JP7668866B2 - Water-based ink composition for ballpoint pens - Google Patents

Description

The present invention relates to an aqueous ink composition for ballpoint pens. Furthermore, the present invention relates to an aqueous ink composition for ballpoint pens that can produce handwriting with excellent brilliance and color development on paper for a long period of time, a ballpoint pen refill containing the same, and a ballpoint pen.

Water-based ballpoint pens capable of producing metallic luster-like handwriting have been known and are widely used for a variety of purposes, from lettering to drawing. In such ballpoint pens, plate-shaped luster pigments such as plate-shaped (scale-shaped) metal powders and pearl pigments are often used as reflective pigments in the ink components, because the resulting handwriting has high brightness.
In addition, in order to adjust the hue of the ink, general-purpose pigments are added to the ink or the surface of the plate-like luster pigment is colored (see, for example, Patent Documents 1 and 2).
As described in Patent Document 1, when a general-purpose color pigment is added to the ink, the paper surface has permeability, so that only the plate-shaped glitter pigment with a large particle size is layered on the surface of the paper during writing, and the color pigment permeates the paper surface, making it difficult to obtain handwriting of the desired hue. In addition, when a plate-shaped glitter pigment whose surface has been colored is used, it is not necessary to consider the above-mentioned penetration of the color pigment, but in order to color the entire ink, it is necessary to increase the particle size of the plate-shaped glitter pigment used or to increase the amount added, so that settling of the plate-shaped glitter pigment occurs during storage, and the ink dischargeability is likely to decrease.

In recent years, since a single ballpoint pen can produce handwriting in different tones such as black, red, and blue, multi-color (multi-core) ballpoint pens that house ballpoint pen refills of multiple colors in the barrel are widely used. Ballpoint pens with thin barrels tend to be preferred for their ease of use, and such ballpoint pens often house thin refills because the internal volume of the barrel is small. However, thin refills often have ink reservoirs that are thin and thin-walled, and depending on the material of the ink reservoir, the ink reservoir may not be able to suppress the permeation of volatile solvents such as water. Over time, the volatile solvents in the ink in the refill may permeate the ink reservoir and evaporate out of the refill, causing the ink to thicken excessively or the insoluble components of the ink to aggregate, resulting in poor ink discharge. This tendency is more pronounced in ink reservoir tubes made of synthetic resins such as polyethylene terephthalate (PET), and furthermore, in inks that use photoluminescent pigments as colorants, large amounts of plate-shaped photoluminescent pigments are often added to the ink to produce handwriting with excellent photoluminescence. However, inks that contain a large amount of solid matter such as pigments have a relatively small amount of liquid in the ink, so when the solvent evaporates, the ink thickens and the solid matter aggregates significantly, making the ink ejection properties even more likely to deteriorate.

As such, ballpoint pens that use plate-shaped photoluminescent pigments in their inks can have difficulty in achieving good writing performance and stability over time, so improvements are needed.

Japanese Patent Application Publication No. 11-29734 JP 2003-12973 A

The present invention provides a ballpoint pen refill that has a slender, thin-walled ink reservoir and contains highly luminous water-based ink that uses plate-shaped lustrous pigments, and that can produce vivid handwriting that is excellent in lustrousness and color development and is suppressed from smearing or being interrupted, stably over a long period of time on paper surfaces of various hues, as well as a ballpoint pen refill and a ballpoint pen that contain the same.

The water-based ink composition for ballpoint pens of the present invention contains water, a water-soluble organic solvent, a plate-shaped glittering pigment, a coloring pigment, one or more water-dispersible polymers selected from the group consisting of acrylic acid-based polymers, urethane-based polymers, and olefin-based polymers, a water-soluble copolymer of acrylic acid and a sulfonic acid-based monomer, and a thickener, wherein, when the total mass of the water-dispersible polymers is X and the total mass of the copolymers of acrylic acid and sulfonic acid-based monomers is Y, Y/X is 0.1 to 1.0, the content of the water-dispersible polymers is 0.5 to 3 mass% based on the total mass of the ink composition, A is the sum of the total mass of the plate-shaped glittering pigment and the total mass of the coloring pigment, and B is the total mass of the water-dispersible polymers, B/A is 0.1 to 0.4, and the viscosity of the ink composition at 20°C is 800 to 1000 at 3.84 sec-1. The ink composition is required to be a water-based ink composition for a ballpoint pen, having a viscosity of 1,600 mPa·s and a shear thinning index n of 0.15 to 0.5 at 20° C.
Furthermore, the present invention provides a ballpoint pen refill containing the above-mentioned water-based ink composition.
A further feature is a ballpoint pen containing the ballpoint pen refill.

The present invention provides a ballpoint pen refill with a slender, thin-walled ink reservoir and containing a highly luminous water-based ink that uses plate-shaped photoluminescent pigments, and an aqueous ink composition for ballpoint pens that is excellent in photoluminescence and color development on paper surfaces of various hues and can stably produce vivid handwriting with reduced smearing and interruptions over a long period of time, as well as a ballpoint pen refill and a ballpoint pen that contain the same.

FIG. 2 is a cross-sectional view showing an example of a ballpoint pen refill of the present invention. 1 is a cross-sectional view showing an example of a pen tip (ballpoint pen tip) provided in a ballpoint pen refill of the present invention. 2A is a cross-sectional view taken along the line XX in FIG.

The following is a detailed description of an embodiment of the present invention. In this specification, the terms "parts," "%," and "ratio" used to indicate the composition are based on mass unless otherwise specified.

The ballpoint pen refill according to the present invention comprises a pen tip and an ink reservoir, and contains an aqueous ink composition (hereinafter, sometimes referred to as "ink composition" or "composition") containing a plate-shaped photoluminescent pigment in the ink reservoir, and an ink backflow preventive body is filled on the end surface of the aqueous ink composition. Each element constituting the aqueous ink composition and ballpoint pen refill according to the present invention will be described below.
The average particle size of the plate-like pigment in the present invention is a value calculated by assuming that the minimum value on the particle size axis in a particle size distribution diagram is 0.5 μm when measured by a laser diffraction method (volume basis).

The water-based ink composition contains water, a water-soluble organic solvent, a plate-shaped photoluminescent pigment, a color pigment, one or more water-dispersible polymers selected from acrylic acid polymers, urethane polymers, and olefin polymers, which are water-dispersible, a water-soluble copolymer of acrylic acid and a sulfonic acid monomer, and a thickener, and has an ink viscosity and shear thinning index within a specific range.

The plate-shaped luster pigment may be a plate-shaped or scaly pigment that exhibits luster by reflecting light in handwriting, and examples thereof include pearl pigments, aluminum pigments, and metal or metal oxide coated glass flakes. One or more of these may be selected and blended into the ink.

Specifically, the pearl pigments include natural products such as fish scale foil, and synthetic products in which the surface of natural mica, synthetic mica, silica, etc. is coated with a metal oxide, with the latter being generally more widely used. Pearl pigments exhibit a variety of colors depending on the type of metal oxide that coats the mica surface and the thickness of the coating. Commercially available pearl pigments include, for example, Iriodin 100 (silver), Iriodin 111 (silver), Iriodin 151 (silver), Iriodin 153 (silver), Iriodin 201 (gold), Iriodin 217 (copper red), Iriodin 289 (blue), Iriodin 302 (gold), Iriodin 504 (wine red), Iriodin 530 (copper) [all manufactured by Merck Japan Ltd.], and Ultimica SB-100 (silver) [all manufactured by Topy Industries Ltd.]. In addition, there are cholesteric liquid crystal type photoluminescent pigments such as HELICONE HCS and HCXS (both manufactured by Wacker Chemie).

The aluminum pigment can be obtained as a paste of very thin, scaly aluminum particles by crushing and grinding aluminum flakes together with a petroleum-based solvent such as higher fatty acid or mineral spirits in a ball mill or the like. Commercially available products include Alpaste WXM-0630, EMERAL EMR-D5660, and EMERAL WJC-U75C (all manufactured by Toyo Aluminum Co., Ltd.).
Alternatively, thin film aluminum obtained by vacuum deposition may be finely pulverized, and examples of commercially available products include METALURE W-52012 IL, Ultravario Aqua PG-24001 (both manufactured by ECKART), LG neo Silver #500 (silver), and LG neo Gold #500 (gold) (both manufactured by Oike Kogyo Co., Ltd.).

The metal-coated glass flakes are obtained by coating the glass surface with silver or nickel using an electroless plating method, while the metal oxide-coated glass flakes are obtained by coating the surface of the glass flakes with titanium dioxide using a liquid phase method. By changing the thickness of this titanium oxide film, colors such as silver, yellow, red, blue, and green can be obtained. Commercially available metal or metal oxide-coated glass flakes include Metashine 2040PS, Metashine 2020PS, Metashine 5090NS, and Metashine 5090RC (all manufactured by Nippon Sheet Glass Co., Ltd.).

These plate-shaped luster pigments can be used alone or in combination with two or more types depending on the desired hue and luminance. The amount of the plate-shaped luster pigment used is 1.0 to 20% by weight, preferably 1.5 to 10% by mass, based on the total amount of the ink composition.

In addition, there is no particular limit to the particle size of the plate-shaped luster pigment used in the ink composition, but a particle size is selected that does not cause the ballpoint pen to be used to be unable to write with the ink, or to block the ink ejection groove (ink outlet hole) during writing, making writing impossible. If the particle size is too small, it is difficult to obtain a sense of luster in the handwritten state, and if it is too large, there is a strong tendency for the ink to be ejected with difficulty and for the ink to wear down, so a particularly preferred average particle size is in the range of 3 to 25 μm.

The aqueous ink composition contains at least one water-dispersible polymer selected from the group consisting of acrylic acid polymers, urethane polymers, and olefin polymers, which have water dispersibility. The water-dispersible polymer is in the form of an emulsion.
The water-dispersible polymer adsorbs to the plate-like glittering pigment and the coloring pigment, suppressing aggregation of the pigments and suppressing deterioration of ink dischargeability, and also adsorbs the coloring pigment to the plate-like glittering pigment or the paper surface via the water-dispersible polymer, suppressing penetration of the coloring pigment from the paper surface into the interior, forming handwriting that is suppressed in smearing and discontinuity and has excellent glittering and color development properties of the coloring pigment. The water-dispersible polymer may be neutralized with an alkaline substance such as sodium hydroxide, ammonia, or alkanolamine.

Examples of acrylic acid-based polymers that can be used include polyacrylic acid, polycarboxylic acid, acrylic acid/maleic acid copolymer, acrylic acid/sulfonic acid monomer copolymer, acrylic acid/unsaturated carboxylic acid copolymer, and styrene/acrylic acid copolymer.

Specific examples of the acrylic acid polymers include Joncryl PDX-7182, Joncryl PDX-7630A, Joncryl PDX-7692, and Joncryl 7787 (all manufactured by BASF Japan), Boncoat 5400EF (all manufactured by DIC Corporation), Mowinyl 7525 (all manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), Neocryl A-639, and Neocryl A-6016 (all manufactured by Kusumoto Chemical Industry Co., Ltd.), and one or more of these may be used.

The urethane polymer is not particularly limited in type, and examples thereof include reaction products of polyisocyanate and polyol such as polyether, polyester, and polycarbonate.
The urethane polymer has an amorphous portion and a crystalline urethane bond in the molecule that interact with the color pigment and the plate-like luster pigment, so that the color pigment is prevented from being absorbed by the paper surface during writing, and it is possible to form handwriting with a vivid color tone and high color development. In particular, a self-emulsifying emulsion having an anionic functional group in the molecule is more useful because it exerts a high effect regardless of the pH of the ink.
Specific examples of such compounds include NeoRez R-972, R-2170, R-966, R-967, R-986, R-9603, and R-9404 (all manufactured by Kusumoto Chemical Industries, Ltd.), Eukoat UX-485, UWS-145, and Euplen UXA-307 (all manufactured by Sanyo Chemical Industries, Ltd.), Hydran AP-40N and APX-101H (all manufactured by DIC Corporation), and Superflex 150, 460, 470, and 820 (all manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.). One or more of these compounds may be used.

The olefin polymer is not particularly limited in type, and examples thereof include polyethylene, polypropylene, ethylene-(meth)acrylic acid copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, etc., and emulsions formed by dispersing these in a medium are used. In particular, self-emulsifying emulsions having an anionic functional group in the molecule are more useful because they exhibit high effects regardless of the pH of the ink.
Specific examples include ZAICHXEN L, ZAICHXEN A, and ZAICHXEN A-GH (all manufactured by Sumitomo Seika Chemicals Co., Ltd.), HYTEC E-4A, HYTEC E-5403, and HYTEC E-9460 (all manufactured by Toho Chemical Industry Co., Ltd.), and one or more of these may be used.

The emulsion containing the water-dispersible polymer preferably has a film-forming temperature (MFT) of 60° C. or higher, more preferably 70° C. or higher, and further preferably 80° C. or higher.
When the film-forming temperature is within the above range, when the ballpoint pen refill is exposed to excessive temperature changes, the water-dispersible polymer in the ink forms a film, causing the pigment to aggregate, which in turn reduces the ink dischargeability and leads to smearing or interruption of handwriting.

Among the water-dispersible polymers, acrylic acid-based polymers are suitable for ink compositions because they are easily adsorbed not only to color pigments, but also to plate-shaped luster pigments and paper surfaces, and as a result, the color pigments are adsorbed to the plate-shaped luster pigments and paper surfaces, making it easier to prevent the color pigments from penetrating into the paper from the surface, and thus improving the luster and color development of handwriting.

The content of the water-dispersible polymer is preferably 0.1 to 5% by mass, and more preferably 0.5 to 3% by mass, based on the total mass of the ink composition. When the content is within this range, the ink composition is prevented from thickening excessively while improving the dispersion stability of the plate-shaped photoluminescent pigment and color pigment, and handwriting with excellent photoluminescence and color development and with reduced smearing and discontinuities is easily formed.

The ink composition further contains a water-soluble copolymer of acrylic acid and a sulfonic acid monomer, which further suppresses the penetration of the color pigment from the paper surface into the interior and the aggregation of the plate-shaped lustrous pigment, making it easier to form handwriting with excellent color development and lustrous properties while suppressing smearing and interruption of the handwriting.
The copolymer is made water-soluble by neutralizing a copolymer of acrylic acid and a sulfonic acid monomer with an alkaline substance such as sodium hydroxide, ammonia, alkanolamine, etc., and is applied to an ink composition. A specific example thereof is a neutralized copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid, and products available under the trade names Aron A-6012, A-6016, A-6017, and A-6020 (all of which are sodium salts of copolymers of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid, manufactured by Toagosei Co., Ltd.) can be used.
The copolymer of acrylic acid and a sulfonic acid monomer that can be used in the ink composition is not limited to the above.
The copolymers may be used in combination of two or more kinds.

The content of the copolymer of acrylic acid and sulfonic acid monomer is preferably 0.05 to 2% by mass, more preferably 0.1 to 1% by mass, based on the total mass of the ink composition. When the content is within the above range, excessive thickening of the ink composition is prevented, which reduces the ink dischargeability from the pen tip, and handwriting with excellent brilliance and color development is easily formed.

In addition, in the aqueous ink composition, when the total mass of the water-dispersible polymer is X and the total mass of the copolymer of acrylic acid and sulfonic acid monomer is Y, Y/X is preferably 0.1 to 1.0, more preferably 0.2 to 0.8. Particularly preferably 0.3 to 0.6. When the total mass ratio is within the above range, the color pigment is prevented from penetrating into the paper from the surface and the plate-shaped photoluminescent pigment is prevented from agglomerating, making it easy to form excellent handwriting with excellent color development and photoluminescence.

As the color pigment, inorganic pigments such as carbon black and ultramarine, organic pigments such as copper phthalocyanine blue and benzidine yellow, and water-dispersed pigment products which are finely and stably dispersed in an aqueous medium in advance using a surfactant or the like are used, for example, C.I. Pigment Blue 15:3B [product name: S.S. Blue GLL, pigment content 22%, manufactured by Sanyo Dye Co., Ltd.], C.I. Pigment Red 146 [product name: S.S. Pink FBL, pigment content 21.5%, manufactured by Sanyo Dye Co., Ltd.], C.I. Pigment Yellow 81 [product name: TC Yellow FG, pigment content about 30%, manufactured by Dainichiseika Color & Chemicals Co., Ltd.], C.I. Pigment Red 220/166 (product name: TC Red FG, pigment content: about 35%, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.).
As the fluorescent pigment, there can be used a fluorescent pigment in the form of fine particles of synthetic resin in which various fluorescent dyes are solid-dissolved in a resin matrix.
Other examples include phosphorescent pigments, white pigments such as titanium dioxide, thermochromic compositions, photochromic compositions, and capsule pigments in which perfumes and the like are directly or microencapsulated.

The thermochromic composition is preferably a reversible thermochromic composition comprising (i) an electron-donating color-forming organic compound, (ii) an electron-accepting compound, and (iii) a reaction medium that determines the temperature at which the color-forming reaction between the two occurs, and is applied as a reversible thermochromic microcapsule pigment by encapsulating it in microcapsules.
As the reversible thermochromic composition, there can be used a heat-discoloring type microcapsule pigment in which a reversible thermochromic composition having a relatively small hysteresis width (ΔH=1 to 7° C.) is encapsulated in a microcapsule, and the reversible thermochromic composition changes color around a predetermined temperature (discoloration point) as described in JP-B-51-44706, JP-B-51-44707, JP-B-1-29398, etc., and exhibits a discolored state in a temperature range above the high-temperature discoloration point and a colored state in a temperature range below the low-temperature discoloration point, and of the two states, only one specific state exists in the room temperature range, and the other state is maintained while the heat or cold required to express that state is applied, but returns to the state exhibited in the room temperature range when the application of the heat or cold is removed.
Further, there are those exhibiting relatively large hysteresis characteristics (ΔH=8 to 50° C.) as described in JP-B-4-17154, JP-A-7-179777, JP-A-7-33997, JP-A-8-39936, etc., and those exhibiting large hysteresis characteristics as described in JP-A-2006-137886, JP-A-2006-188660, JP-A-2008-45062, JP-A-2008-280523, etc. In other words, the shape of the curve plotting the change in color density due to temperature change will change color along a path that is significantly different when the temperature is increased from a lower temperature side than the color change temperature range than when the temperature is decreased from a higher temperature side than the color change temperature range, and the colored state in a low temperature range below the complete color development temperature, or the decolored state in a high temperature range above the complete decolorization temperature, can also be applied to heat-discolorable microcapsule pigments that encapsulate a reversible thermochromic composition that has color memory properties in a specific temperature range.
Specifically, the reversible thermochromic composition having color memory has a complete color-developing temperature that is a temperature that can only be obtained in a freezer or in a cold region, i.e., −50 to 0° C., preferably −40 to −5° C., more preferably −30 to −10° C., and a complete decolorization temperature that is a temperature obtained from frictional heat produced by a friction body or a familiar heating body such as a hair dryer, i.e., 50 to 95° C., preferably 50 to 90° C., more preferably 60 to 80° C., and a ΔH value of 40 to 100° C., thereby allowing the composition to effectively function in maintaining the color exhibited under normal conditions (daily living temperature range).

Furthermore, if necessary, a dye soluble in an aqueous medium can be used in combination.
As the dye, an acid dye, a basic dye, a direct dye, etc. can be used. As the acid dye, New Coccine (C.I. 16255), Tartrazine (C.I. 19140), Acid Blue Black 10B (C.I. 20470), Guinea Green (C.I. 42085), Brilliant Blue FCF (C.I. 42090), Acid Violet 6B (C.I. 42640), Soluble Blue (C.I. 42755), Naphthalene Green (C.I. 44025), Eosin (C.I. 45380), Phloxine (C.I. 45410), Erythrosine (C.I. 45430), Nigrosine (C.I. 50420), Acid Flavin (C.I. 56205), etc. can be used.
Examples of basic dyes that can be used include chrysoidine (C.I. 11270), methyl violet FN (C.I. 42535), crystal violet (C.I. 42555), malachite green (C.I. 42000), Victoria blue FB (C.I. 44045), rhodamine B (C.I. 45170), acridine orange NS (C.I. 46005), and methylene blue B (C.I. 52015).
Examples of direct dyes that can be used include Congo Red (C.I. 22120), Direct Sky Blue 5B (C.I. 24400), Violet BB (C.I. 27905), Direct Deep Black EX (C.I. 30235), Kayalas Black G Conc (C.I. 35225), Direct Fast Black G (C.I. 35255), and Phthalocyanine Blue (C.I. 74180).

The color pigments can be used alone or in a suitable mixture of two or more, and are preferably used in the range of 0.1 to 20% by mass, and more preferably 0.5 to 15% by mass, in the ink composition.

In addition, in order to suppress blurring and interruption of handwriting while improving the color development and brilliance of handwriting, in the aqueous ink composition, when the sum of the total mass of the color pigment and the total mass of the plate-like brilliance pigment is A and the total mass of the water-dispersible polymer is B, B/A is preferably 0.05 to 0.5, and more preferably 0.1 to 0.4.

Furthermore, a general-purpose pigment dispersant can be used in the ink composition. As the pigment dispersant, a water-soluble resin or a surfactant can be used. Examples of the water-soluble resin include water-soluble maleic acid resin, water-soluble styrene resin, water-soluble styrene-maleic acid resin, polyvinylpyrrolidone, polyvinyl alcohol, water-soluble urethane resin, etc. Furthermore, the surfactant can be selected from anionic, cationic, nonionic, and amphoteric surfactants.

A thickener is added to the ink composition, which can prevent the particulate components (plate-shaped luster pigment, color pigment) from settling and the writing from bleeding during storage.
Any known thickener can be used as the thickener, but a substance capable of imparting shear thinning properties to the ink composition (shear thinning agent) is preferred.
By using a shear thinning agent in the ink composition, it is possible to improve the anti-settling stability of the particles and the suppression of bleeding of handwriting without impairing the ink dischargeability during writing.

As the shear thinning agent, a substance that is soluble or dispersible in water is effective, and examples thereof include xanthan gum, welan gum, succinoglycan (average molecular weight: about 1 to 8 million), which is an organic acid-modified heteropolysaccharide whose constituent monosaccharides are glucose and galactose, guar gum, locust bean gum and its derivatives, hydroxyethyl cellulose, alginic acid alkyl esters, polymers with a molecular weight of 100,000 to 150,000 and whose main component is an alkyl ester of methacrylic acid, glucomannan, carbohydrates with gelling ability extracted from seaweed such as agar and carrageenin, benzylidene sorbitol and benzylidene xylitol or derivatives thereof, crosslinkable acrylic acid polymers, poly N-vinyl carboxylic acid amide, inorganic fine particles, nonionic surfactants with an HLB value of 8 to 12, metal salts and amine salts of dialkyl sulfosuccinic acid, etc. Furthermore, stable shear thinning can be imparted even when N-alkyl-2-pyrrolidone and anionic surfactants are added in combination to the ink composition.

The content of the thickener is preferably 0.01 to 3% by mass, and more preferably 0.1 to 1% by mass, based on the total mass of the ink composition. When the content of the thickener is within this range, it is easy to achieve both the ink ejection properties during writing, the pigment's anti-settling stability, and the suppression of bleeding of handwriting.

In order to prevent the ink dischargeability from decreasing due to excessive evaporation of water from the ink contained in the refill, a conventional water-soluble organic solvent that is compatible with water is used in the aqueous ink composition. Specific examples of the water-soluble organic solvent include ethanol, propanol, butanol, glycerin, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thiodiethylene glycol, polyethylene glycol, propylene glycol, butylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, sulfolane, 2-pyrrolidone, and N-methyl-2-pyrrolidone.
The water-soluble organic solvents may be used alone or in combination of two or more kinds, and are preferably used in an amount of 1 to 20% by mass, more preferably 5 to 15% by mass.
When the content of the organic solvent is within the above range, excessive evaporation of water can be easily suppressed without excessively increasing the ink viscosity, so that good ink ejection properties can be maintained and handwriting that is free of smudges and interruptions can be easily formed over a long period of time.

In addition, the water content is preferably 40 to 80% by mass, and more preferably 45 to 70% by mass, based on the total mass of the ink composition, in order to improve the fluidity of the ink composition and improve the ink ejection properties from the pen tip.

The ink composition preferably contains a phosphate ester surfactant.
The phosphate ester surfactant also adsorbs to the surface of the ball and to the surface of the ball receiving seat of the ballpoint pen tip, forming a lubricating layer made of the phosphate ester surfactant on the surface of the ball and the surface of the ball receiving seat, making the ball rotate more smoothly when writing.
Furthermore, the phosphate surfactant can also be adsorbed to the surface of the pigment, making it easier to inhibit the aggregation and sedimentation of the pigment.

式中、Ｘ_１、Ｘ_２、Ｘ_３は、下記式（２）に示す官能基、または水酸基であり、Ｘ_１、Ｘ_２、Ｘ_３の少なくとも１種は、式（２）に示す官能基である。

式中、Ｒ_１は炭化水素基、Ｒ_２はアルキレン基である。また、ｎは１以上の整数である。 The phosphate ester surfactant used in the ink composition is a compound represented by the following formula (1).

In the formula, X ₁ , X ₂ and X ₃ are a functional group shown in the following formula (2) or a hydroxyl group, and at least one of X ₁ , X ₂ and X ₃ is a functional group shown in formula (2).

In the formula, _R1 is a hydrocarbon group, _R2 is an alkylene group, and n is an integer of 1 or more.

The preferred phosphate ester surfactant for the ink composition is a phosphate ester surfactant in which the hydrocarbon group is an alkyl group, an alkenyl group, or an aryl group, and more preferably, the phosphate ester surfactant in which the hydrocarbon group is an alkyl group, an alkenyl group, or an aryl group, and the alkylene group is an ethylene group. A particularly preferred phosphate ester surfactant is a phosphate ester surfactant in which the hydrocarbon group is an alkyl group, and the alkylene group is an ethylene group, that is, polyoxyethylene alkyl ether phosphate. The use of the polyoxyethylene alkyl ether phosphate makes the ball rotate more smoothly during writing, improves the ink dischargeability during writing, and makes it easier to prevent the pigment from coagulating and settling. This is because the polyoxyethylene alkyl ether phosphate has a high affinity not only to the ball and the ball tip, but also to the pigment, and exerts the effects of excellent lubricating layer formation and pigment dispersibility on the ball surface and the ball tip surface. In particular, ballpoint pens that use the plate-like luster pigment as the ink colorant can struggle to provide a smooth writing feel or good ink discharge; however, polyoxyethylene alkyl ether phosphate is interposed between the plate-like luster pigment and the ball surface and the ball seat surface, and the pigment is adsorbed to the ball surface and the ball seat surface, so that the pigment acts as a roller when the ball rotates during writing, thereby making the ball rotate smoothly and providing a good writing feel and ink discharge.
The phosphate ester surfactant may be an alkali metal salt or an amine salt.

The content of the phosphate ester surfactant is preferably 0.01 to 5% by mass, and more preferably 0.1 to 3% by mass, based on the total mass of the ink composition. By keeping the content of the phosphate ester surfactant in the ink composition within this range, it becomes easier to make the ball spin smoother while improving the dissolution stability of the phosphate ester surfactant, and it also becomes easier to suppress pigment aggregation and sedimentation.

In addition, water-soluble resins can be added to the ink composition to impart adhesion and viscosity to the paper surface. Examples of the water-soluble resins include alkyd resins, styrene-maleic acid copolymers, cellulose derivatives, polyvinylpyrrolidone, polyvinyl alcohol, dextrin, etc. One or more of the water-soluble resins can be used in combination, and are used in the range of 1 to 30% by weight in the ink composition.

In addition, the ink composition may contain, as necessary, inorganic salts such as sodium carbonate, sodium phosphate, and sodium acetate; pH adjusters such as organic basic compounds such as water-soluble amine compounds; rust inhibitors such as benzotriazole, tolyltriazole, 2,5-dimercapto-1,3,4-thiadiazole, and saponin; preservatives or antifungal agents such as carbolic acid, the sodium salt of 1,2-benzthiazolin-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, and 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine; wetting agents such as urea, nonionic surfactants, sorbitol, mannitol, sucrose, glucose, reduced starch hydrolysates, and sodium pyrophosphate; defoamers; and fluorine-based surfactants and nonionic surfactants that improve the penetration of the ink.
Furthermore, air bubbles can be removed chemically by adding ascorbic acids, erythorbic acids, α-tocopherol, catechins, synthetic polyphenols, kojic acid, alkylhydroxylamines, oxime derivatives, α-glucosylrutin, α-lipoic acid, phosphonates, phosphinates, sulfites, sulfoxylates, dithionites, thiosulfates, thiourea dioxide, or the like.
Furthermore, dextrin can be used to improve the resistance of the pen tip to drying up.
Furthermore, by adding a thickening inhibitor such as an oligomer of N-vinyl-2-pyrrolidone, an oligomer of N-vinyl-2-piperidone, N-vinyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, ε-caprolactam, or an oligomer of N-vinyl-ε-caprolactam, the functionality in the retractable form can be improved.
Furthermore, lubricants can be used, such as metal soaps, polyalkylene glycol fatty acid esters, ethylene oxide-added cationic surfactants, phosphate ester-based surfactants, β-alanine-type surfactants, N-acylamino acids, N-acylmethyltaurines, 2,5-dimercapto-1,3,4-thiadiazoles and their salts and oligomers, 3-amino-5-mercapto-1,2,4-triazole, thiocarbamate salts, dimethyldithiocarbamate salts, α-lipoic acid, condensates of N-acyl-L-glutamic acid and L-lysine and their salts, and the like.

It is important that the viscosity of the aqueous ink composition at 20° C. is 800 to 1600 mPa·s at a shear rate of 3.84 sec ⁻¹ , and it is preferably 1000 to 1500 mPa·s.
The viscosity can be measured, for example, using a rheometer "DHR-2" manufactured by TA Instruments.

It is also important that the shear thinning index n of the aqueous ink composition at 20° C. is 0.15 to 0.5, preferably 0.2 to 0.4, and more preferably 0.25 to 0.35. Here, the shear thinning index n refers to n in the viscosity formula S=αD ⁿ , where S is the shear stress (dyn/cm ² =0.1 Pa), D is the shear rate (sec ⁻¹ ), and α is the viscosity coefficient.
The shear thinning index n can be measured, for example, using a rheometer "DHR-2" manufactured by TA Instruments Co., Ltd., and n is calculated by applying the shear rates of 3.84 sec ^-1 , 38.4 sec ^-1 and 384 sec ^-1 and the shear stresses obtained at those shear rates to the above formula.
When the viscosity and shear thinning index of the aqueous ink composition are within the above-mentioned numerical ranges, settling and aggregation of the plate-like photoluminescent pigment and colored pigment when left to stand can be suppressed, while the ink can be discharged well from the pen tip when writing, and clear handwriting with excellent color development and photoluminescence can be produced with suppressed smearing and discontinuities.

The surface tension of the aqueous ink composition is preferably 25 to 55 mN/m in an environment of 20° C. If the surface tension is within the above range, it is possible to improve the writing properties by suppressing smearing, interruption, bleeding, etc. of handwriting. In terms of improving the writing properties, the surface tension of the aqueous ink composition is more preferably 30 to 50 mN/m.
The surface tension is determined in an environment of 20° C. by measuring with a surface tension meter manufactured by Kyowa Interface Science Co., Ltd. using a platinum plate by the vertical plate method.

The pH of the aqueous ink composition is preferably 6 to 10, and more preferably 7 to 9. When the pH of the aqueous ink composition is within the above range, the dispersibility of the colorant is easily improved.
In the present invention, the pH value can be measured at 20° C. using, for example, a pH meter "D-51" manufactured by Horiba, Ltd.

The aqueous ink composition can be produced by any conventional method. Specifically, the components are mixed in the required amounts and mixed with various stirrers such as a propeller stirrer, homodisper, or homomixer, or various dispersers such as a bead mill, to produce the composition.

The aqueous ink composition contains at least water, a water-soluble organic solvent, a plate-shaped photoluminescent pigment, a coloring pigment, one or more water-dispersible polymers selected from acrylic acid-based polymers, urethane-based polymers and olefin-based polymers having water-dispersibility, and a thickener. By controlling the viscosity and shear thinning index to be within a specific range, the dispersion stability and ink dischargeability of the plate-shaped photoluminescent pigment and the coloring pigment are improved, and the coloring pigment is prevented from sinking from the paper surface into the interior of the paper, thereby forming vivid handwriting with excellent color development and photoluminescence and with reduced smearing and discontinuities.
The pigment dispersion stability is maintained even after long periods of aging or when the water content in the ink decreases over time and the concentrations of the plate-shaped photoluminescent pigment and color pigment increase. Furthermore, even when the water content in the ink decreases, the aqueous ink composition is prevented from excessively thickening and good ink discharge properties are maintained, so that the aqueous ink composition can form the above-mentioned vivid handwriting for a long period of time.

The ballpoint pen refill of the present invention contains the above-mentioned water-based ink composition in an ink reservoir tube to which a ballpoint pen tip is attached directly or via a holder, and is filled with an ink backflow prevention body (liquid plug) that follows the ink as it is consumed.

The structure and shape of the pen tip (ballpoint pen tip) are not particularly limited. For example, there is a structure in which a ball holding chamber for holding a ball formed by cutting metal with a drill or the like, an ink flow hole formed in the center of the bottom wall of the ball holding chamber, and a plurality of ink flow grooves extending radially from the ink flow hole are provided, and the tip tip of the tip body is crimped inward to make a part of the ball held in the ball holding chamber protrude from the tip edge and hold the ball rotatably. Another example is a so-called pipe-type ballpoint pen tip structure, which has a ball holding part in which the ball is rotatably held by a crimped part formed by pressing and deforming the tapered tip of a metal pipe inward in the radial direction, and a plurality of inward protrusions formed by pressing and deforming the side wall near the tip of the pipe inward in the radial direction.

The pipe may, for example, have a straight cylindrical tip (straight cylindrical body) and an outer diameter and an inner diameter that expand behind the tip. The shape of the pipe may be a straight cylindrical body as a whole.

Considering the need to improve the ink ejection properties from the ballpoint pen tip, the ballpoint pen tip is preferably a pipe-type ballpoint pen tip in which the tip of the pipe is a straight cylinder and the outer and inner diameters of the tip expand behind the tip (hereinafter, sometimes referred to as a pipe-type ballpoint pen tip with a shape that expands behind the tip).

A pipe-type ballpoint pen tip with a shape that expands in diameter at the rear of the tip has a wide ink flow path formed behind the ball-holding chamber inside the ballpoint pen tip, allowing for abundant ink to be supplied to the ball-holding chamber. A ballpoint pen refill equipped with such a ballpoint pen tip provides good ink ejection from the pen tip, excellent brilliance and color development, and is easy to produce clear handwriting with reduced cutting and smudging.

The material of the ballpoint pen tip and the ball held by the ballpoint pen tip is preferably selected from stainless steel, cemented carbide based on tungsten carbide, silicon carbide, alumina, zirconia, silicon nitride, etc., taking into consideration the good wear resistance of the ball and the ball seat.

The ball diameter is 0.2 to 0.7 mm, preferably 0.3 to 0.5 mm, and more preferably 0.3 to 0.45 mm.

Ballpoint pen refills with a ball diameter of 0.7 mm or less, especially less than 0.5 mm, have a small ink ejection volume and may not produce clear handwriting. However, the pipe-type ballpoint pen tip with a shape that expands in diameter at the rear of the tip, even when equipped with a ball with such an outer diameter, has good ink ejection properties and makes it easy to form clear handwriting with reduced smearing and interruptions, so it can be preferably used in combination with a ball with a ball diameter in the above range.

The ballpoint pen tip may have a resilient member disposed within the tip that resilients the rear end of the ball forward. This allows the ball to be retracted by writing pressure when writing, allowing the ink to flow out, and when not writing, the ball can be pressed against the inner edge of the tip tip to create a tight fit, making it easy to prevent ink leakage when not in use.

Examples of the resilient member include a thin metal wire spring, a thin metal wire spring having a straight portion (rod portion) at one end, a linear plastic processed body, and the like.
It is configured so as to be pressable with a resilient force of 10 g or more and 40 g or less.

Ink reservoir tubes to which a ballpoint pen tip is attached directly or via a holder are made of molded components of synthetic resins such as polyethylene, polypropylene, polyethylene terephthalate, or ethylene-vinyl acetate copolymer resins, because these have low water vapor permeability, good productivity, and transparency that allows excellent visibility of the filled ink.
Examples of the polyethylene include low-density polyethylene, linear short-chain branched polyethylene, metallocene-catalyzed linear short-chain branched polyethylene, and high-density polyethylene, and examples of the polypropylene include homopolymer polypropylene, random copolymer polypropylene, and block copolymer polypropylene, all of which can be preferably used. Among these, polypropylene is preferably used because it has excellent strength and heat resistance, low moisture permeability, and is easily inhibited from thickening the ink due to evaporation of moisture over time.
The ink reservoir tube is obtained by subjecting the synthetic resin to extrusion molding or injection molding.
The surface of the resin may be coated with another material.

The ink reservoir tube made of the synthetic resin may be single-layered or multi-layered, but it is preferable for the ink reservoir tube to have a multi-layered structure with a layer that prevents the permeation of gases such as oxygen, in order to prevent the ink from deteriorating over time. Furthermore, if necessary, the inner surface of the ink reservoir can be treated with an ink-repellent agent by applying a silicone resin or fluororesin to prevent the ink from adhering to the inner wall of the ink reservoir tube.

The ink reservoir has an outer diameter of 2.5 to 4 mm and a wall thickness of 0.3 to 1 mm.
An ink reservoir tube whose outer diameter and wall thickness are within the above-mentioned ranges is slender yet capable of balancing a sufficient ink capacity with high strength. Therefore, when a ballpoint pen refill equipped with the above-mentioned ink reservoir tube is contained in a composite retractable ballpoint pen which contains multiple ballpoint pen refills within a barrel and in which the writing tip of one of the ballpoint pen refills protrudes and retracts from the front end opening of the barrel by activation of the retraction mechanism, the ballpoint pen can be made to be a highly practical ballpoint pen which is capable of writing a sufficient distance while having a slim outer diameter of the barrel.
In ballpoint pen refills having the ink reservoir tube, water from the ink contained therein tends to volatilize out of the refill over time through the ink reservoir tube, and as a result, the ink dischargeability tends to decrease due to the aggregation of solids and excessive thickening of the ink caused by the decrease in the amount of water. In particular, when the ink in the ballpoint pen refill contains a large amount of solids such as pigments, such as plate-shaped glittering pigment ink, this tendency is remarkable, and the ink dischargeability tends to deteriorate. However, although the ink composition is an ink using a plate-shaped glittering pigment, even after a long period of time or when the amount of water in the composition decreases over time, excessive thickening of the ink viscosity is suppressed, and good dispersibility of the plate-shaped glittering pigment and coloring pigment is maintained. Therefore, the ballpoint pen refill of the present invention containing the ink composition maintains good ink dischargeability even though it has the ink reservoir tube, and can stably form handwriting with excellent glitter and color development of the coloring pigment for a long period of time.
In addition, in a ballpoint pen refill having the ink reservoir, the ink plug is less likely to deform when an impact is applied to the ink plug, so that ink leakage from the rear end of the refill when the ballpoint pen refill is dropped can be suppressed. This makes the ballpoint pen refill excellent in storage properties.
The ink reservoir tube preferably has an outer diameter of 2.5 to 3.5 mm and a wall thickness of 0.5 to 0.8 mm.

Furthermore, an ink backflow prevention member (liquid plug) is disposed at the rear end of the ink composition filled in the ink reservoir tube.
The ink backflow preventer is a viscous liquid that uses a non-volatile medium as a base oil and has a high viscosity due to the addition of solids such as silica, aluminum silicate, swellable mica, and fatty acid amide.
Examples of non-volatile media used for the base oil include petrolatum, spindle oil, castor oil, olive oil, refined mineral oil, liquid paraffin, polybutene, α-olefin, α-olefin oligomer or cooligomer, dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, polyether-modified silicone oil, fatty acid-modified silicone oil, etc., and polybutene is preferably used because it is likely to increase in viscosity when the solid is added, the solid is unlikely to separate over time, and further has low water vapor permeability, making it easy to suppress ink thickening over time due to water evaporation. Polybutene preferably has a kinetic viscosity of 1000 to 10000 mm ² s ^-1 at 40°C, more preferably 1500 to 5000 mm ² s ^-1 , and even more preferably 2000 to 4000 mm ² s ^-1 . By using such polybutene as the base oil for the plug, the plug is able to easily follow the ink when it is ejected during writing, making it easier to prevent ink ejection from being hindered, and also making it easier to prevent the plug from deforming and ink from leaking from the rear end of the refill if the ballpoint pen refill falls and the weight of the ink composition is applied to the plug.
The ink backflow preventive material can be prepared by kneading the polybutene with the silica, aluminum silicate, swellable mica, fatty acid amide, etc., in a kneading machine such as a three-roll mill or a kneader.
The kinematic viscosity can be measured in accordance with JIS K 2283:2000 "Crude oil and petroleum products - Kinematic viscosity test method and viscosity index calculation method."

In addition, a ballpoint pen refill may be provided with a solid plug in addition to the ink backflow preventer to prevent ink from flowing back.
Examples of solid plugs include solid plugs made of resin, such as polyethylene, polypropylene, and polymethylpentene.

The ballpoint pen refill of the present invention is equipped with a cap-type, knock-type, rotating-type, sliding-type or other retractable mechanism, and is attached to a retractable ballpoint pen configured so that the pen tip can be retracted from the tip hole of the barrel.

When applying the retractable type to a ballpoint pen, the structure and shape of the retractable ballpoint pen are not particularly limited, and any structure can be used as long as the writing tip provided on the ballpoint pen refill is stored in the barrel while being exposed to the outside air, and the writing tip protrudes from the barrel opening by the operation of the retractable mechanism. Examples of the operation method of the retractable mechanism include a knock type, a rotation type, a slide type, and the like. The knock type can be exemplified by a configuration having a knock part at the rear end of the barrel or the side of the barrel, and the writing tip protrudes from the barrel front end opening by pressing the knock part, or a configuration in which the writing tip protrudes from the barrel front end opening by pressing a clip part provided on the barrel. The rotation type can be exemplified by a configuration having a rotating part at the rear of the barrel, and the writing tip protrudes from the barrel front end opening by rotating the rotating part. The sliding type may be exemplified by a configuration having a sliding part on the side of the barrel, and by operating the slide, the writing tip part is made to protrude and retract from the front end opening of the barrel, or a configuration in which the writing tip part is made to protrude and retract from the front end opening of the barrel by sliding a clip part provided on the barrel. The retractable ballpoint pen may be a composite type retractable ballpoint pen (hereinafter sometimes referred to as a composite type retractable ballpoint pen) in which a plurality of ballpoint pen refills are accommodated in the barrel, and the writing tip part of any of the ballpoint pen refills is made to protrude and retract from the front end opening of the barrel by the operation of the retractable mechanism.
Furthermore, by using a transparent, colored transparent, or translucent molded body as the barrel, it is possible to check the ink color, the remaining amount of ink, etc.

The ballpoint pen refill of the present invention is slim, yet has excellent brilliance and color development, and can produce vivid handwriting without smudges or interruptions for a long period of time, making it suitable for use in composite retractable ballpoint pens, for which slim ballpoint pen refills are suitable.

An example of a ballpoint pen refill according to this embodiment is described below with reference to the drawings.

Ballpoint Pen Refill An embodiment of the ballpoint pen refill is shown in FIGS.
The ballpoint pen refill 1 of this embodiment comprises a ballpoint pen tip 2 which rotatably holds a ball 4 at its front end, a spring 5 housed inside the ballpoint pen tip 2, a holder 6 to which the ballpoint pen tip 2 is press-fitted at its front end, and an ink reservoir tube 7 to which the rear part of the holder is press-fitted at its front end opening.
In this embodiment, "front" refers to the pen tip ball side, and "rear" refers to the opposite side.

Ballpoint Pen Tip The ballpoint pen tip 2 comprises a tip body 3 and a ball 4. The tip body 3 comprises a metallic cylinder comprising a small-diameter cylindrical section 31 rotatably holding the ball 4 at its front end, a tapered cylindrical section 32 integrally connected to the rear of the small-diameter cylindrical section 31 and gradually increasing in diameter toward the rear, and a large-diameter cylindrical section 33 integrally connected to the rear of the tapered cylindrical section 32. The metallic cylinder is made of austenitic stainless steel such as SUS304, SUS305, or SUS321.

On the inner surface near the front end of the small diameter tube portion 31 of the tip body 3, a plurality of (for example, four) inward protrusions 31b are formed at equal intervals in the circumferential direction by inward pressing deformation. The inward protrusions 31b form a ball receiving seat. In addition, the front end of the tip body 3 is circumferentially pressed inward to form an inward front edge portion 31a. A ball holding portion that rotatably holds the ball 4 is formed between the front surface of the inward protrusions 31b (ball receiving seat) and the rear surface of the front edge portion 31a. Between the inward protrusions 31b, an ink circulation hole 31c is formed that extends radially outward from the center and penetrates in the axial direction. That is, the ink circulation hole 31c is formed in the ball receiving seat. The ballpoint pen tip 2 may be a type in which a ball receiving seat is formed by cutting at the front end of the metal tip body 3.

A right cylindrical inner surface is formed on the inner surface of the small diameter cylindrical portion 31 rearward of the inward protruding portion 31b. A right cylindrical inner surface is formed on the inner surface of the large diameter cylindrical portion 33.

Tapered Inner Surface The tapered cylindrical portion 32 has an inner surface that is tapered (or conical) and gradually expands in diameter toward the rear.

Spring The spring 5 has a front rod portion 51 and a rear coil portion 52 which are integrally connected to each other by a single metal wire (for example, a stainless steel wire having a wire diameter of 0.11 mm).

Rod portion The rod portion 51 extends linearly in the axial direction, and is inserted into the ink flow hole 31c of the ball receiving seat 31b. The front end of the rod portion 51 abuts against approximately the center of the rear surface of the ball 4, and the ball 4 is directly urged forward by the rod portion 51. This brings the ball 4 into close contact with the inner peripheral surface of the front end edge portion 31a, preventing ink leakage from the front end of the tip body 3 and ink evaporation.

Coil section The coil section 52 is formed by winding a wire in a spiral shape. A tightly wound section where the wire is tightly wound is formed at the front and rear ends of the coil section 52. An effective winding section with gaps between the wire is formed in the middle section of the coil section 52 excluding the front and rear ends. The elastic force with which the spring 5 urges the ball 4 forward (specifically, the load when the ball 4 is pressed backward by 0.01 mm) is set in the range of 14 grams to 25 grams (preferably 15 grams to 22 grams).

Holder The holder 6 is a cylindrical body obtained by injection molding of a synthetic resin (e.g., polypropylene). The holder 6 comprises a tapered front portion 61 to which the ballpoint pen tip 1 is attached, a flange portion 62 that abuts against the front end surface of the ink reservoir 7, and a rear portion 63 that is press-fitted into the front end opening of the ink reservoir 7. The rear portion of the tip body 3 is press-fitted and fixed into the mounting hole of the front portion 61 of the holder 6. A step portion 64 is protruded from the rear end of the inner surface of the mounting hole, and the rear end of the tip body 3 is engaged with the step portion 64, and the rear end of the spring 5 (the rear end of the coil portion 52) is engaged with the step portion 64.

Ink reservoir tube The ink reservoir tube 7 is a cylinder with both ends open, obtained by extrusion molding of a synthetic resin (e.g., polypropylene). The ink reservoir tube 7 has an outer diameter of 2.5 to 4 mm and a wall thickness of 0.3 to 1 mm, and is filled with ink 71 and an ink backflow preventer 72 made of a high-viscosity fluid that advances as the ink 71 is consumed. The ink 71 is the aqueous ink composition related to the ballpoint pen refill of the present invention. The ink backflow preventer 72 may be a high-viscosity fluid made by mixing a solid material with polybutene as a base oil having a kinetic viscosity of 1000 to 10000 mm ² s ^-1 at 40°C.

Ball The ball 4 has a diameter A in the range of 0.2 mm to 0.7 mm (preferably 0.3 mm to 0.5 mm, and more preferably 0.3 mm to 0.45 mm). Specifically, balls 4 are prepared in a number of sizes according to the desired handwriting width, and balls with diameters of, for example, 0.2 mm, 0.25 mm, 0.3 mm, 0.4 mm, 0.5 mm, and 0.7 mm are used.

The amount of axial movement of the ball 4 in the ball holding part is preferably in the range of 0.02 mm to 0.05 mm in order to obtain smooth ink flow. The amount of axial movement of the ball 4 in the ball holding part varies depending on the diameter A of the ball 4, and is set in the range of 5% to 15% (preferably 8% to 12%) of the diameter A of the ball 4, thereby obtaining smooth ink flow and sufficient ball exposure.

The material of the ball 4 may be stainless steel, a cemented carbide based on tungsten carbide, silicon carbide, alumina, zirconia, silicon nitride, or the like.
The amount E of exposure of the ball 4 forward in the axial direction is set in the range of 22% to 32% of the diameter A of the ball 4. The amount E of exposure of the ball 4 forward in the axial direction is measured in a state where the ball 4 is pressed backward against the forward bias of the spring and the ball 4 is in contact with each inward protrusion 31b (ball receiving seat). When the diameter A is within the above range (particularly when the diameter A of the ball 4 is 0.3 mm to 0.45 mm), a common spring 6 is used to obtain a plurality of types of ballpoint pen tips 2 by using a plurality of types of balls 4 with different diameters.

Small Diameter Cylinder Portion When the diameter A of ball 4 is within the above-mentioned range (particularly when the diameter A of ball 4 is 0.3 mm to 0.45 mm), the inner diameter B of the right cylindrical inner surface of the small diameter cylinder portion 31 is set to be larger than the diameter A of ball 4. Specifically, the inner diameter B of the small diameter cylinder portion 31 is set to be larger than the diameter A of ball 4 by 0.03 mm to 0.06 mm.

The axial length F of the inner surface of the straight cylinder behind the inward protrusion of the small diameter cylinder portion 31 is set to be smaller than the diameter A of the ball 4. This allows ink to be supplied abundantly to the rear surface of the ball 4, resulting in smooth ink flow.

Tapered cylinder section When the diameter A of the ball 4 is within the above range (particularly when the diameter A of the ball 5 is 0.3 mm to 0.45 mm), the angle α of the tapered inner surface of the tapered cylinder section 32 (the angle α of the conical inner surface centered on the axis) is set to 30 degrees to 40 degrees. The axial length G of the tapered inner surface is set to be greater than the diameter A of the ball 4. Specifically, the axial length G of the tapered inner surface is set to 1.1 to 5.0 times (preferably 2 to 4.5 times) the diameter A of the ball 4. The tapered cylinder section 32 properly connects the small diameter cylinder section 31 and the large diameter cylinder section 33 to obtain smooth ink flowability.

Large-diameter cylindrical portion When the diameter A of the ball 4 is in the above-mentioned range (particularly when the diameter A of the ball 4 is 0.3 mm to 0.45 mm), the inner diameter C of the straight cylindrical inner surface of the large-diameter cylindrical portion 33 is set to 0.9 mm or more (preferably 1 mm or more), and the outer diameter D of the straight cylindrical inner surface of the large-diameter cylindrical portion 33 is set to 1.2 mm or more (preferably 1.3 mm or more). The axial length H of the straight cylindrical inner surface of the large-diameter cylindrical portion 333 is set in the range of 4.0 mm to 5.0 mm.

In addition, when the diameter A of the ball 4 is within the above range (particularly when the diameter A of the ball 4 is 0.3 mm to 0.45 mm), and multiple types of balls 4 with different diameters are used to obtain multiple types of ballpoint pen tips 1, the inner diameter C of each large diameter cylindrical portion 33 is set to be the same, and the outer diameter D of each large diameter cylindrical portion 33 is set to be the same, so that the shape of the attachment portion of the ballpoint pen tip 2 to the holder 6 can be standardized, and the manufacturing process can be simplified.

Summary The ballpoint pen refill 1 of the present embodiment has at least the following configuration requirements.
The ballpoint pen refill 1 of this embodiment includes a ballpoint pen tip 2 that rotatably holds a ball 4 at its front end, a spring 5 that is accommodated and disposed inside the ballpoint pen tip 2, a holder 6 to which a rear portion 63 of the ballpoint pen tip 2 is fixed, and an ink reservoir 7 to whose front end opening the rear portion 63 of the holder 6 is fixed.
The ink reservoir 7 is made of synthetic resin.
The ink reservoir 7 has an outer diameter of 2.5 to 4 mm and a wall thickness of 0.3 to 1 mm.
The inside of the ink reservoir 7 is filled with ink 71 and an ink backflow prevention body 72 made of a high-viscosity fluid that advances as the ink 71 is consumed.
The ballpoint pen tip 2 is provided with a tip body 3 made of a metallic cylinder having a small diameter tube portion 31 in the shape of a straight cylinder, the ball 4 being rotatably supported at the front end thereof, a tapered tube portion 32 which is integrally connected to the rear of the small diameter tube portion 31 and which gradually expands in diameter as it advances rearward, and a large diameter tube portion 33 in the shape of a straight cylinder which is integrally connected to the rear of the tapered tube portion 32.
The elastic force of the spring 5 that biases the ball 4 forward is set in the range of 14 g to 25 g.
The diameter A of the ball 4 is set in the range of 0.2 mm to 0.7 mm.
The amount of axial movement of the ball 4 of the ball holding portion is set in the range of 0.02 mm to 0.05 mm,
The inner diameter B of the straight cylindrical inner surface of the small diameter cylinder portion 31 rearward of the ball receiving seat 31b is set to be 0.03 mm to 0.06 mm larger than the diameter A of the ball 4,
The axial length F of the right cylindrical inner surface of the small diameter cylindrical portion 31 rearward of the ball receiving seat 31b is set to be smaller than the diameter A of the ball 4,
The inner diameter C of the right cylindrical inner surface of the large diameter tubular portion 33 is set to 0.9 mm or more.

Examples will be described below, but the present invention is not limited to these examples.
The compositions of the glittering inks for ballpoint pen refills of the Examples and Comparative Examples are shown in the following table. The numerical values for the compositions in the table indicate parts by weight.
The average particle size is measured using a laser particle size distribution analyzer LA-300 (volume basis) manufactured by Horiba, Ltd., and the median size is taken as the average particle size. In this case, the particle size of the plate-shaped bright pigment is calculated by setting the minimum value on the particle size axis in the particle size distribution diagram to 0.5 μm.

The contents of the ingredients in the table are explained according to the note numbers.
(1) Aluminum powder paste, manufactured by Toyo Aluminum Co., Ltd., product name: Alpaste WXM-0630 (aluminum powder content: 60 mass%, average particle size: 7 μm)
(2) Aluminum powder paste, manufactured by Toyo Aluminum Co., Ltd., product name: Alpaste EMERAL EMR-D5660H (aluminum powder content: 60 mass%, average particle size: 9 μm)
(3) Pearl pigment, product name: Iriodin 221 (average particle size: 15 μm), manufactured by Merck Japan Ltd.
(4) Water dispersion of blue pigment having an average particle size of 0.2 μm (solid content: 20% by mass)
(5) Magenta pigment dispersion having an average particle size of 0.2 μm (solid content: 20% by mass)
(6) Yellow pigment dispersion having an average particle size of 0.2 μm (solid content: 16% by mass)
(7) Trade name: Phloxine, manufactured by Hodogaya Chemical Industry Co., Ltd. (8) Olefin-based polymer emulsion [water dispersion, trade name: ZAIXXEN L, manufactured by Sumitomo Seika Chemicals Co., Ltd., active ingredient: 25% by mass]
(9) Urethane-based polymer emulsion [water dispersion, manufactured by Kusumoto Chemical Industries, Ltd., product name: NeoRez R-2170, active ingredient: 40% by mass]
(10) Acrylic acid-based polymer emulsion [water dispersion, manufactured by Kusumoto Chemical Industries, Ltd., product name: NeoCryl A-639, active ingredient: 42% by mass]
(11) Acrylic acid polymer emulsion [Kusumoto Chemical Industries, Ltd., product name: NeoCryl A-6016, active ingredient: 45% by mass]
(12) Aqueous solution of sodium salt of copolymer of acrylic acid and sulfonic acid monomer [manufactured by Toagosei Co., Ltd., trade name: Aron A-6017 (solid content: 40% by mass)]
(13) Polyoxyethylene alkyl ether phosphate [manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name: Plysurf M208F]
(14) Succinoglycan (15) Dextrin [manufactured by Sanwa Starch Co., Ltd., trade name: Sandec #100]

Preparation of Ink Each component was added to water and stirred at 2000 rpm for 1 hour at 20° C. using a disperser, after which a shear thinning agent was added and stirred for a further 1 hour to prepare each ink.

Preparation of ink backflow preventive agent 1.5 parts of fatty acid amide as a thickener was added to 98.5 parts of polybutene as a base oil, and then the mixture was kneaded with a three-roll mill to obtain an ink backflow preventive agent.

The ink compositions of the examples and comparative examples were used to prepare ballpoint pen refills according to the embodiment. The ink reservoir was made of polypropylene resin, and the outer diameter of the ink reservoir was 3.07 mm and the wall thickness was 0.69 mm.
The ball diameter was 0.4 mm, and the amount of ink contained in the ballpoint pen was 0.15 g.
The ink backflow preventive body (liquid plug) was prepared by kneading 98.5 parts of polybutene and 1.5 parts of fatty acid amide with a three-roll mill.

Preparation of Ballpoint Pen The ballpoint pen refill was attached to an exterior (product number: LHKC15C-NC, manufactured by Pilot Corporation) for a pen with the product name: HI-TEC-C COLETO (manufactured by Pilot Corporation) to prepare a ballpoint pen.

The following tests were carried out using the ballpoint pens prepared in the above-mentioned preparation of ballpoint pens.
Evaluation of blurred and interrupted handwriting The ballpoint pens that were confirmed to be writable were used to continuously write 20 spiral circles on JIS P3201 writing paper A using an automatic writing tester to confirm the condition of the handwriting (10 pens were tested each). The tester was used under the following conditions: writing load 100 g, writing angle 70°, and writing speed 4 m/min.
◯...Can produce good handwriting without smudges or breaks.
△: Slight blurring and interruptions are observed.
×: There is noticeable blurring and interruption.
Evaluation of brilliance and color development of handwriting Ten spiral circles were handwritten in succession on black paper, and the handwriting was visually inspected and subjected to a sensory evaluation of brilliance and color development.
◎…Vivid metallic luster and color.
◯: The metallic luster is clear and the hue is visible.
△: The metallic luster is clear, but the hue is slightly difficult to see.
×: The metallic luster is clear, but the hue is unclear.
Evaluation of storage stability After the ballpoint pens that were confirmed to be writable were left in a thermostatic chamber at 50° C. for 30 days, a spiral circle was written by hand and the handwriting was visually confirmed. The writing paper used was the writing paper A, and the writing load, writing angle and writing speed were the same as those in the writing test.
〇…As with the early stages, there are no smudges or breaks in the handwriting.
△: Compared to the initial state, the handwriting is more easily smudged and broken, but this does not cause any problems in practical use.
×: Writing is impossible, or the handwriting is noticeably smudged or broken compared to the initial state.
The results of each of the above tests are shown in the following table.

(Application example)
Preparation of Multi-Color Ballpoint Pen Each of the ballpoint pen refills containing the ink compositions of Examples 5, 6, and 10 was attached to an exterior (product number: LHKC15C-NC, manufactured by Pilot Corporation) for a pen with the product name: HI-TEC-C COLETO [manufactured by Pilot Corporation] to prepare a composite type retractable ballpoint pen (slide type).
The ballpoint pen allows easy attachment/detachment and sliding of each ballpoint pen refill, and allows writing with excellent brilliance and vivid red, blue and yellow hues to be formed over a long period of time without smearing or interruption.

Reference symbols for ballpoint pen refills shown in Figures 1 to 3: 1 ballpoint pen refill; 2 ballpoint pen tip (pen tip)
Reference Signs List 3: Tip body 31: Small diameter cylindrical portion 31a: Front end edge portion 31b: Inward protrusion portion 31c: Ink flow hole 32: Tapered cylindrical portion 33: Large diameter cylindrical portion 4: Ball 5: Spring 51: Rod portion 52: Coil portion 6: Holder 61: Front portion 62: Flange portion 63: Rear portion 64: Step portion 7: Ink reservoir tube 71: Ink 72: Ink backflow prevention body (liquid plug)
A: diameter of ball 4; B: inner diameter of the straight cylindrical inner surface of small diameter cylindrical portion 31; C: inner diameter of large diameter cylindrical portion 33; D: outer diameter of large diameter cylindrical portion 33; E: amount of ball 4 exposed forward in the axial direction; F: axial length of the straight cylindrical inner surface behind the inward protrusion of small diameter cylindrical portion 31; G: axial length of the tapered inner surface of tapered cylindrical portion 32; H: axial length of the straight cylindrical inner surface of large diameter cylindrical portion 33

Claims (3)

An ink composition comprising water, a water-soluble organic solvent, a plate-like effective pigment, a color pigment, at least one water-dispersible polymer selected from the group consisting of an acrylic acid polymer, a urethane polymer, and an olefin polymer, a water-soluble copolymer of acrylic acid and a sulfonic acid monomer, and a thickener,
wherein the total mass of the water-dispersible polymer is X and the total mass of the copolymer of acrylic acid and a sulfonic acid monomer is Y, Y/X is 0.1 to 1.0;
The content of the water-dispersible polymer is 0.5 to 3 mass% based on the total mass of the ink composition,
the sum of the total mass of the plate-like bright pigment and the total mass of the color pigment is A, and the total mass of the water-dispersible polymer is B, B/A is 0.1 to 0.4;
The ink composition has a viscosity of 800 to 1600 mPa·s at 3.84 sec-1 at 20°C, and a shear thinning index n of 0.15 to 0.5 at 20°C. A ballpoint pen refill containing the aqueous ink composition according to claim 1. A ballpoint pen containing the ballpoint pen refill according to claim 2.

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