JPH0524365A - Heat-sensitive recording material - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a heat-sensitive recording material having improved oil resistance and plasticizer resistance. A heat-sensitive recording layer is mainly composed of at least one electron-donating color-forming dye and an electron-accepting color-developing compound that reacts with the dye under heating to form a color on a sheet-like support and an adhesive. In the heat-sensitive recording material provided, the color-developing compound is selected from 4,4′-dihydroxydiphenylsulfone, 4-hydroxy-4′-isopropoxydiphenylsulfone, and bis- (3-allyl-4-hydroxyphenyl) sulfone. And at least one hydroquinone diglycidyl ether.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a heat-sensitive recording material.
More specifically, it relates to a heat-sensitive recording material having excellent storage stability.

[0002]

2. Description of the Related Art A heat-sensitive recording material generally comprises a sheet-like support made of paper, synthetic paper, plastic film or the like, on which a color-forming dye such as an electron-donating leuco dye and an electron-accepting phenolic compound are formed. 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 decreases, and in severe cases, the recording disappears. For example, when a heat-sensitive label having a pressure-sensitive adhesive (adhesive) layer 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 is transferred from the back surface of the label. There was a problem that the bar code or characters printed on the label became unreadable due to migration or migration of the plasticizer from the film that was in direct contact with the label surface.
Further, even when oil such as edible oil or industrial oil comes into contact with the above label, there is a problem that the recording portion disappears or becomes unreadable as in the case of the plasticizer.

In order to solve this problem, an attempt is made to provide an overcoat layer on the surface of the heat-sensitive layer (Jitsuko Sho 59-9909).
However, if there are minute defects in the overcoat layer, oil or plasticizer penetrates from that part and diffuses into the thermosensitive coloring layer, making the entire printed area unreadable after a long time. There was a point.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat-sensitive recording material which is excellent in storability and has little decoloration of the printed portion even after contact with oil or a plasticizer after printing.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted extensive research including a search for materials in order to solve the above-mentioned problems. As a result, an electron-donating color-forming dye and the dye are formed on a sheet-like support. A heat-sensitive recording material comprising an electron-accepting color-developing compound that reacts under heat to develop a color, and a heat-sensitive recording layer containing an adhesive as a main component.
4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, bis-
By containing at least one electron-accepting color-developing compound selected from (3-allyl-4-hydroxyphenyl) sulfone and hydroquinone diglycidyl ether, oil resistance and plasticizer resistance are significantly improved. And found the present invention. Furthermore, the present inventors have further sought to improve the oil resistance and plasticizer resistance by containing di-p-methylbenzyl oxalate, which is known to be effective as a sensitizer, in the heat-sensitive recording layer. In addition, they have found that by providing a protective layer containing a water-soluble polymer and a pigment on the heat-sensitive recording layer, the oil resistance and plasticizer resistance are almost perfect.

In the present invention, in order to improve oil resistance, hydroquinone diglycidyl ether (melting point 86 ° C.)
To use. Although the oil resistance can be significantly improved by using hydroquinone diglycidyl ether, its mechanism is not always clear. A color forming dye, a color developing compound, and hydroquinone diglycidyl ether are mixed in a molecular state by heating and melting, and then an epoxy group is polymerized by reacting with the color forming dye or the color developing compound in some way. It is considered that the solubility in oils and plasticizers is reduced.

Hydroquinone diglycidyl ether is 0.1 to 2 parts by weight per 1 part by weight of the electron-donating color forming dye,
It is preferably used in a proportion of 0.3 to 0.6 part by weight.

The hydroquinone diglycidyl ether used in the present invention has the advantage that it is excellent in oil resistance, but it has the drawback that the printed part is bleeding due to polyvinyl chloride wrap resistance and the characters are difficult to read. The present inventors have considered that the advantages of this substance in oil resistance are effectively utilized, and have studied that the printed part does not have bleeding even when it is in contact with a polyvinyl chloride wrap film for a long time. The object was achieved by combining with a specific electron-accepting color-developing compound.

Various kinds of electron-accepting color-developing compounds have been known so far, but a sulfone-containing phenolic substance is used in order to improve the drawback that the printed part is bleeded by polyvinyl chloride wrap. And at least one selected from 4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, and bis- (3-allyl-4-hydroxyphenyl) sulfone. .. These electron-accepting color-developing compounds are electron-donating color-forming dyes 1
It is used in a proportion of 1 to 5 parts by weight, preferably 1.5 to 3 parts by weight, based on parts by weight.

The electron-donating color forming dye contained in the heat-sensitive recording layer is a triarylmethane compound,
3,3-bis (P-dimethylaminophenyl) -6-dimethylaminophthalide, 4,4′-bis-dimethylaminobenzhydrin benzyl ether, N-2,4,5-trichlorophenyl as diphenylmethane compounds Leuco auramine, N-2,4,5-trichlorophenyl leuco auramine, Rhodamine B-anilinolactam, 3-diethylamino-7 as a xanthene compound.
-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-anilinofluorane, 3- (N-isoamyl-
N-ethylamino) -6-methyl-7-anilinofluorane and the like.

Of these, 3-dibutylamino-6-methyl-7-anilinofluorane and 3- (N-isoamyl-N-ethylamino) -6-methyl-7-anilinofluorane are particularly preferred. These color-forming dyes can be used alone or in combination of two or more, and are appropriately selected and used depending on the use of the heat-sensitive recording material and desired properties.

As the sensitizer for improving the sensitivity of the heat-sensitive recording material, for example, parabenzyl biphenyl, dibenzyl terephthalate, phenyl 1-hydroxy-2-naphthoate, dibenzyl oxalate, di-o-chlorobenzyl adipate, 1 , 2-di (3-methylphenoxy) ethane,
Although di-p-chlorobenzyl oxalate, di-p-methylbenzyl oxalate, 1,2-bis (3,4-dimethylphenyl) ethane and the like can be used, di-p-methylbenzyl oxalate is used in the present invention. By using, it is possible to further improve the oil resistance and the plasticizer resistance. Di-p-methylbenzyl oxalate is used in an amount of 0.5 to 4 parts by weight, preferably 1 to 2 parts by weight, based on 1 part by weight of the electron-donating color forming dye.

It is permissible to add a preservability improver to supplement the preservability. Phenolic compounds are effective as such a preservative improving agent, and, for example, 1,3,5-tris (4-t-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanuric acid,
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)]
Examples thereof include bisphenol and 4,4 ′-[1,3-phenylenebis (1-methylethylidene)] bisphenol.

These organic heat-fusible substances are obtained by using water as a dispersion medium and 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 water-soluble synthetic polymer compound such as a maleic anhydride copolymer salt and the like, as well as a surfactant and the like are dispersed into 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, UV absorbers.

Water-soluble adhesives are generally used as the adhesive, and polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer,
Examples include polyacrylic acid, starch, casein, gelatin and the like. Further, for the purpose of imparting water resistance to these binders, a water resistant agent such as glyoxal may be added, or a hydrophobic emulsion, specifically, a styrene-butadiene rubber latex, an acrylic resin emulsion or the like may be added.

The inorganic pigments include kaolin, calcined kaolin, talc, wax, diatomaceous earth, calcium carbonate, aluminum hydroxide, magnesium hydroxide, titanium oxide,
Examples include barium carbonate, and examples of organic pigments include urea, phenol, epoxy, melamine, and guanamine resins. Examples of the wax include paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, and higher fatty acid amides such as stearic acid amide, ethylenebisstearic acid amide, 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 heat-sensitive color developing layer coating material is applied on one surface of the sheet-shaped support so as to have an amount of 3 to 8 g / m ² (dry), whereby a heat-sensitive recording layer is formed.

In the present invention, the protective layer provided on the heat-sensitive recording layer comprises a water-soluble polymer for imparting oil resistance and plasticizer resistance, a pigment mainly for suppressing sticking with the thermal head, Crosslinking agents, waxes, metal soaps and the like can be used.

Examples of the water-soluble polymer include polyvinyl alcohol, acetoacetylated polyvinyl alcohol,
Examples thereof include modified polyvinyl alcohol such as carboxy-modified polyvinyl alcohol, starch, casein, gelatin, glue, polyamide, polyacrylamide, hydroxyethyl cellulose, methyl cellulose, and styrene-maleic anhydride copolymer salt.

In order to impart water resistance to these adhesives, it is effective to use a crosslinking agent such as melamine, epoxy, aziridine, glyoxal, dimethylolurea, polyaldehyde or zirconium salt in combination.

Examples of the pigment include inorganic pigments such as calcium carbonate, clay, calcined kaolin, talc, titanium oxide, magnesium carbonate, zinc oxide, aluminum silicate, calcium silicate, silica and aluminum hydroxide, starch particles, wheat 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 and metal soaps include paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, higher fatty acid amides such as stearic acid amide, ethylenebisstearic acid amide, higher fatty acid ester, and higher fatty acid polyvalent metal. Salts such as zinc stearate, aluminum stearate, calcium stearate, zinc oleate and the like are mentioned.

In addition, various additives such as an oil repellent, an antifoaming agent, a viscosity modifier, and a surfactant 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 , preferably 1 to 4 g / m ² . When the amount is less than 0.1 g / m ² , the effect as a protective layer is poor and 6 g / m ²
In the above cases, the color development sensitivity decreases. Further, the protective layer may be a multilayer having two or more layers.

The sheet-like support 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-based synthetic paper, synthetic fiber paper, synthetic resin film and the like can be appropriately used.

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 to form the heat-sensitive recording layer and the protective layer. May be used.

To suppress the penetration of oil and plasticizer from the back side,
A back layer may be provided for curl control. In addition, various modifications such as providing an undercoat layer under the heat-sensitive recording layer may be allowed if necessary.

[0031]

EXAMPLES The present invention will be described more specifically below with reference to examples. Formation of heat-sensitive layer (1) Preparation of color-forming dye dispersion A Component Amount (parts by weight) 3- (N-ethyl-N-isoamylamino) -6-40 methyl-7-anilinofluorane 10% polyvinyl alcohol 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) Parabenzyl biphenyl 40 Polyvinyl alcohol 10% liquid 40 (Polymerization degree 500, Saponification degree 90%) Water 20

(4) Preparation of Hydroquinone Diglycidyl Ether Dispersion D Component Amount (parts by weight) Hydroquinone diglycidyl ether 20 Polyvinyl alcohol 10% liquid 20 (Polymerization degree 500, Saponification degree 90%) Water 60 The composition was separately dispersed with a vertical sand mill (manufactured by AIMEX CORPORATION, sand grinder).

(5) Preparation of Pigment Dispersion E Component Amount (parts by weight) Light calcium carbonate 40 (Brilliant 15, Shiroishi Industry Co., Ltd.) Sodium hexametaphosphate 0.7% solution 60 This composition was dispersed with a cowles disperser. did.

Further, as the dispersions F and G, 20% zinc stearate dispersion and 20% stearic amide dispersion were prepared. A 10% aqueous solution of polyvinyl alcohol was used as a binder.

The weight ratio after drying using these dispersions and a binder is A: B: C: D: E: F: G: polyvinyl alcohol = 10: 20: 20: 5: 25: 5. :
It was mixed so as to be 5:10 to prepare a coating liquid.

This coating solution was applied onto one surface of a high-quality paper of 50 g / m ² so that the coating amount after drying would be 7.5 g / m ^2, and dried to form a thermosensitive coloring layer to form a thermosensitive recording paper. A was created.

During the procedure for preparing the thermosensitive recording paper A, the same operation was performed except that 4,4'-dihydroxydiphenylsulfone in the color-developing compound dispersion B was changed to 4-hydroxy-4'-isopropyloxydiphenylsulfone. Thermal recording paper B was prepared.

During the procedure for preparing the thermosensitive recording paper A, the 4,4'-dihydroxydiphenylsulfone in the color-developing compound dispersion B was mixed with bis- (3-allyl-4-hydroxyphenyl).
The same operation was performed except that the thermosensitive recording paper C was used.
It was created.

A thermosensitive recording paper D was prepared by the same procedure except that para-benzyl biphenyl in the sensitizer dispersion C was changed to di-p-methylbenzyl oxalate in the procedure for preparing the thermosensitive recording paper A.

For the purpose of comparison, in the procedure for preparing the thermal recording paper A,
The same operation was performed except that the 4,4′-dihydroxydiphenylsulfone in the color-developing compound dispersion liquid B was changed to 2,2-bis (4′-hydroxyphenyl) propane, to prepare a heat-sensitive recording paper E.

For the purpose of comparison, in the procedure for preparing the thermal recording paper A,
Except for the dispersion D, the same operation was carried out with the rest of the compounding ratio as it was to prepare a thermosensitive recording paper F.

Formation of protective layer As an adhesive, polyvinyl alcohol (Nippon Gosei Co., Ltd., NH-18, saponification degree 98.0 to 99.0),
Kaolinite clay (UW-90, manufactured by EMC), glyoxal, and 20% zinc stearate were used as pigments, and a protective layer coating solution was prepared so that the dry weight ratio was 50: 35: 5: 10. This coating solution was applied onto the previously obtained thermal recording papers A, D and E so that the coating amount after drying would be 2.0 g / m ^2, and dried to provide a protective layer. It was created. The seven types of heat-sensitive recording materials thus obtained were subjected to smoothing treatment with a super calender and then subjected to a plasticizer resistance test.

The plasticizer resistance test was carried out by a high-speed thermal facsimile manufactured by Matsushita Electric Transport Co., Ltd .: UF60, and then printed by Mitsui Toatsu Co., Ltd.
Put PVC vinyl wrap film, KMA on the coloring part,
After applying a load of 0 g / cm ² and keeping it at 20 ° C. and 65% RH for 1 week, the degree of decoloring was visually judged. The results are shown in Table 1. ◎ means that decoloring was not observed at all
○ indicates that the color was slightly decolored but was sufficiently readable, △ indicates that the color was decolorized but legible, and × indicates that the color was completely decolorized. .. The PVC resistance shows the result of evaluation of bleeding. ○ indicates that no bleeding was observed, × indicates that bleeding is severe,
Indicates that it was difficult to read.

[0046]

[Table 1]

[0047]

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to produce a heat-sensitive recording material having excellent plasticizer resistance and vinyl chloride resistance.

Claims (1)

Claims: 1. A sheet-like support comprising an electron-donating color-forming dye as a main component, an electron-accepting color-developing compound that reacts with the dye under heating to form a color, and an adhesive. A heat-sensitive recording material provided with a heat-sensitive recording layer containing 4,4′-dihydroxydiphenyl sulfone, 4
-Hydroxy-4'-isopropoxydiphenyl sulfone and bis- (3-allyl-4-hydroxyphenyl) sulfone, and at least one electron-accepting color developing compound and hydroquinone diglycidyl ether are contained. Thermosensitive recording material.