JPH05201135A - Heat-sensitive recording material - Google Patents

Abstract

PURPOSE:To provide a heat-sensitive recording material whose recording image possessing an absorption in a near infrared ray sphere is superior in light resistance and a texture part has few discoloration. CONSTITUTION:In a heat-sensitive recording material obtained by providing one after the other a recording layer and protective layer containing colorless or light-colored basic dye and a coloration agent, the inside of the recording layer contains basic dye wherein a recording image possesses absorption in a near infrared ray sphere, an ultraviolet absorbing agent is involved and the inside of the protective layer is made to contain a microcapsule which has no color development function substantially.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has excellent characteristics for an optical character (or mark) reader having a reading wavelength range in the near infrared region, and has excellent light resistance of a recorded image and a background portion. The present invention relates to a thermosensitive recording medium.

[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 both color-forming substances into contact with each other by heat to obtain a recorded image is often used. Are known. Since such a thermal recording medium is relatively inexpensive, the recording device 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.

On the other hand, in recent years, the number of cases in which a recorded image is read by an optical character reading device (including mark reading) has increased remarkably in combination with the rationalization of office processing, and particularly, an optical having a reading wavelength in the near infrared region. In many cases, a character reading device is used. For example, in the distribution industry, in order to quickly respond to the needs of consumers, as the POS (point of sales) system is expanded, it is increasingly used as a thermal recording label. A small and inexpensive device having a reading wavelength in the near infrared region is used.

However, recorded images (black color image, blue color image, red color image, green color image, etc.) obtained by the above-mentioned thermosensitive recording medium.
Can read as a lead color for an optical character reader having a reading wavelength range in the visible range (400 to 700 nm), but can read in the near infrared range (700 to 11 nm).
It could not be applied to an optical character reader having a reading wavelength range of (00 nm) because it all functions as a dropout color regardless of the color tone.

Therefore, as a basic dye used in a heat-sensitive recording material, a dye suitable for an optical character reader utilizing light in the near infrared region is being developed. For example, a divinyl group-containing phthalide derivative (special (Kosho 58-5940)
And a phthalide derivative having a fluorene skeleton (JP-A-59-59
-199757) is proposed. However, when these compounds are used in a thermal recording material for POS labels, there is a problem in storage stability, and in particular, the contrast between the printed portion and the background portion tends to be lowered due to the influence of room light. Generally, the thermal recording material for labels includes water, a plasticizer,
A protective layer is provided on the recording layer to prevent the recording layer from being deteriorated by oil or the like, and the water resistance and chemical resistance of the recording layer are improved. However, as described above, in the case of a POS label using a dye suitable for an optical character reading device, since the stability of the dye against indoor light is poor, the contrast between the printed part and the background part of the label after the indoor light is radiated is low. There is also a possibility that it will decrease and cause misreading by the reading device. Therefore, in order to prevent yellowing due to light on the background of the thermal recording medium,
Although it was considerably improved by using an aromatic secondary amine type antioxidant and a hindered phenol type antioxidant in the heat-sensitive recording layer, the long-term light resistance is not sufficient yet. Therefore, there is a strong demand for a thermosensitive recording medium that does not cause yellowing of the background even when exposed to room light or sunlight for a long time.

On the other hand, conventionally, a method of adding a finely pulverized ultraviolet absorber to the heat-sensitive recording layer or the protective layer has been proposed for the purpose of preventing yellowing of the background portion of the heat-sensitive recording material due to light. However, the finely pulverized UV absorber has a poor UV absorption efficiency and cannot provide a sufficient effect. If the amount of the UV absorber used in the heat-sensitive recording layer is increased, background fog may occur, or the recording density may decrease. Will also 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.

[0007]

In view of the present situation, the present invention provides a thermal recording for a POS label having excellent characteristics for an optical character (or mark) reading device having a reading wavelength range in the near infrared region. The present invention provides a heat-sensitive recording material which is excellent in light fastness with little light fading of a recorded image and light discoloration of a background portion.

[0008]

DISCLOSURE OF THE INVENTION The inventors of the present invention recorded a thermosensitive recording medium in which a recording layer containing a colorless or light-colored basic dye and a coloring agent, and a protective layer were sequentially provided on a support. A thermal recording material containing a basic dye whose recorded image has absorption in the near infrared region in the layer, and also containing an ultraviolet absorber and having microcapsules having substantially no color-forming ability in the protective layer. It has been found that the light resistance of the recording portion can be improved and the discoloration of the background portion can be suppressed by providing the above.

[0009]

[Action]

In the heat-sensitive recording material of the present invention, the basic dye having a recorded image having absorption in the near infrared region is not particularly limited, but specific examples thereof include the following compounds.

3,3-bis [1,1-bis (4-pyrrolidinophenyl) ethylene-2-yl] -4,5,6,7
-Tetrabromophthalide, 3,3-bis [1- (4methoxyphenyl) -1- (4-dimethylaminophenyl)
Ethylene-2-yl] -4,5,6,7-tetrachlorophthalide, 3,3-bis [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2-
Il] -4,5,6,7-tetrachloridophthalide, bis [p- (dimethylaminostyryl) -o-methylsulfonyl] methane, 3,6-bis (dimethylamino) fluorene-9-spiro-3 ' -(6-Dimethylamino) phthalide, 3,6-bis (diethylamino) fluorene-
9-spiro-3 '-(6-diethylamino) phthalide,
3- [1,1-bis (p-diethylaminophenyl) ethylene-2-yl] -6-dimethylaminophthalide, 3
-Bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl) ethylene-2-yl] -3-diethylaminophenyl-4,5,6,7-tetrachlorophthalide, 3- (4 -Diethylamino-2-methoxyphenyl) -3- [4- (4-dimethylaminophenyl)
-4- (4-chlorophenyl) -1,3-butanedienyl] benzophthalide, 3-p- (p-anilinoanilino) anilino-6-methyl-7-chlorofluorane, 3
-P- [di (n-butyl) aminoanilino] -6-methylfluorane, 3- (p-dimethylaminoanilino) anilino-6-methylfluorane and the like.

These various basic dyes may be used alone or in combination.
It is possible to use a mixture of two or more kinds, but 0.01 to ² g per 1 m ^{2 in the} recording layer, more preferably 0.05
It is necessary to contain about 1 g. And above all,
3,3-bis [1- (4-methoxyphenyl) -1-
(4-Dimethylaminophenyl) ethylene-2-yl]
-4,5,6,7-tetrachlorophthalide has a whiteness,
It is more preferable because it has excellent light resistance.

In the present invention, it is preferable to use a basic dye having an absorption wavelength in the visible region in combination with the near-infrared dye in the recorded image. Specific examples thereof include various known basic dyes. Specific examples of such basic dyes include the following. 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) phthalide, 3- (p
-Dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-methylindole-3-
Yl) phthalide, 3,3-bis (1,2-dimethylindol-3-yl) -5-dimethylaminophthalide,
3,3-bis (1,2-dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis (9
-Ethylcarbazol-3-yl) -6-dimethylaminophthalide, 3,3-bis (2-phenylindole-
3-yl) -6-dimethylaminophthalide, 3-p-dimethylaminophenyl-3- (1-methylpyrrole-3
-Yl) -6-dimethylaminophthalide and other triallylmethane dyes, 4,4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucoauramine, N-2,4,5-tri Diphenylmethane dyes such as chlorophenyl leuco auramine, benzoyl leuco methylene blue, thiazine dyes such as p-nitrobenzoyl leuco methylene blue, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, Spiro dyes such as 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho (6'-methoxybenzo) spiropyran, 3-propyl-spiro-dibenzopyran, rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) Lactam, Damin (o- chloroanilino)
Lactam dyes such as lactam, 3-dimethylamino-7
-Methoxyfluorane, 3-diethylamino-6-methoxyfluorane, 3-diethylamino-7-methoxyfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3 -Diethylamino-6,7-dimethylfluorane, 3- (N-ethyl-p-toluidino) -7-methylfluorane, 3-diethylamino-7-N-acetyl-N-methylaminofluorane, 3-diethylamino-
7-N-methylaminofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-N-methyl-N-benzylaminofluorane,
3-diethylamino-7-N-chloroethyl-N-methylaminofluorane, 3-diethylamino-7-diethylaminofluorane, 3- (N-ethyl-p-toluidino) -6-methyl-7-phenylaminofluorane, Three
-(N-ethyl-p-toluidino) -6-methyl-7-
(P-Toluidino) fluorane, 3-dimethylamino-
6-methyl-7-phenylaminofluorane, 3-diethylamino-6-methyl-7-phenylaminofluorane, 3-di (n-butyl) amino-6-methyl-7-phenylaminofluorane, 3-di (N-Pentyl) amino-6-methyl-7-phenylaminofluorane, 3-
Diethylamino-7- (2-carbomethoxy-phenylamino) fluorane, 3- (N-cyclohexyl-N-
Methylamino) -6-methyl-7-phenylaminofluorane, 3- (N-cyclopentyl-N-ethylamino) -6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-phenyl Aminofluorane,
3-piperidino-6-methyl-7-phenylaminofluorane, 3-diethylamino-6-methyl-7-xylidinofluorane, 3-diethylamino-7- (o-chlorophenylamino) fluorane, 3-di (n- Butyl)
Amino-7- (o-chlorophenylamino) fluorane, 3-pyrrolidino-6-methyl-7-p-butylphenylaminofluorane, 3-diethylamino-7- (o
-Fluorophenylamino) fluorane, 3-dibutylamino-7- (o-fluorophenylamino) fluorane, 3- (N-methyl-Nn-amyl) amino-6-
Methyl-7-phenylaminofluorane, 3- (N-ethyl-Nn-amyl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-N-isoamyl) amino-6- Methyl-7-phenylaminofluorane, 3- (N-methyl-Nn-hexyl) amino-
6-methyl-7-phenylaminofluorane, 3- (N
-Ethyl-N-n-hexyl) amino-6-methyl-7
-Phenylaminofluorane, 3- (N-ethyl-N-
Fluoran dyes such as β-ethylhexyl) amino-6-methyl-7-phenylaminofluorane and 3- (N-ethyl-N-tetrahydrofurfuryl) amino-6-methyl-7-anilinofluorane. Two or more kinds of these basic dyes can be used in combination, if necessary.

The amount of the above dye having an absorption wavelength in the visible region is 0.01 to ² g, preferably 0.05 to 1 g per 1 m ² of the heat sensitive layer. In addition, various known compounds are used as the color developing agent that reacts with the basic dye, and specific examples thereof include the following.
2,2-bis (4-hydroxyphenyl) -4-methylpentane, 1,3-bis [1- (4-hydroxyphenyl) -1-methylethyl] benzene, 1,4-bis [1
-(4-hydroxyphenyl) -1-methylethyl] benzene, 4-tert-butylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol,
4-hydroxyacetophenone, 4-tert-octylcatechol, 2,2'-dihydroxydiphenyl, 4,
4'-isopropylidene bis (2-tert-butylphenol), 4,4'-sec-butylidene diphenol, 4
-Phenylphenol, 4,4'-isopropylidenediphenol, 4,4'-cyclohexylidenediphenol, 2,2'-methylenebis (4-chlorophenol), hydroquinone, hydroquinone monobenzyl ether, 4-hydroxybenzophenone, 2 , 4-dihydroxybenzophenone, 2,4,4'-trihydroxybenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone, bis (3-tert-butyl-4-hydroxy-6-methylphenyl) sulfide, Screw (2
-Methyl-4-hydroxy-6-tert-butylphenyl) sulfide, 4,4'-dihydroxydiphenyl sulfide, 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-
Hydroxy-4'-methyldiphenyl sulfone, 4-hydroxy-4'-methoxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone,
4-hydroxy-3 ', 4'-tetramethyldiphenyl sulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 3,4-dihydroxydiphenyl sulfone, 3,4 -Dihydroxy-4'-methyldiphenyl sulfone, 4,4'-methylenebis (oxyethylenethio) diphenol, 1,5-di (4-hydroxyphenylthio) -3-oxapentane, bis (4-hydroxyphenylthioethoxy) ) Methane, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, 4-hydroxybenzoic acid-se
c-Butyl, pentyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, phenylpropyl 4-hydroxybenzoate, 4-hydroxy Phenethyl benzoate,
4-hydroxybenzoic acid-p-chlorobenzyl, 4-hydroxybenzoic acid-p-methoxybenzyl, novolac type phenolic resin, phenolic compounds such as phenolic polymers, benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid , Terephthalic acid, 3-sec-butyl-4-
Hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid, 3-tert-butylsalicylic acid, 3-benzylsalicylic acid, 3- (α-methylbenzyl) salicylic acid, 3-
Chlor-5- (α-methylbenzyl) salicylic acid, 3,
5-di-tert-butylsalicylic acid, 3-phenyl-5-
Aromatic carboxylic acids such as (α, α-dimethylbenzyl) salicylic acid and 3,5-di-α-methylbenzylsalicylic acid, and these phenolic compounds, aromatic carboxylic acids and, for example, zinc, magnesium, aluminum, calcium, titanium , Salts with polyvalent metals such as manganese, tin and nickel, and organic acid substances such as antipyrine complex of zinc thiocyanate. Among them, 4-hydroxy-
4'-isopropoxydiphenyl sulfone, 1,5-di (4-hydroxyphenylthio) -3-oxapentane, and bis (4-hydroxyphenylthioethoxy) methane are preferable because they have various storability. The amount of the above-mentioned color developing agent to be used is not particularly limited, but it is desirable that it is contained in an amount of about 50 to 1000% by weight based on the basic dye.

In particular, a basic dye having absorption in the near infrared region tends to deteriorate the recorded image due to the action of light, air oxidation, etc., but the recording layer contains an aromatic secondary amine anti-aging agent and / or an antioxidant. The addition of a hindered phenolic antioxidant stabilizes the recorded image. Specific examples of the aromatic secondary amine anti-aging agent include the followings. Phenyl-1-naphthylamine, 4,4'-dioctyldiphenylamine, 4,4'-bis (α, α-dimethylbenzyl) diphenylamine, p- (p-toluenesulfonylamide) diphenylamine, N, N'-di-2- Naphthyl-p-phenylenediamine, N, N'-
Diphenyl-p-phenylenediamine, N-phenyl-
N'-isopropyl-p-phenylenediamine, N-phenyl-N '-(1,3-dimethylbutyl) -p-phenylenediamine, N-phenyl-N'-(3-methacryloyloxy-2-hydroxypropyl)- p-phenylenediamine and the like. Of course, it is not limited to these, and two or more kinds can be used in combination.

Among them, N, N'-di-2-naphthyl-p
-Phenylenediamine is preferably used because it has less stains on the background after light exposure and has an appropriate melting point. The amount of the above-mentioned aromatic primary amine anti-aging agent is not particularly limited, but it is preferably 10 to 500% by weight, preferably 10 to 500% by weight, with respect to the basic dye whose recorded image has absorption in the near infrared region. Is preferably adjusted to be in the range of about 20 to 200% by weight.

Specific examples of the hindered phenolic antioxidant include the followings. 2,2 '
-Methylenebis (4-methyl-6-tert-butylphenol), 2,2'-methylenebis (4-ethyl-6-te
rt-butylphenol), 2,2'-methylenebis (4,6-di-tert-butylphenol), 2,2'-
Ethylidene bis (4,6-di-tert-butylphenol), 2,2'-ethylidene bis (4-methyl-6-te)
rt-butylphenol), 2,2'-ethylidene bis (4-ethyl-6-tert-butylphenol), 2,
2 '-(2,2-propylidene) bis (4,6-di-te
rt-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) and the like. Of course, it is not limited to these, and two or more kinds can be used in combination. Among these, 2,2'-methylenebis (4-methyl-6-
tert-butylphenol), 2,2'-methylenebis (4-ethyl-6-tert-butylphenol), 2,
2'-ethylidene bis (4,6-di-tert-butylphenol), 4,4'-thiobis (2-methyl-6-tert
-Butylphenol) is particularly preferably used.

Although the amount of the hindered phenolic antioxidant used is not particularly limited, it is 10 to 50 with respect to the basic dye whose recorded image has absorption in the near infrared region.
It is desirable to adjust the amount to be in the range of 0% by weight, preferably 20 to 200% by weight. Basic dyes, colorants, aromatic secondary amine anti-aging agents in the present invention,
The heat-sensitive recording layer coating liquid containing a hindered phenolic antioxidant and the like is generally prepared by dispersing water with a stirring medium such as a ball mill, attritor, or sand mill using water as a dispersion medium. In such coating liquid,
Usual binders such as starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, acetoacetyl group-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, amide resin, etc. For 10-40
%, Preferably about 15 to 30% by weight.

Further, various auxiliary agents can be added to the coating liquid as needed, and examples thereof include dioctylsulfosuccinic acid sodium salt, dodecylbenzenesulfonic acid sodium salt, lauryl alcohol sulfate / sodium salt, and fatty acid. A dispersant such as a metal salt, an ultraviolet absorber such as a benzophenone type, an antifoaming agent, a fluorescent dye, a coloring dye and the like are appropriately added.

If necessary, waxes such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, kaolin, clay, talc, calcium carbonate, calcined kaolin, titanium oxide, diatomaceous earth, and fine particles Inorganic pigments such as anhydrous silica and activated clay can be added, and a sensitizer can be used in combination depending on the purpose.

Specific examples of the sensitizer include fatty acid amides such as stearic acid amide, stearic acid methylenebisamide, oleic acid amide, palmitic acid amide and coconut fatty acid amide, and 2- (2'-hydroxy-5'-. Methylphenyl) benzotriazole, 2-hydroxy-
4-benzyloxybenzophenone, 1,2-di (3-
Methylphenoxy) ethane, 1,2-diphenoxyethane, 1-phenoxy-2- (4-methylphenoxy) ethane, 1-phenoxy-2- (4-methoxyphenoxy) ethane, 1-phenoxy-2- (4- Chlorophenoxy) ethane, 1- (2-methylphenoxy) -2-
(4-Methoxyphenoxy) ethane, naphthylbenzyl ether, benzyl-4-methylthiophenyl ether, 4-methylthiophenyl-4'-chlorobenzyl ether, 4-methylthiophenyl-4'-bromobenzyl ether, 4-methylthiophenyl-4 ′ -Methylbenzyl ether, 4-methylthiophenyl-2′-methylbenzyl ether, 4-methylthiophenyl-4′-
Butyl benzyl ether, 4-methylthiophenyl-
4'-methoxybenzyl ether, oxalic acid dibenzyl ester, oxalic acid-di-p-methyl-benzyl ester, oxalic acid-di-p-chlorobenzyl ester, terephthalic acid dimethyl ester, terephthalic acid dibutyl ester, terephthalic acid dibenzyl Examples thereof include esters, dibutyl isophthalate, phenyl 1-hydroxynaphthoate and various known heat-fusible substances.

Among these sensitizers, 1,2-di (3-methylphenoxy) ethane, 1,2-diphenoxyethane, 1-phenoxy-2- (4-methylphenoxy) ethane, 1- ( 2-methylphenoxy) -2- (4
-Methoxyphenoxy) ethane, oxalic acid dibenzyl ester, oxalic acid-di-p-methyl-benzyl ester, and oxalic acid-di-p-chlorobenzyl ester are particularly preferable because of their excellent sensitizing effect. Although the amount of the sensitizer used is not particularly limited, it is generally desirable to adjust the amount within a range of about 4 parts by weight or less relative to 1 part by weight of the color developing agent.

Specific examples of the ultraviolet absorbent contained in the microcapsules according to the present invention include the following. Salicylic acid-based UV 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-hydroxy-4-methoxy-5-sulfobenzophenone, etc. Benzophenone-based UV absorber, 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 "-tetrahydrophthalimidomethyl)
-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, methyl-3
-[3-tert-Butyl-5- (2H-benzotriazol-2-yl) -4-hydroxyphenyl] propionate and benzotriazole-based UV absorber such as a condensate of polyethylene glycol (molecular weight about 300), 2 ' −
Cyanoacrylate-based UV absorbers such as 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 (1,2,2,6,6) 6
-Pentamethyl-4-piperidyl) ester and other hindered amine UV absorbers 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 ultraviolet absorbers, benzotriazole type ultraviolet absorbers are preferable, and 2- (2 ') is particularly preferable.
-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, methyl-3- [3-tert-
Butyl-5- (2H-benzotriazol-2-yl)
A condensate of -4-hydroxyphenyl] propionate and polyethylene glycol (molecular weight of about 300) is more preferably used because it exhibits a particularly remarkable effect of improving light resistance.

The present invention is characterized in that the ultraviolet absorber is encapsulated in microcapsules and contained in the protective layer, and has a low melting point which has been difficult to use in the past in terms of background fog and storability. Since a UV absorber or a UV absorber that is liquid at room temperature can be used by enclosing it in a microcapsule, the range of choice can be greatly expanded.

Although the amount of the ultraviolet absorber used is not particularly limited, it is preferably in the protective layer in an amount of about 10 to 500% by weight based on the basic dye in the recording layer.
More preferably, it is desirable to adjust the content to be in the range of about 20 to 300% by weight.

The present invention has a significant feature in that the protective layer formed on the recording layer contains microcapsules containing the above-mentioned ultraviolet absorber and having substantially no color-forming ability. Is. Various heat-sensitive recording materials and pressure-sensitive recording materials using microcapsules containing a colorless or light-colored basic dye together with a purple ray absorbing agent have been proposed.These microcapsules also contain a basic dye. Therefore, not only the coloring phenomenon occurs with the increase of the light irradiation amount, but also the sufficient light resistance improving effect cannot be exhibited for a long period of time.

The microcapsules used in the present invention can be prepared by various known methods. Generally, a core substance (oil-based liquid) obtained by dissolving a solid ultraviolet absorber at an ordinary temperature in an organic solvent as described above is used. It is prepared by a method of emulsifying and dispersing in an aqueous medium and forming a wall film made of a polymer material around oily droplets. Specific examples of the polymer material that forms the wall film of the microcapsule include, for example, polyurethane resin, polyurea resin, polyamide resin, polyester resin, polycarbonate resin, aminoaldehyde resin, melamine resin,
Examples thereof include 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. Exerts an excellent accompanying effect that it also fulfills the function of, and has a lower refractive index than other microcapsules consisting of wall films and ordinary pigments, and its shape is spherical,
Even if it is mixed in a large amount in the protective layer, there is no fear of causing a decrease in the density of a recorded image (so-called whitening phenomenon) due to diffused reflection of light, and therefore it is preferably used.

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 have a formulation in which the wall film material is added after emulsifying the core substance, so that the wall film thickness can be controlled without being influenced by the particle size of the emulsion. Capsules with aminoaldehyde resin wall membranes used in the present invention generally include urea, thiourea, alkylureas, ethylene urea, acetoguanamine, benzoguanamine, melamine, guanidine,
Biuret, at least one amine such as cyanamide, at least one aldehyde such as formaldehyde, acetaldehyde, paraformaldehyde, hexamethylenetetramine, glutaraldehyde, glyoxal, furfural or the initial condensation product obtained by condensing them It is produced by the in-situ polymerization method used.

As an emulsifying agent (protective colloidal agent) used for microencapsulation, various anions, nonions, cations, amphoteric water-soluble polymer compounds and the like are used. Examples of the anionic polymer compound include -CO
Natural polymer compounds such as gum arabic, carrageenan, sodium alginate, pectic acid, tragacanth gum, almond gum, agar, etc. having O ⁻ , —OPO ₃ ²⁻ , —SO ₃ ^— groups, carboxymethyl cellulose, sulfated cellulose, sulfated Methylcellulose, carboxymethylated starch, phosphorylated starch, semi-synthetic polymer compounds such as ligninsulfonic acid, maleic anhydride (including hydrolyzed ones)
Copolymers, polymers and copolymers of acrylic acid, methacrylic acid or crotonic acid, polymers and copolymers of vinylbenzenesulfonic acid or 2-acrylamido-2-methylpropanesulfonic acid, and polymers or copolymers thereof. Partial amide derivative or partial esterified product of polymer,
Examples thereof include synthetic polymer compounds such as carboxy-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, and phosphoric acid-modified polyvinyl alcohol. More specifically, maleic anhydride (including hydrolyzed) copolymers include methyl vinyl ether-maleic anhydride copolymer, ethylene-maleic anhydride copolymer, and styrene-maleic anhydride copolymer. , Α-methylstyrene-maleic anhydride copolymer, vinyl acetate-maleic anhydride copolymer, methacrylamide-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer and the like, acrylic acid copolymer Examples of the combination, the methacrylic acid copolymer or the crotonic acid copolymer include methyl acrylate-acrylic acid copolymer (hereinafter abbreviated as "copolymer"), ethyl acrylate-acrylic acid, methyl acrylate-methacrylic acid,
Methyl methacrylate-acrylic acid, methyl methacrylate-methacrylic acid, methyl acrylate-acrylamide-
Acrylic acid, acrylonitrile-acrylic acid, acrylonitrile-methacrylic acid, hydroxyethyl acrylate-acrylic acid, hydroxyethyl methacrylate-methacrylic acid, vinyl acetate-acrylic acid, vinyl acetate-methacrylic acid, acrylamide-acrylic acid, acrylamide-methacrylic acid, methacrylic Amide-acrylic acid,
Examples thereof include copolymers of methacrylamide-methacrylic acid, vinyl acetate-crotonic acid, and the like, and as vinylbenzenesulfonic acid or 2-acrylamido-2-methyl-propanesulfonic acid copolymer, methyl acrylate-vinylbenzenesulfonic acid. (Or a salt thereof) copolymer, vinyl acetate-vinylbenzenesulfonic acid copolymer, acrylamido-vinylbenzenesulfonic acid copolymer, acryloylmorpholine-vinylbenzenesulfonic acid copolymer, vinylpyrrolidone-vinylbenzenesulfonic acid copolymer Coalescing,
Examples thereof include vinylpyrrolidone-2-methyl-propanesulfonic acid copolymer.

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.

The amount of the emulsifier used is not particularly limited, but generally, in the case of polyurethane / polyurea resin, it is 1 to 50% by weight based on the total of the wall film agent, the ultraviolet absorber and the organic solvent. %, Preferably 3 to 3
It may be adjusted in the range of about 0% by weight. In the case of an aminoaldehyde resin, the amount of the emulsifier used is generally 1 to 20 parts by weight, more preferably 3 to 10 parts by weight, based on 100 parts by weight of the hydrophobic core substance.

The organic solvent is not particularly limited and may 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. 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. Incidentally, among the high-boiling-point hydrophobic media as described above, tricresyl phosphate, 1-methyl-1-phenyl-1-xylylmethane and 1-phenyl-1-tolylmethane are related to the ultraviolet absorber used in the present invention. It is preferable because it exhibits excellent solubility. 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, etc., but is not particularly limited. Since it is preferable that the ultraviolet absorber is in a sufficiently dissolved state, when the capsule wall film is a polyurethane / polyurea resin, the organic solvent, the ultraviolet absorber and the microcapsule wall film material are used in combination with the organic solvent. It is desirable to adjust the ratio so that it is generally in the range of 10 to 60% by weight, preferably 20 to 60% by weight. When the UV absorber used is a solid at room temperature, it is 50 to 2000% by weight, preferably 100 to 10% by weight of the UV absorber.
It is desirable to adjust it to be within the range of 00% by weight,
If the ultraviolet absorber used is a liquid at room temperature, it is used appropriately.

The amount of the capsule wall film material to be used is not particularly limited either, but the organic solvent in the microcapsules may exude due to long-term storage, and the storability of the thermosensitive recording medium may be deteriorated. 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 absorber used in the microencapsulation should be appropriately selected according to the kind of the ultraviolet absorber 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, considering the absorption efficiency of ultraviolet rays and the image quality of a recorded image.
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.

Further, a preservative improving agent may be used in combination for the purpose of further enhancing preservability of the recorded image as long as the effect is not impaired. Specific examples of such a shelf life improver include, for example, 4,4′-butylidene bis (6-tert-butyl-m-cresol), 1- [α-methyl-α-
(4'-Hydroxyphenyl) ethyl] -4- [α ',
α'-bis (4 "-hydroxyphenyl) ethyl] benzene, 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-
Hindered phenols such as 3,5-dibromophenyl) propane, 2,2-bis (4-hydroxy-3,5-dichlorophenyl) propane and 2,2-bis (4-hydroxy-3,5-dimethylphenyl) propane Compound,
Epoxy compounds such as 1,4-diglycidyloxybenzene, 4,4′-diglycidyloxydiphenyl sulfone, diglucidyl terephthalate, cresol novolac type epoxy resin, phenol novolac type epoxy resin, bisphenol A type epoxy resin, N, N ′ -Di-2-
Examples thereof include naphthyl-p-phenylenediamine and 2,2'-methylenebis (4,6-di-tert-butylphenyl) sodium phosphate.

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.
Further, in the coating liquid for the protective layer, if necessary, a lubricant such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, a surfactant such as sodium dioctylsulfosuccinate (dispersant, wetting agent). Agents), antifoaming agents, and various auxiliaries such as water-soluble polyvalent metal salts such as potassium alum and aluminum acetate can be appropriately added. 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 heat-sensitive recording layer and the protective layer is not particularly limited, and suitable examples include air knife coating, varibar blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating and die coating. The coating liquid for recording layer is applied and dried on the support by the coating method, and then the coating liquid for protective layer is further applied and dried on the recording layer. The support is appropriately selected from paper, plastic film, synthetic paper, non-woven fabric, metal vapor deposition and the like.
The coating amount of the recording layer coating liquid is 2 to 12 g / dry weight.
m ² , preferably about 3 to 10 g / m ² , and the coating amount of the protective layer coating liquid is adjusted to a dry weight of 0.1 to 20 g / m ² , preferably about 0.5 to 10 g / m ^2. It

If desired, a protective layer may be provided on the back side of the thermosensitive recording medium to further improve the storage stability. Furthermore, an undercoat layer may be provided on the support, or smoothing treatment such as super calendering may be performed after coating each layer,
Alternatively, various well-known techniques in the field of heat-sensitive recording material production may be added as necessary, such as processing the back surface of the recording material with an adhesive to form an adhesive label.

[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 the mixture was reacted at 60 ° C. for 3 hours with stirring to prepare a microcapsule dispersion having a wall film made of a polyurethane / polyurea resin containing an ultraviolet absorber.

Preparation of solution B 3,3-bis [1- (4-methoxyphenyl) -1-
(4-Dimethylaminophenyl) ethylene-2-yl]
-3,4,5,6,7-tetrachlorophthalide, N,
N'-di-2-naphthyl-p-phenylenediamine 3
Parts, 5 parts of a 5% aqueous solution of methylcellulose, and 40 parts of water
Part of the composition is sand-milled to have an average particle size of 1.5μ.
It was crushed until it reached m.

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 55 parts of water was ground by a sand mill until the average particle diameter became 1.5 μm. did.

Preparation of solution D 3-di (n-butyl) amino-6-methyl-7-phenylaminofluorane 10 parts, 1,2-di (3-methylphenoxy) ethane 25 parts, 5% aqueous solution of methylcellulose 5 Parts and 55 parts of water were pulverized with a sand mill until the average particle diameter became 1.5 μm.

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 sand milled to give an average particle size of 1 It was pulverized to 0.5 μm.

Formation of Recording Layer 50 parts of B solution, 90 parts of C solution, 60 parts of D solution, 5 parts of E solution, 15 parts of calcium carbonate, 160 parts of 10% polyvinyl alcohol aqueous solution were mixed and stirred to obtain a coating solution. A heat-sensitive layer was obtained by coating and drying a 60 g / m ² base paper so that the coating amount after drying was 6 g / m ² .

Formation of protective layer 220 parts of solution A, 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 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-amylphenyl) benzotriazole was used.

Example 4 In the preparation of solution A, 3 parts of ethyl acetate and 2- (2'-hydroxy-5'-) were used instead of 12 parts of tricresyl phosphate.
Instead of 2 parts of methylphenyl) benzotriazole,
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 12 parts of 2- (2'-hydroxy-3'-dodecyl-5'-methylphenyl) benzotriazole was used.

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

Example 8 In the preparation of solution A, 3 parts of 1-phenyl-1-methyl-1-xylylmethane and 2-part instead of 3 parts of ethyl acetate were prepared.
Instead of 12 parts of (2'-hydroxy-3'-dodecyl-5'-methylphenyl) benzotriazole, 2-
6 parts of (2'-hydroxy-3'-dodecyl-5'-methylphenyl) benzotriazole and methyl-3- [3
-Tert-butyl-5- (2H-benzotriazole-2
A thermosensitive recording medium was obtained in the same manner as in Example 5 except that 6 parts of a condensate of -yl) -4-hydroxyphenyl] propionate and polyethylene glycol (molecular weight about 300) was used.

Example 7 In the preparation of solution B, N, N'-di-2-naphthyl-p-
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 3 parts of 4,4′-bis (α, α-dimethylbenzyl) diphenylamine was used instead of 3 parts of phenylenediamine.

Example 8 In the preparation of solution B, 3,3-bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl) ethylene-2-yl] -4,5,6,7- Instead of 3 parts of tetrachlorophthalide, 3,3-bis [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2-yl] -4,5,6,7-tetra A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 3 parts of chlorophthalide was used.

Example 9 Preparation of solution B, 3,3-bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl) ethylene-2-yl] -4,5,6,7- Instead of 3 parts of tetrachlorophthalide, 3,3-bis [1,1-bis (4
-Pyrrolidinophenyl) ethylene-2-yl] -4,
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 3 parts of 5,6,7-tetrabromophthalide was used.

Example 10 In preparation of solution B, 3- (4-diethylamino-2-methoxyphenyl) -3- [1- (4-dimethylaminophenyl) -1- (4-chlorophenyl) -1,3-butadienyl was used. A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 3 parts of benzophthalide was added and used.

Example 11 In the preparation of solution C, 30 parts of bis (4-hydroxyphenylthioethoxy) methane was used instead of 30 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone,
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 12 Instead of 30 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone in the preparation of the liquid C, 4,4'-
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 30 parts of isopropylidenediphenol was used.

Example 13 In place of 10 parts of 3-di (n-butyl) amino-6-methyl-7-phenylaminofluorane in the preparation of solution D, 3- (N-ethyl-N-isoamyl) amino-6 was used. −
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 10 parts of methyl-7-phenylaminofluorane was used.

Example 14 Instead of 10 parts of 2,2'-methylenebis (4-methyl-6-tert-butylphenol) in the preparation of solution E,
A thermal recording material was obtained in the same manner as in Example 1 except that 10 parts of 2,2'-ethylidene bis (4,6-di-tert-butylphenol) was used.

Example 15 In the solution E preparation, 10 parts of 2,2'-methylenebis (4-methyl-6-tert-butylphenol) was used instead of
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 10 parts of 2,2'-methylenebis (4-ethyl-6-tert-butylphenol) was used.

Example 16 Preparation of solution 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 prepare an aqueous medium for capsule production. Separately, 16 parts of 2- (2'-hydroxy-5'-methylphenyl) was dissolved in 100 parts of tricresyl phosphate, and the resulting solution was used as a capsule core substance in the above-mentioned aqueous medium for producing a capsule using a TK homomixer [Model HV-M]. , Manufactured by Tokushu Kika Kogyo Co., Ltd.] and emulsified and dispersed at 10,000 rpm for 15 minutes.

A 30% aqueous solution of a commercially available melamine-formaldehyde initial condensate 19 as a wall film material was added to this emulsified dispersion.
After adding 0 parts and reacting at 90 ° C. for 3 hours while continuing stirring, the temperature was lowered to room temperature and an ultraviolet absorber was included.
A melamine-formaldehyde resin wall membrane capsule having an average particle diameter of 2 μm was prepared.

55 parts of F liquid, polyvinyl alcohol modified with acetoacetyl group [trade name: Gocefimer Z-20
0, manufactured by Nihon Gosei Co., Ltd.], 150 parts of 10% aqueous solution, 15 parts of kaolin (trade name: manufactured by UW-90 EMC), 6 parts of 30% zinc stearate dispersion and 30 parts of water are mixed and stirred to obtain a protective layer. The coating liquid was applied and dried on the recording layer used in Example 1 so that the coating amount after drying was 6 g / m ^2, and calendered to obtain a thermosensitive recording medium.

Example 17 In the preparation of solution F, after reacting at 90 ° C. for 3 hours, pH was adjusted.
Was lowered to 3.5, and the mixture was kept at 80 ° C for 3 hours with stirring, and then
After cooling, a melamine-formaldehyde resin wall membrane capsule having an average particle diameter of 2.5 μm was prepared, and the capsule liquid 55
Example 16 except that the protective layer coating solution was prepared using
A thermosensitive recording medium was obtained in the same manner as described above.

Example 18 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 thermal recording material was obtained in the same manner as in Example 16 except that 58 parts of 3'-dodecyl-5'-methylphenyl) benzotriazole was used.

Example 19 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.

Formation of Thermal Sensitive Recording Material 60 g / m ² of high-quality paper was coated and dried with the solution G so that the coating amount after drying was 7 g / m ^2, and then used for the recording layer used 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 20 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.

Example 21 In the preparation of solution B, N, N'-di-2-naphthyl-p-
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 3 parts of phenylenediamine was not used.

Example 22 Instead of 10 parts of 2,2'-methylenebis (4-methyl-6-tert-butylphenol) in the preparation of solution E,
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 4,4'-thiobis (2-methyl-6-tert-butylphenol) was used.

Comparative Example 1 2- (2'-hydroxy-3'-dodecyl-5'-methylphenyl) benzotriazole 1 in the preparation of solution A
A thermosensitive recording medium was obtained in the same manner as in Example 5 except that 12 parts of diisopropylnaphthalene was used instead of 2 parts.

Comparative Example 2 Preparation of H Solution A composition comprising 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.

Formation of Thermal Recording Material In the formation of the protective layer, the above H was used in place of 220 parts of the liquid A.
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, instead of 10 parts of 2- (2'-hydroxy-5'-methylphenyl) benzotriazole,
A thermosensitive recording medium was obtained in the same manner as in Comparative Example 4 except that 10 parts of 2- (2'-hydroxy-3 ', 5'-di-tert-amylphenyl) benzotriazole was used.

The following 25 evaluation tests were conducted on the thus obtained 25 kinds of thermal recording materials, and the results are shown in [Table 1]. [Evaluation] 1 [Color development] Thermal printer (Texas Instruments, PC
The reflection density of the recorded image obtained by printing with -100A type) was measured with a Macbeth densitometer (RD-914 type, manufactured by Macbeth Co.), and the reflectance at a wavelength of 900 nm of the recorded image was measured by a spectrophotometer (JASCO Corporation). It was measured by a UVIDEC model 590 manufactured by K.K.

2 [Light resistance] After the above recorded image was left under a fluorescent lamp for 30 days, the reflection density of the recorded image was measured by a Macbeth densitometer (Macbeth RD-9).
14 type), and the reflectance of the recorded image at a wavelength of 900 nm is measured by a spectrophotometer (Jasco Corporation, UVIDEC5).
90 type).

3 [Underground Discoloration] After the recording paper was left under a fluorescent lamp for 30 days, the undercolor discoloration was visually evaluated. ○ Almost no discoloration of the background. △ 〃 There is a little. × 〃 Large.

[0087]

[Table 1]

[0088]

As is clear from the results of [Table 1], all of the thermosensitive recording materials of the present invention were excellent in light resistance of recorded images and had less discoloration on the background.

Claims (6)

[Claims] 1. A thermosensitive recording medium comprising a support, on which a recording layer containing a colorless or light-colored basic dye and a coloring agent, and a protective layer are successively provided, and a recorded image is recorded in the near infrared region. A heat-sensitive recording material comprising a protective layer containing microcapsules containing a basic dye having absorption, an ultraviolet absorber, and substantially no color-developing ability. 2. The heat-sensitive recording material according to claim 1, wherein the recording layer contains an aromatic secondary amine-based antioxidant and / or a hindered phenol-based antioxidant. 3. The average particle size of the microcapsules is 0.1 to 10.
The thermal recording medium according to claim 1 or 2, 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 a polyurethane-polyurea resin or an aminoaldehyde resin. 5. An aromatic secondary amine-based antioxidant is N,
The heat-sensitive recording material according to claim 2, which is N'-di-2-naphthyl-p-phenylenediamine. 6. The hindered phenolic antioxidant is 2,
2'-methylenebis (4-methyl-6-tert-butylphenol), 2,2'-methylenebis (4-ethyl-6)
-Tert-butylphenol), 2,2-ethylidene bis (4,6-di-tert-butylphenol, 4,4'-thiobis (2-methyl-6-tert-butylphenol)). The heat-sensitive recording material described.