Composite coloring particles

Abstract

To provide an ink composition having excellent dispersion stability and writing performance.SOLUTION: Provided are a composite colored particle including a resin particle carrying a positive electric charge on a particle surface, a colored particle carrying a negative electric charge on a particle surface, and a low-density particle, the colored particle and the low-density particle forming a composite with the resin particle through Coulomb force; a water-based ink composition containing the composite colored particles dispersed in a water-based medium; and a writing instrument loaded with the water-based ink composition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ink composition for a writing instrument, a colorant contained therein, and a writing instrument equipped with the ink composition. [Background technology]

[0002] Ink compositions containing various dyes or pigments dissolved or dispersed in a solvent as colorants are used in writing instrument inks. Furthermore, when writing instruments such as ballpoint pens and marking pens are stored without being used for a long period of time, the colorants contained in the ink composition settle, causing a change in concentration. Writing with such a writing instrument can result in lighter or smudged lines. To prevent changes in writing density due to settling of ink composition components during long-term storage of writing instrument inks, the colorants contained in the ink composition must have dispersion stability.

[0003] Patent Document 1 describes an aqueous ink composition for a ballpoint pen, which contains a colorant, water, and a polysaccharide complex, the polysaccharide complex consisting of multiple polysaccharides, each having two or more types of monosaccharides as constituent monosaccharides. This provides an aqueous ink composition for a ballpoint pen that has shear thinning properties, and that, even when a pigment is used as the colorant, suppresses pigment sedimentation and aggregation without excessively increasing the ink viscosity, thereby preventing ink separation and a decrease in writing density, and enables the formation of clear writing over a long period of time without smearing, cracking, or bleeding, as well as a ballpoint pen containing the same.

[0004] Patent Document 2 discloses an aqueous ink composition for a writing instrument, which comprises at least a pigment, water, and a galactoxyloglucan partially free of galactose in the side chain. This composition prevents the ink viscosity from decreasing due to external heat, and prevents the pigment from flocculating or settling, resulting in lighter or darker handwriting. In particular, the composition inhibits the decrease in ink viscosity and the flocculation and settling of the pigment when the writing instrument is carried in a breast pocket with the writing tip facing up (upright position) or when transported in summer, resulting in no blurring or lighter handwriting. It also provides a writing instrument containing the composition, which exhibits excellent pigment dispersion stability in a temperature range exceeding the temperature range of the living environment.

[0005] The methods described in these documents all focus on the aqueous medium contained in the ink composition and attempt to improve the dispersion stability of the pigment by improving the physical properties of the medium, but are not inventions that improve the dispersion stability of the pigment itself. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2021-8595 A, pages 3-4 [Patent Document 2] JP 2021-31679 A, ​​pages 3-4 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to provide an aqueous ink composition that suppresses sedimentation of a colorant during ink storage and has excellent dispersion stability over time, as well as a writing instrument that has excellent writing properties and bleeding resistance. Another object of the present invention is to provide a method for producing composite colored particles that are blended as a colorant in the aqueous ink composition. [Means for solving the problem]

[0008] As a result of extensive research into the dispersion stability of the colorants used, the inventors came up with the idea of ​​combining resin particles with colorant particles and low-density particles by utilizing Coulomb force, and thus completed the present invention. That is, the present invention relates to composite colored particles comprising resin particles having a positive charge on their particle surfaces, colored particles having a negative charge on their particle surfaces, and low-density particles having a negative charge on their particle surfaces, in which the colored particles and low-density particles are combined with the resin particles 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, a dispersion containing colored particles having a negative charge on the particle surface, and a dispersion containing low-density 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, a colorant with improved dispersion stability can be obtained. An ink composition incorporating the composite colored particles of the present invention exhibits good dispersion stability, writing performance, and bleeding resistance. As a result, an ink composition with excellent long-term dispersion stability and a writing instrument such as a ballpoint pen or marking pen with excellent writing performance and bleeding resistance are provided. A writing instrument incorporating the ink composition of the present invention has excellent writing performance and does not undergo changes in writing density or smearing even when stored unused for a long period of time. Furthermore, according to the present invention, composite colored particles with excellent dispersion stability to be incorporated into the ink composition and a manufacturing method suitable for industrial production thereof are provided. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram illustrating an example of the present invention, showing that a resin particle 3 having a positive charge on its particle surface is combined with a colored particle 1 having a negative charge on its particle surface and a low-density particle 2 having a negative charge on its particle surface by Coulomb force to form a large-diameter composite colored particle of the present invention. [Figure 2] FIG. 2 is a particle size frequency distribution diagram of the composite colored particles P-1 obtained by carrying out the composite step and the deagglomeration step in Example 1. As shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] The composite colored particles of the present invention are stable composite particles having a structure in which resin particles having a positive charge on the particle surface (hereinafter, sometimes referred to as cationic resin particles), colored particles having a negative charge on the particle surface (hereinafter, sometimes referred to as anionic colored particles), and low-density particles having a negative charge on the particle surface (hereinafter, sometimes referred to as anionic low-density particles) are bonded by Coulomb force.

[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] 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 that of the anionic colored particles can be measured by a dynamic light scattering method.

[0016] <Cationic resin particles> The resin particles used in the present invention are resin particles having a positive charge on the particle surface (cationic resin particles). As such resin particles, resin particles made of a polymer modified with a cationic group can be used, specifically, 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] Furthermore, cationic resin particles of acrylic resin can be prepared by copolymerizing (meth)acrylic monomers or mixtures of (meth)acrylic monomers and styrene-based comonomers with amino group-containing monomers such as N-substituted aminoalkyl (meth)acrylates (e.g., dimethylaminoethyl (meth)acrylate or diethylaminoethyl (meth)acrylate) or N-substituted aminoalkyl (meth)acrylamides (e.g., dimethylaminopropyl (meth)acrylamido), 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] <Anionic colored particles> In the present invention, colored particles having a negative charge on the particle surface (anionic colored particles) are used, which include resin particles having a negative charge on the particle surface and containing a dye (hereinafter sometimes referred to as anionic dye particles), and pigment particles having a negative charge on the particle surface (hereinafter sometimes referred to as anionic pigment particles).

[0031] The anionic colored particles used in the present invention may have any particle size, but are preferably fine particles having a particle size of 0.01 to 1.0 μm, particularly 0.05 to 0.5 μm, and more preferably at least 95% by mass of which are fine particles having a particle size within the range of 0.01 to 0.5 μm, particularly 0.05 to 0.3 μm. It is preferable that the anionic color particles have a particle diameter within this range, since they can be combined with the cationic resin particles to form good composite color particles.The shape of the anionic color particles is preferably spherical, and particularly spherical.

[0032] [Anionic dye particles] The anionic dye particles used in the present invention 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. In particular, anionic dye microparticles in which a dye is encapsulated inside or on the surface of anionic resin microparticles are preferred.

[0033] As the resin particles used to produce anionic dye particles in which a dye is encapsulated inside or on the surface of resin particles having anionic properties, particles made of a resin to which functional groups having anionic properties (hereinafter also referred to as anionic groups) are chemically bonded or particles made of a resin to which anionic groups are physically attached can be used.

[0034] The resin constituting the anionic dye particles 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.

[0035] In the production of anionic dye particles, when an anionic group is introduced into resin particles, a reagent having an anionic group or a precursor thereof may be directly bonded to the resin, or may be indirectly bonded 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.

[0036] Resin particles containing anionic groups can be used to produce anionic dye particles. These particles can be made from a resin composition 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 their surfaces. Examples of anionic groups include carboxyl groups, sulfonic acid groups, and phosphate groups.

[0037] 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.

[0038] As a chemical treatment for introducing anionic groups onto the resin surface, a method for introducing anionic groups such as carboxyl groups, sulfonic acid groups, or phosphoric acid groups into the resin by a coupling reaction using a diazonium salt can also be used.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The dye used in the production of anionic dye particles can be any of acid dyes, basic dyes, direct dyes, and oil-soluble dyes, and can be either naturally occurring or synthetic dyes. Two or more types of non-anionic or anionic dyes can be mixed and used, or a non-anionic dye and an anionic dye can be mixed and used.

[0043] Acid dyes include eosin, fuoxin, acid red, water blue, brilliant blue FCF, and nigrosin.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.).

[0048] The anionic dye particles may contain 0.2 to 50% by mass, preferably 0.5 to 20% by mass, and more preferably 1.0 to 10% by mass of the dye relative to the total amount of the anionic dye particles.

[0049] [Anionic pigment particles] The pigment particles used in the present invention are resin particles having a negative charge on the particle surface (hereinafter, sometimes referred to as anionic pigment particles). As such pigment particles, pigment particles made of a solid pigment modified with an anionic group can be used.

[0050] Anionic pigment particles can be particles primarily composed of inorganic or organic pigments. Inorganic pigments include titanium oxide, iron oxide, metal powder, calcined, and extender pigments. Organic pigments include azo, phthalocyanine, quinacridone, anthraquinone, dioxazine, indigo-thioindigo, perinone-perylene, isoindolenon, aniline black, azo-methine azo, and carbon black pigments. Inorganic and organic pigments can also be used in combination.

[0051] In the present invention, the anionic pigment particles may be those in which a reagent having an anionic functional group (hereinafter referred to as an anionic group) or a precursor thereof is chemically bonded or physically attached to the surface of the pigment particles. Alternatively, the anionic pigment particles may be those in which an anionic group is generated by chemically reacting the surface of the pigment particles. Examples of the anionic group include a carboxyl group, a sulfonic acid group, and a phosphate group.

[0052] When an anionic group is chemically bonded to the surface of a pigment particle, the anionic group may be bonded directly to the compound constituting the pigment, or may be bonded to the compound constituting the pigment via another atomic group. Examples of other atomic groups that indirectly bond the anionic group to the compound constituting the pigment include linear or branched alkylene groups having 1 to 12 carbon atoms, phenylene groups, naphthylene groups, carbonyl groups, ester groups, ether groups, amide groups, amino groups, azo groups, and sulfonyl groups.

[0053] When anionic groups are physically attached to the surface of pigment particles, it is preferred to treat the pigment surface with an anionic dispersant or to coat the pigment surface with an anionic resin or the like. As a method for treating the surface of a pigment with a dispersant, there is a method in which an anionic polymer dispersant is supplied to a pigment dispersion liquid, and the anionic polymer dispersant is allowed to adhere to the pigment surface.

[0054] Methods for coating a pigment with a resin include a method in which an anionic monomer is supplied to a pigment dispersion and polymerized to coat the pigment surface, and a method in which the pigment is introduced into a solution of an anionic resin and the solvent is removed to coat the pigment surface.

[0055] When anionic groups are generated on the particle surface by chemical treatment of the pigment, the anionic groups are generated by a chemical reaction of the pigment. Examples of acidic groups introduced onto the pigment surface include sulfonic acid groups, phosphoric acid groups, carboxyl groups, and hydroxyl groups.

[0056] The chemical treatment for introducing anionic groups onto the pigment surface can be carried out by a gas phase method, a liquid phase method, or a combination of these methods.

[0057] In the case of oxidation treatment by a gas phase method, ozone or air is used as an oxidizing agent, and oxidation is carried out by bringing the oxidizing agent into contact with a pigment such as carbon black.

[0058] When oxidation treatment is performed by a liquid phase method, an oxidizing agent such as hydrogen peroxide, nitric acid, sulfuric acid, a chlorate, or a persulfate can be used. For example, a pigment having acidic groups on its surface can be obtained by adding the pigment to an aqueous solution containing the oxidizing agent and stirring the mixture. By controlling the amount of oxidizing agent used and the reaction temperature, acidic groups can be introduced uniformly onto the surface of a pigment such as carbon black.

[0059] Further examples of the method include a method in which an anionic group such as a sulfonic acid group, a phosphoric acid group, or a carboxyl group is introduced onto the surface of a pigment such as carbon black by a coupling reaction using a diazonium salt; a method in which an anionic group is introduced onto the surface of the pigment by contacting the pigment with free oxygen at high temperature; and a method in which an anionic group is introduced onto the surface of the pigment by treating the surface of the pigment with bromine and water under normal pressure or under pressure. <Anionic low-density particles>

[0060] The low-density particles used in the present invention are particles with a low apparent density that have a negative charge on the particle surface. As the low-density particles, organic or inorganic low-density particles can be used, and one type may be used alone, or two or more types may be used in combination.

[0061] The apparent density of low-density particles is 0.1 g / cm 3 ~1.4g / cm 3 It is preferable that the density is 0.1 g / cm 3 ~1.0g / cm 3 In the present invention, the apparent density is the mass of a particle relative to the volume that the particle occupies in a liquid, and is equal to the true density when the particle is a solid particle, but when the particle is a hollow particle, the volume occupied by the voids is not excluded from the particle volume.

[0062] Because the low-density particles have a low apparent density, when they are compounded with the composite colored particles by Coulomb force, they can reduce the apparent density of the entire composite colored particles, and as a result, can prevent the composite colored particles from settling in the ink composition.

[0063] Anionic low-density resin particles can be used as organic low-density particles. Anionic low-density resin particles are particles that have anionic properties on the particle surface and are made of a low-density resin. Examples of low-density resins that make up anionic low-density resin particles include polymers and copolymers containing olefins such as ethylene, propylene, or styrene. Examples of anionic groups include sulfonic groups, carboxyl groups, and phosphate groups.

[0064] The anionic low-density resin particles can be obtained, for example, by (co)polymerizing at least a portion of a monomer having an anionic group, or by coating at least a portion of the surface of the low-density resin particles with a material having an anionic group.

[0065] As the low-density resin particles, dense particles made of a low-density resin without voids can be used. In this case, the density (true density) of the low-density resin constituting the dense particles is preferably as low as possible, specifically, 1.4 g / cm. 3 Below, especially 1.0 g / cm 3 The following is preferred: As the dense particles, polyolefin-based resin particles are preferably used, with polyethylene-based particles and polypropylene-based particles being particularly preferred.

[0066] Furthermore, hollow resin particles are preferably used as low-density resin particles. Hollow resin particles are resin particles with a hollow structure having voids inside. The porosity of hollow resin particles is preferably 20% to 80%, more preferably 35% to 70%. When hollow particles are used, a low apparent density can be obtained, but if the apparent density is too low and the thickness of the shell layer constituting the particle becomes thin, the particles become more susceptible to breakage, making it difficult to stably obtain composite colored particles.

[0067] Examples of the structure of hollow resin particles include a core / shell structure. The thickness of the shell layer of the core / shell structure is preferably 10 nm or more and 20 nm or less, and more preferably 12 nm or more and 15 nm or less. When the shell layer of the hollow resin particles is 10 nm or more thick, the hollow structure is less likely to break, making it possible to obtain composite colored particles with a stable density. Furthermore, when the shell layer of the hollow resin particles is 20 nm or less thick, it is possible to obtain composite colored particles with a low density. The porosity of the hollow resin particles and the thickness of the shell layer of the core / shell structure are measured, for example, using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0068] Commercially available anionic hollow resin particles can be used as the low-density resin particles. Examples of commercially available products include styrene-acrylic resins under the trade name Ropeake OP-62 (average particle size: 450 nm, hollow ratio: 33%), Ropeake OP-84J (average particle size: 550 nm, hollow ratio: 20%, solid content: 42.5%), Ropeake OP-91, Ropeake HP-1055 (average particle size: 1,000 nm, hollow ratio: 55%), Ropeake HP-91 (average particle size: 1,000 nm, hollow ratio: 50%), and Ropeake ULTRA (average particle size: 380 nm, hollow ratio: 45%) (all manufactured by The Dow Chemical Company);

[0069] Examples of cross-linked styrene-acrylic resins include trade names SX-863(A), SX-864(B), SX-866(A), SX-866(B) (average particle size: 300 nm, hollow ratio: 30%), and SX-868 (average particle size: 500 nm) (all manufactured by JSR Corporation), and trade names Ropeake ULTRA E (average particle size: 380 nm, hollow ratio: 45%) and Ropeake ULTRA DUAL (average particle size: 380 nm, hollow ratio: 45%) (all manufactured by The Dow Chemical Company); and examples of modified styrene-acrylic resins include trade names Nipol MH5055 (average particle size: 500 nm) and Nipol MH8101 (average particle size: 1 μm) (all manufactured by Zeon Corporation).

[0070] The inorganic low-density particles are preferably hollow inorganic particles made of inorganic oxides having a hollow structure with unfilled voids inside, and particularly preferably hollow glass particles and hollow silica particles. The porosity of the hollow inorganic particles is preferably 20% to 80%, more preferably 35% to 70%.

[0071] As the low-density particles of the present invention, commercially available hollow inorganic particles to which anionic groups have been added can be used. Examples of commercially available low-density inorganic particles include silica particles having a hollow structure inside, such as Silinax (manufactured by Nittetsu Mining Co., Ltd.).

[0072] Anionic groups can be imparted to the surfaces of hollow glass particles by, for example, coating at least a portion of the surface of the commercially available hollow glass particles with a material such as a resin having anionic groups. Examples of anionic groups include sulfonic, carboxyl, and phosphate groups. <Complex>

[0073] In the present invention, composite colored particles can be produced by combining resin particles having a positive charge on their particle surfaces with colored particles and anionic low-density particles having a negative charge on their particle surfaces through Coulomb force. Figure 1 shows a schematic diagram of cationic resin particles, anionic colored particles, and anionic low-density particles combining through Coulomb force to form large composite colored particles.

[0074] 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 dispersion containing anionic colored particles and an emulsion containing anionic low-density particles.

[0075] The compounding ratio of the cationic resin particles to the anionic colored particles in the composite forming step is 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, as the mass ratio of cationic resin particles to anionic colored particles (excluding the aqueous medium, etc.). The compounding ratio of the cationic resin particles to the anionic low-density particles is 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, as the mass ratio of cationic resin particles to anionic low-density particles (excluding the aqueous medium, etc.).

[0076] In the composite forming step, a resin emulsion containing cationic resin particles, a dispersion containing anionic colored particles, and anionic low-density particles are prepared. Each emulsion and dispersion is preferably an aqueous emulsion in which particles are dispersed in an aqueous medium. The density of the aqueous medium used is preferably close to the density of the particles.

[0077] The medium of each aqueous emulsion is a mutually compatible water-soluble medium, preferably water, a water-soluble organic solvent, or a mixture thereof. The content of the aqueous medium in each aqueous emulsion is preferably 1 to 50% by mass, more preferably 3 to 30% by mass, and even more preferably 5 to 20% by mass, based on the total amount of the emulsion or dispersion.

[0078] Examples of water-soluble organic solvents that can be used include alkylene glycols, polyalkylene glycols, glycol ethers, monohydric or polyhydric alcohols such as acetin and diacetin, lactams such as ε-caprolactam, 2-pyrrolidone and N-methylpyrrolidone, lactones such as ε-caprolactone and δ-valerolactone, and sulfoxides such as dimethyl sulfoxide.

[0079] Among the above-mentioned water-soluble organic solvents, polyhydric alcohols and lactams are preferred, specifically propylene glycol, 1,3-butanediol, 1,2-hexanediol, 3-methoxy-3-methyl-1-butanol, 3-methoxy-1-butanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-butoxy-2-propanol, triethylene glycol monobutyl ether, and 2-pyrrolidone, which may be used alone or in combination of two or more.

[0080] Next, the cationic resin particle emulsion is mixed with an anionic color particle dispersion and an anionic low-density particle emulsion. The order of mixing is arbitrary, but it is preferable to mix the resin emulsion containing cationic resin particles with the dispersion containing anionic color particles, and then mix this with the emulsion containing anionic low-density particles. The anionic color particle dispersion and the anionic low-density particle emulsion can be mixed with the cationic resin particle emulsion separately, but it is also preferable to mix the anionic color particle dispersion and the anionic low-density particle emulsion in advance and then mix them with the cationic resin particle emulsion.

[0081] The emulsions can be mixed by placing each emulsion in a container equipped with a stirring device such as a mechanical stirrer or a magnetic stirrer, and stirring the mixture. At this time, components required to form the ink composition may be added.

[0082] In the composite process, the cationic resin particles, anionic colorant particles, and anionic low-density particles contained in each emulsion or dispersion are electrostatically bonded by Coulomb force to effectively form large-sized composite colorant particles. The composite colorant particles obtained in this manner contain very little colorant fine particles with a particle size of less than 0.1 μm, which is effective in achieving the effects of the present invention.

[0083] 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, for example. 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.

[0084] 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 composite color particles can be controlled by adjusting the stirring conditions used to break down the aggregates. The above-described method for producing composite colored particles can be successfully implemented industrially.

[0085] 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 with a dispersion containing colored particles having a negative charge on the particle surface and a dispersion containing low-density particles, and then a deagglomeration step of breaking down the aggregates produced in the compounding step.

[0086] The particle diameter of the composite colored particles of the present invention is preferably such that at least 95% of the particles have a particle size in the range of 0.2 μm to 3.0 μm, more preferably such that at least 95% of the particles have a particle size 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 preferably less than 3%, more preferably less than 1%, in terms of particle frequency.

[0087] The apparent density of the composite colored particles of the present invention is 0.6 g / cm 3 ~1.8g / cm 3 and preferably 0.7 g / cm 3 ~1.4g / cm 3 More preferably, it is 0.8 g / cm 3 ~1.2g / cm 3 The apparent density of the composite colored particles can be measured, for example, by the method of Z8807:2012.

[0088] <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, an anti-rust agent, a preservative, an antibacterial agent, a lubricant, and a solvent as a dispersion medium.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] <Dispersion medium> The aqueous ink composition contains an aqueous medium as a dispersion medium to stabilize the dispersion state of the composite colored particles and ensure usability as an ink for a writing instrument. 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.

[0095] As the dispersion medium, a hydrophilic dispersion medium consisting of water such as tap water, purified water, distilled water, or ion-exchanged water, a water-soluble organic solvent, or a mixed solution thereof can be used, and preferably, a mixed solution consisting of water and at least one water-soluble organic solvent can be used.

[0096] Examples of water-soluble organic solvents that can be used in the aqueous medium 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.

[0097] 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, , aqueous ink composition This can prevent the occurrence of aggregation over time.

[0098] 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).

[0099] The density of the aqueous medium is preferably close to the apparent density of the composite colored particles to be blended. Specifically, it is 0.6 g / cm 3 ~1.8g / cm 3 , more preferably 0.7 g / cm 3 ~1.4g / cm 3 , and more preferably 0.8 g / cm 3 ~1.2g / cm3 Combining an aqueous medium having a similar density with the composite colored particles is suitable for preventing the colored particles from settling and separating in the ink during storage, and for obtaining an aqueous ink composition for a writing instrument that has excellent dispersion stability over time.

[0100] 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 mixer such as a homomixer or a disper, etc. If necessary, coarse particles in the aqueous ink composition may be removed by filtration or centrifugation.

[0101] <Writing instruments> The aqueous ink composition of the present invention is used by being mounted on a felt-tip pen or marking pen having a fiber tip, felt tip, or plastic tip at the writing tip, or a ballpoint pen having 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 of being excellent in dispersion stability and writing performance. [Example]

[0102] 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.

[0103] <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. (Resin Particles A-1) As the cation-modified vinyl acetate resin, a cation-modified vinyl acetate resin emulsion (Viniblan 1008, manufactured by Nissin Chemical Industry Co., Ltd.) was used. (Resin Particles A-2) As the cation-modified acrylic resin, a cation-modified polyvinyl alcohol-acrylic resin emulsion (Movinyl 6950; manufactured by Japan Coating Resin Co., Ltd.) was used. (Resin Particles A-3) As the cation-modified urethane resin, a cation-modified urethane emulsion (Superflex 620, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was used. (Resin Particles A-4) For comparison, an emulsion of a nonionic modified vinyl acetate resin (Viniblan 1002; manufactured by Nissin Chemical Industry Co., Ltd.) was used.

[0104] <Colored particles> As the anionic colored particles, colored resin dispersions in which anionic colored particles obtained by the methods of Preparation Examples 1 to 3 below were dispersed in an aqueous medium were used.

[0105] Preparation example 1 (colored particles B-1) A 2-liter flask was equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas inlet tube, and a 1000-ml separatory funnel for introducing monomers, and was placed in a warm water bath. 329.5 parts of distilled water, 5 parts of glycerin monomethacrylate (manufactured by NOF Corporation, Blenmer GLM), 5 parts of sodium 2-sulfoethyl methacrylate (manufactured by Mitsubishi Chemical Corporation, acrylic ester SEM-Na), 20 parts of a polymerizable surfactant (manufactured by ADEKA Corporation, ADEKA REASOAP SE-10N, ether sulfate), and 0.5 parts of ammonium persulfate were then charged, and the internal temperature was raised to 50°C while introducing nitrogen gas.

[0106] 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 as another monomer with 40 parts of a metal complex oil-soluble dye (Suninyl Blue GLS, manufactured by Clariant Co., Ltd.) and 10 parts of triallyl isocyanurate (TAIC, manufactured by Nippon Kasei Co., Ltd.) as a crosslinking agent. This prepared solution was added from the separatory funnel to the flask maintained at about 50°C 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 anionic resin dye particles B-1 made of anionic resin encapsulating a dye.

[0107] The anionic dye particles thus obtained had a measured zeta potential of −58 mV, indicating anionic properties, and an average particle size of 0.04 μm.

[0108] Preparation example 2 (colored particles C-1) Ion-exchanged water, water-soluble organic solvent, viscosity modifier, pH adjuster, dispersant, and pigment were added to a vessel in the above-mentioned ratio, premixed for 2 hours with a stirrer, dispersed in a 1 mm zirconia bead mill, centrifuged to remove impurities, and then filtered under reduced pressure using a microfilter (pore size 5.0 μm; manufactured by Millipore Corporation) to obtain an emulsion of anionic resin-modified carbon black particles (C-1) with a pH of 8.9. The anionic resin-modified pigment particles C-1, consisting of anionic resin-modified carbon black, had an average particle size of 0.1 μm.

[0109] Pigment: Carbon black (MCF88; manufactured by Mitsubishi Chemical Corporation) 10% by mass Dispersant: 10% by mass of α-methylstyrene-acrylic copolymer (Joncryl 61J, manufactured by Johnson & Johnson, 30% by mass aqueous solution) pH adjuster: aminomethylpropanol 0.1% by mass Viscosity modifier: Polyvinylpyrrolidone 5% by mass Water-soluble organic solvent: propylene glycol monoethyl ether 5% by mass Ion-exchanged water 69.9% by mass

[0110] Preparation example 3 (colored particles C-2) Anionic pigment particles C-2, whose surfaces are anionically modified, were prepared using an emulsion of self-dispersing carbon black (product name CAB-O-JET200; manufactured by Cabot Specialty Corporation), in which acidic groups were attached to the surface of the carbon black.

[0111] <Low density particles> As the anionic low-density particles, low-density particle emulsions in which anionic low-density particles obtained by the methods of Preparation Examples 4 to 6 below were dispersed in an aqueous medium were used.

[0112] Preparation example 4 (low density particles D-1) As low-density particles D-1 made of anionic dense resin particles, anionic dense modified polyethylene resin particles (trade name Chemipearl A-100, manufactured by Mitsui Chemicals, Inc., density 0.89 g / cm) were used. 3 An emulsion of 40% solids was prepared.

[0113] Preparation example 5 (low density particles D-2) To prepare low-density particles D-2 made of anionic hollow resin, an emulsion of hollow crosslinked modified styrene-acrylic resin particles with anionic properties (product name: Ropeake ULTRA E, manufactured by Dow Chemical Company, hollowness: 45%, refractive index: 1.6, volume average particle size: 500 nm) with a solids concentration of 30% was prepared.

[0114] Preparation example 6 (low density particles D-3) As low-density particles D-3 made of anionic hollow inorganic material, hollow microspheres made of silica particles with a hollow structure (product name: Silinax, manufactured by Nittetsu Mining Co., Ltd.; apparent density: 0.13 g / cm) were used. 3 , particle diameter (median diameter) 130 nm, glass thickness 15 nm) were used and mixed in the following composition to adsorb an anionic dispersant, thereby producing an emulsion of anionic modified low-density particles D-3 having a solids concentration of 30 mass %.

[0115] Micro hollow spheres (product name: Silinax, manufactured by Nittetsu Mining Co., Ltd.) 8% by mass Joncryl 63J (BASF JAPAN) 6% by mass Bioden S (Nippon Soda Co., Ltd.) 0.2% by mass Triethanolamine 1.4% by mass Propylene glycol 15% by mass, distilled water, balance

[0116] Examples 1 to 5, Comparative Examples 1 to 2 The anionic colored particle emulsions B-1, C-1, and C-2 prepared in Preparation Examples 1 to 3 were added to the various cationic resin particle emulsions A-1 to A-4 in the combinations and mass ratios (mass ratio of solids) shown in Table 1, and then the anionic low-density particle emulsions D-1 to D-3 prepared in Preparation Examples 4 to 6 were added (or not added) and mixed using a stirrer to obtain aqueous dispersions R-1 to R-7. Next, the mixture was deagglomerated by vigorous stirring using a homomixer to obtain composite colored particles P-1 to P-5 containing anionic low-density particles as examples, and composite colored particles Q-1 and Q-2 not containing anionic low-density particles as comparative examples, all in the form of aqueous dispersions with a solids concentration of 20 mass%.

[0117] Furthermore, the particle size frequency distribution was measured for the composite colored particles prepared in Examples 1 to 5 and Comparative Examples 1 and 2 after the deagglomeration operation, 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.

[0118] The particle size distributions of the cationic resin particles, cationic low-density resin particles, and 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.).

[0119] [Table 1]

[0120] [Table 2]

[0121] Examples 11 to 19 and Comparative Examples 11 to 12 Using emulsions of composite colored particles P-1 to P-5 as examples and Q-1 to Q-2 as comparative examples, pH adjusters, thickeners, lubricants, rust inhibitors, preservatives, and dispersants were blended and mixed in the combinations and weight ratios shown in Table 3, and some aggregates were removed to prepare dispersions of aqueous ink compositions.

[0122] The ink compositions of Examples 11 to 19 are aqueous ink compositions of the present invention. The ink composition of Comparative Example 11 is an example in which cationic resin particles are not used, and the ink composition of Comparative Example 12 is an example in which anionic low-density particles are not used.

[0123] [Evaluation of aqueous ink compositions for writing instruments] [Making a ballpoint pen] Ballpoint pens were prepared using the aqueous ink compositions obtained in Examples 1 to 5 and Comparative Examples 1 to 5. Specifically, refills were prepared consisting of a transparent polypropylene ink reservoir (inner diameter 3.8 mm, length 113 mm) and a stainless steel tip equipped with a 0.5 mm diameter cemented carbide ball, and 0.8 g of each aqueous ink composition was filled into each refill. The rear end of the ink reservoir was filled with an ink follower whose main component was mineral oil. The resulting refills were loaded into the barrel of a ballpoint pen (manufactured by Mitsubishi Pencil Co., Ltd., product name: Signo UM-100) to prepare the ballpoint pen.

[0124] <Evaluation of Ink Composition> Using each of the ballpoint pens of the above-mentioned Examples and Comparative Examples, the dispersion stability and writing properties were evaluated by the following evaluation methods.

[0125] (1) Evaluation of dispersion stability Each ballpoint pen was capped, stood upright with the nib facing downwards, and left to stand in a room at 25°C for 60 days, after which the refill was removed and the state of the filled ink was observed and evaluated. Dispersion stability evaluation criteria: A: No aggregates were observed in any part of the refill. B: A small amount of agglomerates was observed on the surface or bottom of the refill. C: Large aggregates were found on the surface or bottom of the refill.

[0126] (2) Evaluation of writability Each ballpoint pen was placed vertically with the tip facing downwards with the cap on and left to stand in a room at 25°C for 60 days, after which the handwriting was evaluated by writing on writing paper A conforming to the old JISP3201 using a writing tester conforming to ISO standard 141415-1. The writing conditions were a temperature of 20°C, a pen angle of 70 degrees, a pen tip load of 100 g, and a writing speed of 4 m / min. Handwriting evaluation criteria: A: No smearing or cracking of handwriting was observed. B: Blurred handwriting and cracks were observed in some areas. C: The handwriting was noticeably blurred and cracked.

[0127] (3) Evaluation of bleeding resistance Using the ballpoint pen prepared above, a straight line was drawn on PPC paper at 25°C and 60% RH with a load of 100 g and a writing angle of 60°. At the final point, the tip of the ballpoint pen was held on the PPC paper for 10 seconds without removing it from the paper, and then the ballpoint pen was removed from the paper. The maximum diameter of the ink remaining on the paper at the final point was measured with a magnifying glass. The smallness of the measured diameter was taken as the degree of contact DC, and the bleed resistance was evaluated according to the following evaluation criteria. Evaluation criteria: A: The diameter of the ink on the paper is less than 1.0 mm B: The diameter of the ink on the paper is 1.0 mm or more and less than 2.0 mm C: The diameter of the ink on the paper is 2.0 mm or more

[0128] The evaluation results are shown in Table 3. In Examples 11 to 19, the aqueous ink compositions containing the composite colored particles of the present invention exhibited good dispersion stability and writing properties.

[0129] [Table 3] [Industrial Applicability]

[0130] An ink composition containing the composite colored particles of the present invention can be suitably used in writing instruments such as felt-tip pens, marking 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]

[0131] 1. Colored particles with negative charges on the particle surface 2 Low density particles with negative charges on the particle surface 3. Resin particles with positive charges on the particle surface

Claims

1. Composite colored particles comprising resin particles having a positive charge on the particle surface, colored particles having a negative charge on the particle surface, and low-density particles having a negative charge on the particle surface and an apparent density of 0.1 g / cm 3 to 1.0 g / cm 3 , wherein the low-density particles are low-density resin particles modified with an anionic functional group, hollow resin particles, or hollow inorganic particles, and the colored particles and low-density particles are composited with the resin particles by Coulomb force.

2. The apparent density of the composite colored particles is 0.6 g / cm ３ ~1.8g / cm ３ 2. The composite colored particle according to claim 1, wherein

3. 3. The composite colored particles according to 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.

4. 4. The composite colored particles according to claim 1, wherein the low-density particles are hollow resin particles or hollow inorganic particles.

5. 4. The composite colored particles according to claim 1, wherein the low-density particles are made of a polymer or copolymer containing an olefin modified with an anionic functional group.

6. 6. The composite colored particles according to claim 1, wherein the resin particles having a positive charge on the particle surface are particles made of a polymer modified with a cationic group.

7. 7. The composite colored particles according to claim 1, wherein the colored particles having a negative charge on the particle surface are made of fine particles of a pigment or a colorant-containing resin modified with an anionic functional group.

8. The composite colored particles according to any one of claims 1 to 7, wherein the colored particles having a negative charge on the particle surface are particles in which a dye is encapsulated inside or on the surface of at least one anionic resin selected from the group consisting of an acrylic resin, a urea resin, a urethane resin, and a urea-urethane resin, each of which has anionic properties.

9. 9. An ink composition comprising the composite colored particles according to claim 1 dispersed in a medium.

10. A writing instrument equipped with the ink composition according to claim 9.

11. A method for producing composite colored particles in which the colored particles and the low-density particles are composited with the resin particles by Coulomb force, the method comprising a composite step of mixing a resin emulsion containing resin particles having a positive charge on the particle surface with a dispersion containing colored particles having a negative charge on the particle surface and an emulsion containing low-density particles having an apparent density of 0.1 g / cm 3 to 1.0 g / cm 3.

12. The method for producing composite colored particles according to claim 11, further comprising a deagglomeration step of crushing aggregates.

13. 13. The method for producing composite colored particles according to claim 11, wherein at least 95% of the composite colored particles have a particle size within the range of 0.2 μm to 3.0 μm.

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