Thermal recording media

Abstract

The present invention provides at least Synthetic resin film support layer; A thermosensitive color-forming layer containing a leuco dye and a color developer; one or more protective layers disposed on the thermosensitive color-forming layer opposite the synthetic resin film support layer; A barrier back layer provided on the synthetic resin film support layer on the side opposite to the thermosensitive color developing layer. wherein the barrier back layer contains polyvinyl alcohol characterized by a saponification degree of at least 70%.

Description

[Technical Field]

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

[0002] Known thermosensitive recording media use a color-forming agent system in which a dye such as a leuco dye in one layer of the medium (thermosensitive color-forming layer) reacts with another component, a so-called "color developer," to produce a colored product when heat is applied.

[0003] Thermal recording materials are used in a wide range of applications, including information processing (electronic desk calculator and computer output), medical equipment recording devices, low- and high-speed facsimiles, automatic ticket vending machines (railroad and admission tickets), thermal copiers, and labels and tabs for POS systems. To meet the requirements for a variety of applications, such as labels affixed to the surface of moisture-resistant packaging materials or labels that can be peeled off after application, thermal recording materials must simultaneously satisfy a variety of properties, including physical strength to resist bending and breakage, dimensional stability, and water insolubility. For these reasons, synthetic paper and synthetic resin films are often used as the support for thermal recording materials.

[0004] In particular, in the field of labels and tabs for POS systems, thermosensitive recording materials with an adhesive layer on the back are often used. There are a variety of adhesives used on the back, including adhesives for permanent adhesion, adhesives for peeling and re-adhesion, and adhesives that maintain adhesion at low temperatures, such as those used for labels on frozen foods.

[0005] When synthetic paper or plastic film, which has a smoother surface than paper, is used as the support, the thermosensitive recording material may curl, especially when an adhesive layer is provided. Furthermore, when a backing layer is provided between the support and the adhesive layer, the adhesive strength between the backing layer and the support may decrease, and peeling may occur at the portion where the adhesive strength is decreased.

[0006] The causes of peeling and curling of thermal recording materials have not yet been fully elucidated, but it is thought that when the support is synthetic paper or plastic film, low molecular weight components such as plasticizers, tackifiers (adhesive agents), and emulsifiers contained in the adhesive used in the adhesive layer migrate to the back layer or support, thereby reducing the adhesive strength with the back layer or imparting plasticity to one side of the support.

[0007] Patent Document 1 provides a heat-sensitive recording material comprising a support, a heat-sensitive recording layer provided on one surface of the support, and a back layer provided on the other surface of the support, wherein the support has a surface formed of a resin, and the back layer contains a combination of a core-shell acrylic resin and an oxazoline resin and / or a reaction product thereof. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] European Patent Application Publication No. 2675626 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to provide a thermosensitive recording medium that has excellent adhesion between the support layer and the barrier back layer, excellent water resistance and stability of the barrier back layer coating, and reduced curling of the barrier back layer even when an adhesive is applied thereon. The anti-curl effect is particularly improved by the composition of the barrier back layer composition of the present invention. [Means for solving the problem]

[0010] In this context, the present invention provides at least A synthetic resin film support layer (10); a thermosensitive color-forming layer (40) containing a leuco dye and a color developer; one or more protective layers (50) provided on the thermosensitive color-forming layer (40) on the side opposite to the synthetic resin film support layer (10); one barrier back layer (20) provided on the synthetic resin film support layer (10) on the side opposite to the thermosensitive coloring layer (40); A thermosensitive recording medium (1) comprising: The present invention relates to a thermosensitive recording medium (1), in which the barrier back layer (20) contains polyvinyl alcohol characterized by a saponification degree of at least 70%.

[0011] In a preferred embodiment of the present invention, the amount of polyvinyl alcohol, expressed as dry weight relative to 100% of the combined dry weight of all components of the barrier back layer (20), is at least 5%, more preferably at least 10%. Furthermore, the amount of polyvinyl alcohol, expressed as dry weight relative to 100% of the combined dry weight of all components of the barrier back layer (20), is preferably at most 40%, more preferably at most 30%, even more preferably at most 25%, even more preferably at most 20%, and most preferably at most 15%.

[0012] In a preferred embodiment of the present invention, the polyvinyl alcohol is used in the barrier back layer (20): a core-shell acrylic emulsion comprising a hydrophilic shell polymer containing a carboxylic acid and a hydrophobic core polymer; and Oxazoline Crosslinker Used in combination with

[0013] In a preferred embodiment of the present invention, the synthetic resin film support layer (10) has a thickness of at least 60 μm and at most 105 μm.

[0014] In a preferred embodiment of the present invention, the synthetic resin film support layer (10) is biaxially oriented polypropylene (BOPP). Preferably, hollowed BOPP, which has small cavities created during film manufacturing, is used for the support layer (10). When there are no small cavities, BOPP typically has a density of 0.90 g / cm. 3It may exhibit a density slightly exceeding 0.65 g / cm 3 In the present invention, hollowed BOPP with a density of at least 0.70 g / cm is available. 3 , up to 0.80 g / cm 3 It is preferred to use hollowed BOPP having a density of at least 0.72 g / cm. More preferably, the hollowed BOPP has a density of at least 0.72 g / cm. 3 , up to 0.79 g / cm 3 and particularly preferably at least 0.74 g / cm 3 , up to 0.78 g / cm 3 It is believed that the BOPP film used as the support layer (10) can contribute to the image sensitivity and / or suppression of curling of the thermosensitive recording medium of the present invention when the density is in an appropriate range.

[0015] In a preferred embodiment of the present invention, the synthetic resin film support layer (10) comprises two protective layers (51) and (52).

[0016] In a preferred embodiment of the present invention, the barrier back layer (20) contains an antistatic agent. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 shows a method for evaluating the curl of a thermosensitive recording material (thermosensitive recording medium) sample in the context of the present invention, in which a hot melt adhesive is applied to the barrier back layer of the sample, the sample is fixed to a stem fixed straight on a support without contact between the label and the support, and the sample is exposed to an environment of 50°C and 70% relative humidity for 72 hours, where FIG. 1 is a front view. [Figure 2] FIG. 2 shows a method for evaluating the curl of a thermosensitive recording material (thermosensitive recording medium) sample in the context of the present invention, in which a hot melt adhesive is applied to the barrier back layer of the sample, the sample is fixed to a stem fixed straight on the support without contact between the label and the support, and the sample is exposed to an environment of 50°C and 70% relative humidity for 72 hours, where FIG. 2 is a top view. [Figure 3]3 is a schematic diagram of an illustrative, non-limiting example of a thermosensitive recording medium according to one embodiment of the present invention. In this type of embodiment, the thermosensitive recording medium (1) has a thermosensitive color-forming layer (40) disposed on a synthetic resin film support layer (10) in contact with the synthetic resin film support layer (10), and the thermosensitive color-forming layer (40) also in contact with a protective layer (50). On the opposite side of the synthetic resin film support layer (10) from the thermosensitive color-forming layer (40), there is a barrier back layer (20). [Figure 4] Figure 4 is a schematic diagram of an illustrative, non-limiting example of a thermal recording medium according to a further embodiment of the present invention, where, in addition to the layers described above in relation to Figure 3, there is a "base layer" (30) between the synthetic resin support layer (10) and the thermal layer (40). [Figure 5] Figure 5 is a schematic diagram of an illustrative, non-limiting example of a thermosensitive recording medium according to a further embodiment of the present invention, where there is no "underlayer" and in addition to the layers described above in relation to Figure 3 there are two protective layers (51) and (52). [Figure 6] Figure 6 is a schematic diagram of an illustrative, non-limiting example of a thermosensitive recording medium according to a further embodiment of the present invention, where, in addition to the layers described above in relation to Figure 3, there is an "underlayer" (30) and two protective layers (51) and (52). DETAILED DESCRIPTION OF THE INVENTION

[0018] Synthetic resin support layer The support layer in the present invention is a support having a surface formed of a resin, examples of which include synthetic paper containing synthetic resin as a main component, plastic film, laminated paper, and coated paper. Among these, synthetic paper is preferred. The synthetic paper is not particularly limited and may be appropriately selected depending on the intended purpose. Examples include synthetic paper made from synthetic fibers such as polyethylene, polypropylene, polyethylene terephthalate, and polyamide; and products obtained by bonding the above synthetic paper to part, the surface, or both surfaces of paper. The synthetic paper may be manufactured according to the intended use or may be selected from commercially available products. Examples of commercially available products include polypropylene films such as biaxially oriented polypropylene (BOPP) films. Examples of suitable polypropylene film products include PL-100 from NanYa Plastics, FPH-95 from YUPO CORPORATION, 100 LH344 from Jindal Films, and SP-PG-10075 from Lichang Plastics.

[0019] The preferred thickness of the synthetic resin support layer in the present invention is at least 60 μm and at most 105 μm. A film thickness at the upper end of this range, i.e., 105 μm, may be preferred to achieve a high enough stiffness to provide good label jetting properties.

[0020] Furthermore, the density of the support whose surface is formed of resin is preferably 60 g / m 3 ~150g / m 3 More preferably, the support has a density of 60 g / m 3 ~90g / m 3 When the support has a low density, better color development can be obtained. When the support has a low density, there are many voids inside the support, which provides excellent heat insulation, and the heat energy applied from the thermal head is effectively absorbed by the heat-sensitive recording layer, thereby improving the color development of the heat-sensitive recording material. The preferred density is at least 70 g / m to achieve the best balance between heat insulation and rigidity. 3 , up to 80g / m 3 , preferably about 75 g / m 3 is.

[0021] The wettability index of the support surface on the back layer side is preferably 0.03 N / m (30 dyn / cm) or more, more preferably 0.04 N / m (40 dyn / cm) or more. If the wettability index is less than 0.03 N / m (30 dyn / cm), it may be difficult to form a coating film of the back layer.

[0022] Primer layer Generally, in the technical field of thermosensitive recording media, the term "undercoat" is understood by those skilled in the art to refer to a layer between the support and the thermosensitive color-forming layer. Also, the term "underlayer" may be used synonymously with "priming layer" by those skilled in the art.

[0023] In the present invention, the undercoat layer may or may not be provided; that is, the undercoat layer is merely an option in the present invention, and the thermosensitive recording medium of the present invention may or may not include such an undercoat layer.

[0024] In the thermosensitive recording medium of the present invention, when a subbing layer is used, the technical effects sought by using the subbing layer include, in particular, improving the adhesion between the substrate and the thermal layer and improving print quality.

[0025] As mentioned above, the thermosensitive recording medium of the present invention may optionally include a subbing layer disposed between the support and the thermosensitive color forming layer.

[0026] When present in the thermosensitive recording medium of the present invention, the undercoat layer comprises a binder resin, and the undercoat layer may further comprise other components such as fillers and other additives.

[0027] The binder resin to be used in the undercoat layer may be either a water-dispersible resin or a water-soluble resin, and specific examples thereof include conventionally known water-soluble polymers and aqueous polymer emulsions.

[0028] The water-soluble polymer that can be used as the binder resin in the undercoat layer is not particularly limited and can be appropriately selected depending on the intended purpose. Examples include polyvinyl alcohol, starch and its derivatives, cellulose derivatives such as methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose, polyvinylpyrrolidone, alkali salts of styrene-maleic anhydride copolymers, alkali salts of isobutylene-maleic anhydride copolymers, sodium alginate, gelatin, and casein. These may be used alone or in combination.

[0029] The aqueous polymer emulsion that can be used as the binder resin of the undercoat layer is not particularly limited and can be appropriately selected depending on the intended purpose. Examples include latex of styrene-butadiene copolymer, and emulsions of vinyl acetate resin, acrylic resin, and polyurethane resin. These may be used alone or in combination.

[0030] When an undercoat layer is used in the thermosensitive recording medium of the present invention, an inorganic filler may be used in the undercoat layer, or may be omitted. When an inorganic filler is used, examples thereof include aluminum hydroxide, calcium carbonate, aluminum oxide, zinc oxide, titanium dioxide, silica, barium sulfate, talc, kaolin, alumina, and clay. These may be used alone or in combination. Among these, aluminum hydroxide, calcium carbonate, kaolin, and clay are preferred in terms of the liquid properties in the coating liquid, the stability of dispersed particles, and water solubility.

[0031] To improve print quality, it is known to use hollow particles with a hollow ratio (%) of 50% or more, or even 80% or more, or even 90% or more, where the hollow ratio (%) is (inner diameter of hollow particle / outer diameter of hollow particle) × 100, as components contained in the undercoat layer of a thermosensitive recording medium. Each of these hollow particles has an outer shell made of a thermoplastic resin, and may contain air or other gases therein. Typically, the volume average particle size is 1 μm to 10 μm, and the outer shell is most commonly made of a thermoplastic resin made from polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylate, polyacrylonitrile, and polybutadiene, or a copolymer resin thereof.

[0032] When an undercoat layer is used in the thermosensitive recording medium of the present invention, the deposition amount of the first undercoat layer in the thermosensitive recording medium is 0.4 g / m 2 ~10g / m 2 is suitable, and more preferably 0.6 g / m 2 ~4g / m 2 is.

[0033] Typically, an important function of a subbing layer in conventional thermosensitive recording media is to fill in and compensate for the unevenness of the support, particularly a paper support. Such subbing layers are typically selected as low-cost layers that, through their constituent components, ensure a smoother surface before coating with an expensive thermal layer. This approach optimizes the use of thermal layer materials and avoids their loss. The subbing layer has been modified to improve preprint characteristics and sensitivity by adding hollow fillers to reflect heat back to the thermosensitive color-forming layer without loss to the paper support. However, in the present invention, a subbing layer is generally not required because the synthetic resin film support layer is smoother than the paper support of other thermosensitive recording media. Therefore, in a preferred embodiment of the present invention, one side of the synthetic resin film support layer is in contact with one side of the thermosensitive layer, and no subbing layer is present between the synthetic resin film support layer and the thermosensitive color-forming layer. However, in the present invention, when the base layer of the thermosensitive recording medium is a synthetic resin film support layer in the form of a thin polymer film, an undercoat layer may be used to effectively utilize the generated heat to improve sensitivity, improve adhesion between the support and the thermosensitive layer, and prevent the recording layer material from penetrating into the support.

[0034] Heat-sensitive coloring layer In the thermosensitive recording medium of the present invention, the thermosensitive coloring layer is located on the support layer and contains a leuco dye, a color developer, and a hydrophobic resin. The thermosensitive coloring layer may be in contact with one side of the synthetic resin film support layer, or, as described above, an undercoat layer may be present between the support layer and the thermosensitive coloring layer.

[0035] Heat-sensitive coloring layer - leuco dye and color developer The thermosensitive color forming layer comprises a color forming system in which a leuco dye in one layer of the medium reacts with another component, a so-called "color developer," to produce a colored product upon the application of heat.

[0036] Leuco dyes are compounds that exhibit electron donating properties and can be used alone or in combination of two or more. However, leuco dyes themselves are colorless or light-colored dye precursors, and known leuco compounds can be used. Examples of leuco compounds include triphenylmethanephthalide compounds, triarylmethane compounds, fluoran compounds, phenothiazine compounds, thiofluoran compounds, xanthene compounds, indophthalyl compounds, spiropyran compounds, azaphthalide compounds, chlormenopyrazole compounds, methine compounds, rhodamine anilinolactam compounds, rhodamine lactam compounds, quinazoline compounds, diazaxanthene compounds, and bislactone compounds. Specific examples of such compounds, taking into consideration color development, background fogging, and image fading due to humidity, heat, or light exposure, are as follows: 2-anilino-3-methyl-6-diethylaminofluoran, 2-anilino-3-methyl-6-(di-n-butylamino)fluoran, 2-anilino-3-methyl-6-(di-n-pentylamino)fluoran, 2-anilino-3-methyl-6-(Nn-propyl-N-methylamino)fluoran, 2-anilino-3-methyl-6-(N-isopropyl-N-methylamino)fluoran, 2-anilino-3-methyl-6-(N-isobutyl-N-methylamino)fluoran, 2-anilino-3-methyl-6-(Nn-amyl-N-methylamino)fluoran, 2-anilino-3-methyl-6-(N-sec-butyl-N-ethylamino)fluoran, Amino)fluoran, 2-anilino-3-methyl-6-(Nn-amyl-N-ethylamino)fluoran, 2-anilino-3-methyl-6-(N-isoamyl-N-ethylamino)fluoran, 2-anilino-3-methyl-6-(N-cyclohexyl-N-methylamino)fluoran, 2-anilino-3-methyl-6-(N-methyl-p-toluidino)fluoran, 2-anilino-3-methyl-6-(N-methyl-p-toluidino)fluoran, 2-(m-trichloromethylanilino)-3-methyl-6-diethylaminofluoran, 2-(m-trifluoromethylanilino)-3-methyl-6-diethylaminofluoran, 2-(m-trifluoromethylanilino)-3-methyl-6-(N-cyclohexyl-N-methylamino)fluoran, 2-(2,4-dimethylanilino)-3-methyl-6-diethylaminofluoran, 2-(N-ethyl-p-toluidino)-3-methyl-6-(N-ethylanilino)fluoran, 2-(N-methyl-p-toluidino)-3-methyl-6-(N-propyl-p-toluidino)fluoran, 2-anilino-6-(Nn-hexyl-N-ethylamino)fluoran, 2-(o-chloranilino)-6-diethylaminofluoran, 2-(o-bromoanilino)-6-diethylaminofluoran, 2-(o-chloranilino)-6-dibutylaminofluoran, 2-(o-fluoranilino)-6-diethylaminofluoran 2-(m-trifluoromethylanilino)-6-diethylaminofluoran, 2-(p-acetylanilino)-6-(Nn-amyl-Nn-butylamino)fluoran, 2-benzylamino-6-(N-ethyl-p-toluidino)fluoran, 2-benzylamino-6-(N-methyl-2,4-dimethylanilino)fluoran, 2-benzylamino-6-(N-ethyl-2,4-dimethylanilino)fluoran, 2-dibenzylamino-6-(N-methyl-p-toluidino)fluoran, 2-dibenzylamino Amino-6-(N-ethyl-p-toluidino)fluoran, 2-(di-p-methylbenzylamino)-6-(N-ethyl-p-toluidino)fluoran, 2-(α-phenylethylamino)-6-(N-ethyl-p-toluidino)fluoran, 2-methylamino-6-(N-methylanilino)fluoran, 2-methylamino-6-(N-ethylanilino)fluoran, 2-methylamino-6-(N-propylanilino)fluoran, 2-ethylamino-6-(N-methyl-p-toluidino)fluoran, 2-methylamino-6-(N-methyl-2,4-di methylanilino)fluoran, 2-ethylamino-6-(N-methyl-2,4-dimethylanilino)fluoran, 2-dimethylamino-6-(N-methylanilino)fluoran, 2-dimethylamino-6-(N-ethylanilino)fluoran, 2-diethylamino-6-(N-methyl-p-toluidino)fluoran, benzoleuco methylene blue, 2-[3,6-bis(diethylamino)]-6-(o-chloranilino)xanthylbenzoic acid lactum, 2-[3,6-bis(diethylamino)]-9-(o-chloranilino)xanthylbenzoic acid lactum, 3,3-bis(p-dimethylaminophenyl)phthalide, 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)-6-diethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)-6-chlorophthalide, 3,3-bis(p-dibutylaminophenyl)phthalide, 3-(2-methoxy-4-dimethylaminophenyl)-3-(2-hydroxy-4,5-dichlorophenyl)phthalide, 3-(2-hydroxy-4-dimethylaminophenyl)-3-(2-methoxy-5-chlorophenyl)phthalide, 3 -(2-hydroxy-4-dimethoxyaminophenyl)-3-(2-methoxy-5-chlorophenyl)phthalide, 3-(2-hydroxy-4-dimethoxyaminophenyl)-3-(2-methoxy-5-nitrophenyl)phthalide, 3-(2-hydroxy-4-diethylaminophenyl)-3-(2-methoxy-5-methylphenyl)phthalide, 3,6-bis(dimethylamino)fluorene spiro(9,3')-6'-dimethylaminophthalide, 6'-chloro-8'-methoxy-benzoindolinospiropyran, and 6'-bromo-2'-methoxybenzoindolinospiropyran. These may be used alone or in combination.

[0037] The amount of the leuco dye contained in the thermosensitive color developing layer is preferably 3% by mass to 20% by mass.

[0038] As the color developer, various electron-accepting materials are suitably used, which react with the leuco dye to develop color upon heating, such as phenolic compounds, organic or inorganic acid compounds, and their esters or salts. Specific examples thereof include bisphenol A, tetrabromobisphenol A, gallic acid, salicylic acid, 3-isopropyl salicylate, 3-cyclohexyl salicylate, 3-5-di-tert-butyl salicylate, 3,5-di-α-methylbenzyl salicylate, 4,4'-isopropylidenediphenol, 1,1'-isopropylidenebis(2-chlorophenol), 4,4'-isopropylidenebis(2,6-dibromophenol), 4,4'-isopropylidenebis(2,6-dichlorophenol), 4,4'-isopropylidenebis(2-methylphenol), 4,4'-isopropylidenebis(2,6-dimethylphenol), 4,4'-isopropylidenebis(2-tert-butylphenol), 4,4'-sec-butylidenediphenol, Phenol, 4,4'-cyclohexylidenebisphenol, 4,4'-cyclohexylidenebis(2-methylphenol), 4-tert-butylphenol, 4-phenylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, 3,5-xylenol, thymol, methyl-4-hydroxybenzoate, 4-hydroxyacetophenone, novolak phenolic resin, 2,2'-thiobis(4,6-dichlorophenol), catechol, resorcinol, hydroquinone, pyrogallol, fluoroglycine, fluoroglycine carboxylate, 4-tert-octylcatechol, 2,2'-methylenebis(4-chlorophenol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2,2'-Dihydroxydiphenyl, ethyl p-hydroxybenzoate, propyl p-hydroxybenzoate, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate, p-hydroxybenzoate-p-chlorobenzyl, p-hydroxybenzoate-o-chlorobenzyl, p-hydroxybenzoate-p-methylbenzyl, p-hydroxybenzoate-n-octyl, benzoic acid, zinc salicylate, 1-hydroxy-2-naphthoic acid, 2-hydroxy-6-naphthoic acid, zinc 2-hydroxy-6-naphthoate, 4-hydroxydiphenyl sulfone, 4-hydroxy-4'-chlorodiphenyl sulfone, bis(4-hydroxyphenyl) sulfide, 2-hydroxy-p-toluic acid, zinc 3,5-di-tert-butylsalicylate, tin 3,5-di-tert-butylsalicylate, tartaric acid, oxalic acid Acid, maleic acid, citric acid, succinic acid, stearic acid, 4-hydroxyphthalic acid, boric acid, thiourea derivatives, 4-hydroxythiophenol derivatives, bis(4-hydroxyphenyl)acetate, bis(4-hydroxyphenyl)ethyl acetate, bis(4-hydroxyphenyl)acetate-n-propyl, bis(4-hydroxyphenyl)acetate-n-butyl, bis(4-hydroxyphenyl)phenyl acetate, bis(4-hydroxyphenyl)benzyl acetate, bis(4-hydroxyphenyl)phenethyl acetate, bis(3-methyl-4-hydroxyphenyl)acetate, bis(3-methyl-4-hydroxyphenyl)methyl acetate, bis(3-methyl-4-hydroxyphenyl)acetate-n-propyl, 1,7-bis(4-hydroxyphenylthio)3,5-dioxaheptane, 1,5-bis(4-hydroxyphenylthio)3-oxaheptane, dimethyl 4-hydroxyphthalate, 4-hydroxy-4'-methoxydiphenyl sulfone, 4-hydroxy-4'-ethoxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-propoxydiphenyl sulfone, 4-hydroxy-4'-butoxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-sec-butoxydiphenyl sulfone, 4-hydroxy-4'-tert-butoxydiphenyl sulfone, 4-hydroxy-4'-benzyloxydiphenyl sulfone, 4-hydroxy-4'-phenoxydiphenyl sulfone, 4-hydroxy-4'-(m-methylbenzo Examples of the 4,4'-hydroxyphenylsulfone include 4-hydroxy-4'-(p-methylbenzoxy)diphenylsulfone, 4-hydroxy-4'-(o-methylbenzoxy)diphenylsulfone, 4-hydroxy-4'-(p-chlorobenzoxy)diphenylsulfone, 4-hydroxy-4'-oxyaryldiphenylsulfone, 4-hydroxy-4-allyloxydiphenylsulfone, N-(2-((phenylcarbamoyl)amino)phenyl)benzenesulfonamide, 4,4'-sulfonylbisphenol, polymers of 1,1'-oxybis[2-chloroethane], 2-(4-hydroxyphenylsulfonyl)phenol, (bis(3-allyl-4-hydroxyphenyl)sulfone), and 2,2'-diallyl-4,4'-sulfonyldiphenol. These may be used alone or in combination.

[0039] In the thermosensitive coloring layer, the mixing ratio of the color developer to the leuco dye is preferably 0.5 to 10 parts by weight, more preferably 1 to 5 parts by weight, of the color developer to 1 part by weight of the leuco dye.

[0040] The thickness of the thermosensitive coloring layer varies depending on the composition of the thermosensitive coloring layer and the intended use of the thermosensitive recording medium, and cannot be uniformly defined, but is preferably 1 μm to 50 μm, more preferably 2 μm to 20 μm.

[0041] In addition to the above-mentioned leuco dye and developer, other materials commonly used in thermal recording materials, such as binders, fillers, heat-fusible materials, crosslinking agents, pigments, surfactants, fluorescent brighteners, and lubricants, may be added to the thermal coloring layer as appropriate.

[0042] A binder may be used as needed to improve layer adhesion and coating properties. The binder is not particularly limited and may be appropriately selected depending on the intended purpose. Specific examples of binder resins include starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, salts of diisobutylene-maleic anhydride copolymers, salts of styrene-maleic anhydride copolymers, salts of ethylene-acrylic acid copolymers, salts of styrene-acrylic copolymers, and salt emulsions of styrene-butadiene copolymers. These binders may be used alone or in combination. A preferred binder formulation for the thermosensitive color-forming layer of the present invention is a combination of polyvinyl alcohol and aliphatic polyurethane.

[0043] The filler is not particularly limited and is appropriately selected depending on the intended purpose. Examples thereof include inorganic pigments such as calcium carbonate, aluminum oxide, zinc oxide, titanium dioxide, silica, aluminum hydroxide, barium sulfate, talc, kaolin, alumina, and clay, as well as known organic pigments. Among these, acidic pigments (those that exhibit acidity in aqueous solution) such as silica, alumina, and kaolin are preferred, and silica is particularly preferred from the viewpoint of color density.

[0044] The heat-meltable material is not particularly limited and is appropriately selected depending on the intended purpose. Examples thereof include fatty acid amides such as stearic acid and behenic acid; fatty acid amides such as stearic acid amide, erucic acid amide, palmitic acid amide, behenic acid amide, and palmitic acid amide; N-substituted amides such as N-lauryl lauric acid amide, N-stearyl stearic acid amide, and N-oleyl stearic acid amide; bis fatty acid amides such as methylene bisstearic acid amide, ethylene bisstearic acid amide, ethylene bislauric acid amide, ethylene biscapric acid amide, and ethylene bisbehenic acid amide; hydroxyl fatty acid amides such as hydroxystearic acid amide, methylene bishydroxystearic acid amide, ethylene bishydroxyl stearic acid amide, and hexamethylene bishydroxystearic acid amide; metal salts of fatty acids such as zinc stearate, aluminum stearate, calcium stearate, zinc palmitate, and zinc behenate;p-benzylbiphenyl, terphenyl, triphenylmethane, benzyl p-benzyloxybenzoate, β-benzyloxynaphthalene, β-naphthoic acid phenyl, 1-hydroxy-2-naphthoic acid phenyl, 1-hydroxy-2-naphthoic acid methyl, diphenyl carbonate, benzyl terephthalate, 1,4-dimethoxynaphthalene, 1,4-diethoxynaphthalene, 1,4-dibenzyloxynaphthalene, 1,2-diphenoxyethane, 1,2-bis(4-methylphenoxyethane), 1,4-diphenoxy-2-butene, 1,2-bis(4-methoxyphenylthio)ethane, dibenzoylmethane, 1,4-diphenylthiobutane, 1,4-diphenylthio-2-butene, 1,3-bis(2-vinyloxyethoxy)benzene Examples of suitable hydroxybenzoates include 1,4-bis(2-vinyloxyethoxy)benzene, p-(2-vinyloxyethoxy)biphenyl, p-aryloxybiphenyl, dibenzoyloxymethane, dibenzoyloxypropane, dibenzyl sulfide, 1,1-diphenylethanol, 1,1-diphenylpropanol, p-benzyloxybenzyl alcohol, 1,3-phenoxy-2-propanol, N-octadecylcarbamoyl-p-methoxycarbonylbenzene, N-octadecylcarbamoylbenzene, 1,2-bis(4-methoxyphenoxy)propane, 1,5-bis(4-methoxyphenoxy)-3-oxapentane, dibenzyl oxalate, bis(4-methylbenzyl) oxalate, and bis(4-chlorobenzyl) oxalate. These may be used alone or in combination.

[0045] Furthermore, it is generally preferable to incorporate diacetone-modified polyvinyl alcohol into the thermosensitive color-forming layer, and when N-aminopolyacrylamide is added as a crosslinking agent to the thermosensitive color-forming layer and protective layer, the crosslinking reaction occurs easily, improving water resistance without the need to add a separate crosslinking agent that may inhibit color development.

[0046] When synthetic paper is used as the support layer, a combination of polyvinyl alcohol and an aliphatic urethane dispersion is preferred to enhance adhesion of all layers to the synthetic paper support, as discussed above with respect to the selection of binders for the thermosensitive color forming layer.

[0047] The thermosensitive coloring layer can be formed by a known method. For example, a leuco dye and a color developer are pulverized and dispersed together with a binder and other components using a dispersing machine such as a ball mill, attritor, or sand mill to a particle size of 1 μm to 3 μm. The resulting dispersion is mixed with a filler and a heat-fusible material (sensitizer) dispersion according to a predetermined formulation, as needed, to prepare a coating liquid for the thermosensitive coloring layer. The coating liquid thus prepared is then applied to a support.

[0048] protective layer To obtain various properties such as good compatibility with a thermal head (e.g., anti-sticking, anti-scratching), and water resistance or plasticizer resistance, it is preferable to provide at least one protective layer on the thermosensitive layer. By stacking multiple different protective layers, it is possible to focus on compatibility or barrier properties, respectively. The protective layer in the thermosensitive recording medium of the present invention is not particularly limited and can be appropriately selected depending on the intended purpose.

[0049] The protective layer usually contains at least a binder, and each protective layer may contain a crosslinking agent, an inorganic filler, a lubricant, and a surfactant.

[0050] The binder for each protective layer is not particularly limited and can be appropriately selected depending on the intended purpose. The same binder can be used for each protective layer, or different binders can be used for each protective layer. Examples of binders that can be used in the protective layer include polyvinyl alcohol, modified polyvinyl alcohol, starch and its derivatives, cellulose derivatives, polyvinylpyrrolidone, polyethyleneimine, sodium alginate, gelatin, and casein. Acrylic binders can also be used. Hydrophobic resins that can be used as binders for the protective layer include those that are usually provided as aqueous emulsions during the preparation of the protective layer, such as urethane resins, epoxy resins, vinyl acetate (co)polymers, vinylidene chloride (co)polymers, vinyl chloride (co)polymers, and styrene-butadiene copolymers.

[0051] The crosslinking agent is not particularly limited as long as it can react with the binder to reduce the water solubility of the binder. Examples of crosslinking agents include glyoxal derivatives, methylol derivatives, epichlorohydrin, polyamide epichlorohydrin, epoxy compounds, aziridine compounds, hydrazine, hydrazide derivatives, oxazoline derivatives, and carbodiimide derivatives. One of these crosslinking agents may be used alone, or two or more of these crosslinking agents may be used in combination. Among these crosslinking agents, polyamide epichlorohydrin is preferred because of its high safety in handling and the short curing time required for water-resistant treatment. The content of polyamide epichlorohydrin is not particularly limited and can be selected appropriately depending on the intended purpose, but is preferably 10 to 80 parts by weight, more preferably 20 to 60 parts by weight, per 100 parts by weight of the binder.

[0052] The thickness of the protective layer is preferably 0.2 μm to 10 μm, more preferably 0.5 μm to 5 μm. In a non-limiting exemplary embodiment of the present invention, a protective layer having a dry thickness of 2.5 μm can be used, and if added during the manufacturing process, the initial wet thickness of this layer is about 6 μm. If multiple protective layers are applied, the thickness of each individual protective layer must be lower. The preferred maximum cumulative thickness of all protective layers combined is 10 μm for the dried final product.

[0053] When used, the inorganic filler in the protective layer is not particularly limited and is appropriately selected depending on the intended purpose. Examples of inorganic fillers include aluminum hydroxide, calcium carbonate, aluminum oxide, zinc oxide, titanium dioxide, silica, barium sulfate, talc, kaolin, alumina, and clay. These may be used alone or in combination. Among these, aluminum hydroxide and calcium carbonate are particularly preferred. This is because a protective layer containing such an inorganic filler has excellent abrasion resistance against a thermal head when printing for a long period of time. The amount of inorganic filler in the second protective layer is not particularly limited and is appropriately selected depending on the intended purpose. The amount of inorganic filler varies depending on the type of filler, but is preferably 50 to 500 parts by mass per 100 parts by mass of the binder resin.

[0054] When a lubricant is used, it is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include higher fatty acids such as zinc stearate, calcium stearate, Montan acid wax, polyethylene wax, carnauba wax, paraffin wax, ester wax, and metal salts thereof; higher fatty acid amides, higher fatty acid esters, animal waxes, vegetable waxes, mineral waxes, and petroleum waxes.

[0055] The surfactant is not particularly limited and can be appropriately selected depending on the intended purpose. Examples of surfactants include anionic surfactants, nonionic surfactants, amphoteric surfactants, and fluorine-based surfactants. One of these surfactants may be used alone, or two or more of these surfactants may be used in combination. Examples of anionic surfactants include polyoxyethylene alkyl ether acetates, dodecylbenzenesulfonates, laurates, and polyoxyethylene alkyl ether sulfates. One of these anionic surfactants may be used alone, or two or more of these anionic surfactants may be used in combination. Examples of nonionic surfactants include acetylene glycol surfactants, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl esters, and polyoxyethylene sorbitan fatty acid esters. One of these nonionic surfactants may be used alone, or two or more of these nonionic surfactants may be used in combination. 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. One of these acetylene glycol surfactants may be used alone, or two or more of these acetylene glycol surfactants may be used in combination.

[0056] The method for forming the first protective layer, the second protective layer, or any subsequent protective layer is not particularly limited and may be appropriately selected depending on the intended purpose, and examples thereof include blade coating, roll coating, wire bar coating, die coating, and curtain coating.

[0057] middle class The intermediate layer is a layer that can be provided between the thermosensitive color developing layer and the protective layer, but such an intermediate layer is not essential to the present invention and is merely optional.

[0058] The intermediate layer containing a water-soluble resin can prevent coloring of the thermosensitive recording layer due to ultraviolet irradiation performed to form the protective layer or due to reaction between the protective layer and the pigment in the thermosensitive coloring layer. In addition, the intermediate layer, like the first protective layer, can also improve the resistance of the background.

[0059] When used, the intermediate layer contains a water-soluble resin. The water-soluble resin is not particularly limited and can be appropriately selected depending on the intended purpose. Examples of water-soluble resins include polyvinyl alcohol resins, starch or starch derivatives; 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 copolymers, acrylamide-acrylic acid ester-methacrylic acid ternary copolymers, styrene-maleic anhydride copolymer alkali salts, isobutylene-maleic anhydride copolymer alkali salts, polyacrylamide, sodium alginate, gelatin, and casein; emulsions of polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid esters, vinyl chloride-vinyl acetate copolymers, polybutyl methacrylate, and ethylene-vinyl acetate copolymers; and latexes of styrene-butadiene copolymers and styrene-butadiene-acrylic copolymers. These water-soluble resins may be used alone or in combination. Among these water-soluble resins, polyvinyl alcohol resins are preferred, and polyvinyl alcohol resins having a molecular weight of 15,000 or less are more preferred.

[0060] The other components of the intermediate layer are not particularly limited and can be selected appropriately depending on the intended purpose. Examples of other components include a crosslinking agent and a surfactant. One of these other components may be used alone, or two or more of these other components may be used in combination. Both the crosslinking agent and the surfactant that can be used in the intermediate layer may be selected from the same types as those described above for the protective layer.

[0061] The method for forming the intermediate layer is not particularly limited and can be appropriately selected depending on the intended purpose. For example, the intermediate layer can be formed by the following steps (1) and (2). Step (1): A water-soluble resin, and optionally a crosslinking agent and a surfactant are mixed to prepare an intermediate layer coating liquid. Step (2): The intermediate layer coating liquid is applied onto the thermosensitive recording layer and dried.

[0062] The coating method is not particularly limited and can be appropriately selected depending on the intended purpose. Examples of the coating method include blade coating, gravure coating, gravure offset coating, bar coating, roll coating, knife coating, air knife coating, comma coating, U comma coating, AKKU coating, smooth coating, microgravure coating, reverse roll coating, four-roll or five-roll coating, dip coating, curtain coating, slide coating, and die coating.

[0063] The amount of the intermediate layer that remains after drying is not particularly limited and can be appropriately selected depending on the intended purpose. Preferably, the amount is, for example, 0.4 g / m 2 More than 3.0g / m 2 Less than 0.5 g / m, more preferably 0.5 g / m 2 More than 1.5g / m 2 Below 0.5 g / m, particularly preferably 2 More than 1.0g / m 2 The following is the result.

[0064] Barrier Back Layer A barrier back layer is provided under the support layer of the thermosensitive recording medium of the present invention, and this barrier back layer is arranged on the surface of the support opposite to the surface on which the thermosensitive layer is arranged, or, if an undercoat layer is present between the support and the thermosensitive layer, on the surface opposite to the surface on which the undercoat layer is located.

[0065] The barrier back layer contains polyvinyl alcohol (PVA). In the present invention, "polyvinyl alcohol" includes modified polyvinyl alcohols commonly used by those skilled in the art. Polyvinyl alcohol is often produced industrially by polymerizing vinyl acetate followed by saponification (ester hydrolysis). In addition to the main monomer residue (-CH-CHO-), a certain proportion of (-CH-CHO-CO-Me) groups is present. In polyvinyl alcohols that can be used in the barrier back layer of the thermosensitive recording medium of the present invention, the saponification range is at least 70%, typically 70% to 99%, i.e., 70% to 99% of (-CH-CHO-) units are contained in the polymer chain. Within the framework of the present invention, it has been recognized that the use of a barrier back layer containing polyvinyl alcohol with a degree of saponification (ester hydrolysis) of less than 70% may result in a thermosensitive recording medium with poor curl resistance.

[0066] In the present invention, the degree of polymerization of polyvinyl alcohol is not particularly limited and may be, for example, in the range of 400 to 2000, i.e., an average of 400 to 2000 monomer units are present in the polymer chain. As mentioned above, in the case of a perfect PVA homopolymer, all such monomer units are (-CH-CHOH-). However, PVA materials commercially available and used by those skilled in the art typically contain some residual ester groups and / or other main chain or side chain modifications.

[0067] In the context of the present invention, polyvinyl alcohol products obtained from the copolymerization of vinyl acetate with other monomers such as itaconic acid can be used for the barrier back layer, with (-CH2-C(CO2M)(CH2CO2M)-) monomer residues (M=H or metal ions such as Na, depending on the pH / degree of neutralization) occurring in the polymer chain. Other modified PVAs that can be used in the present invention include sulfone-modified PVA, diacetone-modified PVA, and acetoacetyl-modified PVA. Another type of modified PVA that can be used for the barrier back layer of the thermal recording medium of the present invention is amide-modified PVA. A non-limiting example of a suitable amide-modified PVA in this context is a saponified copolymer of N-(2-acetyl-1,1-dimethyl)ethylacrylamide, vinyl alcohol, and vinyl acetate, which has the following structure: [ka] Such an amide-modified PVA is sold by Japan VAM & POVAL Co., LTD as product DM-17.

[0068] In the present invention, the barrier back layer may contain substantially only PVA as the water-soluble resin, or may contain only PVA, including modified PVA. However, other polymers can be used in combination with the PVA used in the barrier back layer of the present invention. Examples of other polymers that can be used in combination with PVA include latex of styrene-butadiene copolymer; emulsions of vinyl acetate resin, acrylic resin (e.g., acrylic acid-acrylic acid ester copolymer latex), (meth)acrylamide resin, and polyurethane resin.

[0069] In certain embodiments that have been found to be effective in improving backside anchoring, polyvinyl alcohol is used in the barrier back layer with the following crosslinking agents: a core-shell acrylic emulsion comprising a hydrophilic shell polymer containing a carboxylic acid and a hydrophobic core polymer; and Oxazoline Crosslinker Used in combination with

[0070] The core-shell acrylic emulsion is preferably a core-shell acrylic resin having a core essentially containing a polymer material having a highly hydrophilic group such as an acrylonitrile group, and a shell essentially containing a copolymer of a hydrophilic polymer material such as methacrylamide and (meth)acrylic acid. The core-shell acrylic resin exhibits excellent barrier properties, water resistance, and film-forming properties after being crosslinked with a specific crosslinking agent.

[0071] Such core-shell type acrylic resins are known in the art from JP-A-06-227119, JP-A-09-254555, and JP-A-2000-158815. As the core-shell type acrylic resin, for example, a commercially available product under the name BARIASTAR (manufactured by Mitsui Chemicals, Inc.) can be used.

[0072] Oxazoline resins have a molecular structure consisting of a polymer chain (acrylic or styrene) backbone to which oxazoline groups, which are weak Lewis bases, are grafted. The oxazoline groups bond to the core-shell acrylic resin through various reactions with carboxyl groups present on the surface of the core-shell acrylic resin, such as cleaving the ring structure of the oxazoline group to bond to the carboxyl group or directly bonding to the carboxyl group, resulting in crosslinking or graft copolymerization. As a result, barrier properties, water resistance, solvent resistance, heat resistance, and strength are improved. Oxazoline resins are particularly effective in preventing peeling of the back layer due to low-molecular-weight substances such as emulsifiers and tackifiers. Oxazoline resins are highly reactive with carboxyl groups, but their reactivity at room temperature is lower than that of aziridine groups, suppressing gelation and improving the stability of the back layer coating solution.

[0073] In the present invention, to observe effective curl resistance properties, the amount of polyvinyl alcohol, expressed as dry weight relative to 100% dry weight of all components of the barrier back layer (20), is preferably at least 5%, more preferably at least 10%. Also, to optimize water resistance, the amount of polyvinyl alcohol, expressed as dry weight relative to 100% dry weight of all components of the barrier back layer (20), is preferably at most 40%, more preferably at most 25%, even more preferably at most 20%, and even more preferably at most 15%.

[0074] In a preferred embodiment, the barrier back layer may contain an antistatic agent.

[0075] The optional antistatic filler for the barrier back layer may be selected from, for example, conventional ionically conductive antistatic agents and electronically conductive antistatic agents. Specific examples of ionically conductive antistatic agents include inorganic salts such as sodium chloride; anionic polymers such as sodium polystyrene sulfonate; and resins containing quaternary ammonium salts, which are electrolyte cations. Specific examples of electronically conductive antistatic agents include conductive metal oxides, such as conductive metal compounds such as conductive tin oxide and antimony oxide; and conductive polymers such as polyaniline. Antistatic agents using surfactants may also be used. Among these antistatic agents, polystyrene sulfonate in particular reacts with aziridine to crosslink, thereby improving water resistance. Additionally, salts copolymerized with maleic acid are also effective in terms of both antistatic properties and water resistance.

[0076] Antistatic agents using surfactants are relatively inexpensive, available in a wide variety of types, and have excellent antistatic properties. However, many antistatic agents using surfactants exhibit conductivity due to the surfactant itself absorbing moisture. Furthermore, many conductive metal oxides are highly hygroscopic. Therefore, these antistatic agents are susceptible to the effects of humidity, which can reduce the water resistance of the resulting back layer. Antistatic agents using acrylic polymers have the advantage of being less likely to affect the water resistance of the resulting barrier back layer.

[0077] The amount of the antistatic agent is preferably 25 parts by mass or less relative to 5 to 100 parts by mass of the solid content of the barrier back layer. 10 It can be less than Ωcm.

[0078] The method for forming the barrier back layer is not particularly limited and may be appropriately selected depending on the intended purpose. The barrier back layer is preferably formed by applying a coating liquid for the barrier back layer to the support.

[0079] The coating method is not particularly limited and may be appropriately selected depending on the intended purpose, and examples thereof include blade coating, roll coating, wire bar coating, die coating, and curtain coating.

[0080] The thickness of the barrier back layer is not particularly limited and may be appropriately selected depending on the intended purpose, and is preferably 0.1 μm to 10 μm, more preferably 0.5 μm to 5 μm.

[0081] Adhesive layer The thermosensitive recording medium of the present invention may be provided with an adhesive layer (sometimes called a tacky layer). However, such an adhesive layer is not essential to the present invention and is merely optional.

[0082] The adhesive layer can be provided on the surface of the synthetic resin film support layer opposite to the surface on which the protective layer is formed.

[0083] In a possible application of the present invention, the adhesive layer can be useful, for example, for attaching the thermosensitive recording medium to a food package. The method for forming the adhesive layer is not particularly limited. Examples of such methods include general coating methods and lamination methods. The average thickness of the adhesive layer is not particularly limited and can be appropriately selected depending on the intended purpose, but is preferably 0.1 μm or more and 20 μm or less.

[0084] The material of the adhesive layer is not particularly limited and can be appropriately selected depending on the intended purpose. Examples of materials for the adhesive layer include urea resins, melamine resins, phenolic resins, epoxy resins, vinyl acetate resins, vinyl acetate-acrylic copolymers, ethylene-vinyl acetate copolymers, acrylic resins, polyvinyl ether resins, vinyl chloride-vinyl acetate copolymers, polystyrene resins, polyester resins, polyurethane resins, polyamide resins, chlorinated polyolefin resins, polyvinyl butyral resins, acrylic ester copolymers, methacrylic ester copolymers, natural rubber, cyanoacrylate resins, and silicone resins. One of these materials may be used alone, or two or more of these materials may be used in combination. These materials may be crosslinked with a crosslinking agent. The material for the adhesive layer may be a hot melt type.

[0085] Image recording method To record an image on the thermal recording medium of any of the embodiments of the present invention, an image recording method using either one of an image recording unit, a thermal head or a laser, can be used.

[0086] The thermal head is not particularly limited in shape, structure, and size, and may be appropriately selected depending on the intended purpose.

[0087] The laser is not particularly limited and can be selected depending on the intended purpose. In a preferred embodiment, a CO2 laser emitting light with a wavelength of 9.3 μm to 10.6 μm can be used. By using a CO2 laser emitting light with a wavelength of 9.3 μm to 10.6 μm, a satisfactory laser print image can be obtained without using a photothermal conversion agent such as a phthalocyanine pigment. Other types of lasers, such as a fiber laser diode array (FLDA), may also be used. [Example]

[0088] The present invention will be specifically described below based on examples and comparative examples. However, it should be noted that the present invention is not limited to these examples. In the following examples, unless otherwise specified, the unit "parts" means "parts by mass" and the unit "%" means "% by mass".

[0089] Example 1 A 10% by weight aqueous solution of polyvinyl alcohol (Mowiol 28-99; available from Kuraray Europe GmbH) was applied to the substrate so that the amount of polyvinyl alcohol remaining after drying was 1.0 g / m 2 The solutions were applied in this order to a thermosensitive recording material (product name: 150LCS-HW, thickness: 104 μm, available from Ricoh Company Ltd.) on the side opposite the thermosensitive layer, and then dried to obtain the thermosensitive recording medium of Example 1. The 150LCS-HW film consists of a biaxially oriented polypropylene (BOPP) support layer, an underlayer, a thermosensitive color-forming layer, and a protective layer. In the 150LCS-HW thermosensitive recording material, the BOPP support layer is a PL-100 BOPP layer provided by Nanya, a supplier, and has a coating weight of 0.78 g / cm. 3 It has a density of

[0090] Examples 2 to 9 As shown in Table 1 below, the thermosensitive recording media of Examples 2 to 9 were obtained in the same manner as in Example 1 by changing the type of polyvinyl alcohol (Examples 1 to 8 used Poval® brand PVA available from Kuraray Europe GmbH, and Example 9 used amide-modified PVA DM-17 available from JAPAN VAM & POVAL Co. LTD). [Table 1] Example 10 1) Preparation of barrier back layer solution [A1] A 20% core-shell acrylic emulsion (product name: Bariastar B-2000 available from Mitsui Chemicals, Inc.) (41 parts by weight), a 25% oxazoline crosslinker (product name: Epocros WS-700 available from Nippon Shokubai Co., Ltd.) (20 parts by weight), a 10% aqueous polyvinyl alcohol solution (product name: Mowiol 28-99 available from Kuraray Europe GmbH) (16 parts by weight), and 28 parts by weight of water were mixed and stirred to obtain a barrier back layer [A1]. 2) Preparation of application medium After drying, the amount of [A1] remaining on the surface is 1.0 g / m 2 The film was coated in this order onto a biaxially oriented polypropylene (BOPP) support (product name: Jindal 100 LH243, 100 μm thick, available from Jindal Films BV) with the matte side so that the film had a coating weight of 0.74 g / cm. The 100 LH243 BOPP support layer, provided by the supplier Jindal, had a coating weight of 0.74 g / cm. 3 It has a density of The coated support sheet was cured for 15 hours in an environment of 40° C. and 10% relative humidity to obtain Example 10.

[0091] Example 11 A thermosensitive recording medium of Example 11 was obtained in the same manner as in Example 10, except that the BOPP support was replaced with a thermosensitive recording material (product name: 150LCS-R, thickness 103 μm, available from Ricoh Industrie France SAS) and the [A1] liquid was applied to the side opposite the thermosensitive layer. The 150LCS-R film consists of a biaxially oriented polypropylene (BOPP) support layer, a thermosensitive color-forming layer, and two protective layers. In the 150LCS-R thermosensitive recording material, the BOPP support layer is a 100 LH243 BOPP layer provided by the supplier Jindal, with a density of 0.74 g / cm. 3 It has a density of

[0092] Example 12 A thermosensitive recording medium of Example 12 was obtained in the same manner as in Example 11, except that the thermosensitive recording material 150LCS-R was replaced with the thermosensitive recording material 150LCS-HW.

[0093] Examples 13 to 15 Thermosensitive recording media of Examples 13 to 15 were obtained in the same manner as in Example 12, except that the parts by mass of polyvinyl alcohol in the barrier back layer were changed as follows. [Table 2] Example 16 1) Preparation of barrier back layer solution [B1] 50% styrene-butadiene copolymer (product name: DL295 available from Trinseo France SAS) (25 parts by weight), 10% aqueous polyvinyl alcohol solution (product name: Mowiol 28-99 available from Kuraray Europe GmbH) (25 parts by weight), and 50 parts by weight of water were mixed and stirred to obtain a barrier back layer [B1]. 2) Preparation of thermal recording media The amount of [B1] remaining after drying is 1.0 g / m 2The solutions were applied in this order to a thermosensitive recording material (product name: 150LCS-HW, thickness: 104 μm, available from Ricoh Company Ltd.) on the side opposite the thermosensitive layer, and then dried. In this way, a thermosensitive recording sheet was prepared. This thermosensitive recording sheet was cured for 15 hours in an environment of 40° C. and 10% relative humidity to prepare a thermosensitive recording medium of Example 16.

[0094] Comparative Example 1 The same support layer (150LCS-HW) as in Example 1 was used, but no layer was provided on the side opposite to the thermosensitive layer, to obtain a thermosensitive recording medium of Comparative Example 1.

[0095] Comparative Examples 2 to 9 As shown in the table below, thermosensitive recording media of Comparative Examples 2 to 9 were obtained in the same manner as in Example 1, except that the type of PVA or binder was changed. [Table 3] Comparative Example 10 A thermosensitive recording medium of Comparative Example 10 was obtained in the same manner as in Example 10, except that the liquid [A1] was replaced with 33% by mass of an aliphatic urethane dispersion (NeoRez R-600; available from DSM Coating Resins BV).

[0096] Comparative Example 11 The BOPP support was replaced with a thermosensitive recording material (150LCS-R, thickness 103 μm, available from Ricoh Industrie France), and a 33% by mass aliphatic urethane dispersion was applied to the side opposite the thermosensitive layer, to obtain a thermosensitive recording medium of Comparative Example 11 in the same manner as in Comparative Example 10.

[0097] Comparative Example 12 1) Preparation of barrier back layer solution [C1] A 20% core-shell acrylic emulsion (product name: Bariastar B-2000 available from Mitsui Chemicals, Inc.) (41 parts by weight), a 25% oxazoline crosslinker (product name: Epocros WS-700 available from Nippon Shokubai Co., Ltd.) (20 parts by weight), and 28 parts by weight of water were mixed and stirred to obtain a barrier back layer [C1]. 2) Preparation of thermal recording media A thermosensitive recording medium of Comparative Example 12 was obtained in the same manner as in Example 12, except that the liquid [A1] was replaced with the liquid [C1].

[0098] Characterization of the obtained thermal recording medium uniformity After coating the barrier backing layer and before drying, the uniformity of the barrier backing layer was evaluated according to the following criteria: A value of "A" indicates that the barrier layer uniformity is at an acceptable level; a value of "B" indicates that all other tests cannot be performed. A: No defects in the uniformity of the coating liquid B: Holes or depressions in the coating liquid

[0099] curl Hot melt adhesive (RH1, available from UPM Raflatac OY) was applied at a hot melt adhesive amount of 17.5 g / m 2 The coating was applied onto the barrier layer of a sample of a thermal recording material having a width of 5 cm and a length of 5 cm so as to obtain the above value, and curling was evaluated.

[0100] A sample of the thermal recording material with the hot melt adhesive attached is fixed onto the stem in the center of the label, and the stem is fixed straight onto the support so that the label and the support do not come into contact (see Figure 1). The assembly was placed in an environment of 50°C and 70% relative humidity for 72 hours. After 72 hours, the curl was calculated by measuring the distance between the top two corners of the thermal recording material (length 1) and the distance between the bottom two corners of the thermal recording material (length 2). The final curl value was obtained by calculating the average of length 1 and length 2 (see Figures 1 and 2). The evaluation was carried out according to the following evaluation criteria: A value of "A" or "B" indicates that the curl effect is at an acceptable level. A: Higher than 4.8cm B: Between 4.5cm and 4.8cm C: Less than 4.5cm

[0101] Adhesion of the barrier back layer The adhesion of the barrier back layer was evaluated by applying an 18 mm wide, 6 cm long piece of cellophane tape (product name CT405AP-18, available from Nichiban Co., Ltd.) to the barrier back layer of the thermal recording medium along the coating flow direction and rubbing it with a finger 10 times to avoid introducing air bubbles. The tape was then removed by: i) slowly peeling it off at a 90-degree angle; ii) quickly peeling it off at a 90-degree angle. Evaluation was performed according to the following evaluation criteria. A value of "A" or "B" indicates that the adhesion of the barrier back layer is at an acceptable level. A: No peeling occurred in either step (i) or (ii). B: No peeling occurred in step (i), but peeling of the barrier back layer occurred in step (ii). C: Peeling of the barrier back layer occurred in step (i).

[0102] Water resistance of the barrier back layer A sample of the thermal recording medium measuring 7 cm in length (in the direction of the coating) and 5 cm in width was immersed in a beaker filled with 250 mL of water for 30 minutes to evaluate the barrier water resistance. After 30 minutes, the sample was removed from the beaker and rubbed back and forth 10 times with a finger on the barrier back layer in the direction of the coating. Evaluation was performed according to the following criteria: "A" indicates that the water resistance of the barrier back layer is at an acceptable level. A: The barrier back layer was not removed even after rubbing back and forth with a finger 10 times. B: The barrier back layer was removed while rubbing with a finger. [Table 4] [Explanation of symbols]

[0103] 1. Thermal recording media 10 Synthetic resin support layer 20 Barrier back layer 30 Base layer 40 Thermosensitive coloring layer 50, 51, 52 Protective layer (multiple protective layers may be present) This application is based on and claims priority from European Patent Application No. 22305146.7, filed February 10, 2022, the entire contents of which are incorporated herein by reference.

Claims

1. at least, a synthetic resin film support layer; a heat-sensitive color-forming layer containing a leuco dye and a color developer; one or more protective layers disposed on the thermosensitive color-forming layer on the side opposite to the synthetic resin film support layer; one barrier back layer provided on the synthetic resin film support layer on the side opposite to the thermosensitive color developing layer; A thermal recording medium comprising: the barrier back layer contains polyvinyl alcohol characterized by a saponification degree of at least 70%, the amount of polyvinyl alcohol, expressed as dry weight relative to 100% dry weight of all components of the barrier back layer, is at least 10%; A thermal recording medium, wherein the polyvinyl alcohol is used in the barrier back layer in combination with a core-shell acrylic emulsion containing a hydrophilic shell polymer containing a carboxylic acid and a hydrophobic core polymer; and an oxazoline crosslinking agent.

2. 2. The thermosensitive recording medium according to claim 1, wherein the amount of polyvinyl alcohol is 20% at most, expressed as a dry weight relative to 100% of the total dry weight of all components of the barrier back layer.

3. 2. The thermosensitive recording medium according to claim 1, wherein the amount of polyvinyl alcohol is 15% at most, expressed as dry weight relative to 100% dry weight of all components of the barrier back layer.

4. 4. The thermosensitive recording medium according to claim 1, wherein the synthetic resin film support layer has a thickness of at least 60 [mu]m and at most 105 [mu]m.

5. 4. The thermosensitive recording medium according to claim 1, wherein the synthetic resin film support layer contains biaxially oriented polypropylene (BOPP).

6. 6. The thermosensitive recording medium according to claim 5, wherein the biaxially oriented polypropylene (BOPP) of the synthetic resin film support layer is hollowed BOPP.

7. The hollow biaxially oriented polypropylene (BOPP) of the synthetic resin film support layer has a density of at least 0.70 g / cm ３ , up to 0.80 g / cm ３ The thermosensitive recording medium according to claim 6, having a density of

8. 4. The thermosensitive recording medium according to claim 1, wherein the synthetic resin film support layer comprises two protective layers.

9. The thermosensitive recording medium according to claim 1 , wherein the barrier back layer contains an antistatic agent.

Images