JPH04191085A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material of high quality reduced in thermal fog and improved in recording sensitivity and image preservability by adding bis(p-methylbenzyl)oxalate and 1,2-bix(3,4-dimethylphenyl)ethane to a thermal recording layer as a color forming accelerator. CONSTITUTION:A thermal recording material is formed by providing a thermal recording layer containing a colorless electron donating color forming dye precursor and an electron acceptive developing compound allowing said dye precursor to form a color through the contact reaction with the dye precursor under heating on a support and, as a color forming accelerator, bis(p- methybenzyl)oxalate and 1,2-bis(3,4-dimethylphenyl)ethane are added to the thermal recording layer. When bis(p-methylbenzyl)oxalate and 1,2-bis(3,4- dimethylphenyl)ethane are compounded within the range of 1:0.1-0.1:1, effect is confirmed and, especially, at the time of 1:1, effect becomes max. The proper compounding amount of two compounds in the thermal recording layer is 1-50% by wt. of the total solid from the aspect of the development of sensitizing effect but the pref. compounding amount is 20-35wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a heat-sensitive recording material that has excellent recording sensitivity and excellent storage stability.

[Prior art] Thermal recording method allows color images to be obtained simply by heating.
Furthermore, the advantages of this recording device, such as its ability to be made relatively simple and compact, have been highly evaluated, and it has been widely used as a variety of information recording methods.

Particularly in recent years, improvements have been made in facsimile printers that use such thermal recording methods, and high-speed recording, which was previously considered difficult, has become possible. As the speed of such devices increases, the heat-sensitive recording materials used therein are required to further improve the recording sensitivity, and many proposals have been made in this regard. Such a heat-sensitive recording material is one in which a heat-sensitive recording layer containing a binder and a thermochromic substance as the main components is formed as a single layer or in multiple layers on a support made of paper, plastic film, synthetic paper, etc. is commonly used.

In order to improve the recording sensitivity of heat-sensitive recording materials having such a structure, it has been proposed to add a low-melting thermofusible substance (sensitizer). For example, the addition of higher fatty acids or higher fatty acid esters (Japanese Patent Publication No. 49-17748), the addition of stearic acid amide or oleic acid amide (Japanese Patent Publication No. 54-139740), and the addition of phthalate esters (Japanese Patent Publication No. 1974-139740). Bo37-116690), pencil biphenyl (JP 60-82382), naphthol derivatives (JP 58-87094), and recently bis(P-methylbenzyl oxalate).
(Japanese Unexamined Patent Publication No. 2-25377) has been proposed.

[Problem to be solved by the invention] However, the effects of the low melting point thermofusible components that have been proposed in the past are not sufficient, and the addition of low melting point components tends to cause a decrease in the concentration of the colored part during storage. There was a problem.

Therefore, research into a low melting point component that improves sensitivity and does not cause a decrease in the density of the colored portion during storage led to the present invention.

[Means for Solving the Problems] The present invention uses, as a heat-sensitive recording layer, an electron-accepting color-developing compound that develops color by contact reaction with a substantially colorless electron-donating color-forming dye precursor under heating. In a heat-sensitive recording material in which a color-forming layer is provided on a support, by containing bisoxalate (P-methylpencil) and 3-phenyl-1-1'-biphenyl as a color development accelerator in the heat-sensitive recording layer. configured.

Color development in the heat-sensitive recording layer is caused by contact between the dye precursor and the color-developing compound, but the low-melting compound added to promote this reaction quickly dissolves due to the heat received during printing, forming the dye precursor. It is believed that sensitivity is improved by dissolving color-developing compounds and/or color-developing compounds.

Therefore, as a result of wide and deep studies to find a low melting point compound that is compatible with both the dye precursor and the color developing compound, it was not possible to find a single compound that met the purpose.

Therefore, we investigated the combination of two or more types of low-melting point compounds. 1
It has been found that the sensitivity is improved more than when only the different types are added, but fatty acid-based low melting point compounds that have a sensitizing effect cannot be added in large quantities because they tend to cause a decrease in image density after storage. Therefore, we conducted intensive research on combinations of aromatic low-melting point compounds that have a sensitizing effect, but when two or more low-melting point compounds are mixed, the melting point decreases greatly and thermal fog is likely to occur. 3-dibutylamino-6-methyl-7-anilinofluorane, 3-(N-isoamyl-N-ethylamino)-6-methyl-7-anilinofluorane, and 2.2゛ as a color developing compound. - When using bis(4-hydroxyphenyl)propane, the combination of bis(P-methylbenzyl) oxalate and 3-phenyl-1-1゛-biphenyl as a low melting point compound allows for rapid progress without causing heat loss. It was found that the sensitivity was improved.

Bis(P-methylbenzyl) oxalate used in the present invention
and 3-phenyl-1-1'-biphenyl is 1:0.1 to 0.1 to bis(P-methylbenzyl oxalate).
The effect is observed when the ratio is up to 1:1, but the effect is particularly greatest when the ratio is 1:1.

The appropriate amount of these two compounds in the heat-sensitive recording layer is 1 to 50% by weight based on the total solid content from the viewpoint of developing a sensitizing effect, but preferably 20 to 35% by weight.

Examples of the dye precursor used in the present invention include various derivatives such as triarylmethane, diphenylmethane, and xanthine. Specific examples include (1) triarylmethane compounds, such as 3.
3-bis(P-dimethylaminophenyl)-6-dimethylaminophthalide.

(2) As a diphenylmethane compound, for example, 4.4
°-bis-dimethylaminobenzhydrin benzyl ether, N-2,4,5-trichlorophenyl leuco auramine, N-2,4 °5-trichlorophenyl leuco auramine, etc.

(3) As a xanthine compound, for example, rhodamine B
-anilinolactam, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-phthylaminofluorane, 3-diethylamino-7-(2-
chloroanilino)fluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-ethyl-tolylamino-6-methyl-7-anilifluorane, 3-cyclohexyl-methylamino-6-methyl-7- Anilinofluorane, 3-diethylamine-6-crow-7-(β
-ethoxyethyl)aminofluorane, 3-diethylamino-6-chloro-7-(γ-chloropropyl)aminofluorane, 3-ethyl-isoamylamino-6-methyl-7-anilinofluorane, 3-cyphthylaminofluorane Examples include no-7-chloroanilinofluorane.

Among these, 3-dibutylaminol 6-methyl-huanilitofluoran and 3-(N-isoamyl-N-ethylamino)-6-methyl-7-anilinofluoran are particularly preferred.

These may be used alone or as a mixture of two or more.

The dye precursor is appropriately selected and used depending on the use and desired properties of the heat-sensitive recording material.

Examples of the color developer used in the present invention include phenol derivatives and aromatic carboxylic acid derivatives. To specifically illustrate this, examples of phenols include p-octylphenol, p-tert-butylphenol, p-phenylphenol, 1.1°-bis(p-hydroxyphenyl)propane, and 2,2°-bis (p-hydroxyphenyl)pentane, 1,1'-bis(p-hydroxyphenyl)hexane, 2,2'-bis(p-hydroxyphenyl)hexane, 1,1'-bis(p-hydroxyphenyl)-2 -ethyl-hexane, 2,2゛-
Examples include bis(4-hydroxy-3,5-dichlorophenyl)propane and dihydroxydiphenyl ether.

In addition, examples of aromatic carboxylic acid derivatives include p-hydroxybenzoic acid, butyl p-hydroxybenzoate, 3,5-di-tert-butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid, and the above carboxylic acids. Examples include polyvalent metal salts.

In order to achieve the effects of the present invention, 2,2'-bis(4-hydroxyphenyl)propane is preferred. In preparing the dispersion of the above-mentioned dye precursor, color developer compound, and low melting point compound, surfactants, polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, and styrene-maleic anhydride copolymer may be used within the range that does not impair the effects of the present invention. Water-soluble synthetic polymer compounds such as hydroxyethyl cellulose, starch derivatives, gelatin, and water-soluble natural polymer compounds or their derivatives such as casein are used, and various auxiliaries such as antifoaming agents are added. You can also do that.

The dye precursor dispersion, color developer dispersion, and low melting point compound dispersion are prepared using a sand grinder, attritor, or
It is made into a dispersion liquid using various wet crushers such as ball mills and Kobo mills.

In the present invention, when preparing a paint for a heat-sensitive recording layer, separately prepared dispersions of a dye precursor, a color developing compound, and a low melting point compound are mixed with each other, and this is mixed as desired.
Add inorganic pigments, waxes, metallic soaps, and if necessary, ultraviolet absorbers, antioxidants, or latex binders.

There is no problem in adding the above additives during the dispersion operation of each dispersion.

Examples of waxes contained in the heat-sensitive recording layer include paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, and higher fatty acid amides such as stearic acid amide, ethylene bisstearamide, and higher fatty acid esters.

Examples of metal soaps include higher fatty acid polyvalent metal salts, ie, zinc stearate, aluminum stearate, calcium stearate, zinc oleate, and the like.

Examples of inorganic pigments include kaolin, calcined kaolin, talc, waxite, diatomaceous earth, calcium carbonate, aluminum hydroxide, magnesium hydroxide, magnesia, titanium oxide, barium carbonate, and the like.

These are applied to the support together with a binder.

Binders are generally water-soluble, such as polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, ethylene-maleic anhydride copolymer,
Examples include styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, polyacrylic acid, polyacrylic acid, starch, casein, gelatin, and the like. Further, for the purpose of imparting water resistance to these binders, a water resistance imparting agent may be added, or a hydrophobic emulsion, specifically, a styrene-butadiene rubber lux, an acrylic resin emulsion, etc. may be added.

The coating liquid is applied to one surface of the sheet-like support at a rate of 3 to 8 g/bo (dry), thereby forming a heat-sensitive recording layer. The heat-sensitive recording layer can be formed using any of the known coating methods such as the air knife method, Flade method, gravure method, roll coater method, spray method, dip method, bar method, and extrusion method. good.

The support material used in the present invention is not particularly limited, and for example, paper, synthetic #M string, synthetic paper, synthetic resin film, etc. can be used as appropriate.

[Example] The invention will be further illustrated by examples.

Example 1 A coating section for forming a heat-sensitive recording layer was prepared by the following steps.

■Ingredients for preparing dye precursor dispersion Amount (parts by weight) 3-dibutylamino-6-methylniar fluorane 10 parts Polyvinyl alcohol 10% solution 30 parts (polymerization degree 500
, degree of saponification 90%) Bis(P-methylbenzyl) oxalate 10 parts 3-phenyl-1-1"-biphenyl 10 parts water
40 parts of this composition was charged into a vertical sand mill (manufactured by Igarashi Kikai Seizo Co., Ltd., sand grinder), and a diameter of 1.211R was placed there as a dispersion media.
A dispersion and refinement operation was performed for 30 minutes using + glass beads, and then the composition was charged into a model sand mill (Ultra Visco Mill, manufactured by Igarashi Kikai Seizo Co., Ltd.), and a glass with a diameter of 0.6+N11 was added as a dispersion medium. A dispersion and refinement operation was performed using beads for 30 minutes.

■Preparation components of color developer dispersion Amount (parts by weight) 2.2'
-Bis(p-hydroxy) 20 parts Phenyl)propane 10% polyvinyl alcohol 20 parts (molecular fi 500, degree of saponification 90%) Water 60 parts This composition was dispersed by the same method as the method for preparing the dye precursor dispersion.

■Preparation of heat-sensitive recording layer coating solution 100 parts of the above dye precursor dispersion and 1 part of the color developer dispersion
00 parts, 40 parts of rhusium carbonate and 100 parts of a 10% polyvinyl alcohol aqueous solution were mixed and stirred to prepare a coating liquid.

This coating solution was applied onto one side of a 50 g/rd base paper so that the coating amount after drying was 7.5 g/rd, dried to form a heat-sensitive coloring layer, and then supercalendered to form a heat-sensitive coloring layer. Manufactured recording paper.

The heat resistance, recording sensitivity, and image preservation solution concentration of the obtained thermal recording paper were measured. The results of these measurements are shown in Table 1. Recording sensitivity is made by Matsushita Densen, high-speed thermal facsimile: U
After printing at F60, the color density was measured, and the image was stored in an atmosphere of 60° C. and 50% for 24 hours, and then the density was measured again. For thermal testing, a heat-sensitive recording layer was attached to a heating plate at 70°C, and the color density was measured at that time. The respective concentrations were measured using a Macbeth thermometer RD-914.

Example 2 A thermosensitive recording paper was prepared in the same manner as in Example 1 except that the following dye precursor dispersion was used.

■Preparation components of dye precursor dispersion Amount (parts by weight) 3-dibutylamino-6-methyl-7-anilinofluorane 10 parts Polyvinyl alcohol 10% solution 30 parts (polymerization degree 500
, degree of saponification 90%) Bis(P-methylbenzyl) oxalate 10 parts 3-phenyl-1-1"-biphenyl 10 parts water
40 parts Example 3 Thermographic paper 8 was prepared in the same manner as in Example 1 except that the following dye precursor dispersion was used.

■ Components for preparing dye precursor dispersion Amount (parts by weight) 3-dibutylamino-6-methyl-7-anilinofluorane 9.5 parts 3-(
N-isoamyl-N-ethylamino)-6-methyl-7-anilite fluorane 0.5 parts Polyvinyl alcohol 10% solution 30 parts (polymerization degree 50
0, degree of saponification 90%) Bis(P-methylbenzyl) oxalate 10 parts 3-phenyl-1-1′-biphenyl 10 parts water
40 parts Comparative Example 1 A thermosensitive recording paper was prepared in the same manner as in Example 1 except that the following dye precursor dispersion was used.

Component Amount (parts by weight) 3-dibutylamino-6-methyl-7-anilinofluorane 10 parts Polyvinyl alcohol 10% solution 30 parts (polymerization degree 500
, degree of saponification 90%) 3-phenyl-1-1'-biphenyl 20 parts water
40 parts Comparative Example 2 Example 8 except that the following dye precursor dispersion was used! A thermosensitive recording paper was prepared in the same manner as in Example 1.

■Preparation components of dye precursor dispersion Amount (parts by weight) 3-dibutylamino-6-methyl-7-anilinofluorane 10 parts Polyvinyl alcohol 10% solution 30 parts (polymerization degree 500
, degree of saponification 90%) 20 parts of bis(P-methylbenzyl) oxalate water
40 copies (blank below) Table 1 [Effects of the Invention] By the method of the present invention, it has become possible to produce a high-quality heat-sensitive recording material with little thermal fluctuation and good recording sensitivity and image storage stability.

Claims (1)

[Claims] A heat-sensitive recording material comprising, on a support, a color-forming layer containing an electron-accepting color-developing compound that develops color by contacting and reacting with a substantially colorless electron-donating color-forming dye precursor under heating, Bis(P-methylbenzyl) oxalate and 3-phenyl-1-1' are used as color development accelerators in the heat-sensitive recording layer.
- A heat-sensitive recording material characterized by containing biphenyl.