Ink composition for thermochromatic writing instrument and writing instrument accommodating the same

Abstract

To provide: an ink composition for a thermochromatic writing instrument by which it is difficult to visually recognize a discolored handwriting in addition to convenience that it is possible to form a handwriting while visually observing the handwriting, and it is possible to confirm a history of the handwriting after discoloring the handwriting by ultraviolet irradiation; and a writing instrument accommodating the ink composition for the thermochromatic writing instrument.SOLUTION: An ink composition for a thermochromatic writing instrument contains a medium, a thermochromatic material that discolors from colored to colorless, and a fluorescent material that emits fluorescence under irradiation of ultraviolet light. A writing instrument 1 accommodates the ink composition for the thermochromatic writing instrument.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to an ink composition for a thermochromic writing instrument and a writing instrument containing the same. More specifically, the present invention relates to an ink composition for a thermochromic writing instrument capable of confirming the history of writing and a writing instrument containing the same.

Background Art

[0002] Conventionally, there has been disclosed an aqueous ink composition for a writing instrument containing a microcapsule pigment in which a reversible thermochromic composition composed of at least (a) an electron-donating color-forming organic compound, (b) an electron-accepting compound, and (c) a reaction medium for controlling the color-forming reaction of (a) and (b) is encapsulated in microcapsules, and a fluorescent brightening agent (see, for example, Patent Document 1). The handwriting obtained by a writing instrument containing the ink composition can be decolorized by heating, is not visible under sunlight or indoor light, and emits light by ultraviolet irradiation, so that the history of the handwriting can be confirmed, and it can be used for security purposes such as forgery prevention and password, and for memorization and play. However, since the fluorescent brightening agent exhibits white color, the decolorized handwriting written on paper other than white is always visible, which causes problems in the above-mentioned use for confirming the history.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide an ink composition for a thermochromic writing instrument that can form handwriting while confirming the handwriting because the handwriting can be visually observed in a normal use state, and that can confirm the history of the handwriting by ultraviolet irradiation when the handwriting is decolorized, and a writing instrument containing the same.

Means for Solving the Problem

[0005] The present invention requires an ink composition for a thermochromic writing instrument containing a medium, a thermochromic material that changes color from colored to colorless, and a fluorescent substance that emits fluorescence when irradiated with ultraviolet light. Furthermore, the thermochromic material is at least a reversible thermochromic composition composed of (a) an electron-donating color-forming organic compound, (b) an electron-accepting compound, and (c) a reaction medium that controls the color-forming reaction between (a) and (b), encapsulated in microcapsules to form a microcapsule pigment. The pigment exhibits hysteresis characteristics with respect to the color density-temperature curve, shows the interconvertibility between the colored state and the colorless state, and the retention temperature ranges of both states are in the normal temperature range. When the temperature rises from the colored state, the pigment starts to decolorize when it reaches temperature t3, and becomes completely colorless in the temperature range of temperature t4 or higher, which is higher than temperature t3. When the temperature drops from the colorless state, the pigment starts to color when it reaches temperature t2, which is lower than temperature t3, and becomes completely colored in the temperature range of temperature t1 or lower, which is lower than temperature t2. The pigment shows hysteresis characteristics in which the colored state and the colorless state are selectively retained in the temperature range between temperature t2 and temperature t3. Temperature t1 is in the range of -50 to 5 °C, and temperature t4 is in the range of 40 to 95 °C. The fluorescent substance is encapsulated in microcapsules to form a microcapsule pigment, or resin particles in which the fluorescent substance is dispersed in a thermoplastic or thermosetting resin are used, etc. are required. Furthermore, a writing instrument containing the ink composition for a thermochromic writing instrument, a writing instrument provided with a friction member, etc. are required.

Advantages of the Invention

[0006] The present invention can provide an ink composition for a thermochromic writing instrument and a writing instrument containing the same, which are rich in practicality. In addition to the convenience of being able to form handwriting while visually observing it, the decolored handwriting is difficult to visually recognize, and the history of the handwriting can be confirmed by ultraviolet irradiation after the handwriting is decolorized.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0008] As the thermochromic material, an inorganic material such as Ag2HgI4 or Cu2HgI4, a liquid crystal, a heat - decoloring type reversible thermochromic material containing three components of an electron - donating color - forming organic compound, an electron - accepting compound, and an organic compound medium that reversibly causes the color - forming reaction between the two, or a heat - coloring type reversible thermochromic material containing three components of an electron - donating color - forming organic compound, an electron - accepting compound, and an organic compound medium that reversibly causes the color - forming reaction between the two is used. Among them, a reversible thermochromic material containing an electron - donating color - forming organic compound, an electron - accepting compound, and an organic compound medium that reversibly causes the color - forming reaction between the two will be described. The reversible thermochromic material includes at least three essential components of (a) an electron - donating color - forming organic compound, (b) an electron - accepting compound, and (c) a reaction medium that determines the color - forming temperature of the two, which is a heat - decoloring type (decolors upon heating and colors upon cooling) reversible thermochromic composition. As the reversible thermochromic composition, those described in Japanese Patent Publication No. Sho 51-44706, Japanese Patent Publication No. Sho 51-44707, Japanese Patent Publication No. Hei 1-29398, etc. change color before and after a predetermined temperature (color change point). In the temperature range above the high-temperature-side color change point, it shows a decolorized state, and in the temperature range below the low-temperature-side color change point, it shows a colored state. Among these two states, only a specific one exists at room temperature, and the other state is maintained while heat or thermo-cold applied to develop the state is being applied, but returns to the state presented at room temperature when the application of heat or thermo-cold stops. A heat-decolorizing type (decolorizes by heating and colors by cooling) reversible thermochromic composition having a relatively small characteristic of hysteresis width (ΔH = 1 to 7 °C) can be applied (see Figure 1).

[0009] Also, a heat-decolorizing type (decolorizes by heating and colors by cooling) reversible thermochromic composition described in Japanese Patent Publication No. Hei 4-17154, Japanese Patent Laid-Open No. Hei 7-179777, Japanese Patent Laid-Open No. Hei 7-33997, Japanese Patent Laid-Open No. Hei 8-39936, Japanese Patent Laid-Open No. 2005-1369, Japanese Patent Laid-Open No. 2008-280523, etc., showing a relatively large characteristic of hysteresis width (ΔH) of 8 °C to 80 °C, that is, the shape of the curve plotting the change in coloring density due to temperature change varies greatly depending on whether the temperature is increased from the low-temperature side of the color change temperature range or decreased from the high-temperature side of the color change temperature range. A colored state in a low-temperature range below the complete coloring temperature (t1) or a decolorized state in a high-temperature range above the complete decolorizing temperature (t4) has color memory in a specific temperature range [temperature range between t2 and t3 (substantially two-phase holding temperature range)] can also be applied (see Figure 2).

[0010] The hysteresis characteristics in the color density-temperature curve of the reversible thermochromic composition will be described. In FIG. 2, the vertical axis represents color density and the horizontal axis represents temperature. The change in color density due to temperature change proceeds along the arrow. Here, A is a point indicating the density at temperature t4 (hereinafter referred to as the complete decolorization temperature) at which the complete decolorization state is reached, B is a point indicating the density at temperature t3 (hereinafter referred to as the decolorization start temperature) at which decolorization starts, C is a point indicating the density at temperature t2 (hereinafter referred to as the color development start temperature) at which color development starts, and D is a point indicating the density at temperature t1 (hereinafter referred to as the complete color development temperature) at which the complete color development state 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, where there is a large difference in color density, is the substantial discoloration temperature range. Also, the length of line segment EF is a measure indicating the contrast of discoloration, and the length of line segment HG passing through the midpoint of line segment EF is the temperature width indicating the degree of hysteresis (hereinafter referred to as the hysteresis width ΔH). When this ΔH value is small, only a specific one of the two states in the normal temperature range can exist before and after discoloration. Also, when 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, 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 makes it easier to maintain the discolored state in the normal temperature range.

[0011] The components (a), (b), and (c) contained in the reversible thermochromic composition will be specifically described below. The component (a), i.e., the electron-donating color-forming organic compound, is a component that determines color and is a compound that donates electrons to the component (b), which is a developer, and develops color. Examples of the electron-donating color-forming organic compound include phthalide compounds, fluoran compounds, styrylnaphthyridine compounds, diazolidinone compounds, pyridine compounds, quinazoline compounds, bisquinazoline compounds, etc. Among these, phthalide compounds, fluoran compounds, styrylnaphthyridine compounds, and diazolidinone compounds are preferred. Examples of the phthalide compound include diphenylmethane phthalide compounds, phenylindolyl phthalide compounds, indolyl phthalide compounds, diphenylmethane azaphthalide compounds, phenylindolyl azaphthalide compounds, and their derivatives. Among these, phenylindolyl azaphthalide compounds and their derivatives are preferred. These compounds are exemplified 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-diethylaminofluorane, 2-(3-Trifluoromethylanilino)-6-dipentylaminofluorane, 2-(Dibenzylamino)-6-diethylaminofluorane, 2-(N-Methylanilino)-6-(N-ethyl-N-p-tolylamino)fluorane, 1,3-Dimethyl-6-diethylaminofluorane, 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-N-p-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-N-i-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-indol-3-yl)-1(3H)-isobenzofuranone 4,5,6,7-Tetrachloro-3-[4-(diethylamino)-2-ethoxyphenyl]-3-(1-ethyl-2-methyl-1H-indol-3-yl)-1(3H)-isobenzofuranone 4,5,6,7-Tetrachloro-3-[4-(diethylamino)-2-ethoxyphenyl]-3-(1-pentyl-2-methyl-1H-indol-3-yl)-1(3H)-isobenzofuranone 4,5,6,7-Tetrachloro-3-[4-(diethylamino)-2-methylphenyl]-3-(1-ethyl-2-methyl-1H-indol-3-yl)-1(3H)-isobenzofuranone 3′,6′-Bis[phenyl(2-methylphenyl)amino]-spiro[isobenzofuran-1(3H),9′-[9H]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-methoxy-quinazoline, 4,4′-(ethylenedioxy)-bis[2-(4-diethylaminophenyl)quinazoline] etc. can be mentioned. In addition, as fluorans, in addition to the above-mentioned compounds having a substituent on the phenyl group forming the xanthene ring, compounds having a substituent on the phenyl group forming the xanthene ring and also having a substituent (for example, an alkyl group such as a methyl group, a halogen atom such as a chloro group) on the phenyl group forming the lactone ring, which exhibit blue or black, may also be used.

[0012] The component (b), i.e., the electron-accepting compound, is a compound that receives electrons from the component (a) and functions as a color former for the component (a). Examples of the electron-accepting compound include compounds selected from the group of compounds having an active proton and their derivatives, the group of pseudo-acidic compounds (compounds that are not acids but act as acids in the composition to cause the component (a) to develop color), the group of compounds having an electron hole, etc. Among these, compounds selected from the group of compounds having an active proton are preferred. Examples of the compound having an active proton and its derivatives include compounds having a phenolic hydroxyl group 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, and azole-based compounds and their derivatives, 1,2,3-triazoles and their derivatives. Among these, compounds having a phenolic hydroxyl group are preferred because they can exhibit effective thermochromic properties. The compounds having phenolic hydroxyl groups widely include from monophenol compounds to polyphenol compounds, and further include bis-type, tris-type phenols, etc. and phenol-aldehyde condensation resins, etc. Among the compounds having phenolic hydroxyl groups, those having at least two benzene rings are preferred. Further, these compounds may have substituents, and examples of the substituents include an alkyl group, an aryl group, an acyl group, an alkoxycarbonyl group, a carboxy group and its ester or amide group, a halogen group, etc. Examples of the metal contained 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, etc.

[0013] Specific examples are given below. Phenol, o - Cresol, Tertiary Butyl Catechol, 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 - Dihydroxydiphenyl Sulfone, Bis(4 - hydroxyphenyl) Sulfide, 1,1 - Bis(4 - hydroxyphenyl) Ethane, 1,1 - Bis(4 - hydroxyphenyl) Propane, 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) - 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) 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, 2,2-Bis(4-hydroxyphenyl)ethyl propionate, 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, 3,3-bis(3-methyl-4-hydroxyphenyl)butane, etc. The compound having the phenolic hydroxyl group can exhibit the most effective thermochromic properties, but it may also be a compound selected from aromatic carboxylic acids, aliphatic carboxylic acids having 2 to 5 carbon atoms, metal carboxylates, acidic phosphate esters and their metal salts, 1, 2, 3-triazole and its derivatives.

[0014] The component (c) of the reaction medium that reversibly causes the electron transfer reaction between the components (a) and (b) in a specific temperature range will be described. Examples of the component (c) include alcohols, esters, ketones, ethers, and acid amides. When applying the component (c) to microencapsulation and secondary processing described later, low molecular weight compounds are likely to evaporate outside the capsules when subjected to high heat treatment. Therefore, compounds having 10 or more carbon atoms are preferably used to stably retain them inside the capsules. As the alcohols, aliphatic monohydric saturated alcohols having 10 or more carbon atoms are effective. Specifically, decyl alcohol, undecyl alcohol, dodecyl alcohol, tridecyl alcohol, tetradecyl alcohol, pentadecyl alcohol, hexadecyl alcohol, heptadecyl alcohol, octadecyl alcohol, eicosyl alcohol, docosyl alcohol, etc. can be mentioned.

[0015] As esters, esters having 10 or more carbon atoms are effective, and include esters obtained from any combination of monocarboxylic acids having an aliphatic, alicyclic or aromatic ring and monohydric alcohols having an aliphatic, alicyclic or aromatic ring, esters obtained from any combination of polycarboxylic acids having an aliphatic, alicyclic or aromatic ring and monohydric alcohols having an aliphatic, alicyclic or aromatic ring, and esters obtained from any combination of monocarboxylic acids having an aliphatic, alicyclic or aromatic ring and polyhydric alcohols having an aliphatic, alicyclic or aromatic ring. Specifically, ethyl caprylate, octyl caprylate, stearyl caprylate, myristyl capric acid, docosyl capric acid, 2-ethylhexyl laurate, n-decyl laurate, 3-methylbutyl myristate, myristyl myristate, cetyl myristate, isopropyl palmitate, neopentyl palmitate, nonyl palmitate, cyclohexyl palmitate, n-butyl stearate, 2-methylbutyl stearate, 3,5,5-trimethylhexyl stearate, n-undecyl stearate, pentadecyl stearate, stearyl stearate, cyclohexylmethyl stearate, isopropyl behenate, hexyl behenate, lauryl behenate, behenyl behenate, cetyl benzoate, stearyl p-tert-butylbenzoate, dimyristyl phthalate, distearyl phthalate, dimyristyl oxalate, dicitrate oxalate, dicetyl malonate, dilauryl succinate, dilaury glutamate, diundecyl adipate, dilaury azelate, di-(n-nonyl) sebacate, di-neopentyl 1,18-octadecylmethylenedicarboxylate, ethylene glycol dimyristate, propylene glycol dilaurate, propylene glycol distearate, hexylene glycol dipalmitate, 1,5-pentanediol distearate, 1,2,6-hexanetriol trimyristate, 1,4-cyclohexanediol didecyl, 1,4-cyclohexanedimethanol dimyristate, xylene glycol dicaprinate, xylene glycol distearate, etc. are included.

[0016] Also effective are ester compounds selected from esters of saturated fatty acids and branched aliphatic alcohols, esters of unsaturated fatty acids or saturated fatty acids having a branch or substituent and aliphatic alcohols that are branched or have 16 or more carbon atoms, cetyl butyrate, stearyl butyrate, and behenyl butyrate. Specifically, 2-ethylhexyl butyrate, 2-ethylhexyl behenate, 2-ethylhexyl myristate, 2-ethylhexyl capric acid, 3,5,5-trimethylhexyl laurate, 3,5,5-trimethylhexyl palmitate, 3,5,5-trimethylhexyl stearate, 2-methylbutyl caproate, 2-methylbutyl caprylate, 2-methylbutyl capric acid, 1-ethylpropyl palmitate, 1-ethylpropyl stearate, 1-ethylpropyl behenate, 1-ethylhexyl laurate, 1-ethylhexyl myristate, 1-ethylhexyl palmitate, 2-methylpentyl caproate, 2-methylpentyl caprylate, 2-methylpentyl capric acid, 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 capric acid, 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, 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, behenyl butyrate, etc. can be mentioned.

[0017] Furthermore, in order to discolor while showing large hysteresis characteristics with respect to the color density-temperature curve and impart color memory depending on temperature change, a carboxylic acid ester compound showing a ΔT value (melting point - cloud point) of 5°C or more and less than 50°C described in Japanese Patent Publication No. 4-17154, for example, a carboxylic acid ester containing a substituted aromatic ring in the molecule, an ester of a carboxylic acid containing an unsubstituted aromatic ring and an aliphatic alcohol having 10 or more carbon atoms, a carboxylic acid ester containing a cyclohexyl group in the molecule, an ester of a fatty acid having 6 or more carbon atoms and an unsubstituted aromatic alcohol or phenol, an ester of a fatty acid having 8 or more carbon atoms and a branched aliphatic alcohol, an ester of a dicarboxylic acid and an aromatic alcohol or a branched aliphatic alcohol, dibenzyl cinnamate, heptyl stearate, didecyl adipate, dilauryl adipate, dimyristyl adipate, dicetyl adipate, distearyl adipate, trilaurin, trimyristin, tristearin, dimyristin, distearin and the like can be mentioned.

[0018] A fatty acid ester compound obtained from an odd-numbered aliphatic monohydric alcohol having 9 or more carbon atoms and an aliphatic carboxylic acid having an even number of carbon atoms, and a fatty acid ester compound having a total carbon number of 17 to 23 obtained from n-pentyl alcohol or n-heptyl alcohol and an even-numbered aliphatic carboxylic acid having 10 to 16 carbon atoms are also effective. Specifically, examples include 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 capric acid, n-nonyl capric acid, n-undecyl capric acid, n-tridecyl capric acid, n-pentadecyl capric acid, n-pentyl laurate, n-heptyl laurate, n-nonyl laurate, n-undecyl laurate, n-tridecyl laurate, n-pentadecyl laurate, n-pentyl myristate, n-heptyl myristate, n-nonyl myristate, 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-undecyl eicosanoate, n-tridecyl eicosanoate, n-pentadecyl eicosanoate, n-nonyl behenate, n-undecyl behenate, n-tridecyl behenate, n-pentadecyl behenate, and the like.

[0019] As the ketones, aliphatic ketones having 10 or more carbon atoms in total are effective, and examples include 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-henicosanone, 2-docosanone, laurone, stearone, and the like. Furthermore, arylalkyl ketones having a total carbon number of 12 to 24, such as n-octadecanophenone, n-heptadecanophenone, n-hexadecanophenone, n-pentadecanophenone, n-tetradecanophenone, 4-n-dodecylacetophenone, n-tridecanophenone, 4-n-undecylacetophenone, n-laurophenone, 4-n-decanoylacetophenone, n-undecanophenone, 4-n-nonylacetophenone, n-decanophenone, 4-n-octylacetophenone, n-nonanophenone, 4-n-heptylacetophenone, n-octanophenone, 4-n-hexylacetophenone, 4-n-cyclohexylacetophenone, 4-tert-butylpropiophenone, n-heptaphenone, 4-n-pentylacetophenone, cyclohexyl phenyl ketone, benzyl-n-butyl ketone, 4-n-butylacetophenone, n-hexanophenone, 4-isobutylacetophenone, 1-acetonaphthone, 2-acetonaphthone, cyclopentyl phenyl ketone, etc. may be mentioned.

[0020] As the ethers, aliphatic ethers having a total carbon number of 10 or more 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, undecanediol diethyl ether, etc.

[0021] Examples of acid amides include acetamide, propionamide, butyramide, caproamide, caprylamide, capric amide, lauric amide, myristic amide, palmitic amide, stearic amide, behenic amide, oleic amide, erucic amide, benzamide, caproanilide, caprylanilide, capric anilide, lauric anilide, myristic anilide, palmitic anilide, stearic anilide, behenic anilide, oleic anilide, erucic anilide, N-methylcaproamide, N-methylcaprylamide, N-methylcapric amide, N-methyllauramide, N-methylmyristamide, N-methylpalmitamide, N-methylstearamide, N-methylbehenamide, N-methyloleamide, N-methylierucamide, N-ethyllauramide, N-ethylmyristamide, N-ethylpalmitamide, N-ethylstearamide, N-ethyloleamide, N-butyllauramide, N-butylmyristamide, N-butylpalmitamide, N-butylstearamide, N-butyloleamide, N-octyllauramide, N-octylmyristamide, N-octylpalmitamide, N-octylstearamide, N-octyloleamide, N-dodecyllauramide, N-dodecylmyristamide, N-dodecylpalmitamide, N-dodecylstearamide, N-dodecyloleamide, dilauric amide, dimyristic amide, dipalmitic amide, distearic amide, dioleic amide, trilauric amide, trimyristic amide, tripalmitic amide, tristearic amide, trioleic amide, succinamide, adipamide, glutaramide, malonamide, azelaic amide, maleic amide, N-methylsuccinamide, N-methyladipamide, N-methylglutaramide, N-methylmalonamide, N-methylazelaic amide, N-ethylsuccinamide, N-ethyladipamide, N-ethylglutaramide, N-ethylmalonamide, N-ethylazelaic amide, N-butylsuccinamide,Examples include N-butyl adipamide, N-butyl glutarate, N-butyl malonate, N-octyl adipamide, N-dodecyl adipamide, and the like.

[0022] Further, as the component (c), a compound represented by the following general formula (1) can also be used. [Chemical formula] [In the formula, R1 represents a hydrogen atom or a methyl group, m represents an integer of 0 to 2, either one of X1 and X2 is -(CH2) n OCOR2 or -(CH2) n COOR2, the other represents a hydrogen atom, n represents an integer of 0 to 2, R2 represents an alkyl group or alkenyl group having 4 or more carbon atoms, Y1 and Y2 represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a methoxy group, or a halogen, and r and p represent an integer of 1 to 3. ] Among the compounds represented by the formula (1), when R1 is a hydrogen atom, a reversible thermochromic composition having a wider hysteresis width can be obtained, which is preferable. Further, when R1 is a hydrogen atom and m is 0, it is more preferable. Among the compounds represented by the formula (1), a compound represented by the following general formula (2) is more preferably used. [Chemical formula] In the formula, R represents an alkyl group or alkenyl group having 8 or more carbon atoms, preferably an alkyl group having 10 to 24 carbon atoms, more preferably an alkyl group having 12 to 22 carbon atoms. Specific examples of the compound 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.

[0023] Furthermore, as the component (c), a compound represented by the following general formula (3) can also be used.

Chemical formula

[0024] Furthermore, as the component (c), a compound represented by the following general formula (4) can also be used.

Chemical formula

[0025] Furthermore, a compound represented by the following general formula (5) can also be used as the component (c). [Chemical formula] (In the formula, R represents an alkyl group or alkenyl group having 1 to 21 carbon atoms, and n represents an integer of 1 to 3.) Examples of the compound 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, diesters of 1,4-bis(2-hydroxyethoxy)benzene and propionic acid, diesters of 1,4-bis(2-hydroxyethoxy)benzene and valeric acid, diesters of 1,4-bis(2-hydroxyethoxy)benzene and caproic acid, diesters of 1,4-bis(2-hydroxyethoxy)benzene and caprylic acid, diesters of 1,4-bis(2-hydroxyethoxy)benzene and capric acid, diesters of 1,4-bis(2-hydroxyethoxy)benzene and lauric acid, and diesters of 1,4-bis(2-hydroxyethoxy)benzene and myristic acid.

[0026] Furthermore, a compound represented by the following general formula (6) can also be used as the component (c).

Chemical formula

[0027] Furthermore, a compound represented by the following general formula (7) can also be used as the component (c).

Chemical formula

[0028] Furthermore, a compound represented by the following general formula (8) can also be used as the component (c).

Chemical formula

[0029] Furthermore, a compound represented by the following general formula (9) can also be used as the component (c). [Chemical formula] (In the formula, R represents any one of an alkyl group having 4 to 22 carbon atoms, an alkenyl group having 4 to 22 carbon atoms, a cycloalkylalkyl group, and a cycloalkyl group; X represents any one of a hydrogen atom, an alkyl group, an alkoxy group, and a halogen atom; Y represents any one of a hydrogen atom, an alkyl group, an alkoxy group, and a halogen atom; and n represents 0 or 1.) Examples of the compound include octyl p-hydroxybenzoate benzoate, decyl p-hydroxybenzoate benzoate, heptyl p-hydroxybenzoate p-methoxybenzoate, dodecyl p-hydroxybenzoate o-methoxybenzoate, and cyclohexylmethyl p-hydroxybenzoate benzoate.

[0030] Furthermore, a compound represented by the following general formula (10) can also be used as the component (c). [Chemical formula] (In the formula, R represents any one of 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, and an alkenyl group having 3 to 18 carbon atoms; X represents any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, and a halogen atom; Y represents any one of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a methoxy group, an ethoxy group, and a halogen atom.) Examples of the compound include nonyl p-hydroxybenzoate phenoxyethyl ether, decyl p-hydroxybenzoate phenoxyethyl ether, undecyl p-hydroxybenzoate phenoxyethyl ether, and dodecyl vanillate phenoxyethyl ether.

[0031] Furthermore, a compound represented by the following general formula (11) can also be used as the component (c). [Chemical formula] (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 of 1 to 3.) Examples of the compound 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.

[0032] Furthermore, a compound represented by the following general formula (12) can also be used as the component (c). [Chemical formula] (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 of 1 to 3.) Examples of the compound 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.

[0033] Furthermore, a specific alkoxyphenol compound having a linear or branched alkyl group with 3 to 18 carbon atoms can be used as the electron-accepting compound (Japanese Patent Application Laid-Open No. 11-129623, Japanese Patent Application Laid-Open No. 11-5973), a specific hydroxybenzoic acid ester can be used (Japanese Patent Application Laid-Open No. 2001-105732), or a gallic acid ester or the like can be used (Japanese Patent Publication No. 51-44706, Japanese Patent Application Laid-Open No. 2003-253149), and a heat-developing type (develops color upon heating and fades upon cooling) reversible thermochromic composition can also be applied (see Figure 3).

[0034] The ratio of each component of the reversible thermochromic composition depends on the concentration, the color-changing temperature, the color-changing form, and the types of each component. Generally, the component ratio at which desired properties can be obtained is in the range of (i) 1 part by mass of component 1, (ii) 0.1 to 100 parts by mass, preferably 0.1 to 50 parts by mass, more preferably 0.5 to 20 parts by mass of component 2, and (iii) 1 to 800 parts by mass, preferably 5 to 200 parts by mass, more preferably 10 to 100 parts by mass of component 3 (all of the above ratios are in parts by mass).

[0035] Furthermore, various light stabilizers can be added as needed. The light stabilizer is contained to prevent photo-degradation of the reversible thermochromic composition composed of components (i), (ii), and (iii), and is contained in a ratio of 0.3 to 24% by mass, preferably 0.3 to 16% by mass, based on 1% by mass of component 1. Among the light stabilizers, the ultraviolet absorber effectively cuts off the ultraviolet rays contained in sunlight and the like, and prevents photo-degradation caused by the excited state due to the photoreaction of component (i). Also, antioxidants, singlet oxygen quenchers, superoxide anion quenchers, ozone quenchers, etc. suppress the oxidation reaction by light. The light stabilizer may be used alone or in combination of two or more.

[0036] The reversible thermochromic composition can be encapsulated in microcapsules and used as a reversible thermochromic microcapsule pigment, or dispersed in a thermoplastic or thermosetting resin and used as reversible thermochromic resin particles. Note that microencapsulation methods include known interfacial polymerization, in-situ polymerization, in-liquid hardening coating, phase separation from aqueous solutions, phase separation from organic solvents, melt dispersion cooling, air suspension coating, spray drying, etc., which are appropriately selected according to the application. Furthermore, a secondary resin film can be provided on the surface of the microcapsules according to the purpose to impart durability or modify the surface properties for practical use. Examples of the resin constituting the microcapsules include urea resin, urethane resin, ureaurethane resin, epoxy resin, melamine resin, benzoguanamine resin, isocyanate resin, etc. The microcapsule pigment preferably has a mass ratio of inclusion / wall film in the range of 7 / 1 to 1 / 1. When the ratio of the wall film is within the above range, it is possible to prevent a decrease in color density and vividness during color development. More preferably, the mass ratio of inclusion / wall film is 6 / 1 to 1 / 1. By encapsulating the microcapsules, a chemically and physically stable pigment can be formed.

[0037] The average particle diameter of the reversible thermochromic microcapsule pigment or reversible thermochromic resin particles is not particularly limited, but is preferably in the range of 0.1 to 5 μm, more preferably 0.3 to 5 μm, still more preferably 0.3 to 4 μm, and particularly preferably 0.5 to 3 μm. For the measurement of the average particle diameter, the particle region is determined using image analysis type particle size distribution measurement software [manufactured by Mountech Co., Ltd., product name: MacView], the equivalent diameter of the projection area circle (Heywood diameter) is calculated from the area of the particle region, and the value is measured as the average particle diameter of the particles equivalent to an equal-volume sphere. When the particle diameter of all or most of the particles exceeds 0.2 μm, it is also possible to measure the average particle diameter of the particles equivalent to an equal-volume sphere by the Coulter method using a particle size distribution measuring device [manufactured by Beckman Coulter, Inc., product name: Multisizer 4e]. Furthermore, based on the numerical values measured using the above-described software or the measuring device according to the Coulter method, the volume-based particle diameter and the average particle diameter may be measured using a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba, Ltd., product name: LA-960V2) that has been calibrated.

[0038] As the fluorescent substance, it is a substance that is colorless before being irradiated with ultraviolet light and emits light when irradiated with ultraviolet light. Examples of the fluorescent substance that emits light with ultraviolet light include ultraviolet fluorescent dyes and ultraviolet fluorescent pigments. Examples of the ultraviolet fluorescent dye include dyes such as fluorescein, coumarin-based, oxazole-based, pyrazoline-based, thiadiazole-based, spiropyran-based, pyrenesulfonic acid-based, benzimidazole-based, and diaminostilbene-based dyes. Examples of the ultraviolet fluorescent pigment include fluorescent substances activated with copper such as ZnS:Cu and ZnS:Cu,Al, fluorescent substances activated with silver such as (ZnCd)S:Ag+In2O3, fluorescent substances activated with gold such as ZnS:Au and ZnS:Au,Cu, fluorescent substances activated with manganese such as Zn2SiO4:Mn and Zn2SiO4:Mn,As, BaAl 12 O 19 :Mn, fluorescent substances activated with europium such as Sr5(PO4)3Cl:Eu, Y2O2S:Eu, Y2O3:Eu, YVO4:Eu, (Y,Gd)BO3:Eu, Sr5(PO4)3Cl:Eu, BaMgAl 10 O 17 :Eu, BaMgAl 14 O 23 :Eu, BaMg2Al 14 O 24 :Eu, BaMgAl 16 O 27 :Eu, fluorescent substances activated with terbium such as LaPO4:Tb, CeMgAl 11 O 19 :Tb, Gd2O2S:Tb, Y3Al5O 12 :Tb, fluorescent substances activated with cerium such as Y3Al5O 12 :Ce, Y2SiO3:Ce, Lu3Al5O 12:Inorganic UV fluorescent pigments include fluorescent substances activated with Ce and zinc such as ZnO:Zn, fluorescent substances composed of calcium sulfide activated with cadmium and bismuth, fluorescent substances composed of strontium sulfide activated with samarium, fluorescent substances composed of calcium tungstate activated with lead, and the like. The fluorescent substance is a substance that is colorless before being irradiated with ultraviolet rays and emits light when irradiated with ultraviolet rays. In the case of a fluorescent substance that also emits blue light, the history of the handwriting can also be confirmed by irradiating with light from a blue LED or the like. As the blue light, a light source with a peak emission wavelength in the range of 400 to 495 nm and mainly irradiating blue light is used.

[0039] In addition to containing the fluorescent substance in a medium, the fluorescent substance can be used as a fluorescent microcapsule pigment in which the fluorescent substance is encapsulated in microcapsules, or as fluorescent resin particles in which the fluorescent substance is uniformly or locally dispersed in a thermoplastic or thermosetting resin, or can be contained in a reversible thermochromic microcapsule pigment, or can be contained in the wall film of a reversible thermochromic microcapsule pigment. Note that the fluorescent microcapsule pigment in which the fluorescent substance is encapsulated in microcapsules has excellent dispersion stability in an ink using an aqueous medium. For microencapsulation, the same method as that for the reversible thermochromic microcapsule pigment can be used.

[0040] The content of the fluorescent substance is 0.01 to 30% by mass, preferably 0.05 to 20% by mass, more preferably 0.1 to 10% by mass in the total amount of the ink composition. If it is less than 0.01% by mass, when irradiating with light using an irradiator, the effect of confirming the history of the handwriting is poor, and even if an amount exceeding 30% by weight is added, the effect of confirming the history of the handwriting when irradiating with light using an irradiator cannot be further improved, so no further addition is required.

[0041] The medium is an organic solvent, water, water and a water-soluble organic solvent, and various additives can be added. As the organic solvent, general-purpose solvents applicable to oil-based inks can be used, but it is preferable to use a medium-boiling 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 the organic solvent within the 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, hexylene glycol, etc. In addition, as co-solvents, low-boiling 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, ethylene glycol monoethyl ether acetate, etc., and high-boiling solvents such as ethylene glycol monophenyl ether can be used. Examples of the water-soluble organic solvent 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, sulfolane, 2-pyrrolidone, N-methyl-2-pyrrolidone, and the like.

[0042] Examples of the ink composition for a thermochromic writing instrument comprising at least the thermochromic material, the fluorescent substance, and the medium include shear-thinning viscosity-imparting ink containing a shear-thinning viscosity-imparting agent, and cohesive ink in which a microcapsule pigment is suspended in a gently aggregated state by containing a water-soluble polymer flocculant.

[0043] By adding the shear-thinning viscosity-imparting agent, aggregation and sedimentation of the microcapsule pigment and resin particles can be suppressed, and bleeding of the handwriting can be suppressed, so that good handwriting can be formed. Furthermore, when the writing instrument filled with the ink is in the form of a ballpoint pen, ink leakage from the gap between the ball and the tip when not in use can be prevented, and backflow of the ink when the writing tip is left upward (in the upright state) can be prevented. Examples of the shear-thinning viscosity-imparting agent include xanthan gum, welan gum, succinoglycan (average molecular weight: about 1 million to 8 million) which is an organic acid-modified heteropolysaccharide whose constituent monosaccharides are glucose and galactose, guar gum, locust bean gum and its derivatives, hydroxyethyl cellulose, alkyl alginates, polymers with a molecular weight of 100,000 to 150,000 mainly composed of alkyl esters of methacrylic acid, glucomannan, thickening polysaccharides having a gelling ability extracted from seaweeds 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 alkyl phenyl ethers, nonionic surfactants with an HLB value of 8 to 12 such as fatty acid amides, salts of dialkyl or dialkenyl sulfosuccinic acid. Mixtures of N-alkyl-2-pyrrolidone and anionic surfactants, and mixtures of polyvinyl alcohol and acrylic resins can be exemplified.

[0044] Examples of the water-soluble polymer flocculant include polyvinyl pyrrolidone, polyethylene oxide, water-soluble polysaccharides and the like. Examples of the water-soluble polysaccharides include tragacanth gum, guar gum, pullulan, cyclodextrin, water-soluble cellulose derivatives and the like. Specific examples of the water-soluble cellulose derivatives include methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose and the like. In the ink composition of the present invention, any water-soluble polymer that exhibits a loose bridging action between the microcapsule pigment particles can be applied, and among them, water-soluble cellulose derivatives function effectively.

[0045] In addition, when a water-soluble resin is added, the adhesiveness and viscosity to the paper surface can be imparted. Examples of the water-soluble resin include alkyd resin, acrylic resin, styrene maleic acid copolymer, cellulose derivative, polyvinylpyrrolidone, polyvinyl alcohol, dextrin, etc. Polyvinyl alcohol is preferably used. Furthermore, as for the polyvinyl alcohol, a partially saponified polyvinyl alcohol having a saponification degree of 70 to 89 mol% is more preferably used because the ink is rich in solubility even in the acidic range. The addition amount of the water-soluble resin is added in the range of 0.3 to 3.0% by mass, preferably 0.5 to 1.5% by mass in the ink.

[0046] When the ink composition of the present invention is filled and used in a ballpoint pen, higher fatty acids such as oleic acid, nonionic surfactants having long-chain alkyl groups, polyether-modified silicone oils, tri(alkoxycarbonylmethyl esters) of thio-phosphorous acid, and lubricants such as tri(alkoxycarbonylethyl esters) of thio-phosphorous acid, phosphoric acid monoesters of polyoxyethylene alkyl ethers or polyoxyethylene alkyl aryl ethers, phosphoric acid diesters of polyoxyethylene alkyl ethers or polyoxyethylene alkyl aryl ethers, or their metal salts, ammonium salts, amine salts, alkanolamine salts, etc. are preferably added to prevent wear of the ball receiving seat. In addition, pH adjusters such as inorganic salts such as sodium carbonate, sodium phosphate, and sodium acetate, organic basic compounds such as water-soluble amine compounds, rust preventives such as benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, and saponin, phenol, sodium salt of 1,2-benzothiazolin-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine, etc. preservatives or fungicides, urea, nonionic surfactants, reducing or non-reducing starch hydrolyzates, oligosaccharides such as trehalose, sucrose, cyclodextrin, glucose, dextrin, sorbitol, mannitol, sodium pyrophosphate, etc. wetting agents, defoaming agents, dispersants, and fluorosurfactants or nonionic surfactants that improve the ink permeability may be added.

[0047] The ink is filled into writing instruments such as ballpoint pens and marking pens with a ballpoint pen tip or a marking pen tip attached to the writing tip portion for practical use.

[0048] When filling a ballpoint pen, the structure and shape of the ballpoint pen itself are not particularly limited. For example, an ink storage tube filled with shear-thinning ink in a shaft cylinder can be exemplified. The ink storage tube communicates with a tip having a ball attached to the tip portion, and a liquid plug for preventing backflow is in close contact with the end face of the ink.

[0049] More specifically, regarding the ballpoint pen tip, a tip that holds a ball in a ball holding portion obtained by pressing and deforming the vicinity of the tip of a metal pipe inward from the outer surface, or a tip that holds a ball in a ball holding portion formed by cutting a metal material with a drill or the like, a tip provided with a resin ball seat inside a metal or plastic tip, or a tip in which the ball held by the tip is biased forward by a spring body can be applied. Further, the ball can be made of cemented carbide, stainless steel, ruby, ceramic, resin, rubber, etc., with a diameter of about 0.3 to 3.0 mm, preferably 0.3 to 1.5 mm, more preferably 0.4 to 1.0 mm, and can be applied.

[0050] As the ink storage tube for storing the ink, for example, a molded body made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, nylon, etc. is used. In addition to directly connecting the tip to the ink storage tube, the ink storage tube and the tip may be connected via a connecting member. In addition, the ink storage tube may be in the form of a refill, and the refill may be housed in the shaft cylinder, or the shaft cylinder itself with a tip attached to the tip may be used as the ink storage body, and the ink may be directly filled into the shaft cylinder. The ballpoint pen obtained as described above may be a retractable ballpoint pen in addition to a ballpoint pen with a cap, and its shape is not particularly limited. The retractable ballpoint pen has a writing tip provided on the ballpoint pen refill housed in the shaft cylinder with the writing tip exposed to the outside air, and any structure can be used as long as the writing tip protrudes from the shaft cylinder opening by the operation of the retracting mechanism. Examples of the operation method of the retracting mechanism include a knock type, a rotary type, a slide type, etc. The knock type has a knock portion on the rear end portion or the side surface of the shaft cylinder, and by pressing the knock portion, the ballpoint pen tip is configured to protrude and retract from the front end opening of the shaft cylinder, or by pressing the clip portion provided on the shaft cylinder, the ballpoint pen tip is configured to protrude and retract from the front end opening of the shaft cylinder. The rotary type has a rotating portion on the rear portion of the shaft cylinder, and by rotating the rotating portion, the ballpoint pen tip is configured to protrude and retract from the front end opening of the shaft cylinder. The slide type has a slide portion on the side surface of the shaft cylinder, and by operating the slide, the ballpoint pen tip is configured to protrude and retract from the front end opening of the shaft cylinder, or by sliding the clip portion provided on the shaft cylinder, the ballpoint pen tip is configured to protrude and retract from the front end opening of the shaft cylinder.

[0051] An ink backflow prevention body can be filled at the rear end of the ink contained in the ink storage tube. The ink backflow prevention body composition consists of a non-volatile liquid or a hardly volatile liquid. Specifically, there are petrolatum, spindle oil, castor oil, olive oil, refined mineral oil, liquid paraffin, polybutene, α-olefin, oligomers or co-oligomers of α-olefin, dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, polyether-modified silicone oil, fatty acid-modified silicone oil, etc., and one kind or two or more kinds can be used in combination.

[0052] It is preferable to add a thickener to the non-volatile liquid and / or hardly volatile liquid to thicken it to a suitable viscosity. Examples of the thickener include silica with a hydrophobic surface treatment, fine particle silica with a methylated surface treatment, aluminum silicate, swelling mica, clay-based thickeners such as bentonite and montmorillonite with a hydrophobic treatment, fatty acid metal soaps such as magnesium stearate, calcium stearate, aluminum stearate, zinc stearate, tribenzylidene sorbitol, fatty acid amide, amide-modified polyethylene wax, hydrogenated castor oil, dextrin-based compounds such as fatty acid dextrin, and cellulose-based compounds. Furthermore, the liquid ink backflow prevention body and a solid ink backflow prevention body can also be used in combination.

[0053] When filling the ink composition into a marking pen, the structure and shape of the marking pen itself are not particularly limited. For example, an ink storage body composed of a fiber aggregate is built in a shaft cylinder, and a pen tip composed of a fiber processed body with a capillary gap formed is directly or via a relay member attached to the shaft cylinder, and the ink storage body of the marking pen in which the cohesive ink is impregnated in the ink storage body of the marking pen where the ink storage body and the pen tip are connected, or a marking pen in which the pen tip and the ink storage tube are arranged via a valve body that is opened by pressing the pen tip, and the ink is directly stored in the ink storage tube can be exemplified.

[0054] The pen tip is a porous member with communicating pores having a porosity generally selected from the range of 30 to 70%, such as a resin processed body of fibers, a fusion processed body of heat-meltable fibers, or a felt body. One end is processed into a shape according to the purpose, such as a bullet shape, a rectangular shape, or a chisel shape, and is put into practical use. The ink storage body is formed by converging crimped fibers in the longitudinal direction, and is incorporated in a covering body such as a plastic cylinder or a film, and is configured by adjusting the porosity to generally range from 40 to 90%. In addition, although a pumping type can be used for the valve body, it is preferably set to a spring pressure that can be pressed and opened by the pen pressure. The marking pen obtained as described above may be an emerging type marking pen in addition to a marking pen equipped with a cap, and its shape is not particularly limited.

[0055] Furthermore, the forms of the ballpoint pen and the marking pen are not limited to those described above, and may be a composite writing instrument (such as a double-headed type or a pen tip feeding type) with different forms of pen tips attached or pen tips for discharging inks of different color tones attached.

[0056] The handwriting formed by the writing instrument containing the ink composition can be discolored by friction with a finger or application of a friction body. As the friction body, an elastic body such as an elastomer or a plastic foam that is rich in elasticity and can generate appropriate friction and frictional heat during friction is suitable, but a plastic molded body, a stone material, a wood material, a metal material, or a fabric may also be used. Although it is also possible to rub the handwriting using an eraser, since eraser dust is generated during friction, preferably a friction body as described above is used. As the material of the friction body, a silicone resin or an SEBS resin (styrene-ethylene-butadiene-styrene block copolymer) of a styrene-based resin is preferably used. However, since the silicone resin tends to adhere to the portion erased by friction and the handwriting tends to be repelled when writing repeatedly, the SEBS resin is more preferably used. The friction member can be combined with a member (friction member) of an arbitrary shape separate from the writing instrument to obtain a writing instrument set. However, by fixing the friction member (friction member) to the writing instrument, it is excellent in portability. The location where the friction member is fixed is not particularly limited. However, in the case of a ballpoint pen equipped with a cap, it can be provided at the tip (top) of the cap or at the rear end of the shaft cylinder (the part where the writing tip is not provided). In the case of a retractable ballpoint pen, it can be provided at the tip of the shaft cylinder or at the rear end of the shaft cylinder. Furthermore, a small protrusion of an arbitrary shape can be provided on a part of the cap or a part of the shaft cylinder to serve as a friction member.

Example

[0057] Next, the ink composition for a thermochromic writing instrument of the present invention and the writing instrument containing the same will be described. In addition, the blending in the examples is shown in parts by mass. Example 1 Preparation of microcapsule pigment (A) As a component, 2.0 parts of 4,5,6,7-tetrachloro-3-[4-(dimethylamino)-2-methylphenyl]-3-(1-ethyl-2-methyl-1H-indol-3-yl)-1(3H)-isobenzofuranone, (B) As a component, 3.0 parts of 4,4′-(2-ethylhexane-1,1-diyl)diphenol, 5.0 parts of 2,2-bis(4′-hydroxyphenyl)-hexafluoropropane, (C) As a component, 50.0 parts of 4-benzyloxyphenylethyl caprate. A microcapsule pigment suspension containing a reversible thermochromic composition having color memory was obtained. The suspension was centrifuged to isolate the microcapsule pigment. The average particle diameter of the microcapsule pigment is 1.8 μm, the complete decoloring temperature is 55 °C, and the complete coloring temperature is -20 °C, and it reversibly changes color from blue to colorless with temperature change.

[0058] Preparation of ink composition for thermochromic writing instrument 10.0 parts of the microcapsule pigment, 2.5 parts of the fluorescent microcapsule pigment obtained by encapsulating Zn2SiO4:Mn as a fluorescent substance in microcapsules, 0.3 part of xanthan gum (shear-thinning viscosity-imparting agent), 10 parts of urea, 10 parts of glycerin, 0.5 part of a phosphate ester-based surfactant, 0.6 part of a nonionic penetrant, 0.1 part of a modified silicone-based defoaming agent, 0.1 part of a fungicide, 0.5 part of triethanolamine, and 55.4 parts of water were used to prepare an ink composition for a thermochromic writing instrument.

[0059] Production of the writing instrument (see Figure 2) The ink 2 (pre-cooled to -20°C or lower to cause the microcapsule pigment to develop a blue color) was suction-filled into a pipe (ink storage tube 3) made of polypropylene resin, and connected to a ball pen tip 5 holding a 0.5 mm stainless steel ball at the tip via a resin intermediate member 4 (holder). Next, an ink backflow preventer 6 (liquid plug) was filled from the rear end of the polypropylene pipe, and a tail plug 7 was further fitted to the rear part of the pipe to form a refill 8. Further, the refill was incorporated into a shaft cylinder 9 (composed of a front shaft cylinder and a rear shaft cylinder), and after fitting a cap 10, a degassing treatment was performed by centrifugation to obtain a writing instrument 1 (ball pen). Note that an SEBS resin is attached as a friction member 11 to the rear part of the rear shaft cylinder.

[0060] When writing on writing paper using the writing instrument, a blue handwriting could be formed, and the handwriting was maintained at room temperature (25°C). When the blue handwriting was rubbed with a friction body provided on the writing instrument, the blue handwriting disappeared, and this state was maintained at room temperature (25°C). When the area where the handwriting existed was irradiated with light using an ultraviolet irradiator, the erased handwriting emitted green light and could be visually recognized, and the history could be confirmed. Also, when irradiated with light using an irradiator that irradiates blue light using a blue LED, the erased handwriting emitted light and could be visually recognized, and the history could be confirmed.

[0061] Example 2 Preparation of the microcapsule pigment (A) component: 1.0 part of 2-(dibutylamino)-8-(dipentylamino)-4-methyl-spiro[5H-[1]benzopyrano[2,3-g]pyrimidine-5,1′(3′H)-isobenzofuran]-3-one; (B) component: 3.0 parts of 4,4′-(2-ethylhexane-1,1-diyl)diphenol, 5.0 parts of 2,2-bis(4′-hydroxyphenyl)-hexafluoropropane; (C) component: 50.0 parts of 4-benzyloxyphenylethyl capricate; and as the fluorescent substance, 1.0 part of BaMgAl 10 O 17 :Eu. A microcapsule pigment suspension encapsulating a reversible thermochromic composition having color memory was obtained. The suspension was centrifuged to isolate the microcapsule pigment. The average particle diameter of the microcapsule pigment is 2.3 μm, the complete decolorization temperature is 58°C, and the complete color development temperature is -20°C, and it reversibly changes color from pink to colorless with temperature change.

[0062] Preparation of Thermochromic Ink Composition for Writing Instruments A thermochromic ink composition for writing instruments was prepared from 12.5 parts of the microcapsule pigment, 0.3 part of succinoglycan (shear-thinning viscosity-imparting agent), 10 parts of urea, 10 parts of glycerin, 0.5 part of a phosphate ester surfactant, 0.6 part of a nonionic penetrant, 0.1 part of a modified silicone defoaming agent, 0.1 part of a fungicide, 0.5 part of triethanolamine, and 65.4 parts of water.

[0063] Manufacture of Writing Instrument (see Figure 2) The ink 2 (pre-cooled to -20°C or below to develop the microcapsule pigment into pink) was suction-filled into a pipe (ink storage tube 3) made of polypropylene resin and connected to a ball pen tip 5 holding a 0.5 mm stainless steel ball at the tip via a resin intermediate member 4 (holder). Next, an ink backflow prevention body 6 (liquid plug) was filled from the rear end of the polypropylene pipe, and a tail plug 7 was further fitted to the rear part of the pipe to form a refill 8. Further, the refill was incorporated into a shaft cylinder 9 (comprising a front shaft cylinder and a rear shaft cylinder), and after fitting a cap 10, a degassing treatment was performed by centrifugation to obtain a writing instrument 1 (ballpoint pen). Note that an SEBS resin is attached as a friction member 11 to the rear part of the rear shaft cylinder.

[0064] When writing on writing paper using the writing instrument, pink-colored handwriting could be formed, and the handwriting was retained at room temperature (25°C). When the pink-colored handwriting was rubbed with a friction body provided on the writing instrument, the handwriting was erased, and this state was retained at room temperature (25°C). When the area where the handwriting existed was irradiated with light using an ultraviolet irradiation tool, the erased handwriting emitted light in blue and could be visually recognized, and the history could be confirmed. Also, when irradiated with light using an irradiation tool that irradiates blue light using a blue LED, the erased handwriting emitted light and could be visually recognized, and the history could be confirmed.

[0065] Example 3 Preparation of microcapsule pigment A microcapsule pigment suspension containing a reversible thermochromic composition having color memory, which consists of 3.0 parts of 1,3-dimethyl-6-diethylaminofluorane as component (a), 3.0 parts of 4,4′-(2-ethylhexane-1,1-diyl)diphenol as component (b), 5.0 parts of 2,2-bis(4′-hydroxyphenyl)-hexafluoropropane, and 50.0 parts of 4-benzyloxyphenylethyl caprate as component (c), was obtained. The suspension was centrifuged to isolate the microcapsule pigment. The average particle diameter of the microcapsule pigment was 2.0 μm, the complete erasing temperature was 60°C, and the complete coloring temperature was -20°C, and it reversibly changed color from orange to colorless with temperature change.

[0066] Preparation of thermochromic writing ink composition 20.0 parts of the microcapsule pigment (pre-cooled to -20°C or lower and developed to an orange color), 1.0 part of fluorescent resin particles in which Y2O2S:Eu is dispersed in a resin as a fluorescent substance, 0.5 part of hydroxyethyl cellulose, 0.2 part of a comb-shaped polymer dispersant [manufactured by Nippon Lubrizol Corporation, trade name: Solsperse 43000], 1.0 part of an organic nitrogen-sulfur compound [manufactured by Hokusei Chemical Industry Co., Ltd., trade name: Hoksid R-150, a mixture of 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one], 0.5 part of polyvinyl alcohol, 25.0 parts of glycerin, 0.02 part of an antifoaming agent, and 51.78 parts of water were mixed to obtain an ink composition for a thermochromic writing instrument.

[0067] Production of a writing instrument (see Figure 5) The ink composition was impregnated into an ink reservoir 12 in which a polyester sliver was coated with a synthetic resin film, and the ink composition was housed in a shaft cylinder 9 made of polypropylene resin. A marking pen tip 5 (bullet type) made of polyester fiber was assembled in a connected state to the tip of the shaft cylinder via a relay member 4 (holder), and a cap 10 was attached to obtain a writing instrument 1 (marking pen). The cap was provided with an SEBS resin as a friction member 11 at the top.

[0068] When writing on writing paper using the writing instrument, an orange handwriting could be formed, and the handwriting was maintained at room temperature (25°C). When the orange handwriting was rubbed with a friction body provided on the writing instrument, the orange handwriting was erased, and this state was maintained at room temperature (25°C). When the location where the handwriting existed was irradiated with light using an ultraviolet irradiator, the erased handwriting emitted red light and was visually recognized, and the history could be confirmed. Also, when irradiated with light using an irradiator that irradiates blue light using a blue LED, the erased handwriting emitted light and was visually recognized, and the history could be confirmed.

[0069] Example 4 Preparation of microcapsule pigment As component (a), 2.0 parts of 4,5,6,7 - tetrachloro - 3 - [4 - (dimethylamino) - 2 - methylphenyl] - 3 - (1 - ethyl - 2 - methyl - 1H - indol - 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, and as component (c), 50.0 parts of 4 - benzyloxyphenylethyl caprate were used to obtain a microcapsule pigment suspension containing a reversible thermochromic composition having color memory properties. The suspension was centrifuged to isolate the microcapsule pigment. The average particle diameter of the microcapsule pigment was 1.8 μm, the complete decolorization temperature was 55°C, and the complete color development temperature was - 20°C. It reversibly changes color from blue to colorless with temperature changes.

[0070] Preparation of Ink Composition for Thermochromic Writing Instruments 20.0 parts of the microcapsule pigment, 2.0 parts of a fluorescent microcapsule pigment encapsulating Lu3Al5O 12 :Ce in microcapsules, 0.3 part of succinoglycan (shear - thinning viscosity - imparting agent), 10 parts of urea, 5 parts of glycerin, 0.5 part of a phosphate - ester - based surfactant, 0.6 part of a nonionic penetrant, 0.1 part of a modified silicone - based defoaming agent, 0.1 part of a fungicide, 0.5 part of triethanolamine, and 60.9 parts of water were used to prepare an ink composition for thermochromic writing instruments.

[0071] Production of Ball - Pen Refill The ink 2 (pre - cooled to - 20°C or lower to develop the microcapsule pigment into blue) was suction - filled into a pipe (ink - containing tube 3) made of polypropylene resin and connected to a ball - pen tip 5 holding a 0.5 - mm stainless - steel ball at the tip via a resin intermediate member 4 (holder). Next, an ink back - flow prevention body (liquid stopper) was filled from the rear end of the polypropylene pipe, and a tail stopper was further fitted to the rear part of the pipe to make a refill. The refill was incorporated into the barrel 9 to obtain a writing instrument 1 (retractable ballpoint pen) (see Fig. 6). Note that a SEBS resin is provided as the friction member 11 at the tip of the barrel. In the retractable ballpoint pen, the writing tip provided on the ballpoint pen refill is housed in the barrel with the tip exposed to the outside air, and the writing tip protrudes from the front end opening of the barrel by the operation of the retracting mechanism (knock mechanism) provided at the rear end of the barrel. When writing on writing paper with the ballpoint pen tip protruding from the front end opening of the barrel by operating the retracting mechanism of the writing instrument, a blue handwriting can be formed, and the handwriting was maintained at room temperature (25°C). Next, when the handwriting was rubbed with the friction body provided on the writing instrument with the ballpoint pen tip housed in the barrel by operating the retracting mechanism, the blue handwriting was erased, and this state was maintained at room temperature (25°C). When the area where the handwriting existed was irradiated with light using an ultraviolet irradiator, the erased handwriting emitted yellow light and was visible, and the history could be confirmed. Also, when irradiated with light using an irradiator that irradiates blue light using a blue LED, the erased handwriting emitted light and was visible, and the history could be confirmed.

Explanation of symbols

[0072] t1 Complete color development temperature of the heat-decolorizable reversible thermochromic composition t2 Color development start temperature of the heat-decolorizable reversible thermochromic composition t3 Decolorization start temperature of the heat-decolorizable reversible thermochromic composition t4 Complete decolorization temperature of the heat-decolorizable reversible thermochromic composition T1 Complete decolorization temperature of the heat-colorizable reversible thermochromic composition T2 Decolorization start temperature of the heat-colorizable reversible thermochromic composition T3 Color development start temperature of the heat-colorizable reversible thermochromic composition T4 Complete color development temperature of the heat-colorizable reversible thermochromic composition ΔH Hysteresis width 1 Writing instrument 2 Ink 3 Ink storage tube 4 Relay member 5 Chip 6 Ink backflow prevention body 7 Tail plug 8 Refill 9 Shaft cylinder 10 Cap 11 Friction member 12 Ink storage body

Claims

1. An ink composition for a thermochromic writing instrument, comprising a medium, a thermochromic material that changes color from colored to colorless, and a fluorescent substance that emits fluorescence when irradiated with ultraviolet light.

2. The thermochromic material is a microcapsule pigment in which 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) is encapsulated in microcapsules. The pigment exhibits hysteresis characteristics with respect to the color density-temperature curve and exhibits mutability between a colored state and a colorless state, and the holding temperature ranges of both states are both in the normal temperature range. In the process of the temperature rising from the colored state, when the temperature t ３ is reached, the decolorization starts, and when the temperature is higher than t ３ and reaches t ４ or higher, it completely becomes colorless. In the process of the temperature dropping from the colorless state, when the temperature is lower than t ３ and reaches t ２ , the coloring starts, and when the temperature is lower than t ２ and reaches t １ or lower, it completely becomes colored. The pigment exhibits hysteresis characteristics in which the colored state and the colorless state are selectively retained 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. The ink composition for a thermochromic writing instrument according to claim 1.

3. The ink composition for a thermochromic writing instrument according to claim 1 or 2, wherein the fluorescent substance is a microcapsule pigment encapsulated in microcapsules or resin particles in which the fluorescent substance is dispersed in a thermoplastic or thermosetting resin.

4. A writing instrument containing the ink composition for a thermochromic writing instrument according to claim 1 or 2.

5. The writing instrument according to claim 4, provided with a friction member.

Images