment Blue 64, CI Pigment Blue 15: 6) can be used for the back layer from the viewpoint of improving the hue. Further, a hardener may be used for the back layer. Examples of the hardener include T.W. H. There are various methods described in “THE THEORY OF THE PHOTOGRAPHIC PROCESS 4th EDITION” by James (pages 77 to 87), and vinyl sulfone compounds are preferred.

(Method for producing thermosensitive recording material)
Hereinafter, the method for producing the heat-sensitive recording material of the present invention will be described.
In the heat-sensitive recording material of the present invention, a heat-sensitive recording layer forming coating solution is applied onto a support to form a heat-sensitive recording layer. If necessary, a protective layer-forming coating solution is applied on the heat-sensitive recording layer. The protective layer can be formed by coating, and other layers can be formed as necessary.
Here, the heat-sensitive recording layer and the protective layer may be formed at the same time. In this case, the heat-sensitive recording layer-forming coating solution and the protective-layer-forming coating solution are simultaneously coated on the support to form heat. A recording layer and a protective layer can be simultaneously formed thereon.

As the support used here, the support described above used in the heat-sensitive recording material of the present invention can be used. Further, as the heat-sensitive recording layer forming coating solution, the above-mentioned heat-sensitive recording layer coating solution can be used. Further, the protective layer-forming coating solution is also for the protective layer containing the pigment and the binder described above. A coating solution can be used.
Moreover, as said other layer, other layers, such as the intermediate | middle layer mentioned above and undercoat, are mentioned.
In order to sequentially form an undercoat layer, thermosensitive recording layer, intermediate layer, protective layer, etc. on the support, blade coating method, air knife coating method, gravure coating method, roll coating coating method, spray coating method, dip coating method A known coating method such as a bar coating method, a slide coating method using an extrusion die, or the like is used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not restrict | limited at all by these Examples. In the following, “%” represents “% by mass” unless otherwise specified.

[Example 1]
(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. .

  The average particle size is determined by dispersing a 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. After being poured into warm water and adjusted so that the light transmittance is 72 ± 1%, ultrasonic treatment is performed for 30 seconds, and a laser diffraction particle size distribution measuring apparatus (trade name “LA700” manufactured by Horiba, Ltd.) The average particle diameter of the pigment particles corresponding to 50% volume of the total pigment measured by “)” is used, and the average particle diameters described below all represent the average particle diameter measured by the same method.

(2) Preparation of coating solution for protective layer As a coating solution for protective layer,
・ 5% polyvinyl alcohol aqueous solution …… 430g
(Product name “PVA124C” manufactured by Kuraray Co., Ltd.)
・ 72% sodium dodecylbenzenesulfonate aqueous solution ............ 5g
・ 50% acetylene glycol surfactant aqueous solution …… 5.5g
(Product name “Surfinol 104E” manufactured by Nisshin Chemical Co., Ltd.)
・ "Surflon S131S" (Asahi Glass Co., Ltd.) ... 10g
・ Polyoxyethylene alkyl phosphate ester …… 2g
(Plysurf A217E manufactured by Daiichi Kogyo Seiyaku Co., Ltd., melting point 35 ° C.)
・ The above 18% pigment dispersion …… 245g
・ 20.5% zinc stearate dispersion …… 21g
(Product name “F115” manufactured by Chukyo Yushi Co., Ltd.)
・ 18% stearic acid dispersion ………… 31g
(Product name “Cerosol 920” manufactured by Chukyo Yushi Co., Ltd.)
・ 35% silicone oil dispersion ……… 41.5g
(Product name “BY22-840” manufactured by Toray Dow Corning Co., Ltd.)
・ 5% styrene-maleic acid copolymer ammonium salt aqueous solution …… 110g
(Product name “Polymaron 385” manufactured by Arakawa Chemical Co., Ltd.)
・ 20% colloidal silica ………… 53g
(Product name "Snowtex O" manufactured by Nissan Chemical Co., Ltd.)
・ 4% boric acid aqueous solution …… 70g
・ 2% acetic acid aqueous solution ………… 30g
-Compound of the above structural formula [002] (50% aqueous solution) 22g
Were mixed, and water was added thereto to adjust the concentration to 12% to obtain a desired protective layer coating solution. The total mass of the lubricant (A) liquid or melting point of 40 ° C. or lower contained in the protective layer coating solution is 16.53 g, and the total mass of the solid lubricant (B) at normal temperature is 11.24 g. Yes, the mass ratio (A) :( B) of both is 59.5: 40.5.

(Preparation of coating solution for thermosensitive recording layer)
According to the following procedure, a microcapsule liquid having an electron donating dye precursor as a core substance and a solid dispersion of a developer 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 [202], 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 the compound represented by the following structural formula [207] 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 Takeda Pharmaceutical Co., Ltd.) was added and mixed. This solution was added to a 5.9% polyvinyl alcohol aqueous solution (trade name “MP-103, manufactured by Kuraray Co., Ltd.”). ”) After being added to 300 g of the aqueous phase, emulsification and dispersion were carried out at a rotational speed of 15000 rpm using an ace homogenizer (manufactured by Nippon Seiki Co., Ltd.). 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 solution A 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 [202], 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] were added to 110 g of ethyl acetate, heated to 70 ° C. and dissolved, and then cooled to a temperature of 45 ° C. To this was added 65.5 g of capsule wall material (trade name “Takenate D127N” manufactured by Takeda Pharmaceutical Co., Ltd.) and mixed. This solution was added to a 5.9% aqueous polyvinyl alcohol solution (trade name “MP” manufactured by Kuraray Co., Ltd.). -103 ") was added to 275 g of the aqueous phase, and then emulsified and dispersed at a rotational speed of 15000 rpm using an ace homogenizer (manufactured by Nippon Seiki Co., Ltd.). 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 solution B having a diameter of 0.3 μm was obtained.

(3) Preparation of solid dispersion of developer Add developer 1 shown below (exemplary compound: (A)), developer 2, and ultraviolet absorber to the aqueous phase of the formulation shown below. And dispersed into fine particles with a Dynomill manufactured by Shinmaru Enterprise Co., to obtain a developer solid dispersion having a particle size of 0.21 μm. The concentration of the obtained developer solid dispersion was adjusted with water so that the solid content was 18%. The particle size of the developer solid dispersion is such that the test liquid diluted to 0.5% by mass with water added to the solid dispersion is poured into warm water at 40 ° C., and the light transmittance is 70 ± 1%. After being adjusted so as to be, particles treated with ultrasonic waves for 30 seconds and measured with a laser diffraction particle size distribution measuring device (trade name: LA910, manufactured by Horiba, Ltd.), particles corresponding to 50% volume of the total solid content The average particle diameter.

(Formulation of solid dispersion of developer)
-Component A-
Developer 1 (Exemplary Compound: (A)) 7.3 g
Developer 2 (compound having the following structural formula and amorphous properties) 7.3 g
Ultraviolet absorber (the following structural formula) 1.2g

-Component B (aqueous phase)-
Protective colloid 1 24.8g
(8% polyvinyl alcohol, “PVA217C” manufactured by Kuraray Co., Ltd.)
Protective colloid 2 7.2g
(15% polyvinyl alcohol, “PVA205” manufactured by Kuraray Co., Ltd.)
Protective colloid 3 7.2g
(15% polyvinyl alcohol, “MP203” manufactured by Kuraray Co., Ltd.)
Surfactant (2% aqueous solution) (the following structural formula) 12.7 g

(4) Preparation of coating liquid A for thermosensitive recording layer 160 g of the above microcapsule A liquid (solid content concentration 25%), 30 g of the above microcapsule B liquid (solid content concentration 28%), solid dispersion of the above developer (solid) 710 g (partial concentration 18%), 7.2 g of 50% aqueous solution of the compound represented by the structural formula [002], and 25.5 g of colloidal silica (trade name “Snowtex O” manufactured by Nissan Chemical Co., Ltd.) Then, the concentration was adjusted to 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%), solid dispersion of the above developer (solid) 725 g, concentration of 18%), 6.5 g of 50% aqueous solution of the compound represented by the structural formula [001], and 23.5 g of colloidal silica (trade name “Snowtex O” manufactured by Nissan Chemical Co., Ltd.) Then, the concentration was adjusted to 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 1 kg of lime-processed gelatin and dissolved, a 5% solution of di-2-ethylhexylsulfosuccinic acid Na salt (“Nissan Rapisol B90” manufactured by NOF Corporation) (water / methanol = 1 / 137 g of 1 volume mixed solvent), 25 g of 3.5% 1,2-benzisothiazolin-3-one aqueous solution, 1080 g of 3.0% poly (sodium p-vinylbenzenesulfonate) (molecular weight: about 400,000) Was added to prepare a target intermediate layer coating solution.

(Preparation of coating solution A for the back layer)
UV absorption containing 1 kg of lime-processed gelatin, 180 g of gelatin dispersion containing 12% of spherical PMMA particles having an average particle size of 5.7 μm, and compounds represented by the following structural formulas [501] to [505] with the following contents 1028 g of the emulsion of the agent [wherein the ultraviolet absorber content per kg of the emulsion is 14.9 g of the compound represented by the structural formula [501] and 12.7 g of the compound represented by the structural formula [502]. 14.9 g of the compound represented by the structural formula [503], 21.1 g of the compound represented by the structural formula [504], and 44.5 g of the compound represented by the structural formula [505]. And 0.98 g of 1,2-benzisothiazolin-3-one, 16.4 g of poly (sodium p-vinylbenzenesulfonate) (molecular weight: about 400,000), compound 3 represented by the following structural formula [506] .79 g, 1448 mL of 20% latex solution of polyethyl acrylate, 52.2 g of N, N-ethylene-bis (vinylsulfonylacetamide), and 17.4 g of 1,3-bis (vinylsulfonylacetamide) propane, water added to above The total amount was adjusted to 21.03 liters to prepare the desired back layer coating solution (A).

(Preparation of coating solution B for back layer)
10 kg of gelatin dispersion containing 1 kg of lime-processed gelatin and 15% of spherical PMMA particles having an average particle size of 0.7 μm, 2.09 g of 1,2-benzisothiazolin-3-one, p-tert-octylphenoxypolyoxyethylene- 9.53 g of sodium ethylene sulfonate, 57.9 g of sodium polyacrylate (molecular weight: about 100,000), 22.9 g of poly (sodium p-vinylbenzenesulfonate) (molecular weight: about 400,000), N-propyl-N- Polyoxyethylene-perfluorooctanesulfonamide sodium butyl sulfonate 0.37 g, hexadecyloxy-nonyl (ethyleneoxy) -ethanol 8.97 g, 1N sodium hydroxide 28.1 g, M, M-ethylene-bis (vinylsulfonylacetamide) ) 18.0 g and 1 3- (vinyl sulfonyl acetamide) propane 6.0 g, adjusted to be 26.59 l of total volume by adding water to the above, the back layer coating solution for the purpose of (B) was prepared.

(Preparation of thermal recording material)
(1) Production of Back Layer A transparent PET support (thickness of 175 μm) prepared by blue staining with chromaticity coordinates defined by the method described in JIS-Z8701 with X = 0.2850 and Y = 0.29995 is prepared. From the side close to the support, the coating amount is 51.4 mL / m ² and 14.7 mL / m ² in the order of the back layer coating solution (A) and the back layer coating solution (B), respectively. A simultaneous multilayer coating was applied by a slide bead method and dried. The coating and drying conditions are as follows. The coating speed was 160 m / min, the distance between the coating die tip and the support was 0.10 to 0.30 mm, and the pressure in the decompression chamber was set 200 to 900 Pa lower than the atmospheric pressure. The support was neutralized with an ion wind before coating. In the subsequent chilling zone, the coating liquid is cooled with a wind at a dry bulb temperature of 10 to 20 ° C., then conveyed in a non-contact manner, and dried at a dry bulb temperature of 23 to 45 ° C. and a wet bulb temperature by a helical contactless drying device. It dried with the dry wind of 15-21 degreeC.

(2) Formation of thermosensitive recording layer From the side close to the support, the thermosensitive recording layer coating solution (A) and the thermosensitive recording layer coating are formed on the side opposite to the back layer of the support coated with the above back layer. The coating amounts of the liquid (B), the intermediate layer coating solution, and the protective layer coating solution were 41.3 mL / m ² , 22.5 mL / m ² , 24.7 mL / m ² , 27.5 mL / and simultaneous multilayer coating and drying by a slide bead method such that m ^2, the heat-sensitive recording layer on a support (a), the heat-sensitive recording layer (B), an intermediate layer, a protective layer, and the present invention having a backing layer A transparent thermosensitive recording material was obtained. The coating solution for each layer was adjusted to a temperature range of 33 ° C to 37 ° C. The drying conditions are as follows. 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 the wet bulb temperature 17-23 degreeC, and humidity was adjusted by the humidity 40-60% at the temperature of 25 degreeC after drying.

[Example 2]
Developer 1 (7.3 g) of Component A in “(3) Preparation of solid dispersion of developer” in Example 1 was changed to Developer 3 (Exemplary Compound (B)) (7.3 g). A heat-sensitive recording material of Example 2 was produced in the same manner as Example 1 except for the change. The particle size of the developer solid dispersion was 0.28 μm.

[Comparative Example 1]
Except for changing the developer A (7.3 g) of component A in “(3) Preparation of solid dispersion of developer” in Example 1 to a developer (7.3 g) having the following structure: A thermosensitive recording material was produced in the same manner as in Example 1. The particle size of the developer solid dispersion was 0.32 μm.

[Comparative Example 2]
Except for changing the developer A (7.3 g) of component A in “(3) Preparation of solid dispersion of developer” in Example 1 to a developer (7.3 g) having the following structure: A thermosensitive recording material was produced in the same manner as in Example 1. The particle size of the developer solid dispersion was 0.24 μm.

[Comparative Example 3]
Except for changing the developer A (7.3 g) of component A in “(3) Preparation of solid dispersion of developer” in Example 1 to a developer (7.3 g) having the following structure: A thermosensitive recording material was produced in the same manner as in Example 1. The particle size of the developer solid dispersion was 0.38 μm.

[Comparative Example 4]
The addition amount of developer 2 was set to 14.6 g without adding developer A (7.3 g) of component A in “(3) Preparation of solid dispersion of developer” in Example 1. A thermosensitive recording material was prepared in the same manner as in Example 1 except for the above. The particle size of the developer solid dispersion was 0.35 μm.

[Comparative Example 5]
Example 1 except that the addition amount of the developer A of component A in “(3) Preparation of solid dispersion of developer” in Example 1 was 14.6 g, and the developer 2 was not added. A thermosensitive recording material was produced in the same manner as described above. The particle size of the developer solid dispersion was 0.28 μm.

(Test evaluation)
The heat-sensitive recording material obtained above was evaluated by the following method. The evaluation results are shown in Table 1 below.
(1) Measurement of haze value The haze values of the heat-sensitive recording materials of Examples 1-2 and Comparative Examples 1-5 were measured with a haze meter (device name: HGM-2DP, manufactured by Suga Test Instruments Co., Ltd.). A haze value of 55% or more is judged to be unusable from the viewpoint of transparency. Preferably, it is 50% or less. In Table 1, “◯” indicates that the haze value is less than 55%, and “x” indicates that it is 55% or more.

(2) Measurement of color density Using a thermal head (trade name: KGT, 260-12MPH8, manufactured by Kyocera Corporation), the obtained thermal recording material was subjected to a head pressure of 10 kg / cm ² and a recording energy of 70 mJ / mm ² . The sensitivity was evaluated from the optical density (OD) at the time of printing. The larger the value of OD, the better, 1.2 or more is more preferable, and 1.3 or more is more preferable. The optical density OD was measured in a visual filter mode using a transmission densitometer (Macbeth TD904: manufactured by Macbeth). In Table 1, “◯” indicates that OD is 1.2 or more, and “×” indicates less than 1.2.

  From Table 1, it can be seen that the heat-sensitive recording materials of Examples 1 and 2 obtained good results in both sensitivity and haze, and were able to achieve both high sensitivity and haze. In contrast, the heat-sensitive recording materials of Comparative Examples 1 to 5 were inferior in at least one of sensitivity and haze.

Claims (5)

A thermosensitive recording material having a thermosensitive recording layer comprising a microcapsule encapsulating a colorless or light-colored electron-donating dye precursor and at least two solid-dispersed developers on a support,
A heat-sensitive recording material comprising a compound represented by the following general formula (1) and a compound having an amorphous property as the two kinds of solid dispersion developers.

[In General Formula (1), R ¹ and R ² each independently represents an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an aralkyl group, an alkoxy group, or a halogen atom. ]   2. The heat-sensitive recording material according to claim 1, wherein the wall material of the microcapsule is made of polyurethane, polyurea, or a composite of both.   The heat-sensitive recording material according to claim 1, wherein the support is a polymer film, and the haze value of the heat-sensitive recording material is 55% or less.   The thermosensitive recording material according to any one of claims 1 to 3, wherein the support is a polyethylene terephthalate film having a thickness of 100 µm or more.   The developer contained in the solid dispersion is solid-dispersed with one or more water-soluble polymers selected from partially saponified polyvinyl alcohol and gelatin. The heat-sensitive recording material according to Item.