Aqueous ink composition and ballpoint pen

Abstract

This aqueous ink composition comprises: a pigment having a specific surface area of at most 260 m2 / g; and a phosphoric acid ester having an HLB value of at least 8.5, wherein when the average particle diameter of the pigment is defined as A nm, the content of the pigment in the aqueous ink composition is defined as B mass%, the specific surface area of the pigment is defined as C m2 / g, and the content of the phosphoric acid ester in the aqueous ink composition is defined as D mass%, (B×C) / (A×D)<600 is satisfied.

Description

Water-based ink composition and ballpoint pen

[0001] This invention relates to an aqueous ink composition and a ballpoint pen.

[0002] When writing on paper contaminated with hand oils using a water-based ballpoint pen, a phenomenon where the pen cannot write properly may occur. To solve such writing problems, for example, a water-based pigment ink for ballpoint pens has been proposed that contains at least water, a pigment, and a cross-linked poly-N-vinylcarboxylic acid amide or a cross-linked polyacrylic acid or a salt thereof, and is characterized by containing an alkylbenzene sulfonate, thereby minimizing the frictional resistance between the ball and the ball seat of the ballpoint pen tip, making the ball rotate smoothly and providing sufficient writing performance even on oily surfaces (Patent Document 1). Another example is a water-based ballpoint pen ink that contains at least a colorant, water, a polymer, and an unsaturated fatty acid with an unsaturation degree of 4 or higher, which aims to eliminate writing problems caused by skipped lines even when writing on paper contaminated with hand oils (Patent Document 2).

[0003] Japanese Patent Publication No. 2003-73605 Japanese Patent Publication No. 2015-160916

[0004] However, after long-term storage, especially under severe conditions where the nib tends to dry out, writing on paper with hand oils on it may result in skipping at the beginning of writing, or writing with high pressure may cause a decrease in writing quality or wear on the tip's resting surface.

[0005] The object of the present invention is to provide an aqueous ink composition that does not cause smudging at the start of writing (initial stroke) when writing on paper that has been stored for a long period of time and has been soiled with hand oils, and that does not cause a decrease in writing quality or wear of the tip's seat even when writing under high pressure, and to provide a ballpoint pen equipped with this aqueous ink composition.

[0006] As a result of diligent research, the inventors discovered that the above objective can be achieved by using a combination of materials that satisfy predetermined conditions, and thus completed the present invention.

[0007] In other words, according to the present invention, (1) the specific surface area is 260 m² ２ An aqueous ink composition comprising a pigment of less than or equal to / g and a phosphate ester with an HLB value of 8.5 or higher, wherein the average particle size of the pigment is A nm, the content of the pigment in the aqueous ink composition is B mass%, and the specific surface area of ​​the pigment is C m ２ (1) an aqueous ink composition in which the content of the phosphate ester in the aqueous ink composition is D by mass%, such that (B × C) / (A × D) < 600, (2) the aqueous ink composition according to (1) having a dissolved oxygen concentration of less than 7 mg / L, (3) a ballpoint pen equipped with the aqueous ink composition according to (1) or (2), wherein the surface roughness Ra of the ball is 0.1 to 10 nm, and (4) a ballpoint pen equipped with the aqueous ink composition according to (1) or (2), wherein the ballpoint pen has a pipe tip structure.

[0008] According to the present invention, it is possible to provide an aqueous ink composition that does not cause smudging at the start of writing (initial stroke) when writing on paper that has been stored for a long period of time and has been soiled with hand oils, and that does not cause a decrease in writing quality or wear of the tip's seat even when writing under high pressure, and a ballpoint pen equipped with this aqueous ink composition.

[0009] This figure shows a pipe-shaped tip of a ballpoint pen according to an embodiment. This figure shows a bullet-shaped tip of a ballpoint pen according to an embodiment.

[0010] The aqueous ink composition of the present invention will be described below. The aqueous ink composition of the present invention has a specific surface area of ​​260 m². ２ An aqueous ink composition comprising a pigment of less than or equal to / g and a phosphate ester with an HLB value of 8.5 or higher, wherein the average particle size of the pigment is A nm, the content of the pigment in the aqueous ink composition is B mass%, and the specific surface area of ​​the pigment is C m ２ When the content of the phosphate ester in the aqueous ink composition is D by mass, (B × C) / (A × D) < 600.

[0011] (Pigments) As pigments used in the present invention, water-insoluble colorants can be used. Such pigments can be conventionally known inorganic and organic pigments such as titanium dioxide, pseudo-pigments obtained by coloring resin emulsions with dyes or pigments, white plastic pigments, luminous pigments, pigments obtained by using silica or mica as a base material and coating the surface with multiple layers of iron oxide or titanium dioxide, colored resin particles, etc., without limitation.

[0012] Examples of inorganic pigments that can be used include carbon black, titanium black, zinc oxide, red iron oxide, aluminum, chromium oxide, iron black, cobalt blue, iron yellow, viridian, zinc sulfide, lithopone, cadmium yellow, vermilion, cadmium red, lead yellow, molybdide orange, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine, precipitated barium sulfate, barite powder, calcium carbonate, lead white, navy blue, navy blue, manganese violet, aluminum powder, brass powder, etc.

[0013] Examples of organic pigments include azo lakes, insoluble azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, and nitroso pigments. Examples of such organic pigments include 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. Examples include I. Pigment Violet 23, C.I. Pigment Violet 50, and C.I. Pigment Green 7.

[0014] The colored resin particles are not particularly limited as long as they are composed of colored resin particles, and examples include: 1) colored resin particles having dyes such as direct dyes, acid dyes, basic dyes, food dyes, fluorescent dyes, salt-making dyes, and oil-soluble dyes in the resin particles; 2) colored resin particles in which a coloring agent consisting of an inorganic pigment such as carbon black and titanium dioxide, or an organic pigment such as phthalocyanine pigments and azo pigments is dispersed in the resin particles; 3) composite colored resin particles in which the surface of the resin particles is coated with a pigment or colored resin particles; 4) colored resin particles that are heat-changeable using leuco dyes, etc. (leuco dye-encapsulated particles); and 5) colored resin particles that are photochromic using photochromic dyes (compounds), fluorescent dyes, etc.

[0015] Examples of the resin components of the colored resin particles described in 1) and 2) above include at least one selected from polymers or copolymers thereof such as acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, styrene, acrylonitrile, and butadiene, as well as benzoguanamine, phenolic resin, epoxy resin, urethane resin, and urea resin, and may be subjected to crosslinking or other treatments as necessary.

[0016] The colored resin particles described in 1) and 2) above may contain resins having OH groups, and the resins having OH groups are contained in the matrix. Examples of resins having OH groups include terpene phenol resins, rosin phenol resins, alkyl phenol resins, phenol novolac resins, cresol novolac resins, butyral resins, polyvinyl alcohol resins, polyol-modified xylene resins, ethylene oxide-modified xylene resins, maleic acid resins, hydroxyl-modified acrylic resins, hydroxyl-modified styrene acrylic resins, carboxyl-modified acrylic resins, and carboxyl-modified styrene acrylic resins.

[0017] The colored resin particles described in 1) and 2) above can be produced, for example, by conventionally known methods such as emulsion polymerization, suspension polymerization, interfacial polymerization, and phase separation.

[0018] Composite colored resin particles, in which the surface of the resin particles described in 3) above is coated with pigment or colored resin particles, can be manufactured by compounding cationic resin particles with anionic pigment or the colored resin particles described in 1) to 2) above using Coulomb force.

[0019] The compounding method involves preparing a resin emulsion containing cationic resin particles on the particle surface and a dispersion containing anionic pigment or colored resin particles. Preferably, the particles in each emulsion and dispersion are dispersed in an aqueous medium. Next, the cationic resin emulsion and the anionic pigment or colored resin particle dispersion are mixed. For mixing each emulsion (dispersion), a method of adding each to a container equipped with a stirring device such as a mechanical stirrer or magnetic stirrer and stirring can be employed.

[0020] Examples of the thermochromic colored resin particles described in 4) above include thermochromic colored resin particles (leuco dye-encapsulated particles) produced by microencapsulating a thermochromic composition containing at least a leuco dye that functions as a color developer, a color developer that is a component capable of causing 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).

[0021] Examples of microencapsulation methods include interfacial polymerization, interfacial polycondensation, insitu polymerization, liquid curing coating, phase separation from aqueous solutions, phase separation from organic solvents, melt-dispersion-cooling, air suspension coating, and spray drying, which can be appropriately selected depending on the application.

[0022] For example, in a phase separation method from an aqueous solution, thermochromic colored resin particles can be produced by a method including the following steps, particularly a method including the following steps in this order: (1) heating and melting a leuco dye, a developer, and a color change temperature regulator; (2) adding the heated and melted leuco dye, developer, and color change temperature regulator to an emulsifier solution, heating and stirring to disperse them into oil droplets and prepare a dispersion; (3) gradually adding a resin raw material capable of forming a wall film, such as a urethane resin, epoxy resin, or amino resin, for example, an amino resin solution, specifically an amino resin solution such as a methylolmelamine aqueous solution, urea solution, or benzoguanamine solution, to the above dispersion, reacting the resin raw material to form a capsule film, thereby obtaining a thermochromic microcapsule pigment; and (4) filtering the dispersion containing the thermochromic microcapsule pigment.

[0023] In these thermochromic colored resin particles, the color development temperature and decolorization temperature of each color can be set to a suitable temperature by appropriately combining the types and amounts of leuco dyes, color developers, and color change temperature adjusters.

[0024] As the photochromic colored resin particles described in 5) above, for example, photochromic colored resin particles can be used that consist of at least one or more photochromic substances selected from photochromic dyes (compounds), fluorescent dyes, etc., and a resin such as a terpene phenol resin. Furthermore, examples of photochromic colored resin particles include those produced by microencapsulating a photochromic composition containing at least one or more photochromic substances 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 (for example, 0.1 to 6 μm). The microencapsulation method can be the same as that used for producing the thermochromic resin particles described above.

[0025] These photochromic colored resin particles 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 to develop color in an ultraviolet irradiation environment (irradiation with wavelengths of 200 to 400 nm, or an irradiation environment with sunlight including ultraviolet rays) by suitably using the above-mentioned photochromic substance.

[0026] Each of the colored resin particles described in 1) to 5) above can be used as a fluorescent pigment, a microcapsule pigment of a thermochromic pigment or a photochromic pigment, or a microsphere (colorant). Furthermore, each of the colored resin particles described in 1) to 5) above can be manufactured using each manufacturing method, and commercially available products may also be used if available. These pigments can be used individually or in mixtures of two or more types.

[0027] The average particle size of the pigment used in the present invention is not particularly limited, but is preferably 30 nm or more, more preferably 40 nm or more, even more preferably 60 nm or more, preferably 1000 nm or less, more preferably 500 nm or less, and even more preferably 300 nm or less.

[0028] Here, the average particle size of the pigment is the 50th percentile particle size (D50 value) of the cumulative particle size distribution calculated by volume-based measurement using the laser diffraction method with the LA-960 series laser diffraction / scattering particle size distribution analyzer (product name) manufactured by Horiba, Ltd. The shape of the pigment particles incorporated into the ink composition of the present invention may be spherical or non-spherical.

[0029] If the average particle size of the pigment is too small, a large amount of phosphate ester will be adsorbed onto the pigment. This will result in insufficient phosphate ester adsorbed onto the tip seat, impairing the lubrication of the ball's rotation. This can lead to poor writing performance on paper with hand oils after long-term storage, such as skipping at the beginning of writing, and may also cause a decrease in writing quality and wear of the tip seat when writing under high pressure.

[0030] The content of the pigment is not particularly limited, but is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 4% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less, based on the total amount of the aqueous ink composition.

[0031] If the content of the pigment is too large, the amount of the phosphate ester adsorbed on the pigment increases, so that when writing on paper with fingerprints attached after long-term storage, bleeding (initial writing) occurs, resulting in deterioration of fingerprint writing properties, or when the writing pressure is high, there is a risk of deterioration of the writing feel in high-load writing or wear of the tip receiving seat.

[0032] The specific surface area of the pigment used in the present invention is 260 m ２ / g or less, preferably 240 m ２ / g or less, more preferably 200 m ２ / g or less, and preferably 1 m ２ / g or more, more preferably 5 m ２ / g or more, still more preferably 10 m ２ / g or more. Here, the specific surface area of the pigment is the BET specific surface area measured using a specific surface area measuring device. More specifically, the pigment is sampled, precisely weighed using an electronic balance, dried while degassing at 110°C for 30 minutes, and then the BET specific surface area can be measured by the BET single-point method using a fully automatic specific surface area measuring device (manufactured by Mountech Co., Ltd., Macsorb model HM-1208).

[0033] If the specific surface area of the pigment is too large, the amount of the phosphate ester adsorbed on the pigment increases, so that the amount of the phosphate ester adsorbed on the tip receiving seat is insufficient, the lubricity of the ball rotation is impaired, and when writing on paper with fingerprints attached after long-term storage, bleeding (initial writing) occurs, resulting in deterioration of fingerprint writing properties, or when the writing pressure is high, there is a risk of deterioration of the writing feel in high-load writing or wear of the tip receiving seat.​​(Phosphate ester) The phosphate ester used in the present invention has an HLB value of 8.5 or more, preferably 9 or more, more preferably 10 or more, preferably 17 or less, more preferably 15 or less, and even more preferably 14 or less. The phosphate ester has a function as a lubricant.

[0035] Here, the HLB value is a value calculated by the Kawakami method [HLB value = 7 + 11.7 log (MW / MO), MW: total sum of the formula weights of the hydrophilic part, MO: total sum of the formula weights of the lipophilic part].

[0036] Examples of the phosphate ester include phosphate esters of polyoxyethylene alkyl ether or polyoxyethylene alkyl aryl ether. These phosphate esters may be used alone or in combination of two or more.

[0037] Specifically, phosphate esters that can be used include NIKKOL DDP-6 [HLB value: 9 (manufactured by Nikko Chemicals Co., Ltd.)], NIKKOL DDP-8 [HLB value: 11.5 (manufactured by Nikko Chemicals Co., Ltd.)], NIKKOL DDP-10 [HLB value: 13.5 (manufactured by Nikko Chemicals Co., Ltd.)], Phosphanol RS-410 [HLB value: 9 (manufactured by Toho Chemical Industry Co., Ltd.)], Phosphanol RS-610 [HLB value: 10.5 (manufactured by Toho Chemical Industry Co., Ltd.)], Phosphanol RS-710 [HLB value: 13.3 (manufactured by Toho Chemical Industry Co., Ltd.)], and the like. These can be used as they are or as salts neutralized with an alkali metal or an organic base, and one kind can be used alone or two or more kinds can be used in combination.

[0038] The content of these phosphate esters is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more, and preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less based on the total amount of the aqueous ink composition.

[0039] If the content of the phosphate ester is too low, when writing on paper with fingerprints after long-term storage, the writing performance may deteriorate, such as scratching during the first writing, or when the writing pressure is high, the writing feel may decrease in high-load writing, and there is a risk of causing wear of the tip receiving seat.

[0040] (Aqueous ink composition) The aqueous ink composition of the present invention contains a pigment having a specific surface area of 260 m ２ / g or less and a phosphate ester having an HLB value of 8.5 or more as described above.

[0041] Further, when the average particle diameter of the pigment is Anm, the content of the pigment in the aqueous ink composition is B mass%, the specific surface area of the pigment is Cm ２ / g, and the content of the phosphate ester in the aqueous ink composition is D mass%, (B×C) / (A×D) < 600.

[0042] Further, (B×C) / (A×D) is less than 600, preferably less than 400, and more preferably less than 200. Also, (B×C) / (A×D) is preferably 0.1 or more, more preferably 1.0 or more, and even more preferably 2.0 or more.

[0043] If (B×C) / (A×D) is too large, due to an increase in the amount of phosphate ester adsorbed on the pigment, the amount of phosphate ester adsorbed on the tip receiving seat is insufficient, the lubricity of the ball rotation is impaired, and when writing on paper with fingerprints after long-term storage, the writing performance may deteriorate, such as scratching during the first writing, or when the writing pressure is high, the writing feel may decrease in high-load writing, and there is a risk of causing wear of the tip receiving seat.

[0044] In addition to the above-mentioned pigment pigment and phosphate ester, the aqueous ink composition of the present invention contains water (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.) as a solvent. Also, within a range that does not impair the effects of the present invention, a water-soluble solvent, a pigment dispersant, a thickener, a pH adjuster, an anti-rust agent, a preservative, etc. may be appropriately contained. Also, a lubricant other than the above-mentioned phosphate ester may be contained as necessary.

[0045] Examples of water-soluble solvents include 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. These may be used individually or in combination of two or more. The content of the water-soluble solvent is preferably 5 to 40% by mass of the total amount of the ink composition.

[0046] Examples of pigment dispersants include polyacrylic acid, acrylic acid copolymers, and maleic acid resins. Specifically, resins such as acrylic resins, styrene-acrylic resins, and styrene-maleic acid resins can be used in the form of water-soluble salts. For example, salts can be formed with alkali metals such as sodium and potassium. Salts can also be formed with aliphatic primary to tertiary amines such as mono, di, or trimethylamine, alcohol amines such as mono, di, or trippropanolamine, methylethanolamine, methylpropanolamine, and dimethylethanolamine, and amines such as ammonia, morpholine, and N-methylphorin. Among these, styrene-acrylic resin is preferred.

[0047] As a thickening agent, at least one selected from the group consisting of synthetic polymers, cellulose, and polysaccharides is preferable. Specifically, examples include gum arabic, tragacanth gum, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, xanthan gum, gelan gum, succinoglycan, dieutan gum, dextran, methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, starch glycolic acid and its salts, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylic acid and its salts, polyethylene hydroxide, copolymers of vinyl acetate and polyvinylpyrrolidone, styrene-acrylic acid copolymers and their salts, etc. Among these, xanthan gum is preferred.

[0048] Examples of pH adjusting agents include ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, alkali metal salts of carbonic acid or phosphoric acid such as sodium tripolyphosphate and sodium carbonate, alkali metal hydrates such as sodium hydroxide, and N,N-bis(2-hydroxyethyl)glycine. Among these, triethanolamine is preferred.

[0049] As rust inhibitors, benzotriazole, toltriazole, dicyclohexylammonium nitride, saponins, etc., can be used. Among these, benzotriazole is preferred.

[0050] Examples of preservatives include isothiazolines such as benzoisothiazoline (also known as 1,2-benzoisothiazoline-3-one), isothiazolinone (also known as 1,2-thiazoline-3-one), methylisothiazolinone (also known as 2-methyl-4-isothiazoline-3-one), and octylisothiazolinone (2-n-octyl-4-isothiazoline-3-one), as well as pentachlorophenol sodium and 2,3,5,6-tetrachloro-4 (methyl sulfur Examples include ionyl pyridine, parahydroxybenzoic acid esters, phenol, sodium benzoate, sodium dehydroacetate, potassium sorbate, morpholine, cresol, hexahydro-1,3,5-tris(2-hydroxyethyl)-1,3,5-triazine, 2-bromo-2-nitropropane-1,3-diol, 2-pyridinethiol-1-oxide sodium, sodium pyrithione, and 2-(4-thiozolyl)benzimidazole.

[0051] Other lubricants besides phosphate esters include nonionic types such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, and higher fatty acid esters of polyoxyalkylenes, which are also used as surface treatment agents for pigments; anionic types such as alkyl sulfonates and alkyl allyl sulfonates of higher fatty acid amides; derivatives of polyalkylene glycols; fluorinated surfactants; and polyether-modified silicones.

[0052] Pigment dispersants, thickeners, pH adjusters, rust inhibitors, preservatives, and lubricants other than phosphate esters may each be used individually or in combination of two or more. Furthermore, commercially available products of these may be used if they are available.

[0053] The amounts of water-soluble solvents, pigment dispersants, thickeners, pH adjusters, rust inhibitors, preservatives, and lubricants other than phosphate esters are not particularly limited, but the amount of each component of pigment dispersant, thickener, pH adjuster, rust inhibitor, and preservative relative to the total amount of the aqueous ink composition is preferably 0.1% by mass or more, preferably 10% by mass or less, and more preferably 5% by mass or less.

[0054] The aqueous ink composition of the present invention can be manufactured using conventionally known methods and is no different from the manufacturing methods of other aqueous ink compositions. That is, the aqueous ink composition of the present invention can be manufactured by blending a pigment, a phosphate ester, water, and, if necessary, a pigment dispersant, a thickener, a pH adjuster, a rust inhibitor, a preservative, and a lubricant other than the phosphate ester, according to the application of the ink, and mixing and stirring. During mixing and stirring, a mixer or, furthermore, a bead mill, homomixer, homogenizer, etc., which can apply strong shear, can be used to set the stirring conditions to suitable conditions. In addition to mixing and stirring, if necessary, steps such as filtration or centrifugation may be performed to remove coarse particles from the aqueous ink composition.

[0055] The dissolved oxygen concentration in the aqueous ink composition of the present invention is preferably less than 7 mg / L, more preferably less than 6 mg / L, and even more preferably less than 4 mg / L, under the condition of a measurement temperature of 25°C. Here, the dissolved oxygen concentration can be measured using a needle-type oxygen concentration meter MicroxTX3 (manufactured by PreSense). If the dissolved oxygen concentration is too high, the phosphate ester will be taken away by the microbubbles that form after long-term storage, which may worsen the writing performance on paper with hand oils on it, such as causing smudging at the beginning of writing.

[0056] The pH of the aqueous ink composition of the present invention is preferably 6 to 10. The pH of the aqueous ink composition can be measured using a commercially available pH meter or the like.

[0057] Furthermore, the viscosity of the aqueous ink composition of the present invention is preferably measured at a temperature of 25°C and a shear rate of 383 s⁻¹. －１ Under these conditions, the viscosity is 2 to 200 mPa·s. Here, the viscosity of the aqueous ink composition can be measured by steady flow measurement using a rheometer MCR-302 (manufactured by Anton Paar) with a cone plate (diameter: 25 mm, angle: 2°).

[0058] (Ballpoint pen) The aqueous ink composition of the present invention is preferably used in a ballpoint pen equipped with a pen tip such as a ballpoint pen tip. The structure of the ballpoint pen tip is not particularly limited, but examples include a pipe tip (sometimes called a needle tip) and a bullet-shaped tip.

[0059] As shown in Figure 1, the pipe tip 2 has a structure in which the tip of a thin tube 4 made of a metal material such as stainless steel is crimped inward, and a ball 6 is rotatably enclosed inside. Furthermore, by pressing and deforming the area near the tip at four or more locations, the inner protrusions serve as receiving seats 8, and the gaps between the multiple protrusions are formed as ink flow paths.

[0060] As shown in Figure 2, the bullet-shaped tip 10 is formed by cutting a metal material such as stainless steel to create a tapered tip, and has a structure in which a ball 12 is rotatably enclosed at the tip. In addition, a receiving seat (not shown) and an ink channel (not shown) are formed on the inner surface near the tip.

[0061] Among these options, a pipe tip is preferable because it has a small receptacle and good ink ejection, resulting in a smoother writing experience.

[0062] Furthermore, the surface roughness Ra of the ball in the ballpoint pen is preferably 0.1 nm or more, more preferably 0.3 nm or more, even more preferably 0.5 nm or more, preferably 10 nm or less, more preferably 6.0 nm or less, and even more preferably 4.0 nm or less. Here, the surface roughness Ra was measured using a non-contact surface shape measuring instrument (Zygo NewView 7200) with a lens magnification of 50x, an evaluation length of 100 μm, and a Gaussian filter of 25 μm, with all other conditions conforming to JIS B0601 (Geometric specifications of products - surface properties). If the surface roughness Ra is too large, the ball bearing tends to wear down easily, and if the surface roughness Ra is too small, there is a risk that the writing performance with hand oil will deteriorate, such as when writing on paper with hand oil on it, causing smudging at the beginning of writing.

[0063] In the present invention, a ballpoint pen having a dynamic friction coefficient in the range of 0.1 to 0.25 during writing is more preferable from the viewpoint of resistance to wear on the writing surface. The dynamic friction coefficient is determined by using a surface quality measuring instrument (HEIDON-14D, Shinto Chemical Co., Ltd.) to measure the frictional resistance three times during a 10 cm linear motion under the conditions of a writing speed of 3.3 m / min, a load of 100 g, and a writing angle of 90°, and then calculating the friction coefficient from the average value. Standard paper (Shiraoi) is used as the writing paper.

[0064] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following, "parts" refers to mass unless otherwise specified.

[0065] (Examples 1-9 and Comparative Examples 1-3) Each aqueous ink composition was prepared by conventional methods according to the formulations shown in Table 1 below. Here, "remainder" in Table 1 refers to the remaining amount of the formulation when 100 parts of the aqueous ink composition are charged, for example, in Example 1 it is 83.2 parts. The colored resin particles used in Example 3 and the heat-changed particles used in Example 4 were manufactured as follows.

[0066] (Production of colored resin particles) 12.5 parts by mass of ethyl acetate was heated to 60°C, and 3.5 parts by mass of oil-soluble black dye (Oil Black 860; manufactured by Orient Chemical Industry Co., Ltd.) and 0.5 parts by mass of terpene phenol resin (YS Polystar N125; manufactured by Yasuhara Chemical Co., Ltd.) were added and stirred. Next, 8 parts by mass of isocyanurate modified hexamethylene diisocyanate (TLA-100; manufactured by Asahi Kasei Chemicals Corporation) was added as a prepolymer to prepare an oil phase solution. 200 parts by mass of distilled water was heated to 60°C, and 15 parts by mass of polyvinyl alcohol (PVA-205; manufactured by Kuraray Co., Ltd.) was added as a dispersant to prepare an aqueous phase solution. The oil phase solution was added to the aqueous phase solution maintained at 60°C, and interfacial polymerization was carried out using a homogenizer for 6 hours. The resulting mixture was centrifuged to recover the solid content, yielding colored resin particles with an average particle size of 2.1 μm.

[0067] (Preparation of heat-changed particles) One part by mass of methyl-3',6'-bisdiphenylaminofluorane as a leuco dye, two parts by mass of 2,2-bis(2-hydroxy-5-biphenylyl)propane as a color developer, and 24 parts by mass of bis(4-hydroxyphenyl)phenylmethanedicaprylate as a color change temperature adjuster were mixed and heated and melted at 100°C to obtain 27 parts by mass of a homogeneous composition. The obtained thermal solution composition was gradually added, while heating and stirring, to 100 parts by mass of a 90°C, pH 4 aqueous solution in which 40 parts by mass of methyl vinyl ether / maleic anhydride copolymer resin (Gantzletz AN-179: manufactured by ISP Co., Ltd.) was dissolved as a protective colloid, and dispersed into oil droplets with a diameter of approximately 0.5 to 1.0 μm. Next, 20 parts by mass of methylol melamine (Sumitex Resin M-3: aqueous solution containing 80% of the active ingredient; manufactured by Sumitomo Chemical Co., Ltd.) was gradually added as a capsule membrane material, and the mixture was heated at 90°C for 30 minutes to microencapsulate it. The resulting mixture was centrifuged to recover the solid content, and thermochromic particles with an average particle size of 0.72 μm were obtained.

[0068] The water-based ballpoint pen ink compositions obtained in Examples 1 to 9 and Comparative Examples 1 to 3 were used to prepare ballpoint pens using the method described below, and their initial writing performance, resistance to ballpoint pen wear, and writing feel were evaluated using the evaluation method described below. The results are shown in Table 1 below.

[0069] (Ballpoint Pen Manufacturing) Each aqueous ink composition obtained above was filled into a refill consisting of a polypropylene ink reservoir tube (inner diameter 4.0 mm, length 113 mm), a stainless steel tip (carbide ball, ball diameter 0.5 mm), and a connector connecting the reservoir tube to a pipe tip (see Figure 1) or a bullet-shaped tip (see Figure 2). Next, an ink-following body consisting of mineral oil, polybutene, and olefin-based elastomer was loaded into the trailing end of the ink. This refill was loaded into the barrel of a ballpoint pen (Signo UM-100, Mitsubishi Pencil Co., Ltd.) to manufacture an aqueous ballpoint pen. The surface roughness Ra of the balls of the ballpoint pens used is shown in Table 1. [Measured and calculated using the non-contact surface shape measuring instrument (Zygo NewView 7200) mentioned above.]

[0070] <Evaluation Method> (Initial Writing Performance) Each water-based ballpoint pen obtained above was left to stand horizontally for 7 days in an environment of 25°C and 65% humidity with the pen tip exposed. Then, 10 consecutive circles with a diameter of 4 cm were written on the following hand-grease paper and evaluated according to the evaluation criteria below. (Preparation of Hand-Grease Paper) Artificial hand grease prepared with the following formulation was uniformly applied to the test paper shown in JIS S 6061:2010 7.3, and then thoroughly dried at room temperature to prepare the test paper. (Artificial Hand-Grease Formulation) Squalane 3% by mass Isopropyl myristate 6% by mass Olive oil 12% by mass Cholesterol 0.5% by mass Palmitic acid 0.5% by mass Oleic acid 4% by mass Isostearic acid 4% by mass Acetone 70% by mass (Evaluation Criteria) A: All writing was completely successful. B: A total of more than 0 mm and less than or equal to 20 mm of unwriting area was observed. C: An area exceeding 20 mm was found to be unusable for writing.

[0071] (Resistance to Seat Abrasion) Using each of the water-based ballpoint pens obtained above, a mechanical writing test was conducted in which spiral writing was performed up to a writing distance of 1000m (end of writing), and the following evaluation criteria were used for evaluation. Writing conditions: load 150gf, writing angle 80 degrees, writing speed 4.5mm / min (Evaluation criteria) A: All pens can write without any problems. B: Some skipping occurs, but writing is possible until the end of writing. C: All pens are severely worn and cannot write midway through.

[0072] (Writing feel) Using each of the water-based ballpoint pens obtained above, the writing feel was evaluated before and after the machine writing test used in the evaluation above, with a writing distance of 300m in a spiral pattern, according to the following evaluation criteria. Writing conditions: 150gf, writing angle 80 degrees, writing speed 4.5mm / min (Evaluation criteria) A: Same writing feel. B: Slightly worse writing feel. C: Significantly worse writing feel.

[0073] (Coefficient of Dynamic Friction) For each ballpoint pen, a surface texture measuring instrument (HEIDON-14D, Shinto Chemical Co., Ltd.) was used to measure the frictional resistance three times during a 10 cm linear motion under the conditions of a writing speed of 3.3 m / min, a load of 100 g, and a writing angle of 90°. The coefficient of friction was calculated from the average value. Standard paper (Shiraoi) was used as the writing paper.

[0074]

[0075] As shown in Table 1, the specific surface area is 260 m². ２ An aqueous ink composition comprising a pigment of less than or equal to / g and a phosphate ester with an HLB value of 8.5 or higher, wherein the average particle size of the pigment is A nm, the content of the pigment in the aqueous ink composition is B mass%, and the specific surface area of ​​the pigment is C m ２ When the content of the phosphate ester in the aqueous ink composition is D by mass%, a ballpoint pen equipped with an aqueous ink composition in which (B × C) / (A × D) < 600 was found to have excellent initial writing performance, resistance to wear on the pen tip, and writing feel.

[0076] The aqueous ink composition of the present invention can be suitably used in ballpoint pens, particularly ballpoint pens having a pipe tip structure.

Claims

1. Specific surface area is 260 m² ２ An aqueous ink composition comprising a pigment of less than or equal to / g and a phosphate ester with an HLB value of 8.5 or higher, wherein the average particle size of the pigment is A nm, the content of the pigment in the aqueous ink composition is B mass%, and the specific surface area of ​​the pigment is C m ２ An aqueous ink composition in which, when the content of the phosphate ester in the aqueous ink composition is D by mass%, (B × C) / (A × D) < 600.

2. The aqueous ink composition according to claim 1, wherein the dissolved oxygen concentration is less than 7 mg / L.

3. A ballpoint pen equipped with the aqueous ink composition according to claim 1 or 2, wherein the surface roughness Ra of the ball is 0.1 to 10 nm.

4. A ballpoint pen equipped with the aqueous ink composition according to claim 1 or 2, the ballpoint pen having a pipe tip structure.

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