JPWO2009034768A1 - Thermal recording material - Google Patents

Abstract

Provided is a thermal recording material excellent in offset printability without impairing thermal recording properties. A heat-sensitive recording layer containing a leuco dye and a colorant is provided on the support, and a protective layer containing a pigment and a binder resin is provided as the outermost surface layer on the side where the heat-sensitive recording layer is provided. In the heat-sensitive recording material, the protective layer contains a water-soluble copolymer of a hydrophobic monomer and polycarboxylic acid or a salt thereof in an amount of 0.1 to 4.8% by mass with respect to the total solid content of the protective layer. It is characterized by. The water-soluble copolymer preferably has an acid value of 200 or more.

Description

  The present invention relates to a heat-sensitive recording material utilizing a color reaction between a leuco dye and a color former, and more particularly to a heat-sensitive recording material excellent in offset printability.

  A thermal recording medium that uses a color reaction between a leuco dye and a colorant to obtain a recorded image by heat is relatively inexpensive, and the recording apparatus is compact and easy to maintain. It is widely used as a recording medium for various printers such as POS label, ATM, CAD, handy terminal, various ticket sheets as well as a recording medium for outputs of various computers and printers for scientific measuring instruments.

  In general, a heat-sensitive recording material is provided with a heat-sensitive recording layer containing a leuco dye and a colorant on a support such as paper or a plastic film, and further provided with a protective layer for protecting the heat-sensitive recording layer. . The protective layer is provided to protect the heat-sensitive recording layer and the printed portion obtained by heat-sensitive recording from water, oil, and a plasticizer, and generally contains a pigment such as kaolin, aluminum hydroxide, calcium carbonate or silica. It is constituted by adhering onto a heat-sensitive recording layer with a binder resin. As the binder resin, a water-soluble resin such as polyvinyl alcohol or starch is usually used as a main component from the viewpoints of transparency and adhesiveness.

  By the way, in heat-sensitive recording media used for food labels used in tickets, supermarkets, etc., general-purpose matters may be pre-printed in advance on the surface where a color image appears due to heat. Pre-printing will be done on the protective layer. As pre-printing, offset printing is usually performed because the printed image is clear and suitable for mass printing. Therefore, the thermal recording material to be preprinted in this way is required to have not only the original thermal recording property but also excellent offset printing suitability.

  Offset printing is a printing method in which ink transferred from a plate to a blanket is transferred again to a sheet using a plate in which water is applied to a non-image portion to prevent ink from being applied. Since the ink transferred from the blanket contains water, the paper to be printed absorbs the water quickly to separate the ink from the water, thereby ensuring a clear printed image.

  However, in the case of a thermal recording material, the protective layer to be offset printed has a property of not absorbing water or oil for the original purpose of protecting the thermal recording layer. In particular, the water-soluble resin that is the main component of the protective layer tends to get wet preferentially to the water contained in the ink rather than the oleophilic ink used in offset printing. Since the protective layer is first wetted with water, a water film is formed on the surface of the protective layer, so that a so-called water loss phenomenon is likely to occur, in which hydrophobic ink is not fixed. As a result, a clear printed image cannot be obtained.

For these reasons, a protective layer that can ensure offset printing suitability has been studied. For example, JP-A-4-82777 (Patent Document 1) pays attention to the fact that the wettability of the ink on the surface of the protective layer is important for offset printing. As a protective layer with good loss, it has been proposed that the value of P represented by the following formula is 40 dyne / cm or less.
P = γ ₁ cos θ ₁ −γ ₂ cos θ ₂
θ ₁ : Contact angle of the protective layer surface with water γ ₁ : Surface tension of water θ ₂ : Contact angle of the protective layer surface with linseed oil γ ₂ : Surface tension of linseed oil

  As a constitution of the protective layer satisfying such requirements, it has been proposed to contain a water-soluble molecule and a crosslinking agent, and further to contain paraffin wax. For example, it can be seen from Comparative Examples 3 and 4 in Table 1 that when the crosslinking agent is not included, the value of P increases and the printing water loss test concentration decreases.

  JP-A-4-14481 (Patent Document 2) pays attention to the fact that the contact angle with water is an indicator of the wettability, and the thermal recording in which the contact angle with water on the surface of the protective layer is 45 ° or more. Materials have been proposed. In addition, it is described that a cross-linking agent, a wax, or the like is added to make the contact angle of the protective layer with water 45 ° or more. Specifically, when the amount of paraffin wax is insufficient (Comparative Examples 1 and 3 in Table 1), the contact angle with water becomes small and the printing water loss test is inferior, that is, the ink transferability is low. It is shown.

JP-A-4-82777 JP-A-4-14481

  However, when paraffin wax is included, the wettability of the protective layer is adjusted to improve the ink transfer property, resulting in poor adhesion of the offset printed portion. Further, during thermal recording, the paraffin wax partially melts and adheres to the thermal head, resulting in a head residue, which may cause a printing failure. Therefore, there is a need for a heat-sensitive recording material having improved offset printing suitability without using paraffin wax and without impairing heat-sensitive recording properties.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a thermal recording material excellent in offset printing suitability without impairing thermal recording properties.

  That is, the heat-sensitive recording material of the present invention is provided with a heat-sensitive recording layer containing a leuco dye and a colorant on a support, and a pigment and a binder as the outermost surface layer on the side where the heat-sensitive recording layer is provided. In the heat-sensitive recording material provided with a protective layer containing a resin, the protective layer contains a water-soluble copolymer of a hydrophobic monomer and a polycarboxylic acid or a salt thereof in an amount of 0. 0 relative to the total solid content of the protective layer. It is characterized by containing 1 to 4.8% by mass. The water-soluble copolymer preferably has an acid value of 200 or more.

  The protective layer preferably has a contact angle of 70 to 110 ° after 0.1 second with respect to water based on ASTM D5725, and the content of paraffin wax in the protective layer is based on the total solid content of the protective layer. It is preferable that it is 4 mass% or less.

  The binder resin preferably contains a polyvinyl alcohol-based resin in an amount of 20 to 70% by mass with respect to the total solid content of the protective layer, and contains an acrylic resin in an amount of 3 to 50% by mass with respect to the total solid content of the protective layer. It is preferable.

  As the pigment, kaolin and / or calcium carbonate is preferably contained in an amount of 5 to 65% by mass based on the total solid content of the protective layer, and as the pigment, amorphous silica primary particles having a particle diameter of 3 to 70 nm are aggregated. It is preferable to contain 1 to 40% by mass of secondary particles having an average particle diameter of 30 to 1300 nm based on the total solid content of the protective layer.

  The heat-sensitive recording material may have an offset printing part.

  The heat-sensitive recording material of the present invention has excellent heat-sensitive recording properties and also has an offset printability.

  In the heat-sensitive recording material of the present invention, a heat-sensitive recording layer containing a leuco dye and a colorant is provided on a support, and a pigment and a binder resin are used as the outermost surface layer on the side where the heat-sensitive recording layer is provided. In the heat-sensitive recording material provided with the protective layer, the protective layer contains a water-soluble copolymer of a hydrophobic monomer and polycarboxylic acid or a salt thereof in an amount of 0.1 to 4 with respect to the total solid content of the protective layer. It is characterized by containing 8 mass%. Hereinafter, each layer will be described in order.

[Protective layer]
First, the protective layer which is a characteristic part of the thermosensitive recording material of the present invention will be described.
The protective layer constituting the heat-sensitive recording material of the present invention contains a pigment and a binder resin, and further includes a water-soluble copolymer of a hydrophobic monomer and a polycarboxylic acid (hereinafter, this water-soluble copolymer is referred to as “hydrophobic polycarboxylic acid copolymer”). May be abbreviated) or a salt thereof. That is, protection is formed by coating and drying a coating liquid in which a pigment, a binder resin, a hydrophobic polycarboxylic acid copolymer or a salt thereof is dispersed in an aqueous medium.

  The pigment prevents the binder resin from adhering to the thermal head because the protective layer becomes sticky with thermal energy during thermal recording. The kind of pigment used for the protective layer of the present invention is not particularly limited, and conventionally known pigments can be used. Examples include kaolin, light calcium carbonate, heavy calcium carbonate, calcined kaolin, titanium oxide, magnesium carbonate, aluminum hydroxide, amorphous silica, colloidal silica, synthetic layered mica, and urea-formalin resin filler plastic pigments. .

  Of the pigments, kaolin, amorphous silica, and calcium carbonate are preferably used. By having kaolin and / or calcium carbonate, the contact angle after 0.1 second with respect to water based on ASTM D5725 can be increased, and ink transferability can be improved. The content of kaolin and / or calcium carbonate is preferably about 5 to 65% by mass and more preferably about 10 to 65% by mass with respect to the total solid content of the protective layer.

  Amorphous silica is preferably used as a pigment for the protective layer because of its excellent affinity with printing ink. That is, by containing amorphous silica in the protective layer, the ink transferred onto the protective layer can be captured in the protective layer. This helps to increase the fixability of the printing ink. In addition, during thermal recording, the preprinted printed part may melt due to the heat of the thermal head, but the protective layer absorbs the melted printing ink component to prevent ink from adhering to the thermal head. Helps prevent sticking.

  As the amorphous silica used in the present invention, it is preferable to use amorphous silica of secondary particles having an average particle diameter of 30 to 1300 nm obtained by agglomerating primary silica particles having a particle diameter of 3 to 70 nm. Amorphous silica that has become secondary particles having such a specific particle size has the advantage of improving the recording sensitivity because of its excellent barrier properties and high transparency of the protective layer. Colloidal silica is substantially composed of primary particles, and is different from amorphous silica in that secondary particles that are aggregates of the primary particles are substantially absent.

  The primary particle diameter of the amorphous silica used in the present invention is more preferably 5 to 50 nm, and further preferably 7 to 40 nm.

Here, the particle diameter Dp of the primary particles can be calculated from the following formula.
Dp (nm) = 3000 / Asp (1)
Equation (1) is derived on the assumption that the shape of the silica primary particles is a true sphere and the density of the silica is d = 2 (g / m ³ ). In the formula, Asp represents a specific surface area obtained by the formula (2).
Asp (m ² / g) = SA × n (2)
In the formula, SA represents the surface area of one primary particle, and n represents the number of primary particles per gram.

  The specific surface area referred to here is a vacuum adsorption / desorption isotherm of a powder sample dried at 105 ° C. using a specific surface area measuring device (SA3100 type manufactured by Coulter) for 2 hours at 200 ° C. B. measured and calculated. E. T specific surface area.

  The specific surface area is a surface area per unit mass (per 1 g) of amorphous silica, and the primary particle diameter decreases as the value of the specific surface area increases. When the primary particle size is reduced, the pores formed from the primary particles (that is, the pores formed in the secondary particles obtained by agglomerating the primary particles) are reduced, and the capillary pressure is increased. Therefore, it is considered that the melted ink component is quickly absorbed and sticking is suppressed. Further, the secondary particles formed from the primary particles are also complicated, and it is assumed that a capacity capable of sufficiently absorbing the melted ink component can be secured. As for the upper limit of the particle diameter of the primary particles, the smaller the value, the better the head residue and the sticking resistance.

  Amorphous silica preferably used in the present invention is obtained by agglomerating amorphous silica primary particles having a primary particle diameter in the above range to form secondary particles having an average particle diameter of 30 to 1300 nm. More preferably, it is 40-900 nm, More preferably, it is 50-700 nm. Secondary particles having an average particle size of less than 30 nm are difficult to produce, and if the secondary particle size is less than 30 nm, the volume of pores formed is too small to penetrate the melted ink component, and sticking May occur. On the other hand, when the secondary particle diameter exceeds 1300 nm, the transparency may be lowered, and the recording sensitivity may be lowered, or the barrier property may be lowered.

Here, the average particle size of the secondary particles means that the silica aqueous dispersion obtained by the above method is adjusted to a solid content concentration of 5% by mass, and immediately after stirring and dispersing 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 × 5 cm visual field in 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 method for producing amorphous silica as the secondary particles having the above particle diameter is not particularly limited. For example, it is obtained by a bulk raw material such as commercially available synthetic amorphous silica or a chemical reaction in a liquid phase. The obtained precipitate or the like can be obtained by a method of pulverizing by a mechanical means, a sol-gel method by hydrolysis of a metal alkoxide, a high temperature hydrolysis in a gas phase, or the like. 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.

  The content of the amorphous silica in the protective layer as described above is preferably about 1 to 40% by mass, more preferably about 2 to 30% by mass with respect to the total solid content of the protective layer. If the amorphous silica content is too high, the barrier properties may be reduced.

  As the binder resin, it is preferable to use a polyvinyl alcohol resin and / or an acrylic resin.

  Polyvinyl alcohol resins are preferably used because of their high barrier properties against plasticizers and the like. Of the polyvinyl alcohol resins, various modified polyvinyl alcohols such as acetoacetyl-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and diacetone-modified polyvinyl alcohol are preferably used. Such modified polyvinyl alcohol is obtained by imparting water resistance to polyvinyl alcohol by modification, and can prevent peeling of the protective layer by dampening water in offset printing when performing offset printing.

  The content ratio of the polyvinyl alcohol-based resin is preferably 20 to 70% by mass and more preferably 20 to 60% by mass with respect to the total solid content of the protective layer. If the content of the polyvinyl alcohol resin is too high, the hydrophilicity of the protective layer becomes too high, and even if a predetermined amount of pigment, hydrophobic polycarboxylic acid copolymer or salt thereof is contained, there is a tendency that ink transferability cannot be secured. Because it is.

  Acrylic resin is preferably used as a binder resin because it has good adhesion to offset printing ink and the printing density increases even with a small amount of ink.

  The acrylic resin used in the present invention is a water-insoluble polymer mainly composed of an acrylic monomer and / or a methacrylic monomer (hereinafter collectively referred to as “(meth) acryl” unless distinction is made between acrylic and methacrylic). In the range which does not impair the characteristic as an acrylic resin binder, the monomer which can be copolymerized with a (meth) acrylic-type monomer may be contained.

  Examples of the (meth) acrylic monomer include (meth) acrylic acid such as acrylic acid and methacrylic acid; methyl (meth) acrylate, ethyl (meth) acrylate, hydroxyethyl acrylate, butyl acrylate, acrylic acid 2- C1-C10 alkyl or C1-C10 hydroxyalkyl ester alkyl or hydroxyalkyl ester of acrylic acid and methacrylic acid such as ethylhexyl and octyl acrylate; dimethylaminoethyl methacrylate, trimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, triethylaminoethyl methacrylate, etc. Amino derivatives of (meth) acrylic acid alkyl esters; acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylate (Meth) acrylonitrile; de, acrylamide diacetone acrylamide, (meth) glycidyl acrylate and the like.

  Monomers that can be copolymerized with acrylic monomers include ethylenically unsaturated carboxylic acids such as itaconic acid, maleic acid, fumaric acid, and crotonic acid, or their C1-C10 monoalkyl esters; styrene, vinyltoluene, vinylbenzene, and the like. Aromatic vinyl compounds; vinyl esters of carboxylic acids such as vinyl acetate; vinyl halides such as vinyl chloride, vinylidene chloride and vinylidene fluoride; α-olefins such as ethylene and propylene; dienes such as butadiene; vinyl pyrrolidone and the like And heterocyclic vinyl compounds.

  The acrylic resin preferably used in the present invention is a copolymer obtained by combining two or more of the above acrylic monomers, and preferably has a glass transition temperature (Tg) containing (meth) acrylonitrile and (meth) acrylic ester as constituent monomers. A copolymer having a temperature of -10 ° C to 100 ° C, particularly 0 to 80 ° C is preferred.

  The content of (meth) acrylonitrile in the acrylic resin used in the present invention is preferably about 20 to 80% by mass of a copolymer, more preferably about 30 to 70% by mass. The content of the vinyl monomer copolymerizable with (meth) acrylonitrile in the acrylic resin used in the present invention is preferably about 80 to 20% by mass, more preferably about 70 to 30% by mass.

  In addition to (meth) acrylonitrile and (meth) acrylic esters, other acrylic monomers, vinyl monomers containing one or more (especially one or two) carboxyl groups in the molecule (carboxyl group-containing vinyl monomers) Copolymers containing) are also preferably used.

  When the acrylic resin used in the present invention contains a carboxyl group-containing vinyl monomer, the content of the carboxyl group-containing vinyl monomer in the copolymer is preferably 1 to 10% by mass, more preferably 2 to 8% by mass.

  As an acrylic resin containing another acrylic monomer, a quaternary copolymer containing (meth) acrylic acid or (meth) acrylamide is preferably used. Among them, a quaternary copolymer having a glass transition temperature Tg of about 30 to 100 ° C., particularly about 30 to 70 ° C. is particularly preferable. The content of each constituent acrylic monomer in such a quaternary copolymer is not particularly limited, but (meth) acrylic acid is 1 to 10% by mass (particularly about 2 to 8% by mass), and (meth) acrylamide 1 to 50% by mass. % (Particularly about 2 to 45% by mass), (meth) acrylonitrile 20 to 80% by mass (particularly about 30 to 70% by mass), and (meth) acrylic ester 1 to 50% by mass (particularly about 2 to 45% by mass). It is preferable to be in the range.

  3-50 mass% is preferable and, as for the content rate of the acrylic resin with respect to the total solid of a protective layer, 4-40 mass% is more preferable. When the content of the acrylic resin is too high, the barrier property against a plasticizer or the like tends to be lowered.

  The protective layer according to the present invention further includes a water-soluble copolymer of a hydrophobic monomer and a polycarboxylic acid (hydrophobic polycarboxylic acid copolymer) or a salt thereof.

  Examples of the hydrophobic monomers include vinyl group-containing compounds such as aromatic vinyl compounds such as styrene, vinyl toluene and vinyl benzene, vinyl esters of carboxylic acids such as vinyl acetate, and vinyl halides such as vinyl chloride and vinylidene chloride; (Meth) acrylic acid such as methyl (meth) acrylate, ethyl (meth) acrylate, hydroxyethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate Alkyl esters of diene compounds such as butadiene and isobutylene can be used.

  Examples of the polycarboxylic acid include unsaturated dicarboxylic acids having double bonds such as itaconic acid, maleic acid, fumaric acid, citraconic acid, and mesaconic acid, unsaturated polycarboxylic acids such as unsaturated tricarboxylic acid, and anhydrides thereof. Is used. These may be used alone or in combination of two or more. Carboxylic anhydride may be hydrolyzed with an acid or a base after copolymerization.

  Examples of the salt of the hydrophobic polycarboxylic acid water-soluble copolymer include alkali metal salts such as sodium salt and potassium salt, ammonium salt and the like.

The water-soluble copolymer of the hydrophobic polycarboxylic acid used in the present invention is such that the polycarboxylic acid and the hydrophobic monomer are in a mass ratio of polycarboxylic acid: hydrophobic monomer = 40: 60 to 99.8: 0. The copolymer contained in the range of 2 shows water solubility.
As long as the water solubility of the hydrophobic polycarboxylic acid copolymer is not impaired, a part of the polycarboxylic acid may be replaced with ethylenically unsaturated monocarboxylic acid such as (meth) acrylic acid, itaconic acid, maleic acid, fumaric acid, etc. A monoalkyl ester of an unsaturated dicarboxylic acid may be substituted. Substitution with a monoalkyl ester of an ethylenically unsaturated monocarboxylic acid and / or unsaturated dicarboxylic acid is preferably less than 20% by weight of the polycarboxylic acid.

  By containing the hydrophobic polycarboxylic acid copolymer as described above in the protective layer, ink transferability and ink adhesion can be improved. Although the mechanism is not clear, the hydrophobic groups contained in the hydrophobic polycarboxylic acid copolymer are arranged on the surface side of the protective layer and repels the water on the surface of the protective layer, so that water preferentially wets the surface of the protective layer over the ink. It is estimated that excellent ink transfer properties can be obtained as a result.

  In the case of a thermal recording material that is offset printed, it is not sufficient to evaluate the offset printability only by ink transferability. This is because even if the ink transfer property is good, the printed part is peeled off if the ink adhesion is bad. For example, when used for food labels, products with labels attached to films are stacked and arranged on a display stand. In such a laminated state, when the ink adhesion of the label printing unit is poor, when the product placed on the top is taken up, it is placed on the packaging film of the product placed on the bottom. This causes a problem that the printed part of the label of the product is peeled off.

  The hydrophobic polycarboxylic acid copolymer used in the present invention further has an acid value of 200 or more, preferably 300 to 950, more preferably 400 to 900, and particularly preferably 400 to 850. If it is less than 300, the heat resistance tends to be inferior, and the head residue tends to increase, for example, adhering to the thermal head during thermal recording. On the other hand, if the acid value exceeds 950, the contact angle may decrease and ink transferability required may not be satisfied.

  Here, the acid value is expressed in mg of sodium hydroxide required to neutralize the acidic component contained in 1 g of the sample. Therefore, it means that the higher the acid value, the higher the content of polycarboxylic acid in the water-soluble copolymer, and the higher the degree of hydrophilicity.

  The water-soluble copolymer of the hydrophobic polycarboxylic acid as described above is preferably contained in an amount of 0.1 to 4.8% by mass, and 0.1 to 4.5% by mass based on the total solid content of the protective layer. More preferred is 0.1 to 4.2% by mass. If it is less than 0.1% by mass, the effect of improving ink transferability cannot be obtained. On the other hand, if it exceeds 4.8% by mass, the contact angle increases too much, and the ink adhesion decreases.

  For the protective layer, further known auxiliaries such as lubricants, antifoaming agents, wetting agents, preservatives, fluorescent whitening agents, dispersing agents, thickening agents, coloring agents, antistatic agents, crosslinking agents, surfactants Various auxiliary agents such as may be contained as appropriate. When the protective layer is formed simultaneously with the heat-sensitive recording layer by curtain coating or the like, it is preferable to reduce the surface tension of the protective layer by adding a surfactant.

  On the other hand, the content of paraffin wax in the protective layer according to the present invention is preferably 4% by mass or less, more preferably 3% by mass or less, and most preferably no paraffin wax with respect to the total solid content of the protective layer. It is not. Paraffin wax can increase the contact angle of the protective layer and contribute to the improvement of ink transferability, but if the wax content becomes too high, the ink adhesion becomes poor. In addition, the heat resistance of the protective layer is lowered, and this causes a printing failure such as adhesion of the protective layer melt to the thermal head during thermal recording. On the other hand, the protective layer according to the present invention having the above configuration can increase the contact angle to a predetermined range without containing paraffin wax, and can ensure excellent ink transfer properties and ink adhesion.

  The protective layer is formed by coating and drying a protective layer coating solution obtained by dissolving and dispersing the above components in water. The coating solution for the protective layer is prepared by mixing and stirring with an aqueous solution of a hydrophobic polycarboxylic acid copolymer, a pigment dispersion, an acrylic resin, an aqueous polyvinyl alcohol solution, and various auxiliary agents.

The coating amount is not particularly limited, but in general, it is preferably about 0.2 to 5 g / m ² , particularly about 0.3 to 3.5 g / m ² after drying.

  The protective layer formed by applying the coating liquid having the components as described above preferably has a contact angle after 70 seconds with water based on ASTM D5725 of 70 to 110 °, more preferably 70. ~ 100 °. If the contact angle is too low, water loss phenomenon tends to occur during offset printing, and it is difficult to obtain a dark and clear printed image. On the other hand, if the contact angle becomes too high, the ink adhesion may be lowered.

(Thermosensitive recording layer)
The heat-sensitive recording layer of the present invention contains a leuco dye, a color former and an adhesive.

  The leuco dye can be used alone or in combination of two or more. For example, leuco dyes such as triphenylmethane, fluoran, phenothiazine, auramine, spiropyran, and indolylphthalide are preferred. Used. Specific examples of leuco dyes include, for example, 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- (N-ethyl-p-toluidino) -6-methyl-7- (P-Toluidino) fluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-di (n-butyl) amino-6-methyl-7-anilinofluora 3-di (n-butyl) amino-7- (o-chloroanilino) fluorane, 3-di (n-pentyl) amino-6-methyl-7-anilinofluorane, 3- (N-cyclohexyl-N- Methylamino) -6-methyl-7-anilinofluorane, 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, and 3,6-bis (dimethylamino) fluorene-9-spiro-3 '-(6'-dimethylamino) Phthalide, and the like.

  As a coloring agent, it can use individually or in mixture of 2 or more types. 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, 2,2 ′-[4- (4-hydroxyphenylsulfonyl) phenoxy] diethyl Ether, 1,4-bis [α-methyl-α- (4′-hydroxyphen Nyl) ethyl] benzene and other phenolic compounds, Np-tolylsulfonyl-N′-phenylurea, 4,4′-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylmethane, Np -Tolylsulfonyl-N'-3- (p-tolylsulfonyloxy) phenylurea, 4,4'-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylsulfone, 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) propyl Oxy] zinc salicylate, 5- [p- (2-p-methoxyphenoxyethoxy) kumi (L) Zinc salts of aromatic carboxylic acids such as salicylic acid.

  Furthermore, it is preferable that a sensitizer is contained. Examples of the sensitizer include stearamide, stearic acid methylenebisamide, stearic acid ethylenebisamide, p-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-diphenoxy Ethane, 1- (4-methoxyphenoxy) -2- (3-methylphenoxy) ethane, 2-naphthylbenzyl ether, 1- (2-naphthyloxy) -2-phenoxyethane, 1,3-di (naphthyloxy) Propane, dibenzyl oxalate, di-p-methyl-benzyl oxalate, di-p-chlorobe oxalate Jill, dibutyl terephthalate, dibenzyl terephthalate, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole. These may be used alone or in combination of two or more.

  Furthermore, a pigment may be contained. 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, 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 to the above components, the heat-sensitive recording layer may further include a lubricant, an antifoaming agent, a wetting agent, an antiseptic, a fluorescent whitening agent, a dispersing agent, a thickening agent, a coloring agent, an antistatic agent, and a surface active agent. You may contain well-known adjuvants, such as an agent. When the thermal recording layer is formed simultaneously with the protective layer by curtain coating or the like, it is preferable to reduce the surface tension of the thermal recording layer by adding a surfactant.

  In the heat-sensitive recording layer of the present invention, the content of the leuco dye in the heat-sensitive recording layer is generally 5 to 20% by mass, and the content of the developer is generally 5 to 40% by mass. When a sensitizer is included, the content of the sensitizer is preferably 5 to 40% by mass. Lubricants and pigments are preferably contained in a content of 5 to 20% by mass and 10 to 50% by mass, respectively, and the content of the adhesive is generally about 5 to 20% by mass.

  The heat-sensitive recording layer is formed by applying a heat-sensitive recording layer coating liquid in which the above components are dispersed and dissolved in water. The thermal recording layer coating solution is prepared by separately pulverizing and dispersing each component together with an aqueous adhesive solution with a dispersing machine such as a ball mill, and then mixing and stirring with a sensitizer, a pigment, and various auxiliary agents as necessary.

The coating amount is not particularly limited, but generally it is preferably about 1.5 to 10 g / m ² , particularly about ² to 8 g / m ² in terms of mass after drying.

[Support]
The support used for the heat-sensitive recording material of the present invention is not particularly limited, and a known support conventionally used in the field of heat-sensitive recording materials can be used. Specifically, it can be selected from paper, coated paper coated with pigment, latex, etc. on the surface, synthetic paper having a multilayer structure made of polyolefin resin, plastic film, or composite sheet thereof.

[Thermal recording material]
The heat-sensitive recording material of the present invention is formed by coating and drying the heat-sensitive recording layer coating liquid on a support to form a heat-sensitive recording layer, and further coating and drying a protective layer coating liquid on the heat-sensitive recording layer. Thus, the protective layer coating liquid can be formed.

  As the coating method, for example, any conventionally known coating methods such as air knife coating, varibar blade coating, pure blade coating, gravure coating, rod coating, short dwell coating, curtain coating, and die coating can be adopted. In particular, if the thermal recording layer and the protective layer are formed simultaneously using the curtain coating method, there is an advantage that the process can be omitted, and if the thermal recording layer and the protective layer are sequentially formed using the curtain coating method, the barrier property is improved. There are advantages.

  An undercoat layer can be provided between the support and the heat-sensitive recording layer as necessary. In this case, as a component constituting the undercoat layer, known pigments, adhesives, various auxiliaries and the like can be used.In particular, when calcined kaolin and organic fine hollow particles or organic foamable particles are used in combination, It is preferably used because the recording sensitivity is improved and sticking is excellent.

Further, another protective layer may be provided between the thermosensitive recording layer and the protective layer. The protective layer containing a predetermined amount of the hydrophobic polycarboxylic acid according to the present invention may be the outermost layer.
Further, a layer having inkjet suitability, an antistatic layer, a barrier layer, and the like may be provided on the back surface of the support depending on the purpose.

  The above heat-sensitive recording material may be previously printed on the outermost protective layer. Since the thermal recording material of the present invention is excellent in offset printability and excellent in ink adhesion in a printed portion that has been offset printed, the pre-printed portion can be used as a pre-printed thermal recording material even in the distribution process. A clear image is retained, and an excellent preprinted image is retained even after thermal recording. In addition, since the heat-sensitive recording material of the present invention is excellent in heat resistance of the protective layer, it does not contaminate the head due to adhesion of head debris by heat-sensitive recording. As a result, the head lasts long and good thermal recording can be performed over a long period of time.

  As the ink used for printing, an ultraviolet curable ink is often used. In the present invention, however, offset printing using an ultraviolet curable ink is particularly effective.

  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.

[Measurement evaluation method]
(1) Thermal recording part density 1
Using a thermal evaluation machine (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermal recording medium was colored at 0.24 mJ / dot, and the density of the recording part was measured using a Macbeth densitometer (trade name: RD-914, It was measured in the visual mode of Macbeth.

(2) Thermal recording part density 2
Using a label printer (trade name: HP3600, manufactured by Teraoka Seiko Co., Ltd.), each thermal recording medium is colored with a printing speed of 45 mm / second and a set thermal head resistance value of 800Ω (thermal head resistance value of 617Ω), and the density of the recording area is adjusted. The measurement was performed in the visual mode of a Macbeth densitometer (trade name: RD-914, manufactured by Macbeth).

(3) Contact angle After dropping pure water on the blank paper portion, the contact angle 0.1 seconds later was measured using a dynamic contact angle measuring device (trade name: FIBRO DAT1100, manufactured by FIBRO systemmab).

(4) Offset printing suitability (4-1) Ink transfer property Offset printing was performed on the protective layer of the heat-sensitive recording medium using an RI printer. After printing by using 0.5 cc of water added to 0.25 g of UV ink (trade name: Best Cure UV NVR Crimson, manufactured by T & K) and emulsifying the ink by kneading the ink and water with an ink kneading roller for 1 minute. The solid uniformity of the printed part was evaluated as follows.
○: Printed on one side.
X: The printing part is printed in spots.

(4-2) Ink adhesion In the same manner as the above ink transfer property, a cellophane tape is attached to the obtained printed portion, and then the printed portion after the cellophane tape is peeled off is visually observed, as follows. evaluated.
○: No peeling of the printed part ×: There is peeling of the printed part

(4-3) Density of printing solid part The solid part of the obtained printing part was measured with a red filter of a Macbeth densitometer (trade name: RD-914, manufactured by Macbeth Co., Ltd.) in the same manner as the ink transfer property. A high printing solid part concentration means that the ink transfer property and ink adhesion are excellent, and a solid part concentration of 0.7 or less is practically unacceptable.

(5) Thermal recording property-presence / absence of head residue Each thermal recording medium was printed using a label printer (trade name: HP3600, manufactured by Teraoka Seiko Co., Ltd.) with a printing speed of 45 mm / second and a set thermal head resistance value of 800Ω (thermal head resistance value of 617Ω). After the color was developed, the state of the thermal head was visually observed and evaluated as follows.
○: No head residue is attached on the heating element of the thermal head.
Δ: Head debris is slightly attached on the heating element of the thermal head, but there is no practical problem.
X: Head debris adheres to the heating element of the thermal head.

(Preparation of coating solution for undercoat layer)
In preparing the thermal recording material, the following two types of undercoating liquids were used.
(1) Preparation of undercoat layer coating liquid U1 To a dispersion obtained by dispersing 85 parts of calcined clay (trade name: Ansilex, Engelhard) in 320 parts of water, a styrene-butadiene copolymer emulsion ( Undercoat layer coating liquid U1 was obtained by mixing and stirring 40 parts of a solid content concentration of 50%) and 50 parts of a 10% aqueous solution of oxidized starch.

(2) Preparation of undercoat coating liquid U2 In a dispersion obtained by dispersing 60 parts of calcined clay (trade name: Ansilex, Engelhard) in 320 parts of water, fine hollow particles (trade name: AE852, Undercoat layer coating liquid U2 by mixing and stirring 96 parts of JSR, solid content of 26%), 40 parts of styrene-butadiene copolymer emulsion (solid content of 50%) and 50 parts of 10% aqueous solution of oxidized starch. Got.

[Preparation of thermal recording layer coating solution]
(1) Preparation of thermal recording layer coating liquid H1 (1-1) Leuco dye dispersion 3- (N-ethyl-N-isopentylamino) -6-methyl-7-anilinofluorane, 10 parts of methylcellulose A composition comprising 5 parts of a 5% aqueous solution and 15 parts of water was pulverized with a sand mill until the average particle size became 1.5 μm to obtain a leuco dye dispersion.

(1-2) Colorant Dispersion Solution A composition comprising 10 parts of 3,3′-diallyl-4,4′-dihydroxydiphenylsulfone, 5 parts of a 5% aqueous solution of methylcellulose, and 15 parts of water was averaged by a sand mill. Was pulverized to obtain a colorant dispersion.
(1-3) Sensitizer dispersion liquid A composition comprising 20 parts of 1,2-di (3-methylphenoxy) ethane, 5 parts of a 5% aqueous solution of methylcellulose, and 55 parts of water in a sand mill has an average particle size of 1. A sensitizer dispersion was obtained by pulverizing to 5 μm.

(1-4) Preparation of coating solution for heat-sensitive recording layer 25 parts of leuco dye dispersion prepared above, 50 parts of colorant dispersion, 50 parts of sensitizer dispersion, 30 parts of 20% aqueous solution of oxidized starch, light A composition comprising 10 parts of calcium carbonate, 50 parts of a 10% aqueous solution of polyvinyl alcohol, and 10 parts of water was mixed and stirred to obtain a thermal recording layer coating liquid H1.

(2) Thermal recording layer coating liquid H2
Further, 0.35 part of an aqueous solution of sodium di (2-ethylhexyl) sulfosuccinate (trade name: SN wet OT-70, concentration 70%, manufactured by San Nopco) was added to the coating liquid H1 for the thermal recording layer, and the thermal recording layer was added. The coating liquid was H2.

[Thermal recording material No. Preparation and evaluation of 1 to 12]
(1) Thermal recording material No. 1:
U1 was used as the undercoat layer coating solution. The H1 was used as a heat-sensitive recording layer coating solution.
As the protective layer coating solution, a solution prepared as follows was used.
400 parts of a 10% aqueous solution of acetoacetyl-modified polyvinyl alcohol (trade name: Goosefimmer Z-200, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), acrylic resin (trade name: AM2250, copolymer of acrylic acid alkyl ester and acrylonitrile, 20 parts of an aqueous emulsion having a solid content of 50%, manufactured by Showa Polymer Co., Ltd., 92 parts of a 50% kaolin dispersion (trade name: UW90, manufactured by Huber), 10 parts of a 30% zinc stearate dispersion, a hydrophobic monomer And 5 parts by weight of a water-soluble copolymer of polycarboxylic acid (ammonium salt of fumaric acid 90% by weight and 2-ethylhexyl acrylate copolymer (fumaric acid / AEH copolymer), solid content concentration 20%) Were mixed and stirred to obtain a coating solution for a protective layer. The content ratio (% by mass) of each component in the protective layer constituted using this protective layer coating solution is as follows.
Acetoacetyl-modified polyvinyl alcohol (abbreviated as PVA): 40%
Acrylic resin AM2250 (abbreviated as Ac1): 10%
Kaolin: 46%
Zinc stearate: 3%
Ammonium salt of fumaric acid / AEH copolymer (abbreviated as P1): 1%

The undercoat layer coating liquid U1 was applied and dried on one surface of a 48 g / m ² base paper so that the coating amount after drying was 9.0 g / m ² to form an undercoat layer. Next, the thermal recording layer coating liquid H1 was applied and dried with a rod coater so that the coating amount after drying was 5.0 g / m ² on the undercoat layer. The coating solution for the protective layer prepared above was applied and dried with a rod coater so that the coating amount after drying was 2 g / m ² on the obtained heat-sensitive recording layer. After that, it was processed by a super calendar, and a thermal recording body having a surface smoothness of 1500 to 2500 seconds was prepared with a Wangken type smoothness meter. Based on the above evaluation method, the thermal recording portion density 1, contact angle, ink transfer Property, ink adhesion, and presence of head residue. The results are also shown in Table 1.

Thermal recording material No. 2-7:
In the protective layer coating solution, no change was made except that the types and blending amounts of the binder resin, pigment, and hydrophobic polycarboxylic acid were changed as shown in Table 1. In the same manner as in No. 1, a thermal recording material was prepared, and based on the above evaluation method, the thermal recording portion density 1, contact angle, ink transferability, ink adhesion, and presence of head residue were evaluated. The results are also shown in Table 1.

The binder resin, pigment, and hydrophobic polycarboxylic acid shown in Table 1 are as follows.
Ac2: acrylic resin (trade name: Barrier Star OT-1035-1, (meth) acrylonitrile / (meth) acrylic acid alkyl / (meth) acrylic acid 2-hydroxyethyl / (meth) acrylic acid / (meth) acrylamide) Polymer, solid concentration 25%, manufactured by Mitsui Chemicals)
Silica: Silica dispersion (Silojet 703A, average particle diameter of secondary particles 300 nm, particle diameter of primary particles 10 nm, solid content concentration 20%)
CaCO ₃ : 50% light calcium carbonate dispersion (trade name: Brilliant 15, manufactured by Shiraishi Calcium Co., Ltd.)
P2: Orotan 165A (trade name), aqueous solution of ammonium salt of styrene / maleic anhydride / isobutylene terpolymer, solid concentration 21.8%, manufactured by Rohm and Haas P3: copolymer of maleic acid / isobutylene Ammonium salt (maleic acid content 55%, isobutylene content 45%), solid content concentration 20%
P4: Polymeron 1353 (trade name), manufactured by Arakawa Chemical Co., Ltd., aqueous dispersion with a solid content of 20%

Thermal recording material No. 8:
Except for using the undercoat layer coating liquid U2, the thermal recording material No. A thermal recording material was prepared in the same manner as in No. 2, and based on the above evaluation method, the thermal recording portion density 1, contact angle, ink transferability, ink adhesion, and presence of head residue were evaluated. The results are also shown in Table 1.

Thermal recording material No. 9:
The heat-sensitive recording layer coating liquid H2 was used. In the protective layer coating solution used in 2, the acrylic resin (Ac1) and the hydrophobic polycarboxylic acid copolymer content were changed as shown in Table 1, and a di (2-ethylhexyl) sodium sulfosuccinate aqueous solution (trade name) : SN wet OT-70, concentration 70%, the above) A coating liquid containing 0.35 part (corresponding to 0.2% content in the protective layer) was used. Further, in the creation of heat-sensitive recording material, a thermal recording layer coating solution and protective layer coating solution, a two-layer simultaneous curtain coater so that the coating amount after each drying and ^{5.0g / m 2, 2g / m} 2 And dried. In other cases, the thermal recording material No. A thermal recording material was prepared in the same manner as in No. 2, and based on the above evaluation method, the thermal recording portion density 1, contact angle, ink transferability, ink adhesion, and presence of head residue were evaluated. The results are also shown in Table 1.

Thermal recording material No. 10:
The heat-sensitive recording layer coating liquid H2 was used. In the protective layer coating liquid used in No. 3, 35 parts of Ac2 is used for the acrylic resin as the binder resin (corresponding to 9% content in the protective layer), and 10 parts of P2 (corresponding to 2% content in the protective layer) ) And further di (2-ethylhexyl) sodium sulfosuccinate aqueous solution (trade name: SN wet OT-70, concentration 70%, supra) 0.35 parts (corresponding to 0.2% content in the protective layer) A protective layer coating solution was used. Further, in the creation of heat-sensitive recording material, a thermal recording layer coating solution and protective layer coating solution, a two-layer simultaneous curtain coater so that the coating amount after each drying and ^{5.0g / m 2, 2g / m} 2 And dried. In other cases, the thermal recording material No. A thermal recording material was prepared in the same manner as in No. 3, and the thermal recording part density 1, contact angle, ink transferability, ink adhesion, and presence of head residue were evaluated based on the above evaluation methods. The results are also shown in Table 1.

Thermal recording material No. 11, 12:
In the protective layer coating solution, No. 1 except that the composition of the protective layer was changed as shown in Table 1 by changing the type and blending amount of the binder resin, pigment, and hydrophobic polycarboxylic acid copolymer. In the same manner as in No. 1, a thermal recording material was prepared, and based on the above evaluation method, the thermal recording portion density 1, contact angle, ink transferability, ink adhesion, and presence of head residue were evaluated. The results are also shown in Table 1.

Thermal recording material No. 13:
In the coating liquid for the protective layer, no hydrophobic polycarboxylic acid was blended, paraffin wax was blended (content ratio in the protective layer 10%), and the amount of pigment was changed. A thermal recording material was prepared in the same manner as in No. 1, and the thermal recording portion density 1, contact angle, ink transferability, ink adhesion, and presence of head residue were evaluated based on the above evaluation methods. The results are also shown in Table 1.

As can be seen from Table 1, the protective layer (No. 11) containing no hydrophobic polycarboxylic acid copolymer had a contact angle of 62 ° and had a slightly hydrophilic surface. Therefore, the ink transfer property could not be satisfied.
On the other hand, if the content of the hydrophobic polycarboxylic acid is too high (No. 12), the contact angle becomes 115 ° and the hydrophobicity becomes too high, or the ink adhesion is poor and the offset printability cannot be satisfied. It was.
No. 1 to 10 are all heat-sensitive recording materials having a protective layer containing a hydrophobic polycarboxylic acid copolymer, the contact angle is in the range of 70 to 110 °, and offset printability (ink transfer properties, ink adhesion) ). Also, the density of the thermal recording part was satisfactory.
On the other hand, no. Reference numeral 13 denotes a heat-sensitive recording material having a protective layer whose contact angle is adjusted to 85 ° by blending paraffin wax instead of the hydrophobic polycarboxylic acid copolymer. The ink transferability was excellent, but the ink adhesion was inferior, and further head debris was confirmed.

[Thermal recording material No. 21-25]
Undercoat layer coating solution U1 was used. The thermal recording layer coating liquid H1 was used.
Thermal recording material No. In the protective layer coating solution prepared in step 1, 112 parts of 50% kaolin dispersion (trade name: UW90, supra) is used without using an acrylic resin (trade name: AM2250, supra), and further hydrophobic. The type of the polycarboxylic acid copolymer was changed as shown in Table 2, and the thermal recording material No. 21-25 were created. The acid value of the used hydrophobic polycarboxylic acid copolymer is as shown in Table 2. The prepared thermal recording material No. About 21-25, based on the said evaluation method, the contact angle, the thermal recording part density | concentration 2, the printing solid part density | concentration, and the presence or absence of the head residue were evaluated. The results are shown in Table 2.

  Thermal recording material No. The contact angle of No. 25 is 70 ° or less and the solid portion density is low. All of Nos. 21 to 24 had a contact angle of 70 ° or more and satisfied the solid portion density. It can be seen that as the contact angle increases, the solid density of offset printing tends to increase, and the ink transfer property tends to be excellent.

On the other hand, regarding the adhesion of the head residue, when the acid value of the hydrophobic polycarboxylic acid copolymer is low, the adhesion tends to increase. Thermal recording material No. No. 24 is a thermal recording material No. 24. The contact angle was larger than 21 and the ink transferability was excellent, but the adhesion of head residue was observed.
The thermal recording material No. When the contact angle of 25 was less than 70 °, the ink transferability was poor, the printing solid portion density could not achieve a practically acceptable level, the acid value was less than 200, and the head residue was often attached.

  Since the thermal recording material of the present invention is excellent in both thermal recording properties and offset printing properties, it is useful as a thermal recording material on which general items requiring printing are printed in advance.

Claims (9)

A heat-sensitive recording layer containing a leuco dye and a colorant is provided on the support, and a protective layer containing a pigment and a binder resin is provided as the outermost surface layer on the side where the heat-sensitive recording layer is provided. In a thermal recording medium,
The protective layer contains a water-soluble copolymer of a hydrophobic monomer and a polycarboxylic acid or a salt thereof in an amount of 0.1 to 4.8% by mass based on the total solid content of the protective layer. body. The heat-sensitive recording material according to claim 1, wherein the water-soluble copolymer has an acid value of 200 or more. The heat-sensitive recording material according to claim 1 or 2, wherein the protective layer has a contact angle after 70 seconds with water based on ASTM D5725 of 70 to 110 °. The thermosensitive recording material according to claim 1, wherein the content of paraffin wax in the protective layer is 4% by mass or less with respect to the total solid content of the protective layer. The heat-sensitive recording material according to any one of claims 1 to 4, wherein the binder resin contains a polyvinyl alcohol resin in an amount of 20 to 70 mass% with respect to the total solid content of the protective layer. The heat-sensitive recording material according to any one of claims 1 to 5, wherein the binder resin contains an acrylic resin in an amount of 3 to 50 mass% with respect to the total solid content of the protective layer. The heat-sensitive recording material according to claim 1, wherein the pigment contains kaolin and / or calcium carbonate in an amount of 5 to 65 mass% based on the total solid content of the protective layer. The secondary pigment having an average particle diameter of 30 to 1300 nm obtained by agglomerating amorphous silica primary particles having a particle diameter of 3 to 70 nm as the pigment is contained in an amount of 1 to 40% by mass based on the total solid content of the protective layer. The heat-sensitive recording material according to any one of 1 to 7. The thermal recording body according to claim 1, wherein the thermal recording body has an offset printing section.