JP5668580B2 - Thermal recording material - Google Patents

Description

  The present invention relates to a heat-sensitive recording material utilizing a color development reaction between a leuco dye and a developer.

  A heat-sensitive recording material is known that utilizes a color-forming reaction between a colorless or light-colored leuco dye and an organic or inorganic developer to bring a color-developing image into contact with both color-forming substances by heat. Such a heat-sensitive recording material is relatively inexpensive, and the recording device is compact and relatively easy to maintain, so that it is used not only as a recording medium for facsimiles and various printers but also in a wide range of fields.

  With the expansion of the field of use and the diversification and high performance of recording devices, the usage environment of recording media is becoming harsh, and not only the image quality and recording sensitivity of recorded images but also storage stability can be satisfied at the same time. It has been demanded.

  Conventionally, in order to improve the image quality and recording sensitivity of the thermal recording paper, it has been proposed to introduce an undercoat layer containing plastic hollow particles between the support and the thermal recording layer. For example, a first undercoat layer containing hollow fine particles and a second undercoat layer containing an organic filler and / or an inorganic filler are provided between the base material and the heat-sensitive recording layer (Patent Document 1). Organic micro hollow particles having a film thickness / particle diameter ratio of 0.15 or less are provided as an undercoat layer between the organic micro hollow particle layer and the heat sensitive recording layer. Is known as a second undercoat layer, and Mayer bar coating is described as a coating method (Patent Document 2). Further, the under layer containing plastic hollow particles is blade coating, and two or more layers including a thermosensitive coloring layer provided on the under layer are simultaneously applied by a curtain coating method (Patent Document 3). ) Has also been proposed.

  In addition, an improvement in image quality and recording sensitivity by improving the smoothness after coating the undercoat layer has been proposed. For example, a first intermediate layer and a second intermediate layer are provided between the support and the heat-sensitive recording layer, and the first intermediate layer has a Wang Ken type smoothness of 700 seconds or more (Patent Document 4). Between the recording layers, an undercoat layer containing an inorganic pigment other than silica having a shape index of 3 to 10 (ratio of pigment particle diameter measured by laser method and precipitation method (laser method / precipitation method)) is provided ( Patent document 5) etc. are proposed.

  However, the undercoat layer using hollow particles has good image quality and recording sensitivity, but has low storage stability, and the use of a pigment having a large shape index and the calender treatment after the undercoat layer improve the smoothness of the coating layer. There is a drawback that the cushioning property is insufficient and the image quality is lowered.

  On the other hand, in order to obtain a heat-sensitive recording material having good recording sensitivity, image quality, storability, etc., an undercoat layer is formed by a blade coating method, and then a heat-sensitive recording layer containing a specific developer and a protective layer are simultaneously multilayered by a curtain coating method. It is applied so that the center line surface roughness of the thermal recording surface is 2.0 μm or less (Patent Document 6), and the thermal recording layer contains a specific dye precursor and a pigment having an average particle size of 1.5 μm or less ( Patent Document 7) has been proposed.

  However, these are all improvements from the heat-sensitive recording layer, and the present situation is that satisfactory results are not necessarily obtained with respect to the improvement in storage stability from the undercoat layer.

Japanese Patent Laid-Open No. 62-117787 JP-A-1-285383 JP 2010-94981 A JP 2000-108518 A JP 2005-254471 A JP 2003-182246 A JP 2005-262714 A

  The main object of the present invention is to provide a thermal recording material excellent in recording sensitivity, image quality, and chemical resistance.

  As a result of intensive studies in view of the above-described conventional technology, the present inventors have solved the above problems. That is, the present invention relates to the following thermal recording material.

  Item 1: A thermosensitive recording medium comprising an anchor layer, an undercoat layer and a thermosensitive recording layer containing a leuco dye and a developer on a support, wherein the anchor layer contains an inorganic pigment having an aspect ratio of 20 to 100 and plastic hollow particles And an undercoat layer containing an oil-absorbing pigment having an oil absorption of 40 to 120 ml / 100 g.

  Item 2: The heat-sensitive recording material according to Item 1, wherein the inorganic pigment contained in the anchor layer is kaolin.

  Item 3: The thermal recording material according to Item 1 or 2, wherein the mass ratio of the inorganic pigment and the plastic hollow particles contained in the anchor layer is 95/5 to 20/80.

  Item 4: The heat-sensitive recording material according to any one of Items 1 to 3, wherein the undercoat layer further contains plastic hollow particles.

  Item 5: The heat-sensitive recording material according to Item 4, wherein the mass ratio of the oil-absorbing pigment and the plastic hollow particles contained in the undercoat layer is 20/80 to 50/50.

  Item 6: The heat-sensitive recording material according to any one of Items 1 to 5, wherein the oil-absorbing pigment contained in the undercoat layer is calcined kaolin.

Item 7: The heat-sensitive recording material according to any one of Items 1 to 6, wherein the coating amount after drying of the anchor layer is 4 to 15 g / m ² .

Item 8: The heat-sensitive recording material according to any one of Items 1 to 7, wherein the coating amount after drying of the undercoat layer is 0.5 to 10 g / m ² .

  Item 9: An anchor layer is formed by applying a coating solution for an anchor layer containing an inorganic pigment having an aspect ratio of 20 to 100 and plastic hollow particles, and applying the blade onto the support, followed by drying. Using an undercoat layer coating solution containing an oil-absorbing pigment in an amount of 40 to 120 ml / 100 g and a thermal recording layer coating solution containing a leuco dye and a developer, simultaneous multilayer curtain coating and drying are carried out on the anchor layer. Item 9. The heat-sensitive recording material according to any one of Items 1 to 8, wherein the undercoat layer and the heat-sensitive recording layer are formed.

  The heat-sensitive recording material of the present invention is excellent in recording sensitivity, image quality, and chemical resistance.

  The anchor layer in the present invention contains an inorganic pigment having an aspect ratio of 20 to 100 and plastic hollow particles. By using an inorganic pigment having a high aspect ratio and plastic hollow particles in combination, the coating surface can be smoothed and the thickness of the coating layer laminated thereon can be made uniform. This makes it possible to achieve both improvement in image quality and improvement in chemical resistance.

  The hollow plastic particles are conventionally known, for example, fine hollow particles having a thermoplastic polymer as a shell, and a copolymer mainly composed of acrylic resin, styrene resin, acrylic-styrene resin, vinylidene chloride resin and acrylonitrile. Examples thereof include particles made of a resin, a copolymer resin mainly composed of isobornyl methacrylate and acrylonitrile, and the like.

  About the inorganic pigment used together with the plastic hollow particles, those having an aspect ratio of 30 to 100 are more preferable. Among inorganic pigments, kaolin having an aspect ratio of 20 to 100 is particularly preferable from the viewpoints of image quality, recording sensitivity, and economy. The aspect ratio is the ratio of the particle diameter to the thickness. The larger the value, the thinner the particle shape and the larger the particle shape. If the aspect ratio is less than 20, the coverage of the support becomes low, so that the smoothness after coating becomes insufficient, the image quality deteriorates, and the chemical resistance also decreases. A product having an aspect ratio exceeding 100 is technically difficult to manufacture, for example, in kaolin, and may affect the image quality in terms of concealment.

  The mass ratio between the inorganic pigment and the plastic hollow particles is preferably 95/5 to 20/80, and more preferably 90/10 to 30/70. By setting the mass ratio of the inorganic pigment to 95 or less, the cushioning property of the anchor layer can be improved and the image quality and recording sensitivity can be improved. On the other hand, by setting it to 20 or more, the oil absorption of the anchor layer can be sufficiently exhibited, and image defects due to head wrinkles and the like can be reduced.

The coating amount after drying of the anchor layer is preferably ^{4~15g / m 2, 5~12g / m} 2 is more preferable. By setting it to 4 g / m ² or more, even if an inorganic pigment having a high aspect ratio is used, sufficient coverage of the support can be obtained, and image quality and chemical resistance can be improved. On the other hand, if it exceeds 15 g / m ² , no significant effect on the improvement of image quality and chemical resistance can be seen any more, and if it is 15 g / m ² or less, the effect of improving the surface strength can be obtained.

  In the present invention, a specific pigment is contained in the anchor layer, but other pigments can be used as long as the desired effects of the present invention are not impaired. As other pigments, both inorganic and organic pigments can be used. Specific examples include kaolin, clay, calcium carbonate, magnesium carbonate, aluminum hydroxide, barium sulfate, talc, calcined clay, calcined kaolin, and titanium oxide. Inorganic pigments such as zinc oxide, diatomaceous earth, particulate anhydrous silica, activated clay, styrene microballs, nylon powder, polyethylene powder, urea-formalin resin filler, styrene-methacrylic acid copolymer resin, polystyrene resin, raw starch particles, etc. An organic pigment is mentioned.

  The anchor layer can contain an adhesive. As the adhesive, for example, any of a water-soluble adhesive and a water-dispersible adhesive can be used. Examples of the water-soluble adhesive include polyvinyl alcohol, modified polyvinyl alcohol, starch and derivatives thereof, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, and ethylcellulose, polyacrylic acid soda, polyvinylpyrrolidone, and acrylic acid. Water-soluble polymers such as amide-acrylic acid ester copolymer, acrylic acid amide-acrylic acid ester-methacrylic acid copolymer, styrene-maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, and casein Is mentioned. Water dispersible adhesives include polyvinyl acetate, polyurethane, styrene-butadiene copolymer, styrene-butadiene-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride-acetic acid Examples thereof include latex of water-insoluble polymers such as vinyl copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, silylated urethane, acrylic-silicon composite, and acrylic-silicon-urethane composite. These can be used alone or in combination of two or more.

  The amount of the adhesive used is not particularly limited, and is determined in consideration of the coating strength and the recording sensitivity of the heat-sensitive recording layer, but 3 to 50 parts by mass with respect to 100 parts by mass of the pigment contained in the anchor layer. Preferably, 5-30 mass parts is more preferable, and 7-20 mass parts is especially preferable. In addition, the anchor layer coating solution may contain auxiliary agents such as various known thickeners, waxes, antifoaming agents, and surfactants as necessary.

  The anchor layer is generally prepared by mixing an anchor layer coating solution prepared by mixing plastic hollow particles and an inorganic pigment having an aspect ratio of 20 to 100, and, if necessary, an adhesive and an auxiliary agent with water as a medium. It is formed by coating and drying.

  The method for applying the anchor layer coating solution is not particularly limited, but in the present invention, it is particularly preferable to select the blade coating method. Thereby, unevenness on the surface of the anchor layer can be reduced, the coating thickness of the undercoat layer and the heat-sensitive recording layer formed on the anchor layer can be made uniform, and the image quality and chemical resistance can be improved.

  The anchor layer in the present invention is not limited to the type of the support, but can exhibit even more excellent effects, particularly on a support with low smoothness that is inferior in coverage of the coating layer. Specifically, the image quality can be effectively improved on a support having a Beck smoothness (JIS P8119) of 30 to 100 seconds. By setting it to 30 seconds or more, sufficient coverage with the anchor layer can be obtained. On the other hand, since the smoothness of the support itself is high by setting it to 100 seconds or less, the effect of providing the anchor layer becomes relatively small, so that a sufficient effect can be obtained in improving the image quality.

  The blade coating method is not limited to the coating method using blades represented by the bevel type and the vent type, but also includes the rod blade method and the bill blade method, and is not limited to the off-machine coater. You may apply with the installed on-machine coater. After forming the anchor layer, a known smoothing process such as a calendar may be applied to the surface of the anchor layer as necessary.

  The heat-sensitive recording material of the present invention comprises an undercoat layer between the anchor layer and the heat-sensitive recording layer. The undercoat layer in the invention contains an oil-absorbing pigment having an oil absorption of 40 to 120 ml / 100 g based on JIS K 5101.

  The oil absorption amount of the oil absorbing pigment is more preferably 60 to 120 ml / 100 g. When the oil absorption exceeds 120 ml / 100 g, the adhesive component in the heat-sensitive recording layer penetrates and is absorbed by the oil-absorbing pigment, and the surface strength is significantly reduced. On the other hand, if it is less than 40 ml / 100 g, the heat insulating property is poor and the recording sensitivity is lowered.

  Specific examples of the oil-absorbing pigment include calcined diatomaceous earth, aluminum silicate, calcium carbonate, magnesium carbonate, aluminum hydroxide, calcined kaolin, amorphous silica, and talc. Of these, calcined kaolin is preferred from the viewpoint of improving recording sensitivity and image quality.

  As the pigment for the undercoat layer, any other inorganic and organic pigments can be used in combination with the oil-absorbing pigment as long as the effects of the present invention are not impaired. Examples of other pigments include kaolin, clay, calcium carbonate, magnesium carbonate, aluminum hydroxide, barium sulfate, talc, calcined clay, titanium oxide, zinc oxide, diatomaceous earth, fine particulate anhydrous silica, activated clay, and styrene. Examples thereof include organic pigments such as microballs, nylon powder, polyethylene powder, urea-formalin resin filler, styrene-methacrylic acid copolymer resin, polystyrene resin, and raw starch particles. Among these, the combined use with plastic hollow particles is preferable. As a plastic hollow particle, it can select suitably from what can be used for an anchor layer.

  The mass ratio of the oil-absorbing pigment and the plastic hollow particles is preferably 20/80 to 50/50, more preferably 30/70 to 45/55. By setting the mass ratio of the oil-absorbing pigment to 20 or more, the oil-absorbing property of the undercoat layer can be sufficiently exhibited, and image defects such as head wrinkles can be reduced. On the other hand, by setting it to 50 or less, image quality and chemical resistance can be improved.

  The undercoat layer is generally used for an undercoat layer prepared by mixing water with a specific pigment, if necessary, plastic hollow particles, and various auxiliary agents such as an antifoaming agent, a thickener, and a wax. It is formed on the anchor layer using a coating liquid.

0.5-10 g / m < ² > is preferable and, as for the coating amount after drying of a subbing layer, 1-8 g / m < ² > is more preferable. By setting it as 0.5 g / m < ² > or more, the effect of this invention can fully be exhibited, and surface strength can be improved by setting it as 10 g / m < ² > or less. The undercoat layer can be divided into two or more layers as necessary, and the composition and coating amount of each layer may be the same or different.

  In the present invention, a specific pigment is contained in the undercoat layer, but other pigments can be used as long as the desired effects of the present invention are not impaired. As other pigments, both inorganic and organic pigments can be used. Specific examples include kaolin, clay, calcium carbonate, magnesium carbonate, aluminum hydroxide, barium sulfate, talc, calcined clay, titanium oxide, and zinc oxide. Inorganic pigments such as diatomaceous earth, particulate anhydrous silica, activated clay, organic pigments such as styrene microballs, nylon powder, polyethylene powder, urea-formalin resin filler, styrene-methacrylic acid copolymer resin, polystyrene resin, raw starch particles, etc. Can be mentioned.

  Examples of adhesives that can be used for the undercoat layer include starches such as oxidized starch, acid-modified starch, phosphate esterified starch, enzyme-modified starch, cation-modified starch, esterified starch, etherified starch, and vinyl acetate-modified grafted starch. , Cellulose derivatives such as methylcellulose, ethylcellulose, carboxymethylcellulose, methoxycellulose, hydroxyethylcellulose and hydroxypropylmethylcellulose, fully (or partially) saponified polyvinyl alcohol, silicon modified polyvinyl alcohol, diacetone modified polyvinyl alcohol, carboxy modified polyvinyl alcohol, acetoacetyl modified polyvinyl Polyvinyl alcohols such as alcohol, polyacrylic acid soda, polyacrylamide, polyvinylpyrrolidone, acrylic acid amide-acrylic acid Stealth copolymer, acrylic acid amide-acrylic acid ester-methacrylic acid copolymer, styrene-maleic anhydride copolymer alkali salt, isobutylene-maleic anhydride copolymer alkali salt, sodium alginate, gelatin, casein, etc. Adhesive, polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic ester, polybutyl methacrylate, styrene-butadiene copolymer, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate copolymer, styrene-butadiene -Water-insoluble polymers such as acrylic copolymers. When a water-insoluble polymer is used as an adhesive, it may be used as a water-dispersible adhesive in a latex state or the like.

  In the present invention, the undercoat layer is preferably formed by a curtain coating method. In order to stabilize the curtain film by adjusting the surface tension, it is preferable to add a surfactant such as dioctyl sulfosuccinic acid sodium salt to the coating solution for the undercoat layer. As the range of the surface tension, the static surface tension measured by a platinum plate method at 25 ° C. is preferably adjusted to 25 to 36 mN / m, more preferably 26 to 34 mN / m. By setting the static surface tension to 25 mN / m or more, defects due to bubbles can be hardly generated. On the other hand, by setting the static surface tension to 36 mN / m or less, curtain film stability can be improved.

  The heat-sensitive recording layer in the present invention contains various known leuco dyes and developers. In addition, you may contain a sensitizer, a preservability improving agent, a pigment, various adjuvants, etc. as needed. Specific examples of leuco dyes include, for example, 3-diethylamino-6-methyl-7-anilinofluorane, 3-di (n-butyl) amino-6-methyl-7-aniline as a leuco dye that gives a black color. Linofluorane, 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-trifluoromethylani Lino) fluorane, 3- (N-isoamyl-N-ethylamino) -7- (o-chloroanilino) fluorane, 3- (N-ethyl-N-2-tetrahydrofurfurylamino) -6 -Methyl-7-anilinofluorane, 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 Examples include methyl-7-anilinofluorane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3-di (n-butylamino) -7- (2-chloroanilino) fluorane. Further, if necessary, a leuco dye that develops a color tone different from black, for example, a color tone such as red, magenta, orange, blue, green, etc., may be used.

  The leuco dye is not limited to these, and two or more kinds can be used in combination. The ratio of the leuco dye used is not particularly limited, and is preferably about 3 to 30% by mass in the total solid content of the heat-sensitive recording layer.

  In the present invention, when the leuco dye is used as a solid dispersion fine particle state, water is used as a dispersion medium, modified polyvinyl alcohol such as polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, sulfone-modified polyvinyl alcohol, methylcellulose, carboxymethylcellulose, hydroxypropylmethylcellulose, In addition to water-soluble polymers such as styrene-maleic anhydride copolymer salts and derivatives thereof, various wet pulverizers such as sand mills, attritors, ball mills, cobo mills, as well as surfactants and antifoaming agents as necessary. To obtain a dispersion liquid dispersed in a dispersion medium, and this dispersion liquid can be used for the preparation of a thermal recording layer coating liquid. 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 use the leuco dye as solid fine particles. . In any case, the average particle size of the dispersed particles of the leuco dye used in the solid dispersed fine particle state is preferably 0.2 to 3.0 μm, more preferably 0.3 to 0.3 in order to obtain appropriate recording sensitivity. 1.0 μm.

  As a method of using the leuco dye in the present invention, it can be used as composite particles composed of an organic polymer and a leuco dye, in addition to the solid dispersed fine particle state. The composite particles can be produced by a known method. As a specific example, for example, in the case of a method for producing composite particles in which the organic polymer is at least one of polyurea and polyurea-polyurethane, the composite particles are leuco dye, and at least one of polyurea and polyurea-polyurethane by polymerization. A polymer-forming raw material such as a polyisocyanate compound capable of forming a seed is dissolved and mixed in a water-insoluble organic solvent having a boiling point of 100 ° C. or lower, and this organic solvent solution is a hydrophilic protective colloid solution such as polyvinyl alcohol. Emulsified and dispersed so that the average particle size is about 0.5 to 3 μm, and after mixing a reactive substance such as polyamine if necessary, this emulsified dispersion is heated to volatilize and remove the organic solvent, and then The polymer-forming raw material can be prepared by polymerizing. Alternatively, the leuco dye is dissolved in a polymer-forming raw material, and this solution is emulsified and dispersed to an average particle size of about 0.5 to 3 μm by the above method, and then the polymer-forming raw material is polymerized. Can be prepared.

  As the developer, a known compound can be used. 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'-allyloxydiphe Rulsulfone, 3,3′-diallyl-4,4′-dihydroxydiphenylsulfone, bis (p-hydroxyphenyl) butyl acetate, phenolic compounds such as methyl bis (p-hydroxyphenyl) acetate, 4-hydroxybenzophenone, 4- Dimethyl hydroxyphthalate, methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, 4-hydroxybenzoate-sec-butyl, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, Phenolic compounds such as chlorophenyl 4-hydroxybenzoate and 4,4′-dihydroxydiphenyl ether, or benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, salicylic acid, 3-tert-butylsalicylic acid, -Aromatic carboxylic acids such as isopropylsalicylic acid, 3-benzylsalicylic acid, 3- (α-methylbenzyl) salicylic acid, 3,5-di-tert-butylsalicylic acid, and these phenolic compounds, aromatic carboxylic acids and, for example, zinc, Organic acidic substances such as salts with polyvalent metals such as magnesium, aluminum and calcium, Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea, Np-toluenesulfonyl-N ′ -P-butoxycarbonylphenylurea, Np-tolylsulfonyl-N'-phenylurea, 4,4'-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylsulfone, 4,4'- Bis (p-toluenesulfonylaminocarbonylamino) diphenylmethane, etc. Urea compounds.

  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 types of the leuco dye and the developer, and is not particularly limited, but generally 1 mass of leuco dye. Preferably, about 1 to 7 parts by mass, more preferably about 1 to 6 parts by mass of the developer is used.

  Furthermore, 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 size 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 an amount that does not decrease the color density, that is, 50% by mass or less based on the total solid content of the heat-sensitive recording layer.

  Furthermore, the heat-sensitive recording layer can contain a sensitizer for increasing the recording sensitivity. 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, oxalic acid-di-p-methylbenzyl, oxalic acid-di-p-chlorobenzyl, p-benzylbiphenyl, tolylbiphenyl ether, di (p-methoxyphenoxyethyl) ether, 1,2-di (3 -Mechi Phenoxy) 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- Examples include acetoacetyl-p-toluidine, di (β-biphenylethoxy) benzene, p-di (vinyloxyethoxy) benzene, 1-isopropylphenyl-2-phenylethane, and the like. The content of these sensitizers is not particularly limited, but it is generally desirable to adjust in a range of about 4 parts by mass or less with respect to 1 part by mass of the developer.

  Further, the heat-sensitive recording layer may contain a storability improving agent for improving the storability of the recorded image. 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, 1,1,3-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'-tetrabromodiphenyl sulfone, 4,4'-dihydroxy-3,3', 5,5'- Tetramethyldiphenylsulfone, 2,2-bis (4-hydroxy-3,5-dibromophenyl) propane, 2,2-bis (4-hydroxy-3,5-dichlorophenyl) propane, 2,2-bis (4- Hindered phenol compounds such as hydroxy-3,5-dimethylphenyl) propane, N, N′-di-2-naphthyl-p-phenylenediamine, 2,2′-methylenebi (4,6-di -tert- butylphenyl) phosphate sodium, and the like.

The heat-sensitive recording layer generally uses water as a dispersion medium, and a dispersion obtained by dispersing a leuco dye and a developer, and if necessary, a sensitizer and a storage stabilizer together or separately, and further, an adhesive, an interface It is formed on the undercoat layer using a heat-sensitive recording layer coating solution prepared by mixing an activator, an auxiliary agent and the like. The coating amount of the heat-sensitive recording layer coating composition is not particularly limited, is preferably about 1~12g / ^{m 2} of the coating amount after drying, more preferably 2~10g / ^{m 2,} 2.5~5.5g / ^{m 2} is particularly preferred. The heat-sensitive recording layer can be divided into two or more layers as necessary, and the composition and coating amount of each layer may be the same or different.

  As the adhesive used in the thermal recording coating liquid, for example, any of a water-soluble adhesive and a water-dispersible adhesive can be used. Examples of the water-soluble adhesive include polyvinyl alcohol, modified polyvinyl alcohol, starch and derivatives thereof, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, and ethylcellulose, polyacrylic acid soda, polyvinylpyrrolidone, and acrylic acid. Examples include amide-acrylic acid ester copolymers, acrylic acid amide-acrylic acid ester-methacrylic acid copolymers, styrene-maleic anhydride copolymer alkali salts, polyacrylamide, sodium alginate, gelatin, and casein. Water dispersible adhesives include polyvinyl acetate, polyurethane, styrene-butadiene copolymer, styrene-butadiene-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride-acetic acid Examples thereof include latex of water-insoluble polymers such as vinyl copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, silylated urethane, acrylic-silicon composite, and acrylic-silicon-urethane composite. These can be used alone or in combination of two or more.

  In the coating solution for the heat sensitive recording layer, an auxiliary agent such as a crosslinking agent, waxes, metal soap, colored dye, colored pigment, fluorescent dye, oil repellent, antifoaming agent and viscosity modifier may be included as necessary. Can do.

  Examples of the crosslinking agent include aldehyde compounds such as glyoxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, dimethylol urea compounds, aziridine compounds, blocked isocyanate compounds, and adipic acid dihydrazides. Examples thereof include dihydrazide compounds, inorganic compounds such as ammonium persulfate, ferric chloride, magnesium chloride, sodium tetraborate, potassium tetraborate and boric acid, boric acid triesters, boron polymers, and the like. These can be used alone or in combination of two or more. These crosslinking agents are preferably used in the range of 0.1 to 10% by mass in the total solid content of the heat-sensitive recording layer.

  Examples of the wax include waxes such as paraffin wax, carnauba wax, microcrystalline wax, polyolefin wax and polyethylene wax, and higher fatty acid amides such as stearic acid amide and ethylenebisstearic acid amide, higher fatty acid esters, and derivatives thereof. Can be mentioned.

  Examples of the metal soap include higher fatty acid polyvalent metal salts such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate.

  In the present invention, the heat-sensitive recording layer is preferably formed by a curtain coating method. A surfactant is preferably added to the thermal recording layer coating liquid in order to stabilize the curtain film by adjusting the surface tension. As the range of the surface tension, the static surface tension measured by a platinum plate method at 25 ° C. is preferably adjusted to 25 to 36 mN / m, more preferably 26 to 34 mN / m. By setting the static surface tension to 25 mN / m or more, defects due to bubbles can be hardly generated. On the other hand, by setting the static surface tension to 36 mN / m or less, curtain film stability can be improved.

  In this invention, a protective layer can also be provided as needed. 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 the present invention, any one of a water-soluble adhesive and a water-dispersible adhesive can be used as the adhesive. The adhesive can be appropriately selected from those that can be used for the heat-sensitive recording layer. The effect of the present invention can be further enhanced by containing 15 to 50% by mass of polyvinyl alcohol having a polymerization degree of 1000 to 3000 as a water-soluble adhesive in the total solid content of the protective layer. Examples of the polyvinyl alcohol having a polymerization degree of 1000 to 3000 include fully saponified or partially saponified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol. Among these, acetoacetyl-modified polyvinyl alcohol and diacetone-modified polyvinyl alcohol are preferable because they can improve the barrier property of the protective layer surface and improve the storage stability such as chemical resistance.

  The total content of the water-soluble adhesive is preferably about 10 to 80% by mass, more preferably about 20 to 75% by mass in the total solid content of the protective layer. By setting it as 10 mass% or more, the outstanding barrier property can be obtained, and also generation | occurrence | production of paper dust can be prevented by improving surface strength. On the other hand, by setting it to 80% by mass or less, sticking that is a recording failure can be suppressed.

  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 content ratio of the pigment is about 5 to 80% by mass in the total solid content of the protective layer, and particularly preferably about 10 to 70% by mass. By setting the content to 5% by mass or more, the sliding with the thermal head can be improved, and sticking and head wrinkles can be suppressed. On the other hand, by setting it to 80% by mass or less, the barrier property can be improved.

  As an auxiliary agent, for example, a lubricant such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, sodium alkylbenzenesulfonate, sodium dioctylsulfosuccinate, sulfonate-modified polyvinyl alcohol, acetylene glycol, fluorine, Surfactants such as silicone, phosphate ester, ether type surfactants, amphoteric surfactants such as betaine, aminocarboxylate, imidazoline derivatives, glyoxal, boric acid, dialdehyde starch, methylol urea, Water resistant agents (crosslinking agents) such as epoxy compounds and hydrazine compounds, hydrophobic polycarboxylic acid copolymers, ultraviolet absorbers, fluorescent dyes, colored dyes, mold release agents, antioxidants and the like can be mentioned. The usage-amount of auxiliary agent can be suitably set from a wide range.

The protective layer is generally formed on the heat-sensitive recording layer using a protective layer coating liquid prepared by mixing water, a dispersion medium, and a pigment, an adhesive, and, if necessary, an auxiliary agent. The coating amount of the protective layer coating composition is not particularly limited, 0.3 to 10 / ^{m 2} approximately by dry weight, in particular 0.5 to 8 g / ^{m 2} approximately. The protective layer can be divided into two or more layers as necessary, and the composition and the coating amount of each layer may be the same or different.

  In the present invention, the protective layer is preferably formed by a curtain coating method. In order to adjust the surface tension and stabilize the curtain film, it is preferable to add a surfactant to the protective layer coating liquid. As the range of the surface tension, the static surface tension measured by a platinum plate method at 25 ° C. is preferably adjusted to 25 to 36 mN / m, more preferably 26 to 34 mN / m. By setting the static surface tension to 25 mN / m or more, defects due to bubbles can be hardly generated. On the other hand, by setting the static surface tension to 36 mN / m or less, curtain film stability can be improved.

  After application of each of the above coating liquids, it is dried, and after that, it is preferably smoothed by calendaring and used. In the present invention, a smoothing process using a super calendar can be performed in an arbitrary process after the formation of each layer or after the formation of a specific layer.

  Since the curtain coating method is a non-contact type contour coating, a layer having a uniform thickness can be obtained. On the other hand, a contact coating method such as a blade coating method, a bar coating method, or an air knife coating method is affected by the surface properties (unevenness) of the support, and therefore the film thickness is non-uniform. For this reason, with the same coating amount, an undercoat layer formed by a curtain coating method, a heat-sensitive recording layer, and a protective layer provided if necessary can have a uniform thickness, and a good image quality can be obtained. In addition, the storability of the recorded image can be improved and the barrier property can be improved.

  The curtain coating method is not particularly limited. For example, the curtain coating method is a method in which the coating liquid is allowed to flow down and freely drop and applied to the support without contact. For example, a slide curtain method using a slide hopper type curtain coating device, a couple curtain And publicly known methods such as the twin curtain method. Further, as described in JP-A-2006-247611, the coating liquid is ejected downward from the curtain head to form a coating liquid layer on the slope, and the coating liquid is applied from the downward curtain guide portion of the slope. It is also possible to transfer the coating liquid layer onto the web surface by forming a curtain.

  In the present invention, it is preferable that two or more layers including at least an undercoat layer and a thermosensitive recording layer are formed by simultaneous multilayer curtain coating. Examples of combinations of coating solutions in which two or more layers are simultaneously applied are, for example, a combination of an undercoat layer coating solution and a thermal recording layer coating solution, an undercoat layer coating solution and a thermal recording layer coating solution, and, if necessary, a protective layer The combination with the coating liquid for an application etc. are mentioned. A method in which two or more coating liquid layers are formed and applied at the same time, or, for example, a coating liquid for an undercoat layer is applied by a curtain system, and a coating liquid for a thermal recording layer is further curtaind when the undercoat layer is wet. The method of applying by is preferable.

  The support in the present invention is not particularly limited, and examples thereof include high-quality paper, art paper, synthetic paper, PET film, non-woven medium-quality paper, coated paper, cast-coated paper, glassine paper, resin-laminated paper, and polyolefin-based synthetic paper. In addition to synthetic fiber paper, non-woven fabric, synthetic resin film, etc., various transparent supports can be appropriately selected and used.

  In the present invention, in order to further increase the added value of the product, a multicolor thermal recording material can be obtained. In general, a multicolor thermal recording material is an attempt to use a difference in heating temperature or a difference in heat energy, and is generally configured by laminating a high-temperature coloring layer and a low-temperature coloring layer that develop colors in different colors on a support. When these are roughly classified, a multicolor thermosensitive recording material is produced using two types, a decoloring type and a coloring type, a method using a microcapsule, and composite particles comprising an organic polymer and a leuco dye. There is a way.

  Furthermore, in the present invention, in order to increase the added value of the heat-sensitive recording material, it is possible to obtain a heat-sensitive recording material that has been subjected to processing to give higher functions. For example, it can be used as pressure-sensitive adhesive paper, re-moistened adhesive paper, and delayed tack paper by applying a coating such as a pressure-sensitive adhesive, a re-humidifying adhesive, and a delayed tack type pressure-sensitive adhesive to the back surface opposite to the thermosensitive recording layer. . 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 as a thermal transfer paper, an ink jet paper, a carbonless paper, an electrostatic recording paper, and a 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. The average particle diameter was measured using a laser diffraction particle size distribution analyzer SALD-2200 (manufactured by Shimadzu Corporation).

Example 1
Preparation of anchor layer coating solution Kaolin (trade name: Contour 1500, aspect ratio 60, Imeris Minerals Japan) 80 parts, plastic hollow particle emulsion (trade name: AE852, solid content concentration 26%, hollow ratio 80%, average particle size 1.0 μm, manufactured by JSR) 80 parts, styrene-butadiene-acrylonitrile copolymer latex (trade name: PT-1004A, solid content concentration 43%, manufactured by Nippon Zeon Co., Ltd.) 20 parts as an adhesive, A composition comprising 40 parts of a 5% aqueous solution of carboxymethylcellulose (trade name: Cellogen 7A, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 60 parts of water was mixed and stirred to obtain an anchor layer coating solution.

Preparation of coating solution for undercoat layer 40 parts of calcined kaolin with oil absorption of 110 ml / 100 g, plastic hollow particle emulsion (trade name: AE852, solid content concentration 26%, hollow ratio 80%, average particle size 1.0 μm, manufactured by JSR Corporation ) 230 parts, 30 parts of styrene-butadiene-acrylonitrile copolymer latex (trade name: PT-1004A, solid concentration 43%, manufactured by Nippon Zeon Co., Ltd.) as an adhesive, fully saponified polyvinyl alcohol (trade name: PVA124, polymerization degree 2400) A composition comprising 30 parts of a 15% aqueous solution of Kuraray Co., Ltd., 2 parts of a 5% aqueous solution of sodium dioctylsulfosuccinate (trade name: SN wet OT-70, manufactured by San Nopco), and 60 parts of water are mixed and stirred. Thus, an undercoat layer coating solution was obtained.

Preparation of mixed dispersion of leuco dye and sensitizer (liquid A) 3-di (n-butyl) amino-6-methyl-7-anilinofluorane 25 parts, 1,2-di (3-methyl A composition comprising 20 parts of phenoxy) ethane, 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 0.9 μm, and a leuco dye / sensitizer dispersion. (Liquid A) was obtained.

・ 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 was mixed with a sand mill. Were pulverized until the average particle size became 1.5 μm to obtain a developer dispersion (liquid B).

Preparation of coating solution for heat-sensitive recording layer 60 parts of A solution, 70 parts of B solution, 10 parts of 60% aqueous dispersion of light calcium carbonate (trade name: Brilliant 15, manufactured by Shiroishi Chemical Co., Ltd.), aluminum hydroxide (trade name) : Heidilite H42, Showa Denko Co., Ltd.) 60% aqueous dispersion 15 parts, heavy calcium carbonate (trade name: Softon 2200, Okutama Kogyo Co., Ltd.) 60% aqueous dispersion 10 parts, fully saponified polyvinyl alcohol (Product) Name: 60 parts of 15% aqueous solution of PVA-124, polymerization degree 2400, saponification degree 98.5 mol%, manufactured by Kuraray Co., Ltd., 30 parts of 30% aqueous dispersion of zinc stearate, glycerin ester emulsion defoamer (product) Name: Nopco 1407K, manufactured by San Nopco) 5% aqueous dispersion, dioctyl sulfosuccinate sodium salt (trade name: SN wet OT-70, manufactured by San Nopco) 5 parts of 10% aqueous solution and 90 parts of water were sequentially added, mixed and stirred to obtain a thermal recording layer coating solution.

(Preparation of thermal recording material)
The anchor layer coating solution was applied to one side of a high-quality paper having a basis weight of 60 g / m ² (Beck smoothness 80 seconds) using a blade coater so that the coating amount after drying was 7 g / m ² and dried. Thereafter, the coating solution for the undercoat layer was applied and dried using a rod blade coater so as to be 3 g / m ^2, and the coating solution for the thermosensitive recording layer was applied using a rod blade coater so as to be 4 g / m ² , After drying, a super calendar process was performed to obtain a heat-sensitive recording material.

Example 2
Example 1 except that bulk paper (Beck smoothness 32 seconds) having a basis weight of 55 g / m ² was used in place of the high-quality paper (Beck smoothness 80 seconds) of the basis weight 60 g / m ² of Example 1. A heat-sensitive recording material was obtained in the same manner.

Example 3
In the preparation of the anchor layer coating liquid of Example 1, kaolin (trade name: Varisurf HX, aspect ratio) was used instead of 80 parts of kaolin (trade name: Contour 1500, aspect ratio 60, manufactured by Imeris Minerals Japan). 100, manufactured by Imerizu Minerals Japan Co., Ltd.) was used in the same manner as in Example 1 except that 80 parts were used.

Example 4
In the preparation of the anchor layer coating solution of Example 1, kaolin (trade name: Astra plate, aspect ratio) was used instead of 80 parts of kaolin (trade name: Contour 1500, aspect ratio 60, manufactured by Imeris Minerals Japan). 34, Imeris Minerals Japan Co.) was used in the same manner as in Example 1 except that 80 parts were used.

Example 5
In the preparation of the anchor layer coating solution of Example 1, kaolin (trade name: Capim NP, aspect ratio) was used instead of 80 parts of kaolin (trade name: Contour 1500, aspect ratio 60, manufactured by Imerizu Minerals Japan). (20, manufactured by Imerizu Minerals Japan Ltd.) A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 80 parts were used.

Example 6
In the preparation of the anchor layer coating liquid of Example 1, 95 parts of 80 parts of kaolin (trade name: Contour 1500, aspect ratio 60, manufactured by Imeris Minerals Japan Ltd.) and plastic hollow particle emulsion (trade name: AE852) Heat-sensitive material in the same manner as in Example 1 except that 80 parts were changed to 20 parts and 60 parts of water were changed to 100 parts), solid content concentration 26%, hollow ratio 80%, average particle diameter 1.0 μm, manufactured by JSR Corporation). A record was obtained.

Example 7
In the preparation of the anchor layer coating solution of Example 1, 80 parts of kaolin (trade name: Contour 1500, aspect ratio 60, manufactured by Imeris Minerals Japan Co., Ltd.) was added to 30 parts, and a plastic hollow particle emulsion (trade name: AE852). Heat-sensitive material in the same manner as in Example 1 except that 80 parts were changed to 250 parts and 60 parts of water were changed to 0 parts, with a solid content concentration of 26%, a hollowness of 80%, an average particle size of 1.0 μm, manufactured by JSR) A recording material was obtained.

Example 8
In the preparation of the coating liquid for the undercoat layer of Example 1, 40 parts of calcined kaolin was mixed with 50 parts of plastic hollow particle emulsion (trade name: AE852, solid content concentration 26%, hollow ratio 80%, average particle diameter 1.0 μm, A thermosensitive recording material was obtained in the same manner as in Example 1 except that 230 parts (made by JSR) was changed to 200 parts.

Example 9
In the preparation of the coating solution for the undercoat layer of Example 1, 40 parts of calcined kaolin was added to 30 parts, and a plastic hollow particle emulsion (trade name: AE852, solid content concentration 26%, hollow ratio 80%, average particle diameter 1.0 μm, A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 230 parts (made by JSR) were changed to 260 parts and 60 parts of water were changed to 20 parts.

Example 10
In the preparation of the coating liquid for the undercoat layer of Example 1, 40 parts of calcined kaolin was added to 100 parts, and a plastic hollow particle emulsion (trade name: AE852, solid content concentration 26%, hollow ratio 80%, average particle diameter 1.0 μm, A thermosensitive recording material was obtained in the same manner as in Example 1 except that 230 parts (made by JSR) were changed to 0 parts and 60 parts of water were changed to 200 parts.

Example 11
A thermosensitive recording material was obtained in the same manner as in Example 1 except that the coating amount of the anchor layer was changed from 7 g / m ² to 4.5 g / m ² in the production of the thermosensitive recording material of Example 1.

Example 12
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that in the production of the heat-sensitive recording material of Example 1, the coating amount of the undercoat layer was changed from 3 g / m ² to 0.5 g / m ² .

Example 13
In the production of the heat-sensitive recording material of Example 1, the undercoat layer and the heat-sensitive recording layer were simultaneously coated with a multi-layer curtain using a slide hopper type curtain coating apparatus and dried, and then subjected to the supercalendering process in the same manner as in Example 1. A heat-sensitive recording material was obtained.

Example 14
Preparation of coating solution for protective layer A dispersion obtained by dispersing 50 parts of kaolin (trade name: UW-90, manufactured by Engelhard) in 100 parts of water was mixed with acetoacetyl-modified polyvinyl alcohol (trade name: Gocepha). 600 parts of 10% aqueous solution of Immer Z-200, manufactured by Nippon Synthetic Chemical Co., Ltd., 30 parts of a 30% aqueous dispersion of zinc stearate, and sodium dioctylsulfosuccinate (trade name: SN Wet OT-70, manufactured by San Nopco) A composition comprising 10 parts of a 10% aqueous solution was mixed and stirred to obtain a protective layer coating solution.

-Preparation of heat-sensitive recording material On one side of a high-quality paper (Beck smoothness 80 seconds) with a basis weight of 60 g / m ² , the coating amount after drying the anchor layer coating liquid of Example 1 is 7 g / m ^2. After coating and drying using a blade coater, the undercoat layer coating solution, the thermal recording layer coating solution and the protective layer coating solution of Example 1 were applied onto the anchor layer using a slide hopper curtain coating device. A coating liquid layer composed of an undercoat layer coating liquid, a thermosensitive recording layer coating liquid and a protective layer coating liquid in this order is formed from the support side, and the solid content coating amount of each layer is 3.0 g / m ^{2 of the} undercoat layer. After simultaneous multilayer curtain coating and drying so that the thermal recording layer was 3.0 g / m ² and the protective layer was 2.5 g / m ² , supercalendering was performed to obtain a thermal recording material.

Comparative Example 1
In the preparation of the coating liquid for anchor layer of Example 1, 80 parts of kaolin (trade name: Contour 1500, aspect ratio 60, manufactured by Imeris Minerals Japan) was added to 100 parts, and a plastic hollow particle emulsion (trade name: AE852). (Soluble content concentration 26%, hollow rate 80%, average particle size 1.0 μm, manufactured by JSR) Heat-sensitive recording was carried out in the same manner as in Example 1 except that 80 parts was 0 parts and 60 parts of water was 100 parts. Got the body.

Comparative Example 2
In the preparation of the thermal recording material of Example 1, the undercoat layer coating solution was not used, and in the preparation of the anchor layer coating solution, kaolin (trade name: Contour 1500, aspect ratio 60, manufactured by Imeris Minerals Japan Ltd.) ) A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 80 parts of calcined kaolin was used instead of 80 parts.

Comparative Example 3
In the preparation of the anchor layer coating liquid of Example 1, kaolin (trade name: UW90, aspect ratio 10) was used instead of 80 parts of kaolin (trade name: Contour 1500, aspect ratio 60, manufactured by Imerizu Minerals Japan). The product was obtained in the same manner as in Example 1 except that 80 parts (manufactured by BASF) were used.

  The thermosensitive recording material thus obtained was subjected to the following evaluation test. The results are shown in Table 1.

(Recording sensitivity and image quality)
Using a thermal recording simulator (TH-PMD, manufactured by Okura Electric Co., Ltd.), recording was performed at an applied energy of 0.15 mJ / dot, and the density of the solid recording part was measured with a Macbeth densitometer (trade name: RD914, manufactured by Macbeth). Measured in visual mode. Further, the recording image quality of the solid recording portion was visually evaluated.
A: There is no white spot and the image quality is extremely excellent.
○: Almost no white spots are seen and the image quality is good.
Δ: White spots are observed, but the image quality is at a practical level.
X: Remarkably many white spots are observed, and the image quality is poor, which is a practical problem.

(chemical resistance)
Using the thermal recording simulator (TH-PMD, manufactured by Okura Electric Co., Ltd.), the recording portion of the thermal recording body colored with an applied energy of 0.27 mj / dot is placed on an acrylic cylinder having a diameter of 5 cm with a vinyl chloride wrap film (trade name) : High essoft TM350, manufactured by Nippon Carbide Industries Co., Ltd.) and wound for 24 hours at room temperature, and then the density of the recorded part was measured with a Macbeth densitometer (trade name: RD914, manufactured by Macbeth). Measured in visual mode. Further, the storage ratio of the recording part was determined 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

  According to the present invention, an inorganic pigment and a plastic having an aspect ratio of 20 to 100 in a thermosensitive recording medium comprising an anchor layer, an undercoat layer, and a thermosensitive recording layer containing a leuco dye and a developer on a support. By containing hollow particles and an undercoat layer containing an oil-absorbing pigment having an oil absorption of 40 to 120 ml / 100 g, a thermal recording material excellent in recording sensitivity, image quality and chemical resistance can be provided. In particular, it is possible to provide a heat-sensitive recording material excellent in image quality on a support having low smoothness, which has been conventionally difficult to use due to the poor coverage of the coating layer.

Claims (9)

  A thermosensitive recording medium comprising an anchor layer, an undercoat layer and a thermosensitive recording layer containing a leuco dye and a developer on a support, the anchor layer containing an inorganic pigment having an aspect ratio of 20 to 100 and plastic hollow particles, A heat-sensitive recording material, wherein the layer contains an oil-absorbing pigment having an oil absorption of 40 to 120 ml / 100 g.   The heat-sensitive recording material according to claim 1, wherein the inorganic pigment contained in the anchor layer is kaolin.   The heat-sensitive recording material according to claim 1 or 2, wherein the mass ratio of the inorganic pigment and the plastic hollow particles contained in the anchor layer is 95/5 to 20/80.   The heat-sensitive recording material according to claim 1, wherein the undercoat layer further contains plastic hollow particles.   The heat-sensitive recording material according to claim 4, wherein the mass ratio of the oil-absorbing pigment and the plastic hollow particles contained in the undercoat layer is 20/80 to 50/50.   The heat-sensitive recording material according to any one of claims 1 to 5, wherein the oil-absorbing pigment contained in the undercoat layer is calcined kaolin. The heat-sensitive recording material according to claim 1, wherein the anchor layer has a coating amount after drying of 4 to 15 g / m ² . The heat-sensitive recording material according to claim 1, wherein the coating amount after drying of the undercoat layer is 0.5 to 10 g / m ² .   Using an anchor layer coating solution containing an inorganic pigment with an aspect ratio of 20 to 100 and plastic hollow particles, the anchor layer is formed by applying a blade onto the support and drying, and an oil absorption amount of 40 to Using an undercoat layer coating solution containing 120 ml / 100 g of an oil-absorbing pigment and a thermal recording layer coating solution containing a leuco dye and a developer, simultaneous multi-layer curtain coating and drying are performed on the anchor layer. The heat-sensitive recording material according to claim 1, wherein a layer and a heat-sensitive recording layer are formed.