Microcapsule pigment and ink composition for writing instruments

Abstract

To provide a thermally discoloring microcapsule pigment having excellent color development of a drawn line during writing and decolorization property that does not leave a written trace on a paper surface even by thermal erasure due to friction heat and has excellent thermal discoloration property and a writing ink composition containing the microcapsule pigment.SOLUTION: A microcapsule pigment of the present invention is characterized in that at least one leuco pigment, a discoloration temperature adjusting agent, and at least one selected from diphenylacetic acid, 3,3-diphenylpropionic acid and triphenylacetic acid as a color development agent. A writing ink composition of the present invention is characterized in that the microcapsule pigment having the above described structure is contained.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a thermochromic microcapsule pigment which exhibits excellent color development when drawn and excellent decolorization properties, leaving no trace on the paper even when thermally erased by frictional heat or the like, and an ink composition for a writing instrument containing the microcapsule pigment. [Background technology]

[0002] 2. Description of the Related Art Thermochromic (thermal erasable) ink compositions capable of erasing written lines by heating have been known. This thermochromic ink composition typically contains a mixture of a leuco dye that has been brought into a colored state by a color developer consisting of an acid, and a reaction medium that changes the colored state of the leuco dye to a colorless state at a specified temperature, dispersed in a dispersion medium, and uses a microencapsulated pigment in which each of these materials is microencapsulated.

[0003] Examples of conventional thermochromic microcapsule pigments include: (1) A reversible thermochromic microencapsulated pigment in which a reversible thermochromic composition is encapsulated in a microcapsule, the composition comprising (a) an electron-donating organic color-forming compound, (b) a specific hydroxybenzoic acid ester compound represented by the general formula and a specific hydroxyphenyl acetate ester compound represented by the general formula as an electron-accepting compound, (c) a compound selected from chain hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, and halogenated hydrocarbons as a reaction medium for reversibly inducing the electron donor-acceptor reaction of (a) and (b), and (d) a styrene-based compound having a softening point of 5° C. or higher and a weight-average molecular weight of 200 to 100,000, which becomes a colored state when heated from a decolorized state and becomes a decolorized state when cooled from the colored state (see, for example, Patent Document 1), (2) A reversible thermochromic microencapsulated pigment in which a reversible thermochromic composition that changes from a decolorized state to a colored state by heating is encapsulated in a microcapsule, the reversible thermochromic composition comprising (a) an electron-donating organic color-forming compound, (b) a specific hydroxybenzoic acid ester compound represented by the general formula as an electron-accepting compound, (c) a compound selected from chain hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, and halogenated hydrocarbons as a reaction medium for reversibly inducing the electron donor / acceptor reaction of (a) and (b), (d) a styrene-based compound having a softening point of 5° C. or higher and a weight-average molecular weight of 200 to 100,000, and (e) a specific compound selected from the general formula (e.g., see Patent Document 2), etc. are known.

[0004] However, depending on the color developer selected from the specific hydroxybenzoic acid ester compounds and specific hydroxyphenyl acetate ester compounds used in the above Patent Documents 1 and 2, there are issues with the color development of drawn lines during writing and the tendency for written marks to remain on the paper surface even after erasure by thermal friction, and further improvements and higher functionality are currently desired. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-84454 A (Claims, Examples, etc.) [Patent Document 2] JP 2017-14328 A (Claims, Examples, etc.) Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the above-mentioned problems and current state of the prior art, and aims to solve these problems, and to provide a thermochromic microencapsulated pigment that exhibits excellent color development in lines drawn during writing and has excellent erasing properties, such that even after erasing by thermal friction, the writing is erased cleanly without leaving any trace on the paper surface, and an ink composition for a writing instrument containing this microencapsulated pigment. [Means for solving the problem]

[0007] Means for Solving the Problems of the Prior Art The present inventors have conducted intensive research in view of the above-mentioned problems and have found that the above-mentioned objective microencapsulated pigment and ink composition for a writing instrument can be obtained by using a microencapsulated pigment containing at least a leuco dye, a discoloration temperature regulator, and a specific color developer, thereby completing the present invention.

[0008] That is, the microencapsulated pigment of the present invention is characterized by containing at least a leuco dye, a discoloration temperature regulator, and at least one color developer selected from diphenylacetic acid, 3,3-diphenylpropionic acid, and triphenylacetic acid. The content of the color developer is preferably 0.1 to 20% by mass based on the total amount of the microcapsulated pigment. The ink composition for a writing instrument of the present invention is characterized by containing the microcapsulated pigment having the above-mentioned composition. Effect of the Invention

[0009] According to the present invention, there are provided a thermochromic microencapsulated pigment which exhibits excellent color development in lines drawn when written, leaves no trace on the paper even when thermally erased by frictional heat or the like, and has excellent decolorization properties, and an ink composition for a writing instrument containing this microencapsulated pigment. The objects and advantages of the invention will be realized and obtained by means of the elements and combinations particularly pointed out in the claims. Both the foregoing general description and the following detailed description are exemplary and explanatory but are not restrictive of the invention as claimed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments of the present invention will be described in detail. However, it should be noted that the technical scope of the present invention is not limited to the embodiments described in detail below, but extends to the inventions described in the claims and their equivalents.

[0011] <Microcapsule pigment> The microencapsulated pigment of the present invention is characterized by containing at least a leuco dye, a discoloration temperature regulator, and at least one color developer selected from diphenylacetic acid, 3,3-diphenylpropionic acid, and triphenylacetic acid.

[0012] The leuco dye that can be used is not particularly limited as long as it is an electron donating dye and functions as a color former. Specifically, from the viewpoint of obtaining an ink having excellent color development characteristics, conventionally known dyes such as triphenylmethane, spiropyran, fluoran, diphenylmethane, rhodamine lactam, indolylphthalide, leucoauramine, and pyridine can be used alone (one type) or in a mixture of two or more types (hereinafter simply referred to as "at least one type"). Specifically, 6-(dimethylamino)-3,3-bis[4-(dimethylamino)phenyl]-1(3H)-isobenzofuranone, 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)phthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 1, 3-Dimethyl-6-diethylaminofluoran, 2-Chloro-3-methyl-6-dimethylaminofluoran, 3-Dibutylamino-6-methyl-7-anilinofluoran, 3-Diethylamino-6-methyl-7-anilinofluoran, 3-Diethylamino-6-methyl-7-xylidinofluoran, 2-(2-chloroanilino)-6-dibutylaminofluoran, 3,6-Dimethoxyfluoran, 3,6-Di-n-butoxyfluoran, 1,2-Benzo- 6-diethylaminofluoran, 1,2-benz-6-dibutylaminofluoran, 1,2-benz-6-ethylisoamylaminofluoran, 2-methyl-6-(Np-tolyl-N-ethylamino)fluoran, 2-(N-phenyl-N-methylamino)-6-(Np-tolyl-N-ethylamino)fluoran, 2-(3'-trifluoromethylanilino)-6-diethylaminofluoran, 3-chloro-6-cyclohexylaminofluoran, 2- Examples of the fluoran include methyl-6-cyclohexylaminofluoran, 3-di(n-butyl)amino-6-methoxy-7-anilinofluoran, 3,6-bis(diphenylamino)fluoran, methyl-3',6'-bisdiphenylaminofluoran, chloro-3',6'-bisdiphenylaminofluoran, 3-methoxy-4-dodecoxystyrinoquinoline, and 4,4'-bis(diethylamino)benzophenone, and at least one of these can be used. These leuco dyes have a lactone skeleton, a pyridine skeleton, a quinazoline skeleton, a bisquinazoline skeleton, or the like, and exhibit coloration by opening the skeleton (ring), and if commercially available products of these are available, they can also be used. It is preferable to use a leuco dye that changes from colored to colorless by heat.

[0013] The developer that can be used is a component that has the ability to cause the above-mentioned leuco dye to develop color, and in the present invention, the developer described below is used as a component that can achieve the intended effect of the present invention. The color developer used in the present invention is at least one selected from diphenylacetic acid, 3,3-diphenylpropionic acid, and triphenylacetic acid. These color developers exhibit superior color development of drawn lines during writing and superior erasability without leaving any trace of writing on the paper even after erasing by thermal frictional heat, compared to conventionally known color developers (this point will be described in more detail in the examples below). The diphenylacetic acid, 3,3-diphenylpropionic acid, and triphenylacetic acid used are known substances, and their production methods are known. However, it was not previously known that they could be used as color developers for thermochromic microencapsulated pigments and the like, or that they could exert the above-mentioned effects.

[0014] The color change temperature regulator that can be used in the present invention is a substance that controls the color change temperature during color development of the leuco dye and the developer. The discoloration temperature regulator that can be used may be any of those known in the art, specifically, alcohols, esters, ketones, ethers, acid amides, azomethines, fatty acids, and hydrocarbons. For example, 4,4'-(hexafluoroisopropylidene)bisphenol dicaprate, 4,4'-(hexafluoroisopropylidene)bisphenol dilaurate, 4,4'-(hexafluoroisopropylidene)bisphenol dimyristate, 4,4'-(hexafluoroisopropylidene)bisphenol dipalmiate, 4,4'-(hexafluoroisopropylidene)bisphenol diundecanoate, 4,4'-(hexafluoroisopropylidene)bisphenol ditridecanoate, 4,4'-(isopropylidene)bisphenol dicaprate, 4,4'-(isopropylidene)bisphenol dilaurate, 4,4'-(isopropylidene)bisphenol dimyristate, At least one of the following may be mentioned: 4,4'-(isopropylidene)bisphenol dipalmiate, 4,4'-(isopropylidene)bisphenol diundecanoate, 4,4'-(isopropylidene)bisphenol ditridecaate, 4,4'-methylenebisphenol dicaprate, 4,4'-methylenebisphenol dilaurate, 4,4'-methylenebisphenol dimyristate, 4,4'-methylenebisphenol dipalmiate, 4,4'-methylenebisphenol diundecanoate, 4,4'-methylenebisphenol ditridecanoate, 4,4'-methylenebisphenol ditridecanoate, and 4,4'-methylenebisphenol ditridecanoate.

[0015] The microencapsulated pigment of the present invention can be produced by microencapsulating at least the leuco dye, the specific color developer, and the discoloration temperature regulator so that the average particle size is 0.3 to 10 μm. Examples of the microencapsulation method include an interfacial polymerization method, an interfacial polycondensation method, an in situ polymerization method, a liquid hardening coating method, a phase separation method from an aqueous solution, a phase separation method from an organic solvent, a melting dispersion cooling method, an air suspension coating method, and a spray drying method, and can be appropriately selected depending on the application.

[0016] For example, in the phase separation method from an aqueous solution, the above-mentioned leuco dye, developer, and discoloration temperature regulator are heated and melted, then added to an emulsifier solution, and heated and stirred to disperse them into oil droplets. Next, a resin raw material or the like is used as a capsule membrane agent, and each liquid such as an amino resin solution, specifically a methylolmelamine aqueous solution, a urea solution, or a benzoguanamine solution is gradually added and allowed to react, and the dispersion is then filtered to produce the desired thermochromic microcapsule pigment.

[0017] The contents of these leuco dyes, color developers, and discoloration temperature regulators vary depending on the types of leuco dyes, color developers, and discoloration temperature regulators used, the microencapsulation method, etc., but it is preferable that the leuco dye is 0.1 to 20 mass % (hereinafter simply referred to as "%) of the total amount of the microencapsulated pigment, the specific color developers mentioned above are 0.1 to 20%, and the discoloration temperature regulator is 30 to 80%, with the remainder being the amount of capsule membrane agent, etc. The content of the leuco dye may be appropriately selected depending on the desired color density, etc., and is adjusted within the above-mentioned specified range. If the content of the developer is less than 0.1%, the color development is poor, while if it exceeds 20%, the decolorization is poor. The content of the discoloration temperature regulator may be appropriately selected depending on the desired hysteresis width and color density during color development, etc., and is preferably adjusted within the above-mentioned specified range.

[0018] The microencapsulated pigment of the present invention can be configured so that the color-developing temperature (for example, color develops at 0°C or higher) and the color-discoloring temperature (for example, color disappears at 50°C or higher) of each color can be set to a suitable temperature by suitably combining the types and amounts of the above-mentioned leuco dye, the above-mentioned specific color developer, and the color-discoloring temperature regulator. A microencapsulated pigment that changes from colored to colorless when exposed to heat such as frictional heat is preferable.

[0019] In the microcapsule pigment of the present invention, from the viewpoint of further improving the line density, storage stability, and writing property, it is preferable that the wall film is formed of a urethane resin, a urea resin, a urethane / urea resin, an epoxy resin, or an amino resin. For example, the urethane resin may be a compound of an isocyanate and a polyol. For example, the urea resin may be a compound of an isocyanate and an amine. For example, the urethane / urea resin may be a compound of an isocyanate and a polyol / amine. For example, the epoxy resin may be a compound of an epoxy resin and an amine. For example, the amino resin may be a melamine resin, a benzoguanamine resin, or the like. The thickness of the wall of the microcapsule color material is appropriately determined depending on the required strength of the wall and the line density.

[0020] The average particle size of the microcapsulated pigment of the present invention is preferably 0.3 to 10 μm, more preferably 0.5 to 3 μm, from the viewpoints of colorability, color development, easy decolorization, stability, and suppression of adverse effects on writing properties. The "average particle size" specified in the present invention (including examples) is the D50 value calculated on a volume basis using a particle size distribution analyzer HRA9320-X100 (manufactured by Nikkiso Co., Ltd.). If the average particle size is less than 0.3 μm, sufficient line density cannot be obtained, whereas if it exceeds 10 μm, the writing properties deteriorate and the dispersion stability of the microencapsulated pigment decreases, which is undesirable. The average particle size of the microencapsulated pigment falling within the above range (0.3 to 10 μm) varies depending on the microencapsulation method. In a method such as phase separation from an aqueous solution, the microencapsulated pigment can be prepared by appropriately combining stirring conditions during production.

[0021] The microencapsulated pigment of the present invention thus constituted has excellent color development properties for lines drawn during writing, and also leaves no traces of writing on the paper surface or the like even when thermally erased due to frictional heat or the like, resulting in a thermochromic microencapsulated pigment with excellent erasing properties. The pigment can be suitably used as a thermochromic colorant for writing instruments, and as will be described later, even when used as a pigment in an ink composition for a writing instrument whose solvent type is aqueous or oil-based, the above-mentioned effects can be exhibited without being affected by the solvent type, etc.

[0022] <Ink composition for writing instruments> The ink composition for a writing instrument of the present invention is characterized by containing the microencapsulated pigment having the above-mentioned composition, and can be used as an ink composition for a writing instrument, such as a water-based or oil-based ballpoint pen or marking pen. The content of the microencapsulated pigment of the present invention is preferably 5 to 30%, and more preferably 10 to 25%, based on the total amount of each water-based or oil-based ink composition. If the content of the microencapsulated pigment is less than 5%, the coloring strength and color development will be insufficient, whereas if it exceeds 30%, blurring will occur, which is undesirable.

[0023] <Water-based ink composition for writing instruments> In the aqueous ink composition for writing instruments of the present invention, in addition to the above-mentioned microencapsulated pigment, the remainder contains water (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.) as a solvent, and may also contain water-soluble organic solvents, thickeners, lubricants, rust inhibitors, preservatives, antibacterial agents, and the like, as appropriate depending on the application of each writing instrument (for a ballpoint pen, a marking pen, etc.), within the scope of the invention's effects.

[0024] Examples of the water-soluble organic solvent that can be used include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, 3-butylene glycol, thiodiethylene glycol, and glycerin, as well as ethylene glycol monomethyl ether and diethylene glycol monomethyl ether, which can be used alone or in combination.

[0025] The usable thickener is preferably at least one selected from the group consisting of synthetic polymers, cellulose, and polysaccharides.Specific examples of the thickener include gum arabic, tragacanth gum, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, xanthan gum, welan gum, succinoglycan, diutan gum, dextran, methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, starch glycolic acid and its salts, propylene glycol alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylic acid and its salts, carboxyvinyl polymer, polyethylene oxide, copolymer of vinyl acetate and polyvinylpyrrolidone, crosslinked acrylic acid polymer and its salts, non-crosslinked acrylic acid polymer and its salts, styrene acrylic acid copolymer and its salts, etc.

[0026] Examples of lubricants include nonionic lubricants such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, polyoxyalkylene higher fatty acid esters, and alkyl phosphate esters, which are also used as surface treatment agents for pigments, anionic lubricants such as alkyl sulfonates and alkyl aryl sulfonates of higher fatty acid amides, derivatives of polyalkylene glycols, fluorine-based surfactants, polyether-modified silicones, etc. Examples of rust inhibitors include benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, and saponins, while examples of preservatives or antibacterial agents include phenol, sodium omadine, sodium benzoate, and benzimidazole-based compounds.

[0027] This aqueous ink composition for writing instruments can be produced by a conventional method, for example, by blending the above-mentioned microcapsulated pigment and each of the above-mentioned aqueous components in a predetermined amount, stirring and mixing them with a stirrer such as a homomixer or a disperser, etc. If necessary, coarse particles in the ink composition can be removed by filtration or centrifugation. Good too.

[0028] <Oil-based ink composition for writing instruments> In the ink composition for a writing instrument of the present invention, the oil-based ink composition preferably contains the microencapsulated pigment having the above-mentioned constitution and at least one selected from polypropylene glycol, polybutylene glycol, and polyoxypropylene diglyceryl ether as a main solvent. By selecting and using such a solvent as the main solvent, it acts to prevent the aggregation of the microencapsulated pigment over time.

[0029] The polypropylene glycol and polybutylene glycol used may have any degree of polymerization. In order to further exert the effects of the present invention, however, it is preferable to use polypropylene glycol having a degree of polymerization (weight average) in the range of 400 to 700, and it is preferable to use polybutylene glycol having a degree of polymerization (weight average) in the range of 500 to 700. The polyoxypropylene diglyceryl ether [POP(n) diglyceryl ether] used in the present invention is obtained by addition polymerization of polyoxypropylene to the hydroxyl groups of diglycerin. In the present invention, the number of moles (n) of oxypropylene added in the polyoxypropylene diglyceryl ether [POP(n) diglyceryl ether] is preferably 4 to 25, more preferably 4 to 14, in order to further exert the effects of the present invention.

[0030] The content of these main solvents is preferably 50 to 100% based on the total amount of solvents in the ink composition, and more preferably 80 to 100%. By making the content of the main solvent 50% or more, it is possible to suppress the occurrence of aggregation over time as much as possible. In addition to the main solvents described above, solvents that are compatible with the main solvents, such as glycerin, diglycerin, and propylene glycol, may be appropriately contained within a range that does not impair the effects of the present invention.

[0031] In addition to the above-mentioned microencapsulated pigment and main solvent, this oil-based ink composition for writing instruments may contain, depending on the application of each writing instrument (for ballpoint pen, marking pen, etc.), and as necessary, resins, dispersants, rust inhibitors, preservatives, lubricants, etc. that are compatible with the oil-based ink without adversely affecting it. Examples of resins that can be used include ketone resins, styrene resins, styrene-acrylic resins, terpene phenol resins, rosin-modified maleic acid resins, rosin phenol resins, alkylphenol resins, phenol-based resins, styrene-maleic acid resins, rosin-based resins, acrylic resins, urea aldehyde-based resins, maleic acid-based resins, cyclohexanone-based resins, polyvinyl butyral, polyvinylpyrrolidone, and the like.

[0032] As the dispersant that can be used, a dispersant capable of dispersing the microcapsulated pigment can be selected from the resins listed above, and a surfactant or oligomer can also be contained as long as it is suitable for the purpose. Specific examples of the dispersant include synthetic resins such as polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl butyral, polyvinyl ether, styrene-maleic acid copolymer, ketone resin, hydroxyethyl cellulose and its derivatives, and styrene-acrylic acid copolymer, as well as PO·EO adducts and polyester amine oligomers. As the rust inhibitor, preservative and lubricant, the various rust inhibitors, preservatives and lubricants used in the aqueous solution described above can be used.

[0033] This oil-based ink composition for writing instruments can be produced by a conventional method, for example, by blending the above-mentioned microcapsule pigment and each of the above-mentioned oil-based components in a predetermined amount, stirring and mixing them with a stirrer such as a homomixer or a disperser, etc. If necessary, coarse particles in the ink composition can be removed by filtration or centrifugation. Good too.

[0034] In the ink composition for a writing instrument of the present invention thus configured, an aqueous or oil-based ink is formulated which contains a microencapsulated pigment which contains at least a leuco dye, the specific color developer and a discoloration temperature regulator. When this ink is loaded onto a writing instrument such as a ballpoint pen or marking pen, the ink composition has excellent color development when drawn, and when the ink is erased by heat such as friction, no traces are left on the paper, resulting in an ink composition for a writing instrument which has excellent erasing properties. EXAMPLES

[0035] Next, the present invention will be described in more detail with reference to a production example of a microcapsule pigment, and examples and comparative examples of an ink composition for a writing instrument, but the present invention is not limited to the following examples, etc. In the following, the unit of blending "parts" means parts by mass.

[0036] (Production Examples 1 to 8: Production of Microcapsule Pigments A-1 to A-8) Microcapsule pigments A-1 to A-8 were manufactured by the following manufacturing methods using the dyes (leuco dyes A and B), color developers (five types, including diphenylacetic acid, 3,3-diphenylpropionic acid, and triphenylacetic acid), and discoloration temperature regulators (three types) in the compositions shown in Table 1 below.

[0037] (Production Example 1: Formulation of Microcapsule Pigment A-1) One part of methyl-3',6'-bisdiphenylaminofluoran as leuco dye A, one part of diphenylacetic acid as developer, and 24 parts of bis(4-hydroxyphenyl)phenylmethane dicaprylate as color-changing temperature regulator were heated and melted at 100°C to obtain 26 parts of homogeneous composition. The homogeneous hot solution of 26 parts of the composition obtained above was gradually added to 100 parts of a 90°C aqueous solution in which 40 parts of methyl vinyl ether-maleic anhydride copolymer resin (Ganzlets AN-179: manufactured by ISP Co., Ltd.) as a protective colloid agent was dissolved at pH 4 with NaOH, while heating and stirring to disperse the mixture into oil droplets with a diameter of about 0.5 to 1.0 μm. Next, 20 parts of melamine resin (Sumitex Resin M-3, manufactured by Sumitomo Chemical Co., Ltd.) as a capsule film agent were gradually added, and the mixture was heated at 90°C for 30 minutes to perform microencapsulation, thereby obtaining a microcapsule dispersion of a reversible thermochromic composition in which the film agent is melamine resin. The hue was deep blue in the colored state, and was completely colorless with no residual color in the decolorized state.

[0038] (Production Example 2: Formulation of Microcapsule Pigment A-2) In the above A-1 formulation, leuco dye A was replaced with leuco dye B (4,4'-bis(diethylamino)benzophenone), the amount of diphenylacetic acid as the developer was changed to 0.3 parts, and the color-changing temperature regulator was replaced with 4,4'-isopropylidenebisphenol dimyristate, but the rest of the formulation was the same as A-1 above to obtain a microcapsule dispersion of a reversible thermochromic composition. The hue was deep yellow in the colored state, and completely colorless with no residual color in the decolorized state.

[0039] (Production Example 3: Formulation of Microcapsule Pigment A-3) A microcapsule dispersion of a reversible thermochromic composition was obtained in the same manner as in the above-mentioned A-1 formulation, except that diphenylacetic acid was replaced with 3,3-diphenylpropionic acid as the developer and 4,4'-isopropylidenebisphenol dimyristate was used as the color-changing temperature regulator. The hue was deep blue in the colored state, and completely colorless with no residual color in the decolorized state.

[0040] (Production Example 4: Formulation of Microcapsule Pigment A-4) In the above-mentioned A-2 formulation, except that 0.3 parts of diphenylacetic acid was replaced with 8 parts of 3,3-diphenylpropionic acid as the developer and 4,4'-ethylidenebisphenol dilaurate was used as the color-changing temperature regulator, a microcapsule dispersion of a reversible thermochromic composition was obtained in the same manner as in the above-mentioned A-2 formulation. The hue was deep yellow in the colored state, and completely colorless with no residual color in the decolorized state.

[0041] (Production Example 5: Formulation of Microcapsule Pigment A-5) A microcapsule dispersion of a reversible thermochromic composition was obtained in the same manner as in the above-mentioned A-1 formulation, except that 1 part of diphenylacetic acid was replaced with 0.3 parts of triphenylacetic acid as a developer. The hue was deep blue in the colored state, and completely colorless with no residual color in the decolored state.

[0042] (Production Example 6: Formulation of Microcapsule Pigment A-6) In the above-mentioned A-2 formulation, except that 0.3 parts of diphenylacetic acid was replaced with 1 part as the color developer and 4,4'-ethylidenebisphenol dilaurate was used as the color-changing temperature regulator, a microcapsule dispersion of a reversible thermochromic composition was obtained in the same manner as in the above-mentioned A-2 formulation. The hue was deep yellow in the colored state, and completely colorless with no residual color in the decolorized state.

[0043] (Production Example 7: Formulation of Microcapsule Pigment A-7) A microcapsule dispersion of a reversible thermochromic composition was obtained in the same manner as in the above-mentioned A-1 formulation, except that in the above-mentioned A-1 formulation, 1 part of diphenylacetic acid was replaced with 1 part of 4-hydroxybenzoic acid dodecyl as the color developer, and 4,4'-isopropylidenebisphenol dimyristate was used as the color-changing temperature regulator. The hue was deep blue in the colored state, and completely colorless with no residual color in the decolorized state.

[0044] (Production Example 8: Formulation of Microcapsule Pigment A-3) In the above formulation of A-2, except that 0.3 parts of diphenylacetic acid was replaced with 1 part of 4-hydroxyphenyl dodecyl acetate as the color developer and 4,4'-ethylidene bisphenol dilaurate was used as the color-changing temperature regulator, a microcapsule dispersion of a reversible thermochromic composition was obtained in the same manner as in the above formulation of A-2. The hue was deep yellow in the colored state, and completely colorless with no residual color in the decolorized state.

[0045] (Examples 1 to 12 and Comparative Examples 1 to 2: Preparation of ink compositions for writing instruments) Each water-based and oil-based ink composition for ballpoint pens was prepared by a conventional method according to the formulation shown in Table 2 below (microcapsule pigments: A-1 to A-6, each blending component of the water-based ink in Examples 1 to 6 and Comparative Example 1, each blending component of the oil-based ink in Examples 7 to 12 and Comparative Example 2). Each microcapsule pigment A-1 to A-8 was extracted as a microcapsule pigment by filtering and drying each microcapsule dispersion and used.

[0046] (Production of water-based and oil-based ballpoint pens) Using each ink composition obtained above, prepare a water-based ballpoint pen and an oil-based ballpoint pen.Specifically, use the shaft of a ballpoint pen [manufactured by Mitsubishi Pencil Co., Ltd., product name: Signo UM-100], fill the refill with each of the water-based and oil-based inks described above, and fill the ink follower mainly composed of mineral oil at the ink rear end, and prepare a water-based ballpoint pen and an oil-based ballpoint pen. Using each of the ballpoint pens obtained in Examples 1 to 12 and Comparative Examples 1 and 2, the drawn line density and the color development / erasing properties of the drawn line were evaluated by the following evaluation method. The results are shown in Table 2 below.

[0047] (Evaluation method for line density) Each pen was used to write a freehand spiral on writing paper conforming to the ISO standard, and the line density was then visually evaluated according to the following criteria. Evaluation criteria: A: The color is deep black. B: The color is slightly light in density. C: The color is low in density. D: No color development.

[0048] (Evaluation method for color development / erasability of drawn lines) Each pen was used to write a freehand spiral on ISO standard writing paper, and the writing paper was thoroughly rubbed with an eraser-like friction tool made by SEBS to observe its condition. The writing paper was then stored in an environment of -10°C for 1 hour, after which the condition of the drawn lines was evaluated according to the following criteria. Evaluation criteria: A: In the decolorized state, the color is completely erased, and after storage at -10℃, the color returns to the hue before decolorization. B: A small amount of color remains after erasing, or the line density is slightly lighter after storage at -10°C. C: Color remains even after erasing, or the line density is low after storage at -10℃. D: No decolorization

[0049] [Table 1]

[0050] [Table 2]

[0051] As is clear from the results of Tables 1 and 2 above, the water-based and oil-based ink compositions for writing instruments containing the microencapsulated pigment of the present invention in Examples 1 to 12 of the present invention are superior in line density and color development of drawn lines compared to the water-based and oil-based ink compositions for writing instruments in Comparative Examples 1 and 2 which are outside the scope of the present invention, and no traces of writing remain on the paper even when thermally erased by frictional heat, confirming that they are ink compositions for writing instruments containing a thermochromic microencapsulated pigment with excellent erasing properties. [Industrial Applicability]

[0052] Thus, a microencapsulated pigment and an ink composition for a writing instrument, which are suitable for use in a water-based or oil-based writing instrument such as a ballpoint pen or a marking pen, can be obtained.

Claims

1. The microcapsule pigment contains at least a leuco dye, a discoloration temperature regulator, and a color developer, and the wall film is formed from a urethane resin, a urea resin, a urethane / urea resin, an epoxy resin, or an amino resin, and is characterized in that the color developer contains at least one selected from diphenylacetic acid, 3,3-diphenylpropionic acid, and triphenylacetic acid, and the content of the color developer is 0.1 to 20% by mass based on the total amount of the microcapsule pigment.

2. 2. An ink composition for a writing instrument, comprising the microcapsulated pigment according to claim 1.

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