Heat-sensitive data storage media

Abstract

Invention details;

Description

Thermal recording medium

[0001] The present invention relates to a thermosensitive recording medium, and more particularly to a thermosensitive recording medium which has low safety concerns and is excellent in color development, light resistance, and heat resistance.

[0002] Thermal recording media develop color through a chemical reaction when heated by a thermal head or the like, resulting in a recorded image. They are used in a wide range of applications, including as recording media for facsimiles, automatic ticket vending machines, and scientific measuring instruments, as well as for thermal recording labels and receipt paper for POS systems in retail stores and the like.

[0003] As mentioned above, thermal recording media are widely used. Therefore, various performance characteristics are required of thermal recording media. For example, when reading a barcode with a barcode reader, color development is required to improve the accuracy of the barcode reader. Furthermore, when exposed to strong light, including ultraviolet light, for a long period of time, the thermal recording media is required to have a property (light resistance) that prevents yellowing. Furthermore, excellent heat resistance is also required so that the color development of the printed areas does not decrease even when heated in a microwave oven or the like, while preventing color development in the non-printed areas.

[0004] As such a thermosensitive recording medium, for example, a thermosensitive recording medium has been proposed, which comprises a support and a thermosensitive recording layer containing a colorless or pale-colored electron-donating leuco dye and an electron-accepting color developer, the thermosensitive recording layer containing a phenolic color developer such as 4-hydroxy-4'-isopropoxydiphenyl sulfone as the color developer, and further containing a phenolic UV absorber having a phenolic hydroxyl group such as 2-(3'-t-butyl-2'-hydroxy-5'-methylphenyl)-5-chlorobenzotriazole as the UV absorber (see, for example, Patent Documents 1 to 3).

[0005] JP 2009-066897 A JP 2018-134818 A JP 2017-177577 A

[0006] There are safety concerns about the compounds having a phenolic hydroxyl group (phenolic compounds), such as the phenolic color developers and ultraviolet absorbers used in the above Patent Documents 1 to 3. Therefore, in recent years, from the viewpoint of environmental friendliness, there has been a demand for thermal recording media that use additives, such as color developers and ultraviolet absorbers, that do not have a phenol skeleton.

[0007] The present invention has been made in light of the above-mentioned circumstances, and aims to provide a thermal recording medium that has low safety concerns regarding endocrine disrupting substances, has excellent color development and light resistance, and also has excellent heat resistance.

[0008] As a result of extensive research to achieve the above object, the present inventors have found that by incorporating a color developer that does not have a phenol skeleton (non-phenolic color developer) and a specific ultraviolet absorber that does not have a phenol skeleton (non-phenolic ultraviolet absorber) in the thermal recording layer, it is possible to provide a thermal recording medium that has low safety concerns such as endocrine disrupting substances, and that is excellent in color development and light resistance, as well as heat resistance. The present invention was completed based on this finding.

[0009] That is, one aspect of the present invention provides a thermosensitive recording medium having a thermosensitive recording layer laminated on a substrate, wherein the thermosensitive recording layer contains a color former, a non-phenolic color developer, and a non-phenolic ultraviolet absorber.

[0010] Conventional thermosensitive recording media generally contain phenolic compounds as color developers and ultraviolet absorbers. However, phenolic compounds are considered endocrine disruptors and are therefore of concern regarding safety. In contrast, the thermosensitive recording media of the present invention contain non-phenolic compounds as color developers and ultraviolet absorbers in the thermosensitive recording layer. Therefore, the above-mentioned concerns do not arise. Furthermore, even when such non-phenolic compounds are used, the thermosensitive recording media of the present invention exhibit excellent color development, light resistance, and heat resistance.

[0011] In the thermal recording medium of the present invention, the non-phenolic ultraviolet absorber contains an oxalic acid anilide ultraviolet absorber, which can particularly improve light resistance.

[0012] In one embodiment of the thermosensitive recording medium of the present invention, the non-phenolic color developer preferably 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 R 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 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 may be the 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 R each independently represents a hydrogen atom or a substituent. 18 represents a substituent. o represents an integer of 0 to 4. When o is 2 or more, a plurality of R 18 may be the same or different.)

[0013] In one embodiment of the thermosensitive recording medium of the present invention, the non-phenolic color developer preferably 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).)

[0014] According to this configuration, a thermosensitive recording medium having excellent color development and heat resistance can be provided.

[0015] In another embodiment of the thermosensitive recording medium of the present invention, the content of the non-phenolic color developer relative to the entire thermosensitive recording layer is preferably 10% by mass or more and 50% by mass or less, which makes it possible to provide a thermosensitive recording medium having excellent color development properties and heat resistance.

[0016] In another embodiment of the thermosensitive recording medium of the present invention, the content of the non-phenolic ultraviolet absorber in the thermosensitive recording layer is preferably 5% by mass or more and 15% by mass or less, and this configuration makes it possible to provide a thermosensitive recording medium that is excellent in color development and heat resistance, as well as in light resistance, even when a non-phenolic ultraviolet absorber is used.

[0017] According to the present invention, it is possible to provide a thermosensitive recording medium which has low safety concerns regarding endocrine disrupting substances and is excellent in color development and light resistance, and further has excellent heat resistance.

[0018] FIG. 1 is a schematic cross-sectional view showing one embodiment of the thermosensitive recording medium of the present invention.

[0019] 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 ultraviolet absorber. The non-phenolic ultraviolet absorber contains an oxalic acid anilide ultraviolet absorber.

[0020] Hereinafter, an embodiment of the thermosensitive recording medium of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the following embodiments.

[0021] FIG. 1 is a schematic cross-sectional view showing one embodiment of the thermosensitive recording medium of the present invention.

[0022] As shown in FIG. 1, the thermosensitive recording material 1 of this embodiment has a laminated 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.

[0023] In this embodiment, the substrate 2 functions as a support for the thermal recording medium 1. Examples of the substrate 2 that can be used include fine paper, art paper, coated paper, kraft paper, and other types of paper, such as laminated paper formed by laminating a thermoplastic resin such as polyethylene to these paper substrates; synthetic paper; and porous materials such as nonwoven fabric. Transparent synthetic resin films, such as polypropylene film, polyethylene terephthalate film, polystyrene film, and polycarbonate film, can also be used. While the thickness of the substrate 2 is not particularly limited, a substrate 2 with excellent coatability can be obtained by adjusting the thickness of the substrate 2 to approximately 10 μm to 100 μm. Furthermore, a substrate 2 with excellent transparency can also be obtained.

[0024] In this embodiment, the undercoat layer 6 has functions such as heat insulation to prevent the dissipation of heat given from the thermal head, cushioning, etc. The undercoat layer 6 is formed, for example, by adding hollow particles as a filler to a binder.

[0025] By providing such a heat-insulating undercoat layer 6 on the thermal recording medium 1, the printing sensitivity is improved, and therefore the increase in the voltage applied to the thermal head can be suppressed, and as a result, burn-in of the thermal head can be suppressed.

[0026] The average particle size of the hollow particles added as a filler to the undercoat layer 6 is preferably 1 μm to 100 μm. This range improves the heat insulating properties of the undercoat layer 6. Here, the average particle size refers to the weight average particle size measured by laser diffraction. Measurement of the average particle size by laser diffraction can be performed using, for example, a Microtrac Bell product under the trade name "MT3300EX-II."

[0027] The hollow percentage of the hollow particles is preferably 30% to 99%. This range improves the heat insulating properties of the undercoat layer 6. The higher the hollow percentage of the hollow particles, the greater the heat insulating effect. This allows the color former to effectively develop color with a small amount of heat. In other words, increasing the hollow percentage improves the print quality of the thermal recording medium 1.

[0028] Here, the hollow ratio of the hollow particles is calculated by the following formula: Hollow ratio = {(volume of voids) / (volume of hollow particles)} x 100

[0029] The content of the hollow particles in the undercoat layer 6 is preferably 40 to 90 parts by mass relative to 100 parts by mass of the undercoat layer.

[0030] The material constituting the hollow particles is, for example, a thermoplastic resin, such as a polystyrene-based resin, a polyvinyl chloride-based resin, a polyvinylidene chloride-based resin, a polyvinyl acetate-based resin, a polyacrylate-based resin, a polyacrylonitrile-based resin, or a polybutadiene-based resin.

[0031] Note that fillers other than hollow particles may also be used for the undercoat layer 6. Examples include 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-formalin resin particles, polyolefin resin particles, etc. Furthermore, these fillers can be used alone or in combination of two or more.

[0032] Examples of the binder contained in the undercoat layer 6 include an acrylic-styrene copolymer, a styrene-butadiene copolymer, an acrylic-butadiene-styrene copolymer, a vinyl acetate resin, a vinyl acetate-acrylic acid copolymer, a styrene-acrylic acid ester copolymer, an acrylic acid ester-based resin, and a polyurethane-based resin.

[0033] Furthermore, as the binder, water-soluble polymers such as polyvinyl alcohol, starch and derivatives thereof, cellulose derivatives such as methoxycellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide-acrylic acid ester copolymers, acrylamide-acrylic acid ester-methacrylic acid terpolymers, alkali salts of styrene-maleic anhydride copolymers, alkali salts of isobutylene-maleic anhydride copolymers, polyacrylamide, sodium alginate, gelatin, and casein may be used.

[0034] The coating amount (dry weight) of the undercoat layer 6 is preferably 1 g / m 2 ~10g / m 2 is.

[0035] The thickness of the undercoat layer 6 is preferably 1 μm to 20 μm.

[0036] When the coating amount and thickness of the undercoat layer 6 are adjusted to fall within the above ranges, the undercoat layer 6 properly exhibits its heat insulating function.

[0037] In this embodiment, the thermosensitive recording layer 3 is a layer that develops color through a 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 color former, a non-phenolic color developer, and a non-phenolic ultraviolet absorber.

[0038] As the color former, a color former that develops color upon heating is a component that develops color through a chemical reaction when heated by a thermal head or the like, and forms a recorded image on the thermal recording medium 1 of this embodiment. As the color former that develops color upon heating, a commonly used known leuco dye can be used. Examples of the leuco dye include 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-toluidino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-p-toluidino)-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-isopentyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethoxypropyl-N-ethyl)amino-6-methyl-7-anilinofluoran, 3-(N-cyclohexyl-N-methyl)amino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-n-propyl)amino-6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-anilinofluoran Nilinofluoran, 3-diethylamino-6-methyl-7-p-toluidinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-8-methylfluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluoran, 3-diethylamino-7-(o-chloroanilino)fluoran, 3-diethylamino-7-chlorofluoran, 3-dibutylamino-6-methyl-7-bromofluoran, 3-dibutylamino-7-(o-chloroanilino)fluoran, 3-dipentylamino-6-methyl-7-anilinofluoran, 3-dimethylamino-5-methyl-7-methylfluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, crystal violet lactone, and the like can be used alone or in combination of two or more.

[0039] The particle size of the color former is preferably 0.1 to 1.0 μm. Because the color former reacts by melting, as the particle size increases, the reaction slows down and the sensitivity characteristics decrease. On the other hand, as the particle size decreases, the risk of color development at an unexpected temperature due to the heat generated when drying the paint increases. In this embodiment, by setting the particle size of the color former within the above range, the sensitivity characteristics and color development temperature of the color former can be appropriately adjusted. Here, the particle size refers to the 50% average particle size measured using a microtrack laser analysis / scattering particle size analyzer.

[0040] In this embodiment, in order to obtain excellent color development, the color former is preferably contained in an amount of about 10 to 20% by mass relative to the entire thermosensitive recording layer 3. The color developer, which will be described later, is preferably contained in a ratio of 1 to 3 parts by dry weight of 1 part color former to 1 part color former.

[0041] In this embodiment, the thermosensitive recording layer 3 contains a non-phenolic color developer rather than the conventionally widely used phenolic color developer. Non-phenolic color developers are various electron-accepting substances that react with the leuco dyes described above upon heating to cause the leuco dyes to develop color, and are compounds that do not have a phenolic hydroxyl group. The thermosensitive recording layer 3 contains a non-phenolic color developer, which intentionally avoids the use of phenolic color developers, which are endocrine disruptors and therefore pose safety concerns. In this embodiment, the thermosensitive recording layer 3 contains a non-phenolic color developer rather than a phenolic color developer, allowing the leuco dyes to develop color efficiently. Note that the thermosensitive recording layer 3 may inevitably contain trace amounts of phenolic compounds as impurities, etc., to the extent that they do not pose safety concerns as endocrine disruptors. Cases in which the thermosensitive recording layer 3 inevitably contains such trace amounts of phenolic compounds are considered to be within the scope of the present invention.

[0042] As such a non-phenolic color developer, any known color developer that does not have a phenolic hydroxyl group can be used without any particular limitation, and examples thereof include 2,2-bis[(4-methyl-3-phenoxycarbonylaminophenyl)urea]diphenyl sulfone, 4,4'-bis(p-tolylsulfonylaminocarbonylamino)diphenylmethane, 2'-(3-phenylureido)benzenesulfonanilide, and N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea.

[0043] The above-mentioned non-phenolic color developers can also be used as the color developer. However, the present inventors have found that compounds represented by the following formulas (1) and (2) are suitable from the viewpoint of further improving the heat resistance of the thermal recording medium 3.

[0044] (In formula (1), R 1 , R 2 , R 3 , R 4 , R 5 , R 7 , R 8 , R 9 , R 10 , and R 11 R 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 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 may be the same or different.)

[0045] (In formula (2), R 13 , R 14 , R 15 , R 16 , R 17 , R 19 , R 20 , R 21 , R 22 , and R 23 R each independently represents a hydrogen atom or a substituent. 18represents a substituent. o represents an integer of 0 to 4. When o is 2 or more, a plurality of R 18 may be the same or different.)

[0046] As the "substituent", an organic group other than a hydrogen atom can be used without any 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, and an arylamino group.

[0047] The above-mentioned "halogen atom" includes a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0048] Examples of the "alkyl (group)" include straight-chain or branched-chain alkyl groups having 1 to 12 carbon atoms, such as a methyl group, ethyl group, normal propyl group, isopropyl group, normal butyl group, isobutyl group, secondary butyl group, tertiary butyl group, normal pentyl group, isopentyl group, tertiary pentyl group, neopentyl group, 2,3-dimethylpropyl group, 1-ethylpropyl group, 1-methylbutyl group, 2-methylbutyl group, normal hexyl group, isohexyl group, 2-hexyl group, 3-hexyl group, 2-methylpentyl group, 3-methylpentyl group, normal heptyl group, normal octyl group, normal nonyl group, normal decyl, normal undecyl group, and normal dodecyl group.

[0049] Examples of the "alkoxy group" include straight-chain or branched-chain alkoxy groups having 1 to 8 carbon atoms, such as a methoxy group, an ethoxy group, a normal propoxy group, an isopropoxy group, a normal butoxy group, a secondary butoxy group, a tertiary butoxy group, a normal pentyloxy group, an isopentyloxy group, a tertiary pentyloxy group, a neopentyloxy group, a 2,3-dimethylpropyloxy group, a 1-ethylpropyloxy group, a 1-methylbutyloxy group, a normal hexyloxy group, an isohexyloxy group, a normal heptyloxy group, and a normal octyloxy group.

[0050] Examples of the above-mentioned "aryl (group)" include aromatic hydrocarbon groups having 6 to 10 carbon atoms, such as a phenyl group, a 1-naphthyl group, and a 2-naphthyl group.

[0051] In the above "dialkylamino group," the two alkyl groups may be the same or different.

[0052] The compound represented by formula (1) is preferably a compound represented by the following formula (1a), from the viewpoint of imparting excellent color development and heat resistance to the thermosensitive recording medium 1. Specific examples include N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-xylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(mesitylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(o-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m-toluenesulfonyloxy)phenyl]urea, and N,N'-di-[3-(benzenesulfonyloxy)phenyl]urea, all of which are represented by the following formula (1b).

[0053] (The symbols in formula (1a) are the same as those in formula (1).)

[0054] The compound represented by formula (2) is preferably a compound represented by the following formula (2a), from the viewpoint of imparting excellent color development and heat resistance to the thermal recording medium 1. Specifically, there can be mentioned [3-(3-phenylureido)phenyl]-4-methylbenzenesulfonate represented by the following formula (2b).

[0055] (The symbols in formula (2a) are the same as those in formula (2).)

[0056] In this embodiment, the thermosensitive recording layer 3 may contain a single non-phenolic color developer, or may contain two or more types of non-phenolic color developers.

[0057] By using at least one or both of the compound represented by the above general formula (1) and the compound represented by the above general formula (2) as a non-phenolic color developer in the thermal recording layer 3, the heat resistance and color development of the thermal recording material 1 can be improved.

[0058] In this embodiment, the content of the non-phenolic color developer in the entire thermosensitive recording layer 3 is preferably 10% by mass or more and 50% by mass or less. A configuration in which the content of the non-phenolic color developer is 10% by mass or more is preferred in that it can prevent poor color development (low optical density) due to a lack of color developer. Furthermore, a configuration in which the content of the non-phenolic color developer is 50% by mass or less is preferred in that it can prevent poor color development (low optical density) due to an excess of color developer (i.e., a lack of dye).

[0059] In this embodiment, as described above, a phenolic color developer is not intentionally used as a color developer in the thermosensitive recording layer 3. However, trace amounts of phenolic compounds may be unavoidably contained as impurities in non-phenolic color developers. Examples of such impurities include compounds in which sulfonic acid esters (-SO2-O-) and alkoxy groups, aryloxy groups, alkylcarbonyloxy groups, and the like contained as substituents in non-phenolic color developers represented by the above formulas (1) and / or (2) are wholly or partially hydrolyzed. Phenol compounds contained as such impurities may also function as color developers.

[0060] In this embodiment, the above-mentioned phenolic compounds, which may be inevitably contained as impurities in the thermosensitive recording layer 3, may be contained in trace amounts at the ppm level (for example, about 100 ppm or less relative to the entire thermosensitive recording layer 3) that can be detected by instrumental analysis. At such trace amounts, there are no safety concerns such as endocrine disruptors, and it is considered that the compounds do not substantially function as color developers.

[0061] In this embodiment, the thermosensitive recording layer 3 contains a non-phenolic UV absorber rather than the conventionally widely used phenolic UV absorber. A non-phenolic UV absorber is a substance that absorbs UV light and is a compound that does not have a phenolic hydroxyl group. The thermosensitive recording layer 3 contains a non-phenolic UV absorber, which is intended to avoid the use of phenolic compounds that are endocrine disruptors and therefore pose safety concerns. In this embodiment, the thermosensitive recording layer 3 contains a non-phenolic UV absorber rather than a phenolic UV absorber, thereby improving the light resistance and heat resistance of the thermosensitive recording medium 1. Note that the thermosensitive recording layer 3 of this embodiment may also contain a phenolic UV absorber to an extent that does not raise safety concerns as an endocrine disruptor and does not affect color development, light resistance, or heat resistance, which is within the scope of the present invention.

[0062] As such a non-phenolic UV absorber, any known UV absorber that does not have a phenolic hydroxyl group can be used without any particular limitation. For example, an oxalic acid anilide UV absorber can be used. The present inventors have found that a compound represented by the following formula (3) is suitable from the viewpoint of further improving the light resistance and heat resistance of the thermal recording medium 1.

[0063] (In formula (3), R 24 , R 25 , R 26 , R 27 , R 28 , R 29 , R 30 , R 31 , R 32 , and R 33 each independently represents a hydrogen atom or a substituent.

[0064] In formula (3), R 24 ~R 33 The definition and examples of the substituent represented by are the same as those in formula (1).

[0065] Specific examples of the compound represented by formula (3) include oxalic acid bisanilide, 2-ethoxy-2'-ethyloxalic acid bisanilide, (N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)ethanediamide), 2-ethoxy-5-t-butyl-2'-ethyloxalic acid bisanilide, 2-ethoxy-3'-dodecyloxalic acid bisanilide, etc. In this embodiment, the thermosensitive recording layer 3 may contain a single non-phenolic ultraviolet absorber, or may contain two or more types of non-phenolic ultraviolet absorbers.

[0066] In this embodiment, the content of the non-phenolic UV absorber in the entire thermosensitive recording layer 3 is not particularly limited, but is preferably 5% by mass or more and 15% by mass or less. A non-phenolic UV absorber content of 5% by mass or more is preferable in that it can impart excellent light resistance to the thermosensitive recording medium 1 of this embodiment. A non-phenolic UV absorber content of 15% by mass or less is preferable in that it can impart excellent color development properties to the thermosensitive recording medium 1 of this embodiment.

[0067] In this embodiment, the content of the non-phenolic ultraviolet absorber relative to the total amount of ultraviolet absorbers contained in the thermosensitive recording layer 3 is not particularly limited, but from the viewpoint of improving light resistance and heat resistance while reducing safety concerns such as endocrine disrupting substances, it is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more.

[0068] In this embodiment, the content of the oxalic acid anilide-based ultraviolet absorber relative to the total amount of ultraviolet absorbers contained in the thermosensitive recording layer 3 is not particularly limited, but from the viewpoint of improving light resistance and heat resistance while reducing safety concerns such as endocrine disrupting substances, it is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more.

[0069] Furthermore, the heat-sensitive recording layer 3 may contain additives such as binders, sensitizers, lubricants, fillers, storage improvers, and pigments, as needed.

[0070] Examples of binders 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, polyacrylic acid esters, 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, polyvinylpyrrolidone, acrylic acid esters, acrylonitrile, methyl vinyl ether, etc. These binders can be used alone or in combination of two or more.

[0071] Examples of sensitizers include those that are solid at room temperature and preferably have a melting point of about 70° C. or higher, such as stearic acid, stearic acid amide, stearic acid anilide, methylolstearic acid amide, methylenebisstearic acid amide, ethylenebisstearic acid amide, 1-benzyloxynaphthalene, 2-benzyloxynaphthalene, 2,6-diisopropylnaphthalene, 1,2-diphenoxyethane, 1,2-diphenoxymethylbenzene, 1,2-bis(3,4-dimethylphenol)ethane, 1,2-bis(3-methylphenoxy)ethane, 1,2-bis(4-methylphenoxy)ethane, di(p-chlorobenzyl oxalate), di(p-methylbenzyl) 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.

[0072] 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, and oils such as silicone oil and whale oil. These lubricants can be used alone or in combination of two or more.

[0073] 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-formalin resin particles, polyolefin resin particles, etc. These fillers can be used alone or in combination of two or more.

[0074] Examples of the storage improver include sodium 2,2'-methylenebis(4,6-di-t-butylphenyl)phosphite, 4,4,butylidenebis(3-methyl-6-t-butylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, tris(2,6-dimethyl-4-t-butyl-3-hydroxy benzyl) isocyanurate, 4-(2-methylglycyloxy)-4'-benzyloxydiphenyl sulfone, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), diethylthiourea, zinc dibutyldithiocarbamate, 4,4'-thiobis(6-t-butyl-m-cresol), and a urea-urethane compound represented by the following formula (4):

[0075]

[0076] These preservatives may be used alone or in combination of two or more. Known surfactants may also be contained.

[0077] Fresh foods such as meat and fish are sold in packs wrapped in plastic wrap, with a label affixed to the pack showing the price and other information. Packs are usually stacked for display, meaning that the label may come into contact with the plastic wrap that encases another pack. This plastic wrap contains a plasticizer to impart plasticity. If packs are left stacked for a long period of time, the plasticizer may migrate to the label, affecting the printing. Therefore, it is preferable for a thermosensitive recording medium to have excellent "plasticizer resistance," i.e., a property that makes it difficult for the printing to fade even if the plasticizer migrates.

[0078] In this embodiment, from the viewpoint of print storage stability, particularly plasticizer resistance, the thermosensitive recording layer 3 preferably contains a storage stability improver, and particularly preferably contains a urea-urethane compound represented by the above formula (4). By containing a storage stability improver, particularly a urea-urethane compound represented by formula (4), the thermosensitive recording layer 3 increases the reaction efficiency between the leuco dye and the developer, making it easier to generate an electron transfer complex and less likely to cause a reverse reaction, resulting in excellent color development of the thermosensitive recording medium and less reduction in color density, and is thought to result in excellent print storage stability, particularly plasticizer resistance.

[0079] The urea-urethane compound represented by formula (4) is specifically three types represented by the following formulas (4a) to (4c), which may be used alone or in combination of two or more types.

[0080]

[0081] In this embodiment, when the thermosensitive recording layer 3 contains a storage stability improver, the content of the storage stability improver relative to the entire thermosensitive recording layer 3 is preferably 1% by mass or more and 20% by mass or less. A configuration in which the content of the storage stability improver is 1% by mass or more is preferred in that it can suppress a decrease in color density due to plasticizers and the like, thereby improving print storage stability, particularly plasticizer resistance. Furthermore, a configuration in which the content of the storage stability improver is 20% by mass or less is preferred in that it prevents poor color development (low optical density).

[0082] In this embodiment, when the thermosensitive recording layer 3 contains a storage stability improver, the content ratio of the storage stability improver to the non-phenolic color developer (storage stability improver / non-phenolic color developer) is preferably 1 / 20 to 1 / 1. A configuration in which the content ratio is 1 / 1 or less is preferred in that it can prevent poor color development (low optical density). Furthermore, a configuration in which the content ratio is 1 / 20 or more is preferred in that it can suppress a decrease in color development density due to plasticizers and the like, thereby improving print storage stability, particularly plasticizer resistance.

[0083] In this embodiment, when the thermosensitive recording layer 3 contains a ureaurethane compound represented by formula (4), the content of the ureaurethane compound represented by formula (4) in the entire thermosensitive recording layer 3 is preferably 1% by mass or more and 20% by mass or less. A configuration in which the content of the ureaurethane compound is 1% by mass or more is preferred in that it can suppress a decrease in color density due to plasticizers and the like, and provides excellent print storage stability, particularly plasticizer resistance. Furthermore, a configuration in which the content of the ureaurethane compound is 20% by mass or less is preferred in that it prevents poor color development (low optical density).

[0084] In this embodiment, when the thermosensitive recording layer 3 contains a ureaurethane compound represented by formula (4), the content ratio of the ureaurethane compound represented by formula (4) to the non-phenolic color developer (ureaurethane compound / non-phenolic color developer) is preferably 1 / 20 to 1 / 1. A configuration in which the content ratio is 1 / 1 or less is preferred in that it can prevent poor color development (low optical density). Furthermore, a configuration in which the content ratio is 1 / 20 or more is preferred in that it can suppress a decrease in color development density due to plasticizers and the like, and provides excellent print storage stability, particularly plasticizer resistance.

[0085] In this embodiment, the content of the urea-urethane compound represented by formula (4) relative to the total amount of the storage stability improver contained in the thermosensitive recording layer 3 is not particularly limited, but is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more, from the viewpoints of being able to suppress a decrease in color density due to a plasticizer or the like and of providing excellent print storage stability, in particular, plasticizer resistance.

[0086] In this embodiment, by providing the intermediate layer 4 on the thermosensitive recording layer 3, it is possible to obtain a thermosensitive recording medium 1 that is excellent in water resistance, chemical resistance, plasticizer resistance, and the like.

[0087] Examples of materials that can be used to form the intermediate layer 4 include aqueous resins such as polyvinyl alcohol, modified polyvinyl alcohol, starch, modified starch, casein, gelatin, glue, gum arabic, polyamide, polyacrylamide, modified polyacrylamide, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl acetate, polyacrylic esters, styrene-maleic anhydride copolymers, isobutylene-maleic anhydride copolymers, diisobutylene-maleic anhydride copolymers, vinyl acetate-maleic anhydride copolymers, methyl vinyl-maleic anhydride copolymers, isopropylene-maleic anhydride copolymers, styrene-butadiene copolymers, maleic acid copolymers, polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinyl acetate copolymers, polyurethane, polystyrene, polyvinylpyrrolidone, acrylic esters, acrylonitrile, and methyl vinyl ether polyvinyl alcohol. The term "aqueous resin" refers to a resin component in which the compound is dispersed or dissolved in water. These materials can be used alone or in combination.

[0088] The transparency of the resin can be improved by using a resin having a water-soluble portion, such as a polyvinyl alcohol (PVA) resin, which is a resin having a hydroxy group as a hydrophilic structural unit, or a resin having a core-shell structure in which hydrophobic core particles are coated with a water-soluble shell polymer, such as a core-shell acrylic resin.

[0089] As the core-shell type resin, for example, a core-shell type acrylic resin commercially available under the name "Barrier Star (manufactured by Mitsui Chemicals Inc.)" can be used.

[0090] The coating amount (dry weight) of the intermediate layer 4 is preferably 0.3 g / m 2 ~10g / m 2 is.

[0091] The topcoat layer 5 improves the thermal head compatibility of the thermal recording medium 1 with a thermal head, thereby ensuring smooth color development in the thermal recording layer 3. Specifically, this means that color development in the thermal recording layer 3 is carried out so as to minimize problems such as the accumulation of deposits on the thermal head and distortion of the surface of the thermal recording medium 1 due to heat.

[0092] In this embodiment, the top coat layer 5 of the thermal recording medium 1 serves to reduce thermal head wear and prevent shortening of the thermal head's lifespan without adding elastic particles or the like. This means improving thermal head suitability. It is also necessary to improve the top coat layer 5's sticking resistance to the thermal head. Here, sticking resistance means that the components of the top layer of the thermal recording medium are less likely to melt due to the heat of the thermal head and stick to the thermal head. More specifically, it means that the thermal recording medium is less likely to suffer from problems such as partial printing failure or distortion of the printed surface.

[0093] The top coat layer 5 of this embodiment has depressions on its surface, such as evaporation holes due to evaporation of water, and cracks, which reduce the contact area between the surface of the top coat layer 5 and the thermal head.

[0094] In this way, in order to generate recesses, particularly cracks, on the surface of the top coat layer 5, a coating liquid containing hydrophobic resin particles is used as the coating liquid for forming the top coat layer 5.

[0095] That is, in this embodiment, the top coat layer 5 uses, as a binder, an emulsion of hydrophobic resin particles, for example, an emulsion in which hydrophobic acrylic resin particles are dispersed in water.

[0096] In this way, the binder of the top coat layer 5 is an emulsion of hydrophobic resin particles, and no water-soluble polymer is used.

[0097] A coating liquid containing a water-soluble polymer is less likely to aggregate when applied and dried, and a flexible coating film is formed, so that cracks due to shrinkage do not occur in the top coat layer 5 .

[0098] In contrast, when an emulsion of hydrophobic resin particles is applied and dried, the hydrophobic resin particles aggregate and shrink due to evaporation, causing cracks that become depressions on the surface of the top coat layer 5.

[0099] These cracks are formed by shrinkage due to aggregation of hydrophobic resin particles, and therefore remain within the top coat layer 5 and do not reach the intermediate layer 4 .

[0100] In addition, in this embodiment, in order to form evaporation holes on the surface of the top coat layer 5 due to evaporation of water, which will become depressions, the three layers of the thermal recording layer 3, the intermediate layer 4, and the top coat layer 5 are simultaneously coated using a curtain coater.

[0101] In the curtain coater, the coating liquids for forming the thermosensitive recording layer 3, intermediate layer 4, and top coat layer 5 are ejected from a plurality of slits, respectively, and the layered coating liquids are continuously run. At this time, the coating liquids are allowed to fall freely onto the undercoat layer 6 formed in advance on the substrate 2 and coated thereon.

[0102] In such simultaneous coating of three layers by a curtain coater, when the top coat layer 5 dries, the hydrophobic resin particles begin to aggregate as described above, causing cracks, which then allow water vapor to escape through the cracks, drying and solidifying the semi-dry intermediate layer 4 and thermosensitive recording layer 3. Most of the water vapor in the intermediate layer 4 and thermosensitive recording layer 3 is released through the cracks, but some of the water vapor is released by forming evaporation holes in the top coat layer 5. As a result, the cracks and evaporation holes are formed near the top coat layer 5.

[0103] In this embodiment, the evaporation holes formed in the top coat layer 5 are limited to the intermediate layer 4. Therefore, even if oil or the like adheres to the surface of the top coat layer 5, which is the uppermost layer, it does not reach the thermosensitive recording layer 3, and the thermosensitive recording layer 3 does not become discolored or otherwise become discolored.

[0104] The top coat layer 5 may contain additives such as a lubricant, a crosslinking agent, a dispersant, an antifoaming agent, a water-resistant agent, and a filler, as required.

[0105] Examples of the lubricant include polyethylene, zinc stearate, etc. Examples of the cross-linking agent include zirconium carbonate, etc.

[0106] Examples of fillers include 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-formalin resin particles, and polyolefin resin particles. These fillers can be used alone or in combination of two or more. The particle diameter of the filler contained in the top coat layer 5 is preferably 1.0 μm or less.

[0107] In this embodiment, the thermal recording medium 1 is manufactured using, as the coating liquid for forming the top coat layer 5, an aqueous dispersion suspension containing an emulsion of a hydrophobic acrylic resin dispersed in water, polyethylene wax as a lubricant, and calcium carbonate as a pigment in a dry mass ratio of 4:3:3.

[0108] The coating amount (dry weight) of the top coat layer 5 is 1 g / m 2 Let's say.

[0109] According to this embodiment, as described above, the surface of the top coat layer 5, which is the uppermost layer of the thermal recording medium 1, is formed with cracks that become recesses and moisture evaporation holes, resulting in an uneven surface of the top coat layer 5. This reduces the contact area between the top coat layer 5 and the thermal head, reduces thermal head wear, improves thermal head suitability, and improves sticking resistance.

[0110] The thickness of the top coat layer 5 is adjusted to, for example, less than 1 μm. In this embodiment, it is adjusted to about 0.8 μm. This shortens the distance from the surface of the top coat layer 5 to the thermosensitive recording layer 3, allowing heat from the thermal head to be efficiently conducted to the thermosensitive recording layer 3. Furthermore, the thin thickness contributes to cost reduction.

[0111] Furthermore, because the cracks on the surface of the top coat layer 5 propagate in the thickness direction within the top coat layer 5, the cracks cause the top coat layer 5 to be divided in a direction perpendicular to the thickness direction, i.e., in the horizontal direction. This suppresses the dissipation of heat from the thermal head in the horizontal direction. As a result, the heat from the thermal head is efficiently conducted to the underlying thermal recording layer 3 located in the thickness direction.

[0112] In order to reduce the contact area between the top coat layer 5 and the thermal head, the roughly circular moisture evaporation holes preferably have an average diameter of 2 μm or more.

[0113] The average diameter of the evaporation holes is determined by observing the surface of the top coat layer 5 with an electron microscope (SEM) and calculating the average diameter of the evaporation holes per unit area, for example, 1 mm 2 The number of evaporation holes is calculated by measuring the diameter of the evaporation holes per 1 mm. 2 Preferably, there are 30 or more, and more preferably 40 or more per unit area.

[0114] In the thermosensitive recording medium 1 of this embodiment, the surface of the top coat layer 5 can be made to have, for example, a large number of evaporation holes and a small number of cracks by adjusting the composition of the top coat layer 5. Alternatively, the surface of the top coat layer 5 can be made to have only a large number of evaporation holes without cracks.

[0115] In this embodiment, the three layers of the thermosensitive recording layer 3, the intermediate layer 4, and the top coat layer 5 are simultaneously coated in multiple layers using a curtain coater, but this is not limited to simultaneous multilayer coating, and the thermosensitive recording layer 3, the intermediate layer 4, and the top coat layer 5 may be formed individually and sequentially.

[0116] In this embodiment, the undercoat layer 6 and the intermediate layer 4 are formed on the substrate 2, but in other embodiments of the present invention, at least one of the undercoat layer 6 and the intermediate layer 4 may be omitted.

[0117] The thermosensitive recording medium of the above embodiment has a thermosensitive recording layer having the above-described structure, and therefore has excellent light resistance, color development properties, and heat resistance.

[0118] The whiteness change (%) of the thermosensitive recording medium of this embodiment, as shown by the following formula, is preferably −5% or more, more preferably −4.5% or more, and even more preferably −4% or more, from the viewpoint of excellent lightfastness and suppressing a decrease in whiteness due to light irradiation. Whiteness change (%) = whiteness after leaving for 100 hours at an illuminance of 5000 Lux - whiteness before test The whiteness is determined in accordance with JIS P 8148. The minus sign (-) in the whiteness change (%) indicates the amount of decrease in whiteness, and the closer to 0%, the less the decrease in whiteness and the more excellent the lightfastness.

[0119] The absolute value of Δb shown by the following formula for the thermosensitive recording medium of this embodiment is preferably 2.3 or less, more preferably 2.2 or less, even more preferably 2.1 or less, and particularly preferably 2 or less, from the viewpoint of excellent light resistance and suppressing yellowing or bluing (bluishness) due to light irradiation. Δb = b value after leaving for 100 hours at an illuminance of 5000 Lux - b value before test. The b value is the L defined in JIS Z8781-4:2013. * a * b * It represents chromaticity (b value) in color space. The b value indicates a change from blue to yellow, with a larger b value indicating a yellower color and a smaller b value indicating a bluer color. Δb indicates the amount of change in the b value, with a positive value indicating yellowing and a negative value indicating blueing. Therefore, the closer the absolute value of Δb is to 0, the less yellowing or blueing occurs, indicating excellent lightfastness.

[0120] The dynamic sensitivity (OD value) of the printed portion of the thermosensitive recording medium of this embodiment at 0.16 mj / dot is preferably 0.5 or more, more preferably 0.6 or more, from the viewpoint of excellent color development. The dynamic sensitivity (OD value) of the printed portion of the thermosensitive recording medium of this embodiment at 0.20 mj / dot is preferably 1 or more, more preferably 1.1 or more, from the viewpoint of excellent color development. The dynamic sensitivity (OD value) of the printed portion of the thermosensitive recording medium of this embodiment at 0.40 mj / dot is preferably 1.3 or more, more preferably 1.4 or more, from the viewpoint of excellent color development. The dynamic sensitivity (OD value) is measured in the examples described below, and a higher value indicates better color development.

[0121] The OD value of the non-printed area in the heat resistance evaluation example of the thermal recording medium of this 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 allowing the printed area to be clearly identified even after cooking with heat in a microwave oven or the like.

[0122] In the following examples and comparative examples, a thermal recording medium containing a non-phenolic color developer and a non-phenolic UV absorber in the thermal recording layer was prepared, and the color development, light resistance, and heat resistance were evaluated. However, the present invention is not limited to these examples.

[0123] (Examples 1 to 6, Comparative Examples 1 to 3) (Preparation of Thermal Recording Medium) <Undercoat Layer> The substrate was a 70 g / m 2 A coating liquid for an undercoat layer was prepared by mixing and stirring 70 parts by mass of hollow particles (solid content concentration 26.5%, Ropeake HP-1055: Rohm and Haas Japan Co., Ltd.), 10 parts by mass of modified styrene butadiene latex (solid content concentration 49%), and 20 parts by mass of water onto a sheet of high-quality paper (thickness: 80 μm) of 1000 kJ / cm², and then drying the mixture until the coating weight upon drying was 3.0 g / m². 2 An undercoat layer having a thickness of 5 μm was formed.

[0124] <Thermal Recording Layer> A coating liquid for forming a thermal recording layer shown in Table 1 was prepared, and the prepared coating liquid for forming a thermal recording layer was applied to the undercoat layer described above in an amount of 4.0 g / m2 in terms of dry weight. 2 After coating, the mixture was dried to form a thermosensitive recording layer having a thickness of 3.5 μm on the undercoat layer. In Table 1, the numerical values ​​of each compounded material indicate the weight ratio when dried.

[0125] The leuco dye used was 3-dibutylamino-6-methyl-7-anilinofluorolane with a particle size of 0.6 to 0.7 μm, the developer 1 was [3-(3-phenylureido)phenyl]-4-methylbenzenesulfonate represented by the above formula (2b), and the developer 2 was N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea represented by the above formula (1b). The ultraviolet absorber 1 was N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)ethanediamide (manufactured by SONGWON), an oxalic acid anilide, and the ultraviolet absorber 2 was α-3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl)-1-oxopropyl-ω-hydroxypoly(oxyethylene), a benzotriazole (phenol).

[0126] The sensitizer used was 1,2-bis(3-methylphenoxy)ethane (dispersed in a PVA aqueous solution to give a dispersion with a solids concentration of 20%), the binder used was a styrene-acrylic copolymer emulsion, the pigment used was calcium carbonate (dispersed in a 5% aqueous solution of sodium hexametaphosphate to give a dispersion with a solids concentration of 30%), and the lubricant used was a zinc stearate emulsion.

[0127] <Intermediate layer> An acrylic emulsion (solid concentration 30%) was applied onto the above-mentioned heat-sensitive recording layer and dried to give a coating weight of 1.6 g / m 2 An intermediate layer having a thickness of 1.5 μm was formed.

[0128] <Top Coat Layer> A liquid obtained by mixing and stirring 40 parts by mass of acrylic emulsion (solid content concentration 20%), 5 parts by mass of calcium carbonate, 15 parts by mass of polyethylene wax (solid content concentration 40%), and 40 parts by mass of water was applied onto the intermediate layer and dried to a coating weight of 1.0 g / m2 when dried. 2 A top coat layer having a thickness of 0.9 μm was formed.

[0129] By the above method, the thermosensitive recording media of Examples 1 to 6 and Comparative Examples 1 to 3 were prepared.

[0130]

[0131] (Lightfastness Evaluation) In the lightfastness evaluation, the optical density (OD value of printed area / OD value of non-printed area), yellowing (yellowing), and whiteness changes were measured for the printed and non-printed areas of each thermosensitive recording medium in each Example and Comparative Example. The procedure for lightfastness evaluation is described below.

[0132] Printing was performed on the prepared thermal recording medium using a thermal paper printing tester (manufactured by Okura Engineering Co., Ltd., product name: Pulse Simulator TH-M2 / PP) under the following conditions: printing speed 50 mm / sec, applied voltage 17.0 V, head resistance value 870 Ω, pulse width 0.488 to 1.394 ms, and printing energy 0.40 mJ / dot.

[0133] The distance from the fluorescent lamp was confirmed using an illuminance meter so that the illuminance was 5,000 Lux, and the thermal recording medium printed as described above was left at that position for 100 hours.

[0134] The optical densities (OD value of printed area / OD value of non-printed area) of the printed and non-printed areas of the sample thermal recording medium before the test and after the above-mentioned storage period were measured using a spectrophotometer (product name: eXact, manufactured by Videojet X-Rite Inc.).

[0135] The whiteness (%) and color tone (L, a, b) of the sample of the thermosensitive recording medium were measured before the test and after the above-mentioned storage period. The whiteness was measured in accordance with JIS P 8148 using a photovoltaic reflection densitometer (manufactured by Tokyo Denshoku Co., Ltd., product name: TC-6DS / A).

[0136] The color tone (L, a, b) was measured using a color difference meter (trade name: SpectroEye, manufactured by Videojet X-Rite Inc.).

[0137] The measurement results of the above test are shown in Table 2. In the measurement results in Table 2, a larger optical density (OD value) in the printed and non-printed areas (i.e., lower light reflectance) indicates more color development (color development closer to black), while a smaller value (i.e., higher light reflectance) indicates insufficient color development. The whiteness (%) increases as the value increases. Of the color tone indicators (L, a, b), (L) indicates a change from black to white, and the larger the (L) value, the closer the color is to white. (a) indicates a change from green to red, and the larger the (a) value, the closer the color is to red. (b) indicates a change from blue to yellow, and the larger the (b) value, the closer the color is to yellow. The lightfastness of each thermal recording medium was evaluated based on these color changes.

[0138] (Dynamic Sensitivity Evaluation) In the dynamic sensitivity test, printing was performed on each thermosensitive recording medium in each Example and Comparative Example using different printing energies, and the optical density (OD value of the printed area) at each printing energy was measured. Based on the measurement results, the dynamic sensitivity of each thermosensitive recording medium in each Example and Comparative Example was evaluated. The procedure for the dynamic sensitivity test is described below.

[0139] The prepared thermal recording medium was printed using a thermal paper printing tester (manufactured by Okura Engineering Co., Ltd., trade name: Pulse Simulator TH-M2 / PP) under the following conditions: printing speed 50 mm / sec, applied voltage 17.0 V, head resistance value 870 Ω, pulse width 0.488 to 1.394 ms, and printing energy 0.16 mJ / dot, 0.20 mJ / dot, and 0.40 mJ / dot. The optical density (OD value) under each printing energy condition was measured using a spectrophotometer (manufactured by X-rite, trade name: eXact).

[0140] The measurement results of the above test are shown in Table 2. As with the above light fastness test, in the measurement results in Table 2, a larger optical density (OD value) indicates better color development, and a smaller value indicates insufficient color development. For example, if the optical density (OD value) is large despite the low printing energy, it is evaluated as "good color development." On the other hand, if the optical density (OD value) is small despite the high printing energy, it is evaluated as "poor color development." In other words, the dynamic sensitivity test is an evaluation of color development.

[0141] (Heat Resistance Evaluation) In the heat resistance test, heat was applied to the printed and non-printed areas of each thermosensitive recording medium in each Example and Comparative Example, and the optical density (OD value of the printed area) of the printed and non-printed areas was measured. From the measurement results, the heat resistance of each thermosensitive recording medium in each Example and Comparative Example was evaluated. The procedure for the heat resistance test is described below.

[0142] Printing was performed on the prepared thermal recording medium using a thermal paper printing tester (manufactured by Okura Engineering Co., Ltd., product name: Pulse Simulator TH-M2 / PP) under the following conditions: printing speed 50 mm / sec, applied voltage 17.0 V, head resistance value 870 Ω, pulse width 0.488 to 1.394 ms, and printing energy 0.40 mJ / dot.

[0143] A container (diameter: 12 cm, capacity: 220 cc) containing 100 g of water was covered with a vinyl chloride wrap (thickness: 10 μm), and a sample of the thermal recording medium printed above (length: 3 cm, width: 4 cm) was attached to the wrap.

[0144] Next, ten through holes were made in the wrap using a safety pin to allow steam to escape during heating. The through holes were made to avoid the sample area and to ensure that the distance between the through holes was uniform.

[0145] Next, the container was heated for 1 minute in a microwave oven (1500 W), and then the optical densities of the printed and non-printed areas of the sample thermosensitive recording medium (OD value of printed area / OD value of non-printed area) were measured using a spectrophotometer (manufactured by X-rite, product name: eXact).

[0146] The results of the above test are shown in Table 2. In this heat resistance evaluation, a low optical density (OD value) in the non-printed area and a high optical density (OD value) in the printed area indicate that the thermosensitive recording medium has a low response to heat. In other words, the optical density (OD value) represents the degree of color development in the printed or non-printed area when the thermosensitive recording medium is heated in a microwave oven and steam heat is applied to the thermosensitive recording medium. Therefore, it is preferable that the non-printed area not develop color as much as possible, so a low optical density (OD value) can be evaluated as having "good heat resistance." On the other hand, the printed area is checked to ensure that the colored portion does not disappear due to steam heat. Specifically, a high optical density (OD value) in the printed area indicates that the printed area does not respond much to heat.

[0147]

[0148] <Verification Results> The following was confirmed from the results shown in Table 2. [Examples 1 to 4 and Comparative Examples 1 and 2] Examples 1 to 4 and Comparative Examples 1 and 2, which contain the same color developer 1, will be examined.

[0149] (1) In the lightfastness test, Examples 1 to 4 showed smaller whiteness changes and higher whiteness after the test than Comparative Example 1. This is presumably due to the inclusion of UV absorber 1 (non-phenolic UV absorber) in Examples 1 to 4. On the other hand, Comparative Example 2, which contained the same developer 1 as Examples 1 to 4 but a different UV absorber 2 (phenolic UV absorber) from Examples 1 to 4, showed a whiteness change of -3.60. This is smaller than the whiteness change of Examples 1 to 3. Therefore, it appears that Examples 1 to 3 have inferior lightfastness compared to Comparative Example 2. In other words, it is thought that the inclusion of a conventionally widely used phenolic UV absorber in the thermal recording layer provides superior lightfastness. However, the whiteness after the test for Comparative Example 2 was 77.4%, which is clearly smaller than the whiteness of Examples 1 to 4. Furthermore, the difference in whiteness change between Examples 1 to 3 and Comparative Example 2 was only slight, at 0.90, 0.30, and 0.80, respectively. Therefore, even though a non-phenolic UV absorber was contained, it can be said that the degree of change in whiteness was similar to that of Comparative Example 2. Moreover, when comparing Example 4 and Comparative Example 2, the amount of change in whiteness was smaller in Example 4. This indicates that at least Example 4 has better lightfastness than Comparative Example 2. Furthermore, there was not much difference in the optical density (OD value) after the test between Examples 1 to 4 and Comparative Examples 1 and 2. From these results, it was confirmed that the thermal recording materials of Examples 1 to 4 containing a non-phenolic UV absorber have lightfastness similar to that of Comparative Example 2 containing phenolic UV absorber 2. Furthermore, as shown in Example 4, it was confirmed that by adjusting the content of the non-phenolic UV absorber, the thermal recording materials have better lightfastness than thermal recording materials containing phenolic UV absorbers.

[0150] (2) In the dynamic sensitivity test (color development), when the printing energy was set to 0.40 mJ / dot, the optical densities (OD values) of Examples 1 to 3 and Comparative Examples 1 and 2 were 1.55 and 1.56, respectively, whereas Example 4 was 1.50, which was lower than the others. However, when the printing energy was set to 0.16 mJ / dot and 0.20 mJ / dot, there was no significant difference in the optical densities (OD values) of Examples 1 to 4 and Comparative Examples 1 and 2. From these results, it was confirmed that the thermal recording materials of Examples 1 to 4, which contain a non-phenolic UV absorber, have color development comparable to that of Comparative Example 2, which contains a phenolic UV absorber.

[0151] (3) In the heat resistance test, the optical density (OD value) of the printed area of ​​Examples 1 to 4 was 1.50 to 1.52, and the optical density (OD value) of the non-printed area was 0.06 for all examples. The optical density (OD value) of the printed area of ​​Comparative Example 1 was 1.50, and the optical density (OD value) of the non-printed area was 0.06, which were similar to Examples 1 to 4. In contrast, the optical density (OD value) of the printed area of ​​Comparative Example 2 was 1.54, and the optical density (OD value) of the non-printed area was 0.35, which were higher than those of Examples 1 to 4. In particular, the optical density (OD value) of the non-printed area of ​​Comparative Example 2 was significantly higher than those of Examples 1 to 4. As described above, in the heat resistance test, the lower the optical density (OD value) of the non-printed area, the better the heat resistance can be determined to be. Therefore, it can be said that at least the non-printed areas in Examples 1 to 4 have better heat resistance than the non-printed areas in Comparative Example 2. From these findings, it was confirmed that the thermosensitive recording materials of Examples 1 to 4, which contain a non-phenolic UV absorber, have heat resistance comparable to that of Comparative Example 1, which does not contain any UV absorber. Furthermore, it was confirmed that the heat resistance is clearly better than that of the thermosensitive recording material of Comparative Example 2, which contains phenolic UV absorber 2.

[0152] [Examples 5-6 and Comparative Example 3] Examples 5-6 and Comparative Example 3, which contain the same color developer 2, will be examined.

[0153] (4) In the light resistance test, the whiteness change in Examples 5 and 6 was smaller than that in Comparative Example 3. In addition, the whiteness after the test was also greater than that in Comparative Example 3. From these findings, it was confirmed that Examples 5 and 6, which contain a non-phenolic ultraviolet absorber, are more effective in suppressing the decrease in whiteness than Comparative Example 3, which does not contain an ultraviolet absorber.

[0154] (5) In the dynamic sensitivity test, the optical density (OD value) of Example 5 and Comparative Example 3 at each printing energy was comparable. The optical density (OD value) of Example 6 tended to be lower than that of Comparative Example 3, but the decrease was only about 5 to 10%, demonstrating color development suitable for use as a thermal recording medium. From these results, it was confirmed that even if a non-phenolic UV absorber was contained, the color development was comparable to that of Comparative Example 3, which did not contain a UV absorber.

[0155] (6) In the heat resistance test, the optical density (OD value) of the printed area and the optical density (OD value) of the non-printed area were the same for Examples 5 and 6 and Comparative Example 3. This confirmed that even though the non-phenolic UV absorber was contained, the heat resistance was comparable to that of Comparative Example 3, which did not contain a UV absorber.

[0156] [Conclusion] The above measurement results did not confirm that thermal recording media containing non-phenolic color developers and non-phenolic UV absorbers were inferior in lightfastness, color development, and heat resistance to thermal recording media containing phenolic UV absorbers. Furthermore, it was found that adding a non-phenolic UV absorber to a thermal recording media improves lightfastness while maintaining good heat resistance, and can suppress loss of whiteness and yellowing. Furthermore, non-phenolic color developers and non-phenolic UV absorbers are safer than phenolic counterparts. Therefore, using non-phenolic color developers and non-phenolic UV absorbers is extremely effective from an environmental perspective.

[0157] Variations of the present invention are described below. [Appendix 1] A thermosensitive recording medium having a thermosensitive recording layer laminated on a substrate, wherein the thermosensitive recording layer contains a color former, a non-phenolic color developer, and a non-phenolic ultraviolet absorber, and the non-phenolic ultraviolet absorber contains an oxalic acid anilide ultraviolet absorber. [Appendix 2] The thermosensitive recording medium according to Appendix 1, wherein the non-phenolic color 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 R 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 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 may be the 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 R each independently represents a hydrogen atom or a substituent. 18 represents a substituent. o represents an integer of 0 to 4. When o is 2 or more, a plurality of R 18 may be the same or different.) [Appendix 3] The thermosensitive recording material according to appendix 1 or 2, wherein the non-phenolic color 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).) (Each symbol in formula (2a) is the same as in formula (2).) [Appendix 4] The thermosensitive recording material according to any one of Appendices 1 to 3, wherein the content of the non-phenolic color developer relative to the entire thermosensitive recording layer is 10% by mass or more and 50% by mass or less. [Appendix 5] The thermosensitive recording material according to any one of Appendices 1 to 4, wherein the content of the non-phenolic ultraviolet absorber relative to the entire thermosensitive recording layer is 5% by mass or more and 15% by mass or less.

[0158] As explained above, the present invention is particularly useful for thermosensitive recording media on which bar codes and the like are printed.

[0159] 1 Thermosensitive recording medium 2 Substrate 3 Thermosensitive recording layer 4 Intermediate layer 5 Topcoat layer 6 Undercoat layer

Claims

DEPCT6808 / 05 / 25681. A thermally sensitive recording medium in which the thermally sensitive recording layer is placed on top of a thermally sensitive recording substrate consisting of a phenolic-free pigment, an imaging agent, and a phenolic-free ultraviolet absorber. The phenolic-free ultraviolet absorber is composed of an oxanilide-based ultraviolet absorber.2.A heat-sensitive recording medium under claim 1 in which the non-phenolic imaging agent is composed of compounds represented by the following formula(1) and / or compounds represented by the following formula(2): [Formula 1](Chemical Formula)(1) in which each R1, R2, R3, R4, R5, R7, R8, R9, R10 and R11 each independently represent a hydrogen atom or substituent; each R6 and R12 each independently represent a substituent; m represents an integer 0 to 4. When m is 2 or more, more than one R6 is the same or different, n represents an integer 0 to 4; and when n is 2 or more, more than one R12 is the same or different [Formula 2](Chemical Formula)(2) where each R13, R14, R15, R16, R17, R19, R20, R21, R22 and R23 each independently represents a hydrogen atom or substituent; R18 represents a substituent; o represents an integer 0 to 4; and when o is 2 or more, more than one R18 is the same or different. 3.

4. Any one of the thermally sensitive media under claims 1 through 3 in which the amount of non-phenolic imaging agent is not less than 10 percent by mass and not more than 50 percent by mass relative to the total volume of the thermally sensitive media layer; 5. Any one of the thermally sensitive media under claims 1 through 4 in which the amount of non-phenolic imaging agent is not less than 5 percent by mass and not more than 15 percent by mass relative to the total volume of the thermally sensitive media layer;

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