Thermal recording layer and thermal recording body

Abstract

To provide a thermal recording layer or thermal recording material in which discoloration over time is suppressed even in printed areas printed with low energy. [Solution] The thermal recording layer 4 contains animal-derived zinc stearate. The stearic acid in the above animal-derived zinc stearate is stearic acid derived from animal fats and oils. The content of the above animal-derived zinc stearate is 0.1 to 2% by mass based on 100% by mass of the total solids content of the thermal recording layer 4. Preferably, the thermal recording layer 4 contains a dye and a color developer having a specific structure.

Description

Technical Field

[0001] The present invention relates to a heat-sensitive recording layer and a heat-sensitive recording medium.

Background Art

[0002] A heat-sensitive recording medium develops color by a chemical reaction upon heating by a thermal head or the like, and a recorded image is obtained. It is used not only as a recording medium for facsimiles, automatic ticket vending machines, scientific measuring instruments, etc., but also as a heat-sensitive recording label used for various products such as food pouches, and is used in a wide range of applications.

[0003] Due to its nature, the printed portion of a heat-sensitive recording medium using such a chemical reaction may fade over time. Such fading of the printed portion over time causes a problem that the recorded information becomes unreadable over time.

[0004] By the way, zinc stearate may be blended in a recording layer, which is a layer presenting a recorded image in a heat-sensitive recording medium, for the purpose of improving the matching suitability with a thermal head (see, for example, Patent Document 1). Here, zinc stearate has properties of melting by heat from a thermal head and excellent mold release properties, and is thus used as a so-called lubricant. When zinc stearate is used as a lubricant in this way, as disclosed in Patent Document 1, it is usually blended in the recording layer at 3% by weight or more.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Under the above background, a thermal recording medium that can maintain the density of the printing portion even over time is desired. However, especially when the applied energy is low, it has been difficult to prevent the discoloration of the printing portion.

[0007] The present invention has been conceived under such circumstances, and its object is to provide a thermal recording layer in which discoloration over time is suppressed even in a printed portion printed with low energy, and a thermal recording medium provided with such a thermal recording layer.

Means for Solving the Problems

[0008] As a result of intensive studies to achieve the above object, the present inventors have found that a thermal recording layer containing a very small amount of animal-derived zinc stearate and a thermal recording medium provided with the above thermal recording layer are less likely to discolor over time even when printed with low energy. The present invention has been completed based on these findings.

[0009] That is, the present invention is a thermal recording layer containing animal-derived zinc stearate, where the zinc stearate of the above animal-derived zinc stearate is stearic acid derived from animal fats and oils, and the content ratio of the above animal-derived zinc stearate is 0.1 to 2% by mass based on 100% by mass of the total solid content of the above thermal recording layer, and provides a thermal recording layer.

[0010] The above thermal recording layer preferably contains a dye and a developer. The above developer preferably contains a compound represented by the following formula (1) and / or a compound represented by the following formula (2).

[0011]

Chemical formula

[0012] [ka] (In formula (2), R 2 This represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may have substituents, and multiple R 2 They may be the same or different. 2 This represents a monovalent hydrocarbon group having 1 to 4 carbon atoms, and multiple A 2 (These values ​​may be the same or different. q represents an integer between 0 and 4, and multiple qs may be the same or different.)

[0013] The thermal recording layer described above preferably contains a lubricant. The mass ratio of the content of the animal-derived zinc stearate to the content of the lubricant (animal-derived zinc stearate / lubricant) is preferably 0.01 to 1.

[0014] Furthermore, the present invention provides a thermal recording body in which a substrate, the thermal recording layer, and a top coat layer are laminated in this order. [Effects of the Invention]

[0015] The thermal recording layer and thermal recording material of the present invention can suppress the fading of the printed area over time, even when printed at low energy. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic cross-sectional view showing one embodiment of the thermal recording body of the present invention. [Figure 2] This graph shows the change over time in the decolorization rate of the printed area in the thermal recording materials prepared in Examples 1-3 and Comparative Examples 1-3. [Figure 3] This graph shows the change over time in the decolorization rate of the printed area in the thermal recording materials prepared in Examples 4-5 and Comparative Example 4. [Modes for carrying out the invention]

[0017] [Thermal recording layer] The thermal recording layer of the present invention contains animal-derived zinc stearate in an amount ranging from 0.1% to 2% by mass relative to 100% by mass of the total solid content of the thermal recording layer. Generally, zinc stearate is used as a lubricant in the field of thermal recording materials, but surprisingly, it has been found that including animal-derived zinc stearate, in particular, can suppress the fading of the printed area. In this specification, "animal-derived zinc stearate" means that the stearic acid is derived from animal fats and oils. Also, "vegetable-derived zinc stearate" means that the stearic acid is derived from vegetable fats and oils. The mechanism of action regarding the prevention of fading is unknown, but since both animal fats and vegetable fats are naturally occurring fats and oils, it is known that even after impurities are removed by refining, there are slight differences in the types and amounts of trace components (metal components and organic components such as tocopherols and vitamins) in the fats and oils. Therefore, it is presumed that trace components contained in animal fats may contribute to stabilizing the color-developing components within the thermal recording layer, thereby preventing the printed area from fading over time.

[0018] Hereinafter, one embodiment of the thermal recording layer 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.

[0019] Figure 1 shows one embodiment of the thermal recording layer of the present invention. As shown in Figure 1, the thermal recording layer 4 can constitute a part of the thermal recording body 1. The thermal recording body 1 will be described later.

[0020] The thermal recording layer 4 is a layer that develops color when heated by a thermal head or the like, and forms a recorded image. The thermal recording layer 4 contains at least animal-derived zinc stearate, and may further contain other components as needed. Examples of these other components include dyes, color developers, preservation enhancers, lubricants, sensitizers, binders, fillers, crosslinking agents, and surface tension modifiers.

[0021] The content of the above-mentioned animal-derived zinc stearate is 0.1 to 2% by mass based on 100% by mass of the total solid content of the thermal recording layer 4, and may be 0.1 to 1.5% by mass, 0.1 to 1.3% by mass, 0.1 to 1.0% by mass, 0.1 to 0.8% by mass, 0.1 to 0.6% by mass, or 0.1 to 0.4% by mass. Furthermore, the lower limit of the above-mentioned content may be 0.3% by mass or 0.5% by mass.

[0022] In this specification, the above-mentioned animal-derived zinc stearate is used primarily for the purpose of preventing discoloration of the printed area, and therefore does not fall under the category of lubricants described later.

[0023] Examples of the above dyes include 2'-bromo-6'-(dibutylamino)-3'-methylspiro[isobenzofuran-1(3H),9'-[9H]xanthene]-3-one, 3-(1-ethyl-2-methylindole-3-yl)-3-(4-diethylamino-2-methylphenyl)-4-azaphthalide, 6-(dimethylamino)-3,3-bis[4-(dimethylamino)phenyl]-1(3H)-isobenzofuranone, 1,2-dihydro-1-ethyl-8-[N-(4-methylphenyl)-N-ethylamino]-2,2,4-trimethylspiro[11H]-chromeno(2,3-g)quinoline-11,3'-phthalide, 2'-[bis(phenylmethyl)amino]-6'-(diethylamino)-spiro[isobenzofuran-1(3H),9'-(9H)xanthene]-3-one, 2-anilino-6-(dibutylamino)-3-methylfluorane, 2-aniline-3methyl-6-(N-methyl-p-toluidino)fluorane, 3-(N-isobutyl-N-ethyl)amino-6-methyl-7-anilinofluorane, 3-(N-isopentyl-N-ethyl)amino-6-methyl-7-o-chloroanilinofluorane, 3-(N-methyl-Np-toluidino)-6-methyl -7-anilinofluorane, 3-(N-ethyl-Np-toluidino)-6-methyl-7-anilinofluorane, 3-(N-ethyl-N-isopentyl)amino-6-methyl-7-anilinofluorane, 3-(N-ethoxypropyl-N-ethyl)amino-6-methyl-7-anilinofluorane, 3-(N-cyclohexyl-N-methyl)amino-6-methyl-7-anilinofluorane, 3-(N-methyl-Nn-propyl)amino No-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-p-toluidinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-8-methylfluorane, 3-diethylamino-7-(m-trifluoromethylanilino)fluorane, 3-diethylamino-7-(o-chloroanilino) Fluorane, 3-diethylamino-7-chlorofluorane, 3-dibutylamino-6-methyl-7-bromofluorane, 3-dibutylamino-7-(o-chloroanilino)fluorane, 3-dipentylamino-6-methyl-7-anilinofluorane, 3-dimethylamino-5-methyl-7-methylfluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, crystal violet lactone, etc. can be used. These dyes can be used individually or in combination of two or more.

[0024] The average particle diameter of the above dye is preferably 0.1 to 1.0 μm. Generally, since the dye melts and reacts, when the average particle diameter is reduced, the sensitivity characteristics tend to improve. On the other hand, when the average particle diameter is increased, it tends to be easier to suppress unexpected color development due to heat during drying or the like. When the average particle diameter is within the above range, the sensitivity characteristics and color development temperature of the dye can be adjusted more appropriately.

[0025] The content ratio of the above dye is preferably 1% by mass or more, more preferably 3% by mass or more, and still more preferably 5% by mass or more with respect to 100% by mass of the total solid content of the heat-sensitive recording layer 4. Further, the content ratio is preferably 40% by mass or less, more preferably 30% by mass or less with respect to 100% by mass of the total solid content of the heat-sensitive recording layer 4.

[0026] The above color developer is not particularly limited, and known phenolic color developers and non-phenolic color developers can be used. Among them, from the viewpoints of color development efficiency and prevention of decolorization, phenolic color developers are preferred. As the above phenolic color developer, for example, a compound represented by the following formula (1) is preferred.

[0027]

Chemical formula

[0028] In the above formula (1), A 1 represents a monovalent hydrocarbon group having 1 to 4 carbon atoms, and a plurality of A 1 may be the same or different. p represents an integer of 0 to 4, and a plurality of p may be the same or different. R 1 represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may have a substituent.

[0029] In the above formula (1), -OR 1 is directly bonded to the carbon atom constituting the benzene ring. The substitution position of -OR 1 may be the 2-position, 3-position, or 4-position, and is preferably the 4-position. In this specification, in the above formula (1), the carbon atom bonded to the sulfonyl group (-SO2-) is taken as the 1-position.

[0030] In the above equation (1), R 1 In this specification, the "monovalent hydrocarbon group having 1 to 12 carbon atoms that may have substituents" includes, for example, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, an alicyclic alkyl group having 3 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, or a monovalent group having 4 to 12 carbon atoms formed by bonding two or more different groups from these groups. 1 In the phrase "monovalent hydrocarbon group having 1 to 12 carbon atoms," the number of carbon atoms refers to the total number of carbon atoms, including the carbon atoms in the substituents, if the substituents contain carbon atoms.

[0031] The above-mentioned "linear alkyl group having 1 to 12 carbon atoms" may be a linear saturated alkyl group or a linear unsaturated alkyl group. Examples of the above-mentioned "linear alkyl group having 1 to 12 carbon atoms" include a methyl group, an ethyl group, an n-propyl group, an allyl group, an n-butyl group, a 3-butenyl group, an n-hexyl group, a lauryl group, and the like.

[0032] The above-mentioned "branched alkyl group having 3 to 12 carbon atoms" may be a branched saturated alkyl group or a branched unsaturated alkyl group. Examples of the above-mentioned "branched alkyl group having 3 to 12 carbon atoms" include i-propyl group, i-butyl group, s-butyl group, t-butyl group, and 2-ethylhexyl group.

[0033] The above-mentioned "alicyclic alkyl group having 3 to 12 carbon atoms" may be either an alicyclic saturated alkyl group or an alicyclic unsaturated alkyl group. Examples of the above-mentioned "alicyclic alkyl group having 3 to 12 carbon atoms" include a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, and the like.

[0034] Examples of the above-mentioned "aryl groups having 6 to 12 carbon atoms" include unsubstituted aryl groups such as phenyl, 1-naphthyl, and 2-naphthyl groups.

[0035] Examples of the above-mentioned "monovalent groups having 4 to 12 carbon atoms, formed by the bonding of two or more distinct groups" include "monovalent groups having 7 to 12 carbon atoms, formed by the bonding of an aryl group with one or more linear alkyl groups," "monovalent groups having 9 to 12 carbon atoms, formed by the bonding of an aryl group with one or more branched alkyl groups," and "monovalent groups having 4 to 12 carbon atoms, formed by the bonding of an alicyclic alkyl group with one or more linear alkyl groups."

[0036] The above-mentioned "substituent" is a group having at least one atom other than carbon atoms and hydrogen atoms (heteroatom). In this specification, the heteroatom in the "substituent" is assumed to be bonded to a carbon atom in the "carbon 1 to 12 hydrocarbon group". Specific examples of the above-mentioned "substituent" include halogen atoms, hydroxyl groups, alkoxy groups, oxo groups (=O), etc. The above-mentioned "substituent" may or may not contain carbon atoms. If the above-mentioned "substituent" contains carbon atoms, the number of carbon atoms in the substituent is preferably 1 to 6, and more preferably 1 to 4. There may or may not be multiple above-mentioned "substituents".

[0037] In the above equation (1), R 1 R is preferably one of the following: a linear alkyl group having 1 to 12 carbon atoms which may have substituents, a branched alkyl group having 3 to 12 carbon atoms which may have substituents, or an alicyclic alkyl group having 3 to 12 carbon atoms which may have substituents, and more preferably a linear alkyl group having 1 to 12 carbon atoms which may have substituents. Specifically, R 1 The group is preferably one of the following: methyl group, ethyl group, n-propyl group, allyl group, n-butyl group, 3-butenyl group, n-hexyl group, i-propyl group, i-butyl group, s-butyl group, t-butyl group, or 2-ethylhexyl group, and more preferably one of the following: ethyl group, n-propyl group, or i-propyl group.

[0038] In the above formula (1), A 1 Among the carbon atoms that make up the benzene ring, -OR 1Alternatively, an -OH group may bond to a carbon atom that is not bonded to it. In formula (1) above, A 1 Examples of monovalent hydrocarbon groups having 1 to 4 carbon atoms include alkyl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, and t-butyl groups.

[0039] In the above formula (1), p is preferably an integer between 0 and 2, more preferably an integer between 0 and 1, and even more preferably 0.

[0040] In formula (1) above, -OH is directly bonded to a carbon atom constituting the benzene ring. The substitution position of -OH may be at position 2, position 3, or position 4, and is preferably at position 4.

[0041] The compound represented by formula (1) above preferably includes, more specifically, the compound represented by formula (1a) below.

[0042] [ka]

[0043] The above non-phenolic color developer is preferably a compound represented by the following formula (2).

[0044] [ka]

[0045] In equation (2) above, R 2 This represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may have substituents, and multiple R 2 They may be the same or different. 2 This represents a monovalent hydrocarbon group having 1 to 4 carbon atoms, and multiple A 2 The values ​​of q may be the same or different. q represents an integer between 0 and 4, and multiple qs may be the same or different.

[0046] In equation (2) above, multiple R 2-SO3- is directly bonded to the carbon atoms that make up the benzene ring. Multiple R 2 The substitution position of -SO3- may be the same or different between one benzene ring and the other. 2 -SO3- substitution position and R on the other benzene ring 2 The substitution positions of the -SO3- groups are preferably the same, and more preferably both are at position 3. In this specification, in formula (2) above, the carbon atom on the benzene ring bonded to the nitrogen atom of the urea group (-NH-CO-NH-) is defined as position 1.

[0047] In equation (2) above, R 2 In the "monovalent hydrocarbon group having 1 to 12 carbon atoms that may have substituents" in R, examples of "monovalent hydrocarbon group having 1 to 12 carbon atoms" include linear alkyl groups having 1 to 12 carbon atoms, branched alkyl groups having 3 to 12 carbon atoms, alicyclic alkyl groups having 3 to 12 carbon atoms, aryl groups having 6 to 12 carbon atoms, or monovalent groups having 4 to 12 carbon atoms formed by bonding two or more different groups from these groups. Furthermore, multiple "monovalent hydrocarbon groups having 1 to 12 carbon atoms that may have substituents" may be the same or different from each other. Note that in this specification, the above R 2 In the phrase "carbon hydrocarbon groups with 1 to 12 carbon atoms," the number of carbon atoms refers to the total number of carbon atoms, including the carbon atoms in the substituents if the substituents contain carbon atoms.

[0048] The above-mentioned "linear alkyl group having 1 to 12 carbon atoms" may be a linear saturated alkyl group or a linear unsaturated alkyl group. Examples of the above-mentioned "linear alkyl group having 1 to 12 carbon atoms" include a methyl group, an ethyl group, an n-propyl group, an allyl group, an n-butyl group, a 3-butenyl group, an n-hexyl group, a lauryl group, and the like.

[0049] The above-mentioned "branched alkyl group having 3 to 12 carbon atoms" may be a branched saturated alkyl group or a branched unsaturated alkyl group. Examples of the above-mentioned "branched alkyl group having 3 to 12 carbon atoms" include i-propyl group, i-butyl group, s-butyl group, t-butyl group, and 2-ethylhexyl group.

[0050] The above-mentioned "alicyclic alkyl group having 3 to 12 carbon atoms" may be either an alicyclic saturated alkyl group or an alicyclic unsaturated alkyl group. Examples of the above-mentioned "alicyclic alkyl group having 3 to 12 carbon atoms" include a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, and the like.

[0051] Examples of the above-mentioned "aryl groups having 6 to 12 carbon atoms" include unsubstituted aryl groups such as phenyl, 1-naphthyl, and 2-naphthyl groups.

[0052] Examples of the above-mentioned "monovalent groups having 4 to 12 carbon atoms, formed by the bonding of two or more distinct groups" include "monovalent groups having 7 to 12 carbon atoms, formed by the bonding of an aryl group with one or more linear alkyl groups," "monovalent groups having 9 to 12 carbon atoms, formed by the bonding of an aryl group with one or more branched alkyl groups," and "monovalent groups having 4 to 12 carbon atoms, formed by the bonding of an alicyclic alkyl group with one or more linear alkyl groups."

[0053] The above-mentioned "monovalent group having 7 to 12 carbon atoms bonded to an aryl group and one or more linear alkyl groups" is preferably "a monovalent group having 7 to 12 carbon atoms bonded to a phenyl group and one to three linear alkyl groups having 1 to 4 carbon atoms." Specifically, examples include p-tolyl group, m-tolyl group, o-tolyl group, 2,5-dimethylphenyl group, 2,4-dimethylphenyl group, 3,5-dimethylphenyl group, 2,3-dimethylphenyl group, 3,4-dimethylphenyl group, mesitylene group, p-ethylphenyl group, etc. Alternatively, aralkyl groups such as benzyl group, 1-phenylethyl group, 2-phenylethyl group, 3-phenylpropyl group, p-methylbenzyl group, m-methylbenzyl group, m-ethylbenzyl group, and p-ethylbenzyl group may also be used. Furthermore, the above-mentioned "monovalent group having 7 to 12 carbon atoms, formed by bonding a phenyl group to 1 to 3 linear alkyl groups having 1 to 4 carbon atoms" may have substituents as described below.

[0054] The above-mentioned "monovalent group having 9 to 12 carbon atoms bonded to an aryl group and one or more branched alkyl groups" is preferably a "monovalent group having 7 to 12 carbon atoms bonded to a phenyl group and one or two branched alkyl groups having 3 to 4 carbon atoms." Specifically, examples include pi-propylphenyl group and pt-butylphenyl group. Furthermore, the above-mentioned "monovalent group having 7 to 12 carbon atoms bonded to a phenyl group and one or two branched alkyl groups having 3 to 4 carbon atoms" may have substituents as described later.

[0055] The above-mentioned "monovalent group having 4 to 12 carbon atoms bonded to an alicyclic alkyl group and one or more linear alkyl groups" is preferably a "monovalent group having 7 to 12 carbon atoms bonded to an alicyclic alkyl group having 6 to 12 carbon atoms and one to three linear alkyl groups having 1 to 4 carbon atoms." Specifically, examples include the 4-methylcyclohexyl group and the 4-methylcyclooctyl group. Furthermore, the above-mentioned "monovalent group having 7 to 12 carbon atoms bonded to an alicyclic alkyl group having 6 to 12 carbon atoms and one to three linear alkyl groups having 1 to 4 carbon atoms" may have substituents as described later.

[0056] The above "substituent" has the same meaning as described in formula (1) above, and the same group is included. When the above "substituent" contains a carbon atom, the number of carbon atoms in the substituent is preferably 1 to 6, and more preferably 1 to 4. There may be multiple above "substituents" or none. The substitution positions of the multiple "substituents" are on the R of one of the benzene rings. 2 and R on the other benzene ring 2 The R on one of the benzene rings may be the same or different from each other. 2 The substitution position of the substituent in and the R on the other benzene ring 2 It is preferable that the substitution positions of the substituents in the compound are the same.

[0057] In the above formula (2), the above R 2 In particular, a monovalent group having 7 to 10 carbon atoms, formed by bonding a phenyl group to 1 to 3 linear alkyl groups having 1 to 4 carbon atoms, is preferred, and a monovalent group having 7 to 10 carbon atoms, formed by bonding a phenyl group to 1 linear alkyl group having 1 to 4 carbon atoms, is more preferred. Specifically, the above R 2 The preferred R is a p-tolyl group, m-tolyl group, o-tolyl group, 2,5-dimethylphenyl group, 2,4-dimethylphenyl group, 3,5-dimethylphenyl group, 2,3-dimethylphenyl group, 3,4-dimethylphenyl group, or mesitylene group, with the p-tolyl group being more preferred. 2 In that case, the color development and the effect of preventing discoloration of the printed area can be improved.

[0058] In the above formula (2), A 2 Among the carbon atoms constituting the benzene ring, the above R 2 -SO3- can bond to carbon atoms that are not bonded. Also, A 2 If there are two or more A 2 The substitution positions may be the same or different between one benzene ring and the other.

[0059] A above 2Examples of hydrocarbon groups having 1 to 4 carbon atoms include alkyl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, and t-butyl groups.

[0060] In formula (2) above, q is preferably an integer between 0 and 2, more preferably an integer between 0 and 1, and even more preferably 0.

[0061] The compounds represented by formula (2) above include, but are not limited to, the following specific compounds.

[0062] In other words, the compounds represented by formula (2) above include N,N'-di-[3-(o-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-toluenesulfonyloxy)-4-methylphenyl]urea, N,N'-di-[3-(p-xylenesulfonyloxy)phenyl]urea, and N,N'-di-[3-(m-xylenesulfonyloxy)phenyl]urea. Examples include N,N'-di-[3-(mesitylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-4-methylphenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-4-ethylphenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-5-methylphenyl]urea, and N,N'-di-[3-(benzenesulfonyloxy)-4-propylphenyl]urea. Among these, the compound represented by formula (2) above, namely N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, is particularly preferred.

[0063] [ka]

[0064] The above-mentioned color developer may contain the compound represented by formula (1) alone, or it may contain two or more compounds represented by formula (1). Furthermore, the above-mentioned color developer may contain the compound represented by formula (2) alone, or it may contain two or more compounds represented by formula (2). In addition, the above-mentioned color developer may contain both the compound represented by formula (1) and the compound represented by formula (2). It is preferable that the above-mentioned color developer contains the compound represented by formula (1) and / or the compound represented by formula (2). Furthermore, other color developers (other color developers) may be included insofar as they do not impair the effects of the present invention.

[0065] Other color developers include, for example, 3-[(3-phenylureido)phenyl]-4-methylbenzenesulfonate (trade name: TG-MD), N-3-[(p-toluenesulfonyl)oxy]phenyl-N'-(p-toluenesulfonyl)-urea (trade name: PF-201), N-[2-(3-phenylureido)phenyl]-benzenesulfonamide (trade name: NKK-1304), and 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophosphate) Known non-phenol colorants such as [phenyl)ureido]diphenylsulfone (trade name: UU), 4,4'-isopropylidenediphenol (BPA), 4,4'-dihydroxydiphenylsulfone (BPS), 4-allyloxy-4'-hydroxydiphenylsulfone (trade name: BPS-MAE), bis(3-allyl-4-hydroxyphenyl)sulfone (trade name: TGSA), 2,2'-diallyl-4,4'-sulfonyldiphenol (trade name: TG-SH), 4-Hydroxy-4'-Isopropoxydiphenylsulfone (trade name: D-8), N-(m-tolylaminocarbonyl)-methionine, N-(m-tolylaminocarbonyl)-phenylalanine and N-(phenylaminocarbonyl)-phenylalanine, 1,1-bis(p-hydroxyphenyl)cyclohexane, 1,1-bis(p-hydroxyphenyl)propane, 2,2-bis(p-hydroxyphenyl)propane, 2,2-bis(p-hydroxyphenyl) Phenyl)butane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 2,2'-methylenebis(4-chlorophenol), 2,2-bis(4-hydroxyphenyl)-4-methylpentane, poly(4-hydroxybenzoic acid), benzyl 4-hydroxybenzoate, 2,4-bis(phenylsulfonyl)phenol, 3,5-bis(α-methylbenzyl)salicylic acid, bis[4-(n-octyloxycarbonylamino)salicylate zinc], 4,Known color developers include 4'-bis(p-tolylsulfonylaminocarbonylamino)diphenylmethane, 4-hydroxybenzenesulfonanilide, N-(2-hydroxyphenyl)-2-[(4-hydroxyphenyl)thio]acetamide, N-(4-hydroxyphenyl)-2-[(4-hydroxyphenyl)thio]acetamide, 4-[4-(4-{4-[4-(1-methylethoxy)phenylsulfonyl]phenoxy}butoxy)phenylsulfonyl]phenol, and 4-tert-butylphenol-formaldehyde polycondensate. These other color developers can be used individually or in combination of two or more.

[0066] The content of the compound represented by formula (1) above is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on 100% by mass of the total amount of developer in the thermal recording layer 4. The above total content may be substantially 100% by mass, based on 100% by mass of the total amount of developer in the thermal recording layer 4. Furthermore, the content of the compound represented by formula (2) above is preferably within the above range, based on 100% by mass of the total amount of developer in the thermal recording layer 4.

[0067] The content of the above-mentioned color developer is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, based on 100% by mass of the total solid content of the thermal recording layer 4. Furthermore, the content is preferably 40% by mass or less, and more preferably 30% by mass or less, based on 100% by mass of the total solid content of the thermal recording layer 4.

[0068] Examples of the above preservatives include urea urethane compounds, 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, and tris(2,6-dimethyl Examples include 4-t-butyl-3-hydroxybenzyl) 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, and 4,4'-thiobis(6-t-butyl-m-cresol). The above preservatives can be used individually or in combination of two or more.

[0069] The above urea-urethane compound is preferably a urea-urethane compound having two or more urea bonds and two or more urethane bonds in its molecule. Specifically, the above urea-urethane compound preferably includes a compound represented by the following formula (3). It is presumed that the above urea-urethane compound improves the reaction efficiency between the dye and the color developer, making it easier to form electron transfer complexes and making the reverse reaction less likely to occur, thereby improving color development and suppressing decolorization.

[0070] [ka]

[0071] The content of the above-mentioned preservation improver is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on 100% by mass of the total solid content of the thermal recording layer 4. Furthermore, the content is preferably 40% by mass or less, and more preferably 30% by mass or less, based on 100% by mass of the total solid content of the thermal recording layer 4.

[0072] Examples of the above-mentioned lubricants include hydrocarbon waxes such as paraffin, polyethylene, and polystyrene; ester waxes such as carnauba wax; oils such as silicone oil and whale oil; fatty acids such as oleic acid and stearic acid; and metal soaps such as vegetable zinc stearate. These lubricants can be used individually or in combination of two or more.

[0073] The content of the above lubricant is preferably 1% by mass or more, and more preferably 2% by mass or more, based on 100% by mass of the total solid content of the thermal recording layer 4. Furthermore, the content is preferably 20% by mass or less, and more preferably 10% by mass or less, based on 100% by mass of the total solid content of the thermal recording layer 4.

[0074] The mass ratio of the content of the above-mentioned animal-derived zinc stearate to the content of the above-mentioned lubricant (animal-derived zinc stearate / lubricant) is preferably 0.01 to 1, may be 0.02 to 0.8, 0.05 to 0.5, or 0.1 to 0.3.

[0075] The mass ratio of the content of the above-mentioned animal-derived zinc stearate to the content of the above-mentioned dye (animal-derived zinc stearate / dye) is preferably 0.001 to 0.2, may be 0.005 to 0.15, 0.01 to 0.1, or 0.01 to 0.5.

[0076] The mass ratio of the content of the above-mentioned animal-derived zinc stearate to the content of the above-mentioned color developer (animal-derived zinc stearate / color developer) is preferably 0.001 to 0.1, may be 0.002 to 0.08, 0.005 to 0.05, or 0.01 to 0.03.

[0077] The mass ratio of the dye content to the developer content (dye / developer) is preferably 0.05 to 5, may be 0.1 to 2.5, 0.15 to 1.5, 0.2 to 1, or 0.3 to 0.7.

[0078] The mass ratio of the content of the preservative enhancer to the content of the color developer (preservative enhancer / color developer) is preferably 0.05 to 5, may be 0.1 to 2.5, 0.15 to 1.5, 0.2 to 1, or 0.3 to 0.7.

[0079] Examples of the sensitizers mentioned above include known sensitizers such as higher fatty acid amides like stearate amide, methylol stearate amide, methylenebisstearate amide, and ethylenebisstearate amide; higher fatty acid anilides like stearate anilide; aromatic ethers such as 1,2-diphenoxyethane, 1,4-diphenoxybutane, 1,2-di(3-methylphenoxyethane), and 1,2-di(4-methoxyphenoxyethane); 1-benzyloxynaphthalene, 2-benzyloxynaphthalene, 2,6-diisopropylnaphthalene; di(p-chlorobenzyl) oxalate, di(p-methylbenzyl) oxalate, dibenzyl oxalate, p-benzylbiphenyl, m-terphenyl, diphenylsulfone, p-benzyloxybenzoate benzyl, dibenzyl terephthalate, and p-toluenesulfonamide. The above-mentioned sensitizer is preferably solid at room temperature and pressure (e.g., 25°C, 1 atm), and more preferably has a melting point of 70°C or higher. The above-mentioned sensitizer can be used alone or in combination of two or more types.

[0080] The content of the above-mentioned sensitizer is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on 100% by mass of the total solid content of the thermal recording layer 4. Furthermore, the content is preferably 40% by mass or less, and more preferably 30% by mass or less, based on 100% by mass of the total solid content of the thermal recording layer 4.

[0081] Examples of the above-mentioned binders include known resins. Specifically, these include acrylic resins such as acrylic resins, styrene-acrylic resins, acrylic-urethane resins, acrylamide resins, and vinyl acetate-acrylic resins; maleic acid resins such as maleic acid resins, styrene-maleic acid resins, and olefin-maleic acid resins; styrene-butadiene rubber (SBR); and polyvinyl alcohol resins (PVA) such as fully saponified polyvinyl alcohol resins and partially saponified polyvinyl alcohol resins. Other examples of the above-mentioned binders include starch, casein, gelatin, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, and hydroxypropylcellulose. The above-mentioned binders may be modified by known methods. The above-mentioned binders can be used alone or in combination of two or more types.

[0082] In this specification, "acrylic resin" means a resin obtained by homopolymerizing acrylic monomers (monomers having a (meth)acryloyl group) (acrylic resin), and / or a resin obtained by copolymerizing an acrylic monomer with another monomer (a monomer other than an acrylic monomer that can copolymerize with an acrylic monomer). Here, the acrylic monomer and the other monomer may each be one type or two or more types. Also, when simply referred to as "acrylic," unless otherwise specified, it means (meth)acrylic acid (salt) and / or (meth)acrylic acid ester. Here, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid. Also, "(meth)acrylic acid (salt)" means (meth)acrylic acid and / or (meth)acrylic acid salt.

[0083] The salts in the above-mentioned (meth)acrylate salts are not particularly limited and include, for example, ammonium salts such as ammonia; alkanolamine salts such as triethanolamine, diethanolamine, and monoethanolamine; alkylamine salts such as methylamine, ethylamine, diethylamine, and triethylamine; polyamine salts such as diethyleneamine and diethylenetriamine; alkali metal salts such as lithium, sodium, and potassium; alkaline earth metal salts such as magnesium and calcium; and polyvalent metal salts such as zinc and iron. These salts can be used individually or in combination of two or more.

[0084] The composition containing the above-mentioned binder may be a solid, an emulsion, or a solution. From the viewpoint of excellent handling and coating properties, it is preferable to be an emulsion or a solution.

[0085] The content of the above-mentioned binder is preferably 3% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, based on 100% by mass of the total solid content of the thermal recording layer 4. Furthermore, the content of the above-mentioned binder is preferably 70% by mass or less, and more preferably 50% by mass or less, based on 100% by mass of the total solid content of the thermal recording layer 4.

[0086] Examples of the above-mentioned fillers include inorganic fillers such as kaolin, calcined kaolin, aluminum oxide, aluminum silicate, heavy calcium carbonate, light calcium carbonate, titanium dioxide, barium sulfate, silica gel, activated clay, talc, clay, kaolinite, diatomaceous earth, white carbon, magnesium carbonate, magnesium oxide, magnesium hydroxide, aluminum hydroxide, and zinc oxide; and organic fillers such as hollow particles and non-hollow particles. The above-mentioned fillers can be used individually or in combination of two or more types.

[0087] The content of the above-mentioned filler is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on 100% by mass of the total solid content of the thermal recording layer 4. Furthermore, the content of the above-mentioned filler is preferably 30% by mass or less, and more preferably 20% by mass or less, based on 100% by mass of the total solid content of the thermal recording layer 4.

[0088] Examples of the crosslinking agents include inorganic crosslinking agents such as zirconium compounds, and organic crosslinking agents such as epichlorohydrin resins and oxazoline compounds. Examples of the zirconium compounds include zirconium carbonate, zirconium ammonium carbonate, and zirconium acetate. Examples of the epichlorohydrin resins include polyamide epichlorohydrin resins, polyamine epichlorohydrin resins, and polyamide polyamine epichlorohydrin resins. Among these, epichlorohydrin resins are preferred as the crosslinking agent. The crosslinking agents can be used alone or in combination of two or more.

[0089] The content of the above crosslinking agent is preferably 0.01% by mass or more, and more preferably 0.1% by mass or more, based on 100% by mass of the total solid content of the thermal recording layer 4. Furthermore, the content is preferably 5% by mass or less, and more preferably 3% by mass or less, based on 100% by mass of the total solid content of the thermal recording layer 4.

[0090] Examples of the surface tension modifiers mentioned above include surfactants. Known surfactants can be used as appropriate, including anionic surfactants such as sodium dioctyol succinate, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, and alkyl ether sulfates; nonionic surfactants such as acetylene glycol surfactants and polyoxyalkylene alkyl ethers. These surface tension modifiers can be used individually or in combination of two or more.

[0091] For example, the coating amount (dry mass) of the thermal recording layer 4 is 0.3 g / m². 2 ~10g / m 2Preferably, and more preferably, 2.0 g / m 2 ~6.0g / m 2 Therefore, if the above coating amount is within the above range, it is easier to achieve more appropriate color development. In this specification, "dry mass" refers to the mass of non-volatile components (solids) excluding solvents (volatile components) such as water contained in the coating liquid or its raw materials.

[0092] [Method for manufacturing a thermal recording layer] The thermal recording layer of the present invention can be manufactured by known or conventional methods. For example, a thermal recording layer can be manufactured by preparing a coating solution for forming a thermal recording layer by a conventional method, coating it onto one surface of a substrate or the like, and drying it.

[0093] (Preparation process) The method for preparing the above coating solution is not particularly limited. For example, it can be prepared by pre-dispersing all the materials contained in the thermal recording layer in the same solvent. Alternatively, the dye and developer, which react with each other, may be prepared as separate dispersions and then mixed to form the coating solution for the thermal recording layer. In this case, the other components may be added to either the dispersion containing the dye or the dispersion containing the developer, or to both. Examples of methods for preparing the above coating solution for the thermal recording layer include stirring, ultrasonic treatment, crushing treatment using a ball mill, bead mill, sand mill, high-pressure homogenizer, etc. One of these methods may be used, or two or more may be used.

[0094] (Coating process) The method of applying the above coating liquid is not particularly limited and includes methods such as direct application to the target surface of a substrate or the like, or application to a release film and then transfer to the target surface of the substrate or the like. Examples of coating methods include air knife coating, barrier blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, die coating, and gravure coating. Hand application using a wire bar is also acceptable. One of these methods may be used, or two or more may be used.

[0095] (drying process) The method for drying the above-mentioned coating liquid is not particularly limited and includes, for example, heat drying, room temperature drying, and vacuum drying. One of these methods may be used, or two or more may be used.

[0096] As described above, a thermal recording layer can be obtained. The thermal recording layer of the present invention can suppress the decrease in optical density of the printed area over time, even when printed at low energy. For this reason, it is possible to prevent the printed area from fading over time, even in miniaturized printers or when using high-speed printing or energy-saving settings.

[0097] [Thermal recording media] The thermal recording body of the present invention comprises at least the thermal recording layer of the present invention described above. The thermal recording body may also comprise other layers besides the thermal recording layer. Examples of these other layers include a substrate, an anchor layer, an intermediate layer, and a topcoat layer. The anchor layer is located between the substrate and the thermal recording layer and can improve the anchoring ability of the thermal recording layer to the substrate. The intermediate layer is located between the thermal recording layer and the topcoat layer and functions as a protective layer to protect the thermal recording layer. The topcoat layer is located on one surface of the thermal recording body of the present invention and can improve thermal head suitability.

[0098] The thermal recording body of the present invention preferably comprises a substrate and a topcoat layer as the other layers. The substrate functions as a support for the thermal recording layer and the topcoat layer, thereby increasing the strength of the thermal recording body of the present invention and providing excellent handling properties. The thermal recording body of the present invention comprising the substrate and the topcoat layer preferably has a structure in which the substrate, the thermal recording layer, and the topcoat layer are laminated in this order.

[0099] Hereinafter, one embodiment of the thermal recording body 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.

[0100] Figure 1 is a schematic cross-sectional view showing one embodiment of the thermal recording body of the present invention. The thermal recording body 1 shown in Figure 1 comprises a substrate 2, an anchor layer 3, a thermal recording layer 4, an intermediate layer 5, and a top coat layer 6 in this order. The top coat layer 6 is located on one surface of the thermal recording body 1, and the substrate 2 is located on the other surface of the thermal recording body 1. Note that the thermal recording body 1 shown in Figure 1 does not necessarily have to include one or more layers selected from the group consisting of the substrate 2, anchor layer 3, intermediate layer 5, and top coat layer 6.

[0101] (base material) Examples of base material 2 include high-quality paper, art paper, coated paper, kraft paper, laminated paper (a paper base material laminated with a thermoplastic resin such as polyethylene), porous materials such as nonwoven fabrics, resin films, and synthetic paper. Examples of resins constituting the resin film and synthetic paper include polypropylene, polyethylene, polyethylene terephthalate, polystyrene, and polycarbonate. Only one type of resin may be used, or two or more types may be used. The resin film may be stretched or not. Furthermore, base material 2 may be a single layer or a multi-layered layer with the same composition or different thicknesses.

[0102] The thickness of the substrate 2 is not particularly limited, but is preferably 5 μm to 150 μm, and more preferably 10 μm to 100 μm. When the thickness is within the above range, it is easier to achieve more appropriate coating properties and support properties, and handling properties may be better.

[0103] (Anchor layer) The anchor layer 3 is a layer intended to improve the adhesion between the substrate 2 and the thermal recording layer 4. The anchor layer 3 may be omitted if it is not needed, in which case the thermal recording layer 4 can be directly laminated on one side of the substrate 2. The anchor layer 3 preferably contains a binder, and may also contain other components. Examples of these other components include antistatic agents, surface tension modifiers, and fillers.

[0104] Examples of the binders mentioned above include those similar to the binders listed in the section on thermal recording layer 4. These binders can be used alone or in combination of two or more types.

[0105] The content of the above-mentioned binder is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on 100% by mass of the total solid content of the anchor layer 3. Furthermore, the content of the above-mentioned binder may be 99% by mass or less, 95% by mass or less, or 90% by mass or less, based on 100% by mass of the total solid content of the anchor layer 3.

[0106] Examples of the above-mentioned antistatic agents include low-molecular-weight antistatic agents such as surfactants; high-molecular-weight antistatic agents such as acrylic-styrene copolymers; and conductive metal compounds such as tin oxide. These antistatic agents can be used individually or in combination of two or more.

[0107] Examples of the surface tension modifiers mentioned above include those similar to the surface tension modifiers listed in the section on thermal recording layer 4. These surface tension modifiers can be used alone or in combination of two or more types.

[0108] The above-mentioned filler may be, for example, the same as the filler listed in the section on thermal recording layer 4. The above-mentioned filler can be used alone or in combination of two or more types.

[0109] The coating amount (dry mass) of the anchor layer 3 is preferably, for example, 0.1 g / m². 2 ~10g / m 2 And more preferably 0.2 g / m 2 ~5.0g / m 2 Therefore, if the amount of coating is within the above range, it is easier to achieve more appropriate properties such as heat insulation, cushioning, and adhesion between the substrate 2 and the heat-sensitive recording layer 4.

[0110] (Middle class) The intermediate layer 5 is a layer that has the function of improving the barrier properties of the thermal recording body 1, such as water resistance, chemical resistance, plasticizer resistance, and oil resistance. The intermediate layer 5 contains, for example, a binder such as a resin. The intermediate layer 5 may further contain other components as needed. Examples of these other components include crosslinking agents and surface tension modifiers.

[0111] Examples of the binders mentioned above include those similar to the binders listed in the section on thermal recording layer 4. These binders can be used alone or in combination of two or more types.

[0112] The above-mentioned binder may be a resin having a water-soluble portion or a resin without a water-soluble portion. Examples of resins having a water-soluble portion include polyvinyl alcohol (PVA) resin and core-shell type resins. In this specification, "core-shell type resin" means a resin having a structure in which hydrophobic core particles are coated with a water-soluble shell polymer.

[0113] Examples of the crosslinking agent include those similar to those listed in the section on thermal recording layer 4. Examples of the surface tension modifier include those similar to those listed in the section on thermal recording layer 4. These materials can be used individually or in combination of two or more.

[0114] For example, the coating amount (dry mass) of the intermediate layer 5 is 0.1 g / m². 2 ~10g / m 2 Preferably, and more preferably, 1.0 g / m 2 ~5.0g / m 2 That is the case.

[0115] (Top coat layer) The top coat layer 6 is a layer intended to improve the matching of the thermal recording body 1 with respect to the thermal head, that is, to improve the slipperiness of the head and suppress the adhesion of debris to the head. It is preferable that the thermal recording body 1 has the top coat layer 6 on one end face. The top coat layer 6 may contain, for example, a binder, a filler, a lubricant, a crosslinking agent, a surface tension modifier, etc. These materials can be used individually or in combination of two or more types.

[0116] Examples of the binders mentioned above include those similar to the binders listed in the section on thermal recording layer 4. Among these, acrylic resins are preferred as the binders. The content of the binder is preferably 10% by mass or more, and more preferably 20% by mass or more, based on 100% by mass of the total solid content of the top coat layer 6. Furthermore, the content of the binder is preferably 70% by mass or less, and more preferably 60% by mass or less, based on 100% by mass of the total solid content of the top coat layer 6.

[0117] Examples of the above-mentioned fillers include those similar to those listed in the section on thermal recording layer 4. The content of the above-mentioned filler is preferably 10% by mass or more, and more preferably 20% by mass or more, based on 100% by mass of the total solid content of the top coat layer 6. Furthermore, the content of the above-mentioned filler is preferably 60% by mass or less, and more preferably 50% by mass or less, based on 100% by mass of the total solid content of the top coat layer 6.

[0118] Examples of the above-mentioned lubricant include those similar to the lubricant listed in the section on thermal recording layer 4. The content of the above-mentioned lubricant is preferably 1% by mass or more, and more preferably 5% by mass or more, based on 100% by mass of the total solid content of the top coat layer 6. Furthermore, the content of the above-mentioned lubricant is preferably 40% by mass or less, and more preferably 30% by mass or less, based on 100% by mass of the total solid content of the top coat layer 6.

[0119] Examples of the crosslinking agents mentioned above include those similar to those listed in the section on thermal recording layer 4. In particular, inorganic crosslinking agents are preferred, and zirconium compounds are more preferred, from the viewpoint of improving heat resistance and suitability for thermal heads by forming a crosslinked structure containing metal ions. The content of the crosslinking agent is preferably 0.5% by mass or more, and more preferably 1% by mass or more, based on 100% by mass of the total solid content of the top coat layer 6. Furthermore, the content of the crosslinking agent is preferably 20% by mass or less, and more preferably 10% by mass or less, based on 100% by mass of the total solid content of the top coat layer 6.

[0120] For example, the coating amount (dry mass) of the topcoat layer 6 is 0.1 g / m². 2 ~10g / m 2 Preferably, and more preferably, 1.0 g / m 2 ~5.0g / m 2 That is the case.

[0121] [Method for manufacturing thermal recording media] The thermal recording material of the present invention can be manufactured by known or conventional methods. For example, a method for manufacturing the thermal recording material 1 shown in Figure 1 will be described. First, coating liquids for forming each layer are prepared by a conventional method.

[0122] (Preparation process) The method for preparing the above coating solution is not particularly limited; for example, the coating solution can be prepared for each layer by pre-dispersing all the materials in the same solvent. Also, similar to the preparation of the coating solution for the thermal recording layer, if the materials contain materials that can react with each other, one material and the other materials may be prepared as separate dispersions and then mixed together to form the coating solution. Examples of methods for preparing the above coating solution include stirring, ultrasonic treatment, crushing treatment using a ball mill, bead mill, sand mill, high-pressure homogenizer, etc. These methods can be used individually or in combination of two or more.

[0123] (Coating process) The method of applying the above coating liquid is not particularly limited and includes methods such as direct application to the substrate or application to a release film and then transfer to the substrate. Examples of coating methods include air knife coating, barrier blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, die coating, and gravure coating. Hand application using a wire bar is also acceptable. These methods can be used individually or in combination of two or more.

[0124] (drying process) The method for drying the above-mentioned coating liquid is not particularly limited and includes, for example, heat drying, room temperature drying, and vacuum drying. These methods can be used individually or in combination of two or more.

[0125] In this manner, an anchor layer 3, a thermal recording layer 4, an intermediate layer 5, and a top coat layer 6 are sequentially formed on one surface of the substrate 2. The thermal recording body 1 can be manufactured in this way. [Examples]

[0126] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples. Unless otherwise specified, the masses mentioned in the examples refer to the mass of each component in a dry state.

[0127] Example 1 (Preparation of thermal recording media) <Anchor layer> An anchor layer coating solution (solid content concentration 11% by mass) containing an acrylic resin as a binder and water as a solvent was prepared by conventional methods. The above anchor layer coating solution was applied to one surface of the synthetic paper substrate by conventional methods and dried, resulting in a coating amount of 0.4 g / m². 2 An anchor layer of (dry mass) was formed.

[0128] <Thermal recording layer> Solution A (solid content 32% by mass) was prepared by a conventional method, containing 34.0% by mass of 2-anilino-6-(dibutylamino)-3-methylfluorane (ODB-2) as a dye, 48.2% by mass of 1,2-di(3-methylphenoxyethane) as a sensitizer, 7.1% by mass of a carboxyl group-containing acrylic resin and 10.1% by mass of an alkali-soluble acrylic resin as binders, 0.1% by mass of a surfactant as a surface tension modifier, 0.1% by mass of an antifoaming agent, 0.2% by mass of a preservative, and water. Next, a solution B (solid content concentration 40% by mass) containing 90.2% by mass of 4-hydroxyphenyl (4'-n-propoxyphenyl) sulfone as a color developer, 9.0% by mass of acrylic resin as a binder, 0.1% by mass of a surfactant as a surface tension modifier, 0.3% by mass of an antifoaming agent, 0.4% by mass of a thickening agent, and water was prepared by a conventional method.

[0129] Next, a thermal recording layer coating solution (solid content 35% by mass) was prepared by conventional methods, containing 30.9 parts by mass of solution A, 0.3 parts by mass of epichlorohydrin resin as a crosslinking agent, 0.3 parts by mass of a surfactant as a surface tension modifier, 23.6 parts by mass of solution B, 10.1 parts by mass of a urea urethane compound (compound represented by formula (3) above) as a preservation improver, 22.9 parts by mass of modified SBR (Tg: -3℃) as a binder, 9.4 parts by mass of kaolin as a filler, 2.7 parts by mass of polyethylene wax (average particle size: 1.3 μm, softening point: approximately 110℃) as a lubricant, 0.30 parts by mass of animal zinc stearate (derived from animal fats and oils, average particle size: 5.5 μm, softening point: 120℃) (manufactured by Chukyo Oils Co., Ltd., product name: Hydrin O-128), and water. By applying the above-mentioned thermal recording layer coating solution to the surface of the anchor layer using a conventional method and drying it, the coating amount is 4.8 g / m². 2 A thermal recording layer of (dry mass) was formed. Note that the part-of-mass values ​​in this paragraph also represent the part-of-mass (i.e., the part-of-mass as solid content) of each material in its dry state.

[0130] <Middle class> An acrylic resin emulsion (solid content concentration 12% by mass) is applied to the above-mentioned thermal recording layer by a conventional method and dried, resulting in a coating amount of 1.8 g / m². 2 An intermediate layer of (dry mass) was formed.

[0131] <Top coat layer> A topcoat coating solution (solid content 16% by mass) was prepared by conventional methods, containing 11.1% by mass of zinc stearate and 4.9% by mass of polyethylene wax as lubricants, 39.9% by mass of acrylic resin emulsion as a binder, 30.7% by mass of calcium carbonate and 6.8% by mass of polymethyl methacrylate (PMMA) particles as fillers, 0.2% by mass of a preservative, 4.8% by mass of zirconium ammonium carbonate as a crosslinking agent, 1.0% by mass of a surfactant as a surface tension modifier, 0.6% by mass of an antifoaming agent, and water. The above topcoat coating solution was applied to the surface of the above intermediate layer by conventional methods and dried, resulting in a coating amount of 1.6 g / m². 2A topcoat layer of (dry mass) was formed.

[0132] Examples 2-3 In the process of preparing the thermal recording layer, the thermal recording bodies of Examples 2 and 3 were prepared in the same manner as in Example 1, except that the amount of animal-derived zinc stearate was changed to the amount shown in Table 1.

[0133] Comparative Example 1 A thermal recording material for Comparative Example 1 was prepared in the same manner as in Example 1, except that the animal-derived zinc stearate was not incorporated in the thermal recording layer preparation process.

[0134] Comparative Examples 2-3 In the process of preparing the thermal recording layer, as shown in Table 1, plant-derived zinc stearate (derived from vegetable oil, average particle size: 5.5 μm, softening point: 120°C) (manufactured by Chukyo Oils Co., Ltd., product name: Hydrin P-647) or paraffin wax (average particle size: 1.0 μm, softening point: approximately 75°C) (manufactured by Chukyo Oils Co., Ltd., product name: Hydrin L-700) was used instead of animal-derived zinc stearate, and the amount was changed to 1.3 parts by mass. The thermal recording materials of Comparative Examples 2 and 3 were prepared in the same manner as in Example 1.

[0135] Example 4 The thermal recording material of Example 4 was prepared in the same manner as in Example 1, except that (N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea) was used as the color developer instead of 4-hydroxyphenyl (4'-n-propoxyphenyl)sulfone in the process of preparing the thermal recording layer.

[0136] Example 5 The thermal recording material of Example 5 was prepared in the same manner as in Example 4, except that the amount of animal-derived zinc stearate used in the thermal recording layer preparation process was changed to the amount shown in Table 2.

[0137] Comparative Example 4 A thermal recording material for Comparative Example 4 was prepared in the same manner as in Example 4, except that the animal-derived zinc stearate was not incorporated in the thermal recording layer preparation process.

[0138] [evaluation] The thermal recording materials prepared in the examples and comparative examples were evaluated as follows. The results are shown in Tables 1 and 2. Some of the results are also illustrated in Figures 2 and 3.

[0139] (Evaluation of changes in discoloration over time) A thermal paper printing test device (manufactured by Okura Engineering Co., Ltd., device name: Pulse Simulator TH-M2 / PP) was used to print on a thermal recording material. The printing speed was set to 50 mm / sec, the applied voltage to 17.0 V, the head resistance to 870 Ω, and the pulse width to 0.488 to 1.394 ms. Furthermore, the applied energy was set to the value listed in Table 1 or Table 2 (0.20 mJ / dot, 0.22 mJ / dot, or 0.26 mJ / dot). A printed thermal recording material was prepared and used as a test specimen. The optical density (printed area density) of the printed area of ​​the test specimen immediately after printing was measured using a spectrophotometer (manufactured by X-rite, device name: eXact). The measured value at this time was defined as the immediate optical density X0. Subsequently, the specimens were left standing at 23°C and 50% humidity, and the optical density of the printed area of ​​the test specimen was measured using the spectrophotometer described above 2 hours, 24 hours, and 4 days after printing. The optical density of the printed area at these times was defined as Y1 at 2 hours, Y2 at 24 hours, and Y3 at 4 days, respectively. The rate of change in decolorization of the printed area (decolorization rate) was then calculated using the following formula, where Y represents one of Y1 to Y3. The rate of change in decolorization (decolorization rate) [%] = (X0 - Y) / X0 × 100

[0140] [Table 1]

[0141] As shown in Table 1, when the thermal recording layer contained animal-derived zinc stearate and the developer was a phenol-based developer (Examples 1-3), the decrease in optical density was suppressed even when printing was done at low energies such as 0.26 mJ / dot or 0.22 mJ / dot. Therefore, the thermal recording layers of the examples were evaluated as having excellent anti-fading effects on the printed area. In particular, when the applied energy was 0.26 mJ / dot, the decrease in optical density was almost completely suppressed (Figure 2). On the other hand, when the thermal recording layer did not contain animal-derived zinc stearate (Comparative Examples 1-3), a significant decrease in optical density was observed after 2 hours when the applied energy was 0.22 mJ / dot, and after 24 hours when the applied energy was 0.26 mJ / dot (Figure 2). In particular, although plant-derived zinc stearate had physical properties such as average particle size and softening point that were the same as animal-derived zinc stearate, no anti-fading effect was confirmed. Therefore, it was found that preventing the fading of the printed area was difficult with plant-derived zinc stearate or paraffin wax, and that suppression of print fading was achieved by animal-derived zinc stearate.

[0142] [Table 2]

[0143] As shown in Table 2, when the thermal recording layer contained animal-derived zinc stearate and the developer was a non-phenolic developer (Examples 4-5), the decrease in optical density was suppressed even when printing at low energies such as 0.22 mJ / dot or 0.20 mJ / dot (Figure 3). For this reason, the thermal recording layers of the examples were evaluated as having excellent anti-fading effects on the printed area. On the other hand, when the thermal recording layer did not contain animal-derived zinc stearate (Comparative Example 4), a decrease in optical density over time was observed (Figure 3), and it was evaluated that it was difficult to prevent the printing area from fading.

[0144] In summary, the configuration of the present invention and its variations are described below. [Note 1] The thermal recording layer contains animal-derived zinc stearate. The stearic acid in the above-mentioned animal-derived zinc stearate is stearic acid derived from animal fats and oils. The thermal recording layer has a content of 0.1 to 2% by mass of the animal-derived zinc stearate, relative to 100% by mass of the total solid content of the thermal recording layer. [Note 2] The thermal recording layer according to Note 1, wherein the thermal recording layer comprises a dye and a developer, and the developer comprises a compound represented by formula (1) and / or a compound represented by formula (2). [Note 3] The thermal recording layer according to Note 1 or 2, wherein the thermal recording layer contains a lubricant, and the mass ratio of the content of the animal-derived zinc stearate to the content of the lubricant (animal-derived zinc stearate / lubricant) is 0.01 to 1. [Note 4] A thermal recording body in which a base material, a thermal recording layer described in any one of Notes 1 to 3, and a top coat layer are laminated in this order. [Explanation of Symbols]

[0145] 1. Thermal recording medium 2 Base material 3 Anchor layer 4. Thermal recording layer 5. Middle Class 6. Top coat layer

Claims

1. The thermal recording layer contains animal-derived zinc stearate, The stearic acid in the aforementioned animal-derived zinc stearate is stearic acid derived from animal fats and oils. The thermal recording layer has a content of 0.1 to 2% by mass of the total solid content of the thermal recording layer, where the content of the animal-derived zinc stearate is 100% by mass.

2. The thermal recording layer comprises a dye and a color developer. The thermal recording layer according to claim 1, wherein the color developer comprises a compound represented by the following formula (1) and / or a compound represented by the following formula (2). 【Chemistry 1】 (In formula (1), A １ This represents a monovalent hydrocarbon group having 1 to 4 carbon atoms, and multiple A １ p may be the same or different. p represents an integer from 0 to 4, and multiple p may be the same or different. １ (This represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may have substituents.) 【Chemistry 2】 (In formula (2), R ２ This represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may have substituents, and a plurality of R ２ They may be the same or different. A ２ This represents a monovalent hydrocarbon group having 1 to 4 carbon atoms, and multiple A ２ (These values ​​may be the same or different. q represents an integer between 0 and 4, and multiple q values ​​may be the same or different.)

3. The thermal recording layer contains a lubricant, The thermal recording layer according to claim 1 or 2, wherein the mass ratio of the content of the animal-derived zinc stearate to the content of the lubricant (animal-derived zinc stearate / lubricant) is 0.01 to 1.

4. A thermal recording body comprising a base material, a thermal recording layer according to claim 1 or 2, and a top coat layer laminated in this order.

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