Thermochromic learning tool set

Abstract

This invention provides a thermochromic learning tool set that allows users to record the process of arriving at the correct answer to a learning problem, as well as the resulting answer, and to erase the written content, while also allowing for repeated exposure and concealment of pre-set correct answers on the learning tool. [Solution] A learning tool set comprising a writing instrument containing a thermochromic writing instrument ink composition which contains a heat-decolorizing reversible thermochromic pigment, which changes from a colored state to a colorless state upon heating, and which retains the colorless state at room temperature, and a learning sheet 13 on which a problem display section 15 and an answer display section 16 corresponding to the problem display section are provided on the surface of the sheet 14, wherein the answer display section contains a heat-developing reversible thermochromic pigment, which changes from a colorless state to a colored state upon heating, and from a colored state to a colorless state upon cooling.

Description

Technical Field

[0001] The present invention relates to a thermochromic learning tool set. More specifically, it relates to a thermochromic learning tool set comprising a writing instrument and a learning tool on which questions and answers to the questions are described.

Background Art

[0002] Conventionally, there has been disclosed a learning tool in which an answer portion of a learning tool on which questions and answers are displayed is covered with a reversible thermochromic material that changes color from colored to colorless due to a temperature change (see, for example, Patent Document 1 or 2). In the learning tool, the reversible thermochromic material can visualize an invisible answer in a colored state by a simple means such as touching, simplifies the structure of the learning tool, and enables quick confirmation of the correct answer. However, since the learning tool only visually recognizes the correct answer by a simple means such as touching without going through the process of deriving the correct answer or filling in the derived answer, the learning effect is poor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention aims to solve the problems of this type of learning tool in which the correct answer appears, that is, it is possible to go through the process of deriving the correct answer to the question and fill in the derived answer, the filled-in content can be decolorized, and a thermochromic learning tool set rich in learning effect that can repeatedly hide and reveal the correct answer provided in advance in the learning tool is to be provided. [Means for solving the problem]

[0005] The present invention provides a learning tool set comprising a writing instrument containing a thermochromic writing instrument ink composition which contains a heat-decolorizing reversible thermochromic pigment, which changes from a colored state to a colorless state upon heating, and which retains the colorless state at room temperature, and a learning sheet which has a problem display section and an answer display section corresponding to the problem display section on its surface, wherein the answer display section contains a heat-developing reversible thermochromic pigment, which changes from a colorless state to a colored state upon heating, and from a colored state to a colorless state upon cooling. Furthermore, the heat-decolorizing type reversible thermochromic pigment and the heat-developing type reversible thermochromic pigment are microcapsule pigments that exhibit hysteresis characteristics with respect to a color density-temperature curve and exhibit tautomorphism between a colored state and a colorless state, wherein the heat-decolorizing type reversible thermochromic pigment, in the process of the temperature rising from the colored state, begins to decolorize when it reaches temperature t3 and becomes completely colorless in the temperature range of temperature t4 or higher, and in the process of the temperature falling from the colorless state, begins to color when it reaches temperature t2 and becomes colorless below temperature t1 or lower. The requirements include: becoming fully colored in a certain temperature range, exhibiting hysteresis characteristics in which a colored state and a colorless state are selectively maintained in a temperature range between temperatures t2 and t3, with temperature t1 being in the range of -50 to 5°C and temperature t4 being in the range of 40 to 95°C; the heat-developing reversible thermochromic pigment, in the process of rising from a colorless state, begins to color when it reaches temperature T3 and becomes fully colored at temperatures above temperature T4, in the process of falling from a colored state, begins to decolorize when it reaches temperature T2 and becomes completely decolorized when it reaches temperature T1, with temperature T4 being in the range of 40 to 95°C and temperature T1 being above 20°C; being equipped with a friction body; and being equipped with a friction member in a writing instrument. [Effects of the Invention]

[0006] The present invention provides a highly practical thermochromic learning tool set that allows users to record the process of arriving at the correct answer to a learning tool problem, as well as the resulting answer, and to erase the recorded content, while also allowing for repeated exposure and concealment of pre-set correct answers on the learning tool. [Brief explanation of the drawing]

[0007] [Figure 1] This graph illustrates the hysteresis characteristics in the color density-temperature curve of a reversible thermochromic composition that has color memory properties and heat-decolorizing properties. [Figure 2] This graph illustrates the hysteresis characteristics in the color density-temperature curve of a heat-activated, reversible thermochromic composition. [Figure 3] This is a longitudinal cross-sectional diagram illustrating one embodiment of the writing instrument of the present invention. [Figure 4] This is a longitudinal cross-sectional diagram illustrating another embodiment of the writing instrument of the present invention. [Figure 5] This is a longitudinal cross-sectional diagram illustrating another embodiment of the writing instrument of the present invention. [Figure 6] This is a top view showing one embodiment of the learning sheet of the present invention. [Figure 7] Figure 6 is a top view showing the learning sheet with writing done using a writing instrument. [Figure 8] Figure 7 is a top view showing the state in which the answer display section of the learning sheet is revealed. [Modes for carrying out the invention]

[0008] This invention relates to a writing instrument containing a thermochromic ink composition that includes a heat-decolorizing reversible thermochromic pigment, which changes from a colored state to a colorless state upon heating, and maintains the colorless state at room temperature. As the aforementioned heat-decolorizing reversible thermochromic pigment, a heat-decolorizing reversible thermochromic pigment is used that includes a reversible thermochromic composition comprising three components: an electron-donating color-developing organic compound, an electron-accepting compound, and an organic compound medium that reversibly causes the color-developing reaction between the two. (The pigment decolorizes when heated and develops color when cooled.) Examples of the aforementioned reversible thermochromic composition include those 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. 2006-137880, Japanese Patent Publication No. 2008-280523, International Publication No. 2010 / 131684, International Publication No. 2010 / 131684, International Publication No. 2012 / 046837, International Publication No. 2014 / 200053, International Publication No. 2015 / 119161, International Publication No. 2016 / 027664, International Publication No. 2017 / 022471, International Publication No. 2018 / 155583, etc. The described hysteresis width (ΔH) is relatively large, ranging from 25°C to 80°C. That is, the shape of the curve plotting the change in color intensity due to temperature changes follows a significantly different path when the temperature is increased from a temperature below the color change temperature range compared to when it is decreased from a temperature above the color change temperature range. This allows for the application of a heat-decolorizing, reversible thermochromic composition that exhibits color memory in a specific temperature range [the temperature range between t2 and t3 (effectively the two-phase retention temperature range)], either in the colored state at low temperatures below the complete color development temperature (t1) or in the decolorized state at high temperatures above the complete decolorization temperature (t4) (see Figure 1).

[0009] The hysteresis characteristics in the color density-temperature curve of the aforementioned reversible thermochromic composition will be described. In Figure 1, the vertical axis represents color density and the horizontal axis represents temperature. The change in color density due to temperature changes progresses along the arrows. Here, A represents the density at the temperature t4 (hereinafter referred to as the complete decolorization temperature) where complete decolorization is reached, B represents the density at the temperature t3 (hereinafter referred to as the decolorization start temperature) where decolorization begins, C represents the density at the temperature t2 (hereinafter referred to as the color development start temperature) where color development begins, and D represents the density at the temperature t1 (hereinafter referred to as the complete color development temperature) where complete color development is reached. The discoloration temperature range is the temperature range between t1 and t4, and can exhibit either a colored state or a decolorized state. The temperature range between t2 and t3, which is the region with a large difference in color density, is the effective discoloration temperature range. Furthermore, the length of line segment EF is a measure of the contrast of the discoloration, and the length of line segment HG passing through the midpoint of line segment EF is the temperature range indicating the degree of hysteresis (hereinafter referred to as the hysteresis range ΔH). If this ΔH value is small, only one of the two states before and after discoloration can exist in the normal temperature range (normal living temperature range). Also, if the ΔH value is large, it becomes easier to maintain each state before and after discoloration. Here, the complete color development temperature t1 is in the range of -50 to 5°C, preferably -50 to 0°C, more preferably -50 to -5°C, which is a temperature not reached at normal living temperatures, and the complete decolorization temperature t4 is in the range of 40 to 95°C, preferably 45 to 95°C, more preferably 50 to 95°C, which can be obtained by simple methods such as rubbing with a finger or rubbing with a friction object, thereby allowing the discolored state to be maintained in the room temperature range. The room temperature range is defined as the temperature range between 5°C and 25°C.

[0010] The components (a), (b), and (c) contained in the reversible thermochromic composition are described in detail below. The aforementioned component (a), i.e., the electron-donating chromogenic organic compound, is a component that determines the color and is a compound that produces color by donating electrons to component (b), which is a color developer. Examples of the aforementioned electron-donating colorimetric organic compounds include phthalide compounds, fluorane compounds, styrinoquinoline compounds, diazalodamine lactone compounds, pyridine compounds, quinazoline compounds, and bisquinazoline compounds, among which phthalide compounds, fluorane compounds, styrinoquinoline compounds, and diazalodamine lactone compounds are preferred. Examples of the phthalide compounds include diphenylmethanephthalide compounds, phenylindolylphthalide compounds, indolylphthalide compounds, diphenylmethaneazaphthalide compounds, phenylindolylazaphthalide compounds, and their derivatives. Among these, phenylindolylazaphthalide compounds and their derivatives are preferred. Examples of these compounds are given below. 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-Diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)phthalide, 3,3-Bis(1-n-butyl-2-methylindol-3-yl)phthalide, 3,3-Bis(2-ethoxy-4-diethylaminophenyl)-4-azaphthalide, 3-(2-Ethoxy-4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 3-(2-Hexyloxy-4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 3-[2-Ethoxy-4-(N-ethylanilino)phenyl]-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 3-(2-Acetamido-4-diethylaminophenyl)-3-(1-propylindol-3-yl)-4-azaphthalide, 3,6-Bis(diphenylamino)fluoran, 3,6-Dimethoxyfluoran, 3,6-Di-n-butoxyfluoran, 2-Methyl-6-(N-ethyl-N-p-tolylamino)fluoran, 3-Chloro-6-cyclohexylaminofluoran, 2-Methyl-6-cyclohexylaminofluoran, 2-(2-Chloroamino)-6-dibutylaminofluoran, 2-(2-Chloroanilino)-6-di-n-butylaminofluoran, 2-(3-Trifluoromethylanilino)-6-diethylaminofluoran, 2-(3-Trifluoromethylanilino)-6-dipentylaminofluoran, 2-(Dibenzylamino)-6-diethylaminofluoran, 2-(N-Methylanilino)-6-(N-ethyl-N-p-tolylamino)fluoran, 1,3-Dimethyl-6-diethylaminofluoran, 2-Chloro-3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-diethylaminofluorane, 2-anilino-3-methoxy-6-diethylaminofluorane, 2-anilino-3-methyl-6-di-n-butylaminofluorane, 2-anilino-3-methoxy-6-di-n-butylaminofluorane, 2-Xylidino-3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-(N-ethyl-Np-tolylamino)fluorane, 1,2-Benz-6-diethylaminofluorane, 1,2-Benz-6-(N-ethyl-N-isobutylamino)fluorane, 1,2-Benz-6-(N-ethyl-N-isoamylamino)fluorane, 2-(3-methoxy-4-dodecoxystyryl)quinoline, Spiro[5H-(1)benzopyrano(2,3-d)pyrimidine-5,1′(3′H)isobenzofuran]-3′-one,2-(diethylamino)-8-(diethylamino)-4-methyl, Spiro[5H-(1)benzopyrano(2,3-d)pyrimidine-5,1′(3′H)isobenzofuran]-3′-one,2-(di-n-butylamino)-8-(di-n-butylamino)-4-methyl, Spiro[5H-(1)benzopyrano(2,3-d)pyrimidine-5,1′(3′H)isobenzofuran]-3′-one,2-(di-n-butylamino)-8-(diethylamino)-4-methyl, Spiro[5H-(1)benzopyrano(2,3-d)pyrimidine-5,1′(3′H)isobenzofuran]-3′-one,2-(di-n-butylamino)-8-(N-ethyl-Ni-amylamino)-4-methyl, Spiro[5H-(1)benzopyrano(2,3-d)pyrimidine-5,1′(3′H)isobenzofuran]-3′-one,2-(dibutylamino)-8-(dipentylamino)-4-methyl, 4,5,6,7-Tetrachloro-3-[4-(dimethylamino)-2-methoxyphenyl]-3-(1-butyl-2-methyl-1H-indole-3-yl)-1(3H)-isobenzofuranone, 4,5,6,7-Tetrachloro-3-[4-(diethylamino)-2-ethoxyphenyl]-3-(1-ethyl-2-methyl-1H-indole-3-yl)-1(3H)-isobenzofuranone, 4,5,6,7-Tetrachloro-3-[4-(diethylamino)-2-ethoxyphenyl]-3-(1-pentyl-2-methyl-1H-indole-3-yl)-1(3H)-isobenzofuranone, 4,5,6,7-tetrachloro-3-[4-(diethylamino)-2-methylphenyl]-3-(1-ethyl-2-methyl-1H-indole-3-yl)-1(3H)-isobenzofuranone, 3′,6′-bis[phenyl(2-methylphenyl)amino]-spiro[isobenzofuran-1(3H),9′-[9H]xanthene]-3-one, 3′,6′-bis[phenyl(3-methylphenyl)amino]-spiro[isobenzofuran-1(3H),9′-[9H]xanthene]-3-one, 3′,6′-bis[phenyl(3-ethylphenyl)amino]-spiro[isobenzofuran-1(3H),9′-[9H]xanthene]-3-one, 2,6-bis(2′-ethyloxyphenyl)-4-(4′-dimethylaminophenyl)pyridine, 2,6-Bis(2′,4′-diethyloxyphenyl)-4-(4′-dimethylaminophenyl)pyridine, 2-(4′-dimethylaminophenyl)-4-methoxyquinazoline, 4,4′-(ethylenedioxy)-bis[2-(4-diethylaminophenyl)quinazoline] Examples include: In addition to the aforementioned compounds having substituents on the phenyl group forming the xanthene ring, fluoranes may also be compounds exhibiting blue or black coloration, having substituents on the phenyl group forming the xanthene ring and also substituents (for example, alkyl groups such as methyl groups, halogen atoms such as chloro groups) on the phenyl group forming the lactone ring.

[0011] The aforementioned 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). The electron-accepting compounds include compounds selected from the group of compounds having active protons and their derivatives, the group of pseudoacidic compounds (compounds that are not acids but act as acids in the composition to cause component (a) to develop color), and the group of compounds having electron vacancies. Among these, compounds selected from the group of compounds having active protons are preferred. Examples of compounds having active protons and their derivatives include compounds having phenolic hydroxyl groups and their metal salts, carboxylic acids and their metal salts, preferably aromatic carboxylic acids, aliphatic carboxylic acids having 2 to 5 carbon atoms and their metal salts, acidic phosphate esters and their metal salts, as well as azol compounds and their derivatives, 1,2,3-triazoles and their derivatives. Among these, compounds having phenolic hydroxyl groups are preferred because they can exhibit effective thermal color change properties. The aforementioned compounds having phenolic hydroxyl groups broadly include monophenol compounds to polyphenol compounds, and further include bis-type and tris-type phenols, as well as phenol-aldehyde condensation resins. Among the compounds having phenolic hydroxyl groups, those having at least two benzene rings are preferred. These compounds may also have substituents, and examples of substituents include alkyl groups, aryl groups, acyl groups, alkoxycarbonyl groups, carboxyl groups and their esters or amide groups, halogen groups, and the like. Examples of metals included in the metal salt of the compound having the active proton include sodium, potassium, calcium, zinc, zirconium, aluminum, magnesium, nickel, cobalt, tin, copper, iron, vanadium, titanium, lead, and molybdenum.

[0012] Specific examples are given below. Phenol, o-cresol, tert-butylcatechol, nonylphenol, n-octylphenol, n-dodecylphenol, n-stearylphenol, p-chlorophenol, p-bromophenol, o-phenylphenol, n-butyl p-hydroxybenzoate, n-octyl p-hydroxybenzoate, resorcinol, dodecyl gallate, 4,4-dihydroxydiphenylsulfone, bis(4-hydroxyphenyl)sulfide, 1,1-bis(4-hydroxyphenyl)ethane, 1,1-bis(4-hydroxyphenyl)propane, 1 1,1-bis(4-hydroxyphenyl)n-butane, 1,1-bis(4-hydroxyphenyl)n-pentane, 1,1-bis(4-hydroxyphenyl)n-hexane, 1,1-bis(4-hydroxyphenyl)n-heptane, 1,1-bis(4-hydroxyphenyl)n-octane, 1,1-bis(4-hydroxyphenyl)n-nonane, 1,1-bis(4-hydroxyphenyl)n-decane, 1,1-bis(4-hydroxyphenyl)n-dodecane, 1,1-bis(4-hydroxyphenyl)-2-methylpropane, 1,1-bis(4-hydroxyphenyl) Phenyl)-3-methylbutane, 1,1-bis(4-hydroxyphenyl)-3-methylpentane, 1,1-bis(4-hydroxyphenyl)-2,3-dimethylpentane, 1,1-bis(4-hydroxyphenyl)-2-ethylbutane, 1,1-bis(4-hydroxyphenyl)-2-ethylhexane, 1,1-bis(4-hydroxyphenyl)-3,7-dimethyloctane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, 1-phenyl-1,1-bis(4-hydroxyphenyl) 2,2-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyphenyl)n-butane, 2,2-bis(4-hydroxyphenyl)n-pentane, 2,2-bis(4-hydroxyphenyl)n-hexane, 2,2-bis(4-hydroxyphenyl)n-heptane, 2,2-bis(4-hydroxyphenyl)n-octane, 2,2-bis(4-hydroxyphenyl)n-nonane, 2,2-bis(4-hydroxyphenyl)n-decane, 2,2-bis(4-hydroxyphenyl)n-dodecane, 2,Examples include 2-bis(4-hydroxyphenyl)ethylpropionate, 2,2-bis(4-hydroxyphenyl)-4-methylpentane, 2,2-bis(4-hydroxyphenyl)-4-methylhexane, 2,2-bis(4-hydroxyphenyl)hexafluoropropane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 9,9-bis(4-hydroxy-3-methylphenyl)fluorene, 1,1-bis[2-(4-hydroxyphenyl)-2-propyl]benzene, bis(2-hydroxyphenyl)methane, 1,1,1-tris(4-hydroxyphenyl)ethane, and 3,3-bis(3-methyl-4-hydroxyphenyl)butane. The compound having the phenolic hydroxyl group exhibits the most effective thermal color change properties, but compounds selected from aromatic carboxylic acids and aliphatic carboxylic acids having 2 to 5 carbon atoms, carboxylic acid metal salts, acidic phosphate esters and their metal salts, 1,2,3-triazoles and their derivatives may also be used.

[0013] The component (c) of the reaction medium that causes the electron transfer reaction by the components (a) and (b) described above to occur reversibly in a specific temperature range will now be explained. Examples of component (c) include alcohols, esters, ketones, ethers, and acid amides. In order to exhibit large hysteresis characteristics with respect to the color density-temperature curve and change color, thereby providing color memory depending on temperature changes, carboxylic acid ester compounds exhibiting a ΔT value (melting point-cloud point) of 5°C or higher and less than 50°C as described in Japanese Patent Publication No. 4-17154, such as carboxylic acid esters containing a substituted aromatic ring in the molecule, esters of carboxylic acids containing an unsubstituted aromatic ring and aliphatic alcohols having 10 or more carbon atoms, carboxylic acid esters containing a cyclohexyl group in the molecule, esters of fatty acids having 6 or more carbon atoms and unsubstituted aromatic alcohols or phenols, esters of fatty acids having 8 or more carbon atoms and branched aliphatic alcohols, esters of dicarboxylic acids and aromatic alcohols or branched aliphatic alcohols, dibenzyl cinnamate, heptyl stearate, didecyl adipate, dilauryl adipate, dimyristyl adipate, dicetyl adipate, distearyl adipate, trilaurin, trimiristine, tristearin, dimyristine, distearin, etc.

[0014] Fatty acid ester compounds obtained from an odd-numbered aliphatic monohydric alcohol with 9 or more carbon atoms and an even-numbered aliphatic carboxylic acid, and fatty acid ester compounds with a total of 17 to 23 carbon atoms obtained from n-pentyl alcohol or n-heptyl alcohol and an even-numbered aliphatic carboxylic acid with 10 to 16 carbon atoms are also effective. Specifically, n-pentadecyl acetate, n-tridecyl butyrate, n-pentadecyl butyrate, n-undecyl caproate, n-tridecyl caproate, n-pentadecyl caproate, n-nonyl caprylate, n-undecyl caprylate, n-tridecyl caprylate, n-pentadecyl caprylate, n-heptyl caprate, n-nonyl caprate, n-undecyl caprate, n-tridecyl caprate, n-pentadecyl caprate, n-pentyl laurate, n-heptyl laurate, n-nonyl laurate, n-undecyl laurate, n-tridecyl laurate, n-pentadecyl laurate, n-pentyl myristate, n-heptyl myristate, myristic acid Examples include n-nonyl palmitate, n-undecyl myristate, n-tridecyl myristate, n-pentadecyl myristate, n-pentyl palmitate, n-heptyl palmitate, n-nonyl palmitate, n-undecyl palmitate, n-tridecyl palmitate, n-pentadecyl palmitate, n-nonyl stearate, n-undecyl stearate, n-tridecyl stearate, n-pentadecyl stearate, n-nonyl eicosanoate, n-undersi eicosanoate, n-tridecyl eicosanoate, n-pentadecyl eicosanoate, n-nonyl behenate, n-undecyl behenate, n-tridecyl behenate, and n-pentadecyl behenate.

[0015] Effective ketones include aliphatic ketones with a total carbon number of 10 or more, such as 2-decanone, 3-decanone, 4-decanone, 2-undecanone, 3-undecanone, 4-undecanone, 5-undecanone, 2-dodecanone, 3-dodecanone, 4-dodecanone, 5-dodecanone, 2-tridecanone, 3-tridecanone, 2-tetradecanone, 2-pentadecanone, 8-pentadecanone, 2-hexadecanone, 3-hexadecanone, 9-heptadecanone, 2-pentadecanone, 2-octadecanone, 2-nonadecanone, 10-nonadecanone, 2-eicosanone, 11-eicosanone, 2-heneicosanone, 2-docosanone, laurone, and stearone. Furthermore, arylalkyl ketones with a total carbon number of 12 to 24, such as n-octadecanophenone, n-heptadecanophenone, n-hexadecanophenone, n-pentadecanophenone, n-tetradecanophenone, 4-n-dodecacetophenone, n-tridecanophenone, 4-n-undecanoacetophenone, n-laurophenone, 4-n-decanoacetophenone, n-undecanophenone, 4-n-nonylacetophenone, n-decanophenone, 4-n-octylacetophenone, n-nonylacetophenone Examples include nophenone, 4-n-heptylacetophenone, n-octanophenone, 4-n-hexylacetophenone, 4-n-cyclohexylacetophenone, 4-tert-butylpropiophenone, n-heptaphenone, 4-n-pentylacetophenone, cyclohexylphenyl ketone, benzyl-n-butyl ketone, 4-n-butylacetophenone, n-hexanophenone, 4-isobutylacetophenone, 1-acetonaphthone, 2-acetonaphthone, and cyclopentylphenyl ketone.

[0016] As for ethers, aliphatic ethers with a total of 10 or more carbon atoms are effective, and examples include dipentyl ether, dihexyl ether, diheptyl ether, dioctyl ether, dinonyl ether, didecyl ether, diundecyl ether, didodecyl ether, ditridecyl ether, ditetradecyl ether, dipentadecyl ether, dihexadecyl ether, dioctadecyl ether, decanediol dimethyl ether, undecanediol dimethyl ether, dodecanediol dimethyl ether, tridecanediol dimethyl ether, decanediol diethyl ether, and undecanediol diethyl ether.

[0017] Acid amides include acetamide, propionic acid amide, butyrate amide, caproic acid amide, caprylic acid amide, capric acid amide, lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, benzamide, caproic acid anilide, caprylic acid anilide, capric acid anilide, lauric acid anilide, myristic acid anilide, palmitic acid anilide, stearic acid anilide, behenic acid anilide, oleic acid anilide, erucic acid anilide, caproic acid N-methylamide, Caprylic acid N-methylamide, capric acid N-methylamide, lauric acid N-methylamide, myristate acid N-methylamide, palmitic acid N-methylamide, stearate N-methylamide, behenic acid N-methylamide, oleic acid N-methylamide, erucate N-methylamide, laurate N-ethylamide, myristate acid N-ethylamide, palmitic acid N-ethylamide, stearate N-ethylamide, oleic acid N-ethylamide, laurate N-butylamide, myristate acid N-butylamide, palmitic acid N-butylamide, stear N-butylamide phosphate, N-butylamide oleate, N-octylamide laurate, N-octylamide myristate, N-octylamide palmitate, N-octylamide stearate, N-octylamide oleate, N-dodecylamide laurate, N-dodecylamide myristate, N-dodecylamide palmitate, N-dodecylamide stearate, N-dodecylamide oleate, dilaurate, dimyristateamide, dipalmitamide, distearate, dioleamide, trilaurate, tri Myristic acid amide, tripalmitic acid amide, tristearic acid amide, trioleic acid amide, succinic acid amide, adipic acid amide, glutaric acid amide, malonic acid amide, azelaic acid amide, maleic acid amide, succinic acid N-methylamide, adipic acid N-methylamide, glutaric acid N-methylamide, malonic acid N-methylamide, azelaic acid N-methylamide, succinic acid N-ethylamide, adipic acid N-ethylamide, glutaric acid N-ethylamide, malonic acid N-ethylamide, azelaic acid N-ethylamide, succinic acid N-butylamide,Examples include N-butylamide adipic acid, N-butylamide glutarate, N-butylamide malonate, N-octylamide adipic acid, and N-dodecylamide adipic acid.

[0018] Furthermore, the compound represented by the following general formula (1) can also be used as component (c) above. [ka] [In the formula, R1 represents a hydrogen atom or a methyl group, m represents an integer from 0 to 2, and either X1 or X2 is -(CH2)] n OCOR2 or -(CH2) n COOR2, the other side represents a hydrogen atom, n is an integer from 0 to 2, R2 represents an alkyl group or alkenyl group with 4 or more carbon atoms, Y1 and Y2 represent a hydrogen atom, an alkyl group with 1 to 4 carbon atoms, a methoxy group, or a halogen, and r and p are integers from 1 to 3. Among the compounds represented by formula (1) above, the case where R1 is a hydrogen atom is preferred because it yields a reversible thermochromic composition with a wider hysteresis width, 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 compound represented by the following general formula (2) is more preferably used. [ka] In the formula, R represents an alkyl 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. Specific examples of the aforementioned compounds include 4-benzyloxyphenylethyl octanoate, 4-benzyloxyphenylethyl nonanoate, 4-benzyloxyphenylethyl decanoate, 4-benzyloxyphenylethyl undecanoate, 4-benzyloxyphenylethyl dodecanoate, 4-benzyloxyphenylethyl tridecanoate, 4-benzyloxyphenylethyl tetradecanoate, 4-benzyloxyphenylethyl pentadecanoate, 4-benzyloxyphenylethyl hexadecanoate, 4-benzyloxyphenylethyl heptadecanoate, and 4-benzyloxyphenylethyl octadecanoate.

[0019] Furthermore, the compound represented by the following general formula (3) can also be used as component (c). [ka] (In the formula, R represents an alkyl or alkenyl group having 8 or more carbon atoms, m and n each represent an integer from 1 to 3, and X and Y represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, and a halogen, respectively.) Specific examples of the aforementioned compounds include 1,1-diphenylmethyl octanoate, 1,1-diphenylmethyl nonanoate, 1,1-diphenylmethyl decanoate, 1,1-diphenylmethyl undecanoate, 1,1-diphenylmethyl dodecanoate, 1,1-diphenylmethyl tridecanoate, 1,1-diphenylmethyl tetradecanoate, 1,1-diphenylmethyl pentadecanoate, 1,1-diphenylmethyl hexadecanoate, 1,1-diphenylmethyl heptadecanoate, and 1,1-diphenylmethyl octadecanoate.

[0020] Furthermore, the compound represented by the following general formula (4) can also be used as component (c). [ka] (In the formula, X represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a methoxy group, or a halogen atom; m represents an integer from 1 to 3; and n represents an integer from 1 to 20.) The aforementioned compounds include diesters of malonic acid and 2-[4-(4-chlorobenzyloxy)phenyl)]ethanol, succinic acid and 2-(4-benzyloxyphenyl)ethanol, succinic acid and 2-[4-(3-methylbenzyloxy)phenyl)]ethanol, glutaric acid and 2-(4-benzyloxyphenyl)ethanol, glutaric acid and 2-[4-(4-chlorobenzyloxy)phenyl)]ethanol, adipic acid and 2-(4-benzyloxyphenyl)ethanol, pimelic acid and 2-(4-benzyloxyphenyl)ethanol, suberic acid and 2-(4-benzyloxyphenyl)ethanol, and suberic acid and 2-[4-(3-methylbenzyloxy) Examples include diesters of 2-(4-(4-chlorobenzyloxy)phenyl)) ethanol, diesters of suberic acid and 2-(4-(2,4-dichlorobenzyloxy)phenyl)) ethanol, diesters of suberic acid and 2-(4-dichlorobenzyloxy)phenyl)) ethanol, diesters of azelaic acid and 2-(4-benzyloxyphenyl) ethanol, diesters of sebacic acid and 2-(4-benzyloxyphenyl) ethanol, diesters of 1,10-decanedicarboxylic acid and 2-(4-benzyloxyphenyl) ethanol, diesters of 1,18-octadecanedicarboxylic acid and 2-(4-benzyloxyphenyl) ethanol, and diesters of 1,18-octadecanedicarboxylic acid and 2-(4-methylbenzyloxy)phenyl)) ethanol.

[0021] Furthermore, the compound represented by the following general formula (5) can also be used as component (c). [ka] (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.) The aforementioned compounds include diesters of 1,3-bis(2-hydroxyethoxy)benzene and capric acid, diesters of 1,3-bis(2-hydroxyethoxy)benzene and undecanoic acid, diesters of 1,3-bis(2-hydroxyethoxy)benzene and lauric acid, diesters of 1,3-bis(2-hydroxyethoxy)benzene and myristic acid, diesters of 1,4-bis(hydroxymethoxy)benzene and butyric acid, diesters of 1,4-bis(hydroxymethoxy)benzene and isovaleric acid, diesters of 1,4-bis(2-hydroxyethoxy)benzene and acetic acid, Examples include diesters of 4-bis(2-hydroxyethoxy)benzene with propionic acid, 1,4-bis(2-hydroxyethoxy)benzene with valeric acid, 1,4-bis(2-hydroxyethoxy)benzene with caproic acid, 1,4-bis(2-hydroxyethoxy)benzene with caprylic acid, 1,4-bis(2-hydroxyethoxy)benzene with capric acid, 1,4-bis(2-hydroxyethoxy)benzene with lauric acid, and 1,4-bis(2-hydroxyethoxy)benzene with myristic acid.

[0022] Furthermore, the compound represented by the following general formula (6) can also be used as component (c). [ka] (In the formula, X represents 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; m represents an integer from 1 to 3; and n represents an integer from 1 to 20.) Examples of the aforementioned compounds include diesters of succinic acid and 2-phenoxyethanol, diesters of suberic acid and 2-phenoxyethanol, diesters of sebacic acid and 2-phenoxyethanol, diesters of 1,10-decanedicarboxylic acid and 2-phenoxyethanol, and diesters of 1,18-octadecanedicarboxylic acid and 2-phenoxyethanol.

[0023] Furthermore, the compound represented by the following general formula (7) can also be used as component (c). [ka] (In the formula, R represents any of a C4 to C22 alkyl group, a cycloalkylalkyl group, a cycloalkyl group, or a C4 to C22 alkenyl group; X represents any of a hydrogen atom, a C1 to C4 alkyl group, a C1 to C4 alkoxy group, or a halogen atom; and n represents 0 or 1.) Examples of the aforementioned compounds include decyl 4-phenylbenzoate, lauryl 4-phenylbenzoate, myristyl 4-phenylbenzoate, cyclohexylethyl 4-phenylbenzoate, octyl 4-biphenylacetate, nonyl 4-biphenylacetate, decyl 4-biphenylacetate, lauryl 4-biphenylacetate, myristyl 4-biphenylacetate, tridecyl 4-biphenylacetate, pentadecyl 4-biphenylacetate, cetyl 4-biphenylacetate, cyclopentyl 4-biphenylacetate, cyclohexylmethyl 4-biphenylacetate, hexyl 4-biphenylacetate, and cyclohexylmethyl 4-biphenylacetate.

[0024] Furthermore, the compound represented by the following general formula (8) can also be used as component (c). [ka] (In the formula, R represents any of an alkyl group having 3 to 18 carbon atoms or an aliphatic acyl group having 3 to 18 carbon atoms; X represents any of 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 any of a hydrogen atom or a methyl group; and Z represents any of 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.) Examples of the aforementioned compounds include phenoxyethyl 4-butoxybenzoate, phenoxyethyl 4-pentyloxybenzoate, phenoxyethyl 4-tetradecyloxybenzoate, esters of phenoxyethyl 4-hydroxybenzoate and dodecanoic acid, and dodecyl ether of phenoxyethyl vanillate.

[0025] Furthermore, the compound represented by the following general formula (9) can also be used as component (c). [ka] (In the formula, R represents any of the following: 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 any of the following: a hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom; Y represents any of the following: a hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom; and n represents 0 or 1.) Examples of the aforementioned compounds include benzoic acid esters of octyl p-hydroxybenzoate, decyl p-hydroxybenzoate, p-methoxybenzoic acid ester of heptyl p-hydroxybenzoate, o-methoxybenzoic acid ester of dodecyl p-hydroxybenzoate, and benzoic acid ester of cyclohexylmethyl p-hydroxybenzoate.

[0026] Furthermore, the compound represented by the following general formula (10) can also be used as component (c). [ka] (In the formula, R represents any of the following: an alkyl group having 3 to 18 carbon atoms, a cycloalkylalkyl group having 6 to 11 carbon atoms, a cycloalkyl group having 5 to 7 carbon atoms, or an alkenyl group having 3 to 18 carbon atoms; X represents any of the following: a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, or a halogen atom; and Y represents any of the following: a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a methoxy group, an ethoxy group, or a halogen atom.) Examples of the aforementioned compounds include phenoxyethyl ether of nonyl p-hydroxybenzoate, phenoxyethyl ether of decyl p-hydroxybenzoate, phenoxyethyl ether of undecyl p-hydroxybenzoate, and phenoxyethyl ether of dodecyl vanillate.

[0027] Furthermore, the compound represented by the following general formula (11) can also be used as component (c). [ka] (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.) Examples of the aforementioned compounds include diesters of 1,3-bis(2-hydroxyethoxy)benzene and cyclohexanecarboxylic acid, diesters of 1,4-bis(2-hydroxyethoxy)benzene and cyclohexanepropionic acid, and diesters of 1,3-bis(2-hydroxyethoxy)benzene and cyclohexanepropionic acid.

[0028] Furthermore, the compound represented by the following general formula (12) can also be used as component (c). [ka] (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 aforementioned compounds include diesters of 4-phenylphenol ethylene glycol ether and cyclohexanecarboxylic acid, diesters of 4-phenylphenol diethylene glycol ether and lauric acid, diesters of 4-phenylphenol triethylene glycol ether and cyclohexanecarboxylic acid, diesters of 4-phenylphenol ethylene glycol ether and octanoic acid, diesters of 4-phenylphenol ethylene glycol ether and nonanoic acid, diesters of 4-phenylphenol ethylene glycol ether and decanoic acid, and diesters of 4-phenylphenol ethylene glycol ether and myristic acid.

[0029] The proportion of each component in the reversible thermochromic composition depends on the concentration, discoloration temperature, discoloration form, and type of each component, but generally, the component ratios that yield the desired properties are in the range of (a) 1 part of component, (b) 0.1 to 100 parts, preferably 0.1 to 50 parts, more preferably 0.5 to 20 parts, and (c) 1 to 800 parts, preferably 5 to 200 parts, more preferably 10 to 100 parts (all proportions are in parts by mass).

[0030] Furthermore, various light stabilizers can be added as needed. The aforementioned light stabilizers are included to prevent photodegradation of the reversible thermochromic composition consisting of components (a), (b), and (c), and are included in a ratio of 0.3 to 24% by mass, preferably 0.3 to 16% by mass, per 1% by mass of component (a). Furthermore, among the light stabilizers, the ultraviolet absorber effectively cuts ultraviolet rays contained in sunlight, etc., and prevents photodegradation caused by the excitation state due to the photoreaction of component (a). In addition, antioxidants, singlet oxygen quenchers, superoxide anion quenchers, ozone quenchers, etc., suppress oxidation reactions caused by light. The aforementioned light stabilizers may be used alone or in combination of two or more types.

[0031] The aforementioned reversible thermochromic composition can be used as a reversible thermochromic microcapsule pigment (reversible thermochromic pigment) by encapsulating it in microcapsules, or as reversible thermochromic resin particles (reversible thermochromic pigment) by dispersing the reversible thermochromic composition in a thermoplastic or thermosetting resin. Microencapsulation can be performed using known methods such as interfacial polymerization, in situ polymerization, liquid curing coating, phase separation from aqueous solutions, phase separation from organic solvents, melt-dispersion-cooling, air suspension coating, and spray drying, and can be appropriately selected depending on the application. Furthermore, depending on the purpose, a secondary resin coating can be applied to the surface of the microcapsules to provide durability or modify the surface properties for practical use. Examples of resins that constitute the microcapsules include urea resin, urethane resin, urea-urethane resin, epoxy resin, melamine resin, benzoguanamine resin, and isocyanate resin. The microcapsule pigment is preferably in the range of encapsulation / wall film = 7 / 1 to 1 / 1 (mass ratio). By having the wall film ratio within this range, a decrease in color density and vividness during color development can be prevented. More preferably, the encapsulation / wall film ratio is 6 / 1 to 1 / 1 (mass ratio). By encapsulating the pigment in the aforementioned microcapsules, a chemically and physically stable pigment can be constructed.

[0032] The average particle size of the reversible thermochromic pigment is not particularly limited, but is preferably in the range of 0.1 to 5 μm, more preferably 0.3 to 5 μm, even more preferably 0.3 to 4 μm, and particularly preferably 0.5 to 3 μm. The average particle diameter was measured using image analysis-based particle size distribution measurement software [Mountec Co., Ltd., product name: MacView] to determine the particle area, calculate the projected area circle equivalent diameter (Heywood diameter) from the area of ​​the particle area, and then measure the average particle diameter of particles equivalent to an equivolute sphere based on that value. Furthermore, if the particle size of all or most of the particles exceeds 0.2 μm, it is also possible to measure the average particle size of particles equivalent to equivolute spheres using the Coulter method with a particle size distribution analyzer [Beckman Coulter, Ltd., product name: Multisizer 4e]. Furthermore, volume-based particle diameter and average particle diameter may be measured using a laser diffraction / scattering particle size distribution analyzer (manufactured by Horiba, Ltd., product name: LA-960V2) that has been calibrated based on the values ​​measured using the above-mentioned software or Coulter method measuring device.

[0033] The medium of the aforementioned thermochromic writing instrument ink composition is an organic solvent, water, water, and a water-soluble organic solvent, and various additives can be added. As the aforementioned organic solvent, a general-purpose one used for oil-based inks can be used, but it is preferable to use a medium-boiling point solvent with a boiling point in the range of 95°C to 220°C, preferably in the range of 140°C to 200°C, as the main solvent (i.e., containing 50% or more). Examples of organic solvents within the aforementioned boiling point range include n-octane, isooctane, n-heptane, methylcyclohexane, ethylcyclohexane, toluene, xylene, ethylene glycol monoisopropyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, 3-methoxybutanol, 3-methyl-3-methoxybutanol, 3-methyl-1,3-butanediol, 1,3-butanediol, and hexylene glycol. In addition, low-boiling point solvents such as ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, ethylene glycol alkyl (C1-3) ether, ethylbenzene, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, ethyl propionate, methyl lactate, ethyl lactate, dimethyl carbonate, propylene glycol methyl ether acetate, and ethylene glycol monoethyl ether acetate, as well as high-boiling point solvents such as ethylene glycol monophenyl ether, can be used as auxiliary solvents. Examples of the aforementioned water-soluble organic solvents include ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, glycerin, 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, sulforane, 2-pyrrolidone, and N-methyl-2-pyrrolidone.

[0034] Examples of ink compositions for thermochromic writing instruments comprising at least the aforementioned heat-decolorizing reversible thermochromic pigment and a medium include shear-thinning inks containing a shear-thinning agent and coagulating inks containing a water-soluble polymer flocculant to suspend microcapsule pigments in a loosely aggregated state.

[0035] By adding the aforementioned shear-reducing viscosity-imparting agent, aggregation and sedimentation of microcapsule pigments and resin particles can be suppressed, and bleeding of the handwriting can be suppressed, resulting in the formation of good handwriting. Furthermore, if the writing instrument filled with the ink composition is in the form of a ballpoint pen, it is possible to prevent ink leakage from the gap between the ball and the tip when not in use, and to prevent ink backflow when the writing tip is left upright. The aforementioned shear-thickening agent may include xanthan gum, gellan gum, succinoglycans (average molecular weight approximately 1 to 8 million) whose constituent monosaccharides are organic acid-modified heteropolysaccharides of glucose and galactose, guar gum, locust bean gum and its derivatives, hydroxyethylcellulose, alkyl alginates, polymers with a molecular weight of 100,000 to 150,000 mainly composed of alkyl esters of methacrylic acid, glucomannan, gelling polysaccharides extracted from seaweed such as agar and carrageenan, benzylidene sorbitol and benzylidene xylitol or their derivatives, crosslinkable acrylic acid polymers, inorganic fine particles, polyglycerin fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyethylene glycol fatty acid esters, polyoxyethylene alkyl ethers, polyoxypropylene alkyl ethers, polyoxyethylene alkylphenyl ethers, nonionic surfactants with an HLB value of 8 to 12 such as fatty acid amides, and salts of dialkyl or dialkenyl sulfosuccinate. Examples include a mixture of N-alkyl-2-pyrrolidone and anionic surfactant, and a mixture of polyvinyl alcohol and acrylic resin.

[0036] Examples of the aforementioned water-soluble polymer flocculants include polyvinylpyrrolidone, polyethylene oxide, and water-soluble polysaccharides. Examples of the aforementioned water-soluble polysaccharides include tragacanth gum, guar gum, pullulan, cyclodextrin, and water-soluble cellulose derivatives. Specific examples of water-soluble cellulose derivatives include methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, and hydroxypropylmethylcellulose. In the ink composition of the present invention, any water-soluble polymer that exhibits a loose bridging effect between microcapsule pigment particles can be used, but water-soluble cellulose derivatives are particularly effective.

[0037] Furthermore, adding a water-soluble resin can impart adhesion and viscosity to the paper surface. Examples of the water-soluble resin include alkyd resins, acrylic resins, styrene-maleic acid copolymers, cellulose derivatives, polyvinylpyrrolidone, polyvinyl alcohol, and dextrin, with polyvinyl alcohol being preferred. Furthermore, among the polyvinyl alcohols, partially saponified polyvinyl alcohol with a degree of saponification of 70-89 mol% is more preferably used because it is highly soluble even in acidic inks. The amount of the water-soluble resin added to the ink is preferably in the range of 0.3 to 3.0% by mass, more preferably 0.5 to 1.5% by mass.

[0038] Furthermore, when the ink composition is used by filling it into a ballpoint pen, it is preferable to add a lubricant such as a higher fatty acid like oleic acid, a nonionic surfactant having a long-chain alkyl group, a polyether-modified silicone oil, thiophosphite triesters such as thiophosphite tri(alkoxycarbonylmethyl ester) or thiophosphite tri(alkoxycarbonylethyl ester), phosphate monoesters of polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether, phosphate diesters of polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether, or metal salts, ammonium salts, amine salts, or alkanolamine salts thereof to prevent wear of the ball bearing seat. Furthermore, pH adjusters such as inorganic salts like sodium carbonate, sodium phosphate, and sodium acetate, and organic basic compounds such as water-soluble amine compounds, rust inhibitors such as benzotriazole, tolyltriazole, dicyclohexylammonium nitride, diisopropylammonium nitride, and saponins, preservatives or fungicides such as carbolic acid, sodium salt of 1,2-benzthiazolin 3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl parahydroxybenzoate, and 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine may be added. Additionally, fluorinated surfactants or nonionic surfactants that improve ink penetration may be added.

[0039] The aforementioned ink composition is used by filling writing instruments such as ballpoint pens and marking pens, which have a ballpoint pen tip or marking pen tip attached to the writing end, into the writing instrument. When filling a ballpoint pen, the structure and shape of the ballpoint pen itself are not particularly limited. For example, one could consider a ballpoint pen having an ink reservoir filled with shear-reducing ink inside the barrel, the ink reservoir communicating with a tip to which a ball is attached, and a backflow prevention stopper tightly fitted to the end face of the ink reservoir.

[0040] To explain the ballpoint pen tip in more detail, the tip can be one in which a ball is held in a ball-holding portion formed by pressing the tip of a metal pipe inward from the outer surface, or one in which a ball is held in a ball-holding portion formed by cutting a metal material with a drill or the like, one in which a resin ball-receiving seat is provided inside a metal or plastic tip, or one in which the ball held in the tip is biased forward by a spring. Furthermore, the ball can be made of materials such as cemented carbide, stainless steel, ruby, ceramic, resin, or rubber, with a diameter of approximately 0.3 to 3.0 mm, preferably 0.3 to 1.5 mm, and more preferably 0.4 to 1.0 mm.

[0041] The ink container tube that holds the ink is, for example, a molded body made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon. In addition to directly connecting the tip to the ink storage tube, the ink storage tube and the tip may also be connected via a connecting member. Furthermore, the ink reservoir may be in the form of a refill, with the refill housed inside the barrel, or the barrel itself, with a tip attached to its end, may be used as the ink reservoir, with ink directly filled into the barrel. The ballpoint pen obtained in the manner described above may be a ballpoint pen with a cap, or a retractable ballpoint pen, and its shape is not particularly limited. A retractable ballpoint pen can be used as long as the writing tip, which is attached to the ballpoint pen refill, is stored inside the barrel and exposed to the outside air, and the writing tip protrudes from the barrel opening when the retractable mechanism is activated. Examples of operating methods for the retraction mechanism include knocking, rotating, and sliding mechanisms. The aforementioned retractable pen may be configured such that it has a retractable part at the rear end or side of the barrel, and the ballpoint pen tip extends and retracts from the front end opening of the barrel by pressing the retractable part, or by pressing a clip provided on the barrel to extend and retract the ballpoint pen tip from the front end opening of the barrel. The aforementioned rotary type may be exemplified by having a rotating part at the rear of the barrel, and by rotating the rotating part, the ballpoint pen tip can be extended and retracted from the opening at the front of the barrel. The aforementioned sliding mechanism may be exemplified by having a sliding part on the side of the barrel, and by operating the slide, the ballpoint pen tip can be extended and retracted from the opening at the front of the barrel, or by sliding a clip part provided on the barrel, the ballpoint pen tip can be extended and retracted from the opening at the front of the barrel.

[0042] An ink backflow prevention body can be filled into the rear end of the ink contained in the aforementioned ink storage tube. The aforementioned ink backflow prevention composition consists of a non-volatile liquid or a low-volatility liquid. Specifically, examples include petrolatum, spindle oil, castor oil, olive oil, refined mineral oil, liquid paraffin, polybutene, α-olefin, α-olefin oligomer or co-oligomer, dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, polyether-modified silicone oil, fatty acid-modified silicone oil, etc., and one or more of these can be used in combination. The non-volatile liquid and / or non-volatile liquid is preferably thickened to a suitable viscosity by adding a thickening agent. Examples of the thickening agent include silica with a hydrophobic surface treatment, fine particle silica with a methylated surface treatment, aluminum silicate, swellable mica, clay-based thickening agents such as hydrophobic treated bentonite and montmorillonite, fatty acid metal soaps such as magnesium stearate, calcium stearate, aluminum stearate, and zinc stearate, tripenzylidene sorbitol, fatty acid amides, amide-modified polyethylene wax, hydrogenated castor oil, dextrin compounds such as fatty acid dextrins, and cellulose compounds. Furthermore, the liquid ink backflow prevention body and the solid ink backflow prevention body can be used in combination.

[0043] Furthermore, when filling a marking pen with an ink composition, the structure and shape of the marking pen itself are not particularly limited. For example, a marking pen may have an ink-absorbing body made of a fiber bundle built into the barrel, and a pen tip made of a fiber processed body with capillary gaps attached to the barrel directly or via an intermediate member, with the ink-absorbing body and the pen tip connected, and the ink-absorbing body being impregnated with a cohesive ink. Another example is a marking pen in which the pen tip and an ink-storage tube are arranged via a valve that is released when the pen tip is pressed, and the ink is directly stored in the ink-storage tube.

[0044] The aforementioned pen tip is a porous material with interconnected pores, selected from materials such as resin-processed fibers, fused heat-meltable fibers, and felt, with a porosity generally ranging from 30% to 70%. One end is processed into a shape suitable for the purpose, such as a bullet shape, rectangle, or chisel shape, for practical use. The aforementioned ink-absorbing material is constructed by bundling crimped fibers in the longitudinal direction and embedding it in a covering such as a plastic cylinder or film, adjusting the porosity to approximately 40-90%. Furthermore, while the valve body can be of the pumping type, it is preferable that it be set to a spring pressure that allows it to be released by pressing with pen pressure. The marking pen obtained in the manner described above may be a marking pen with a cap, or a retractable marking pen, and its shape is not particularly limited.

[0045] Furthermore, the form of the ballpoint pen or marking pen is not limited to those described above, and may also be a multi-function writing instrument (such as a double-ended or retractable-tip type) equipped with pen tips of different shapes or pen tips that dispense inks of different colors.

[0046] The writing produced by a writing instrument containing the aforementioned ink composition can be erased by friction with a finger or by applying a friction material. The friction body is preferably an elastic material such as an elastomer or plastic foam that is highly elastic and can generate appropriate friction and frictional heat during friction, but it may also be a plastic molded body, stone, wood, metal, or fabric. While it is also possible to use an eraser to rub away the ink, this generates eraser residue, so it is preferable to use a friction material as described above. As the material of the friction body, silicone resin and styrene-based resins such as SEBS resin (styrene-ethylene-butadiene-styrene block copolymer) are preferably used. However, silicone resin tends to adhere to the area erased by friction, and the writing tends to be repelled when writing repeatedly, so SEBS resin is more preferably used. While a thermochromic learning tool set can be obtained by combining a writing instrument with a separate, arbitrarily shaped component (friction element), attaching the friction element to the writing instrument provides superior portability. The location where the friction member is fixed is not particularly limited, but in the case of a ballpoint pen with a cap, it can be provided at the tip (top) of the cap or at the rear end of the barrel (the part without a writing tip), and in the case of a retractable ballpoint pen, it can be provided at the tip of the barrel or at the rear end of the barrel. Furthermore, a small protrusion of any shape can be provided on part of the cap or part of the barrel to serve as a friction member.

[0047] The learning sheet is provided with a question display section and an answer display section corresponding to the question display section on its surface. The material of the sheet is not particularly limited and can include, for example, paper, synthetic paper, synthetic leather, leather, plastic, glass, ceramics, metal, wood, stone, etc. Paper and synthetic paper are preferably used. The problem display area provided on the surface of the sheet consists of letters, numbers, symbols, pictures, sentences, etc., containing a non-discoloring coloring agent. The non-coloring coloring agent can be a general dye or pigment, and as a dye, acid dyes, basic dyes, or direct dyes can be used. The aforementioned pigments can include inorganic pigments such as carbon black and ultramarine, organic pigments such as azo pigments, phthalocyanine pigments, indigo pigments, thioindigo pigments, threne pigments, quinacridone pigments, anthraquinone pigments, throne pigments, diketopyrrolopyrrole pigments, dioxazine pigments, perylene pigments, perinone pigments, isoindolinone pigments, and fluorescent pigments. The non-coloring colorant can be dispersed in a vehicle containing water and / or an organic solvent and various additives as needed to prepare printing inks and inkjet inks used in screen printing, offset printing, process printing, gravure printing, etc., and then printed to form a problem indication area on a sheet.

[0048] Near the problem display section, there is an answer display section containing a heat-activated, reversible thermochromic pigment that becomes colored when heated from a colorless state and becomes colorless when cooled from the colored state. The answer can be visually confirmed by rubbing it with a finger or applying a friction object to activate the color. The friction body can be the aforementioned friction body or a friction member provided on a writing instrument.

[0049] The answer display section contains a heat-activated, reversible thermochromic pigment and consists of characters, numbers, symbols, pictures, sentences, etc., corresponding to the answer in the question display section. The aforementioned heat-activated, reversible thermochromic pigment can be dispersed in a vehicle containing water and / or an organic solvent and various additives as needed to prepare printing inks and inkjet inks used in screen printing, offset printing, process printing, gravure printing, etc., and then printed to form an answer display area on a sheet.

[0050] The following describes reversible thermochromic pigments that change color when heated. The electron-donating colored organic compound used in the aforementioned reversible thermochromic composition is the same as the electron-donating colored organic compound used in a heat-decolorizing reversible thermochromic pigment. As the electron-accepting compound in (b) above, an alkoxyphenol compound represented by the following general formula (13) as described in Japanese Patent Publication No. 11-129623 can be used. [ka] (R indicates an alkyl group.) Examples of the aforementioned compounds include pn-propyloxyphenol, pn-butyloxyphenol, pn-pentyloxyphenol, pn-hexyloxyphenol, pn-heptyloxyphenol, pn-octyloxyphenol, pn-nonyloxyphenol, pn-decyloxyphenol, pn-undecyloxyphenol, pn-dodecyloxyphenol, pn-tridecyloxyphenol, pn-tetradecyloxyphenol, pn-pentyldecyloxyphenol, pn-hexyldecyloxyphenol, pn-heptyldecyloxyphenol, and pn-octyldecyloxyphenol.

[0051] Furthermore, as the electron-accepting compound, a hydroxybenzoic acid ester compound represented by the following general formula (14) described in Japanese Patent Publication No. 2001-105732 can also be used. [ka] (In the formula, R represents a linear or side-chain alkyl group having 13 to 22 carbon atoms, and X, Y, and Z consist of one or two hydroxyl groups and the remaining atoms are hydrogen.) The aforementioned compounds include tridecyl 3-hydroxybenzoate, tetradecyl 3-hydroxybenzoate, pentadecyl 3-hydroxybenzoate, hexadecyl 3-hydroxybenzoate, heptadecyl 3-hydroxybenzoate, octadecyl 3-hydroxybenzoate, nonadecyl 3-hydroxybenzoate, eicosyl 3-hydroxybenzoate, heneicosyl 3-hydroxybenzoate, docosyl 3-hydroxybenzoate, and 4-hydroxybenzoate. Tridecyl hydroxybenzoate, tetradecyl 4-hydroxybenzoate, pentadecyl 4-hydroxybenzoate, hexadecyl 4-hydroxybenzoate, heptadecyl 4-hydroxybenzoate, octadecyl 4-hydroxybenzoate, nonadecyl 4-hydroxybenzoate, eicosyl 4-hydroxybenzoate, heneicosyl 4-hydroxybenzoate, docosyl 4-hydroxybenzoate, tridecyl 3,4-dihydroxybenzoate, 3,4- Tetradecyl dihydroxybenzoate, pentadecyl 3,4-dihydroxybenzoate, hexadecyl 3,4-dihydroxybenzoate, heptadecyl 3,4-dihydroxybenzoate, octadecyl 3,4-dihydroxybenzoate, nonadecyl 3,4-dihydroxybenzoate, eicosyl 3,4-dihydroxybenzoate, heneicosyl 3,4-dihydroxybenzoate, docosyl 3,4-dihydroxybenzoate, tridecyl 3,5-dihydroxybenzoate Examples include sil esters, tetradecyl 3,5-dihydroxybenzoate, pentadecyl 3,5-dihydroxybenzoate, hexadecyl 3,5-dihydroxybenzoate, heptadecyl 3,5-dihydroxybenzoate, octadecyl 3,5-dihydroxybenzoate, nonadecyl 3,5-dihydroxybenzoate, eicosyl 3,5-dihydroxybenzoate, heneicosyl 3,5-dihydroxybenzoate, and docosyl 3,5-dihydroxybenzoate.

[0052] Furthermore, as the electron-accepting compound, a gallic acid ester compound described in Japanese Patent Publication No. 2003-253149 can also be used. Examples of the aforementioned compounds include dodecyl gallate, tridecyl gallate, tetradecyl gallate, pentadecyl gallate, hexadecyl gallate, octadecyl gallate, eicosyl gallate, and behenyl gallate.

[0053] Examples of reaction media that control the color reactions described in (c) (a) and (b) above include hydrocarbons, halogenated hydrocarbons, sulfides, ethers, ketones, esters, acid amides, alcohols, waxes, and the like. Examples of the aforementioned hydrocarbons include chain hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, etc. Examples of saturated chain hydrocarbons include pentadecane, hexadecane, heptadecane, octadecane, nonadecane, eicosane, heneicosane, docosane, tricosane, tetracosane, pentacosane, hexacosane, heptacosane, octacosane, nonacosane, and triacontane. Examples of unsaturated chain hydrocarbons include 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 1-heneicosene, 1-docosene, 1-tricocene, 1-tetracosene, 1-pentacosene, 1-hexacosene, 1-heptacosene, 1-octacosene, 1-nonacosene, and 1-triaconthene. Examples of alicyclic hydrocarbons include cyclooctane, cyclododecane, n-pentadecylcyclohexane, n-octadecylcyclohexane, n-nonadecylcyclohexane, and decahydronaphthalene. Examples of aromatic hydrocarbons include dodecylbenzene, biphenyl, ethylbiphenyl, 4-benzylbenzene, phenyltolylmethane, diphenylethane, 1,3-diphenylbenzene, dibenzyltoluene, methylnaphthalene, 2,7-diisopropylnaphthalene, methyltetralin, naphthylphenylmethane, and others.

[0054] Examples of the halogenated hydrocarbons include 1-bromodecane, 1-bromoundecane, 1-bromododecane, 1-bromotridecane, 1-bromotetradecane, 1-chlorotetradecane, 1-bromopentadecane, 1-bromohexadecane, 1-chlorohexadecane, 1-iodohexadecane, 1-bromoheptadecane, 1-bromooctadecane, 1-chlorooctadecane, 1-iodooctadecane, 1-bromoeicosane, 1-chloroeicosane, 1-bromodocosane, and 1-chlorodocosane.

[0055] Examples of the aforementioned sulfides include di-n-octyl sulfide, di-n-nonyl sulfide, di-n-decyl sulfide, di-n-dodecyl sulfide, di-n-tetradecyl sulfide, di-n-hexadecyl sulfide, di-n-octadecyl sulfide, octyldodecyl sulfide, diphenyl sulfide, dibenzyl sulfide, ditolyl sulfide, diethylphenyl sulfide, dinaphthyl sulfide, 4,4'-dichloro-diphenyl sulfide, and 2,4,5,4'-tetrachloro-diphenyl sulfide.

[0056] Examples of the aforementioned ethers include aliphatic ethers with a total of 10 or more carbon atoms, such as dipentyl ether, dihexyl ether, diheptyl ether, dioctyl ether, dinonyl ether, didecyl ether, diundecyl ether, didodecyl ether, ditridecyl ether, ditetradecyl ether, dipentadecyl ether, dihexadecyl ether, dioctadecyl ether, decanediol dimethyl ether, undecanediol dimethyl ether, dodecanediol dimethyl ether, tridecanediol dimethyl ether, decanediol diethyl ether, undecanediol diethyl ether, etc. Examples of alicyclic ethers include s-trioxane, etc. Examples of aromatic ethers include phenyl ether, benzylphenyl ether, dibenzyl ether, di-p-tolyl ether, 1-methoxynaphthalene, 3,4,5-trimethoxytoluene, etc.

[0057] The aforementioned ketones include aliphatic ketones with a total carbon number of 10 or more, such as 2-decanone, 3-decanone, 4-decanone, 2-undecanone, 3-undecanone, 4-undecanone, 5-undecanone, 6-undecanone, 2-dodecanone, 3-dodecanone, 4-dodecanone, 5-dodecanone, 2-tridecanone, 3-tridecanone, 2-tetradecanone, 2-pentadecanone, 8-pentadecanone, 2-hexadecanone, 3-hexadecanone, 9-heptadecanone, 2-pentadecanone, 2-octadecanone, 2-nonadecanone, 10-nonadacanone, 2-eicosanone, 11-eicosanone, 2-heneicosanone, 2-docosanone, laurone, stearone, etc. Arylalkyl ketones with a total of 12 to 24 carbon atoms, for example, n-octadecanophenone, n-heptadecanophenone, n-hexadecanophenone, n-pentadecanophenone, n-tetradecanophenone, 4-n-dodecacetophenone, n-tridecanophenone, 4-n-undecanoacetophenone, n-laurophenone, 4-n-decanoacetophenone, n-undecanophenone, 4-n-nonylacetophenone, n-decanophenone, 4-n-octylacetophenone, n- Examples include nanophenone, 4-n-heptylacetophenone, n-octanophenone, 4-n-hexylacetophenone, 4-n-cyclohexylacetophenone, 4-tert-butylpropiophenone, n-heptaphenone, 4-n-pentylacetophenone, cyclohexylphenyl ketone, benzyl-n-butyl ketone, 4-n-butylacetophenone, n-hexanophenone, 4-isobutylacetophenone, 1-acetonaphthone, 2-acetonaphthone, cyclopentylphenyl ketone, etc. Examples of arylaryl ketones include benzophenone, benzylphenyl ketone, dibenzyl ketone, etc. Examples of alicyclic ketones include cyclooctanone, cyclododecanone, cyclopentadecanone, 4-tert-butylcyclohexanone, etc.

[0058] As the esters, esters having 10 or more carbon atoms are effective, and esters obtained from any combination of a monohydric carboxylic acid having an aliphatic and alicyclic or aromatic ring and a monohydric alcohol having an aliphatic and alicyclic or aromatic ring, esters obtained from any combination of a polyhydric carboxylic acid having an aliphatic and alicyclic or aromatic ring and a monohydric alcohol having an aliphatic and alicyclic or aromatic ring, and any combination of a monohydric carboxylic acid having an aliphatic and alicyclic or aromatic ring and a polyhydric alcohol having an aliphatic and alicyclic or aromatic ring. Examples of esters obtained from this include, specifically, ethyl caprylate, octyl caprylate, stearyl caprylate, myristyl caprate, stearyl caprate, docosyl caprate, 2-ethylhexyl laurate, n-decyl laurate, 3-methylbutyl myristate, cetyl myristate, isopropyl palmitate, neopentyl palmitate, nonyl palmitate, cyclohexyl palmitate, n-butyl stearate, 2-methylbutyl stearate, and 3,5,5-trimethylhexyl stearate. Syl, n-undecyl stearate, pentadecyl stearate, stearyl stearate, cyclohexylmethyl stearate, isopropyl behenate, hexyl behenate, lauryl behenate, behenyl behenate, cetyl benzoate, p-tert-butyl stearyl benzoate, dimyristyl phthalate, distearyl phthalate, dimyristyl oxalate, dicetyl oxalate, dicetyl malonate, dilauryl succinate, dilauryl glutarate, diundecyl adipate, dilauryl azelaate, di-(n-no) sebacate Examples include dineopentyl 1,18-octadecylmethylenedicarboxylic acid, ethylene glycol dimyristate, propylene glycol dilaurate, propylene glycol distearate, hexylene glycol dipalmitate, 1,5-pentanediol dimyristate, 1,2,6-hexanetriol trimyristate, 1,4-cyclohexanediol didecyl, 1,4-cyclohexanedimethanol dimyristate, xylene glycol dicaprinate, xylene glycol distearate, etc. Furthermore, ester compounds selected from saturated fatty acids and branched aliphatic alcohols, unsaturated fatty acids or branched or substituted saturated fatty acids and branched or aliphatic alcohols with 16 or more carbon atoms, cetyl butyrate, stearyl butyrate, and behenyl butyrate are also effective.Specifically, 2-ethylhexyl butyrate, 2-ethylhexyl behenate, 2-ethylhexyl myristate, 2-ethylhexyl caprate, 3,5,5-trimethylhexyl laurate, 3,5,5-trimethylhexyl palmitate, 3,5,5-trimethylhexyl stearate, 2-methylbutyl caproate, 2-methylbutyl caprylate, 2-methylbutyl caprate, 1-ethylpropyl palmitate, 1-ethylpropyl stearate, 1-ethylpropyl behenate, 1-ethylhexyl laurate Xyl, 1-ethylhexyl myristate, 1-ethylhexyl palmitate, 2-methylpentyl caproate, 2-methylpentyl caprylate, 2-methylpentyl caprate, 2-methylpentyl laurate, 2-methylbutyl stearate, 2-methylbutyl stearate, 3-methylbutyl stearate, 1-methylheptyl stearate, 2-methylbutyl behenate, 3-methylbutyl behenate, 1-methylheptyl stearate, 1-methylheptyl behenate, 1-ethylpentyl caproate, 1-Ethylpentyl palmitate, 1-Methylpropyl stearate, 1-Methyloctyl stearate, 1-Methylhexyl stearate, 1,1-Dimethylpropyl laurate, 1-Methylpentyl caprate, 2-Methylhexyl palmitate, 2-Methylhexyl stearate, 2-Methylhexyl behenate, 3,7-Dimethyloctyl laurate, 3,7-Dimethyloctyl myristate, 3,7-Dimethyloctyl palmitate, 3,7-Dimethyloctyl stearate, 3,7-Dimethyloctyl behenate Examples include thiooctyl oleate, stearyl oleate, behenyl oleate, stearyl linoleate, behenyl linoleate, 3,7-dimethyloctyl erucate, stearyl erucate, isostearyl erucate, cetyl isostearate, stearyl isostearate, 2-methylpentyl 12-hydroxystearate, 2-ethylhexyl 18-bromostearate, isostearyl 2-ketomyristate, 2-ethylhexyl 2-fluoromyristate, cetyl butyrate, stearyl butyrate, and behenyl butyrate. Furthermore, examples of carboxylic acid ester compounds disclosed in Japanese Patent Publication No. 4-17154 include carboxylic acid esters containing a substituted aromatic ring in the molecule, esters of carboxylic acids containing an unsubstituted aromatic ring and aliphatic alcohols having 10 or more carbon atoms, carboxylic acid esters containing a cyclohexyl group in the molecule, esters of fatty acids having 6 or more carbon atoms and unsubstituted aromatic alcohols or phenols, fatty acids having 8 or more carbon atoms and branched aliphatic alcohols or esters, esters of dicarboxylic acids and aromatic alcohols or branched aliphatic alcohols, dibenzyl cinnamate, heptyl stearate, didecyl adipate, dilauryl adipate, dimyristyl adipate, dicetyl adipate, distearyl adipate, trilaurin, trimiristine, tristearin, dimyristine, distearin, and the like. Fatty acid ester compounds obtained from an odd-numbered aliphatic monohydric alcohol with 9 or more carbon atoms and an even-numbered aliphatic carboxylic acid, and fatty acid ester compounds with a total of 17 to 23 carbon atoms obtained from n-pentyl alcohol or n-heptyl alcohol and an even-numbered aliphatic carboxylic acid with 10 to 16 carbon atoms are also effective. Specifically, n-pentadecyl acetate, n-tridecyl butyrate, n-pentadecyl butyrate, n-undecyl caproate, n-tridecyl caproate, n-pentadecyl caproate, n-nonyl caprylate, n-undecyl caprylate, n-tridecyl caprylate, n-pentadecyl caprate, n-heptyl caprate, n-nonyl caprate, n-undecyl caprate, n-tridecyl caprate, n-pentadecyl caprate, n-pentyl laurate, n-heptyl laurate, n-nonyl laurate, n-undecyl laurate, n-tridecyl laurate, n-pentadecyl laurate, n-pentyl myristate, n-heptyl myristate, myris Examples include n-nonyl tinate, n-undecyl myristate, n-tridecyl myristate, n-pentadecyl myristate, n-pentyl palmitate, n-heptyl palmitate, n-nonyl palmitate, n-undecyl palmitate, n-tridecyl palmitate, n-pentadecyl palmitate, n-nonyl stearate, n-undecyl stearate, n-tridecyl stearate, n-pentadecyl stearate, n-nonyl eicosanoate, n-undersi eicosanoate, n-tridecyl eicosanoate, n-pentadecyl eicosanoate, n-nonyl behenate, n-undecyl behenate, n-tridecyl behenate, and n-pentadecyl behenate.

[0059] Examples of the aforementioned alcohols include aliphatic monohydric saturated alcohols, such as decyl alcohol, undecyl alcohol, dodecyl alcohol, tridecyl alcohol, tetradecyl alcohol, pentadecyl alcohol, hexadecyl alcohol, heptadecyl alcohol, octadecyl alcohol, eicosyl alcohol, docosyl alcohol, etc.; aliphatic unsaturated alcohols, such as allyl alcohol, oleyl alcohol, etc.; alicyclic alcohols, such as cyclopentanol, cyclohexanol, cyclooctanol, cyclododecanol, 4-tert-butylcyclohexanol, etc.; aromatic alcohols, such as 4-methylbenzyl alcohol, benzhydrol, etc.; and polyhydric alcohols, such as polyethylene glycol, etc.

[0060] Examples of the acid amides include the following compounds: acetamide, propionic acid amide, butyrate amide, caproic acid amide, caprylic acid amide, capric acid amide, lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, benzamide, caproic acid anilide, caprylic acid anilide, capric acid anilide, lauric acid anilide, myristic acid anilide, palmitic acid anilide, stearic acid anilide, behenic acid anilide, oleic acid anilide, erucic acid anilide, caproic acid N-methylamide, caprylic acid N-methylamide, capric acid N-methylamide, lauric acid N-methylamide, myristate acid N-methylamide, palmitic acid N-methylamide, stearate N-methylamide, behenate N-methylamide, oleic acid N-methylamide, erucate N-methylamide, laurate N-ethylamide, myristate acid N-ethylamide, palmitic acid N-ethylamide, stearate N-ethylamide, oleic acid N-ethylamide, laurate N-butylamide, myristate acid N-butylamide, palmitic acid N-butylamide, stear N-butylamide phosphate, N-butylamide oleate, N-octylamide laurate, N-octylamide myristate, N-octylamide palmitate, N-octylamide stearate, N-octylamide oleate, N-dodecylamide laurate, N-dodecylamide myristate, N-dodecylamide palmitate, N-dodecylamide stearate, N-dodecylamide oleate, dilaurate, dimyristateamide, dipalmitamide, distearate, dioleamide, trilauric acid Amides, trimyristinamide, tripalmitamide, tristearic acid amide, trioleamide, succinamide, adipic acid amide, glutaramide, malonamide, azelaic acid amide, maleic acid amide, succinate N-methylamide, adipic acid N-methylamide, glutaric acid N-methylamide, malonate N-methylamide, azelaic acid N-methylamide, succinate N-ethylamide, adipic acid N-ethylamide, glutaric acid N-ethylamide, malonate N-ethylamide, azelaic acid N-ethylamide,Examples include N-butylamide succinate, N-butylamide adipic acid, N-butylamide glutarate, N-butylamide malonate, N-octylamide adipic acid, and N-dodecylamide adipic acid.

[0061] Examples of waxes and medium molecular weight polymers include paraffin wax, microcrystalline wax, petrolactam, oxidized paraffin wax, oxidized petrolactam, shellac, sugarcane wax, carnauba wax, candelilla wax, castor wax, hydrogenated beef tallow, hydrogenated fish oil, hydrogenated rapeseed oil, montan wax, palm wax, malted bark, senna wax, wolf fat, etc. Oxidized polyethylene wax, montanic acid wax, ethylene vinyl acetate copolymer wax, ethylene acrylic copolymer wax, vinyl ether wax, etc. Palm oil, babassu oil, liquid paraffin, polybutene, polybutadiene, polystyrene oligomers, etc.

[0062] Furthermore, the (c) component may be an aliphatic hydrocarbon having 17 or more carbon atoms, or the (c) component may be a hydrocarbon selected from chain hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, and halogenated hydrocarbons, and a compound selected from alcohols, esters, ethers, ketones, and acid amides having a melting point of 50°C or higher, or the hydrocarbon may be a styrene compound having a softening point of 5°C or higher and a weight-average molecular weight of 200 to 100,000, or the hydrocarbon may be a styrene polymer having a softening point of -10°C or higher and a weight-average molecular weight of 200 to 100,000, and an alkoxyphenyl compound, or the hydrocarbon may be a linear dibasic acid compound having 3 to 22 carbon atoms, and an alcohol, ester, ether, ketone, acid amide, or aromatic hydrocarbon having a melting point of 50°C or higher.

[0063] The hysteresis characteristics in the color density-temperature curve of the aforementioned reversible thermochromic composition will be described. In Figure 2, the vertical axis represents color density and the horizontal axis represents temperature. The color density changes with temperature along the arrows. Here, A represents the density at temperature T1 (hereinafter referred to as the complete decolorization temperature) where the color is completely decolorized, C represents the density at temperature T2 (hereinafter referred to as the decolorization start temperature) where the color can be maintained, B represents the density at temperature T3 (hereinafter referred to as the color development start temperature) where the color can be maintained, and D represents the density at temperature T4 (hereinafter referred to as the complete color development temperature) where the color is completely developed. Furthermore, the temperature range (hysteresis range ΔH) can be determined in the same manner as in Figure 1.

[0064] The aforementioned heat-color-developing reversible thermochromic composition is prepared by a method similar to that used for heat-decolorizing reversible thermochromic pigments, using reversible thermochromic microcapsule pigments (reversible thermochromic pigments) or reversible thermochromic resin particles (reversible thermochromic pigments), with an average particle size similar to that of heat-decolorizing reversible thermochromic pigments. The aforementioned heat-activated, reversible thermochromic pigment begins to develop color when the temperature rises from a colorless state, reaching a temperature T3 and becoming fully colored at a temperature of T4 or higher. When the temperature decreases from the colored state, it begins to decolorize when the temperature reaches T2 and becomes completely decolorized when the temperature reaches T1. The temperature T4 is in the range of 40 to 95°C, preferably 45 to 95°C, more preferably 50 to 95°C, and the temperature T1 is above 20°C, preferably above 20°C and below T3, more preferably above 25°C and below T3 (see Figure 2).

[0065] The writing produced by a writing instrument containing the aforementioned heat-decolorizing, reversible thermochromic pigment ink composition maintains its colored state at room temperature. The aforementioned handwriting becomes colorless when heated to a complete decolorization temperature t4 in the range of 40 to 95°C, and remains colorless until cooled to a complete color development temperature t1 in the range of -50 to 5°C. Using the aforementioned writing instrument, answers to the problem display section of the learning tool, as well as the process leading to the answer, can be written in the blank spaces of the learning tool. On the other hand, the heat-activated, reversible thermochromic pigment provided in the answer display section of the learning tool is colorless at room temperature and is not visible. The colorless answer display area can be heated by simple methods such as rubbing it with a finger or a friction object. When it reaches the full color development temperature T4, which is in the range of 40 to 95°C, it will develop color, and the answer will become visible in color. The aforementioned colored answer will disappear and become invisible at room temperature (20°C) because the complete decolorization temperature T1 is above 20°C. Therefore, the user can form the answer corresponding to the problem display section of the learning tool by writing the answer and, if necessary, the process leading to the answer using a writing instrument, and can confirm whether the answer is correct or incorrect by heating the answer display section and visually checking the answer (correct answer). The correct answer becomes invisible at room temperature, and the answer formed with the writing instrument can be made colorless by heating, so the learning material can be reused.

[0066] Preferably, the problem display section provided on the sheet surface of the learning tool has multiple problem display sections and multiple answer display sections corresponding to the problem display sections. Furthermore, the learning tool may consist of multiple sheets, the multiple learning sheets may be separate, holes may be punched in each learning tool and they may be connected with a ring-shaped member, or one side of the learning tools may be bound together to form a booklet. By connecting the various learning materials together or creating a booklet format, a highly portable learning material set can be obtained. [Examples]

[0067] Examples are shown below, but the present invention is not limited to these examples. Note that the part in the example refers to the part by mass. Example 1 (See Figures 3, 6 to 8) Preparation of reversible thermochromic pigments that decolorize when heated A microcapsule pigment suspension was obtained containing a reversible thermochromic composition with color memory properties, comprising (a) 2.0 parts of 4,5,6,7-tetrachloro-3-[4-(dimethylamino)-2-methylphenyl]-3-(1-ethyl-2-methyl-1H-indole-3-yl)-1(3H)-isobenzofuranone as component (b) 3.0 parts of 4,4′-(2-ethylhexane-1,1-diyl)diphenol and 5.0 parts of 2,2-bis(4′-hydroxyphenyl)-hexafluoropropane as component (c) 50.0 parts of 4-benzyloxyphenylethyl caprate as component (c). The suspension was centrifuged to isolate the reversible thermochromic microcapsule pigment (heat-decolorizing reversible thermochromic pigment). The average particle size of the microcapsule pigment is 1.8 μm, the complete decolorization temperature (t4) is 55°C, and the complete color development temperature (t1) is -20°C. The pigment reversibly changes color from blue to colorless with temperature changes.

[0068] Preparation of reversible thermochromic pigments that develop color when heated A microcapsule pigment suspension was obtained containing a reversible thermochromic composition comprising: (a) 3.0 parts of 3′,6′-bis[phenyl(3-methylphenyl)amino]-spiro[isobenzofuran-1(3H),9'-[9H]xanthene]-3-one; (b) 16.0 parts of docosyl 4-hydroxybenzoate; (c) 30.0 parts of pentadecane; (d) 2.0 parts of eicosanedioic acid; (e) 1.0 part of p-terphenyl; and (f) 20.0 parts of styrene-α-methylstyrene copolymer (trade name: Picolastic A-75). The suspension was centrifuged to isolate the reversible thermochromic microcapsule pigment (heat-activated reversible thermochromic pigment). The average particle size of the microcapsule pigment is 2.5 μm, the complete color development temperature (T4) is 63°C, and the complete decolorization temperature (T1) is 30°C. It reversibly changes color from colorless to blue with temperature changes.

[0069] Preparation of thermochromic ink compositions for writing instruments A thermochromic writing instrument ink composition was prepared consisting of 22.5 parts of the aforementioned heat-decolorizing reversible thermochromic pigment, 0.3 parts of xanthan gum (shear viscosity reducing agent), 10 parts of urea, 10 parts of glycerin, 0.5 parts of a phosphate ester surfactant, 0.6 parts of a nonionic penetration agent, 0.1 part of a modified silicone defoaming agent, 0.1 part of a fungicide, 0.5 parts of triethanolamine, and 55.4 parts of water.

[0070] Manufacturing of writing instruments The ink 2 (pre-cooled to -20°C or below to develop a reversible thermochromic pigment that turns blue) is drawn into a polypropylene resin pipe (ink storage tube 3) and connected to a ballpoint pen tip 5 holding a 0.5 mm stainless steel ball at its tip via a resin relay member 4 (holder). Next, an ink backflow prevention body 6 (liquid stopper) was filled into the rear end of the polypropylene pipe, and then a tail plug 7 was fitted to the rear of the pipe to form a refill 8. Furthermore, the refill was assembled into the barrel 9 (consisting of a front barrel and a rear barrel), and after fitting the cap 10, a degassing process was performed by centrifugation to obtain a writing instrument 1 (ballpoint pen). Furthermore, SEBS resin is attached as a friction member 11 to the rear of the rear axle cylinder.

[0071] Making learning materials On a sheet 14 made of synthetic paper, the letters, numbers, and symbols of "Problem 2 × 2 =" were printed using a blue screen printing ink consisting of 5 parts blue pigment, 1 part viscosity modifier, 0.2 parts defoamer, and 93.8 parts water to form a problem display section 15. Next, using a reversible thermochromic screen printing ink consisting of 30 parts of the heat-activated reversible thermochromic pigment, 50 parts of acrylic resin emulsion (45% solids), 1 part of viscosity modifier, 0.2 parts of defoamer, and 18.8 parts of water, the number "4" was printed to the right of the problem display area to form the answer display area (reversible thermochromic image) 16, thereby obtaining the learning tool 13. Furthermore, a rectangular frame and the word "correct answer" are formed around the answer display area using the blue screen printing ink.

[0072] Making a thermochromic learning tool set A thermochromic learning tool set consisting of the aforementioned writing instrument 1 and learning tool 13 was obtained. Problem display of the aforementioned learning tool After checking the section, I used a writing instrument to write the number "4" as the answer to the problem on the learning material (handwriting 17). The handwriting 17 formed by the aforementioned writing instrument was maintained at room temperature (25°C). Next, when the answer display section 16 was rubbed using the friction element provided on the writing instrument, the heat-activated reversible thermochromic pigment changed color, revealing the number "4," thus confirming the correct answer to the question. Furthermore, the answer display area fades and becomes invisible when left at room temperature (25°C), and the handwriting of the number "4" also fades and becomes invisible when rubbed with the friction material. This state is maintained at room temperature (25°C), so the learning tool returns to its initial state, allowing for repeated learning using a writing instrument.

[0073] Example 2 Preparation of reversible thermochromic pigments that decolorize when heated A microcapsule pigment suspension was obtained containing a reversible thermochromic composition with color memory properties, comprising (a) 3.0 parts of 1,3-dimethyl-6-diethylaminofluorane as component, (b) 5.0 parts of 2,2-bis(4-hydroxyphenyl)hexafluoropropane as component, and (c) 50.0 parts of 4-biphenylacetate as component. The suspension was centrifuged to isolate the microcapsule pigment (heat-decolorizing, reversible thermochromic pigment). The average particle size of the microcapsule pigment is 2.0 μm, the complete decolorization temperature (t4) is 47°C, and the complete color development temperature (t1) is -10°C. The pigment reversibly changes color from orange to colorless with temperature changes.

[0074] Preparation of reversible thermochromic pigments that develop color when heated A microcapsule pigment suspension was obtained containing a reversible thermochromic composition comprising (a) 3.0 parts of 1,3-dimethyl-6-diethylaminofluorane as component, (b) 8.0 parts of tetradecyl gallate as component, and (c) 20.0 parts of cetyl caprate and 5.0 parts of myristyl alcohol as component. The suspension was centrifuged to isolate the reversible thermochromic microcapsule pigment (heat-activated reversible thermochromic pigment). The average particle size of the microcapsule pigment is 2.0 μm, the complete color development temperature (T4) is 43°C, and the complete decolorization temperature (T1) is 22°C. It reversibly changes color from colorless to orange with temperature changes.

[0075] Preparation of thermochromic ink compositions for writing instruments A thermochromic writing instrument ink composition was obtained by mixing 21.0 parts of the aforementioned heat-decolorizing reversible thermochromic pigment (pre-cooled to -10°C or below to develop an orange color), 0.5 parts of hydroxyethylcellulose, 0.2 parts of a comb-type polymer dispersant [manufactured by Nippon Lubrizol Co., Ltd., trade name: Solspers 43000], 1.0 part of an organic nitrogen sulfur compound [manufactured by Hokko Chemical Industry Co., Ltd., trade name: Hokuside R-150, a mixture of 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one], 0.5 parts of polyvinyl alcohol, 25.0 parts of glycerin, 0.02 parts of an antifoaming agent, and 51.78 parts of water.

[0076] Manufacturing of writing instruments (see Figure 4) The ink composition is impregnated into an ink-absorbing body 12 made of polyester sliver coated with a synthetic resin film, housed in a barrel 9 made of polypropylene resin, and a marking pen tip 5 (bullet-shaped) made of polyester fiber is attached to the tip of the barrel via a connecting member 4 (holder). The cap 10 is then attached to obtain a writing instrument 1 (marking pen). The aforementioned cap has SEBS resin attached to its top as a friction member 11.

[0077] Making learning materials On a sheet made of synthetic paper, the letters, numbers, and symbols of "Problem 2 × 3 =" were printed using a blue screen printing ink consisting of 5 parts orange pigment, 1 part viscosity modifier, 0.2 parts defoamer, and 93.8 parts water to form the problem display area. Next, using a reversible thermochromic screen printing ink consisting of 30 parts of the heat-activated reversible thermochromic pigment, 50 parts of acrylic resin emulsion (45% solids), 1 part of viscosity modifier, 0.2 parts of defoamer, and 18.8 parts of water, the number "6" was printed to the right of the problem display area to form the answer display area (reversible thermochromic image) and obtain a learning tool. Furthermore, a rectangular frame and the word "correct answer" are formed around the answer display area using the orange screen printing ink.

[0078] Making a thermochromic learning tool set A thermochromic learning tool set consisting of the aforementioned writing instrument and learning tool was obtained. After checking the problem display section of the learning tool, I used a writing instrument to write the number "4" as the answer to the problem on the learning tool (handwriting). The handwriting formed by the aforementioned writing instrument was maintained at room temperature (20°C). Next, by rubbing the answer display area with the friction element provided on the writing instrument, the heat-activated, reversible thermochromic pigment changed color, revealing the number "6," thus confirming the correct answer to the question. Furthermore, the answer display area fades and becomes invisible when left at room temperature (20°C), and the handwriting of the number "4" also fades and becomes invisible when rubbed with the friction material. This state is maintained at room temperature (20°C), so the learning tool returns to its initial state, allowing for repeated learning using a writing instrument.

[0079] Example 3 Preparation of reversible thermochromic pigments that decolorize when heated A microcapsule pigment suspension was obtained containing a reversible thermochromic composition with color memory properties, comprising (a) 2.0 parts of 4,5,6,7-tetrachloro-3-[4-(dimethylamino)-2-methylphenyl]-3-(1-ethyl-2-methyl-1H-indole-3-yl)-1(3H)-isobenzofuranone as component (b) 5.0 parts of 2,2-bis(4-hydroxyphenyl)hexafluoropropane as component (c) 50.0 parts of 4-biphenyl acetate as component (c). The suspension was centrifuged to isolate the microcapsule pigment (heat-decolorizing, reversible thermochromic pigment). The average particle size of the microcapsule pigment is 2.0 μm, the complete decolorization temperature (t4) is 47°C, and the complete color development temperature (t1) is -10°C. The pigment reversibly changes color from blue to colorless with temperature changes.

[0080] Preparation of reversible thermochromic pigments that develop color when heated A microcapsule pigment suspension was obtained containing a reversible thermochromic composition comprising (a) 2.0 parts of 4,5,6,7-tetrachloro-3-[4-(dimethylamino)-2-methylphenyl]-3-(1-ethyl-2-methyl-1H-indole-3-yl)-1(3H)-isobenzofuranone as component, (b) 10.0 parts of n-tetradoxy p-oxybenzoic acid as component, and (c) 20.0 parts of n-docosane as component. The suspension was centrifuged to isolate the reversible thermochromic microcapsule pigment (heat-activated reversible thermochromic pigment). The average particle size of the microcapsule pigment is 2.5 μm, the complete color development temperature (T4) is 44°C, and the complete decolorization temperature (T1) is 27°C. It reversibly changes color from colorless to blue with temperature changes.

[0081] Preparation of thermochromic ink compositions for writing instruments A thermochromic writing instrument ink composition was prepared consisting of 10.0 parts of the aforementioned heat-decolorizing reversible thermochromic pigment (pre-cooled to -10°C or below to develop blue color), 12.0 parts of the heat-developing reversible thermochromic pigment, 0.3 parts of succinoglycan (shear viscosity reducing agent), 10 parts of urea, 5 parts of glycerin, 0.5 parts of a phosphate ester surfactant, 0.6 parts of a nonionic penetration agent, 0.1 parts of a modified silicone defoaming agent, 0.1 parts of a fungicide, 0.5 parts of triethanolamine, and 60.9 parts of water.

[0082] Manufacturing of writing instruments (see Figure 5) The ink 2 is suction-filled into a polypropylene resin pipe (ink storage tube 3), and connected to a ballpoint pen tip 5 holding a 0.5 mm stainless steel ball at its tip via a resin relay member 4 (holder). Next, an ink backflow prevention device (liquid stopper) was filled into the rear end of the polypropylene pipe, and then a tail plug was fitted to the rear of the pipe to create a refill. The refill was incorporated into the barrel 9 to obtain a writing instrument 1 (retractable ballpoint pen). Furthermore, SEBS resin is provided as a friction member 11 at the tip of the shaft cylinder. The aforementioned retractable ballpoint pen has a structure in which the writing tip, provided on the ballpoint pen refill, is stored inside the barrel while exposed to the outside air, and the writing tip protrudes from the opening at the front of the barrel when a retractable mechanism (knock mechanism) provided at the rear end of the barrel is activated.

[0083] Making learning materials On a sheet made of synthetic paper, the words "Chemical formula for water" were printed using a blue screen printing ink consisting of 5 parts black pigment, 1 part viscosity modifier, 0.2 parts defoamer, and 93.8 parts water to form the problem display area. Next, using a reversible thermochromic screen printing ink consisting of 30 parts of the heat-activated reversible thermochromic pigment, 50 parts of acrylic resin emulsion (45% solids), 1 part of viscosity modifier, 0.2 parts of defoamer, and 18.8 parts of water, the chemical formula "H2O" was printed on the right side of the problem display area to form the answer display area (reversible thermochromic image) and thus a learning tool was obtained. Furthermore, a rectangular frame and the word "correct answer" are formed around the answer display area using the blue screen printing ink.

[0084] Making a thermochromic learning tool set A thermochromic learning tool set consisting of the aforementioned writing instrument and learning tool was obtained. After checking the problem display section of the learning aid, I used a writing instrument to write "H2O" as the answer to the problem on the learning aid (handwriting). The handwriting formed by the aforementioned writing instrument was maintained at room temperature (25°C). Next, by rubbing the answer display area with the friction element provided on the writing instrument, the heat-activated, reversible thermochromic pigment changed color, revealing the chemical formula "H2O," thus confirming the correct answer to the question. Furthermore, the answer display area fades and becomes invisible when left at room temperature (25°C), and the "H2O" writing also fades and becomes invisible when rubbed with a friction material. This state is maintained at room temperature (25°C), so the learning tool returns to its initial state, allowing for repeated learning using a writing instrument.

[0085] Example 4 Manufacturing of writing instruments The thermochromic writing instrument ink composition obtained in Example 1 (pre-cooled to -20°C or below to develop a reversible thermochromic pigment that turns blue when heated) was suction-filled into a polypropylene resin pipe (ink storage tube), and connected to a ballpoint pen tip holding a 0.5 mm stainless steel ball at its tip via a resin relay member (holder). Next, an ink backflow prevention body (liquid stopper) was filled into the rear end of the polypropylene pipe, and a tail plug was fitted to the rear of the pipe to form a refill. Furthermore, the refill was assembled into the barrel (consisting of a front barrel and a rear barrel), a cap was fitted, and then degassed by centrifugal treatment to obtain a writing instrument (ballpoint pen).

[0086] Making a thermochromic learning tool set A thermochromic learning tool set was obtained by combining the aforementioned writing instrument, the learning tool obtained in Example 1, and a friction body made of SEBS resin. After checking the problem display section of the learning tool, I used a writing instrument to write the number "4" as the answer to the problem on the learning tool (handwriting). The handwriting formed by the aforementioned writing instrument was maintained at room temperature (25°C). Next, by rubbing the answer display area with a friction tool, the heat-activated, reversible thermochromic pigment changed color, revealing the number "4," thus confirming the correct answer to the question. Furthermore, the answer display area fades and becomes invisible when left at room temperature (25°C), and the handwriting of the number "4" also fades and becomes invisible when rubbed with the friction material. This state is maintained at room temperature (25°C), so the learning tool returns to its initial state, allowing for repeated learning using a writing instrument.

[0087] Example 5 Making learning materials A booklet-type learning tool was obtained by gluing together one side of the learning tool obtained in Example 1 and the learning tool obtained in Example 2.

[0088] Making a thermochromic learning tool set A thermochromic learning tool set was obtained by combining the aforementioned learning tool with the writing instrument obtained in Example 1. After checking the problem display section of the learning tool, the student used a writing instrument to write a number as the answer to the problem on the learning tool (handwriting). The handwriting formed by the aforementioned writing instrument was maintained at room temperature (25°C). Next, by rubbing the answer display area with the friction element provided on the writing instrument, the heat-activated, reversible thermochromic pigment changes color, revealing a number and allowing the user to confirm the correct answer to the question. Furthermore, the answer display area fades and becomes invisible when left at room temperature (25°C), and the handwriting also fades and becomes invisible when rubbed with the friction material. This state is maintained at room temperature (25°C), so the learning tool returns to its initial state, allowing for repeated learning using a writing instrument. [Explanation of symbols]

[0089] t1 Complete color development temperature of a reversible thermochromic composition that decolorizes when heated t2: Onset temperature of color development for reversible thermochromic composition that decolorizes by heating. t3 Decolorization start temperature of a reversible thermochromic composition that decolorizes by heating Complete decolorization temperature of a reversible thermochromic composition of the t4 heat-decolorizing type. Complete decolorization temperature of a T1 heat-activated, reversible thermochromic composition Decolorization onset temperature of a T2 heat-activated, reversible thermochromic composition T3 heat-activated reversible thermochromic composition color development start temperature Complete color development temperature of T4 heat-activated reversible thermochromic composition ΔH Hysteresis width 1 writing implements 2 inks 3 ink storage tubes 4. Intermediate members 5 chips 6. Ink backflow prevention element 7. Tail plug 8 refills 9 Shaft tube 10 caps 11 Friction members 12 Ink absorber 13 Learning Tools 14 sheets 15 Question display area 16 Answer display area 17 Handwriting

Claims

1. A learning tool set comprising a writing instrument containing a thermochromic writing instrument ink composition that includes a heat-decolorizing reversible thermochromic pigment, which changes from a colored state to a colorless state upon heating, and maintains the colorless state at room temperature, and a learning sheet having a problem display section and an answer display section corresponding to the problem display section on its surface, wherein the answer display section contains a heat-developing reversible thermochromic pigment, which changes from a colorless state to a colored state upon heating, and from a colored state to a colorless state upon cooling.

2. The heat-decoloring type reversible thermochromic pigment and the heat-coloring type reversible thermochromic pigment are microcapsule pigments that exhibit hysteresis characteristics with respect to the color density-temperature curve of a reversible thermochromic composition comprising at least (a) an electron-donating color-forming organic compound, (b) an electron-accepting compound, and (c) a reaction medium that controls the color-forming reaction of (a) and (b), and are encapsulated in microcapsules and exhibit mutability between a colored state and a colorless state. In the process of the temperature rising from the colored state, the heat-decoloring type reversible thermochromic pigment starts to decolor when the temperature reaches t ３ and becomes completely colorless in the temperature range above t ４ . In the process of the temperature dropping from the colorless state, it starts to color when the temperature reaches t ２ and becomes completely colored in the temperature range below t １ . It shows hysteresis characteristics in which the colored state and the colorless state are selectively maintained in the temperature range between the temperature t ２ and the temperature t ３ . The temperature t １ is in the range of -50 to 5°C, and the temperature t ４ is in the range of 40 to 95°C. In the process of the temperature rising from the colorless state, the heat-coloring type reversible thermochromic pigment starts to color when the temperature reaches T ３ and becomes completely colored at a temperature above T ４ . In the process of the temperature dropping from the colored state, it starts to decolor when the temperature reaches T ２ and becomes completely colorless when the temperature reaches T １ . The temperature T ４ is in the range of 40 to 95°C, and the temperature T １ is a temperature exceeding 20°C. The thermochromic learning tool set according to claim 1.

3. A thermochromic learning tool set according to claim 1 or 2, comprising a friction element.

4. A thermochromic learning tool set according to claim 1 or 2, wherein the writing instrument is equipped with a friction member.

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