Oil-in-water ink composition for writing instrument

Abstract

Provided is an oil-in-water ink composition for a writing instrument, having: an aqueous phase and oil droplets dispersed in the aqueous phase in the form of an oil-in-water emulsion, wherein the oil droplets contain an oil phase and inorganic particles, and the ratio of the density of the oil droplets to the density of the aqueous phase is in the range of 0.85-1.15.

Description

Oil-in-water ink composition for writing instruments

[0001] This invention relates to an oil-in-water droplet type ink composition for writing instruments.

[0002] One of the characteristics of water-based ballpoint pens is their light writing feel, but on the other hand, they often cause scratching. Also, while water-soluble dyes used as coloring agents have the advantage of high coloring power and freedom in color mixing, they have poor weather resistance, and the lines tend to bleed if water comes into contact with them.

[0003] Oil-based ballpoint pens have the advantage of not scratching when writing and minimizing ink bleeding, but they often have a heavy writing feel. Furthermore, the oil-soluble dyes used as coloring agents are water-resistant, preventing the bleeding that occurs when water comes into contact with the ink.

[0004] In recent years, oil-based ballpoint pens have been developed that improve writing feel by reducing the viscosity of the oil-based ink. However, low-viscosity oil-based ink flows out more when writing, which worsens the drying time of the lines and can cause ink to bleed through to the back of the paper and result in blotting.

[0005] To address these challenges, an aqueous ballpoint pen ink composition has been disclosed in which the ink properties are those of an oil-in-water emulsion (O / W emulsion), which can achieve both the smooth writing feel of the aqueous phase and the water resistance of oil-soluble dyes.

[0006] Patent Document 1 discloses an aqueous ballpoint pen ink composition in which an oil phase is contained in an aqueous phase in the form of an oil-in-water emulsion, wherein at least one of the oil phase or the aqueous phase contains a coloring agent, and the oil phase contains, among the components constituting the oil phase, an estolide which is a fatty acid oligomer formed by the condensation of fatty acids having hydroxyl groups or by the condensation of a fatty acid having hydroxyl groups and a fatty acid not having hydroxyl groups, or an ester of the estolide and an alcohol.

[0007] Patent Document 2 discloses an O / W type emulsion ink composition for ballpoint pens, which is an emulsion dispersion in water containing an oil-soluble dye as a coloring agent, an organic solvent in which the dye is dissolved and whose solubility in 100 g of water at 20°C is 5 g or less, a sucrose fatty acid ester with an HLB of 8 or less, and an oily component containing at least a sodium salt of acyl lactic acid having 8 or more carbon atoms.

[0008] Japanese Patent Publication No. 2013-221051 Japanese Patent Publication No. 2010-275402

[0009] In the field of oil-in-water ink compositions for writing instruments, long-term storage stability at high temperatures has been a challenge, particularly due to phase separation caused by the floating of oil droplets and the sedimentation of the contents.

[0010] The present invention provides a novel oil-in-water droplet ink composition for writing instruments in which phase separation and sedimentation of contents are suppressed after long-term storage at high temperatures.

[0011] The present inventors, after diligent study, found that the above problems could be solved by the following means, and thus completed the present invention. That is, the present invention is as follows: <Aspect 1> An oil-in-water emulsion ink composition for writing instruments, comprising an aqueous phase and oil droplets dispersed in the aqueous phase, wherein the oil droplets contain an oil phase and inorganic particles, and the ratio of the density of the oil droplets to the density of the aqueous phase is in the range of 0.85 to 1.15. <Aspect 2> The density of the inorganic particles is 2.0 g / cm³. ３ 6.0g / cm or more ３ The oil-in-water ink composition for writing instruments according to Embodiment 1, which is within the following range: <Embodiment 3> The oil-in-water ink composition for writing instruments according to Embodiment 1 or 2, wherein the particle size of the inorganic particles, as measured by dynamic light scattering, is 10 nm or more and 400 nm or less. <Embodiment 4> The oil-in-water ink composition according to any one of Embodiments 1 to 3, wherein the content of inorganic particles in the oil droplet is 0.1% or more and 30% or less relative to the mass of the oil droplet. <Embodiment 5> The oil-in-water ink composition according to any one of Embodiments 1 to 4, wherein the particle size of the oil droplet, as measured by dynamic light scattering, is 50 nm or more and 1000 nm or less. <Embodiment 6> The density of the oil phase component constituting the oil droplet is 0.8 g / cm³３ 1.05 g / cm or less ３ An oil-in-water ink composition according to any one of Aspects 1 to 5, which is in the following range: <Aspect 7> The oil-phase component constituting the oil droplets contains at least one selected from the group consisting of hydrocarbon oils, ester oils, higher alcohols, fatty acids, and silicone oils. An oil-in-water ink composition according to any one of Aspects 1 to 6. <Aspect 8> A writing instrument including an ink storage unit having the oil-in-water ink composition for writing instruments according to any one of Aspects 1 to 7.

[0012] According to the present invention, it is possible to provide a novel oil-in-water ink composition for writing instruments in which generation of phase separation and sedimentation of the contents are suppressed after long-term storage at high temperatures.

[0013] 《Oil-in-Water Ink Composition for Writing Instruments》 The oil-in-water ink composition for writing instruments of the present invention has an aqueous phase and oil droplets dispersed in the aqueous phase in the state of an oil-in-water emulsion. The oil droplets contain an oil phase and inorganic particles, and the ratio of the density of the oil droplets to the density of the aqueous phase is within the range of 0.85 to 1.15.

[0014] The present inventors have found that by including inorganic particles in the oil droplets in the above configuration, particularly by making the density of the oil droplets and the density of the aqueous phase close to each other, the oil droplets can be well dispersed in the aqueous phase, thereby suppressing the generation of phase separation and sedimentation of the contents.

[0015] The oil-in-water ink composition of the present invention may further contain a coloring material. This coloring material may be contained in at least one of the oil droplets and the aqueous phase.

[0016] Further, the oil-in-water ink composition of the present invention may contain any other optional components.

[0017] Hereinafter, each component of the present invention will be described.

[0018] 〈Oil Droplets〉 The oil droplets are dispersed in the aqueous phase and, together with the aqueous phase, are in the state of an oil-in-water emulsion. The oil droplets contain an oil phase and inorganic particles.

[0019] The ratio of the density of the oil droplets to the density of the aqueous phase is within the range of 0.85 to 1.15. In particular, this ratio may be 0.85 or more, 0.90 or more, or 0.95 or more, and may also be 1.15 or less, 1.10 or less, or 1.05 or less. Regarding the present invention, "the density of the oil droplets" means the density of the entire oil droplets including the oil phase and inorganic particles constituting the oil droplets.

[0020] The content rate of the oil droplets may be 1% by mass or more and 35% by mass or less with respect to the mass of the oil-in-water type ink composition. This content rate may be 1% by mass or more, 3% by mass or more, 5% by mass or more, 7% by mass or more, 9% by mass or more, or 10% by mass or more, and may also be 35% by mass or less, 33% by mass or less, 31% by mass or less, 27% by mass or less, 25% by mass or less, 22% by mass or less, 20% by mass or less, 17% by mass or less, 15% by mass or less, or 12% by mass or less.

[0021] The particle diameter of the oil droplets may be 50 nm or more and 1000 nm or less. This particle diameter may be 50 nm or more, 70 nm or more, 100 nm or more, 130 nm or more, 150 nm or more, 180 nm or more, 200 nm or more, or 220 nm or more, and may also be 1000 nm or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 400 nm or less, 380 nm or less, 350 nm or less, 320 nm or less, or 300 nm or less.

[0022] Here, in the present invention, "the particle diameter" is, in principle, the value of the median diameter (D50) calculated on a volume basis in the scattering intensity distribution measured by the dynamic light scattering method. Exceptionally, for particles whose particle diameter cannot be measured by the dynamic light scattering method, for example, particles with a D50 exceeding 5 μm, the median diameter (D50) calculated on a volume basis in the laser diffraction method can be adopted.

[0023] (Oil phase) Generally, the oil phase is a liquid component constituting the oil droplets. The oil phase may contain oil phase components.

[0024] The density of the oil phase components is not particularly limited as long as the above ratio regarding the density of the oil droplets and the aqueous phase is satisfied. For example, 0.50 g / cm ３ or more and 1.05 g / cm３ It may be as follows. This density is 0.50 g / cm ３ or more, 0.60 g / cm ３ or more, 0.70 g / cm ３ or more, 0.80 g / cm ３ or more, 0.85 g / cm ３ or more, 0.90 g / cm ３ or more, or 0.95 g / cm ３ or more and may be 1.05 g / cm ３ or less, 1.00 g / cm ３ or less, 0.90 g / cm ３ or less, 0.80 g / cm ３ or less, 0.70 g / cm ３ or less, or 0.60 g / cm ３ or less. Among them, the density of the oil phase component is preferably 0.80 g / cm ３ or more from the viewpoint of satisfying the above ratio regarding the density of the oil droplets and the aqueous phase. When the oil phase component is composed of a mixture, the above density may be a weighted average obtained by weighting the density of each component with the content rate of each component.

[0025] As the oil phase component, for example, at least one selected from the group consisting of hydrocarbon oils, ester oils, higher alcohols, fatty acids, and silicone oils can be used.

[0026] As the hydrocarbon oil, for example, polyolefins such as polybutene, olefin oligomers, aromatic hydrocarbons, and liquid paraffin can be used.

[0027] As the ester oil, for example, the estolide or ester mentioned below can be used.

[0028] Generally, higher alcohols with six or more carbon atoms can be used, such as n-hexanol, methylamyl 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, etc.

[0029] As fatty acids, for example, the fatty acids mentioned below can be used.

[0030] Examples of silicone oils that can be used include dimethyl silicone oil and methylphenyl silicone oil.

[0031] In particular, examples of oil phase components include estolides, which are fatty acid oligomers formed by the condensation of fatty acids having hydroxyl groups or by the condensation of fatty acids having hydroxyl groups and fatty acids not having hydroxyl groups, or esters of such estolides with alcohols. The oil phase may also contain the fatty acids not having hydroxyl groups themselves in the estolide or ester.

[0032] Furthermore, the oil phase may further contain resins and / or organic solvents to adjust its viscosity. The resins and organic solvents referred to here are those in the aqueous phase.

[0033] (Estolides or Esters) The estolides or esters that can be used in the oil phase may be fatty acid oligomers formed by the condensation of fatty acids having hydroxyl groups or by the condensation of a fatty acid having hydroxyl groups and a fatty acid not having hydroxyl groups, or esters of such estolides with alcohols.

[0034] Various conventionally used fatty acids can be used as the fatty acids having hydroxyl groups in the above-mentioned estolides or esters. Among these, it is preferable to use castor oil fatty acids whose main component is ricinoleic acid, or hydrogenated castor oil fatty acids whose main component is 12-hydroxystearic acid. These fatty acids may be used individually or in combination.

[0035] Furthermore, fatty acids that do not have hydroxyl groups include capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, melissic acid, oleic acid, linoleic acid, and linolenic acid. In addition, coconut oil fatty acids, palm oil fatty acids, olive oil fatty acids, beef tallow fatty acids, and hydrogenated beef tallow fatty acids containing these components can also be used.

[0036] In this invention, a fatty acid oligomer obtained by condensing fatty acids having hydroxyl groups as described above, or a fatty acid oligomer (estolide) obtained by condensing a fatty acid having hydroxyl groups with a fatty acid not having hydroxyl groups is used. Here, "fatty acid oligomer" refers to a condensate of two or more units. Dimers to heptamers are preferred. Monomers may be present in the fatty acid oligomer, but from the viewpoint of solubility in the oil phase, it is preferable that the average of the fatty acid oligomer as a whole be 1.5 units or more, preferably 2.0 units or more.

[0037] The content of the above-mentioned estrid or ester may be 50% by mass or more, 60% by mass or more, or 70% by mass or more, with respect to the mass of the oil phase, and may also be 90% by mass or less, or 85% by mass or less.

[0038] Furthermore, the oil phase may further contain other oil phase components. These other oil phase components may include, for example, fatty acids themselves that do not have hydroxyl groups in the estolide or ester described above.

[0039] (Inorganic particles) Inorganic particles are contained within the oil droplets.

[0040] The density of inorganic particles is 2.0 g / cm³. ３ 6.0g / cm or more ３From the viewpoint of satisfying the above ratio of the densities of the oil droplet and the aqueous phase, the following range is preferable. This density is, for example, 2.0 g / cm³. ３ The above is sufficient, and also 6.0 g / cm³. ３ Below, 5.5g / cm ３ Below, 5.0g / cm ３ Below, 4.5g / cm ３ Below, 4.0g / cm ３ Below, 3.5g / cm ３ Below, 3.0g / cm ３ The following, or 2.5 g / cm³ ３ The following is acceptable:

[0041] Examples of such inorganic particles include silicon dioxide (silica: density 2.1 g / cm³). ３ ), calcium oxide (density 3.34 g / cm³) ３ ), magnesium oxide (density 3.65 g / cm³) ３ ), aluminum oxide (alumina: density 4.0 g / cm³) ３ ), titanium dioxide (density 4.26 g / cm³) ３ ), niobium oxide (density 4.47 g / cm³) ３ ), molybdenum oxide (density 4.69 g / cm³) ３ ), manganese dioxide (density 5.03 g / cm³) ３ ), chromium oxide (density 5.21 g / cm³) ３ ), iron oxide (density 5.24 g / cm³) ３ ), zinc oxide (density 5.61 g / cm³) ３ ), and zirconium oxide (zirconia: density 5.68 g / cm³). ３ ) etc. can be used.

[0042] The particle size of the inorganic particles may be between 10 nm and 400 nm. This particle size may be between 10 nm and 20 nm, 30 nm and 40 nm and 50 nm and 60 nm and 70 nm and 80 nm and 90 nm and 100 nm and also between 400 nm and below, 370 nm and below, 350 nm and below, 320 nm and below, 300 nm and below, 270 nm and below, 250 nm and below, 220 nm and below, 200 nm and below, 190 nm and below, 180 nm and below, 170 nm and below, 160 nm and below, 150 nm and below, 140 nm and below, 130 nm and below, or 120 nm and below. In particular, a particle size of 70 nm and above is preferred from the viewpoint of suppressing phase separation after long-term storage at high temperatures, and a particle size of 190 nm and below is preferred from the viewpoint of suppressing sedimentation after long-term storage at high temperatures.

[0043] The content of inorganic particles in the oil droplet is not particularly limited as long as it satisfies the above ratio of the density of the oil droplet to the density of the aqueous phase, and may be, for example, 0.1% by mass or more and 30% by mass or less with respect to the mass of the oil droplet. This content may be 0.1% by mass or more, 0.3% by mass or more, 0.5% by mass or more, 0.7% by mass or more, 1% by mass or more, 2% by mass or more, 3% by mass or more, or 4% by mass or more, and may also be 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, 12% by mass or less, 10% by mass or less, 8% by mass or less, or 5% by mass or less.

[0044] <Aqueous Phase> The aqueous phase contains at least water. The aqueous phase may also further contain emulsifier components. The presence of emulsifier components allows the aqueous phase and the oil droplets dispersed in the aqueous phase to exist in the form of an oil-in-water emulsion.

[0045] The aqueous phase may further contain colorants, resins, organic solvents, etc.

[0046] (Water) Distilled water and deionized water can be used as the water source.

[0047] The water content may be more than 50% by mass, 55% or more by mass, 60% or more by mass, 65% or more by mass, or 70% or more by mass, relative to the mass of the oil-in-water ink composition for writing instruments, and may also be 90% or less by mass, 85% or less by mass, 80% or less by mass, or 75% or less by mass.

[0048] Furthermore, the water content may be more than 50% by mass, 55% or more by mass, 60% or more by mass, 65% or more by mass, 70% or more by mass, 75% or more by mass, or 80% or more by mass, relative to the mass of the aqueous phase, and may also be 90% or less by mass, or 85% or less by mass.

[0049] (Emulsifier component) Any emulsifier can be used as the emulsifier component, for example, an emulsifier having one or more aromatic rings in its molecular skeleton can be used.

[0050] The aromatic emulsifier that can be used in the ink composition of the present invention is not particularly limited as long as it has one or more aromatic rings, and for example, polycyclic phenyl-type nonionic surfactants such as polyoxyethylene distyrenated phenyl ether, polyoxyethylene monotyrenated phenyl ether, and polyoxyethylene cumylphenyl ether, and ionic surfactants such as their sulfates can be used.

[0051] From the viewpoint of suppressing the coalescence of oil droplets by the long chain of ethylene oxide (EO), the number of moles of ethylene oxide (EO) added to the emulsifier described above is preferably 40 mol or more, 45 mol or more, or 50 mol or more.

[0052] In addition to the emulsifiers mentioned above, emulsifiers with a low number of ethylene oxide addition moles that are strongly oriented towards the oil phase, specifically those with a number of ethylene oxide addition moles of 3 mol or more, 4 mol or more, or 5 mol or more, and 15 mol or less, 12 mol or less, or 10 mol or less, may also be used. Combining an emulsifier strongly oriented towards the oil phase with one strongly oriented towards the aqueous phase can be preferable from the viewpoint of increasing the micelle concentration at the interface and improving the stability of the emulsion.

[0053] Regarding the HLB value (hydrophilic-lipophilic balance value), it is preferable to use at least one emulsifier with an HLB value of 15 or higher for nonionic surfactants, from the viewpoint of suppressing excessive mixing of emulsifier into the oil droplets.

[0054] In addition to surfactants having aromatic rings in their molecules, any other emulsifiers with different structures may be added as emulsifier components. Examples of such emulsifiers include polyoxyethylene hydrogenated castor oil, linear hydrocarbon-type nonionic surfactants such as polyoxyethylene alkyl (C10-C18) esters, and sorbitan derivatives.

[0055] The amount of emulsifier component may be 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, 20 parts by mass or more, 25 parts by mass or more, 30 parts by mass or more, 35 parts by mass or more, 40 parts by mass or more, or 45 parts by mass or more per 100 parts by mass of oil droplets, and may also be 150 parts by mass or less, 140 parts by mass or less, 130 parts by mass or less, 120 parts by mass or less, 110 parts by mass or less, 100 parts by mass or less, 90 parts by mass or less, 80 parts by mass or less, 70 parts by mass or less, 65 parts by mass or less, 60 parts by mass or less, or 55 parts by mass or less.

[0056] (Resin) Any resin can be used as the resin, especially resins used for fixing the coating film. For example, sulfamide resins, maleic acid resins, terpene resins, terpene phenol resins, ester gums, xylene resins, alkyd resins, phenol resins, rosin, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl alcohol, acrylic resins, melamine resins, nitrocellulose resins, urea resins, etc., and derivatives thereof can be used.

[0057] The resin content can be adjusted according to the desired viscosity of the aqueous phase. For example, it may be 1% by mass or more, 2% by mass or more, or 3% by mass or more relative to the mass of the aqueous phase, or it may be 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, 10% by mass or less, 7% by mass or less, or 5% by mass or less.

[0058] (Organic Solvents) Examples of organic solvents that can be used include aromatics, alcohols, polyhydric alcohols, glycol ethers, hydrocarbons, esters, etc. These solvents may be used individually or in combination.

[0059] 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, alkylsulfonate phenyl ester, butyl phthalate, ethylhexyl phthalate, tridecyl phthalate, ethylhexyl trimellitate, diethylene glycol dibenzoate, and dipropylene glycol dibenzoate.

[0060] 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, methylamyl alcohol, 2-ethylbutanol, n-heptanol, 2-heptanol, 3-heptanol, n-octanol, nonanol, n-decanol, undecanol, n-decanol, tetradecanol, heptadecanol, cyclohexanol, 2-methylcyclohexanol, etc.

[0061] Examples of polyhydric alcohols that can be used include ethylene glycol, diethylene glycol, 3-methyl-1,3-butanediol, triethylene glycol, dipropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, hexylene glycol, octylene glycol, and the like.

[0062] 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-ethyl butyl 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-methoxy-3-methyl-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, tetrapropylene glycol monobutyl ether, and the like.

[0063] Examples of hydrocarbons that can be used include linear hydrocarbons such as hexane, isohexane, heptane, octane, nonane, and decane, and cyclic hydrocarbons such as cyclohexane, methylcyclohexane, and ethylcyclohexane.

[0064] 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, 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 triglyceride, tributyl citrate, octyl oxystearate, propylene glycol monolicinolate, methyl 2-hydroxyisobutyrate, 3-methoxybutyl acetate, etc. can be used.

[0065] The content of the organic solvent can be adjusted according to the desired viscosity of the oil droplets. For example, it may be 1% by mass or more, 2% by mass or more, or 3% by mass or more relative to the mass of the oil droplets, and may also be 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, 10% by mass or less, 7% by mass or less, or 5% by mass or less.

[0066] <Coloring agents> Various coloring agents that can be used in conventional inks can be used as coloring agents, such as dyes, pigments, or mixtures of dyes and pigments. These coloring agents may be used individually or in mixtures.

[0067] Water-soluble dyes and water-insoluble dyes can be used as dyes.

[0068] As water-soluble dyes, all dyes that dissolve or disperse in water can be used, for example, acid dyes such as eosin, foxine, water yellow #6-C, acid red, water blue #105, brilliant blue FCF, and negrosine NB; direct dyes such as direct black 154, direct sky blue 5B, and violet BB; and basic dyes such as rhodamine and methyl violet.

[0069] Water-insoluble dyes are dyes that are insoluble in water at room temperature. Examples of such water-insoluble dyes include salt-forming dyes, disperse dyes, and oil-soluble dyes, and among these, salt-forming dyes are preferred from the viewpoint of color development.

[0070] Examples of salt-forming dyes include dyes having chemical structures such as azo, metal complex azo, anthraquinone, and metal phthalocyanine. For example, Valifast® Black 1807, Valifast® Blue 2620, Valifast® Brown 2402, Valifast® Green 1501, Valifast® Orange 2210, Valifast® Pink 2310, Valifast® Red 1355, Valifast® Violet 1701, and Valifast® Yellow 1101 from Orient Chemical Industry Co., Ltd. can be used.

[0071] As the disperse dye, at least one dye selected from, for example, C.I. Disperse Yellow 198, C.I. Disperse Yellow 42, C.I. Disperse Red 92, C.I. Disperse Violet 26, C.I. Disperse Violet 35, C.I. Disperse Blue 60, and C.I. Disperse Blue 87 can be used.

[0072] Examples of oil-soluble dyes that can be used include Oil Black 860, Oil Blue 613, Oil Brown BB, Oil Green 530, Oil Orange 201, Oil Pink 312, Oil Red 5B, Oil Scarlet 318, and Oil Yellow 105 from Orient Chemical Industry Co., Ltd.

[0073] As pigments, conventionally known inorganic and organic pigments such as titanium dioxide, resin particle pigments containing pigments or dyes, pseudo-pigments obtained by coloring resin emulsions with dyes or pigments, white plastic pigments, luminous pigments, 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, etc. can be used without limitation.

[0074] 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.

[0075] 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.

[0076] Examples of thermochromic pigments include thermochromic pigments 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 develop the color of the leuco dye, 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 particle size is predetermined (for example, 0.1 to 6 μm). This particle size may be, for example, 0.1 μm or more, 0.2 μm or more, 0.3 μm or more, 0.5 μm or more, 0.7 μm or more, or 0.9 μm or more, and may also be 6 μm or less, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less.

[0077] As photochromic particles, for example, photochromic particles composed 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 can be used. Alternatively, photochromic particles can be 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 particle size (for example, 0.1 to 6 μm).

[0078] These photochromic 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.

[0079] Examples of microencapsulation methods for the above-mentioned thermochromic pigments and photochromic particles 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.

[0080] For example, in a phase separation method from an aqueous solution, a thermochromic microcapsule pigment 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 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, for example, an amino resin solution, specifically an amino resin solution such as an aqueous solution of methylolmelamine, a urea solution, or a 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.

[0081] In this thermochromic pigment, 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, developer agents, and color change temperature adjusters.

[0082] These colorants can be used individually or in mixtures of two or more. Furthermore, the particle size of these colorants, such as water-dispersible pigments, resin particle pigments, pseudo-pigments, white plastic pigments, multi-layer coated pigments, thermochromic pigments, and photochromic particles, varies depending on the ball diameter, ink composition, viscosity, etc., but a particle size of 0.02 to 6 μm is desirable. This particle size may be, for example, 0.02 μm or more, 0.05 μm or more, 0.07 μm or more, 0.10 μm or more, 0.20 μm or more, 0.30 μm or more, 0.50 μm or more, 0.70 μm or more, or 0.90 μm or more, and may also be 6 μm or less, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less.

[0083] The content of these colorants can be appropriately increased or decreased depending on the ink line density, but may be 0.1% by mass or more, 0.3% by mass or more, 0.5% by mass or more, 0.7% by mass or more, 0.9% by mass or more, or 1.0% by mass or more, relative to the total amount of the oil-in-water droplet type ink composition, and preferably 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less.

[0084] <Other Components> Other components include, for example, dispersants, leveling agents, rust inhibitors, preservatives, lubricants, pH adjusters, and surface modifiers. As leveling agents, for example, fluorine-based surfactants and silicone oils can be used. As lubricants, for example, phosphate esters can be used. As pH adjusters, for example, amines such as triethanolamine can be used. As surface modifiers, silicone-based surface modifiers can be used.

[0085] 《Writing Instruments》 The writing instrument contains the above-described oil-in-water ink composition for writing instruments. The writing instrument may comprise an ink reservoir, a writing section, and a holding section, in which case the ink reservoir may store oil-in-water ink. The writing instrument may be a ballpoint pen.

[0086] <Ink Storage Section> The ink storage section stores the above-mentioned oil-in-water ink composition for writing instruments.

[0087] Any type of ink storage unit can be used as long as it can store ink and supply ink to the writing unit. It may be a direct-ink type with a collector structure (ink holding mechanism), or it may be a cotton-filled ink storage unit.

[0088] Furthermore, the ink reservoir may be integrated with the writing section. In particular, if the writing instrument is a ballpoint pen, the ink reservoir may be a refill for the writing instrument.

[0089] In particular, when the ink storage section is a ballpoint pen refill, the thickness of the outer wall of the ink storage section, i.e., the value of (outer diameter - inner diameter) / 2 of the ink storage section, is preferably 0.3 mm or more, 0.5 mm or more, or 0.7 mm or more, and also 2.0 mm or less, 1.8 mm or less, 1.5 mm or less, or 1.2 mm or less, from the viewpoint of suppressing the generation of air bubbles and obtaining a stable writing flow rate.

[0090] <Writing section> The writing section may be a writing section having a ballpoint pen tip at its front.

[0091] A ballpoint pen tip may consist of a ball and a holder that rotatably holds the ball. The ball may be made of any material used for ballpoint pen balls, such as stainless steel, cemented carbide, or ceramics. The shape of the ballpoint pen tip is not particularly limited and may be, for example, bullet-shaped or needle-shaped.

[0092] Furthermore, to improve the stability of the writing flow and the writing feel, it is more preferable that the surface roughness Ra of the ball of the ball pen tip be less than 15 nm, less than 12 nm, or less than 10 nm.

[0093] In this invention (including the embodiments described later), the "surface roughness Ra" was measured using a non-contact surface shape measuring instrument (NewView 7200, Zygo Corporation) with a lens magnification of 50x, an evaluation length of 100 μm, and a Gaussian filter of 25 μm. All other conditions were met in accordance with JIS B0601 (Geometric specifications of products - surface properties).

[0094] <Holding part> The holding part may be a part that allows the writing instrument of the present invention to be held by hand, and may have a hollow structure that can house the ink storage part. The holding part may have a shape such as cylindrical or polygonal tube.

[0095] The present invention will be specifically described by examples and comparative examples, but the present invention is not limited thereto.

[0096] <Example 1> 7.5 parts by mass of condensed fatty acid ester (Minerasol LB-601, Ito Oil Co., Ltd., density 0.96 g / cm³) ３ ), 2 parts by mass of oleic acid (Lunaq OV, Kao Corporation, density 0.895 g / cm³) ３ ), and 0.5 parts by mass of dl-α-tocopherol (tocopherol, Mitsubishi Chemical Corporation, density 0.95 g / cm³) as an antioxidant. ３ After heating the mixture to a temperature of 50°C to 60°C while stirring to dissolve it, silicon dioxide particles (inorganic particle A, density 2.1 g / cm³) are added as inorganic particles. ３ A mixture of particles (with a particle size of 110 nm) was obtained to obtain 10.5 parts by mass of an oily solution.

[0097] Separately, an emulsifier solution was prepared by dissolving 5 parts by mass of polyoxyethylene styrene-phenyl ether (Newcol N780 (ethylene oxide 80 molar adduct), Nippon Emulsifier Co., Ltd.) as an emulsifier component in 35 parts by mass of purified water while stirring. Next, the emulsifier solution was gradually added to the oily solution to invert the phase from water in oil (w / o) to oil in water (o / w) to obtain an oil in water emulsion.

[0098] Subsequently, while stirring, the pigment dispersion was added to this oil-in-water emulsion to obtain 100 parts by mass of the writing instrument ink composition of Example 1. The pigment dispersion consisted of 7 parts by mass of carbon black as a pigment, 1 part by mass of styrene acrylic resin as a dispersant, 2 parts by mass of glycerin as an organic solvent, 0.6 parts by mass of phosphate ester as a lubricant, 0.6 parts by mass of triethanolamine as a pH adjuster, 0.5 parts by mass of methylisothiazolinone as a preservative, and 38.3 parts by mass of water.

[0099] <Examples 2-9 and Comparative Examples 1-6> Except for changing the type and content of each component as shown in Tables 1-4, oil-in-water ink compositions for writing instruments were prepared in the same manner as in Example 1 for Examples 2-9 and Comparative Examples 1-6. Details of the components shown in Tables 1-4 are as follows: Inorganic particles B: Aluminum oxide particles, density 4.0 g / cm³ ３ Inorganic particles C: Titanium dioxide particles, particle size 100 nm, density 4.26 g / cm³３ Inorganic particles D: zinc oxide particles, particle size 180 nm, density 5.61 g / cm³ ３ Inorganic particles E: silicon dioxide particles, particle size 80 nm, density 2.1 g / cm³ ３ Inorganic particles F: silicon dioxide particles, particle size 340 nm, density 2.1 g / cm³ ３ , particle size 30 nm Inorganic particles G: cerium oxide particles, density 7.65 g / cm ３ , particle size 90nm

[0100] The particle size of the oil droplets in the obtained oil-in-water ink composition for writing instruments was measured by dynamic light scattering. The measurement was performed using cumulant analysis of the scattering intensity distribution calculated with a particle size analyzer (concentrated particle size analyzer FPAR-1000, manufactured by Otsuka Electronics Co., Ltd.).

[0101] Furthermore, the density of the oil droplets and the density of the aqueous phase in the obtained oil-in-water ink composition for writing instruments were calculated by a weighted average of the densities of the materials used.

[0102] 《Evaluation》 Ballpoint pens were manufactured by filling each of the prepared oil-in-water ink compositions for writing instruments into a ballpoint pen. Specifically, the barrel of a ballpoint pen (Signo UM-100, Mitsubishi Pencil Co., Ltd.) was used, and the above-mentioned ink composition and an ink-following body were loaded into a refill consisting of a polypropylene ink reservoir tube with an outer diameter of 60 mm, an inner diameter of 3.8 mm, and a length of 113 mm, a stainless steel tip (carbide ball, ball diameter 0.38 mm, surface roughness less than 10 nm), and a connector connecting the reservoir tube and the tip. The following evaluation tests were conducted using these.

[0103] <Phase separation state after long-term storage at high temperatures> The ink was left to stand for four weeks in a 60°C environment, and the presence or absence of suspended particles was checked. The evaluation results are as follows: A: No suspended particles were present. B: A small amount of suspended particles were observed. C: Suspended particles were clearly observed.

[0104] <Sedimentation status after long-term storage at high temperatures> The ink was left to stand for four weeks in a 60°C environment, and the presence or absence of sediment was checked. The evaluation results are as follows: A: No sediment was present. B: A small amount of sediment was observed. C: Sediment was clearly observed.

[0105] Tables 1 to 4 show the configurations and evaluation results of the examples and comparative examples.

[0106]

[0107]

[0108]

[0109]

[0110] Tables 1 to 4 show that the oil-in-water ink compositions for writing instruments in the examples, where the ratio of the density of the oil droplets to the density of the aqueous phase is in the range of 0.85 to 1.15, can be seen to suppress the formation of phase separation and the sedimentation of contents after long-term storage at high temperatures.

Claims

1. An oil-in-water ink composition for writing instruments, comprising an aqueous phase and oil droplets dispersed in the aqueous phase in the form of an oil-in-water emulsion, wherein the oil droplets contain an oil phase and inorganic particles, and the ratio of the density of the oil droplets to the density of the aqueous phase is in the range of 0.85 to 1.

15.

2. The density of the inorganic particles is 2.0 g / cm³. ３ 6.0g / cm or more ３ An oil-in-water droplet type ink composition for writing instruments according to claim 1, within the following range.

3. The oil-in-water droplet ink composition for writing instruments according to claim 1 or 2, wherein the particle size of the inorganic particles, as measured by dynamic light scattering, is 10 nm or more and 400 nm or less.

4. The oil-in-water ink composition according to any one of claims 1 to 3, wherein the content of inorganic particles in the oil droplet is 0.1% or more and 30% or less relative to the mass of the oil droplet.

5. The oil-in-water droplet type ink composition according to any one of claims 1 to 4, wherein the particle size of the oil droplets, as measured by dynamic light scattering, is 50 nm or more and 1000 nm or less.

6. The density of the oil phase component constituting the oil droplet is 0.8 g / cm³. ３ 1.05g / cm or more ３ An oil-in-water droplet type ink composition according to any one of claims 1 to 5, within the following range.

7. The oil-in-water ink composition according to any one of claims 1 to 6, wherein the oil phase component constituting the oil droplet contains at least one selected from the group consisting of hydrocarbon oil, ester oil, higher alcohol, fatty acid, and silicone oil.

8. A writing instrument comprising an ink storage section having the oil-in-water droplet type ink composition for writing instruments described in any one of claims 1 to 7.

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