JPH0723024B2 - Thermal recording sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat-sensitive recording sheet, and more particularly to a heat-sensitive recording sheet excellent in stability of a color image.

2. Description of the Related Art A heat-sensitive recording sheet using a colorless or light-colored color-forming substance and a color-developing substance capable of coloring the color-forming substance under heat is disclosed in Japanese Patent Publication No.
-4160, Japanese Patent Publication No. 45-14039, etc., and is widely used. Usually, a heat-sensitive recording sheet is prepared by dispersing a leuco dye and a color developing agent such as a phenolic substance in the form of fine particles, and then mixing them together, and then adding an auxiliary agent such as a binder, a sensitizer, a filler, and a lubricant. As a coating liquid, which is applied to a support such as paper, film, synthetic paper, etc., and one or both of the leuco dye and the color developer are dissolved by heating and a color reaction is obtained by a chemical reaction caused by contact. . To obtain such color development recording, a thermal printer having a built-in thermal head is used. Thermal recording is better than other recording methods (1)
No noise is generated during recording (2) No need for development, fixing, etc. (3) Maintenance-free (4) Machines are relatively inexpensive, and the field of fax machines, computer output, calculators, and other printer fields,
It is widely used in the fields of medical measurement recorders, automatic ticket vending machines, and heat-sensitive recording labels.

However, such a heat-sensitive recording sheet containing a combination of a leuco dye and a phenolic substance has a drawback that the color image portion is discolored (plasticizer resistance) due to contact with a plasticizer and oils and fats.

Problems to be Solved by the Invention A color-developed image obtained by a thermosensitive recording method using a thermosensitive recording sheet having a thermosensitive color-developing layer containing a color-developing substance and a color-developing substance as main components on a support is a plasticizer, oils There is a demand for the development of a thermal recording sheet that does not cause discoloration due to factors such as the above.

Means for Solving the Problems As a result of intensive studies to improve the above-mentioned drawbacks of the thermosensitive recording sheet, the present inventors have developed a thermosensitive coloring layer containing a color-developing substance and a color-developing substance as main components. In a thermosensitive recording sheet formed on a support, the thermosensitive coloring layer is provided with an overcoat layer comprising pectins and a water-soluble polymer compound and / or a water-insoluble polymer compound as described above. The present invention has been completed by finding that the defects of the recording sheet are improved.

The pectins used in the present invention are natural carbohydrates (polysaccharides) existing as constituents of plant cell tissues,
Its main components are partially methylated polygalacturonic acid and amide of its carboxyl group, sodium, potassium,
Alternatively, it is a polysaccharide having a degree of polymerization of 150 to 500, which is composed of a calcium salt or the like.

Pectin is roughly classified into high methoxyl pectin and low methoxyl pectin according to its degree of esterification, but pectin can also be used for the purpose of the present invention.

Specific examples of the water-soluble polymer compound or the water-insoluble polymer compound include methyl cellulose, methoxy cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, carboxy group-modified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, and silica modified. Polyvinyl alcohol, alkali salt of acrylic acid / styrene copolymer, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, starch and its derivatives, casein, gelatin, styrene-
Alkaline salt of maleic anhydride copolymer, water-soluble polymer compound such as alkali salt of iso (or diiso) butylene-maleic anhydride copolymer, or polyvinyl acetate, vinyl chloride / vinyl acetate copolymer, polystyrene, poly Examples of the water-insoluble polymer compound include acrylic acid ester, polyurethane, and styrene / butadiene / acrylic acid type copolymer.

For the overcoat layer of the present invention, a coating solution is prepared from the above-mentioned pectins and a water-soluble polymer compound or / and a water-insoluble polymer compound as an aqueous solution or water-based emulsion thereof, for example, on a heat-sensitive recording layer with a coater. Obtained by applying.

The mixing ratio of the water-soluble polymer compound and / or the water-insoluble polymer compound with respect to pectins in the coating liquid is usually the former 1 to the latter 0.1 to 10 (weight ratio). The proportion of the solid content of the pectin, the water-soluble polymer compound and / or the water-insoluble polymer compound in the coating liquid is preferably 1 to 30%, more preferably 3 to 15% (weight ratio). The thickness of this overcoat layer is usually 0.2μ-8μ,
The thickness is preferably 0.5 to 5 μ, and when the thickness is 0.2 μ or less, the plasticizer resistance is not sufficiently improved, and when it is 8 μ or more, the coloring sensitivity may decrease.

Even if the pectins used in the present invention are applied alone as an overcoat layer on a thermosensitive recording sheet, the plasticizer resistance is improved, but the water resistance is not sufficient, and therefore such an overcoat layer is provided. When the thermal recording sheet is submerged in water, the overcoat layer peels off. It is also possible to use the pectins in the overcoat layer after making them water resistant with alkaline earth ions such as calcium and magnesium, but since the adhesiveness to the thermal recording sheet is insufficient, the overcoat layer may still be submerged in water. It causes the drawback of peeling.

Therefore, in order to obtain sufficient plasticizer resistance and water resistance, it is essential to mix and apply the pectins and the water-soluble polymer compound and / or the water-insoluble polymer compound. Furthermore, in order to impart sufficient plasticizer resistance and water resistance, alkaline earth ions that make pectin water resistant are used in combination, or water-soluble polymer compounds and / or cross-linking water-insoluble polymer compounds are cross-linked. Agents and the like can also be used in combination. Agents for making pectin water resistant include calcium chloride, calcium acetate, calcium oxalate, calcium lactate, calcium citrate, calcium tartrate, magnesium chloride, magnesium acetate, magnesium oxalate, magnesium lactate, magnesium citrate, calcium tartrate. An aqueous solution of the above, an aqueous solution containing calcium or magnesium, or the like is used. By applying these aqueous solutions on the overcoat layer of the present invention, water resistance can be made complete.

As a cross-linking agent for cross-linking a water-soluble polymer compound and / or a water-insoluble polymer compound, formalin, glyoxal, glycine, glycidyl ester, glycidyl ether, dimethylol urea, ketene dimer, dialdehyde starch, melamine resin, Polyamide resin, polyamide epoxy resin, ketone-aldehyde resin, polyethyleneimine resin, boric acid, borax, ammonium chloride, aluminum sulfate, ammonium zirconium carbonate, Ti, Zr,
Alkoxides such as Al are used.

Next, the thermal recording sheet to be provided with the overcoat layer of the present invention will be described. This heat-sensitive recording sheet is known per se. Normally, a coating solution prepared from a color-developing substance, a color-developing substance and, if necessary, a binder, a filler, and other additives is applied to paper, film, synthetic paper, etc. It was done.

Xanthene compounds, triarylmethane compounds, spiropyran compounds, diphenylmethane compounds, thiazine compounds, fluorene compounds, and the like are used as the color-developing substance, and specific examples thereof are given.

2-anilino-3-methyl-6-diethylaminofluorane as a xanthene compound, 2-anilino-3-
Methyl-6- (methylcyclohexylamino) -fluorane, 2-anilino-3-methyl-6- (ethylisobenthylamino) fluorane, 2-anilino-3-methyl-6-dibutylaminofluorane, 2- (p -Chloroanilino) -3-methyl-6-diethylaminofluorane, 2- (p-fluoroanilino) -3-methyl-6-
Diethylaminofluorane, 2-anilino-3-methyl-6- (p-toluidinoethylamino) fluorane, 2
-(P-toluidino) -3-methyl-6-diethylaminofluorane, 2- (o-chloroanilino) -6-dibutylaminofluorane, 2- (o-fluoroanilino)
-6-diethylaminofluorane, 2- (o-fluoroanilino) -6-dibutylaminofluorane, 2-anilino-3-methyl-6-piperidinofluorane, 2-anilino-3-methyl-6- Pyrrolidinofluorane, 2-
Ethoxyethylamino-3-chloro-6-diethylaminofluorane, 2-anilino-3-chloro-6-diethylaminofluorane, 2-chloro-6-diethylaminofluorane, 2-methyl-6-diethylaminofluorane, tria 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide as a reel methane compound (also known as crystal bioleptlactone),
3,3-bis- (p-dimethylaminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3- (1,2
-Dimethylaminoindol-3-yl) phthalide, etc.,
3-methyl-3-spiro-dinaphthopyran as spiropyran-based compound, 1,3,3-trimethyl-6'-nitro-8'-methoxyspiro (indoline-2,2'-benzopyran), etc. as diphenylmethane-based compound N-
Halophenyl-leuco auramine, benzoyl leuco methylene blue as a thiazine-based compound, 3,6-bis (dimethylamino) fluorene spiro (9,3 ')-6'-dimethylaminophthalide [3,6- Bis (dimethylamino) fluorene spiro (9,
3 ')-6'-pyrrolidinophthalide], [3-dimethylamino-6-diethylamino-fluorenspiro (9,
3 ')-6'-pyrrolidinophthalide] and the like, and these leuco dyes may be used alone or in combination.

Also, as the color-developing substance, p-octylphenol, p-te
rt-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, Novolac-type phenol resin, benzyl p-hydroxybenzoate, ethyl p-hydroxybenzoate,
Dimethyl 4-hydroxyphthalate, ethyl 5-hydroxyisophthalate, 3,5-di-tert-butylsalicylic acid,
In the case of 3,5-di-α-methylbenzyl salicylic acid and the like and aromatic carboxylic acids, polyvalent metal salts thereof can be mentioned.

As the binder, methyl cellulose, methoxy cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, silica-modified polyvinyl alcohol, styrene acrylate copolymer alkali salt, polyvinylpyrrolidone, Polyacrylamide, polyacrylic acid, starch and its derivatives, casein, gelatin, alkali salt of styrene-maleic anhydride copolymer, iso (or diiso)
Butylene-water-soluble substances such as alkali salts of maleic anhydride copolymer or polyvinyl acetate, vinyl chloride / vinyl acetate copolymer, polystyrene, polyacrylic ester,
Wastewater-soluble emulsions such as polyurethane and styrene / butadiene / acrylic acid type copolymers are used.

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

As the sensitizer, waxes such as animal and plant waxes, polyethylene waxes, synthetic waxes and higher fatty acids, higher fatty acid amides, higher fatty acid metal salts, acetylated aromatic amines, aromatic ether compounds, biphenyl derivatives, etc. at room temperature. A solid substance having a melting point of 80 ° C. or higher is preferable.

Other additives include lubricants such as zinc stearate, calcium stearate and aluminum stearate,
Various kinds of surfactants, antifoaming agents and the like are added as needed.

Paper, synthetic paper, film or the like is used as the support on which the thermosensitive coloring layer is provided.

The heat-sensitive recording sheet of the present invention is widely used for facsimiles, computer output, printers such as calculators, recorders for medical measurement, tickets for vending machines, heat-sensitive recording labels and the like. Further, it can also be used for a magnetic recording chip, a card or the like having a magnetic recording layer provided on the surface of the thermosensitive recording sheet support opposite to the thermosensitive coloring layer.

Examples The present invention will be described in more detail with reference to Examples.

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

Then [A] solution: [B] was: [C] solution were mixed at a ratio of 6:47:47 with thermosensitive coloring layer forming liquid dry solids in the prepared fine paper surface of the basis weight about 50 g / m ² and Of 10 g / m ² ; dried to obtain a thermosensitive recording paper. The following examples were carried out using this thermosensitive recording paper.

Example 1 A composition represented by the following A was dissolved in water to give a solid content of 3
% Of the aqueous solution, and the resulting thermal recording paper obtained in the above-mentioned Reference Example was coated with a bar coater so as to have a dry thickness of 2 μ (overcoat). ) Got.

Example 2 A thermal recording sheet (paper) of the present invention was obtained by further coating a 2% aqueous solution of calcium lactate on the thermal coated paper coated with the overcoat of Example 1 to a dry thickness of 0.2 μm.

Example 3 A composition represented by the following B was dissolved in water to give a solid content of 3
%, The aqueous solution was prepared, and overcoated in the same manner as in Example 1 to obtain a thermosensitive recording sheet of the present invention.

Example 4 Instead of using composition B in example 3, the following composition C
A thermal recording sheet (paper) of the present invention was obtained in the same manner as in Example 3 except that was used.

Example 5 Instead of using composition B in example 3, the following composition D
A thermal recording sheet (paper) of the present invention was obtained in the same manner as in Example 3 except that was used.

Example 6 Instead of using composition B in example 3, the following composition E
A thermal recording sheet (paper) of the present invention was obtained in the same manner as in Example 3 except that was used.

The thermal recording sheet (paper) of the present invention obtained as described above and the thermal recording sheet before overcoat obtained in Reference Example for comparison (Comparative Example 1). The thermal recording sheet obtained in Reference Example was acetoacetylated polyvinyl alcohol. [Nippon Synthetic Chemical Industry Co., Ltd.
Made by mixing 6 parts of Gosef Eyemer Z100] and 0.05 parts of glyoxal [manufactured by Nippon Synthetic Chemical Industry Co., Ltd., 40% aqueous solution] and overcoated so that the dry thickness becomes 2 μ (Comparative Example 2 ), The thermal recording paper obtained in Reference Example was overcoated with pectin [Red Rib bon 3G manufactured by Unipectin Co., Ltd.] to a dry thickness of 2 μ (Comparative Example 3), and on Comparative Example 3, A performance test was carried out by using a 2% calcium lactate aqueous solution coated to a dry thickness of 0.2 μm (Comparative Example 4). The results are shown in the table below.

[Coloring Density] The coloring density when the recording sheet was pressed at 140 ° C. for 5 seconds using a hot plate was measured with a Macbeth reflection densitometer RD-914.

[Plasticizer test]

The polyvinyl chloride lap film was pressed and contacted (about 20 g / cm ² ) from both sides of the color-developed thermosensitive recording paper and allowed to stand at room temperature for 7 days, and the image density was measured and displayed as a ratio to the image density before the test. .

[Water resistance test]

The color-developed thermosensitive recording paper was allowed to stand in water at room temperature for 24 hours, and then the thermosensitive recording paper was rubbed with a fingertip to observe the peeling state of the overcoat layer. The crosses are terrible with peeling, △
The mark shows a part of peeling, and the ○ mark shows that there is no peeling.

As is clear from the above comparative tests, the heat-sensitive recording sheet of the present invention has excellent plasticizer resistance and good water resistance with almost no loss in color density as compared with known recording sheets.

Effects of the Invention In a thermosensitive recording sheet mainly composed of a color-forming substance and a color-developing substance capable of developing the color when heated, it is possible to remarkably reduce the decrease in the density of the color-developed image due to the plasticizer without substantially impairing the color-developing density. done.

Claims (1)

[Claims] 1. A heat-sensitive recording sheet comprising a support and a heat-sensitive color-forming layer comprising a color-forming substance and a color-developing substance capable of developing a color when the color-forming substance is heated as a main component, on the heat-sensitive color-developing layer. And a water-soluble polymer compound and / or a water-insoluble polymer compound provided with an overcoat layer.