Microcapsule pigments, and ink compositions for writing instruments containing them.

Abstract

To provide a microcapsule pigment in which leuco dye is used.SOLUTION: Provided is a microcapsule pigment that contains at least a leuco dye, a developer represented by the following formula (I), and a color change temperature regulator. [In the formula, R1 is H or a C1-8 alkyl group, phenyl group, benzyl group, tolyl group, xylyl group; R2 is a C2-12 alkyl group, phenyl group, benzyl group, tolyl group, xylyl group; any one of A1 and A2 is a C1-2 alkyl group and the other is H; any one of B1 and B2 is a C1-2 alkyl group and the other is H.].SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to microcapsule pigments, ink compositions for writing instruments containing the same, and more specifically, to leuco dyes, thermochromic microcapsule pigments utilizing the color development and decolorization mechanisms of these dyes, ink compositions for writing instruments containing the same, and writing instruments. [Background technology]

[0002] Conventionally, ink compositions for writing instruments that utilize the color development and decolorization mechanisms of leuco dyes typically use pigments in which the above dyes are microencapsulated.

[0003] For example, 1) an ink composition for a thermochromic color memory writing instrument comprising at least a microcapsule pigment containing a homogeneous compatible solution of an ester compound represented by a specific formula, as a reaction medium to control the color reaction of (a) and (b), and a solvent (see, for example, Patent Document 1), 2) A reversible thermochromic composition comprising (a) an electron-donating chromogenic organic compound, (b) 2,2′-dimethyl-4,4′(fluorene-9,9-diyl)diphenol as an electron-accepting compound, and (c) a reaction medium that reversibly causes the electron transfer reaction of components (a) and (b) to occur in a specific temperature range, and a reversible thermochromic microcapsule pigment containing the same (see, for example, Patent Document 2). 3) A thermochromic pigment composition comprising (A) at least one electron-donating dye compound, (B) at least one electron-accepting compound, and (C) at least one compound represented by specific formula (I), wherein (B) is known to be 2,2-bis(4-hydroxy-3-methylphenyl)propane (bisphenol C) (see, for example, Patent Document 3).

[0004] However, as described in the above-mentioned Patent Documents 1 to 3, this type of color development effect is limited to specific compounds as the electron-accepting compounds (developers) that control the color development effect, and is only exhibited in systems in which these compounds are applied as components. As a result, there are still challenges such as a low degree of freedom in selecting the developer (electron-accepting compound) and a limited degree of freedom in selecting materials. Therefore, improvements in manufacturing efficiency and diversification of thermal discoloration are still insufficient, and there is a strong demand for microcapsule pigments with even better color development and erasure (decolorization) properties. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2005-213361 (Claims, Examples, etc.) [Patent Document 2] Japanese Patent Publication No. 2018-123204 (Claims, Examples, etc.) [Patent Document 3] Japanese Patent Publication No. 2020-517759 (Claims, Examples, etc.) [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In view of the problems and current state of the prior art described above, the present invention aims to resolve these issues by increasing the degree of freedom in selecting materials when selecting a color developer, expanding the degree of freedom in setting the amount thereof, reducing the burden of manufacturing, improving the diversification of thermal discoloration, further increasing the usability of microcapsule pigments, and providing a microcapsule pigment with even better color development and erasability (decolorization) properties, an ink composition for writing instruments containing the same, and a writing instrument. [Means for solving the problem]

[0007] In view of the above-mentioned conventional problems, the present inventors conducted diligent research and, as a result, discovered that by including at least a leuco dye, a specific color developer, and a color change temperature adjuster, the above-mentioned microcapsule pigment, an ink composition for writing instruments containing the same, and a writing instrument can be obtained, thus completing the present invention.

[0008] In other words, the microcapsule pigment of the present invention is characterized by comprising at least a leuco dye, a color developer represented by the following formula (I), and a color change temperature adjuster. [ka] [In formula (I) above, R1 is a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, a phenyl group, a benzyl group, a tolyl group, or a xylyl group; R2 is an alkyl group having 2 to 12 carbon atoms, a phenyl group, a benzyl group, a tolyl group, or a xylyl group; either A1 or A2 is an alkyl group having 1 to 2 carbon atoms, and the other is a hydrogen atom; either B1 or B2 is an alkyl group having 1 to 2 carbon atoms, and the other is a hydrogen atom; R1 and R2 may be the same or different.] In the above formula (I), R1 is preferably a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, R2 is preferably an alkyl group having 2 to 8 carbon atoms, a phenyl group, a benzyl group, or a phenethyl group, and A1 or A2 is preferably a methyl group and B1 or B2 is preferably a methyl group. The above-mentioned microcapsule pigments preferably have an average particle size in the range of 0.1 to 5.0 μm. The ink composition for writing instruments of the present invention is characterized by containing a microcapsule pigment having the above-described structure. The writing instrument of the present invention is characterized by incorporating the above-described ink composition for writing instruments. [Effects of the Invention]

[0009] According to the present invention, there are provided microcapsule pigments that increase the degree of freedom in material selection when selecting a developer, expand the degree of freedom in setting when adjusting the amount of the developer, reduce the manufacturing load, improve the diversification of thermochromic properties, further increase the utilization of microcapsule pigments, and additionally have excellent color-developing properties and erasing (decoloring) properties; ink compositions for writing instruments containing the same; and writing instruments. The objects and effects of the present invention are recognized and obtained particularly by using the constituent elements and combinations thereof pointed out in the claims. Both the foregoing general description and the following detailed description are exemplary and explanatory, and are not intended to limit the present invention described in the claims. [BRIEF DESCRIPTION OF THE DRAWINGS]

[0010] [Figure 1] (a) to (e) are drawings showing structural formulas of respective compounds that are specific examples of the developer represented by formula (I) used in the microcapsule pigment of the present invention. [Figure 2] (f) to (j) are a continuation from FIG. 1, and are drawings showing structural formulas of respective compounds that are specific examples of the developer represented by formula (I) used in the microcapsule pigment of the present invention. [MODE FOR CARRYING OUT THE INVENTION]

[0011] Hereinafter, 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 detailed below, and extends to the invention described in the claims and equivalents thereof. Furthermore, the present invention can be implemented based on the content disclosed in the present specification and common general technical knowledge in the art (including design matters and obvious matters).

[0012] The microcapsule pigment of the present invention is characterized by comprising at least a leuco dye, a developer represented by the following formula (I), and a discoloration temperature regulator. [Chemical Formula] [In the above formula (I), R1 is a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a phenyl group, a benzyl group, a tolyl group, or a xylyl group; R2 is an alkyl group having 2 to 12 carbon atoms, a phenyl group, a benzyl group, a tolyl group, or a xylyl group; one of A1 and A2 is an alkyl group having 1 to 2 carbon atoms, and the other is a hydrogen atom; one of B1 and B2 is an alkyl group having 1 to 2 carbon atoms, and the other is a hydrogen atom; and R1 and R2 may be the same or different from each other.]]

[0013] <Leuco dye> 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 excellent in color development properties, conventionally known ones such as triphenylmethane-based, spiropyran-based, fluorane-based, diphenylmethane-based, rhodamine lactam-based, indolylphthalide-based, and leucoauramine-based dyes can be used alone (one type) or as a mixture of two or more types (hereinafter simply referred to as "at least one type"). Examples of leuco dyes that can be used include 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-methylindole-3-yl)phthalide, and 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2 -methylindole-3-yl)-4-azaphthalide, 1,3-dimethyl-6-diethylaminofluorane, 2-chloro-3-methyl-6-dimethylaminofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-xylidinofluorane, 2-(2-chloroanilino)-6-dibutylaminofluorane, 3,6- Dimethoxyfluorane, 3,6-di-n-butoxyfluorane, 1,2-benz-6-diethylaminofluorane, 1,2-benz-6-dibutylaminofluorane, 1,2-benz-6-ethylisoamylaminofluorane, 2-methyl-6-(Np-tolyl-N-ethylamino)fluorane, 2-(N-phenyl-N-methylamino)-6-(Np-tolyl-N-ethylamino)fluorane, 2-(3'-trifluoromethyl Examples include anilino)-6-diethylaminofluorane, 3-chloro-6-cyclohexylaminofluorane, 2-methyl-6-cyclohexylaminofluorane, 3-di(n-butyl)amino-6-methoxy-7-anilinofluorane, 3,6-bis(diphenylamino)fluorane, 3-methoxy-4-dodecoxystylinoquinoline, 3-diethylamino-6-methyl-7-m-trifluoromethylphenylaminofluorane (BLACK 100), 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluorane (S-205), and 3-(N-ethyl-p-methylphenylamino)-6-methyl-7-anilinofluorane (ETAC), and at least one of these can be used. In addition to the aforementioned compounds having substituents on the phenyl group forming the xanthene ring, fluoranes may also be compounds exhibiting blue or black color, having substituents on the phenyl group forming the xanthene ring and also substituents (for example, alkyl groups such as methyl groups, halogen atoms such as chloro groups) on the phenyl group forming the lactone ring. Furthermore, pyridine compounds, quinazoline compounds, bisquinazoline compounds, etc., that produce yellow to red coloration can also be used. These leuco dyes possess structures such as lactone, pyridine, quinazoline, and bisquinazoline skeletons, and they exhibit color development when these skeletons (rings) open.

[0014] <Color Developer> The color developer represented by formula (I) used in the present invention is a component that has the ability to cause the above-mentioned leuco dye to develop color. In formula (I) above, R1 is a hydrogen atom or a linear or branched alkyl group having 1 to 8 carbon atoms, a phenyl group, a benzyl group, a tolyl group, or a xylyl group. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, and so on. R2 is a linear or branched alkyl group having 2 to 12 carbon atoms, a phenyl group, a benzyl group, a tolyl group, or a xylyl group. Either A1 or A2 is a C1-C2 alkyl group and the other is a hydrogen atom, and either B1 or B2 is a C1-C2 alkyl group and the other is a hydrogen atom. R1 and R2 may be the same or different. Preferably, in order to further exhibit the effects of the present invention, in formula (I) above, R1 is a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, R2 is an alkyl group having 2 to 8 carbon atoms, a phenyl group, or a benzyl group, A1 or A2 is preferably a methyl group and B1 or B2 is preferably a methyl group, and particularly preferably the total number of carbon atoms of R1 and R2 is in the range of 4 to 8.

[0015] Examples of color developers that can be specifically used are the compounds shown by the structural formulas (a) to (j) in Figures 1 and 2. Specifically, 1,1-bis(4-hydroxy-3-methylphenyl)-2-ethylhexane [Figure 1(a)], 1,1-bis(4-hydroxy-3-methylphenyl)-2-ethylbutane [Figure 1(b)], 1,1-bis(4-hydroxy-3-methylphenyl)-2-methylpentane [Figure 1(c)], 1,1-bis(4-hydroxy-3-methylphenyl)-2-phenylethane [Figure 1(d)], 1,1-bis(4-hydroxy-3-methylphenyl)-3-phenylpropane [Figure 1(e)], 1,1-bis(4 These are 1,1-(4-hydroxy-3-methylphenyl)-5-methylpentane [Figure 1(f)], 1,1-(4-hydroxy-3-methylphenyl)-6-methylhexane [Figure 1(g)], 1,1-(4-hydroxy-3-methylphenyl)-7-methylheptane [Figure 1(h)], 1,1-(4-hydroxy-3-methylphenyl)-8-methyloctane [Figure 1(i)], and 1,1-(4-hydroxy-3-methylphenyl)-9-methylnonane [Figure 1(j)], and at least one of these can be used. The color developer represented by the above formula (I) is manufactured using a known method and exhibits a color development effect that is equal to or better than conventional color developers consisting of triphenylmethane-based compounds or compounds such as bis(4-hydroxy-3-methylphenyl). This increases the freedom of material selection and expands the freedom of setting the amount of the color developer.

[0016] In the present invention, by using one or more of these color developers in combination, or by using conventionally known color developers in combination within a range that does not impair the properties of the color developers of the present invention, the color density during color development can be adjusted more freely than in the conventional method. Therefore, the amount used can be arbitrarily selected according to the desired color density and is not particularly limited, but it is generally preferable to select an amount in the range of 0.1 to 100 parts by mass per 1 part by mass of the leuco dye mentioned above.

[0017] <Color change temperature adjuster> The color change temperature adjusting agent used in the present invention is a substance that controls the color change temperature in the color development of the leuco dye and the color developer shown in (I) above. Conventional known color change temperature regulators can be used. Specifically, these include alcohols, esters, ketones, ethers, acid amides, azomethines, fatty acids, hydrocarbons, and the like.

[0018] Specific examples of color change temperature modifiers that can be used include 4-benzyloxyphenylethyl octanoate, 4-benzyloxyphenylethyl nonanoate, 4-benzyloxyphenylethyl decanoate, 4-benzyloxyphenylethyl undecanoate, 4-benzyloxyphenylethyl dodecanoate, 4-benzyloxyphenylethyl tridecanoate, 4-benzyloxyphenylethyl tetradecanoate, 4-benzyloxyphenylethyl pentadecanoate, and 4-benzyloxyphenylethyl hexadecanate. Dyloxyphenylethyl, 4-benzyloxyphenylethyl heptadecanoate, 4-benzyloxyphenylethyl octadecanoate, 1,1-diphenylmethyl octanoate, 1,1-diphenylmethyl nonanoate, 1,1-diphenylmethyl decanoate, 1,1-diphenylmethyl undecanoate, 1,1-diphenylmethyl dodecanoate, 1,1-diphenylmethyl tridecanoate, 1,1-diphenylmethyl tetradecanoate, 1,1-diphenylmethyl pentadecanoate, 1,1-diphenylmethyl hexadecanoate Methyl, 1,1-diphenylmethyl heptadecanoate, 1,1-diphenylmethyl octadecanoate, diester of malonic acid with 2-[4-(4-chlorobenzyloxy)phenyl)]ethanol, diester of succinic acid with 2-(4-benzyloxyphenyl)ethanol, diester of succinic acid with 2-[4-(3-methylbenzyloxy)phenyl)]ethanol, diester of glutaric acid with 2-(4-benzyloxyphenyl)ethanol, diester of glutaric acid with 2-[4-(4-chlorobenzyloxy)phenyl] Diesters of ethanol (phenyl) and 2-(4-benzyloxyphenyl)ethanol, diesters of adipic acid and 2-(4-benzyloxyphenyl)ethanol, diesters of pimelic acid and 2-(4-benzyloxyphenyl)ethanol, diesters of suberic acid and 2-(4-benzyloxyphenyl)ethanol, diesters of suberic acid and 2-[4-(3-methylbenzyloxy)phenyl)]ethanol, diesters of suberic acid and 2-[4-(4-chlorobenzyloxy)phenyl)]ethanol, diesters of suberic acid and 2-[4-(2,Diester of 4-dichlorobenzyloxy(phenyl)ethanol, diester of azelaic acid and 2-(4-benzyloxyphenyl)ethanol, diester of sebacic acid and 2-(4-benzyloxyphenyl)ethanol, 1,10-decanedicarboxylic acid and 2-(4-benzyloxyphenyl), Examples include diesters with ethanol, diesters of 1,18-octadecanedicarboxylic acid and 2-(4-benzyloxyphenyl)ethanol, and diesters of 1,18-octadecanedicarboxylic acid and 2-[4-(2-methylbenzyloxy)phenyl)]ethanol. Diesters of 1,3-bis(2-hydroxyethoxy)benzene and capric acid, diesters of 1,3-bis(2-hydroxyethoxy)benzene and undecanoic acid, diesters of 1,3-bis(2-hydroxyethoxy)benzene and lauric acid, diesters of 1,3-bis(2-hydroxyethoxy)benzene and myristic acid, diesters of 1,4-bis(hydroxymethoxy)benzene and butyric acid, diesters of 1,4-bis(hydroxymethoxy)benzene and isovaleric acid, diesters of 1,4-bis(2-hydroxyethoxy)benzene and acetic acid, and 1,4-bis( Examples include diesters of 2-hydroxyethoxy)benzene with propionic acid, 1,4-bis(2-hydroxyethoxy)benzene with valeric acid, 1,4-bis(2-hydroxyethoxy)benzene with caproic acid, 1,4-bis(2-hydroxyethoxy)benzene with caprylic acid, 1,4-bis(2-hydroxyethoxy)benzene with capric acid, 1,4-bis(2-hydroxyethoxy)benzene with lauric acid, and 1,4-bis(2-hydroxyethoxy)benzene with myristic acid.Diester of succinic acid and 2-phenoxyethanol, diester of suberic acid and 2-phenoxyethanol, diester of sebacic acid and 2-phenoxyethanol, diester of 1,10-decanedicarboxylic acid and 2-phenoxyethanol, diester of 1,18-octadecanedicarboxylic acid and 2-phenoxyethanol, diester of succinic acid and 2-phenoxyethanol, diester of suberic acid and 2-phenoxyethanol, diester of sebacic acid and 2-phenoxyethanol, diester of 1,10-decanedicarboxylic acid and 2-phenoxyethanol, diester of 1,18-octadecanedicarboxylic acid and 2-phenoxyethanol, decyl phenylbenzoate, lauryl phenylbenzoate, 4-phenylbenzoic acid Examples include myristyl acid, cyclohexylethyl phenylbenzoate, octyl 4-biphenylacetate, nonyl 4-biphenylacetate, decyl 4-biphenylacetate, lauryl 4-biphenylacetate, myristyl 4-biphenylacetate, tridecyl 4-biphenylacetate, pentadecyl 4-biphenylacetate, cetyl 4-biphenylacetate, cyclopentyl 4-biphenylacetate, cyclohexylmethyl 4-biphenylacetate, hexyl 4-biphenylacetate, cyclohexylmethyl 4-biphenylacetate, phenoxyethyl 4-butoxybenzoate, phenoxyethyl 4-pentyloxybenzoate, phenoxyethyl 4-tetradecyloxybenzoate, esters of phenoxyethyl 4-hydroxybenzoate and dodecanoic acid, and dodecyl ether of phenoxyethyl vanillate. The aforementioned compounds include benzoic acid esters of octyl p-hydroxybenzoate, benzoic acid esters of decyl p-hydroxybenzoate, p-methoxybenzoic acid esters of heptyl p-hydroxybenzoate, o-methoxybenzoic acid esters of dodecyl p-hydroxybenzoate, benzoic acid esters of cyclohexylmethyl p-hydroxybenzoate, and bis(4-hydroxyphenyl)phenylmethane dicaprylate (C7H. 15 ), bis(4-hydroxyphenyl)phenylmethanedilaureate (C 11 H 23 ), bis(4-hydroxyphenyl)phenylmethanedimyristate (C 13 H 27), bis(4-hydroxyphenyl)phenylethane dimyristate (C 13 H 27 ), bis(4-hydroxyphenyl)phenylmethane dipalmitate (C 15 H 30 ), bis(4-hydroxyphenyl)phenylmethane dibehenate (C 21 H 43 ), bis(4-hydroxyphenyl)phenylethylhexylidene dimyristate (C 13 H 27 ), and the like, and at least one type thereof may be cited.

[0019] The used amount of the discoloration temperature adjusting agent may be appropriately selected according to the desired hysteresis width, color density at the time of color development, and the like, and is not particularly limited, but it is usually preferably used in a range of about 1 to 1000 parts by mass relative to 1 part by mass of the leuco dye. Furthermore, as long as the various properties of the ink composition of the present invention are not impaired, conventionally known discoloration temperature adjusting agents for this type of thermochromic composition can also be used in combination.

[0020] <Microcapsule Pigment> The microcapsule pigment of the present invention can be produced by microencapsulating a thermochromic composition containing at least a leuco dye, the developer represented by the above formula (I), and a discoloration temperature adjusting agent, preferably so as to have an average particle diameter of 0.1 to 1.0 μm. Examples of the microencapsulation method include an interfacial polymerization method, an interfacial polycondensation method, an in-situ polymerization method, an in-liquid curing coating method, a phase separation method from an aqueous solution, a phase separation method from an organic solvent, a melt dispersion cooling method, an air suspension coating method, a spray drying method, and the like, and can be appropriately selected according to the application.

[0021] For example, in the phase separation method from aqueous solutions, a leuco dye, a color developer, and a color change temperature regulator are heated and melted, then added to an emulsifier solution, heated and stirred to disperse them into oil droplets, and then a resin raw material is used as a capsule membrane agent. For example, an amino resin solution, specifically an aqueous solution of methylolmelamine, a urea solution, or a benzoguanamine solution, is gradually added and the mixture is continued to react. After preparing the mixture, the dispersion is filtered to produce the desired thermochromic microcapsule pigment.

[0022] The content of these leuco dyes, developers, and color change temperature regulators varies depending on the type of leuco dye, developer, and color change temperature regulator used, as well as the microencapsulation method. However, for every 1 unit of dye, the mass ratio is 0.1 to 100 units of developer and 1 to 100 units of color change temperature regulator. In addition, the mass ratio of the capsule membrane to the capsule contents is 0.1 to 1 unit. In the microcapsule pigments of the present invention, the color development temperature and decolorization temperature of each color can be set to a suitable temperature by suitably combining the types and amounts of leuco dyes, color developers, and color change temperature adjusters.

[0023] From the viewpoint of further improving the line density, storage stability, and writing properties of the microcapsule pigment of the present invention, it is preferable that the wall film be formed of a urethane resin, epoxy resin, or amino resin. Examples of urethane resins include compounds of isocyanates and polyols. Examples of epoxy resins include compounds of epoxy resins and amines. Examples of amino resins include melamine resin, urea resin, and benzoguanamine resin, and more preferably, from the viewpoint of manufacturability, storage stability, and writing properties, it is desirable that the wall film be formed of a melamine resin. The thickness of the microcapsule pigment's wall film is determined appropriately according to the required wall film strength and line density. Furthermore, in order for the wall film to be formed of amino resin, suitable amino resin raw materials (melamine resin, urea resin, benzoguanamine resin, etc.), as well as dispersants, protective colloids, etc., should be selected when using each microencapsulation method.

[0024] The average particle size of the microcapsule pigment of the present invention is preferably 0.1 to 5.0 μm, and more preferably 0.3 to 1.0 μm, from the viewpoint of colorability, color development, ease of decolorization, stability, and suppression of adverse effects on writing performance. The "average particle size" as defined in the present invention (including examples, etc.) is the value obtained by measuring the average particle size using a particle size distribution analyzer [particle size analyzer N4Plus (manufactured by COULTER)]. If the average particle size is less than 0.1 μm, sufficient line density cannot be obtained. On the other hand, if it exceeds 5.0 μm, deterioration of writing performance and a decrease in the dispersion stability of microcapsule pigments occur, which is undesirable. The average particle size range of microcapsule pigments (0.1 to 5.0 μm) varies depending on the microencapsulation method, but in methods such as phase separation from aqueous solutions, they can be prepared by suitably combining the stirring conditions during production of the microcapsule pigment.

[0025] The microcapsule pigment of the present invention, configured in this manner, increases the freedom of material selection when choosing the developer to use in a microcapsule pigment using a leuco dye, expands the freedom of setting the amount thereof, reduces the burden of manufacturing, improves the diversification of thermal color change, and further increases the usability of microcapsule pigments. Moreover, it has a color intensity and ease of decolorization that is equal to or better than conventional thermal colorants, and can be suitably used as a thermal colorant for writing instruments. Even when used as a colorant in an ink composition for writing instruments with an aqueous or oil-based solvent, it can exhibit the above effects without being affected by the type of solvent.

[0026] <Ink composition for writing instruments> The ink composition for writing instruments of the present invention is characterized by containing microcapsule pigments having the above-described structure, and can be used as an ink composition for writing instruments such as ballpoint pens and marking pens. The content of the microcapsule pigment of the present invention is preferably 5 to 30% by mass (hereinafter simply referred to as "%"), and more preferably 10 to 25% of the total amount of the ink composition. If the content of these microcapsule pigments is less than 5%, the coloring power and color development will be insufficient, while if it exceeds 30%, streaking is likely to occur, which is undesirable.

[0027] <Water-based ink composition for writing instruments> In the writing instrument ink composition of the present invention, in the aqueous form, in addition to the microcapsule pigment described above, the remainder may contain, as appropriate, a solvent such as water (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.), and depending on the application for each writing instrument (for ballpoint pens, marking pens, etc.), a water-soluble organic solvent, a thickener, a lubricant, a rust inhibitor, a preservative, or an antibacterial agent, to the extent that the effects of the present invention are not impaired.

[0028] Examples of water-soluble organic solvents 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.

[0029] The thickening agents that can be used are preferably at least one selected from the group consisting of synthetic polymers, cellulose, and polysaccharides. Specifically, examples include gum arabic, tragacanth gum, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, xanthan gum, gelan gum, succinoglycan, dieutan 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 hydroxide, 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, and the like.

[0030] Examples of lubricants include nonionic compounds such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, higher polyoxyalkylene fatty acid esters, and alkyl phosphate esters, which are also used as surface treatment agents for pigments; anionic compounds such as alkyl sulfonates and alkyl allyl sulfonates of higher fatty acid amides; derivatives of polyalkylene glycols; fluorinated surfactants; and polyether-modified silicones. Examples of rust inhibitors include benzotriazole, tolyltriazole, dicyclohexylammonium nitride, and saponins, while examples of preservatives or antibacterial agents include phenol, sodium omazine, sodium benzoate, and benzimidazole compounds.

[0031] Conventional methods can be used to produce this aqueous ink composition for writing instruments. For example, it can be obtained by mixing predetermined amounts of the above-mentioned microcapsule pigment and other components in the aqueous solution, and stirring and mixing them using a stirrer such as a homomixer or disper. Furthermore, if necessary, coarse particles in the ink composition may be removed by filtration or centrifugation.

[0032] <Oil-based ink composition for writing instruments> In the writing instrument ink composition of the present invention, in the case of an oil-based ink, it is preferable to contain a microcapsule pigment having the above-described configuration, and to also contain at least one selected from polypropylene glycol, polybutylene glycol, and polyoxypropylene diglyceryl ether as the main solvent. By selecting and using these solvents as the main solvent, it is possible to prevent the aggregation of the microcapsule pigment over time.

[0033] While polypropylene glycol and polybutylene glycol of various degrees of polymerization can be used, to further enhance the effects of the present invention, it is preferable to use polypropylene glycol with a degree of polymerization (weight average) in the range of 400 to 700, and polybutylene glycol with a degree of polymerization (weight average) in the range of 500 to 700. Furthermore, the polyoxypropylene diglyceryl ether [POP(n) diglyceryl ether] used in the present invention is obtained by addition polymerization of polyoxypropylene to the hydroxyl group of diglycerin. In the present invention, the number of moles (n) of oxypropylene added to the polyoxypropylene diglyceryl ether [POP(n) diglyceryl ether] is preferably 4 to 25, and more preferably 4 to 14, in order to further exhibit the effects of the present invention.

[0034] The content of these main solvents is preferably 50-100% of the total amount of solvent in the ink composition, and more preferably 80-100%. By having a main solvent content of 50% or more, the occurrence of aggregation over time can be suppressed as much as possible. In addition to the main solvents mentioned above, solvents that are compatible with the main solvents, such as glycerin, diglycerin, and propylene glycol, can be appropriately included as long as they do not impair the effects of the present invention.

[0035] In addition to the microcapsule pigment and main solvent mentioned above, this oil-based ink composition for writing instruments may contain resins, dispersants, rust inhibitors, preservatives, lubricants, etc., that are compatible with the oil-based ink without adversely affecting it, depending on the application for each writing instrument (e.g., ballpoint pens, marking pens, etc.) and as needed. 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, phenolic resins, styrene-maleic acid resins, rosin-based resins, acrylic resins, urea aldehyde-based resins, maleic acid-based resins, cyclohexanone-based resins, polyvinyl butyral, and polyvinylpyrrolidone.

[0036] As for the dispersants that can be used, those resins that can disperse microcapsule pigments can be selected from the resins listed above, and surfactants and oligomers can also be included if they are suitable for the purpose. Specific examples of dispersants include polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl butyral, polyvinyl ether, styrene-maleic acid copolymer, ketone resin, synthetic resins such as hydroxyethylcellulose and its derivatives, and styrene-acrylic acid copolymer, as well as PO·EO adducts and polyester amine oligomers. Furthermore, the various water-based rust inhibitors, preservatives, and lubricants mentioned above can be used as rust inhibitors, preservatives, and lubricants.

[0037] Conventional methods can be used to produce this oil-based ink composition for writing instruments. For example, it can be obtained by blending predetermined amounts of the above-mentioned microcapsule pigment and other oil-based components, and stirring and mixing them using a stirrer such as a homomixer or disper. Furthermore, if necessary, coarse particles in the ink composition may be removed by filtration or centrifugation.

[0038] The ink composition for writing instruments of the present invention, configured in this manner, is used by being mounted on a marking pen body equipped with a fiber tip, a felt tip, or a plastic tip at the writing end, or on a ballpoint pen body equipped with a ballpoint pen tip at the writing end. The present invention provides an ink composition and writing instrument for writing instruments that contain an aqueous or oil-based ink containing a microcapsule pigment comprising at least a leuco dye, a color developer represented by formula (I) above, and a color change temperature adjuster. When writing on paper or the like with a writing instrument such as a ballpoint pen or marking pen equipped with this ink, the microcapsule pigment does not aggregate or change color over time, the writing can change color well, and the ink composition and writing instrument have excellent color development and erasability (decolorization). [Examples]

[0039] Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples. In the following, "parts" as a blending unit means parts by mass.

[0040] [Microcapsule pigments: Formulations for A-1 to A-11, see Table 1 below] (Microcapsule pigment: A-1) Colorants were obtained using combinations of leuco dye, developer, and color-changing temperature regulator in the amounts shown in Table 1 below. Specifically, 1 part of ETAC (manufactured by Yamada Chemical Industries Co., Ltd.) was used as a leuco dye, 3 parts of the developer shown in Figure 1(a) was used as a color developer, and 24 parts of myristyl myristate was used as a color change temperature regulator. These were heated and melted at 100°C to obtain 27 parts of a homogeneous composition. A homogeneous hot solution of 27 parts of the composition obtained above was gradually added to 100 parts of a 90°C aqueous solution prepared by dissolving 40 parts of methyl vinyl ether-maleic anhydride copolymer resin [Ganzletz AN-179: manufactured by ISP Co., Ltd.] in NaOH at pH 4 as a protective colloidal agent. The mixture was heated and stirred to disperse the solution into oil droplets with a diameter of approximately 0.5 to 5.0 μm. Next, 20 parts of melamine resin (Sumitex Resin M-3: manufactured by Sumitomo Chemical Co., Ltd.) as a capsule membrane agent was gradually added, and the mixture was heated at 90°C for 30 minutes to microencapsulate the solution, obtaining a microcapsule dispersion of a reversible thermochromic hysteresis composition with melamine resin as the membrane agent. After cooling this dispersion to room temperature, acid was added, filtered, and washed with water. The mixture was then dried using a spray dryer to obtain a powder-like microcapsule pigment with an average particle size of 2.3 μm. The hue exhibited a deep black color when the color was developed (for example, at room temperature of 25°C), and became completely colorless with no residual color when the color was decolorized.

[0041] (Microcapsule pigments: A-2~A-11) Powdered microcapsule pigments were obtained using combinations of leuco dye, developer, and color-changing temperature regulator in the amounts shown in Table 1 below, with the rest of the process being the same as in the formulation of A-1 above. Table 1 below shows the average particle size and hue (color development state) of the obtained microcapsule pigments A-2 to A-11. It should be noted that even with microcapsule pigments A-2 to A-11, there was no residual color in the decolorized state, and they became completely colorless.

[0042] [Table 1]

[0043] (Examples 1-8 and Comparative Examples 1-3) (Ink formulation) Using the microcapsule pigments (A-1 to A-11) obtained in the above manufacturing example, aqueous ballpoint pen ink compositions were prepared by conventional methods according to the formulations shown in Table 2 below.

[0044] (Making a ballpoint pen) A ballpoint pen was manufactured using each of the ink compositions obtained above. Specifically, the barrel of a ballpoint pen [Mitsubishi Pencil Co., Ltd., product name: UF-202] was used, and the above inks were filled into a refill consisting of a polypropylene ink reservoir tube with an inner diameter of 3.8 mm and a length of 90 mm, a stainless steel tip (carbide alloy ball, ball diameter 0.5 mm), and a connector connecting the reservoir tube and the tip. An ink-following body mainly composed of mineral oil was loaded at the rear end of the ink to manufacture the ballpoint pen. The ballpoint pens obtained in Examples 1-8 and Comparative Examples 1-3 were used to evaluate color development and erasability using the following evaluation methods. These results are shown in Table 2 below.

[0045] (Method for evaluating color development) After writing a five-turn spiral on PPC paper using the above pen, the color development of the written lines was visually evaluated based on the following evaluation criteria. Evaluation criteria: A: Very rich and vibrant B: Dark C: Slightly thin D: Thin

[0046] (Method for evaluating extinction ability) Using the above pen, a spiral of five turns was written on PPC paper. Then, an eraser consisting of the cap of a UF-202-05 (manufactured by Mitsubishi Pencil Co., Ltd.) and a load of 500g were attached to a reciprocating machine, and the machine was moved back and forth five times over the written line (paint film). The degree of erasure (discoloration state) was evaluated based on the evaluation criteria below. Evaluation criteria: A: It's completely gone. B: It's not completely gone, but it's gone. C: There are many areas that cannot be erased. D: It won't disappear.

[0047] [Table 2]

[0048] As is clear from the results in Tables 1 and 2 above, the writing instrument ink compositions of Examples 1 to 8, which represent the present invention, were found to have satisfactory color development and decolorization properties. This increases the freedom of material selection when choosing the developer to use in microcapsule pigments using leuco dyes, expands the freedom of setting the amount, reduces the burden of manufacturing, improves the diversification of thermal discoloration, further increases the usability of microcapsule pigments, and confirms that microcapsule pigments with even better color development and erasability (decolorization) properties can be obtained, as well as writing instrument ink compositions containing these excellent microcapsule pigments and writing instruments equipped with these ink compositions. [Industrial applicability]

[0049] Microcapsule pigments and ink compositions for writing instruments, as well as writing instruments themselves, suitable for use in ballpoint pens, markers, and other writing instruments, can be obtained.

Claims

1. A microcapsule pigment characterized by comprising at least a leuco dye, a color developer represented by the following formula (I), and a color change temperature adjuster. 【Chemistry 1】 [In the above formula (I), R1 is a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a phenyl group, a benzyl group, a tolyl group, or a xylyl group. If R1 is a hydrogen atom, R2 is a phenyl group, a benzyl group, a tolyl group, or a xylyl group. If R1 is an alkyl group having 1 to 8 carbon atoms, R2 is a phenyl group, a benzyl group, a tolyl group, or a xylyl group. Furthermore, if R1 is a phenyl group, a benzyl group, a tolyl group, or a xylyl group, R2 is a alkyl group having 2 to 12 carbon atoms, a phenyl group, a benzyl group, a tolyl group, or a xylyl group. Either A1 or A2 is an alkyl group having 1 to 2 carbon atoms, and the other is a hydrogen atom. Either B1 or B2 is an alkyl group having 1 to 2 carbon atoms, and the other is a hydrogen atom.]

2. The microcapsule pigment according to claim 1, characterized in that the average particle size is in the range of 0.1 to 5.0 μm.

3. An ink composition for writing instruments characterized by containing the microcapsule pigment described in claim 1 or 2.

4. A writing instrument characterized by incorporating the writing instrument ink composition described in claim 3.

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