JPH0714660B2 - Thermal recording material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a high-sensitivity heat-sensitive recording material having excellent thermal response.

(B) Prior Art A heat-sensitive recording material generally comprises a support and a heat-sensitive recording layer mainly composed of an electron-donating, usually colorless or light-colored dye precursor and an electron-accepting developer. By heating with a head, a hot pen, a laser beam, etc., the dye precursor and the developer react instantaneously to obtain a recorded image, which is disclosed in JP-B-43-4160 and JP-B-45-14039. It is disclosed. Such a heat-sensitive recording material has the advantages that recording can be obtained with a relatively simple device, maintenance is easy, and noise is not generated.
It is used in a wide range of fields such as printers, computer terminals, labels, ticket vending machines, etc. In particular, in the case of facsimiles, the demand for the heat-sensitive system has greatly increased, and at the same time, the speed is being increased to reduce the transmission cost. Corresponding to the speeding up of such a facsimile, there has been a demand for higher sensitivity of the thermal recording material.

Accelerated fax is standard A4 originals from a few seconds to 20
Since the data is transmitted and received in seconds, the current flowing through the facsimile thermal head is repeated for a very short time of less than a few milliseconds, and the thermal energy generated thereby is transmitted to the thermal recording sheet to carry out the image forming reaction. .

In order to carry out the image forming reaction with the heat energy transferred in such a short time, it is necessary that the heat sensitive recording material has excellent thermal responsiveness. In order to improve the thermal response, it is necessary to improve the compatibility between the developer and the dye precursor. A sensitizer is used for this if necessary. When the sensitizer melts itself by the transferred heat energy, the sensitizer has a function of dissolving or encapsulating a dye precursor and a developer in the vicinity to accelerate the color-forming reaction. It is also one of the methods to improve the sensitivity of the thermal recording material.

As such a method, waxes are disclosed in JP-A-48-19231, JP-A-49-34842, JP-A-50-149353,
In JP-A-52-106746 and JP-A-53-5636, nitrogen-containing compounds, carboxylic acid esters and the like are disclosed in JP-A-57-6459.
No. 3, JP-A-58-87094 discloses naphthol derivatives,
JP-A-57-64592, JP-A-57-185187, JP-A-57-1
91089 and JP-A-58-110289 disclose naphthoic acid derivatives, JP-A-57-148688, JP-A-57-182483, JP-A-58-112788, and JP-A-58-162379. Is a benzoic acid ester derivative, JP-A-60-122193 discloses parabenzyl biphenyl, and JP-A-61-272189 discloses 4-benzoic acid ester derivative.
It is disclosed that allyloxybiphenyl and the like, diphenoxyethanes are added in JP-A-60-56588, and sulfides are added in JP-A-61-242884.

However, the thermal recording materials produced by using these methods are still insufficient in terms of color density and color density.

Further, JP-A-61-193881 discloses the addition of a compound having a suitable melting point, a low viscosity at the melting point, and a good compatibility with a dye precursor as a sensitizer. According to the findings of the present inventor, the ability of the sensitizer to dissolve the dye precursor is closely related to the structure and functional group of the sensitizer, but no correlation with the sensitivity was observed. For example, a compound having an ester group and naphthalene have a large ability to dissolve a dye precursor, but these do not necessarily have high sensitivity. Conversely, a dye precursor can be dissolved in hydrocarbons and monoethers. Some had good sensitivity even though they had a small ability to play. Therefore, at present, it is difficult to predict the sensitivity from these physical properties, and to date, no sensitizer having a satisfactory thermal response has been known. (C) Object of the present invention Various sensitizers were investigated for the purpose of obtaining a highly sensitive thermosensitive recording material having excellent responsiveness.

(D) Structure of the Invention In a heat-sensitive recording material containing a color developing agent that reacts with a normally colorless or light-colored dye precursor upon heating to develop the dye precursor, 2,5-diphenylfuran ( Melting point: 91 ° C), 2,4-diphenylfuran (melting point: 111 ° C), 3,
4-diphenylfuran (melting point: 109 ° C), 2,5-diphenylthiophene (melting point: 153 ° C), 2,4-diphenylthiophene (melting point: 150 ° C), 3,4-diphenylthiophene (melting point:
116 ° C.) and 2-phenyl-5- (4-chlorophenyl) furan (melting point: 123 ° C.) at least one kind, and thereby a highly sensitive thermal recording material excellent in thermal response could be obtained. . The above-mentioned sensitizer can be easily obtained by a known method.

The sensitizer according to the present invention is usually added in an amount of 5% by weight or more based on the color developer. A preferred amount is 10 to 400% by weight, especially 2
0 to 300% by weight is preferred. If the addition amount is less than 5% by weight, the sensitivity improving effect is not sufficient, and if the addition amount is more than 400% by weight, an economically disadvantageous case may occur, and since the amount of the heat fusible substance increases, a diluting effect appears, which is sufficient. It is impossible to obtain good color density.

The main components used in the heat-sensitive recording material of the present invention will be specifically described below, but the present invention is not limited thereto.

Examples of the dye precursor include triphenylmethane-based, fluorane-based, diphenylmethane-based, thiazine-based and spiropyran-based compounds. For example, 3,3-bis (P-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindole-3-
Yl) -4-azaphthalide, 3-diethylamino-6-
Methyl-7-chlorofluorane, 3-diethylamino-
7-chlorofluorane, 3- (N-cyclohexylamino) -7-methylfluorane, 3-diethylamino-7
-Methylfluorane, 3-diethylamino-6-chloro-7-methylfluorane, 3-diethylamino-7-anilinofluorane, 3-diethylamino-6-methyl-
7-dibenzylaminofluorane, 3- (N-ethyl-
N-P-toluidino) -7-anilinofluorane, 3-
Diethylamino-7- (O-chloroanilino) fluorane, 3-dibutylamino-7- (O-chloroanilino)
Fluoran, 3-diethylamino-6-methyl-7-anilinofluorane, 3- (N-ethyl-NP-toluidino) -6-methyl-7-aninolifluorane, 3-
(N-methyl-N-cyclohexylamino) -6-methyl-7-aninolifluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-pyrrolidino-6-
Methyl-7-anilinofluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, 3- (N-ethyl-N-isopentylamino) -6
-Methyl-7-aninolifluorane, 3-diethylamino-6-methyl-7- (P-phenetidino) fluorane, 3-dibutylamino-7- (O-fluoroanilino) fluorane, and the like.

As the developer, an acidic substance generally used for thermal paper,
That is, an electron-accepting compound is used, and in particular, a phenol derivative, an aromatic carboxylic acid derivative, an N, N′-diarylthiourea derivative, a polyvalent metal compound such as zinc, and the like.

Among the above-mentioned phenol derivatives, bisphenols in which one hydroxyl group may be substituted are particularly preferable as the developer, which is represented by the following structural formula.

Structural formula (However, X is Represents R ₁ represents a hydroxyl group, a lower alkoxy group, hydrogen, a lower alkyl group, or halogen. R ₂ and R ₃ represent hydrogen, a lower alkyl group, a lower alkenyl group, or halogen. R ₄ and R ₅ represent hydrogen, a lower alkyl group, or a lower alkoxycarbonyl group. R ₄ and R ₅ may combine to form a ring. ) Specific examples of the compound represented by the above structural formula include, for example, 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis (4-hydroxyphenyl) butane, and 1,1-bis (4-hydroxy). Phenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) pentane, 2,2-bis (4-hydroxyphenyl) hexane, methyl 2,2-bis (4-hydroxyphenyl) acetate, 2,2-bis ( 4-hydroxyphenyl) ethyl acetate, 2,2-bis (4-hydroxyphenyl) butyl acetate, bis (4-hydroxyphenyl) sulfone, bis (4-hydroxyphenyl) sulfoxide, bis (4-hydroxyphenyl) sulfide, 4 -Hydroxy-4'-isopropyloxydiphenyl sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 4-hydr Xy-4'-chlorodiphenyl sulfone, 2,2-bis (3-t-butyl-4-hydroxyphenyl) propane, 2,2-bis (3-chloro-4-hydroxyphenyl) propane, bis (3-allyl -4-hydroxyphenyl) sulfone, bis (3-t-butyl-4-hydroxy-5-methylphenyl) sulfide, 4-hydroxydiphenylsulfone and the like.

Specific examples of other preferable developers include, for example, benzyl 4-hydroxybenzoate, 1,7-bis (hydroxyphenylthio) -3,5-dioxaheptane, N, N'-bis (3-chlorophenyl). ) Thiourea, zinc thiocyanate, N, N'-bis (3-trifluoromethylphenyl) thiourea, lauryl gallate, stearyl gallate, behenyl gallate, zinc hydroxynaphthoate, salicylanilide, 4-hydroxyphthalic acid Dimethyl, metal salts such as zinc 5-t-butylsalicylic acid, dimethyl 6-hydroxy-2,3-naphthalene dicarboxylate, methyl 4-hydroxybenzoate, 4-hydroxybenzoic acid, benzyl 2,4-dihydroxybenzoate, Benzyl 3,4-dihydroxybenzoate, chlorosalicylanilide 4-t-butylbenzoate, 4-hydroxy Isopropyl benzoate, 2-phenoxyethyl 4-hydroxybenzoate, benzoic acid, novolac type phenol resin, 2,2'-dihydroxybiphenyl, 1-naphthol, 2-naphthol, bis (2-hydroxy-5-chlorophenyl) methane, 1,1-bis (2-hydroxy-5-methylphenyl) dodecane, 4-phenylphenol, 4-t-butylphenol, phenol 1,5-bis (3-hydroxyphenoxy) pentane, 1,2-bis (3-hydroxyphenoxy) ethane, 1,2-bis (4-hydroxyphenoxy) ethane, 1- (2,4-dihydroxyphenyl)- 1-phenylethane, 4-hydroxybenzoic acid stearyl, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 3- (2-phenoxyethoxy) phenol, 3,4-dihydroxy-4'-methyldiphenyl sulfone, and the like.

As the binder, starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, styrene-maleic anhydride copolymer, ethylene-water-soluble binder such as anhydrous-maleic acid copolymer, Examples include latex-based water-soluble binders such as styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, and methyl acrylate-butadiene copolymer.

Examples of the pigment include diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, and urea-formalin resin.

In addition, for the purpose of preventing head wear and sticking, higher fatty acid metal salts such as zinc stearate and calcium stearate, waxes such as paraffin, oxidized paraffin, polyethylene, oxidized polyethylene, stearic acid amide, and castor wax, Examples thereof include dispersants such as sodium dioctylsulfosuccinate, ultraviolet absorbers such as benzophenone-based and benzotriazole-based, and surfactants and fluorescent dyes.

Paper is mainly used as a support for the heat-sensitive recording material according to the present invention, but various non-woven fabrics, plastic films, synthetic papers, metal foils, etc., or a composite sheet in which these are combined can be optionally used.

(E) Examples The present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following examples.

Example 3 20 g of 3- (N-ethyl-N-isopentylamino) -6-methyl-7-anilinofluorane was dispersed in a ball mill together with 80 g of a 1% polyvinyl alcohol aqueous solution. Meanwhile, 50 g of 2,2-bis (4-hydroxyphenyl) propane
Was dispersed with 200 g of a 1% aqueous solution of polyvinyl alcohol by a ball mill, and 50 g of 2,5-diphenylfuran was further dispersed with 200 g of a 1% aqueous solution of polyvinyl alcohol in the same manner.

After mixing these three dispersions, add 40
% Dispersion 125 g, 25% zinc stearate dispersion 40 g, 10% polyvinyl alcohol aqueous solution 300 g,
It was sufficiently stirred to obtain a coating liquid. The coating solution was applied to a base paper having a basis weight of 49 g / m ^{2 so} that the solid content was 6 g / m ² , dried and treated with a super calendar to obtain a heat-sensitive recording material.

Comparative Example Instead of 50 g of 2,5-diphenylfuran used in the examples, N was used.
A heat-sensitive recording material was obtained in the same manner as in Example except that 50 g of hydroxymethylstearic acid amide was used.

Evaluation The thermal recording materials obtained in Examples and Comparative Examples were printed with a facsimile machine FACOM FAX-621C manufactured by Fujitsu Ltd., and the optical density of the obtained images was measured with Macbeth RD-514. The results are tabulated.

(F) Effect of the invention As shown in the table, the use of the sensitizer according to the present invention makes it possible to obtain a highly sensitive heat-sensitive recording material having excellent thermal response.

Claims (1)

[Claims] 1. A heat-sensitive recording material containing a colorless or light-colored dye precursor and a developer which reacts when heated to develop the color of the dye precursor, which comprises 2,5-diphenylfuran, 2,4
-Diphenylfuran, 3,4-diphenylfuran, 2,5-diphenylthiophene, 2,4-diphenylthiophene, 3,4
-Diphenylthiophene and 2-phenyl-5- (4-
A heat-sensitive recording material containing at least one of chlorophenyl) furan.