Heat-sensitive recording body

Abstract

The purpose of the present invention is to provide a heat-sensitive recording body having excellent transparency.　A heat-sensitive recording body according to the present invention is characterized by comprising a thermal layer that contains a fatty acid-based wax. The fatty acid-based wax is preferably a solubilized fatty acid-based wax and / or a fatty acid-based wax in the form of an emulsion. Further, the fatty acid-based wax is preferably a solubilized fatty acid-based wax. Further, the solubilized fatty acid-based wax preferably contains a solubilizing agent.

Description

Thermal recording medium

[0001] The present invention relates to a thermosensitive recording medium.

[0002] Thermal recording media develop color through a chemical reaction when heated by a thermal head or the like, resulting in a recorded image. They are used in a wide range of applications, including as recording media for facsimiles, automatic ticket vending machines, and scientific measuring instruments, as well as for thermal recording labels and receipt paper for POS systems in retail stores and the like.

[0003] In particular, when using thermal recording media as labels for food containers such as bento boxes or as food packaging films, there is a problem that the contents cannot be seen if an opaque thermal recording media is used, so there is a demand for thermal recording media with excellent transparency so that the contents can be clearly seen.

[0004] As a thermosensitive recording medium with excellent transparency, for example, a thermosensitive recording medium has been proposed in which the thermosensitive recording layer contains a dispersant having a carboxyl group and a crosslinking agent whose main component is an epichlorohydrin-modified polyamide polyamine resin or an organic compound containing an oxazoline group, and it has also been disclosed that transparency can be further improved by using a material with a small particle size (see, for example, Patent Document 1).

[0005] International Publication No. 2021 / 106076

[0006] However, research into thermosensitive recording media with excellent transparency has not yet been sufficient, and there is room for further research.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a thermosensitive recording medium having excellent transparency.

[0008] As a result of extensive research to solve the above problems, the present inventors have found that by incorporating a fatty acid wax into the thermal layer, it is possible to provide a thermosensitive recording medium with excellent transparency. The present invention was completed based on these findings.

[0009] That is, the present invention provides a thermosensitive recording medium having a thermal layer containing a fatty acid-based wax. The thermosensitive recording medium has excellent transparency due to the thermal layer containing a fatty acid-based wax.

[0010] The fatty acid wax is preferably a solubilized fatty acid wax and / or an emulsion of fatty acid wax, which can further improve transparency.

[0011] The fatty acid wax is preferably a solubilized fatty acid wax, which can further improve transparency.

[0012] The solubilized fatty acid wax preferably contains a solubilizer, which can further improve transparency.

[0013] The thermal layer preferably contains a surfactant and / or a solvent, which can further improve transparency.

[0014] The thermal layer preferably further contains a wax other than the fatty acid wax and having an average particle size of 1 μm or less. By having such a configuration, transparency can be further improved.

[0015] The content of the fatty acid wax is preferably 0.1% by mass or more and 5% by mass or less relative to 100% by mass of the dry mass of the thermal layer, which can further improve transparency.

[0016] The present invention also provides a method for producing a thermal recording medium, which comprises the steps of preparing a thermal layer coating material using a solubilized fatty acid wax and / or an emulsion of fatty acid wax, and applying and drying the thermal layer coating material to form a thermal layer. The thermal recording medium produced by this method has excellent transparency.

[0017] According to the present invention, a thermosensitive recording medium having excellent transparency can be provided.

[0018] 1 is a schematic cross-sectional view showing one embodiment of a thermosensitive recording medium of the present invention.

[0019] [Thermal Recording Medium] The thermal recording medium of the present invention is a thermal recording medium having a thermal layer containing a fatty acid-based wax.

[0020] The thermosensitive recording medium of the present invention may include a substrate and an anchor layer. When the thermosensitive recording medium of the present invention includes a substrate and an anchor layer, the thermosensitive recording medium of the present invention preferably includes the substrate, the anchor layer, and the thermal layer in this order. The thermosensitive recording medium of the present invention may also include layers other than the above-mentioned layers. Examples of layers other than the above-mentioned layers include a backcoat layer, an intermediate layer, and a topcoat layer.

[0021] Hereinafter, an embodiment of the thermosensitive recording medium of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the following embodiments.

[0022] FIG. 1 is a schematic cross-sectional view showing one embodiment of the thermosensitive recording medium of the present invention.

[0023] As shown in FIG. 1, the thermosensitive recording medium 1 of this embodiment comprises a substrate 2, an anchor layer 3, and a thermal layer 4 in this order.

[0024] (Substrate) In this embodiment, the substrate 2 functions as a support for the thermal recording medium 1. The substrate 2 may be, for example, a transparent synthetic resin film. Examples of the transparent synthetic resin film include polypropylene film, polyethylene terephthalate film, polystyrene film, and polycarbonate film. The transparent synthetic resin film may be a biaxially oriented film or a heat-sealable film. The substrate 2 may be a single layer or a multi-layer. The thickness of the substrate 2 is preferably, for example, 5 μm to 150 μm, and more preferably 10 μm to 100 μm. A thickness within the above range is preferred because of its excellent coatability and transparency. Among the substrates described above, biaxially oriented polypropylene (OPP) film and heat-sealable polyethylene terephthalate (HS-PET) film are suitable for use from the viewpoints of improving transparency and providing functionality.

[0025] (Anchor Layer) In this embodiment, the anchor layer 3 functions as a layer that enhances adhesion between the substrate 2 and the thermal layer 4. The material for forming the anchor layer 3 is not particularly limited, and only a binder can be used. The anchor layer 3 may also contain other components, such as a pigment. Furthermore, if the anchor layer is not required, it may not be provided.

[0026] The binder contained in the anchor layer 3 is not particularly limited, and examples thereof include modified styrene-acrylic resin, acrylic emulsion, styrene-acrylic copolymer, modified styrene-butadiene latex, styrene-butadiene copolymer (SBR), acrylic-butadiene-styrene copolymer, vinyl acetate resin, vinyl acetate-acrylic acid copolymer, polyurethane resin, etc. Here, acrylic means acrylic acid (salt) and acrylic ester, and acrylic acid (salt) means acrylic acid and acrylic acid salt.

[0027] The binder is preferably one or more selected from the group consisting of modified styrene-acrylic resin, acrylic emulsion, styrene-acrylic copolymer, acrylic-butadiene-styrene copolymer, and vinyl acetate-acrylic acid copolymer, and more preferably one or more selected from the group consisting of modified styrene-acrylic resin and acrylic emulsion. Among these, when the modified styrene-acrylic resin is used, modified styrene-acrylic acid (salt) resin is preferred. These binders can be used alone or in combination of two or more.

[0028] The salt of the acrylic acid salt is not particularly limited, and examples thereof include ammonium salts such as ammonia; alkanolamine salts such as triethanolamine, diethanolamine, and monoethanolamine; alkylamine salts such as methylamine salt, ethylamine salt, diethylamine salt, and triethylamine salt; polyamine salts such as diethyleneamine salt and diethylenetriamine salt; alkali metal salts such as lithium, sodium, and potassium; alkaline earth metal salts such as magnesium and calcium; and polyvalent metal salts such as zinc and iron. Among these, ammonium salts are particularly preferred. These salts can be used alone or in combination of two or more.

[0029] Other binders that can be used include, for example, polyvinyl alcohol, starch and derivatives thereof, cellulose derivatives such as methoxycellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose, water-soluble polymers such as sodium polyacrylate, polyvinylpyrrolidone, acrylamide-acrylic acid ester copolymers, acrylamide-acrylic acid ester-methacrylic acid terpolymers, alkali salts of styrene-maleic anhydride copolymers, alkali salts of isobutylene-maleic anhydride copolymers, polyacrylamide, sodium alginate, gelatin, and casein. These binders can be used alone or in combination of two or more.

[0030] The content of the binder is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 50% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, relative to 100% by mass of the dry mass of the anchor layer 3. The content of the binder may be substantially 100% by mass, relative to 100% by mass of the dry mass of the anchor layer 3. When the content of the binder is within the above range, this is preferable from the viewpoint of further enhancing the adhesion between the substrate 2 and the thermal layer 4.

[0031] In this specification, the term "dry mass" refers to the mass of non-volatile components (solids) obtained by drying to remove solvents (volatile components) such as water contained in the paint and its raw materials.

[0032] The coating amount (dry mass) of the anchor layer 3 is preferably 0.3 g / m 2 ~5.0g / m 2 and more preferably 0.5 g / m 2 ~2.0 g / m 2 is.

[0033] The thickness of the anchor layer 3 is, for example, preferably 0.3 μm to 5.0 μm, and more preferably 0.5 μm to 2.0 μm.

[0034] In the present embodiment, when the coating amount and thickness of the anchor layer 3 are within the above ranges, the adhesion between the substrate 2 and the thermal layer 4 tends to be further improved, which is preferable.

[0035] In this embodiment, when the anchor layer 3 is provided, the material for forming the anchor layer 3 can be selected depending on the type of the substrate 2. For example, when a polypropylene film is used as the substrate 2, the anchor layer 3 preferably contains a modified styrene-acrylic resin as a binder, more preferably a modified styrene-acrylic acid (salt) resin, and even more preferably a modified styrene-acrylic acid (ammonium salt) resin. Furthermore, from the viewpoints of improving transparency and imparting functionality, the polypropylene film is particularly preferably a biaxially oriented polypropylene (OPP) film.

[0036] Furthermore, when a polyethylene terephthalate film is used as the substrate 2, the anchor layer 3 preferably contains an acrylic emulsion as a binder. Examples of the acrylic emulsion include a commercially available material such as "AQUENCE EPIX BC AD81B" (manufactured by Henkel Japan Co., Ltd.). Furthermore, from the viewpoints of improving transparency and providing functionality, the polyethylene terephthalate film is particularly preferably a heat-sealable polyethylene terephthalate (HS-PET) film. The combination of the substrate 2 and anchor layer 3 is preferred because it tends to further improve adhesion between the substrate 2 and the thermal layer 4 and further improve the transparency of the thermal recording medium 1.

[0037] (Thermal Layer) In this embodiment, the thermal layer 4 functions as a layer that develops color when heated. The thermal layer 4 contains at least a fatty acid wax.

[0038] It is preferable to use materials with a small average particle size in order to improve the transparency of the thermal recording medium 1. By using materials with a small average particle size, diffuse reflection of light caused by the particles is suppressed, which tends to improve the transparency of the thermal recording medium 1.

[0039] In this specification, the term "average particle size" refers to the particle size at 50% of the cumulative value in the particle size distribution measured by a laser diffraction / scattering method (D50, median diameter). Measurement of the average particle size by the laser diffraction / scattering method can be performed using, for example, a Microtrac-Bell product under the trade name "MT3300EX-II." Hereinafter, "average particle size" refers to the median diameter measured by the above method.

[0040] The fatty acid wax has the function of improving the transparency of the thermal recording medium. Specifically, when forming the thermal layer 4, the fatty acid wax penetrates into the voids between particles of other components and seals them, thereby suppressing diffuse reflection of light in the voids, which is thought to result in further improving the transparency of the thermal recording medium. Examples of the fatty acid wax include fatty acids, fatty acid salts, fatty acid amides, and fatty acid esters. These fatty acid waxes can be used alone or in combination of two or more.

[0041] Examples of the fatty acids include higher fatty acids having 10 to 22 carbon atoms. Examples of the higher fatty acids include higher saturated fatty acids having 10 to 22 carbon atoms, such as capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, and behenic acid; and higher unsaturated fatty acids having 10 to 22 carbon atoms, such as palmitoleic acid, oleic acid, elaidic acid, linoleic acid, and linolenic acid. These fatty acids may have a substituent. Examples of the substituent include a hydroxy group.

[0042] Examples of the fatty acid salts include salts obtained by neutralizing the fatty acids. Examples of the salts include alkali metal salts such as lithium, sodium, and potassium; alkaline earth metal salts such as magnesium and calcium; and polyvalent metal salts such as zinc and iron. Specific examples of the fatty acid salts include sodium stearate, potassium stearate, magnesium stearate, calcium stearate, zinc stearate, iron stearate, sodium oleate, potassium oleate, magnesium oleate, calcium oleate, zinc oleate, and iron oleate.

[0043] Examples of the fatty acid amides include amidation reaction products of the fatty acids with ammonium or amines. Examples of the amines include diamines such as ethylenediamine and hexamethylenediamine. Specific examples of the fatty acid amides include capric acid amide, lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, arachidic acid amide, behenic acid amide, palmitoleic acid amide, oleic acid amide, elaidic acid amide, linoleic acid amide, linolenic acid amide, N,N'-ethylenebis(stearic acid amide), and N,N'-hexamethylenebis(stearic acid amide).

[0044] Examples of the fatty acid esters include esterification products of the fatty acids with monohydric and / or polyhydric alcohols. Examples of the monohydric and / or polyhydric alcohols include monohydric alcohols such as ethanol and propanol, and polyhydric alcohols such as propylene glycol, glycerin, and sorbitol.

[0045] In this embodiment, the fatty acid wax is preferably a solubilized fatty acid wax and / or an emulsion-type fatty acid wax, and more preferably a solubilized fatty acid wax. In this specification, solubilized fatty acid wax means that it is soluble in the thermal layer or a coating material for the thermal layer. The use of the solubilized fatty acid wax and / or an emulsion-type fatty acid wax tends to improve the transparency of the thermal recording medium. In particular, the solubilized fatty acid wax is soluble in the thermal layer or a coating material for the thermal layer, which in turn tends to improve the transparency of the thermal recording medium.

[0046] The solubilized fatty acid wax may be soluble in the thermal layer or thermal layer coating material by itself, or may be soluble in the thermal layer or thermal layer coating material as a mixture of the fatty acid wax and a solubilizing agent. Examples of the solubilizing agent include surfactants, solvents, and solvents used in thermal layer coating materials. Examples of the solvent used in the thermal layer coating material include organic solvents and water, with water being preferred. When the solubilized fatty acid wax contains a solvent used in the thermal layer coating material, it may contain a portion of the solvent or the entire amount of the solvent. From the perspectives of ease of handling and ease of solubilization, the solubilized fatty acid wax preferably contains a fatty acid wax and a solubilizing agent. The solubilizing agent is preferably one or more selected from the group consisting of surfactants, solvents, and solvents used in thermal layer coating materials. Furthermore, the solubilizer preferably contains a surfactant and / or a solvent and a portion of the solvent in the thermal layer paint, and it is also preferable that the solubilizer contains a surfactant and / or a solvent but does not contain the solvent in the thermal layer paint.

[0047] The emulsion-like fatty acid wax is a compound that self-emulsifies the fatty acid wax, and may be a compound that disperses by itself in the solvent of the thermal layer paint to form an emulsion, or may be a compound that disperses in the solvent of the thermal layer paint with the aid of a surfactant or the like to form an emulsion. In this specification, the emulsion-like fatty acid wax refers to a fatty acid wax that forms a stable emulsion. Furthermore, forming a stable emulsion means that, for example, when left standing for 24 hours at room temperature and normal pressure, no changes in state such as separation or precipitation of components are observed, and the emulsion state can be maintained.

[0048] In this embodiment, the thermal layer 4 may contain components other than the fatty acid-based wax, such as dyes, color developers, fillers, binders, dispersants, crosslinkers, waxes other than the fatty acid-based wax (other waxes), surfactants, solvents, etc. It is preferable that the thermal layer 4 contains a surfactant and / or a solvent. The surfactant is not particularly limited, and any component that has the function of improving the solubility of the fatty acid-based wax may be used. Examples of the surfactant include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. These surfactants may be used alone or in combination of two or more.

[0049] Examples of the anionic surfactant include alkylbenzenesulfonic acid and / or its salt, alkylsulfonic acid and / or its salt, alkyl sulfate and / or its salt, and alkyl ether sulfate and / or its salt. Examples of the alkyl group contained in the anionic surfactant include alkyl groups having 10 to 22 carbon atoms. Examples of the alkyl group include saturated hydrocarbon groups and unsaturated hydrocarbon groups. The alkyl group may have a substituent. Examples of the substituent include a hydroxy group. Examples of the salt include ammonium salts such as ammonia; alkanolamine salts such as triethanolamine; alkali metal salts such as lithium, sodium, and potassium; alkaline earth metal salts such as magnesium and calcium; and polyvalent metal salts such as zinc and iron.

[0050] Examples of the nonionic surfactant include polyoxyethylene alkyl ethers, polyoxypropylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene alkyl esters, polyoxyethylene polyoxypropylene glycols, sorbitan alkyl esters, polyoxyethylene sorbitan alkyl esters, glycerin alkyl esters, polyoxyethylene glycerin alkyl esters, and polyoxyethylene hydrogenated castor oil. The alkyl group contained in the nonionic surfactant is not particularly limited, and examples include alkyl groups having 10 to 22 carbon atoms. Examples of the alkyl group include saturated hydrocarbon groups and unsaturated hydrocarbon groups. The alkyl group may have a substituent. Examples of the substituent include a hydroxy group.

[0051] The solvent is not particularly limited, and may be any component that functions to improve the solubility of the fatty acid wax. Examples of the solvent include glycol ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, and propylene glycol; ethers such as diisopropyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and 1,4-dioxane; alcohols such as methanol, ethanol, n-propanol, isopropanol, 2-ethylhexanol, and benzyl alcohol; and amines such as monoethanolamine, diethanolamine, and triethanolamine. Among these, from the viewpoints of ease of handling and solubilizing the fatty acid wax, the solvent is preferably one or more selected from the group consisting of glycol ethers, glycols, ethers, and alcohols, more preferably one or more selected from the group consisting of glycol ethers and glycols, and even more preferably glycol ethers. When the solvent is a glycol ether, diethylene glycol monobutyl ether is particularly preferred. These solvents can be used alone or in combination.

[0052] In this specification, compounds that fall under the category of fatty acid waxes and may also fall under other components such as surfactants and solvents are classified only as fatty acid waxes and not as other components. Compounds that do not fall under the category of fatty acid waxes and may also fall under surfactants and solvents are classified only as surfactants and not as solvents.

[0053] The average particle size of the fatty acid wax is preferably 1.0 μm or less. When the average particle size of the fatty acid wax is within the above range, the transparency of the thermosensitive recording medium 1 tends to be further improved, which is preferable.

[0054] The content of the fatty acid wax is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, based on 100% by mass of the dry mass of the thermal layer 4. The content of the fatty acid wax is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less, based on 100% by mass of the dry mass of the thermal layer 4. When the content of the fatty acid wax is within the above range, the transparency of the thermal recording medium 1 tends to be further improved, which is preferable.

[0055] In this specification, the term "content of fatty acid wax" refers to the total content of the dry mass of the fatty acid wax and the dry mass of the soluble agent when the fatty acid wax contains a solubilizer. When the fatty acid wax is in an emulsion state and contains a surfactant, the term refers to the content of the dry mass of the emulsion containing the surfactant.

[0056] In this embodiment, from the viewpoint of further improving the long-term water resistance of the thermal recording medium 1, the thermal layer 4 preferably contains a wax other than the fatty acid-based wax (other wax). Examples of waxes other than the fatty acid-based wax that can be used include polystyrene, polyethylene, and paraffin. Of these, from the viewpoint of further improving the long-term water resistance and transparency of the thermal recording medium 1, the wax other than the fatty acid-based wax is preferably one or more selected from the group consisting of polystyrene and polyethylene, and polystyrene is more preferred. These waxes can be used alone or in combination of two or more.

[0057] The average particle size of the wax other than the fatty acid wax is preferably 0.1 μm or more. The average particle size of the wax other than the fatty acid wax is preferably 1.0 μm or less, more preferably 0.6 μm or less, even more preferably 0.55 μm or less, even more preferably 0.4 μm or less, and particularly preferably 0.3 μm or less. When the average particle size of the wax other than the fatty acid wax is within the above range, the transparency of the thermal recording medium 1 tends to be further improved, which is preferable.

[0058] The content of waxes other than the fatty acid waxes is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, relative to 100% by mass of the dry mass of the thermal layer 4. The content of waxes other than the fatty acid waxes is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less, relative to 100% by mass of the dry mass of the thermal layer 4. When the content of waxes other than the fatty acid waxes is within the above range, the transparency of the thermal recording medium 1 tends to be further improved, which is preferable.

[0059] In this embodiment, the types of wax contained in the thermal layer 4 are, for example, preferably 1 to 5 types, more preferably 1 to 2 types, and even more preferably 2 types. When the types of wax contained are two, a particularly preferred combination is one each of fatty acid wax and polystyrene.

[0060] The ratio of the dry mass of the wax other than the fatty acid wax to the dry mass of the fatty acid wax (dry mass of wax other than the fatty acid wax / dry mass of fatty acid wax) when the dry mass of the fatty acid wax is taken as 1 is preferably 0.1 or more, more preferably 0.5 or more. Furthermore, the ratio of the dry mass of the wax other than the fatty acid wax to the dry mass of the fatty acid wax (dry mass of wax other than the fatty acid wax / dry mass of fatty acid wax) when the dry mass of the fatty acid wax is taken as 1 is preferably 10 or less, more preferably 5 or less, and even more preferably 2 or less. Furthermore, the ratio of the dry mass of the wax other than the fatty acid wax to the dry mass of the fatty acid wax (dry mass of wax other than the fatty acid wax / dry mass of fatty acid wax) when the dry mass of the fatty acid wax is taken as 1 is particularly preferably 1. When the ratio of the dry mass of the wax other than the fatty acid wax to the dry mass of the fatty acid wax is within the above range, the transparency and long-term water resistance of the thermosensitive recording medium 1 tend to be further improved, which is preferable.

[0061] The total wax content is preferably 0.2% by mass or more, more preferably 1% by mass or more, and even more preferably 1.5% by mass or more, based on 100% by mass of the dry mass of the thermal layer 4. The total wax content is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less, based on 100% by mass of the dry mass of the thermal layer 4. When the total wax content is within the above range, the transparency of the thermosensitive recording medium 1 tends to be further improved, which is preferable.

[0062] Examples of the dye include 3-dibutylamino-6-methyl-7-anilinofluoran, 3-(N-isobutyl-N-ethyl)amino-6-methyl-7-anilinofluoran, 3-(N-isopentyl-N-ethyl)amino-6-methyl-7-o-chloroanilinofluoran, 3-(N-ethyl-N-p-toluidino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isopentyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethoxypropyl-N-ethyl)amino-6-methyl-7-anilinofluoran, 3-(N-cyclohexyl-N-methyl)amino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-n-propyl)amino-6-methyl-7-anilinofluoran, 3-diethyl Examples of dyes that can be used include 3-diethylamino-6-methyl-7-p-toluidinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-8-methylfluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluoran, 3-diethylamino-7-(o-chloroanilino)fluoran, 3-diethylamino-7-chlorofluoran, 3-dibutylamino-6-methyl-7-bromofluoran, 3-dibutylamino-7-(o-chloroanilino)fluoran, 3-dipentylamino-6-methyl-7-anilinofluoran, 3-dimethylamino-5-methyl-7-methylfluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, and crystal violet lactone. These dyes can be used alone or in combination of two or more.

[0063] The average particle size of the dye is, for example, preferably 0.1 μm to 1.0 μm, more preferably 0.1 μm to 0.6 μm, even more preferably 0.1 μm to 0.55 μm, still more preferably 0.1 μm to 0.4 μm, and particularly preferably 0.1 μm to 0.3 μm. When the average particle size of the dye is within the above range, the transparency of the thermal recording medium 1 tends to be further improved, which is preferable.

[0064] The content of the dye is preferably 5% by mass or more and 50% by mass or less, more preferably 8% by mass or more and 35% by mass or less, and even more preferably 10% by mass or more and 25% by mass or less, relative to 100% by mass of the dry mass of the thermal layer 4.

[0065] Examples of the color developer include 4-hydroxyphenyl(4'-n-propoxyphenyl)sulfone, 3-[(3-phenylureido)phenyl]-4-methylbenzenesulfonate, N,N-di-[3-(p-toluenesulfonyloxy)phenyl]urea, 1,1-bis(p-hydroxyphenyl)cyclohexane, 1,1-bis(p-hydroxyphenyl)propane, 2,2-bis(p-hydroxyphenyl)propane, 2,2-bis(p-hydroxyphenyl)butane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 2,2'-methylenebis(4-chlorophenol), 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 2,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone, 4-hydroxy-4'-allyloxydiphenyl sulfone, bis(3-allyl-4-hydroxyphenyl)sulfone, poly(4-hydroxybenzoic acid), benzyl 4-hydroxybenzoate, 2,4-bis(phenylsulfonyl)phenol, α-{4-[(4-hydroxyphenyl)sulfonyl]phenyl}-ω-hydroxypoly(degree of polymerization n=1 to 7)(oxyethyleneoxyethyleneoxy-p-phenylenesulfonyl-p-phenylene)2,2-bis[(4-methyl-3-phenoxycarbonylaminophenyl)urea]diphenyl sulfone, 3,Examples of the usable surfactant include 5-bis(α-methylbenzyl)salicylic acid, bis[4-(n-octyloxycarbonylamino)zinc salicylate], 4,4'-bis(p-tolylsulfonylaminocarbonylamino)diphenylmethane, 4-hydroxybenzenesulfonanilide, 2'-(3-phenylureido)benzenesulfonanilide, N-(2-hydroxyphenyl)-2-[(4-hydroxyphenyl)thio]acetamide, N-(4-hydroxyphenyl)-2-[(4-hydroxyphenyl)thio]acetamide, 4-[[4-[4-[4-[[4-(1-methylethoxy)phenyl]sulfonylphenoxy]butoxy]phenyl]sulfonyl]phenol, 4-tert-butylphenol-formaldehyde polycondensate, N-(p-toluenesulfonyl)N'-(3-p-toluenesulfonyloxyphenyl)urea, and 1-phenyl-3-(4-methylphenylsulfonyl)urea. These color developers can be used alone or in combination of two or more.

[0066] The average particle size of the developer is, for example, preferably 0.1 μm to 1.0 μm, more preferably 0.1 μm to 0.6 μm, even more preferably 0.1 μm to 0.55 μm, still more preferably 0.1 μm to 0.4 μm, and particularly preferably 0.1 μm to 0.3 μm. When the average particle size of the developer is within the above range, the transparency of the thermosensitive recording medium 1 tends to be further improved, which is preferable.

[0067] The content of the developer is preferably 20% by mass or more and 70% by mass or less, more preferably 25% by mass or more and 60% by mass or less, and even more preferably 30% by mass or more and 50% by mass or less, relative to 100% by mass of the dry mass of the thermal layer 4.

[0068] Examples of the filler that can be used include kaolin, calcined kaolin, aluminum hydroxide, magnesium hydroxide, aluminum oxide, magnesium oxide, aluminum silicate, calcium carbonate, magnesium carbonate, titanium oxide, barium sulfate, silica gel, activated clay, talc, clay, diatomaceous earth, white carbon, zinc oxide, silicon oxide, colloidal silica, polystyrene resin particles, urea-formalin resin particles, polyolefin resin particles, etc. These fillers can be used alone or in combination of two or more.

[0069] The average particle size of the filler is, for example, preferably 0.1 μm to 1.0 μm, more preferably 0.1 μm to 0.6 μm, even more preferably 0.1 μm to 0.55 μm, still more preferably 0.1 μm to 0.4 μm, and particularly preferably 0.1 μm to 0.3 μm. When the average particle size of the filler is within the above range, the transparency of the thermosensitive recording medium 1 tends to be further improved, which is preferable.

[0070] The content of the filler is preferably 0.1% by mass or more and 30% by mass or less, more preferably 1% by mass or more and 20% by mass or less, and even more preferably 5% by mass or more and 15% by mass or less, relative to 100% by mass of the dry mass of the thermal layer 4.

[0071] Examples of the binder include styrene-butadiene copolymer (SBR), polyvinyl alcohol, modified polyvinyl alcohol, starch, casein, gelatin, polyamide, polyacrylamide, modified polyacrylamide, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl acetate, polyacrylic acid ester, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, diisobutylene-maleic anhydride copolymer, vinyl acetate-maleic anhydride copolymer, methyl vinyl-maleic anhydride copolymer, isopropylene-maleic anhydride copolymer, styrene-butadiene copolymer, polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinyl acetate copolymer, polyurethane, polystyrene, polyvinylpyrrolidone, acrylic acid ester, acrylonitrile, methyl vinyl ether, etc. These binders can be used alone or in combination of two or more.

[0072] The content of the binder is preferably 5% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 40% by mass or less, and even more preferably 20% by mass or more and 30% by mass or less, relative to 100% by mass of the dry mass of the thermal layer 4.

[0073] As the dispersant, a dispersant having a carboxyl group is preferred. As the dispersant having a carboxyl group, styrene-acrylic polymers such as styrene-acrylic acid (salt) polymers and styrene-acrylic acid ester polymers; styrene-maleic acid (salt) resins, styrene-maleic acid ester resins, etc. can be used. Among them, styrene-acrylic polymers are preferred, styrene-acrylic acid (salt) polymers are more preferred, and styrene-acrylic acid (ammonium salt) polymers are even more preferred. These dispersants can be used alone or in combination of two or more.

[0074] The salt of the acrylate contained in the dispersant having a carboxyl group is not particularly limited, and examples thereof include ammonium salts such as ammonia; alkanolamine salts such as triethanolamine, diethanolamine, and monoethanolamine; alkylamine salts such as methylamine salt, ethylamine salt, diethylamine salt, and triethylamine salt; polyamine salts such as diethyleneamine salt and diethylenetriamine salt; alkali metal salts such as lithium, sodium, and potassium; alkaline earth metal salts such as magnesium and calcium; and polyvalent metal salts such as zinc and iron. Among these, ammonium salts are particularly preferred.

[0075] The content of the dispersant is preferably 5% by mass or more and 30% by mass or less, more preferably 7% by mass or more and 18% by mass or less, and even more preferably 10% by mass or more and 15% by mass or less, relative to 100% by mass of the dry mass of the thermal layer 4.

[0076] Examples of the crosslinking agent that can be used include epichlorohydrin-modified polyamide polyamine resins, organic compounds containing oxazoline groups, etc. These crosslinking agents can be used alone or in combination of two or more.

[0077] The content of the crosslinking agent is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.3% by mass or more and 5% by mass or less, and even more preferably 0.5% by mass or more and 2% by mass or less, relative to 100% by mass of the dry mass of the thermal layer 4.

[0078] When a dispersant having a carboxyl group is used as the dispersant and an epichlorohydrin-modified polyamide polyamine resin is used as the crosslinker, the azetidinium ring (AZR) in the epichlorohydrin-modified polyamide polyamine resin crosslinker reacts with the carboxyl group of the dispersant to form a crosslinked structure in the thermal layer 4. This crosslinked structure is thought to improve the film-forming properties of the thermal layer 4 and fill voids in the thermal layer 4. As a result, the transparency of the thermal layer 4 is further improved, making it possible to obtain a thermal recording medium 1 with improved transparency.

[0079] Furthermore, when a dispersant having a carboxyl group is used as the dispersant and an organic compound containing an oxazoline group is used as the crosslinker, the oxazoline group of the organic compound containing the oxazoline group, which is the crosslinker, reacts with the carboxyl group of the dispersant to form a crosslinked structure in the thermal layer 4. This crosslinked structure is thought to improve the film-forming properties of the thermal layer 4 and fill voids in the thermal layer 4. As a result, the transparency of the thermal layer 4 is further improved, making it possible to obtain a thermal recording medium 1 with improved transparency.

[0080] The coating amount (dry mass) of the thermal layer 4 is preferably 0.5 g / m 2 ~10.0g / m 2 and more preferably 1.0 g / m 2 ~8.0g / m 2 and more preferably 2.0 g / m 2 ~6.0g / m 2 and more preferably 3.0 g / m 2 ~6.0g / m 2 and more preferably 3.5 g / m 2 ~5.5g / m 2 and more preferably 4.0 g / m 2 ~5.0g / m 2 and particularly preferably 4.5 g / m 2 When the coating amount is within the above range, the transparency of the thermosensitive recording medium 1 tends to be further improved, which is preferable.

[0081] The thickness of the thermal layer 4 is, for example, preferably 2 μm to 6 μm, and more preferably 3 μm to 5 μm.

[0082] The thermosensitive recording medium 1 of this embodiment has the above-described structure and is therefore excellent in transparency.

[0083] In the thermal recording medium 1 of this embodiment, the haze value of the laminate having the substrate 2 and the thermal layer 4 on both end faces is preferably 40% or less, more preferably 38% or less, and even more preferably 37% or less, when measured by the method described in the examples. If the haze value of the laminate having the substrate 2 and the thermal layer 4 on both end faces is within the above range, it is preferable because it has better transparency.

[0084] [Method for producing a thermal recording medium] The method for producing a thermal recording medium of the present invention is not particularly limited. For example, the thermal recording medium can be produced by dispersing the components to be contained in the thermal layer in a solvent such as water to prepare a coating material for the thermal layer by a known or conventional method, applying the obtained coating material by a known or conventional method, and then drying the coating material by a known or conventional method.

[0085] (Preparation Step) In the preparation step, the thermal layer coating material may be prepared by dispersing all of the components in the same solvent in advance. Alternatively, a color former and a color developer that react with each other may be prepared as separate dispersions and then mixed to form the thermal layer coating material. In this case, the other components may be added to either the dispersion containing the dye or the dispersion containing the color developer, or to both. The method for preparing the coating material is not particularly limited, and examples include stirring, ultrasonic treatment, and crushing treatment using a ball mill, bead mill, sand mill, high-pressure homogenizer, etc. These methods may be used alone or in combination of two or more.

[0086] In the method for producing a thermal recording medium of the present invention, from the viewpoint of further improving the transparency of the thermal recording medium, it is preferable to include a step of preparing a thermal layer coating material using a solubilized fatty acid wax and / or an emulsion-type fatty acid wax. Of these, it is more preferable to include a step of preparing a thermal layer coating material using a solubilized fatty acid wax. By microparticulating or solubilizing the fatty acid wax into an emulsion-type, the permeability of the fatty acid wax into the voids between the particles of other components is improved, and the voids are more effectively sealed, thereby further suppressing diffuse reflection of light in the voids, which is presumably the result of further improving the transparency of the thermal recording medium.

[0087] The method for obtaining the solubilized fatty acid wax is not particularly limited, and can be obtained, for example, by adding a solubilizer to the fatty acid wax and mixing. Regarding the solubilizer, all of the contents described in the section on [Thermal Recording Material] may be used. The mixing method is also not particularly limited, and examples include stirring, ultrasonic treatment, and crushing treatment using a ball mill, bead mill, sand mill, high-pressure homogenizer, etc. These methods can be used alone or in combination of two or more.

[0088] The solubilized fatty acid wax is preferably a transparent liquid. For example, a transparent liquid solubilized fatty acid wax can be prepared by mixing the fatty acid wax with the solubilizing agent. Such a solubilized fatty acid wax can further improve the permeability into the thermal layer or the thermal layer coating material, thereby further improving the transparency of the thermal recording medium. Furthermore, unlike an emulsion in which the wax exists as particles in the medium, such a solubilized fatty acid wax does not exist as particles, thereby further improving the transparency of the thermal recording medium.

[0089] (Coating Step) In the coating step, examples of a method for applying the thermal layer coating material obtained above include a method of directly applying the coating material to a substrate, and a method of applying the coating material to a release liner or the like and then transferring the coating material to a substrate. The coating method is not particularly limited, and examples thereof include air knife coating, barrier blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, die coating, and gravure coating. These methods can be used alone or in combination of two or more.

[0090] (Drying step) The method for drying the applied coating material is not particularly limited, and examples thereof include heat drying, room temperature drying, vacuum drying, etc. A thermal layer can be formed by drying the applied coating material using these methods. These methods can be used alone or in combination of two or more.

[0091] If the thermosensitive recording medium of the present invention includes layers other than the thermal layer, the above methods for forming the layers may be used. For example, as shown in FIG. 1 , a thermosensitive recording medium 1 including a substrate 2, an anchor layer 3, and a thermal layer 4 in this order can be manufactured by forming the anchor layer 3 on the substrate 2 and then forming the thermal layer 4 on the anchor layer 3. The anchor layer coating material may be prepared by dispersing all of the components contained in the anchor layer 3 in the same solvent in advance. Alternatively, if the anchor layer 3 contains components that react with each other, the components may be prepared as separate dispersions and then mixed together. The preparation method is not particularly limited, and examples include stirring, ultrasonic treatment, and crushing using a ball mill, bead mill, sand mill, high-pressure homogenizer, etc. These methods can be used alone or in combination. The anchor layer coating material obtained above can be applied to the substrate 2 by directly applying it to the substrate 2, for example. The method for applying the anchor layer coating material is not particularly limited, and examples thereof include air knife coating, barber blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, die coating, and gravure coating. These methods can be used alone or in combination of two or more. The applied anchor layer coating material is then dried to form an anchor layer 3 on the substrate 2. Examples of the drying method include heat drying, room temperature drying, and vacuum drying. These methods can be used alone or in combination of two or more. A thermal layer 4 is then formed on the anchor layer 3 using the same procedure as above, thereby obtaining the thermosensitive recording material 1 shown in FIG. 1.

[0092] In the method for producing a thermosensitive recording medium of the present invention, the layers may be simultaneously coated by, for example, a curtain coater, or may be formed individually and sequentially. Alternatively, some layers may be simultaneously coated and some layers may be formed individually and sequentially.

[0093] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples and is limited only by the claims.

[0094] A thermosensitive recording medium having an anchor layer and a thermal layer laminated in this order on a substrate was prepared by the following steps. (Example 1) (Preparation of Thermosensitive Recording Medium) <Anchor Layer> A coating material for the anchor layer was prepared by adding water to a modified styrene-acrylic acid (ammonium salt) resin (manufactured by BASF Japan Ltd., product name: JONCRYL PDX7430) so that the dry mass was 10% by mass. The coating material for the anchor layer was applied to a biaxially oriented polypropylene (OPP) film (thickness: 40 μm) as a substrate, and then dried to obtain a coating amount of 0.5 to 2.0 g / m2 in terms of dry mass. 2 An anchor layer having a thickness of 0.5 to 2 μm was formed.

[0095] <Thermal layer> A coating material for the thermal layer, prepared to a dry mass of 23% by mass using water as a solvent so that the dry mass of each compounded material would be the composition shown in Table 1, was applied onto the anchor layer, and then dried at 50°C, resulting in a coating amount of 4.0 g / m2 in terms of dry mass. 2 A thermal layer of 1000 ppm was formed to prepare a thermosensitive recording medium of Example 1. In Table 1, the numerical values ​​of each compounded material indicate the mass ratio after drying (dry mass). Unless otherwise specified, when the compounded material (fatty acid wax, etc.) contains a surfactant and a solvent, the numerical values ​​of each compounded material in Table 1 indicate the mass ratio after drying, including the surfactant and solvent.

[0096] As a compounding material, Wax 1 was used, which was a solubilized fatty acid wax (manufactured by Nissin Chemical Laboratory Co., Ltd., product name: R-053D). Wax 1 contained a fatty acid wax as the main component, an anionic surfactant and a polyoxyethylene alkyl ether as surfactants, and water as a solvent. Wax 1 was also readily soluble in water. The dye used was 3-dibutylamino-6-methyl-7-anilinofluoran with an average particle size of 0.15 μm, the developer used was 4-hydroxyphenyl(4'-n-propoxyphenyl)sulfone (manufactured by Mitsubishi Chemical Corporation, product name: Tomilac KN) with an average particle size of 0.15 μm, the filler used was kaolin with an average particle size of 0.4 μm, the binder used was SBR with a glass transition temperature Tg of -3°C, the dispersant used was a styrene-acrylic acid (ammonium salt) polymer, and the crosslinker used was epichlorohydrin-modified polyamide polyamine resin.

[0097] (Example 2) In the thermal layer, Wax 5 (polystyrene wax with an average particle diameter of 0.2 μm) was used as a wax other than the fatty acid-based wax, and the blending amounts of each blending material were adjusted so that the dry mass of each blending material had the composition shown in Table 1. The thermal recording material of Example 2 was prepared in the same manner as in Example 1 above, except that Wax 5 (polystyrene wax with an average particle diameter of 0.2 μm) was used as a wax other than the fatty acid-based wax, and the blending amounts were adjusted so that the dry mass of each blending material had the composition shown in Table 1.

[0098] Example 3 A thermosensitive recording medium for Example 3 was prepared in the same manner as in Example 2, except that Wax 1 in the thermal layer was replaced with Wax 2, an emulsion of a fatty acid-based wax (manufactured by Chukyo Yushi Co., Ltd., product name: Highmicron L-271). Wax 2 contained 20% to 30% by dry weight of a fatty acid amide as the main component, less than 1.0% by dry weight of triethanolamine as a solvent, and water as a solvent. Wax 2 was also dispersible in water. The average particle diameter of the fine particles contained in the emulsion of Wax 2 was measured and found to be 0.87 μm.

[0099] Example 4 A thermosensitive recording medium of Example 4 was prepared in the same manner as in Example 2, except that Wax 1 in the thermal layer was replaced with Wax 3, an emulsion of fatty acid wax (manufactured by Nissin Chemical Laboratory Co., Ltd., product name: New Wax E-50). Wax 3 contained a fatty acid wax as the main component, 10% to 20% by dry weight of solid paraffin as other components, and water as the solvent. Wax 3 was also dispersible in water. The average particle diameter of the fine particles contained in the emulsion of Wax 3 was measured and found to be 0.18 μm.

[0100] Example 5 A thermosensitive recording medium for Example 5 was prepared in the same manner as in Example 2, except that Wax 1 in the thermal layer was replaced with Wax 4, a solubilized fatty acid wax. Wax 4 was prepared by heating an emulsion of Wax 3 (manufactured by Nissin Chemical Laboratory Co., Ltd., product name: New Wax E-50) at 50°C to evaporate the water, and adding 3 g of diethylene glycol monobutyl ether as a solvent to 1 g of the resulting solids. This was used as the solubilized fatty acid wax. In Example 5, the diethylene glycol butyl ether was treated as a solvent for solubilizing the fatty acid wax, so the value for Wax 4 in Example 5 in Table 1 indicates the dry mass ratio including the diethylene glycol butyl ether.

[0101] The waxes 1 and 4 were transparent liquids.

[0102] Comparative Example 1 A thermosensitive recording medium for Comparative Example 1 was prepared in the same manner as in Example 2, except that in the thermal layer, Wax 1 was changed to Wax 6 and Wax 5 to Wax 7. Wax 6 was a polyethylene wax with an average particle size of 1.3 μm, and Wax 7 was a paraffin with a melting point of 46° C. and an average particle size of 0.3 μm.

[0103] According to the above method, the thermosensitive recording media of Examples 1 to 5 and Comparative Example 1 were prepared and used for measuring the haze value described below.

[0104] (Haze Measurement) The haze value of each thermal recording medium was measured from the thermal layer side of the thermal recording medium (a laminate having a substrate and a thermal layer at both end faces) using a haze meter (manufactured by Nippon Denshoku Co., Ltd., product name: NDH7000). The haze values ​​obtained for each thermal recording medium prepared in each Example and Comparative Example are shown in Table 1.

[0105] The above measurement was carried out according to the method of JIS K7136:2000.

[0106]

[0107] The following was confirmed from Table 1.

[0108] The thermal recording materials of Examples 1 to 5, which contained a fatty acid wax as the wax in the thermal layer, had lower haze values ​​than the thermal recording material of Comparative Example 1, which did not contain a fatty acid wax, confirming the tendency for the use of a fatty acid wax as the wax to improve the transparency of the thermal recording material. Furthermore, the thermal recording material of Example 5, which was obtained using Wax 4, a solubilized fatty acid wax obtained by solubilizing Wax 3 with a solvent, had a lower haze value than the thermal recording material of Example 4, which was obtained using Wax 3, an emulsion-like fatty acid wax, confirming improved transparency. The detailed mechanism of the improvement in transparency achieved by solubilizing the fatty acid wax before use is unknown, but it is presumed that solubilizing Wax 3, which existed as particles large enough to be seen with the naked eye, improved the penetration of the blended materials into the voids between the particles.

[0109] In summary, the configuration of the present invention and its variations are described below. [Appendix 1] A thermosensitive recording medium having a thermal layer containing a fatty acid wax. [Appendix 2] The thermosensitive recording medium of Appendices 1, wherein the fatty acid wax is a solubilized fatty acid wax and / or an emulsion of fatty acid wax. [Appendix 3] The thermosensitive recording medium of any one of Appendices 1 and 2, wherein the fatty acid wax is a solubilized fatty acid wax. [Appendix 4] The thermosensitive recording medium of any one of Appendices 2 and 3, wherein the solubilized fatty acid wax contains a solubilizer. [Appendix 5] The thermosensitive recording medium of any one of Appendices 1 to 4, wherein the solubilized fatty acid wax is a transparent liquid. [Appendix 6] The thermosensitive recording medium of any one of Appendices 1 to 5, wherein the thermal layer contains a surfactant and / or a solvent. [Appendix 7] The thermosensitive material according to any one of Appendices 1 to 6, wherein the thermal layer further contains a wax other than the fatty acid-based wax, the wax having an average particle size of 1 μm or less. [Appendix 8] The thermosensitive material according to Appendices 7, wherein the wax other than the fatty acid-based wax is one or more of polystyrene, polyethylene, and paraffin. [Appendix 9] The thermosensitive recording material according to any one of Appendices 1 to 8, wherein the content of the fatty acid-based wax is 0.1% by mass or more and 5% by mass or less, relative to 100% by mass of the dry mass of the thermal layer. [Appendix 10] A method for producing a thermosensitive recording material according to any one of Appendices 1 to 9, comprising the steps of preparing a thermal layer coating material using a solubilized fatty acid-based wax and / or an emulsion of fatty acid-based wax, and applying and drying the thermal layer coating material to form a thermal layer. [Appendix 11] A method for producing a thermal recording medium according to any one of Appendices 1 to 9, comprising the steps of preparing a thermal layer coating material using a transparent liquid solubilized fatty acid wax, and applying and drying the thermal layer coating material to form a thermal layer.

[0110] The thermosensitive recording medium of the present invention has excellent transparency and can be particularly suitably used in applications where visibility of the contents is required, such as labels for food containers such as lunch boxes and food packaging films.

[0111] 1 Thermosensitive recording medium 2 Substrate 3 Anchor layer 4 Thermal layer

Claims

1. A thermal recording medium having a thermal layer containing a fatty acid-based wax.

2. The heat-sensitive recording medium according to claim 1, wherein the fatty acid wax is a solubilized fatty acid wax and / or an emulsion of fatty acid wax.

3. The heat-sensitive recording medium according to claim 1, wherein the fatty acid wax is a solubilized fatty acid wax.

4. The thermal recording medium according to claim 3, wherein the solubilized fatty acid wax contains a solubilizing agent.

5. The thermal recording medium according to any one of claims 1 to 4, wherein the thermal layer contains a surfactant and / or a solvent.

6. The heat-sensitive recording medium according to any one of claims 1 to 4, wherein the thermal layer further contains a wax other than the fatty acid wax and having an average particle size of 1 µm or less.

7. A thermal recording medium according to any one of claims 1 to 4, wherein the content of the fatty acid wax is from 0.1% by mass to 5% by mass, based on 100% by mass of the dry mass of the thermal layer.

8. A method for producing a thermal recording medium according to any one of claims 1 to 4, comprising the steps of: preparing a thermal layer coating material using a solubilized fatty acid wax and / or an emulsion of fatty acid wax; and applying and drying the thermal layer coating material to form a thermal layer.

Images