JPH0259783B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-sensitive recording material, and particularly to a heat-sensitive recording material that has high heat sensitivity and is suitable for high-speed recording.

In recent years, the amount of information has increased with the diversification of information.
In order to record this information, various recording methods and recording materials have been researched, developed, and put into practical use in the field of information recording. Among them, the thermal recording method allows a recorded image to be obtained by simply heating the thermal recording material, and does not require a complicated development process.The manufacturing and storage management of the thermal recording material is better than that of other recording materials. In many cases, inexpensive paper is used as a support for heat-sensitive recording materials, and the recording material obtained in this case also has the advantage of having a feel similar to that of plain paper. It is widely used in computer output, printers such as calculators, recorders for various measuring instruments, facsimiles, automatic ticket vending machines, thermal copying machines, etc.

Thermal recording materials used for this purpose include:
Conventionally, a heat-sensitive coloring layer containing a leuco dye that is colorless or light-colored at room temperature and an organic acidic substance such as a phenol compound that develops color by reacting with the leuco dye when heated is supported on paper, synthetic paper, synthetic resin film, etc. One that is placed on the body is known.

However, in the field of information recording, the recording speed can be improved by heating the thermal head in a short time and producing sufficient density with a low voltage. There has been a strong demand for the development of recording materials.

In view of this, the present inventors have conducted extensive research on heat-sensitive recording materials that have excellent thermal responsiveness and are capable of recording clear images with good density even during high-speed recording, and have found that leuco dyes and The general formula (In the formula, R ₁ to _{R 6} represent hydrogen or a hydrocarbon group having 1 to 4 carbon atoms) by containing a hydride or partial hydride of a compound having a melting point of 50 to 200°C, The present invention was completed based on the discovery that these compounds act as color development accelerators, significantly improving thermal responsiveness and achieving the object.

The leuco dye used as a coloring agent in the present invention is a substance that is colorless or light-colored at room temperature and develops a color by reacting with an acidic substance under heating, such as 3,3-bis(p-dimethylaminophenyl )-Triallylmethane dyes such as 6-dimethylaminophthalide, diphenylmethane dyes such as 4,4'-bis-dimethylaminobenzhydrylbenzyl ether, and fluoran dyes such as 7-diethylamino-3-chlorofluorane. , thiazine dyes such as benzoylleucomethylene blue, and 3-
Examples include spiro dyes such as methyl spirodinaphthopyran, as well as leuco auramine dyes, indoline dyes, indigo dyes, and the like.

The organic acidic substance used together with the leuco dye is a substance that becomes a color developer when it comes into contact with the leuco dye when heated, and includes various phenol compounds, organic acids, and the like. These are preferably solid at room temperature and liquefied or vaporized at 50°C or higher. Examples of these organic acidic substances include phthalic anhydride, gallic acid, salicylic acid, 4,4'-isopropylidene diphenol, 4,4'-isopropylidene bis(2-chlorophenol), and 4,4'-isopropylidene. Redenbis(2-t-butylphenol), 4,4′-sec-butylidenediphenol,
4,4'-(1-Methyl-n-hexylidene)diphenol, 4-phenyl phenol, 4-hydroxydiphenoxide, methyl-4-hydroxybenzoate, phenyl-4-hydroxybenzoate, 4-hydroxy acetophenone, salicylic acid Anilide, 4,4'-cyclohexylidene
Diphenol, 4,4'-cyclohexylidene bis(2-methylphenol), 4,4'-benzylidene diphenol, 4,4'-thiobis(6-t-butyl-3-methylphenol), novolak type phenolic resin , halogenated novolac type phenolic resin, α-naphthol, β-naphthol and the like.

The thermosensitive coloring layer containing the leuco dye and the organic acidic substance contains one or more compounds of the hydride or partial hydride of the compound represented by the above general formula and having a melting point of 50 to 200°C. urge

A hydride or partial hydride of the compound represented by the above general formula used in the present invention with a melting point of 50 to
The compound, which has a temperature of 200°C, is contained in the heat-sensitive coloring layer and acts as a coloring accelerator, and its mechanism of action is that it has a melting point or sublimation point lower than both the leuco dye and/or the organic acidic substance. , leuco dye and/or organic acidic substance, it is thought that it dissolves one or both of them and promotes the reaction between them. Therefore, compounds with melting points in the range of 50 to 200°C are preferred.

The above general formula (In the formula, R ₁ to _{R 6} represent hydrogen or a hydrocarbon group having 1 to 4 carbon atoms.) As the hydride or partially hydride of the compound represented by the formula, terphenyl and its alkyl substituted product, preferably 1 or 2 Examples include hydrides or partially hydrides of methyl or ethyl substituted products. Examples of these hydrides or partially hydrogenated compounds having a melting point of 50 to 200°C include 1,3-dicyclohexylcyclohexane (octadecahydro-m-terphenyl), 1,4
-dicyclohexylcyclohexane (octadecahydro-p-terphenyl), 1,4-dicyclohexylbenzene, 4-cyclohexyl-1-phenylcyclohexane, 1,4-dicyclohexen-1-ylbenzene, 1-cyclohexyl-4
-(p-toluyl)cyclohexane, 1,3-dicyclohexyl-5-methylbenzene, 1,4-
dicyclohexyl-2,5-dimethylbenzene,
1,5-dicyclohexyl-2,4-dimethylbenzene, 1,4-dicyclohexyl-2,6-dimethylbenzene, 1,5-dicyclohexyl-
2,3-dimethylbenzene, 1,4-bis(1-
Examples include compounds such as methylcyclohexyl)benzene. These compounds can be used alone or in combination of two or more.

The color development accelerator made of these compounds varies depending on the leuco dye used, the type of organic acidic substance, etc., but is used in amounts of 0.5 to 30% per 1 part by weight of the leuco dye.
Parts by weight are used, preferably 1 to 10 parts by weight. It may also be used in combination with a conventionally known color accelerator.

Various additives can be added to the heat-sensitive recording material of the present invention depending on its use. The additives mainly include binders that isolate and fix the leuco dye dispersed in fine particles and the organic acidic substance from each other, such as polyvinyl alcohol (PVA), methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, and polyacrylic acid. , casein, gelatin, starch, or derivatives thereof.
In addition to the above-mentioned binders, white pigments such as calcium carbonate, kaolin, clay, talc, and titanium oxide, fatty acid metal salts, etc. are also used for the purpose of improving the whiteness of the heat-sensitive coloring layer, the slipperiness of writing instruments, and preventing staining. be.

These materials can be mixed or separately used to make paper,
It is coated onto a support such as a film to form a heat-sensitive coloring layer.

The present invention will be specifically described below based on Examples and Comparative Examples.

Example 1 (1) Preparation of Solution A 15 parts by weight of crystal violet lactone, 50 parts by weight of p-dicyclohexylbenzene, and 500 parts by weight of a 10% PVA aqueous solution were ground and mixed in a ball mill for 5 hours to prepare Solution A.

(2) Preparation of Solution B 75 parts by weight of bisphenol A and 500 parts by weight of a 15% PVA aqueous solution were pulverized and mixed in a ball mill for 5 hours to prepare Solution B.

(3) Preparation of thermal recording paper Prepare a coating liquid by mixing 100 parts by weight of liquid A and 100 parts by weight of liquid B. Apply this coating liquid to a base paper of 50 g/m ² and dry it. A thermal recording paper with a coating weight of 5 g/m ² was obtained.

Examples 2 and 3 Instead of p-dicyclohexylbenzene in Example 1, 1,3-dicyclohexylcyclohexane (octadecahydro-m-terphenyl) was used in Example 2, and 1,4-dicyclohexyl- A thermosensitive recording paper was obtained in exactly the same manner as in Example 1 except that 2,5-dimethylbenzene was used in each case.

Comparative example Crystal violet lactone 15 parts by weight and 10 parts by weight
%PVA aqueous solution and 250 parts by weight of the 15% PVA aqueous solution to prepare solution A. Prepare solution B using 75 parts by weight of bisphenol A and 500 parts by weight of the 15% PVA aqueous solution.
A coating liquid was prepared by mixing 200 parts by weight, and a heat-sensitive recording paper with a dry coating weight of 5 g/m ² was prepared in the same manner as in the above example.

Each heat-sensitive recording paper obtained in each of the above Examples and Comparative Examples was colored in the range of 60 to 130°C using a stamp-type color tester, and the color density was measured using a reflection densitometer (Sakura Digital Reflection Densitometer PDA-45). did.
The results are shown in Figure 1.

As is clear from FIG. 1, it was found that the thermal recording paper of each example had a better rise in reflection density with respect to a rise in temperature than that of the comparative example, and had excellent thermal responsiveness.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between temperature and reflection density of the thermal recording paper of each Example and Comparative Example.

Claims (1)

[Scope of Claims] 1. A heat-sensitive recording material provided on a support with a heat-sensitive coloring layer containing a leuco dye that is colorless or light-colored at room temperature and an organic acidic substance that develops color by reacting with the leuco dye when heated, The above heat-sensitive coloring layer has the general formula (wherein R ₁ to _{R 6} represent hydrogen or a hydrocarbon group having 1 to 4 carbon atoms) is selected from the group consisting of hydrides or partially hydrides of compounds having a melting point of 50 to 200°C. 1. A heat-sensitive recording material characterized by containing one or more kinds of compounds.