JP2008068554A - Heat-sensitive recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-sensitive recording medium which can obtain high sensitivity even at a high printing speed and is almost free from a sticking phenomenon. <P>SOLUTION: This heat-sensitive recording medium keeps a support overlaid with an undercoat layer composed mainly of a pigment and an adhesive and a heat-sensitive recording layer containing a leuco dye and a coloring agent in that order. The pigment contained in the undercoat layer comprises a secondary particle, with 30 to 1,000 nm in average particle diameter, which is made up of a flocculated amorphous silica primary particle with 3 to 70 nm in particle diameter. The content of the secondary particle is preferably 1 to 70 mass% to the total solid content of the undercoat layer. <P>COPYRIGHT: (C)2008,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.

  In order to improve the recording sensitivity and image quality of the heat-sensitive recording material, an undercoat layer containing a pigment and a binder is provided between the support and the heat-sensitive recording layer, and a void is formed to make it porous or bulky. It is known to grant. 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 paper (see Patent Document 2). Furthermore, in order to reduce 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).

  In recent years, there has been a demand for higher sensitivity and reduced sticking due to further higher printing speed. Sticking is a phenomenon in which heat from the printer head adheres to the head due to the adhesiveness of the melted components, and printing is skipped without printing, and printing sound is increased. In order to cope with higher printing speed and higher sensitivity, there is a method of increasing the smoothness of the thermal recording medium and effectively using the heat from the head, but sticking is likely to occur. Also, sticking is likely to occur by increasing the content of a hot melt such as a sensitizer.

  For this reason, it has been proposed to reduce sticking by adding an oil-absorbing pigment to the heat-sensitive recording layer to absorb the hot melt (see Patent Document 4). However, in recent high-speed printers, it is difficult to achieve a high balance between high speed, high sensitivity, and sticking only by improving the oil absorption of the thermosensitive recording layer.

Japanese Patent Laid-Open No. 4-290789 JP 2004-122483 A JP 2005-103864 A JP 59-22794 A

  In view of such circumstances, it is an object of the present invention to provide a heat-sensitive recording material that can obtain high sensitivity even when high-speed printing is performed and has good sticking.

  As a result of intensive studies to solve the above problems, the present inventor has found that the above problems can be solved by using specific silica for the undercoat layer, and has completed the present invention.

  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, A heat-sensitive recording material comprising secondary particles having an average particle diameter of 30 to 1000 nm formed by agglomerating amorphous silica primary particles having a particle diameter of 3 to 70 nm.
Item 2: A protective layer mainly composed of a pigment and an adhesive may be provided on the thermosensitive recording layer.
Item 3: The secondary particles are preferably 1 to 70% by mass with respect to the total solid content of the undercoat layer.
Item 4: The undercoat layer is preferably formed of two or more layers.

  The heat-sensitive recording material of the present invention provides a heat-sensitive recording material which can obtain high sensitivity even when high-speed printing is performed and has good sticking.

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

In the thermal recording material of the present invention,
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, a particle size of 3 as a pigment in the undercoat layer. It contains secondary particles having an average particle diameter of 30 to 1000 nm formed by aggregation of amorphous silica primary particles of ˜70 nm.

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.

  By using secondary particles having an average particle diameter of 30 to 1000 nm formed by agglomerating amorphous silica primary particles having a particle diameter of 3 to 70 nm as the pigment of the undercoat layer of the present invention, the hot melt in the thermal recording medium can be quickly obtained. Since it is absorbed, sticking is suppressed. Further, since the bulk is high, there is an advantage that the recording sensitivity is improved.

  The method for producing secondary particles having an average particle diameter of 30 to 1000 nm obtained by agglomerating amorphous silica primary particles having a particle diameter of 3 to 70 nm used in the present invention is not particularly limited. For example, general commercially available synthetic amorphous silica is used. Such as bulk materials, precipitates obtained by chemical reaction in liquid phase by mechanical means, sol-gel method by hydrolysis of metal alkoxide, high temperature hydrolysis in gas phase, etc. Obtainable. Examples of the mechanical means include an ultrasonic wave, a high-speed rotary mill, a roller mill, a container drive medium mill, a medium agitation mill, a jet mill, a sand grinder, and a wet medialess atomizer. When mechanically pulverizing, it is preferable to pulverize in water to obtain an aqueous silica dispersion.

Here, the particle diameter Dp of the primary particles can be calculated from the following formula.
Asp (m ² / g) = SA × n (1)
In the above formula (1), Asp represents the specific surface area, SA represents the surface area of one primary particle, and n represents the number of primary particles per gram.
Dp (nm) = 3000 / Asp (2)
In the above formula (2), Dp represents the particle size of the primary particles, and Asp represents the specific surface area.
The above formula (2) is derived assuming that the shape of the silica is a true sphere and the density of the silica is d = 2 (g / cm ³ ).
More specifically, the derivation method is as follows. That is, the specific surface area Asp is calculated by the surface area / (volume × density). Here, the unit of density is g / cm ³ . Assuming that the shape of the primary particle is a true sphere and the diameter is Dp (nm), the surface area of the primary particle is 4π (Dp / 2) ² and the volume is (1/3) × 4π (Dp / 2). ) Since it is ³ , the specific surface area Asp = 6 / (Dp × d). Here, assuming that the density of silica is d = 2 (g / cm ³ ) based on the general value of silica, Asp (m ² / g) = 6 / (Dp × 10 ⁻⁹ × 2 × 10 ⁶ ) = 3000 / Dp. Therefore, the particle diameter Dp (nm) of the primary particles = 3000 / Asp, that is, calculated by the above formula (2).
The particle diameter of the amorphous silica primary particles used in the present invention is 3 to 70 nm, preferably 5 to 50 nm, more preferably 7 to 40 nm.
The specific surface area is a surface area per unit mass of amorphous silica (that is, per 1 g). As can be seen from the above formula (1), the larger the specific surface area, the smaller the primary particle diameter. When the primary particle size is reduced, the pores formed from the primary particles (that is, the pores formed in the secondary particles formed by aggregation of the primary particles) are reduced, and the capillary pressure is increased. Therefore, it is considered that the melted color developing component is rapidly absorbed and sticking is suppressed. In addition, the secondary particles formed from the primary particles are complicated, and it is presumed that a capacity capable of sufficiently absorbing the molten coloring component can be secured. About the particle diameter of a primary particle, it is 3-70 nm, Preferably it is 5-50 nm, More preferably, it is 7-40 nm. As for the upper limit of the primary particle size, the smaller the value, the better the head wrinkle suppression and the sticking resistance.

Here, the specific surface area of the amorphous silica was measured by measuring the nitrogen adsorption and desorption isotherm of the powder sample obtained by drying the fine pigment (that is, the amorphous silica used in the present invention) at 105 ° C. Measured after vacuum degassing at 200 ° C. for 2 hours using an apparatus (SA3100 type manufactured by Coulter). E. The T specific surface area is calculated.
From the above, the particle size of the primary particles of the amorphous silica used in the present invention is calculated from the above formula (1) by actually measuring the specific surface area using the above specific surface area measuring device (SA3100 type manufactured by Coulter). It is a thing.

  Moreover, the average particle diameter of a secondary particle is 30-1000 nm, Preferably it is 40-700 nm, More preferably, it is 50-500 nm. Secondary particles having an average particle diameter of less than 30 nm are difficult to produce, and if the average particle diameter is less than 30 nm, the volume of pores formed is too small to penetrate the melted coloring component, which is effective for sticking. May decrease. On the other hand, if the thickness exceeds 1000 nm, the strength decreases, and paper dust may be generated or printing may not be possible in the printing process of the thermal recording medium.

Here, the average particle diameter of the secondary particles refers to the dispersion immediately after the aqueous dispersion of silica obtained by the above method is adjusted to a solid content concentration of 5% by mass and stirred and dispersed at 5000 rpm for 30 minutes with a homomixer. Is coated on a polyester film having been subjected to hydrophilic treatment so that the weight after drying is about 3 g / m ² and dried to obtain a sample, which is observed with an electron microscope (SEM and TEM) and is 10,000 to 400,000 times larger An electron micrograph is taken and the martin diameter of secondary particles in a 5 cm square of the electron micrograph is measured and averaged (see “Fine Particle Handbook”, Asakura Shoten, p52, 1991).

  In addition, the stirring and dispersion in the homomixer is merely performed for uniform dispersion in order to improve the measurement accuracy, and the size of the secondary particles changes substantially before and after the stirring and dispersion in the homomixer. It is not considered.

  The content of secondary particles in the undercoat layer is preferably about 1 to 70% by mass, more preferably about 2 to 60% by mass with respect to the total solid content of the undercoat layer. More preferably, it is about 5-50 mass%. If it is the said 1-70 mass% range, the said desired effect will be easy to be acquired.

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 kaolin, light calcium carbonate, heavy calcium carbonate, calcined kaolin, titanium oxide, magnesium carbonate, aluminum hydroxide, colloidal silica, synthetic layered mica, clay, organic hollow particles, and thermally expandable particles. And plastic pigments such as urea-formalin resin filler.
In addition, colloidal silica is substantially composed of primary particles, and secondary particles that are aggregates of the primary particles are substantially absent.
In addition, use of calcined kaolin, organic hollow particles, thermally expandable particles, and light calcium carbonate is preferable because the color development sensitivity is good. The amount used is about 15 to 80% by mass, preferably about 20 to 75% by mass, based on the total solid content of the undercoat layer.

  The average particle size of the pigment used in combination with the specific silica used in the present invention is preferably about 0.01 to 5 μm, particularly about 0.02 to 3 μm. Here, the average particle diameter of the pigment is a 50% value measured by a laser diffraction particle size distribution analyzer (trade name: SALD2000, manufactured by Shimadzu Corporation).

  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 thermally 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 and acrylonitrile by an in situ polymerization method. Can be given. Examples of the low boiling point hydrocarbon include ethane and propane.

  When two or more kinds selected from the specific silica and inorganic pigment, organic hollow particles and thermally expandable particles used in the present invention are used in combination, the total amount is 40 to 90% by mass with respect to the total solid content of the undercoat layer. In particular, it is preferably about 50 to 80% by mass.

  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, polyvinyl acetate, polyurethane, styrene-butadiene copolymer, polyacrylic acid, polyacrylate ester, vinyl chloride-vinyl acetate copolymer, Latex of hydrophobic polymers such as ethylene methacrylate-vinyl acetate copolymer, styrene-butadiene-acrylic copolymer, silylated urethane, acrylic-silicon composite, acrylic-silicon-urethane composite emulsion, etc. It is also possible to use one kind or two or more kinds in combination.

  The content of the adhesive in the undercoat layer is preferably 3 to 35% by mass, more preferably 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 auxiliary agents include surfactants such as sodium alkylbenzene sulfonate, sodium dioctyl sulfosuccinate, sulfone-modified polyvinyl alcohol, sodium polyacrylate, glyoxal, boric acid, dialdehyde starch, methylol 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, colored dyes, mold release agents, oxidation An inhibitor etc. are mentioned. The usage-amount of auxiliary agent can be suitably set from a wide range.

  The method for preparing the undercoat layer coating solution is not particularly limited, and the concentration of the coating solution is not particularly limited, but is preferably 20 to 50% by mass, and preferably 35 to 45% by mass. If it is less than 20% by mass, 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. Leading to a decline. On the other hand, if it exceeds 50% by mass, the viscosity of the coating material 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 may be appropriately adjusted so as to be about 7 to 35 g / m ² as the total thickness of the undercoat layer is 6 to 30 μm. However, it is particularly preferable to apply the coating in two or more layers since the penetration of the paint is suppressed during the application of the heat-sensitive layer, and the image quality and the color development sensitivity are 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.

Heat-sensitive recording layer In the heat-sensitive recording layer of the present invention, various known leuco dyes, colorants, sensitizers, pigments, adhesives, and various auxiliary agents can be used.
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-methyl-benzyl oxalate, di-p-oxalate Rubenjiru, dibutyl terephthalate, dibenzyl terephthalate, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole.

  Examples of the pigment include calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, calcined clay, talc, and surface-treated inorganic fine powder such as calcium carbonate and silica, In addition, organic fine powders such as urea-formalin resin, styrene-methacrylic acid copolymer, polystyrene resin and the like can be mentioned.

  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, And polyvinyl acetate, polyurethane, styrene-butadiene copolymer, polyacrylic acid, polyacrylate ester, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene- Vinyl copolymer acid, 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 pigments 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 20% 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 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 water-soluble polymers 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 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, synthetic mica, or aluminum hydroxide is preferable 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 will be poor, causing sticking and 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 Agents, glyoxal, boric acid, dialdehyde starch, methylol urea, epoxy compounds, hydrazine compounds, etc., 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 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 to 3.0 g / ^{m 2} approximately, preferably 0.8~2.5g / ^{m 2} approximately, the thickness of the protective layer 0.4 It is about -2.5 micrometers, More preferably, it is about 0.6-2.0 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, if it exceeds 3.0 g / m ² , the thickness also exceeds 2.5 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 silica dispersion)
Commercially available silica (trade name: Fineseal X-45, average secondary particle size 4500 nm, primary particle size 12 nm, specific surface area 260 m ² / g, manufactured by Tokuyama Corporation) is dispersed in water with a sand grinder and then wet medialess. Using a atomizer (trade name: Nanomizer, manufactured by Yoshida Kikai Kogyo Co., Ltd.), pulverization and dispersion were repeated to obtain a 20% silica dispersion having a primary particle diameter of 12 nm and a secondary particle average particle diameter of 300 nm.

(1a) Preparation of coating solution for undercoat layer Obtained by dispersing 70 parts of calcined kaolin (trade name: Ansilex, Engelhard, oil absorption 90 ml / 100 g) in 50 parts of 20% silica dispersion and 80 parts of water. 28 parts of a styrene-butadiene copolymer emulsion (solid content 50%), 25 parts of a 20% aqueous solution of oxidized starch, 1 part of carboxymethylcellulose (trade name: Serogen AG gum, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) Were mixed and stirred to obtain a coating solution for an undercoat layer.

(2a) Preparation of each component / A solution preparation (preparation of leuco dye dispersion)
A composition consisting of 10 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 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 0.5 μm to obtain a liquid B.

・ C liquid preparation (preparation of sensitizer dispersion)
A composition consisting of 20 parts of di-p-methylbenzyl oxalate, 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 0.5 μm to obtain a liquid C.

(Preparation of thermal recording layer coating solution)
Liquid A 25 parts, Liquid B 50 parts, Liquid C 50 parts, 20% silica dispersion 20 parts, oxidized starch 20% aqueous solution 30 parts, and acetoacetyl-modified polyvinyl alcohol (trade name: Goosefimmer Z-200, Japan A composition comprising 50 parts of a 10% aqueous solution (manufactured by Synthetic Chemical Industry Co., Ltd.) was mixed and stirred to obtain a thermal recording layer coating solution.

(1d) Preparation 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 11.0 g / m ^2. Thus, an undercoat layer was formed. The thermal recording layer coating solution was applied and dried on the resulting undercoat layer so that the coating amount after drying was 5.0 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
(2a) 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.

(2b) Preparation of thermosensitive recording material In the preparation of the thermosensitive recording material of Example 1, after forming the thermosensitive recording layer, the coating amount after drying the protective layer coating liquid on the thermosensitive recording layer was 2.0 g / m. ^A heat-sensitive recording material was obtained in the same manner as in Example 1 except that a protective layer was formed by coating and drying so as to be ² .

Example 3
In the production of the thermal recording material of Example 1, as the undercoat layer, the undercoat layer coating solution was applied and dried by a blade coating method so that the coating amount after drying was 6.0 g / m ^2. Form the coating layer, and apply and dry the coating solution for the undercoat layer on the first undercoat layer by the rod coating method so that the coating amount after drying is 5.0 g / m ² without further winding. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the second undercoat layer was formed.

Example 4
In the production of the heat-sensitive recording material of Example 2, as the undercoat layer, the undercoat layer coating solution was applied and dried by a blade coating method so that the coating amount after drying was 6.0 g / m ^2. The undercoat layer coating solution is applied and dried on the first undercoat layer by the rod coating method so that the coating amount after drying is 5.0 g / m ² without further winding. A heat-sensitive recording material was obtained in the same manner as in Example 2 except that the two undercoat layers were formed.

Example 5
A thermosensitive recording material was obtained in the same manner as in Example 2 except that the following coating solution was used as the coating solution for the undercoat layer in the production of the thermosensitive recording material of Example 2.

(5a) Preparation of coating liquid for undercoat layer In 150 parts of silica dispersion, fine hollow particles (trade name: AE-851, manufactured by JSR Corporation, hollow ratio 55%, solid content 26%, average particle diameter 0.9 μm) 192 Part, 36 parts of styrene-butadiene copolymer emulsion (solid content 50%) and 2 parts of carboxymethylcellulose (trade name: Serogen AG gum, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) are mixed and stirred to obtain a coating solution for an undercoat layer. It was.

Example 6
Instead of 192 parts of fine hollow particles (trade name: AE-851, manufactured by JSR, hollow ratio 55%, solid content 26%, average particle size 0.9 μm) in the production of the thermal recording material of Example 5, hollow A thermosensitive recording material was obtained in the same manner as in Example 5 except that 125 parts of resin particles (hollow rate 90%, solid content 40%, average particle size 3.5 μm) were used.

Example 7
In the production of the heat-sensitive recording material of Example 2, 70 parts of calcined kaolin (trade name: Ancilex, Engelhard, Inc., oil absorption 90 ml / 100 g) and 50 parts of 20% silica dispersion were used. Ansilex, Engelhard, Inc., oil absorption 90 ml / 100 g) was used in the same manner as in Example 5 except that 78 parts and 10 parts of 20% silica dispersion were used.

Comparative Example 1
A thermosensitive recording material was obtained in the same manner as in Example 2 except that the following coating solution was used as the coating solution for the undercoat layer in the production of the thermosensitive recording material of Example 2.
To a dispersion obtained by dispersing 80 parts of calcined kaolin (trade name: Ansilex, Engelhard, oil absorption 90 ml / 100 g) in 100 parts of water, styrene-butadiene copolymer emulsion (solid content 50%) 28 parts, 25 parts of 20% aqueous solution of oxidized starch, and 1 part of carboxymethylcellulose (trade name: Cellogen AG gum, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) were mixed and stirred to obtain a coating solution for an undercoat layer.

Comparative Example 2
A thermosensitive recording material was obtained in the same manner as in Example 2 except that the following coating solution was used as the coating solution for the undercoat layer in the production of the thermosensitive recording material of Example 2.
Fine hollow particles (trade name: AE-851, manufactured by JSR Corporation, hollow ratio 55%, solid content 26%, average particle size 0.9 μm) 300 parts, styrene-butadiene copolymer emulsion (solid content 50%) 36 parts Then, 2 parts of carboxymethylcellulose (trade name: Cellogen AG gum, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) were mixed and stirred to obtain a coating solution for an undercoat layer.

  The following evaluations were performed on the nine types of thermal 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), each thermal recording medium was colored at 0.20 mJ / dot, and the density of the recording area was measured with a Macbeth densitometer (trade name: RD-914, It was measured in the visual mode of Macbeth. When the density of the recording part is high, the recording sensitivity is high.

-Sticking Black solid printing was performed using a thermal evaluation machine (trade name: VP-35, manufactured by Seiko Co., Ltd.), and the state of sticking 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.
(Triangle | delta): Sticking is seen in some places and there is a problem in practical use.
X: Sticking is severe and there is a very practical problem.

Claims (4)

  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, a particle diameter of 3 as a pigment in the undercoat layer A heat-sensitive recording material comprising secondary particles having an average particle diameter of 30 to 1000 nm formed by agglomeration of amorphous silica primary particles of ˜70 nm.   The thermosensitive recording material according to claim 1, wherein a protective layer mainly comprising a pigment and an adhesive is provided on the thermosensitive recording layer.   The heat-sensitive recording material according to claim 1 or 2, wherein the secondary particles are 1 to 70 mass% with respect to the total solid content of the undercoat layer.   The heat-sensitive recording material according to claim 1, wherein the undercoat layer is formed of two or more layers.