JP2024062227A - Dispersion of colored resin particles for water-based inks and water-based ink composition for writing instruments using the same - Google Patents

Abstract

[Problem] To provide a dispersion of colored resin particles for aqueous inks that have excellent dispersion stability over time, an aqueous ink composition for writing implements that uses the same, and a writing implement equipped with the same. [Solution] A dispersion of colored resin particles for aqueous inks that are composed of at least a (meth)acrylate cyclohexyl monomer and a basic dye or an oil-soluble dye, characterized in that the measured zeta potential of the surface of the colored resin particles is in the range of -20 to +20 mV. [Selected Figure] None

Description

The present invention relates to a dispersion of colored resin microparticles for aqueous inks, and an aqueous ink composition for writing instruments using the same, which is suitable for writing instruments such as felt-tip pens, marking pens, and ballpoint pens.

It has been known in the past to dye a resin emulsion having a specific polymer structure with a dye and use it as a coloring material also called a pseudo pigment.
For example, there are known: 1) an aqueous dispersion of colored resin microparticles for aqueous inks prepared by emulsion polymerization of a vinyl monomer having an acidic functional group in which a water-soluble basic dye is dissolved in the presence of a polymerizable surfactant (see, for example, Patent Document 1); and 2) an aqueous ink composition for writing instruments using a dispersion of colored resin microparticles for aqueous inks in which colored resin microparticles composed of at least a carboxyl group-containing vinyl monomer (A) having a solubility in water of 10 mass % or less as an acidic functional group, an ester monomer (B) of acrylic acid or methacrylic acid with a linear or cyclic alcohol having 2 to 18 carbon atoms, and a basic dye or an oil-soluble dye are dispersed in water (see, for example, Patent Document 2).

However, the aqueous inks for writing instruments that use the dispersions of colored resin microparticles for aqueous inks described in Patent Documents 1 and 2 above as coloring materials are limited in the amount of dye that can be encapsulated. As a result, the density of the lines drawn tends to be somewhat insufficient. On the other hand, if a large amount of dye is added during the synthesis of the colored resin microparticles, polymerization is inhibited, and stable colored resin microparticles cannot be obtained.

Therefore, the applicant of the present application has disclosed colored resin microparticles that are excellent in stability and have sufficient line drawing density by preparing a dispersion of colored resin microparticles for aqueous inks in which the colored resin microparticles are composed of at least cyclohexyl (meth)acrylate monomer and a basic dye or an oil-soluble dye, and the content of the cyclohexyl (meth)acrylate monomer and the content of the basic dye or the oil-soluble dye are each within a specific range and dispersed in water (see, for example, Patent Document 3).

This dispersion of colored resin microparticles for aqueous inks is excellent in stability and produces colored resin microparticles with sufficient line drawing density even when the amount of dye that can be encapsulated is large. In order to obtain high dispersing power, however, an anionic surfactant is used as the polymerizable surfactant to form the colored microparticles by charge repulsion.
In this case, in the case of a water-based ink formulation system that is sensitive to electric charge, for example, a water-based ink formulation system of cellulose nanofiber (such as a gel formed by a hydrogen bond network of CNF) that is capable of realizing stable written lines without smearing or ink pooling even in writing conditions where it was previously difficult to draw clean lines, such as fast writing or left-handed writing, when the colored resin microparticles described in Patent Document 3 are used, there are currently some issues, such as the fact that the initial state of stable dispersion of the formulation cannot be maintained due to the electric charge of the particles.

JP-A-10-259337 (claims, examples, etc.) JP 2016-196623 A (Claims, Examples, etc.) JP 2019-112561 A (Claims, Examples, etc.)

In view of the problems of the above-mentioned conventional techniques, the present invention seeks to solve these problems, and aims to provide a dispersion of colored resin microparticles for aqueous inks that has excellent light resistance, can maintain a stable initial state of dispersion of colored resin microparticles even in aqueous ink formulations that are sensitive to electric charges, and is less irritating even in unstable systems (ionic systems), without impairing sufficient line density, and has excellent dispersion stability without compromising the density of drawn lines; and to provide an aqueous ink composition for writing instruments that uses this as a coloring material and is suitable for writing instruments such as felt-tip pens, marking pens, and ballpoint pens, and a writing instrument equipped with this.

In view of the above-mentioned problems, the present inventors have conducted intensive research and have discovered that by using colored resin microparticles composed of at least a specific monomer and a basic dye or an oil-soluble dye, and by setting the measured zeta potential of the surface of the colored resin microparticles within a specific range, it is possible to obtain a dispersion of colored resin microparticles for aqueous inks, an aqueous ink composition for writing instruments using the same, and a writing instrument, which are all of the above-mentioned objectives, and have thus completed the present invention.

That is, the dispersion of colored resin microparticles for aqueous ink of the present invention is characterized in that the colored resin microparticles are composed of at least a cyclohexyl (meth)acrylate monomer and a basic dye or an oil-soluble dye, and the measured zeta potential of the surface of the colored resin microparticles is in the range of -20 to +20 mV.
The colored resin fine particles preferably have an average particle size of 20 to 300 nm.
The aqueous ink composition for a writing instrument of the present invention is characterized by containing the dispersion of colored resin microparticles for an aqueous ink having the above-mentioned constitution, a water-soluble organic solvent, and water.
The writing instrument of the present invention is characterized in that it is equipped with the above-mentioned aqueous ink composition for a writing instrument.

According to the present invention, a dispersion of colored resin microparticles for aqueous inks is provided, which has excellent light resistance and can maintain an initial stable dispersion state of colored resin microparticles even in aqueous ink formulations that are sensitive to electric charge, and is less irritating even in unstable systems (ionic systems) without impairing sufficient line density.The present invention also provides an aqueous ink composition for writing instruments that is suitable for writing instruments such as felt-tip pens, marking pens, and ballpoint pens using this as a colorant, and a writing instrument equipped with this.
The objects and advantages of the invention will be realized and obtained by means of the elements and combinations particularly pointed out in the claims. Both the foregoing general description and the following detailed description are exemplary and explanatory but are not restrictive of the invention as claimed.

The following describes in detail the embodiments of the present invention for each invention. However, please note that the technical scope of the present invention is not limited to the embodiments described in detail below, but extends to the inventions described in the claims and their equivalents. In addition, the present invention can be implemented based on the contents disclosed in this specification and common technical knowledge in the relevant field (including design matters and obvious matters).
The dispersion of colored resin microparticles for aqueous ink of the present invention is characterized in that the colored resin microparticles are composed of at least a cyclohexyl (meth)acrylate monomer and a basic dye or an oil-soluble dye, and the measured zeta potential of the surface of the colored resin microparticles is in the range of -20 to +20 mV.

The cyclohexyl (meth)acrylate monomer used in the present invention is used because it can provide stable colored resin microparticles with excellent deep color development even when the amount of dye that can be encapsulated is large, and the obtained colored resin microparticles have a sufficient line density as a coloring material for writing instruments, etc. If other (meth)acrylic acid compounds such as n-butyl (meth)acrylate are used, the effects of the present invention cannot be achieved.
The expression "(meth)acrylic acid" above means "acrylic acid and/or methacrylic acid." Methods for producing cyclohexyl (meth)acrylate monomer are known, and cyclohexyl (meth)acrylate can be produced by conventional methods, for example, an esterification method in which (meth)acrylic acid and cyclohexanol are esterified using a catalyst such as an inorganic acid, an organic sulfonic acid, or a strongly acidic ion exchange resin, or an ester exchange method in which an organometallic compound containing titanium, tin, or the like is used as a catalyst.

In the present invention, in addition to the above-mentioned cyclohexyl (meth)acrylate monomer, from the viewpoint of obtaining colored resin microparticles having excellent color development properties, it is preferable to use a hydrophobic vinyl monomer or an aqueous monomer other than the above-mentioned cyclohexyl (meth)acrylate monomer.
As the hydrophobic vinyl monomer, for example, at least one monomer such as esters of acrylic acid or methacrylic acid other than the above-mentioned cyclohexyl (meth)acrylate monomer, styrene, methylstyrene and other styrenes can be used.
Examples of hydrophobic vinyl monomers that can be used include at least one of methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, styrene, methylstyrene, and the like (each alone or a mixture of two or more).
Examples of aqueous monomers that can be used include at least one of glycerin monomethacrylate, sodium 2-sulfoethyl methacrylate, polyethylene glycol monomethacrylate, polypropylene glycol monomethacrylate, polyethylene glycol-propylene glycol monomethacrylate, polyethylene glycol-tetramethylene glycol monomethacrylate, propylene glycol-polybutylene glycol monomethacrylate, and the like (each alone or a mixture of two or more).

Examples of basic dyes used in the present invention include at least one of the following basic dyes: di- and triarylmethane dyes; quinoneimine dyes such as azine (including nigrosine), oxazine, and thiazine; xanthene dyes; triazole azo dyes; thiazole azo dyes; benzothiazole azo dyes; azo dyes; methine dyes such as polymethine, azomethine, and azamethine; anthraquinone dyes; and phthalocyanine dyes. Water-soluble basic dyes are preferred.

Specific examples of the basic dye that can be used include dyes of each color number listed in the COLOR INDEX, such as C.I. Basic Yellow (-1, -2, -9, -80, etc.), C.I. Basic Orange (-1, -2, -7, -34, etc.), C.I. Basic Red (-1, -2, -3, -53, etc.), C.I. Basic Violet (-1, -2, -3, -39, etc.), C.I. Basic Blue (-1, -2, -5, -88, etc.), C.I. Basic Green (-1, -4, -6, -10, etc.), C.I. Basic Brown (-1, -2, -4, -15, etc.), and C.I. Basic Black (-1, -2, -7, -8, etc.).
In addition, commercially available products of these dyes can also be used. Yellow basic dyes include AIZEN CATHILON YELLOW GLH (trade name of Hodogaya Chemical Co., Ltd.), red basic dyes include AIZEN CATHILON RED BLH, AIZEN CATHILON RED RH (all of which are trade names of Hodogaya Chemical Co., Ltd.), Diacryl Supra Brilliant Red 2G (trade name of Mitsubishi Chemical Co., Ltd.), Sumiacryl Red B (trade name of Sumitomo Chemical Co., Ltd.), blue basic dyes include AIZEN CATHILON TURQUOISE BLUE LH (trade name of Hodogaya Chemical Co., Ltd.), and green basic dyes include Diacryl Supra Brilliant Green Examples of brown basic dyes include Janus Brown R (product name of Nippon Kagaku Co., Ltd.) and AIZEN CATHILON BROWN GH (product name of Hodogaya Chemical Co., Ltd.).

In addition, examples of the oil-soluble dyes used in the present invention include commercially available monoazos, disazos, metal complex monoazos, anthraquinones, phthalocyanines, triarylmethanes, etc. In addition, salt-forming oil-soluble dyes in which the functional groups of acidic and basic dyes are replaced with hydrophobic groups can also be used.
Examples of the yellow color include C.I. Solvent Yellow 114 and 116; examples of the orange color include C.I. Solvent Orange 67; examples of the red color include C.I. Solvent Red 122 and 146; examples of the blue color include C.I. Solvent Blue 5, 36, 44, 63, 70, 83, 105, and 111; and examples of the black color include C.I. Solvent Black 3, 7, 27, and 29.
Specific examples of 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 Co., Ltd.), blue dye Saninyl Blue GLS (manufactured by Clariant), red dye SOC-1-0100 (manufactured by Orient Chemical 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 Co., Ltd.).

The dispersion of colored resin microparticles for aqueous ink of the present invention is a dispersion in water of colored resin microparticles composed of at least a cyclohexyl (meth)acrylate monomer and a basic dye or an oil-soluble dye, and the measured zeta potential of the surface of the colored resin microparticles is desirably in the range of −20 to +20 mV, preferably in the range of −15 to +15 mV, more preferably in the range of −13 to +13, and particularly preferably in the range of −10 to +10 mV.
In the present invention (including the Examples described later), "measurement of the zeta potential of the surface of colored resin fine particles" refers to a value obtained by the following measurement method.
The zeta potential V was measured using a zeta potential measuring device DT-300 (manufactured by Disoersion Technology, Inc.).
The zeta potential V is a value measured by the electrophoretic light scattering method. For example, the zeta potential V was measured by diluting the obtained dispersion of colored resin particles for aqueous ink with water so that the solid content concentration of the dispersion was 40 g/L. The obtained measurement sample was used for measurement by the above-mentioned zeta potential measuring device (Zetasizer Nano ZS) using the electrophoretic light scattering method. The measurement was performed three times, and the average value was taken as the zeta potential V.

By setting the measured zeta potential of the surface of the colored resin microparticles in the range of -20 to +20 mV, even in a water-based ink formulation system that uses a thickener such as polysaccharide fiber and is sensitive to electric charge, the initial state in which the dispersion of the colored resin microparticles is stable can be maintained, and further, even in a water-based ink formulation system that is unstable such as an ionic system, there is little irritation, so that a dispersion of colored resin microparticles for water-based inks having excellent dispersion stability can be obtained without impairing sufficient line density.
Furthermore, if the colorant is a dye, it will strongly bind to the ionic substances present in the ink, and may cause precipitation during long-term storage. However, the present invention makes it possible to obtain a dispersion of colored resin microparticles for aqueous inks that has excellent dispersion stability and light resistance.
If the measured zeta potential value is outside the range of −20 to +20 mV, the effects of the present invention cannot be exhibited, and if the measured zeta potential value is less than −20 mV, the ink will become less viscous and the dispersion will become poor. On the other hand, if the measured zeta potential value exceeds +20 mV, the ink will become less viscous and the dispersion will become poor, which is also undesirable.

In order to make the zeta potential measurement value fall within the range of -20 to +20 mV, for example, the colored resin microparticles for aqueous inks are obtained by emulsion polymerization or the like, and by using a nonionic polymerizable surfactant (type, amount, etc.) as the polymerizable surfactant used during emulsion polymerization, a dispersion of colored resin microparticles for aqueous inks having a predetermined zeta potential can be obtained.
The dispersion of colored resin microparticles for aqueous ink of the present invention can be produced, for example, by dissolving the basic dye or oil-soluble dye in the cyclohexyl (meth)acrylate monomer or in a mixed monomer containing the cyclohexyl (meth)acrylate monomer and another hydrophobic vinyl monomer, and using ammonium persulfate, potassium persulfate, hydrogen peroxide, or the like as a polymerization initiator, or a polymerization initiator further combined with a reducing agent, and using a nonionic polymerizable surfactant (type, suitable amount) as the polymerizable surfactant, thereby obtaining a dispersion of colored resin microparticles for aqueous ink having a target zeta potential measurement value within the range of -20 to +20 mV.

Examples of nonionic polymerizable surfactants that can be used include Aqualon AN-10, AN-20, AN-30, and AN-5065 (all of which are polyoxyethylene styrenated propenyl phenyl ethers: EO addition mole numbers of 10, 20, 30, 40, and 50) manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Aqualon RN-10, RN-20, RN-30, and RN-50 (all of which are polyoxyethylene propenyl phenyl ethers (nonylphenyl type): EO addition mole numbers of 10, 20, 30, and 50) manufactured by Kao Corporation, Latemul PD-420, PD-430, and PD-450 (all of which are polyoxyalkylene alkenyl ethers) manufactured by NOF Corporation, Blenmer PE-90, PE-200, and PE-350 (all of which are PEG monomethacrylates: EO addition mole numbers of 2, 4.5, and 8) and Blenmer AE-200 and AE-400 (all of which are PEG monomethacrylates) manufactured by NOF Corporation. Acrylate: EO addition mole number 4.5, 10), Blenmar PP-1000, PP-500, PP-800 (above, PPG monomethacrylate: PO addition mole number 4 to 6, 9, 13), Blenmar AP-200, AP-400, AP-550, AP-800 (above, PPG monoacrylate: PO addition mole number: 3.5, 6, 9, 13), NOF Corporation's Uniox PKA-5001, PKA-500 2, PKA-5003, PKA-5004, Unisafe PKA-5014F, ADEKA CORPORATION's ADEKA REASOAP ER-10, ER-20, ER-30, ER-40 (all alkyl type: EO added mole number: 10, 20, 30, 40), ADEKA REASOAP NE-10, NE-20, NE-30 (all alkylphenol type: (nonylphenyl type) EO added mole number: 10, 20, 30), and the like.
The amount of these nonionic polymerizable surfactants used may be any amount that results in the zeta potential measurement value falling within the range of −20 to +20 mV, and varies depending on the type of basic dye and oil-soluble dye used, but is preferably 0.01 to 50% by mass, and more preferably 0.1 to 50% by mass, based on the total amount of the monomers.

Furthermore, in the present invention, within a range that does not impair the effects of the present invention, crosslinking agents such as triallyl isocyanurate, triallyl isocyanurate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, pentaerythritol acrylate, ditrimethylolpropane acrylate, dipentaerythritol acrylate, methoxylated bisphenol A methacrylate, pentaerythritol methacrylate, ditrimethylolpropane methacrylate, dipentaerythritol methacrylate, and ethoxylated polyglycerin methacrylate may be used, and, if necessary, polyoxyethylene-1-(allyloxymethyl)-alkyl ether ammonium sulfate, ether sulfate, polyoxyethylene nonylpropenyl phenyl ether ammonium sulfate, polyoxyethylene terephthalic acid ester ... The polyoxyethylene styrene-based copolymer can be produced by emulsion polymerization using a polymerizable surfactant (emulsifier) such as oxyethylene nonylpropenyl phenyl ether, ammonium polyacrylate, styrene-maleic acid copolymer ammonium, polyoxyethylene alkyl ether, polyoxyethylene styrenated phenyl ether, polyoxyethylene polyoxypropylene glycol, polyoxyalkylene decyl ether, polyoxyethylene tridecyl ether, alkylbenzene sulfonate, dioctyl sulfosuccinate, sodium lauryl sulfate, polyoxyethylene alkyl ether phosphate, polyoxyethylene styrenated phenyl ether phosphate, polyoxyethylene styrenated phenyl ether sulfate, or polyoxyethylene alkyl ether sulfate.
The content of the crosslinking agent such as the triallyl isocyanurate is preferably 0 to 50% by mass, and more preferably 0.1 to 25% by mass, based on the total amount of the monomers.
Although the dyeing was carried out simultaneously with the polymerization, dyeing may be carried out after the polymerization by dissolving a basic dye or an oil-soluble dye.
It is preferable to further use a crosslinking agent such as the above-mentioned triallyl isocyanurate, since this improves the heat resistance, mechanical properties, hydrolysis resistance, and weather resistance of the colored resin particles.

In the present invention, during the emulsion polymerization, a suitable amount of dicyclopenta(ten)yl (meth)acrylate monomer may be further mixed with the cyclohexyl (meth)acrylate monomer, etc., to carry out the emulsion polymerization. When this dicyclopenta(ten)yl (meth)acrylate monomer is further mixed and then emulsion polymerized, the stability is not easily impaired even if the water in the dispersion evaporates, and a dispersion of colored resin microparticles for aqueous inks having even better stability can be obtained.
Dicyclopenta(ten)yl (meth)acrylate monomers which may be used include dicyclopentanyl acrylate monomer, dicyclopentenyl acrylate, dicyclopentanyl methacrylate monomer, dicyclopentenyl methacrylate.
In the present invention, in the emulsion polymerization, in addition to the above-mentioned cyclohexyl (meth)acrylate monomer, other hydrophobic vinyl monomers, and the like, monomers having a reactive crosslinking group such as an epoxy group, a hydroxymethylamide group, an isocyanate group, and the like, and polyfunctional monomers having two or more vinyl groups may be blended in appropriate amounts to cause crosslinking.

In the present invention, among the polymer components constituting the colored resin microparticles for aqueous ink, the content of the cyclohexyl (meth)acrylate monomer must be 30% by mass or more, preferably 30 to 95% by mass, and more preferably 30 to 70% by mass, based on the total polymer components constituting the colored resin microparticles.
In the present invention, the term "total polymer components" refers to the polymerizable components constituting the colored resin microparticles, and specifically refers to the total amount of the cyclohexyl (meth)acrylate monomer used, the other monomer components used, and the crosslinking agent described below.
By making the content of the cyclohexyl (meth)acrylate monomer 30% by mass or more based on the total polymer components, the effects of the present invention can be exerted. On the other hand, if this content is less than 30% by mass, the stability over time will be inferior, which is not preferable.

Furthermore, among the polymer components constituting the colored resin microparticles for aqueous ink, the content of other monomer components than the cyclohexyl (meth)acrylate monomer is the remainder of the total amount of the cyclohexyl (meth)acrylate monomer and the crosslinking agent described below.
The content of the other monomer components is preferably 5 to 85% by mass based on the total polymer components, from the viewpoints of further exerting the effects of the present invention, dispersibility, and reactivity.

In the present invention, the content of the basic dye or oil-soluble dye is required to be preferably 15% by mass or more, and is preferably 15 to 50% by mass, and more preferably 15 to 40% by mass, based on the total polymer components, from the viewpoints of color development, obtaining sufficient line density, stability, and the like.
By making the content of this dye 15% or more, sufficient color development and sufficient line density can be achieved, while if the content of the dye is less than 15% by mass, the color development is insufficient and the effects of the present invention cannot be achieved.

In the present invention, in the above-mentioned preferred embodiment, specifically, by dissolving the above-mentioned basic dye or oil-soluble dye in at least the cyclohexyl (meth)acrylate monomer and emulsion-polymerizing the same, or by polymerizing a mixed monomer containing at least the cyclohexyl (meth)acrylate monomer and other monomer components and then dissolving a basic dye or oil-soluble dye to dye the resulting mixture, a dispersion of colored resin microparticles for aqueous ink can be obtained, in which the measured zeta potential falls within the range of -20 to +20 mV and 20 to 50 mass % of colored resin microparticles are dispersed in water as a resin solid content.
This dispersion of colored resin microparticles can maintain an initial state in which the dispersion of the colored resin microparticles is stable, even in aqueous ink formulations that are sensitive to electric charges, and is less irritating even in unstable systems (ionic systems), so it is a colorant that has excellent dispersion stability without compromising sufficient line density, and is useful as a colorant for aqueous ink compositions for writing instruments, such as felt-tip pens, marking pens, and ballpoint pens.

In the present invention, the average particle size of the colored resin particles in the dispersion of colored resin particles for aqueous ink obtained varies depending on the cyclohexyl (meth)acrylate monomer, the type and content of other monomers used, the polymerization conditions during polymerization, etc., but is preferably 20 to 300 nm, more preferably 40 to 150 nm, and even more preferably 60 to 110 nm.
It is desirable that:
By setting the average particle size within the above preferred range, clogging does not occur in the core of a writing instrument such as a felt-tip pen, a marking pen, or a ballpoint pen, and further, excellent storage stability is achieved.
The "average particle size" as defined in the present invention is a histogram average particle size based on scattered light intensity distribution, and in the present invention (including the examples described later), it is a value _D50 measured using a particle size distribution measuring device [FPAR1000 (manufactured by Otsuka Electronics Co., Ltd.)].

The aqueous ink composition for writing instruments of the present invention is characterized by containing at least a dispersion of colored resin particles having the above-mentioned characteristics, a water-soluble organic solvent, and water.
Examples of the water-soluble organic solvent that can be used include ethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 2,3-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol, 2,5-hexanediol, 3-methyl-1,3-butanediol, and 2-methylpentanediol. and at least one of alkylene glycols such as 1,2,4-diol, 3-methylpentane-1,3,5-triol, and 1,2,3-hexanetriol; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; glycerols such as glycerol, diglycerol, and triglycerol; lower alkyl ethers of glycols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol mono-n-butyl ether; N-methyl-2-pyrrolidone, and 1,3-dimethyl-2-imidalidinone.

In addition, water-soluble solvents such as alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, tert-butyl alcohol, isobutyl alcohol, hexyl alcohol, octyl alcohol, nonyl alcohol, decyl alcohol, and benzyl alcohol, amides such as dimethylformamide and diethylacetamide, and ketones such as acetone can also be mixed.
The content of these water-soluble organic solvents varies depending on the type of writing instrument, such as a felt-tip pen, a marking pen, or a ballpoint pen, but is preferably 1 to 40% by mass relative to the total amount of the ink composition, and is particularly effective in ink compositions with a content of 10% by mass or less in order to further improve the drying properties of drawn lines, and more preferably 3 to 8% by mass.

The content of water (tap water, purified water, ion-exchanged water, distilled water, pure water, etc.) is preferably 30 to 90% by mass, and more preferably 40 to 60% by mass, based on the total amount of the ink composition.
The content of the colored resin particles varies depending on the type of writing instrument and the outflow mechanism (pen core, ballpoint pen), but is preferably 1 to 30% by mass in terms of solid content based on the total amount of the aqueous ink composition for writing instruments.

In the aqueous ink composition for writing instruments containing the dispersion of colored resin microparticles having the above-mentioned characteristics of the present invention, polysaccharide fibers can be used as a thickener, and examples of such polysaccharide raw materials include polysaccharides such as cellulose or cellulose derivatives, chitin, and chitosan. Although the hydrogen bonding force due to the hydroxyl groups of the polysaccharide fibers is weak, they tend to form aggregate structures due to weak hydrogen bonds, which tend to affect the formulation system of the aqueous ink, which is sensitive to electric charges, and it is difficult to maintain the initial state in which the dispersion of the colored resin microparticles is stable. By using the colored resin microparticles of the present invention, it is possible to obtain a high dispersion stability effect even when polysaccharide fibers are used as a thickener.

Further examples of thickening agents other than the above polysaccharide fibers include xanthan gum, welan gum, succinoglycan, which is an organic acid-modified heteropolysaccharide whose constituent monosaccharides are glucose and galactose, guar gum, locust bean gum and its derivatives, hydroxyethylcellulose, alginic acid alkyl esters, polymers having a molecular weight of 100,000 to 150,000 and consisting mainly of alkyl esters of methacrylic acid, glucomannan, thickening polysaccharides with gelling ability extracted from seaweed such as agar and carrageenin, benzylidene sorbitol and benzylidene xylitol or derivatives thereof, alkali-swelling association-type thickeners, crosslinked acrylic acid polymers, inorganic fine particles, nonionic surfactants with an HLB value of 8 to 12, such as polyglycerin fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyethylene glycol fatty acid esters, polyoxyethylene alkyl ethers, polyoxypropylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, fatty acid amides, and salts of dialkyl or dialkenyl sulfosuccinic acid. Examples include a mixture of N-alkyl-2-pyrrolidone and an anionic surfactant, and a mixture of polyvinyl alcohol and an acrylic resin. These thickeners may be used alone or in combination of two or more. Even the above-mentioned thickeners do not affect the formulation of the aqueous ink, so the dispersion of the colored resin microparticles of the present invention can be suitably used.

The amount of these thickeners varies depending on the type of writing instrument (ballpoint pen, marking pen, felt tip pen, etc.), but it is preferable that the amount of solids contained in the ink composition is 0.01 to 15% by mass, and more preferably 0.05 to 10% by mass.

In the aqueous ink composition for writing instruments of the present invention, preservatives or antifungal agents, pH adjusters, defoamers, wetting agents, and the like can be appropriately selected and used as necessary within the scope that does not impair the effects of the present invention.
For example, the pH adjuster may be at least one of ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, aminomethylpropanol, sodium tripophosphate, alkali metal salts of carbonate or phosphoric acid such as sodium carbonate, and alkali metal hydroxides such as sodium hydroxide.
Examples of the preservative or antifungal agent include at least one of phenol, sodium omadine, sodium pentachlorophenol, 1,2-benzisothiazolin-3-one, 2,3,5,6-tetrachloro-4(methylphonyl)pyridine, alkali metal salts of benzoic acid, sorbic acid, and dehydroacetic acid, and benzimidazole compounds.
Examples of wetting agents include at least one type of phosphate esters, polyalkylene glycol derivatives such as polyoxyethylene lauryl ether, fatty acid alkali salts, nonionic surfactants, fluorine-based surfactants such as perfluoroalkyl phosphate esters, polyether-modified silicones such as polyethylene glycol adducts of dimethylpolysiloxane, acetylene glycols, and acetylene derivatives selected from ethylene oxide adducts thereof.

In the present invention, in order to further enhance the light resistance effect, the effect of preventing deterioration due to ultraviolet rays, and the effect of light stability, the colored resin microparticles may contain an ultraviolet absorber and/or a light stabilizer together with the basic dye or oil-soluble dye.
The ultraviolet absorbent that can be used may be a conventionally known one, for example, a benzotriazole-based absorbent, a triazine-based absorbent, a salicylic acid derivative-based absorbent, a benzophenone-based absorbent, etc., and the above ultraviolet absorbent is preferably one having a polymerizable unsaturated group.

Specific examples of benzotriazole-based absorbents include 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-5'-t-butylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-t-butylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole, and 2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole. Benzotriazole, 2-(2'-hydroxy-3',5'-di-t-amylphenyl)benzotriazole, 2-(2'-hydroxy-4'-octoxyphenyl)benzotriazole, 2-{2'-hydroxy-3'-(3",4",5",6"-tetrahydrophthalimidomethyl)-5'-methylphenyl}benzotriazole, 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole, etc.

Specific examples of triazine-based absorbents include 2,4-bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-isooctyloxyphenyl)-1,3,5-triazine, 2-[4((2-hydroxy-3-dodecyloxypropyl)-oxy)-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[4-((2-hydroxy-3-tridecyloxypropyl)-oxy)-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, and 2-(2,4-dihydroxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine.

Specific examples of salicylic acid derivative-based absorbents include phenyl salicylate, p-octylphenyl salicylate, and 4-tert-butylphenyl salicylate.
Specific examples of benzophenone-based absorbents include 4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-2'-carboxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone trihydrate, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-octadecyloxybenzophenone, and naphthalene. sodium 2,2'-dihydroxy-4,4'-dimethoxy-5-sulfobenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 4-dodecyloxy-2-hydroxybenzophenone, 5-chloro-2-hydroxybenzophenone, resorcinol monobenzoate, 2,4-dibenzoylresorcinol, 4,6-dibenzoylresorcinol, hydroxydodecylbenzophenone, 2,2'-dihydroxy-4(3-methacryloxy-2-hydroxypropoxy)benzophenone, and the like.

Examples of commercially available ultraviolet absorbents include "Tinuvin 900", "Tinuvin 928", "Tinuvin 348-2", "Tinuvin 479", "Tinuvin 405", "Tinuvin 400" (all of which are product names manufactured by BASF, Tinuvin is a registered trademark), and "RUVA-93" (all of which are product names manufactured by Otsuka Chemical Co., Ltd.).
The content of the ultraviolet absorber in the colored resin microparticles can be 1 to 50% by mass, and preferably 10 to 40% by mass, based on the total amount of the particles excluding the solvent, from the standpoints of color development, light resistance, and stability.

Examples of light stabilizers that can be suitably used include hindered amine-based light stabilizers, hindered phenol antioxidants, phenol-based radical scavengers, sulfur-based antioxidants, phosphorus-based antioxidants, triazine-based compounds, benzotriazole-based compounds, phenol-based ultraviolet absorbers, malonic acid ester-based ultraviolet absorbers, oxanilide-based ultraviolet absorbers, and benzophenone-based compounds.
A more preferred embodiment of the light stabilizer is a polymerizable (reactive) light stabilizer having the above-mentioned methacrylic group, and a polymerizable (reactive) light stabilizer that can be easily polymerized with the above-mentioned (meth)methacrylic acid ester or the like and can incorporate a light-stable functional group into a polymer chain can be suitably used, and the light stabilizer does not volatilize or dissolve, and colored resin microparticles having high safety and long-term stable light stability can be obtained. Note that even a non-polymerizable light stabilizer can be included in the colored resin microparticles to impart the desired light stability.

As the hindered amine-based light stabilizer, a conventionally known compound such as a hindered piperidine compound can be used. The hindered amine-based light stabilizer may be one having a polymerizable unsaturated group.
Specific examples of the hindered amine-based light stabilizer include monomer-type stabilizers such as bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate, bis(N-methyl-2,2,6,6-tetramethyl-4-piperidinyl)sebacate, 4-benzoyloxy-2,2',6,6'-tetramethylpiperidine, and bis(1,2,2,6,6-pentamethyl-4-piperidyl){[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl}butylmalonate; Examples of known polymerizable compounds include oligomer types such as 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol and succinic acid polyesterified products, and 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate and 2,2,6,6-tetramethyl-4-piperidyl methacrylate.

In addition, examples of commercially available hindered amine light stabilizers include "Tinuvin 765", "Tinuvin 770DF", "Tinuvin 144", "Tinuvin 622SF", "Tinuvin 152" (all manufactured by BASF, product names, Tinuvin \ Tinuvin are registered trademarks), "ADK STAB LA-52", "ADK STAB LA-57", "ADK STAB LA-63P", "ADK STAB LA-72", "ADK STAB LA-77Y", "ADK STAB LA-81", "ADK STAB LA-82", "ADK STAB LA-87" (all manufactured by ADEKA Corporation, product names, ADK STAB \ ADKSTAB and ADK STAB are registered trademarks), and the like.
The content of the light stabilizer in the colored resin microparticles can be 1 to 50% by mass, and preferably 10 to 40% by mass, based on the total amount of the particles excluding the solvent, from the standpoints of color development, light resistance, and stability.

In the present invention, in order to further improve stability over time, antiseptic properties, coloring properties, and fragrance, the colored resin microparticles may contain, in addition to the above-mentioned colorants, preservatives, reducing agents, colorants containing dyes or pigments other than basic dyes or oil-soluble dyes, coloring materials containing thermochromic substances, fragrances, etc.

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

The writing instrument of the present invention is equipped with an aqueous ink composition for writing instruments having the above-mentioned composition, and is equipped, for example, with a ballpoint pen tip, fiber tip, felt tip, plastic tip including a brush-type tip, fiber core, porous core including a sintered core, a sponge core capable of application at a large flow rate, or a pen tip portion such as a brush or writing brush, a ballpoint pen, a marking pen, etc.
The ballpoint pen may be one in which the aqueous ink composition for a writing instrument having the above-mentioned composition is contained in an ink container (refill) for the ballpoint pen, and a substance that is incompatible with the aqueous ink composition for a writing instrument having the above-mentioned composition contained in the ink container and has a low specific gravity compared to the aqueous ink composition, such as polybutene, silicone oil, mineral oil, etc., is contained as an ink follower.
The structure of the ballpoint pen or marking pen is not particularly limited and may be a known one, for example, 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 of the above-mentioned structure, a direct liquid type equipped with a valve structure, or a padding type equipped with an ink container. Furthermore, the structure of the writing instrument configured as above may be either a knock type or a cap type.

The aqueous ink composition for writing instruments of the present invention thus constituted contains at least the dispersion of colored resin microparticles for aqueous inks constituted as above, a water-soluble solvent, and water, so that even when a thickener is contained, an aqueous ink composition for writing instruments suitable for felt-tip pens, marking pens, ballpoint pens, and other writing instruments having sufficient line density and excellent dispersion stability over time can be obtained.

Furthermore, by using the colored resin microparticles of the present invention, it is possible to increase the degree of freedom in ink design. Specifically, it is possible to design ink without imposing restrictions on the surface tension value in the initial state at the time of ink production. Depending on the colored resin microparticles used, the surface tension may be reduced during ink production due to the action of the activator exposed on the particle surface.
In this case, in a direct ink type writing instrument having a collector structure (ink retention mechanism), a design is required in which the surface tension value is set higher from the initial state in order to prevent the ink from flowing directly or from blowing out. If the initial surface tension value is low, there will be limitations on the mechanical design when mounting the ink.
The colored resin particles of the present invention can maintain high copolymerization of the surfactant while maintaining high sedimentation resistance and dispersion stability, so that an aqueous dispersion can be obtained with a small amount of free surfactant. Therefore, by using the colored resin particles of the present invention, it is possible to increase the freedom of ink design and mechanism design without being affected by the free surfactant and without decreasing the initial surface tension value.

Next, the present invention will be described in more detail with reference to manufacturing examples, examples, and comparative examples, but the present invention is not limited to the following examples.

[Production Examples 1 to 12: Production of Dispersions of Colored Resin Fine Particles (Particles 1 to 12)]
Dispersions of colored resin particles were prepared according to the following Preparation Examples 1 to 12. In the following, "parts" refers to parts by mass. The total amount (total amount) of each component in Preparation Examples 1 to 12 was 500 parts.

(Production Example 1)
A 2-liter flask was equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas inlet tube, and a 1000 ml separating funnel for monomer introduction, and set in a warm water bath. 329.5 parts of distilled water, 5 parts of glycerin monomethacrylate (Blenmer GLM, manufactured by NOF Corporation), 5 parts of 2-sulfoethyl sodium methacrylate (acrylic ester SEM-Na, manufactured by Mitsubishi Chemical Corporation), 20 parts of a nonionic polymerizable surfactant (ADEKA Corporation, ADEKA REASOAP ER-30) and 0.5 parts of ammonium persulfate were then charged, and the internal temperature was raised to 50° C. while introducing nitrogen gas.

On the other hand, a liquid was prepared by mixing a monomer mixture consisting of 55 parts of cyclohexyl methacrylate monomer and 35 parts of n-butyl methacrylate as another monomer with 40 parts of an oil-soluble dye (Savinyl Blue GLS, manufactured by Clariant) and 10 parts of a crosslinking agent (triallyl isocyanurate, manufactured by Nippon Kasei Chemical Industry Co., Ltd., "TAIC").
This preparation liquid was added from the separating funnel to the flask kept at about 50° C. over a period of 3 hours with stirring to carry out emulsion polymerization. The mixture was further aged for 5 hours to complete the polymerization, thereby obtaining a dispersion of colored resin particles for aqueous ink (particles 1).
The content of the cyclohexyl methacrylate monomer was 50.0% by mass relative to the total polymer components constituting the colored resin microparticles, and the content of the oil-soluble dye was 30.8% by mass relative to the total polymer components. The average particle diameter of the colored resin microparticles was 40 nm. The zeta potential of the surface of the colored resin microparticles (particle 1) was -1.7 mV.

(Production Example 2)
A colored fine particle aqueous dispersion for aqueous ink (particles 2) was obtained in the same manner as in Production Example 1, except that in Production Example 1, 340.5 parts of distilled water, 30 parts of the amount of cyclohexyl methacrylate monomer, 45 parts of n-butyl methacrylate, and 20 parts of an oil-soluble dye [Oil Pink 314, manufactured by Orient Chemical Industry Co., Ltd.], 12 parts of an oil-soluble dye [Valifast Red 3312, manufactured by Orient Chemical Industry Co., Ltd.], and 12 parts of an oil-soluble dye [Valifast Pink 2310N, manufactured by Orient Chemical Industry Co., Ltd.] were used.
The content of the cyclohexyl methacrylate monomer was 31.6% by mass relative to the total polymer components constituting the colored resin microparticles, and the content of the oil-soluble dye was 38.3% by mass relative to the total polymer components. The average particle diameter of the colored resin microparticles was 82 nm. The zeta potential of the surface of the colored resin microparticles (particles 2) was +13.4 mV.

(Production Example 3)
A colored fine particle aqueous dispersion for aqueous ink (particles 3) was obtained in the same manner as in Production Example 1, except that in Production Example 1, 333.5 parts of distilled water, 60 parts of the amount of cyclohexyl methacrylate monomer, 30 parts of n-butyl methacrylate, and 25 parts of an oil-soluble dye [Oil Yellow 129, manufactured by Orient Chemical Industry Co., Ltd.] and 11 parts of an oil-soluble dye [Valifast Yellow 1108, manufactured by Orient Chemical Industry Co., Ltd.] were used.
The content of the cyclohexyl methacrylate monomer was 54.5% by mass relative to the total polymer components constituting the colored resin particles, and the content of the oil-soluble dye was 27.7% by mass relative to the total polymer components. The average particle diameter of the colored resin particles was 65 nm. The zeta potential of the surface of the colored resin particles (particles 3) was -8.1 mV.

(Production Example 4)
A colored fine particle aqueous dispersion for aqueous ink (particles 4) was obtained in the same manner as in Production Example 1, except that in Production Example 1, 309.5 parts of distilled water, 60 parts of cyclohexyl methacrylate monomer, 35 parts of n-butyl methacrylate, 30 parts of nonionic polymerizable surfactant (ADEKA Corporation, ADEKA REASOAP ER-30) were used, and 10 parts of oil-soluble dye (Valifast Red 3312, Orient Chemical Industry Co., Ltd.), 25 parts of oil-soluble dye (Valifast Black 1821, Orient Chemical Industry Co., Ltd.), and 10 parts of oil-soluble dye (Oil Yellow 105M, Orient Chemical Industry Co., Ltd.) were used.
The content of the cyclohexyl methacrylate monomer was 52.2% by mass relative to the total polymer components constituting the colored resin microparticles, and the content of the oil-soluble dye was 31.0% by mass relative to the total polymer components. The average particle diameter of the colored resin microparticles was 132 nm. The zeta potential of the surface of the colored resin microparticles (particles 4) was +2.1 mV.

(Production Example 5)
An aqueous dispersion of colored fine particles for aqueous ink (particles 5) was obtained in the same manner as in Production Example 1, except that 55 parts of cyclohexyl acrylate monomer was used instead of 55 parts of cyclohexyl methacrylate monomer.
The content of the cyclohexyl acrylate monomer was 50.0% by mass based on the total polymer components constituting the colored resin particles, the content of the oil-soluble dye was 30.8% by mass based on the total polymer components, and the average particle size of the colored resin particles was 51 nm.
The zeta potential of the surface of the colored resin fine particles (particles 5) was +1.1 mV.

(Production Example 6)
A colored fine particle aqueous dispersion for aqueous ink (particles 6) was obtained in the same manner as in Production Example 2, except that the distilled water was changed to 332.5 parts, the dyes were changed to 12 parts of an oil-soluble dye [Oil Pink 314, manufactured by Orient Chemical Industry Co., Ltd.], 15 parts of an oil-soluble dye [Valifast Red 3312, manufactured by Orient Chemical Industry Co., Ltd.], 5 parts of an oil-soluble dye [Valifast Pink 2310N, manufactured by Orient Chemical Industry Co., Ltd.], 45 parts of n-butyl methacrylate was replaced by 45 parts of methyl methacrylate, and 20 parts of RUVA-93 was used as an ultraviolet absorber.
The content of the cyclohexyl methacrylate monomer was 29.8% by mass relative to the total polymer components constituting the colored resin particles, and the content of the oil-soluble dye was 26.2% by mass relative to the total polymer components. The average particle diameter of the colored resin particles was 91 nm. The zeta potential of the surface of the colored resin particles (particles 6) was -3.1 mV.

(Production Example 7)
An aqueous dispersion of colored fine particles for aqueous ink (particles 7) was obtained in the same manner as in Production Example 3, except that the amount of distilled water was 336.5 parts, and that the dyes used were an oil-soluble dye [Oil Yellow 129, manufactured by Orient Chemical Industry Co., Ltd.] (30 parts), an oil-soluble dye [Valifast Yellow 1108, manufactured by Orient Chemical Industry Co., Ltd.] (30 parts), and n-butyl methacrylate (30 parts) and styrene (30 parts).
The content of the cyclohexyl methacrylate monomer was 54.5% by mass relative to the total polymer components constituting the colored resin microparticles, and the content of the oil-soluble dye was 25.4% by mass relative to the total polymer components. The average particle diameter of the colored resin microparticles was 70 nm. The zeta potential of the surface of the colored resin microparticles (particles 7) was -1.9 mV.

(Production Example 8)
A colored fine particle aqueous dispersion for aqueous ink (particles 8) was obtained in the same manner as in Production Example 4, except that in Production Example 4, 270.5 parts of distilled water, 90 parts of cyclohexyl methacrylate monomer, 25 parts of n-butyl methacrylate, and 15 parts of an oil-soluble dye [Valifast Red 3312, manufactured by Orient Chemical Industry Co., Ltd.], 10 parts of an oil-soluble dye [Valifast Black 1821, manufactured by Orient Chemical Industry Co., Ltd.], 15 parts of an oil-soluble dye [Oil Yellow 105M, manufactured by Orient Chemical Industry Co., Ltd.], and 24 parts of a light stabilizer Adeka STAB LA-82 were used.
The content of the cyclohexyl methacrylate monomer was 61.3% by mass relative to the total polymer components constituting the colored resin particles, and the content of the oil-soluble dye was 22.2% by mass relative to the total polymer components. The average particle diameter of the colored resin particles was 110 nm. The zeta potential of the surface of the colored resin particles (particles 8) was -1.6 mV.

(Production Example 9)
An aqueous dispersion of colored fine particles for aqueous ink (particles 9) was obtained in the same manner as in Production Example 1, except that the distilled water was changed to 324.5 parts, the crosslinking agent was changed to 0 (zero) parts (not used), and the ultraviolet absorber Tinuvin 900 was changed to 15 parts.
The content of the cyclohexyl methacrylate monomer was 55.0% by mass relative to the total polymer components constituting the colored resin particles, and the content of the oil-soluble dye was 33.3% by mass relative to the total polymer components. The average particle diameter of the colored resin particles was 55 nm. The zeta potential of the surface of the colored resin particles (particles 9) was -1.2 mV.

(Production Example 10)
An aqueous dispersion of colored microparticles for aqueous ink (particles 10) was obtained in the same manner as in Production Example 6, except that in Production Example 6, the amount of cyclohexyl methacrylate monomer was changed to 30 parts, n-butyl methacrylate was changed to 45 parts, and the light stabilizer Tinuvin 765 was changed to 20 parts.
The content of the cyclohexyl methacrylate monomer was 0% by mass relative to the total polymer components constituting the colored resin particles, and the content of the oil-soluble dye was 27.8% by mass relative to the total polymer components. The average particle diameter of the colored resin particles was 175 nm. The zeta potential of the surface of the colored resin particles (particle 10) was -14.2 mV.

(Production Example 11)
An aqueous dispersion of colored fine particles for aqueous ink (particles 11) was obtained in the same manner as in Production Example 5, except that no cyclohexyl methacrylate monomer was used (content: zero), and 100 parts of cyclohexyl acrylate monomer and 20 parts of a nonionic polymerizable surfactant [ADEKA CORPORATION, ADEKA REASOAP ER-30] were used instead of 20 parts of a nonionic polymerizable surfactant [Kao Corporation, LATEMURU PD-420].
The content of the cyclohexyl acrylate monomer was 50.0% by mass relative to the total polymer components constituting the colored resin particles, and the content of the oil-soluble dye was 36.4% by mass relative to the total polymer components. The average particle diameter of the colored resin particles was 343 nm. The zeta potential of the surface of the colored resin particles (particles 12) was −20.8 mV.

(Production Example 12)
A colored fine particle aqueous dispersion for aqueous ink (particles 12) was obtained in the same manner as in Production Example 6, except that no cyclohexyl methacrylate monomer was used (content: zero), the amount of n-butyl methacrylate was 75 parts, and 20 parts of a nonionic polymerizable surfactant (ADEKA CORPORATION, ADEKA REASOAP ER-30) was replaced with 20 parts of a nonionic polymerizable surfactant (Kao Corporation, LATEMURU PD-420).
The content of the cyclohexyl acrylate monomer was 31.6% by mass relative to the total polymer components constituting the colored resin particles, and the content of the oil-soluble dye was 33.7% by mass relative to the total polymer components. The average particle diameter of the colored resin particles was 298 nm. The zeta potential of the surface of the colored resin particles (particle 12) was +3.9 mV.

The dispersions of colored resin microparticles for water-based inks obtained in Production Examples 1 to 12 above each had a resin solid content of 20 to 40% by mass.

[Examples 1 to 10 and Comparative Examples 1 and 2: Preparation of aqueous ink compositions for writing instruments]
Using the dispersions of each of the colored resin fine particles (particles 1 to 12) produced in Production Examples 1 to 12 above, aqueous ink compositions for writing instruments were prepared by a conventional method according to the blending compositions (total amount 100 mass%) shown in Table 1 below.

For each of the resulting aqueous ink compositions for writing instruments (total amount 100% by mass), the dispersion stability over time was evaluated and the surface tension was measured by the following evaluation method.
The evaluation results of Examples 1 to 10 and Comparative Examples 1 and 2 are shown in Table 1 below.

(Method of evaluating dispersion stability over time)
Each of the ink compositions prepared in Examples 1 to 10 and Comparative Examples 1 and 2 obtained above was filled into a glass vial, the lid was closed, and the ink was stored in an environment of 50°C. After a certain period of time, the period during which no aggregation or sedimentation was observed in the ink in the vial was defined as the "period during which stability is maintained", and was evaluated according to the following evaluation criteria.
Evaluation criteria:
A: More than 6 months
B: 3 months or more but less than 6 months
C: Less than 3 months
D: Less than one month

(Measurement of surface tension value)
The surface tension of each of the ink compositions (at 25° C.) prepared in Examples 1 to 10 and Comparative Examples 1 and 2 obtained above was measured using a surface tension measuring device: CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.

(Evaluation of Light Fastness)
(Mechanical evaluation): At 25°C and 65%, the pen was set at 60°, a load of 200g was applied, the PPC paper in contact was moved spirally at a speed of 4.5m/min, and the written line was cut out to a specified size. The paper test piece was irradiated with 50W/ ^m2 (300-400nm) xenon arc light according to JIS L 0843 for 5 hours using a Suga Test Instruments xenon weather meter X25, and the degree of fading was judged according to the following criteria.
Evaluation criteria:
A+: No change in hue, and the spiral is legible
A: There is a slight change in hue, but the spiral is legible.
B: There is a noticeable change in hue, and although it is quite faint, the spiral is still legible.
C: The spiral is unreadable.

From an examination of Table 1 above, it is apparent that Examples 1 to 10, which are within the scope of the present invention, are superior in stability over time compared to Comparative Examples 1 and 2, which are outside the scope of the present invention.
By using the colored resin microparticles of Examples 1 to 10 of the present invention, it has become possible to design ink without placing restrictions on the surface tension value in the initial state at the time of ink production, which has traditionally been the case in which the surface tension was reduced during ink production, and it has been confirmed that this further increases the freedom of ink design and mechanism design.

Furthermore, after the evaluation of the stability over time of Examples 1 to 10 obtained above (after 7 months for Examples 1 to 10), ballpoint pens and marking pens having the following configurations were prepared using the aqueous ink compositions for writing instruments, and the writing performance of each writing instrument was evaluated by writing on writing paper.
(Writing implement: ballpoint pen production)
A ballpoint pen (manufactured by Mitsubishi Pencil Co., Ltd., collector specification, direct ink type, ball diameter: 0.5 mm, product name: Uni-ball Eye, UB-150) was filled with the ink to prepare an aqueous ballpoint pen.
(Writing implement: Making a marking pen)
Each of the above aqueous ink compositions was loaded into a marking pen (manufactured by Mitsubishi Pencil Co., Ltd., trade name: Propus Wind PUS-102T, pen tip, thick: PE resin sintered core, thin: PET fiber core) to prepare a marking pen.
It was confirmed that the ballpoint pens and marking pens containing the CNFs prepared above were free of smearing or bleeding, had sufficient line density, and produced clear lines.

A dispersion of colored resin microparticles for aqueous inks suitable for writing instruments such as felt-tip pens, marking pens, and ballpoint pens, an aqueous ink composition for writing instruments using this, and a writing instrument can be obtained.

Claims (4)

A dispersion of colored resin particles for aqueous inks, which are composed of at least cyclohexyl (meth)acrylate monomer and a basic dye or an oil-soluble dye, and which is characterized in that the measured zeta potential of the surface of the colored resin particles is in the range of -20 to +20 mV. The dispersion of colored resin microparticles for aqueous ink according to claim 1, characterized in that the average particle diameter of the colored resin microparticles is 20 to 300 nm. An aqueous ink composition for writing instruments, comprising a dispersion of colored resin microparticles for aqueous inks according to claim 1 or 2, a water-soluble organic solvent, and water. A writing instrument equipped with the aqueous ink composition for writing instruments according to claim 3.