Oil droplet-in-water type ink composition for writing instruments

Abstract

An oil droplet-in-water type ink composition for writing instruments according to the present invention has an aqueous phase and an oil phase dispersed in the aqueous phase. The oil phase and / or the aqueous phase contains a colorant. The oil phase contains a rust inhibitor having a molecular weight of 90-500.

Description

Oil-in-water ink composition for writing instruments

[0001] The present invention relates to an oil-in-water ink composition for a writing instrument.

[0002] A feature of water-based ballpoint pens is that they have a light writing feel, but they often have a scratchy feel. Furthermore, the water-soluble dyes used as colorants have the advantage of high coloring power and flexibility in toning, but they have the problem of poor weather resistance and the tendency for the lines to bleed when water gets on them.

[0003] Oil-based ballpoint pens have the advantage of not feeling scratchy when writing and not bleeding the lines, but they often have a heavy writing feel. In addition, the oil-soluble dyes used as colorants are water-resistant, so they do not bleed when water gets on the lines.

[0004] As a means for achieving both the good writing feel of an aqueous ballpoint pen and the water resistance of an oil-soluble dye, an ink composition for an oil-in-water ballpoint pen, which has the ink property of an oil-in-water emulsion (O / W emulsion), has been developed.

[0005] Patent Document 1 discloses an aqueous ballpoint pen ink composition in which an oil phase is contained in the form of an oil-in-water emulsion relative to an aqueous phase, wherein at least one of the oil phase and the aqueous phase contains a colorant, and the oil phase contains, among the components constituting the oil phase, an estolide, which is a fatty acid oligomer formed by condensation of fatty acids having hydroxyl groups with each other or condensation of fatty acids having hydroxyl groups with fatty acids not having hydroxyl groups, or an ester of the estolide with an alcohol.The aqueous ballpoint pen ink composition is said to be able to improve storage stability by preventing phase separation even when stored for long periods at high or low temperatures.

[0006] On the other hand, water-based ballpoint pens have a problem in that the ball portion is easily corroded, and over time, the written lines become faint or writing becomes impossible. In response to this problem, water-based ballpoint pen ink compositions containing various anti-rust agents have been disclosed.

[0007] Patent Document 2 discloses a pigment ink for a water-based ballpoint pen, which is characterized by adding diisopropylammonium nitrite as a rust inhibitor to the pigment ink for a water-based ballpoint pen, which is composed of a pigment, a dispersant, and an aqueous medium. Benzotriazole and its derivatives, which are commonly used as rust inhibitors, can sometimes cause a decrease in the rust inhibitor effect due to the adsorption of the benzotriazole and its derivatives to pigment particles, but the pigment ink for the water-based ballpoint pen is said to have no decrease in the rust inhibitor effect.

[0008] JP 2013-221051 A JP 9-87568 A

[0009] Like aqueous ballpoint pens, ballpoint pens containing oil-in-water ink compositions may experience corrosion of the ball and holder over time. Similar to the addition of a rust inhibitor to the aqueous medium in Patent Document 2, a certain degree of rust prevention effect can be achieved by including a rust inhibitor in the aqueous phase of an ink for an oil-in-water ballpoint pen. However, when a ballpoint pen containing the oil-in-water ink composition is stored for a long period of time, particularly under high humidity, the occurrence of the corrosion may not be suppressed. Furthermore, when the pen is stored for a long period of time at low temperatures, the rust inhibitor precipitates, causing blurring during writing.

[0010] Therefore, the present invention provides a novel oil-in-water ink composition that does not or is less likely to corrode the ball and holder of a ballpoint pen even when the ballpoint pen is stored for a long period of time under high humidity and / or low temperature conditions.

[0011] After extensive investigation, the present inventors have found that the above problems can be solved by the following means, and have completed the present invention. That is, the present invention is as follows: <Aspect 1> An oil-in-water ink composition having an aqueous phase and an oil phase dispersed in the aqueous phase, wherein at least one of the oil phase and the aqueous phase contains a colorant, and the oil phase contains a rust inhibitor having a molecular weight of 90 to 500. <Aspect 2> The oil-in-water ink composition according to Aspect 1, wherein the rust inhibitor has an octanol / water partition coefficient LogP of -1.0 or greater. <Aspect 3> The oil-in-water ink composition according to Aspect 1 or 2, wherein the total content of the rust inhibitor in the oil phase is greater than the total content of the rust inhibitor in the aqueous phase. <Aspect 4> The oil-in-water ink composition according to any one of Aspects 1 to 3, wherein the content of the oil phase is 1% by mass or greater and 35% by mass or less, relative to the mass of the oil-in-water ink composition. Aspect 5: The oil-in-water ink composition according to any one of Aspects 1 to 4, wherein the particle diameter of the oil droplets constituting the oil phase, as measured by dynamic light scattering, is 100 nm or more and 1000 nm or less. Aspect 6: A writing instrument comprising an ink reservoir containing the oil-in-water ink composition according to any one of Aspects 1 to 5. Aspect 7: The writing instrument according to Aspect 6, which is a ballpoint pen. Aspect 8: The writing instrument according to Aspect 7, which is a ballpoint pen having a ball made of tungsten carbide and a holder made of stainless steel.

[0012] According to the present invention, it is possible to provide a novel oil-in-water ink composition that does not or is less likely to cause corrosion of the ball and holder of a ballpoint pen, even when the ballpoint pen is stored for a long period of time under high humidity and / or low temperature conditions.

[0013] FIG. 1 is a side cross-sectional view of the writing portion of a writing instrument (ballpoint pen) of the present invention.

[0014] Oil-in-water ink composition The oil-in-water ink composition of the present invention has an aqueous phase and an oil phase dispersed in the aqueous phase, wherein at least one of the oil phase and the aqueous phase contains a colorant, and the oil phase contains a rust inhibitor having a molecular weight of 90 or more and 500 or less.

[0015] The present inventors, in investigating the composition of an oil-in-water ink composition that would not or would be less susceptible to corrosion of the ball part even when a writing instrument is stored under high humidity for an extended period of time, have found that a significant rust-preventing effect can be obtained by incorporating a rust inhibitor with a molecular weight of 90 or more into the oil phase of the oil-in-water ink composition. Without wishing to be bound by theory, this is thought to be because the oil phase comes into contact with the ball part and holder part preferentially over the water phase, and the inclusion of a rust inhibitor in the oil phase makes it easier for the rust inhibitor to adsorb to the ball part and holder part, and therefore any rust inhibitor with a molecular weight of 90 or more will exhibit a rust-preventing effect, regardless of its type.

[0016] Furthermore, the present inventors have found that when the molecular weight of the rust inhibitor in the oil-in-water ink composition is 500 or less, the rust inhibitor does not precipitate or is less likely to precipitate even when stored at low temperatures for a long period of time.

[0017] Each component of the present invention will be described below.

[0018] The oil-in-water ink composition of the present invention has an aqueous phase and an oil phase dispersed in the aqueous phase.

[0019] The pH of the oil-in-water ink composition of the present invention may be 6.0 or more and 10.0 or less, and may be 6.0 or more, 6.5 or more, 7.0 or more, or 7.5 or more, and may be 10.0 or less, 9.5 or less, 9.0 or less, 8.5 or less, or 8.5 or less.

[0020] <Oil Phase> The oil-in-water ink composition of the present invention has an oil phase dispersed in an aqueous phase. In particular, the oil phase may be present in the form of an oil-in-water emulsion.

[0021] The content of the oil phase may be from 1% to 35% by mass, relative to the mass of the oil-in-water ink composition. This content 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 be 35% by mass or less, 30% 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.

[0022] The particle size of the oil droplets constituting the oil phase may be 100 nm or more and 1000 nm or less, and may be 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, or may 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.

[0023] In the present invention, the "particle size" of the oil droplets is the value of the histogram mean particle size (D50) calculated on a volume basis in the scattering intensity distribution measured by dynamic light scattering.

[0024] The oil phase may contain an oil phase component. Examples of the oil phase component include an estolide, which is a fatty acid oligomer formed by condensation of fatty acids having hydroxyl groups or condensation of a fatty acid having hydroxyl groups and a fatty acid having no hydroxyl groups, or an ester of such an estolide with an alcohol. The oil phase may also contain the fatty acid having no hydroxyl groups in the estolide or ester itself.

[0025] The oil phase may further contain a resin and / or an organic solvent to adjust the viscosity. For the resin and organic solvent, the description of the aqueous phase below can be referred to.

[0026] (Rust inhibitor) The oil phase contains a rust inhibitor having a molecular weight of 90 or more and 500 or less. When the molecular weight of the rust inhibitor is 90 or more, sufficient rust prevention effect can be obtained even when stored for a long period of time under high humidity. Furthermore, when the molecular weight of the rust inhibitor is 500 or less, precipitation of the rust inhibitor can be suppressed even when stored for a long period of time under low temperature. This molecular weight may be 95 or more, 100 or more, 110 or more, 120 or more, 150 or more, or 200 or more, or may be 500 or less, 450 or less, 400 or less, 350 or less, or 300 or less.

[0027] The rust inhibitor has an octanol / water partition coefficient Log P of -1.0 or more. Dissolution of the rust inhibitor in the oil phase provides a high rust prevention effect. This octanol / water partition coefficient Log P may be -0.8 or more, -0.6 or more, -0.4 or more, -0.2 or more, 0.0 or more, 0.3 or more, 0.5 or more, 1.0 or more, 2.0 or more, 3.0 or more, 4.0 or more, 5.0 or more, or 6.0 or more. Furthermore, this partition coefficient Log P may be 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, or 6.0 or less.

[0028] Here, the octanol / water partition coefficient Log P is an index that represents the lipophilicity of a substance, and the higher the Log P, the higher the lipophilicity. Log P can be measured by the flask permeation method in accordance with JIS-Z-7260. It can also be calculated using ChemDraw (manufactured by CambridgeSoft).

[0029] Examples of the rust inhibitor include 1,2,3-benzotriazole, 4-methylbenzotriazole, 5-methylbenzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]benzotriazole, carboxybenzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]4-methylbenzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]5-methylbenzotriazole, 2,2'-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol, 1-(1',2'-dicarboxyethyl)benzotriazole, 1-(2,3-dicarboxypropyl)benzotriazole, 1-(2-ethylhexylaminomethyl)benzotriazole, 2,6-bis[(1H-benzotriazol-1-yl)methyl]-4-methylphenol, 5-methylbenzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl] ... Benztriazole, 5-carboxybenzotriazole, diisopropylammonium nitrite, dicyclohexylammonium nitrite, 3-(diisobutoxy-thiophosphorylsulfanyl)-2-methylpropionic acid, 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone-5,5'-disulfonic acid, 2-hydroxy-4-diethylamino-2'-hydroxycarbonylbenzophenone, 2,4,6-trimercapto-s-triazine, 2-dibutylamino-4,6-dimercapto-s-triazine, thioglycolic acid, laurylthiopropionic acid, dithiodiglycolic acid, thiodipropionic acid, dithiodipropionic acid, 1-(2-hydroxyethylthio)-2 propanol, thiodiglycol, and the like can be used.

[0030] The total content of the rust inhibitor in the oil phase may be greater than the total content of the rust inhibitor in the aqueous phase. A high content of the rust inhibitor in the oil phase improves the rust prevention effect and also suppresses precipitation of the rust inhibitor. Here, "the total content of the rust inhibitor in the oil phase" refers to the total amount of the rust inhibitor contained in the entire oil phase of a specific amount of the oil-in-water ink composition, and "the total content of the rust inhibitor in the aqueous phase" refers to the total amount of the rust inhibitor contained in the entire aqueous phase of a specific amount of the oil-in-water ink composition.

[0031] The content of the rust inhibitor may be 0.05% by mass or more and 3.0% by mass or less, relative to the mass of the oil-in-water ink composition. From the viewpoint of ensuring rust prevention, the content is preferably 0.05% by mass or more, 0.1% by mass or more, 0.5% by mass or more, 1.0% by mass or more, or 1.5% by mass or more, relative to the mass of the oil phase. From the viewpoint of suppressing precipitation at low temperatures, the content is preferably 3.0% by mass or less, 2.5% by mass or less, or 2.0% by mass or less.

[0032] The content of the rust inhibitor may be 0.5% by mass or more and 25.0% by mass or less, relative to the mass of the oil phase. From the viewpoint of ensuring rust prevention, the content is preferably 0.5% by mass or more, 0.7% by mass or more, 1.0% by mass or more, 3.0% by mass or more, 5.0% by mass or more, or 10.0% by mass or more, relative to the mass of the oil phase. From the viewpoint of suppressing precipitation at low temperatures, the content is preferably 25.0% by mass or less, 20.0% by mass or less, 15.0% by mass or less, or 12.0% by mass or less.

[0033] (Estolide or Ester) The estolide or ester that can be used in the oil phase may be an estolide, which is a fatty acid oligomer obtained by condensation of fatty acids having hydroxyl groups or condensation of a fatty acid having a hydroxyl group and a fatty acid not having a hydroxyl group, or an ester of the estolide with an alcohol.

[0034] As the fatty acid having a hydroxyl group in the estolide or ester, various conventionally used fatty acids can be used, and among them, it is preferable to use castor oil fatty acids whose main component is ricinoleic acid, hydrogenated castor oil fatty acids whose main component is 12-hydroxystearic acid, etc. These fatty acids may be used alone or in combination.

[0035] Furthermore, examples of fatty acids that do not have a hydroxyl group include capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachic acid, behenic acid, lignoceric acid, cerotic acid, melissic acid, oleic acid, linoleic acid, and linolenic acid. Furthermore, coconut oil fatty acids, palm oil fatty acids, olive oil fatty acids, beef tallow fatty acids, and hydrogenated beef tallow fatty acids that contain these components can also be used.

[0036] In the present invention, a fatty acid oligomer obtained by condensing the above-mentioned fatty acids having hydroxyl groups, or a fatty acid oligomer (estolide) obtained by condensing a fatty acid having a hydroxyl group with a fatty acid having no hydroxyl group, is used. Here, "fatty acid oligomer" refers to a condensation product of dimer or more. Dimers to heptamers are preferred. Although monomers may be mixed in the fatty acid oligomer, from the viewpoint of solubility in the oil phase, it is preferable that the average fatty acid oligomer as a whole is 1.5-mer or more, preferably 2.0-mer or more.

[0037] The content of the estolide or ester may be 50% by mass or more, 60% by mass or more, or 70% by mass or more, and may be 90% by mass or less, or 85% by mass or less, based on the mass of the oil phase.

[0038] The oil phase may further contain other oil phase components, such as the fatty acids themselves that do not have a hydroxyl group in the above-mentioned estolides or esters.

[0039] <Aqueous Phase> The oil-in-water ink composition of the present invention has an aqueous phase. The aqueous phase contains at least water. The aqueous phase may further contain an emulsifier component. The presence of the emulsifier component allows the aqueous phase and the oil phase dispersed in the aqueous phase to exist in the state of an oil-in-water emulsion.

[0040] The aqueous phase may further contain a colorant, a resin, an organic solvent, and the like.

[0041] (Water) As the water, distilled water and ion-exchanged water can be used.

[0042] The water content may be greater than 50% by mass, 55% by mass or more, 60% by mass or more, 65% by mass or more, or 70% by mass or more, and may be 90% by mass or less, 85% by mass or less, 80% by mass or less, or 75% by mass or less, based on the mass of the oil-in-water ink composition.

[0043] The water content may be more than 50% by mass, 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, or 80% by mass or more, and may be 90% by mass or less, or 85% by mass or less, based on the mass of the aqueous phase.

[0044] (Emulsifier Component) As the emulsifier component, any emulsifier can be used, for example, an emulsifier having one or more aromatic rings in the molecular skeleton.

[0045] 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. For example, polycyclic phenyl-type nonionic surfactants such as polyoxyethylene distyrenated phenyl ether, polyoxyethylene monostyrenated phenyl ether, and polyoxyethylene cumyl phenyl ether, and ionic surfactants such as sulfates thereof can be used.

[0046] The number of moles of ethylene oxide (EO) added to the emulsifier is preferably 40 mol or more, 45 mol or more, or 50 mol or more, from the viewpoint of suppressing coalescence of oil phase particles by the long ethylene oxide chain.

[0047] In addition to the above emulsifiers, emulsifiers with a low ethylene oxide addition mole number that are strongly oriented toward the oil phase, specifically emulsifiers with an ethylene oxide addition mole number 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 with a strong ethylene oxide addition mole number toward the oil phase with an emulsifier with a strong ethylene oxide addition mole number toward the aqueous phase may be preferable from the viewpoint of increasing the micelle concentration at the interface and improving the stability of the emulsion.

[0048] With regard to the HLB value (hydrophilic-lipophilic balance), it is preferable to use one or more emulsifiers with an HLB value of at least 15 for nonionic surfactants, from the viewpoint of preventing excessive incorporation of the emulsifier into the oil phase.

[0049] As the emulsifier component, in addition to surfactants having an aromatic ring in the molecule, any emulsifier having a different structure may be added and used. Examples of such emulsifiers include linear hydrocarbon-type nonionic surfactants such as polyoxyethylene hydrogenated castor oil and polyoxyethylene alkyl (C10 to C18) esters, and sorbitan derivatives.

[0050] The content of the 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, relative to 100 parts by mass of the oil phase, and may 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.

[0051] (Resin) As the resin, any resin, particularly a resin used for fixing a coating film, can be used, such as a sulfonamide resin, a maleic acid resin, a terpene resin, a terpene phenol resin, an ester gum, a xylene resin, an alkyd resin, a phenol resin, a rosin, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl alcohol, an acrylic resin, a melamine resin, a nitrocellulose resin, a urea resin, or a derivative thereof.

[0052] The resin content can be adjusted depending on the desired viscosity of the aqueous phase, and may be, for example, 1% by mass or more, 2% by mass or more, or 3% by mass or more, and 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, relative to the mass of the aqueous phase.

[0053] (Organic Solvent) Examples of the 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.

[0054] 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.

[0055] 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, and 2-methylcyclohexanol.

[0056] 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, and octylene glycol.

[0057] 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-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, and tetrapropylene glycol monobutyl ether.

[0058] 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.

[0059] 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 usable surfactants 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, and 3-methoxybutyl acetate.

[0060] The content of the organic solvent can be adjusted depending on the desired viscosity of the oil phase, and may be, for example, 1% by mass or more, 2% by mass or more, or 3% by mass or more, and 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, relative to the mass of the oil phase.

[0061] <Colorant> In the oil-in-water ink composition of the present invention, at least one of the oil phase and the aqueous phase contains a colorant.

[0062] As the colorant, various colorants that can be used in conventional inks can be used, such as dyes, pigments, or mixtures of dyes and pigments, etc. These colorants can be used alone or in combination.

[0063] The dye may be a water-soluble dye, including any dye that dissolves or disperses in water, such as acid dyes like eosin, fuoxin, water yellow #6-C, acid red, water blue #105, brilliant blue FCF, and nigrosine NB; direct dyes like direct black 154, direct sky blue 5B, and violet BB; and basic dyes like rhodamine and methyl violet.

[0064] The water-insoluble dye is a dye that is insoluble in water at room temperature. Examples of such water-insoluble dyes include salt-forming dyes, disperse dyes, and oil-soluble dyes. Among these, salt-forming dyes are preferred from the viewpoint of color development.

[0065] Examples of the salt-forming dye include dyes having azo, metal complex azo, anthraquinone, and metal phthalocyanine chemical structures. For example, Valifast (registered trademark) Black 1807, Valifast (registered trademark) Blue 2620, Valifast (registered trademark) Brown 2402, Valifast (registered trademark) Green 1501, Valifast (registered trademark) Orange 2210, Valifast (registered trademark) Pink 2310, Valifast (registered trademark) Red 1355, Valifast (registered trademark) VIOLET 1701, and Valifast (registered trademark) Yellow 1101, all of which are manufactured by Orient Chemical Industry Co., Ltd., can be used.

[0066] As the disperse dye, 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. At least one dye selected from Disperse Blue 87 can be used.

[0067] 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, all of which are manufactured by Orient Chemical Industry Co., Ltd.

[0068] Examples of pigments that can be used without limitation include conventionally known inorganic and organic pigments such as titanium oxide, resin particle pigments containing pigments or dyes, pseudopigments in which resin emulsions are colored with dyes or pigments, white plastic pigments, luster pigments, pigments in which silica or mica is used as a base material and the surface is multi-coated with iron oxide, titanium oxide, or the like, thermochromic pigments, photochromic particles, and the like.

[0069] 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.

[0070] 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.

[0071] Examples of thermochromic pigments include those 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 during 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). This average 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, or may 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.

[0072] Examples of photochromic particles that can be used include photochromic 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 particles include photochromic 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, so as to have a predetermined average particle size (e.g., 0.1 to 6 μm).

[0073] By suitably using the above-mentioned photochromic substance, the photochromic particles can be made to have the property of being colorless in an indoor lighting environment (indoor lighting equipment selected from incandescent lamps, fluorescent lamps, lamps, white LEDs, etc.) and becoming colored in an ultraviolet ray irradiation environment (irradiation with light having a wavelength of 200 to 400 nm, or irradiation with sunlight containing ultraviolet rays).

[0074] In the present invention (including the examples), the "average particle size" is appropriately selected depending on the size of the particles to be measured. For particles less than approximately 1 μm, it is the histogram mean particle size (D50) calculated on a volume basis in the scattering intensity distribution measured by dynamic light scattering, and for particles 1 μm or larger, it is the median diameter (D50) calculated on a volume basis by laser diffraction. The average particle size can be measured using a particle size analyzer [Microtrac HRA9320-X100 (Nikkiso Co., Ltd.)].

[0075] Examples of methods for microencapsulating the thermochromic pigment and the photochromic particles include interfacial polymerization, interfacial polycondensation, in situ polymerization, liquid hardening coating, phase separation from an aqueous solution, phase separation from an organic solvent, melt-dispersion cooling, air suspension coating, and spray drying, and can be appropriately selected depending on the application.

[0076] For example, in the phase separation method from an aqueous solution, a thermochromic microcapsule pigment can be produced by a method comprising the following steps, particularly a method comprising carrying out 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 heating and stirring to disperse them into oil droplets to produce a dispersion; (3) gradually adding, as a capsule film agent, a resin raw material capable of forming a wall film such as a urethane resin, an epoxy resin, or an amino resin, for example, an amino resin solution, specifically, an amino resin solution such as a methylolmelamine aqueous solution, a urea solution, or a 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.

[0077] In this thermochromic pigment, 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 regulator.

[0078] These colorants can be used alone or in combination of two or more. The average particle diameter of water-dispersible pigments, resin particle pigments, pseudopigments, white plastic pigments, multi-coated pigments, thermochromic pigments, photochromic particles, and the like varies depending on the ball diameter, ink composition, viscosity, and other factors, but is preferably 0.02 to 6 μm. This average particle diameter 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, or may 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.

[0079] The content of these colorants can be increased or decreased as appropriate depending on the line density of the ink, 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 ink composition, and is 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.

[0080] <Other Components> Examples of other components include thickeners, dispersants, leveling agents, preservatives, lubricants, pH adjusters, and surface conditioners. Examples of leveling agents that can be used include fluorine-based surfactants, silicone oils, and acetylene-based surfactants. Examples of lubricants that can be used include phosphate esters. Examples of pH adjusters that can be used include amines such as triethanolamine. Examples of surface conditioners that can be used include silicon-based surface conditioners.

[0081] <Writing Instrument> The writing instrument includes an ink reservoir containing the oil-in-water ink composition described above. The writing instrument may be a ballpoint pen. The writing instrument may have a writing part and a holder part.

[0082] <Ink Storage Unit> The ink storage unit stores the oil-in-water ink composition.

[0083] The ink storage section can be any type that can store ink and supply ink to the writing section, and it can be a direct liquid type with a collector structure (ink retention mechanism) or a padded type ink storage section.

[0084] The ink reservoir may also be integral with the writing element, and in particular when the writing instrument is a ballpoint pen, the ink reservoir may be a refill for the writing instrument.

[0085] In particular, when the ink storage section is a ballpoint pen refill, it is preferable that 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 0.3 mm or more, 0.5 mm or more, or 0.7 mm or more, and 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 bubbles and obtaining a stable writing flow rate.

[0086] <Writing Part> The writing part can be a writing part having a ballpoint pen tip at the tip.

[0087] The ballpoint pen tip may have a ball made of tungsten carbide and a holder made of stainless steel, which rotatably holds the ball.

[0088] For the purpose of improving the stability of the writing flow rate and the writing feel, it is more preferable that the surface roughness Ra of the ball of the ballpoint pen tip is less than 15 nm, less than 12 nm, or less than 10 nm.

[0089] The "surface roughness Ra" in the present invention (including the examples described later) was measured using a non-contact surface profiler (NewView 7200, Zygo Corporation) under the following conditions: lens magnification: 50x, evaluation length: 100 μm, Gaussian filter: 25 μm; and other conditions were measured in accordance with JIS B0601 (geometric characteristics specifications of products - surface properties).

[0090] Specifically, for example, as shown in FIG. 1, a ballpoint pen tip 10 is composed of a ball 12 and a holder 14.

[0091] 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 accommodate the ink storage part. The holding part may have a shape such as a cylindrical or polygonal tube.

[0092] The present invention will be specifically explained with reference to examples and comparative examples, but the present invention is not limited to these.

[0093] Preparation of Oil-in-Water Ink Composition Example 1 7.5 parts by mass of a condensed fatty acid ester (Minerazol LB-601, Ito Oil Mills, Ltd., Ester A), 2 parts by mass of oleic acid (Lunac OV, Kao Corporation), 0.5 parts by mass of dl-α-tocopherol as an antioxidant, and 0.5 parts by mass of 1,2,3-benzotriazole as a rust inhibitor were mixed, and the mixture was heated to a temperature of 50°C to 60°C while stirring to obtain an oily solution in which the components were completely dissolved.

[0094] Separately, an emulsifier solution was prepared by dissolving 5 parts by mass of polyoxyethylene styrenated phenyl ether (Newcol N780, Nippon Nyukazai Co., Ltd.) as an emulsifier component in purified water with stirring. The emulsifier solution was then gradually added to the oily solution, resulting in phase inversion from a water-in-oil (w / o) emulsion to an oil-in-water (o / w) emulsion.

[0095] Thereafter, a pigment dispersion was added to this oil-in-water emulsion with stirring, yielding 100 parts by mass of a writing instrument ink composition of Example 1. The pigment dispersion consisted of 7 parts by mass of carbon black as a colorant (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 a phosphoric acid ester as a lubricant, 0.6 parts by mass of triethanolamine as a pH adjuster, and 73.3 parts by mass of water. Details of the emulsifier solution, pigment dispersion components, and additive components used are shown in Tables 1 and 2.

[0096] Examples 2 to 8 and Comparative Examples 1 to 4 Writing instrument ink compositions of Examples 2 to 8 and Comparative Examples 1 to 4 were prepared in the same manner as Example 1, except that the mass and content of each component was changed as shown in Tables 1 and 2. Details of the rust inhibitors shown in Tables 1 and 2 are as follows. Rust inhibitor A: 1,2,3-benzotriazole (molecular weight: 119, octanol / water partition coefficient (Log P): 0.5) Rust inhibitor B: dicyclohexylammonium nitrite (molecular weight: 228, octanol / water partition coefficient (Log P): 4.4) Rust inhibitor C: laurylthiopropionic acid (molecular weight: 274, octanol / water partition coefficient (Log P): 6.0) Rust inhibitor D: 1,2,4-triazole (molecular weight: 69, octanol / water partition coefficient (Log P): -0.6) Rust inhibitor E: thiazolidine (molecular weight: 89, octanol / water partition coefficient (Log P): 0.3) Rust inhibitor F: saponin (molecular weight: 1105, octanol / water partition coefficient (Log P): -2.7)

[0097]

[0098]

[0099] <Evaluation> <Writing feel after long-term storage under high humidity> The prepared ballpoint pen was stored in a landscape position at a humidity of 80% for 120 days. After storage, writing was carried out using the ballpoint pen, and the writing feel was evaluated sensorily. The evaluation criteria are as follows: A: Very smooth. B: Smooth. C: Felt a little heavy. D: Heavy.

[0100] <Precipitation resistance after low-temperature storage> The prepared ballpoint pens were stored in a horizontal position in an open chamber set at a temperature of -5°C for 60 days. After storage, the ballpoint pens were returned to room temperature, and writing was performed using the ballpoint pens, and the writing feel was evaluated sensorily. The evaluation criteria are as follows: A: No smearing occurred. B: Smearing occurred, but the drawn lines were fully recognizable. C: Smearing occurred to the extent that it significantly affected the recognizability of the drawn lines. D: Almost no ink came out.

[0101] The configurations and evaluation results of the examples and comparative examples are shown in Tables 3 and 4.

[0102]

[0103]

[0104] From Examples 1 to 8 and Comparative Example 1, it can be seen that by including a rust inhibitor in the oil phase, rust prevention is enhanced and precipitation at low temperatures is also suppressed.

[0105] From Examples 1 to 8 and Comparative Examples 2 to 4, it can be seen that when the molecular weight of the rust inhibitor is 90 or more and 500 or less, the rust prevention properties are improved and precipitation at low temperatures is also suppressed.

[0106] 10 Ballpoint pen tip 12 Ball 14 Holder

Claims

1. An oil-in-water ink composition having an aqueous phase and an oil phase dispersed in the aqueous phase, wherein at least one of the oil phase and the aqueous phase contains a colorant, and the oil phase contains a rust inhibitor having a molecular weight of 90 or more and 500 or less.

2. The oil-in-water ink composition according to claim 1, wherein the rust inhibitor has an octanol / water partition coefficient Log P of -1.0 or more.

3. The oil-in-water ink composition according to claim 1 or 2, wherein the total content of the rust inhibitor in the oil phase is greater than the total content of the rust inhibitor in the aqueous phase.

4. The oil-in-water ink composition according to any one of claims 1 to 3, wherein the content of the oil phase is 1% by mass or more and 35% by mass or less, based on the mass of the oil-in-water ink composition.

5. The oil-in-water ink composition according to any one of claims 1 to 4, wherein the particle diameter of the oil droplets constituting the oil phase, as measured by dynamic light scattering, is 100 nm or more and 1000 nm or less.

6. A writing instrument comprising an ink reservoir containing the oil-in-water ink composition of any one of claims 1 to 5.

7. The writing instrument according to claim 6, which is a ballpoint pen.

8. The writing instrument according to claim 7, which is a ballpoint pen having a ball made of tungsten carbide and a holder made of stainless steel.

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