JPH0645258B2 - 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 having less dust adhered to a thermal head and excellent in stability of a color image.

2. Description of the Related Art A heat-sensitive recording sheet using a colorless or light-colored coloring substance and a color-developing substance capable of coloring the coloring substance under heat is disclosed in Japanese Patent Publication No.
No. 3-4160, Japanese Patent Publication No. 45-14039, etc. Usually, a thermosensitive 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, mixing them, and then adding an auxiliary agent such as a binder, a sensitizer, a filler and a lubricant. It is applied as a coating liquid on a support such as paper, film, synthetic paper, etc., and one or both of the leuco dye and the color developer are melted by heating and a color reaction is obtained by a chemical reaction caused by contact. is there. A thermal printer or the like having a built-in thermal head is used to obtain such color recording. The thermal recording method has the following characteristics: (1) No noise during recording (2) Phenomenon, no need for fixing, etc. (3) Maintenance-free (4) Machines are relatively inexpensive, etc. It is widely used in the field of printers, printers such as calculators, recorders for medical measurement, vending machines, and thermosensitive recording labels.

However, such a heat-sensitive recording sheet that is a combination of a leuco dye and a phenolic substance (1) has dust on the thermal head at the time of recording (2) fading in the colored image portion due to contact with plasticizers and oils ( It has the drawback of being resistant to plasticizers.

Problems to be Solved by the Invention In a thermosensitive recording method using a thermosensitive recording sheet in which a thermosensitive coloring layer containing a color-developing substance and a color-developing substance as main components is formed on a support, a thermal head does not have a trace when heat-developed and is obtained. It is desired to develop a heat-sensitive recording sheet in which the formed color image does not fade due to plasticizers, oils and fats.

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 found that a colloidal inorganic silicate and a self-crosslinking acrylic emulsion are formed on the thermosensitive coloring layer. The present invention has been completed by finding that the above-mentioned drawbacks of the heat-sensitive recording sheet are ameliorated by applying the following coating liquid and then drying it to form an overcoat layer.

The colloidal inorganic silicate used in the present invention means a compound which is a water-insoluble inorganic silicate and whose fine particles swell in water and can be dispersed in a colloidal state.

Specific examples thereof include colloidal aluminum silicates such as kaolin, kibushi clay, bentonite, colloidal magnesium silicates such as sepiolite, colloidal magnesium aluminum silicates such as attapulgite, colloidal fluorine-containing magnesium silicates such as dimonite. Etc.

The self-crosslinking acrylic emulsion used in the present invention has a functional group reactive with the polymer or copolymer itself, and this functional group undergoes a crosslinking reaction to form a nodular polymer structure. It is an emulsion consisting of polymers or copolymers obtained from esters. Polymers or copolymers having such reactive functional groups are overcoat layers, which crosslink with the evaporation of the solvent to form a film. Examples of the crosslinking reaction include carboxyl group, hydroxyl group, amino group, epoxide group, amide group or N-methylolamide group in polymers or copolymers of acrylic acid, methacrylic acid or their esters or modified products thereof. An example is a reaction between functional groups. This cross-linking reaction also includes a carboxyl group, a hydroxyl group, an amino group, an N-methylol group, which these reactive groups and a cross-linking agent optionally used have.
It may be a reaction with an N-methylol ether group, an isocyanate group, an epoxy group, an aldehyde group, or a reaction between these groups and a metal ion or a metal compound.

The colloidal inorganic silicate used in the present invention is also useful for forming a crosslinking reaction.

Specific examples of the self-crosslinking acrylic polymer are shown below, and alkyl represents alkyl having 10 or less carbon atoms such as methyl, ethyl, propyl, butyl, and 2-ethylhexyl. Vinyl acetate-acrylic acid copolymer, vinyl acetate-methacrylic acid copolymer, vinyl acetate-alkyl acrylate copolymer, vinyl acetate-alkyl methacrylate copolymer, acrylonitrile-acrylic acid copolymer, acrylonitrile-acrylic acid -Alkyl acrylate copolymer, acrylonitrile-alkyl methacrylate copolymer, acrylonitrile-methacrylic acid-alkyl acrylate-alkyl methacrylate-styrene copolymer, acrylonitrile-dialkylaminoalkyl methacrylate-acrylamide copolymer, acrylic acid Metallic salts such as methacrylic acid copolymers, acrylic acid-alkyl acrylate copolymers (ammonium, Li, Na, K, Mg, C
a, a salt such as Al), acrylic acid-alkyl acrylate-
Acrylamide copolymer, acrylic acid-methacrylamide-styrene copolymer, methacrylic acid-alkyl acrylate-alkyl methacrylate copolymer, methacrylic acid metal salt-alkyl acrylate-alkyl methacrylate copolymer (ammonium, Li, Na, K, Mg, Ca, A
1), methacrylic acid-alkyl acrylate-alkyl methacrylate-acrylamide copolymer, methacrylic acid-alkyl methacrylate copolymer, alkyl acrylate-acrylamide-styrene copolymer, alkyl methacrylate-alkyl acrylate -Maleic anhydride copolymer, methacrylic acid-alkyl acrylate-maleic anhydride light metal salt copolymer (ammonium, Li, Na,
K, Mg, Ca, Al salts), alkyl acrylate-
Styrene-maleic anhydride light metal salt copolymer (ammonium, Li, Na, K, Mg, Ca, Al, etc. salts), alkyl methacrylate-fumaric acid copolymer, alkyl acrylate-itaconic acid light metal salt copolymer (Ammonium,
Examples thereof include modified products obtained by introducing the above-described functional groups into a copolymer such as Li, Na, K, Mg, Ca, and Al). In the present invention, these modified products are used as an aqueous emulsion by optionally using an emulsifier or the like.

Further, as a cross-linking agent used if necessary, epoxy compounds, polyamines, polyhydric alcohols, aldehydes,
Examples include polyvalent metal compounds.

The overcoat layer can be obtained by preparing a coating solution containing the above-mentioned colloidal inorganic silicate and a self-crosslinking emulsion, applying the coating solution on the heat-sensitive recording layer with a coater, and heating and drying if necessary. The thickness of this overcoat layer is 0.5-8 μm, preferably 1-5 μm,
If it is 0.5μ or less, the prevention of dust adhesion to the thermal head during recording and the improvement of the plasticizer resistance are not sufficient, and 8μ
With the above, the coloring sensitivity is lowered.

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, and a coating liquid consisting of a color-developing substance, a color-developing substance, a binder, a filler, and other additive substances is usually applied to paper, film,
It is applied to synthetic paper.

Xanthene compounds, triarylmethane compounds, spiropyran compounds, diphenylmethane compounds, thiazine compounds and the like are used as the color-developing substance, and specific examples thereof are given. 2-anilino-3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6- (methylcyclohexylamino) -fluorane, 2-anilino-3 as xanthene compounds
-Methyl-6- (ethylisopentylamino) 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 and the like, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide as a triarylmethane compound (alias: Crystal violet lactone), 3,3-bis- (p-
Dimethylaminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3- (1,2-dimethylaminoindol-3-yl) phthalide, and the like 3-methyl-3-spiro-dinaphthopyran as a spiropyran-based compound ,
1,3,3-trimethyl-6'-nitro-8'-methoxyspiro (indoline-2,2'-benzopyran),
Examples thereof include N-halophenyl-leuco auramine as a diphenyl methane compound, benzoyl leuco methylene blue as a thiazine compound, and these leuco dyes may be used alone or in a mixture.

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, novolak type phenol resin, p
-Benzyl hydroxybenzoate, ethyl p-hydroxybenzoate, dimethyl 4-hydroxyphthalate, ethyl 5-hydroxyisophthalate, 3,5-di-tert-butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid, etc. In the case of aromatic carboxylic acids, polyvalent metal salts thereof can be mentioned.

As the binder, methyl cellulose, methoxy cellulose, hydroxyethyl cellulose, carboxydimethyl cellulose, polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, starch and its derivatives, casein, gelatin, styrene-maleic anhydride copolymer Water-soluble substances such as alkali salts of polymers, alkali salts of iso (or diiso) butylene-maleic anhydride copolymers, or polyvinyl acetate, vinyl chloride / vinyl acetate copolymers,
A water-insoluble emulsion such as polystyrene, polyacrylic acid ester, polyurethane, styrene / butadiene / acrylic acid type copolymer, and self-crosslinking acrylic polymer is 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.

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 outputs, printers such as calculators, recorders for medical measurement, tickets for automatic ticket vending machines, heat-sensitive recording labels and the like. Further, it is also used for a magnetic recording kiss, 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. In the following examples, the "self-crosslinking acrylic emulsion" means an aqueous emulsion of a modified product obtained by introducing the functional group as described above into the copolymer described in each.

Example 1. Liquids [A] to [C] were prepared by separately pulverizing and dispersing a mixture having the following composition using a sand grinder so as to have an average particle size of 1 to 3 μm.

Then, [A] liquid: [B] liquid: [C] liquid is 6:47:47.
To prepare a thermosensitive color forming layer forming liquid, and the basis weight is about 50
A thermosensitive recording paper was obtained by coating the surface of a high-quality paper of g / m ^{2 so} that the dry solid content was 10 g / m ² and drying. Next, a compound containing a colloidal hydrous aluminum silicate as a main component (Kunipine F manufactured by Kunimine Industries Co., Ltd.) and a self-crosslinking acrylic emulsion (animonium methacrylate salt-ethyl acrylate-methyl methacrylate copolymer as a main component). (A coating liquid) was mixed at a solid content weight ratio of 1: 5 to obtain a dry thickness of 2 μ and overdried to obtain a heat-sensitive recording sheet (paper) of the present invention.

Example 2. Instead of the colloidal hydrous aluminum silicate-based compound used in Example 1, a colloidal fluorine-containing magnesium silicate-based compound (manufactured by Topy Industries, Ltd.,
A thermosensitive recording sheet (paper) of the present invention was obtained in the same manner as in Example 1 except that Dimonite) was used.

Example 3. In Example 1, as a coating liquid, colloidal hydrous aluminum silicate and a self-crosslinking acrylic emulsion (ammonium methacrylate salt-butyl acrylate-methyl methacrylate copolymer as a main component) were used in a solid component weight ratio of 1 :. A thermal recording sheet (paper) of the present invention was obtained by treating in the same manner as in Example 1 except that the mixture of 3 was used (however, the thickness of the coating film was 3 μm).

Example 4. In Example 1, colloidal magnesium fluorinated silicate and a self-crosslinking acrylic emulsion (ammonium methacrylate salt-methyl acrylate-methyl methacrylate copolymer) as a coating liquid were used as a coating liquid at a solid content weight ratio of 1 A heat-sensitive recording sheet (paper) of the present invention was obtained in the same manner as in Example 1 except that the mixture of 1: 1 was used (however, the thickness of the coating film was 3 μm).

Example 5. The self-crosslinking acrylic emulsion used in Example 1 and the self-crosslinking acrylic emulsion used in Example 4 and a compound mainly containing colloidal hydrous aluminum silicate (Kunipia G, manufactured by Kunimine Industries Co., Ltd.) A thermosensitive recording sheet (paper) of the present invention was obtained in the same manner as in Example 1 except that a mixture having a weight ratio of 1: 1: 1 was used so that the dry thickness was 3 μm.

Examples 6-15. A coating solution was prepared from the self-crosslinking acrylic emulsion shown in the table and the colloidal inorganic silicate by substantially the same method as in Example 1, and the coating solution was overcoated on the thermosensitive color developing layer to obtain the thermosensitive recording sheet (paper of the present invention. ) Got.

This overcoated thermal recording sheet was found to have improved dust adhesion and plasticity resistance with almost no loss in color density, as compared with the non-overcoated thermal recording sheet.

Coloring Test and Comparative Test The thermosensitive recording sheet (paper) of the present invention obtained as described above and a base paper before overcoat for comparison (Comparative Example 1)
And the self-crosslinking acrylic emulsion used in Example 1 (ammonium methacrylate salt, ethyl acrylate, methyl methacrylate copolymer as the main component) was used to obtain a dry thickness of 2μ. A performance test was performed using the coated product (Comparative Example 2). The results are shown in the table below.

Color density The color density when a recording sheet was pressed at 140 ° C. for 5 seconds using a hot plate was measured with a Macbeth reflection densitometer RD-914.

Adhesion of residue The presence or absence of residue on the thermal head when printed with OKIFAX 7800 (manufactured by Oki Electric Co., Ltd.) for a certain period of time was visually judged.

Plasticizer resistance test Polyvinyl chloride wrap film was pressure contacted (approx. 20 g / cm ² ) from both sides of the developed thermosensitive recording paper and left at room temperature for 7 days, then the image density was measured and compared with the image density before the test. Displayed as a percentage.

As is clear from the above comparative tests, the thermal recording sheet of the present invention has improved dust adhesion and plasticizer resistance with almost no loss in color density as compared with known recording sheets.

Effects of the Invention In a thermosensitive recording sheet containing a color-developing substance and a color-developing substance that develops this color when heated, the adhesion of dust at the time of coloring is reduced with almost no loss of color density, and a color image formed by a plasticizer is formed. It was possible to significantly reduce the decrease in concentration.

Claims (1)

[Claims] 1. A coating liquid comprising a colloidal inorganic silicate and a self-crosslinking acrylic emulsion is applied on the thermosensitive coloring layer,
Next, a thermosensitive recording sheet characterized by being dried and provided with an overcoat layer