JPH05208556A - Thermal recording material - Google Patents

Abstract

PURPOSE:To markedly improve storage stability, especially, light fastness, in a thermal recording material having a thermal recording layer containing a basic dye forming a blue color and a developer, by providing a protective layer containing microcapsules containing an ultraviolet absorber and having no color forming capacity. CONSTITUTION:In a thermal recording material wherein a thermal recording layer containing a basic dye forming a blue color and a developer is provided on a support, a protective layer containing microcapsules containing an ultraviolet absorber and substantially having no color forming capacity is provided on the recording layer. As the basic dye forming a blue color, 3,3-bis(p- dimethylaminophenyl)-6-dimethylaminophthalide or 3-(4-diethylamino-2- methylphenyl)-3-(4-diethylaminophenyl)-6-dimethylaminophthalide is used. The microcapsules have membranes of polyurethene/polyurea resin or aminoaldehyder resin and the average particle size thereof is 0.1-3mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material capable of obtaining a blue recording image, and more particularly to a heat-sensitive recording material having excellent storage stability, particularly light resistance.

[0002]

2. Description of the Related Art A heat-sensitive recording material which utilizes a color reaction between a colorless or light-colored basic dye and an organic or inorganic color-forming agent to bring a recording image by contacting both color-forming substances with heat is often used. Are known. Such a thermal recording material is relatively inexpensive,
In addition, since the recording equipment is compact and its maintenance is easy,
It is used not only as a recording medium for facsimiles and various computers, but also in a wide range of fields.

Conventionally, a basic dye which mainly develops black color has been used in a thermosensitive recording medium, but recently, along with the remarkable progress of the thermosensitive recording system, its fields of use and forms have been diversified. Not only as a recording medium for heat-sensitive faxes and printers, new applications such as large-scale advertisements in stores and presentations are being pioneered and commercialized. In addition to the conventional black color, there is a demand for a heat-sensitive recording material for such an application, which is capable of obtaining a vivid blue-based recording image that is noticeable. However, the triphenylmethane dye, which is usually used as a basic dye that develops blue color, has a drawback that the recorded image is significantly faded by light as compared with a dye that develops black color and cannot be handled outdoors. Therefore, there is a strong demand for a blue color thermosensitive recording material having excellent light resistance.

Conventionally, there has been proposed a method of adding finely pulverized ultraviolet absorber to a heat-sensitive recording layer or a protective layer for the purpose of preventing yellowing of the background portion of a heat-sensitive recording material due to light. With a crushed UV absorber, it may not be possible to obtain a sufficient effect even if it is used in a small amount, probably because of its poor UV absorption efficiency.
If it is used in a large amount in the heat-sensitive recording layer, background fog may occur, or new defects such as decrease in recording density may occur. Further, when a finely pulverized ultraviolet absorber is added to the protective layer, the ultraviolet absorber is eluted by the influence of plasticizers and oils and fats to impair the function of the protective layer, and as a result the storage stability of the recorded image is deteriorated. I will end up.

[0005]

DISCLOSURE OF THE INVENTION The object of the present invention is to significantly improve the light resistance of not only the background but also the recorded image without causing new defects such as a decrease in recording density and a reduction in storage stability of a recorded image. An object is to provide an improved blue color thermosensitive recording medium.

[0006]

SUMMARY OF THE INVENTION The present invention comprises:
A heat-sensitive recording material provided with a heat-sensitive recording layer containing a basic dye that develops blue color and a coloring agent, wherein the recording layer contains a microcapsule containing an ultraviolet absorber and having substantially no color-forming ability. A heat-sensitive recording material is provided with a protective layer.

[0007]

The following compounds may be mentioned as specific examples of the basic dye that develops blue color used in the present invention.
3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2)
-Methylphenyl) -3- (4-dimethylaminophenyl) -6-dimethylaminophthalide, 3-diethylamino-7-dibenzylamino-benzo [a] fluorane,
3-diethylamino-7-amino-benzo [a] fluorane, 3,3-bis (p-dimethylaminophenyl) phthalide, 1-oxy-1,3,3-tris (p-dimethylaminophenyl) phthalane, 3- Diethylamino-9
-Amino-benzo [a] fluorane, 3,7-bis (dimethylamino) -10-benzoylphenothiazine, 3
-Diethylamino-7- (N-methylanilino) -10
-Benzoylphenoxazine, 10- (3 ', 4',
5'-trimethoxybenzoyl) -3,7-bis (dimethylamino) phenothiazine, 3-methyl-di-β-naphthospiropyran, spiro [3-methyl-benzo (5,5
6-a) chromene-2,2'-γ-diethylaminochromene] and the like. Of course, it is not limited to these, and two or more kinds may be used in combination as required.

Among these basic dyes, 3,3-
Bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl) -6
-Dimethylaminophthalide and 3-diethylamino-
7-Dibenzylamino-benzo [a] fluorane is more preferably used because a recorded image having a vivid color tone and high color density can be obtained.

In the present invention, for the purpose of adjusting the color tone of the recorded image, various known basic dyes capable of developing other color tones may be used in combination.

Various materials are known as a colorant used in combination with the basic dye as described above, for example, activated clay, attapulgite, colloidal silica, inorganic acidic substances such as aluminum silicate, 4-cumylphenol, Hydroquinone monobenzyl ether, 4,4'-isopropylidenediphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 4,4'-dihydroxydiphenyl-2,2-butane, 4,4'-dihydroxydiphenylmethane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 2,2-bis (4-hydroxyphenyl) heptane, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxy) Phenylthio) -3-oxapentane, 1,1-bis (4-hydroxyphenyl) Yl) -1-phenyl ethane,
1,4-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, 1,3-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, 4,4 ′ -Dihydroxydiphenyl sulfide, di (4-hydroxy-3-methylphenyl) sulfine,
4,4'-dihydroxydiphenyl sulfone, 2,4 '
-Dihydroxydiphenyl sulfone, 4-hydroxy-
4'-methyldiphenyl sulfone, 4-hydroxy-
4'-isopropoxydiphenyl sulfone, bis (3-
Allyl-4-hydroxyphenyl) sulfone, 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone, 4-hydroxy-3 ', 4'-tetramethylene diphenyl sulfone, 3,4-dihydroxyphenyl-p-
Tolyl sulfone, benzyl 4-hydroxybenzoate, butyl bis (p-hydroxyphenyl) acetate, bis (p-
Hydroxyphenyl) acetic acid methyl, (4-hydroxyphenylthio) acetic acid-2- (4-hydroxyphenylthio) ethyl ester, di (p-hydroxyphenylthioethyl) ether, N, N'-di-m-chlorophenylthiourea , Phenolic compounds such as N- (phenoxyethyl) -4-hydroxyphenylsulfonamide, 4-
[2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 4- {3- (p-tolylsulfonyl) propyloxy] salicylic acid, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] salicylic acid, p-chloro Aromatic carboxylic acids such as benzoic acid, and salts of these aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin and nickel; and antipyrine complexes of zinc thiocyanate such as Examples include organic acidic substances.

The use ratio of the basic dye and the color developing agent is appropriately selected according to the types of the basic dye and the color developing agent to be used, and is not particularly limited, but the basic dye 1 is generally used. 1 to 70 parts by weight, preferably 2 to 100 parts by weight
About 40 parts by weight of coloring agent is used. A coating material for a heat-sensitive recording layer containing these is generally prepared by using water as a dispersion medium and dispersing them together or separately by a stirrer / pulverizer such as a ball mill, an attritor or a sand mill.

In such a coating liquid, as a binder,
Starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, carboxy modified polyvinyl alcohol, acetoacetyl group modified polyvinyl alcohol, silicon modified polyvinyl alcohol,
Diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt, ethylene / acrylic acid copolymer salt, styrene / acrylic acid copolymer salt, styrene / butadiene copolymer emulsion, urea resin, At least one of melamine resin, amide resin, polyurethane resin and the like is blended in the range of 5 to 40% by weight, preferably 15 to 30% by weight, based on the total solid content of the recording layer.

If desired, various auxiliary agents can be added to the coating liquid. For example, dispersants such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, and fatty acid metal salts. , Zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, and other waxes,
Kaolin, clay, calcium carbonate, calcined clay, calcined kaolin, titanium oxide, diatomaceous earth, fine anhydrous silica,
Various pigments such as inorganic pigments such as activated clay, styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, organic pigments such as raw starch particles, defoaming agents, fluorescent dyes, coloring dyes, etc. are appropriately added. ..

Further, if necessary, a sensitizer may be used in combination, and specific examples of the sensitizer include stearic acid amide, methoxycarbonyl-N-stearic acid benzamide, N-benzoylstearic acid amide, N
-Eicosanoic acid amide, ethylenebisstearic acid amide, behenic acid amide, methylenebisstearic acid amide, N-methylolstearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, benzyl p-benzyloxybenzoate, 1- Phenyl hydroxy-2-naphthoate, dibenzyl oxalate, oxalate-di-p-methylbenzyl, oxalate-di-p-chlorobenzyl, 2-naphthylbenzyl ether, m-terphenyl, p-benzylbiphenyl, tolylbiphenyl Ether, di (p-methoxyphenoxyethyl) ether, 1,2-di (3-methylphenoxy)
Ethane, 1,2-di (4-methylphenoxy) ethane,
1,2-di (4-methoxyphenoxy) ethane, 1,2
-Di (4-chlorophenoxy) ethane, 1,2-diphenoxyethane, 1- (4-methoxyphenoxy) -2-
(2-Methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p-acetotoluidide, p-acetophenetizide, N-acetoacetyl-p-toluidine, di (β-biphenyl) Examples include ethoxy) benzene, p-di (vinyloxyethoxy) benzene and 1-isopropylphenyl-2-phenylethane. The amount of the sensitizer used is not particularly limited, but it is generally desirable to adjust the amount in the range of 4 to 80 parts by weight, preferably 4 to 30 parts by weight, relative to 10 parts by weight of the color developing agent.

In the present invention, it is also possible to further improve the storability of the recorded image by using a storability improver in the recording layer coating solution. Specific examples of such storability improver include the following. Is mentioned. 2,2'-methylenebis (4-
Methyl-6-tert-butylphenol), 2,2'-ethylenebis (4-methyl-6-tert-butylphenol) 2,2'-methylenebis (4-ethyl-6-tert-)
Butylphenol), 2,2'-methylenebis (4,6
-Di-tert-butylphenol), 2,2'-ethylidenebis (4,6-di-tert-butylphenol), 2,
2'-ethylidene bis (4-methyl-6-tert-butylphenol), 2,2'-ethylidene bis (4-ethyl-6-tert-butylphenol), 2,2 '-(2,2
-Propylidene) bis (4,6-di-tert-butylphenol), 2,2'-methylenebis (4-methoxy-6)
-Tert-butylphenol), 2,2'-methylenebis (6-tert-butylphenol), 4,4'-thiobis (3-methyl-6-tert-butylphenol), 4,
4'-thiobis (2-methyl-6-tert-butylphenol), 4,4'-thiobis (5-methyl-6-tert-
Butylphenol), 4,4'-thiobis (2-chloro-6-tert-butylphenol), 4,4'-thiobis (2-methoxy-6-tert-butylphenol), 4,
4'-thiobis (2-ethyl-6-tert-butylphenol), 4,4'-butylidenebis (6-tert-butyl-m-cresol), 1,1,3-tris (2-methyl-4-hydroxy-) 5-cyclohexylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4′-thiobis (3-methylphenol), 4,4′- Dihydroxy-3,3 ', 5,5'-tetrabromodiphenyl sulfone, 4,4'-dihydroxy-3,3', 5,5'-
Tetramethyldiphenyl sulfone, 2,2-bis (4-
Hydroxy-3,5-dibromophenyl) propane,
2,2-bis (4-hydroxy-3,5-dichlorophenyl) propane, 2,2-bis (4-hydroxy-3,
Hindered phenol compounds such as 5-dimethylphenyl) propane, 1- [α-methyl-α- (4′-hydroxyphenyl) ethyl] -4- [α ′, α′-bis (4 ″)
-Hydroxyphenyl) ethyl] benzene, 1,4-diglycidyloxybenzene, 4,4'-diglycidyloxydiphenyl sulfone, diglycidyl terephthalate,
Epoxy compounds such as cresol novolac type epoxy resin, phenol novolac type epoxy resin, bisphenol A type epoxy resin, N, N'-di-2-naphthyl-
Examples thereof include p-phenylenediamine and 2,2'-methylenebis (4,6-di-tert-butylphenyl) sodium phosphate.

Among the above-mentioned storability improvers, the compounds represented by the following [Chemical formula 1] or [Chemical formula 2] exhibit a particularly remarkable effect in combination with the specific basic dye of the present invention. Therefore, it is more preferably used.

[0017]

[Chemical 1]

[In the formula, R ₁ represents an optionally substituted alkylene group or an optionally substituted cycloalkylene group, and R ₂ and R ₃ are each a hydrogen atom, a halogen atom, or a substituted atom. A good alkyl group or an optionally substituted alkoxyl group is shown. ]

[0019]

[Chemical 2]

[In the formula, R ₄ , R ₅ and R ₆ each represent a hydrogen atom, a halogen atom, an optionally substituted alkyl group or an optionally substituted alkoxyl group. ]

The amount of the storability improver used is not particularly limited, but it is adjusted within the range of 1 to 300 parts by weight, preferably 10 to 200 parts by weight, relative to 100 parts by weight of the basic dye. Is desirable.

The method for forming the heat-sensitive recording layer is not particularly limited and includes, for example, air knife coating, varibar blade coating, pure blade coating,
Apply the coating liquid for the recording layer on the support by a suitable coating method such as rod blade coating, short dwell coating, curtain coating, or die coating.
It is formed by a method such as drying. The support is appropriately selected from paper, plastic film, synthetic paper, non-woven fabric, metal vapor deposition and the like. The recording layer coating solution 2~12g / m ² coating amount by dry weight of, is regulated preferably in the range of about 3 to 10 g / m ^2.

The present invention has a significant feature in that a protective layer containing a microcapsule containing an ultraviolet absorber and having substantially no color forming ability is provided on the heat-sensitive recording layer thus formed. is there. Incidentally, various thermal recording media and pressure-sensitive recording media using microcapsules containing both a basic dye and an ultraviolet absorber have been proposed, but these microcapsules also contain a basic dye. Not only does the coloring phenomenon occur with an increase in the irradiation amount of light, but also the effect of sufficiently improving the light resistance cannot be exhibited for a long period of time.

Specific examples of the ultraviolet absorbent used in the present invention include the following. Salicylic acid type ultraviolet absorbers such as phenyl salicylate, p-tert-butylphenyl salicylate, p-octylphenyl salicylate, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-
4-octyloxybenzophenone, 2-hydroxy-
4-dodecyloxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-
Benzophenone-based UV absorbers such as hydroxy-4-methoxy-5-sulfobenzophenone, 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" -tetrahydrophthalimide -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-3'-undecyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy- 3'-undecyl-5'-methylphenyl) benzotriazole, 2-
(2'-hydroxy-3'-tridecyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tetradecyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy- 3'-pentadecyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3'-hexadecyl-
5'-methylphenyl) benzotriazole, 2-
[2'-hydroxy-4 '-(2 "-ethylhexyl)
Oxyphenyl] benzotriazole, 2- [2'-hydroxy-4 '-(2 "-ethylheptyl) oxyphenyl] benzotriazole, 2- [2'-hydroxy-
4 '-(2 "-ethyloctyl) oxyphenyl] benzotriazole, 2- [2'-hydroxy-4'-
(2 "-Propyloctyl) oxyphenyl] benzotriazole, 2- [2'-hydroxy-4 '-(2"-
Propylheptyl) oxyphenyl] benzotriazole, 2- [2′-hydroxy-4 ′-(2 ″ -propylhexyl) oxyphenyl] benzotriazole, 2-
[2'-hydroxy-4 '-(1 "-ethylhexyl)
Oxyphenyl] benzotriazole, 2- [2'-hydroxy-4 '-(1 "-ethylheptyl) oxyphenyl] benzotriazole, 2- [2'-hydroxy-
4 '-(1 "-ethyloctyl) oxyphenyl] benzotriazole, 2- [2'-hydroxy-4'-
(1 ″ -propyloctyl) oxyphenyl] benzotriazole, 2- [2′-hydroxy-4 ′-(1 ″-
Propylheptyl) oxyphenyl] benzotriazole, 2- [2′-hydroxy-4 ′-(1 ″ -propylhexyl) oxyphenyl] benzotriazole, polyethylene glycol (molecular weight about 300) and methyl-3-
[3-tert-butyl-5- (2H-benzotriazol-2-yl) -4-hydroxyphenyl] propionate-containing benzotriazole-based UV absorbers such as condensation products,
Cyanoacrylate-based ultraviolet absorbers such as 2'-ethylhexyl-2-cyano-3,3-diphenylacrylate and ethyl-2-cyano-3,3-diphenylacrylate, bis (2,2,6,6-tetramethyl- 4-piperidyl) sebacate, succinic acid-bis (2,2,6,6-
Tetramethyl-4-piperidyl) ester, 2- (3,
5-di-tert-butyl) malonic acid-bis (1,2,2,2)
Hindered amine UV absorbers such as 6,6-pentamethyl-4-piperidyl) ester.

Of course, the present invention is not limited to these, and two or more kinds may be used in combination if necessary. In the heat-sensitive recording material of the present invention, since the ultraviolet absorbent is used by being encapsulated in microcapsules, it is a low-melting ultraviolet absorbent which has been difficult to use in terms of background fog and storability, and at room temperature. Liquid UV absorbers can also be used,
The range of choice is greatly expanded.

Among these ultraviolet absorbers, benzotriazole type ultraviolet absorbers are preferable, and particularly 2- (2 '
-Hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-
5'-methylphenyl) -5-chlorobenzotriazole, 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-
A condensate with hydroxyphenyl] propionate exhibits a particularly remarkable effect of improving light resistance and is therefore more preferably used.

The amount of the ultraviolet absorber used is not particularly limited, but the basic dye 100 in the heat-sensitive recording layer is used.
The amount is preferably about 10 to 500 parts by weight, more preferably 20 to 300 parts by weight, relative to the parts by weight.

The microcapsules used in the present invention can be prepared by various known methods. In general, cores obtained by dissolving a solid or liquid UV absorber at room temperature as described above in an organic solvent as needed. It is prepared by a method of emulsifying and dispersing a substance in an aqueous medium to form a wall film made of a polymer substance around oily droplets. Specific examples of the polymer substance that forms the wall film of the microcapsule include, for example, polyurethane resin, polyurea resin, polyamide resin, polyester resin, polycarbonate resin, aminoaldehyde resin,
Examples thereof include melamine resin, polystyrene resin, styrene-acrylate copolymer resin, styrene-methacrylate copolymer resin, gelatin and polyvinyl alcohol. Among these, in particular, the microcapsules having a wall film made of polyurethane / polyurea resin or aminoaldehyde resin are excellent in heat resistance, and therefore inorganic pigments added to the protective layer for the purpose of preventing sticking to the thermal head. It also has an excellent collateral effect of also fulfilling the function of, and has a lower refractive index than other microcapsules consisting of wall films and ordinary pigments, and its spherical shape, so a large amount is contained in the protective layer. It is preferably used because there is no fear that the density of the recorded image will be reduced (so-called whitening phenomenon) due to diffused reflection of light even if it is blended.

The microcapsules having a wall film composed of polyurethane / polyurea resin are a core substance for encapsulating a capsule wall film material such as a polyvalent isocyanate and a polyol which reacts therewith, or an adduct of a polyvalent isocyanate and a polyol. It is manufactured by emulsifying and dispersing it in an aqueous medium in which a protective colloid substance such as polyvinyl alcohol is dissolved, and raising the liquid temperature to cause a polymer forming reaction at the oil droplet interface.

Examples of the polyvalent isocyanate compound include m-phenylene diisocyanate, p-phenylene diisocyanate, 2,6-tolylene diisocyanate,
2,4-tolylene diisocyanate, naphthalene-1,
4-diisocyanate, diphenylmethane-4,4'-
Diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, xylylene-1,4
-Diisocyanate, 4,4'-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, cyclohexylene-1,2-diisocyanate, cyclohexylene-1, Diisocyanates such as 4-diisocyanate, 4,4 ′, 4 ″ -triphenylmethane triisocyanate, triisocyanates such as toluene-2,4,6-triisocyanate, 4,4′-dimethyldiphenylmethane-2,2 ′ , 5,5'-Tetraisocyanate and other tetraisocyanates, addition product of hexamethylene diisocyanate and trimethylolpropane, addition of 2,4-tolylene diisocyanate and trimethylolpropane , An adduct of xylylene diisocyanate and trimethylolpropane, an isocyanate prepolymer of adduct of trimethylolpropane resin isocyanate and hexane triol.

Examples of the polyol compound include ethylene glycol, 1,3-propanediol, 1,4
-Butanediol, 1,5-pentanediol, 1,6
-Hexanediol, 1,7-heptanediol, 1,
8-octanediol, propylene glycol, 2,3
-Dihydroxybutane, 1,2-dihydroxybutane,
1,3-dihydroxybutane, 2,2-dimethyl-1,
3-propanone diol, 2,4-pentane diol,
2,5-hexanediol, 3-methyl-1,5-pentanediol, 1,4-cyclohexanedimethanol,
Dihydroxycyclohexane, diethylene glycol,
1,2,6-trihydroxyhexane, phenylethylene glycol, 1,1,1-trimethylolpropane,
Aromatic polyols such as hexanetriol, pentaerythritol and glycerin, aromatic polyhydric alcohols such as 1,4-di (2-hydroxyethoxy) benzene and 1,3-di (2-hydroxyethoxy) benzene, and alkylene oxides Condensation product, p-xylylene glycol, m-xylylene glycol, α, α′-dihydroxy-p-diisopropylbenzene, 4,4′-dihydroxydiphenylmethane, 2- (p, p′-dihydroxydiphenylmethyl) benzyl alcohol 4,4'-isopropylidenediphenol, 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfide, ethylene oxide adduct of 4,4'-isopropylidenediphenol, 4,4'-isopropylidene Of ridenediphenol Examples include propylene oxide adducts.

Of course, the polyisocyanate compound and the polyol compound are not limited to the above compounds, and two or more kinds may be used in combination, if necessary. Among the polyvalent isocyanate compounds used in the present invention or the adducts of the polyvalent isocyanate compounds and the polyol compounds, those having three or more isocyanate groups in the molecule are particularly preferable.

The microcapsules having a wall film made of an aminoaldehyde resin are manufactured by a formulation in which the wall film material is added after emulsification of the core substance, so that the thickness of the wall film is controlled regardless of the particle size of the emulsion. The merit that can be done is also demonstrated.
Capsules having an aminoaldehyde resin wall film generally include at least one amine such as urea, thiourea, alkylurea, ethyleneurea, acetoguanamine, benzoguanamine, melamine, guanidine, biuret, and cyanamide, and formaldehyde, acetaldehyde, and paraformaldehyde. , Hexamethylenetetramine, glutaraldehyde, glyoxal, furfural and the like, or an in-situ polymerization method using an initial condensate obtained by condensing them.

Milk used for microencapsulation
As an agent (protective colloid agent), various anions and
Nion, cation or amphoteric water-soluble polymer compound etc. are used
To be done. Examples of the anionic polymer compound include -C
OO^-, -SO₃ ^-, -OPO ₃ ^2-Arabi with groups etc.
Agum, carrageenan, sodium alginate, pectin
Natural such as acid, tragacanth gum, almond gum, agar
Polymer compounds, carboxymethyl cellulose, sulfated cellulose
Lulose, sulfated methyl cellulose, carboxymethyl
Semi-synthesis of modified starch, phosphorylated starch, lignin sulfonic acid, etc.
Polymer compounds, maleic anhydride (including hydrolyzed ones)
Mu) Copolymer, acrylic acid, methacrylic acid or black
Polymers and copolymers of tonic acid, vinylbenzene sulfone
Acid or 2-acrylamido-2-methylpropane
Polymers and copolymers of rufonic acid, and these polymers
Or partial esterification of copolymers or copolymers
Products, carboxy-modified polyvinyl alcohol, sulfonic acid
Modified polyvinyl alcohol, phosphoric acid modified polyvinyl alcohol
Examples thereof include synthetic polymer compounds such as Cole. More concrete
In general, maleic anhydride (including hydrolyzed ones)
As the polymer, methyl vinyl ether-maleic anhydride
Acid copolymer, ethylene-maleic anhydride copolymer, styrene
Len-maleic anhydride copolymer, α-methylstyrene-
Maleic anhydride copolymer, vinyl acetate-maleic anhydride
Copolymer, methacrylamide-maleic anhydride copolymer
And an isobutylene-maleic anhydride copolymer.
Acrylic acid copolymer, methacrylic acid copolymer or
Is crotonic acid copolymer, methyl acrylate
Acrylic acid copolymer (hereinafter abbreviated as "copolymer"), acrylic
Ethyl acrylate-acrylic acid, methyl acrylate-methacrylic acid
Acid, methyl methacrylate-acrylic acid, methacrylic acid
Methyl-methacrylic acid, methyl acrylate-acrylic acid
Mido-acrylic acid, acrylonitrile-acrylic acid, acrylic
Acrylonitrile-methacrylic acid, hydroxyethyl ac
Lilate-acrylic acid, hydroxyethyl methacrylate
To-methacrylic acid, vinyl acetate-acrylic acid, vinyl acetate
-Methacrylic acid, acrylamide-acrylic acid, acetic acid
Rylamide-methacrylic acid, methacrylamide-acrylic
Acid, methacrylamide-methacrylic acid, vinyl acetate-
Examples include copolymers such as crotonic acid, vinylbenzene
Rufonic acid or 2-acrylamido-2-methyl-propyl
Methyl acrylate as lopan sulfonic acid copolymer
-Vinylbenzenesulfonic acid (or salt thereof) copolymer,
Vinyl acetate-vinylbenzene sulfonic acid copolymer, acetic acid
Rylamide-vinylbenzene sulfonic acid copolymer, acetic acid
Liloylmorpholine-vinylbenzene sulfonic acid copolymerization
Body, vinylpyrrolidone-vinylbenzene sulfonic acid copolymer
Combined, vinylpyrrolidone-2-methyl-propanesulfone
Examples thereof include acid copolymers.

Examples of the nonionic polymer compound include semi-synthetic polymer compounds such as hydroxyethyl cellulose, methyl cellulose, pullulan, soluble starch, and oxidized starch having a —OH group, and synthetic polymer compounds such as polyvinyl alcohol. Examples of the cationic polymer compound include cation-modified polyvinyl alcohol and the like. Examples of the amphoteric polymer compound include gelatin and the like.

Although the amount of the emulsifier used is not particularly limited, in general, when a polyurethane / polyurea resin is used as the wall film material, the total of the wall film material, the ultraviolet absorber and the organic solvent is used. However, it may be adjusted in the range of 1 to 50% by weight, preferably 3 to 30% by weight. When the aminoaldehyde resin is used as the wall film material, the amount of the emulsifier used is the hydrophobic core substance 100.
It is adjusted in the range of 1 to 20 parts by weight, preferably 3 to 10 parts by weight with respect to parts by weight.

The organic solvent is not particularly limited and can be appropriately selected from various high boiling point hydrophobic media used in the field of pressure-sensitive copying paper, and specifically, for example, phosphoric acid can be used. Phosphates such as tricresyl, octyldiphenyl phosphate, dibutyl phthalate,
Phthalates such as dioctyl phthalate, carboxylic esters such as butyl oleate, various fatty acid amides, alkylated naphthalenes such as diethylene glycol dibenzoate, monoisopropyl naphthalene and diisopropyl naphthalene, 1-methyl-1-phenyl- 1-
Alkylated benzenes such as tolylmethane, 1-methyl-1-phenyl-1-xylylmethane, 1-phenyl-1-tolylmethane, alkylated biphenyls such as isopropyl biphenyl, xenoxyalkanes such as o-phenylphenol glycidyl ether, Examples thereof include acrylic acid esters such as trimethylolpropane triacrylate, esters of polyhydric alcohols and unsaturated carboxylic acids, chlorinated paraffins, and kerosene. Of course, these may be used in combination of two or more. Among the high boiling point hydrophobic media as described above, tricresyl phosphate and 1-
Phenyl-1-tolylmethane is preferable because it exhibits excellent solubility in relation to the ultraviolet absorber used in the present invention. Further, generally, the lower the viscosity of the mixture of the capsule wall film material, the ultraviolet absorber and the organic solvent, the smaller the particle size after emulsification and the sharper the particle size distribution. Therefore, if necessary, the viscosity of the mixture is decreased. A low boiling point solvent may be used together for the purpose. Specific examples of the low boiling point solvent include ethyl acetate, butyl acetate and methylene chloride.

The amount of the organic solvent used is not particularly limited and should be appropriately adjusted according to the type and amount of the ultraviolet absorber used, the type of the organic solvent and the like. However, since it is preferable that the ultraviolet absorbent is sufficiently dissolved in the microcapsules, in the case of polyurethane / polyurea resin, the total amount of the organic solvent, the ultraviolet absorbent, and the microcapsule wall film material is Therefore, it is desirable to adjust the ratio of the organic solvent to be in the range of generally 10 to 60% by weight, preferably 20 to 60% by weight. In the case of amino aldehyde resin,
It is desirable to adjust the amount of the ultraviolet absorber in the range of 50 to 2000% by weight, preferably 100 to 1000% by weight. When the ultraviolet absorber that is liquid at room temperature is used, the organic solvent is not always essential, and may be appropriately adjusted within the above range if necessary.

The amount of the capsule wall film material to be used is not particularly limited either. However, since the organic solvent in the microcapsules may seep out during long-term storage and deteriorate the storability of the thermosensitive recording medium, It is preferable to use a larger amount of the wall film material than the microcapsules, and in the case of polyurethane / polyurea resin, the wall film is used for the total of the organic solvent, the ultraviolet absorber and the microcapsule wall film material. The proportion of wood is 35 to 70% by weight, preferably 3
It is desirable to select it so as to be in the range of 5 to 60% by weight. In the case of an aminoaldehyde resin, the wall film material is 30 to 300 with respect to the total of the ultraviolet absorber and the organic solvent used as necessary. % By weight, preferably 35-200% by weight
It is desirable to select the range so that

Further, the amount of the ultraviolet absorbent used in the microencapsulation should be appropriately selected according to the kind of the ultraviolet absorbent and the organic solvent used and is not particularly limited, but a remarkable effect is obtained. Therefore, in the case of polyurethane / polyurea resin, the amount of the ultraviolet absorber is about 3 to 50% by weight, preferably about 3 to 20% by weight, based on the total of the three of the organic solvent, the ultraviolet absorber and the microcapsule wall membrane material. It is desirable to mix so that
In the case of an aminoaldehyde resin, it is 3 to 75% by weight, preferably 3 to 75% by weight based on the total of the three components of the ultraviolet absorber, the microcapsule wall film material and the organic solvent used as necessary.
It is desirable to mix the ultraviolet absorber in an amount of about 50% by weight.

In the microcapsules used in the present invention, an antioxidant, an oil-soluble fluorescent dye, a release agent and the like can be added, if necessary, in addition to the ultraviolet absorber. Further, at the time of microencapsulation, a tin compound, a polyamide compound, an epoxy compound, a polyamine compound or the like can be used together as a reaction accelerator. When a polyamine compound is used, it is desirable to use an aliphatic polyamine compound in terms of light resistance.

The average particle size of the microcapsules used in the present invention is 0.1 to 3 μm, preferably 0.3 to 2.5 μm, in consideration of the absorption efficiency of ultraviolet rays and the quality of recorded images.
It is desirable to adjust it so that it is within the range. Also,
The content of the microcapsules in the protective layer should be appropriately selected depending on the type of the ultraviolet absorber, the concentration in the capsules, and the desired quality, etc., but generally with respect to the total solid content of the protective layer. 5 to 80% by weight, preferably 20 to 70% by weight.

As described above, the thermosensitive recording medium of the present invention has a protective layer containing microcapsules containing an ultraviolet absorber. The protective layer is water-soluble or water-dispersible with the microcapsules. It is composed mainly of a binder made of a polymer compound. Specific examples of the binder include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, carboxy modified polyvinyl alcohol, acetoacetyl group modified polyvinyl alcohol, silicon modified polyvinyl alcohol, diisobutylene. Maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt, ethylene / acrylic acid copolymer salt, styrene / acrylic acid copolymer salt, styrene / butadiene copolymer emulsion, urea resin, melamine resin, Examples thereof include amide resins and polyurethane resins. Among them, acetoacetyl group-modified polyvinyl alcohol and carboxy-modified polyvinyl alcohol can form a strong film. Preferably used for.

A pigment may be added to the protective layer, if necessary, to improve printability and sticking. Specific examples thereof include calcium carbonate,
Inorganic pigments such as zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, talc, kaolin, clay, calcined kaolin, colloidal silica, styrene microballs, nylon powder, polyethylene powder, urea. Examples thereof include formalin resin fillers and organic pigments such as raw starch particles. It is generally desirable to adjust the amount used in the range of about 5 to 300 parts by weight with respect to 100 parts by weight of the binder component.

The method for preparing the coating liquid for forming the protective layer is not particularly limited, and generally, water is used as the dispersion medium, and the specific microcapsules (dispersion liquid), the binder, the pigment added as necessary, and the like. It is prepared by mixing. Furthermore, in the protective layer coating liquid, zinc stearate, calcium stearate, polyethylene wax,
Lubricants such as carnauba wax, paraffin wax and ester wax, surfactants (dispersing agents and wetting agents) such as sodium dioctylsulfosuccinate, defoaming agents, various auxiliaries such as water-soluble polyvalent metal salts such as potassium alum and aluminum acetate. Can also be added as appropriate. Further, in order to further improve the water resistance, a curing agent such as glyoxal, boric acid, dialdehyde starch, and an epoxy compound can be used in combination.

The method for forming the protective layer is not particularly limited, and for example, suitable coating methods such as air knife coating, varibar blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, die coating and the like can be used. It is formed by a method such as coating the coating liquid for the protective layer on the recording layer and drying. The coating amount of the protective layer coating liquid is adjusted to a dry weight of 0.1 to 20 g / m ² , preferably 0.5 to 10 g / m ² .

In the present invention, the light resistance can be further enhanced by adding a finely pulverized ultraviolet absorber or an ultraviolet absorber encapsulated in the above-mentioned microcapsules to the heat-sensitive recording layer. Further, if necessary, a protective layer may be provided on the back side of the thermosensitive recording medium to further improve the storability. Further, in the field of heat-sensitive recording medium production, an undercoat layer may be provided on the support, smoothing treatment such as super calendering may be applied after coating each layer, or adhesive treatment may be applied to the back surface of the recording medium to form an adhesive label. Various known techniques can be added as necessary.

[0048]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In addition, "part" and "%" in an example show "weight part" and "weight%", respectively, unless there is particular notice.

Example 1 Preparation of Liquid A In a stirring and mixing vessel equipped with a heating device, 60 parts of an 8% aqueous solution of polyvinyl alcohol [trade name: PVA-217, manufactured by Kuraray Co., Ltd.] was added to prepare an aqueous medium for producing microcapsules. did. Separately, 12 parts of tricresyl phosphate were added with 2- (2 '
-Hydroxy-5'-methylphenyl) benzotriazole 2 parts, (3: 1) adduct of xylylene diisocyanate and trimethylolpropane [trade name: Takenate D
-110 N, manufactured by Takeda Pharmaceutical Co., Ltd., containing 25% of ethyl acetate] 18 parts were dissolved to obtain a solution, which was then added to the above-mentioned aqueous medium for capsule production using TK Homomixer [Model HV-M, Tokushu Kika Kogyo Co., Ltd.]. Manufactured by the above method, and emulsified and dispersed while cooling so that the average particle diameter becomes 2 μm. Next, 50 parts of water was added to this emulsified dispersion and reacted at 60 ° C. for 3 hours while stirring to obtain a dispersion of microcapsules having a wall film made of a polyurethane / polyurea resin containing an ultraviolet absorber.

Preparation of solution B 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide 10 parts, methyl cellulose 5%
A composition consisting of 5 parts of an aqueous solution and 40 parts of water was pulverized with a sand mill until the average particle size became 1.5 μm. Preparation of Solution C A composition consisting of 30 parts of 4-hydroxy-4′-isopropoxydiphenyl sulfone, 5 parts of a 5% aqueous solution of methylcellulose, and 80 parts of water was pulverized with a sand mill until the average particle diameter became 1.5 μm.

Preparation of Solution D A composition comprising 20 parts of 1,2-di (3-methylphenoxy) ethane, 5 parts of a 5% aqueous solution of methylcellulose, and 55 parts of water was sand-milled until the average particle size reached 1.5 μm. Crushed. Preparation of solution E A composition comprising 10 parts of 2,2′-methylenebis (4-methyl-6-tert-butylphenol), 5 parts of a 5% aqueous solution of methylcellulose, and 40 parts of water was used to obtain an average particle size of 1.5 μm in a sand mill. Crushed until

Formation of Recording Layer 55 parts of solution B, 115 parts of solution C, 24 parts of solution D, 20 parts of solution E,
The recording layer coating liquid obtained by mixing and stirring 80 parts of a 10% polyvinyl alcohol aqueous solution and 35 parts of calcium carbonate
The coating amount after drying on one side of 0g / m ² of high quality paper is 6g / m
^A recording layer was formed by coating and drying so as to be ² .

Formation of Protective Layer 220 parts of A liquid, 150 parts of 10% aqueous solution of acetoacetyl group-modified polyvinyl alcohol [trade name: Gocefimer Z-200, manufactured by Nippon Gosei Kagaku], kaolin [trade name: UW-90] , Manufactured by EMC Inc.] 15 parts, 6 parts of a 30% zinc stearate aqueous dispersion, and 30 parts of a composition are mixed and stirred to obtain a coating solution for a protective layer, which is applied onto a recording layer after drying. After coating and drying so that the amount becomes 6 g / m ² ,
Super calendering was performed to obtain a heat sensitive recording material.

Example 2 In preparation of solution A, 2 parts of 2- (2'-hydroxy-5'-methylphenyl) benzotriazole was used instead of 2 parts.
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 2 parts of-(2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -5-chlorobenzotriazole was used.

Example 3 In the preparation of solution A, 3 parts of ethyl acetate was used instead of 12 parts of tricresyl phosphate, and 2 parts instead of 2 parts of 2- (2'-hydroxy-5'-methylphenyl) benzotriazole. -(2'-hydroxy-3'-dodecyl-
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 12 parts of 5'-methylphenyl) benzotriazole was used.

Example 4 Preparation of solution A: 2- (2'-hydroxy-3'-dodecyl-5'-methylphenyl) benzotriazole 1
Instead of 2 parts, 2- [2'-hydroxy-4 '-(2
A thermosensitive recording medium was obtained in the same manner as in Example 3 except that 12 parts of -ethylhexyl) oxyphenyl] benzotriazole was used.

Example 5 In the preparation of solution B, 3,3-bis (p-dimethylaminophenyl)-was used instead of 10 parts of 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide.
Same as Example 3 except that 5 parts of 6-dimethylaminophthalide and 5 parts of 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl) -6-dimethylaminophthalide were used. A thermosensitive recording medium was obtained.

Example 6 In preparation of solution B, 3-diethylamino-7-dibenzylamino-benzo [a] was used instead of 10 parts of 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide. A thermosensitive recording medium was obtained in the same manner as in Example 3 except that 10 parts of fluoran was used.

Example 7 Preparation of Liquid F In a stirring and mixing vessel equipped with a heating device, 150 parts of a 5% aqueous solution of polyacrylic acid was added to adjust the pH of the system to 4.5 to obtain an aqueous medium for capsule production. Separately, a solution obtained by dissolving 16 parts of 2- (2'-hydroxy-5'-methylphenyl) benzotriazole in 100 parts of tricresyl phosphate was used as a capsule core substance, and this was used in the above-mentioned aqueous medium for capsule production to prepare TK. The mixture was emulsified and dispersed at 10,000 rpm for 15 minutes while cooling using a homomixer [Model HV-M, manufactured by Tokushu Kika Kogyo Co., Ltd.]. To this emulsion dispersion, 190 parts of a 30% aqueous solution of a commercially available melamine-formaldehyde resin initial condensate as a wall film material was added, and the mixture was reacted at 90 ° C. for 3 hours while continuing stirring, and then the temperature was lowered to room temperature to obtain an ultraviolet absorber. A dispersion liquid of microcapsules containing a melamine-formaldehyde resin wall film having an average particle diameter of 2 μm was obtained.

Preparation of thermosensitive recording medium 55 parts of F liquid, 150 parts of 10% aqueous solution of polyvinyl alcohol modified by acetoacetyl group [trade name: Gocefimer Z-200, manufactured by Nippon Gosei Co., Ltd.], kaolin (trade name: UW)
-90, manufactured by EMC) 15 parts, zinc stearate 30
% Of an aqueous dispersion and 30 parts of water were mixed and stirred, and the coating solution for protective layer obtained on the thermosensitive recording layer obtained in the same manner as in Example 1 had a coating amount of 6 g / m ² after drying. After coating and drying, a super calender treatment was performed to obtain a heat sensitive recording material.

Example 8 In the preparation of solution F, 58 parts of diisopropylnaphthalene was used instead of 100 parts of tricresyl phosphate, and
Instead of 16 parts of (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-
A thermosensitive recording medium was obtained in the same manner as in Example 7 except that 58 parts of 3'-dodecyl-5'-methylphenyl) benzotriazole was used.

Example 9 Preparation of liquid G A composition consisting of 100 parts of calcined clay [trade name: Ansilex, manufactured by EMC, oil absorption: 110 ml / 100 g], 100 parts of a 10% aqueous solution of polyvinyl alcohol, and 200 parts of water was prepared. By mixing and stirring, a coating liquid for the undercoat layer was obtained. Preparation of thermal recording material 60 g / m ² of high quality paper was coated with solution G so that the coating amount after drying was 7 g / m ² and dried, and then used for the recording layer prepared in the same manner as in Example 1. The coating material and the coating liquid for protective layer were applied and dried so that the applied amount after drying was 6 g / m ^2, and then super calendering treatment was carried out to obtain a thermosensitive recording medium.

Example 10 In the preparation of solution C, 30 parts of bis (4-hydroxyphenylthioethoxy) methane was used in place of 30 parts of 4-hydroxy-4'-isopropoxydiphenylsulfone,
Further, a thermosensitive recording medium was prepared in the same manner as in Example 1 except that 20 parts of bis (4-hydroxyphenylthioethoxy) methane was used instead of 20 parts of 1,2-di (3-methylphenoxy) ethane in the preparation of the D liquid. Got

Example 11 Thermal recording was carried out in the same manner as in Example 1 except that 20 parts of 2-naphthylbenzyl ether was used in place of 20 parts of 1,2-di (3-methylphenoxy) ethane in the preparation of solution D. Got the body

Example 12 In the formation of the protective layer, 150 parts of a 10% aqueous solution of carboxy-modified polyvinyl alcohol was used in place of 150 parts of a 10% aqueous solution of acetoacetyl group-modified polyvinyl alcohol, and 15 parts of calcium carbonate was used instead of 15 parts of kaolin.
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that parts were used.

Comparative Example 1 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 2- (2'-hydroxy-5'-methylphenyl) benzotriazole was not used in the preparation of solution A.

Comparative Example 2 Preparation of H Solution A composition consisting of 10 parts of 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 5 parts of a 5% aqueous solution of methylcellulose, and 40 parts of water was sand milled to obtain an average particle diameter. Was pulverized to 1.5 μm. Preparation of thermosensitive recording medium In the formation of the protective layer, the above H was used in place of 220 parts of A liquid.
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 40 parts of the liquid was used.

Comparative Example 3 In the preparation of solution H, 10 parts of 2- (2'-hydroxy-5'-methylphenyl) benzotriazole was used instead of
A thermosensitive recording medium was obtained in the same manner as in Comparative Example 2 except that 10 parts of 2- (2'-hydroxy-3 ', 5'-di-tert-amylphenyl) -5-chlorobenzotriazole was used.

The following 15 evaluation tests were conducted on the thus obtained 15 kinds of thermal recording materials, and the results are shown in Table 1. [Color development] Thermal recording material evaluation machine [Product name: TH-PMD,
Okura Electric Co., Ltd.] applied voltage 24V, pulse time 2
The color of each thermosensitive recording medium was developed in ms, and the color density of the obtained recorded image was measured by a Macbeth densitometer [RD-914 type, manufactured by Macbeth Co.]. A blue filter was used for measuring the recording density by a Macbeth densitometer. [Light resistance] After recording, the thermosensitive recording medium was exposed to direct sunlight for 2 days, and then the density of the printed portion was measured again with a Macbeth densitometer.

[0070]

[Table 1]

[0071]

As is clear from the results shown in Table 1, each of the blue-based heat-sensitive recording materials of the present invention was a recording material having extremely excellent light resistance of recorded images.

Claims (5)

[Claims] 1. A heat-sensitive recording material comprising a support and a heat-sensitive recording layer containing a basic dye that develops blue color and a coloring agent. A heat-sensitive recording material comprising a protective layer containing microcapsules that have no color-developing ability. 2. A basic dye which develops blue color is 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-methylphenyl) -3- (. 4-dimethylaminophenyl) -6-
Dimethylaminophthalide, or 3-diethylamino-
The thermosensitive recording medium according to claim 1, which is at least one selected from 7-dibenzylamino-benzo [a] fluorane. 3. The average particle size of the microcapsules is 0.1 to 10.
The heat-sensitive recording material according to claim 1, which has a thickness of 3 μm. 4. The heat-sensitive recording material according to claim 1, wherein the microcapsules are microcapsules having a wall film made of polyurethane polyurea resin. 5. The heat-sensitive recording material according to claim 1, wherein the microcapsule is a microcapsule having a wall film made of an aminoaldehyde resin.