JP2006289703A - Thermal recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-sensitive recording material which has little change in recording sensitivity due to a change in environmental humidity of the heat-sensitive recording material, and which is excellent in moisture resistance preservation and heat-resistant background fogging property.
SOLUTION: In a heat-sensitive recording layer in which a heat-sensitive recording layer containing a leuco dye and a colorant is provided on a support, the heat-sensitive recording layer contains the leuco dye in a form in which composite particles are formed with a hydrophobic resin. 2,4'-dihydroxydiphenylsulfone as a colorant and 2-[(4-hydroxyphenyl) methyl] -6-[(2-hydroxyphenyl) methyl] -4- (sec-butyl) phenol And a specific compound such as 2,6-bis [(4-hydroxyphenyl) methyl] -4- (sec-butyl) phenol.
[Selection figure] None

Description

  The present invention relates to a heat-sensitive recording material utilizing a color reaction between a leuco dye and a color former, and more particularly to a heat-sensitive recording material with little fluctuation in recording sensitivity due to a change in environmental humidity.

  2. Description of the Related Art Conventionally, a heat-sensitive recording material using a color development reaction caused by heat between a leuco dye and a color former is well known. Such a thermal recording medium is relatively inexpensive, and the recording device is compact and relatively easy to maintain, so that it is not only used as a recording medium for facsimiles and various computers, but also for ultrasonic image diagnosis and X-ray image diagnosis. In addition to recording media used for printers of medical diagnostic devices such as CAD, it is also used as recording media for CAD plotters.

A method of using composite particles obtained by microencapsulating a leuco dye and a hydrophobic organic solvent with a wall film material made of a hydrophobic resin such as polyurea or polyurethane in order to enhance the storage stability of the recording part of the thermal recording medium (Patent Document) 1 and 2), a method using composite particles obtained by polymerizing acrylic hydrophobic resin such as methacrylate on the surface of leuco dye (see Patent Document 3), and leuco dye from polyurea or polyurethane-polyurea resin. There have been proposed methods using composite particles obtained by inclusion in a hydrophobic resin (see Patent Documents 4 and 5).
However, a thermal recording medium using a leuco dye and a colorant, depending on the material used, changes the recording sensitivity when the moisture in the thermal recording layer changes with the humidity change in the environment in which the recording medium is used. There is a drawback that it is difficult to always obtain a constant recording density in the region, and this defect becomes remarkable particularly when a support such as a synthetic resin film is used. For this reason, a thermal recording medium for medical diagnosis is required that can be recorded with multiple gradations, and that the recording density of the halftone area is always constant regardless of the humidity change of the environment. There is a strong demand for improvement.

  The use of 2,4'-dihydroxydiphenylsulfone as a colorant for a heat-sensitive recording material has been known for a long time (see Patent Document 6), and a recorded image can be obtained by using such a colorant and a specific fluorene leuco dye. A method (Patent Document 7) for obtaining a heat-sensitive recording material having improved storage stability is also proposed. In addition, thermal recording with enhanced storage stability of recorded images by using a phenol trinuclear such as 2,6-bis [(2-hydroxy-5-methylphenyl) methyl] -4-methylphenol as a colorant. A method for obtaining a body (Patent Document 8) has also been proposed.

JP 60-244594 A (Claim 1) JP 61-86283 A (Example 1) JP 2000-158822 A (Claims 1 and 7) JP-A-9-263057 (Claim 1) JP-A-2003-266951 (Claim 1) JP 63-3991 A (Claim 1) Japanese Unexamined Patent Publication No. 63-4990 (Example 4) JP-A-6-115255 (Example 9)

  SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive recording material that is less susceptible to changes in recording sensitivity due to changes in environmental humidity of the heat-sensitive recording material, and that is excellent in moisture-resistant storage and heat-resistant background fogging.

  The present invention relates to a thermosensitive recording medium in which a thermosensitive recording layer containing a leuco dye and a colorant is provided on a support, and the thermosensitive recording layer contains the leuco dye in a form in which composite particles are formed with a hydrophobic resin. The colorant contains at least one compound represented by the following general formula (1) (hereinafter referred to as a specific compound) and 2,4′-dihydroxydiphenylsulfone.

［式中、Ｒはｎ−ブチル基、ｉｓｏ−ブチル基、ｓｅｃ−ブチル基またはｔｅｒｔ−ブチル基を表す。］

[Wherein, R represents an n-butyl group, an iso-butyl group, a sec-butyl group or a tert-butyl group. ]

  The heat-sensitive recording material of the present invention has the advantage that the recording sensitivity varies little due to the environmental humidity change of the heat-sensitive recording material, and exhibits excellent effects in moisture resistance storage resistance and heat-resistant background fogging.

In the present invention, the leuco dye is used in the form of composite particles made of a hydrophobic resin in the heat-sensitive recording layer, and at least 2,4'-dihydroxydiphenylsulfone and the specific compound are contained as a colorant. Is extremely important, and by adopting such a configuration, there is little fluctuation in recording sensitivity due to environmental humidity change of the thermosensitive recording material, and further, an effect excellent in moisture-resistant storage stability and heat-resistant background fogging property can be obtained.
Although the compound represented by the general formula (1) may be used alone, it is preferable to use the following general formulas (2) and (3) in combination.

［式中、Ｒ_１、Ｒ_２はｎ−ブチル基、ｉｓｏ−ブチル基、ｓｅｃ−ブチル基またはｔｅｒｔ−ブチル基を表す。］
上記一般式（２）及び（３）の併用比率は特に限定するものではないが、質量比で７０：３０〜３０：７０程度が好ましい。
また、上記一般式（２）及び（３）で表される化合物として、２−［（４−ヒドロキシフェニル）メチル］−６−［（２−ヒドロキシフェニル）メチル］−４−（ｓｅｃ−ブチル）フェノールと２，６−ビス［（４−ヒドロキシフェニル）メチル］−４−（ｓｅｃ−ブチル）フェノールを併用すると特に環境湿度変化による記録感度の変動が少なく好ましい。
尚、本発明の呈色剤として、前記の特定の３核体化合物以外に合成時の副生成物として生成される多核体の混合物が含有されていてもよい。
本発明は、各種の呈色剤のうちで前記特定の化合物が感熱記録体の環境湿度変化による記録感度の変動を抑制するという特異な効果を見出してなされたものであり、このため呈色剤として前記特定の化合物を使用しない場合には、記録感度、特に中間調領域の記録感度が、感熱記録体を使用する環境の湿度変化に左右される記録体になってしまう。また、２，４′−ジヒドロキシジフェニルスルホンを併用することにより、記録画像の耐湿保存性が向上し、更に記録濃度を高めることもできる。なお、前記特定の化合物と２，４′−ジヒドロキシジフェニルスルホンとの併用比率は８０：２０〜３０：７０程度が好ましい。

[Wherein R ₁ and R ₂ represent an n-butyl group, an iso-butyl group, a sec-butyl group, or a tert-butyl group. ]
The combined ratio of the general formulas (2) and (3) is not particularly limited, but is preferably about 70:30 to 30:70 in terms of mass ratio.
In addition, as the compounds represented by the general formulas (2) and (3), 2-[(4-hydroxyphenyl) methyl] -6-[(2-hydroxyphenyl) methyl] -4- (sec-butyl) When phenol and 2,6-bis [(4-hydroxyphenyl) methyl] -4- (sec-butyl) phenol are used in combination, the change in recording sensitivity due to changes in environmental humidity is particularly small.
In addition to the specific trinuclear compound, the colorant of the present invention may contain a mixture of polynuclear bodies produced as a by-product during synthesis.
The present invention has been made by finding the specific effect that among the various colorants, the specific compound suppresses the change in recording sensitivity due to the environmental humidity change of the heat-sensitive recording material. When the specific compound is not used, the recording sensitivity, particularly the recording sensitivity in the halftone region, becomes a recording body that depends on the humidity change in the environment where the thermal recording body is used. Further, by using 2,4′-dihydroxydiphenyl sulfone together, the moisture-preserving stability of the recorded image is improved, and the recording density can be further increased. The combined ratio of the specific compound and 2,4′-dihydroxydiphenylsulfone is preferably about 80:20 to 30:70.

The present invention further provides 4,4′-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylsulfone and 4,4′-bis (Np-tolylsulfonylaminocarbonylamino) as colorants. By containing at least one compound selected from diphenylmethane, there is an effect of adjusting the recording density of the halftone region, which is preferable.
At least one compound selected from 4,4′-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylsulfone and 4,4′-bis (Np-tolylsulfonylaminocarbonylamino) diphenylmethane Is preferably 15 to 75% by mass with respect to the specific compound.

In the present invention, the specific compound and 2,4′-dihydroxydiphenylsulfone are selectively used as a colorant, but other colorants may be used depending on the purpose within a range not inhibiting the desired effect of the present invention. A colorant can also be used in combination. Examples of such other colorants include 4,4′-isopropylidenediphenol, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, benzyl 4-hydroxybenzoate, and 4,4′-dihydroxy. Diphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, 4-hydroxy-4'-allyloxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenylsulfone , 3,4-dihydroxyphenyl-4'-methylphenylsulfone, bis (4-hydroxyphenylthioethoxy) methane, phenol compounds such as bis (p-hydroxyphenyl) acetic acid butyl, N- (p-toluenesulfonyl) carbamoyl acid -P-cumylphenyl ester, N- ( p-tolylsulfonyl) -N′-phenylurea, N- (o-tolyl) -p-tolylsulfamide, etc., a compound having —SO ₂ NHCO— bond in the molecule, zinc p-chlorobenzoate, 4- [ Zinc 2- (p-methoxyphenoxy) ethyloxy] salicylate, zinc 4- [3- (p-tolylsulfonyl) propyloxy] salicylate, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] zinc salicylate, etc. Examples thereof include zinc salts of aromatic carboxylic acids.

  The use ratio of the colorant is not particularly limited, but is preferably about 10 to 60% by mass with respect to the total solid content of the heat-sensitive recording layer. If the total use ratio of the colorants is less than 10% by mass, the recording sensitivity may be lowered, and if it exceeds 60% by mass, the maximum recording density may be lowered due to a decrease in the ratio of the leuco dye.

  Depending on the purpose, it does not impair the desired effect of the present invention, and may contain a preservability improver, such as 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 2,2′-ethylidenebis ( 4,6-di-tert-butylphenol), 1,4-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, 1,3-bis [α-methyl-α- (4′- Hydroxyphenyl) ethyl] benzene, 4,4'-thiobis (2-methyl-6-tert-butylphenol), 1,3,5-tris (4-tert-butyl-3-hydroxy-2,6 Dimethylbenzyl) isocyanuric acid and the like. In addition, the usage ratio of the storage stability improving agent is preferably about 10 to 40% by mass with respect to the total colorants.

The form in which the leuco dye specified in the present invention is made into composite particles with a hydrophobic resin is, for example, a form in which one or more leuco dyes and a hydrophobic organic solvent are encapsulated in a resin film to form a microcapsule. It includes a form in which a hydrophobic resin is polymerized on the surface of the above leuco dye particles, or a form in which one or more leuco dyes are dispersed in solid resin particles. The volume average particle size of the composite particles is preferably about 0.5 to 3.0 μm.
It is preferable that the hydrophobic resin forming the composite particles is a urea-based resin or a urea-urethane-based resin from the viewpoint of obtaining a heat-sensitive recording material excellent in heat resistance, particularly heat-resistant background fogging.

  Specific examples of the leuco dye in the composite particles include 3- [2,2-bis (1-ethyl-2-methylindol-3-yl) vinyl] -3- (4-diethylaminophenyl) phthalide, 3, 3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl) -6-dimethylaminophthalide, 3- Cyclohexylamino-6-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6,8-dimethylfluorane, 3-diethylamino-6,7-dimethylfluorane, 3-diethylamino -7-chlorofluorane, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluorane, -Di (n-butyl) amino-6-methyl-7-anilinofluorane, 3-di (n-pentyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-p- Toluidino) -6-methyl-7-anilinofluorane, 3-di (n-butyl) amino-6-chloro-7-anilinofluorane, 3-diethylamino-6-methyl-7- (3-toluidino) Fluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3,3-bis (4-diethylamino-2-ethoxyphenyl) -4- Azaphthalide, 3,3-bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl) ethylene-2-yl] -4,5,6,7-tetrachlorophthalide, 3-p- (P-di Tilaminoanilino) anilino-6-methyl-7-chlorofluorane, 3-p- (p-chloroanilino) anilino-6-methyl-7-chlorofluorane, 3- [1,1-bis (1-ethyl) -2-methylindol-3-yl)]-3-p-diethylaminophenylphthalide, 3,3-bis (1-n-butyl-2-methylindol-3-yl) phthalide, 3,6-bis ( And dimethylamino) fluorene-9-spiro-3 ′-(6′-dimethylamino) phthalide.

  The total content ratio of the leuco dye in the composite particles is about 10 to 70% by mass, preferably about 35 to 60% by mass, based on the total solid content of the composite particles.

  The leuco dye in the composite particles is highly separable from the outside, there is little background fogging due to heat and humidity, and the color image is not decolored, and the leuco dye is dissolved in isocyanate or an organic solvent, so the transparency of the thermal recording layer is high. This is superior to the case where the leuco dye is used in a solid fine particle state.

  Although it does not specifically limit as hydrophobic resin which forms a composite particle, For example, urea type resin, urethane type resin, urea-urethane type resin, styrene type resin, acrylic resin etc. are mentioned. Of these, urea-based resins, urethane-based resins, and urea-urethane-based resins are preferable because they have excellent heat-resistant background fogging properties as described above.

  When preparing composite particles in which a leuco dye is dispersed in a urea resin or a urea-urethane resin, for example, an oily solution in which a polyvalent isocyanate compound and a leuco dye are dissolved in a hydrophilic protective colloid solution such as polyvinyl alcohol. In addition, it is obtained by accelerating the polymerization reaction of the polyvalent isocyanate compound after emulsification and dispersion so that the average particle diameter is about 0.5 to 3 μm, and is a preferable composite particle because of excellent recording sensitivity.

  The polyisocyanate compound is a compound that forms polyurea or polyurea-polyurethane by reacting with water, and may be a polyisocyanate compound alone, or a polyisocyanate compound and a polyol or polyamine that reacts with the polyisocyanate compound Or an adduct of a polyvalent isocyanate compound and a polyol, or a multimer such as a biuret or isocyanurate. A leuco dye is dissolved in these polyvalent isocyanate compounds, and this solution is emulsified and dispersed in an aqueous medium containing a protective colloidal substance such as polyvinyl alcohol, and further, if necessary, a reactive substance such as polyamine is mixed, By heating this emulsified dispersion, the polymer-forming raw material is polymerized to polymerize, thereby forming composite particles composed of a leuco dye and a polymer substance.

  Specific examples of the polyvalent isocyanate compound include, for example, p-phenylene diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate, naphthalene-1,4-diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, 3,3′-dimethyldiphenylmethane-4,4′-diisocyanate, xylylene-1,4-diisocyanate, tetramethylxylylene diisocyanate, 4,4′-diphenylpropane diisocyanate, Hexamethylene diisocyanate, butylene-1,2-diisocyanate, cyclohexylene-1,2-diisocyanate, cyclohexylene-1,4-diisocyanate, 4,4 ', 4 "-triphenylmethane Examples include reisocyanate, toluene-2,4,6-triisocyanate, trimethylolpropane adduct of hexamethylene diisocyanate, trimethylolpropane adduct of 2,4-tolylene diisocyanate, trimethylolpropane adduct of xylylene diisocyanate, and the like. It is done.

  Specific examples of the polyol compound include, for example, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,7-heptanediol, 1,8-octanediol, propylene glycol, and 1,3-dihydroxy. Butane, 2,2-dimethyl-1,3-propanediol, 2,5-hexanediol, 3-methyl-1,5-pentanediol, 1,4-cyclohexanedimethanol, dihydroxycyclohexane, diethylene glycol, phenylethylene glycol, Pentaerythritol, 1,4-di (2-hydroxyethoxy) benzene, 1,3-di (2-hydroxyethoxy) benzene, p-xylylene glycol, m-xylylene glycol, 4,4′-isopropylidenediphenol 4,4'-dihydroxy Diphenyl sulfone, and the like.

  Specific examples of the polyamine compound include ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, p-phenylenediamine, m-phenylenediamine, 2,5-dimethylpiperazine, triethylenetriamine, and triethylene. Examples include tetramine and diethylaminopropylamine.

Of course, the polyvalent isocyanate compound, the adduct of polyvalent isocyanate and polyol, the polyol compound, and the like are not limited to the above compounds, and two or more kinds may be used in combination as necessary.
Further, in the composite particles, an aromatic organic compound (sensitizer) having a melting point of about 40 to 150 ° C. for increasing the recording sensitivity, an ultraviolet absorber for increasing light resistance, and a hindered phenol as a stabilizer, A hindered amine or the like can also be contained.

  The content ratio of the composite particles in the heat-sensitive recording layer is about 10 to 60% by mass, preferably about 20 to 50% by mass, based on the total solid content of the heat-sensitive recording layer. The ratio of the composite particles and the colorant in the heat-sensitive recording layer is about 50 to 300 parts by weight, preferably about 100 to 200 parts by weight with respect to 100 parts by weight of the composite particles.

  In addition, the heat-sensitive recording layer may contain a sensitizer that can be contained in the composite particles, an ultraviolet absorber for enhancing light resistance, and a hindered phenol, hindered amine, or the like as a stabilizer. it can.

The heat-sensitive recording layer is generally obtained by drying a coating liquid for a heat-sensitive recording layer prepared by mixing and stirring composite particles, a specific colorant, an adhesive, and an auxiliary agent on a support, using water as a medium. It is formed by coating and drying so that the coating amount is about 3 to 25 g / m ² .

  The heat-sensitive recording layer may have a structure of a multilayer color forming layer in which a plurality of leuco dyes are arranged in different layers, or a structure of a single layer color forming layer in which a plurality of leuco dyes are contained in the same layer. . However, in the case of a heat-sensitive recording medium having a transparent support, a single-layer color forming layer in which a plurality of leuco dyes are contained in the same layer is preferred from the viewpoint of haze.

  The method for forming the heat-sensitive recording layer is not particularly limited. For example, known appropriate application such as air knife coating, varibar blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, die coating, gravure coating, etc. Formed by the method.

  Examples of the adhesive compounded in the thermal recording layer coating liquid include polyvinyl alcohols such as partially saponified or fully saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol. Starch and its derivatives, cellulose derivatives such as hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose, ethylcellulose, polyvinylpyrrolidone, acrylamide-acrylic acid ester copolymer, acrylamide-acrylic acid ester-methacrylic acid ester copolymer, styrene -Water-soluble adhesives such as maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, casein, gelatin, Vinyl acetate-based latex in beauty, urethane latex, acrylic latex, styrene - butadiene latex, and the like.

  Examples of the auxiliary agent include surfactants such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate / sodium salt, and fatty acid metal salts, and waxes such as polyethylene wax, carnauba wax, paraffin wax, and ester wax. , Kaolin, clay, talc, calcium carbonate, calcined kaolin, titanium oxide, amorphous silica, pigments such as aluminum hydroxide, glyoxal, formalin, glycine, glycidyl ester, glycidyl ether, dimethylol urea, ketene dimer, dialdehyde starch, melamine Water resistance agents such as resins, polyamide resins, polyamide-epichlorohydrin resins, ketone-aldehyde resins, borax, boric acid, ammonium zirconium carbonate, epoxy compounds, etc. Other defoaming agents, fluorescent dyes, coloring dyes and the like.

  The support on which the heat-sensitive recording layer is provided is not particularly limited, and examples thereof include high-quality paper, laminated paper, polyethylene terephthalate, polypropylene and polyethylene. The thickness is about 20 to 200 μm and may be colored. In particular, when a transparent film is used as a support, the improvement effect of the present invention such as a change in recording sensitivity due to a change in environmental humidity and an image quality can be exhibited. In addition, an anchor coat layer can be provided on the surface or a corona discharge treatment can be performed to enhance the adhesion to the heat-sensitive recording layer. Further, a conductive treatment with a conductive agent may be performed.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Unless otherwise specified, “parts” and “%” represent “parts by mass” and “mass%”, respectively.

Example 1
-Liquid A dispersion (preparation of composite particle dispersion)
11 parts of 3-diethylamino-6-methyl-7- (3-toluidino) fluorane, 6 parts of 3-diethylamino-6,8-dimethylfluorane and 3,3-bis (4-diethylamino-2-ethoxy) as leuco dyes 5 parts of phenyl) -4-azaphthalide and 10 parts of 2-hydroxy-4-octyloxybenzophenone as an ultraviolet absorber, 2 parts of dicyclohexylmethane-4,4′-diisocyanate (Desmodur W, manufactured by Sumitomo Bayer Urethane Co., Ltd.) , M-tetramethylxylylene diisocyanate (manufactured by Mitsui Takeda Chemical Co., Ltd., TMXDI) is dissolved by heating (150 ° C.) in a mixed solvent, and this solution is polyvinyl alcohol (Kuraray Co., Ltd., Poval PVA-217EE) 8.5. And ethylene oxide of acetylene glycol as a surfactant. The mixture was gradually added to 100 parts of an aqueous solution containing 1.5 parts of an id adduct (manufactured by Nissin Chemical Co., Ltd., Olphine E1010), and emulsified and dispersed by stirring at a rotational speed of 10,000 rpm using a homogenizer. To this emulsified dispersion, an aqueous solution obtained by dissolving 30 parts of water and 2.5 parts of a polyamine compound (manufactured by Shell International Petroleum, Epicure T) in 22.5 parts of water was added and homogenized. The emulsified dispersion was heated to 75 ° C. and subjected to a polymerization reaction for 7 hours to prepare a leuco dye-containing composite particle dispersion having an average particle size of 0.8 μm (by laser light diffraction method). In addition, it diluted with water so that the leuco dye containing composite particle dispersion liquid might be 25%.

-Liquid B dispersion (Preparation of colorant dispersion)
A composition comprising 42 parts of 2,4'-dihydroxydiphenylsulfone, 60 parts of a 10% aqueous solution of sulfone-modified polyvinyl alcohol, and 18 parts of water was pulverized using an ultraviscomil until the average particle size was 0.28 μm. A colorant dispersion was obtained.

・ C liquid dispersion (Preparation of colorant dispersion)
42 parts of 2-[(4-hydroxyphenyl) methyl] -6-[(2-hydroxyphenyl) methyl] -4- (sec-butyl) phenol, 60 parts of a 10% aqueous solution of sulfone-modified polyvinyl alcohol, and 18 parts of water The composition consisting of was pulverized with an ultra visco mill until the average particle size became 0.30 μm to obtain a colorant dispersion.

-Liquid D dispersion (preparation of colorant dispersion)
A composition comprising 42 parts of 4,4′-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylsulfone, 60 parts of a 10% aqueous solution of sulfone-modified polyvinyl alcohol, and 18 parts of water A colorant dispersion was obtained by pulverizing until the average particle size was 0.30 μm.

(Preparation of thermal recording layer coating solution)
From 88 parts of A liquid, 42 parts of B liquid, 50 parts of C liquid, 28 parts of D liquid, 80 parts of styrene-butadiene latex (Smartex PA-9280, manufactured by A & L Japan) with a solid content of 48% and 70 parts of water The resulting composition was mixed and stirred to obtain a thermal recording layer coating solution.

(Preparation of coating solution for protective layer)
Ionomer-type urethane resin latex [Dainippon Ink & Chemicals, Hydran (registered trademark) AP-30F, solid concentration 20%], 100 parts, acetoacetyl-modified polyvinyl alcohol [Nippon Synthetic Chemicals, Goseifamer (registered) Trademark) Z-410, polymerization degree: about 2300, saponification degree: about 98 mol%] 8% aqueous solution 500 parts, polyamidoamine epichlorohydrin 25% aqueous solution 5 parts, kaolin with an average particle size of 0.8 μm (Engelhard) , UW-90) 60% slurry, stearic acid amide (manufactured by Chukyo Yushi Co., Ltd., Himicron L-271, solid concentration 25%) 26 parts, stearyl phosphate potassium salt (Matsumoto Yushi Seiyaku Co., Ltd., woopol) 1800, solid concentration 35%) 4 parts, perfluoroalkylethylene oxide adduct [Seimi Michal Co., was obtained Surflon 10% aqueous solution 15 parts (R) S-145], and a composition comprising 300 parts of water were mixed and stirred by a protective layer coating solution.

(Preparation of thermal recording material)
On a single side of a blue transparent polyethylene terephthalate film (trade name: Melinex 912, thickness 175 μm, manufactured by Teijin DuPont), the coating amount after drying with a slot die coater is 20 g / m ^2. A thermosensitive recording layer is provided by coating and drying, and the coating solution for the protective layer is coated and dried using a slot die coater so that the coating amount after drying is 3.5 g / m ^2. A heat-sensitive recording material was obtained by providing a layer.

Example 2
-Liquid E dispersion (Preparation of colorant dispersion)
A composition comprising 42 parts of 2,6-bis [(4-hydroxyphenyl) methyl] -4- (sec-butyl) phenol, 60 parts of a 10% aqueous solution of sulfone-modified polyvinyl alcohol, and 18 parts of water A colorant dispersion was obtained by pulverizing until the average particle size was 0.30 μm.
A thermosensitive recording material was obtained in the same manner as in Example 1 except that 50 parts of E solution was used instead of 50 parts of C solution in the preparation of the thermal recording layer coating liquid of Example 1.

Example 3
・ F liquid dispersion (Preparation of colorant dispersion)
2-[(4-hydroxyphenyl) methyl] -6-[(2-hydroxyphenyl) methyl] -4- (sec-butyl) phenol 21 parts, 2,6-bis [(4-hydroxyphenyl) methyl]- A composition comprising 21 parts of 4- (sec-butyl) phenol, 60 parts of a 10% aqueous solution of sulfone-modified polyvinyl alcohol, and 18 parts of water was pulverized with an ultraviscomil until the average particle size became 0.30 μm. A colorant dispersion was obtained.
A thermosensitive recording material was obtained in the same manner as in Example 1 except that 50 parts of the F liquid was used instead of 50 parts of the C liquid in the preparation of the thermal recording layer coating liquid of Example 1.

Example 4
・ G liquid dispersion (Preparation of colorant dispersion)
An average particle diameter of a composition comprising 42 parts of 4,4′-bis (Np-tolylsulfonylaminocarbonylamino) diphenylmethane, 60 parts of a 10% aqueous solution of sulfone-modified polyvinyl alcohol, and 18 parts of water using Ultraviscomil Was pulverized to a colorant dispersion of 0.30 μm.
In the preparation of the heat-sensitive recording layer coating liquid of Example 1, heat sensitivity was the same as Example 1 except that 50 parts of F liquid and 28 parts of G liquid were used instead of 50 parts of C liquid and 28 parts of D liquid. A record was obtained.

Example 5
In the preparation of the heat-sensitive recording layer coating liquid of Example 1, Example 1 was used except that instead of 42 parts of B liquid, 50 parts of C liquid and 28 parts of D liquid, 55 parts of B liquid and 65 parts of F liquid were used. In the same manner, a heat-sensitive recording material was obtained.

Comparative Example 1
In the preparation of the heat-sensitive recording layer coating liquid of Example 1, 88 parts of Liquid A, 120 parts of Liquid B, 80 parts of styrene-butadiene latex (Smartex PA-9280, manufactured by Japan A & L) with a solid content concentration of 48% and A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 70 parts of water was used.

Comparative Example 2
In the preparation of the heat-sensitive recording layer coating solution of Example 1, 88 parts of Liquid A, 120 parts of Liquid F, 80 parts of styrene-butadiene latex (Smartex PA-9280, manufactured by A & L Japan) having a solid content of 48% and A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 70 parts of water was used.

Comparative Example 3
In the preparation of the thermal recording layer coating liquid of Example 1, 88 parts of Liquid A, 120 parts of Liquid H below, styrene-butadiene latex having a solid content concentration of 48% (Smartex PA-9280, manufactured by A & L Japan) 80 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the amount was 70 parts.
・ H liquid dispersion (preparation of colorant dispersion)
A composition comprising 42 parts of 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone, 60 parts of a 10% aqueous solution of sulfone-modified polyvinyl alcohol, and 18 parts of water was prepared using Ultraviscomyl and an average particle size of 0. The colorant dispersion was obtained by grinding to 30 μm.

Comparative Example 4
In the preparation of the heat-sensitive recording layer coating solution of Example 1, 88 parts of liquid A, 120 parts of the following liquid I, styrene-butadiene latex having a solid content of 48% (Smartex PA-9280, manufactured by A & L Japan) 80 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the amount was 70 parts.
・ I liquid dispersion (preparation of colorant dispersion)
A composition consisting of 42 parts of 4-hydroxy-4'-isopropoxydiphenylsulfone, 60 parts of a 10% aqueous solution of sulfone-modified polyvinyl alcohol, and 18 parts of water was used to obtain an average particle size of 0.30 μm using Ultraviscomyl. By pulverizing, a colorant dispersion was obtained.

Comparative Example 5
In the preparation of the heat-sensitive recording layer coating liquid of Example 1, the same procedure as in Example 1 was conducted, except that 30 parts of the following leuco dye dispersion and 140 parts of water were used instead of 88 parts of Liquid A and 70 parts of water. A heat-sensitive recording material was obtained.

(Preparation of leuco dye dispersion)
3-diethylamino-6-methyl-7- (3-toluidino) fluorane 11 parts, 3-diethylamino-6,8-dimethylfluorane 6 parts, and 3,3-bis (4-diethylamino-2-ethoxyphenyl)- A composition comprising 5 parts of 4-azaphthalide, 10 parts of 2-hydroxy-4-octyloxybenzophenone, 20 parts of a 10% aqueous solution of sulfone-modified polyvinyl alcohol, and 46 parts of water, and an average particle size of 0 using Ultraviscomyl Milled to 6 μm.

The thermosensitive recording material thus obtained was evaluated as follows, and the results are shown in Table 1.
(Recording sensitivity)
After leaving the thermal recording medium in an environment of 23 ° C. and 20% RH for 24 hours and in an environment of 23 ° C. and 50% RH for 24 hours, the thermal printing printer UP-DF500 (manufactured by Sony Corporation) is used in each environment. And recorded in the gradation mode. Among the recorded images of all 16 gradations recorded in an environment of 23 ° C. and 50% RH, the density of the recorded portion and the unrecorded portion of the 9th and 16th gradation (step) was measured. Further, the density of the recording portion of the ninth gradation (step) recorded in an environment of 23 ° C. and 20% RH was measured.
In addition, the density | concentration of an unrecorded part and a recording part was measured in the visual mode of the Macbeth densitometer (brand name: TR-927J type, Macbeth company make).

(Change in recording sensitivity due to environmental humidity change)
The recording density of the ninth gradation (step) recorded in the environment of 23 ° C. and 50% RH obtained in the above recording sensitivity measurement, and the nine gradations recorded in the environment of 23 ° C. and 20% RH ( Step) From the density of the recording part of the eye, the variation percentage was obtained by the following formula, and this was evaluated as the fluctuation of the recording sensitivity due to the environmental humidity change.
Percentage fluctuation = (23 ° C./20% RH value−23 ° C./50% RH value) × 100/23 ° C./50% RH value

(Evaluation of heat-resistant surface fogging property)
After the heat-sensitive recording material was treated in an environment of 60 ° C. and 20% RH for 24 hours, the unrecorded portion was measured in a visual mode of a Macbeth densitometer (trade name: TR-927J type Macbeth).

(Evaluation of moisture storage resistance)
The thermal recording medium is allowed to stand for 24 hours in an environment of 23 ° C. and 50% RH, and then recorded in a gradation mode using a thermal printing printer UP-DF500 (manufactured by Sony Corporation), and in an environment of 40 ° C. and 90% RH. Then, the density of the recording portion of the 16th gradation (step) after the processing was measured.
The density of the recording part was measured in a visual mode of a Macbeth densitometer (trade name: TR-927J type, manufactured by Macbeth).

In a heat-sensitive recording material in which a heat-sensitive recording layer containing a leuco dye and a colorant is provided on a support, the heat-sensitive recording layer contains the leuco dye in a form in which composite particles are formed with a hydrophobic resin. 2,4'-dihydroxydiphenylsulfone and 2-[(4-hydroxyphenyl) methyl] -6-[(2-hydroxyphenyl) methyl] -4- (sec-butyl) phenol or 2,6 By containing a specific compound such as -bis [(4-hydroxyphenyl) methyl] -4- (sec-butyl) phenol, there is little change in recording sensitivity due to environmental humidity changes of the heat-sensitive recording material, and moisture storage stability In addition, it is possible to provide a heat-sensitive recording material excellent in heat-resistant background fogging property, and to apply to a medical transparent heat-sensitive recording material.

Claims (9)

In a heat-sensitive recording material in which a heat-sensitive recording layer containing a leuco dye and a colorant is provided on a support, the heat-sensitive recording layer contains the leuco dye in a form in which composite particles are formed with a hydrophobic resin. A heat-sensitive recording material comprising at least one compound represented by the following general formula (1) and 2,4'-dihydroxydiphenylsulfone:

[Wherein, R represents an n-butyl group, an iso-butyl group, a sec-butyl group or a tert-butyl group. ] The thermosensitive recording material according to claim 1, wherein the ratio of the compound represented by the general formula (1) to 2,4'-dihydroxydiphenylsulfone is 80:20 to 30:70. In the heat-sensitive recording layer, further from 4,4′-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylsulfone and 4,4′-bis (Np-tolylsulfonylaminocarbonylamino) diphenylmethane The heat-sensitive recording material according to claim 1, comprising at least one selected compound. At least one compound selected from 4,4′-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylsulfone and 4,4′-bis (Np-tolylsulfonylaminocarbonylamino) diphenylmethane The heat-sensitive recording material according to claim 1, wherein is contained in an amount of 15 to 75% by mass relative to the compound represented by the general formula (1). The compound represented by the following general formula (2) and the compound represented by the following general formula (3) among the compounds represented by the above general formula (1) is used in combination. A heat-sensitive recording material according to 1.

[Wherein R ₁ and R ₂ represent an n-butyl group, an iso-butyl group, a sec-butyl group, or a tert-butyl group. ] The heat-sensitive recording material according to claim 5, wherein the combined ratio of the compounds represented by the general formulas (2) and (3) is 70:30 to 30:70. The compound represented by the general formulas (2) and (3) is 2-[(4-hydroxyphenyl) methyl] -6-[(2-hydroxyphenyl) methyl] -4- (sec-butyl) phenol. The heat-sensitive recording material according to claim 5 or 6, which is 2,6-bis [(4-hydroxyphenyl) methyl] -4- (sec-butyl) phenol. The thermosensitive recording material according to any one of claims 1 to 7, wherein the hydrophobic resin forming the composite particles is a urea resin or a urea-urethane resin. The heat-sensitive recording material according to claim 1, wherein the support is a transparent film.