JPH0698831B2 - Thermal recording - Google Patents

Description

The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material having high whiteness and excellent suitability for high-speed recording.

[Prior Art] A heat-sensitive recording material utilizing a heat-coloring reaction of a normally colorless or light-colored leuco dye with a phenol or an organic acid is disclosed in JP-B-43-4160, JP-B-45-14039, and JP-A-48-14039. 227
It was announced in Issue No. 36 and has been put to practical use. In recent years, such a thermosensitive recording medium has been widely used as various information recording materials because of the advantages that a color image is formed by simply heating and the recording apparatus can be made relatively compact. . In particular, thermal facsimiles, thermal printers, and the like using such thermal recording media have been improved in their apparatus, and high-speed printing and high-speed image formation, which have been difficult in the past, are now possible. With the increase in the speed of such fields of equipment and hardware, the thermal recording medium used is required to have a significantly higher recording sensitivity than ever before. Many proposals have been made to meet this requirement, but most of them relate to the combination of a basic dye and a color former, and also a heat-fusible substance.

When a heat-sensitive recording material containing such a heat-fusible substance is heated,
First, the heat-fusible substance is melted, and the dye and the color developer are dissolved therein, so that they are mixed with each other at a molecular level to induce a color-forming reaction. Therefore, these heat-fusible substances must have an appropriate melting point (preferably 60 to 140 ° C.) as well as excellent compatibility with dyes and color formers. Further, in order not to reduce the whiteness of the thermosensitive recording medium, it is desirable that these heat fusible substances are extremely sparingly soluble in water, and further, they have properties such as low sublimability. desirable. The latter is considered to be deeply related to the phenomenon of so-called whitening, in which the coloring portion of the heat-sensitive recording material becomes dusty over time, which is an extremely important property for practical use of the heat-sensitive recording material. Becomes
Although many of these heat-fusible substances have been proposed in the past,
Few materials satisfy all of the above conditions, and new materials have been demanded.

The present invention provides a novel heat-fusible substance to be used with the above-mentioned leuco dye and color-developing agent, and applying it to a thermosensitive recording medium
It is an object of the present invention to significantly improve the recording sensitivity of the recording medium and prevent deterioration of various recording-related qualities.

[Means for solving problems]

As a result of repeated studies to achieve this object, the present inventors have two acetylacetoxy groups represented by the following compound [I] or general formula [II] in one molecule as a heat-fusible substance. Using at least one of the organic compounds, (In the above formula, X represents a divalent alkylene group, an oxygen atom, a sulfur atom, or a sulfonyl group.) Compared with higher fatty acid amides such as stearic acid amide and palmitic acid amide, which have been conventionally proposed as heat fusible substances. In order to complete the present invention, it was found that extremely high recording sensitivity can be obtained without causing a decrease in whiteness and without experiencing a phenomenon such as whitening that deteriorates the quality of a colored image with time. I arrived.

The present invention provides a thermosensitive recording material having a thermosensitive coloring layer utilizing a color reaction between a colorless or monochromatic basic leuco dye and a coloring agent, wherein the compound [I] is contained in the coloring layer of the thermosensitive recording material.
Alternatively, it is a thermosensitive recording medium containing at least one compound represented by the general formula [II].
Specific heat-fusible substance as described above (hereinafter referred to as sensitizer)
However, the reason for improving the color development sensitivity of the thermosensitive recording material containing it is not clear, but one of the reasons is that these compounds themselves have the ability to develop a basic leuco dye although they are weak. Presumed. Further, it is considered that it is the low sublimation property that does not reduce the whiteness because it is poorly soluble in water, and therefore the phenomenon that the recorded image quality such as whitening is deteriorated is extremely low. Not sticky. The following may be mentioned as specific examples of the heat-fusible substance constituting the present invention.

These compounds having an acetylacetoxy group can be easily synthesized in high yield from the corresponding phenol and diketene as shown in the reaction formula below.

In the above formula, X is selected from a divalent alkylene group, an oxygen atom, a sulfur atom and a sulfonyl group. Examples of the divalent alkylene group include a methylene group, a 2,2-propylidene group, a 1,1-cyclohexylidene group, and the like. Although X has various possibilities other than the above-mentioned functional groups, according to the systematic research of the inventors, the compound having an acetoacetyl group which constitutes the present invention is one of the synthetic raw materials. It has a suitable melting point as a sensitizer only when a phenol derivative having a valence of 130 ° C or higher is used. For example, a compound represented by the structural formula [II] in which X is a 2,2-butylidene group, which is synthesized from 2,2-bis (p-hydroxyphenyl) butane (melting point: 126 ° C.) in which X is a 2,2-butylidene group. Has a melting point of less than 50 ° C. and is not preferable as a sensitizer.

Any one of the compounds having an acetylacetonyl group constituting the present invention may be used together with a leuco dye and a color developer, or two or more kinds thereof may be used in combination in the thermosensitive color developing layer. Also, within the range that does not inhibit the desired effects of the present invention,
It can also be used in combination with other so-called sensitizers. The amount of the compound of the present invention used is 10 to 1,000% by weight, preferably 50 to 300% by weight, based on the color developing agent.

The thermosensitive coloring layer using the compound of the present invention is mainly a leuco dye,
It comprises a color developer consisting of phenols or organic acids, and the compound of the present invention. Further, the thermosensitive coloring layer preferably contains an inorganic pigment, and may further contain waxes, if necessary. In addition, a binder for fixing these components to the support is contained as an essential component.

The leuco dye may be a conventionally known one, for example, the following.

Crystal violet lactone, 3- (N-ethyl-)
N-isopentylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6methyl-7
-(O, p-dimethylanilino) fluorane, 3- (N
-Ethyl-p-toluidino) -6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3- (N-cyclohexyl-N-methylamino) -6-methyl-7-anilinofluorane,
3-diethylamino-7- (o-chloroanilino) fluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino-6
-Methyl-7-chlorofluorane, 3-diethylamino-6-methylfluorane, 3-cyclohexylamino-
6-chlorofluorane.

The coloring agent composed of phenols or organic acids may be the same as the conventionally known ones, and the following are examples thereof.

Bisphenol A, benzyl P-hydroxybenzoate,
N-Butyl di (4-hydroxyphenyl) acetate, bisphenol S, 4-hydroxy-4'-isopropyloxydiphenyl sulfone, 1,1-di (4-hydroxyphenyl) cyclohexane, 1,7-di (hydroxyphenylthio) -3,5-dioxaheptane.

As the so-called sensitizer which can be used in combination with the compound of the present invention, a heat-fusible organic compound having a melting point of 50 to 150 ° C. is used.
The following is a typical example.

1-hydroxy-2-naphthoic acid phenyl ester, p
-Benzyl biphenyl, benzyl naphthyl ether, dibenzyl terephthalate, benzyl p-benzyloxybenzoate, diphenyl carbonate, ditolyl carbonate, m-terphenyl, ethylene glycol-m-tolyl ether.

The organic or inorganic pigments used in the color forming layer include calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay,
Examples include inorganic fine powders of talc, surface-treated calcium carbonate, silica and the like, as well as fine powders of organic total such as urea-formalin resin, styrene / methacrylic acid copolymer and polystyrene resin.

Further, the color forming layer of the present invention may optionally contain various waxes. They may be known ones such as paraffin, amide wax, bisimide wax, and metal salt of superabsorbent fatty acid. Regarding the adhesive,
Polyvinyl alcohol, starch and its derivatives of various molecular weights, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylic acid amide / acrylic acid ester copolymer, acrylic acid amide / acrylic Acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate,
Water-soluble polymers such as gelatin and casein, polyvinyl acetate, polyurethane, styrene / butadiene copolymer,
Polyacrylic acid, polyacrylic acid ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer, styrene / butadiene /
A latex such as an acrylic copolymer can be used.

A mixture of these materials, which is colored by heating, can be applied to paper, coated paper with viscosity, plastic, etc. coated on the surface, or synthetic paper mainly made of plastic, or synthetic film. Make a recording body. The coating amount is preferably 1 to 10 g / m ^{2 and} particularly preferably ² to 7 g / m ² when the coating layer is dried.

As described above, the thermal recording material obtained by the present invention is excellent in high-speed recording suitability, has high whiteness, and does not exhibit unfavorable properties such as whitening in a recorded image portion.

Hereinafter, the present invention will be specifically described with reference to examples. Unless otherwise specified, the numbers indicate parts by weight.

〔Example〕

Synthesis Example 1 20.2 g of bis (p-hydroxyphenyl) ether and 17.
0 g of diketene is dissolved in 50 ml of tetrahydrofuran (THF), to which a few drops of pyridine are added. An exothermic reaction occurs after a few minutes of induction. After standing for 1 day, THF was distilled off to obtain a white solid. This solid was recrystallized from toluene to obtain 18.6 g of white crystals. As a result of nuclear magnetic resonance analysis, it was confirmed to be the target compound.

Synthesis Example 2 25.0 g of bis (p-hydroxyphenyl) sulfone and 17.
0 g of diketene is dissolved in 50 ml of THF, to which a few drops of pyridine are added. An exothermic reaction occurs after a few minutes of induction. 1
Light yellow crystals precipitate after standing for a day. This was recrystallized from THF to obtain 38.3 g of white crystals. As a result of nuclear magnetic resonance analysis,
It was confirmed to be the target compound.

Example 1 Preparation of Dispersion A 3- (N-Isopentyl-Nethylamino) -6-methyl-7-anilinofluorane 20 Polyvinyl alcohol 10% solution 10 Water 70 This composition was sand-grinded to an average particle size of 1 μm. Crushed.

Preparation of Dispersion B 4,4′-Isopropylidene diphenol 10 Compound (A) of the present invention 10 Polyvinyl alcohol 10% liquid 10 Water 70 This composition was ground to an average particle size of 1 μm with a sand grinder.

Preparation of coloring layer 40 parts of solution A, 160 parts of solution B, 40 parts of calcium carbonate pigment, 3
20 parts of 0% paraffin dispersion and 180 parts of 10% polyvinyl alcohol aqueous solution were mixed and stirred to obtain a coating liquid. This coating solution was applied to a base paper of 50 g / m ² so that the coating amount after drying was 7.5 g / m ^2, and dried to obtain a thermosensitive recording paper.

Example 2 Preparation of Pigmented Undercoat Paper 20 parts of a styrene-butadiene copolymer emulsion (solid content 50%) was added to a dispersion obtained by dispersing 85 parts of calcined clay (trade name: Ansilex) in 320 parts of water, 10 parts. A coating solution obtained by mixing 50 parts of a% oxidized starch aqueous solution was coated on a base paper of 48 g / m ² so that the coating amount after drying was 7.0 g / m ² to obtain a pigment-undercoated paper.

Formation of coloring layer 50 parts of A dispersion, 200 parts of B dispersion, 25 parts of calcium carbonate, 3
20 parts of 0% paraffin dispersion and 180 parts of 10% aqueous solution of polyvinyl alcohol were mixed and stirred to obtain a coating liquid. The obtained coating liquid on the pigment-undercoated paper, the coating amount after drying is 5.0 g / m ²
And dried to obtain a heat-sensitive recording paper.

Example 3 A thermosensitive recording paper was obtained in the same manner as in Example 2 except that the compound (C) was used instead of the compound (A) of the present invention in the preparation of solution B.

Comparative Example 1 A thermosensitive recording paper was obtained in the same manner as in Example 1 except that stearic acid amide was used instead of the present invention (A) in the preparation of solution B.

Comparative Example 2 A thermosensitive recording paper was obtained in the same manner as in Example 2 except that stearic acid amide was used instead of the invention (A) in the preparation of the liquid B.

Comparative Example 3 A thermosensitive recording paper was obtained in the same manner as in Example 2 except that 1-hydroxy-2-naphthoic acid phenyl ester was used instead of the present invention (A) in the preparation of solution B.

The six types of heat-sensitive recording papers obtained as described above were treated by a super calendar so that the surface smoothness was 600 to 1,000 seconds as measured by a Beck smoothness meter. For the sample thus obtained, measurement of recording sensitivity,
The color density of the uncolored portion of the recording layer surface was measured, and a whitening comparison test was conducted. The results are shown in Table 1.

Recording sensitivity was 120 ° C using Toyo Seiki's thermal tilt tester.
A sample was heated at a pressure of 2.5 kg / cm ² for 100 msec, and the color density at that time was measured with a Macbeth densitometer RD-914, and the value was used as a value representative of the recording sensitivity of thermal paper. Uncolored area (blank area) on recording layer
Was measured with the same densitometer and used as a representative value of whiteness.

For whitening, the sample is developed at a temperature of 150 ° C with the above tester,
The printed part was left in an environment of 40 ° C and 90% for 24 hours, and the change in the surface was sensory evaluated. In the table, ∘ indicates that no change was observed in the color printed part, and x indicates that the printed surface became dusty, that is, whitening occurred.

[Advantages of the Invention] The heat-sensitive recording material of the present invention, which uses a novel heat-fusible material, is excellent in high-speed recording property, has high whiteness, and does not induce an undesirable phenomenon such as whitening. , Has a very balanced quality.

Claims (1)

[Claims] 1. A thermosensitive recording medium which utilizes a color reaction between a colorless or light-colored basic dye and a color former, and is represented by the following compound [I] or general formula [II] in the thermosensitive color developing layer. A heat-sensitive recording material comprising at least one organic compound having two acetylacetoxy groups in one molecule. (X in the above formula represents a divalent alkylene group, an oxygen atom, a sulfur atom, or a sulfonyl group.)