Thermosensitive recording body

Abstract

The present application aims to provide a heat-sensitive recording body having good transparency while suppressing curling. A heat-sensitive recording body (1) has a base material (2) containing a transparent resin film, a heat-sensitive recording layer (3), and a protective layer (4) formed in this order on one surface of the base material (2), and a back-coating layer (5) containing a core-shell type resin and a polyamide epichlorohydrin resin formed on the other surface of the base material (2). The protective layer (4) preferably contains a top-coating layer (6) and an intermediate layer (7) formed between the top-coating layer (6) and the heat-sensitive recording layer (3).

Description

thermal recording device Technical Field

[0001] This invention relates to a thermal recording device. Background Technology

[0002] Thermal recorders produce color by being heated by a thermal printhead, thus recording an image. Thermal recorders are widely used in a variety of applications, including printers for outputting fax machines, automatic ticket vending machines, scientific measuring instruments, and CRT medical measuring instruments.

[0003] When this thermal recorder is used, for example, as a label or packaging film for various containers containing food, the contents of the container are obscured by the label or packaging film, making it difficult for consumers to identify the contents.

[0004] Therefore, the applicant in this case has constructed a thermal recorder by making the film used for labels and packaging transparent. That is, in order to be able to identify the contents of the container, the film used for labels and packaging should be transparent, and a thermal recorder with excellent transparency has been proposed (see, for example, Patent Document 1).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 6202599 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] In recent years, the problem of plastic waste has become increasingly serious. As an environmental countermeasure, de-plasticization has gained attention, requiring a reduction in the amount of plastic used.

[0010] Therefore, in the thermal recorder and the like proposed in the aforementioned Patent Document 1, it is also desirable to reduce the amount of plastic used by thinning the substrate film.

[0011] However, if the substrate film is thinned, the stress caused by the thermal recording layer and other components formed on the substrate film increases. As a result, the thermal recorder may curl towards the printing side where the thermal recording layer is formed.

[0012] This invention was made in view of this actual situation, and its purpose is to provide a thermal recorder that has good transparency while suppressing curling.

[0013] Methods for solving problems

[0014] To achieve the above objectives, the present invention is configured as follows.

[0015] (1) The thermal recorder of the present invention has a substrate, a thermal recording layer and a protective layer sequentially stacked on one side of the substrate, and a back coating is formed on the other side of the substrate. The substrate includes a transparent resin film and the back coating contains a core-shell type resin and a polyamide epichlorohydrin resin.

[0016] According to the present invention, the thermal recorder exhibits superior film-forming properties compared to conventional emulsions because the back coating contains a core-shell type resin. Generally, in the case of conventional emulsions, the emulsion consists of particles that fuse together to form a film after drying. However, in the case of a core-shell type resin, the film-forming properties are further improved because the shell portion, which has a water-soluble component, partially dissolves before drying and is not composed of particles. Therefore, even when the thermal recording layer and protective layer are laminated, they can withstand stress, resulting in the suppression of curling. Furthermore, since the aforementioned back coating contains polyamide epichlorohydrin resin as a crosslinking agent for crosslinking the core-shell type resin, transparency is improved compared to oxazoline-based crosslinking agents, as described later.

[0017] (2) In a preferred embodiment of the present invention, the protective layer comprises a top coating layer and an intermediate layer formed between the top coating layer and the thermal recording layer.

[0018] According to this embodiment, the top coating improves the compatibility of the thermal recording layer with the thermal head, thereby enabling proper color development in the thermal recording layer.

[0019] In addition, due to the presence of an intermediate layer, it can provide shielding against water and oil.

[0020] (3) In another embodiment of the present invention, the intermediate layer contains a core-shell type resin and a polyamide epichlorohydrin resin.

[0021] According to this embodiment, the intermediate layer contains a core-shell type resin, which is a resin having a water-soluble portion. Therefore, when the coating liquid for forming the intermediate layer is applied to the thermal recording layer and then dried, the core-shell type resin having a water-soluble portion penetrates into the thermal recording layer to form a smooth intermediate layer. As a result, diffuse reflection of light at the thermal recording layer is suppressed, and the transparency of the thermal recorder is improved.

[0022] Furthermore, in the intermediate layer serving as a protective layer on one side of the substrate and the back coating on the other side of the substrate, a polyamide epichlorohydrin resin is used as a crosslinking agent in addition to a core-shell type resin. As a result, the stress on one side of the substrate and the other side is offset, thus effectively suppressing curling.

[0023] (4) In another embodiment of the present invention, the dynamic surface tension of the coating liquid used to form the back coating layer at 50 msec is 51 mN / m or less.

[0024] According to this embodiment, since the dynamic surface tension of the coating liquid used to form the back coating layer is less than 51 mN / m at 50 msec, its adaptability to coating the substrate becomes excellent. As a result, the coated surface becomes a uniform surface without unevenness. Consequently, there is no unevenness in transparency, and stress can also be obtained.

[0025] (5) In another embodiment of the present invention, the thickness of the substrate is 10 μm or more and 50 μm or less.

[0026] According to this embodiment, since the thickness of the transparent resin film used as the substrate is as thin as 50 μm or less, the amount of resin material used can be reduced to achieve plasticization.

[0027] Invention Effects

[0028] According to the present invention, since the back coating contains a core-shell type resin, it exhibits better film-forming properties compared to conventional emulsions. Therefore, even when the thermal recording layer and protective layer are laminated, they can withstand stress, resulting in the suppression of curling. Furthermore, since the aforementioned back coating contains polyamide epichlorohydrin resin as a crosslinking agent for crosslinking the core-shell type resin, its transparency is improved compared to oxazoline-based crosslinking agents, as described later. Attached Figure Description

[0029] Figure 1 is a schematic cross-sectional view of a thermal recorder according to an embodiment of the present invention. Detailed Implementation

[0030] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0031] Figure 1 is a schematic cross-sectional view of a thermal recording device according to an embodiment of the present invention. In this embodiment, a thermal recording layer 3, which emits color upon heating, is laminated on the upper surface of one side of a substrate 2. Furthermore, a protective layer 4 is laminated on the surface of the thermal recording layer 3, and a back coating layer 5 is formed on the lower surface of the other side of the substrate 2. The protective layer 4 includes a top coating layer 6 constituting a surface layer and an intermediate layer 7 formed between the top coating layer 6 and the thermal recording layer 3.

[0032] The following is an explanation of the structure of each layer.

[0033] [Substrate]

[0034] As the substrate 2, a transparent synthetic resin film can be used, such as a polypropylene film, polyethylene terephthalate film, polystyrene film, polycarbonate film, etc. Furthermore, the substrate 2 can be a single layer or multiple layers. The thickness of the film is not particularly limited; however, a thickness of approximately 10 μm to 100 μm is preferred as it provides excellent coatability and transparency to the substrate 2. Additionally, to reduce the amount of resin material used and achieve plasticization, the thickness of the substrate 2 is preferably 50 μm or less, more preferably 40 μm or less.

[0035] [Thermal Recording Layer]

[0036] The materials used to form the thermal recording layer 3 include color-developing agents, colorants, fillers, binders, and lubricants that develop color upon heating.

[0037] To improve the transparency of the thermal recorder 1, materials with small particle sizes are preferably used. Using such small-particle-size materials suppresses diffuse reflection of light, thereby improving the transparency of the thermal recorder.

[0038] Specifically, as leuco dyes used as color-developing agents, 3-(N-isobutyl-N-ethyl)amino-6-methyl-7-aniline fluorane, 3-(N-isopentyl-N-ethyl)amino-6-methyl-7-o-chloroaniline fluorane, 3-(N-ethyl-N-p-toluidine)-6-methyl-7-aniline fluorane, 3-(N-ethyl-N-isopentyl)amino-6-methyl-7-aniline fluorane, 3-(N-ethoxypropyl-N-ethyl)amino-6-methyl-7-aniline fluorane, 3-(N-cyclohexyl-N-methyl)amino-6-methyl-7-aniline fluorane, 3-(N-methyl-N-n-propyl)amino-6-methyl-7-aniline fluorane, and 3-dibutylamino Examples of leuco dyes include 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-p-toluidine, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-8-methylfluorane, 3-diethylamino-7-(m-trifluoromethylanilino)fluorane, 3-diethylamino-7-(o-chloroanilino)fluorane, 3-diethylamino-7-chlorofluorane, 3-dibutylamino-6-methyl-7-bromofluorane, 3-dibutylamino-7-(o-chloroanilino)fluorane, 3-dipentylamino-6-methyl-7-anilinofluorane, 3-dimethylamino-5-methyl-7-methylfluorane, 3-pyrrolidinyl-6-methyl-7-anilinofluorane, and crystal violet lactone. These leuco dyes can be used alone or in combination of two or more.

[0039] The preferred particle size of the aforementioned color-developing agent is 0.1 μm to 1.0 μm. Here, particle size refers to the 50% average particle size measured using a Microtrac laser-scattering particle size analyzer. Hereafter, "particle size" refers to the 50% average particle size measured using a Microtrac laser-scattering particle size analyzer.

[0040] As the colorimetric agents mentioned above, for example, 1,1-bis(p-hydroxyphenyl)cyclohexane, 1,1-bis(p-hydroxyphenyl)propane, 2,2-bis(p-hydroxyphenyl)propane, 2,2-bis(p-hydroxyphenyl)butane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 2,2'-methylenebis(4-chlorophenol), 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 2,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'- n-Propoxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone, 4-hydroxy-4′-allyloxydiphenyl sulfone, bis(3-allyl-4-hydroxyphenyl) sulfone, poly(4-hydroxybenzoic acid), benzyl 4-hydroxybenzoate, 2,4-bis(phenylsulfonyl)phenol, α-{4-[(4-hydroxyphenyl)sulfonyl]phenyl}-ω-hydroxy poly(degree of polymerization n = 1-7) (oxyethylene) (2,2-bis[(4-methyl-3-phenoxycarbonylaminophenyl)urea]diphenyl sulfone), 3,5-bis(α-methylbenzyl)salicylic acid, bis[4-(n-octyloxycarbonylamino)zinc salicylate], 4,4'-bis(p-tolylsulfonylaminocarbonylamino)diphenylmethane, 4-hydroxybenzenesulfonylaniline, 2'-(3-phenylurea)benzenesulfonylaniline, N-(2-hydroxyphenyl)-2-[(4-hydroxyphenyl)thio] Acetamide, N-(4-hydroxyphenyl)-2-[(4-hydroxyphenyl)thio]acetamide, 4-[[4-[4-[4-[4-(1-methylethoxy)phenyl]sulfonylphenoxy]butoxy]phenyl]sulfonyl]phenol, 4-tert-butylphenol-formaldehyde condensate, N-(p-toluenesulfonyl)N'-(3-p-toluenesulfonyloxyphenyl)urea, 1-phenyl-3-(4-methylphenylsulfonyl)urea, etc., preferably have a particle size of 0.1 μm or more and 1.0 μm or less. These color developers can be used alone or in combination of two or more.

[0041] As fillers as described above, examples include aluminum hydroxide, magnesium hydroxide, aluminum oxide, magnesium oxide, aluminum silicate, calcium carbonate, magnesium carbonate, titanium dioxide, barium sulfate, silica gel, activated clay, talc, clay, kaolin, calcined kaolin, diatomaceous earth, silica, zinc oxide, silicon dioxide, colloidal silica, polystyrene resin particles, urea-formaldehyde resin particles, and polyolefin resin particles, etc., preferably with a particle size of 1.0 μm or less. These fillers can be used alone or in combination of two or more.

[0042] Examples of binders that can be used include polyvinyl alcohol, modified polyvinyl alcohol, starch, casein, gelatin, polyamide, polyacrylamide, modified polyacrylamide, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl acetate, polyacrylate, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, diisobutylene-maleic anhydride copolymer, vinyl acetate-maleic anhydride copolymer, methyl vinyl-maleic anhydride copolymer, isopropylene-maleic anhydride copolymer, styrene-butadiene copolymer, polyvinyl chloride, polyvinylidene chloride-vinyl acetate copolymer, polyurethane, polystyrene, polyvinylpyrrolidone, acrylate, acrylonitrile, methyl vinyl ether, etc. These binders can be used alone or in combination of two or more.

[0043] Examples of sensitizers that can be used include stearic acid, stearamide, stearic aniline, hydroxymethylstearamide, methylene bis-stearamide, ethylene bis-stearamide, 1-benzyloxynaphthalene, 2-benzyloxynaphthalene, 2,6-diisopropylnaphthalene, 1,2-diphenoxyethane, 1,2-diphenoxymethylbenzene, 1,2-bis(3,4-dimethylphenyl)ethane, 1,2-bis(3-methylphenoxy)ethane, 1,2-bis(4-methylphenoxy)ethane, di(p-chlorobenzyl) oxalate, di(p-methylbenzyl) oxalate, dibenzyl oxalate, p-benzylbiphenyl, m-terphenyl, diphenyl sulfone, benzyl p-benzyloxybenzoate, dibenzyl terephthalate, and p-toluenesulfonamide. These sensitizers can be used alone or in combination of two or more.

[0044] As the aforementioned lubricants, for example, fatty acid waxes such as paraffin wax and oleic acid, polyolefin waxes such as polyethylene wax, metallic soaps such as zinc stearate, ester waxes such as carnauba wax, silicone oil, whale oil, and other oils can be used, and their particle size is preferably 0.5 μm or less. These lubricants can be used alone or in combination of two or more.

[0045] To improve the transparency of the thermal recording layer 1, it is known that containing paraffin wax in the thermal recording layer 3 is particularly effective. This paraffin wax is a low-melting-point paraffin wax with a melting point below the color development temperature of the thermal recording layer 3, preferably below 80°C, and more preferably below 50°C.

[0046] The particle size of this low-melting-point paraffin is preferably 0.5 μm or less, as described above. The paraffin content, on a dry weight basis, is preferably, for example, 0.1 g / m³. 2 ~1.0g / m 2 .

[0047] When a low-melting-point paraffin wax is applied to the substrate 2 and dried, the wax melts and penetrates into the gaps between the surface irregularities of the particles constituting the thermal recording layer 3. This process suppresses diffuse reflection of light at the thermal recording layer 3 and improves the transparency of the thermal recorder 1.

[0048] [Protective layer]

[0049] The protective layer 4 in this embodiment has a top coating layer 6 and an intermediate layer 7.

[0050] The intermediate layer 7 provides water and oil shielding, improving the water resistance and chemical resistance of the thermal recording layer 3. The top coating layer 6 enhances the compatibility of the thermal recording layer 3 with the thermal head, thereby enabling proper color development within the thermal recording layer 3.

[0051] The intermediate layer 7 is mainly formed of resin. The resin described above can be, for example, a resin with a water-soluble portion or a resin without a water-soluble portion. Specifically, examples include acrylic resins such as acrylic resins, styrene-acrylic resins, acrylic-polyurethane resins, acrylic-amide resins, and vinyl acetate-acrylic resins; epichlorohydrin resins such as polyamide epichlorohydrin resins, polyamine epichlorohydrin resins, and polyamide polyamine epichlorohydrin resins; maleic acid resins such as maleic acid resins, styrene-maleic acid resins, and olefin-maleic acid resins; styrene-butadiene (SBR) resins; acrylonitrile-butadiene-styrene resins; vinyl acetate resins; fully saponified polyvinyl alcohol resins, partially saponified polyvinyl alcohol resins, diacetone-modified polyvinyl alcohol resins, acetoacetyl-modified polyvinyl alcohol resins, sulfonic acid-modified polyvinyl alcohol resins, olefin-modified polyvinyl alcohol resins, acrylonitrile-modified polyvinyl alcohol resins, pyrrolidone-modified polyvinyl alcohol resins, silanol-modified polyvinyl alcohol resins, and cationic-modified polyvinyl alcohol resins, etc. Alternatively, these resins can be modified resins obtained using known methods. These resins can be used alone or in combination of two or more. Furthermore, the compositions forming these resins can be solids, emulsions, or solutions. From the viewpoint of excellent coatability, emulsions or solutions are preferred.

[0052] It should be noted that, in this specification, the term "acrylic resin" refers to a resin obtained by polymerizing acrylic monomers (acrylic resin), or a resin obtained by copolymerizing acrylic monomers with other monomers (monomers other than acrylic monomers capable of copolymerizing with acrylic monomers). Here, the aforementioned other monomers can be two or more types. Furthermore, when abbreviated as "acrylic," unless otherwise specified, it refers to (meth)acrylic acid (salt) and / or (meth)acrylate. Here, "(meth)acrylic acid" refers to acrylic acid and / or methacrylic acid, and "(meth)acrylic acid (salt)" refers to (meth)acrylic acid and / or (meth)acrylate salts.

[0053] The salts in the above-mentioned (meth)acrylates are not particularly limited, and examples include ammonium salts such as ammonia; alkylamine salts such as triethanolamine, diethanolamine, and monoethanolamine; alkylamine salts such as methylamine, ethylamine, diethylamine, and triethylamine; polyamine salts such as diethyleneamine and diethylenetriamine; alkali metal salts such as lithium, sodium, and potassium; alkaline earth metal salts such as magnesium and calcium; and polyvalent metal salts such as zinc and iron. These salts can be used alone or in combination of two or more.

[0054] To improve the transparency of the thermal recorder 1, the resin of the intermediate layer 7 can be a resin with a water-soluble portion, such as polyvinyl alcohol (PVA), which belongs to the category of resins with hydroxyl groups as hydrophilic structural units, or a resin with carboxyl groups as hydrophilic structural units (carboxyl-containing resins). In this specification, "carboxyl-containing resin" refers to a resin in which a carboxyl group is contained in the structure of the polymer or copolymer forming the resin. Furthermore, the carboxyl group in a carboxyl-containing resin can be a free carboxyl group or an anhydride group (specifically a dicarboxylic anhydride group). Additionally, the anhydride group can be partially ring-opened to become a carboxyl group. In a carboxyl-containing resin, part or all of the carboxyl group can be neutralized by a base. Furthermore, to efficiently form a crosslinked structure with the crosslinking agent described later and further improve film-forming properties, a resin with reactive structural units is preferred. In this invention, "reactive structural unit" refers to a reactive structural unit capable of forming a crosslinked structure with other materials; representative examples include carboxyl groups, azathiolated rings, and oxazoline groups.

[0055] In this embodiment, the intermediate layer 7 preferably comprises at least one resin selected from carboxyl-containing resins and epichlorohydrin-based resins. From the viewpoint of forming the crosslinked structure described later, further improving film-forming properties, improving transparency, and suppressing curling, it is more preferable to include carboxyl-containing resins and epichlorohydrin-based resins.

[0056] As the aforementioned carboxyl-containing resin, it is preferably selected from at least one of acrylic resins and maleic acid resins, more preferably from acrylic resins. As the aforementioned acrylic resin, it is preferably selected from at least one of acrylic resins, styrene-acrylic resins, acrylic-polyurethane resins, acrylic-amide resins, and vinyl acetate-acrylic resins, more preferably from at least one of acrylic resins, styrene-acrylic resins, and acrylic-polyurethane resins, and even more preferably from at least one of acrylic resins and styrene-acrylic resins.

[0057] The epichlorohydrin resin described above is preferably selected from at least one of polyamide epichlorohydrin resin, polyamine epichlorohydrin resin, and polyamide polyamine epichlorohydrin resin, more preferably selected from at least one of polyamide epichlorohydrin resin and polyamide polyamine epichlorohydrin resin, and even more preferably polyamide epichlorohydrin resin.

[0058] Alternatively, from the viewpoint of further improving the transparency and curl suppression of the thermal recorder 1, the resin of the intermediate layer 7 preferably contains a core-shell structure resin in which hydrophobic core particles are coated with a water-soluble shell polymer, i.e., a core-shell type resin. There are no particular limitations on the core-shell type resin; for example, a carboxyl-containing resin with a core-shell structure (a core-shell type carboxyl-containing resin) is preferred. Here, the core-shell type carboxyl-containing resin is considered to contain carboxyl groups at least in the structure of the water-soluble shell polymer. Generally, a core-shell type resin is a resin obtained by forming hydrophobic core particles and a water-soluble shell polymer through a multi-stage polymerization reaction. Examples of resins forming the core particles and the shell polymer are the same as those described above. Therefore, regarding the resin in the core-shell type resin, all descriptions of the above-described resins can be cited.

[0059] Specifically, the core-shell type carboxyl-containing resin described above is preferably selected from at least one of core-shell type acrylic resins and core-shell type maleic acid resins, more preferably from core-shell type acrylic resins. The core-shell type acrylic resin described above is preferably selected from at least one of core-shell type acrylic resins, core-shell type styrene-acrylic resins, core-shell type acrylic-polyurethane resins, core-shell type acrylic-amide resins, and core-shell type vinyl acetate-acrylic resins, more preferably from at least one of core-shell type acrylic resins, core-shell type styrene-acrylic resins, and core-shell type acrylic-polyurethane resins, further preferably from at least one of core-shell type acrylic resins and core-shell type styrene-acrylic resins, and particularly preferably from core-shell type acrylic resins. It should be noted that, for example, resins marketed under the name Barrierstar (manufactured by Mitsui Chemicals Co., Ltd.) can be cited as examples of this core-shell type acrylic resin. It should be noted that the epichlorohydrin resin described above is a non-core-shell type resin.

[0060] Water-soluble polyvinyl alcohol and core-shell type acrylic resins exhibit good film-forming properties. Furthermore, when a coating solution for forming an intermediate layer is applied to the thermal recording layer 3 and then dried, the water-soluble portion of the resin penetrates the thermal recording layer 3, forming a smooth intermediate layer 7. This suppresses diffuse reflection of light at the thermal recording layer 3, thereby improving the transparency of the thermal recording layer 3.

[0061] Furthermore, even resins with water-soluble components cannot adequately suppress curling if they have poor film-forming properties. In this regard, the aforementioned core-shell type resin, with its hydrophobic core particles coated by a water-soluble shell polymer, exhibits superior film-forming properties compared to conventional emulsions. Typically, in the case of conventional emulsions, the emulsion consists of particles that fuse together to form a film after drying. On the other hand, in the case of core-shell type resins, the shell portion with water-soluble components partially dissolves before drying and is not composed of particles, thus further enhancing film-forming properties. Therefore, even with a laminated back coating, it can withstand stress, resulting in effective suppression of curling.

[0062] The intermediate layer 7 in this embodiment preferably includes a crosslinking agent. Examples of crosslinking agents include organic crosslinking agents such as cationic crosslinking agents and non-cationic crosslinking agents; and inorganic crosslinking agents such as zirconium carbonate. Examples of cationic crosslinking agents include polyamide epichlorohydrin resins, polyamine epichlorohydrin resins, and polyamide polyamine epichlorohydrin resins. Examples of non-cationic crosslinking agents include oxazoline compounds such as polymers containing oxazoline groups. Cationic crosslinking agents are preferred, and epichlorohydrin resins are more preferred. Here, the preferred types of epichlorohydrin resins are the same as those mentioned above. These crosslinking agents can be used alone or in combination of two or more.

[0063] Generally, crosslinking agents have reactive structural units as described above. Because the reactive structural units in the crosslinking agent react with reactive structural units in other materials to form a crosslinked structure, film-forming properties are further improved, and transparency and curl suppression can be further enhanced. For example, when the crosslinking agent is an epichlorohydrin resin, the azacyclic butyronium ring (AZR) in the epichlorohydrin resin acts as a reactive structural unit and reacts with other materials (e.g., the carboxyl groups in the aforementioned carboxyl-containing resin) to form a crosslinked structure. Thus, from the viewpoint of further improving film-forming properties, the intermediate layer 7 of this embodiment preferably comprises a carboxyl-containing resin and an epichlorohydrin resin. Furthermore, it is also preferable to include a core-shell type resin and an epichlorohydrin resin. Moreover, it is more preferable to include a core-shell type carboxyl-containing resin and an epichlorohydrin resin. Here, the preferred types of the aforementioned carboxyl-containing resin, the aforementioned core-shell type carboxyl-containing resin, and the aforementioned epichlorohydrin resin are the same as those described for the aforementioned carboxyl-containing resin, the aforementioned core-shell type carboxyl-containing resin, and the aforementioned epichlorohydrin resin.

[0064] The resin content relative to 100% of the dry weight of the intermediate layer 7 is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. Within the above ranges, film-forming properties become better, and transparency and curl suppression can be further improved.

[0065] The content ratio of the core-shell type resin relative to 100% by dry mass of the resin in the intermediate layer 7 is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. Furthermore, the content ratio of the core-shell type resin relative to 100% by dry mass of the resin in the intermediate layer 7 is preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less. Within the above range, film-forming properties become better, and transparency and curl suppression can be further improved. Additionally, the content ratio of the core-shell type resin relative to 100% by dry mass of the intermediate layer 7 is preferably within the above range.

[0066] The crosslinking agent content is preferably 3% by mass or more, more preferably 6% by mass or more, and even more preferably 10% by mass or more, relative to 100% by mass of the dried resin in the intermediate layer 7. Furthermore, the crosslinking agent content is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, relative to 100% by mass of the dried resin in the intermediate layer 7. Within the above ranges, film-forming properties become better, and transparency and curl suppression can be further improved. Additionally, the crosslinking agent content is preferably within the above range relative to 100% by mass of the dried resin in the intermediate layer 7.

[0067] In addition, the intermediate layer 7 may further contain other materials besides those mentioned above. Examples of such other materials include wetting agents.

[0068] The coating amount (dry weight) of the intermediate layer 7 described above is preferably, for example, 0.3 g / m². 2 ~10g / m 2 More preferably 0.5 g / m 2 ~5.0g / m 2 Further preferred is 1.0 g / m 2 ~4.0g / m 2 .

[0069] In this embodiment, the intermediate layer 7 uses a core-shell type acrylic resin, similar to the back coating layer 5, and uses polyamide epichlorohydrin resin as a crosslinking agent. This will be explained in detail later with examples provided.

[0070] The top coating 6 uses substances such as fillers, lubricants, and crosslinking agents added to the binder.

[0071] Regarding the resins used as the binders mentioned above, examples include acrylic resins. Other resins mentioned in the section on intermediate layer 7 can also be cited. These resins can be used alone or in combination of two or more. As for the lubricants mentioned above, examples include polyethylene and zinc stearate. Other lubricants mentioned in the section on thermal recording layer 3 can also be cited. These lubricants can be used alone or in combination of two or more.

[0072] Examples of crosslinking agents mentioned above include zirconium carbonate. Other crosslinking agents mentioned in the section on intermediate layer 7 may also be cited. These crosslinking agents can be used alone or in combination of two or more.

[0073] Examples of fillers mentioned above include colloidal silica, calcium carbonate, polymethyl methacrylate (PMMA), and polystyrene (PS). Other fillers mentioned in the section on thermal recording layer 3 may also be cited. These fillers can be used alone or in combination of two or more.

[0074] The particle size of these fillers is preferably below 1.0 μm. To improve transparency, colloidal silica with small particle size is preferred as a filler.

[0075] [Back coating]

[0076] The back coating 5, formed on the non-printing side of the substrate 2 opposite to the thermal recording layer 3, is mainly formed of resin, containing at least a core-shell type resin and a polyamide-epoxychlorohydrin resin. It should be noted that the aforementioned polyamide-epoxychlorohydrin resin is a non-core-shell type resin.

[0077] The resin contained in the back coating 5 of this embodiment can be entirely described in the section on the intermediate layer 7. Furthermore, the resin contained in the back coating 5 can be a resin having a water-soluble portion or a resin without a water-soluble portion. Preferably, it is a resin having a water-soluble portion. Here, polyvinyl alcohol can be cited as an example of a resin having a water-soluble portion, as described above. However, while transparency can be improved in this case, polyvinyl alcohol has poor water resistance, and therefore the back coating may peel off in humid environments.

[0078] By further improving the water resistance of the thermal recorder 1, curl suppression can be further improved. Therefore, in this embodiment, the back coating 5 contains a core-shell type resin as a resin having a water-soluble portion. There are no particular limitations on the core-shell type resin described above; for example, a core-shell type resin containing carboxyl groups is preferred. The preferred types of the core-shell type resin containing carboxyl groups described above are the same as those given in the intermediate layer 7. That is, the core-shell type resin containing carboxyl groups described above is preferably selected from at least one of core-shell type acrylic resins and core-shell type maleic acid resins, and more preferably a core-shell type acrylic resin. The core-shell type acrylic resin described above is preferably selected from at least one of core-shell type acrylic resins, core-shell type styrene-acrylic resins, core-shell type acrylic-polyurethane resins, core-shell type acrylic-amide resins, and core-shell type vinyl acetate-acrylic resins; more preferably selected from at least one of core-shell type acrylic resins, core-shell type styrene-acrylic resins, and core-shell type acrylic-polyurethane resins; even more preferably selected from at least one of core-shell type acrylic resins and core-shell type styrene-acrylic resins; and particularly preferably selected from core-shell type acrylic resins.

[0079] In addition, polyamide epichlorohydrin resin is used as a crosslinking agent for crosslinking core-shell type acrylic resins.

[0080] Even resins with water-soluble components cannot adequately suppress curling if they have poor film-forming properties. In this regard, core-shell type acrylic resins, which coat hydrophobic core particles with water-soluble shell polymers, exhibit excellent film-forming properties compared to general emulsions. Therefore, even when laminated with thermal recording layers and protective layers, they can withstand their stresses, resulting in effective curl suppression. Furthermore, due to the hydrophobic core, there is no degradation in water resistance.

[0081] Furthermore, by using polyamide epichlorohydrin resin as a crosslinking agent for crosslinking core-shell type acrylic resins, as shown in the comparative transparency test described later, transparency is improved compared to oxazoline-based crosslinking agents.

[0082] The resin content relative to 100% of the dry weight of the back coating 5 is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. Within the above ranges, film-forming properties become better, and transparency and curl suppression can be further improved.

[0083] The content ratio of the core-shell type resin relative to 100% by dry mass of the resin in the back coating 5 is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. Furthermore, the content ratio of the core-shell type resin relative to 100% by dry mass of the resin in the back coating 5 is preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less. Within the above range, film-forming properties become better, and transparency and curl suppression can be further improved. Additionally, the content ratio of the core-shell type resin relative to 100% by dry mass of the back coating 5 is preferably within the above range.

[0084] The crosslinking agent content is preferably 3% by mass or more, more preferably 6% by mass or more, and even more preferably 10% by mass or more, relative to 100% by mass of the dried resin in the back coating layer 5. Furthermore, the crosslinking agent content is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, relative to 100% by mass of the dried resin in the back coating layer 5. Within the above ranges, film-forming properties become better, and transparency and curl suppression can be further improved. Additionally, the crosslinking agent content is preferably within the above range relative to 100% by mass of the dried resin in the back coating layer 5.

[0085] Furthermore, the back coating 5 may contain other materials besides those mentioned above. Examples of such other materials include wetting agents, fillers, lubricants, and preservatives.

[0086] As the aforementioned wetting agents, nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, fluorinated surfactants, etc., can be used. These surfactants can be used alone or in combination of two or more.

[0087] For example, acetylenic diol surfactants, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl esters, and polyoxyethylene sorbitan fatty acid esters can be used as nonionic surfactants.

[0088] Examples of alkynyldiol surfactants include alkynyldiol and its epoxide alkane adducts. Other examples of alkynyldiols include 2,4,7,9-tetramethyl-5-decyn-4,7-diol, 3,6-dimethyl-4-octyyn-3,6-diol, 3,5-dimethyl-1-hexyn-3-diol, and 2,5,8,11-tetramethyl-6-dodecyn-5,8-diol.

[0089] As anionic surfactants, for example, polyoxyethylene alkyl ether sulfuric acid or its salts, polyoxyethylene alkyl ether acetic acid or its salts, dodecylbenzene sulfonic acid or its salts, alkyl sulfuric acid or its salts, alkane sulfonic acid or its salts, etc., can be used.

[0090] As the aforementioned wetting agent, a nonionic surfactant is preferred, an alkynyl glycol-based surfactant is more preferred, and an alkylene glycol epoxide adduct is even more preferred.

[0091] Wetting agents can typically be used to adjust wettability and other properties using their HLB values. From the viewpoint of further improving the coatability of the back coating 5, the HLB value of the wetting agent is preferably 4 or higher, more preferably 6 or higher, and even more preferably 6 or higher and 16 or lower.

[0092] The coating amount (dry weight) of the back coating layer 5 is preferably, for example, 0.3 g / m³. 2 ~10g / m 2 More preferably 0.5 g / m 2 ~5.0g / m 2 Further preferred is 1.0 g / m 2 ~4.0g / m 2 .

[0093] In this embodiment, from the viewpoint of further suppressing the curling of the thermal recorder, when viewed from the substrate serving as the support, it is preferable that the stress that may be generated in one surface is more equal to the stress that may be generated in the surface on the opposite side. Therefore, both the back coating layer 5 and the intermediate layer 7 preferably contain a core-shell type resin, more preferably the same type of core-shell type resin, and even more preferably the same type of core-shell type resin. Additionally, both the back coating layer 5 and the intermediate layer 7 preferably contain a polyamide-epoxy resin. Furthermore, both the back coating layer 5 and the intermediate layer 7 preferably contain the same type of core-shell type resin and polyamide-epoxy resin, more preferably the same type of core-shell type resin and polyamide-epoxy resin. Additionally, both the back coating layer 5 and the intermediate layer 7 preferably contain a core-shell type acrylic resin and a polyamide-epoxy resin, more preferably a core-shell type acrylic resin and a polyamide-epoxy resin.

[0094] Here, "same kind" refers to structural units that share common reactivity. For example, "same kind" core-shell resins refer to structural units that share reactivity such as carboxyl groups derived from acrylic monomers.

[0095] The mass ratio of the core-shell type resin in the intermediate layer 7 to the core-shell type resin in the back coating layer 5 (content of core-shell type resin per unit area (dry weight) in the intermediate layer 7 / content of core-shell type resin per unit area (dry weight) in the back coating layer 5) is preferably 0.2 to 4, more preferably 0.3 to 3, even more preferably 0.5 to 2, and particularly preferably 0.7 to 1.5. Within the above range, when observed from the substrate, the stress that may be generated in one surface is more equal to the stress that may be generated in the surface on the opposite side, and curl suppression can be further improved.

[0096] The mass ratio of polyamide epichlorohydrin resin in the intermediate layer 7 to that in the back coating layer 5 (content of polyamide epichlorohydrin resin per unit area (dry weight) in the intermediate layer 7 / content of polyamide epichlorohydrin resin per unit area (dry weight) in the back coating layer 5) is preferably 0.2 to 4, more preferably 0.3 to 3, even more preferably 0.5 to 2, and particularly preferably 0.7 to 1.5. Within the above range, when observed from the substrate, the stress that may be generated in one surface is more equal to the stress that may be generated in the surface on the opposite side, and curl suppression can be further improved.

[0097] The ratio of the coating amount (dry weight) of the intermediate layer 7 to the coating amount (dry weight) of the back coating layer 5 (coating amount (dry weight) per unit area of ​​the intermediate layer 7 / coating amount (dry weight) per unit area of ​​the back coating layer 5) is preferably 0.3 to 3, more preferably 0.5 to 2, and even more preferably 0.7 to 1.5. Within the above range, when observed from the substrate, the stress that may be generated in one surface is more equal to the stress that may be generated in the surface on the opposite side, and curl suppression can be further improved.

[0098] When a curling test is performed on the thermal recorder 1 (a laminate with a back coating 5 and a top coating 6 as its two end faces) according to the method described in the embodiment, regarding the curling height, it is preferable that the curling is 6 mm or less under at least one of the three conditions specified in (B), and under at least one of the subsequent conditions in (C). Furthermore, it is more preferable that the curling is 6 mm or less under at least two of the three conditions specified in (B), and under at least two of the subsequent conditions in (C). Furthermore, it is even more preferable that the curling is 6 mm or less under all three conditions specified in (B), and under all the subsequent conditions in (C).

[0099] Regarding the back coating 5 and the substrate 2 of the thermal recorder 1 in this embodiment, the haze value of the laminate of the back coating 5 and the substrate 2 is preferably 7 or less, more preferably 6 or less, and even more preferably 5 or less when measured using the method described in the embodiment.

[0100] Regarding the back coating 5 and the substrate 2 of the thermal recorder 1 in this embodiment, when a water-resistant ink adhesion test is performed on the laminate of the back coating 5 and the substrate 2 using the method described in the embodiment, it is preferable that no ink falls off after immersion in water for 1 minute, more preferably that no ink falls off after immersion in water for 2 minutes, and even more preferably that the ink falls off by less than 50% after immersion in water for 5 minutes.

[0101] Example

[0102] The present invention will now be described in further detail based on specific embodiments; however, the following embodiments do not limit the present invention in any way.

[0103] The inventors of this case prepared a coating liquid for forming a back coating by combining the main agent, crosslinking agent, and wetting agent shown in Table 1 below as shown in combinations No. 1 to No. 5. Each combination was prepared such that the concentration of the solid component was 18.5%.

[0104]

[0105] In compound No.1, relative to the core-shell type acrylic resin 100 as the main agent, by weight ratio at dryness, it is compounded with polyamide epichlorohydrin resin 18 as a crosslinking agent and acetylenic diol surfactant 1.3 with an HLB value of 13 to 14 as a wetting agent.

[0106] Here, HLB (Hydrophile-Lipophile-Balance) is a value that indicates the degree of affinity of a surfactant for water and oil. If the HLB value is greater than 7, the surfactant is highly hydrophilic; if it is less than 7, the surfactant is highly hydrophobic (lipophilic).

[0107] In compound No.2, relative to the core-shell type acrylic resin 100 as the main agent, by weight ratio at dryness, an oxazoline-based crosslinking agent, specifically oxazoline WS300 (manufactured by Nippon Shokubai Co., Ltd.), 18, and an alkynyldiol-based surfactant with an HLB value of 13 to 14 as a wetting agent, are added.

[0108] In formulation No. 3, only core-shell type acrylic resin 100 is set as the main agent, without crosslinking agents or wetting agents.

[0109] In compound No.4, relative to the core-shell type acrylic resin 100 as the main agent, by weight ratio at dryness, it is compounded with polyamide epichlorohydrin resin 18 as a crosslinking agent and 0.16 of alkynyl diol surfactant with an HLB value of 8 as a wetting agent.

[0110] In compound No. 5, relative to the core-shell type acrylic resin 100 as the main agent, by weight ratio at dryness, it is compounded with polyamide epichlorohydrin resin 18 as a crosslinking agent and 0.32 of alkynyl diol surfactant with an HLB value of 8 as a wetting agent.

[0111] The inventors of this case appropriately selected the coating liquids used for forming the back coating of No. 1 to No. 5 mentioned above to prepare samples and conducted tests on curling, transparency, ink adhesion and dynamic surface tension.

[0112] The following is a description of each experiment.

[0113] <Curling Experiment>

[0114] The inventors of this case produced a thermal recorder of the embodiment shown in Figure 1 above and a comparative example thermal recorder without the back coating 5, and conducted a comparative test on the curling of the two thermal recorders.

[0115] In the embodiment, the back coating 5 is formed using the coating film for forming the back coating of the matching No.1 in Table 1 above.

[0116] The embodiments and comparative examples are identical in structure except for the presence or absence of the back coating 5. That is, the structures of the substrate 2, the thermal recording layer 3, the intermediate layer 7, and the top coating 6 are common in both embodiments and comparative examples.

[0117] The following is a detailed description of the structure of the substrate 2, the thermal recording layer 3, the intermediate layer 7 and the top coating layer 6. However, this structure is the same as that of the aforementioned patent document 1 (Japanese Patent No. 6202599) previously filed by the applicant in this case.

[0118] Therefore, the thermal recorder, excluding the back coating 5, has the same excellent transparency as the thermal recorder described in Patent Document 1.

[0119] First, a PET (polyethylene terephthalate) film with a thickness of 25 μm was used as the substrate 2.

[0120] The thermal recording layer 3 uses 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone with a particle size of 0.4 μm as the color developer, and kaolin with a particle size of 0.4 μm is used as the filler. Additionally, SBR with a glass transition temperature (Tg) of -3 °C is used as the binder. Paraffin wax with a melting point of 46 °C and a particle size of 0.2 μm is used as the lubricant. 2-aniline-3-methyl-6-(N-methyl-p-toluidine)fluorane with a particle size of 0.5 μm is used as the dye.

[0121] Based on the weight ratio at the time of drying, the color developer, kaolin, SBR, paraffin, and dye were set to 25, 10, 20, 4, and 12, respectively, with the overall ratio set to 74.

[0122] The coating solution for forming the thermal recording layer of this compound was prepared and applied to the aforementioned PET film to achieve a coating weight of 4.5 g / m² (dry weight). 2 After coating in a certain manner, the thermal recording layer 3 is obtained by drying.

[0123] The intermediate layer 7 uses a core-shell type acrylic resin as a binder, a polyamide epichlorohydrin resin as a crosslinking agent, and an acetylenic diol surfactant with an HLB value of 13-14 as a wetting agent.

[0124] Based on the weight ratio at dryness, the core-shell type acrylic resin, polyamide epichlorohydrin resin, and acetylenic diol surfactant with an HLB value of 13-14 were set to 100, 18, and 1.3, respectively, with the overall ratio set to 119.3.

[0125] A coating solution for forming the intermediate layer of this compound is prepared and applied to the thermal recording layer 3 such that the coating amount is 2.0 g / m² (dry weight). 2 After being coated in this manner, it is dried to form the intermediate layer 7.

[0126] The top coating 6 uses polyethylene (PE) with a particle size of 0.12 μm and zinc stearate (St-Zn) with a particle size of 5.5 μm as lubricants. Acrylic resin is used as a binder, and zirconium carbonate is used as a crosslinking agent. Colloidal silica with a particle size of several nm and colloidal silica with a particle size of tens of nm are used as fillers.

[0127] Based on the weight ratio when dry, polyethylene (PE), zinc stearate (St-Zn), acrylic resin, zirconium carbonate, colloidal silica with a particle size of several nm, and colloidal silica with a particle size of tens of nm are set to 10, 5, 50, 5, 15, and 30, respectively, and the overall ratio is set to 130.

[0128] The coating liquid for forming the top coating layer of this compound is prepared on the intermediate layer 7 so that the coating amount is 1.5 g / m² based on dry weight. 2 The top coating is applied and dried in a specific manner to form the top coating 6.

[0129] Thus, a comparative example thermal recorder, namely the thermal recorder described in Patent Document 1 with excellent transparency, was obtained. This thermal recorder was cut into pieces with a flow direction of 70 mm and a width direction of 240 to 320 mm, and these were designated as comparative example samples.

[0130] Similarly, a thermal recording layer 3, an intermediate layer 7, and a top coating 6 are formed on the substrate 2, and then a coating layer with a dry weight of 2.0 g / m² is formed on the lower surface of the substrate 2. 2 The above-mentioned coating liquid for forming the back coating layer No.1 is applied and dried to form the back coating layer 5.

[0131] The thermal recorder of the embodiment is obtained in this way. The thermal recorder is cut into sections of 70 mm in the flow direction and 240–320 mm in the width direction, and these sections are designated as samples of the embodiment.

[0132] A curling test was conducted using samples from the embodiments and comparative examples prepared as described above. The conditions and results of the curling test are shown in Table 2 below.

[0133]

[0134] The curling test was conducted as shown below.

[0135] (A) Before the start of the test, each sample of the example and comparative example used in the test was placed at a temperature of 23°C and a relative humidity of 50% for 24 hours.

[0136] (B) Subsequently, under the conditions shown in Table 2, namely, at a temperature of 30 degrees Celsius and humidity of low, medium, and high, specifically relative humidity of 35%, 67%, and 98%, the samples of the Examples and Comparative Examples were placed for 24 hours to evaluate the curling state of each sample.

[0137] (C) The samples of the examples and comparative examples for which the curling state was evaluated in (B) above were further placed at a temperature of 23°C and a relative humidity of 50% for 2 hours, as shown in Table 2, and the curling state was evaluated again.

[0138] In the evaluation of the curling state, samples with a maximum curling height of less than 3 mm at the end are set to 0, samples with a curling height greater than 3 mm but less than 6 mm are set to △, and samples with a curling height greater than 6 mm are set to ×.

[0139] Regarding the samples of the embodiment with the back coating 5, the curling height of each sample after being placed for 24 hours under the conditions described in (B) above was 0, which was less than 3 mm.

[0140] Furthermore, for each sample of the embodiment with the back coating 5, the curling height after being placed for 2 hours under the conditions described in (C) above was 0.

[0141] In contrast, in the comparative example sample without a back coating, the curling height after being placed for 24 hours under the conditions of 30 degrees Celsius and 35% relative humidity in the above (B) was 7 mm or more.

[0142] Furthermore, under the conditions described in (C) above, the curling height of the comparative example sample after being left for 2 hours was 7 mm or more ×.

[0143] In the comparative examples where the back coating 5 was not formed, there were cases where the curl height was 7 mm or more. However, in the examples where the back coating 5 was formed, even if the substrate was thin, such as a PET (polyethylene terephthalate) film with a thickness of 25 μm, the curl height was 3 mm or less. There were no cases where the curl height was greater than 3 mm.

[0144] In the embodiments, the back coating, as described above, contains a core-shell type acrylic resin with a water-soluble portion obtained by coating hydrophobic core particles with a water-soluble shell polymer as the main agent, thus exhibiting good film-forming properties and being able to suppress curling.

[0145] In addition, since polyamide epichlorohydrin resin is used as a crosslinking agent, it has excellent shielding properties, water resistance, and film-forming properties, and can suppress curling caused by high temperature and high humidity and humidity changes.

[0146] <Comparative Experiment on Transparency>

[0147] The coating solutions No. 1, 2, and 3 in Table 1 above for forming the back coating layer have a dry weight of 2.5 g / m³. 2 The coating was applied to a 25 μm thick PET (polyethylene terephthalate) film used as a substrate and dried. The transparency was then evaluated. The transparency of the substrate alone (without the coating) was also evaluated at this time.

[0148] The transparency was evaluated by measuring haze according to JIS K 7136.

[0149] The measurement results are shown in Table 3 below.

[0150]

[0151] Table 3 shows the total light transmittance (TT), parallel line transmittance (PT), and diffuse (scattered) light component (DIF) calculated using the following formulas.

[0152] HAZE (%) = DIF / TT × 100

[0153] = (TT-PT) / TT×100

[0154] As shown in Table 3, the sample obtained by coating with the back coating solution No.1, namely the back coating solution shown in Table 1 above, which is a core-shell type acrylic resin as the main agent, combined with polyamide epichlorohydrin resin as a crosslinking agent and acetylenol surfactant, has a haze value of 4.35 (%) and the highest transparency.

[0155] The haze value of the sample obtained by coating with the back coating liquid of No. 3, that is, the back coating liquid shown in Table 1 above, which is a core-shell type acrylic resin as the main agent and does not contain any crosslinking agent or surfactant, is 4.92 (%), and the transparency is the second highest.

[0156] In contrast, the sample with the coating solution for forming the back coating of No. 2, namely the coating solution for forming the back coating shown in Table 1 above, which contains an oxazoline-based crosslinking agent and an alkynyl glycol-based surfactant in the core-shell type acrylic resin as the main agent, had the highest haze value of 8.28 (%) and low transparency.

[0157] It should be noted that the haze value is 3.48% only for the substrate without coating liquid, that is, only for PET (polyethylene terephthalate) film.

[0158] It can be seen that, compared with the haze value of sample No. 2, which used an oxazoline-based crosslinking agent (8.28%), the haze value of sample No. 1, which used polyamide epichlorohydrin resin as the crosslinking agent (4.35), was lower and the transparency was better.

[0159] Compared to the haze value of 4.92 for compound No. 3, which uses only core-shell type acrylic resin without crosslinking agent, the haze value of 4.35 for compound No. 1, which uses polyamide epichlorohydrin resin as crosslinking agent, is lower and has better transparency.

[0160] The sample obtained by coating with a back coating solution containing a core-shell type acrylic resin and a polyamide epichlorohydrin resin as a crosslinking agent, as described in No. 1, has the lowest haze value and the best transparency.

[0161] <Test on ink adhesion>

[0162] The coating solutions No. 1, 2, and 3 in Table 1 above for forming the back coating layer have a dry weight of 2.0 g / m³. 2 A PET (polyethylene terephthalate) film, serving as the substrate, is coated. A gravure ink for surface printing is then printed onto this coated surface to create a sample. The gravure ink used is the Raijin series manufactured by DIC Graphics Co., Ltd.

[0163] Regarding the ink's adhesion, tests were conducted on ink adhesion and water-resistant ink adhesion when immersed in water.

[0164] In the ink adhesion test, transparent tape was pasted on the printed surface of the sample, and the presence or absence of ink detachment when peeled along the 180° direction was determined. Samples that did not detach were marked as 0.

[0165] In the water-resistant ink adhesion test, the sample was immersed in water for 1 minute, then removed and gently wiped dry. Transparent tape was then applied to the printed surface, and the presence or absence of ink detachment when peeled along a 180° direction was determined. Samples with no ink detachment were marked as 0, samples with less than 50% detachment were marked as △, and samples with more than 50% detachment were marked as ×.

[0166] Alternatively, immerse the sample in water for 2 minutes, then remove it and gently wipe off the moisture. Apply transparent tape to the printed surface and determine whether ink is detached when peeled at a 180° angle.

[0167] Similarly, the presence or absence of ink detachment was determined for samples immersed in water and removed after 5 minutes, and for samples immersed in water and removed after 10 minutes.

[0168] That is, in the test of water-resistant ink adhesion, the sample was immersed in water for four different times: 1 minute, 2 minutes, 5 minutes and 10 minutes.

[0169] The experimental results are presented in Table 4 below.

[0170]

[0171] In the ink adhesion test, the samples that used the coating liquids for forming the back coating of No. 1, 2 and 3 did not experience any ink detachment, and all were 0.

[0172] In the water-resistant ink adhesion test, for samples coated with the back coating forming liquid of No. 3 (as shown in Table 1 above), which is a core-shell type acrylic resin as the main agent without any crosslinking agent or surfactant, the ink loss of the sample immersed in water for 1 minute was less than 50% (△). Furthermore, the ink loss of the samples immersed in water for 2 minutes, 5 minutes, and 10 minutes was all more than 50% (×).

[0173] In contrast, in samples coated with the No. 1 back coating solution—that is, a back coating solution containing a core-shell type acrylic resin as the main agent, a polyamide epichlorohydrin resin as a crosslinking agent, and an acetylenol-based surfactant—no ink detachment was observed in samples immersed in water for 1 minute or 2 minutes (○). Furthermore, the ink detachment in the sample immersed in water for 5 minutes was less than 50% (△). The ink detachment in the sample immersed in water for 10 minutes was more than 50% (×).

[0174] In the samples obtained using the coating solution for forming the back coating of No. 2 (i.e., a core-shell type acrylic resin containing an oxazoline crosslinking agent and an alkynyl glycol surfactant), similar to the coating solution for forming the back coating of No. 1, no ink was detached after immersion in water for 1 minute or 2 minutes (○). Furthermore, the ink detachment of the sample immersed in water for 5 minutes was less than 50% (△). The ink detachment of the sample immersed in water for 10 minutes was more than 50% (×).

[0175] Compared to samples obtained by coating with a back coating solution containing only core-shell type acrylic resin No. 3, samples obtained by coating with a back coating solution containing a crosslinking agent No. 1 and samples obtained by coating with a back coating solution containing No. 2 exhibit better water-resistant ink adhesion.

[0176] Regarding the sample obtained by coating with the back coating liquid of formulation No. 1 using polyamide epichlorohydrin resin as a crosslinking agent and the sample obtained by coating with the back coating liquid of formulation No. 2 using an oxazoline-based crosslinking agent, the ink adhesion is the same as described above.

[0177] <Experiment for the Measurement of Dynamic Surface Tension>

[0178] The dynamic surface tensions of the coatings used for forming the back coating layer in Table 1 above, specifically those with formulations No. 1, 3, 4, and 5, were measured. This dynamic surface tension was determined using the maximum bubble pressure method (BUBBLE PRESSURE method). Specifically, a KRUSS BP-2 BUBBLE PRESSURE dynamic surface tension meter was used.

[0179] In addition, the above-mentioned coating solutions in combination with No. 1, 3, 4, and 5 have a dry weight of 2.5 g / m³. 2 A 25 μm thick PET (polyethylene terephthalate) film was coated onto a substrate and dried at 50°C for 1 minute. The surface quality of the coated surface was then visually evaluated. Specifically, samples with a uniform and good coating surface were designated as 0, while samples with uneven thickness and thin sections were designated as △.

[0180] The results of dynamic surface tension measurement and surface quality evaluation are presented in Table 5 below.

[0181]

[0182] The back coating liquid of formulation No. 4 in Table 1 above, which is prepared by combining polyamide epichlorohydrin resin 18 as a crosslinking agent and 0.16% acetylenic diol surfactant with an HLB value of 8 as a wetting agent, in a dry weight ratio relative to the core-shell type acrylic resin 100 as the main agent, has a dynamic surface tension of 51 mN / m at 50 msec. The coating liquid of formulation No. 4 exhibits good coating adaptability, with a uniform coating surface without unevenness, which is considered good.

[0183] The back coating liquid of the formulation No. 5 in Table 1 above, which is a back coating liquid prepared by combining polyamide epichlorohydrin resin 18 as a crosslinking agent and 0.32 acetylenic diol surfactant with an HLB value of 8 as a wetting agent in a dry weight ratio relative to the core-shell type acrylic resin 100 as the main agent, has a dynamic surface tension of 46 mN / m at 50 msec.

[0184] Furthermore, the back coating forming liquid of the formulation No. 1 in Table 1 above, which is a back coating forming liquid obtained by combining polyamide epichlorohydrin resin 18 as a crosslinking agent and acetylenic diol surfactant 1.3 with an HLB value of 13 to 14 as a wetting agent in a dry weight ratio relative to the core-shell type acrylic resin 100 as the main agent, has a dynamic surface tension of 35 mN / m at 50 msec.

[0185] The coating adaptability of the coating liquid for forming the back coating at 50 msec is good, which is lower than that of the coating liquid for forming the back coating of No.4 (51 mN / m). The coating surfaces are uniform without unevenness, and all are good.

[0186] In contrast, the back coating liquid of formulation No. 3 in Table 1 above, which is a back coating liquid consisting only of core-shell type acrylic resin 100 as the main agent without crosslinking agents or wetting agents, has a dynamic surface tension of 58 mN / m at 50 msec, which is higher than the dynamic surface tension of 51 mN / m of the back coating liquid of formulation No. 4. The coating liquid of formulation No. 3 has poor coating adaptability, and the thickness of its coating surface is uneven, with thin sections.

[0187] In order to obtain a surface finish with good coating adaptability and uniform coating surface as described above, it is preferable that the dynamic surface tension of the coating liquid used to form the back coating layer is 51 mN / m or less at 50 msec.

[0188] As shown above, according to this embodiment, since the back coating contains a core-shell type acrylic resin and a polyamide epichlorohydrin resin, it has good film-forming properties and can suppress curling even when the substrate is thin. Since the transparent resin film serving as the substrate can be thinned in this way, the amount of resin material used can be reduced, thus achieving plasticization.

[0189] In addition, since it contains polyamide epichlorohydrin resin as a crosslinking agent for crosslinking core-shell type acrylic resins, its transparency is improved compared to oxazoline-based crosslinking agents.

[0190] Since the thermal recorder, which includes the substrate 2 (excluding the back coating 5 in FIG1), the thermal recording layer 3, the top coating 6, and the intermediate layer 7, has excellent transparency as the thermal recorder described in Patent Document 1 above, the thermal recorder 1 of this embodiment with the back coating 5 also has excellent transparency.

[0191] Therefore, when the thermal recorder 1 of this embodiment is attached to the container, for example as a packaging film, the contents of the container can be visually inspected through the film.

[0192] In another embodiment of the present invention, an anchoring layer may be provided to improve the adhesion between the substrate 2 and the back coating 5 in FIG1.

[0193] In summary, the structure and variations of the present invention are described below.

[0194] [Note 1] A thermal recorder has a substrate, a thermal recording layer and a protective layer sequentially stacked on one side of a substrate, and a back coating is formed on the other side of the substrate. The substrate includes a transparent resin film, and the back coating contains a core-shell type resin and a polyamide epichlorohydrin resin.

[0195] [Note 2] According to the thermal recording medium described in Note 1, the protective layer comprises a top coating layer and an intermediate layer formed between the top coating layer and the thermal recording layer.

[0196] [Note 3] According to the thermal recorder described in Note 2, the above-mentioned intermediate layer contains a core-shell type resin and a crosslinking agent.

[0197] [Note 4] According to the thermal recorder described in Note 3, the crosslinking agent is polyamide epichlorohydrin resin.

[0198] [Appendix 5] According to any one of Appendices 1 to 4, the content of the core-shell type resin contained in the back coating is 50% by mass or more relative to 100% by dry mass of the back coating.

[0199] [Appendix 6] According to any one of Appendices 1 to 5, the proportion of the polyamide epichlorohydrin resin contained in the back coating is 3% by mass or more relative to 100% by dry mass of the back coating.

[0200] [Appendix 7] According to any one of Appendices 3 to 6, the content of the core-shell type resin contained in the intermediate layer is 50% by mass or more relative to 100% by dry mass of the intermediate layer.

[0201] [Appendix 8] According to any one of Appendices 3 to 7, the crosslinking agent contained in the intermediate layer is 3% by mass or more relative to 100% by dry mass of the intermediate layer.

[0202] [Note 9] According to the thermal recorder described in Notes 3 to 8, the back coating layer and the intermediate layer contain the same core-shell type resin.

[0203] [Note 10] According to the thermal recorder described in Note 9, the aforementioned core-shell type resin is a core-shell type acrylic resin.

[0204] [Note 11] According to any one of Notes 1 to 10, the dynamic surface tension of the coating liquid used to form the back coating layer is 51 mN / m or less at 50 msec.

[0205] [Note 12] According to any one of Notes 1 to 11, the thickness of the substrate is 10 μm or more and 50 μm or less.

[0206] Explanation of reference numerals in the attached figures

[0207] 1 Thermal recorder, 2 Substrate, 3 Thermal recording layer, 4 Protective layer, 5 Back coating, 6 Top coating, 7 Intermediate layer.

Claims

1. A thermal recorder having a substrate, a thermal recording layer and a protective layer sequentially laminated on one side of a substrate, and a back coating layer formed on the other side of the substrate, the substrate comprising a transparent resin film, the protective layer comprising a top coating layer and an intermediate layer formed between the top coating layer and the thermal recording layer, the back coating layer comprising a core-shell resin and a polyamide-epoxychlorohydrin resin, and the intermediate layer comprising a core-shell resin and a polyamide-epoxychlorohydrin resin.

2. The thermal recorder according to claim 1, wherein, The dynamic surface tension of the coating liquid used to form the back coating layer is less than 51 mN / m at 50 msec.

3. The thermal recorder according to claim 1 or 2, wherein, The thickness of the substrate is more than 10 μm and less than 50 μm.

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