Water-based ballpoint pen ink composition

Abstract

To provide an ink composition for a water-based ballpoint pen, which has stable ink discharge properties even when used with a so-called fine-point ballpoint pen, has excellent glittering of drawn lines, and does not cause the ball to fall off, and to provide the water-based ballpoint pen. [Solution] The aqueous ink composition for a ballpoint pen of the present invention is characterized by containing at least an aluminum pigment and 8 to 25 mass % of dense urethane particles having an average particle size of 0.3 to 10 μm. The aqueous ballpoint pen of the present invention is characterized by being equipped with the aqueous ballpoint pen ink composition having the above-described configuration.

Description

[Technical field]

[0001] The present invention relates to a water-based ink composition for a ballpoint pen that contains an aluminum pigment. [Background technology]

[0002] Conventionally, water-based ballpoint pens using aluminum powder as a pigment have been able to produce brilliant lines, but their performance depends on the size of the aluminum powder. Larger aluminum pigments produce a strong sense of brilliance, but are more likely to cause problems such as clogging in gaps within the chip. In particular, in the case of so-called fine ballpoint pens with a ball diameter of φ0.5 mm or less, the gap is smaller, so the above-mentioned problems are more likely to occur. In addition, fine ballpoint pens have a problem in that it is difficult to obtain a sense of brilliance because the ink ejection volume is small.

[0003] Known inventions of water-based ballpoint pens and the like that attempt to solve these problems include, for example, 1) writing implements such as ballpoint pens that contain spherical resin particles such as acrylic resin, styrene-acrylic copolymer, polyolefin, etc., in order to suppress agglomeration of metal particles (see, for example, Patent Document 1), 2) glittering ink compositions for ballpoint pens that contain microcapsule particles, etc., in order to prevent wear on the receiving seat, and ballpoint pens that have the same built in (see, for example, Patent Documents 2 and 3), and 3) a ballpoint pen that holds the ball of the ballpoint pen tip in a movable and rotatable manner within a predetermined clearance range (see, for example, Patent Document 4).

[0004] However, even if the technical contents (inventions) of the above Patent Documents 1 to 4 are known, the current situation is that sufficient effects have not yet been obtained in the case of so-called fine ballpoint pens with a ball diameter of φ0.5 mm or less, and compared with ballpoint pens with a ball diameter of more than φ0.5 mm, the ball retention force is smaller and the ball tends to fall off easily depending on the usage conditions. In addition, although it is possible to compensate for this by designing the ballpoint pen tip, there may be adverse effects such as a deterioration in writing feel and a decrease in ink ejection. Furthermore, the ball is held in place by crimping the tip of the holder in which the ball is stored, but there are issues with this, such as the fact that the holding force decreases due to wear on the crimped part when writing, or local stress distortion caused by solid matter getting caught between the inner surface of the crimped part and the ball, and that the ball may fall out due to impact, making it impossible to write with. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-125841 A (Claims, Examples, etc.) [Patent Document 2] JP 2014-118527 A (Claims, Examples, etc.) [Patent Document 3] JP 2017-119862 A (Claims, Examples, etc.) [Patent Document 4] JP-A-11-28887 (claims, examples, Figure 1, etc.) Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the above-mentioned problems of the conventional art and aims to solve them, and has an object to provide an ink composition for an aqueous ballpoint pen, and an aqueous ballpoint pen, which have stable ink ejection properties even when used with a so-called fine point ballpoint pen, have excellent sparkle in the lines drawn, and do not cause the ball to fall off. [Means for solving the problem]

[0007] In view of the above-mentioned problems in the conventional art, the present inventors conducted intensive research and found that the above-mentioned objective aqueous ballpoint pen ink composition, etc. can be obtained by incorporating at least an aluminum pigment and a specific amount of particles having specific physical properties and an average particle size within a specific range, and thus completed the present invention.

[0008] That is, the aqueous ink composition for ballpoint pens of the present invention is characterized by containing at least an aluminum pigment and 8 to 25 mass % of dense urethane particles having an average particle size of 0.3 to 10 μm. 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. Effect of the Invention

[0009] According to the present invention, there are provided an ink composition for an aqueous ballpoint pen, which has stable ink ejection properties even when used with a so-called fine point ballpoint pen, has excellent sparkle in the drawn lines, and does not cause the ball to fall off, and an aqueous ballpoint pen. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is an enlarged vertical cross-sectional view showing an example of a ballpoint pen tip of an aqueous ballpoint pen equipped with the aqueous ballpoint pen ink composition of the present invention. [Diagram 2] FIG. 2 is a vertical cross-sectional view showing the ballpoint pen tip of FIG. [Diagram 3] FIG. 2 is a vertical cross-sectional view showing another example of a ballpoint pen tip. [Figure 4] 3 is a vertical cross-sectional view showing a state in which the ballpoint pen tip of FIG. 2 is attached to an ink containing tube (refill). [Diagram 5] FIG. 5 is a vertical cross-sectional view showing an example of an embodiment of a water-based ballpoint pen of the present invention, in which the ink reservoir (refill) of FIG. 4 is attached to a barrel to form a water-based ballpoint pen. [Figure 6]FIG. 5 is a vertical sectional view showing another embodiment of the water-based ballpoint pen of the present invention, in which the ink reservoir (refill) of FIG. 4 is attached to a knock-type barrel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] 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 an aluminum pigment and 8 to 25 mass % of dense urethane particles having an average particle size of 0.3 to 10 μm.

[0012] The aluminum pigment that can be used in the present invention is generally produced by pulverizing and grinding aluminum in a ball mill or an attritor mill using a grinding aid in the presence of a grinding medium, and is used as a pigment for aqueous inks, but there are no particular limitations on the production method, properties (powder, paste, etc.), particle size (average particle diameter, thickness), etc., and for example, any aluminum pigment that is commercially available for use in aqueous inks can be used. Preferably, in order to further exert the effects of the present invention, the average particle size is 20 μm or less, and more preferably, 5 to 16 μm.

[0013] Examples of commercially available aluminum pigments that can be used include the WXM series, in which the aluminum surface is treated for rust prevention with a phosphorus-based compound, the WL series, in which the aluminum surface is treated for rust prevention with a molybdenum compound, the EMR series, in which the surfaces of aluminum flakes are coated with high-density silica (all manufactured by Toyo Aluminum Co., Ltd.), and SW-120PM (all manufactured by Asahi Kasei Chemicals Corporation), and these can be used alone or in combination of two or more types.

[0014] The content of these aluminum pigments is preferably 0.1 to 20 mass% (hereinafter, "mass%" will be simply referred to as "%"), and more preferably 2 to 10%, based on the total amount of the aqueous ink composition for writing instruments (hereinafter, simply referred to as "total amount of ink composition"). If the content of this aluminum pigment is less than 0.1%, the sense of brilliance is not obtained, whereas if it exceeds 20%, the writing feel is deteriorated and the stability of the ink may be impaired.

[0015] The urethane particles used in the present invention are dense and have an average particle size of 0.3 to 10 μm. In the present invention, "dense solid" refers to particles such as hollow particles and microcapsule particles that have no voids (including monovoid, polyvoid, and porous) within them, and thus the particles are packed tightly with no voids. The average particle size of the urethane particles used is 0.3 to 10 μm, with the lower limit being preferably 0.5 μm or more, more preferably 0.9 μm or more, and particularly preferably 1.0 μm or more, while the upper limit is preferably 8 μm or less, more preferably 6 μm or less. If the average particle size is less than 0.3 μm, the particles will cover the surface of the aluminum pigment in the written line, which may impair the brilliance of the pigment. On the other hand, if the average particle size exceeds 10 μm, it will be difficult to stabilize the dispersion of the particles, and the inside of the tip will tend to become clogged, which is undesirable. In the present invention, the "average particle size" refers to the D50 value calculated on a volume basis by a laser diffraction method. Here, the average particle size can be measured by a laser diffraction method using, for example, a particle size distribution analyzer HRA9320-X100 manufactured by Nikkiso Co., Ltd.

[0016] In the present invention, as described above, it is important that the urethane particles used are of a certain size (within the above-mentioned range of average particle size) and are dense particles. In the present invention, by using dense solid particles, the strength of the particles can be easily controlled compared to particles such as microcapsules. The urethane particles used preferably have a 10% strength of 30 MPa or less as measured by a microcompression test. This allows the urethane particles to be soft even when dense, and because they are soft, they have the property of not causing the ball to fall off even when they are caught between the rivet and the ball. Furthermore, if the 10% strength is 5 MPa or more, the ink can flow out more stably. That is, by setting the 10% strength to 5 to 30 MPa, it is possible to highly simultaneously achieve good ink outflow stability and the property of preventing ball dropping out. In the present invention, the "microcompression test" can be carried out using, for example, MCT-510 manufactured by Shimadzu Corporation. In this case, the average value of five particles can be used. This 10% strength can be calculated using the following formula. C(x) = (2.48 × P) / (π × d 2 ) C(x): 10% strength (MPa) P: Test force at 10% displacement of particle diameter (N) d: Particle diameter (mm)

[0017] The urethane-based particles used may be any particles that are dense and have the above-mentioned average particle size, and moreover, it is particularly preferable that the 10% strength measured by a microcompression test has the above-mentioned characteristics. The urethane-based particles may be either commercially available products or those produced by the production method described below, and furthermore, the urethane-based particles may be colored so long as they have the above-mentioned characteristics. When the urethane particles of the present invention are colored and used as a coloring material (colorant), the amount of the particles added can be reduced because the coloring property is higher than that of microcapsule particles. Microcapsule particles have problems such as a limited amount of coloring material that can be encapsulated and the shell inhibiting coloring. In the present invention, the colored urethane particles function as a colorant, thereby improving the flexibility of ink formulation. In addition, in the present invention, when the urethane-based particles are not colored and the ink composition does not contain other colorants, the hue of the ink composition is the aluminum pigment + uncolored urethane-based particles, and therefore is silver (aluminum pigment + uncolored urethane-based particles).

[0018] The urethane-based particles used are polymers or copolymers having urethane bonds, 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.) and urethane-urea particles. It is preferable to use urethane particles obtained by the following method. The urethane particles can be produced by the following steps: 1) preparing an oil phase containing an organic solvent, and an isocyanate monomer or isocyanate prepolymer, and, if coloring is required, a water-insoluble dye; 2) preparing an aqueous phase by mixing water and a dispersant; and 3) mixing the oil phase and the aqueous phase to emulsify the components of the oil phase, followed by polymerization.

[0019] 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 the organic solvent to a predetermined temperature, adding a water-insoluble dye if coloring is desired, stirring, then adding the above-mentioned monomer or prepolymer, and further adding other organic solvents as necessary. Examples of the organic solvent that can be used include phenyl glycol, benzyl alcohol, ethylene glycol monobenzyl ether, ethyl acetate, etc. In addition, alkylsulfonic acid phenyl ester, ethylhexyl phthalate, tridecyl phthalate, ethylhexyl trimellitate, diethylene glycol dibenzoate, dipropylene glycol dibenzoate, liquid xylene resin, etc. can also be used.

[0020] 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. In this manufacturing method, the above-mentioned 10% strength can be adjusted by selecting the isocyanate components (monomer or prepolymer, auxiliary monomer, auxiliary prepolymer) used, adjusting the content, etc. The average particle size can be adjusted by controlling the stirring conditions during polymerization.

[0021] The water-insoluble dye used for coloring 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, but from the viewpoint of color development, it is preferable to use salt forming dyes. Examples of the salt forming dye include dyes having azo, metal complex azo, anthraquinone and metal phthalocyanine chemical structures. For example, Valifast (registered trademark) Black 1807, Valifast (registered trademark) Blue 2620, Valifast (registered trademark) Brown 2402, Valifast (registered trademark) Green 1501, Valifast (registered trademark) Orange 2210, Valifast (registered trademark) Pink 2310, Valifast (registered trademark) Red 1355, Valifast (registered trademark) VIOLET 1701 and Valifast (registered trademark) Yellow 1101 manufactured by Orient Chemical Industry Co., Ltd. can be used.

[0022] As the disperse dye, for example, at least one dye selected from CI Disperse Yellow 198, CI Disperse Yellow 42, CI Disperse Red 92, CI Disperse Violet 26, CI Disperse Violet 35, CI Disperse Blue 60, and CI Disperse Blue 87 can be used. As the oil-soluble dye, for example, Oil Black 860, Oil Blue 613, Oil Brown BB, Oil Green 530, Oil Orange 201, Oil Pink 312, Oil Red 5B, Oil Scarlet 318, Oil Yellow 105, etc. manufactured by Orient Chemical Industry Co., Ltd. can be used.

[0023] The aqueous phase can be prepared by mixing water and a dispersant, such as, but not limited to, polyvinyl alcohol.

[0024] 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 colored urethane-based particles and uncolored urethane-based particles.

[0025] In addition to the above emulsion polymerization, urethane particles may be prepared by a phase separation method. This method comprises preparing a dye-containing solution, preparing a protective colloid-containing solution, and polymerizing an isocyanate monomer or an isocyanate when coloring the particles. 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.

[0026] 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.

[0027] These dense urethane particles can be used alone or in combination of two or more kinds, and the content thereof is 8 to 25% based on the total amount of the ink composition, and preferably 10 to 18%. If the content of the dense urethane particles is less than 8%, the effect of the present invention cannot be achieved, whereas if it exceeds 25%, the stability of the ink may be impaired, which is undesirable.

[0028] The aqueous ballpoint pen ink composition of the present invention contains at least the above-mentioned aluminum pigment and 8 to 25 mass % of dense urethane particles having an average particle size of 0.3 to 10 μm. In addition to these components, the composition may also contain, for example, other pigments, colorants such as dyes, water-soluble organic solvents, and the remainder of the solvent water (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.), and, as necessary, may also contain various components typically used in aqueous ink compositions for writing instruments, such as thickeners, lubricants, rust inhibitors, preservatives or antibacterial agents, pH adjusters, etc., within ranges that do not impair the effects of the present invention.

[0029] In the present invention, in addition to the above-mentioned aluminum pigment and urethane-based particles when colored, coloring materials (colorants) such as other pigments and dyes can be used in combination as complementary color components, if necessary. Usable coloring materials include dyes that dissolve or disperse in water, conventionally known inorganic and organic pigments such as titanium oxide, and pigments having a silica or mica base material and a multilayer coating of iron oxide, titanium oxide, or the like on the surface. These can be used in an appropriate amount within a range that does not impair the effects of the present invention. Examples of dyes include acid dyes such as eosin, fuoxin, water yellow #6-C, acid red, water blue #105, brilliant blue FCF, and nigrosine NB; direct dyes such as direct black 154, direct sky blue 5B, and violet B00B; and basic dyes such as rhodamine and methyl violet.

[0030] Examples of organic pigments include azo lakes, insoluble azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, and nitroso pigments. More specifically, inorganic pigments such as carbon black, titanium black, zinc oxide, red iron oxide, chromium oxide, iron black, cobalt blue, iron oxide yellow, viridian, zinc sulfide, lithopone, cadmium yellow, vermilion, cadmium red, yellow lead, molybdate orange, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine blue, precipitated barium sulfate, baryte powder, calcium carbonate, lead white, navy blue, Prussian blue, manganese violet, and brass powder; CI Pigment Blue 15, CI Pigment Blue 17, CI Pigment Blue 27, CI Pigment Red 5, CI Pigment Red 22, CI Pigment Red 38, CI Pigment Red 48, CI Pigment Red 49, CI Pigment Red 53, CI Pigment Red 57, CI Pigment Red 81, CI Pigment Red 82, CI Pigment Red 83, CI Pigment Red 84, CI Pigment Red 85, CI Pigment Red 86, CI Pigment Red 87, CI Pigment Red 88, CI Pigment Red 89, CI Pigment Red 90, CI Pigment Red 91, CI Pigment Red 92, CI Pigment Red 93, CI Pigment Red 94, CI Pigment Red 95, CI Pigment Red 96, CI Pigment Red 97, CI Pigment Red 98, CI Pigment Red 99, CI Pigment Red 100, CI Pigment Red 101, CI Pigment Red 102, CI Pigment Red 103, CI Pigment Red 104, CI Pigment Red 105, CI Pigment Red 106, Examples of organic pigments that can be used as pigments include CI Pigment Red 104, CI Pigment Red 146, CI Pigment Red 245, CI Pigment Yellow 1, CI Pigment Yellow 3, CI Pigment Yellow 12, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 17, CI Pigment Yellow 34, CI Pigment Yellow 55, CI Pigment Yellow 74, CI Pigment Yellow 95, CI Pigment Yellow 166, CI Pigment Yellow 167, CI Pigment Orange 5, CI Pigment Orange 13, CI Pigment Orange 16, CI Pigment Violet 1, CI Pigment Violet 3, CI Pigment Violet 19, CI Pigment Violet 23, CI Pigment Violet 50, and CI Pigment Green 7. These coloring materials can be used alone or in combination of two or more.

[0031] Examples of the water-soluble organic solvent 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. These can be used alone or in combination of two or more. The content of these water-soluble organic solvents is appropriately adjusted depending on the application of the aqueous ink composition for writing instruments, and is in the range of 1% to 30% based on the total amount of the ink composition.

[0032] 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, etc.

[0033] Examples of the lubricant include nonionic lubricants such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, and higher polyoxyalkylene fatty acid esters, which are also used as surface treatment agents for pigments; anionic lubricants such as phosphate esters, alkyl sulfonates of higher fatty acid amides, and alkyl aryl sulfonates; derivatives of polyalkylene glycols, fluorine-based surfactants, and polyether-modified silicones.

[0034] Examples of the rust inhibitor include benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, and saponins, and examples of the preservative or antibacterial agent include phenol, sodium omadine, sodium benzoate, benzisothiazoline, and benzimidazole compounds. Examples of the pH adjuster include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide; amine compounds such as triethanolamine, diethanolamine, monoethanolamine, dimethylethanolamine, morpholine, and triethylamine; and ammonia.

[0035] The aqueous ink composition for ballpoint pens of the present invention contains at least the above-mentioned aluminum pigment and 8 to 25 mass % of dense urethane particles having an average particle size of 0.3 to 10 μm. The other components are appropriately combined depending on the structure of the ballpoint pen, etc., and stirred and mixed with a stirrer such as a homomixer, homogenizer or disper, and if necessary, coarse particles in the ink composition can be removed by filtration or centrifugation, to prepare the aqueous ink composition for ballpoint pens. The resulting aqueous ballpoint pen ink composition of the present invention is loaded into a ballpoint pen equipped with a ballpoint pen tip and then used.

[0036] The reason why the aqueous ink composition for a ballpoint pen of the present invention thus constituted has stable ink ejection properties, provides excellent sparkle in the drawn lines, and is free from ball dropout, even when used with a so-called fine tip ballpoint pen having a ball diameter of φ0.5 mm or less, is presumed to be as follows. The aqueous ink composition for ballpoint pens of the present invention contains at least an aluminum pigment and 8 to 25% of urethane particles having an average particle size of 0.3 to 10 μm. By containing 8 to 25% of these urethane particles, it is presumed that the aluminum pigments are prevented from flocculating, and even if the urethane particles get stuck between the inner surface of the crimped portion and the ball, local stress distortion does not occur, and the ball retention force does not decrease, so that an aqueous ink composition for ballpoint pens is obtained that has stable ink discharge properties, has excellent glittering of drawn lines, and does not cause the ball to fall off.

[0037] An example of the aqueous ballpoint pen of the present invention is one in which the aqueous ballpoint pen ink composition having the above-mentioned composition is contained in an ink container (refill) for a ballpoint pen, and at least one 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 ballpoint pen is not particularly limited, and may be, for example, 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-described configuration.

[0038] In the water-based ballpoint pen of the present invention, as shown in FIG. 1, when the ball diameter in the water-based ballpoint pen is D and the maximum ball projection dimension is L, the value of X represented by the following formula (I) is preferably 27 to 37, and more preferably 28 to 36. X = (L / D) x 100 ………(I) D: ball diameter, L: maximum ball projection dimension, L = (ball projection dimension l + clearance m) It is even more preferable that the value of X is represented by the above formula (I) and that the ball has a diameter (φ) of 0.5 mm or less, more preferably 0.3 mm or less, and particularly preferably 0.29 mm or less. By providing an aqueous ballpoint pen with this structure, in combination with the ink composition for an aqueous ballpoint pen having the above-mentioned properties, it is possible to obtain an aqueous ballpoint pen that exhibits even better ball flying resistance and even better writing feel.

[0039] Specific examples of the water-based ballpoint pen of the present invention having a ballpoint pen tip with the above-mentioned characteristics include the water-based ballpoint pens shown in Figs. FIG. 2 is an example of a ballpoint pen tip having a ball with a ball diameter (φ) of 0.5 mm or less, more preferably 0.3 mm or less, and particularly preferably 0.29 mm or less. FIG. 3 shows another example of the ballpoint pen tip of FIG. 2. FIG. 4 is a drawing showing the ballpoint pen tip of FIG. 2 attached to an ink containing tube (refill). FIG. 5 is a drawing showing the ink containing tube (refill) having the ballpoint pen tip of FIG. 4 attached to a barrel to form an aqueous ballpoint pen. FIG. 6 is a drawing showing another example of the aqueous ballpoint pen of FIG. 5 (a knock-type aqueous ballpoint pen body).

[0040] FIG. 2 shows a bullet-shaped ballpoint pen tip A having a tapered tip and a hollow holder 11 rotatably holding a ball 10 having a ball diameter of, for example, 0.29 mm or less at its tip. An aqueous ballpoint pen C having this ballpoint pen tip A can be obtained by connecting the rear end of the ballpoint pen tip A to an ink reservoir 25 via a joint member 20 having a backflow prevention mechanism (or directly) as shown in FIG. 4 to form a refill 30, and storing the refill 30 in a shaft 33 having an anti-slip member 32 as shown in FIG. 5. A ferrule 31 is fixed to the tip of the shaft 33. Also, the reference numeral 26 in FIG. 4 denotes the above-mentioned aqueous ballpoint pen ink composition of the present invention, 27 denotes the above-mentioned ink follower, and the reference numeral 35 in FIG. 5 denotes a cap. In this water-based ballpoint pen C, the water-based ballpoint pen ink composition 30 of the present invention filled in the ink reservoir 25 is supplied to the ball 10 through the ink flow path 12 which tapers gradually.

[0041] 3 shows a needle-shaped ball tip B in which the tip of a thin tube 15 made of metal or the like is crimped on the inside to rotatably hold a ball 16 having a diameter (ball diameter) of, for example, 0.29 mm or less. As with the above, the rear end of this ballpoint pen tip B is connected to an ink reservoir tube and a shaft body (not shown) to form an aqueous ballpoint pen. FIG. 6 is a vertical cross-sectional view showing an example of a knock-type water-based ballpoint pen body in which an ink reservoir (refill) having the ballpoint pen tip of FIG. 2 is attached to a knock-type barrel. This knock-type water-based ballpoint pen body E has a ballpoint pen tip 40 as shown in Fig. 2, and a refill 47 connected to an ink containing tube 46 via a joint member 45 having a backflow prevention mechanism is housed in a knock-type shaft body 50 having an anti-slip member 48. The reference numeral 41 in the figure denotes a coil spring member having a thin wire-like tip housed in the tip, and the tip urges the ball outward by the elastic force of the coil spring. The reference numeral 42 in the figure denotes the ink composition for water-based ballpoint pens of the present invention, 43 denotes an ink follower having the above-mentioned characteristics, 51 denotes a knock portion, and 52 denotes a coating member that protects the tip portion of the tip.

[0042] The ball material is not particularly limited as long as it has a ball diameter (φ) of 0.5 mm or less, more preferably 0.3 mm or less, and particularly preferably 0.29 mm or less, and examples of the ball material include those made of metal members such as ultra-hard metal members, ceramic members, and further those having a thin film coating member applied to the surface of these members to improve durability, corrosion resistance, etc. The lower limit of the ball diameter is about 0.1 mm from the viewpoint of manufacturing technology, etc. The holder may be made of metal such as nickel silver, brass, or stainless steel, or synthetic resin. The ink reservoir tube may be made of a transparent or semi-transparent synthetic resin that allows the remaining ink level to be checked, but may also be made of metal. The water-based ballpoint pen of the present invention is not limited to the structure of the ballpoint pen tip shown in Figures 2 and 3, and the structure of the water-based ballpoint pen body including the ballpoint pen tip is not particularly limited as long as it uses a ballpoint pen tip having a ball with a ball diameter (φ) of 0.5 mm or less, more preferably 0.3 mm or less, and particularly preferably 0.29 mm or less, and can be applied to water-based ballpoint pens of various structures including knock-type. In addition, the material, size (inner diameter, length), etc. of the ball holder, ink storage tube, and joint member (front barrel) are appropriately set according to the tip structure, ball diameter, ink follower, etc.

[0043] In the aqueous ballpoint pen of the present invention thus configured, even in an aqueous ballpoint pen equipped with a ballpoint pen tip having a ball with a ball diameter (φ) of 0.5 mm or less, more preferably 0.3 mm or less, and particularly preferably 0.29 mm or less, by using the ink composition for an aqueous ballpoint pen of the present invention, the aqueous ballpoint pen has stable ink ejection properties, excellent glittering of drawn lines, and is free of ball falling off. In particular, in the aqueous ballpoint pen of the present invention, as shown in Fig. 1, when the ball diameter in the aqueous ballpoint pen is D and the maximum ball projection dimension is L, by using a ballpoint pen tip having a value of X represented by the above formula (I) of 27 to 37, in combination with the ink composition for aqueous ballpoint pens of the present invention, an aqueous ballpoint pen can be obtained that has stable ink discharge properties, excellent glittering of drawn lines, does not cause ball dropping, and further exhibits ball skip resistance and further improves writing feel. In this aqueous ballpoint pen, the smaller the ball diameter (φ), the more the effects of the present invention can be exhibited, and the present invention can be suitably used for aqueous ballpoint pens having a ball diameter of 0.5 mm or less, more preferably 0.3 mm or less, and particularly preferably 0.29 mm or less. EXAMPLES

[0044] Next, the present invention will be described in more detail with reference to Production Examples (production of urethane-based particles, etc.), Examples, and Comparative Examples (preparation of an aqueous ink composition for a ballpoint pen). However, the present invention is not limited to the following Examples. <Preparation of urethane particles A to F and melamine particles G> Urethane particles A to F and melamine particles G were produced using the blending compositions shown in Table 1 below and the method described below.

[0045] (Production Example 1: Urethane Particles A) 12.5 parts by mass of ethyl acetate as an organic solvent was heated to 60°C, and 8 parts by mass of isocyanurate modified hexamethylene diisocyanate (TLA-100, manufactured by Asahi Kasei Chemicals) as a prepolymer was added thereto 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. Next, 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 particles (uncolored) A.

[0046] (Production Example 2: Urethane Particles B) 11.5 parts by mass of ethylene glycol monobenzyl ether as an organic solvent was heated to 60°C, and 7.2 parts by mass of a prepolymer of diphenylmethane diisocyanate (3 moles) and trimethylolpropane (1 mole) adduct (D-109, manufactured by Mitsui Chemicals) was added thereto 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 particles (red particles) B.

[0047] (Production Example 3: Urethane Particles C) Urethane-based particles (blue particles) were obtained in the same manner as for urethane-based particles B, except that 2.8 parts by mass of a water-insoluble dye (Valifast Red 1355, manufactured by Orient Chemical Industries Co., Ltd.) was replaced with 2.4 parts by mass of a water-insoluble dye (Valifast Blue 2620, manufactured by Orient Chemical Industries Co., Ltd.), 11.5 parts by mass of ethylene glycol monobenzyl ether was replaced with 9.6 parts by mass of benzyl alcohol, and 7.2 parts by mass of a diphenylmethane diisocyanate (3 mol) to trimethylolpropane (1 mol) adduct (D-109, manufactured by Mitsui Chemicals Co., Ltd.) was replaced with 7 parts by mass of an allophanate modified product of hexamethylene diisocyanate (D-178NL, manufactured by Mitsui Chemicals Co., Ltd.).

[0048] (Production Example 4: Urethane Particles D) Urethane-based particles (uncolored) D were obtained in the same manner as for urethane-based particles A, except that the amount of isocyanurate-modified hexamethylene diisocyanate (TLA-100, Asahi Kasei Chemicals Corporation) was changed from 8 parts by mass to 15 parts by mass.

[0049] (Production Example 5: Urethane Particles E) In Production Example 2, the stirring conditions during polymerization were changed to obtain urethane-based particles (red particles) E having a different average particle size.

[0050] (Production Example 6: Urethane Particles F) In Production Example 3, the stirring conditions during polymerization were changed to obtain urethane-based particles (blue particles) F having a different average particle size.

[0051] (Production Example 7: Melamine Particles G) Melamine particles (uncolored) G were obtained in the same manner as in the production of urethane particles A, except that 12.5 parts by mass of ethyl acetate was replaced with 20 parts by mass of benzyl alcohol and 8 parts by mass of isocyanurate modified hexamethylene diisocyanate (TLA-100, manufactured by Asahi Kasei Chemicals Corporation) was replaced with 7 parts by mass of methylol melamine.

[0052] The 10% strength (MPa) and average particle size (μm) of the obtained urethane particles A to F and melamine particles G were measured by the following methods. The results are shown in Table 1 below. (Method of measuring 10% strength) The calculation was performed using Shimadzu Corporation's MCT-510 according to the above formula. (Method of measuring average particle size) Measurements were performed using a particle size distribution analyzer HRA9320-X100 manufactured by Nikkiso Co., Ltd.

[0053] Preparation of Water-Based Ballpoint Pen Ink Composition (Examples 1 to 8 and Comparative Examples 1 to 3) A water-based ink composition for a ballpoint pen was prepared by a conventional method using the blending composition (total amount 100% by mass) shown in Table 2 below. For each of the obtained aqueous ink compositions for writing instruments (total amount 100% by mass), the ink discharge properties (line drawing evaluation, ink flow rate) and ball retention were evaluated by the following evaluation methods using an aqueous ballpoint pen having the following composition. The results are shown in Table 2 below.

[0054] <Preparation of water-based ballpoint pen> The ink compositions for water-based ballpoint pens of Examples 1 to 8 and Comparative Examples 1 to 3 were filled into refills consisting of a polypropylene ink reservoir (inner diameter 4 mm, length 113 mm), a stainless steel tip (carbide alloy ball, ball diameter 0.38 mm) conforming to Figs. 1 and 2, and a joint connecting the reservoir and the tip. An ink follower consisting of mineral oil, polybutene, and an olefin-based elastomer was then loaded into the rear end of the ink. Each refill was loaded into the barrel of a ballpoint pen (UM-151, manufactured by Mitsubishi Pencil Co., Ltd.) to prepare each water-based ballpoint pen. The value of X in the above formula (I) was in the range of 27-37 when the ball diameter D (0.38 mm) and the maximum ball projection dimension L of the water-based ballpoint pens used in the Examples and Comparative Examples were taken as D (0.38 mm) and L, respectively.

[0055] [Ink ejection performance (line drawing evaluation, ink flow rate)] Writing was done with a φ0.38 mm ballpoint pen (in accordance with JIS S6061) until all the ink was consumed, and the drawn line and ink flow rate were evaluated every 100 m according to the following evaluation criteria (A to C). <Evaluation criteria for line drawing> A: Has sufficient brilliance B: The shine is slightly weak C: Lack of brilliance <Ink flow rate evaluation criteria> A: A constant flow rate was maintained until the end. B: The flow rate decreased slightly in the latter half. C: Writing became impossible midway through, or the flow rate dropped drastically.

[0056] [Ball Possession] After writing 200m with the same ballpoint pen as above, the pen was dropped from a height of 1.8m with the tip facing upwards and evaluated according to the following criteria (A, C). n=50 pens <Ball possession evaluation criteria> A: The ball was in possession the whole time. C: A ballpoint pen fell off.

[0057] [Table 1]

[0058] [Table 2]

[0059] Considering Tables 1 and 2 above, it is clear that Examples 1 to 8, which are within the scope of the present invention, are superior in ink ejection properties (line drawing evaluation, ink flow rate) and ball retention compared to Comparative Examples 1 to 3, which are outside the scope of the present invention. Specifically, Examples 1 and 4 to 6 used uncolored urethane-based particles together with aluminum pigment, and it was confirmed that only the aluminum pigment in Comparative Examples 1 to 3 was superior in ink ejection properties (line drawing evaluation, ink flow rate) and ball retention compared to the aluminum pigment + melamine particles or acrylic particles. Furthermore, it was confirmed that the inks using colored urethane particles (blue, red) together with the aluminum pigments of Examples 2, 3, 7, and 8 also had excellent color development, as well as excellent ink ejection properties (line drawing evaluation, ink flow rate) and ball retention. [Industrial Applicability]

[0060] An aqueous ballpoint pen ink composition suitable for ballpoint pens can be obtained. [Explanation of symbols]

[0061] A Ballpoint pen tip C Ballpoint Pen 10 Ball 30 Refill

Claims

1. The ink composition for a water-based ballpoint pen contains at least 0.1 to 20% by mass of an aluminum pigment having an average particle size of 20 μm or less, and 8 to 25% by mass of dense urethane-based colored particles colored with a salt-forming dye having an average particle size of 0.3 to 10 μm.

2. 2. An aqueous ballpoint pen comprising the ink composition for aqueous ballpoint pens according to claim 1.

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