Composite colored particles

Abstract

Provided is an ink composition that is excellent in bleed prevention and wiping resistance and is suitable for industrial production. The present invention relates to a composite coloring particle including a resin particle having a positive charge on the surface of the particle and a pigment particle having a negative charge on the surface of the particle, the aforementioned resin particle and the aforementioned pigment particle being complexed by electrostatic interaction, and an aqueous ink composition in which the aforementioned composite coloring particle is dispersed in an aqueous medium, and a writing instrument equipped with the aforementioned aqueous ink composition. Furthermore, the present invention relates to a method for producing a composite coloring particle, including a complexing step of mixing a resin emulsion including a resin particle having a positive charge on the surface of the particle and a pigment dispersion including a pigment particle having a negative charge on the surface of the particle.

Description

Technical Field

[0001] This invention relates to composite coloring particles for writing instruments and ink compositions containing the same. Background Technology

[0002] Writing instruments use inks made by dissolving or dispersing various dyes or pigments as coloring materials in solvents. In particular, pigment inks have superior ink adhesion and covering power compared to dye inks.

[0003] For ink compositions used in writing instruments, it is necessary to prevent ink bleeding and ensure the durability of the ink strokes due to penetration of the raw materials. To this end, a composite powder has been proposed, in which pigment particles are mechanically bonded or fixed to the surface of resin particles.

[0004] For example, Patent Document 1 discloses an ink composition for writing instruments, characterized in that it is formed from a colorant, a dispersant, and an aqueous medium, wherein the colorant is a composite particle of spherical resin particles and pigment. The composite particle is formed as follows: resin particles and pigment are ground together, causing the pigment particles to adhere to the resin particles, which are softened by the frictional heat generated at this time.

[0005] Furthermore, Patent Document 2 discloses a water-based pigment ink composition for writing instruments, which at least includes a composite powder containing microparticles of titanium dioxide with an average particle size of less than 0.1 μm fixed on the surface of resin particles such as polyethylene, polypropylene, and polymethyl methacrylate as a coloring material. These composite particles can be obtained by mixing microparticles of titanium dioxide with resin particles in an automatic mortar, ball mill, spray mill, atomizer, etc., grinding them, and / or applying mechanical impact force using a hammer mill, mixer, etc., thereby causing the microparticles of titanium dioxide to be adsorbed onto the surface of the resin particles or discharged from the surface of the resin particles, thus fixing them.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 63-218778

[0009] Patent Document 2: Japanese Patent Application Publication No. 6-192611 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] When writing on surfaces made of fibrous materials such as cloth, ink often seeps into the fibers, resulting in visible ink penetration. Furthermore, the ink may disappear or become faint when wiped away. Therefore, the ink used in writing instruments must be resistant to these issues.

[0012] Furthermore, writing instruments are commodities produced in large quantities as daily necessities; therefore, the ink used for them must be produced industrially in a high-quality manner.

[0013] However, composite particles obtained by mixing pigment particles and resin particles and applying mechanical impact forces such as grinding to bond or fix them often contain a considerable amount of uncomposite, particulate residues of raw materials. Even after compounding, the raw materials easily detach from each other, inevitably leading to ink bleeding. Furthermore, methods of mechanically processing solids to obtain uniform solids require significant power and processing time, making them unsuitable for industrial production. In particular, grinding easily results in uneven size and shape of the product, and uneven ink compositions cannot provide good writing performance.

[0014] The objective of this invention is to provide composite coloring particles that prevent ink bleeding and have excellent writing properties such as rub resistance and initial writing properties, suitable for industrial production, and an ink composition in which the composite coloring particles are dispersed.

[0015] Solution for solving the problem

[0016] The inventors conducted in-depth research and, focusing on the adverse effects of pigment particles on ink bleeding, thus completing this invention.

[0017] That is, the present invention relates to a composite coloring particle, which comprises resin particles having a positive charge on the particle surface and pigment particles having a negative charge on the particle surface, wherein the resin particles and the pigment particles are composited through electrostatic interaction.

[0018] In addition, the present invention relates to an aqueous ink composition in which the aforementioned composite coloring particles are dispersed in an aqueous medium, and a writing instrument equipped with the aqueous ink composition.

[0019] Furthermore, the present invention relates to a method for manufacturing composite colored particles, which includes the following composite process: mixing a resin emulsion containing resin particles having a positive charge on the particle surface and a pigment dispersion containing pigment particles having a negative charge on the particle surface.

[0020] It should be noted that, in this invention, "having positive (negative) charge on the particle surface" means that the particle has positive (negative) charge at least on its surface, including the case where only the particle surface has positive (negative) charge, and the case where both the particle surface and interior have positive (negative) charge.

[0021] The effects of the invention

[0022] According to the present invention, there are: composite coloring particles that are excellent in preventing ink bleeding and resisting wiping, and suitable for industrial production, and an ink composition in which the composite coloring particles are dispersed.

[0023] According to the present invention, a water-based ink writing instrument with excellent writing performance is provided. Attached Figure Description

[0024] Figure 1 This is a schematic diagram for illustrating the present invention. It shows that resin particles with positive charges on their surfaces and pigment particles with negative charges on their surfaces are combined through electrostatic interactions to form large-diameter composite colored particles.

[0025] Figure 2 This is a frequency distribution diagram of the particle size of the cationic modified vinyl acetate resin used in Example 1.

[0026] Figure 3 This is a frequency distribution diagram of the particle size of the anionic modified carbon black particles used in Example 1.

[0027] Figure 4 This is a frequency distribution diagram of the composite colored particles A-1 before deaggregation in Example 1.

[0028] Figure 5 The frequency distribution diagram of the particle size of the composite colored particles A-1 obtained by deaggregation in Example 1 is shown. Detailed Implementation

[0029] The embodiments of the present invention will be described in detail below. However, technical features may be added or modified within the scope of the present invention without departing from the spirit of the invention. The scope of protection of the present invention is not limited to the described embodiments, but includes the invention described in the claims and its equivalents.

[0030] <Resin Particles>

[0031] The resin particles used in this invention are resin particles with a positive charge on their surface (hereinafter, sometimes referred to as cationic resin particles). As such resin particles, resin particles containing polymers modified with cationic groups can be used. Specifically, examples include resin particles that generate a positive charge by attaching or reacting a reagent onto the resin particles, and resin particles that are cationicized by coexisting monomers containing functional groups or precursors that have a positive charge during the preparation of the resin particles.

[0032] The resin particles used in this invention are preferably composed primarily of at least one polymer selected from vinyl acetate resins, acrylic resins, and urethane resins. Resin particles containing the aforementioned polymers and having a positively charged particle surface modified with cationic groups are suitable.

[0033] Cationic resin particles of vinyl acetate-based resins

[0034] The preferred cationic resin particles of vinyl acetate-based resins are those containing a cationic emulsifier, a polymer containing cationic groups, or a copolymer containing cationic monomers. Such cationic resin particles are manufactured as follows: during emulsion polymerization using vinyl acetate monomers, or a mixture of vinyl acetate monomers and comonomers such as vinyl chloride or (meth)acrylic acid monomers that can copolymerize with vinyl acetate monomers, a cationic emulsifier is used, or a polymer containing cationic groups is used as a protective colloid, or a cationic monomer is added for reverse emulsion polymerization.

[0035] Cationic resin particles of vinyl acetate-based resins can preferably be produced by emulsion polymerization using a cationic surfactant as a cationic emulsifier. Examples of cationic surfactants include alkylbenzyl ammonium chloride such as tetradecyl dimethyl benzyl ammonium chloride, alkylbenzyl ammonium chloride such as octadecyl dimethyl benzyl ammonium chloride, alkylpyridinium ammonium chloride such as lauryl pyridinium chloride, stearyltrimethyl ammonium chloride, tetraalkyl ammonium chloride such as dioleenyl dimethyl ammonium chloride, and EO addition-type ammonium chlorides such as alkylbis(2-hydroxyethyl)methyl ammonium chloride and polyoxyethylene alkylmethyl ammonium chloride, where the alkyl group has 8 to 18 carbon atoms and the ethylene oxide addition number is 2 to 15 molar. The amount of cationic surfactant used in the emulsion polymerization is preferably 1 to 10 parts by weight, more preferably 2 to 5 parts by weight, relative to 100 parts by weight of the monomer.

[0036] Alternatively, by using nonionic surfactants for emulsion polymerization and then adding cationic substances, such as cationic surfactants, polyoxyethylene alkylamines, or polyethyleneimine, cationic resin particles of vinyl acetate-based resins can also be produced.

[0037] Furthermore, amino-containing monomers such as dimethylaminoethyl methacrylate or diethylaminoethyl methacrylate (N-substituted aminoalkyl methacrylates), or dimethylaminopropyl methacrylamide (N-substituted aminoalkyl (meth)acrylamides), can be added to (meth)acrylic acid monomers or mixtures of (meth)acrylic acid monomers and styrene-based comonomers, and copolymerized. Then, quaternization with an alkylating agent can be performed to produce cationic resin particles of vinyl acetate-based resins. As alkylating agents, alkyl halides such as octyl chloride, octyl bromide, dodecyl chloride, dodecyl bromide, tetradecyl chloride, tetradecyl bromide, hexadecyl chloride, and hexadecyl bromide are used.

[0038] Cationic resin particles of acrylic resins

[0039] Cationic resin particles made from acrylic resins are preferably those containing a cationic emulsifier, a polymer having cationic groups, or a copolymer containing cationic monomers. Such cationic resin particles are manufactured as follows: During emulsion polymerization using (meth)acrylic monomers, or a mixture of (meth)acrylic monomers and comonomers such as styrene monomers that can copolymerize with (meth)acrylic monomers, a cationic emulsifier is used, or a polymer having cationic groups is used as a protective colloid, or a cationic monomer is added for reverse emulsion polymerization.

[0040] Emulsion polymerization using a cationic surfactant as a cationic emulsifier is preferred, thereby enabling the production of cationic resin particles from acrylic resins. Examples of cationic surfactants include alkylbenzyl ammonium chloride such as tetradecyl dimethyl benzyl ammonium chloride, alkylbenzyl ammonium chloride such as octadecyl dimethyl benzyl ammonium chloride, alkylpyridinium ammonium chloride such as lauryl pyridinium chloride, stearyltrimethyl ammonium chloride, tetraalkyl ammonium chloride such as dioleenyl dimethyl ammonium chloride, and EO addition-type ammonium chlorides such as alkylbis(2-hydroxyethyl)methyl ammonium chloride and polyoxyethylene alkylmethyl ammonium chloride, where the alkyl group has 8 to 18 carbon atoms and the ethylene oxide addition number is 2 to 15 molar. 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, relative to 100 parts by weight of the monomer.

[0041] Alternatively, after emulsion polymerization using nonionic surfactants, adding cationic substances, such as cationic surfactants, polyoxyethylene alkylamines, and polyethyleneimine, can also produce cationic resin particles of acrylic resins.

[0042] Furthermore, amino-containing monomers such as dimethylaminoethyl methacrylate or diethylaminoethyl methacrylate (N-substituted aminoalkyl methacrylates), or dimethylaminopropyl methacrylamide (N-substituted aminoalkyl (meth)acrylamides), can be added to (meth)acrylic acid monomers or mixtures of (meth)acrylic acid monomers and styrene-based comonomers, and copolymerized. Then, quaternization is performed using an alkylating agent to produce cationic resin particles of acrylic resins. Alkyl halides such as octyl chloride, octyl bromide, dodecyl chloride, dodecyl bromide, tetradecyl chloride, tetradecyl bromide, hexadecyl chloride, and hexadecyl bromide are used as alkylating agents.

[0043] Cationic resin particles of carbamate resins

[0044] As cationic resin particles of urethane-based resins, cationic resin particles of urethane-based resins having quaternary ammonium groups are preferred. These cationic resin particles can be prepared, for example, by reacting a polyol, a polyisocyanate, and a tertiary amino-containing polyol in a solvent or without a solvent to prepare a dispersion of polyurethane; subsequently, the tertiary amino groups in the polyurethane are protonated by an acid or quaternized by an alkylating agent, thereby producing cationic resin particles of urethane-based resins having quaternary ammonium groups.

[0045] As another preparation method, a polyol, a polyisocyanate, and a tertiary amino-containing polyol are reacted in a solvent or without solvent at a specified ratio to prepare a urethane prepolymer with isocyanate groups at the ends. The urethane prepolymer is then chain-extended with a polyamine to prepare a dispersion of polyurethane resin particles. Next, the tertiary amino groups in the polyurethane resin are protonated by an acid or quaternized by an alkylating agent. This produces cationic resin particles of a urethane-based resin with quaternary ammonium groups.

[0046] The preferred alkylating agent for quaternizing tertiary amino groups is a reagent that adds an alkyl group to an amino group to generate a quaternary ammonium cation, and is an alkyl halide such as octyl chloride, octyl bromide, dodecyl chloride, dodecyl bromide, tetradecyl chloride, tetradecyl bromide, hexadecyl chloride, hexadecyl bromide, etc.

[0047] The cationic resin particles used in this invention preferably have a low content of microparticles and uniform particle size. Specifically, in terms of particle size distribution, it is preferable that at least 95% of the particles have a particle size in the range of 0.1 μm to 3.0 μm, and more preferably that at least 95% of the particles have a particle size in the range of 0.1 μm to 2.0 μm.

[0048] It should be noted that the particle size distribution defined in this invention is measured as follows: For resin particles and composite coloring particles, the particle size distribution is measured according to JIS Z 8825:2013, using laser diffraction / scattering method, for example, using a particle size distribution analyzer MICROTRACHRA9320-X100 (manufactured by Nikkiso Co., Ltd.). Furthermore, the particle size distribution of pigment particles is measured according to JIS Z 8828:2019, using dynamic light scattering method, for example, using a thick particle size analyzer FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd.).

[0049] <pigment particles>

[0050] The pigment particles used in this invention are resin particles with a negative charge on their surface (hereinafter, sometimes referred to as anionic pigment particles). As such pigment particles, pigment particles containing solid pigments modified with anionic groups can be used.

[0051] As anionic pigment particles, particles with inorganic pigments as the main component or particles with organic pigments as the main component can be used. Examples of inorganic pigments include titanium dioxide-based, iron oxide-based, metal powder-based, sintered, and extender-based pigments. Examples of organic pigments include azo-based, phthalocyanine-based, quinacridone-based, anthraquinone-based, dioxazine-based, indigo / thiodigo-based, violet ketone / perylene-based, isoindolinone-based, aniline black-based, azo-azomethyl alkali-based, and carbon black-based pigments. Combinations of inorganic and organic pigments can also be used.

[0052] The pigment particles used in this invention can be of any particle size, but preferably 0.05 to 0.5 μm, more preferably at least 95% by mass of which have a particle size in the range of 0.05 to 0.3 μm.

[0053] In this invention, anionic pigment particles can be formed by chemically binding anionic functional groups (hereinafter referred to as anionic groups) or their precursors to the surface of the pigment particles or by physically attaching them to the surface of the pigment particles. Alternatively, anionic pigment particles can be formed by chemically reacting the pigment particles to generate anionic groups. Examples of anionic groups include carboxylic acid groups, sulfonic acid groups, and phosphate groups.

[0054] When anionic groups are chemically bonded to the surface of pigment particles, the anionic groups can directly bind to the compounds constituting the pigment, or they can bind to the compounds constituting the pigment through the assistance of other atomic groups. Examples of other atomic groups that indirectly bind anionic groups to the compounds constituting the pigment include straight-chain or branched alkylene groups, phenylene groups, naphthylene groups, carbonyl groups, ester groups, ether groups, amide groups, amino groups, azo groups, sulfonyl groups, etc., having 1 to 12 carbon atoms.

[0055] When anionic groups are physically attached to the surface of pigment particles, it is preferable to treat the pigment surface with a dispersant or to cover the pigment surface with resin.

[0056] One method for surface treatment of pigment dispersants is to supply an anionic polymeric dispersant to the pigment dispersion, thereby allowing the anionic polymeric dispersant to adhere to the pigment surface.

[0057] As a method for coating pigments with resin, the following methods can be cited: a method of supplying anionic monomers to a pigment dispersion and polymerizing them to cover the pigment surface; and a method of adding pigments to a solution of anionic resin and removing the solvent to cover the pigment surface.

[0058] In cases where anionic groups are generated on the surface of pigment particles through chemical treatment, anionic groups are generated through a chemical reaction of the pigment. Examples of acidic groups introduced onto the pigment surface include sulfonic acid groups, phosphate groups, carboxylic acid groups, and hydroxyl groups.

[0059] Chemical treatment that introduces anionic groups onto the surface of pigments can be carried out by gas-phase methods, liquid-phase methods, or combinations thereof.

[0060] In the case of oxidation treatment by gas phase method, the following method can be used: ozone or air is used as an oxidant to contact pigments such as carbon black, thereby oxidizing them.

[0061] In the case of oxidation treatment via liquid phase method, hydrogen peroxide, nitric acid, sulfuric acid, chlorate, or persulfate can be used as oxidants. For example, pigments are added to an aqueous solution containing the aforementioned oxidants and stirred to obtain pigments with acidic groups on their surface. By controlling the amount of oxidant and the reaction temperature, acidic groups can be uniformly introduced onto the surface of pigments such as carbon black.

[0062] Furthermore, the following methods can be cited: introducing anionic groups such as sulfonic acid groups, phosphoric acid groups, and carboxylic acid groups onto the surface of pigments such as carbon black through a coupling reaction based on diazonium salts; introducing anionic groups onto the surface of pigments by contacting them with free oxygen at high temperatures; or introducing anionic groups onto the surface of pigments by treating the pigment surface with bromine and water under normal or high pressure.

[0063] <Complex>

[0064] In this invention, composite coloring particles can be manufactured by combining cationic resin particles and anionic pigment particles through electrostatic interaction. Figure 1 The schematic diagram shows a case where resin particles with positive charges on their surfaces and pigment particles with negative charges on their surfaces combine through electrostatic interaction to form large-diameter composite colored particles.

[0065] The composite coloring particles of the present invention are stable composite particles with a structure in which cationic resin particles and anionic pigment particles are combined through electrostatic interaction.

[0066] Specifically, the composite coloring particles of the present invention can be manufactured by a composite process of mixing a resin emulsion containing cationic resin particles and a pigment dispersion containing anionic pigment particles.

[0067] The mixing ratio of cationic resin particles to anionic pigment particles in the compounding process is, based on the mass ratio of pigment particles to resin particles (excluding aqueous media, etc.), preferably selected from 0.1 / 1 to 50 / 1, more preferably selected from 0.5 / 1 to 10 / 1, and even more preferably selected from 1 / 1 to 5 / 1.

[0068] First, a resin emulsion containing resin particles with a positive charge on their surface and a pigment dispersion containing pigment particles with a negative charge on their surface are prepared. Each emulsion is preferably an aqueous emulsion in which the particles are dispersed in an aqueous medium.

[0069] The medium for the aqueous emulsion is preferably water, a water-soluble organic solvent, or a mixture thereof, which are mutually miscible. The content of the aqueous medium in the resin emulsion or pigment dispersion relative to the total emulsion is preferably 1 to 50% by mass, more preferably 3 to 30% by mass, and even more preferably 5 to 20% by mass.

[0070] As a water-soluble organic solvent, monohydric alcohols such as alkylene glycols, (poly)alkylene glycols, glycol ethers, glyceryl acetate, glyceryl diacetate, etc., as well as polyhydric alcohols, ε-caprolactam, 2-pyrrolidone, N-methylpyrrolidone, ε-caprolactone, δ-valerolactone, etc., lactones such as dimethyl sulfoxide, etc. can be used.

[0071] Among the aforementioned compounds, polyols and compounds having a lactam structure are preferred as water-soluble organic solvents. Specifically, examples of such water-soluble organic solvents include 1,2-alkylene glycols such as 1,2-hexanediol, 2-pyrrolidone, propylene glycol, butyl ethyl propylene glycol, 1,3-butanediol, 3-methoxy-3-methyl-1-butanol, 3-methoxy-1-butanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-butoxy-2-propanol, and triethylene glycol monobutyl ether, which can be used alone or in mixtures of two or more (hereinafter referred to as "at least one").

[0072] Next, the resin emulsion and pigment dispersion are mixed. The emulsions can be mixed by adding them to a container equipped with a stirring device, such as a mechanical stirrer or magnetic stirrer, and stirring. At this time, components required to form the ink composition may also be added.

[0073] After the cationic resin and anionic pigment contained in each emulsion are mixed, they are electrostatically bonded by Coulomb forces to effectively form large-diameter composite coloring particles. The resulting composite coloring particles contain extremely low amounts of pigment particles with a diameter of less than 0.1 μm, thus effectively achieving the desired effect of the invention.

[0074] At this point, a large number of composite coloring particles may aggregate to form aggregates with a particle size exceeding 10 μm. These aggregates can cause ink blockage and skipping when used in writing instruments. Therefore, it is preferable to add a deagglomeration process to break down these aggregates and disperse them among the individual composite coloring particles.

[0075] That is, a preferred embodiment of the method for manufacturing composite colored particles of the present invention is a method for manufacturing composite colored particles, which includes the following steps: a compositeization step of mixing a resin emulsion containing resin particles having a positive charge on the particle surface and an aqueous medium and a pigment dispersion containing pigment particles having a negative charge on the particle surface and an aqueous medium; and a deagglomeration step of breaking down aggregates.

[0076] As a deagglomeration process to break down oversized aggregates, examples include stirring using mixers such as homogenizers, dispersion mixers, supermixers, and homogenizers. Through this deagglomeration process, the aggregates are broken down and transformed into individual composite coloring particles, generating a dispersion of these particles. The particle size of the pigment particles can be controlled by adjusting the stirring conditions during aggregate breakdown.

[0077] The composite coloring particles of the present invention preferably have at least 95% within the range of 0.2 μm to 3.0 μm, more preferably at least 95% within the range of 0.2 μm to 2.0 μm. The content of particles smaller than 0.1 μm in the composite coloring particles, expressed as frequency, is less than 3%, preferably less than 1%. The frequency of the particles can be determined by dynamic light scattering, for example using a particle size distribution analysis device.

[0078] <Water-based ink composition>

[0079] The composite coloring particles of the present invention, based on the required characteristics of writing instruments (ballpoint pens, felt-tip pens, brushes, markers, etc.), are dispersed together with other components in an aqueous medium to form an aqueous ink composition for writing instruments. Examples of these other components include pH adjusters, thickeners, lubricants, rust inhibitors, preservatives, antibacterial agents, surfactants, and solvents as the dispersion medium.

[0080] That is, the water-based ink composition of the present invention is a water-based ink composition containing at least the composite coloring particles of the present invention.

[0081] The content of the composite coloring particles of the present invention in the water-based 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, which is preferred in order to ensure the hue of the ink and prevent blurring during writing.

[0082] Examples of pH adjusters for adjusting the pH of ink compositions include amines such as monoethanolamine, diethanolamine, triethanolamine, triisopropanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, and morpholine; ureas such as urea, thiourea, and tetramethylurea; urea esters such as urethane and methyl urethane; biuret, dimethyl biuret, and tetramethyl biuret; quaternary ammonium compounds such as tetramethylammonium hydroxide; inorganic hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide; and inorganic salts such as sodium carbonate, potassium carbonate, and lithium carbonate. At least one of these can be used.

[0083] As thickeners compounded in water-based ink compositions, synthetic polymers, cellulose derivatives, and polysaccharides can be used, for example. Specifically, examples include gum arabic, tragacanth gum, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, xanthan gum, vesicular gum, succinyl polysaccharide, Diutan gum, dextran, methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, fermented cellulose, oxidized cellulose, starch glycolic acid and its salts, propylene glycol alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylic acid and its salts, carboxyvinyl polymers, polyethylene oxide, copolymers of vinyl acetate and polyvinylpyrrolidone, cross-linked acrylic polymers and their salts, non-cross-linked acrylic polymers and their salts, and styrene-acrylic acid copolymers and their salts; at least one of these can be used.

[0084] Examples of lubricants that can be formulated into water-based ink compositions include nonionic lubricants such as fatty acid esters of polyols, higher fatty acid esters of sugars, higher fatty acid esters of polyoxyalkylene, alkyl phosphates, and alkyl polyoxyalkylene phosphates; anionic lubricants such as alkyl sulfonates and alkyl allyl sulfonates of higher fatty acid amides; fluorinated lubricants; and silicone lubricants such as polyether-modified silicone.

[0085] As rust inhibitors compounded in water-based ink compositions, benzotriazole, toluenetriazole, dicyclohexyl nitrite, saponins, etc., can be used. As preservatives or antibacterial agents compounded in water-based ink compositions, phenols, benzoic acids, benzimidazoles, isothiazolones, triazines, bromonitols, thiabendazoles, zinc pyrithione, carbendazim, and thiamethoxam can be used.

[0086] When the water-based ink composition used with a writing instrument is placed with the cap removed, the initial strokes sometimes exhibit bleed-out characteristics.

[0087] To address this, the composite coloring particles, which are simultaneously formulated with the composite coloring particles of the present invention and a surfactant in an aqueous ink composition, are stabilized in the medium to prevent aggregation. Therefore, in the aforementioned case, good handwriting (initial writeability) is provided from the very beginning of writing, which is preferable.

[0088] That is, one preferred embodiment of the water-based ink composition of the present invention is a water-based ink composition that at least includes the composite coloring particles of the present invention, and a nonionic surfactant or anionic surfactant.

[0089] The surfactants used in the formulation are preferably nonionic or anionic surfactants. Fluorinated, acetylene-based, or organosilicon-based nonionic or anionic surfactants are preferred. Mixtures of nonionic and anionic surfactants may also be formulated.

[0090] Specifically, at least one (either alone or in mixtures of two or more) of the following can be cited: acetylene-based surfactants selected from acetylene glycols, their epoxide adducts and acetylene alcohols; fluorinated surfactants such as perfluoroalkyl phosphates; and polyether-modified organosilicon surfactants such as dimethyl polysiloxane polyethylene glycol adducts.

[0091] The total amount of nonionic or anionic surfactants in the water-based ink composition is in the range of 0.01 to 10% by mass, preferably 0.1 to 8% by mass, and more preferably 0.3 to 6% by mass. When the amount of surfactant is less than 0.01% by mass, it is difficult to obtain an improvement in initial writeability. When the amount is 10% by mass or more, bleeding may sometimes occur in the ink.

[0092] Commercially available nonionic surfactants include: NIKKOL BL-21 (polyoxyethylene (21) lauryl ether), NIKKOL BL-25 (polyoxyethylene (25) lauryl ether), NIKKOL BC-15 (polyoxyethylene (15) hexadecyl ether), NIKKOL BC-20 (polyoxyethylene (20) hexadecyl ether), NIKKOL BC-23 (polyoxyethylene (23) hexadecyl ether), NIKKOL BC-25 (polyoxyethylene (25) hexadecyl ether), NIKKOL BC-30 (polyoxyethylene (30) hexadecyl ether), NIKKOL BC-40 (polyoxyethylene (40) hexadecyl ether), NIKKOL BS-20 (polyoxyethylene (20) stearyl ether), NIKKOL BO-15V (polyoxyethylene (15) oil ether), NIKKOL... BO-20V (polyoxyethylene (20) oil ether), NIKKOL BO-50V (polyoxyethylene (50) oil ether), NIKKOL BB-20 (polyoxyethylene (20) betaine), NIKKOL BB-30 (polyoxyethylene (30) betaine), NIKKOL BD-10 (polyoxyethylene (10) (C12~15) synthetic alkyl ether) (all manufactured by Nikko Chemicals Co., Ltd.)

[0093] Emulgen 120 (polyethylene (12) lauryl ether), Emulgen 123P (polyethylene (23) lauryl ether), Emulgen 130K (polyethylene (41) lauryl ether), Emulgen 147 (polyethylene (19) lauryl ether), Emulgen 150 (polyethylene (47) lauryl ether), Emulgen 210P (polyethylene (7) hexadecyl ether), Emulgen 220 (polyethylene (13) hexadecyl ether), Emulgen 350 (polyethylene (50) stearyl ether), Emulgen 430 (polyethylene (30) oil ether), Emulgen 4085 (polyethylene (85) monotetradecyl ether), Emulgen 2025G (polyethylene (25) octyl dodecyl ether) (all manufactured by Kao Corporation) and other polyethylene alkyl ethers,

[0094] Similar to PBC-34 (polyoxyethylene (20) polyoxypropylene (4) hexadecyl ether), similar to PBC-44 (polyoxyethylene (20) polyoxypropylene (8) hexadecyl ether) (all manufactured by Nikko Chemicals Co., Ltd.), etc., polyoxyethylene polyoxypropylene alkyl ethers, NIKKOL MYS-25 (polyethylene glycol monostearate (25 ethylene oxide)), NIKKOL MYS-45 (polyethylene glycol monostearate (45 ethylene oxide)), NIKKOL MYS-55 (polyethylene glycol monostearate (55 ethylene oxide)), NIKKOL CDS-600P (polyethylene glycol distearate) (all manufactured by Nikko Chemicals Co., Ltd.).

[0095] Emanon 3199B (polyethylene glycol monostearate (141 ethylene oxide)), Emanon 3299V (dipolyethylene glycol stearate (140 ethylene oxide)), Emanon 3299RV (polyethylene glycol distearate (250 ethylene glycol oxide)) (all manufactured by Kao Corporation) and other polyethylene glycol fatty acid esters, NIKKOL TL-10 (polyoxyethylene (20) dehydrated sorbitan monocoquercetin fatty acid ester), NIKKOL TP-10 (polyoxyethylene (20) dehydrated sorbitan monopalmitate), NIKKOL TO-10M, NIKKOL TO-10 (all manufactured by Nikko Chemicals Co., Ltd.), NIKKOL TI-10 (polyoxyethylene (20) dehydrated sorbitan monoisostearate) (all manufactured by Nikko Chemicals Co., Ltd.)

[0096] RHEODOL TW-L120, RHEODOL Super TW-L120 (polyoxyethylene (20) dehydrated sorbitan monolaurate), RHEODOL TW-P120 (polyoxyethylene (20) dehydrated sorbitan monopalmitate), RHEODOL TWO120 (polyoxyethylene (20) dehydrated sorbitan monooleate) and other polyoxyethylene dehydrated sorbitan fatty acid esters, NIKKOL HCO-80 (polyoxyethylene (80) hydrogenated castor oil), HCO-100 (polyoxyethylene (100) hydrogenated castor oil) (and other polyoxyethylene hydrogenated castor oils manufactured by Nikko Chemicals Co., Ltd.), NIKKOL Decaglyn 1-L (monolarate decaglycerate) (manufactured by Nikko Chemicals Co., Ltd.) polyglycerol fatty acid esters,

[0097] RYOTO Sugar Ester S-1570 (sucrose stearate), RYOTO Sugar Ester S-1670 (sucrose stearate), RYOTO Sugar Ester P-1570 (sucrose palmitate), RYOTO Sugar Ester P-1670 (sucrose palmitate), RYOTO Sugar Ester M-1695 (sucrose myristate), RYOTO Sugar Ester O-1570 (sucrose oleate), RYOTO Sugar Ester L-1695 (sucrose laurate) (all manufactured by Mitsubishi Chemical Foods Corporation) and other sucrose fatty acid esters; Pluronic L10, Pluronic L31, Pluronic L61, Pluronic L62, Pluronic 10R5, Pluronic 17R2, Pluronic 25R2 (poly(ethylene oxide)poly(propylene oxide) block copolymers) (all manufactured by BASF Japan Ltd.).

[0098] ADEKA Pluronic L-23, ADEKA Pluronic L-31, ADEKA Pluronic L-44, ADEKAPluronic L-61, ADEKA Pluronic L-62, ADEKA Pluronic L-64, ADEKA Pluronic L-71, ADEKA Pluronic L-72, ADEKA Pluronic L-101, ADEKA Pluronic L-121, ADEKA PluronicP-84, ADEKA Pluronic P-85, ADEKA Pluronic P-103, ADEKA Pluronic F-68, ADEKAPluronic F-88, ADEKA Pluronic F-108 (polyoxyethylene polyoxypropylene condensate) (above, manufactured by ADEKA Corporation).

[0099] These nonionic surfactants can be used alone or in combination of two or more.

[0100] Commercially available anionic surfactants that can be used include alkylbenzene sulfonates, polyoxyethylene alkyl ether sulfates, alkyl sulfate esters, and higher alkyl sulfates. Specific examples include: Lipon LH-200, Lipon LS-250, Lipon PS-230, Lipon PS-260, Lipon PS-860 (linear alkyl (C12-14) benzenesulfonate), Lipon LH-900 (branched alkyl (C12-14) benzenesulfonic acid), Lipolan PJ-400CJ, Lipolan LB-440, Lipolan LJ-441, K Lipolan PJ-400C (α-olefin (C14) sulfonate), Lipolan LB-840, and Lipolan PB-800CJ (α-olefin (C14-18) sulfonate) (all manufactured by Lion Corporation).

[0101] LUNOX S-40TD (triethanolamine dodecylbenzenesulfonate) (manufactured by Toho Chemical Industries, Co., Ltd.), NEOPELEX G-15, NEOPELEX G-25, NEOPELEX G-65 (sodium dodecylbenzenesulfonate), NEOPELEX GS (dodecylbenzenesulfonic acid) (manufactured by Kao Corporation), and other alkylbenzenesulfonates; SUNNOLLMT-1430 (sodium polyoxyethylene alkyl (C12) ether sulfate), SUNNOL TD-3130 (sodium polyoxyethylene alkyl (C13) ether sulfate) (manufactured by Lion Corporation); EMAL 20C, EMAL 270J, EMAL 20CM, EMAL D-3-D, EMAL D-4-D, EMAL 20T; LATEMUL E-118B, LATEMUL E-150, LATEMUL WX (sodium polyoxyethylene lauryl ether sulfate) (manufactured by Kao Corporation), and other polyoxyethylene alkyl ether sulfates.

[0102] SUNNOL EH-1145M (alkyl (C8) sulfate ethanolamine), SUNNOL LM-1130 (alkyl (C12) sulfate sodium), SUNNOL LM-1140T (alkyl (C12) sulfate triethanolamine) (all manufactured by Lion Corporation) and other alkyl sulfate salts.

[0103] ALSCOPE LN-90PW, ALSCOPE LS-40T, ALSCOPE LS-30 (Lauryl Sulfate), ALSCOPE LS-25B (Ammonium Lauryl Sulfate), ALSCOPE A-225B, ALSCOPE DA-330S, ALSCOPE N-335T, ALSCOPE NS-230, ALSCOPE TH-330K, ALSCOPE TH-370N (Polyoxyethylene Alkyl Ether Sulfate) (all manufactured by Toho Chemical Industries, Co., Ltd.), EMAL 0, EMAL 0S, EMAL 10S, EMAL 2FG, EMAL 2F-30 (Sodium Lauryl Sulfate) (all manufactured by Kao Corporation) and other high-grade alkyl sulfates.

[0104] These anionic surfactants can be used alone or in combination of two or more.

[0105] In the water-based ink composition of the present invention, a dispersion medium is incorporated to stabilize the state of the contained components and ensure its usability as a writing instrument ink. The dispersion medium can be a hydrophilic dispersion medium formed from water such as tap water, purified water, distilled water, ion-exchanged water, or pure water, or a water-soluble organic solvent or a mixture thereof. A mixture formed from water and at least one water-soluble organic solvent is preferred.

[0106] The amount of aqueous medium in the aqueous ink composition is preferably 3 to 300 parts by weight, more preferably 5 to 100 parts by weight, relative to 100 parts by weight of composite coloring particles.

[0107] As a water-soluble organic solvent, alcohols, glycols, or their derivatives can be used, for example. Specifically, examples include methanol, ethanol, propanol, butanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, polyethylene glycol, 3-butanediol, thiodiethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, glycerol, and diglycerol; at least one of these can be used. Preferably, a mixed solvent is prepared by mixing a water-soluble organic solvent in a ratio of 5 to 200 parts by weight relative to 100 parts by weight of water.

[0108] Additionally, hydrophilic nonionic polymers can be used as dispersion media. For example, polyethers can be used as nonionic polymers compounded in the aqueous ink composition. Specifically, examples include polypropylene glycol, polybutane glycol, and polyoxypropylene diglyceride; at least one of these can be used. Using these nonionic polymers as the main solvent can prevent the aggregation of thermochromic microcapsules over time.

[0109] The polyethers such as polypropylene glycol and polybutylene glycol mixed in the water-based ink composition can be of various degrees of polymerization. However, from the perspective of further maximizing the effects of the present invention, it is preferred to use a polymer of polypropylene glycol with a degree of polymerization in the range of 400 to 700 (weight average) and a polymer of polybutylene glycol with a degree of polymerization in the range of 500 to 700 (weight average).

[0110] A water-based ink composition for writing instruments can be manufactured, for example, by mixing a specified amount of composite coloring particles and each component of the water-based ink composition using a mixer such as a homogenizer or disperser. Further, if necessary, coarse particles in the water-based ink composition can be removed by filtration or centrifugation.

[0111] <Writing Tools>

[0112] The ink composition of the present invention is used in writing instruments such as ballpoint pens, markers, brushes, and fountain pens. Writing instruments incorporating the ink composition of the present invention have the following advantages: when written on paper or other surfaces, they exhibit excellent writing performance, including line density, bleed resistance, smudge resistance, and initial writing properties.

[0113] Example

[0114] The present invention will be further described in detail according to the embodiments, but the present invention is not limited to the embodiments, etc. It should be noted that, in the following, "parts" in compounding refers to parts by mass. The particle size distribution of resin particles and composite coloring particles was determined using a MICROTRAC HRA9320-X100 particle size distribution analyzer (manufactured by Nikkiso Co., Ltd.) according to the laser diffraction / scattering method. In addition, the particle size distribution of pigment particles was determined using a thick-film particle size analyzer FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd.) according to the dynamic light scattering method.

[0115] <Cationic Resin Particles>

[0116] Aqueous emulsions of vinyl acetate-based resins, acrylic resins, or urethane-based resins are used as emulsions for cationic resin particles.

[0117] A cationic modified vinyl acetate resin emulsion (VINYBLAN 1008; manufactured by Nissin Chemical Co., Ltd.) was used as a vinyl acetate-based resin emulsion. A cationic modified polyvinyl alcohol-acrylic resin emulsion (MOWINYL 6950; manufactured by apan Coating Resin Co., Ltd.) was used as an acrylic resin emulsion. A cationic urethane emulsion (SUPERFLEX 620; manufactured by DKS Co., Ltd.) was used as a urethane-based resin emulsion. A nonionic modified vinyl acetate resin emulsion (VINYBLAN 1002; manufactured by Nissin Chemical Co., Ltd.) was used as a comparison.

[0118] <Anionic pigment particles>

[0119] An aqueous emulsion of anionic carbon black or organic pigment obtained according to the method described in Reference Examples 1 to 4 below is used as an anionic pigment dispersion.

[0120] Reference Example 1

[0121] Pigment: Carbon black (MCF88; manufactured by Mitsubishi Chemical Corporation) 10% by mass

[0122] Dispersant: α-methylstyrene-acrylic acid copolymer (Joncryl 61J, manufactured by Johnson, 30% by mass aqueous solution) 10% by mass

[0123] pH adjuster: 0.1% by mass of aminomethylpropanol

[0124] Viscosity modifier: Polyvinylpyrrolidone 5% by mass

[0125] Water-soluble organic solvent: 5% by mass of propylene glycol monoethyl ether

[0126] Water: 69.9% by mass of purified water

[0127] In a container, water, water-soluble organic solvent, viscosity modifier, pH adjuster, dispersant, and pigment were added sequentially at the aforementioned mixing ratio. The mixture was premixed in a mixer for 2 hours, then dispersed in a 1 mm zirconia bead mill. Impurities were removed by centrifugation, and the mixture was further filtered under reduced pressure using a microfilter (5.0 μm pore size; Millipore) to obtain an emulsion of anionic modified carbon black particles 1 with a pH of 8.9. The average particle size of anionic modified carbon black particles 1 was 0.1 μm.

[0128] See Example 2

[0129] Self-dispersible carbon black (CAB-O-JET200; manufactured by Cabot Specialty Chemicals Inc.) with acidic groups imparted to its surface was dispersed in an aqueous solution of aminomethylpropanol to obtain an emulsion of anionic modified carbon black particles 2 with pH 8.5.

[0130] See Example 3

[0131] Pigment: Phthalocyanine Blue 5187 (manufactured by Dainippon Seika Co., Ltd.) 10% by weight

[0132] Dispersant: α-methylstyrene-acrylic acid copolymer (Joncryl 63J, manufactured by BASF Corporation, 30% by mass aqueous solution) 10% by mass

[0133] pH adjuster: 0.1% by mass of aminomethylpropanol

[0134] Viscosity modifier: Polyvinylpyrrolidone 5% by mass

[0135] Water-soluble organic solvent: 5% by mass of propylene glycol monoethyl ether

[0136] Water: 69.9% by mass of purified water

[0137] In a container, water, water-soluble organic solvent, viscosity modifier, pH adjuster, dispersant, and pigment are added sequentially according to the aforementioned mixing ratio. The mixture is premixed in a mixer for 2 hours, dispersed in a 1 mm zirconia bead mill, impurities are removed by centrifugation, and further filtered under reduced pressure using a microfilter (5.0 μm pore size; manufactured by Millipore) to obtain an emulsion of anionic modified phthalocyanine blue particles with pH 8.9.

[0138] See Example 4

[0139] Pigment: Carbon black (MCF88; manufactured by Mitsubishi Chemical Corporation) 10% by mass

[0140] pH adjuster: 0.1% by mass of aminomethylpropanol

[0141] Viscosity modifier: Polyvinylpyrrolidone 5% by mass

[0142] Water-soluble organic solvent: 5% by mass of propylene glycol monoethyl ether

[0143] Water: 79.9% by mass of purified water

[0144] In a container, water, water-soluble organic solvent, viscosity modifier, pH adjuster and pigment are added sequentially according to the aforementioned mixing ratio. The mixture is premixed in a mixer for 2 hours, dispersed in a 1 mm zirconia bead mill, impurities are removed by centrifugation, and further filtered under reduced pressure using a microfilter (5.0 μm pore size; Millipore) to obtain an emulsion of unmodified carbon black particles with pH 8.9.

[0145] Examples 1-6, Comparative Examples 1-2

[0146] The various cationic resin particle emulsions and the various anionic pigment dispersions prepared in the reference examples were mixed using the combinations and mass ratios (mass ratios of solids) shown in Table 1, and then mixed using a mixer. Next, the mixture was vigorously stirred using a homogenizer to deaggregate the mixture, resulting in emulsions A-1 to A-6 containing the composite coloring particles of the present invention, and emulsions C-1 to C-2 as comparative examples.

[0147] [Table 1]

[0148]

[0149] The frequency distribution of particle size of the cationic modified vinyl acetate resin used in Example 1 is illustrated in the figure. Figure 2 The frequency distribution of particle size of anion-modified carbon black particles is shown in the figure. Figure 3 Similarly, the frequency distribution of the particle size of the composite colored particles before deaggregation in Example 1 is illustrated in the figure. Figure 4 The frequency distribution of the particle size of the composite colored particles A-1 after deaggregation is shown in the figure. Figure 5 These figures show that the carbon black pigment used as a raw material contains a large number of small-diameter pigment particles, while the composite coloring particles obtained in this invention contain virtually no small-diameter pigment particles.

[0150] Table 2 shows the frequency distribution diagram of the particle size of the composite colored particles prepared in Examples 1-6 and Comparative Examples 1-2, determined by the aforementioned method, and the results of calculating the frequency of the composite colored particles within a specific particle size range in the overall composite colored particles.

[0151] [Table 2]

[0152]

[0153] Examples 11-19 and Comparative Examples 11-12

[0154] Using composite coloring particles A-1 to A-6, or emulsions containing C-1 to C-2 as comparative examples, respectively, pH adjuster, thickener, lubricant, rust inhibitor, preservative and dispersion medium were mixed in the combinations and weight ratios shown in Table 3 and mixed. A portion of the aggregates was filtered to prepare ink compositions.

[0155] The ink compositions of Examples 11-19 are embodiments of the water-based ink compositions of the present invention. The ink composition of Comparative Example 11 is a comparative example that does not use cationic resin particles, and the ink composition of Comparative Example 12 is a comparative example that does not use anionic pigment particles.

[0156] <Evaluation of Ink Compositions>

[0157] Ballpoint pens were manufactured using the prepared ink compositions. Specifically, ballpoint pens were made by filling commercially available ballpoint pens (trade name: PROCKEY PM-120T; manufactured by Mitsubishi Pencil Co., Ltd., with ultrafine and superfine nibs) with the ink compositions manufactured in Examples 1-8 and Comparative Examples 1-5. Using the superfine side of each of the aforementioned ballpoint pens, the writing performance, such as line density, bleed, erasing resistance, and initial writing properties, was evaluated using the following methods. The results are shown in Table 3.

[0158] 1) Line density

[0159] 1-1) Writing on paper

[0160] Using various pens, write spirals by hand on the surface of writing paper according to ISO standards, then visually inspect the surface of the paper to evaluate the density of the writing lines based on the following criteria.

[0161] 1-2) Writing about cloth

[0162] Using various pens, write "Mitsubishi Pencil" on the surface of cotton cloth (Kanakin No. 3; JIS color fastness test (according to JIS L0803)) by hand, then visually examine the surface of the paper to evaluate the density of the written lines according to the following criteria.

[0163] Evaluation criteria for writing lines:

[0164] A: The color of the lines is noticeably darker.

[0165] B: The lines are dark in color.

[0166] C: The color of the lines is slightly lighter.

[0167] D: The color of the lines is noticeably lighter.

[0168] 2) Resistance to leaching

[0169] 2-1) Bleeding from the paper

[0170] Using various pens, write spirals by hand on the surface of writing paper according to ISO standards, then visually inspect the surface of the paper to evaluate the bleeding of the writing lines based on the following criteria.

[0171] 2-2) Leakage from the fabric

[0172] Using various pens, write "Mitsubishi Pencil" on the surface of cotton cloth (Kanakin No. 3; JIS color fastness test (according to JIS L0803)) by hand, and then visually evaluate the bleeding state of the writing lines by observing the surface of the paper according to the following criteria.

[0173] Evaluation criteria for exudation status:

[0174] A: No wires are leaking out.

[0175] B: Slight lines are seeping out.

[0176] C: There are quite a few lines seeping out.

[0177] D: The lines show obvious bleeding.

[0178] 3) Abrasion resistance

[0179] Using various pens, write the words "Mitsubishi Pencil" by hand on the surface of coated paper (manufactured by Yupo Corporation), and allow the ink to dry. Place a wiping paper (manufactured by Nippon Paper Crecia Co., Ltd.) on the ink, place a 500g weight on it, and rub the ink by moving the wiping paper and the weight horizontally back and forth 5 times. Evaluate the condition of the ink afterward according to the following criteria.

[0180] Evaluation criteria for abrasion resistance:

[0181] A: There are no missing parts in the handwriting.

[0182] B: There are one or two thin, missing lines in the handwriting.

[0183] C: There are obvious gaps in the handwriting.

[0184] D: The more difficult the characters are to recognize, the greater the gaps.

[0185] 4) Initial draft

[0186] Using the aforementioned pens, after placing them at 25°C and 60%RH for one week without caps, write straight lines on PPC paper and evaluate the initial writeability using the following evaluation criteria.

[0187] Evaluation criteria for initial drafts:

[0188] A: The ability to write without ink from the very first stroke, creating a "flying white" effect.

[0189] B: From the beginning of the stroke, confirm the ink dry-out effect up to 10mm.

[0190] C: From the beginning of the stroke, confirm the dry white effect of ink exceeding 10mm.

[0191] As shown in the examples in Table 3, the ink composition containing the composite coloring particles of the present invention exhibits good writing performance in terms of line (handwriting) concentration, bleed-through, rub-resistantness, and initial writing properties.

[0192] [Table 3]

[0193]

[0194] Examples 20-24 and Comparative Examples 13-14

[0195] Using composite coloring particles A-1, in addition to pH adjusters, thickeners, lubricants, rust inhibitors, corrosion inhibitors and dispersion media, various surfactants are mixed in the combinations and weight ratios shown in Table 4, and the mixture is then filtered to prepare an ink composition.

[0196] The surfactants used are as described below.

[0197] Example 20: Acetylene-based nonionic surfactant (manufactured by Nissin Chemical Industry Co., Ltd.; SURFYNOL 104)

[0198] Example 21: Fluorinated nonionic surfactant (manufactured by Chemours Company; Capstone FS-10)

[0199] Example 22: Organosilicon-based nonionic surfactant (manufactured by Shin-Etsu Chemical Co., Ltd.; KF-6011)

[0200] Example 23, Comparative Example 13: Polyoxyethylene alkyl ether sulfate type anionic surfactant (manufactured by DKS Co., Ltd.; HITENOL NF-13)

[0201] Example 24: Polyoxyethylene styrene-based nonionic surfactant (manufactured by Kao Corporation; Emulgen A-90)

[0202] Comparative Example 14: Quaternary ammonium salt cationic surfactant (manufactured by Lion Specialty Chemicals Co., Ltd.; Lipocard 16-29)

[0203] Using the prepared ink compositions, ballpoint pens were manufactured according to the same method as in the aforementioned examples. The writing performance, including line density, bleed, erasability, and initial writing properties, was evaluated. The results are shown in Table 4.

[0204] The ink compositions of Examples 20-24 are embodiments of the aqueous ink compositions of the present invention. The ink composition of Comparative Example 13 is a comparative example in which the amount of surfactant is excessive, and the ink composition of Comparative Example 14 is a comparative example in which a cationic surfactant is used as the surfactant.

[0205] As shown in the examples in Table 4, the ink composition containing an appropriate amount of the composite coloring particles of the present invention and an anionic or nonionic surfactant as a surfactant exhibits extremely good writing performance in terms of line (handwriting) concentration, bleed-through, rub-resistantness, and initial writing properties.

[0206] [Table 4]

[0207]

[0208] Industrial availability

[0209] According to the present invention, composite coloring particles with excellent usability and ink compositions formulated therein can be advantageously produced industrially. The ink compositions of the present invention are suitable for use in writing instruments such as ballpoint pens and fountain pens.

Claims

1. A water-based ink composition for a writing instrument, comprising composite coloring particles, said composite coloring particles comprising resin particles having a positive charge on their surface and pigment particles having a negative charge on their surface. The composite coloring particles are manufactured by a manufacturing method including the following steps: (i) A compounding process comprising a resin emulsion containing resin particles with positive charges on their surfaces and an aqueous medium, and a pigment dispersion containing pigment particles with negative charges on their surfaces and an aqueous medium; and, (ii) A deagglomeration process that breaks down aggregates with a particle size exceeding 10 µm by using a mixer. At least 95% of the composite coloring particles have a particle size in the range of 0.2 μm to 3.0 μm, and the frequency of particles smaller than 0.1 μm in the composite coloring particles is less than 3%. The resin particles and the pigment particles are combined through electrostatic interaction.

2. The water-based ink composition according to claim 1, wherein, The mass ratio of resin particles to pigment particles is 0.1 / 1 to 50 / 1.

3. The water-based ink composition according to claim 1, wherein, The resin particles contain polymers modified with cationic groups.

4. The water-based ink composition according to claim 3, wherein, The polymer is selected from at least one of the groups consisting of acrylic resins and vinyl acetate resins.

5. The water-based ink composition according to claim 3, wherein, The polymer is a urethane resin.

6. The water-based ink composition according to any one of claims 1 to 5, wherein, Pigment particles contain solid pigments modified with anionic groups.

7. The aqueous ink composition according to claim 6, further comprising a nonionic surfactant.

8. The aqueous ink composition according to claim 6, further comprising anionic surfactant.

9. The water-based ink composition according to claim 1, wherein, The resin particles comprise cationic resin particles of urethane resins having quaternary ammonium groups.

10. A writing instrument comprising the water-based ink composition according to any one of claims 1 to 9.

11. A method for manufacturing composite colored particles, comprising: (i) Composite process: A resin emulsion containing resin particles with positive charge on the particle surface and an aqueous medium is mixed with a pigment dispersion containing pigment particles with negative charge on the particle surface and an aqueous medium. and, (ii) Deagglomeration process: Agglomerates with a particle size exceeding 10 µm are broken up by stirring with a mixer. At least 95% of the composite colored particles have a particle size in the range of 0.2 μm to 3.0 μm, and the frequency of particles smaller than 0.1 μm in the composite colored particles is less than 3%.

12. The method for manufacturing composite colored particles according to claim 11, wherein, In the (i) compounding process, at least 95% of the resin particles have a particle size in the range of 0.1 to 3.0 μm, and at least 95% of the pigment particles have a particle size in the range of 0.05 to 0.3 μm.

13. The method for manufacturing composite colored particles according to claim 11, wherein, In the (i) compounding process, the mass ratio of resin particles to pigment particles is 0.1 / 1 to 50 / 1.

14. The method for manufacturing composite colored particles according to claim 11, wherein, (ii) The deagglomeration process is a process of stirring using a homogenizer, dispersion mixer, super mixer, or homogenizer.

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