JP7530710B2 - Water-based ballpoint pen ink composition - Google Patents

Description

The present invention relates to an aqueous ink composition for ballpoint pens that does not increase ink viscosity much even in low temperature environments and is less likely to cause writing defects.

Conventionally, as ink compositions for aqueous ballpoint pens using colored particles, for example, 1) an ink composition for aqueous ballpoint pens containing a microcapsule pigment that encapsulates a pigment with a high specific gravity or a pigment that is somewhat difficult to disperse, and a poorly water-soluble medium that has specific physical properties (see, for example, Patent Document 1); 2) a glittering ink composition for ballpoint pens that contains a plate-shaped glittering pigment, a coloring pigment, microcapsule particles that encapsulate an oil-based solvent, water, and one or more salts or emulsions selected from a salt of an acrylic acid polymer, or an emulsion of an olefin polymer, a urethane polymer, and an acrylic acid polymer (see, for example, Patent Document 2); and 3) an ink composition for aqueous ballpoint pens that contains styrene-acrylonitrile resin particles, a colorant, an alkyl sulfate, a phosphate ester surfactant, and water (see, for example, Patent Document 3).

The above Patent Document 1 aims to provide an aqueous ballpoint pen ink composition that makes it easier to disperse pigments with high specific gravity or pigments that are somewhat difficult to disperse, the above Patent Document 2 aims to provide a glittering ballpoint pen ink composition that can maintain vivid handwriting and stability over time, and the above Patent Document 3 aims to provide an aqueous ballpoint pen ink composition that has excellent dispersion stability and can produce good handwriting, but these patent documents do not disclose or suggest anything about writability in low-temperature environments.

In general, when writing with a ballpoint pen in a low-temperature environment, it is often impossible to write normally. The cause of this is thought to be that at low temperatures, the ink viscosity increases, making it difficult to eject from the pen tip, resulting in poor ink transfer. In particular, the current situation is that with aqueous ballpoint pen ink compositions that contain materials with large particle sizes, the ink has poor fluidity, making this phenomenon even more likely to occur.

JP 2017-122168 A (Claims, Examples, etc.) JP 2017-119862 A (Claims, Examples, etc.) JP 2019-116576 A (Claims, Examples, etc.)

The present invention is made in view of the problems and current state of the prior art described above, and aims to solve these problems, and to provide an ink composition for an aqueous ballpoint pen and an aqueous ballpoint pen that have a small increase in ink viscosity even in a low-temperature environment and are less likely to cause writing defects.

In view of the above-mentioned problems and current situation, the inventors conducted intensive research and discovered that the above-mentioned objective aqueous ballpoint pen ink composition can be obtained by containing at least specific colored resin particles having an average particle size within a specified range and a specific surfactant, and thus completed the present invention.

That is, the aqueous ballpoint pen ink composition of the present invention is characterized by containing at least urethane-based colored particles having an average particle size of 0.5 to 6 μm, and an acetylene-based surfactant.
The above-mentioned aqueous ballpoint pen ink composition preferably has a contact angle between the polyethylene terephthalate film and the ink of 40° or less.
The water-based ballpoint pen of the present invention is characterized by being equipped with the water-based ballpoint pen ink composition having the above-mentioned configuration.
The surface roughness of the ball of the water-based ballpoint pen is preferably less than 10 nm.

The present invention provides an ink composition for an aqueous ballpoint pen that shows little increase in ink viscosity even in low-temperature environments and is less likely to cause writing defects, and an aqueous ballpoint pen equipped with the ink composition.

Hereinafter, an embodiment of the present invention will be described in detail.
The aqueous ballpoint pen ink composition of the present invention is characterized by containing at least urethane-based colored resin particles having an average particle size of 0.5 to 6 μm, and an acetylene-based surfactant.

<Urethane-based colored resin particles>
The urethane-based colored resin particles used in the present invention are not particularly limited as long as they are composed of colored urethane-based resin particles, and examples thereof include 1) urethane-based colored resin particles colored with a dye or pigment, 2) urethane-based colored resin particles made thermochromic using a leuco dye, etc., and 3) urethane-based colored resin particles made photochromic using a photochromic dye (compound), a fluorescent dye, etc., which serves as a photochromic dye.

The urethane-based colored resin particles 1) above are composed of a polymer or copolymer having at least a urethane bond, and are obtained by reacting an isocyanate component (including a diisocyanate component) with a polyol component (including a diol component), and examples thereof include at least one type of urethane particles (polyester-type urethane particles, polycarbonate-type urethane particles, polyether-type urethane particles, etc.), urethane-urea particles, etc.
The urethane-based colored resin particles may be, for example, those obtained by the following production method.
The above-mentioned urethane-based colored resin particles can be produced by the steps of: a) preparing an oil phase containing an organic solvent, an isocyanate monomer or isocyanate prepolymer, and a water-insoluble dye; b) preparing an aqueous phase by mixing water and a dispersant; and c) mixing the oil phase and the aqueous phase to emulsify the oil phase components, followed by polymerization. When no water-insoluble dye is used, the resulting particles can be used as white urethane-based colored resin particles.

The oil phase contains an organic solvent, an isocyanate monomer or an isocyanate prepolymer, and, when colored, a water-insoluble dye. A plurality of kinds of organic solvents may be contained.
This oil phase can be prepared by heating an organic solvent to a predetermined temperature, adding a water-insoluble dye and stirring, then adding the above-mentioned monomer or prepolymer, and further adding another organic solvent as necessary.
Examples of the organic solvent that can be used include phenyl glycol, benzyl alcohol, ethylene glycol monobenzyl ether, and ethyl acetate. In addition, alkylsulfonic acid phenyl ester, ethylhexyl phthalate, tridecyl phthalate, ethylhexyl trimellitate, diethylene glycol dibenzoate, dipropylene glycol dibenzoate, and liquid xylene resin can also be used.

As the isocyanate monomer or prepolymer, for example, hexamethylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, isophorone diisocyanate, isocyanate prepolymer, etc. can be used.
As the isocyanate prepolymer, it is preferable to use a trimer such as the above-mentioned triol adduct of the isocyanate or an isocyanurate modified product from the viewpoint of good curing by polymerization. In addition to the trimer, a dimer such as the above-mentioned allophanate modified product of the isocyanate can be used as an auxiliary prepolymer.
The average particle size can be adjusted by controlling the stirring conditions during polymerization.

The water-insoluble dye is a dye that is insoluble in water at room temperature. For example, salt-forming dyes, disperse dyes, oil-soluble dyes, etc. can be used. From the viewpoint of color development, it is preferable to use salt-forming dyes having a chemical structure of an azo type, a metal complex azo type, an anthraquinone type, or a metal phthalocyanine type.
The aqueous phase can be prepared by mixing water and a dispersant, such as, but not limited to, polyvinyl alcohol.
In the emulsification and polymerization process, the components of the oil phase are emulsified, and in the polymerization process, the oil phase is added to the aqueous phase and emulsified and mixed while heating to a predetermined temperature using a homogenizer or the like, thereby obtaining urethane-based colored resin particles.

In addition to the above emulsion polymerization, the urethane-based colored resin particles may be prepared by a phase separation method. This production method includes preparing a dye-containing solution, preparing a protective colloid-containing solution, and polymerizing an isocyanate monomer or an isocyanate.
The dye-containing solution can be prepared by dissolving the water-insoluble dye in an organic solvent under heating. The water-insoluble dye and the organic solvent can be the same as those used in the emulsion polymerization.
The protective colloid-containing solution can be prepared by dissolving a protective colloid in water. As the protective colloid, for example, a methyl vinyl ether-maleic anhydride copolymer can be used.
In the case of coloring, polymerization of an isocyanate monomer or an isocyanate prepolymer can be produced by adding a dye-containing solution to a protective colloid-containing solution heated to a predetermined temperature and dispersing it in the form of oil droplets, adding the above-mentioned isocyanate monomer or isocyanate prepolymer thereto, and stirring while maintaining the temperature.

Examples of the thermochromic urethane-based colored resin particles of 2) above include thermochromic urethane-based colored resin particles produced by microencapsulating a thermochromic composition containing at least a leuco dye which is an electron-donating dye and functions as a color former, a color developer which is a component capable of causing the leuco dye to develop color, and a color change temperature regulator which can control the color change temperature in the color development of the leuco dye and the color developer, so as to have a predetermined average particle size.
As the microencapsulation method, for example, interface polymerization method, interface polycondensation method, in situ polymerization method, liquid hardening coating method, phase separation method from aqueous solution, phase separation method from organic solvent, melting dispersion cooling method, air suspension coating method, spray drying method, etc. can be mentioned, and can be appropriately selected according to the application.For example, in the phase separation method from aqueous solution, similar to the above 1) phase separation method, after heating and melting leuco dye, color developer, and discoloration temperature regulator, put into emulsifier solution, heat and stir to disperse in oil droplets, and then gradually put in the urethane resin raw material of the wall membrane exemplified in the above 1) as an encapsulation membrane agent, and continue to react and prepare, and then filter this dispersion to produce thermochromic urethane-based colored resin particles made of thermochromic microcapsule pigment.In this thermochromic urethane-based colored resin particle, the type, amount, etc. of leuco dye, color developer, and discoloration temperature regulator can be suitably combined to set the color development temperature and decolorization temperature of each color to a suitable temperature.
The thermochromic urethane-based colored resin particles are preferably reversible thermochromic. The reversible thermochromic type may be a heat-discoloring type that is decolorized by heating from a colored state, a color memory-retaining type that alternately retains a colored state or a decolored state in a specific temperature range, or a heat-coloring type that is colored by heating from a decolored state and returns to the decolored state by cooling from the colored state, and may be composed of various types alone or in combination.

Examples of the photochromic urethane-based colored resin particles of the above 3) include photochromic urethane-based colored resin particles composed of at least one selected from photochromic dyes (compounds), fluorescent dyes, etc., and resins such as terpene phenol resins, and photochromic urethane-based colored resin particles produced by microencapsulating a photochromic composition containing at least one selected from photochromic dyes (compounds), fluorescent dyes, etc., an organic solvent, and additives such as antioxidants, light stabilizers, and sensitizers, so as to have a predetermined average particle size. As the microencapsulation method, it can be prepared in the same manner as the production of the above-mentioned thermochromic resin particles.
By suitably using a photochromic dye (compound), fluorescent dye, or the like, the photochromic urethane-based colored resin particles can be made to have the property of being colorless in an indoor lighting environment (indoor lighting equipment selected from incandescent lamps, fluorescent lamps, lamps, white LEDs, and the like) and developing color in an ultraviolet ray irradiation environment (irradiation with light having a wavelength of 200 to 400 nm, or irradiation with sunlight containing ultraviolet rays).
The above urethane-based colored resin particles 1) to 3) can be used as a normal coloring material for ballpoint pens, such as fluorescent pigments, thermochromic pigments, photochromic pigments, and microencapsulated pigments (coloring materials). In addition, the above urethane-based colored resin particles 1) to 3) can be urethane-based colored resin particles produced by known production methods, and if commercially available products are available, they may be used.
From the standpoint of coloring power, dispersion stability, etc., it is desirable to use these urethane-based colored resin particles having an average particle size of 0.5 to 6 μm, and preferably 1 to 5 μm.
In the present invention (including the examples described later), the "average particle size" refers to the particle size (D50) at 50% cumulative volume in the particle size distribution calculated based on the volume standard measured by a laser diffraction method. Here, the measurement of the average particle size by the laser diffraction method can be performed using, for example, a particle size distribution analyzer HRA9320-X100 manufactured by Nikkiso Co., Ltd.

The content of these urethane-based colored resin particles is preferably 3 to 30% of the total amount of the ink composition, and more preferably 10 to 30%. If the content of these urethane-based colored resin particles is less than 3%, the desired line density cannot be obtained, and if it exceeds 30%, the writing feel becomes heavy and the lines are prone to smearing, which is undesirable.

The acetylene-based surfactant used in the present invention is contained in order to exert the effects of the present invention, and includes at least one type selected from acetylene glycols, their alkylene oxide adducts, and acetylene alcohols (each alone or a mixture of two or more types, the same applies below).
Specific examples of the acetylene glycols, their alkylene oxide adducts, and acetylene alcohols that can be used include at least one selected from the following formulas (I) to (VI).

〔上記式（Ｉ）～（ＩＩＩ）中のＲ１、Ｒ２は、それぞれ炭素数１～８の直鎖又は分岐鎖を有するアルキル基であり、ｍ、ｎ、ｘ、ｙは１～１００の数である。〕

〔上記式（ＩＶ）～（ＶＩ）中、Ｒ３、Ｒ４、Ｒ５は、水素原子、直鎖又は分岐鎖を有する炭素数０～１０の炭素鎖を表し、該炭素鎖には不飽和結合を含んでもいてもよく、Ｒ６は、炭素数２～５のアルキレン基、Ｒ７は、炭素数１～５のアルキレン基を表す。〕

[In the above formulas (I) to (III), R1 and R2 are each a linear or branched alkyl group having 1 to 8 carbon atoms, and m, n, x, and y are numbers from 1 to 100.]

[In the above formulas (IV) to (VI), R3, R4, and R5 each represent a hydrogen atom or a straight or branched carbon chain having 0 to 10 carbon atoms, which may contain an unsaturated bond, R6 represents an alkylene group having 2 to 5 carbon atoms, and R7 represents an alkylene group having 1 to 5 carbon atoms.]

Examples of acetylene glycols and alkylene oxide adducts thereof that can be used include acetylene glycol represented by the above formula (I), a derivative (adduct) of acetylene glycol represented by the above formula (II) with ethylene oxide (EO) added thereto, and a derivative (adduct) of acetylene glycol represented by the above formula (III) with ethylene oxide (EO) or propylene oxide (PO) added thereto.
Examples of the linear or branched alkyl group having 1 to 8 carbon atoms represented by R1 and R2 in the above formulas (I) to (III) include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a pentyl group, a hexyl group, a heptyl group, and an octyl group.

Examples of the acetylene glycol of formula (I) above include 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, 5,8-dimethyl-6-dodecyne-5,8-diol, 2,4,7,9-tetramethyl-5-dodecyne-4,7-diol, 8-hexadecyne-7,10-diol, 7-tetradecyne-6,9-diol, 2,3,6,7-tetramethyl-4-octyne-3,6-diol, 3,6-diethyl-4-octyne-3,6-diol, and 2,5-dimethyl-3-hexyne-2,5-diol. Examples of the alkylene oxide (EO, PO) adducts of the acetylene glycol of formula (II) and formula (III) above include alkylene oxide derivatives of the acetylene glycol.

The synthesis methods of each compound listed in the above formulas (I) to (III) are known and can be obtained by various methods, and commercially available products may be used. For example, examples of acetylene glycols and their alkylene oxide adducts include commercially available Surfynol 104 [2,4,7,9-tetramethyl-5-dodecyne-4,7-diol, manufactured by Nissin Chemical Industry Co., Ltd.], Surfynol 104E (ethylene glycol), 104H (ethylene glycol), 104A (2-ethylhexanol), etc., which are obtained by diluting Surfynol 104 with various solvents, Surfynol 104 series such as 104S containing silica particles, and EO adducts of Surfynol 104 such as 420, 440, 465, 485, DF110D, DF37, DF58, DF75, and DF220.

The acetylene alcohols represented by the above formulas (IV) to (VI) have an acetylene group (-C≡C-) and a hydroxyl group (-OH) in the molecular structure.
R3, R4, and R5 in the above general formulae (IV) to (VI) each include a hydrogen atom, a linear or branched alkyl group, an alkenyl group, an aryl group, and an aralkyl group. Here, the alkyl group and the alkenyl group may be linear, branched, or cyclic, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, a cyclopentyl group, a cyclohexyl group, a vinyl group, a propenyl group, an allyl group, a hexenyl group, an octenyl group, a cyclopentenyl group, and a cyclohexenyl group. The aryl group may have a substituent such as a lower alkyl group on the aromatic ring, and examples thereof include a phenyl group, a tolyl group, a xylyl group, and a naphthyl group. Furthermore, the aralkyl group may have a substituent such as a lower alkyl group on the aromatic ring. Examples of the aralkyl group include a benzyl group, a phenethyl group, and a naphthylmethyl group.
R6 in the formula (V) represents an alkylene group having 2 to 5 carbon atoms, which may be linear, branched, or cyclic, but is preferably linear. Examples of the linear alkylene group include an ethylene group, a trimethylene group, a tetramethylene group, and a pentamethylene group.
Furthermore, R7 in the above general formula (VI) represents an alkylene group having 1 to 5 carbon atoms, and the alkylene group is a methylene group (having 1 carbon atom), and when the alkylene group has 2 or more carbon atoms, it is the same as R6 in the above general formula (V).

Specific examples of the acetylene alcohols of the above formula (IV) or derivatives thereof include 2-butyn-1-ol, 3-butyn-2-ol, 2-decyn-1-ol, 3,6-dimethyl-1-heptyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, 3,4-dimethyl-1-pentyn-3-ol, 1,1-diphenyl-2-propyn-1-ol, 3-ethyl-1-heptyn-3-ol, 4-ethyl-1-octyn-3-ol, 3-ethyl-1-pentyn-3-ol, 1-ethynyl-1-cyclohexanol, 9-ethynyl-9-fluorenol, 1-heptyn-3-ol, 1-ethyl-1-cyclohexan ... At least one of 1-phenyl-2-propyn-1-ol, 3-phenyl-2-propyn-1-ol, 2-propyn-1-ol, and 1,1,3-triphenyl-2-propyn-1-ol may be mentioned.
Specific examples of the acetylene alcohols of formula (V) or derivatives thereof include at least one of 3-butyn-1-ol, 3-decyn-1-ol, 9-decyn-1-ol, 3-heptyn-1-ol, 3-hexyn-1-ol, 5-hexyn-1-ol, 3-nonyn-1-ol, 3-octyn-1-ol, 3-pentyn-1-ol, 4-pentyn-1-ol, 5-phenyl-4-pentyn-1-ol, and 10-undecyn-1-ol.

Specific examples of the acetylene alcohols of the above formula (VI) or derivatives thereof include at least one of 4-heptyn-2-ol, 5-heptyn-3-ol, 5-hexyn-3-ol, and 4-pentyn-2-ol.
Among the compounds specifically listed in the above formulas (IV) to (VI), it is preferable to use 3-methyl-1-butyn-3-ol, 3-methyl-1-pentyn-3-ol, and 3,5-dimethyl-1-hexyn-3-ol from the viewpoints of usability, cost, safety, and further exerting the effects of the present invention.
The synthesis methods of each of the compounds listed in the above formulas (IV) to (VI) are known and can be obtained by various production methods, and commercially available products may also be used. For example, examples of acetylene alcohols include commercially available Surfynol 61 (3,5-dimethyl-1-hexyne-3-ol), Olfine A (2,5-dimethylhexane-2,5-diol), Olfine B (3-methyl-1-butyne-3-ol), Olfine P (3-methyl-1-pentyne-3-ol), Olfine PD-002W, EXP. 4200, WE-003, SPC, and other olfins manufactured by Nissin Chemical Industry Co., Ltd.

The content (active ingredient amount) of these acetylene surfactants is preferably 0.1 to 3.0% of the total amount of the ink composition, and more preferably 0.3 to 2.0%. If the content of this acetylene surfactant is less than 0.1%, the effect of the present invention may not be fully exerted, while if it exceeds 3.0%, bleeding and show-through on the paper surface are likely to occur, which is undesirable.

<Water-based ballpoint pen ink composition>
The aqueous ballpoint pen ink composition of the present invention is characterized by containing the above-mentioned urethane-based colored resin particles having an average particle size of 0.5 to 6 μm and an acetylene-based surfactant, and may further contain a water-soluble solvent and, if necessary, a general-purpose colorant in addition to the above-mentioned urethane-based colored resin particles.

Examples of water-soluble solvents that can be used include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, 3-butylene glycol, thiodiethylene glycol, and glycerin, as well as ethylene glycol monomethyl ether and diethylene glycol monomethyl ether, which can be used alone or in combination. The content of this water-soluble solvent is preferably 5 to 40% of the total amount of the ink composition.

Usable colorants include water-soluble dyes and pigments, such as inorganic pigments and organic pigments, which can be used in appropriate amounts as needed, provided that the effects of the present invention are not impaired.
As the water-soluble dye, any of direct dyes, acid dyes, food dyes and basic dyes can be used in an appropriate amount within a range that does not impair the effects of the present invention.

The ink composition for aqueous ballpoint pens of the present invention is characterized by containing at least the above-mentioned urethane-based colored resin particles having an average particle size of 0.5 to 6 μm and an acetylene-based surfactant, and may contain colorants other than the above-mentioned colored resin particles, a water-soluble solvent, and water (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.) as the solvent as the remainder, as well as dispersants, lubricants, thickeners, pH adjusters, rust inhibitors, preservatives, or antibacterial agents, etc., as appropriate, within the scope of not impairing the effects of the present invention.

Usable dispersants include nonionic and anionic surfactants and water-soluble resins, and preferably water-soluble polymers.
Examples of lubricants that can be used include nonionic lubricants such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, polyoxyalkylene higher fatty acid esters, and alkyl phosphate esters, which are also used as surface treatment agents for pigments; anionic lubricants such as phosphoric acid esters, alkyl sulfonates of higher fatty acid amides, and alkyl aryl sulfonates; polyalkylene glycol derivatives; and polyether-modified silicones.
The usable thickener is preferably at least one selected from the group consisting of synthetic polymers, cellulose, and polysaccharides, and specifically includes gum arabic, tragacanth gum, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, xanthan gum, welan gum, succinoglycan, diutan gum, dextran, methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, starch glycolic acid and its salts, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylic acid and its salts, polyethylene oxide, copolymers of vinyl acetate and polyvinylpyrrolidone, styrene-acrylic acid copolymers and its salts, and the like.

Examples of pH adjusters include ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, alkali metal salts of carbonates and phosphoric acids such as sodium tripolyphosphate and sodium carbonate, and hydrates of alkali metals such as sodium hydroxide. Examples of rust inhibitors include benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, saponins, and the like. Examples of preservatives or antibacterial agents include phenol, sodium omadine, sodium benzoate, thiazoline compounds, benzimidazole compounds, and the like.
The above-mentioned components such as dispersants, lubricants, thickeners, pH adjusters, rust inhibitors, preservatives, and antibacterial agents may be used alone or in combination of two or more. In addition, commercially available products of these may be used if available.

The aqueous ink composition for ballpoint pens of the present invention can be prepared by appropriately combining at least the urethane-based colored resin particles having an average particle size of 0.5 to 6 μm, an acetylene-based surfactant, a water-soluble solvent, and other components according to the intended use of the ink for ballpoint pens, stirring and mixing the mixture with a stirrer such as a homomixer, homogenizer, or disperser, and, if necessary, removing coarse particles from the ink composition by filtration or centrifugation.

The water-based ink composition for ballpoint pens of the present invention can be produced in a manner similar to that of other water-based ink compositions.
That is, the aqueous ink composition for a ballpoint pen of the present invention can be produced by mixing and stirring at least the above-mentioned urethane-based colored resin particles having an average particle size of 0.5 to 6 μm, the acetylene-based surfactant, the water-soluble solvent, and other components using a mixer or the like, and further using, for example, a bead mill, homomixer, homogenizer, or the like that can apply strong shear, while setting the stirring conditions to suitable conditions.
Furthermore, the pH (25° C.) of the aqueous ballpoint pen ink composition of the present invention is preferably adjusted to 5 to 10 with a pH adjuster or the like from the viewpoints of usability, safety, the stability of the ink itself, and compatibility with the ink container, and is more preferably 6 to 9.5.

The aqueous ballpoint pen ink composition of the present invention is loaded into a ballpoint pen equipped with a pen tip portion such as a ballpoint pen tip.
The aqueous ballpoint pen of the present invention may, for example, be one in which the aqueous ballpoint pen ink composition having the above composition is contained in an ink container (refill) for a ballpoint pen equipped with a ball having a diameter of 0.18 to 2.0 mm, and a substance that is incompatible with the aqueous ink composition contained in the ink container and has a low specific gravity relative to the aqueous ink composition, such as polybutene, silicone oil, mineral oil, etc., is contained as an ink follower. The structure of the aqueous ballpoint pen used is not particularly limited as long as it is equipped with a ball having a diameter within the above range, and in particular, it is desirable to fill an ink container of a polypropylene tube with the above aqueous ink composition, and finish it into an aqueous ballpoint pen refill with a stainless steel tip (the ball is made of a super steel alloy) at the tip.
Furthermore, the present invention may be a direct ink type ballpoint pen having a collector structure (ink retention mechanism) in which the barrel itself serves as an ink container and is filled with the aqueous ballpoint pen ink composition having the above-mentioned configuration.

It is preferable that the surface roughness Ra of the ball of the water-based ballpoint pen is less than 10 nm, and it is particularly preferable that the surface roughness Ra of the writing ball is 4 nm or less.
In this case, if the surface roughness Ra of the writing ball is 10 nm or more, the writing feel will gradually deteriorate. Note that the "surface roughness Ra" in this invention (including the examples described later) is set using a non-contact surface shape measuring device (NewView7200 manufactured by Zygo) under the conditions of a lens magnification of 50 times, an evaluation length of 100 μm, and a Gaussian filter of 25 μm, and the rest is in accordance with JIS B0601 (product geometric characteristic specifications - surface properties).
The water-based ballpoint pen of the present invention can further exert the effects of the present invention without impairing the writing feel, and can also use a ball with small surface roughness.

In addition, in the present invention, in order to achieve further effects of the present invention, it is preferable that the ink composition has a contact angle between the polyethylene terephthalate film (PET film surface, writing surface) and the ink of 40° or less. In order to achieve a contact angle between the writing surface and the ink of 40° or less, the ink composition can be prepared by suitably combining the acrylic colored resin particle type having a predetermined average particle size range, the acetylene surfactant type, and the respective contents thereof. In the present invention (including the examples described below), an automatic contact angle measuring instrument (DM500 manufactured by Kyowa Interface Science Co., Ltd.) was used to measure the contact angle.

The ink composition for aqueous ballpoint pens of the present invention thus constituted is characterized by containing at least the urethane-based colored resin particles having an average particle size of 0.5 to 6 μm and an acetylene-based surfactant, and the acetylene-based surfactants represented by the formulas (I) to (VI) have the effect of providing a low contact angle and enhancing wettability. It has been confirmed that by using these acetylene-based surfactants, even ink that has become highly viscous in a low-temperature environment and is difficult to eject from the pen tip becomes more easily attached to the ball due to its high wettability, and writing defects are less likely to occur. In addition, if the ball surface roughness is large, the ink wetting is improved, but on the other hand, the writing feel is deteriorated. With the ink composition for aqueous ballpoint pens and the aqueous ballpoint pen of the present invention, it is possible to apply a ball with a small surface roughness, and it is possible to achieve both a good writing feel and writing ability in a low-temperature environment to an even higher degree.

Next, the present invention will be explained in more detail with reference to Production Examples 1-2 of the colored resin particles used, Examples 1-6 of the water-based ballpoint pen ink composition, and Comparative Examples 1-2, but the present invention is not limited to the following Examples. In addition, the average particle diameter (D50: μm) of the colored resin particles obtained in Production Examples 1-2 was measured using a particle size distribution analyzer HRA9320-X100 manufactured by Nikkiso Co., Ltd.

[Production Example 1: Production of urethane-based colored resin particles 1]
11.5 parts by mass of ethylene glycol monobenzyl ether as an organic solvent was heated to 60 ° C., and 2.8 parts by mass of a water-insoluble dye (Valifast Red 1355, manufactured by Orient Chemical Industries Co., Ltd.) and 7.2 parts by mass of a diphenylmethane diisocyanate (3 moles) trimethylolpropane (1 mole) adduct (D-109, manufactured by Mitsui Chemicals, Inc.) as a prepolymer were added to prepare an oil phase solution. Meanwhile, 200 parts by mass of distilled water was heated to 60 ° C., and 15 parts by mass of polyvinyl alcohol (PVA-205, manufactured by Kuraray Co., Ltd.) as a dispersant was dissolved therein to prepare an aqueous phase solution. The oil phase solution was added to the aqueous phase solution at 60 ° C., and the mixture was emulsified and mixed by stirring with a homogenizer for 6 hours to complete the polymerization. The obtained dispersion was centrifuged to obtain urethane-based colored particles (red particles).
The average particle size (D50) of the colored resin particles was 3.2 μm.

[Production Example 2: Production of urethane-based colored resin particles 2]
As an oil phase solution, 11.6 parts of ethylene glycol monobenzyl ether and 1.8 parts of a dispersant (DISPERBYK-111, manufactured by BYK Japan) were heated to 60 ° C., and 2.0 parts of a pigment (carbon black, Cabot Mogul L, manufactured by Cabot Corporation) and 0.2 parts of Synergist (phthalocyanine pigment derivative, Solsperse 5000, manufactured by Lubrizol Corporation) were added and thoroughly dispersed. Next, 9.0 parts by mass of a trimethylolpropane adduct of xylylene diisocyanate (Takenate D110N, manufactured by Mitsui Chemicals, Inc.) was added as a prepolymer to prepare an oil phase solution. As an aqueous phase solution, 600 parts by mass of distilled water was heated to 60 ° C., and 15 parts by mass of polyvinyl alcohol (PVA-205, manufactured by Kuraray Co., Ltd.) was dissolved therein as a dispersant to prepare an aqueous phase solution.
The oil phase solution was added to the aqueous phase solution at 60° C., and the mixture was emulsified and mixed by stirring with a homogenizer for 6 hours to complete the polymerization. The resulting dispersion was centrifuged to obtain colored resin particles. The average particle size (D50) of the colored resin particles was 2.1 μm.

[Examples 1 to 6 and Comparative Examples 1 to 2]
Using the urethane-based colorable resin particles of Production Examples 1 and 2 above, and with the blending compositions shown in Table 1 below, each water-based ink composition for a ballpoint pen was prepared by a conventional method.
For the aqueous ballpoint pen ink compositions obtained in Examples 1 to 6 and Comparative Examples 1 and 2, the contact angle between the ink and the PET film surface was measured by the method described above, and the writability at low temperature (5°C) was evaluated by the evaluation method described below.
The results are shown in Table 1 below.

(Method for evaluating writability at low temperature (5°C))
Ten circles, each 4 cm in diameter, were drawn consecutively on test paper as specified in JIS S 6061:2010, 7.3, in an environment of 5°C using a ballpoint pen (UM-100 made by Mitsubishi Pencil Co., Ltd., ball diameter 0.5 mm, surface roughness 4 nm) filled with each ink, and the results were evaluated according to the following evaluation criteria.
<Evaluation criteria>
A: I was able to write everything down perfectly.
B: The area where writing was not possible was found to be more than 0 mm and 20 mm or less.
C: A portion that could not be written on was found to be more than 20 mm long.

As is clear from the results in Table 1 above, the ink compositions for aqueous ballpoint pens of Examples 1 to 6, which fall within the scope of the present invention, show less increase in ink viscosity even in low-temperature environments compared to Comparative Examples 1 and 2, which fall outside the scope of the present invention, and it has been confirmed that these ink compositions for aqueous ballpoint pens and aqueous ballpoint pens equipped with them are less prone to writing defects.

An ink composition suitable for water-based ballpoint pens is obtained.

Claims (3)

The water-based ballpoint pen is characterized in that it is equipped with an ink composition for water-based ballpoint pens, the ink composition containing at least 0.1 to 3.0% by mass of an acetylene-based surfactant and 3 to 30% by mass of urethane-based colored particles having an average particle size of 0.5 to 6 μm, based on the total amount of the ink composition, and has a ball diameter of 0.5 to 2.0 mm. The aqueous ballpoint pen according to claim 1, characterized in that the ink composition for the aqueous ballpoint pen has a contact angle between the polyethylene terephthalate film and the ink of 40° or less. The water-based ballpoint pen according to claim 1 or 2, characterized in that the surface roughness of the ball of the water-based ballpoint pen is less than 10 nm.