JPH0648040A - Thermosensitive recording medium - Google Patents

Abstract

PURPOSE:To improve printability by laminating a thermosensitive coloring layer containing a dye, a developer, and an adhesive and an overcoat layer containing a specified amount of a surfactant with an HLB value of 1-3.9 one after another on a support. CONSTITUTION:A colorless or slightly colored electron donating dye, an electron accepting developer, and an adhesive are dispersed in a aqueous solution of polyvinyl alcohol as a binder to prepare a coating liquid for a thermosensitive coloring layer. On the other hand, a surfactant with an HLB value of 1-3.9 of 0.1-5wt.% of 100 pts.wt. total solid content and a specified amount of calcium carbonate are dispersed in an aqueous solution of polyvinyl alcohol as a binder to prepare a coating solution for an overcoat layer. The coating liquid for the coloring layer is applied on a substrate including a paper sheet and a synthetic resin film, and the coated layer is dried to form the thermosensitive coloring layer. Additionally, the coating liquid for the overcoat layer is applied on the coloring layer, and the coated layer is dried to form the overcoat layer, thereby producing a thermosensitive recording medium.

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 excellent printability which can be used for a heat-sensitive label for POS and the like.

[0002]

2. Description of the Related Art A heat-sensitive recording material is generally composed of paper, synthetic paper, plastic film or the like on one side thereof, and a colorless or light-coloring substance such as an electron-donating color-forming dye and an electron-accepting substance. A thermosensitive coloring layer containing a color-developing compound such as a phenolic compound and an adhesive as main components, and melting the color-developing dye and the electron-accepting color-developing compound by heat energy. By doing so, a reaction occurs and a color recorded image can be obtained.
Such a heat-sensitive recording method has advantages such as a compact recording apparatus, low cost, and easy maintenance, and is not only used as a recording medium for a facsimile, an automatic ticket vending machine, or a scientific measuring machine, POS label, CAD, CR
Widely used in various printers and plotters for medical images.

In a conventional thermal recording material such as a POS label, a high content of a pigment or the like has been added to improve the printability of the overcoat layer to increase the oil absorption and improve the ink receptivity of the printing ink. However, when the pigment in the overcoat layer is blended in a high amount, the plasticizer in the film penetrates into the heat-sensitive layer through the overcoat layer when it comes into contact with a vinyl chloride wrap film after printing, and the recorded image is erased. Was not always practical because it leads to.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the printability of a thermal recording material without adding a high amount of pigment in the overcoat layer.

[0005]

The present inventors have completed the present invention as a result of studying the improvement of the ink receptivity of the printing ink without depending on the method of highly blending the pigment. That is, the present invention provides a thermosensitive color-forming layer containing a colorless or light-colored electron-donating color-forming dye and an electron-accepting color-developing compound for coloring the color-forming dye on heating and an adhesive as main components. And an HLB value of 1 or more and 3.9 on the thermosensitive coloring layer.
The following surfactants were added in an amount of 0.
The present invention relates to a thermosensitive recording medium characterized by comprising an overcoat layer containing 1 to 5 parts by weight.

The HLB value is WDGriffin (J.Soc.Cosm) as an index showing the degree of hydrophilicity and lipophilicity of a surfactant.
etic Chem., 5,294 (1954)), and is widely used as a measure of hydrophilicity and lipophilicity of surfactants. The smaller the number, the stronger the lipophilicity. Although the mechanism for improving the ink receptivity of the printing ink by the addition of a surfactant having an HLB value of 1 or more and 3.9 or less is not always clear, the lipophilicity of the surface of the overcoat layer increases,
It is believed that the oil-based printing ink improves the inking property.

As a surfactant having an HLB value of 1 or more and 3.9 or less, ethylene glycol distearate (HLB value =
1.3), ethylene glycol monostearate (HLB value =
2.9), propylene glycol monostearate (HLB
Value = 3.4) alkylene glycol ester type, sorbitan monooleate (HLB value = 1.8), sorbitan tristearate (HLB value = 2.1), sorbitan sesquioleate (HLB value = 3.7), sorbitan trioleate (HLB)
Value = 1.8), sorbitan ester type, glyceryl dioleate (HLB value = 1.8), glyceryl monooleate (HLB value = 3.4), glyceryl monostearate (HLB value)
= 3.8), diglyceryl sesquioleate (HLB value = 3.
5), glyceryl ester type such as decaglyceryl dekaoleate (HLB value = 3.0), others, lanolin alcohol (HLB value = 1.0), oleic acid (HLB value = 1.0), sucrose distearate (HLB value = 3.0), etc. Is mentioned.

Such a surfactant having an HLB value of 1 or more and 3.9 or less is used as the total solid content of the overcoat layer coating material of 100.
It can be used between 0.1 and 5 parts by weight relative to parts by weight. Furthermore, it is preferable to use 0.5 to 3 parts by weight. When the amount of the surfactant having an HLB value of 1 or more and 3.9 or less is less than 0.1 part by weight, the printability is not improved, and when it is more than 5 parts by weight, a coating such as a pinhole is applied when the coating material is applied. Defects are likely to occur. Also,
If the HLB value is less than 1, the lipophilicity is too strong to dissolve in the paint and easily separate, and if the HLB value is 4 or more, the effect of improving the ink receptivity of the printing ink is poor, which does not always meet the purpose of the present invention. Disappear.

The resin used for imparting the vinyl chloride wrap film resistance to the overcoat layer of the present invention is, for example, polyvinyl alcohol, oxidized starch, modified starch, gum arabic, gelatin, casein, chitosan, methyl cellulose, hydroxyethyl cellulose. , Hydroxymethyl cellulose, polyvinylpyrrolidone, polyacrylic acid salt, polyacrylic amide, styrene-maleic anhydride copolymer salt, methyl vinyl ether-maleic anhydride copolymer salt, isopropylene-maleic anhydride copolymer salt, and the like, Other aqueous resins include, for example, styrene-butadiene latex, acrylic emulsion, emulsion of vinyl acetate-acrylic ester copolymer,
Polyurethane emulsions, polyvinyl chloride emulsions, polyvinylidene chloride emulsions, emulsions of methacrylic acid ester copolymers and emulsions of acrylic acid ester copolymers can be used. These resins may be used alone or in combination of two or more.

Examples of the pigment used in the overcoat layer of the present invention include calcium carbonate, magnesium carbonate,
Inorganic pigments such as kaolin, clay, talc, calcined clay, silica, diatomaceous earth, synthetic aluminum silicate, zinc oxide, titanium oxide, aluminum hydroxide and barium sulfate, and urea-formalin resin, styrene-methacrylic acid copolymer Examples thereof include fine particles of organic resin such as polystyrene resin.

If necessary, auxiliary additive components such as a dispersant, a cross-linking agent and a lubricant may be added to the overcoat layer. Examples of the cross-linking agent include glyoxal, aldehyde compounds such as polyaldehydes, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, dimethylol urea, and ammonium persulfate, ferric chloride, and magnesium chloride. Inorganic compounds can be used. Examples of the lubricant include fatty acid amides such as stearic acid amide, ethylenebisstearic acid amide, oleic acid amide, palmitic acid amide, coconut fatty acid amide, behenic acid amide, and methylol stearic acid amide, as well as zinc stearate and stearate. Calcium phosphate, polyethylene wax, carnauba wax, paraffin wax, ester wax and the like can be used.

As a coating method, a Meyer bar method, an air knife method, a blade method, a reverse roll method, a slit die method, or the like can be used. The overcoat layer in the present invention has a coating amount after drying of 0.5 to 10.
It is preferable that the coating amount is 0 g / m ² , preferably 2.0 to 8.0 g / m ² . If the coating amount is less than 0.5 g / m ² , the coating film is not formed uniformly, so coating defects such as pinholes are likely to exist. If the coating amount is more than 10.0 g / m ² , the recording sensitivity decreases. However, the printed matter may become unreadable. The recording sensitivity can be improved by smoothing the surface of the overcoat layer using a super calendar, a gloss calendar, a machine calendar or the like.

The support material used in the present invention is not particularly limited and, for example, paper, synthetic fiber paper, synthetic resin film and the like can be appropriately used. Generally, the coating amount of the thermosensitive color forming layer provided on the support is preferably 3 to 10 g / m ² . As the coating method, the same method as for the overcoat layer can be used. As the color-forming dye, a colorless or light-colored electron-donating dye capable of reacting with an electron-accepting color-developing compound under heating to form a color is used.

Examples of the color forming dye include 3,3-bis (P-dimethylaminophenyl) -6-dimethylaminophthalide as a triarylmethane-based compound and 4,4'-bis- as a diphenylmethane-based compound. Dimethylaminobenzhydrin benzyl ether, N-2,
4,5-Trichlorophenyl leuco auramine, N-
2,4,5-Trichlorophenyl leuco auramine, as a xanthene compound, rhodamine B-anilinolactam, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-butylaminofluorane, 3- ( N-isoamyl-N-ethyl) amino-6
-Methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 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 and the like.

Examples of the electron-accepting color developing compound that can be used in the present invention include phenol derivatives and aromatic carboxylic acid derivatives. Specific examples thereof include p-octylphenol and p-tert as phenols.
-Butylphenol, p-phenylphenol, 2,
2'-bis (p-hydroxyphenyl) propane, 2,
2'-bis (p-hydroxyphenyl) pentane, 1,
1'-bis (p-hydroxyphenyl) hexane, 2,
2'-bis (p-hydroxyphenyl) hexane, 1,
1'-bis (p-hydroxyphenyl) -2-ethylhexane, 2,2'-bis (4-hydroxy-3,5-dichlorophenyl) propane, dihydroxydiphenyl ether, 4,4'-dihydroxydiphenylsulfone,
4-hydroxy-4'-isopropyloxydiphenyl sulfone, bis (3-allyl-4-hydroxyphenyl) sulfone and the like can be mentioned. Examples of the aromatic carboxylic acid derivative include p-hydroxybenzoic acid, butyl p-hydroxybenzoate, 3,5-di-tert-butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid, and the above carboxylic acids. And polyvalent metal salts thereof.

Among these electron-accepting color-developing compounds,
Sulfone-containing phenolic substances, especially 4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, and bis- (3-allyl-4-hydroxyphenyl) sulfone are good in storage stability. Gives more favorable results. These electron-accepting color-developing compounds are used in a proportion of 1 to 5 parts by weight, preferably 1.5 to 3 parts by weight, based on 1 part by weight of the entire electron-donating color-forming dye.

A sensitizer can be used to improve the sensitivity of the heat-sensitive recording material. For example, dibenzyl terephthalate, di-o-chlorobenzyl adipate, dibenzyl oxalate, di-p-chlorobenzyl oxalate, di-p-methylbenzyl oxalate, phenyl 1-hydroxy-2-naphthoate, 1,2- Bis (3,4-dimethylphenyl) ethane, parabenzyl biphenyl, 1,2-di (3
-Methylphenoxy) ethane and the like can be used. These sensitizers are used in an amount of 0.5 to 4 parts by weight, more preferably 1 to 2 parts by weight, based on 1 part by weight of the entire electron-donating color forming dye. A normal resin can be used as the adhesive,
For example, the one used for the overcoat layer can be used.

In order to strengthen the water resistance of the coating film, a resin containing a reactive group such as an acetoacetyl group, a carboxyl group or an amide may be used in combination with a crosslinking agent. As the cross-linking agent, for example, the chemical used for the overcoat layer can be used. The thermosensitive coloring layer may contain a pigment, particularly a white pigment, if necessary. As such a pigment, for example, the one used for the overcoat layer can be used. If necessary, the thermosensitive coloring layer may be supplemented with auxiliary additives which are conventionally used in thermosensitive recording materials, such as a dispersant, a surfactant and a storability improver.

Phenolic compounds are effective as the storability improver, for example, 1,3,5-tris (4-t-).
Butyl-3-hydroxy-2,6-dimethylbenzyl)
Isocyanuric acid, 1,1,3-tris (2-methyl-4)
-Hydroxy-5-t-butylphenyl) butane, 1,
1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1-bis (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4,4 '-( 1-phenylethylidene) bisphenol, 4,4 '-[1,4-phenylenebis (1-methylethylidene)] bisphenol, 4,4'-[1,3
-Phenylenebis (1-methylethylidene)] bisphenol and the like. A back layer may be provided to suppress the penetration of oil or plasticizer from the back surface and to control curl. In addition, various kinds of modifications such as providing an undercoat layer under the heat-sensitive recording layer may be carried out if necessary.

[0020]

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to these examples. In each example, “part” means “part by weight”. Formation of thermosensitive coloring layer / coloring dye dispersion liquid A 3- (N-isoamyl-N-ethyl) amino-6-methyl-7-anilinofluorane 50 parts Polyvinyl alcohol 10% aqueous solution 50 parts water 10 parts Receptive color-developing compound dispersion liquid B 4-hydroxy-4'-isopropoxydiphenyl sulfone 50 parts Polyvinyl alcohol 10% aqueous solution 50 parts Water 10 parts ・ Sensitizer dispersion liquid C di-p-methylbenzyl oxalate 50 Parts polyvinyl alcohol 10% aqueous solution 50 parts water 10 parts The preparation compositions of solutions A, B and C were separately pulverized with a sand grinder to an average particle size of 1.5 μm.

Liquid A, liquid B, liquid C, calcium carbonate 60%
Slurry (liquid D), zinc stearate 30% dispersion liquid (E
Liquid), polyvinyl alcohol 10% aqueous solution (F liquid), S
The weight ratio of BR latex [L-1537, solid content 50%, manufactured by Asahi Kasei Co., Ltd.] (liquid G) was A: B:
C: D: E: F: G = 10: 20: 20: 25: 5:
The mixture was mixed at 5:15 to obtain a thermosensitive coloring layer coating material.
The thermosensitive coloring layer coating composition was applied onto one surface of a high-quality paper having a basis weight of 50 g / m ² so that the coating amount after drying was 7.0 g / m ^2, and dried to obtain a thermosensitive coloring layer.

As an adhesive for forming the overcoat layer , polyvinyl alcohol (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., Gohsenol NH-17Q (polymerization degree 170
0, fully saponified type)), kaolinite clay as a pigment, glyoxal as a cross-linking agent, and zinc stearate, and surfactants having different HLB values as shown in Table 1 are added. It was used as an overcoat layer paint. The dry blending ratio of each paint is shown in Table 1. The coating liquid for overcoat layer was applied on the thermosensitive coloring layer so that the coating amount after drying was 2.0 g / m ^2, and the coating liquid was dried. After that, super calendering was performed so that the Beck smoothness was 1100 seconds to obtain a heat-sensitive recording material.

Test Method The separated state of the overcoat layer paint was visually determined. The state in which the surfactant was separated from the aqueous phase and became an oil film state and existed in the upper layer portion of the coating material was described as "Yes" in Table 1.
In addition, the thermal recording material obtained as described above was used for UV curable ink (manufactured by Dainippon Ink and Chemicals Incorporated MV seal) using a printing tester RI-II type manufactured by Akira Seisakusho.
After printing with 59 Indigo Z), the ink was irradiated with UV (ultraviolet light), and it was visually inspected whether the ink was uniformly inked (ink inking property). The test results are shown in Table 1.

[0024]

[Table 1]

[0025]

As described above, according to the present invention, by providing the above-mentioned overcoat layer, it is possible to provide a heat-sensitive recording material having good printability without depending on a high pigment content in the overcoat layer. It is clear that

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Eri Kawamoto 1-10-6 Shinonome, Koto-ku, Tokyo Oji Paper Co., Ltd. Product Research Laboratory

Claims (1)

[Claims] 1. A thermosensitive coloring layer containing a colorless or light-colored electron-donating color-forming dye and an electron-accepting color-developing compound for coloring the color-forming dye by heating and an adhesive as main components. An overcoat layer containing 0.1 to 5 parts by weight of a surfactant having an HLB value of 1 or more and 3.9 or less with respect to 100 parts by weight of the total solid content is provided on the thermosensitive coloring layer. And a thermal recording medium.