JPH05221141A - Thermal recording material - Google Patents

Abstract

PURPOSE:To produce a thermal recording material having high whiteness and excellent in preservation stability of recorded image. CONSTITUTION:In a thermal recording material wherein a thermal coloring layer containing a colorless or light-colored electron donative coloring dye, an electron acceptive compound for thermally developing the coloring dye, and a binder, as main components, is provided on a supporting sheet, the electron donative coloring dye contains 3-(N,N-dibutyl)amino-6-methyl-7- phenylaminofluoran while the electron acceptive color developing compound is selected from 4,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'- isopropyloxydiphenylsulfon, bis(3-allyl-4-hydroxyphenyl)sulfon, and 4-(2-methyl- glycidyloxy)-4'-benzyloxydiphenylsulfon is further contained therein. An overcoat containing water soluble polymer and pigment may be applied thereon.

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 heat-sensitive recording material having high whiteness 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 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 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 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 the heat-sensitive level attached to the film is contacted with oils such as edible oil and industrial oil, there is a problem that the recorded 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 thermosensitive color developing layer (Jitsuko Sho 59-99).
No. 09), but if the overcoat layer has minute defects, even if oil or a plasticizer penetrates from that part, it diffuses into the thermosensitive coloring layer and the entire printing part disappears after a long time. There was a problem that caused it.

Further, a method has been proposed in which a diphenyl sulfone derivative having a glycidyl group is added to the thermosensitive color developing layer (JP-A-62-164579).

However, when such a compound is added to the heat-sensitive color-developing layer, the storability of the recording area is improved, but there is a problem that background fog is likely to occur under high temperature or high humidity conditions.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat-sensitive recording material which is excellent in the preservability of the recording portion and which does not cause background fog. Furthermore, it is an object of the present invention to provide a heat-sensitive recording material having higher storage stability by providing an overcoat layer.

[0009]

The present invention provides a colorless or light-colored electron-donating color-forming dye on a sheet-like support, an electron-accepting color-developing compound for coloring the color-forming dye by heating, and a binder. A thermosensitive recording material comprising a thermosensitive coloring layer containing as a main component, 3- (N, N-dibutyl) amino-6-methyl-7-phenylamino as the electron-donating coloring dye in the thermosensitive coloring layer. At least one electron-accepting property containing fluorane and selected from 4,4′-dihydroxydiphenylsulfone, 4-hydroxy-4′-isopropyloxydiphenylsulfone, and bis (3-allyl-4-hydroxyphenyl) sulfone In a heat-sensitive recording material containing a developer compound and 4- (2-methyl-glycidyloxy) -4'-benzyloxydiphenylsulfone To.

The colorless or light-colored electron-donating color-forming dye contained in the heat-sensitive color-developing layer is a triarylmethane compound such as 3,3-bis (P-dimethylaminophenyl) -6-dimethylaminophthalide. As the diphenylmethane compound, 4,4′-bis-dimethylaminobenzhydrin benzyl ether, N-2,4,5-trichlorophenylleukoauramine, N-2,4,5-
Trichlorophenyl leuco auramine, as a xanthene-based 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-ani Rinofluorane, 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-
Although many materials such as 7-anilinofluorane are known, in the present invention, 3- (N, N-dibutyl) amino-6-methyl-7-phenylaminofluorane is an essential component.

This color-forming dye has the advantage of being superior in whiteness to other dyes, but has the drawback of fading when stored for a long period of time. In the present invention, as a result of intensive studies on a heat-sensitive recording material which has high whiteness and is free from background fog after storage and decoloration of a printed portion, 3- (N, N-dibutyl) amino-6-methyl-7- Phenylaminofluorane and 4,4'-dihydroxydiphenyl sulfone,
At least one electron-accepting color-developing compound selected from 4-hydroxy-4′-isopropyloxydiphenylsulfone and bis (3-allyl-4-hydroxyphenyl) sulfone and 4- (2-methyl-glycidyloxy)- The combination effective in containing the 4'-benzyloxydiphenyl sulfone was found to be specifically effective for the purposes of the present invention.

In the present invention, 1 to 5 parts by weight, preferably 1.5 to 5 parts by weight, relative to 1 part by weight of 3- (N, N-dibutyl) amino-6-methyl-7-phenylaminofluorane.
At least one electron accepting electron microscope selected from 4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropyloxydiphenyl sulfone, and bis (3-allyl-4-hydroxyphenyl) sulfone in a proportion of 3 parts by weight. Blend with a color compound. Furthermore 4- (2-
Methyl-glycidyloxy) -4′-benzyloxydiphenyl sulfone is 0.05 to 1 part by weight, preferably 1 part by weight of 3- (N, N-dibutyl) amino-6-methyl-7-phenylaminofluorane. Is 0.1 to 0.
It is desirable to mix them in a ratio of 5 parts by weight.

As sensitizers 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,
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 polyacrylamide, polyvinylpyrrolidone, polyvinylalcohol, carboxymethylcellulose, and styrene using water as a dispersion medium and various wet pulverizers such as a sand grinder, an attritor, a ball mill and a cobomill. -In addition to water-soluble synthetic polymer compounds such as maleic anhydride copolymer salts and their derivatives, 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 binders, inorganic or organic pigments, waxes, metal soaps and, if necessary, ultraviolet absorbers, storability improvers and fluorescent dyes. Can be mentioned.

Water-soluble binders are generally used, and polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer,
Examples thereof include polyacrylic acid, starch, casein, gelatin and the like and their derivatives. Also, a hydrophobic emulsion, specifically styrene-butadiene rubber latex,
It is also possible to add an acrylic resin emulsion or the like.

The inorganic pigments include 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 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.

It is permissible to add a storability improver to supplement the storability. Phenolic compounds are effective as such a preservative improving agent, and, for example, 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-methylethylidene)] bisphenol, 4,4 '-[1,3-
Examples thereof include phenylene bis (1-methylethylidene)] bisphenol.

In the present invention, in the overcoat 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 depending on 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, 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,
In addition to microcrystalline wax and polyethylene wax, higher fatty acid amides such as stearic acid amide, ethylenebisstearic acid amide, higher fatty acid ester,
Examples thereof include higher fatty acid polyvalent metal salts, that is, zinc stearate, aluminum stearate, calcium stearate, zinc oleate and the like.

Other additives such as oil repellents, defoamers, viscosity modifiers, surfactants and fluorescent dyes 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 multi-layer structure of two or more layers.

The support material used in the present invention is not particularly limited and includes, for example, high-quality paper, medium-quality paper, glossy paper, oil-resistant paper, coated paper, art paper, cast coated paper, lightly 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. Further, if necessary, various modifications such as providing an undercoat layer under the heat-sensitive recording layer are allowed.

[0030]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples. In addition, "parts" and "%" in Examples and Comparative Examples represent "parts by weight" and "% by weight", respectively.

Formation of Heat Sensitive Layer (1) Preparation of Coloring Dye Dispersion Liquid A Component Parts by Weight 3- (N, N-dibutyl) amino-6-methyl-7-phenylfluorane 40 Polyvinyl alcohol 10% liquid 40 (Polymerization Water 20 (2) Preparation of color-developing compound dispersion B Component 4 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 Parts by Weight Parabenzyl biphenyl 40 Polyvinyl alcohol 10% solution 40 (Polymerization degree 500, Saponification degree 90%) Water 20 (4) Preparation of storage stability improver dispersion D Ingredients Weight part 4- (2-methyl-glycidyloxy) -4'-benzyloxydiphenyl sulfone 40 Polyvinyl alcohol 10% liquid 40 (Polymerization degree 50 , Saponification degree 90%) vertical sand mill water 20 These compositions (Imex Co.
Manufactured and separately dispersed by a sand grinder.

(5) Preparation of Pigment Dispersion Liquid E Ingredients 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.

Further, a 20% zinc stearate dispersion as a dispersion F liquid and a 20% stearic acid amide dispersion as a dispersion G liquid were prepared. 10% polyvinyl alcohol (polymerization degree 1700, saponification degree 98.5%) as a binder
An aqueous solution was used.

Example 1-Thermal paper A-The weight ratio of these dispersions and a binder after drying was A: B: C: D: E: F: G: polyvinyl alcohol = 10: 20. : 20: 3: 30: 5: 5: 10 to prepare a coating solution.

Comparative Example 1-Heat-sensitive paper B-3- (N, N-dibutyl) amino-6-methyl-7-phenylaminofluorane in Example 1 was replaced with 3-N-methylcyclohexylamino-6-methyl- A coating liquid was prepared by the same method except that 7-phenylaminofluorane was used.

Comparative Example 2-Heat Sensitive Paper C-A coating solution was prepared in the same manner as in Example 1 except that 4,4'-dihydroxydiphenyl sulfone was replaced with bisphenol-A.

Comparative Example 3-Heat-sensitive paper D- 4- (2-methyl-glycidyloxy) -in Example 1
A coating solution was prepared without adding 4′-benzyloxydiphenylsulfone.

These coating solutions were coated on one side 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,
B, C and D were prepared.

Example 2 Formation of Protective Layer As an adhesive, polyvinyl alcohol (Nippon Gosei Co., Ltd., NH-18, saponification degree: 98.0 to 99.
0), kaolinite clay as a pigment (UW-90, E
MC), glyoxal, and 20% zinc stearate, and the dry weight ratio is 50: 35: 5: 10.
A protective layer coating solution was prepared so that

The coating amount of this coating solution after drying was 2.0 g / m 2.
² was applied onto the thermal recording paper A obtained in Example 1 and dried to form a protective layer to prepare a thermal recording paper E.

Comparative Examples 4, 5 and 6 Thermal papers B, C and D were processed in the same manner as in Example 2 to prepare thermal papers F, G and H.

The four kinds of heat-sensitive recording materials thus obtained were subjected to smoothing treatment with a super calendar to a Beck smoothness of 1200 seconds and evaluated.

[0043]

[Table 1] Change in whiteness over time: 30 sheets of white paper in an environment of 20 ° C and 65%
It is stored for a day, and the change in whiteness before and after that is measured with the blue filter of the Hunter whiteness meter.

Vinyl chloride resistance: After printing with UF60 manufactured by Matsushita Electric Transport Co., Ltd., affixing it to a vinyl chloride wrap film, covering it with a vinyl chloride wrap film, and visually evaluating the image after one week at 25 ° C. did.

Evaluation method x: Recording and printing cannot be read at all.

Δ: Some recording print remains, but it is difficult to read and there is a problem in practical use.

◯: Recording print is not erased at all.

Long-term storability: The print density storage ratio for examining the long-term storability was measured by printing with UF60 manufactured by Matsushita Electric Transport Co., Ltd. (acceleration test) and then measured with a RD-100R densitometer manufactured by Macbeth. The sample was put in an environment of 40 ° C. and 90% RH, the concentration after 24 hours was examined, and the concentration was calculated by the following formula.

Print density storage ratio (%) = (density after test) /
(Initial concentration) x 100

[0050]

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

Claims (2)

[Claims] 1. A heat-sensitive color-developing comprising, as a main component, a colorless or light-colored electron-donating color-forming dye, an electron-accepting color-developing compound for coloring the color-forming dye by heating, and a binder on a sheet-like support. In a thermosensitive recording material having a layer, the electron-donating color-forming dye in the thermosensitive color-developing layer is 3
-(N, N-dibutyl) amino-6-methyl-7-phenylaminofluorane-containing and 4,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-isopropyloxydiphenylsulfone, bis (3-allyl) At least one electron-accepting color-developing compound selected from -4-hydroxyphenyl) sulfone and 4- (2
-Methyl-glycidyloxy) -4'-benzyloxydiphenyl sulfone. 2. The thermosensitive recording material according to claim 1, wherein a protective layer containing a water-soluble polymer and a pigment is provided on the thermosensitive coloring layer.