JP2010046878A - Thermal recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording medium which is excellent in sticking, recording sensitivity, recording image quality, the heat resistance of an unrecorded part, and the preservation stability of a recorded image even in printing by a high-speed printer. <P>SOLUTION: In the thermal recording medium in which an undercoat layer containing a pigment and an adhesive as main components and a thermal recording layer containing a leuco dye and a coloring agent are formed sequentailly on the support as the pigment in the undercoat layer baked Kaoline in an amount of 40-85 mass% and organic fine hollow particles or organic hollow particles selected from organic expandable particles in an amount of 5-40 mass% of the total solid content of the undercoat layer. As the coloring agent in the thermal recording layer, as the coloring agent in the thermal recording layer, N-p-toluenesulfonyl-N'-3-(p-toluenesulfonyl oxy)phenylurea is used and adipic acid dihydrazide is contained. <P>COPYRIGHT: (C)2010,JPO&INPIT

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.

  As the field of use expands, the usage environment of thermal recording media is becoming more severe. There is a demand for products that simultaneously satisfy the quality such as the heat resistance of the unrecorded part, the storage stability of the recorded image, and the suitability for high-speed printing.In general, if the heat resistance of the unrecorded part is improved, the storage stability of the recorded image, The present situation is that satisfactory print quality is not obtained because high-speed printability deteriorates.

  There is also a need for high sensitivity, high image quality, and reduced sticking in high-speed printing. Sticking is a phenomenon in which a molten component having adhesiveness adheres to the head due to heat from the printer head, and printing is skipped or printing sound is increased. There is a method to increase the smoothness of the thermal recording medium and effectively use the heat from the thermal head in order to cope with higher sensitivity and higher image quality of high-speed printing. However, sticking is likely to occur because of high adhesion. . Further, by increasing the content of a hot melt such as a sensitizer, the storage stability of a recorded image is inferior and sticking is likely to occur.

According to Patent Document 1, it is proposed that the thermal responsiveness is improved by providing a hollow fine particle and a layer containing 1 to 10 parts by weight of filler with respect to 1 part by weight of the fine particle as an under layer for the thermosensitive coloring layer. Has been.
However, nothing is described about the heat resistance of the unrecorded portion and the storage stability of the recorded image.

According to Patent Document 2, Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea is used as a colorant, and aluminum hydroxide, amorphous silica, kaolin and talc are used as white pigments. It has been proposed that recording sensitivity and heat resistance are improved by using at least one selected from the above.
However, the heat resistance of the unrecorded part is slightly inferior.

According to Patent Document 3, Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea or the like is used as a colorant, and a specific hindered phenol polymer is used as a preservative improver. Therefore, it has been proposed that the background fogging is small and the light resistance and moisture resistance are improved.
However, the effect of improving the heat resistance of the unrecorded portion is not described, and the balance between high sensitivity, high image quality and sticking in high-speed printing is inferior.

  According to Patent Document 4, there is a description of containing calcined kaolin and hollow resin particles as an undercoat layer, but the effect of improving the heat resistance of unrecorded portions is not described, and high sensitivity, high image quality and sticking of high-speed printing are not described. The balance is also expected to improve.

  According to Patent Document 5, a technique is described in which Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea is used as a colorant, and a specific amount of organic pigment is used in the undercoat layer. However, further improvements are desired.

JP 60-248390 A JP 2002-160461 A JP 2003-118234 A JP 2007-203471 A JP 2007-86927 A

  None of them have been able to obtain sticking, recording sensitivity, recording image quality, heat resistance of an unrecorded portion, and storage stability of recorded images in recent high-speed printers.

  In view of such circumstances, the present invention provides a thermal recording material that is excellent in sticking, recording sensitivity, and recording image quality even in printing by a high-speed printer, and excellent in heat resistance of an unrecorded portion and storage stability of a recorded image. It is in.

  As a result of intensive studies to solve the above problems, the present inventor, as a pigment in the undercoat layer, 40 to 85% by mass of calcined kaolin and fine hollow particles or expandable particles with respect to the total solid content of the undercoat layer 5 to 40% by mass of hollow particles selected from the group consisting of Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea as a colorant in the heat-sensitive recording layer, and adipine It has been found that the above problems can be solved by containing an acid dihydrazide, and the present invention has been completed.

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

Item 1: In a heat-sensitive recording body in which an undercoat layer mainly composed of a pigment and an adhesive and a heat-sensitive recording layer containing a leuco dye and a colorant are sequentially provided on a support, the pigment in the undercoat layer, The colorant in the heat-sensitive recording layer contains 40 to 85% by mass of calcined kaolin and 5 to 40% by mass of hollow particles selected from fine hollow particles or expandable particles with respect to the total solid content of the undercoat layer. And Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea, and further containing adipic acid dihydrazide.
Item 2: The heat-sensitive recording material according to Item 1, wherein the heat-sensitive recording layer contains at least one selected from aluminum hydroxide, amorphous silica, kaolin and talc as a pigment.
Item 3: The heat-sensitive recording material according to Item 1 or 2, wherein the content of adipic acid dihydrazide in the heat-sensitive recording layer is 0.2 to 5% by mass with respect to the total solid content of the heat-sensitive recording layer.
Item 4: The heat-sensitive recording material according to any one of Items 1 to 3, wherein a protective layer mainly composed of a pigment and an adhesive is provided on the heat-sensitive recording layer.
Item 5: The heat-sensitive recording material according to Item 4, comprising at least one selected from acetoacetyl-modified polyvinyl alcohol and diacetone-modified polyvinyl alcohol as an adhesive for the protective layer.

  The heat-sensitive recording material of the present invention is excellent in sticking, recording sensitivity, and recording image quality even when printing with a high-speed printer, and has excellent effects in heat resistance of unrecorded portions and storage stability of recorded images.

  Hereinafter, the present invention will be described in more detail.

  In the heat-sensitive recording material of the present invention, in the heat-sensitive recording material, an undercoat layer mainly composed of a pigment and an adhesive, and a heat-sensitive recording layer containing a leuco dye and a colorant are sequentially provided on the support. As a pigment in the layer, containing 40 to 85% by mass of calcined kaolin and 5 to 40% by mass of organic hollow particles selected from organic fine hollow particles or organic foamable particles with respect to the total solid content of the undercoat layer, Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea is used as a colorant in the heat-sensitive recording layer and further contains adipic acid dihydrazide.

As a method for forming the undercoat layer, generally known application methods such as air knife coating, blade coating, gravure coating, rod coating, bar coating, short dwell coating, curtain coating, and die coating can be adopted.

Since the calcined kaolin used in the present invention has many voids among inorganic pigments, it is excellent in the sensitivity of the heat-sensitive recording material and in the printing strength, and has been preferably used conventionally.
In addition, the organic micro hollow particles or organic foamable particles are superior in recording sensitivity because they have higher heat insulating properties than inorganic pigments. However, the space between the particles is small, and the ability to absorb the hot melt is low.

  In the present invention, the effects of the present invention are obtained by using calcined kaolin and organic hollow particles, which are known materials as the material for the undercoat layer, in a specific ratio.

  40 to 85% by mass of calcined kaolin, preferably 45 to 80% by mass, and 5 to 40% by mass of organic hollow particles selected from organic fine hollow particles or organic foamable particles, based on the total solid content of the undercoat layer, The content is preferably 10 to 35% by mass. When the organic hollow particle exceeds 40% by mass, sticking occurs, and when it is less than 5% by mass, the effect of improving the recording sensitivity and recording image quality is hardly seen.

  The average particle size of the calcined kaolin is preferably about 0.01 to 5 μm, particularly preferably about 0.02 to 3 μm.

  Moreover, when organic hollow particles are used, conventionally known particles, for example, particles having a hollow ratio of about 50 to 99% in which the film material is made of an acrylic resin, a styrene resin, a vinylidene chloride resin, or the like can be exemplified. 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 4 μm.

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

  Among the organic hollow particles, the fine hollow particles have good image quality with a high-speed printer and are particularly preferably used.

In addition, if necessary, other known pigments can be added to the undercoat layer as long as the desired effects of the present invention are not impaired. Examples of such other pigments include plastic pigments such as kaolin, light calcium carbonate, heavy calcium carbonate, titanium oxide, magnesium carbonate, aluminum hydroxide, silica, colloidal silica, synthetic layered mica, clay, and urea-formalin resin filler. Etc.
Further, when light calcium carbonate is used, it is preferably used because the heat resistance of an unrecorded portion is improved. The amount used is about 1 to 15% by mass, preferably about 2 to 10% by mass, based on the total solid content of the undercoat layer.

  The total amount of the pigment in the undercoat layer of the present invention is preferably about 45 to 90% by mass, particularly about 50 to 85% by mass, based on the total solid content of the undercoat layer.

  Examples of the adhesive used in the coating solution 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 tacrolate, ethylene-vinyl acetate copolymer, and latex of hydrophobic polymer such as styrene-butadiene-acrylic copolymer, silylated urethane, acrylic-silicon complex, and acrylic-silicon-urethane complex emulsion. It is also possible to use one type or two or more types in combination.

  The content of the adhesive in the undercoat layer is preferably about 3 to 35% by mass, more preferably about 5 to 30% by mass with respect to the total solid content of the undercoat layer. If it is less than 3% by mass, the strength of the coating layer may be insufficient, and if it exceeds 35% by mass, the recording sensitivity may be lowered.

  Examples of the auxiliary agent include surfactants such as sodium alkylbenzene sulfonate, sodium dioctyl sulfosuccinate, sulfone-modified polyvinyl alcohol, sodium polyacrylate, glyoxal, boric acid, dialdehyde starch, dimethylol urea, epoxy compound, zirconium compound, Water resistance agents (crosslinking agents) such as hydrazine compounds, zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax and other lubricants, UV absorbers, fluorescent dyes, thickeners, coloring dyes, mold release Agents, antioxidants and the like. 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 preferably about 20 to 50%, preferably about 25 to 45%. If it is less than 20%, the viscosity of the coating liquid becomes low, and uneven penetration tends to occur, resulting in unevenness of the undercoat layer, resulting in a decrease in image quality and a decrease in coating speed. Leads to. On the other hand, if it is 50% or more, the viscosity of the coating becomes too high and processing becomes difficult.

  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 total thickness of the undercoat layer is suitably about 3.5 to 30 μm, and the total coating amount of the undercoat layer is suitably about 4 to 35 g / m ^2. However, it is particularly preferable to apply the coating in two or more layers because the penetration of the paint during the thermal recording layer coating is suppressed and the image quality is improved and the color development sensitivity is improved. When divided into two layers, the coating amount per layer is preferably about 2.5 to 10 g / m ² . Further, a smoothing process such as a super calendar may be performed according to the required quality.

Thermosensitive recording layer The thermosensitive recording layer of the present invention uses a leuco dye, Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea as a colorant, and further contains adipic acid dihydrazide.

  Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea is excellent in storage stability of recorded images, but is slightly inferior in heat resistance of unrecorded portions. It is preferable to use adipic acid dihydrazide because the heat resistance of the unrecorded portion is improved.

  The content of Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea is preferably about 5 to 40% by mass, particularly 10 to 35% by mass based on the total solid content of the thermosensitive recording layer. % Is preferred. If it is about 5-40 mass%, a desired effect will be easy to be acquired.

  The content of adipic acid dihydrazide is preferably about 0.2 to 5% by mass, particularly preferably about 0.3 to 4% by mass, based on the total solid content of the heat-sensitive recording layer. If it is less than 0.2% by mass, it is difficult to obtain a desired effect, and if it exceeds 5% by mass, the recording sensitivity may be lowered.

Other known colorants can be added as long as the desired effects of the present invention are not impaired. 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, 2,2 ′-[4- (4-hydroxyphenylsulfonyl) phenoxy] diethyl ether, 1,1-bis (4-hydroxyphenyl) -1-phenyl Ethane, 1,4-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] Phenolic compounds such as benzene, Np-tolylsulfonyl-N′-phenylurea, 4,4′-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylmethane, Np-tolylsulfonyl- Compounds having a sulfonyl group and a ureido group in the molecule such as N′-p-butoxyphenylurea, zinc 4- [2- (p-methoxyphenoxy) ethyloxy] salicylate, 4- [3- (p-tolylsulfonyl) Zinc salts of aromatic carboxylic acids such as propyloxy] zinc salicylate and 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] salicylic acid.
Among these, 2,2 ′-[4- (4-hydroxyphenylsulfonyl) phenoxy] diethyl ether is particularly preferably used because it has good heat resistance in the unrecorded portion and good recording storage stability.

  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.

In the heat-sensitive recording layer of the present invention, various known sensitizers, pigments, adhesives, various auxiliaries and the like can be used.
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, magnesium 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.

  Among these, aluminum hydroxide, amorphous silica, kaolin and talc are preferable, and aluminum hydroxide is particularly excellent in paint stability and heat resistance of unrecorded parts when a thermal recording layer coating solution is prepared, Preferably used.

  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-acetic acid Cycloalkenyl copolymers, and styrene - butadiene - latex of a hydrophobic polymer such as an acrylic copolymer.

  In addition, as the various auxiliary agents, known agents such as a lubricant, 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 5 to 20% by mass, and the content of the colorant is generally about 5 to 40% by mass. When a sensitizer is included, the content of the sensitizer is preferably about 10 to 40% by mass. The lubricants and the pigment are preferably contained in a content of about 5 to 20% by mass and about 10 to 50% by mass, respectively, and the content of the adhesive is generally about 5 to 30% 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, a 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 heat-sensitive recording layer coating liquid may be applied, for example, in a two-layer curtain simultaneously with the undercoat layer coating liquid or the protective layer coating liquid described later. Further, the undercoat layer coating solution, the thermosensitive recording layer coating solution, and the protective layer coating solution may be simultaneously applied in a three-layer curtain. By simultaneously applying each layer, the coating process is omitted, which is preferable in terms of time and economy.

The coating amount of the thermal recording layer coating liquid is not particularly limited, and a desired quality can be achieved if the dry weight is about 1 to 15 g / m ² , particularly about ² to 10 g / m ² .

Protective layer In the heat-sensitive recording material of the present invention, a protective layer may be 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 these, acetoacetyl-modified polyvinyl alcohol and diacetone-modified polyvinyl alcohol are preferably used 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 polymer and / or synthetic resin emulsion is preferably about 20 to 80% by mass, and more preferably about 25 to 75% by mass, based on the total solid content of the protective layer.

  If the content is less than 20% 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 carbonates such as calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, amorphous silica, synthetic mica, aluminum hydroxide, barium sulfate, talc, kaolin, calcined kaolin, nylon resin filler, urea / formalin Organic pigments such as resin fillers and raw starch particles can be mentioned.

  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 of the pigment is about 5 to 80% by mass, particularly preferably about 10 to 70% by mass, based on the total solid content of the protective layer.

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

  As 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 Agent, glyoxal, boric acid, dialdehyde starch, methylol urea, epoxy compound, hydrazine compound, etc., waterproofing agent (crosslinking agent), hydrophobic polycarboxylic acid copolymer, UV absorber, fluorescent dye, coloring dye, release agent Examples thereof include a mold agent and an antioxidant. The usage-amount of auxiliary agent can be suitably set from a wide range.

  The method for applying the protective layer coating liquid is not particularly limited, and known means such as air knife coating, blade coating, rod coating, short dwell coating, curtain coating, and die coating can be used.

The coating amount of the protective layer coating solution, dry weight 0.5~3.5g / ^{m 2} approximately, preferably 0.8~3.0g / ^{m 2} approximately, the thickness of the protective layer 0.4 It is about -3.0 micrometers, More preferably, it is about 0.6-2.5 micrometers.

When it is less than 0.5 g / m ² , the thickness is less than 0.4 μm, and the effect of protecting the heat-sensitive recording layer is lost, and it cannot function as a protective layer. On the other hand, when it exceeds 3.5 g / m ² , the thickness also exceeds 3.0 μm, the recording sensitivity is lowered, and there is a possibility that it becomes unreadable when printed with low energy.

Support As a support used in the heat-sensitive recording material of the present invention, a pulp mainly composed of LBKP, NBKP, DIP, etc., if necessary, a paper filler, a paper strength enhancer, a yield improver, a sizing agent, etc. A base paper blended with a small amount of a water-soluble polymer and made into a basis weight of about 30 to 150 g / m ² by a paper machine 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.

  In the present invention, after various layers are formed or after all layers are formed, a smoothing process such as supercalendering is performed, or a protective layer is formed on the back side of the support of the thermal recording medium as necessary. A coating layer for printing, a magnetic recording layer, an antistatic layer, a thermal transfer recording layer, an ink jet recording layer, etc. are provided, an adhesive treatment is applied to the back surface of the support to process it into an adhesive label, or a perforation is formed on the thermal recording medium. Various known techniques in the heat-sensitive recording material manufacturing field, such as putting in, 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
-Preparation of coating solution for undercoat layer 55 parts of calcined kaolin (trade name: Ansilex, Engelhard, Inc., oil absorption 90 ml / 100 g), organic fine hollow particles (trade name: AE852, manufactured by Nippon Synthetic Rubber, solid content) Concentration 26%) 96 parts, 40% polyacrylic acid 2.5 parts and water 80 parts dispersed in a dispersion, styrene-butadiene copolymer emulsion (solid content 50%) 32 parts, carboxymethylcellulose (Product name: Serogen AG gum, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 3 parts were mixed and stirred to obtain a coating solution for undercoat layer.

-Solution A preparation (preparation of leuco dye dispersion)
A composition consisting of 15 parts of 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 5 parts of a 5% aqueous solution of methylcellulose, and 15 parts of water was sand milled with an average particle size of 0.5 μm. A liquid A was obtained by grinding until

・ B liquid preparation (preparation of colorant dispersion)
A composition comprising 15 parts of Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea, 5 parts of a 5% aqueous solution of methylcellulose, and 15 parts of water is averaged to 0.5 μm in a sand mill. The liquid B was obtained by pulverizing.

・ C liquid preparation (preparation of sensitizer dispersion)
A composition comprising 15 parts of di (4-methylphenoxy) ethane, 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 0.5 μm to obtain a liquid C.

-Preparation of coating solution for heat-sensitive recording layer A part 15 parts, B part 30 parts, C part 15 parts, 35% adipic acid dihydrazide aqueous solution 2.5 parts, 50% aluminum hydroxide dispersion 17.2 parts, styrene-butadiene For a thermosensitive recording layer, a composition comprising 6.9 parts of a copolymer emulsion (solid content concentration 50%) and 42.9 parts of a 10% aqueous solution of polyvinyl alcohol (trade name: PVA117, manufactured by Kuraray Co., Ltd.) was mixed and stirred. A coating solution was obtained.

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.) and 25 parts of zinc stearate (trade name: Hydrin Z-8-36, solid content concentration 36%, manufactured by Chukyo Yushi Co., Ltd.) are mixed and stirred. A protective layer coating solution was obtained.

・ Preparation of thermosensitive recording material On one side of a 48 g / m ² base paper, an undercoat layer coating solution is applied and dried by a blade coating method so that the coating amount after drying is 11.0 g / m ^2. A layer was formed. On the resulting undercoat layer, the thermal recording layer coating solution was applied and dried so that the coating amount after drying was 3.5 g / m ² to form a thermal recording layer. On the thermosensitive recording layer, the protective layer coating solution was further applied and dried so that the coating amount after drying was 2.5 g / m ² to form a protective layer, and then a linear pressure of 78 N / m was applied. A heat-sensitive recording material was obtained by smoothing with a super calendar under conditions.

Example 2
In the preparation of the coating liquid for the undercoat layer of Example 1, 55 parts of calcined kaolin (trade name: Ancilex, supra) and 96 parts of organic micro hollow particles (trade name: AE852, supra) were used instead of calcined kaolin. A thermal recording material was obtained in the same manner as in Example 1 except that 75 parts (trade name: Ansilex, supra) and 20 parts of organic micro hollow particles (trade name: AE852, supra) were used.

Example 3
In the preparation of the coating solution for the undercoat layer of Example 1, 75 parts of calcined kaolin (trade name: Ancilex, supra) and 96 parts of organic micro hollow particles (trade name: AE852, supra) were used instead of calcined kaolin. A thermosensitive recording material was obtained in the same manner as in Example 1 except that 40 parts (trade name: Ansilex, supra) and 153 parts of organic micro hollow particles (trade name: AE852, supra) were used.

Example 4
A thermosensitive recording material was obtained in the same manner as in Example 1 except that the amount of the 35% adipic acid dihydrazide aqueous solution was increased from 2.5 parts to 14.6 parts in the preparation of the thermosensitive recording layer coating liquid of Example 1.

Example 5
In preparation of the coating liquid for protective layer of Example 1, diacetone modified polyvinyl alcohol (trade name: DF-10, Japanese vinegar) instead of acetoacetyl modified polyvinyl alcohol (trade name: Goosefimmer Z-200, supra). A thermosensitive recording material was obtained in the same manner as in Example 1 except that Vipovar was used.

Example 6
In the production of the thermal recording material of Example 1, a thermal recording material was obtained in the same manner as in Example 1 except that the protective layer coating solution was not applied.

Comparative Example 1
In the preparation of the coating liquid for the undercoat layer of Example 1, 55 parts of calcined kaolin (trade name: Ancilex, supra) and 96 parts of organic micro hollow particles (trade name: AE852, supra) were used instead of calcined kaolin. (Product name: Ancilex, supra) A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 80 parts were used.

Comparative Example 2
In the preparation of the coating liquid for the undercoat layer of Example 1, instead of 55 parts of calcined kaolin (trade name: Ancilex, supra) and 96 parts of organic micro hollow particles (trade name: AE852, supra), calcined kaolin ( A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 30 parts of product name: Ancilex, supra) and 192 parts of organic micro hollow particles (trade name: AE852, supra) were used.

Comparative Example 3
A thermosensitive recording material was obtained in the same manner as in Example 1 except that adipic acid dihydrazide was not used in the preparation of the thermosensitive recording layer coating solution of Example 1.

Comparative Example 4
In the liquid B preparation of Example 2, 15 parts of 4-isopropoxy-4′-hydroxydiphenylsulfone was used instead of 15 parts of Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea. A thermosensitive recording material was obtained in the same manner as in Example 1 except that it was used.

  The following evaluations were carried out on the 10 heat-sensitive recording materials thus obtained, and the results are shown in Table 1.

Recording sensitivity Using a thermal evaluation machine (trade name: Barrabe 300, manufactured by Sato Co., Ltd.), each thermal recording body was colored at 0.21 mJ / dot, and the density of the recording part was measured with a Macbeth densitometer (trade name: RD-914, It was measured in the visual mode of Macbeth.

-Recording image quality The image quality of prints developed with recording sensitivity (0.21 mJ / dot) was visually evaluated as follows.
A: There is no omission and the image quality is excellent.
○: Some omissions are seen, but the image quality is good.
×: Many omissions are seen and the image quality is poor.

Sticking Black solid printing was performed using a thermal evaluation machine (trade name: VP-35, manufactured by Seiko Co., Ltd.), and the sticking situation at that time was visually evaluated as follows.
A: Good without sticking (printing skipped and horizontal lines seen).
○: Some sticking was observed at the beginning, but no good after that.
Δ: Sticking is seen in some places and there is a problem.
X: Sticking is intense and very problematic.

-Heat resistance The fog of the blank paper portion after being treated at 90 ° C for 24 hours was measured in a visual mode of a Macbeth densitometer (trade name: RD-914, manufactured by Macbeth).

・ Storage stability of recorded images (oil resistance)
The print density developed with a recording sensitivity (0.21 mJ / dot) was coated with salad oil, and the recording density after being allowed to stand for 24 hours was measured in the visual mode of a Macbeth densitometer (trade name: RD-914, manufactured by Macbeth). .

Claims (5)

  In a heat-sensitive recording body in which an undercoat layer mainly composed of a pigment and an adhesive and a heat-sensitive recording layer containing a leuco dye and a colorant are sequentially provided on a support, the pigment of the undercoat layer is used as a pigment in the undercoat layer. The colorant in the heat-sensitive recording layer contains 40 to 85% by mass of calcined kaolin and 5 to 40% by mass of organic hollow particles selected from organic fine hollow particles or organic foamable particles with respect to the total solid content. And Np-toluenesulfonyl-N′-3- (p-toluenesulfonyloxy) phenylurea, and further containing adipic acid dihydrazide.   The heat-sensitive recording material according to claim 1, wherein the heat-sensitive recording layer contains at least one selected from aluminum hydroxide, amorphous silica, kaolin and talc as a pigment.   The heat-sensitive recording material according to claim 1 or 2, wherein the content of adipic acid dihydrazide in the heat-sensitive recording layer is 0.2 to 5% by mass with respect to the total solid content of the heat-sensitive recording layer.   The heat-sensitive recording material according to claim 1, wherein a protective layer mainly composed of a pigment and an adhesive is provided on the heat-sensitive recording layer.   The heat-sensitive recording material according to claim 4, comprising at least one selected from acetoacetyl-modified polyvinyl alcohol and diacetone-modified polyvinyl alcohol as an adhesive for the protective layer.