Oil-in-water ink composition for writing instruments

Abstract

This oil-in-water ink composition for writing instruments includes an oil phase in an aqueous phase in a state of oil droplets in water, the oil phase containing a resin and a polar lubricating oil, and the resin content being more than 0.5 mass% relative to the mass of the oil phase.

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] In recent years, oil-based ballpoint pens have been developed that improve the writing experience by reducing the viscosity of the oil-based ink. However, low-viscosity oil-based ink tends to run out in large amounts, which makes it difficult for the ink to dry properly and causes ink to bleed through to the back of the paper, resulting in blobbing.

[0005] In response to these problems, an aqueous ballpoint pen ink composition has been disclosed, which has an oil-in-water emulsion (O / W emulsion) as an ink property that can achieve both the good writing feel of the aqueous phase and the water resistance of the oil-soluble dye.

[0006] Patent Document 1 discloses an aqueous ink composition for a ballpoint pen, in which an oil phase is contained in the 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 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 a fatty acid having a hydroxyl group with a fatty acid not having a hydroxyl group, or an ester of the estolide with an alcohol.

[0007] Patent Document 2 discloses an aqueous ink composition for a ballpoint pen, in which an oil phase is contained in an aqueous phase in the form of an oil-in-water emulsion, wherein the oil phase or the oil phase and the aqueous phase contain a colorant, and the oil phase contains a fatty acid having 6 to 22 carbon atoms among the components constituting the oil phase.

[0008] JP 2013-221051 A JP 2013-203790 A

[0009] The present invention provides a novel oil-in-water ink composition for a writing instrument that can improve the direct current resistance while suppressing the writing feel at the start of writing and the blurring of drawn lines.

[0010] After extensive research, the present inventors have found that the above problems can be solved by the following means, and have completed the present invention. Specifically, the present invention is as follows: <Aspect 1> An oil-in-water ink composition for a writing instrument, wherein an oil phase is contained in a water phase in the form of oil-in-water droplets, the oil phase contains a resin and a polar lubricating oil, and the content of the resin is greater than 0.5% by mass relative to the mass of the oil phase. <Aspect 2> The oil-in-water ink composition for a writing instrument according to Aspect 1, wherein the oil phase further contains a fatty acid having 10 or more carbon atoms or an alcohol having 10 or more carbon atoms. <Aspect 3> The oil-in-water ink composition for a writing instrument according to Aspect 2, wherein the fatty acid is a straight-chain fatty acid. <Aspect 4> The oil-in-water ink composition for a writing instrument according to Aspect 2 or 3, wherein the content of the fatty acid is 15% by mass or greater relative to the mass of the oil phase. Aspect 5: The oil-in-water ink composition for a writing instrument according to any one of Aspects 1 to 4, wherein the polar lubricating oil is an ester-based lubricating oil or a polyglycol-based lubricating oil. Aspect 6: The oil-in-water ink composition for a writing instrument according to Aspect 5, wherein the polar lubricating oil is an estolide, which is a fatty acid oligomer formed by condensation of hydroxyl-containing fatty acids with each other or condensation of a hydroxyl-containing fatty acid with a non-hydroxyl-containing fatty acid, or an ester of the estolide with an alcohol. Aspect 7: The oil-in-water ink composition for a writing instrument according to any one of Aspects 1 to 6, wherein the polar lubricating oil has an acid value of 150 or less. Aspect 8: The oil-in-water ink composition for a writing instrument according to any one of Aspects 1 to 7, wherein the resin has a glass transition temperature of 100°C or less. Aspect 9: The oil-in-water ink composition for a writing instrument according to any one of Aspects 1 to 8, wherein the resin is selected from the group consisting of a styrene-acrylic resin, a polyester resin, and a ketone resin. Aspect 10: The oil-in-water ink composition for a writing instrument according to any one of Aspects 1 to 9, wherein the aqueous phase does not contain a resin.

[0011] According to the present invention, it is possible to provide a novel oil-in-water ink composition for a writing instrument that can suppress blurring of drawn lines and improve the writing feel at the start of writing while improving DC resistance.

[0012] Oil-in-water ink composition for a writing instrument The oil-in-water ink composition for a writing instrument of the present invention comprises an oil phase contained in an aqueous phase in the form of oil droplets in water, the oil phase containing a resin and a polar lubricating oil, and the resin content is greater than 0.5% by mass relative to the mass of the oil phase.

[0013] The present inventors have found that the above-described configuration can improve DC resistance while suppressing the initial writing feel and blurring of drawn lines. Specifically, by incorporating a resin in the oil phase at the above-described content, when the writing instrument is not in use, the ink composition dries at the tip of the writing tip, such as the ballpoint of a ballpoint pen, to form a resin coating. Furthermore, because the oil phase is stably dispersed in the oil-in-water ink composition, uneven distribution of the resin can be suppressed compared to when the resin is incorporated into the aqueous phase. As a result, the oil-in-water ink composition of the present invention can maintain good DC resistance even after long-term storage.

[0014] Furthermore, by containing the resin in the oil phase at the above content, such DC resistance can be obtained without excessively increasing the resin content of the entire ink composition, thereby suppressing adverse effects on writing performance. Furthermore, by containing a polar lubricating oil in the oil phase together with the resin, a smooth writing feel can be obtained due to the affinity between the polar lubricating oil and the tip of the writing part, such as the ball of a ballpoint pen.

[0015] Each component of the present invention will be described below.

[0016] <Oil Phase> The oil phase is dispersed in the water phase in the state of an oil-in-water emulsion, and contains a resin and a polar lubricating oil.

[0017] The oil phase may further contain, as a solvent, a fatty acid having 10 or more carbon atoms, particularly a straight-chain fatty acid.

[0018] The oil phase may also contain other optional ingredients, such as colorants and oxygen scavengers.

[0019] From the viewpoint of writing properties, it is preferable that the oil phase does not contain any organic solvent other than fatty acids and alcohols having 10 or more carbon atoms. Examples of such organic solvents include the organic solvents listed for the aqueous phase.

[0020] (Polar lubricating oil) The polar lubricating oil refers to a substance known as a lubricating oil that has a polar group. Examples of such polar lubricating oils include ester-based lubricating oils and polyglycol-based lubricating oils.

[0021] Examples of ester-based lubricating oils include estolides, which are fatty acid oligomers formed by condensation of fatty acids having hydroxyl groups or condensation of fatty acids having hydroxyl groups and fatty acids not having hydroxyl groups, and esters of such estolides with alcohols.

[0022] As the fatty acid having a hydroxyl group in the estolide or ester that can be used in the oil phase, various conventionally used fatty acids can be used, and among them, it is preferable to use castor oil fatty acid whose main component is ricinoleic acid, hydrogenated castor oil fatty acid whose main component is 12-hydroxystearic acid, etc. These fatty acids may be used alone or in combination.

[0023] 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.

[0024] In the present invention, the above-mentioned fatty acid oligomers obtained by condensing fatty acids having hydroxyl groups, or fatty acid oligomers (estolides) obtained by condensing fatty acids having hydroxyl groups with fatty acids not having hydroxyl groups, can be used. Here, "fatty acid oligomer" refers to a condensation product of dimers 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.

[0025] The content of the polar lubricating oil may be 50% or more, 60% or more, or 70% or more, and may be 90% or less, or 85% or less, based on the mass of the oil phase.

[0026] (Resin) In the oil phase, the resin may be dissolved in the polar lubricating oil, or may be dispersed in the polar lubricating oil as a resin emulsion.

[0027] The resin may be any resin that can be used to fix the coating film, such as sulfonamide resin, maleic acid resin, terpene resin, terpene phenol resin, ester gum, xylene resin, alkyd resin, phenol resin, rosin, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl alcohol, acrylic resin, melamine resin, nitrocellulose resin, urea resin, or derivatives thereof. These resins may be used alone or in combination. Among them, styrene acrylic resin, polyester resin, and ketone resin are preferred from the viewpoint of DC resistance.

[0028] The acid value of the resin is preferably 0 KOHmg / g or more and 150 KOHmg / g or less from the viewpoint of promoting the formation of a resin coating. This acid value may be 150 KOHmg / g or less, 140 KOHmg / g or less, 130 KOHmg / g or less, 120 KOHmg / g or less, 110 KOHmg / g or less, 100 KOHmg / g or less, 90 KOHmg / g or less, 80 KOHmg / g or less, 70 KOHmg / g or less, or 60 KOHmg / g or less, or may be 0 KOHmg / g or more, 5 KOHmg / g or more, or 7 KOHmg / g or more. Here, "acid value" refers to the number of milligrams (mg) of potassium hydroxide required to neutralize the free fatty acids present in 1 g of sample. This acid value may be determined by referring to a catalog value.

[0029] The glass transition temperature (Tg) of the resin may be 0° C. or higher and 100° C. or lower. From the viewpoint of obtaining a DC resistance effect, the glass transition temperature is preferably 0° C. or higher, 5° C. or higher, 10° C. or higher, 15° C. or higher, 20° C. or higher, 25° C. or higher, 30° C. or higher, 35° C. or higher, 40° C. or higher, 45° C. or higher, 50° C. or higher, 55° C. or higher, or 65° C. or higher. From the viewpoint of suppressing blurring at the start of writing, the glass transition temperature is preferably 100° C. or lower, 95° C. or lower, 90° C. or lower, 85° C. or lower, 80° C. or lower, 75° C. or lower, or 70° C. or lower.

[0030] The glass transition temperature (Tg) can be determined in accordance with JIS K7121-1987. Specifically, for example, a 5 mg sample can be used and evaluated by raising the temperature at a rate of 10°C / min in an air atmosphere. In this case, the sample condition adjustment may be performed in accordance with JIS K7121, "Measurement of glass transition temperature after a certain heat treatment."

[0031] The resin content is greater than 0.5% by mass relative to the mass of the oil phase. This content is preferably 0.5% by mass or more, 1% by mass or more, 2% by mass or more, 3% by mass or more, 4% by mass or more, 5% by mass or more, 8% by mass or more, 10% by mass or more, 12% by mass or more, 15% by mass or more, or 16% by mass or more relative to the mass of the oil phase, from the viewpoint of promoting film formation at the pen tip and thereby improving DC resistance. This content may be 35% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, or 18% by mass or less, and a content of 30% by mass or less is particularly preferred from the viewpoint of achieving a moderate viscosity of the oil phase and thereby improving the initial writing feel and storage stability.

[0032] (Fatty Acid or Alcohol) The fatty acid is a fatty acid having 10 or more carbon atoms, particularly a straight-chain fatty acid. For such a fatty acid, reference can be made to the description of the fatty acid without a hydroxyl group given in relation to the estolide polar lubricating oil.

[0033] The alcohol has 10 or more carbon atoms. Examples of the alcohol that can be used include linear alcohols such as n-decanol, undecanol, n-decanol, tetradecanol, and heptadecanol, and branched alcohols such as 2-butyl-1-octanol, 2-hexyl-1-decanol, 2-octyl-1-decanol, 2-hexyl-1-dodecanol, 2-octyl-1-dodecanol, 8-methyl-(4-methylhexyl)-decanol, and 5,7,7-trimethyl-2-(1,3,3-trimethylbutyl)-octanol.

[0034] The content of the fatty acid or alcohol may be, for example, 1% by mass or more, 2% by mass or more, 3% by mass or more, 5% by mass or more, 7% by mass or more, 10% by mass or more, 12% by mass or more, or 15% by mass or more, and may be 30% by mass or less, 25% by mass or less, 20% by mass or less, or 17% by mass or less, relative to the mass of the oil phase. In particular, when the content of the fatty acid is 15% by mass or more, good writability can be obtained.

[0035] (Oxygen scavenger) The oxygen scavenger in the oil phase of the present invention may be any, but is preferably a water-insoluble oxygen scavenger from the viewpoint of affinity with the components of the oil phase. The oxygen scavenger may be present in a dissolved state or a dispersed state in the oil phase.

[0036] The water-insoluble oxygen scavenger is generally an oxygen scavenger having a solubility in water of less than 5 mg / L. It is preferable to use an organic water-insoluble oxygen scavenger as such a water-insoluble oxygen scavenger, in view of not affecting the color of the ink. Examples of such organic water-insoluble oxygen scavenger include tocopherol, terpene aldehyde, and derivatives thereof. Examples of derivatives that can be used include fatty acid esters such as formates, acetates, and propionates. The water-insoluble oxygen scavenger may be at least one selected from these.

[0037] The content of the oxygen scavenger may be 3% by weight or more and 20% by weight or less, based on the weight of the oil phase. This content may be 3% by weight or more, 4% by weight or more, or 5% by weight or more, based on the weight of the oil phase, and may be 20% by weight or less, 15% by weight or less, 13% by weight or less, 10% by weight or less, 8% by weight or less, or 6% by weight or less.

[0038] (Colorant) 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. These colorants can be used alone or in combination.

[0039] As the dye, a water-insoluble dye can be used. A water-insoluble dye is a dye that is insoluble in water at room temperature, particularly a dye that has a solubility in water of 1 g / L or less at 20°C. Examples of such water-insoluble dyes that can be used include salt-forming dyes, disperse dyes, and oil-soluble dyes. Among these, salt-forming dyes are preferred from the viewpoint of color development properties.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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 an oxygen scavenger, a light stabilizer, and a sensitizer, so as to have a predetermined average particle size (e.g., 0.1 to 6 μm).

[0048] 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).

[0049] 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.)].

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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 mass of the oil-in-water ink composition for a writing instrument, 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.

[0055] <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.

[0056] 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.

[0057] 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 the oil phase f particles by the long ethylene oxide chain.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] The content of the emulsifier 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.

[0062] <Aqueous Phase> The aqueous phase contains at least water. The aqueous phase may contain a colorant.

[0063] In order to improve the writing performance of the oil-in-water ink for a writing instrument, it is preferable that the aqueous phase has a low resin content. Specifically, the resin content in the aqueous phase is preferably 1.5% by mass or less, 1.2% by mass or less, 1.0% by mass or less, 0.5% by mass or less, 0.3% by mass or less, or 0.1% by mass or less, based on the mass of the aqueous phase, or the aqueous phase is preferably free of resin. Examples of such resins include the resins listed for the oil phase.

[0064] The aqueous phase may further contain a resin, an organic solvent, and the like.

[0065] (Water) Purified water, ion-exchanged water, etc. can be used as the water.

[0066] (Organic Solvent) The organic solvent in the aqueous phase is not particularly limited as long as it is an organic solvent that can be dissolved in water, and for example, alcohols, polyhydric alcohols, glycol ethers, etc. can be used. These solvents can be used alone or in combination. As these solvents, those listed for the oil phase can be used.

[0067] 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, and 2-methylcyclohexanol.

[0068] 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.

[0069] 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.

[0070] (Colorant) 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. These colorants can be used alone or in combination.

[0071] 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.

[0072] As the pigment, those mentioned for the oil phase can be used.

[0073] 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.

[0074] <Other Components> Examples of other components include dispersants, leveling agents, rust inhibitors, antiseptics, lubricants, and surface conditioners. Examples of leveling agents that can be used include fluorine-based surfactants, silicone oils, and phosphate ester surfactants. Examples of surface conditioners that can be used include silicon-based surface conditioners.

[0075] <Writing Instrument> A writing instrument contains the oil-in-water ink composition for a writing instrument. The writing instrument may include an ink reservoir, a writing portion, and a holding portion, and in this case, the ink reservoir may store the oil-in-water ink. The writing instrument may be a ballpoint pen.

[0076] <Ink Storage Unit> The ink storage unit stores the oil-in-water ink composition for a writing instrument described above.

[0077] 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.

[0078] The ink reservoir may also be integral with the writing element, and in particular where the writing instrument is a ballpoint pen, the ink reservoir may be a refill for the writing instrument.

[0079] 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 intrusion of oxygen into the ink and thereby suppressing the generation of bubbles.

[0080] <Writing Part> The writing part can be a writing part having a ballpoint pen tip at the tip.

[0081] A ballpoint pen tip may be composed of a ball and a holder that rotatably holds the ball. The ball may be composed of any material used for ballpoint pen balls, such as stainless steel, cemented carbide, ceramics, etc. The shape of the ballpoint pen tip is not particularly limited, and may be, for example, bullet-shaped or needle-shaped.

[0082] Furthermore, from the viewpoint of writing feel, it is desirable that the surface roughness Ra of the ball is less than 10 nm, and it is particularly preferable that the surface roughness Ra of the writing ball is 4 nm or less.

[0083] 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).

[0084] 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.

[0085] The present invention will be specifically explained with reference to examples and comparative examples, but the present invention is not limited to these.

[0086] Preparation of Oil-in-Water Ink Composition for Writing Instruments Example 1 7.5 parts by mass of a condensed fatty acid ester (Minerazol LB-601, Ito Oil Mills, Ltd., Ester A) as a polar lubricant, 2 parts by mass of oleic acid (Lunac OV, Kao Corporation) as a fatty acid, 0.5 parts by mass of dl-α-tocopherol (Tocopherol, Mitsubishi Chemical Corporation, Tocopherol A) as an oxygen scavenger, and 2 parts by mass of a styrene acrylic resin (Joncryl 63J, BASF) as a resin were mixed, and the mixture was heated to a temperature of 50°C to 60°C with stirring to completely dissolve the ingredients, thereby obtaining 12 parts by mass of an oily solution.

[0087] Separately, 5 parts by mass of polyoxyethylene styrenated phenyl ether (Newcol N780 (ethylene oxide 80 mol adduct), Nippon Nyukazai Co., Ltd.) as an emulsifier component was dissolved in 35 parts by mass of purified water with stirring to prepare an emulsifier solution. 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), thereby obtaining an oil-in-water emulsion.

[0088] Thereafter, a pigment dispersion was added to this oil-in-water emulsion with stirring, yielding 100 parts by mass of the writing instrument ink composition of Example 1. The pigment dispersion consisted of 6.7 parts by mass of carbon black as the pigment, 2 parts by mass of ethylene glycol as the organic solvent, 0.6 parts by mass of a 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 37.6 parts by mass of water. Details of the emulsifier solution, pigment dispersion components, and additive components used are shown in Table 1.

[0089] Examples 2 to 9 and Comparative Examples 1 to 6 Oil-in-water ink compositions for writing instruments of Examples 2 to 9 and Comparative Examples 1 to 6 were prepared in the same manner as in Example 1, except that the type and content of each component was changed as shown in Tables 1 to 4. Details of the components shown in Tables 1 to 4 are as follows. Ester B: condensed fatty acid ester (Minerazol LB-601, Ito Oil Mills, Ltd.) Ester C: ricinoleic acid derivative ester (KF-825E, KF Trading Co., Ltd.) PPG: polypropylene glycol (Uniol D-4000, NOF Corporation) Paraffin: liquid paraffin (liquid paraffin No. 150-S, Sanko Chemical Industry Co., Ltd.) Silicone: silicone oil (KF-96, Shin-Etsu Silicones Co., Ltd.) Styrene acrylic: styrene acrylic resin (Joncryl 63J, BASF, Tg: 73°C) Polyester: polyester resin (Elitel UE-9200, Unitika Ltd., Tg: 65°C) Ketone: ketone resin (Variplus SK, TEGO, Tg: 90°C) Emulsion: polyester resin emulsion (Elitel KT8803, Unitika Ltd.)

[0090] <Evaluation> Each of the prepared oil-in-water ink compositions for writing instruments was filled into a ballpoint pen to prepare a ballpoint pen. Specifically, a ballpoint pen (Signo UM-100, Mitsubishi Pencil Co., Ltd.) was used, and the refill consisted 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 alloy ball, ball diameter 0.38 mm, surface roughness less than 10 nm), and a joint connecting the reservoir tube and the tip. The ink composition and an ink follower were loaded into the rear end of the ink. These were used to carry out the following evaluation tests.

[0091] <Direct Current Resistance> The prepared ballpoint pen was placed in an environment of 25°C and 60% relative humidity, and left facing down with the cap removed for one day. The initial resistance to direct current was evaluated by visually observing leakage of ink from the tip of the ballpoint pen. The evaluation criteria are as follows: A: No leakage at all. B: Leakage was observed to the extent that droplets formed around the ballpoint pen tip. C: Liquid dripped from the ballpoint pen tip.

[0092] The ballpoint pens thus produced were stored for one week in an environment of 25° C. and 60% relative humidity, and then the same test as above was carried out to evaluate the DC resistance after long-term storage.

[0093] <Writing Feel> Writing was carried out and the writing feel was evaluated sensorily. The evaluation criteria are as follows: A: The writing feel was smooth. B: There was a slight scratchy feeling. C: There was a significant scratchy feeling.

[0094] <Smearing of drawn lines> A machine writing test was conducted in which a 1000 m (final stroke) spiral was written under conditions of a load of 100 gf, a writing angle of 75 degrees, and a writing speed of 4.5 mm / min, and the appearance of the drawn lines was evaluated visually. The evaluation criteria are as follows: A: No smearing of the drawn lines was observed. B: Slight smearing of the drawn lines was observed. C: Significant smearing of the drawn lines was observed.

[0095] The configurations and evaluation results of the examples and comparative examples are shown in Tables 1 to 4.

[0096]

[0097]

[0098]

[0099] It can be seen from Tables 1 to 4 that the oil-in-water ink composition for a writing instrument of the present invention, i.e., the oil phase is contained in the form of oil droplets in water relative to the aqueous phase, the oil phase contains a resin and a polar lubricating oil, and the resin content is greater than 0.5% by mass relative to the mass of the oil phase, can improve the direct current resistance while suppressing the feeling of writing at the start of writing and the blurring of drawn lines.

Claims

1. An oil-in-water type ink composition for writing instruments, wherein an oil phase is contained in an aqueous phase in the form of oil droplets in water, the oil phase contains a resin and a polar lubricating oil, and the content of the resin is more than 0.5% by mass based on the mass of the oil phase.

2. The oil-in-water type ink composition for writing instruments according to claim 1, wherein the oil phase further contains a fatty acid having 10 or more carbon atoms or an alcohol having 10 or more carbon atoms.

3. The oil-in-water type ink composition for writing instruments according to claim 2, wherein the fatty acid is a linear fatty acid.

4. The oil-in-water type ink composition for writing instruments according to claim 2 or 3, wherein the content of the fatty acid is 15% by mass or more based on the mass of the oil phase.

5. The oil-in-water type ink composition for writing instruments according to any one of claims 1 to 4, wherein the polar lubricating oil is an ester-based lubricating oil or a polyglycol-based lubricating oil.

6. The oil-in-water type ink composition for writing instruments according to claim 5, wherein the polar lubricating oil is an estolide which is a fatty acid oligomer obtained by condensation of fatty acids having a hydroxyl group 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 and an alcohol.

7. The oil-in-water type ink composition for writing instruments according to any one of claims 1 to 6, wherein the acid value of the polar lubricating oil is 150 or less.

8. The oil-in-water type ink composition for writing instruments according to any one of claims 1 to 7, wherein the glass transition temperature of the resin is 100°C or less.

9. The oil-in-water type ink composition for writing instruments according to any one of claims 1 to 8, wherein the resin is selected from the group consisting of a styrene acrylic resin, a polyester resin, and a ketone resin.

10. The oil-in-water type ink composition for writing instruments according to any one of claims 1 to 9, wherein the aqueous phase does not contain a resin.

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