JP2014218053A - Thermal recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal recording medium which indicates development color tone of yellow, has high color optical density, and is superior in a keeping quality and light resistance of coloring image.SOLUTION: A thermal recording medium with a thermal recording layer containing a dye precursor and developer on a backing contains the dye precursor having pyridine skeleton for a molecular structure specific as the dye precursor. The dye precursor having the pyridine skeleton is preferable to be chosen one kind from the following group: 4-[2-(2-butoxyphenyl)-6-phenyl-4-pyridinyl]-N, N-dimethylbenzeneamine; 4-[2-(2-pentyloxyphenyl)-6-phenyl-4-pyridinyl]-N, N-dimethylbenzeneamine; and 4-[2-(2-hexyloxyphenyl)-6-phenyl-4-pyridinyl]-N, N-dimethylbenzeneamine.

Description

  The present invention utilizes a reaction between a dye precursor and a developer, and a portion colored by thermal energy from a thermal head or a thermal stamp shows a yellow color tone, has a high color density, and stores a color image. The present invention relates to a heat-sensitive recording material having high properties.

  A heat-sensitive recording material is known which uses a reaction between a dye precursor and a developer and causes both substances to react with each other by thermal energy to obtain a recorded image. Such a heat-sensitive recording material is relatively inexpensive, and since the recording device is compact and easy to maintain, it is used not only as a recording medium for facsimiles and printers but also in a wide range of fields.

  However, the performance and quality required with the expansion of applications are diversifying, and there is a demand for a thermal recording material that exhibits a yellow color tone, has a high color density, and has a high color image preservability.

  Examples of the heat-sensitive recording material showing a yellow color tone include a heat-sensitive recording material using a specific heat-sensitive recording material, a two-color heat-sensitive recording material having different hues in a low-temperature recording region and a high-temperature recording region (see Patent Documents 1 to 6). However, in the present situation, satisfactory results are not necessarily obtained with respect to color density, color image preservability and light resistance.

JP-A-5-169830 Japanese Patent Laid-Open No. 5-193254 JP-A-6-255251 JP 2001-219657 A JP 2001-219659 A JP 2004-142173 A

  The main object of the present invention is to provide a heat-sensitive recording material that exhibits a yellowish color tone, has a high color density, and is excellent in storage stability and light resistance of a color image.

  As a result of extensive studies, the present inventors have solved the above problems by using a dye precursor having a pyridine skeleton in the molecular structure represented by the following general formula (1) in the heat-sensitive recording layer. It was. That is, the present invention relates to the following thermal recording material.

  Item 1: In a thermosensitive recording medium comprising a thermosensitive recording layer containing a dye precursor and a developer on a support, a pyridine skeleton is represented in the molecular structure represented by the following general formula (1) as the dye precursor. A heat-sensitive recording material comprising a dye precursor.

（式中、Ｒ^１及びＲ^２は水素原子もしくは炭素数１〜８のアルコキシ基を表し、Ｒ^３は炭素数１〜４のアルキル基を表す。Ｒ^１及びＲ^２は同一であっても、異なっていてもよい。但し、Ｒ^１及びＲ^２は同時に水素原子である場合を除く。）

(In the formula, R ¹ and R ² represent a hydrogen atom or an alkoxy group having 1 to 8 carbon atoms, R ³ represents an alkyl group having 1 to 4 carbon atoms. Even if R ¹ and R ² are the same, They may be different, except that R ¹ and R ² are simultaneously hydrogen atoms.)

  Item 2: The dye precursor having the pyridine skeleton is 4- [2- (2-butoxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2- (2-pentyl) Oxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2- (2-hexyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine 4- [2- (2-octyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2,6-bis (2-butoxyphenyl) -4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2,6-bis (2-pentyloxyphenyl) -4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2,6 Bis (2-hexyloxyphenyl) -4-pyridinyl] -N, N-dimethylbenzenamine and 4- [2,6-bis (2-octyloxyphenyl) -4-pyridinyl] -N, N-dimethylbenzene Item 2. The heat-sensitive recording material according to Item 1, which is at least one selected from the group consisting of amines.

  Item 3: The developer is 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy-4′-n-propoxydiphenylsulfone, 4-hydroxy-4′-allyloxydiphenylsulfone, bis (3-allyl -4-hydroxyphenyl) sulfone, 4,4'-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylsulfone, Np-tolylsulfonyl-N'-p-butoxycarbonylphenylurea, N -(P-toluenesulfonyl) -N '-(3-p-toluenesulfonyloxyphenyl) urea, N- (p-toluenesulfonyl) -N'-phenylurea, 4,4'-bis (3-tosylureido) diphenylmethane Item 3. The thermal recording material according to Item 1 or 2, which is at least one selected from

  The heat-sensitive recording material of the present invention exhibits a yellow color tone, has a high color density, and is excellent in color image storage and light resistance.

  The present invention is represented by the following general formula (1) as a dye precursor that develops a yellowish color tone in a thermosensitive recording medium comprising a thermosensitive recording layer containing a dye precursor and a developer on a support. It contains a dye precursor having a pyridine skeleton in its molecular structure.

（式中、Ｒ^１及びＲ^２は水素原子もしくは炭素数１〜８のアルコキシ基を表し、Ｒ^３は炭素数１〜４のアルキル基を表す。Ｒ^１及びＲ^２は同一であっても、異なっていてもよい。但し、Ｒ^１及びＲ^２は同時に水素原子である場合を除く。）

(In the formula, R ¹ and R ² represent a hydrogen atom or an alkoxy group having 1 to 8 carbon atoms, R ³ represents an alkyl group having 1 to 4 carbon atoms. Even if R ¹ and R ² are the same, They may be different, except that R ¹ and R ² are simultaneously hydrogen atoms.)

In the general formula (1), when R ¹ and R ² are simultaneously hydrogen atoms, the color density is low. R ¹ and R ² represent a hydrogen atom or an alkoxy group having 1 to 8 carbon atoms which may be branched; R ³ represents an alkyl group having 1 to 4 carbon atoms which may be branched; and R ¹ and R 2 ² may be the same or different, but at least R ¹ and R ² are preferable because a linear saturated hydrocarbon group can be easily introduced industrially.

In the present invention, from the viewpoint of increasing the color density and improving the storage stability and light resistance of the color image, in the general formula (1), either R ¹ or R ² is an alkoxy group having 4 to 8 carbon atoms. Is preferably represented. Furthermore, from the viewpoint of further increasing the color density, it is preferable that either R ¹ or R ² represents a hydrogen atom.

  The dye precursor having the pyridine skeleton is 4- [2- (2-butoxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2- (2-pentyloxyphenyl). ) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2- (2-hexyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine, 4 -[2- (2-octyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2,6-bis (2-butoxyphenyl) -4-pyridinyl] -N , N-dimethylbenzenamine, 4- [2,6-bis (2-pentyloxyphenyl) -4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2,6-bi (2-Hexyloxyphenyl) -4-pyridinyl] -N, N-dimethylbenzenamine and 4- [2,6-bis (2-octyloxyphenyl) -4-pyridinyl] -N, N-dimethylbenzenamine One type selected from the group consisting of is preferable. Among these, from the viewpoint of further improving the storability of the color image, 4- [2- (2-butoxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2 -(2-pentyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine and 4- [2- (2-hexyloxyphenyl) -6-phenyl-4-pyridinyl] -N One selected from the group consisting of N, dimethylbenzeneamine is preferred.

  In the present invention, the form of the dye precursor contained in the heat-sensitive recording layer is not particularly limited, and may be contained in the heat-sensitive recording layer in the form of solid dispersed fine particles. May be contained in the heat-sensitive recording layer in a form in which composite fine particles containing a polymer compound such as a photosensitive resin are formed.

  When the dye precursor is used in the form of solid dispersed fine particles, for example, water is used as a dispersion medium and pulverized by various wet pulverizers such as a sand mill, an attritor, a ball mill, and a cobo mill to obtain a dispersion. In addition to water-soluble polymer compounds such as polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, modified polyvinyl alcohols such as sulfone-modified polyvinyl alcohol, methylcellulose, carboxymethylcellulose, styrene-maleic anhydride copolymer salts and derivatives thereof, are necessary. Depending on the above, it can be dispersed in a dispersion medium in the presence of a surfactant, an antifoaming agent or the like to form a dispersion. What is necessary is just to prepare the coating liquid for forming a thermosensitive recording layer using this dispersion liquid. In addition, after dissolving the dye precursor in an organic solvent, this solution is emulsified and dispersed in water using the above water-soluble polymer compound as a stabilizer, and then the organic solvent is evaporated from the emulsion to make the dye precursor into solid dispersed fine particles. Can also be used. In any case, the volume average particle diameter of the solid dispersion fine particles of the dye precursor used in the form of the solid dispersion fine particles is preferably about 0.2 to 3.0 μm, more preferably in order to obtain appropriate recording sensitivity. Is about 0.3 to 1.0 μm.

As a form in which composite fine particles containing a dye precursor and a hydrophobic resin are formed,
(1) A form in which one or more dye precursors are microencapsulated using a hydrophobic resin as a wall film,
(2) A form in which one or more dye precursors are contained in a base material made of a hydrophobic resin obtained from a polyvalent isocyanate or the like,
(3) A form in which a compound having an unsaturated carbon bond is polymerized on the surface of one or more dye precursor fine particles,
Etc. For example, a method described in JP-A-60-244594 can be cited as a method for producing the particles having the form (1). Examples of the method for producing particles having the form (2) include the method described in JP-A-9-263057. Examples of the method for producing the particles having the form (3) include the method described in JP-A No. 2000-158822.

  In addition to the dye precursor, the composite fine particles contain, as necessary, an ultraviolet absorber, an antioxidant, a release agent, which will be described later, and a sensitizer known as a thermal recording material. May be.

  The content ratio of the dye precursor is preferably about 5 to 30% by mass, more preferably about 7 to 30% by mass, and still more preferably about 7 to 25% by mass in the total solid content of each thermosensitive recording layer. The color density can be improved by setting it to 5% by mass or more. Heat resistance can be improved by setting it as 30 mass% or less.

  The developer contained in the heat-sensitive recording layer in the present invention is selected from those having the property of being liquefied or dissolved by an increase in temperature and having the property of causing color development upon contact with the dye precursor. Specific examples include organic acidic substances such as phenol compounds, aromatic carboxylic acids, and polyvalent metal salts of these compounds.

  The developer usually exists in the form of composite fine particles, microcapsules, and solid dispersed fine particles. The content of the developer is preferably about 30 to 1500 parts by weight, more preferably about 50 to 1000 parts by weight, and still more preferably 100 to 600 parts per 100 parts by weight of the total dye precursor in each thermosensitive recording layer. About 200 parts by mass, particularly preferably about 140 to 600 parts by mass, and most preferably about 200 to 500 parts by mass. The composite fine particles can be prepared by a method similar to the method of preparing the composite fine particles containing the dye precursor.

  As typical developers, for example, 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4′-sec-butylidene diphenol, 4-phenylphenol, 4,4′-dihydroxy Diphenylmethane, 4,4′-isopropylidene diphenol, 4,4′-dihydroxydiphenyl ether, 4,4′-cyclohexylidene diphenol, 1,1-bis (4-hydroxyphenyl) ethane, 1,1-bis (4 -Hydroxyphenyl) -1-phenylethane, 4,4'-dihydroxydiphenyl sulfide, 4,4'-thiobis (3-methyl-6-tert-butylphenol), 4,4'-dihydroxydiphenylsulfone, 2,4 ' -Dihydroxydiphenylsulfone, 4-hydroxy -4'-isopropoxydiphenylsulfone, 4-hydroxy-4'-n-propoxydiphenylsulfone, 4-hydroxy-4'-allyloxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 4,4 '-Bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylsulfone, 4- [4'-(1'-methylethyloxy) phenyl] sulfonylphenol, N- (p-toluenesulfonyl) -N '-(3-p-toluenesulfonyloxyphenyl) urea, Np-tolylsulfonyl-p-butoxycarbonylphenylurea, N- (p-toluenesulfonyl) -N'-phenylurea, 4,4'-bis ( And compounds such as 3-tosylureido) diphenylmethane .

  Further, in the present invention, compounds that can be used as a developer include 4-hydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, and 4-hydroxybenzoic acid-sec-butyl. Phenyl compounds such as phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, 4,4′-dihydroxydiphenyl ether, or benzoic acid, p-tert-butyl Benzoic acid, trichlorobenzoic acid, terephthalic acid, salicylic acid, 3-tert-butylsalicylic acid, 3-isopropylsalicylic acid, 3-benzylsalicylic acid, 3,5- (α-methylbenzyl) salicylic acid, 3,5-di-tert-butylsali Aromatic carboxylic acids such as Le acid, and the phenolic compounds, aromatic carboxylic acid and, for example, zinc, magnesium, aluminum, organic acidic substances of salts with polyvalent metals such as calcium and the like.

  Among these developers, 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy-4′-n-propoxydiphenylsulfone, 4-hydroxy-4′-allyloxydiphenylsulfone, bis (3-allyl -4-hydroxyphenyl) sulfone, 4,4'-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylsulfone, Np-tolylsulfonyl-N'-p-butoxycarbonylphenylurea, N -(P-toluenesulfonyl) -N '-(3-p-toluenesulfonyloxyphenyl) urea, N- (p-toluenesulfonyl) -N'-phenylurea, 4,4'-bis (3-tosylureido) diphenylmethane At least one selected from the group consisting of Thereby, a more vivid yellowish color tone can be obtained, and the effects of the present invention can be exhibited without regret. Furthermore, 4-hydroxy-4′-isopropoxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, N- (p-toluenesulfonyl) -N ′-(3-p-toluenesulfonyloxyphenyl) urea 4,4′-bis (3-tosylureido) diphenylmethane, N- (p-toluenesulfonyl) -N′-phenylurea, Np-tolylsulfonyl-N′-p-butoxycarbonylphenylurea Species are preferred.

  In the present invention, a preservability improving agent can be further contained in the heat-sensitive recording layer mainly in order to further improve the preservability of the color image. Examples of such preservability improvers include 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 (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4 ′-[1,4-phenylenebis (1-methylethylidene) ] Phenols such as bisphenol and 4,4 '-[1,3-phenylenebis (1-methylethylidene)] bisphenol, 4-benzyloxyphenyl-4'-(2-methyl-2,3-epoxypropyloxy) ) Phenylsulfone, 4- (2-methyl-1,2-epoxyethyl) diphenylsulfone, and 4- (2-ethyl-1,2-epoxyethyl) ) At least one selected from epoxy compounds such as diphenylsulfone and isocyanuric acid compounds such as 1,3,5-tris (2,6-dimethylbenzyl-3-hydroxy-4-tert-butyl) isocyanuric acid is used. be able to. Of course, the storage stability improving agent is not limited to these, and two or more kinds of compounds may be used in combination as required.

  In the present invention, a sensitizer can be further contained in the heat-sensitive recording layer in order to improve the recording sensitivity. As the sensitizer, a compound conventionally known as a sensitizer for a thermal recording material can be used. For example, parabenzylbiphenyl, dibenzyl terephthalate, phenyl 1-hydroxy-2-naphthoate, dioxalate Benzyl ester, di-o-chlorobenzyl adipate, 1,2-diphenoxyethane, 1,2-di (3-methylphenoxy) ethane, di-p-methylbenzyl oxalate, di-p-chlorooxalate Benzyl ester, 2-naphthylbenzyl ether, diphenylsulfone, 1,2-diphenoxymethylbenzene, 1,2-bis (3,4-dimethylphenyl) ethane, 1,3-bis (2-naphthoxy) propane, metater Phenyl, diphenyl, benzophenone and the like can be mentioned.

  Auxiliaries such as developers, preservatives, and sensitizers used in the heat-sensitive recording layer are dispersed in water in the same manner as when the dye precursor is used in the form of solid dispersed fine particles. What is necessary is just to mix with this in the case of preparation of a coating liquid. Moreover, these adjuvants can be dissolved in a solvent and emulsified in water using a water-soluble polymer compound as an emulsifier. Further, the preservability improver and the sensitizer may be contained in the composite fine particles containing the dye precursor.

  In order to improve the whiteness of the heat-sensitive recording layer and improve the uniformity of the image, a fine pigment having a high whiteness and an average particle diameter of 10 μm or less can be contained in the heat-sensitive recording layer. For example, calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcined clay, silica, diatomaceous earth, synthetic aluminum silicate, zinc oxide, titanium oxide, aluminum hydroxide, barium sulfate, surface treated inorganic pigments such as calcium carbonate and silica In addition, organic pigments such as urea-formalin resin, styrene-methacrylic acid copolymer resin, and polystyrene resin can be used.

  As other component materials constituting the heat-sensitive recording layer, a binder is used, and if necessary, a crosslinking agent, waxes, metal soaps, colored dyes, colored pigments, fluorescent dyes and the like can be used. Examples of the binder include polyvinyl alcohol and derivatives thereof, starch and derivatives thereof, cellulose derivatives such as hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose, and ethylcellulose, polyacrylic acid soda, polyvinylpyrrolidone, and acrylamide-acrylic acid ester copolymer. Water-soluble polymer materials such as acrylamide-acrylic acid ester-methacrylic acid ester copolymer, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, casein, gelatin and derivatives thereof, and Polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic ester, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate Butadiene copolymer, styrene - - emulsion and styrene polymers such as butadiene - can be given latex water-insoluble polymer such as an acrylic copolymer.

  Examples of the crosslinking agent include aldehyde compounds such as glyoxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, glyoxylate, dimethylol urea compounds, aziridine compounds, blocked isocyanate compounds, Examples thereof include inorganic compounds such as ammonium sulfate, ferric chloride, magnesium chloride, sodium tetraborate, and potassium tetraborate, or boric acid, boric acid triesters, boron-based polymers, hydrazide compounds, and glyoxylate. These may be used individually by 1 type and may be used in combination of 2 or more type. The amount of the crosslinking agent used is preferably in the range of about 1 to 10 parts by mass with respect to 100 parts by mass of the total solid content of the thermosensitive recording layer. Thereby, the water resistance of the thermosensitive recording layer can be improved.

  Examples of the wax include waxes such as paraffin wax, carnauba wax, microcrystalline wax, polyolefin wax, and polyethylene wax, and higher fatty acid amides such as stearic acid amide and ethylenebisstearic acid amide, higher fatty acid esters, and derivatives thereof. Can be mentioned.

  Examples of the metal soap include higher fatty acid polyvalent metal salts such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate. Further, if necessary, various auxiliary agents such as an oil repellent, an antifoaming agent and a viscosity modifier can be further added to the heat-sensitive recording layer as long as the effects of the present invention are not impaired.

  Furthermore, the light resistance can be greatly improved by incorporating microcapsules enclosing an ultraviolet absorber or solid dispersed fine particles of the ultraviolet absorber in the heat-sensitive recording layer.

  Specific examples of the ultraviolet absorber include salicylic acid-based ultraviolet absorbers such as phenyl salicylate, p-tert-butylphenyl salicylate, p-octylphenyl salicylate, 2,4-dihydroxybenzophenone, 2-hydroxy-4-octyloxy Benzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-dodecyloxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2- Examples thereof include benzophenone-based ultraviolet absorbers such as hydroxy-4-methoxy-5sulfobenzophenone.

  Furthermore, 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-5′-tert-butylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-butylphenyl) benzotriazole, 2- (2′-hydroxy-3′-tert-butyl-5′-methylphenyl) -5-chlorobenzotriazole, 2- (2′-hydroxy-3) ', 5'-di-tert-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3', 5'-di-tert-amylphenyl) benzotriazole, 2- [2'-hydroxy -3 ′-(3 ″, 4 ″, 5 ″, 6 ″ -tetrahydrophthalimido-methyl) -5′-methylphenyl] benzotriazole, 2- (2 ′ Hydroxy-5′-tert-octylphenyl) benzotriazole, 2- [2′-hydroxy-3 ′, 5′-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (2′- Hydroxy-3'-dodecyl-5'-methylphenyl) benzotriazole, 2- [2'-hydroxy-4 '-(2 "-ethylhexyl) oxyphenyl] benzotriazole, polyethylene glycol (molecular weight about 300) and methyl-3 -[3-tert-butyl-5- (2H-benzotriazol-2-yl) -4-hydroxyphenyl] benzoic acid UV absorbers such as condensates with propionate, 2'-ethylhexyl-2-cyano- 3,3-diphenyl acrylate, ethyl-2-cyano-3,3-diphenyl acrylate It may be mentioned ultraviolet absorbent cyanoacrylate such bets, and the like. Of course, not limited thereto, may be used in combination of two or more depending also required.

  Among these ultraviolet absorbers, benzotriazole-based ultraviolet absorbers are preferable, and in particular, 2- (2′-hydroxy-5′-methylphenyl) benzotriazole and 2- (2′-hydroxy-3′-tert-butyl-5). -Methylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3'-dodecyl-5'-methylphenyl) benzotriazole, 2- [2'-hydroxy-4 '-(2 "-ethylhexyl) A condensate of oxyphenyl] benzotriazole, polyethylene glycol (molecular weight about 300) and methyl-3- [3-tert-butyl-5- (2H-benzotriazol-2-yl) -4-hydroxyphenyl] propionate is In particular, it is more preferable because it exhibits a remarkable light resistance improvement effect.

  The content ratio of the microcapsules encapsulating the ultraviolet absorber or the solid dispersed fine particles of the ultraviolet absorber is not particularly limited, but is preferably about 5 to 70% by mass in the total solid content of the heat-sensitive recording layer. Especially preferably, it adjusts to the range of about 15-50 mass%. Light resistance can be improved by setting it as 5 mass% or more. If it exceeds 70% by mass, the light resistance is saturated, so that it is preferably about 70% by mass or less from the viewpoint of improving the recording sensitivity. It should be noted that the light resistance can be improved more effectively when the microcapsules encapsulating the ultraviolet absorber or the solid dispersed fine particles of the ultraviolet absorber are contained in the protective layer, which will be described later, rather than in the thermal recording layer. it can.

  The microcapsules encapsulating the ultraviolet absorber can be prepared by various known methods. In general, the core substance obtained by dissolving the above-described solid or liquid ultraviolet absorber in an organic solvent as required at room temperature ( Oily liquid) is prepared by a method of emulsifying and dispersing an oily liquid in an aqueous medium to form a wall film made of a polymer substance around oily droplets. Specific examples of the polymer substance that becomes the wall film of the microcapsule include, for example, polyurethane resin, polyurea resin, polyamide resin, polyester resin, polycarbonate resin, aminoaldehyde resin, melamine resin, polystyrene resin, styrene-methacrylate copolymer resin, Examples thereof include styrene-acrylate resin, gelatin, polyvinyl alcohol and the like.

The heat-sensitive recording layer in the present invention uses, for example, water as a dispersion medium, a specific dye precursor, a developer, if necessary, a preservability improver, a sensitizer and the like, or a dispersion in which they are separately dispersed, The coating amount for the heat-sensitive recording layer prepared by mixing a pigment, a binder, a cross-linking agent, and other auxiliaries, if necessary, is preferably about ² to 12 g / m ² , more preferably 2 to 2 by dry weight. 8 g / ^{m 2} approximately, are formed further preferably such that the 2~7g / ^{m 2} approximately, coating and drying on a support.

  The support in the present invention is not particularly limited in type, shape, dimensions, etc., for example, high-quality paper (acidic paper, neutral paper), medium-quality paper, coated paper, art paper, cast-coated paper, glassine paper, resin In addition to laminated paper, polyolefin-based synthetic paper, synthetic fiber paper, non-woven fabric, synthetic resin film, etc., various transparent supports can be appropriately selected and used.

In the present invention, an undercoat layer can be provided between the support and the heat-sensitive recording layer as necessary. Thereby, the recording sensitivity can be further increased. The undercoat layer supports an undercoat layer coating liquid containing an oil-absorbing pigment having an oil absorption of 70 ml / 100 g or more, particularly about 80 to 150 ml / 100 g, at least one of organic hollow particles and thermally expandable particles, and a binder. It is formed by applying and drying on top. Here, the oil absorption is a value determined according to the method described in JIS K 5101. By using a pigment having a high porosity such as silica or calcined kaolin for the undercoat layer, the recording sensitivity of the thermosensitive recording layer can be increased. Further, the inclusion of a plastic pigment, hollow particles, foam, etc. in the undercoat layer is effective in improving the recording sensitivity of the thermosensitive recording layer formed thereon. The coating amount of the undercoat layer coating solution is preferably about 3 to ²⁰ g / m ² by dry weight, and more preferably about 4 to 12 g / m ² .

  The binder in the undercoat layer can be appropriately selected from those that can be used for the heat-sensitive recording layer. Among these binders, starch-vinyl acetate graft copolymer, polyvinyl alcohol, styrene-butadiene latex and the like are preferable from the viewpoint of improving barrier properties.

  In the present invention, it is desirable to provide a protective layer containing a water-soluble polymer material and a pigment as used in conventionally known thermal recording media on the thermal recording layer. As the water-soluble polymer material and the pigment, materials exemplified in the above-mentioned heat-sensitive recording layer can be used. At this time, it is more desirable to add a crosslinking agent to impart water resistance to the protective layer.

  In the present invention, the light resistance can be greatly improved by incorporating the microcapsules encapsulating the ultraviolet absorber or the solid dispersed fine particles of the ultraviolet absorber in the protective layer. In particular, microcapsules having a wall film made of polyurethane-polyurea resin or aminoaldehyde resin are excellent in heat resistance, and are therefore added to the thermal recording layer or protective layer for the purpose of preventing sticking to the thermal head. In addition to the excellent accompanying effect of fulfilling the function of an inorganic pigment, the refractive index is lower than that of other wall membrane microcapsules and ordinary pigments, and the shape is spherical. Even if it is contained in a large amount, it is preferably used because it does not cause a decrease in density due to irregular reflection of light.

  Further, by including a pigment, it is possible to prevent the adhesion of the residue to the thermal head and the sticking. As the oil absorption amount of the pigment, it is preferable to use a pigment of 50 ml / 100 g or more. The pigment content is preferably an amount that does not decrease the color density, that is, 50% by mass or less of the total solid content of the protective layer.

The protective layer is a protective layer coating solution prepared by mixing, for example, water as a dispersion medium and mixing a binder, and if necessary, a crosslinking agent, a pigment, and other auxiliaries. to 15 g / ^{m 2,} more preferably about so that 0.5 to 8 g / ^{m 2} approximately, is formed by applying and drying a heat-sensitive recording layer.

  In the present invention, a resin layer cured with an electron beam or ultraviolet light can be provided on the heat-sensitive recording layer or the protective layer. Examples of resins that can be cured with an electron beam are described in JP-A Nos. 58-177392 and 58-177392. In such a resin, auxiliary agents such as a non-electron beam curable resin, a pigment, an antifoaming agent, a leveling agent, a lubricant, a surfactant, and a plasticizer can be appropriately added. In particular, it is preferable to add pigments such as calcium carbonate and aluminum hydroxide, and lubricants such as waxes and silicon because this helps prevent sticking to the thermal head.

  In the present invention, in order to increase the added value of the heat-sensitive recording material, it can be further processed to obtain a heat-sensitive recording material having a higher function. For example, a pressure-sensitive adhesive paper, a re-humidified adhesive paper, or a delayed tack paper can be obtained by applying coating processing on the back surface with a pressure-sensitive adhesive, a re-humidified adhesive, a delayed tack type pressure-sensitive adhesive, or the like. In particular, the anti-counterfeit recording material of the present invention that has been subjected to adhesive processing is useful as a heat-sensitive label. In addition, by using the back surface, a function as a thermal transfer paper, an ink jet recording paper, a carbonless paper, an electrostatic recording paper, and a zeography paper can be added to form a recording paper capable of double-sided recording. Of course, a double-sided thermal recording material can also be used. Further, a back layer can be provided for suppressing permeation of oil and plasticizer from the back surface of the heat-sensitive recording material, and for curling control and antistatic.

  Examples of methods for forming each layer on the support include air knife method, blade method, gravure method, roll coater method, spray method, dipping method, bar method, curtain method, slot die method, slide die method, and extrusion method. Any of the known coating methods may be used.

  In the present invention, it is preferable that at least one layer formed on the support is a layer formed by a curtain coating method. Thereby, a layer having a uniform thickness can be formed, and the recording sensitivity can be increased, and the barrier property against oil, plasticizer, alcohol, etc. can be increased. The curtain coating method is a method in which the coating liquid is allowed to flow and fall freely, and is applied to the support in a non-contact manner, and known methods such as a slide curtain method, a couple curtain method, and a twin curtain method can be employed. There is no particular limitation. In the curtain coating method, a layer having a more uniform thickness can be formed by simultaneous multilayer coating. In simultaneous multi-layer coating, each coating solution is laminated and then applied, and then dried to form each layer. After applying a coating solution that forms the lower layer, the lower surface coating surface is wet without drying. In a state, you may apply | coat the coating liquid which forms an upper layer on a lower layer coating surface, and it may be made to dry after that, and may form each layer. In the present invention, an embodiment in which a heat-sensitive recording layer and a protective layer are simultaneously applied in multiple layers is preferable from the viewpoint of improving barrier properties.

  Smoothing the heat-sensitive recording surface using a known smoothing method such as a super calendar or a soft calendar has an effect of increasing the recording sensitivity. The heat-sensitive recording surface may be applied to either a metal roll or an elastic roll of the calendar.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Unless otherwise specified, “part” and “%” indicate “part by mass” and “% by mass”, respectively. Moreover, the volume average particle diameter of the pigment mix | blended with a color developer, a dye precursor, and a protective layer was measured using laser diffraction type particle size distribution analyzer SALD-2200 (made by Shimadzu Corporation).

Example 1
-Preparation of Dye Precursor Dispersion (Liquid A) As a dye precursor that develops a yellow color tone, 4- [2- (2-octyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N- 40 parts of dimethylbenzeneamine, 40 parts of a 10% aqueous solution of polyvinyl alcohol (polymerization degree 500, saponification degree 88%) and 20 parts of water are mixed, and the average particle size is 0 using a vertical sand mill (manufactured by Imex). The mixture was pulverized to a thickness of 7 μm to obtain a dye precursor dispersion (hereinafter also referred to as “liquid A”).

-Preparation of developer dispersion (liquid B) 40 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone, 40 parts of a 10% aqueous solution of polyvinyl alcohol (polymerization degree 500, saponification degree 88%), and water 20 parts The mixture was mixed and pulverized using a vertical sand mill (manufactured by IMEX Co., Ltd.) until the volume average particle size became 1.5 μm to obtain a developer dispersion (hereinafter also referred to as “B solution”).

Preparation of sensitizer dispersion (liquid C) 40 parts of 1,2-di (3-methylphenoxy) ethane, 40 parts of 10% aqueous solution of polyvinyl alcohol (polymerization degree 500, saponification degree 88%), and water 20 parts Were mixed using a vertical sand mill (manufactured by Imex Co., Ltd.) so as to have an average particle size of 1.0 μm to obtain a sensitizer dispersion (hereinafter also referred to as “C solution”).

-Preparation of coating solution for heat sensitive recording layer 19 parts of solution A, 5 parts of styrene-butadiene latex (trade name: L1571, manufactured by Asahi Kasei Co., Ltd., solid content concentration 48%), 10% aqueous solution of polyvinyl alcohol (trade name: POVAL (registered) Trademark) PVA-110 (manufactured by Kuraray Co., Ltd.) 25 parts, liquid B 25 parts, liquid C 11 parts, 5% surfactant aqueous solution (trade name: SN Wet OT-70, San Nopco) 2 parts, and water 17 parts A composition for thermal recording layer was obtained by mixing the composition.

-Preparation of Kaolin Dispersion (Liquid D) Kaolin (trade name: UW-90 (registered trademark), manufactured by BASF) 80 parts, 40% aqueous solution of sodium polyacrylate (trade name: Aron T-50, Toagosei Co., Ltd.) 1 part) and 53 parts of water were mixed and pulverized using a sand mill until the volume average particle diameter became 1.6 μm to obtain a kaolin dispersion (hereinafter also referred to as “D liquid”).

-Preparation of coating solution for protective layer D part 25 parts, acetoacetyl-modified polyvinyl alcohol (trade name: Gohsephimer (registered trademark) Z-200, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., degree of polymerization: about 1000, degree of saponification: about 98 mol%) 15% aqueous solution, paraffin wax (trade name: Hydrin P-7, manufactured by Chukyo Yushi Co., Ltd., solid content concentration 30%) 7.5 parts, 5% surfactant aqueous solution (trade name: SN wet) OT-70 (manufactured by San Nopco) 5 parts, Glyoxal (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., solid content concentration 40%) 0.3 part, and a composition comprising 12.5 parts of water and a coating solution for protective layer Got.

-Preparation of thermosensitive recording material The coating amount of the thermal recording layer coating liquid and the protective layer coating liquid after drying on one side of a synthetic paper (trade name: FPG-80, manufactured by YUPO Corporation, thickness 80 μm). There was coated and dried at Meyer bar so as to ^{5g / m 2, 3g / m} 2, subjected to super calender treatment to obtain a heat-sensitive recording material.

Example 2
In the preparation of the liquid A of Example 1, 4- [2- (2-octyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine is used as a dye precursor that develops a yellowish color tone. Instead of 4- [2- (2-butoxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine, a thermosensitive recording material was obtained in the same manner as in Example 1. It was.

Example 3
In preparation of the B liquid of Example 1, it replaced with 4-hydroxy-4'-isopropoxy diphenyl sulfone, and it carried out similarly to Example 1 except having used bis (3-allyl-4-hydroxyphenyl) sulfone. A heat-sensitive recording material was obtained.

Example 4
In the preparation of the liquid A of Example 1, 4- [2- (2-octyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine is used as a dye precursor that develops a yellowish color tone. Instead of 4- [2- (2-hexyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine, a thermosensitive recording medium was prepared in the same manner as in Example 1. Obtained.

Example 5
In the preparation of the liquid A of Example 1, 4- [2- (2-octyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine is used as a dye precursor that develops a yellowish color tone. Instead of 4- [2- (2-pentyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine, a thermosensitive recording medium was prepared in the same manner as in Example 1. Obtained.

Example 6
In the preparation of the liquid A of Example 1, 4- [2- (2-octyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine is used as a dye precursor that develops a yellowish color tone. Instead of 4- [2,6-bis (2-butoxyphenyl) -4-pyridinyl] -N, N-dimethylbenzenamine, a thermosensitive recording material was obtained in the same manner as in Example 1. It was.

Example 7
In preparing the liquid B of Example 1, N- (p-toluenesulfonyl) -N ′-(3-p-toluenesulfonyloxyphenyl) urea was used instead of 4-hydroxy-4′-isopropoxydiphenylsulfone. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that.

Example 8
Example 1 except that Np-tolylsulfonyl-N′-p-butoxycarbonylphenylurea was used in place of 4-hydroxy-4′-isopropoxydiphenylsulfone in the preparation of the liquid B of Example 1. In the same manner, a heat-sensitive recording material was obtained.

Comparative Example 1
In the preparation of the liquid A of Example 1, 4- [2- (2-octyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine is used as a dye precursor that develops a yellowish color tone. Instead of 1- (4-n-dodecyloxy-3-methoxyphenyl) -2- (2-quinolyl) ethylene, a thermosensitive recording material was obtained in the same manner as in Example 1.

Comparative Example 2
In the preparation of the liquid A of Example 1, 4- [2- (2-octyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine is used as a dye precursor that develops a yellowish color tone. Instead of 4- (2,6-diphenyl-4-pyridinyl) -N, N-dimethylbenzenamine, a thermosensitive recording material was obtained in the same manner as in Example 1.

  The thermosensitive recording material thus obtained was evaluated as follows. The results were as shown in Table 1.

(Color density)
Using a thermal recording simulator (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), recording was performed under the condition of applied energy of 0.968 mJ / dot, and an x-rite spectral densitometer (trade name: trade name: X-rite 528, manufactured by X-Rite Co., Ltd., using color measurement) was used to measure the Y concentration.

(Preservation of color image)
Using a thermal recording simulator (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), recording was performed under the condition of applied energy of 0.968 mJ / dot, and a thermal recording body having a recording portion was measured at 50 ° C. and 80% RH. After processing for 24 hours in an environment, the Y density of the recording part was measured with an x-rite spectral densitometer (trade name: x-rite 528, manufactured by X-Rite, color measurement used), and recorded according to the following formula The residual ratio of the color density of the part was determined. The remaining ratio of the color density is preferably 50% or more, more preferably 70% or more, still more preferably 80% or more, and particularly preferably 90% or more.
Residual rate of color density (%) = [(color density after treatment) / (color density before treatment)] × 100

(Light resistance of color images)
Using a thermal recording simulator (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), recording was performed under the condition of applied energy of 0.968 mJ / dot, and a thermal recording body having a recording portion was 5000 lux under a fluorescent lamp. After 100 hours of irradiation treatment, the Y density of the recording part was measured with an x-rite spectral densitometer (trade name: x-rite 528, manufactured by X-Rite, color measurement used), and the storability of the above color image was measured. In the same manner as described above, the residual ratio of the color density in the recording area was obtained. The remaining ratio of the color density is preferably 50% or more, more preferably 70% or more, still more preferably 80% or more, and particularly preferably 90% or more.

  The heat-sensitive recording material of the present invention has a high color density, exhibits a vivid yellowish color tone, and is excellent in preservability of a developed color image, so that it uses a clear yellowish hue, a ticket, ticket, ticket, bag, label It is suitable for applications such as coupons.

Claims (3)

In a heat-sensitive recording material comprising a heat-sensitive recording layer containing a dye precursor and a developer on a support, a dye precursor having a pyridine skeleton in the molecular structure represented by the following general formula (1) as the dye precursor A heat-sensitive recording material comprising a recording material.

(In the formula, R ¹ and R ² represent a hydrogen atom or an alkoxy group having 1 to 8 carbon atoms, R ³ represents an alkyl group having 1 to 5 carbon atoms. Even if R ¹ and R ² are the same, They may be different, except that R ¹ and R ² are simultaneously hydrogen atoms.)   The dye precursor having the pyridine skeleton is 4- [2- (2-butoxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2- (2-pentyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2- (2-hexyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2- (2-octyloxyphenyl) -6-phenyl-4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2,6-bis (2-butoxyphenyl) -4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2,6-bis (2-pentyloxyphenyl) -4-pyridinyl] -N, N-dimethylbenzenamine, 4- [2,6-bis From 2-hexyloxyphenyl) -4-pyridinyl] -N, N-dimethylbenzenamine and 4- [2,6-bis (2-octyloxyphenyl) -4-pyridinyl] -N, N-dimethylbenzenamine The heat-sensitive recording material according to claim 1, which is at least one selected from the group consisting of:   The developer is 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy-4′-n-propoxydiphenylsulfone, 4-hydroxy-4′-allyloxydiphenylsulfone, bis (3-allyl-4- Hydroxyphenyl) sulfone, 4,4′-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylsulfone, Np-tolylsulfonyl-N′-p-butoxycarbonylphenylurea, N- (p -Toluenesulfonyl) -N ′-(3-p-toluenesulfonyloxyphenyl) urea, N- (p-toluenesulfonyl) -N′-phenylurea, 4,4′-bis (3-tosylureido) diphenylmethane The heat-sensitive recording material according to claim 1 or 2, wherein the heat-sensitive recording material is at least one kind.