JP2755396B2 - Thermal recording material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heat-sensitive recording material which has excellent heat responsiveness and little scum on a thermal head.

(B) Prior Art A thermosensitive recording material is generally provided with a thermosensitive recording layer mainly composed of an electron-donating, usually colorless or pale-colored dye precursor and an electron-accepting developer on a support. By heating with a head, a hot pen, a laser beam, etc., the dye precursor and the color developer react instantaneously to obtain a recorded image, which is disclosed in JP-B-43-4160, JP-B-45-14039, etc. Have been. Such heat-sensitive recording materials have the advantages of being able to record with a relatively simple device, being easy to maintain, and having no noise.They are measurement recorders, facsimile machines, printers, computer terminals, and labels. It is used in a wide range of fields such as ticket vending machines. Particularly in the facsimile field, the demand for the heat-sensitive system has been greatly increased, and accordingly, high-speed operation for reducing transmission cost and low energy consumption for reducing the price by reducing the size of the facsimile are being promoted. Speed up such facsimile
Higher sensitivity of heat-sensitive recording materials has been demanded in response to lower energy. On the other hand, the dot density of the conventional thermal head was generally 8 dots / mm, but the dot density has been increased to 16 dots / mm, for example, and the dot area has also become smaller. As a result, it has been required more than ever to obtain good printability, that is, to obtain an image in which the dots of the head are faithfully reproduced.

In order to meet these demands, if the recording paper is strongly treated with a super calender in order to improve the adhesion of the recording paper to the thermal head, a defect such as so-called background fog, which lowers the whiteness, occurs.

JP-A-56-27394 proposes to provide an undercoat layer between the heat-sensitive layer and the base paper, whereby a high-density image can be obtained with a small applied energy without performing a strong super calendering process. High sensitivity has become possible. It is considered that the application of the undercoat layer is effective in smoothing the surface after the application of the heat-sensitive coating layer by filling the unevenness of the support to form a smoother surface.

As described above, the application of the undercoat layer has improved the sensitivity more than before. However, in recent years, there has been a demand for higher sensitivity and an improvement in dot reproducibility. It has become impossible to cope with it simply by applying a coat layer.

(C) Problems to be Solved by the Invention The present invention addresses the demands for higher sensitivity and improved dot reproducibility that could not be solved by such conventional techniques. The purpose is to provide a good thermal paper.

(D) Means for Solving the Problem The constitution of the present invention relates to a thermosensitive recording material containing a dye precursor and a color developing agent for developing the dye precursor when heated,
Between the support and the heat-sensitive recording layer, porous particles made of a styrene-acrylic copolymer resin having an outer diameter of 5 μm or less are coated as a first undercoat layer, and a pigment is further coated on the second undercoat layer. It is characterized by being coated as a layer.

That is, coating the porous particles made of a styrene-acrylic copolymer resin as the undercoat layer means that the unevenness of the support is simply reduced as in the case of the undercoat layer on which the pigment is applied. In addition to showing the effect of making, the thermal insulation from the porous particles, the thermal energy from the thermal head escapes to the outside of the system,
It is thought that it shows the effect of applying heat energy to the heat-sensitive layer more effectively, and because of the elasticity of the porous particle layer, the adhesion between the heat-sensitive paper surface and the heat head is improved and excellent dot reproduction It is thought to show sex. In the present invention, such porous particles having an outer diameter of 5 μm or less are used, and more preferably, porous particles having an outer diameter of 2 μm or less, most preferably 1 μm or less are used. However, when a material having an outer diameter of 5 μm or more is used, it is not possible to obtain a heat-sensitive recording medium excellent in thermal response, which is the object of the present invention. Such porous particles can be obtained by agglomerating fine particles in a polymerization process.

In the first layer, other pigments can be used in combination to such an extent that the effect of the porous particles made of styrene-acrylic copolymer resin is not impaired. Examples of such pigments include polyethylene and polystyrene. Organic pigments such as ethylene-vinyl acetate, urea-formaldehyde resin, diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, zinc hydroxide, barium sulfate And the like, and these can be used alone or in combination of two or more. The amount of other pigments used in combination is not particularly limited, but is preferably 50% by weight or less.

When a heat-sensitive recording layer is applied directly on a porous particle layer made of a styrene-acrylic copolymer resin, a coloring component dissolved by heat energy from a thermal head is sucked into the porous particle layer to form a color. The resulting image may be concealed, resulting in a decrease in image density, sticking to the thermal head and sticking during printing. For this purpose, further coating an oil-absorbing inorganic pigment layer as a second undercoat layer on the porous particle layer prevents them and at the same time further smoothing the surface by coating the first layer. It is considered that there is also a smoothing action.

As the pigment used in the second layer of the present invention, pigments usually used for coated paper and the like can be used, for example, calcium carbonate, kaolin, calcined kaolin, zinc oxide, titanium oxide,
Examples include aluminum hydroxide, zinc hydroxide, barium sulfate, and silicon oxide. Among them, pigments having an oil absorption of 70 ml / 100 g or more, particularly calcined kaolin and silicon oxide are preferred pigments.

Porous particles of the first layer in the present invention is effective if it is smeared 1 g / m ² or more, the characteristics of the paper, for example, coating layer thickness becomes thicker rather than when it is too much smear thermosensitive properties Therefore, if the thickness of the base paper is reduced and the thickness of the smear paper is made uniform, there will be a problem with the strength of the waist.
A smear of g / m ² is preferred. The smear amount of the oil-absorbing inorganic pigment in the second layer is most preferably 1 to 10 g / m ² in order to function as the second layer without impairing the effect of the first layer. If the amount of smear of the second layer is increased, the heat transfer becomes poor, and the heat insulation and elasticity of the first layer may not be fully utilized.

By providing a heat-sensitive layer on the undercoat layer coated as described above, desired characteristics can be obtained.

The dye precursor used in the present invention is not particularly limited as long as it is generally used for pressure-sensitive recording paper or heat-sensitive recording paper. Specific examples include: (1) triarylmethane compounds 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3,3-bis (p-dimethyl Aminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3- (1,
2-dimethylindol-3-yl) phthalide, 3-
(P-dimethylaminophenyl) -3- (2-methylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-phenylindole-3-
Yl) phthalide, 3,3-bis (1,2-dimethylindol-3-yl) -5-dimethylaminophthalide, 3,3-bis (1,2-dimethylindol-3-yl) -6-dimethyl Aminophthalide, 3,3-bis (9-ethylcarbazol-3-yl) -5-dimethylaminophthalide, 3,3
-Bis (2-phenylindol-3-yl) -5-dimethylaminophthalide, 3-p-dimethylaminophenyl-3- (1-methylpyrrol-2-yl) -6-dimethylaminophthalide and the like.

(2) Diphenylmethane compounds 4,4'-bis-dimethylaminophenylbenzhydryl benzyl ether, N-halophenyl leuco auramine, 2,4,5-trichlorophenyl leuco auramine and the like.

(3) Xanthene compounds Rhodamine B Anilinolactam, Rhodamine Bp-
Chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-
Octylaminofluoran, 3-diethylamino-7-
Phenylfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-6-chloro-7-methylfluoran, 3-diethylamino-7- (3,4-dichloroanilino) fluoran, 3-diethylamino-7
-(2-chloroanilino) fluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3- (N
-Ethyl-N-tolyl) amino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-tolyl) amino-6 Methyl-7-phenethylfluoran, 3-diethylamino-7- (4-nitroanilinofluoran,
3-dibutylamino-6-methyl-7-anilinofluoran, 3- (N-methyl-N-propyl) amino-6
Methyl-7-anilinofluoran, 3- (N-ethyl-
N-isoamyl) amino-6-methyl-7-anilinofluoran, 3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluoran, 3- (N
-Ethyl-N-tetrahydrofuryl) amino-6-methyl-7-anilinofluoran and the like.

(4) Thiazine-based compounds benzoyl leucomethylene blue, p-nitrobenzoyl leucomethylene blue and the like.

(5) Spiro compound 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3,3'-dichlorospirodinaphthopyran, 3-benzylspirodinaphthopyran, 3-methylnaphtho- (3-methoxybenzo) ) Spiropyran, 3-propylspirobenzopyran and the like, and these can be used alone or as a mixture of two or more.

As the color developer used in the present invention, an electron-accepting substance generally used for thermal paper is used, and in particular, a phenol derivative, an aromatic carboxylic acid derivative or a metal compound thereof, N, N'-diarylthiourea Derivatives and the like are used. Among them, particularly preferred are phenol derivatives, specifically, p-phenylphenol, p-hydroxyacetophenone, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, 4-hydroxy-4'-benzenesulfonyloxydiphenylsulfone, 1,1-bis (p-hydroxyphenyl) propane, 1,1-bis (p
-Hydroxyphenyl) pentane, 1,1-bis (p-hydroxyphenyl) hexane, 1,1-bis (p-hydroxyphenyl) cyclohexane, 2,2-bis (p-hydroxyphenyl) propane, 2,2-bis (P-hydroxyphenyl) butane, 2,2-bis (p-hydroxyphenyl) hexane, 1,1-bis (p-hydroxyphenyl) -2-ethylhexane, 2,2-bis (3-chloro-
4-hydroxyphenyl) propane, 1,1-bis (p-
(Hydroxyphenyl) -1-phenylethane, 1,3-di [2- (p-hydroxyphenyl) -2-propyl] benzene, 1,3-di [2- (3,4-dihydroxyphenyl)
-2-propyl] benzene, 1,4-di [2- (p-hydroxyphenyl) -2-propyl] benzene, 4,4'-
Dihydroxydiphenyl ether, 4,4'-dihydroxydiphenylsulfone, 3,3'-dichloro-4,4'-dihydroxydiphenylsulfone, 3,3'-diallyl-4,4 '
-Dihydroxydiphenylsulfone, 3,3'-dichloro-4,4'-dihydroxydiphenylsulfide, methyl 2,2-bis (4-hydroxyphenyl) acetate, butyl 2,2-bis (4-hydroxyphenyl) acetate, 4 , 4'-thiobis (2-t-butyl-5-methylphenol), bis (3-allyl-4-hydroxyphenyl) sulfone,
4-hydroxy-4'-isopropyloxydiphenylsulfone, 3,4-dihydroxy-4'-methyldiphenylsulfone, benzyl p-hydroxybenzoate, p
-Chlorobenzyl hydroxybenzoate, propyl p-hydroxybenzoate, butyl p-hydroxybenzoate,
-Dimethyl hydroxyphthalate, benzyl gallate, stearyl gallate, salicylanilide, 5-chlorosalicylanilide and the like.

Other pigments in the heat-sensitive coating layer 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. As additives, as additives, waxes such as N-hydroxymethyl stearamide, stearamide, palmitamide, naphthol derivatives such as 2-benzyloxynaphthalene, p-benzylbiphenyl, 4-allyloxybiphenyl, etc. Biphenyl derivative of 1,2-bis (3-methylphenoxy) ethane, 2,2
Polyether compounds such as 2′-bis (4-methoxyphenoxy) diethyl ether and bis (4-methoxyphenyl) ether, diphenyl carbonate, dibenzyl oxalate,
Carbonic acid or oxalic acid diester derivatives such as oxalic acid di (p-fluorobenzyl) ester can be added.

In addition, higher fatty acid metal salts such as zinc stearate, calcium stearate, etc., paraffin, paraffin oxide, polyethylene, polyethylene oxide, stearamide,
A wax such as caster wax, a dispersant such as dioctyl sodium sulfosuccinate, an ultraviolet absorber such as benzophenone or benzotriazole, a surfactant, and a fluorescent dye are added as necessary.

In the present invention, as the adhesive used for the first undercoat layer, the second undercoat layer, and the heat-sensitive recording layer, various adhesives that are generally used can be used. For example, starches, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, acrylamide / acrylate copolymer acrylamide / acrylate / methacrylic acid 3 Water-soluble adhesives such as copolymers, alkali salts of styrene / maleic anhydride copolymers, alkali salts of ethylene / maleic anhydride copolymers, polyvinyl acetate, polyurethane, polyacrylate, styrene / butadiene Latexes such as copolymers, acrylonitrile / butadiene copolymers, methyl acrylate / butadiene copolymers, ethylene / vinyl acetate copolymers and the like can be mentioned. As the support used in the present invention, paper is mainly used, but a nonwoven fabric, plastic film, synthetic paper, metal foil, or the like, or a sheet obtained by applying a pigment or the like thereto, or a composite sheet obtained by combining these is optionally used. Can be.

(E) Example Next, the present invention will be described in more detail with reference to examples.

Note that all parts and percentages shown below are based on weight.
The value indicating the amount of smear is the amount of smear after drying unless otherwise specified.

Example 1 Preparation of Solution A (First Layer Coating Solution) A mixture having the following composition was stirred to prepare a first layer coating solution.

XMRP-100 (porous particle emulsion made of Mitsui Toatsu Chemical's styrene-acrylic copolymer resin, particle diameter;
About 1.0 μm, solid content: 40%) 100 parts Styrene butadiene copolymer latex (50% aqueous dispersion) 20 parts Water 20 parts Preparation of solution B (coating solution for second layer) A mixture having the following composition was stirred. Thus, a coating solution for the second layer was prepared.

Ansilex (calcined kaolin manufactured by Engelhard Co.) 100 parts Styrene butadiene copolymer latex (50% aqueous dispersion) 24 parts MS4600 (Nippon Shokuhin phosphate esterified starch, 10%
(Aqueous solution) 60 parts Water 52 parts Preparation of heat-sensitive coating liquid A mixture having the following composition was pulverized and dispersed by a sand mill until the average particle diameter became about 1 μm to prepare [Liquid C] and [Liquid D].

[Solution C] 3-Dibutylamino-6-methyl-7-anilinofluoran 40 parts 10% aqueous solution of polyvinyl alcohol 20 parts Water 40 parts [Solution D] bisphenol A 50 parts Benzyloxynaphthalene 50 parts 10% aqueous solution of polyvinyl alcohol 50 Part water 100 parts Next, a heat-sensitive coating liquid was prepared by the following formulation using the prepared [liquid C] and [liquid D].

[Solution C] 50 parts [Solution D] 250 parts Zinc stearate (40% dispersion) 25 parts 10% aqueous solution of polyvinyl alcohol 216 parts Calcium carbonate 50 parts Water 417 parts Basis weight of each coating solution prepared in this way 40 g A thermosensitive recording material was prepared by smearing the following amounts on a / m ² base paper with a Meyer bar.

First layer 8 g / m ² Second layer 3 g / m ² Thermosensitive layer 5.5 g / m ² Example 2 In Example 1, a mixture having the following composition was stirred to prepare a coating solution for the first layer. A thermosensitive recording material was prepared by smearing in the same manner as in Example 1 except that it was prepared and smeared at 8 g / m ² .

XMRP-140 (porous particle emulsion made of Mitsui Toatsu Chemical's styrene-acrylic copolymer resin, particle diameter;
About 0.5 μm, solid content: 40%) 100 parts Styrene butadiene copolymer latex (50% aqueous dispersion) 20 parts Water 20 parts Example 3 In Example 1, a mixture having the following composition was stirred to obtain a first mixture. A thermosensitive recording material was prepared by smearing in the same manner as in Example 1 except that a coating solution for a layer was prepared and smeared at 8 g / m ² .

XMRP-170 (porous particle emulsion made of Mitsui Toatsu Chemical's styrene-acrylic copolymer resin, particle diameter;
About 0.9 μm, solid content; 40%) 100 parts Styrene butadiene copolymer latex (50% aqueous dispersion) 10 parts Water 20 parts Comparative Example 1 8 g / m ^{2 of the} coating solution for the first layer in Example 1 was applied. rear,
The heat-sensitive coating material was smeared directly as in Example 1 without smearing the second layer to prepare a heat-sensitive recording material.

Example 4 The preparation was performed in the same manner as in Example 1 except that 100 parts of Ultra White-90 (coating kaolin manufactured by Engelhard Co.) was used instead of 100 parts of Ansilex in the preparation of solution B (coating solution for the second layer). A thermal recording material was prepared by smearing in the same manner as in Example 1.

Comparative Example 2 Among the coating liquids prepared in Example 1, the coating liquid for the first layer and the coating liquid for the second layer were not smeared, and the heat-sensitive coating liquid was directly applied to the base paper at 5.5 g / m ^2.
A smeared comparative recording material was prepared.

Comparative Example 3 Of the coating liquids prepared in Example 1, the coating liquid for the first layer was applied without coating the coating liquid for the first layer, 8 g / m ² was applied directly on the base paper, and the heat-sensitive coating liquid was applied thereon. Was coated at 5.5 g / m ² to prepare a heat-sensitive recording material for comparison.

Comparative Example 4 Of the coating liquids prepared in Example 1, the coating liquid for the second layer was directly applied to the base paper at 11 g / m ² without coating the coating liquid for the first layer, and the heat-sensitive coating liquid was applied thereon. Was coated at 5.5 g / m ² to prepare a heat-sensitive recording material for comparison.

The heat-sensitive recording material thus prepared was treated with a super calendar at a Beck smoothness of 400 to 500 seconds, and the recording density, printability, and the degree of scum adhesion were compared with a GIII fax tester. The test machine used was a thermal head with a dot density of 8 dots / mm and a head resistance of 185 Ω, made by Okura Electric (TH-PMD), with a head voltage of 15 V, energizing time of 0.10 ms and
Printed at 0.12ms. Note that the recording density
It was measured with a -918 reflection densitometer. These results are
It is shown in the table.

(F) Effect As is clear from the results in Table 1, the heat-sensitive recording material of the present invention has a heat-sensitive coating layer formed on an undercoat layer having porous particles made of a styrene-acrylic copolymer resin. As a result, the thermal responsiveness was superior to that of the conventional thermal recording material, and the sensitivity and dot reproducibility were improved.

Furthermore, by providing a coating layer made of an oil-absorbing inorganic pigment between the porous particle layer made of a styrene-acrylic copolymer resin and the heat-sensitive layer, the sensitivity can be improved without increasing the head residue and dot reproducibility. Improvement was achieved.

Claims (3)

(57) [Claims] 1. A heat-sensitive recording material containing a dye precursor and a color developer which causes the dye precursor to develop a color when heated, wherein a styrene-acrylic material having an outer diameter of 5 μm or less is provided between the support and the heat-sensitive recording layer. A heat-sensitive recording material, wherein porous particles made of a copolymer resin are applied as a first undercoat layer, and a pigment is applied thereon as a second undercoat layer. 2. The heat-sensitive recording material according to claim 1, wherein the pigment used as the second undercoat layer is an oil-absorbing inorganic pigment. 3. The heat-sensitive recording material according to claim 2, wherein the oil-absorbing inorganic pigment used as the second undercoat layer has an oil absorption of 70 ml / 100 g or more.