JPH0259785B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a heat-sensitive recording sheet with excellent thermal responsiveness and image storage stability. A heat-sensitive recording sheet generally has a heat-sensitive recording layer on a support, the main components of which are an electron-donating, usually colorless or light-colored dye precursor and an electron-accepting developer. By heating with light etc., the dye precursor and developer react instantly,
This allows recorded images to be obtained, and is designated as Special Publication No. 43-4160.
It is disclosed in Japanese Patent Publication No. 14039/1983. These heat-sensitive recording sheets have the advantages of being able to record with a relatively simple device, being easy to maintain, and producing no noise. It is used in a wide range of fields such as , labels, ticket vending machines, etc. The basic properties required of a thermosensitive recording sheet include sufficient color image density and sensitivity, and no deterioration of the color image over time.
In addition, in recent years, the speed of printing and recording has been increasing, and as the speed of recording devices themselves has increased, we have also developed recording sheets that can cope with this, that is, thermal recording sheets with excellent thermal responsiveness that can produce high-density colored images with low thermal energy. is desired. In order to improve the thermal responsiveness of a thermosensitive recording sheet, it is necessary to lower the melting point of the color developer and improve its compatibility with the dye precursor. A sensitizer may also be used if necessary. When the sensitizer melts due to the transferred thermal energy, it dissolves or encapsulates nearby dye precursors and color developers to promote the color reaction. Improving thermal responsiveness is also one way to make a heat-sensitive recording sheet highly sensitive. Conventionally, methods have been known in which various sensitizers are incorporated into the recording layer in order to obtain colored images with high density. For example, urea, phthalic anhydride, acetalinide, etc. were listed in Japanese Patent Publication No. 43-4160;
The issue includes natural and synthetic waxes such as beeswax, carnauba wax, and paraffin wax.
No. 17748 discloses a method of adding salicylic acid, phthalic acid motobenzyl ester, etc. However, they have poor thermal responsiveness and cannot provide sufficient density, and even if high-density images are obtained, they have disadvantages such as poor storage stability and deterioration over time, so that no satisfactory product has been obtained. As a result of various studies on sensitizers for obtaining heat-sensitive recording sheets with excellent heat responsiveness and image storage stability, the present inventor discovered that the sensitizers react with normally colorless or light-colored dye precursors when heated, and the dye precursors react with the dye precursors. To obtain a heat-sensitive recording sheet excellent in various properties by containing a compound represented by the following general formula [] in the recording layer of the heat-sensitive recording sheet containing a color developer that develops color. was completed. (However, R represents an aralkyl group.) The compounds represented by the above general formula [] used in the present invention include 2,2-bis(4-benzyloxyphenyl)propane, 2,2-bis(4-benzyloxyphenyl)propane, and 2,2-bis(4-benzyloxyphenyl)propane. −
Examples include phenethyloxythiphenyl) propane. The main components used in the heat-sensitive recording sheet of the present invention will be specifically explained, but the present invention is not limited thereto unless it exceeds the gist of the present invention. As a dye precursor, triphenylmethane type,
Examples include fluoran-based, diphenylmethane-based, thiazine-based, and spiropyran-based compounds. For example, crystal violet lactone, 3-diethylamino-7-methylfluorane, 3-diethylamino-6-chloro-7-methylfluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7 -anilinofluorane, 3-diethylamino-7-(2-
chloroanilino)fluoran, 3-dibutylamino-7-(2-chloroanilino)fluoran, 3
-diethylamino-7-(3-chloroanilino)
Fluoran, 3-diethylamino-6-methyl-
7-anilinofluorane, 3-(N-ethyl-P
-toluidino)-6-methyl-7-anilinofluorane, 3-(N-methylcitalohexylamino)
-3-methyl-7-anilinofluorane, 3-piperidino-3-methyl-7-anilinofluorane, and the like. As the color developer, acidic substances generally used for thermal paper can be used, such as phenol, p-t
-butylphenol, p-phenylphenol,
naphthol, p-hydroxyacetophenone,
2,2'-dihydroxydiphenol, 4,4'-isopropylidene (2-t-butylphenol),
4,4'-isopropylidenediphenol, 4,
Examples include 4'-cyclohexylidene diphenol, novolak type phenolic resin, benzoic acid, pt-butylbenzoic acid, p-hydroxybenzoic acid, p-hydroxybenzoic acid benzyl ester, p-hydroxybenzoic acid methyl ester, and the like. As binders, starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol,
Styrene-maleic anhydride copolymer, ethylene/
Examples include water-soluble binders such as maleic anhydride copolymers, latex-type water-soluble binders such as styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, and methyl acrylate-butadiene copolymers. Examples of pigments include diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, urea-formalin resin, and the like. In addition, higher fatty acid metal salts such as zinc stearate and calcium stearate, paraffin,
Waxes such as paraffin oxide, polyethylene, polyethylene oxide, stearamide, castor wax, dispersants such as sodium dioclesulfosuccinate, ultraviolet absorbers such as benzophenone and benzotriazole, and surfactants, Examples include fluorescent dyes. Although paper is mainly used as the support for the heat-sensitive recording sheet of the present invention, various nonwoven fabrics, plastic films, synthetic papers, metal foils, etc., or composite sheets made of a combination of these can also be used as desired. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples. Example 1 3-(N-methyl-N-cyclohexylamino)
-20g of -6-methyl-7-anilinofluorane
% polyvinyl alcohol aqueous solution for 24 hours in a ball mill. On the other hand, 2,2-bis(4-
Hydroxyphenyl) propane (50 g) was mixed with 75 g of 2% polyvinyl alcohol aqueous solution in a ball mill for 24 hours.
Spread out time. Further, 20 g of 2,2-bis(4-benzyloxyphenyl)propane was dispersed with 40 g of a 2% polyvinyl alcohol aqueous solution in a ball mill for 24 hours. These dispersions were mixed, 100 g of a 50% dispersion of calcium carbonate was added, 50 g of a 20% dispersion of zinc stearate, 250 g of a 12% aqueous polyvinyl alcohol solution, and 200 g of water were mixed and stirred to obtain a coating liquid. . Next, this coating liquid was applied to a base paper having a basis weight of 50 g/m ² so that the amount of the dye precursor was 0.5 g/m ² and dried, and then treated with a supercalender to obtain a heat-sensitive recording sheet. Comparative Example 1 A thermosensitive recording sheet was obtained in the same manner as in Example 1 except that 2,2-bis(4-benzyloxyphenyl)propane in Example 1 was removed. Comparative Example 2 A thermosensitive recording sheet was obtained in the same manner as in Example 1 except that stearamide was used in place of 2,2-bis(4-benzyloxyphenyl)propane. Test Printed using Fujitsu's Huacom Fax 621C.
After obtaining a colored image, the following storage test was conducted.
The results are shown in Table 1. The density of the colored image was measured using a Macbeth densitometer RD514. (a) Color image density was measured. (b) Heat resistance test: After storing for 24 hours in an environment of 60°C, the image density was measured and the image preservation rate was determined. Image survival rate (%) = Image density after test / Image density before test x 100 (c) Humid heat resistance test: After storing for 24 hours in an environment of 40℃ and 90% relative humidity, the image density was measured, and the image density was measured. The survival rate was determined.

[Table] As is clear from Table 1, by using the compound according to the present invention, a heat-sensitive recording sheet with excellent heat responsiveness and image storage stability was obtained.

Claims (1)

[Claims] 1. A compound represented by the following general formula is used in a heat-sensitive recording sheet containing a normally colorless or light-colored dye precursor and a color developer that reacts with the dye precursor when heated to develop color. A heat-sensitive recording sheet that is characterized by: general formula (However, R represents an aralkyl group)