Color developer and thermal recording material

Abstract

To provide a color developer that provides a heat-sensitive recording material that has a low environmental load and achieves both excellent color development sensitivity and storage stability, and also to provide a heat-sensitive recording material obtained by using the color developer.SOLUTION: Provided is a color developer containing a compound represented by the following formula (1). (In the formula (1) above, a, b, c, A, B, and C are as follows. a is an integer selected from 1 to 5, b is an integer selected from 0 to 4, c is an integer selected from 0 to 5, A is each independently a fluoro group or a fluoroalkyl group, and B and C are each independently an alkyl group, a fluoro group, a fluoroalkyl group, a carboxyl group, an ester group, a carbonyl group, or a nitrile group. However, the sum of a and b is 1 or more and 5 or less, and when B and / or C is a carboxyl group, the substitution position of the carboxyl group is the o-position).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a color developer and a heat-sensitive recording material obtained by using the color developer. [Background technology]

[0002] In general, thermal recording materials having a thermal recording layer mainly composed of a colorless or light-colored basic (electron-donating) leuco dye (hereinafter sometimes abbreviated as "dye") and an electron-accepting developer (hereinafter sometimes abbreviated as "developer") that reacts with the dye to develop color when heated, have been widely used.

[0003] Many of the compounds used as such developers are compounds that mainly have a phenol structure, such as 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), bis(4-hydroxyphenyl)sulfone (bisphenol S), etc. On the other hand, due to concerns about environmental impact, studies are also being conducted to use compounds that do not have a phenol structure as developers.

[0004] Patent Document 1 discloses a thermal recording medium using a compound having a sulfonylurea structure as a color developer. Patent Document 2 discloses a thermal recording medium using a compound having a diphenylurea structure having an alkoxy group on the phenyl group as a color developer. Patent Document 3 discloses a thermal recording medium using a compound having a diphenylurea structure having a carboxyl group on the phenyl group as a color developer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4601174 [Patent Document 2] Patent No. 3339043 [Patent Document 3] Japanese Patent Publication No. 08-216526 Summary of the Invention [Problem to be solved by the invention]

[0006] The color developer having a sulfonylurea structure described in Patent Document 1 is known to have high aqueous toxicity, and there is a need to develop a non-phenol color developer with lower environmental impact. In addition, according to the studies of the present inventors, the color developer having a sulfonylurea structure described in Patent Document 1 tends to have a significantly lower color development sensitivity as the particle size of the color developer increases, and in order to reduce the load of the wet grinding process, there has been a need for a color developer that shows excellent color development sensitivity even when the particle size of the color developer is large. Furthermore, according to the present inventors' investigations, when a compound having a diphenylurea structure with an alkoxy group on the phenyl group shown in the above Patent Document 2 is used as a developer, a thermal recording material with excellent storage stability of the color-developing portion was not obtained. Furthermore, according to the present inventors' investigations, when a compound having a diphenylurea structure with a carboxyl group on the phenyl group shown in the above Patent Document 3 is used as a developer, a thermal recording material with excellent color-developing sensitivity was not obtained. That is, the object of the present invention is to provide a color developer that can replace a sulfonylurea structure, has a low environmental impact, and can provide a thermal recording material that has both excellent color-developing sensitivity and storage stability, and a thermal recording material obtained by using the color developer. [Means for solving the problem]

[0007] As a result of intensive research, the present inventors have found that the above problems can be solved by using a urea compound having a specific substituent as a color developer. do.

[0008] [1] A color developer comprising a compound represented by the following formula (1): [ka] (In the above formula (1), a, b, c, A, B, and C are as follows. a is an integer selected from 1 to 5; b is an integer selected from 0 to 4; c is an integer selected from 0 to 5; Each A is independently a fluoro group or a fluoroalkyl group; B and C each independently represent an alkyl group, a fluoro group, a fluoroalkyl group, a carboxyl group, an ester group, a carbonyl group, or a nitrile group. However, the sum of a and b is between 1 and 5, When B and / or C is a carboxyl group, the substitution position of the carboxyl group is the o-position. [2] The color developer according to [1], wherein in the formula (1), at least one A is a fluoro group or a trifluoromethyl group. [3] The color developer according to [1] or [2], wherein in the formula (1), at least one A is a trifluoromethyl group. [4] The color developer according to any one of [1] to [3], wherein a is 1 in the formula (1). [5] The color developer according to any one of [1] to [4], wherein in the formula (1), c is an integer selected from 1 to 5, and at least one C is a fluoro group or a trifluoromethyl group. [6] The color developer according to any one of [1] to [5], wherein in the formula (1), c is an integer selected from 1 to 5, and at least one C is a trifluoromethyl group. [7] The color developer according to any one of claims [1] to [6], wherein in formula (1), c is 1. [8] A thermosensitive recording material having a support and a thermosensitive recording layer provided on the support, the thermosensitive recording layer containing the color developer according to any one of [1] to [7]. [9] The heat-sensitive recording material according to any one of [1] to [8], wherein the heat-sensitive recording layer contains a leuco dye.

[10] The heat-sensitive recording material according to any one of [1] to [9], wherein the heat-sensitive recording layer contains a sensitizer.

[11] The heat-sensitive recording material according to any one of [1] to

[10] , wherein the heat-sensitive recording layer contains a stabilizer.

[12] An ink containing the developer according to any one of [1] to [7].

[13] A writing instrument containing the ink described in

[12] . Effect of the Invention

[0009] According to the present invention, there are provided a color developer capable of providing a heat-sensitive recording material excellent in color development sensitivity and storage stability, and a heat-sensitive recording material obtained by using said color developer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described in detail below, but the present invention is not limited to the following description, and can be modified as desired without departing from the gist of the present invention. In the present invention, when a numerical value or physical property value is enclosed before and after "~", the value before and after the "~" is included.

[0011] [Developer] A color developer according to one embodiment of the present invention is a color developer containing a compound represented by the following formula (1). In this specification, the compound represented by formula (1) may be referred to as "compound (1)". [ka] (In the above formula (1), a, b, c, A, B, and C are as follows. a is an integer selected from 1 to 5; b is an integer selected from 0 to 4; c is an integer selected from 0 to 5; Each A is independently a fluoro group or a fluoroalkyl group; B and C each independently represent an alkyl group, a fluoro group, a fluoroalkyl group, a carboxyl group, an ester group, a carbonyl group, or a nitrile group. However, the sum of a and b is between 1 and 5, When B and / or C is a carboxyl group, the substitution position of the carboxyl group is the o-position.

[0012] The color developer according to the present embodiment has a remarkable effect of being excellent in color development sensitivity and storage stability. It is presumed that the above-mentioned color developer has such an excellent effect due to the following reasons. That is, by introducing a fluoro group or a fluoroalkyl group as a substituent into the diphenylurea compound, the acidity and / or hydrogen bond donating ability of the NH site is improved, and the color development sensitivity is improved by making it easier to react with the leuco dye, and at the same time, the storage stability is improved by stabilizing the color development state. In addition, it is considered that the absence of an electron-donating substituent such as an alkoxy group as a substituent increases the stability of the color development state in which the leuco dye and the color developer react, and improves the storage stability. In addition, it is considered that the presence of a fluoro group or a fluoroalkyl group as a substituent appropriately suppresses association and / or crystallinity, thereby effectively increasing amorphous stability without excessively reducing the energy required for melting, and thus increasing the storage stability of the metastable color development state. In addition, by having a fluoro group or a fluoroalkyl group as a substituent, it is believed that the ease of mixing (compatibility) at the molecular level with the leuco dye or sensitizer can be appropriately adjusted, thereby achieving both high color development sensitivity and storage stability. In addition, by having a hydrophilic portion due to a highly polar urea group and a hydrophobic portion due to a fluoro group or a fluoroalkyl group in the molecule, it is believed that the storage stability under various storage conditions can be improved at the same time. Specifically, it is believed that the color development sensitivity can be increased while resistance to heat, moisture, alcohol, oil, grease, etc. can be increased at the same time.

[0013] In the above formula (1), a is an integer selected from 1 to 5, and is preferably 3 or less, more preferably 2 or less, and particularly preferably 1. When a is large, the hydrophobicity increases, and the hydrophobicity in water increases. It is believed that the color development sensitivity decreases due to a decrease in dispersibility in the solvent, an increase in molecular weight making it difficult for the molecules to move when melted, or an excessive decrease in compatibility with the leuco dye and sensitizer. In the above formula (1), the carbon number of the fluoroalkyl group in A is 1 to 12. The carbon number is preferably 6 or less, more preferably 4 or less, and particularly preferably 1. There is no limitation on the position or number of fluoro groups in the fluoroalkyl group. If the carbon number is large, the hydrophobicity is too high, and the dispersibility in water is reduced, or the molecular weight is large, and the molecule is difficult to move when melted, or the compatibility with the leuco dye and the sensitizer is too low, and the color development sensitivity is reduced. Each A is independently a fluoro group or a fluoroalkyl group, and when a is 2 or more, all A may be the same substituent or may be different, and it is more preferable that all A are the same substituent. As A, a fluoro group or a trifluoromethyl group is preferable because it provides moderate hydrophobicity and compatibility, and a trifluoromethyl group is particularly preferable because it is easy to realize high color development sensitivity due to high compatibility.

[0014] The substitution position of the fluoro group or fluoroalkyl group in A is not particularly limited, but is preferably the o-position or m-position, since it suppresses crystallinity and provides appropriate amorphous stability. On the other hand, the m-position or p-position is preferred, since it is spatially separated from the adjacent NH moiety and does not inhibit reactivity with the leuco dye. The m-position is particularly preferred, since it is easy to achieve both appropriate amorphousness and reactivity. Note that when a is 2 or more, it is preferred that at least one A is in the m-position.

[0015] In the above formula (1), b is an integer selected from 0 to 4, preferably 3 or less, more preferably 2 or less, particularly preferably 1 or less, and even more preferably 0. In the above formula (1), the number of carbon atoms in the alkyl group in B is 1 to 12. The carbon number is preferably 6 or less, more preferably 4 or less, and particularly preferably 1. If the carbon number is large, it is considered that the hydrophobicity becomes too high, resulting in a decrease in dispersibility in water, a lower melting point resulting in a decrease in stability of the white part, and a decrease in storage stability of the colored part. In the above formula (1), the fluoroalkyl group in B is the same as that in A. In the above formula (1), the carboxyl group in B is bonded to the urea group at the o-position. When the carboxyl group is bonded to the o-position, intramolecular hydrogen bonding can be formed between the adjacent urea group, weakening the intermolecular hydrogen bonding, thereby suppressing crystallinity, suppressing an excessively high melting point, and increasing compatibility with the leuco dye, thereby increasing color development sensitivity.

[0016] In the above formula (1), the ester group in B is represented by the following formula (2). [ka] In the above formula (2), R 1 is an alkyl group having 1 to 12 carbon atoms. If the number of carbon atoms is large, the melting point decreases and the stability of the white part decreases, and the storage stability of the colored part decreases, so the number of carbon atoms is preferably 6 or less, more preferably 4 or less, more preferably 2 or less, and particularly preferably 1 (methyl group).

[0017] In the above formula (1), the carbonyl group in B is represented by the following formula (3). [ka] In the above formula (3), R 2 R is an alkyl group having 1 to 12 carbon atoms or an optionally substituted phenyl group. If the number of carbon atoms is large, the melting point decreases, the stability of the white part decreases, and the storage stability of the colored part decreases, so the number of carbon atoms is preferably 6 or less, more preferably 4 or less, more preferably 2 or less, and particularly preferably 1 (methyl group). 2 is preferably a methyl group, a phenyl group, an o-tolyl group, a m-tolyl group or a p-tolyl group. In formulas (2) and (3), * indicates the bonding site to the carbon of the benzene ring.

[0018] For B, a fluoro group, a trifluoromethyl group, an ester group having 1 to 2 carbon atoms, a carboxyl group, or a nitrile group is preferable because it is easy to increase the color development sensitivity, and in particular, a fluoro group, a trifluoromethyl group, or a carboxyl group is more preferable because it has good compatibility with the leuco dye, a fluoro group or a trifluoromethyl group is even more preferable, and a trifluoromethyl group is particularly preferable.

[0019] In the above formula (1), c is an integer selected from 0 to 5, and is preferably 3 or less, more preferably 2 or less, and particularly preferably 1 or less. In the above formula (1), the alkyl group, fluoroalkyl group, carboxyl group, ester group and carbonyl group in C are the same as those in B.

[0020] In C, a fluoro group, a trifluoromethyl group, an ester group having 1 to 2 carbon atoms, a carboxyl group, or a nitrile group is preferable because it is easy to increase the color development sensitivity, and a fluoro group, a trifluoromethyl group, or a carboxyl group is more preferable because it has good compatibility with the leuco dye, a fluoro group or a trifluoromethyl group is even more preferable, and a trifluoromethyl group is particularly preferable.

[0021] In a particularly preferred embodiment of the developer according to the present embodiment, in the above formula (1), a is 1, A is a fluoro group or a trifluoromethyl group, b is 0, c is 0 or 1, and C is a fluoro group or a trifluoromethyl group. When the substitution positions of A and C are both o-positions, the steric hindrance around the urea structure becomes large, thereby decreasing the reactivity with the leuco dye, and therefore it is preferable that the substitution position of at least one of A and C is not the o-position.

[0022] Specific examples of the above formula (1) include, but are not limited to, the following. [ka] [ka] [ka]

[0023] [Use of developer] The color developer of the present embodiment can be used as ink for writing instruments, and writing instruments containing the ink (for example, friction ballpoint pens and fountain pens), etc.

[0024] [Thermal recording material] Another embodiment of the thermosensitive recording material of the present invention is a thermosensitive recording material having a support and a thermosensitive recording layer provided on the support, and the thermosensitive recording layer contains the color developer according to the embodiment of the present invention. The "thermosensitive recording material" may be in any form, such as paper, film, synthetic paper, or card, as long as it has a thermosensitive recording layer on a support. The thermosensitive recording material has a thermosensitive recording layer on a support, but may have a protective layer, an underlayer, a back layer, an intermediate layer, or the like, as described below, if necessary. Here, "on the support" refers to at least one side of the support, and is usually one side. Also, "on the support" means that the layer is present on at least a part of the support.

[0025] [Thermal recording layer] Another embodiment of the heat-sensitive recording material of the present invention has a heat-sensitive recording layer, and the heat-sensitive recording layer contains a color developer according to an embodiment of the present invention. The heat-sensitive recording layer may contain, in addition to the color developer according to the embodiment of the present invention, a leuco dye, a color developer other than the color developer according to the embodiment of the present invention (hereinafter, sometimes referred to as "other color developers"), a sensitizer, a stabilizer, a binder, a crosslinking agent, a pigment, a lubricant, other additives, etc.

[0026] <Leuco dye> In this embodiment, the heat-sensitive recording layer preferably contains a leuco dye. The leuco dye is usually basic, and any leuco dye known in the art of pressure-sensitive or heat-sensitive recording paper can be used. Specific examples of the leuco dye include triphenylmethane-based leuco dyes, fluoran-based leuco dyes, and the like. Preferred are leuco dyes, fluorene-based leuco dyes, divinyl-based leuco dyes, etc. Typical examples of colorless or pale-colored dyes (dye precursors) are shown below. These leuco dyes (leuco dye precursors) may be used alone or in combination of two or more. The leuco dye is preferably used in an amount of 10 to 200 parts by weight, more preferably 15 to 150 parts by weight, and even more preferably 20 to 100 parts by weight, per 100 parts by weight of the developer according to the embodiment of the present invention.

[0027] Examples of triphenylmethane leuco dyes include 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (also known as crystal violet lactone); 3,3-bis(p-dimethylaminophenyl)phthalide (also known as malachite green lactone); and the like.

[0028] Fluoran leuco dyes include 3-diethylamino-6-methylfluoran; 3-diethylamino-6-methyl-7-anilinofluoran; 3-diethylamino-6-methyl-7-(o,p-dimethylanilino)fluoran; 3-diethylamino-6-methyl-7-chlorofluoran; 3-diethylamino-6-methyl-7-(m-trifluoromethylanilino)fluoran; 3-diethylamino-6-methyl-7-(o-chloroanilino)fluoran; 3-diethylamino-6-methyl-7-(p-chloroanilino)fluoran. 3-Diethylamino-6-methyl-7-(o-fluoroanilino)fluoran;3-Diethylamino-6-methyl-7-(m-methylanilino)fluoran;3-Diethylamino-6-methyl-7-octylanilinofluoran;3-Diethylamino-6-methyl-7-octylaminofluoran;3-Diethylamino-6-methyl-7-benzylaminofluoran;3-Diethylamino-6-methyl-7-dibenzylaminofluoran;3-Diethylamino-6-chloro-7-methylfluoran;3-Diethylamino-6-chloro -7-Anilinofluoran;3-Diethylamino-6-chloro-7-p-methylanilinofluoran;3-Diethylamino-6-ethoxyethyl-7-anilinofluoran;3-Diethylamino-7-methylfluoran;3-Diethylamino-7-chlorofluoran;3-Diethylamino-7-(m-trifluoromethylanilino)fluoran;3-Diethylamino-7-(o-chloroanilino)fluoran;3-Diethylamino-7-(p-chloroanilino)fluoran;3-Diethylamino-7-(o-fluoroanilino)fluoran Fluoran;3-Diethylamino-benzo[a]fluoran;3-Diethylamino-benzo[c]fluoran;3-Dibutylamino-6-methyl-fluoran;3-Dibutylamino-6-methyl-7-anilinofluoran;3-Dibutylamino-6-methyl-7-(o,p-dimethylanilino)fluoran;3-Dibutylamino-6-methyl-7-(o-chloroanilino)fluoran;3-Dibutylamino-6-methyl-7-(p-chloroanilino)fluoran;3-Dibutylamino-6-methyl-7-(o-fluoroanilino)fluoran;3-Dibutylamino-6-methyl-7-(m-trifluoromethylanilino)fluoran;3-Dibutylamino-6-methyl-chlorofluoran;3-Dibutylamino-6-ethoxyethyl-7-anilinofluoran;3-Dibutylamino-6-chloro-7-anilinofluoran;3-Dibutylamino-6-methyl-7-p-methylanilinofluoran;3-Dibutylamino-7-(o-chloroanilino)fluoran;3-Dibutylamino-7-(o-fluoroanilino)fluoran;3-Dipentylamino-6-methyl-7-anilinofluoran 3-Di-pentylamino-6-methyl-7-(p-chloroanilino)fluoran;3-Di-pentylamino-7-(m-trifluoromethylanilino)fluoran;3-Di-pentylamino-6-chloro-7-anilinofluoran;3-Di-pentylamino-7-(p-chloroanilino)fluoran;3-Pyrrolidino-6-methyl-7-anilinofluoran;3-Piperidino-6-methyl-7-anilinofluoran;3-(N-methyl-N-propylamino)-6-methyl-7-anilinofluoran;3-(N-methyl-N-cyclohexylamino) -6-Methyl-7-anilinofluoran;3-(N-ethyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran;3-(N-ethyl-N-xylamino)-6-methyl-7-(p-chloroanilino)fluoran;3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluoran;3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran;3-(N-ethyl-N-isoamylamino)-6-chloro-7-anilinofluoran;3-(N-ethyl-N-tetrahydrofurfurylamino)-6- Methyl-7-anilinofluoran;3-(N-ethyl-N-isobutylamino)-6-methyl-7-anilinofluoran;3-(N-ethyl-N-ethoxypropylamino)-6-methyl-7-anilinofluoran;3-Cyclohexylamino-6-chlorofluoran;2-(4-oxahexyl)-3-dimethylamino-6-methyl-7-anilinofluoran;2-(4-oxahexyl)-3-diethylamino-6-methyl-7-anilinofluoran;2-(4-oxahexyl)-3-dipropylamino-6-methyl-7-anilinofluoran;2-METHYL-6-P-(P-DIMETHYLAMINOPHENYL) AMINOANILINOFLUORAN;2-METHOXY-6-P-(P-DIMETHYLAMINOPHENYL) AMINOANILINOFLUORAN;2-CHLORO-3-METHYL-6-P-(P-PHENYLAMINOPHENYL) AMINOANILINOFLUORAN;2-CHLORO-6-P-(P-DIMETHYLAMINOPHENYL) AMINOANILINOFLUORAN;2-NITRO-6-P-(P-DIETHYLAMINOPHENYL) AMINOANILINOFLUORAN;2-AMINO-6-P-(P-DIETHYLAMINOPHENYL) AMINOANILINOFLUORAN;2-DIETHYLAMINO-6-P-(P-DIETHYLAMINOPHENYL) AMINOANILINOFLUORAN;2-PHENYL 2-benzyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 2-hydroxy-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 3-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran; 3-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran; 3-diethylamino-6-p-(p-dibutylaminophenyl)aminoanilinofluoran; 2,4-dimethyl-6-[(4-dimethylamino)anilino]fluoran, and the like.

[0029] Examples of fluorene-based leuco dyes include 3,6,6'-tris(dimethylamino)spiro[fluorene-9,3'-phthalide]; 3,6,6'-tris(diethylamino)spiro[fluorene-9,3'-phthalide]; and the like.

[0030] Examples of divinyl leuco dyes include 3,3-bis[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl]-4,5,6,7-tetrabromophthalide; 3,3-bis[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl]-4,5,6,7-tetrachlorophthalide; 3,3-bis[1,1-bis(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrabromophthalide; and 3,3-bis[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide.

[0031] Other leuco dyes include 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide; 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-octyl-2-methylindol-3-yl)-4-azaphthalide; 3-(4-cyclohexylethylamino-2-methoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide; 3,3-bis(1-ethyl-2-methylindol-3-yl)phthalide; 3,6- Bis(diethylamino)fluoran-γ-(3'-nitro)anilinolactam;3,6-Bis(diethylamino)fluoran-γ-(4'-nitro)anilinolactam;1,1-Bis[2',2',2”,2”-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2,2-dinitrileethane;1,1-Bis[2',2',2”,2”-tetrakis-(p-dimethylaminophenyl)-ethenyl]-2-β-naphthoylethane;1,1-Bis[2',2',2”,2”-tetrakis(p-dimethylaminophenyl)ethenyl] -2,2-diacetylethane; bis[2,2,2',2'-tetrakis(p-dimethylaminophenyl)ethenyl]-methylmalonic acid dimethyl ester, and the like.

[0032] <Other developers> The thermosensitive recording layer may contain a color developer other than the color developer according to the embodiment of the present invention, within a range that does not impair the effects of the present invention. As the other color developer, any color developer known in the field of conventional pressure-sensitive or thermosensitive recording paper can be used, and although there is no particular limitation, an electron-accepting color developer is preferable. The other color developer may be used alone or in combination of two or more kinds. When the other color developer is used, the amount of the other color developer is preferably 1 to 5000 parts by weight, more preferably 5 to 1000 parts by weight, and even more preferably 10 to 500 parts by weight, based on 100 parts by weight of the color developer according to the embodiment of the present invention. By using other color developers, it is possible to obtain an excellent heat-sensitive recording material which maintains high color development sensitivity and further improves image preservation properties such as heat resistance, moisture resistance, and water resistance. As the other color developer, any of those known in the field of conventional pressure-sensitive or heat-sensitive recording paper can be used, and there is no particular limitation. As the other color developer, bisphenol-based compounds, urea-based compounds, and novolak-type phenol-based compounds are preferable.

[0033] Bisphenol compounds include 4,4'-isopropylidenediphenol, 2,2'-bis(4-hydroxy-3-methylphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 4,4'-dihydroxydiphenyl sulfide, di(4-hydroxy-3-methylphenyl) sulfide, 2,2'-thiobis(3-tert-octylphenol), 2,2'-thiobis(4-tert-octylphenol), 4,4'-dihydroxydiphenyl sulfone, and 2,4'-dihydroxydiphenyl. Examples of such bisphenol sulfone include sulfone, 4-hydroxy-4'-propoxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-allyloxydiphenyl sulfone, bis(3-allyl-4-hydroxyphenyl)sulfone, 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone, 3,4-dihydroxyphenyl-4'-methylphenyl sulfone, 2,4-bis(phenylsulfonyl)phenol, the bisphenol sulfone crosslinked compounds described in Japanese Patent No. 3913820, and the bisphenol sulfone derivatives described in Japanese Patent No. 4004289.

[0034] Examples of urea compounds include 4,4'-bis(3-(phenoxycarbonylamino)methylphenylureido)diphenylsulfone, N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea described in Japanese Patent No. 4601174, 4,4'-bis(3-tosylureido)diphenylmethane described in Japanese Patent Publication No. 2011-105638, and N-[2 -(3-phenylureido)phenyl]benzenesulfonamide, N-[2-(acetoxy)phenyl]-N'-phenylurea, N-[3-(acetoxy)phenyl]-N'-phenylurea, N-[2-(benzoyloxy)phenyl]-N'-phenylurea, N-[3-(benzoyloxy)phenyl]-N'-phenylurea described in JP2017-165091A, Examples of amino acid derivatives include the above-mentioned N-(m-tolylaminocarbonyl)-phenylalanine, N-(p-toluenesulfonyl)-phenylalanine, N-(benzyloxycarbonyl)-valine, N-(m-tolylaminocarbonyl)-methionine, N-(m-tolylaminocarbonyl)-tyrosine, N-(m-tolylaminocarbonyl)-phenylglycine, N-(m-tolylaminocarbonyl)-valine, N-(m-tolylaminocarbonyl)-cysteine-S-benzyl, N-(m-tolylaminocarbonyl)-β-alanine, N-phenylaminothiocarbonyl-glycylglycine, N-(p-toluenesulfonylaminocarbonyl)-phenylalanine-methyl ester, N-(p-toluenesulfonyl)-β-alanine, N-(p-tolylaminocarbonyl)-methionine, and N-(phenylaminocarbonyl)-methionine.

[0035] Examples of the novolak-type phenolic compound include the phenol-formalin condensates described in WO 02 / 098674.

[0036] In addition to the compounds listed above, inorganic acidic substances such as activated clay, attapulgite, colloidal silica, and aluminum silicate, hydroquinone monobenzyl ether, benzyl 4-hydroxybenzoate, aminobenzenesulfonamide derivatives described in JP-A-8-59603, bis(4-hydroxyphenylthioethoxy)methane, 1,5-di(4-hydroxyphenylthio)-3-oxapentane, butyl bis(p-hydroxyphenyl)acetate, methyl bis(p-hydroxyphenyl)acetate, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 1,4-bis[α-methyl-α-(4'-hydroxyphenyl)ethyl]benzene, 1,3-bis[α-methyl-α-(4'-hydroxyphenyl)ethyl]benzene, and the compounds disclosed in WO 02 / 081229 are also usable. , the compounds described in JP-A-2002-301873, thiourea compounds such as N,N'-di-m-chlorophenylthiourea, p-chlorobenzoic acid, stearyl gallate, zinc bis[4-(octyloxycarbonylamino)salicylate] dihydrate, 4-[2-(p-methoxyphenoxy)ethyloxy]salicylic acid, 4-[3-(p-tolylsulfonyl)propyloxy]salicylic acid, 5-[p-(2-p-methoxyphenoxyethoxy)cumyl]salicylic acid, and salts of these aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel, and the like, as well as antipyrine complexes of zinc thiocyanate and complex zinc salts of terephthalaldehydic acid and other aromatic carboxylic acids. Examples of the metal chelate complexes include metal double salts of higher fatty acids and polyvalent hydroxy aromatic compounds, as described in JP-A-10-258577.

[0037] Among the other color developers mentioned above, 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-propoxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-allyloxydiphenyl sulfone, bis(3-allyl-4-hydroxyphenyl)sulfone, 4,4'-isopropylidenediphenol, 2,2'-bis(4-hydroxy-3-methylphenyl)propane, diphenyl sulfone crosslinked type compounds described in Patent No. 3913820, compounds described in Japanese Patent No. 4004289, diphenyl sulfone derivatives described in WO 02 / 098674, phenol-formalin condensates described in WO 02 / 098674, 4,4'-bis(3-(phenoxycarbonylamino)methylphenylureido)diphenyl sulfone, N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea described in Japanese Patent No. 4601174, 4,4'-bis(3-tosylureido)diphenylmethane described in JP 2011-105638 A, N-[2 Preferred are N-(m-tolylaminocarbonyl)-phenylalanine and N-(m-tolylaminocarbonyl)-methionine described in WO 2017 / 047572, and more preferred are 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-propoxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-allyloxydiphenyl sulfone, bis(3-allyl-4-hydro More preferred are N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)sulfone, bisphenolsulfone bridged compounds described in Japanese Patent No. 3913820, bisphenolsulfone derivatives described in Japanese Patent No. 4004289, N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea described in Japanese Patent No. 4601174, 4,4'-bis(3-tosylureido)diphenylmethane described in JP-A-2011-105638, and N-[2-(3-phenylureido)phenyl]benzenesulfonamide described in JP-A-2016-165835.By using these, it is possible to improve image storage stability (heat resistance, plasticizer resistance, moisture resistance, water resistance, grease resistance) while maintaining the color development sensitivity of the heat-sensitive recording material.

[0038] <Sensitizer> In this embodiment, a known sensitizer may be used. The sensitizer is not particularly limited, but examples thereof include 1,2-di-(3-methylphenoxy)ethane, 2-benzyloxynaphthalene, fatty acid amides having 10 to 21 carbon atoms (e.g., stearic acid amide, palmitic acid amide, etc.), ethylene bisamide, montanic acid wax, polyethylene wax, p-benzylbiphenyl, diphenyl sulfone, 4-biphenyl-p-tolyl ether, m-terphenyl, 1,2-diphenoxyethane, dibenzyl oxalate, di(p-chlorobenzyl) oxalate, di(p-methylbenzyl) oxalate, dibenzyl terephthalate, p-benzyloxybenzoate, and the like. Benzyl benzoate, di-p-tolyl carbonate, phenyl-α-naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy-2-naphthoic acid phenyl ester, o-xylene-bis-(phenyl ether), 4-(m-methylphenoxymethyl)biphenyl, 4,4'-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxymethane, 1,2-di(3-methylphenoxy)ethylene, bis[2-(4-methoxy-phenoxy)ethyl]ether, methyl p-nitrobenzoate, phenyl p-toluenesulfonate, and the like can be used. Among these, 1,2-di-(3-methylphenoxy)ethane, 1,2-diphenoxyethane, fatty acid amides having 10 to 21 carbon atoms (e.g., stearic acid amide, palmitic acid amide, etc.), 2-benzyloxynaphthalene, diphenylsulfone, p-toluenesulfonamide, and oxalic acid-di-p-methylbenzyl ester are preferred, and 1,2-di-(3-methylphenoxy)ethane, which shows high color development sensitivity even at low energy, is particularly preferred. These sensitizers may be used alone or in combination of two or more. When a sensitizer is used, the amount of the sensitizer is preferably 25 to 250 parts by weight, more preferably 50 to 150 parts by weight, based on 100 parts by weight of the color developer according to the embodiment of the present invention.

[0039] <Stabilizer> In order to improve the image preservation property of the heat-sensitive recording material, a stabilizer may be used in the heat-sensitive recording layer. The stabilizer is an agent that has the effect of improving the image preservation property. Examples of the stabilizer include hindered phenol compounds, ultraviolet absorbers (e.g., benzophenone compounds, triazole compounds), and antioxidants. Among these, hindered phenol compounds are preferred in terms of improving the image preservation property (heat resistance, moisture resistance, water resistance, plasticizer resistance, etc.) of the recording part. The hindered phenol compound is a compound having, in one molecule, usually 1 or more and 15 or less, preferably 2 or more and 6 or less hydroxyphenyl groups. The molecular weight of the hindered phenol compound is usually 200 or more and 2000 or less, preferably 250 or more and 1800 or less, more preferably 300 or more and 1500 or less. The melting point of the hindered phenol compound is preferably 100°C or more and 300°C or less. Furthermore, in at least one of the hydroxyphenyl groups contained in the hindered phenol compound, when the position of the phenolic hydroxyl group is taken as the 1st position, it is preferable that the carbon atom at either the 2nd or 6th position is bonded to a hydrogen atom (i.e., there is no substituent at the 2nd or 6th position).

[0040] Specific examples of the hindered phenol compound include tris(hydroxyphenyl)alkanes and 1,1,3-tris-substituted butane compounds described in JP-B-39-4469 and JP-A-56-40629, etc. These may be used in combination of two or more kinds. The hindered phenol compounds may be used alone or in combination of two or more. In the case where a hindered phenol compound is used in the thermal recording material, the content thereof is preferably 1 to 100 parts by weight, more preferably 1 to 70 parts by weight, and further preferably 1 to 50 parts by weight, relative to 100 parts by weight of the color developer according to the embodiment of the present invention. If the content of the hindered phenol compound is less than this range, the moisture resistance, water resistance, and heat resistance of the recorded portion may decrease, and color development of the blank portion due to heating may not be suppressed. If the content is more than this range, the color development sensitivity may decrease, and the plasticizer resistance of the recorded portion may decrease.

[0041] <Binder> It is preferable to use a binder to form the thermal recording layer. Examples of the binder include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, other modified polyvinyl alcohols, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polystyrene, styrene copolymers such as styrene-maleic anhydride copolymers and styrene-butadiene copolymers, cellulose derivatives such as ethyl cellulose and acetyl cellulose, casein, gum arabic, oxidized starch, etherified starch, dialdehyde starch, esterified starch, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid esters, polyvinyl butyral, polyamide resins, silicone resins, petroleum resins, terpene resins, ketone resins, and coumarone resins. The amount of binder used is suitably about 5 to 25% by weight based on the solid content of the heat-sensitive recording layer. The binder is generally used as a solution, emulsion, dispersion, paste, or a combination thereof. Solvents for the solution, emulsion, or dispersion, or media for the paste, include, for example, water, alcohols, ketones, esters, hydrocarbons, and the like.

[0042] <Crosslinking agent> Examples of the crosslinking agent include glyoxal, methylol melamine, melamine formaldehyde resin, melamine urea resin, polyamine epichlorohydrin resin, polyamide epichlorohydrin resin, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, borax, boric acid, alum, ammonium chloride, etc. When a crosslinking agent is used, the amount thereof is preferably 0.5 to 500 parts by weight relative to 100 parts by weight of the color developer according to the embodiment of the present invention.

[0043] <Pigments> Examples of the pigment include inorganic or organic pigments such as silica (excluding colloidal silica), calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, talc, titanium oxide, aluminum hydroxide, etc. When a pigment is used, the amount of the pigment used is preferably 25 to 1000 parts by weight based on 100 parts by weight of the color developer according to the embodiment of the present invention.

[0044] <Lubricant> Examples of the lubricant include fatty acid metal salts such as zinc stearate and calcium stearate, waxes, silicone resins, etc. When a lubricant is used, the amount of the lubricant used is preferably 0.5 to 500 parts by weight based on 100 parts by weight of the color developer according to the embodiment of the present invention.

[0045] <Other additives> Examples of other additives include dispersants, defoamers, fluorescent dyes, etc. When other additives are used, the amount of the additives is determined based on 100 parts by weight of the color developer according to the embodiment of the present invention. The amount is preferably 0.5 to 500 parts by weight.

[0046] [Support] The shape, structure, size, material, etc. of the support used in the thermal recording material are not particularly limited and can be appropriately selected according to the purpose. Examples of the shape of the support include sheet, roll, and flat plate. The support may have a single-layer structure or a laminated structure. The size of the support can be appropriately selected according to the intended use of the thermal recording material. Examples of the material of the support include plastic film, synthetic paper, wood-free paper, waste paper pulp, recycled paper, one-sided gloss paper, greaseproof paper, coated paper, art paper, cast-coated paper, lightly coated paper, resin-laminated paper, and release paper. A composite sheet combining these may also be used as the support. The thickness of the support is not particularly limited and can be appropriately selected depending on the purpose, and is preferably from 30 to 2,000 μm, more preferably from 50 to 1,000 μm.

[0047] [Protective layer] In the thermal recording material, a protective layer may be provided on the thermal recording layer. In general, when a protective layer is provided on the thermal recording layer to improve the image storage stability of the thermal recording material, the color development sensitivity decreases. However, since the color developer used in the thermal recording material has good color development sensitivity, the color development sensitivity required for thermal paper can be maintained even if a protective layer is provided on the thermal recording layer. The types and amounts of various components used in the protective layer are determined according to the required performance and recording suitability, and are not particularly limited.

[0048] [Underlayer, back layer, middle layer] In the thermal recording material, an underlayer mainly composed of a pigment and a binder may be provided between the support and the thermal recording layer in order to further increase the color development sensitivity. Also, in order to correct curling of the thermal recording material, a back layer may be provided on the surface of the support opposite to the surface on which the thermal recording layer is present. One embodiment of the layers in the thermal recording material of the present invention includes, but is not limited to, a layered embodiment in the order of protective layer / thermal recording layer / under layer / support / back layer. Furthermore, an intermediate layer may be formed between the support and the under layer, between the under layer and the thermosensitive recording layer, between the thermosensitive recording layer and the protective layer, and / or between the support and the back layer.

[0049] [Method of manufacturing thermal recording material] The thermal recording material can be produced by applying a coating liquid containing a basic leuco dye and a color developer according to an embodiment of the present invention, and other color developers, hindered phenol compounds, sensitizers, etc., as necessary, to at least a portion of at least one side of a support and drying the coating liquid to form a thermal recording layer. This coating liquid can be applied according to a well-known conventional technique. There is no particular limitation on the coating means, and for example, an off-machine coater or an on-machine coater equipped with various coaters such as an air knife coater, a rod blade coater, a bent blade coater, a bevel blade coater, a roll coater, or a curtain coater can be used.

[0050] The coating liquid for forming the thermosensitive recording layer can be prepared by, for example, mixing the color developer according to the embodiment of the present invention, and, if necessary, a leuco dye, other color developers, a hindered phenol compound, a sensitizer, etc., and then pulverizing the mixture to a particle size of several microns or less using a grinder such as a ball mill, an attritor, or a sand grinder, or an appropriate emulsifying device, and then adding a binder, etc. to the mixture. The solvent used in this coating liquid can be water, alcohol, etc. The solid content of the coating liquid is usually 20 to 40% by weight. The coating amount of the thermal recording layer can be appropriately selected depending on the composition and the application of the thermal recording material. However, the dry weight is usually 1 to 20 g / m 2 , preferably 2 to 12 g / m 2 The range is.

[0051] Similarly to the above-mentioned thermosensitive recording layer, the protective layer, underlayer, back layer and intermediate layer can also be formed by applying and drying a coating liquid containing the constituent components thereof. Furthermore, the thermosensitive recording material on which each layer has been formed may be subjected to a treatment known in the art (for example, a smoothing treatment using a supercalender or the like).

[0052] [Uses of thermal recording materials] The heat-sensitive recording material of the present embodiment can be suitably used for applications such as paper, film, and IC cards. EXAMPLES

[0053] In the following examples and comparative examples, a paper having an underlayer on one side of a support was used, and a thermosensitive recording layer (thermosensitive coloring layer) was formed on the underlayer. In the following examples and comparative examples, "parts" and "%" respectively refer to "parts by weight" and "% by weight" unless otherwise specified.

[0054] <Comparative Synthesis Example 1> Synthesis of 1-(3-(trifluoromethyl)phenyl)-3-(4-methoxyphenyl)urea [ka] With reference to a known document (Journal of American Chemical Society, 2016, Vol. 138 (No. 40), pp. 13314-13325), the target product was obtained by the same operation as in the synthesis example of 1,3-di-m-tolylurea, except that 3-(trifluoromethyl)phenylisocyanate (purchased from Tokyo Chemical Industry Co., Ltd.) was used in place of m-tolylisocyanate in the same molar ratio, and 4-methoxyaniline (purchased from Tokyo Chemical Industry Co., Ltd.) was used in place of m-toluidine in the same molar ratio. The chemical shifts (δ ppm) in the proton NMR spectrum (400 MHz) measured in deuterated DMSO solvent were as follows: δ:3.72(s,3H),6.88(d,2H,J=9.2Hz),7.28(d,1H,J=7.6Hz),7.37(d,2H,J=9.2Hz),7.47-7.57(m,2H),8.00(s,1H),8.58(s,1H),8.95(s,1H)

[0055] <Comparative Synthesis Example 2> Synthesis of 1-(3-(trifluoromethyl)phenyl)-3-(4-carboxyphenyl)urea [ka] With reference to a known document (Journal of American Chemical Society, 2016, Vol. 138 (No. 40), pp. 13314-13325), the target product was obtained by the same operation as in the synthesis example of 1,3-di-m-tolylurea, except that 3-(trifluoromethyl)phenylisocyanate (purchased from Tokyo Chemical Industry Co., Ltd.) was used in place of m-tolylisocyanate in the same molar ratio, and 4-aminobenzoic acid (purchased from Tokyo Chemical Industry Co., Ltd.) was used in place of m-toluidine in the same molar ratio. The chemical shifts (δ ppm) in the proton NMR spectrum (400 MHz) measured in deuterated DMSO solvent were as follows: δ:7.34(d,1H,J=7.2Hz),7.53(t,1H,J=8.0Hz),7.57-7.59(m,3H),7.88(d,2H,J=8.8Hz),8.03(s,1H),9.18(d,2H,J=7.6Hz)

[0056] <Comparative Synthesis Example 3> Synthesis of N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea [ka]

[0057] The target compound was obtained by a similar operation with reference to Synthesis Example 4 in Patent Document 1 (Patent No. 4601174). The chemical shifts (δ ppm) in the proton NMR spectrum (400 MHz) measured in deuterated DMSO solvent were as follows: δ:2.40(s,6H),6.57-6·61(m,1H), 7.18-7.26(m,3H), 7.44(d,4H,J=8.4Hz), 7.72(d,2H,J=8.4Hz), 7.85(d,2H,J=8.4Hz),9.09(s,1H),10.8(brs,1H)

[0058] <Synthesis Example 1> Synthesis of 1,3-di(3-(trifluoromethyl)phenyl)urea [ka] With reference to a known document (Journal of American Chemical Society, 2016, Vol. 138 (No. 40), pp. 13314-13325), the target product was obtained by the same operation as in the synthesis example of 1,3-di-m-tolylurea, except that 3-(trifluoromethyl)phenylisocyanate (purchased from Tokyo Chemical Industry Co., Ltd.) was used in place of m-tolylisocyanate in the same molar ratio, and 3-(trifluoromethyl)aniline (purchased from Tokyo Chemical Industry Co., Ltd.) was used in place of m-toluidine in the same molar ratio. The melting point was 201-202°C. Chemical analysis of proton NMR spectrum (400MHz) measured in deuterated DMSO solvent. The calorie shifts (δ ppm) were as follows: δ:7.33(d,2H,J=7.6Hz),7.52(t,2H,J=8.0Hz),7.60(d,2H,J=8.4Hz),8.02(s,2H),9.18(s,2H)

[0059] <Synthesis Example 2> Synthesis of 1-(3-(trifluoromethyl)phenyl)-3-(2-fluorophenyl)urea [ka] With reference to a known document (Journal of American Chemical Society, 2016, Vol. 138 (No. 40), pp. 13314-13325), the target product was obtained by the same operation as in the synthesis example of 1,3-di-m-tolylurea, except that 3-(trifluoromethyl)phenylisocyanate (purchased from Tokyo Chemical Industry Co., Ltd.) was used in place of m-tolylisocyanate in the same molar ratio, and 2-fluoroaniline (purchased from Tokyo Chemical Industry Co., Ltd.) was used in place of m-toluidine in the same molar ratio. The melting point was 195-198°C. The chemical shifts (δ ppm) in the proton NMR spectrum (400 MHz) measured in deuterated DMSO solvent were as follows: δ:7.02-7.07(m,1H),7.12-7.20(m,1H),7.22-7.30(m,1H),7.32-7.37(m,1H) ,7.50-7.57(m,2H),8.05(s,1H),8.10-8.15(m,1H),8.65(s,1H),9.42(s,1H)

[0060] <Synthesis Example 3> Synthesis of 1-(3-(trifluoromethyl)phenyl)-3-(2-carboxyphenyl)urea [ka] With reference to a known document (Journal of American Chemical Society, 2016, Vol. 138 (No. 40), pp. 13314-13325), the target product was obtained by the same operation as in the synthesis example of 1,3-di-m-tolylurea, except that 3-(trifluoromethyl)phenylisocyanate (purchased from Tokyo Chemical Industry Co., Ltd.) was used in place of m-tolylisocyanate in the same molar ratio, and 2-aminobenzoic acid (purchased from Tokyo Chemical Industry Co., Ltd.) was used in place of m-toluidine in the same molar ratio. The melting point was 182-186°C. The chemical shifts (δ ppm) in the proton NMR spectrum (400 MHz) measured in deuterated DMSO solvent were as follows: δ:7.04-7.07(m,3H),7.13-7.15(m,1H),7.53(m,1H),7.86-7.93(m,2H),8.27(d,1H,J=7.6Hz),9.60(s,1H),10.29(s,1H),13.34(brs,1H)

[0061] <Synthesis Example 4> Synthesis of 1-(2-(trifluoromethyl)phenyl)-3-(2-carboxyphenyl)urea [ka] With reference to a known document (Journal of American Chemical Society, 2016, Vol. 138 (No. 40), pp. 13314-13325), the target product was obtained by the same operation as in the synthesis example of 1,3-di-m-tolylurea, except that 2-(trifluoromethyl)phenylisocyanate (purchased from Tokyo Chemical Industry Co., Ltd.) was used in place of m-tolylisocyanate in the same molar ratio, and 2-aminobenzoic acid (purchased from Tokyo Chemical Industry Co., Ltd.) was used in place of m-toluidine in the same molar ratio. The melting point was 189-191°C. The chemical shifts (δ ppm) in the proton NMR spectrum (400 MHz) measured in deuterated DMSO solvent were as follows: δ:7.02-7.17(m,3H),7.20-7.27(m,1H),7.48-7.56(m,1H),7.82-7.96(m,2H),8.26-8.29(m,1H),9.60(s,1H),10.29(s,1H),13.4(brs,1H)

[0062] <Synthesis Example 5> Synthesis of 1-(2-fluorophenyl)-3-(2-carboxyphenyl)urea [ka] With reference to the publicly known document (Journal of American Chemical Society, 2016, Vol. 138, No. 40, pp. 13314 - 13325), 2-fluorophenyl isocyanate (purchased from Tokyo Chemical Industry Co., Ltd.) was used in the same molar ratio instead of m-tolyl isocyanate, and 2-aminobenzoic acid (purchased from Tokyo Chemical Industry Co., Ltd.) was used in the same molar ratio instead of m-toluidine. The target product was obtained by the same operation as the synthesis example of 1,3-di-m-tolylurea. The melting point was 180 °C. The chemical shifts (δ ppm) in the proton NMR spectrum (400 MHz) measured in a deuterated DMSO solvent were as follows. δ: 7.02 - 7.17 (m, 3H), 7.20 - 7.27 (m, 1H), 7.49 - 7.56 (m, 1H), 7.82 - 7.88 (m, 1H), 7.92 - 7.97 (m, 1H), 8.24 - 8.29 (m, 1H), 9.59 (s, 1H), 10.28 (s, 1H), 13.3 (brs, 1H)

[0063] <Coating liquid for the thermosensitive recording layer> The following Liquid A to Liquid E were each prepared. In Liquid A and Liquid B, wet grinding was performed with a Ready Mill (RMB - 02) manufactured by Imex Co., Ltd. until the average particle diameter of each component reached 0.5 μm. Here, the average particle diameter is the average diameter based on the volume distribution and was measured with a laser diffraction / scattering particle size distribution measuring device (Microtrac MT3000II) manufactured by Nikkiso Co., Ltd.

[0064] <Liquid A> · 1,3 - bis(3-(trifluoromethyl)phenyl)urea: 40.0 parts · Polyvinyl alcohol (10% aqueous solution): 50.0 parts · Water: 10.0 parts <Liquid B> · 3 - dibutylamino - 6 - methyl - 7 - anilinofluoran (manufactured by Yamamoto Chemical Industry Co., Ltd., trade name "ODB - 2"): 36.5 parts · Polyvinyl alcohol (10% aqueous solution): 60.0 parts · Water: 3.5 parts <Liquid C> · Calcium carbonate dispersion with 60% solids content (manufactured by Okutama Kogyo Co., Ltd., product name "Tamapal TP-123CS") <Liquid D> · Zinc stearate dispersion with 36% solids content (manufactured by Chukyo Yushi Co., Ltd., product name "Hydrin Z-8-36") <Liquid E> · 10% Aqueous solution of polyvinyl alcohol (10% aqueous solution of "Gosenol NH-18" manufactured by Mitsubishi Chemical Corporation)

[0065] [Example 1] Each liquid was mixed at the following ratios to prepare a coating liquid for the heat-sensitive recording layer. Liquid A: 18.89 parts Liquid B: 10.00 parts Liquid C: 17.87 parts Liquid D: 6.00 parts Liquid E: 19.62 parts Next, an underlayer was provided on one side of high-quality paper as the support, and on the underlayer, the coating liquid of the heat-sensitive recording layer was applied and dried (using a forced-air dryer at 60 °C for 2 minutes) so that the dry weight of the heat-sensitive recording layer became 3 g / m 2 to form a heat-sensitive recording layer. Then, the support on which the underlayer and the heat-sensitive recording layer were formed was processed with a supercalender so that the smoothness became 500 - 1000 seconds to obtain a heat-sensitive recording material. This was smoothed by applying a pressure of 1 kgf / cm 2 with a supercalender to obtain a heat-sensitive recording material.

[0066] [Example 2] A heat-sensitive recording material was manufactured in the same manner as in Example 1, except that 1,3-di(3-(trifluoromethyl)phenyl)urea in Liquid A was changed to 1-(3-(trifluoromethyl)phenyl)-3-(2-fluorophenyl)urea.

[0067] [Example 3] A heat-sensitive recording material was manufactured in the same manner as in Example 1, except that 1,3-di(3-(trifluoromethyl)phenyl)urea in Liquid A was changed to 1-(3-(trifluoromethyl)phenyl)-3-(2-carboxyphenyl)urea.

[0068] [Example 4] The 1,3-di(3-(trifluoromethyl)phenyl)urea in solution A was changed to 1-(2-(trifluoromethyl)phenyl)-3-(2-carboxyphenyl)urea. Except for the above, the same procedure as in Example 1 was followed to produce a heat-sensitive recording material.

[0069] [Example 5] A heat-sensitive recording material was produced in the same manner as in Example 1, except that 1,3-di(3-(trifluoromethyl)phenyl)urea in solution A was changed to 1-(2-fluorophenyl)-3-(2-carboxyphenyl)urea.

[0070] [Comparative Example 1] A heat-sensitive recording material was produced in the same manner as in Example 1, except that 1,3-di(3-(trifluoromethyl)phenyl)urea in solution A was changed to 1-(3-(trifluoromethyl)phenyl)-3-(4-methoxyphenyl)urea.

[0071] [Comparative Example 2] A heat-sensitive recording material was produced in the same manner as in Example 1, except that 1,3-di(3-(trifluoromethyl)phenyl)urea in solution A was changed to 1-(3-(trifluoromethyl)phenyl)-3-(4-carboxyphenyl)urea.

[0072] <Color development sensitivity> Gradation patterns were printed using an Okura Electric thermal printer (TH-M2 / PS), and the image density was measured with an X-Rite spectrodensitometer (eXact) at applied energies of 0.26mJ / dot and 0.36mJ / dot. The results are shown in Table 1. Note that the higher the image density in this test, the better the color development sensitivity.

[0073] <Heat resistance> A checkered pattern was printed on the thermal recording material using an Okura Electric thermal printer (TH-M2 / PS) with an applied energy of 0.36 mJ / dot. The thermal recording material was left in an environment at 60°C for 24 hours, after which the image density was measured using an X-Rite spectrodensitometer (eXact). Table 1 shows the image retention rate calculated from the image density using the following formula. Image retention rate (%) = 100 x (image density after test) / (image density before test)

[0074] <Moisture resistance> A checkered pattern was printed on the thermal recording material using an Okura Electric thermal printer (TH-M2 / PS) with an applied energy of 0.36 mJ / dot. The thermal recording material was left for 24 hours in an environment with a temperature of 40°C and a humidity of 90%, after which the image density was measured using an X-Rite spectrodensitometer (eXact). Table 1 shows the image retention rate calculated from the image density using the following formula. Image retention rate (%) = 100 x (image density after test) / (image density before test)

[0075] <Alcohol resistance> A thermal recording material printed in a checkerboard pattern with an applied energy of 0.36 mJ / dot using an Okura Electric thermal printer (TH-M2 / PS) was immersed in 25% ethanol water for 20 minutes, removed and left at room temperature for 24 hours, after which the image density was measured with an X-Rite spectrodensitometer / colorimeter (eXact). Table 1 shows the image retention rate calculated from the image density using the following formula. Image retention rate (%) = 100 x (image density after test) / (image density before test)

[0076] <Oil resistance> A drop of vegetable oil (manufactured by Nisshin Oillio Group, Inc.) was dropped onto the printed area of ​​a thermal recording material that had been printed in a checkerboard pattern using an Okura Electric thermal printer (TH-M2 / PS) with an applied energy of 0.36 mJ / dot, and the material was lightly wiped off and left at 20°C for 24 hours. The print density of the printed area was then measured using an X-Rite spectrodensitometer (eXact). Table 1 shows the results. The image retention rate was calculated from the image density using the following formula. Image retention rate (%) = 100 x (image density after test) / (image density before test)

[0077] <Grease resistance> A drop of skin milk (Nivea Kao Corporation) was dropped onto the printed area of ​​a thermal recording material that had been printed in a checkerboard pattern with an applied energy of 0.36 mJ / dot using an Okura Electric thermal printer (TH-M2 / PS), and the material was lightly wiped off and left at 20°C for 24 hours, after which the print density of the printed area was measured with an X-Rite spectrodensitometer (eXact). Table 1 shows the image retention rate calculated from the image density using the following formula. Image retention rate (%) = 100 x (image density after test) / (image density before test)

[0078] [Table 1]

[0079] As is clear from the results in Table 1, Examples 1 to 5 generally have high retention rates after durability tests. In particular, Examples 1 and 3 to 5 have improved heat resistance, moisture resistance, alcohol resistance, oil resistance, and grease resistance compared to Comparative Example 1, which used a conventional color developer. Moreover, Example 2 has improved heat resistance and grease resistance compared to Comparative Example 1, which used a conventional color developer. As is clear from the results in Table 1, Examples 1 to 5 have improved color development sensitivity compared to Comparative Example 2, which used a conventional color developer. It can be seen that the color development sensitivity (saturation sensitivity) at a large amount of heat is also improved. Moreover, it can be seen that Examples 1 and 2 have good color development sensitivity at a small amount of heat, and therefore are also excellent in dynamic sensitivity.

[0080] As described above, by using a color developer consisting of a compound corresponding to formula (1), it is possible to provide a well-balanced thermal recording material that is excellent in color development sensitivity as well as in the retention rate of image density after durability testing.

[0081] Next, the average particle size of the component used as the developer after wet grinding was changed as follows. The above color development sensitivity test was carried out, and the relative density ratio to the image density when the average particle diameter D50 of the developer was 0.5 μm at an image density of 0.36 mJ / dot printing energy was calculated. The relative concentration ratio refers to the ratio of the image density when a developer having a specific particle diameter D50 is used to the image density when a developer having a standard particle diameter D50 is used. For example, a relative concentration ratio of 4.0 / 0.5 is the ratio of the image density when the developer has a particle diameter D50 of 4.0 μm to the image density when the developer has a particle diameter D50 of 0.5 μm.

[0082] [Example 1b] A heat-sensitive recording material was produced in the same manner as in Example 1.

[0083] [Example 6] to [Example 9] A heat-sensitive recording material was produced in the same manner as in Example 1b, except that wet grinding was carried out until the average particle diameter D50 reached the values ​​shown in Table 2.

[0084] [Comparative Example 3] A heat-sensitive recording material was produced in the same manner as in Example 1, except that 1,3-di(3-(trifluoromethyl)phenyl)urea in solution A was changed to N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea.

[0085] [Comparative Example 4] to [Comparative Example 6] A heat-sensitive recording material was produced in the same manner as in Comparative Example 3, except that wet grinding was carried out until the average particle diameter D50 reached the values ​​shown in Table 2.

[0086] [Table 2]

[0087] As described above, the present invention makes it possible to provide a thermal recording material which has higher color development sensitivity and a smaller rate of decrease in image density even when the particle size becomes larger, compared to the case where a developer having a sulfonylurea structure as described in Patent Document 1 is used.

Claims

1. A color developer comprising a compound represented by the following formula (1): 【Chemistry 1】 (In the above formula (1), a, b, c, A, B, and C are as follows. a is an integer selected from 1 to 5; b is an integer selected from 0 to 4; c is an integer selected from 0 to 5; Each A is independently a fluoro group or a fluoroalkyl group; B's each independently represent an alkyl group, a fluoro group, a fluoroalkyl group, a carboxyl group, an ester group, a carbonyl group, or a nitrile group; Each C is independently a fluoro group, a fluoroalkyl group, a carboxyl group, an ester group, a carbonyl group, or a nitrile group. However, the sum of a and b is between 1 and 5, The substitution position of A is the o-position or m-position; When B and / or C is a carboxyl group, the substitution position of the carboxyl group is the o-position; When C is a fluoro group, the substitution position of the fluoro group is the o-position or m-position; When C is a fluoroalkyl group, the substitution position of the fluoroalkyl group is the o-position or m-position.

2. 2. The developer according to claim 1, wherein in said formula (1), at least one A is a fluoro group or a trifluoromethyl group.

3. 3. The color developer according to claim 1, wherein at least one A in the formula (1) is a trifluoromethyl group.

4. The color developer according to any one of claims 1 to 3, wherein a is 1 in the formula (1).

5. 5. The developer according to claim 1, wherein in said formula (1), c is an integer selected from 1 to 5, and at least one C is a fluoro group or a trifluoromethyl group.

6. 6. The color developer according to claim 1, wherein in the formula (1), c is an integer selected from 1 to 5, and at least one C is a trifluoromethyl group.

7. The color developer according to any one of claims 1 to 6, wherein c is 1 in the formula (1).

8. A heat-sensitive recording material having a support and a heat-sensitive recording layer provided on the support, the heat-sensitive recording layer containing the color developer according to any one of claims 1 to 7.

9. The heat-sensitive recording material according to claim 8 , wherein the heat-sensitive recording layer comprises a leuco dye.

10. 10. The heat-sensitive recording material according to claim 8, wherein the heat-sensitive recording layer comprises a sensitizer.

11. The heat-sensitive recording material according to any one of claims 8 to 10, wherein the heat-sensitive recording layer contains a stabilizer.

12. An ink comprising the developer according to any one of claims 1 to 7.

13. A writing implement containing the ink according to claim 12.

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