Thermal recording medium

Abstract

To provide a thermal recording medium excellent in suppressing generation of black dots.SOLUTION: A thermal recording medium of the present invention is formed by laminating a thermal layer containing non-phenolic developer on a substrate, where the thermal layer contains crosslinking agent and / or thickener, and furthermore satisfies any one of the following aspects (1) to (3). Aspect (1): the thermal layer contains the thickener, and the content ratio of the thickener is 0.07 mass% or more for dry mass 100 mass% of the thermal layer. Aspect (2): the thermal layer contains cationic crosslinking agent as the crosslinking agent, and the content ratio of the cationic crosslinking agent is 0.30 mass% or more for dry mass 100 mass% of the thermal layer. Aspect (3): the thermal layer contains non-cationic crosslinking agent as the crosslinking agent.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Thermal recording media develop color through a chemical reaction when heated by a thermal head or the like, producing a recorded image. They are used for a wide range of purposes, not only as recording media for facsimiles, automatic ticket vending machines, and scientific measuring instruments, but also as thermal recording labels and receipt paper for POS systems in retail stores, etc.

[0003] The above-mentioned thermal recording medium generally includes a thermal layer containing a color developer. As the color developer, many phenol-based color developers have been proposed, but in recent years, there have been concerns about the safety of phenol-based color developers as endocrine disruptors, and from the viewpoints of safety and environmental friendliness, there is a demand for thermal recording mediums using color developers that do not contain a phenol skeleton (non-phenol-based color developers).

[0004] As a non-phenol-based color developer, for example, a color developer made of an N,N'-diaryl urea derivative has been proposed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 044462 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a thermal recording medium having a thermal layer containing a non-phenolic color developer is colored, dark spots may appear in the color, resulting in black spots large enough to be visible to the naked eye.

[0007] Accordingly, an object of the present invention is to provide a thermal recording medium in which the generation of black dots is suppressed.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the present inventors have found the following. That is, 1. In a thermal recording medium in which a thermal layer containing a non-phenolic developer is laminated on a substrate, the generation of black dots is further suppressed by containing a crosslinking agent and / or a thickening agent in the thermal layer. 2. By satisfying any one or more of the following aspects (1) to (3), the generation of black dots is further suppressed. Aspect (1): The thermal layer contains the thickening agent, and the content ratio of the thickening agent is 0.07% by mass or more based on 100% by mass of the dry mass of the thermal layer. Aspect (2): The thermal layer contains a cationic crosslinking agent as the crosslinking agent, and the content ratio of the cationic crosslinking agent is 0.30% by mass or more based on 100% by mass of the dry mass of the thermal layer. Aspect (3): The thermal layer contains a non-cationic crosslinking agent as the crosslinking agent. The present invention has been completed based on these findings.

[0009] That is, the present invention is a thermal recording medium in which a thermal layer containing a non-phenolic developer is laminated on a substrate, the thermal layer contains a crosslinking agent and / or a thickening agent, and further satisfies any one or more of the following aspects (1) to (3). Aspect (1): The thermal layer contains the thickening agent, and the content ratio of the thickening agent is 0.07% by mass or more based on 100% by mass of the dry mass of the thermal layer. Aspect (2): The thermal layer contains a cationic crosslinking agent as the crosslinking agent, and the content ratio of the cationic crosslinking agent is 0.30% by mass or more based on 100% by mass of the dry mass of the thermal layer. Aspect (3): The thermal layer contains a non-cationic crosslinking agent as the crosslinking agent.

[0010] The above non-phenolic color former preferably contains a compound represented by the following formula (1) and / or a compound represented by the following formula (2). By having such a configuration, the generation of black spots can be further suppressed.

Chemical formula

Chemical formula

[0011] The above non-phenolic color developer preferably contains a compound represented by the following formula (1a) and / or a compound represented by the following formula (2a). By having such a configuration, the generation of black spots can be further suppressed.

Chemical formula

Chemical formula

[0012] The above non-phenolic color developer preferably contains a urethane-urea compound. By having such a configuration, the generation of black spots can be further suppressed.

[0013] The above urethane-urea compound is preferably a urethane-urea compound represented by the following formula (3). By having such a configuration, the generation of black spots can be further suppressed.

Chemical formula

[0014] According to the present invention, it is possible to provide a thermal recording medium in which the generation of black dots is suppressed. [Brief Description of the Drawings]

[0015]

Figure 1

[0016] Hereinafter, embodiments of the thermal recording medium according to the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the following embodiments.

[0017] [First Embodiment] [Thermal Recording Medium] FIG. 1 is a schematic cross-sectional view showing an embodiment (first embodiment) of the thermal recording medium of the present invention.

[0018] As shown in FIG. 1, the thermal recording medium 1 of the present embodiment includes a substrate 2, an anchor layer 3, a thermal layer 4, an intermediate layer 5, and a top coat layer 6 in this order. Here, the substrate 2 and the anchor layer 3 are laminated so as to be in direct contact with each other. Further, the anchor layer 3 and the thermal layer 4 are laminated so as to be in direct contact with each other. Furthermore, the intermediate layer 5 and the top coat layer 6 are laminated so as to be in direct contact with each other.

[0019] The thermal recording medium 1 of the present embodiment contains a non-phenolic developer in the thermal layer 4 and satisfies at least the following aspect (1). Aspect (1): The thermal layer 4 contains the thickener, and the content ratio of the thickener is 0.07% by mass or more with respect to 100% by mass of the dry mass of the thermal layer 4.

[0020] The thermal recording medium 1 of the present embodiment may further satisfy any one or more of the following aspects (2) and (3). Among them, it is preferable to satisfy the above aspect (1) and the following aspect (2). Aspect (2): The thermal layer 4 contains a cationic crosslinking agent as the crosslinking agent, and the content ratio of the cationic crosslinking agent is 0.30% by mass or more with respect to 100% by mass of the dry mass of the thermal layer 4. Aspect (3): The thermal layer 4 contains a non-cationic crosslinking agent as the crosslinking agent.

[0021] (Base material) In the present embodiment, the base material 2 functions as a support of the thermal recording medium 1. As the base material 2, for example, fine paper, art paper, coated paper, kraft paper, papers such as laminated paper obtained by laminating a thermoplastic resin such as polyethylene on these paper bases, synthetic paper, and porous materials such as non-woven fabric can be used. Further, for example, synthetic resin films such as polypropylene film, polyethylene terephthalate film, polystyrene film, and polycarbonate film can be used. Further, the base material 2 may be a single layer or a multi-layer. The thickness of the base material 2 is not particularly limited, but for example, it is preferably 5 μm to 150 μm, more preferably 10 μm to 100 μm. If the thickness is within the above range, it tends to be excellent in coatability and supportability and is preferable.

[0022] (Anchor layer) In the present embodiment, the anchor layer 3 functions as a layer having functions such as heat insulation and cushioning properties that prevent heat dissipation given from the thermal head when the base material 2 is a material with high heat dissipation such as paper, and functions as a layer that enhances the adhesion between the base material 2 and the thermal layer 4 when the base material 2 is a material with low adhesion to the thermal layer 4 such as a synthetic resin film. The material for forming the anchor layer 3 is not particularly limited, and for example, it can be formed only from a binder. Further, the anchor layer 3 may contain other materials, for example, it may contain a filler or the like. When the anchor layer is not required, it may not be provided.

[0023] Examples of the above binder include modified styrene-acrylic resins, acrylic resins, styrene-acrylic copolymers, modified styrene-butadiene latexes, styrene-butadiene copolymers (SBR), acrylic-butadiene-styrene copolymers, vinyl acetate resins, vinyl acetate-acrylic copolymers, polyurethane resins, and the like. The composition for forming the above binder may be an emulsion or a solution. From the viewpoint of excellent coatability, an emulsion is more preferable. Here, "acrylic" means acrylic acid (salt) and / or acrylate unless otherwise specified, and "acrylic acid (salt)" means acrylic acid and / or acrylate salt. These binders can be used alone or in combination of two or more.

[0024] The salt in the above acrylate is not particularly limited. Examples 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 diethylenetriamine salt and diethylenetriamine salt; alkali metal salts such as lithium, sodium, and potassium; alkaline earth metal salts such as magnesium and calcium; polyvalent metal salts such as zinc and iron. These salts can be used alone or in combination of two or more.

[0025] In addition, examples of the binder other than those described above include completely or partially saponified polyvinyl alcohol; starch and its derivatives; cellulose derivatives such as methoxycellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose; water-soluble polymers such as sodium polyacrylate, polyvinyl pyrrolidone, acrylamide-acrylic acid ester copolymer, acrylamide-acrylic acid ester-methacrylic acid terpolymer, alkali salt of styrene-maleic anhydride copolymer, alkali salt of isobutylene-maleic anhydride copolymer, polyacrylamide, sodium alginate, gelatin, and casein.

[0026] The content ratio of the above binder is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, and particularly preferably 90% by mass or more with respect to 100% by mass of the dry mass of the anchor layer 3. Further, the content ratio of the binder with respect to 100% by mass of the dry mass of the anchor layer 3 may be substantially 100% by mass. When the content ratio is within the above range, it is preferable from the viewpoint of further enhancing the adhesion between the base material 2 and the thermal layer 4.

[0027] In this specification, the "dry mass" means the mass of the non-volatile component (solid content) obtained by removing solvents (volatile components) such as water contained in the paint and its raw materials by drying.

[0028] Examples of the filler include inorganic fillers such as calcined kaolin, aluminum oxide, aluminum silicate, heavy calcium carbonate, light calcium carbonate, titanium oxide, barium sulfate, silica gel, activated clay, talc, clay, kaolinite, diatomaceous earth, white carbon, magnesium carbonate, magnesium oxide, magnesium hydroxide, and zinc oxide; and organic fillers such as hollow particles, polystyrene resin particles, urea-formalin resin particles, and polyolefin resin particles. These fillers can be used alone or in combination of two or more.

[0029] The coating amount (dry mass) of the anchor layer 3 is, for example, preferably 0.1 g / m 2 ~5 g / m 2 and more preferably 0.2 g / m 2 ~2.0 g / m 2 and even more preferably 0.3 g / m 2 ~0.6 g / m 2 .

[0030] The thickness of the anchor layer 3 is, for example, preferably 0.1 μm to 5 μm, more preferably 0.2 μm to 2.0 μm, and even more preferably 0.3 μm to 0.6 μm.

[0031] When the coating amount and thickness of the anchor layer 3 in this embodiment are within the above ranges, the adhesion between the substrate 2 and the thermal layer 4 tends to be further improved, which is preferable.

[0032] (Thermal layer) In this embodiment, the thermal layer 4 functions as a layer that develops color when heated by a thermal head or the like. The thermal layer 4 contains at least a non-phenolic developer and a thickener.

[0033] The non-phenolic developer is not particularly limited, and known ones can be used. Among them, as the non-phenolic developer, a compound having an N,N'-diarylurea skeleton, that is, an N,N'-diarylurea derivative is preferable, and an N,N'-diarylurea derivative having one or more sulfonic acid ester structures (-S(=O)2-O-) in the molecule is more preferable. The N,N'-diarylurea derivative may be an N,N'-diarylurea derivative (excluding urethane-urea compounds), or an N,N'-diarylurea derivative having one or more sulfonic acid ester structures in the molecule (excluding urethane-urea compounds). The N,N'-diarylurea derivative having one or more sulfonic acid ester structures in the molecule is preferably a compound represented by the following formula (1) and / or a compound represented by the following formula (2). [Chemical formula] (In formula (1), R 1 , R 2 , R 3 , R 4 , R 5 , R 7 , R 8 , R 9 , R 10 , and R 11 each independently represents a hydrogen atom or a substituent. R 6 , and R 12 each independently represents a substituent. m represents an integer from 0 to 4. When m is 2 or more, the plurality of R 6 may be the same or different. n represents an integer from 0 to 4. When n is 2 or more, the plurality of R 12 may be the same or different.) [Chemical formula] (In formula (2), R 13 , R 14 , R 15 , R 16 , R 17 , R 19 , R 20 , R 21 , R 22 , and R 23 each independently represents a hydrogen atom or a substituent. R 18 represents a substituent. o represents an integer from 0 to 4. When o is 2 or more, the plurality of R 18 may be the same or different.)

[0034] As the above-mentioned "substituent", an organic group other than a hydrogen atom can be used without particular limitation. For example, a halogen atom, a nitro group, an amino group, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an alkylcarbonyloxy group, an alkylcarbonylamino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, an arylamino group, etc. can be mentioned.

[0035] Examples of the above-mentioned "halogen atom" include a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom.

[0036] Examples of the above-mentioned "alkyl (group)" include linear or branched alkyl groups having 1 to 12 carbon atoms, such as a methyl group, an ethyl group, a normal propyl group, an isopropyl group, a normal butyl group, an isobutyl group, a secondary butyl group, a tertiary butyl group, a normal pentyl group, an isopentyl group, a tertiary pentyl group, a neopentyl group, a 2,3-dimethylpropyl group, a 1-ethylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a normal hexyl group, an isohexyl group, a 2-hexyl group, a 3-hexyl group, a 2-methylpentyl group, a 3-methylpentyl group, a normal heptyl group, a normal octyl group, a normal nonyl group, a normal decyl group, a normal undecyl group, and a normal dodecyl group.

[0037] Examples of the above-mentioned "alkoxy group" include linear or branched alkoxy groups having 1 to 8 carbon atoms, such as a methoxy group, an ethoxy group, a normal propoxy group, an isopropoxy group, a normal butoxy group, a secondary butoxy group, a tertiary butoxy group, a normal pentyloxy group, an isopentyloxy group, a tertiary pentyloxy group, a neopentyloxy group, a 2,3-dimethylpropyloxy group, a 1-ethylpropyloxy group, a 1-methylbutyloxy group, a normal hexyloxy group, an isohexyloxy group, a normal heptyloxy group, and a normal octyloxy group.

[0038] Examples of the above-mentioned "aryl (group)" include aromatic hydrocarbon groups having 6 to 10 carbon atoms, such as a phenyl group, a 1-naphthyl group, and a 2-naphthyl group.

[0039] In the above-mentioned "dialkylamino group", the two alkyl groups may be the same or different.

[0040] As the compound represented by the formula (1), from the viewpoint of imparting excellent color developability and the like to the thermal recording material 1 and further suppressing the generation of black spots, the compound represented by the following formula (1a) is preferable. Specifically, N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-xylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(mesitylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(o-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)phenyl]urea, etc. represented by the following formula (1b) can be mentioned.

[0041] [Chemical formula] (Each symbol in the formula (1a) is the same as that in the formula (1).) [Chemical formula]

[0042] As the compound represented by the formula (2), from the viewpoint of imparting excellent color developability and the like to the thermal recording material 1 and further suppressing the generation of black spots, the compound represented by the following formula (2a) is preferable. Specifically, 3-[(3-phenylureido)phenyl]-4-methylbenzenesulfonate represented by the following formula (2b) is preferable.

[0043] [Chemical formula] (Each symbol in the formula (2a) is the same as that in the formula (2).) [Chemical formula]

[0044] In the present embodiment, the thermal layer 4 may contain the above non-phenolic developer alone or may contain two or more thereof.

[0045] By containing, as the non-phenolic color former, the compound represented by the above formula (1) and / or the compound represented by the above formula (2), the thermal layer 4 imparts excellent color developability and the like to the thermal recording medium 1, and can further suppress the generation of black spots.

[0046] Examples of the non-phenolic color former include, in addition to the non-phenolic color formers listed above, for example, urethane-urea compounds; urea compounds such as 2,2-bis[(4-methyl-3-phenoxycarbonylaminophenyl)urea] diphenyl sulfone, 4,4'-bis(p-tolylsulfonylaminocarbonylamino)diphenylmethane, 2'-(3-phenylureido)benzenesulfonanilide, and N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea. In the present specification, the "urethane-urea compound" means a compound having one or more urea bonds (-NH-C(=O)-NH-) and one or more urethane bonds (-NH-C(=O)-O-) in the molecule, and the "urea compound" means a compound having one or more urea bonds in the molecule.

[0047] In the present embodiment, from the viewpoint of further improving color developability and print storage stability, the non-phenolic color former preferably contains a urethane-urea compound. Further, the non-phenolic color former more preferably contains a urethane-urea compound in addition to an N,N'- diarylurea derivative (excluding urethane-urea compounds) having one or more sulfonic acid ester structures in the molecule. By using two or more non-phenolic color formers in combination as described above, it is possible to impart more excellent color developability and print storage stability to the thermal recording medium 1 than when used alone.

[0048] As the urethane-urea compound, a urethane-urea compound having two or more urea bonds and two or more urethane bonds in the molecule is preferable, and specifically, a urethane-urea compound represented by the following formula (3) is more preferable.

Chemical formula

[0049] As the urea urethane compound represented by formula (3), from the viewpoint of further improving the color developability and print storage stability, the compound represented by the following formula (3a) is preferable. Specifically, the compound represented by the following formula (3b) is exemplified. [Chemical formula] (Each symbol in formula (3a) is the same as in formula (3).) [Chemical formula]

[0050] When the thermal layer 4 contains a urethane-urea compound, the reaction efficiency between the dye and the developer is increased, the formation of an electron transfer complex is facilitated, and the reverse reaction is less likely to occur. As a result, the color developability of the thermal recording medium becomes more excellent, and the color density is less likely to decrease. Therefore, it is considered that the print storage property, particularly the plasticizer resistance, is excellent. In general, when the thermal layer 4 contains a urethane-urea compound, the number of black dots tends to increase compared to the case where it does not contain. However, by satisfying the configuration of the present invention, it is possible to achieve both suppression of black dot generation and improvement of color developability and print storage property.

[0051] In the present embodiment, the content ratio of the non-phenolic developer is preferably 10% by mass or more and 50% by mass or less, more preferably 15% by mass or more and 35% by mass or less, based on 100% by mass of the dry mass of the thermal layer 4. The fact that the content ratio is 10% by mass or more is preferable from the viewpoint that the color developability is further improved because there is sufficient developer. Also, the fact that the content ratio is 50% by mass or less is preferable from the viewpoint that the ratio to the dye becomes a more appropriate range and the color developability is further improved.

[0052] In the present embodiment, the content ratio of the N,N'- diarylurea derivative (excluding the urethane-urea compound) is preferably 5% by mass or more and 35% by mass or less, more preferably 10% by mass or more and 30% by mass or less, based on 100% by mass of the dry mass of the thermal layer 4. Also, the total content ratio of the compound represented by the above formula (1) and / or the compound represented by the above formula (2) with respect to 100% by mass of the non-phenolic developer in the thermal layer 4 is preferably within the above range.

[0053] In the present embodiment, the content ratio of the urethane-urea compound is preferably 1% by mass or more and 30% by mass or less, more preferably 5% by mass or more and 15% by mass or less, based on 100% by mass of the dry mass of the thermal layer 4.

[0054] In this embodiment, the content ratio of the non-phenolic color former is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, based on 100% by mass of the color former in the thermal layer 4. Also, the content ratio of the non-phenolic color former with respect to 100% by mass of the color former in the thermal layer 4 may be 100% by mass. When the content ratio is within the above range, it can be more excellent in terms of safety and environmental compatibility.

[0055] In this embodiment, the content ratio of the above N,N'-diarylurea derivative (excluding urethane-urea compounds) is preferably 40% by mass or more, more preferably 50% by mass or more, still more preferably 55% by mass or more, based on 100% by mass of the non-phenolic color former in the thermal layer 4. Also, the content ratio of the above N,N'-diarylurea derivative (excluding urethane-urea compounds) is preferably 95% by mass or less, more preferably 90% by mass or less, still more preferably 80% by mass or less, particularly preferably 75% by mass or less, based on 100% by mass of the non-phenolic color former in the thermal layer 4. Also, the total content ratio of the compound represented by the above formula (1) and / or the compound represented by the above formula (2) with respect to 100% by mass of the non-phenolic color former in the thermal layer 4 is preferably within the above range.

[0056] In the present embodiment, the total content ratio of the above N,N'- diarylurea derivative (excluding the ureauurethane compound) and the ureauurethane compound is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, based on 100% by mass of the non - phenolic color former in the thermal layer 4. Further, the total content ratio of the above N,N'- diarylurea derivative (excluding the ureauurethane compound) and the ureauurethane compound may be 100% by mass based on 100% by mass of the non - phenolic color former in the thermal layer 4. Also, the total content ratio of the compound represented by the above formula (1) and / or the compound represented by the above formula (2) and the ureauurethane compound with respect to 100% by mass of the non - phenolic color former in the thermal layer 4 is preferably within the above range.

[0057] In the present embodiment, when the dry mass of the above N,N'- diarylurea derivative (excluding the ureauurethane compound) in the thermal layer 4 is taken as 1, the ratio of the dry mass of the ureauurethane compound in the thermal layer 4 (dry mass of the ureauurethane compound / dry mass of the N,N'- diarylurea derivative (excluding the ureauurethane compound)) is preferably 0.1 or more and 5 or less, more preferably 0.2 or more and 2 or less, still more preferably 0.3 or more and 1 or less. Also, when the total dry mass of the compound represented by the above formula (1) and / or the compound represented by the above formula (2) in the thermal layer 4 is taken as 1, the ratio of the dry mass of the ureauurethane compound in the thermal layer 4 (dry mass of the ureauurethane compound / total dry mass of the compound represented by the above formula (1) and / or the compound represented by the above formula (2)) is preferably within the above range.

[0058] In this embodiment, the thermal layer 4 contains a thickener. By including the thickener, the generation of black spots is suppressed. The thickener is not particularly limited, and known thickeners can be used. Examples of the thickener include alkali-soluble thickeners; inorganic thickeners such as bentonite and silica; cellulose thickeners such as hydroxyethyl cellulose, methyl cellulose, and carboxymethyl cellulose; natural product thickeners such as xanthan gum, sodium alginate, guar gum, carrageenan, and casein; non-ionic polymer thickeners such as polyvinyl alcohol, polyethylene oxide, polypropylene oxide, polyvinyl pyrrolidone, and polyacrylamide; surfactant thickeners such as amine oxide and alkanolamide, etc.

[0059] From the viewpoints of thickening effect and handleability, at least one selected from the group consisting of alkali-soluble thickeners, cellulose thickeners, and non-ionic polymer thickeners is preferable as the thickener, and an alkali-soluble thickener is more preferable. Among the alkali-soluble thickeners, at least one selected from the group consisting of HASE (Hydrophobically modified Alkali-Soluble Emulsion) type thickeners and ASE (Alkali-Soluble Emulsion) type thickeners is preferable. These thickeners can be used alone or in combination of two or more.

[0060] Regarding the phenomenon that the generation of black spots is suppressed when the thermal layer 4 contains the above thickener, the detailed mechanism of action is unknown. However, since the viscosity of the paint for the thermal layer tends to increase when the thermal layer 4 contains the above thickener, the dye and the developer are stably dispersed in the paint for the thermal layer, and aggregation is suppressed. As a result, it is possible that the generation of black spots is further suppressed.

[0061] As the thickener, an acrylic (co)polymer or the like is preferable. The acrylic (co)polymer contains (meth)acrylic acid (salt) and / or an alkyl (meth)acrylate as main monomer components. Further, the acrylic copolymer may contain other monomer components in addition to the main monomer components. Examples of the other monomer components include carboxylic acids (salts) such as maleic acid (salt); carboxylic acid alkyl esters such as maleic acid alkyl ester; and monomer components such as associative monomers including alkoxypolyethylene glycol (meth)acrylate, nonylphenoxypolyethylene glycol (meth)acrylate, and tristyrylphenoxypolyethylene glycol (meth)acrylate. In the present specification, "(co)polymer" means a polymer and / or a copolymer, and "(meth)acrylic" means acrylic and / or methacrylic.

[0062] Among them, as the thickener, at least one selected from the group consisting of an acrylic (co)polymer of an HASE type thickener and an acrylic (co)polymer of an ASE type thickener is preferable. Examples of such thickeners include Primar TT-935, Primar TT-615, Acrysol RM-7, Acrysol DR-130, Acrysol DR-180, Acrysol ASE-60 (manufactured by Dow Chemical Japan Co., Ltd.), Aron A-7075, Aron A-7055, Aron B-500, Aron B-300K (manufactured by Toagosei Co., Ltd.), and the like.

[0063] In this embodiment, the content ratio of the thickener is 0.07% by mass or more, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, still more preferably 0.3% by mass or more, and particularly preferably 0.4% by mass or more with respect to 100% by mass of the dry mass of the thermal layer 4. Also, the content ratio of the thickener is preferably 5% by mass or less, more preferably 3% by mass or less, and still more preferably 2% by mass or less with respect to 100% by mass of the dry mass of the thermal layer 4. The fact that the content ratio is 0.07% by mass or more is preferable from the viewpoint that the viscosity of the paint for the thermal layer is appropriately improved and the generation of black spots is more suppressed. Also, the fact that the content ratio is 5% by mass or less is preferable from the viewpoint that the viscosity of the paint for the thermal layer is within an appropriate range and the stability of the paint for the thermal layer is further improved.

[0064] Further, the thermal layer 4 of this embodiment may contain other materials, and examples thereof include dyes that develop color by heating, binders, waxes, sensitizers, dispersants, phenolic developers, preservative improvers, surfactants, defoamers, fillers, crosslinking agents, and antiseptics.

[0065] Examples of such dyes include 3-dibutylamino-6-methyl-7-anilinofluoran, 2-anilino-3-methyl-6-(N-methyl-p-toluidino)fluoran, 3-(N-isobutyl-N-ethyl)amino-6-methyl-7-anilinofluoran, 3-(N-isopentyl-N-ethyl)amino-6-methyl-7-o-chloroanilinofluoran, 3-(N-methyl-N-p-toluidino)-6-methyl-7-anilinofluoran, 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-dibutylamino-6-methyl-7-anilinofluoran, 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, crystal violet lactone, etc. These dyes can be used alone or in combination of two or more kinds.

[0066] The average particle size of the above dye is preferably 0.1 to 1.0 μm. Since the color former melts and reacts, as the particle size increases, the reaction becomes sluggish and the sensitivity characteristics decrease. On the other hand, as the particle size decreases, the risk of unexpected coloring at a temperature due to the heat when drying the paint increases. In this embodiment, by setting the average particle size of the dye within the above range, the sensitivity characteristics and the coloring temperature of the dye can be appropriately adjusted. In this specification, the average particle size refers to the particle size (D50, median diameter) at the integrated value of 50% in the particle size distribution measured by the laser diffraction / scattering method. The measurement of the average particle size by the laser diffraction / scattering method can be performed, for example, using the product name "MT3300EX-II" manufactured by Microtrac Bell Co., Ltd. Hereinafter, the "average particle size" refers to the median diameter measured by the above method.

[0067] Examples of the above binder include modified styrene-butadiene copolymer, modified styrene-acrylic copolymer, polyvinyl alcohol, modified polyvinyl alcohol, starch, modified starch, casein, gelatin, glue, gum arabic, polyamide, polyacrylamide, modified polyacrylamide, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl acetate, polyacrylate 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, polyvinyl pyrrolidone, (meth)acrylate ester, (meth)acrylonitrile, methyl vinyl ether, etc. These binders can be used alone or in combination of two or more.

[0068] As the wax, for example, higher fatty acid metal salts such as zinc stearate and calcium stearate, paraffin, oxidized paraffin, polyethylene, oxidized polyethylene, etc. can be used. These waxes can be used alone or in combination of two or more.

[0069] As the sensitizer, all those known in the field of conventional thermal recording paper can be used and are not particularly limited. For example, 1,2-bis(3-methylphenoxy)ethane, 1,2-bis(3-methylphenoxy)ethane, waxes, higher fatty acids, higher fatty acid amides, higher fatty acid anilides, naphthol derivatives, naphthalene derivatives, aromatic ethers, aromatic carboxylic acid derivatives, aromatic sulfonic acid ester derivatives, carbonic acid or oxalic acid diester derivatives, biphenyl derivatives, polyether derivatives, terphenyl derivatives, sulfone derivatives, etc. can be used. These sensitizers can be used alone or in combination of two or more. The above sensitizer is preferably solid at normal temperature, and more preferably has a melting point of about 70 °C or higher.

[0070] The dispersant is not particularly limited, and known ones can be used. Among them, from the viewpoint of being likely to form a crosslinked structure with the crosslinking agent described later, a dispersant having a carboxyl group is preferred. As the dispersant having a carboxyl group, acrylic (co)polymers such as acrylic acid (salt) polymers, acrylic acid (salt)·acrylic acid ester copolymers; styrene·acrylic acid (salt) copolymers, styrene·acrylic acid (salt)·acrylic acid ester copolymers, etc. of styrene·acrylic type copolymers; styrene·maleic acid (salt) copolymers, styrene·maleic acid (salt)·maleic acid ester copolymers, etc. can be used. Among them, at least one selected from the group consisting of acrylic (co)polymers and styrene·acrylic type copolymers is preferred. These dispersants can be used alone or in combination of two or more.

[0071] The salt in the acrylate contained in the dispersant having the carboxyl group is not particularly limited. For example, 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; polyvalent metal salts such as zinc and iron, etc. Among them, ammonium salts are preferred.

[0072] The content ratio of the above dispersant is preferably 1% by mass or more and 30% by mass or less, more preferably 2% by mass or more and 20% by mass or less, still more preferably 3% by mass or more and 15% by mass or less, and particularly preferably 3% by mass or more and 10% by mass or less, based on 100% by mass of the dry mass of the thermal layer 4.

[0073] From the viewpoint of easily forming a crosslinked structure with the crosslinking agent described later, the acid value of the above dispersant is preferably 100 mgKOH / g or more, more preferably 150 mgKOH / g or more, and still more preferably 200 mgKOH / g or more. By including a dispersant having an acid value within the above range in the thermal layer 4, a crosslinked structure can be efficiently formed, so that the viscosity of the paint for the thermal layer is further improved, and as a result, the generation of black spots and water swelling can be further suppressed. The acid value can be determined by a test method based on, for example, JIS K0070:1992 for the dried dispersant.

[0074] The phenolic color former is not particularly limited, and known ones can be used. For example, 2,6-bis[(2-hydroxy-5-methylphenyl)methyl]-4-methylphenol, 2,6-bis[(4-hydroxy-2,3,5-trimethylphenyl)methyl]-4-methylphenol, 2,6-bis[(hydroxy-phenyl)methyl]-butylphenol, etc. can be mentioned. When it is desired to obtain a heat-sensitive recording body that does not contain a phenolic color former, it is preferable not to use the above-mentioned phenolic color former. However, if not, the above-mentioned phenolic color former may be used.

[0075] As the above-mentioned storage stability improver, for example, sodium-2,2'-methylenebis(4,6-di-t-butylphenyl)phosphite, 4,4, butylidenebis(3-methyl-6-t-butylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, tris(2,6-dimethyl-4-t-butyl-3-hydroxybenzyl)isocyanurate, 4-(2-methylglycyloxy)-4'-benzyloxydiphenylsulfone, 2,2’-methylenebis(4-methyl-6-t-butylphenol), 2,2’-methylenebis(4-ethyl-6-t-butylphenol), diethylthiourea, zinc dibutyldithiocarbamate, 4,4’-thiobis(6-t-butyl-m-cresol), etc. can be used. These storage stability improvers can be used alone or in combination of two or more. Also, known ultraviolet absorbers, etc. may be added.

[0076] As the above-mentioned filler, for example, inorganic fillers such as calcium carbonate, diatomaceous earth, talc, kaolin, calcined kaolin, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, etc.; organic fillers such as hollow particles, urea-formalin resin, etc. can be used. These fillers can be used alone or in combination of two or more.

[0077] Examples of the crosslinking agent include organic crosslinking agents such as cationic crosslinking agents and non-cationic crosslinking agents; inorganic crosslinking agents such as zirconium carbonate. Examples of the cationic crosslinking agent include epichlorohydrin-based resins such as polyamide-epichlorohydrin resin, polyamine-epichlorohydrin resin, and polyamidepolyamine-epichlorohydrin resin. Examples of the non-cationic crosslinking agent include oxazoline-based compounds such as oxazoline group-containing polymers and oxazoline group-containing low-molecular-weight compounds. The non-cationic crosslinking agent is preferably an oxazoline group-containing polymer. These crosslinking agents can be used alone or in combination of two or more.

[0078] In this embodiment, since the thermal layer 4 contains a crosslinking agent, the generation of blistering can be further suppressed. The above "blistering" is a problem that is likely to occur particularly when a synthetic resin film is used as the base material. For example, it is considered that blistering occurs when ammonia or the like remaining in the thermal layer 4 after layer formation redissolves other materials. Since blistering causes ink or layer peeling, it is preferable to prevent its occurrence.

[0079] Regarding the phenomenon that the generation of black spots is suppressed by increasing the content ratio of the crosslinking agent in the thermal layer 4, the detailed mechanism of action is unknown. Generally, the above crosslinking agent reacts with the functional groups of other materials in the paint for the thermal layer to form a crosslinked structure. For example, when the crosslinking agent is a polyamide-epichlorohydrin resin, the azetidinium ring (AZR) in the polyamide-epichlorohydrin resin reacts with the functional groups of other materials (for example, the carboxyl group of the dispersant) to form a crosslinked structure. Similarly, when the crosslinking agent is an oxazoline group-containing polymer, the oxazoline group in the oxazoline group-containing polymer reacts with the functional groups of other materials (for example, the carboxyl group of the dispersant) to form a crosslinked structure. Therefore, when the thermal layer 4 contains the above crosslinking agent, a crosslinked structure is formed in the paint for the thermal layer, and the viscosity of the paint for the thermal layer tends to increase. Therefore, similar to the case of the above thickener, as the viscosity of the paint for the thermal layer increases due to the action of the crosslinking agent, the dye and the developer are more stably dispersed in the paint for the thermal layer, and aggregation is more suppressed. As a result, it is possible that the generation of black spots is more suppressed.

[0080] In the present embodiment, from the viewpoint of further suppressing the generation of black spots and swelling, it is preferable that the thermal layer 4 contains a crosslinking agent. As the above crosslinking agent, a cationic crosslinking agent and / or a non-cationic crosslinking agent is preferable, and a cationic crosslinking agent is more preferable.

[0081] As the above cationic crosslinking agent, an epichlorohydrin-based resin is preferable. Further, as the above epichlorohydrin-based resin, at least one selected from the group consisting of polyamide-epichlorohydrin resin and polyamide polyamine-epichlorohydrin resin is preferable, and polyamide-epichlorohydrin resin is more preferable.

[0082] In this embodiment, the content ratio of the cationic crosslinking agent is preferably 0.01% by mass or more, more preferably 0.10% by mass or more, and still more preferably 0.15% by mass or more, based on 100% by mass of the dry mass of the thermal layer. Also, the content ratio of the cationic crosslinking agent is preferably 5% by mass or less, more preferably 3% by mass or less, and still more preferably 2% by mass or less, based on 100% by mass of the dry mass of the thermal layer. When the content ratio is 0.01% by mass or more, the crosslinked structure in the paint for the thermal layer is sufficiently formed, and the generation of black spots and swelling is further suppressed. Also, when the content ratio is 5% by mass or less, the crosslinked structure of the paint for the thermal layer is formed within an appropriate range, and the stability of the paint for the thermal layer can be further improved.

[0083] As the glass transition temperature of the non-cationic crosslinking agent, for example, -50°C to 150°C is preferable, more preferably 0°C to 100°C, and still more preferably 40°C to 90°C. Also, as the number average molecular weight of the non-cationic crosslinking agent, for example, 5000 to 1,000,000 is preferable, more preferably 5000 to 500,000, and still more preferably 10,000 to 100,000.

[0084] In this embodiment, the content ratio of the non-cationic crosslinking agent is preferably 0.01% by mass or more, more preferably 0.10% by mass or more, still more preferably 0.20% by mass or more, still more preferably 0.30% by mass or more, and particularly preferably 0.40% by mass or more, based on 100% by mass of the dry mass of the thermal layer. Also, the content ratio of the non-cationic crosslinking agent is preferably 5% by mass or less, more preferably 3% by mass or less, and still more preferably 2% by mass or less, based on 100% by mass of the dry mass of the thermal layer. When the content ratio is 0.01% by mass or more, the crosslinked structure in the paint for the thermal layer is sufficiently formed, and the generation of black spots and swelling is further suppressed. Also, when the content ratio is 5% by mass or less, the crosslinked structure of the paint for the thermal layer is formed within an appropriate range, and the stability of the paint for the thermal layer can be further improved.

[0085] (Intermediate layer) In this embodiment, by providing the intermediate layer 5 on the thermal layer 4, a thermal recording medium 1 excellent in water resistance, oil resistance, chemical resistance, plasticizer resistance, etc. can be obtained. If the intermediate layer is not necessary, it may not be provided. The material for forming the intermediate layer 5 is not particularly limited, and for example, it can be formed of a resin. Further, the intermediate layer 5 may contain other materials, for example, a surfactant, an antifoaming agent, a crosslinking agent, etc. may be contained.

[0086] The resin is not particularly limited, and examples thereof include water-soluble resins such as styrene-acrylic resins, acrylic resins, polyvinyl alcohol (PVA) resins; SBR resins, etc. These resins can be used alone or in combination of two or more.

[0087] The resin may be a core-shell type resin in which hydrophobic core particles are coated with a water-soluble shell polymer. As the core-shell type resin, for example, those commercially available under the name of Barrier Star (manufactured by Mitsui Chemicals, Inc.) can be used.

[0088] The content ratio of the resin is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, still more preferably 80% by mass or more, particularly preferably 90% by mass or more with respect to 100% by mass of the dry mass of the intermediate layer 5. When the content ratio is within the above range, it is preferable from the viewpoint that the water resistance, chemical resistance, plasticizer resistance, etc. of the obtained thermal recording medium 1 are more excellent.

[0089] The coating amount (dry mass) of the intermediate layer 5 is, for example, preferably 0.3 g / m 2 ~10 g / m 2 and more preferably 0.5 g / m 2 ~5.0 g / m 2 is.

[0090] The thickness of the intermediate layer 5 is, for example, preferably 0.3 μm to 20 μm, more preferably 0.5 μm to 5.0 μm.

[0091] When the coating amount and thickness of the intermediate layer 5 in this embodiment are within the above ranges, it is preferable from the viewpoint that the resulting thermal recording medium 1 has more excellent water resistance, chemical resistance, plasticizer resistance, etc.

[0092] (Top coat layer) In this embodiment, the top coat layer 6 functions as a layer that further improves the color development property of the thermal layer 4 by improving the matching property of the thermal recording medium 1 with respect to the thermal head. When the top coat layer is not required, it may not be provided. The material for forming the top coat layer 6 is not particularly limited, and for example, it can be formed using a binder, a crosslinking agent, a filler, a wax, a surfactant, an antifoaming agent, etc. Further, the top coat layer 6 may contain other materials.

[0093] Examples of the binder include acrylic resins and the like. Examples of the wax include polyethylene, zinc stearate, and the like. Examples of the crosslinking agent include zirconium carbonate and the like.

[0094] Examples of the filler include colloidal silica, calcium carbonate, zirconium carbonate, polymethyl methacrylate (PMMA), polystyrene (PS), and the like. Note that the particle diameter of these fillers is preferably 1.0 μm or less.

[0095] The coating amount (dry mass) of the top coat layer 6 is, for example, preferably 0.3 g / m 2 ~10 g / m 2 and more preferably 0.5 g / m 2 ~5.0 g / m 2 is.

[0096] The thickness of the top coat layer 6 is, for example, preferably 0.3 μm to 20 μm, and more preferably 0.5 μm to 5.0 μm.

[0097] When the coating amount and thickness of the top coat layer 6 in the present embodiment are within the above ranges, it is preferable from the viewpoint that the color developability and the like of the obtained thermal recording medium 1 are more excellent.

[0098] Regarding the thermal recording medium 1 of the present embodiment, when the number of black dots of the laminate having the base material 2 and the thermal layer 4 at both end faces is measured by the method described in the examples, it is preferably 80 or less, more preferably 50 or less, still more preferably 40 or less, still more preferably 30 or less, still more preferably 20 or less, still more preferably 15 or less, and particularly preferably 10 or less. When the number of the above black dots is within the above range, the generation of black dots is sufficiently suppressed and the printing quality is more excellent.

[0099] [Method for manufacturing thermal recording medium] The method for manufacturing the thermal recording medium of the present embodiment is not particularly limited. For example, by dispersing the materials contained in the thermal layer in a solvent such as water, a paint for the thermal layer is prepared by a known or conventional method, and then the obtained paint is applied by a known or conventional method and then dried by a known or conventional method to manufacture it.

[0100] [Preparation step] In the preparation step, all the materials may be previously dispersed in the same solvent to prepare the above paint for the thermal layer. Also, a color former and a developer that react with each other may be prepared as separate dispersions and then mixed to obtain a paint for the thermal layer. At that time, other materials may be added to either the dispersion containing the dye or the dispersion containing the developer, or to both. The method for preparing the above paint is not particularly limited, and examples thereof include pulverization treatment using stirring, ultrasonic treatment, ball mill, bead mill, sand mill, high-pressure homogenizer, etc. These methods can be used alone or in combination of two or more.

[0101] The viscosity (rotation speed: 6 rpm) of the above-mentioned paint for the thermal layer (dry mass 34% by mass) at 25°C is preferably 110 to 1500 mPa·s, more preferably 250 to 1400 mPa·s, and even more preferably 300 to 1300 mPa·s. The above viscosity is a value measured using a B-type viscometer.

[0102] (Coating process) In the coating process, examples of the method of coating the paint for the thermal layer obtained above include directly coating the substrate, or coating on a release liner or the like and then transferring it to the substrate. The coating method is not particularly limited, and examples include air knife coating, bar blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, die coating, gravure coating, and the like. These methods can be used alone or in combination of two or more.

[0103] (Drying process) The method of drying the paint coated above is not particularly limited, and examples include heat drying, normal temperature drying, vacuum drying, and the like. By drying the paint coated by these methods, a thermal layer can be formed. These methods can be used alone or in combination of two or more.

[0104] As a method for forming other layers other than the thermal layer, the above content can be incorporated. For example, as shown in FIG. 1, as a method for manufacturing a thermal recording medium 1 including a base material 2, an anchor layer 3, a thermal layer 4, an intermediate layer 5, and a top coat layer 6 in this order, for example, an anchor layer 3 is formed on the base material 2, and then a thermal layer 4 is formed on the anchor layer 3, and then an intermediate layer 5 is formed on the thermal layer 4, and then a top coat layer 6 is formed on the intermediate layer 5. As a method for preparing the above-mentioned paint for the anchor layer, the paint for the intermediate layer, and the paint for the top coat layer, the paint may be prepared for each layer. For example, all the materials contained in the layer may be dispersed in the same solvent in advance for preparation. When components that react with each other are included, each material may be prepared as a separate dispersion and then the two are mixed and prepared. The above preparation method is not particularly limited, and examples include crushing treatment using stirring, ultrasonic treatment, ball mill, bead mill, sand mill, high-pressure homogenizer, etc. These methods can be used alone or in combination of two or more. As a method for applying the paint for the anchor layer obtained above to the base material 2, for example, a method of directly applying it on the base material 2 can be mentioned. The method for applying the paint for the anchor layer is not particularly limited, and examples include air knife coating, bar blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, die coating, gravure coating, etc. Also, these methods can be used alone or in combination of two or more. Next, the anchor layer 3 can be formed on the base material 2 by drying the paint for the anchor layer applied above. As the above drying method, for example, heat drying, normal temperature drying, vacuum drying, etc. can be mentioned. Also, these methods can be used alone or in combination of two or more. Next, the thermal layer 4, the intermediate layer 5, and the top coat layer are formed on the anchor layer 3, on the thermal layer 4, and on the intermediate layer 5, respectively, in the same procedure as above, whereby the thermal recording medium 1 shown in FIG. 1 can be obtained.

[0105] In the method for manufacturing the heat-sensitive recording medium of the present embodiment, each layer may be simultaneously coated in multiple layers using, for example, a curtain coater or the like, or may be sequentially formed individually. Further, some layers may be simultaneously coated and some layers may be sequentially formed individually.

[0106] [Second Embodiment] [Heat-Sensitive Recording Medium] Next, an embodiment (second embodiment) of the heat-sensitive recording medium according to the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, the heat-sensitive recording medium 1 of the present embodiment includes a base material 2, an anchor layer 3, a thermal layer 4, an intermediate layer 5, and a top coat layer 6 in this order. This embodiment has the same configuration as the first embodiment except for the thermal layer 4. That is, the configurations of the base material 2, the anchor layer 3, the intermediate layer 5, and the top coat layer 6 of the present embodiment, as well as the method for manufacturing the heat-sensitive recording medium 1, are all the same as those described in the first embodiment. Therefore, the description thereof will be omitted, and only the configuration of the thermal layer 4 will be described in detail.

[0107] The heat-sensitive recording medium 1 of the present embodiment contains a non-phenolic developer in the thermal layer 4 and satisfies at least the following aspect (2). Aspect (2): The thermal layer 4 contains a cationic crosslinking agent as the crosslinking agent, and the content ratio of the cationic crosslinking agent is 0.30% by mass or more with respect to 100% by mass of the dry mass of the thermal layer 4.

[0108] The heat-sensitive recording medium 1 of the present embodiment may further satisfy any one or more of the following aspects (1) and (3). Among them, it is preferable to satisfy aspect (1) and aspect (2). Aspect (1): The thermal layer 4 contains the thickener, and the content ratio of the thickener is 0.07% by mass or more with respect to 100% by mass of the dry mass of the thermal layer 4. Aspect (3): The thermal layer 4 contains a non-cationic crosslinking agent as the crosslinking agent.

[0109] Regarding the above non-phenolic color developer, it is exactly the same as the content described in the first embodiment. That is, the above non-phenolic color developer is preferably an N,N'-diarylurea derivative, and more preferably an N,N'-diarylurea derivative having one or more sulfonic acid ester structures in the molecule. Specifically, it is preferably a compound represented by the above formula (1) and / or a compound represented by the above formula (2). These non-phenolic color developers can be used alone or in combination of two or more.

[0110] As the compound represented by the above formula (1), a compound represented by the above formula (1a) is preferable. Specifically, N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-xylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(mesitylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(o-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)phenyl]urea, etc. represented by the above formula (1b) can be mentioned. Also, as the compound represented by the above formula (2), a compound represented by the above formula (2a) is preferable. Specifically, 3-[(3-phenylureido)phenyl]-4-methylbenzenesulfonate represented by the above formula (2b) is preferable.

[0111] The above non-phenolic color developer is preferably a urethane-urea compound. It is more preferable that the above non-phenolic color developer contains an N,N'-diarylurea derivative (excluding urethane-urea compounds) and a urethane-urea compound.

[0112] As the above urethane-urea compound, a urethane-urea compound having two or more urea bonds and two or more urethane bonds in the molecule is preferable. Specifically, the urethane-urea compound represented by the above formula (3) is preferable, and the compound represented by the above formula (3a) is more preferable. Specifically, the compound represented by the above formula (3b) can be mentioned.

[0113] In the present embodiment, the content ratio of the non-phenolic color former is preferably 10% by mass or more and 50% by mass or less, more preferably 15% by mass or more and 35% by mass or less, based on 100% by mass of the dry mass of the thermal layer 4.

[0114] In the present embodiment, the content ratio of the N,N'-diarylurea derivative (excluding the urethane-urea compound) is preferably 5% by mass or more and 35% by mass or less, more preferably 10% by mass or more and 30% by mass or less, based on 100% by mass of the dry mass of the thermal layer 4. Further, the total content ratio of the compound represented by the above formula (1) and / or the compound represented by the above formula (2) is preferably within the above range with respect to 100% by mass of the non-phenolic color former in the thermal layer 4.

[0115] In the present embodiment, the content ratio of the urethane-urea compound is preferably 1% by mass or more and 30% by mass or less, more preferably 5% by mass or more and 15% by mass or less, based on 100% by mass of the dry mass of the thermal layer 4.

[0116] In the present embodiment, the content ratio of the non-phenolic color former is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, based on 100% by mass of the color former in the thermal layer 4. Further, the content ratio of the non-phenolic color former may be 100% by mass with respect to 100% by mass of the color former in the thermal layer 4.

[0117] In the present embodiment, the content ratio of the above N,N'- diarylurea derivative (excluding the ureauurethane compound) is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 55% by mass or more with respect to 100% by mass of the non-phenolic color former in the thermal layer 4. Further, the content ratio of the above N,N'- diarylurea derivative (excluding the ureauurethane compound) is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, and particularly preferably 75% by mass or less with respect to 100% by mass of the non-phenolic color former in the thermal layer 4. Further, the total content ratio of the compound represented by the above formula (1) and / or the compound represented by the above formula (2) is preferably within the above range with respect to 100% by mass of the non-phenolic color former in the thermal layer 4.

[0118] In the present embodiment, the total content ratio of the above N,N'- diarylurea derivative (excluding the ureauurethane compound) and the ureauurethane compound is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more with respect to 100% by mass of the non-phenolic color former in the thermal layer 4. Further, the total content ratio of the above N,N'- diarylurea derivative (excluding the ureauurethane compound) and the ureauurethane compound may be 100% by mass with respect to 100% by mass of the non-phenolic color former in the thermal layer 4. Further, the total content ratio of the compound represented by the above formula (1) and / or the compound represented by the above formula (2) and the ureauurethane compound is preferably within the above range with respect to 100% by mass of the non-phenolic color former in the thermal layer 4.

[0119] In the present embodiment, when the dry mass of the N,N'- diarylurea derivative (excluding the urethane - urea compound) in the thermal layer 4 is taken as 1, the ratio of the dry mass of the urethane - urea compound in the thermal layer 4 (dry mass of the urethane - urea compound / dry mass of the N,N'- diarylurea derivative (excluding the urethane - urea compound)) is preferably 0.1 or more and 5 or less, more preferably 0.2 or more and 2 or less, and even more preferably 0.3 or more and 1 or less. Further, when the total dry mass of the compound represented by the above formula (1) and / or the compound represented by the above formula (2) in the thermal layer 4 is taken as 1, the ratio of the dry mass of the urethane - urea compound in the thermal layer 4 (dry mass of the urethane - urea compound / total dry mass of the compound represented by the above formula (1) and / or the compound represented by the above formula (2)) is preferably within the above range.

[0120] Regarding the above cationic cross - linking agent, except for the content of the content ratio, it is exactly the same as the content described in the first embodiment. That is, as the above cationic cross - linking agent, an epichlorohydrin - based resin is preferable. As the above epichlorohydrin - based resin, at least one selected from the group consisting of polyamide - epichlorohydrin resin and polyamide - polyamine - epichlorohydrin resin is preferable, and polyamide - epichlorohydrin resin is more preferable. These cross - linking agents can be used alone or in combination of two or more.

[0121] The content ratio of the cationic crosslinking agent is 0.30% by mass or more, preferably 0.40% by mass or more, more preferably 0.50% by mass or more, and even more preferably 0.60% by mass or more, based on 100% by mass of the dry mass of the thermal layer. Also, the content ratio of the cationic crosslinking agent is preferably 5% by mass or less, more preferably 3% by mass or less, and particularly preferably 2% by mass or less, based on 100% by mass of the dry mass of the thermal layer. When the content ratio of the cationic crosslinking agent is 0.3% by mass or more, the crosslinked structure in the paint for the thermal layer is sufficiently formed, and the occurrence of water swelling and black spots is more suppressed. Also, when the content ratio of the cationic crosslinking agent is 5% by mass or less, the crosslinked structure of the paint for the thermal layer is formed within an appropriate range, and the stability of the paint for the thermal layer can be further improved.

[0122] From the viewpoint of further suppressing the occurrence of black spots, the thermal layer 4 of the present embodiment preferably contains a thickener. Regarding the above thickener, except for the content ratio, it is all the same as the content described in the first embodiment. That is, as the above thickener, at least one selected from the group consisting of an alkali-soluble type thickener, a cellulose-based thickener, and a nonionic polymer type thickener is preferable, and an alkali-soluble type thickener is more preferable. Among the above alkali-soluble type thickeners, in particular, at least one selected from the group consisting of a HASE type thickener and an ASE type thickener is preferable. These thickeners can be used alone or in combination of two or more. Also, as the above thickener, an acrylic-based (co)polymer or the like is preferable. Among them, as the above thickener, at least one selected from the group consisting of an acrylic-based (co)polymer of a HASE type thickener and an acrylic-based (co)polymer of an ASE type thickener is preferable.

[0123] The content ratio of the above thickener is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.2% by mass or more, still more preferably 0.3% by mass or more, and particularly preferably 0.4% by mass or more with respect to 100% by mass of the dry mass of the thermal layer 4. Also, the content ratio of the above thickener is preferably 5% by mass or less, more preferably 3% by mass or less, and still more preferably 2% by mass or less with respect to 100% by mass of the dry mass of the thermal layer 4. When the content ratio of the thickener is 0.01% by mass or more, the viscosity of the paint for the thermal layer is appropriately improved, and the generation of black spots is further suppressed. Also, when the content ratio of the thickener is 5% by mass or less, the viscosity of the paint for the thermal layer falls within an appropriate range, and the stability of the paint for the thermal layer can be further improved.

[0124] The thermal layer 4 of the present embodiment preferably contains a dispersant. The above dispersant is exactly the same as the content described in the first embodiment. That is, as the above dispersant, a dispersant having a carboxyl group is preferable. Specifically, at least one selected from the group consisting of acrylic (co)polymers and styrene-acrylic copolymers is preferable. These dispersants can be used alone or in combination of two or more.

[0125] The content ratio of the above dispersant is preferably 1% by mass or more and 30% by mass or less, more preferably 2% by mass or more and 20% by mass or less, still more preferably 3% by mass or more and 15% by mass or less, and particularly preferably 3% by mass or more and 10% by mass or less with respect to 100% by mass of the dry mass of the thermal layer 4.

[0126] From the viewpoint of easily forming a crosslinked structure, the acid value of the above dispersant is preferably 100 mgKOH / g or more, more preferably 150 mgKOH / g or more, and still more preferably 200 mgKOH / g or more.

[0127] The thermal layer 4 of the present embodiment may contain other materials. For example, dyes that develop color upon heating, binders, waxes, sensitizers, phenolic developers, storage improvers, surfactants, defoamers, fillers, non-cationic crosslinking agents, inorganic crosslinking agents, and preservatives, etc. can be mentioned. These examples and preferred embodiments are the same as those described in the first embodiment. In this specification, the above "embodiment" shall include all of the type, average particle diameter, melting point, acid value, glass transition temperature, number average molecular weight, content ratio, and content ratio (ratio of dry mass).

[0128] Regarding the thermal recording medium 1 of the present embodiment, when the number of black dots in the laminate having the base material 2 and the thermal layer 4 at both end faces is measured by the method described in the examples, it is preferably 80 or less, more preferably 50 or less, still more preferably 40 or less, still more preferably 30 or less, still more preferably 20 or less, still more preferably 15 or less, and particularly preferably 10 or less. When the number of black dots is within the above range, the generation of black dots is sufficiently suppressed and the printing quality is excellent.

[0129] [Third Embodiment] [Thermal Recording Medium] Next, an embodiment (first embodiment) of the thermal recording medium according to the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, the thermal recording medium 1 of the present embodiment includes a base material 2, an anchor layer 3, a thermal layer 4, an intermediate layer 5, and a top coat layer 6 in this order. This embodiment has the same configuration as the first embodiment except for the thermal layer 4. That is, regarding the configurations of the base material 2, the anchor layer 3, the intermediate layer 5, and the top coat layer 6 of the present embodiment, as well as the manufacturing method of the thermal recording medium 1, since they are all the same as those described in the first embodiment, the description will be omitted and only the configuration of the thermal layer 4 will be described in detail.

[0130] The thermal recording medium 1 of the present embodiment contains a non-phenolic developer in the thermal layer 4 and satisfies at least the following aspect (3). Aspect (3): The thermal layer 4 contains a non-cationic crosslinking agent as the crosslinking agent.

[0131] The thermal recording medium 1 of this embodiment may further satisfy any one or more of the following aspects (1) and (2). Aspect (1): The thermal layer 4 contains the thickener, and the content ratio of the thickener is 0.07% by mass or more with respect to 100% by mass of the dry mass of the thermal layer 4. Aspect (2): The thermal layer 4 contains a cationic crosslinking agent as the crosslinking agent, and the content ratio of the cationic crosslinking agent is 0.30% by mass or more with respect to 100% by mass of the dry mass of the thermal layer 4.

[0132] Regarding the non-phenolic developer, it is exactly the same as the content described in the first embodiment. That is, the non-phenolic developer is preferably an N,N'-diarylurea derivative, and more preferably an N,N'-diarylurea derivative having one or more sulfonic acid ester structures in the molecule. Specifically, it is preferably the compound represented by the above formula (1) and / or the compound represented by the above formula (2). These non-phenolic developers can be used alone or in combination of two or more.

[0133] As the compound represented by the above formula (1), the compound represented by the above formula (1a) is preferable. Specifically, N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-xylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(mesitylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(o-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)phenyl]urea, etc. represented by the above formula (1b) can be mentioned. Further, as the compound represented by the above formula (2), the compound represented by the above formula (2a) is preferable. Specifically, 3-[(3-phenylureido)phenyl]-4-methylbenzenesulfonate represented by the above formula (2b) is preferable.

[0134] The above non-phenolic color developer is preferably a urethane-urea compound. More preferably, the above non-phenolic color developer contains an N,N'-diarylurea derivative (excluding urethane-urea compounds) and a urethane-urea compound.

[0135] As for the above urethane-urea compound, a urethane-urea compound having two or more urethane bonds and two or more urea bonds in the molecule is preferred. Specifically, the urethane-urea compound represented by the above formula (3) is preferred, and the compound represented by the above formula (3a) is more preferred. Specifically, the compound represented by the above formula (3b) can be mentioned.

[0136] In the present embodiment, the content ratio of the above non-phenolic color developer is preferably 10% by mass or more and 50% by mass or less, more preferably 15% by mass or more and 35% by mass or less, based on 100% by mass of the dry mass of the thermal layer 4.

[0137] In the present embodiment, the content ratio of the above N,N'-diarylurea derivative (excluding urethane-urea compounds) is preferably 5% by mass or more and 35% by mass or less, more preferably 10% by mass or more and 30% by mass or less, based on 100% by mass of the dry mass of the thermal layer 4. Also, the total content ratio of the compound represented by the above formula (1) and / or the compound represented by the above formula (2) with respect to 100% by mass of the non-phenolic color developer in the thermal layer 4 is preferably within the above range.

[0138] In the present embodiment, the content ratio of the urethane-urea compound is preferably 1% by mass or more and 30% by mass or less, more preferably 5% by mass or more and 15% by mass or less, based on 100% by mass of the dry mass of the thermal layer 4.

[0139] In the present embodiment, the content ratio of the non-phenolic color former is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, based on 100% by mass of the color former in the thermal layer 4. Further, the content ratio of the non-phenolic color former may be 100% by mass based on 100% by mass of the color former in the thermal layer 4.

[0140] In the present embodiment, the content ratio of the N,N'- diarylurea derivative (excluding the urethane-urea compound) is preferably 40% by mass or more, more preferably 50% by mass or more, still more preferably 55% by mass or more, based on 100% by mass of the non-phenolic color former in the thermal layer 4. Further, the content ratio of the N,N'- diarylurea derivative (excluding the urethane-urea compound) is preferably 95% by mass or less, more preferably 90% by mass or less, still more preferably 80% by mass or less, particularly preferably 75% by mass or less, based on 100% by mass of the non-phenolic color former in the thermal layer 4. Further, the total content ratio of the compound represented by the above formula (1) and / or the compound represented by the above formula (2) is preferably within the above range based on 100% by mass of the non-phenolic color former in the thermal layer 4.

[0141] In the present embodiment, the total content ratio of the N,N'- diarylurea derivative (excluding the urethane-urea compound) and the urethane-urea compound is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, based on 100% by mass of the non-phenolic color former in the thermal layer 4. Further, the total content ratio of the N,N'- diarylurea derivative (excluding the urethane-urea compound) and the urethane-urea compound may be 100% by mass based on 100% by mass of the non-phenolic color former in the thermal layer 4. Further, the total content ratio of the compound represented by the above formula (1) and / or the compound represented by the above formula (2) and the urethane-urea compound is preferably within the above range based on 100% by mass of the non-phenolic color former in the thermal layer 4.

[0142] In this embodiment, when the dry mass of the above N,N'- diarylurea derivative (excluding the ureauurethane compound) in the thermal layer 4 is taken as 1, the ratio of the dry mass of the ureauurethane compound in the thermal layer 4 (dry mass of the ureauurethane compound / dry mass of the N,N'- diarylurea derivative (excluding the ureauurethane compound)) is preferably 0.1 or more and 5 or less, more preferably 2 or more and 2 or less, still more preferably 0.3 or more and 1 or less. Further, when the total dry mass of the compound represented by the above formula (1) and / or the compound represented by the above formula (2) in the thermal layer 4 is taken as 1, the ratio of the dry mass of the ureauurethane compound in the thermal layer 4 (dry mass of the ureauurethane compound / total dry mass of the compound represented by the above formula (1) and / or the compound represented by the above formula (2)) is preferably within the above range.

[0143] The examples and preferred embodiments of the above non-cationic crosslinking agent are exactly the same as the content described in the first embodiment. That is, the above non-cationic crosslinking agent is preferably an oxazoline group-containing polymer. Further, the glass transition temperature of the above non-cationic crosslinking agent is, for example, preferably -50°C to 150°C, more preferably 0°C to 100°C, still more preferably 40°C to 90°C. Further, the number average molecular weight of the above non-cationic crosslinking agent is, for example, preferably 5,000 to 1,000,000, more preferably 5,000 to 500,000, still more preferably 10,000 to 100,000.

[0144] In this embodiment, the content ratio of the above non-cationic crosslinking agent is preferably 0.01% by mass or more, more preferably 0.10% by mass or more, still more preferably 0.20% by mass or more, still more preferably 0.30% by mass or more, particularly preferably 0.40% by mass or more, based on 100% by mass of the dry mass of the thermal layer. Further, the content ratio of the above non-cationic crosslinking agent is preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 2% by mass or less, based on 100% by mass of the dry mass of the thermal layer.

[0145] From the perspective of further suppressing the occurrence of black dots, the thermal layer 4 of this embodiment preferably contains a thickener. Regarding the above thickener, except for the content ratio, it is exactly the same as the content described in the first embodiment. That is, as the above thickener, at least one selected from the group consisting of an alkali-soluble thickener, a cellulose-based thickener, and a nonionic polymer thickener is preferable, and an alkali-soluble thickener is more preferable. Among the above alkali-soluble thickeners, in particular, at least one selected from the group consisting of a HASE type thickener and an ASE type thickener is preferable. These thickeners can be used alone or in combination of two or more. Further, as the above thickener, an acrylic (co)polymer or the like is preferable. In particular, as the above thickener, at least one selected from the group consisting of an acrylic (co)polymer of a HASE type thickener and an acrylic (co)polymer of an ASE type thickener is preferable.

[0146] The content ratio of the above thickener is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.2% by mass or more, still more preferably 0.3% by mass or more, and particularly preferably 0.4% by mass or more with respect to 100% by mass of the dry mass of the thermal layer 4. Also, the content ratio of the above thickener is preferably 5% by mass or less, more preferably 3% by mass or less, and still more preferably 2% by mass or less with respect to 100% by mass of the dry mass of the thermal layer 4. When the above content ratio is 0.01% by mass or more, the viscosity of the paint for the thermal layer is appropriately improved, and the occurrence of black dots is further suppressed. Also, when the above content ratio is 5% by mass or less, the viscosity of the paint for the thermal layer is within an appropriate range, and the stability of the paint for the thermal layer can be further improved.

[0147] The thermal layer 4 of this embodiment preferably contains a dispersant. Regarding the above dispersant, it is exactly the same as the content described in the first embodiment. That is, as the above dispersant, a dispersant having a carboxyl group is preferable. Specifically, at least one selected from the group consisting of an acrylic (co)polymer and a styrene-acrylic copolymer is preferable. These dispersants can be used alone or in combination of two or more.

[0148] The content ratio of the above dispersant is preferably 1% by mass or more and 30% by mass or less, more preferably 2% by mass or more and 20% by mass or less, still more preferably 3% by mass or more and 15% by mass or less, and particularly preferably 3% by mass or more and 10% by mass or less with respect to 100% by mass of the dry mass of the above thermal layer 4.

[0149] From the viewpoint of easily forming a crosslinked structure, the acid value of the above dispersant is preferably 100 mgKOH / g or more, more preferably 150 mgKOH / g or more, and still more preferably 200 mgKOH / g or more.

[0150] The thermal layer 4 of the present embodiment may contain other materials. For example, dyes that develop color by heating, binders, waxes, sensitizers, dispersants, phenolic developers, preservative improvers, surfactants, defoamers, fillers, cationic crosslinking agents, inorganic crosslinking agents, and preservatives can be mentioned. These examples and preferred embodiments are the same as those described in the first embodiment.

[0151] Regarding the thermal recording medium 1 of the present embodiment, when the number of black dots in the laminate having the base material 2 and the thermal layer 4 at both end faces is measured by the method described in the examples, it is preferably 80 or less, more preferably 50 or less, still more preferably 40 or less, still more preferably 30 or less, still more preferably 20 or less, still more preferably 15 or less, and particularly preferably 10 or less. When the number of black dots is within the above range, the generation of black dots is sufficiently suppressed and the printing quality is more excellent.

[0152] Although the thermal recording medium according to the present invention has been described in detail with reference to the first to third embodiments, the thermal recording medium according to the present invention is not limited to these embodiments. For example, as the first to third embodiments, a thermal recording medium including a base material, an anchor layer, a thermal layer, an intermediate layer, and a top coat layer has been exemplified, but it may not include one or more of the anchor layer, the intermediate layer, and the top coat layer. Further, the thermal recording medium according to the present invention may include another layer (such as a back coat layer). The above back coat layer is a layer provided on the surface of the above base material opposite to the surface provided with the above thermal layer.

Example

[0153] Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited by these examples and is limited only by the description in the claims.

[0154] A thermal recording medium in which an anchor layer, a thermal layer, an intermediate layer, and a top coat layer are laminated in this order on a substrate was produced by the following steps. (Example 1) (Production of Thermal Recording Medium) <Anchor Layer> Water was added to a modified styrene-acrylic acid (ammonium salt) resin (manufactured by BASF Japan Ltd., trade name: Joncryl series) so that the dry mass became 10% by mass, thereby preparing a coating material for the anchor layer. The above coating material for the anchor layer was applied onto synthetic paper (thickness: 90 μm) as a substrate, and then dried, whereby an anchor layer having a coating amount of 0.2 to 2.0 g / m 2 as the dry mass and a thickness of 0.2 to 2 μm was formed.

[0155] <Thermal Layer> As a dye, 35% by mass of 2'-anilino-6'-(dibutylamino)-3'-methylspiro[phthalide-3,9'-xanthene], as a sensitizer, 48% by mass of 1,2-bis(3-methylphenoxy)ethane, as a dispersant 1, 7% by mass of an acrylic copolymer (manufactured by BASF Japan Ltd., trade name: Joncryl series, acid value: 240 mgKOH / g), as a dispersant 2, 10% by mass of an acrylic copolymer (manufactured by BASF Japan Ltd., trade name: Joncryl series, acid value: 65 mgKOH / g), and water as a solvent were mixed to prepare Agent A (dry mass 32% by mass) by a conventional method. The numerical values of the above respective compounding materials indicate the mass during drying.

[0156] Next, as color developer 1, 24.7% by mass of 3-[(3-phenylureido)phenyl]-4-methylbenzenesulfonate, 5.0% by mass of dispersant 1, as thickener 1, 0.1% by mass of an acrylic (co)polymer (manufactured by Rohm and Haas Japan Co., Ltd., trade name: ASE95NP), and water as a solvent were mixed to prepare a color developer 1 dispersion (dry mass 39.5% by mass). Then, as color developer 2, 13.5% by mass of the ureaurethane compound represented by the above formula (3b), 38.7% by mass of a styrene-butadiene copolymer as a binder, 12.6% by mass of hollow particles as a filler, 3.6% by mass of polyethylene wax as wax 1, and 1.8% by mass of a special anionic surfactant as wax 2 were added, and Agent B was prepared by a conventional method. The numerical values of the above respective compounding materials indicate the mass at the time of drying.

[0157] Next, 27.2% by mass of the above Agent A, 65.6% by mass of the above Agent B, 6.9% by mass of 1,2-bis(3-methylphenoxy)ethane as a sensitizer, and 0.25% by mass of an acrylic copolymer (manufactured by The Dow Chemical Company Japan Ltd., trade name: Primal TT-935) as thickener 2 were mixed, and a coating material for the thermal layer (dry mass 34% by mass) was prepared by a conventional method. The above coating material for the thermal layer was applied onto the above anchor layer and dried to form a thermal layer with a coating amount of 4.8 g / m as dry mass. 2 Also, the viscosity of the above coating material for the thermal layer with the liquid temperature in the range of 22°C to 26°C was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., model name: RB-80L) under the conditions of a rotation speed of 6 rpm and a measurement time of 3 minutes. The measurement results of the viscosity of the coating material for the thermal layer at this time are shown in Table 1. The numerical values of the above respective compounding materials indicate the mass at the time of drying.

[0158] <Intermediate layer> As a binder, 100 parts by mass of an acrylic resin, 6 parts by mass of an epichlorohydrin-based resin as a cationic crosslinking agent, and water as a solvent were mixed to prepare a coating material for the intermediate layer. The above coating material for the intermediate layer was applied onto the above thermal layer and then dried to obtain a coating amount of 1.6 g / m as dry mass.2 An intermediate layer was formed.

[0159] <Top coat layer> As a binder, 46 parts by mass of an acrylic resin, as a filler, 36 parts by mass of calcium carbonate, as a wax, 13 parts by mass of a special anionic surfactant, as a filler, 8 parts by mass of methyl methacrylate (PMMA), as a wax, 6 parts by mass of polyethylene wax, 6 parts by mass of a zirconium compound as a crosslinking agent, and water as a solvent were mixed to prepare a top coat layer paint. The top coat layer paint was applied onto the intermediate layer and then dried, whereby the coating amount was 1.6 g / m as the dry mass 2 of the top coat layer was formed, and the thermosensitive recording medium of Example 1 was produced.

[0160] [Measurement of the number of black dots] In the measurement of the number of black dots, the laminate of the substrate, the anchor layer, and the thermal layer obtained by the above procedure was allowed to stand in a dryer furnace set at 130 °C for 15 minutes and heated to cause color development. The laminate after color development was observed from the thermal layer side, and the number of black dots per 1 cm 2 was measured. Thereafter, the measurement of the number of black dots per 1 cm 2 was carried out a total of 3 times, and the number of black dots per 3 cm 2 was measured. At this time, the black dots having a major axis of 150 μm or more that were visually observable were measured. The total number of black dots per the above 3 cm 2 is shown in Table 1 described later.

[0161] (Examples 2 to 16 and Comparative Examples 1 to 2) In the thermal layer, except that the mass of each compounding material during drying was changed to the composition shown in Table 1, Table 2, Table 3, or Table 4 described later to prepare a thermal layer paint, the thermosensitive recording media of Examples 2 to 16 and Comparative Examples 1 to 2 were produced in the same manner as in Example 1 above, and the viscosity and the number of black dots of the thermal layer paint were measured. The measurement results of the viscosity of the thermal layer paint and the measurement results of the number of black dots at this time are shown in Table 1, Table 2, Table 3, or Table 4.

[0162]

Table 1

[0163] As the compounding material, for the thickener 3, an acrylic copolymer (manufactured by Toagosei Co., Ltd., trade name: A-7075) was used.

[0164]

Table 2

[0165] As the compounding materials, for the crosslinking agent 1, a polyamide-epichlorohydrin resin which is a cationic crosslinking agent was used, and for the crosslinking agent 2, a polyamide-epichlorohydrin resin which is a cationic crosslinking agent was used.

[0166]

Table 3

[0167]

Table 4

[0168] As the compounding material, for the crosslinking agent 3, an oxazoline group-containing polymer (manufactured by Nippon Shokubai Co., Ltd., trade name: Epocross WS-700) which is a non-cationic crosslinking agent was used.

[0169] As shown in Table 1, when the thermal layer does not contain a crosslinking agent and the content ratio of the thickener is less than 0.07% by mass (Comparative Example 1), the number of black dots was 12, whereas when the thermal layer does not contain a crosslinking agent and the content ratio of the thickener is 0.07% by mass or more (Examples 1 to 5), the number of black dots was 11 or less. At this time, it was confirmed that as the content ratio of the thickener increased, the viscosity of the paint for the thermal layer and the number of black dots tended to decrease. For this reason, it is considered that when the above thermal layer contains a thickener, there is an effect of further suppressing the generation of black dots.

[0170] As shown in Table 2, even when the thermal layer contains a crosslinking agent, differences were observed in the tendency of black dots to occur depending on the content ratio of the thickener. That is, when the content ratio of the thickener contained in the thermal layer was less than 0.07% by mass (Comparative Example 2), the number of black dots was 90, whereas when the content ratio of the thickener was 0.07% by mass or more (Examples 6 to 9), the number of black dots was 15 or less. Thus, it was confirmed that as the content ratio of the thickener increased, the viscosity of the thermal layer paint and the number of black dots tended to decrease. Therefore, even when the thermal layer contains a crosslinking agent, including a thickener has the effect of suppressing the generation of black dots, and it is considered that increasing the content ratio of the thickener further enhances the above effect.

[0171] As shown in Table 3, when the content ratio of the thickener contained in the thermal layer was less than 0.07% by mass and the thermal layer contained a cationic crosslinking agent as the crosslinking agent, differences were observed in the tendency of black dots to occur depending on the content ratio of the cationic crosslinking agent. That is, when the thermal layer contained Crosslinking Agent 1, which is a cationic crosslinking agent, and the content ratio was less than 0.30% by mass (Comparative Example 2), the number of black dots was 90, whereas when the content ratio of Crosslinking Agent 1 was 0.30% by mass or more (Examples 10 to 12), the number of black dots was 31 or less. Further, when Crosslinking Agent 1 was changed to Crosslinking Agent 2 and the content ratio of Crosslinking Agent 2 was 0.30% by mass or more (Examples 13 to 14), the number of black dots was 32 or less. In any case, it was confirmed that as the content ratio of the crosslinking agent increased, the viscosity of the thermal layer paint and the number of black dots tended to decrease. Therefore, when the thermal layer contains a cationic crosslinking agent as the crosslinking agent, it is considered that increasing the content ratio of the cationic crosslinking agent has the effect of suppressing the generation of black dots.

[0172] As shown in Table 4, even when the thermal layer contains a crosslinking agent, there were differences in the tendency of black dots to occur depending on the type of crosslinking agent. That is, when the thermal layer contained a cationic crosslinking agent (Comparative Example 2), the number of black dots was 90, whereas when the thermal layer contained a non-cationic crosslinking agent (Examples 15 to 16), the number of black dots was 17 or less. At this time, it was confirmed that as the content ratio of the crosslinking agent increased, the viscosity of the paint for the thermal layer and the number of black dots tended to decrease. Therefore, even when the thermal layer contains a crosslinking agent, by using a non-cationic crosslinking agent as the type of crosslinking agent, there is an effect of suppressing the generation of black dots, and it is considered that by further increasing the content ratio of the non-cationic crosslinking agent, the above effect is further enhanced.

[0173] As a summary of the above, the configuration of the present invention and its variations are appended below. [Appendix 1] A thermal recording medium in which a thermal layer containing a non-phenolic developer is laminated on a substrate, wherein the thermal layer contains a crosslinking agent and / or a thickening agent, and further satisfies any one or more of the following aspects (1) to (3). Aspect (1): The thermal layer contains the thickening agent, and the content ratio of the thickening agent is 0.07% by mass or more with respect to 100% by mass of the dry mass of the thermal layer. Aspect (2): The thermal layer contains a cationic crosslinking agent as the crosslinking agent, and the content ratio of the cationic crosslinking agent is 0.30% by mass or more with respect to 100% by mass of the dry mass of the thermal layer. Aspect (3): The thermal layer contains a non-cationic crosslinking agent as the crosslinking agent. [Appendix 2] The thermal recording medium according to Appendix 1, wherein the non-phenolic developer contains the compound represented by the above formula (1) and / or the compound represented by the above formula (2). [Appendix 3] The thermal recording medium according to Appendix 1 or 2, wherein the non-phenolic developer contains the compound represented by the above formula (1a) and / or the compound represented by the above formula (2a). [Supplementary Note 4] The thermal recording material according to any one of Supplementary Notes 1 to 3, wherein the non-phenolic color former contains a urethane-urea compound. [Supplementary Note 5] The thermal recording material according to Supplementary Note 4, wherein the urethane-urea compound is the urethane-urea compound represented by the above formula (3). [Supplementary Note 6] The thermal recording material according to any one of Supplementary Notes 1 to 5, which satisfies the above aspect (1) and the above aspect (2). [Supplementary Note 7] The thermal recording material according to Supplementary Note 6, wherein the cationic crosslinking agent is a polyamide-epichlorohydrin resin. [Supplementary Note 8] The thermal recording material according to any one of Supplementary Notes 1 to 7, which satisfies the above aspect (1) and the above aspect (3). [Supplementary Note 9] The thermal recording material according to Supplementary Note 8, wherein the non-cationic crosslinking agent is an oxazoline group-containing polymer.

Industrial Applicability

[0174] The thermal recording material of the present invention is a thermal recording material provided with a thermal layer containing a non-phenolic color former, and is a thermal recording material in which the generation of black spots is suppressed. Therefore, it can be suitably used even in situations where environmental response is required.

Explanation of Symbols

[0175] 1 Thermal recording material 2 Base material 3 Anchor layer 4 Thermal layer 5 Intermediate layer 6 Top coat layer

Claims

1. A thermal recording medium having a thermal layer containing a non-phenolic color former laminated on a substrate, wherein the thermal layer contains a crosslinking agent and / or a thickening agent, and further satisfies any one or more of the following aspects (1) to (3). Aspect (1): The thermal layer contains the thickening agent, and the content ratio of the thickening agent is 0.07% by mass or more based on 100% by mass of the dry mass of the thermal layer. Aspect (2): The thermal layer contains a cationic crosslinking agent as the crosslinking agent, and the content ratio of the cationic crosslinking agent is 0.30% by mass or more based on 100% by mass of the dry mass of the thermal layer. Aspect (3): The thermal layer contains a non-cationic crosslinking agent as the crosslinking agent.

2. The thermal recording medium according to Claim 1, wherein the non-phenolic color former contains a compound represented by the following formula (1) and / or a compound represented by the following formula (2). 【Chemical 1】 (In formula (1), R 1 , R 2 , R 3 , R 4 , R 5 , R 7 , R 8 , R 9 , R 10 , and R 11 each independently represents a hydrogen atom or a substituent. R 6 , and R 12 each independently represents a substituent. m represents an integer from 0 to 4. When m is 2 or more, the plurality of R 6 may be the same or different. n represents an integer from 0 to 4. When n is 2 or more, the plurality of R 12 may be the same or different.) 【Chemical formula 2】 (In formula (2), R 13 , R 14 , R 15 , R 16 , R 17 , R 19 , R 20 , R 21 , R 22 , and R 23 each independently represents a hydrogen atom or a substituent. R 18 represents a substituent. o represents an integer from 0 to 4. When o is 2 or more, the plurality of R 18 may be the same or different.)

3. The thermal recording medium according to Claim 1 or 2, wherein the non-phenolic color former contains a compound represented by the following formula (1a) and / or a compound represented by the following formula (2a). [Chemical Formula 3] (Each symbol in formula (1a) is the same as in formula (1).) [Chemical Formula 4] (Each symbol in formula (2a) is the same as in formula (2).)

4. The thermal recording medium according to Claim 1 or 2, wherein the non-phenolic color former contains a urethane-urea compound.

5. The thermal recording medium according to Claim 4, wherein the urethane-urea compound is a urethane-urea compound represented by the following formula (3). [Chemical Formula 5] (In formula (3), R 24 , R 25 , R 26 , R 27 , R 28 , R 33 , R 34 , R 35 , R 36 , and R 37 each independently represent a hydrogen atom or a substituent. R 29 , R 30 , R 31 , and R 32 each independently represent a substituent. p represents an integer from 0 to 4. When p is 2 or more, the plurality of R 29 may be the same or different. q represents an integer from 0 to 4. When q is 2 or more, the plurality of R 30 may be the same or different. r represents an integer from 0 to 4. When r is 2 or more, the plurality of R 31 may be the same or different. s represents an integer from 0 to 4. When s is 2 or more, the plurality of R 32 may be the same or different.)

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