Water-based ballpoint pens and ink compositions for water-based ballpoint pens

Abstract

To provide an aqueous ballpoint pen which suppresses leakage of ink, has an excellent writing feel, and forms thick handwriting.SOLUTION: An aqueous ballpoint pen has a ballpoint pen tip at a tip portion of an ink storage cylinder, and stores an ink composition for aqueous ballpoint pens containing water, a colorant and organic resin particles in the ink storage cylinder, where the organic resin particles are olefinic resin particles, and when the ink consumption of the aqueous ballpoint pen per 100 m is represented by A (mg) and the ball diameter is represented by B (mm), the relationship of 110≤A / B≤600 holds.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a water-based ballpoint pen, and more particularly to a water-based ballpoint pen that suppresses ink leakage, has excellent writing feel, and produces dark writing lines.

Background Art

[0002] As a ballpoint pen ink composition used in conventional ballpoint pens, as disclosed in Patent Document 1, Japanese Patent No. 3338222 "Ink for a direct liquid knock-type water-based ballpoint pen", which improves moisture retention and prevents ink from leaking or dripping from the pen tip even when the pen is left uncapped, or as disclosed in Patent Document 2, Japanese Patent Publication No. 6-47661 "Ballpoint pen ink composition", which has an ink viscosity of 50 to 2000 cps, are disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when these water-based ballpoint pen inks are used to form retractable ballpoint pens or ballpoint pens in the cap-off state, there is a risk of ink dripping due to ink leakage from the tip of the chip when the ballpoint pen is in a downward state.

[0005] By the way, ballpoint pens displayed in a display case are taken out by a user, used for test writing or checking knock operation, etc., and then returned to the same display case.

[0006] In the case of ballpoint pens with a retractable cap, if the pen is returned to the display case with the ballpoint tip extended, the ball on the tip will come into contact with the bottom of the display case. As the process of testing the pen and returning it to the display case is repeated, multiple pens will be stacked on top of the first pen returned. As a result, the weight of the stacked pens causes the ball to move towards the bottom wall of the ball-holding chamber due to the impact of the ballpoint tip contacting the bottom of the display case. This creates a gap between the ball and the inner wall of the tip, through which ink can drip, causing ink leakage and staining the display case, as well as the pens in other cases.

[0007] To address the aforementioned ink leakage, increasing the ink viscosity reduces ink consumption, resulting in a darker writing line and a poorer writing experience. Alternatively, a tip-based solution involves using a coil spring or similar mechanism to constantly press the ball against the inner wall of the tip, thereby closing the tiny gap between the ball and the tip and suppressing ink dripping. However, this increases manufacturing costs, can easily lead to poor ball rotation, and negatively impacts the writing experience.

[0008] The present invention aims to provide a water-based ballpoint pen that suppresses ink leakage, offers excellent writing feel, and produces dark, bold lines. [Means for solving the problem]

[0009] To solve the above problems, the present invention 1. A water-based ballpoint pen having a ballpoint pen tip at the front of an ink reservoir, and containing an aqueous ballpoint pen ink composition comprising water, a colorant, and organic resin particles in the ink reservoir, wherein the organic resin particles are olefin-based resin particles, and when the ink consumption per 100m of the aqueous ballpoint pen is A (mg) and the ball diameter is B (mm), the relationship 110 ≤ A / B ≤ 600 holds true. 2. The water-based ballpoint pen according to paragraph 1, characterized in that the amount of movement of the ball of the ballpoint pen tip in the longitudinal axis direction is 20 to 50 μm. 3. The water-based ballpoint pen according to paragraph 1 or 2, characterized in that the olefin resin particles are polyethylene resin particles. 4. The ink viscosity of the water-based ballpoint pen ink composition is such that, at 20°C and a shear rate of 1.92 sec, -1 A water-based ballpoint pen according to any one of paragraphs 1 to 3, characterized in that the pressure is 500 to 5000 mPa·s. 5. The water-based ballpoint pen according to any one of paragraphs 1 to 4, characterized in that the coloring agent is pigment particles, and when the average particle diameter of the olefin resin particles is X μm and the average particle diameter of the pigment particles is Y μm, Y / X ≤ 1.0. 6. The aqueous ballpoint pen according to any one of paragraphs 1 to 5, characterized in that the aqueous ballpoint pen ink composition contains a phosphate ester surfactant or a fatty acid. 7. A retractable water-based ballpoint pen characterized in that a water-based ballpoint pen described in any one of paragraphs 1 to 6 is slidably disposed inside the barrel, and the tip of the ballpoint pen tip can extend and retract from the tip of the barrel. [Effects of the Invention]

[0010] This invention has made it possible to obtain a water-based ballpoint pen that suppresses ink leakage even when the ballpoint pen is returned to the display case with the ballpoint pen tip protruding, creating a gap between the ball and the inner wall of the tip, while also providing a smooth writing experience and dark lines. [Best Mode for Carrying Out the Invention]

[0011] The present invention is characterized by a water-based ballpoint pen having a ballpoint pen tip at the front of an ink reservoir, and containing an aqueous ballpoint pen ink composition consisting of water, a colorant, and organic resin particles in the ink reservoir, wherein the organic resin particles are olefin-based resin particles, and when the ink consumption per 100m of the water-based ballpoint pen is A (mg) and the ball diameter is B (mm), the relationship 110 ≤ A / B ≤ 600 is observed.

[0012] In this invention, darker lines can be achieved by increasing ink consumption. However, increasing ink consumption presents challenges in writing performance, such as ink leakage, smudging, and blotting due to the gap between the ball and the inner wall of the tip. Therefore, the relationship between the specifications of the ballpoint pen tip and ink consumption was investigated. It was found that as the ball diameter increases, the gap between the ball and the inner wall of the tip increases, affecting ink leakage. Thus, the relationship between ink consumption per 100m and ball diameter is important. The inventors of this invention investigated and found that when the ink consumption per 100m of a water-based ballpoint pen is A (mg) and the ball diameter is B (mm), the relationship 110 ≤ A / B ≤ 600 results in dark lines, improved writing feel, and good writing performance without smudging or blotting. Regarding ink consumption, a spiral writing test was conducted using five test samples at a writing speed of 4 m / min, under the conditions of 20°C, a writing angle of 65°, a writing load of 100 g, and on JIS P3201 writing paper. The average value of the ink consumption per 100 m was defined as the ink consumption per 100 m. Furthermore, while there are no particular limitations on the ball diameter, balls of approximately 0.1 to 2.0 mm are used.

[0013] However, while it is possible to achieve good writing performance by setting the relationship between ink consumption per 100m and ball diameter to 110 ≤ A / B ≤ 600, and it is possible to suppress ink leakage to some extent, as mentioned above, in the case of a ballpoint pen with a retractable cap, if the ballpoint pen tip is returned to the display case with the ballpoint pen tip extended, and the ballpoint pen is returned to the same display case after being used for test writing, etc., multiple ballpoint pens will be stacked on top of the ballpoint pen that was returned first. As a result, it is not sufficient to suppress ink leakage due to the weight of the stacked multiple ballpoint pens. Therefore, the inventor of the present invention conducted diligent research and found that by using olefin-based resin particles among resin particles, it was possible to significantly improve ink leakage suppression while also improving the writing feel.

[0014] The olefin resin particles used in this invention, when included, create a physical obstruction in the gap between the ball and the inner wall of the tip, thereby suppressing ink leakage. Furthermore, because the olefin resin particles have lower hardness compared to inorganic materials, they partially deform and adhere closely to each other, forming a weak aggregate structure that suppresses ink leakage. Moreover, because the olefin resin particles are hydrocarbon compounds and nonpolar, aggregation easily occurs in water, and it is easy to form an optimized aggregate structure that suppresses ink leakage without causing problems such as insufficient ink volume. Therefore, it is presumed that an ink leakage suppression effect can be obtained while maintaining ink consumption. Furthermore, because the olefin resin particles have a high melting point, they tend to exist stably even in high-temperature environments, and in high-pressure environments, they are easily deformed but not easily altered. Therefore, they remain stable even when sandwiched between the ball and the ball seat, providing a cushioning effect, improving writing feel, and suppressing wear of the ball seat, making them suitable for use.

[0015] Therefore, in the present invention, the relationship between ink consumption per 100m and ball diameter is set to 110 ≤ A / B ≤ 600, and by including olefin resin particles in the aqueous ink composition, even if the ballpoint pen is returned to the display case with the ballpoint pen tip protruding, creating a gap between the ball and the inner wall of the tip, ink leakage is suppressed, and it is possible to achieve a smooth writing feel, dark lines, and good writing performance.

[0016] Furthermore, regarding the relationship between ink consumption per 100m and ball diameter, to improve darker lines and writing feel, it is preferable to have A / B ≤ 120. To improve writing performance by including olefin resin particles, which can reduce ink dripping, bleeding, and blotting from the gap between the ball and the tip, it is preferable to have A / B ≤ 500. Therefore, it is preferable to have 120 ≤ A / B ≤ 500, and considering darker lines and ink dripping, it is preferable to have 150 ≤ A / B ≤ 450. To give a specific example, if the ball diameter is B (mm) = 1.0 (mm), the ink consumption A (mg) per 100m can be set to A = 110 to 600 (mg), thus achieving the relationship 110 ≤ A / B ≤ 600.

[0017] (Olefin resin particles) Examples of materials for the olefin resin particles include polyolefins such as polyethylene, polypropylene, and polybutene, as well as mixtures thereof. Among these, considering ink leakage suppression and improving writing feel, it is preferable to use polyethylene. Specifically, examples include low-density polyethylene, high-density polyethylene, low-molecular-weight polyethylene, modified polyethylene, modified high-density polyethylene, etc. Among them, considering the ink leakage suppression effect, low-density polyethylene, low-molecular-weight polyethylene, and modified polyethylene are preferable. In particular, low-density polyethylene has a lower melting point and a softer property than other types of polyethylene. Therefore, polyethylene particles are likely to adhere closely, it is difficult to form gaps between particles, and it is difficult for ink to leak. Thus, low-density polyethylene is preferable. Furthermore, because low-density polyethylene is soft, it is easy to obtain a cushioning effect between the ball and the ball seat, which improves the writing feel and suppresses wear of the ball seat. Therefore, it can be suitably used. The olefin resin particles may contain materials other than polyolefins as required.

[0018] Regarding the average particle diameter of the olefin resin particles, the smaller the average particle diameter, the easier it is for them to adhere to each other and form a weak aggregation structure, and the easier it is to suppress ink leakage. Therefore, it is preferably 10 μm or less, more preferably 8 μm or less. Considering relaxing the rotational resistance of the ball, improving the writing feel, and suppressing wear of the ball seat, it is even more preferably 7 μm or less. Also, because an aggregation structure is formed by hydrogen bonds, even if the particles themselves are relatively small, it is easy to form a macroscopic aggregation structure. Therefore, an excellent ink leakage suppression effect can be obtained even when using a finer particle diameter. On the other hand, if the average particle diameter is too small, the ink leakage suppression effect is likely to be inferior. Therefore, the average particle diameter is preferably 0.1 μm or more, more preferably 3 μm or more. Also, the average particle diameter can be measured by the particle diameter (D50) at 50% volume accumulation of the particle size distribution measured by the laser diffraction method using a laser diffraction type particle size distribution measuring machine (trade name "Microtrac HRA9320-X100", manufactured by Nikkiso Co., Ltd.) or the Coulter counter method (manufactured by Coulter).

[0019] Regarding the shape of the olefin resin particles, spherical or irregular-shaped particles can be used. Considering reducing the frictional resistance, spherical resin particles are preferred. The spherical resin particles referred to here are not limited to true spheres, and may also be substantially spherical resin particles, substantially ellipsoidal resin particles, etc.

[0020] Also, the olefin resin particles are preferably made into an olefin dispersion preliminarily dispersed in water or the like. Regarding the pH value of the olefin dispersion, 7 to 11 is preferred. This is because it is easy to improve the dispersion stability of the olefin resin particles and the stability against ink components such as colorants and surfactants. Considering more, a pH value of 7 to 10 is more preferred.

[0021] Specific examples of the olefin resin particles include Chem Pearl M-200 (low-density polyethylene dispersion, average particle diameter 6 μm, pH value 9), W-100 (low-molecular-weight polyethylene dispersion, average particle diameter 3 μm, pH value 9), W-200 (low-molecular-weight polyethylene dispersion, average particle diameter 6 μm, pH value 9), W300 (low-molecular-weight polyethylene dispersion, average particle diameter 3 μm, pH value 9), W-310 (low-molecular-weight polyethylene dispersion, average particle diameter 9.5 μm, pH value 8), W-400 (low-molecular-weight polyethylene dispersion, average particle diameter 4 μm, pH value 9), W-800 (low-molecular-weight polyethylene dispersion, average particle diameter 8 μm, pH value 9), W900 (low-molecular-weight polyethylene dispersion, average particle diameter 0.6 μm, pH value 11), S300 (average particle diameter 0.5 μm, carboxylic acid-modified polyolefin dispersion, pH value 10), SA100 (average particle diameter 1 μm, carboxylic acid-modified polyolefin dispersion, pH value 10) (manufactured by Mitsui Chemicals, Inc.), Nopco Maru MS-40 (average particle diameter 1.0 μm, polyethylene paraffin wax), Nopco Maru PEM-17 (average particle diameter 0.01 μm, polyethylene wax) (manufactured by San Nopco Ltd.), CERAFLOUR950 (modified polyethylene resin, average particle diameter 9 μm), 925 (modified polyethylene resin, average particle diameter 6 μm), 929 (modified polyethylene resin, average particle diameter 8 μm) (manufactured by BYK Co., Ltd.), etc.

[0022] Furthermore, the content of the olefin resin particles is more preferably 0.01 to 10.0% by mass relative to the total amount of the ink composition. This is because if the content of the olefin resin particles is less than 0.01% by mass, it is difficult to suppress ink leakage, and if it exceeds 10.0% by mass, the aggregated structure tends to become stronger, which tends to affect the writing feel and drying performance. Further considerations suggest that 0.02 to 5.0% by mass is preferable, 0.03 to 1.0% by mass is particularly preferable, and most preferably 0.05 to 0.5% by mass is preferable.

[0023] Furthermore, it is preferable that the amount of movement (clearance) of the ball in the vertical axis direction of the ballpoint pen tip used in the present invention be 15 to 50 μm. This is because if it is less than 15 μm, it becomes difficult to set the relationship 110 ≤ A / B, making it difficult to obtain dark writing lines and a good writing feel, and if it exceeds 50 μm, it becomes difficult to set the relationship A / B ≤ 600, which tends to affect the ink drip performance. Considering this further, it is preferable to set it to 20 to 45 μm, and if considering it even further, it is preferable to set it to 25 to 40 μm. The amount of movement (clearance) of the ball in the vertical axis direction of a ballpoint pen tip refers to the distance the ball can move along the vertical axis direction of the ballpoint pen tip body.

[0024] Regarding ink viscosity, under conditions of 20°C and a shear rate of 1.92 sec, -1 The ink viscosity is preferably between 500 and 5000 mPa·s. This is because if the ink viscosity is less than 500 mPa·s, the viscosity is too low, making it difficult to suppress ink leakage. If it exceeds 5000 mPa·s, the writing quality, ball bearing wear suppression, and writing quality tend to be poor, ink consumption is low, and it is difficult to obtain dark lines. Considering all these factors, 1000 to 3500 mPa·s is preferable.

[0025] Furthermore, it is preferable to use a shear viscosity modifier as an ink viscosity modifier. Examples of shear viscosity modifiers include cross-linked acrylic acid polymers and polysaccharides such as xanthan gum, gellan gum, succinoglycan, guar gum, locust bean gum, λ-carrageenan, cellulose derivatives, and dieutan gum. Examples of associated thickeners include polyester-based, polyether-based, urethane-modified polyether-based, and polyaminoplast-based thickeners depending on the associated hydrophobic group, as well as alkali-swelling associated thickeners and nonionic associated thickeners. These shear viscosity modifiers may be used individually or in combination of two or more types.

[0026] Among shear viscosity-reducing agents, polysaccharides or associated thickeners are preferable when considering the effect of suppressing ink leakage. Furthermore, among polysaccharides, xanthan gum and succinoglycans are preferred because, when used in combination with olefin resin particles, they make it easier to form a three-dimensional structure, thereby providing a better ink leakage suppression effect. Furthermore, regarding the associate type thickener, an alkali-swelling associate type thickener is preferred. This is because, among associate type thickeners, it has a high efficiency in developing ink viscosity, and also has high adsorption properties to the olefin-based resin particles. It is easier to form a crosslinked structure, and a denser three-dimensional structure is formed, which improves ink leakage suppression and pigment dispersibility, thereby improving the ink's stability over time.

[0027] Furthermore, alkali-swelling-associating thickeners include polymerizable resins of monomers or copolymers containing various polymerizable monomers having carboxyl groups, such as acrylic acid, methacrylic acid, and maleic acid, as the mechanism for exhibiting alkali-swelling properties. These are preferred because they have stable swelling properties over a long period of time, which can be expected to improve ink leakage suppression and pigment dispersibility, thereby improving the long-term stability of the ink. In particular, those composed of three monomers, vinyl acetate, methyl metal relate, and methacrylic acid, are preferred.

[0028] Furthermore, the content of the shear viscosity reducing agent is more preferably 0.01 to 5.0% by mass relative to the total amount of the ink composition. This is because if the content of the shear viscosity reducing agent is less than 0.01% by mass, the ink thickening effect is insufficient, making it difficult to suppress ink leakage, and if it exceeds 5.0% by mass, the ink viscosity tends to increase, which can easily affect the suppression of ball bearing wear, writing responsiveness, writing feel, and dry-up performance. Further considerations suggest that 0.1 to 2.0% by mass is preferable, and most preferably 0.1 to 1.0% by mass.

[0029] The colorants used in this invention are not particularly limited, but examples of pigments include inorganic, organic, and processed pigments. Specifically, examples include carbon black, aniline black, ultramarine, lead yellow, titanium dioxide, iron oxide, phthalocyanine, azo, quinacridone, quinophthalone, surene, triphenylmethane, perinone, perylene, dioxazine, microcapsules, aluminum pigments, pearl pigments, fluorescent pigments, phosphorescent pigments, and complementary pigments. As for dyes, direct dyes, acid dyes, basic dyes, metal-containing dyes, and various salt-forming type dyes can be used. These pigments and dyes may be used individually or in combination of two or more.

[0030] Regarding the coloring agent, it is preferable that it contains carbon black with an oil absorption capacity of 100g or more. This is because oil absorption capacity is a substitute characteristic that represents the structure of the carbon black, and the larger the oil absorption capacity, the larger the structure. Carbon black with an oil absorption capacity of 100g or more has a large structure, which suppresses penetration into the paper surface, and the carbon black itself remains on the paper surface, resulting in a dark and clear writing line. Furthermore, the oil absorption capacity of the carbon black is preferably 100 to 300g ( / 100g), because if it exceeds 300g ( / 100g), sedimentation of the carbon black tends to occur. Furthermore, if you want to make the writing line darker and consider suppressing the sedimentation of the carbon black, an oil absorption capacity of 120 to 200g ( / 100g) is preferable. The oil absorption capacity of carbon black is a property that indicates the structure of carbon black, and refers to the amount of DBP (dibutyl phthalate) absorbed by a certain amount of dried carbon black, which is measured by the test method specified in JIS K6221.

[0031] Among these colorants, it is preferable to use pigment particles with an average particle diameter of 1 μm or less. This is because, when using olefin resin particles with an average particle diameter of 10 μm or less, if gaps occur between the olefin resin particles when they are in close contact with each other, it may affect ink leakage. By using pigment particles with an average particle diameter of 1 μm or less, these gaps can be filled, making it easier to suppress ink leakage. More specifically, pigment particles with an average particle diameter of 0.5 μm or less are preferable. Furthermore, while spherical or irregularly shaped pigment particles can be used, spherical pigment particles are preferable, and more preferably spherical pigment resin particles, in order to reduce frictional resistance. The term "spherical pigment particles" here is not limited to perfectly spherical particles; approximately spherical pigment particles or approximately ellipsoidal pigment particles are also acceptable. Furthermore, the average particle size of pigment particles can be measured using the laser diffraction method with a laser diffraction particle size distribution analyzer (product name "MicrotracHRA9320-X100", Nikkiso Co., Ltd.), specifically the particle size at 50% volume accumulation (D50).

[0032] Furthermore, when the average particle diameter of the olefin resin particles is X μm and the average particle diameter of the pigment particles is Y μm, it is preferable that the relationship Y / X ≤ 1.0. This is because when the olefin resin particles are in close contact with each other and gaps occur between them, these gaps are difficult to fill, which can easily affect ink leakage. More specifically, it is preferable that the relationship Y / X ≤ 0.5, and more preferably 0.001 ≤ Y / X ≤ 0.5.

[0033] Furthermore, it is preferable to use dextrin to suppress ink leakage. This is because, when dextrin is used, the ink at the pen tip forms a film when it dries, which effectively suppresses ink leakage through the gap between the ball and the inner wall of the tip.

[0034] Furthermore, a weight-average molecular weight of dextrin between 5,000 and 120,000 is more preferable. If the weight-average molecular weight exceeds 120,000, the film formed on the pen tip becomes hard, and the writing tends to be streaky when starting to write after drying. On the other hand, if the weight-average molecular weight is less than 5,000, the hygroscopicity tends to be high, the film on the pen tip tends to be soft, and it tends to be difficult to obtain a sufficient ink leakage suppression effect. Moreover, if the weight-average molecular weight is less than 20,000, the film tends to be thin, so a weight-average molecular weight between 20,000 and 120,000 is most preferable.

[0035] The dextrin content is preferably 0.1 to 5.0% by mass relative to the total amount of the ink composition. This is because if the content is less than 0.1% by mass, the ink leakage effect tends not to be sufficiently obtained, and if it exceeds 5.0% by mass, it tends to be difficult to dissolve in the ink. If solubility in the ink is considered more important, 0.1 to 3.0% by mass is preferred, and if ink leakage is considered more important, 1.0 to 3.0% by mass is most preferred.

[0036] Furthermore, water-soluble solvents are used, taking into consideration the solubility of water and the prevention of water evaporation and drying. Examples include polyhydric alcohol solvents such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, and glycerin; alcohol-based solvents such as methanol, ethanol, 1-propanol, 2-propanol, isopropanol, isobutanol, t-butanol, allyl alcohol, 3-methyl-1-buty-3-ol, ethylene glycol monomethyl ether acetate, and other higher alcohols; and glycol ether-based solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 3-methoxybutanol, and 3-methoxy-3-methylbutanol. Among these, polyhydric alcohol solvents are preferred when considering the solubility with the olefin resin particles used in the present invention. A polyhydric alcohol solvent is a solvent in which two or more hydroxyl groups are bonded to opposite carbon atoms of an aliphatic or alicyclic compound, and among these, it is most preferable that it contains at least a polyhydric alcohol having divalent or trivalent hydroxyl groups. These may be used individually or in mixtures of two or more.

[0037] Regarding the content of the water-soluble solvent, considering solubility, ink leakage, and bleeding, 0.1 to 25.0% by mass of the total ink composition is preferable. However, considering ink leakage as in the present invention, 7.0 to 20.0% by mass or less is preferable. This is because hydrogen bonding by the solvent can easily disrupt the aggregated structure, which can affect the ink leakage suppression effect of the olefin resin particles.

[0038] Furthermore, it is preferable to use phosphate ester surfactants and fatty acids in order to improve lubricity and make the ball rotation smoother, thereby reducing wear on the ball seat and improving writing quality. In particular, it is preferable to use phosphate ester surfactants that have a phosphate group. This is because the phosphate group adsorbs to metal, further improving lubricity and making it easier to reduce wear on the ball seat and improve writing quality. Examples of phosphate ester surfactants include styrene-phenol, nonylphenol, lauryl alcohol, tridecyl alcohol, octylphenol, and hexanol. Among these, it is preferable to use phosphate ester surfactants that do not have a phenyl skeleton, as those with a phenyl skeleton tend to affect lubricity due to steric hindrance. If lubricity is a priority, lauryl alcohol and tridecyl alcohol phosphate ester surfactants are preferred. These may be used individually or in combination of two or more types.

[0039] Furthermore, specific examples of phosphate ester surfactants include Prysurf A212C (tridecyl alcohol-based), A208B (lauryl alcohol-based), A213B (lauryl alcohol-based), A208F (short-chain alcohol-based), A215C (tridecyl alcohol-based), and A219B (lauryl alcohol-based) from the Prysurf series (Daiichi Kogyo Seiyaku Co., Ltd.). Specific examples of fatty acids include OS Soap, NS Soap, FR-14, and FR-25 (Kao Corporation). These phosphate ester surfactants and fatty acid salts may be used individually or in combination of two or more types.

[0040] Furthermore, in order to produce darker handwriting using pigment particles, it is preferable to use one or more surfactants selected from silicone-based surfactants, acetylene glycol-based surfactants, fluorine-based surfactants, and dialkyl sulfosuccinates. This is because improved penetration into the paper allows the pigment particles to remain on the paper surface, making it easier to obtain darker, clearer handwriting. Therefore, as in the present invention, using the surfactants in a relationship of 110 ≤ A / B ≤ 600 makes it easier to obtain darker, clearer handwriting. Among these, it is preferable to use fluorine-based surfactants, because they can reduce surface tension the most and easily improve penetration into the paper, making it easier to obtain darker handwriting.

[0041] Furthermore, silicone-based surfactants include polyether-modified, methylstyryl-modified, alkyl-modified, higher fatty acid ester-modified, hydrophilic special-modified, fluorine-modified, and silicone oils such as dimethyl and methylphenyl. Fluorine-based surfactants include perfluoro group butyl sulfonates, perfluoro group-containing carboxylates, perfluoro group-containing phosphate esters, perfluoro group-containing phosphate ester type formulations, perfluoroalkyl ethylene oxide adducts, perfluoro group / hydrophilic group / lipophilic group-containing oligomers, perfluoro group / hydrophilic group-containing oligomers, perfluoro group / lipophilic group-containing oligomers, perfluoroalkyl betaine, and perfluoroalkylamine oxide compounds. Among these, perfluoroalkyl ethylene oxide adducts are preferred. This is because fluorine-based surfactants of perfluoroalkyl ethylene oxide adducts can easily produce darker handwriting, making them preferable to use. In addition, the presence of an ethylene oxide group increases hydrophilicity, making them more soluble in water and tending to improve stability over time. These may be used individually or in combination of two or more types.

[0042] Other additives may be included as desired. Specifically, pH adjusters may be added to improve the long-term stability and lubricity of the colorants, as well as fixatives such as acrylic resin emulsions, urethane resin emulsions, and styrene-butadiene resin emulsions, pigment dispersants such as acidic resins, antibacterial agents such as 1,2-benzoisothiazolin-3-one, humectants such as urea and sorbitol, rust inhibitors such as benzotriazole, and chelating agents such as ethylenediaminetetraacetic acid. These can be used individually or in combination of two or more.

[0043] Furthermore, the pH value of the water-based ballpoint pen ink composition is preferably between 7.0 and 11.0. This is because if the pH value is below 7 and in the acidic range, it will affect the stability of ink components such as olefin resin particles, colorants, and surfactants, and will also affect the corrosion of metal ballpoint pen tips and balls. Similarly, if the pH value exceeds 10 and is strongly alkaline, it will also affect the stability of the ink components. Considering these factors, a pH value of 7.0 to 10.0 is more preferable.

[0044] Furthermore, to improve lubrication and obtain darker lines, it is preferable to set the arithmetic mean roughness (Ra) of the ball surface to 0.1 to 5 nm. This is because if the arithmetic mean roughness (Ra) exceeds this range, the ball surface becomes too rough, increasing the rotational resistance between the ball and the ball seat, which tends to result in poor writing quality. Conversely, if it falls below this range, insufficient ink adheres to the ball surface, making it difficult to obtain dark lines. Therefore, to improve writing quality and obtain dark lines, it is preferable to set the arithmetic mean roughness (Ra) of the ball surface to 0.1 to 5 nm. Taking this into consideration, it is preferable to set the arithmetic mean roughness (Ra) of the ball surface to 0.1 to 4 nm.

[0045] Regarding the arithmetic mean roughness of the ball surface, the arithmetic mean roughness (Ra) is calculated by taking a sample of the roughness curve measured by a surface roughness measuring instrument (model name SPI3800N, manufactured by Seiko Epson), extracting a reference length in the direction of the mean line, summing the absolute values ​​of the deviations from the mean line to the measurement curve for this sampled portion, and then averaging the result.

[0046] Furthermore, while the ball material is not particularly limited, examples include cemented carbide balls with tungsten carbide as the main component, as well as silicon carbide, alumina, zirconia, and silicon nitride. In particular, cemented carbide balls are preferred because they are low-cost, and ink adheres easily to the ball surface, making them advantageous when writing on writing surfaces with hand oils.

[0047] The present invention will now be explained with reference to examples. Example 1 Pigment dispersion (colored resin particles: average particle size 0.4 μm, solid content 34%) 20.0 parts by mass Water 59.2 parts by mass Olefin resin particles (low-density polyethylene dispersion, average particle size 6 μm, pH value 9, solid content 40%) 0.5 parts by mass Polyhydric alcohol (glycerin) 10.0 parts by mass Dextrin (weight-average molecular weight: 100,000) 1.0 part by mass Urea 5.0 parts by mass pH adjuster (triethanolamine) 2.0 parts by mass Ethylenediaminetetraacetic acid (EDTA) 0.5 parts by mass Lubricant (phosphate ester surfactant) 1.0 part by mass Rust inhibitor (benzotriazole) 0.5 parts by mass Shear viscosity reducing agent (succinoglycan) 0.3 parts by mass

[0048] A base ink was prepared by heating and stirring a pigment dispersion, water, olefin resin particles, polyhydric alcohol solvent, dextrin, urea, pH adjuster, ethylenediaminetetraacetic acid, lubricant, and rust inhibitor using a magnetic hot stirrer.

[0049] Subsequently, the base ink prepared above was heated, a shear viscosity reducing agent was added, and the mixture was thoroughly mixed and stirred using a homogenizer stirrer until it became uniform, thereby obtaining the aqueous ballpoint pen ink composition of Example 1. The ink viscosity of Example 1 was measured using a Brookfield DV-II viscometer (CPE-42 rotor) at 20°C with a shear rate of 1.92 sec. -1 When the ink viscosity was measured under the condition of a rotation speed of 0.5 rpm, it was found to be 1600 mPa·s. Furthermore, the pH value of Example 1 was measured at 20°C using an IM-40S pH meter (manufactured by Toa DKK Co., Ltd.), and the pH value was 8.5.

[0050] Examples 2-20 Examples 2 to 20 were obtained using the same procedure as in Example 1, except that the ink formulation was changed as shown in the table. The ink formulations and evaluation results are shown in the table. [Table 1] [Table 2]

[0051] Comparative Examples 1-8 Aqueous ballpoint pen ink compositions for Comparative Examples 1 to 8 were obtained using the same procedure as in Example 1, except that the ink formulation was changed as shown in the table. The ink formulations and evaluation results are shown in the table. [Table 3]

[0052] Testing and evaluation The aqueous ballpoint pen ink compositions prepared in Examples 1-20 and Comparative Examples 1-8 were filled into refills (1.0 g) in an ink reservoir (made of polypropylene) equipped with a ballpoint pen tip (made of polypropylene) that rotatably holds a 0.7 mm diameter ball at the tip of the ink reservoir via a tip holder (the ball's longitudinal axis movement of the ball tip is 30 μm, and the arithmetic mean roughness (Ra) of the ball surface is 1 nm). These refills were then mounted in a gel ink ballpoint pen (product name: G-knock) manufactured by Pilot Corporation, and the following tests and evaluations were performed. The writing feel and ink density were evaluated using JIS P3201 writing paper A as the writing test paper, and the following test methods were used. Furthermore, a spiral writing test was conducted using the water-based ballpoint pen ink composition of Example 1 as a water-based ballpoint pen. When the ink consumption per 100m was A (mg) and the ball diameter was B (mm), A = 170 (mg) and the ball diameter was B = 0.7 (mm), resulting in A / B = 243.

[0053] Ink Leakage Test: A 40g weight was attached to a gel ink ballpoint pen, the ballpoint pen tip was extended and pointed downwards, and the ball of the ballpoint pen tip was kept in contact with the bottom of a ballpoint pen display case. The pen was left for one day in an environment of 20°C and 65% RH, and the amount of ink leakage from the tip of the ballpoint pen was measured. Ink leakage of less than 5mg ···◎ Ink leakage of 5-15 mg ···○ Ink leakage exceeding 15mg but less than 30mg ···△ Ink leakage of 30mg or more... ×

[0054] Handwriting density: Handwriting was observed from documents written by hand. Thick and clear handwriting ···◎ Those with dark handwriting ···○ The handwriting is of a practically acceptable darkness. ···△ Faint handwriting ···×

[0055] Writing feel: Evaluated through a sensory test using handwriting. Extremely smooth ···◎ Smooth ···○ Smoothness that is acceptable for practical use...△ Heavy items ···×

[0056] As shown in the table, Examples 1 to 20 showed good performance in terms of ink leakage, ink density, and writing feel. Furthermore, when the water-based ballpoint pen ink compositions of Examples 1 to 20 were used in a gel ink ballpoint pen with a ballpoint pen tip specification that did not include elastic components such as coil springs, good performance was obtained in terms of ink leakage, ink density, and writing feel.

[0057] Furthermore, when a gel ink ballpoint pen with a ballpoint pen tip specification changed to one with a ball diameter of 1.0 mm was tested using the water-based ballpoint pen ink compositions of Examples 5, 6, and 9, good performance was obtained in terms of ink leakage, line density, and writing feel, achieving performance equivalent to or better than that of Examples 5, 6, and 9. Therefore, when using a ball with a ball diameter of 0.9 mm or more and increasing the ink discharge amount, a large gap is created between the ball and the inner wall of the tip, making it prone to ink leakage. However, the effects of the present invention are remarkable and it is suitable for use in such cases.

[0058] As shown in the table, in Comparative Examples 1, 2, 6, 7, and 8, ink leakage was severe and problematic in practical use because olefin-based resin particles were not used.

[0059] In comparative examples 3 and 4, A / B < 110, indicating a poor balance between ink consumption per 100m and ball diameter, resulting in faint lines and a poor writing experience.

[0060] In Comparative Example 5, 600

[0061] ​Generally, the ballpoint pen tip of a water-based gel ballpoint pen is equipped with a valve mechanism to suppress ink leakage. This mechanism uses an elastic member such as a coil spring to directly or via a pressing body to press a ball, which is rotatably held at the tip of the pen tip, against the inner wall of the tip edge. The pressure applied during writing creates a gap between the inner wall of the tip edge and the ball, allowing ink to flow out. The minute gap at the tip of the pen tip is also closed when not in use. However, by using a ballpoint pen ink composition that has a particularly high effect in suppressing ink leakage, as in the present invention, ink leakage can be suppressed even without the elastic member such as a coil spring. As a result, the resistance between the ball and the elastic member is eliminated, improving writing feel, improving ink fluidity, improving ink followability, and further reducing the number of parts, thus making it more effective. In particular, ink leakage suppression is considered even more important in retractable ballpoint pens, so this invention can be suitably used in such pens. [Industrial applicability]

[0062] The present invention can be used as a water-based ballpoint pen, and more specifically, it can be widely used as a water-based ballpoint pen with a cap, retractable pen, etc.

Claims

1. A water-based ballpoint pen having a ballpoint pen tip at the front of an ink reservoir, and containing an aqueous ballpoint pen ink composition comprising water, pigment particles, and organic resin particles in the ink reservoir, The organic resin particles are olefin-based resin particles made of low-density polyethylene, with an average particle diameter of 10 μm or less, and their content is 0.02 to 5.0% by mass relative to the total amount of the ink composition. When the average particle diameter of the olefin resin particles is X μm and the average particle diameter of the pigment particles is Y μm, then Y / X ≤ 1.

0. The viscosity of the aforementioned water-based ballpoint pen ink composition is 1.92 sec at 20°C. －１ In that case, the pressure is 500 to 5000 mPa·s. When the ink consumption per 100 m of the aforementioned water-based ballpoint pen is A (mg) and the ball diameter of the ballpoint pen tip is B (mm), the relationship 110 < A / B ≤ 600 is characterized. Water-based ballpoint pen.

2. The average particle diameter Y μm of the pigment particles is 1.0 μm or less, and the average particle diameter X μm of the olefin resin particles is 4 μm or more and 10 μm or less. The water-based ballpoint pen according to claim 1.

3. The ink composition further comprises a phosphate ester surfactant or a fatty acid. A water-based ballpoint pen according to claim 1 or 2.

4. The ink composition further comprises a phosphate ester surfactant that does not have a phenyl skeleton. A water-based ballpoint pen according to claim 1 or 2.

5. The ink composition further comprises a shear viscosity reducing agent. A water-based ballpoint pen according to any one of claims 1 to 4.

6. A water-based ballpoint pen according to any one of claims 1 to 5 is slidably disposed inside the barrel, A retractable water-based ballpoint pen characterized in that the tip of the ballpoint pen tip can extend and retract from the tip of the barrel.

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