JPH05270134A - Thermal recording sheet - Google Patents

Abstract

PURPOSE:To obtain a thermal recording sheet of high quality having high sensitivity, reduced in the adhesion amount of refuse and excellent in printing quality. CONSTITUTION:In a thermal recording sheet obtained by providing two or more in termediate layers based on pigment whose oil absorbancy due to JIS K5101 is 50ml/100g or more and a binder on a support and providing a thermal color forming layer on the intermediate layers, carboxymethyl cellulose and/or hydroxyethyl cellulose is added to the uppermost intermediate layer in an amount of 0.3-30% by wt. of the pigment of the intermediate layer and fine fibrous cellulose is added to the lowermost intermediate layer. By this constitution, the thermal recording sheet of high quality having high sensitivity, reduced in the adhesion amount of refuse and excellent in printing quality is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording sheet, and more specifically, a JI sheet between a support and a heat-sensitive recording layer.
The present invention relates to a heat-sensitive recording sheet provided with two or more intermediate layers containing an inorganic pigment having an oil absorption of 50 ml / 100 g or more according to the SK5101 method and a binder as main components.

[0002]

2. Description of the Related Art Conventionally, many methods are known for thermal recording. For example, a heat-sensitive recording material using an electron-donating colorless dye and an electron-accepting compound is disclosed in JP-B-43-41.
No. 60, Japanese Patent Publication No. 45-14039, etc., and these thermal recording systems have recently been applied to various fields such as facsimiles, printers, word processors, and labels, and their needs are expanding. In recent years, especially in the field of facsimiles and word processors, with the downsizing of devices and high-speed printing, there has been a demand for color development with low applied energy, that is, high sensitivity and runnability, and improved print quality.

In order to increase the sensitivity, a compound having a low melting point with good compatibility between an electron-donating colorless dye and an electron-accepting compound, a so-called sensitizer (JP-A-60-82382, JP-B-63-42590). Japanese Patent Publication No. 57-52915), or providing an intermediate layer of a pigment having a high oil absorption property (Japanese Patent Publication No. 57-52915).
The electron-donating colorless dye and the electron-accepting compound are atomized (Japanese Patent Application Laid-Open No. 58-76293) and the like, but generally the higher the sensitivity, the more the adhesion of dust. In order to improve the adhesion of dust, a method such as adding an inorganic pigment to the intermediate layer or the heat-sensitive layer has been carried out, but it may not be satisfactory in some cases. Also,
Since the improvement of print quality is largely due to the good adhesion with the heating element, there is a method of smoothing the surface by calendering with a strong pressure, but increasing the gloss of the heat-sensitive layer more than necessary. , Caused fog due to friction,
The appearance of the product tends to be poor, and it is the current situation that nothing satisfying these requirements has been obtained.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat-sensitive recording sheet which has good thermal response, high sensitivity, little dust adhesion, and good print quality.

[0005]

The present inventor has conducted diligent studies to improve these drawbacks, and as a result, JI on the support.
An intermediate layer mainly composed of an inorganic pigment having an oil absorption of 50 ml / 100 g or more as determined by the SK5101 method and a binder is provided, and an electron-donating colorless or light-colored dye and an electron acceptor that develops the dye by heating on the intermediate layer. In the heat-sensitive recording paper provided with a coloring layer containing a polymerizable compound and a binder as a main component, the intermediate layer has two or more layers, and carboxymethyl cellulose and / or hydroxyethyl cellulose is added to the intermediate layer in an amount of 0. Containing from 3% to 3% by weight,
In addition, by including the microfibrous cellulose in the lowermost layer, it became possible to achieve the purpose.

The amount of carboxymethyl cellulose and / or hydroxyethyl cellulose in the top layer is preferably 0.3 to 3% by weight, based on the pigment in the top layer of the intermediate layer, below 0.3% by weight. If the effect is not clear and the amount is more than 3% by weight, the viscosity of the coating solution for the intermediate layer increases and the coating becomes difficult. Carboxymethyl cellulose is a cellulose ether prepared by reacting alkali cellulose with chloroacetate, and is usually commercially available as sodium salt sodium cellulose glycolate. Hydroxyethyl cellulose is a cellulose ether produced by reacting alkali cellulose with ethylene oxide or ethylene chlorohydroline. The microfibrous cellulose in the lowermost layer is, for example, about 1% of the fibrous cellulose obtained by chemically or physically pulping using a conventionally known technique.
To 10 wt% suspension through a small diameter orifice, giving a high velocity with a pressure difference of at least 3000 pai (pounds per square inch) and performing a cutting action by physical impact force, and repeating the above steps to suspend the suspension. The one described in JP-A-56-100801, which is obtained from the step of stabilizing the suspension, can be used. Quantitatively, it is preferable to use 1 to 10% by weight based on the pigment of the intermediate layer.
If it is less than 10% by weight, the effect is unclear, and if it is more than 10% by weight, the fluidity of the coating layer increases, and it tends to be difficult to apply.

As a pigment for the intermediate layer, JIS K5101 is highly porous and has a high heat insulating property in terms of sensitivity and improvement of dust adhesion.
Inorganic powder having an oil absorption amount of 50 ml / 100 g or more according to the method is used, and examples thereof include calcined kaolin, activated clay, silica,
Calcium carbonate and diatomaceous earth are mainly used, and kaolin and talc can be used together. Examples of the water-based adhesive include styrene-butadiene latex, acrylic resin emulsion, styrene-maleic anhydride polymer, polyvinyl alcohol, hydroxyethyl cellulose, starch, starch derivative, casein, gelatin and the like, and other dispersants and antifoaming agents. , Lubricants, etc. can be added, and those used for general coated paper can be used.

The thermosensitive coloring layer provided on the support contains an electron-donating colorless dye, an electron-accepting compound, and a sensitizer (sensitizer) as main components, but if necessary waxes,
Metal soaps, ultraviolet absorbers and the like may be added, and pigments and the like may be further mixed.

The electron-donating colorless dye used in the present invention is not particularly limited as long as it is used for general pressure-sensitive recording paper, heat-sensitive recording paper and the like. Specific examples include (1) 3,3 as triarylmethane compounds
-Bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone) 3,3-bis (p-dimethylaminophenyl) 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-dimethylindole-3)
-Yl) -6-dimethylaminophthalide, 3,3-bis- (9-ethylcarbazol-3-yl) -5-dimethylaminophthalide, 3,3-bis- (2-phenylindol-3-yl) ) -5-Dimethylaminotalide, 3-
p-dimethylaminophenyl-3- (1-methylpyrrol-2-yl) -6-dimethyl-aminophthalide and the like.
(2) 4,4'-as the diphenylmethane compound
Bis-dimethylaminobenzhydrin benzyl ether, N-halophenyl leuco auramine, N-2,4
5-trichlorophenyl leuco auramine and the like. (3)
As the xanthene compound, rhodamine B-anilinolactam, rhodamine B-p-nitroanilinolactam,
Rhodamine B-p-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-octylaminofluorane, 3-diethylamino-7-phenylfluorane, 3-diethylamino-7-3. , 4-dichloroanilinofluorane, 3
-Diethylamino-7- (2-chloroanilino) fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-ethyl-tolylamino-6- Methyl-7-anilinofluorane, 3-ethyl-tolylamino-6-methyl-7-phenethylfluorane, 3-diethylamino-7- (4-nitroanilino) fluorane, 3
-Dibutylamino-6-methyl-7-anilinofluorane and the like. (4) Benzoyl leuco methylene blue, p-nitrobenzoyl leuco methylene blue and the like as thiazine compounds. (5) As the spiro compound, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-
Dinaphthopyran, 3,3'-dichloro-spiro-dinaphthopyran, 3-benzylspiro-dinaphthopyran, 3-
Mention may be made of methylnaphtho- (3-methoxy-benzo) -spiropyran, 3-propyl-spiro-dibenzopyran and the like, or mixtures thereof. These are determined by the application and the desired properties.

The electron accepting compound used in the present invention is preferably a phenol derivative or an aromatic carboxylic acid derivative, and particularly preferably bisphenols. Specifically, as phenols, p-octylphenol, p
-Tert-butylphenol, p-phenylphenol,
1,1-bis (p-hydroxyphenyl) propane,
2,2-bis (p-hydroxyphenyl) propane,
1,1-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-bis (4-hydroxy-3,5-
Dichlorophenyl) propane and the like can be mentioned. As the aromatic carboxylic acid derivative, p-hydroxybenzoic acid,
Ethyl p-hydroxybenzoate, butyl p-hydroxybenzoate, 3,5-di-tert-butylsalicylic acid, 3,
Examples of 5-di-α-methylbenzyl salicylic acid and carboxylic acid include polyvalent metal salts thereof.

Examples of the waxes include paraffin wax, coconut wax, microcrystalline wax, polyethylene wax, higher fatty acid amide,
Examples thereof include stearic acid amide, ethylene bis stearamide, and higher fatty acid ester.

Examples of the metal soap include higher fatty acid polyvalent metal salts, that is, zinc stearate, aluminum stearate, calcium stearate, zinc oleate and the like.

The sensitizer for improving the sensitivity is preferably a sensitizer having a melting point of 80 to 140 ° C., a relatively sharp melting range and good thermal response, and specifically, 2- (P-methylbenzyloxy). ) Naphthalene, oxalic acid-bis (P-methylbenzyl), esters of benzoic acid and terephthalic acid,
Sensitizers such as naphthalene sulfonates, naphthyl ether derivatives, anthryl ether derivatives, aliphatic ethers, phenanthrene, and fluorene can be used in combination. Also, the above waxes can be used together as a sensitizer.

These are dispersed and applied in a binder (adhesive). The binder is generally water-soluble, polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, Examples thereof include polyacrylic acid, starch derivatives, casein, gelatin and the like. In addition, a water resistance agent (gelling agent, cross-linking agent) may be added to these binders for the purpose of imparting water resistance, or an emulsion of a hydrophobic polymer, specifically, styrene-butadiene rubber latex, acrylic resin emulsion, etc. It can also be added.

Paper is generally used as the support, but it is also possible to use resin film, synthetic paper, woven cloth or the like. As an apparatus used for coating the intermediate layer and the heat-sensitive recording layer, a coater head such as a blade coater, an air knife coater, a roll coater, a rod coater or a curtain coater can be used.

Further, in order to improve the surface smoothness of the coated product, a machine calender, a super calender, a gloss calender, a brushing machine or the like can be used.

The coating amount of each intermediate layer is not particularly limited, but if it is too small, its effect is small, and if the paper thickness is considered to be constant, if it is too large, the strength of the paper becomes weak, and the economy is low. Since it is not desirable, 3 to 20 g / m ^{2 is} preferable, and 5 to 10 g / m ² is suitable. The coating amount of the heat-sensitive recording layer on the support is not limited, but is usually 3 to 15 g / m ² , preferably 4 to 10 g / m ^{2 as} a dry weight.
The range is.

A protective layer may be further provided on the heat-sensitive recording layer for solvent resistance and the like.

[0019]

The heat-sensitive recording sheet obtained by the method of the present invention comprises, as described above, two or more intermediate layers composed mainly of an inorganic pigment having an oil absorption of 50 ml / 100 g or more according to the JISK5101 method and a binder as described above. Provided, the uppermost layer contains 0.3% to 3% by weight of carboxymethyl cellulose or hydroxyethyl cellulose with respect to the pigment of the intermediate layer, and further contains the microfibrous cellulose in the lowermost layer, preferably, 1 to 10% by weight with respect to the bottom layer pigment
By including a color-forming layer containing an electron-donating dye and an electron-accepting compound capable of coloring the dye by heating and a binder as a main component on the intermediate layer, which is contained, A high-sensitivity, low-dust deposit and good print quality was obtained.

With respect to color development sensitivity, this is because the fine fibrous cellulose present in the lowermost layer of the intermediate layer diffuses into the layer, which increases the porosity of the coating layer, resulting in a higher heat insulating effect and the applied energy. It is presumed that this can be efficiently used for the color development reaction. In addition, for the improvement of printing quality,
This microfibrous cellulose imparts an excellent leveling property to the coating liquid due to the effect of moderate water retention and capillarity, and a coating layer with extremely good smoothness can be obtained, so that the coloring layer finally obtained. It is considered that this is because it has the effect of improving the uniform adhesion between the heat-sensitive recording sheet and the heating element including. Therefore, by performing the calendering treatment with the minimum necessary pressure, the effect of improving the printing quality is exhibited without generating abnormal friction fog or gloss. Also, even with cellulose, it has not been processed into fine fibers,
In so-called cellulose powder and microcrystalline cellulose,
The above effect was not obtained. Regarding the adhesion of dust, if the pigment in the color forming layer is reduced or the fineness of the dye is increased to improve the color development sensitivity at the time of thermal recording, the color development is improved, but the melt adhered to the thermal head tends to increase. is there. However, when carboxymethyl cellulose and / or hydroxyethyl cellulose was contained in the uppermost layer of the intermediate layer, the effect of reducing the amount of residue attached to the heating element was observed. This is because when forming the intermediate layer, the carboxymethyl cellulose or hydroxyethyl cellulose that had been swollen by water during the transition from the wet state to the dry state was dried and shrunk to form a porous structure in the intermediate layer, resulting in coloration during heat-sensitive recording. It is believed to promote absorption of the melt in the layer.

[0021]

EXAMPLES The present invention will now be described in more detail by way of examples. All parts and% shown below are based on weight. Unless otherwise stated, the value indicating the smear amount indicates the smear amount after drying.

Example 1 Preparation of Intermediate Layer 1 Ansilex (calcined kaolin manufactured by Engelhard, oil absorption amount according to JIS K5101 method: 80 ml / 100 g) 100 parts 10% sodium hexametaphosphate 4 parts 20% MS4600 (phosphorylated starch made by Nippon Foods Co., Ltd.) ) 30 parts 48% styrene-butadiene copolymer latex 40 parts 2% MFC (Daicel microfibrous cellulose suspension) 250 parts by stirring and dispersion to form a coating solution for the intermediate layer 1 and a smear amount of 8 g on a base paper of 40 g / m ^2. The intermediate layer 1 was coated so as to have a concentration of 0.5 g / m ² . Preparation of mid layer 2 Ansilex (oil absorption 80 ml / 100 g according to JIS K5101 method, manufactured by Engelhard, calcined kaolin) 100 parts 10% sodium hexametaphosphate 4 parts 20% MS4600 (phosphorylated starch manufactured by Nippon Shokuhin) 30 parts 48% styrene Butadiene-based copolymer latex 40 parts 2% carboxymethyl cellulose 50 parts Water 90 parts by stirring to make a coating solution for the intermediate layer 2 and apply it on the intermediate layer 1 so that the amount of smear is 5.0 g / m ² A laminated intermediate layer composed of was obtained.

Preparation of Coloring Layer (1) Preparation of Solution A 3-Dibutylamino-6-methyl-7-anilinofluorane 35 parts 5% PVA 105 parts Solution A was used with Dynomill (manufactured by Shinmaru Enterprises). It was pulverized to a volume average diameter of 0.5 μm. (2) Preparation of Solution B Bisphenol A 40 parts 2-Benzyloxynaphthalene 55 parts 5% PVA 100 parts 40% Zinc stearate emulsion 20 parts Solution B was used with Dynomill (manufactured by Shinmaru Enterprises Co., Ltd.) to obtain a volume average diameter of 1. It was crushed to 1 μm. (3) Preparation of solution C Light calcium carbonate 35 parts 10% Sodium hexametaphosphate 3.5 parts Water 63 parts A, B and C solutions are mixed, and further 10% PVA solution is made to be 20% of the total solids. To prepare a coating solution for the color forming layer.

This coating solution for color forming layer was coated on the intermediate layer obtained by sequentially laminating the two layers described above so that the amount of smear was 3 g / m ^{2, and} was calendered with a calender to give Beck smoothness of 550 to 650 seconds. A recording sheet was obtained.

Example 2 A thermosensitive recording sheet was obtained in the same manner as in Example 1, except that the 2-benzyloxynaphthalene of the solution B was replaced by bis (P-methylbenzyl oxalate).

Example 3 A thermosensitive recording sheet was obtained in the same manner as in Example 2, except that the amount of the microfibrous cellulose suspension in the intermediate layer 1 was changed to 50 parts.

Example 4 A thermosensitive recording sheet was obtained in the same manner as in Example 2, except that the amount of the microfibrous cellulose suspension in the intermediate layer 1 was changed to 500 parts.

Example 5 A thermosensitive recording sheet was obtained in the same manner as in Example 1 except that hydroxyethyl cellulose was used as the intermediate layer 2 for carboxymethyl cellulose.

Comparative Example 1 A thermosensitive recording sheet was obtained in the same manner as in Example 1 except that the carboxymethyl cellulose of the intermediate layer 2 was omitted.

Comparative Example 2 A thermosensitive recording sheet was obtained in the same manner except that the fine fibrous cellulose suspension of the intermediate layer 1 of Example 1 was omitted.

Comparative Example 3 A thermosensitive recording sheet was obtained in the same manner as in Example 1 except that the fine fibrous cellulose of the intermediate layer 1 and the carboxymethyl cellulose of the intermediate layer 2 were removed.

Comparative Example 4 A thermosensitive recording sheet was obtained in the same manner as in Example 1 except that the amount of carboxymethyl cellulose in the intermediate layer 2 was changed to 300 parts.

Next, the heat-sensitive recording sheets of Examples 1 to 5 and Comparative Examples 1 to 4 were evaluated for print density, amount of dust adherence and print quality, and the results are shown in Table 1.

[0034]

[Table 1]

The print density was 10 ms / Li using a test machine manufactured by Okura Electric Co., Ltd. with a head having a head resistance of 2816Ω.
It was printed at an energy of 0.2 w / dot with ne and evaluated at a pulse width of 1.2 ms. The print density was measured with a Macbeth densitometer, and the higher the value, the higher the density, and the better.

A dust adhesion tester was a facsimile UF-32 manufactured by Matsushita Electric Industrial Co., Ltd., and the amount of dust adhered to the thermal head after 30 m printing was visually evaluated. O indicates a level at which there is almost no residue of dust, Δ indicates a level at which there is some residue of dust, but there is no practical problem, and X indicates a level at which there is a lot of residue of dust and there is a problem in practical use.

The dot reproducibility of the print quality was judged by printing the ruled lines in a high speed mode with a word processor WD-A560 manufactured by Sharp Corporation and visually observing the frequency of the breaks in the ruled lines. ◯ is good with almost no discontinuity, Δ is a little but practically no problem, and a lot of X are bad impression.

[0038]

As is apparent from the examples, the heat-sensitive recording sheet obtained in the present invention has high sensitivity, a small amount of dust attached, and excellent print quality.

Claims (2)

[Claims] 1. An intermediate layer mainly composed of an inorganic pigment having an oil absorption of 50 ml / 100 g or more according to JIS K5101 method and a binder is provided on a support, and an electron-donating colorless or pale dye is further provided on the intermediate layer. In a heat-sensitive recording sheet provided with a color-developing layer containing an electron-accepting compound and a binder as a main component for coloring the dye by heating, the intermediate layer has two or more layers, and the uppermost layer is carboxymethyl cellulose and / or hydroxyethyl cellulose. Is contained in the uppermost layer of the intermediate layer in an amount of 0.3% to 3% by weight, and the lowermost layer contains fine fibrous cellulose. 2. The heat-sensitive recording sheet according to claim 1, wherein the pigment in the lowermost layer contains 1 to 10% by weight of microfibrous cellulose.