JPH06104380B2 - 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.

[Conventional technology]

Thermosensitive recording materials utilizing the heat-coloring reaction of usually colorless or light-colored leuco dyes with phenols or organic acids are disclosed in Japanese Examined Patent Publication No. 43-4160, Japanese Examined Publication No. 45-14039, and Japanese Unexamined Patent Publication No. 48-27736. Has been widely used. 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, the heat-fusible substance is first melted, and the dye and the developer are dissolved therein, whereby the two are mixed at the molecular level and a color reaction occurs. Is induced. 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 to prevent the whiteness of the heat-sensitive recording material from being lowered, 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, in particular,
It is considered that the heat-colored portion of the heat-sensitive recording material is deeply related to the phenomenon of so-called whitening, which becomes dusty with time, which is an extremely important property for practical use of the heat-sensitive recording material. Although many of these heat-fusible substances have been proposed in the past, few satisfy all of the above conditions, and new materials have been demanded.

The present invention provides a novel heat-fusible substance to be used together with the above-mentioned leuco dye and color-developing agent, and applies it to a heat-sensitive recording material, greatly improving the recording sensitivity of the recording material, and recording. The purpose is not to reduce the quality involved.

[Means for solving problems]

The present inventors have conducted extensive research to achieve this object, and as a result, as a heat-fusible substance, a compound of the general formula [I] or [II] (In the above formula, R represents an alkyl group, an aryl group or an aralkyl group, and the benzene ring may be substituted with two or more.) The organic compound having an acetylacetoxy group represented by Compared with higher fatty acid amides such as stearic acid amide and palmitic acid amide, which have been proposed as fusible substances, there is a phenomenon such as whitening that does not cause a decrease in whiteness and deteriorates the quality of a colored image with time. The inventors have found that extremely high recording sensitivity can be obtained without experience, and have completed the present invention.

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 thermosensitive recording material has the above general formula [I] in the coloring layer.
Alternatively, it is a thermosensitive recording medium containing at least one compound represented by [II]. It is not clear why the specific heat-fusible substance (hereinafter referred to as a sensitizer) as described above improves the color-developing sensitivity of the thermosensitive recording medium containing it, but these compounds themselves are also weak bases. It is presumed that one of the reasons is the ability to develop a sex leuco dye. 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. Specific examples of the sensitizer constituting the present invention include the following.

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

The substituent R is a hydrocarbon selected from an alkyl group, an aryl group or an aralkyl group as described above. Further restrictions on R are made by the melting points of compounds of the invention having R. That is, the melting point of the compound constituting the present invention is required to be 60 ° C. or higher in order to exhibit the desired performance as a sensitizer. As a result of a systematic study, the present inventors have found that there is a correlation between the melting points of the phenol derivative and naphthols, which are one of the starting materials for the compound of the present invention, and the melting points of the compounds having an acetoacetoxy group formed. . That is, when the melting point of the starting phenol derivative or naphthols is 80 ° C. or lower, the melting point of the acetylacetoxy compound formed does not reach the temperature preferable as the sensitizer. This is not directly related to the size of the substituent R. For example, among the specific examples of the compounds constituting the present invention described above, p-tert.octylphenol, p-phenylphenol and 2-naphthol, which are the raw materials of (A) (B) (D), have melting points of 83% respectively.
° C, 165 ° C and 121 ° C. On the other hand, for example, as raw material 2,
4,6 trimethylphenol (melting point 72 ℃), p-cumylphenol (melting point 73 ℃), o-phenylphenol (melting point)
When used at 59 ° C., none of these acetylacetated products have melting points of 50 ° C. and are unsuitable as sensitizers.

As the heat-fusible substance constituting the present invention, any one kind of compound may be used together with a leuco dye and a coloring agent.
You may use together 1 or more types. Further, it may be used in combination with other sensitizers within a range that does not impair the desired effects of the present invention. The amount of the compound of the present invention used is 10 with respect to the color developer.
-1000% by weight, preferably 50-300% by weight.

The thermosensitive coloring layer using the compound of the present invention is mainly a leuco dye,
It comprises a colorant consisting of phenols or organic acids, and the compound of the present invention. Further, the color forming 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-6-methyl-
7- (o, p-dimethylanilino) fluorane, 3- (N
-Ethyl-p-toluidino) -6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-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- Chlorofluoran.

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

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.

Here, as the sensitizer that 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. Is.

p-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 V di-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,
Inorganic fine powders such as talc and surface-treated calcium carbonate and silica, as well as organic fine powders such as urea-formalin resin, styrene / methacrylic acid copolymer and polystyrene resin can be mentioned.

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 higher 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 Water-soluble polymers such as acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, casein, polyvinyl acetate, polyurethane, styrene / butadiene copolymer Polymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer, styrene / butadiene / acrylic copolymerization A latex such as a body can be used.

Mixtures of these materials, which are colored by heating, can be applied to paper, coated paper with clay, plastic, etc. coated on the surface, or synthetic paper mainly made of plastic, or plastic film, and heat-sensitive. Make a recording body. The coating amount is 1 to 10 when the coating layer is dry.
preferably ^{g / m 2, 2~7g / m} 2 is particularly preferred.

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. The numbers represent parts by weight unless otherwise specified.

〔Example〕

Synthesis Example 1 25.5 g of p-phenylphenol and 13.0 g of diketene were added to 60 parts.
Dissolve in ml tetrahydrofuran (THF) and add a few drops of pyridine. An exothermic reaction occurs after a few minutes of induction. Crystals formed from the solution after standing for 1 day. The crystals were separated by filtration and recrystallized from THF to obtain 29.0 g of white crystals. As a result of mass spectrometry and nuclear magnetic resonance analysis, it was confirmed to be the target compound [B].

Synthesis Example 2 14.4 g of 2-naphthol and 9.0 g of diketene are 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. After standing for 1 day, THF was distilled off to obtain a yellow solid. This solid was recrystallized from toluene and 15.7 g
White crystals were obtained. As a result of mass spectrometry and nuclear magnetic resonance analysis, it was confirmed to be the target compound [D].

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.

Dispersion B Preparation 4,4′-Isopropylidenediphenol 10 Inventive Compound (B) 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 and 10% of a styrene-butadiene copolymer emulsion (solid content 50%) was added to a dispersion liquid obtained by dispersing 85 parts of calcined clay (trade name: Ansilex) in 320 parts of water. A coating solution obtained by mixing 50 parts of an 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 (D) was used in place of the compound (B) 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 compound (B) of the present invention in the preparation of solution B.

Comparative Example 2 A thermal recording paper was obtained in the same manner as in Example 2 except that stearic acid amide was used in place of the compound (B) of the present invention in the preparation of solution B.

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

The six types of thermal recording papers obtained as described above were treated with a super calendar so that the surface smoothness was 600 to 1000 seconds as measured by a Beck smoothness meter. For the sample thus obtained, measurement of recording sensitivity,
The color density of the uncolored portion on 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 RD-914 to obtain a value representative of the recording sensitivity of thermal paper. The density of the uncolored part (white paper part) of the recording paper 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 color-developed part was left in an environment of 40 ° C and 90% for 24 hours, and the surface change was sensory evaluated. In the table, ∘ indicates that no change was observed in the color printed portion, and x indicates that so-called whitening occurred such that the printed surface became dusty.

[Advantages of the Invention] As described above, since the thermosensitive recording material of the present invention uses the novel heat-fusible material, it is excellent in high-speed recording suitability, has high whiteness, and is not preferable such as whitening. It does not induce a phenomenon and has a very well balanced property in terms of quality.

Claims (1)

[Claims] 1. A thermosensitive recording medium having a thermosensitive color developing layer utilizing a color reaction between a colorless or pale basic dye and a color developing agent, wherein the thermosensitive color developing layer contains a compound represented by the general formula [I] or [II]. ] (In the above formula, R represents an alkyl group, an aryl group or an aralkyl group, and the benzene ring may be substituted with two or more.) At least one organic compound having an acetylacetoxy group represented by A thermal recording material characterized by.