JP2010023252A - Thermosensitive recording body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermosensitive recording body particularly excellent in recording sensitivity, light stability, storage stability of the recorded image, and print recording property. <P>SOLUTION: The thermosensitive recording body is comprised of a thermosensitive layer containing at least leuco dye and color developing agent, a middle layer, and a protection layer, which are all sequentially laminated on the support body thereof, containing aqueous UV-absorbing polymer in the middle layer at 1 to 60 percent by mass of the total dissolved solid thereof, containing aqueous acrylic polymer and polyvinyl alcohol in total at 30 to 90 percent by mass of the total dissolved solid of the middle layer as adhesive for the middle layer, the polyvinyl alcohol characteristically being at 30 to 99 percent by mass of the total dissolved solid of the aqueous acrylic polymer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

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

  However, since the heat-sensitive recording material is a reversible reaction that develops color when the leuco dye and the colorant are melted and brought into contact with heat, the recorded image is faded by contact with chemicals, etc. Such information may not be confirmed. In addition, exposure to room light or sunlight often changes the structure of the leuco dye, resulting in discoloration of the background and often reduces the commercial value of the thermal recording material.

  In order to solve such problems caused by light, a technique has been proposed in which an inorganic pigment such as zinc oxide having an ultraviolet blocking effect is contained in a heat-sensitive recording layer or a protective layer (see Patent Document 1). However, an inorganic pigment having an ultraviolet blocking effect has a high visible light blocking property and conceals a recorded image, so that it is difficult to apply such as a decrease in recording density.

  In addition, a technique in which an ultraviolet absorber is contained in a heat-sensitive recording layer or a protective layer has been proposed (see Patent Document 2). Since a general organic ultraviolet absorber is insoluble in water, it is applied as an aqueous dispersion finely pulverized using water as a medium. Since the finely pulverized ultraviolet absorber has a low ultraviolet absorption effect, it needs to be contained in a large amount in order to exhibit sufficient light resistance. However, if it is contained in a large amount, problems such as generation of background fogging due to heat and humidity and fading of recorded images occur. In addition, when it is contained in the protective layer, there is a risk of causing a recording failure such that recording becomes impossible because the ultraviolet absorber is welded to the recording head by heat during recording and the soot accumulates. .

  In addition, a technique for containing an ultraviolet absorbing polymer in a heat-sensitive recording layer or a protective layer has been proposed (see Patent Document 3). However, since the UV-absorbing polymer does not have any influence on the color development mechanism, when it is contained in the heat-sensitive recording layer, there is a risk of background fogging due to heat or humidity. In order to avoid these problems, if the content is decreased, the expected ultraviolet absorption effect is also decreased, so that actual application is difficult. Furthermore, it is difficult to say that the heat resistance is sufficient, and when it is contained in the protective layer, the ultraviolet absorber is welded to the recording head by the heat at the time of recording, so that the soot is deposited, and the recording becomes impossible. There is a risk of recording failure.

In addition, in a heat-sensitive recording material in which an intermediate layer and a protective layer are sequentially laminated on a heat-sensitive recording layer, techniques for imparting an ultraviolet absorbing effect or an ultraviolet blocking effect to the intermediate layer have been proposed (Patent Documents 4 to 5). reference). When using ultraviolet blocking inorganic pigments or finely pulverized organic UV absorbers to obtain UV absorbing effects or UV blocking effects, there are problems such as a decrease in recording density, occurrence of background fogging, and fading of recorded images. appear. In addition, when an ultraviolet absorbing polymer is used, there is a risk that the preservability of a recorded image is lowered due to poor barrier properties. In order to maintain the storage stability of the recorded image, it is necessary to take measures such as improving the barrier property of the protective layer. For this purpose, it has been studied to improve the barrier properties such as increasing the content of the adhesive in the protective layer, particularly polyvinyl alcohol, or increasing the total solid content of the protective layer. There is concern about a decrease in recording density due to deterioration in transmission. Moreover, in order to maintain the storability of the recorded image, it is possible to obtain a certain level of effect by using a high-performance product for the color former contained in the heat-sensitive recording layer, but there is a possibility that it may lead to an increase in cost. Is hard to say. Thus, even if the intermediate layer is provided, it is difficult to develop a thermal recording material that has some problems, has ideal light resistance, and has no problem with the storability of recorded images and print recording characteristics. It is the actual situation.
JP-A-62-18626 JP 50-104650 A JP-A-7-137453 JP 61-242878 A JP 2001-54978 A

  An object of the present invention is to provide a heat-sensitive recording material excellent in recording sensitivity, light resistance, storability of recorded images, and print recording characteristics.

  As a result of intensive studies to solve the above problems, the inventor uses a specific amount of a water-based ultraviolet absorbing polymer in the intermediate layer, and uses a specific amount of a water-based acrylic polymer and polyvinyl alcohol as an adhesive for the intermediate layer. In particular, the present inventors have found that a heat-sensitive recording material excellent in recording sensitivity, light resistance, recorded image storability, and print recording characteristics can be obtained, and further earnestly studied to complete the present invention.

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

Item 1: In a heat-sensitive recording material obtained by sequentially laminating a heat-sensitive recording layer containing at least a leuco dye and a colorant on a support, an intermediate layer, and a protective layer, the intermediate layer is coated with a water-based ultraviolet absorbing polymer. 1 to 60% by mass with respect to the solid content, and 30 to 90% by mass with respect to the total solid content of the intermediate layer as a total amount of the aqueous acrylic polymer and polyvinyl alcohol as an adhesive for the intermediate layer, and the aqueous acrylic polymer A heat-sensitive recording material, wherein the polyvinyl alcohol is 30 to 99% by mass relative to the total solid content.
Item 2: The heat-sensitive recording material according to Item 1, wherein the aqueous ultraviolet absorbing polymer is an aqueous ultraviolet absorbing polymer obtained by polymerizing a benzotriazole ultraviolet absorbing monomer or a benzophenone ultraviolet absorbing monomer.
Item 3: The aqueous acrylic polymer is a copolymer resin emulsion, and the copolymer resin constituting the copolymer emulsion is:
(1) comprising (i) (meth) acrylonitrile and (ii) a vinyl monomer copolymerizable with (meth) acrylonitrile, and
(2) The solubility parameter is 12.0 or more,
The vinyl monomer (ii) contains at least one carboxyl group-containing vinyl monomer, and the proportion of the carboxyl group-containing vinyl monomer is 1 to 10 mass in the total mass of the copolymer resin. Item 3. The heat-sensitive recording material according to Item 1 or 2, which is%.
Item 4: As a protective layer adhesive, a water-based acrylic polymer and polyvinyl alcohol are contained as a total amount in an amount of 30 to 80% by mass based on the total solid content of the protective layer, and 20 to 20% of the polyvinyl alcohol is based on the total solid content of the water-based acrylic polymer. Item 4. The thermal recording material according to any one of Items 1 to 3, which is 99% by mass.
Item 5: The water-based acrylic polymer contained as an adhesive for the protective layer is a copolymer resin emulsion, and the copolymer resin constituting the copolymer emulsion is:
(1) comprising (i) (meth) acrylonitrile and (ii) a vinyl monomer copolymerizable with (meth) acrylonitrile, and
(2) The solubility parameter is 12.0 or more,
The vinyl monomer (ii) contains at least one carboxyl group-containing vinyl monomer, and the proportion of the carboxyl group-containing vinyl monomer is 1 to 10 mass in the total mass of the copolymer resin. Item 5. The thermal recording material according to any one of Items 1 to 4, which is%.
Item 6: The heat-sensitive recording material according to any one of Items 1 to 5, wherein the heat-sensitive recording layer, the intermediate layer, and the protective layer do not contain a curing agent.

  The heat-sensitive recording material of the present invention has the effect of being excellent in recording sensitivity, light resistance, preservability of recorded images, and print recording characteristics.

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

  The heat-sensitive recording material of the present invention is a heat-sensitive recording material obtained by sequentially laminating a heat-sensitive recording layer containing at least a leuco dye and a colorant, an intermediate layer, and a protective layer on a support. 1-60 mass% of the polymer is contained with respect to the total solid content of the intermediate layer, and 30-90 mass% with respect to the total solid content of the intermediate layer as a total amount of the water-based acrylic polymer and polyvinyl alcohol as the adhesive of the intermediate layer, And polyvinyl alcohol exists in the range of 30-99 mass% with respect to the water-based acrylic polymer total solid amount, It is characterized by the above-mentioned.

  The heat-sensitive recording material of the present invention imparts an effect excellent in light resistance and print recording characteristics by incorporating an aqueous ultraviolet absorbing polymer in the intermediate layer in an amount of 1 to 60% by mass based on the total solid content of the intermediate layer. . Further, as an adhesive for the intermediate layer, the aqueous acrylic polymer and polyvinyl alcohol are contained in a total amount of 30 to 90% by mass based on the total solid content of the intermediate layer, and the polyvinyl alcohol is 30 to 99 based on the total solid amount of the aqueous acrylic polymer. By containing it in an amount of mass%, it is possible to impart excellent storability of recorded images.

  In a heat-sensitive recording material using a water-based ultraviolet absorbing polymer, if a water-based ultraviolet absorbing polymer is contained in the heat-sensitive recording layer, there is a risk of background fogging due to heat or humidity. In addition, when a water-based UV-absorbing polymer is contained in the protective layer, a recording failure occurs such that recording becomes impossible because the UV absorber is welded to the recording head due to heat during recording and the soot accumulates. There is a risk of doing. In order to eliminate these problems, it is best to include a water-based ultraviolet absorbing polymer only in the intermediate layer in the heat-sensitive recording layer in which the heat-sensitive recording layer, the intermediate layer, and the protective layer are sequentially laminated.

  The water-based ultraviolet absorbing polymer is a polymer obtained by polymerizing an ultraviolet absorbing monomer having ultraviolet absorbing properties and a copolymerizable monomer (vinyl compound) copolymerizable with the ultraviolet absorbing monomer.

  Various methods can be used for polymerization, and emulsion polymerization is particularly preferable. In the emulsion polymerization, the heat of polymerization caused by the water around the micelles can be reduced, so that there is a manufacturing advantage that the temperature can be easily adjusted. In terms of quality, a polymer having a high degree of polymerization can be obtained. Furthermore, since the produced polymer is obtained as an emulsion emulsified in water as a dispersion medium, it can be added to the paint as it is.

  Any UV-absorbing monomer can be used as long as it has UV-absorbing monomers, but benzotriazole-based UV-absorbing monomers or benzophenone-based UV-absorbing monomers are preferred.

Specific examples of such benzotriazole-based ultraviolet absorbing monomers include the following.
2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3′-tert-butyl-5′-methylphenyl) -5-chlorobenzotriazole, 2- (2 ′ -Hydroxy-3 ', 5'-di-tert-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-5'-tert-butylphenyl) -5-chlorobenzotriazole, 2- (2 '-Hydroxy-3', 5'-di-tert-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert-amylphenyl) benzotriazole, 2- (2′-hydroxy-5′-tert-octylphenyl) benzotria 2- (2′-hydroxy-3 ′, 5′-di-tert-benzylphenyl) benzotriazole, 2- [2′-hydroxy-3 ′-(3 ″, 4 ″, 5 ″, 6) “-Tetrahydrophthalimidomethyl) -5′-methylphenyl] benzotriazole, 2- [2′-hydroxy-3 ′, 5′-bis (α, α-diethylbenzyl) phenyl] -2H-benzotriazole, 2- ( 2′-hydroxy-3′-dodecyl-5′-methylphenyl) benzotriazole, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2′-hydroxy-3 ′, 5′-bis ( α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (3,5-di-tert-butyl-2-hydroxyphenyl) benzotriazole, 2- (3-tert-butyl -5-methyl-2-hydroxyphenyl) -5-chlorobenzotriazole, 2- (3,5-di-tert-butyl-2-hydroxyphenyl) -5-chlorobenzotriazole, 2- (3,5-di -Tert-amyl-2-hydroxyphenyl) benzotriazole, 2- (2'-hydroxy-5'-tert-octylphenyl) benzotriazole, 2- (5-tert-butyl-2-hydroxyphenyl) benzotriazole, 2 -(5-tert-octyl-2-hydroxyphenyl) benzotriazole and the like.

Specific examples of such benzophenone-based ultraviolet absorbing monomers include the following.
2-hydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, 2-hydroxy-4-n-octyloxybenzophenone, 2-hydroxy-4-n-octoxybenzophenone 2-hydroxy-4-n-dodecyloxybenzophenone, 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, 2,2 4,4-tetrahydroxybenzophenone, sodium benzophenone-2-hydroxy-4-methoxy-5-sulfonate, and the like.

Specific examples of such copolymer monomers include the following.
Styrene, methyl methacrylate (MMA), ethylene vinyl acetate, vinyl acetate, methacrylonitrile, vinyl alcohol, vinyl pyrrolidone, ethyl acrylate, acrylic ester, methacrylic ester, acrylonitrile, alkyl methacrylate, ethyl methacrylate, methacrylonitrile, glycidyl methacrylate , Glycidyl methacrylate, styrene-butadiene, styrene-isoprene, styrene-isobutylene, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl ( (Meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, lauryl tridecyl ( Acrylate), tridecyl (meth) acrylate, seryl stearyl (meth) acrylate, stearyl (meth) acrylate, ethylhexyl (meth) acrylate, octyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, methacrylic acid, Hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, dimethylaminomethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate, glycidyl (meth) acrylate, tetrahydrofurfuryl (meth) ) Acrylate, ethylene di (meth) acrylate, diethylene glycol (meth) acrylate, triethylene glycol di (meth) acrylate , Tetraethylene glycol di (meth) acrylate, decaethylene glycol (meth) acrylate, pentadecaethylene (meth) acrylate, pentacontahector ethylene glycol (meth) acrylate, butylene di (meth) acrylate, allyl (meth) acrylate, trimethylol Propane tri (meth) acrylate, hexanediol di (meth) acrylate, tripropylene glycol di (meth) acrylate, pentaerythritol tetra (meth) acrylate, pentaerythritol hexa (meth) acrylate, dipentaerythritol hexa (meth) acrylate, 1 , 6-hexanediol di (meth) acrylate, neopentyl glycol penta (meth) acrylate, phosphazene hexa (meth) acrylate Etc.

  Furthermore, a crosslinkable monomer can also be used as a copolymerization monomer. Intraparticle crosslinking can be provided by the crosslinking monomer. As a result, the compatibility with the hydrophilic resin and the improvement of the solvent resistance can be expected by making the coating film surface hydrophilic.

Specific examples of such a crosslinkable monomer include the following.
Triallylamine, ethyl dimethacrylate, divinylbenzene, diethylene glycol dimethacrylate, neopentyl glycol diacrylate, methylolpropane trimethacrylate, 1,6-hexanediol diacrylate, 1,3-butylene dimethacrylate, pentamethacrylate Epoxy-containing monomers such as erythritol, allyl trimethacrylate, glycidyl acrylate, glycidyl methacrylate, glycidyl clonate, glycidyl acrylic ether, N-methylol acrylamide, N-methylol methacrylamide, N-methylol crotonamide, N- (2- Hydroxyethyl) methacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, poly Carboxymethyl ethylene monoacrylate, polyoxypropylene monomethacrylate, methacrylic amine, aminostyrene, allylamine, acrylic acid, methacrylic acid, crotonic acid, maleic acid, or maleic anhydride.

  As an adhesive for the intermediate layer, the aqueous acrylic polymer and polyvinyl alcohol are contained in a total amount of 30 to 90% by mass with respect to the total solid content of the intermediate layer, and 30 to 99 polyvinyl alcohol is included with respect to the total solid amount of the aqueous acrylic polymer. By containing the content by mass%, it is possible to impart excellent recording image storage stability.

  Although the water-based ultraviolet absorbing polymer has improved barrier properties as compared with finely pulverized organic ultraviolet absorbers, it is still not perfect and needs to be used in combination with other resins. As the resin to be used in combination, any adhesive can be used as long as it can be generally used for a heat-sensitive recording material. In particular, it has been found that various resistances are further improved by using a water-based acrylic polymer and polyvinyl alcohol in combination from the viewpoint of compatibility and solvent resistance.

  For example, water-based acrylic polymers are excellent in barrier properties against polyethylene glycol, but are poor in barrier properties against alcohols and oils. Polyvinyl alcohol is excellent in barrier properties against alcohol and oil, but poor in barrier properties against polyethylene glycol.

  The solvent alcohol mentioned here may come into contact with the thermal recording medium as a disinfectant, the oil may come into contact with the thermal recording medium as an edible oil or machine oil, and polyethylene glycol is used as a non-freezing liquid. Used for writing instruments such as fluorescent pens and fluorescent pens, and may come into contact with thermal recording media. If the thermal recording material does not have barrier properties against various solvents, the recorded image may be faded.

  In order to eliminate these problems, the barrier property against any solvent can be improved by using a water-based acrylic polymer and polyvinyl alcohol together. Moreover, 30-90 mass% is contained with respect to the total solid content of the intermediate layer as a total amount of the water-based acrylic polymer and polyvinyl alcohol, and 30-99 mass% of polyvinyl alcohol is contained with respect to the total solid content of the water-based acrylic polymer. And found that the effect is more prominent.

Furthermore, as a water-based acrylic polymer, a copolymer resin emulsion, the copolymer resin constituting the copolymer emulsion,
(1) comprising (i) (meth) acrylonitrile and (ii) a vinyl monomer copolymerizable with (meth) acrylonitrile, and
(2) The solubility parameter is 12.0 or more,
The vinyl monomer (ii) contains at least one carboxyl group-containing vinyl monomer, and the proportion of the carboxyl group-containing vinyl monomer is 1 to 10 mass in the total mass of the copolymer resin. It has been found that not only the storability of the recorded image is improved, but also the strength against water is increased and a strong water-resistant coating film strength can be imparted when using the copolymer resin emulsion characterized by .

Specific examples of the polyvinyl alcohol used in the present invention include the following.
Examples thereof include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol.

  When using the modified polyvinyl alcohol, it is also possible to use a curing agent such as glyoxal, dimethylol urea, glycidyl ether of polyhydric alcohol, aldehyde compound, epichlorohydrin modified product, zirconium ammonium carbonate and the like. However, when a curing agent is used, there are background discoloration of the thermal recording paper over time and environmental problems.

Therefore, it is preferable to use fully saponified polyvinyl alcohol or partially saponified polyvinyl alcohol. When at least one of fully saponified polyvinyl alcohol or partially saponified polyvinyl alcohol is used, it is usually difficult to obtain a water-resistant coating film strength. However, a water-based acrylic polymer is a copolymer resin emulsion, and the copolymer emulsion constituting the copolymer emulsion is used. Polymer resin is
(1) comprising (i) (meth) acrylonitrile and (ii) a vinyl monomer copolymerizable with (meth) acrylonitrile, and
(2) The solubility parameter is 12.0 or more,
The vinyl monomer (ii) contains at least one carboxyl group-containing vinyl monomer, and the proportion of the carboxyl group-containing vinyl monomer is 1 to 10 mass in the total mass of the copolymer resin. %, When a copolymer resin emulsion characterized by the above is used, a water-resistant coating film strength having no problem can be obtained due to the water resistance of a strong water-based acrylic polymer.

  The copolymer resin emulsion will be described in more detail.

-Component of copolymer resin The copolymer resin constituting the copolymer resin emulsion used in the present invention comprises (i) (meth) acrylonitrile and (ii) a vinyl monomer copolymerizable with (meth) acrylonitrile. As a polymerization component.

(I) The proportion of (meth) acrylonitrile in the (meth) acrylonitrile copolymer resin is not particularly limited as long as the effect of the present invention is achieved, but is preferably about 20 to 80% by mass, and more preferably 30 to 30%. It is about 70% by mass.
When the ratio of (meth) acrylonitrile is 20% by mass or more, sufficient water resistance is obtained, and the sticking resistance is not hindered. Moreover, if it is 80 mass% or less, there is no possibility that manufacturing (polymerization) stability of an emulsion may be inferior, and Tg of copolymer resin does not become higher than necessary. In addition, there is no possibility that the film forming property of the emulsion and the binding property to the filler will be hindered.

(Ii) Vinyl monomers copolymerizable with (meth) acrylonitrile Examples of vinyl monomers copolymerizable with (meth) acrylonitrile include:
(A) a carboxyl group-containing vinyl monomer,
(B) alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, (meth ) 2-hydroxyethyl acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2-aminoethyl (meth) acrylate, 2- (N-methylamino) (meth) acrylate ) Ethyl, (meth) acrylic acid esters such as 2- (N, N-dimethylamino) ethyl (meth) acrylate, glycidyl (meth) acrylate,
(C) vinyl esters such as vinyl acetate and vinyl propionate;
(D) aromatic vinyl monomers such as styrene, α-methylstyrene, divinylbenzene,
(E) N-substituted unsaturated carboxylic acid amides such as (meth) acrylamide, N-methylol (meth) acrylamide,
(F) a heterocyclic vinyl compound such as vinylpyrrolidone,
(G) vinylidene halide compounds such as vinylidene chloride and vinylidene fluoride;
(H) α-olefins such as ethylene and propylene,
(I) One or a combination of two or more selected from the group consisting of dienes such as butadiene may be mentioned.

The ratio of the vinyl monomer copolymerizable with (meth) acrylonitrile in the copolymer resin is not particularly limited as long as the effect of the present invention is exhibited, but is preferably about 80 to 20% by mass, and more preferably. Is about 70 to 30% by mass.
If the ratio of the vinyl monomer copolymerizable with (meth) acrylonitrile is 20% by mass or more, there is no fear that the production (polymerization) stability of the emulsion is inferior, and the Tg of the copolymer resin does not become higher than necessary. In addition, there is no possibility that the film forming property of the emulsion and the binding property to the filler will be hindered. Moreover, if it is 80 mass% or less, sufficient water resistance will be obtained and it will not interfere with sticking resistance.

The vinyl monomer copolymerizable with (meth) acrylonitrile in the present invention contains at least one vinyl monomer containing one or more carboxyl groups.
Examples of carboxyl group-containing vinyl monomers include ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, ethylenically unsaturated dicarboxylic acids such as itaconic acid, maleic acid, and fumaric acid, and monocarboxylic acids thereof. The 1 type, or 2 or more types of combination chosen from the group which consists of alkylesters is mentioned.

  The carboxyl group-containing vinyl monomer in the copolymer resin of the present invention is essential for ensuring the polymerization stability of the copolymer resin when preparing the copolymer resin emulsion, and is neutralized with a base after polymerization. As a result, the resin particle surface layer is hydrated and softened, and the film-forming property of the copolymer resin emulsion is improved. It also has a function of enhancing the dispersibility and binding properties of various fillers added as necessary. Furthermore, the carboxyl group also acts as a reactive group with a crosslinking agent used in combination as necessary.

  The ratio of the carboxyl group-containing vinyl monomer is preferably in the range of 1 to 10% by mass, more preferably 2 to 8% by mass, based on the total mass of the copolymer resin. When the content is 1% by mass or more, the polymerization stability of the copolymer resin is not lost, the softening of the resin particles is good even during neutralization, and the film-forming property of the copolymer resin emulsion is excellent. If the content is 10% by mass or less, the heat-sensitive recording layer has sufficient water resistance, and further, there is no fear of gelation due to dissolution of resin particles during neutralization.

-Solubility parameter In this invention, the solubility parameter of the copolymer resin which comprises a copolymer resin emulsion shall be 12.0 or more. The solubility parameter is described in, for example, Iwanami Dictionary of Physical Chemistry, 4th edition.

  When the solubility parameter is 12.0 or more, the heat resistance against heat received from the thermal head during use (adhesiveness to the thermal head) is improved, and the internal cohesive force of the resin can be increased. If the solubility parameter is less than 12.0, the thermal sensitivity of the thermal recording layer increases due to insufficient internal cohesion of the resin, so that the thermal recording layer is easily softened and the running stability of the thermal head is lacking. The upper limit of the solubility parameter is not particularly set, but in consideration of the characteristics of the copolymer resin used in the present invention and industrial production efficiency, a range of 14.0 or less is preferable.

When the solubility parameter is 14.0 or less, the hydrophilicity of the copolymer resin is increased, there is no fear that the water resistance is greatly reduced, and the production of the copolymer resin emulsion is facilitated.
The solubility parameter in the present invention is a value calculated from the molecular structure of each copolymer component, the total evaporation energy of atomic groups, and the molar volume ratio of the copolymer component.
The solubility parameter calculation method is described in Journal of Technology Coatings VOL. 55, No696, P.I. According to description of 100-101, it can calculate based on the following formula 1.
δ = [(ΣΔe _i ) (X) / (ΣΔv _i ) (X)] Equation ^0.5 (1)
(Δ: solubility parameter, X: molar fraction of monomer used for copolymerization, Δe _i : evaporation energy of each monomer, Δv _i : molar volume)
A copolymer resin having a specific solubility parameter can be prepared by selecting a monomer as a copolymer component and setting a blending ratio.

Other properties of copolymer resin emulsion The average primary particle diameter of the copolymer resin emulsion (number average particle diameter by dynamic light scattering method, measuring device: trade name: LPA3100, manufactured by Otsuka Electronics Co., Ltd.) is not particularly limited, but preferably Is about 50 to 500 nm, more preferably about 70 to 300 nm.

  When the average particle size is 50 nm or more, the viscosity of the emulsion does not increase significantly. Therefore, it is not necessary to reduce the resin concentration at the time of manufacture, and the drying property of the thermal recording layer coating liquid is not slowed. Therefore, there is an economic advantage that the productivity of the thermal recording material is not hindered. On the other hand, when the thickness is 500 nm or less, the surface of the thermosensitive recording layer becomes dense, and a desired effect is easily exhibited.

  Adjustment of the average particle diameter can be easily performed by knowledge of those skilled in the art. For example, the average particle diameter can be adjusted by appropriately selecting the composition of the raw material monomer of the copolymer resin emulsion and the type of the surfactant.

-Manufacturing method of copolymer resin emulsion The said copolymer resin emulsion can be manufactured in accordance with the method currently disclosed by international publication 2004/016440, for example.
In producing a copolymer resin emulsion, an emulsifier can be used as necessary to impart stability of the emulsion.
Examples of the emulsifier include anionic surfactants such as higher alcohol sulfates, alkylbenzene sulfonates, aliphatic sulfonates, alkyl diphenyl ether sulfonates, polyethylene glycol alkyl ester types, alkyl phenyl ether types, alkyl ethers. 1 type (s) or 2 or more types selected from the group which consists of nonionic surfactants, such as a type | mold, can be used.
The amount of the emulsifier used is not particularly limited, but is preferably the minimum amount in consideration of the water resistance of the resin.

In producing the copolymer resin emulsion, a polymerization initiator may be used as necessary.
Polymerization initiators include persulfates, hydrogen peroxide, organic hydroperoxides, water-soluble initiators such as azobiscyanovaleric acid, oil-soluble initiators such as azobisisobutyronitrile and benzoyl peroxide, or reducing agents. Is used in combination with a redox initiator. There is no restriction | limiting in particular about the usage-amount of a polymerization initiator, Although what is necessary is just to follow a well-known technique, Usually, 0.1-10 mass parts with respect to 100 mass parts of vinyl monomers, Preferably it is about 0.1-5 mass parts. It is.

Further, when producing a copolymer resin emulsion, a molecular weight modifier (chain transfer agent) may be used as necessary. Examples of molecular weight regulators include mercaptans such as octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, low molecular halogen compounds, and the like.
The copolymer resin emulsion is prepared by neutralization with a base. Although the neutralizing agent in that case can be selected suitably, it is preferable to use aqueous ammonia. Aqueous ammonia can easily be detached at a relatively low temperature, so that the water resistance can be obtained in a short time after the heat-sensitive recording layer is formed.

  The intermediate layer uses water as a medium, and the intermediate layer coating solution obtained by mixing and stirring the water-based ultraviolet absorbing polymer, water-based acrylic polymer, polyvinyl alcohol, and optionally added pigments and various auxiliary agents, is used as the heat-sensitive recording layer. It can be obtained by coating and drying on top.

  Examples of the pigment contained in the intermediate layer include inorganic pigments such as calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, amorphous silica, synthetic mica, aluminum hydroxide, barium sulfate, talc, kaolin, clay, and calcined kaolin. And organic pigments such as nylon resin filler, urea / formalin resin filler, and raw starch particles.

  Of these, kaolin or aluminum hydroxide is preferable because it has a small decrease in barrier properties against chemicals such as plasticizers and oils, and also a small decrease in recording density.

  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, fluorescent dyes, colored dyes, release agents, antioxidants and the like. The usage-amount of auxiliary agent can be suitably set from a wide range.

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

The coating amount of the intermediate layer coating solution is 0.5 to 5.0 g / m ² , preferably 0.8 to 3.5 g / m ² , more preferably 1.0 to 2.5 g / m ^{2 in} terms of dry weight. Degree.

When the dry weight is in the range of 0.5 to 5.0 g / m ² , a heat-sensitive recording material excellent in recording sensitivity, light resistance, and recorded image storage stability can be obtained.

  Various known materials can be used as the leuco dye and the colorant contained in the heat-sensitive recording layer of the present invention. Specific examples of the leuco dye include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide and 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl). ) -6-dimethylaminophthalide, blue coloring dyes such as 3-diethylamino-7-dibenzylamino-benzo [a] fluorane, 3- (N-ethyl-Np-tolyl) amino-7-N- Green coloring dyes such as methylanilinofluorane, 3-diethylamino-7-anilinofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino- Red coloring dyes such as 6-methyl-7-chlorofluorane and 3-diethylamino-6,8-dimethylfluorane; Ru-N-isoamyl) amino-6-methyl-7-anilinofluorane, 3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl -7-anilinofluorane, 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 3-di (n-pentyl) amino-6-methyl-7-anilinofluorane, 3-di (n-butyl) amino-7- (o-fluorophenylamino) fluorane, 3- (N-ethyl-p-toluidino) -6-methyl-7-anilinofluorane, 3- (N-ethyl) Black coloring dyes such as -N-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3,3-bis [1- ( 4- Toxiphenyl) -1- (4-dimethylaminophenyl) ethylene-2-yl] -4,5,6,7-tetrachlorophthalide, 3-p- (p-dimethylaminoanilino) anilino-6-methyl -7-chlorofluorane, 3-p- (p-chloroanilino) anilino-6-methyl-7-chlorofluorane, 3,6-bis (dimethylamino) fluorene-9-spiro-3 '-(6'- And a dye having an absorption wavelength in the near infrared region such as (dimethylamino) phthalide. Of course, it is not limited to these, Moreover, it is also possible to use 2 or more types together.

Specific examples of the colorant include, for example, 4,4′-dihydroxydiphenylmethane, 4,4′-isopropylidenediphenol (bisphenol A), hydroquinone, 4,4′-cyclohexylidene bisphenol, 4,4 ′-( 1,3-dimethylbutylidene) bisphenol, 2,2-bis (4-hydroxyphenyl) -4-methyl-pentane, 4,4′-dihydroxydiphenyl sulfide, 4,4′-dihydroxydiphenyl sulfone, 2,4 ′ -Dihydroxydiphenylsulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxy-4'-allyloxydiphenylsulfone, 4-hydroxy-4'-benzyloxydiphenylsulfone, 2,4-bis (phenylsulfonyl) phenol 2,2 ′-[4- (4-hydroxyphene Rusulfonyl) phenoxy] diethyl ether, 1,3,3-trimethyl-1- (p-hydroxyphenyl) -6-hydroxyindane, 4-hydroxy-4'-methoxydiphenylsulfone, 4-hydroxy-4'-isopropoxy Diphenylsulfone, 4-hydroxy-3 ′, 4′-trimethylenediphenylsulfone, 4-hydroxy-3 ′, 4′-tetramethylenediphenylsulfone, 3,4-dihydroxy-4′-methyldiphenylsulfone, bis (3- Allyl-4-hydroxyphenyl) sulfone, 1,3-di [2- (4-hydroxyphenyl) -2-propyl] benzene, hydroquinone monobenzyl ether, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, 4 -Tolyl hydroxybenzoate, p-hydroxy-N- 2-Phenoxyethyl) benzenesulfonamide, 1,8-bis (4-hydroxyphenylthio) -3,6-dioxa-octane, (4-hydroxyphenylthio) acetic acid-2- (4-hydroxyphenylthio) ethyl ester , Novolak-type phenol resins, phenolic compounds such as phenol polymers, N- (p-tolylsulfonyl) carbamoyl acid-p-cumylphenyl ester, 4,4′-bis (Np-tolylsulfonylaminocarbonylamino) Diphenylmethane, Np-tolylsulfonyl-N′-p-butoxycarbonylphenylurea, Np-tolylsulfonyl-N′-phenylurea, Np-tolylsulfonyl-N′-3- (p-tolylsulfonyloxy) ) Having a —SO ₂ NH— bond in the molecule such as phenylurea, 4 , 4′-bis [(4-methyl-3-phenoxycarbonylaminophenyl) ureido] diphenylsulfone, zinc p-chlorobenzoate, zinc 4- [2- (p-methoxyphenoxy) ethyloxy] salicylate, 4- [3 Examples include zinc salts of aromatic carboxylic acids such as zinc (p-tolylsulfonyl) propyloxy] salicylate and zinc 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] salicylate. Of course, it is not limited to these, Moreover, it is also possible to use 2 or more types together.

  The amount of the leuco dye and the colorant to be used is appropriately selected according to the type of leuco dye or colorant to be used, and is not particularly limited. A colorant of about 1000% by mass, preferably about 100 to 500% by mass is used.

  The heat-sensitive recording layer may contain a storability improving agent for increasing the storage stability of the recorded image and a sensitizer for increasing the recording sensitivity. Specific examples of such preservability improvers include, for example, 2,2′-methylenebis (4-methyl-6-tert-butylphenol), 4,4′-thiobis (2-methyl-6-tert-butylphenol), 4, 4′-butylidenebis (6-tert-butyl-m-cresol), 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,1,3-tris (2 -Methyl-4-hydroxy-5-cyclohexylphenyl) butane, 2,2-bis (4-hydroxy-3,5-dibromophenyl) propane, 2,2-bis (4-hydroxy-3,5-dimethylphenyl) Hindered phenol compounds such as propane, 1,4-diglycidyloxybenzene, 4,4′-diglycidyloxydiphenylsulfone, Jiruokishi -4 '- (2-methyl-glycidyloxy) diphenylsulfone, diglycidyl terephthalate, cresol novolac type epoxy resin, phenol novolak type epoxy resins, epoxy compounds such as bisphenol A type epoxy resins. Of course, it is not limited to these, Moreover, it is also possible to use 2 or more types together.

  Specific examples of the sensitizer include, for example, stearamide, methylenebisstearate, dibenzyl terephthalate, benzyl p-benzyloxybenzoate, 2-naphthylbenzyl ether, m-terphenyl, 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-chlorophenoxy) ) Ethane, 1,2-diphenoxyethane, 1- (4-methoxyphenoxy) -2- (3-methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p-acetoluidide P-acetophenetide, N-acetoacetyl-p-toluidine, (Β-biphenylethoxy) benzene, p-di (vinyloxyethoxy) benzene, 1-isopropylphenyl-2-phenylethane, oxalic acid di-p-chlorobenzyl ester, oxalic acid di-p-methylbenzyl ester, oxalic acid Examples thereof include dibenzyl ester. Of course, it is not limited to these, Moreover, it is also possible to use 2 or more types together.

  Although the usage-amount of these preservatives and a sensitizer is not specifically limited, Generally it is about 50-400 mass% with respect to the total amount of colorant solids.

  In the heat-sensitive recording layer, if necessary, kaolin, calcium carbonate, amorphous silica, titanium oxide, aluminum hydroxide, calcined kaolin, zinc oxide and other pigments, zinc stearate, calcium stearate and other lubricants, and fluorescent dyes A surfactant or the like can also be added.

  The heat-sensitive recording layer generally uses water as a dispersion medium, and uses a cellulose-based polymer material or a water-soluble polymer such as polyvinyl alcohol as a dispersant. In water, an ultrasonic wave, a ball mill, a sand mill, a high-speed jet mill, a roller mill, a sand grinder After dispersing the leuco dye, the colorant and, if necessary, the sensitizer, using a disperser such as a nanomizer or attritor, the adhesive and the pigment dispersed in the predetermined particle diameter are dispersed. The heat-sensitive recording layer coating solution prepared by addition is formed by coating and drying on a support.

  The method for applying the thermal recording layer coating liquid is not particularly limited, and conventionally known methods such as air knife coating, varibar blade coating, pure blade coating, gravure coating, rod blade coating, short dwell coating, curtain coating, die coating, etc. Any of these coating methods can be employed.

The coating amount of the heat-sensitive recording layer coating solution, 1 to 15 g / ^{m 2} by dry weight, and preferably from 2 to 10 g / ^{m 2,} more preferably 3 to 7 g / ^{m 2} approximately.

  In the heat-sensitive recording material of the present invention, a protective layer is provided on the intermediate layer in order to suppress the generation of head wrinkles, improve the storage stability, and improve the running property during recording.

  Examples of the adhesive in the protective layer coating liquid include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, casein, polyvinyl alcohol, carboxy-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, Diisobutylene / maleic anhydride copolymer salt, monovalent salt of styrene / maleic anhydride copolymer, monovalent salt of ethylene / acrylic acid copolymer, monovalent salt of styrene / acrylic acid copolymer And water-dispersible adhesives such as vinyl acetate latex, styrene / butadiene latex, acrylic latex, and urethane latex.

  In particular, in order to impart barrier properties to various solvents, it is preferable to use a water-based acrylic polymer and polyvinyl alcohol in combination with the intermediate layer. Moreover, 30-80 mass% is contained with respect to the total solid content of a protective layer as a total amount of a water-based acrylic polymer and polyvinyl alcohol, and polyvinyl alcohol is contained at 20-99 mass% with respect to the total solid content of the water-based acrylic polymer. And found that the effect is more prominent.

  Furthermore, it is an emulsion of a copolymer resin having a solubility parameter of 12.0 or more including (meth) acrylonitrile and a vinyl monomer copolymerizable therewith, and the vinyl monomer having a carboxyl group in the total solid content of the copolymer resin. It has been found that when a water-based acrylic polymer having at least one kind of 1 to 10% by mass is used, not only the barrier property is improved, but also the strength against water is increased and a strong water-resistant coating film strength can be imparted.

  When the modified polyvinyl alcohol is used as the polyvinyl alcohol, a curing agent such as glyoxal, dimethylol urea, glycidyl ether of polyhydric alcohol, aldehyde compound, epichlorohydrin modified product, zirconium ammonium carbonate or the like may be used. However, when a curing agent is used, there are background discoloration of the thermal recording paper over time and environmental problems.

  Therefore, it is preferable to use fully saponified polyvinyl alcohol or partially saponified polyvinyl alcohol. When at least one of fully saponified polyvinyl alcohol or partially saponified polyvinyl alcohol is used, it is usually difficult to obtain a water-resistant coating film strength, but the solubility includes (meth) acrylonitrile and a vinyl monomer copolymerizable therewith as an aqueous acrylic polymer. When the emulsion is a copolymer resin having a parameter of 12.0 or more, and an aqueous acrylic polymer in which at least one vinyl monomer having a carboxyl group is 1 to 10% by mass in the total solid content of the copolymer resin is used. Therefore, a water-resistant coating film having no problem can be obtained due to the water resistance of a strong water-based acrylic polymer.

  The protective layer uses water as a medium, and the protective layer coating solution obtained by mixing and stirring the above-mentioned adhesive, and optionally added pigments and various auxiliary agents, is applied onto the intermediate layer and dried. Obtainable.

  Examples of the pigment include inorganic pigments such as calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, amorphous silica, synthetic mica, aluminum hydroxide, barium sulfate, talc, kaolin, clay, calcined kaolin, nylon resin filler, urea -Organic pigments such as formalin resin filler and raw starch particles.

  Of these, kaolin or aluminum hydroxide is preferable because it has a small decrease in barrier properties against chemicals such as plasticizers and oils, and also a small decrease in recording density.

  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, fluorescent dyes, colored dyes, release agents, antioxidants and the like. The usage-amount of auxiliary agent can be suitably set from a wide range.

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

The coating amount of the protective coating solution is about 0.5 to 5.0 g / m ² , preferably 0.8 to 3.5 g / m ² , more preferably about 1.0 to 3.0 g / m ² by dry weight. It is.

When the dry weight is in the range of 0.5 to 5.0 g / m ² , a thermosensitive recording material excellent in recording sensitivity, storability of recorded images, and print recording characteristics can be obtained.

  In the present invention, an undercoat layer can be provided between the support and the heat-sensitive recording layer for the purpose of imparting excellent barrier properties and improving recording sensitivity.

  The undercoat layer comprises at least one selected from the group consisting of oil-absorbing pigments, fine hollow particles and thermally expandable particles having an oil absorption of 70 ml / 100 g or more, particularly about 80 to 150 ml / 100 g, and an adhesive as a main component. It is formed by applying and drying a coating liquid on a support. Here, the oil absorption is a value determined according to the method of JISK 5101-2004.

  Various types of oil-absorbing pigments can be used. Specific examples include inorganic pigments such as calcined kaolin, amorphous silica, light calcium carbonate, and talc. The average particle size of these oil-absorbing pigments (50% value by laser diffraction particle size distribution, measuring device: trade name: SALD2000, manufactured by Shimadzu Corporation) is about 0.01 to 5 μm, particularly about 0.02 to 3 μm. Is preferred.

  The amount of the oil-absorbing pigment used can be selected from a wide range, but generally it is preferably 2 to 90% by mass, particularly preferably about 5 to 85% by mass, based on the total solid content of the undercoat layer.

  Examples of the fine hollow particles include 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. Here, the hollowness is a value obtained by (d / D) × 100. In the formula, d represents the inner diameter of the minute hollow particles, and D represents the outer diameter of the minute hollow particles. The average particle diameter of the fine hollow particles is preferably about 50 to 10 μm, particularly about 1 to 3 μm, based on a 50% value based on laser diffraction particle size distribution, measuring device: trade name: SALD2000, manufactured by Shimadzu Corporation.

  The amount of the fine hollow particles used can be selected from a wide range, but generally it is preferably 2 to 90% by mass, particularly preferably about 5 to 70% by mass, based on the total solid content of the undercoat layer.

  When the oil-absorbing inorganic pigment is used in combination with the fine hollow particles, the oil-absorbing inorganic pigment and the fine hollow particles are used within the above-mentioned use amount range, and the total amount of the oil-absorbing inorganic pigment and the organic hollow particles is the entire undercoat layer. It is preferable that it is 5-95 mass% with respect to solid content, especially about 10-92 mass%.

  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. Is mentioned. Examples of the low boiling point hydrocarbon include ethane and propane.

  The amount of the heat-expandable particles can be selected from a wide range, but generally it is preferably 1 to 80% by mass, particularly preferably about 2 to 70% by mass, based on the total solid content of the undercoat layer.

  Further, as the adhesive, an adhesive used for the heat-sensitive recording layer can be used as appropriate, and starch, various polyvinyl alcohols, styrene-butadiene copolymers and the like are particularly preferable.

  The use ratio of the adhesive can be selected within a wide range, but generally it is preferably used in an amount of about 2 to 30% by mass, particularly about 3 to 25% by mass, based on the total solid content of the undercoat layer.

  When forming the undercoat layer, two or more coating layers may be laminated and formed. By laminating two or more layers, the air permeability during the formation of the heat-sensitive recording layer can be increased, and the barrier properties when the intermediate layer and the protective layer are formed are improved. In the case of the same coating amount, the above effect is greater when the undercoat layer is formed with two layers than with one layer.

The coating amount of the undercoat layer coating solution is preferably about 3 to 20 g / m ² by dry weight, and preferably about 5 to 16 g / m ² .

  The method for applying the coating solution for the undercoat layer is not particularly limited, and for example, known means such as air knife coating, varibar blade coating, pure blade coating, rod coating, short dwell coating, curtain coating, die coating, etc. may be used. it can.

  Examples of the support used in the heat-sensitive recording material of the present invention include paper (neutral paper, acid paper), coated paper coated with pigment, latex, etc. on the surface, and synthetic paper having a multilayer structure made of polyolefin resin. , A plastic film, or a composite sheet thereof.

  When producing the heat-sensitive recording material of the present invention, a smoothing process such as supercalendering after forming each layer, and an adhesive layer and a barrier layer on the back surface of the support may be provided as necessary. Various known techniques in the heat-sensitive recording material production field such as printing or perforating the heat-sensitive recording material of the present invention can be added as necessary.

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

Example 1
-Preparation of coating solution for undercoat layer Dispersion obtained by dispersing 85 parts of calcined kaolin (trade name: Ansilex, Engelhard, Inc., oil absorption 90 ml / 100 g) in 200 parts of water (average particle size: 0.00). 6 μm) and 40 parts of a styrene-butadiene copolymer emulsion (solid content concentration 50%) and 50 parts of a 10% aqueous solution of oxidized starch were mixed and stirred to obtain a coating solution for an undercoat layer.

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

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

-Preparation of coating solution for heat-sensitive recording layer 20 parts of solution A, 50 parts of solution B, 10 parts of 50% dispersion of aluminum hydroxide (trade name: Hygielite H-42M, manufactured by Showa Denko KK), polyvinyl alcohol (trade name) : PVA-110, polymerization degree 1000, manufactured by Kuraray Co., Ltd.) A composition comprising 50 parts of a 10% aqueous solution was mixed and stirred to obtain a thermal recording layer coating solution.

-Preparation of coating solution for intermediate layer 20 parts of 50% dispersion of kaolin (trade name: UW-90, manufactured by Engelhard), copolymer resin (copolymerization component: (meth) acrylonitrile / (meth) acrylic acid alkyl / (Meth) acrylic acid 2-hydroxyethyl / (meth) acrylic acid / (meth) acrylamide, ratio of (meth) acrylic acid: 5% by mass with respect to the total mass of the copolymer resin, solubility parameter: 12.8, average particle 40 parts of emulsion (trade name: Barrier Star OT1043Z-1, solid content concentration 25%, manufactured by Mitsui Chemicals), 50 parts of 10% aqueous solution of polyvinyl alcohol (trade name: PVA-110, supra), Water-based UV-absorbing polymer copolymerized with benzotriazole-based UV absorber (trade name: ULS-1635MH, solid content concentration 30%, UV in resin An intermediate layer coating solution was obtained by mixing and stirring 20 parts of a line-absorbing skeleton amount of 50% (manufactured by Yushi Kogyo Co., Ltd.).

-Preparation of coating liquid for protective layer 20 parts of 50% dispersion of kaolin (trade name: UW-90, manufactured by Engelhard), 40 parts of emulsion of copolymer resin (trade name: Barrier Star OT1043Z-1, supra) , 30 parts of a 10% aqueous solution of polyvinyl alcohol (trade name: PVA-110, supra) and 4 parts of zinc stearate (trade name: Hydrin Z-8-36, solid content concentration 36%, manufactured by Chukyo Yushi Co., Ltd.) The mixture was stirred to obtain a protective layer coating solution.

・ Preparation of thermosensitive recording material On one side of a 48 g / m ² base paper, the coating solution for the undercoat layer was applied and dried so that the coating amount after drying was 8.0 g / m ² , and then dried on the undercoat layer. The thermosensitive recording layer coating solution was applied and dried so that the amount of coating was 5.0 g / m ² . Coating amount after drying to heat-sensitive recording layer is coated and dried the intermediate layer coating liquid so that 2.0 g / m ^2, so that the coating amount after drying the intermediate layer is 2.0 g / m ² The protective layer coating solution was applied and dried. Thereafter, it was treated with a super calender to obtain a heat-sensitive recording material having a surface smoothness of 1000 to 4000 seconds with a Oken type smoothness meter.

Example 2
In the intermediate layer coating solution of Example 1, instead of 20 parts of a water-based UV-absorbing polymer copolymerized with a benzotriazole-based UV absorber (trade name: ULS-1635MH, supra), a benzotriazole-based UV absorber was co-polymerized. The same as Example 1 except that 40 parts of polymerized water-based UV absorbing polymer (trade name: New Coat UVA-1025W, solid content concentration 40%, UV absorbing skeleton amount in resin 10%, Shin-Nakamura Chemical Co., Ltd.) were used. A heat-sensitive recording material was obtained.

Example 3
In the intermediate layer coating liquid of Example 1, a benzophenone ultraviolet absorber was copolymerized instead of 20 parts of an aqueous ultraviolet absorber polymer (trade name: ULS-1635MH, supra) copolymerized with a benzotriazole ultraviolet absorber. The same procedure as in Example 1 was carried out except that 20 parts of an aqueous UV absorbing polymer (trade name: ULS-635MH, solid content concentration 30%, UV absorbing skeleton amount in the resin 50%, manufactured by Yushi Kogyo Co., Ltd.) were used. A heat-sensitive recording material was obtained.

Example 4
In place of the protective layer coating liquid of Example 1, 150 parts of a 30% dispersion of kaolin (trade name: UW-90, supra), acetoacetyl-modified polyvinyl alcohol (trade name: Goosephimer Z-200, front 1) 600 parts of 10% aqueous solution, 25 parts of zinc stearate (trade name: Hydrin Z-8-36, solid concentration 36%, manufactured by Chukyo Yushi Co., Ltd.), 5% aqueous solution of aldehyde compound (trade name: Glyoxal) 1 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the protective layer coating liquid obtained by mixing and stirring the parts was used.

Comparative Example 1
In the coating liquid for intermediate layer of Example 1, the same procedure as in Example 1 was conducted except that a water-based ultraviolet absorbing polymer (trade name: ULS-1635MH, supra) copolymerized with a benzotriazole-based ultraviolet absorber was not used. A heat-sensitive recording material was obtained.

Comparative Example 2
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that polyvinyl alcohol (trade name: PVA-110, supra) was not used in the intermediate layer coating solution of Example 1.

Comparative Example 3
In the intermediate layer coating liquid of Example 1, 10% of polyvinyl alcohol (trade name: PVA-110, supra) was used without using a copolymer resin emulsion (trade name: Barrier Star OT1043Z-1, supra). A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 100 parts of the aqueous solution was used.

Comparative Example 4
In the intermediate layer coating solution of Example 1, 15 parts of a copolymer resin emulsion (trade name: Barrier Star OT1043Z-1, supra), 10% aqueous solution of polyvinyl alcohol (trade name: PVA-110, supra). A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 20 parts were used.

Comparative Example 5
In the intermediate layer coating solution of Example 1, 20 parts of a copolymer resin emulsion (trade name: Barrier Star OT1043Z-1, supra), 10% aqueous solution of polyvinyl alcohol (trade name: PVA-110, supra) 100 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the parts were used.

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

1. Recording sensitivity 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). (Manufactured by Macbeth).

2. Light resistance Using a xenon weather meter (manufactured by Suga Test Instruments Co., Ltd.), the thermal recording medium was irradiated for 8 hours at a black panel temperature of 63 ° C., a humidity of 50% RH, and an irradiation illuminance of 390 W / m ² in a wavelength range of 300 to 700 nm. The density of the part was measured with a blue filter of a Macbeth densitometer (trade name: RD-914, manufactured by Macbeth). Furthermore, the blank paper portion was visually observed and evaluated as follows.
○: No discoloration or very thin discoloration, but there is no practical problem without impairing product aesthetics.
(Triangle | delta): Color development is somewhat conspicuous, product aesthetics are impaired, and there is a problem in practical use.
X: Strong discoloration, greatly impairs product aesthetics, and has practical problems.

3. Ethanol barrier property Ethanol was applied and left on the heat-sensitive recording material, and the state of the heat-sensitive recording material after drying was visually observed and evaluated as follows.
○: There is no color development or a slight color development, but there is no practical problem.
Δ: A colored portion is conspicuous, and a part of the recorded contents cannot be visually recognized, which is problematic in practical use.
×: Color development was observed in most part, the recorded contents could not be visually recognized, and there was a problem in practical use.

4). Polyethylene glycol barrier property A 50% polyethylene glycol 400 solution was applied and left on the heat-sensitive recording material, and the condition of the heat-sensitive recording material after drying was visually observed and evaluated as follows.
◯: There was no fading of the recorded image, or a slight fading of the recorded image was observed, but the recorded contents could be visually confirmed, and there was no practical problem.
Δ: Fading of the recorded image is seen, part of the recorded content cannot be visually recognized, and there is a problem in practical use.
X: The recorded image is severely faded, the recorded content cannot be visually recognized, and there is a problem in practical use.

5). Thermal recording property-presence or absence of head residue Using a label printer (trade name: HP3600, manufactured by Teraoka Seiko Co., Ltd.), each thermal recording medium is colored at a printing speed of 45 mm / second and a set thermal head resistance value of 800Ω (thermal head resistance value of 617Ω). Then, 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.

Claims (6)

  In a heat-sensitive recording material obtained by sequentially laminating a heat-sensitive recording layer containing at least a leuco dye and a colorant, an intermediate layer, and a protective layer on a support, an aqueous ultraviolet absorbing polymer is added to the intermediate layer with a total solid content. 1 to 60% by mass of the aqueous acrylic polymer and polyvinyl alcohol as a total amount of the intermediate layer, and 30 to 90% by mass with respect to the total solid content of the intermediate layer. Wherein the polyvinyl alcohol is 30 to 99% by mass.   2. The heat-sensitive recording material according to claim 1, wherein the aqueous ultraviolet absorbing polymer is an aqueous ultraviolet absorbing polymer obtained by polymerizing a benzotriazole ultraviolet absorbing monomer or a benzophenone ultraviolet absorbing monomer. The water-based acrylic polymer is a copolymer resin emulsion, and the copolymer resin constituting the copolymer emulsion is:
(1) comprising (i) (meth) acrylonitrile and (ii) a vinyl monomer copolymerizable with (meth) acrylonitrile, and
(2) The solubility parameter is 12.0 or more,
The vinyl monomer (ii) contains at least one carboxyl group-containing vinyl monomer, and the proportion of the carboxyl group-containing vinyl monomer is 1 to 10 mass in the total mass of the copolymer resin. The heat-sensitive recording material according to claim 1 or 2, wherein the heat-sensitive recording material is%.   As a protective layer adhesive, the aqueous acrylic polymer and polyvinyl alcohol are contained in a total amount of 30 to 80% by mass based on the total solid content of the protective layer, and the polyvinyl alcohol is 20 to 99 based on the total solid content of the aqueous acrylic polymer. The heat-sensitive recording material according to claim 1, wherein the heat-sensitive recording material is a mass%. The water-based acrylic polymer contained as the protective layer adhesive is a copolymer resin emulsion, and the copolymer resin constituting the copolymer emulsion is:
(1) comprising (i) (meth) acrylonitrile and (ii) a vinyl monomer copolymerizable with (meth) acrylonitrile, and
(2) The solubility parameter is 12.0 or more,
The vinyl monomer (ii) contains at least one carboxyl group-containing vinyl monomer, and the proportion of the carboxyl group-containing vinyl monomer is 1 to 10 mass in the total mass of the copolymer resin. The heat-sensitive recording material according to claim 1, which is%.   The heat-sensitive recording material according to any one of claims 1 to 5, wherein the heat-sensitive recording layer, the intermediate layer, and the protective layer do not contain a curing agent.