Water-based ink composition for ballpoint pens and ballpoint pens containing the same.

Abstract

The objective is to provide a water-based ink composition for ballpoint pens and a ballpoint pen containing this composition, which can suppress ink blotting and stably produce good writing lines by using a polymer composed of three monomers—vinyl acetate, methyl methacrylate, and methacrylic acid—and a polyalkylene oxide in combination in a water-based ink. [Solution] A water-based ink composition for ballpoint pens comprising at least a colorant, water, a shear viscosity reducing agent, and a polyalkylene oxide, wherein the shear viscosity reducing agent is a polymer composed of three monomers: vinyl acetate, methyl methacrylate, and methacrylic acid.

Description

Technical Field

[0001] The present invention relates to an aqueous ink composition for ballpoint pens and a ballpoint pen containing the same.

Background Art

[0002] Conventionally, aqueous inks having shear-thinning properties have been widely known. An ink having shear-thinning properties shows a high viscosity when the ink is stationary without shear stress and is stably held in the ballpoint pen mechanism. When writing, due to the high shear stress caused by the rotation of the ball, the viscosity decreases near the ball, and the ink is transferred to the paper surface. The ink transferred to the paper surface has a small shear stress and returns to a high-viscosity state again, so that bleeding of the handwriting, which is a problem of conventional aqueous ink compositions, does not occur.

[0003] Examples of these aqueous inks having shear-thinning properties include an aqueous ink composition for ballpoint pens containing xanthan gum and an aqueous ink composition for ballpoint pens in which a polymer composed of three monomers of vinyl acetate, methyl methacrylate, and methacrylic acid is added as a shear-thinning agent (see, for example, Patent Documents 1 and 2).

[0004] In the aqueous ink composition for ballpoint pens using xanthan gum described in Patent Document 1, writing defects such as streaks in the handwriting may occur after a long period of time. In addition, excess ink that did not transfer to the paper surface during writing and did not return inside the ballpoint pen tip accumulated at the tip of the ballpoint pen tip, and "bleeding" occurred due to the excess ink accumulated at the tip falling onto the paper surface. On the other hand, in the aqueous ink composition for ballpoint pens using the polymer described in Patent Document 2, although writing defects such as streaks in the handwriting do not occur after a long period of time, bleeding may occur.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Publication No. 59-074175 [Patent Document 2] Japanese Patent Publication No. 2003-253184 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] This disclosure aims to solve the problems of the past by providing an aqueous ink composition for ballpoint pens and a ballpoint pen containing the same, which can suppress ink smudging and stably produce good writing by using a polymer composed of three monomers: vinyl acetate, methyl methacrylate, and methacrylic acid, and a polyalkylene oxide in combination in an aqueous ink. [Means for solving the problem]

[0007] [1] A water-based ink composition for ballpoint pens comprising at least a colorant, water, a shear viscosity reducing agent, and a polyalkylene oxide, wherein the shear viscosity reducing agent is a polymer composed of three monomers: vinyl acetate, methyl methacrylate, and methacrylic acid.

[0008] [2] The aqueous ink composition for ballpoint pens according to [1], wherein the coloring agent is a pigment.

[0009] [3] The aqueous ink composition for ballpoint pens according to [1] or [2], wherein the polyalkylene oxide is polyethylene oxide.

[0010] [4] The water-based ink composition for ballpoint pens according to any one of [1] to [3], wherein the weight-average molecular weight of the polyalkylene oxide is 2 million to 6 million.

[0011] [5] The aqueous ink composition for ballpoint pens according to any one of [1] to [4], wherein the content of the polyalkylene oxide is 0.01% to 1.0% by mass with respect to the total amount of the aqueous ink composition.

[0012] A ballpoint pen containing an aqueous ink composition for ballpoint pens as described in any of [6] [1] to [5]. [Effects of the Invention]

[0013] According to this disclosure, when a polymer composed of three monomers, vinyl acetate, methyl methacrylate, and methacrylic acid, is used as a shear viscosity-reducing agent in an aqueous ink, the use of polyalkylene oxide in combination can suppress ink blotting and stably produce good handwriting. [Modes for carrying out the invention]

[0014] Specific embodiments of the present invention will be described in detail below. However, the embodiments are not limited to those described below.

[0015] In this specification, "parts," "%," and "ratio" indicating content are based on mass unless otherwise specified.

[0016] The aqueous ink composition for ballpoint pens of this disclosure (hereinafter referred to as "aqueous ink," "ink composition," or "ink" as may be used) comprises at least a colorant, water, a shear viscosity reducing agent, and a polyalkylene oxide, wherein the shear viscosity reducing agent is a polymer composed of three monomers: vinyl acetate, methyl methacrylate, and methacrylic acid.

[0017] By using a polymer composed of three monomers—vinyl acetate, methyl methacrylate, and methacrylic acid—and polyalkylene oxide in a water-based ink, excess ink that does not transfer to the paper surface during writing and does not return to the ballpoint pen tip accumulates at the tip of the pen tip. This excess ink then drips onto the paper, suppressing the "blotting" effect and resulting in a smooth writing line.

[0018] <Polymer composed of three monomers: vinyl acetate, methyl methacrylate, and methacrylic acid> The aqueous ink of the present disclosure contains a polymer composed of three monomers: vinyl acetate, methyl methacrylate, and methacrylic acid (hereinafter, sometimes referred to as "polymer"). The polymer composed of three monomers: vinyl acetate, methyl methacrylate, and methacrylic acid of the present disclosure can impart shear thinning viscosity to the aqueous ink.

[0019] The polymer composed of three monomers: vinyl acetate, methyl methacrylate, and methacrylic acid of the present disclosure has a weight ratio of each monomer in the range of 20 to 60% by weight of vinyl acetate, 10 to 15% by weight of methyl methacrylate, and 20 to 35% by weight of methacrylic acid, and the weight average molecular weight of the polymer is preferably in the range of 500,000 to 6,000,000, and more preferably the weight ratio of each monomer is in the range of 20 to 60% by weight of vinyl acetate, 10 to 15% by weight of methyl methacrylate, and 20 to 35% by weight of methacrylic acid, and the weight average molecular weight of the polymer is in the range of 1,100,000 to 6,000,000. By having the above weight ratio and average molecular weight, good writing performance can be exhibited.

[0020] In addition, since the polymer of the present disclosure is of the alkali swelling type, at the time of ink preparation, an alkaline pH adjuster or the like is mixed into a mixture of a colorant, a polymer, and various additives in a solvent in advance to adjust the ink to be alkaline, and a preparation method for imparting shear thinning viscosity is preferred. The pH of the prepared ink composition is preferably more than 7 and 12 or less, and more preferably more than 7 and 11 or less.

[0021] The content of the polymer composed of three monomers: vinyl acetate, methyl methacrylate, and methacrylic acid is preferably 0.05 to 20% by mass, more preferably 0.1 to 10% by mass, and still more preferably 0.1 to 5% by mass based on the total amount of the aqueous ink composition. By having a content of 0.05 mass% or more, it is easy to obtain a desired shear thinning viscosity, and by being 20 mass% or less, it is easy to stabilize the ink ejection property.

[0022] <Polyalkylene oxide> The aqueous ink of the present disclosure contains a polyalkylene oxide. By containing a polyalkylene oxide, it is possible to suppress bleeding without impairing the shear thinning viscosity of the polymer composed of three monomers of vinyl acetate, methyl methacrylate, and methacrylic acid.

[0023] Examples of the polyalkylene oxide include polyethylene oxide, polypropylene oxide, and the like. These polyalkylene oxides may be used alone or in combination of two or more.

[0024] The weight average molecular weight of the polyalkylene oxide is not particularly limited, but from the point of being less likely to affect the physical properties of the ink, it is preferably in the range of 2 million to 6 million, more preferably in the range of 2.5 million to 5.5 million, and even more preferably in the range of 3 million to 5 million.

[0025] The content of the polyalkylene oxide is not particularly limited, but with respect to the total amount of the aqueous ink composition, 0.01 to 1 mass% is preferable, 0.05 to 0.5 mass% is more preferable, and 0.1 to 0.3 mass% is even more preferable. By setting the content to 0.01 mass% or more, bleeding can be more suppressed, and by setting the content to 1 mass% or less, dry-up can be suppressed. Note that "dry-up" refers to a phenomenon in which when the tip end portion of the ballpoint pen tip (hereinafter, sometimes referred to as "pen tip") is left exposed, the ink dries at the tip end portion, and the rewritability such as the writing trace being blurred during writing deteriorates.

[0026] <Polyethylene oxide> Among polyalkylene oxides, polyethylene oxide is preferred due to its superior solubility in water and pigment dispersion stability.

[0027] The weight-average molecular weight of polyethylene oxide is not particularly limited, but is preferably in the range of 2 million to 6 million, more preferably in the range of 2.5 million to 5.5 million, and even more preferably in the range of 3 million to 5 million, as it does not significantly affect the physical properties of the ink.

[0028] The polyethylene oxide content is preferably 0.01 to 1% by mass, more preferably 0.05 to 0.5% by mass, and even more preferably 0.1 to 0.3% by mass, based on the total amount of the aqueous ink composition. By setting the content to 0.01% by mass or more, crying can be further suppressed, and by setting the content to 1% by mass or less, drying out can be suppressed.

[0029] <Coloring agent> As colorants, any dyes, pigments, and resin particles that can be dissolved or dispersed in an aqueous medium can be used. In other words, the colorant may contain one or more selected from the group consisting of dyes, pigments, and resin particles.

[0030] <dye> Examples of dyes include acid dyes, basic dyes, direct dyes, reactive dyes, vat dyes, sulfur dyes, alloy dyes, cationic dyes, and disperse dyes.

[0031] <Pigments> When a pigment is used as a coloring agent in the aqueous ink of this disclosure, the aggregation and sedimentation of the pigment in the aqueous ink can be effectively suppressed by using a polymer composed of three monomers: vinyl acetate, methyl methacrylate, and methacrylic acid, in combination with a polyalkylene oxide.

[0032] Examples of pigments include inorganic pigments, organic pigments, luminescent pigments, fluorescent pigments, and phosphorescent pigments. Furthermore, water-dispersible pigments can also be used, in which the pigment is finely and stably dispersed in an aqueous medium using at least one of a surfactant and a resin beforehand.

[0033] Furthermore, a pigment dispersant may be used as needed. Examples of pigment dispersants include anionic and nonionic surfactants; anionic polymers such as polyacrylic acid and styrene-acrylic acid; and nonionic polymers such as PVP and PVA.

[0034] Furthermore, the pigment may be a self-dispersing pigment. Self-dispersing pigments are pigments that can be dispersed in an aqueous medium without the use of dispersants such as resins or surfactants. By subjecting the pigment to physical or chemical treatment to form hydrophilic functional groups on its surface, it becomes possible to disperse the pigment in an aqueous medium without the use of dispersants. Applicable pigments include carbon black, benzimidazoline pigments, condensed azo pigments, isoindolinone pigments, quinophthalone pigments, quinacridone pigments, phthalocyanine pigments, and aluminum.

[0035] Furthermore, the pigment may be a microencapsulated pigment. Microcapsule pigments contain a core substance encased in a wall film formed by a wall-forming material. By encapsulating the core substance in microcapsules, it is isolated and protected from the external environment, thereby improving the water resistance and light resistance of the core substance.

[0036] Examples of core materials include colored compositions comprising a coloring material and a medium. Examples of colored compositions include those in which a dye or pigment as a coloring material is dissolved or dispersed in an aqueous or oily medium. The dyes or pigments described above may be used.

[0037] Examples of aqueous media include tap water, deionized water, ultrafiltered water, and distilled water. Examples of oily media include monobasic acid esters, dibasic acid monoesters, dibasic acid diesters, esters such as partial or complete esters of polyhydric alcohols, aromatic hydrocarbons such as alkylbenzenes and alkylnaphthalenes, higher alcohols, ketones, and ethers. Aqueous or oily media may be used individually or in combination of two or more types.

[0038] As the coloring composition, a photochromic material that changes color depending on the presence or absence of light irradiation may be used. This color change may be reversible or irreversible, but a reversible photochromic material is preferred because it can repeatedly exhibit color changes depending on the presence or absence of light irradiation. Examples of photochromic materials used in colored compositions include colored compositions in which a photochromic compound as a coloring material is dissolved in an oligomer as a medium, i.e., reversible photochromic compositions consisting of at least a photochromic compound and an oligomer. By encapsulating the reversible photochromic composition in microcapsules, reversible photochromic microcapsule pigments can be formed.

[0039] Examples of photochromic compounds include conventionally known spirooxazine derivatives, spiropyran derivatives, naphthopyran derivatives, etc., which develop color when irradiated with sunlight or light containing ultraviolet light such as ultraviolet light, or with purple or blue light having a peak emission wavelength in the range of 400 to 495 nm, and lose their color when irradiation is stopped. Examples include the compounds described in Japanese Patent Publication No. 2021-120493 and International Publication No. 2020 / 137469. Furthermore, photochromic compounds having optical memory properties (color memory photochromic properties) can also be used. Examples of such photochromic compounds include diarylethene derivatives, and for example, the compound described in Japanese Patent Application Publication No. 2021-120493 can be cited.

[0040] Examples of oligomers include styrene-based oligomers, acrylic-based oligomers, terpene-based oligomers, and terpene-phenol-based oligomers. By dissolving photochromic compounds in various oligomers, both lightfastness and color intensity can be improved, and the sensitivity to color change can also be adjusted. Oligomers can be used individually or in combination of two or more types.

[0041] Furthermore, a thermochromic material that changes color with temperature changes may be used as the coloring composition. This color change may be reversible or irreversible, but a reversible thermochromic material is preferred because it can repeatedly exhibit color changes due to temperature changes. Examples of thermochromic materials used in colored compositions include colored compositions comprising at least (a) an electron-donating chromogenic organic compound as a coloring material and (b) an electron-accepting compound as a medium. Furthermore, examples of colored compositions comprising at least a homogeneous compatible solution of component (a) as a coloring material and component (b) as a medium, and a reaction medium that determines the temperature at which the color reaction of components (a) and (b) occurs, i.e., a reversible thermochromic composition comprising at least (a) an electron-donating chromogenic organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color reaction of components (a) and (b) occurs. Reversible thermochromic microcapsule pigments can be formed by encapsulating the reversible thermochromic composition in microcapsules.

[0042] As the reversible thermochromic composition, a heat-decolorizing type reversible thermochromic composition having a relatively small hysteresis width (ΔH) (ΔH = 1 to 7°C), as described in Japanese Patent Publication No. 51-44706, Japanese Patent Publication No. 51-44707, Japanese Patent Publication No. 1-29398, etc., can be used. This reversible thermochromic composition changes color before and after a predetermined temperature (color change point), exhibiting a decolorized state in the temperature range above the high-temperature color change point and a colored state in the temperature range below the low-temperature color change point. Of the two states, only one specific state exists in the room temperature range, and the other state is maintained as long as the heat or cold required to bring about that state is applied, but returns to the state exhibited in the room temperature range when the application of heat or cold is stopped. Furthermore, as a reversible thermochromic composition, a heat-decolorizing type reversible thermochromic composition having a large hysteresis width (ΔH = 8 to 80°C) as described in Japanese Patent Publication No. 4-17154, Japanese Patent Application Publication No. 7-179777, Japanese Patent Application Publication No. 7-33997, Japanese Patent Application Publication No. 8-39936, Japanese Patent Application Publication No. 2005-1369 can also be used. In this reversible thermochromic composition, the shape of the curve plotted for the change in color intensity due to temperature change follows a significantly different path depending on whether the temperature is raised from a temperature lower than the color change temperature range or lowered from a temperature higher than the color change temperature range. The colored state at temperatures below the complete color development temperature t1, or the decolorized state at high temperatures above the complete decolorization temperature t4, exhibits color memory in a specific temperature range [the temperature range between the color development start temperature t2 and the decolorization start temperature t3 (essentially a two-phase retention temperature range)]. Furthermore, "heat-decolorizing type" means that it decolorizes when heated and develops color when cooled.

[0043] When applying the above-described reversible thermochromic composition with color memory properties, the reversible thermochromic composition can be specifically configured such that the complete color development temperature t1 is a temperature that can only be obtained in a freezer or cold region, and the complete decolorization temperature t4 is a temperature that can be obtained from frictional heat from a friction body or a familiar heating element such as a hair dryer, and the ΔH value is specified to be 40 to 100°C, thereby effectively maintaining the color exhibited under normal conditions (daily living temperature range). Temperatures that can only be obtained in a freezer or cold region are in the range of -50 to 0°C, preferably -40 to -5°C, and more preferably -30 to -10°C. The temperature obtained from readily available heating elements such as hair dryers is 50 to 95°C, preferably in the range of 50 to 90°C, and more preferably in the range of 60 to 80°C.

[0044] As a reversible thermochromic composition, a heat-activated, reversible thermochromic composition using gallic acid ester, as described in Japanese Patent Publication No. 51-44706, Japanese Patent Application Publication No. 2003-253149, etc., can also be used. Furthermore, "heat-activated coloring type" means that the color develops when heated and disappears when cooled.

[0045] The reversible thermochromic composition is a compatible mixture containing the above-mentioned components (a), (b), and (c) as essential components. The proportion of each component depends on the concentration, discoloration temperature, discoloration form, and type of each component, but generally, the component ratios that yield the desired properties are in the range of 1 part (a) to 0.1 to 100 parts (b), preferably 0.1 to 50, more preferably 0.5 to 20 parts (c), and 1 to 800 parts (c), preferably 5 to 200, more preferably 5 to 100, and even more preferably 10 to 100 parts (c).

[0046] Examples of wall-forming materials, i.e., resins that constitute the wall film, include urea resins, urethane resins, urea-urethane resins, epoxy resins, melamine resins, benzoguanamine resins, isocyanate resins, and the like.

[0047] Microcapsule pigments may contain various additives, such as antioxidants, ultraviolet absorbers, infrared absorbers, solubilizers, preservatives, and fungicides, to the extent that they do not affect their function.

[0048] Microencapsulated pigments can be manufactured by microencapsulation methods. Examples of conventional microencapsulation methods include isocyanate-based interfacial polymerization, melamine-formaldehyde-based in situ polymerization, liquid curing coating, phase separation from aqueous solutions, phase separation from organic solvents, melt-dispersion-cooling, air suspension coating, and spray drying. These methods are selected appropriately depending on the application. Furthermore, depending on the purpose, a secondary resin coating can be applied to the surface of the microcapsule pigment to provide durability or modify its surface properties for practical use.

[0049] The reversible thermochromic microcapsule pigment or the reversible photochromic microcapsule pigment preferably has a core material:wall film mass ratio of 7:1 to 1:1. By having the core material to wall film mass ratio within the above range, a decrease in color density and vividness during color development can be prevented. More preferably, the core material:wall film mass ratio is 6:1 to 1:1.

[0050] Reversible thermochromic microcapsule pigments or reversible photochromic microcapsule pigments can also be made into microcapsule pigments that exhibit a color change behavior from a first color to a second color by incorporating a non-color-changing coloring agent such as a general dye or pigment into the microcapsule.

[0051] <Resin particles> When resin particles are used as a colorant in the aqueous ink of this disclosure, the aggregation and sedimentation of resin particles in the aqueous ink can be effectively suppressed by using a polymer and polyalkylene oxide in combination.

[0052] Examples of resin particles include resin particles containing at least one of the above-mentioned dyes, pigments, thermochromic materials, and photochromic materials.

[0053] Examples of resin particles containing dyes include colored resin particles in which the dye is homogeneously dissolved or dispersed within the resin particles, and colored resin particles in which the dye is deposited onto the resin particles.

[0054] Examples of resin particles containing pigments include colored resin particles in which the pigment is homogeneously dispersed within the resin particles, and colored resin particles in which the surface of the resin particles is coated with pigment. Here, the pigment may be surface-treated by various conventionally known methods for the purpose of improving its dispersibility and adsorption to the resin constituting the resin particles.

[0055] Examples of resin particles containing a thermochromic material or a photochromic material include colored resin particles in which a reversible thermochromic composition is homogeneously dispersed (hereinafter, sometimes referred to as "reversible thermochromic resin particles") and colored resin particles in which a reversible photochromic composition is homogeneously dispersed (hereinafter, sometimes referred to as "reversible photochromic resin particles").

[0056] The resin constituting the resin particles can be any thermoplastic resin or thermosetting resin without any particular limitations. Examples of thermoplastic resins include polystyrene, acrylic resin, polyester, polyvinyl chloride, polybutadiene, polymethyl methacrylate, acrylic-urethane copolymer resin, polyethylene, polypropylene, polyacrylonitrile, polyacetal, ethylene-propylene copolymer resin, ethylene-vinyl acetate copolymer resin, styrene-acrylic copolymer resin, styrene-butadiene copolymer resin, styrene-acrylonitrile copolymer resin, and acrylonitrile-butadiene copolymer resin. Examples of thermosetting resins include epoxy resin, epoxy acrylate resin, xylene resin, toluene resin, guanamine resin, benzoguanamine resin, melamine resin, urethane resin, phenolic resin, alkyd resin, polyamide, polyimide, polyamide ester, urea resin, silicone resin, and unsaturated polyester.

[0057] The resin particles may be solid resin particles with no voids inside, or hollow resin particles with voids inside.

[0058] Resin particles can be produced by pulverization, spray drying, or polymerization in which a dye, pigment, thermochromic material, and photochromic material are polymerized in an aqueous or oily medium. Examples of polymerization methods include suspension polymerization, suspension polycondensation, dispersion polymerization, and emulsion polymerization.

[0059] The shape of the resin particles is not particularly limited and can include spherical, ellipsoidal, or nearly spherical shapes, as well as polygonal and flattened shapes, with spherical resin particles being preferred.

[0060] Reversible thermochromic resin particles or reversible photochromic resin particles can also be made into resin particles that exhibit a color change behavior from a first color to a second color by incorporating non-color-changing colorants such as general dyes or pigments into the resin particles.

[0061] It is preferable to use a reversible thermochromic composition or a reversible photochromic composition as a microcapsule pigment by encapsulating it in microcapsules. This is because encapsulating it in microcapsules allows for the formation of a chemically or physically stable pigment, and furthermore, under various usage conditions, the reversible thermochromic composition or reversible photochromic composition maintains the same composition and can exert the same effects.

[0062] The colorants disclosed herein may be used individually or in combination of two or more.

[0063] When the coloring agent is a reversible thermochromic microcapsule pigment or a reversible photochromic microcapsule pigment, or a reversible thermochromic resin particle or a reversible photochromic resin particle, the average particle size of these coloring agents is not particularly limited, but is preferably in the range of 0.01 to 5 μm, more preferably 0.1 to 3 μm, and even more preferably 0.5 to 3 μm. When the average particle size of the colorant is 5 μm or less, good ink ejection is easily obtained when used in a ballpoint pen, and when the average particle size is 0.01 μm or more, it is easier to obtain high-density color development in the handwriting.

[0064] The average particle diameter was measured using image analysis-based particle size distribution measurement software [Mountec Co., Ltd., product name: MacView] to determine the particle area, calculate the projected area circle equivalent diameter (Heywood diameter) from the area of ​​the particle area, and then measure the average particle diameter of particles equivalent to an equivolute sphere based on that value.

[0065] Furthermore, if the particle size of all or most of the particles exceeds 0.2 μm, it is also possible to measure the average particle size of particles equivalent to equivolute spheres using the Coulter method with a particle size distribution analyzer [Beckman Coulter, Ltd., product name: Multisizer 4e].

[0066] Furthermore, volume-based particle diameter and average particle diameter may be measured using a laser diffraction / scattering particle size distribution analyzer (manufactured by Horiba, Ltd., product name: LA-960V2) that has been calibrated based on the values ​​measured using the above-mentioned software or measuring device using the Coulter method.

[0067] The colorant content is not particularly limited, but is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 3 to 10% by mass, relative to the total amount of water-based ink. By limiting the content to 20% by mass or less, stable ink discharge performance of the writing instrument containing the ink composition can be obtained, and by limiting the content to 0.5% by mass or more, excellent color development of the handwriting can be obtained.

[0068] When the colorant is a reversible thermochromic microcapsule pigment or a reversible photochromic microcapsule pigment, or a reversible thermochromic resin particle or a reversible photochromic resin particle, the content of the colorant relative to the total amount of the ink composition is preferably in the range of 5 to 40% by mass, more preferably 10 to 40% by mass, and even more preferably 10 to 30% by mass. By setting the content to 40% by mass or less, stable ink discharge performance of the writing instrument containing the ink composition can be obtained, and by setting the content to 5% by mass or more, excellent color development of the writing can be obtained, and the color-changing function can also be fully satisfied.

[0069] <Water> There are no particular restrictions on the type of water that can be used; for example, tap water, deionized water, purified water, distilled water, ultrafiltered water, pure water, deep-sea water, groundwater, etc. The water content is not particularly limited, but is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, and even more preferably 20 to 70% by mass, relative to the total amount of water-based ink.

[0070] <Other additives> The aqueous inks of this disclosure may further contain various additives as needed. Examples of additives include water-soluble organic solvents, water-soluble resins, pH adjusters, rust inhibitors, preservatives, fungicides, wetting agents, defoamers, dispersants, surfactants, and lubricants.

[0071] The ink may further contain a water-soluble organic solvent to adjust its viscosity. Examples of water-soluble organic solvents include 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, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, sulforane, 2-pyrrolidone, and N-methyl-2-pyrrolidone. Water-soluble organic solvents can be used individually or in combination of two or more, and are used in an amount of 2 to 60% by mass, preferably 5 to 35% by mass.

[0072] The material may further contain a water-soluble resin for the purpose of providing adhesion and viscosity to the paper surface. As the water-soluble resin, for example, one or more of the following may be used: alkyd resin, acrylic resin, styrene-maleic acid copolymer, cellulose derivative, polyvinylpyrrolidone, polyvinyl alcohol, dextrin, etc.

[0073] In addition, as needed, pH adjusters such as inorganic salts like sodium carbonate, sodium phosphate, and sodium acetate, and organic basic compounds such as water-soluble amine compounds, rust inhibitors such as benzotriazole, tolyltriazole, dicyclohexylammonium nitride, diisopropylammonium nitride, and saponins, preservatives or fungicides 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, urea, nonionic surfactants, reduced or non-reduced starch hydrolysates, oligosaccharides such as trehalose, humectants such as sucrose, cyclodextrin, glucose, dextrin sorbitin, mannitol, and sodium pyrophosphate, defoamers, dispersants, and fluorinated surfactants or nonionic surfactants to improve ink penetration may be used. Other examples of lubricants include metal soaps, polyalkylene glycol fatty acid esters, ethylene oxide-additive cationic surfactants, phosphate ester surfactants, thiocarbamates, and dimethyldithiocarbamates. Suitable lubricants include monophosphate esters of polyoxyethylene alkyl ethers or polyoxyethylene alkylaryl ethers, diphosphate esters of polyoxyethylene alkyl ethers or polyoxyethylene alkylaryl ethers, and their metal salts, ammonium salts, amine salts, and alkanolamine salts.

[0074] The aqueous ink composition of this disclosure is filled into a ballpoint pen having a ballpoint pen tip attached to the writing end. The structure and shape of the ballpoint pen itself are not particularly limited, and conventional general-purpose designs can be applied. For example, when the ink composition is low viscosity, an ink retaining member is attached to the front of the barrel, and the ink composition is directly contained within the barrel. Alternatively, a structure can be described in which the ink composition is impregnated into a porous body or a fibrous material and contained within. Furthermore, an example of a ballpoint pen can be described in which an ink storage tube filled with the ink composition is located inside the barrel, the ink storage tube is connected to a tip with a ball attached to its end, and an ink backflow prevention body is closely attached to the end face of the ink to prevent backflow.

[0075] To explain ballpoint pen tips in more detail, some tips are made by holding a ball in a ball-holding portion formed by pressing the tip of a metal pipe inward from the outer surface, or by holding a ball in a ball-holding portion formed by cutting a metal material with a drill or the like, or by biasing the ball held in a tip made of a metal pipe or metal material forward (outward) with an elastic body. Furthermore, the ball can be made of cemented carbide, stainless steel, ruby, ceramic, etc., and is preferably made of a diameter in the range of 0.1 mm to 2.0 mm.

[0076] The ink container for housing the aqueous ink composition of this disclosure is preferably made of a molded body made of a thermoplastic resin such as polyethylene, polypropylene, or polyethylene terephthalate, in terms of low ink evaporation and productivity. Furthermore, by using a transparent, colored transparent, or translucent molded body as the ink container, the ink color and remaining ink amount can be checked. In addition to directly connecting the tip to the ink reservoir tube, the ink reservoir tube and the tip may also be connected via a connecting member. The ink reservoir may take the form of a refill, with the refill housed inside the barrel, or the barrel itself, with a tip attached to its end, may be used as the ink reservoir, with the ink directly filled into the barrel.

[0077] Furthermore, the ink backflow prevention body, which is filled at the rear end of the ink composition packed in the ink storage tube, can be either liquid or solid. Examples of liquid ink backflow prevention bodies (liquid stoppers) include non-volatile media such as polybutene, α-olefin co-oligomer, silicone oil, and refined mineral oil. If desired, silica, aluminum silicate, swelling mica, fatty acid amides, etc., can be added to the media. Examples of solid ink backflow prevention bodies include resin molded products. Liquid and solid ink backflow prevention bodies can also be used in combination.

[0078] The ballpoint pen may be either a capped or retractable type. For retractable ballpoint pens, any structure in which the writing tip provided on the ballpoint pen refill is stored inside the barrel (outer barrel) and exposed to the outside air, and the writing tip protrudes from the barrel opening when the retractable mechanism is activated, can be used. Methods of operating the retraction mechanism include knocking, rotating, and sliding mechanisms. A retractable pen may have a retractable mechanism at the rear end or side of the barrel, and pressing the retractable mechanism causes the writing tip of the ballpoint pen refill to extend and retract from the opening at the front of the barrel. Alternatively, pressing a clip on the barrel may cause the writing tip of the ballpoint pen refill to extend and retract from the opening at the front of the barrel. A rotating type can be exemplified by having a rotating part at the rear of the barrel, and by rotating this part, the writing tip of the ballpoint pen refill can be extended and retracted from the opening at the front of the barrel. A sliding type may be exemplified by having a sliding part on the side of the barrel, which allows the writing tip of the ballpoint pen refill to extend and retract from the opening at the front of the barrel by operating the slide, or by sliding a clip part provided on the barrel, which allows the writing tip of the ballpoint pen refill to extend and retract from the opening at the front of the barrel. The retractable ballpoint pen may also be a composite type retractable ballpoint pen (refillable) that houses multiple ballpoint pen refills inside the barrel. [Examples]

[0079] The ink compositions of the examples and comparative examples are shown in the table below. Note that the composition values ​​in the table represent parts by mass.

[0080] [Table 1]

[0081] The contents of the raw materials listed in the table are explained according to the note numbers. (1) Blue pigment dispersion [PigmentBlue15:3B, 24% by mass water dispersion, manufactured by Sanyo Shiki Co., Ltd., product name: Sandye Super Blue GLL-E] (2) Black pigment dispersion [30% solids content, manufactured by Sanyo Pigment Co., Ltd., product name: Sandye Super Black CE] (3) Polymer composition emulsion [polymer composed of three monomers: vinyl acetate, methyl methacrylate, and methacrylic acid, with an active ingredient content of 30%] (4) Polyethylene oxide [Weight-average molecular weight: 5 million, manufactured by Meisei Chemical Industry Co., Ltd., product name: Alcox E-240] (5) Polyethylene oxide [Weight-average molecular weight: 3 million, manufactured by Meisei Chemical Industry Co., Ltd., product name: Alcox E-100] (6) Phosphate ester surfactant [Manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Prysurf AL] (7) Preservative [Manufactured by Arcsarda Japan Co., Ltd., Product name: Proxel XL-2(S)]

[0082] <Preparation of Ink Composition> Each ink composition was prepared by adding components other than triethanolamine to water, stirring at 2000 rpm in a disperser at 20°C for 1 hour, and then adding triethanolamine and stirring for another hour.

[0083] <Preparation of the ink backflow prevention device> An ink backflow prevention body was prepared by adding 1.5 parts of fatty acid amide as a thickening agent to 98.5 parts of polybutene as a base oil, and then kneading the mixture using a three-roll mill.

[0084] <Making a ballpoint pen> The ink compositions of the examples and comparative examples were filled into ballpoint pen refills, each in which a stainless steel tip holding a 0.7 mm diameter cemented carbide ball was fitted to one end of a polypropylene pipe. After placing a prepared ink backflow prevention body at the rear end, the ballpoint pen refill was assembled into a barrel (cap type) to produce sample ballpoint pens.

[0085] The following tests were conducted using the prepared sample ballpoint pens. <Written Exam> Each ballpoint pen sample, confirmed to be writable, was used in an automatic writing tester to continuously write 12 spiral circles on a report sheet of paper (writing paper A conforming to JIS P3201). The presence or absence of bulges and the condition of the tip were visually observed. The test machine was used under the following conditions: writing load of 100g, writing angle of 65°, and writing speed of 4m / min. The test results are shown in Table 2. ◎: No signs of crying were found in the handwriting. ○: There is a slight smudge in the handwriting, but it does not affect its practical use. △: The handwriting is smudged and has practical problems. ×: The handwriting often contains many tear-shaped characters.

[0086] [Table 2]

[0087] After removing the caps from the caps and leaving the sample ballpoint pens containing the water-based inks of Examples 1-9 (which were confirmed to be writable) horizontally at 60°C for 14 days, the handwriting was examined when 12 spiral circles were continuously written in a single line on a report sheet. The handwriting from the ballpoint pens containing the water-based inks of Examples 1-8 was good, with no skipping or breaks observed. In contrast, while some skipping and breaks were observed at the beginning of writing in Example 9, these were not seen in the handwriting at the end of writing. These results confirm that a polyalkylene oxide (polyethylene oxide) content of 1.0% by mass or less results in good resistance to drying up.

Claims

1. A water-based ink composition for ballpoint pens comprising at least a colorant, water, a shear viscosity reducing agent, and a polyalkylene oxide, wherein the shear viscosity reducing agent is a polymer composed of three monomers: vinyl acetate, methyl methacrylate, and methacrylic acid.

2. The aqueous ink composition for ballpoint pens according to claim 1, wherein the coloring agent is a pigment.

3. The aqueous ink composition for ballpoint pens according to claim 1 or 2, wherein the polyalkylene oxide is polyethylene oxide.

4. The aqueous ink composition for ballpoint pens according to any one of claims 1 to 3, wherein the weight-average molecular weight of the polyalkylene oxide is 2 million to 6 million.

5. The aqueous ink composition for ballpoint pens according to any one of claims 1 to 4, wherein the content of the polyalkylene oxide is 0.01 to 1.0% by mass with respect to the total amount of the aqueous ink composition.

6. A ballpoint pen containing the aqueous ink composition for ballpoint pens according to any one of claims 1 to 5.

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