JPS639997B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in heat-sensitive recording paper whose main components are a colorless or light-colored organic dye generally called a leuco compound and an organic acid such as a phenol compound that develops a color by reacting with the leuco compound.
More specifically, 2-naphthyl benzoate (existing chemical substance registration number 4-358) is used as a coloring accelerator in thermal recording paper containing the above-mentioned two-component color-forming reactants.
The present invention relates to a novel heat-sensitive recording paper characterized in that the color development characteristics and storage stability of the heat-sensitive recording paper are improved by incorporating the present invention into the recording layer. A thermosensitive recording paper containing a leuco compound and an organic acid is already known, for example, from Japanese Patent Publication No. 14039/1983. This recording paper is based on the principle that thermal energy is applied to the recording layer to soften or melt the leuco compound, organic acid, and binder, and the two coloring components are brought into contact to cause a coloring reaction. It is used in fields such as Although the recording characteristics of the recording paper differ depending on the use, for example, in order to increase the recording speed, it is necessary to improve the recording apparatus and to promote the color development of the recording paper itself. A commonly used method for promoting color development is to include a low melting point substance in the recording layer. As low melting point substances, i.e. color accelerators or sensitizers, urea, phthalic anhydride,
In JP-A-48-19231, paraffin wax, carnauba wax, beeswax, wood wax, higher fatty acids, higher fatty acid esters are used, and in JP-A-49-17748, salicylic acid, anisic acid,
Phthalic acid monophenyl ester, phthalic acid monobenzyl ester, and fatty acid amide have recently been widely used as color accelerators. That is, Japanese Patent Publication No. 51-27599 describes the sensitizing effect of fatty acid amide by combining paraffin or microwax with fatty acid amide.
No. 139740 also describes the sensitizing effect of fatty acid amides such as stearic acid amide and oleic acid amide, and is well known. The present inventors confirmed the effects of these known color accelerators, and investigated at least 180 types of substances in order to find substances with even better properties.
As a result of extensive and deep studies, 2-naphthyl benzoate was discovered as a new color accelerator. succeeded in finding. The substance is not only excellent in the effect of promoting color development, but also has other properties as a thermal recording paper, such as background density, background fogging after storage, and discoloration, which do not pose any practical problems. It could be confirmed. The object of the present invention can be achieved when the content of 2-naphthyl benzoate is 1 to 30% by weight of the total solid content of the heat-sensitive recording layer. Next, substances other than the color development accelerator used in the present invention will be described. (1) Leuco compounds Even if they are colorless or light-colored, they are substances that develop color by reacting with organic acids, such as triphenylmethane, triphenylmethanephthalide, fluoran, leucoolamine, diphenylmethane, phenothiazine, and phenoxazine. , spiropyran series, indoline series, and indico series derivatives. (2) Organic acid A substance that is solid at room temperature, melts when heated, and becomes a color developer when it comes into contact with a leuco compound, and includes various phenolic substances, fatty acids, aromatic carboxylic acids, and the like. (3) Binder A water-soluble binder is mainly used to isolate and fix the coloring agent dispersed in fine particles from each other, such as polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, and casein. , gelatin, starch and their derivatives. (4) Other additives In addition to the components (1) to (3) above, the whiteness of the recording layer,
In order to improve writing properties, white pigments such as calcium carbonate, carrion, clay talc, and titanium oxide are added to prevent staining, and fatty acid metal salts are added to prevent head abrasion and staining. You can also.
Further, in combination with the color development accelerator according to the present invention, a known color development accelerator can be added and contained in the recording layer. Next, examples of the present invention will be shown. Example Liquids A and B having the following compositions were separately dispersed for 5 hours using a paint shaker (manufactured by Toyo Seiki). A liquid: Leuco dye PSD-150 (Shin Nisso Kako) 5g 2-naphthyl benzoate (Mitsui Toatsu Fine Co., Ltd.)
Mitsui NAPB Co., Ltd.) 8g Aluminum hydroxide 20g Zinc stearate 5g Polyvinyl alcohol 12% solution 35g Water 52g Solution B: Bisphenol A 15g Kaolin 20g Zinc stearate 3g Polyvinyl alcohol 12% solution 35g Water 52g Next, A solution 125g , add 125 g of liquid B, 50 g of 12% polyvinyl alcohol solution, and 40 g of water, mix, stir, and adjust to make a coating liquid. Next, apply this coating liquid to the surface of 50 g/m ² of high-quality paper using a Meyer bar and dry it. The mixture was coated and dried to a coating weight of 8 g/m ² to obtain heat-sensitive recording paper. Comparative Example Among the formulations of liquid A used in the examples, excluding the color development accelerator 2-naphthyl benzoate according to the present invention,
A thermosensitive recording paper was obtained in the same manner as in the example. Reference example Among the formulations of liquid A used in the examples, benzoic acid-
8 g of 2-naphthyl was added to Amide AP-1 (Nippon Kasei Co., Ltd.)
Stearic acid amide/palmitic acid amide =
7/3) 4g and methylolamide (methylolated product of stearamide from Nippon Kasei Co., Ltd.) 4
A thermosensitive recording paper was obtained in the same manner as in the example except for replacing with g. The heat-sensitive recording papers obtained in the above Examples, Comparative Examples, and Reference Examples were surface-treated with a test supercalender so that the recording surface had a Bekk smoothness of 500 seconds. Next, the storage stability of the thermal recording paper obtained by surface treatment, such as background density, background fogging (density) and discoloration (including when fingerprints are attached) after storage at 55°C and 80% RH for 24 hours, commercially available Tables 1 and 2 show the results of measuring the recording density by performing solid recording with a facsimile machine while varying the applied voltage. The concentration was measured using a Macbeth densitometer model RD514.

【table】

[Table] Perform solid recording.
From the results in Table 2, it is clear that the color development promoting effect of the color development accelerator according to the present invention is significantly increased by comparison with Examples and Comparative Examples. Further, in comparison with fatty acid amide type as a reference example, the excellent effect of the color development accelerator 2-naphthyl benzoate according to the present invention can be seen. Furthermore, from the results shown in Table 1, it is clear that the background concentration and storage stability are equal to or higher than those of fatty acid amide-based products commonly used in the past. It was demonstrated that there was no problem in practical use and that it was a better color accelerator.

Claims (1)

[Claims] 1. A thermosensitive recording paper whose main components are a leuco compound and an organic acid that develops a color by reacting with the leuco compound, characterized in that the recording layer contains 2-naphthyl benzoate as a color development accelerator. Recording paper.