JPH05124359A - Thermal recording material - Google Patents

Abstract

PURPOSE:To improve the preservability of a recording image by providing a recording layer containing a colorless or light-colored basic dye and a composite zinc salt of terephthalaldehyde acid and other aromatic carboxylic acid being a developer on a support. CONSTITUTION:A colorless or light-colored basic dye, a composite zinc salt of terephthalaldehyde acid and other aromatic carboxylic acid and a hindered phenol compound are introduced into a stirring grinder such as a ball mill in a predetermined amount ratio along with water being a dispersing medium to be subjected to dispersing and grinding treatment to prepare a coating solution for a recording layer. This coating solution is applied to a support such as paper, synthetic paper or a plastic film and dried to form a recording layer to obtain a thermal recording material. As a pref. example of the hindered phenol compound compounded with the recording layer, there is 2,2'-methylenebis (4-methyl-6-tert-butylphenol) or 2, 2'-methylenebis (4-ethyl-6-tert-butylphenol).

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, and more particularly to a heat-sensitive recording material which is excellent in recording density and storability of recorded images and has less background fog.

[0002]

2. Description of the Related Art Conventionally, a heat-sensitive recording material which utilizes a color reaction between a colorless or light-colored basic dye and a color-developing agent and reacts both color-forming substances with heat energy of a heat-sensitive head to obtain a recorded image is often used. Are known. Since such a thermal recording medium is relatively inexpensive and the recording device is compact and its maintenance is relatively easy, it is used not only as a recording medium for facsimiles and various computers but also in a wide range of fields.

In recent years, recording speeds of 10 seconds or less in A4 size for thermal fax and 120 characters / second or more for thermal printer have become possible, and there is a further demand for higher sensitivity of the thermal recording material. In addition, with the expansion of the POS (Point of sales) system aimed at labor saving in the retail industry,
The use of thermographic labels is increasing. However, since an organic coloring agent such as bisphenol A is used in a normal thermosensitive recording medium, for example, when human skin oils, oils or solvents contact the recording layer, the recording density is lowered, or the background fogging is caused. There is a drawback that it causes unnecessary color development called as.
Further, the thermal recording label is generally used by sticking it on a wrapping film such as a vinylidene chloride film, and thus the recording density is rapidly lowered due to the influence of the plasticizer contained in the wrapping film. There is also.
Various proposals have been made for the purpose of improving such drawbacks, such as a method of providing a protective layer on the recording layer, a method of adding a preservative improving agent to the recording layer, and a method of using a new color former. However, all of them are accompanied by new drawbacks or do not always have a sufficiently satisfactory effect, so that further improvement is strongly demanded.

[0004]

In view of the above situation, the present inventors previously proposed a heat-sensitive recording material using a zinc salt of terephthalaldehyde acid as a color developing agent in Japanese Patent Application No. 2-289301. Such a heat-sensitive recording material has excellent storability of a recorded image with respect to a plasticizer, oil, solvent, etc., and exhibits extremely excellent characteristics such as little background fog. It was found that the shelf life was not always sufficient. For this reason, the present inventors have conducted extensive studies to further improve these points, and as a result, use a complex zinc salt of terephthalaldehyde acid and another aromatic carboxylic acid as a colorant,
Moreover, it has been found that the use of a hindered phenol compound in combination remarkably improves such a difficulty, and has completed the present invention.

[0005]

SUMMARY OF THE INVENTION The present invention comprises:
In a thermosensitive recording medium provided with a recording layer containing a colorless or light-colored basic dye and a coloring agent, the recording layer contains a complex zinc salt of terephthalaldehyde acid and another aromatic carboxylic acid as a coloring agent. The heat-sensitive recording material is characterized by using at least one kind of hindered phenol compound.

[0006]

The terephthalaldehydic acid constituting the complex zinc salt used in the present invention is a compound represented by the following [Chemical formula 1].

[0007]

[Chemical 1]

Other aromatic carboxylic acids which form a complex zinc salt together with terephthalaldehyde acid include benzoic acid derivatives, naphthoic acid derivatives, phthalic acid derivatives, phthalic acid monoester derivatives, phthalamic acid derivatives, orthobenzoylbenzoic acid. Examples thereof include derivatives and salicylic acid derivatives, and specific examples thereof include the following compounds. Of course, the present invention is not limited to these specific examples, and two or more kinds of aromatic carboxylic acids can be used in combination, if necessary.

Benzoic acid, o-toluic acid, p-toluic acid, m-toluic acid, o-chlorobenzoic acid, p-chlorobenzoic acid, o-bromobenzoic acid, p-bromobenzoic acid,
2,4-dichlorobenzoic acid, 3,4-dichlorobenzoic acid, 3,5-dichlorobenzoic acid, 2,6-dichlorobenzoic acid, o-nitrobenzoic acid, p-nitrobenzoic acid, 2,
4-dinitrobenzoic acid, 3,4-dinitrobenzoic acid,
3,5-dinitrobenzoic acid, 2,6-dinitrobenzoic acid, 2-chloro-4-nitrobenzoic acid, 2-chloro-5
-Nitrobenzoic acid, 4-chloro-2-nitrobenzoic acid,
4-chloro-3-nitrobenzoic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, gallic acid, p -Cyanobenzoic acid,
m-trifluoromethylbenzoic acid, 2,4-dimethylbenzoic acid, 3,4-dimethylbenzoic acid, 3,5-dimethylbenzoic acid, o-ethoxybenzoic acid, p-ethoxybenzoic acid, 3,5-dimethoxybenzoic acid Acid, pn-propoxybenzoic acid, 3,4,5-trimethoxybenzoic acid, p-phenoxybenzoic acid, o-phenylbenzoic acid, p-phenylbenzoic acid, o-cumylbenzoic acid, p-cumylbenzoic acid, 2,4-dicumylbenzoic acid, 4,6-dicumylbenzoic acid, p-acetylbenzoic acid, 2-cyclohexylbenzoic acid, 4- (2-phenoxyethoxy) benzoic acid, 2-
Benzoic acid derivatives such as ethoxymethyl-4- (p-chlorophenoxy) benzoic acid, 2-benzylbenzoic acid and 4- (p-methylbenzyloxy) benzoic acid.

Naphthoic acid derivatives such as 1-naphthoic acid, 2-naphthoic acid, 1-hydroxy-2-naphthoic acid, 2-hydroxy-1-naphthoic acid and 2-hydroxy-3-naphthoic acid.

Phthalic acid, isophthalic acid, terephthalic acid,
3-nitrophthalic acid, 4-nitrophthalic acid, 4-chlorophthalic acid, 4-bromophthalic acid, 4,5-dichlorophthalic acid, 3,6-dichlorophthalic acid, tetrachlorophthalic acid, tetrabromophthalic acid, 3,6- Dibromo-4,5
-Phthalic acid derivatives such as dichlorophthalic acid.

Monomethyl ester, monoethyl ester, monopropyl ester, monobutyl ester, monostearyl ester, monobenzyl ester, mono-p-chlorobenzyl ester, mono-p-methylphenyl ester, mono-2 of the above phthalic acid derivative. , 4-dimethylphenyl ester, mono-p-chlorophenyl ester, mono-m-methoxyphenyl ester, mono-p-
Methoxyphenyl ester, mono-m-ethoxyphenyl ester, mono-p-ethoxyphenyl ester, mono-1-naphthyl ester, mono-2-naphthyl ester, monocyclohexyl ester, mono-2-methylcyclohexyl ester, mono-3- Methyl cyclohexyl ester, mono-2-hydroxyethyl ester, mono-2-hydroxybutyl ester, mono-2-hydroxy-1-methylpropyl ester, mono-4-hydroxybutyl ester, mono-2,3-dihydroxypropyl ester, Mono-2- (2-hydroxyethoxy)
Phthalic acid monoester derivatives such as ethyl ester and mono-p-methylbenzyl ester.

Phthalamic acid, 3-chlorophthalamic acid, 4-chlorophthalamic acid, 4-bromophthalamic acid, 4,5-dichlorophthalamic acid, 3,6-dichlorophthalamic acid, tetrachlorophthalamic acid , Tetrabromophthalamic acid, 3,6-dibromo-4,5
-Phthalamic acid derivatives such as dichlorophthalamic acid,
Furthermore, N-methyl and N of these phthalamic acid derivatives
-Ethyl, N-butyl, N-cyclohexyl, N-benzyl, Np-chlorobenzyl, Np-methylbenzyl, N-phenyl, N-1-naphthyl, N-2-naphthyl, N, N-diethyl , N-methyl-N-benzyl,
Phthalamic acid derivatives such as N, N-pentamethylene.

2-benzoylbenzoic acid, 2- (4'-methylbenzoyl) benzoic acid, 2- (2'-hydroxy-)
5'-methylbenzoyl) benzoic acid, 2- (4'-hydroxybenzoyl) benzoic acid, 2- (2'-hydroxybenzoyl) benzoic acid, 2- (3'-methyl-4'-hydroxybenzoyl) benzoic acid , 2- (2'-hydroxy-5'-tert-butylbenzoyl) benzoic acid, 2-
(2'-hydroxy-5'-tert-octylbenzoyl) benzoic acid, 2- (2'-hydroxy-5'-cyclohexylbenzoyl) benzoic acid, 2- (2 ', 4'-dihydroxybenzoyl) benzoic acid, 2 -(2'-hydroxy-5'-phenylbenzoyl) benzoic acid, 2-
(4'-cyclohexylbenzoyl) benzoic acid, 2-
(4'-phenylbenzoyl) benzoic acid, 2- (4'-
Chlorobenzoyl) benzoic acid, 2- (2 ', 4'-dichlorobenzoyl) benzoic acid, 2- (2'-hydroxy-
5'-chlorobenzoyl) benzoic acid, 2- (3'-methyl-4'-hydroxybenzoyl) benzoic acid, 2-
Orthobenzoylbenzoic acid derivatives such as (4'-bromobenzoyl) benzoic acid.

5-tert-octylsalicylic acid, 3,5-
Di-tert-butylsalicylic acid, 3-chloro-5-cumylsalicylic acid, 3-methyl-5-tert-octylsalicylic acid, 3-methyl-5-α-methylbenzylsalicylic acid,
3-methyl-5-cumylsalicylic acid, 3,5-di-tert
-Amylsalicylic acid, 3-phenyl-5-benzylsalicylic acid, 3-phenyl-5-tert-octylsalicylic acid, 3-phenyl-5-α-methylbenzylsalicylic acid, 3,5-di-tert-octylsalicylic acid, 3,5 −
Di (α-methylbenzyl) salicylic acid, 3,5-dicumylsalicylic acid, 4-methyl-5- (α-methylbenzyl) salicylic acid, 4-methyl-5-cumylsalicylic acid,
3- (α-methylbenzyl) -6-methylsalicylic acid,
3- (α-methylbenzyl) -6-phenylsalicylic acid, 3-triphenylmethylsalicylic acid, 3-diphenylmethylsalicylic acid, 4-n-dodecylsalicylic acid, 4
-Tert-dodecylsalicylic acid, 4-n-pentadecylsalicylic acid, 4-n-peptadecylsalicylic acid, 5-
(1,3-Diphenylbutyl) salicylic acid, 5-n-octadecylsalicylic acid, 5-dodecylsulfonylsalicylic acid, 5-dodecylsulfosalicylic acid, 3-methyl-5
-Salicylic acid derivatives such as dodecylsulfosalicylic acid.

Among the above-mentioned aromatic carboxylic acids,
Benzoic acid derivatives, phthalic acid derivatives and orthobenzoylbenzoic acid derivatives are preferred. In particular, an isophthalic acid derivative,
A benzoic acid derivative represented by the following general formula [Chemical Formula 2] and an orthobenzoyl benzoic acid derivative represented by the following general formula [Chemical Formula 3], particularly isophthalic acid, p-toluic acid, and 2- (4'-chloro) Benzoyl) benzoic acid is preferable because it exhibits a more remarkable effect.

[0017]

[Chemical 2]

[Wherein R ₁ , R ₂ and R ₃ are each a hydrogen atom, a halogen atom, a C _{1 to} C ₄ alkyl group, or C ₁ to
A C ₄ alkoxyl group is shown. ]

[0019]

[Chemical 3]

[Wherein R ₄ and R ₅ are each a hydrogen atom,
Halogen atom, an alkyl group of C ₁ -C _4. In the composite zinc salt of the present invention, the ratio of terephthalaldehyde acid and other aromatic carboxylic acid is not particularly limited, but preferably 0.5 to 2 equivalents, most preferably 1 equivalent to terephthalaldehyde acid. It is desirable to use 1 equivalent of an aromatic carboxylic acid. Here, for example, “using 1 equivalent of an aromatic carboxylic acid to 1 equivalent of terephthalaldehyde acid” means that 1 mol of terephthalaldehyde acid has 1 carboxyl group in the molecule.
It means that 1 mol of the aromatic carboxylic acid having one carboxyl group is used, while 0.5 mol of the aromatic carboxylic acid having two carboxyl groups is used.

The complex zinc salt of terephthalaldehyde acid and other aromatic carboxylic acid is, for example, an alkali metal salt of terephthalaldehyde acid and other aromatic carboxylic acid in water or a mixed medium of water and an organic solvent. It can be produced by a method of reacting an alkali metal salt with a zinc compound, a method of wet co-milling terephthalaldehyde acid, another aromatic carboxylic acid, and a zinc compound.
Although the above method has some difficulty in operability during production, it is advantageous in terms of the yield and purity of zinc chloride. On the other hand, the above-mentioned method is somewhat difficult in terms of the yield and purity of zinc chloride, but has the advantage that a composite zinc salt can be produced very easily.

The organic solvent used in the above method is preferably one having a low solubility in water and a high solubility of the produced composite zinc salt, and examples thereof include aromatic compounds, halides and ester compounds. Be done.
More specifically, toluene, xylene, trichlene, ethyl acetate and the like can be exemplified. Further, as the zinc compound for preparing the composite zinc salt, zinc oxide, zinc hydroxide, zinc carbonate, zinc sulfate, zinc chloride, etc. can be used, but zinc sulfate or zinc chloride is used in the above method. Zinc oxide is particularly preferably used in the above method. The amount of the zinc compound used is not particularly limited, but it is desirable to use it so that it is approximately equivalent to the carboxyl groups of both terephthalaldehyde acid and other aromatic carboxylic acid.

In the present invention, if the complex zinc salt of terephthalaldehyde acid and other aromatic carboxylic acid is the main component, zinc containing only a small amount of terephthalaldehyde acid or aromatic carboxylic acid as a by-product. Even if it contains a salt, the desired effect is sufficiently exhibited.

As described above, the present invention has an important feature in that a complex zinc salt of terephthalaldehyde acid and another aromatic carboxylic acid is used as a colorant and at least one hindered phenol compound is used in combination. It is a thing. As such a hindered phenol compound, a compound in which at least one ortho position of the phenolic hydroxyl group is substituted with a branched alkyl group or a cycloalkyl group is preferably used, and specific examples thereof include the following.
2,5-di-tert-butylhydroquinone, 2,5-di-tert-octylhydroquinone, 2,2'-methylenebis (4-methyl-6-tert-butylphenol),
4,4'-butylidene bis (6-tert-butyl-3-methylphenol), 2,2'-methylenebis (4-ethyl-6-tert-butylphenol), 2,4-di-tert
-Butyl-3-methylphenol, 4,4'-thiobis (6-tert-butyl-3-methylphenol), 1,
1,3-tris (5-tert-butyl-4-hydroxy-
2-methylphenyl) butane, 1,1,3-tris (5
-Cyclohexyl-4-hydroxy-2-methylphenyl) butane, bis (3,5-dimethyl-4-hydroxyphenyl) sulfone, 1,3,5-tris (4-tert-
Butyl-3-hydroxy-2,6-dimethylbenzyl)
Isocyanuric acid, etc.

Among these hindered phenol compounds, 2,2'-methylenebis (4-methyl-6-te)
rt-butylphenol), 2,2'-methylenebis (4
-Ethyl-6-tert-butylphenol), 4,4'-
Butylidene bis (6-tert-butyl-3-methylphenol), 4,4'-thiobis (6-tert-butyl-3-
Methylphenol), 1,1,3-tris (5-tert-
Butyl-4-hydroxy-2-methylphenyl) butane, and 1,1,3-tris (5-cyclohexyl-)
4-Hydroxy-2-methylphenyl) butane does not cause new problems such as background fog, and maintains or improves the excellent properties of the specific color developing agent of the present invention and heat resistance of a recorded image. It is more preferably used because it can greatly improve the humidity resistance.

The amount of the hindered phenol compound used is not particularly limited, but in general, a composite zinc salt of terephthalaldehyde acid and other aromatic carboxylic acid 1
It is desirable to use them together in a ratio of about 20 to 300 parts by weight with respect to 00 parts by weight.

In the present invention, various known compounds can be used as the colorless or light-colored basic dye constituting the heat-sensitive recording layer, and specific examples thereof include the following. 3,3
-Bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) phthalide, 3- (4-dimethylaminophenyl) -3- (4-diethylamino-2- Methylphenyl) -6-dimethylaminophthalide, 3- (p-dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- ( 2-methylindol-3-yl) phthalide, 3,3-bis (1,2-dimethylindole-
3-yl) -5-dimethylaminophthalide, 3,3-bis (1,2-dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis (9-ethylcarbazole-3-) Yl) -6-dimethylaminophthalide,
3,3-bis (2-phenylindol-3-yl)-
6-dimethylaminophthalide, 3- (p-dimethylaminophenyl) -3- (1-methylpyrrol-3-yl)
-6-Dimethylaminophthalide, 3- (p-dibenzylaminophenyl) -3- (1,2-dimethylindol-3-yl) -7-azaphthalide, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-
2-Methylindol-3-yl) -7-azaphthalide, 3,3-bis (1-ethyl-2-methylindol-3-yl) phthalide, N-butyl-3- {bis [4-
Triarylmethane dyes such as (N-methylanilino) phenyl] methyl} carbazole, 4,4'-bis (dimethylamino) benzhydrylbenzyl ether, N-
Diphenylmethane dyes such as halophenyl-leuco auramine, N-2,4,5-trichlorophenyl leuco auramine, 4,4'-bis (dimethylamino) benzhydryl-p-toluenesulfinic acid ester, 3,3
-Bis [1,1-bis (4-pyrrolidinophenyl) ethylene-2-yl] -4,5,6,7-tetrabromophthalide, 3,3-bis [1- (4-methoxyphenyl)-
1- (4-dimethylaminophenyl) ethylene-2-yl] -4,5,6,7-tetrachlorophthalide, 3,3
-Bis [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2-yl] -4,5,
Divinylphthalide dyes such as 6,7-tetrachlorophthalide, 3,7-bis (diethylamino) -10-benzoylphenoxazine, benzoyl leuco methylene blue, thiazine dyes such as p-nitrobenzoyl leuco methylene blue, 3-methyl Spirodi Naphthopyran, 3-
Ethylspirodinaphthopyran, 3-phenylspirodinaphthopyran, 3-benzylspirodinaphthopyran, 3-
Methylnaphtho (6'-methoxybenzo) spiropyran,
Spiro dyes such as 3-propylspirodibenzopyran, di-β-naphthospiropyran, 3-methyl-di-β-naphthospiropyran, rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine (o- Lactam dyes such as chloroanilino) lactam, 3-diethylamino-6-methylfluorane, 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-methylamino) fluorane, 3-diethylamino-7-N- Methylaminofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7- (N-methyl-N-
Benzylamino) fluorane, 3-diethylamino-7
-(N-β-chloroethyl-N-methylamino) fluorane, 3-diethylamino-7-diethylaminofluorane, 4-benzylamino-8-diethylaminobenzo [a] fluorane, 3- [4- (4-dimethylaminoanim Rino) anilino] -7-chloro-6-methylfluorane, 8- [4- (4-dimethylaminoanilino) anilino] benzo [a] fluorane, 3- (N-ethyl-p-
Toluidino) -6-methyl-7-phenylaminofluorane, 3- (N-ethyl-p-toluidino) -6-methyl-7- (p-toluidino) fluorane, 3-diethylamino-6-methyl-7-phenyl Aminofluorane,
3-Dimethylamino-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-ethyl-N-
Isoamylamino) -6-methyl-7-phenylaminofluorane, 3- (N-cyclohexyl-N-methylamino) -6-methyl-7-phenylaminofluorane,
3-pyrrolidino-6-methyl-7-phenylaminofluorane, 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- (N-ethyl-N-tetrahydrofurfurylamino) -6-methyl-7-phenylaminofluorane, 3- (N-methyl-N-propylamino) -6
-Methyl-7-phenylaminofluorane, 3-pyrrolidino-6-methyl-7-p-butylphenylaminofluorane, 3- (N-ethyl-N-isobutylamino)-
6-methyl-7-phenylaminofluorane, 3- (N
-Methyl-N-n-hexylamino) -6-methyl-7
-Phenylaminofluorane, 3- (N-ethyl-N-
n-hexylamino) -6-methyl-7-phenylaminofluorane, 3- (N-ethyl-N-cyclopentylamino) -6-methyl-7-phenylaminofluorane, 3- [N- (3-ethoxy) Propyl) -N-methylamino] -6-methyl-7-phenylaminofluorane, 3- [N-ethyl-N- (3-ethoxypropyl)
Amino] -6-methyl-7-phenylaminofluorane, 3-diethylamino-7- [m- (trifluoromethyl) phenylamino] fluorane, 3-diethylamino-7- (o-fluorophenylamino) fluorane,
Fluorane dyes such as 3-di (n-butyl) amino-7- (o-fluorophenylamino) fluorane and 3-diethylamino-6-chloro-7-phenylaminofluorane, 3,6-bis (dimethylamino) Fluorene-9
-Spiro-3 '-(6'-dimethylamino) phthalide,
3-Diethylamino-6- (N-allyl-N-methylamino) fluorene-9-spiro-3 '-(6'-dimethylamino) phthalide, 3,6-bis (dimethylamino)
-Spiro [fluorene-9,6'-6'H-chromeno (4,3-b) indole], 3,6-bis (dimethylamino) -3'-methyl-spiro [fluorene-9,
6'-6'H-chromeno (4,3-b) indole],
3,6-bis (diethylamino) -3'-methyl-spiro [fluorene-9,6'-6'H-chromeno (4,3
-B) Indole] and other fluorene dyes, etc. Of course, the dyes are not limited to these dyes, and two or more dyes may be used in combination. Among these basic dyes, 3-di (n-butyl) amino-6-methyl-7-phenylaminofluorane can exert the characteristics of the specific color-imparting agent of the present invention at all. , Preferably used.

In the heat-sensitive recording material of the present invention, the ratio of the basic dye to be contained in the recording layer and the specific color developing agent is determined by the type of basic carboxylic acid used and the aromatic carboxylic acid constituting the complex zinc salt. It should be appropriately selected according to the like and is not particularly limited, but generally 0.5 to 50 parts by weight, preferably 1 to 10 parts by weight, more preferably 1 to 10 parts by weight of the complex zinc salt with respect to 1 part by weight of the basic dye. Is preferably adjusted to a range of about 1 to 5 parts by weight.

In the present invention, a specific complex zinc salt is used as a coloring agent, but bisphenol A, 4-hydroxy- is used as long as the desired effect of the present invention is not impaired.
It is also possible to use a known phenolic colorant such as 4'-isopropoxydiphenyl sulfone or benzyl 4-hydroxybenzoate together.

Further, in the present invention, a sensitizer may be added to the recording layer, if necessary, and specific examples of such a sensitizer include stearic acid amide, stearic acid methylenebisamide, and oleic acid amide. , Fatty acid amides such as palmitic acid amide and coconut fatty acid amide, 2-
UV absorbers such as (2'-hydroxy-5'-methylphenyl) benzotriazole and 2-hydroxy-4-benzyloxybenzophenone, 1,2-di (3-methylphenoxy) ethane, 1,2-diphenoxyethane 1
-Phenoxy-2- (4-methylphenoxy) ethane,
Ethers such as 1- (4-methoxyphenoxy) -2- (2-methylphenoxy) ethane, parabenzyl biphenyl, naphthylbenzyl ether, benzyl-4-methylthiophenyl ether, 1-hydroxy-2-naphthoic acid phenyl ester, Oxalic acid dibenzyl ester,
Oxalic acid-di-p-methylbenzyl ester, oxalic acid-di-p-chlorobenzyl ester, terephthalic acid dimethyl ester, terephthalic acid dibutyl ester, terephthalic acid dibenzyl ester, isophthalic acid dibutyl ester, and other known esters And the heat fusible substance. Among these, 1,2-di (3-methylphenoxy) ethane, 1,2-diphenoxyethane, 1-phenoxy-2- (4-methylphenoxy) ethane, 1- (4-methoxyphenoxy) -2 -(2-Methylphenoxy) ethane is preferably used because it exhibits particularly remarkable effects in combination with the color former of the present invention. The amount of the sensitizer used is not particularly limited, but it is generally desirable to adjust the amount within the range of about 4 parts by weight or less with respect to 1 part by weight of the color developer.

In order to prepare a coating liquid for a recording layer containing these substances, water is generally used as a dispersion medium, and a basic dye, a specific dye, is added by a stirring / grinding machine such as a ball mill, an attritor, or a vertical or horizontal sand mill. A composite zinc salt, a hindered phenol compound, etc. are dispersed together or separately to prepare a coating liquid. In the coating liquid, starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, arabic gum, polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt are used as adhesives. , Ethylene / acrylic acid copolymer salt,
A styrene / acrylic acid copolymer salt, a styrene / butadiene copolymer emulsion or the like is used in an amount of 10 to 40% by weight, preferably 15 to 30% by weight, based on the total solid content.

Furthermore, various auxiliaries can be added to the coating liquid, for example, sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate / sodium salt, alginate, fatty acid metal salt and the like. Dispersants, UV absorbers, other defoamers, fluorescent dyes, coloring dyes and the like. In addition, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, and ester wax, kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, fine anhydrous silica, and active as required. It is also possible to add an inorganic pigment such as clay.

In the present invention, the method for forming the heat-sensitive recording layer is not particularly limited, and the heat-sensitive recording layer can be formed according to a conventionally well-known technique, for example, air knife coating, varibar blade coating, pure blade coating. It can be formed by a method of coating and drying the coating liquid on the support by short dwell coating, curtain coating or the like. The coating amount of the coating liquid is also not particularly limited, and is usually ² to 12 g / m ² , preferably 3 to 10 g in dry weight.
The range is / m ² . The support is appropriately selected and used from paper, synthetic paper, plastic film and the like.

In the present invention, it is possible to further improve the storability of a recorded image by providing a resin layer on the thermal recording material and / or on the back surface side thereof, if necessary.
Further, various known techniques in the field of heat-sensitive recording material production, such as providing an undercoat layer on the support to improve image quality and sensitivity, or subjecting the back surface of the recording material to an adhesive label to process it into an adhesive label, can be appropriately added. It is a thing. Further, the image quality and the image density can be improved by performing a super calendering process after forming the recording layer.

[0035]

EXAMPLES 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. Unless otherwise specified, "parts" and "%" in the examples mean "parts by weight" and "% by weight", respectively.

Example 1 Preparation of Liquid A A composition comprising 35 parts of 3-di (n-butyl) amino-6-methyl-7-phenylaminofluorane, 5 parts of a 5% aqueous solution of methylcellulose, and 60 parts of water was sand milled. And pulverized until the average particle diameter becomes 2 μm. Preparation of liquid B 15 parts terephthalaldehyde acid, 8.3 isophthalic acid
Parts, 8.1 parts of zinc oxide, 45 parts of a 10% aqueous solution of a dispersant (sulfon group-modified polyvinyl alcohol, trade name: Gocelan L-3266, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), and 25 parts of water.
The average particle size is 2μm in a sand mill
The resulting mixture was pulverized to obtain a mixed zinc salt dispersion containing a composite zinc salt of terephthalaldehyde acid and isophthalic acid as a main component.

Preparation of Solution C A composition consisting of 7 parts of 1,1,3-tris (5-cyclohexyl-4-hydroxy-2-methylphenyl) butane, 1 part of a 5% aqueous solution of methylcellulose, and 12 parts of water was sand-milled. It was pulverized until the average particle diameter became 2 μm. Formation of recording layer Liquid A 100 parts, liquid B 101.4 parts, liquid C 20 parts, polyvinyl alcohol (trade name: PVA110, manufactured by Kuraray Co., Ltd.)
Of 100% of 10% aqueous solution, 10 parts of finely particulate silica, 33 parts of 30% aqueous zinc stearate dispersion, and 57 parts of water were mixed and stirred to prepare a coating liquid for heat-sensitive recording layer. The obtained coating liquid was applied to a base paper of 50 g / m ² and the coating amount after drying was 5 g / m ^2.
It was applied and dried so as to be m ² . Further, it was subjected to smoothing treatment with a super calender to obtain a thermal recording paper.

Example 2 In the preparation of solution C, 4,4'-butylidenebis (6-tert-butyl-) was used instead of 1,1,3-tris (5-cyclohexyl-4-hydroxy-2-methylphenyl) butane. A thermosensitive recording paper was obtained in the same manner as in Example 1 except that 3-methylphenol) was used.

Example 3 In the preparation of solution C, 4,4'-thiobis (6-tert-butyl-) was used instead of 1,1,3-tris (5-cyclohexyl-4-hydroxy-2-methylphenyl) butane.
A thermosensitive recording paper was obtained in the same manner as in Example 1 except that 3-methylphenol) was used.

Example 4 In the preparation of solution C, 2,2'-methylenebis (4-methyl-6) was used instead of 1,1,3-tris (5-cyclohexyl-4-hydroxy-2-methylphenyl) butane.
-Tert-butylphenol) Example 1
A thermosensitive recording paper was obtained in the same manner as in (1).

Example 5 In the preparation of solution C, 2,2'-methylenebis (4-ethyl-6) was used instead of 1,1,3-tris (5-cyclohexyl-4-hydroxy-2-methylphenyl) butane.
-Tert-butylphenol) Example 1
A thermosensitive recording paper was obtained in the same manner as in (1).

Example 6 In the preparation of solution B, p was replaced by 8.3 parts of isophthalic acid.
A thermosensitive recording paper was obtained in the same manner as in Example 1 except that 13.6 parts of toluic acid was used.

Example 7 In the preparation of solution B, 2 parts instead of 8.3 parts of isophthalic acid were prepared.
A thermal recording paper was obtained in the same manner as in Example 1 except that 26.1 parts of-(4'-chlorobenzoyl) benzoic acid was used.

Example 8 Preparation of liquid D 15 g of terephthalaldehyde acid, 8.3 isophthalic acid
g and 4 g of sodium hydroxide were added to 200 ml of water, and heated to 70 ° C. and stirred to dissolve. Then, a solution prepared by dissolving 28.8 g of zinc sulfate heptahydrate in 500 ml of water was added dropwise to this solution over 20 minutes. After completion of dropping, the mixture was stirred for 1 hour and then cooled to 50 ° C., 300 ml of ethyl acetate was added to dissolve the precipitate, and then the ethyl acetate phase was separated. Ethyl acetate was distilled off from the separated ethyl acetate solution under reduced pressure to obtain a mixed zinc salt whose main component was a complex zinc salt of terephthalaldehyde acid and isophthalic acid. Then, 35 parts of the obtained mixed zinc salt, 45 parts of a 10% aqueous solution of a dispersant (sulfone group-modified polyvinyl alcohol, trade name: Gocelan L-3266, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), and water 20
The average particle size of the composition consisting of 2 parts is 2 with a sand mill.
It was pulverized until it became μm. Formation of recording layer 1 part of A solution 100 parts, D solution 100 parts, C solution 20 parts, polyvinyl alcohol (trade name: PVA110, manufactured by Kuraray Co., Ltd.)
A thermosensitive recording layer coating liquid was prepared by mixing and stirring 100 parts of a 0% aqueous solution, 10 parts of fine particle silica, 33 parts of a 30% aqueous dispersion of zinc stearate, and 57 parts of water. The obtained coating solution was applied to a base paper of 50 g / m ² and the coating amount after drying was 5 g / m ²
Was applied and dried. Further, it was subjected to smoothing treatment with a super calender to obtain a thermal recording paper.

Comparative Example 1 A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the liquid C was not used in forming the recording layer.

Comparative Example 2 A thermosensitive recording paper was obtained in the same manner as in Example 8 except that the D liquid was not used in forming the recording layer.

Comparative Example 3 A thermal recording paper was obtained in the same manner as in Example 1 except that isophthalic acid was not used and the amount of zinc oxide used was 4.1 parts in the preparation of the liquid B.

Comparative Example 4 In the same manner as in Example 8 except that 35 parts of bisphenol A was used instead of 35 parts of the mixed zinc salt containing the complex zinc salt of terephthalaldehyde acid and isophthalic acid as the main components in the preparation of the D liquid. A thermosensitive recording paper was obtained.

The 12 types of thermal recording papers thus obtained were subjected to the following evaluation tests, and the results are shown in Table 1. [Recording Density] The recording density of the color image obtained by printing with a thermal printer (Okura Simulator, applied energy 0.4 mJ / dot) was measured by a Macbeth densitometer (Macbeth RD-
100R type). [Plasticizer resistance] Vinylidene chloride wrap film (manufactured by Mitsui Toatsu Chemicals, Inc.) on polypropylene pipe (40 mmφ)
Is wrapped in three layers, the recording layer of the heat-sensitive recording paper after printing is placed on the outer side of the layer, the vinylidene chloride wrap film is further wrapped in three layers and left at room temperature for 3 days, The density of the recorded image was measured with a Macbeth densitometer to evaluate the plasticizer resistance.

[Oil resistance] Cottonseed oil was dropped on the heat-sensitive recording paper after printing, and the condition of the recorded image after standing at room temperature for 24 hours was visually evaluated. [Heat resistance] The heat-sensitive recording paper after printing was treated under a dry condition at 60 ° C for 24 hours, and then the condition of the recorded image was visually evaluated. [Moisture resistance] The heat-sensitive recording paper after printing was processed for 24 hours under the conditions of 50 ° C. and 75% RH, and then the condition of the recorded image was visually evaluated.

[Evaluation Criteria] Evaluation criteria for oil resistance, heat resistance and moisture resistance were as follows.

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[Table 1]

[0053]

As is clear from the results shown in Table 1, the thermosensitive recording medium of the present invention is extremely excellent in the storability of recorded images, particularly in plasticizer resistance, heat resistance and humidity resistance, and also in recording sensitivity. It was a thermosensitive recording medium.

Claims (2)

[Claims] 1. A thermosensitive recording medium comprising a support and a recording layer containing a colorless or light-colored basic dye and a coloring agent, wherein terephthalaldehyde acid and other aromatic compounds are used as the coloring agent in the recording layer. A heat-sensitive recording material comprising a complex zinc salt with a carboxylic acid and at least one hindered phenol compound. 2. A hindered phenol compound is 2,2 '.
-Methylenebis (4-methyl-6-tert-butylphenol), 2,2'-methylenebis (4-ethyl-6-te
rt-butylphenol), 4,4'-butylidenebis (6-tert-butyl-3-methylphenol), 4,
4'-thiobis (6-tert-butyl-3-methylphenol), 1,1,3-tris (5-tert-butyl-4-)
Hydroxy-2-methylphenyl) butane, 1,1,3
-Tris (5-cyclohexyl-4-hydroxy-2-
The thermosensitive recording medium according to claim 1, which is methylphenyl) butane.