JPH03270976A - Thermal recording material - Google Patents

Abstract

PURPOSE:To enhance thermal response and preservability and to prevent the generation of background fog by adding a 2,6-naphthalenedicarboxylic diester derivative having a specific m.p. to a thermal color forming layer. CONSTITUTION:The thermal recording material is obtained by providing a thermal color forming layer containing a leuco dye colorless or light-colored at room temp. and an org. acidic substance reacting with the leuco dye to form a color on a support and a 2,6-nephthalenedicarboxylic diester derivative having an m.p. of 80-150 deg.C is added to the thermal color forming layer. This 2,6-naphthalenedicarboxylic diester derivative has an m.p. lower than that of both of or either one of the leuco dye and the org. acidic substance and solubility to the leuco dye and/or the org. acidic substance to dissolve one or both of them to develop action accelerating the reaction of both of them.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a heat-sensitive recording material, and particularly to a heat-sensitive recording material with excellent heat sensitivity and storage stability.

[Conventional technology]

BACKGROUND ART In recent years, the amount of information has increased with the increasing use of information, and various recording methods and recording materials have been researched and put into practical use in the field of information recording for recording this information. Among them, the thermal recording method is: 1. A recorded image can be obtained by simply heating the thermal recording material, and no complicated development process is required. 2. The manufacturing and storage management of the thermal recording material is similar to that of other recording materials. In many cases, inexpensive paper is used as a support for heat-sensitive recording materials, but in this case, the resulting recording material has a feel similar to that of plain paper. It has the advantages of computer output, printers such as calculators, recorders of various measuring instruments, etc.
It is used in many fields such as facsimiles, automatic ticket issuing machines, and thermal copying machines.

Heat-sensitive recording materials used for these purposes have conventionally contained leuco dyes that are colorless or light-colored at room temperature and organic acidic substances such as phenolic compounds that react with the leuco dyes to develop color when heated. It is known that a heat-sensitive coloring layer is provided on a support such as paper, synthetic paper, synthetic resin film, etc.
0 and Special Publication No. 45-14.039).

However, these conventional heat-sensitive recording materials have a problem in that their thermal responsiveness is insufficient and sufficient color density cannot be obtained when used for high-speed recording.

In addition, in the field of information recording, we have made it possible to heat the thermal head in a short time and produce sufficient density with a low voltage, thereby increasing the recording speed and making it possible to cope with high-speed recording. is requested to do so.

Therefore, in an attempt to solve these problems with conventional heat-sensitive recording materials, it has been proposed to add a thermoplastic substance to the heat-sensitive coloring layer to improve thermal responsiveness (Japanese Patent Application Laid-Open No. Publication No. 51-27.599 and Japanese Unexamined Patent Publication No. 4
8-49.231 and Japanese Patent Publication No. 63-30, 878).

However, even with such technology, as the demand for high-speed recording has become even higher in recent years, fully satisfactory results regarding the thermal response have not yet been obtained. However, if the sensitivity of a heat-sensitive recording material is increased, there is a problem that so-called background fogging (self-coloring due to heat during storage) is likely to occur when used for facsimile or the like.

[Problem to be solved by the invention]

The present invention was devised in view of this point of view, and its purpose is to provide a heat-sensitive recording material that has excellent thermal responsiveness, has excellent storage stability, and is resistant to background fogging. It is in.

[Means to solve the problem]

That is, the present invention provides a heat-sensitive recording material in which a heat-sensitive coloring layer is provided on a support, which contains a leuco dye that is colorless or light-colored at room temperature, and an organic acidic substance that reacts with the leuco dye to develop color when heated. The thermosensitive coloring layer has a melting point of 8.
This is a heat-sensitive recording material containing one or a mixture of two or more selected from 2°6-phthalenecyclodicarboxylic acid diester derivatives having a temperature of 0 to 150°C.

In the present invention, the leuco dye used as a coloring agent is colorless or light-colored at room temperature, and is a substance that develops color by reacting with an acidic substance under heating. Triallylmethane dyes such as 6-dimethylaminophthalide, diphenylmethane dyes such as 4,4°-bisdimethylaminobenzhydride benzyl ether, thiazine dyes such as benzoyl leucomethylene blue, and 3-methyl spirodi Examples include spiro dyes such as naphthopyran, and other dyes such as leuco auramine dyes, indoline dyes, and indigo dyes.

The organic acidic substance used together with the leuco dye is a substance that becomes a color developer when heated and comes into contact with the leuco dye, and includes various phenolic compounds and organic acids. Organic acidic substances used for this purpose include:
Preferably, it is solid at room temperature and liquefies or vaporizes at 50° C. or higher.

Specific examples of such organic acidic substances include phthalic anhydride, gallic acid, salicylic acid, 4゜4゜-isopropylidene (2-chlorophenol), 4.4゛-isopropylidene (2-1-butylphenol), etc. ), 4.4
'-5ee-butylidenephenol, 4,4'(I-methyl-〇-hexylidene)diphenol, 4phenylphenol, 4-hydroxydiphenoxidemethyl-4-
Hydroxybenzoate, 4-hydroxyacetophenone salicylic acid anilide, 4,4' cyclohexylidene diphenol, 4,4'-cyclohexylidene bis(2-
methylphenol), 4,4'-benzylidenephenol, 4,4'-thiobis(6-t-butyl-3-methylphenol), novolac type phenol resin, halogenated novolac type phenol resin, α-naphthol, β-naphthol, etc. can be mentioned.

One type or a mixture of two or more selected from 2゜6-naphthalene dicarboxylic acid diester derivatives having a melting point of 80 to 150°C is added to the heat-sensitive coloring layer containing the leuco dye and organic acidic substance. . This 2,6-naphthalene dicarboxylic acid diester derivative has a melting point lower than both the leuco dye and/or the organic acidic substance, and has solubility in the leuco dye and/or the organic acidic substance. Or, in order to dissolve both and promote the reaction between them, that is, to exhibit an action as a color development promoter, the melting point is 80 to 150.
It is necessary to be within the range of °C.

Preferred 2,6-naphthalene dicarboxylic acid diester derivatives are those represented by the following general formula. Examples of the substituent R include lower alkyl groups, aryl groups, and the like.

Specific examples of 2,6-naphthalene dicarboxylic acid diester derivatives having such substituents include 2,6-
Diethyl naphthalene dicarboxylate (mp: 126℃)
, 2.6-naphthalene dicarboxylic acid diisopropyl (m
p: 120°C), di-n-propyl 2,6-naphthalene dicarboxylate, di-tert-butyl 2,6-naphthalene dicarboxylate, and the like.

These 2,6-naphthalene dicarboxylic acid diester derivatives may be used alone or in combination with each other.
You may use a combination of two or more species as a mixture.

The amount of the 2,6-naphthalene dicarboxylic acid diester derivative used varies depending on the type of leuco dye and organic acid substance used, but is usually 0.5 to 30 parts by weight per 1 part by weight of the leuco dye. , preferably 1-10 parts by weight.

Furthermore, various additives can be added to the heat-sensitive recording material of the present invention depending on its use.

Examples of such additives include polyvinyl alcohol (PVA), methyl cellulose, carboxymethyl cellulose, polyacrylic acid, casein, gelatin, and starch, which fix the leuco dye dispersed in fine particles and the organic acidic substance while separating them from each other. Alternatively, binders such as these derivatives, white pigments such as calcium carbonate, kaolin, clay, talc, titanium oxide, etc., and aliphatic metal salts added for the purpose of whiteness of the heat-sensitive coloring layer, slipperiness of writing instruments, and stickiness. There is. These additives are mixed or applied separately to a support such as a paper film to form a thermosensitive coloring layer.

[For production]

In the heat-sensitive recording material of the present invention, the 2,6-naphthalene dicarboxylic acid diester derivative contained in the heat-sensitive coloring layer is a leuco dye and/or an organic acid substance constituting the heat-sensitive coloring layer. It is believed that it has a lower melting point or sublimation point and is soluble in leuco dyes and/or acidic substances, and acts as a color development accelerator that dissolves one or both of them and promotes the reaction between them.

〔Example〕

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

Example 1 (1) Preparation of Solution A 10 parts by weight of 3-dibutylamino-6-methyl-7-anilinofluorane (ODB-2), 50 parts by weight of calcium carbonate
part by weight, 100 parts by weight of a 5wt

(2) Preparation of liquid B 10 parts by weight of bisphenol A, 10 parts by weight of diethyl 2,6-naphthalene dicarboxylate, 50 parts by weight of 5wtX-PVA aqueous solution, and 30 parts by weight of water were ground and mixed in a sand mill, and the average particle size was 2.5. /, #n liquid B was prepared.

(3) Preparation of heat-sensitive recording paper 30 parts by weight of liquid A, 20 parts by weight of liquid B, and paraffin wax emulsion (manufactured by Chukyo Qufu ■: Hydrin P-7)
A coating liquid was prepared by mixing 5 parts by weight, and this coating liquid was applied onto a base paper and dried to obtain a thermal recording paper with a dry coating weight of 6 g/m.

The thermosensitive recording paper thus obtained was subjected to a dynamic color development test and a static color development test at 70°C. The results are shown in Table 1.

The dynamic coloring test uses a printing tester (manufactured by Taishoku Denki Kogyo Co., Ltd.), and the static coloring test uses a stamp-type coloring tester (daiei Kagaku Seiki (ready made)), and the color density is reflected. Densitometer (
Roku Konishi Photo Industry (Structure: Sakura Digital Reflection Densitometer PD)
A-45).

Example 2 Example 1 above except that diisopropyl 2,6-naphthalene dicarboxylate was used in place of diethyl 2,6-naphthalene dicarboxylate when preparing Solution B of Example 1.
A thermosensitive recording paper was prepared in exactly the same manner as above, and a color development test was conducted in the same manner as in Example 1 above. The results are shown in Table 1.

Comparative Example When preparing Solution B of Example 1, 1 stearamide was added in place of diethyl 2,6-naphthalene dicarboxylate.
A thermosensitive recording paper was prepared in exactly the same manner as in Example 1 above, except that 0 parts by weight was used, and a color development test was conducted in the same manner as in Example 1 above. The results are shown in Table 1.

Table 1 [Effects of the Invention] The color accelerator for heat-sensitive recording materials of the present invention, which is composed of 2.6-naphthalene dicarboxylic acid diester, has excellent thermal responsiveness and heat resistance.

Claims (1)

[Claims] (1) In a heat-sensitive recording material provided on a support, a heat-sensitive color-forming layer containing a leuco dye that is colorless or light-colored at room temperature and an organic acidic substance that reacts with the leuco dye to develop color when heated, the heat-sensitive color-forming layer , the melting point is 80-150℃
1. A heat-sensitive recording material comprising one or a mixture of two or more selected from 2,6-naphthalene dicarboxylic acid diester derivatives.