Ink composition for water-based ballpoint pens and water-based ballpoint pens using the same

Abstract

To provide an ink composition for an aqueous ball point pen which is suppressed in abrasion of a ball seat at a high writing pressure (writing load of 300-500 gf), and has an excellent writing feeling by improving lubricity between a ball and a ball seat of a ball point pen tip and smoothing rotation of a ball in the ink composition for an aqueous ball point pen, and has an excellent writing property by suppressing point unevenness.SOLUTION: An ink composition for an aqueous ball point pen contains water, a coloring agent, polyoxyalkylene glyceryl ether, and a guar gum derivative.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an ink composition for a water-based ballpoint pen and an aqueous ballpoint pen using the same. [Background technology]

[0002] Ballpoint pens equipped with ballpoint pen tips using tip bodies made of stainless steel or other materials are well known. These tip bodies are made of stainless steel in consideration of abrasion resistance, corrosion resistance, cost, and the like. Furthermore, in order to improve the writing feel and prevent blurring and skipping of handwriting, Japanese Patent Laid-Open Publication No. 2006-282870 ("Water-Based Ink Composition for Ballpoint Pens"), Japanese Patent Laid-Open Publication No. 7-62288 ("Ink Composition for Water-Based Ballpoint Pens"), and Japanese Patent Laid-Open Publication No. 2003-192972 ("Ink for Water-Based Ballpoint Pens") propose ink compositions for water-based ballpoint pens containing various lubricants and the like. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] "JP 2006-282870 A" [Patent Document 2] "Unexamined Japanese Patent Publication No. 7-62288" [Patent Document 3] "JP Patent Publication No. 2003-192972" Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses that the inclusion of an isoprene sulfonic acid-acrylic acid copolymer allows for stable, uninterrupted ink ejection, resulting in a light writing feel and suppressing broken lines and smearing of handwriting. Patent Document 2 discloses that the inclusion of dibenzylidene sorbitol allows the ink to flow easily with the rotation of the ball, enabling smooth writing and improving writing performance such as smearing. Patent Document 3 discloses that the inclusion of N-acylamino acid and N-acylmethyltaurine improves the writing feel by adsorbing to the tip seat and reducing friction between the ball and tip seat as the ball rotates during writing. While this resulted in a somewhat smooth writing feel, it also accelerated wear on the ball seat, leaving room for improvement.

[0005] Furthermore, in recent years, ballpoint pen inks have become less viscous to improve the writing feel, but when writing with high writing pressure (high writing pressure resistance, writing load of 300-500 gf), the lubricity is easily affected, and the ball seat wears out, which can easily affect writing performance. Therefore, in order to further reduce the writing resistance between the writing tip and the writing surface, there is a demand for improved lubricity and improved resistance to high writing pressure.

[0006] The object of the present invention is to solve the above problems and to provide an aqueous ink composition for a ballpoint pen that has improved lubricity under high writing pressure (writing load of 300 to 500 gf), suppresses wear of the ball seat, improves writing feel, and suppresses dot unevenness, thereby providing excellent writing properties. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides "1. An ink composition for a water-based ballpoint pen, comprising water, a colorant, a polyoxyalkylene glyceryl ether, and a guar gum derivative. 2. The aqueous ink composition for a ballpoint pen according to claim 1, wherein the polyoxyalkylene glyceryl ether has an average number of moles of alkylene oxide added of 1 to 30. 3. The aqueous ballpoint pen ink composition according to item 1 or 2, wherein the weight-average molecular weight of the guar gum derivative is 500,000 to 5,000,000. 4. The aqueous ink composition for a ballpoint pen according to any one of items 1 to 3, characterized in that the aqueous ink composition for a ballpoint pen contains a surfactant. 5. The ink viscosity of the aqueous ballpoint pen ink composition is 20°C and a shear rate of 384 sec -1 5. The aqueous ballpoint pen ink composition according to any one of items 1 to 4, wherein the viscosity of the ink is 70 to 1000 mPa·s. 6. An aqueous ballpoint pen, comprising: a barrel containing the aqueous ballpoint pen ink composition according to any one of items 1 to 5; and a ballpoint pen tip at the tip of the barrel. [Effects of the Invention]

[0008] The present invention provides an aqueous ink composition for a ballpoint pen that has excellent writing properties by improving the lubricity between the ball and the ball seat of the ballpoint pen tip, thereby smoothing the rotation of the ball and thereby suppressing wear of the ball seat under high writing pressure (writing load of 300 to 500 gf), improving the writing feel, and further suppressing dot unevenness. BEST MODE FOR CARRYING OUT THE INVENTION

[0009]

[0023] In the present specification, the terms "parts," "%," "ratio," and the like, which indicate the composition, are based on mass unless otherwise specified, and the content is the mass % of the constituent components based on the mass of the ink composition.

[0010] The present invention is characterized by an aqueous ink composition for a ballpoint pen, which comprises water, a colorant, a polyoxyalkylene glyceryl ether, and a guar gum derivative. Each of these components is described below.

[0011] In the present invention, the combined use of polyoxyalkylene glyceryl ether and guar gum derivative improves the lubrication between the ball and the ball seat of the ballpoint pen tip, allowing the ball to rotate smoothly, thereby suppressing wear of the ball seat under high writing pressure (writing load of 300 to 500 gf), improving the writing feel, and further suppressing uneven dots, resulting in excellent writing performance.

[0012] (Polyoxyalkylene glyceryl ether) The polyoxyalkylene glyceryl ether used in the present invention is obtained by addition polymerization of alkylene oxide to glycerin or polyglycerin, and examples thereof include polyoxyalkylene glyceryl ether, polyoxyalkylene diglyceryl ether, and polyoxyalkylene triglyceryl ether.

[0013] Polyoxyalkylene glyceryl ether is a compound that has alkylene oxide in its structure and is hydrophilic and lipophilic. The highly polar hydrophilic group in its structure makes it easy to adsorb to the metal material of the ballpoint pen tip, forming a lubricating layer that improves lubricity, suppressing wear on the ball seat even under high writing pressure (writing load 300 to 500 gf) and improving the writing feel. When used in combination with a guar gum derivative (described later) and water, it swells in the ink and forms a dense three-dimensional structure, forming a viscous ink fluid lubrication layer. This creates an appropriate film thickness between the ball and the ball seat of the ballpoint pen tip, suppressing wear on the ball seat even under high writing pressure (writing load 300 to 500 gf) and improving the writing feel. Furthermore, it suppresses unevenness in the writing, resulting in excellent writing performance.

[0014] Furthermore, because polyoxyalkylene glyceryl ethers generally have low volatility, they can improve writing performance even when the writing tip is left exposed to the atmosphere. Furthermore, when pigment particles or resin particles are used as colorants, the polar groups in the polyoxyalkylene glyceryl ether structure adsorb to the particle surfaces, enabling the pigment particles or resin particles to be stably dispersed in the ink.

[0015] Furthermore, polyoxyalkylene glyceryl ethers include polyoxyethylene glyceryl ether, polyoxypropylene glyceryl ether, etc. Among these, polyoxyethylene glyceryl ethers are preferred because they have an ethylene group, which provides an excellent balance of hydrophilicity and lipophilicity, and they are stably dissolved in the aqueous ink composition, providing stability over time and making it easier to achieve the effects of the present invention stably over a long period of time. For this reason, it is preferred to use polyoxyethylene glyceryl ether.

[0016] In consideration of suppressing wear of the ball seat under high writing pressure (writing load of 300 to 500 gf), improving the writing feel, and further improving writing performance and stability over time, the polyoxyalkylene glyceryl ether preferably has an average number of alkylene oxide added moles (average number of alkylene oxide added moles) of 1 to 30, and in consideration of stability over time due to ink moisture absorption, the average number of alkylene oxide added moles is preferably 1 to 30. Furthermore, in consideration of suppressing wear of the ball seat under high writing pressure, improving the writing feel, and improving stability over time, the average number of alkylene oxide added moles is preferably 1 to 20, and more preferably 1 to 15.

[0017] In particular, in consideration of suppressing wear of the ball seat under high writing pressure, the average number of moles of ethylene oxide added is preferably 1 to 30, more preferably 1 to 20, even more preferably 1 to 15, still more preferably 2 to 8, and particularly preferably 3 to 7. In consideration of easily achieving the effects of the present invention, the structure of the polyoxyalkylene glyceryl ether is preferably a structure represented by the following formula (Chemical Formula 1) or (Chemical Formula 2). [ka] [ka] In the formula, m, n, o, p, w, x, y, and z each independently represent the number of alkylene oxides added. Here, m+n+o+p is the average number of moles of propylene oxide added, and w+x+y+z is the average number of moles of ethylene oxide added.

[0018] Among these, polyoxyalkylene glyceryl ether represented by Chemical Formula 2 is preferred because it is easily dissolved and stable in aqueous ink and therefore has a large effect on the improvement of the present invention.

[0019] The weight-average molecular weight of the polyoxyalkylene glyceryl ether is preferably 3,000 or less. This is because a weight-average molecular weight that is too large can affect stability over time and can increase the viscosity of the ink composition, affecting the writing feel and writing performance. Considering stability over time, writing performance, and writing performance, the weight-average molecular weight is preferably 1,500 or less. Furthermore, considering the prevention of ball seat wear under high writing pressure (writing load of 300 to 500 gf) and the writing performance, the weight-average molecular weight is preferably 1,000 or less, and more preferably 800 or less. Considering the prevention of ball seat wear under high writing pressure, the weight-average molecular weight is preferably 500 or less. On the other hand, a weight-average molecular weight that is too small can affect the prevention of ball seat wear under high writing pressure and pigment dispersibility, so the weight-average molecular weight is preferably 100 or more, and more preferably 200 or more. The weight average molecular weight is a value obtained by GPC (gel permeation chromatography) in terms of polystyrene.

[0020] Furthermore, if the content of polyoxyalkylene glyceryl ether is less than 1% by mass of the total ink composition, there is a risk that the effects of suppressing wear of the ball seat under high writing pressure, writing feel, writing performance, and pigment dispersibility may not be obtained, while if it exceeds 50% by mass, there is a risk that the stability over time and writing feel may be affected, so the content is preferably 1 to 50% by mass, more preferably 5 to 45% by mass, of the total ink composition. Furthermore, in consideration of the balance between suppressing wear of the ball seat and stability over time, 10 to 40% by mass is preferred, and 15 to 40% by mass is most preferred.

[0021] (Guar gum derivatives) The guar gum derivative used in the present invention is compatible with and stably dissolved in polar solvents such as polyoxyalkylene glyceryl ether, and can therefore be used in combination with guar gum derivatives. In the present invention, by mixing with water and polyoxyalkylene glyceryl ether, the ink swells in the ink, forming a three-dimensional structure, resulting in an ink thickening effect. Furthermore, these components form a viscous ink fluid lubrication layer, forming an appropriate film thickness between the ball and the ball seat of the ballpoint pen tip, suppressing ball seat wear even under high writing pressure (writing load 300-500 gf) and improving writing feel. Furthermore, when using a ballpoint pen, strong shear is likely to be applied during writing, and the three-dimensional structure temporarily dissolves due to impacts such as shearing of the ball. Therefore, shear reduces the ink viscosity, improving writing feel and suppressing unevenness in writing, thereby maintaining good writing performance, making it suitable for use in ballpoint pens. Furthermore, when pigment particles or resin particles are used, the high-density three-dimensional structure makes it easy for the pigment particles or resin particles to be dispersed stably, and the dispersion stability of the particles can be easily maintained.

[0022] Examples of guar gum derivatives include hydroxyalkyl guar gum, carboxymethyl hydroxyalkyl guar gum, and cationized guar gum. In consideration of compatibility with polyoxyalkylene glyceryl ether and in order to more easily obtain the effects of the present invention, hydroxyalkyl guar gum is preferred, and from this perspective, hydroxypropyl guar gum is even more preferred.

[0023] Hydroxyalkyl guar gum is highly compatible with polyoxyalkylene glyceryl ether, and thus provides stable swelling action in the ink. To facilitate the effects of the present invention, guar gum is used as a raw material and reacted with sodium hydroxide and propylene oxide, and the degree of substitution of the hydroxyalkyl is preferably in the range of 0.1 to 2.0, more preferably in the range of 0.3 to 1.5, and even more preferably in the range of 0.5 to 1.3.

[0024] The weight-average molecular weight of the guar gum derivative is preferably 500,000 to 5,000,000, taking into consideration that the guar gum derivative swells in the ink and easily forms a stable three-dimensional structure, and compatibility stability when mixed with water and polyoxyalkylene glyceryl ether, and more preferably the weight-average molecular weight is 1,000,000 to 3,000,000.

[0025] The content of the guar gum derivative is more preferably 0.1 to 3% by mass of the total amount of the ink composition. This is because within this range, sufficient swelling action in the ink is easily obtained, and the desired ball seat wear prevention, writing feel, and writing performance are easily obtained. From further consideration, the content is preferably 0.1 to 1.5% by mass, more preferably 0.1 to 1% by mass, and even more preferably 0.2 to 0.7% by mass.

[0026] (coloring agent) The colorant used in the present invention is not particularly limited and may be a dye, a pigment, or the like, and may be appropriately selected and used. A dye and a pigment may be used in combination.

[0027] As the dyes used in the aqueous ink composition, direct dyes, acid dyes, basic dyes, metal-containing dyes, various salt-forming dyes, etc. can be used. (a) Direct dyes include Direct Yellow 4, 26, 44, 50, and 85; Direct Red 1, 2, 4, 23, 31, 37, 39, 75, 80, 81, 83, 225, 226, and 227; Direct Blue 1, 3, 15, 41, 71, 86, 106, and 119; and Direct Orange 6. (b) Acid dyes include The colors are Acid Black 1, 2, 24, 26, 31, 52, 107, Acid Orange 56, Acid Yellow 3, 7, 17, 19, 23, 42, 49, 61, 92, Acid Red 8, 9, 14, 18, 51, 52, 73, 87, 92, 94, Acid Blue 1, 7, 9, 22, 62, 90, 103, Acid Green 3, 9, 16, 25, 27, Acid Violet 15, 17, etc.; (c) Basic dyes include CI Basic Yellow 1, 2, 21, 7, 40, CI Basic Orange 2, 14, 32, CI Basic Red 1, 1:1, 2, 9, 14, CI Basic Violet 1, 3, 7, 10, 11:1, CI Basic Blue 3, 7, 26, Basic Green 4, CI Basic Brown 12, CI Basic Black 2, methyl violet, Victoria Blue FB, malachite green, and rhodamine series; (d) Other dyes include disperse dyes such as Disperse Yellow 82, 121, and Disperse Blue 7.

[0028] Pigments used in aqueous ink compositions include inorganic, organic, and processed pigments, and specific examples include carbon black, aniline black, ultramarine, yellow lead, titanium oxide, iron oxide, phthalocyanine-based, azo-based, quinacridone-based, diketopyrrolopyrrole-based, quinophthalone-based, threne-based, triphenylmethane-based, perinone-based, perylene-based, dioxazine-based, metallic pigments, pearl pigments, fluorescent pigments, and phosphorescent pigments. These dyes and pigments may be used alone or in combination of two or more.

[0029] Pigments are preferably used as colorants. This is because, in the case of ballpoint pens, pigment particles can penetrate into the gap between the ball and the tip body, acting like a bearing, thereby suppressing metal-to-metal contact, improving lubricity, improving writing feel, and reducing wear on the ball seat. The use of guar gum derivatives, as in the present invention, gives the ink a three-dimensional structure, reducing the ink viscosity during writing, which facilitates metal-to-metal contact between the ball and the tip body, improving lubricity and reducing wear on the ball seat. Therefore, pigments are preferred. Furthermore, the synergistic effect of the lubricating layer formed by the surfactant, described below, and the pigment particles and bearing action makes it easier to maintain lubricity and improve writing feel. Furthermore, in the case of a ballpoint pen, pigment particles create a physical obstacle in the gap between the ball and the inner wall of the tip, which makes it easy to suppress ink leakage. Pigments are also preferred because they provide excellent handwriting durability, especially excellent light resistance.

[0030] The pigment preferably contains carbon black, because the pigment particles themselves tend to provide a bearing effect between the ball and the ball seat. Furthermore, it is preferable to use carbon black with an oil absorption of 50 to 300 ml ( / 100 g). This is because oil absorption is a substitute characteristic that indicates the structure of the carbon black, and the higher the oil absorption, the larger the structure. Carbon black with an oil absorption of 50 to 300 ml ( / 100 g) has a structure of a size suitable for the gap between the ball and ball seat, which can be expected to provide an efficient bearing effect and easily suppress ball seat wear. It also has a structure of a size suitable for pigment dispersion stability, which facilitates pigment dispersion stability. Furthermore, the carbon black itself remains on the paper surface, which facilitates dark, clear handwriting. Furthermore, considering ball seat wear suppression and pigment dispersibility, the oil absorption of carbon black is preferably 100 to 250 ml ( / 100 g), and more preferably 120 to 200 ml ( / 100 g). The oil absorption of carbon black is a characteristic 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. It is measured using the test method specified in JIS K6221.

[0031] Considering pigment dispersibility, it is preferable to use a pigment with an average particle size of 1 μm or less, and even more preferably an average particle size of 0.5 μm or less. Furthermore, while spherical or irregularly shaped pigment particles can be used, spherical pigment particles are preferred in consideration of reducing frictional resistance and thereby suppressing wear of the ball seat. The spherical pigment particles referred to here are not limited to true spheres, but may also be approximately spherical or approximately ellipsoidal. The average particle size of pigment particles can be measured by the particle size at 50% cumulative volume (D50) of the particle size distribution measured by laser diffraction using a laser diffraction particle size distribution analyzer (product name "MicrotracHRA9320-X100", Nikkiso Co., Ltd.).

[0032] The content of the colorant is preferably 1 to 30% by mass of the total amount of the ink composition, because if it is less than 1% by mass, it tends to be difficult to obtain thick handwriting, and if it exceeds 30% by mass, it is likely to affect the solubility and dispersibility in the ink.

[0033] (water) The water used in the present invention is not particularly limited, and for example, conventional water such as ion-exchanged water, distilled water, and tap water can be used.

[0034] Furthermore, water-soluble solvents are used in consideration of water dissolution stability and prevention of water evaporation and drying. Examples of water-soluble solvents 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-butyn-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 in consideration of the dissolution stability of the polyoxyalkylene glyceryl ether and guar gum derivative used in the present invention. Polyhydric alcohol solvents are solvents in which two or more hydroxyl groups are bonded to different carbon atoms of an aliphatic or alicyclic compound. Among these, polyhydric alcohol solvents containing at least a polyhydric alcohol having a divalent or trivalent hydroxyl group are preferred. These may be used alone or in combination of two or more.

[0035] The content of the water-soluble solvent is preferably 0.1 to 25 mass %, more preferably 3 to 20 mass %, based on the total amount of the ink composition, taking into consideration solubility, ink leakage, bleeding, and the like.

[0036] (surfactant) In the present invention, considering the improvement of lubricity, the prevention of ball seat wear, and the improvement of writing feel, it is preferable that the ink contains a surfactant. Examples of such surfactants include silicone-based surfactants, fluorine-based surfactants, phosphate ester surfactants, and fatty acids. Among these, it is preferable to contain a fatty acid or phosphate ester surfactant. This is because surfactants with a fatty acid group or a phosphate group have an adsorption power to metals, and by adsorbing to the ball or tip body, etc., they have a lubricating effect. Furthermore, when used in combination with a guar gum derivative and water, they swell in the ink and form a dense three-dimensional structure, forming a viscous ink fluid lubricating layer. This forms an appropriate film thickness between the ball and the ball seat of the ballpoint pen tip, forming a lubricating layer with a higher lubrication effect, which makes it easier to achieve ball seat wear prevention.

[0037] Furthermore, types of fatty acids include lauric acid, myristic acid, stearic acid, oleic acid, ricinoleic acid, linoleic acid, and salts thereof, such as alkali metal salts, ammonium salts, and amine salts. The fatty acid preferably has a carbon number of 12 to 24. This is because, within this range, the lubricity of the ball is likely to be improved, wear of the ball seat is likely to be suppressed, and the writing feel is likely to be improved. From this perspective, a carbon number of 16 to 20 is preferred, and from the perspective of suppressing wear of the ball seat under higher writing pressure, linoleic acid or a salt thereof is preferred.

[0038] Examples of types of phosphate ester surfactants include styrenated phenols, nonylphenols, lauryl alcohols, tridecyl alcohols, octylphenols, and short-chain alcohols. Among these, phenyl skeletons tend to affect lubrication due to steric hindrance, so in consideration of suppressing wear of the ball seat under high writing pressure and improving writing feel, it is preferable to use linear alcohols such as lauryl alcohols and tridecyl alcohols as phosphate ester surfactants. These may be used alone or in combination of two or more.

[0039] If the content of the surfactant is less than 0.1% by mass of the total ink composition, it will be difficult to achieve the desired effect of suppressing ball seat wear and improving writing feel, and if it exceeds 5.0% by mass, the ink may become unstable over time. Therefore, the content is preferably 0.1 to 5.0% by mass of the total ink composition, and more particularly, 0.5 to 3.0% by mass of the total ink composition is preferable.

[0040] In addition to the surfactants described above, it is preferable that the ink contains a polyethylene glycol surfactant. This is because the presence of a polyethylene glycol surfactant on the surface of the pigment particles or around the pigment particles makes it easier to form a lubricating layer when the pigment particles enter between the ball and the ball seat of the ballpoint pen tip, thereby providing a lubricating effect and making it easier to suppress wear of the ball seat. Furthermore, the presence of a polyethylene glycol surfactant on the surface of the pigment particles or around the pigment particles makes it possible to maintain the dispersion stability of the pigment. As described above, it is preferable to use the pigment as a pigment dispersion in which pigment particles are dispersed in a polyethylene glycol surfactant and a solvent.

[0041] The weight average molecular weight of the polyethylene glycol surfactant is preferably 5000 or less. This is because within this range, the surfactant is likely to dissolve stably in the ink, and it is easy to suppress ball seat wear and maintain stable pigment dispersibility. From a more specific perspective, the weight average molecular weight is preferably 4000 or less, and more preferably 3000 or less. Furthermore, the weight average molecular weight is preferably 500 or more. This is because the surfactant is likely to be present on the surface of pigment particles and between the ball and the ball seat of the ballpoint pen tip, and it is easy to suppress ball seat wear and improve pigment dispersibility. From a more specific perspective, the weight average molecular weight is preferably 1000 or more.

[0042] The content of the polyethylene glycol surfactant is preferably 0.1 to 5% by mass of the total amount of the ink composition. This is because within this range, it is easy to obtain the effects of suppressing wear of the ball seat and excellent pigment dispersibility. From further considerations, 0.3 to 3% by mass is more preferable, and 0.5 to 2% by mass is more preferable.

[0043] For these pigments, in consideration of pigment dispersibility, it is preferable to use a pigment dispersion in which the pigment is dispersed using a polyethylene glycol-based surfactant and a solvent, and from a more particular consideration, it is preferable to use an aqueous pigment dispersion in which the pigment is dispersed using a polyethylene glycol-based surfactant, water, and a polyhydric alcohol, and it is further preferable to use an aqueous pigment dispersion in which the pigment is previously dispersed using a polyethylene glycol-based surfactant, water, and a polyhydric alcohol.

[0044] (resin particles) In the present invention, it is preferable for the inkjet printhead to contain resin particles. This is because the presence of the resin particles between the ball and the ball seat provides a cushioning effect, which helps prevent relatively hard pigment particles from coming into contact with the ball or the ball seat, reducing friction between the ball and the ball seat and suppressing wear on the ball seat. Furthermore, the resin particles are preferable because they control the flow of the composition in the gap between the ball and the inner wall of the tip end, making it easier to suppress ink leakage. In this case, since the resin particles have a lower hardness than inorganic materials, they partially deform and adhere to each other, which is thought to cause the relatively small resin particles to form a weak cohesion structure with each other, suppressing ink leakage.

[0045] Resin particles that can achieve such effects include olefin-based resin particles, acrylic-based resin particles, styrene-butadiene-based resin particles, polyester-based resin particles, vinyl acetate-based resin particles, and resin particles having amino groups. Of these, olefin-based resin particles and resin particles having amino groups are preferred because they are highly effective in suppressing wear of the ball seat and ink leakage from the pen tip.

[0046] Examples of materials for the olefin resin particles include polyolefins such as polyethylene, polypropylene, and polybutene, as well as mixtures thereof. Among these, polyethylene is preferred in terms of improving ball seat wear prevention and ink leakage prevention, and specific examples include low-density polyethylene, high-density polyethylene, low-molecular-weight polyethylene, modified polyethylene, and modified high-density polyethylene. Among these, low-density polyethylene, low-molecular-weight polyethylene, and modified polyethylene are preferred in terms of ball seat wear prevention and ink leakage prevention, and low-density polyethylene has a lower melting point than other types of polyethylene. Low-density polyethylene is particularly suitable because it has a lower melting point than other types of polyethylene, and its soft nature makes it easier to achieve a cushioning effect between the ball and ball seat, thereby reducing ball seat wear. Furthermore, its softness makes it easier for polyethylene particles to adhere to each other, making it less likely for gaps to form between the particles and reducing ink leakage. Low density refers to a density of 0.90 to 0.94 (g / cm3), and in order to further suppress ball seat wear and ink leakage, the density of the polyethylene is preferably 0.91 to 0.93 (g / cm3). The olefin-based resin particles may contain materials other than polyolefin, if necessary.

[0047] The olefin resin particles may be spherical or irregularly shaped, but spherical resin particles are preferred in view of reducing frictional resistance. The spherical resin particles referred to here are not limited to true spheres, and may be approximately spherical resin particles or approximately oval-spherical resin particles.

[0048] Resin particles having amino groups include benzoguanamine-formaldehyde resin particles, nylon resin particles, melamine resin particles, urethane resin particles, etc. Among these, benzoguanamine-formaldehyde resin particles and melamine resin particles are preferred in terms of lubricity and ink leakage prevention.

[0049] Furthermore, in consideration of suppressing wear of the ball seat and suppressing ink leakage, the content of the resin particles is preferably 0.01 to 5 mass% of the total amount of the ink composition, and from further consideration, it is more preferably 0.1 to 3 mass%, and even more preferably 0.1 to 1.5 mass%.

[0050] The average particle size of the resin particles is preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 7 μm or less, because a smaller average particle size reduces ball rotation resistance, reduces ball seat wear, and facilitates adhesion between particles to form a weakly aggregated structure and inhibit ink leakage. On the other hand, if the average particle size is too small, the effects of inhibiting ball seat wear and ink leakage are likely to be poor. Therefore, the average particle size is preferably 0.1 μm or more, more preferably 1 μm or more, and even more preferably 3 μm or more. The average particle size can be measured by laser diffraction using a laser diffraction particle size distribution analyzer (trade name "MicrotracHRA9320-X100", Nikkiso Co., Ltd.) or by measuring the particle size at 50% cumulative volume (D50) of the particle size distribution measured using a Coulter counter method (manufactured by Coulter).

[0051] Furthermore, it is preferable that the ink contains a shear thinning agent as an ink viscosity modifier other than the guar gum derivative. Examples of shear thinning agents include crosslinked acrylic acid polymers, polysaccharides such as xanthan gum, welan gum, succinoglycan, guar gum, locust bean gum, λ-carrageenan, cellulose derivatives, diutan gum, and oxidized cellulose, and associative thickeners such as polyesters, polyethers, urethane-modified polyethers, and polyaminoplasts, as well as alkali-swelling associative thickeners and nonionic associative thickeners, depending on the associative hydrophobic group. These shear thinning agents may be used alone or in combination of two or more.

[0052] pH adjusters are used to adjust the pH to improve pigment dispersion stability and prevent corrosion of metal parts that come into contact with the water-based ink. Examples of pH adjusters include basic inorganic compounds such as ammonia, sodium carbonate, sodium phosphate, and sodium hydroxide, basic organic compounds such as sodium acetate, triethanolamine, and diethanolamine, lactic acid, and citric acid. Among these, basic organic compounds are preferred, and weakly basic triethanolamine is preferred.

[0053] Examples of preservatives and rust inhibitors include phenol, sodium benzoate, potassium sorbate, propyl parahydroxybenzoate, 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine, 2-pyridinethiol-1-oxide sodium, 1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, and benzotriazole.

[0054] Other additives may be added as desired, specifically, fixing agents such as acrylic resin emulsions, urethane resin emulsions, styrene-butadiene resin emulsions, acrylic resins, styrene-acrylic resins, cellulose resins, and polyvinyl acetate resins, moisturizing agents such as urea and sorbitol, chelating agents such as ethylenediaminetetraacetic acid, foam inhibitors, and antifoaming agents, etc. These may be used alone or in combination of two or more.

[0055] Ink viscosity is measured at a shear rate of 384 sec under a 20°C environment. -1The ink viscosity is preferably 70 to 1000 mPa·s. This is because, within this range, the present invention forms a three-dimensional structure, forming an ink fluid lubrication layer, and an appropriate film thickness is formed between the ball and the ball seat of the ballpoint pen tip. Even under high writing pressure (writing load 300 to 500 gf), it is possible to form an ink fluid lubrication layer suitable for suppressing ball seat wear and improving writing feel. From further consideration, a viscosity of 100 to 700 mPa·s is preferable, and even more preferably 150 to 500 mPa·s.

[0056] In the case of the present invention, when the composition contains water, a colorant, a polyoxyalkylene glyceryl ether, and a guar gum derivative, the viscosity index n can be used as an index. The viscosity index n is calculated by the following equation: S=αD n where S is the shear stress (dyn / cm 2 =0.1 Pa), D is the shear rate (s -1 ), α indicates the viscosity coefficient. The viscosity index n is measured at 20°C using a Brookfield DV-II viscometer (CPE-42 rotor) at a shear rate of 1.92 sec -1 (Rotation speed 0.5 rpm) and shear rate 384 sec -1 The ink viscosity can be measured and calculated at a rotation speed of 100 rpm. The viscosity index n is preferably 0.4 to 0.8 when considering the suppression of ball seat wear even under high writing pressure (writing load of 300 to 500 gf), the writing feel, writing performance, and pigment dispersibility.The viscosity index n is preferably 0.5 to 0.7 when considering the balance between the suppression of ball seat wear and the writing feel, writing performance, and pigment dispersibility.

[0057] The material used for the balls is not particularly limited, but examples include cemented carbide balls mainly composed of tungsten carbide, metal balls such as stainless steel, ceramic balls such as silicon carbide, silicon nitride, alumina, silica, and zirconia, and ruby ​​balls.

[0058] The ball diameter is not particularly limited, but a ball of about 0.1 to 2.0 mm is used. When the ball diameter is 0.5 mm or less, the contact area between the ball and the ball seat tends to be small, and the load per unit area at a constant load increases. Furthermore, when writing the same distance, the smaller the ball diameter, the more the ball rotates, which tends to cause severe wear to the ball seat. Therefore, it is effective to use the water-based ballpoint pen ink composition used in the present invention. Furthermore, when the ball diameter is 0.4 mm or less, the wear to the ball seat tends to progress, so it is more effective and preferable.

[0059] Furthermore, to suppress wear of the ball seat and improve writing performance, the arithmetic mean roughness (Ra) of the ball surface is preferably 0.1 to 10 nm. This is because if the arithmetic mean roughness (Ra) exceeds this range, the ball surface becomes too rough, which tends to increase the rotational resistance between the ball and ball seat, affecting writing performance and ball seat wear. Conversely, if the arithmetic mean roughness (Ra) is below this range, the pigment is not sufficiently applied to the ball surface, which tends to affect writing performance, such as blurring of handwriting. Therefore, to suppress wear of the ball seat, improve writing performance, and obtain sufficient writing performance, the arithmetic mean roughness (Ra) of the ball surface is preferably 0.1 to 10 nm, and more preferably 0.1 to 8 nm.

[0060] The arithmetic mean roughness of the ball surface is calculated by taking a reference length from the roughness curve measured using a surface roughness measuring instrument (Seiko Epson model SPI3800N) in the direction of the mean line, and then adding up and averaging the absolute values ​​of the deviations from the mean line of this sampled section to the measurement curve.

[0061] The present invention will now be described with reference to examples. Example 1 Pigment dispersion (carbon black oil absorption: 170 ml / 100 g, primary particle size: 21 nm) 60.0 parts by mass (Main ingredients of pigment dispersion: carbon black 12 parts by weight, polyethylene glycol surfactant 3 parts by weight, polyhydric alcohol 6 parts by weight) Water 6.2 parts by mass Polyoxyalkylene glyceryl ether ((Chemical Formula 2), polyoxyethylene diglyceryl ether) 30.0 parts by mass pH adjuster (triethanolamine) 2.0 parts by mass Phosphate ester surfactant 1.0 parts by mass Rust inhibitor (benzotriazole) 0.5 parts by mass Guar gum derivative 0.33 parts by mass

[0062] For the aqueous ballpoint pen ink composition of Example 1, water, a polyhydric alcohol, a pigment, and a polyethylene glycol surfactant were mixed in advance and dispersed in a disperser to prepare a pigment dispersion. Then, the pigment dispersion, water, a polyoxyalkylene glyceryl ether, a pH adjuster, a phosphate ester surfactant, and a rust inhibitor were heated and stirred with a magnetic hot stirrer to prepare a base ink.

[0063] Thereafter, the guar gum derivative was added to the base ink prepared above while heating it, and the mixture was thoroughly mixed and stirred using a homogenizer stirrer until it became uniform, thereby obtaining the aqueous ink composition for a ballpoint pen of Example 1. The ink viscosity of Example 1 was measured at a shear rate of 384 sec at a temperature of 20°C using a Brookfield DV-II viscometer (CPE-42 rotor). -1 (Rotation speed 100 rpm), shear rate 1.92 sec -1 The ink viscosity was measured under the conditions of 0.5 rpm (rotation speed) and was found to be 200 mPa·s and 1600 mPa·s, respectively. The viscosity index n was 0.61.

[0064] Examples 2 to 15, Comparative Examples 1 to 2 Except for changing the ink components and tip specifications as shown in the table, water-based ballpoint pen ink compositions and water-based ballpoint pen refills of Examples 2 to 2 were obtained in the same manner as in Example 1. The evaluation results are shown in the table. The ink viscosity of Examples 2 and 3 was measured at a shear rate of 384 sec at 20°C using a Brookfield DV-II viscometer (CPE-42 rotor). -1(Rotation speed 100 rpm), shear rate 1.92 sec -1 The ink viscosity was measured under the condition of 0.5 rpm (rotation speed) and the viscosity index n was calculated, and the following results were obtained. Example 2: Shear rate 384sec -1 :300mPa·s Shear rate 1.92sec -1 :3200mPa·s Viscosity index n:0.55 Example 3: Shear rate 384sec -1 :360mPa·s Shear rate 1.92sec -1 :3400mPa·s Viscosity index n:0.58 Example 4: Shear rate 384sec -1 :150mPa·s Shear rate 1.92sec -1 :600mPa·s Viscosity index n:0.74 [Table 1] [Table 2]

[0065] Testing and Evaluation The aqueous ink compositions for ballpoint pens prepared in Examples and Comparative Examples were filled into an ink reservoir (made of polypropylene) equipped with a ballpoint pen tip that rotatably holds a ball at the tip of the ink reservoir via a tip holder, and the refill (1.0 g) was attached to a gel ink ballpoint pen (trade name: G-knock) manufactured by Pilot Corporation, and the following tests and evaluations were carried out. The abrasion resistance test under high writing pressure and the evaluation of writing feel were carried out using JIS P3201 writing paper A as the writing test paper, using the following test methods.

[0066] Abrasion resistance test under high writing pressure (ball seat abrasion test): One week after assembling the ballpoint pen, the abrasion of the ball seat after the writing test was measured on JIS P3201 writing paper at 20°C with a load of 400 gf, a writing angle of 65°, and a running test machine at 4 m / min. Ball seat wear of less than 5 μm Wear of the ball seat is 5 μm or more and less than 10 μm. Wear of the ball seat is 10 μm or more but less than 20 μm, but writing is possible... △ The ball seat is badly worn, causing poor writing.

[0067] Writing feel: Evaluation was carried out by a sensory test using handwriting. Very smooth... Smooth ○ Smooth enough for practical use △ Heavy items ×

[0068] Writability test: The writing was observed after the test using a running tester with a load of 100 gf, a writing angle of 70°, and a speed of 4 m / min. No or few uneven dots in the handwriting...◎ There are some uneven spots in the writing, but it is not a problem for practical use. There are uneven spots in the handwriting, which affect its practical use. There are many uneven dots in the handwriting... ×

[0069] Pigment dispersibility test: The ink compositions of Examples 1 to 15 and Comparative Examples 1 and 2 were placed in tightly closed glass test tubes with a diameter of 15 mm and left to stand at 50°C for 30 days. Each ink composition was then sampled on a glass slide and observed using an optical microscope, and the pigment dispersibility of the ink composition was evaluated according to the following evaluation criteria. No agglomerates were observed and the product was in a good condition with uniform dispersion. A small amount of agglomerates was observed, but this was at a level that would not cause any problems in practical use. Aggregates were observed, and the level was of concern for practical use. Sedimentation of aggregates was observed. ×

[0070] As can be seen from the results in the table, Examples 1 to 15 achieved good levels of performance in the high writing pressure abrasion resistance test (ball seat abrasion test), writing feel, writing performance test, and pigment dispersibility test. In addition, in Examples 1 to 15, as a writing performance test, after handwriting, the tip was left in an environment of 20°C and 65% RH for 24 hours with the tip end protruding, and then handwriting was performed again, with almost no smearing, resulting in good results.

[0071] As can be seen from the results in the table, in Comparative Examples 1 and 2, the abrasion resistance test under high writing pressure was poor because polyoxyalkylene glyceryl ether and a guar gum derivative were not used in combination.

[0072] In the present invention, as in the examples, a refill in which an ink reservoir is filled with an ink composition for a water-based ballpoint pen is attached to a barrel and used as a ballpoint pen, but the present invention is not limited to this form, and the ink reservoir may be used as a barrel and filled with an ink composition for a water-based ballpoint pen, and used as a ballpoint pen as is. [Industrial Applicability]

[0073] The present invention can be used as a ballpoint pen for water-based inks, and more specifically, can be widely used as a ballpoint pen for water-based inks such as a cap type or a retractable type.

Claims

1. 1. A water-based ink composition for a ballpoint pen, comprising water, a colorant, a polyoxyalkylene glyceryl ether, and a guar gum derivative, wherein the guar gum derivative is a hydroxyalkyl guar gum, and the polyoxyalkylene glyceryl ether is a polyethylene glyceryl ether.

2. An ink composition for a water-based ballpoint pen as described in claim 1, characterized in that the degree of hydroxyalkyl substitution of the hydroxyalkyl guar gum is in the range of 0.1 to 2.

0.

3. An ink composition for a water-based ballpoint pen as described in claim 1 or 2, characterized in that the average number of moles of ethylene oxide added to the polyoxyethylene glyceryl ether is 1 to 30.

4. An ink composition for an aqueous ballpoint pen described in any one of claims 1 to 3, characterized in that the weight average molecular weight of the hydroxyalkyl guar gum is 500,000 to 5,000,000.

5. 5. The water-based ink composition for a ballpoint pen according to claim 1, further comprising a surfactant.

6. The ink viscosity of the aqueous ballpoint pen ink composition is 20°C, a shear rate of 384 sec －１ 6. The water-based ink composition for a ballpoint pen according to claim 1, wherein the viscosity of the ink composition is 70 to 1000 mPa·s.

7. 7. A water-based ballpoint pen comprising: a barrel containing the ink composition for a water-based ballpoint pen according to claim 1; and a ballpoint pen tip at the tip of the barrel.

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