Water-based ballpoint

Abstract

To provide a water-based ball-point pen which suppresses the wear of a ball seat by improving lubricity between a ball and the ball seat of a ball-point pen tip to make the rotation of the ball smooth, is excellent in pigment dispersibility, and makes deep and clear handwriting.SOLUTION: The present invention relates to a water-based ballpoint pen including a container cylinder containing an ink composition for a water-based ballpoint pen, and a ballpoint pen tip at a tip of the container cylinder, wherein the ink composition for a water-based ballpoint pen contains water, pigments, a styrene-acrylic resin, and a polyethylene glycol-based surface active agent, the pigments are carbon black having an oil absorption of 50 to 300ml ( / 100g), and the ball surface has an arithmetic average roughness (Ra) of 0.1 to 5nm. It is assumed that: SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous ballpoint pen, and more particularly to an aqueous ballpoint pen that improves the lubrication between the ball and the ballpoint pen tip, suppresses wear of the ball seat, and has excellent pigment dispersibility. [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 experience and suppressing line breakage and smearing. Patent Document 2 discloses that the inclusion of dibenzylidene sorbitol facilitates ink flow due to the rotation of the ball, enabling smooth writing and improving writing performance, such as reducing smearing. Patent Document 3 discloses that the inclusion of N-acylamino acid and N-acylmethyltaurine improves writing experience by adsorbing to the tip seat and reducing friction between the ball and tip seat as the ball rotates during writing. While this approach provided a certain degree of smooth writing feel, it also accelerated wear on the ball seat, leaving room for improvement. In particular, with fine-point water-based ballpoint pens with a diameter of 0.5 mm or less, the contact area between the ball and ball seat tends to be small, increasing the load per unit area at a given load, and causing severe wear on the ball seat, leading to poor writing performance. A solution to this problem was desired.

[0005] Furthermore, in the case of aqueous inks that are intended to contain pigments, such as those disclosed in Patent Documents 1 to 3, stability in pigment dispersibility is also required.

[0006] The object of the present invention is to solve the above problems and to provide an aqueous ballpoint pen that improves lubricity, suppresses wear of the ball seat, and has excellent pigment dispersibility. [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 pigment, a styrene-acrylic resin, and a polyethylene glycol surfactant. 2. The water-based ink composition for a ballpoint pen according to item 1, wherein the styrene-acrylic resin has an acid value of 100 to 300 (mgKOH / g). 3. The water-based ink composition for a ballpoint pen according to claim 1 or 2, characterized in that the polyethylene glycol surfactant is represented by the general formula (Chemical Formula 1). [ka] 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 fatty acid or a phosphate ester surfactant. 5. The aqueous ballpoint pen ink composition according to any one of items 1 to 4, wherein the pigment is carbon black. 6. The aqueous ink composition for a ballpoint pen according to any one of items 1 to 5, characterized in that the aqueous ink composition for a ballpoint pen contains olefin-based resin particles or resin particles having an amino group. 7. The ink viscosity of the aqueous ballpoint pen ink composition is 20°C and a shear rate of 1.92 sec -1 7. The aqueous ballpoint pen ink composition according to any one of items 1 to 6, wherein the viscosity is 500 to 5000 mPa·s. 8. An aqueous ballpoint pen comprising a barrel containing the aqueous ballpoint pen ink composition according to any one of items 1 to 7, and a ballpoint pen tip at the tip of the barrel. [Effects of the Invention]

[0008] To provide an aqueous ballpoint pen which improves the lubrication between a ball and a ball seat of a ballpoint pen tip, smooths the rotation of the ball, suppresses the wear of the ball seat, has excellent pigment dispersibility, and produces thick, clear handwriting. BEST MODE FOR CARRYING OUT THE INVENTION

[0009] The present invention is characterized by an aqueous ballpoint pen having a barrel containing an ink composition for an aqueous ballpoint pen and a ballpoint pen tip at the tip of the barrel, The water-based ballpoint pen ink composition comprises water, a pigment, a styrene-acrylic resin, and a polyethylene glycol-based surfactant; the pigment is carbon black having an oil absorption of 50 to 300 ml ( / 100 g), Furthermore, the arithmetic mean roughness (Ra) of the ball surface is 0.1 to 5 nm. The following describes each of these components.

[0010] In the present invention, by using a pigment, a polyethylene glycol surfactant, and a styrene acrylic resin in combination, the lubrication between the ball and the ball seat of the ballpoint pen tip is improved, allowing the ball to rotate smoothly, thereby suppressing wear of the ball seat and further improving the dispersion stability of the pigment. In terms of suppressing wear of the ball seat, the pigment particles themselves provide a bearing effect between the ball and the ball seat of the ballpoint pen tip, but in addition, a lubricating effect is obtained through the cushioning action of a specific styrene acrylic resin, improving lubricity. Furthermore, the presence of a polyethylene glycol-based surfactant on the pigment surface and around the pigment means that if a pigment particle gets in between the ball and the ball seat, a lubricating effect is obtained through the lubricating layer of polyethylene glycol-based surfactant. Therefore, the bearing effect created by the pigment particles themselves between the ball and the ball seat, the cushioning effect of the styrene acrylic resin, and the synergistic lubricating effect of the lubricating layer made of polyethylene glycol-based surfactant work together to provide an even greater lubricating effect, thereby improving the lubricity between the ball and the ball seat of the ballpoint pen tip and allowing the ball to rotate more smoothly, making it possible to reduce wear on the ball seat more than before. In addition, with regard to pigment dispersibility, the polyethylene glycol surfactant acts to disperse the pigment, and the styrene acrylic resin also acts to disperse the pigment auxiliary, thereby making it possible to further improve pigment dispersibility.

[0011] (Polyethylene glycol surfactant) The inclusion of a polyethylene glycol surfactant on the pigment surface or in the vicinity of the pigment allows the formation of a lubricating layer when pigment particles get into the gap between the ball and the ball seat of the ballpoint pen tip, providing a lubricating effect and suppressing wear of the ball seat. Furthermore, the presence of a polyethylene glycol surfactant on the pigment surface or in the vicinity of the pigment allows the dispersion stability of the pigment to be maintained.

[0012] Examples of polyethylene glycol surfactants include polyethylene glycol ether and polyethylene glycol ester, but polyethylene glycol ether is preferred in terms of suppressing ball seat wear and pigment dispersibility, and the use of general formula (Chemical Formula 1) is preferred in terms of further suppressing ball seat wear. This is because alkyl groups such as R1 and R2 are easily adsorbed to the pigment surface and tend to maintain their adsorption action for a long period of time, making it easier to obtain a lubricating effect and suppress ball seat wear. Furthermore, because the alkyl groups are adsorbed to the pigment surface, pigment particles do not come into direct contact with each other, making it harder for the pigment to aggregate and making it easier to improve pigment dispersibility. [ka]

[0013] Among the polyethylene glycol surfactants represented by the general formula (Chemical Formula 1), the number of carbon atoms in the alkyl groups such as R1 and R2 in (Chemical Formula 1) is preferably 4 to 20. This is because within this range, they are easily adsorbed to the pigment surface, and it is easy to suppress abrasion of the ball seat and improve pigment dispersibility. From further consideration, the number of carbon atoms in the alkyl group is preferably 5 to 18, and more preferably 8 to 15. Furthermore, for the ethylene oxide group -(CH2-CH2-O)m- in the general formula (Chemical Formula 1), the number of moles of ethylene oxide added, m, is preferably 10 to 40. This is because, within the above range, a cushioning effect is easily achieved between the ball and the ball seat, and the effect of suppressing wear of the ball seat is easily obtained. Furthermore, in order to obtain stability in aqueous inks, it is preferable that the hydrophilic ethylene oxide chain is within a specific range. From further considerations, the number of moles of ethylene oxide added, n, is preferably 20 to 40, and more preferably 30 to 40.

[0014] The weight average molecular weight of the polyethylene glycol surfactant is preferably 5000 or less. This is because within the above 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 pigment surface or 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.

[0015] 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.

[0016] (styrene acrylic resin) By including styrene-acrylic resin, the three-dimensional structure of the styrene group provides a cushioning effect between the ball and ball seat, reducing friction between the ball and ball seat and suppressing wear of the ball seat. The carboxyl group is easily adsorbed to metal, and the three-dimensional structure of the styrene group provides the effect of suppressing wear of the ball seat. Furthermore, the adsorption of the styrene group on the pigment surface facilitates repulsion of pigment particles, making it easier to maintain pigment dispersion stability. Examples of styrene-acrylic resins include styrene-acrylic resins and their salts, such as alkali metal salts, ammonium salts, and amine salts. However, considering the suppression of wear of the ball seat and pigment dispersibility, it is preferable to use ammonium salts of styrene-acrylic resins. Examples of styrene-acrylic resins include the Joncryl series (manufactured by BASF Japan).

[0017] The mass average molecular weight of the styrene acrylic resin is preferably 1000 to 18000. This is because, within this range, a cushioning effect is obtained between the ball and the ball seat, while the resin is likely to be dissolved stably in the ink and an appropriate ink viscosity is likely to be maintained, which makes it easier to suppress abrasion of the ball seat and maintain pigment dispersibility.Taking this into consideration, the mass average molecular weight is preferably 1500 to 8000, more preferably 4000 to 8000, and even more preferably 5000 to 7000.

[0018] The acid value (mgKOH / g) of the styrene-acrylic resin is preferably 100 to 300 (mgKOH / g). This range facilitates stable dissolution in the ink, making it easier to suppress ball seat wear and maintain stable pigment dispersion. Furthermore, ink flow is good and the effect of stabilizing ejection from the tip of the ballpoint pen is also obtained, resulting in a ballpoint pen with excellent lubricity, a good writing feel, and good writing performance (reduced handwriting smearing and bleeding). From a more specific perspective, the acid value (mgKOH / g) is preferably 150 to 300. To further improve ink flow, lubricity, and writing performance, 150 to 300 is preferred, with 200 to 250 being more preferred. Furthermore, in consideration of the effects of the present invention, the glass transition temperature (Tg) of the styrene-acrylic resin is preferably 80 to 200° C., more preferably 100 to 200° C., and even more preferably 120 to 180° C. The glass transition temperature (Tg) can be determined by differential scanning calorimetry.

[0019] The content of the styrene-acrylic resin is more preferably 0.1 to 10% by mass of the total amount of the ink composition. This is because within this range, it is easy to obtain effects such as suppressing wear of the ball seat and excellent pigment dispersibility. From further considerations, the content is preferably 0.3 to 7% by mass, more preferably 0.5 to 5% by mass, and even more preferably 0.5 to 3% by mass.

[0020] The colorant used in the present invention contains a pigment, which is effective in the present invention because the pigment particles themselves provide a bearing effect between the ball and the ball seat. Examples of pigments include inorganic, organic, and processed pigments, and specific examples include carbon black, aniline black, ultramarine, yellow lead, titanium oxide, iron oxide, phthalocyanine-based, azo-based, quinacridone-based, quinophthalone-based, threne-based, triphenylmethane-based, perinone-based, perylene-based, dioxazine-based, microcapsules, aluminum pigments, pearl pigments, fluorescent pigments, phosphorescent pigments, and complementary color pigments. 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 even more 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.

[0021] The pigment preferably contains carbon black, because the pigment particles themselves tend to produce a bearing effect between the ball and the ball seat, and it is preferable to use carbon black as a pigment dispersion using a polyethylene glycol surfactant and a solvent, as described above. 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.

[0022] 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.).

[0023] In the present invention, in consideration of improving lubricity, suppressing wear of the ball seat, and improving the writing feel, it is preferable to contain a fatty acid or a phosphate ester surfactant. This is because those having a fatty acid group or a phosphate group have an adhesive force to metals, and by adsorbing to the ball or tip body, etc., they have a lubricating effect. Furthermore, the lubricating effect due to the cushioning effect of the styrene acrylic resin and the synergistic effect with the lubricating layer of the polyethylene glycol surfactant form a lubricating layer with a higher lubricating effect, making it easier to achieve a wear-suppressing effect on the ball seat. In particular, using a fatty acid and a phosphate ester surfactant in combination is preferable because it makes it easier to achieve an even greater lubricating effect.

[0024] 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 preferable, and from the perspective of suppressing wear of the ball seat, linoleic acid or a salt thereof is preferred.

[0025] 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 ball seat wear and improving writing feel, it is preferable to use linear alcohol-based phosphate ester surfactants such as lauryl alcohols and tridecyl alcohols. These may be used alone or in combination of two or more.

[0026] If the content of fatty acid or phosphate ester 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.

[0027] (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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] The olefin resin particles are preferably dispersed in water or the like to form an olefin dispersion, and the pH value of the olefin dispersion is preferably 7 to 11. This is because it is easy to improve the dispersion stability of the olefin resin particles and the stability to ink components such as pigments and surfactants. From this perspective, a pH value of 7 to 10 is more preferable.

[0032] 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.

[0033] 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%.

[0034] 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).

[0035] Furthermore, when the average particle diameter of the 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 the larger particle diameter of the resin particles facilitates cushioning and reduces wear of the ball seat. Furthermore, when gaps occur between the resin particles due to their close contact with each other, these gaps are difficult to fill, which can affect ink leakage. From further consideration, it is preferable that the relationship Y / X≦0.5, more preferably 0.001≦Y / X≦0.5, with 0.001≦Y / X≦0.3 being preferred and 0.001≦Y / X≦0.1 being preferred.

[0036] (solvent) The solvent used in the present invention includes water, a water-soluble solvent, and the like. The water is not particularly limited, and for example, conventional water such as ion-exchanged water, distilled water, and tap water can be used.

[0037] 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 with the polyethylene glycol surfactant and styrene-acrylic resin 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, it is preferable to use at least a polyhydric alcohol having a divalent or trivalent hydroxyl group. These solvents may be used alone or in combination.

[0038] The content of the water-soluble solvent is preferably 0.1 to 25 mass %, more preferably 7 to 20 mass %, based on the total amount of the ink composition, taking into consideration solubility, ink leakage, bleeding, and the like.

[0039] The ink preferably contains a shear thinning agent as a viscosity modifier. 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, and diutan gum, and associative thickeners such as polyesters, polyethers, urethane-modified polyethers, and polyaminoplasts, which are based on the associative hydrophobic group, alkali-swelling associative thickeners, and nonionic associative thickeners. These shear thinning agents may be used alone or in combination of two or more.

[0040] Among shear thinning agents, polysaccharides are preferably used in consideration of pigment dispersion stability and ink leakage suppression effect, and among polysaccharides, xanthan gum and succinoglycan are preferably used.

[0041] Furthermore, the content of the shear thinning 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 thinning agent is less than 0.01% by mass, the ink thickening effect is insufficient, making it difficult to stabilize the pigment dispersion and prevent ink leakage. If the content exceeds 5.0% by mass, the ink viscosity tends to increase, which can affect ball seat wear prevention, writing tracking, writing feel, and dry-up performance. From further considerations, the content is preferably 0.1 to 2.0% by mass, and most preferably 0.1 to 1.0% by mass.

[0042] In addition, it is preferable that the ink contains dextrin in order to improve writing performance and easily suppress ink leakage. This is because the coating formed when the pen tip dries does not become too hard, suppressing smearing at the start of writing, and the coating formed suppresses evaporation of solvents and the like in the composition, preventing the coating on the pen tip from becoming excessively hard. Furthermore, the formation of a coating when the ink on the pen tip dries provides the effect of suppressing ink leakage from gaps in the pen tip.

[0043] Examples of starches that can be used as raw materials for dextrin include cornstarch (dent cornstarch), waxy cornstarch, sweet potato starch, potato starch, tapioca (cassava starch), wheat starch, and rice starch (glutinous rice starch and non-glutinous rice starch). As the starch that can be used as raw materials for dextrin, waxy cornstarch and sweet potato starch are preferred in terms of writing performance and ink leakage suppression effect, and waxy cornstarch is even more preferred in terms of writing performance and ink leakage suppression effect.

[0044] Regarding the dextrose equivalent (DE) of the dextrin, in consideration of the ease of dissolution and stability in the ink, a dextrin with a dextrose equivalent (DE) of 2 to 25 is preferred. Furthermore, in consideration of the writing performance and the effect of suppressing ink leakage, a dextrose equivalent (DE) of 2 to 15 is preferred, and even more preferably 6 to 13. Dextrose equivalent is an index showing the degree of decomposition when starch is hydrolyzed with acid or enzymes, and is known as a relative measure with the reducing power of dextrose (glucose) set at 100. In this specification, dextrose equivalent is abbreviated as "DE" (Dextrose equivalent). A DE of 0 indicates starch, and the closer to 0, the more similar the properties to starch. Conversely, the closer the DE is to 100, the more hydrolysis of starch has progressed. The DE of dextrin can be measured by the Somogyi-Nelson method. Furthermore, for example, if the manufacturer's guaranteed or measured value of the DE of dextrin is known, that value can be used as the DE value of the dextrin.

[0045] The content of dextrin is preferably 0.1 to 5% by mass of the total amount of ink composition. This is because if it is less than 0.1% by mass, it is difficult to obtain sufficient writing performance and ink leakage suppression effect, and if it exceeds 5% by mass, it is difficult to dissolve in the ink. In consideration of solubility in the ink, 0.1 to 3% by mass is preferable, and in consideration of writing performance and ink leakage, 0.5 to 3% by mass is preferable.

[0046] 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.

[0047] 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.

[0048] Other additives may be added as desired, specifically, fixing agents such as acrylic resin emulsions, urethane resin emulsions, and styrene-butadiene resin emulsions, surfactants such as silicone surfactants, acetylene glycol surfactants, and fluorine surfactants, moisturizing agents such as urea and sorbitol, and chelating agents such as ethylenediaminetetraacetic acid, etc. These may be used alone or in combination of two or more.

[0049] The pH value of the aqueous ballpoint pen ink composition is preferably 7 to 11. This is because a pH value below 7, which is in the acidic range, can affect the stability of ink components such as pigments, styrene acrylic resins, and polyethylene glycol surfactants, and can affect corrosion of the metallic ballpoint pen tip and ball. Similarly, a pH value above 11, which is more strongly alkaline, can affect the stability of the ink components. From this perspective, a pH value of 7 to 10 is more preferable.

[0050] Furthermore, the amount of movement (clearance) of the ball in the vertical direction of the ballpoint pen tip used in the present invention is preferably 15 to 50 μm. This is because if it is less than 15 μm, it becomes difficult to obtain thick handwriting or good lubrication, and if it exceeds 50 μm, it is likely to have an effect on suppressing ink leakage. Taking this into consideration, a value of 20 to 45 μm is more preferable, and even more preferably a value of 20 to 40 μm. The amount of movement (clearance) of the ball in the ballpoint pen tip in the vertical axis direction indicates the distance that the ball can move in the vertical axis direction of the ballpoint pen tip body.

[0051] Ink viscosity is measured at a shear rate of 1.92 sec under a 20°C environment. -1 The ink viscosity is preferably 500 to 5000 mPa·s. This is because if the ink viscosity is less than 500 mPa·s, the ink viscosity is too low, making it difficult to stabilize pigment dispersion and prevent ink leakage, while if it exceeds 5000 mPa·s, the writing feel and ball seat wear prevention and writing feel tend to deteriorate, ink consumption is low, and it is difficult to obtain thick handwriting. From these considerations, a viscosity of 1000 to 3500 mPa·s is preferable.

[0052] 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.

[0053] 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.

[0054] 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, more preferably 0.1 to 5 nm, and particularly preferably 0.1 to 3 nm.

[0055] 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.

[0056] In the present invention, when the ink consumption per 100 m of an aqueous ballpoint pen is A (mg) and the ball diameter is B (mm), in consideration of suppressing wear on the ball seat and improving the writing feel and writing performance (suppressing smeared handwriting and smeared marks), it is preferable that the ratio be 150≦A / B≦500, and more particularly, 200≦A / B≦450, and even more preferably 220≦A / B≦400. In particular, a ball diameter of 0.5 (mm) or less is preferable because it is easier to suppress wear on the ball seat and improve the writing feel and writing performance (suppressing smeared handwriting and smeared marks) in a balanced manner, and a ball diameter of 0.4 (mm) or less is even more preferable. In the present invention, a spiral writing test is performed using five test samples at a writing speed of 4 m / min on JIS P3201 writing paper at a temperature of 20°C, a writing angle of 65°, and a writing load of 100 g, and the average ink consumption per 100 m is defined as the ink consumption per 100 m.

[0057] 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) 30.0 parts by mass (Major ingredients: carbon black 6 parts by weight, polyethylene glycol surfactant 1.5 parts by weight, polyhydric alcohol 3.0 parts by weight) Styrene acrylic resin (acid value 215 (mgKOH / g), molecular weight 6200, glass transition temperature (Tg: 136°C) 1.5 parts by mass Water 48.5 parts by mass Polyhydric alcohol (glycerin) 10.0 parts by mass Resin particles (low-density polyethylene dispersion, average particle size 6 μm, pH value 9, solid content 40%) 1.0 parts by mass Dextrin (derived from waxy cornstarch, DE: 6-8) 1.0 parts by mass pH adjuster (triethanolamine) 2.0 parts by mass Phosphate ester surfactant 1.0 parts by mass Fatty acid (linoleic acid) 1.0 parts by mass Rust inhibitor (benzotriazole) 0.5 parts by mass Shear thinning agent (xanthan gum) 0.4 parts by mass

[0058] For the aqueous ballpoint pen ink composition of Example 1, water, polyhydric alcohol, pigment, and polyethylene glycol surfactant were mixed in advance and dispersed in a disperser to prepare a pigment dispersion. Then, the pigment dispersion, water, polyhydric alcohol, resin particles, dextrin, pH adjuster, phosphate ester surfactant, fatty acid, and rust inhibitor were heated and stirred with a magnetic hot stirrer to prepare a base ink.

[0059] Thereafter, while heating the base ink prepared above, a shear thinning agent was added and the mixture was thoroughly mixed and stirred using a homogenizer mixer until a uniform state was achieved, thereby obtaining the aqueous ballpoint pen ink composition of Example 1. The ink viscosity of Example 1 was measured at a shear rate of 1.92 sec at 20°C using a Brookfield DV-II viscometer (CPE-42 rotor). -1The ink viscosity was measured at 0.5 rpm and was found to be 2500 mPa·s. The pH value of Example 1 was measured at 20° C. using an IM-40S pH meter (manufactured by DKK-Toa Corporation) and was found to be 8.6.

[0060] Examples 2 to 23, Comparative Examples 1 to 5 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 23 were obtained in the same manner as in Example 1. The evaluation results are shown in the table. [Table 1] [Table 2] [Table 3]

[0061] Testing and Evaluation The aqueous ink compositions for ballpoint pens prepared in the 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 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. In addition, a spiral writing test was conducted on aqueous ballpoint pens using the ink compositions for aqueous ballpoint pens and aqueous ballpoint pen refills of Examples 1, 3, 8, 19, and 20. When the ink consumption per 100 m was A (mg) and the ball diameter was B (mm), the A / B ratios were as follows: Example 1: A=125 (mg), B=0.38 (mm) A / B=328 Example 3: A=110 (mg), B=0.38 (mm) A / B=263 Example 8: A = 95 (mg), B = 0.38 (mm) A / B = 250 Example 19: A = 150 (mg), B = 0.5 (mm) A / B = 300 Example 20: A = 160 (mg), B = 0.7 (mm) A / B = 228

[0062] Abrasion resistance test: One month after assembling the ballpoint pen, the abrasion of the ball seat after a writing test was measured on JIS P3201 writing paper at 20°C using a running tester with a load of 100gf, a writing angle of 65°, and a speed of 4m / min. The evaluation was carried out by calculating the wear suppression rate (wear suppression amount) of the ball seat using Comparative Examples 1 to 3, which do not contain styrene acrylic resin, as the standard for each ball diameter. Specifically, the amount of wear suppression in the examples and comparative examples was measured and compared for each ball diameter. Ball diameter 0.38 (mm) The wear suppression rate (wear suppression amount) of the ball seat of Comparative Example 1 was compared with that of Examples 1 to 18 and Examples 21 to 23. Measurement examples: Example 1: 16.8 μm, Comparative Example 1: 29 μm Ball seat wear reduction rate: 42% (29μm-16.8μm) / 29μm, Rating: ◎◎ Ball diameter 0.5 (mm) The wear suppression rate (wear suppression amount) of the ball seat in Comparative Example 2 and Example 19 was compared. Measurement examples: Example 19: 8.5 μm, Comparative Example 2: 10 μm Ball seat wear reduction rate: 15% (10μm-8.5μm) / 10μm, Evaluation: Good When the ball diameter was 0.7 (mm), the wear suppression rate (amount of wear suppression) of the ball seat in Comparative Example 3 and Example 20 was compared. Measurement examples: Example 20: 5.5 μm, Comparative Example 3: 6 μm Ball seat wear reduction rate: 8% (6μm-5.5μm) / 6μm, Evaluation: △ Ball seat wear reduction rate is 40% or more ◎◎ Ball seat wear reduction rate is 20% or more and less than 40%. Ball seat wear reduction rate is 10% or more but less than 20%. The ball seat wear reduction rate is 1% or more but less than 10%...△ Ball seat wear reduction rate is less than 1% ×

[0063] Pigment dispersibility test: The ink compositions of Examples 1 to 23 and Comparative Examples 1 to 5 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 to evaluate the pigment dispersibility of the ink composition according to the following evaluation criteria. The results are summarized in Table 2. 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. ×

[0064] Ink leakage test: A 40g weight was attached to a gel ink ballpoint pen, with the ballpoint pen tip protruding and pointing 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 leaking from the tip of the ballpoint pen was measured. Ink leakage is less than 5 mg. Ink leakage amount is 5 to 15 mg. Ink leakage amount is more than 15 mg but less than 30 mg △ Ink leakage of 30 mg or more: ×

[0065] Writing feel: Evaluation was carried out by a sensory test using handwriting. Very smooth... Smooth ○ Smooth enough for practical use △ Heavy items ×

[0066] As can be seen from the results in the table, Examples 1 to 23 achieved good levels of performance in the abrasion resistance test, pigment dispersibility test, ink leakage test, and writing feel. Furthermore, when the handwriting in the abrasion resistance test was observed in Examples 1, 6, 8, 9, and 10, a comparison of the writing properties (inhibition of smearing of handwriting and blobbing) showed that Examples 1, 6, 9, and 10 had better writing properties (inhibition of smearing of handwriting and blobbing) than Example 8. This is because the acid value of the styrene acrylic resin was 150 to 300 (mgKOH / g),

[0067] As can be seen from the results in the table, in Comparative Examples 1 to 5, since a styrene acrylic resin or a polyethylene glycol surfactant was not used, the abrasion resistance test, the pigment dispersibility test, and the writing feel were poor.

[0068] In the present invention, when the aqueous ink composition for a ballpoint pen is used in a ballpoint pen, it is more preferable to provide a coil spring that presses the ball on the inner wall of the tip edge of the ballpoint pen tip, thereby maintaining the sealing properties of the tip of the ballpoint pen tip and making it easier to prevent ink leakage from gaps at the tip edge. In addition, as in the examples, a refill in which an ink composition for a water-based ballpoint pen is filled in an ink storage tube is attached to a barrel and used as a ballpoint pen, but this is not limited to this form, and the ink storage tube 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]

[0069] 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. A water-based ballpoint pen comprising a barrel containing an ink composition for a water-based ballpoint pen and a ballpoint pen tip at the tip of the barrel, The water-based ballpoint pen ink composition comprises water, a pigment, a styrene-acrylic resin, and a polyethylene glycol-based surfactant; the pigment is carbon black having an oil absorption of 50 to 300 ml ( / 100 g), Furthermore, the arithmetic mean roughness (Ra) of the ball surface is 0.1 to 5 nm. A water-based ballpoint pen.

2. 2. The water-based ballpoint pen according to claim 1, wherein the styrene-acrylic resin has a mass average molecular weight of 1,500 to 8,000.

3. 3. The water-based ballpoint pen according to claim 1, wherein the styrene-acrylic resin has an acid value of 100 to 300 (mgKOH / g).

4. 4. The water-based ballpoint pen according to claim 1, wherein the polyethylene glycol surfactant is represented by the general formula (Chemical Formula 1). 【Chemistry 1】

5. 5. The aqueous ballpoint pen according to claim 1, wherein the ink composition for the aqueous ballpoint pen contains a fatty acid or a phosphate ester surfactant.

6. 6. The water-based ballpoint pen according to claim 1, wherein the ink composition for the water-based ballpoint pen contains resin particles.

7. 7. The water-based ballpoint pen according to claim 6, wherein the resin particles have an average particle size of 10 μm or less.

8. The ink viscosity of the aqueous ballpoint pen ink composition is 20°C, a shear rate of 1.92 sec －１ The water-based ballpoint pen according to any one of claims 1 to 7, characterized in that the viscosity of the ink is 500 to 5000 mPa·s.

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