JPH0647311B2 - Thermal recording material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material in which a heat-sensitive color forming layer is provided on a support having an undercoat layer.

(Prior Art) Regarding thermal recording, many methods have been known for a long time. For example, a heat-sensitive recording material using an electron-donating dye precursor and an electron-accepting compound is disclosed in JP-B-45-14039.
It is disclosed in Japanese Examined Patent Publication No. 43-4160. A heat-sensitive recording material containing a diazo compound is disclosed in Japanese Patent Application No. 59-19.
0886 and the like. In recent years, these thermal recording systems have been applied to various fields such as facsimiles, printers and labels, and their needs are expanding. Along with that, conventionally,
Undesired characteristics have come to be required for thermal recording. One of them is the reproducibility of printing dots. Generally, thermal recording paper is printed by heating it with a minute heating element of about 100 μm × 200 μm called a thermal head. At this time, it is possible to faithfully reproduce the shape of the minute heating element as a color-developing material, which leads to high printing quality. I have come to realize that it is important to get. This is called printing dot reproducibility.

(Object of the Invention) It is an object of the present invention to provide a thermal recording material of high print quality with good dot reproducibility.

(Structure of the Invention) An object of the present invention is to provide a thermosensitive coloring layer on an undercoat layer on a support which is provided with an undercoat layer containing a pigment and a binder as main components and containing 1 to 10% by weight of wax. It was achieved by a heat-sensitive recording material characterized by: As a similar attempt, an example of adding wax to the undercoat layer is disclosed in Japanese Patent Laid-Open No. Sho 5
No. 9-204594, the present inventors have found that when the wax amount of the undercoat layer is 1% by weight or more and 10% by weight or less with respect to the pigment amount of the undercoat layer, a heat-sensitive recording material having a good dot reproducibility is obtained. I found that I could get it. Curiously, no such effect is seen in areas below 1 weight percent and above 10 weight percent. In particular, if it exceeds 20% by weight, the dot reproducibility is deteriorated.

Examples of waxes that can be used in the undercoat layer of the present invention include:
Polyethylene wax, carnauba wax, paraffin wax, microcrystalline wax, candinal wax, montan wax, fatty acid amide and the like can be mentioned. These have a melting point of 40 ° C. or higher and 120 ° C. or lower, preferably 50 ° C. or higher and 100 ° C. or lower.
As the pigment that can be used in the undercoat layer of the present invention, all the general organic or inorganic pigments can be used, but especially JIS-
It is preferable that the oil absorption defined by K5101 is 40 CC / 100 g or more, specifically calcium carbonate, barium sulfate, titanium oxide, talc, wax, kaolin, calcined kaolin, aluminum hydroxide, amorphous silica, urea. Formalin resin powder, polyethylene resin powder and the like can be mentioned.

Examples of the binder used in the undercoat layer include a water-soluble polymer and a water-insoluble binder, and the binder may be used alone or in combination of two or more.

As the water-soluble polymer, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, starches, gelatin, gum arabic, casein, styrene-maleic anhydride copolymer hydrolyzate, ethylene-maleic anhydride copolymer hydrolyzate, isobutylene -Maleic anhydride copolymer hydrolyzate, polyvinyl alcohol,
Examples thereof include carboxy-modified polyvinyl alcohol and polyacrylamide.

As the water-insoluble binder, synthetic rubber latex or synthetic resin emulsion is generally used, and examples thereof include styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex, and vinyl acetate emulsion. .

The amount of the binder used is 3 to 100%, preferably 5 to 50% with respect to the pigment. An anti-decoloring agent, a surfactant, etc. may be further added to the undercoat layer.

Next, a method for producing a typical thermal recording material of the present invention will be described. As an example, an electron donating dye precursor (hereinafter, color former),
In a system using an electron-accepting compound (hereinafter referred to as a developer), a color-forming agent and a color-developing agent are separately dispersed to several microns or less by a ball mill, a sand mill or the like, and mixed to obtain a heat-sensitive coating liquid.

The color former and the color developer are generally dispersed together with an aqueous solution of a water-soluble polymer such as polyvinyl alcohol, and if necessary, a sensitizer can also be dispersed and added. The sensitizer may be added to either or both of the color former and the developer, and may be dispersed at the same time.

Examples of the color former used in the present invention include triarylmethane compounds, diphenylmethane compounds, xanthene compounds, thiazine compounds, spiropyran compounds, and the like. Examples of some of these include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (ie, crystal violet letolactone),
3,3-bis (p-dimethylaminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3- (1,
3-dimethylindol-3-yl) phthalide, 3-
There are (p-dimethylaminophenyl) -3- (2-methylindol-3-yl) phthalide and the like, and diphenylmethane compounds include 4,4′-bis-dimethylaminobenzhydrin benzyl ether and N-halophenyl. -Leuco auramine, N-2,4,5-trichlorophenyl leuco auramine and the like, and xanthene compounds include rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine B (p
-Chloroanilino) lactam, 2-dibenzylamino-
6-diethylaminofluorane, 2-anilino-6-diethylaminofluorane, 2-anilino-3-methyl-
6-diethylaminofluorane, 2-anilino-3-methyl-6-N-cyclohexyl-N-methylaminofluorane, 2-anilino-3-methyl-6-N-ethyl-
N-isoamylaminofluorane, 2-o-chloroanilino-6-diethylaminofluorane, 2-m-chloroanilino-6-diethylaminofluorane, 2- (3.
4-dichloroanilino) -6-diethylaminofluorane, 2-octylamino-6-diethylaminofluorane, 2-dihexylamino-6-diethylaminofluorane, 2-m-trichloromethylanilino-6-diethylaminofluorane, 2-butylamino-3-chloro-
6-diethylaminofluorane, 2-ethoxyethylamino-3-chloro-6-diethylaminofluorane, 2
-Anilino-3-chloro-6-diethylaminofluorane, 2-diphenylamino-6-diethylaminofluorane, 2-anilino-3-methyl-6-diphenylaminofluorane, 2-anilino-3-methyl-5-chloro- 6-diethylaminofluorane, 2-anilino-3-
Methyl-6-diethylamino-7-ethylfluorane,
2-anilino-3-methoxy-6-dibutylaminofluorane, 2-o-chloroanilino-6-dibutylaminofluorane, 2-p-chloroanilino-3-ethoxy-
6-diethylaminofluorane, 2-phenyl-6-diethylaminofluorane, 2-o-chloroanilino-6
-P-Butylanilinofluorane, 2-anilino-3-
Pentadecyl-6-diethylaminofluorane, 2-anilino-3-ethyl-6-dibutylaminofluorane,
2-anilino-3-ethyl-6-N-ethyl-N-isoisylaminofluorane, 2-anilino-3-ethyl-
6-N-ethyl-N-γ-methoxypropylaminofluorane, 2-anilino-3-phenyl-6-diethylaminofluorane, 2-diethylamino-3-phenyl-
6-diethylaminofluorane, 2-anilino-3-methyl-6-N-isoamyl-N-ethylaminofluorane, and the like, and thiazine-based compounds include benzoyl leuco methylene blue, p-nitrobenzyl leuco methylene blue, and spiro. Examples of the compound include 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3,3'-dichloro-spiro-dinaphthopyran, 3-benzylspiro-dinaphthopyran, 3-methyl-naphtho- (3-methoxy- Benzo) -spiropyran, 3-propyl-spiro-dibenzopyran and the like.
These are used alone or in combination in order to adjust the hue or improve the image storability.

The color developer used in the present invention includes 2,2-bis (4 '
-Hydroxyphenyl) propane (bisphenol A), 2,2-bis (4-hydroxyphenyl) pentane, 2,2-bis (4'-hydroxy-3 ', 5'-dichlorophenyl) propane, 1 , 1-bis (4'-hydroxyphenyl) cyclohexane, 2,2-bis (4 '
-Hydroxyphenyl) hexane, 1,1-bis (4 '
-Hydroxyphenyl) propane, 1,1-bis (4 '
-Hydroxyphenyl) butane, 1,1-bis (4'-
Hydroxyphenyl) pentane, 1,1-bis (4'-
Hydroxyphenyl) hexane, 1,1-bis (4'-
Hydroxyphenyl) heptane, 1,1-bis (4'-
Hydroxyphenyl) octane, 1,1-bis (4'-
Hydroxyphenyl) -2-methyl-pentane, 1,1
-Bis (4-hydroxyphenyl) -2-ethyl-hexane, bisphenols of 1,1-bis (4'-hydroxyphenyl) dodecane, 3,5-di-α-methylbenzylsalicylic acid, 3,5 −
Salicylic acids such as di-tertiarybutylsalicylic acid and 3-α, α-dimethylbenzylsalicylic acid or polyvalent metal salts thereof (particularly zinc and aluminum are preferred), p-hydroxybenzoic acid benzyl ester, p-hydroxylbenzoic acid-2 Examples thereof include oxybenzoic acid esters such as ethylhexyl ester, phenols such as p-phenylphenol, 3,5-diphenylphenol, cumylphenol, and bisphenols are particularly preferable.

Examples of the sensitizer include organic compounds having a melting point of 70 ° C or higher and 150 ° C or lower. Specific examples of the compound include compounds represented by the following general formulas (I) to (IV).

In the formula, R _{1 to} R ₄ each represent a phenyl group, a benzyl group, and a lower alkyl or halogen or hydroxy or alkoxy substitution product thereof, and R ₅ and R ₆ each represent an alkyl group having 12 to 24 carbon atoms. , R ₇
Represents hydrogen or a phenyl group.

When the phenyl group or benzyl group represented by R ₁ to R ₄ in the general formulas (II) to (III) is substituted with a lower alkyl group, the carbon number thereof is 1 or more and 8 or less, preferably 1 or more. It is 3 or less. Also, when substituted with halogen, preferred is chlorine or fluorine.

In the formula, R ₈ represents a divalent group, preferably an alkylene group, an alkylene group having an ether bond, an alkylene group having a carbonyl group, an alkylene group having a halogen atom,
An alkylene group having an unsaturated bond, more preferably an alkylene group, or an alkylene group having an ether bond is shown.
A and B represent O or S, and A and B may be the same or different. Further, X, Y, Z, X ', Y', and Z'may be the same or different, and a hydrogen atom, an alkyl group, a lower alkoxy group, a lower aralkyl group, a halogen atom, an alkyloxycarbonyl group, an aralkyloxy group. Indicates a carbonyl group.

Specifically, benzyl p-benzyloxybenzoate, β
-Naphthylbenzyl ether, β-naphthoic acid phenyl ester, 1-hydroxy-2-naphthoic acid phenyl ester, β-naphthol (p-chlorobenzyl) ether, β-naphthol (p-methylbenzyl) ether,
α-naphthylbenzyl ether, 1,4-butanediol-p-methylphenyl ether, 1,4-butanediol-p-methylphenyl ether, 1,4-butanediol-p-isopropylphenyl ether, 1, 4-
Butanediol-pt-octylphenyl ether,
2-phenoxy-1-p-tolyl-oxy-ethane, 1
-Phenoxy-2- (4-ethylphenoxy) ethane,
1-phenoxy-2- (4-chlorophenoxy) ethane, 1,4-butanediol diphenyl ether,
(4,4′-methoxyphenylthio) ethane and the like can be mentioned.

The heat fusible substances may be used alone or as a mixture.

Examples of the binder, pigment and wax include the water-soluble polymer, water-insoluble binder, pigment and wax exemplified as the binder for the undercoat layer.

As the metal soap, higher fatty acid metal salts are used, such as zinc stearate, calcium stearate, and aluminum stearate.

If necessary, an antioxidant, a UV absorber, an image storability improver, etc. may be added thereto.

Examples of the image storability improver include phenols or derivatives thereof in which at least one of 2- or 6-positions is substituted with an alkyl group, and among them, at least one of 2- or 6-positions is substituted with a branched alkyl group. Preferred are phenols and their derivatives. Further, those having a plurality of phenol groups in the molecule are preferable, and those having 2 to 3 phenol groups are particularly preferable.

(Examples of the Invention) Examples are shown below, but the present invention is not limited thereto. Each heat-sensitive recording material was coated with a heat-sensitive coating liquid on each support with a wire bar so that the dry coating amount was 6 g / m ^2.
Obtained by drying in an oven at 0 ° C.

(Preparation of heat-sensitive coating liquid) 2-anilino-3-methyl-N-methyl-
20 g each of N-cyclohexylaminofluorane, bisphenol A as a color developer, and β-naphthylbenzyl ether as a sensitizer were dispersed in a ball mill for 24 hours together with 100 g of an aqueous solution of 5% polyvinyl alcohol (Kuraray PVA-105) to obtain a volume average. The particle size was 3 μm or less.
Calcium carbonate as a pigment (Unibur70 Shiraishi Industry)
80 g were dispersed in a homogenizer together with 160 g of a 0.5% sodium hexametaphosphate solution and used. Each dispersion liquid prepared as described above was treated with 2-anilino-3-
5 g of methyl-6-N-methyl-N-cyclohexylaminofluorane dispersion, 10 g of bisphenol A dispersion,
It was obtained by mixing 10 g of the β-naphthylbenzyl ether dispersion liquid and 15 g of the calcium carbonate dispersion liquid and further adding 3 g of 21% zinc stearate emulsion.

(Example 1) A method for preparing a base paper for undercoating will be described below. Using calcined kaolin (Ansilex90 Engelhard Co.) as a pigment, 8
0 g was dispersed by a homogenizer together with 160 g of a 0.5% sodium hexametaphosphate solution. To 60 g of this dispersion, 8 g of 48% styrene-butadiene latex (manufactured by Sumitomo Nogataku Co., Ltd.) and 3 g of 30% paraffin wax dispersion (Hidrin P-7, manufactured by Chukyo Yushi Co., Ltd.) were respectively added to obtain a coating liquid having a basis weight of 50 g / 6 g / m ² of dry coating amount on high-quality paper of m ²
A wire bar was applied to give m ² and dried in an oven at 50 ° C. to obtain an undercoat base paper. The heat-sensitive coating liquid was applied to this undercoat paper to obtain a heat-sensitive recording material.

(Example 2) An undercoat base paper was prepared by changing the amount of the Paraffin wax dispersion used in Example 1 to 6 g to obtain a heat-sensitive recording material.

(Example 3) Instead of the paraffin wax dispersion of Example 1, 1.8 g of 50% microcrystalline wax dispersion (Cellosol 967 manufactured by Chukyo Yushi Co., Ltd.) was used to prepare an undercoat base paper to obtain a heat-sensitive recording material.

Comparative Example 1 A base paper for undercoating was prepared without adding the paraffin wax dispersion of Example 1 to obtain a heat-sensitive recording material.

(Comparative Example 2) A thermal recording material was obtained by preparing an undercoat base paper by changing the amount of the Paraffin wax dispersion used in Example 1 to 12 g.

(Comparative Example 3) An undercoated base paper was prepared by changing the amount of the Paraffin wax dispersion used in Example 1 to 24 g to obtain a heat-sensitive recording material.

Color density is 30m with Kyocera printing tester
It was printed at J / mm ² and the color density was measured with a Macbeth densitometer.

Dot reproducibility is printing energy 2 with a Kyocera printing tester.
Dots were printed at 5 mJ / mm ² and the area of 40 dots was obtained using an image analyzer. The standard deviation of the areas divided by the average value was used as the value of dot reproducibility. The smaller this value, the better the dot reproducibility.

The above results are shown in Table 1.

Claims (1)

[Claims] 1. A thermosensitive color-forming layer is provided on an undercoat layer on a support comprising a pigment and a binder as main components and an undercoat layer containing 1 to 10% by weight of wax for the pigment. Thermal recording material