Water-based ink composition for writing instruments and writing instruments containing the same

Abstract

The present invention provides an aqueous ink composition for writing instruments that uses a microcapsule pigment that suppresses the hard cake formation of the microcapsule pigment in the aqueous ink composition over a long period of time and has excellent redispersibility, as well as a writing instrument incorporating this composition. [Solution] An aqueous ink composition for a writing instrument containing the same, comprising a wall film composed of an isocyanate compound and a polymer comprising at least one of the constituent units represented by formula (I) and the constituent unit represented by formula (II) in the specification, a microcapsule pigment enclosing a core material, catechins, and water.

Description

[Technical Field]

[0001] This invention relates to an aqueous ink composition for writing instruments. Furthermore, it relates to an aqueous ink composition for writing instruments and a writing instrument using microcapsule pigments. [Background technology]

[0002] Traditionally, writing instrument inks have sometimes used microcapsule pigments, in which various coloring components are encapsulated in microcapsules (wall films) as the core material, depending on the purpose of adjusting specific gravity or stabilization. For example, microcapsule pigments have been disclosed in which pigments such as titanium dioxide, which has a high specific gravity, or carbon black, which has some difficulty in dispersibility, are encapsulated in microcapsules. These microcapsule pigments consist of a water-insoluble medium and the aforementioned pigment as a core material, encapsulated in a shell layer (wall film) composed of a trimethylolpropane adduct of xylylene diisocyanate and hexamethylenediamine (see, for example, Patent Document 1). Furthermore, a microcapsule pigment is disclosed in which a reversible thermochromic composition, comprising an electron-donating chromogenic organic compound, an electron-accepting compound, and a reaction medium (desensitizer) that reversibly induces an electron transfer reaction between the electron-donating chromogenic organic compound and the electron-accepting compound in a specific temperature range, is used as a core material and encapsulated in a film (wall film) composed of a polyvalent isocyanate and xylylenediamine (see, for example, Patent Document 2).

[0003] These microcapsule pigments are difficult to maintain a uniform dispersion state in aqueous ink compositions. In particular, in low-viscosity ink compositions, the microcapsule pigments tend to settle and aggregate. Depending on the difference in specific gravity between the microcapsule pigments and the vehicle, ink separation may occur, and over time, the microcapsule pigments may form hard cakes. Furthermore, when hard cakes form in the ink, there is a problem in that redispersion of the microcapsule pigments becomes difficult. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-122168 [Patent Document 2] Japanese Patent Application Publication No. 7-40660 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention aims to provide an aqueous ink composition for writing instruments that uses a microcapsule pigment that suppresses the hard cake formation of the microcapsule pigment in the aforementioned aqueous ink composition for a long period of time and has excellent redispersibility, as well as a writing instrument containing it. [Means for solving the problem]

[0006] The present invention requires an aqueous ink composition for writing instruments comprising a microcapsule pigment containing a core material in a wall film composed of an isocyanate compound and a polymer comprising at least one of the structural units represented by the following formula (I) and the following formula (II), catechins, and water. [ka] [In the formula, n1 represents an integer of 0 or 1, and X1 represents one of the following: hydrogen halide, carboxylic acid, sulfuric acid, sulfuric acid ester, phosphoric acid, sulfonic acid, or amide sulfuric acid.] [ka] [In the formula, n2 represents an integer of 0 or 1, and X2 represents one of the following: hydrogen halide, carboxylic acid, sulfuric acid, sulfuric acid ester, phosphoric acid, sulfonic acid, or amide sulfuric acid.] Furthermore, the ink composition must contain the catechins in an amount of 0.05 to 1.0% by mass, and the catechins must be at least one compound selected from those represented by the following formula (A). [ka] [In the formula, R 1 ~R 4 Each of these independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, with at least one being a hydrogen atom. 5 R represents a residue obtained by removing the OH group from a hydrogen atom or a carboxyl group of gallic acid. 6 [This represents a hydrogen atom or a hydroxyl group.] Furthermore, the requirements are that the microcapsule pigment is added in an amount of 10 to 35% by mass of the total amount of the ink composition, the core material is a thermochromic material that changes color when heated, and the thermochromic material is a reversible thermochromic composition comprising (a) an electron-donating color-developing organic compound, (b) an electron-accepting compound, and (c) a reaction medium that controls the color reaction of (a) and (b). Furthermore, the requirements include a writing instrument containing the aqueous ink composition for writing instruments described in any of the above, and comprising a friction member that changes the color of the writing made by the writing instrument due to frictional heat. [Effects of the Invention]

[0007] In this invention, by using a microcapsule pigment with a wall film composed of an isocyanate compound and a polymer having specific structural units, in combination with catechins, the hard cake formation of the microcapsule pigment is suppressed even when the aqueous ink composition is stored for a long period of time, and the redispersibility is excellent, resulting in an aqueous ink composition for writing instruments and a writing instrument containing it that can produce good writing lines without smudging or variations in shading over a long period of time. [Modes for carrying out the invention]

[0008] In this invention, we have found that by using a microcapsule pigment whose wall film has excellent redispersibility in an aqueous medium, and by using catechins in combination to create an aqueous ink, the catechins suppress the deterioration of the wall film over long periods of time in the aqueous ink. Therefore, even when various additives are applied to the ink composition, the wall film's property of being resistant to hard cake formation can be maintained for a long period of time, and the microcapsule pigment can permanently maintain a state of excellent redispersibility.

[0009] The microcapsule pigment consists of a core material and a wall film encapsulating the core material, and the wall film is composed of an isocyanate compound described below and a polymer having specific structural units. Each component constituting the microcapsule pigment according to the present invention will be described below.

[0010] The isocyanate compound according to the present invention is used as a wall film forming material of the microcapsule pigment. The isocyanate compound is not particularly limited, and an aliphatic isocyanate compound, an aromatic isocyanate compound, or the like can be used, but an aromatic isocyanate compound is preferred. Further, a compound having two or more isocyanate groups (-NCO) in one molecule is preferred, and specifically, a bifunctional diisocyanate compound, a trifunctional triisocyanate compound, and a tetrafunctional tetraisocyanate compound can be mentioned.

[0011] Examples of isocyanate compounds include m-phenylenediisocyanate, p-phenylenediisocyanate, 2,6-tolylenediisocyanate, 2,4-tolylenediisocyanate, naphthalene-1,4-diisocyanate, naphthalene-1,5-diisocyanate, diphenylmethane-4,4′-diisocyanate, hydrogenated diphenylmethane diisocyanate, 3,3′-dimethylbiphenyl-4,4′-diisocyanate, 3,3′-dimethoxybiphenyl-4,4′-diisocyanate, and 3,3′-dimethyldiphenylmethane-4,4 ′-Diisocyanate, 1,4-Xylylenediisocyanate, 1,3-Xylylenediisocyanate, Tetramethyl-m-Xylylenediisocyanate, Tetramethyl-p-Xylylenediisocyanate, Hydrogenated Xylylenediisocyanate, 4-Chloro-1,3-Xylylenediisocyanate, 2-Methyl-1,3-Xylylenediisocyanate, Diphenylpropane-4,4′-Diisocyanate, Diphenylhexafluoropropane-4,4′-Diisocyanate, Trimethylenediisocyanate, Hexamethylenediisocyanate, Trimethyl Diisocyanates such as hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, trans-1,4-cyclohexylene diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, 1,4-bis(isocyanatomethyl)cyclohexane, 1,3-bis(isocyanatomethyl)cyclohexane, isophorone diisocyanate, lysine diisocyanate, diphenyl ether-4,4′-diisocyanate, 2,6-diisocyanatocaproic acid, norbornane diisocyanate, etc. Examples of triisocyanate compounds include triisocyanate compounds such as 4,4′,4″-triphenylmethane triisocyanate, toluene-2,4,6-triisocyanate, tris(isocyanatophenyl)thiophosphate, 1,6,11-undecanetriyltriisocyanate, 4-(isocyanatomethyl)octane-1,8-diyldiisocyanate, 1,3,6-hexamethylene triisocyanate, and lysine triisocyanate; and tetraisocyanate compounds such as 4,4′-dimethyldiphenylmethane-2,2′,5,5′-tetraisocyanate. The isocyanate compound can be used alone or in combination of two or more kinds.

[0012] The isocyanate compound according to the present invention may be a polymer or an adduct using the above isocyanate compound. Examples of the polymer or adduct include a dimer of a diisocyanate compound, a trimer of a diisocyanate compound (a biuret form or an isocyanurate form), an adduct (an adduct form) obtained by adding a diisocyanate compound to a compound having three or more active hydrogen groups in one molecule (for example, a polyol, a polyamine, a polythiol, etc.), a formalin condensate of benzene isocyanate, a polymer of an isocyanate compound having a polymerizable group such as methacryloyloxyethyl isocyanate, and the like.

[0013] Examples of the polymer or adduct of the isocyanate compound include a dimer of 2,4-tolylene diisocyanate, a biuret form or an isocyanurate form of hexamethylene diisocyanate, an isocyanurate form of 2,4-tolylene diisocyanate and hexamethylene diisocyanate, a trimethylolpropane adduct of hexamethylene diisocyanate, a trimethylolpropane adduct of 2,4-tolylene diisocyanate, a trimethylolpropane adduct of 1,4-xylylene diisocyanate, a trimethylolpropane adduct of 1,3-xylylene diisocyanate, a hexanetriol adduct of 2,4-tolylene diisocyanate, polymethacryloyloxyethyl isocyanate, polymethylene polyphenyl polyisocyanate, and the like.

[0014] The polymer according to the present invention is used as a curing agent that acts on the isocyanate compound which is a wall film forming material, and contains at least one of a structural unit represented by the following formula (I) and a structural unit represented by the following formula (II). Such a polymer is a cationic polymer (cationic polymer) that exhibits cationicity in an aqueous medium such as water.

[0015]

Chemical formula

[0016] Examples of hydrogen halides for X1 or X2 include hydrogen chloride (hydrochloric acid), hydrogen bromide, and hydrogen iodide; examples of carboxylic acids include acetic acid, propionic acid, and butyric acid; examples of sulfuric acid esters include methyl sulfuric acid and ethyl sulfuric acid; and examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, 1-propanesulfonic acid, and 1-butanesulfonic acid.

[0017] The microcapsule pigment according to the present invention can have its surface positively charged by using a polymer containing at least one of the constituent units shown in formula (I) and formula (II). This causes electrostatic repulsion between the microcapsule pigments, which suppresses the dense aggregation of the microcapsule pigments into a hard cake, resulting in a microcapsule pigment with excellent redispersibility.

[0018] Examples of monomers that form the constituent unit shown in formula (I) include allylamine or its salts. Examples of monomers that form the constituent unit shown in formula (II) include diallylamine or its salts.

[0019] As the polymer according to the present invention, a polymer having the structural unit shown in formula (I) above can be used, and for example, the polymer shown in formula (1) below can be exemplified. The polymer represented by the following formula (1) is an allylamine polymer or a polymer of an allylamine salt. [ka] (In the formula, n1 represents an integer of 0 or 1, X1 represents one of the following: hydrogen halide, carboxylic acid, sulfuric acid, sulfuric acid ester, phosphoric acid, sulfonic acid, or amide sulfuric acid, and n represents a natural number.)

[0020] The mass-average molecular weight of the polymer represented by formula (1) is in the range of 500 to 200,000, where n represents the degree of polymerization required for the mass-average molecular weight to be 500 to 200,000. The mass-average molecular weight is preferably in the range of 1,000 to 150,000, and more preferably in the range of 1,500 to 100,000.

[0021] The polymer according to the present invention is preferably a polymer in formula (1) where n1 is 0 or 1 and X1 is hydrochloric acid, acetic acid, or amidosulfuric acid, and more preferably a polymer where n1 is 0 or 1 and X1 is hydrochloric acid. Such polymers are excellent at positively charging the surface of the microcapsule pigments and generating electrostatic repulsion between the microcapsule pigments, which makes it easier to suppress the dense aggregation of microcapsule pigments into hard cakes and to improve redispersibility.

[0022] Examples of polymers represented by formula (1) include products manufactured by Nitto Boseki Medical Co., Ltd., with product names: PAA-01, PAA-03, PAA-05, PAA-08, PAA-15C, PAA-25, PAA-HCL-01, PAA-HCL-03, PAA-HCL-05, PAA-HCL-3L, PAA-HCl-10L, PAA-SA, etc.

[0023] As the polymer according to the present invention, a polymer having the structural unit shown in formula (II) above can be used, and for example, the polymer shown in formula (2) below can be exemplified. The polymer represented by formula (2) below is a diallylamine polymer or a polymer of a salt of diallylamine. [ka] (In the formula, n² represents an integer of 0 or 1, X² represents one of the following: hydrogen halide, carboxylic acid, sulfuric acid, sulfuric acid ester, phosphoric acid, sulfonic acid, or amide sulfuric acid, and n represents a natural number.)

[0024] The mass-average molecular weight of the polymer represented by formula (2) is in the range of 500 to 200,000, where n represents the degree of polymerization required for the mass-average molecular weight to be 500 to 200,000. The mass-average molecular weight is preferably in the range of 1,000 to 150,000, more preferably 2,000 to 100,000, and even more preferably 5,000 to 50,000.

[0025] The polymer according to the present invention is preferably a polymer in formula (2) where n2 is 0 or 1 and X2 is hydrochloric acid, acetic acid, or amidosulfuric acid, and more preferably a polymer where n2 is 0 or 1 and X2 is hydrochloric acid. Such polymers are excellent at positively charging the surface of the microcapsule pigments and generating electrostatic repulsion between the microcapsule pigments, which makes it easier to suppress the dense aggregation of microcapsule pigments into hard cakes and to improve redispersibility.

[0026] Examples of polymers represented by formula (2) include products manufactured by Nitto Boseki Medical Co., Ltd., such as PAS-21 and PAS-21CL.

[0027] The polymer according to the present invention can be a polymer having both the structural unit shown in formula (I) and the structural unit shown in formula (II) above, for example, the polymer shown in formula (3) below can be exemplified. The polymer represented by formula (3) below is a copolymer of allylamine or a salt of allylamine and diallylamine or a salt of diallylamine. [ka] (In the formula, n1 and n2 each independently represent an integer of 0 or 1, X1 and X2 each independently represent one of the following: hydrogen halide, carboxylic acid, sulfuric acid, sulfuric acid ester, phosphoric acid, sulfonic acid, or amide sulfuric acid, and m and n each independently represent a natural number.)

[0028] The mass-average molecular weight of the polymer represented by formula (3) is in the range of 500 to 200,000, where m and n represent the degree of polymerization required to achieve a mass-average molecular weight of 500 to 200,000. The mass-average molecular weight is preferably in the range of 1,000 to 150,000, more preferably 5,000 to 150,000, and even more preferably 10,000 to 100,000.

[0029] The polymer according to the present invention is preferably one in which n1 and n2 are both 0 in formula (3), or n1 and n2 are both 1 and X1 and X2 are both hydrochloric acid, acetic acid, or amidosulfuric acid, and more preferably one in which n1 and n2 are both 1 and X1 and X2 are both hydrochloric acid or acetic acid.

[0030] Examples of polymers represented by formula (3) include those manufactured by Nitto Boseki Medical Co., Ltd., with product names: PAA-D11, PAA-D11-HCL, PAA-D41-HCL, PAA-D19-HCL, PAA-D19A, etc.

[0031] The polymer according to the present invention may contain other structural units other than those represented by formula (I) and formula (II). Other constituent units include, for example, the constituent unit shown in formula (III) below, acrylamide-derived constituent units, and sulfur dioxide-derived constituent units (sulfonyl group, -SO2-). [ka] (In the formula, X3 -R3 represents one of the following: a halide ion, carboxylate ion, sulfate ion, sulfate ester ion, phosphate ion, or sulfonate ion. R3 and R3' each independently represent an alkyl group having 1 to 3 carbon atoms.

[0032] X3 - Examples of halide ions include chloride ions, bromide ions, and iodide ions; examples of carboxylic acid ions include acetate ions, propionate ions, and butyrate ions; examples of sulfate ester ions include methyl sulfate ions and ethyl sulfate ions; and examples of sulfonate ions include methanesulfonate ions, ethanesulfonate ions, 1-propanesulfonate ions, and 1-butanesulfonate ions.

[0033] Regarding R3 and R3', examples of alkyl groups having 1 to 3 carbon atoms include methyl, ethyl, n-propyl, and isopropyl groups.

[0034] As an example of a polymer containing the constituent unit shown in formula (III) above, the polymer shown in formula (4) below can be cited. [ka] (In the formula, n1 represents an integer of 0 or 1, X1 represents one of hydrogen halides, carboxylic acids, sulfuric acid, sulfuric acid esters, phosphoric acid, sulfonic acid, or amide sulfuric acid, X3 - (where R3 represents one of the following: halide ion, carboxylate ion, sulfate ion, sulfate ester ion, phosphate ion, or sulfonate ion; R3 and R3' each independently represent an alkyl group having 1 to 3 carbon atoms; and m and n each independently represent a natural number.)

[0035] The mass average molecular weight of the polymer represented by the formula (4) is in the range of 500 to 200,000, and m and n represent the degree of polymerization necessary for the mass average molecular weight to be 500 to 200,000. The mass average molecular weight is preferably in the range of 1,000 to 100,000, more preferably in the range of 5,000 to 50,000, and still more preferably in the range of 10,000 to 20,000.

[0036] As the polymer according to the present invention, a polymer in which n1 is 0 in the formula (4) and R3 and R3′ are each independently a methyl group or an ethyl group is preferable, n1 is 0, R3 and R3′ are both methyl groups, and X3 - is a chloride ion, or a polymer in which n1 is 0, one of R3 and R3′ is a methyl group, the other is an ethyl group, and X3 - is ethyl sulfate ion (C2H5SO4 - ) is more preferable.

[0037] Specific examples of the polymer represented by the formula (4) include those manufactured by Nitto Boehringer Ingelheim Co., Ltd., product name: PAA-1123, etc.

[0038] Examples of the polymer containing a structural unit derived from acrylamide as other structural units include, for example, a polymer represented by the following formula (5).

Chemical formula

[0039] The mass average molecular weight of the polymer represented by the formula (5) is in the range of 500 to 200,000, and m and n represent the degree of polymerization necessary for the mass average molecular weight to be 500 to 200,000. The mass average molecular weight is preferably in the range of 1,000 to 100,000, more preferably in the range of 2,000 to 50,000, and still more preferably in the range of 5,000 to 20,000.

[0040] The polymer according to the present invention is preferably a polymer in formula (5) where n2 is 1 and X2 is one of hydrochloric acid, acetic acid, or amidosulfuric acid, and more preferably a polymer in which n2 is 1 and X2 is hydrochloric acid.

[0041] Examples of polymers represented by formula (5) include PAS-2141CL, manufactured by Nitto Boseki Medical Co., Ltd.

[0042] As an example of a polymer containing sulfur dioxide-derived structural units (sulfonyl group, -SO2-) as other structural units, the polymer represented by the following formula (6) can be cited. [ka] (In the formula, n² represents an integer of 0 or 1, X² represents one of the following: hydrogen halide, carboxylic acid, sulfuric acid, sulfuric acid ester, phosphoric acid, sulfonic acid, or amide sulfuric acid, and n represents a natural number.)

[0043] The mass-average molecular weight of the polymer represented by formula (6) is in the range of 500 to 200,000, where n represents the degree of polymerization required for the mass-average molecular weight to be 500 to 200,000. The mass-average molecular weight is preferably in the range of 1,000 to 50,000, more preferably 1,500 to 25,000, and even more preferably 2,000 to 10,000.

[0044] The polymer according to the present invention is preferably a polymer in formula (6) where n2 is 1 and X2 is one of hydrochloric acid, acetic acid, or amidosulfuric acid, and more preferably a polymer where n2 is 1 and X2 is hydrochloric acid or acetic acid.

[0045] Examples of polymers represented by formula (6) include products manufactured by Nitto Boseki Medical Co., Ltd., such as PAS-92 and PAS-92A.

[0046] As the polymer according to the present invention, a polymer obtained by partially modifying a primary amine of a polymer having a constituent unit in formula (I) above where n1 is 0 can also be used, for example, the polymer shown in formula (7) below can be exemplified. [ka] (In the formula, R represents one of the following: an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, or an amino group; and m and n each independently represent natural numbers.)

[0047] Examples of alkyl groups having 1 to 3 carbon atoms include methyl, ethyl, n-propyl, and isopropyl groups, while examples of alkoxy groups having 1 to 3 carbon atoms include methoxy, ethoxy, n-propoxy, and isopropoxy groups.

[0048] The mass-average molecular weight of the polymer represented by formula (7) is in the range of 500 to 200,000, where m and n represent the degree of polymerization required to achieve a mass-average molecular weight of 500 to 200,000. The mass-average molecular weight is preferably in the range of 1,000 to 150,000, more preferably 1,500 to 100,000, and even more preferably 5,000 to 50,000.

[0049] Examples of polymers represented by formula (7) include those manufactured by Nitto Boseki Medical Co., Ltd., with product names: PAA-U5000, PAA-U7030, PAA-AC5050A, PAA-N5000, PAA-N5050CL, etc.

[0050] The mass-average molecular weight of the polymer according to the present invention is the value obtained by GPC (gel permeation chromatography) on a polyethylene glycol basis.

[0051] The amount of polymer blended with the isocyanate compound in the microcapsule pigment according to the present invention is not particularly limited, but it is preferable that the polymer be blended in the range of 1 to 30 parts by mass per 100 parts by mass of the isocyanate compound, more preferably in the range of 2 to 25 parts by mass, and even more preferably in the range of 3 to 20 parts by mass. By ensuring that the amount of polymer blended with the isocyanate compound is within the above range, it becomes easier to positively charge the surface of the microcapsule pigment, thereby improving the redispersibility of the microcapsule pigment.

[0052] The wall film of the microcapsule pigment according to the present invention is mainly composed of a urea resin (polyurea) or urea urethane resin (polyurea urethane), which is formed by a polymerization reaction of an isocyanate compound, a polymer having specific structural units, and a compound having a hydroxyl group (-OH) as needed.

[0053] Examples of compounds having a hydroxyl group (-OH), i.e., alcohol-based compounds, include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, glycerin, catechol, resorcinol, hydroquinone, and other polyols having two or more hydroxyl groups. Alcohol compounds can be used individually or in combination of two or more.

[0054] Examples of core materials include colored compositions consisting of a coloring material and a medium. Examples of colored compositions include those in which dyes or pigments, as coloring materials, are dissolved or dispersed in an aqueous or oily medium.

[0055] Examples of dyes include acid dyes, basic dyes, direct dyes, oil-soluble dyes, and disperse dyes. Examples of pigments include inorganic pigments, organic pigments, luminescent pigments, fluorescent pigments, and phosphorescent pigments. Pigment dispersants may also be used as needed. Examples of pigment dispersants include anionic and nonionic surfactants; anionic polymers such as polyacrylic acid and styrene-acrylic acid; and nonionic polymers such as PVP and PVA.

[0056] Examples of aqueous media include tap water, deionized water, ultrafiltered water, and distilled water. Examples of oily media include monobasic acid esters, dibasic acid monoesters, dibasic acid diesters, esters such as partial or complete esters of polyhydric alcohols, aromatic hydrocarbons such as alkylbenzenes and alkylnaphthalenes, higher alcohols, ketones, and ethers. Aqueous media or oil-based media can be used individually or in combination of two or more.

[0057] As a coloring composition, a thermochromic material that changes color with temperature can also be used. This color change may be reversible or irreversible, but a reversible thermochromic material is preferred because it can repeatedly exhibit color changes with temperature. Examples of thermochromic materials used as coloring compositions include coloring compositions comprising at least (a) an electron-donating chromogenic organic compound as a coloring material and (b) an electron-accepting compound as a medium. Furthermore, examples of coloring compositions comprising at least a homogeneous compatibility of component (a) as a coloring material and component (b) as a medium, and a reaction medium that determines the temperature at which the color reaction of components (a) and (b) occurs, i.e., reversible thermochromic compositions comprising 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 components (a) and (b) occurs.

[0058] As a reversible thermochromic composition, a heat-decolorizing type reversible thermochromic composition having 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., can be used. Heat-decolorizing type means that it decolorizes when heated and develops color when cooled. This reversible thermochromic composition changes color before and after a predetermined temperature (color change point), exhibiting 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. 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.

[0059] As a reversible thermochromic composition, a heat-decolorizing type reversible thermochromic composition having 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 can also be used. Heat-decolorizing type means that it decolorizes when heated and develops color when cooled. This reversible thermochromic composition exhibits color memory properties in a specific temperature range (a temperature range between the color onset temperature t2 and the decolorization temperature t3 (essentially a two-phase retention temperature range)). The shape of the curve plotting the change in color intensity due to temperature changes follows a significantly different path depending on whether the temperature is raised from a temperature lower than the color change temperature range or from a temperature higher than the color change temperature range. The colored state at temperatures below the complete color development temperature t1, or the decolorized state at temperatures above the complete decolorization temperature t4, is determined to be color-memory.

[0060] Furthermore, when applying the above-described reversible thermochromic composition having color memory properties to the present invention, the reversible thermochromic composition can be specifically configured such that the complete color development temperature t1 is a temperature that can only be obtained in a freezer, a cold region, etc., and the complete decolorization temperature t4 is a temperature that can be obtained from frictional heat from a friction body, a familiar heating element such as a hair dryer, and the ΔH value is specified to be 40 to 100°C, thereby effectively maintaining the color exhibited under normal conditions (daily living temperature range).

[0061] Temperatures that can only be obtained in freezers, cold regions, etc., are in the range of -50 to 0°C, preferably -40 to -5°C, and more preferably -30 to -10°C. The temperature obtained from readily available heating elements such as hair dryers is 50 to 95°C, preferably in the range of 50 to 90°C, and more preferably in the range of 60 to 80°C.

[0062] As a reversible thermochromic composition, a heat-activated reversible thermochromic composition using gallic acid ester, as described in Japanese Patent Publication No. 51-44706, Japanese Patent Application Publication No. 2003-253149, etc., can also be used. Heat-activated means that it develops color when heated and disappears when cooled.

[0063] The reversible thermochromic composition is a miscible comprising the above-mentioned components (a), (b), and (c) as essential components. The proportion of each component depends on the concentration, discoloration temperature, discoloration form, or type of each component. 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 proportions are in parts by mass).

[0064] As a coloring composition, a photochromic material that changes color upon irradiation with light can also be used. This color change may be reversible or irreversible, but a reversible photochromic material is preferred because it can repeatedly exhibit color changes upon irradiation with light. Examples of photochromic materials used as coloring compositions include, for example, a coloring composition in which a photochromic compound as a coloring material is dissolved in a medium, that is, a reversible photochromic composition consisting of at least a photochromic compound and a medium.

[0065] Examples of photochromic compounds include conventionally known spirooxazine derivatives, spiropyran derivatives, naphthopyran derivatives, etc., which develop color when irradiated with sunlight, ultraviolet light, or blue light with a peak emission wavelength in the range of 400 to 495 nm, and lose their color when irradiation is stopped. Examples include the compounds described in Japanese Patent Publication No. 2021-120493 and International Publication No. 2020 / 137469. Furthermore, photochromic compounds having optical memory properties (color memory photochromic properties) can also be used. Examples of such photochromic compounds include diarylethene derivatives, and for example, the compound described in Japanese Patent Application Publication No. 2021-120493 can be cited.

[0066] Examples of media include various oligomers such as styrene-based oligomers, acrylic-based oligomers, terpene-based oligomers, and terpene-phenol-based oligomers. By dissolving photochromic compounds in various oligomers, both lightfastness and color intensity can be improved, and the sensitivity to color change can also be adjusted. Oligomers can be used individually or in combination of two or more types.

[0067] Styrene oligomers are compounds having a styrene skeleton or their hydrogenated derivatives, and examples include low molecular weight polystyrene, styrene-α-methylstyrene copolymer, α-methylstyrene polymer, and α-methylstyrene-vinyltoluene copolymer. Examples of acrylic oligomers include acrylic acid ester copolymers. Terpene oligomers are compounds that have a terpene skeleton, and examples include α-pinene polymers, β-pinene polymers, and d-limonene polymers. Terpene phenol oligomers are compounds obtained by copolymerizing cyclic terpene monomers with phenols or their hydrogenated derivatives, such as α-pinene-phenol copolymers.

[0068] Reversible thermochromic materials or reversible photochromic materials can be encapsulated in microcapsules to form reversible thermochromic microcapsule pigments or reversible photochromic microcapsule pigments, thereby creating chemically and physically stable pigments. Furthermore, under various usage conditions, the reversible thermochromic materials or reversible photochromic materials can maintain the same composition and exhibit the same effects.

[0069] The microcapsule pigment according to the present invention may also contain various additives such as antioxidants, ultraviolet absorbers, infrared absorbers, solubilizers, preservatives, and fungicides, to the extent that they do not affect its function. If the microcapsule pigment according to the present invention includes a reversible thermochromic microcapsule pigment or a reversible photochromic microcapsule pigment, a microcapsule pigment exhibiting a color change behavior from colored (1) to colored (2) can be obtained by incorporating a non-coloring colorant such as a general dye or pigment into the microcapsule.

[0070] The microcapsule pigment according to the present invention exhibits excellent redispersibility even when containing a core material with a high specific gravity. Microcapsule pigments containing a core material with a high specific gravity tend to settle over time and form a hard cake, but the microcapsule pigment according to the present invention can suppress the formation of a hard cake due to settling over time.

[0071] Examples of microcapsule pigments containing a core material with a high specific gravity include microcapsule pigments containing a colored composition using titanium dioxide, carbon black, or a luminous pigment as a coloring material, or reversible thermochromic microcapsule pigments containing a reversible thermochromic composition with a large hysteresis width (ΔH).

[0072] The microcapsule pigment according to the present invention is preferably a reversible thermochromic microcapsule pigment in which component (c) in the reversible thermochromic composition is in the range of 60 to 90% by mass of the total amount of the reversible thermochromic composition, the mass-average molecular weight of component (c) is 250 or more, and the specific gravity of the fully colored reversible thermochromic microcapsule pigment in 20°C, relative to water, is 1.05 to 1.20. Such reversible thermochromic microcapsule pigments possess a reversible thermochromic function, becoming decolorized at temperatures above the high-temperature color change point (complete decolorization temperature) and becoming colored at temperatures below the low-temperature color change point (complete color development temperature). Furthermore, they exhibit a large hysteresis width (ΔH), allowing them to maintain a colored or decolorized state within a specific temperature range. For this reason, they are widely used not only in the writing instrument field but also in a wide range of other fields. However, reversible thermochromic microcapsule pigments with a large hysteresis width (ΔH) often use compounds containing two or more benzene rings in the molecule as component (c), which tends to increase their specific gravity, making them prone to settling over time and forming hard cakes, thus posing a problem in redispersion. The microcapsule pigment according to the present invention has a wall film composed of an isocyanate compound and the aforementioned polymer, which allows for easy redispersion even when encapsulating a core material with a high specific gravity. Furthermore, since the reversible thermochromic function of the reversible thermochromic composition is less likely to be impaired by the external environment, it is preferable to apply the above-mentioned reversible thermochromic microcapsule pigment as the microcapsule pigment according to the present invention.

[0073] Considering the redispersibility of the microcapsule pigment according to the present invention, a reversible thermochromic microcapsule pigment is more preferable in which component (c) in the reversible thermochromic composition is in the range of 65 to 85% by mass of the total amount of the reversible thermochromic composition, the mass-average molecular weight of component (c) is 250 or more, and the specific gravity of the fully colored reversible thermochromic microcapsule pigment in 20°C with water as the reference is 1.05 to 1.20 (preferably 1.10 to 1.20, more preferably 1.12 to 1.15). Furthermore, a reversible thermochromic microcapsule pigment is even more preferable in which component (c) in the reversible thermochromic composition is in the range of 70 to 85% by mass of the total amount of the reversible thermochromic composition, the mass-average molecular weight of component (c) is 250 or more, and the specific gravity of the fully colored reversible thermochromic microcapsule pigment in 20°C with water as the reference is 1.05 to 1.20 (preferably 1.10 to 1.20, more preferably 1.12 to 1.15). The specific gravity of reversible thermochromic microcapsule pigments can be measured by the following method.

[0074] <Method for measuring the specific gravity of reversible thermochromic microcapsule pigments> 1. Add 30 ml of glycerin aqueous solution and 1 g of fully colored reversible thermochromic microcapsule pigment to a screw-capsule bottle, mix, and prepare a reversible thermochromic microcapsule pigment dispersion. 2. Adjust the temperature of 30 ml of the above 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 dispersion. If it is confirmed that 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 previous glycerin solution, and observe the state of the dispersion again. If you observe that most of the microcapsule pigment has floated to the surface of the liquid, repeat steps 1 and 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 settled on the surface or floating. The specific gravity of the glycerin aqueous solution at this point should be measured and used as the specific gravity of the reversible thermochromic microcapsule pigment. The specific gravity of the glycerin aqueous solution can be measured using the hydrometer method described in JIS K0061, Section 7.1, after adjusting the temperature of the aqueous solution to 20°C.

[0075] The microencapsulated pigments according to the present invention can be manufactured by a microencapsulation method. Examples of microencapsulation methods include in situ polymerization, liquid curing coating, phase separation from aqueous solutions, phase separation from organic solvents, melt-dispersion-cooling, air suspension coating, and spray drying. The microencapsulation method is appropriately selected depending on the application, but interfacial polymerization is preferred.

[0076] The present invention provides a method for producing microcapsule pigments by interfacial polymerization, comprising an emulsification step of dispersing a core material and an oily component (oil phase) containing an isocyanate compound as a wall-forming material in an aqueous medium (aqueous phase) to prepare an emulsion, and a polymerization step of polymerizing the wall-forming material at the interface between the oil phase and the aqueous phase to form the wall of a microcapsule. After adding the oil phase to the aqueous phase and emulsifying it using mechanical force, a polymer is added as a curing agent, and the temperature of the system is increased as needed to induce interfacial polymerization at the interface between the oil phase and the aqueous phase, thereby forming microcapsules. Desolvation can be performed simultaneously or after the completion of the interfacial polymerization reaction. After the interfacial polymerization reaction and desolvation, the microcapsule pigment can be separated from the aqueous phase, washed, and then dried to obtain the microcapsule pigment.

[0077] While there are no particular limitations on the aqueous medium, water or deionized water can be used.

[0078] The aqueous phase may contain protective colloids such as water-soluble polymers beforehand. Examples of water-soluble polymers include conventionally known anionic polymers, nonionic polymers, and amphoteric polymers, which can be selected and used as appropriate. Preferably, the water-soluble polymers are polyvinyl alcohol, gelatin, and cellulose-based polymers.

[0079] The aqueous phase may also contain a surfactant. Examples of surfactants include anionic or nonionic surfactants, preferably those that do not react with the protective colloid to cause precipitation or aggregation. Preferred surfactants include sodium alkylbenzene sulfonates such as sodium lauryl sulfate; sodium dioctyl sulfosuccinate; and polyalkylene glycols such as polyoxyethylene nonylphenyl ether.

[0080] Depending on the purpose, a secondary resin film may be applied to the surface of the microcapsule pigment according to the present invention to provide durability or modify its surface properties for practical use.

[0081] The microcapsule pigment according to the present invention preferably has a core material:wall film mass ratio of 7:1 to 1:1, and a decrease in color density and vividness during color development is prevented by having the core material to wall film mass ratio within the above range. More preferably, the core material:wall film mass ratio is 6:1 to 1:1.

[0082] Furthermore, the microcapsule pigment according to the present invention may also be a microcapsule pigment in which a wall film is made of a resin selected from urea resin, urethane resin, urea-urethane resin, epoxy resin, melamine resin, benzoguanamine resin, etc., and a wall film made of an isocyanate compound and the aforementioned polymer is provided on the surface of the microcapsule pigment.

[0083] The average particle size of the microcapsule pigment is not particularly limited, but 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. If the average particle size exceeds 5 μm, it becomes difficult to adjust the dispersion state in the ink, and good ink discharge performance is difficult to obtain 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.

[0084] The average particle diameter is measured by using image analysis-based particle size distribution measurement software [Mountec Co., Ltd., product name: MacView] to determine the particle area, calculating the projected area circle equivalent diameter (Heywood diameter) from the area of ​​the particle area, and then measuring the average particle diameter of particles equivalent to an equivolute sphere based on that value. 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 an equivolute sphere 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.

[0085] The microcapsule pigments according to the present invention can be used by mixing one or more types as appropriate, and are used in an amount of 10 to 35% by weight, preferably 15 to 30% by weight, in the ink composition. Since the individual concentrations of the microcapsule pigments are lower than those of general-purpose colorants, use within the above range is preferable from a practical standpoint regarding ink concentration. Therefore, the present invention is effective because the ink tends to undergo high solid differentiation and form a hard cake.

[0086] Furthermore, it is possible to use colorants (dyes and general pigments) that can be dissolved or dispersed in an aqueous medium to impart a desired hue to the handwriting without thermal or light discoloration, and to express a wide range of hues. For example, as dyes, acid dyes, basic dyes, and direct dyes can be used. As general pigments, inorganic pigments such as carbon black and ultramarine, organic pigments such as copper phthalocyanine blue and benzidine yellow, and water-dispersible pigment products that are finely and stably dispersed in an aqueous medium using surfactants can be used. Furthermore, metallic pigments such as metal powders and pearl pigments, fluorescent pigments, phosphorescent pigments, and white pigments such as titanium dioxide can also be applied. These can also be encapsulated in microcapsule pigments.

[0087] Catechins are a general term for polyoxy derivatives of 3-oxyflavans, and because they have irregular carbon atoms at positions 2 and 3, there are four isomers: d-, 1-, d-epi-, and 1-epi-, as well as their racemic mixtures. The catechins used in the present invention are preferably compounds represented by the general formula (A), and the R in the formula 1 ~R 4 Each of these independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and at least one of them has a hydrogen atom. Furthermore, R 5 R represents a residue obtained by removing the OH group from a hydrogen atom or a carboxyl group of gallic acid. 6 represents a hydrogen atom or a hydroxyl group. In particular, R 1 ~R 4 Some use hydrogen atoms, and furthermore, R 5 and R 6 Some use hydrogen atoms, or R 5 R is defined as the residue obtained by removing the OH group from the carboxyl group of gallic acid. 6 Using hydrogen atoms yields a high level of effectiveness.

[0088] In this invention, by using a cationic polymer as the wall material for the microcapsule, a positively charged three-dimensional polymer structure is formed on the wall surface, creating a highly redispersible microcapsule. Furthermore, the bulky phenolic hydroxyl groups of catechins act on the microcapsule wall, protecting the wall while maintaining the three-dimensional structure. As a result, the wall surface can control the reactions it receives from other media, suppressing the degradation of the wall components. Therefore, the wall, with its highly redispersible structure, can maintain its performance over a long period even in aqueous inks, and hard cake formation can be suppressed for a longer period compared to when the microcapsule pigment alone is used.

[0089] More specifically, examples of catechins include (+)-catechin, (-)-epicatechin, (-)-catechin, (+)-epicatechin, (-)-epigallocatechin, (-)-epicatechin gallate, (-)-epigallocatechin gallate, (+)-gallocatechin, and (+)-gallocatechin gallate.

[0090] The catechins according to the present invention are blended in an amount of 0.05 to 1.0% by mass, preferably 0.08 to 0.8% by mass, relative to the total amount of the ink composition. Although an effect can be obtained even at less than 0.05% by mass, 0.05% by mass or more is preferable to achieve the desired performance under all conditions, and further additions beyond 1.0% by mass are not necessary as no further effects can be obtained.

[0091] There are no particular restrictions on the type of water used in water-based inks; for example, tap water, deionized water, ultrafiltered water, and distilled water are examples. The water content relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 35 to 95% by mass, and more preferably in the range of 40 to 90% by mass.

[0092] In addition to the essential components described above, the aqueous ink composition of the present invention may contain optional components as long as they do not impair the effects of the present invention. For example, conventional water-soluble organic solvents that are compatible with water can be used. Specifically, examples include ethanol, propanol, butanol, glycerin, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thiodiethylene glycol, hexylene glycol, 1,3-butanediol, neoprene glycol, polyethylene glycol, propylene glycol, butylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, 2-pyrrolidone, and N-methyl-2-pyrrolidone. Furthermore, the aforementioned water-soluble organic solvent may be used individually or in combination of two or more types, and is used in an amount of 2 to 60% by mass, preferably 5 to 35% by mass, in the ink composition.

[0093] Furthermore, a water-soluble resin can be added to provide adhesion 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. One or more water-soluble resins can be used in combination, and they are used in an amount of 1 to 20% by mass in the ink composition, provided that they do not impair drying resistance.

[0094] In addition, if necessary, pH adjusters such as organic basic compounds, rust inhibitors such as benzotriazole, toltriazole, and saponins, preservatives or fungicides such as carbolic acid, sodium salt of 1,2-benzthiazolin 3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl parahydroxybenzoate, and 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine, wetting agents such as urea, sorbitol, mannitol, sucrose, glucose, and sodium pyrophosphate, defoamers, antioxidants, and fluorinated or nonionic surfactants to improve ink penetration may be used. Furthermore, lubricants can be added, and examples include metal soaps, polyalkylene glycol fatty acid esters, ethylene oxide-additive cationic surfactants, phosphate ester surfactants, N-acyl amino acid surfactants, dicarboxylic acid-type surfactants, β-alanine-type surfactants, 2,5-dimercapto-1,3,4-thiadiazole and its salts or oligomers, 3-amino-5-mercapto-1,2,4-triazole, thiocarbamate, dimethyldithiocarbamate, α-lipoic acid, condensates of N-acyl-L-glutamic acid and L-lysine and their salts. Furthermore, shear-reducing agents such as xanthan gum, gellan gum, succinoglycan, and guar gum can also be added. Furthermore, the functionality of the retractable ballpoint pen form can be enhanced by adding thickening inhibitors such as N-vinyl-2-pyrrolidone oligomer, N-vinyl-2-piperidone oligomer, N-vinyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, ε-caprolactam, and N-vinyl-ε-caprolactam oligomer.

[0095] The aqueous ink composition of the present invention is filled into marking pens and ballpoint pens equipped with a fiber tip, felt tip, plastic tip, or ballpoint pen tip at the writing end. The marking pens and ballpoint pens may be of the cap type, which has a cap that covers the pen tip, or they may be of the retractable type, which has a retractable mechanism such as a push-button type, twist-button type, or slide-button type, and the pen tip can be stored inside the barrel.

[0096] When filling a marking pen, the structure and shape of the marking pen itself are not particularly limited. For example, a marking pen tip (bullet-shaped, chisel-shaped, brush-pen-shaped, etc.) such as a fiber tip, felt tip, or plastic tip, or a fountain pen-type metal tip, can be attached to the writing tip, and ink can be impregnated into an ink-absorbing body made of fiber bundles housed inside the barrel, supplying ink to the writing tip. Another example is a marking pen in which ink is directly housed inside the barrel, and a predetermined amount of ink is supplied to the writing tip via a comb-shaped ink flow rate adjustment member or an ink flow rate adjustment member made of fiber bundles (the ink storage part may be in the form of a cartridge). Yet another example is a marking pen in which ink is directly housed inside the barrel, and a predetermined amount of ink is supplied to the writing tip by a valve mechanism. In addition to a cap type, a retractable type can be made by providing an airtight opening and closing lid on the pen tip retraction hole, or by using an ink component with a highly moist composition. In addition to having a single pen tip, a double-ended design may also be available, with pen tips of different thicknesses and shapes at both ends of the barrel. Furthermore, in the aforementioned double-ended design, one end may be a ballpoint pen.

[0097] When filling a ballpoint pen, the structure and shape of the ballpoint pen itself are not particularly limited. Examples include a structure in which ink is impregnated into an ink-absorbing body made of fiber bundles housed inside the barrel and supplied to the writing tip; a structure in which ink is directly housed inside the barrel and an ink flow rate adjustment member with comb-shaped grooves or an ink flow rate adjustment member made of fiber bundles is interposed (the ink storage part may be in the form of a cartridge); and a ballpoint pen having an ink storage tube filled with an ink composition inside the barrel, the ink storage tube communicating with a tip to which a ball is attached, and further having a liquid stopper in close contact with the end face of the ink to prevent backflow. A solid stopper can also be used in combination with the liquid stopper.

[0098] The ballpoint pen tip can be a straight metal pipe, or a metal pipe with a tapered inner diameter at the front of the writing section that has been tapered to narrow the inner diameter at the front, with a ball held in a ball-holding portion formed by pressing the tip of the pipe inward from the outer surface; or a ball held in a ball-holding portion formed by cutting a metal material with a drill or the like; or a ball held in a tip formed by cutting a metal pipe or metal material is biased forward by a spring. Furthermore, the balls used are those made of cemented carbide, stainless steel, ruby, ceramic, etc., with an outer diameter of 0.1 to 2.0 mm, preferably 0.2 to 1.2 mm, and more preferably 0.28 to 1.0 mm.

[0099] The barrel for containing the water-based ink according to the present invention is preferably made of a thermoplastic resin such as polyethylene, polypropylene, or polyethylene terephthalate, in terms of low ink evaporation and productivity. The tip can be directly connected to the barrel, or it can be connected to the barrel and tip via a connecting member. Furthermore, it can be configured as a replaceable cartridge type. When the ink composition is low viscosity, the ink composition can be contained within the barrel by either attaching an ink retaining member to the front of the barrel and directly containing the ink composition within the barrel, or by impregnating a porous body or a fibrous material with the ink composition and then containing it.

[0100] Furthermore, by using a transparent, colored transparent, or translucent molded body for the barrel, the ink color and ink level can be checked. In the form of a ballpoint pen, the barrel may be in the form of a ballpoint pen refill, with the refill housed inside the outer barrel, or the barrel itself, with a tip attached to the end, may be used as the ink reservoir, with ink directly filled into the barrel.

[0101] Furthermore, the ballpoint pen using the aforementioned barrel can be either a capped or retractable type. As for retractable ballpoint pens, any structure in which the writing tip provided on the ballpoint pen refill is housed inside the outer barrel while exposed to the outside air, and the writing tip protrudes from the opening of the outer barrel when the retractable mechanism is activated, can be used. Examples of operating methods for the retraction mechanism include knocking, rotating, and sliding mechanisms. A retractable pen may have a retractable mechanism at the rear end or side of the outer barrel, and pressing the retractable mechanism causes the writing tip of the ballpoint pen refill to extend and retract from the opening at the front end of the outer barrel. Alternatively, pressing a clip on the outer barrel can cause the writing tip of the ballpoint pen refill to extend and retract from the opening at the front end of the outer barrel. A rotary type can be exemplified by having a rotating part (such as a rear shaft) on the outer shaft, and by rotating this part, the writing tip of the ballpoint pen refill extends and retracts from the opening at the front end of the outer shaft. A sliding type may be exemplified by having a sliding part on the side of the barrel, which allows the writing tip of the ballpoint pen refill to extend and retract from the opening at the front of the outer barrel by operating the slide, or by sliding a clip part provided on the outer barrel, which allows the writing tip of the ballpoint pen refill to extend and retract from the opening at the front of the outer barrel. Furthermore, a retractable ballpoint pen may be a composite type that houses multiple ballpoint pen refills in addition to one that houses a single ballpoint pen refill within the outer barrel. Also, the ink reservoir that makes up the ballpoint pen refill may be made of resin or metal.

[0102] An ink backflow prevention device can also be filled into the trailing end of the ink contained in the ballpoint pen refill. The ink backflow prevention body can be either liquid or solid. Examples of liquid ink backflow prevention bodies include non-volatile media such as polybutene and silicone oil, and silica, aluminum silicate, etc., can be added to the media if desired. Furthermore, resin molded products can be used as solid ink backflow prevention bodies. Furthermore, the liquid and solid ink backflow prevention devices can be used in combination.

[0103] Furthermore, along with the writing instrument, a friction member can be used to erase or change the color of the writing by generating frictional heat. As the friction material, an elastic body containing an elastomer that is highly elastic and can generate appropriate friction and frictional heat during friction is preferred. Although it is also possible to rub the ink away with an eraser, eraser residue is generated during friction, so the aforementioned friction material is preferred. Materials used for friction components include silicone-containing resins, styrene-based copolymer-containing resins, polyester-based resins, and the like. While a writing instrument set can be created by combining a friction element with a separate, arbitrarily shaped component (friction body) from the writing instrument, attaching the friction element to the writing instrument's exterior results in a form that is highly portable. In the case of capped writing instruments, there are no particular limitations on where the friction element can be provided. For example, the cap itself may be formed from the friction element, the barrel itself from the friction element, the clip itself may be formed from the friction element if a clip is provided, or the friction element may be provided at the tip (top) of the cap or the rear end of the barrel (the part opposite the cap side where the writing tip is not provided). In the case of retractable writing instruments, the location where the friction element is provided is not particularly limited, but for example, the barrel itself may be formed from the friction element, or if a clip is provided, the clip itself may be formed from the friction element, or the friction element may be provided near the barrel opening (pen tip side), at the rear end of the barrel (the part without the writing tip), or at the knock mechanism. [Examples]

[0104] Examples are described below, but the present invention is not limited to these examples. Table 1 shows the composition of the aqueous inks of the examples and comparative examples. The numerical values ​​of the composition in the table represent parts by mass. Furthermore, the average particle diameter was measured using the Coulter method with a particle size distribution analyzer (Beckman Coulter, Ltd., product name: Multisizer 4e) as the average particle diameter of particles equivalent to an equivolute sphere.

[0105] [Table 1]

[0106] [Table 2]

[0107] The contents of the raw materials listed in the table are explained according to the footnote numbers. (1) A reversible thermochromic composition comprising (a) 2 parts of 3-(4-diethylamino-2-hexyloxyphenyl)-3-(1-ethyl-2-methylindole-3-yl) as component (a), 5 parts of 2,2-bis(4-hydroxyphenyl)hexafluoropropane and 3 parts of 1,1-bis(4-hydroxyphenyl)-2-ethylhexane as component (b), and 50 parts of 4-benzyloxyphenylethyl caprate as component (c), with 25 parts of aromatic isocyanate prepolymer as a wall film forming material and 4 co-solvents After adding to a mixed solution consisting of 0 parts of and , the mixture is emulsified and dispersed in an 8% polyvinyl alcohol aqueous solution, and stirring is continued while heating. Then, 2.5 parts of allylamine polymer (mass average molecular weight: 3,000) is added as a curing agent (polymer), and stirring is continued to prepare a microcapsule dispersion. From this microcapsule dispersion, a reversible thermochromic microcapsule pigment with an average particle size of 2.0 μm is obtained by centrifugation (complete color development temperature t1: -20℃, complete decolorization temperature t4: 62℃, reversibly changing color from blue to colorless with temperature changes). (2) A reversible thermochromic microcapsule pigment obtained in the same manner as in (1), except that the polymer was changed to an allylamine polymer (mass-average molecular weight: 5,000) and the amount added was 4 parts. (Complete color development temperature t1: -20°C, complete decolorization temperature t4: 62°C, reversibly changes color from blue to colorless with temperature changes) (3) A reversible thermochromic microcapsule pigment obtained in the same manner as in (1), except that the polymer was changed to an allylamine polymer (mass-average molecular weight: 8,000) and the amount added was 1.5 parts. (Complete color development temperature t1: -20°C, complete decolorization temperature t4: 61°C, reversibly changes color from blue to colorless with temperature changes) (4) A reversible thermochromic microcapsule pigment obtained by the same method as in (1), except that the polymer was changed to an allylamine hydrochloride polymer (mass-average molecular weight: 5,000) (complete color development temperature t1: -20°C, complete decolorization temperature t4: 62°C, reversibly changes color from blue to colorless with temperature change). (5) A reversible thermochromic microcapsule pigment obtained by the same method as in (1), except that the polymer was changed to an allylamine hydrochloride polymer (mass-average molecular weight: 15,000) (complete color development temperature t1: -20°C, complete decolorization temperature t4: 61°C, reversibly changes color from blue to colorless with temperature change). (6) A reversible thermochromic microcapsule pigment obtained by the same method as in (1), except that the polymer was changed to an allylamine hydrochloride-diallylamine hydrochloride copolymer (mass-average molecular weight: 20,000) (complete color development temperature t1: -20°C, complete decolorization temperature t4: 62°C, reversibly changes color from blue to colorless with temperature change). (7) A reversible thermochromic microcapsule pigment obtained by the same method as in (1), except that the polymer was changed to an allylamine acetate-diallylamine acetate copolymer (mass-average molecular weight: 40,000). (The pigment has a complete color development temperature t1: -20°C and a complete decolorization temperature t4: 62°C, and reversibly changes color from blue to colorless with temperature changes.) (8) A reversible thermochromic microcapsule pigment obtained by the same method as in (1), except that the polymer was changed to a diallylamine polymer (mass-average molecular weight: 5,000) (complete color development temperature t1: -20°C, complete decolorization temperature t4: 62°C, reversibly changes color from blue to colorless with temperature change). (9) A reversible thermochromic microcapsule pigment obtained by the same method as in (1), except that the polymer was changed to a diallylamine hydrochloride copolymer (mass-average molecular weight: 50,000) (complete color development temperature t1: -20°C, complete decolorization temperature t4: 61°C, reversibly changes color from blue to colorless with temperature change). (10) A reversible thermochromic microcapsule pigment obtained by the same method as in (1), except that the polymer was changed to a diallylamine hydrochloride-sulfur dioxide copolymer (mass-average molecular weight: 5,000) (complete color development temperature t1: -20°C, complete decolorization temperature t4: 61°C, reversibly changes color from blue to colorless with temperature change). (11) A reversible thermochromic microcapsule pigment obtained by the same method as in (1), except that the polymer was changed to a diallylamine acetate-sulfur dioxide copolymer (mass-average molecular weight: 5,000) (complete color development temperature t1: -20°C, complete decolorization temperature t4: 61°C, reversibly changes color from blue to colorless with temperature change). (12) A composition consisting of 10 parts azo red pigment and 10 parts stearyl myristate is added to a mixed solution consisting of 30 parts aromatic isocyanate prepolymer as a wall-forming material and 50 parts co-solvent. The mixture is then emulsified and dispersed in a 6% aqueous polyvinyl alcohol solution, and stirring is continued while heating. Then, 4 parts allylamine acetate-diallylamine acetate copolymer (mass average molecular weight: 40,000) is added as a curing agent (polymer), and stirring is continued to prepare a microcapsule dispersion. Microcapsule pigments with an average particle size of 2.0 μm (exhibiting red color) are obtained from the microcapsule dispersion by centrifugation. (13) A reversible thermochromic composition comprising (a) 2 parts of 3-(4-diethylamino-2-hexyloxyphenyl)-3-(1-ethyl-2-methylindole-3-yl) as component (a), 5 parts of 2,2-bis(4-hydroxyphenyl)hexafluoropropane and 3 parts of 1,1-bis(4-hydroxyphenyl)-2-ethylhexane as component (b), and 50 parts of 4-benzyloxyphenylethyl caprate as component (c), with an aromatic isocyanate prepolymer as the wall film forming material. - After adding to a mixed solution consisting of 25 parts of - and 40 parts of a co-solvent, the mixture is emulsified and dispersed in an 8% polyvinyl alcohol aqueous solution, and stirring is continued while heating. Then, 2.5 parts of xylylenediamine are added as a curing agent, and stirring is continued to prepare a microcapsule dispersion. A reversible thermochromic microcapsule pigment with an average particle size of 2.0 μm is obtained from this microcapsule dispersion by centrifugation (complete color development temperature t1: -20℃, complete decolorization temperature t4: 62℃, reversibly changing color from blue to colorless with temperature changes). (14) A composition consisting of 10 parts azo red pigment and 10 parts stearyl myristate is added to a mixed solution consisting of 30 parts aromatic isocyanate prepolymer as a wall-forming material and 50 parts co-solvent. The mixture is then emulsified and dispersed in a 6% aqueous polyvinyl alcohol solution, and stirring is continued while heating. Then, 4 parts xylylenediamine is added as a curing agent, and stirring is continued to prepare a microcapsule dispersion. From this microcapsule dispersion, a microcapsule pigment with an average particle size of 2.0 μm (exhibiting red color) is obtained by centrifugation. (15) Manufactured by Kyowa Hakko Bio Co., Ltd., Product name: Glutathione (16) Manufactured by Toyo Fermentation Co., Ltd., Product name: α-Lipoic Acid (17) Manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Product name: Prysurf AL (18) Manufactured by Arcsarda Japan, Product name: Proxel XL-2

[0108] Preparation of marking pen ink (ballpoint pen ink A) The raw materials were mixed in the proportions specified in Examples 1-6, 9, and 12 and Comparative Examples 1-6 and 9. The mixture was stirred at 2000 rpm for 1 hour in a disperser at 20°C, and then filtered to obtain a marking pen ink composition (ballpoint pen ink composition A).

[0109] Making a marking pen The marking pen ink composition is impregnated into an ink-absorbing body made of polyester sliver coated with a synthetic resin film, housed in a barrel made of polypropylene resin, and assembled to connect a processed tip (bullet-shaped plastic pen) with numerous ink guide holes formed in polyester resin to the tip of the barrel via a holder, and a cap is attached to obtain a marking pen. A friction member made of an elastic material containing styrene elastomer is provided on the top of the cap.

[0110] Making ballpoint pen A A ballpoint pen A is manufactured by filling the pen-type writing instrument exterior, which has a stainless steel tip holding a 0.7 mm diameter cemented carbide ball (comb-shaped ink reservoir), with the ink reservoir at the rear (sealed side) by fitting a pen core (comb-shaped ink reservoir) to the front (open side) of the barrel, and then fitting a cap onto it.

[0111] Preparation of ballpoint pen ink B Ballpoint pen ink composition B was obtained by mixing each raw material except succinoglycan in the proportions specified in Examples 7, 8, 10, 11 and Comparative Examples 7, 8, stirring at 2000 rpm in a disper at 20°C for 1 hour, adding a thickener, stirring for another hour, and then filtering.

[0112] Preparation of an ink backflow prevention device An ink backflow prevention body was obtained by adding 1.5 parts of fatty acid amide as a thickening agent to 98.5 parts of polybutene as a base oil, and then kneading the mixture using a three-roll machine.

[0113] Making Ballpoint Pen B Ballpoint pen B was manufactured by filling a ballpoint pen refill, in which a stainless steel tip (containing a spring that presses the ball toward the writing section) holding a 0.4 mm diameter cemented carbide ball was fitted to one end of a transparent polypropylene pipe, with each of the aforementioned ink compositions, and then placing the ink backflow prevention body at the rear end of the refill. Finally, the ballpoint pen refill was assembled into the barrel and the cap was attached. A friction member made of an elastic material containing styrene elastomer is provided at the rear end of the barrel.

[0114] The following tests were conducted using each of the obtained ink compositions and writing instruments. Ink stability test Each ink was sealed in a container and left in a 50°C incubator for 15 and 30 days. After cooling to room temperature, the condition of the ink was visually inspected. Written exam After confirming that each writing instrument was capable of writing, it was left in a 50°C environment for 30 days, then allowed to cool to room temperature. Twelve spiral circles were then continuously written by hand on JIS P3201 writing paper A. The results of each test are shown below.

[0115] [Table 3]

[0116] [Table 4]

[0117] The evaluation of the test results is as follows: Ink stability test ○: No change from before the exam. △: Some aggregation of microcapsule pigments was observed. ×: Hard cake formation and layer separation were observed due to aggregation of microcapsule pigments. Written examination (A and B are considered passing grades) A: Shows good, dark handwriting. B: Some areas of the handwriting showed slight blurring or skipping of lines. C: The handwriting is faint, the lines are broken, or it is impossible to write.

Claims

1. An aqueous ink composition for writing instruments comprising a microcapsule pigment containing a core material, catechins, and water, with a wall film composed of an isocyanate compound and a polymer comprising at least one of the structural units represented by the following formula (I) and the structural unit represented by the following formula (II). 【Chemistry 1】 [In the formula, n1 represents an integer of 0 or 1, X １ This represents one of the following: hydrogen halide, carboxylic acid, sulfuric acid, sulfuric acid ester, phosphoric acid, sulfonic acid, or amide sulfuric acid. 【Chemistry 2】 [In the formula, n² represents an integer of 0 or 1, X ２ This represents one of the following: hydrogen halide, carboxylic acid, sulfuric acid, sulfuric acid ester, phosphoric acid, sulfonic acid, or amide sulfuric acid.

2. The aqueous ink composition for writing instruments according to claim 1, wherein the catechins are contained in an amount of 0.05 to 1.0% by mass in the ink composition.

3. The aqueous ink composition for writing instruments according to claim 1 or 2, wherein the catechins are at least one selected from the compounds represented by the following formula (A). 【Transformation 3】 [In the formula, R １ ~R ４ Each of these independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and at least one of them is a hydrogen atom. ５ R represents a residue obtained by removing the OH group from a hydrogen atom or a carboxyl group of gallic acid. ６ [This represents a hydrogen atom or a hydroxyl group.]

4. The aqueous ink composition for writing instruments according to claim 1 or 2, wherein the microcapsule pigment is added in an amount of 10 to 35% by mass of the total amount of the ink composition.

5. The aqueous ink composition for writing instruments according to claim 1, wherein the core material is a thermochromic material that changes color when heated.

6. The aqueous ink composition for writing instruments according to claim 5, wherein the thermochromic material is a reversible thermochromic composition comprising (a) an electron-donating color-developing organic compound, (b) an electron-accepting compound, and (c) a reaction medium that controls the color-developing reactions of (a) and (b).

7. A writing instrument containing the aqueous ink composition for writing instruments described in any one of claims 1 to 6.

8. A writing instrument comprising a friction member that changes the color of the writing produced by a writing instrument containing the aqueous ink composition for writing instruments described in claim 5 by frictional heat.

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