JP2724585B2 - Thermal recording material - Google Patents

Description

Description: 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 storage stability of a color image.

2. Description of the Related Art A heat-sensitive recording material using a colorless or light-colored color-forming substance and a color-developing substance capable of coloring the color-forming substance when heated is disclosed in
No. -4160 and Japanese Patent Publication No. 45-14039 and widely used. In general, a thermosensitive recording material is obtained by separately dispersing a developer such as a leuco dye and a phenolic substance into fine particles, and then mixing and mixing the two with a binder, a sensitizer, a filler,
Additives such as lubricants are added to form a coating solution, which is applied to a support such as paper, film, or synthetic paper. A color recording is obtained by the reaction, and an ordinary sheet-like heat-sensitive recording material is prepared. A thermal printer with a built-in thermal head or the like is used for coloring the heat-sensitive recording sheet. In this thermal recording method, (1) no noise is generated during recording as compared with other recording methods. (2) There is no need for development and fixing. (3) Maintenance-free.
(4) Widely used in the facsimile field, computer output, printers such as calculators, recorders for medical measurement, automatic ticket vending machines, thermosensitive labeling, etc. Have been.

However, such a heat-sensitive recording material comprising a combination of a leuco dye and a phenolic substance has a drawback in that a color image disappears or fades due to contact with a solubilizer, oils and fats, and water. In recent years, with the expansion of POS systems such as retail stores and supermarkets, the use of labels and station automation systems for train tickets has been increasing, and various improvements have been studied for this shortcoming. is there.

Problems to be Solved by the Invention A color image obtained in a thermal recording method using a thermal recording material in which a thermal coloring layer having a color developing substance and a color developing substance as main components is formed on a support is a solvating agent, an oil or fat and the like. It is desired to develop a heat-sensitive recording material that does not disappear or discolor due to water or the like.

Means for Solving the Problems The present inventors have conducted intensive studies to improve the above-mentioned drawbacks of the thermosensitive recording material, and as a result, have supported a thermosensitive coloring layer containing a coloring material and a coloring material as main components. As described above, in the thermosensitive recording material formed on the body, an overcoat layer containing pectins, inbutylene-N-phenylmaleimide maleic anhydride copolymer and an epoxy compound as essential components is provided on the thermosensitive coloring layer. The present inventors have found that the disadvantages of various heat-sensitive recording materials are improved and completed the present invention.

The pectins used in the present invention are natural carbohydrates (polysaccharides) present as components of plant cell tissues.
The main component thereof is a partially methylated product of polygalacturonic acid and an amide, sodium, potassium, or calcium salt of a carboxyl group thereof, and is a polysaccharide having a degree of polymerization of 150 to 500.

Pectin is roughly classified into high methoxyl pectin and low methoxyl pectin according to the degree of esterification, and any pectin can be used for the purpose of the present invention. Even if pectins are applied alone as an overcoat layer on a heat-sensitive recording sheet, the plasticizer resistance is improved, but the water resistance is not sufficient, so the heat-sensitive recording sheet provided with such an overcoat layer Has a drawback that the overcoat layer peels off when submerged in water. In addition, pectins can be used for the overcoat layer after making them water-resistant with alkaline earth ions such as calcium and magnesium.However, since the adhesiveness to the heat-sensitive recording sheet is insufficient, the overcoat layer is still immersed in water. The disadvantage of peeling occurs.

For this reason, when using pectins, water-soluble polymer compounds and / or polymer compounds having poor water solubility such as methylcellulose, methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, polyvinyl alcohol, and carboxy-modified polysaccharide are used to obtain water resistance. Vinyl alcohol, acetoacetylated polyvinyl alcohol, silica-modified polyvinyl alcohol, alkali salts of acrylic acid / styrene copolymer, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, starch and derivatives thereof, casein, gelatin, styrene
Water-soluble polymer compounds such as alkali salts of maleic anhydride copolymers, alkali salts of iso (or diiso) butylene-maleic anhydride copolymers or polyvinyl acetate, vinyl chloride / vinyl acetate copolymers, polystyrene, poly It has been proposed to mix a water-insoluble polymer compound such as an acrylate ester, a polyurethane, or a styrene / butadiene / acrylic acid copolymer, but sufficient performance has not been obtained.

Isobutylene used with pectins in the present invention
The N-phenylmaleimide-maleic anhydride copolymer is obtained by, for example, isobutylene, N-phenylmaleimide and maleic anhydride in a weight ratio of isobutine: N-phenylmaleimide: maleic anhydride 50:45 to 20: 5 to 30. They are obtained by co-weighting and usually have a molecular weight of 20,000 to 80,000. In the heat-sensitive material of the present invention, such a copolymer can be used as it is. Further, in the present invention, an epoxy compound is contained in the overcoat layer as an essential component in order to strengthen and promote crosslinking.
Specific examples of epoxy compounds include polyamide epoxy resin, ethylene polyethylene glycol diglycidyl ether, propylene polypropylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, phenol glycidyl ether, lauryl alcohol glycidyl ether, sorbitol, and polyglycidyl ether. 1.3 bis (N, N-diglycidylaminomethyl) cyclohexane, N,
N, N ', N-tetraglycidyl m-xylene and the like can be mentioned.

The overcoat layer in the present invention is the above-mentioned pectins and isobutylene-N-phenylmaleimide-maleic anhydride copolymer, an epoxy compound, a water-soluble polymer compound of the preceding example, a water-soluble polymer compound, and a water-soluble polymer compound. A crosslinking agent for crosslinking them, an inorganic pigment, a filler fatty acid metal salt, various surfactants, and the like can be added. Then, an overcoat layer is provided by preparing a coating solution of these compositions as an aqueous solution, an aqueous emulsion or an aqueous dispersion, and applying the coating solution to the heat-sensitive recording layer with a coater or the like. The mixing ratio of isobutylene-N-phenylmaleimide-maleic anhydride copolymer to pectins in the coating liquid (weight ratio, the same applies hereinafter) is usually more preferably at a ratio of 0.05 to 10 with respect to the former 1 with respect to the latter. 0.1 to 5. The amount of the epoxy compound to be used is preferably 0.01 to 0.5, preferably 0.05 to 0.2, based on 1 of the total solid components. Pectins, isobutylene-N.
The proportion of the solid component such as phenylmaleimide-maleic anhydride copolymer is 1 to 30%, more preferably 3 to 15%.
(Weight ratio). The thickness of the overcoat layer is preferably from 0.2g / m ² ~8g / m ² at normal dry solids 0.5 g / m ² to 5
a g / m ^2, in 0.2 g / m ² or less in some the resistance improved plasticizer resistance also not 8 g / m ² or more is sufficient, there is a possibility that the decrease in color developing sensitivity occurs.

Next, the heat-sensitive recording material to be provided with the overcoat layer of the present invention will be described. This thermosensitive recording material is applied to paper, film, synthetic paper, etc. by applying a coating liquid prepared from a known color developing substance, a color developing substance and, if necessary, a binder, a filler, and other additive substances. It was done.

Here, as the coloring substance, a xanthene compound, a triarylmethane compound, a spiropyran compound, a diphenylmethane compound, a thiazine compound, a fluorene compound or the like is used, and specific examples thereof are given.

2-anilino-3-methyl-6-diethylaminofluoran and 2-anilino-3 as xanthene compounds
-Methyl-6- (methylcyclohexylamiso) -fluoran, 2-anilino-3-methyl-6- (ethylisobentylamino) fluoran, 2-anilino-3-methyl-6-dibutylaminofluoran, 2- ( p-chloroanilino) -3-methyl-6-diethylaminofluoran, 2- (p-fluoroanilino) -3-methyl-6-
Diethylaminofluoran, 2-anilino-3-methyl-6- (p-toluidinoethylamino) fluoran, 2
-(P-toluidino) -3-methyl-6-diethylaminofluoran, 2- (o-chloroanilino) -6-dibutylaminofluoran, 2- (o-fluoroanilino)
-6-diethylaminofluoran, 2- (o-fluoroanilino) -6-dibutylaminofluoran, 2-anilino-3-methyl-6-biperidinofluoran, 2-anilino-3-methyl-6 Pyrrolidinofluoran, 2-
Ethoxyethylamino-3-chloro-6-diethylaminofluoran, 2-anilino-3-chloro-6-diethylaminofluoran, 2-chloro-6-diethylaminofluoran, 2-methyl-6-diethylaminofluoran and the like; 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone) as a reel methane compound;
3,3-bis- (p-dimethylaminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3- (1,2
-Dimethylaminoindol-3-yl) phthalide and the like;
Examples of diphenylmetas compounds such as 3-methyl-3-spiro-dinaphthopyran and 1,3,3-trimethyl-6'-nitro-8'-methoxyspiro (indoline-2,2'-benzopyran) as spiropyran compounds N-halophenyl-leuco auramine, benzoyl leucomethylene blue as a thiazine compound, 3,6-bis (dimethylamino) fluorene spiro (9,3 ')-6'-dimethylaminophthalide as a fluorene compound [3, 6
-Bis (dimethylamino) fluorenespiro (9,3 ')
-6'-pyrrolidinophthalide], [3-dimethylamino-6-diethylamino-fluorenespiro (9,3 ')-
6'-pyrrolidinophthalide], and these leuco dyes are used alone or in combination.

Examples of the color-developing substances include p-octylphenol and p-octylphenol.
tert-butylphenol, p-phenylphenol, 1,
1-bis (p-hydroxyphenyl) propane, 2,2-bis- (p-hydroxyphenyl) -propane, 1,1-bis (p-hydroxyphenyl) cyclohexane, 4,4'-
Thiobisphenol, 4,4'-sulfonyldiphenol, bis- (3-allyl-4-hydroxyphenyl)-
Sulfone, novolak type phenol resin, benzyl p-hydroxybenzoate, ethyl p-hydroxybenzoate,
Dimethyl 4-hydroxyphthalate, ethyl 5-hydroxyisophthalate, 3,5-di-tert-butylsalicylic acid,
Examples of 3,5-di-α-methylbenzylsalicylic acid and the like and aromatic carboxylic acids include polyvalent metal salts thereof.

Examples of the binder include methylcellulose, methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, silica-modified polyvinyl alcohol, alkali salts of styrene acrylate copolymer, and polyvinylpyrrolidone. , Polyacrylamide, polyacrylic acid, starch and derivatives thereof, casein, gelatin, styrene
Water-soluble ones such as an alkali salt of a maleic anhydride copolymer, an alkali salt of an iso (or diiso) butylene-maleic anhydride copolymer, or polyvinyl acetate, a vinyl chloride / vinyl acetate copolymer, polystyrene, and polyacryl Water-insoluble emulsions such as acid esters, polyurethanes, and styrene / butadiene / acrylic acid copolymers are used.

Calcium carbonate, magnesium carbonate,
Examples include magnesium oxide, silica, white carbon, talc, clay, alumina, magnesium hydroxide, aluminum hydroxide, aluminum oxide, barium sulfate, polystyrene resin, and urea-formalin resin.

As sensitizers, animal and plant waxes, polyethylene waxes, waxes such as synthetic waxes and higher fatty acids,
Those which are solid at room temperature and have a melting point of 80 ° C. or higher, such as higher fatty acid amides, higher fatty acid metal salts, acetylated aromatic amines, aromatic ether compounds, and biphenyl derivatives are preferred.

As other additives, lubricants such as zinc stearate, calcium stearate and aluminum stearate, various surfactants, antifoaming agents and the like are added as required.

The heat-sensitive recording material of the present invention is prepared using the above-mentioned material by the following method, for example. That is, first, a color-forming compound and a color-developing compound are separately separated by a ball mill, an attritor, and a sand mill together with a binder, water or other additives as necessary, a protective colloid substance such as polyvinyl alcohol, a surfactant, and the like. After being pulverized and dispersed by a disperser such as the above (usually, pulverization and dispersion are carried out by containing about 5 to 70% of a coloring compound or a developing compound).
The mixture is mixed to prepare a thermosensitive coloring layer coating solution, and the solution is coated on a support such as paper, plastic sheet, synthetic paper, or the like with a bar coater or the like at a concentration of 5 to 40 g / m ² . (The ratio of the color-forming compound to the color-developing compound is usually 1: 1 to 1:10 in terms of dry weight ratio.) After drying, the solid content concentration is adjusted to about 1 to 30% on the thermosensitive coloring layer. The above-mentioned overcoat layer coating solution is applied by a bar coater or the like and dried to obtain the heat-sensitive recording material of the present invention. If necessary, an intermediate layer may be further provided between the thermosensitive coloring layer and the overcoat layer of the present invention, and a protective layer may be further formed on the overcoat layer of the present invention. A binder for preparing the color-forming layer or a combination of a binder with a usual filler and fine particle resin is used.

The heat-sensitive recording material of the present invention in which an overcoat layer containing a pectin and isobutylene-N-phenylmaleimide-maleic anhydride copolymer and also an epoxy compound is provided on the heat-sensitive color-forming layer has a higher color development than conventionally known ones. The plasticizer resistance and water resistance of the image are remarkably excellent.

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. `` Parts '' in the examples
Indicates parts by weight.

Reference Example (Preparation of Thermosensitive Recording Paper) [A] to [C] liquids were prepared by separately pulverizing and dispersing a mixture of the following compositions using a sand grinder so that the average particle diameter became 1 to 3 µm. did.

Next, 10 parts of [A] liquid, 55 parts of [B] liquid, and 30 parts of [C] liquid
And a water-containing carboxylated SB latex copolymer (solid content = 50%) at a mixing ratio of 5 parts to prepare a thermosensitive coloring layer forming solution, and a dry solid content of about 50 g / m ^{2 on} a high quality paper surface. It was applied to 9 g / m ² and dried to obtain a thermosensitive recording paper. The following examples were carried out using this heat-sensitive recording paper.

Example 1 The following composition was mixed and dissolved to prepare an overcoat solution, and the heat-sensitive recording paper obtained in Reference Example had a dry solid content of 2 g / m ^2.
Was applied using a bar coater to obtain the heat-sensitive recording material of the present invention.

Example 2 A heat-sensitive recording material of the present invention was obtained in the same manner as in Example 1 except that pectin having an esterification degree of 42 to 48% was used instead of low methoxyl pectin having an esterification degree of 18 to 30%. Was.

Example 3 A heat-sensitive recording material of the present invention was obtained in the same manner as in Example 1 except that high methoxyl pectin having a degree of esterification of 70 to 76% was used instead of low methoxyl pectin.

Example 4 The following composition was mixed and dissolved to prepare an overcoat solution, and the heat-sensitive recording paper obtained in Reference Example had a dry solid content of 3 g / m ^2.
Was applied using a bar coater and dried to obtain the heat-sensitive recording material of the present invention.

Example 5 The following composition was mixed and dissolved to prepare an overcoat solution, and the heat-sensitive recording paper obtained in Reference Example had a dry solid content of 2 g / m ^2.
Was applied using a bar coater and dried to obtain the heat-sensitive recording material of the present invention.

Example 6 A heat-sensitive recording material of the present invention was prepared in the same manner as in Example 5 except that 0.1 part of 1,3 bis (N, N-diglycidylaminomethyl) cyclohexane was used in place of ethylene glycol diglycidyl ether in Example 5. Obtained.

Comparative Example 1 Same as Example 1 except that the same amount of 15% carboxyl group-modified PVA was used in place of the aqueous NH ₄ salt solution of the 15% isobutylene-N-phenylmaleimide-maleic anhydride copolymer of Example 1. Thus, a heat-sensitive recording material for comparison was obtained.

Comparative Example 2 In the same manner as in Example 4 except that the same amount of an aqueous 15% casein solution was used instead of the aqueous NH ₄ salt solution of the 15% isobutylene-N-phenylmaleimide-maleic anhydride copolymer of Example 4. A heat-sensitive recording material for comparison was obtained.

Comparative Example 3 A vinyl acetate-acrylic copolymer emulsion (solid content = 45) was used in place of the aqueous NH ₄ salt solution of the 20% isobutylene-N.phenylmaleimide-maleic anhydride copolymer of Example 5.
%) A heat-sensitive recording material was obtained in the same manner as in Example 5, except that 5 parts were used.

1) Color density Density of the sample printed with a thermal test printer (D-805P) manufactured by Ishida Koki Co., Ltd. Measured with a Macbeth reflection densitometer (RD-914 type) 2) Sodium-resistant agent Thermal test A sample printed by a printer was sandwiched from both sides with a PVC wrap film, and the printed portion was left at 40 ° C. for 15 hours under a load of 0.3 kg / cm ² , and the printed portion was measured with an upper Macbeth reflection densitometer. The value was expressed as a percentage of the density after the test with respect to the color density before the test.

3) Water resistance After the sample developed by the thermal test printer was left in water at room temperature for 24 hours, the sample was rubbed with a fingertip and the peeling state of the overcoat layer was observed. ×
The mark indicates severe peeling, the mark Δ indicates partial peeling, and the mark ○ indicates no peeling.

As is clear from the above-mentioned quality performance tests, the heat-sensitive recording material of the present invention is characterized by having excellent solvability and water resistance of a color image.

Effect of the Invention A heat-sensitive recording material containing a color-forming substance and a color-developing substance capable of developing color when heated, as a main component, has excellent soviability resistance and water resistance.

Claims (1)

(57) [Claims] 1. A heat-sensitive recording material comprising, on a support, a heat-sensitive coloring layer mainly comprising a color-forming substance and a color-developing substance capable of causing the color-forming substance to develop a color when heated. A heat-sensitive recording material comprising an overcoat layer containing an inbutylene-N-phenylmaleimide-maleic anhydride copolymer and an epoxy compound as essential components.