TWI895513B - Reversible thermochromic composition and reversible thermochromic microcapsule pigment encapsulated therein - Google Patents

Abstract

The present invention provides a reversible thermochromic composition and a reversible thermochromic microcapsule pigment containing the composition, which exhibit excellent contrast between the colored and decolorized states and, consequently, excellent lightfastness in the colored state. The present invention relates to a reversible thermochromic composition and a reversible thermochromic microcapsule pigment containing the composition. The composition comprises (a) an electron-donating color-developing organic compound, (b) an electron-accepting compound having a specific structure, and (c) a reaction medium that reversibly causes the electron donation reaction between components (a) and (b) to occur within a specific temperature range.

Description

Reversible thermochromic composition and reversible thermochromic microcapsule pigment encapsulated therein

The present invention relates to a reversible thermochromic composition and a reversible thermochromic microcapsule pigment encapsulating the composition. More specifically, the invention relates to a reversible thermochromic composition that exhibits a colorless state at temperatures above its high-temperature lateral color shift point and a color-developing state at temperatures below its low-temperature lateral color shift point, and a reversible thermochromic microcapsule pigment encapsulating the composition.

Previously, a reversible thermochromic composition that changes color from a color-developing state to a colorless state was disclosed. This composition essentially comprises an electron-donating color-developing organic compound, an electron-accepting compound, and a reaction medium that reversibly causes the electron-donating color-developing organic compound and the electron-accepting compound to undergo an electron-donating/accepting reaction within a specific temperature range. For example, Patent Document 1 discloses this reversible thermochromic composition, particularly regarding the use of compounds of specific structures, either alone or in combination, as color-developing agents for the electron-accepting compound.

Reversible thermochromic compositions are required to have excellent contrast, meaning a higher density in the color-developed state and a lower density in the decolorized state. Furthermore, they are required to have excellent lightfastness during color development, meaning that even when exposed to light, the decrease in color density over time in the color-developed state is suppressed. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Publication No. 2010-126549

[Identify the problem you want to solve]

The present invention, developed based on the aforementioned background technology, aims to provide a reversible thermochromic composition having a high density in the color-developing state and a low density in the color-decolorizing state, thereby exhibiting excellent light resistance, and a reversible thermochromic microcapsule pigment encapsulated therein. [Technical Solution]

The reversible thermochromic composition of the present invention comprises: (a) an electron-donating color-developing organic compound, (b) a combination of a compound represented by formula (I) and a compound selected from the group consisting of compounds represented by formulas (IIa) to (IIc) as an electron-accepting compound, and (c) a reaction medium that causes the electron donation and acceptance reaction between components (a) and (b) to reversibly occur within a specific temperature range. [Chemistry 1] (In the formula, R ¹¹ is a hydrogen atom, a linear or branched alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, an aryl group having 6 to 10 carbon atoms, or an aryl-substituted alkyl group having 7 to 11 carbon atoms (herein, the methylene group (-CH ₂ -) in the above alkyl group may be substituted with an oxy group (-O-)), R ¹² and R ¹³ are independently a linear or branched alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aryl-substituted alkyl group having 7 to 11 carbon atoms, or a halogen atom, and n11, n12, and n13 are independently 0 to 2) [Chemistry 2] (In the formula, ^Ra1 and ^Ra2 are independently a hydrogen atom, or a linear or branched alkyl group with 1 to 17 carbon atoms that may be substituted with a fluorine atom (herein, the methylene group ( _-CH2- ) in the above alkyl group may be substituted with an oxy group (-O-) or a carbonyl group (-CO-)), ^Ra3 and ^Ra4 are independently a linear or branched alkyl group with 1 to 4 carbon atoms that may be substituted with a fluorine atom or a hydroxyl group, an alkenyl group with 2 to 4 carbon atoms, or a halogen atom, and Na3 and Na4 are independently 0 to 2) [Chemistry 3] (wherein, ^Rb1 and ^Rb2 are independently a hydroxyl group, a linear or branched alkoxy group having 1 to 9 carbon atoms, a linear or branched alkyl group having 1 to 10 carbon atoms which may be substituted with a fluorine atom, an alkenyl group having 2 to 10 carbon atoms, or a halogen atom, nb1 is 0 to 3, and nb2 is 0 to 2) [Chemistry 4] (wherein, R ^c1 is a hydrogen atom, or a linear or branched alkyl group with 1 to 6 carbon atoms, L is a single bond, a linear or branched alkylene group with 1 to 3 carbon atoms, an aryl-substituted alkylene group with 7 to 9 carbon atoms, or an arylene group with 6 to 10 carbon atoms, R ^c2 , R ^c3 , and R ^c4 are each independently a linear or branched alkyl group with 1 to 4 carbon atoms which may be substituted with a fluorine atom, a cyclic alkyl group with 3 to 7 carbon atoms, a linear or branched alkoxy group with 1 to 3 carbon atoms, an alkenyl group with 2 to 4 carbon atoms, or a halogen atom, and nc2 , nc3 , and nc4 are each independently 0 to 3)

The reversible thermochromic microcapsule pigment of the present invention encapsulates the aforementioned reversible thermochromic composition. The reversible thermochromic liquid composition of the present invention contains the aforementioned reversible thermochromic microcapsule pigment and a vehicle. The solid writing material or solid makeup of the present invention contains the aforementioned reversible thermochromic microcapsule pigment and a shaping agent. The reversible thermochromic molding resin composition of the present invention contains the aforementioned reversible thermochromic microcapsule pigment and a molding resin. The reversible thermochromic laminate of the present invention comprises a support and a reversible thermochromic layer containing the aforementioned reversible thermochromic microcapsule pigment. The writing instrument of the present invention is a writing instrument containing a reversible thermochromic microcapsule pigment and a medium, and is filled with ink. [Effects of the Invention]

The present invention provides a reversible thermochromic composition having a high density in the color-developing state and a low density in the color-decoloring state, an excellent contrast between the color-developing and color-decoloring states, and excellent light fastness in the color-developing state, and a reversible thermochromic microcapsule pigment encapsulated therein.

Examples of the reversible thermochromic composition of the present invention include heat-decolorizing (decolorizing by heating and developing color by cooling) reversible thermochromic compositions containing at least three essential components: (a) an electron-donating color-developing organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color development reaction between components (a) and (b) occurs. As the reversible thermochromic composition, a heat-decolorizing type (decolorizing by heating and recoloring by cooling) reversible thermochromic composition described in Japanese Patent Publication No. 51-44706, Japanese Patent Publication No. 51-44707, Japanese Patent Publication No. 1-29398, etc. can be used (see FIG1 ). The heat-decolorizing type reversible thermochromic composition has a specific temperature (color change point) as the boundary. The color changes back and forth. It appears achromatic in the temperature range above the high-temperature color change point and appears colored in the temperature range below the low-temperature color change point. At room temperature, only one of these two states exists. The other state is maintained during the heating or cooling required to display the state. However, if no heating or cooling is applied, it returns to the state displayed at room temperature. It also has a small hysteresis width (ΔH) (ΔH = 1-7°C).

Furthermore, reversible thermochromic compositions of the heat-erasable type (which erases color by heating and develops color by cooling) described in Japanese Patent Publication No. 4-17154, Japanese Patent Publication No. 7-179777, Japanese Patent Publication No. 7-33997, Japanese Patent Publication No. 8-39936, Japanese Patent Publication No. 2005-1369, etc. can also be used (see FIG. 2 ). The reversible thermochromic composition of the heat-decolorizable type exhibits a relatively wide hysteresis width (ΔH = 8-70°C) and changes color along the following path: the path is a curve plotting the change in color density caused by temperature change, and the shape of the curve differs significantly when the temperature is increased toward the lower side of the color change temperature range and when the temperature is decreased toward the higher side of the color change temperature range. The color development state in the temperature range below the complete color development temperature _t1 or the color reduction state in the high temperature range above the complete color reduction temperature _t4 exhibits color memory within a specific temperature range [the temperature range between the color development start temperature _t2 and the color reduction start temperature _t3 (substantially two-phase retention temperature range)].

The components (a), (b), and (c) are described in detail below.

Component (a), the electron-donating color-developing organic compound, is the component that determines color. It is the compound that donates electrons to component (b), the color developer, thereby developing color.

Examples of the electron-donating color-developing organic compound include phthalide lactone compounds, fluorescent yellow matrix compounds, styrylquinoline compounds, diazolidine rose bengalactamide compounds, pyridine compounds, quinazoline compounds, and bisquinazoline compounds.

Examples of phthalide lactone compounds include diphenylmethanephthalide lactone compounds, phenylindolylphthalide lactone compounds, indolylphthalide lactone compounds, diphenylmethane azaphthalide lactone compounds, phenylindolyl azaphthalide lactone compounds, and their derivatives. Among these, phenylindolyl azaphthalide lactone compounds and their derivatives are preferred. Furthermore, examples of fluorescent yellow matrix compounds include amino fluorescent yellow matrix compounds, alkoxy fluorescent yellow matrix compounds, and their derivatives.

The following are examples of compounds that can be used as component (a): 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalolide, 3-(4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)phthalolide, 3,3-bis(1-n-butyl-2-methylindol-3-yl)phthalolide, 3,3-bis(2-ethoxy-4-diethylaminophenyl)-4-azaphthalolide, 3-(2-ethoxy-4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalolide, 3-(2-hexyloxy-4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalolide, 3-[2-Ethoxy-4-(N-ethylanilino)phenyl]-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 3-(2-acetamido-4-diethylaminophenyl)-3-(1-propyl-2-methylindol-3-yl)-4-azaphthalide, 3,6-Bis(diphenylamino)fluorescent yellow matrix, 3,6-Bis(N-phenyl-N-p-toluidinyl)fluorescent yellow matrix, 3,6-Dimethoxyfluorescent yellow matrix, 3,6-Di-n-butoxyfluorescent yellow matrix, 2-Methyl-6-(N-ethyl-N-p-toluidinyl)fluorescent yellow matrix, 3-Chloro-6-cyclohexylaminofluorescent yellow matrix, 2-Methyl-6-cyclohexylamino fluorescent yellow matrix, 2-Chloroamino-6-di-n-butylamino fluorescent yellow matrix, 2-(2-Chloroanilino)-6-di-n-butylamino fluorescent yellow matrix, 2-(3-Trifluoromethylanilino)-6-diethylamino fluorescent yellow matrix, 2-(3-Trifluoromethylanilino)-6-di-n-pentylamino fluorescent yellow matrix, 2-Dibenzylamino-6-diethylamino fluorescent yellow matrix, 2-(N-Methylanilino)-6-(N-ethyl-N-p-toluinyl) fluorescent yellow matrix, 1,3-Dimethyl-6-diethylamino fluorescent yellow matrix, 2-Chloro-3-methyl-6-diethylamino fluorescent yellow matrix, 2-anilino-3-methyl-6-diethylamino fluorescent yellow matrix, 2-anilino-3-methoxy-6-diethylamino fluorescent yellow matrix, 2-anilino-3-methyl-6-di-n-butylamino fluorescent yellow matrix, 2-anilino-3-methoxy-6-di-n-butylamino fluorescent yellow matrix, 2-dimethylamino-3-methyl-6-diethylamino fluorescent yellow matrix, 2-anilino-3-methyl-6-(N-ethyl-N-p-toluidinyl) fluorescent yellow matrix, 6-diethylamino-1,2-benzofluorescent yellow matrix, 6-(N-ethyl-N-isobutylamino)-1,2-benzofluorescent yellow matrix, 6-(N-ethyl-N-isopentylamino)-1,2-benzofluorescent yellow matrix, 2-(3-methoxy-4-dodecyloxyphenyl)quinoline, 2-diethylamino-8-diethylamino-4-methylspiro[5H-[1]benzopyrano[2,3-d]pyrimidin-5,1'(3'H)-isobenzofuran]-3'-one, 2-di-n-butylamino-8-di-n-butylamino-4-methylspiro[5H-[1]benzopyrano[2,3-d]pyrimidin-5,1'(3'H)-isobenzofuran]-3'-one, 2-Di-n-butylamino-8-diethylamino-4-methylspiro[5H-[1]benzopyrano[2,3-d]pyrimidine-5,1'(3'H)-isobenzofuran]-3'-one, 2-Di-n-butylamino-8-(N-ethyl-N-isopentylamino)-4-methylspiro[5H-[1]benzopyrano[2,3-d]pyrimidine-5,1'(3'H)-isobenzofuran]-3'-one, 2-Di-n-butylamino-8-di-n-pentylamino-4-methylspiro[5H-[1]benzopyrano[2,3-d]pyrimidine-5,1'(3'H)-isobenzofuran]-3'-one, 4,5,6,7-tetrachloro-3-(4-dimethylamino-2-methoxyphenyl)-3-(1-n-butyl-2-methyl-1H-indol-3-yl)-1(3H)-isobenzofuranone, 4,5,6,7-tetrachloro-3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methyl-1H-indol-3-yl)-1(3H)-isobenzofuranone, 4,5,6,7-tetrachloro-3-(4-diethylamino-2-ethoxyphenyl)-3-(1-n-pentyl-2-methyl-1H-indol-3-yl)-1(3H)-isobenzofuranone, 4,5,6,7-tetrachloro-3-(4-diethylamino-2-methylphenyl)-3-(1-ethyl-2-methyl-1H-indol-3-yl)-1(3H)-isobenzofuranone, 3',6'-bis[phenyl(2-methylphenyl)amino]spiro[isobenzofuran-1(3H),9'-[9H] ]-3-one, 3',6'-bis[phenyl(3-methylphenyl)amino]spiro[isobenzofuran-1(3H),9'-[9H] ]-3-one, 3',6'-bis[phenyl(3-ethylphenyl)amino]spiro[isobenzofuran-1(3H),9'-[9H] ]-3-one, 2,6-bis(2'-ethoxyphenyl)-4-(4'-dimethylaminophenyl)pyridine, 2,6-bis(2',4'-diethoxyphenyl)-4-(4'-dimethylaminophenyl)pyridine, 2,6-bis(2,4-diethoxyphenyl)-4-[4-bis(4-methoxyphenyl)aminophenyl]pyridine, 2-(4'-dimethylaminophenyl)-4-methoxyquinazoline, 4,4'-ethylenedioxy-bis[2-(4-diethylaminophenyl)quinazoline]

Furthermore, as a fluorescent yellow matrix, in addition to forming In addition to compounds having substituents on the phenyl group of the ring, A blue or black compound having a substituent on the phenyl group of the ring and a substituent (e.g., an alkyl group such as a methyl group, a halogen atom such as a chlorine atom) on the phenyl group forming the lactone ring.

Component (b), i.e., the electron-accepting compound, is a compound that accepts electrons from component (a) and functions as a color developer for component (a). Component (b) is a combination of a compound represented by formula (I) and a compound selected from the group consisting of compounds represented by formulas (IIa) to (IIc).

The compound represented by formula (I) is shown below. In the formula, R ¹¹ is a hydrogen atom, a linear or branched alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, an aryl group having 6 to 10 carbon atoms, or an aryl-substituted alkyl group having 7 to 11 carbon atoms (herein, the methylene group (-CH ₂ -) in the alkyl group may be substituted with an oxy group (-O-)). Preferably, it is a hydrogen atom, a linear or branched alkyl group having 1 to 3 carbon atoms, or an aryl-substituted alkyl group having 7 or 8 carbon atoms. More preferably, it is an isopropyl group or a benzyl group, and even more preferably, it is an isopropyl group. Furthermore, in the present invention, the term "aryl" also includes an aryl group substituted with an alkyl group (e.g., tolyl). The same applies to the following aryl groups. ^R12 and ^R13 are each independently a fluorine-substituted, linear or branched alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aryl-substituted alkyl group having 7 to 11 carbon atoms, or a halogen atom. Preferably, they are a linear or branched alkyl group having 1 to 4 carbon atoms (more preferably a methyl group), an alkenyl group having 2 to 4 carbon atoms (more preferably a 2-propenyl group), an aryl-substituted alkyl group having 7 or 8 carbon atoms (more preferably a methylbenzyl group, a benzyl group, or a phenethyl group), or a halogen atom (more preferably a chlorine atom or a bromine atom). n11, n12, and n13 are each independently 0 to 2, preferably 1, and preferably 0 or 1. In a further preferred embodiment, the hydroxyl group is present at the 4-position (para-position) of at least one benzene ring.

As a specific example of (I), the following can be cited. Bis(4-hydroxyphenyl)sulfone, 4-benzyloxy-4'-hydroxydiphenylsulfone, 4-(4-methylbenzyloxy)-4'-hydroxydiphenylsulfone, 4-(4-n-propylbenzyloxy)-4'-hydroxydiphenylsulfone, 4-(4-isopropylbenzyloxy)-4'-hydroxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 4-hydroxydiphenylsulfone, 4-methyl-4'-hydroxydiphenylsulfone, 4-n-propyl-4'-hydroxydiphenylsulfone, 4-isopropyl-4'-hydroxydiphenylsulfone, 4-methoxy-4'-hydroxydiphenylsulfone, 4-n-Propoxy-4'-hydroxydiphenylsulfone, 4-Isopropoxy-4'-hydroxydiphenylsulfone, 4-(2-Propyleneoxy)-4'-hydroxydiphenylsulfone, 4-(β-Phenoxyethoxy)-4'-hydroxydiphenylsulfone, Bis[4-hydroxy-3-(2-propenyl)phenyl]sulfone, Bis(3,5-dibromo-4-hydroxyphenyl)sulfone, Bis(4-hydroxy-3-n-propylphenyl)sulfone, Bis(4-hydroxy-3-methylphenyl)sulfone, 3',4'-dihydroxy-4-methyldiphenylsulfone, 3,4,4'-trihydroxydiphenylsulfone, Bis(3,4-dihydroxyphenyl)sulfone, 2,3,4-trihydroxydiphenylsulfone, 3-Benzyl-4-benzyloxy-4'-hydroxydiphenylsulfone, 3-Phenethyl-4-phenylethoxy-4'-hydroxydiphenylsulfone, 3-Methylbenzyl-4-methylbenzyloxy-4'-hydroxydiphenylsulfone, 4-Benzyloxy-3'-benzyl-4'-hydroxydiphenylsulfone, 4-Phenethoxy-3'-phenethyl-4'-hydroxydiphenylsulfone, 4-Methylbenzyloxy-3'-methylbenzyl-4'-hydroxydiphenylsulfone

The compound represented by formula (IIa) is shown below. In the formula, ^Ra1 and ^Ra2 are each independently a hydrogen atom, or a linear or branched alkyl group having 1 to 17 carbon atoms which may be substituted with a fluorine atom (herein, the methylene group ( _-CH2- ) in the alkyl group may be substituted with an oxy group (-O-) or a carbonyl group (-CO-)). Preferably, they are each independently a hydrogen atom, or a linear or branched alkyl group having 1 to 11 carbon atoms which may be substituted with a fluorine atom. More preferably, at least one of ^Ra1 and ^Ra2 is a linear or branched alkyl group having 5 to 9 carbon atoms. Further preferably, ^Ra1 and ^Ra2 are each independently a hydrogen atom, a branched alkyl group having 5 to 9 carbon atoms, and the other is a hydrogen group or a methyl group. R ^a3 and R ^a4 are each independently a linear or branched alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, or a halogen atom, which may be substituted with a fluorine atom or a hydroxyl group. Preferably, they are linear or branched alkyl groups having 1 to 4 carbon atoms (more preferably a methyl group), or a halogen atom (more preferably a fluorine atom). na3 and na4 are each independently 0 to 2, preferably 0 or 1, and more preferably 0. In a further preferred embodiment, the hydroxyl group is located at the 4-position (para-position) of the benzene ring.

As a specific example of (IIa), the following can be cited. 1,1-Bis(4-hydroxyphenyl)n-hexane, 1,1-Bis(4-hydroxyphenyl)n-octane, 1,1-Bis(4-hydroxyphenyl)n-decane, 1,1-Bis(4-hydroxyphenyl)-2-methylpropane, 1,1-Bis(4-hydroxyphenyl)-2-ethylbutane, 1,1-Bis(4-hydroxyphenyl)-2-ethylhexane, 2,2-Bis(4-hydroxyphenyl)propane, 2,2-Bis(4-hydroxyphenyl)n-heptane, 2,2-Bis(4-hydroxyphenyl)n-dodecane, 2,2-Bis(4-hydroxyphenyl)-4-methylhexane, 2,2-Bis(4-hydroxyphenyl)hexafluoropropane, 2,2-Bis(4-hydroxy-3-methylphenyl)butane, 2,2-Bis(4-hydroxy-3-isopropylphenyl)propane, 2,2-Bis(3-fluoro-4-hydroxyphenyl)propane

The compound represented by formula (IIb) is shown below. In the formula, ^Rb1 and ^Rb2 are independently a hydroxyl group, a linear or branched alkoxy group having 1-9 carbon atoms, a linear or branched alkyl group having 1-10 carbon atoms which may be substituted with a fluorine atom, an alkenyl group having 2-10 carbon atoms, or a halogen atom. Preferably, they are a hydroxyl group, a linear or branched alkyl group having 1-8 carbon atoms, more preferably a hydroxyl group, or a linear or branched alkyl group having 3-6 carbon atoms, and even more preferably, a hydroxyl group, an isobutyl group, a sec-butyl group, or a tert-butyl group. nb1 is 0-3, preferably 1. nb2 is 0-2, preferably 1. In a further preferred embodiment, the hydroxyl group is present at the 2-position (ortho-position) and the 4-position (para-position) of a benzene ring.

As a specific example of (IIb), the following can be cited. 2,4-Dihydroxybenzophenone, 4,4'-Dihydroxybenzophenone, 2,4-Dihydroxy-4'-n-propylbenzophenone, 2,4-Dihydroxy-4'-n-butylbenzophenone, 2,4-Dihydroxy-4'-isobutylbenzophenone, 2,4-Dihydroxy-4'-sec-butylbenzophenone, 2,4-Dihydroxy-4'-tert-butylbenzophenone, 2,4-Dihydroxy-4'-n-hexylbenzophenone, 2,4-Dihydroxy-2',4'-dimethylbenzophenone, 2,4-Dihydroxy-2',4',6'-trimethylbenzophenone, 2,4-Dihydroxy-2'-methoxybenzophenone, 2,4-Dihydroxy-4'-ethoxybenzophenone, 2,4-Dihydroxy-2',4'-dimethoxybenzophenone, 2,4-Dihydroxy-3',4'-diethoxybenzophenone

The compound represented by formula (IIc) is shown below. [Chemistry 8] In the formula, R ^c1 is a hydrogen atom, or a linear or branched alkyl group having 1 to 6 carbon atoms, preferably a hydrogen atom or a methyl group. L is a single bond, a linear or branched alkylene group having 1 to 3 carbon atoms, an aryl-substituted alkylene group having 7 to 9 carbon atoms, or an arylene group having 6 to 10 carbon atoms, preferably a single bond, an ethylene group, or a group represented by formula (i), more preferably a single bond or a group represented by formula (i). [Chemistry 9] (The benzene ring in the group represented by formula (i) is bonded to the designated carbon atom in formula (IIc)) R ^c2 , R ^c3 , and R ^c4 are each independently a fluorine-substituted linear or branched alkyl group having 1 to 4 carbon atoms, a cyclic alkyl group having 3 to 7 carbon atoms, a linear or branched alkoxy group having 1 to 3 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, or a halogen atom, preferably a linear or branched alkyl group having 1 to 4 carbon atoms (more preferably a methyl group), a linear or branched alkoxy group having 1 to 3 carbon atoms (more preferably a methoxy group or an ethoxy group), a cyclohexyl group, or a halogen atom (more preferably a fluorine atom). nc2 , nc3 , and nc4 are each independently 0 to 3, preferably 0 or 1, and more preferably 0. In a further preferred embodiment, the hydroxyl group is present at the 4-position (para-position) of each benzene ring.

As a specific example of (IIc), the following can be cited. 4,4',4''-methylenetriphenol, 4,4'-[(4-hydroxyphenyl)methylene]bis(2-methylphenol), 4,4'-[(4-hydroxyphenyl)methylene]bis(2-cyclohexyl-5-methylphenol), 4,4',4''-ethylenetriphenol, 4,4',4''-ethylenetri(2-methylphenol), 4,4'-[1-{4-[1-(4-hydroxyphenyl)-1-methylethyl]phenyl}ethylene]bisphenol, 4,4'-[1-{4-[1-(4-hydroxy-3-methylphenyl)-1-methylethyl]phenyl}ethylene]bis(2-methylphenol), 4,4'-[(3-ethoxy-4-hydroxyphenyl)methylene]bisphenol, 4,4'-[3-(5-cyclohexyl-4-hydroxy-2-methylphenyl)-3-phenyl)propylene]bis(2-cyclohexyl-5-methylphenol), 4,4'-[(4-hydroxyphenyl)methylene]bis(2-isopropylphenol), 4,4'-[1-{4-[1-(3-fluoro-4-hydroxyphenyl)-1-methylethyl]phenyl}ethylene]bisphenol, 4,4'-[3-(2,5-dimethyl-4-hydroxyphenyl)butyl]bis(2,5-dimethylphenol), 1,1,3-tris(4-hydroxyphenyl)propane, 1,2,2-tris(4-hydroxyphenyl)propane, 1,3,3-tris(4-hydroxyphenyl)butane, 1,4,4-Tris(4-hydroxyphenyl)pentane, 2,2-Bis(3-methyl-4-hydroxyphenyl)-1-(4-hydroxyphenyl)propane, 1-(3-methyl-4-hydroxyphenyl)-2,2-bis(4-hydroxyphenyl)propane, 1-(3-methyl-4-hydroxyphenyl)-3,3-bis(4-hydroxyphenyl)butane, 3,3-bis(3-methyl-4-hydroxyphenyl)-1-(4-hydroxyphenyl)butane, 1,1,3-Tris(3-methyl-4-hydroxyphenyl)propane, 1,3,3-Tris(3-methyl-4-hydroxyphenyl)butane, 4,4'-[4-(4-Hydroxyphenyl)-2-butylene]bis(2-methylphenol)

By combining a compound represented by formula (I) and a compound selected from the group consisting of compounds represented by formulas (IIa) to (IIc) as component (b), the properties of each compound can be utilized to provide a reversible thermochromic composition with excellent light resistance in the color-developed state. Specifically, even in the color-developed state, the decrease in density can be suppressed after exposure to light for a certain period of time.

Among the compounds represented by formula (I), from the perspective of easily improving the light resistance of the reversible thermochromic composition, preferably, n11 is 1, n12 and n13 are each 0 or 1, and when n12 and n13 are each 0, ^R11 is a linear or branched alkyl group having 1 to 3 carbon atoms, or an aryl-substituted alkyl group having 7 or 8 carbon atoms, and the hydroxyl group is present at the 4-position (para-position) of the benzene ring. When n12 and n13 are each 1, ^R11 is a hydrogen atom, ^R12 and ^R13 are alkenyl groups having 2 to 4 carbon atoms, and the hydroxyl group is present at the 4-position (para-position) of the benzene ring. More preferred are compounds wherein n11 is 1, n12 and n13 are each 0, ^R11 is a linear or branched alkyl group having 1 to 3 carbon atoms, and the hydroxyl group is located at the 4-position (para-position) of the benzene ring. Even more preferred are compounds wherein n11 is 1, n12 and n13 are each 0, ^R11 is an isopropyl group, and the hydroxyl group is located at the 4-position (para-position) of the benzene ring.

Furthermore, by combining a compound represented by formula (I) and a compound selected from the group consisting of compounds represented by formulas (IIa) to (IIc) as component (b), a reversible thermochromic composition having excellent light resistance in the color-developing state and excellent color density can be provided.

Among the compounds represented by formulas (IIa) to (IIc), compounds represented by formula (IIa) or (IIb) are preferred because they easily form reversible thermochromic compositions with superior light resistance. Furthermore, compounds represented by formula (IIa) are more preferred because they exhibit a greater difference between color development density and color loss density, that is, an excellent contrast between the color development state and the color loss state. Specifically, a combination of a compound represented by formula (I) and a compound represented by formula (IIa) as component (b) is preferred from the perspective of light resistance or the contrast between the color development state and the color loss state. In terms of reducing the color loss density of the reversible thermochromic composition compared to using the compound represented by formula (I) alone as component (b), the compound represented by (IIa) in combination with the compound represented by formula (I) is preferably a compound in which at least one of ^Ra1 and ^Ra2 is a linear or branched alkyl group having 3 to 9 carbon atoms, na3 and na4 are each 0, and the hydroxyl group is located at the 4-position (para-position) of the benzene ring. Furthermore, preferably, ^Ra1 and ^Ra2 are each independently a branched alkyl group having 5 to 9 carbon atoms, and the other is a hydrogen atom or a methyl group, and na3 and na4 are each 0, and the hydroxyl group is located at the 4-position (para-position) of the benzene ring. That is, the best combination to be used is a compound represented by formula (I) in which n11 is 1, n12 and n13 are respectively 0, ^R11 is an isopropyl group, and a hydroxyl group is present at the 4-position (para-position) of the benzene ring; and a compound represented by formula (IIa) in which one of R ^a1 and R ^a2 is a linear or branched alkyl group having 5 to 9 carbon atoms and the other is a hydrogen atom or a methyl group, n3 and n4 are respectively 0, and a hydroxyl group is present at the 4-position (para-position) of the benzene ring.

In a preferred embodiment of the present invention, component (b) comprises only a combination of a compound represented by formula (I) and a compound represented by formula (IIa). In this case, the mass ratio of the compound represented by formula (I) to the compound represented by formula (IIa) is preferably in the range of 1:0.5 to 1:5, more preferably 1:1 to 1:3. By maintaining the mass ratio of the compound represented by formula (I) to the compound represented by formula (IIa) within this range, a reversible thermochromic composition with a large difference between the color development density and the color elimination density, that is, an excellent contrast between the color development state and the color elimination state, is easily obtained.

In a more preferred embodiment of the present invention, component (b) comprises only a combination of a compound represented by formula (I), a compound represented by formula (IIa), and a compound represented by formula (IIb). This allows for a higher effect in terms of light resistance or the contrast between the colored state and the decolorized state. In this case, the content of the compound represented by formula (IIb) is preferably 5-25% by mass, more preferably 10-20% by mass, based on the total mass of component (b). The compound represented by formula (IIb) in combination with the compound represented by formula (I) and the compound represented by formula (IIa) is preferably one in which nb1 is 1, nb2 is 1, and ^Rb1 and ^Rb2 are independently hydroxy, isobutyl, sec-butyl, or tert-butyl. More preferably, nb1 is 1, nb2 is 1, ^Rb1 is isobutyl, sec-butyl, or tert-butyl, and ^Rb2 is hydroxy, wherein the hydroxyl group is located at the 2-position (ortho-position) and the 4-position (para-position) of the benzene ring.

In either case, the content of the compound represented by formula (IIa) is preferably 30-90% by mass, more preferably 40-80% by mass, and even more preferably 45-75% by mass, based on the total mass of component (b). By being within this range, a reversible thermochromic composition having an excellent contrast between the color-developing state and the decolorized state can be easily obtained.

Component (c), a reaction medium that reversibly causes the electron transfer reaction between component (a) and component (b) to occur within a specific temperature range, will be described. Examples of component (c) include alcohols, esters, ketones, ethers, and amides. When the reversible thermochromic composition of the present invention is used for microencapsulation and secondary processing, low-molecular-weight compounds evaporate out of the capsule upon high heat treatment. Therefore, to stably retain them within the capsule, compounds with 10 or more carbon atoms are preferably used.

As alcohols, effective ones are aliphatic monohydric saturated alcohols having 10 or more carbon atoms.

As esters, those having 10 or more carbon atoms are effective, and examples thereof include esters obtained from any combination of a monocarboxylic acid having an aliphatic, alicyclic, or aromatic ring and a monohydric alcohol having an aliphatic, alicyclic, or aromatic ring; esters obtained from any combination of a polycarboxylic acid having an aliphatic, alicyclic, or aromatic ring and a monohydric alcohol having an aliphatic, alicyclic, or aromatic ring; and esters obtained from any combination of a monocarboxylic acid having an aliphatic, alicyclic, or aromatic ring and a polyhydric alcohol having an aliphatic, alicyclic, or aromatic ring.

Also effective are ester compounds selected from esters of saturated fatty acids and branched aliphatic alcohols, esters of unsaturated fatty acids or saturated fatty acids having branches or substituents and branched or carbon-containing aliphatic alcohols, cetyl butyrate, stearyl butyrate, and behenyl butyrate.

Furthermore, in order to achieve color change with a greater hysteresis characteristic in the color density-temperature curve and provide color memory according to temperature changes, carboxylic acid ester compounds described in Japanese Patent Publication No. 4-17154 that exhibit a ΔT value (melting point-clouding point) of 5°C or more and less than 50°C can be exemplified.

Also effective are fatty acid ester compounds obtained from an odd-numbered aliphatic monohydric alcohol having 9 or more carbon atoms and an aliphatic carboxylic acid having an even carbon number, and fatty acid ester compounds having a total carbon number of 17 to 23 obtained from n-pentanol or n-heptanol and an even-numbered aliphatic carboxylic acid having 10 to 16 carbon atoms.

As the ketones, effective ones are aliphatic ketones having a total carbon number of 10 or more, and arylalkyl ketones having a total carbon number of 12 to 24 are exemplified.

As the ethers, effective ones are aliphatic ethers having a total carbon number of 10 or more.

Examples of the alcohols, esters, ketones, ethers, and amides include compounds described in Japanese Patent Application Laid-Open No. 2020-100710.

Furthermore, the component (c) may be a compound represented by the following formula (1). [In the formula, _R1 represents a hydrogen atom or a methyl _group , m represents an integer from 0 to 2, either _X1 or _X2 represents -( _CH2 ) _nOCOR2 or ( _CH2 ) _nCOOR2 , the other represents a hydrogen atom, n represents an integer from 0 to 2, _R2 represents _an alkyl group or alkenyl group having 4 or more carbon atoms, _Y1 and _Y2 each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a methoxy group, or a halogen atom, and r and p each independently represent an integer from 1 to 3] Among the compounds represented by formula (1), the case where _R1 is a hydrogen atom is preferred because a reversible thermochromic composition having a wider hysteresis width can be obtained, and the case where _R1 is a hydrogen atom and m is 0 is even more preferred. Furthermore, among the compounds represented by formula (1), the compounds represented by the following formula (2) are more preferred. (wherein R represents an alkyl group or alkenyl group having 8 or more carbon atoms, preferably an alkyl group having 10 to 24 carbon atoms, and more preferably an alkyl group having 12 to 22 carbon atoms)

Furthermore, the component (c) may be a compound represented by the following formula (3). (wherein, R represents an alkyl or alkenyl group having 8 or more carbon atoms, m and n each independently represent an integer of 1 to 3, and X and Y each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a halogen atom)

Furthermore, the component (c) may be a compound represented by the following formula (4). (In the formula, X represents any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a methoxy group, and a halogen atom; m represents an integer from 1 to 3; and n represents an integer from 1 to 20)

Furthermore, the component (c) may be a compound represented by the following formula (5). (In the formula, R represents an alkyl or alkenyl group having 1 to 21 carbon atoms, and n represents an integer from 1 to 3)

Furthermore, the component (c) may be a compound represented by the following formula (6). (In the formula, X represents any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, and a halogen atom; m represents an integer from 1 to 3; and n represents an integer from 1 to 20)

Furthermore, the component (c) may be a compound represented by the following formula (7). (wherein, R represents any one of an alkyl group having 4 to 22 carbon atoms, a cycloalkylalkyl group, a cycloalkyl group, and an alkenyl group having 4 to 22 carbon atoms; X represents any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, and a halogen atom; and n represents 0 or 1)

Furthermore, the component (c) may be a compound represented by the following formula (8). (In the formula, R represents an alkyl group having 3 to 18 carbon atoms or an aliphatic acyl group having 3 to 18 carbon atoms, X represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 or 2 carbon atoms, or a halogen atom, Y represents a hydrogen atom or a methyl group, and Z represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 or 2 carbon atoms, or a halogen atom)

Furthermore, the component (c) may be a compound represented by the following formula (9). (In the formula, R represents an alkyl group having 4 to 22 carbon atoms, an alkenyl group having 4 to 22 carbon atoms, a cycloalkylalkyl group, or a cycloalkyl group; X represents a hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom; Y represents a hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom; and n represents 0 or 1)

Furthermore, the component (c) may be a compound represented by the following formula (10). (In the formula, R represents any one of an alkyl group having 3 to 18 carbon atoms, a cycloalkyl group having 6 to 11 carbon atoms, a cycloalkyl group having 5 to 7 carbon atoms, and an alkenyl group having 3 to 18 carbon atoms; X represents any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, and a halogen atom; and Y represents any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a methoxy group, an ethoxy group, and a halogen atom)

Furthermore, the component (c) may be a compound represented by the following formula (11). (In the formula, R represents a cycloalkyl group having 3 to 8 carbon atoms or a cycloalkylalkyl group having 4 to 9 carbon atoms, and n represents an integer from 1 to 3)

Furthermore, the component (c) may be a compound represented by the following formula (12). (In the formula, R represents an alkyl group having 3 to 17 carbon atoms, a cycloalkyl group having 3 to 8 carbon atoms, or a cycloalkylalkyl group having 5 to 8 carbon atoms; X represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a methoxy group, an ethoxy group, or a halogen atom; and n represents an integer from 1 to 3)

Examples of the compounds represented by formulae (2) to (12) include compounds described in Japanese Patent Application Laid-Open No. 2020-100710.

Furthermore, reversible thermochromic compositions that utilize gallic acid esters (Japanese Patent Publication No. 51-44706, Japanese Patent Publication No. 2003-253149) as electron-accepting compounds (developing color upon heating and losing color upon cooling) and reversible thermochromic microcapsule pigments encapsulating these compositions can also be used (see FIG3 ).

The reversible thermochromic composition of the present invention is a phase solution containing the aforementioned components (a), (b), and (c) as essential components. The ratio of the components is affected by density, color change temperature, color change morphology, or the type of each component. Generally, the ratio of components to achieve the desired properties is: relative to 1 component (a), component (b) is 0.1-100, preferably 0.1-50, more preferably 0.5-20, and component (c) is 5-200, preferably 5-100, more preferably 10-100 (all the above ratios are in parts by mass).

Furthermore, various light stabilizers may be blended into the reversible thermochromic composition as needed. Light stabilizers are included to prevent photodegradation of the reversible thermochromic composition comprising components (a), (b), and (c). They are blended in an amount of 0.3 to 24 parts by mass, preferably 0.3 to 16 parts by mass, per 1 part by mass of component (a). Among the light stabilizers, ultraviolet absorbers effectively block ultraviolet light contained in sunlight and other sources, preventing photodegradation caused by the excited state resulting from the photoreaction of component (a). Antioxidants, singlet oxygen quenchers, superoxide anion quenchers, ozone quenchers, and the like inhibit oxidation reactions induced by light. Light stabilizers can be used alone or in combination of two or more.

The reversible thermochromic composition of the present invention is effective when used directly. However, it can also be encapsulated in microcapsules to form reversible thermochromic microcapsule pigments (hereinafter sometimes referred to as "microcapsule pigments" or "pigments"), or dispersed in thermoplastic resins or thermosetting resins to form reversible thermochromic resin particles (hereinafter sometimes referred to as "resin particles"). The reversible thermochromic composition is preferably encapsulated in microcapsules to form reversible thermochromic microcapsule pigments. This is because microcapsulation creates a chemically and physically stable pigment. Consequently, the reversible thermochromic composition maintains the same composition and exhibits the same effects under various usage conditions. Furthermore, microencapsulation methods include the well-known isocyanate-based interfacial polymerization method, the melamine-formalin-based in-situ polymerization method, the liquid curing coating method, the phase separation method from aqueous solutions, the phase separation method from organic solvents, the melt dispersion cooling method, the in-air suspension coating method, and the spray drying method. The appropriate method should be selected depending on the application. Furthermore, depending on the purpose, a secondary resin coating can be applied to the surface of the microcapsule to impart durability or modify surface properties for practical application. For reversible thermochromic microcapsule pigments, the optimal mass ratio of the inner material to the outer film is 7:1 to 1:1. By maintaining this mass ratio within this range, a decrease in color density and clarity during color development can be prevented. The optimal mass ratio of the inner material to the membrane is 6:1 to 1:1.

The average particle size of reversible thermochromic microencapsulated pigments or resin particles is preferably 0.01 to 50 μm, more preferably 0.1 to 30 μm, and even more preferably 0.5 to 20 μm. If the average particle size of the microencapsulated pigment or resin particles exceeds 50 μm, dispersion stability and processing compatibility may be poor when incorporated into inks, coatings, or resins. On the other hand, if the average particle size is less than 0.01 μm, high-density color development may be difficult to achieve. When using microencapsulated pigments or resin particles in writing inks, the average particle size is preferably 0.01-5 μm, more preferably 0.05-4 μm, even more preferably 0.1-3 μm, and most preferably 0.5-3 μm. If the average particle size of the pigment or resin particles exceeds 5 μm, good ink release properties may be difficult to achieve when used in writing instruments. On the other hand, if the average particle size is less than 0.01 μm, high-density color development may be difficult. The average particle size is determined using image analysis particle size distribution measurement software [Mac View, manufactured by Mountech Co., Ltd.]. The particle area is then determined, and the projected area circle equivalent diameter (Heywood diameter) is calculated from the area of the particle area. This value is then used as the average particle size of particles equivalent to a sphere of equal volume. Alternatively, if the particle size of all or most particles exceeds 0.2 μm, the average particle size of particles equivalent to a sphere of equal volume can be measured using the Coulter method using a particle size distribution measurement device [Multisizer 4e, manufactured by Beckman Coulter Co., Ltd.]. Furthermore, using the above software or the values measured using a Coulter method measuring device as a reference, a calibrated laser diffraction/scattering particle size distribution measuring device [manufactured by Horiba, Ltd., product name: LA-300] can be used to measure volume-based particle size and average particle size.

Reversible thermochromic colorants such as reversible thermochromic compositions, reversible thermochromic microcapsule pigments, or resin particles can be dispersed in a medium containing water and/or an organic solvent and, if necessary, various additives to prepare an ink composition (hereinafter sometimes referred to as "ink"). This can be used as a reversible thermochromic liquid composition for printing inks used in screen printing, offset printing, color printing, gravure printing, coating machines, and soft fabric printing; coatings used in brush coating, spray coating, electrostatic coating, electrodeposition coating, shower coating, roll coating, and dip coating; inkjet inks; UV-curable inks; inks for writing instruments such as markers, ballpoint pens, fountain pens, and ink pens; inks for painting tools; inks for stamps; drawing tools; cosmetics; and fiber coloring liquids.

Various additives can be added to the reversible thermochromic liquid composition. Examples of additives include resins, crosslinking agents, hardeners, desiccants, plasticizers, viscosity modifiers, dispersants, UV absorbers, antioxidants, light stabilizers, anti-precipitants, lubricants, gelling agents, defoaming agents, matting agents, penetrants, pH adjusters, foaming agents, coupling agents, humectants, mold inhibitors, preservatives, and rust inhibitors.

Examples of writing mediums used in writing inks include oil-based media containing an organic solvent, or aqueous media containing water and, if necessary, an organic solvent. In the case of aqueous media, a water-soluble organic solvent compatible with water can be added to the writing ink. The water-soluble organic solvent inhibits evaporation of water from the ink, prevents fluctuations in the specific gravity of the media, maintains good dispersion stability of the reversible thermochromic microencapsulated pigment, and stabilizes the structure of the loose aggregates formed by the polymer coagulant or the polymer coagulant and dispersant described below. Examples of organic solvents include ethanol, propanol, butanol, glycerol, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thiodiethylene glycol, polyethylene glycol, propylene glycol, butylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, cyclobutanesulfonate, 2-pyrrolidone, and N-methyl-2-pyrrolidone.

When writing instrument ink contains a water-soluble organic solvent, the water-soluble organic solvent is preferably blended in a range of 1-40% by mass, more preferably 5-30% by mass, and even more preferably 10-25% by mass relative to the total ink volume. If the blend ratio of the water-soluble organic solvent exceeds 40% by mass, the ink viscosity tends to increase. On the other hand, if the blend ratio is less than 1% by mass, the water evaporation suppression effect is reduced.

When writing ink contains a water-soluble organic solvent and the hysteresis width (ΔH) of the reversible thermochromic microencapsulated pigment used in the writing ink is large, the specific gravity of the microencapsulated pigment is greater than 1. When adjusting the specific gravity of the medium, using a water-soluble organic solvent with a specific gravity greater than water facilitates specific gravity adjustment. Therefore, it is preferred to use a water-soluble organic solvent with a specific gravity exceeding 1.1, such as glycerin.

Shear-thinning agents can be added to writing inks. Inks containing this agent (shear-thinning inks) can inhibit the aggregation and sedimentation of microencapsulated pigments and prevent bleeding, resulting in superior handwriting. Furthermore, when this shear-thinning ink is contained in a ballpoint pen, it prevents ink from leaking out of the gap between the ball and the pen tip when the pen is not in use, and prevents backflow of ink when the pen is held upright with the writing tip facing upward.

Examples of shear-thinning agents include: Samsonite gum, Brunei gum, organic acid-modified heteropolysaccharides composed of glucose and galactose (average molecular weight of about 1 million to 8 million), Alcagum, guar gum, locust bean gum and its derivatives, hydroxyethyl cellulose, alginic acid alkyl esters, polymers with a molecular weight of 100,000 to 150,000 based on alkyl esters of methacrylic acid, thickening polysaccharides with gelling ability extracted from seaweed such as glucomannan, agar or carrageenan, benzylidene sorbitol and benzylidene xylitol or Derivatives of these, cross-linked acrylic acid polymers, inorganic microparticles, polyglycerol fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyethylene glycol fatty acid esters, polyoxyethylene castor oil, polyoxyethylene lanolin/lanolin alcohol/beeswax derivatives, polyoxyethylene alkyl ethers/polyoxypropylene alkyl ethers, polyoxyethylene alkylphenyl ethers, fatty amides, and other non-ionic surfactants with an HLB value of 8-12, salts of dialkyl or dienyl sulfosuccinic acids, mixtures of N-alkyl-2-pyrrolidone and anionic surfactants, and mixtures of polyvinyl alcohol and acrylic resins.

Furthermore, a polymer coagulant can be added to writing ink. Ink containing a polymer coagulant (cohesive ink) allows the microcapsule pigment to form loose aggregates through the polymer coagulant, inhibiting aggregation caused by contact between microcapsule pigments, thereby improving the dispersibility of the microcapsule pigment.

Examples of polymeric flocculants include polyvinyl pyrrolidone, polyethylene oxide, and water-soluble polysaccharides. Examples of water-soluble polysaccharides include astragalus gum, guar gum, branched starch, cyclodextrin, and water-soluble cellulose derivatives. Further examples of water-soluble cellulose derivatives include methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, and hydroxypropylmethylcellulose. Among the above polymeric flocculants, hydroxyethylcellulose is preferred due to its excellent dispersibility.

The polymer coagulant is preferably blended in a range of 0.1-1% by mass, and more preferably 0.3-0.5% by mass, relative to the total ink volume. Within this range, the microencapsulated pigment forms loose aggregates, effectively enhancing the pigment's dispersibility.

Furthermore, by adding a dispersant to writing ink, the dispersibility of microencapsulated pigments can be improved. Also, a polymer coagulant and a dispersant can be used together. When used together, the dispersibility of microencapsulated pigments can be improved, and the dispersibility of loose aggregates of microencapsulated pigment formed by the polymer coagulant can be further enhanced.

Examples of dispersants include polyvinyl pyrrolidone, polyvinyl butyral, polyvinyl ether, styrene-maleic acid copolymers, ketone resins, hydroxyethyl cellulose and its derivatives, synthetic resins such as styrene-acrylic acid copolymers, acrylic polymers, PO (propylene oxide)/EO (ethylene oxide) adducts, and polyester amine oligomers. Among these dispersants, acrylic polymer dispersants are preferred for their excellent dispersibility in microencapsulated pigments. Acrylic polymer dispersants with carboxyl groups are more preferred, and acrylic polymer dispersants with a comb-shaped structure and carboxyl groups on the side chains are even more preferred. Preferred dispersants are acrylic polymers with a comb-shaped structure containing multiple carboxyl groups on the side chains. A specific example is Solsperse 43000, manufactured by Japan Lubrizol Co., Ltd. The dispersant should be added in an amount preferably between 0.01 and 2% by weight, more preferably between 0.1 and 1.5% by weight, relative to the total ink volume. If the dispersant content exceeds 2% by weight, the microencapsulated pigment may easily settle or float when subjected to external vibrations. On the other hand, if the content is less than 0.01% by weight, the dispersibility improvement effect may be limited.

Furthermore, by adding a water-soluble resin to writing ink, the writing can be made more firmly fixed to the paper or have better adhesion. Examples of water-soluble resins include alkyd resins, acrylic resins, styrene-maleic acid copolymers, cellulose derivatives, polyvinyl pyrrolidone, polyvinyl alcohol, and dextrin. Among these water-soluble resins, polyvinyl alcohol is preferred due to its excellent stability as an acrylic polymer dispersant. Furthermore, partially saponified polyvinyl alcohol with a saponification degree of 70 to 89 mol% is more preferred due to its high solubility in acidic regions. The water-soluble resin is preferably added in an amount of 0.3 to 3.0 mass%, more preferably 0.5 to 1.5 mass%, relative to the total ink volume.

Furthermore, when the viscosity of the medium used in writing inks is relatively low, by adding a specific gravity adjuster, the microencapsulated pigment can be prevented from settling or floating in the ink and becoming localized, thereby improving the dispersion stability of the microencapsulated pigment.

When the difference in specific gravity between the vehicle and pigment is minimal, pigment dispersion stability is maximized. A specific gravity adjuster is used to bring the vehicle's specific gravity closer to that of the pigment. The specific gravity of a vehicle is affected by the specific gravity of the water-soluble substances dissolved in it and the amount of water-soluble substances added. Therefore, adding more specific gravity adjusters with a higher specific gravity to the vehicle and allowing them to dissolve further increases the vehicle's specific gravity.

Examples of specific gravity adjusters include oxyacids and salts of Group VI elements with atomic weights ranging from 90 to 185. These specific gravity adjusters adjust the specific gravity of the medium to approximate that of the heavier pigment. Even with low-viscosity inks, they can prevent localization of the pigment, which can occur due to external stimuli such as vibration, causing precipitation or lifting.

The oxyacids and their salts are selected from the group consisting of oxyacids of transition metal elements and their salts. The oxyacid radical ions are formed by oxygen atoms typically coordinating with metal atoms in a four- or six-fold manner, forming tetrahedral or octahedral configurations. The oxyacids and their salts may be polyacids and polyacid salts thereof. Polyacids include isopolyacids and heteropolyacids, and polyacid salts include isopolyacid salts and heteropolyacid salts.

Examples of specific gravity adjusters include single oxyacids and their salts, isopolyacids and their salts, and heteropolyacids and their salts. Single oxyacids include molybdic acid and tungstic acid. Further examples of single oxyacid salts include sodium molybdate, potassium molybdate, ammonium molybdate, sodium tungstate, potassium tungstate, ammonium tungstate, lithium tungstate, and magnesium tungstate. Examples of isopoly acids include metamolybdic acid, secondary molybdic acid, metatungstate acid, secondary tungstate acid, and isotungstate acid. Examples of isopoly acid salts include sodium metamolybdate, potassium metamolybdate, ammonium metamolybdate, secondary molybdate, potassium secondary molybdate, ammonium secondary molybdate, sodium metatungstate, potassium metatungstate, ammonium metatungstate, barium metatungstate, sodium secondary tungstate, and sodium isotungstate. Examples of polyacids include molybdenum phosphate, molybdenum silicic acid, tungsten phosphate, and tungsten silicic acid. Examples of polyacid salts include sodium molybdenum phosphate, sodium molybdenum silicic acid, sodium tungsten phosphate, and sodium tungsten silicic acid. The above-mentioned oxyacids and their salts may be used alone or in combination of two or more.

Among the above-mentioned specific gravity adjusters, preferred are metatungstate, secondary tungstate, sodium metatungstate, potassium metatungstate, ammonium metatungstate, barium metatungstate, sodium secondary tungstate, sodium isotungstate, tungsten phosphate, silicic tungstate, sodium tungsten phosphate, and sodium silicic tungstate. More preferred are sodium isotungstate, sodium metatungstate, and sodium secondary tungstate. Sodium isotungstate, sodium metatungstate, and sodium secondary tungstate are not only highly safe but also inherently have high specific gravities. Therefore, they can be easily adjusted to the specific gravity of liquids with high specific gravity by adjusting the added amount, making them ideal for use.

The specific gravity adjuster should be added in a range of 2-20% by weight, more preferably 5-15% by weight, relative to the total ink volume. If the specific gravity adjuster exceeds 20% by weight, the microencapsulated pigment will tend to aggregate. On the other hand, if the specific gravity adjuster is less than 2% by weight, the vehicle's specific gravity adjustment effect will be poor. The microencapsulated pigment:specific gravity adjuster ratio is preferably 1:0.05-4.0, more preferably 1:0.075-2.0, and even more preferably 1:0.1-1.5.

The vehicle formulated with the aforementioned specific gravity adjuster is particularly effective for microencapsulated pigments with higher specific gravity. Even with low-viscosity inks, it can inhibit pigment precipitation in the ink when subjected to external stimuli such as vibration, thereby improving the dispersion stability of the microencapsulated pigment. The specific gravity of microencapsulated pigments is affected by particle size, the ingredients and their content within the microcapsules, the composition and thickness of the capsule membrane, the pigmentation state of the microencapsulated pigment, and temperature. The optimal specific gravity, when the microencapsulated pigment is fully colored, is 1.05-1.20 relative to water at 20°C. This type of pigment exhibits a large hysteresis width (ΔH), allowing it to be decolorized by heating and remain decolorized within a specific temperature range. However, since pigments with large hysteresis widths (ΔH) often use compounds with two or more aromatic rings as component (c), their specific gravity tends to be high, making them prone to sedimentation and separation in the ink. This is particularly true when stimulated by external vibrations. However, when formulated with the aforementioned specific gravity adjuster, even with low ink viscosity, the microencapsulated pigment can be prevented from sedimenting and localizing, thereby improving the dispersion stability of the pigment and making it suitable for use. Considering the dispersion stability of the pigment in the ink, the specific gravity of the microencapsulated pigment, when fully colored, relative to water at 20°C, is preferably 1.10-1.20, and more preferably 1.12-1.15. The specific gravity of the microencapsulated pigment can be measured using the following method.

(Method for Determining the Specific Gravity of Microencapsulated Pigments) 1. Place 30 ml of a glycerin-water solution and 1 g of fully colored microencapsulated pigment in a screw-top bottle and mix to obtain a microencapsulated pigment dispersion. 2. Adjust the temperature of the 30 ml microencapsulated pigment dispersion to 20°C and centrifuge at 1000 rpm for 30 seconds. Alternatively, a cooling/tabletop centrifuge [Kokusan Co., Ltd., product name: H103N] can be used as a centrifuge. 3. Observe the microencapsulated pigment dispersion. If most of the microencapsulated pigment settles to the bottom of the beaker, repeat steps 1 and 2 using an aqueous solution with a higher glycerin concentration than the current glycerin-water solution and observe the dispersion. Once the microcapsule pigment is confirmed to be mostly suspended on the liquid surface, repeat steps 1 and 2 using a glycerin solution with a lower glycerin concentration and observe the dispersion. Repeat this series of steps until you can visually confirm that the microcapsule pigment is not mostly floating to the liquid surface or settling, but rather that the glycerin solution is uniformly colored except near the surface or the bottom of the screw-top bottle. Measure the specific gravity of the glycerin solution at which this state is observed and use it as the specific gravity of the microcapsule pigment. The specific gravity of the glycerin solution can be measured using the floating balance method described in JIS K0061, Section 7.1, on an aqueous solution conditioned at 20°C.

Furthermore, the vehicle formulated with the aforementioned specific gravity adjuster has a specific gravity in the range of 1.00 to 1.30, preferably 1.05 to 1.20, and more preferably 1.08 to 1.18, at 20°C, based on water. Furthermore, the specific gravity of the vehicle relative to the specific gravity of the aforementioned pigment is preferably 0.90 to 1.20 times, and more preferably 0.95 to 1.10 times. When the specific gravity of the vehicle is within this range, and when the specific gravity of the vehicle relative to the specific gravity of the pigment is within this range, even when the ink has a low viscosity, even when subjected to external stimuli such as vibration, the pigment can be further prevented from settling and localizing within the ink, thereby further improving the dispersion stability of the pigment.

When the writing medium is an aqueous medium, the medium contains at least water, and the water content relative to the total amount of ink is preferably in the range of 30-80 mass %, more preferably 40-70 mass %.

Furthermore, when the writing instrument ink is used in a ballpoint pen, it is preferred to add a lubricant such as a higher fatty acid such as oleic acid, a non-ionic surfactant having a long-chain alkyl group, a polyether-modified polysilicone oil, a thiophosphite triester such as tris(alkoxycarbonylmethyl) thiophosphite or tris(alkoxycarbonylethyl) thiophosphite, a phosphate monoester of polyoxyethylene alkyl ether or polyoxyethylene alkyl aryl ether, a phosphate diester of polyoxyethylene alkyl ether or polyoxyethylene alkyl aryl ether, or metal salts, ammonium salts, amine salts, or alkanolamine salts of these to the ink to prevent wear of the ballpoint pen holder.

In addition, additives such as wetting agents, resins, resin particles, pH adjusters, rust inhibitors, surfactants, wetting agents, defoaming agents, viscosity adjusters, preservatives, and mold inhibitors can be added as needed.

In the aforementioned writing instrument ink, the reversible thermochromic microencapsulated pigment is preferably blended in a range of 5-40% by weight, more preferably 10-40% by weight, and even more preferably 10-30% by weight relative to the total ink volume. By maintaining the microencapsulated pigment blend ratio within this range, the desired color density can be achieved while preventing a decrease in ink flowability.

The ink composition of the present invention can be produced by any known method. Specifically, the required amounts of the aforementioned components can be blended and mixed using a stirrer such as a propeller, a homogenizer, or a homomixer, or a disperser such as a bead mill.

When the writing ink of the present invention is used in a ballpoint pen, its viscosity, measured at 20°C and a rotational speed of 1 rpm (shear rate of 3.84 sec ^-1 ), is preferably 1 to 2000 mPa·s, more preferably 3 to 1500 mPa·s, and even more preferably 500 to 1000 mPa·s, in order to inhibit the precipitation or aggregation of the microencapsulated pigment. Furthermore, when measured at 20°C and a rotational speed of 100 rpm (shear rate of 384 sec ^-1 ), the viscosity is preferably 1-200 mPa·s, more preferably 10-100 mPa·s, and even more preferably 20-50 mPa·s for good ink flow from the ballpoint pen tip. By maintaining the viscosity within this range, the dispersion stability of the microencapsulated pigment and the fluidity of the ink within the ballpoint pen mechanism can be maintained at a high level. Viscosity was measured using a rheometer (TA Instruments, Discovery HR-2, tapered plate (40 mm diameter, 1° angle)) at 20°C at a rotational speed of 1 rpm (shear rate of 3.84 sec ^-1 ) or 100 rpm (shear rate of 384 sec ^-1 ).

When the writing instrument ink of the present invention is used in a ballpoint pen, its surface tension at 20°C is preferably 20-50 mN/m, more preferably 25-45 mN/m. Maintaining the surface tension within this range can help prevent bleeding of the writing line and penetration into the paper surface, and improve the ink's wettability on the paper surface. Surface tension is measured using a surface tension meter (DY-300, manufactured by Kyowa Interface Science Co., Ltd.) at 20°C using the vertical plate method with a platinum plate.

When the writing instrument ink of the present invention is used in a ballpoint pen, its pH is preferably 3 to 10, more preferably 4 to 9. Maintaining the pH within this range can suppress aggregation or precipitation of the microencapsulated pigment contained in the ink in low-temperature environments. The pH value is measured using a pH meter [manufactured by DKK Toa Co., Ltd., product name: IM-40S] at 20°C.

When the writing instrument ink of the present invention is used in marker pens, its viscosity, measured at 20°C and 30 rpm, is preferably 1-20 mPa·s, more preferably 1-10 mPa·s, and even more preferably 1-5 mPa·s. Maintaining the viscosity within this range improves the fluidity of the ink and the dispersion stability of the microencapsulated pigment. Viscosity values are measured using a BL-type rotational viscometer [manufactured by Toki Industry Co., Ltd., product name: TVB-M Viscometer, L-type rotor] at 20°C.

When the writing instrument ink of the present invention is used in a marker, its surface tension at 20°C is preferably 25-50 mN/m, more preferably 25-45 mN/m, and even more preferably 35-45 mN/m. Maintaining the surface tension within this range can help prevent bleeding of the writing line and penetration into the paper surface, and improve the ink's wettability on the paper surface. Surface tension is measured using a surface tension meter (DY-300, manufactured by Kyowa Interface Science Co., Ltd.) at 20°C using the vertical plate method with a glass plate.

When the writing instrument ink of the present invention is used in a marker, its pH is preferably 3-8, more preferably 4-7, and even more preferably 5-6. Maintaining the pH within this range can suppress aggregation or precipitation of the microencapsulated pigment contained in the ink in low-temperature environments. The pH value is measured using a pH meter [manufactured by DKK Toa Co., Ltd., product name: IM-40S] at 20°C.

The writing ink is contained in a writing instrument equipped with a pen tip and an ink refill mechanism. Examples of such writing instruments include various types of writing instruments, such as ballpoint pens, markers, fountain pens, ink pens, and calligraphy pens.

There are no particular limitations on the type of writing instrument pen tip, and various types of nibs can be used. Among these various nibs, examples of ballpoint pen nibs include those in which a ball is held by a ball-holding portion formed by pressing and deforming the vicinity of the front end of a metal tube from the outside toward the inside; those in which a ball is held by a ball-holding portion formed by cutting metal material using a drill, etc.; nibs in which a resin ball holder is provided within a metal or plastic nib; and those in which a spring is used to urge the ball held by the nib forward. The materials for the ballpoint pen tip and ball are not particularly limited. Examples include superhard alloys (ultrahard), stainless steel, ruby, ceramics, resins, and rubber. The diameter of the ball is preferably 0.1 to 3.0 mm, more preferably 0.2 to 2.0 mm, and even more preferably 0.3 to 1.0 mm. The ball may also be surface-treated with DLC (diamond-like carbon) coating.

Examples of marker pen tips include: conventionally used porous members with interconnected pores and a porosity ranging from approximately 30% to 70% such as processed fiber resins, fused heat-meltable fibers, and felts; or extruded synthetic resins with multiple axially extending ink outlets, with one end processed into a shape suitable for the intended purpose, such as a cannonball, rectangle, or chisel.

Examples of a pen tip (pen body) in the form of a fountain pen include a metal plate such as a stainless steel plate or a gold alloy plate cut into a tapered shape and then bent or folded, or a resin molded into the shape of a pen tip. Furthermore, the pen body may have a slit in the center or a bulb at the tip.

Examples of ink refill mechanisms include ink containers or ink absorbing bodies that can be directly refilled with writing ink. The ink container, for example, is formed from a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon, or a metal tubular body. Besides being directly connected to the pen tip, the ink container and pen tip can also be connected via a connecting member. The ink absorbing body is a fiber bundle formed by longitudinally bundling curled fibers. It is embedded in a covering such as a plastic cylinder or film, and has a porosity adjusted to approximately 40% to 90%.

When filling a ballpoint pen with writing ink, the structure and shape of the ballpoint pen itself are not particularly limited. For example, a ballpoint pen may have an ink container filled with shear-thinning ink within a barrel, the ink container being connected to a ballpoint pen tip having a ball mounted at the front end, and a liquid plug for preventing backflow being in close contact with the end face of the ink.

An ink backflow preventer composition is filled at the rear end of the ink filled in the ink container. The ink backflow preventer composition comprises a non-volatile liquid and/or a low-volatile liquid. Examples include petroleum jelly, tablet oil, castor oil, olive oil, refined mineral oil, liquid wax, polybutene, α-olefins, α-olefin oligomers or cooligomers, dimethyl polysilicone oil, methylphenyl polysilicone oil, amino-modified polysilicone oil, polyether-modified polysilicone oil, and fatty acid-modified polysilicone oil. The ink backflow preventer composition may be used alone or in combination of two or more.

It is preferred to add a thickener to the ink backflow prevention composition to increase its viscosity to a preferred level. Examples of such thickeners include hydrophobic silica, methylated microparticles, aluminum silicate, expanded mica, hydrophobic clay-based thickeners such as bentonite or montmorillonite, fatty acid metal soaps such as magnesium stearate, calcium stearate, aluminum stearate, and zinc stearate, tribenzylidene sorbitol, fatty amides, amide-modified polyethylene wax, hydrogenated castor oil, dextrin-based compounds such as fatty acid dextrin, and cellulose-based compounds. Furthermore, the above-mentioned liquid ink backflow prevention composition and solid ink backflow prevention composition can also be used in combination.

Alternatively, the barrel itself may serve as the ink filling mechanism, for example, a ballpoint pen in which ink is directly filled into the barrel and a ballpoint pen tip is attached to the front end of the barrel.

A ballpoint pen having a ballpoint pen tip and an ink filling mechanism may further have an ink supply mechanism for supplying the ink filled in the ink filling mechanism to the pen head.

There is no particular limitation on the ink supply mechanism, and examples thereof include: (1) a mechanism having an ink guide core including a fiber bundle as an ink flow regulating body, which supplies ink to the pen tip; (2) a mechanism having a comb-groove-shaped ink flow regulating body, which is interposed to supply ink to the pen tip; (3) a mechanism in which a plurality of disc bodies are arranged in parallel with comb-groove-shaped intervals, and a narrow ink guide groove and a ventilation groove wider than the groove are provided that penetrate the disc body in the axial direction, an ink guide core for guiding ink from the ink filling mechanism to the pen tip is arranged at the axis to form a pen core, and ink is supplied to the pen tip via the pen core.

The material for the refill is not particularly limited, as long as it is a synthetic resin that can be injection-molded into a comb-grooved structure with multiple discs. Examples of such synthetic resins include general-purpose polycarbonate, polypropylene, polyethylene, and acrylonitrile-butadiene-styrene copolymer (ABS resin). In particular, acrylonitrile-butadiene-styrene copolymer (ABS resin) is particularly preferred due to its high moldability and ease of achieving refill performance.

When the ballpoint pen is provided with the above-mentioned ink supply mechanism, the above-mentioned ink absorbing body may be used as the ink filling mechanism in addition to the above-mentioned ink container or barrel.

The structure of a ballpoint pen for storing writing ink includes the following examples: (1) a ballpoint pen having a tip connected to an ink container directly or via a connecting member, filled with writing ink, and an ink backflow prevention member filled on the end face of the ink container, and a ballpoint pen replacement refill thus formed is stored in a barrel; (2) a ballpoint pen having the following mechanism, i.e., a barrel directly filled with writing ink, an ink flow regulating member or an ink flow regulating member interposed as a comb groove. (1) a mechanism for supplying ink to the pen tip by means of an ink-conducting core comprising a fiber bundle or the like in a body; (2) a mechanism for supplying ink to the pen tip by means of an ink-conducting core comprising a fiber bundle or the like in a body; (3) a mechanism for supplying ink to the pen tip by means of an ink-conducting core comprising a fiber bundle or the like in a body; (4) a mechanism for supplying ink to the pen tip by means of an ink-conducting core comprising a fiber bundle or the like in a body; (5) a mechanism for supplying ink to the pen tip by means of an ink-conducting core comprising a fiber bundle or the like in a body; (6) a mechanism for supplying ink to the pen tip by means of an ink-conducting core comprising a fiber bundle or the like in a body; (7) a mechanism for supplying ink to the pen tip by means of an ink-conducting core comprising a fiber bundle or the like in a body; (8) a mechanism for supplying ink to the pen tip by means of an ink-conducting core comprising a fiber bundle or the like in a body; (9) a mechanism for supplying ink to the pen tip by means of an ink-conducting core comprising a fiber bundle or the like in a body; (10) a mechanism for supplying ink to the pen tip by means of an ink-conducting core comprising a fiber bundle or the like in a body; (11) a mechanism for supplying ink to the pen tip by means of an ink-conducting core comprising a fiber bundle or the like in a body; (12) a mechanism for supplying ink to the pen tip by means of an ink-conducting core comprising a fiber bundle or the like in a body; (13) a mechanism for supplying ink to the pen tip by means of an ink-conducting core comprising a fiber bundle or the like in a body; (14) a mechanism for supplying ink to the pen tip by means of an ink-conducting core comprising a fiber bundle or the like in a body; (15) a mechanism for supplying ink to the pen tip by means of an ink-conducting core comprising a fiber bundle or the

When filling a marker with writing ink, the structure and shape of the marker itself are not particularly limited. For example, a marker may include an ink absorbing body filled with agglomerated ink within a barrel, with the ink absorbing body connected to the marker tip. In addition to directly connecting the ink absorbing body to the marker tip, the ink absorbing body and the marker tip may also be connected via a connecting member.

A marker pen having a marker pen tip and an ink filling mechanism may further have an ink supply mechanism for supplying the ink filled in the ink filling mechanism to the pen head.

The ink supply mechanism is not particularly limited. For example, in addition to the ink supply mechanism of the above-mentioned ballpoint pen, the following can also be mentioned: (4) a mechanism having an ink flow regulating body by a valve mechanism, which supplies ink to the pen tip by opening the valve. The valve mechanism can use a conventional suction type that is opened by pressing the pen tip, and is preferably set to a spring pressure that can be pressed open by the pen pressure.

In the case where the marker is equipped with an ink supply mechanism, in addition to the above-mentioned ink absorbing body, an ink container that can be directly filled with writing ink can also be used as the ink filling mechanism. Alternatively, the barrel itself can be used as the ink filling mechanism and directly filled with writing ink.

The structure of a marker pen for accommodating writing ink includes the following examples: (1) an ink absorbing body comprising a fiber bundle impregnated with writing ink is accommodated in a shaft, and a marker pen tip comprising a fiber processed body or a resin formed body having capillary gaps is connected to the shaft directly or via a connecting member in such a manner that the ink absorbing body and the pen tip are connected; (2) a marker pen having the following mechanism, i.e., a mechanism in which the shaft is directly filled with writing ink, an ink flow regulating body in the form of a comb groove or an ink guide core comprising a fiber bundle as the ink flow regulating body is interposed, and ink is supplied to the pen tip; (3) a marker pen having the following mechanism, i.e., , a mechanism in which the barrel is directly filled with writing ink and the ink is supplied to the pen tip via the above-mentioned pen core; (4) a marker pen having a pen tip and an ink container through a valve mechanism that opens by pressing the pen tip, and the ink container is directly filled with writing ink; (5) a marker pen tip comprising a fiber processed body or a resin formed body with a capillary gap formed on an ink container containing an ink absorbing body comprising a fiber cluster impregnated with writing ink, the ink absorbing body and the pen tip are connected directly or via a connecting member to form a marker pen replacement core, and the marker pen replacement core is accommodated in the barrel, etc.

Furthermore, the aforementioned ballpoint pen or marker can also be manufactured in the form of a detachable ink cartridge. In this case, the writing instrument can be used by replacing the ink cartridge with a new one after the ink in the cartridge has run out. The ink cartridge can be one that is connected to the writing instrument body and also serves as the writing instrument's shaft, or one that is connected to the writing instrument body and then protected by a shaft (rear shaft). Furthermore, in addition to being used as a standalone ink cartridge, the latter can also be one in which the writing instrument body and ink cartridge are connected to each other before use, or one in which the user of the writing instrument connects the ink cartridge inside the shaft and begins use by disconnecting the cartridge from the shaft.

Furthermore, when a ballpoint pen or marker is directly filled with writing ink, it is preferable to incorporate a stirring element, such as stirring beads, into the ink container or cylinder filled with ink to facilitate redispersion of the microcapsule pigment. Examples of the shape of the stirring element include spheres and rods. The material of the stirring element is not particularly limited and includes, for example, metal, ceramics, resin, and glass.

Furthermore, it is preferable to provide a pen cap on a writing instrument such as a ballpoint pen or a marker so as to cover the writing tip (tip end), or to provide a retractable mechanism that allows the writing tip to be extended and retracted from the writing instrument body (shaft). This can prevent the writing tip from drying out and becoming inoperable, or from becoming contaminated or damaged. Any writing instrument equipped with a retractable mechanism can be used as long as the writing tip is housed within a shaft while exposed to the outside air, and the writing tip is protruded from the shaft opening by the operation of the retractable mechanism. For example, a writing instrument equipped with a retractable mechanism (retractable writing instrument) can be manufactured by adopting the following structure: the refill for a ballpoint pen or marker pen is housed within the shaft, and the retractable mechanism is operated to protrude from the shaft opening. Furthermore, when a retractable mechanism is provided in a writing instrument, a composite retractable writing instrument (retractable ballpoint pen or retractable marker) may be provided in which a plurality of refillable ballpoint pen refills or refillable marker refills are accommodated in a shaft, and the writing tip of any refill refill is retracted from the opening of the shaft by the operation of the retractable mechanism.

As an extension and retraction mechanism, for example, there can be exemplified: (1) a side-sliding extension and retraction mechanism in which an operating portion (pen clip) movable in the front-back direction is protruded from the side wall of the rear portion of the shaft and radially outwardly disposed, and the writing tip portion is extended and retracted from the front end opening of the shaft by sliding the operating portion forward; (2) a side-sliding extension and retraction mechanism in which the writing tip portion is extended and retracted from the shaft by pressing the operating portion disposed at the rear end of the shaft forward. (1) a rear end press-type retractable mechanism for extending and retracting the front end opening of the shaft; (2) a side press-type retractable mechanism for extending and retracting the writing tip from the front end opening of the shaft by pressing an operating portion protruding from the outer surface of the side wall of the shaft radially inward; (3) a side press-type retractable mechanism for extending and retracting the writing tip from the front end opening of the shaft by pressing an operating portion protruding from the outer surface of the side wall of the shaft radially inward; (4) a rotary retractable mechanism for extending and retracting the writing tip from the front end opening of the shaft by rotating an operating portion at the rear of the shaft.

Furthermore, the shape of a ballpoint pen or marker is not limited to the above-mentioned structure. In addition to being equipped with nibs of different shapes or nibs that discharge inks of different colors, it can also be a composite writing instrument (two-headed or nib-continuous discharge type, etc.) that is equipped with nibs of different shapes and discharges inks of different colors from each nib.

Using a writing instrument containing the aforementioned writing ink, the handwriting on the writing surface changes color due to friction generated by the finger or by a heating or cooling tool. Examples of heating tools include electrically heated color-changing tools equipped with a resistive heating element such as a PTC (positive temperature coefficient) element, heated color-changing tools filled with a medium such as warm water, heated color-changing tools using steam or laser light, and applications using a hair dryer. Friction members and friction bodies are preferred for their ease of color change. Examples of cooling tools include electrically cooled color-changing tools using a Peltier element, cooled color-changing tools filled with a refrigerant such as cold water or ice chips, and applications using refrigerants, refrigerators, or freezers.

Friction members and friction bodies are preferably elastic materials such as elastomers or plastic foams that are highly elastic and generate moderate friction heat when rubbed. Plastic moldings, stone, wood, metal, and cloth are also possible. Also, a standard eraser, such as those used to erase pencil marks, can be used to rub the marks. However, this produces eraser shavings, so it is preferable to use friction members and friction bodies that produce little eraser shavings. Examples of materials for friction members and friction bodies include silicone resins and SEBS resins (styrene-ethylene-butadiene-styrene block copolymer). Silicone resins tend to adhere to areas that are easily erased by friction, and tend to resist re-sticking when writing repeatedly. Therefore, SEBS resin is more suitable.

The friction member or friction body can be a member of any shape separate from the writing tool, but by being installed in the writing tool, it can be made highly portable. In addition, a writing tool and a friction member or friction body of any shape separate from the writing tool can be combined to obtain a writing tool kit.

In the case of a writing instrument with a pen cap, the location where the friction member or friction body is provided is not particularly limited. For example, the friction member may be formed as the pen cap itself, or as the shaft barrel itself, or as the pen clip itself if provided, or may be provided at the front end (top) of the pen cap or the rear end (the portion not provided with the writing tip) of the shaft barrel. In the case of a telescopic writing instrument, the location where the friction member or friction body is provided is not particularly limited. For example, the friction member may form the shaft barrel itself, or further, in the case of a pen clip, the friction member may form the pen clip itself, or the friction member or friction body may be provided near the opening of the shaft barrel, at the rear end of the shaft barrel (the portion not provided with the writing tip), or at the pressing portion.

Furthermore, the above ink can also be used as a stamp ink. The medium for stamp ink can be water, or, if necessary, a water-soluble organic solvent. When using microencapsulated pigments in stamp ink, glycerin or propylene glycol are preferred water-soluble organic solvents.

The water-soluble organic solvent should be added in an amount of 30-60% by weight, more preferably 30-55% by weight, and even more preferably 40-50% by weight relative to the total ink volume. By maintaining the water-soluble organic solvent ratio within this range, the ink will not dry out or absorb moisture, making it easier to produce a clear seal image. If the water-soluble organic solvent ratio exceeds 60% by weight, its hygroscopicity will increase, causing bleeding or streaking in the seal image, making it difficult to produce a clear seal image. On the other hand, if the ratio is less than 30% by weight, the seal surface will dry out, blurring the seal image, and making it difficult to produce a clear seal image.

Furthermore, organic solvents may be used as the medium. Examples of organic solvents include castor oil fatty acid alkyl esters, solvent-based solvents, alkylene glycol-based solvents, ester-based solvents, hydrocarbon-based solvents, halogenated hydrocarbon-based solvents, alcohol-based solvents, ether-based solvents, ketone-based solvents, propionic acid-based solvents, highly polar solvents, and mixtures thereof.

Furthermore, a thickener can be added to the stamp ink. Among these thickeners, alkali-soluble acrylic emulsions are preferred. When using an alkali-soluble acrylic emulsion as a thickener, the ink's pH is preferably between 6 and 11, more preferably between 7 and 11, and even more preferably between 7 and 10.

Furthermore, by adding a binder resin to stamp ink, the fixation of the stamp image can be improved or the viscosity of the ink can be adjusted. Examples of binder resins include resin emulsions, alkali-soluble resins, and water-soluble resins.

In addition, additives such as wetting agents, resins, resin particles, pH adjusters, rust inhibitors, surfactants, wetting agents, defoaming agents, viscosity adjusters, preservatives, and mold inhibitors may be added as needed.

Reversible thermochromic microencapsulated pigments should be incorporated into stamp inks at a ratio of preferably 10-40% by weight, more preferably 10-35% by weight, and even more preferably 10-30% by weight, relative to the total ink weight. If the microencapsulated pigment ratio exceeds 40% by weight, the dispersion stability of the microencapsulated pigment in the ink may be reduced. On the other hand, if the ratio is less than 10% by weight, the color density may be reduced.

The aforementioned seal ink can be used as ink for ink pads or for seals with materials having continuous air holes. For example, by impregnating an ink pad with ink, an ink pad can be obtained that supplies ink to the surface of a contacting seal. Alternatively, a seal can be obtained by impregnating the ink into the material of a seal with continuous air holes.

The aforementioned stamp can form a stamp image on a variety of surfaces. Furthermore, the stamp image formed by the stamp ink can change color through friction with the finger or application of the aforementioned heating or cooling tools. For a simple method of color change, the aforementioned friction member or friction body is preferably used as the heating tool.

The friction member or friction body can be a member of any shape separate from the seal, but by being installed on the seal, it can be made highly portable. In addition, a seal and a friction member or friction body of any shape separate from the seal can be combined to obtain a seal set.

When applying or printing a reversibly thermochromic liquid composition, the material of the support is not particularly limited; all materials are effective. Examples include paper, synthetic paper, fiber, cloth, synthetic leather, leather, plastic, glass, ceramic, metal, wood, and stone. The shape of the support is not limited to being flat; it may also be concave and convex. By providing a reversible thermochromic layer containing a reversible thermochromic colorant on the support, a reversible thermochromic laminate (reversible thermochromic printed material) can be obtained. When a non-thermochromic coloring layer (non-thermochromic image) is pre-formed on the support, the reversible thermochromic layer can be used to conceal the coloring layer or image in response to temperature changes, thereby providing a variety of changing patterns.

Furthermore, by melt-blending a reversibly thermochromic colorant with a shaping agent and then forming it, a reversibly thermochromic solid molded article for coating can be produced, which can be used as a solid writing medium or solid cosmetic. Examples of solid writing mediums include crayons, pencil refills, automatic pencil refills, and solid gel markers. Examples of solid cosmetics include powders, eyeliners, eyebrow pencils, eyeshadows, and lipsticks.

Examples of solid writing materials include waxes, gelatinizers, and clay minerals. Preferred solid writing materials contain at least one of polyolefin wax, sucrose fatty acid ester, or dextrin fatty acid ester, as they tend to increase writing density.

Furthermore, to ensure excellent mechanical strength and thermochromic properties of the solid writing medium, and to facilitate handling during production, the plasticizer preferably has a mass average molecular weight (Mw) of 2,000 to 50,000, more preferably 10,000 to 30,000. Furthermore, a number average molecular weight (Mn) of 1,000 to 10,000 is particularly preferred. The mass average molecular weight and number average molecular weight are values measured by gel permeation chromatography (GPC) using polystyrene as a standard.

The content of the solidifying agent relative to the total weight of the solid writing medium is preferably within a range of 0.2-70% by weight, more preferably 0.5-40% by weight. By maintaining the solidifying agent content within this range, the shape of the solid writing medium can be easily achieved, and the density of the writing can be increased. If the content of the solidifying agent exceeds 70% by weight, sufficient writing density will be difficult to achieve. On the other hand, if the content is less than 0.2% by weight, the shape of the core material for writing cannot be achieved.

Furthermore, by adding fillers to solid writing materials, the strength of the material can be increased or the writing feel can be adjusted. Among these fillers, talc or calcium carbonate are preferred due to their excellent formability and minimal impairment of thermochromic properties when using microencapsulated pigments.

The filler content is preferably within the range of 10-65% by mass relative to the total weight of the solid writing medium. If the filler content exceeds 65% by mass, the color rendering and writing feel may be reduced. On the other hand, if the filler content is less than 10% by mass, the strength of the solid writing medium may be reduced.

Furthermore, by adding a binder resin to the solid writing medium, its strength can be enhanced. Preferred binder resins include ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, and polyvinyl alcohol. Combining these resins with polyester polyols can improve molding stability. The binder resin is preferably added in an amount of 0.5 to 5% by weight relative to the total weight of the solid writing medium.

Furthermore, by blending a hindered amine compound into a solid writing medium, the residual image left after erasing the writing surface becomes less visible. This ensures rewritability without damaging the surface, improving market value.

In addition, additives such as viscosity regulators, mold inhibitors, preservatives, antibacterial agents, UV inhibitors, antioxidants, lubricants, and fragrances may be added as needed.

The solid writing medium can be used as a writing medium alone, or it can be used as an inner core and provided with an outer shell covering its outer circumference to form a core-sheath structure (double-layer core).

If necessary, additives such as non-thermochromic colorants, mold inhibitors, preservatives, antibacterial agents, UV absorbers, antioxidants, lubricants, and fragrances may also be added to the casing.

The solid writing medium can be written on a variety of writing surfaces. Furthermore, because it uses a reversible thermochromic colorant, the writing on the writing surface changes color through finger friction or application of the aforementioned heating or cooling tools. For a simple method of color change, the aforementioned friction member and friction body are preferred as heating tools.

The friction member or body can be a member of any shape separate from the solid writing medium or the outer casing of a solid writing instrument containing the solid writing medium. However, by attaching the member to the solid writing medium or the outer casing of the solid writing instrument containing the solid writing medium, the writing instrument can be made highly portable. A specific example is a configuration in which the friction member is attached to a pencil or crayon with an outer casing made of wood or paper. Furthermore, a solid writing medium kit can be obtained by combining the solid writing medium with a friction member or body of any shape separate from the solid writing medium.

Furthermore, reversible thermochromic colorants can be melt-blended with thermoplastic resins, thermosetting resins, waxes, and the like to form granules, powders, or pastes, which can then be used as reversible thermochromic molding resin compositions. Using commonly used methods such as injection molding, extrusion molding, blow molding, or casting, these reversible thermochromic molding resin compositions can be molded into 3D shapes, films, sheets, plates, filaments, rods, tubes, and other shapes of any desired design. Furthermore, by melt-blending with thermoplastic resins, carbon powders and powder coatings can be obtained.

Furthermore, by mixing non-thermochromic colorants such as conventional dyes and pigments into the above-mentioned reversible thermochromic liquid composition, coating solid molded body, and molding resin composition, a color change behavior from colored (1) to colored (2) can be exhibited.

Lightfastness can also be enhanced by depositing a layer containing a light stabilizer and/or a transparent metallic gloss pigment on the molded or laminated body, or by providing a topcoat to enhance durability. Light stabilizers include, for example, UV absorbers, antioxidants, singlet oxygen quenchers, superoxide anion quenchers, and ozone quenchers. Transparent metallic gloss pigments include those in which the surface of a core material (natural mica, synthetic mica, glass sheets, aluminum oxide, or transparent films) is coated with a metal oxide such as titanium oxide.

Specific examples of products using a reversible thermochromic composition and microencapsulated pigments or resin particles encapsulating the composition include the following. (1) Toys: Dolls and animal figures, hair for dolls and animal figures, doll houses and furniture, clothing, hats, handbags, shoes and other accessories for dolls, decorative toys, plush toys, drawing toys, picture books for toys, jigsaw puzzles, building blocks, block toys, clay toys, liquid toys, spinning tops, kites, musical instrument toys, cooking toys, gun toys, hunting toys, background toys, simulated vehicles, toys of animals, plants, buildings, food, etc. (2) Clothing: T-shirts, training clothes, overalls, dresses, swimsuits, raincoats, ski suits and other clothing, shoes and bags and other footwear, handkerchiefs, towels, bath towels and other cloth daily necessities, gloves, ties, hats, neck scarves, scarves, etc. (3) Interior decorations Curtains, curtain ropes, tablecloths, cushions, backrests, carpets, blankets, chair covers, chairs, felt cushions, decorative frames, artificial flowers, photo frames, etc. (4) Furniture Bedding, pillows, mattresses and other bedding, lighting fixtures, air conditioners, etc. (5) Decorations Rings, bracelets, headwear, earrings, hairpins, artificial nails, ribbons, scarves, watches, glasses, etc. (6) Stationery Writing tools, stamp tools, erasers, pads, rulers, notepads, tape, etc. (7) Daily necessities Lipstick, eye shadow, powder, eyeliner, eyebrow pencil, nail polish, hair dye, artificial nails, artificial nail paint and other cosmetics, toothbrushes, etc. (8) Kitchen supplies Cups, plates, chopsticks, spoons, forks, pots, frying pans, etc. (9) Others Calendars, signs, cards, recording materials, various printed materials for anti-counterfeiting, picture books, handbags, packaging containers, embroidery thread, sports equipment, fishing gear, coasters, musical instruments, hand warmers, coolers, bags such as wallets, umbrellas, vehicles, buildings, temperature measuring meters, teaching tools, etc. [Examples]

Unless otherwise specified, "parts" and "%" in the examples represent "parts by mass" and "% by mass", respectively.

<Example 101> Preparation of a Reversible Thermochromic Composition Component (a) (2 parts) of 2,6-bis(2',4'-diethoxyphenyl)-4-(4'-dimethylaminophenyl)pyridine (A-1); (b) (3 parts) of 4-isopropoxy-4'-hydroxydiphenylsulfone (I-1); (7 parts) of 1,1-bis(4-hydroxyphenyl)-2-ethylhexane (IIa-1); and (c) (25 parts) of behenyl alcohol (C-1) and 25 parts of stearyl stearate (C-2) were mixed and dissolved under heating to obtain a reversible thermochromic composition that reversibly changes color. The reversible thermochromic composition was added to a mixed solution containing 35 parts of an aromatic isocyanate prepolymer (as the membrane material) and 40 parts of a cosolvent. The mixture was then emulsified and dispersed in an 8% aqueous polyvinyl alcohol solution. After heating and continuous stirring, 2.5 parts of a water-soluble aliphatic modified amine was added and further stirred to prepare a microcapsule dispersion. Microcapsule pigment with an average particle size of 2.0 μm was obtained from this microcapsule dispersion by centrifugal separation.

<Examples 102-107 and Comparative Examples 101-107> Microencapsulated pigments were obtained in the same manner as in Example 101, except that the types and amounts of components (a), (b), and (c) were changed to those listed in Table 1. The color tone of the resulting microencapsulated pigments in the developed state was as shown in Table 1, with the color changing from the developed state to the decolorized state. The values for components (a), (b), and (c) in the table are expressed in parts by mass, and the values for density retention are expressed in %.

[Table 1] Table 1 Embodiment Comparative example Embodiment Comparative example Embodiment Comparative example Embodiment Comparative example Embodiment Comparative example Embodiment Comparative example Embodiment Comparative example 101 101 102 102 103 103 104 104 105 105 106 106 107 107 Composition (a) A-1 2 2 2 2 2 2 2 2 2 2 A-2 6.5 6.5 6.5 6.5 (b) I-1 3 10 3 10 5 10 I-2 5 10 5 10 I-3 5 10 I-4 5 10 IIa-1 7 7 5 5 5 IIc-1 5 5 (c) C-1 25 25 C-2 25 25 C-3 50 50 50 50 50 50 50 50 C-4 50 50 50 50 Hue Yellow Yellow Yellow Yellow Yellow Yellow Yellow Yellow Yellow Yellow black black black black Reviews Density retention 69.2 44.7 68.4 43.6 63.0 49.7 59.3 49.7 57.4 41.9 91.8 68.2 89.1 78.8 Components (a), (b), and (c) in the table are the compounds shown below. A-1 2,6-Bis(2',4'-diethoxyphenyl)-4-(4'-dimethylaminophenyl)pyridine A-2 2-(3-trifluoromethylanilino)-6-di-n-pentylamino fluorescent yellow matrix I-1 4-isopropoxy-4'-hydroxydiphenylsulfone I-2 Bis[4-hydroxy-3-(2-propenyl)phenyl]sulfone I-3 4-benzyloxy-4'-hydroxydiphenylsulfone I-4 4-n-propoxy-4'-hydroxydiphenylsulfone IIa-1 1,1-Bis(4-hydroxyphenyl)-2-ethylhexane IIc-1 4,4'-[1-{4-[1-(4-hydroxyphenyl)-1-methylethyl]phenyl}ethylene]bisphenol C-1 Behenyl alcohol C-2 Stearyl Stearate C-3 4-Benzyloxyphenyl Ethyl Decanoate C-4 Cyclohexyl Methyl 4-Felbinacetate

[Color Change Temperature Measurement] Reversible thermochromic inks were prepared by mixing 40 parts of each microcapsule pigment obtained in Examples 101-107 and Comparative Examples 101-107, 52 parts of ethylene-vinyl acetate copolymer emulsion, 5 parts of a thickener, and 3 parts of a leveling agent. These inks were used to screen-print a full-screen pattern on high-quality paper to obtain samples for color change temperature measurement. Each of these samples was placed in the measurement section of a colorimeter (TC-3600, manufactured by Tokyo Denshoku Co., Ltd.) and heated and cooled at a rate of 2°C/minute. Brightness values were measured as color densities at various temperatures, and color density-temperature curves were generated. From the color density-temperature curve, the complete color development temperature t ₁ , the color development start temperature t ₂ , the color loss start temperature t ₃ , the complete color loss temperature t ₄ , and ΔH (hysteresis width: (temperature between t ₃ and t ₄ ) - (temperature between t ₁ and t ₂ )) were calculated. The results are shown in Table 2 below. The values in the table are expressed in "°C."

[Table 2] Table 2 Embodiment Comparative example Embodiment Comparative example Embodiment Comparative example Embodiment Comparative example Embodiment Comparative example Embodiment Comparative example Embodiment Comparative example 101 101 102 102 103 103 104 104 105 105 106 106 107 107 t ₁ 48 49 -20 -20 -20 -20 -20 -20 -20 -20 -20 -20 -20 -20 t ₂ 54 54 -14 -12 -13 -12 -13 -10 -13 -12 -15 -14 -13 -14 t ₃ 54 53 48 56 44 57 52 57 52 58 40 40 40 50 t ₄ 58 59 62 62 63 62 64 62 64 62 60 60 60 60 ΔH 5.0 4.5 72.0 75.0 70.0 75.5 74.5 74.5 74.5 76.0 67.5 67.0 66.5 72.0

[Lightfastness Evaluation] Reversible thermochromic inks were prepared by mixing 40 parts of each microcapsule pigment from Examples 101-107 and Comparative Examples 101-107, 52 parts of ethylene-vinyl acetate copolymer emulsion, 5 parts of a thickener, and 3 parts of a leveling agent. The inks were used to screen-print full-screen patterns on high-quality paper to obtain test samples. Each test sample was cooled to a temperature below _t1 to achieve a fully colored state. The sample was then placed in the measuring section of a fluorescent spectrodensitometer (manufactured by Konica Minolta Co., Ltd., product name: FD-7) to measure the absolute density of the fully colored state (hereinafter referred to as "initial density"). Next, each density test specimen was exposed to light at a temperature not exceeding t ₃ for 10 hours using a xenon lightfastness tester [Suga Test Instruments, product name: Table Sun XT75] at an irradiance of 170 w/m ^2. After removal from the light-exposed specimens and cooling to a temperature below t ₁ , when the specimens were fully colored, they were placed in the measuring section of the aforementioned fluorescent spectrodensitometer and the absolute density of the fully colored specimens after light exposure (hereinafter referred to as "density after light exposure") was measured. The density retention ratio [(density after light exposure) / (initial density) × 100] was calculated from the initial density and the density after light exposure. A higher density retention ratio indicates better lightfastness. The results are shown in Table 1.

<Examples 201-205, 301, 302, and Comparative Example 201> A microencapsulated pigment was obtained in the same manner as in Example 101, except that the types and amounts of components (a), (b), and (c) were changed to those listed in Table 3. The color tone of the resulting composition or microencapsulated pigment in the developed state was as shown in Table 3, with the color changing from the developed state to the decolorized state. The values for components (a), (b), and (c) in the table are expressed in parts by mass, and the values for density retention are expressed in %.

[Table 3] Table 3 Embodiment Comparative example Embodiment Comparative example Embodiment Comparative example 101 102 201 202 203 204 301 302 101 102 106 106 205 201 Composition (a) A-1 2 2 2 2 2 2 2 2 2 2 A-2 6.5 6.5 A-3 4 4 (b) I-1 3 3 5 5 5 5 2 1 10 10 5 10 3 8 IIa-1 7 7 7 7 5 IIa-2 5 IIa-3 5 IIa-4 5 IIb-1 5 1 2 IIc-1 5 (c) C-1 25 25 C-2 25 25 C-3 50 50 50 50 50 50 50 50 C-4 50 50 50 50 Hue Yellow Yellow Yellow Yellow Yellow Yellow Yellow Yellow Yellow Yellow black black black black Reviews Color density 1.59 1.58 1.76 1.66 1.72 1.64 1.69 1.77 1.50 1.49 1.48 1.07 1.36 0.95 Achromatic density 0.09 0.11 0.74 0.19 0.33 0.20 0.17 0.18 0.30 0.31 0.09 0.11 0.03 0.05 Density retention 69.2 68.4 56.3 67.5 54.1 71.3 79.3 80.2 44.7 43.6 91.8 68.2 94.9 93.7 Components (a), (b), and (c) in the table are the compounds shown below. A-1 2,6-Bis(2',4'-diethoxyphenyl)-4-(4'-dimethylaminophenyl)pyridineA-2 2-(3-Trifluoromethylanilino)-6-di-n-pentylamino fluorescent yellow matrixA-3 2-anilino-3-methyl-6-(N-ethyl-N-p-toluinyl) fluorescent yellow matrixI-1 4-isopropoxy-4'-hydroxydiphenylsulfoneIIa-1 1,1-Bis(4-hydroxyphenyl)-2-ethylhexaneIIa-2 2,2-Bis(4-hydroxyphenyl)propaneIIa-3 1,1-Bis(4-hydroxyphenyl)-2-methylpropaneIIa-4 2,2-Bis(4-hydroxyphenyl)hexafluoropropaneIIb-1 2,4-Dihydroxy-4'-tert-butylbenzophenone IIc-1 4,4'-[1-{4-[1-(4-hydroxyphenyl)-1-methylethyl]phenyl}ethylene]bisphenol C-1 Behenyl alcohol C-2 Stearyl stearate C-3 4-Benzyloxyphenylethyl decanoate C-4 Cyclohexylmethyl 4-felbinacetate

Color Change Temperature Measurement: 40 parts of each microcapsule pigment obtained in Examples 201-205, 301, 302, and Comparative Example 201, 52 parts of ethylene-vinyl acetate copolymer resin emulsion, 5 parts of a thickener, and 3 parts of a leveling agent were mixed to prepare a reversible thermochromic ink. This ink was used to screen-print a full-screen pattern on high-quality paper to obtain a sample for color change temperature measurement. For each sample for color change temperature measurement, t ₁ , t ₂ , t ₃ , t ₄ , and ΔH were determined using the same measurement method as above. The results are shown in Table 4 below. The values in the table are expressed in degrees Celsius.

[Table 4] Table 4 Embodiment Comparative example 201 202 203 204 205 301 302 201 t _l -20 -20 -20 -20 -20 -20 -20 -20 t ₂ -12 -14 -14 -14 -14 -12 -13 -8 t ₃ 57 53 55 55 40 56 56 36 t ₄ 62 60 61 60 60 63 62 61 ΔH 75.5 73.5 75.0 74.5 67.0 75.5 75.5 62.5

Density Measurement: Reversible thermochromic inks were prepared by mixing 40 parts of each microcapsule pigment obtained in Examples 101, 102, 106, 201-205, 301, and 302, and Comparative Examples 101, 102, 106, and 201, 52 parts of ethylene-vinyl acetate copolymer emulsion, 5 parts of a thickener, and 3 parts of a leveling agent. The inks were used to screen-print a full-screen pattern on high-quality paper to obtain samples for density measurement. Density measurement samples of Examples 101, 102, 106, 201 to 205, 301, and 302, and Comparative Examples 101, 102, 106, and 201, which had been cooled to a temperature below _t1 and were in a completely colored state, were placed in the measuring section of a fluorescent spectrodensitometer [manufactured by Konica Minolta Co., Ltd., product name: FD-7 model] to measure the absolute density of the colored state (hereinafter referred to as "colored density"). Furthermore, the density measurement samples of Examples 101, 102, 106, 201-205, 301, and 302, and Comparative Examples 101, 102, 106, and 201, which had been heated to a temperature of _t4 or higher and completely decolorized, were placed in the measurement section of the aforementioned fluorescent spectrodensitometer, and the absolute density of the decolorized state (hereinafter referred to as "decolorization density") was measured. The results are shown in Table 3.

[Lightfastness Evaluation] A reversible thermochromic ink was prepared by mixing 40 parts of each of the microencapsulated pigments 201-205, 301, 302, and Comparative Example 201, 52 parts of ethylene-vinyl acetate copolymer resin emulsion, 5 parts of a thickener, and 3 parts of a leveling agent. The ink was used to screen-print a full-screen pattern on high-quality paper to obtain test samples. The density retention of each of these test samples was determined using the same measurement method as above. The results are shown in Table 3.

Application Example 1 Preparation of a Reversible Thermochromic Writing Instrument (Reversible Thermochromic Marker) 23 parts of the microcapsule pigment from Example 102 (pre-cooled to below -20°C to develop a yellow color) were mixed with 0.4 parts of a polymeric flocculant (hydroxyethyl cellulose) [Dow Chemical Japan Co., Ltd., product name: CELLOSIZE WP-09], 0.4 parts of an acrylic polymer dispersant [Japan Lubrizol Co., Ltd., product name: Solsperse 43000], and a preservative (sodium 2-pyridinethiol 1-oxide) [Lonza Co., Ltd., product name: Sodium A reversible thermochromic liquid composition for writing ink was prepared in an aqueous vehicle containing 0.2 parts of [Omadine], 0.2 parts of a preservative (3-iodo-2-propynyl N-butylcarbamate) [Lonza Co., Ltd., product name: Glycacil 2000], 30 parts of glycerin, 0.01 parts of a defoaming agent, 0.03 parts of a pH adjuster (10% diluted phosphoric acid solution), and 45.76 parts of water. The writing ink was impregnated into an ink reservoir composed of polyester fiber bundles coated with a synthetic resin film. The ink was then housed in a polypropylene resin barrel. A polyester fiber resin-finished pen body (edge-shaped) was attached to the front end of the barrel via a resin holder, and a pen cap was attached to produce a marker. Furthermore, a SEBS resin is attached to the rear end of the shaft as a friction member. When the aforementioned marker is used to write on paper, creating yellow text (handwriting), the handwriting appears yellow at room temperature (25°C). However, when the friction member is used to rub the text, the text fades and becomes colorless. This state is maintained unless the paper is cooled below -20°C. Furthermore, if the paper is placed in a freezer and cooled below -20°C, the text changes color again, returning to yellow. This color change is reproducible.

Application Example 2: Preparation of a Reversible Thermochromic Solid Writing Instrument: 40 parts of the microcapsule pigment of Example 103, 35 parts of filler (talc), 10 parts of a shaping agent (side-chain crystalline polyolefin) [manufactured by HOKOKU CORPORATION, product name: HS Crysta 4100], 10 parts of a shaping agent (polyolefin wax) [manufactured by Sanyo Chemical Industries, Ltd., product name: Sanwax 131-P (softening point 110°C, needle penetration 3.5)], 2 parts of a styrene-acrylic acid copolymer, 2 parts of polyvinyl alcohol, and 1 part of a hindered amine light stabilizer were mixed in a kneader to prepare a mixture for the inner core. Next, 69 parts of filler (talc), 10 parts of sucrose fatty acid ester, 10 parts of shaping agent (polyolefin wax), and 10 parts of ethylene-vinyl acetate copolymer were kneaded by a kneader to prepare a shell mixture. The shell mixture was wound around the outer surface of the core mixture so as to form the core, and the shell mixture was compressed by a press to form an outer diameter of 3 mm, 60 mm long (core is 2 mm, with the outer shell covering 0.5 mm thick), thereby producing a core-sheath solid writing material. Furthermore, the above dimensions are set values. After compression molding, the material is cooled to -20°C and then returned to room temperature to produce the solid writing material. The solid writing material is then housed and formed within a circular outer shaft (wooden shaft) to produce a pencil. Furthermore, a cylindrical friction body composed of SEBS resin is fixed to the rear end of the pencil via a metal connecting member, producing a solid writing tool with a friction body (a pencil with a friction body). When yellow text (handwriting) is written on paper using the aforementioned solid writing instrument, it appears yellow at room temperature (25°C). However, rubbing the text with a friction member causes it to fade and become colorless. This state is maintained as long as the paper is not cooled below -20°C. Furthermore, if the paper is placed in a freezer and cooled below -20°C, the text changes color again, returning to yellow. This color change is reproducible.

Application Example 3 Preparation of a Reversible Thermochromic Stamp Mix 20 parts of the microcapsule pigment from Example 104 (pre-cooled to below -20°C to develop a yellow color), 50 parts of glycerin, 1.5 parts of an alkali-soluble acrylic emulsion [Primal DR73, manufactured by Rohm and Haas Japan Co., Ltd.], 0.9 parts of triethanolamine, 10 parts of a 50% aqueous solution of polyvinyl pyrrolidone, 0.2 parts of a silicone defoamer, 0.5 parts of a pen leveler, 0.2 parts of a preservative, and 16.7 parts of water to prepare a reversible thermochromic liquid composition for use as a stamp ink. Impregnate a stamping material with continuous pores with the ink, adhere the ink to the stamp substrate with the printed surface of the material exposed, and attach a cap to produce a stamp. Furthermore, a SEBS resin, acting as a friction member, is attached to the rear end of the stamp substrate. When this stamp is repeatedly pressed against the surface to be stamped (paper), the ink flows smoothly from the stamping surface to the surface to be stamped, preventing the stamp image from bleeding through and creating a continuous, clear stamp image. The stamp image appears yellow at room temperature (25°C). However, rubbing it with the friction member causes it to fade to colorless, a state that is maintained as long as it is not cooled below -20°C. Furthermore, if the paper is placed in a freezer and cooled below -20°C, the stamp image changes color again, returning to yellow, and this color change is reproducible.

Application Example 4 Preparation of Reversibly Thermochromic Printed Articles (Reversibly Thermochromic T-shirts) 30 parts of the microcapsule pigment from Example 105 (pre-cooled to below -20°C to develop a yellow color) were uniformly mixed with an aqueous vehicle containing 60 parts of an acrylic emulsion (45% solids), 0.2 parts of a defoaming agent, 1 part of a viscosity modifier, and 8.8 parts of water to prepare a reversibly thermochromic liquid composition for use as a printing ink. This printing ink was used to print multiple star-shaped patterns on a white cotton T-shirt as a support using a 100-mesh screen. The resulting composition was then dried and cured to form a reversibly thermochromic layer, producing a reversibly thermochromic printed article (reversibly thermochromic T-shirt). At room temperature (25°C), multiple yellow star patterns can be seen on the T-shirt's surface. This pattern remains unchanged at body temperature or ambient temperature. However, when heated to above 64°C, the portion with the printed star pattern becomes colorless, making the yellow star pattern invisible. Furthermore, when cooled to below -20°C, the yellow star pattern becomes visible again. This change can be repeated. Also, by heating the T-shirt with an iron, for example, partially decolorizing the star pattern, creating a pattern that decolorizes only a desired star pattern, allowing the T-shirt's pattern to be changed at will. Furthermore, this color change can be maintained at room temperature (25°C). After the entire T-shirt is heated to above 64°C to completely decolorize the star pattern, it can be cooled to below -20°C to recolor the star pattern.

Application Example 5 Preparation of Reversible Thermochromic Prints 30 parts of the microcapsule pigment from Example 106 (preliminarily cooled to below -20°C to develop a black color), 5 parts of a red dye, and 65 parts of a linseed oil-based offset ink medium were mixed to prepare a reversible thermochromic liquid composition for offset printing. The offset printing ink was applied to both the front and back sides of high-quality paper as the printing medium. The ink was dried and hardened to form a date (thermochromic image). Furthermore, the thermochromic images on the front and back sides were formed so that they did not overlap. Subsequently, non-color-shifting black offset printing ink was applied to the paper and dried and hardened to form a grid line (non-color-shifting image), thereby producing a reversible thermochromic print. The reversible thermochromic printed material initially takes the form of a notepad with a black date. However, by rubbing the thermochromic image anywhere on the surface with a friction member, frictional heat is generated, which causes the material to change color to red. This color change is maintained at room temperature (25°C), making it useful for scheduling weekends. Furthermore, the date on the back of the color-changing area does not change color due to heat conduction when the thermochromic image on the front changes color, allowing for accurate scheduling.

Application Example 6 Preparation of Reversible Thermochromic Recording Material (Information Display Card) 40 parts of the microcapsule pigment from Example 107 (pre-cooled to below -20°C to develop a black color) were uniformly mixed with an aqueous medium containing 50 parts of a urethane resin emulsion, 3 parts of a leveling agent, and 1 part of a thickener to prepare a reversible thermochromic liquid composition for printing ink. A transparent thickening coating layer composed of a urethane resin and an isocyanate-based hardener was applied to the surface of a transparent polyester film (25 μm thick) with an adhesive layer provided on the back side as a support. The above-mentioned printing ink was screen-printed on top of the film and dried to harden, thereby forming a reversible thermochromic layer. A transparent protective layer composed of epoxy acrylate oligomer, polyester acrylate oligomer, and acrylate monomer is then applied on top. This layer is then irradiated with ultraviolet light to polymerize, creating a reversible thermochromic recording material. This recording material is then laminated to a white polyester film (188 μm thick) as a substrate, allowing it to be used as an information display card. The reversible thermochromic recording material is temporarily cooled to below -20°C to allow the reversible thermochromic layer to completely transform to black. After this, text information is printed using a thermal printer equipped with a thermal head. The recording material clearly displays white text (hollow text) against a black background. As long as the temperature remains above -20°C and below 60°C, the white text is visible. Furthermore, if the recording material is cooled to below -20°C, the reversible thermochromic layer will completely turn black, making the white hollow text indiscernible. A thermal printer can be used to re-print the white hollow text on the reversible thermochromic layer from this state, allowing the recording material to be reused multiple times.

Application Example 7 Production of Dolls with Hair Using Reversibly Thermochromic Composite Fibers 5 parts of the microcapsule pigment from Example 201, 1 part of a dispersant, 94 parts of nylon 12 (melting point 180°C), and 0.1 part of a conventional blue pigment were melt-mixed at 200°C using an extruder to prepare a reversibly thermochromic molding resin composition in the form of particles for the core. The aforementioned pellets were fed to an extruder for core molding, while natural nylon 12 pellets were fed to an extruder for sheath molding. Using a composite fiber spinning apparatus, the fibers were spun from an 18-hole nozzle at 200°C, with a core:sheath volume ratio of 6:4. This produced 18 reversibly thermochromic composite fibers consisting of single yarns with an outer diameter of 90 μm. When the reversibly thermochromic composite fibers were temporarily cooled to below -20°C to allow the microencapsulated pigment to fully develop, they exhibited a green color, a mixture of the yellow color created by the microencapsulated pigment and the blue color created by the conventional pigment. By conventionally attaching reversibly thermochromic composite fibers to the doll's head, a toy doll with hair made with reversibly thermochromic composite fibers is produced. The doll's hair does not change color due to body temperature or ambient temperature. However, when heated to 62°C or higher, it changes from green to blue. Cooling to -20°C or lower returns it to green again. This change is reproducible. Also, by heating the hair with a hairdryer, for example, partially decolorizing the hair, creating a pattern where only a specific area is decolorized, the hair color can be changed at will. Furthermore, this color change can be maintained at room temperature (25°C). After the entire hair is heated to 62°C or higher to decolorize, it can be cooled to -20°C or lower to recolor green.

Application Example 8 Preparation of a Reversible Thermochromic Writing Instrument (Reversible Thermochromic Ballpoint Pen) Mix 25 parts of the microcapsule pigment from Example 202 (pre-cooled to below -20°C to develop a yellow color), 0.3 parts of a shear-thinning agent (Sansen Gum), 10 parts of urea, 10 parts of glycerin, 0.5 parts of a non-ionic penetrant [San Nopco Co., Ltd., product name: Nopco SW-WET-366], 0.1 parts of a modified polysilicone defoamer [San Nopco Co., Ltd., product name: Nopco 8034], and 0.1 parts of a phosphate surfactant [Daichi Kogyo Seiyaku Co., Ltd., product name: Plysurf] A reversible thermochromic liquid composition for writing ink was prepared by combining 0.5 parts of AL, 0.5 parts of a pH adjuster (triethanolamine), 0.2 parts of a mold inhibitor (Lonza Co., Ltd., product name: Proxel XL-2), and 52.9 parts of water. The writing ink was suctioned into an ink reservoir made of polypropylene tubing. The ink was then connected to a ballpoint pen tip holding a 0.5 mm diameter superhard steel ball via a resin holder. A viscoelastic ink backflow preventer (liquid plug) composed primarily of polybutylene was then added to the rear end of the ink reservoir to create a refill. The refill was then assembled into a barrel to produce a retractable ballpoint pen. The aforementioned ballpoint pen has the following structure: the pen tip, located in the refill, is housed within the barrel while exposed to the outside atmosphere. A clip-shaped retractable mechanism (sliding mechanism) located on the rear sidewall of the barrel is actuated to cause the pen tip to protrude from the front opening of the barrel. Furthermore, a SEBS resin serving as a friction member is attached to the rear end of the barrel. When writing on paper using the aforementioned ballpoint pen, yellow text (handwriting) appears yellow at room temperature (25°C). However, rubbing the text with the friction member causes the text to fade and become colorless. This state is maintained as long as the temperature is not cooled below -20°C. Furthermore, if the paper is placed in a freezer and cooled to below -20°C, the displayed text will change color again to yellow, and this color change can be repeated.

Application Example 9 Preparation of a Reversible Thermochromic Plug 2.5 parts of the microcapsule pigment from Example 203 (pre-cooled to below -20°C to develop a yellow color) and 1.5 parts of a standard blue pigment were mixed in an oil-based vehicle containing 12.5 parts of a vinyl chloride-vinyl acetate copolymer, 38.3 parts of xylene, 45 parts of butyl acetate, and 0.2 parts of a viscosity modifier to prepare a reversible thermochromic liquid composition for spray coating. This coating was spray-coated onto a white plug (compliant with household electrical standards) as a support. The coating was dried to form a reversible thermochromic layer, producing a reversible thermochromic plug. The reversible thermochromic plug appears green at room temperature (25°C) and turns blue at temperatures above 59°C. This blue color change is maintained until the temperature drops below -20°C. This allows visual confirmation of the plug's temperature history, including instances where it has overheated to temperatures exceeding 61°C.

Application Example 10 Preparation of a Reversible Thermochromic Writing Instrument (Reversible Thermochromic Ballpoint Pen) Mix 25 parts of the microcapsule pigment from Example 204 (pre-cooled to below -20°C to develop a yellow color), 0.3 parts of a shear-thinning agent (Sansen Gum), 10 parts of urea, 10 parts of glycerin, 0.5 parts of a non-ionic penetrant [San Nopco Co., Ltd., product name: Nopco SW-WET-366], 0.1 parts of a modified polysilicone defoamer [San Nopco Co., Ltd., product name: Nopco 8034], and 0.1 parts of a phosphate surfactant [Daichi Kogyo Seiyaku Co., Ltd., product name: Plysurf] A reversible thermochromic liquid composition for writing ink was prepared by combining 0.5 parts of ethanolamine, 0.5 parts of a pH adjuster (triethanolamine), 0.2 parts of a mildew inhibitor (Lonza Co., Ltd., product name: Proxel XL-2), and 52.9 parts of water. The writing ink was then suctioned into an ink reservoir made of a polypropylene tube. The ink was then attached to the tip of a ballpoint pen, which held a 0.5 mm diameter stainless steel ball, via a resin holder. Next, a viscoelastic ink backflow preventer (liquid plug) composed primarily of polybutene is filled from the rear end of the ink reservoir tube. The tail plug is then fitted into the rear end of the tube. The front and rear shafts are then installed, and the cap is attached. The pen is then degassed by centrifugal separation to create a ballpoint pen. Furthermore, SEBS resin is attached to the rear end of the rear shaft as a friction member. When writing with this ballpoint pen on paper, yellow text (handwriting) appears yellow at room temperature (25°C). However, rubbing the text with the friction member causes the text to fade and become colorless. This state is maintained as long as the pen is not cooled to below -20°C. Furthermore, if the paper is placed in a freezer and cooled to below -20°C, the displayed text will change color again to yellow, and this color change can be repeated.

Application Example 11 Preparation of a Reversible Thermochromic Writing Instrument (Reversible Thermochromic Marker) 20 parts of the microcapsule pigment from Example 205 (pre-cooled to below -20°C to develop a black color) were mixed with 0.4 parts of a polymeric coagulant (hydroxyethyl cellulose) [Dow Chemical Japan Co., Ltd., product name: CELLOSIZE EP-09], 0.4 parts of an acrylic polymer dispersant [Japan Lubrizol Co., Ltd., product name: Solsperse 43000], and a preservative (sodium 2-pyridinethiol 1-oxide) [Lonza Co., Ltd., product name: Sodium A reversible thermochromic liquid composition for writing ink was prepared in an aqueous medium containing 0.2 parts of oxynitrite, 0.2 parts of a preservative (3-iodo-2-propynyl N-butylcarbamate) [Lonza Co., Ltd., product name: Glycacil 2000], 18 parts of glycerin, 0.2 parts of a defoaming agent, 1 part of a pH adjuster (10% diluted phosphoric acid solution), 8 parts of a specific gravity adjuster (sodium polytungstate) (SOMETU, product name: SPT), and 46.6 parts of water. The writing ink is impregnated into an ink reservoir made of polyester fiber bundles coated with a synthetic resin film. This ink is then housed in a polypropylene resin barrel. A resin-processed pen body (bullet-shaped) composed of an extruded polyacetal resin body with multiple axially extending ink outlets is attached to the barrel's front end via a holder. A pen cap is then attached to create a marker. A SEBS resin friction member is attached to the top of the cap. When writing with this marker on paper, black text (writing) appears black at room temperature (25°C). However, rubbing the text with the friction member causes it to fade and become colorless. This color remains unchanged unless cooled to -20°C or below. Furthermore, if the paper is placed in a freezer and cooled to below -20°C, the displayed text will change color again to black, and this color change can be repeated.

Application Example 12 Preparation of a Reversible Thermochromic Writing Instrument (Reversible Thermochromic Marker) 23 parts of the microcapsule pigment from Example 302 (pre-cooled to below -20°C to develop a yellow color) were mixed with 0.4 parts of a polymeric coagulant (hydroxyethyl cellulose) [Dow Chemical Japan Co., Ltd., product name: CELLOSIZE WP-09], 0.4 parts of an acrylic polymer dispersant [Japan Lubrizol Co., Ltd., product name: Solsperse 43000], and a preservative (sodium 2-pyridinethiol 1-oxide) [Lonza Co., Ltd., product name: Sodium A reversible thermochromic liquid composition for writing ink was prepared in an aqueous medium containing 0.2 parts of oxydimidine, 0.2 parts of a preservative (3-iodo-2-propynyl N-butylcarbamate) [Lonza Co., Ltd., product name: Glycacil 2000], 30 parts of glycerin, 0.01 parts of a defoaming agent, 0.03 parts of a pH adjuster (10% diluted phosphoric acid solution), and 45.76 parts of water. The writing ink is impregnated into an ink reservoir made of polyester fiber bundles coated with a synthetic resin film. This ink is then housed in a polypropylene resin barrel. A polyester fiber resin body (bullet-shaped) is attached to the barrel's tip via a resin holder, and a cap is attached to create a marker. Furthermore, a SEBS resin is attached to the top of the cap as a friction member. When using this marker to write on paper, yellow text (handwriting) appears yellow at room temperature (25°C). However, rubbing the text with the friction member causes the text to fade and become colorless. This color remains unchanged unless cooled to -20°C or below. Furthermore, if the paper is placed in a freezer and cooled to below -20°C, the displayed text will change color again to yellow, and this color change can be repeated.

_t1 : Complete color development temperature _t2 : Color development start temperature _t3 : Color loss start temperature _t4 : Complete color loss temperature _T1 : Complete _{color loss temperature T2: Color loss start temperature T3: Color development start temperature T4 : Complete} color development temperature ΔH: Hysteresis width

Figure 1 is a graph illustrating the hysteresis characteristics of the color density-temperature curve of a reversible thermochromic composition that undergoes thermal decolorization. Figure 2 is a graph illustrating the hysteresis characteristics of the color density-temperature curve of a reversible thermochromic composition that undergoes thermal decolorization and has color memory. Figure 3 is a graph illustrating the hysteresis characteristics of the color density-temperature curve of a reversible thermochromic composition that undergoes thermal color development.

Claims (17)

A reversible thermochromic composition comprising: (a) an electron-donating color-developing organic compound; (b) a combination of a compound represented by formula (I) and a compound selected from the group consisting of compounds represented by formulas (IIa) to (IIc) as an electron-accepting compound; and (c) a reaction medium that causes the electron donation and acceptance reaction between component (a) and component (b) to reversibly occur within a specific temperature range; [Chemical 1] (In the formula, R ¹¹ is a linear or branched alkyl group with 1 to 3 carbon atoms, n11 is 1, n12 and n13 are 0, and the hydroxyl group is located at the 4-position of the benzene ring) [Chemistry 2] (In the formula, one of ^Ra1 and ^Ra2 is a branched alkyl group with 5 to 9 carbon atoms, the other is a hydrogen atom or a methyl group, Na3 and Na4 are 0, and the hydroxyl group is located at the 4-position of the benzene ring) [Chemistry 3] (In the formula, ^Rb1 is a linear or branched alkyl group with 3 to 6 carbon atoms, ^Rb2 is a hydroxyl group, nb1 is 1, nb2 is 1, and the hydroxyl group is located at the 2nd and 4th positions of a benzene ring) [Chemistry 4] (wherein, R ^c1 is a hydrogen atom, or a linear or branched alkyl group having 1 to 6 carbon atoms, L is a single bond, a linear or branched alkylene group having 1 to 3 carbon atoms, an aryl-substituted alkylene group having 7 to 9 carbon atoms, or a group represented by formula (i), R ^c2 , R ^c3 , and R ^c4 are each independently a linear or branched alkyl group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, a cyclic alkyl group having 3 to 7 carbon atoms, a linear or branched alkoxy group having 1 to 3 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, or a halogen atom, and nc2 , nc3 , and nc4 are each independently 0 to 3, [Chemistry 5] (The benzene ring in the group represented by formula (i) is bonded to the carbon atom indicated in formula (IIc)). The composition of claim 1 comprises a combination of a compound represented by formula (I) and a compound represented by formula (IIa) as component (b). The composition of claim 1 comprises a combination of a compound represented by formula (I) and a compound represented by formula (IIb) as component (b), and in formula (IIb), R ^b1 is isobutyl, sec-butyl, or tert-butyl. The composition of any one of claims 1 to 3, wherein in formula (I), R ¹¹ is isopropyl. The composition of claim 2 further comprising a compound represented by formula (IIb) as component (b). The composition of claim 5, wherein in formula (IIb), R ^b1 is isobutyl, sec-butyl or tert-butyl. The composition of claim 1 or 2, wherein the content of the compound represented by formula (IIa) is 30-90 mass % based on the total mass of component (b). The composition of claim 5 or 6, wherein the content of the compound represented by formula (IIb) is 5-25 mass % based on the total mass of component (b). A reversible thermochromic microcapsule pigment comprising the composition of any one of claims 1 to 8. A reversible thermochromic liquid composition comprises the reversible thermochromic microcapsule pigment of claim 9 and a medium. The reversible thermochromic liquid composition of claim 10 is selected from the group consisting of printing ink, writing ink, painting ink, stamp ink, inkjet ink, paint, UV-curable ink, drawing tools, cosmetics, and fiber coloring liquid. A solid writing material or solid cosmetic comprising the reversible thermochromic microcapsule pigment of claim 9 and a formulator. A reversible thermochromic molding resin composition comprises the reversible thermochromic microcapsule pigment of claim 9 and a molding resin. A reversible thermochromic molded article is formed by molding the reversible thermochromic moldable resin composition of claim 13. A reversible thermochromic laminate comprises a support and a reversible thermochromic layer containing the reversible thermochromic microcapsule pigment of claim 9. A writing implement containing the reversible thermochromic liquid composition of claim 10. The writing instrument of claim 16 is provided with a friction component, and the friction component changes the color of the handwriting formed by the writing instrument by frictional heat.