JPS6360714B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a thermal recording paper, and more particularly to a thermal recording paper with improved stability of colored images against plasticizers. It has been known for a long time that a color-forming substance such as crystal violet lactone reacts with an acidic substance to form a color, and it is also known, for example, in US Pat. No. 3,539,375, to thermally develop a color using these substances. . However, colored images obtained by a thermal reaction between a coloring substance and an acidic substance such as a phenolic substance or an organic acid are generally very unstable against changes in light, temperature, and humidity. In addition, various plasticizers used in rubber, plastics, etc. such as dioctyl phthalate, dibutyl phthalate,
dihexyl phthalate, butylbenzyl phthalate,
It is unstable to tricresyl phosphate, dioctyl adipate, etc., and has the major drawback that if the above-mentioned colored image comes into contact with rubber, plastic, etc. to which these plasticizers have been added, the image will disappear or change color. have. It is of course important to improve the stability of colored images against changes in light, temperature, humidity, etc., and therefore there are still problems to be solved at least simultaneously or independently. , when in contact with plasticizers used in plastics, etc.
The present invention relates to a thermosensitive recording paper that has stability of colored images against plasticizers (hereinafter referred to as plasticizer resistance). In recent years, the use of thermal recording paper has increased as a recording medium used at the input/output end of information equipment such as facsimiles, computers, and telex, as well as in transportation-related fields such as labor-saving equipment at railway stations. As a result, there are increasing opportunities for these thermosensitive recording papers to directly or indirectly come into contact with plastic sheets containing various plasticizers, commuter pass holders, etc. Recently, it has also been used on tags for supermarkets, etc.
Opportunities for contact with plastic film are also increasing. Therefore, we colored thermal recording paper and used it for a long time.
There was an urgent need to improve the reliability of recording media when brought into contact with plasticizers. Efforts have been made to improve these required performances, but the current situation is that nothing with satisfactory performance has yet been obtained. As a result of intensive research aimed at improving this drawback, the present inventors discovered that adding a sulfonyl diphenol compound to the recording layer of thermal recording paper improves the plasticizer resistance of the coloring area and filed an application. (Special application 1986-135214). They also filed a separate application (filed on February 16, 1982) with the discovery that plasticizer resistance can also be improved by adding zinc oxide and polyvinylpyrrolidone to the recording layer. Based on these results, the present inventors conducted further research and determined that the plasticizer resistance of the coloring area would be improved by simultaneously adding a sulfonyl diphenol compound, polyvinylpyrrolidone, and zinc oxide to the recording layer of thermal recording paper. find ways to improve,
The present invention has now been accomplished. That is, the present invention provides at least a colorless to light-colored color-forming substance, an acidic substance that causes the dye to color when heated,
A thermal recording paper comprising a water-soluble binder and a pigment, characterized in that the acidic substance is a sulfonyl diphenol compound, 5 wt% or more of the water-soluble binder is polyvinylpyrrolidone, and 5 wt% or more of the pigment is zinc oxide. This paper relates to thermal recording paper. Examples of using sulfonyl diphenol compounds as color developers in pressure-sensitive recording compositions include
-Described in Publication No. 9309. Furthermore, the use of zinc oxide as a pigment for thermal recording paper is well known, as described in, for example, Japanese Patent Publication No. 18635/1983, and the use of polyvinylpyrrolidone as a binder for thermal recording paper is also known as described in Japanese Patent Publication No. 3680/1983. This is a matter that is publicly known from publications such as the above. However, in the present invention, by simultaneously applying a sulfonyl diphenol compound, zinc oxide, and polyvinylpyrrolidone to the recording layer of heat-sensitive recording paper, a heat-sensitive material with excellent plasticizer resistance that cannot be obtained when these substances are used alone can be obtained. Since recording paper can be obtained, such an effect was completely unexpected. The acidic substances used in the present invention are limited to sulfonyl diphenol compounds, such as 4,4'-sulfonyl diphenol, 2,4'-sulfonyl diphenol, 3,3'-dichloro-4,4'-sulfonyl diphenol, Phenol, 3,3',5,5'-tetrabromo-
Examples include 4,4'-sulfonyldiphenol and 3,3'-diamino-4,4'-sulfonyldiphenol. Among them, 4,4'-sulfonyldiphenol has excellent plasticizer resistance when used in combination with polyvinylpyrrolidone and zinc oxide, has little fogging on the skin, and has no odor. Also, among the sulfonyl diphenol compounds, it is the most preferred because it can be obtained in large quantities at low cost. The polyvinylpyrrolidone and zinc oxide used in the present invention are usually commercially available and are not particularly limited, but polyvinylpyrrolidone has slightly different plasticizer resistance effects depending on the molecular weight, and the smaller the molecular weight, the better the plasticizer resistance. The effect tends to be remarkable, and the effect tends to decrease for large ones. Therefore, the molecular weight of polyvinylpyrrolidone used in the present invention is preferably
40000 or less. The mixing ratio of these substances in the paint varies depending on the physical properties required for the paint and the finished thermal recording paper, but in order to maintain plasticizer resistance, polyvinylpyrrolidone should be added to the total binder solid content. Zinc oxide is required in an amount of 5 to 100 wt% based on the total pigment solid content. The amount of these used is 100wt each if judged only from the point of plasticizer resistance.
% is the best combination, but when the thermal recording paper is exposed to high temperature and humidity, the background tends to darken, so in order to maintain plasticizer resistance and to satisfy the stability of the background against temperature and humidity, The preferred usage range is polyvinylpyrrolidone at 10 to 50 wt% based on the total binder solid content, and zinc oxide at 30 to 50 wt% based on the total pigment content.
It is 70wt%. The colorless or light-colored color-forming substance used in the present invention is a substance that develops color by reacting with an acidic substance under heat, such as triphenylmethane, triphenylmethane phthalide, fluoran, leucoolamine, Examples include various leuco compounds such as spiropyrans. Examples of binders other than polyvinylpyrrolidone used in the present invention include water-soluble binders such as casein, gelatin, modified starch, carboxymethylcellulose, hydroxyethylcellulose, polyvinyl alcohol, styrene-maleic anhydride copolymer and its alkaline solution, polyacrylamide, Examples include latexes of styrene-butadiene copolymers, polyvinyl acetate, and polyacrylic esters. Pigments other than zinc oxide used in the present invention include white pigments such as calcium carbonate, kaolin, clay, talc, and titanium oxide. The thermal recording paper of the present invention may contain other additives in the recording layer as necessary, such as various waxes and fatty acid amides to improve recording properties, various fatty acid metal salts to prevent staining, and various additives to improve water resistance. It is also possible to add a waterproofing agent or the like. As the support used in the present invention, various types of paper including high-quality paper, medium-quality paper, and coated paper can be used, and the type and weightage thereof are not limited at all. The support used in the present invention is most commonly paper, but other supports such as synthetic resin film, film laminated paper, and woven fabric sheets can also be used. The thermal recording paper of the present invention is produced as follows. Color forming substances, acidic substances, zinc oxide and other pigments, sensitivity modifiers and other additives are mixed in an aqueous medium containing an appropriate concentration of polyvinylpyrrolidone and other binders using a pulverizer such as a ball mill or sand grinder. The mixture is crushed and dispersed to obtain a heat-sensitive paint. It is advantageous in terms of color development efficiency to make each component material as fine as possible, and preferably to have a particle size of 1 to 3 microns. The heat-sensitive paint thus obtained is applied to a support and dried to obtain the heat-sensitive recording paper of the present invention. The heat-sensitive recording paper of the present invention thus obtained exhibits excellent plasticizer resistance against various plasticizers,
Even if a colored image is brought into contact with these plasticizers for a long period of time, the image will not fade or change color. The present invention will be explained in more detail with reference to Examples. Example 1 (a) Production of heat-sensitive recording composition

【table】

[Table] After separately dispersing liquids A and B in a centrifugal ball mill for 4 hours, liquids A and B were mixed to prepare a paint. (b) This paint was applied to 50 g/m ² of general paper so that the coating amount after drying was 8 g/m ² to obtain thermal recording paper. (c) Next, this thermosensitive recording paper was examined for plasticizer resistance according to the following procedure. First, heat-sensitive recording paper was tested with a static color tester (stamp type) at a pressure of 2 kg/cm ² .
Color was developed at a temperature of 120°C for 1 second. Next, as a plasticizer resistance test, a commercially available plastic eraser was placed on the colored area of the thermosensitive recording paper, and a 300 g weight was placed on top of the eraser and left for one day. Thereafter, the density of the colored portion before and after the test was measured using a Macbeth reflection densitometer RD-514, and the results shown in the table were obtained. Example 2 10 parts by weight of the 20 parts by weight of zinc oxide in Solutions A and B of Example 1 were replaced with clay, and 15 parts by weight of the 20 parts by weight of 10% polyvinylpyrrolidone aqueous solution were replaced with a 10°C aqueous solution of polyvinyl alcohol. A thermosensitive recording paper was obtained in exactly the same manner as in Example 1 except for the above, and the plasticizer resistance test was conducted in the same manner. The results are shown in the table. Comparative Examples 1 to 3 Except for changing the combinations of 4,4'-sulfonyldiphenol, zinc oxide, and polyvinylpyrrolidone in Solutions A and B of Example 1 as shown in the table,
A thermosensitive recording paper was obtained in exactly the same manner as in Example 1, and the plasticizer resistance test was conducted in the same manner. The results are shown in the table. Reference examples 1 to 2 For reference, 4, in liquid A and liquid B of Example 1
Thermosensitive recording paper was obtained in exactly the same manner as in Example 1, except that the combination of 4'-sulfonyldiphenol, zinc oxide, and polyvinylpyrrolidone was changed as shown in the table, and the plasticizer resistance was tested in the same manner. I did this. The results are shown in the table.

[Table] Poor From the results in the table, it is clear that the thermal recording paper of the present invention is not only superior to the comparative examples, but also superior to the reference examples.

Claims (1)

[Claims] 1. In thermal recording paper consisting of at least a colorless or light-colored color-forming substance, an acidic substance that causes the dye to develop color when heated, a water-soluble binder, and a pigment, the acidic substance is a sulfonyl diphenol compound, and the acidic substance is 5wt% or more of the water-soluble binder. is polyvinylpyrrolidone, and 5wt% or more of the pigment is zinc oxide.