JP5333109B2 - Thermal recording material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording material excellent in color developing sensitivity, chemical resistance, and sticking-proof properties. <P>SOLUTION: The thermal recording material includes sequentially on a support: an under coat layer containing a pigment and a binder as principal components; a thermal recording layer containing a leuco dye and a developer; and a protective layer where the under coat layer contains 1-10 mass% of a styrene-acrylic based copolymer resin obtained from a styrene-acrylic based copolymer resin emulsion based on an under coat total solid content, and further a coating liquid for the thermal recording layer and a coating liquid for a protective layer are applied and dried by a simultaneous multilayer curtain coating method, and thereby the thermal recording layer and the protective layer are formed. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a heat-sensitive recording material.

  A heat-sensitive recording material is known which utilizes a color reaction between a colorless or light leuco dye and an organic or inorganic developer to bring a coloring image into contact with both coloring substances by heat. Such heat-sensitive recording materials are relatively inexpensive, and since the recording equipment is compact and relatively easy to maintain, they are used not only as recording media for facsimiles and various printers but also in a wide range of fields.

  On the other hand, methods such as an air knife coating method, a blade coating method, a rod coating method, a roll coating method, and a bar coating method are used as a method for coating a coating liquid on a substrate such as paper or film. The heat-sensitive recording material prepared by this method has poor coating quality, soaking of the upper coating liquid into the lower layer, upper pinholes caused by repelling during upper coating, etc. In addition to problems such as variations, there are problems such as a limitation in high-speed coating and a decrease in productivity caused by multiple coatings.

  In contrast to these coating methods, the curtain coating method is a method in which a free fall curtain of coating liquid is formed, and this is applied by colliding with a support (see Patent Document 1). It is known that it has aptitude. Moreover, it is also possible to form a coating film composed of a plurality of coating liquid films and apply it on a curtain, and the productivity of multilayer coating can be greatly improved. This curtain coating method is a method in which the coating liquid is applied in a film form from a slit-shaped coater lip on a substrate, and the coating properties of the coating liquid and the wettability to the substrate are improved to prevent uneven coating and coating. In order to prevent defects, fine adjustment is required for static surface tension, dynamic surface tension, viscosity, and the like (see Patent Document 2). From such a viewpoint, the uniform stability of the coating itself is extremely important, and the performance and production efficiency of the heat-sensitive recording material obtained thereby are greatly affected.

  Simultaneous multilayer coating by the curtain coating method has an advantage that productivity can be greatly improved because a plurality of layers can be applied simultaneously as described above. However, after laminating a plurality of coating liquid films, it is necessary to apply, dry and solidify on the support. When the layer structure is disturbed when the coating liquid is laminated or dried and interlayer mixing occurs, the function of each layer is not fully exhibited, and the quality as a heat-sensitive recording material is impaired. For example, when the heat-sensitive recording layer and the protective layer are applied at the same time, if the interlayer mixing occurs, the film thickness of the protective layer becomes non-uniform, resulting in poor chemical resistance against plasticizers, alcohol, etc., and insufficient sticking prevention There are also disadvantages.

  Conventionally, in the field of photographic light sensitive materials where simultaneous multilayer coating is performed by the curtain coating method, gelatin is usually contained as a binder in the coating liquid, and cooling is performed immediately after the coating film is transferred onto the support. As a result, the gelatin in the coating solution gels and the coating solution is immobilized, so that mixing between layers does not occur.

  On the other hand, in the case of heat-sensitive recording materials, there is a problem that various properties such as color development properties and image stability are greatly deteriorated when gelatin is added so that the coating liquid is immobilized by cooling. No method has been found to immobilize the coating liquid without impairing the above characteristics, and interlayer mixing cannot be prevented by a method similar to that for photographic photosensitive materials.

  Several methods have been disclosed in order to develop a good layer separation state by preventing interlayer mixing in information recording materials such as heat-sensitive recording materials and ink jet recording materials. For example, a method of increasing the viscosity over time when two adjacent coating liquids contact or mix (see Patent Document 3), the viscosity of the coating liquid constituting a multi-layer coating liquid film is 100 mPa · s or more, A method of making the surface tension of the lowermost coating liquid of a plurality of coating liquid films 18 to 45 mN / m (see Patent Document 4) is disclosed. Also, a method of drying a plurality of curtain-coated films in a state where the angle between the support and the horizontal plane is 45 degrees or less (see Patent Document 5), and drying a plurality of curtain-coated films within 2 minutes after coating. And the like (see Patent Document 6).

  However, in the method of increasing the viscosity of two adjacent coating liquids described in Patent Document 3, agglomerates are formed by the reaction of the two layers, and coating defects occur, or continuous operation can be performed for a long time due to gelation of the paint. It becomes difficult. Further, even with the method described in Patent Document 4, barrier properties against plasticizers, alcohols, and the like, and sticking resistance are still insufficient. Further, the methods described in Patent Document 5 and Patent Document 6 have a large facility restriction and may have poor quality.

  On the other hand, as a method for improving dot reproducibility and color developability, a method of containing a styrene resin compound in the undercoat layer (Patent Document 7) or a method of containing an alkyl ketene dimer in the undercoat layer (Patent Document 8) is also disclosed. ing. Furthermore, a method for improving the image quality by forming a uniform undercoat layer by preventing the undercoat paint from penetrating into the base paper by applying a water retention agent such as sodium alginate to the undercoat layer coating is also disclosed. (Patent Document 9 and Patent Document 10).

  However, none of the methods described in Patent Document 7 and Patent Document 8 has a level of preservability with respect to chemicals such as plasticizers and alcohols that is not practical enough. Further, even with the method of forming a uniform undercoat layer described in Patent Document 9 or Patent Document 10, although the image quality is improved, it is not possible to suppress uneven penetration into the undercoat layer of the thermal recording layer coating liquid. Further, the protective layer applied and formed thereon has a non-uniform thickness and does not have a sufficient effect on the barrier properties.

Japanese Patent Publication No.49-24133 JP-A-57-39985 International Publication WO01 / 076884 JP 2001-18526 A JP 2001-138632 A JP 2001-113226 A JP-A-4-314590 Japanese Patent Laid-Open No. 7-179041 JP-A-2005-280117 Republished patent WO2005 / 007419

  An object of the present invention is to provide a heat-sensitive recording material excellent in color development sensitivity, chemical resistance, and sticking resistance.

  As a result of various studies on the above problems, the present inventors have completed the present invention on a support.

  That is, the present invention provides the following heat-sensitive recording material.

Item 1: A heat-sensitive recording material having an undercoat layer mainly composed of a pigment and a binder, a heat-sensitive recording layer containing a leuco dye and a developer, and a protective layer on a support, wherein the undercoat layer is styrene-acrylic. A styrene-acrylic copolymer resin obtained from a copolymer resin emulsion is contained in an amount of 1 to 10% by mass based on the total solid content of the undercoat layer, and the heat-sensitive recording layer and the protective layer further comprise a heat-sensitive recording layer coating solution and a protective layer. A heat-sensitive recording material, which is formed by coating and drying a layer coating solution by a simultaneous multilayer curtain coating method.
Item 2: The heat-sensitive recording material according to Item 1, wherein the styrene-acrylic copolymer resin is contained in an amount of 2 to 8% by mass based on the total solid content of the undercoat layer.
Item 3: The heat-sensitive recording material according to Item 1 or 2, wherein the styrene-acrylic copolymer resin emulsion is anionic.
Item 4: The heat-sensitive recording material according to any one of Items 1 to 3, comprising a calcined kaolin having an oil absorption (based on JIS K 5101) of 90 ml / 100 g or more as a pigment of the undercoat layer.
Item 5: The heat-sensitive recording material according to any one of Items 1 to 4, further comprising 10 to 100% by mass of plastic hollow particles as a pigment for the undercoat layer based on the calcined kaolin.
Item 6: The heat-sensitive recording material according to any one of Items 1 to 5, wherein the undercoat layer is formed by applying and drying an undercoat layer coating solution by a blade coating method.
Item 7: The heat-sensitive recording material according to any one of Items 1 to 6, wherein the coating liquid for the heat-sensitive recording layer has a Brookfield viscosity (60 rpm) at 25 ° C. of 200 to 1500 mPa · s.
Item 8: Polyvinyl alcohol having a polymerization degree of 500 or more is contained as a main water-soluble adhesive in the coating solution for the thermosensitive recording layer, and the content of the polyvinyl alcohol is 3 to 30 with respect to the total solid content of the thermosensitive recording layer. Item 8. The heat-sensitive recording material according to any one of Items 1 to 7, which is mass%.
Item 9: The heat-sensitive recording material according to any one of Items 1 to 8, wherein the coating solution for the heat-sensitive recording layer contains a dialkylsulfosuccinate represented by the following general formula (1).

（式中、Ｒ^１、Ｒ^２は同一または異なる炭素数２〜２０の脂肪族または脂環式炭化水素基を表し、Ｍは水素原子またはカチオン、ｘは１または２を表す）

(Wherein R ¹ and R ² represent the same or different aliphatic or alicyclic hydrocarbon groups having 2 to 20 carbon atoms, M represents a hydrogen atom or a cation, and x represents 1 or 2)

  According to the present invention, it is possible to provide a heat-sensitive recording material excellent in color development sensitivity, chemical resistance and sticking resistance.

  Hereinafter, the heat-sensitive recording material of the present invention will be described in detail. In the present invention, in the heat-sensitive recording material having an undercoat layer mainly composed of a pigment and a binder, a heat-sensitive recording layer containing a leuco dye and a developer, and a protective layer on the support, the undercoat layer is made of styrene-acrylic. 1 to 10% by mass of a styrene-acrylic copolymer resin obtained from a copolymer copolymer resin emulsion with respect to the total solid content of the undercoat layer, and the thermosensitive recording layer and the protective layer are a thermosensitive recording layer coating solution, The protective layer coating liquid is formed by applying and drying by a simultaneous multilayer curtain coating method.

(Undercoat layer)
In the present invention, an undercoat layer containing a pigment and a binder as main components and further containing a specific amount of a styrene-acrylic copolymer resin obtained from a styrene-acrylic copolymer resin emulsion between the support and the thermosensitive recording layer. When the thermal recording layer and the protective layer are formed on the undercoat layer by applying and drying the thermal recording layer coating liquid and the protective layer coating liquid by the simultaneous multilayer curtain coating method, In particular, the color development sensitivity and the sticking resistance are good.

  The styrene-acrylic copolymer resin used in the present invention is a resin obtained from a styrene-acrylic copolymer resin emulsion and is obtained from a styrene-acrylic copolymer resin salt (so-called solution type). Compared with a copolymer resin, the chemical resistance of the recording part is excellent. Examples of acrylic monomers obtained by copolymerization with styrene include acrylic acid, acrylic acid such as methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and octyl acrylate. Alkyl or hydroxyalkyl esters of acids, and also methacrylic acid, methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, alkyl or hydroxyalkyl esters of methacrylic acid such as octyl methacrylate, etc. Can be given.

  The styrene-acrylic copolymer resin emulsion may be either anionic or cationic, but an anionic emulsion is more preferable for achieving the effects of the present invention.

  The styrene-acrylic copolymer resin obtained from the styrene-acrylic copolymer resin emulsion contains 1 to 10% by mass, more preferably 2 to 8% by mass, based on the total solid content of the undercoat layer. And most preferably 2-7% by mass. If the content of the styrene-acrylic copolymer resin obtained from the styrene-acrylic copolymer resin emulsion is 1 to 10% by mass relative to the total solid content of the undercoat layer, interlayer mixing can be effectively suppressed. The coating uniformity is improved, the barrier property of the protective layer is improved, and further excellent chemical resistance can be exhibited. If it is less than 1% by mass, the effect of improving chemical resistance cannot be obtained, and if it exceeds 10% by mass, the ability to absorb the hot melt, which is the role of the undercoat layer, decreases, and sticks to the thermal head. There is concern about the occurrence of sticking.

  In the present invention, it is preferable that the main component of the pigment of the undercoat layer contains calcined kaolin having an oil absorption amount (based on JIS K 5101) of 90 ml / 100 g or more because color development sensitivity can be improved by imparting heat insulation. More preferably, the combined use of calcined kaolin and plastic hollow particles having an oil absorption (based on JIS K 5101) of 90 ml / 100 g or more is preferable from the viewpoint of the balance between color development sensitivity and sticking.

  Here, as the plastic hollow particles, conventionally known ones, for example, micro hollow particles having a thermoplastic polymer as a shell, mainly composed of acrylic resin, styrene resin, styrene-acrylic resin, vinylidene chloride resin and acrylonitrile. And particles having a hollow ratio of about 50 to 99%, such as a copolymer resin mainly composed of isobornyl methacrylate and acrylonitrile. Here, the hollow ratio is a ratio of the inner diameter to the outer diameter, and is expressed by the following formula.

  Hollow ratio (%) = (inner diameter of hollow particle / outer diameter of hollow particle) × 100

  The content of the plastic hollow particles is preferably 10 to 100% by mass, more preferably 10 to 70% by mass, and most preferably 15 to 70% by mass with respect to the calcined kaolin. By setting the coating amount to 100% by mass or less, interlayer coating can be effectively suppressed and coating uniformity can be improved when the coating solution for the heat-sensitive recording layer and the coating solution for the protective layer are simultaneously applied by the curtain coating method. This improves the barrier properties and can exhibit even better chemical resistance. Moreover, it is excellent in the ability to absorb the hot melt and can improve the effect of suppressing sticking to the thermal head, so-called sticking. On the other hand, when the content is 10% by mass or more, the recording sensitivity and the image quality are improved, and the effect of suppressing intermixing between the heat-sensitive recording layer and the protective layer can be improved.

  Moreover, as long as the effect of this invention is not impaired, all the general inorganic and organic pigments can be added as a pigment in undercoat. Specific examples include aluminum oxide, calcined diatomaceous earth, aluminum silicate, calcium carbonate, magnesium carbonate, barium sulfate, aluminum hydroxide, kaolin, amorphous silica, talc and the like. Moreover, a solid plastic particle can also be contained in the range which does not impair the effect of this invention. The total amount of the pigment containing the hollow plastic particles and the calcined kaolin is preferably 40 to 90% by mass with respect to the total solid content of the undercoat layer.

  Examples of the binder for the undercoat layer include water-soluble polymers and aqueous binders. These may be used alone or in combination of two or more. Examples of the water-soluble polymer include starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol, acrylamide, carboxymethyl cellulose, and casein. As the aqueous binder, synthetic rubber latex and synthetic resin emulsion are common. Yes, for example, styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex, vinyl acetate emulsion and the like.

  The amount of binder used in the undercoat layer is determined in view of the coating strength and the recording sensitivity of the heat-sensitive recording layer, but is preferably 3 to 100% by mass, and preferably 5 to 50%, based on the pigment contained in the undercoat layer. % By mass is more preferable, and 7 to 40% by mass is particularly preferable. Moreover, you may add a thickener, a wax, an antifoamer, surfactant, etc. in the coating liquid for undercoat layers as needed.

  The undercoat layer in the present invention can be applied according to a conventionally known technique. For example, an off-machine coating machine or an on-machine coating machine equipped with various coaters such as an air knife coater, a blade coater, a roll coater, and a curtain coater can be used as appropriate. It is. The undercoat layer may be applied simultaneously with the heat-sensitive recording layer and the protective layer, or after the undercoat layer is applied, the undercoat layer may be dried and then the heat-sensitive recording layer and the protective layer may be applied simultaneously. Thus, the effect of the present invention can be maximized by applying and drying by a blade coating method capable of imparting uniform orientation to the components in the coating liquid. Here, the method using a blade coater is not limited to a coating method using a bevel type or a vent type blade, but also includes a rod blade method, a bill blade method, and the like. It may be used after being subjected to a smoothing process.

The coating amount of the undercoat layer is not particularly limited, depending on the characteristics of the heat-sensitive recording material is preferably 2 g / ^{m 2} or more, 3 g / ^{m 2} or more preferably, 4~10g / ^{m 2} is particularly preferred.

  In general, when a coating film composed of a plurality of coating liquids of a heat-sensitive recording layer and a protective layer is applied simultaneously on the undercoat layer, the heat-sensitive recording layer that constitutes the coating liquid film between application and drying is completed. The moisture of the coating liquid for the ink moves into the undercoat layer, and the moisture of the coating liquid for the protective layer, which is an upper layer, moves to the thermosensitive recording layer. At this time, components other than water contained in the protective layer also move to the heat-sensitive recording layer side due to the movement of moisture, and mixing between layers occurs. Quality degradation such as property becomes a problem. The reason why excellent chemical resistance can be obtained in the present invention is that the styrene-acrylic copolymer resin obtained from the styrene-acrylic copolymer resin emulsion is applied from the application of the coating liquid for the undercoat layer until the drying is finished. To move upward and align with the surface of the undercoat layer, increase the hydrophobicity of the surface of the undercoat layer, suppress the infiltration of moisture in the coating liquid for the thermal recording layer, and as a result, the coating liquid for the thermal recording layer and the protective layer This is thought to be because the interfacial mixing of the coating liquid was suppressed and the barrier property of the protective layer was improved. At this time, the emulsion type styrene-acrylic resin is more effective than the solution type. This is presumably because the water-soluble resin has a slower movement during drying than the emulsion and scatters to the entire undercoat layer, so that the hydrophobicity of the surface layer is lower than that of the emulsion.

(Thermosensitive recording layer)
In the present invention, the thermal recording layer coating liquid preferably has a Brookfield type viscosity (B type viscosity) at 25 ° C. and 60 rpm of 200 to 1500 mPa · s, particularly about 300 to 1200 mPa · s. It is preferable. If it is less than 200 mPa · s, the heat-sensitive recording layer coating liquid is likely to be partially and non-uniformly absorbed into the undercoat layer, so that the thickness of the protective layer tends to be non-uniform and the barrier properties are considered to be reduced. On the other hand, if it exceeds 1500 mPa · s, bubbles in the heat-sensitive recording layer coating liquid are difficult to escape, so that coating defects due to bubbles occur or streaky coating unevenness tends to occur in the flow direction. The protective layer is not evenly applied and the barrier property is lowered, and printing unevenness is likely to occur.

  Further, by preparing a coating solution for a thermal recording layer containing 3 to 30% by mass of polyvinyl alcohol having a polymerization degree of 500 or more as a main water-soluble adhesive of the thermal recording layer with respect to the total solid content of the thermal recording layer. A coating liquid having a Brookfield viscosity (B type viscosity) at 25 ° C. and 60 rpm of 200 to 1500 mPa · s was obtained, and the quality was excellent by the simultaneous multilayer curtain coating method with the coating liquid for the protective layer. A heat-sensitive recording material can be produced with high productivity.

  As the polyvinyl alcohol having a polymerization degree of 500 or more, any of unmodified and modified, complete saponification and partial saponification can be used. Examples of the modified polyvinyl alcohol include acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol.

  Specific examples of water-soluble adhesives other than polyvinyl alcohol having a polymerization degree of 500 or more added to the heat-sensitive recording layer include, for example, oxidized starch, acid-modified starch, phosphate esterified starch, enzyme-modified starch, cation-modified starch, Starches such as esterified starch, etherified starch and vinyl acetate modified grafted starch, polyvinyl alcohol having a polymerization degree of less than 500, cellulose derivatives such as methylcellulose, ethylcellulose, carboxymethylcellulose, methoxycellulose, hydroxyethylcellulose and hydroxypropylmethylcellulose, polyacryl Acid soda, polyacrylamide, polyvinylpyrrolidone, acrylic acid amide / acrylic acid ester copolymer, acrylic acid amide / acrylic acid ester / methacrylic acid copolymer, styrene / maleic anhydride copolymer Alkali salts, isobutylene-maleic anhydride copolymer alkali salts, sodium alginate, gelatin, casein, their content must not exceed the content of the polyvinyl alcohol of polymerization degree of 500 or more. In addition to water-soluble adhesives, polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic ester, polybutyl methacrylate, styrene / butadiene copolymer, vinyl chloride / vinyl acetate copolymer, ethylene / vinyl acetate copolymer Further, latex such as styrene / butadiene / acrylic copolymer can be used in combination.

  Further, in order to improve the whiteness and image uniformity, the heat-sensitive recording layer may contain a fine pigment having a high whiteness and an average particle diameter of 10 μm or less. Specific examples of the pigment include, for example, kaolin, clay, calcium carbonate, magnesium carbonate, aluminum hydroxide, barium sulfate, talc, calcined clay, calcined kaolin, titanium oxide, zinc oxide, diatomaceous earth, particulate anhydrous silica, activated clay, etc. Organic pigments such as inorganic pigments, styrene microballs, nylon powder, polyethylene powder, urea-formalin resin filler, styrene-methacrylic acid copolymer resin, polystyrene resin, raw starch particles and the like can be mentioned. The pigment content is preferably 50% by mass or less with respect to the total solid content of the heat-sensitive recording layer, in such an amount that does not decrease the color density.

  Furthermore, in the present invention, in order to improve chemical resistance, a partially saponified polyvinyl alcohol having a polymerization degree of 300 to 2400 as a thermal recording layer coating liquid is used in an amount of 0.3 to 10 mass based on the total solid content of the thermal recording layer. % Content is preferable. Partially saponified polyvinyl alcohol acts as a protective colloid agent for the color forming component, and is considered to further improve chemical resistance. Here, as the purpose of partially saponified polyvinyl alcohol, it is a protective colloid agent, not for viscosity adjustment, so it is not necessary to have a polymerization degree of 500 or more described in the above-mentioned polyvinyl alcohol, and it may be a polymerization degree of 300 or more. . When the partially saponified polyvinyl alcohol is in the range of 0.3 to 10% by mass, the chemical resistance is further improved, and the decrease in color development sensitivity can be suppressed. Further, when the degree of polymerization of partially saponified polyvinyl alcohol is in the range of 300 to 2400, the decrease in coating strength is suppressed, the viscosity of the thermal recording layer coating liquid does not increase, and the coating suitability is less likely to decrease. . The saponification degree of partially saponified polyvinyl alcohol is 75 to 90 mol%, preferably about 80 to 89 mol%. When the saponification degree exceeds 90 mol%, the ability as a protective colloid agent is insufficient. Polyvinyl alcohol having a saponification degree of less than 75 mol% is not preferable because the foam of the coating liquid increases.

  As the partially saponified polyvinyl alcohol having a polymerization degree of 300 to 2400, both unmodified and modified can be used. Examples of the modified polyvinyl alcohol include acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol.

  The heat-sensitive recording layer of the present invention contains various known leuco dyes and developers. In addition, you may contain a sensitizer, a pigment, various adjuvants, etc. as needed.

  For example, as leuco dyes that give black color, 3-diethylamino-6-methyl-7-anilinofluorane, 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 3-di (N-pentyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamylamino) -6-methyl-7-arininofluorane, 3- (N-ethyl-p -Toluidino) -6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, 3- ( N-isoamyl-N-ethylamino) -7- (o-chloroanilino) fluorane, 3- (N-ethyl-N-2-tetrahydrofurfurylamino) -6-methyl-7-anilinov Oran, 3-diethylamino-6-chloro-7-anilinofluorane, 3- (Nn-hexyl-N-ethylamino) -6-methyl-7-anilinofluorane, 3- [N- (3 -Ethoxypropyl) -N-ethylamino] -6-methyl-7-anilinofluorane, 3- [N- (3-ethoxypropyl) -N-methylamino] -6-methyl-7-anilinofluorane , 3-diethylamino-7- (2-chloroanilino) fluorane, 3-di (n-butyl) amino-7- (2-chloroanilino) fluorane, and the like can be used. If necessary, as the leuco dye, a leuco dye that develops a color tone different from that of black, for example, a color tone such as red, magenta, orange, blue, and green may be used.

  The leuco dye used in the present invention is not limited to these, and two or more kinds may be used in combination. The amount of the leuco dye used is about 3 to 30% by mass with respect to the total solid content of the thermosensitive recording layer.

  In the present invention, when the leuco dye is used in a solid fine particle state, the leuco dye is pulverized by various wet pulverizers such as a sand grinder, an attritor, a ball mill, and a cobo mill using water as a dispersion medium. In addition to modified polyvinyl alcohols such as polyvinylpyrrolidone, polyvinyl alcohol, and sulfone-modified polyvinyl alcohol, water-soluble synthetic polymer compounds such as methyl cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose, styrene-maleic anhydride copolymer salts and derivatives thereof, If necessary, it can be dispersed in a dispersion medium together with a surfactant, an antifoaming agent and the like to form a dispersion, and this dispersion can be used for the preparation of a thermal recording layer coating solution.

  Alternatively, after dissolving the leuco dye in a solvent, the solution is emulsified and dispersed in water using the water-soluble polymer as a stabilizer, and then the solvent is evaporated from the emulsion to form a dye precursor in solid fine particles. . In any case, the average particle size of the dispersed particles of the leuco dye used in the solid fine particle state is preferably about 0.2 to 3.0 μm, more preferably 0.3 to 3.0 in order to obtain appropriate color development sensitivity. It is about 1.0 μm.

  In the present invention, as a method of using the leuco dye, it can be used as a composite particle composed of an organic polymer and a leuco dye, in addition to the above-mentioned solid fine particle state. The composite particles can be produced by a known method. For example, a method for producing composite particles in which the organic polymer is at least one of polyurea and polyurea-polyurethane will be described. The composite particles are prepared by dissolving and mixing a leuco dye and a polymer-forming raw material that forms at least one of polyurea and polyurea-polyurethane by polymerization in a water-insoluble organic solvent having a boiling point of 100 ° C. or less. Is emulsified and dispersed in a hydrophilic protective colloid solution such as polyvinyl alcohol so that the average particle size is about 0.5 to 3 μm, and if necessary, a reactive substance such as polyamine is further mixed, and then this emulsified dispersion is heated. The organic solvent is volatilized and removed, and then the polymer-forming raw material is polymerized, or the leuco dye is dissolved in the polymer-forming raw material, and this solution is used as described above. And after the emulsion is dispersed to an average particle size of about 0.5 to 3 μm, the polymer-forming raw material is polymerized.

  In the present invention, a known compound can be used as the developer used in the heat-sensitive recording layer. Specific examples of the developer include 4-tert-butylphenol, 4-acetylphenol, 4-tert-octylphenol, 4,4′-sec-butylidenediphenol, 4-phenylphenol, 4,4′- Dihydroxydiphenylmethane, 4,4′-isopropylidene diphenol, 4,4′-cyclohexylidene diphenol, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 4,4′-dihydroxydiphenyl sulfide, 4 , 4′-thiobis (3-methyl-6-tert-butylphenol), 4,4′-dihydroxydiphenylsulfone, 2,4′-dihydroxydiphenylsulfone, 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy -4'-allyloxydiph Nyl sulfone, phenolic compounds such as bis (3-allyl-4-hydroxyphenyl) sulfone, bis (p-hydroxyphenyl) butyl acetate, methyl bis (p-hydroxyphenyl) acetate, 4-hydroxybenzophenone, 4-hydroxyphthal Dimethyl acid, methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, 4-hydroxybenzoate-sec-butyl, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, 4- Phenolic compounds such as chlorophenyl hydroxybenzoate and 4,4′-dihydroxydiphenyl ether, or benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, salicylic acid, 3-tert-butylsalicylic acid, 3- Aromatic carboxylic acids such as sopropylsalicylic acid, 3-benzylsalicylic acid, 3- (α-methylbenzyl) salicylic acid, 3,5-di-tert-butylsalicylic acid, and these phenolic compounds, aromatic carboxylic acids and eg zinc, Organic acidic substances such as salts with polyvalent metals such as magnesium, aluminum and calcium, Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea, N- (p-toluenesulfonyl)- And urea compounds such as N ′-(p-butoxycarbonyl) urea and Np-toluenesulfonyl-N′-phenylurea.

  In the present invention, the use ratio of the leuco dye and the developer in the heat-sensitive recording layer should be appropriately selected according to the kind of the leuco dye and developer used, and is not particularly limited, but generally 1 mass of leuco dye. About 1 to 7 parts by mass, preferably about 1 to 6 parts by mass of the developer is used. Preparation of coating solution for heat-sensitive recording layer containing these substances is generally carried out using water as a dispersion medium, and stirring or ball mill, attritor, sand mill, etc., and dispersing leuco dye and developer together or separately. By doing so, it is prepared as a coating solution.

  Furthermore, a sensitizer can be used in combination according to the purpose. Specific examples of the sensitizer include stearic acid amide, methoxycarbonyl-N-stearic acid benzamide, N-benzoyl stearic acid amide, N-eicosanoic acid amide, ethylene bistearic acid amide, behenic acid amide, and methylenebisstearic acid. Amide, N-methylol stearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, benzyl p-benzyloxybenzoate, phenyl 1-hydroxy-2-naphthoate, 2-naphthylbenzyl ether, m-terphenyl, Oxalic acid dibenzyl ester, oxalic acid-di-p-methylbenzyl ester, oxalic acid-di-p-chlorobenzyl ester, p-benzylbiphenyl, tolylbiphenyl ether, di (p-methoxyphenoxyethyl) ether 1,2-di (3-methylphenoxy) ethane, 1,2-di (4-methylphenoxy) ethane, 1,2-di (4-methoxyphenoxy) ethane, 1,2-di (4-chlorophenoxy) ) Ethane, 1,2-diphenoxyethane, 1- (4-methoxyphenoxy) -2- (2-methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p-acetoluidide , P-acetophenetide, N-acetoacetyl-p-toluidine, di (β-biphenylethoxy) benzene, p-di (vinyloxyethoxy) benzene, 1-isopropylphenyl-2-phenylethane, etc. . The amount of these sensitizers to be used is not particularly limited, but it is generally desirable to adjust in a range of 4 parts by mass or less with respect to 1 part by mass of the developer.

  Further, as long as the desired effect is not impaired, other storability improving agents can be used in combination in order to further improve the storability of the recorded image according to the purpose. Specific examples of such preservability improvers include, for example, 2,2′-methylenebis (4-methyl-6-tert-butylphenol), 2,2′-ethylenebis (4-methyl-6-tert-butylphenol), 2 2,2'-methylenebis (4-ethyl-6-tert-butylphenol), 2,2'-methylenebis (4,6-di-tert-butylphenol), 2,2'-ethylidenebis (4,6-di-tert) -Butylphenol), 2,2'-ethylidenebis (4-methyl-6-tert-butylphenol), 2,2'-ethylidenebis (4-ethyl-6-tert-butylphenol), 2,2 '-(2, 2-propylidene) bis (4,6-di-tert-butylphenol), 2,2′-methylenebis (4-methoxy-6-tert-butyl) Ruphenol), 2,2'-methylenebis (6-tert-butylphenol), 4,4'-thiobis (3-methyl-6-tert-butylphenol), 4,4'-thiobis (2-methyl-6-tert) -Butylphenol), 4,4'-thiobis (5-methyl-6-tert-butylphenol), 4,4'-thiobis (2-chloro-6-tert-butylphenol), 4,4'-thiobis (2-methoxy) -6-tert-butylphenol), 4,4'-thiobis (2-ethyl-6-tert-butylphenol), 4,4'-butylidenebis (6-tert-butyl-m-cresol), 1- [α-methyl -Α- (4′-hydroxyphenyl) ethyl] -4- [α ′, α′-bis (4 ″ -hydroxyphenyl) ethyl] benzene, 1 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 4,4 '-Thiobis (3-methylphenol), 4,4'-dihydroxy-3,3', 5,5'-tetrabromodiphenylsulfone, 4,4'-dihydroxy-3,3 ', 5,5'-tetra Methyldiphenylsulfone, 2,2-bis (4-hydroxy-3,5-dibromophenyl) propane, 2,2-bis (4-hydroxy-3,5-dichlorophenyl) propane, 2,2-bis (4-hydroxy) -Hindered phenol compounds such as 3,5-dimethylphenyl) propane, N, N'-di-2-naphthyl-p-phenylenediamine, 2,2'-methylenebis 4,6-di -tert- butylphenyl) phosphate sodium, and the like.

  Various auxiliary agents can be added to the thermal recording layer coating liquid as necessary. For example, surfactants, waxes, metal soaps, antifoaming agents, fluorescent dyes, colored dyes, crosslinking agents, viscosity modifiers, and the like are added as appropriate.

  In the present invention, in order to further increase the added value of the product, a multicolor thermosensitive recording material can be used. In general, multicolor thermal recording materials are an attempt to utilize the difference in heating temperature or thermal energy, and are generally constructed by sequentially laminating a high-temperature coloring layer and a low-temperature coloring layer that develop colors in different colors on a support. These are roughly divided into two types: decoloring type and additive type, producing multicolor thermal recording materials using a method using microcapsules and composite particles composed of organic polymer and dye precursor. There is a way to do it.

  In the present invention, since the heat-sensitive recording layer is formed by a curtain coating method, a surfactant is added to the heat-sensitive recording layer coating liquid in order to stabilize the curtain film by adjusting the surface tension. Surfactants include, for example, sulfosuccinic acid alkali metal salts, alkylbenzene sulfonates, acetylene glycol compounds, fluorine surfactants, silicon surfactants, phosphate ester surfactants, and ether type surfactants. Or amphoteric surfactants such as betaines, aminocarboxylates, and imidazoline derivatives, and the like. From the viewpoint of curtain film stability, dialkylsulfosuccinic acid represented by the following general formula (1) is particularly preferable. Salts are preferred. Further, the salt is preferably an alkali metal salt or an ammonium salt, and the alkyl group is preferably 2 to 20 carbon atoms, more preferably 4 to 10 carbon atoms. Specifically, an isobutyl group, a hexyl group, a cyclohexyl group, an octyl group, an isooctyl group, and a 2-ethylhexyl group are preferable. The addition amount of the surfactant is preferably about 0.05 to 3.0% by mass with respect to the total solid content of the thermosensitive recording layer. If it is less than 0.05% by mass, the effect of addition is small and the surface tension is not sufficiently lowered, and the curtain film is likely to be cut. If it exceeds 3.0% by mass, the coating liquid tends to foam and causes coating defects. From the balance between the effect and the physical properties of the paint, the more preferable content of the surfactant is about 0.10 to 2.0% by mass.

（式中、Ｒ^１、Ｒ^２は同一または異なる炭素数２〜２０の脂肪族または脂環式炭化水素基を表し、Ｍは水素原子またはカチオン、ｘは１または２を表す）

(Wherein R ¹ and R ² represent the same or different aliphatic or alicyclic hydrocarbon groups having 2 to 20 carbon atoms, M represents a hydrogen atom or a cation, and x represents 1 or 2)

In the present invention, simultaneous multilayer coating of the heat-sensitive recording layer and the protective layer by the curtain coating method can increase the stability of the curtain film, further improve the production efficiency, and further reduce the energy consumption during production. This is preferable. In the present invention, the curtain coating method used in the application of the heat-sensitive recording layer is a method in which the coating liquid is allowed to flow down and freely fall and is applied to the support in a non-contact manner, such as a slide curtain method, a couple curtain method, a twin curtain method. A known method such as a curtain method can be adopted and is not particularly limited. Further, as described in Japanese Patent Application Laid-Open No. 2006-247611, the paint is ejected downward from the curtain head to form a paint layer on the slope, and the paint curtain is formed from the downward curtain guide portion of the slope. The paint layer can also be transferred onto the web surface. The coating amount of the thermal recording layer coating liquid is not particularly limited, and a desired quality can be achieved if the dry weight is about 1 to 12 g / m ² , particularly about ² to 10 g / m ² . The heat-sensitive recording layer can be divided into two or more layers as required, and the composition and coating amount of each layer can be changed. It should be noted that various conditions such as coating concentration, coating speed, curtain film width, drop angle, and the like are desirably adjusted appropriately according to each curtain coating method and coating apparatus. Since these curtain coating methods are non-contact contour coating, a coating layer having a uniform thickness can be obtained. On the other hand, contact type coating such as blade, bar, and air knife coating is affected by the surface properties (unevenness) of the support, and therefore the film thickness becomes non-uniform. For this reason, with the same coating amount, a heat-sensitive recording layer formed by curtain coating can obtain better image quality and also improve image storability.

(Protective layer)
In the present invention, at least one protective layer is provided on the thermosensitive recording layer. As the protective layer, a protective layer that has been used in conventionally known thermal recording media can be used. The protective layer is mainly composed of a pigment and an adhesive. In particular, a lubricant such as polyolefin wax or zinc stearate is preferably added to the protective layer for the purpose of preventing sticking to the thermal head, and an ultraviolet absorber can also be included. In addition, the added value of the product can be increased by providing a glossy protective layer.

  In this invention, the effect of this invention can be improved further by containing 15-50 mass% of polyvinyl alcohol of 1000-3000 degree of polymerization as a water-soluble adhesive with respect to the total solid of a protective layer. Examples of the polyvinyl alcohol having a polymerization degree of 1000 to 3000 include fully saponified or partially saponified polyvinyl alcohol, polyvinyl alcohol such as acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol. .

  Among them, acetoacetyl-modified polyvinyl alcohol and diacetone-modified polyvinyl alcohol are preferably used because they can improve the surface barrier properties and improve the storage stability such as chemical resistance.

  The total amount of the water-soluble polymer is preferably about 10 to 80% by mass, and more preferably about 20 to 75% by mass, based on the total solid content of the protective layer.

  If it is less than 10% by mass, not only the barrier property is not sufficient, but also the surface strength is lowered, leading to deterioration of paper dust and the like. On the other hand, if it exceeds 80% by mass, sticking may be deteriorated.

  Adhesives other than water-soluble polymers include polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylate ester, polybutyl methacrylate, styrene / butadiene copolymer, vinyl chloride / vinyl acetate copolymer, ethylene / vinyl acetate copolymer Polymers and latexes such as styrene / butadiene / acrylic copolymers can be used in combination.

  Examples of the pigment include inorganic pigments such as calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, amorphous silica, synthetic mica, aluminum hydroxide, barium sulfate, talc, kaolin, clay, calcined kaolin, nylon resin filler, urea -Organic pigments such as formalin resin filler and raw starch particles.

  Of these, kaolin and aluminum hydroxide are preferred because they have a small decrease in barrier properties against chemicals such as plasticizers and oils, and a small decrease in recording density.

  The usage-amount of a pigment is about 5-80 mass% with respect to the total solid of a protective layer, and the range of about 10-70 mass% is especially preferable.

  If it is less than 5% by mass, slipping with the thermal head is deteriorated, causing sticking or deteriorating head wrinkles. On the other hand, when it exceeds 80 mass%, barrier property will worsen and the function as a protective layer will fall significantly.

  As the auxiliary agent, for example, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, sodium alkylbenzene sulfonate, sodium dioctyl sulfosuccinate, sulfone-modified polyvinyl alcohol, sodium acrylate glycol polyacrylate compound , Surfactants such as fluorosurfactants, silicon surfactants, phosphate ester surfactants, ether surfactants, or amphoteric surfactants such as betaines, aminocarboxylates, and imidazoline derivatives, Glyoxal, boric acid, dialdehyde starch, methylol urea, epoxy compound, hydrazine compound, etc., water resistance (crosslinking agent), hydrophobic polycarboxylic acid copolymer, UV absorber, fluorescent dye, coloring dye Mold release agents, antioxidants, and the like. The usage-amount of auxiliary agent can be suitably set from a wide range.

  In the present invention, the protective layer is applied simultaneously with the heat-sensitive recording layer to increase the curtain flow rate, thereby stabilizing the curtain film and suppressing the occurrence of coating defects. This is preferable in that the production efficiency can be increased and the energy consumption during production can be further reduced. Although it does not specifically limit as a coating device used for curtain coating, An extrusion hopper type curtain coating device, a slide hopper type curtain coating device, or the method described in Japanese Patent Application Laid-Open No. 2006-247611 mentioned above can be used.

The coating amount of the protective layer coating liquid is not particularly limited, and a desired quality can be achieved if the dry weight is about 0.3 to 10 g / m ² , particularly about 0.5 to 8 g / m ² . The protective layer can be divided into two or more layers as required, and the composition and coating amount of each layer can be changed.

  After application of the coating liquid, it is dried, and thereafter, it is preferably smoothed by calendaring and used.

  In the present invention, in order to increase the added value of the heat-sensitive recording material, it can be further processed to obtain a heat-sensitive recording material having a higher function. For example, it can be used as a pressure-sensitive adhesive paper, a re-humidified adhesive paper, or a delayed tack paper by applying a coating process such as a pressure-sensitive adhesive, a re-humidifying adhesive, or a delayed tack type pressure-sensitive adhesive on the back surface. Or it can also be set as the thermosensitive recording body which has a layer which can be magnetic-recorded in a back surface by giving magnetic processing. In particular, those subjected to adhesive processing and magnetic processing are useful for applications such as heat-sensitive labels and heat-sensitive magnetic tickets. In addition, by using the back surface, a function of thermal transfer paper, ink jet paper, carbonless paper, electrostatic recording paper, and xerographic paper can be added to the recording material to enable double-sided recording. Of course, a double-sided thermal recording material can also be used.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples. Unless otherwise specified, “part” and “%” in the examples represent “part by mass” and “% by mass”, respectively.

Example 1
(Preparation of coating solution for undercoat layer)
60 parts of calcined kaolin having an oil absorption of 110 ml / 100 g, 80 parts of plastic hollow particle emulsion (trade name: AE852, solid content concentration 26%, hollow rate 80%, average particle size 1.0 μm, manufactured by JSR), light magnesium carbonate 1 20 parts of a styrene / butadiene / acrylonitrile copolymer latex having a solid content concentration of 50% as an adhesive, 20 parts of a 5% aqueous solution of carboxymethylcellulose (trade name: Cellogen 7A, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), oxidized starch (trade name) : 25 parts of a 20% aqueous solution of Oji Ace A (manufactured by Oji Cornstarch Co., Ltd.), 20 parts of an anionic styrene-acrylic copolymer resin emulsion (trade name: Polymeralon E-100, solid content concentration 30%, Arakawa Chemical Industries, Ltd.) And 90 parts of water were uniformly mixed and stirred to obtain an undercoat layer coating solution.

(Preparation of dye precursor / sensitizer dispersion (liquid A))
25 parts of 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 20 parts of 1,2-di (3-methylphenoxy) ethane, 25 parts of a 20% aqueous solution of sulfone-modified polyvinyl alcohol, and A composition comprising 30 parts of water was pulverized with a sand mill until the average particle size became 0.9 μm to obtain a dye precursor dispersion (liquid A).

(Preparation of developer dispersion (liquid B))
A composition comprising 45 parts of 2,2′-bis (4-hydroxyphenyl) propane, 25 parts of a 20% aqueous solution of sulfone-modified polyvinyl alcohol and 30 parts of water is pulverized with a sand mill until the average particle size becomes 1.5 μm. As a result, a developer dispersion (liquid B) was obtained.

(Preparation of thermal recording layer coating solution)
A 50% aqueous dispersion 50 of A part 40 parts, B part 50 parts, C part 10 parts, kaolin (primary kaolin, trade name: UW-90, manufactured by Engelhard, average particle diameter d ₅₀ ; 0.32 μm) Parts, 20 parts of 15% aqueous solution of fully saponified polyvinyl alcohol (trade name: PVA-110, polymerization degree 1000, saponification degree 98.5 mol%, manufactured by Kuraray Co., Ltd.), partially saponified polyvinyl alcohol (trade name: PVA-205, polymerization degree) 500, 30 parts of 15% aqueous solution of saponification degree 88.0 mol%, manufactured by Kuraray Co., Ltd., styrene / butadiene copolymer latex (trade name: L-1571, solid content concentration 48%, manufactured by Asahi Kasei Chemicals Co., Ltd.), adipic acid 10 parts of 30% aqueous dispersion of dihydrazide, 10 parts of 30% aqueous dispersion of zinc stearate, and dioctyl sulfosuccinate sodium salt (trade name: SN Wet 5 parts of a 10% aqueous solution of OT-70 (manufactured by San Nopco) were sequentially added, mixed and stirred to obtain a coating solution for a thermosensitive recording layer having a B-type viscosity of 700 mPa · s at 25 ° C.

(Preparation of coating solution for protective layer)
To 50 parts of a 50% aqueous dispersion of kaolin (primary kaolin, trade name: UW-90, manufactured by Engelhard, average particle size d ₅₀ ; 0.32 μm), acetoacetyl-modified polyvinyl alcohol (trade name: Goosefimer) 600 parts of 10% aqueous solution of Z-410, polymerization degree 2400, manufactured by Nippon Synthetic Chemical Co., Ltd., zinc stearate (trade name: Hydrin Z-8-36, solid content concentration 36%, manufactured by Chukyo Yushi Co., Ltd.), further A protective layer coating solution was obtained by mixing and stirring 20 parts of a 5% aqueous solution of dioctyl sulfosuccinic acid sodium salt (trade name: SN Wet OT-70, manufactured by San Nopco).

(Preparation of undercoat layer)
On one surface of woodfree paper having a basis weight of 60 g / m ^2, coated with a subbing layer coating solution in a blade coater as the coating amount after drying of 7 g / m ^2, to obtain an undercoat layer-coated base paper and dried .

(Preparation of thermal recording material)
On the base paper coated with the undercoat layer prepared above, the thermal recording layer coating liquid and the protective layer coating liquid are applied from the lower layer side to the thermal recording layer coating liquid and the protective layer coating liquid using a slide hopper type curtain coating apparatus. coating solution sequentially coating film composed of the formation of, so that the solid content coating amount of each layer is a heat-sensitive recording layer 4.0 g / ^{m 2,} and the protective layer 2.0 g / ^{m 2,} coating speed 600 meters / min At the same time, a multi-layer curtain was applied and dried, followed by supercalendering to obtain a heat sensitive recording material.

Example 2
Cationic styrene-acrylic copolymer resin instead of 20 parts of anionic styrene-acrylic copolymer resin emulsion (trade name: Polymeralon E-100, supra) in the preparation of the undercoat layer coating solution of Example 1 A thermosensitive recording material was obtained in the same manner as in Example 1 except that 20 parts of emulsion (trade name: Polymeralon 1603, solid content concentration 30%, manufactured by Arakawa Chemical Industries, Ltd.) was used to obtain a coating solution for an undercoat layer. It was.

Example 3
In the preparation of the undercoat layer coating solution of Example 1, the anionic styrene-acrylic copolymer resin emulsion (trade name: Polymalon E-100, supra) was reduced from 20 parts to 6 parts to prepare an undercoat layer coating. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the liquid was obtained.

Example 4
In the preparation of the undercoat layer coating solution of Example 1, an anionic styrene-acrylic copolymer resin emulsion (trade name: Polymeron E-100, supra) was increased from 20 parts to 30 parts for use in the undercoat layer. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the coating liquid was obtained.

Example 5
In the preparation of the undercoat layer coating solution of Example 1, 80 parts of calcined kaolin having an oil absorption of 110 ml / 100 g was added, and the plastic hollow particle emulsion (trade name: AE852, supra) was not added, and the undercoat layer coating was added. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the liquid was obtained.

Example 6
In the preparation of the coating solution for the undercoat layer of Example 1, 60 parts of calcined kaolin having an oil absorption of 110 ml / 100 g was not added, and 250 parts of a plastic hollow particle emulsion (trade name: AE852, supra) was added. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the layer coating solution was obtained.

Example 7
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that in preparing the undercoat layer of Example 1, a base paper coated with the undercoat layer was obtained by applying and drying using a curtain coater instead of a blade coater. It was.

Comparative Example 1
In the preparation of the undercoat layer coating solution of Example 1, the same procedure as in Example 1 was conducted except that 20 parts of an anionic styrene-acrylic copolymer resin emulsion (trade name: Polymeron E-100, supra) was not added. Thus, a heat-sensitive recording material was obtained.

Comparative Example 2
Example 1 Example 1 except that the anionic styrene-acrylic copolymer resin emulsion (trade name: Polymalon E-100, supra) was increased from 20 parts to 50 parts in the preparation of the undercoat layer coating liquid of Example 1. In the same manner, a heat-sensitive recording material was obtained.

Comparative Example 3
In the preparation of the coating liquid for the undercoat layer of Example 1, in place of 20 parts of an anionic styrene-acrylic copolymer resin emulsion (trade name: Polymeron E-100, supra), sodium alginate (trade name: Kelgin HV, A thermosensitive recording material was obtained in the same manner as in Example 1 except that 5 parts of 2% aqueous solution was added.

Comparative Example 4
Instead of 20 parts of an anionic styrene-acrylic copolymer resin emulsion (trade name: Polymalon E-100, supra) in the preparation of the undercoat layer coating solution of Example 1, an anionic styrene-acrylic copolymer resin A thermosensitive recording material was obtained in the same manner as in Example 1 except that 24 parts of salt (trade name: SE2066, solid concentration 25%, manufactured by Seiko PMC Co., Ltd.) was used to obtain an undercoat layer coating solution.

Comparative Example 5
Cationic styrene-acrylic copolymer resin instead of 20 parts of anionic styrene-acrylic copolymer resin emulsion (trade name: Polymeralon E-100, supra) in the preparation of the undercoat layer coating solution of Example 1 A thermosensitive recording material was obtained in the same manner as in Example 1 except that 30 parts of salt (trade name: Polymeralon 360, solid content concentration 20%, manufactured by Arakawa Chemical Industries, Ltd.) was used to obtain a coating solution for an undercoat layer. It was.

Comparative Example 6
Instead of 20 parts of anionic styrene-acrylic copolymer resin emulsion (trade name: POLYMALON E-100, supra) in the preparation of the undercoat layer coating solution of Example 1, an anionic styrene-maleic acid copolymer resin A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 24 parts of salt (trade name: Polymeralon 385, solid content concentration 25%, manufactured by Arakawa Chemical Industries Ltd.) was used to obtain a coating solution for an undercoat layer. It was.

Comparative Example 7
Instead of 20 parts of an anionic styrene-acrylic copolymer resin emulsion (trade name: POLYMALON E-100, supra) in the preparation of the undercoat coating solution for Example 1, an anionic olefin-maleic acid copolymer resin was used. A thermosensitive recording material was obtained in the same manner as in Example 1 except that 24 parts of salt (trade name: Polymeron 1329, solid content concentration 25%, manufactured by Arakawa Chemical Industry Co., Ltd.) was used to obtain an undercoat layer coating solution. It was.

Comparative Example 8
In the preparation of the coating solution for the undercoat layer of Example 1, an anionic paraffin wax emulsion (trade name) was used instead of 20 parts of the anionic styrene-acrylic copolymer resin emulsion (trade name: Polymeron E-100, supra). : Size pine W116H, solid content concentration 31%, manufactured by Arakawa Chemical Industries, Ltd.) was used in the same manner as in Example 1 except that an undercoat layer coating solution was obtained.

Comparative Example 9
In the preparation of the undercoat layer coating liquid of Example 1, an anionic rosin aqueous solution type sizing agent (trade name: POLYMALON E-100, supra) instead of 20 parts of an anionic styrene-acrylic copolymer resin emulsion (trade name: A thermosensitive recording material was obtained in the same manner as in Example 1 except that 20 parts of trade name: Size Pine E, 30% concentration, manufactured by Arakawa Chemical Industries, Ltd.) was used to obtain a coating solution for an undercoat layer.

Comparative Example 10
In the preparation of the coating liquid for the undercoat layer of Example 1, a cationic alkyl ketene dimer emulsion (product) was used instead of 20 parts of an anionic styrene-acrylic copolymer resin emulsion (trade name: Polymeron E-100, supra). Name: Size Pine K921, 20% concentration, manufactured by Arakawa Chemical Industries, Ltd.) 30 parts were used to obtain a thermosensitive recording material in the same manner as in Example 1 except that an undercoat layer coating solution was obtained.

Comparative Example 11
In the preparation of the undercoat layer coating liquid of Example 1, instead of 20 parts of an anionic styrene-acrylic copolymer resin emulsion (trade name: POLYMALON E-100, supra), an alkenyl succinic anhydride sizing agent (product Name: Size Pine SA864, manufactured by Arakawa Chemical Industries, Ltd., 100% concentration) was used in the same manner as in Example 1 except that an undercoat layer coating solution was obtained.

Comparative Example 12
In the production of the heat-sensitive recording material of Example 1, in place of the slide hopper type curtain coating device, the heat-sensitive recording layer and the protective layer were sequentially applied and dried by using a rod bar coating device. A thermosensitive recording material was obtained in the same manner.

  The obtained thermal recording material was subjected to the following evaluation tests, and the results are shown in Table 1.

(Recording sensitivity)
Using a thermal recording simulator (TH-PMD, manufactured by Okura Electric Co., Ltd.), recording was performed at an applied energy of 0.27 mJ / dot, and the density of the solid recording portion was visualized by a Macbeth densitometer (trade name: RD914, manufactured by Macbeth). Measured in mode. The recording unit is required to be 1.30 or more practically.

(chemical resistance)
The printed portion of the heat-sensitive recording material colored at 0.27 mj / dot was wrapped around an acrylic cylinder having a diameter of 5 cm so as to be sandwiched from above and below with a vinyl chloride film (trade name: HiES Soft TM350, manufactured by Nippon Carbide Industries, Ltd.) After leaving for 24 hours in an environment of 40 ° C., the density of the printed portion was measured in a visual mode of a Macbeth densitometer (trade name: RD914, manufactured by Macbeth). In addition, the storage ratio of the printed part was obtained by the following formula. There is no problem if the recording density after PVC film processing is 1.00 or higher and the storage rate is 75% or higher.
Storage rate (%) = measured value (recording density) ÷ recording density before processing × 100

(Sticking)
Black solid printing was performed using a thermal evaluation machine (VP-35, manufactured by Seiko Co., Ltd.), and the state of sticking at that time (the printing jumped and a horizontal line was seen) was visually evaluated.
○: Good without sticking.
(Triangle | delta): Although sticking is seen in some places, it is a practical use level.
X: Sticking is intense, which is a practical problem.

  According to the present invention, an undercoat layer containing a styrene-acrylic copolymer resin obtained from a styrene-acrylic copolymer resin emulsion, the main component being a pigment and a binder, between the support and the thermosensitive recording layer. When the thermal recording layer and the protective layer are formed on the undercoat layer by applying and drying the thermal recording layer coating liquid and the protective layer coating liquid by the simultaneous multilayer curtain coating method, the chemical resistance Can be improved, and a heat-sensitive recording material having excellent sensitivity and sticking property can be provided.

Claims (9)

  In a heat-sensitive recording material having an undercoat layer mainly composed of a pigment and a binder, a heat-sensitive recording layer containing a leuco dye and a developer, and a protective layer on a support, the undercoat layer is a styrene-acrylic copolymer resin. The styrene-acrylic copolymer resin obtained from the emulsion is contained in an amount of 1 to 10% by mass based on the total solid content of the undercoat layer, and the heat-sensitive recording layer and the protective layer further comprise a heat-sensitive recording layer coating solution and a protective layer coating. A heat-sensitive recording material formed by applying and drying a liquid by a simultaneous multilayer curtain coating method.   The heat-sensitive recording material according to claim 1, wherein the styrene-acrylic copolymer resin is contained in an amount of 2 to 8% by mass based on the total solid content of the undercoat layer.   The heat-sensitive recording material according to claim 1 or 2, wherein the styrene-acrylic copolymer resin emulsion is anionic.   The heat-sensitive recording material according to any one of claims 1 to 3, comprising a calcined kaolin having an oil absorption (based on JIS K 5101) of 90 ml / 100 g or more as a pigment of the undercoat layer.   The heat-sensitive recording material according to any one of claims 1 to 4, further comprising 10 to 100% by mass of plastic hollow particles as a pigment for the undercoat layer based on the calcined kaolin.   The heat-sensitive recording material according to claim 1, wherein the undercoat layer is formed by applying and drying an undercoat layer coating solution by a blade coating method.   The heat-sensitive recording material according to claim 1, wherein the coating liquid for the heat-sensitive recording layer has a Brookfield type viscosity (60 rpm) at 25 ° C. of 200 to 1500 mPa · s.   The polyvinyl alcohol having a polymerization degree of 500 or more is contained as a main water-soluble adhesive of the coating solution for the thermal recording layer, and the content of the polyvinyl alcohol is 3 to 30% by mass with respect to the total solid content of the thermal recording layer. The thermosensitive recording material according to any one of claims 1 to 7. The heat-sensitive recording material according to any one of claims 1 to 8, wherein the heat-sensitive recording layer coating liquid contains a dialkylsulfosuccinate represented by the following general formula (1).

(Wherein R ¹ and R ² represent the same or different aliphatic or alicyclic hydrocarbon groups having 2 to 20 carbon atoms, M represents a hydrogen atom or a cation, and x represents 1 or 2).