JPH04314590A - Thermosensitive recording material - Google Patents

Abstract

PURPOSE:To improve a dot reproducibility and color forming properties to obtain a high-quality recording in a thermosensitive recording material provided with a color forming layer containing an electron donative colorless dye and an electron accepting compound. CONSTITUTION:In a thermal recording material in which an undercoat layer mainly composed of a pigment and a binder is provided on a substrate, and a thermal color-forming layer is provided on said undercoat layer, a thermal recording material incorporating a styrene resin compound in said undercoat layer.

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 material, and more particularly to a heat-sensitive recording material having a heat-sensitive coloring layer and an undercoat layer.

0002

2. Description of the Related Art Regarding thermal recording, many methods have been known for a long time. For example, heat-sensitive recording materials using electron-donating dye precursors and electron-accepting compounds are
14039, Japanese Patent Publication No. 43-4160, etc. Further, heat-sensitive recording materials using diazo compounds are disclosed in Japanese Patent Application Laid-Open No. 190886/1986. In recent years, these thermal recording systems have been widely used in fax machines, printers,
It is used in many fields such as labels, medical image output, and prepaid cards, and needs are expanding.

[0003] Along with this, new characteristics have come to be required for thermosensitive recording. One of them is the reproducibility of printed dots. Generally, thermal recording is 100 microns x 2
This is done by heating the heat-sensitive recording material to develop color using a thermal head, which is an assembly of minute heating elements with a size of about 0.00 microns. Therefore, in order to perform high-quality recording without blurring or bleeding, it is important that the colored portion after heating faithfully reproduce the shape of the micro heating element. This is called print dot reproducibility.

Conventionally, in order to improve dot reproducibility,
Countermeasures such as smoothing the support with an undercoat layer and (2) providing the undercoat with heat insulation properties have been considered effective. The method includes incorporating hydrophobic polymer particles, which have lower thermal conductivity than general inorganic pigments, into the undercoat layer (disclosed in JP-A-59-204595, JP-A-60-2397, etc.); In order to add air insulation, hollow fine particles are included in the undercoat layer (Japanese Patent Application Laid-open No. 171685/1985,
It has been proposed to provide an undercoat layer consisting of a highly oil-absorbing pigment and hydrophobic polymer particles (as disclosed in JP-A No. 61-89883, etc.).

However, at present, these methods do not provide sufficient dot reproducibility.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-quality heat-sensitive recording material with good print dot reproducibility.

[0007]

[Means for Solving the Problems] An object of the present invention is to provide a heat-sensitive recording material in which an undercoat layer containing a pigment and a binder as main components is provided on a support, and a heat-sensitive coloring layer is provided on the undercoat layer. This was achieved using a heat-sensitive recording material characterized by containing a styrene resin compound in its layer.

[0008] As the pigment that can be used in the undercoat layer of the present invention, all general organic or inorganic pigments can be used, but in particular, pigments with an oil absorption of 40 cc as specified by JIS-K5101 can be used.
/100g or more, and specific examples include calcium carbonate, barium sulfate, titanium oxide, talc, waxite, kaolin, calcined kaolin, aluminum hydroxide, amorphous silica, urea-formalin resin powder, polyethylene resin powder, etc. can be mentioned. These may be used alone or in combination.

[0009] The binder used in the undercoat layer is as follows:
Examples include water-soluble polymers and water-insoluble binders, which may be used alone or in combination of two or more.

Examples of water-soluble polymers include methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, starches, gelatin, gum arabic, casein, styrene-maleic anhydride copolymer hydrolyzate, and ethylene-maleic anhydride copolymer hydrolyzate. Examples include polyvinyl alcohol, isobutylene-maleic anhydride copolymer hydrolyzate, polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and polyacrylamide.

As the water-insoluble binder, synthetic rubber latex or synthetic resin emulsion is generally used, such as styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-
Examples include butadiene rubber latex and vinyl acetate emulsion. The amount of binder used is 3 to 100% by weight, preferably 5 to 5% by weight, based on the pigment contained in the undercoat layer.
It is 0% by weight.

The styrenic resin compound that can be used in the present invention is one that is generally used as a sizing agent for paper manufacturing and a paper strength enhancer. Depending on the modification method, both cationic and anionic types exist, and either can be used in the present invention. The amount of the styrene resin compound used is 0.2 to 20% by weight, preferably 0.5 to 5% by weight, based on the pigment contained in the undercoat layer.

The undercoat layer coating liquid of the present invention is obtained by mixing a binder and a styrene resin compound with the pigment dispersion. Furthermore, a mold release agent, a waterproofing agent, a surfactant, aluminum sulfate, etc. may be added as necessary. The obtained undercoat layer coating liquid is applied onto a support using a device such as a bar coater, an air knife coater, a blade coater, etc., and dried to obtain the undercoat layer of the present invention. The dry coating amount of the undercoat layer is preferably 1 to 20 g/m2, more preferably 5 g/m2.
~15g/m2. After applying the undercoat layer, calendering may be performed as necessary.

Next, a typical thermosensitive color forming layer of the present invention will be described. As an example, a heat-sensitive color forming layer using an electron-donating dye precursor (hereinafter referred to as a color former) and an electron-accepting compound (hereinafter referred to as a color developer) will be described. coloring agent,
The color developer is dispersed separately, generally together with an aqueous solution of a water-soluble polymer such as polyvinyl alcohol, to a size of several microns or less using a ball mill, sand mill, or the like. These dispersions are mixed after dispersion, and oil-absorbing pigments, binders, waxes, metal soaps, antioxidants, ultraviolet absorbers, surfactants, antistatic agents, etc. are added as necessary to form a heat-sensitive coloring layer coating solution. shall be.

The heat-sensitive recording material of the present invention is obtained by coating the heat-sensitive coloring layer coating solution obtained by the above method on the above-mentioned undercoat layer,
Obtained by drying. At this time, smoothness may be imparted by calendering if necessary.

Examples of color formers used in the present invention include triphenylmethane phthalide compounds, fluoran compounds, phenothiazine compounds, indolyl phthalide compounds, leucoauramine compounds, rhodamine lactam compounds, and triphenylmethane phthalide compounds. There are various compounds such as phenylmethane compounds, triazene compounds, spiropyran compounds, and fluorene compounds. Specific examples of phthalides are U.S. Reissue Patent Specification No. 23,024, U.S. Patent Specification No. 3,
No. 491,111, No. 3,491,112, No. 3
, No. 491,116 and No. 3,509,174,
Specific examples of fluorans are given in U.S. Patent No. 3,624,
No. 107, No. 3,627,787, No. 3,641
, No. 011, No. 3,462,828, No. 3,68
No. 1,390, No. 3,920,510, No. 3,9
No. 59,571, specific examples of spirodipyrans are given in U.S. Patent No. 3,971,808, and pyridine and pyrazine compounds are given in U.S. Patent No. 3,775,424.
No. 3,853,869, No. 4,246,31
No. 8, specific examples of fluorene compounds are given in Japanese Patent Application No. 61-24.
No. 0989, etc. Among these, 2-arylamino-3-H, halogen-, alkyl-, or alkoxy-6-substituted aminofluorane which produces black color is particularly effective. Specific examples include 2-anilino-3-methyl-6-
Diethylaminofluorane, 2-anilino-3-methyl-6-N-cyclohexyl-N-methylaminofluorane, 2-p-chloroanilino-3-methyl-6-dibutylaminofluorane, 2-anilino-3-methyl- 6-
Dioctylaminofluorane, 2-anilino-3-chloro-6-diethylaminofluorane, 2-anilino-3
-Methyl-6-N-ethyl-N-isoamylaminofluorane, 2-anilino-3-methyl-6-N-ethyl-
N-dodecylaminofluorane, 2-anilino-3-methoxy-6-dibutylaminofluorane, 2-o-chloroanilino-6-dibutylaminofluorane, 2-p-
Chloroanilino-3-ethyl-6-N-ethyl-N-isoamylaminofluorane, 2-o-chloroanilino-
6-p-butylanilinofluorane, 2-anilino-3
-pentadecyl-6-diethylaminofluorane, 2-
Anilino-3-ethyl-6-dibutylaminofluorane, 2-o-toluidino-3-methyl-6-diisopropylaminofluorane, 2-anilino-3-methyl-6-
N-isobutyl-N-ethylaminofluorane, 2-anilino-3-methyl-6-N-ethyl-N-tetrahydrofurfurylaminofluorane, 2-anilino-3-chloro-6-N-ethyl-N- Isoamylaminofluorane, 2-anilino-3-methyl-6-N-methyl-N-
γ-Ethoxypropylaminofluorane, 2-anilino-3-methyl-6-N-ethyl-N-γ-ethoxypropylaminofluorane, 2-anilino-3-methyl-6
-N-ethyl-N-γ-propoxypropylaminofluorane and the like.

Examples of the color developer used in the present invention include 2
, 2-bis(4'-hydroxyphenyl)propane (common name 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'-hydroxy) phenyl)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, 1,1-bis(4'-hydroxyphenyl) Dodecane, 1,4-bis(p-hydroxyphenylcumyl)benzene, 1,3-bis(p-
hydroxyphenylcumyl)benzene, bis(p-hydroxyphenyl)sulfone, bis(3-allyl-4-
Bisphenols such as hydroxyphenyl) sulfone, bis(p-hydroxyphenyl)acetic acid benzyl ester, 3,5-di-α-methylbenzyl salicylic acid, 3,
5-di-tert-butylsalicylic acid, 3-α-α-
Salicylic acid derivatives such as dimethylbenzyl salicylic acid and 4-(β-p-methoxyphenoxyethoxy) salicylic acid, or polyvalent metal salts thereof (particularly preferred are zinc and aluminum), benzyl erther p-hydroxybenzoate,
Oxybenzoic acid esters such as p-hydroxybenzoic acid-2-ethylhexyl ester and β-resorcinic acid-(2-phenoxyethyl) ester, p-phenylphenol, 3,5-diphenylphenol, cumylphenol, 4-hydroxy Examples include phenols such as -4'-isopropoxy-diphenylsulfone and 4-hydroxy-4'-phenoxy-diphenylsulfone. Among these, bisphenols are particularly preferred for the purpose of improving dot reproducibility. The color developer is preferably used in an amount of 50 to 800% by weight, more preferably 100% by weight of the color former.
~500% by weight. Further, two or more of the above electron-accepting compounds may be used in combination.

Further, the heat-sensitive recording material of the present invention contains a thermofusible substance (hereinafter referred to as a sensitizer) in any layer constituting the heat-sensitive recording material in order to improve thermal responsiveness. Good too. Examples of sensitizers include benzyl p-benzyloxybenzoate, β-naphthyl-benzyl ether, stearamide, stearyl urea, p-benzylbiphenyl, di(2-methylphenoxy)ethane, di(2-methoxy) phenoxy)ethane, β-naphthol-(p-methylbenzyl) ether, α-naphthyl-benzyl ether, 1,4-butanediol-p-methylphenyl ether, 1,4-butanediol-p-isopropylphenyl ether, 1 , 4-butanediol-p-tertiary octylphenyl ether, 1-phenoxy-2-
(4-ethylphenoxy)ethane, 1-phenoxy-2
-(4-Chlorphenoxy)ethane, 1,4-butanediol phenyl ether, diethylene glycol-bis-(4-methoxyphenyl) ether, 4-ethoxyphenyl-p-chlorobenzyl ether, 1(4-methoxy-phenoxy)- 2-phenoxy-propane, 1,3
-bis-(4-methoxyphenoxy)propane, 3-methyl-4-chlorophenyl-p-methoxybenzyl ether, 3,5-dimethyl-4-chlorophenyl-p-methoxybenzyl ether, 4-chlorophenyl-p- Examples include methoxybenzyl ether, 1-phenoxy-2(4-methoxy-phenoxy)-propane, oxalic acid dibenzyl ester, oxalic acid di(p-methylbenzyl) ester, and the like. These sensitizers may be used alone or in combination. In order to obtain sufficient thermal responsiveness, it is preferably used in an amount of 10 to 200% by weight, more preferably 20 to 150% by weight, based on the color developer. The sensitizer can be added to either the color former, the color developer, or both and dispersed at the same time, or a thermal eutectic with the color former or color developer can be prepared in advance, cooled, and then dispersed. good.

The binder is preferably a compound that dissolves at least 5% by weight in water at 25°C.
Polyvinyl alcohol (including modified polyvinyl alcohols such as carboxy-modified, itaconic acid-modified, maleic acid-modified, silica-modified, etc.), methylcellulose, carboxymethylcellulose, starches (including modified starch), gelatin, gum arabic, casein, styrene-maleic anhydride Examples include acid copolymer hydrolysates, polyacrylamide, and saponified vinyl acetate-polyacrylic acid copolymers. These binders are used not only for dispersion but also for the purpose of improving coating film strength. For this purpose, styrene-butadiene copolymers, vinyl acetate copolymers,
Synthetic polymer latex binders such as acrylonitrile/butadiene copolymer, methyl acrylate/butadiene copolymer, and polyvinylidene chloride can also be used together. In addition, a suitable crosslinking agent for the binder may be added depending on the type of binder, if necessary.

Examples of pigments include calcium carbonate, barium sulfate, lithopone, rosite, kaolin, silica, and amorphous silica. As the metal soap, higher fatty acid metal salts are used, such as zinc stearate, zinc myristate, calcium stearate, and aluminum stearate.

Examples of wax include montan wax, paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, and the like.

[0022] Furthermore, a protective layer may be provided on the heat-sensitive coloring layer, if necessary. As the protective layer, any one known as a protective layer for heat-sensitive recording materials can be used. Furthermore, if necessary, a back coat layer may be provided on the opposite side of the support of the heat-sensitive recording material from the heat-sensitive coloring layer. As the back coat layer, any material known as a back coat layer for heat-sensitive recording materials can be used. The present invention will be specifically explained below with reference to Examples.
The present invention is not limited to the following examples.

[0023] The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to the following Examples.

[0024]

【Example】

(Preparation of heat-sensitive coating liquid) As a coloring agent, 2-anilino-3-
Methyl-6-N-dibutyl-aminofluorane, bisphenol A as a color developer, β-naphthyl- as a sensitizer
20 g of each benzyl ether was dispersed with 100 g of a 5% polyvinyl alcohol (Kuraray PVA-105) aqueous solution in a ball mill overnight to obtain an average particle size of 1.5 μm or less to obtain each dispersion. In addition, calcium carbonate 80
g was dispersed in a homogenizer together with 160 g of a 0.5% sodium hexametaphosphate solution to obtain a pigment dispersion. Each dispersion prepared as above was mixed with 5 g of color former dispersion, 10 g of color developer dispersion, 10 g of sensitizer dispersion, and 5 g of calcium carbonate dispersion, and then a 21% zinc stearate emulsion was added. 3 g was added to obtain a heat-sensitive coating liquid.

(Example 1) The method for preparing the base paper for undercoat is shown below. As the pigment, 80 g of calcined kaolin (manufactured by Engelhard, Ancirex-90) was dispersed with 160 g of a 0.5% aqueous solution of sodium hexametaphosphate using a homogenizer. 48% styrene was added to 60g of this dispersion.
Butadiene latex (manufactured by Sumitomo Naugatuck) 8g,
A coating liquid obtained by adding 4.5 g of a 20% cationic styrene resin compound (Polymaron 360 manufactured by Arakawa Chemical Co., Ltd.) was applied to a high-quality paper with a basis weight of 50 g/m2 in a dry coating amount of 8 g.
/m2 using a wire bar and dried in an oven at 50°C to obtain an undercoat base paper. The above heat-sensitive coating liquid was applied to this undercoat paper using a wire bar to a dry coating amount of 6 g/m2, and dried in an oven at 50°C.
A heat-sensitive recording material of the present invention was obtained.

(Example-2) Cationic styrenic resin compound of Example-1 (Polymaron 360 manufactured by Arakawa Chemical Co., Ltd.)
A heat-sensitive recording material was obtained in the same manner except that 4.5 g of a 20% cationic styrenic resin compound (N-PPS, manufactured by Arakawa Chemical Co., Ltd.) was used instead of the undercoat coating solution.

(Example 3) Cationic styrenic resin compound of Example 1 (Polymaron 360 manufactured by Arakawa Chemical Co., Ltd.)
A heat-sensitive recording material was obtained in the same manner, except that 4.5 g of a 20% anionic styrenic resin compound (Polymaron 1308, manufactured by Arakawa Chemical Co., Ltd.) was used to prepare the undercoating liquid instead of using .

(Comparative Example-1) Cationic styrenic resin compound of Example-1 (Polymaron 360 manufactured by Arakawa Chemical Co., Ltd.)
A heat-sensitive recording material was obtained in the same manner except that the undercoating liquid was not used.

(Comparative Example-2) Cationic styrenic resin compound of Example-1 (Polymaron 360 manufactured by Arakawa Chemical Co., Ltd.)
A heat-sensitive recording material was obtained in the same manner, except that 3 g of a 30% paraffin wax dispersion (Hidrin P-7, manufactured by Chukyo Yushi Co., Ltd.) was used to prepare the undercoating liquid instead of using .

(Comparative Example-3) Cationic styrenic resin compound of Example-1 (Polymaron 360 manufactured by Arakawa Chemical Co., Ltd.)
Instead of using β-
A heat-sensitive recording material was obtained in the same manner except that 6 g of the naphthyl benzyl ether dispersion was used to prepare the undercoating liquid.

(Comparative Example 4) A heat-sensitive recording material was obtained by directly coating a heat-sensitive coloring layer on a high-quality paper having a basis weight of 50 g/m 2 .

The heat-sensitive recording material obtained as described above was surface-treated with a calender and the smoothness was adjusted to Bekk smoothness of 400±50 seconds to obtain a heat-sensitive recording material.

Dot reproducibility was determined by printing dots using a Kyocera printing tester with a printing energy of 15 mJ/mm2, using an image analysis device to determine the area of each of the 40 dots, and calculating the (standard deviation ÷ average value) of the area for dot reproduction. The value was taken as the gender value. The smaller this value is, the better the dot reproducibility is.

The color density was determined using a Kyocera printing tester with a printing energy of 20 mJ while using a pressure roll.
/mm2, and the color density was measured using a Macbeth reflection densitometer.

[0035]

【Effect of the invention】

[Table 1]

From the results in Table 1, it can be seen that the recording material of the present invention has excellent dot reproducibility, high recording sensitivity, and extremely high quality printing can be obtained.

Claims (1)

[Claims] Claim 1: A heat-sensitive recording material comprising an undercoat layer containing a pigment and a binder as main components on a support, and a heat-sensitive coloring layer provided on the undercoat layer, wherein the undercoat layer contains a styrene resin compound. A heat-sensitive recording material characterized by: