Heat-sensitive recording medium

Abstract

To provide a heat-sensitive recording medium having excellent capability of suppressing fading of printed images and superior heat resistance in non-image regions while exhibiting high sensitivity.SOLUTION: A heat-sensitive recording medium comprises a support and a heat-sensitive recording layer disposed on one side of the support, the heat-sensitive recording layer comprising a leuco dye, a color developer, and a carboxylic acid compound.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Thermal recording methods using thermal recording media do not require processes such as development and fixing, and have the advantage of being able to record in a short time using relatively simple equipment and at low cost compared to other recording methods. For these reasons, thermal recording media are widely used in a variety of fields, for example, in the POS field for fresh food, boxed lunches, and prepared dishes, in the copying field for books and documents, in the communication field such as facsimiles, in the ticket issuing field for ticket vending machines, receipts, and invoices, and in baggage tags in the airline industry.

[0003] Phenol-based color developers such as 4,4'-isopropylidenediphenol, which are excellent in preserving the background and image and in color development sensitivity, are widely used as color developers for thermal recording media. However, concerns have arisen over the use of phenol-based color developers because they are endocrine disruptors. In recent years, from the perspective of environmental friendliness, there has been a demand for thermal recording media that use color developers that do not have a phenol skeleton (non-phenol-based color developers).

[0004] For example, a thermosensitive recording medium using N-phenylureido-phenyl-benzenesulfonamides as a non-phenolic color developer has been proposed (see, for example, Patent Documents 1 and 2). Also, a thermosensitive recording medium using N-phenylureido-phenyl-benzenesulfonamides in combination with a specific color developer has been proposed for the purpose of improving the stability of printed image areas (see, for example, Patent Document 3).

[0005] Furthermore, in order to improve the storage stability of printed images, thermosensitive recording media using sulfonylurea derivatives as non-phenolic color developers have been proposed (see, for example, Patent Documents 3 to 5). Also, in order to further improve the storage stability of printed images, thermosensitive recording media using a combination of sulfonylurea derivatives and urea ureido compounds have been proposed (see, for example, Patent Documents 6 to 7). It has also been shown that sulfonylamidophthalic acid diamide compounds can also be used as non-phenolic color developers (see, for example, Patent Document 8). Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a thermosensitive recording medium that is excellent in the effect of suppressing fading of printed images, excellent in the heat resistance of non-image areas, and has high sensitivity. [Means for solving the problem]

[0007] The thermosensitive recording medium of the present invention as a means for solving the above problems comprises: A thermosensitive recording medium having a support and a thermosensitive recording layer disposed on one side of the support, The thermosensitive recording layer contains a leuco dye, a color developer represented by general formula (1) or general formula (2), and a carboxylic acid compound represented by at least one selected from general formulas (A) to (E).

[0008] [ka] (In general formula (1), R1's each independently represent any one of a linear or branched alkyl group having 1 to 3 carbon atoms, a phenyl group, a naphthyl group, a benzyl group, a phenylethyl group, a phenylpropyl group, and a phenyl group or a naphthyl group substituted at one or more positions with a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, a carboxy group, and an alkyl group having 1 to 3 carbon atoms and a linear or branched structure; and R2's each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms and a linear or branched structure.)

[0009] [ka] (In general formula (2), each R3 independently represents any one of hydrogen, a linear or branched alkyl group having 1 to 3 carbon atoms, a linear or branched alkoxy group having 1 to 3 carbon atoms, a benzyl group, a phenyl group, a naphthyl group, a phenylethyl group, a phenylpropyl group, and a phenyl group and a naphthyl group substituted at one or more positions with an alkyl group having a linear or branched structure having 1 to 3 carbon atoms.)

[0010] [ka]

[0011] [ka]

[0012] [ka] (In the general formula (C), R4 represents an alkyl group having a linear or branched structure and having 1 to 5 carbon atoms.)

[0013] [ka]

[0014] [ka] (In general formula (E), Ar represents a phenyl group, a naphthyl group, or a phenyl group or naphthyl group substituted at one or more positions with a linear or branched alkyl group having 1 to 3 carbon atoms, a phenyl group, a naphthyl group, a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, or a carboxy group; and each n independently represents 1 or 2.) [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a thermosensitive recording medium that is excellent in the effect of suppressing fading of printed images, excellent in the heat resistance of non-image areas, and has high sensitivity. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 shows an example of the results of DSC analysis when 1-naphthoic acid is used as the carboxylic acid compound. [Figure 2] FIG. 2 shows an example of the results of DSC analysis when acetylsalicylic acid is used as the carboxylic acid compound. [Figure 3] FIG. 3 shows an example of the results of DSC analysis when 3-nitrobenzoic acid is used as the carboxylic acid compound. [Figure 4] FIG. 4 shows an example of the results of DSC analysis when 3-phenoxybenzoic acid is used as the carboxylic acid compound. [Figure 5] FIG. 5 shows an example of the results of DSC analysis when 1-naphthaleneacetic acid is used as the carboxylic acid compound. [Figure 6] FIG. 6 shows an example of the results of DSC analysis when diphenylacetic acid is used as the carboxylic acid compound. [Figure 7] FIG. 7 shows an example of the results of DSC analysis when 4-hydroxy-4'-isopropoxydiphenyl sulfone is used as the phenolic compound. [Figure 8] FIG. 8 shows an example of the results of DSC analysis when a leuco dye / a color developer represented by general formula (2) is used. [Figure 9] FIG. 9 is a schematic cross-sectional view showing a thermosensitive recording medium according to one embodiment of the present invention. [Figure 10] FIG. 10 is a schematic cross-sectional view showing a thermosensitive recording medium according to another embodiment of the present invention. [Figure 11] FIG. 11 is a schematic cross-sectional view showing a thermosensitive recording medium according to another embodiment of the present invention. [Figure 12] FIG. 12 is a schematic cross-sectional view showing a thermosensitive recording medium according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The thermosensitive recording media described in Patent Documents 1 to 3 use N-phenylureido-phenyl-benzenesulfonamides as color developers, which causes problems such as discoloration of printed images and reduced heat resistance of non-printed areas when they come into contact with PVC wrap or various chemicals. Furthermore, the thermosensitive recording media described in Patent Documents 3 to 8 use sulfonylurea derivatives as color developers, which improve the storage stability of printed images, but have the problem of reduced thermal responsiveness and inability to support high-speed printing.

[0018] The thermosensitive recording medium of the present invention can fully resolve the various concerns in the prior art. The color developer represented by general formula (1) contained in the thermosensitive recording layer of the thermosensitive recording medium of the present invention has a structure containing a plurality of urea groups, and is therefore capable of forming strong hydrogen bonds. The color developer represented by general formula (2) contained in the thermosensitive recording layer of the thermosensitive recording medium of the present invention is a sulfonamide phthalic acid diamide derivative, and since it has three or more amide bonds in its molecule, it is capable of forming strong hydrogen bonds similar to those of a urea group. When the crystalline structure that collapses upon melting cools and solidifies, these strong hydrogen bonds are predicted to form a molecular aggregate-like state. That is, it is predicted that multiple molecules of the color developer represented by general formula (1) or general formula (2) are linked together to form a large molecular aggregate. This large molecular aggregate and the leuco dye contained in the thermal recording layer form a color-developing solid solution, resulting in a state in which the color of the leuco dye is maintained by the polymer compound. This is predicted to prevent contact with chemicals such as PVC wrap, oil, hand lotion, and alcohol, as well as inhibit the elution of the colored leuco dye, resulting in high chemical resistance.

[0019] On the other hand, these color developers require a lot of heat energy when heated and melted because the intermolecular bonding force of hydrogen bonds is too strong, and they have the property of being difficult to form a eutectic with other molecules. In other words, these color developers are difficult to form a eutectic with leuco dyes, and may have poor color-developing response (thermal sensitivity). Generally, in order to improve this color-developing response (thermal sensitivity), a method of using a heat-melting substance, a phenolic compound, or a diphenylurea compound in combination has been considered. However, because the heat-melting substance does not have the affinity to cleave the strong hydrogen bonds of the sulfonylurea compound, the eutectic point depression effect is difficult to manifest, and the effect of improving thermal sensitivity is minimal. Furthermore, although phenolic compounds and diphenylurea compounds are likely to form a eutectic with the color developer due to the effect of the urea group, this is insufficient.

[0020] In contrast, the carboxylic acid compound contained in the thermosensitive recording layer of the thermosensitive recording medium of the present invention has stronger acid strength and reactivity than the phenol group or urea group, and therefore is more likely to interact with the hydrogen bonds of the sulfonylurea compound. This behavior was analyzed using a differential scanning calorimeter (DSC). The results are shown in Figures 1 to 8. [Differential scanning calorimetry (DSC) analysis] Measurement was performed using a differential scanning calorimeter DSC6100 (manufactured by SII NanoTechnology Inc.) under the following conditions. Sample: Leuco dye / developer represented by general formula (1) or general formula (2) / carboxylic acid compound or phenolic compound = 1 / 2 / 1 (weight ratio) mixture Leuco dye: 3-dibutylamino-6-methyl-7-anilinofluoran Developer represented by general formula (1): N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea Developer represented by general formula (2): 5-(N-3-methylphenylsulfonylamido)-(N',N''-bis(3-methylphenyl)isophthalic acid diamide Carboxylic acids: 1-naphthoic acid, acetylsalicylic acid, 3-nitrobenzoic acid, 3-phenoxybenzoic acid, 1-naphthalene acid, diphenylacetic acid Phenolic compounds: 4-hydroxy-4'-isopropoxydiphenyl sulfone Heating rate: 20℃ / min Temperature range: 30℃~250℃ ·Reference material: α-Al2O3

[0021] FIG. 1 shows an example of a DSC analysis result when 1-naphthoic acid is used as the carboxylic acid compound. FIG. 2 shows an example of a DSC analysis result when acetylsalicylic acid is used as the carboxylic acid compound. FIG. 3 shows an example of a DSC analysis result when 3-nitrobenzoic acid is used as the carboxylic acid compound. FIG. 4 shows an example of a DSC analysis result when 3-phenoxybenzoic acid is used as the carboxylic acid compound. FIG. 5 shows an example of a DSC analysis result when 1-naphthalene acid is used as the carboxylic acid compound. FIG. 6 shows an example of a DSC analysis result when diphenylacetic acid is used as the carboxylic acid compound. FIG. 7 shows an example of a DSC analysis result when 4-hydroxy-4'-isopropoxydiphenyl sulfone is used as the phenolic compound. FIG. 8 shows an example of a DSC analysis result when a leuco dye / developer represented by general formula (2) is used. When 1-naphthoic acid, acetylsalicylic acid, 3-nitrobenzoic acid, 3-phenoxybenzoic acid, 1-naphthalene acid, and diphenylacetic acid were used, one endothermic peak was observed, indicating that the sulfonylurea compound and the carboxylic acid compound were in a eutectic state. When 4-hydroxy-4'-isopropoxydiphenyl sulfone was used, two endothermic peaks were observed, indicating that the sulfonylurea compound and the phenolic compound were not sufficiently eutectic. Figure 8 shows data for a mixture of a leuco dye and a developer represented by general formula (2). The peak temperature in Figure 8 is close to the higher peak temperature in Figure 7, which indicates that eutectic formation between phenolic compounds and sulfonylurea compounds is less likely to occur. Furthermore, the data in Figs. 1 to 6 show that the endothermic peak temperature is 100°C or higher, indicating excellent heat resistance.

[0022] As shown in Figures 1 to 8, by using a color developer represented by general formula (1) or general formula (2) in combination with a carboxylic acid compound, it is possible to realize a thermosensitive recording medium that is excellent in the effect of suppressing fading of printed images and in the heat resistance of non-image areas, as well as being highly sensitive.

[0023] The present invention will be described in detail below.

[0024] (thermal recording medium) The thermosensitive recording medium of the present invention has a support and a thermosensitive recording layer disposed on the support, and may also have a protective layer, an intermediate layer, a back layer, an undercoat layer, an adhesive layer, a release layer, and other layers as necessary.

[0025] <Support> Examples of the support include non-wood paper supports, recycled pulp (containing 50% or more recycled pulp), synthetic paper, polyethylene film, and laminated paper.

[0026] The support is not particularly limited and can be appropriately selected depending on the purpose, and may be transparent or opaque. When the support is transparent (hereinafter, sometimes referred to as a "transparent support"), it may be in the form of a polymer material that exists in the form of a thin film. The support may also be colored.

[0027] The material used for the transparent support is not particularly limited and can be appropriately selected depending on the purpose. Examples include ionomer film (IO), polyethylene film (PE), poly(vinyl chloride) film (PVC), poly(vinylidene chloride) film (PVDC), poly(vinyl alcohol) film (PVA), polypropylene film (PP) including biaxially oriented (double-stretched) polypropylene (BOPP), polyester film, poly(ethylene terephthalate) film (PET), polyethylene naphthalate (PEN) film, polycarbonate film (PC), polystyrene film (PS), polyacrylonitrile film (PAN), ethylene-vinyl acetate copolymer film (EVA), ethylene-vinyl alcohol copolymer film (EMAA), nylon film (NY), polyamide film (PA), triacetyl cellulose film (TAC), norbornane film (NB), Arton film, polyethylene (PE), and polymethyl methacrylate (PMMA).

[0028] The total light transmittance of the transparent support is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 60% or more, more preferably 70% or more, and even more preferably 90% or more.

[0029] The total light transmittance of the support is not particularly limited and can be appropriately selected depending on the purpose, and can be measured, for example, with a haze meter (manufactured by SUGA Corporation).

[0030] The haze value of the transparent support is not particularly limited and can be appropriately selected depending on the purpose, but it is preferably less than 3.

[0031] The haze value of the support is not particularly limited and can be appropriately selected depending on the purpose, and can be measured, for example, with a haze meter (manufactured by SUGA Corporation).

[0032] The average thickness of the support is not particularly limited and can be appropriately selected depending on the composition of the support and the thermosensitive recording layer and the intended use, but is preferably 30 μm to 250 μm, more preferably 50 μm to 200 μm. The average thickness of the transparent support is not particularly limited and can be appropriately selected depending on the composition of the support and the thermosensitive recording layer and the intended use, but is preferably 20 μm to 100 μm, more preferably 40 μm to 70 μm.

[0033] The method for measuring the average thickness of the support is not particularly limited and can be appropriately selected depending on the purpose. For example, it can be measured using a haze meter (manufactured by SUGA Corporation) or an electronic micrometer (manufactured by Anritsu Corporation).

[0034] <Thermal recording layer> The heat-sensitive recording layer is disposed on a support. The thermosensitive recording layer contains a leuco dye, a color developer represented by general formula (1) or general formula (2), and a carboxylic acid compound represented by at least one selected from general formulas (A) to (E), and may contain other components for the thermosensitive recording layer, if necessary.

[0035] [ka] (In general formula (1), R1's each independently represent any one of a linear or branched alkyl group having 1 to 3 carbon atoms, a phenyl group, a naphthyl group, a benzyl group, a phenylethyl group, a phenylpropyl group, and a phenyl group or a naphthyl group substituted at one or more positions with a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, a carboxy group, and an alkyl group having 1 to 3 carbon atoms and a linear or branched structure; and R2's each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms and a linear or branched structure.)

[0036] [ka] (In general formula (2), each R3 independently represents any one of hydrogen, a linear or branched alkyl group having 1 to 3 carbon atoms, a linear or branched alkoxy group having 1 to 3 carbon atoms, a benzyl group, a phenyl group, a naphthyl group, a phenylethyl group, a phenylpropyl group, and a phenyl group and a naphthyl group substituted at one or more positions with an alkyl group having a linear or branched structure having 1 to 3 carbon atoms.)

[0037] [ka]

[0038] [ka]

[0039] [ka] (In the general formula (C), R4 represents an alkyl group having a linear or branched structure and having 1 to 5 carbon atoms.)

[0040] [ka]

[0041] [ka] (In general formula (E), Ar represents a phenyl group, a naphthyl group, or a phenyl group or naphthyl group substituted at one or more positions with a linear or branched alkyl group having 1 to 3 carbon atoms, a phenyl group, a naphthyl group, a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, or a carboxy group; and each n independently represents 1 or 2.)

[0042] <<Leuco dye>> The leuco dye is not particularly limited and can be appropriately selected depending on the purpose from those used in known thermosensitive recording media, and examples thereof include leuco compounds of triphenylmethane-based, fluoran-based, phenothiazine-based, auramine-based, spiropyran-based, and indolinophthalide-based dyes.

[0043] Specific examples of leuco dyes include 3,3-bis(p-dimethylaminophenyl)-phthalide, 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (also known as crystal violet lactone), 3,3-bis(p-dimethylaminophenyl)-6-diethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)-6-chlorophthalide, 3,3-bis(p-dibutylaminophenyl)phthalide, 3-cyclohexylamino-6-chlorofluoran, 3-dimethylamino-5,7-dimethylfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-7-methylfluoran, 3-diethylamino-7,8-benzfluoran, 3-diethylamino-6-methyl-7-chlorofluoran, and 3-(Np-tolyl-N-ethylamino)-6-methyl-7 -Anilinofluoran, 2-{N-(3'-trifluoromethylphenyl)amino}-6-diethylaminofluoran, 2-{3,6-bis(diethylamino)-9-(o-chloroanilino)xanthylbenzoic acid lactam}, 3-diethylamino-6-methyl-7-(m-trichloromethylanilino)fluoran, 3-diethylamino-7-(o-chloroanilino)fluoran, 3-pyrrolidino-6 -methyl-7-anilinofluoran, 3-di-n-butylamino-7-o-chloroanilino)fluoran, 3-N-methyl-N,n-amylamino-6-methyl-7-anilinofluoran, 3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-(N,N-diethylamino)-5-methyl-7-(N,N-Dibenzylamino)fluoran, Benzoyl Leucomethylene Blue, 6'-Chloro-8'-methoxy-benzoindolino-spiropyran, 6'-Bromo-3'-methoxy-benzoindolino-spiropyran, 3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-chlorophenyl)phthalide, 3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-nitrophenyl)phthalide, 3-(2'-hydroxy-4'-diethylaminophenyl)-3-(2'-methoxy-5'-methyl Phenyl)phthalide, 3-(2'-methoxy-4'-dimethylaminophenyl)-3-(2'-hydroxy-4'-chloro-5'-methylphenyl)phthalide, 3-(N-ethyl-N-tetrahydrofurfuryl)amino-6-methyl-7-anilinofluoran, 3-N-ethyl-N-(2-ethoxypropyl)amino-6-methyl-7-anilinofluoran, 3-N-methyl-N-isobutyl-6-methyl-7-anilinofluoran, 3-morpholino-7-(N-propyl-trifluoromethylanilino)fluoran, 3-pyrrolidino-7-trifluoro Methylanilinofluoran, 3-diethylamino-5-chloro-7-(N-benzyl-trifluoromethylanilino)fluoran, 3-pyrrolidino-7-(di-p-chlorophenyl)methylaminofluoran, 3-diethylamino-5-chloro-7-(α-phenylethylamino)fluoran, 3-(N-ethyl-p-toluidino)-7-(α-phenylethylamino)fluoran, 3-diethylamino-7-(o-methoxycarbonylphenylamino)fluoran, 3-diethylamino-5-methyl-7-(α-phenylethylamino)fluoran, 3 -Diethylamino-7-piperidinofluoran, 2-chloro-3-(N-methyltoluidino)-7-(pn-butylanilino)fluoran, 3-di-n-butylamino-6-methyl-7-anilinofluoran, 3,6-bis(dimethylamino)fluorenespiro(9,3')-6'-dimethylaminophthalide, 3-(N-benzyl-N-cyclohexylamino)-5,6-benzo-7-α-naphthylamino-4'-bromofluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3-diethylamino-6-methyl-7-mesitidino-4',5'-Benzofluoran, 3-N-methyl-N-isopropyl-6-methyl-7-anilinofluoran, 3-N-ethyl-N-isoamyl-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-(2',4'-dimethylanilino)fluoran, 3-morpholino-7-(N-propyl-trifluoromethylanilino)fluoran, 3-pyrrolidino-7-trifluoromethylanilinofluoran, 3-diethylamino-5-chloro-7 -(N-benzyl-trifluoromethylanilino)fluoran, 3-pyrrolidino-7-(di-p-chlorophenyl)methylaminofluoran, 3-diethylamino-5-chloro-(α-phenylethylamino)fluoran, 3-(N-ethyl-p-toluidino)-7-(α-phenylethylamino)fluoran, 3-diethylamino-7-(o-methoxycarbonylphenylamino)fluoran, 3-diethylamino-5-methyl-7-(α-phenylethylamino)fluoran (N-phenylamino)fluoran, 3-diethylamino-7-piperidinofluoran, 2-chloro-3-(N-methyltoluidino)-7-(pN-butylanilino)fluoran, 3,6-bis(dimethylamino)fluorenespiro(9,3')-6'-dimethylaminophthalide, 3-(N-benzyl-N-cyclohexylamino)-5,6-benzo-7-α-naphthylamino-4'-bromofluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3 -N-ethyl-N-(-2-ethoxypropyl)amino-6-methyl-7-anilinofluoran, 3-N-ethyl-N-tetrahydrofurfurylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-mesitidino-4',5'-benzofluoran, 3-(p-dimethylaminophenyl)-3-{1,1-bis(p-dimethylaminophenyl)ethylene-2-yl}phthalide, 3-(p-dimethylaminophenyl)-3-{1,1-bis(p-dimethylaminophenyl)ethylene-2-yl}phthalide1-Bis(p-dimethylaminophenyl)ethylene-2-yl}-6-dimethylaminophthalide, 3-(p-dimethylaminophenyl)-3-(1-p-dimethylaminophenyl-1-phenylethylene-2-yl)phthalide, 3-(p-dimethylaminophenyl)-3-(1-p-dimethylaminophenyl-1-p-chlorophenylethylene-2-yl)-6-dimethylaminophthalide, 3-(4'-dimethylamino-2'-methoxy)-3-(1'-p-dimethylaminophenyl-1'-p-chlorophenyl-1',3'-butadien-4'-yl)benzophthalide, 3-(4'-dimethylamino-2'-benzyloxy)-3-(1''-p-dimethylaminophenyl) Examples of such compounds include 3-dimethylaminophenyl-1'-phenyl-1',3'-butadien-4'-yl)benzophthalide, 3-dimethylamino-6-dimethylamino-fluorene-9-spiro-3'-(6'-dimethylamino)phthalide, 3,3-bis(2-(p-dimethylaminophenyl)-2-p-methoxyphenyl)ethenyl)-4,5,6,7-tetrachlorophthalide, 3-bis{1,1-bis(4-pyrrolidinophenyl)ethylene-2-yl}-5,6-dichloro-4,7-dibromophthalide, bis(p-dimethylaminostyryl)-1-naphthalenesulfonylmethane, and bis(p-dimethylaminostyryl)-1-p-tolylsulfonylmethane. These may be used alone or in combination of two or more.

[0044] The content of the leuco dye is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of image density, it is preferably 3% by mass or more and 30% by mass or less relative to the total mass of the thermosensitive recording layer.

[0045] The leuco dye may be a suitably synthesized product or a commercially available product. Commercially available leuco dyes include, for example, ODB2 (3-dibutylamino-6-methyl-7-anilinofluoran, manufactured by Yamamoto Chemical Industry Co., Ltd.).

[0046] <<Developer>> The color developer contained in the thermosensitive recording layer of the present invention includes a color developer represented by general formula (1) or general formula (2), and may contain other color developers as needed.

[0047] [ka] (In general formula (1), R1's each independently represent any one of a linear or branched alkyl group having 1 to 3 carbon atoms, a phenyl group, a naphthyl group, a benzyl group, a phenylethyl group, a phenylpropyl group, and a phenyl group or a naphthyl group substituted at one or more positions with a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, a carboxy group, and an alkyl group having 1 to 3 carbon atoms and a linear or branched structure; and R2's each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms and a linear or branched structure.)

[0048] [ka] (In general formula (2), each R3 independently represents any one of hydrogen, a linear or branched alkyl group having 1 to 3 carbon atoms, a linear or branched alkoxy group having 1 to 3 carbon atoms, a benzyl group, a phenyl group, a naphthyl group, a phenylethyl group, a phenylpropyl group, and a phenyl group and a naphthyl group substituted at one or more positions with an alkyl group having a linear or branched structure having 1 to 3 carbon atoms.)

[0049] The color developer in the present invention is a non-phenolic color developer that does not have a phenol skeleton. The thermosensitive recording medium of the present invention is superior in terms of environmental impact because it contains in the thermosensitive recording layer a color developer represented by general formula (1) or general formula (2) as a non-phenolic color developer, rather than a phenolic color developer which is an endocrine disruptor.

[0050] The color developer represented by general formula (1) is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of color-developing performance, it is preferably a color developer represented by formula (1-1).

[0051] [ka]

[0052] The color developer represented by general formula (2) is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of color-developing performance, it is preferably a color developer represented by formula (2-1).

[0053] [ka]

[0054] The content of the developer represented by general formula (1) or general formula (2) is not particularly limited and can be selected appropriately depending on the purpose. From the viewpoint of color-developing performance, however, it is preferably 1 part by mass or more and 20 parts by mass or less, and more preferably 2 parts by mass or more and 10 parts by mass or less, per 1 part by mass of leuco dye.

[0055] The analytical method for confirming whether or not the thermosensitive recording layer contains a color developer represented by general formula (1) or general formula (2) is not particularly limited and can be selected appropriately depending on the purpose. For example, confirmation can be made by identifying the retention time in liquid chromatography analysis.

[0056] The color developer represented by general formula (1) or general formula (2) may be suitably synthesized or may be a commercially available product. Commercially available color developers represented by general formula (1) or general formula (2) include, for example, S-176 (N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, manufactured by Sanko Co., Ltd.) and PF-425 (5-(N-3-methylphenylsulfonylamido)-(N',N''-bis-(3-methylphenyl)isophthalic acid diamide, manufactured by B.A.S.F.S.A.).

[0057] The other color developers are not particularly limited and can be appropriately selected from known non-phenolic color developers, and examples thereof include color developers represented by general formulas (3) to (8), urea urethane (UU), etc.

[0058] [ka] (In general formula (3), X and Z each independently represent any one of a linear or branched alkyl group having 1 to 5 carbon atoms, a phenyl group, a naphthyl group, a benzyl group, a phenylethyl group, a phenylpropyl group, indoline, indole, thiophene, benzothiophene, pyrrole, pyridine, and a phenyl group or a naphthyl group substituted at one or more positions with a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, a carboxy group, or an alkyl group having 1 to 3 carbon atoms and a linear or branched structure; and Y represents any one of a tolylene group, a xylylene group, a naphthylene group, a hexamethylene group, and a -φ-CH2-φ- group, where -φ- represents a phenylene group.)

[0059] [ka] (In general formula (4), X and Y each independently represent any of a linear or branched alkyl group having 1 to 5 carbon atoms, a phenyl group, a naphthyl group, a benzyl group, a phenylethyl group, a phenylpropyl group, indoline, indole, thiophene, benzothiophene, pyrrole, pyridine, and a phenyl group or naphthyl group substituted at one or more positions with a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, a carboxy group, or a linear or branched alkyl group having 1 to 3 carbon atoms.)

[0060] [ka] (In general formula (5), X and Y each independently represent any of a linear or branched alkyl group having 1 to 5 carbon atoms, a phenyl group, a naphthyl group, a benzyl group, a phenylethyl group, a phenylpropyl group, indoline, indole, thiophene, benzothiophene, pyrrole, pyridine, a phenyl group, a naphthyl group substituted at one or more positions with a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, a carboxy group, and a linear or branched alkyl group having 1 to 3 carbon atoms.)

[0061] [ka] (In general formula (6), Z and Y each independently represent any of a linear or branched alkyl group having 1 to 5 carbon atoms, a phenyl group, a naphthyl group, a benzyl group, a phenylethyl group, a phenylpropyl group, indoline, indole, thiophene, benzothiophene, pyrrole, pyridine, and a phenyl group or naphthyl group substituted at one or more positions with a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, a carboxy group, or a linear or branched alkyl group having 1 to 3 carbon atoms.)

[0062] [ka] In the general formula (7), the hydrogen atoms of the benzene ring are each independently selected from a linear or branched alkyl group having 1 to 5 carbon atoms, a phenyl group, a naphthyl group, a benzyl group, a phenylethyl group, a phenylpropyl group, indoline, indole, thiophene, benzothiophene, pyrrole, pyridine, a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, a carboxy group, and a linear or branched alkyl group having 1 to 3 carbon atoms. represents one of a phenyl group and a naphthyl group substituted at one or more positions, γ represents one of -SO2-, -O-, -(S)n-, -(CH2)n-, -CO-, -CONH-, -O-φ-C(CH3)2-φ-O-, -C(CH3)2-φ-C(CH3)2-, -O-φ-O-, -O-φ-φ-O-, and -O-φ-SO2-φ-O-, or represents absence, and n represents 1 or 2. Note that -φ- represents a phenylene group.

[0063] [ka] (In general formula (8), the hydrogen atoms of the benzene ring are each independently substituted by a linear or branched alkyl group having 1 to 5 carbon atoms, a phenyl group, a naphthyl group, a benzyl group, a phenylethyl group, a phenylpropyl group, indoline, indole, thiophene, benzothiophene, pyrrole, pyridine, a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, a carboxy group, or a linear or branched alkyl group having 1 to 3 carbon atoms.) represents one or more substituted phenyl or naphthyl groups, δ represents one or more of -SO2-, -O-, -(S)n-, -(CH2)n-, -CO-, -CONH-, -NH-, -CH(COOR5)-, -C(CF3)2-, and -CR6R7-, or is absent, R5, R6, and R7 represent alkyl groups having a linear or branched structure and having 1 to 5 carbon atoms, and n represents 1 or 2. Note that -φ- represents a phenylene group.

[0064] The content of other color developers is not particularly limited and can be set appropriately within a range that does not impair the effects of the present invention. From the viewpoint of color density, however, it is preferably less than 2 parts by weight, more preferably less than 0.5 parts by weight, per 1 part by weight of leuco dye.

[0065] As other color developers, appropriately synthesized ones or commercially available products may be used. Other commercially available color developers include, for example, Urea Urethane (UU, manufactured by Chemipro Chemical Co., Ltd.) and NKK-1304 (N-[2-[[(phenylamino)carbonyl]amino]phenyl]benzenesulfonamide, manufactured by Nippon Soda Co., Ltd.).

[0066] <<Carboxylic acid compounds>> The carboxylic acid compound contained in the thermosensitive recording layer of the present invention is represented by at least one selected from the general formulae (A) to (E). These may be used alone or in combination of two or more.

[0067] [ka]

[0068] [ka]

[0069] [ka] (In the general formula (C), R4 represents an alkyl group having a linear or branched structure and having 1 to 5 carbon atoms.)

[0070] [ka]

[0071] [ka] (In general formula (E), Ar represents a phenyl group, a naphthyl group, or a phenyl group or naphthyl group substituted at one or more positions with a linear or branched alkyl group having 1 to 3 carbon atoms, a phenyl group, a naphthyl group, a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, or a carboxy group; and each n independently represents 1 or 2.)

[0072] The carboxylic acid compound is not particularly limited and can be appropriately selected depending on the purpose. However, from the viewpoints of suppressing fading of printed images, excellent heat resistance of non-image areas, and high sensitivity, it is preferable to use at least one selected from 1-naphthoic acid, acetylsalicylic acid, 3-nitrobenzoic acid, 3-phenoxybenzoic acid, 1-naphthaleneacetic acid, and diphenylacetic acid. Furthermore, when a developer represented by general formula (2) is used as the developer, it is preferable that the developer is at least one selected from 1-naphthoic acid, 3-nitrobenzoic acid, 3-phenoxybenzoic acid, and diphenylacetic acid, from the viewpoint of improving vinyl wrap resistance.

[0073] The content of the carboxylic acid compound is not particularly limited and can be selected appropriately depending on the purpose, but is preferably 0.01 parts by mass or more and 3.00 parts by mass or less, more preferably 0.05 parts by mass or more and 3.00 parts by mass or less, and even more preferably 0.05 parts by mass or more and 2.00 parts by mass or less, relative to 1 part by mass of the color developer represented by general formula (1) or (2). When the content of the carboxylic acid compound is 0.05 parts by mass or more relative to 1 part by mass of the color developer represented by general formula (1) or (2), the color-forming energy is lowered, that is, the sensitivity is improved. When the content of the carboxylic acid compound is 3.00 parts by mass or less per part by mass of the color developer represented by the general formula (1) or (2), the PVC wrap resistance is improved.

[0074] The analytical method for determining whether or not a carboxylic acid compound is contained in the thermosensitive recording layer is not particularly limited and can be selected appropriately depending on the purpose. For example, it can be determined by infrared absorption analysis or retention time in liquid chromatography.

[0075] The carboxylic acid compound may be suitably synthesized or may be a commercially available product. Examples of commercially available carboxylic acid compounds include 1-naphthoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), acetylsalicylic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), 3-nitrobenzoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), 3-phenoxybenzoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), 1-naphthaleneacetic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), and diphenylacetic acid (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0076] <<Other components for the thermal recording layer>> Examples of other components for the heat-sensitive recording layer include heat-fusible substances, binder resins for the heat-sensitive recording layer, auxiliary additives, surfactants, lubricants, and fillers. The content of other components for the thermosensitive recording layer is not particularly limited, and can be set appropriately within a range that does not impair the effects of the present invention.

[0077] -Thermofusible substance- The heat-fusible substance is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include fatty acids such as stearic acid and behenic acid; fatty acid amides such as stearic acid amide and palmitic acid amide; fatty acid metal salts such as zinc stearate, aluminum stearate, calcium stearate, zinc palmitate and zinc behenate; p-benzylbiphenyl, terphenyl, triphenylmethane, benzyl p-benzyloxybenzoate, β-benzyloxynaphthalene, and β-phenyl naphthoate. Esters, 1-hydroxy-2-naphthoic acid phenyl ester, 1-hydroxy-2-naphthoic acid methyl ester, diphenyl carbonate, terephthalic acid dibenzyl ester, terephthalic acid dimethyl ester, 1,4-dimethoxynaphthalene, 1,4-diethoxynaphthalene, 1,4-dibenzyloxynaphthalene, 1,2-bis(phenoxy)ethane, 1,2-bis(3-methylphenoxy)ethane, 1,2-bis(4-methylphenoxy)ethane, 1,4-bis(phenoxy)butane benzene, 1,4-bis(phenoxy)-2-butene, 1,2-bis(4-methoxyphenylthio)ethane, dibenzoylmethane, 1,4-bis(phenylthio)butane, 1,4-bis(phenylthio)-2-butene, 1,2-bis(4-methoxyphenylthio)ethane, 1,3-bis(2-vinyloxyethoxy)benzene, 1,4-bis(2-vinyloxyethoxy)benzene, p-(2-vinyloxyethoxy)biphenyl, p-aryloxybiphenyl, p-propargyloxybiphenyl dibenzoyloxymethane, 1,3-dibenzoyloxypropane, dibenzyl disulfide, 1,1-diphenylethanol, 1,1-diphenylpropanol, p-(benzyloxy)benzyl alcohol, 1,3-diphenoxy-2-propanol, N-octadecylcarbamoyl-p-methoxycarbonylbenzene, N-octadecylcarbamoylbenzene, oxalic acid dibenzyl ester, 1,5-bis(p-methoxyphenyloxy)-3-oxapentane, and the like. These may be used alone or in combination of two or more.

[0078] -Binder resin for thermal recording layers- The binder resin for the heat-sensitive recording layer is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include polyvinyl alcohol resin, starch or derivatives thereof; cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose; water-soluble polymers such as sodium polyacrylate, polyvinylpyrrolidone, 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; emulsions such as polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid ester, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, and ethylene-vinyl acetate copolymer; and latexes such as styrene-butadiene copolymer and styrene-butadiene-acrylic copolymer. These may be used alone or in combination of two or more.

[0079] -Auxiliary additives- The auxiliary additives are not particularly limited and can be appropriately selected depending on the purpose. For example, various hindered phenol compounds or hindered amine compounds which have electron accepting properties but relatively little color-forming ability may be added. Specific examples of auxiliary additives include 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 4,4'-butylidenebis(6-tert-butyl-2-methylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, 4,4'-thiobis(6-tert-butyl-2-methylphenol), tetrabromobisphenol A, tetrabromobisphenol S, 4,4'-thiobis(2-methylphenol), 4,4'-thiobis(2-chlorophenol), tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, and tetrakis(1,2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate.

[0080] -Surfactants- The surfactant is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include anionic surfactants, nonionic surfactants, amphoteric surfactants, and fluorine surfactants. These may be used alone or in combination of two or more.

[0081] Examples of anionic surfactants include polyoxyethylene alkyl ether acetates, dodecylbenzenesulfonates, laurates, and salts of polyoxyethylene alkyl ether sulfates. These may be used alone or in combination of two or more.

[0082] Examples of nonionic surfactants include acetylene glycol surfactants, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, and polyoxyethylene sorbitan fatty acid esters. Examples of acetylene glycol surfactants include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyne-3-diol, and 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol. These may be used alone or in combination of two or more.

[0083] - Lubricant - The lubricant is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include higher fatty acids or metal salts thereof, higher fatty acid amides, higher fatty acid esters, animal waxes, vegetable waxes, mineral waxes, and petroleum waxes.

[0084] -Filler- The filler is not particularly limited and can be appropriately selected depending on the purpose. Examples of the filler include inorganic fine powders such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, kaolin, talc, surface-treated calcium, and surface-treated silica; and organic fine powders such as urea-formalin resin, styrene-methacrylic acid copolymer, polystyrene resin, and vinylidene chloride resin.

[0085] The average thickness of the thermosensitive recording layer is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of color density, it is preferably 3 μm or more and 15 μm or less.

[0086] The method for measuring the average thickness of the thermosensitive recording layer is not particularly limited and can be appropriately selected depending on the purpose. For example, it can be measured by the same method as that for measuring the average thickness of the support.

[0087] <<Method of manufacturing the thermal recording layer>> The method for producing the thermosensitive recording layer is not particularly limited and can be appropriately selected from known methods, for example, the following methods. The leuco dye, the developer generally represented by (1) or (2), the carboxylic acid compound, and other components for the thermosensitive recording layer are pulverized and dispersed using a dispersing machine such as a ball mill, attritor, or sand mill until the dispersed particle size is 0.1 μm to 3 μm. Then, they are mixed with fillers and other materials as needed to prepare a thermosensitive recording layer coating liquid. The thermosensitive recording layer coating liquid is applied to a support and dried to obtain a thermosensitive recording layer.

[0088] The method for applying the heat-sensitive recording layer coating liquid onto the support is not particularly limited and can be appropriately selected depending on the purpose, and examples include blade coating, gravure coating, gravure offset coating, bar coating, roll coating, knife coating, air knife coating, comma coating, U comma coating, AKKU coating, smoothing coating, microgravure coating, reverse roll coating, four to five roll coating, dip coating, single-layer curtain coating, multi-layer simultaneous curtain coating, slide coating, and die coating. Among these, from the viewpoints of economy and improving the uniformity of the coating layer, a method of coating a thermosensitive recording layer and a protective layer by a simultaneous multilayer curtain coating method, and a method of coating a thermosensitive recording layer, a protective layer, and an intermediate layer by a simultaneous multilayer curtain coating method are preferred.

[0089] The amount of the heat-sensitive recording layer adhered to the support after drying is not particularly limited and can be appropriately selected depending on the purpose. However, from the viewpoint of color density, it is preferable that the amount is 0.5 g / m 2 More than 20.0g / m 2 Less than 1.0 g / m is preferred 2 More than 10.0g / m 2 The following is more preferred:

[0090] <Protective layer> The thermosensitive recording medium of the present invention may have a protective layer on the side of the thermosensitive recording layer where the support is not disposed. The protective layer preferably contains a binder resin for the protective layer and a crosslinking agent, and may contain other components for the protective layer as required.

[0091] -Binder resin for protective layer- The binder resin for the protective layer is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include water-soluble resins, water-soluble resin emulsions, hydrophobic resins, ultraviolet-curable resins, and electron beam-curable resins. Examples of water-soluble resins include polyvinyl alcohol, modified polyvinyl alcohol, starch or derivatives thereof, cellulose derivatives such as methoxycellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide-acrylic acid ester copolymers, acrylamide-acrylic acid ester-methacrylic acid terpolymers, alkali salts of styrene-maleic anhydride copolymers, alkali salts of isobutylene-maleic anhydride copolymers, polyacrylamide, modified polyacrylamide, methyl vinyl ether-maleic anhydride copolymers, carboxy-modified polyethylene, polyvinyl alcohol-acrylamide block copolymers, melamine-formaldehyde resins, urea-formaldehyde resins, sodium alginate, gelatin, and casein. Among these, modified polyvinyl alcohol is preferred. Examples of modified polyvinyl alcohols include diacetone-modified polyvinyl alcohol; acetoacetyl-modified polyvinyl alcohol; carboxylic acid-modified polyvinyl alcohols such as itaconic acid-modified polyvinyl alcohol and maleic acid-modified polyvinyl alcohol. These may be used alone or in combination of two or more.

[0092] -Crosslinking agent- The crosslinking agent is not particularly limited and can be appropriately selected depending on the purpose as long as it can reduce the solubility of the water-soluble resin in water by reacting with the water-soluble resin, and examples thereof include glyoxal derivatives, methylol derivatives, epichlorohydrin, polyamide epichlorohydrin, epoxy compounds, aziridine compounds, hydrazine, hydrazide derivatives, oxazoline derivatives, carbodiimide derivatives, etc. Among these, polyamide epichlorohydrin is preferred because it is highly safe to handle and the curing time required for water resistance is short. These may be used alone or in combination of two or more.

[0093] The content of polyamide epichlorohydrin as a crosslinking agent is not particularly limited and can be selected appropriately depending on the purpose, but is preferably 10 parts by mass or more and 60 parts by mass or less, and more preferably 20 parts by mass or more and 50 parts by mass or less, per 100 parts by mass of the binder resin for the protective layer.

[0094] -Other ingredients for the protective layer- Other components for the protective layer are not particularly limited and can be selected appropriately depending on the purpose, and examples include pigments (fillers), heat-fusible substances, auxiliary additives, surfactants, lubricants, and pressure color-developing inhibitors. The auxiliary additives, surfactants, and lubricants may be the same as those described in the section "Other components for the heat-sensitive recording layer."

[0095] Examples of pigments include inorganic pigments such as zinc oxide, calcium carbonate, barium sulfate, titanium oxide, lithopone, talc, rosewood, kaolin, aluminum hydroxide, and calcined kaolin, and organic pigments such as cross-linked polystyrene resin, urea resin, silicone resin, cross-linked polymethyl methacrylate resin, and melamine-formaldehyde resin.

[0096] The average thickness of the protective layer is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of barrier performance and printer matching, it is preferably 0.5 μm or more and 5 μm or less, and more preferably 1 μm or more and 3 μm or less.

[0097] The method for measuring the average thickness of the protective layer is not particularly limited and can be appropriately selected depending on the purpose. For example, the average thickness of the protective layer can be measured by the same method as that for measuring the average thickness of the thermosensitive recording layer.

[0098] The method for producing the protective layer is not particularly limited and can be appropriately selected depending on the purpose. For example, the same method as described in the section <<Method for producing the thermosensitive recording layer>> can be used.

[0099] <Middle class> The thermosensitive recording medium of the present invention may have an intermediate layer between the protective layer and the thermosensitive recording layer.

[0100] The intermediate layer preferably contains a binder, and may also contain an inorganic filler and a surfactant. The binder is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include polyvinyl alcohol, modified polyvinyl alcohol, starch and derivatives thereof, cellulose derivatives, polyvinylpyrrolidone, polyethyleneimine, sodium alginate, gelatin, casein, and acrylic binders. Hydrophobic resins that can be used as binders also include those in emulsion or water-soluble form, such as urethane resins, epoxy resins, vinyl acetate (co)polymers, vinylidene chloride (co)polymers, vinyl chloride (co)polymers, and styrene-butadiene copolymers. Among these, polyvinyl alcohol and modified polyvinyl alcohol are preferred.

[0101] The intermediate layer may have a single layer structure or a laminated structure. If the intermediate layer is a laminated structure, the same binder can be used in each intermediate layer, or different binders can be used in different layers.

[0102] The average thickness of the intermediate layer is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of barrier performance, it is preferably 0.2 μm or more and 10 μm or less, more preferably 0.5 μm or more and 5 μm or less. When the intermediate layer has a laminated structure, the total thickness (average value) of the intermediate layer is preferably 5 μm or less.

[0103] The method for measuring the average thickness of the intermediate layer is not particularly limited and can be appropriately selected depending on the purpose. For example, it can be measured by the same method as the method for measuring the average thickness of the support.

[0104] The method for producing the intermediate layer is not particularly limited and can be appropriately selected depending on the purpose. For example, the same methods as those described in the section <<Method for producing the thermosensitive recording layer>> can be used.

[0105] <Back layer> The thermosensitive recording medium of the present invention may have a back layer on the support on the side where the thermosensitive recording layer is not disposed.

[0106] The back layer preferably contains a filler for the back layer and a binder resin, and may contain other components such as a lubricant and a color pigment, if necessary. The binder resin and lubricant may be the same as those described in the section <<Other components for the heat-sensitive recording layer>>.

[0107] As the filler for the back layer, for example, an inorganic filler or an organic filler can be used. The inorganic filler is not particularly limited and can be appropriately selected depending on the purpose. Examples of the inorganic filler include carbonates, silicates, metal oxides, and sulfate compounds. The organic filler is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include silicone resin, cellulose, epoxy resin, nylon resin, phenolic resin, polyurethane resin, urea resin, melamine resin, polyester resin, polycarbonate resin, styrene resin, acrylic resin, polyethylene resin, formaldehyde resin, and polymethyl methacrylate resin.

[0108] The average thickness of the back layer is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of preventing the substrate from curling, it is preferably 0.1 μm or more and 20 μm or less, more preferably 0.3 μm or more and 10 μm or less.

[0109] The method for measuring the average thickness of the back layer is not particularly limited and can be appropriately selected depending on the purpose. For example, it can be measured by the same method as that for measuring the average thickness of the support.

[0110] <Undercoat layer> The thermosensitive recording medium of the present invention may have an undercoat layer between the support and the thermosensitive recording layer.

[0111] The undercoat layer preferably contains thermoplastic hollow resin particles and an adhesive resin, and may contain other components as required.

[0112] Thermoplastic hollow resin particles are minute hollow particles that have a thermoplastic resin (thermoplastic substance) shell and contain air or other gases inside, and are already in a foamed state.

[0113] The thermoplastic resin is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include styrene-acrylic resin, polystyrene resin, acrylic resin, polyethylene resin, polypropylene resin, polyacetal resin, chlorinated polyether resin, polyvinyl chloride resin, and copolymer resin mainly composed of vinylidene chloride and acrylonitrile. Among these, styrene-acrylic resin and copolymer resins mainly composed of vinylidene chloride and acrylonitrile are preferred from the viewpoints of high hollowness, small variation in particle size, and suitability for blade coating.

[0114] The thermoplastic material is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include phenol-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins, furan resins, unsaturated polyester resins produced by addition polymerization, and crosslinked MMA resins.

[0115] The average particle size (particle outer diameter) of the thermoplastic hollow resin particles is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.2 μm to 20 μm, more preferably 2 μm to 5 μm. In addition, it is preferable that the distribution peak is uniform with little variation. If the average particle size of the thermoplastic hollow resin particles is 0.2 μm or more, it is technically difficult to make them hollow, and this can solve the problem of the undercoat layer being insufficient in effect. If the average particle size of the thermoplastic hollow resin particles is 20 μm or less, the smoothness of the undercoat layer surface after drying decreases, which eliminates the problem of having to apply a large amount of the thermosensitive recording layer coating liquid in order to make the thermosensitive recording layer uniform.

[0116] The hollowness of the thermoplastic hollow resin particles is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 50% to 95%, more preferably 80% to 95%. If the hollow ratio of the thermoplastic hollow resin particles is 50% or more, the heat insulating properties will be insufficient, and the thermal energy from the thermal head will be released outside the thermal recording medium through the support, resulting in insufficient sensitivity improvement. This can eliminate such problems. In this specification, the "hollowness" refers to the ratio of the outer diameter to the inner diameter (diameter of the hollow portion) of a hollow particle, and is expressed by the following formula. Hollowness (%) = (inner diameter of hollow particle / outer diameter of hollow particle) x 100

[0117] The amount of the thermoplastic hollow resin particles to be applied is not particularly limited and can be selected appropriately depending on the purpose. However, from the viewpoint of maintaining sensitivity and uniformity of application, it is preferable to apply the amount of the thermoplastic hollow resin particles to the support 1 m. 2 1g to 3g per serving is preferred. Thermoplastic hollow resin particle coating amount: 1g / m 2 If this is the case, sufficient sensitivity can be obtained. Thermoplastic hollow resin particle coating amount: 3g / m 2 If it is less than this, the bonding strength between the layers is improved.

[0118] <Adhesive layer> The thermosensitive recording medium of the present invention may have an adhesive layer on the support on the side where the protective layer is not provided. The thermosensitive recording medium of the present invention may have an adhesive layer, which allows the thermosensitive recording medium to be attached to, for example, food packaging. Thus, the thermosensitive recording medium of the present invention may have an adhesive layer attached to a support or backing layer, which is useful for providing a label with an adhesive layer. A peelable liner may then be attached to the adhesive layer and removed prior to final attachment to the product to be labeled. The adhesive layer may also provide antistatic properties.

[0119] The material for the adhesive layer is not particularly limited and can be selected appropriately depending on the purpose, and examples include urea resin, melamine resin, phenolic resin, epoxy resin, vinyl acetate resin, vinyl acetate-acrylic copolymer, ethylene-vinyl acetate copolymer, acrylic resin, polyvinyl ether resin, vinyl chloride-vinyl acetate copolymer, polystyrene resin, polyester resin, polyurethane resin, polyamide resin, chlorinated polyolefin resin, polyvinyl butyral resin, acrylic acid ester copolymer, methacrylic acid ester copolymer, natural rubber, cyanoacrylate resin, and silicone resin. These may be used alone or in combination of two or more. These materials may be crosslinked with a crosslinking agent.

[0120] The adhesive layer material may be of the hot melt type. In one aspect of the present invention, a label comprising the thermosensitive recording medium of the present invention is in the form of a silicone linerless (SLL) label.

[0121] The average thickness of the adhesive layer is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.1 μm or more and 20 μm or less.

[0122] The method for measuring the average thickness of the adhesive layer is not particularly limited and can be appropriately selected depending on the purpose. For example, it can be measured by the same method as the method for measuring the average thickness of the support.

[0123] The method for producing the adhesive layer is not particularly limited and can be appropriately selected depending on the purpose. For example, known coating methods and lamination methods can be used.

[0124] Here, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. In each drawing, the same components are denoted by the same reference numerals, and redundant explanations may be omitted. Furthermore, the number, position, shape, etc. of the components are not limited to the present embodiment, and the number, position, shape, etc. may be any number, position, shape, etc. that is preferable for implementing the present invention.

[0125] FIG. 9 is a schematic cross-sectional view showing a thermosensitive recording medium according to one embodiment of the present invention. The thermosensitive recording medium 1 has a support 13, a thermosensitive recording layer 12 disposed on one side of the support 13, and a protective layer 11 on the side of the thermosensitive recording layer 12 where the support 13 is not disposed.

[0126] FIG. 10 is a schematic cross-sectional view showing a thermosensitive recording medium according to one embodiment of the present invention. The thermosensitive recording medium 1 has a support 13, a thermosensitive recording layer 12 arranged on one side of the support 13, a protective layer 11 arranged on the side of the thermosensitive recording layer 12 where the support 13 is not arranged, and a back layer 15 on the side of the support 13 where the thermosensitive recording layer 12 is not arranged.

[0127] FIG. 11 is a schematic cross-sectional view showing a thermosensitive recording medium according to another embodiment of the present invention. The thermosensitive recording medium 1 has a support 13, a thermosensitive recording layer 12 arranged on one side of the support 13, a protective layer 11a arranged on the side of the thermosensitive recording layer 12 opposite the support 13, and an intermediate layer 11b arranged between the protective layer 11a and the thermosensitive recording layer 12.

[0128] FIG. 12 is a schematic cross-sectional view showing a thermosensitive recording medium according to another embodiment of the present invention. The thermosensitive recording medium 1 has a support 13, a thermosensitive recording layer 12 arranged on one side of the support 13, an undercoat layer 14 arranged between the support 13 and the thermosensitive recording layer 12, and a protective layer 11 arranged on the side of the thermosensitive recording layer 12 where the support 13 is not arranged.

[0129] The shape of the thermosensitive recording medium of the present invention is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include label, sheet, and roll shapes.

[0130] The embodiment of the thermosensitive recording medium of the present invention is not particularly limited and can be appropriately selected depending on the purpose. For example, it may be used as a label, and a layer for printing information such as letters, marks, pictures, barcodes, or two-dimensional codes such as QR Code (registered trademark) may be provided on the protective layer or support. Specific embodiments of the thermosensitive recording medium of the present invention are as follows.

[0131] <Thermal recording label> One embodiment of the thermosensitive recording medium of the present invention is a thermosensitive recording label. The thermosensitive recording label comprises a support, a thermosensitive recording layer disposed on one side of the support, an adhesive layer disposed on the side of the support where the thermosensitive recording layer is not disposed, and a release paper on the adhesive layer, and may further comprise other layers as necessary. The adhesive layer may be provided on the entire label or only on a part of the label.

[0132] <Linerless thermal recording medium with release layer> One embodiment of the thermosensitive recording medium of the present invention is a linerless thermosensitive recording medium with a release layer. A linerless thermosensitive recording medium with a release layer comprises a support, a thermosensitive recording layer disposed on one side of the support, a release layer disposed on the top layer of the surface on which the thermosensitive recording layer is disposed, and an adhesive layer disposed on the support on the side on which the thermosensitive recording layer is not disposed, and may further comprise other layers as necessary.

[0133] The release layer is preferably a layer formed using a material that has good releasability from the adhesive layer, and more preferably a layer containing silicon. The linerless thermosensitive recording medium with a release layer of this embodiment can be handled in the form of a roll wound so that the adhesive layer is superimposed on the release layer.

[0134] <Linerless thermal recording medium without release layer> One embodiment of the thermosensitive recording medium of the present invention is a linerless thermosensitive recording medium without a release layer. A linerless thermosensitive recording medium without a release layer comprises a support, a thermosensitive recording layer disposed on one side of the support, and an adhesive layer disposed on the support on the side where the thermosensitive recording layer is not disposed, the adhesive layer being a thermosensitive adhesive layer that becomes adhesive when heated, and may have other layers as necessary.

[0135] The heat-sensitive adhesive layer preferably contains a thermoplastic resin and a heat-meltable substance, and may contain a tackifier as needed. The thermoplastic resin provides adhesive strength and bonding strength. The heat-melting substance is solid at room temperature and does not impart plasticity to the resin, but melts when heated, causing the resin to swell or soften, thereby exhibiting adhesiveness. The tackifier has the function of improving adhesiveness.

[0136] <Thermal magnetic recording paper> One embodiment of the thermosensitive recording medium of the present invention is thermosensitive magnetic recording paper. The thermosensitive magnetic recording paper comprises a support, a thermosensitive recording layer disposed on one side of the support, and a magnetic recording layer disposed on the side of the support where the thermosensitive recording layer is not disposed, and may further comprise other layers as necessary.

[0137] The magnetic recording layer is formed by coating a support with iron oxide, barium ferrite, or the like and vinyl chloride resin, urethane resin, nylon resin, or the like, or by vapor deposition, sputtering, or the like without using resin. The magnetic recording layer is preferably provided on the support on the side where the thermosensitive recording layer is not provided, but may also be provided between the support and the thermosensitive recording layer or on at least a part of the thermosensitive recording layer.

[0138] (Recording method) The recording method using the thermosensitive recording medium of the present invention is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a thermal head and a laser. The thermal head is not particularly limited in shape, structure, size, etc., and can be appropriately selected depending on the purpose. The laser is not particularly limited and can be appropriately selected depending on the purpose. Examples include CO2 lasers and semiconductor lasers having a wavelength of 9.3 μm or more and 10.6 μm or less.

[0139] (Goods) The article according to the present invention comprises a thermal recording medium. As the thermosensitive recording medium, the thermosensitive recording medium of the present invention can be suitably used. Here, "having a thermosensitive recording medium" means a state in which the thermosensitive recording medium of the present invention is attached or mounted.

[0140] The article is not particularly limited as long as it has the thermosensitive recording medium of the present invention and can be appropriately selected depending on the purpose, and examples thereof include packaging materials, wrapping materials, wrapping paper, etc. More specifically, examples thereof include packaging materials for fresh foods, lunch boxes, prepared dishes, books, documents, etc.

[0141] [Application] The thermosensitive recording medium of the present invention has excellent PVC wrap resistance and heat resistance of printed images, and is highly sensitive, and therefore can be used in a wide range of applications, such as in the POS field for fresh food, bento boxes, prepared dishes, etc.; in the copying field for books, documents, etc.; in the communication field such as facsimiles; in the ticket issuing field for ticket vending machines, receipts, invoices, etc.; and in the airline industry, for baggage tags, pill cases, pill bottles, etc. [Example]

[0142] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples and comparative examples, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0143] <Preparation of Dispersion for Coating Thermosensitive Recording Layer> The leuco dye dispersion [Liquid A], developer dispersion [Liquids B1 and B2], carboxylic acid compound dispersion [Liquids C1 to C6], and comparative compound dispersion [Liquids C7 to C10] were dispersed using a sand grinder so that the volume average particle diameter was 0.5 μm for [Liquid A], 1.0 μm for [Liquids B1 and B2], and 1.0 μm for [Liquids C1 to C10], to prepare dispersions for coating the thermosensitive recording layer. The compositions of the respective solutions are as follows:

[0144] -Leuco dye dispersion liquid [liquid A]- Leuco dye (3-dibutylamino-6-methyl-7-anilinofluoran) (ODB2, manufactured by Yamamoto Chemical Co., Ltd.): 20 parts by mass 40 parts by weight of 10% itaconic acid-modified polyvinyl alcohol aqueous solution (25-88KL, manufactured by Kuraray Co., Ltd.) Surfactant (Newco1290, manufactured by Nippon Nyukazai Co., Ltd., solids concentration 100%): 0.2 parts by mass Ion-exchanged water: 40 parts by weight

[0145] - Developer dispersion liquid [B1 liquid] - N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea (S-176, manufactured by Sanko Co., Ltd.): 20 parts by mass 20 parts by weight of 10% itaconic acid-modified polyvinyl alcohol aqueous solution (25-88KL, manufactured by Kuraray Co., Ltd.) Amorphous silica (Mizukasil P527, manufactured by Mizusawa Industrial Chemicals Co., Ltd.): 15 parts by mass Surfactant (PD-001, manufactured by Nissin Chemical Industry Co., Ltd., solid content concentration 100% by mass): 0.2 parts by mass Ion-exchanged water: 65 parts by weight

[0146] - Developer dispersion liquid [B2 liquid] - 5-(N-3-methylphenylsulfonylamido)-(N',N''-bis(3-methylphenyl)isophthalic acid diamide (PF-425, manufactured by B.A. SF.SA): 20 parts by mass 20 parts by weight of 10% itaconic acid-modified polyvinyl alcohol aqueous solution (25-88KL, manufactured by Kuraray Co., Ltd.) Amorphous silica (Mizukasil P527, manufactured by Mizusawa Industrial Chemicals Co., Ltd.): 15 parts by mass Surfactant (PD-001, manufactured by Nissin Chemical Industry Co., Ltd., solid content concentration 100% by mass): 0.2 parts by mass Ion-exchanged water: 65 parts by weight

[0147] -Carboxylic acid compound dispersion liquid [Liquid C1]- 1-Naphthoic acid (Tokyo Chemical Industry Co., Ltd.): 20 parts by mass 20 parts by weight of a 10% by weight aqueous solution of sulfone-modified polyvinyl alcohol (Gohselan L-3266, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) Surfactant (PD-001, manufactured by Nissin Chemical Industry Co., Ltd., solid content concentration 100% by mass): 0.2 parts by mass Ion-exchanged water: 35 parts by weight

[0148] -Carboxylic acid compound dispersion liquid [Liquid C2]- Acetylsalicylic acid (Tokyo Chemical Industry Co., Ltd.): 20 parts by weight 20 parts by weight of a 10% by weight aqueous solution of sulfone-modified polyvinyl alcohol (Gohselan L-3266, manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.) Surfactant (PD-001, manufactured by Nissin Chemical Industry Co., Ltd., solid content concentration 100% by mass): 0.2 parts by mass Ion-exchanged water: 35 parts by weight

[0149] -Carboxylic acid compound dispersion liquid [C3 liquid]- 3-Nitrobenzoic acid (Tokyo Chemical Industry Co., Ltd.): 20 parts by mass 20 parts by weight of a 10% by weight aqueous solution of sulfone-modified polyvinyl alcohol (Gohselan L-3266, manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.) Surfactant (PD-001, manufactured by Nissin Chemical Industry Co., Ltd., solid content concentration 100% by mass): 0.2 parts by mass Ion-exchanged water: 35 parts by weight

[0150] -Carboxylic acid compound dispersion liquid [C4 liquid]- 3-phenoxybenzoic acid (Tokyo Chemical Industry Co., Ltd.): 20 parts by mass 20 parts by weight of a 10% by weight aqueous solution of sulfone-modified polyvinyl alcohol (Gohselan L-3266, manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.) Surfactant (PD-001, manufactured by Nissin Chemical Industry Co., Ltd., solid content concentration 100% by mass): 0.2 parts by mass Ion-exchanged water: 35 parts by weight

[0151] -Carboxylic acid compound dispersion liquid [C5 liquid]- Naphthalene acetic acid (Tokyo Chemical Industry Co., Ltd.): 20 parts by weight 20 parts by weight of a 10% by weight aqueous solution of sulfone-modified polyvinyl alcohol (Gohselan L-3266, manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.) Surfactant (PD-001, manufactured by Nissin Chemical Industry Co., Ltd., solid content concentration 100% by mass): 0.2 parts by mass Ion-exchanged water: 35 parts by weight

[0152] -Carboxylic acid compound dispersion liquid [C6 liquid]- Diphenylacetic acid (Tokyo Chemical Industry Co., Ltd.): 20 parts by weight 20 parts by weight of a 10% by weight aqueous solution of sulfone-modified polyvinyl alcohol (Gohselan L-3266, manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.) Surfactant (PD-001, manufactured by Nissin Chemical Industry Co., Ltd., solid content concentration 100% by mass): 0.2 parts by mass Ion-exchanged water: 35 parts by weight

[0153] -Comparative compound dispersion [C7 liquid]- Urea-urethane compound (UU, manufactured by Chemipro Chemical Co., Ltd.): 20 parts by mass 20 parts by weight of a 10% by weight aqueous solution of sulfone-modified polyvinyl alcohol (Gohselan L-3266, manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.) Surfactant (PD-001, manufactured by Nissin Chemical Industry Co., Ltd., solid content concentration 100% by mass): 0.2 parts by mass Ion-exchanged water: 35 parts by weight

[0154] -Comparative compound dispersion liquid [C8 liquid]- N-[2-(3-phenylureido)phenyl]benzenesulfonamide (NKK-1304, manufactured by Nippon Soda Co., Ltd.): 20 parts by mass 20 parts by weight of a 10% by weight aqueous solution of sulfone-modified polyvinyl alcohol (Gohselan L-3266, manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.) Surfactant (PD-001, manufactured by Nissin Chemical Industry Co., Ltd., solid content concentration 100% by mass): 0.2 parts by mass Ion-exchanged water: 35 parts by weight

[0155] -Comparative compound dispersion liquid [C9 liquid]- 4-Nitrophthalic acid (Tokyo Chemical Industry Co., Ltd.): 20 parts by mass 20 parts by weight of a 10% by weight aqueous solution of sulfone-modified polyvinyl alcohol (Gohselan L-3266, manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.) Surfactant (PD-001, manufactured by Nissin Chemical Industry Co., Ltd., solid content concentration 100% by mass): 0.2 parts by mass Ion-exchanged water: 35 parts by weight

[0156] -Comparative compound dispersion liquid [C10 liquid]- 2-Chlorobenzoic acid (Tokyo Chemical Industry Co., Ltd.): 20 parts by mass 20 parts by weight of a 10% by weight aqueous solution of sulfone-modified polyvinyl alcohol (Gohselan L-3266, manufactured by The Nippon Synthetic Chemical Industry Co., Ltd.) Surfactant (PD-001, manufactured by Nissin Chemical Industry Co., Ltd., solid content concentration 100% by mass): 0.2 parts by mass Ion-exchanged water: 35 parts by weight

[0157] <Preparation of Undercoat Layer Coating Solution [Solution D]> The materials were mixed to prepare an undercoat layer coating solution having the following composition: Hollow particles (a copolymer of acrylonitrile, methacrylonitrile, and isobornyl methacrylate, hollow ratio 90%, volume average particle diameter 4.4 μm, solid content concentration 33% by mass, manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.): 20 parts by mass Styrene / butadiene copolymer latex (solid content concentration 47.5% by mass, Smartex PA-8076, manufactured by Nippon A&L Co., Ltd.): 20 parts by mass 20 parts by weight of 10% polyvinyl alcohol aqueous solution (PVA117, manufactured by Kuraray Co., Ltd.) Ion-exchanged water: 40 parts by weight

[0158] <Preparation of protective layer coating solution [Solution E]> 30 parts by weight of aluminum hydroxide, 30 parts by weight of a 10% by weight aqueous solution of itaconic acid-modified polyvinyl alcohol (25-88KL, manufactured by Kuraray Co., Ltd.), and 40 parts by weight of ion-exchanged water were stirred and dispersed using a sand grinder to a volume average particle size of 0.5 μm to obtain a mixed solution. The mixed solution and various other materials were mixed and stirred to prepare a protective layer coating solution [Solution E]. The composition of the protective layer coating solution [Solution E] was as follows: ·Mixed liquid: 30 parts by mass 50 parts by weight of 10% itaconic acid-modified polyvinyl alcohol aqueous solution (25-88KL, manufactured by Kuraray Co., Ltd.) Crosslinking agent solution (polyamide epichlorohydrin resin, solid content concentration 25% by mass, WS525, manufactured by Nippon PMC Co., Ltd.): 8 parts by mass Montan acid ester wax dispersion (solid content concentration 30% by mass, J206, manufactured by Chukyo Yushi Co., Ltd.): 5 parts by mass Ion-exchanged water: 15 parts by weight

[0159] Example 1 2.5 parts by mass of [Liquid A], 10.0 parts by mass of [Liquid B1], 5.0 parts by mass of [Liquid C1], and 10 parts by mass of a 10% by mass aqueous solution of itaconic acid-modified polyvinyl alcohol (25-88KL, manufactured by Kuraray Co., Ltd.) were mixed and stirred to prepare [Thermal Recording Layer Coating Liquid of Example 1]. As a support, a basis weight of 60 g / m 2 The amount of [Liquid D] adhered to the paper surface after drying was 3.0 g / m 2 The coating was then dried to form an undercoat layer. On the undercoat layer, the coating solution for the thermosensitive recording layer of Example 1 was applied in an amount of 3.0 g / m2 after drying. 2 The mixture was then dried to form a heat-sensitive recording layer. After drying, [Liquid E] is applied to the thermal recording layer at a deposition rate of 2.5 g / m 2 The coating was then dried to form a protective layer. Next, the surface was treated with a supercalender to achieve a surface smoothness of 1,500 to 2,500 seconds, and the film was sealed in a high-density polyethylene bag and cured for a predetermined period of time in an environment of 40°C to obtain the thermosensitive recording medium of Example 1.

[0160] <Evaluation of dynamic color development characteristics> Printing was performed using a thermal printer MP104 (MARKPOINT) with the applied energy varied from 0.96 mJ / dot to 13.0 mJ / dot in 1.34 mJ / dot increments. Image density was measured using a Macbeth densitometer RD-914, and the energy value at which the image density reached 1.0 was calculated. The calculated energy values ​​were evaluated based on the evaluation criteria for dynamic color development characteristics. Note that a smaller energy value indicates better sensitivity (thermal responsiveness). The results are shown in Table 1. -Evaluation criteria for dynamic color development characteristics- ◎: Energy value is 6.5mJ / dot or less 〇: Energy value is over 6.5mJ / dot and 8.0mJ / dot or less ×: Energy value exceeds 8.0 mJ / dot

[0161] <Evaluation of PVC wrap resistance> Printing was performed using a thermal printer MP104 (MARKPOINT) with an applied energy of 8.99 mJ / dot. A vinyl chloride wrap (Shin-Etsu Chemical Co., Ltd.) was attached to the test sample, and the sample was stored for 48 hours at 60°C under a 5 kg load. The image density of the printed area after storage was measured using a Macbeth RD-914 densitometer. The measured image density was evaluated based on the evaluation criteria for vinyl chloride wrap resistance. Note that the higher the image density of the printed area, the less likely it was to be discolored by the vinyl chloride wrap, indicating a better effect in preventing the printed image from fading. The results are shown in Table 1. -Evaluation criteria for PVC wrap resistance- ◎: Image density of the printed area is 1.0 or more ○: Image density of the printed area is 0.8 or more and less than 1.0 ×: Image density of printed area is less than 0.8

[0162] <Evaluation of water-resistant PVC wrap> Printing was performed using a thermal printer MP104 (MARKPOINT) with an applied energy of 8.99 mJ / dot. The test sample was immersed in water for 5 minutes, then a PVC wrap (Shin-Etsu Chemical Co., Ltd.) was attached and the sample was stored for 48 hours at 60°C under a 5 kg load. The image density of the printed area after storage was measured using a Macbeth RD-914 densitometer. The measured image density was evaluated based on the evaluation criteria for water-resistant PVC wrap. Note that the higher the image density of the printed area, the less likely it was to be discolored by the PVC wrap, indicating a better effect in preventing the printed image from fading. The results are shown in Table 1. -Evaluation criteria for water-resistant PVC wrap- ◎: Image density of the printed area is 0.8 or more ○: Image density of the printed area is 0.5 or more and less than 0.8 ×: Image density of printed area is less than 0.5

[0163] <Evaluation of heat resistance> Printing was performed using a thermal printer MP104 (MARKPOINT) with an applied energy of 8.99 mJ / dot. The test sample was placed in a thermostatic chamber at 100°C and left to stand for 1 hour. The image density of the non-printed areas was measured using a Macbeth densitometer RD-914. The measured image density was evaluated based on the heat resistance evaluation criteria. Note that a lower image density in the non-printed areas indicates less discoloration in a high-heat environment. The results are shown in Table 1. -Heat resistance evaluation criteria- ◎: Image density of non-printed area is 0.2 or less ○: Image density of non-printed area is over 0.2 and 0.4 or less ×: Image density of non-printed area exceeds 0.4

[0164] (Examples 2 to 15 and Comparative Examples 1 to 12) A thermosensitive recording medium was prepared in the same manner as in Example 1, except that the composition was changed as shown in Table 1, and various evaluations were carried out. The results are shown in Table 1.

[0165] [Table 1]

[0166] It was confirmed that the thermosensitive recording media of Examples 1 to 15, compared to the thermosensitive recording media of Comparative Examples 1 to 12, are thermosensitive recording media that can simultaneously suppress fading of printed images and improve heat resistance of non-image areas, while also achieving high sensitivity suitable for high-speed printing.

[0167] The present invention includes, for example, the following aspects. <1> A thermosensitive recording medium having a support and a thermosensitive recording layer disposed on one side of the support, The thermosensitive recording layer is a thermosensitive recording medium characterized by containing a leuco dye, a color developer represented by the following general formula (1) or the following general formula (2), and a carboxylic acid compound represented by at least one selected from the following general formulas (A) to (E). [ka] (In general formula (1), R1's each independently represent any one of a linear or branched alkyl group having 1 to 3 carbon atoms, a phenyl group, a naphthyl group, a benzyl group, a phenylethyl group, a phenylpropyl group, and a phenyl group or a naphthyl group substituted at one or more positions with a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, a carboxy group, and an alkyl group having 1 to 3 carbon atoms and a linear or branched structure; and R2's each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms and a linear or branched structure.) [ka] (In general formula (2), each R3 independently represents any one of hydrogen, a linear or branched alkyl group having 1 to 3 carbon atoms, a linear or branched alkoxy group having 1 to 3 carbon atoms, a benzyl group, a phenyl group, a naphthyl group, a phenylethyl group, a phenylpropyl group, and a phenyl group and a naphthyl group substituted at one or more positions with an alkyl group having a linear or branched structure having 1 to 3 carbon atoms.) [ka] [ka] [ka] (In the general formula (C), R4 represents an alkyl group having a linear or branched structure and having 1 to 5 carbon atoms.) [ka] [ka] (In general formula (E), Ar represents a phenyl group, a naphthyl group, or a phenyl group or naphthyl group substituted at one or more positions with a linear or branched alkyl group having 1 to 3 carbon atoms, a phenyl group, a naphthyl group, a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, or a carboxy group; and each n independently represents 1 or 2.) <2> The color developer represented by the general formula (1) is represented by the following formula (1-1): [ka] The color developer represented by the general formula (2) is represented by the following formula (2-1): <1> 1. The thermosensitive recording medium according to claim 1. [ka] <3> The carboxylic acid compound is at least one selected from 1-naphthoic acid, acetylsalicylic acid, 3-nitrobenzoic acid, 3-phenoxybenzoic acid, 1-naphthaleneacetic acid, and diphenylacetic acid. <1> or <2> 1. The thermosensitive recording medium according to claim 1. <4> The content of the carboxylic acid compound is 0.05 parts by mass or more and 3.00 parts by mass or less relative to 1 part by mass of the color developer. <1> from <3> 1. The thermosensitive recording medium according to claim 1, wherein the first and second layers are arranged parallel to each other. <5> The support further has a back layer on the side where the heat-sensitive recording layer is not disposed. <1> from <4> 1. The thermosensitive recording medium according to claim 1, wherein the first and second layers are arranged parallel to each other. <6> an undercoat layer is further provided between the support and the thermosensitive recording layer; <1> from <5> 1. The thermosensitive recording medium according to claim 1, wherein the first and second layers are arranged parallel to each other. <7> The undercoat layer contains hollow particles. <6> The thermal recording medium is as described above. <8> The recording medium further comprises a protective layer on the side of the thermosensitive recording layer where the support is not disposed. <1> from <7> 1. The thermosensitive recording medium according to claim 1, wherein the first and second layers are arranged parallel to each other. <9> an intermediate layer is further provided between the protective layer and the thermosensitive recording layer; <8> 1. The thermosensitive recording medium according to claim 1. <10> the thermosensitive recording layer, the intermediate layer, and the protective layer are formed by simultaneous coating using a curtain coating method. <9> 1. The thermosensitive recording medium according to claim 1.

[0168] <1> from <10> The thermosensitive recording medium according to any one of the above items can solve the various problems encountered in the prior art and achieve the object of the present invention. [Explanation of symbols]

[0169] 1. Thermal recording media 11 Protective layer 12. Thermal recording layer 13 Support [Prior art documents] [Patent documents]

[0170] [Patent Document 1] Patent No. 5887423 [Patent Document 2] Patent No. 7143952 [Patent Document 3] Patent No. 6751479 [Patent Document 4] Patent No. 7046984 [Patent Document 5] Patent No. 4601174 [Patent Document 6] Japanese Patent Publication No. 2022-067451 [Patent Document 7] Patent No. 6960562 [Patent Document 8] Special Publication No. 2022-546097

Claims

1. A thermosensitive recording medium having a support and a thermosensitive recording layer disposed on one side of the support, The thermosensitive recording medium is characterized in that the thermosensitive recording layer contains a leuco dye, a color developer represented by the following general formula (1) or the following general formula (2), and a carboxylic acid compound represented by at least one selected from the following general formulas (A) to (E): 【Chemical 1】 (In general formula (1), each R1 independently represents any one of a linear or branched alkyl group having 1 to 3 carbon atoms, a phenyl group, a naphthyl group, a benzyl group, a phenylethyl group, a phenylpropyl group, and a phenyl group or a naphthyl group substituted at one or more positions with a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, a carboxy group, or an alkyl group having 1 to 3 carbon atoms and a linear or branched structure; and R2 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms and a linear or branched structure.) 【Chemistry 2】 (In general formula (2), each R3 independently represents any one of hydrogen, a linear or branched alkyl group having 1 to 3 carbon atoms, a linear or branched alkoxy group having 1 to 3 carbon atoms, a benzyl group, a phenyl group, a naphthyl group, a phenylethyl group, a phenylpropyl group, and a phenyl group and a naphthyl group substituted at one or more positions with an alkyl group having a linear or branched structure having 1 to 3 carbon atoms.) 【Chemistry 3】 【Chemistry 4】 【Chemistry 5】 (In general formula (C), R4 represents an alkyl group having a linear or branched structure and having 1 to 5 carbon atoms.) 【Chemistry 6】 【Chemistry 7】 (In general formula (E), Ar represents a phenyl group, a naphthyl group, or a phenyl group or naphthyl group substituted at one or more positions with an alkyl group having 1 to 3 carbon atoms and a linear or branched structure, a phenyl group, a naphthyl group, a halogen group, a nitro group, an amino group, a sulfo group, a hydroxy group, or a carboxy group; and n's each independently represent 1 or 2.)

2. The color developer represented by the general formula (1) is represented by the following formula (1-1): 【Chemistry 8】 2. The thermosensitive recording medium according to claim 1, wherein the color developer represented by the general formula (2) is represented by the following formula (2-1): 【Chemistry 9】

3. 3. The thermosensitive recording medium according to claim 1, wherein the carboxylic acid compound is at least one selected from the group consisting of 1-naphthoic acid, acetylsalicylic acid, 3-nitrobenzoic acid, 3-phenoxybenzoic acid, 1-naphthaleneacetic acid, and diphenylacetic acid.

4. 3. The thermosensitive recording medium according to claim 1, wherein the content of the carboxylic acid compound is 0.05 parts by mass or more and 3.00 parts by mass or less with respect to 1 part by mass of the color developer.

5. 3. The thermosensitive recording medium according to claim 1, further comprising a back layer on the side of the support where the thermosensitive recording layer is not disposed.

6. 3. The thermosensitive recording medium according to claim 1, further comprising an undercoat layer between the support and the thermosensitive recording layer.

7. The thermosensitive recording medium according to claim 6 , wherein the undercoat layer contains hollow particles.

8. 3. The thermosensitive recording medium according to claim 1, further comprising a protective layer on the side of the thermosensitive recording layer opposite to the support.

9. 9. The thermosensitive recording medium according to claim 8, further comprising an intermediate layer between the protective layer and the thermosensitive recording layer.

10. The thermosensitive recording medium according to claim 9 , wherein the thermosensitive recording layer, the intermediate layer, and the protective layer are formed by simultaneous coating using a curtain coating method.

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