Water-based ink composition for writing instruments

Abstract

To provide an aqueous ink composition for writing instruments that has a pigment-containing colored resin particle to prevent the falling of a pigment, so that the clogging of an ink channel is prevented and the writing feel is improved.SOLUTION: An aqueous ink composition for writing instruments has a colored resin particle at least having a pigment and a synergist.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aqueous ink composition for a writing instrument, which contains colored resin particles encapsulating a pigment. [Background technology]

[0002] Conventionally, many attempts have been made to use resin particles containing pigments as coloring agents in inks for writing instruments. Conventionally, examples of colored resin particles containing this pigment include an ink composition for a writing instrument in which the colorant is a composite particle of spherical resin particles and a pigment (see, for example, Patent Document 1), and an ink composition for a writing instrument containing a pigment coated with a resin (see, for example, Patent Document 2).

[0003] Furthermore, known methods for producing colored resin particles encapsulating a pigment include a method for producing a pigment composition (colored resin particles) comprising a first step of mixing a crude pigment or a ground crude pigment obtained by dry-grinding the crude pigment, an alkali salt of a carboxyl group-containing acrylic resin, and water and / or an aqueous solvent, a second step of mechanically dispersing the mixture obtained in the first step, a third step of adding an acid to the dispersion obtained in the second step to precipitate a resin on the pigment, and a fourth step of adding an alkali to the precipitate obtained in the third step to re-neutralize it (see, for example, Patent Document 3).

[0004] However, such coloring agents composed of colored resin particles containing pigments often suffer from the pigment falling off in the writing instrument ink composition or during use or storage of the writing instrument in which the ink composition is mounted. This fallen pigment can cause problems such as clogging of the ink flow path and a gradual deterioration in the writing feel. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 63-218778 A (claims, examples, etc.) [Patent Document 2] JP 2003-268287 A (Claims, Examples, etc.) [Patent Document 3] JP-A-9-217019 (Claims, Examples, etc.) Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the above-mentioned problems of the conventional technology and aims to solve them, and has an object to provide an aqueous ink composition for writing instruments that contains colored resin particles encapsulating a pigment that is less likely to fall off, thereby preventing clogging of the ink flow path and providing a good writing feel. [Means for solving the problem]

[0007] In view of the above-mentioned problems in the prior art, the present inventors conducted intensive research and discovered that the above-mentioned aqueous ink composition for use in writing instruments can be obtained by incorporating a synergist (pigment derivative) in colored resin particles containing a pigment, thereby completing the present invention.

[0008] That is, the aqueous ink composition for a writing instrument of the present invention is characterized by containing colored resin particles that contain at least a pigment and a synergist. The synergist / pigment mass ratio is preferably 0.01 to 0.2. The resin component of the colored resin particles is preferably a urethane-based resin. Effect of the Invention

[0009] According to the present invention, there is provided an aqueous ink composition for a writing instrument which does not clog ink flow paths and has a good writing feel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described in detail. The aqueous ink composition for a writing instrument of the present invention is characterized by containing colored resin particles that contain at least a pigment and a synergist.

[0011] <Pigments> There is no particular limitation on the type of pigment that can be used, and any of the inorganic and organic pigments commonly used in aqueous ink compositions for writing instruments can be used. Examples of inorganic pigments include carbon black, titanium oxide, zinc oxide, iron oxide, chromium oxide, and ultramarine. Examples of organic pigments include azo lakes, insoluble azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dye lakes, nitro pigments, and nitroso pigments. These may be used alone or in combination of two or more.

[0012] The content of these pigments in the colored resin particles is preferably from 5 to 40% by mass, more preferably from 10 to 35% by mass, and particularly preferably from 15 to 25% by mass. If the pigment content is less than 5% by mass, the coloring power may be insufficient and the visibility of the drawn lines may decrease, whereas if it exceeds 40% by mass, the amount of pigment may be excessive, resulting in poor color reproducibility.

[0013] <Synergist> The synergist (pigment derivative) used in the present invention is used to facilitate the incorporation of the pigment into the resin particles during the formation of the colored resin particles, and to prevent the pigment from falling off from the colored resin particles, and is a derivative having the same structure as the pigment, and is a compound having a strong interaction with the pigment. In addition, the synergist also has a strong interaction with the dispersant described below, which is preferably used during the preparation of the colored resin particles. By containing at least a pigment and a synergist in the colored resin particles, the synergist has a similar structure (common skeleton) to the pigment and is therefore adsorbed to the pigment surface, and the synergist is also adsorbed to the resin of the colored resin particles, making it easier for the pigment to enter the resin particles and less likely to fall off. The interaction of such synergists is said to be van der Waals force, and it is assumed that strong and practical adsorption can be achieved because it acts on the entire flat and wide surface of the pigment skeleton. Incidentally, synergists are usually used as a dispersion aid for pigments in liquid media, but in the present invention, the effects of the present invention can only be achieved by incorporating synergists together with the pigments in the colored resin particles to be formed.

[0014] The synergist that can be used may be an optimum synergist depending on the pigment used. For example, a commercially available synergist for the color of the pigment, specifically carbon black, yellow pigment, azo pigment, or phthalocyanine pigment, may be used. Examples of such commercially available synergists having an acidic functional group include Solsperse 5000 (phthalocyanine pigment derivative), Solsperse 12000 (phthalocyanine pigment derivative), and Solsperse 22000 (azo pigment derivative) manufactured by Lubrizol Corporation, BYK-SYNERGIST 2100 (phthalocyanine pigment derivative), BYK-SYNERGIST 2105 (yellow pigment derivative) manufactured by BYK-Chemie Japan, and EFKA6745 (phthalocyanine pigment derivative) manufactured by BASF Japan Ltd. anine pigment derivative), EFKA6750 (azo pigment derivative), Synergist Yello-8020, 8404, 9043, 4827 (yellow pigment derivative), Synergist Red-3953, 4327, 4474, 4858, 4966, 5507, 5525, 5909, 6006, 6547 (azo pigment derivative), Synergist Blue-6831, 7215, 7438, 7854, 0785, 0785A (phthalocyanine pigment derivative), Synergist Violet-6965, 7349, 7572, 7988 (phthalocyanine pigment derivative), and the like manufactured by Dispersion Materials Research Institute. These may be used alone or in combination of two or more.

[0015] The content of these synergists in the colored resin particles varies depending on the type of pigment used and the amount used, and in order to favorably exert the effect of the synergist and the effect of the present invention, it is preferable that the pigment and synergist used are in a certain blend ratio, and the mass ratio of synergist / pigment is preferably 0.01 to 0.2, more preferably 0.05 to 0.15. If the mass ratio of synergist / pigment is less than 0.01, the effect of preventing the pigment from falling off in the colored resin particles may be weakened, while if the mass ratio exceeds 0.2, the pigment may aggregate in the colored resin particles, resulting in poor writing feel.

[0016] <Colored resin particles> The colored resin particles of the present invention can be composed of a microencapsulated pigment containing at least the above-mentioned pigment and synergist, and can be produced, for example, by microencapsulating at least the above-mentioned pigment and synergist to a predetermined particle size, specifically, by encapsulating the particles in a shell layer (shell body) composed of a wall-forming substance (wall material). Examples of the microencapsulation method include an interfacial polymerization method, an interfacial polycondensation method, an in situ polymerization method, a liquid hardening coating method, a phase separation method from an aqueous solution, a phase separation method from an organic solvent, a melting dispersion cooling method, an air suspension coating method, and a spray drying method.

[0017] From the standpoint of ease of preparation and quality, the resin component (shell component) constituting the microcapsules is preferably a thermosetting resin such as epoxy resin, urethane, urea, or urea-urethane, and particularly preferably a urethane-based resin such as urethane, urea, or urea-urethane, because it is possible to increase the amount of components encapsulated, there are fewer restrictions on the types of encapsulated components, and they have excellent redispersibility. The urethane (polyurethane resin), urea (polyurea resin), and urea-urethane (polyurea resin / polyurethane resin) used to form the shell layer are formed by reaction between an isocyanate component and an amine component or an alcohol component, etc. The epoxy resin used to form the shell layer is formed by reaction with a curing agent such as an amine component, etc.

[0018] Examples of isocyanate components that can be used include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, polymeric diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, 3,3'-dimethyldiphenyl-4,4'-diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, transcyclohexa 1,4-diisocyanate, diphenyl ether diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, 2,6-diisocyanate caproic acid, tetramethyl-m-xylylene diisocyanate, tetramethyl-p-xylylene diisocyanate, trimethylhexamethylene diisocyanate, triphenylmethane triisocyanate, tris(isocyanatophenyl)thiophosphate, isocyanate alkyl 2,6-diisocyanatocapronate, 1,6,11-undecane triisocyanate 1,8-diisocyanate-4-isocyanate methyl octane, 1,3,6-hexamethylene triisocyanate, and bicycloheptane triisocyanate. Also, m-phenylene diisocyanate, p-phenylene diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate, naphthalene-1,4-diisocyanate, diphenylmethane-4,4'-diisocyanate, 3,3'-dimethoxy-4,4-biphenyl-diisocyanate, 3,3'-dimethylphenylmethane-4,4'-diisocyanate, xylylene-1,4-diisocyanate, 4,4'-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, cyclohexylene-1,2- Examples of the isocyanate include diisocyanates such as cyclohexylene-1,4-diisocyanate, triisocyanates such as 4,4',4''-triphenylmethane triisocyanate and toluene-2,4,6-triisocyanate, tetraisocyanates such as 4,4'-dimethyldiphenylmethane-2,2',5,5'-tetraisocyanate, and isocyanate prepolymers such as an adduct of hexamethylene diisocyanate and trimethylolpropane, an adduct of 2,4-tolylene diisocyanate and trimethylolpropane, an adduct of xylylene diisocyanate and trimethylolpropane, and an adduct of tolylene diisocyanate and hexanetriol. These isocyanate components may be used alone or in combination.

[0019] Specific examples of the amine component that can be used include aliphatic amines such as ethylenediamine, hexamethylenediamine, diaminocyclohexane, piperazine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, iminobispropylamine, diaminoethyl ether, 1,4-diaminobutane, pentamethylenediamine, 2-methylpiperazine, 2,5-dimethylpiperazine, 2-hydroxytrimethylenediamine, diethylaminopropylamine, diaminopropylamine, diaminopropane, 2-methylpentamethylenediamine, and xylenediamine, m-phenylenediamine, triaminobenzene, 3,5-tolylenediamine, diaminodiphenylamine, diaminonaphthalene, t-butyltoluenediamine, diethyltoluenediamine, and diaminophenol. Among these, aromatic amines such as phenylenediamine, diaminophenol, and triaminobenzene are preferred.

[0020] Specific examples of the alcohol component that can be used include polyols having two or more hydroxyl groups, such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, glycerin, catechol, resorcinol, and hydroquinone. These alcohol components may be used alone or in combination. Furthermore, an alcohol component and an amine component may be used in combination.

[0021] The shell layer can be formed by, for example, 1) dispersing at least one monomer component of urethane, urea, or urethane urea and a pigment component to form a shell layer by interfacial polymerization, or 2) by a production method including an emulsification step of dispersing an oily component (oil phase) containing an isocyanate component in a water-based solvent (aqueous phase) to prepare an emulsion, and an interfacial polymerization step of adding at least one of an amine component and an alcohol component to the emulsion to perform interfacial polymerization.

[0022] In the above-mentioned manufacturing method 2), a solvent can be used when preparing the emulsion. For example, phenyl glycol, benzyl alcohol, ethylene glycol monobenzyl ether, ethyl acetate, alkylsulfonic acid phenyl ester, ethylhexyl phthalate, Examples of the resin that can be used include tridecyl phthalate, ethylhexyl trimellitate, diethylene glycol dibenzoate, dipropylene glycol dibenzoate, liquid xylene resin, etc. These may be used alone or in combination. On the other hand, the aqueous phase used to emulsify the oily phase may contain a protective colloid in advance. As the protective colloid, a water-soluble polymer can be used, which can be appropriately selected from known anionic polymers, nonionic polymers, and amphoteric polymers, but it is particularly preferable to add polyvinyl alcohol, gelatin, and a cellulose-based polymer compound. The aqueous phase may contain a surfactant. The surfactant may be appropriately selected from anionic or nonionic surfactants that do not react with the protective colloid to cause precipitation or aggregation. Preferred surfactants include sodium alkylbenzenesulfonate (e.g., sodium lauryl sulfate), dioctyl sodium sulfosuccinate, polyalkylene glycol (e.g., polyoxyethylene nonylphenyl ether), and the like. The oily phase prepared as above is added to the aqueous phase, emulsified by mechanical force, and then the temperature of the system is increased as necessary to cause interfacial polymerization at the interface of the oily droplets, which can be turned into particles. In addition, desolvation can be performed simultaneously or after the end of the interfacial polymerization reaction. Capsule particles can be obtained by separating the particles from the aqueous phase after the interfacial polymerization reaction and desolvation, washing them, and then drying them.

[0023] The epoxy resin used to form the shell layer is formed by reacting with a curing agent such as an amine component, and can be formed by using any of the above-mentioned microencapsulation methods, for example, by interfacial polymerization. The epoxy resin that can be used is an epoxy resin having two or more epoxy groups in one molecule, and can be generally used without being limited by molecular weight, molecular structure, etc., and examples thereof include aromatic epoxy resins such as bisphenol A type epoxy resins such as bisphenol A diglycidyl ether type epoxy resins, bisphenol F type epoxy resins, novolac type epoxy resins, cresol novolac type epoxy resins, and biphenyl type epoxy resins, naphthalene type multifunctional epoxy resins, polycarboxylic acid glycidyl ether type epoxy resins, polycarboxylic acid glycidyl ester type epoxy resins, cyclohexane polyether type epoxy resins, cyclohexane derivatives such as hydrogenated bisphenol A type epoxy resins, and alicyclic epoxy resins such as dicyclopentadiene type epoxy resins, which can be used alone or in combination of two or more kinds.

[0024] In the present invention, when the colored resin particles are formed, it is preferable to use a dispersant together with the pigment and synergist. Examples of dispersants that can be used include AJISPER PB821, AJISPER PB822, and AJISPER PB711 (all manufactured by Ajinomoto Fine-Techno Co., Ltd.), DISPARLON DA-705, DISPARLON DA-325, DISPARLON DA-725, DISPARLON DA-703-50, and DISPARLON DA-234 (manufactured by Kusumoto Chemicals Co., Ltd.), DISPERBYK-111, DISPERBYK-2000, DISPERBYK-2001, and DI SPERBYK-2020, DISPERBYK-2050, DISPERBYK-215 0 (manufactured by BYK-Chemie Japan), EFKA4010, EFKA4009, EFKA4015, EFKA4047, EFKA4050, EFKA4055, EFKA4060, EFKA4080, EFKA4520 (manufactured by BASF Japan), TEGO Dispers 655, TEGO Dispers 685, TEGO Dispers 690 (manufactured by Evonik Japan), and other commonly known dispersants that are commercially available can also be used, and the dispersants are not limited to the above examples. The content of these dispersants in the colored resin particles varies depending on the type of pigment and synergist used, and the synergistic effect of the pigment and synergist and the effect of the present invention are preferably exhibited. From the viewpoint of stability, the content is preferably from 2 to 20 mass %, and more preferably from 3 to 15 mass %.

[0025] In the present invention, by forming a shell layer by each of the above-mentioned forming means, colored resin particles comprising at least a pigment and a microencapsulated pigment encapsulating a synergist can be obtained. In the present invention, the contents of at least the pigment and synergist vary depending on the dispersibility, specific gravity, and particle size that can be arbitrarily controlled, color development, etc., but the above-mentioned aqueous phase components (water, PVA) and oil phase components (solvent) used in the production do not substantially remain when the colored resin particles are formed. Therefore, by adjusting each of the raw materials (pigment, synergist, dispersant, resin component, etc.) used in the production of the colored resin particles to within a suitable range, and polymerizing the above-mentioned pigment, synergist, dispersant, and resin component (remainder), colored resin particles in which each component is within the above-mentioned predetermined preferred range can be obtained. In the present invention, the colored resin particles composed of the microcapsule pigment containing at least the above-mentioned pigment and synergist can be adjusted to a predetermined average particle size, for example, an average particle size of 0.1 to 30 μm, depending on the application of the writing instrument (ballpoint pen, marking pen), and preferably, the range of 0.5 to 20 μm satisfies the practicality of each of the above-mentioned applications. In the present invention (including the examples described later), the "average particle size" refers to the particle size (D50) at 50% cumulative volume in the particle size distribution calculated based on the volume standard measured by the laser diffraction method. Here, the measurement of the average particle size by the laser diffraction method can be performed using, for example, a particle size distribution analyzer HRA9320-X100 manufactured by Nikkiso Co., Ltd.

[0026] <Water-based ink composition for writing instruments> The aqueous ink composition for writing instruments of the present invention is characterized by containing at least the colored resin particles having the above-mentioned composition, i.e., colored resin particles containing at least a pigment and a synergist, and is used as an ink composition for writing instruments such as aqueous ballpoint pens and marking pens. In the present invention, the content of the colored resin particles having the above characteristics is preferably 3 to 24% by mass, and more preferably 10 to 20% by mass, based on the total amount of the aqueous ink composition for writing instruments. If the content of the colored resin particles is less than 3% by mass, the coloring power will be insufficient and the visibility of the written lines will be reduced. On the other hand, if the content exceeds 24% by mass, the viscosity will increase, which may reduce the fluidity of the ink, which is not preferable.

[0027] The water-based ink composition for a writing instrument of the present invention contains, in addition to the colored resin particles having the above-mentioned characteristics, at least a general-purpose colorant other than the colored resin particles having the above-mentioned characteristics, and a water-soluble solvent. Usable colorants include water-soluble dyes, pigments within the range that does not impair the effects of the present invention, such as inorganic pigments, organic pigments, plastic pigments, hollow resin particles having voids inside the particles as white pigments, and resin particles dyed with basic dyes (pseudo pigments) that have excellent color development and dispersibility, which can be used in appropriate amounts. As the water-soluble dye, any of direct dyes, acid dyes, food dyes and basic dyes can be used in an appropriate amount within a range that does not impair the effects of the present invention.

[0028] Examples of the water-soluble solvent that can be used include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, and glycerin, as well as ethylene glycol monomethyl ether and diethylene glycol monomethyl ether, which can be used alone or in combination. The content of the water-soluble solvent is preferably 5 to 40% by mass of the total amount of the aqueous ink composition for writing instruments.

[0029] The aqueous ink composition for a writing instrument of the present invention may contain, in addition to the colored resin particles having the above-mentioned characteristics, a colorant other than the colored resin particles, and a water-soluble solvent, the remainder being water as a solvent (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.), as well as dispersants, lubricants, pH adjusters, rust inhibitors, preservatives or antibacterial agents, thickeners, and the like, as appropriate, within the scope of the effects of the present invention.

[0030] Usable dispersants include nonionic and anionic surfactants and water-soluble resins, and preferably water-soluble polymers. The polymer dispersant is not particularly limited, and any known polymer dispersant may be used, and any polymer dispersant obtained from known materials and methods may be used. Examples of the lubricant include nonionic lubricants such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, polyoxyalkylene higher fatty acid esters, and alkyl phosphates, which are also used as surface treatment agents for pigments; anionic lubricants such as alkyl sulfonates and alkyl aryl sulfonates of higher fatty acid amides; derivatives of polyalkylene glycols, fluorine-based surfactants, and polyether-modified silicones.

[0031] Examples of pH adjusters include ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, alkali metal salts of carbonates and phosphoric acids such as sodium tripolyphosphate and sodium carbonate, and hydrates of alkali metals such as sodium hydroxide. Examples of rust inhibitors include benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, and saponins, while examples of preservatives or antibacterial agents include phenol, sodium omadine, sodium benzoate, thiazoline compounds, and benzimidazole compounds. Examples of thickeners include carboxymethylcellulose (CMC) or its salts, fermented cellulose, crystalline cellulose, polysaccharides, etc. Examples of polysaccharides that can be used include xanthan gum, guar gum, hydroxypropylated guar gum, casein, gum arabic, gelatin, amylose, agarose, agaropectin, arabinan, curdlan, callose, carboxymethyl starch, chitin, chitosan, quince seed, glucomannan, gellan gum, tamarind seed gum, dextran, nigeran, hyaluronic acid, pustulan, funoran, HM pectin, porphyran, laminaran, lichenan, carrageenan, alginic acid, tragacanth gum, alkaloid gum, succinoglycan, locust bean gum, tara gum, etc., and these may be used alone or in combination of two or more. In addition, if these commercially available products are available, they may be used.

[0032] The aqueous ink composition for a writing instrument of the present invention can be prepared by appropriately combining the colored resin particles having the above-mentioned characteristics, the water-soluble solvent, and other components depending on the application of the ink for the writing instrument (for a ballpoint pen, a marking pen, etc.), stirring and mixing them with a stirrer such as a homomixer, a homogenizer, or a disper, and further, if necessary, removing coarse particles in the ink composition by filtration or centrifugation.

[0033] The aqueous ink composition for writing instruments of the present invention is loaded onto ballpoint pens, marking pens, etc. equipped with a pen tip such as a ballpoint tip, fiber tip, felt tip, or plastic tip. The ballpoint pen in the present invention may be prepared by containing the aqueous ink composition for writing instruments having the above-mentioned composition in an ink container (refill) for a ballpoint pen, and containing a substance that is incompatible with the aqueous ink composition contained in the ink container and has a small specific gravity relative to the aqueous ink composition, such as polybutene, silicone oil, mineral oil, etc., as an ink follower. For example, the ballpoint pen can be prepared by filling the aqueous ink composition for writing instruments into an aqueous ballpoint pen container equipped with a ballpoint pen tip having a ball with a diameter of 0.18 to 2.0 mm. The structure of the ballpoint pen and the marking pen is not particularly limited. For example, the barrel itself may be The ink container may be a direct ink type ballpoint pen or marking pen having a collector structure (ink retention mechanism) in which the aqueous ink composition for writing instruments having the above-mentioned configuration is filled in the barrel.

[0034] Furthermore, the pH (25°C) of the aqueous ink composition for a writing instrument of the present invention is preferably adjusted to 5 to 10 using a pH adjuster or the like, from the viewpoints of usability, safety, the stability of the ink itself, and compatibility with the ink container, and is more preferably adjusted to 6 to 9.5.

[0035] In the aqueous ink composition for writing instruments of the present invention thus constituted, the colored resin particles used contain a synergist, which increases the affinity of the pigment to the resin, making it difficult for the pigment to fall off, preventing clogging of the ink flow path, and providing a good writing feel, and a writing instrument equipped with the same can be obtained. As a result, the colored resin particles of the present invention can be suitably used as a coloring agent for aqueous ink compositions for writing instruments, and the desired aqueous ink composition for writing instruments can be obtained by suitably combining and preparing each of the blending components for ballpoint pens, marking pens, etc. EXAMPLES

[0036] The present invention will now be described in more detail with reference to Production Examples, Examples and Comparative Examples, but the present invention is not limited to the following Examples. In the following Production Examples, "parts" refers to "parts by mass". Next, the present invention will be described in more detail with reference to Production Examples 1 to 8 of the colored resin particles used, Examples 1 to 4 of the water-based ink composition for writing instruments, and Comparative Examples 1 to 4. However, the present invention is not limited to the following Examples. The average particle size (D50: μm) of the colored resin particles obtained in Production Examples 1 to 8 was measured using a particle size distribution analyzer HRA9320-X100 manufactured by Nikkiso Co., Ltd. In the following Production Examples 1 to 4, "parts" refers to "parts by mass."

[0037] [Production Example 1: Colored resin particles 1] As an oil phase solution, 11.6 parts of ethylene glycol monobenzyl ether and 1.8 parts of a dispersant (DISPERBYK-111, manufactured by BYK Japan) were heated to 60°C, while 2.0 parts of a pigment (carbon black, Cabot Mogul L, manufactured by Cabot Corporation) and 0.2 parts of Synergist (phthalocyanine pigment derivative, Solsperse 5000, manufactured by Lubrizol Corporation) were added and thoroughly dispersed. Next, 9.0 parts by mass of a trimethylolpropane adduct of xylylene diisocyanate (Takenate D110N, manufactured by Mitsui Chemicals, Inc.) was added as a prepolymer to prepare an oil phase solution. The aqueous phase solution was prepared by heating 600 parts by mass of distilled water to 60° C. and dissolving 15 parts by mass of polyvinyl alcohol (PVA-205, manufactured by Kuraray Co., Ltd.) as a dispersant therein. The oil phase solution was added to the aqueous phase solution at 60° C., and the mixture was emulsified and mixed by stirring with a homogenizer for 6 hours to complete the polymerization. The resulting dispersion was centrifuged to obtain colored resin particles. The average particle size (D50) of the colored resin particles was 2.1 μm. Note that water, solvent, and PVA did not substantially remain as particle components (this also applies to the following manufacturing examples).

[0038] [Production Example 2: Colored resin particles 2] Colored resin particles 2 were obtained in the same manner as in Production Example 1 above, except that the pigment in Production Example 1 was replaced with 2.0 parts of PV Fast Blue L6472 (Clariant Japan), the dispersant was replaced with 1.0 part of TEGO Dispers 685 (Evonik Japan), and the synergist was replaced with 0.2 parts of a phthalocyanine pigment derivative (Solsperse 12000, Lubrizol). The average particle size (D50) of the colored resin particles was 2.7 μm.

[0039] [Production Example 3: Colored resin particles 3] Colored resin particles 3 were obtained in the same manner as in Production Example 1 above, except that the pigment in Production Example 1 was replaced with 2.5 parts of Yellow 4G-PT VP2669 (Clariant Japan), the dispersant was replaced with 0.5 parts of AJISPER 821 (Ajinomoto Fine-Techno Co., Ltd.), and the synergist was replaced with 0.15 parts of an azo pigment derivative (EFKA6750, BASF Japan). The average particle size (D50) of the colored resin particles was 3.2 μm.

[0040] [Production Example 4: Colored resin particles 4] Colored resin particles 4 were obtained in the same manner as in Production Example 1 above, except that the pigment in Production Example 1 was replaced with 2.0 parts of Novoperm Orange HL70 (Clariant Japan), the dispersant with 0.4 parts of EFKA PX4340 (BASF Japan), and the synergist with 0.14 parts of a yellow pigment derivative (BYK-SYNERGIST 2105, BYK-Chemie Japan). The average particle size (D50) of the colored resin particles was 1.3 μm.

[0041] [Production Examples 5-8: Colored resin particles 5-8] Colored resin particles 5 to 8 were obtained in the same manner as in Production Examples 1 to 4, except that no synergist was used (excluding the synergist), respectively. The average particle diameters (D50) of the colored resin particles 5 to 8 were 1.9 μm, 2.4 μm, 3.4 μm, and 1.5 μm, respectively.

[0042] [Examples 1 to 4 and Comparative Examples 1 to 4] Using the colorable resin particles 1 to 8 of Production Examples 1 to 8 and the blending compositions shown in Table 1 below, aqueous ink compositions for writing instruments were prepared by a conventional method. For each of the aqueous ink compositions for writing instruments obtained in Examples 1 to 4 and Comparative Examples 1 to 4 above, writing instruments (aqueous ballpoint pens and aqueous marking pens) were prepared by the following method, and the ink consumption stability and writing feel were evaluated by the following evaluation methods. The results are shown in Table 1 below.

[0043] (Preparation of Water-Based Ballpoint Pens; Examples 1 to 3, Comparative Examples 1 to 3) Water-based ballpoint pens were prepared using the ink compositions of Examples 1 to 3 and Comparative Examples 1 to 3 obtained above. Specifically, the shaft of a ballpoint pen [manufactured by Mitsubishi Pencil Co., Ltd., product name: Signo UM-151] was used, and the inks were filled into a refill consisting of a polypropylene ink reservoir tube with an inner diameter of 3.8 mm and a length of 113 mm, a ballpoint pen tip (holder: stainless steel, ball: carbide ball, ball diameter 0.38 mm), and a joint connecting the reservoir tube and the tip, and an ink follower made of polybutene was filled into the rear end of the ink, followed by degassing by centrifugation (500G, 5 minutes), to prepare water-based ballpoint pens (five of each type).

[0044] (Preparation of water-based marking pens; Example 4, Comparative Example 4) Water-based marking pens were prepared using the ink compositions of Example 4 and Comparative Example 4 obtained above. Specifically, a marking pen having a plastic tip as a writing part (manufactured by Mitsubishi Pencil Co., Ltd., product name: PEM-SY) was used, and the built-in ink occlusion body was filled with each of the inks described above to prepare water-based marking pens (five of each).

[0045] <Evaluation method for ink consumption stability; ballpoint pen> The pen was spirally written to the end in a mechanical writing test under the following writing conditions, and was evaluated according to the following evaluation criteria: Writing conditions: 100 gf, writing angle 75 degrees, writing speed 4.5 m / min. Evaluation criteria: A: You can write until all the ink is used up, and the ink consumption is stable. there was. B: Variation in ink consumption was observed. C: A significant decrease in ink consumption was observed.

[0046] <Evaluation method for ink consumption stability; felt tip pen> The pen was spirally written to the end in a mechanical writing test under the following writing conditions, and was evaluated according to the following evaluation criteria: Writing conditions: 50 gf, writing angle 65 degrees, writing speed 4.2 m / min. Evaluation criteria: A: I was able to write until all the ink was used up, and the ink consumption was stable. B: Variation in ink consumption was observed. C: A significant decrease in ink consumption was observed.

[0047] <How to evaluate writing feel; ballpoint pen> A 400m spiral was written in a mechanical writing test under the following writing conditions, and the change in writing feel before and after writing was evaluated according to the following evaluation criteria: Writing conditions: 100gf, writing angle 75 degrees, writing speed 4.5m / min. Evaluation criteria: A: The writing feel does not change. B: The writing feel has deteriorated slightly. C: The writing quality has significantly deteriorated.

[0048] <How to evaluate writing feel; marking pen> In a mechanical writing test under the following writing conditions, 400m of spiral writing was performed, and the change in writing feel before and after writing was evaluated according to the following evaluation criteria. Writing conditions: 50gf, writing angle 65 degrees, writing speed 4.2m / min Evaluation criteria: A: The writing feel does not change. B: The writing feel has deteriorated slightly. C: The writing quality has significantly deteriorated.

[0049] [Table 1]

[0050] As is clear from the results in Table 1 above, it was confirmed that the aqueous ink compositions for writing instruments of Examples 1 to 4, which fall within the scope of the present invention, are aqueous ink compositions for writing instruments and writing instruments (aqueous ballpoint pens and marking pens) equipped with them, which are excellent in ink consumption stability and writing feel, compared to Comparative Examples 1 to 4, which fall outside the scope of the present invention. [Industrial Applicability]

[0051] Thus, an aqueous ink composition for writing instruments suitable for aqueous ballpoint pens, marking pens, etc. can be obtained.

Claims

1. The writing instrument is characterized by being equipped with an aqueous ink composition for a writing instrument, which contains colored resin particles containing at least a pigment and a synergist, the resin component of the colored resin particles being a urethane-based resin, and the mass ratio of synergist / pigment being 0.01 to 0.

2.

2. 2. The writing instrument according to claim 1, which is a ballpoint pen.

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