JP7679201B2 - Oil-based ink composition for writing instruments, water-based ink composition for writing instruments, and ballpoint pen - Google Patents

Description

The present invention relates to an oil-based ink composition for a writing instrument, a water-based ink composition for a writing instrument, and a ballpoint pen.

In recent years, there has been a rapid increase in user demand for writing instruments (especially ballpoint pens) that meet the needs of users, such as the writing feel, writing performance (initial writing performance), and stable, continuous writing, depending on the ink and functions used. Ballpoint pens can be broadly categorized into oil-based ballpoint pens, water-based ballpoint pens, gel ink ballpoint pens, etc.

Oil-based inks come in a variety of colors, including black, red, blue, pink, green, and orange, and are usually produced by dissolving or dispersing colorants in organic solvents. In order to further improve writing performance, resins, surfactants, additives, etc. are added depending on the application.

Dyes, pigments, and mixtures of these are used as colorants in oil-based inks. For example, oil-based inks that use pigments have excellent durability when writing, but the pigments tend to clump and settle in the ink, which can cause defects in the writing. In contrast, oil-based inks that use dyes have the characteristic that the dyes are easily soluble in solvents, so they are less likely to clump and settle compared to pigments, but they tend to have inferior water resistance and weather resistance.

As for dyes, various dyes such as acid dyes and basic dyes, as well as processed dyes such as salt-forming dyes, are known. For example, inks using methine dyes as colorants (Patent Document 1) and inks using a mixture of dyes and pigments (Patent Document 2) have been reported.

On the other hand, water-based inks use dispersed pigments and oil-based dyes in addition to water-soluble dyes as colorants.

In recent years, cellulose nanofibers, which can be obtained by chemically or mechanically defibrating plant fibers, have been attracting attention, and research into their use in various fields is being actively conducted. Examples of using cellulose nanofibers for writing instruments have been reported (Patent Documents 3 and 4). In addition, a method of incorporating a colorant by emulsion polymerization of a monomer has been reported (Patent Documents 5 and 6).

Japanese Patent Application Publication No. 08-20669 JP 2015-30753 A JP 2017-105907 A JP 2017-125135 A JP 2016-196623 A JP 2019-112561 A

The dyes described in Patent Documents 1 and 2 tend to aggregate easily, and when the ink solvent at the tip of the ball tip evaporates, the ink thickens, which can cause smudging when writing begins. In addition, depending on the usage environment, there are issues such as a poor writing feel (handwriting density does not change and handwriting continues to be produced stably) and low handwriting robustness.

In addition, when a dye is used that is incompatible with the carrier (resin or cellulose nanofiber), the dye and carrier each aggregate, and the carrier is not uniformly dyed with the dye. In addition, an ink composition containing such a carrier in an unevenly dyed state has the problem of poor storage stability.

The present invention relates to a medium containing an alcohol or a glycol ether,
a resin present in a dissolved state in the medium; and a colorant containing a compound represented by the following general formula (1):
The present invention relates to an oil-based ink composition for a writing instrument, which contains the above compound.

[R ₁ and R ₂ each independently represent a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 12 carbon atoms;
_R3 represents a linear alkyl group having 1 to 4 carbon atoms or a branched alkyl group having 3 to 4 carbon atoms;
_R4 represents any functional group selected from the group consisting of a t-butyl group, an iso-propyl group, a phenyl group, and a benzyl group.
The present invention also relates to an aqueous medium, and a carrier dispersed in the aqueous medium.
A water-based ink composition for a writing instrument comprising:
The present invention relates to an aqueous ink composition for a writing instrument, characterized in that the carrier carries a compound represented by the above general formula (1).

The present invention provides an oil-based ink composition for writing instruments in which aggregation of the colorant is suppressed even under low and high temperature conditions.

In addition, by using the oil-based ink composition for writing instruments, it is possible to provide a ballpoint pen that suppresses the phenomenon of smearing at the beginning of writing, has a good writing feel with less skipping and smearing in the handwriting, and has high handwriting fastness.

The present invention also provides an aqueous ink composition for writing instruments that has high dispersion stability of the carrier in an aqueous medium.

Furthermore, by using the above-mentioned aqueous ink composition for writing instruments, it is possible to provide a ballpoint pen that suppresses the phenomenon of smearing at the beginning of writing, has a good writing feel with less skipping and smearing in the handwriting, and has high handwriting fastness.

The following describes in detail the embodiments of the present invention.

[Coloring agent]
First, the compound represented by formula (1) used as a colorant will be described.

[R ₁ and R ₂ each independently represent a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 12 carbon atoms;
_R3 represents a linear alkyl group having 1 to 4 carbon atoms or a branched alkyl group having 3 to 4 carbon atoms;
_R4 represents any functional group selected from the group consisting of a t-butyl group, an iso-propyl group, a phenyl group, and a benzyl group.
When the substituent at the 2-position of the [1,2,4]triazolo[1,5-a]pyridine ring has a branched structure such as a heptan-3-yl group (Conventional Dye X below) as described in the prior art, repulsion occurs between the alkylamino group of the thiazole ring due to steric interaction. It is believed that this repulsive effect causes the molecules to spread out overall, bringing them closer to each other and facilitating aggregation through hydrogen bonding.

In contrast, in the compound represented by general formula (1), the substituent at the 2-position of the [1,2,4]triazolo[1,5-a]pyridine ring has a branched alkyl group, a phenyl group, or a benzyl group, with one methylene group in between. Therefore, the steric interaction between the alkylamino group of the thiazole ring and the ring is alleviated by the presence of one methylene group. This makes the entire molecule smaller. As a result, it is believed that aggregation is suppressed because it becomes difficult for other molecules to approach the nitrogen atom that promotes hydrogen bonding.

In other words, it is speculated that by using a compound represented by general formula (1) as a colorant, aggregation of the colorant in an oil-based ink composition for a writing instrument can be suppressed even under low and high temperature conditions. Also, in an aqueous ink composition for a writing instrument, the carrier carrying general formula (1) has high dispersion stability in an aqueous medium.

[Compound represented by general formula (1)]
First, the compound represented by formula (1) will be described.

In general formula (1), the linear alkyl group having 1 to 12 carbon atoms, the branched alkyl group having 3 to 12 carbon atoms, and the cyclic alkyl group having 3 to 12 carbon atoms for R ₁ and R ₂ are not particularly limited, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, a 2-ethylhexyl group, and a cyclohexyl group.

Among these, a branched alkyl group is preferable, and a 2-ethylhexyl group is more preferable. It is particularly preferable that both R ₁ and R ₂ are 2-ethylhexyl groups.

In general formula (1), the linear alkyl group having 1 to 4 carbon atoms in R ₃ is not particularly limited, but examples thereof include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, etc. Examples of branched alkyl groups having 3 to 4 carbon atoms include an isopropyl group, a sec-butyl group, a tert-butyl group, etc. Among these, a methyl group, an ethyl group, and an n-butyl group are preferred, and a methyl group in particular has the greatest effect.

In the general formula (1), _R4 represents any functional group selected from the group consisting of a t-butyl group, an isopropyl group, a phenyl group, and a benzyl group. Among these, a t-butyl group or a phenyl group is preferable.

The compound represented by general formula (1) can be synthesized by referring to the known method described in the patent document (JP-A-08-245896).

Preferable examples of the compound of the present invention represented by general formula (1) are shown below in (1-1) to (1-15), but the present invention is not limited to these.

The compound represented by the above general formula (1) may be used alone or in combination with two or more other compounds to adjust the color tone, etc., depending on the application.

Among these compounds, (1-1), (1-2), (1-4), (1-5), (1-6), (1-8), (1-10), (1-12), and (1-14) are preferred. In particular, when (1-2), (1-4), (1-5), and (1-6) are used in which R ₁ and R ₂ are 2-ethylhexyl groups and R ₃ is a methyl group, the effects of the present invention are particularly remarkable.

The amount of the compound represented by general formula (1) is appropriately selected depending on the application, but is preferably 1 to 50% by mass of the total amount of the ink composition. More preferably, it is 2 to 45% by mass, and even more preferably, it is 5 to 40% by mass.

In addition, the compound represented by general formula (1) may be used alone as a colorant, but other known colorants may also be used in combination.

The colorants (dyes, pigments) that can be used in combination are determined according to the purpose and application of the ink, taking into consideration factors such as hue, printing sensitivity, light resistance, storage stability, and solubility with the resin.

Known dyes that can be used in combination are not particularly limited, but examples include acid dyes, basic dyes, metal complex dyes, salt-forming dyes, azine dyes, condensed azo compounds, azo metal complexes, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, perylene compounds, methine compounds, allylamide compounds, phthalocyanine dyes, triphenylmethane dyes, basic dye lake compounds, oxazine compounds, thiazine compounds, xanthene compounds, etc.

Specific examples include NIGROSIN BASE EX-BP, NUBIAN BLACKPA-2800, VALIFAST BLACK 1805, VALIFAST BLACK 1807, VALIFAST BLACK 1815, VALIFAST BLACK 1821, Oil Blue 613, VALIFAST RED 1308, VALIFAST RED 1320, VALIFAST RED 1355, VALIFAST RED 1360, VALIFAST BLUE 1601, VALIFAST BLUE 1605, VALIFAST BLUE 1621, VALIFAST YELLOW 1101, VALIFAST YELLOW 1151 (all manufactured by Orient Chemical Industry Co., Ltd.), Aizen Spilon Blue 2BNH, Aizen Spilon Red C-GH, Aizen Spilon Red C-BH, Aizen Spilon Yellow C-GHN new, Aizen Spilon Yellow GRLH special, Aizen S.P.T. Blue-121 (all manufactured by Hodogaya Chemical Co., Ltd.), and the like. Known pigments that can be used in combination are not particularly limited, but examples include carbon black, aniline black, titanium dioxide pigments, phthalocyanine, quinacridone, diketopyrrole, azo, dioxane, quinophthalone, triphenylmethane, perylene, perinone, metallic pigments, pearl pigments, fluorescent pigments, phosphorescent pigments, etc. It is preferable that the pigment has an average particle size of 30 nm to 700 nm after dispersion in the medium.

Specific examples include FUJI FAST RED 8800 (C.I. Pigment Red 254) and FUJI FAST RED 2200 (C.I. Pigment Red 170) (both manufactured by Fuji Pigment Co., Ltd.).

The amount of pigment to be added is 0.5 to 25% by mass, preferably 0.5 to 20% by mass, based on the total amount of the ink composition, and can be added as needed.

The colorant, including the compound represented by formula (1) and the dyes and pigments that can be used in combination, is selected appropriately depending on the application, but it is preferable to mix them in the range of 1 to 50% by mass based on the total amount of the ink composition.

<Oil-based ink composition for writing instruments>
Next, the oil-based ink composition for a writing instrument according to the present invention will be described.

The oil-based ink composition for writing instruments contains a colorant containing a compound represented by general formula (1), a medium containing an alcohol or glycol ether, and a resin present in a dissolved state in the medium.

In addition to the above components, additives may be added as appropriate to the extent that they do not impair the properties for various applications. The additives will be described later.

[Media]
The "medium" in the present invention is alcohol or glycol ether. The medium is selected according to the purpose and use of the ink, and is not particularly limited, and one or more kinds may be used.

The following are some suitable alcohols:

For example, alkyl monoalcohols having no substituents, such as ethanol, isopropanol, n-butanol, isobutanol, tert-butanol, sec-butanol, 2-methyl-2-butanol, 3-pentanol, octanol, and cyclohexanol; alkyl monoalcohols having substituents, such as 2-phenoxyethanol and 3-methyl-3-methoxy-1-butanol; alkyl polyhydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, 3-methyl-1,3-butanediol, and 1,3-butanediol; and aromatic alcohols, such as benzyl alcohol. Examples of the substituents in alkyl monoalcohols having a substituent include alkoxy groups and aryloxy groups.

Further examples include glycol ether alcohols such as ethylene glycol monobutyl ether, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether, and triethylene glycol monobutyl ether.

In particular, 3-methyl-3-methoxy-1-butanol, 1,3-butanediol, and propylene glycol monomethyl ether are preferably used.

Glycol ethers can also be used. Glycol ethers include monoalcohol monoethers, but these are described as alcohols. Examples of diethers include ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dipropylene glycol, ethylene glycol diethyl ether, diethylene glycol diethyl ether, and diethylene glycol dipropyl ether.

In addition to alcohol and glycol ether, the medium may also contain water; ester solvents such as 3-methyl-3-methoxybutyl acetate, butyl acetate, and methyl propionate.

The amount of medium used varies depending on the type of writing instrument (ballpoint pen, felt tip pen, marking pen, etc.), but is preferably 1 to 70% by mass, more preferably 3 to 60% by mass, and particularly preferably 5 to 30% by mass, based on the total amount of the ink composition.

[resin]
The oil-based ink composition for writing instruments contains a resin that is present in a dissolved state in the medium in order to adjust the viscosity of the ink and improve the scratch resistance.

The resin is determined according to the purpose and use of the ink, and is not particularly limited, but examples include butyral resin, ketone resin, polyvinylpyrrolidone resin, styrene resin, styrene-acrylic resin, styrene-maleic acid resin, terpene resin, acrylic resin, polyvinyl acetal resin, polyvinyl butyral resin, terpene phenol resin, rosin modified maleic resin, rosin phenol resin, maleic acid resin, phenol resin, xylene resin, urea resin, polyamide resin, phenoxy resin, cellulose-based resin, etc. These resins may be used alone, or two or more types may be used in combination as necessary.

In the present invention, butyral resins and ketone resins are preferably used to provide a writing feel that does not cause smearing.

Examples of butyral resins include low polymerization types such as S-LEC BL-1, BL-2, and BL-10, and high polymerization types such as BH-3, BH-6, BX-1, BX-5, and BH-S (all manufactured by Sekisui Chemical Co., Ltd.).

Examples of ketone resins include Ketone Resin K-90 (manufactured by Arakawa Chemical Industries, Ltd.), Hilac 901, Hilac 110H, and Hilac 111 (all manufactured by Hitachi Chemical Co., Ltd.).

An example of a polyvinylpyrrolidone resin is Polyvinylpyrrolidone K-90 (manufactured by Nippon Shokubai Co., Ltd.).

The amount of resin blended is preferably 1 to 50% by mass, more preferably 3 to 30% by mass, and particularly preferably 5 to 25% by mass, based on the total amount of the ink composition. Within the above range, viscosity adjustment is easy, wear on the pen tip can be prevented, and a stable and good writing feel can be obtained. Furthermore, since film-forming properties can be appropriately suppressed, ink solidification can be suppressed even if the pen tip is left exposed for a long period of time, and the "blurring phenomenon" when starting to write can be suppressed.

[Additives]
Furthermore, if necessary, additives may be added within a range that does not adversely affect the ink, such as rust inhibitors, surfactants, lubricants, wetting agents, UV absorbers, defoamers, antioxidants, pH adjusters, leveling agents, preservatives, and cellulose nanofibers.

Anti-rust agents include, but are not limited to, benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, saponin, ethylenediaminetetraacetic acid, metal salt compounds, and phosphate ester compounds.

The surfactant is not particularly limited, but examples thereof include cationic surfactants, anionic surfactants, nonionic surfactants, amphoteric surfactants, silicone-based surfactants, and fluorine-based surfactants.

The lubricant is not particularly limited, but examples thereof include higher fatty acids, silicone oils, glycerin fatty acid esters, castor oil, phosphate esters and their metal salts, ammonium salts, etc., and are effective in preventing wear of the ball receiving seat of the ball tip of a ballpoint pen. These lubricants may be used alone or in combination of two or more kinds. Furthermore, fine particles such as silica fine particles and alumina fine particles may be added to improve lubricity.

Humectants include, but are not limited to, glycerin, sorbitan compounds, polysaccharides, urea, etc.

Examples of ultraviolet absorbers include, but are not limited to, 2-(2'-hydroxy-3'-t-butyl-5'-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, and p-benzoic acid-2-hydroxybenzophenone.

Antifoaming agents include, but are not limited to, silicone compounds such as dimethylpolysiloxane, mineral oils, and fluorine-based compounds.

Antioxidants include, but are not limited to, dibutylhydroxytoluene, nordihydroxytoluene, flavonoids, butylhydroxyanisole, ascorbic acid derivatives, α-tocopherol, and catechins.

Examples of pH adjusters include, but are not limited to, alkalizing agents such as sodium hydroxide, alkanolamines, oxyethylene alkylamines, polyoxyethylene alkylamines, laurylamine, N,N-dimethylstearinamine, N,N-dimethylstearylamine, N,N-dimethyloctylamine, and ammonium, and acidic compounds such as alkylbenzenesulfonic acid, methanesulfonic acid, dialkylsulfosuccinic acid, naphthalenesulfonic acid, oleic acid, and naphthalenesulfonic acid-formaldehyde condensates.

Leveling agents are not particularly limited, but examples include acetylene glycol, acetylene alcohol, and silicone surfactants.

[Manufacturing method]
The oil-based ink composition for a writing instrument can be produced by a known method.

For example, the medium, the compound represented by formula (1), the resin, and, if necessary, other colorants and additives are mixed at an appropriate temperature range, and the mixture is stirred and mixed using a mixer, roll, homogenizer, disperser, or the like. In addition, a media-type dispersing machine such as a rotary shear homogenizer, ball mill, sand mill, or attritor, and a high-pressure counter-collision type dispersing machine can also be used.

Oil-based ink compositions for writing instruments need to have a certain amount of solids content; if the solids content is too low, the ink will have low viscosity, which can lead to ink dripping.

That is, the viscosity of the oil-based ink composition for writing instruments is preferably in the range of 100 to 3,000 mPa·s at a shear rate of 38.30 (1/s) in an atmosphere of 24.5 to 25.5°C.

[Writing implements]
The oil-based ink composition for writing instruments is used by filling it into a ballpoint pen, a felt tip pen, or a marking pen.

Explain about ballpoint pens.

The structure and shape of the ballpoint pen are not particularly limited. For example, there is a ballpoint pen having an ink reservoir tube with a ball tip attached to a ball receiving seat at the tip, which is connected to the tip, housed inside the barrel, and the tip protruding from the tip of the barrel. After the oil-based ballpoint pen ink composition is filled from the opening of the ink reservoir tube through the base end, the opening at the base end is closed with a backflow prevention plug or backflow prevention body.

As the ball rolls over the writing medium, the ink composition for the oil-based ballpoint pen is supplied to the surface of the ball through the gap between the ball tip and the ball, soaking into the writing medium and forming a handwritten mark.

<Water-based ink composition for writing instruments>
Next, the water-based ink composition for a writing instrument will be described.

The aqueous ink composition for writing instruments contains an aqueous medium and a carrier dispersed in the aqueous medium, and is characterized in that the carrier supports a compound represented by general formula (1).

[Career]
The carrier supports the compound represented by general formula (1), and the state of support may be such that the compound represented by general formula (1) is dispersed throughout the carrier, is encapsulated within the carrier, or is present on the carrier surface.

The main components constituting the carrier are not particularly limited, but examples include resins, cellulose nanofibers, etc.

[resin]
The method for producing resin particles carrying the compound represented by general formula (1) is not particularly limited, but examples thereof include a bulk resin crushing method, a suspension polymerization method, an emulsion polymerization method, a mini-emulsion polymerization method, and a phase inversion emulsification method.

The lump resin crushing method is a method in which a lump resin obtained by polymerizing in advance so as to contain the compound represented by general formula (1) is physically crushed using a crusher or the like.

The suspension polymerization method is a method in which a polymerizable monomer in which a compound represented by general formula (1) is dissolved is suspended in a liquid state in an aqueous medium in the presence of a dispersant, and the droplets are polymerized in this state.

The emulsion polymerization method is a method in which a polymerizable monomer is polymerized in an aqueous medium in the presence of a compound represented by general formula (1).

The mini-emulsion polymerization method is a method in which a polymerizable monomer is dissolved or dispersed in a compound represented by general formula (1) and vigorously stirred in an aqueous medium in the presence of a surfactant to form resin particles.

The transfer emulsification method involves dissolving the compound represented by general formula (1) and a resin in a solvent, vigorously stirring the mixture in an aqueous medium in the presence of a surfactant to form resin particles, and then distilling off the solvent.

Examples of methods for making the compound represented by general formula (1) present on the surface of pre-produced resin particles include a physical dyeing method in which the compound represented by general formula (1) is attached to the surface of the resin particles, and a chemical swelling method in which the resin particles are swollen with an organic solvent and mixed with the compound represented by general formula (1), thereby allowing the compound represented by general formula (1) to penetrate into the interior of the resin.

Among the above, emulsion polymerization, mini-emulsion polymerization, and phase inversion emulsification are preferred from the viewpoint of being able to sufficiently reduce the particle size of the resin particles and obtaining a resin with a high degree of coloration in order to solve the problems of the present invention.

The aqueous ink composition for writing instruments can be obtained by mixing a dispersion of a carrier carrying general formula (1) in an aqueous medium, and, if necessary, other colorants and additives, at an appropriate temperature range, and stirring and mixing with a mixer, roll, homogenizer, disperser, etc. It can also be prepared using a media-type disperser such as a rotary shear homogenizer, ball mill, sand mill, or attritor, and a high-pressure counter-impingement type disperser.

It is preferable that the carrier is in a state in which the compound represented by general formula (1) is encapsulated. To encapsulate such a compound represented by general formula (1) in a carrier, for example, the carrier can be produced by polymerizing the compound represented by general formula (1) using a hydrophobic monomer in which the compound represented by general formula (1) is dissolved, or by polymerizing the compound represented by general formula (1) using a hydrophobic monomer adsorbed on the surface of the compound.

A detailed study of the former is reported in Colloid and Polymer Science (December 2003, Vol. 282, pp. 119-126). A specific example of the latter is a method in which a dispersion of a coloring material and a dispersion of a hydrophobic monomer that have been separately prepared are mixed and then polymerized. A detailed study of this method is reported in "Encapsulation of Carbon Black by Miniemulsion Polymerization," Macromolecular Chemistry and Physics (January 2001, Vol. 202, pp. 51-60).

The content of the compound represented by general formula (1) is preferably 0.4 to 20 times the content of the resin and cellulose nanofiber constituting the carrier in terms of mass ratio. When the content of the compound represented by general formula (1) is within the above range, the occurrence of skipped lines, blurring, and clogging of the tip of the lead can be more effectively suppressed.

The resin constituting the carrier is selected according to the application, but for example, a resin obtained by copolymerizing hydrophilic polymerizable monomers such as acrylic acid, methacrylic acid, N-(2-hydroxyethyl)acrylamide, N-vinylpyrrolidone, and polymerizable monomers having ammonium salts with lipophilic polymerizable monomers such as acrylic acid esters, methacrylic acid esters, vinyl acetate, styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-t-butylstyrene, 4-methoxystyrene, 4-chlorostyrene, and N-vinylcarbazole in an appropriate mixing ratio by a known method can be used.

Examples of (meth)acrylic acid esters include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and diethylaminoethyl (meth)acrylate. Other examples include monofunctional acrylates such as polyethylene glycol monoacrylate, polyethylene glycol monomethacrylate, polypropylene glycol monoacrylate, polypropylene glycol monomethacrylate, phenoxyethyl acrylate, and phenoxyethyl methacrylate; polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, polypropylene glycol dimethacrylate, trimethylolethane triacrylate, trimethylolethane trimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, and trimethylolpropane diacrylate. acrylate, trimethylolpropane dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, dipentaerythritol hexaacrylate, dipentaerythritol hexamethacrylate, dipentaerythritol pentaacrylate, dipentaerythritol pentamethacrylate, hexanediol diacrylate, hexanediol dimethacrylate, trimethylolpropane tri(acryloyloxypropyl)ether, etc.

When polymerizing the polymerizable monomer to obtain the resin that constitutes the carrier, an oil-soluble initiator, a water-soluble initiator, a photopolymerization initiator, a photoacid generator, etc. can be used.

Examples of oil-soluble initiators include, but are not limited to, azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 1,1'-azobis(cyclohexane-1-carbonitrile), and 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile; and peroxide initiators such as acetylcyclohexylsulfonyl peroxide, diisopropyl peroxycarbonate, decanonyl peroxide, lauroyl peroxide, stearoyl peroxide, propionyl peroxide, acetyl peroxide, t-butylperoxy-2-ethylhexanoate, benzoyl peroxide, t-butylperoxyisobutyrate, cyclohexanone peroxide, methyl ethyl ketone peroxide, dicumyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, and cumene hydroperoxide.

Water-soluble initiators include, but are not limited to, ammonium persulfate, potassium persulfate, 2,2'-azobis(N,N'-dimethyleneisobutyromidine) hydrochloride, 2,2'-azobis(2-aminodinopropane) hydrochloride, azobis(isobutylamidine) hydrochloride, 2,2'-azobisisobutyronitrile sodium sulfonate, ferrous sulfate, or hydrogen peroxide.

Examples of photopolymerization initiators include vicinal polyketoaldonyl compounds, α-carbonyl compounds, acionoin ethers, polyquinone compounds, combinations of triaryl imidazole dimer and p-aminophenyl ketone, trioxadiazole compounds, etc. Among these, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone (trade name: Irgacure 369, manufactured by BASF) is preferred.

As the photoacid generator, known photoacid generators such as salts of onium ions, such as sulfonium, iodonium, selenium, ammonium, and phosphonium, with anions can be used.

Examples of sulfonium ions include triphenylsulfonium, tri-p-tolylsulfonium, tri-o-tolylsulfonium, tris(4-methoxyphenyl)sulfonium, 1-naphthyldiphenylsulfonium, diphenylphenacylsulfonium, phenylmethylbenzylsulfonium, 4-hydroxyphenylmethylbenzylsulfonium, dimethylphenacylsulfonium, and phenacyltetrahydrothiophenium.

Examples of the iodonium ions include diphenyliodonium, di-p-tolyliodonium, bis(4-dodecylphenyl)iodonium, bis(4-methoxyphenyl)iodonium, and (4-octyloxyphenyl)phenyliodonium.

Examples of selenium ions include triarylselenium ions such as triphenylselenium, tri-p-tolylselenium, tri-o-tolylselenium, tris(4-methoxyphenyl)selenium, 1-naphthyldiphenylselenium, tris(4-fluorophenyl)selenium, tri-1-naphthylselenium, and tri-2-naphthylselenium.

Examples of ammonium ions include tetraalkylammonium ions such as tetramethylammonium, ethyltrimethylammonium, diethyldimethylammonium, triethylmethylammonium, tetraethylammonium, trimethyl-n-propylammonium, trimethylisopropylammonium, trimethyl-n-butylammonium, and trimethylisobutylammonium.

Examples of phosphonium ions include tetraphenylphosphonium, tetra-p-tolylphosphonium, tetrakis(2-methoxyphenyl)phosphonium, triphenylbenzylphosphonium, triphenylphenacylphosphonium, triphenylmethylphosphonium, triethylbenzylphosphonium, and tetraethylphosphonium.

Examples of the anion include perhalogen acid ions such as ClO ₄ ^- and BrO ₄ ^- ; halogenated sulfonate ions such as FSO ₃ ^- and ClSO ₃ ^- ; sulfate ions such as CH ₃ SO ₄ ^- , CF ₃ SO ₄ ^- and HSO ₄ ^- ; carbonate ions such as HCO ₃ ^- and CH ₃ CO ₃ ^- ; aluminate ions such as AlCl ₄ ^- and AlF ₄ ^- _; hexafluorobismuthate ion, carboxylate ions such as CH ₃ COO ^- , CF ₃ COO ^- , C ₆ H ₅ ^{COO - ,} CH ₃ C ₆ H ₄ COO ^- , _{C 6 F 5 COO} ^- and CF ₃ C ₆ H ₄ COO ^- _; Examples include, but are not limited to, arylborates such as ₂ CH ₂ B(C ₆ H ₅ ) ₃ ^-- ; thiocyanate, and nitrate.

The concentration of the polymerization initiator is preferably 0.01% by mass or more and 10% by mass or less, and more preferably 0.03% by mass or more and 5% by mass or less, based on the total mass of the monomer components.

The emulsifier used during polymerization of the polymerizable monomer is not particularly limited, and may be a cationic surfactant, an anionic surfactant, a nonionic surfactant, or the like.

Specific examples of cationic surfactants include dodecyl ammonium chloride, dodecyl ammonium bromide, dodecyl trimethyl ammonium bromide, dodecyl pyridinium chloride, dodecyl pyridinium bromide, and hexadecyl trimethyl ammonium bromide.

Anionic surfactants include fatty acid soaps such as sodium stearate and sodium dodecanoate, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and sodium lauryl sulfate.

Further examples of nonionic surfactants include dodecyl polyoxyethylene ether, hexadecyl polyoxyethylene ether, nonylphenyl polyoxyethylene ether, lauryl polyoxyethylene ether, sorbitan monooleate polyoxyethylene ether, monodecanoyl sucrose, and lauric acid monoglyceride (manufactured by Taiyo Kagaku Co., Ltd.).

The resin content in the carrier is preferably 5 to 50% by mass, and more preferably 10 to 40% by mass, based on the mass (total solids) of the aqueous ink composition for writing instruments. By being in the above range, the sensitivity to light exposure and the strength of the drawing paper can be further improved, and the adhesion of the aqueous ink composition for writing instruments is also improved.

[Cellulose nanofiber]
The cellulose nanofibers contained in the carrier are selected according to the intended use, but for example, are obtained by subjecting plant fibers to chemical and/or mechanical fiber defibration treatment, and are ultrafine fibers with an average width of about several nm to 20 nm and an average length of about 0.5 μm to several μm. The size (fiber diameter) of these cellulose nanofibers varies depending on the type of cellulose nanofiber. In addition, a fiber diameter is selected that falls within a suitable range in terms of thickening action, stability over time, color development, etc., within a range that does not impair the characteristics in various applications.

Materials that contain cellulose fibers include plants such as wood, bamboo, kenaf, hemp, jute, wood pulp, waste paper, crystalline cellulose, agricultural waste, and recycled pulp, animals such as sea squirts, algae, and microorganisms.

Equipment used for defibration processing includes rotary shear homogenizers, high-pressure homogenizers, high-pressure homogenizers, ball mills, sand mills, attritors, high-pressure opposed collision type dispersers, grinders, conical refiners, etc.

Cellulose nanofibers are commercially available and can be used. Examples of commercially available products include Rheocrysta I-2AX, CNF 03, and CNF 04 (manufactured by Daiichi Chemical Industry Co., Ltd.), ELLEX-S (manufactured by Daio Paper Co., Ltd.), and nanoforest-S (manufactured by Chuetsu Pulp Industry Co., Ltd.).

The amount of cellulose nanofiber is preferably 0.001 to 40 parts by mass, more preferably 0.01 to 10 parts by mass, and even more preferably 0.05 to 5 parts by mass, per 100 parts by mass of the aqueous medium contained in the aqueous ink composition for writing instruments.

There are no particular limitations on the method for supporting the compound represented by general formula (1) on the cellulose nanofibers. For example, the cellulose nanofibers are contacted with the compound represented by general formula (1) in an aqueous medium, and then heated or oxidized as necessary, and the medium is then distilled off to obtain dyed cellulose nanofibers. When contacting, a pH adjuster, a color developer, a dispersant, etc. may be added.

The aqueous coloring liquid may be the same system used when dyeing the cellulose nanofibers, or it may be a liquid in which the colored cellulose nanofibers are extracted by drying and then dispersed again in an aqueous medium.

[Media]
When preparing an aqueous ink composition for writing instruments, it is preferable to use a mixture of water and a water-soluble organic solvent as the aqueous medium. Examples of the water-soluble organic solvent to be contained in the aqueous medium include alcohol, polyhydric alcohol, polyglycol, glycol ether, nitrogen-containing polar solvent, and sulfur-containing polar solvent. Specific examples include ethylene glycol, diethylene glycol, triethylene glycol, 3-methyl-1,3-butanediol, 1,3-butanediol, polyethylene glycol, glycerin, ethylene glycol monomethyl ether, and diethylene glycol monomethyl ether. These water-soluble organic solvents contribute to maintaining the moisture retention of the ink for writing instruments, improving the solubility of coloring materials, and effectively penetrating the ink for writing instruments into recording paper. In the aqueous medium in the ink for writing instruments, the ratio of water to the water-soluble organic solvent (based on mass) is preferably water/water-soluble organic solvent=9/1 to 1/9. More preferably, it is 8/2 to 2/8, and even more preferably, it is 7/3 to 3/7. In this way, the dispersibility or solubility of the colorant containing compound (1) in the ink can be improved.

[Additives]
The aqueous ink composition for writing instruments can be suitably used in aqueous ballpoint pens, gel inks for aqueous ballpoint pens, felt tip pens, marking pens, and the like, and additives such as dispersants, lubricants, pH adjusters, rust inhibitors, preservatives, and antibacterial agents may be appropriately added within a range that does not impair the properties in various applications.

Lubricants are not particularly limited, but examples include nonionic lubricants such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, and alkyl phosphate esters, 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.

The pH adjuster is not particularly limited, but examples include sodium hydroxide, urea, monoethanolamine, diethanolamine, triethanolamine, sodium tripolyphosphate, sodium carbonate, and alkali metal salts of phosphoric acid. For example, from the viewpoints of usability, safety, and the stability of the ink itself, it is preferable to adjust the pH to 4 to 11, and more preferably 5 to 10.

Anti-rust agents include, but are not limited to, benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, saponin, and phosphate ester compounds.

Preservatives or antibacterial agents are not particularly limited, but examples include phenol, sodium benzoate, benzimidazole compounds, sodium omadine, sodium pentachlorophenol, sodium sorbate, and 1,2-benzisothiazolin-3-one.

The aqueous ink composition for writing instruments may also contain a pigment.

The pigments that can be used are not particularly limited, but can be selected from inorganic and organic pigments that are conventionally used in writing instruments such as water-based ballpoint pens.

Examples of inorganic pigments include carbon black and metal powder.

Examples of organic pigments include azo pigments, phthalocyanine pigments, perylene pigments, and quinacridone pigments. The content is 0.1 to 50 parts by mass, and preferably 0.5 to 30 parts by mass, per 100 parts by mass of the aqueous medium.

When a pigment is used in combination, it is preferable to use a dispersant. As a dispersant, ionic surfactants, nonionic surfactants, polymeric surfactants, water-soluble resins, etc. can be used as long as they do not impair the characteristics of the application.

[Manufacturing method]
The aqueous ink composition for a writing instrument can be produced by a known method.

For example, the aqueous ink composition for writing instruments and, if necessary, other colorants and additives are mixed at an appropriate temperature range, and the mixture is stirred and mixed using a mixer, roll, homogenizer, disperser, etc. Alternatively, a media-type dispersing machine such as a rotary shear homogenizer, ball mill, sand mill, or attritor, and a high-pressure counter-impingement type dispersing machine can also be used.

The aqueous ink composition for writing instruments produced in this manner is filled into ballpoint pens, felt tip pens, and marking pens.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the text, "parts" and "%" refer to "parts by mass" and "% by mass" unless otherwise specified.

The compound represented by the general formula (1) was synthesized by a known method. The obtained compound was identified using a ¹ H nuclear magnetic resonance spectroscopic analysis ( ¹ H-NMR) device (ECA-400, manufactured by JEOL Ltd.) and an LC/TOF MS device (LC/MSD TOF, manufactured by Agilent Technologies).

<Production of Oil-Based Ink Composition for Writing Instruments>
[Examples 1 to 22, Comparative Examples 1 to 14]
The constituent materials used were shown in Tables 1 and 2. First, a resin was added to a medium and dissolved by heating to 70° C., and then the mixture was cooled to room temperature. A colorant and other constituent materials were added, and the mixture was dispersed for 3 hours using an attritor (manufactured by Mitsui Mining Co., Ltd.) to produce an oil-based ink composition for a writing instrument.

The comparative compounds (1) to (6) in Table 2 are the following compounds.

[Evaluation of dissolution stability]
20 mL of each of the oil-based ink compositions for writing instruments obtained above was added to a 50 mL sample bottle, sealed, and left for one month under low temperature (0° C.) and high temperature (60° C.) conditions to evaluate the dissolution stability of the ink composition. The presence or absence of aggregates in the ink composition was visually observed using a phase contrast microscope (BX53, manufactured by Olympus Corporation).
A: The ink composition is free of aggregates.
B: A small amount of agglomerates were generated in the ink composition.
C: Coagulation occurred in the ink composition.

[Evaluation of blurring (initial writing ability) when writing]
Each of the oil-based ink compositions for writing instruments obtained above was filled into an ink reservoir made of polypropylene tube having an inner diameter of 1.2 mm and a length of 140 mm. A ballpoint pen for evaluation test was prepared by using this ink reservoir and a phosphor bronze tip (ball diameter 0.7 mm).

The cap was removed from the test ballpoint pen and it was left for 1 hour under low temperature (0°C) and high temperature (60°C) conditions with a humidity of 65%, after which a circle was handwritten on it using JIS P3201 writing paper.

The blurring at the beginning of writing was evaluated according to the following criteria.
A: No smearing occurred under both low temperature (0° C.) and high temperature (60° C.) conditions.
B: Slight smearing occurred under either or both of the low temperature (0° C.) and high temperature (60° C.) conditions.
C: Clear smearing occurred under either or both of the low temperature (0° C.) and high temperature (60° C.) conditions.

[Writing feel evaluation]
The ballpoint pens thus produced were used to evaluate the writing experience. The writing experience was evaluated based on the following criteria: whether there were skipped or smudged lines in the writing, and whether the writing density did not change and the writing continued to be stable.
A: Under both low temperature (0° C.) and high temperature (60° C.) conditions, there is no skipping or smearing of lines in the handwriting, and there is no change in the density of the handwriting.
B: Under at least one of the low temperature (0° C.) and high temperature (60° C.) conditions, slight skipping or smearing of lines in handwriting occurred, or slight change in handwriting density occurred.
C: At least one of the low temperature (0° C.) and high temperature (60° C.) conditions clearly caused skipping or smearing of lines in the handwriting, and a change in the handwriting density occurred.

[Evaluation of handwriting robustness]
For the evaluation of handwriting fastness, the ballpoint pen was used to write 20 cm at a constant writing pressure to create an image sample. The image sample was placed in a xenon test device (Atlas Weather-O-Meter Ci4000, manufactured by Toyo Seiki Seisakusho Co., Ltd.) and exposed for 10 hours under the following conditions: (illuminance: 0.28 W/ ^m2 at 340 nm, black panel temperature: 40°C, relative humidity: 50%). The spectra before and after exposure were read with a scanner, and the initial optical density was defined as OD ₀ , and the optical density after 5 hours of exposure was defined as OD _5. The optical density residual rate was defined as follows:

Optical density residual rate (%) = (OD ₅ /OD ₀ ) × 100
The evaluation criteria are as follows:
A: Optical density residual rate is 85% or more; B: Optical density residual rate is 70% or more and less than 85%; C: Optical density residual rate is less than 70%. The evaluation results are shown in Table 3.

As described above, by using the compound of the present invention, it is possible to provide an oil-based ink composition for a writing instrument in which aggregation of the colorant is suppressed even under low and high temperature conditions. Furthermore, by using such an oil-based ink composition for a writing instrument, it is possible to provide a ballpoint pen that suppresses the phenomenon of smearing at the start of writing, has a good writing feel with less skipping and smearing in the handwriting, and has high handwriting fastness.

<Production of Water-Based Ink Composition for Writing Instruments>
<Example 23>
5 parts of compound (1-2), 1 part of methanol, and 0.5 parts of cellulose nanofiber (LEOCRYSTA I-2AX) were added, followed by the addition of 99 parts of ion-exchanged water. The mixture was heated to an internal temperature of 80°C and stirred for 2 hours while removing methanol. After cooling to room temperature, a dispersion treatment was carried out with a homogenizer for 5 minutes to prepare an aqueous ink composition for writing instruments in which cellulose nanofiber dyed with compound (1) was dispersed in the medium.

<Examples 24 to 44, Comparative Examples 15 to 32>
An aqueous ink composition for a writing instrument containing cellulose nanofibers dyed with a compound and an aqueous ink composition for a comparative example writing instrument were prepared by the same procedure as in Example 23, except that the compounds and cellulose nanofibers were changed to those shown in Table 4. The cellulose nanofibers are available from Rheocrysta I-2AX, CNF 03, CNF 04 (Dai-ichi Kogyo Seiyaku Co., Ltd.), ELLEX-S (Daioh Paper Co., Ltd.), and nanoforest-S (Chuetsu Pulp Industry Co., Ltd.).

Comparative compounds (1) to (3) are the same as those described above.

<Example 45>
10 g of cyclohexyl methchlorate, 8 g of n-butyl methacrylate, 2 g of triallyl isocyanurate, and 0.5 g of 2,2'-azobis-(2-methylbutyronitrile) were mixed and stirred at 100 rpm for 1 hour. The mixture obtained was added dropwise to 70 g of an aqueous solution (concentration 0.3%) of 0.05 g of lauric acid monoglyceride (manufactured by Taiyo Kagaku Co., Ltd.), and stirred at 300 rpm for 1 hour. The mixture was dispersed with a homogenizer for 1 hour (Dispersion A).

10 g of compound (1-5) was added to 110 g of an aqueous solution of lauric acid monoglyceride (concentration 2.7%), stirred at 300 rpm for 2 hours, and then dispersed with a homogenizer for 1 hour (dispersion liquid B).

20 g of dispersion A and 80 g of dispersion B were mixed and stirred at 300 rpm for 1 hour. The mixture was then dispersed with a homogenizer for 5 minutes and stirred for 1 hour. After stirring, the mixture was polymerized at 70°C for 8 hours under a nitrogen atmosphere to obtain a dispersion containing a carrier in which compound (1-5) was dispersed in resin particles. This was filtered through a 5.0 μm filter to remove coarse particles, thereby obtaining an aqueous ink composition for writing instruments. The average particle size of the resin particles in the resulting aqueous ink composition for writing instruments was 58 nm.

<Examples 46 to 50>
In Example 45, the same procedure was repeated except that the materials used were changed to those shown in Table 5, to prepare aqueous ink compositions for writing instruments in which the compound represented by general formula (1) was dispersed or encapsulated in the carrier.

[Dispersion Stability Evaluation]
20 mL of each of the aqueous ink compositions for writing instruments obtained above was added to a 50 mL sample bottle, which was then sealed and left for one month under low temperature (0° C.) and high temperature (60° C.) conditions to evaluate the dispersion stability of the ink composition. The presence or absence of aggregates in the ink composition was observed using a phase contrast microscope (BX53, manufactured by Olympus Corporation).
A: No agglomerates are observed in the ink composition.
B: A small amount of agglomerates was generated in the ink composition.
C: Coagulation was clearly observed in the ink composition.

[Evaluation of blurring (initial writing ability) when writing]
Each of the water-based ink compositions for writing instruments obtained above was filled into an ink reservoir made of polypropylene tube having an inner diameter of 1.2 mm and a length of 140 mm. A ballpoint pen for evaluation test was prepared by using this ink reservoir and a phosphor bronze tip (ball diameter: 0.7 mm).

The cap was removed from the test ballpoint pen, and the pen was left to stand for 1 hour under low temperature (0°C) and high temperature (60°C) conditions with a humidity of 65%, after which a circle was handwritten on the pen using JIS P3201 writing paper. The degree of smearing at the start of writing was evaluated according to the following criteria.
A: No smearing occurred under both low temperature (0° C.) and high temperature (60° C.) conditions.
B: Scratches occurred under either or both low temperature (0° C.) and high temperature (60° C.) conditions.
C: Obvious smearing occurred under either or both low temperature (0° C.) and high temperature (60° C.) conditions.

[Writing feel evaluation]
The ballpoint pens thus produced were used to evaluate the writing experience. The writing experience was evaluated based on the following criteria: whether there were skipped or smudged lines in the writing, and whether the writing density did not change and the writing continued to be stable.
A: Under both low temperature (0° C.) and high temperature (60° C.) conditions, there is no skipping or smearing of lines in the handwriting, and there is no change in the density of the handwriting.
B: Under at least one of the low temperature (0° C.) and high temperature (60° C.) conditions, slight skipping or smearing of lines in handwriting occurred, or slight change in handwriting density occurred.
C: At least one of the low temperature (0° C.) and high temperature (60° C.) conditions clearly caused skipping or smearing of lines in the handwriting, and a change in the handwriting density occurred.

[Evaluation of handwriting robustness]
The ballpoint pen was used to create an image sample, which was written at a constant writing pressure of 20 cm. The image sample was placed in a xenon test device (Atlas Weatherometer Ci4000, manufactured by Toyo Seiki Seisakusho Co., Ltd.) and exposed for 10 hours under the following conditions: (illuminance: 0.28 W/ ^m2 at 340 nm, black panel temperature: 40°C, relative humidity: 50%). The spectra before and after exposure were read with a scanner, and the initial optical density was defined as OD ₀ , and the optical density after 5 hours of exposure was defined as OD _5. The optical density residual rate was defined as follows:

Optical density residual rate (%) = (OD ₅ /OD ₀ ) × 100
The evaluation criteria are as follows:
A: Optical density residual rate was 85% or more; B: Optical density residual rate was 70% or more and less than 85%; C: Optical density residual rate was less than 70%. The evaluation results are shown in Tables 6 and 7.

As shown by the above results, the present invention provides an aqueous ink composition for writing instruments that has high dispersion stability of the carrier in an aqueous medium. Furthermore, by using such an aqueous ink composition for writing instruments, it is possible to provide a ballpoint pen that suppresses the phenomenon of smearing at the start of writing, has a good writing feel with less skipping and smearing in the handwriting, and has high handwriting robustness.

The oil-based ink composition for writing instruments of the present invention suppresses aggregation of the colorant even under low and high temperature conditions. In addition, the water-based ink composition for writing instruments of the present invention has excellent dispersion stability of the carrier.

A ballpoint pen containing the oil-based ink composition for writing instruments or the water-based ink composition for writing instruments of the present invention suppresses the phenomenon of smearing at the start of writing, has a good writing feel with less skipping and smearing in the handwriting, and has high handwriting fastness.

Claims (6)

A medium containing an alcohol or a glycol ether,
a resin present in a dissolved state in the medium; and a colorant containing a compound represented by the following general formula (1):
An oil-based ink composition for a writing instrument comprising:

[R ₁ and R ₂ each represent a 2-ethylhexyl group or an n-butyl group;
_R3 represents a linear alkyl group having 1 to 4 carbon atoms or a branched alkyl group having 3 to 4 carbon atoms;
_R4 represents any functional group selected from the group consisting of a t-butyl group, an iso-propyl group, a phenyl group, and a benzyl group. 2. The oil-based ink composition for writing instruments according to claim 1 , wherein the resin comprises a butyral resin or a ketone resin. A ballpoint pen comprising the oil-based ink composition for a writing instrument according to claim 1 or 2 . an aqueous medium; and a carrier dispersed in the aqueous medium;
A water-based ink composition for a writing instrument comprising:
The aqueous ink composition for writing instruments is characterized in that the carrier carries a compound represented by general formula (1).

[R ₁ and R ₂ each represent a 2-ethylhexyl group or an n-butyl group ;
_R3 represents a linear alkyl group having 1 to 4 carbon atoms or a branched alkyl group having 3 to 4 carbon atoms;
_R4 represents any functional group selected from the group consisting of a t-butyl group, an iso-propyl group, a phenyl group, and a benzyl group. The aqueous ink composition for writing instruments according to claim 4 , wherein the carrier is a resin or a cellulose nanofiber. A ballpoint pen comprising the aqueous ink composition for a writing instrument according to claim 4 or 5 .