Composite coloring particles

Abstract

To provide an aqueous ink composition which is excellent in blur prevention of handwriting and scratch resistance, and is suitable industrial production, composite coloring particles blended with the same, and a method for producing composite coloring particles.SOLUTION: There are provided composite coloring particles which contain resin particles 2 having positive electric charge on the surface of the particle and dye-containing particles 1 having negative electric charge on the surface of the particles, and are obtained by compounding the resin particles and the dye-containing particles with a Coulomb force; an aqueous ink composition in which the composite coloring particles are dispersed in the aqueous medium; and a writing instrument containing the aqueous ink composition. There is also provided a method for producing composite coloring particles which includes a compounding step of mixing a resin emulsion containing resin particles having positive electric charge on the surface of the particles, with a coloring resin dispersion containing dye-containing particles having negative electric charge on the surface of the particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ink composition for a writing instrument and to composite colored particles contained therein. [Background technology]

[0002] Ink compositions in which various dyes or pigments are dissolved or dispersed in a solvent as colorants are used for writing instrument inks. In particular, aqueous ink compositions can be written with light writing pressure, but their properties as writing instruments are inferior to those of oil-based ink compositions, and improvements are needed.

[0003] For example, Patent Document 1 discloses an O / W emulsion ink composition for ballpoint pens that provides excellent water resistance to handwriting and good handwriting drying and nib drying resistance, and that includes an oil-based ink component comprising at least an oil-soluble dye as a colorant and an organic solvent that dissolves the dye and has a solubility of 5 g or less in 100 g of water at 20° C., an emulsifier component, a sugar alcohol that is solid at 20° C., and water, with the oil-based ink component being emulsified and dispersed in water. It states that an ink composition can be obtained that provides excellent water resistance to handwriting and good handwriting drying and nib drying resistance.

[0004] Patent Document 2 also discloses a method for producing microcapsules in which a functional substance such as a dye, a maleic anhydride copolymer, methylol melamine, and an organic amine salt having 6 or more carbon atoms are emulsified and dispersed in an aqueous medium, and the resulting aqueous emulsion dispersion is subjected to thermal condensation polymerization, thereby encapsulating the functional substance in a coating containing a methylol melamine condensate of a maleic anhydride copolymer and a compound of a maleic anhydride copolymer and an organic amine having 6 or more carbon atoms. The microcapsules obtained in this manner rapidly release the functional substance such as a dye when pressure is applied. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-136742 A [Patent Document 2] JP 2017-12998 A Summary of the Invention [Problem to be solved by the invention]

[0006] When writing on the surface of a fibrous material such as cloth using a writing instrument loaded with ink, the ink often soaks into the fibers, causing the handwriting to appear smudged. Furthermore, when the handwriting is rubbed, it may disappear or fade. Therefore, inks used in writing instruments are required to have the ability to resist these problems, and improvements to this end are continually being made. Furthermore, since writing instruments are mass-produced commodities for daily use, the ink and its components used in them must be industrially produced with good quality.

[0007] The present invention aims to provide an aqueous ink composition that prevents bleeding of handwriting and provides excellent abrasion resistance, and a writing instrument incorporating the same. In particular, the present invention aims to provide composite colored particles to be incorporated into the aqueous ink composition and a method for producing the same. [Means for solving the problem]

[0008] As a result of extensive research, the present inventors came up with the idea of ​​combining a colorant and resin particles by utilizing Coulomb force, and have completed the present invention. That is, the present invention relates to composite colored particles comprising resin particles having a positive charge on the particle surface and dye-containing particles having a negative charge on the particle surface, the resin particles and the dye-containing particles being composited by Coulomb force.

[0009] The present invention also relates to an aqueous ink composition in which the composite colored particles are dispersed in an aqueous medium, and a writing instrument equipped with the aqueous ink composition. Furthermore, the present invention relates to a method for producing composite colored particles, which includes a compounding step of mixing a resin emulsion containing resin particles having a positive charge on the particle surface with a colored resin dispersion containing dye-containing particles having a negative charge on the particle surface.

[0010] In the present invention, the Coulomb force refers to the attractive force (electrostatic force) acting between charged particles whose charge signs are positive and negative. Furthermore, "having a positive (or negative) charge on the particle surface" means that the particle has a positive (or negative) charge at least on the surface, and includes cases where only the particle surface has a positive (or negative) charge, and cases where the particle surface has a positive (or negative) charge due to the particle interior having a positive (or negative) charge. [Effects of the Invention]

[0011] According to the present invention, there are provided an aqueous ink composition that has excellent writing properties, prevents bleeding of written marks, and provides excellent abrasion resistance of written marks, and a writing instrument such as a ballpoint pen or a marking pen that incorporates the same. According to the present invention, there are provided composite colored particles to be incorporated into the aqueous ink composition, and a method for producing the same that is suitable for industrial production. [Brief explanation of the drawings]

[0012] [Figure 1] Fig. 1 is a schematic diagram for explaining an example of the present invention, showing that resin particles having a positive charge on their particle surfaces and dye-containing particles having a negative charge on their particle surfaces are combined by Coulomb force to form large composite colored particles. [Figure 2] FIG. 2 is a particle size frequency distribution diagram of the composite colored particles P-1 obtained by deagglomeration in Example 1.

[0013] In the present invention, the particle size distribution of the cationic resin particles and the composite colored particles can be measured by a laser diffraction method, and the particle size distribution of the anionic dye-containing particles can be measured by a dynamic light scattering method. DETAILED DESCRIPTION OF THE INVENTION

[0014] The following describes in detail the embodiments of the present invention. However, the components of the present invention can be added or modified without departing from the spirit of the present invention, and the technical scope of the present invention is not limited to the described embodiments, but extends to the inventions set forth in the claims and their equivalents.

[0015] <Cationic resin particles> The resin particles used in the present invention are resin particles having a positive charge on the particle surface (hereinafter, sometimes referred to as cationic resin particles). As such resin particles, resin particles made of a polymer modified with a cationic group can be used. Specifically, there are resin particles obtained by attaching or reacting a reagent to resin particles to generate a positive charge, and resin particles obtained by preparing resin particles in the presence of a monomer containing a positively charged functional group or its precursor, and cationizing the resulting polymer.

[0016] The resin particles used in the present invention are preferably made of a polymer having a cationic group, and are preferably composed mainly of at least one polymer selected from vinyl acetate resins, acrylic resins, and urethane resins, which are modified with cationic groups.

[0017] Vinyl acetate cationic resin particles The cationic resin particles of vinyl acetate resin are preferably those polymerized by adding a cationic auxiliary such as a cationic monomer or a cationic emulsifier in addition to vinyl acetate monomer. For example, they are prepared by polymerizing vinyl acetate monomer alone or a mixture of vinyl acetate monomer and a comonomer copolymerizable with vinyl acetate monomer, such as vinyl chloride or a (meth)acrylic monomer, using a cationic emulsifier, using a polymer having a cationic group as a protective colloid, or adding a cationic monomer to perform reverse phase emulsion polymerization.

[0018] Preferably, cationic resin particles of vinyl acetate resins can be prepared by emulsion polymerization using a cationic surfactant as a cationic emulsifier. Examples of cationic surfactants include alkylbenzyl ammonium chlorides such as tetradecyl dimethylbenzyl ammonium chloride and octadecyl dimethylbenzyl ammonium chloride, alkyl pyridinium ammonium chlorides such as lauryl pyridinium chloride, tetraalkyl ammonium chlorides such as stearyl trimethyl ammonium chloride and dioleyl dimethyl ammonium chloride, and EO-added ammonium chlorides having an alkyl group with 8 to 18 carbon atoms and 2 to 15 times the molar amount of ethylene oxide added, such as alkyl bis(2-hydroxyethyl)methyl ammonium chloride and polyoxyethylene alkyl methyl ammonium chloride. The amount of cationic surfactant used in emulsion polymerization is preferably 1 to 10 parts by weight, more preferably 2 to 5 parts by weight, per 100 parts by weight of monomer.

[0019] Alternatively, cationic resin particles of vinyl acetate resin can be prepared by emulsion polymerization using a nonionic surfactant and then adding a cationic substance, such as a cationic surfactant, polyoxyethylene alkylamine, or polyethyleneimine.

[0020] Furthermore, cationic vinyl acetate resin particles can be produced by copolymerizing a (meth)acrylic monomer or a mixture of a (meth)acrylic monomer and a styrene comonomer with an amino group-containing monomer, such as an N-substituted aminoalkyl (meth)acrylate (e.g., dimethylaminoethyl (meth)acrylate or diethylaminoethyl (meth)acrylate, or an N-substituted aminoalkyl (meth)acrylamide (e.g., dimethylaminopropyl (meth)acrylamide), followed by quaternization with an alkylating agent. Examples of alkylating agents include alkyl halides such as octyl chloride, octyl bromide, dodecyl chloride, dodecyl bromide, tetradecyl chloride, tetradecyl bromide, hexadecyl chloride, and hexadecyl bromide.

[0021] Acrylic cationic resin particles The cationic resin particles of an acrylic resin are preferably those polymerized by adding a cationic auxiliary such as a cationic monomer or a cationic emulsifier in addition to an acrylic monomer. For example, they can be prepared by using a cationic emulsifier, a polymer having a cationic group as a protective colloid, or adding a cationic monomer to carry out reverse phase emulsion polymerization when polymerizing a (meth)acrylic monomer alone or a mixture of a (meth)acrylic monomer and a comonomer copolymerizable with the (meth)acrylic monomer.

[0022] Preferably, cationic resin particles of an acrylic resin can be prepared by emulsion polymerization using a cationic surfactant as a cationic emulsifier. Examples of cationic surfactants include alkylbenzyl ammonium chlorides such as tetradecyl dimethyl benzyl ammonium chloride and octadecyl dimethyl benzyl ammonium chloride, alkyl pyridinium ammonium chlorides such as lauryl pyridinium chloride, tetraalkyl ammonium chlorides such as stearyl trimethyl ammonium chloride and dioleyl dimethyl ammonium chloride, and EO-added ammonium chlorides having an alkyl group with 8 to 18 carbon atoms and 2 to 15 times the molar amount of ethylene oxide added, such as alkyl bis(2-hydroxyethyl)methyl ammonium chloride and polyoxyethylene alkyl methyl ammonium chloride. The amount of cationic surfactant used in emulsion polymerization is preferably 1 to 10 parts by weight, more preferably 2 to 5 parts by weight, per 100 parts by weight of monomer.

[0023] Alternatively, cationic resin particles of an acrylic resin can be prepared by emulsion-polymerizing an acrylic monomer using a nonionic surfactant and then adding a cationic substance, such as a cationic surfactant, polyoxyethylene alkylamine, or polyethyleneimine.

[0024] Furthermore, cationic acrylic resin particles can be prepared by copolymerizing a (meth)acrylic monomer or a mixture of a (meth)acrylic monomer and a styrene-based comonomer with an amino group-containing monomer, such as an N-substituted aminoalkyl (meth)acrylate (e.g., dimethylaminoethyl (meth)acrylate or diethylaminoethyl (meth)acrylate, or an N-substituted aminoalkyl (meth)acrylamide (e.g., dimethylaminopropyl (meth)acrylamide), followed by quaternization with an alkylating agent. Examples of alkylating agents include alkyl halides such as octyl chloride, octyl bromide, dodecyl chloride, dodecyl bromide, tetradecyl chloride, tetradecyl bromide, hexadecyl chloride, and hexadecyl bromide.

[0025] Urethane-based cationic resin particles The cationic resin particles of urethane resin are preferably cationic resin particles of urethane resin having quaternized ammonium groups. These cationic resin particles can be prepared, for example, by reacting a polyol, a polyisocyanate, and a tertiary amino group-containing polyol in a solvent or without a solvent to prepare a polyurethane dispersion, and then protonating the tertiary amino groups in the polyurethane with an acid or quaternizing them with an alkylating agent.

[0026] Another method involves reacting a polyol, a polyisocyanate, and a tertiary amino group-containing polyol in a predetermined ratio in a solvent or without solvent to produce a urethane prepolymer having isocyanate groups at its terminals, followed by chain extension of the urethane prepolymer using a polyamine to produce a dispersion of urethane resin particles. The tertiary amino groups in the urethane resin are then protonated with an acid or quaternized with an alkylating agent. This produces cationic resin particles of a urethane resin having quaternized ammonium groups.

[0027] The alkylating agent for quaternizing a tertiary amino group is a reagent that adds an alkyl group to an amino group to produce a quaternary ammonium cation, and alkyl halides such as octyl chloride, octyl bromide, dodecyl chloride, dodecyl bromide, tetradecyl chloride, tetradecyl bromide, hexadecyl chloride, and hexadecyl bromide are preferably used.

[0028] The cationic resin particles used in the present invention preferably have a small content of fine particles and a uniform particle size. Specifically, in terms of particle size distribution, it is preferable that at least 95% of the particles have a particle size within the range of 0.1 μm to 3.0 μm, and more preferably that at least 95% of the particles have a particle size within the range of 0.1 μm to 2.0 μm.

[0029] <Anionic dye-containing particles> The dye-containing particles used in the present invention are resin particles that have a negative charge on the particle surface and contain a dye (sometimes simply referred to as dye-containing particles). The dye-containing particles include particles in which a dye is encapsulated inside or on the surface of anionic resin particles, and particles in which anionic dye is encapsulated inside or on the surface of resin particles, and particularly preferred are fine particles in which a dye is encapsulated inside or on the surface of anionic resin particles.

[0030] The resin particles used to produce particles having a dye encapsulated inside or on the surface of anionic resin particles may be particles made of a resin to which functional groups having anionic properties (hereinafter referred to as anionic groups) are chemically bonded, or particles made of a resin to which anionic groups are physically attached.

[0031] The resin constituting the resin particles having an anionic group may be a thermoplastic resin or a thermosetting resin, and preferably at least one resin selected from the group consisting of an acrylic resin, a urea resin, a urethane resin, and a urea-urethane resin. The resin structure may be linear or branched.

[0032] When an anionic group is chemically bonded to the surface of a resin particle, a reagent having an anionic group or a precursor thereof may be bonded directly to the resin, or may be bonded indirectly to the resin via another atomic group. Examples of the other atomic group that bonds the anionic group to the resin include a linear or branched alkylene group having 1 to 12 carbon atoms, a phenylene group, a naphthylene group, a carbonyl group, an ester group, an ether group, an amide group, an amino group, an azo group, and a sulfonyl group.

[0033] Resin particles in which anionic groups are directly bonded to the resin can be particles made of a resin obtained by polymerizing a monomer mixture containing a monomer having an anionic group, or a monomer mixture containing an auxiliary such as an emulsifier having an anionic group, together with a dye in a dissolved or dispersed state. Furthermore, resin particles can be chemically treated to form anionic groups on the particle surface. Examples of anionic groups include carboxyl groups, sulfonic acid groups, and phosphate groups.

[0034] An acrylic resin having an anionic group can be obtained, for example, by polymerizing (meth)acrylic acid having a carboxyl group or a (meth)acrylic acid ester having an anionic group such as a carboxyl group or a sulfonic acid group as a monomer. A urea resin having an anionic group can be obtained, for example, by polymerizing a compound having an anionic group in at least one of a combination of a polyisocyanate compound and a polyamine compound. A urethane resin having an anionic group can be obtained, for example, by polymerizing a compound having an anionic group in at least one of a combination of a polyisocyanate compound and a polyol compound. A urea-urethane resin having an anionic group can be obtained, for example, by polymerizing a compound having an anionic group in at least one of a combination of a polyisocyanate compound, a polyamine compound, and a polyol compound.

[0035] The chemical treatment for introducing anionic groups onto the resin surface can be carried out by carrying out a coupling reaction with a diazonium salt to introduce anionic groups such as carboxyl groups, sulfonic acid groups, or phosphoric acid groups into the resin.

[0036] Furthermore, anionic groups such as carboxyl groups can be introduced into the resin by subjecting the resin to oxidation treatment using a gas phase method, a liquid phase method, or a combination of these. When oxidation treatment is performed using a gas phase method, ozone or oxygen can be used as an oxidizing agent, and the resin can be brought into contact with the oxidizing agent to oxidize it.

[0037] When the oxidation treatment is performed by a liquid phase method, chlorine, hydrogen peroxide, nitric acid, sulfuric acid, chlorate, persulfate, or the like can be used as the oxidizing agent. For example, by introducing a resin into an aqueous solution containing the oxidizing agent, a resin having anionic groups on the surface can be obtained.

[0038] When anionic groups are physically attached to the surface of resin particles, examples of the method include a method in which an anionic polymer dispersant is supplied to a dispersion of resin particles to attach the anionic polymer dispersant to the resin surface, and a method in which resin particles are introduced into a solution of an anionic agent, and then the solvent is removed to coat the resin surface with the anionic agent.

[0039] The dyes used may be acid dyes, basic dyes, direct dyes, or oil-soluble dyes, and may be naturally derived or synthetic dyes. Two or more types of non-anionic or anionic dyes may be mixed and used, or a non-anionic dye and an anionic dye may be mixed and used.

[0040] Acid dyes include eosin, fuoxin, acid red, water blue, brilliant blue FCF, and nigrosin.

[0041] Examples of basic dyes include di- or triarylmethane dyes such as methyl violet; quinoneimine dyes such as azines (including nigrosine), oxazines, and thiazines; xanthene dyes such as rhodamine; triazole azo dyes; thiazole azo dyes; benzothiazole azo dyes; azo dyes; methine dyes such as polymethine, azomethine, and azamethine; anthraquinone dyes; and phthalocyanine dyes, of which water-soluble basic dyes are preferred.

[0042] Direct dyes include Direct Black 154 and Direct Sky Blue. Examples of oil-soluble dyes include monoazo dyes, diazo dyes, metal complex monoazo dyes, anthraquinone dyes, phthalocyanine dyes, and triarylmethane dyes. Salt-forming oil-soluble dyes in which the functional group of an acid-basic dye is substituted with a hydrophobic group can also be used.

[0043] Examples of oil-soluble dyes include CI Solvent Yellow 114 and 116 for yellows, CI Solvent Orange 67 for oranges, CI Solvent Red 122 and 146 for reds, CI Solvent Blue 5, 36, 44, 63, 70, 83, 105 and 111 for blues, and CI Solvent Black 3, 7, 27 and 29 for blacks.

[0044] Commercially available oil-soluble dyes include blue dye SBN Blue 701 (manufactured by Hodogaya Chemical Co., Ltd.), blue dye Oil Blue 650 (manufactured by Orient Chemical Industry Co., Ltd.), blue dye Saninyl Blue GLS (manufactured by Clariant Co., Ltd.), red dye SOC-1-0100 (manufactured by Orient Chemical Industry Co., Ltd.), Oil Black 860, Oil Pink 314, Oil Yellow 3G, Varifast Pink 2310N, Varifast Red 3312, Varifast Yellow CGHNnew, Varifast Yellow 1108, and Varifast Black 3830 (manufactured by Orient Chemical Industry Co., Ltd.).

[0045] The dye content of the dye-containing particles can be 0.2 to 50% by mass, preferably 0.5 to 20% by mass, and more preferably 1.0 to 10% by mass, based on the dye-containing particles.

[0046] The anionic dye-containing particles used in the present invention are preferably fine particles having a particle diameter of 0.01 to 1.0 μm, and more preferably fine particles with at least 95% by mass having a particle diameter in the range of 0.01 to 0.5 μm. Having a particle diameter in this range is preferable because it forms good composite colored particles when combined with cationic resin particles. The shape of the anionic dye-containing particles is preferably spherical, particularly true spherical.

[0047] <Complex> In the present invention, composite colored particles can be produced by combining cationic resin particles and anionic dye-containing particles through Coulomb force. Figure 1 shows a schematic diagram of the formation of large composite colored particles by combining resin particles with positive charges on their surfaces and dye-containing particles with negative charges on their surfaces through Coulomb force.

[0048] The composite colored particles of the present invention are stable composite particles having a structure in which cationic resin particles and anionic dye-containing particles are bound by Coulomb force. The composite colored particles of the present invention can be produced by a composite step in which a resin emulsion containing cationic resin particles is mixed with a colored resin dispersion containing anionic dye-containing particles.

[0049] The compounding ratio of the cationic resin particles to the anionic dye-containing particles in the composite forming step is, in terms of the mass ratio of resin particles to dye-containing particles (excluding aqueous media, etc.), preferably selected from the range of 1 / 0.1 to 1 / 50, more preferably 1 / 0.5 to 1 / 10, and even more preferably 1 / 1 to 1 / 5.

[0050] In the compounding step, a resin emulsion containing resin particles having a positive charge on the particle surface and a colored resin dispersion containing dye-containing particles having a negative charge on the particle surface are prepared. In each emulsion and dispersion, the particles are preferably dispersed in an aqueous medium.

[0051] The media for each of the aqueous emulsions and dispersions are mutually compatible aqueous media, preferably water, a water-soluble organic solvent, or a mixed solution thereof. The content of the aqueous medium in the resin emulsion and colored resin dispersion is preferably 1 to 50 mass %, more preferably 3 to 30 mass %, and even more preferably 5 to 20 mass %, based on the total amount of the emulsion or dispersion. The density of the aqueous medium used is preferably close to the density of the particles.

[0052] Examples of usable water-soluble organic solvents include ethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 2,3-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, 2,5-hexanediol, 3-methyl-1,3-butanediol, and 2-methylpentanediol. alkylene glycols such as 2,4-diol, 3-methylpentane-1,3,5-triol, and 1,2,3-hexanetriol; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; glycerols such as glycerol, diglycerol, and triglycerol; lower alkyl ethers of glycols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol mono-n-butyl ether; N-methyl-2-pyrrolidone; and 1,3-dimethyl-2-imidalidinone.

[0053] Other water-soluble solvents that can be mixed include alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, tert-butyl alcohol, isobutyl alcohol, hexyl alcohol, octyl alcohol, nonyl alcohol, decyl alcohol, and benzyl alcohol, amides such as dimethylformamide and diethylacetamide, and ketones such as acetone. The content of these water-soluble organic solvents varies depending on the type of writing implement, such as a felt-tip pen, marking pen, or ballpoint pen, and is preferably 1 to 40% by mass of the total amount of the ink composition.

[0054] Next, the cationic resin emulsion and the anionic colored resin dispersion are mixed. The emulsions (dispersions) can be mixed by placing them in a container equipped with a stirring device such as a mechanical stirrer or a magnetic stirrer and stirring them. At this time, components necessary for forming the ink composition may be added.

[0055] When the resin particles and dye-containing particles contained in each emulsion are mixed, they are electrostatically bonded by Coulomb force to effectively form large-sized composite colored particles. The composite colored particles thus obtained contain very little colorant particles with a particle size of less than 0.1 μm, which is effective in achieving the effects of the present invention.

[0056] In this case, some of the composite color particles may aggregate together to form ultra-large composite color particle aggregates with particle diameters exceeding 10 μm. Since ultra-large aggregates can cause problems such as ink clogging and smearing when used in writing instruments, it is preferable to add a deagglomeration step to break down such aggregates and disperse them into individual composite color particles.

[0057] The deagglomeration process can be carried out using a stirrer such as a homomixer, disperser mixer, ultramixer, or homogenizer. The deagglomeration process breaks down ultra-large aggregates into individual composite color particles, producing a good dispersion of the composite color particles. The particle size of the dye-containing particles can be controlled by adjusting the stirring conditions used to break down the aggregates. The above-described method for producing dye-containing particles can be successfully carried out industrially.

[0058] That is, one preferred embodiment of the method for producing composite colored particles of the present invention is a method for producing composite colored particles, which includes a compounding step of mixing a resin emulsion containing resin particles having a positive charge on the particle surface and an aqueous medium with a colored resin dispersion containing dye-containing particles having a negative charge on the particle surface and an aqueous medium, and a deaggregation step of breaking down the aggregates.

[0059] Preferably, at least 95% of the composite colored particles of the present invention are in the range of 0.2 μm to 3.0 μm, more preferably at least 95% are in the range of 0.2 μm to 2.0 μm. The content of fine particles smaller than 0.1 μm in the composite colored particles is less than 3%, preferably less than 1%, in terms of particle frequency.

[0060] <Water-based ink composition> The composite colored particles of the present invention are dispersed in an aqueous medium containing other components added according to the required properties of the writing instrument (ballpoint pen, marking pen, etc.), to form an aqueous ink composition for the writing instrument. The other components constituting the aqueous medium include a pH adjuster, a thickener, a lubricant, an anti-rust agent, a preservative, an antibacterial agent, and a solvent as a dispersion medium.

[0061] The content of the composite colored particles of the present invention in the aqueous ink composition is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 3 to 20% by mass, relative to the total amount of the ink composition, in order to ensure the hue of the ink and prevent smearing during writing.

[0062] Examples of pH adjusters for adjusting the pH of the ink composition include amines such as monoethanolamine, diethanolamine, triethanolamine, triisopropanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, and morpholine; ureas such as urea, thiourea, and tetramethylurea; allophanates such as allophanate and methylalophanate; biurets such as biuret, dimethylbiuret, and tetramethylbiuret; quaternary ammoniums such as tetramethylammonium hydroxide; inorganic hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide; and inorganic salts such as sodium (hydrogen)carbonate, potassium (hydrogen)carbonate, and lithium (hydrogen)carbonate; and at least one of these can be used.

[0063] Examples of thickeners that can be used in the aqueous ink composition include synthetic polymers, cellulose, and polysaccharides. Specific examples 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 glycolate and its salts, propylene glycol alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylic acid and its salts, carboxyvinyl polymer, polyethylene oxide, copolymers of vinyl acetate and polyvinylpyrrolidone, crosslinked acrylic acid polymers and their salts, non-crosslinked acrylic acid polymers and their salts, and styrene-acrylic acid copolymers and their salts. At least one of these can be used.

[0064] Antirust agents that can be incorporated into the aqueous ink composition include benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, saponins, etc. Preservatives or antibacterial agents that can be incorporated into the aqueous ink composition include phenols, benzoic acids, benzimidazoles, isothiazolones, triazines, bronopoles, thiabendazoles, zinc pyrithiones, carbendazims, omadines, etc.

[0065] Examples of lubricants that can be incorporated into the aqueous ink composition include nonionic lubricants such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, polyoxyalkylene higher fatty acid esters, alkyl phosphates, and alkyl polyoxyalkylene phosphates; anionic lubricants such as alkyl sulfonates and alkyl aryl sulfonates of higher fatty acid amides; fluorine-based lubricants; and silicone-based lubricants such as polyether-modified silicones.

[0066] <Dispersion medium> A dispersion medium is blended into the aqueous ink composition to stabilize the dispersion state of the composite colored particles and ensure usability as an ink for writing instruments. The dispersion medium can be water (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.), a hydrophilic dispersion medium consisting of a water-soluble organic solvent, or a mixed solution thereof, and preferably a mixed solution consisting of water and at least one water-soluble organic solvent. The density of the dispersion medium used is preferably close to the density of the composite colored particles. The amount of the aqueous medium in the aqueous ink composition is preferably 3 to 300 parts by mass, and more preferably 5 to 100 parts by mass, per 100 parts by mass of the composite colored particles.

[0067] Examples of water-soluble organic solvents that can be used include alcohols, glycols, and derivatives thereof. Specific examples include methanol, ethanol, propanol, butanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, polyethylene glycol, 3-butylene glycol, thiodiethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, glycerin, and diglycerin, and at least one of these can be used. A mixed solvent in which 5 to 200 parts by mass of a water-soluble organic solvent is mixed with 100 parts by mass of water is preferred.

[0068] Furthermore, a hydrophilic nonionic polymer can be used as the dispersion medium. For example, polyether can be used as the nonionic polymer blended in the aqueous ink composition. Specific examples include polypropylene glycol, polybutylene glycol, and polyoxypropylene diglyceryl ether, and at least one of these can be used. By using these nonionic polymers as the main solvent, 、 The occurrence of aggregation over time can be prevented.

[0069] Polyethers such as polypropylene glycol and polybutylene glycol that are blended into the aqueous ink composition can be used with various degrees of polymerization. However, in order to further enhance the effects of the present invention, it is preferable to use polypropylene glycol polymers with a degree of polymerization in the range of 400 to 700 (weight average), and it is preferable to use polybutylene glycol polymers with a degree of polymerization in the range of 500 to 700 (weight average).

[0070] The aqueous ink composition for writing instruments can be produced, for example, by blending predetermined amounts of the composite colored particles and each component to be blended in the aqueous ink composition, and stirring and mixing them with a stirrer such as a homomixer or a disper, etc. If necessary, coarse particles in the aqueous ink composition may be removed by filtration or centrifugation.

[0071] <Writing implements> The aqueous ink composition of the present invention is used by being mounted on a felt-tip pen or marking pen equipped with a fiber tip, felt tip or plastic tip at the writing tip, or a ballpoint pen equipped with a ballpoint pen tip at the writing tip, and a writing instrument equipped with the aqueous ink composition of the present invention has the advantage that when used to write on paper or the like, it prevents bleeding or show-through of the handwriting due to penetration into the material, and provides excellent writing performance such as washing fastness of the handwriting. [Example]

[0072] The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the following, "parts" in the formulations refer to parts by mass.

[0073] <Resin particles> As the emulsion of cationic resin particles, aqueous emulsions of cation-modified vinyl acetate resin, cation-modified acrylic resin, and cation-modified urethane resin were used. As the (A-1) cation-modified vinyl acetate resin, a cation-modified vinyl acetate resin emulsion (Viniblan 1008; manufactured by Nissin Chemical Industry Co., Ltd.) was used. As the (A-2) cation-modified acrylic resin, a cation-modified polyvinyl alcohol-acrylic resin emulsion (Movinyl 6950; manufactured by Japan Coating Resin Co., Ltd.) was used. As the (A-3) cation-modified urethane resin, a cation-modified urethane emulsion (Superflex 620; manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was used. (A-4) For comparison, an emulsion of nonionic modified vinyl acetate resin (Viniblan 1002; manufactured by Nissin Chemical Industry Co., Ltd.) was used.

[0074] <Dye-containing particles> As the anionic dye-containing particles, colored resin dispersions in which dye-containing particles obtained by the methods of Production Examples 1 to 3 below were dispersed in an aqueous medium were used.

[0075] [Production Example 1: Particle B-1] While heating 17 parts of triethylene glycol distearate (trade name: Estepearl 30, melting point 44-51°C, manufactured by Nikko Chemicals Co., Ltd.), 4 parts of a metal complex oil-soluble dye (trade name: VALIFAST BLACK 3830, manufactured by Orient Chemical Industry Co., Ltd.) to 65°C was added and thoroughly dispersed. Next, 4 parts of methyl ethyl ketone was added, followed by 7 parts of a trimethylolpropane-modified xylylene diisocyanate (trade name: D-110N, manufactured by Mitsui Chemicals, Inc.), and the mixture was stirred at 65°C to prepare an oil phase solution. Meanwhile, 10 parts of polyvinyl alcohol (trade name: PVA-205, manufactured by Kuraray Co., Ltd.) and 20 parts of an anion-modified polyvinyl alcohol having a sulfonate group (trade name: Gohsenex L-3266, manufactured by Mitsubishi Chemical Corporation) were dissolved in 600 parts of distilled water heated to 65°C to prepare an aqueous phase solution. The oil phase solution was added to the obtained aqueous phase solution, and 6 parts of hexamethylenediamine was added and mixed by stirring to complete the emulsion polymerization, thereby obtaining an emulsion of dye-containing particles B-1 consisting of an anionic urea-urethane resin encapsulating an oil-soluble dye.

[0076] The dye-containing resin particles B-1 thus obtained had anionic properties, with a measured surface potential of −28 mV, and an average particle size of 0.12 μm.

[0077] [Production Example 2: Particle B-2] A 2-liter flask was fitted with a stirrer, a reflux condenser, a thermometer, a nitrogen gas inlet tube, and a 1000-ml separatory funnel for monomer introduction, and set in a warm water bath. 329.5 parts of distilled water, 5 parts of glycerin monomethacrylate (trade name: Blemmer GLM, manufactured by NOF Corporation), 5 parts of sodium 2-sulfoethyl methacrylate having a sulfonate group (trade name: Acrylate SEM-Na, manufactured by Mitsubishi Chemical Corporation), 20 parts of an anionic polymerizable surfactant (trade name: Adeka Reasoap SE-10N, ether sulfate, manufactured by ADEKA Corporation), and 0.5 parts of ammonium persulfate were then charged, and the internal temperature was raised to 50°C while introducing nitrogen gas.

[0078] Separately, a liquid was prepared by mixing a mixed monomer consisting of 55 parts of cyclohexyl methacrylate monomer and 35 parts of n-butyl methacrylate with 40 parts of a metal complex oil-soluble dye (trade name: Suninyl Blue GLS, manufactured by Clariant Co., Ltd.) and 10 parts of triallyl isocyanurate (trade name: TAIC, manufactured by Nippon Kasei Co., Ltd.) as a crosslinking agent. The resulting solution was added to the flask, which was kept at about 50°C, through the separatory funnel over a period of 3 hours with stirring to carry out emulsion polymerization. The mixture was then aged for a further 5 hours to terminate the polymerization, yielding an emulsion of dye-containing particles B-2 made of an anionic acrylic resin encapsulating an oil-soluble dye.

[0079] The dye-containing resin particles B-2 obtained had anionic properties, with a measured surface potential of −58 mV, and an average particle size of 0.04 μm.

[0080] [Production Example 3: Particle B-3 (for comparative example)] 4 parts of methyl ethyl ketone and 17 parts of triethylene glycol distearate (trade name: Estepearl 30, melting point 44-51°C, manufactured by Nikko Chemicals Co., Ltd.) were heated to 65°C, and 10.4 parts of oil-soluble red dye (trade name: OIL SCARLET #308, manufactured by Orient Chemical Industry Co., Ltd.) were added and thoroughly dispersed. 7 parts of a trimethylolpropane-modified xylylene diisocyanate (trade name: D-110N, manufactured by Mitsui Chemicals, Inc.) were then added and stirred at 65°C to prepare an oil phase solution. Meanwhile, 15 parts of polyvinyl alcohol (trade name: PVA-205, manufactured by Kuraray Co., Ltd.) were dissolved in 600 parts of distilled water heated to 65°C to prepare an aqueous phase solution. The oil phase solution was then added to the resulting aqueous phase solution, and 6 parts of hexamethylenediamine were added. The mixture was stirred and mixed to complete emulsion polymerization, yielding an emulsion of dye-containing particles B-3 composed of a nonionic urea-urethane resin encapsulating an oil-soluble dye.

[0081] Examples 1 to 6, Comparative Examples 1 to 2 The various resin particle emulsions mentioned above and Manufacturing exampleThe various dye-containing particle emulsions prepared in the above were blended in the combinations and mass ratios (mass ratio of solids) shown in Table 1 and mixed using a stirrer to obtain aqueous dispersions R-1 to R-8. Next, deagglomeration was carried out by vigorous stirring using a homomixer to obtain composite colored particles P-1 to P-6 as examples and C-1 to C-2 as comparative examples, all in the form of aqueous dispersions with a solids concentration of 20 mass%.

[0082] A frequency distribution diagram of the particle sizes of the cationically modified vinyl acetate resin used in Example 1 is shown in Figure 2, and a frequency distribution diagram of the particle sizes of the anionic dye-containing particles is shown in Figure 3. A frequency distribution diagram of the particle sizes of the composite colored particles before deagglomeration in Example 1 is shown in Figure 4, and a frequency distribution diagram of the particle sizes of the composite colored particles after deagglomeration is shown in Figure 5.

[0083] Furthermore, the particle size frequency distribution was measured for the composite colored particles produced in Examples 1 to 6 and Comparative Examples 1 and 2, and the frequency ratio (%) of composite colored particles having a specific particle size range to the total composite colored particles was calculated. The results are shown in Table 2. From these figures and tables, it is clear that the composite colored particles of the present invention are composed of large particle diameters and contain almost no small particle diameters containing dye.

[0084] The particle size distributions of the cationic resin particles and the composite colored particles were measured by laser diffraction using a particle size distribution analyzer (Microtrac HRA9320-X100, manufactured by Nikkiso Co., Ltd.). The particle size distribution of the anionic dye-containing particles was measured by dynamic light scattering using a concentrated particle size analyzer (FPAR-1000, manufactured by Otsuka Electronics Co., Ltd.).

[0085] Examples 11 to 19 and Comparative Examples 11 to 12 Dispersions of composite colored particles P-1 to P-6 were used as examples, and C-1 to C-2 were used as comparative examples. A pH adjuster, a preservative, and a dispersion medium were blended and mixed in the combinations and weight ratios shown in Table 3, and some of the aggregates were removed to prepare dispersions of aqueous ink compositions.

[0086] The ink compositions of Examples 11 to 19 are aqueous ink compositions of the present invention. The ink composition of Comparative Example 11 is a comparative example in which cationic resin particles are not used, and the ink composition of Comparative Example 12 is a comparative example in which anionic dye-containing particles are not used.

[0087] <Evaluation of Ink Composition> A felt-tip pen was prepared using each of the prepared aqueous ink compositions. Specifically, the ink reservoir of a commercially available felt-tip pen (product name: Procky PM-120T; manufactured by Mitsubishi Pencil Co., Ltd., extra-fine point + fine point) was filled with each of the ink compositions prepared in Examples 1 to 8 and Comparative Examples 1 to 5 to prepare a felt-tip pen. Writing was performed using the round tip on the fine point side of each of the prepared felt-tip pens, and writing properties such as the density of the drawn line (handwriting) during writing, bleeding resistance, and abrasion resistance were tested and evaluated using the methods described below. The results are shown in Table 3.

[0088] 1) Line density 1-1) Writing on paper Using each felt-tip pen, a spiral was handwritten on the surface of writing paper conforming to ISO standards, and then the surface of the paper was visually inspected to evaluate the density of the written lines according to the following criteria. 1-2) Writing on fabric Using each felt-tip pen, the words "Mitsubishi Pencil" were handwritten on the surface of cotton cloth (Kanakin No. 3; for JIS dye fastness testing (JIS L 0803 compliant)), and the surface of the paper was then visually inspected to evaluate the density of the written lines according to the following criteria.

[0089] Evaluation criteria for handwriting: A: The color of the lines is significantly darker. B: The lines are dark. C: The line color is slightly light. D: The color of the lines is noticeably light.

[0090] 2) Anti-bleeding 2-1) Bleeding onto paper Using each felt-tip pen, a spiral was handwritten on the surface of writing paper conforming to ISO standards, and then the surface of the paper was visually inspected to evaluate the bleeding state of the written lines according to the following criteria. 2-2) Bleeding onto fabric Using each felt-tip pen, the word "Mitsubishi Pencil" was handwritten on the surface of cotton cloth (Kanakin No. 3; for JIS color fastness test (JIS L 0803 compliant)). cotton cloth The surface of the ink was visually inspected to evaluate the bleeding state of the written lines according to the following criteria.

[0091] Smearing evaluation criteria: A: The lines do not bleed. B: There is slight bleeding of the lines. C: There is considerable bleeding of the lines. D: There is noticeable bleeding of the lines.

[0092] 3) Scratch resistance The characters "Mitsubishi Pencil" were handwritten on the surface of coated paper (Yupo Corporation) using each felt-tip pen and allowed to dry. A waste paper (Kimwipe; Nippon Paper Crecia Co., Ltd.) was placed on the handwriting, and a 500 g weight was placed on top. The waste paper and the weight were then moved back and forth horizontally five times to rub off the handwriting. The condition of the handwriting was then evaluated according to the following criteria.

[0093] Scratch resistance rating criteria: A: No defects were found in the handwriting. B: There were a few thin lines missing from the handwriting. C: There was a clear defect in the handwriting. D: There was a large defect that made it difficult to read the text.

[0094] [Table 1]

[0095] [Table 2]

[0096] [Table 3]

[0097] As is clear from the above examples, the ink composition using the composite colored particles of the present invention was excellent in the density of the drawn lines (handwriting), the anti-bleeding properties and the abrasion resistance. [Industrial Applicability]

[0098] An ink composition containing the composite colored particles of the present invention can be suitably used in writing instruments such as felt-tip pens, ballpoint pens, etc. According to the present invention, composite colored particles that impart excellent usability to ink compositions can be produced industrially advantageously. [Explanation of symbols]

[0099] 1. Dye-containing particles with negative charges on the particle surface 2. Resin particles with positive charges on the particle surface

Claims

1. A writing instrument equipped with an aqueous ink composition comprising resin particles having a positive charge on their particle surface and dye-containing particles having a negative charge on their particle surface, the dye-containing particles being colored particles in which an oil-soluble dye is incorporated inside or on the surface of anionic resin particles, and composite colored particles formed by the resin particles and the dye-containing particles being combined by Coulomb force are dispersed in an aqueous medium.

2. 2. The writing implement of claim 1, wherein at least 95% of the composite colored particles have a particle size within the range of 0.2 μm to 3.0 μm.

3. 3. The writing implement according to claim 1, wherein the positively charged resin particles are particles made of a polymer modified with a cationic group.

4. 4. The writing implement according to claim 3, wherein the polymer modified with a cationic group is at least one selected from the group consisting of vinyl acetate resins, acrylic resins, and urethane resins.

5. 5. The writing implement according to claim 1, wherein the dye-containing particles are colored particles in which a dye is encapsulated inside or on the surface of anionic resin particles.

6. 6. The writing implement according to claim 1, wherein the positively charged resin particles are composed of at least one resin selected from the group consisting of acrylic resins, urea resins, urethane resins, and urea-urethane resins.

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