JPH0336036B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a heat-sensitive recording medium, and more particularly to a heat-sensitive recording medium that has excellent suitability for high-speed recording and improved storage stability. [Prior Art] A thermosensitive recording paper containing a normally colorless or light-colored color-forming substance (hereinafter referred to as a leuco compound) and a color developer 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 The recording properties of the recording paper differ depending on the application, but in order to increase the recording speed, for example, it is necessary to improve the recording device and promote the color development of the recording paper itself, and in recent years, thermal paper has been developed in this direction. It has been demanded. Conventionally, bisphenol A has been commonly used as a color developer, but bisphenol A has a high melting point of 157°C and is not suitable for high-speed recording, so it is necessary to add various sensitizers to improve its suitability for high-speed recording. Although several methods have been proposed, there are still none that are sufficiently effective. In addition, many proposals have been made for color developers with lower melting points to improve suitability for high-speed recording, and practical ones include P-hydroxybenzoic acid ester (Japanese Patent Application Laid-open No. 144193/1983) and 4-hydroxyphthalic acid diester. (Unexamined Japanese Patent Publication No. 58-153692), etc. can be considered. However, all of these materials have the disadvantage that the resulting images have significantly poor fading resistance. Therefore, the addition of various chemicals such as antioxidants has been proposed in order to improve the fading property, but nothing satisfactory has been obtained. [Problems to be Solved by the Invention] Therefore, the present inventor has conducted intensive research with the aim of obtaining a heat-sensitive recording medium that has excellent high-speed recording performance and excellent storage stability, and has accomplished the present invention. It came to this. [Means for Solving the Problems] That is, the present invention provides a heat-sensitive recording material having a heat-sensitive recording layer containing a leuco compound and a color developer that causes the leuco compound to develop color when heated. 2-(4-hydroxyphenyl)
-2-(2'-hydroxyphenyl)propane The present invention relates to a heat-sensitive recording material characterized by containing the following. 2-(4-hydroxyphenyl)-2- of the present invention
(2′-Hydroxyphenyl)propane has a melting point of 111
℃, and thermal paper using this color developer has the following characteristics. (1) Excellent high-speed recording performance. (2) The sharpness of the obtained image is extremely high. (3) A thermosensitive recording medium with high whiteness can be obtained. (4) There is little debris adhesion to the head, and there are no problems with states king or piling. In general, monophenolic color developers can provide thermosensitive recording materials with high whiteness, but they have strong thermochromic properties and have difficulty in fading. On the other hand, bis- or triphenol-based color developers have extremely weak thermochromism and are satisfactory in terms of fading resistance, but have the disadvantage that the whiteness of the resulting heat-sensitive recording material is reduced. It is still not clear why the heat-sensitive recording material using the color developer of the present invention has the above characteristics. In the present invention, the object can be achieved by containing the color developer of the present invention in an amount of 1 to 40% by weight in the total solid content of the heat-sensitive recording layer. It is also possible to use the color developer of the present invention in combination with other known color developers. Next, the substances used in the present invention will be described. (1) Leuco compounds Colorless or light-colored substances that develop color by reacting with color developers, including triphenylmethane, triphenylmethanephthalide, fluoran, leucoolamine, diphenylmethane, phenothiazine, and phenoxazine. , spiropyran derivatives, indoline derivatives, indigo derivatives, and the like. Examples include, but are not limited to, the following. Crystal violet lactone (blue),
3-diethylamino-6-methyl-7-anilinofluorane (black), 3-(N-ethyl-P-
triidino)-6-methyl-7-anilinofluorane (black), 3-diethylamino-6-
Methyl-7-(ortho, p-dimethylanilino)fluoran (black), 3-pyrrolidino-
6-methyl-7-anilinofluorane (black),
3-piperidino-6-methyl-7-anilinofluorane (black), 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-anilinofluorane (black), 3-diethylamino-7 -(ortho-chloroanilino)fluoran (black), 3-diethylamino-7-(meta-trifluoromethylanilino)fluoran (black), 3-diethylamino-6-methyl-chlorofluoran (red), 3-diethylamino-
6-Methyl-fluorane (red), 3-cyclohexylamino-6-chlorofluorane (orange), 3-(N-isoamyl-N-ethylamino)-6-methyl-7-anilinofluorane (black). (2) Color development accelerator In order to improve the recording characteristics of the heat-sensitive recording medium of the present invention, conventionally known color development accelerators such as fatty acid amide such as stearamide, terephthalic acid ester, terephenyl, tribenzylamine, and benzyl maldene can be used. Acid, parabenzyl biphenyl, etc. are used. (3) Binders Examples of the binders used in the present invention include polyvinyl alcohol, casein, starch and modified starch, carboxymethyl cellulose, hydroxyethyl cellulose, polyvinylpyrrolidone, styrene-maleic anhydride copolymer and its alkaline solution, Polyacrylamide, styrene-butadiene copolymer, polyvinyl acetate,
Examples include, but are not limited to, latexes of polyacrylic esters, gelatin, and gelatin. (4) Storage stabilizer By adding a storage stabilizer to the recording medium of the present invention, it is possible to further improve storage stability. Storage stabilizers used in the present invention include 4,
4-Butylidene-bis(3-methyl-6-t-
butylphenol) (melting point 208℃, same below),
2,2'-methylene-bis(4-methyl-6-t
-butylphenol) (120℃), 2,2'-methylene-bis(4-ethyl-6-t-butylphenol) (119℃), 2,5-di-t-butyl-hydroquino (202℃), 2, 5-di-t-amyl-hydroquinone (172°C), bis(3-methyl-4-
Hydroxy-5-tert-butyl-benzyl) sulfide (115°C), bis-[3,3'-bis-
(4'-hydroxy-3'-t-butylphenol)-butyric acid] glycol ester (165°C), 4,
4'-Methylene-bis(2,6-di-t-butylphenol (154℃), 2,6-bis(2'-hydroxy-3'-t-butyl-5-methylbenzyl)-4-methylphenol (171℃), 2,
2'-iso-butylidene-bis-(4,6-di-
methylphenol) (160℃), bis[2-(2-
Hydroxy-5-methyl-3-t-butyl-benzyl)-4-methyl-6-t-butyl-phenyl] terephthalate (240°C), 2-hydroxy-4-methoxy-4'-chlorobenzophenone (112 °C), 2-hydroxy-4-methoxy-
2'-carboxybenzophenone (166°C), tris(3,5-di-t-butyl-4-hydroxy-phenyl) isocyanate (221°C), tris[β-(3,5-di-t-butyl) -4-hydroxy-phenyl)propionyl-oxyethyl]
Isocyanate (126℃), 1,3,5-tri-
Methyl-2,4,6-tris(3,5-di-t)
-butyl-4-hydroxy-benzyl)benzene (244°C), N,N'-hexamethylene-bis(3,5-di-t-butyl-4-hydroxy-
hydrocinnamide) (156°C), 1,1,3-tris(2-methyl-4-hydroxy-5-t-
butylphenyl)butane (185°C), 2,2'-dihydroxy-3,3'-di(α-methyl-cyclohexyl)-5,5'-dimethyl-diphenylmethane (130°C), and various phenolic resins. (5) Other additives The heat-sensitive recording material of the present invention may contain other additives in the heat-sensitive layer as necessary, such as pigments such as clay, calcium carbonate, aluminum hydroxide, talc, titanium oxide, and zinc oxide, and waxes. It is also possible to add various fatty acid metal salts to prevent stickiness, water resistance agents, surfactants, etc. to improve water resistance. (6) Substrate The substrate used in the present invention is generally paper such as high-quality paper, medium-quality paper, or coated paper, but other materials such as glass fiber sheets, plastic sheets, film laminated paper, and nonwoven fabrics are also used. It can be used as a base. The heat-sensitive recording material of the present invention is produced as follows. A system containing a color-forming substance and a system containing a color developer of the present invention are separately pulverized in an aqueous medium containing a binder, and then mixed to obtain a heat-sensitive composition paint. The heat-sensitive recording material of the present invention is obtained by coating or impregnating a substrate with the paint thus prepared and drying it. [Effects of the Invention] The heat-sensitive recording material of the present invention thus obtained has many characteristics as described above, including high-speed recording performance and storage stability, and is extremely useful. [Example] Below, the effects of the present invention will be explained in more detail with reference to Examples. Example 1 (a) Production of heat-sensitive recording material Liquids A and B having the following compositions were separately dispersed in a paint shaker (manufactured by Toyo Seiki) for 10 hours. Solution A: 3-(N-cyclohexyl-N-methyl)amino-6-methyl-7-anilinofluorane 5g Aluminum hydroxide 28g Zinc stearate 5g Polyvinyl alcohol 12% solution 35g Water 52g Solution B: 2-(4 -Hydroxyphenyl)-2-(2'-hydroxyphenyl)propane 15g Kaolin 20g Zinc stearate 3g Polyvinyl alcohol 12% solution 35g Water 52g Next, 125g of Part A, 125g of Part B, 50g of 12% polyvinyl alcohol, and water. Add 40g and mix, stir and adjust to make a coating liquid. Next, apply this coating liquid to the surface of 50g/ ^m2 high-quality paper using a Maya bar so that the coating amount after drying is 8g/ ^m2 . A thermosensitive recording material was obtained. Example 2 Among the formulations of liquid A used in Example 1, 3-(N-
3-(N-methyl)amino-6-methyl-7-anilinofluorane instead of cyclohexyl-N-methyl)amino-6-methyl-7-anilinofluorane
isoamyl-N-ethyl)amino-6-methyl-
Example 1 except that 7-anilinofluorane was used.
A thermosensitive recording material was obtained in the same manner as in the above. Comparative Examples 1, 2 Among the formulations of liquid B used in Example 1, 2-(4-
A thermosensitive recording material was obtained in the same manner as in Example 1 except that P-hydroxybenzoic acid benzyl ester was used instead of 4-hydroxyphthalic acid (hydroxyphenyl)-2-(2'-hydroxyphenyl)propane. Example 1 except that dimethyl ester was used
Thermal recording bodies were obtained in the same manner as in Comparative Examples 1 and 2, respectively. Comparative Example 3 In the A liquid formulation used in Example 1, 5 g of aluminum hydroxide was replaced with stearamide, and B
2-(4-hydroxyphenyl)-2 in liquid formulation
A thermal recording material was obtained in the same manner as in Example 1 except that -(2'-hydroxyphenyl)propane was replaced with bisphenol A, and this was used as a thermal recording material of Comparative Example 3. The heat-sensitive recording bodies obtained in the above Examples and Comparative Examples were surface-treated with a test super calender so that the recording surface had a Bekk smoothness of 500 seconds. Next, regarding the heat-sensitive recording material obtained by surface treatment, the commercially available G facsimile machine FACOM FAX621C
(manufactured by Fujitsu Ltd.), recording power 0.85W/dot, power supply time
Printing was performed under conditions of 0.45 msec and a cycle of about 5 msec/, and the image density and background density at the time of printing were measured using Macbeth Densitometer RD-514. The storage stability is the concentration after storage for 48 hours in a constant temperature and humidity room maintained at 40°C and 90%. In addition, a facsimile machine (manufactured by Toshiba) was attached to the obtained heat-sensitive recording medium.
Copix-6500) was used to print at high speed to check for gas adhesion and states king phenomenon. Thermal head voltage is 12.6V. Table results were obtained for Examples and Comparative Examples.

[Table] ◎...Good, △...Slightly poor, ×...Poor The above demonstrates that the heat-sensitive recording material of the present invention has excellent characteristics.

Claims (1)

[Scope of Claims] 1. In a heat-sensitive recording material having a heat-sensitive recording layer containing a normally colorless or light-colored color-forming substance and a color developer that causes the color-forming substance to develop color when heated, the color developer is represented by the following formula. 2-(4-hydroxyphenyl)-2-(2'-hydroxyphenyl)propane A heat-sensitive recording material characterized by containing.