Aqueous ink composition for writing instruments, and writing instrument and refill containing the same

Abstract

To provide a water-based ink composition for a writing utensil, capable of forming colored and colorful handwriting having a metallic luster tone without permeating a coloring pigment into a writing surface by adding an anion-modified polyvinyl alcohol, excellent in water resistance, and hardly causing bleeding even when brought into contact with water, and further to provide the writing utensil and a refill containing the ink composition.SOLUTION: The water-based ink composition for writing utensils comprises at least a color pigment, a bright pigment, resin particles, an anion-modified polyvinyl alcohol and water, wherein the content of the resin particles is less than 5 mass% based on the total mass of the ink composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based ink composition for a writing instrument, and a writing instrument and refill containing the same. [Background technology]

[0002] Conventionally, aqueous ink compositions for writing instruments and writing instruments and refills containing the same have been used in normal living environments, and handwriting may come into contact with moisture such as water droplets and sweat. In particular, in the case of aqueous inks, contact with moisture can cause the coloring components of the handwriting to bleed onto the writing surface, resulting in bleeding or fading of the handwriting. This bleeding of the coloring components onto the paper surface not only impairs the visibility and color of pictures and characters, but also causes problems such as soiling the paper surface. Furthermore, aqueous ink compositions using glittering pigments such as metal powders or pearlescent pigments are widely used for writing letters, drawings, etc. because they can produce handwriting with a metallic luster, but when a coloring pigment is used as a coloring component, there is a problem that the coloring pigment penetrates into the writing surface such as the paper surface, making the hue of the formed handwriting insufficiently visible. In particular, when the ink is contained in a ballpoint pen or the like with a small ballpoint diameter to form thin handwriting or lines, the penetration of the coloring pigment makes the handwriting even more difficult to see, and there are cases in which handwriting is formed that appears to be made only of uncolored glittering pigment.

[0003] As aqueous ink compositions using the above-mentioned luster pigments, for example, aqueous inks using aluminum powder pigments (e.g., Patent Document 1), aqueous inks using pearl pigments (e.g., Patent Document 2), and aqueous inks using luster pigments to which acrylic acid polymers or salts thereof, olefin polymers, or urethane polymers have been added (e.g., Patent Document 3) have been disclosed.

[0004] However, in the aqueous ink compositions described in Patent Documents 1 and 2, the color pigment penetrates into the paper surface, forming handwriting that appears to consist only of the glitter pigment. Furthermore, when the handwriting comes into contact with water, the color pigment may bleed out.

[0005] Furthermore, in the water-based ink of Patent Document 3, the addition of acrylic acid polymers or their salts, olefin polymers, or urethane polymers suppresses the penetration of color pigments into the paper surface, and colored handwriting with a metallic luster is obtained. However, when the formed handwriting comes into contact with a large amount of water or when the handwriting is written on a writing surface such as paper with a coating applied to its surface, the color pigment may bleed out onto the writing surface. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 8-151547 [Patent Document 2] Japanese Patent Application Publication No. 7-118592 [Patent Document 3] Japanese Patent Application Publication No. 2017-119862 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention solves the conventional problems by providing an aqueous ink composition for a writing instrument that can form colored handwriting with a metallic luster tone without the color pigment, which is a coloring component, penetrating into a writing surface such as paper, and that furthermore does not bleed when the formed handwriting comes into contact with water or on any writing surface, and has excellent water resistance, and a writing instrument containing the same. [Means for solving the problem]

[0008] (1) An aqueous ink composition for a writing instrument, comprising at least a color pigment, a luster pigment, resin particles, an anion-modified polyvinyl alcohol, and water, wherein the content of the resin particles is less than 5% by mass based on the total mass of the ink composition.

[0009] (2) The aqueous ink composition for a writing instrument according to (1), wherein the anion-modified polyvinyl alcohol is a sulfonic acid group-modified polyvinyl alcohol and / or a carboxyl group-modified polyvinyl alcohol.

[0010] (3) The aqueous ink composition for a writing instrument according to (1) or (2), wherein the resin particles are at least one type selected from microcapsule particles.

[0011] (4) The aqueous ink composition for a writing instrument according to any one of (1) to (3), further comprising a shear thinning agent.

[0012] (5) A writing instrument containing the aqueous ink composition for a writing instrument according to any one of (1) to (4).

[0013] (6) The writing instrument according to (5), wherein the writing instrument is a ballpoint pen.

[0014] (7) A refill containing the aqueous ink composition for a writing instrument according to any one of (1) to (4). [Effects of the Invention]

[0015] According to the present invention, by adding an anion-modified polyvinyl alcohol, it is possible to provide a water-based ink composition for a writing instrument, which is capable of forming colored, colorful handwriting with a metallic luster without the color pigment penetrating the writing surface, and which has excellent water resistance and does not bleed even when it comes into contact with moisture, as well as a writing instrument and a refill containing the same. DETAILED DESCRIPTION OF THE INVENTION

[0016] Specific embodiments of the present invention will be described in detail below. However, the present invention is not limited to the embodiments described below.

[0017] In this specification, "parts," "%," "ratio," and the like indicating the composition are based on mass unless otherwise specified.

[0018] The aqueous ink composition for a writing instrument of the present invention (hereinafter sometimes referred to as "aqueous ink composition" or "aqueous ink") contains at least a color pigment (hereinafter sometimes simply referred to as "pigment"), a luster pigment, resin particles, anion-modified polyvinyl alcohol, and water, and is characterized in that the content of the resin particles is less than 5 mass% based on the total amount of the ink composition.

[0019] <Coloring pigments> The color pigment is not particularly limited, and any known pigment can be used, as long as it is a pigment other than a metal powder pigment such as aluminum powder or a pigment having brilliance such as a pearl pigment. Examples of suitable pigments include inorganic pigments, organic pigments, extender pigments, processed pigments, fluorescent pigments, phosphorescent pigments, and complementary color pigments. Specific examples of inorganic pigments include carbon black, graphite, titanium oxide, zinc oxide, iron black, yellow iron oxide, red iron oxide, composite oxide pigments, Prussian blue, ultramarine, talc, mica, and kaolin. Specific examples of organic pigments include azo pigments, indigo pigments, phthalocyanine pigments, quinacridone pigments, thioindigo pigments, threne pigments, perinone pigments, perylene pigments, phthalone pigments, dioxane pigments, isoindolinone pigments, metal complex pigments, methine azomethine pigments, and diketopyrrolopyrrole pigments. Specific examples of fluorescent pigments include inorganic fluorescent pigments and organic fluorescent pigments. Furthermore, water-dispersed pigments dispersed using surfactants, self-dispersed pigments, pigment dispersions in which pigments are dispersed in solvents, and lake pigments insolubilized by adding metal salts to dyes can also be used. Specific examples of water-dispersible pigments include CI Pigment Blue 15:3B (product name: SS Blue GLL-E, solids content 24%, manufactured by Sanyo Pigment Co., Ltd.), CI Pigment Red 146 (product name: SSPink FBL, solids content 21.5%, manufactured by Sanyo Pigment Co., Ltd.), CI Pigment Yellow 81 (product name: TC Yellow FG, solids content approximately 30%, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), and CI Pigment Red 220 / 166 (product name: TC Red FG, solids content approximately 35%, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.).

[0020] These color pigments may be used alone or in combination of two or more.

[0021] <Brilliant pigments> The luster pigment is not particularly limited as long as it exhibits luster by reflecting light in handwriting, and any known luster pigment can be used. Examples include metal powder pigments made of simple substances such as aluminum, chromium, copper, silver, nickel, tin, zinc, and indium, metal compounds, intermetallic compounds, alloys, and mixtures thereof; glass flake pigments coated with metal or metal oxide; pearl pigments with pearlescent luster such as bismuth oxychloride and fish scale foil; and glitter pigments.

[0022] The shape of the bright pigment is not particularly limited and can be appropriately selected. In the water-based ink of the present invention, in order to maintain the metallic luster of the handwriting while taking into consideration excellent jetting properties, it is preferable that the ink be in a plate-like shape such as a thin flake or scale shape.

[0023] The bright pigment may be an appropriately prepared product or a commercially available product. The method for producing the bright pigment is not particularly limited, and the pigment may be produced by a known production method.

[0024] For example, an aluminum pigment can be obtained as a paste of very thin, flaky aluminum particles by crushing and grinding aluminum flakes together with a petroleum-based solvent such as a higher fatty acid or mineral spirits in a ball mill or the like. Commercially available products include Alpaste WXM-0630, EMERAL EMR-D5660H, EMERAL EMR-D6390, and WJC-U75C (all manufactured by Toyo Aluminum Co., Ltd.). Alternatively, thin film aluminum obtained by vacuum deposition may be finely pulverized, and commercially available products include METALURE W-52012 IL and Ultravario Aqua PG-24001 (both manufactured by ECKART), LG neo Silver #500 (silver), and LG neo Gold #500 (gold) (both manufactured by Oike Kogyo Co., Ltd.).

[0025] Furthermore, pearlescent pigments are mainly classified into natural products such as fish scale foil and synthetic products in which the surface of natural mica, synthetic mica, silica, etc. is coated with a metal oxide such as titanium oxide. Synthetic pearlescent pigments include interference pearlescent pigments and colored pearlescent pigments, and they exhibit a variety of color tones depending on the type of metal oxide coated on the surface of a base material such as mica and the thickness of the coating film. Commercially available products include, for example, Iriodin 100 (silver), 111 (silver), 153 (silver), 201 (gold), 217 (copper), 289 (blue), 302 (gold), 504 (wine red), and 530 (copper) (all manufactured by Merck Japan Ltd.), and Ultimica SB-100 (silver) (all manufactured by Topy Industries Ltd.). Further, there are HELICONE HCS and HCXS (both manufactured by Wacker Chemie) which are called cholesteric liquid crystal type bright pigments.

[0026] Further, examples of glass flake pigments that can be used include metal-coated glass flake pigments in which the glass surface of glass flakes is coated with silver or nickel by electroless plating, and metal oxide-coated glass flake pigments in which the surface of glass flakes is coated with titanium dioxide by a liquid phase method. These glass flake pigments can be obtained in colors such as silver, yellow, red, blue, and green by changing the thickness of the titanium oxide film. Commercially available products include Metashine 2040PS, 2020PS, 5090NS, and 5090RC (all manufactured by Nippon Sheet Glass Co., Ltd.).

[0027] These bright pigments may be used alone or in combination of two or more depending on the desired hue and brightness. Furthermore, in order to ensure excellent ink ejection stability and obtain the desired hue, the amount of the luster pigment added is preferably from 1.0 to 20% by mass, more preferably from 1.0 to 16.0% by mass, and even more preferably from 3.0 to 8.0% by mass, relative to the total amount of the aqueous ink composition.

[0028] The particle size of the luster pigment used in the present invention is not particularly limited, but it is preferable to select a particle size that does not cause the luster pigment to clog the ejection groove (ink outlet hole) of the writing implement, resulting in poor writing. Furthermore, if the particle size is too small, it becomes difficult to obtain a sense of brilliance in handwriting, and if it is too large, it may hinder ink dischargeability or promote wear of the ball seat, so it is particularly preferable that the average particle size is in the range of 3 to 25 μm.

[0029] Furthermore, when a plate-shaped bright pigment is used, the aspect ratio (average particle diameter / average thickness) is preferably greater than 1, more preferably at least 5, and even more preferably at least 10. On the other hand, in consideration of the dispersibility of the bright pigment, the aspect ratio is preferably no greater than 200, and more preferably no greater than 100. The average particle size of the bright pigment is a volume-based average particle size (median size), and can be measured, for example, using a laser particle size distribution analyzer LA-300 (volume-based) manufactured by Horiba, Ltd.

[0030] <Resin particles> By adding resin particles to the water-based ink of the present invention, the jetting properties of the water-based ink can be improved, and further, wear of the ball and ball seat caused by the luminescent pigment or coloring pigment, as well as wear between the ball and the ball seat, can be suppressed.

[0031] The material of the resin particles is not particularly limited and can be appropriately selected and used. Examples include urethane-based resin particles, 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 an amino group. Examples of resin particles include microcapsule particles, spherical resin particles, and solid resin particles.

[0032] From the viewpoint of ink ejection stability and long-term storage stability, these resin particles are used in an amount of less than 5% by mass relative to the total amount of the aqueous ink composition. If the amount is 5% by mass or more, the resin particles may aggregate together in the ink reservoir or at the pen tip, causing unstable ejection and resulting in smeared handwriting or poor writing performance.

[0033] <Microcapsule particles> The microcapsule particles not only improve the ejection properties of the water-based ink, but also suppress abrasion of the ball and ball seat caused by the luminous pigment and colored pigment, and abrasion between the ball and the ball seat. Furthermore, they suppress the settling of the luminous pigment and colored pigment in the ink reservoir tube, providing excellent dispersion stability and enabling the formation of handwriting that does not cause smearing or uneven coloring over the long term.

[0034] Microcapsule particles are obtained by encapsulating the dispersion in a shell made of a wall-forming substance using a conventionally known microencapsulation method. Examples of wall-forming substances include gelatin, shellac, gum arabic, rosin, rosin ester, ethyl cellulose, carboxymethyl cellulose, paraffin, tristearin, polyvinyl alcohol, polyethylene, polypropylene, acrylic resins, vinyl resins, polyisobutene, polyurethane, polybutadiene, polyester, polyamide, epoxy resins, phenolic resins, silicone resins, polystyrene, and melamine resins, which can be used alone or in combination of two or more. Examples of the microencapsulation method include an interfacial polymerization method, an interfacial polycondensation method, an in situ polymerization method, a coacervation method, a liquid hardening coating method, a phase separation method from an aqueous solution, a phase separation method from an organic solvent, a melting dispersion cooling method, an air suspension coating method, and a spray drying method, and any of these methods can be appropriately selected.

[0035] The substances contained in the microcapsule particles may be substances that are liquid or solid under normal temperature and pressure, such as lipophilic compounds. Specific examples of lipophilic compounds include aromatic hydrocarbons, esters, ketones, higher alcohols, and ethers. The lipophilic compounds may be used singly or in combination of two or more. In this specification, normal temperature and normal pressure are 20°C, 1.01325 x 10 5 Refers to Pa.

[0036] The microcapsule particles can be microencapsulated to have an average particle size of 0.2 to 5 μm, preferably 0.5 to 3 μm. By setting the average particle size to 0.2 μm or more, aggregation of the bright pigment can be effectively suppressed with a small amount. Furthermore, by setting the average particle size to 5 μm or less, deterioration in the ejection properties of the microcapsule particles can be suppressed. The average particle size of microcapsules is the average particle size (median diameter) of particles equivalent to a sphere of equal volume. This can be optimally measured using a laser diffraction / scattering particle size distribution analyzer, LA-300, manufactured by Horiba, Ltd., which is a laser diffraction / scattering particle size distribution analyzer calibrated by a direct measurement method. Direct measurement methods used for calibration include: (i) Image analysis methods that measure the area (2D) of individual particles from images taken with a microscope to determine their equivalent diameter; or (ii) The Coulter method (electrical detection zone method) uses a Coulter counter to pass a constant current through a tiny aperture in the detector, and measures the equivalent diameter from the change in impedance that occurs when a particle passes through the aperture. The laser measurement method is calibrated based on the values ​​obtained by these methods. The average particle diameter can be measured by image analysis, for example, by determining the particle region using image analysis particle size distribution measurement software "MacView" manufactured by Mountech Co., Ltd., calculating the diameter equivalent to a circle with a projected area (Heywood diameter) from the area of ​​the particle region, and measuring the average particle diameter of particles equivalent to a sphere with an equal volume using this value. The Coulter method can be used to measure the average particle size when the particle size of all or most of the particles exceeds 0.2 μm. For example, the method can be performed using a particle size distribution analyzer, such as the Beckman Coulter Multisizer 4e.

[0037] The content of the microcapsule particles is less than 5% by mass based on the total amount of the ink composition. If the content is 5% by mass or more, the resin particles may aggregate together in the ink reservoir or at the pen tip, making the ink ejection unstable and resulting in smeared handwriting or poor writing performance.

[0038] <Anion-modified polyvinyl alcohol> In the present invention, by containing an anionic modified polyvinyl alcohol, the color pigment does not penetrate into the writing surface such as paper, and colored, colorful handwriting with a metallic luster is obtained, and further, the ink has excellent water resistance and is less likely to bleed even when it comes into contact with moisture.

[0039] The reason for this is not clear, but it is thought to be as follows. By having anionic substituents such as sulfonic acid groups or carboxyl groups (hereinafter sometimes referred to as "anionic groups"), the polyvinyl alcohol having anionic groups adsorbs to the luster pigment and color pigment in the writing marks formed on the writing surface, and serves to bind the luster pigment and color pigment together, preventing the color pigment from penetrating the writing surface and maintaining the luster pigment and color pigment together, resulting in a colored writing mark with a metallic luster. Furthermore, by having a polyvinyl alcohol structure, a film is formed so as to cover the tethered luster pigment and color pigment, making it difficult for moisture to penetrate between the luster pigment and color pigment, and the coloring component does not flow out even when it comes into contact with moisture, thereby maintaining the colored metallic luster tone. Furthermore, in aqueous inks, anionic polyvinyl alcohol is adsorbed onto the surfaces of resin particles such as microcapsule particles, thereby suppressing aggregation of solids in the aqueous ink composition, which is thought to prevent smearing and poor writing.

[0040] The anion-modified polyvinyl alcohol is not particularly limited, and any known polyvinyl alcohol substituted with an anion group can be appropriately selected and used. For example, carboxyl group-modified polyvinyl alcohol, sulfonic acid group-modified polyvinyl alcohol, etc. may be mentioned.

[0041] The anion-modified polyvinyl alcohol may be appropriately synthesized, or a commercially available product may be used. Examples of methods for synthesizing anion-modified polyvinyl alcohol include a method in which an anionic group is introduced by synthesizing a compound having an anionic group with polyvinyl alcohol, and a method in which a compound having an anionic group is polymerized with vinyl acetate and all or part of the vinyl acetate is saponified. Commercially available carboxyl group-modified polyvinyl alcohols include "GOSENEX T-330," "GOSENEX T-330H," and "GOSENEX T-350," all manufactured by Mitsubishi Chemical Corporation. Commercially available sulfonic acid group-modified polyvinyl alcohols include "GOSENEX L-3266" and "GOSENEX CKS-50," all manufactured by Mitsubishi Chemical Corporation.

[0042] The anion-modified polyvinyl alcohol may be fully saponified polyvinyl alcohol, intermediately saponified polyvinyl alcohol, or partially saponified polyvinyl alcohol, depending on the degree of saponification. The degree of saponification of the polyvinyl alcohol used in the present invention is not particularly limited, but is preferably 85% or more in consideration of obtaining colored handwriting with a metallic luster.

[0043] The composition ratio of the structure having an anionic group in the polyvinyl alcohol is not particularly limited, and the desired effect can be obtained as long as the polyvinyl alcohol is anion-modified and has an anionic group.

[0044] These anion-modified polyvinyl alcohols may be used alone or in combination of two or more. The content of anion-modified polyvinyl alcohol is preferably 0.3% by mass or more and 5.0% by mass or less, based on the total amount of the ink composition, and in consideration of excellent water resistance, it is more preferably 0.5% by mass or more and 3.0% by mass or less.

[0045] <Water> The water is not particularly limited, and examples thereof include tap water, ion-exchanged water, purified water, distilled water, ultrafiltered water, pure water, deep sea water, and groundwater.

[0046] <Shear thinning agent> The water-based ink of the present invention preferably further contains a shear thinning agent. By adding a shear thinning agent to the water-based ink, it is possible to improve the sedimentation resistance of the particle components (luminescent pigments, color pigments, resin particles, and microcapsule particles) during storage.

[0047] As the shear thinning agent, a substance that is soluble or dispersible in water is effective, and examples thereof include xanthan gum, welan gum, succinoglycan (average molecular weight: about 1,000,000 to 8,000,000) which is an organic acid-modified heteropolysaccharide whose constituent monosaccharides are glucose and galactose, guar gum, locust bean gum and its derivatives, hydroxyethyl cellulose, alginic acid alkyl esters, polymers having a molecular weight of 100,000 to 150,000 and containing as the main component an alkyl ester of methacrylic acid, glucomannan, and seaweed such as agar and carrageenin. Examples of such surfactants include carbohydrates having gelling properties extracted from the above, benzylidene sorbitol and benzylidene xylitol or derivatives thereof, alkali-thickening acrylic resins, crosslinkable acrylic acid polymers, poly-N-vinylcarboxylic acid amides, inorganic fine particles, nonionic surfactants with an HLB value of 8 to 12, and metal salts and amine salts of dialkyl sulfosuccinic acid. Furthermore, stable shear thinning properties can be imparted to the ink composition even when N-alkyl-2-pyrrolidone and anionic surfactants are added in combination.

[0048] <Other additives> Furthermore, if necessary, conventional water-soluble organic solvents that are compatible with water can be used, such as ethanol, propanol, butanol, glycerin, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thiodiethylene glycol, polyethylene glycol, propylene glycol, butylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, sulfolane, 2-pyrrolidone, and N-methyl-2-pyrrolidone. The water-soluble organic solvents can be used alone or in combination of two or more kinds, and are used in an amount of from 2% by mass to 60% by mass, preferably from 5% by mass to 35% by mass.

[0049] Furthermore, a water-soluble resin can be added to impart adhesiveness and viscosity to the paper surface. Examples of the water-soluble resin include alkyd resin, styrene-maleic acid copolymer, cellulose derivative, polyvinylpyrrolidone, polyvinyl alcohol, and dextrin. The water-soluble resins can be used alone or in combination of two or more, and are used in an amount of 1% by mass to 30% by mass in the ink composition.

[0050] In addition, various additives may be used as necessary. Specifically, pH adjusters such as inorganic salts such as sodium carbonate, sodium phosphate, and sodium acetate; organic basic compounds such as water-soluble amine compounds; rust inhibitors such as benzotriazole, tolyltriazole, 2,5-dimercapto-1,3,4-thiadiazole, and saponin; preservatives or antifungal agents such as carbolic acid, sodium salt of 1,2-benzthiazolin-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl parahydroxybenzoate, and 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine; wetting agents such as urea, nonionic surfactants, sorbitol, mannitol, sucrose, glucose, reduced starch hydrolysates, and sodium pyrophosphate; antifoaming agents; and fluorine-based surfactants and nonionic surfactants that improve the penetration of the ink may be used. Furthermore, air bubbles can also be removed chemically by adding ascorbic acids, erythorbic acids, α-tocopherol, catechins, synthetic polyphenols, kojic acid, alkylhydroxylamines, oxime derivatives, α-glucosylrutin, α-lipoic acid, phosphonates, phosphinates, sulfites, sulfoxylates, dithionites, thiosulfates, thiourea dioxide, or the like. Furthermore, by adding a thickening inhibitor such as an oligomer of N-vinyl-2-pyrrolidone, an oligomer of N-vinyl-2-piperidone, N-vinyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, ε-caprolactam, or an oligomer of N-vinyl-ε-caprolactam, the functionality in the retractable form can be improved. Furthermore, lubricants can be used, such as metal soaps, polyalkylene glycol fatty acid esters, ethylene oxide-added cationic surfactants, phosphate ester surfactants, β-alanine surfactants, N-acylamino acids, N-acylmethyltaurine, 2,5-dimercapto-1,3,4-thiadiazole, salts and oligomers thereof, 3-amino-5-mercapto-1,2,4-triazole, thiocarbamate, dimethyldithiocarbamate, α-lipoic acid, condensates of N-acyl-L-glutamic acid and L-lysine, and salts thereof.

[0051] <Writing implements> The structure and shape of the writing instrument to be filled with the aqueous ink composition for writing instruments of the present invention are not particularly limited, and conventional general-purpose ones can be applied, and the composition can be used for various writing instruments such as ballpoint pens with ballpoint pen tips, marking pens and felt-tip pens with fiber tips, felt tips, plastic tips, etc. as tips, and fountain pens with metal tips. The water-based ink of the present invention may also be a refill for a writing instrument in which the ink tip is accommodated in an ink reservoir tube to which the ink tip is attached directly or via a connecting member. Taking into consideration the ejection stability of the ink, the writing implement containing the water-based ink composition of the present invention is preferably a ballpoint pen.

[0052] <Ballpoint pens and ballpoint pen refills> When the water-based ink of the present invention is applied to a ballpoint pen, the structure of the writing tip of the ballpoint pen to be filled can be a conventional, general-purpose mechanism, and examples thereof include a tip in which a ball is held in a ball-holding portion formed by deforming the vicinity of the tip of a metal pipe by pressing inward from the outer surface, a tip in which a ball is held in a ball-holding portion formed by cutting a metal material with a drill or the like, a tip in which a resin ball receiving seat is provided inside a metal or plastic tip body, and a tip in which the ball held in the tip is urged forward by a spring body.

[0053] The materials for the tip and ball are not particularly limited, and general-purpose materials such as cemented carbide, stainless steel, ruby, ceramic, resin, rubber, etc. can be used, and the ball can also be surface-treated with a DLC coating, etc. The diameter of the balls used is preferably in the range of 0.1 mm to 2.0 mm, and more preferably 0.2 mm to 1.0 mm. In particular, with small ball diameters of 0.5 mm or less, the number of ball rotations relative to the writing distance is large, and therefore, inks using conventional glitter pigments are prone to seat wear. However, in the ink of the present invention, the resin particles and microcapsule particles are thought to act as rollers, and since writing can be done without seat wear even when using the small-diameter ball, the ink of the present invention functions more effectively in small-diameter ballpoint pens. Therefore, even small diameter ballpoint pens such as 0.5 mm, 0.4 mm, 0.38 mm, 0.35 mm, 0.3 mm, 0.28 mm, 0.25 mm, and 0.18 mm can exhibit excellent writing performance. Furthermore, among the ball materials, cemented carbide balls, which have high hardness, are prone to seat wear, and therefore the water-based ink composition of the present invention is particularly useful.

[0054] The ink filling mechanism may be, for example, an ink reservoir or ink storage body that can be directly filled with ink. The ink reservoir may be a molded body made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon, or a metal tubular body. Alternatively, the barrel itself may be used as the ink filling mechanism, and the ink may be directly filled into the barrel, and the barrel may be connected directly or via a connecting member to a ballpoint pen tip.

[0055] In addition, a ballpoint pen refill (hereinafter sometimes referred to as "refill") can be formed by connecting a ballpoint pen tip to an ink container directly or via a connecting member and directly filling the ink container with ink. By housing this refill in a barrel, a ballpoint pen can be formed.

[0056] Furthermore, an ink backflow preventer may be filled at the rear end of the ink filled in the ink reservoir. The ink backflow preventer may be a liquid stopper or a solid stopper, and a liquid stopper and a solid stopper may be used in combination.

[0057] The liquid plug is made of a non-volatile or hardly volatile liquid, such as petrolatum, spindle oil, castor oil, olive oil, refined mineral oil, liquid paraffin, polybutene, α-olefin, α-olefin oligomer or co-oligomer, dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, polyether-modified silicone oil, fatty acid-modified silicone oil, etc. It is preferable to add a thickener to non-volatile liquids and hardly-volatile liquids to thicken them to a suitable viscosity. Examples of such thickeners include clay-based thickeners such as silica with a hydrophobic surface treatment, fine particle silica with a methylated surface, aluminum silicate, swellable mica, and hydrophobically treated bentonite and montmorillonite; fatty acid metal soaps such as magnesium stearate, calcium stearate, aluminum stearate, and zinc stearate; dextrin-based compounds such as tribenzylidene sorbitol, fatty acid amides, amide-modified polyethylene wax, hydrogenated castor oil, and fatty acid dextrins; and cellulose-based compounds. These non-volatile or hardly-volatile liquids may be used alone or in combination of two or more.

[0058] Examples of solid plugs include solid plugs made of resin moldings such as polyethylene, polypropylene, and polymethylpentene, and sponges.

[0059] The ballpoint pen containing the water-based ink may be of either a cap type or a retractable type. Any retractable ballpoint pen can be used as long as the writing tip provided on the ballpoint pen refill is stored inside the outer barrel while exposed to the outside air, and the writing tip protrudes from the outer barrel opening when the retractable mechanism is activated. Examples of the method of operating the retractable mechanism include a knock type, a rotation type, and a slide type. The knock type may have a knock portion at the rear end or side surface of the outer shaft, and pressing the knock portion causes the writing tip of the ballpoint pen refill to protrude and retract from the opening at the front end of the outer shaft, or may have a clip portion provided on the outer shaft that is pressed to cause the writing tip of the ballpoint pen refill to protrude and retract from the opening at the front end of the outer shaft. The rotating type can be exemplified by a configuration in which the outer shaft has a rotating part (rear shaft, etc.), and the writing tip of the ballpoint pen refill appears and disappears from the front end opening of the outer shaft by rotating the rotating part. The sliding type can be exemplified by a configuration in which a sliding portion is provided on the side of the barrel, and the writing tip of the ballpoint pen refill is caused to protrude and retract from the opening at the front end of the outer barrel by operating the sliding portion, or by sliding a clip portion provided on the outer barrel, the writing tip of the ballpoint pen refill is caused to protrude and retract from the opening at the front end of the outer barrel. The retractable ballpoint pen may be a composite type retractable ballpoint pen that accommodates a plurality of ballpoint pen refills in addition to one that accommodates a single ballpoint pen refill in the outer barrel. Furthermore, the ink may be assisted in ejecting ink during writing by applying pressure such as compressed air to the ink.

[0060] In addition, in a ballpoint pen in which the ink composition is filled directly into the barrel itself, if the ink has a low viscosity, the ballpoint pen may further be provided with an ink supply mechanism for supplying the ink filled in the ink filling mechanism to the pen tip. The ink supply mechanism is not particularly limited, and examples include: (1) a mechanism that has an ink guide core made of a fiber bundle or the like as an ink flow rate regulator and supplies ink to the pen tip through this; (2) a mechanism that has a comb-shaped ink flow rate regulator and supplies ink to the pen tip through this; and (3) a mechanism that supplies ink to the pen tip through a pen core consisting of multiple disks arranged in parallel with comb-shaped intervals, with slit-shaped ink guide grooves running vertically through the disks in the axial direction and wider ventilation grooves than the grooves, and an ink guide core arranged in the axial center to guide ink from the ink filling mechanism to the pen tip.

[0061] The material of the pen core is not particularly limited, and synthetic resins that can be injection molded into a structure in which many discs are arranged in a comb-like groove pattern can be used. For example, from the viewpoint of obtaining high moldability and excellent pen core performance, acrylonitrile-butadiene-styrene copolymer (ABS resin) is preferably used.

[0062] The writing implement according to the present invention may also be in the form of an ink cartridge, which has a detachable structure. In this case, after the ink contained in the ink cartridge of the writing instrument has been used up, the writing instrument can be used again by replacing it with a new ink cartridge.

[0063] Ink cartridges that are connected to the writing instrument body and also serve as the barrel that makes up the writing instrument, or that cover and protect the barrel (rear barrel) after being connected to the writing instrument body, are used. In the latter case, the ink cartridge may be used alone, or the writing instrument may have the ink cartridge connected to the main body of the writing instrument before use, or may be stored in the barrel in an unconnected state so that the user of the writing instrument can connect the ink cartridge in the barrel when using it and begin use. [Example]

[0064] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Table 1 shows the compositions of the water-based inks of the examples and comparative examples. The composition values ​​in the table are in parts by mass. The average particle size of the bright pigment is measured using a laser particle size distribution measuring instrument LA-300 (volume basis) manufactured by Horiba, Ltd., and the median diameter is taken as the average particle size. The average particle size of the microcapsule particles was measured using a laser diffraction particle size distribution analyzer (manufactured by Horiba, Ltd., device name: LA-300) calibrated by the Coulter method (electrical detection zone method), and the average particle size (median size) and particle size based on volume were measured.

[0065] [Table 1]

[0066] The contents of the ingredients in the table are explained according to the note numbers. (1) Red pigment dispersion [Pigment Red 146, 21.5% by mass water dispersion, manufactured by Sanyo Pigment Co., Ltd., product name: Sandye Super Pink FBL] (2) Blue pigment dispersion [Pigment Blue 15:3B, 24% by mass water dispersion, manufactured by Sanyo Shiki Co., Ltd., product name: Sandye Super Blue GLL-E] (3) Aluminum powder paste [plate-shaped, average particle diameter: 7 μm, manufactured by Toyo Aluminum Co., Ltd., product name: Alpaste WXM-0630] (4) Aluminum powder paste [plate-shaped, average particle diameter: 9 μm, manufactured by Toyo Aluminum Co., Ltd., product name: Alpaste EMERAL EMR-D5660H] (5) Pearl pigment [plate-shaped, average particle size: 15 μm, manufactured by Merck Japan, product name: Iriodin 221] (6) Carboxyl-modified polyvinyl alcohol [manufactured by Mitsubishi Chemical Corporation, trade name: Gohsenex T-330] (7) Sulfonic acid group-modified polyvinyl alcohol [manufactured by Mitsubishi Chemical Corporation, trade name: Gohsenex L-3266] (8) Sulfonic acid group-modified polyvinyl alcohol [manufactured by Mitsubishi Chemical Corporation, trade name: Gohsenex CKS-50] (9) Polyvinyl alcohol [manufactured by Kuraray Co., Ltd., product name: Kuraray Poval 3-88] (10) Sodium salt of acrylic acid / sulfonic acid monomer copolymer [manufactured by Toagosei Co., Ltd., product name: Aron A-6017] (11) Carboxyl group-containing polyolefin emulsion [manufactured by Sumitomo Seika Chemicals Co., Ltd., product name: ZAIKUSEN A-GH] (12) Spherical resin particles [manufactured by Soken Chemical & Engineering Co., Ltd., trade name: Chemisnow MP-2200, average particle diameter 0.35 μm] (13) Microcapsule particles (average particle diameter: 2 μm, wall-forming material: urethane resin) encapsulating cetyl ethylhexanoate (specific gravity: 0.85) using interfacial polymerization. (14) Microcapsule particles (average particle size: 0.5 μm, wall-forming material: melamine resin) encapsulating isocetyl myristate (specific gravity: 0.86) using in situ polymerization. (15) Phosphate ester [manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name: Plysurf M208F] (16) Shear thinning agent [manufactured by Sansho Co., Ltd., product name: LEOSAN]

[0067] <Ink preparation> Each component was added to water and stirred at 2000 rpm in a disper at 20°C for 1 hour, after which a shear thinning agent was added and stirred for a further 1 hour to prepare each ink.

[0068] Preparation of ink backflow preventive 1.5 parts of fatty acid amide as a thickener was added to 98.5 parts of polybutene as a base oil, and then the mixture was kneaded with a three-roll mill to obtain an ink backflow preventive.

[0069] <Making a ballpoint pen> 1.0 g of the ink compositions of the above Examples and Comparative Examples was filled into a ballpoint pen refill having a stainless steel cutting tip holding a 0.4 mm diameter cemented carbide ball fitted to one end of a polypropylene pipe, and the ink backflow preventer was placed at the rear end of the ink. The ballpoint pen refill was then incorporated into the outer barrel and a cap was attached to prepare a sample ballpoint pen.

[0070] The following tests were carried out using the sample ballpoint pen and ink composition. The results obtained are shown in Table 1. <Written exam> After confirming that the sample ballpoint pens were writable, spiral circles were written continuously on JIS P3201 writing paper A using an automatic writing tester to check the condition of the writing and whether the ink filled in could be completely consumed (five pens of each type were tested). The tester was used under the conditions of a writing load of 100 g, a writing angle of 70°, and a writing speed of 4 m / min. Evaluations of "A" and "B" were considered to be acceptable. A: Good handwriting was formed and all the ink contained was used up. B: Some samples had skipped or smudged lines in the writing, but all of the ink contained was able to be written. C: Some samples became unusable midway through writing and ink remained. D: For all samples, the handwriting was skipped or faded, making it impossible to write halfway through and leaving ink behind.

[0071] <Handwriting Verification Test 1> Ten spiral circles were handwritten in succession on black paper (Hokuetsu Corporation, product name: Kishu Color High-Quality Black, medium-weight paper), and the handwriting was visually inspected and the hue was evaluated sensorily. A rating of "A" or "B" was considered acceptable. A: It has a clear brilliance and a vivid hue was obtained. B: There are some areas where color unevenness occurs, but the hue obtained is not problematic for practical use. C: No coloring was observed, and only a metallic luster was observed. D: No writing was formed and the hue could not be evaluated.

[0072] <Written Verification Test 2> After confirming that the sample ballpoint pens were writable, they were left in an environment of 50°C for 30 days with the pen tip facing downwards, and then 10 spiral circles were handwritten in succession on black paper (manufactured by Hokuetsu Corporation, product name: Kishu Color Wood-Stick Black, medium weight) at room temperature. The handwriting was visually inspected and the hue was evaluated. A rating of "A" or "B" was considered acceptable. A: It has a clear brilliance and a vivid hue was obtained. B: There are some areas where color unevenness occurs, but the hue obtained is not problematic for practical use. C: No coloring was observed, and only a metallic luster was observed. D: No writing was formed and the hue could not be evaluated.

[0073] <Water resistance test 1> Ten spiral circles were handwritten in succession on synthetic paper [Yupo Corporation, product name: New Yupo FGS (thickness: 200 μm)], and after one hour of writing, the paper was immersed in a plastic basin filled with tap water for 15 minutes and visually inspected for bleeding of the color pigment. A rating of "A" or "B" was considered a pass. A: No bleeding of color pigments was observed. B: There were some areas where the hue was lighter, but there was no bleeding of the color pigment, and it was not a problem in practical use. C: The color pigment bled out slightly, and the hue was lighter than before immersion. D: The color pigment bled out, the hue was lost, and the paper surface was stained with the bled color pigment. E: No mark was formed, and water resistance could not be evaluated.

[0074] <Water resistance test 2> Ten spiral circles were handwritten in succession on JIS P3201 writing paper A, and after one hour of writing, the paper was immersed in a plastic basin filled with tap water for one hour, and the state of bleeding of the color pigment was checked visually. Evaluations of "A" and "B" were considered passing. A: No bleeding of color pigments was observed. B: There were some areas where the hue was lighter, but there was no bleeding of the color pigment, and it was not a problem in practical use. C: The color pigment bled out slightly, and the hue was lighter than before immersion. D: The color pigment bled out, the hue was lost, and the paper surface was stained with the bled color pigment. E: No mark was formed, and water resistance could not be evaluated.

Claims

1. An aqueous ink composition for a writing instrument, comprising at least a color pigment, a luster pigment, resin particles, anion-modified polyvinyl alcohol, and water, wherein the content of the resin particles is less than 5 mass% based on the total mass of the ink composition.

2. 2. The aqueous ink composition for a writing instrument according to claim 1, wherein the anion-modified polyvinyl alcohol is a sulfonic acid group-modified polyvinyl alcohol and / or a carboxyl group-modified polyvinyl alcohol.

3. 3. The aqueous ink composition for a writing instrument according to claim 1, wherein the resin particles are microcapsule particles.

4. The aqueous ink composition for a writing instrument according to claim 1 , further comprising a shear thinning agent.

5. A writing instrument containing the aqueous ink composition for a writing instrument according to any one of claims 1 to 4.

6. 6. The writing instrument according to claim 5, wherein the writing instrument is a ballpoint pen.

7. A refill containing the aqueous ink composition for a writing instrument according to any one of claims 1 to 4.

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