JP2009166264A - Thermal recording material - Google Patents

Abstract

The present invention relates to a heat-sensitive recording material using a color reaction between a leuco dye and a colorant, and particularly excellent in blank paper quality, good image quality even when printed with low energy, and excellent barrier properties. The present invention relates to a thermal recording medium.
In a heat-sensitive recording body in which an undercoat layer, a heat-sensitive recording layer, and a protective layer are sequentially provided on a paper support, the undercoat layer is formed on at least the first undercoat layer and the first undercoat layer. It has a multilayer structure composed of a second undercoat layer, the first undercoat layer is formed by coating and drying by a blade coating method, and the second and subsequent undercoat layers are applied by a rod coating method and A heat-sensitive recording material formed by drying and containing a specific amount of a specific soap-free polyethylene dispersion in the heat-sensitive recording layer coating liquid.
[Selection figure] None

Description

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

  A heat-sensitive recording material that utilizes a color reaction between a leuco dye and a color former to obtain a recorded image by heat is well known. Such a thermal recording medium is relatively inexpensive, and the recording device is compact and easy to maintain. Therefore, it is not only used as a recording medium for output of facsimiles and various computers, printers of scientific measuring devices, etc. It is widely used as a recording medium for various printers such as labels, ATMs, CAD, handy terminals, and various ticket sheets.

In addition, the printing speed of printers increases year by year, and it is desired that printing can be performed even with lower printing energy. Therefore, in order to improve the recording sensitivity and image quality of the thermal recording medium, an undercoat layer containing a pigment and a binder is provided between the support and the thermal recording layer, and a void is formed to make it porous or bulky. It is known to give For example, in order to obtain a uniform and stable undercoat layer structure, it has been proposed to apply an undercoat layer coating solution having a specific viscosity by blade coating (see Patent Document 1). In addition, it has been proposed that the variation in the thickness of the undercoat layer be within a certain range in order to improve the image quality of the thermal recording paper (see Patent Document 2). Further, in order to lower the static friction coefficient of the surface, it has been proposed to form two or more undercoat layers by blade coating (see Patent Document 3).
However, in recent years, the printing speed has been further increased, and the demand for high sensitivity and high image quality of thermal recording media has been increasing. Only high-smooth base paper can be used, or an undercoat layer is simply provided. However, sufficient quality cannot be obtained.
As a method of providing the undercoat layer, the undercoat layer usually exhibits a heat insulating effect and improves the recording sensitivity as the coating amount increases, but the higher the coating amount, the more difficult it is to obtain a uniform coating layer, and the subsequent formation. It is difficult to make the heat-sensitive recording layer and the protective layer uniform. Also, after forming the undercoat layer as a uniform coating layer and subsequently forming a uniform heat-sensitive recording layer, so-called scratches that occur due to rubbing the heat-sensitive recording layer, particularly during coating of the protective layer coating, are likely to occur. Become. As a result, the blank paper quality and image quality are deteriorated, or the barrier performance of the protective layer is deteriorated.
In addition, in the thermal recording material market, which is shifting to a mature market, manufacturing costs have become an important issue, and low-productivity coating methods and coating methods that tend to cause coating defects are high. Even when a quality product is obtained, it is difficult to actually manufacture the product.

Japanese Patent Laid-Open No. 4-290789 JP 2004-122483 A JP 2005-103864 A

  An object of the present invention is to provide a heat-sensitive recording material that is excellent in white paper quality, provides good image quality even when printed with low energy, and has excellent barrier properties.

  As a result of intensive studies to solve the above problems, the present inventors have a specific average particle diameter range in the thermal recording layer coating liquid as a means for preventing scratches during coating of the protective layer coating. By including a specific amount of a specific dispersion, the above-described problems can be solved.

  That is, the present invention provides the following thermal recording material.

  Item 1: In a heat-sensitive recording body in which an undercoat layer, a heat-sensitive recording layer, and a protective layer are sequentially provided on a paper support, the undercoat layer is formed on at least the first undercoat layer and the first undercoat layer. It has a multilayer structure composed of two undercoat layers, the first undercoat layer is formed by coating and drying by a blade coating method, and the second and subsequent undercoat layers are applied and dried by a rod coating method. The heat-sensitive recording layer coating liquid contains a soap-free polyethylene dispersion, and the average particle size of the dispersion is in the range of 1 to 8 μm, A thermal recording material, wherein the dispersion is contained in an amount of 1 to 5% by mass relative to the total solid content of the thermal recording layer.

  The heat-sensitive recording material of the present invention does not cause coating defects such as scratches when coating the protective layer coating material, is excellent in blank paper quality, provides good image quality even when printed with low energy, and has excellent barrier properties. Is.

In the thermal recording body in which an undercoat layer, a thermal recording layer, and a protective layer are sequentially provided on both sides of the undercoat paper support, the undercoat layer having the multilayer structure is formed on at least one side of the paper support, In that case, by forming a thermosensitive recording layer on the undercoat layer having a multilayer structure, it is possible to provide a thermosensitive recording medium that has high recording sensitivity on at least one side and that can provide good image quality even when printed with low energy. It becomes.

  In the present invention, the undercoat layer comprises at least two layers. The number of undercoat layers is not particularly limited as long as it is 2 or more, but the upper limit may be about 4 layers, particularly preferably 2 layers. When the undercoat layer has a multilayer structure of two or more layers, the barrier property is improved and the uneven penetration of the heat-sensitive recording layer can be greatly reduced. As a result, the coloring component contained in the heat-sensitive recording layer can effectively utilize the printing energy received from the surface layer during printing, so the recording sensitivity is high and good image quality can be obtained even when printing with low energy. It is done. If there is little penetration unevenness in the protective layer, the effective component for protecting the surface layer of the heat-sensitive recording layer is increased and the barrier property is improved, so that an effect excellent in plasticizer resistance and barrier property can be obtained.

  The undercoat layer is usually at least one selected from the group consisting of I) an oil-absorbing pigment having an oil absorption of 70 ml / 100 g or more, particularly about 80 to 150 ml / 100 g, II) organic hollow particles, and III) thermally expandable particles. In addition, an undercoat layer coating liquid containing an adhesive as a main component can be formed on a support by coating and drying.

  By using at least one pigment selected from the group consisting of the oil-absorbing pigment, organic hollow particles, and thermally expandable particles, the gap in the undercoat layer is increased, and heat energy is provided when a thermal recording layer or the like is provided thereon. Therefore, it is possible to obtain a high color density because it is possible to prevent the diffusion of the ink in the direction of the base paper and to effectively use the printing energy.

  Here, the oil absorption is a value determined according to the method of JIS K5101-2004.

  Various oil-absorbing pigments can be used, and specific examples include inorganic pigments such as calcined kaolin and silica.

  The average particle diameter of the oil-absorbing pigment is preferably about 0.05 to 5 μm, particularly preferably about 0.08 to 3 μm. Here, the average particle diameter is a 50% D value measured by a laser diffraction particle size distribution analyzer (trade name: SALD2200, manufactured by Shimadzu Corporation).

  Moreover, as an organic hollow particle, a conventionally well-known thing, for example, the particle | grains whose hollow rate consists of an acrylic resin, a styrene resin, a vinylidene chloride resin etc. about 50-99% can be illustrated. Here, the hollowness is a value obtained by (d / D) × 100. In the formula, d represents the inner diameter of the organic hollow particles, and D represents the outer diameter of the organic hollow particles.

  The average particle diameter of the organic hollow particles is preferably about 0.5 to 10 μm, particularly preferably about 0.7 to 2 μm. In addition, this average particle diameter is measured by the same measuring method as the average particle diameter of the oil-absorbing pigment.

  Various types of thermally expandable particles can be used. Specific examples include thermally expandable fine particles obtained by microencapsulating a low-boiling point hydrocarbon with a copolymer such as vinylidene chloride or acrylonitrile by an in situ polymerization method. Is mentioned. Examples of the low boiling point hydrocarbon include ethane, propane, n-butane, and the like.

  In the present invention, the pigment component constituting the undercoat layer can be composed of only an oil-absorbing pigment, organic hollow particles, or thermally expandable particles. Also, for example, two or more of the above pigments can be used in combination, such as a combination of an oil-absorbing pigment and organic hollow particles, or a combination of an oil-absorbing pigment and thermally expandable particles.

  When two or more of the above pigments are used in combination, the amount of each pigment used can be selected from a wide range. For example, in the combination of the oil absorbing pigment and the organic hollow particles, the organic hollow is used with respect to the oil absorbing pigment. About 20 to 180% by mass of particles, particularly about 25 to 120% by mass, or a combination of oil-absorbing pigment and thermally expandable particles, about 1 to 160% by mass of thermally expandable particles, particularly 10 It is preferable to adjust and use together in the range of about ~ 120% by mass.

  When using together 1 type, or 2 or more types chosen from an oil-absorbing pigment, an organic hollow particle, and a thermally expansible particle, the total amount is about 40-90 mass% with respect to undercoat layer total solid, Especially 50-85. It is preferably about mass%.

  As the pigment used in the undercoat layer, in addition to the oil-absorbing inorganic pigment, the organic hollow particles, and the heat-expandable particles, various known coating pigments may be used as long as the effects of the present invention are not impaired. Examples thereof include kaolin, heavy calcium carbonate, titanium oxide, magnesium carbonate, aluminum hydroxide, synthetic mica, talc, and solid organic pigments.

  Examples of the adhesive used in the coating liquid for the undercoat layer include polyvinyl alcohols having various molecular weights, modified polyvinyl alcohols, starches and derivatives thereof, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate , Polyvinylpyrrolidone, acrylic acid amide-acrylic acid ester copolymer, acrylic acid amide-acrylic acid ester-methacrylic acid terpolymer, styrene-maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, And water-soluble polymer materials such as casein, and polyvinyl acetate, polyurethane, styrene-butadiene copolymer, polyacrylic acid, polyacrylate ester, vinyl chloride-vinyl acetate copolymer, polybutyl Examples include tachylate, ethylene-vinyl acetate copolymer, styrene-butadiene-acrylic copolymer, silylated urethane, acrylic-silicon composite, latex of hydrophobic polymer such as acrylic-silicon-urethane composite, and the like. It is also possible to use 1 type or 2 types or more together.

  The content of the adhesive in the undercoat layer is preferably about 3 to 55% by mass, more preferably about 5 to 45% by mass with respect to the total solid content of the undercoat layer. By setting it as 3 mass% or more, the intensity | strength of a coating layer can be improved. On the other hand, when the content is 35% by mass or less, the target void of the undercoat layer can be increased, and the recording sensitivity can be improved.

  As the auxiliary agent, for example, surfactants such as sodium alkylbenzene sulfonate, sodium dioctyl sulfosuccinate, sulfone-modified polyvinyl alcohol, sodium polyacrylate, glyoxal, boric acid, dialdehyde starch, methylol urea, epoxy compound, hydrazine compound, etc. Water-resistant agents (crosslinking agents), zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax and other lubricants, ultraviolet absorbers, fluorescent dyes, coloring dyes, mold release agents, antioxidants, etc. It is done. The usage-amount of auxiliary agent can be suitably set from a wide range.

  The method for preparing the coating solution for the undercoat layer is not particularly limited, and the concentration of the coating solution is not particularly limited, but is usually about 20 to 50% by mass, preferably about 35 to 45% by mass. . By setting the content to 20% by mass or more, the viscosity of the coating liquid can be increased, the occurrence of uneven penetration and hence unevenness of the undercoat layer can be suppressed, and the image quality can be improved. At the same time, the coating speed can be increased to improve productivity. Moreover, by setting it as 50 mass% or less, the viscosity of a coating material can be made moderate and a process can be made easy.

  About the coating liquid for undercoat layers in this invention, it is preferable that the viscosity in 8800 rpm of the Hercules viscometer in liquid temperature 25 degreeC is about 15-40 mPa * s. Moreover, it is preferable that the viscosity at 60 rpm of the BL viscometer at a liquid temperature of 25 ° C. is about 500 to 2000 mPa · s. By setting the viscosity to 15 mPa · s or more or 500 mPa · s or more, it is possible to suppress the occurrence of uneven penetration, and as a result, it is easy to obtain a high-sensitivity, high-quality heat-sensitive recording material, and at the same time, productivity can be increased. Further, by setting the viscosity to 40 mPa · s or 2000 mPa · s or less, respectively, coating can be easily performed, and as a result, a desired heat-sensitive recording material can be easily obtained.

  Adjustment of the viscosity of the undercoat layer coating solution may be appropriately performed by selecting the types and blending amounts of pigments, adhesives, auxiliaries and the like used in the preparation of the undercoat layer coating solution.

The coating amount of the undercoat layer is not particularly limited, and the thickness of one undercoat layer is about 3 to 12 μm (preferably about 5 to 10 μm), and the total thickness of the undercoat layer is about 6 to 30 μm (preferably 10 What is necessary is just to adjust suitably so that it may become (about 25 micrometers). The coating amount after drying per layer is about 1 to 15 g / m ² , more preferably about 2.5 to 10 g / m ² . The total coating amount of the undercoat layer is about ² to 35 g / m ² , more preferably about 7 to ²⁰ g / m ² .

  In particular, the ratio of the coating amount after drying of the first undercoat layer and the second undercoat layer is preferably about 2: 8 to 8: 2, more preferably about 4: 6 to 6: 4. . By setting it within this range, the undercoat layer can exhibit a function as a sufficient heat insulating layer and can enhance the effect of suppressing excessive penetration during coating of the thermal recording layer. Can be formed.

  In the present invention, as the coating method for forming the undercoat layer, it is easy to obtain a coating surface with high smoothness, excellent high-speed coating suitability, and few coating defects. The blade coating method and the second undercoat layer and thereafter form the undercoat layer using the rod coating method.

  The blade coating method applies the paint to the paper by roll or fountain method, and then presses a thin steel plate with a thickness of several millimeters typified by the bevel type and vent type to scrape the paint. This is a method for controlling.

  The rod coating method is a method of controlling the coating amount by scraping off the coated paint by rotating and pressing a metal cylinder instead of a thin steel plate.

  As a method for applying the undercoat layer in the present invention, when the first undercoat layer is formed by coating and drying by a blade coating method, a uniform and highly smooth coated surface is obtained, and further the second undercoat layer is obtained. After that, when it is formed by coating and drying by the rod coating method, a uniform and highly smooth coated surface with few coating defects can be obtained. The heat-sensitive recording material of the present invention can achieve high sensitivity and high image quality by the interaction of these coating methods.

  In forming the undercoat layer, for example, in the case of forming the two undercoat layers, the first layer is applied to the base paper fed from the unwinder and dried, and then the second layer is directly used without passing through the winding process. A method of winding after coating and drying is preferred. That is, after forming the first undercoat layer, it is preferable to continuously form the second undercoat layer without winding up the first undercoat layer-forming paper support. After the first layer is applied and before the second undercoat layer is applied, once the winding process is performed, the back surface of the base paper comes into contact, which may adversely affect the surface of the first undercoat layer. On the other hand, since the second undercoat layer can be formed in a state in which the surface of the first undercoat layer is highly smooth by not performing the winding step during the formation of the undercoat layer, the coating layers after the second undercoat layer are A highly smooth coated surface is formed.

  In the present invention, the smoothness of the undercoat layer after application of the undercoat layer is preferably about 200 to 1200 seconds, more preferably about 300 to 1000 seconds. The smoothness is measured with a Oken type smoothness meter (J.TAPPI No.5-2: 2000).

  In this invention, in order to make smoothness into the said range, after forming the undercoat layer after the 2nd layer by a rod coating method, you may perform smoothing processes, such as a super calendar.

Heat-sensitive recording layer In the heat-sensitive recording layer of the present invention, various known leuco dyes, colorants, sensitizers, pigments, adhesives, various auxiliary agents such as the polyethylene dispersion of the present invention, and the like can be used.

  By adding soap-free polyethylene dispersion to the thermal recording layer coating solution, scratches are generated when the rod or blade is rubbed against the thermal recording layer during coating of protective layer paint such as rod coating or blade coating. Can be suppressed. Soap-free polyethylene dispersion is obtained by adding a small amount of ethylenically unsaturated carboxylic acid monomer, for example, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, maleic anhydride, styrene sulfonic acid, etc. After the polymerization reaction, it is obtained by neutralizing with an alkali.

  The average particle size of the dispersion is 1 to 8 μm, preferably 1.5 to 6 μm. If the average particle size is less than 1 μm, the effect of suppressing scratches cannot be obtained, and if it exceeds 8 μm, the surface smoothness of the heat-sensitive recording layer formed is inferior and the image quality deteriorates in the heat-sensitive recording material on which the protective layer is formed. Further, the content of the dispersion is 1 to 5% by mass, preferably 1 to 3% by mass with respect to the total solid content of the heat-sensitive recording layer. If the content is less than 1% by mass, the effect of suppressing scratches cannot be obtained, and if it exceeds 5% by mass, uneven coating tends to occur during the formation of the protective layer, resulting in poor white paper quality. The emulsion does not use an emulsifier. If the emulsifier is contained, it is not preferable because the effect of the emulsifier causes background fogging or the like, and the water resistance of the heat-sensitive recording layer decreases. The average particle diameter is a value measured by a Coulter counter method.

  Specific examples of the leuco dye include 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide, crystal violet lactone, 3- (N-ethyl-N-isopentylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (o , P-dimethylanilino) fluorane, 3- (N-ethyl-Np-toluidino) -6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3 -Di (n-butyl) amino-6-methyl-7-anilinofluorane, 3- (N-cyclohexyl-N-methylamino) -6-methyl-7-anilinofur Lan, 3-diethylamino-7- (o-chloroanilino) fluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino- 6-methylfluorane, 3-cyclohexylamino-6-chlorofluorane, 3- (N-ethyl-N-hexylamino) -6-methyl-7- (p-chloroanilino) fluorane, 3-di (n-pentyl) ) Amino-6-methyl-7-anilinofluorane, 3- (N-isoamyl-N-ethylamino) -7- (o-chloroanilino) fluorane, 3- (N-ethyl-N-2-tetrahydrofurfuryl) Amino) -6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7-anilinofluorane, -(Nn-hexyl-N-ethylamino) -6-methyl-7-anilinofluorane, 3- [N- (3-ethoxypropyl) -N-ethylamino] -6-methyl-7-ani Linofluorane, 3- [N- (3-ethoxypropyl) -N-methylamino] -6-methyl-7-anilinofluorane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3- (N -Ethyl-p-toluidino) -6-methyl-7- (p-toluidino) fluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-diethylamino-7- (o-fluoroanilino) fluorane , 3- (4-dimethylamino) alinino-5,7-dimethylfluorane and the like. Of these, one can be used alone, or two or more can be used in combination.

  As the color former, one kind or a mixture of two or more kinds can be used. Specific examples of the colorant include, for example, 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy-4′-allyloxydiphenylsulfone, 4,4′-isopropylidenediphenol, 4,4′-cyclohexylene. Dendiphenol, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 2,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxydiphenylsulfone, 3,3'-diallyl-4,4'- Dihydroxydiphenylsulfone, 4-hydroxy-4′-methyldiphenylsulfone, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α-methyl-α- (4′-hydroxyphenyl) ) Ethyl] phenolic compounds such as benzene, Np-tolylsulfonyl-N′-fe Nylurea, 4,4′-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylmethane, Np-tolylsulfonyl-N′-p-butoxyphenylurea, etc., sulfonyl group and ureido in the molecule Compounds having a group, zinc 4- [2- (p-methoxyphenoxy) ethyloxy] salicylate, zinc 4- [3- (p-tolylsulfonyl) propyloxy] salicylate, 5- [p- (2-p-methoxyphenoxy) Ethoxy) cumyl] zinc salts of aromatic carboxylic acids such as salicylic acid.

  As a sensitizer, it can use individually or in combination of 2 or more types. Specific examples of the sensitizer include, for example, stearamide, stearic acid methylenebisamide, stearic acid ethylenebisamide, 4-benzylbiphenyl, p-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- (3-methylphenoxy) ethane, 2-naphthylbenzyl ether, 1- (2-naphthyloxy) -2-phenoxyethane, 1,3-di (naphthyl) Oxy) propane, dibenzyl oxalate, di-p-methylbenzyl oxalate, di-p-chloro oxalate Benzyl, dibutyl terephthalate, dibenzyl terephthalate, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole.

  Examples of the pigment include inorganic fine particles such as calcium carbonate, amorphous silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, kaolin, calcined kaolin, talc, and surface-treated calcium carbonate and silica. Examples thereof include powders and organic fine powders such as urea-formalin resin, styrene-methacrylic acid copolymer and polystyrene resin.

  Adhesives include polyvinyl alcohols of various molecular weights, modified polyvinyl alcohols, starches and derivatives thereof, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose, polyacrylic acid soda, polyvinylpyrrolidone, acrylic acid amide-acrylic acid Water-soluble polymer materials such as ester copolymers, acrylic acid amide-acrylic acid ester-methacrylic acid terpolymers, styrene-maleic anhydride copolymer alkali salts, polyacrylamide, sodium alginate, gelatin, and casein, Polyvinyl acetate, polyurethane, styrene-butadiene copolymer, polyacrylic acid, polyacrylate ester, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate. Alcohol copolymer, and styrene - butadiene - latex of a hydrophobic polymer such as an acrylic copolymer.

  In addition, as the various auxiliary agents, known ones such as an antifoaming agent, a wetting agent, an antiseptic, a fluorescent whitening agent, a dispersing agent, a thickening agent, a coloring agent, and an antistatic agent can be used.

  In the heat-sensitive recording layer of the present invention, the content of the leuco dye in the heat-sensitive recording layer is generally about 3 to 50% by mass (preferably about 5 to 20% by mass), and the content of the colorant is generally 3%. It is about -60 mass% (preferably 5-40 mass%). The content of the adhesive is generally about 3 to 50% by mass (preferably about 5 to 30% by mass).

  When a sensitizer is included, the content of the sensitizer is preferably about 10 to 40% by mass, and the pigment is preferably included with a content of about 2 to 50% by mass.

  The preparation method and coating method of the heat-sensitive recording layer coating liquid of the present invention can be prepared by generally known methods. For example, the heat-sensitive recording layer coating liquid is a leuco dye and a colorant separately pulverized and dispersed together with an aqueous adhesive solution by a dispersing machine such as a ball mill, and then mixed with a sensitizer, pigment, and various auxiliary agents as necessary. To prepare. Next, the thermal recording layer coating solution may be applied and dried on the undercoat layer by a known method.

  The coating method for the thermal recording layer coating liquid is not particularly limited. For example, any conventionally known coating methods such as air knife coating, blade coating, gravure coating, rod coating, short dwell coating, curtain coating, and die coating are adopted. it can.

The coating amount of the heat-sensitive recording layer coating solution is not particularly limited and includes, 1 to 15 g / ^{m 2} approximately by dry weight, the desired quality can be achieved if particular 2 to 10 g / ^{m 2} approximately.

Protective layer In the heat-sensitive recording material of the present invention, a protective layer is provided on the heat-sensitive recording layer in order to improve storability and to improve runnability during recording.

  The protective layer is preferably composed mainly of a water-soluble polymer and / or a synthetic resin emulsion.

  Examples of the water-soluble polymer include fully saponified or partially saponified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, and the like, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose and the like. Cellulose resins, gelatin, casein, alkali salts of styrene / maleic anhydride copolymers, alkali salts of ethylene / acrylic acid copolymers, alkali salts of styrene / acrylic acid copolymers, and the like.

  Examples of the synthetic resin emulsion include latexes such as styrene-butadiene latex, acrylic latex, and urethane latex.

  Among them, modified polyvinyl alcohol having a degree of polymerization of 1000 or more is preferably used because it can improve the surface barrier properties and improve the storage stability such as chemical resistance.

  The total content of the water-soluble polymer and / or synthetic resin emulsion is preferably about 30 to 80% by mass, and more preferably about 40 to 75% by mass, based on the total solid content of the protective layer.

  If it is less than 30% 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.

  When the water-soluble polymer and the synthetic resin emulsion are used in combination, the usage ratio of the synthetic resin emulsion is about 5 to 100 parts by mass with respect to 100 parts by mass of the water-soluble polymer.

  The protective layer is a thermosensitive recording layer obtained by mixing and stirring the water-soluble polymer and / or synthetic resin emulsion, and optionally added pigments and various auxiliary agents using water as a medium. It can be obtained by coating and drying on top.

  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 or aluminum hydroxide is preferred because it has 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 10-60 mass% is especially preferable.

  If it is less than 5% by mass, the sliding with the thermal head becomes worse, causing sticking or worsening of the head wrinkles. On the other hand, when it exceeds 80% by mass, the barrier property is deteriorated, and the function as a protective layer is significantly lowered.

  As an auxiliary agent, for example, zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax and other lubricants, alkylbenzene sulfonate sodium, dioctyl sulfosuccinate sodium, sulfone-modified polyvinyl alcohol, polyacrylic acid sodium and the like surface activity Agents, glyoxal, boric acid, dialdehyde starch, methylol urea, epoxy compounds, hydrazine compounds, water resistance agents (crosslinking agents), UV absorbers, fluorescent dyes, coloring dyes, mold release agents, antioxidants, etc. Can be mentioned. The usage-amount of auxiliary agent can be suitably set from a wide range.

  The method for applying the protective layer coating solution is not particularly limited, and for example, known means such as air knife coating, varibar coating, blade coating, rod coating, short dwell coating, curtain coating, and die coating can be used. The effect of the present invention can be obtained when using varibar coating, blade coating, and rod coating in the coating method, and the resulting thermal recording material has excellent white paper quality and good image quality even when printed at low energy. It is obtained and has excellent barrier properties.

The coating amount of the protective coating liquid is about 0.5 to 3.0 g / m ² by dry weight, preferably about 0.8 to 2.0 g / m ² .

If it is less than 0.5 g / m ² , the effect of protecting the heat-sensitive recording layer is lost, and it cannot function as a protective layer. On the other hand, if it exceeds 3.0 g / m ² , the recording sensitivity will be reduced and it will not be compatible with high-speed printers.

The support used in the heat-sensitive recording material of the present invention includes, as necessary, a pulp mainly composed of LBKP, NBKP, DIP (waste paper pulp), a paper filler, a paper strength enhancer, a yield improver, and a sizing agent. Or the like together with a small amount of water-soluble polymer, and a base paper made by a paper machine to a basis weight of about 30 to 150 g / m ² is suitable. As the filler internally added to the base paper, known materials can be used, and examples thereof include kaolin, talc, titanium oxide, white carbon, calcium carbonate and the like. The filler content is appropriately adjusted according to paper strength and stiffness, but is preferably 10% by mass or less.

  When manufacturing waste paper pulp, a nonionic surfactant is used during the deinking process, which may cause difficulties in the background fog resistance of the heat-sensitive recording material and the storage stability of the recording portion over time. However, with the two or more undercoat layers formed in the present invention, those having good quality can be obtained.

  In the present invention, after various layers are formed or after all layers are formed, a smoothing process such as supercalendering is performed, or the back side of the support of the thermal recording medium is protected if necessary. Layer, printing coating layer, magnetic recording layer, antistatic layer, thermal transfer recording layer, ink jet recording layer, etc., and the back side of the support is processed into an adhesive label by applying an adhesive treatment to the thermal recording medium Various known techniques in the thermal recording material manufacturing field, such as putting eyes on, can be added as necessary. Furthermore, the heat-sensitive recording layer in the heat-sensitive recording material can be configured to be capable of multicolor recording.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. Further, “parts” and “%” in the examples indicate “parts by mass” and “% by mass”, respectively, unless otherwise specified.

Example 1
(1a) Preparation of coating solution for undercoat layer Styrene-butadiene was added to a dispersion obtained by dispersing 85 parts of calcined kaolin (trade name: Ancilex, Engelhard, Inc., oil absorption 90 ml / 100 g) in 100 parts of water. 40 parts of latex (50% solid content) of copolymer, 50 parts of 10% aqueous solution of oxidized starch, and 1 part of carboxymethylcellulose (trade name: Serogen AG gum, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) are mixed and stirred to form an undercoat layer A coating solution was obtained. The viscosity of the coating solution for the undercoat layer was 1380 mPa · s (60 rpm of BL viscometer) and 34 mPa · s (8800 rpm of Hercules viscometer, using Bob E type).

(1b) Preparation of each component / A solution preparation (preparation of leuco dye dispersion)
A composition consisting of 10 parts of 3- (N-ethyl-p-toluidino) -6-methyl-7-anilinofluorane, 5 parts of a 5% aqueous solution of methylcellulose, and 15 parts of water in a sand mill has an average particle size of 0. A liquid A was obtained by pulverizing to 3 μm.

・ B liquid preparation (preparation of colorant dispersion)
A composition consisting of 10 parts of 2,4′-dihydroxydiphenylsulfone, 5 parts of a 5% aqueous solution of methylcellulose, and 15 parts of water was pulverized with a sand mill until the average particle size became 0.3 μm to obtain a liquid B.

・ C liquid preparation (preparation of sensitizer dispersion)
A composition consisting of 20 parts of di-p-methylbenzyl oxalate ester, 5 parts of a 5% aqueous solution of methylcellulose, and 55 parts of water was pulverized with a sand mill until the average particle size became 0.3 μm to obtain a liquid C.

(1c) Preparation of coating liquid for heat-sensitive recording layer A part 25 parts, B part 50 parts, C part 50 parts, fine particle amorphous silica dispersion (trade name: Silojet 703A, average particle diameter 0.3 μm, solid content concentration 20 parts of 20%, manufactured by Grace Devison Co., Ltd.), 30 parts of 20% aqueous solution of oxidized starch, and 50% of 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol (trade name: GOHSEIMER Z-200, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) Part, a soap-free polyethylene dispersion (trade name: Chemipearl W-400, average particle size 4 μm, solid content concentration 40%, manufactured by Mitsui Chemicals Co., Ltd.) Got.

(1d) Preparation of coating solution for protective layer To a dispersion obtained by dispersing 50 parts of kaolin (trade name: UW-90, manufactured by Engelhard) in 100 parts of water, acetoacetyl-modified polyvinyl alcohol (trade name: Protected by mixing and stirring 600 parts of a 10% aqueous solution of Goosefimmer Z-200, supra) and 25 parts of zinc stearate (trade name: Hydrin Z-8-36, solid content 36%, manufactured by Chukyo Yushi Co., Ltd.) A layer coating solution was obtained.

(1e) Production of thermosensitive recording medium A coating solution for an undercoat layer was applied and dried on one side of a 48 g / m ² base paper by a blade coating method so that the coating amount after drying was 7.0 g / m ^2. Then, the first undercoat layer is formed, and the coating solution for the undercoat layer is formed on the first undercoat layer by the rod coating method so that the coating amount after drying is 8.0 g / m ² without further winding. And dried to form a second undercoat layer. The coating solution for the heat-sensitive recording layer was applied and dried by the rod coating method so that the coating amount after drying was 5.0 g / m ² on the resulting two-layered undercoat layer. Further, the protective layer coating solution was applied and dried by a rod coating method so that the coating amount after drying was 1.3 g / m ² . Thereafter, a smoothing process was performed with a super calender under a pressure condition of linear pressure of 78 N / m to obtain a heat-sensitive recording material.

Example 2
In the preparation of the thermal recording layer coating liquid of Example 1, a soap-free polyethylene dispersion (trade name: Chemipearl W) was used instead of 2 parts of soap-free polyethylene dispersion (trade name: Chemipearl W-400, supra). A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 4 parts of -700, an average particle diameter of 1 μm, a solid content concentration of 40%, manufactured by Mitsui Chemicals, Inc. were used.

Example 3
In the preparation of the thermal recording layer coating liquid of Example 1, a soap-free polyethylene dispersion (trade name: Chemipearl W) was used instead of 2 parts of soap-free polyethylene dispersion (trade name: Chemipearl W-400, supra). A thermosensitive recording material was obtained in the same manner as in Example 1 except that 2 parts of -200, average particle size 6 μm, solid content 40%, manufactured by Mitsui Chemicals Co., Ltd. were used.

Example 4
In the preparation of the thermal recording layer coating liquid of Example 1, a soap-free polyethylene dispersion (trade name: Chemipearl W) was used instead of 2 parts of soap-free polyethylene dispersion (trade name: Chemipearl W-400, supra). A thermosensitive recording material was obtained in the same manner as in Example 1 except that 3 parts of -500, average particle size 2.5 μm, solid content 40%, manufactured by Mitsui Chemicals Co., Ltd. were used.

Comparative Example 1
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the second undercoat layer was not formed in the production of the heat-sensitive recording material of Example 1.

Comparative Example 2
In the production of the heat-sensitive recording material of Example 1, the heat-sensitive recording material was prepared in the same manner as in Example 1 except that the coating amount of the first undercoat layer was 15.0 g / m ² and the second undercoat layer was not formed. Got.

Comparative Example 3
A thermosensitive recording material was obtained in the same manner as in Example 1 except that Chemipearl W-400 (supra) was omitted in the preparation of the thermosensitive recording layer coating solution of Example 1.

Comparative Example 4
In the preparation of the heat-sensitive recording layer coating liquid of Example 1, a soap-free polyethylene dispersion (trade name: Chemipearl W-900, average particle size 0.6 μm, solid content) instead of Chemipearl W-400 (supra) A heat-sensitive recording material was obtained in the same manner as in Example 1 except that it was changed to 40%, manufactured by Mitsui Chemicals.

Comparative Example 5
In the preparation of the heat-sensitive recording layer coating liquid of Example 1, a heat-sensitive recording material was obtained in the same manner as in Example 1 except that the blending number of Chemipearl W-400 (supra) was changed from 2 parts to 0.2 parts. It was.

Comparative Example 6
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the heat-sensitive recording layer coating liquid of Example 1, the number of blended parts of Chemipearl W-400 (supra) was changed from 2 parts to 10 parts.

Comparative Example 7
In the preparation of the thermal recording layer coating liquid of Example 1, a soap-free polyethylene dispersion (trade name: Chemipearl W-410, average particle size 9.5 μm, instead of 2 parts of Chemipearl W-400 (supra), A thermosensitive recording material was obtained in the same manner as in Example 1 except that 2 parts (solid content 40%, manufactured by Mitsui Chemicals, Inc.) were used.

  The following evaluations were performed on the 11 types of thermal recording materials thus obtained, and the results are shown in Table 1.

-Scratches In the thermal recording material, scratches were visually observed and evaluated as follows.
A: There is no occurrence of scratches.
○: Scratch does not occur at all, but there is no practical problem.
(Triangle | delta): Generation | occurrence | production of a scratch is seen and there exists a problem practically.
X: Scratches are observed on the entire surface, which is problematic in practical use.

・ Image quality Using a thermal evaluation machine (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermal recording medium was colored at 0.16 mJ / dot, and the color development status was observed with a microscope and evaluated as follows. did.
A: The dots are uniformly colored and there is no shading unevenness.
○: Slightly uncolored portions of the dots are seen, but there is no practical problem.
Δ: A clear dot non-colored portion is observed, and the unevenness in density is large even by visual evaluation, which is problematic in practical use.
X: There are many dot non-colored portions, and shading unevenness is intense.

Barrier property A 50% strength ethanol solution was applied to the background of the heat-sensitive recording medium and left standing, and the color development state of the heat-sensitive recording body after drying was visually observed and evaluated as follows.
A: There was no color development and the barrier property was excellent.
○: A very slightly colored portion was observed, but there was no practical problem.
Δ: The area of the colored portion and the degree of color development are larger than those of ○, which is problematic in practical use.
X: Color development is observed in most parts, the color development level is severe, and there is a problem in practical use.

Claims (1)

  In a heat-sensitive recording body in which an undercoat layer, a heat-sensitive recording layer, and a protective layer are sequentially provided on a paper support, the undercoat layer is at least a first undercoat layer and a second undercoat layer formed on the first undercoat layer. The first undercoat layer is formed by coating and drying by a blade coating method, and the second and subsequent undercoat layers are further applied and dried by a rod coating method. The heat-sensitive recording layer coating liquid contains a soap-free polyethylene dispersion, the dispersion has an average particle diameter in the range of 1 to 8 μm, and the dispersion is 1 to 5% by mass of the thermosensitive recording layer based on the total solid content of the thermosensitive recording layer.