Reversible thermochromic aqueous ink composition for writing instruments and writing instruments containing the same

Abstract

To provide a reversible thermochromic aqueous ink composition for a writing instrument and a writing instrument using the same, capable of achieving excellent stability of a non thermochromic colorant, even when an excessive temperature change occurs on an ink composition, and capable of exhibiting a change of a color of a handwriting formed of a writing instrument using the ink composition before the temperature change occurs, from a chromatic color (1) to a chromatic color (2), and being excellent in practical utility, and to provide the writing instrument storing the same.SOLUTION: There is provided a reversible thermochromic aqueous ink composition for a writing instrument which includes at least: a reversible thermochromic micro capsule pigment which includes a reversible thermochromic composition formed of (a) an electron donative coloration organic compound, (b) an electron reception compound, and (c) a reaction medium determining an origination temperature of a color reaction of both the components (a) and (b); an acidic dye; and water, where, pH of the ink composition is in a range of 3-7. There is also provided the writing instrument storing the same.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a reversible thermochromic aqueous ink composition for writing instruments and a writing instrument containing the same. More specifically, the present invention relates to a reversible thermochromic aqueous ink composition for writing instruments in which the color of the writing formed by the writing instrument is hardly changed even against excessive temperature changes, and a writing instrument containing the same.

Background Art

[0002] Conventionally, a non-thermochromic colorant is blended in a reversible thermochromic ink in which a reversible thermochromic microcapsule pigment is dispersed in an aqueous medium or in a reversible thermochromic microcapsule pigment, and the reversible thermochromic microcapsule pigment is suspended in a gently aggregated state. An ink absorber composed of a fiber aggregate housed in a shaft cylinder is filled with an aggregated ink, and a writing instrument configured to be able to flow out by a fiber pen body composed of a fiber processed body is disclosed (for example, see Patent Document 1). The above writing instrument has good ink flowability and storage stability over time, and the reversible thermochromic microcapsule pigment reversibly changes color from the coloring state to the decoloring state due to temperature changes such as frictional heat by a friction body, and a colored (1) to a colored (2) can be formed. However, when an excessive temperature change occurs in the ink housed in the above writing instrument, the stability of the non-thermochromic colorant is impaired, and the color of the writing formed by the writing instrument changes, and the change from colored (1) to colored (2) shown by the writing before the temperature change may be difficult to appear. In particular, the color of the writing by only the non-thermochromic colorant, that is, the color of the writing when the reversible thermochromic microcapsule pigment is in the decoloring state may fade and become invisible.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention aims to provide a reversible thermochromic aqueous ink composition for writing instruments, which exhibits a change from colored (1) to colored (2) even when excessive temperature changes occur in the ink composition, and in which the color of the writing formed by the writing instrument does not easily change before and after temperature changes, and a writing instrument containing the same. [Means for solving the problem]

[0005] The present invention comprises at least a reversible thermochromic microcapsule pigment containing a reversible thermochromic composition comprising (a) an electron-donating color-developing organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color reaction between the two occurs, an acid dye, and water, wherein the pH of the ink composition is in the range of 3 to 7. Furthermore, it exhibits an intermutation color change from a color (1) which is a mixture of the color produced by the reversibly thermochromic microcapsule pigment and the color produced by the acid dye, to a color (2) which is produced solely by the acid dye. Reversible thermochromic water-based ink composition for writing instruments things The requirements are as follows: When P1 is the content of the reversible thermochromic microcapsule pigment relative to the total mass of the ink composition, and P2 is the content of the acid dye relative to the total mass of the ink composition, the relationship between P2 and P1 must satisfy 0.003 ≤ P2 / P1 ≤ 0.05, and the ink must contain a polymer flocculant and an acrylic polymer dispersant. Furthermore, the requirements include a writing instrument containing the ink composition. The requirements also include a friction member that changes the color of the writing made by the writing instrument due to frictional heat, a marking pen having a marking pen tip made of a resin processed body or resin molded body with capillary gaps formed therein, and a marking pen having an ink-absorbing body made of a fiber bundle inside the barrel, wherein the ink-absorbing body and the marking pen tip are connected, and the ink composition is impregnated into the ink-absorbing body. Furthermore, the requirement is a writing instrument set consisting of the aforementioned writing instrument and memo paper. In addition, the requirement is that the memo paper has a ToDo entry section and also has stickers. [Effects of the Invention]

[0006] The present invention provides a highly practical reversible thermochromic aqueous ink composition for writing instruments and a writing instrument containing the same, which exhibits excellent stability of the non-thermochromic colorant even when excessive temperature changes occur in the ink composition, and can produce a change from colored (1) to colored (2) in the handwriting formed by a writing instrument using the ink composition before the temperature change occurs. [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 decolorizes upon heating. [Figure 2] 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 3] This graph illustrates the hysteresis characteristics in the color density-temperature curve of a heat-activated, reversible thermochromic composition. [Modes for carrying out the invention]

[0008] The reversible thermochromic aqueous ink composition for writing instruments according to the present invention (hereinafter sometimes referred to as "ink composition" or "ink") consists of at least a reversible thermochromic microcapsule pigment, an acidic dye, and water, and the pH of the ink composition is in the range of 3 to 7. The components constituting the ink composition according to the present invention are described below.

[0009] The ink composition according to the present invention comprises, as a coloring agent, a reversible thermochromic microcapsule pigment (hereinafter sometimes referred to as "microcapsule pigment") containing a reversible thermochromic composition.

[0010] The reversible thermochromic composition comprises at least (a) an electron-donating chromogenic organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color reaction of component (a) and component (b) occurs. As a reversible thermochromic composition, you can use a reversible thermochromic composition of the heat-decolorizing type (decolorizes when heated and develops color when cooled) that has a relatively small hysteresis width (ΔH) (ΔH = 1 to 7°C), as described in Japanese Patent Publication No. 51-44706, Japanese Patent Publication No. 51-44707, Japanese Patent Publication No. 1-29398, etc., which changes color before and after a predetermined temperature (color change point), exhibits a decolorized state in the temperature range above the high-temperature color change point and a colored state in the temperature range below the low-temperature color change point, and of the two states, only one specific state exists in the room temperature range, and the other state is maintained as long as the heat or cold required to bring about that state is applied, but returns to the state exhibited in the room temperature range when the application of heat or cold is stopped (see Figure 1).

[0011] Furthermore, it is also possible to use a reversible thermochromic composition that exhibits a large hysteresis width (ΔH = 8 to 80°C) as described in Japanese Patent Publication No. 4-17154, Japanese Patent Application Publication No. 7-179777, Japanese Patent Application Publication No. 7-33997, Japanese Patent Application Publication No. 8-39936, Japanese Patent Application Publication No. 2005-1369, etc., and in which the shape of the curve plotted for the change in color intensity due to temperature change follows a significantly different path when the temperature is raised from a temperature lower than the color change temperature range and when it is lowered from a temperature higher than the color change temperature range, and in which the colored state in the temperature range below the complete color development temperature t1, or the decolorized state in the high temperature range above the complete decolorization temperature t4, has color memory in a specific temperature range [the temperature range between the color development start temperature t2 and the decolorization start temperature t3 (essentially a two-phase holding temperature range)] (see Figure 2).

[0012] The following provides a detailed explanation of each component (a), (b), and (c).

[0013] (a) Component, i.e., the electron-donating chromogenic organic compound, is the component that determines the color and is a compound that produces color by donating electrons to component (b), which is the color developer.

[0014] Examples of the electron-donating color-forming organic compounds include phthalide compounds, fluoran compounds, styrylnaphthyridine compounds, diazarhodamine lactone compounds, pyridine compounds, quinazoline compounds, bisquinazoline compounds, and the like. Examples of the phthalide compounds 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 preferable. Examples of the fluoran compounds include aminofluoran compounds, alkoxyfluoran compounds, and their derivatives.

[0015] Examples of the compounds that can be used for the component (a) are shown below. 3,3-Bis(4-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-n-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-propyl-2-methylindol-3-yl)-4-azaphthalide, 3,6-Bis(diphenylamino)fluoran, 3,6-Bis(N-phenyl-N-p-tolylamino)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-Chloroamino-6-di-n-butylaminofluoran, 2-(2-Chloroanilino)-6-di-n-butylaminofluoran, 2-(3-Trifluoromethylanilino)-6-diethylaminofluoran, 2-(3-Trifluoromethylanilino)-6-di-n-pentylaminofluoran, 2-Dibenzylamino-6-diethylaminofluoran, 2-N-Methylanilino-6-(N-ethyl-N-p-tolylamino)fluoran, 1,3-Dimethyl-6-diethylaminofluoran, 2-Chloro-3-methyl-6-diethylaminofluoran, 2-Anilino-3-methyl-6-diethylaminofluoran, 2-Anilino-3-methoxy-6-diethylaminofluoran, 2-Anilino-3-methyl-6-di-n-butylaminofluoran, 2-Anilino-3-methoxy-6-di-n-butylaminofluoran, 2-Xylidino-3-methyl-6-diethylaminofluoran, 2-Anilino-3-methyl-6-(N-ethyl-N-p-tolylamino)fluoran, 6-Diethylamino-1,2-benzofluorane, 6-(N-Ethyl-N-isobutylamino)-1,2-benzofluorane, 6-(N-Ethyl-N-isopentylamino)-1,2-benzofluorane, 2-(3-Methoxy-4-dodecoxystyryl)quinoline, 2-Diethylamino-8-diethylamino-4-methylspiro[5H-[1]benzopyrano[2,3-d]pyrimidine-5,1′(3′H)-isobenzofuran]-3′-one, 2-di-n-butylamino-8-di-n-butylamino-4-methylspiro[5H-[1]benzopyrano[2,3-d]pyrimidine-5,1′(3′H)-isobenzofuran]-3′-one, 2-di-n-butylamino-8-diethylamino-4-methylspiro[5H-[1]benzopyrano[2,3-d]pyrimidine-5,1′(3′H)-isobenzofuran]-3′-one, 2-di-n-butylamino-8-(N-ethyl-N-isoamylamino)-4-methylspiro[5H-[1]benzopyrano[2,3-d]pyrimidine-5,1′(3′H)-isobenzofuran]-3′-one, 2-di-n-butylamino-8-di-n-pentylamino-4-methylspiro[5H-[1]benzopyrano[2,3-d]pyrimidine-5,1′(3′H)-isobenzofuran]-3′-one, 4,5,6,7-Tetrachloro-3-(4-dimethylamino-2-methoxyphenyl)-3-(1-n-butyl-2-methylindole-3-yl)-1(3H)-isobenzofuranone, 4,5,6,7-Tetrachloro-3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindole-3-yl)-1(3H)-isobenzofuranone, 4,5,6,7-Tetrachloro-3-(4-diethylamino-2-ethoxyphenyl)-3-(1-n-pentyl-2-methylindole-3-yl)-1(3H)-isobenzofuranone, 4,5,6,7-Tetrachloro-3-(4-diethylamino-2-methylphenyl)-3-(1-ethyl-2-methylindole-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, 2,6-bis(2,4-diethyloxyphenyl)-4-[4-bis(4-methyloxyphenyl)aminophenyl]pyridine, 2-(4′-dimethylaminophenyl)-4-methoxyquinazoline, 4,4′-Ethylenedioxy-bis[2-(4-diethylaminophenyl)quinazoline]

[0016] Furthermore, fluoranes may include not only compounds having substituents on the phenyl group forming the xanthene ring, but also compounds that exhibit a blue or black color, having substituents on the phenyl group forming the xanthene ring and also on the phenyl group forming the lactone ring (for example, alkyl groups such as methyl groups, halogen atoms such as chlorine atoms).

[0017] (b) Component, i.e., the electron-accepting compound, is a compound that accepts electrons from component (a) and functions as a color developer for component (a). Examples of electron-accepting compounds include compounds selected from the group of compounds having active protons, the group of pseudoacidic compounds (compounds that are not acids but act as acids in reversible thermochromic products to cause the color of component (a)), and the group of compounds having electron vacancies. Among the above components (b), compounds selected from the group of compounds having active protons are preferred.

[0018] Examples of compounds having active protons include compounds having a phenolic hydroxyl group and their derivatives, carboxylic acids and their derivatives, acidic phosphate esters and their derivatives, azole compounds and their derivatives, 1,2,3-triazoles and their derivatives, cyclic carbosulfoimides, C2-C5 halohydrins, sulfonic acids and their derivatives, and inorganic acids. As for carboxylic acids and their derivatives, aromatic carboxylic acids and their derivatives, or C2-C5 aliphatic carboxylic acids and their derivatives are preferred. Examples of pseudoacidic compounds include metal salts of compounds having a phenolic hydroxyl group, metal salts of carboxylic acids, metal salts of acidic phosphate esters, metal salts of sulfonic acids, aromatic carboxylic acid anhydrides, aliphatic carboxylic acid anhydrides, mixed anhydrides of aromatic carboxylic acids and sulfonic acids, cycloolefin dicarboxylic acid anhydrides, urea and its derivatives, thiourea and its derivatives, guanidine and its derivatives, and halogenated alcohols. Examples of compounds containing electron vacancies include borates, borate esters, and inorganic salts.

[0019] Among the components of (b) above, compounds having a phenolic hydroxyl group are preferred because they can more effectively exhibit thermal discoloration properties. Compounds having a phenolic hydroxyl group broadly include monophenol compounds to polyphenol compounds, and further include bisphenol compounds, trisphenol compounds, phenol-aldehyde condensation resins, etc. It is preferable that compounds having a phenolic hydroxyl group have at least two benzene rings. Furthermore, compounds having a phenolic hydroxyl group may have substituents such as alkyl groups, aryl groups, acyl groups, alkoxycarbonyl groups, carboxyl groups and their esters or amide groups, halogen atoms, etc.

[0020] Examples of metals contained in metal salts of compounds having a phenolic hydroxyl group include sodium, potassium, calcium, zinc, zirconium, aluminum, magnesium, nickel, cobalt, tin, copper, iron, vanadium, titanium, lead, and molybdenum.

[0021] The following are examples of compounds that can be used in component (b). Phenol, o-cresol, 4-np-nonylphenol, 4-n-octylphenol, 4-n-dodecylphenol, 4-n-stearylphenol, 4-chlorophenol, 4-bromophenol, 2-phenylphenol, 4-hydroxybenzoate n-butyl, 4-hydroxybenzoate n-octyl, resorcinol, 4-tert-butylcatechol, 2,4-dihydroxy-4′-tert-butylbenzophenone, dodecyl gallate, 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) 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, 2,2-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, 2,2-Bis(4-hydroxy-3-methylphenyl)butane, 9,9-Bis(4-hydroxy-3-methylphenyl)fluorene, 1,3-Bis[2-(4-hydroxyphenyl) -2-propyl]benzene, bis(2-hydroxyphenyl)methane, 4,4′-dihydroxydiphenylsulfone, 4-isopropoxy-4′-hydroxydiphenylsulfone, bis(4-hydroxyphenyl)sulfide, 1,1,1-tris(4-hydroxyphenyl)ethane, 4,4′-[1-{4-[1-(4-hydroxyphenyl)-1-methylethyl]phenyl}ethylidene]bisphenol, 4,4′-[4-(4-hydroxyphenyl)-sec-butylidene]bis(2-methylphenol),

[0022] The (c) component of the reaction medium that causes the electron transfer reaction between components (a) and (b) to occur reversibly in a specific temperature range will be described. (h) Examples of components include alcohols, esters, ketones, ethers, and acid amides. When applying the reversible thermochromic composition according to the present invention to microencapsulation and secondary processing, low molecular weight compounds evaporate outside the capsule when subjected to high heat treatment. Therefore, compounds with 10 or more carbon atoms are preferably used to stably retain them inside the capsule.

[0023] As for alcohols, monohydric aliphatic saturated alcohols with 10 or more carbon atoms are effective.

[0024] Effective esters include those having 10 or more carbon atoms, such as esters obtained from any combination of aliphatic and alicyclic or aromatic monocarboxylic acids and aliphatic and alicyclic or aromatic monohydric alcohols; esters obtained from any combination of aliphatic and alicyclic or aromatic polycarboxylic acids and aliphatic and alicyclic or aromatic monohydric alcohols; and esters obtained from any combination of aliphatic and alicyclic or aromatic monocarboxylic acids and aliphatic and alicyclic or aromatic polyhydric alcohols.

[0025] Furthermore, ester compounds selected from esters of saturated fatty acids and branched aliphatic alcohols, esters of unsaturated fatty acids or branched or substituted saturated fatty acids with branched or carbon-16 or more aliphatic alcohols, cetyl butyrate, stearyl butyrate, and behenyl butyrate are also effective.

[0026] Furthermore, to demonstrate significant hysteresis characteristics with respect to the color density-temperature curve, resulting in discoloration and providing color memory depending on temperature changes, examples include 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.

[0027] Furthermore, 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, as well as 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.

[0028] Effective ketones include aliphatic ketones with a total of 10 or more carbon atoms, as well as arylalkyl ketones with a total of 12 to 24 carbon atoms.

[0029] As for ethers, aliphatic ethers with a total of 10 or more carbon atoms are effective.

[0030] Examples of the alcohols, esters, ketones, ethers, and acid amides mentioned above include the compounds described in Japanese Patent Publication No. 2020-100710.

[0031] Furthermore, component (c) may be a compound represented by the following formula (1). [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 or alkenyl group with 4 or more carbon atoms, Y1 and Y2 each independently represent one of the following: a hydrogen atom, an alkyl group with 1 to 4 carbon atoms, a methoxy group, or a halogen atom, and r and p each independently represent an integer from 1 to 3. Among the compounds represented by formula (1), when R1 is a hydrogen atom, a reversible thermochromic composition with a wider hysteresis width is obtained, which is preferable, and it is even more preferable when R1 is a hydrogen atom and m is 0. Furthermore, among the compounds represented by formula (1), the compounds represented by the following formula (2) are more preferred. [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.)

[0032] Furthermore, component (c) may be a compound represented by the following formula (3). [ka] (In the formula, R represents an alkyl or alkenyl group having 8 or more carbon atoms, m and n each independently represent an integer from 1 to 3, and X and Y each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a halogen atom.)

[0033] Furthermore, component (c) may be a compound represented by the following formula (4). [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.)

[0034] Furthermore, component (c) may be a compound represented by the following formula (5). [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.)

[0035] Furthermore, component (c) may be a compound represented by the following formula (6). [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.)

[0036] Furthermore, component (c) may be the compound shown in formula (7) below. [ka] (In the formula, R represents any of the following: an alkyl group having 4 to 22 carbon atoms, a cycloalkylalkyl group, a cycloalkyl group, or an alkenyl group having 4 to 22 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 4 carbon atoms, or a halogen atom; and n represents 0 or 1.)

[0037] Furthermore, component (c) may be a compound represented by the following formula (8). [ka] (In the formula, R represents an alkyl group having 3 to 18 carbon atoms or an aliphatic acyl group having 3 to 18 carbon atoms; X represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 or 2 carbon atoms, or a halogen atom; Y represents a hydrogen atom or a methyl group; and Z represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 or 2 carbon atoms, or a halogen atom.)

[0038] Furthermore, component (c) may be a compound represented by the following formula (9). [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.)

[0039] Furthermore, component (c) may be a compound represented by the following formula (10). [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.)

[0040] Furthermore, component (c) may be a compound represented by the following formula (11). [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.)

[0041] Furthermore, component (c) may be a compound represented by the following formula (12). [ka] (In the formula, R represents one of the alkyl groups having 3 to 17 carbon atoms, cycloalkyl groups having 3 to 8 carbon atoms, or cycloalkylalkyl groups having 5 to 8 carbon atoms; X represents one of the 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.)

[0042] Examples of compounds represented by formulas (2) to (12) include those described in Japanese Patent Publication No. 2020-100710.

[0043] Furthermore, a reversible thermochromic composition that changes color upon heating and disappears upon cooling can also be applied, using gallic acid esters (Japanese Patent Publication No. 51-44706, Japanese Patent Application Publication No. 2003-253149) as an electron-accepting compound (see Figure 3).

[0044] The reversible thermochromic composition is a compatible mixture containing the above-mentioned components (a), (b), and (c) as essential components. The proportion of each component 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 1 part of component (a) to 0.1 to 100 parts of component (b), preferably 0.1 to 50 parts, more preferably 0.5 to 20 parts, and 1 to 800 parts of component (c), preferably 5 to 200 parts, more preferably 5 to 100 parts, and even more preferably 10 to 100 parts (all of the above proportions are in parts by mass).

[0045] The reversible thermochromic composition may contain various light stabilizers as needed. Light stabilizers are included to prevent photodegradation of the reversible thermochromic composition consisting of components (a), (b), and (c), and are blended in a ratio of 0.3 to 24% by mass, preferably 0.3 to 16% by mass, per 1% by mass of component (a). Among the light stabilizers, ultraviolet absorbers effectively cut ultraviolet rays contained in sunlight, etc., and prevent 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. Light stabilizers can be used individually or in combination of two or more types.

[0046] By encapsulating the reversible thermochromic composition in microcapsules to create a reversible thermochromic microcapsule pigment, a chemically and physically stable pigment can be constructed. Furthermore, under various usage conditions, the reversible thermochromic composition maintains the same composition and exhibits the same effects.

[0047] Microencapsulation can be performed using known methods such as interfacial polymerization of isocyanates, in situ polymerization of melamine-formaldehyde systems, liquid curing coating, phase separation from aqueous solutions, phase separation from organic solvents, melt-dispersion-cooling, air suspension coating, and spray drying, and is selected appropriately 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. The reversible thermochromic microcapsule pigment preferably has a mass ratio of encapsulated material to wall film of 7:1 to 1:1. By having the mass ratio of encapsulated material to wall film within this range, a decrease in color density and vividness during color development can be prevented. More preferably, the mass ratio of encapsulated material to wall film is 6:1 to 1:1.

[0048] The average particle size of the reversible thermochromic microcapsule pigment is preferably in the range of 0.01 to 5 μm, more preferably 0.05 to 4 μm, even more preferably 0.1 to 3 μm, and particularly preferably 0.5 to 3 μm, which satisfies practical requirements. If the average particle size of the microcapsule pigment exceeds 5 μm, it becomes difficult to obtain good ink ejection when used in writing instruments. On the other hand, if the average particle size is less than 0.01 μm, it becomes difficult to exhibit high-concentration color development. The average particle diameter was determined using image analysis-based particle size distribution measurement software [Mountec Co., Ltd., product name: MacView], which was used to identify 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-300) that has been calibrated based on the values ​​measured using the above software or a measuring device using the Coulter method.

[0049] The content of reversible thermochromic microcapsule pigment (hereinafter sometimes referred to as "P1") relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 5 to 40% by mass, more preferably 10 to 40% by mass, and even more preferably 10 to 30% by mass. By having the microcapsule pigment content within the above range, the desired color density can be obtained and a decrease in ink flowability can be prevented.

[0050] The ink composition according to the present invention further comprises an acid dye as a colorant. Examples of acid dyes include Naphthol Green B (CI10020), Naphthol Yellow S (CI10316), Orange 1 (CI14600), Orange 2 (CI15510), Sunset Yellow FCF (CI15985), Fast Red S (CI15620), New Coccine (CI16255), Fast Light Yellow 3G (CI18820), Tartrazine (CI19140), Resorcinol Brown (CI20170), Naphthol Blue Black 10B (CI20470), Acid Blue 1 (CI42045), Fast Green FCF (CI42053), Guinea Green (CI42085), and Bri. Examples include Liant Blue FCF (CI42090), Acid Violet 6B (CI42640), Solubble Blue (CI42755), Naphthalene Green (CI44025), Acid Red 289 (CI45100), Eosin (CI45380), Phloxine (CI45410), Erythrosine (CI45430), Rose Bengal (CI45440), Quinoline Yellow WS (CI47005), Nigrosine (CI50420), Acid Flavin (CI56205), Acidsrol Purple (CI60730), Alizarin Cyanine Green F (CI61570), Indigo Carmine (CI73015), etc. Furthermore, acid dyes may be incorporated during the microencapsulation process and encapsulated together with the reversible thermochromic composition within the microcapsules.

[0051] The content of the acid dye relative to the total mass of the ink composition (hereinafter sometimes referred to as "P2") is not particularly limited, but is preferably in the range of 0.05 to 10% by mass, and more preferably in the range of 0.1 to 5% by mass. Having the acid dye content within the above range makes it easier to obtain handwriting with a suitable density for use as a writing instrument.

[0052] The ink composition according to the present invention uses a reversible thermochromic microcapsule pigment and an acid dye in combination as colorants. Since the reversible thermochromic microcapsule pigment reversibly changes color from a colored state to a decolorized state due to temperature changes, the change from colored (1) to colored (2) is also reversible, resulting in an intermutable color change from colored (1) to colored (2). Here, in the present invention, colored (1) refers to the color shown when the reversible thermochromic microcapsule pigment is in a colored state, and is a color resulting from a mixture of the color from the colored reversible thermochromic microcapsule pigment and the color from the acid dye. Colored (2) refers to the color shown when the reversible thermochromic microcapsule pigment is in a decolorized state, and is a color resulting from the acid dye alone. Intermutational color changes from colored (1) to colored (2) include changes in hue (e.g., from dark to light) and changes in color (e.g., from purple to pink, from green to yellow).

[0053] Specifically, as an interpenetrating color change from colored (1) to colored (2), when a writing instrument containing an ink composition containing a heat-decolorizing type reversible thermochromic microcapsule pigment and an acid dye forms a handprint, the handprint is a mixture of the color from the microcapsule pigment and the color from the acid dye [colored (1')]. When this handprint is heated to a temperature t4 or higher that is the complete decolorization temperature of the microcapsule pigment (reversible thermochromic composition), the microcapsule pigment decolorizes and changes to a color from only the acid dye [colored (2')]. Furthermore, when this handprint is cooled to a temperature t1 or lower that is the complete color development temperature of the microcapsule pigment (reversible thermochromic composition), the microcapsule pigment returns to a color development state and returns to the initial color [colored (1')], thus exhibiting an interpenetrating color change from colored (1) to colored (2). Furthermore, when a writing instrument containing an ink composition containing a decolorized microcapsule pigment and an acid dye is used to form handwriting using a heat-activated, reversible thermochromic microcapsule pigment, the handwriting is initially colored solely by the acid dye [colored (2″)]. When this handwriting is heated to a temperature above the complete color development temperature T4 of the microcapsule pigment (reversible thermochromic composition), the microcapsule pigment develops color, resulting in a mixed color [colored (1″)] of the microcapsule pigment and the acid dye. When this handwriting is cooled to a temperature below the complete decolorization temperature T1 of the microcapsule pigment (reversible thermochromic composition), the microcapsule pigment decolorizes and returns to its initial color [colored (2″)], thus exhibiting an intermutation color change from colored (1) to colored (2).

[0054] The ink composition according to the present invention further comprises water. The type of water used is not particularly limited; for example, tap water, deionized water, ultrafiltered water, distilled water, etc., can be used as examples. The water content relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 10 to 90% by mass, and more preferably in the range of 30 to 80% by mass.

[0055] The ink composition according to the present invention can be formulated with a water-soluble organic solvent that is compatible with water, and has the effect of suppressing moisture evaporation from the pen tip of a writing instrument. Furthermore, it can prevent fluctuations in the specific gravity of the vehicle, maintain good dispersion stability of the reversible thermochromic microcapsule pigment, and stabilize the structure of the polymer flocculant described later, or the loose aggregate formed by the polymer flocculant and the dispersant.

[0056] Examples of water-soluble organic solvents include ethanol, propanol, butanol, 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.

[0057] When an ink composition contains a water-soluble organic solvent, the content of the water-soluble organic solvent relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 1 to 50% by mass, more preferably 5 to 45% by mass, and even more preferably 10 to 40% by mass. If the content of the water-soluble organic solvent exceeds 50% by mass, the ink viscosity tends to increase, reducing the ink discharge performance of the writing instrument containing the ink and making writing problems more likely. On the other hand, if the content is less than 1% by mass, the effect of suppressing water evaporation becomes poor.

[0058] When an ink composition contains a water-soluble organic solvent and the hysteresis width (ΔH) of the reversible thermochromic microcapsule pigment blended into the ink composition is large, the specific gravity of the microcapsule pigment is greater than 1. When adjusting the specific gravity of the vehicle, it is easier to adjust the specific gravity by using a water-soluble organic solvent with a specific gravity greater than water. Therefore, it is preferable to use glycerin or the like as the water-soluble organic solvent, which has a specific gravity of 1.1 or more.

[0059] An ink composition may contain a shear viscosity reducing agent. An ink containing a shear viscosity reducing agent (shear viscosity reducing ink) can suppress the aggregation and sedimentation of microcapsule pigments and also suppress the bleeding of handwriting, thus enabling the formation of good handwriting. When shear-reducing ink is housed in a ballpoint pen-type writing instrument, it is possible to prevent ink leakage from the gap between the ball and the tip when the writing instrument is not in use, and to prevent ink backflow when the writing tip is left upright.

[0060] Examples of shear-thinning agents include xanthan gum, gellan gum, succinoglycans (average molecular weight approximately 1 million to 8 million) whose constituent monosaccharides are organic acid-modified heteropolysaccharides of glucose and galactose, alka gum, 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, and inorganic substances. Examples include fine particles, polyglycerin fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyethylene glycol fatty acid esters, polyoxyethylene castor oil, polyoxyethylene lanolin / lanonine alcohol / beeswax derivatives, polyoxyethylene alkyl ethers / polyoxypropylene alkyl ethers, polyoxyethylene alkylphenyl ethers, nonionic surfactants with an HLB value of 8 to 12 such as fatty acid amides, salts of dialkyl or dialkenyl sulfosuccinate, mixtures of N-alkyl-2-pyrrolidone and anionic surfactants, and mixtures of polyvinyl alcohol and acrylic resins.

[0061] Ink compositions can contain polymer flocculants. In inks containing polymer flocculants (agglomerating inks), the microcapsule pigments form loose aggregates via the polymer flocculant, suppressing contact and aggregation between the microcapsule pigments, thus improving the dispersibility of the microcapsule pigments.

[0062] Examples of polymeric flocculants include polyvinylpyrrolidone, polyethylene oxide, and water-soluble polysaccharides. Examples of water-soluble polysaccharides include tragacanth gum, guar gum, pullulan, cyclodextrin, and water-soluble cellulose derivatives. Examples of water-soluble cellulose derivatives include methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, and hydroxypropylmethylcellulose. Among the polymer flocculants mentioned above, hydroxyethylcellulose is preferred due to its excellent dispersibility.

[0063] When the ink composition contains a polymer flocculant, the content of the polymer flocculant relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.1 to 1% by mass, and more preferably in the range of 0.3 to 0.5% by mass. By having a polymer flocculant content within the above range, the microcapsule pigments can form loose aggregates, and the effect of improving the dispersibility of the microcapsule pigments can be fully exhibited.

[0064] By incorporating a dispersant into the ink composition, the dispersibility of microcapsule pigments can be improved. Furthermore, polymer flocculants and dispersants can be used in combination. When both are used together, the dispersibility of microcapsule pigments can be improved, and the dispersibility of the loose aggregates of microcapsule pigments formed via the polymer flocculant can be further enhanced.

[0065] Examples of dispersants include polyvinylpyrrolidone, polyvinyl butyral, polyvinyl ether, styrene-maleic acid copolymer, ketone resin, hydroxyethylcellulose and its derivatives, synthetic resins such as styrene-acrylic acid copolymer, acrylic polymers, PO·EO adducts, and polyester amine oligomers. Among the above dispersants, acrylic polymer dispersants are preferred due to their excellent dispersibility of microcapsule pigments, acrylic polymer dispersants having carboxyl groups are more preferred, and acrylic polymer dispersants with a comb-like structure having carboxyl groups in their side chains are even more preferred. Particularly preferred as a dispersant is an acrylic polymer dispersant with a comb-like structure having multiple carboxyl groups in its side chains. Specifically, an example is Solspers 43000, manufactured by Lubrizol Nippon Co., Ltd.

[0066] When an ink composition contains a dispersant, the dispersant content relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.01 to 2% by mass, and more preferably in the range of 0.1 to 1.5% by mass. If the dispersant content exceeds 2% by mass, the microcapsule pigments are more likely to settle or float when subjected to external vibrations, etc. On the other hand, if the content is less than 0.01% by mass, the effect of improving dispersibility becomes less apparent.

[0067] By incorporating a water-soluble resin into the ink composition, the ink can be given properties such as adhesion and viscosity to the paper surface. Examples of water-soluble resins include alkyd resins, acrylic resins, styrene-maleic acid copolymers, cellulose derivatives, polyvinylpyrrolidone, polyvinyl alcohol, and dextrin. Among the water-soluble resins mentioned above, polyvinyl alcohol is preferred due to its excellent stability as an acrylic polymer dispersant, and partially saponified polyvinyl alcohol with a degree of saponification of 70-89 mol% is even more preferred because it is highly soluble even in acidic inks.

[0068] When the ink composition contains a water-soluble resin, the content of the water-soluble resin relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.3 to 3% by mass, and more preferably in the range of 0.5 to 1.5% by mass.

[0069] When the viscosity of the vehicle used in the ink composition is low, adding a specific gravity adjuster can suppress the sedimentation or floating and localization of microcapsule pigments in the ink, thereby improving the dispersion stability of the microcapsule pigments.

[0070] The dispersion stability of microencapsulated pigments is maximized when the difference in specific gravity between the vehicle and the microencapsulated pigment is minimal. A specific gravity adjuster brings the specific gravity of the vehicle closer to that of the microencapsulated pigment. The specific gravity of the vehicle depends on the specific gravity of the water-soluble substance dissolved in the vehicle and the amount added. Therefore, by adding and dissolving a larger amount of a specific gravity adjuster with a higher specific gravity in the vehicle, the specific gravity of the vehicle can be increased.

[0071] Examples of specific gravity adjusting agents include oxygen acids and salts of Group 6 elements with atomic weights in the range of 90 to 185. Such specific gravity adjusting agents can adjust the specific gravity of the vehicle to be close to that of the microcapsule pigment, which has a higher specific gravity. This prevents the microcapsule pigment from settling or floating and becoming localized due to external stimuli such as vibration, even though the ink has low viscosity.

[0072] Oxy acids and their salts are selected from the group consisting of oxy acids and their salts of transition metal elements, and it is said that the oxyacid ions form tetrahedra or octahedrons in which oxygen atoms are usually coordinated to metal atoms in a 4 or 6-degree configuration. The oxygen acid and its salt may also be polyacid and its salt, which is a polyate. Polyacids include isopolyacids and heteropolyacids, while polyate includes isopolyate and heteropolyate.

[0073] Examples of specific gravity adjusting agents include individual oxyacids and their salts, isopolyacids and their salts, heteropolyacids and their salts, and the like. Examples of individual oxygen acids include molybdic acid and tungstic acid, and examples of salts of individual oxygen acids include sodium molybdate, potassium molybdate, ammonium molybdate, sodium tungstate, potassium tungstate, ammonium tungstate, lithium tungstate, and magnesium tungstate. Examples of isopolyacids include metamolybdic acid, paramolybdic acid, metatungstic acid, paratungstic acid, and isotungstic acid. Furthermore, examples of isopolyates include sodium metamolybdate, potassium metamolybdate, ammonium metamolybdate, sodium paramolybdate, potassium paramolybdate, ammonium paramolybdate, sodium metatungstate, potassium metatungstate, ammonium metatungstate, barium metatungstate, sodium paratungstate, and sodium isotungstate. Examples of heteropoly acids include molybd phosphate, molybdosilicic acid, tungstonic acid, and tungstosilicate. Furthermore, examples of heteropoly salts include sodium molybd phosphate, sodium molybdosilicate, sodium tungstonic phosphate, and sodium tungstosilicate. The above-mentioned oxygen acids and their salts can be used individually or in appropriate mixtures of two or more types.

[0074] Among the gravity adjusting agents listed above, metatungstic acid, paratungstic acid, sodium metatungstate, potassium metatungstate, ammonium metatungstate, barium metatungstate, sodium paratungstate, sodium isotungstate, tungstonic acid, tungstosilicate, sodium tungstonic acid, and sodium tungstosilicate are preferred, with sodium isotungstate, sodium metatungstate, and sodium paratungstate being more preferred. The sodium isotungstate, sodium metatungstate, and sodium paratungstate mentioned above are not only highly safe but also have a high specific gravity, making it easy to adjust the specific gravity of the liquid according to the amount added, and are therefore suitable for use.

[0075] When an ink composition contains a specific gravity adjuster, the content of the specific gravity adjuster relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 2 to 20% by mass, and more preferably 5 to 15% by mass. If the content of the specific gravity adjuster exceeds 20% by mass, the microcapsule pigments tend to aggregate. On the other hand, if the content is less than 2% by mass, the effect of adjusting the specific gravity of the vehicle becomes poor. Furthermore, the mass ratio of microcapsule pigment to specific gravity adjuster is preferably 1:0.05 to 1:4, more preferably 1:0.075 to 1:2, and even more preferably 1:0.1 to 1:1.5.

[0076] Vehicles containing the above-mentioned specific gravity adjusting agent are particularly effective for microcapsule pigments with high specific gravity. Even with low viscosity ink, they can suppress the sedimentation of microcapsule pigments in the ink when subjected to external stimuli such as vibration, thereby improving the dispersion stability of microcapsule pigments. The specific gravity of microcapsule pigments depends on the particle size, the components encapsulated in the microcapsules and their content, the components and thickness of the capsule wall film, the coloring state of the microcapsule pigments, and the temperature. However, when the microcapsule pigments are in a fully colored state and at 20°C with water as the reference, the specific gravity is preferably 1.05 to 1.20. Such microcapsule pigments exhibit a large hysteresis width (ΔH), and can be decolorized by heating and maintain a decolorized state in a specific temperature range. However, pigments with a large hysteresis width (ΔH) often use compounds with two or more aromatic rings in the molecule as component (c), which tends to increase the specific gravity and make them prone to settling and separating in ink. In particular, microcapsule pigments tend to settle and separate when subjected to external stimuli such as vibration. However, in inks containing the above-mentioned specific gravity adjusting agent, the ink has low viscosity, yet the settling and localization of microcapsule pigments is suppressed, thereby improving the dispersion stability of the microcapsule pigments, and therefore it is preferable to use it. Considering the dispersion stability of microcapsule pigments in ink, the specific gravity of the microcapsule pigment is preferably 1.10 to 1.20, and more preferably 1.12 to 1.15, when the microcapsule pigment is in a fully colored state and is based on water at 20°C. The specific gravity of microcapsule pigments can be measured by the following method.

[0077] (Method for measuring the specific gravity of microencapsulated pigments) 1. Add 30 ml of glycerin aqueous solution and 1 g of fully colored microcapsule pigment to a screw-capsule vial, mix, and prepare a microcapsule pigment dispersion. 2. Heat 30 ml of the microcapsule pigment dispersion to 20°C and centrifuge it in a centrifuge at a rotation speed of 1000 rpm for 30 seconds. A cooled benchtop centrifuge (manufactured by Kokusan Co., Ltd., product name: H103N) can be used as the centrifuge. 3. Observe the microcapsule pigment dispersion. If most of the microcapsule pigment has settled at the bottom of the beaker, repeat steps 1-2 using a glycerin solution with a higher glycerin concentration than the one used in the first step, and observe the state of the dispersion. If you observe that most of the microcapsule pigments are suspended on the liquid surface, repeat steps 1-2 using a glycerin solution with a lower glycerin concentration than the one used in the first step, and observe the state of the dispersion again. The above series of operations should be repeated until it is visually confirmed that the glycerin aqueous solution is uniformly colored, except for the area near the surface and the bottom of the screw-capsule bottle, and that the majority of the microcapsule pigment is not floating or settling on the surface. The specific gravity of the glycerin aqueous solution at this point should be measured and recorded as the specific gravity of the microcapsule pigment. The specific gravity of the glycerin aqueous solution can be measured using the hydrometer method described in JIS K0061, Section 7.1, with the solution heated to 20°C.

[0078] The vehicle containing the above-mentioned specific gravity adjusting agent has a specific gravity in the range of 1.00 to 1.30 at 20°C, with water as the reference substance. Furthermore, the specific gravity is preferably 1.05 to 1.20, and more preferably 1.08 to 1.18. Furthermore, the specific gravity of the vehicle is preferably 0.90 to 1.20 times, and more preferably 0.95 to 1.10 times, compared to the specific gravity of the microcapsule pigment. When the specific gravity of the vehicle is within the above range, and the specific gravity of the vehicle relative to the specific gravity of the microcapsule pigment is within the above range, even when the ink is subjected to external stimuli such as vibration, the sedimentation and localization of the microcapsule pigment within the ink can be further suppressed, even though the ink has low viscosity, thereby further improving the dispersion stability of the microcapsule pigment.

[0079] When the ink composition according to the present invention is used in a ballpoint pen, it is preferable to add a lubricant to the ink, 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), a phosphate monoester of polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether, a phosphate diester of polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether, or a metal salt, ammonium salt, amine salt, or alkanolamine salt thereof, to prevent wear of the ball bearing seat.

[0080] The pH of the ink composition according to the present invention is adjusted to a range of 3 to 7. By adjusting the pH of the ink composition to 3 to 7, i.e., to an acidic to neutral range, it is possible to suppress the loss of stability of the acidic dye and the resulting change in the color of the writing formed by the writing instrument when the ink composition is subjected to excessive temperature changes, and in particular, it is possible to make it less likely for the writing to become lighter in color when the microcapsule pigment is in a decolorized state. In other words, even when excessive temperature changes occur, the ink composition according to the present invention can exhibit the change from colored (1) to colored (2) in the writing formed by a writing instrument containing the ink composition before the temperature change occurred (hereinafter sometimes referred to as "initial writing"). This is presumably because, within the pH range of 3 to 7, the reversible thermochromic microcapsule pigments and acidic dyes interact within the ink composition, making it easier for the acidic dyes to maintain a stable state even when excessive temperature changes occur. The aforementioned effects are more readily observed in cohesive inks, as the microcapsule pigments and acid dyes maintain an interactive state while the microcapsule pigments form loose aggregates via a polymer flocculant, thereby further stabilizing the acid dyes. Therefore, the ink composition according to the present invention preferably contains a polymer flocculant.

[0081] The pH of the ink composition according to the present invention can also be adjusted to an appropriate range by incorporating a pH adjusting agent. Various acidic and basic substances can be used as the pH adjusting agent. Examples of acidic substances include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, carbonic acid, boric acid, lactic acid, citric acid, tartaric acid, and malic acid. Examples of basic substances include ammonia, sodium carbonate, sodium hydrogen phosphate, potassium hydrogen phosphate, sodium hydroxide, potassium hydroxide, and sodium acetate. Alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine can also be used. The pH value was measured using a pH meter (manufactured by Toa DKK Co., Ltd., product name: IM-40S) with the ink placed in a 20°C environment.

[0082] The ink composition according to the present invention may also contain various additives as needed. Examples of additives include wetting agents, resins, resin particles, rust inhibitors, surfactants, humectants, defoamers, viscosity modifiers, preservatives, and fungicides.

[0083] The method for producing the ink composition according to the present invention is not particularly limited, and any conventionally known method can be used. Specifically, the ink composition can be produced by stirring a mixture containing the required amounts of each of the above-mentioned components using various stirrers such as propeller stirrers, homodispersers, or homomixers, or by dispersing it using various dispersers such as bead mills.

[0084] In the present invention, it is preferable that the ratio (P2 / P1) of the content of the reversible thermochromic microcapsule pigment (P1) to the content of the acid dye (P2) satisfies the following formula (*). 0.003 ≤ P2 / P1 ≤ 0.05 (*) Regarding P2 / P1, it is more desirable that 0.0035 ≤ P2 / P1 ≤ 0.04 be satisfied. Having P2 / P1 within the above range facilitates interaction between the reversible thermochromic microcapsule pigment and the acid dye in the ink composition according to the present invention, further improving the effect of the acid dye in maintaining a stable state. As a result, it becomes easier to suppress changes in the color of handwriting formed by a writing instrument when excessive temperature changes occur in the ink composition.

[0085] Furthermore, it is preferable that the ratio P2 / P1 satisfies 0.0035 ≤ P2 / P1 ≤ 0.015. By having P2 / P1 within the above range, the ink composition can be such that the colored (1) (a color resulting from a mixture of the colored microcapsule pigment and the acid dye) is clearly visible in density, and the colored (2) (a color from the acid dye alone) is visible in density. Specifically, when writing is formed using a writing instrument containing an ink composition that includes a heat-activated, reversible thermochromic microcapsule pigment and an acid dye within the above range, the colored (1) writing is clearly visible, and when this writing is heated to a temperature t4 or higher that is above the complete decolorization temperature of the microcapsule pigment (reversible thermochromic composition), the microcapsule pigment decolorizes, and a colored (2) writing of a visible density becomes visible. Writing instruments that exhibit this kind of color change can be used for managing tasks and appointments (to-do lists), and an example of this is explained below.

[0086] When a ToDo is written on paper or other media using the above-mentioned writing instrument, or when a ToDo is written on media using a general writing instrument containing non-thermochromic ink, and then a mark is made on the written area with the above-mentioned writing instrument, the handwriting formed by the writing instrument becomes clearly visible. When these handwriting marks are discolored after the ToDo is completed, the visibility of the handwriting changes significantly before and after discoloration, making it easy to determine and manage whether or not the ToDo has been completed. Here, the discolored handwriting does not become completely invisible, but remains visible to a certain degree of density, so in addition to being able to determine that the ToDo has been completed, it is also possible to review it later.

[0087] When the ink composition according to the present invention is used in a ballpoint pen, its viscosity is not particularly limited, but in an environment of 20°C, at a rotation speed of 1 rpm (shear speed of 3.84 sec), -1When measured under the following conditions, the sedimentation or aggregation of microcapsule pigments can be suppressed, so a pressure of 1 to 2000 mPa·s is preferable, 3 to 1500 mPa·s is more preferable, and 500 to 1000 mPa·s is even more preferable. Also, in an environment of 20°C, with a rotation speed of 100 rpm (shear speed of 384 sec), the pressure can be suppressed. -1 When measured under the conditions described above, the viscosity is preferably 1 to 200 mPa·s, more preferably 10 to 100 mPa·s, and even more preferably 20 to 50 mPa·s, as this allows for good ink discharge from the tip of the ballpoint pen. By having the viscosity within the above range, the dispersion stability of the microcapsule pigment and the ease of ink flow within the ballpoint pen mechanism can be maintained at a high level. Viscosity was measured using a rheometer (TA Instruments, product name: Discovery HR-2, cone plate (diameter 40 mm, angle 1°)) with the ink placed in a 20°C environment at a rotation speed of 1 rpm (shear speed 3.84 sec). -1 ), or rotational speed 100 rpm (shear speed 384 sec -1 These are values ​​measured under the following conditions.

[0088] When the ink composition according to the present invention is used in a ballpoint pen, its surface tension is not particularly limited, but is preferably 20 to 50 mN / m, and more preferably 25 to 45 mN / m, at a temperature of 20°C. Having the surface tension within the above range makes it easy to suppress ink bleeding and show-through on the paper, and also improves the wettability of the ink to the paper. The surface tension was measured using a surface tension meter [Kyowa Interface Science Co., Ltd., product name: DY-300] with the ink placed in a 20°C environment, and measured using the vertical plate method with a platinum plate.

[0089] When the ink composition according to the present invention is used in a marking pen, its viscosity is not particularly limited, but when measured at 20°C and a rotation speed of 30 rpm, it is preferably 1 to 20 mPa·s, more preferably 1 to 10 mPa·s, and even more preferably 1 to 5 mPa·s. By having the viscosity within the above range, the fluidity of the ink and the dispersion stability of the microcapsule pigment can be improved. The viscosity was measured using a BL-type rotational viscometer (manufactured by Toki Sangyo Co., Ltd., product name: TVB-M type viscometer, L-type rotor) with the ink placed in an environment of 20°C.

[0090] When the ink composition according to the present invention is used in a marking pen, its surface tension is not particularly limited, but is preferably 25 to 50 mN / m, more preferably 25 to 45 mN / m, and even more preferably 35 to 45 mN / m at a temperature of 20°C. Having the surface tension within the above range makes it easy to suppress bleeding of the writing line and show-through to the back of the paper, and also improves the wettability of the ink to the paper surface. The surface tension was measured using a surface tension meter [Kyowa Interface Science Co., Ltd., product name: DY-300] with the ink placed in a 20°C environment, and measured using the vertical plate method with a glass plate.

[0091] The ink composition according to the present invention is housed in a writing instrument equipped with a pen tip and an ink filling mechanism. Examples of writing instruments include various types such as ballpoint pens, marking pens, fountain pens, brush pens, and calligraphy pens.

[0092] There are no particular restrictions on the type of pen tip used for writing instruments; pen tips equipped with various types of tips are used. Examples of ballpoint pen tips include, for example, a tip 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; a tip in which a ball is held in a ball-holding portion formed by cutting a metal material with a drill or the like; a tip in which a resin ball seat is provided inside a metal or plastic tip; or a tip in which the ball held in the above tip is biased forward by a spring. The material of the ballpoint pen tip and ball is not particularly limited, and examples include cemented carbide, stainless steel, ruby, ceramic, resin, rubber, etc. The diameter of the ball is preferably 0.1 to 3.0 mm, more preferably 0.2 to 2.0 mm, and even more preferably 0.3 to 1.0 mm. The ball may also be subjected to surface treatment such as DLC coating.

[0093] Examples of marking pen tips include conventional porous materials with interconnected pores selected from a range of approximately 30-70% porosity, such as resin processed fiber bodies, fused heat-meltable fiber bodies, and felt bodies, or extruded synthetic resin bodies having multiple ink outlets extending in the axial direction. One end is processed into a shape such as a bullet shape, rectangle, or chisel shape according to the purpose for practical use.

[0094] Examples of ink filling mechanisms include ink containers or ink absorbers that can be directly filled with ink compositions. The ink container may be a molded body made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon, or a metal tubular body, and the above-mentioned chip may be directly connected to it, or the ink container and the chip may be connected via a connecting member. The ink-absorbing material is a fiber bundle formed by gathering crimped fibers in the longitudinal direction, and is constructed by embedding it in a covering such as a plastic cylinder or film, and adjusting the porosity to be in the range of approximately 40-90%.

[0095] When filling a ballpoint pen with the ink composition according to the present invention, the structure and shape of the ballpoint pen itself are not particularly limited. For example, a ballpoint pen can be exemplified in which an ink reservoir filled with shear-reducing ink is located inside the barrel, the ink reservoir is in communication with a ballpoint pen tip with a ball attached to its tip, and a backflow prevention stopper is tightly fitted to the end face of the ink.

[0096] An ink backflow prevention composition is filled at the trailing end of the ink contained in the ink container. The ink backflow prevention composition consists of a non-volatile liquid and / or a low-volatility liquid, and 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, and fatty acid-modified silicone oil. The ink backflow prevention composition can be used by using one or more types in appropriate combination.

[0097] It is preferable to add a thickening agent to the ink backflow prevention composition to increase its viscosity to a suitable level. Examples of thickening agents 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. The liquid ink backflow prevention composition described above can also be used in combination with the solid ink backflow prevention composition.

[0098] Furthermore, the barrel itself can be used as the ink filling mechanism, and an example of a ballpoint pen can be created in which ink is directly filled into the barrel and a ballpoint pen tip is attached to the front end of the barrel.

[0099] A ballpoint pen having a ballpoint pen tip and an ink filling mechanism may further include an ink supply mechanism for supplying the ink to be filled into the ink filling mechanism to the pen tip.

[0100] The ink supply mechanism is not particularly limited, but examples include: (1) a mechanism that supplies ink to the pen tip using an ink guide core made of a fiber bundle or the like as an ink flow rate regulator; (2) a mechanism that supplies ink to the pen tip using a comb-shaped ink flow rate regulator interposed therebetween; and (3) a mechanism that supplies ink to the pen tip via a pen core in which a number of discs are arranged in parallel with comb-shaped spacing, a slit-shaped ink guide groove that penetrates the discs axially, and a ventilation groove wider than the groove, and an ink guide core that guides ink from the ink filling mechanism to the pen tip is arranged at the axis.

[0101] The material of the pen tip is not particularly limited as long as it is a synthetic resin that can be injection molded into a comb-groove structure with numerous discs. Examples of synthetic resins include general-purpose polycarbonate, polypropylene, polyethylene, and acrylonitrile-butadiene-styrene copolymer (ABS resin). In particular, acrylonitrile-butadiene-styrene copolymer (ABS resin) is preferably used because it has high moldability and makes it easy to obtain the desired pen tip performance.

[0102] If the ballpoint pen is equipped with the above-described ink supply mechanism, in addition to the above-described ink reservoir and barrel, the above-described ink absorbent can also be used as the ink filling mechanism.

[0103] Specific examples of the configuration of a ballpoint pen containing the ink composition according to the present invention include: (1) a ballpoint pen refill in which a ballpoint pen tip is directly or via a connecting member connected to an ink reservoir, the refill is filled with ink, and an ink backflow prevention body is filled on the end face of the ink, and the ballpoint pen refill is housed in the barrel; (2) a ballpoint pen in which ink is directly filled into the barrel and a mechanism is provided to supply ink to the pen tip by interposing an ink flow control body such as a comb-shaped ink flow control body or an ink guide core made of a fiber bundle as an ink flow control body; (3) a ballpoint pen in which ink is directly filled into the barrel and a mechanism is provided to supply ink to the pen tip via the above-mentioned pen core; and (4) a ballpoint pen in which an ink absorbent body made of an ink-impregnated fiber bundle is housed in the barrel and an ink guide core made of a fiber bundle as an ink flow control body is interposed to supply ink to the pen tip.

[0104] When filling a marking pen with the ink composition according to the present invention, the structure and shape of the marking pen itself are not particularly limited. For example, a marking pen can be described as having an ink reservoir filled with cohesive ink inside the barrel, with the ink reservoir communicating with the marking pen tip. In addition to directly connecting the above-mentioned chip to the ink absorber, the ink absorber and the chip may also be connected via a connecting member.

[0105] A marking pen, comprising a marking pen tip and an ink filling mechanism, may further include an ink supply mechanism for supplying ink to be filled into the ink filling mechanism to the pen tip.

[0106] The ink supply mechanism is not particularly limited, but for example, in addition to the ink supply mechanism provided in the ballpoint pen described above, a mechanism is provided that includes an ink flow rate regulator by a valve mechanism, and supplies ink to the pen tip when the valve is opened. The valve mechanism can use a conventional pumping type that opens when pressed by the tip, and it is preferable that the spring pressure is set to allow it to be opened by the pressure of a pen.

[0107] If the marking pen is equipped with the above-described ink supply mechanism, in addition to the above-described ink absorber, an ink container that can be directly filled with ink may also be used as the ink filling mechanism. Alternatively, the barrel itself may be used as the ink filling mechanism to directly fill the ink.

[0108] Specifically, the configuration of a marking pen containing the ink composition according to the present invention includes: (1) a marking pen in which an ink-absorbing body made of a fiber bundle impregnated with ink is contained in the barrel, and a marking pen tip made of a fiber processed body or resin molded body with capillary gaps formed therein is connected to the barrel directly or via a connecting member so that the ink-absorbing body and the tip are connected; (2) a marking pen in which ink is directly filled into the barrel, and an ink-guiding core made of a comb-shaped ink flow rate regulator or a fiber bundle is interposed as an ink flow rate regulator to supply ink to the pen tip; and (3) a marking pen in which ink is directly filled into the barrel. Examples include: (4) a marking pen in which a tip and an ink reservoir are provided via a valve mechanism that opens when the tip is pressed, and ink is directly filled into the ink reservoir; and (5) a marking pen in which a marking pen refill is housed in a barrel, in which a marking pen tip made of a fiber processed body or resin molded body with capillary gaps formed therein is connected to the ink reservoir, which is made of a fiber bundle made of an ink-impregnated fiber bundle, either directly or via a connecting member, so as to connect the ink reservoir and the tip.

[0109] The ballpoint pen or marking pen according to the present invention can also be in the form of an ink cartridge with a detachable structure. In this case, after the ink contained in the ink cartridge of the writing instrument is used up, the writing instrument can be used again by replacing it with a new cartridge. Ink cartridges can be either those that connect to the writing instrument body and also serve as the barrel of the writing instrument, or those that cover and protect the barrel (rear barrel) after being connected to the writing instrument body. In the latter case, the ink cartridge may be used alone, or the writing instrument body and ink cartridge may be connected before use, or the ink cartridge may be housed in the barrel in an unconnected state so that the user can connect it when using the writing instrument to begin use.

[0110] When the ballpoint pen or marking pen according to the present invention is directly filled with ink, it is preferable to incorporate an agitator, such as an agitator ball, into the ink container or barrel in which the ink is filled, in order to facilitate the redispersion of the microcapsule pigment. Examples of the shape of the agitator include a spherical body and a rod-shaped body. The material of the agitator is not particularly limited, and examples include metal, ceramic, resin, glass, etc.

[0111] The writing instrument according to the present invention preferably includes a cap that covers the writing tip (tip), or a retractable mechanism that allows the writing tip to extend and retract from the writing instrument body (barrel), thereby preventing the writing tip from drying out and becoming unusable, and preventing contamination and damage to the writing tip. A writing instrument equipped with a retractable tip mechanism can be any writing instrument in which the writing tip is stored inside the barrel with the tip exposed to the outside air, and the writing tip protrudes from the barrel opening when the retractable tip mechanism is activated. For example, by manufacturing the ballpoint pen refill or marking pen refill described above, and housing the refill inside the barrel so that the writing tip protrudes from the barrel opening when the retractable tip mechanism is activated, a writing instrument equipped with a retractable tip mechanism (retractable writing instrument) can be manufactured. Furthermore, when a writing instrument is equipped with a retractable mechanism, it can also be a composite type of retractable writing instrument (retractable ballpoint pen or retractable marking pen) that houses multiple ballpoint pen refills or marking pen refills inside the barrel, and the writing tip of any of the refills is extended or retracted from the opening of the barrel by the operation of the retractable mechanism.

[0112] Examples of retractable / retractable mechanisms include: (1) a side-slide type retractable / retractable mechanism in which an operating part (clip) that can move in the front-rear direction is provided protruding radially outward from the rear side wall of the barrel, and the writing tip is extended and retracted from the front end opening of the barrel by sliding the operating part forward; (2) a rear-end knock type retractable / retractable mechanism in which the writing tip is extended and retracted from the front end opening of the barrel by pressing an operating part provided at the rear end of the barrel forward; (3) a side-knock type retractable / retractable mechanism in which the writing tip is extended and retracted from the front end opening of the barrel by pressing an operating part that protrudes from the outer surface of the side wall of the barrel radially inward; and (4) a rotary type retractable / retractable mechanism in which the writing tip is extended and retracted from the front end opening of the barrel by rotating an operating part at the rear of the barrel.

[0113] The form of ballpoint pens and marking pens is not limited to the configuration described above. They may also be equipped with tips of different shapes, or pen tips that dispense ink of different tones or hues, or they may be multi-function writing instruments (such as double-ended or retractable-tip types) that are equipped with tips of different shapes and dispense ink of different tones or hues from each tip.

[0114] The writing produced by writing on a surface using a writing instrument containing the ink composition according to the present invention can be discolored by rubbing with a finger or by using a heating or cooling device. Examples of heating devices include electrically heated color change devices equipped with resistance heating elements such as PTC elements, heated color change devices filled with a medium such as hot water, heated color change devices using steam or laser light, and hair dryers. However, friction members and friction bodies are preferred because they can change color by a simple method. Cooling devices include electrically charged cooling devices using Peltier elements, cooling devices filled with refrigerants such as cold water or ice chips, cold storage agents, refrigerators, and freezers.

[0115] As friction members and friction bodies, elastic materials such as elastomers and plastic foams are preferred, as they are highly elastic and capable of generating appropriate friction and frictional heat when rubbed. However, plastic molded products, stone, wood, metal, fabric, etc., can also be used. While it is also possible to use a general eraser, which is used to erase pencil marks, to rub off the marks, eraser residue is generated during rubbing. Therefore, the above-mentioned friction member and friction body, which generate almost no eraser residue, are preferably used. Examples of materials for friction members and friction bodies include silicone resin and SEBS resin (styrene-ethylene-butadiene-styrene block copolymer). Silicone resin tends to adhere to areas erased by rubbing, and the ink tends to be repelled when writing repeatedly; therefore, SEBS resin is more preferably used.

[0116] The friction member or friction body may be a separate component of any shape from the writing instrument, but by attaching it to the writing instrument, portability can be improved. Furthermore, a writing instrument set can be obtained by combining a writing instrument with a separate friction member or friction body of any shape.

[0117] In the case of writing instruments equipped with a cap, the location where a friction member or friction body is provided is not particularly limited. For example, the cap itself may be formed from a friction member, the barrel itself from a friction member, or, if a clip is provided, the clip itself may be formed from a friction member, or a friction member or friction body may be provided at the tip (top) of the cap or the rear end of the barrel (the part without a writing tip). In the case of a retractable writing instrument, the location where a friction member or friction body is provided is not particularly limited. For example, the barrel itself may be formed from a friction member, or if a clip is provided, the clip itself may be formed from a friction member, or a friction member or friction body may be provided near the barrel opening, at the rear end of the barrel (the part without a writing tip), or at the knock mechanism.

[0118] Preferably, the writing instrument containing the ink composition according to the present invention is a writing instrument that has a marking pen tip made of a resin processed body or resin molded body with capillary gaps formed therein as the pen tip. The ink composition according to the present invention is suitable as a writing instrument (marking pen) that can form a line with good color change from colored (1) to colored (2) because the microcapsule pigment and acid dye are in an interacting state even in the capillary gaps of the marking pen tip, and both the microcapsule pigment and acid dye are stably discharged from the pen tip of the writing instrument. More preferably, the writing instrument has an ink absorbent made of a fiber bundle built into the barrel, and the ink absorbent is connected to the marking pen tip, and the ink composition is impregnated into the ink absorbent. In addition to the above-mentioned effect that both the microcapsule pigment and acid dye are stably discharged from the pen tip of the writing instrument, the writing instrument with the above configuration is more preferably used because the ink absorbent made of a fiber bundle can stably hold the microcapsule pigment and acid dye in an interacting state.

[0119] It is preferable to apply an ink containing the aforementioned polymer flocculant (agglomerating ink) to a writing instrument equipped with the marking pen tip described above, or to a writing instrument equipped with a marking pen tip and an ink absorber. This is preferable because it can stably maintain loose aggregates of microcapsule pigments formed via the polymer flocculant in the capillary gaps of the marking pen tip and in the ink absorber, thereby forming good handwriting.

[0120] A writing instrument set can also be obtained by combining the writing instrument according to the present invention with memo paper. It is preferable that the memo paper is equipped with a section for writing To-Do items, making it easy to use the writing instrument according to the present invention for the purpose of managing To-Do items. The memo paper used with the writing instrument may be a single sheet or multiple sheets. Alternatively, the memo paper may be attached to a backing sheet using adhesive or other fastening means. In addition to a To-Do list section, memo paper may also have a memo section or a design. For example, the right half of the memo paper may have a To-Do list section, and the left half may have a memo section or a design. Alternatively, the memo paper with the To-Do list section and the memo paper with the memo section or design may be separate, and each memo paper may be attached to a backing sheet using adhesive or other fastening means. These memo papers, or the memo papers attached to a backing sheet, may be folded to form a booklet.

[0121] The color of the ToDo entry area, memo entry area, or design on the memo paper is preferably the same as the color of the handwriting formed by the writing instrument according to the present invention, which is colored (1) or colored (2). By having the same color for the handwriting from the writing instrument as the color of the ToDo entry area, memo entry area, or design, a sense of unity can be given to the writing instrument set, and its marketability can be enhanced.

[0122] The writing instrument set may also include stickers, which are used to attach memo paper to paper media such as notebooks or diaries. The sticker consists of a sticker material with an adhesive layer on one side of the base material and a release sheet, with the release sheet attached to the adhesive layer of the sticker material. The sticker is not particularly limited, but it is preferable that the adhesive used in the adhesive layer is weakly tacky or slightly tacky, as it allows for easy removal of memo paper attached to paper media. Furthermore, since it is possible to write on it with the writing instrument according to the present invention and it can be easily cut by hand, it is also preferable that the base material of the sticker material be paper or cloth. The sticker material may consist of one sheet or multiple sheets. If there are multiple sheets of sticker material, they may be arranged on a single release sheet independently of each other, or adjacent to each other. Preferably, the color of the sticker material is the same as the color of the handwriting formed by the writing instrument according to the present invention, which is colored (1) or colored (2). Having the same color for the handwriting and the sticker gives the writing instrument set a sense of unity and enhances its marketability. Furthermore, if the sticker materials are provided adjacent to each other, each sticker material may be colored so that the entire sticker forms a gradient between colored (1) and colored (2), allowing the color change of the handwriting formed by the writing instrument to be confirmed by the stickers provided in the writing instrument set.

[0123] A writing instrument set can also be obtained by combining the writing instrument according to the present invention with a plastic sheet (hereinafter referred to as "template") on which a design or character has been die-cut. When writing on paper media such as a notebook or diary using the writing instrument according to the present invention, the template can be used to create ToDo entry fields, memo entry fields, etc., by the user. Although it is also possible to create ToDo entry fields, memo entry fields, etc., by using a template with a general writing instrument using non-thermochromic ink, it is preferable to use the writing instrument according to the present invention because the design can be easily improved by changing the color of the ToDo entry fields, memo entry fields, etc. The template can also be used as a ruler by adding grid lines. Furthermore, by adding dots across the entire template, it becomes easier to align sections such as to-do lists and memo fields.

[0124] The writing instrument according to the present invention can be used for managing to-do lists, as well as for security purposes such as anti-counterfeiting and password protection, as well as for toys and magic tricks.

[0125] Furthermore, it can be used for memorization purposes in combination with a transparent colored sheet (hereinafter sometimes referred to as "sheet"). Specifically, the hue of the colored (1) handwriting (a color resulting from a mixture of the color of microcapsule pigments in their colored state and the color of acid dyes) formed by the writing instrument according to the present invention differs from the hue of the transparent colored sheet, so the handwriting is visible through the transparent colored sheet, and the hue of the colored (2) handwriting (a color from acid dyes only) satisfies the same color relationship as the hue of the transparent colored sheet. Because the hue of the sheet and the hue of the handwriting satisfy the above relationship, even if the sheet is placed on the colored (1) handwriting formed on the paper, the handwriting is visible through the sheet. If the handwriting is discolored to become colored (2), and the sheet is placed on the colored (2) handwriting, it becomes difficult to distinguish between the areas where the handwriting is formed and the white areas on the paper through the sheet, and the handwriting becomes invisible, so it can be applied for memorization purposes. When the color of the transparent colored sheet is darker than the color of the handwriting, it is preferable because it is highly effective in making the handwriting invisible when the sheet is placed on the colored handwriting (2). Even if the hue of the sheet and the hue of the colored element (2) are not the same, if the hue of the colored element (2) is a constituent color obtained by subtractive color mixing of the sheet's hue, the same effect will be achieved.

[0126] Transparent colored sheets are sheet-like materials formed by incorporating a non-thermochromic coloring agent into a transparent resin, or sheet-like materials formed from transparent resin that have been colored. Their size and thickness are not particularly limited; examples include those roughly the size and thickness of a desk mat, a ruler, or a strip of paper.

[0127] Examples of combinations of the sheet's hue and the colored (2) handwriting's hue include orange sheet and yellow handwriting, red sheet and yellow handwriting, green sheet and yellow handwriting, green sheet and light green handwriting, red sheet and orange handwriting, red sheet and pink handwriting, purple sheet and pink handwriting, purple sheet and blue handwriting, green sheet and blue, blue sheet and light blue handwriting, and so on.

[0128] Furthermore, if black characters are pre-formed on the paper using non-thermochromic ink, a marking pen equipped with a chisel-shaped or similar marking pen tip that can color the characters to be memorized can be used in combination with a transparent colored sheet for memorization purposes. Specifically, the hue of the colored (1) handwriting formed by the writing instrument (marking pen) according to the present invention satisfies the complementary color relationship with the hue of the transparent colored sheet, and the hue of the colored (2) handwriting satisfies the same color relationship with the hue of the transparent colored sheet. Because the hue of the sheet and the hue of the handwriting satisfy the above relationship, when black characters are colored with colored (1) and the sheet is placed on top, the colored areas are visible as black through the sheet, making the black characters formed on the paper invisible and thus suitable for memorization purposes. After memorization is complete, if the colored areas are changed to colored (2), the colored areas are not visible when the sheet is placed on top, and the characters in the colored areas become visible again through the sheet, thus preventing the memorized areas from becoming invisible due to the sheet. When the color of the transparent colored sheet is darker than the color of the handwriting, it is preferable because it is highly effective in making the handwriting invisible when the sheet is placed on the colored handwriting (1). Even if the hue of the sheet and the hue of colored (1) are not complementary colors, if the hue of colored (1) and the hue of the sheet are composed of colors that result in black or a color close to black through subtractive color mixing, a similar effect will be achieved.

[0129] Examples of combinations of the sheet's hue and the colored (1) handwriting's hue include a red sheet with green handwriting, a red sheet with blue handwriting, a red sheet with light blue handwriting, a green sheet with red handwriting, a blue sheet with orange handwriting, an orange sheet with purple handwriting, and so on.

[0130] Examples of combinations of the sheet's hue and the colored (2) handwriting's hue include: orange sheet and yellow handwriting, red sheet and yellow handwriting, green sheet and yellow handwriting, red sheet and orange handwriting, red sheet and pink handwriting, purple sheet and pink handwriting, purple sheet and blue handwriting, green sheet and blue handwriting, and so on. [Examples]

[0131] Examples are shown below. Unless otherwise specified, "parts" in the examples refer to "parts by mass."

[0132] Preparation of reversible thermochromic microcapsule pigment A A reversible thermochromic composition consisting of (a) 3 parts of 3′,6′-bis[phenyl(3-methylphenyl)amino]spiro[isobenzofuran-1(3H),9′-[9H]xanthene]-3-one as component (a), 3 parts of 1,1-bis(4-hydroxyphenyl)-2-ethylhexane and 5 parts of 2,2-bis(4-hydroxyphenyl)hexafluoropropane as component (b), and 50 parts of 4-benzyloxyphenylethyl capric acid as component (c) was added to a mixed solution consisting of 35 parts of aromatic isocyanate prepolymer as a wall material and 40 parts of a co-solvent. The mixture was then emulsified and dispersed in an 8% aqueous polyvinyl alcohol solution, and after stirring continued while heating, 2.5 parts of water-soluble aliphatic-modified amine were added, and stirring was continued to prepare a microcapsule dispersion. Reversible thermochromic microcapsule pigment A with an average particle size of 1.9 μm was obtained from the microcapsule dispersion by centrifugation. Microcapsule pigment A had a complete color development temperature t1 of -20°C and a complete decolorization temperature t4 of 60°C, and reversibly changed from blue to colorless with temperature changes.

[0133] Preparation of reversible thermochromic microcapsule pigment B A reversible thermochromic composition comprising (a) 2 parts of 2-di-n-butylamino-8-di-n-pentylamino-4-methylspiro[5H-[1]benzopyrano[2,3-d]pyrimidine-5,1′(3′H)-isobenzofuran]-3′-one as component (a), 3 parts of 1,1-bis(4-hydroxyphenyl)-2-ethylhexane and 5 parts of 2,2-bis(4-hydroxyphenyl)hexafluoropropane as component (b), and 50 parts of 4-benzyloxyphenylethyl caprate as component (c) was added to a mixed solution consisting of 35 parts of aromatic isocyanate prepolymer as a wall material and 40 parts of a co-solvent. The mixture was then emulsified and dispersed in an 8% aqueous polyvinyl alcohol solution, and after continuing to stir while heating, 2.5 parts of a water-soluble aliphatic modified amine were added, and stirring was continued to prepare a microcapsule dispersion. Reversible thermochromic microcapsule pigment B with an average particle size of 2.3 μm was obtained from the microcapsule dispersion by centrifugation. Microcapsule pigment B had a complete color development temperature t1 of -20°C and a complete decolorization temperature t4 of 58°C, and reversibly changed from pink to colorless with temperature changes.

[0134] Example 1 Preparation of ink composition 20 parts of microcapsule pigment A (pre-cooled to below -20°C to develop blue color), 0.25 parts of red acid dye [manufactured by Daiwa Chemical Industries, Ltd., product name: IJ RED 319H], and polymer flocculant (hydroxyethylcellulose) [manufactured by Dow Chemical Japan Ltd., product name: CELLOSIZE] are mixed together. An ink composition was prepared by mixing 0.4 parts of WP-09L, 0.4 parts of an acrylic polymer dispersant [manufactured by Lubrizol Japan Co., Ltd., product name: Solspers 43000], 0.2 parts of a preservative (2-pyridinethiol 1-oxide sodium) [manufactured by Lonza Japan Co., Ltd., product name: sodium omazine], 0.2 parts of a preservative (3-iodo-2-propynyl N-butylcarbamate) [manufactured by Lonza Japan Co., Ltd., product name: Glycasil 2000], 30 parts of glycerin, 0.01 parts of an antifoaming agent, 0.3 parts of a pH adjuster (10% diluted phosphoric acid solution), and 48.24 parts of water in an aqueous vehicle. Furthermore, the content of microcapsule pigment relative to the total mass of the ink composition (P1) was 20, the content of acid dye relative to the total mass of the ink composition (P2) was 0.25, and the ratio of P1 to P2 (P2 / P1) was 0.0125.

[0135] Manufacturing of writing instruments The above ink composition was impregnated into an ink-absorbing body made of polyester sliver coated with a synthetic resin film, and housed in a barrel made of polypropylene resin. A resin-processed pen body (chisel type) made of polyester fiber was assembled to the tip of the barrel via a resin holder, and a cap was attached to create a refillable writing instrument (marking pen). SEBS resin was attached to the rear end of the barrel as a friction member. When writing (handwriting) was created on paper using the marking pen described above, the handwriting appeared bluish-purple at room temperature (25°C). When the handwriting was rubbed with a friction material, the microcapsule pigment A became discolored, and the handwriting turned pink. This state could be maintained as long as the temperature was not cooled below -20°C. Furthermore, when the paper was placed in a freezer and cooled below -20°C, the handwriting reverted to bluish-purple, and this discoloration behavior could be repeatedly reproduced.

[0136] Examples 2-6 and Comparative Examples 1-4 Ink compositions were prepared in the same manner as in Example 1, except that the types and amounts of materials used were changed to those listed in Table 1 below. The values ​​of P1, P2, and P2 / P1 in each ink composition are as shown in Table 1. The writing instruments (marking pens) for Examples 2-5 were prepared in the same manner as in Example 1, and the writing instrument for Example 6 was prepared as described below. The color changes of the handwriting obtained with each writing instrument are shown in Table 1.

[0137] Example 6 Manufacturing of writing instruments An ink-absorbing body made of polyester sliver coated with a synthetic resin film was impregnated with the ink composition of Example 6, housed in a barrel made of polypropylene resin, and assembled to connect a resin-processed polyester fiber pen body (bullet-shaped) to the tip of the barrel via a resin holder. A cap was then attached to create a refillable writing instrument (marking pen). A SEBS resin was attached to the rear end of the barrel as a friction member.

[0138] [Table 1]

[0139] The contents of the materials in Table 1 are explained according to the note numbers. (1) Those that have been pre-cooled to below -20°C to produce a blue color. (2) Those that have been pre-cooled to below -20°C to develop a pink color. (3) Red acid dye [Manufactured by Daiwa Chemical Co., Ltd., Product name: IJ RED 319H] (4)Blue acid dye solution [Manufactured by Orient Chemical Industries, Ltd., Product name: WATER BLUE 106-L (Solid content: 10%)] (5) Yellow acid dye [Manufactured by Sumitomo Chemical Co., Ltd., Product name: Acid Yellow NS] (6) Red basic dye [Manufactured by Hodogaya Chemical Industry Co., Ltd., product name: SWT Red 4] (7) Green basic dye [Manufactured by Hodogaya Chemical Co., Ltd., Product name: Diamond Green GH] (8) Orange basic dye [Manufactured by Hodogaya Chemical Co., Ltd., Product name: SWT Orange 1] (9) Hydroxyethylcellulose [Manufactured by Dow Chemical Japan Ltd., Product name: CELLOSIZE WP-09L] (10) Acrylic polymer dispersants [Manufactured by Lubrizol Japan Co., Ltd., Product name: Solspers 43000] (11) 2-Pyridinethiol 1-oxide sodium [Manufactured by Lonza Japan Co., Ltd., Product name: Sodium Omazine] (12) 3-iodo-2-propynyl N-butylcarbamate [Manufactured by Lonza Japan Co., Ltd., Product name: Glycasil 2000] (13) 10% diluted phosphoric acid solution (14) Sodium polytungstate (Manufactured by SOMETU, product name: SPT-1)

[0140] [Viscosity measurement] The viscosity of each ink composition prepared in Examples 1-6 and Comparative Examples 1-4 was measured using a BL-type rotational viscometer [manufactured by Toki Sangyo Co., Ltd., product name: TVB-M type viscometer with L-type rotor] at room temperature (20°C) and a rotational speed of 30 rpm. The measurement results are shown in Table 2.

[0141] [Surface tension measurement] For each ink composition prepared in Examples 1-6 and Comparative Examples 1-4, the surface tension was measured using an automatic surface tension meter [Kyowa Interface Science Co., Ltd., product name: DY-300] at room temperature (20°C) using the vertical plate method with a glass plate. The measurement results are shown in Table 2.

[0142] [pH measurement] The pH of each ink composition prepared in Examples 1-6 and Comparative Examples 1-4 was measured at room temperature (20°C) using a pH meter [Toa DKK Co., Ltd., product name: IM-40S]. The measurement results are shown in Table 2.

[0143] [Table 2]

[0144] [Written Exam] Using the writing instruments prepared in Examples 1-5 and Comparative Examples 1-4, a 15cm straight line was handwritten parallel to the short side of an A4-sized test sheet (portrait orientation) at room temperature (20°C), with the wide side of the pen in close contact with the paper surface. This was repeated for 5 lines. Using the writing instrument prepared in Example 6, at room temperature (20°C), 12 elliptical circles, approximately 15mm in major axis and 8mm in minor axis, were handwritten in a spiral pattern parallel to the short side of an A4-sized test sheet (portrait orientation), with the circles touching each other. This was repeated for 5 lines. Test paper A conforming to the old JIS P3201 was used. The handwriting samples obtained from the written test (initial samples) showed no defects such as smudging and were clear with excellent color development. Furthermore, when a portion of the handwriting was rubbed with a friction element attached to the rear end of the barrel, the color of the handwriting changed.

[0145] [Heating and Cooling Test] The writing instruments used in the aforementioned written examination were capped and subjected to heating and cooling according to the following procedure. (Heating and cooling procedure) 1. Place each writing instrument in a constant temperature bath set to 80°C and leave it undisturbed for 3 days with the nib facing upwards (upright position). 2. Remove each writing instrument from the constant temperature bath and leave it undisturbed at room temperature (20°C) for 5 hours with the pen tip facing sideways. 3. Place each writing instrument in a constant temperature bath set to -45°C and leave it undisturbed for one day with the pen tip facing sideways. 4. Remove each writing instrument from the constant temperature bath and leave it lying on its side at room temperature (20°C) for one day.

[0146] [Written examination after heating and cooling] Using the writing instruments from Examples 1-5 and Comparative Examples 1-4, after the aforementioned heating and cooling tests, a 15cm straight line was handwritten at room temperature (20°C) parallel to the short side of an A4-sized test sheet (portrait orientation), with the wide side of the pen in close contact with the paper surface. This was repeated for 5 lines. Using the writing instrument from Example 6, at room temperature (20°C), 12 elliptical circles, approximately 15mm in major axis and 8mm in minor axis, were handwritten in a spiral pattern parallel to the short side of an A4-sized test sheet (portrait orientation), with the circles touching each other. This was repeated for 5 lines. Test paper A conforming to the old JIS P3201 was used. The handwriting samples obtained above showed no defects such as smudging. A portion of the handwriting was rubbed with a friction element attached to the rear end of the barrel, causing a change in color.

[0147] The color of the handwriting before and after discoloration, obtained from a written test after heating and cooling, was visually inspected and evaluated according to the following criteria. The evaluation results are shown in Table 3 below, with an evaluation of "A" being considered a passing grade. A: The color of the handwriting before and after discoloration, obtained from the written test after heating and cooling, was the same as, or at the same level as, the color of the handwriting before and after discoloration in the initial handwriting. B: The color of the handwriting before and after discoloration, obtained from the written test after heating and cooling, differed from the color of the handwriting before and after discoloration in the initial handwriting, and was lighter in color compared to the initial handwriting. C: The color of the handwriting before and after discoloration, obtained from the writing test after heating and cooling, differed from the color of the handwriting before and after discoloration in the initial handwriting, and the discolored handwriting obtained from the writing test after heating and cooling was not visible.

[0148] [Table 3] [Explanation of Symbols]

[0149] T1 Full Color Temperature T2 color development start temperature t3 decolorization start temperature t4 complete color erasure temperature T1 complete discoloration temperature T2 decolorization start temperature T3 color development start temperature T4 Full Color Temperature ΔH Hysteresis width

Claims

1. A reversible thermochromic aqueous ink composition for writing instruments comprising at least a reversible thermochromic composition containing a reversible thermochromic microcapsule pigment comprising (a) an electron-donating color-developing organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color reaction between the two occurs, an acid dye, and water, wherein the pH of the ink composition is in the range of 3 to 7, and exhibits an intermodal color change from a colored state (1), which is a mixture of the color from the reversible thermochromic microcapsule pigment in its colored state and the color from the acid dye, to a colored state (2), which is the color from the acid dye alone.

2. The content of the reversible thermochromic microcapsule pigment relative to the total mass of the ink composition is P. １ The content of the acid dye relative to the total mass of the ink composition is P. ２ In that case, P ２ / P １ Regarding this, 0.003 ≤ P ２ / P １ The ink composition according to claim 1, satisfying ≤0.

05.

3. An ink composition according to claim 1 or 2, comprising a polymer flocculant.

4. An ink composition according to any one of claims 1 to 3, comprising an acrylic polymer dispersant.

5. A writing instrument comprising an ink composition according to any one of claims 1 to 4.

6. The writing instrument according to claim 5, further comprising a friction member that changes the color of the writing made by the aforementioned writing instrument due to frictional heat.

7. A marking pen according to claim 5 or 6, comprising a marking pen tip made of a resin processed body or resin molded body having capillary gaps formed therein.

8. The writing instrument according to claim 7, comprising an ink-absorbing body made of a fiber bundle inside the barrel, wherein the ink-absorbing body and the marking pen tip are connected, and the ink-absorbing body is impregnated with an ink composition.

9. A writing instrument set comprising a writing instrument according to any one of claims 5 to 8 and memo paper.

10. The writing instrument set according to claim 9, wherein the memo paper is provided with a To-Do entry field.

11. The writing instrument set according to claim 9 or 10, further comprising a seal.

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