JPS60178086A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material with a high sensitivity excellent in the thermal response by arranging a specified 1,4-dihydroxynaphthalene derivative to be contained as an intensifier into thermal recording material containing a dye precursor and the intensifier. CONSTITUTION:1,4-Dihydroxynaphthalene derivative of the formula (wherein R represents methyl group or ethyl group) is added to a composition for a thermal recording material mainly composed of a colorless or light dye precursor such as triphenylmethane based, fluorane based and diphenylmethane based ones and a developer as acid substance such as phenol at the rate of 5wt% or more, preferably 10-400wt% with respect to the developer. Furthermore, a widely-accepted binder, pigment and other assistants are added to the composition properly and it is provided in a layer on a support of paper, a resin film or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-sensitive recording material, and particularly to a heat-sensitive recording material with improved color development.

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 developer. By heating with a laser source or the like, a dye precursor and a color developer react instantaneously to obtain a recorded image, and are disclosed in Japanese Patent Publication No. 43-4160, Japanese Patent Publication No. 45-14039, etc. Such 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 countries, the demand for heat-sensitive methods is increasing rapidly, and speeds are being increased to reduce transmission costs. In response to the increase in speed of facsimile, there has been a demand for higher sensitivity of heat-sensitive recording materials.

Since high-speed facsimile machines receive and send standard A4 documents in 10 to 20 seconds, the current flowing through the facsimile's thermal head is repeated over a very short period of time (less than a few milliseconds). The generated thermal energy is transmitted to the thermosensitive 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-5
No. 0-149353, JP-A-52-106746, JP-A-53-5636, etc. describe nitrogen-containing compounds, carboxylic acid esters, etc. No. 191089, JP-A-58-1102
No. 89 discloses adding a naphthoic acid derivative.

It is something.

The present inventors investigated various sensitizers in order to obtain a heat-sensitive recording material with even higher sensitivity. As a result, the present inventors developed a color developer that reacts with normally colorless or light-colored dye precursors when heated to develop color from the dye precursors. In the heat-sensitive recording material containing 1,4-dihydroxynaphthalene derivative nη R (wherein R represents a methyl group or an ethyl group) as a sensitizer, the thermal responsiveness can be improved. An excellent, highly sensitive heat-sensitive recording material could be obtained.

It was found that the 1,4-dihydroxynaphthalene derivative according to the present invention has superior thermal responsiveness compared to naphthol derivatives and hydroxynaphthoic acid derivatives, and it was possible to obtain a highly sensitive heat-sensitive recording material that can produce colored images even at low energy.

The sensitizer according to the present invention is usually added in an amount of 5% by weight or more based on the color developer. The preferred amount is 10-400% by weight;
Particularly preferred is 20 to 300% by weight. Addition amount is 5% by weight
If it is less than 400% by weight, the sensitivity improvement effect will not be sufficient, and if it is added 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 it goes without saying that components other than those described below may also be used in the present invention.

Examples of the dye precursor include triphenylmethane-based, fluoran-based, diphenylmethane-based, thiacin-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, 31'ethylamino-7-(210 roanilino)fluorane, 3-dibutylamino-7-(2-chloroanilino)fluoran, 3-diethylamino-7-(
3-chloroanilino)fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluorane, 3-(N-methylcyclo toΦcylamino)−
Examples include 3-methyl-7-anilinofluorane and 3-piperidino-6-methyl-7-anilinofluorane.

As the color developer, acidic substances generally used in thermal paper can be used, such as phenol, p-'Il+-fuyy
-ruphenol, p-phenylphenol, naphthol, p-hydroxyacetophenone, 2,2'-dihydroxydiphenol, 4.4'-1nopropylidene (2-
1-butylphenol), 4,4'-inzolobylidene diphenol, 4,4'-cyclohexylidene diphenol, novolac type phenol resin, benzoic acid, 1)
-1-ditylbenzoic acid, p-hydroxybenzoic acid, p-
Examples include benzyl hydroxybenzoate and methyl p-hydroxybenzoate.

Examples of binders include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, water-soluble binders such as styrene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer, and styrene. -zotazoene copolymer, acrylonitrile-butadiene copolymer, methyl acrylate-
Examples include latex-based water-insoluble binders such as butadiene copolymers.

Examples of the pigment include cinnabar 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, waxes such as paraffin, oxidized paraffin, polyethylene, oxidized polyethylene, stearic acid amide, and castor wax are used to prevent head wear and stickiness. Examples include dispersants such as sodium dioctyl sulfosuccinate, ultraviolet absorbers such as benzophenone and benzotriazole, surfactants, and fluorescent dyes.

Paper is mainly used as the support for the heat-sensitive recording material according to the present invention, but various nonwoven fabrics, plastic films, synthetic papers, metal foils, etc., or composite sheets made of combinations of these can also be used as desired.

Hereinafter, the present invention will be explained in more detail by showing synthesis examples and examples, but the present invention is not limited only to these synthesis examples and examples.

Synthesis Example 1 (Synthesis of 1,4-dimethoxynaphthalene) 425 g of naphthohydroquinone, 1,000 g of dimethyl sulfate
o g into a separable flask, and while stirring while passing nitrogen gas, 2,000 g of a 48.3% by weight aqueous sodium hydroxide solution was added over 2 hours while cooling from the outside so that the internal liquid temperature did not exceed 45°C. dripped. Then take 7 drops of internal fluid.
The temperature was raised to 9-81°C and the reaction was completed for 1 hour.

After cooling, the precipitated crystals were filtered, washed twice with warm water 11 at 60°C, and dried under reduced pressure to obtain 486 g of light brown crystals. Furthermore, it was recrystallized with methanol and a small amount of activated carbon, resulting in white crystals with a melting point of 87.6°C. ! I got 9.

Synthesis Example 2 (Synthesis of 1,4-jethoxynaphthalene) Naphthohydroquinone 84. Charge 330 g of El and diethyl sulfate into a separable flask, and add 488 g of a 48.3% by weight aqueous sodium hydroxide solution while stirring while passing nitrogen gas.
was added dropwise over 20 minutes while cooling from the outside so that the internal liquid temperature did not exceed 45°C. Then, the temperature of the internal solution was raised to 76 to 78°C, and the reaction was completed for 1 hour.

After cooling, the precipitated crystals were filtered and washed with 700 Wt of 60°C warm water.
I! The crystals were washed 3 times with
0 g of pale brown crystals were obtained. Furthermore, it was recrystallized with ethanol and a small amount of activated carbon, and a single point of white crystals with a temperature of 87.8℃ was 68.2℃.
I got g.

Example 1 10 g of 3-diethylamino-6-methy,11/-7-anilite fluorane was dispersed in a ball mill for 24 hours with a 2% polyvinyl alcohol aqueous solution 3 (L9).
, 2-bis(4-hydroxyphenyl)propane 2F
1 of 1,4-dimethoxynaphthalene was dispersed in a ball mill for 24 hours with 75 Il of a 2% polyvinyl alcohol aqueous solution, and then 10.1 l of 1,4-dimethoxynaphthalene was dispersed for 24 hours. F was dispersed with 30 g of an aqueous solution of polyvinyl alcohol for 24 hours using a trap ball mill. These 6
After mixing the seed dispersion, 80y of a 50% dispersion of calcium carbonate was added, followed by 25.9y of a 20y dispersion of zinc stearate, and 180y of a 10% polyvinyl alcohol aqueous solution.
g and 75 g of water were added and thoroughly stirred to prepare a coating liquid.

The basis weight of the coating liquid is 551! The mixture was coated on a base paper of 6 g/77 L2/m2 at a solid coating weight of 6 g/77 L2, dried, and treated with a supercalender to obtain a heat-sensitive recording material.

Example 2 1 in place of 1,4-dimethoxynaphthalene in Example 1
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that , 4-jetoxynaphthalene was used.

Comparative Examples 1 to 5 In place of 1,4-dimethoxynaphthalene in Example 1, 2-benzyloxynaphthalene, 2-benzoyloxynaphthalene, 2-hydroxy-3-naphthoic acid phenyl ester, and 2-hydroxy-6-naphthoic acid were used, respectively. Heat-sensitive recording materials of Comparative Examples 1 to 5 were obtained in the same manner as in Example 1 except that acid anilide and stearamide were used.

Comparative Example 6 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 1,4-jethoxynaphthalene in Example 1 was omitted.

Examples 1 and 2. The heat-sensitive recording materials obtained in Comparative Examples 1 to 6 were evaluated by conducting the following tests.

The results are shown in Table 1.

Test 1 Using a heat-sensitive facsimile tester (manufactured by Matsushita Electronic Components), the applied pulse width was 1.0. Printing was carried out under the conditions of 1.5 and 2.0 milliseconds and an applied voltage of 16.00 volts, respectively, and the color density of the obtained colored images was measured using a Macbeth densitometer RD5i4.

Test 2 The fog density was measured in the same manner as Test 1 after being stored for 24 hours in an environment of 40° C. and 90% relative humidity.

Table 1 From Table 1, it can be seen that the heat-sensitive recording material according to the present invention does not cause background capri during storage and can obtain sufficient color density even with low energy.

Agent Asamura Hajime

Claims (1)

[Scope of Claims] A heat-sensitive recording material containing a normally colorless or light-colored dye precursor and a color developer that reacts with the dye precursor when heated to develop a color, which contains a compound represented by the following general formula. A heat-sensitive recording material characterized by: R (However, R represents a methyl group or an ethyl group.'