JPH0159916B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-sensitive recording material, and more specifically, the present invention relates to a heat-sensitive recording material that includes a color-forming substance that is normally colorless or light-colored and a phenolic substance that causes the color-forming material to develop color when heated. The present invention also relates to an improved thermosensitive recording medium. It has been known that colorless or light-colored color-forming substances, such as lactone or lactam ring-containing leuco dyes, react with phenolic substances to produce color, and these can be used to thermally develop color. A heat-sensitive recording material for this purpose is already known from Japanese Patent Publication No. 14039/1983. This recording material is based on the principle that thermal energy is applied to the recording layer to soften or melt the color-forming substance, phenolic substance, and binder, and the two color-forming components are brought into contact to cause a color reaction. used in the field of In recent years, as recording apparatuses have become faster and consume less energy, there has been a demand for heat-sensitive recording materials with good color development. Various methods have been tried to promote the color development of heat-sensitive recording materials, and one of them is bisphenol A (4,4'-isopropylidene diphenol, melting point 156), which is the most common phenolic substance. JP-A-55-27253 discloses a method of improving the color development of heat-sensitive recording materials by using a phenolic substance having a melting point lower than that of the heat-sensitive recording material (158 DEG C.). On the other hand, JP-A-54-17741, JP-A-Sho
No. 54-74762 contains benzyl p-hydroxybenzoate (melting point 108), which has a lower melting point than bisphenol A.
~113°C) is used as a phenolic substance in a heat-sensitive recording medium.From this, it is possible to use benzyl p-hydroxybenzoate as a phenolic substance in order to improve the color development of a heat-sensitive recording medium. It seemed natural. However, when the present inventors investigated benzyl p-hydroxybenzoate, it was found that although the coloring properties were greatly improved, the storage stability of colored images was inferior to that of bisphenol A. In particular, rubbing the colored area with your finger or cloth and then wiping off a white powder will cause whitening. Fingerprint fading will cause the area to fade if you put a fingerprint on the colored area. Discoloration will occur if the colored area is exposed to sunlight or fluorescent light. The color fading occurred and it could not be put to practical use. The present inventors have made extensive research into a heat-sensitive recording material that improves these drawbacks and has good color development and storage stability, and as a result, the present invention has been completed. That is, the present invention provides a heat-sensitive recording material having a heat-sensitive coloring layer containing a colorless or light-colored color-forming substance and a phenolic substance that causes the color-forming substance to develop color when heated as a color-forming component, in which p-hydroxybenzoin is used as the phenolic substance. using benzyl acid,
Furthermore, 4,4'-butylidene-bis(3-methyl-6-t-butyl-phenol) is contained in the heat-sensitive coloring layer.
and a heat-sensitive recording material characterized by containing a phenol derivative represented by the following general formula (). (In the formula, R ₁ and R ₄ represent a methyl group, t-butyl group, cyclohexyl group, or α-methylcyclohexyl group, R ₂ and R ₃ represent a methyl group or an ethyl group, and R ₅ and R ₆ are hydrogen or an alkyl group having 1 to 8 carbon atoms.) 4,4'-Butylidene-bis(3-methyl-6-t-butyl-phenol) used in the present invention is known as a deterioration inhibitor for rubber, plastic, etc. It is also described in Japanese Patent Publication No. 51-43386 that it can be used in heat-sensitive recording materials to improve light resistance and the like. However, when this substance is used in combination with benzyl p-hydroxybenzoate, although it is slightly effective in light resistance and prevention of whitening, it has no effect on fingerprint fading or fading under high temperature and high humidity. Furthermore, the phenol derivatives represented by the general formula () used in the present invention are also known as anti-aging agents for rubber, plastics, etc., and some compounds are described in the above-mentioned Japanese Patent Publication No. 51-43386. It is stated that the shelf life and storage stability are improved. However, simply using this compound in combination with benzyl p-hydroxybenzoate does not prevent whitening, and the light resistance is extremely poor. Therefore, when benzyl p-hydroxybenzoate is used as a phenolic substance, 4,4'-butylidene-bis(3-methyl-6-t-butyl-phenol) and a phenol derivative represented by the general formula () are combined. It was unexpected that when used in combination, both color development and storage stability were significantly improved. 4,4'-Butylidene-bis(3-methyl-6-
t-butylphenol) and the phenol derivative represented by the general formula () are added in an amount of 0.1 to 5 parts by weight, preferably 0.5 to 7 parts by weight, per 1 part by weight of the color-forming substance. If the amount is less than 0.1 part by weight, the effect of improving storage stability will not be sufficient, and 5
If the weight exceeds the weight, states king is likely to occur. Also, 4,4'-butylidene-bis(3-
The addition ratio of methyl-6-t-butyl-phenol) and the phenol derivative represented by the general formula () is 4,4'-butylidene-bis(3-methyl-6-
The amount of the phenol derivative of the general formula () is 0.3 to 3 parts by weight per 1 part by weight of t-butylphenol. In the case of ratios other than these, whitening, discoloration, etc. cannot be prevented even if either is too large or too small, and the effect of improving storage stability is not achieved. A typical example of the phenol derivative of the general formula () used in the present invention is 2,2'-dihydroxy-3,3'-di(α-methyl-cyclohexyl)-5,5'-dimethyl-diphenylmethane. ,1,
1'-bis(2'-hydroxy-3',5'-dimethylphenyl)butane, 2,2,4-trimethyl-6,
6-bis(2'-hydroxy-3',5'-dimethylphenyl)hexane, 2,2'-methylene-bis(4
-methyl-6-cyclohexyl-phenol),
2,2'-methylene-bis(4-methyl-6-t-
butyl-phenol), 2,2'-methylene-bis(4-ethyl-6-t-butyl-phenol), etc., but these representative examples are not intended to limit the present invention. The color-forming substance, which is normally colorless or light-colored, used in the present invention is a substance that develops color by reacting with a phenolic substance under heat, such as triphenylmethane,
triphenylmethane phthalide, fluoran,
There are various leuco compounds such as leuco auramine type and spiropyran type, but among them, color-forming,
From the viewpoint of storage stability, fluoran-based ones are preferred. For example, for black, 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, etc. can be mentioned. When manufacturing a heat-sensitive coating liquid, an adhesive is added to each of a color-forming substance and a phenolic substance, and the two are mixed and dispersed in a form that separates them from each other to form a heat-sensitive coating liquid, which is then applied onto a support such as paper. stick. Examples of adhesives used in the heat-sensitive recording material of the present invention include casein, gelatin, modified starch,
Examples include carboxymethylcellulose, hydroxyethylcellulose, polyvinyl alcohol, polyvinylpyrrolidone, styrene-maleic anhydride copolymer and its alkaline solution, polyacrylamide, styrene-butadiene copolymer, polyvinyl acetate, polyacrylic acid ester latexes, etc. . The heat-sensitive recording material of the present invention may contain other additives in the recording layer as necessary, such as various fatty acid metal salts to prevent staining, day-color pigments to improve surface whiteness, naturalness, and writability. Fillers, water resistance agents and other phenolic substances are added to improve water resistance. As the support used in the thermal recording medium of the present invention, papers such as wood-free paper, medium-quality paper, and coated paper are generally used, but other materials such as glass fiber sheets, plastic sheets, film laminated paper, and nonwoven fabrics are also used. etc. can also be used. The heat-sensitive recording material of the present invention obtained in this way has significantly improved color development compared to the case where bisphenol A is used as the conventional phenolic substance, and
The storage stability of colored images is also very good. The present invention will be explained in more detail with reference to Examples. Example 1 (a) Production of heat-sensitive recording composition Liquids A and B having the following compositions were separately dispersed in a paint shaker (manufactured by Toyo Seiki Co., Ltd.) for 10 hours.

[Table] Next, 140 parts by weight of liquid A, 140 parts by weight of liquid B, and 80 parts by weight of a 12% polyvinyl alcohol aqueous solution were mixed to obtain a coating liquid. (b) Apply this coating liquid to the surface of high-quality paper with a basis weight of 50 g/m ² using a Mayer bar so that the coating amount after drying is 7 g/m ²
The mixture was coated and dried to obtain a heat-sensitive recording material.
The resulting heat-sensitive recording material has a recording surface with Becque smoothness.
The surface was treated with a test super calender so that the time was 400 seconds. (c) Solid recording was performed on the heat-sensitive recording material thus obtained using a Japanese National Railways Fax manufactured by Matsushita Electric Transmission Equipment Co., Ltd. at an applied voltage of 12 V and a pulse width of 6.5 ms, and the quality evaluation tests shown in the table were performed. The results are shown in the table. Examples 2 to 4 Among the B liquid formulations of Example 1, 4,4'-butylidene-bis(3-methyl-6-t-butyl-phenol) and 2,2'-dihydroxy-3,3'-di( α−
Methyl-cyclohexyl)-5,5'-dimethyl-
A thermosensitive recording material was obtained in the same manner as in Example 1 except that the number of parts of diphenylmethane was changed as shown in the table, and tested to give Examples 2 to 4. The results are shown in the table. Example 5 2,2'-dihydroxy-3,3'-di(α-methyl-cyclohexyl) in the B liquid formulation of Example 1
-5,5'-dimethyl-diphenylmethane 2,
A heat-sensitive recording material was obtained and tested in the same manner as in Example 1 except that 2'-methylene-bis(4-ethyl-6-t-butyl-phenol) was used instead. The results are shown in the table. Comparative Example 1 Of the B liquid formulation of Example 1, 6 parts by weight of 4,4'-butylidene-bis(3-methyl-6-t-butyl-phenol), 2,2'-dihydroxy-3,
3'-di(α-methyl-cyclohexyl)-5,
A heat-sensitive recording material was obtained and tested in the same manner as in Example 1 except that 5'-dimethyl-diphenylmethane was reduced to zero. The results are shown in the table. Comparative Example 2 In the B liquid formulation of Example 1, 4,4'-butylidene-bis(3-methyl-6-t-butyl-phenol) was zero, 2,2'-dihydroxy-3,3'-
A thermosensitive recording material was obtained and tested in the same manner as in Example 1, except that 6 parts by weight of di(α-methyl-cyclohexyl)-5,5'-dimethyl-diphenylmethane was used. The results are shown in the table. Comparative Example 3 Of the B liquid formulation of Example 1, 2,2'-dihydroxy-3,3'-di(α-methyl-cyclohexyl)-5,5'-dimethyl-diphenylmethane was added to 4,
4'-thio-bis(3-methyl-6-t-butyl-
A heat-sensitive recording material was obtained and tested in the same manner as in Example 1 except that phenol was used. The results are shown in the table. Comparative Example 4 Among the B liquid formulations of Example 1, 4,4'-butylidene-bis(3-methyl-6-t-butyl-phenol) and 2,2'-dihydroxy-3,3'-di(α
-Methyl-cyclohexyl)-5,5'-dimethyl-diphenylmethane was reduced to zero Example 1
A thermosensitive recording medium was obtained and tested in the same manner. The results are shown in the table. Comparative Example 5 In the B liquid formulation of Example 1, benzyl p-hydroxybenzoate was replaced with bisphenol A, and 4,
4'-butylidene-bis(3-methyl-6-t-butyl-phenol) and 2,2'-dihydroxy-
3,3'-di(α-methyl-cyclohexyl)-5,
A heat-sensitive recording material was obtained and tested in the same manner as in Example 1 except that 5'-dimethyl-diphenylmethane was reduced to zero. The results are shown in the table.

【table】

[Table] As is clear from the table, the heat-sensitive recording material according to the present invention has good color development and storage stability, but even when benzyl p-hydroxybenzoate is used as the phenolic substance, 4,4'-butylidene - screw (3
- Methyl-6-t-butylphenol) or the phenolic derivative of the general formula (), a thermosensitive recording material with good storage stability cannot be obtained. When conventional bisphenol A is used as the substance, a heat-sensitive recording material with good color development cannot be obtained.

Claims (1)

[Scope of Claims] 1. In a thermosensitive recording material having a thermosensitive coloring layer containing as a coloring component, a normally colorless or light-colored coloring substance and a phenolic substance that causes the coloring substance to develop color when heated, the phenolic substance as p-
Benzyl hydroxybenzoate is used, and 4,4'-butylidene-bis(3-
1. A heat-sensitive recording material containing methyl-6-t-butyl-phenol) and a phenol derivative represented by the following general formula (). (In the formula, R ₁ and R ₄ represent a methyl group, t-butyl group, cyclohexyl group, or α-methylcyclohexyl group, R ₂ and R ₃ represent a methyl group or an ethyl group, and R ₅ and R ₆ are hydrogen or represents an alkyl group having 1 to 8 carbon atoms.)