Aqueous ink composition and ballpoint pen

Abstract

This aqueous ink composition comprises: water; a coloring agent; a water-soluble organic solvent; tropolone and / or a tropolone derivative; and a surfactant. The tropolone and / or the tropolone derivative is contained in an amount of 0.03-3 mass% in the aqueous ink composition.

Description

Water-based ink composition and ballpoint pen

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

[0002] Writing instruments such as ballpoint pens and marking pens that contain aqueous inks are widely used. However, such writing instruments have been subject to problems such as unstable ink flow rate, ink spurting from the ejection port, or, conversely, difficulty in ejecting ink from the ejection port, due to bubbles that form in the aqueous ink over time.

[0003] Therefore, various studies have been conducted on the suppression and removal of bubbles. Patent Document 1 studies the case where at least one selected from 1,3-dimethyl-5-pyrazolone, 3-methyl-5-pyrazolone, and 3-methyl-5-pyrazolin-5-one is blended, and Patent Document 2 studies the case where ascorbic acid is blended.

[0004] JP 2013-91695 A JP 2012-62338 A

[0005] There is also a demand for suppression of bubble generation under various conditions, such as suppression of bubble generation under low temperature conditions or over a long period of time.

[0006] An object of the present invention is to provide an aqueous ink composition that can suppress the generation of bubbles even under low temperature conditions or when subjected to impact after storage over a period of time, and a ballpoint pen that uses this aqueous composition.

[0007] As a result of extensive research, the present inventors have found that the above problems can be solved by using a specific component, and have thus completed the present invention.

[0008] That is, according to the present invention, there are provided: (1) an aqueous ink composition comprising water, a colorant, a water-soluble organic solvent, tropolone and / or a tropolone derivative, and a surfactant, wherein the tropolone and / or the tropolone derivative is contained in an amount of 0.03 to 3 mass % in the aqueous ink composition; (2) the aqueous ink composition according to (1), further comprising an organic acid; (3) the aqueous ink composition according to (1) or (2), further comprising a thickener; (4) the aqueous ink composition according to (3), wherein the colorant is colored resin particles, and the tropolone and / or the tropolone derivative is hinokitiol; and (5) a ballpoint pen equipped with the aqueous ink composition according to (4).

[0009] According to the present invention, it is possible to provide an aqueous ink composition that can suppress the generation of bubbles even under low temperature conditions or when subjected to impact, and a ballpoint pen that uses this aqueous composition.

[0010] The aqueous ink composition of the present invention is an aqueous ink composition containing water, a colorant, a water-soluble organic solvent, tropolone and / or a tropolone derivative, and a surfactant, and the aqueous ink composition contains 0.03 to 3 mass % of the tropolone and / or the tropolone derivative.

[0011] (Colorant) As the colorant used in the aqueous ink composition of the present invention, coloring materials used for writing instruments can be used, such as dyes, pigments, colored resin particles, etc. that are soluble or dispersible in water.

[0012] As the dye, a dye that is soluble or dispersible in water can be used, and examples thereof include acid dyes such as eosin, foxin, 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] As the pigment, any of conventionally known inorganic and organic pigments such as titanium oxide, pseudopigments in which a resin emulsion is colored with a dye or pigment, white plastic pigments, luster pigments, pigments in which a silica or mica base is coated with a multilayer of iron oxide, titanium oxide, or the like on the surface, and the like can be used without any restrictions.

[0014] Examples of inorganic pigments that can be used include 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, yellow lead, molybdate orange, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine, precipitated barium sulfate, baryte powder, calcium carbonate, white lead, dark blue, iron blue, manganese violet, aluminum powder, and brass powder.

[0015] Examples of organic pigments include azo lakes, insoluble azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, nitroso pigments, etc. 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.I. Examples of suitable pigments include C.I. Pigment Violet 23, C.I. Pigment Violet 50, and C.I. Pigment Green 7.

[0016] The colored resin particles are not particularly limited as long as they are composed of colored resin particles, and examples thereof include: 1) colored resin particles in which a colorant consisting of a pigment such as an inorganic pigment such as carbon black or titanium oxide, or an organic pigment such as a phthalocyanine pigment or an azo pigment is dispersed in the resin particles; 2) colored resin particles in which the surfaces of resin particles are coated with a colorant consisting of the above-mentioned pigment; 3) colored resin particles in which a colorant consisting of a dye such as a direct dye, an acid dye, a basic dye, a food dye, or a fluorescent dye is dyed onto the resin particles; 4) microspheres having a matrix composed of a polymer, a resin having an OH group, and a water-insoluble dye; 5) colored resin particles made thermochromic using a leuco dye or the like (leuco dye-encapsulating particles); 6) colored resin particles made photochromic using a photochromic dye (compound), a fluorescent dye, or the like.

[0017] The resin component of the colored resin particles of 1) to 3) above can be, for example, at least one selected from polymers or copolymers of acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, styrene, acrylonitrile, butadiene, etc., benzoguanamine, phenolic resins, epoxy resins, urethane resins, etc., which may be crosslinked or otherwise treated as necessary. Conventional methods such as suspension polymerization and dispersion polymerization can be used to color these resins. The microspheres of 4) above have a polymer matrix, a resin having OH groups, and a water-insoluble dye.

[0018] Examples of polymers constituting the matrix include epoxy polymers, melamine polymers, acrylic polymers, urethane polymers, and urea polymers. One type may be used alone, or two or more types of these may be used in combination.

[0019] The resin having an OH group is contained in the matrix. Examples of the resin having an OH group include terpene phenol resin, rosin phenol resin, alkylphenol resin, phenol novolac resin, cresol novolac resin, butyral resin, polyvinyl alcohol resin, polyol-modified xylene resin, ethylene oxide-modified xylene resin, maleic acid resin, hydroxyl group-modified acrylic resin, hydroxyl group-modified styrene acrylic resin, carboxyl-modified acrylic resin, and carboxyl-modified styrene acrylic resin.

[0020] The water-insoluble dye is a dye that is insoluble in water at room temperature, and examples thereof include salt-forming dyes such as azo dyes, metal complex azo dyes, dyes having anthraquinone and metal phthalocyanine chemical structures, disperse dyes, oil-soluble dyes, etc., but from the viewpoint of color development, it is preferable to use salt-forming dyes. The microspheres can be produced, for example, by the following production processes (emulsion polymerization method, phase separation method).

[0021] The process for preparing microspheres using emulsion polymerization involves preparing an oil phase, preparing an aqueous phase, and mixing the oil phase and aqueous phase to emulsify the components of the oil phase, followed by polymerization.

[0022] The oil phase contains an organic solvent such as phenyl glycol, benzyl alcohol, ethylene glycol monobenzyl ether, or ethyl acetate, the water-insoluble dye, the resin having an OH group, and a monomer or prepolymer. Multiple types of organic solvents may be contained.

[0023] This oil phase can be prepared by adding a water-insoluble dye and a resin having an OH group to an organic solvent while heating the organic solvent to a predetermined temperature and stirring the mixture, then adding a monomer or a prepolymer thereof that constitutes the polymer, such as a melamine monomer, an epoxy monomer, an acrylic monomer, or an isocyanate monomer, and optionally further adding another organic solvent.

[0024] The aqueous phase can be prepared by mixing water and a dispersant, such as, but not limited to, polyvinyl alcohol.

[0025] The emulsification and polymerization step involves first emulsifying the oil phase components, and then polymerizing the oil phase by adding the oil phase to the aqueous phase and emulsifying and mixing the components while heating to a predetermined temperature using a homogenizer, etc. The microsphere preparation step may include other steps, such as classifying the microspheres.

[0026] The process for preparing microspheres by the phase separation method comprises preparing a dye-containing solution, preparing a protective colloid-containing solution, and polymerizing a monomer or prepolymer.

[0027] The dye-containing solution can be prepared by dissolving a water-insoluble dye and a resin having an OH group in an organic solvent under heating. The water-insoluble dye, the resin having an OH group, and the organic solvent can be the same as those mentioned in the microsphere preparation process by emulsion polymerization.

[0028] The protective colloid-containing solution can be prepared by dissolving a protective colloid in water. Examples of the protective colloid include methyl vinyl ether-maleic anhydride copolymer.

[0029] The polymerization of the monomer or prepolymer can be carried out by adding the dye-containing solution to a protective colloid-containing solution heated to a predetermined temperature to disperse it in the form of oil droplets, adding the monomer or prepolymer thereto, and stirring while maintaining the temperature. In this way, the water-insoluble dye and the resin having an OH group are encapsulated in the polymer obtained by polymerizing the monomer or prepolymer.

[0030] In the obtained microspheres, the content of the resin having an OH group in the total amount of the microspheres is preferably 1% by mass or more and 40% by mass or less, and the content of the water-insoluble dye is preferably 10% by mass or more and 45% by mass or less. The average particle size of the microspheres is preferably 0.2 μm or more and 3.0 μm or less.

[0031] Here, the average particle size of the microspheres is the D50 value measured using a particle size analyzer [Microtrac HRA9320-X100 (manufactured by Nikkiso Co., Ltd.)] or the average particle size value calculated by cumulant method analysis in scattering intensity distribution using a concentrated particle size analyzer FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd.).

[0032] Examples of the thermochromic colored resin particles of 5) 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 former, a color developer that is a component capable of causing the leuco dye to develop color, and a color change temperature regulator that can control the color change temperature in the color development of the leuco dye and the color developer, so as to have a predetermined average particle size (e.g., 0.1 to 6 μm).

[0033] Examples of microencapsulation methods include interfacial polymerization, interfacial polycondensation, in situ polymerization, liquid hardening coating, phase separation from an aqueous solution, phase separation from an organic solvent, melting dispersion cooling, air suspension coating, and spray drying, and can be appropriately selected depending on the application.

[0034] For example, in the phase separation method from an aqueous solution, thermochromic colored resin particles can be produced by a method comprising the following steps, particularly a method comprising the following steps in this order: (1) heating and melting a leuco dye, a color developer, and a color change temperature regulator; (2) adding the heated and melted leuco dye, color developer, and color change temperature regulator to an emulsifier solution, and dispersing them into oil droplets by heating and stirring to 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 as a capsule film agent, 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, and reacting this resin raw material to form a capsule film, thereby obtaining a thermochromic microcapsule pigment; and (4) filtering the dispersion containing the thermochromic microcapsule pigment.

[0035] In these thermochromic colored resin particles, the color-developing temperature and decolorizing temperature of each color can be set to an appropriate temperature by appropriately combining the types and amounts of the leuco dye, color developer, and color-change temperature adjuster.

[0036] The photochromic colored resin particles of 6) above can be, for example, photochromic colored resin particles composed of at least one photochromic substance selected from photochromic dyes (compounds), fluorescent dyes, and other photochromic substances, and a resin such as a terpene phenol resin. Examples of photochromic colored resin particles include photochromic colored resin particles produced by microencapsulating a photochromic composition containing at least one photochromic substance selected from photochromic dyes (compounds), fluorescent dyes, and other photochromic substances, 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). The microencapsulation method can be the same as that used to produce the thermochromic resin particles described above.

[0037] By suitably using the above-mentioned photochromic substance, the photochromic colored resin particles can be made to have the property of being colorless in, for example, an indoor lighting environment (a lighting fixture selected from an incandescent lamp, a fluorescent lamp, a lamp, a white LED, etc.) and developing color in an ultraviolet ray irradiation environment (an environment irradiated with light having a wavelength of 200 to 400 nm or sunlight containing ultraviolet rays).

[0038] Each of the colored resin particles 1) to 6) above can be used as a fluorescent pigment, a microencapsulated pigment of a thermochromic pigment or a photochromic pigment, a microsphere, etc. (coloring material). Furthermore, each of the colored resin particles 1) to 6) above can be produced by a corresponding production method, and commercially available products can also be used if available.

[0039] These colorants can be used alone or in combination of two or more. The average particle size of the dyes, pigments, colored resin particles, etc. that are soluble or dispersible in water among these colorants is not particularly limited, but can be, for example, 0.02 to 6 μm.

[0040] The content of these colorants is not particularly limited, but is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 7% by mass or more, in terms of solids mass % of the total amount of the aqueous ink composition, and is preferably 35% by mass or less, more preferably 20% by mass or less, even more preferably 18% by mass or less.

[0041] (Solvent) The aqueous ink composition of the present invention contains water and a water-soluble organic solvent as a solvent. That is, the solvent used in the aqueous ink composition of the present invention is an aqueous solvent containing water. As the aqueous solvent, a mixed solvent of water (e.g., ion-exchanged water, distilled water, tap water, etc.) and a water-soluble organic solvent can be used. By using a water-soluble organic solvent, tropolone and / or a tropolone derivative can be stably dissolved in the aqueous ink composition of the present invention.

[0042] Examples of the water-soluble organic solvent that can be used include aromatics, alcohols, polyhydric alcohols, glycol ethers, hydrocarbons, esters, etc. These solvents may be used alone or in combination.

[0043] Examples of aromatic compounds that can be used include benzyl alcohol, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, propylene glycol monophenyl ether, diethylene glycol monophenyl ether, alkylsulfonic acid phenyl ester, butyl phthalate, ethylhexyl phthalate, tridecyl phthalate, ethylhexyl trimellitate, diethylene glycol dibenzoate, and dipropylene glycol dibenzoate.

[0044] Examples of alcohols that can be used include ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butyl alcohol, 1-pentanol, isoamyl alcohol, sec-amyl alcohol, 3-pentanol, tert-amyl alcohol, n-hexanol, methyl amyl alcohol, 2-ethylbutanol, n-heptanol, 2-heptanol, 3-heptanol, n-octanol, 2-octanol, 2-ethylhexanol, 3,5,5-trimethylhexanol, nonanol, n-decanol, undecanol, n-decanol, trimethylnonyl alcohol, tetradecanol, heptadecanol, cyclohexanol, 2-methylcyclohexanol, and glycerin.

[0045] Examples of polyhydric alcohols that can be used include ethylene glycol, diethylene glycol, propylene glycol, 3-methyl-1,3 butanediol, triethylene glycol, dipropylene glycol, 1,3 propanediol, 1,3 butanediol, 1,5 pentanediol, hexylene glycol, octylene glycol, and glycerin.

[0046] Examples of glycol ethers that can be used include methyl isopropyl ether, ethyl ether, ethyl propyl ether, ethyl butyl ether, isopropyl ether, butyl ether, hexyl ether, 2-ethylhexyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylbutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, 3-methyl-3-methoxy-1-butanol, 3-methoxy-1-butanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol tertiary butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, and tetrapropylene glycol monobutyl ether.

[0047] As the hydrocarbons, for example, straight-chain hydrocarbons such as hexane, isohexane, heptane, octane, nonane, and decane, and cyclic hydrocarbons such as cyclohexane, methylcyclohexane, and ethylcyclohexane can be used.

[0048] Examples of esters include propylene glycol methyl ether acetate, propylene glycol diacetate, 3-methyl-3-methoxybutyl acetate, propylene glycol ethyl ether acetate, ethylene glycol ethyl ether acetate, butyl formate, isobutyl formate, isoamyl formate, propyl acetate, butyl acetate, isopropyl acetate, isobutyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, propyl propionate, isobutyl propionate, isoamyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, propyl isobutyrate, Examples of water-soluble organic solvents that can be used include methyl valerate, ethyl valerate, propyl valerate, methyl isovalerate, ethyl isovalerate, propyl isovalerate, methyl trimethylacetate, ethyl trimethylacetate, propyl trimethylacetate, methyl caproate, ethyl caproate, propyl caproate, methyl caprylate, ethyl caprylate, propyl caprylate, methyl laurate, ethyl laurate, methyl oleate, ethyl oleate, caprylic acid triglyceride, tributyl acetate citrate, octyl oxystearate, propylene glycol monoricinoleate, methyl 2-hydroxyisobutyrate, 3-methoxybutyl acetate, etc. One water-soluble organic solvent may be used alone, or two or more water-soluble organic solvents may be used in combination.

[0049] The total amount of water-soluble organic solvents added is 5% by mass or more, preferably 8% by mass or more, and more preferably 12% by mass or more, based on the total mass of the aqueous ink composition, and is 30% by mass or less, preferably 25% by mass or less, and more preferably 20% by mass or less.

[0050] When the amount of the water-soluble organic solvent added is within the above range, it is possible to prevent the phenomenon of precipitation of tropolone and / or tropolone derivatives during storage at low temperatures due to an addition amount that is too small.

[0051] (Tropolone and / or Tropolone Derivative) The aqueous ink composition of the present invention contains tropolone and / or a tropolone derivative. Examples of tropolone and / or a tropolone derivative include tropolone (chemical formula (1) below), α-thujaplicin (chemical formula (2) below), β-thujaplicin (also known as hinokitiol) (chemical formula (3) below), and γ-thujaplicin (chemical formula (4) below). Among these, tropolone and hinokitiol are preferred, and hinokitiol is even more preferred from the viewpoint of achieving a particularly high bubble generation suppression effect. In particular, when a material that easily traps bubbles, such as colored resin particles, is used as a colorant, the ink itself tends to be prone to bubble generation, so bubble generation can be effectively suppressed. At least one of the above-mentioned tropolone and / or tropolone derivatives can be used, and multiple types may also be used in combination.

[0052]

[0053] The tropolone and / or tropolone derivative salts may be used singly or in combination of two or more.

[0054] The amount of tropolone and / or a tropolone derivative blended is 0.03% by mass or more, preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and 3% by mass or less, preferably 1.5% by mass or less, and more preferably 1% by mass or less, based on the total mass of the aqueous ink composition. When the amount of tropolone and / or a tropolone derivative blended is within the above range, the generation of bubbles in the aqueous ink composition can be suppressed for a long period of time, and the generation of bubbles can also be suppressed when the writing instrument or the like is subjected to an impact after storage or when the writing instrument is used in a knock-type writing instrument. Furthermore, because the compound does not inactivate the preservative, as with other types of bubble suppressors, an improvement in the preservative effect over a long period of time is expected.

[0055] It is preferable that the tropolone and / or tropolone derivative included in the present invention is not in a form that is encapsulated or otherwise enclosed inside particles of a polymer or the like, and when producing (mixing and stirring) the aqueous ink composition of the present invention, it is preferable that the tropolone and / or tropolone derivative is dissolved in its original form in a solvent containing water and a water-soluble organic solvent, preferably in the presence of a surfactant.

[0056] (Surfactant) The aqueous ink composition of the present invention contains a surfactant. By including a surfactant in the aqueous ink composition of the present invention, tropolone and / or a tropolone derivative can be stably dissolved in the aqueous ink composition of the present invention. Examples of the surfactant include nonionic surfactants and anionic surfactants.

[0057] Examples of nonionic surfactants include polyoxyalkylene higher fatty acid esters, higher fatty acid partial esters of polyhydric alcohols, and higher fatty acid esters of sugars. Specific examples include glycerin fatty acid esters, polyglycerin fatty acid esters, propylene glycol fatty acid esters, pentaerythritol fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbit fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyethylene glycol fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene phytosterols, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene styrenated phenyl ethers, polyoxyethylene distyrenated phenyl ethers, polyoxyethylene castor oil, polyoxyethylene lanolin, polyoxyethylene lanolin alcohols, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, and polyoxyethylene alkylphenyl formaldehyde condensates.

[0058] Examples of anionic surfactants include alkylated sulfonates of higher fatty acid amides, alkyl aryl sulfonates, and naphthalene sulfonate-formaldehyde condensates. Specific examples include alkyl sulfates, polyoxyethylene alkyl ether sulfates, N-acylamino acid salts, N-acylmethyl taurine salts, polyoxyethylene alkyl ether acetates, alkyl phosphates such as alkyl phosphate esters, and polyoxyethylene alkyl ether phosphates. Among these, polyoxyethylene castor oil, polyoxyethylene alkyl ethers, or phosphate esters (e.g., alkyl phosphate esters) are preferred. One surfactant may be used alone, or two or more surfactants may be used in combination. If commercially available, these commercially available products may be used.

[0059] The amount of surfactant blended is not particularly limited, but 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, relative to the total amount of the aqueous ink composition, and is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less.

[0060] If a surfactant is not present in the aqueous ink composition of the present invention, the solubility of tropolone and / or tropolone derivatives will be insufficient, and it will be impossible to incorporate the amount of tropolone and / or tropolone derivatives necessary to achieve the effects of the present invention into the aqueous ink composition of the present invention.

[0061] (Organic Acid) The aqueous ink composition of the present invention may contain an organic acid as needed. The presence of an organic acid in the aqueous ink composition of the present invention can achieve a higher effect of suppressing bubble generation. In addition, bubble generation due to impact can be suppressed even at low temperatures where the dissolved oxygen concentration is high.

[0062] Examples of organic acids include at least one of carboxylic acids having a carboxy group (—COOH) and sulfonic acids having a sulfo group. Examples of carboxylic acids having a carboxy group include acetic acid, lactic acid, gluconic acid, fumaric acid, succinic acid, malic acid, tartaric acid, oxalic acid, citric acid, ascorbic acid, and N-acetyl-L-cysteine. Examples of sulfonic acids having a sulfo group include methanesulfonic acid, ethanesulfonic acid, isethionic acid, 1,2-ethanedisulfonic acid, and 1,3-propanedisulfonic acid. Among these, ascorbic acid, citric acid, and N-acetyl-L-cysteine ​​are preferred. Organic acids may also be used in the form of organic acid salts, including alkali metal salts such as lithium, sodium, and potassium salts of organic acids. Organic acids may be used alone or in combination. If commercially available, these products may be used.

[0063] The amount of organic acid blended is not particularly limited, but is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more, relative to the total amount of the aqueous ink composition, and is preferably 3% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less.

[0064] The aqueous ink composition of the present invention may contain a thickener as needed. By adding a thickener, vibration of the ink when an impact is applied to the writing implement can be suppressed, thereby further suppressing the formation of bubbles.

[0065] Examples of thickeners include polysaccharides such as cellulose derivatives, crystalline cellulose, rheozan gum, gellan gum, xanthan gum, and succinoglycan; organic thickeners such as alkali-swelling association emulsions, alkali-swelling emulsions, polyvinylpyrrolidone, and cross-linked acrylic acid polymers; and inorganic thickeners such as montmorillonite clay minerals. Among these, xanthan gum is preferred. One type of thickener may be used alone, or two or more types may be used in combination. Furthermore, if these commercially available products are available, they may be used.

[0066] The amount of thickener blended is not particularly limited, but is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, relative to the total amount of the aqueous ink composition, and is preferably 5% by mass or less, more preferably 4% by mass or less, even more preferably 3% by mass or less.

[0067] (Other Components) In addition to the components described above, the aqueous ink composition of the present invention may further contain other components, such as a dispersant, a rust inhibitor, and a pH adjuster.

[0068] Examples of 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 salts that are water-soluble. 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 tripropanolamine, methylethanolamine, methylpropanolamine, and dimethylethanolamine, as well as amines such as ammonia, morpholine, and N-methylpholine. Among these, styrene-acrylic resins are preferred. Dispersants can be suitably incorporated when using pigments as colorants.

[0069] As the rust inhibitor, benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, saponins, etc. can be used, of which benzotriazole is preferred.

[0070] Examples of pH adjusters include ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, alkali metal salts of carbonate or phosphate such as sodium tripolyphosphate and sodium carbonate, hydrates of alkali metals such as sodium hydroxide, N,N-bis(2-hydroxyethyl)glycine, etc. Among these, triethanolamine is preferred.

[0071] The dispersants, rust inhibitors, and pH adjusters may be used alone or in combination of two or more. Furthermore, if commercially available products are available, they may be used. Furthermore, in order to improve the writing properties of the aqueous ink composition of the present invention, a humectant or a fixing resin (including dispersions) such as a urethane-based, olefin-based, or acrylic-based resin may also be used in combination.

[0072] The amount of other components to be blended is not particularly limited, but each other component can be blended in an amount of preferably 0.1% by mass or more and 5% by mass or less, more preferably 0.2% by mass or more and 4% by mass or less, and even more preferably 0.3% by mass or more and 3% by mass or less, relative to the total amount of the aqueous ink composition.

[0073] The aqueous ink composition of the present invention can be produced by a conventionally known method, and can be produced without any particular changes from the method of producing other aqueous ink compositions. That is, the aqueous ink composition of the present invention can be produced by blending and mixing at least water, a colorant, a water-soluble organic solvent, a tropolone and / or a tropolone derivative, a surfactant, and other components used as needed depending on the intended use of the ink (for ballpoint pens, marking pens, felt-tip pens, etc.). The mixing and stirring can be carried out using a mixer or the like, or further, for example, a bead mill, homomixer, homogenizer, or the like that can apply strong shear, with stirring conditions set to suitable conditions. In addition to the mixing and stirring, if necessary, a step of removing coarse particles from the aqueous ink composition by filtration or centrifugation may be carried out.

[0074] The aqueous ink composition of the present invention can be suitably incorporated into batting-type or direct-fill ballpoint pens, marking pens, felt-tip pens, etc., which have a pen tip such as a ballpoint pen tip, fiber tip, felt tip, or plastic tip and which occlude the aqueous ink composition of the above composition, and from the viewpoint of effectively exhibiting an air bubble generation suppression effect, can be suitably used in knock-type writing instruments and writing instruments which use gel ink. In particular, with knock-type gel ink ballpoint pens, it is conceivable that the usage environment may be such that air bubbles are likely to be generated by the impact of knocking, but the aqueous ink composition of the present invention can effectively suppress the generation of air bubbles.

[0075] 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" are based on mass unless otherwise specified.

[0076] (Production of Leuco Dye-Encapsulating Particles) Leuco dye-encapsulating particles A-1 used in the examples and comparative examples were produced as follows: 1 part of methyl-3',6'-bisdiphenylaminofluoran as a leuco dye, 2 parts of bis(4-hydroxyphenyl)phenylmethane as a color developer, and 24 parts of bis(4-hydroxyphenyl)phenylmethane dicaprylate as a color-changing temperature regulator were heated and melted at 100°C to obtain 27 parts of a homogeneous composition.

[0077] To 27 parts of the homogeneous hot solution of the composition obtained above, 10 parts of isocyanate and 10 parts of polyol were added as encapsulation film agents, and the mixture was stirred and mixed. Next, 60 parts of a 12% aqueous polyvinyl alcohol solution was used as a protective colloid, and the mixture was emulsified at 25°C to prepare a dispersion. Next, 5 parts of a 5% polyamine was used, and the mixture was treated at 80°C for 60 minutes to obtain microcapsules. The microencapsulated aqueous dispersion obtained by the above procedure was spray-dried into a powder to produce leuco dye-encapsulated particles A-1.

[0078] Leuco dye-encapsulating particles A-2 were produced in the same manner as leuco dye-encapsulating particles A-1, except that chloro-3',6'-bisdiphenylaminofluoran was used instead of methyl-3',6'-bisdiphenylaminofluoran as the leuco dye, 1,1-bis(4-hydroxyphenyl)cyclohexane was used instead of bis(4-hydroxyphenyl)phenylmethane as the color developer, and bis(4-hydroxyphenyl)phenylmethane dilaurate was used instead of bis(4-hydroxyphenyl)phenylmethane dicaprylate as the color-changing temperature regulator.

[0079] (Production of Colored Resin Particles) The colored resin particles used in the examples and comparative examples were prepared as follows. 2.4 parts by mass of a water-insoluble dye (ValifastBlue 2620, Orient Chemical Industries Co., Ltd.) was added to 9.6 parts by mass of benzyl alcohol as an organic solvent, and 7 parts by mass of an allophanate-modified hexamethylene diisocyanate (D-178NL, manufactured by Mitsui Chemicals, Inc.) as a prepolymer to prepare an oil phase solution. Meanwhile, 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.) as a dispersant was dissolved therein to prepare an aqueous phase solution. The oil phase solution was added to the aqueous phase solution at 60°C, and the mixture was emulsified and mixed by stirring with a homogenizer for 6 hours to complete the polymerization. The resulting dispersion was centrifuged to obtain urethane-based particles (blue particles) as colored resin particles.

[0080] Example 1 An aqueous ink composition was prepared by mixing and stirring 15 parts of leuco dye-encapsulating particles A-1 and 8 parts of leuco dye-encapsulating particles A-2 as colorants, 0.15 parts of triethanolamine as a pH adjuster, 0.80 parts of a phosphate ester (polyoxyethylene lauryl ether phosphate ester (phosphate ester-type anionic surfactant); Plysurf A219B, HLB value 16) as a surfactant, 0.05 parts of tropolone as a bubble inhibitor, 0.30 parts of N-acetyl-L-cysteine ​​as an organic acid, 0.35 parts of xanthan gum (KELZAN Z, manufactured by Sansho Co., Ltd.) as a thickener, 0.30 parts of benzotriazole as a rust inhibitor, 5.00 parts of glycerin and 10.0 parts of ethylene glycol as water-soluble organic solvents, and 60.05 parts of ion-exchanged water in a conventional manner.

[0081] (Example 2) An aqueous ink composition was prepared in the same manner as in Example 1, except that hinokitiol was used as the bubble inhibitor instead of tropolone, ascorbic acid was used as the organic acid instead of N-acetyl-L-cysteine, and the amounts of each component were changed to those shown in Table 1.

[0082] (Example 3) An aqueous ink composition was prepared in the same manner as in Example 1, except that no organic acid was added, hinokitiol was used instead of tropolone as a bubble inhibitor, and the amount of each component was changed to the amount listed in Table 1.

[0083] Example 4 An aqueous ink composition was prepared by mixing and stirring 15 parts of colored resin particles (urethane-based particles) as a colorant, 0.18 parts of triethanolamine as a pH adjuster, 1.00 parts of a phosphate ester (polyoxyethylene lauryl ether phosphate ester; Plysurf A219B, HLB value 16) as a surfactant, 0.20 parts of hinokitiol as a bubble inhibitor, 0.30 parts of N-acetyl-L-cysteine ​​as an organic acid, 0.35 parts of xanthan gum (KELZAN Z, manufactured by Sansho Co., Ltd.) as a thickener, 0.30 parts of benzotriazole as a rust inhibitor, 5.00 parts of glycerin and 3.00 parts of ethylene glycol as water-soluble organic solvents, and 74.67 parts of ion-exchanged water in a conventional manner.

[0084] Example 5 An aqueous ink composition was prepared in the same manner as in Example 4, except that polyoxyethylene hydrogenated castor oil (Emanon CH-25) was used as the surfactant instead of the phosphate ester, ascorbic acid was used as the organic acid instead of N-acetyl-L-cysteine, and the amounts of each component were changed to those shown in Table 1.

[0085] (Example 6) An aqueous ink composition was prepared in the same manner as in Example 4, except that no organic acid was added, polyoxyethylene hydrogenated castor oil (Emanon CH-25) was used as the surfactant instead of the phosphate ester, and the amounts of each component were changed to those shown in Table 1.

[0086] Example 7 An aqueous ink composition was prepared by mixing and stirring 7.00 parts of carbon black as a colorant, 3.00 parts of a styrene acrylic resin (Joncryl 63J (manufactured by BASF JAPAN)) as a pigment dispersant, 0.40 parts of triethanolamine as a pH adjuster, 1.00 parts of a phosphate ester (polyoxyethylene lauryl ether phosphate ester; Plysurf A219B, HLB value 16) as a surfactant, 1.00 parts of hinokitiol as a bubble inhibitor, 0.30 parts of N-acetyl-L-cysteine ​​as an organic acid, 0.35 parts of xanthan gum (KELZAN Z, manufactured by Sansho Co., Ltd.) as a thickener, 0.30 parts of benzotriazole as a rust inhibitor, 10.00 parts of glycerin and 10.00 parts of propylene glycol as water-soluble organic solvents, and 66.65 parts of ion-exchanged water in a conventional manner.

[0087] Example 8 An aqueous ink composition was prepared in the same manner as in Example 7, except that polyoxyethylene alkyl ether (NIKKOL BL-25) was used as the surfactant instead of the phosphate ester, citric acid was used as the organic acid instead of N-acetyl-L-cysteine, and the amounts of each component were changed to those shown in Table 1.

[0088] (Example 9) An aqueous ink composition was prepared in the same manner as in Example 7, except that no organic acid was added, polyoxyethylene alkyl ether (NIKKOL BL-25) was used as the surfactant instead of the phosphate ester, and the amounts of each component were changed to those shown in Table 1.

[0089] Example 10 7.00 parts of carbon black as a colorant, 3.00 parts of a styrene acrylic resin (Joncryl 63J (manufactured by BASF JAPAN)) as a pigment dispersant, 0.40 parts of triethanolamine as a pH adjuster, 1.50 parts of a phosphate ester (polyoxyethylene lauryl ether phosphate ester; Plysurf A219B, HLB value 16) as a surfactant, 3.00 parts of hinokitiol as a bubble inhibitor, 0.30 parts of N-acetyl-L-cysteine ​​as an organic acid, 8.00 parts of glycerin, 4.00 parts of propylene glycol, and 10.00 parts of ethylene glycol as water-soluble organic solvents, and 62.80 parts of ion-exchanged water were mixed and stirred in a conventional manner to prepare an aqueous ink composition.

[0090] Example 11 An aqueous ink composition was prepared in the same manner as in Example 10, except that polyoxyethylene hydrogenated castor oil (Emanon CH-25) was used as the surfactant instead of the phosphate ester, citric acid was used as the organic acid instead of N-acetyl-L-cysteine, and the amounts of each component were changed to those shown in Table 1.

[0091] (Example 12) An aqueous ink composition was prepared in the same manner as in Example 10, except that no organic acid was added, polyoxyethylene hydrogenated castor oil (Emanon CH-25) was used as the surfactant instead of the phosphate ester, and the amounts of each component were changed to those shown in Table 1.

[0092] Example 13 An aqueous ink composition was prepared in the same manner as in Example 1, except that hinokitiol was further added as a bubble inhibitor and the amounts of each component used were changed to those shown in Table 1.

[0093] Example 14 An aqueous ink composition was prepared in the same manner as in Example 2, except that the amounts of each component used were changed to those shown in Table 1.

[0094] Example 15 An aqueous ink composition was prepared in the same manner as in Example 5, except that glycerin was not added and the amounts of each component used were changed to those shown in Table 1.

[0095] Example 16 An aqueous ink composition was prepared in the same manner as in Example 8, except that propylene glycol was not added and the amounts of each component used were changed to those shown in Table 1.

[0096] Example 17 An aqueous ink composition was prepared in the same manner as in Example 11, except that glycerin was not added and the amounts of each component used were changed to those shown in Table 1.

[0097] Comparative Example 1 An aqueous ink composition was prepared in the same manner as in Example 2, except that no bubble inhibitor was used and the amounts of each component used were changed to those shown in Table 1.

[0098] Comparative Example 2 An aqueous ink composition was prepared in the same manner as in Example 2, except that no surfactant was used and the amounts of each component used were changed to those shown in Table 1.

[0099] (Comparative Example 3) An aqueous ink composition was prepared in the same manner as in Example 5, except that no bubble inhibitor was used, a phosphate ester was used instead of polyoxypolyethylene hydrogenated castor oil (Emanon CH-25), and the amounts of each component were changed to those shown in Table 1.

[0100] Comparative Example 4 An aqueous ink composition was prepared in the same manner as in Example 5, except that no surfactant was used and the amounts of each component used were changed to those shown in Table 1.

[0101] Comparative Example 5 An aqueous ink composition was prepared in the same manner as in Example 7, except that no bubble inhibitor was used, citric acid was used instead of N-acetyl-L-cysteine ​​as the organic acid, and the amounts of each component were changed to the amounts shown in Table 1.

[0102] Comparative Example 6 An aqueous ink composition was prepared in the same manner as in Example 8, except that no surfactant was used and the amounts of each component used were changed to those shown in Table 1.

[0103] Comparative Example 7 An aqueous ink composition was prepared in the same manner as in Example 10, except that no bubble inhibitor was used and the amounts of each component used were changed to those shown in Table 1.

[0104] Comparative Example 8 An aqueous ink composition was prepared in the same manner as in Example 10, except that no surfactant was used and the amounts of each component used were changed to those shown in Table 1.

[0105] <Evaluation Method> Measurements and evaluations in the examples and comparative examples were carried out as follows.

[0106] (Tropolone or Hinokitiol Solubility) The solubility of tropolone or hinokitiol at room temperature in the aqueous ink compositions obtained in Examples and Comparative Examples was evaluated according to the following criteria: A: No precipitation was observed after storage at room temperature for one month. B: Precipitation was observed after storage at room temperature for one month.

[0107] (Solubility of Tropolone or Hinokitiol (After Storage at 0°C for 1 Week)) The aqueous ink compositions obtained in the Examples and Comparative Examples were stored at 0°C for 1 week, and the solubility of tropolone or hinokitiol was evaluated according to the following criteria: A: No precipitation was observed after storage at 0°C for 1 week. B: Precipitation was observed after storage at 0°C for 1 week.

[0108] (Knock Impact Test) Knock impact was applied to knock ballpoint pens equipped with the aqueous ink compositions obtained in Examples and Comparative Examples after storage at room temperature for one day, and the occurrence of bubbles was evaluated after three days according to the following criteria: A: No bubbles were observed B: Minor bubbles of less than 1 mm were observed C: Bubbles of 1 mm to 2 mm were observed D: Bubbles of 2 mm or more or multiple bubbles were observed

[0109] (Knock Impact Test (Low Temperature)) The aqueous ink compositions obtained in the Examples and Comparative Examples were loaded into a knock-type ballpoint pen, stored at 0°C for one day, and then subjected to a knock impact. After three days, the generation of bubbles was evaluated according to the following criteria: A: No bubbles were observed B: Minor bubbles less than 1 mm were observed C: Bubbles of 1 mm to 2 mm were observed D: Bubbles of 2 mm or more or multiple bubbles were observed The evaluation results are shown in Table 1 below.

[0110]

[0111] The results in Table 1 show that aqueous ink compositions containing water, a colorant, a water-soluble organic solvent, tropolone and / or a tropolone derivative, and a surfactant, wherein the aqueous ink composition contains 0.03 to 3 mass % of the tropolone and / or the tropolone derivative, exhibit excellent solubility of the tropolone and / or the tropolone derivative and excellent solubility after storage at −10° C. for 1 week, and showed good results in the knock impact test and in the knock impact test at low temperatures.

[0112] The aqueous ink composition of the present invention can be suitably used in writing instruments such as ballpoint pens, marking pens, and felt-tip pens, and can be particularly suitably used in knock-type writing instruments, more particularly knock-type writing instruments equipped with gel ink.

Claims

1. An aqueous ink composition comprising water, a colorant, a water-soluble organic solvent, tropolone and / or a tropolone derivative, and a surfactant, wherein the aqueous ink composition contains 0.03 to 3% by mass of tropolone and / or a tropolone derivative.

2. The aqueous ink composition according to claim 1, further comprising an organic acid.

3. The aqueous ink composition according to claim 1 or 2, further comprising a thickener.

4. The aqueous ink composition according to claim 3, wherein the colorant is colored resin particles, and the tropolone and / or tropolone derivative is hinokitiol.

5. A ballpoint pen equipped with the aqueous ink composition according to claim 4.

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