JPH0528186B2 - - Google Patents

Description

[Detailed description of the invention]

(A) Industrial Application Field The present invention relates to a highly sensitive heat-sensitive recording material with excellent thermal responsiveness. (B) Prior Art A heat-sensitive recording material 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 color developer. By heating with a thermal head, thermal pen, laser 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 materials have the advantages of being able to record with relatively simple equipment, being easy to maintain, and producing no noise. It is used in a wide range of fields, including automatic ticket vending machines, labels, and train tickets. Particularly in facsimile, the demand for heat-sensitive methods is increasing rapidly, and speeds are being increased to reduce transmission costs. In response to such increased speed of facsimile, there has been a demand for higher sensitivity of heat-sensitive recording materials. Since high-speed facsimile machines can receive and send standard A4 documents in a few seconds to 20 seconds, the current that flows through the facsimile's thermal head is repeated over a very short period of time, less than a few milliseconds, and the thermal energy generated by this is extremely short. is transmitted to a heat-sensitive recording sheet to cause an image-forming reaction. In order to carry out an image forming reaction using thermal energy transmitted in such a short time, it is necessary to use a heat-sensitive recording material with excellent thermal responsiveness. In order to improve thermal responsiveness, it is necessary to improve the compatibility between the color developer and the dye precursor. A sensitizer is used for this purpose if necessary. When the sensitizer itself melts due to the transferred thermal energy, it dissolves or encapsulates nearby dye precursors and color developers to promote the color reaction, so the thermal responsiveness of the sensitizer increases. Improving the compatibility with dye precursors and color developers is also one method for increasing the sensitivity of heat-sensitive recording materials. As such a method, waxes are used in JP-A-48-19231, JP-A-49-34842 and JP-A-Sho.
No. 50-149353, JP-A-52-106746, JP-A-53-
5636, etc., nitrogen-containing compounds, carboxylic acid esters, etc. are described in JP-A-57-64593, JP-A-58-
No. 87094 discloses naphthol derivatives,
-64592, JP-A-57-185187, JP-A-57-
191089 and JP-A-58-110289 disclose naphthoic acid derivatives, JP-A-57-148688 and JP-A-57-
No. 182483, JP-A No. 112788, JP-A-58-
Publication No. 162379 discloses the addition of a benzoic acid ester derivative. However, the heat-sensitive recording materials produced using these methods are still unsatisfactory in terms of color density and color sensitivity. (C) Purpose of the Invention The present inventors investigated various sensitizers with the aim of obtaining a highly sensitive heat-sensitive recording material with further excellent thermal responsiveness. (D) Structure of the Invention In a heat-sensitive recording material containing a color developer that reacts with a normally colorless or light-colored dye precursor upon heating to cause the dye precursor to develop color, a compound represented by the following general formula is used as a sensitizer. By containing this, a highly sensitive heat-sensitive recording material with excellent thermal responsiveness could be obtained. general formula (However, R represents an alkyl group, halogen, alkoxy group, acyloxy group, or acyl group. n represents an integer of 0, 1, or 2.) Specific examples of the compound represented by the above general formula include: Examples include those shown below. The compound of the above general formula can be easily obtained by a known method. The sensitizer according to the present invention is usually added in an amount of 5% by weight or more based on the color developer. Preferred amounts are 10-400% by weight, particularly 20-300% by weight. If the amount added is less than 5% by weight, the effect of improving sensitivity will not be sufficient, and if the amount added is more than 400% by weight, it may be economically disadvantageous. The main components used in the heat-sensitive recording material of the present invention will be specifically explained below, but are not limited thereto. As a dye precursor, triphenylmethane type,
Examples include fluoran-based, diphenylmethane-based, thiazine-based, and spiropyran-based compounds. For example, 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1
-ethyl-2-methylindol-3-yl)-
4-Azaphthalide, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-chlorofluorane, 3-(N-cyclohexylamino)-7-methylfluorane, 3-diethylamino-7-methyl Fluoran, 3-diethylamino-6-chloro-7-methylfluorane, 3-diethylamino-7-anilinofluorane, 3-diethylamino-6-methyl-7-dibenzylaminofluorane, 3-(N-ethyl -N
-p-toluidino)-7-anilinofluorane,
3-diethylamino-7-(o-chloroanilino)
Fluoran, 3-dibutylamino-7-(o-chloroanilino)fluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-
(N-ethyl-N-p-toluidino)-6-methyl-7-anilinofluorane, 3-(N-methyl-
N-cyclohexylamino)-6-methyl-7-
Anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-pyrrolidino-
6-Methyl-7-anilinofluorane, 3-diethylamino-7-(m-trifluoromethylanilino)fluorane, 3-(N-ethyl-N-isopentylamino)-6-methyl-7-anilino Fluoran, 3-diethylamino-6-methyl-7
-(p-phenetidino)fluoran, 3-dibutylamino-7-(o-fluoroanilino)fluoran, and the like. As the color developer, acidic substances generally used in thermal paper, ie, electron-accepting compounds, are used, and in particular, phenol derivatives and aromatic carboxylic acid derivatives are used. Preferred compounds among the phenol derivatives are those having at least one phenolic hydroxyl group, and more preferably phenol derivatives in which both or one of the ortho positions of the phenolic hydroxyl group are unsubstituted. For example, phenol, p-t-butylphenol, p-phenylphenol, 1-naphthol, 2-naphthol, p-hydroxyacetophenone, 2,2'-dihydroxybiphenyl, 4,4'-isopropylidene di Phenol, 4,4'-isopropylidene diphenol, 4,4'-isopropylidene bis(2-
t-butylphenol), 4,4'-isopropylidene bis(2-chlorophenol), 4,4'-cyclohexylidene diphenol, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis (4-hydroxyphenyl)pentane, 2,2
-Bis(4-hydroxyphenyl)hexane, diphenol acetic acid methyl ester, bis(4-hydroxyphenyl)sulfone, bis(3-allyl-
4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 4-hydroxy-4'-isopropyloxydiphenyl sulfone, bis(4-hydroxyphenyl) sulfide, 4,4'-thiobis( 2-t-butyl-5-methyl)phenol, 1,7-bis(4-hydroxyphenylthio)-3,5-dioxyheptane,
There are novolac type phenolic resins, etc., and aromatic carboxylic acid derivatives include, for example, benzoic acid, p
-t-butylbenzoic acid, p-hydroxybenzoic acid, p-hydroxybenzoic acid methyl ester, p
-Hydroxybenzoic acid isopropyl ester, p
-Metal salts such as zinc of hydroxybenzoic acid benzyl ester, lauryl gallic acid ester, stearyl gallic acid ester, salicylanilide, 5-chlorosalicylanilide, 5-t-butylsalicylic acid, metal salts such as zinc of hydroxynaphthoic acid, etc. Can be mentioned. 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-based 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 dioctyl sulfosuccinate, ultraviolet absorbers such as benzophenone and benzotriazole, surfactants, and fluorescent Examples include dyes. Paper is mainly used as the support for the heat-sensitive recording material according to the present invention, but various non-woven fabrics,
Plastic film, synthetic paper, metal foil, etc., or a composite sheet made of a combination of these may be used as desired. (E) Synthesis Examples and Examples The present invention will be explained in more detail with reference to Synthesis Examples and Examples. However, the present invention is not limited to the following synthesis examples and examples. Synthesis Example 1 Synthesis of Compound (1) Dissolve 6.9g of para-cresol in 40ml of acetone,
To this was added 9.4 g of a 34% aqueous sodium hydroxide solution. A solution of 11.2 g of cinnamic acid chloride dissolved in 20 ml of acetone was added dropwise over 10 minutes with stirring, and after continued stirring for 7 minutes, benzene and water were added to separate the layers. The organic layer was washed with an aqueous sodium hydrogen carbonate solution, dried over anhydrous potassium carbonate, and the solvent was distilled off. Residue n-
Treatment with hexane gave crystals of the desired product. This was recrystallized from n-hexane to obtain 11.0 g of the desired product.
mp=98-99℃ Synthesis Example 2 Synthesis of Compound (2) 10.4 g of the target compound was prepared in the same manner as Synthesis Example 1 except that 7.6 g of parachlorophenol was used instead of 6.9 g of para-cresol used in Synthesis Example 1. Obtained. mp=103-104°C Example 1 20 g of 3-diethylamino-6-methyl-7-anilinofluorane was dispersed in a ball mill with 80 g of a 1% aqueous polyvinyl alcohol solution. on the other hand
4.4'-Isopropylidene diphenol 50g 1%
The mixture was dispersed in a ball mill with 200 g of a polyvinyl alcohol aqueous solution, and further, 50 g of compound (1) was similarly dispersed with 200 g of a 1% polyvinyl alcohol aqueous solution. After mixing these three types of dispersions, 250 g of a 40% dispersion of calcium carbonate was added, followed by 40 g of a 25% dispersion of zinc stearate and 490 g of a 9.4% aqueous polyvinyl alcohol solution, and the mixture was sufficiently stirred to form a coating solution. . The coating liquid was applied to a base paper having a basis weight of 55 g/m ² so that the solid content coating amount was 7 g/m ² , dried, and treated with a supercalender to obtain a heat-sensitive recording material. Example 2 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that compound (2) was used instead of compound (1) in Example 1. Comparative Example 1 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the dispersion of compound (1) in Example 1 was omitted. Comparative Example 2 A heat-sensitive recording material was obtained in the same manner as in Example 1, except that N-(hydroxymethyl)stearamide was used instead of compound (1) in Example 1. Example 3 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that benzyl parahydroxybenzoate was used in place of 4,4'-isopropylidene diphenol. Example 4 A heat-sensitive recording material was obtained in the same manner as in Example 3 except that compound (2) was used instead of compound (1) in Example 3. Comparative Example 3 A heat-sensitive recording material was obtained in the same manner as in Example 3 except that the dispersion of compound (1) in Example 3 was omitted. Evaluation The thermal recording materials obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were printed under the conditions of 16.00 volts, 1.5 milliseconds, 2.0 milliseconds, and 2.5 milliseconds, and the optical densities of the colored images obtained were measured using Macbeth. Measured using RD918. The results are shown in the table.

[Table] (F) Effect of the invention As shown in the table, the heat-sensitive recording material using the sensitizer according to the present invention has excellent thermal responsiveness and high sensitivity.

Claims (1)

[Scope of Claims] 1. A heat-sensitive recording material containing a color developer that reacts with a normally colorless or light-colored dye precursor upon heating to cause the dye precursor to develop color, containing a compound represented by the following general formula: A heat-sensitive recording material characterized by: general formula (However, R represents an alkyl group, halogen, alkoxy group, acyloxy group, or acyl group. n represents an integer of 0, 1, or 2.)