JP7603116B2 - Water-based ink composition for writing instruments - Google Patents

Description

The present invention relates to an aqueous ink composition for writing instruments that contains colored resin particles encapsulating a pigment.

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 encapsulating a pigment include an ink composition for a writing instrument in which the colorant is a composite particle of a spherical resin particle 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).

In addition, as a method for producing colored resin particles containing a pigment, for example, a method for producing a pigment composition (colored resin particles) comprising the steps of: 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 the 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).

However, coloring agents composed of colored resin particles containing such 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 it is installed. This fallen pigment can cause problems such as clogging the ink flow path and a gradual deterioration in the writing feel.

JP-A-63-218778 (claims, examples, etc.) JP 2003-268287 A (claims, examples, etc.) JP-A-9-217019 (claims, examples, etc.)

The present invention is made in consideration of the problems of the conventional technology described above and aims to solve them, and aims to provide an aqueous ink composition for writing instruments that contains colored resin particles that encapsulate a pigment that is less likely to fall off, thereby preventing clogging of the ink flow path and providing a good writing feel.

In view of the above-mentioned problems, the present inventors conducted extensive research and discovered that the above-mentioned aqueous ink composition for writing instruments can be obtained by incorporating a synergist (pigment derivative) into colored resin particles that encapsulate a pigment, and thus completed the present invention.

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.
It is preferable that the synergist/pigment mass ratio is 0.01 to 0.2.
The resin component of the colored resin particles is preferably a urethane-based resin.

The present invention provides an aqueous ink composition for writing instruments that does not clog the ink flow path and has a good writing feel.

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.

<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.

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.

<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 a compound having a strong interaction with the pigment. It also has a strong interaction with the dispersant described below that 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.

As the synergist that can be used, an optimum synergist can be used depending on the pigment to be used. Commercially available synergists for the color of the pigment, specifically carbon black, yellow pigment, azo pigment, and phthalocyanine pigment, can 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) and BYK-SYNERGIST 2105 (yellow pigment derivative) manufactured by BYK-Chemie Japan, EFKA6745 (phthalocyanine pigment derivative) and EFKA6750 (azo pigment derivative) manufactured by BASF Japan Ltd., and Synergist 100 (phthalocyanine pigment derivative) manufactured by Dispersion Materials Research Institute. Yello-8020, 8404, 9043, 4827 (yellow pigment derivatives); Synergist Red-3953, 4327, 4474, 4858, 4966, 5507, 5525, 5909, 6006, 6547 (azo pigment derivatives); Synergist Blue-6831, 7215, 7438, 7854, 0785, 0785A (phthalocyanine pigment derivatives); Synergist Violet-6965, 7349, 7572, 7988 (phthalocyanine pigment derivatives), and the like. These may be used alone or in combination of two or more.

The content of these synergists in the colored resin particles varies depending on the type of pigment used and its amount used. In order to obtain the effects of the synergist and the effects of the present invention, it is preferable that the pigment and synergist used are mixed at a constant ratio, and the mass ratio of synergist/pigment is preferably 0.01 to 0.2, and 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 from the colored resin particles may be weakened, while if this mass ratio exceeds 0.2, the pigment may aggregate in the colored resin particles, resulting in a poor writing feel.

<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.

From the standpoints 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.

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, transcyclohexane 1,4-diisocyanate, diphenyl ether diisocyanate, and xylylene diisocyanate. anate, hydrogenated xylylene diisocyanate, 2,6-diisocyanate caproic acid, tetramethyl-m-xylylene diisocyanate, tetramethyl-p-xylylene diisocyanate, trimethylhexamethylene diisocyanate, triphenylmethane triisocyanate, tris(isocyanatephenyl)thiophosphate, isocyanate alkyl 2,6-diisocyanate capronate, 1,6,11-undecane triisocyanate, 1,8-diisocyanate-4-isocyanate methyl octane, 1,3,6-hexamethylene triisocyanate, bicycloheptane triisocyanate, and the like.
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-diisocyanate, 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.

Specific examples of amine components 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 xylylenediamine, as well as 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.

Specific examples of alcohol components 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. An alcohol component may also be used in combination with an amine component.

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 manufacturing 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.

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.

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.
[0033] The epoxy resin that can be used is an epoxy resin having two or more epoxy groups in one molecule, and can be any commonly used epoxy resin 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.

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 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 the like. In addition, conventionally known commercially available dispersants 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 types of pigment and synergist used, and is preferably 2 to 20% by mass, and more preferably 3 to 15% by mass, from the viewpoint of the synergistic action of the pigment and the synergist and of favorably exhibiting the effects of the present invention.

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, and the like. However, the above-mentioned aqueous phase components (water, PVA), oil phase components (solvent), and the like 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 within a suitable range, and polymerizing the above-mentioned pigment, synergist, dispersant, and resin component (remainder), colored resin particles in which each component falls 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 a 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.

<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.

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.

Examples of water-soluble solvents 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 this water-soluble solvent is preferably 5 to 40% by mass of the total amount of the aqueous ink composition for writing instruments.

The aqueous ink composition for writing instruments of the present invention may contain, in addition to the colored resin particles having the above characteristics, a colorant other than the colored resin particles, and a water-soluble solvent, the remainder being water (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.) as a solvent, as well as dispersants, lubricants, pH adjusters, rust inhibitors, preservatives or antibacterial agents, thickeners, etc., as appropriate, within the scope of not impairing the effects of the present invention.

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. In addition, any polymer dispersant obtained by 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.

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, saponins, and the like. Examples of preservatives or antibacterial agents include phenol, sodium omadine, sodium benzoate, thiazoline compounds, benzimidazole compounds, and the like.
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., which may be used alone or in combination of two or more. In addition, if these commercially available products are available, they may be used.

The aqueous ink composition for writing instruments of the present invention can be prepared by appropriately combining the colored resin particles having the above characteristics, the water-soluble solvent, and other components according to the application of the ink for the writing instrument (for ballpoint pens, marking pens, etc.), stirring and mixing them with a stirrer such as a homomixer, homogenizer, or disperser, and further removing coarse particles from the ink composition by filtration or centrifugation, if necessary.

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 or marking pen is not particularly limited, and may be, for example, a direct ink type ballpoint pen or marking pen having a collector structure (ink retention mechanism) in which the barrel itself serves as an ink container and is filled with the aqueous ink composition for writing instruments having the above-described structure.

The pH (25°C) of the aqueous ink composition for writing instruments 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.

In the aqueous ink composition for writing instruments of the present invention thus configured, 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, thereby providing an aqueous ink composition for writing instruments and a writing instrument equipped with the same. 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 formulation components for ballpoint pens, marking pens, etc.

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 aqueous ink composition for a writing instrument, and Comparative Examples 1 to 4. However, the present invention is not limited to the following Examples, etc.
The average particle size (D50: μm) of the colored resin particles and the like 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" means "parts by mass."

[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 a pigment (carbon black, Cabot Mogul L 2.0 parts of Cabot Corporation) and 0.2 parts of Synergist (phthalocyanine pigment derivative, Solsperse 5000, Lubrizol Corporation) were added and thoroughly dispersed. 9.0 parts by mass of a trimethylolpropane adduct (Takenate D110N, manufactured by Mitsui Chemicals, Inc.) was added to prepare an oil phase solution.
The aqueous phase solution was prepared by dissolving 15 parts by mass of polyvinyl alcohol (PVA-205, manufactured by Kuraray Co., Ltd.) as a dispersant in 600 parts by mass of distilled water heated to 60° C. did.
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 were essentially the same as the particle components. (The same applies to the following manufacturing examples.)

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

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

[Production Example 4: Colored resin particles 4]
The pigment of Production Example 1 was mixed with 2.0 parts of Novoperm Orange HL70 (Clariant Japan), 0.4 parts of EFKA PX4340 (BASF Japan) as a dispersant, and 0.5 parts of a yellow pigment derivative (BYK-SYNERGIST 2105, Colored resin particles 4 were obtained in the same manner as in Production Example 1, except that 0.14 parts of BYK-Chemie Japan Co., Ltd. was used instead.
The average particle size (D50) of the colored resin particles was 1.3 μm.

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

[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, 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.

(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 each of the inks was 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: cemented 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 (500 G, 5 minutes) to prepare water-based ballpoint pens (five of each type).

(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).

<Evaluation method for ink consumption stability; ballpoint pen>
The spiral writing was performed until the end in a mechanical writing test under the following writing conditions, and the results were evaluated according to the following evaluation criteria. Writing conditions: 100 gf, writing angle 75 degrees, writing speed 4.5 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.

<Evaluation method for ink consumption stability; felt tip pen>
The spiral writing was performed to the end in a machine writing test under the following writing conditions, and the results were 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.

<How to evaluate writing feel; ballpoint pen>
In a mechanical writing test under the following writing conditions, 400 m 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: 100 gf, writing angle 75 degrees, writing speed 4.5 m/min.
Evaluation criteria:
A: The writing feel does not change.
B: The writing feel has deteriorated slightly.
C: The writing quality was significantly deteriorated.

<How to evaluate writing feel; marking pen>
In a mechanical writing test under the following writing conditions, 400 m 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: 50 gf, writing angle 65 degrees, writing speed 4.2 m/min.
Evaluation criteria:
A: The writing feel does not change.
B: The writing feel has deteriorated slightly.
C: The writing quality was significantly deteriorated.

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, provide aqueous ink compositions for writing instruments and writing instruments (aqueous ballpoint pens and marking pens) equipped with the same that are superior in ink consumption stability and writing feel compared to Comparative Examples 1 to 4, which fall outside the scope of the present invention.

An aqueous ink composition suitable for use in writing instruments such as water-based ballpoint pens and marking pens is obtained.

Claims (2)

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