JP7643188B2 - Color developer and thermal recording material - Google Patents

Description

The present invention relates to a color developer and a heat-sensitive recording material obtained by using the color developer.

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 are widely used.

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

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 with 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 with a carboxyl group on the phenyl group as a color developer.

Patent No. 4601174 Patent No. 3339043 Japanese Patent Application Publication No. 08-216526

The color developer having a sulfonylurea structure described in Patent Document 1 is known to have high aqueous toxicity, and there is a demand for the development of a non-phenol color developer with lower environmental impact. In addition, according to the studies by 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 demand 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 having an alkoxy group on the phenyl group shown in the above Patent Document 2 is used as a color developer, a thermal recording material having 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 having a carboxyl group on the phenyl group shown in the above Patent Document 3 is used as a color developer, a thermal recording material having excellent color development sensitivity was not obtained. That is, the object of the present invention is to provide a color developer that can replace a sulfonylurea structure and provide a thermal recording material having low environmental impact and excellent color development sensitivity and storage stability, and a thermal recording material obtained by using the color developer.

As a result of intensive investigations, the present inventors have found that the above problems can be solved by using a urea compound having a specific substituent as a developer.

（上記式（１）中、ａ、ｂ、ｃ、Ａ、Ｂ、Ｃは下記の通りである。
ａは、１から５から選ばれる整数であり、
ｂは、０から４から選ばれる整数であり、
ｃは、０から５から選ばれる整数であり、
Ａは、それぞれ独立してフルオロ基又はフルオロアルキル基であり、
Ｂ、Ｃは、それぞれ独立してアルキル基、フルオロ基、フルオロアルキル基、カルボキシル基、エステル基、カルボニル基、又はニトリル基である。
ただし、ａとｂの合計は、１以上５以下であり、
Ｂ及び／又はＣがカルボキシル基の場合は、前記カルボキシル基の置換位置はｏ－位である。）
［２］ 前記式（１）中、少なくとも一つのＡがフルオロ基又はトリフルオロメチル基である［１］に記載の顕色剤。
［３］ 前記式（１）中、少なくとも一つのＡがトリフルオロメチル基である［１］又は［２］に記載の顕色剤。
［４］ 前記式（１）中、ａが１である［１］～［３］のいずれかに記載の顕色剤。
［５］ 前記式（１）中、ｃは、１から５から選ばれる整数であり、少なくとも一つのＣがフルオロ基又はトリフルオロメチル基である［１］～［４］のいずれかに記載の顕色剤。
［６］ 前記式（１）中、ｃは、１から５から選ばれる整数であり、少なくとも一つのＣがトリフルオロメチル基である［１］～［５］のいずれかに記載の顕色剤。
［７］ 前記式（１）中、ｃが１である請求項［１］～［６］のいずれかに記載の顕色剤。
［８］ 支持体及び支持体上に設けられた感熱記録層を有する感熱記録材料であって、該感熱記録層が、［１］～［７］のいずれかに記載の顕色剤を含む感熱記録材料。
［９］ 前記感熱記録層がロイコ染料を含む、［１］～［８］のいずれかに記載の感熱記録材料。
［１０］ 前記感熱記録層が増感剤を含む、［１］～［９］のいずれかに記載の感熱記録材料。
［１１］ 前記感熱記録層が安定剤を含む、［１］～［１０］のいずれかに記載の感熱記録材料。
［１２］ ［１］～［７］のいずれかに記載の顕色剤を含むインキ。
［１３］ ［１２］に記載のインキを収容してなる筆記具。 [1] A color developer comprising a compound represented by the following formula (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 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 c in the formula (1) 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 according to [12].

The present invention provides a color developer capable of producing a thermal recording material with excellent color development sensitivity and storage stability, and a thermal recording material obtained using the color developer.

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 "~" is used to express a numerical value or physical property value before and after the value, the value before and after the value is included.

（上記式（１）中、ａ、ｂ、ｃ、Ａ、Ｂ、Ｃは下記の通りである。
ａは、１から５から選ばれる整数であり、
ｂは、０から４から選ばれる整数であり、
ｃは、０から５から選ばれる整数であり、
Ａは、それぞれ独立してフルオロ基又はフルオロアルキル基であり、
Ｂ、Ｃは、それぞれ独立してアルキル基、フルオロ基、フルオロアルキル基、カルボキシル基、エステル基、カルボニル基、又はニトリル基である。
ただし、ａとｂの合計は、１以上５以下であり、
Ｂ及び／又はＣがカルボキシル基の場合は、前記カルボキシル基の置換位置はｏ－位である。） [Color 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)".

(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.

The color developer according to the present embodiment has a remarkable effect of excellent color development sensitivity and storage stability. It is presumed that the above-mentioned color developer has such excellent effects 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 N-H 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, making it possible to achieve both high color development sensitivity and storage stability. In addition, by having a hydrophilic site due to the highly polar urea group and a hydrophobic site due to the fluoro group or fluoroalkyl group in the molecule, it is believed that storage stability under various storage conditions can be simultaneously improved. Specifically, it is believed that it is possible to simultaneously improve resistance to heat, moisture, alcohol, oil, grease, etc. while increasing color development sensitivity.

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. It is considered that if a is large, the hydrophobicity increases, resulting in a decrease in dispersibility in water, the molecular weight increases, resulting in a decrease in the mobility of the molecules during melting, and the compatibility with the leuco dye and sensitizer decreases too much, resulting in a decrease in color development sensitivity.
In the above formula (1), the number of carbon atoms in the fluoroalkyl group in A is 1 to 12. The number of carbon atoms 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 number of carbon atoms is large, the hydrophobicity is too high, and the dispersibility in water is reduced, or the molecular weight is increased, and the molecule becomes 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, but 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.

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

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 number of carbon atoms is preferably 6 or less, more preferably 4 or less, and particularly preferably 1. It is considered that if the number of carbon atoms is large, 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 groups, thereby weakening intermolecular hydrogen bonding, which can suppress crystallinity, suppress an excessively high melting point, and increase compatibility with the leuco dye, thereby increasing color development sensitivity.

上記式（２）中、Ｒ^１は、炭素数１～１２のアルキル基である。炭素数が大きいと融点が下がり白色部の安定性が低下したり、発色部の保存安定性が低下することから、好ましくは炭素数６以下、より好ましくは４以下、より好ましくは２以下、特に好ましくは１（メチル基）である。 In the above formula (1), the ester group in B is represented by the following formula (2).

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, the stability of the white part decreases, and the storage stability of the colored part decreases, so the carbon number is preferably 6 or less, more preferably 4 or less, more preferably 2 or less, and particularly preferably 1 (methyl group).

上記式（３）中、Ｒ^２は、炭素数１～１２のアルキル基又は任意に置換されてもよいフェニル基である。炭素数が大きいと融点が下がり白色部の安定性が低下したり、発色部の保存安定性が低下することから、好ましくは炭素数６以下、より好ましくは４以下、より好ましくは２以下、特に好ましくは１（メチル基）である。Ｒ^２として、好ましくは、メチル基、フェニル基、ｏ－トリル基、ｍ－トリル基又はｐ－トリル基である。
なお、式（２）及び（３）中、＊がベンゼン環の炭素に結合する部位である。 In the above formula (1), the carbonyl group in B is represented by the following formula (3).

In the above formula (3), ^R2 is an alkyl group having 1 to 12 carbon atoms or an optionally substituted phenyl group. If the carbon number 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 carbon number is preferably 6 or less, more preferably 4 or less, more preferably 2 or less, and particularly preferably 1 (methyl group). ^R2 is preferably a methyl group, a phenyl group, an o-tolyl group, an m-tolyl group, or a p-tolyl group.
In the formulas (2) and (3), * indicates the bonding site to the carbon of the benzene ring.

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

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.

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

In a particularly preferred embodiment of the developer according to this 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. If the substitution positions of A and C are both o-positions, the steric hindrance around the urea structure becomes large, decreasing the reactivity with the leuco dye, so it is preferable that the substitution position of at least one of A and C is not the o-position.

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

[Use of color 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.

[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, card, etc., so 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 under layer, a back layer, an intermediate layer, etc., as described below, if necessary. Here, "on the support" refers to at least one side of the support, and is usually one side. Furthermore, "on the support" means that the layer is present on at least a part of the support.

[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 an embodiment of the present invention, a leuco dye, a color developer other than the color developer according to an 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.

<Leuco dye>
In this embodiment, the thermal recording layer preferably contains a leuco dye. The leuco dye is usually basic, and any leuco dye known in the art in the field of pressure-sensitive or thermal recording paper can be used. Specific examples of the leuco dye include triphenylmethane-based leuco dyes, fluoran-based leuco dyes, fluorene-based leuco dyes, and divinyl-based leuco dyes. Specific examples of representative colorless or light-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, relative to 100 parts by weight of the developer according to the embodiment of the present invention.

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], etc.

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; 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-di-pentylamino-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 Amino-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-6-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran; 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, etc.

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], etc.

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; 3,3-bis[1-(4-methoxyphenyl)-1-(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, etc.

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]
bis[2,2,2',2'-tetrakis(p-dimethylaminophenyl)ethenyl]-methylmalonic acid dimethyl ester, and the like.

<Other color developers>
The thermosensitive recording layer may contain a color developer other than the color developer according to the embodiment of the present invention, so long as the effect of the present invention is not impaired. As the other color developer, any color developer known in the field of conventional pressure-sensitive or thermal 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 novolac-type phenol-based compounds are preferable.

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, 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-hydroxyphenyl-4'-benzyloxyphenyl sulfone, 3,4-dihydroxyphenyl-4'-methylphenyl sulfone, 2,4-bis(phenylsulfonyl)phenol, bisphenol sulfone crosslinked compounds described in Japanese Patent No. 3913820, and bisphenol sulfone derivatives described in Japanese Patent No. 4004289 are included.

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 N-[2-(acetoxy)phenyl]-N'-phenylurea, N-[3-(acetoxy)phenyl]-N'-phenylurea, N-[2-(benzoyloxy)phenyl]-N'-phenylurea, N-[3-(benzoyloxy)phenyl]-N'-phenylurea, and N-[3-(benzoyloxy)phenyl]-N'-phenylurea described in WO 2017/047572 are also disclosed. Examples of amino acid derivatives include 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.

Novolak-type phenolic compounds include phenol-formaldehyde condensates described in WO 02/098674.

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, the aminobenzenesulfonamide derivatives described in JP-A-8-59603, bis(4-hydroxyphenylthioethoxy)methane, 1,5-di(4-hydroxyphenylthio)-3-oxapentane, bis(p-hydroxyphenyl)butyl acetate, bis(p-hydroxyphenyl)methyl 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 described in WO 02/081229. , the compounds described in JP-A-2002-301873, thiourea compounds such as N,N'-di-m-chlorophenylthiourea, p-chlorobenzoic acid, stearyl gallate, bis[zinc 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 terephthalaldehyde acid and other aromatic carboxylic acids. Examples include metal chelate complexes of higher fatty acid metal double salts and polyvalent hydroxy aromatic compounds, etc., as described in JP-A-10-258577.

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, and the diphenyl sulfone crosslinked type 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 crosslinked 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 Japanese Patent Publication No. 2011-105638, and N-[2-(3-phenylureido)phenyl]benzenesulfonamide described in Japanese Patent Publication No. 2016-165835. By using these, the color development sensitivity of the thermal recording material can be maintained while improving image storage properties (heat resistance, plasticizer resistance, moisture resistance, water resistance, grease resistance), etc.

<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, diphenylsulfone, 4-biphenyl-p-tolyl ether, m-terphenyl, 1,2-diphenoxyethane, dibenzyl oxalate, di(p-chlorobenzyl) oxalate, di(p-methylbenzyl) oxalate, dibenzyl terephthalate, and p-benzyloxyethane. 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 exhibits 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 developer according to the embodiment of the present invention.

<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).

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-based compound may be used alone or in combination of two or more kinds. When the hindered phenol-based 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 even more 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-based compound is less than this range, the moisture resistance, water resistance, and heat resistance of the recorded part may decrease, and color development of the blank part 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 part may decrease.

<Binder>
In order to form the thermal recording layer, it is preferable to use a binder. 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 the 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.

<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 based on 100 parts by weight of the color developer according to the embodiment of the present invention.

<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.

<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.

<Other additives>
Examples of other additives include dispersants, defoamers, fluorescent dyes, etc. When other additives are used, the amount of the additives 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.

[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.

[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.

[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.

[Method of manufacturing the 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.

The coating liquid for forming the thermosensitive recording layer can be prepared, for example, by blending 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 grinding machine 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 heat-sensitive recording layer can be appropriately selected depending on the composition and the application of the heat-sensitive recording material, but is usually in the range of 1 to 20 g/m ² , preferably 2 to 12 g/m ² in terms of dry weight.

The protective layer, underlayer, back layer and intermediate layer can also be formed by applying and drying a coating liquid containing the components thereof, in the same manner as the above-mentioned thermosensitive recording layer. 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, etc.).

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

In the following examples and comparative examples, paper with an underlayer on one side of the 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 "%" refer to "parts by weight" and "% by weight", respectively, unless otherwise specified.

公知文献（Ｊｏｕｒｎａｌ ｏｆ Ａｍｅｒｉｃａｎ Ｃｈｅｍｉｃａｌ Ｓｏｃｉｅｔｙ ２０１６年，１３８巻（４０号），１３３１４－１３３２５頁）を参考に、ｍ－トリルイソシアネートの代わりに３－（トリフルオロメチル）フェニルイソシアネート（東京化成社より購入）を同じモル比で使用し、ｍ－トルイジンの代わりに４－メトキシアニリン（東京化成社より購入）を同じモル比で使用した以外は１，３－ジ－ｍ－トリルウレアの合成例と同様の操作により、目的物を得た。
重ＤＭＳＯ溶媒中で測定したプロトンＮＭＲスペクトル（４００ＭＨｚ）におけるケミカルシフト（δｐｐｍ）は下記の通りであった。
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） Comparative Synthesis Example 1
Synthesis of 1-(3-(trifluoromethyl)phenyl)-3-(4-methoxyphenyl)urea

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 a 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, 2 H, J = 9.2Hz), 7.47-7.57 (m, 2H), 8.00 (s, 1H), 8.58 (s, 1H), 8.95 (s, 1H)

公知文献（Ｊｏｕｒｎａｌ ｏｆ Ａｍｅｒｉｃａｎ Ｃｈｅｍｉｃａｌ Ｓｏｃｉｅｔｙ ２０１６年，１３８巻（４０号），１３３１４－１３３２５頁）を参考に、ｍ－トリルイソシアネートの代わりに３－（トリフルオロメチル）フェニルイソシアネート（東京化成社より購入）を同じモル比で使用し、ｍ－トルイジンの代わりに４－アミノ安息香酸（東京化成社より購入）を同じモル比で使用した以外は１，３－ジ－ｍ－トリルウレアの合成例と同様の操作により、目的物を得た。
重ＤＭＳＯ溶媒中で測定したプロトンＮＭＲスペクトル（４００ＭＨｚ）におけるケミカルシフト（δｐｐｍ）は下記の通りであった。
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） Comparative Synthesis Example 2
Synthesis of 1-(3-(trifluoromethyl)phenyl)-3-(4-carboxyphenyl)urea

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 a 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)

Comparative Synthesis Example 3
Synthesis of N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea

The target compound was obtained by a similar operation with reference to Synthesis Example 4 of Patent Document 1 (Patent No. 4601174).
The chemical shifts (δ ppm) in the proton NMR spectrum (400 MHz) measured in a 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)

公知文献（Ｊｏｕｒｎａｌ ｏｆ Ａｍｅｒｉｃａｎ Ｃｈｅｍｉｃａｌ Ｓｏｃｉｅｔｙ ２０１６年，１３８巻（４０号），１３３１４－１３３２５頁）を参考に、ｍ－トリルイソシアネートの代わりに３－（トリフルオロメチル）フェニルイソシアネート（東京化成社より購入）を同じモル比で使用し、ｍ－トルイジンの代わりに３－（トリフルオロメチル）アニリン（東京化成社より購入）を同じモル比で使用した以外は１，３－ジ－ｍ－トリルウレアの合成例と同様の操作により、目的物を得た。融点は２０１－２０２℃であった。
重ＤＭＳＯ溶媒中で測定したプロトンＮＭＲスペクトル（４００ＭＨｚ）におけるケミ
カルシフト（δｐｐｍ）は下記の通りであった。
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） <Synthesis Example 1>
Synthesis of 1,3-di(3-(trifluoromethyl)phenyl)urea

With reference to a known document (Journal of American Chemical Society, 2016, Vol. 138 (No. 40), pp. 13314-13325), the target substance was obtained by the same operation as in the synthesis example of 1,3-di-m-tolylurea, except that 3-(trifluoromethyl)phenyl isocyanate (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.
The chemical shifts (δ ppm) in the proton NMR spectrum (400 MHz) measured in a deuterated DMSO solvent 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)

公知文献（Ｊｏｕｒｎａｌ ｏｆ Ａｍｅｒｉｃａｎ Ｃｈｅｍｉｃａｌ Ｓｏｃｉｅｔｙ ２０１６年，１３８巻（４０号），１３３１４－１３３２５頁）を参考に、ｍ－トリルイソシアネートの代わりに３－（トリフルオロメチル）フェニルイソシアネート（東京化成社より購入）を同じモル比で使用し、ｍ－トルイジンの代わりに２－フルオロアニリン（東京化成社より購入）を同じモル比で使用した以外は１，３－ジ－ｍ－トリルウレアの合成例と同様の操作により、目的物を得た。融点は１９５－１９８℃であった。
重ＤＭＳＯ溶媒中で測定したプロトンＮＭＲスペクトル（４００ＭＨｚ）におけるケミカルシフト（δｐｐｍ）は下記の通りであった。
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） <Synthesis Example 2>
Synthesis of 1-(3-(trifluoromethyl)phenyl)-3-(2-fluorophenyl)urea

With reference to a known document (Journal of American Chemical Society, 2016, Vol. 138 (No. 40), pp. 13314-13325), the target substance 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 a 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)

公知文献（Ｊｏｕｒｎａｌ ｏｆ Ａｍｅｒｉｃａｎ Ｃｈｅｍｉｃａｌ Ｓｏｃｉｅｔｙ ２０１６年，１３８巻（４０号），１３３１４－１３３２５頁）を参考に、ｍ－トリルイソシアネートの代わりに３－（トリフルオロメチル）フェニルイソシアネート（東京化成社より購入）を同じモル比で使用し、ｍ－トルイジンの代わりに２－アミノ安息香酸（東京化成社より購入）を同じモル比で使用した以外は１，３－ジ－ｍ－トリルウレアの合成例と同様の操作により、目的物を得た。融点は１８２－１８６℃であった。
重ＤＭＳＯ溶媒中で測定したプロトンＮＭＲスペクトル（４００ＭＨｚ）におけるケミカルシフト（δｐｐｍ）は下記の通りであった。
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） <Synthesis Example 3>
Synthesis of 1-(3-(trifluoromethyl)phenyl)-3-(2-carboxyphenyl)urea

With reference to a known document (Journal of American Chemical Society, 2016, Vol. 138 (No. 40), pp. 13314-13325), the target substance 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 a 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, 2 H), 8.27 (d, 1H, J = 7.6Hz), 9.60 (s, 1H), 10.29 (s, 1H), 13.34 (brs, 1H)

公知文献（Ｊｏｕｒｎａｌ ｏｆ Ａｍｅｒｉｃａｎ Ｃｈｅｍｉｃａｌ Ｓｏｃｉｅｔｙ ２０１６年，１３８巻（４０号），１３３１４－１３３２５頁）を参考に、ｍ－トリルイソシアネートの代わりに２－（トリフルオロメチル）フェニルイソシアネート（東京化成社より購入）を同じモル比で使用し、ｍ－トルイジンの代わりに２－アミノ安息香酸（東京化成社より購入）を同じモル比で使用した以外は１，３－ジ－ｍ－トリルウレアの合成例と同様の操作により、目的物を得た。融点は１８９－１９１℃であった。
重ＤＭＳＯ溶媒中で測定したプロトンＮＭＲスペクトル（４００ＭＨｚ）におけるケミカルシフト（δｐｐｍ）は下記の通りであった。
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） <Synthesis Example 4>
Synthesis of 1-(2-(trifluoromethyl)phenyl)-3-(2-carboxyphenyl)urea

With reference to a known document (Journal of American Chemical Society, 2016, Vol. 138 (No. 40), pp. 13314-13325), the target substance 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 a 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)

公知文献（Ｊｏｕｒｎａｌ ｏｆ Ａｍｅｒｉｃａｎ Ｃｈｅｍｉｃａｌ Ｓｏｃｉｅｔｙ ２０１６年，１３８巻（４０号），１３３１４－１３３２５頁）を参考に、ｍ－トリルイソシアネートの代わりに２－フルオロフェニルイソシアネート（東京化成社より購入）を同じモル比で使用し、ｍ－トルイジンの代わりに２－アミノ安息香酸（東京化成社より購入）を同じモル比で使用した以外は１，３－ジ－ｍ－トリルウレアの合成例と同様の操作により、目的物を得た。融点は１８０℃であった。
重ＤＭＳＯ溶媒中で測定したプロトンＮＭＲスペクトル（４００ＭＨｚ）におけるケミカルシフト（δｐｐｍ）は下記の通りであった。
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） <Synthesis Example 5>
Synthesis of 1-(2-fluorophenyl)-3-(2-carboxyphenyl)urea

With reference to a known document (Journal of American Chemical Society, 2016, Vol. 138 (No. 40), pp. 13314-13325), the target substance was obtained by the same operation as in the synthesis example of 1,3-di-m-tolylurea, except that 2-fluorophenyl isocyanate (purchased from Tokyo Chemical Industry Co., Ltd.) was used in place of m-tolyl isocyanate 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 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)

<Coating liquid for the thermal recording layer>
The following liquids A to E were prepared. Liquids A and B were wet ground using a ready mill (RMB-02) manufactured by Imex until the average particle size of each component became 0.5 μm. The average particle size here is the average size in a volume-based distribution, and was measured using a laser diffraction/scattering particle size distribution analyzer (Microtrac MT3000II) manufactured by Nikkiso Co., Ltd.

<Liquid A>
1,3-di(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 Industries, 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 (manufactured by Okutama Kogyo Co., Ltd., product name "Tamapearl TP-123CS")
<Liquid D>
36% zinc stearate dispersion (manufactured by Chukyo Yushi Co., Ltd., product name "Hydrin Z-8-36")
<Liquid E>
10% polyvinyl alcohol aqueous solution (10% aqueous solution of "GOHSENOL NH-18" manufactured by Mitsubishi Chemical Corporation)

[Example 1]
The coating liquid for the thermal recording layer was prepared by mixing the respective liquids in the ratio shown below.
A liquid: 18.89 parts B liquid: 10.00 parts C liquid: 17.87 parts D liquid: 6.00 parts E liquid: 19.62 parts Next, an under layer was provided on one side of the support of fine paper, and the coating liquid for the thermosensitive recording layer was applied and dried (air blower, 60°C, 2 minutes) on the under layer so that the dry weight of the thermosensitive recording layer was 3 g/ ^m2 to form a thermosensitive recording layer. Next, the support on which the under layer and thermosensitive recording layer were formed was treated with a supercalender to a smoothness of 500 to 1000 seconds to obtain a thermosensitive recording material. This was smoothed with a pressure of 1 kgf/ ^cm2 with a supercalender to obtain a thermosensitive recording material.

[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-(2-fluorophenyl)urea.

[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 1-(3-(trifluoromethyl)phenyl)-3-(2-carboxyphenyl)urea.

[Example 4]
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-(trifluoromethyl)phenyl)-3-(2-carboxyphenyl)urea.

[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.

[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.

[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.

<Color development sensitivity>
Gradation patterns were printed using a thermal printer (TH-M2/PS) manufactured by Okura Electric Co., Ltd., and the image densities at applied energies of 0.26 mJ/dot and 0.36 mJ/dot were measured using a spectrodensitometer/colorimeter (eXact) manufactured by X-Rite Corporation. The results are shown in Table 1. Note that the higher the image density in this test, the better the color development sensitivity.

<Heat resistance>
A thermal recording material was printed in a checkered pattern with an applied energy of 0.36 mJ/dot using a thermal printer (TH-M2/PS) manufactured by Ohkura Electric Co., Ltd., and left to stand for 24 hours in an environment at a temperature of 60° C., after which the image density was measured with a spectrodensitometer/colorimeter (eXact) manufactured by X-Rite Corp. Table 1 shows the image retention rate calculated from the image density using the following formula.
Image retention rate (%)=100×(image density after test)/(image density before test)

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

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

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

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

As is clear from the results in Table 1, Examples 1 to 5 generally had high retention rates after the durability test. In particular, Examples 1 and 3 to 5 had 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 had 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.

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.

Next, the above-mentioned color development sensitivity test was carried out by changing the average particle diameter after wet grinding of the component used as the color developer as follows, and the relative concentration ratio to the image density when the average particle diameter D50 of the color developer was 0.5 μm was calculated at an image density of 0.36 mJ/dot printing energy.
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.

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

[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 value shown in Table 2.

[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 replaced with N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea.

[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 value shown in Table 2.

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

Claims (13)

A color developer comprising a compound represented by the following formula (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 are 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. The developer according to claim 1, wherein in formula (1), at least one A is a fluoro group or a trifluoromethyl group. The developer according to claim 1 or 2, wherein at least one A in formula (1) is a trifluoromethyl group. The developer according to any one of claims 1 to 3, wherein in formula (1), a is 1. The developer according to any one of claims 1 to 4, wherein in formula (1), c is an integer selected from 1 to 5, and at least one C is a fluoro group or a trifluoromethyl group. The developer according to any one of claims 1 to 5, wherein in formula (1), c is an integer selected from 1 to 5, and at least one C is a trifluoromethyl group. The developer according to any one of claims 1 to 6, wherein c in formula (1) is 1. A thermal recording material having a support and a thermal recording layer provided on the support, the thermal recording layer containing the color developer according to any one of claims 1 to 7. The heat-sensitive recording material according to claim 8 , wherein the heat-sensitive recording layer comprises a leuco dye. 10. The thermosensitive recording material according to claim 8 , wherein the thermosensitive recording layer comprises a sensitizer. The heat-sensitive recording material according to any one of claims 8 to 10, wherein the heat-sensitive recording layer contains a stabilizer. An ink containing the developer according to any one of claims 1 to 7. A writing instrument containing the ink according to claim 12.