Thermal recording medium

Abstract

To provide a thermal recording medium having excellent boil resistance in non-printed areas. The thermosensitive recording medium 1 of the present invention has a structure in which a thermosensitive recording layer 4 and a low contact angle layer 5 are laminated in this order on a substrate 2. The low contact angle layer 5 is laminated directly on the thermosensitive recording layer 4. The thermosensitive recording layer 4 contains a compound represented by the following formula (1) as a color developer. Furthermore, the water contact angle of the low contact angle layer 5 is 40° or less. [Formula 1] TIFF0007723462000007.tif35170 In formula (1), R 1 is a hydrocarbon group having 1 to 12 carbon atoms which may have a substituent, and a plurality of R 1 may be the same or different. 1 is a hydrocarbon group having 1 to 4 carbon atoms. 1 If there are two or more, multiple A 1 may be the same or different. n represents an integer of 0 to 4, and multiple n's may be the same or different.

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, resulting in a recorded image. They are used in a wide range of applications, including as recording media for facsimiles, automatic ticket vending machines, scientific measuring instruments, etc., as well as thermal recording labels for various products such as food pouches.

[0003] Incidentally, food pouches are sometimes immersed in hot water (boiled) to disinfect the contents. However, the printed portion of a thermosensitive recording medium usually disappears when boiled, and the non-printed portion of the thermosensitive recording medium may become discolored when boiled, so boiling a food pouch to which a thermosensitive recording medium is affixed has been taboo. For this reason, thermosensitive recording media are sometimes required to have the ability to prevent the printed portion from disappearing even when boiled, i.e., the boil resistance of the printed portion. Similarly, thermosensitive recording media are sometimes required to have the ability to prevent the non-printed portion from becoming discolored even when boiled, i.e., the boil resistance of the non-printed portion.

[0004] As a thermal recording medium with excellent boil resistance in both printed and non-printed areas, for example, a thermal recording medium has been proposed in which an underlayer containing hollow particles with a specific porosity, a thermal recording layer containing a specific color developer, and a top coat layer containing a specific lubricant are laminated in this order on a substrate (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7456711 Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional thermosensitive recording media that are said to have excellent boil resistance may gradually discolor after being removed from hot water, even if the non-printed areas do not show any obvious color development. If the degree of discoloration after boiling is severe, the contrast between the printed and non-printed areas decreases, resulting in problems such as a decrease in the visibility and aesthetics of the printed areas. Therefore, there is a demand for a thermosensitive recording media that can further suppress discoloration of the non-printed areas not only during boiling but also after boiling, i.e., a thermal recording medium with improved boil resistance of the non-printed areas.

[0007] The present invention was conceived under these circumstances, and its object is to provide a thermosensitive recording medium which has excellent boil resistance in the non-printed areas. [Means for solving the problem]

[0008] As a result of extensive research to achieve the above object, the present inventors have found that a thermosensitive recording medium having a low contact angle layer with a low water contact angle of 40° or less on a thermosensitive recording layer containing a specific color developer has excellent boil resistance in the non-printed areas. The present invention was completed based on these findings.

[0009] That is, the present invention provides a thermosensitive recording medium comprising a substrate, a thermosensitive recording layer, and a low contact angle layer in this order, wherein the low contact angle layer is laminated directly on the thermosensitive recording layer, the thermosensitive recording layer contains a compound represented by the following formula (1) as a color developer, and the low contact angle layer has a water contact angle of 40° or less. [ka] (In formula (1), R 1 is a hydrocarbon group having 1 to 12 carbon atoms which may have a substituent, and a plurality of R 1 may be the same or different. 1 is a hydrocarbon group having 1 to 4 carbon atoms. 1 If there are two or more, multiple A 1 may be the same or different. n represents an integer of 0 to 4, and multiple n's may be the same or different.

[0010] The low contact angle layer preferably contains a core-shell type resin as a binder.

[0011] The core-shell resin preferably includes a core-shell acrylic resin.

[0012] In the core-shell resin, the ratio of the mass of the shell portion to the mass of the core portion (mass of the shell portion / mass of the core portion) is preferably 0.5 or more.

[0013] The low contact angle layer may further contain an epichlorohydrin-based resin.

[0014] The content of the binder is preferably 80% by mass or more relative to 100% by mass of the total solid content of the low contact angle layer.

[0015] The heat-sensitive recording layer preferably does not contain a water-soluble resin.

[0016] The thermosensitive recording layer preferably contains, as a filler, one or more selected from the group consisting of kaolin, calcined kaolin, aluminum oxide, aluminum silicate, and kaolinite.

[0017] It is preferable that an anchor layer containing an acrylic resin as a binder is provided between the substrate and the thermosensitive recording layer.

[0018] The content of the binder is preferably 50% by mass or more relative to 100% by mass of the total solid content of the anchor layer.

[0019] The content of the acrylic resin is preferably 70% by mass or more relative to 100% by mass of the total amount of binders in the anchor layer.

[0020] The anchor layer may contain hollow particles as a filler, and when the anchor layer contains the hollow particles, the content of the hollow particles is preferably 10% by mass or less relative to 100% by mass of the total solid content of the anchor layer.

[0021] The anchor layer may not contain hollow particles.

[0022] It is preferable that a top coat layer be provided on the surface of the low contact angle layer opposite to the thermosensitive recording layer.

[0023] The substrate is preferably any one of laminated paper, nonwoven fabric, synthetic resin film, and synthetic paper. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide a thermosensitive recording medium having excellent boil resistance in the non-printed areas. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a schematic cross-sectional view showing one embodiment of a thermosensitive recording medium of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view showing another embodiment of the thermosensitive recording medium of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] [Thermal recording medium] The thermosensitive recording medium of the present invention comprises at least a substrate, a thermosensitive recording layer, and a low contact angle layer. The low contact angle layer is directly laminated on the thermosensitive recording layer. The thermosensitive recording layer also contains at least a color developer. The color developer further contains a compound represented by the following formula (1). The water contact angle of the low contact angle layer is 40° or less.

[0027] [ka]

[0028] In formula (1), R 1 is a hydrocarbon group having 1 to 12 carbon atoms which may have a substituent, and a plurality of R 1 may be the same or different. 1 is a hydrocarbon group having 1 to 4 carbon atoms. 1 If there are two or more, multiple A 1 may be the same or different. n represents an integer of 0 to 4, and multiple n's may be the same or different.

[0029] Hereinafter, an embodiment of the thermosensitive recording medium of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the following embodiments.

[0030] Fig. 1 is a schematic cross-sectional view showing one embodiment of a thermosensitive recording medium of the present invention. In Fig. 1, the thermosensitive recording medium 1 comprises, in this order, a substrate 2, a thermosensitive recording layer 4, and a low contact angle layer 5. In this case, the low contact angle layer 5 is laminated on one side of the thermosensitive recording layer 4 so as to be in direct contact with it.

[0031] FIG. 2 is a schematic cross-sectional view showing another embodiment of the thermosensitive recording medium of the present invention. The thermosensitive recording medium 1 shown in FIG. 2 has a structure in which the thermosensitive recording medium 1 shown in FIG. 1 further comprises an anchor layer 3 and a top coat layer 6. Specifically, the anchor layer 3 is a layer provided between the substrate 2 and the thermosensitive recording layer 4. The top coat layer 6 is a layer provided on the surface of the low contact angle layer 5 opposite the thermosensitive recording layer 4. In this case, the substrate 2 and anchor layer 3, the anchor layer 3 and thermosensitive recording layer 4, and the low contact angle layer 5 and top coat layer 6 are laminated so as to be in direct contact with each other. The thermosensitive recording medium 1 has the top coat layer 6 located on one surface and the substrate 2 located on the other surface.

[0032] (base material) The substrate 2 can function as a support in the thermosensitive recording medium 1 of the present invention. The thermosensitive recording medium 1 has excellent handleability due to the substrate 2. Examples of the substrate 2 that can be used include paper such as high-quality paper, art paper, coated paper, and kraft paper, as well as laminated paper obtained by laminating a thermoplastic resin such as polyethylene to these paper substrates; porous materials such as nonwoven fabric; synthetic resin films; and synthetic paper. Examples of resins that constitute the synthetic resin films and synthetic paper include polypropylene, polyethylene, polyethylene terephthalate, polystyrene, and polycarbonate. Only one type of resin may be used, or two or more types may be used. The synthetic resin film may be stretched or unstretched. The substrate 2 may be a single layer or multiple layers of the same or different compositions, thicknesses, etc.

[0033] The substrate 2 is preferably one of laminated paper, nonwoven fabric, synthetic resin film, or synthetic paper, more preferably one of synthetic resin film or synthetic paper, from the viewpoint of being able to easily maintain strength even after boiling.

[0034] The thickness of the substrate 2 is not particularly limited, but is preferably 5 μm to 150 μm, and more preferably 10 μm to 100 μm. When the thickness is within the above range, the coating property and supportability are more likely to be suitable, and the handling property can be more excellent.

[0035] (Anchor layer) The anchor layer 3 is a layer intended to improve adhesion between the substrate 2 and the thermosensitive recording layer 4. The anchor layer 3 may not be provided if it is not required, in which case the thermosensitive recording layer 4 can be directly laminated on one side of the substrate 2. The anchor layer 3 contains, for example, a binder. The anchor layer 3 may also contain other components. Examples of such other components include an antistatic agent, a wetting agent, and a filler.

[0036] Examples of the binder include known resins, such as acrylic resins, styrene-acrylic resins, acrylic-urethane resins, acrylic-amide resins, and vinyl acetate-acrylic resins; maleic acid resins, such as maleic acid resins, styrene-maleic acid resins, and olefin-maleic acid resins; styrene-butadiene rubber (SBR); and polyvinyl alcohol resins (PVA), such as fully saponified polyvinyl alcohol resins and partially saponified polyvinyl alcohol resins. The binder may be starch, casein, gelatin, polyamide, polyacrylamide, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl acetate, isobutylene-maleic anhydride copolymer, diisobutylene-maleic anhydride copolymer, vinyl acetate-maleic anhydride copolymer, methyl vinyl-maleic anhydride copolymer, isopropylene-maleic anhydride copolymer, styrene-butadiene copolymer, polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinyl acetate copolymer, polyurethane, polystyrene, polyvinylpyrrolidone, acrylonitrile, methyl vinyl ether, or the like. The resin may be a modified resin modified by a known method. These binders may be used alone or in combination of two or more.

[0037] In particular, it is preferable that the binder contains an acrylic resin, from the viewpoint that good adhesion can be achieved even when the substrate contains a resin, and that the binder is less likely to swell even when boiled, resulting in better stability.

[0038] The content of the binder is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, relative to 100% by mass of the total solid content of the anchor layer 3. The content of the binder is preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less, relative to 100% by mass of the total solid content of the anchor layer 3.

[0039] The content of the acrylic resin is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, relative to 100% by mass of the total amount of binders in the anchor layer 3. The content of the acrylic resin may be 100% by mass, relative to 100% by mass of the total amount of binders in the anchor layer 3.

[0040] In this specification, "acrylic resin" refers to a resin (acrylic resin) obtained by homopolymerizing an acrylic monomer (a monomer having a (meth)acryloyl group), and / or a resin obtained by copolymerizing an acrylic monomer with another monomer (a monomer other than the acrylic monomer that is copolymerizable with the acrylic monomer). Here, the acrylic monomer and the other monomer may each be one type or two or more types. Furthermore, when simply referring to "acrylic," unless otherwise specified, it refers to (meth)acrylic acid (salt) and / or (meth)acrylic acid ester. Here, "(meth)acrylic acid" refers to acrylic acid and / or methacrylic acid. Furthermore, "(meth)acrylic acid (salt)" refers to (meth)acrylic acid and / or (meth)acrylic acid salt.

[0041] The salt of the (meth)acrylic acid salt is not particularly limited, and examples thereof include ammonium salts such as ammonia; alkanolamine salts such as triethanolamine, diethanolamine, and monoethanolamine; alkylamine salts such as methylamine salt, ethylamine salt, diethylamine salt, and triethylamine salt; polyamine salts such as diethyleneamine salt and diethylenetriamine salt; alkali metal salts such as lithium, sodium, and potassium; alkaline earth metal salts such as magnesium and calcium; and polyvalent metal salts such as zinc and iron. These salts can be used alone or in combination of two or more.

[0042] The composition forming the resin may be a solid, an emulsion, or a solution, but is preferably an emulsion or a solution from the viewpoint of excellent handling and coatability.

[0043] Examples of the antistatic agent include low molecular weight antistatic agents such as surfactants, high molecular weight antistatic agents such as acrylic-styrene copolymers, conductive metal compounds such as tin oxide, etc. These antistatic agents can be used alone or in combination of two or more.

[0044] The content of the antistatic agent is not particularly limited, and may be, for example, 1% by mass or more or 3% by mass or more relative to 100% by mass of the total solid content of the anchor layer 3. Furthermore, the content of the antistatic agent may be 40% by mass or less or 30% by mass or less relative to 100% by mass of the total solid content of the anchor layer 3.

[0045] Examples of the wetting agent include surfactants. Known surfactants can be used as appropriate, and examples thereof include anionic surfactants such as sodium dioctylsuccinate, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, and alkyl ether sulfate salts; and nonionic surfactants such as acetylene glycol surfactants and polyoxyalkylene alkyl ethers. Among these, acetylene glycol surfactants such as acetylene glycol and alkylene oxide adducts of acetylene glycol are preferred. These wetting agents can be used alone or in combination of two or more.

[0046] Examples of the filler include inorganic fillers such as kaolin, 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, aluminum hydroxide, and zinc oxide; and organic fillers such as hollow particles and non-hollow particles. The filler may or may not contain hollow particles. These fillers may be used alone or in combination of two or more.

[0047] The materials constituting the hollow particles and non-hollow particles are not particularly limited, and examples thereof include thermoplastic resins. Examples of the thermoplastic resins include acrylic resins such as acrylic resins (especially polymethyl methacrylate (PMMA)), acrylonitrile resins, acrylic-polyvinylidene chloride resins, acrylic-polyvinylidene chloride-acrylonitrile resins, acrylic-acrylonitrile resins, styrene-acrylic resins, acrylic-urethane resins, acrylic-amide resins, and vinyl acetate-acrylic resins; polyvinylidene chloride-based resins such as polyvinylidene chloride resins and polyvinylidene chloride-acrylonitrile resins; polystyrene-based resins; urea-formalin resins; polyolefin-based resins such as polyethylene resins and polypropylene resins; polyvinyl chloride-based resins; polyvinyl acetate-based resins; and polybutadiene-based resins. These resins may also be modified resins modified by known methods. These materials constituting the hollow particles and non-hollow particles can be used alone or in combination of two or more.

[0048] The average particle diameter of the hollow particles is not particularly limited, and is preferably 0.5 μm or more, more preferably 1 μm or more, even more preferably 3 μm or more, and particularly preferably 5 μm or more. The average particle diameter is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. When the average particle diameter is within the above range, the heat insulation is more likely to be adequate, and the heat resistance and density of the printed area can be improved. In this specification, the term "average particle diameter" refers to the particle diameter at 50% of the cumulative value in the particle size distribution measured by a laser diffraction / scattering method (D50, median diameter). Measurement of the average particle diameter by the laser diffraction / scattering method can be performed, for example, using a Microtrack Bell product, trade name "MT3300EX-II." Hereinafter, "average particle diameter" refers to the median diameter measured by the above method.

[0049] The content of the filler is not particularly limited and may be, for example, 1% by mass or more, 3% by mass or more, or 5% by mass or more, relative to 100% by mass of the total solid content of the anchor layer 3. The content of the filler may be 40% by mass or less, 30% by mass or less, 20% by mass or less, or 10% by mass or less, relative to 100% by mass of the total solid content of the anchor layer 3. The content of the hollow particles is not particularly limited and may be, for example, within the above range, relative to 100% by mass of the total solid content of the anchor layer 3. The content of the hollow particles is not particularly limited and may be, for example, 5% by mass or less, 3% by mass or less, or 1% by mass or less, relative to 100% by mass of the total solid content of the anchor layer 3.

[0050] The content of the hollow particles is not particularly limited, and may be, for example, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, 5% by mass or less, or 1% by mass or less, relative to 100% by mass of the total amount of the filler. Furthermore, the content may even be 0% by mass relative to 100% by mass of the total amount of the filler.

[0051] The coating amount (dry mass) of the anchor layer 3 is preferably 0.1 g / m2 ~10g / m 2 and more preferably 0.2 g / m 2 ~5.0g / m 2 When the coating weight is within the above range, it is easy to achieve more appropriate heat insulation, cushioning properties, and adhesion between the substrate 2 and the thermosensitive recording layer 4. In this specification, the term "dry mass" refers to the mass of non-volatile components (solid content) excluding solvents (volatile components) such as water contained in the coating liquid and its raw materials.

[0052] (thermal recording layer) The thermosensitive recording layer 4 is a layer that develops color through a chemical reaction when heated by a thermal head or the like, forming a recorded image on the thermosensitive recording medium 1. The thermosensitive recording layer 4 contains at least a color developer. The color developer contains at least a compound represented by the following formula (1). By using such a color developer, it is possible to achieve both good color development properties, i.e., high sensitivity in color development, and good boil resistance, i.e., colorfastness even when boiled. The thermosensitive recording layer 4 may further contain other components as necessary. Examples of such other components include dyes, binders, fillers, lubricants, crosslinking agents, wetting agents, and sensitizers.

[0053] [ka]

[0054] In formula (1), R 1 is a hydrocarbon group having 1 to 12 carbon atoms which may have a substituent, and a plurality of R 1 may be the same or different. 1 is a hydrocarbon group having 1 to 4 carbon atoms. 1 If there are two or more, multiple A 1 may be the same or different. n represents an integer of 0 to 4, and multiple n's may be the same or different.

[0055] In the above formula (1), multiple R 1 -SO3- is directly bonded to the carbon atom that makes up the benzene ring. 1The substitution positions of -SO3- may be the same or different between one benzene ring and the other benzene ring. 1 The substitution position of -SO3- and R on the other benzene ring 1 The substitution positions of -SO3- are preferably the same, and more preferably both are position 3. In this specification, the carbon atom on the benzene ring bonded to the nitrogen atom of the urea group (-NH-CO-NH-) in the above formula (1) is defined as position 1.

[0056] In the above formula (1), the above R 1 Among the "hydrocarbon groups having 1 to 12 carbon atoms which may have a substituent," examples of the "hydrocarbon groups having 1 to 12 carbon atoms" include linear alkyl groups having 1 to 12 carbon atoms, branched alkyl groups having 3 to 12 carbon atoms, alicyclic alkyl groups having 3 to 12 carbon atoms, aryl groups having 6 to 12 carbon atoms, and monovalent groups having 4 to 12 carbon atoms to which two or more different groups from these groups are bonded. Furthermore, multiple "hydrocarbon groups having 1 to 12 carbon atoms which may have a substituent" may be the same or different from each other. In this specification, the above R 1 When the substituent contains carbon atoms, the number of carbon atoms in the "hydrocarbon group having 1 to 12 carbon atoms" refers to the total number of carbon atoms including the number of carbon atoms in the substituent.

[0057] The "straight-chain alkyl group having 1 to 12 carbon atoms" may be a straight-chain saturated alkyl group or a straight-chain unsaturated alkyl group. Examples of the "straight-chain alkyl group having 1 to 12 carbon atoms" include a methyl group, an ethyl group, an n-propyl group, an allyl group, an n-butyl group, a 3-butenyl group, an n-hexyl group, and a lauryl group.

[0058] The "branched alkyl group having 3 to 12 carbon atoms" may be a branched saturated alkyl group or a branched unsaturated alkyl group. Examples of the "branched alkyl group having 3 to 12 carbon atoms" include an i-propyl group, an i-butyl group, an s-butyl group, a t-butyl group, and a 2-ethylhexyl group.

[0059] The "alicyclic alkyl group having 3 to 12 carbon atoms" may be a saturated alicyclic alkyl group or an unsaturated alicyclic alkyl group. Examples of the "alicyclic alkyl group having 3 to 12 carbon atoms" include a cyclopropyl group, a cyclopentyl group, and a cyclohexyl group.

[0060] Examples of the "aryl group having 6 to 12 carbon atoms" include unsubstituted aryl groups such as a phenyl group, a 1-naphthyl group, and a 2-naphthyl group.

[0061] Examples of the above "monovalent group having 4 to 12 carbon atoms in which two or more different groups from among these groups are bonded" include "a monovalent group having 7 to 12 carbon atoms in which an aryl group is bonded to one or more linear alkyl groups", "a monovalent group having 9 to 12 carbon atoms in which an aryl group is bonded to one or more branched alkyl groups", and "a monovalent group having 4 to 12 carbon atoms in which an alicyclic alkyl group is bonded to one or more linear alkyl groups".

[0062] The "monovalent group having 7 to 12 carbon atoms in which an aryl group is bonded to one or more linear alkyl groups" is preferably a "monovalent group having 7 to 12 carbon atoms in which a phenyl group is bonded to one to three linear alkyl groups each having 1 to 4 carbon atoms." Specific examples include p-tolyl, m-tolyl, o-tolyl, 2,5-dimethylphenyl, 2,4-dimethylphenyl, 3,5-dimethylphenyl, 2,3-dimethylphenyl, 3,4-dimethylphenyl, mesitylene, and p-ethylphenyl. Aralkyl groups such as benzyl, 1-phenylethyl, 2-phenylethyl, 3-phenylpropyl, p-methylbenzyl, m-methylbenzyl, m-ethylbenzyl, and p-ethylbenzyl may also be used. Furthermore, the above "monovalent group having 7 to 12 carbon atoms in which a phenyl group is bonded to 1 to 3 linear alkyl groups each having 1 to 4 carbon atoms" may have a substituent as described below.

[0063] The "monovalent group having 9 to 12 carbon atoms in which an aryl group and one or more branched alkyl groups are bonded" is preferably a "monovalent group having 7 to 12 carbon atoms in which a phenyl group and one or two branched alkyl groups each having 3 or 4 carbon atoms are bonded." Specific examples include a pi-propylphenyl group and a pt-butylphenyl group. The "monovalent group having 7 to 12 carbon atoms in which a phenyl group and one or two branched alkyl groups each having 3 or 4 carbon atoms are bonded" may have a substituent as described below.

[0064] The "monovalent group having 4 to 12 carbon atoms in which an alicyclic alkyl group and one or more linear alkyl groups are bonded" is preferably a "monovalent group having 7 to 12 carbon atoms in which an alicyclic alkyl group having 6 to 12 carbon atoms and one to three linear alkyl groups having 1 to 4 carbon atoms are bonded." Specific examples include a 4-methylcyclohexyl group and a 4-methylcyclooctyl group. The "monovalent group having 7 to 12 carbon atoms in which an alicyclic alkyl group having 6 to 12 carbon atoms and one to three linear alkyl groups having 1 to 4 carbon atoms are bonded" may have a substituent as described below.

[0065] The "substituent" is a group having at least one atom other than carbon atoms and hydrogen atoms (heteroatom). In this specification, the heteroatom in the "substituent" is bonded to a carbon atom in the "hydrocarbon group having 1 to 12 carbon atoms". Specific examples of the "substituent" include a halogen atom, a hydroxy group, an alkoxy group, and an oxo group (=O). The "substituent" may or may not contain a carbon atom. When the "substituent" contains a carbon atom, the number of carbon atoms in the substituent is preferably 1 to 6, and more preferably 1 to 4. The "substituent" may or may not be present in plural. The substitution positions of the plural "substituents" are determined by the R on one of the benzene rings. 1 and R on the other benzene ring 1 R on one benzene ring may be the same or different. 1 and the substitution position of the substituent on the other benzene ring 1 The substitution positions of the substituents in are preferably the same.

[0066] In the above formula (1), the above R 1 Among them, a monovalent group having 7 to 10 carbon atoms in which a phenyl group is bonded to one to three linear alkyl groups having 1 to 4 carbon atoms is preferred, and a monovalent group having 7 to 10 carbon atoms in which a phenyl group is bonded to one linear alkyl group having 1 to 4 carbon atoms is more preferred. 1 is preferably a p-tolyl group, a m-tolyl group, an o-tolyl group, a 2,5-dimethylphenyl group, a 2,4-dimethylphenyl group, a 3,5-dimethylphenyl group, a 2,3-dimethylphenyl group, a 3,4-dimethylphenyl group, or a mesitylene group, and among these, a p-tolyl group is more preferred. 1 In this case, the color development property and storage stability can be improved.

[0067] In the above formula (1), the above A 1 is the carbon atom constituting the benzene ring, and the R 1 -SO3- can be attached to the unattached carbon atom. 1 If there are two or more, multiple A 1 The substitution positions of the above A may be the same or different between one benzene ring and the other benzene ring. 1 The substitution positions are preferably the 2-, 4-, 5- and 6-positions.

[0068] Above A 1 Examples of the hydrocarbon group having 1 to 4 carbon atoms include alkyl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, and t-butyl.

[0069] In the above formula (1), n is preferably an integer of 0 to 2, more preferably an integer of 0 to 1, and even more preferably 0.

[0070] Specific examples of the compound represented by the above formula (1) include, but are not limited to, the following compounds.

[0071] That is, examples of the compound represented by the above formula (1) include N,N'-di-[3-(o-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-toluenesulfonyloxy)-4-methyl-phenyl]urea, N,N'-di-[3-(p-xylenesulfonyloxy)phenyl]urea, and N,N'-di-[3-(m-xylenesulfonyloxy)phenyl]urea. , N,N'-di-[3-(mesitylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-4-methyl-phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-4-ethyl-phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-5-methyl-phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-4-propyl-phenyl]urea, etc. Among these, as the compound represented by the above formula (1), the compound represented by the following formula (1a), i.e., N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, is particularly preferred.

[0072] [ka]

[0073] The color developer may contain a single compound represented by formula (1) above, or may contain two or more compounds represented by formula (1). Furthermore, the color developer may contain a color developer other than the compound represented by formula (1) above (another color developer) within a range that does not impair the effects of the present invention.

[0074] Examples of the other color developers include 3-[(3-phenylureido)phenyl]-4-methylbenzenesulfonate (trade name: TG-MD), N-3-[(p-toluenesulfonyl)oxy]phenyl-N'-(p-toluenesulfonyl)-urea (trade name: PF-201), N-[2-(3-phenylureido)phenyl]-benzenesulfonamide (trade name: NKK-1304), 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophen] known non-phenolic color developers such as [(Nyl)ureido]diphenyl sulfone (trade name: UU), 4,4'-isopropylidenediphenol (BPA), 4,4'-dihydroxydiphenyl sulfone (BPS), 4-allyloxy-4'-hydroxydiphenyl sulfone (trade name: BPS-MAE), 4-allyloxy-4'-hydroxy-diphenyl sulfone (trade name: TGSA), and 2,2'-diallyl-4,4'-sulfonyldiphenol (trade name: TG-SH); , 4-hydroxy-4'-isopropoxydiphenyl sulfone (trade name: D-8), N-(m-tolylaminocarbonyl)-methionine, N-(m-tolylaminocarbonyl)-phenylalanine and N-(phenylaminocarbonyl)-phenylalanine, 1,1-bis(p-hydroxyphenyl)cyclohexane, 1,1-bis(p-hydroxyphenyl)propane, 2,2-bis(p-hydroxyphenyl)propane, 2,2-bis(p-hydroxyphenyl)propane, phenyl)butane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 2,2'-methylenebis(4-chlorophenol), 2,2-bis(4-hydroxyphenyl)-4-methylpentane, poly(4-hydroxybenzoic acid), benzyl 4-hydroxybenzoate, 2,4-bis(phenylsulfonyl)phenol, 3,5-bis(α-methylbenzyl)salicylic acid, bis[4-(n-octyloxycarbonylamino)zinc salicylate], 4,Examples of known color developers include 4'-bis(p-tolylsulfonylaminocarbonylamino)diphenylmethane, 4-hydroxybenzenesulfonanilide, N-(2-hydroxyphenyl)-2-[(4-hydroxyphenyl)thio]acetamide, N-(4-hydroxyphenyl)-2-[(4-hydroxyphenyl)thio]acetamide, 4-[4-(4-{4-[4-(1-methylethoxy)phenylsulfonyl]phenoxy}butoxy)phenylsulfonyl]phenol, and 4-tert-butylphenol-formaldehyde polycondensate.

[0075] The content of the compound represented by formula (1) is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, relative to 100% by mass of the total amount of developer in the thermosensitive recording layer 4. The total content may be substantially 100% by mass, relative to 100% by mass of the total amount of developer in the thermosensitive recording layer 4. When the total content is within the above range, it is easy to achieve more appropriate boil resistance. Furthermore, the content of the compound represented by formula (1a) is preferably within the above range, relative to 100% by mass of the total amount of developer in the thermosensitive recording layer 4.

[0076] The content of the color developer is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, relative to 100% by mass of the total solid content of the thermosensitive recording layer 4. The content of the color developer is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less, relative to 100% by mass of the total solid content of the thermosensitive recording layer 4.

[0077] Examples of the dye include 2'-bromo-6'-(dibutylamino)-3'-methylspiro[isobenzofuran-1(3H),9'-[9H]xanthene]-3-one, 3-(1-ethyl-2-methylindol-3-yl)-3-(4-diethylamino-2-methylphenyl)-4-azaphthalide, 6-(dimethylamino)-3,3-bis[4-(dimethylamino)phenyl]-1(3H)-isobenzofuranone, 1,2-dihydro-1-ethyl-8-[N-(4-methylphenyl)-N-ethylamino]-2,2,4-trimethylspiro[11H]-chromeno(2,3-g)quinoline-11,3'-phthalide, 2'-[bis(phenylmethyl)amino]-6'-(diethylamino)-spiro[isobenzofuran-1(3H),9'-(9H)xanthen]-3-one, 3-dibutylamino-6-methyl-7-anilinofluorane, 2-aniline-3methyl-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-Np-toluidino)-6-methyl- 7-Anilinofluoran, 3-(N-ethyl-Np-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-Nn-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 Examples of dyes that can be used include fluoran, 3-diethylamino-7-chlorofluoran, 3-dibutylamino-6-methyl-7-bromofluoran, 3-dibutylamino-7-(o-chloroanilino)fluoran, 3-dipentylamino-6-methyl-7-anilinofluoran, 3-dimethylamino-5-methyl-7-methylfluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, and crystal violet lactone. These dyes can be used alone or in combination of two or more.

[0078] The average particle size of the dye is preferably 0.1 to 1.0 μm. Since dyes generally melt and react, reducing the average particle size tends to improve sensitivity characteristics. On the other hand, increasing the average particle size tends to make it easier to suppress unexpected color development due to heat during drying. When the average particle size is within the above range, the sensitivity characteristics and color development temperature of the dye can be more appropriately adjusted.

[0079] The content of the dye is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, relative to 100% by mass of the total solid content of the thermosensitive recording layer 4. The content of the dye is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less, relative to 100% by mass of the total solid content of the thermosensitive recording layer 4.

[0080] Examples of the binder include the same binders as those listed in the anchor layer section. Among them, styrene butadiene rubber (SBR) and acrylic resins are preferred as the binder. Furthermore, from the viewpoint of improving boil resistance, it is preferred that the thermosensitive recording layer 4 does not contain a water-soluble resin such as PVA. These binders can be used alone or in combination of two or more.

[0081] The content of the binder is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, relative to 100% by mass of the total solid content of the thermosensitive recording layer 4. The content of the binder is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less, relative to 100% by mass of the total solid content of the thermosensitive recording layer 4.

[0082] The content of the water-soluble resin is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, even more preferably 10% by mass or less, still more preferably 5% by mass or less, and particularly preferably 1% by mass or less, relative to 100% by mass of the total amount of the binder. It is also preferable that the content of the water-soluble resin is 0% by mass, relative to 100% by mass of the total amount of the binder.

[0083] Examples of the filler include the same fillers as those listed in the anchor layer section. Among these, the filler is preferably one or more selected from the group consisting of kaolin, calcined kaolin, aluminum oxide, aluminum silicate, and kaolinite, and more preferably one or more selected from the group consisting of kaolin and calcined kaolin. Generally, thermosensitive recording media with excellent resistance to heat (heat resistance) such as boiling may have low color development efficiency. For this reason, the anchor layer may contain hollow particles to improve color development efficiency. However, in one embodiment of the present invention, by including these fillers in the thermosensitive recording layer 4, color development efficiency can be further improved even when the anchor layer 3 does not contain hollow particles. These fillers can be used alone or in combination of two or more.

[0084] The content of the filler is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, relative to 100% by mass of the total solid content of the thermosensitive recording layer 4. The content of the filler is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less, relative to 100% by mass of the total solid content of the thermosensitive recording layer 4.

[0085] Examples of the lubricant include hydrocarbon waxes such as paraffin, polyethylene, and polystyrene; ester waxes such as carnauba wax; oils such as silicone oil and whale oil; fatty acids such as oleic acid and stearic acid; metal soaps such as zinc stearate; etc. These lubricants can be used alone or in combination of two or more.

[0086] The content of the lubricant is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, relative to 100% by mass of the total solid content of the thermosensitive recording layer 4. The content of the lubricant is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, relative to 100% by mass of the total solid content of the thermosensitive recording layer 4.

[0087] Examples of the crosslinking agent include inorganic crosslinking agents such as zirconium compounds; and organic crosslinking agents such as epichlorohydrin resins and oxazoline compounds. Examples of the zirconium compounds include zirconium carbonate, ammonium zirconium carbonate, and zirconium acetate. Examples of the epichlorohydrin resin include polyamide epichlorohydrin resins, polyamine epichlorohydrin resins, and polyamide polyamine epichlorohydrin resins. Among these, epichlorohydrin resins are preferred as the crosslinking agent. These crosslinking agents can be used alone or in combination of two or more.

[0088] The content of the crosslinking agent is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more, relative to 100% by mass of the total solid content of the thermosensitive recording layer 4. The content of the crosslinking agent is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, relative to 100% by mass of the total solid content of the thermosensitive recording layer 4.

[0089] Examples of the wetting agent include the same wetting agents as those listed in the section on the anchor layer. These wetting agents can be used alone or in combination of two or more.

[0090] Examples of the sensitizer include known sensitizers such as higher fatty acid amides such as stearic acid amide, methylol stearic acid amide, methylene bisstearic acid amide, and ethylene bisstearic acid amide; higher fatty acid anilides such as stearic acid anilide; aromatic ethers such as 1,2-diphenoxyethane, 1,4-diphenoxybutane, 1,2-bis(3-methylphenoxy)ethane, and 1,2-bis(4-methoxyphenoxy)ethane; 1-benzyloxynaphthalene, 2-benzyloxynaphthalene, 2,6-diisopropylnaphthalene, di(p-chlorobenzyl)oxalate, di(p-methylbenzyl)oxalate, dibenzyl oxalate, p-benzylbiphenyl, m-terphenyl, diphenyl sulfone, benzyl p-benzyloxybenzoate, dibenzyl terephthalate, and p-toluenesulfonamide. The above sensitizer is preferably a solid at room temperature and normal pressure (for example, 25° C. and 1 atmosphere), and more preferably has a melting point of 70° C. or higher. These sensitizers can be used alone or in combination of two or more.

[0091] The coating amount (dry mass) of the thermosensitive recording layer 4 is, for example, 0.3 g / m 2 ~10g / m 2 is preferred, and more preferably 2.0 g / m 2 ~6.0g / m 2 When the coating amount is within the above range, it is easy to achieve more appropriate color development.

[0092] (Low contact angle layer) The low contact angle layer 5 is a layer that is in direct contact with the thermosensitive recording layer 4. The low contact angle layer 5 has a water contact angle of 40° or less. The low contact angle layer 5 is in direct contact with at least a portion of one side of the thermosensitive recording layer 4. The low contact angle layer 5 is preferably in direct contact with the entirety of one side of the thermosensitive recording layer 4. By satisfying this configuration, the low contact angle layer 5 can improve the boil resistance of the thermosensitive recording medium 1 (particularly the boil resistance of the non-printed area). The following reason is presumed to be the reason: The thermosensitive recording medium 1, which is a laminate of at least the thermosensitive recording layer 4 and the low contact angle layer 5, requires a certain amount of time to completely dry and cool after being removed from the hot water after boiling because the hot water adheres to and penetrates the thermosensitive recording medium 1. Therefore, the thermosensitive recording medium 1 continues to be heated for some time after being removed from the hot water by the hot water that adheres to and penetrates the thermosensitive recording medium 1 and the hot steam that is generated when the hot water evaporates. Generally, it can be said that the smaller the water contact angle of a surface, the more easily water spreads on that surface. Therefore, when the water contact angle of the low contact angle layer 5 is small and water spreads easily, it is presumed that the hot water or water vapor that has adhered or penetrated to the low contact angle layer 5 will quickly adsorb and spread on the low contact angle layer 5, and will be easily discharged from the thermosensitive recording layer 4 along the low contact angle layer 5. As a result, it is thought that the temperature of the thermosensitive recording layer 4 will easily decrease after being removed from the hot water, and discoloration of the non-printed areas will be suppressed.

[0093] In the present invention, the water contact angle of the low contact angle layer 5 is measured 30 seconds after 0.025 g of pure water is dropped onto the surface of the low contact angle layer 5. A microscope such as a digital microscope can be used for the measurement, and specifically, the measurement can be performed by the method described in the Examples. The water contact angle can be adjusted by the type and content of the material constituting the low contact angle layer 5.

[0094] The water contact angle of the low contact angle layer 5 is 40° or less, and may be 38° or less, 35° or less, 33° or less, or 30° or less. When the contact angle is 40° or less, boiling resistance (particularly boiling resistance of non-printed areas) is excellent. Furthermore, the ratio of the water contact angle of the low contact angle layer 5 to the water contact angle of the thermosensitive recording layer 4 (water contact angle of low contact angle layer 5 / water contact angle of thermosensitive recording layer 4) is not particularly limited, and may be, for example, 0.1 to 0.88, 0.2 to 0.85, or 0.3 to 0.8.

[0095] The low contact angle layer 5 contains a binder such as a resin. The low contact angle layer 5 may further contain other components as necessary. Examples of the other components include a crosslinking agent and a wetting agent. The water contact angle can be reduced by using a binder that has high hydrophilicity and film-forming properties.

[0096] Examples of the binder include the same binders as those listed in the anchor layer section. Among them, acrylic resins are preferred as the binder. The acrylic resins have highly hydrophilic moieties such as carboxyl groups and / or ester bonds, which makes it easy to reduce the water contact angle.

[0097] The binder is preferably a core-shell resin, more preferably a core-shell acrylic resin, from the viewpoints of improving the film-forming properties of the low-contact-angle layer 5, ensuring its strength, and suppressing layer peeling due to stress such as boiling. A core-shell resin is a resin having a structure in which hydrophobic core particles (core portions) are coated with a water-soluble shell polymer (shell portion), and is typically obtained by stepwise polymerization of monomers with different compositions. By forming a crosslinked structure within the core particles or adjusting the molecular weight or glass transition temperature, the core particles can be made to be easily or difficult to fuse during film formation. For example, when the low-contact-angle layer 5 is formed using a coating liquid containing a core-shell resin having a shell portion composed of a water-soluble resin component and a core portion with a relatively high glass transition temperature, the shell portions are easily miscible in the coating liquid, facilitating film formation upon drying after coating, thereby improving film-forming properties. Furthermore, because the core portions are difficult to melt, they remain scattered throughout the low-contact-angle layer 5 even after formation, and the hydrophobic properties of the core portions can improve the water resistance of the layer. These binders can be used alone or in combination of two or more. In this specification, a resin that does not have the above-mentioned shell polymer portion may be particularly referred to as a non-core-shell resin.

[0098] From the viewpoint of making the low contact angle layer 5 a hydrophilic and smooth layer and further reducing the water contact angle, it is preferable that the ratio of the mass of the shell portion to the mass of the core portion in the core-shell resin is larger. In the core-shell resin, the ratio of the mass of the shell portion to the mass of the core portion (mass of the shell portion / mass of the core portion) is, for example, preferably 0.5 or more, more preferably 0.7 or more, even more preferably 1 or more, still more preferably 1.5 or more, and particularly preferably 2 or more. Furthermore, the ratio (mass of the shell portion / mass of the core portion) may be, for example, 50 or less, 30 or less, 20 or less, 10 or less, or 5 or less.

[0099] The core-shell acrylic resin is the same resin as that exemplified as the binder in the anchor layer section, and may be a core-shell type resin, such as a core-shell acrylic resin, a core-shell styrene-acrylic resin, a core-shell acrylic-urethane resin, a core-shell acrylic-amide resin, or a core-shell vinyl acetate-acrylic resin.

[0100] The core-shell acrylic resin is preferably a core-shell carboxyl group-containing acrylic resin. The core-shell carboxyl group-containing acrylic resin is considered to have a carboxyl group in the shell polymer, and with such a structure, the carboxyl group reacts with the crosslinking agent to more easily form a crosslinked structure, which can further improve the strength of the low contact angle layer 5.

[0101] When the binder contains a resin, the glass transition temperature of the resin is preferably 15 to 48°C, more preferably 20 to 45°C, and particularly preferably 22 to 40°C. The glass transition temperature of the core portion of the core-shell resin is preferably within the above range. When the glass transition temperature is within the above range, adequate fusion occurs during coating, resulting in good film-forming properties, which is thought to make it easier to set the water contact angle within an appropriate range. Furthermore, when the glass transition temperature is within the above range, excellent film-forming properties are achieved, further suppressing layer peeling when boiled.

[0102] The content of the binder is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, relative to 100% by mass of the total solids content of the low contact angle layer 5. The content may also be 95% by mass or more, 97% by mass or more, 99% by mass or more, or even substantially 100% by mass, relative to 100% by mass of the total solids content of the low contact angle layer 5. When the content is within the above range, the water contact angle is more likely to be in an appropriate range.

[0103] The content of the core-shell resin is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, relative to 100% by mass of the total amount of binders in the low contact angle layer 5. The content may be substantially 100% by mass, relative to 100% by mass of the total amount of binders in the low contact angle layer 5. Furthermore, the content of the core-shell acrylic resin is preferably within the above range, relative to 100% by mass of the total amount of binders in the low contact angle layer 5.

[0104] Examples of the crosslinking agent include the same crosslinking agents as those listed in the section on the thermosensitive recording layer. Among them, epichlorohydrin resins are preferred as the crosslinking agent because they can easily form a crosslinked structure with the acrylic resin. These crosslinking agents can be used alone or in combination of two or more.

[0105] The content of the crosslinking agent may be 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 3% by mass or more, 5% by mass or more, or 10% by mass or more, relative to 100% by mass of the total solids content of the low contact angle layer 5. The content of the crosslinking agent may be 40% by mass or less, or 30% by mass or less, relative to 100% by mass of the total solids content of the low contact angle layer 5. In this specification, the epichlorohydrin-based resin is not included in the content as the binder, but is included in the content as the crosslinking agent.

[0106] Examples of the wetting agent include the same wetting agents as those listed in the section on the anchor layer. These wetting agents can be used alone or in combination of two or more.

[0107] The coating amount (dry mass) of the low contact angle layer 5 is, for example, 0.1 g / m 2 ~10g / m 2 is preferable, and more preferably 1.0 g / m 2 ~5.0g / m 2When the coating amount is within the above range, it is easy to obtain more suitable boil resistance.

[0108] (Top coat layer) The top coat layer 6 is a layer intended to improve the matching of the thermosensitive recording medium 1 with the thermal head, i.e., to improve the slipperiness of the head and to prevent debris from adhering to the head. The top coat layer 6 may not be provided if it is not required. From the viewpoint of improving matching, it is preferable that the thermosensitive recording medium 1 has a top coat layer 6 on one end surface. The top coat layer 6 may contain, for example, a binder, a filler, a lubricant, a crosslinking agent, a wetting agent, etc.

[0109] Examples of the binder include the same binders as those listed in the anchor layer section. Among them, acrylic resins are preferred as the binder. The binder may or may not contain a core-shell type resin. These binders can be used alone or in combination of two or more.

[0110] The content of the binder is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, relative to 100% by mass of the total solid content of the top coat layer 6. The content of the binder is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less, relative to 100% by mass of the total solid content of the top coat layer 6. The content of the resin is preferably within the above range, relative to 100% by mass of the total amount of resin in the top coat layer 6.

[0111] Examples of the filler include the same fillers as those listed in the anchor layer section. Among them, inorganic fillers are preferred. In some cases, organic fillers (e.g., PMMA particles) listed in the anchor layer section may also be added. These binders can be used alone or in combination of two or more.

[0112] The content of the filler is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, relative to 100% by mass of the total solid content of the top coat layer 6. The content of the filler is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less, relative to 100% by mass of the total solid content of the top coat layer 6.

[0113] Examples of the lubricant include the same lubricants as those mentioned in the section on the heat-sensitive recording layer. These lubricants can be used alone or in combination of two or more.

[0114] The content of the lubricant is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, relative to 100% by mass of the total solid content of the top coat layer 6. The content of the lubricant is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less, relative to 100% by mass of the total solid content of the top coat layer 6.

[0115] Examples of the crosslinking agent include the same crosslinking agents as those listed in the section on the thermal recording layer. Among them, inorganic crosslinking agents are preferred, and zirconium compounds are more preferred, from the viewpoint of improving heat resistance and enhancing suitability for thermal heads by forming a crosslinked structure containing metal ions. These crosslinking agents can be used alone or in combination of two or more.

[0116] The content of the crosslinking agent is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, relative to 100% by mass of the total solid content of the top coat layer 6. The content of the crosslinking agent is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, relative to 100% by mass of the total solid content of the top coat layer 6.

[0117] Examples of the wetting agent include the same wetting agents as those listed in the section on the anchor layer. These wetting agents can be used alone or in combination of two or more.

[0118] [Method of manufacturing the thermal recording medium] The method for producing the thermosensitive recording medium of the present invention is not particularly limited, and known or conventional methods can be used. One embodiment of the method for producing the thermosensitive recording medium will be described with reference to FIG. 1. First, the thermosensitive recording layer 4 and the low contact angle layer 5 can be formed by applying a coating liquid containing the components contained in each layer. For example, the coating liquid for the thermosensitive recording layer can be prepared by dispersing the components contained in the thermosensitive recording layer 4 in a solvent such as water. A coating liquid for the low contact angle layer can also be prepared in a similar manner. Next, the coating liquid for the thermosensitive recording layer is applied to one side of the substrate 2 and dried to form the thermosensitive recording layer 4. Further, the coating liquid for the low contact angle layer is applied to the surface of the thermosensitive recording layer 4 and dried to form the low contact angle layer 5. In this manner, the thermosensitive recording medium 1 shown in FIG. 1 can be obtained.

[0119] (Preparation process) The coating liquid for the thermosensitive recording layer may be prepared by dispersing all of the materials in the same solvent in advance. Alternatively, the dye and developer, which react with each other, may be prepared as separate dispersions and then mixed to form the coating liquid for the thermosensitive recording layer. In this case, the other components may be added to either the dispersion containing the dye or the dispersion containing the developer, or to both. Examples of methods for preparing the coating liquid for the thermosensitive recording layer include stirring, ultrasonic treatment, and crushing using a ball mill, bead mill, sand mill, high-pressure homogenizer, etc. The coating liquid for the low contact angle layer may also be prepared by a similar method. These methods may be used alone or in combination of two or more.

[0120] (Coating process) Examples of methods for applying the coating liquid for the thermosensitive recording layer include applying the coating liquid to a release liner and then peeling off the release liner, or applying the coating liquid directly to one side of a substrate when a substrate is used. Examples of coating methods include air knife coating, barber blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, die coating, and gravure coating. Hand coating using a wire bar is also possible. The coating liquid for the low contact angle layer can also be applied by a similar method. These methods can be used alone or in combination of two or more.

[0121] (drying process) Examples of methods for drying the coating liquid for the thermosensitive recording layer that has been applied above include heat drying, room temperature drying, and vacuum drying. These methods can be used alone or in combination of two or more. The thermosensitive recording layer 4 can be formed by these methods. The low contact angle layer 5 can also be formed by the same means.

[0122] When the thermosensitive recording medium of the present invention has layers other than the substrate, the thermosensitive recording layer, and the low contact angle layer, the method for forming the other layers can be the same as described above. For example, the thermosensitive recording medium 1 shown in Fig. 2 can be produced by coating one side of the substrate 2 with an anchor layer coating liquid prepared by dispersing the components contained in the anchor layer 3 in a solvent such as water, drying the coating liquid to form the anchor layer 3, then laminating the thermosensitive recording layer 4 and the low contact angle layer 5 on the anchor layer 3 in the same manner as described above, and then coating the top coat layer coating liquid prepared by dispersing the components contained in the top coat layer 6 in a solvent such as water on the surface of the low contact angle layer 5, drying the coating liquid to form the top coat layer 6.

[0123] In the method for producing a thermosensitive recording medium of the present invention, the layers may be simultaneously coated by, for example, a curtain coater, or may be formed individually and sequentially. Alternatively, some layers may be simultaneously coated and some layers may be formed individually and sequentially. [Example]

[0124] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, the masses described in the examples refer to the masses of each component (i.e., the masses after drying after layer formation).

[0125] Example 1 (Preparation of thermal recording medium) <Anchor layer> A coating liquid for the anchor layer (solid content concentration 11% by mass) was prepared by a standard method by mixing 84% by mass of styrene-acrylic resin as a binder, 15% by mass of an acrylic-styrene copolymer as an antistatic agent, 1% by mass of a surfactant as a wetting agent, and water. The resulting coating liquid for the anchor layer was coated on one side of the synthetic paper substrate by a standard method and dried to a coating weight of 0.4 g / m. 2 An anchor layer of (dry mass) was formed.

[0126] <Thermal recording layer> A dispersion of agent A (solids concentration 39% by mass) was prepared by a standard method by mixing 90% by mass of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea (product name "S-176" manufactured by Sanko Co., Ltd.) as a color developer, 10% by mass of an acrylic resin as a binder, and water. Next, a dispersion of agent B (solids concentration 36% by mass) was prepared by a standard method by mixing 60% by mass of the dispersion of agent A, 15% by mass of kaolin as a filler, 23% by mass of styrene butadiene rubber (SBR) as a binder, 2% by mass of polyethylene as a lubricant, and water. Next, a dispersion of agent C (solids concentration 34% by mass) was prepared by a standard method by mixing 83% by mass of 3-dibutylamino-6-methyl-7-anilinofluoran (ODB-2) as a dye, 17% by mass of an acrylic resin as a binder, and water. Next, 82% by mass of the B agent dispersion, 17% by mass of the C agent dispersion, 1% by mass of polyamide epichlorohydrin resin as a crosslinking agent, and water were mixed to prepare a coating liquid for a thermosensitive recording layer (solid content concentration: 24% by mass) by a conventional method. The obtained coating liquid for a thermosensitive recording layer was applied to the surface of the anchor layer by a conventional method and dried, resulting in a coating amount of 4.4 g / m. 2 (dry weight) of a heat-sensitive recording layer was formed.

[0127] <Low contact angle layer> A coating liquid for a low contact angle layer (solid content concentration 14% by mass) was prepared by a conventional method by adding water to an emulsion containing a core-shell type acrylic resin (resin A). The coating liquid was applied to the surface of the thermosensitive recording layer by a conventional method and dried to obtain a coating amount of 1.6 g / m. 2 (dry weight) of the low contact angle layer A was formed, and the thermosensitive recording medium of Example 1 was obtained.

[0128] Examples 2 to 3, Comparative Examples 1 to 6 The thermosensitive recording materials of Examples 2 and 3 and Comparative Examples 1 to 6 were prepared in the same manner as in Example 1, except that in the process of preparing the low contact angle layer, the resins shown in Table 1 were used instead of Resin A. In Comparative Examples 1 to 6, the layer formed at a position corresponding to the low contact angle layer of the Examples is referred to as a protective layer because it has a high water contact angle, as will be described later.

[0129] Reference example 1 A laminate consisting of a substrate, an anchor layer, and a thermosensitive recording layer was prepared in the same manner as in Example 1, except that the low contact angle layer was not formed.

[0130] [evaluation] The thermosensitive recording media prepared in the Examples and Comparative Examples, and the laminate prepared in the Reference Example were evaluated as follows. The results are shown in Table 1.

[0131] (1) Measurement of water contact angle 0.025 g of pure water was dropped onto the surface of the low contact angle layer, and the contact angle after 30 seconds was measured using a digital microscope (manufactured by Keyence Corporation, device name: VHX-8000). In Reference Example 1, the water contact angle of the thermosensitive recording layer was measured using the same procedure as above.

[0132] (2) Boil test The thermosensitive recording medium or laminate was immersed in boiling water (100°C) for 1 minute.

[0133] (3) Evaluation of layer peeling and dissolution (2) After the boiling test, the thermosensitive recording medium or laminate was visually observed and evaluated based on the following evaluation criteria. [Evaluation criteria] ○: No peeling or dissolution of the layer was observed ×: Either peeling or dissolution of the layer was confirmed.

[0134] (4) Measurement of L value (2) After the boil test, the L value of the non-printed area of the thermal recording medium or laminate was measured using a spectrodensitometer / colorimeter (manufactured by X-rite, device name: eXact).

[0135] (5) Evaluation of boil resistance The evaluation was based on the following evaluation criteria. [Evaluation criteria] 〇: Meet all of the following items 1 and 2 ×: Does not meet one or more of the following criteria 1 and 2 The evaluation result of item 1.(3) is ○ The L value measured in item 2.(4) is 90 or higher.

[0136] [Table 1]

[0137] As shown in Table 1, when no low contact angle layer was laminated (Reference Example 1), the L value of the non-printed area after boiling was the highest (95.07), and the white color of the non-printed area was maintained the longest. This is presumably because, in Reference Example 1, the thermosensitive recording layer was located at the edge of the laminate, and hot water that adhered to and penetrated the laminate evaporated quickly after boiling, allowing the thermosensitive recording layer to cool easily, thereby suppressing color development. Furthermore, even when a low contact angle layer was laminated, when the water contact angle of the low contact angle layer was 40° or less (Examples 1 to 3), the L value was high (91.87 to 93.04), and the white color of the non-printed area was maintained, so the non-printed area was judged to have excellent boil resistance. This is presumably because, when the low contact angle layer has a low water contact angle, the low contact angle layer has excellent water wettability, so hot water and water vapor quickly adsorb to and spread on the low contact angle layer, and are easily expelled from the thermosensitive recording layer along the low contact angle layer, thereby suppressing color development. On the other hand, when the water contact angle of the protective layer formed at the position corresponding to the low contact angle layer in the examples was greater than 40° (Comparative Examples 1 to 3), the L value was lower (86.18 to 87.62) than when the water contact angle was 40° or less, and it was determined that the whiteness retention rate of the non-printed area was inferior and the boil resistance of the non-printed area was inferior.

[0138] Furthermore, when the protective layer was formed solely from a resin with a glass transition temperature of 50°C or higher (Comparative Examples 4 and 5), no examples were found in which the water contact angle was 40° or less, and furthermore, peeling of the layer was confirmed after boiling. The reasons for this are unclear, but the following are possible explanations: First, when the protective layer is formed solely from a resin with a relatively high glass transition temperature, the resin is less likely to fuse during coating, and particulate resin is more likely to remain in the protective layer. Such a protective layer is non-uniform and water-resistant, making it difficult for hot water that adheres to or penetrates the thermosensitive recording medium to be absorbed by the protective layer and to spread. This makes it more likely for water droplets to form between the thermosensitive recording layer and the protective layer. This is thought to facilitate the formation of blisters and promote peeling.

[0139] Furthermore, when the protective layer was formed from PVA, a water-soluble resin (Comparative Example 6), the water contact angle could not be measured accurately because it dissolved in water, and furthermore, dissolution of the layer was observed after boiling.

[0140] The various raw materials shown in Table 1 are as follows: Resin A: Core-shell acrylic resin (glass transition temperature of core: 30°C) Resin B: Core-shell acrylic resin (glass transition temperature of core: 36°C) Resin C: Core-shell acrylic resin (glass transition temperature of core: 36°C) Resin D: Non-core-shell SBR (glass transition temperature: 8°C) Resin E: Non-core-shell styrene acrylic resin (glass transition temperature: 4°C) Resin F: Non-core-shell styrene acrylic resin (glass transition temperature: 14°C) Resin G: Non-core-shell acrylic resin (glass transition temperature: 60°C) Resin H: Non-core-shell acrylic resin (glass transition temperature: 50°C) Resin I: PVA resin (water-soluble resin)

[0141] In summary, the configuration of the present invention and its variations are described below. [Appendix 1] A thermosensitive recording medium comprising a substrate, a thermosensitive recording layer, and a low contact angle layer in this order, wherein the low contact angle layer is laminated directly on the thermosensitive recording layer, the thermosensitive recording layer contains a compound represented by the above formula (1) as a color developer, and the low contact angle layer has a water contact angle of 40° or less. [Appendix 2] The thermosensitive recording material according to Appendix 1, wherein the low contact angle layer contains a core-shell type resin as a binder. [Appendix 3] The thermosensitive recording material according to Appendix 2, wherein the core-shell resin comprises a core-shell acrylic resin. [Appendix 4] The thermosensitive recording material according to appendix 2 or 3, wherein in the core-shell resin, the ratio of the mass of the shell part to the mass of the core part (mass of the shell part / mass of the core part) is 0.5 or more. [Appendix 5] The thermosensitive recording medium according to any one of Appendices 1 to 4, wherein the low contact angle layer further contains an epichlorohydrin-based resin. [Appendix 6] The thermosensitive recording medium according to any one of Appendices 2 to 5, wherein the content of the binder is 80% by mass or more relative to 100% by mass of the total solid content of the low contact angle layer. [Appendix 7] The thermosensitive recording medium according to any one of Appendices 1 to 6, wherein the thermosensitive recording layer does not contain a water-soluble resin. [Appendix 8] The thermosensitive recording medium according to any one of Appendices 1 to 7, wherein the thermosensitive recording layer contains one or more fillers selected from the group consisting of kaolin, calcined kaolin, aluminum oxide, aluminum silicate, and kaolinite. [Appendix 9] The thermosensitive recording medium according to any one of Appendices 1 to 8, further comprising an anchor layer containing an acrylic resin as a binder between the substrate and the thermosensitive recording layer. [Appendix 10] The thermosensitive recording medium according to Appendix 9, wherein the content of the binder is 50% by mass or more relative to 100% by mass of the total solid content of the anchor layer. [Appendix 11] The thermosensitive recording medium according to Appendices 9 or 10, wherein the content of the acrylic resin is 70% by mass or more relative to 100% by mass of the total amount of binder in the anchor layer. [Appendix 12] The anchor layer may contain hollow particles as a filler, and when the anchor layer contains the hollow particles, the content of the hollow particles is 10 mass % or less relative to 100 mass % of the total solid content of the anchor layer. A thermosensitive recording material described in any one of Appendices 9 to 11. [Appendix 13] The thermosensitive recording medium according to any one of Appendices 9 to 12, wherein the anchor layer does not contain hollow particles. [Appendix 14] The thermosensitive recording medium according to any one of Appendices 1 to 13, further comprising a top coat layer on the surface of the low contact angle layer opposite to the thermosensitive recording layer. [Appendix 15] The thermosensitive recording medium according to any one of Appendices 1 to 14, wherein the substrate is any one of laminated paper, nonwoven fabric, synthetic resin film, and synthetic paper. [Explanation of symbols]

[0142] 1. Thermal recording medium 2 Base material 3 Anchor layer 4. Thermal recording layer 5 Low contact angle layer 6 Topcoat layer

Claims

1. A thermosensitive recording medium comprising a substrate, a thermosensitive recording layer, and a low contact angle layer in this order, the low contact angle layer is directly laminated on the thermosensitive recording layer, The thermosensitive recording layer contains a compound represented by the following formula (1) as a color developer: the low contact angle layer has a water contact angle of 40° or less; The low contact angle layer comprises a core-shell type resin as a binder. 【Chemical 1】 (In formula (1), R １ is a hydrocarbon group having 1 to 12 carbon atoms which may have a substituent, and a plurality of R １ may be the same or different. １ is a hydrocarbon group having 1 to 4 carbon atoms. １ If there are two or more, multiple A １ may be the same or different. n represents an integer of 0 to 4, and multiple n's may be the same or different.

2. 2. The thermosensitive recording material according to claim 1, wherein the core-shell resin comprises a core-shell acrylic resin.

3. 2. The thermosensitive recording medium according to claim 1, wherein in the core-shell resin, the ratio of the mass of the shell portion to the mass of the core portion (mass of the shell portion / mass of the core portion) is 0.5 or more.

4. 4. The thermosensitive recording material according to claim 3, wherein the low contact angle layer further contains an epichlorohydrin resin.

5. 5. The thermosensitive recording medium according to claim 1, wherein the content of the binder is 80% by mass or more relative to 100% by mass of the total solid content of the low contact angle layer.

6. 6. The thermosensitive recording medium according to claim 5, wherein the thermosensitive recording layer does not contain a water-soluble resin.

7. 6. The thermosensitive recording medium according to claim 5, wherein the thermosensitive recording layer contains, as a filler, one or more selected from the group consisting of kaolin, calcined kaolin, aluminum oxide, aluminum silicate, and kaolinite.

8. 6. The thermosensitive recording medium according to claim 5, further comprising an anchor layer containing an acrylic resin as a binder between the substrate and the thermosensitive recording layer.

9. 9. The thermosensitive recording medium according to claim 8, wherein the content of the binder is 50% by mass or more relative to 100% by mass of the total solid content of the anchor layer.

10. 9. The thermosensitive recording medium according to claim 8, wherein the content of the acrylic resin is 70% by mass or more relative to 100% by mass of the total amount of the binder in the anchor layer.

11. The anchor layer may contain hollow particles as a filler, 9. The thermosensitive recording material according to claim 8, wherein when the anchor layer contains the hollow particles, the content of the hollow particles is 10% by mass or less relative to 100% by mass of the total solid content of the anchor layer.

12. 9. The thermosensitive recording medium according to claim 8, wherein the anchor layer does not contain hollow particles.

13. 6. The thermosensitive recording medium according to claim 5, further comprising a top coat layer on the surface of said low contact angle layer opposite to said thermosensitive recording layer.

14. 6. The thermal recording medium according to claim 5, wherein the substrate is any one of laminated paper, nonwoven fabric, synthetic resin film, and synthetic paper.

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