JPH05318911A - Thermal recording material - Google Patents

Abstract

PURPOSE:To provide a thermal recording material having high recording sensitivity and forming a recording image excellent in storage stability. CONSTITUTION:Paint for a thermal color forming layer containing a colorless or light-colored electron donating color forming dye, an electron acceptive developing compd. allowing the color forming dye to develop a color by heating and an adhesive based on an urethane emulsion is applied to a sheet like support in a ratio of 7.5g/m<2> to form the thermal color forming layer which is, in turn, dried so that the moisture thereof becomes 7% and, thereafter, calendering is applied to the thermal color forming layer under line pressure of 80kg/cm. Further, a protective layer consisting of polyvinyl alcohol, kaolin clay, glyoxal and zinc stearate is provided on the thermal color forming layer.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a thermal recording material. More specifically, it relates to a thermosensitive recording material having high recording sensitivity and excellent storage stability of recorded images.

[0002]

2. Description of the Related Art A heat-sensitive recording material generally comprises a sheet-like support, which is generally made of paper, synthetic paper, plastic film or the like, and a color-forming dye such as an electron-donating leuco dye and an electron-accepting phenolic compound. A thermosensitive color-developing layer containing such a color-developing compound and an adhesive as a main component is provided, and a color-recorded image can be obtained by reacting these color-developing dye and the color-developing agent with heat energy. it can.

On the other hand, the thermosensitive recording system is highly evaluated for its advantages that a color image can be obtained by simply heating it and that the recording apparatus can be made relatively simple and compact. , Scientific instrument, CD
It is widely used as various information recording systems such as / ATM and POS label printers.

However, the conventional heat-sensitive recording materials have a problem that when they come into contact with oil or a plasticizer, the recording density is lowered, or in the worst case, the recording is completely lost. For example, when a heat-sensitive label having a pressure-sensitive adhesive (adhesive) layer provided on the back surface of a heat-sensitive recording material is applied as a POS label to a vinyl chloride film, polypropylene film, etc., the plasticizer contained in the film causes the back surface of the label to disappear. There is a problem that the bar code or characters printed on the label cannot be read because the plasticizer migrates from the film or the film that comes into direct contact with the label surface. In addition, the thermal label attached to the film,
Even when oils such as edible oil and industrial oil come into contact with each other, there is a problem that the recorded portion disappears or becomes unreadable as in the case of the plasticizer.

To solve this problem, many proposals have been made to provide a chemical-resistant protective layer on the surface of the thermosensitive coloring layer (JP-A-48-051644, JP-A-54-128347, and JP-A-54-128347). JP-A-58-053484, JP-A-60-031996, JP-A-1-230681, and JP-A-2-274589).

However, since the protective layer is provided between the thermosensitive coloring layer and the thermal head, not only the sensitivity is lowered, but also when the water-based protective layer paint is applied onto the thermosensitive coloring layer, If the water resistance is low, it will lead to coating defects such as scratches, so it is necessary to improve the water resistance of the thermosensitive color developing layer. For this reason, a water-proofing agent or a water-resistant emulsion is added, but there is a drawback that the sensitivity is further lowered when such a means is used.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermosensitive recording material which has excellent recording sensitivity and high storability of recorded images.

[0008]

Means for Solving the Problems As a result of repeated research to achieve this object, the present inventors have found that a colorless or light-colored electron-donating color-forming dye on a sheet-like support and the color-forming dye by heating. In a heat-sensitive recording material having a thermosensitive coloring layer containing an adhesive containing, as a main component, an electron-accepting color-developing compound and a hydrophobic emulsion for coloring, and a protective layer containing a water-soluble polymer and a pigment thereon. , A thermosensitive coloring layer containing a coated hydrophobic resin emulsion having a water content of 5 to 8
%, It was found that the above-mentioned drawbacks can be solved by providing a protective layer after calendering in the range of 20 to 200 kg / cm of linear pressure, and the present invention has been completed.

As a means for improving the water resistance of the heat-sensitive color forming layer necessary for coating the protective layer, an adhesive in which a hydrophobic resin is emulsified is used, or a water-soluble resin is water-resistant with a crosslinking agent. There are two ways to do this. When water resistance is obtained with a crosslinking agent, the hydroxyl group is destroyed, so that the hydroxyl group reacts with the hydroxyl group of the color developer, resulting in extremely low sensitivity.
On the other hand, even in the case of an emulsion of a hydrophobic resin, the sensitivity tends to be lowered when added to the extent that water resistance is exhibited, so it is necessary to impart water resistance with a minimum addition amount.

Therefore, as a result of earnest research on a method for increasing the water resistance of the thermosensitive coloring layer without using a crosslinking agent, the density of the thermosensitive coloring layer was increased before the coating of the protective layer and the thermosensitive coloring layer was formed during the coating of the protective layer. As a result of examining the formulation of the thermosensitive coloring layer with the idea of preventing water penetrating into the water, the thermosensitive coloring layer contains an emulsion of a hydrophobic resin, water content of 5 to 8%, and linear pressure of 20 to 200 kg / cm. It was found that by calendering the thermosensitive coloring layer, the density increased and as a result, the water resistance was effectively improved.

According to the present invention, a solid content of 1 has been conventionally required.
The addition amount of 10 parts by weight or more of the hydrophobic resin emulsion per 100 parts by weight varies depending on the coating method and the hydrophobic resin emulsion used, but the effect on the recording sensitivity is small. It turned out that it can improve the sex.

Examples of the hydrophobic resin include alkyl polyacrylate, polyalkyl methacrylate, vinyl acetate-ethylene copolymer, vinyl acetate-alkyl methacrylate, vinyl acetate-methacrylic acid copolymer, vinyl acetate-acrylic acid copolymer. Coalesce, vinyl acetate-alkyl methacrylate copolymer, vinyl acetate-alkyl acrylate copolymer, acrylonitrile-alkyl acrylate copolymer, acrylonitrile-alkyl methacrylate copolymer, styrene-acrylic acid copolymer, Styrene-methacrylic acid copolymer,
Styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, acrylic acid-methacrylic acid copolymer, acrylic acid-alkyl methacrylate copolymer, styrene-alkyl acrylate-alkyl methacrylate copolymer, Examples thereof include an alkyl acrylate-alkyl methacrylate copolymer, a styrene-butadiene-acrylic acid copolymer, a styrene-butadiene-alkyl acrylate copolymer, polyurethane, polyvinyl chloride and the like.

In the present invention, the color-forming material constituting the thermosensitive color-forming layer is not particularly limited, and any combination that causes a color reaction by the thermal energy generated by the thermal head can be used. To a light-colored basic dye in combination with an inorganic or organic acidic substance, a combination of a higher fatty acid metal salt such as ferric stearate and a phenol such as gallic acid, a diazonium compound, a coupler compound and a base upon heat melting An example is a heat-sensitive recording material obtained in combination with a compound exhibiting a volatile atmosphere.

However, a combination of a colorless or light-colored electron-donating color forming dye and an acidic substance is particularly preferable because the recording characteristics are extremely excellent and the effects of the present invention are fully exhibited.

Colorless or light-colored electron-donating color-forming dyes contained in the heat-sensitive color-developing layer include triarylmethane compounds such as 3,3-bis (P-dimethylaminophenyl) -6-dimethylaminophthalide and diphenylmethane. 4,4'-bis-dimethylaminobenzhydrin benzyl ether, N-2,4,5-trichlorophenylleuco auramine, N-2,4,5-trichlorophenyl leuco auramine, as a xanthene compound Rhodamine B-anilinolactam, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-butylaminofluorane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3-
Piperidino-6-methyl-7-anilinofluorane, 3
-Ethyl-tolylamino-6-methyl-7-anilinofluorane, 3-cyclohexyl-methylamino-6-methyl-7-anilinofluorane, 3-diethylamino-
6-chloro-7- (β-ethoxyethyl) aminofluorane, 3-diethylamino-6-chloro-7- (γ-chloropropyl) aminofluorane, 3-dibutylamino-6-methyl-7-anilinoflu Oran, 3- (N-isoamyl-N-ethyl) amino-6-methyl-7-anilinofluorane and the like can be mentioned.

Any electron-accepting color-developing compound may be used as long as it has a property of liquefying or dissolving when the temperature rises and a property of developing a color by contacting with the electron-donating color-forming dye.

Specific examples of typical color developing agents include 4-te
rt-butylphenol, 4-acetylphenol, 4-t
ert-octylphenol, 4,4'-sec-butylidenephenol, 4-phenylphenol, 4,4'-dihydroxydiphenylmethane, 4,4'-isopropylidenediphenol, 4,4'-cyclohexylidenediphenol, 4, 4'-dihydroxydiphenyl sulfide, 4,4'-thiobis (6-tert-butyl-3-methylphenol), 4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy Benzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, sec-butyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, 4-hydroxy Tolyl benzoate, chlorophenyl 4-hydroxybenzoate, 4,4'-dihydroxydiphenyl ether, etc. Examples thereof include enolic compounds.

Further, benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, salicylic acid,
3-tert-butylsalicylic acid, 3-isopropylsalicylic acid, 3-benzylsalicylic acid, 3- (α-methylbenzyl)
Aromatic carboxylic acids such as salicylic acid and 3,5-di-tert-butylsalicylic acid, and organic acids such as salts of these phenolic compounds and aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum and calcium. Examples include substances. The developer is usually mixed and used in an amount of 1 to 5 parts by weight, preferably 1.5 to 3 parts by weight, based on 1 part by weight of the color forming dye.

It is permissible to add a storability improver to supplement the storability. Examples of such a shelf life improver include 1,3,5-tris (4-tert-butyl-3-
Hydroxy-2.6-dimethylbenzyl) isocyanuric acid,
1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1, 1-bis (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4 '-(1-phenylethylidene) bisphenol, 4,4'-[1,4-phenylenebis (1-methyl Ethylidene)] bisphenol, 4,4 ′-[1,3-phenylenebis (1-methylethylidene)] bisphenol and other phenolic compounds and 4- (2-methyl-1,2-epoxyethyl) diphenylsulfone, 4 -(2-Ethyl-1,2-epoxyethyl) diphenylsulfone, 4- (2-methyl-glycidyl) diphenylsulfone, 4- (2-ethyl-glycidyl) diphenylsulfone, 4- (2-butyl-glycidyl) diphenyl Sulfone, 4- (3-methyl-3,4-epoxybutyl) diphenyl Sulfone, 4- (2-methyl-3,4-
Epoxy butyl) diphenyl sulfone, 4- (2-methyl)
-2,3-Epoxybutyl) diphenylsulfone, 4- (2-
Methyl-1,2-epoxyethyloxy) diphenyl sulfone, 4- (2-methyl-2,3-epoxybutyloxy) diphenyl sulfone, 4- (2-methyl-1,2-glycidyloxy) diphenyl sulfone, 4- (2-Methyl-glycidyloxy) 4'-chlorodiphenylsulfone, 4- (2-methyl-glycidyloxy) -4'-bromodiphenylsulfone, 4- (2-methyl-glycidyloxy) -4'-methyldiphenylsulfone , 4- (2-methyl-glycidyloxy)
-2 ', 4'-Dimethyldiphenyl sulfone, 4- (2-methyl
-Glycidyloxy) -2 ', 4'-dichlorodiphenylsulfone, 4- (2-methyl-glycidyloxymethoxy) diphenylsulfone, 4- (2-methyl-glycidyloxy) -4'-(p-methoxybenzyloxy) Examples thereof include diphenyl sulfone derivatives such as diphenyl sulfone.
Of course, it is not limited to these, and two or more kinds of compounds can be used in combination as required.

As a sensitizer for improving the sensitivity of the heat-sensitive recording material, for example, parabenzyl biphenyl, dibenzyl terephthalate, 1-hydroxy-2-phenyl naphthoate, dibenzyl oxalate, di-o-chlorobenzyl adipate, 1,2-di (3-methylphenoxy) ethane, di-p-chlorobenzyl oxalate, di-p-methylbenzyl oxalate, 1,2-bis (3,4-dimethylphenyl) ethane and the like can be used.

These organic heat-fusible substances are prepared by using water as a dispersion medium and using various wet pulverizers such as a sand grinder, an attritor, a ball mill and a cobo mill to obtain polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, carboxymethylcellulose, and styrene. -A maleic anhydride copolymer salt and a water-soluble synthetic polymer compound such as a derivative thereof, and a surfactant and the like are dispersed to prepare a dispersion liquid, which is then used for preparing a thermosensitive coloring layer coating material.

In the present invention, other materials constituting the heat-sensitive recording layer include adhesives, inorganic or organic pigments, waxes, metal soaps, and if necessary, ultraviolet absorbers, storability improvers, fluorescent dyes and the like. Can be mentioned.

A water-soluble resin other than the hydrophobic resin emulsion can be added as the adhesive, and examples of the water-soluble resin include polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, styrene-maleic anhydride copolymer, Examples thereof include isobutylene-maleic anhydride copolymer, polyacrylic acid, starch, casein, gelatin and the like and their derivatives.

The amount of the water-soluble resin blended is preferably 0 to 0.5 parts by weight per 1 part by weight of the hydrophobic resin emulsion, and if it is blended in excess of this amount, the effect of improving the density of the thermosensitive coloring layer by calendaring is not so great.

As the inorganic pigment, kaolin, calcined kaolin, talc, wax, diatomaceous earth, calcium carbonate, aluminum hydroxide, magnesium hydroxide, titanium oxide,
Examples thereof include barium carbonate, and examples of the organic pigment include urea, phenol, epoxy, melamine, guanamine, and styrene resin.

As the wax, paraffin wax,
In addition to carnauba wax, microcrystalline wax, polyethylene wax, higher fatty acid amides such as stearic acid amide, ethylenebisstearic acid amide, and higher fatty acid ester can be used.

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 heat-sensitive color developing layer coating material is applied to one surface of the sheet-like support so that the dry weight is 3 to 8 g / m ² , whereby the heat-sensitive recording layer is formed.

Thereafter, the moisture content is 5 to 8% and the linear pressure is 20 to 200 Kg / c.
Perform calendaring in the m range. When the water content is less than 5%, the whiteness is lowered due to superburn, and when the water content is more than 8%, the heat-sensitive color forming layer is peeled off to the calendar roll. When the linear pressure is 20 Kg / cm, the density of the thermosensitive coloring layer is not sufficiently improved, and when the linear pressure is higher than 200 Kg / cm, super burning occurs.

In the present invention, in the protective layer provided on the heat-sensitive recording layer, a water-soluble polymer, a pigment, a crosslinking agent, a wax, a metal soap or the like can be used according to the purpose.

Examples of the water-soluble polymer include polyvinyl alcohol, acetoacetylated polyvinyl alcohol,
Modified polyvinyl alcohol such as carboxyl modified polyvinyl alcohol, starch, casein, gelatin, glue, polyamide, polyacrylamide, hydroxyethyl cellulose, methyl cellulose, styrene-maleic anhydride copolymer salt, isobutylene-maleic anhydride copolymer salt, etc. be able to.

In order to impart water resistance to these adhesives, melamine resin, epoxy resin, aziridine compound,
A cross-linking agent such as glyoxal, dimethylol urea, polyaldehyde and zirconium salt can also be used in combination. Examples of the pigment include calcium carbonate, clay,
Calcined kaolin, talc, titanium oxide, magnesium carbonate, zinc oxide, aluminum silicate, calcium silicate, silica, inorganic pigments such as aluminum hydroxide, starch particles, flour, silicone resin, urea / formalin resin, phenol resin, melamine / Formalin resin, epoxy resin, guanamine / formalin resin, polystyrene resin and the like can be used.

Examples of waxes include paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, and higher fatty acid amides such as stearic acid amide, ethylenebisstearic acid amide, higher fatty acid ester, and metallic soaps. Fatty acid polyvalent metal salts such as zinc stearate, aluminum stearate, calcium stearate, zinc oleate and the like can be mentioned.

Other additives such as oil repellents, defoamers, viscosity modifiers, surfactants, fluorescent dyes and the like may be added as long as the effects of the present invention are not impaired.

The protective layer has a dry weight of 0.1 to 6 g / m.
² , more preferably 1 to 4 g / m ² . If it is too small, the effect as a protective layer is poor, and if it is too large, the color development sensitivity is reduced. The protective layer may have a multilayer structure of two or more layers.

According to the present invention, since the thermosensitive color developing layer is made smooth, the uniform coating property of the protective layer is improved, so that the same storability can be achieved with a smaller coating amount than before.

The support material used in the present invention is not particularly limited and includes, for example, high quality paper, medium quality paper, coated paper, art paper, cast coated paper, resin laminated paper, polyolefin synthetic paper, synthetic fiber paper. , A synthetic resin film or the like can be appropriately used.

As a method for forming the thermosensitive coloring layer, any of known coating methods such as an air knife method, a blade method, a gravure method, a roll coater method, a spray method, a dip method, a bar method, and an extrusion method can be used. May be. As the method for forming the protective layer, the same coating method as the method for forming the thermosensitive coloring layer can be used.However, such as the air knife method, the gravure method, the roll coater method, the spray method, the dip method and the extrusion method. In the case of lightly scraping off the protective layer coating material coated on the thermosensitive coloring layer, the blending amount of the hydrophobic resin emulsion can be further reduced.

To suppress the penetration of oil and plasticizer from the back side,
A back layer may be provided for curl control. If necessary, an undercoat layer may be provided under the heat-sensitive recording layer, or various modifications may be made such as calendering after coating the protective layer.

[0040]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

Formation of Heat Sensitive Layer (1) Preparation of Coloring Dye Dispersion A Component Amount (parts by weight) 3- (N, N-dibutyl) amino-6-methyl-7-phenylaminofluorane 40 Polyvinyl alcohol 10% solution 40 (Polymerization Degree 500, saponification degree 90%) water 20

(2) Preparation of color-developing compound dispersion B Component Amount (parts by weight) 4,4′-dihydroxydiphenylsulfone 40 Polyvinyl alcohol 10% liquid 40 (Polymerization degree 500, saponification degree 90%) Water 20

(3) Preparation of Sensitizer Dispersion C Component Amount (parts by weight) Oxalic acid di-p-methylbenzyl ester 40 Polyvinyl alcohol 10% liquid 40 (Polymerization degree 500, Saponification degree 90%) Water 20

(4) Preparation of Preservability Improver Dispersion D Component Amount (parts by Weight) 4- (2-Methyl-glycyloxy) -4′-benzyloxydiphenylsulfone 40 Polyvinyl alcohol 10% liquid 40 (Polymerization degree 500 , Saponification degree 90%) Water 20 These compositions were subjected to vertical sand mill (IMEX Co., Ltd.).
And sand grinder).

(5) Preparation of Pigment Dispersion E Component Amount (parts by weight) Light calcium carbonate (Brilliant 15, manufactured by Shiraishi Industry Co., Ltd.) 40 Sodium hexametaphosphate 0.7% solution 60 Dispersed.

Further, 20% zinc stearate dispersion as dispersion F liquid and 20% stearic acid amide dispersion as dispersion G liquid were prepared. The weight ratio after drying using these dispersions was A: B: C: D: E: F: G = 10: 2.
A coating solution was prepared by mixing 6 parts by weight of the hydrophobic resin emulsion described below in a dry weight of 0: 20: 3: 34: 5: 5.

Example 1-Heat-sensitive paper A-Urethane emulsion (trade name: Aizelax S5040N-manufactured by Hodogaya Chemical Co., Ltd.) was used as the hydrophobic resin emulsion, and this coating solution was applied to one side of a high-quality paper of 50 g / m ^2. After coating with a rod blade so that the coating amount after drying becomes 7.5 g / m ² , it is dried so as to have 7% water content to form a thermosensitive coloring layer, and then calendered at a linear pressure of 80 Kg / cm 2. went.

Polyvinyl alcohol (Nippon Gosei Co., Ltd.) was used as an adhesive for forming a protective layer.
Manufactured by NH-18, saponification degree 98.0-99.0), kaolinite clay (UW-90, manufactured by EMC) as a pigment, glyoxal, and a dry weight ratio of 50% zinc stearate. : 35: 5: 10 to prepare a coating solution for the protective layer, which was coated on a heat-sensitive recording paper A with a rod blade and dried to prepare a heat-sensitive recording paper A.

Example 2-Heat-sensitive paper B-Styrene-butadiene emulsion (trade name: L1571-Asahi Kasei Co., Ltd.) as a hydrophobic resin emulsion
The same process as in Example 1 was performed to prepare a thermal paper B except that the thermal paper B was used.

Comparative Example 1-Thermal Paper C-The degree of polymerization was 17 instead of the urethane emulsion in Example 1.
A thermal paper C was prepared in the same manner as in Example 1 except that polyvinyl alcohol having a saponification degree of 00 and a saponification degree of 98.5% was used.

Comparative Examples 2 and 3 After forming the thermosensitive coloring layer, the same treatment as in Examples 1 and 2 was carried out except that calendering was not carried out.
Thermal paper D and E were prepared by calendering at a linear pressure of 80 kg / cm.

[0052]

[Table 1] Sensitivity comparison: Recording is performed in copy mode using a commercially available high-speed facsimile UF60 (manufactured by Matsushita Electric Transmission Co., Ltd.),
The recording density was measured using a Macbeth reflection densitometer (RD-914 type,
(Made by Macbeth), and the recording density was defined as the sensitivity. PVC wrap resistance: After printing with UF60 manufactured by Matsushita Electric Transport Co., Ltd.,
It was attached to a vinyl chloride wrap film, further covered with a vinyl chloride wrap film, and the image after 1 week at 25 ° C. was visually evaluated.

[0053]

According to the present invention, it becomes possible to produce a heat-sensitive recording material having high recording sensitivity and excellent storage stability of recorded images.

Claims (1)

[Claims] 1. A main component comprising an adhesive containing a colorless or light-colored electron-donating color-forming dye on a sheet-like support, an electron-accepting color-developing compound that causes the color-forming dye to develop color upon heating, and a hydrophobic resin emulsion. And a thermosensitive coloring layer contained as
In a heat-sensitive recording material having a water-soluble polymer-containing protective layer formed thereon, a thermosensitive color-forming layer containing a coated hydrophobic resin emulsion has a water content of 5 to 8% and a linear pressure of 20 to 200 Kg / c.
A heat-sensitive recording material characterized by being provided with a protective layer after calendering in the range of m.