JPH0684105B2 - 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 color developer react instantaneously to obtain a recorded image, which is described in JP-B-43-4160 and JP-B-45-14039. It is disclosed. Such a thermal recording material has the advantages that it can be recorded with a relatively simple device, is easy to maintain, and does not generate noise. It is a terminal for measuring recorders, facsimiles, printers, and computer terminals. It is used in a wide range of fields such as automatic ticket vending machines such as labels and tickets. 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, JP-A-52-106746, and JP-A-53-5636. JP-A-57-64593 and JP-A-58-87094 disclose naphthol derivatives, JP-A-57-64593 and JP-A-57-64593.
-64592, JP-A-57-185187, JP-A-57-191089, and JP-A-58-110289 disclose naphthoic acid derivatives,
7-148688, JP-A-57-182483, JP-A-58-112788,
JP-A-58-162379 discloses benzoic acid ester derivatives, JP-A-60-122193 discloses parabenzyl biphenyl, JP-A-61-272189 discloses biphenyls, and JP-A-60- 56588 discloses that diphenoxyethanes are added, and JP-A 61-242884 discloses that sulfides are added.

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

(C) Purpose of the Invention The present inventors have investigated various sensitizers for the purpose of obtaining a highly sensitive heat-sensitive recording material having further excellent thermal response.

(D) Structure of the Invention In a heat-sensitive recording material containing a color developing agent which reacts with a normally colorless or light-colored dye precursor upon heating to develop the dye precursor, a compound represented by the following general formula is used as a sensitizer. By incorporating it, a high-sensitivity heat-sensitive recording material excellent in thermal response could be obtained.

General formula (However, R represents a lower alkyl group.) Specific examples of the compound represented by the above general formula include those shown below.

The compound of the above general formula 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)
Fluorane, 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 benzyl 4-hydroxybenzoate, 1,7-bis (4-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-hydroxy Dimethyl phthalate, metal salts such as zinc 5-t-butylsalicylic acid, dimethyl 6-hydroxy-2,3-naphthalenedicarboxylate, methyl 4-hydroxybenzoate, 4-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid Benzyl, benzyl 3,4-dihydroxybenzoate, 4-t-butylbenzoic acid, 5-chlorosalicylanilide, 4 -Isopropyl hydroxybenzoate, 2-phenoxyethyl 4-hydroxybenzoate, benzoic acid, novolac type phenolic 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 dioctyl sulfosuccinate, benzophenone-based and benzotriazole-based ultraviolet absorbers, 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) Synthetic Examples and Examples The present invention will be described in more detail with reference to synthetic examples and examples. However, the present invention is not limited to the following synthesis examples and examples.

Synthesis example Synthesis of compound (1) Dissolve 10.1 g of 4,4'-dihydroxydiphenyl ether in 50 ml of acetone and add 1.75 g of 36.0% sodium hydroxide aqueous solution.
Was added. While stirring this system, 12.3 g of acetic anhydride was added dropwise over 5 minutes. Then, after stirring for 4 hours and a half, toluene and water were added to separate the layers. The organic layer was washed with an aqueous sodium hydrogen carbonate solution, and the solvent dried over anhydrous potassium carbonate was distilled off. The residue was treated with a mixed solvent of n-hexane and benzene to obtain a target crystal. This was recrystallized with a mixed solvent of n-hexane and benzene to obtain 8.8 g of the desired product.

mp = 111.5-113.0 ° C. Example 20 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% aqueous polyvinyl alcohol solution. Meanwhile, 50 g of 2,2-bis (4-hydroxyphenyl) propane
Was dispersed by a ball mill together with 200 g of a 1% polyvinyl alcohol aqueous solution, and further 50 g of the compound (1) was similarly dispersed together with 200 g of a 1% polyvinyl alcohol aqueous solution.

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 1 A thermosensitive recording material was obtained in the same manner as in Example except that 50 g of N-hydroxymethylstearic acid amide was used instead of 50 g of the compound (1) used in Example.

Evaluation The thermal recording materials obtained in Examples and Comparative Examples 1 and 2 were printed with a FACOM FAX-621C facsimile machine manufactured by Fujitsu Ltd., and the optical densities of the obtained images were measured with a Macbeth RD-514. did. 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 color developing agent which reacts with a normally colorless to light-colored dye precursor upon heating to develop the dye precursor, characterized by containing a compound represented by the following general formula. Heat sensitive recording material General formula (However, R represents a lower alkyl group.)