Oil-based ink composition for ballpoint pen

Abstract

To provide an oil-based ink composition for a ballpoint pen that has excellent stability over time and can achieve a high level of both smooth writing feel and line drawing quality, and to provide an oil-based ballpoint pen.　An oil-based ink composition for a ballpoint pen according to the present disclosure contains at least carbon black, a resin component, and a solvent. The oil-based ink composition for a ballpoint pen is characterized in that the viscosity by rheometer when using a cone plate at 25°C is 1-200 mPa∙s at shear rates of 20-200 s-1, the ratio represented by the viscosity at a shear rate of 20 s-1 / viscosity at a shear rate of 200 s-1 by rheometer at 25°C is 0.90-1.10, and the carbon black has a 90% particle size in a volume-based cumulative particle size distribution of 0.50 μm or less.　Also, an oil-based ballpoint pen according to the present disclosure is characterized by being filled with an oil-based ink composition for a ballpoint pen of the above configuration.

Description

Oil-based ink composition for ballpoint pens

[0001] The present specification relates to an oil-based ink composition for a ballpoint pen and an oil-based ballpoint pen.

[0002] Conventionally, oil-based ink compositions for ballpoint pens have been known that suppress blobbing, improve the writing feel, and improve the quality of ballpoint pens. For example, 1) a ballpoint pen oil-based ink composition in which the viscosity of the ballpoint pen oil-based ink decreases over time, preventing blobbing and direct current, is characterized by previously incorporating into the ballpoint pen ink composition an amount of moisture that will reach an equilibrium state when the ballpoint pen oil-based ink composition absorbs moisture from the air when left in a usage environment (see, for example, Patent Document 1); 2) a ballpoint pen oil-based ink composition in which the ink composition contains at least a colorant, an organic solvent, and a surfactant with an IOB value of 0.01 to 1.0, in order to provide an oil-based ballpoint pen ink composition that has a good writing feel and is capable of suppressing wear of the ball seat (see, for example, Patent Document 2); 3) In order to provide an oil-based ink composition for a ballpoint pen that maintains good ink visibility even after long-term storage, there is known an oil-based ink composition for a ballpoint pen that contains at least a colorant, an organic solvent, water, and one or more organic acid monoglycerides selected from succinic acid monoglyceride, citric acid monoglyceride, and diacetyltartaric acid monoglyceride (see, for example, Patent Document 3).

[0003] However, the oil-based ink compositions for ballpoint pens described in Patent Documents 1 to 3 above have the problem that they are still insufficient in terms of line quality and effect on reducing blobbing. In particular, in the case of inks designed to have a low ink viscosity in order to provide a smooth writing feel, improvements in the smooth writing feel and the ability to draw lines without rubbing are desired.

[0004] On the other hand, the applicant of the present application has proposed an oil-based ink composition for a ballpoint pen that is excellent in suppressing the blobbing phenomenon, has a smooth writing feel, is good in the initial writing property (no rubbing when starting to write), ensures quick drying and a stable ink flow rate, and can also improve bleed-through. The ink composition contains at least a colorant, a resin component, a solvent, and water, and the contents of the solvent and water are 40% by mass or more relative to the total amount of the ink composition, and the resin component contains a resin with a mass average molecular weight of 40,000 or more. In one example, Patent Document 4 proposes an oil-based ink composition for ballpoint pens, characterized in that, if the ink composition contains a resin component, the content of the resin component is 0.5% by mass or less relative to the total amount of the ink composition, the weight loss rate A when the ink composition is left standing in an open state for 2 hours in an environment of 50°C and a relative humidity of 35±5% RH is 25% or more, and the ratio A / B of the weight loss rate A to the weight loss rate B when the ink composition is left standing in an open state for 2 hours in an environment of 50°C and a relative humidity of 85±5% RH is 0.8 to 1.2 (see, for example, Patent Document 4). The oil-based ink composition for ballpoint pens described in Patent Document 4 has excellent properties not previously available, but when the ink viscosity is designed to be low by using carbon black or a diketopyrrolopyrrole pigment as a colorant, there is still room for improvement in terms of smooth writing feel and line drawing quality, and further improvements in a more stable, smooth writing feel and line drawing quality are desired.

[0005] On the other hand, in order to provide an ink composition for an oil-based ballpoint pen and an oil-based ballpoint pen that have excellent pigment dispersibility and can improve the stability of the ink ejection amount of the oil-based ballpoint pen even when the viscosity is reduced, the ink composition for an oil-based ballpoint pen contains an organic solvent including a water-soluble organic solvent, a resin, a colorant including carbon black or a diketopyrrolopyrrole pigment as a pigment, and water, wherein the content of water in the ink composition for an oil-based ballpoint pen is 3 to 10 mass %, the resin includes at least one of a ketone resin and a maleic resin, and the viscosity at 25°C and a shear rate of 7.5 / sec is 7. Known examples include an oil-based ballpoint pen ink composition having a viscosity of less than 1000 mPa·s (see, for example, Patent Document 5), and an oil-based ballpoint pen ink composition comprising an organic solvent including a water-soluble organic solvent, a resin, a colorant including carbon black or a diketopyrrolopyrrole pigment as a pigment, a dispersant, and water, wherein the water content in the oil-based ballpoint pen ink composition is 3 to 10 mass %, the dispersant contains a fatty acid and an aliphatic amine, and the resin contains at least one of a ketone resin and a maleic resin (see, for example, Patent Document 6). The oil-based ballpoint pen ink compositions disclosed in Patent Documents 5 and 6 disclose related technologies of the present disclosure, but in the case of oil-based ballpoint pen ink compositions using carbon black or a diketopyrrolopyrrole pigment as a colorant, the stability over time can become unstable, and as a result, it is still not possible to achieve both a smooth writing feel and high line quality, and further improvements are currently desired.

[0006] JP 2001-311032 A (claims, examples, etc.) JP 2012-219213 A (claims, examples, etc.) JP 2015-196735 A (claims, examples, etc.) JP 2024-3603 A (claims, examples, etc.) JP 2022-154494 A (claims, examples, etc.) JP 2022-154496 A (claims, examples, etc.)

[0007] The present disclosure has been made in view of the problems and current state of the prior art described above and seeks to solve these problems, and aims to provide an oil-based ink composition for ballpoint pens that uses carbon black or a diketopyrrolopyrrole pigment as a coloring material, which has excellent stability over time and can achieve a high degree of both smooth writing feel and line drawing quality, and an oil-based ballpoint pen equipped with this oil-based ink composition.

[0008] In view of the above-mentioned conventional problems, the present inventors have conducted extensive research and have found that, in an oil-based ink composition for a ballpoint pen, the ink composition contains at least carbon black or a diketopyrrolopyrrole pigment, a resin component, a solvent, and water, the viscosity of a rheometer using a cone plate at 25°C is set within a specific range, and the viscosity of the ink composition is maintained at a shear rate of 20 s －１ Viscosity at shear rate 200 s －１ The present inventors have found that the above-mentioned desired oil-based ink composition for ballpoint pens and oil-based ballpoint pens can be obtained by setting the ratio, expressed in terms of time viscosity, within a specific range and limiting the 90% particle size in the cumulative particle size distribution on a volume basis of the carbon black or diketopyrrolopyrrole pigment to a specific value or less, and have thus completed the present disclosure.

[0009] That is, the oil-based ink composition for ballpoint pens of the first disclosure is an oil-based ink composition for ballpoint pens containing at least carbon black, a resin component, and a solvent, and the oil-based ink composition for ballpoint pens has a viscosity measured at 25°C using a cone plate at a shear rate of 20 to 200 s －１ The shear rate of the rheometer is 20 s at 25 ° C. －１ Viscosity at shear rate 200 s －１ The oil-based ink composition for ballpoint pens of the second disclosure is characterized in that the ratio of the viscosity at shear rate to the viscosity at shear rate is 0.90 to 1.10, and the carbon black has a 90% particle size of 0.50 μm or less in a cumulative particle size distribution based on volume.－１ The shear rate of the rheometer is 20 s at 25 ° C. －１ Viscosity at shear rate 200 s －１ The oil-based ballpoint pen of the present disclosure is characterized in that the ratio of viscosity to viscosity at time of application is 0.90 to 1.10, and the diketopyrrolopyrrole pigment (DPP) has a 90% particle size of 0.50 μm or less in a cumulative particle size distribution based on volume. The resin component of the first or second disclosure preferably contains a resin with a mass average molecular weight of less than 40,000. The oil-based ballpoint pen of the present disclosure is characterized in that it is equipped with the oil-based ink composition for ballpoint pens described in the first or second disclosure.

[0010] According to the present disclosure, there is provided an oil-based ink composition for a ballpoint pen that uses carbon black or a diketopyrrolopyrrole pigment as a colorant, which has excellent stability over time, suppresses blobbing, and is capable of achieving both a smooth writing feel and high line quality, and an oil-based ballpoint pen equipped with this oil-based ink composition. The objects and advantages of the present disclosure can be realized and attained by using the elements and combinations particularly pointed out in the claims. Both the general description above and the detailed description below are exemplary and explanatory and do not limit the present disclosure as set forth in the claims.

[0011] FIG. 1 is a longitudinal cross-sectional view showing an example of a main part of a ballpoint pen tip of an oil-based ballpoint pen equipped with the oil-based ink composition for ballpoint pens of the present disclosure.

[0012] The embodiments of the present disclosure are described in detail below. However, it should be noted that the technical scope of the present disclosure is not limited to the respective embodiments detailed below, but extends to the inventions set forth in the claims and their equivalents. The oil-based ink composition for ballpoint pens of the present disclosure is an oil-based ink composition for ballpoint pens containing at least carbon black, a resin component, and a solvent, and the oil-based ink composition for ballpoint pens has a viscosity measured at 25°C using a cone plate at a shear rate of 20 to 200 s －１ The shear rate of the rheometer is 20 s at 25 ° C. －１ Viscosity at shear rate 200 s－１ The oil-based ink composition for ballpoint pens of the second disclosure is characterized in that the ratio of the viscosity at shear rate to the viscosity at shear rate is 0.90 to 1.10, and the carbon black has a 90% particle size of 0.50 μm or less in a cumulative particle size distribution based on volume. The oil-based ink composition for ballpoint pens of the second disclosure is characterized in that the viscosity at shear rate is 20 to 200 s at 25°C using a cone plate rheometer. －１ The shear rate of the rheometer is 20 s at 25 ° C. －１ Viscosity at shear rate 200 s －１ and the diketopyrrolopyrrole pigment (DPP) has a 90% particle size of 0.50 μm or less in a cumulative particle size distribution on a volume basis. The term "the present disclosure" includes both the oil-based ink compositions for ballpoint pens of the first and second disclosures.

[0013] In the present disclosure, the term "average particle size" refers to a value calculated using a laser diffraction / scattering particle size distribution analyzer (LA-960S, manufactured by HORIBA, Ltd. (temperature during measurement: 25°C, 3-methoxy-3-methyl-1-butanol used as a diluent solvent). The 90% particle size (D90) in a cumulative particle size distribution on a volume basis refers to the particle size at which the integrated amount accounts for 90% on a volume basis in a cumulative particle size curve of a particle size distribution measured using a laser diffraction / scattering particle size distribution analyzer, and can be measured using a laser diffraction / scattering particle size distribution analyzer (LA-960S, temperature during measurement: 25°C, 3-methoxy-3-methyl-1-butanol used as a diluent solvent during measurement) manufactured by HORIBA, Ltd. The cumulative particle size distribution on a volume basis can be evaluated from the measurement results using the accompanying software.

[0014] <Coloring Material> The coloring material used in the present disclosure is carbon black in the first disclosure, and diketopyrrolopyrrole pigment (DPP) in the second disclosure. The carbon black used in the first disclosure is not particularly limited as long as the 90% particle size in the cumulative particle size distribution based on volume is 0.50 μm or less. Examples of carbon black that can be used include acetylene black, ketjen black, furnace black, channel black, thermal black, etc., and are used to impart a black coloring effect to the handwriting of the oil-based ink composition, making it visible and forming durable handwriting. From the viewpoint of dispersibility, the carbon black used should have a BET specific surface area of ​​30 to 150 m ２ / g, and more preferably 40 to 100m ２ / g is desirable. The BET specific surface area in the present disclosure is a value measured using a Macsorb model HM-1208 manufactured by Mountech Co., Ltd., by the BET single-point method, under pretreatment conditions of 110°C for 30 minutes, and using nitrogen as the adsorption gas. Specific carbon black that can be used is one that satisfies the above physical properties, and examples of commercially available carbon black include at least one selected from furnace black, channel black, and the like manufactured by Degussa, Mitsubishi Chemical, Cabot Corporation, etc.

[0015] The diketopyrrolopyrrole pigment (DPP) used in the second disclosure is not particularly limited as long as the 90% particle size in the cumulative particle size distribution based on volume in the ink composition is 0.50 μm or less. Examples of diketopyrrolopyrrole pigments (DPP) that can be used include C.I. Pigment Red 254, 255, 264, 272, 291, C.I. Pigment Orange 71, 73, and 81, and are used to impart a red coloring effect to handwriting of an oil-based ink composition, making it visible and forming durable handwriting. Specific examples of diketopyrrolopyrrole pigments (DPP) that can be used include one or more selected from Irgazin Flame Red K3800 (C.I. Pigment Red 272), Irgazin Flame Red L3600 HD (C.I. Pigment Red 272), Irgazin Red L3630 (C.I. Pigment Red 254), Irgazin Flame Red D3656 HD (C.I. Pigment Red 254), Irgazin Flame Red S3625 (C.I. Pigment Red 291), and Fuji Fast Red 8800 (C.I. Pigment Red 254), manufactured by Fuji Color Co., Ltd. Among these, C.I. Pigment Red 272 is preferred for use in oil-based ballpoint pens in terms of high clarity, weather resistance, and fastness.

[0016] In the present disclosure, carbon black is used in the first disclosure and diketopyrrolopyrrole pigment (DPP) is used in the second disclosure, but colorants other than carbon black and diketopyrrolopyrrole pigment (DPP), such as other inorganic pigments, other organic pigments, various dyes, etc. (each alone or in a mixture of two or more, the same applies hereinafter), can be used within the scope that does not impair the effects of the present disclosure. Examples of other inorganic pigments include at least one of titanium oxide, zinc white, red iron oxide, chromium oxide, iron black, cobalt blue, alumina white, iron oxide yellow, viridian, zinc sulfide, cadmium yellow, vermilion, cadmium red, yellow lead, molybdate orange, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine, baryte powder, white lead, Prussian blue, manganese violet, aluminum powder, brass powder, etc. Examples of other organic pigments include at least one of azo lakes, insoluble azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dye lake nitro pigments, and nitroso pigments.

[0017] As the dye, at least one of acid dyes, reactive dyes, basic dyes, disperse dyes, direct dyes, fluorescent dyes, C.I. Basic Yellow 35, C.I. Basic Yellow 40, C.I. Acid Orange 28, C.I. Acid Blue 92, eosin, phloxine, Water Yellow #6-C, Acid Red, Water Blue #105, Brilliant Blue FCF, Nigrosine NB, Direct Black 154, Direct Sky Blue 5B, Violet BB Rhodamine, methyl violet, etc. can also be used. Furthermore, at least one of processed pigments surface-modified with resins or surfactants, dispersed toners, acrylic resins or benzoguanamine resins colored with pigments or dyes and microparticulated, thermochromic microcapsule pigments, and photochromic microcapsule pigments can also be used.

[0018] The content of each of the colorants used in the present disclosure, carbon black in the first disclosure and diketopyrrolopyrrole pigment (DPP) in the second disclosure, varies depending on the type of oil-based ballpoint pen, the ink storage form (fill-in type, direct ink type), dispersibility, storage stability, the amount of ink raw materials blended, etc., but is preferably 2 to 12 mass%, and more preferably 4 to 10 mass%, of the total amount of the ink composition. The amount of colorants other than carbon black used in the first disclosure and the amount of colorants other than diketopyrrolopyrrole pigment (DPP) used in the second disclosure are adjusted within a range that does not impair the effects of the present disclosure, and is preferably 0 to 12 mass%, and more preferably 4 to 10 mass%, of the total amount of the ink composition.

[0019] <Resin Component> The resin component used in the present disclosure may be, for example, at least one of polyvinyl butyral, ketone resin, polyvinylpyrrolidone, polyacetal resin, polyvinyl alcohol resin, cellulose resin, terpene resin, alkyd resin, phenoxy resin, polyvinyl acetate resin, maleic acid resin, styrene-maleic acid resin, alkylphenol resin, rosin-modified resin, terpene phenol resin, styrene-acrylic resin, etc. As the resin component used, it is desirable to use a resin having a mass average molecular weight of less than 40,000 in terms of suppressing blobbing, abrasion resistance, and in the present disclosure, adjusting the ink viscosity and viscosity ratio to within a specific range.

[0020] Usable examples of the resin include at least one of polyvinyl butyral, ketone resin, polyvinylpyrrolidone, polyacetal resin, polyvinyl alcohol resin, cellulose resin, terpene resin, alkyd resin, phenoxy resin, polyvinyl acetate resin, maleic acid resin, styrene-maleic acid resin, alkylphenol resin, rosin-modified resin, terpene phenol resin, and styrene-acrylic resin. Among these, polyvinyl butyral, ketone resin, and polyvinylpyrrolidone having a mass average molecular weight of less than 40,000 are preferred, and polyvinyl butyral and ketone resins having a mass average molecular weight of 20,000 or less are more preferred. In the present disclosure, the mass average molecular weight is a value measured in styrene equivalent terms using a GPC method. Here, the polyvinyl butyral resin is obtained by reacting polyvinyl alcohol (PVA) with butyraldehyde (BA) and has a structure containing butyral groups, acetyl groups, and hydroxyl groups.

[0021] Specific examples of resins that can be used include polyvinyl butyrals manufactured by Sekisui Chemical Co., Ltd. under the trade names Polyvinyl Butyral BL-1, BL-10, BM-1, BM-5, and BH-3, and Mobital B14S and B30T manufactured by Kuraray Co., Ltd. Examples of ketone resins include Ketone Resin K-90 manufactured by Arakawa Chemical Industries, Ltd. and Resin SK manufactured by Degussa Co., Ltd. Examples of polyvinylpyrrolidone include Pitzcol K-17 manufactured by Daiichi Kogyo Seiyaku Co., Ltd. and PVP K90 manufactured by Ashland Co., Ltd.

[0022] The content of these resin components (solids) varies depending on factors such as the type of oil-based ballpoint pen, ink storage form (fill-in type, direct ink type), dispersibility, storage stability, and, in the present disclosure, the ink viscosity and viscosity ratio are adjusted to a specific range, but is preferably 25% by mass or less, more preferably 15% by mass or less, and particularly preferably 1 to 5% by mass, in terms of solids content relative to the total amount of ink composition. When a resin with a mass-average molecular weight of 40,000 or more is used as the resin component, the content of the resin component is preferably 0.5% by mass or less, more preferably 0.4% by mass or less, and particularly preferably 0 (zero) to 0.3% by mass, in terms of solids content relative to the total amount of ink composition, from the standpoint of the effects of the present disclosure and abrasion resistance.

[0023] <Solvent> Examples of solvents that can be used in the present disclosure include aromatics, alcohols, polyhydric alcohols, glycol ethers, hydrocarbons, esters, etc. These solvents may be used alone or in combination of two or more.

[0024] Examples of aromatic compounds that can be used include benzyl alcohol, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, propylene glycol monophenyl ether, diethylene glycol monophenyl ether, alkylsulfonic acid phenyl ester, butyl phthalate, ethylhexyl phthalate, tridecyl phthalate, ethylhexyl trimellitate, diethylene glycol dibenzoate, and dipropylene glycol dibenzoate.

[0025] Examples of alcohols that can be used include ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butyl alcohol, 1-pentanol, isoamyl alcohol, sec-amyl alcohol, 3-pentanol, tert-amyl alcohol, n-hexanol, methyl amyl alcohol, 2-ethylbutanol, n-heptanol, 2-heptanol, 3-heptanol, n-octanol, 2-octanol, 2-ethylhexanol, 3,5,5-trimethylhexanol, nonanol, n-decanol, undecanol, n-decanol, trimethylnonyl alcohol, tetradecanol, heptadecanol, cyclohexanol, and 2-methylcyclohexanol.

[0026] Examples of polyhydric alcohols that can be used include ethylene glycol, diethylene glycol, 3-methyl-1,3 butanediol, triethylene glycol, dipropylene glycol, 1,3 propanediol, 1,3 butanediol, 1,5 pentanediol, hexylene glycol, and octylene glycol.

[0027] Examples of glycol ethers that can be used include methyl isopropyl ether, ethyl ether, ethyl propyl ether, ethyl butyl ether, isopropyl ether, butyl ether, hexyl ether, 2-ethylhexyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylbutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, 3-methyl-3-methoxy-1-butanol, 3-methoxy-1-butanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol tertiary butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, and tetrapropylene glycol monobutyl ether.

[0028] Examples of hydrocarbons that can be used include straight-chain hydrocarbons such as hexane, isohexane, heptane, octane, nonane, and decane, and cyclic hydrocarbons such as cyclohexane, methylcyclohexane, and ethylcyclohexane.

[0029] Examples of esters include propylene glycol methyl ether acetate, propylene glycol diacetate, 3-methyl-3-methoxybutyl acetate, propylene glycol ethyl ether acetate, ethylene glycol ethyl ether acetate, butyl formate, isobutyl formate, isoamyl formate, propyl acetate, butyl acetate, isopropyl acetate, isobutyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, propyl propionate, isobutyl propionate, isoamyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, propyl isobutyrate, Examples of usable surfactants include methyl valerate, ethyl valerate, propyl valerate, methyl isovalerate, ethyl isovalerate, propyl isovalerate, methyl trimethylacetate, ethyl trimethylacetate, propyl trimethylacetate, methyl caproate, ethyl caproate, propyl caproate, methyl caprylate, ethyl caprylate, propyl caprylate, methyl laurate, ethyl laurate, methyl oleate, ethyl oleate, caprylic acid triglyceride, tributyl acetate citrate, octyl oxystearate, propylene glycol monoricinoleate, methyl 2-hydroxyisobutyrate, and 3-methoxybutyl acetate.

[0030] Particularly preferred solvents include 3-methoxy-3-methyl-1-butanol, propylene glycol monomethyl ether, ethyl alcohol, isopropyl alcohol, xylene, etc. The content of these solvents is preferably 30 to 80% by mass, and more preferably 40 to 70% by mass, of the total amount of the ink composition, from the viewpoint of the solubility of the raw materials and, in the present disclosure, adjusting the ink viscosity and viscosity ratio to a specific range.

[0031] In the present disclosure, it is desirable to incorporate water. Purified water, ion-exchanged water, pure water, ultrapure water, etc. may be used, and specifically, the amount of water is preferably 0.5 to 10% by mass relative to the total amount of the ink composition. Ballpoint pen refills incorporating the oil-based ink composition for ballpoint pens of the present disclosure gradually absorb moisture from the air when left unused for many years. Therefore, adding water in advance can suppress changes in physical properties due to moisture absorption. From this perspective, it is desirable to incorporate water. In the present disclosure, the total content of the solvent and water is preferably 40% by mass or more, more preferably 40 to 80% by mass, relative to the total amount of the ink composition. If the total content of the solvent and water is less than 40% by mass, the volatility of the ink decreases, making it more likely for blobs to accumulate around the caulking, which is undesirable.

[0032] <Other Components> The oil-based ink composition for ballpoint pens of the present disclosure may contain other components in appropriate amounts within a range that does not impair the effects of the present disclosure. Examples of other components include leveling agents, rust inhibitors, preservatives, lubricants, etc. Examples of leveling agents that can be used include fluorine-based surfactants, silicone-based surfactants, and phosphate ester-based surfactants. Examples of lubricants include phosphate esters, etc.

[0033] The oil-based ink composition for ballpoint pens of the present disclosure uses the carbon black described above in the first disclosure and the diketopyrrolopyrrole pigment (DPP) described above in the second disclosure. Each oil-based ink composition for ballpoint pens containing these coloring materials, a resin component, and a solvent has a viscosity measured at 25°C using a cone plate at a shear rate of 20 to 200 s －１ The shear rate of the rheometer is 20 s at 25 ° C. －１ Viscosity at shear rate 200 s －１ The ratio of viscosity at room temperature to viscosity at room temperature is 0.90 to 1.10, and the carbon black or diketopyrrolopyrrole pigment (DPP) has a 90% particle size of 0.50 μm or less in the cumulative particle size distribution based on volume.

[0034] In the present disclosure, in an oil-based ink composition for a ballpoint pen using carbon black or a diketopyrrolopyrrole pigment as a coloring material, excellent stability over time, smooth writing feel, and line quality are highly achieved, and in order to effectively exhibit the effects of the present disclosure, 1) the ink composition is heated at 25°C and a shear rate of 20 to 200 s －１ 2) The ink viscosity when using a cone plate (CP25-1, manufactured by Anton Paar) is set to a value within the range of 1 to 200 mPa·s at a shear rate of 20 s in a rheometer (MCR302, manufactured by Anton Paar) at 25°C. －１ Viscosity at shear rate 200 s －１ 2) the ratio of the viscosity at room temperature to the viscosity at room temperature must be 0.90 to 1.10, and 3) the 90% particle size in the cumulative particle size distribution on a volume basis of the carbon black or diketopyrrolopyrrole pigment used as the coloring material must be 0.50 μm or less.

[0035] The condition 1) that the ink viscosity is 200 mPa·s or less is related to the occurrence of blobbing, and by further satisfying this condition, the blobbing phenomenon can be further suppressed and good initial writing performance can be achieved. More preferably, the ink viscosity is 200 mPa·s or less at 25°C and a shear rate of 20 to 200 s －１ It is desirable that the ink viscosity be 1 to 110 mPa·s between these values. The condition of 2) that the ratio be 0.90 to 1.10 is related to the amounts of carbon black, diketopyrrolopyrrole pigment, and resin, and the proportion of volatile solvent, and by further satisfying this condition, it is possible to further improve the suppression of the blobbing phenomenon. 3) Setting the 90% particle size in the cumulative particle size distribution on a volume basis of the carbon black and diketopyrrolopyrrole pigment to 0.50 μm or less is closely related to the effects of the present disclosure and is the most important factor, and can be used as an indicator of the elimination of pigments with large particle sizes, and it is preferable that the 90% particle size be 0.48 μm or less.

[0036] The carbon black and diketopyrrolopyrrole pigment (DPP) satisfying the 90% particle size (D90) in the cumulative particle size distribution based on the volume standard can be adjusted by suitably combining the type of pigment used (characteristics such as BET specific surface area and primary particle size), the type of dispersant, the dispersion conditions described below, and manufacturing conditions such as classification treatment (centrifugation conditions). For example, adjustment can be made by suitably combining the classification method (media dispersion, roll dispersion), media (type, size), dispersion time, etc. The media disperser used is not particularly limited, but examples include Star Mill Nano Getter, Star Mill ZRS (Ashizawa Finetech Co., Ltd., product name), Ultra Apex Mill, Dual Apex Mill (Kotobuki Industries Co., Ltd., product name), Paint Shaker, Pico Grain Mill (Asada Iron Works Co., Ltd., product name), Micromedia (Buehler Co., Ltd., product name), MSC Mill (Nippon Coke and Engineering Co., Ltd., product name), and sand mill. The particle diameter of the dispersion media used can be 0.05 to 2.0 mm, from the viewpoint of improving the efficiency of the dispersion process and obtaining the above-mentioned predetermined cumulative particle size distribution. The material of the dispersion media particles used is not particularly limited, but from the viewpoint of reducing metal impurities in the dispersion, glass beads or ceramic media such as alumina, zirconia, silicon carbide, and silicon nitride can be used. The rotational speed (the peripheral speed of the leading edge of the rotor) and dispersion time of the media disperser are set to a predetermined value depending on the type of carbon black, diketopyrrolopyrrole pigment (DPP), etc. Roll dispersion can be performed by a compression effect utilizing inter-roll pressure and a shear effect between rolls with different peripheral speeds, such as a roll mill. The roll mill is not particularly limited, and a known three-roll mill can be used. The three-roll mill has three rolls (a rear roll, a middle roll, and a front roll) that rotate and come into contact with each other in different directions at a predetermined speed ratio to apply pressure and shear force, thereby dispersing (adjusting) carbon black and diketopyrrolopyrrole pigment (DPP) to have the predetermined cumulative particle size distribution D90 of the present disclosure.

[0037] In order to prepare an oil-based ink composition for a ballpoint pen that satisfies the above conditions 1) to 3), it can be prepared by suitably combining the amount of carbon black or diketopyrrolopyrrole pigment used, the type of resin, and the type of solvent, optimizing the content of each component, and the above-mentioned dispersion (classification) treatment and the kneading method described below.

[0038] The oil-based ink composition for ballpoint pens of the present disclosure can be produced by the following production method, etc. In the first production method, a dispersion containing carbon black (black dispersion) or a dispersion containing diketopyrrolopyrrole pigment (DPP) (red dispersion) having a 90% particle size of 0.50 μm or less in a cumulative particle size distribution on a volume basis is prepared using carbon black in the first disclosure or diketopyrrolopyrrole pigment (DPP) in the second disclosure, a resin component, a solvent, and, if necessary, a dispersant. This black dispersion or red dispersion having the predetermined physical properties is then used to appropriately combine other components (other colorants, solvents, etc.) depending on the intended use of the ballpoint pen ink. The resulting mixture is mixed and stirred using a mixer or the like, or further, for example, a bead mill, homomixer, homogenizer, or the like, which can apply strong shear, under suitable stirring conditions. Furthermore, if necessary, coarse particles in the ink composition are removed by filtration or centrifugation, whereby an oil-based ink composition for a ballpoint pen that satisfies the above conditions 1) to 3) can be produced.

[0039] As a second production method, for example, instead of preparing the black dispersion or red dispersion having the predetermined physical properties of the first production method, carbon black or diketopyrrolopyrrole pigment, resin component, solvent, etc. are effectively combined in predetermined types and amounts, taking into consideration dispersibility, and the mixture is mixed and stirred using a mixer or the like, or further, for example, a bead mill, homomixer, homogenizer, or the like, which can apply strong shear, under suitable stirring conditions, and further, by microfiltration or centrifugation, the carbon black or diketopyrrolopyrrole pigment particles in the ink composition are adjusted to a predetermined diameter or less and the ink viscosity is adjusted to within the respective predetermined ranges, thereby producing an oil-based ink composition for a ballpoint pen that satisfies the above conditions 1) to 3).

[0040] In the present disclosure, as described above, an oil-based ink composition for a ballpoint pen, which is formulated with the carbon black of the first disclosure and the diketopyrrolopyrrole pigment (DPP) of the second disclosure and adjusted to have predetermined physical properties, is mounted in a ballpoint pen equipped with a pen tip such as a ballpoint pen tip. Examples of oil-based ballpoint pens in the present disclosure include those in which the oil-based ink composition for a ballpoint pen having the above-described composition is contained in a ballpoint pen ink container (refill), and the pen can be produced, for example, by filling the oil-based ink composition for a ballpoint pen into the body of an oil-based ballpoint pen equipped with a ballpoint pen tip having a ball with a diameter of 0.18 to 2.0 mm, preferably 0.28 to 1.0 mm.

[0041] In an oil-based ballpoint pen equipped with the oil-based ink composition for ballpoint pens with the physical properties of the present disclosure, in order to further demonstrate the effects of the present disclosure from the structural aspect of the ballpoint pen, the structure of the ballpoint pen tip X fixed to the tip of the ink container (refill) comprises, for example, a ball 10 and a holder 20 for holding the ball 10, as shown in FIG. 1 , a ball house 25 for storing the ball 10 is provided near the tip of the holder 20, and a crimped portion 26 is provided at the tip of the holder 20 to prevent the ball 10 stored in the ball house 25 from jumping out of the ball house 25, and the length of the sealing surface Y between the inner surface of the crimped portion 26 and the ball 10 is preferably 20 to 170 μm, and the diameter of the ball 10 is also preferably 0.28 to 1.0 mm. This, combined with the properties of the oil-based ink composition for ballpoint pens, also contributes to the structure of the ballpoint pen, preventing residual oil-based ink from accumulating near the crimp of the tip as writing progresses, preventing blobs from dripping onto the drawn lines and improving the quality of the drawn lines, further enhancing the effect of reducing blobs. By satisfying the above-mentioned conditions 1) to 3), it is possible to further control excess ink that is not transferred to the paper surface and that affects blobs, preventing the formation of large ink puddles near the crimp, thereby providing an oil-based ink composition for ballpoint pens that is stable over time and can achieve both a smooth writing feel and high-quality drawn lines. The structure of the ballpoint pen is not particularly limited, and it may be, for example, a direct-fill oil-based ballpoint pen equipped with a collector structure (ink retention mechanism) in which the barrel itself serves as the ink reservoir and is filled with the oil-based ink composition for ballpoint pens of the above-mentioned configuration.

[0042] The oil-based ink composition for ballpoint pens of the present disclosure thus configured contains, as a coloring material, carbon black in the first disclosure and a diketopyrrolopyrrole pigment, a resin component, and a solvent in the second disclosure. The oil-based ink composition for ballpoint pens has a viscosity of 20 to 200 s at a shear rate of 20 to 200 s when measured with a rheometer at 25°C using a cone plate. －１The shear rate of the rheometer is 20 s at 25 ° C. －１ Viscosity at shear rate 200 s －１

[0013] By characterizing the oil-based ink composition for ballpoint pens as having an oil-based ink composition with a viscosity ratio of 0.90 to 1.10, expressed in terms of viscosity at room temperature, and the carbon black or diketopyrrolopyrrole pigment both having a 90% particle size in a cumulative particle size distribution on a volume basis of 0.50 μm or less, it is possible to obtain an oil-based ink composition for ballpoint pens that has excellent stability over time and is capable of achieving both a smooth writing feel and high line quality, and an oil-based ballpoint pen equipped with this oil-based ink composition. The oil-based ink composition for ballpoint pens and the oil-based ballpoint pen equipped with this ink composition of the present disclosure have an extremely excellent sustained effect that allows the above-mentioned functional effects of the present disclosure to be exerted, and furthermore, the period during which the effects are exhibited and maintained is long, and they also have excellent stability over time.

[0043] Next, the present disclosure will be explained in more detail using Examples 1 to 17 and Comparative Examples 1 to 13 of oil-based ink compositions for ballpoint pens and oil-based ballpoint pens equipped therewith, but the present disclosure is not limited to the following examples, etc.

[0044] [First Disclosure: Examples 1 to 7 and Comparative Examples 1 to 8: Preparation of Oil-Based Ink Compositions for Ballpoint Pens Containing Carbon Black] Each oil-based ink composition for ballpoint pens was prepared by mixing and stirring black dispersions 1 to 9, dye, solvent, lubricant, water, etc. according to the formulations shown in Table 1 below. The resin components are expressed in terms of solid content. Black dispersions 1 to 9 were prepared by the following method.

[0045] (Preparation of Black Dispersion 1) Carbon black (BET specific surface area: 65 m ２Black Dispersion 1 was prepared by mixing and stirring the following blended ingredients: 15% by mass of polyvinyl butyral (BL-1, mass average molecular weight: 19,000, manufactured by Sekisui Chemical Co., Ltd.; the same applies hereinafter), 15% by mass of resin component; 3.8% by mass of polyvinyl butyral (BL-1, mass average molecular weight: 19,000, manufactured by Sekisui Chemical Co., Ltd.; the same applies hereinafter); and 81.2% by mass of solvent; 3-methoxy-3-methyl-1-butanol. (Preparation of Black Dispersion 2) Using the blended ingredients of Black Dispersion 1, Black Dispersion 2 was prepared by centrifuging at 10,000 G for 15 minutes to have a D90 of 0.50 μm or less. (Preparation of Black Dispersion 3) Using the blended ingredients of Black Dispersion 1, Black Dispersion 3 was prepared by centrifuging at 10,000 G for 30 minutes to have a D90 of 0.50 μm or less.

[0046] (Preparation of Black Dispersion 4) A different carbon black was used in the above Black Dispersion 1, but with a different product name (physical properties). That is, carbon black (BET specific surface area 45 m) ２ Black Dispersion 4 was prepared by mixing and stirring the mixture containing 15% by mass of acrylic resin (1.5% by mass of acrylic resin, PRINTEX #25, manufactured by Degussa), 3.8% by mass of polyvinyl butyral (manufactured by BL-1), and 81.2% by mass of 3-methoxy-3-methyl-1-butanol. The mixture was then dispersed using a bead mill. (Preparation of Black Dispersion 5) Using the same formulation as Black Dispersion 4, Black Dispersion 5 was prepared by centrifuging at 10,000 G for 15 minutes, resulting in a D90 of 0.50 μm or less. (Preparation of Black Dispersion 6) Using the same formulation as Black Dispersion 4, Black Dispersion 6 was prepared by centrifuging at 10,000 G for 30 minutes, resulting in a D90 of 0.50 μm or less.

[0047] (Preparation of Black Dispersion 7) In the above-mentioned Black Dispersion 1, a different carbon black having different physical properties was used. That is, carbon black (BET specific surface area 66 m) ２Black Dispersion 7 was prepared by mixing and stirring a formulation containing 15% by mass of a resin component (Polyvinyl butyral (BL-1) (15% by mass, 1 / g, Raven 1060 Ultra, manufactured by Columbian Chemicals), 3.8% by mass of a resin component, and 81.2% by mass of a solvent (3-methoxy-3-methyl-1-butanol). The mixture was then dispersed using a bead mill. (Preparation of Black Dispersion 8) Using the formulation of Black Dispersion 7, Black Dispersion 8 was prepared by centrifuging at 10,000 G for 15 minutes to have a D90 of greater than 0.50 μm. (Preparation of Black Dispersion 9) Using the formulation of Black Dispersion 7, Black Dispersion 9 was prepared by centrifuging at 10,000 G for 30 minutes to have a D90 of greater than 0.50 μm.

[0048] [Second Disclosure: Examples 8 to 17 and Comparative Examples 9 to 13: Preparation of Oil-Based Ink Compositions for Ballpoint Pens Containing Diketopyrrolopyrrole Pigments] Each oil-based ink composition for ballpoint pens was prepared by mixing and stirring Red Dispersions 1 to 9, dye, solvent, lubricant, water, and the like according to the formulations shown in Table 2 below. The resin components are expressed in terms of solid content. Red Dispersions 1 to 9 were prepared by the following method.

[0049] (Preparation of Red Dispersion 1) A formulation containing 10 mass% of a diketopyrrolopyrrole pigment (CROMOPHTAL DPP FLAME RED FP, manufactured by BASF, C.I. Pigment Red 272), 4.0 mass% of a resin component: polyvinyl butyral (BL-1), 85.7 mass% of a solvent: 3-methoxy-3-methyl-1-butanol, and 0.3 mass% of a dispersant, Aerosil RX50, was mixed and stirred, and then dispersed using a bead mill to prepare Red Dispersion 1. (Preparation of Red Dispersion 2) Using the formulation of Red Dispersion 1, Red Dispersion 2 was prepared by centrifuging at 10,000 G for 15 minutes to give a D90 of 0.50 μm or less. (Preparation of Red Dispersion 3) Using the formulation of Red Dispersion 1, Red Dispersion 3 having a D90 of 0.50 μm or less was prepared by centrifuging at 10,000 G for 30 minutes.

[0050] (Preparation of Red Dispersion 4) A diketopyrrolopyrrole pigment with a different product name (physical properties) was used in Red Dispersion 1. Specifically, a formulation containing 10% by mass of a diketopyrrolopyrrole pigment (Irgazin Red D 3656 HD, manufactured by DIC Corporation, C.I. Pigment Red 254), 4.0% by mass of a resin component: polyvinyl butyral (BL-1), 85.7% by mass of a solvent: 3-methoxy-3-methyl-1-butanol, and 0.3% by mass of a dispersant, Aerosil RX50, was mixed and stirred, and then dispersed using a bead mill to prepare Red Dispersion 4. (Preparation of Red Dispersion 5) Using the formulation of Red Dispersion 4, Red Dispersion 5 was prepared by centrifuging at 10,000 G for 15 minutes to obtain a red dispersion with a D90 of 0.50 μm or less. (Preparation of Red Dispersion 6) Using the formulation of Red Dispersion 4, Red Dispersion 6 having a D90 of 0.50 μm or less was prepared by centrifuging at 10,000 G for 30 minutes.

[0051] (Preparation of Red Dispersion 7) A different diketopyrrolopyrrole pigment was used in the Red Dispersion 1, etc., but with a different product name (physical properties). Specifically, a formulation containing 10% by mass of diketopyrrolopyrrole pigment (Fuji Fast Red 8800, manufactured by Fuji Color Co., Ltd., C.I. Pigment Red 254), 4.0% by mass of resin component: polyvinyl butyral (BL-1), 85.7% by mass of solvent: 3-methoxy-3-methyl-1-butanol, and 0.3% by mass of dispersant Aerosil RX50 was mixed and stirred, and then dispersed using a bead mill to prepare Red Dispersion 7. (Preparation of Red Dispersion 8) Using the formulation of Red Dispersion 7, Red Dispersion 5 was prepared by centrifuging at 10,000 G for 15 minutes to obtain a red dispersion having a D90 of 0.50 μm or less. (Preparation of Red Dispersion 9) Using the formulation of Red Dispersion 7, Red Dispersion 6 having a D90 of 0.50 μm or less was prepared by centrifuging at 10,000 G for 30 minutes.

[0052] The oil-based ink compositions for ballpoint pens obtained in Examples 1 to 7, 8 to 17 and Comparative Examples 1 to 8, 9 to 13 were measured by the following methods at 25°C using a cone plate (CP25-1, Anton Paar) and a shear rate of 20 to 200 s －１ Ink viscosity at 25°C using a cone plate (CP25-1, Anton Paar) and a shear rate of 20 s －１ Viscosity at shear rate 200 s －１ The D90 particle size and average particle size of the carbon black and diketopyrrolopyrrole pigment were calculated using a laser diffraction / scattering particle size distribution analyzer (LA-960S, manufactured by Horiba, Ltd., using 3-methoxy-3-methyl-1-butanol as the dilution solvent during measurement).

[0053] Furthermore, for each of the oil-based ink compositions for ballpoint pens obtained in Examples 1 to 7, 8 to 17, and Comparative Examples 1 to 8, and 9 to 13, the writing performance after a centrifugal test and the writing performance after accelerated aging of the pen body were evaluated by the evaluation methods described below. Oil-based ballpoint pens having the following structures were also prepared, and the writing feel and the effect of suppressing blobbing were evaluated by the evaluation methods described below. These results are shown in Tables 1 and 2 below, respectively.

[0054] [25°C, shear rate 20-200 s －１ Ink viscosity value: Shear rate of 20 s using a rheometer (MCR302, manufactured by Anton Paar) with a cone plate (CP25-1, manufactured by Anton Paar) at 25°C －１ Viscosity at shear rate 200 s －１ Each of the obtained oil-based ink compositions for ballpoint pens was measured at 25°C at a shear rate of 20 to 200 s using a rheometer (MCR302, manufactured by Anton Paar) with a cone plate (CP25-1, manufactured by Anton Paar). －１ The viscosity values ​​of each ink were measured between the shear rate of 20 s and the ink viscosity value of 100 s. －１ / shear rate 200 s －１ ) was calculated.

[0055] (Method for evaluating writing performance after centrifugation test) The prepared ink was filled into an SXR-72-05 tube manufactured by Mitsubishi Pencil Co., Ltd. to obtain an oil-based ballpoint pen refill. Each ballpoint pen refill was prepared, consisting of a ballpoint pen tip with a stainless steel holder, a carbide ball, a ball diameter of 0.5 mm, a clearance (gap) between the ball and the crimped portion of 13 μm, a sealing surface of 70 μm, and a joint connecting the containing tube and the tip. The obtained refill was set in a centrifuge and the pen tip was subjected to 130 G for 84 hours. After removal, 100 spiral strokes of a 20 mm diameter were performed, and the writing performance was evaluated according to the following evaluation criteria. Evaluation criteria: A: The written line was good and there was no smearing or the like. B: The written line smeared within 1 to 5 strokes and then recovered. C: The written line smeared within 6 to 20 strokes and then recovered. D: The written line faded after 20 to 99 laps and then recovered. E: The written line did not recover within 100 laps, or writing was impossible.

[0056] (Method for evaluating the writability of the pen body after accelerated aging) In the same manner as in the method for evaluating the writability after the centrifugal test described above, the ink was filled into a tube to obtain an SXR-72-05 refill. The obtained refill was left facing down in an environment of 50°C and a relative humidity of 80% for 4 months, and then removed. After which spiral writing was performed and the writability was evaluated according to the following evaluation criteria. Evaluation criteria: A: The written line was good and there was no smearing. B: The written line smeared within 1 to 5 revolutions and then recovered. C: The written line smeared within 6 to 20 revolutions and then recovered. D: The written line smeared within 20 to 99 revolutions and then recovered. E: The written line did not recover within 100 revolutions, or writing was impossible.

[0057] (Preparation of oil-based ballpoint pens) Using the barrel of an oil-based ballpoint pen (manufactured by Mitsubishi Pencil Co., Ltd., product name: SA-R), each refill consisting of a polypropylene ink reservoir having an inner diameter of 1.7 mm and a length of 115 mm, a ballpoint pen tip (holder: stainless steel, ball: cemented carbide ball, ball diameter 0.7 mm), a clearance (gap) between the ball and the crimped part of 13 μm, a sealing surface of 70 μm, and a joint connecting the reservoir tube and the tip was filled with each of the oil-based ink compositions obtained above to prepare oil-based ballpoint pens (five of each type).

[0058] (Method for Evaluating Writing Feel) The writing feel was evaluated using the oil-based ballpoint pen prepared above. The writing feel was evaluated by measuring the writing resistance value (Heyden value) using the following method. Using a surface property measuring instrument (HEIDON-14D, Shinto Chemical Co., Ltd.), the writing resistance value (Heyden value) was measured three times during a 10 cm linear motion under conditions of a writing speed of 3.3 m / min, a load of 100 g, and a writing angle of 90°, and the average value was calculated. Standard paper (white paper) was used as the writing paper. A lower writing resistance value (Heyden value) indicates less writing resistance and a better writing feel (writing feel).

[0059] (Method for evaluating the effect of suppressing blobbing) Using the oil-based ballpoint pen, a writing test was carried out on a writing test paper conforming to JIS standard P3201 under the conditions of a writing speed of 4.5 m / min, an angle of 60°, a writing load of 40 g, no rotation, and intermittent writing of one round written and one round rest, using a writing tester conforming to JIS standard S6039-2001, by spiral writing. The effect of suppressing blobbing after writing 5 m was evaluated according to the following criteria. Evaluation criteria: A: No line blobbing or adhesion blobbing, good line condition. B: Almost no line blobbing or adhesion blobbing, good line condition. C: Noticeable blobbing occurred in either the line blobbing or adhesion blobbing. D: Noticeable blobbing occurred in both the line blobbing and adhesion blobbing, resulting in a dirty line.

[0060]

[0061]

[0062] As is clear from the results of the evaluation of writing performance after the centrifuge test, the evaluation of writing performance of the pen body after accelerated aging, the writing feel (writing taste), and the effect of suppressing blobbing in Tables 1 and 2 above, it was confirmed that the oil-based ink compositions for ballpoint pens using carbon black or a diketopyrrolopyrrole pigment as a colorant in Examples 1 to 7 and 8 to 17, which fall within the scope of the present disclosure, are oil-based ink compositions for ballpoint pens and oil-based ballpoint pens that produce good written lines without blurring or the like, have excellent stability over time, and are able to achieve a high degree of both a smooth writing feel and high quality of drawn lines, compared to Comparative Examples 1 to 8 and 9 to 13, which fall outside the scope of the present disclosure.

[0063] An oil-based ink composition for a ballpoint pen suitable for an oil-based ballpoint pen and an oil-based ballpoint pen equipped with the same can be obtained.

Claims

1. An oil-based ink composition for a ballpoint pen containing at least carbon black, a resin component, and a solvent, the oil-based ink composition for a ballpoint pen having a viscosity measured at 25°C using a cone plate at a shear rate of 20 to 200 s －１ The shear rate of the rheometer is 20 s at 25 ° C. －１ Viscosity at shear rate 200 s －１ and the carbon black has a 90% particle size of 0.50 μm or less in a cumulative particle size distribution based on volume.

2. An oil-based ink composition for a ballpoint pen containing at least a diketopyrrolopyrrole pigment (DPP), a resin component, and a solvent, the oil-based ink composition for a ballpoint pen having a viscosity measured at 25°C using a cone plate at a shear rate of 20 to 200 s －１ The shear rate of the rheometer is 20 s at 25 ° C. －１ Viscosity at shear rate 200 s －１ and the diketopyrrolopyrrole pigment (DPP) has a 90% particle size of 0.50 μm or less in a cumulative particle size distribution on a volume basis.

3. The oil-based ink composition for ballpoint pens according to claim 1 or 2, characterized in that it contains a resin having a mass average molecular weight of less than 40,000 as the resin component.

4. An oil-based ballpoint pen, characterized by being equipped with the oil-based ink composition for ballpoint pens according to claim 1 or 2.

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