JP2003072236A - Heat-sensitive recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop a heat-sensitive recording material having less fogging, a high sensitivity and an excellent preservability. SOLUTION: The heat-sensitive recording material comprises a heat-sensitive color developing layer containing a normally colorless or pale color developable compound, a developable compound capable of color-developing the color developable compound by heating and a sensitizer as essential ingredients in such a manner that the heat-sensitive color developing layer contains an oxalic diester and an ethylene acrylic acid copolymer.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a thermal recording material. More specifically, it has high sensitivity and less fog,
The present invention relates to a heat-sensitive recording material having excellent storage stability.

[0002]

2. Description of the Related Art Generally, a heat-sensitive recording material is prepared by separately dispersing a leuco dye and a color developing agent such as a phenolic substance in the form of fine particles and mixing them together, and then adding a binder, a sensitizer, a filler and a lubricant. It is applied as a coating liquid by adding additives such as etc. to paper, film, synthetic paper, etc., and color recording is made by a chemical reaction that occurs when one or both of the leuco dye and the developer melts and is heated by heating. I will get it. A thermal printer or the like having a built-in thermal head is used for coloring the heat-sensitive recording sheet. Compared with other recording methods, this thermal recording method has (1) no noise during recording, (2) no need for development and fixing, (3) maintenance-free, (4) relatively inexpensive machine By the characteristics such as
Facsimile field, computer output, calculator field printer field, medical measurement recorder field,
It is widely used in the fields of automatic ticket vending machines and heat-sensitive recording labels.

In recent years, with the introduction of POS systems in retail stores and supermarkets, and automation systems in transportation facilities, the use of labels, tickets, coupons, etc. has increased. In these applications, heat-sensitive recording materials are required to have further improved storage stability such as heat resistance, water resistance and plasticizer resistance. Further, the demand for high-speed recording is further increased, and development of a thermal recording material capable of sufficiently supporting high-speed recording is strongly desired, but in general, when the sensitivity of the thermal recording material is improved and the thermal response is improved, background fogging occurs. Is more likely to appear. Conventionally, various methods have been proposed in order to improve thermal responsiveness and further improve storability, but none is still satisfactory.

[0004]

The objects of the present invention are as follows.
It is to solve the drawbacks of the prior art. That is, it is to provide a heat-sensitive recording material having high sensitivity, less background fog, and excellent storage stability.

[0005]

The present inventor has completed the present invention as a result of various studies to achieve the above object. That is, the present invention provides (1) a thermosensitive recording material comprising a support, which is usually provided with a colorless or light-colored color-forming compound, and a thermosensitive color-developing layer containing a color-developing compound capable of coloring the color-forming compound under heat as a main component. 2. A heat-sensitive recording material characterized in that the heat-sensitive color developing layer contains an oxalic acid diester and an ethylene / acrylic acid copolymer.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The heat-sensitive color forming layer in the present invention generally comprises a colorless or light-colored color-forming compound, a color-developing compound, an oxalic acid diester and an ethylene / acrylic acid copolymer as main components. In the present invention, the oxalic acid diester functions as a sensitizer and the ethylene / acrylic acid copolymer functions as a binder, but if necessary, other sensitizers (heat-fusible compounds) and binders may be added. They may be used in combination, and if desired, a heat-sensitive color forming layer is prepared by adding a filler and other additives.

In forming the thermosensitive coloring layer in the present invention, the color forming compound is usually 1 to 50% by weight, preferably 5 to 30% by weight, the color developing compound and the oxalic acid diester are usually 1 to 80% by weight, respectively. Preferably 5-40% by weight,
The ethylene / acrylic acid copolymer is usually 0.5 to 50% by weight, preferably 2 to 20% by weight, the sensitizer, the binder and the filler are usually 0 to 80% by weight, other lubricants and surfactants. The antifoaming agent, the ultraviolet absorber, etc. are used in arbitrary proportions, for example, usually 0 to 30% by weight (weight% is the weight ratio of each component in the thermosensitive color developing layer). In a more preferred embodiment, among the above-mentioned compositions, the amount of each of the color-developing compounds to the color-developing compound is usually 0.1.
5 to 20 times, preferably 1 to 5 times, oxalic acid diester is usually 0.5 to 20 times, preferably 1 to 8 times, ethylene / acrylic acid copolymer is 0.5 to 30 times, preferably 1
It is used in a weight ratio range of 10 to 10.

Specific examples of the oxalic acid diester used in the present invention include oxalic acid dibenzyl ester, oxalic acid di (4-methylbenzyl) ester and oxalic acid di (4-chlorobenzyl) ester.

The ethylene / acrylic acid copolymer used in the present invention has, for example, the formula (1)

[0010]

[Chemical 1]

(In the formula (1), m is a number from 600 to 900.
, N is a number from 100 to 400, and m + n is 1,0
It is a numerical value of 00 or less. X is hydrogen, Li, Na,
K, NH _FourAlternatively, it represents an alkanolamine. )
It

The ethylene / acrylic acid copolymer represented by the formula (1) is a compound having a monomer component of ethylene and acrylic acid, a molecular weight of usually 100,000 or less and an acid value of about 150, and is obtained from the market. For example, trade names: Saixen-AC (NH ₄ salt), Saixen-N
(Na salt), Saixen-L (alkanolamine salt)
Etc. Particularly preferable ethylene / acrylic acid copolymers in the present invention include ethylene / acrylic acid ammonium salt and ethylene / acrylic acid sodium salt.

Specific examples of the color forming compound that can be used include:
There is no particular limitation as long as it is one generally used for pressure-sensitive recording paper and heat-sensitive recording paper. Specific examples include, for example, fluoran compounds, triarylmethane compounds,
Examples thereof include spiro compounds, diphenylmethane compounds, thiazine compounds, lactam compounds, fluorene compounds, and the like.

Specific examples of the fluorane compound include 3-diethylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane and 3- (N-methyl). -N-cyclohexylamino) -6-methyl-7-anilinofluorane, 3
-(N-ethyl-N-isopentylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-
Isobutylamino) -6-methyl-7-anilinofluorane, 3- [N-ethyl-N- (3-ethoxypropyl) amino] -6-methyl-7-anilinofluorane,
3- (N-ethyl-N-hexylamino) -6-methyl-7-anilinofluorane, 3-dipentylamino-6
-Methyl-7-anilinofluorane, 3- (N-methyl-N-propylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-tetrahydrofurylamino) -6- Methyl-7-anilinofluorane, 3-
Diethylamino-6-methyl-7- (p-chloroanilino) fluorane, 3-diethylamino-6-methyl-7
-(P-Fluoroanilino) fluorane, 3- [N-ethyl-N- (p-tolyl) amino] -6-methyl-7-
Anilinofluorane, 3-diethylamino-6-methyl-7- (p-toluidino) fluorane, 3-diethylamino-7- (o-chloroanilino) fluorane, 3-dibutylamino-7- (o-chloroanilino) fluorane, 3 -Diethylamino-7- (o-fluoroanilino) fluorane, 3-dibutylamino-7- (o-fluoroanilino) fluorane, 3-diethylamino-7-
(3,4-Dichloroanilino) fluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7-ethoxyethylaminofluorane, 3-diethylamino-6-chloro- 7-anilinofluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7-methylfluorane,
3-diethylamino-7-octylfluorane, 3-
[N-ethyl-N- (p-tolyl) amino] -6-methyl-7-phenethylfluorane and the like can be mentioned.

Specific examples of triarylmethane compounds include, for example, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone or CVL) and 3,3-bis ( p
-Dimethylaminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3- (1,2-dimethylaminoindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-methyl Indole-3-
Yl) phthalide, 3- (p-dimethylaminophenyl)
-3- (2-phenylindol-3-yl) phthalide, 3,3-bis (1,2-dimethylindole-3-
Yl) -5-dimethylaminophthalide, 3,3-bis (1,2-dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis (9-ethylcarbazol-3-yl) -5-dimethylaminophthalide,
3,3- (2-phenylindol-3-yl) -5-
Examples thereof include dimethylaminophthalide and 3-p-dimethylaminophenyl-3- (1-methylpyrrol-2-yl) -6-dimethylaminophthalide.

Specific examples of the spiro compound include, for example, 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3,3'-dichlorospirodinaphthopyran, 3-benzylspirodinaphthopyran, 3- Propyl spirobenzopyran, 3-methylnaphtho- (3-methoxybenzo) spiropyran, 1,3,3-trimethyl-6
-Nitro-8'-methoxyspiro (indoline-2,
2'-benzopyran) and the like are specific examples of the diphenylmethane compound, for example, N-halophenyl-leuco auramine, 4,4-bis-dimethylaminophenylbenzhydrylbenzyl ether, N-2,4,5-triene. Chlorophenyl leuco auramine and the like are specific examples of thiazine compounds such as benzoyl leuco methylene blue and p-nitrobenzoyl leuco methylene blue, and specific examples of lactam compounds are, for example, rhodamine B anilinolactam and rhodamine B-p. -Chloroanilinolactam and the like are specific examples of the fluorene-based compound, for example, 3,6-bis (dimethylamino) fluorene spiro (9,3 ')-6'-dimethylaminophthalide, 3,6-bis ( Dimethylamino) fluorenspyrro (9,3 ′)-6′-pyrroli Nofutarido, 3-dimethylamino-6-diethylamino fluorene spiro (9,
3 ')-6'-pyrrolidinophthalide and the like, respectively. These color forming compounds may be used alone or as a mixture.

As the color-developing compound, any of those generally used for pressure-sensitive recording paper and heat-sensitive recording paper can be used. For example, α-naphthol, β-naphthol, p-octylphenol, 4-t-. Octylphenol, p-
t-butylphenol, p-phenylphenol, 1,
1-bis (p-hydroxyphenyl) propane, 2,2
-Bis- (p-hydroxyphenyl) propane (alias:
Bisphenol A or BPA), 2,2-bis- (p-
Hydroxyphenyl) butane, 1,1-bis- (p-hydroxyphenyl) cyclohexane, 4,4′-thiobisphenol, 4,4′-cyclo-hexylidenediphenol, 2,2′-bis- (2,5 -Dibromo-4-hydroxyphenyl) propane, 4,4'-isopropylidenebis (2-t-butylphenol), 2,2'-methylenebis (4-chlorophenol), 4,4'-dihydroxydiphenylsulfone, 2, 4'-dihydroxydiphenyl sulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, bis (4-hydroxyphenyl) methyl acetate, bis (4-hydroxyphenyl)
Phenolic compounds such as butyl acetate, bis (4-hydroxyphenyl) benzyl acetate, benzyl p-hydroxybenzoate, ethyl p-hydroxybenzoate, dibenzyl 4-hydroxyphthalate, dimethyl 4-hydroxyphthalate, 5-hydroxyisophthalate Aromatic carboxylic acid derivatives such as ethyl acidate, 3,5-di-t-butylsalicylic acid and 3.5-di-α-methylbenzylsalicylic acid, aromatic carboxylic acids or polyvalent metal salts thereof, etc. Examples of the color-developing compound that can be used in combination include those used for heat-sensitive recording paper and heat-sensitive recording paper, but are not limited thereto.

Specific examples of the sensitizer (heat-fusible compound) that can be used in the present invention include waxes such as animal and vegetable waxes and synthetic waxes, higher fatty acids, higher fatty acid amides, higher fatty acid anilides, and naphthalene derivatives. , An aromatic ether, an aromatic carboxylic acid derivative, an aromatic sulfonic acid ester derivative, a carbonic acid diester derivative, a biphenyl derivative, a terphenyl derivative, a sulfone derivative, etc., which are solid at room temperature and have a melting point of about 70 ° C. or higher are used. be able to.

Specific examples of the waxes that can be used in combination include:
For example, wood wax, carnauba wax, shellac, paraffin, montan wax, oxidized paraffin, polyethylene wax, polyethylene oxide and the like. Specific examples of higher fatty acids include stearic acid and behenic acid, and specific examples of higher fatty acid amides. , For example stearic acid amide,
Examples of the higher fatty acid anilide include oleic acid amide, N-methylstearic acid amide, erucic acid amide, methylolbehenic acid amide, methylenebisstearic acid amide, and ethylenebisstearic acid amide. Specific examples of the naphthalene derivative such as anilide include 1-benzyloxynaphthalene, 2-benzyloxynaphthalene, and 1-benzyloxynaphthalene.
Specific examples of aromatic ethers such as hydroxynaphthoic acid phenyl ester include 1,2-diphenoxyethane, 1,4-diphenoxybutane, 1,2-bis (3-methylphenoxy) ethane, 1,2. -Bis (4-
Methoxyphenoxy) ethane, 1,2-bis (3,4-
Dimethylphenyl) ethane, 1-phenoxy-2- (4
-Chlorophenoxy) ethane, 1-phenoxy-2-
Specific examples of the aromatic carboxylic acid derivative include (4-methoxyphenoxy) ethane and the like. Examples thereof include p-hydroxybenzoic acid benzyl ester, p-benzyloxybenzoic acid benzyl ester, and terephthalic acid dibenzyl ester. Specific examples of the acid ester derivative include, for example, p-toluenesulfonic acid phenyl ester,
Phenylmesitylene sulfonate, 4-methylphenyl mesitylene sulfonate and the like, specific examples of carbonic acid diester derivatives include diphenyl carbonate and the like, and specific examples of biphenyl derivatives include p-benzylbiphenyl, p-allyloxybiphenyl and the like. However, specific examples of the terphenyl derivative include, for example, m-terphenyl and the like, and specific examples of the sulfone derivative include, for example, diphenyl sulfone and the like.

The amount of the above-mentioned sensitizer which can be used in combination is preferably within a range not hindering the effects of the present invention, for example, within a range not exceeding the amount of oxalic acid diester used.

Specific examples of the binder that can be used in combination include, for example, methyl cellulose, methoxy cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, sodium carboxymethyl cellulose, cellulose, polyvinyl alcohol (PVA), carboxyl group-modified polyvinyl alcohol, sulfonic acid group-modified polyvinyl alcohol. , Polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, starch and its derivatives, casein, gelatin, water-soluble isoprene rubber, alkali salt of styrene / maleic anhydride copolymer, iso (or diiso) butylene / maleic anhydride copolymer Soluble substances such as alkali salts of polyvinyl acetate, polyvinyl acetate, vinyl chloride / vinyl acetate copolymer, polystyrene, polyacrylic acid ester, polyurethane, styrene Butadiene (SB) copolymers, carboxylated styrene / butadiene (SB) copolymers, styrene / butadiene / acrylic acid copolymers, hydrophobic polymer emulsions such as colloidal silica / acrylic resin composite particles, and the like. To be

Specific examples of usable fillers include calcium carbonate, magnesium carbonate, magnesium oxide, silica, white carbon, talc, clay, alumina, magnesium hydroxide, aluminum hydroxide, aluminum oxide, barium sulfate and polystyrene resin. , Urea-formalin resin and the like.

Other additives include higher fatty acid metal salts such as zinc stearate and calcium stearate for the purpose of preventing thermal head wear and sticking, and phenol derivatives for imparting an antioxidant or antiaging effect. UV absorbers such as benzophenone compounds and benzotriazole compounds, various surfactants, antifoaming agents and the like are added as necessary.

The heat-sensitive recording material of the present invention is prepared by using the above-mentioned material by the following method, for example. That is, according to a conventional method, first, a color-developing compound, a color-developing compound, and an oxalic acid diester are separately pulverized and dispersed together with a binder or, if necessary, other additives in a disperser such as a ball mill, attritor, or sand mill. After mixing (usually water is used as a medium when performing pulverization and dispersion in a wet state), ethylene / acrylic acid / copolymer is added to prepare a coating solution for the thermosensitive color developing layer, which is prepared on paper, plastic sheet, synthetic It is usually coated on a support such as paper by a bar coater, a blade coater, etc. so that the dry weight is 1-20 g / m ² (the ratio of the color forming compound to the color developing compound is usually 1: 1 by dry weight). It is dried (1:10) to obtain the heat-sensitive recording material of the present invention. If necessary, an intermediate layer may be provided between the thermosensitive coloring layer and the support, or an overcoat layer (protective layer) may be provided on the thermosensitive coloring layer. The intermediate layer and the overcoat layer (protective layer) are pulverized and dispersed in the same manner as in the preparation of the coating solution for the thermosensitive color developing layer together with the binder or other additives as necessary, and then the intermediate layer coating solution or the overcoat layer (protective layer) is protected. Layer) After being made into a coating solution, the dry weight of each layer is usually 0.1 to 0.1%.
The coating is applied so as to be about 10 g / m ² .

The heat-sensitive recording material of the present invention, which usually contains a colorless or light-colored compound, a color-developing compound, an oxalic acid diester and an ethylene / acrylic acid copolymer, has a higher sensitivity than that of a conventionally known recording material and the background. Has little fogging and has excellent storage stability.

[0026]

EXAMPLES The present invention will be described in more detail by way of examples, but the present invention is not limited thereto. In the examples, "part" means part by weight and "%" means% by weight.

Example 1 (Formation of Thermosensitive Coloring Layer) A mixture having the following composition was pulverized and dispersed by a sand grinder so that the average particle diameter was 1 μm or less, and the solutions [A], [B] and [B] were respectively prepared. C] liquid was prepared. [A] liquid: 3-dibutylamino-6-methyl-7-anilinofluorane 25 parts 25% PVA aqueous solution 20 parts water 55 parts [B] liquid: 4,4'-dihydroxydiphenylsulfone 25 parts 25% PVA aqueous solution 20 parts Water 55 parts Water 55 parts [C] Solution: Oxalic acid di (4-methylbenzyl) ester 25 parts 25% PVA aqueous solution 20 parts Water 55 parts

Next, a thermosensitive color developing layer coating solution was prepared by mixing in the following proportions, coated on a high-quality paper having a basis weight of 50 g / m ^{2 so} that the dry weight was 8 g / m ^2, and dried to obtain a heat-sensitive material. A colored layer was obtained. [A] liquid 16 parts [B] liquid 32 parts [C] liquid 40 parts 50% calcium carbonate aqueous dispersion 16 parts 30% ethylene / ammonium acrylate emulsion (trade name: XYXEN-AC, Sumitomo Seika Co., Ltd. )) 13 parts (formation of protective layer) Further, a protective layer coating liquid having the following composition ratio is applied onto the thermosensitive color developing layer to give a dry weight of 3 g / m 2.
^It was coated so as to be ² and dried to obtain a heat-sensitive recording material of the present invention with a protective layer. 40% styrene / acrylic acid ester copolymer emulsion 20 parts 5% bentonite aqueous dispersion 40 parts 30% zinc stearate aqueous dispersion 3 parts

Example 2 Instead of the 30% ethylene / acrylic acid ammonium salt emulsion of Example 1, a 30% ethylene / acrylic acid sodium salt emulsion (trade name: Saixen-NC,
Using Sumitomo Seika Co., Ltd., a thermal recording material of the present invention with a protective layer was obtained in the same manner as in Example 1.

Example 3 Instead of the liquid [C] of Example 1, an aqueous dispersion of 25% oxalic acid dibenzyl ester obtained by pulverizing and dispersing in the same manner as in Example 1 was used. Similarly, a thermal recording material of the present invention having a protective layer was obtained.

Example 4 25% 3-dipentylamino-6-obtained by pulverizing and dispersing in the same manner as in Example 1 instead of the liquid [A] of Example 1.
Using a methyl-7-anilinofluorane aqueous dispersion,
A thermal recording material of the present invention with a protective layer was obtained in the same manner as in Example 1.

Example 5 Instead of the liquid [B] of Example 1, a 25% bis (3-allyl-4-hydroxydiphenyl) sulfone aqueous dispersion obtained by pulverizing and dispersing in the same manner as in Example 1 was used. Then, in the same manner as in Example 1, a heat-sensitive recording material of the present invention having a protective layer was obtained.

Example 6 Instead of the liquid [B] of Example 1, pulverization was carried out in the same manner as in Example 1,
Using the 25% 4-hydroxy-4′-isopropoxydiphenylsulfone aqueous dispersion obtained by dispersion, a heat-sensitive recording material of the present invention with a protective layer was obtained in the same manner as in Example 1.

Table 1 shows the quality performance of the heat-sensitive recording materials of the present invention and comparative examples obtained as described above.

Table 1 Quality performance test Background ¹⁾ Color density ²⁾ Heat resistance ³⁾ Water resistance ⁴⁾ Plasticizer resistance ⁵⁾ Example 1 0.05 1.56 1.56 1.35 1.49 Example 2 0.05 1.55 1.55 1.34 1.49 Example 3 0.05 1.60 1.59 1.35 1.50 Example 4 0.04 1.56 1.56 1.35 1.35 49 Example 5 0.04 1.67 1.66 1.37 1.59 Example 6 0.04 1.61 1.60 1.35 1.52

1) Background: A value measured by a Macbeth reflection densitometer RD-914 type (Macbeth reflection density) in the uncolored portion of the sample. 2) Color density: Macbeth reflection density value of the image portion printed by a thermal printer (D-805P) manufactured by Ishida Co., Ltd. 3) Heat resistance: 6 samples of color developed by the above printer
Macbeth reflection density of the image portion after standing in a 0 ° C incubator for 24 hours. 4) Water resistance: Macbeth reflection density of the image portion after the sample developed by the printer was immersed in tap water at room temperature for 24 hours. 5) Plasticizer resistance: P was added to the sample colored by the above printer.
0.0294MP with VC wrap film on both sides
Macbeth reflection density of the image portion after standing at room temperature for 24 hours under a load of a (300 g / cm ² ).

As is apparent from the table, the heat-sensitive recording material of the present invention is excellent in the whiteness of the background and the color density and is excellent in the storage stability such as heat resistance, water resistance and plasticizer resistance.

[0038]

EFFECT OF THE INVENTION A heat-sensitive recording material having high sensitivity, little background fog and excellent storage stability was obtained.

Claims (2)

[Claims] 1. A heat-sensitive recording material comprising a support and a thermosensitive color-developing layer containing a colorless or light-colored color-forming compound as a main component and a color-developing compound capable of coloring the color-forming compound under heat. A heat-sensitive recording material, wherein the heat-sensitive color developing layer contains an oxalic acid diester and an ethylene / acrylic acid copolymer. 2. The heat-sensitive recording material according to claim 1, wherein the ethylene / acrylic acid copolymer is ethylene / acrylic acid ammonium salt or ethylene / acrylic acid sodium salt.