Heat-sensitive recording medium

Abstract

The purpose of the present invention is to provide a heat-sensitive recording medium which has low concern about the safety of endocrine disruptors and the like, excellent color development properties and light resistance, and excellent heat resistance. A heat-sensitive recording material (1) has a configuration in which a heat-sensitive recording layer (3) is laminated on a base material (2). The heat-sensitive recording layer (3) contains a color former, a non-phenolic color developer, and a non-phenolic antioxidant. The non-phenolic antioxidant contains a phosphorus-based antioxidant. The non-phenolic color developing agent preferably contains a compound represented by formula (1) and / or a compound represented by formula (2). (Definitions of the symbols in formulae (1) and (2) are as defined in the description) # imgabs0 # imgabs1 #

Description

Technical Field

[0001] The present invention relates to a thermosensitive recording material, and more particularly to a thermosensitive recording material having low safety concerns and excellent color development properties, light resistance, and heat resistance. Background Art

[0002] Thermal recording media develop colors by chemical reaction when heated by a thermal head, etc., to obtain recorded images. They are used in a wide range of applications, such as thermal recording labels and receipt paper in POS systems of retail stores, etc., as recording media for fax machines, automatic ticket machines, and scientific measuring instruments.

[0003] As described above, thermosensitive recording media are widely used. Therefore, various properties are required for thermosensitive recording media. For example, when a barcode is read by a barcode reader, a color development property that enables the accuracy of reading by the barcode reader to be good is required. In addition, when the thermosensitive recording media is exposed to strong light including ultraviolet rays for a long time, the thermosensitive recording media is required to have the property that it is not easy to turn yellow (light resistance). In addition, it is also required that the color development property of the printed part does not decrease during heating in a microwave oven, and the non-printed part does not easily turn color.

[0004] As such a thermosensitive recording medium, for example, a thermosensitive recording medium has been proposed, wherein a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer is provided on a support, wherein the thermosensitive recording layer contains a phenolic developer such as 2,4'-dihydroxydiphenyl sulfone as the developer, and further contains a phenolic antioxidant having a phenolic hydroxyl group such as 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane as the antioxidant (see, for example, Patent Document 1).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2020-151948 Summary of the invention

[0008] Problems to be solved by the invention

[0009] The safety of compounds having phenolic hydroxyl groups (phenolic compounds) such as phenolic developers and phenolic antioxidants used in Patent Document 1 is a concern as endocrine disruptors. Therefore, in recent years, from the perspective of environmental response, there has been a demand for thermosensitive recording media using additives such as developers and antioxidants that do not have a phenol skeleton.

[0010] The present invention has been made in view of such circumstances, and an object of the present invention is to provide a thermosensitive recording material which has low safety concerns regarding endocrine disruptors, etc., and has excellent color development properties and light resistance, as well as excellent heat resistance.

[0011] Means for solving problems

[0012] The inventors of the present application have conducted intensive research to achieve the above-mentioned purpose, and as a result, have found that by adding a color developer (non-phenolic color developer) without a phenol skeleton and a specific antioxidant (non-phenolic antioxidant) without a phenol skeleton to a thermosensitive recording layer, it is possible to provide a thermosensitive recording material having low safety concerns regarding endocrine disruptors, etc., excellent color development and light resistance, and excellent heat resistance. The present invention was completed based on this finding.

[0013] That is, one aspect of the present invention provides a thermosensitive recording material having a thermosensitive recording layer laminated on a substrate. In the thermosensitive recording material of the present invention, the thermosensitive recording layer contains a color former, a non-phenolic color developer, and a non-phenolic antioxidant.

[0014] Conventional thermosensitive recording media generally contain phenolic compounds as color developers and antioxidants, but there are concerns about the safety of phenolic compounds as endocrine disruptors.

[0015] In contrast, according to the thermosensitive recording medium of the present invention, the developer and antioxidant contained in the thermosensitive recording layer are non-phenolic compounds. Therefore, there is no concern as described above. In addition, even when the non-phenolic compounds as described above are used, the thermosensitive recording medium of the present invention can be a thermosensitive recording medium having excellent color development and light resistance and excellent heat resistance.

[0016] In the thermosensitive recording material of the present invention, the non-phenolic antioxidant contains a phosphorus antioxidant, thereby making it possible to improve light resistance in particular.

[0017] In one embodiment of the thermosensitive recording material of the present invention, the non-phenolic developer preferably contains a compound represented by the following formula (1) and / or a compound represented by the following formula (2).

[0018] [Chemistry 1]

[0019]

[0020] (In formula (1), R 1 , R 2 , R 3 , R 4 , R 5 , R 7 , R 8 , R 9 , R 10 and R11 Each independently represents a hydrogen atom or a substituent. 6 and R 12 Each independently represents a substituent. m represents an integer of 0 to 4. When m is 2 or more, a plurality of R 6 They may be the same or different. n represents an integer of 0 to 4. When n is 2 or more, a plurality of R 12 Can be the same or different.)

[0021] [Chemistry 2]

[0022]

[0023] (In formula (2), R 13 , R 14 , R 15 , R 16 , R 17 , R 19 , R 20 , R 21 , R 22 and R 23 Each independently represents a hydrogen atom or a substituent. 18 represents a substituent. o represents an integer from 0 to 4. When o is 2 or more, a plurality of R 18 Can be the same or different.)

[0024] In one embodiment of the thermosensitive recording material of the present invention, the non-phenolic developer preferably contains a compound represented by the following formula (1a) and / or a compound represented by the following formula (2a).

[0025] [Chemistry 3]

[0026]

[0027] (The symbols in formula (1a) are the same as those in formula (1).)

[0028] [Chemistry 4]

[0029]

[0030] (The symbols in formula (2a) are the same as those in formula (2).

[0031] According to this configuration, a thermosensitive recording material having further excellent color development properties and heat resistance can be provided.

[0032] In another embodiment of the thermosensitive recording material of the present invention, the content of the non-phenolic developer relative to the entire thermosensitive recording layer is preferably 10% by mass or more and 50% by mass or less. This configuration can provide a thermosensitive recording material having excellent color development properties and excellent heat resistance.

[0033] In another embodiment of the thermosensitive recording material of the present invention, the content of the non-phenolic antioxidant is preferably 5% by mass or more and 10% by mass or less relative to the entire thermosensitive recording layer. With this configuration, even if a non-phenolic antioxidant is used, a thermosensitive recording material having excellent color development and heat resistance and excellent light resistance can be provided.

[0034] Effects of the Invention

[0035] According to the present invention, it is possible to provide a thermosensitive recording material which has low safety concerns regarding endocrine disruptors and the like, is excellent in color development and light resistance, and is also excellent in heat resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic cross-sectional view showing one embodiment of the thermosensitive recording material of the present invention. DETAILED DESCRIPTION

[0037] The thermosensitive recording medium of the present invention has a laminated structure in which a thermosensitive recording layer is laminated on a substrate. In the thermosensitive recording medium of the present invention, the thermosensitive recording layer contains a color former, a non-phenolic color developer and a non-phenolic antioxidant. The non-phenolic antioxidant contains a phosphorus antioxidant.

[0038] Hereinafter, one embodiment of the thermosensitive recording material of the present invention will be described in detail based on the drawings; however, the present invention is not limited to the following embodiments.

[0039] Figure 1 This is a schematic cross-sectional view showing one embodiment of the thermosensitive recording material of the present invention.

[0040] The thermosensitive recording medium 1 of this embodiment is as follows Figure 1 As shown, the laminate has a laminate structure in which an undercoat layer 6, a thermosensitive recording layer 3, an intermediate layer 4, and a topcoat layer 5 are laminated in this order on a sheet-like substrate 2.

[0041] In the present embodiment, the substrate 2 functions as a support for the thermosensitive recording body 1. As the substrate 2, for example, paper such as offset paper, art paper, coated paper, kraft paper, laminated paper obtained by laminating thermoplastic resins such as polyethylene on these paper substrates, synthetic paper, and porous materials such as non-woven fabrics can be used. In addition, transparent synthetic resin films such as polypropylene films, polyethylene terephthalate films, polystyrene films, polycarbonate films, etc. can be used. It should be noted that the thickness of the substrate 2 is not particularly limited, but when the thickness of the substrate 2 is adjusted to about 10 μm to 100 μm, a substrate 2 with excellent coating properties can be obtained. In addition, a substrate 2 with excellent transparency can be obtained.

[0042] In this embodiment, the primer layer 6 has functions such as heat insulation and buffering properties for preventing the release of heat provided by the thermal head. The primer layer 6 is formed by adding hollow particles as a filler to a binder, for example.

[0043] By providing such a heat-insulating primer layer 6 on the thermosensitive recording medium 1, the printing sensitivity is improved, and therefore, the increase in the applied voltage of the thermal head can be suppressed, and as a result, the burning of the thermal head can be suppressed.

[0044] The average particle size of the hollow particles added as a filler to the primer layer 6 is preferably 1 μm to 100 μm. If it is within such a range, the thermal insulation of the primer layer 6 is improved. Here, the so-called average particle size is a weight average particle size measured by a laser diffraction method. The measurement of the average particle size based on the laser diffraction method can be performed using, for example, the trade name "MT3300EX-II" manufactured by Microtrac-BEL.

[0045] In addition, the hollow ratio of the hollow particles is preferably 30% to 99%. If it is within this range, the heat insulation of the primer layer 6 is improved. In addition, the greater the hollow ratio of the hollow particles, the higher the heat insulation effect. Therefore, the coloring agent can effectively color with less heat. That is, if the hollow ratio is increased, the printing quality of the thermosensitive recording body 1 is improved.

[0046] Here, the hollow ratio of the hollow particles is calculated by the following formula.

[0047] Hollowness = {(volumetric volume of voids) / (volume of hollow particles)}×100

[0048] The content ratio of the hollow particles in the primer layer 6 is preferably 40 parts by mass to 90 parts by mass relative to 100 parts by mass of the primer layer.

[0049] The material constituting the hollow particles is, for example, a thermoplastic resin, such as polystyrene resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polyacrylate resin, polyacrylonitrile resin, polybutadiene resin, etc.

[0050] It should be noted that fillers other than hollow particles may be used as fillers for the primer layer 6. For example, calcined kaolin, aluminum oxide, aluminum silicate, heavy calcium carbonate, light calcium carbonate, titanium oxide, barium sulfate, silica gel, activated clay, talc, clay, kaolinite, diatomaceous earth, white carbon, magnesium carbonate, magnesium oxide, magnesium hydroxide, zinc oxide, polystyrene resin particles, urea-formaldehyde resin particles, polyolefin resin particles, etc. may be cited. In addition, these fillers may be used alone or in combination of two or more.

[0051] Examples of the binder contained in the primer layer 6 include acrylic-styrene copolymers, styrene-butadiene copolymers, acrylic-butadiene-styrene copolymers, vinyl acetate resins, vinyl acetate-acrylic acid copolymers, styrene-acrylate copolymers, acrylate resins, and polyurethane resins.

[0052] In addition, as binders, water-soluble polymers such as polyvinyl alcohol, starch and its derivatives, cellulose derivatives such as methoxycellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose, sodium polyacrylate, polyvinyl pyrrolidone, acrylamide-acrylate copolymer, acrylamide-acrylate-methacrylic acid terpolymer, styrene-maleic anhydride copolymer alkali salt, isobutylene-maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, and casein can also be used.

[0053] The coating amount (dry weight) of the primer layer 6 is preferably 1 g / m 2 ~10g / m 2 .

[0054] The thickness of the primer layer 6 is preferably 1 μm to 20 μm.

[0055] When the coating amount and thickness of the primer layer 6 are adjusted to the above ranges, the primer layer 6 can appropriately exhibit a heat insulating function.

[0056] In this embodiment, the thermosensitive recording layer 3 is a layer that develops color by chemical reaction when heated by a thermal head or the like, and forms a recorded image on the thermosensitive recording medium 1. In this embodiment, the thermosensitive recording layer 3 contains a coloring agent, a non-phenolic color developer, and a non-phenolic antioxidant.

[0057] The coloring agent that develops color by heating is a component that develops color by chemical reaction when heated by a thermal head or the like, and forms a recorded image in the thermosensitive recording medium 1 of this embodiment. As the coloring agent that develops color by heating, a commonly used and known leuco dye can be used. As the leuco dye, for example, 3-(N-isobutyl-N-ethyl)amino-6-methyl-7-anilinofluoran, 3-(N-isopentyl-N-ethyl)amino-6-methyl-7-o-chloroanilinofluoran, 3-(N-methyl-N-p-toluidinyl)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-p-toluidinyl)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isopentyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethoxypropyl-N-ethyl)amino-6-methyl-7-anilinofluoran, 3-(N-cyclohexyl-N-methyl)amino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-n-propyl)amino-6-methyl-7- Methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-p-toluidinylfluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-8-methylfluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluoran, 3-diethylamino-7-(o-chloroanilino)fluoran, 3-diethylamino-7-chlorofluoran, 3-dibutylamino-6-methyl-7-bromofluoran, 3-dibutylamino-7-(o-chloroanilino)fluoran, 3-dipentylamino-6-methyl-7-anilinofluoran, 3-dimethylamino-5-methyl-7-methylfluoran, 3-pyrrolidinyl-6-methyl-7-anilinofluoran, crystal violet lactone, etc.

[0058] The particle size of the coloring agent is preferably 0.1 to 1.0 μm. Since the coloring agent reacts after melting, the reaction slows down as the particle size increases, and the sensitivity characteristics decrease. On the other hand, as the particle size decreases, the risk of coloring at an unexpected temperature due to the heat when the coating is dried increases. In this embodiment, by setting the particle size of the coloring agent to the range as described above, the sensitivity characteristics and coloring temperature of the coloring agent can be appropriately adjusted. Here, the particle size refers to the 50% average particle size measured by a Microtrac laser analysis-scattering particle size analyzer.

[0059] In this embodiment, in order to obtain excellent color development properties, the color forming agent is preferably contained in an amount of about 10 to 20% by mass relative to the entire thermosensitive recording layer 3. The color developing agent described below is preferably contained in an amount of 1 to 3% relative to the color forming agent 1 in terms of dry weight ratio.

[0060] In the present embodiment, the thermosensitive recording layer 3 does not contain the phenolic color developer commonly used in the past, but contains a non-phenolic color developer. The non-phenolic color developer is a variety of electron accepting substances that react with the leuco dye as described above when heated to make the leuco dye develop color, and is a compound that does not have a phenolic hydroxyl group. In other words, the thermosensitive recording layer 3 contains a non-phenolic color developer, which is a phenolic color developer that is of concern for safety as an endocrine disruptor. In the present embodiment, by containing a non-phenolic color developer in the thermosensitive recording layer 3 instead of a phenolic color developer, the leuco dye can be efficiently developed. It should be noted that the thermosensitive recording layer 3 sometimes inevitably contains a trace amount of phenolic compounds in the form of impurities, etc., to the extent that there is no concern about safety as an endocrine disruptor. In the case where the thermosensitive recording layer 3 inevitably contains such a trace amount of phenolic compounds, it is considered to be included in the scope of the present invention.

[0061] As such a non-phenolic color developer, a known color developer having no phenolic hydroxyl group can be used without particular limitation, and for example, 2,2-bis[(4-methyl-3-phenoxycarbonylaminophenyl)urea]diphenyl sulfone, 4,4'-bis(p-tolylsulfonylaminocarbonylamino)diphenylmethane, 2'-(3-phenylureido)benzenesulfonanilide, N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea, etc. can be used.

[0062] Here, the above-mentioned non-phenolic developer may be used as the developer. However, the present inventors have found that compounds represented by the following formula (1) and the following formula (2) are suitable from the viewpoint of further improving the heat resistance of the thermosensitive recording material 3 .

[0063] [Chemistry 5]

[0064]

[0065] (In formula (1), R 1 , R 2 , R 3 , R 4 , R 5 , R 7 , R 8 , R 9 , R 10 and R 11 Each independently represents a hydrogen atom or a substituent. 6 and R 12 Each independently represents a substituent. m represents an integer of 0 to 4. When m is 2 or more, a plurality of R 6 They may be the same or different. n represents an integer of 0 to 4. When n is 2 or more, a plurality of R 12 Can be the same or different.)

[0066] [Chemistry 6]

[0067]

[0068] (In formula (2), R 13 , R 14 , R 15 , R 16 , R 17 , R 19 , R 20 , R 21 , R 22 and R 23 Each independently represents a hydrogen atom or a substituent. 18 represents a substituent. o represents an integer from 0 to 4. When o is 2 or more, a plurality of R 18 Can be the same or different.)

[0069] As the above-mentioned "substituent", an organic group other than a hydrogen atom can be used without particular limitation, and examples thereof include a halogen atom, a nitro group, an amino group, an alkyl group, an alkoxy group, an aryl group, an aryloxy group, an alkylcarbonyloxy group, an alkylcarbonylamino group, an arylcarbonylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, a monoalkylamino group, a dialkylamino group, an arylamino group, and the like.

[0070] Examples of the "halogen atom" include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.

[0071] Examples of the “alkyl group” include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl, neopentyl, 2,3-dimethylpropyl, 1-ethylpropyl, 1-methylbutyl, 2-methylbutyl, n-hexyl, isohexyl, 2-hexyl, 3-hexyl, 2-methylpentyl, 3-methylpentyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl and other linear or branched alkyl groups having 1 to 12 carbon atoms.

[0072] Examples of the “alkoxy group” include linear or branched alkoxy groups having 1 to 8 carbon atoms, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, n-pentoxy, isopentoxy, tert-pentoxy, neopentoxy, 2,3-dimethylpropoxy, 1-ethylpropoxy, 1-methylbutoxy, n-hexyloxy, isohexyloxy, n-heptyloxy and n-octyloxy.

[0073] Examples of the “aryl group” include aromatic hydrocarbon groups having 6 to 10 carbon atoms, such as phenyl, 1-naphthyl, and 2-naphthyl.

[0074] In the above-mentioned "dialkylamino group", two alkyl groups may be the same or different.

[0075] As the compound represented by formula (1), the compound represented by the following formula (1a) is preferred from the viewpoint of being able to impart excellent color development and heat resistance to the thermosensitive recording material 1. Specific examples thereof include N,N'-bis-[3-(p-toluenesulfonyloxy)phenyl]urea, N,N'-bis-[3-(p-xylenesulfonyloxy)phenyl]urea, N,N'-bis-[3-(mesitylenesulfonyloxy)phenyl]urea, N,N'-bis-[3-(o-toluenesulfonyloxy)phenyl]urea, N,N'-bis-[3-(m-toluenesulfonyloxy)phenyl]urea, and N,N'-bis-[3-(benzenesulfonyloxy)phenyl]urea represented by the following formula (1b).

[0076] [Chemistry 7]

[0077]

[0078] (The symbols in formula (1a) are the same as those in formula (1).)

[0079] [Chemistry 8]

[0080]

[0081] As the compound represented by formula (2), the compound represented by the following formula (2a) is preferred from the viewpoint of being able to impart excellent color development and heat resistance to the thermosensitive recording material 1. Specifically, there can be mentioned [3-(3-phenylureido)phenyl]-4-methylbenzenesulfonate represented by the following formula (2b).

[0082] [Chemistry 9]

[0083]

[0084] (The symbols in formula (2a) are the same as those in formula (2).

[0085] [Chemistry 10]

[0086]

[0087] In the present embodiment, the thermosensitive recording layer 3 may contain a non-phenolic color developer alone or two or more types thereof.

[0088] By using at least one or both of the compound represented by the general formula (1) and the compound represented by the general formula (2) as non-phenolic color developers in the thermosensitive recording layer 3 , the heat resistance and color development properties of the thermosensitive recording material 1 can be improved.

[0089] In this embodiment, the content of the non-phenolic developer relative to the entirety of the thermosensitive recording layer 3 is preferably 10% by mass or more and 50% by mass or less. From the perspective of being able to prevent the lack of color development (lower optical density) caused by insufficient developer, a configuration in which the content of the non-phenolic developer is 10% by mass or more is preferred. In addition, from the perspective of preventing the lack of color development (lower optical density) caused by excessive developer (i.e., insufficient dye), a configuration in which the content of the non-phenolic developer is 50% by mass or less is preferred.

[0090] In this embodiment, as described above, a phenolic developer is not intentionally used as a developer in the thermosensitive recording layer 3. However, a trace amount of a phenolic compound may be inevitably contained as an impurity of a non-phenolic developer. Such impurities include, for example, sulfonate (-SO2-O-), compounds obtained by hydrolysis of all or part of an alkoxy group, an aryloxy group, an alkylcarbonyloxy group, etc. contained as a substituent in the non-phenolic developer represented by the above formula (1) and / or (2). Such a phenolic compound contained as an impurity may also function as a developer.

[0091] In the present embodiment, the above-mentioned phenolic compounds that may inevitably be contained as impurities in the thermal recording layer 3 may be contained, for example, in trace amounts at the ppm level that can be detected by machine analysis (for example, less than 100 ppm relative to the entire thermal recording layer 3). However, it is considered that if it is a trace amount to this extent, there will be no concerns about the safety of endocrine disruptors, etc., and it will not substantially function as a color developer.

[0092] In the present embodiment, the thermosensitive recording layer 3 does not contain the phenolic antioxidant commonly used in the past, but contains a non-phenolic antioxidant. The non-phenolic antioxidant is a substance that prevents oxidation by capturing or decomposing hydroperoxides, and is a compound that does not have a phenolic hydroxyl group. In other words, the thermosensitive recording layer 3 contains a non-phenolic antioxidant, which means that a phenolic compound whose safety is worrying as an endocrine disruptor is not intentionally used. In the present embodiment, by containing a non-phenolic antioxidant in the thermosensitive recording layer 3 instead of a phenolic antioxidant, the light resistance and heat resistance of the thermosensitive recording body 1 can be improved. It should be noted that in the case where the thermosensitive recording layer 3 of the present embodiment contains a phenolic antioxidant to the extent that it does not cause safety concerns as an endocrine disruptor and does not affect the color development, light resistance, and heat resistance, it is considered to be included in the scope of the present invention.

[0093] As such non-phenolic antioxidants, known antioxidants without phenolic hydroxyl groups can be used without particular limitation. Examples thereof include phosphorus antioxidants, aromatic amine antioxidants, sulfur antioxidants, adipic acid, and vitamin C. Furthermore, the inventors of the present application have found that phosphorus antioxidants are suitable from the viewpoint of further improving the light resistance and heat resistance of the thermosensitive recording medium 1.

[0094] The phosphorus-based antioxidant is a compound having a trivalent phosphorus atom in the molecule, and reacts with a hydroperoxide to be oxidized to pentavalent phosphorus, thereby decomposing the hydroperoxide and exhibiting an antioxidant function.

[0095] The phosphorus-based antioxidant may be any compound having a trivalent phosphorus atom in the molecule without particular limitation, and examples thereof include phosphite compounds represented by the following formula (3a) and phosphite compounds represented by the following formula (3b).

[0096] [Chemistry 11]

[0097]

[0098] (In formula (3a), R 24 , R 25 and R 26 Each independently represents a substituted or unsubstituted hydrocarbon group. 24 and R 25 Can be bonded via a linking group.)

[0099] [Chemistry 12]

[0100]

[0101] (In formula (3b), R 27 and R 28 Each independently represents a substituted or unsubstituted hydrocarbon group. )

[0102] In the above formula (3a), R 24 , R 25 and R 26Examples of the substituted or unsubstituted hydrocarbon group include alkyl groups [e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl, 2-ethylhexyl, etc.], cycloalkyl groups [e.g., cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclododecyl, etc.], aryl groups [e.g., phenyl, tolyl, xylyl, naphthyl, 2,6-di-tert-butyl-4-methyl-1-phenyl, 2,4-di-tert-butyl-1-phenyl, etc.], cycloalkyl-alkyl groups [e.g., cyclohexylmethyl, methylcyclohexyl, etc.], aralkyl groups [e.g., benzyl, phenethyl, etc.], halogenated hydrocarbon groups in which one or more hydrogen atoms in the hydrocarbon group are substituted with halogen atoms [e.g., halogenated alkyl groups such as chloromethyl, 3-chloropropyl, 3,3,3-trifluoropropyl, etc.], and groups in which one or more hydrogen atoms bonded to carbon atoms possessed by these groups are substituted with functional groups such as hydroxyl, carboxyl, nitro, substituted or unsubstituted amino, mercapto, etc.

[0103] As bond R 24 and R 25 Specific examples of the linking group include a single bond, an alkylene group [for example, an alkylene group having 1 to 6 carbon atoms (the number of carbon atoms constituting the alkylene group) such as methylene, ethylene, and trimethylene], -O-, -CO-, and a group in which a plurality of these groups are linked.

[0104] Among them, as R 24 , R 25 and R 26 , preferably each independently represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, and more preferably a substituted or unsubstituted alkyl group having 8 to 20 carbon atoms (the number of carbon atoms constituting the alkyl group) (for example, 2-ethylhexyl, stearyl, etc.), an aryl group (for example, phenyl, etc.), or an alkyl-substituted aryl group (for example, 2,6-di-tert-butyl-4-methyl-1-phenyl, 2,4-di-tert-butyl-1-phenyl, etc.).

[0105] In the above formula (3b), R 27 and R 28 The substituted or unsubstituted hydrocarbon group shown in the figure may be, for example, 24 , R 25 and R 26 The substituted or unsubstituted hydrocarbon groups are the same as those exemplified. 27 and R 28 , which are the same or different, are preferably substituted or unsubstituted alkyl, substituted or unsubstituted aryl, and more preferably substituted or unsubstituted alkyl having 8 to 20 carbon atoms (the number of carbon atoms constituting the alkyl group) (e.g. 2-ethylhexyl, stearyl, etc.), aryl (e.g. phenyl, etc.), alkyl-substituted aryl (e.g. 2,6-di-tert-butyl-4-methyl-1-phenyl, 2,4-di-tert-butyl-1-phenyl, etc.).

[0106] More specifically, examples of the phosphorus antioxidant include 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol-diphosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol-diphosphite, tris(2,4-di-tert-butylphenyl)phosphite, tris(mono-, dinonylphenyl)phosphite, tris(2-ethylhexyl)phosphite, triphenyl phosphite, tris(monononylphenyl)phosphite, triisodecyl phosphite, and the like.

[0107] Phosphorus antioxidants may be used alone or in combination of two or more. In addition, as phosphorus antioxidants, for example, commercial products such as trade names "JP-360", "JP-308E" (made by Johoku Chemical Industry (Strain)), trade name "IRGAFOS168" (made by BASF), trade name "Sanko Epoclean" (made by Sanko (Strain)), trade name "Adekastab3010", "Adekastab PEP-36" (made by ADEKA (Strain)), and trade name "CS1680" (made by SONGWON) may be used.

[0108] In the present embodiment, the content of the non-phenolic antioxidant relative to the entirety of the thermosensitive recording layer 3 is not particularly limited, but is preferably 5% by mass or more and 10% by mass or less. From the perspective of being able to impart excellent light resistance to the thermosensitive recording material 1 of the present embodiment, a configuration in which the content of the non-phenolic antioxidant is 5% by mass or more is suitable. From the perspective of being able to impart excellent color development properties to the thermosensitive recording material 1 of the present embodiment, a configuration in which the content of the non-phenolic antioxidant is 10% by mass or less is suitable.

[0109] In the present embodiment, the content of the non-phenolic antioxidant relative to the total amount of the antioxidant contained in the thermal recording layer 3 is not particularly limited, but from the viewpoint of improving light resistance and heat resistance while reducing safety concerns about endocrine disruptors, etc., it is preferably 90% by mass or more, more preferably 95% by mass or more, and further preferably 99% by mass or more.

[0110] In the present embodiment, the content of the phosphorus-based antioxidant relative to the total amount of the antioxidant contained in the thermal recording layer 3 is not particularly limited, but from the viewpoint of improving light resistance and heat resistance while reducing safety concerns about endocrine disruptors, etc., it is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more.

[0111] Furthermore, the thermosensitive recording layer 3 may contain additives such as a binder, a sensitizer, a lubricant, a filler, a storage stability improving agent, and a pigment as necessary.

[0112] Examples of the binder contained in the thermosensitive recording layer 3 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 chloride-vinyl acetate copolymer, polyurethane, polystyrene, polyvinyl pyrrolidone, acrylate, acrylonitrile, methyl vinyl ether, etc. These binders may be used alone or in combination of two or more.

[0113] Examples of the sensitizer include stearic acid, stearic acid amide, stearic acid aniline, hydroxymethyl stearic acid amide, methylene bis stearic acid amide, ethylene bis stearic acid amide, 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, p-toluenesulfonamide, and the like, which are solid at room temperature and preferably have a melting point of about 70° C. or higher. These sensitizers may be used alone or in combination of two or more.

[0114] Examples of lubricants include paraffin wax, fatty acids such as oleic acid, polyolefin waxes such as polyethylene wax, metal soaps such as zinc stearate, ester waxes such as carnauba wax, silicone oil, and oils such as whale oil. These lubricants may be used alone or in combination of two or more.

[0115] Examples of fillers include aluminum hydroxide, magnesium hydroxide, aluminum oxide, magnesium oxide, aluminum silicate, calcium carbonate, magnesium carbonate, titanium oxide, barium sulfate, silica gel, activated clay, talc, clay, kaolin, calcined kaolin, diatomaceous earth, white carbon, zinc oxide, silicon oxide, colloidal silica, polystyrene resin particles, urea-formaldehyde resin particles, and polyolefin resin particles. These fillers may be used alone or in combination of two or more.

[0116] Examples of the storage stability improving agent include sodium 2,2'-methylenebis(4,6-di-tert-butylphenyl)phosphate, 4,4-butylenebis(3-methyl-6-tert-butylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, tris(2,6-dimethyl-4-tert-butyl-3-hydroxybenzyl)isocyanurate, 4-(2-methylglycyloxy)-4'-benzyloxydiphenyl sulfone, 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), diethylthiourea, zinc dibutyldithiocarbamate, 4,4'-thiobis(6-tert-butyl-m-cresol), and a ureaurethane compound represented by the following formula (4).

[0117] [Chemistry 13]

[0118]

[0119] These preservability improving agents may be used alone or in combination of two or more. In addition, a known surfactant may be contained.

[0120] Fresh foods such as meat and fish are sold in the form of packages wrapped in plastic wrap, and labels showing prices and the like are affixed to the plastic wrap. In addition, packages are usually displayed in a stacked manner, so there is a possibility that the label comes into contact with the plastic wrap that wraps other packages. The plastic wrap contains a plasticizer for imparting plasticity. When the stacked packages are left for a long time, the plasticizer transfers to the label, which may affect the printing. Therefore, the thermosensitive recording medium preferably has excellent properties such as the printing is not easily lost even if the plasticizer transfers, that is, "plasticizer resistance".

[0121] In the present embodiment, from the viewpoint of printing storage stability, particularly plasticizer resistance, the thermosensitive recording layer 3 preferably contains a storage stability improving agent, and particularly preferably contains a urea urethane compound represented by the above formula (4).

[0122] It can be considered that by making the thermosensitive recording layer 3 contain a preservation improving agent, especially a urea urethane compound represented by formula (4), the reaction efficiency between the leuco dye and the developer is improved, the electron transfer complex is easily generated, and the reverse reaction is not easy to occur, so that the color development property of the thermosensitive recording body becomes excellent, and the color development concentration is not easy to decrease, and the printing preservation property, especially the plasticizer resistance, is excellent.

[0123] The ureaurethane compound represented by formula (4) is specifically three types represented by the following formulas (4a) to (4c), and these can be used alone or in combination of two or more types.

[0124] [Chemistry 14]

[0125]

[0126] [Chemistry 15]

[0127]

[0128] [Chemistry 16]

[0129]

[0130] In the present embodiment, when the thermosensitive recording layer 3 contains a storage property improving agent, the content of the storage property improving agent relative to the entire thermosensitive recording layer 3 is preferably 1% by mass or more and 20% by mass or less. From the perspective of being able to suppress the decrease in color development concentration caused by plasticizers and the like, and to obtain a thermosensitive recording material having excellent printing storage properties, especially plasticizer resistance, a configuration in which the content of the storage property improving agent is 1% by mass or more is preferred. In addition, from the perspective of preventing a lack of color development (lower optical density), a configuration in which the content of the storage property improving agent is 20% by mass or less is preferred.

[0131] In the present embodiment, when the thermosensitive recording layer 3 contains a storage property improving agent, the content ratio of the storage property improving agent relative to the non-phenolic color developer (storage property improving agent / non-phenolic color developer) is preferably 1 / 20 to 1 / 1. From the perspective of being able to prevent the lack of color development (lower optical density), a configuration in which the above content ratio is 1 / 1 or less is preferred. In addition, from the perspective of being able to suppress the reduction of color development concentration caused by plasticizers and the like, and to achieve a thermosensitive recording medium with excellent printing storage properties, especially plasticizer resistance, a configuration in which the above content ratio is 1 / 20 or more is preferred.

[0132] In the present embodiment, when the thermosensitive recording layer 3 contains the urea urethane compound represented by formula (4), the content of the urea urethane compound represented by formula (4) relative to the entire thermosensitive recording layer 3 is preferably 1% by mass or more and 20% by mass or less. From the perspective of being able to suppress the reduction in color development concentration caused by plasticizers and the like, and to achieve a thermosensitive recording body having excellent printing preservation properties, especially plasticizer resistance, it is preferred that the content of the urea urethane compound is 1% by mass or more. In addition, from the perspective of preventing a lack of color development (lower optical density), it is preferred that the content of the urea urethane compound is 20% by mass or less.

[0133] In the present embodiment, when the thermosensitive recording layer 3 contains the urea urethane compound represented by formula (4), the content ratio of the urea urethane compound represented by formula (4) relative to the non-phenolic color developer (urea urethane compound / non-phenolic color developer) is preferably 1 / 20 to 1 / 1. From the perspective of being able to prevent the lack of color development (lower optical density), a composition in which the above content ratio is 1 / 1 or less is preferred. In addition, from the perspective of being able to suppress the reduction in color development concentration caused by plasticizers, etc., and to achieve a thermosensitive recording body with excellent printing preservation, especially plasticizer resistance, a composition in which the above content ratio is 1 / 20 or more is preferred.

[0134] In the present embodiment, the content of the ureaurethane compound represented by formula (4) relative to the total amount of the preservability enhancer contained in the thermal recording layer 3 is not particularly limited. However, from the perspective of being able to suppress the reduction in color concentration caused by plasticizers and the like and to achieve a thermal recording body with excellent printing preservation properties, especially plasticizer resistance, it is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more.

[0135] In the present embodiment, by providing the intermediate layer 4 on the thermosensitive recording layer 3, it is possible to obtain a thermosensitive recording material 1 having excellent water resistance, chemical resistance, plasticizer resistance, and the like.

[0136] As the material constituting the intermediate layer 4, for example, water-based resins such as polyvinyl alcohol, modified polyvinyl alcohol, starch, modified starch, casein, gelatin, bone glue, gum arabic, 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, maleic acid copolymer, polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinyl acetate copolymer, polyurethane, polystyrene, polyvinyl pyrrolidone, acrylate, acrylonitrile, methyl vinyl ether polyvinyl alcohol can be cited. It should be noted that the so-called "water-based resin" means that these compounds are dispersed in water or the resin component dissolved in water. These materials can be used alone or in combination of two or more.

[0137] The above-mentioned resin uses a resin having a water-soluble portion, such as a polyvinyl alcohol (PVA) resin which is a resin having a hydroxyl group as a hydrophilic structural unit, or a core-shell structured resin in which hydrophobic core particles are coated with a water-soluble shell polymer, such as a core-shell type acrylic resin, thereby improving transparency.

[0138] As the core-shell type resin, for example, a resin sold under the name of "Bariastar (manufactured by Mitsui Chemicals, Inc.)" as a core-shell type acrylic resin can be used.

[0139] The coating amount (dry weight) of the intermediate layer 4 is preferably 0.3 g / m 2 ~10g / m 2 .

[0140] The top coat layer 5 is a layer that improves the thermal head adaptability of the thermal recording medium 1 to the thermal head and smoothly develops the color of the thermal recording layer 3. Specifically, it means that the thermal recording layer 3 develops the color without causing the unfavorable conditions of accumulation of attached materials on the thermal head and deformation of the surface of the thermal recording medium 1 due to heat as much as possible.

[0141] In this embodiment, the top coating layer 5 of the thermal recording medium 1 is responsible for reducing the wear of the thermal head without reducing the life of the thermal head without adding elastic particles. This means the so-called improvement of the adaptability of the thermal head. In addition, the top coating layer 5 needs to improve the anti-sticking property to the thermal head. Here, the so-called anti-sticking property means that it is not easy to produce the undesirable condition that the components of the top layer of the thermal recording medium melt and adhere to the thermal head due to the heat of the thermal head. More specifically, it is not easy to produce the undesirable condition that there is no printing in part of the thermal recording medium or the printing surface is deformed.

[0142] The top coat layer 5 of the present embodiment has evaporation holes and cracks in the form of concave recesses on its surface due to evaporation of water, thereby reducing the contact area between the surface of the top coat layer 5 and the thermal head.

[0143] In order to generate recessed portions, particularly cracks, on the surface of the top coating layer 5 in this manner, a coating liquid containing hydrophobic resin particles is used as the coating liquid for forming the top coating layer 5 .

[0144] That is, in the present embodiment, the top coat layer 5 uses an emulsion of hydrophobic resin particles, for example, an emulsion in which hydrophobic acrylic resin particles are dispersed in water, as a binder.

[0145] In this way, an emulsion of hydrophobic resin particles is used as a binder for the top coat layer 5, and no water-soluble polymer is used.

[0146] The coating liquid containing the water-soluble polymer is unlikely to aggregate when dried after application, and forms a flexible coating film, so that cracks due to shrinkage are not generated in the top coating layer 5 .

[0147] On the other hand, when the emulsion of hydrophobic resin particles is dried after coating, the hydrophobic resin particles agglomerate and shrink due to evaporation, and cracks that become recessed portions are generated on the surface of the top coat layer 5 .

[0148] Since the cracks are formed by shrinkage due to aggregation of the hydrophobic resin particles, they remain in the top coating layer 5 and do not reach the intermediate layer 4 .

[0149] In this embodiment, in order to form evaporation holes that become recessed portions on the surface of the top coat layer 5 due to evaporation of water, the thermosensitive recording layer 3, the intermediate layer 4 and the top coat layer 5 are simultaneously coated using a curtain coater.

[0150] The curtain coater discharges coating liquids for forming the thermosensitive recording layer 3 , the intermediate layer 4 , and the topcoat layer 5 from a plurality of slits, and stacks the coating liquids, and allows the stacked coating liquids to continuously flow.

[0151] In such a three-layer simultaneous coating using a curtain coater, once the top coat layer 5 is dried, cracks are generated due to the aggregation of hydrophobic resin particles as described above, and water vapor is discharged from the cracks, and the semi-dried intermediate layer 4 and the thermosensitive recording layer 3 are dried and solidified. Most of the water vapor in the intermediate layer 4 and the thermosensitive recording layer 3 is released from the cracks, but a part of the water vapor is released by forming evaporation holes in the top coat layer 5. Therefore, cracks and evaporation holes are formed near the top coat layer 5.

[0152] In this embodiment, the evaporation pores formed in the top coat layer 5 stay in the intermediate layer 4. Therefore, even if oil adheres to the surface of the top coat layer 5 as the uppermost layer, it does not reach the thermosensitive recording layer 3, and the thermosensitive recording layer 3 does not discolor.

[0153] The top coat layer 5 may contain additives such as a lubricant, a cross-linking agent, a dispersant, a defoaming agent, a water resistance agent, and a filler as necessary.

[0154] Examples of the lubricant include polyethylene and zinc stearate, and examples of the crosslinking agent include zirconium carbonate.

[0155] As fillers, for example, aluminum hydroxide, aluminum oxide, aluminum silicate, heavy calcium carbonate, light calcium carbonate, titanium oxide, barium sulfate, silica gel, activated clay, talc, clay, kaolinite, diatomaceous earth, white carbon, magnesium carbonate, magnesium oxide, magnesium hydroxide, zinc oxide, polystyrene resin particles, urea-formaldehyde resin particles, polyolefin resin particles, etc. These fillers can be used alone or in combination of two or more. It should be noted that the particle size of the filler contained in the top coating layer 5 is preferably less than 1.0 μm.

[0156] In the present embodiment, as a coating liquid for forming the top coat layer 5, a water-dispersed suspension obtained by mixing an emulsion obtained by dispersing a hydrophobic acrylic resin in water, a polyethylene wax as a lubricant, and calcium carbonate as a pigment at a mass ratio of 4:3:3 when dried is used to produce the thermosensitive recording material 1.

[0157] The coating amount (dry weight) of the top coating layer 5 was set to 1 g / m 2 .

[0158] According to the present embodiment, as described above, cracks that become recessed portions and water evaporation holes are formed on the surface of the top coating layer 5 that is the uppermost layer of the thermal recording medium 1, so that the surface of the top coating layer 5 becomes concavoconvex. As a result, the contact area between the top coating layer 5 and the thermal head is reduced, the wear of the thermal head is reduced, the adaptability of the thermal head is improved, and the anti-blocking property is improved.

[0159] The thickness of the top coating layer 5 is adjusted to, for example, less than 1 μm. In the present embodiment, it is adjusted to about 0.8 μm. Thus, since the distance from the surface of the top coating layer 5 to the thermal recording layer 3 is short, the heat from the thermal head is efficiently conducted to the thermal recording layer 3. In addition, since the thickness is thin, it helps to reduce costs.

[0160] In addition, since the cracks on the surface of the top coating layer 5 develop along the thickness direction of the inside of the top coating layer 5, the top coating layer 5 is cut in a direction perpendicular to the thickness direction, that is, in the lateral direction, by the cracks. As a result, the heat release from the thermal head in the lateral direction is suppressed. As a result, the heat from the thermal head is efficiently conducted to the thermal recording layer 3 located in the lower layer in the thickness direction.

[0161] In order to reduce the contact area between the top coat layer 5 and the thermal head, the average diameter of the substantially circular water evaporation pores is preferably 2 μm or more.

[0162] The average diameter of the evaporation pores is measured by observing the surface of the top coating layer 5 with an electron microscope (SEM) and measuring the average diameter per unit area, for example, per 1 mm 2 The number of evaporation holes is calculated based on the diameter of the evaporation holes in the evaporation holes. For example, the number of evaporation holes with an average diameter of 5 μm or more is calculated based on the diameter of the evaporation holes in the evaporation holes. 2 The number is preferably 30 or more, and the number is more preferably 40 or more.

[0163] In the thermosensitive recording material 1 of this embodiment, the surface of the top coating layer 5 can be made to have a large number of evaporation holes and a small number of cracks by adjusting the formulation of the top coating layer 5. Alternatively, the surface of the top coating layer 5 can be made to have only a large number of evaporation holes without cracks.

[0164] In the present embodiment, although the three layers of the thermosensitive recording layer 3, the intermediate layer 4 and the top coating layer 5 are simultaneously coated in multiple layers using a curtain coater, it is not limited to the simultaneous coating of multiple layers, and each thermosensitive recording layer 3, the intermediate layer 4 and the top coating layer 5 can also be formed separately and sequentially.

[0165] In this embodiment, the primer layer 6 and the intermediate layer 4 are formed on the substrate 2. However, as another embodiment of the present invention, at least one of the primer layer 6 and the intermediate layer 4 may be omitted.

[0166] Since the thermosensitive recording material of the above embodiment has the thermosensitive recording layer having the above configuration, it is excellent in light resistance, color development property, and heat resistance.

[0167] The amount of change (%) of whiteness represented by the following formula of the thermosensitive recording material of the present embodiment is preferably -10% or more, more preferably -9% or more, further preferably -8% or more, and particularly preferably -7% or more, from the viewpoint of excellent light resistance and suppression of decrease in whiteness due to light irradiation.

[0168] Whiteness change (%) = whiteness after 100 hours at 5000 Lux - whiteness before test

[0169] The whiteness is a value obtained in accordance with JIS P 8148.

[0170] A negative value (-) of the whiteness change (%) indicates a decrease in whiteness, and a value closer to 0% indicates a smaller decrease in whiteness and better light resistance.

[0171] The absolute value of Δb represented by the following formula of the thermosensitive recording material of the present embodiment is preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less, from the viewpoint of excellent light resistance and suppression of yellowing or bluish discoloration (bluish color) due to light irradiation.

[0172] Δb = b value after 100 hours under illuminance of 5000 Lux - b value before test

[0173] The b value indicates L specified in JIS Z8781-4:2013 * a * b * Chroma (b value) in color space.

[0174] The b value indicates the change from blue to yellow. The larger the value, the closer to yellow, and the smaller the value, the closer to blue. The above Δb indicates the amount of change in the b value. A positive value indicates yellowing, and a negative value indicates blueing. Therefore, the closer the absolute value of Δb is to 0, the less yellowing and blueing there is, and the better the light resistance.

[0175] The above Δb indicates the degree of yellowing, and a lower value indicates less yellowing and better light resistance.

[0176] The dynamic sensitivity (OD value) of the printed portion of the thermosensitive recording material of the present embodiment at 0.16 mj / dot is preferably 0.3 or more, and more preferably 0.35 or more, from the viewpoint of excellent color development properties.

[0177] The dynamic sensitivity (OD value) of the printed portion of the thermosensitive recording material of the present embodiment at 0.20 mj / dot is preferably 0.9 or more, and more preferably 1 or more, from the viewpoint of excellent color development properties.

[0178] The dynamic sensitivity (OD value) of the printed portion of the thermosensitive recording material of the present embodiment at 0.40 mj / dot is preferably 1.1 or more, and more preferably 1.2 or more, from the viewpoint of excellent color development properties.

[0179] The above-mentioned dynamic sensitivity (OD value) is a value measured in Examples given later, and a higher value indicates better color development.

[0180] The OD value of the non-printing portion in the examples (heat resistance evaluation) listed later regarding the thermosensitive recording material of the present embodiment is preferably 0.2 or less, more preferably 0.18 or less, and even more preferably 0.15 or less, from the viewpoint of excellent heat resistance and being able to clearly identify the printed portion even after heating and cooking in a microwave oven or the like.

[0181] Example

[0182] In the following examples and comparative examples, thermosensitive recording materials containing a non-phenolic color developer and a non-phenolic antioxidant in the thermosensitive recording layer were prepared, and the color development, light resistance, and heat resistance were evaluated. It should be noted that the present invention is not limited to these examples.

[0183] (Examples 1 to 6, Comparative Examples 1 to 2)

[0184] (Production of thermal recording medium)

[0185] <Base coating>

[0186] The basis weight of the substrate is 70g / m 2 On an offset paper (thickness: 80 μm), a coating liquid for an undercoat layer was applied by mixing and stirring a composition of 70 parts by mass of hollow particles (solid content concentration 26.5%, ROPAQUE HP-1055: Rohm & Hass Japan Co., Ltd.), 10 parts by mass of modified styrene butadiene latex (solid content concentration 49%), and 20 parts by mass of water, and the mixture was dried to form a coating amount of 3.0 g / m 2 , a primer layer with a thickness of 5μm.

[0187] <Thermosensitive recording layer>

[0188] The coating liquid for forming a thermosensitive recording layer shown in Table 1 was prepared, and the prepared coating liquid for forming a thermosensitive recording layer was applied to the above-mentioned undercoat layer so that the coating amount was 4.0 g / m in terms of dry weight. 2After that, drying was performed to form a 3.5 μm thick thermosensitive recording layer on the undercoat layer. In Table 1, the numerical values ​​of the respective compounding materials represent the weight ratios when dried.

[0189] In addition, as the compounding material, 3-dibutylamino-6-methyl-7-anilinofluoran having a particle size of 0.6 to 0.7 μm was used as the leuco dye, [3-(3-phenylureido)phenyl]-4-methylbenzenesulfonate represented by the above formula (2b) was used as the developer 1, and N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea represented by the above formula (1b) was used as the developer 2. In addition, phosphorus-based tris(2,4-di-tert-butylphenyl) phosphite (manufactured by SONGWON) was used as the antioxidant 1.

[0190] In addition, 1,2-bis(3-methylphenoxy)ethane (dispersed in a PVA aqueous solution to make a dispersion having a solid content concentration of 20%) was used as a sensitizer, a styrene acrylic copolymer emulsion was used as a binder, calcium carbonate (dispersed in a 5% sodium hexametaphosphate aqueous solution to make a dispersion having a solid content concentration of 30%) was used as a pigment, and a zinc stearate emulsion was used as a lubricant.

[0191] <Middle layer>

[0192] An acrylic emulsion (solid content concentration 30%) was applied on the above-mentioned heat-sensitive recording layer and dried to form a coating amount of 1.6 g / m 2 , an intermediate layer with a thickness of 1.5μm.

[0193] <Top coating>

[0194] A liquid prepared by mixing and stirring an acrylic emulsion (solid content concentration of 20%), 5 parts by mass of calcium carbonate, 15 parts by mass of polyethylene wax (solid content concentration of 40%), and 40 parts by mass of water was applied to the intermediate layer and dried to obtain a coating amount of 1.0 g / m 2 , a top coating layer with a thickness of 0.9 μm.

[0195] Thermosensitive recording materials of Examples 1 to 6 and Comparative Examples 1 and 2 were produced by the above method.

[0196]

[0197] (Lightfastness evaluation)

[0198] In the light resistance evaluation, the optical density (OD value of the printed part / OD value of the non-printed part), yellowing (yellowing), and changes in whiteness were measured for the printed part and the non-printed part of each thermosensitive recording medium in each Example and each Comparative Example. The following is an explanation of the procedure for light resistance evaluation.

[0199] The produced thermosensitive recording medium was printed using a thermal paper printing test device (manufactured by Oakla Engineering, trade name: Pulse Simulator TH-M2 / PP) at a printing speed of 50 mm / sec, an applied voltage of 17.0 V, a thermal head resistance of 870 Ω, a pulse width of 0.488 to 1.394 ms, and a printing energy of 0.40 mJ / dot.

[0200] The distance from the fluorescent lamp was checked using an illuminometer so as to achieve 5000 Lux, and the thermosensitive recording material printed as above was left at this position for 100 hours.

[0201] The optical densities of the printed area and the non-printed area of ​​the thermosensitive recording material sample before the test and after the above-mentioned storage were measured using a spectrophotometer (Videojet X-rite Co., Ltd., trade name: eXact) (OD value of the printed area / OD value of the non-printed area).

[0202] The whiteness (%) and hue (L, a, b) of the thermosensitive recording material samples before and after the test were measured. The whiteness was measured using a photoelectric reflection densitometer (manufactured by Tokyo Denshoku Co., Ltd., trade name: TC-6DS / A) in accordance with JISP 8148.

[0203] The color tone (L, a, b) was measured using a colorimeter (manufactured by Videojet X-rite Co., Ltd., trade name: SpectroEye).

[0204] The measurement results obtained by the above test are shown in Table 2. In the measurement results of Table 2, when the numerical value of the optical density (OD value) of the printed part and the non-printed part is large (that is, the reflectivity of light is low), it means that the color development is further carried out (the color development state is close to black), and when the numerical value is small (that is, the reflectivity of light is large), it means that the color development is insufficient. The larger the numerical value of whiteness (%), the closer it is to white. Among the various indicators of hue (L, a, b), (L) represents the change from black to white, and the larger the numerical value of (L), the closer it is to white. (a) represents the change from green to red, and the larger the numerical value of (a), the closer it is to red. (b) represents the change from blue to yellow, and the larger the numerical value of (b), the closer it is to yellow. The light resistance of each thermal recording medium was evaluated based on these color changes.

[0205] (Dynamic sensitivity evaluation)

[0206] In the dynamic sensitivity test, each thermosensitive recording medium of each embodiment and each comparative example was printed at different printing energies, and the optical density (OD value of the printed portion) at each printing energy was measured. Based on the measurement results, the dynamic sensitivity of each thermosensitive recording medium of each embodiment and each comparative example was evaluated. The procedure of the dynamic sensitivity test is described below.

[0207] The produced thermosensitive recording medium was printed using a thermal paper printing test device (manufactured by Oakla Engineering, trade name: Pulse Simulator TH-M2 / PP) with the settings set to a printing speed of 50 mm / sec, an applied voltage of 17.0 V, a thermal head resistance of 870 Ω, and a pulse width of 0.488 to 1.394 ms. Printing was performed under the printing energy conditions of 0.16 mJ / dot, 0.20 mJ / dot, and 0.40 mJ / dot, and the optical density (OD value) under the printing energy conditions was measured using a spectrophotometer (manufactured by X-rite, trade name: eXact).

[0208] The measurement results obtained by the above test are shown in Table 2. As in the above light resistance test, in the measurement results of Table 2, when the numerical value of the optical density (OD value) is large, it means that the color development is further advanced, and when the numerical value is small, it means that the color development is insufficient. For example, even if the printing energy is small, when the numerical value of the optical density (OD value) is large, it is evaluated as "good color development". On the other hand, even if the printing energy is large, when the numerical value of the optical density (OD value) is small, it is evaluated as "poor color development". That is, the dynamic sensitivity test is an evaluation of color development.

[0209] (Heat resistance evaluation)

[0210] In the heat resistance test, the printing part and the non-printing part of each thermosensitive recording medium of each embodiment and each comparative example were heated, and the optical density (OD value of the printing part) of the printing part and the non-printing part was measured. Based on the measurement results, the heat resistance of each thermosensitive recording medium of each embodiment and each comparative example was evaluated. The procedure of the heat resistance test is described below.

[0211] The produced thermosensitive recording medium was printed using a thermal paper printing tester (manufactured by Oakla Engineering, trade name: Pulse Simulator TH-M2 / PP) at a printing speed of 50 mm / sec, an applied voltage of 17.0 V, a thermal head resistance of 870 Ω, a pulse width of 0.488 to 1.394 ms, and a printing energy of 0.40 mJ / dot.

[0212] A container (diameter: 12 cm, content: 220 cc) containing 100 g of water was covered with a vinyl chloride cling film (thickness: 10 μm), and the sample of the thermosensitive recording material printed as described above (length: 3 cm, width: 4 cm) was attached to the cling film.

[0213] Then, in order to release the steam during heating, 10 through holes were formed in the plastic wrap using a safety pin. It should be noted that the through holes were formed avoiding the sample portion and the distances between the through holes were uniform.

[0214] The container was then heated in a microwave oven (1500 W) for 1 minute, and the optical densities of the printed and non-printed parts of the thermosensitive recording material sample (OD value of the printed part / OD value of the non-printed part) were then measured using a spectrophotometer (manufactured by X-rite, trade name: eXact).

[0215] The measurement results obtained by the above test are shown in Table 2. In the evaluation of the heat resistance, when the value of the optical density (OD value) is small for the non-printing part and large for the printing part, it means that the thermosensitive recording body has a small reaction to heat. That is, it indicates the degree of coloration of the printing part or the non-printing part when the heat caused by steam is applied to the thermosensitive recording body by heating the thermosensitive recording body in a microwave oven. Therefore, since the non-printing part is preferably as colorless as possible, it can be evaluated as "good heat resistance" when the value of the optical density (OD value) is small. On the other hand, it is confirmed that the coloring part of the printing part does not disappear due to the heat caused by steam. Specifically, when the value of the optical density (OD value) of the printing part is large, it means that the reaction to heat is not too large.

[0216]

[0217] <Verification results>

[0218] From the results shown in Table 2, the following conclusions can be confirmed.

[0219] [Examples 1 to 3 and Comparative Example 1]

[0220] Examples 1 to 3 and Comparative Example 1 containing the same developer 1 were examined.

[0221] (1) In the light resistance test, Examples 2 to 3 showed a smaller change in whiteness than Comparative Example 1, and the whiteness after the test was also higher. This is presumably because Examples 2 to 3 contain antioxidant 1 (non-phenolic antioxidant). On the other hand, Example 1, in which the amount of antioxidant 1 blended was 5% less than that of Examples 2 to 3 (7.5% by mass, 10% by mass), showed a whiteness change of -8.2, which was higher than that of Comparative Example 1, but a slight difference of 0.70. Therefore, it can be said that Example 1 showed the same degree of whiteness change as Comparative Example 1. In addition, the absolute values ​​of Δb of Examples 1 to 3 were lower than that of Comparative Example 1, and there was no difference in the optical density (OD value) of the non-printed portion after the test between Examples 1 to 3 and Comparative Example 1.

[0222] From these results, it was confirmed that the thermosensitive recording materials of Examples 1 to 3 containing the non-phenolic antioxidant were superior in light resistance to that of Comparative Example 1 containing no antioxidant.

[0223] (2) In the dynamic sensitivity test (color development property), when the printing energy was set to 0.40 mJ / dot, the optical density (OD value) of Examples 1 to 3 was 1.52 to 1.55, and the optical density (OD value) of Comparative Example 1 was 1.58. When the printing energy was set to 0.20 mJ / dot, the optical density (OD value) of Examples 1 to 3 was 1.07 to 1.16, and the optical density (OD value) of Comparative Example 1 was 1.23. When the printing energy was set to 0.16 mJ / dot, the optical density (OD value) of Examples 1 to 3 was 0.57 to 0.63, and the optical density (OD value) of Comparative Example 1 was 0.64. The optical density (OD value) of Examples 1 to 3 tended to be lower than that of Comparative Example 1. However, the decrease was about 2 to 13%, indicating that the color development property was good enough to be used as a thermal recording medium.

[0224] From these results, it was confirmed that the thermosensitive recording materials of Examples 1 to 3 containing the non-phenolic antioxidant had color development properties comparable to those of Comparative Example 1 containing no antioxidant.

[0225] (3) In the heat resistance test, the optical density (OD value) of the printed part of Examples 1 to 3 was 1.48 to 1.51, and the optical density (OD value) of the non-printed part was 0.11 to 0.12. The optical density (OD value) of the printed part of Comparative Example 1 was 1.52, and the optical density (OD value) of the non-printed part was 0.13. In particular, in the non-printed part, Examples 1 to 3 tended to have a lower increase in optical density (OD value) than Comparative Example 1.

[0226] From these results, it can be confirmed that the heat-sensitive recording materials of Examples 1 to 3 containing non-phenolic antioxidants have improved heat resistance compared with Comparative Example 1 which does not contain any antioxidant.

[0227] [Examples 4 to 6 and Comparative Example 2]

[0228] Examples 4 to 6 and Comparative Example 2 containing the same developer 2 were examined.

[0229] (4) In the light resistance test, the whiteness changes of Examples 4 to 6 were 0 to 0.6, and the whiteness change of Comparative Example 2 was 0.6, and no decrease in whiteness was observed. In addition, the whiteness after the test was also at the same level.

[0230] From these results, it was confirmed that Examples 4 to 6 containing a non-phenolic antioxidant showed comparable light resistance to that of Comparative Example 2 containing no antioxidant.

[0231] (5) In the dynamic sensitivity test, when the printing energy was set to 0.40 mJ / dot, the optical density (OD value) of Examples 4 to 6 was 1.15 to 1.17, and the optical density (OD value) of Comparative Example 2 was 1.20. When the printing energy was set to 0.20 mJ / dot, the optical density (OD value) of Examples 4 to 6 was 0.91 to 0.94, and the optical density (OD value) of Comparative Example 2 was 0.97. When the printing energy was set to 0.16 mJ / dot, the optical density (OD value) of Examples 4 to 6 was 0.35 to 0.42, and the optical density (OD value) of Comparative Example 2 was 0.40. The optical density (OD value) of Examples 4 to 6 tended to be lower than that of Comparative Example 2. However, the decrease was about 13% or less, showing a color development property that can be used well as a thermosensitive recording medium.

[0232] From these results, it was confirmed that the thermosensitive recording materials of Examples 4 to 6 containing the non-phenolic antioxidant had color development properties comparable to those of Comparative Example 2 containing no antioxidant.

[0233] (6) In the heat resistance test, the optical density (OD value) of the printed portion and the optical density (OD value) of the non-printed portion in each of Examples 4 to 6 and Comparative Example 3 were approximately the same.

[0234] From this result, it was confirmed that even if a non-phenolic antioxidant was contained, the heat resistance was comparable to that of Comparative Example 2 which did not contain an antioxidant.

[0235] [in conclusion]

[0236] According to the above measurement results, even if the thermosensitive recording medium contains a non-phenolic color developer and a non-phenolic antioxidant, it is not confirmed that the light resistance, color development and heat resistance are inferior to those of the thermosensitive recording medium without an antioxidant. In addition, it can be seen that if a non-phenolic antioxidant is contained in the thermosensitive recording medium, the light resistance can be improved while the heat resistance of the thermosensitive recording medium is well maintained, and the decrease in whiteness and yellowing can be suppressed.

[0237] Furthermore, non-phenolic color developers and non-phenolic antioxidants are superior in safety compared to phenolic color developers and antioxidants. Therefore, the use of non-phenolic color developers and non-phenolic antioxidants is also very effective from the perspective of environmental protection.

[0238] Hereinafter, modifications of the present invention will be described.

[0239] [Supplementary Note 1]

[0240] A thermosensitive recording medium is characterized in that a thermosensitive recording layer is laminated on a substrate, the thermosensitive recording layer contains a color former, a non-phenolic color developer and a non-phenolic antioxidant, and the non-phenolic antioxidant contains a phosphorus antioxidant.

[0241] [Appendix 2]

[0242] The thermosensitive recording material according to Supplementary Note 1, wherein the non-phenolic developer contains a compound represented by the following formula (1) and / or a compound represented by the following formula (2).

[0243] [Chemistry 17]

[0244]

[0245] (In formula (1), R 1 , R 2 , R 3 , R 4 , R 5 , R 7 , R 8 , R 9 , R 10 and R 11 Each independently represents a hydrogen atom or a substituent. 6 and R 12 Each independently represents a substituent. m represents an integer of 0 to 4. When m is 2 or more, a plurality of R 6 They may be the same or different. n represents an integer of 0 to 4. When n is 2 or more, a plurality of R 12 Can be the same or different.)

[0246] [Chemistry 18]

[0247]

[0248] (In formula (2), R 13 , R 14 , R 15 , R 16 , R 17 , R 19 , R 20 , R 21, R 22 and R 23 Each independently represents a hydrogen atom or a substituent. 18 represents a substituent. o represents an integer from 0 to 4. When o is 2 or more, a plurality of R 18 Can be the same or different.)

[0249] 〔Appendix 3〕

[0250] The thermosensitive recording material according to Appendix 1 or 2, wherein the non-phenolic developer contains a compound represented by the following formula (1a) and / or a compound represented by the following formula (2a).

[0251] [Chemistry 19]

[0252]

[0253] (The symbols in formula (1a) are the same as those in formula (1).)

[0254] [Chemistry 20]

[0255]

[0256] (The symbols in formula (2a) are the same as those in formula (2).

[0257] [Appendix 4]

[0258] The thermosensitive recording material according to any one of Appendixes 1 to 3, wherein the content of the non-phenolic developer is 10% by mass or more and 50% by mass or less based on the entire thermosensitive recording layer.

[0259] 〔Appendix 5〕

[0260] The thermosensitive recording material according to any one of Appendixes 1 to 4, wherein the content of the non-phenolic antioxidant is 5% by mass or more and 10% by mass or less based on the entire thermosensitive recording layer.

[0261] Industrial Applicability

[0262] As described above, the present invention is particularly useful for printing a thermosensitive recording medium such as a barcode.

[0263] Description of Reference Numerals

[0264] 1 Thermosensitive recording medium, 2 substrate, 3 thermosensitive recording layer, 4 intermediate layer, 5 top coating layer, 6 bottom coating layer.

Claims

1. A thermosensitive recording medium, characterized in that A heat-sensitive recording layer is laminated on a substrate. The heat-sensitive recording layer contains a coloring agent, a non-phenolic color developer and a non-phenolic antioxidant. The non-phenolic antioxidant contains a phosphorus antioxidant.

2. The thermosensitive recording medium according to claim 1, wherein The non-phenolic developer contains a compound represented by the following formula (1) and / or a compound represented by the following formula (2): In formula (1), R 1 , R 2 , R 3 , R 4 , R 5 , R 7 , R 8 , R 9 , R 10 and R 11 Each independently represents a hydrogen atom or a substituent; R 6 and R 12 Each independently represents a substituent; m represents an integer of 0 to 4; when m is 2 or more, multiple R 6 can be the same or different; n represents an integer of 0 to 4; when n is 2 or more, multiple R 12 Optional: same or different; In formula (2), R 13 , R 14 , R 15 , R 16 , R 17 , R 19 , R 20 , R 21 , R 22 and R 23 Each independently represents a hydrogen atom or a substituent; R 18 represents a substituent; o represents an integer from 0 to 4; when o is 2 or more, multiple R 18 Optional same or different.

3. The thermosensitive recording medium according to claim 2, wherein The non-phenolic developer contains a compound represented by the following formula (1a) and / or a compound represented by the following formula (2a): The symbols in formula (1a) are the same as those in formula (1); The symbols in formula (2a) are the same as those in formula (2).

4. The thermosensitive recording material according to any one of claims 1 to 3, wherein The content of the non-phenolic developer relative to the entirety of the thermosensitive recording layer is 10% by mass or more and 50% by mass or less.

5. The thermosensitive recording material according to any one of claims 1 to 4, wherein The content of the non-phenolic antioxidant is 5% by mass or more and 10% by mass or less based on the entirety of the thermosensitive recording layer.

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