Oil-based ballpoint pen

Abstract

To obtain an oil-based ballpoint pen that suppresses the ink leakage and improved ink temporal stability, while maintaining dense calligraphy.SOLUTION: An oil-based ballpoint pen characterized in that an oil-based ballpoint pen having a ballpoint pen tip at the tip of the ink receiving cylinder and containing an ink composition for an oil-based ballpoint pen in the ink container, and the amount of ink consumed per 100 meters of the oil-based ballpoint pen is 20 to 70 mg and the oil composition for the oil-based ballpoint pen contains a colorant, an organic solvent and an acrylic ester resin particle.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an oil-based ballpoint pen. [Background technology]

[0002] Conventionally, in order to prevent ink leakage from the gap between the ball and the tip end (writing end) in ink compositions for oil-based ballpoint pens, various technologies have been proposed, such as using a solvent with a vapor pressure of 0.001 mmHg or more at 25°C, using a terpene phenol resin as an ink leakage inhibitor, or using a gelling agent to increase the ink viscosity.

[0003] As ink compositions for such oil-based ballpoint pens, techniques using alcohols, polyhydric alcohols, and glycol ether solvents having a vapor pressure of 0.001 mmHg or more at 25°C are disclosed in JP 2004-107591 A, entitled "Oil-Based Ink Composition for Writing Instruments," and techniques using ink leakage inhibitors are disclosed in JP 10-195365 A, entitled "Oil-Based Ink for Ballpoint Pens," which uses silica having an average primary particle size of 7 to 40 nm, and JP 2007-126528 A, entitled "Oil-Based Ink for Ballpoint Pens," which uses a terpene phenol resin having an OH value of 150 or more. JP 7-196972 A, entitled "Oil-Based Ink Composition for Ballpoint Pens," discloses a technique using hydrogenated castor oil or fatty acid amide wax as a shear thinning agent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] "JP 2004-107591 A" [Patent Document 2] "JP 2007-126528 A" [Patent Document 3] "Unexamined Japanese Patent Publication No. 7-196972" Summary of the Invention [Problem to be solved by the invention]

[0005] However, while Patent Document 1 is effective in suppressing ink leakage to a certain extent, when the ink viscosity is reduced, the solvent used in Patent Document 1 alone is unable to sufficiently suppress ink leakage. Furthermore, Patent Document 2 discloses that the terpene phenol resin with an OH value of 150 or more has poor solubility in oil-based ink due to its high OH value, and therefore fails to exhibit sufficient effectiveness. Furthermore, Patent Document 3 discloses that hydrogenated castor oil and fatty acid amide wax can suppress ink leakage to a certain extent, but the ink viscosity increases when stationary, which tends to result in poor ink tracking and can cause smearing of handwriting, leaving room for improvement. Furthermore, when a new ink leakage inhibitor is used, it may be incompatible with other ink components, which can easily affect stability over time in the ink.

[0006] When increasing the amount of ink consumed to produce thick handwriting, or when reducing the viscosity of oil-based ink to achieve a smooth writing feel, the amount of ink consumed increases accordingly, making it more likely that ink will leak from the gap between the ball and the tip (writing tip), which can be a problem.

[0007] An object of the present invention is to provide an oil-based ballpoint pen that maintains dark handwriting, suppresses ink leakage, and has good ink stability over time. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention "1. An oil-based ballpoint pen having a ballpoint pen tip at the tip of an ink reservoir, and containing an ink composition for an oil-based ballpoint pen in the ink reservoir, wherein the ink consumption per 100 m of the oil-based ballpoint pen is 20 to 70 mg, and the ink composition for an oil-based ballpoint pen contains a colorant, an organic solvent, and acrylic ester resin particles. 2. The oil-based ballpoint pen according to claim 1, wherein the content of the acrylic ester resin particles is 0.1 to 5% by mass based on the total amount of the ink composition. 3. The oil-based ballpoint pen according to item 1 or 2, characterized in that the average particle diameter of the acrylic ester resin particles is 5 μm or less. 4. The oil-based ballpoint pen described in any one of items 1 to 3, wherein the acrylic acid ester resin particles are methacrylic acid ester resin particles. 5. The oil-based ballpoint pen according to any one of items 1 to 4, wherein the amount of movement of the ball in the ballpoint pen tip in the direction of the vertical axis is 3 to 20 μm. 6. An oil-based ballpoint pen according to any one of items 1 to 5, characterized in that the organic solvent is an alcohol solvent, and the content of the alcohol solvent is 50% or more of the total organic solvent content in the oil-based ballpoint pen composition. 7. The oil-based ballpoint pen according to any one of items 1 to 6, characterized in that the ink composition for the oil-based ballpoint pen contains a polyvinyl butyral resin or a ketone resin. [Effects of the Invention]

[0009] This oil-based ballpoint pen can be made to have a large ink consumption, maintain dark writing, suppress ink leakage from the gap between the ball and the tip end, and further have good ink stability over time. DETAILED DESCRIPTION OF THE INVENTION

[0010] A feature of the present invention is that even when the ink consumption of an oil-based ballpoint pen is increased to 20 to 70 mg per 100 m in order to produce thick handwriting, the ink composition for an oil-based ballpoint pen contains acrylate ester resin particles, which stabilizes the acrylate ester resin particles in the ink while suppressing ink leakage, thereby improving the ink stability over time.

[0011] (Acrylate ester resin particles) In the present invention, it has been found that ink leakage can be suppressed by including acrylate ester resin particles in an ink composition for an oil-based ballpoint pen. This is because the acrylate ester particles create a physical barrier in the gap between the ball and the inner wall of the tip, thereby suppressing ink leakage. Furthermore, the acrylate ester particles undergo partial deformation and adhere to each other, creating a structure formed by weak aggregation. This creates a structure in the ink that is highly resistant to ink leakage when left stationary, thereby enabling high ink leakage suppression. Meanwhile, because the structure is formed by weak aggregation, the aggregated structure is broken down by physical actions such as the rotation of the ball during writing. This does not impair the ink flowability during writing, allowing for smooth writing and the production of thick handwriting. Furthermore, acrylate ester resin particles are solvent-stable, and therefore are suitable for use because they can maintain the ink's stability over time while also imparting high solvent resistance and water resistance to handwriting.

[0012] The average particle size of the acrylate resin particles is preferably 5 μm or less, more preferably 3 μm or less, because a smaller average particle size allows particles to adhere to each other, forming a weakly aggregated structure and suppressing ink leakage. Furthermore, considering the dispersion stability of the acrylate resin particles in the ink (ink stability over time), 2 μm or less is preferred, and even more preferably less than 1 μm. On the other hand, since a too small average particle size tends to result in a poor ink leakage suppression effect, the average particle size is preferably 0.1 μm or more, more preferably 0.3 μm or more. The average particle size can be determined by the Coulter Counter method using a Coulter Multisizer™3 (a measuring device manufactured by Beckman Coulter, Inc.) to measure the particle size at 50% cumulative volume (D50) of the particle size distribution measured based on values ​​calibrated using standard samples or other measurement methods.

[0013] Examples of the acrylic acid ester resin particles (polyacrylic acid ester particles) used in the present invention include resin particles of acrylic acid esters and methacrylic acid esters (polyacrylic acid ester particles, polymethacrylic acid ester particles). More specifically, examples include acrylic acid ester resin particles (polyacrylic acid ester particles) such as methyl acrylate, ethyl acrylate, and butyl acrylate, and methacrylic acid ester resin particles (polymethacrylic acid ester particles) such as methyl methacrylate, isopropyl methacrylate, and butyl methacrylate. Methacrylic acid ester resin particles are preferred because they are more stable in ink, thereby improving ink leakage prevention and ink stability over time. Furthermore, the alkyl group in the methacrylic acid ester resin particle structure has a small number of carbon atoms, which makes it more stable in ink. Therefore, the alkyl group preferably has 1 to 6 carbon atoms, and more preferably has 1 to 4 carbon atoms. Considering the ink leakage prevention effect, methyl methacrylate resin particles (polymethyl methacrylate particles) are preferred. These acrylic acid ester resin particles (polyacrylic acid ester particles) may be used alone or in the form of a mixture or copolymer of two or more kinds. Furthermore, the acrylic acid ester resin particles (polyacrylic acid ester particles) may contain at least acrylic acid ester resin particles, and may be a mixture of acrylic acid ester resin particles and other resins, or a copolymer of acrylic acid ester resin particles and other resins.

[0014] As the acrylic acid ester resin particles, it is preferable to use acrylic acid ester resin particles having a crosslinked structure, considering the suppression of ink leakage and the improvement of ink stability over time. This is presumably because the presence of a crosslinked structure forms a stable particle structure, which makes it easier to stabilize in the ink, and furthermore, it makes it easier to form a stable, weak aggregation structure between the acrylic acid ester particles, which makes it easier to improve ink leakage suppression. It is preferable to use a methacrylic acid ester having a crosslinked structure, because it is easier to stabilize in the ink, which makes it easier to improve ink leakage suppression and ink stability over time.

[0015] The acrylic ester resin particles may be spherical or irregularly shaped, but spherical resin particles are preferred in view of the ink leakage suppression effect due to the adhesion between the acrylic ester particles. The spherical resin particles referred to here are not limited to true spheres, and may be approximately spherical resin particles or approximately oval-spherical resin particles.

[0016] Furthermore, the content of the acrylic ester resin particles (polyacrylic ester particles) is more preferably 0.01 to 10% by mass of the total amount of the ink composition. This is because if the content of the acrylic ester resin particles (polyacrylic ester particles) is less than 0.01% by mass, it is difficult to prevent ink leakage, and if it exceeds 10% by mass, the aggregate structure tends to become strong, which is likely to affect the ink's stability over time, writing feel, and writing performance. From further considerations, the content is preferably 0.1 to 5% by mass, particularly preferably 0.1 to 3% by mass, and even more preferably 0.2 to 3% by mass. Furthermore, since the ink leakage suppression effect can be easily obtained even with a small amount of acrylic ester resin particles (polyacrylic ester particles), 0.01 to 2 mass % is preferable, and if the ink leakage suppression effect can be obtained while taking into consideration costs by using even smaller amounts, 0.1 to 1 mass % is preferable, and 0.1 to 0.7 mass % is more preferable.

[0017] (ballpoint pen) Furthermore, the ink consumption of a ballpoint pen per 100 m is preferably 20 to 70 mg. This is because if the ink consumption per 100 m is less than 20 mg, it is difficult to obtain thick handwriting or a good writing feel, and if the ink consumption per 100 m exceeds 70 mg, the gap between the ball and the tip end is likely to affect ink leakage prevention, and writing performance and blobbing are likely to occur. Therefore, in consideration of the balance of the above effects, the ink consumption is preferably 25 to 60 mg, and in consideration of achieving both thicker handwriting and ink leakage prevention, it is preferably 30 to 55 mg. Regarding ink consumption, a spiral writing test was conducted using five test samples at a writing speed of 4 m / min on JIS P3201 writing paper at a writing angle of 70° and a writing load of 200 g at 20°C, and the average ink consumption per 100 m was defined as the ink consumption per 100 m.

[0018] Furthermore, to achieve thicker handwriting and improved ink leakage prevention, it is effective not only to set the ink consumption amount but also to consider the relationship with the ball diameter. Specifically, the ratio of the ink consumption amount (mg) per 100 m of an oil-based ballpoint pen to the ball diameter (mm) (ball diameter:ink consumption amount) is preferably 1:20 to 1:100, a different relationship from the conventional one, because it makes it easier to achieve thicker handwriting and suppress ink leakage. Further considerations make the ratio 1:30 to 1:90 preferable, and 1:40 to 1:80 more preferable. The ball diameter is not particularly limited, but balls of about 0.1 to 2.0 (mm) are used.

[0019] Furthermore, the amount of movement of the ball in the ballpoint pen tip used in the present invention in the vertical direction is preferably 3 to 20 μm, because if it is less than 3 μm, it becomes difficult to obtain thick handwriting or a good writing feel, and if it exceeds 20 μm, it is likely to have an effect on suppressing ink leakage. In the present invention, the amount of movement of the ball of the ballpoint pen tip in the vertical axis direction is the shape of the ballpoint pen tip of the ballpoint pen in its initial state before writing begins.

[0020] Furthermore, to improve ink leakage suppression, it is effective not only to set the movement distance (μm) of the ball in the ballpoint pen tip in the longitudinal direction but also to consider the relationship with the average particle diameter (μm) of the acrylate resin particles. Specifically, the ratio of the movement distance (μm) of the ball in the ballpoint pen tip in the longitudinal direction to the average particle diameter (μm) of the acrylate resin particles (average particle diameter of acrylate resin particles: movement distance of ball in the longitudinal direction) is preferably 1:1 to 1:200, as this makes it easier to suppress ink leakage. A relationship of 1:1 to 1:100 is also preferable, and with further consideration, a ratio of 1:1 to 1:20 is preferable, and a ratio of 1:2 to 1:15 is also preferable.

[0021] (coloring agent) The colorant used in the present invention is not particularly limited and may be a dye, a pigment, or the like, and may be appropriately selected and used. The combined use of a dye and a pigment is preferred because it is easier to obtain the following effects. Examples of dyes include oil-soluble dyes, acid dyes, basic dyes, metal-containing dyes, and various salt-forming dyes thereof, such as salt-forming dyes formed between an acid dye and a basic dye, salt-forming dyes formed between an organic acid and a basic dye, and salt-forming dyes formed between an acid dye and an organic amine. These dyes may be used alone or in combination of two or more. As the dye, it is preferable to use at least a salt-forming dye in consideration of stability over time due to compatibility with the acrylic ester resin particles. Furthermore, in consideration of maintaining stability over time due to stable salt-forming bonds, it is preferable to use a salt-forming dye formed between a basic dye and an organic acid, a salt-forming dye formed between an acid dye and a basic dye, or a salt-forming dye formed between an acid dye and an organic amine.Specific examples of dyes include Balifast Black 1802, Balifast Black 1805, Balifast Black 1807, Balifast Violet 1701, Balifast Violet 1704, Balifast Violet 1705, Balifast Blue 1601, Balifast Blue 1605, Balifast Blue 1613, Balifast Blue 1621, Balifast Blue 1631, Balifast Red 1320, Balifast Red 1355, Balifast Red 1360, Balifast Yellow 1101, Balifast Yellow 1151, Nigrosine Base EXBP, Nigrosine Base EX, BASE OF BASIC DYES ROB-B, BASE OF BASIC DYES RO6G-B, BASE OF BASIC DYES VPB-B, BASE OF BASIC DYES VB-B, and BASE OF BASIC DYES MVB-3 (all manufactured by Orient Chemical Industry Co., Ltd.), Aizen Spiron Black GMH-Special, and Aizen Spiron Violet C-RH, Aizenspiron Blue GNH, Aizenspiron Blue 2BNH, Aizenspiron Blue C-RH, Aizenspiron Red C-GH, Aizenspiron Red C-BH, Aizenspiron Yellow C-GNH, Aizenspiron Yellow C-2GH, SPT Blue 111, SPT Blue GLSH-Special, SPT Red 533, SPT Orange 6, SBN Violet 510, SBN Yellow 530, SRC-BH (all manufactured by Hodogaya Chemical Co., Ltd.), and the like.

[0022] Furthermore, examples of pigments include inorganic, organic, and processed pigments, and specific examples include carbon black, aniline black, ultramarine, yellow lead, titanium oxide, iron oxide, phthalocyanine-based, azo-based, quinacridone-based, diketopyrrolopyrrole-based, quinophthalone-based, threne-based, triphenylmethane-based, perinone-based, perylene-based, dioxazine-based, metallic pigments, pearl pigments, fluorescent pigments, and phosphorescent pigments.

[0023] It is preferable to use a pigment as the colorant, because in the case of a ballpoint pen, the use of pigment particles creates a physical barrier in the gap between the ball and the inner wall of the tip, making it easier to suppress ink leakage. Furthermore, in the present invention, the use of the acrylic ester resin particles forms a coating on the writing tip, and the physical barrier of the pigment creates a synergistic effect, resulting in a higher ink leakage suppression effect and simultaneously achieving a pigment dispersion effect, which is preferable. Pigments are also preferable because they provide excellent handwriting durability, particularly excellent light resistance.

[0024] The content of the colorant is preferably 5.0 to 30.0% by mass relative to the total amount of the ink composition. This is because if it is less than 5.0% by mass, it tends to be difficult to obtain thick handwriting, and if it exceeds 30.0% by mass, it tends to affect the solubility in the ink. Taking these tendencies into consideration, the content is preferably 7.0 to 25.0% by mass, and even more so, 10.0 to 25.0% by mass.

[0025] (organic solvent) Examples of organic solvents that can be used in the present invention include organic solvents that are commonly used in oil-based ballpoint pen inks, such as glycol ether solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol monophenyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, diethylene glycol dimethyl ether, 3-methoxybutanol, and 3-methoxy-3-methylbutanol; glycol solvents such as diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, and ethylene glycol; and alcohol solvents such as benzyl alcohol, methanol, ethanol, 1-propanol, 2-propanol, isopropanol, isobutanol, t-butanol, propargyl alcohol, allyl alcohol, 3-methyl-1-butyn-3-ol, ethylene glycol monomethyl ether acetate, and other higher alcohols.

[0026] Among these organic solvents, in consideration of the dispersion stability with the acrylic ester resin particles, it is preferable to use a water-insoluble organic solvent, which is preferable because it is easy to suppress ink leakage. Among these, alcohol solvents are preferred because they volatilize and dry easily at the tip of the ballpoint pen, making it easier to prevent ink leakage from the outside of the tip. In particular, in the present invention, the inclusion of the acrylic ester resin particles, as described above, provides an ink leakage prevention effect from the inside of the tip due to physical barriers and the formation of a weak aggregation structure, thereby preventing ink leakage from both the inside and outside of the tip of the ballpoint pen, thereby achieving a higher ink leakage prevention effect. Furthermore, aromatic alcohols such as benzyl alcohol are preferred because they stabilize the dispersion of the acrylic ester resin particles. In particular, the content of the alcohol solvent is preferably 50% or more of the total organic solvent content in the oil-based ballpoint pen composition, considering the ease of drying the tip of the ballpoint pen and the ink leakage prevention effect. More particularly, 70% or more is preferred, and 75% or more is more preferred.

[0027] Furthermore, in consideration of improving solubility, writing drying properties, bleeding, etc., the content of the organic solvent is preferably 10.0 to 90.0 mass% of the total amount of the ink composition, and in consideration of drying properties at the tip end, the content is preferably 20.0 to 90.0 mass%, more preferably 40.0 to 70.0 mass%.

[0028] (resin) In order to further improve the ink leakage suppression effect, it is preferable to use a resin as an ink viscosity adjuster. Examples of resins include polyvinyl butyral resin, ketone resin, polyacetal resin, polyvinyl alcohol resin, cellulose resin, terpene resin, alkyd resin, phenoxy resin, polyvinyl acetate resin, etc., but among these, it is preferable to use a polyvinyl butyral resin or a ketone resin, as this makes it easier to improve the ink leakage suppression effect.

[0029] Furthermore, when considering the ink leakage suppression effect and the improvement of writing feel, it is preferable to use a polyvinyl butyral resin. This is because the coating formed by the polyvinyl butyral resin on the outside of the tip tip makes it easier to improve ink leakage. In particular, as described above, the inclusion of the acrylic ester resin particles provides an ink leakage suppression effect from the inside of the tip tip due to physical obstacles and the formation of a weak aggregation structure, and therefore a higher ink leakage suppression effect can be expected due to the ink leakage suppression effect from both the inside and outside of the ballpoint pen tip tip. In addition, polyvinyl butyral resin forms a constantly elastic ink layer between the ball and ball seat, making direct contact difficult and improving the writing feel. Furthermore, when a pigment is used as the colorant, polyvinyl butyral resin is preferably used because it also provides a pigment dispersion effect. Here, the polyvinyl butyral resin is obtained by reacting polyvinyl alcohol (PVA) with butyraldehyde (BA), and has a structure having butyral groups, acetyl groups, and hydroxyl groups. In particular, when the ink consumption of an oil-based ballpoint pen is set to 20 to 70 mg per 100 m, the ink is likely to leak from the gap between the ballpoint pen tip body and the ball, so it is effective to use a polyvinyl butyral resin, and it is even more effective to use the acrylic ester resin particles used in the present invention in combination with a polyvinyl butyral resin.

[0030] Furthermore, the polyvinyl butyral resin preferably has a hydroxyl group content of 20 mol% or more. This is because polyvinyl butyral resins with a hydroxyl group content of less than 20 mol% are insufficient in organic solvents, making it difficult to achieve sufficient lubrication and ink leakage suppression. Furthermore, considering the writing performance due to moisture absorption, it is preferable to use a polyvinyl butyral resin with a hydroxyl group content of 20 mol% or more. Furthermore, considering ink leakage suppression, the hydroxyl group content is preferably 28 mol% or more, and more preferably 32 mol% or more. Furthermore, using a polyvinyl butyral resin with a hydroxyl group content of more than 45 mol% tends to increase moisture absorption, which can affect the stability over time of the ink components. Therefore, polyvinyl butyral resins with a hydroxyl group content of 45 mol% or less are preferred, and polyvinyl butyral resins with a hydroxyl group content of 40 mol% or less are more preferred. The amount of hydroxyl groups (mol %) of the polyvinyl butyral resin refers to the content of hydroxyl groups (mol %) relative to the total molar amount of butyral groups (mol %), acetyl groups (mol %), and hydroxyl groups (mol %).

[0031] Furthermore, with regard to the average degree of polymerization of the polyvinyl butyral resin, if the average degree of polymerization is 200 or more, the ink leakage suppression performance is likely to be improved, and if the average degree of polymerization exceeds 2500, the ink viscosity tends to become too high, affecting the writing feel, so the average degree of polymerization is preferably 200 to 2500. Furthermore, in order to further consider the suppression of ink leakage, the average degree of polymerization is preferably 1500 or less. Here, the average degree of polymerization refers to the number of basic units constituting one molecule of the polyvinyl butyral resin, and a value measured based on the method specified in JIS K6728 (2001 edition) can be used.

[0032] Specific examples of polyvinyl butyral resins include those manufactured by Sekisui Chemical Co., Ltd. under the trade names of S-LEC BH-3 (hydroxyl group amount: 34 mol%, average degree of polymerization: 1700), S-LEC BH-6 (hydroxyl group amount: 30 mol%, average degree of polymerization: 1300), S-LEC BX-1 (hydroxyl group amount: 33±3 mol%, average degree of polymerization: 1700), S-LEC BX-5 (hydroxyl group amount: 33±3 mol%, average degree of polymerization: 2400), S-LEC BM-1 ( Amount of hydroxyl groups: 34 mol%, average degree of polymerization: 650), BM-2 (amount of hydroxyl groups: 31 mol%, average degree of polymerization: 800), BM-5 (amount of hydroxyl groups: 34 mol%, average degree of polymerization: 850), BL-1 (Amount of hydroxyl groups: 36 mol%, average degree of polymerization: 300), BL-1H (Amount of hydroxyl groups: 30 mol%), BL-2 (Amount of hydroxyl groups: 36 mol%, Average degree of polymerization: 450), BL-2H (Amount of hydroxyl groups: 29 mol%), Mobital BL-10 (hydroxyl group amount: 28 mol%), and trade names of Kuraray Co., Ltd.: Mobital B20H (hydroxyl group amount: 26-31 mol%, average polymerization degree: 250-500), Mobital B30T (hydroxyl group amount: 33-38 mol%, average polymerization degree: 400-650), Mobital B30H (hydroxyl group amount: 26-31 mol%, average polymerization degree: 400-650), Mobital B30HH (hydroxyl group amount: 30-34 mol%) %, average degree of polymerization: 400-650), B45H (hydroxyl group amount: 26-31 mol%, average degree of polymerization: 600-850), B60T (hydroxyl group amount: 34-38 mol%, average degree of polymerization: 750-1000), B60H (hydroxyl group amount: 26-31 mol%, average degree of polymerization: 750-1000), B75H (hydroxyl group amount: 26-31 mol%, average degree of polymerization: 1500-1750), etc. These may be used alone or in combination of two or more.

[0033] Furthermore, the combined use of acrylate resin particles and ketone resins can be expected to synergistically suppress ink leakage and also reduce the risk of blobbing. In particular, when the ink consumption of an oil-based ballpoint pen is increased to 20 to 70 mg per 100 m, excess ink tends to cause blobbing and bleeding at the tip. The use of ketone resins is more effective because it suppresses ink creeping and thus helps prevent blobbing and bleeding. Furthermore, considering the suppression of blobbing and bleeding, it is preferable to use ketone resins with cyclic structures such as aromatic ring skeletons (containing benzene rings such as phenyl, acetophenone, and naphthalene groups) or cyclohexane skeletons (containing cyclohexane rings such as cyclohexane and cyclohexanone groups). Furthermore, oil-based ballpoint pens are often used to write on copy paper, which requires a higher writing pressure than normal (high-pressure writing), so there is a need to improve the ability to write with high pressure. Using ketone resins is effective and preferable because it improves lubricity under high writing pressure (writing load of 300 to 500 gf) and makes it easier to further reduce wear on the ball seat.

[0034] If the total content of the resins is less than 1.0% by mass relative to the total amount of the ink composition, the amount of resin film formed may be insufficient and ink leakage suppression performance may be poor, while if it exceeds 40.0% by mass, solubility in the ink may be poor, so the total content of the resins is preferably 1.0 to 40.0% by mass relative to the total amount of the ink composition. Furthermore, in consideration of ink leakage suppression performance, a content of 5.0% by mass or more is preferable, and if it exceeds 30.0% by mass, the ink viscosity may become too high, which may affect the writing feel and writing performance, so 5.0 to 30.0% by mass is preferable.

[0035] Resins other than polyvinyl butyral resins and ketone resins may be used with a stringiness imparting agent as appropriate. In particular, polyvinylpyrrolidone resin is preferably included, since its incorporation improves ink binding properties and helps prevent excess ink from forming at the tip. If the content of the polyvinylpyrrolidone resin is less than 0.01% by mass relative to the total ink composition, it tends to be difficult to prevent excess ink from forming. If it exceeds 3.0% by mass, its solubility in the ink tends to be poor. Therefore, a content of 0.01 to 3.0% by mass relative to the total ink composition is preferred. Considering the above reasons, a content of 0.1 to 2.0% by mass is preferred. Specific examples include PVP K-15, PVP K-30, PVP K-90, and PVP K-120, both of which are products of ISP Japan Co., Ltd. These may be used alone or in combination.

[0036] (surfactant) In the present invention, it is preferable to use a surfactant in order to improve lubricity and writing performance when the tip of the pen is left in the air and dries. This is because the use of a surfactant tends to soften the coating that is formed, improving writing performance and lubricity. Examples of surfactants include fatty acids, fatty acid esters, silicone surfactants, fluorine-based surfactants, and phosphate ester surfactants. Among these, it is preferable to use one or more of fatty acids, silicone surfactants, and phosphate ester surfactants in consideration of the above-mentioned effects.

[0037] The surfactant preferably has an HLB value of 6 to 14 in order to further improve both lubricity and writing performance. This is because an HLB value of more than 14 tends to result in increased hydrophilicity, which tends to result in poor solubility in oil-based inks, making it difficult to obtain the surfactant's effects and lubrication effect. Furthermore, an HLB value of less than 6 tends to result in excessively strong lipophilicity, which tends to affect compatibility with organic solvents, making it difficult for the ink to stabilize over time and further improving writing performance. Furthermore, in consideration of lubricity, the HLB value is preferably 12 or less, and an HLB value of 6 to 12 is preferable. In consideration of better writing performance, an HLB value of 7 to 12 is preferable. The HLB value can be determined by the Griffin method, the Kawakami method, etc. In particular, in retractable writing instruments such as knock-type writing instruments and rotary-type writing instruments, the pen tip is always exposed to the outside, unlike cap-type writing instruments, and therefore the writing performance is easily affected when the writing tip dries, so it is more preferable to use a surfactant with the above HLB value.

[0038] Specific examples of the surfactant include fatty acids such as oleic acid, stearic acid, and linoleic acid; silicone surfactants such as dimethyl silicone, methylphenyl silicone, polyether-modified silicone, and higher fatty acid ester-modified silicone; fluorine-based surfactants such as perfluoro-butyl sulfonate, perfluoro-containing carboxylate, perfluoro-containing phosphate, perfluoro-containing phosphate ester-type compound, perfluoroalkyl betaine, and perfluoroalkylamine oxide compound; and phosphate ester surfactants such as alkoxyethyl group (C n H 2n+1 OCH2CH2O) or alkoxy groups (C m H 2m+1O), a phosphate ester of a polyoxyethylene alkyl ether or a polyoxyethylene alkylaryl ether, a phosphate monoester of a polyoxyethylene alkyl ether or a polyoxyethylene alkylaryl ether, a phosphate diester of a polyoxyethylene alkyl ether or a polyoxyethylene alkylaryl ether, a phosphate triester of a polyoxyethylene alkyl ether or a polyoxyethylene alkylaryl ether, an alkyl phosphate ester, an alkyl ether phosphate ester, or a derivative thereof.

[0039] Furthermore, oil-based ballpoint pens are often used to write on copy paper, and when writing on copy paper, a higher writing pressure than normal (high-pressure writing) is required, so there is a need to improve the high-pressure writing properties. Among surfactants, it is preferable to use a phosphate ester surfactant because it is easy to improve lubrication under high writing pressure (300 to 500 gf). This is because the phosphate group in the phosphate ester surfactant makes the lubricating action easier to work, exerting a greater extreme-pressure effect, improving the lubrication between the ball and the tip body even under high writing pressure (300 to 500 gf), suppressing wear on the ball seat, and making it easier to produce good handwriting without smearing, so it can be used more preferably in the present invention. Furthermore, among the phosphate ester surfactants, in order to improve the lubrication between the ball and the tip body and suppress the wear of the ball seat even under high writing pressure (300 to 500 gf), an alkoxyethyl group (C n H 2n+1 OCH2CH2O) or alkoxyl group (C m H 2m+1 It is preferable to use a phosphate ester surfactant having an alkoxyethyl group (C n H 2n+1 It is preferable to use a phosphate ester surfactant having the formula (OCH2CH2O).

[0040] The phosphate ester surfactants have an alkoxyethyl group (C n H 2n+1 OCH2CH2O), alkoxyl group (C m H 2m+1The carbon chain (n, m) of the terminal alkyl group of the alkoxyethyl group (C n H 2n+1 OCH2CH2O) and alkoxyl groups (C m H 2m+1 If the carbon chain of the terminal alkyl group (O) becomes too long, the writing feel and initial writing performance are good, but it may be difficult to suppress ball seat wear under high writing pressure (writing load 300 to 500 gf). This is because when the carbon chain (n, m) of the terminal alkyl group exceeds 10, especially when the carbon chain (n, m) exceeds 5, steric hindrance is likely to occur between the carbon chains. Even if the phosphate groups adsorbed to the metal of the ballpoint pen tip material are densely packed, the carbon chain arrangement is unlikely to be dense, and a lubricating layer with sufficient lubricity is not obtained, making it difficult to suppress ball seat wear under high writing pressure. Furthermore, because the polarity of the terminal alkyl group is biased toward oil-based solvents, the affinity for organic solvents is poor, which easily affects the solubility stability and easily causes problems with solubility stability in the ink. Therefore, metal salt precipitates are likely to occur due to the influence of metal ions in the metal tip during long-term storage, which tends to deteriorate the ink's stability over time and makes it difficult to achieve the lubricating effect of the present invention. Therefore, the carbon chain (n, m) of the terminal alkyl group is preferably 1 to 10, and from a more particular perspective, the carbon chain (n, m) of the terminal alkyl group is preferably 1 to 5. On the other hand, when the carbon chain (n, m) of the terminal alkyl group is 3 or less, wear of the ball seat under high writing pressure is suppressed well, but the alkyl group does not extend sufficiently in the ink, resulting in a lubricating layer with insufficient cushioning between the ball and the ball seat, which is likely to affect the writing feel and initial writing performance. Therefore, it is preferable to use butoxyethyl acid phosphate (n=4) or butyl acid phosphate (m=4) in which the terminal alkyl group has a butyl group (carbon chain of the terminal alkyl group: 4), as this tends to suppress wear of the ball seat under high writing pressure and improve the writing feel and initial writing performance.

[0041] The content of the surfactant is more preferably 0.1 to 5.0% by mass of the total amount of the ink composition. This is because if it is less than 0.1% by mass, it tends to be difficult to obtain the desired lubricity, and if it exceeds 5.0% by mass, the ink tends to become unstable over time. Taking these tendencies into consideration, the content is preferably 0.3 to 3.0% by mass of the total amount of the ink composition, and even more preferably 0.5 to 3.0% by mass.

[0042] (organic amine) In the present invention, in consideration of the stability of the ink components in the ink, it is preferable to use an organic amine. Examples of such an organic amine include amines having ethylene oxide, such as oxyethylene alkylamines and polyoxyethylene alkylamines, alkylamines, such as laurylamine and stearylamine, and aliphatic amines, such as dimethyl alkylamines, such as distearylamine, dimethyl laurylamine, dimethyl stearylamine and dimethyl octylamine. Among these, in consideration of the stability in the ink, amines having ethylene oxide and dimethyl alkylamines are preferred. In particular, when a phosphate ester surfactant is used, neutralization is preferred because it stabilizes the ink and the effects of the phosphate ester surfactant can be easily obtained.

[0043] Regarding the reactivity of the organic amines with other components in the ink, primary amines are the most reactive, followed by secondary amines and tertiary amines, and therefore, in consideration of the ink stability over time, it is preferable to use secondary amines or tertiary amines. These may be used alone or in combination of two or more.

[0044] The content of the organic amine is preferably 0.1 to 10.0 mass% of the total amount of the ink composition, taking into consideration the stability with the ink components, and furthermore, taking into consideration the neutralization of the phosphate ester surfactant described below, it is preferably 0.2 to 5.0 mass%.

[0045] (fatty acid esters) In addition to the surfactants mentioned above, fatty acid esters are preferably used in consideration of improving lubricity and writing performance when the tip of the tip is left in the air and dries. In particular, fatty acid esters are preferred because they help maintain lubricity even under high writing pressure (writing load of 300 to 500 gf), suppressing wear of the ball seat (high writing pressure writing performance), and improving both the writing feel and writing performance.

[0046] Fatty acid esters are those obtained by esterifying fatty acids with alcohols such as monohydric alcohols and polyhydric alcohols, and among these fatty acid esters, it is preferable to use fatty acid esters having a branched alkyl group in order to further improve writing performance. This is because fatty acid esters having a branched alkyl group have a bulkier structure than straight-chain structures, and the bulkiness of the branched alkyl group makes them more likely to adsorb to the surface of a metal ball or the ball seat of the tip body, forming a thicker lubricating film and further improving lubrication. At the same time, the bulkiness of the branched alkyl group softens the strength of the film formed at the tip end when the ink dries, thereby improving writing performance.

[0047] Furthermore, the fatty acid ester preferably has an acid value of 0.01 to 5 (mgKOH / g), because it has good compatibility with the acidic phosphate ester and other components in the oil-based ink and remains stable in the ink for a long period of time, thereby improving writing performance over a long period of time, improving lubricity over a long period of time, and making it easier to improve the writing feel. From this perspective, the acid value is preferably 0.01 to 2.5 (mgKOH / g), and more preferably 0.05 to 1.0 (mgKOH / g). The acid value is expressed as the number of mg of potassium hydroxide required to neutralize the acidic components (free fatty acids) contained in 1 g of sample.

[0048] The alcohol used in the esterification reaction of the fatty acid ester is preferably a polyhydric alcohol. While the reason for this is unclear, it is presumed that the more hydroxyl groups in the alcohol used in the esterification reaction of the fatty acid ester, the more moisturizing the alcohol is, which softens the strength of the coating formed when the tip end dries and smooths the ball's rotation, thereby preventing blurred writing and improving initial writing performance. Considering further improvement in initial writing performance, polyhydric alcohols with trivalent or higher hydroxyl groups are preferred, and more preferably with tetravalent or higher hydroxyl groups. Furthermore, since too many hydroxyl groups can easily affect stability in oil-based inks, it is preferred that the hydroxyl groups be octavalent or less, and preferably hexavalent or less.

[0049] Specific examples of alcohols used in the esterification reaction of the fatty acid esters include monohydric alcohols such as pentanol, cyclohexanol, hexanol, heptanol, octanol, 2-ethylhexanol, nonanol, isononanol, decanol, lauryl alcohol, myristyl alcohol, stearyl alcohol, and docosanol, and polyhydric alcohols such as ethylene glycol, propylene glycol, polyalkylene glycol, 1,3-propanediol, diethylene glycol, glycerin, 2-methylpropanetriol, neopentyl glycol, trimethylolethane, triethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, and tripentaerythritol. Among these, in order to further improve the writing performance and take into consideration the ink stability over time, it is preferable to contain a fatty acid ester esterified with a pentaerythritol such as pentaerythritol, dipentaerythritol, or tripentaerythritol, and from further consideration, it is preferable to contain a fatty acid ester esterified with dipentaerythritol.

[0050] The content of the fatty acid ester is more preferably 0.1 to 10.0% by mass of the total amount of the ink composition. This is because if it is less than 0.1% by mass, it is difficult to obtain the desired lubricity and writing performance, and if it exceeds 10.0% by mass, the ink tends to become unstable over time. Taking this tendency into consideration, the content is preferably 0.1 to 5.0% by mass, and even more preferably 0.1 to 3.0% by mass, and most preferably 0.3 to 2.0% by mass.

[0051] In addition, as viscosity modifiers, pseudoplasticity imparting agents such as fatty acid amides and hydrogenated castor oil, colorant stabilizers, plasticizers, chelating agents, water, etc. may be used as appropriate. These may be used alone or in combination of two or more.

[0052] The ink viscosity of the ink composition for oil-based ballpoint pens of the present invention is not particularly limited, but is preferably 20°C at a shear rate of 5 sec -1 If the ink viscosity (at rest) exceeds 30,000 mPa·s, the writing performance and writing feel tend to deteriorate. -1 The ink viscosity (at rest) is preferably 30,000 mPa·s or less. -1 If the ink viscosity (at rest) is less than 1000 mPa·s, it is difficult to prevent ink leakage, so if ink leakage is taken into consideration, it is preferably 1000 mPa·s or more. If consideration is given to further improving ink leakage prevention, writing feel, ink tracking performance, and writing start performance, the ink viscosity is more preferably 1500 to 25000 mPa·s, and even more preferably 2000 to 20000 mPa·s, and more preferably 2000 to 15000 mPa·s. Furthermore, in retractable oil-based ballpoint pens such as knock-type oil-based ballpoint pens and rotary-type oil-based ballpoint pens, it is necessary to give more consideration to suppressing ink leakage, and therefore this is effective and preferable.

[0053] The arithmetic mean roughness (Ra) of the ball surface of the ballpoint pen tip used in the present invention is preferably 0.1 to 12 nm. This is because if the arithmetic mean roughness (Ra) is less than 0.1 nm, ink will not spread sufficiently on the ball surface, making it difficult to obtain thick handwriting, and line skips and smears are likely to occur in the handwriting. If the arithmetic mean roughness (Ra) is more than 12 nm, the ball surface will be too rough, resulting in high rotational resistance between the ball and the ball seat, which will likely result in a poor writing feel. Furthermore, writing performance will likely be affected by smears, line skips, and uneven lines. Furthermore, an arithmetic mean roughness (Ra) of 0.1 to 10 nm is more preferable because it allows ink to spread easily on the ball surface, and a value of 2 to 8 nm is even more preferable. Surface roughness can be measured using a Seiko Epson SPI3800N (model number).

[0054] The material used for the balls is not particularly limited, but examples include cemented carbide balls mainly composed of tungsten carbide, metal balls such as stainless steel, ceramic balls such as silicon carbide, silicon nitride, alumina, silica, and zirconia, and ruby ​​balls.

[0055] In addition, materials for ballpoint pen tips include metals such as stainless steel, nickel silver, brass, aluminum bronze, and aluminum, and resins such as polycarbonate, polyacetal, and ABS.However, in consideration of writing feel and workability such as cutting, a tip body made of nickel silver is preferred, and in consideration of wear of the ball seat and stability over time, a tip body made of stainless steel is preferred.

[0056] Example 1 The ink composition for an oil-based ballpoint pen in Example 1 employed a dye as a colorant, benzyl alcohol as an organic solvent, acrylic acid ester resin particles, a phosphate ester surfactant having an alkoxyethyl group as a surfactant, oxyethylene alkylamine as an organic amine, a fatty acid ester having a branched alkyl group, polyvinyl butyral resin, and polyvinylpyrrolidone as a stringiness-imparting agent. A predetermined amount of these ingredients was weighed out, heated to 60°C, and then completely dissolved using a Disper stirrer to obtain an ink composition for an oil-based ballpoint pen. The specific blending amounts are as follows:

[0057] Example 1 (ink formulation) Coloring agent (dye, acid dye and basic dye salt-forming dye) 8.0% by mass Coloring agent (dye, salt-forming dye of organic acid and basic dye) 5.0% by mass Organic solvent (benzyl alcohol) 72.5% by mass Acrylate ester resin particles (crosslinked polymethyl methacrylate particles, average particle size: 0.8 μm) 1.0 mass% Surfactant (alkoxyethyl group (C n H 2n+1 OCH2CH2O:n=4) 1.0% by mass of a phosphate ester surfactant Organic amine (oxyethylene alkylamine) 1.0% by mass Fatty acid ester with branched alkyl group (fatty acid ester esterified with fatty acid and dipentaerythritol) 1.0% by mass Polyvinyl butyral resin 10.0% by mass Spinnability imparting agent (polyvinylpyrrolidone resin) 0.5% by mass

[0058] Examples 2 to 28 As shown in Table 1, ink compositions for oil-based ballpoint pens of Examples 2 to 28 were obtained in the same manner as in Example 1, except that the ink components and tip specifications were changed. The table shows the measurement and evaluation results. The ink viscosities of Examples 1, 9, and 10 were measured using a Brookfield Viscometer RVDVII+Pro CP-52 spindle at a shear rate of 10 sec in an environment of 20°C. -1 , Example 1: ink viscosity = 2000 mPa·s, Example 9: ink viscosity = 5000 mPa·s, Example 10: ink viscosity = 12000 mPa·s.

[0059] Comparative Examples 1 to 4 As shown in the table, except that the ink components and tip specifications were changed, ink compositions for oil-based ballpoint pens of Comparative Examples 1 to 4 were obtained in the same manner as in Example 1. The measurement and evaluation results are shown in the table. [Table 1] [Table 2] [Table 3]

[0060] Testing and Evaluation The ink compositions (0.27 g) for oil-based ballpoint pens prepared in Example 1 and Comparative Example 1 were filled into oil-based ballpoint pen refills equipped with ink reservoirs (polypropylene) and ballpoint pen tips (ball longitudinal axis movement: 10 μm, ball surface arithmetic mean roughness (Ra): 6 nm) that rotatably held a ball with a ball diameter of 0.5 mm. Oil-based ballpoint pens were prepared by filling the ink compositions (0.27 g) prepared in Examples 2 to 28 and Comparative Examples 2 to 4 into oil-based ballpoint pen refills equipped with ink reservoirs (polypropylene) and ballpoint pen tips with modified tip specifications as shown in the table. The following tests and evaluations were carried out using JIS P3201 writing paper as the test paper. The ink consumption per 100 m of Example 1 was 35 mg / 100 m when a spiral writing test was carried out using an oil-based ballpoint pen. The ratio of the ball diameter (mm) to the ink consumption (mg) per 100 m of the oil-based ballpoint pen (ball diameter: ink consumption) was 1:70. The ratio of the average particle diameter (μm) of the acrylic ester resin particles to the movement distance (μm) of the ball in the ballpoint pen tip along the vertical axis (average particle diameter of the acrylic ester resin particles:movement distance of the ball in the vertical axis) was 1:12.5.

[0061] Ink leakage prevention test: The pen was left in an environment of 30°C and 85% RH with the tip facing downwards for 7 days, and ink leakage from the tip was confirmed. No ink droplets at the tip end... The ink droplet at the tip end is within 1 / 4 of the tapered section. The ink droplet at the tip end is between 1 / 4 and 1 / 2 of the tapered section...△ The ink droplet at the tip is more than half the size of the tapered part. ×

[0062] Ink aging test: After one month in a 50°C environment, the ink inside the tip body was observed under a microscope. No deposits, good condition... Precipitation occurred, but no practical problems occurred. A lot of precipitates occurred and there was some blurring...△ Deposits may occur, causing blurring or poor writing. ×

[0063] Thickness of handwriting: Handwritten handwriting was observed. Thick, clear handwriting ◎ Thick handwriting...○ The handwriting is thick enough that it is not a problem for practical use. Light handwriting ×

[0064] Abrasion resistance test under high writing pressure (ball seat abrasion test): The abrasion of the ball seat after the writing test was measured using a running test machine with a load of 400 gf, a writing angle of 70°, and a speed of 4 m / min. Wear of the ball seat is less than 8 μm. Wear of the ball seat is 8 μm or more and less than 15 μm. Wear of the ball seat is 15μm or more but less than 25μm, but writing is possible...△ The ball seat is badly worn, causing poor writing.

[0065] In Examples 1 to 28, good performance was obtained in the ink leakage inhibition test, ink aging test, writing density, and abrasion resistance test under high writing pressure (ball seat abrasion test). In addition, in Examples 23 and 24, the inks using pigments as colorants were observed under a microscope and found to have good pigment dispersibility.

[0066] In Comparative Example 1, the acrylic ester resin particles were not used, and therefore the ink leakage suppression was poor. In Comparative Example 2, a polystyrene resin was used, but it deformed in the ink, resulting in poor ink stability over time and poor ink leakage suppression. In Comparative Example 3, the ink consumption was small, so thick handwriting was not obtained. In Comparative Example 4, the ink consumption was too large, and therefore the effect of suppressing ink leakage was not obtained.

[0067] Furthermore, when a retractable oil-based ballpoint pen (retractable ballpoint pen) such as a knock-type oil-based ballpoint pen or a twist-and-pull type oil-based ballpoint pen is used, ink leakage suppression performance is one of the most important performance characteristics. Therefore, it is effective to use an ink composition for an oil-based ballpoint pen containing acrylic ester resin particles as in the present invention, which can suppress ink leakage from the gap at the writing tip (ink leakage from the gap between the ball and the tip tip) and achieve good ink leakage suppression performance.

[0068] Generally, to prevent ink leakage, ballpoint pen tips for oil-based ballpoint pens are equipped with a valve mechanism in which a ball rotatably held at the tip of the ballpoint pen tip is pressed against the inner wall of the tip edge by a resilient member such as a coil spring, either directly or via a pressing body, to create a gap between the inner wall of the tip edge and the ball due to the pressing force during writing, allowing ink to flow out. The minute gap at the tip edge is also closed when not in use. However, by using an ink composition for oil-based ballpoint pens, which has an exceptionally high ink leakage prevention effect as in the present invention, ink leakage can be prevented even without a resilient member such as a coil spring. This eliminates resistance between the ball and the resilient member, improving writing feel and ink fluidity, thereby improving ink tracking and making it easier to obtain thick handwriting. Furthermore, this reduces the number of parts, enabling cost reduction and is more effective. Since preventing ink leakage is particularly important in retractable ballpoint pens, this composition can be used advantageously. Although no resilient member such as a coil spring was attached to the tip of the oil-based ballpoint pens of Examples 1 to 28, ink leakage could be suppressed and good results were obtained.

[0069] In addition, in this example, for convenience, an oil-based ballpoint pen is exemplified in which an oil-based ballpoint pen refill in which an oil-based ballpoint pen ink composition is directly stored in the barrel is stored, but the oil-based ballpoint pen of the present invention may be a direct-fill type ballpoint pen or an oil-based ballpoint pen in which the barrel serves as an ink storage barrel and the oil-based ballpoint pen ink composition is directly stored in the barrel. In addition, in this example, for convenience, a ballpoint pen tip formed by cutting a wire material is exemplified, but a ballpoint pen tip formed by pressing a pipe material may also be used.

[0070] Furthermore, in this example, an oil-based ballpoint pen in which a ballpoint pen refill containing an oil-based ballpoint pen ink composition in an ink storage tube is disposed in the barrel has been exemplified, but the oil-based ballpoint pen of the present invention may be a direct-fill type oil-based ballpoint pen in which the barrel itself serves as the ink storage tube and the oil-based ballpoint pen ink composition is stored directly in the barrel, or may have a structure in which an ink storage tube containing an oil-based ballpoint pen ink composition (ballpoint pen refill) is used as a ballpoint pen as is. [Industrial Applicability]

[0071] The present invention can be used as an oil-based ballpoint pen, and more specifically, can be widely used as an oil-based ballpoint pen such as a cap type or a retractable type.

Claims

1. An oil-based ballpoint pen having a ballpoint pen tip at the tip of an ink reservoir, and an ink composition for an oil-based ballpoint pen contained in the ink reservoir, wherein the ink consumption per 100 m of the oil-based ballpoint pen is 20 to 70 mg, and the ink composition for an oil-based ballpoint pen contains a colorant, an organic solvent, and acrylic ester resin particles; the content of the acrylic ester resin particles is 0.01 to 10% by mass relative to the total amount of the ink composition; the ratio of the average particle diameter (μm) of the acrylic ester resin particles to the amount of movement (μm) of the ball in the vertical axis direction of the ball of the ballpoint pen tip of the oil-based ballpoint pen (average particle diameter of the acrylic ester resin particles: amount of movement of the ball in the vertical axis direction) is set to a relationship of 1:1 to 1:100, The arithmetic mean roughness (Ra) of the ball surface of the ballpoint pen tip is 0.1 to 10 nm. An oil-based ballpoint pen characterized by:

2. The ink viscosity of the ink composition for oil-based ballpoint pens is 20°C, a shear rate of 5 sec －１ 2. The oil-based ballpoint pen according to claim 1, wherein the viscosity is 1,000 mPa·s or more and 30,000 mPa·s or less.

3. 3. The oil-based ballpoint pen according to claim 1, wherein the acrylic ester resin particles have an average particle size of 5 μm or less.

4. 4. The oil-based ballpoint pen according to claim 1, wherein the acrylic ester resin particles are methacrylic ester resin particles.

5. 5. The oil-based ballpoint pen according to claim 1, wherein the organic solvent is an alcoholic solvent, and the content of the alcoholic solvent is 50% or more of the total organic solvent content in the oil-based ballpoint pen composition.

6. 6. The oil-based ballpoint pen according to claim 1, wherein the ink composition for the oil-based ballpoint pen contains a polyvinyl butyral resin or a ketone resin.

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