Water-based ballpoint pen ink composition

Abstract

To provide an aqueous ink composition for ball-point pens, which maintains smooth writing feeling and is excellent in abrasion suppression of a ball receiving sheet, even when a pen top is held in a down-directed state for a long time.SOLUTION: An aqueous ink composition for ballpoint pens of the present invention comprises at least a coloring material, fine particles having a new Mohs hardness of 3 or more and an average particle size of 30 μm or less, a polyoxyethylene polycyclic phenyl surfactant, and an aqueous solvent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous ink composition for ballpoint pens that maintains a smooth writing feel even when stored for a long period of time with the pen tip facing downwards, and that is excellent in suppressing wear of the ball bearing seat. [Background technology]

[0002] Conventionally, in water-based ballpoint pens, there have been ink compositions for ballpoint pens that can reduce wear on the ball bearing seat due to the rotation of the ball during writing, such as, 1) A ballpoint pen ink characterized by containing at least a pigment as a coloring agent, fine particles with a new Mohs hardness of 4 or higher, and a liquid medium (see, for example, Patent Document 1), 2) An aqueous ink composition for a fine-point ballpoint pen characterized in that the ink composition, which contains at least water, a colorant, and a water-soluble solvent, is blended with one or more ultrafine particles selected from alumina, titanium dioxide, silica, silicon carbide, and tungsten carbide with a particle size of less than 0.1 μm, and the amount of the blended particles is 0.002 to 2% by weight in the ink composition (see, for example, Patent Document 2). These are some of the known facts.

[0003] However, the ink described in Patent Document 1 had several problems: when the pen tip was stored facing downwards for a long period of time, the colorants, such as pigments, accumulated on the pen tip, resulting in wear on the ball bearing seat and a rough writing feel at the beginning of writing. While Patent Document 2 described above is excellent for suppressing ball bearing wear, when the pen tip is stored facing downwards for a long period of time with the above formulation, there were instances where the writing feel and the effect on ball bearing wear were somewhat insufficient.

[0004] On the other hand, an example of a technology that uses polyoxyethylene polycyclic phenyl surfactants in writing instrument inks is, 3) To provide a colored resin particle dispersion with excellent dispersion stability, and an aqueous ink composition for writing instruments that has excellent dispersion stability and produces good handwriting, for example, a colored resin particle dispersion comprising styrene-acrylonitrile resin particles, a colorant, a specific dispersant such as a polyoxyethylene polycyclic phenyl surfactant, and water, and an aqueous ink composition for writing instruments comprising the same (see, for example, Patent Document 3). 4) To provide an aqueous ballpoint pen ink composition that produces good handwriting when written and exhibits excellent dispersion stability of the colorant and storage stability of the ink composition, an aqueous ballpoint pen ink composition comprising a colorant, an acrylic acid copolymer, a specific dispersant such as a polyoxyethylene polycyclic phenyl surfactant, and water, and an aqueous ballpoint pen using the same (see, for example, Patent Document 4). These are some of the known facts.

[0005] However, while Patent Documents 3 and 4 described above are water-based ballpoint pen ink compositions that have excellent dispersion stability and storage stability of the colorant, they do not suppress wear of the ball bearing seat, nor do they recognize the problems that arise when fine particles with a new Mohs hardness of 3 or higher are used and the pen tip is stored in a downward position for a long period of time. Therefore, they differ from the present invention in terms of the problem to be solved and the technical concept (structure and its effects). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2002-206066 (Claims, Examples, etc.) [Patent Document 2] Japanese Patent Publication No. 2007-518838 (Claims, Examples, etc.) [Patent Document 3] Japanese Patent Publication No. 2019-189802 (Claims, Examples, etc.) [Patent Document 4] Japanese Patent Publication No. 2020-180198 (Claims, Examples, etc.) [Overview of the project] [Problems that the invention aims to solve]

[0007] In view of the problems and current state of the prior art described above, the present invention aims to resolve these issues and provides an aqueous ink composition for ballpoint pens that maintains a smooth writing feel even when stored for a long period of time with the pen tip facing downwards, and that is excellent in suppressing wear of the ball bearing seat. [Means for solving the problem]

[0008] In view of the above-mentioned conventional problems, the present inventors conducted diligent research and found that by including at least a colorant, fine particles with specific physical properties having a new Mohs hardness of 7 or higher, a polyoxyethylene polycyclic phenyl surfactant, and a water-soluble solvent, the above-mentioned water-based ballpoint pen ink composition can be obtained, thus completing the present invention.

[0009] In other words, the water-based ballpoint pen ink composition of the present invention is characterized by comprising at least a colorant, fine particles having a new Mohs hardness of 3 or higher and an average particle diameter of 30 μm or less, a polyoxyethylene polycyclic phenyl surfactant, and a water-soluble solvent. It is preferable that the product of the new Mohs hardness of the fine particles and the average particle size (μm) of the fine particles is between 0.02 and 450. The content of the aforementioned fine particles is preferably 0.001 to 5% by mass relative to the total amount of the ink composition. The polyoxyethylene polycyclic phenyl surfactant is preferably a polyoxyethylene distyleninated phenyl ether. Preferably, the content of the polyoxyethylene polycyclic phenyl surfactant is 0.05 to 20% by mass relative to the total amount of the ink composition. It is preferable that the viscosity at 1 rpm measured by a cone-plate type rotational viscometer (1°34′R24 cone) is 50 to 2000 mPa·s (25℃). [Effects of the Invention]

[0010] According to the present invention, an aqueous ink composition for ballpoint pens and an aqueous ballpoint pen equipped with the same are provided, which maintain a smooth writing feel even when stored for a long period of time with the pen tip facing downwards, and which also exhibits excellent wear suppression of the ball bearing seat. The object and effect of the present invention are recognized and obtained, in particular, by using the components and combinations indicated in the claims. Both the general description above and the detailed description below are illustrative and descriptive, and do not limit the present invention as described in the claims. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described in detail below. However, it should be noted that the technical scope of the present invention is not limited to the embodiments described below, but extends to the invention described in the claims and its equivalents. The present invention relates to an aqueous ballpoint pen ink composition characterized by comprising at least a colorant, fine particles having a new Mohs hardness of 3 or higher and an average particle diameter of 30 μm or less, a polyoxyethylene polycyclic phenyl surfactant, and a water-soluble solvent.

[0012] The colorants used in this invention can be any of the following without limitation: all dyes that dissolve or disperse in water, conventionally known inorganic and organic pigments such as titanium dioxide, resin particle pigments containing pigments, pseudo-pigments obtained by coloring resin emulsions with dyes, white plastic pigments, wax particles, hollow resin particles, pigments with silica or mica as a base material and a multi-layer coating of iron oxide or titanium dioxide on the surface, thermochromic pigments, photochromic particles, and composite particles thereof. Examples of dyes include acid dyes such as eosin, foxine, water yellow #6-C, acid red, water blue #105, brilliant blue FCF, and nigrosine NB; direct dyes such as direct black 154, direct sky blue 5B, and violet BB; and basic dyes such as rhodamine and methyl violet.

[0013] Examples of inorganic pigments include azo lakes, insoluble azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, nitroso pigments, etc. More specifically, inorganic pigments such as carbon black, titanium black, zinc white, red iron oxide, aluminum, chromium oxide, iron black, cobalt blue, iron oxide yellow, viridian, zinc sulfide, lithopone, cadmium yellow, vermilion, cadmium red, lead yellow, molybdate orange, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine, precipitated barium sulfate, barite powder, calcium carbonate, lead white, ultramarine white, ultramarine blue, manganese violet, aluminum powder, brass powder, etc., and C.I. Pigment Blue 17, C.I. Pigment Blue 15, C.I. Pigment Blue 17, C.I. Pigment Blue 27, C.I. Pigment Red 5, C.I. Pigment Red 22, C.I. Pigment Red 38, C.I. Pigment Red 48, C.I. Pigment Red 49, C.I. Pigment Red 53, C.I. Pigment Red 57, C.I. Pigment Red 81, C.I. Pigment Red 104, C.I. Pigment Red 146, C.I. Pigment Red 245, C.I. Pigment Yellow 1, C.I. Pigment Yellow 3, C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. Pigment Yellow 17, C.I. Pigment Yellow 34, C.I. Pigment Yellow 55, C.I. Pigment Yellow 74, C.I. Pigment Yellow 95, C.I. Pigment Yellow 166, C.I. Pigment Yellow 167, C.I. Pigment Orange 5, C.I. Pigment Orange 13, C.I. Pigment Orange 16, C.I. Pigment Violet 1, C.I. Pigment Violet 3, C.I. Pigment Violet 19, C.I. Pigment Violet 23, C.I. Pigment Violet 50, C.I. Pigment Green 7, etc. can be mentioned.

[0014] Examples of thermochromic pigments include those produced by microencapsulating a thermochromic composition containing at least a leuco dye that functions as a color developer, a color developer that has the ability to cause the leuco dye to develop color, and a color change temperature adjuster that can control the color change temperature in the color development of the leuco dye and the color developer, so that the composition has a predetermined average particle size (for example, 0.1 to 6 μm). Examples of photochromic particles include photochromic particles composed of at least one selected from photochromic dyes (compounds), fluorescent dyes, etc., and a resin such as a terpene phenol resin, or photochromic particles produced by microencapsulating a photochromic composition containing at least one selected from photochromic dyes (compounds), fluorescent dyes, etc., an organic solvent, and additives such as antioxidants, light stabilizers, and sensitizers, to a predetermined average particle size (e.g., 0.1 to 6 μm).

[0015] In the present invention (including the examples), the "average particle size" is the D50 value measured with a particle size analyzer [Microtrac HRA9320-X100 (manufactured by Nikkiso Co., Ltd.)]. Examples of the method for microencapsulating the thermochromic pigment include, for example, interfacial polymerization method, interfacial polycondensation method, in-situ polymerization method, in-liquid curing coating method, phase separation method from aqueous solution, phase separation method from organic solvent, melt dispersion cooling method, air suspension coating method, spray drying method, etc., and can be appropriately selected according to the application. For example, in the phase separation method from aqueous solution, after heating and melting a leuco dye, a developer, and a discoloration temperature regulator, they are put into an emulsifier solution, heated and stirred to be dispersed in an oil droplet form, and then, as a capsule film agent, a resin raw material whose wall film is a urethane resin, an epoxy resin, an amino resin, etc. is used. For example, each solution such as an amino resin solution, specifically, an aqueous solution of methylol melamine, a urea solution, a benzoguanamine solution, etc. is gradually added, and then continuously reacted and prepared, and the thermochromic microcapsule pigment can be produced by filtering this dispersion liquid. In this thermochromic pigment, by suitably combining the types, amounts, etc. of the leuco dye, the developer, and the discoloration temperature regulator, the color development temperature and the discoloration temperature of each color can be set to suitable temperatures. Also, as the method for microencapsulating the photochromic particles, it can be prepared in the same manner as the production of the above-mentioned thermochromic resin particles. By suitably using a photochromic dye (compound), a fluorescent dye, etc. for these photochromic particles, for example, they can be made to be colorless in an indoor lighting environment (lighting fixtures selected from incandescent lamps, fluorescent lamps, lamps, white LEDs, etc. indoors) and have the property of developing color in an ultraviolet irradiation environment (irradiation with a wavelength of 200 - 400 nm, irradiation environment with sunlight containing ultraviolet rays).

[0016] These color materials can be used alone or in combination of two or more. Among these color materials, the average particle diameters of pigments dispersed in water, resin particle pigments, pseudo pigments, white plastic pigments, pigments with multilayer coating, thermochromic pigments, photochromic particles, etc. vary depending on the ball diameter, ink composition, viscosity, etc., but those with an average particle diameter of 0.02 - 6 μm are desirable. The content of these colorants can be appropriately increased or decreased depending on the ink line density, but it is preferably 0.1 to 40% by mass (hereinafter, "mass%" is referred to as "%"), and more preferably 1 to 10% by mass, relative to the total amount of the ink composition.

[0017] The fine particles used in this invention, which have a new Mohs hardness of 3 or higher and an average particle diameter of 30 μm or less, are included in order to exert a wear-suppressing effect on the ball bearing seat. The fine particles used are not particularly limited, as long as they have a new Mohs hardness of 3 or higher and an average particle diameter of 30 μm or less. The New Mohs hardness scale is synonymous with the Modified Mohs hardness scale. The New Mohs hardness scale is a measure of mineral hardness that determines the hardness of a mineral by comparing it to 15 reference minerals. The reference minerals, in order from softest to hardest (New Mohs hardness 1) to hardest (New Mohs hardness 15), are talc, gypsum, calcite, fluorite, apatite, orthoclase, fused silica, quartz, topaz, garnet, fused zirconia, fused alumina, silicon carbide, boron carbide, and diamond. In this specification, the New Mohs hardness scale is determined by rubbing the sample material (fine particles) to be measured against one of these reference minerals and observing whether or not a scratch is left. For example, if calcite does not scratch the sample material (fine particles) but fluorite does, the New Mohs hardness of that sample material (fine particles) is 3.5 (meaning between 3 and 4). Furthermore, using fine particles with a new Mohs hardness of less than 3 makes it difficult to obtain sufficient effect in suppressing wear of the receiving seat, and thus the effects of the present invention cannot be achieved, which is undesirable.

[0018] When using fine particles with a new Mohs hardness of 3 or higher, ink flows out as the ball rotates during writing, and at the same time, the high pressure during writing embeds the particles into the ball seat. As a result, the surface hardness of the seat increases, suppressing wear of the seat caused by the ball's rotation. Preferably, the new Mohs hardness of the fine particles is between 3 and 15, from the viewpoint of durability and ink flowability. Examples of fine particles with a new Mohs hardness of 3 to 15 include ceramic fine particles, metal fine particles, and resin fine particles such as silicon carbide, alumina, silica, tungsten carbide, titanium oxide, and melamine resin. These can be used individually or in mixtures of two or more types.

[0019] Furthermore, the fine particles used should have an average particle diameter of 30 μm or less, preferably 0.007 to 30 μm, and more preferably 0.01 to 10 μm, from the standpoint of further suppressing wear of the receiving surface and dispersibility in the ink. Fine particles with an average particle diameter exceeding 30 μm are undesirable because they worsen the dispersion stability in the ink and suppress the settling of the fine particles. Furthermore, the shape of the fine particles having the specified new Mohs hardness and average particle diameter is preferably spherical, elliptical, plate-shaped, or rod-shaped, from the standpoint of improving writing feel and ink flow.

[0020] These fine particles can be commercially available, as long as they have the specified new Mohs hardness and average particle size described above. In addition, ceramic fine particles, metal fine particles, resin fine particles, etc., manufactured by known methods can also be used. Furthermore, in the present invention, if the fine particles satisfy the aforementioned new Mohs hardness, and the product of the new Mohs hardness of the fine particles and their average particle diameter (μm) (hereinafter referred to as the "product value") falls within a predetermined range, then when used in an aqueous ballpoint pen ink composition, it is possible to achieve both wear suppression of the bearing surface and dispersion stability, and the effects of the present invention can be exhibited even more favorably. The predetermined range of such product value is preferably 0.02 to 450, and more preferably 0.03 to 150.

[0021] The content of these fine particles having a predetermined new Mohs hardness and average particle size is preferably 0.001 to 5% by mass, more preferably 0.1 to 2% by mass, relative to the total amount of the ink composition. If the content of these fine particles is less than 0.001% by mass, sufficient suppression of seat wear cannot be obtained, while if it exceeds 5% by mass, the writing feel may deteriorate.

[0022] The polyoxyethylene polycyclic phenyl surfactant used in the present invention is an ether having a molecular skeleton that contains "a group having at least two monocyclic aromatic hydrocarbon groups (e.g., a phenyl group, a phenylene group, etc.)" or "a group having at least one polycyclic aromatic hydrocarbon group (e.g., a naphthyl group, etc.)". This polyoxyethylene polycyclic phenyl surfactant is a component that ensures good dispersion stability even during long-term storage of fine particles with the above physical properties. For example, a compound represented by the following formula (1) can be cited. [ka] [In formula (1) above, X is a polycyclic phenyl group; AO is an alkylene oxy group having 2 to 5 carbon atoms; Z is SO3M or a hydrogen atom, M is a hydrogen atom or an organic or inorganic cation; and n is a number from 3 to 120.]

[0023] In formula (1) above, X is a polycyclic phenyl group. Here, "polycyclic phenyl group" means "a group having at least two monocyclic aromatic hydrocarbon groups (e.g., a phenyl group, a phenylene group, etc.)" or "a group having at least one polycyclic aromatic hydrocarbon group (specifically, a group in which at least two benzene rings are fused, such as a naphthyl group, a phenanthryl group, etc.)". Examples of the "polycyclic phenyl group" in formula (1) above are shown in formulas (2) to (5) below.

[0024] [ka] [In the above equations (2) to (5), R 1 R is a chain-like hydrocarbon group having 1 to 3 carbon atoms. 2 , R 3 These are independently hydrogen atoms or chain-like hydrocarbon groups having 1 to 3 carbon atoms. Independently, a hydrogen atom or a chain-like hydrocarbon group having 1 to 3 carbon atoms, or a group represented by formula (6). That is. R 4 , R 5 x is an independent hydrogen atom and a chain-like hydrocarbon group having 1 to 3 carbon atoms. x is an integer between 1 and 3.

[0025]

Chemical formula

[0026] The polyoxyethylene polycyclic phenyl-based surfactant used in the present invention may contain a bisphenol-based polycyclic group represented by formulas (7) to (8).

Chemical formula

[0027] In the above formula (1), as X, a distyrenated phenyl group, a distyrenated methylphenyl group, or a tristyrenated phenyl group is preferable. In the above formula (1), Z represents SO3M or a hydrogen atom, M represents a hydrogen atom, or an organic or inorganic cation, and preferably a hydrogen atom. Examples of the cation represented by M include an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an alkyl-substituted ammonium ion, etc.

[0028] In the above formula (1), n is preferably 3 to 120, more preferably 3 to 20, and particularly preferably 3 to 10. When the upper and lower limit values are within the above range, the stability of the aqueous ballpoint pen ink composition and the dispersion stability of the above-mentioned characteristics of the fine particles can be highly compatible. The production of this polyoxyethylene polycyclic phenyl-based surfactant is known. For example, it is produced by formalin condensation of distyrenated phenol in the presence of formaldehyde to obtain a bis body, and then addition polymerization of ethylene oxide in the presence of a catalyst.

[0029] In the present invention, the length of the ethylene oxide portion in the polyoxyethylene polycyclic phenyl surfactant is preferably such that the number of ethylene oxide moles added is 10 to 120, in order to further exhibit the effects of the present invention. In particular, 20 moles or more is preferred. Preferred polyoxyethylene polycyclic phenyl surfactants include polyoxyethylene distylenide phenyl ether, polyoxyethylene distylenide methylphenyl ether, polyoxyethylene distylenide methylphenyl ether sulfate, polyoxyethylene tristyreneide phenyl ether, polyoxyethylene tripenzyl phenyl ether, polyoxyethylene distylenide cresyl ether, and polyoxyethylene allyl phenyl ether, with polyoxyethylene distylenide phenyl ether being particularly preferred.

[0030] Specific examples of polyoxyethylene polycyclic phenyl surfactants include Emulgen A-60, Emulgen A-90, Emulgen A-500, Emulgen B-66 (Kao Corporation), Newcol 703, Newcol 704, Newcol 706, Newcol 707, Newcol 708, Newcol 709, Newcol 710, Newcol 711, Newcol 712, Newcol 714, Newcol 719, Newcol 723, and Newcol Examples include Ru 729, Newcol 733, Newcol 740, Newcol 747, Newcol 780, Newcol 610, Newcol 2604, Newcol 2607, Newcol 2609, Newcol 2614 (Nippon Emulsifier Co., Ltd.), Neugen EA-87, Neugen EA-137, Neugen EA-157, Neugen EA-167, Neugen EA-177, Neugen EA-197D, and Neugen EA-207D (Daiichi Kogyo Seiyaku Co., Ltd.).

[0031] These polyoxyethylene polycyclic phenyl surfactants can be used individually or in combination of two or more types. The content of these polyoxyethylene polycyclic phenyl surfactants varies depending on the type and amount of fine particles and the type and amount of colorants, but is 0.5 to 20% by mass, preferably 1 to 10% by mass, relative to the total amount of the ink composition. If the content is less than 0.5% by mass relative to the total amount of the ink composition, the long-term stability of the fine particles with the above characteristics will decrease. On the other hand, if it exceeds 20% by mass, the ink viscosity will increase, leading to a decrease in ink flowability and a decrease in the quality of the writing lines, which is undesirable.

[0032] In the present invention, the mass ratio expressed as "content of fine particles (A) with the above physical properties / content of polyoxyethylene polycyclic phenyl surfactant (B)" (hereinafter sometimes referred to as the (A) / (B) ratio) is preferably 0.005 to 10.0, and more preferably 0.05 to 1.5. When the lower and upper limits of this (A) / (B) ratio are within the above range, the abrasion resistance of the water-based ballpoint pen ink composition is further improved, and a smoother and more stable writing feel can be achieved.

[0033] The water-soluble solvent used in this invention is used for various purposes related to the quality of the ink, such as preventing ink freezing at low temperatures and preventing ink drying at the pen tip. Specifically, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, 3-butylene glycol, thiodiethylene glycol, and glycerin, as well as ethylene glycol monomethyl ether and diethylene glycol monomethyl ether, can be used individually or in combination. The content of this water-soluble solvent is preferably 1 to 40% by mass of the total amount of the ink composition.

[0034] The aqueous ballpoint pen ink composition of the present invention is characterized by containing at least the above-mentioned colorant, fine particles having a new Mohs hardness of 3 or higher and an average particle diameter of 30 μm or less, a polyoxyethylene polycyclic phenyl surfactant, and a water-soluble solvent. In addition, the remainder consists of water as a solvent (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.), and may optionally contain dispersants, water-soluble resins, lubricants, thickeners, pH adjusters, rust inhibitors, preservatives, or antibacterial agents, to the extent that they do not impair the effects of the present invention.

[0035] Other dispersants that can be used include nonionic and anionic surfactants other than the polyoxyethylene polycyclic phenyl surfactants mentioned above. The water-soluble resin used can be suitably used in terms of viscosity adjustment and improved adhesion. Specifically, at least one of the following can be used: water-soluble resins having hydrophobic parts in the molecule, such as polyacrylic acid, water-soluble styrene-acrylic resin, water-soluble styrene-maleic acid resin, polyvinyl alcohol, polyvinylpyrrolidone, water-soluble maleic acid resin, water-soluble styrene resin, polyvinylpyrrolidone, polyvinyl alcohol, water-soluble ester-acrylic resin, ethylene-maleic acid copolymer, polyethylene oxide, and water-soluble urethane resin; and resin emulsions such as polyolefin emulsion, acrylic emulsion, vinyl acetate emulsion, urethane emulsion, styrene-butadiene emulsion, and styrene-acrylonitrile emulsion. It is desirable to use at least one of each of these, for a total of two or more types.

[0036] Examples of lubricants that can be used include nonionic types such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, higher fatty acid esters of polyoxyalkylenes, and alkyl phosphate esters, which are also used as surface treatment agents for pigments; anionic types such as phosphate esters, alkyl sulfonates of higher fatty acid amides, and alkyl allyl sulfonates; derivatives of polyalkylene glycols; and polyether-modified silicones. Known thickeners can be used, and specifically, at least one selected from alkali-swelling-associating emulsions, alkali-swelling emulsions, polyvinylpyrrolidone, cellulose derivatives, polysaccharides such as xanthan gum and succinoglycans, cross-linked acrylic acid polymers, crystalline cellulose, rheozan gum, gellan gum, montmorillonite clay minerals, and other inorganic thickeners.

[0037] Examples of pH adjusters include ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, alkali metal salts of carbonic acid and phosphoric acid such as sodium tripolyphosphate and sodium carbonate, and alkali metal hydrates such as sodium hydroxide. Examples of rust inhibitors include benzotriazole, tolyltriazole, dicyclohexylammonium nitride, and saponins, while examples of preservatives or antibacterial agents include phenol, sodium omazine, sodium benzoate, thiazoline compounds, and benzimidazole compounds. Each of the above-mentioned components, such as dispersants, lubricants, thickeners, pH adjusters, rust inhibitors, preservatives, or antibacterial agents, may be used individually or in combination of two or more. Commercially available products containing these components may also be used.

[0038] The water-based ballpoint pen ink composition of the present invention can be manufactured in no particular way compared to the manufacturing methods of other water-based ink compositions. In other words, the aqueous ballpoint pen ink composition of the present invention can be produced by mixing and stirring at least a colorant, fine particles having a new Mohs hardness of 3 or more and an average particle diameter of 30 μm or less, a polyoxyethylene polycyclic phenyl surfactant, a water-soluble solvent, and other components using a mixer or the like, and further, setting the stirring conditions to suitable conditions using, for example, a bead mill, homomixer, homogenizer, etc. that can apply strong shear, and further, if necessary, removing coarse particles from the ink composition by filtration or centrifugation. Furthermore, the pH (at 25°C) of the aqueous ballpoint pen ink composition of the present invention is preferably adjusted to 5 to 10 using a pH adjuster or the like, from the viewpoint of usability, safety, stability of the ink itself, and compatibility with the ink container, and more preferably to 6 to 9.5.

[0039] The viscosity of the water-based ballpoint pen ink composition of the present invention is preferably 50 to 2000 mPa·s (25℃), more preferably 100 to 1000 mPa·s, as measured by a cone-plate type rotational viscometer (1°34′R24 cone) at 1 rpm. If the viscosity is less than 50 mPa·s (at 25°C), the fine particles with the above characteristics are more likely to settle, which can easily clog the pen tip and result in poor initial writing performance. On the other hand, if the viscosity exceeds 2000 mPa·s (at 25°C), the flowability decreases, which can result in poor writing feel.

[0040] The water-based ballpoint pen ink composition of the present invention is used in a ballpoint pen equipped with a pen tip, such as a ballpoint pen tip. Examples of water-based ballpoint pens in the present invention include those in which an aqueous ballpoint pen ink composition having the above composition is contained in a ballpoint pen ink container (refill) equipped with a ball with a diameter of 0.18 to 2.0 mm, and a substance that is incompatible with the aqueous ink composition contained in the ink container and has a lower specific gravity than the aqueous ink composition, such as polybutene, silicone oil, or mineral oil, is contained as an ink-following body. The structure of the water-based ballpoint pen used is not particularly limited as long as it is equipped with a ball with a diameter within the above range, but it is particularly desirable to have an aqueous ballpoint pen in which the above aqueous ink composition is filled into an ink container tube made of polypropylene resin, and the refill has a stainless steel tip (the ball is made of cemented carbide). Furthermore, it may also be a direct-ink type ballpoint pen equipped with a collector structure (ink holding mechanism) in which the barrel itself serves as the ink reservoir and the above-described aqueous ballpoint pen ink composition is filled into the barrel. In particular, the present invention is suitable for use in water-based ballpoint pens having a ball with a diameter of 0.18 to 2.0 mm, as it is expected to suppress wear on the ball bearing.

[0041] The mechanism by which the water-based ballpoint pen ink composition and the water-based ballpoint pen equipped with it maintain a smooth writing feel and exhibit excellent wear suppression of the ball bearing seat, even when stored for a long period of time with the pen tip facing downwards, is presumed to be as follows. In other words, by including fine particles with a new Mohs hardness of 3 or higher and an average particle diameter of 30 μm or less, and a polyoxyethylene polycyclic phenyl surfactant in the water-based ballpoint pen ink composition containing at least a colorant, the ink properties remain unchanged even during long-term storage. As the ball rotates during writing, stable ink flows out, and at the same time, the pressure during writing embeds the fine particles with the above characteristics into the ball seat. As a result, the surface hardness of the seat increases, suppressing wear of the seat caused by the ball's rotation. Even after long-term storage, the fine particles and colorant with the above characteristics are uniformly and stably present in the ink interposed between the ball seat during writing, thus not hindering the ball's rotation or ink properties. Therefore, it is presumed that the water-based ballpoint pen ink composition of the present invention stably suppresses wear of the ball seat and provides a smooth and stable writing experience without impairing other writing performance. The water-based ballpoint pen ink composition of the present invention and the water-based ballpoint pen equipped with it exhibit extremely excellent sustained effects that bring about the effects of the present invention. Moreover, the period and duration of the onset of these effects are long, and furthermore, because it is water-based, it also exhibits excellent stability over time. [Examples]

[0042] Next, the present invention will be described in more detail with reference to Examples 1 to 10 and Comparative Examples 1 to 5 of water-based ballpoint pen ink compositions and water-based ballpoint pens equipped with them. However, the present invention is not limited to the following examples.

[0043] [Examples 1-10 and Comparative Examples 1-5] Each water-based ballpoint pen ink composition was prepared by conventional methods according to the formulation shown in Table 1 below. For each of the obtained aqueous ballpoint pen ink compositions (100% by mass), the viscosity at 1 rpm was measured using a cone-plate type rotational viscometer (1°34′R24 cone) according to the methods described below, and abrasion resistance tests and writing quality evaluations were performed according to the methods described below. These results are shown in Table 1 below.

[0044] (Method for measuring the viscosity of ink compositions) Viscosity measurements using a cone-plate type rotational viscometer were performed using a Tokimec EMD cone-plate type rotational viscometer at 25°C, with an st rotor (1°34'R24 cone) and a rotational speed of 1 rpm.

[0045] Ballpoint pen tips of various ball diameters (0.38 mm superalloy ball, 0.5 mm superalloy ball) were mounted on tubes (both PP tubes with an inner diameter of 3.4 mm) and polypropylene fittings manufactured by Mitsubishi Pencil, filled with the aqueous ink compositions obtained in the examples and comparative examples, filled with polybutene as an ink follower, degassed by centrifugation (500 G, 5 minutes), and then assembled into aqueous ballpoint pens of each ball diameter. Various writing tests (abrasion resistance test, writing feel test) as shown below were then performed.

[0046] Water-based ballpoint pens were stored for 12 weeks under conditions of 50°C and 65% humidity, with the pen tip facing downwards. Writing tests were then conducted using the method described below. Evaluation tests were performed on five ballpoint pens of each ball diameter. 1) Abrasion resistance test: A mechanical writing test will be conducted, with 1000m (end of writing) of spiral writing, and the results will be evaluated according to the following evaluation criteria. Writing conditions: 100gf, writing angle 75 degrees, writing speed 4.5mm / min Evaluation criteria: A: Everything is perfectly usable for writing. B: There is some slight smudging, but it is still usable until the end of writing. C: There is some smudging, but it is still usable until the end of writing. D: At least one or more pipes are experiencing a decrease in flow rate.

[0047] 2) Method for evaluating writing feel Using each of the water-based ballpoint pens obtained above, students performed "spiral writing" freehand on writing paper, and evaluated the writing feel according to the following evaluation criteria. Evaluation criteria: A: Smooth and stable writing feel. B: A relatively rough and hard writing feel. C: It has a rough, hard writing feel, and the lines are slightly breakable and directional. D: It has a rough, hard writing feel, and the lines break noticeably and are directional.

[0048] [Table 1]

[0049] *1 to *3 in Table 1 above are as follows: *1: Manufactured by Mitsubishi Chemical Corporation, average particle size 0.1 μm *2: Blue colored resin particles, average particle size 1.2μm *3: Red heat-discoloring particles, average particle size 3.0 μm, decolorization temperature 60°C

[0050] As is clear from the results in Table 1 above, the two types of water-based ballpoint pens with different ball diameters, each equipped with the water-based ballpoint pen ink compositions of Examples 1 to 10 which fall within the scope of the present invention, were found to have superior wear resistance and writing quality even after long-term storage, compared to Comparative Examples 1 to 5 which fall outside the scope of the present invention, demonstrating a high degree of compatibility. [Industrial applicability]

[0051] An ink composition suitable for water-based ballpoint pens can be obtained.

Claims

1. An ink composition for water-based ballpoint pens, characterized in that it comprises at least a colorant, fine particles selected from group A below having a new Mohs hardness of 3 or more and an average particle diameter of 30 μm or less, a polyoxyethylene polycyclic phenyl surfactant selected from group B below, and a water-soluble solvent, wherein the content of the fine particles (A) is 0.1 to 2% by mass of the total amount of the ink composition, and the mass ratio expressed as the content of the fine particles (A) / content of the polyoxyethylene polycyclic phenyl surfactant (B) is 0.005 to 10.

0. Group A: Silicon carbide, alumina, silica, melamine resin Group B: Polyoxyethylene distylenide phenyl ether, polyoxyethylene distylenide methylphenyl ether, polyoxyethylene tristyreneide phenyl ether, polyoxyethylene tripenzyl phenyl ether, polyoxyethylene distylenide cresyl ether, polyoxyethylene allyl phenyl ether

2. The aqueous ballpoint pen ink composition according to claim 1, characterized in that the product of the new Mohs hardness of the fine particles and the average particle diameter (μm) of the fine particles is between 0.02 and 450.

3. The aqueous ballpoint pen ink composition according to claim 1 or 2, characterized in that the polyoxyethylene polycyclic phenyl surfactant of group A is polyoxyethylene distyrenate phenyl ether.

4. An aqueous ballpoint pen ink composition according to any one of claims 1 to 3, wherein the viscosity at 1 rpm measured by a cone-plate type rotational viscometer (1°34'R24 cone) is 50 to 2000 mPa·s (25°C).

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