Oil-in-water ink composition for writing instruments

Abstract

To provide a novel oil-in-water ink composition for writing instruments that can suppress scratchiness at the start of writing and line skipping while maintaining excellent direct-current resistance.SOLUTION: The oil-in-water ink composition for writing instruments includes an oil phase in an aqueous phase in a state of oil droplets in water, where the oil phase contains a resin and a polar lubricating oil, and where the resin content is more than 0.5 mass% relative to the mass of the oil phase.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous oil-drop type ink composition for writing instruments.

Background Art

[0002] As a characteristic of aqueous ballpoint pens, it can be mentioned that the writing feeling is light, but on the other hand, a scratching feeling is often felt. In addition, water-soluble dyes used as colorants have the advantage of high coloring power and high freedom in color mixing, but have low weather resistance, and when water adheres to the drawn line, there is a problem that the drawn line easily bleeds.

[0003] Oil-based ballpoint pens have the advantage of no scratching feeling during writing and little bleeding on the drawn line, but often have a heavy writing feel. In addition, oil-soluble dyes used as colorants have water resistance, and bleeding does not occur when water adheres to the drawn line as described above.

[0004] In recent years, oil-based ballpoint pens have also been developed in which the viscosity of the oil-based ink is reduced to improve the writing feel. However, since low-viscosity oil-based inks have a large writing outflow amount, the drying property of the drawn line deteriorates, causing ink bleeding through the paper and blobbing.

[0005] In response to such problems, as a means capable of achieving both the good writing feel of the aqueous phase and the water resistance of the oil-soluble dye, an ink composition for aqueous ballpoint pens in which the ink property is an oil-in-water emulsion (O / W emulsion) has been disclosed.

[0006] In Patent Document 1, an ink composition for aqueous ballpoint pens in which an oil phase is contained in a state of an oil-in-water emulsion with respect to an aqueous phase, wherein at least one of the oil phase or the aqueous phase contains a colorant, and the oil phase is an estolide in which fatty acids having a hydroxyl group are condensed with each other or a fatty acid having a hydroxyl group and a fatty acid having no hydroxyl group are condensed among the components constituting the oil phase, or an ester of the estolide and an alcohol. An ink composition for aqueous ballpoint pens characterized by containing is disclosed.

[0007] In Patent Document 2, there is disclosed an aqueous ballpoint pen ink composition in which an oil phase is contained in the form of oil-in-water droplets with respect to an aqueous phase, 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.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention provides a novel aqueous oil-in-water droplet ink composition for writing instruments that can suppress the writing feel during writing and the streaks of the drawn line while improving the DC resistance.

Means for Solving the Problems

[0010] As a result of intensive studies, 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 phase is contained in the form of oil-in-water droplets with respect to an aqueous phase, the oil phase contains a resin and a polar lubricating oil, and the content of the resin is more than 0.5% by mass with respect to the mass of the oil phase, an aqueous oil-in-water droplet ink composition for writing instruments. <Aspect 2> The aqueous oil-in-water droplet ink composition for writing instruments 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 aqueous oil-in-water droplet ink composition for writing instruments according to Aspect 2, wherein the fatty acid is a straight-chain fatty acid. <Aspect 4> The aqueous oil droplet type ink composition for writing instruments according to Aspect 2 or 3, wherein the content of the fatty acid is 15% by mass or more based on the mass of the oil phase. <Aspect 5> The aqueous oil droplet type ink composition for writing instruments 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 aqueous oil droplet type ink composition for writing instruments according to Aspect 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. <Aspect 7> The aqueous oil droplet type ink composition for writing instruments according to any one of Aspects 1 to 6, wherein the acid value of the polar lubricating oil is 150 or less. <Aspect 8> The aqueous oil droplet type ink composition for writing instruments according to any one of Aspects 1 to 7, wherein the glass transition temperature of the resin is 100 ° C or less. <Aspect 9> The aqueous oil droplet type ink composition for writing instruments 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 aqueous oil droplet type ink composition for writing instruments according to any one of Aspects 1 to 9, wherein the aqueous phase does not contain a resin.

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a novel aqueous oil droplet type ink composition for writing instruments that can suppress the writing feel during writing and the streaks of the drawn line while improving the DC resistance.

Modes for Carrying Out the Invention

[0012] 《Aqueous Oil Droplet Type Ink Composition for Writing Instruments》 The aqueous oil droplet type ink composition for writing instruments of the present invention contains an oil phase in the form of oil droplets in water with respect to the aqueous phase, 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.

[0013] The inventors have found that with the above configuration, while improving the DC resistance, it is possible to suppress the writing feel during writing and the streaking of the drawn lines. Specifically, when the resin is contained in the oil phase at the above content rate, when the writing instrument is not in use, the ink composition at the tip of the writing part like the ball of the ballpoint pen dries and a resin film is formed. Further, since the oil phase is stably dispersed in the water-in-oil type ink composition, the uneven distribution of the resin can be suppressed as compared with the case where the resin is contained in the water phase. As a result, the water-in-oil type ink composition of the present invention can maintain good DC resistance even after long-term storage.

[0014] Also, when the resin is contained in the oil phase at the above content rate, such DC resistance can be obtained without excessively increasing the resin content rate of the entire ink composition, so that the adverse effect on the writing performance can be suppressed. Further, when the oil phase contains a polar lubricating oil 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 like the ball of the ballpoint pen.

[0015] Hereinafter, each component of the present invention will be described.

[0016] 〈Oil phase〉 The oil phase is dispersed in a water-in-oil type emulsion state with respect to the water phase, and contains a resin and a polar lubricating oil.

[0017] Further, the oil phase may further contain a fatty acid having 10 or more carbon atoms, particularly a linear fatty acid, as a solvent.

[0018] Further, the oil phase may contain any other components. Examples of other components include a coloring material and an oxygen scavenger.

[0019] Further, from the viewpoint of writing performance, it is preferable that the oil phase does not contain an organic solvent other than a fatty acid and an alcohol having 10 or more carbon atoms. Examples of such an organic solvent include the organic solvents mentioned for the water phase.

[0020] (Polar lubricating oil) The polar lubricating oil means a substance known as a lubricating oil that has a polar group among substances known as lubricating oils. As such polar lubricating oils, ester-based lubricating oils, polyglycol-based lubricating oils, etc. can be used.

[0021] Examples of ester-based lubricating oils include estolides which are fatty acid oligomers obtained by condensation of fatty acids having a hydroxyl group or condensation of a fatty acid having a hydroxyl group and a fatty acid having no hydroxyl group, or esters of such estolides and 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. 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] Examples of fatty acids having no hydroxyl group 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, linolenic acid, etc. Furthermore, coconut oil fatty acid, palm oil fatty acid, olive oil fatty acid, beef tallow fatty acid, hydrogenated beef tallow fatty acid, etc. containing these components can also be used.

[0024] In the present invention, fatty acid oligomers obtained by condensing the above-described fatty acids having a hydroxyl group, or fatty acid oligomers (estolides) obtained by condensing a fatty acid having a hydroxyl group and a fatty acid having no hydroxyl group can be used. Here, the "fatty acid oligomer" means a condensate of dimer or higher. Those of dimer to heptamer are preferable. Monomers may be mixed in the fatty acid oligomer, but from the viewpoint of solubility in the oil phase, it is preferable that the average of the whole fatty acid oligomer is 1.5-mer or more, preferably 2.0-mer or more.

[0025] The content rate of the polar lubricating oil may be 50% or more, 60% or more, or 70% or more with respect to the mass of the oil phase, and may also be 90% or less, or 85% or less.

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

[0027] As the resin, any resin that can be used for fixing the coating film can be used. For example, sulfonamide resin, maleic acid resin, terpene resin, terpene phenol resin, ester gum, xylene resin, alkyd resin, phenol resin, rosin, polyvinyl pyrrolidone, polyvinyl acetal, polyvinyl alcohol, acrylic resin, melamine resin, nitrocellulose resin, urea resin, etc., and derivatives thereof can be used. These resins may be used alone or in combination. Among these resins, it is preferable to use styrene acrylic resin, polyester resin, and ketone resin from the viewpoint of DC resistance.

[0028] From the viewpoint of promoting the formation of the film by the resin, the acid value of the resin is preferably 0 KOHmg / g or more and 150 KOHmg / g or less. 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, and may also be 0 KOHmg / g or more, 5 KOHmg / g or more, or 7 KOHmg / g or more. Here, the "acid value" means the number of milligrams (mg) of potassium hydroxide required to neutralize the free fatty acid present in 1 g of the sample. The value of this acid value may refer to the 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, it is preferable that this glass transition temperature is 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 scratching during writing, it is preferable that this glass transition temperature is 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] Here, the glass transition temperature (Tg) can be determined according to JIS K7121-1987. Specifically, for example, using a 5 mg sample, it can be evaluated by heating at a heating rate of 10°C / min under an air atmosphere. In this case, for the sample conditioning, "When measuring the glass transition temperature after performing a certain heat treatment" in JIS K7121 may be adopted.

[0031] The content of the resin is more than 0.5% by mass based on the mass of the oil phase. From the viewpoint of promoting film formation at the pen tip and thereby improving the DC resistance, it is preferable that this content is 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 based on the mass of the oil phase. 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 particularly being 30% by mass or less is preferable from the viewpoint of making the viscosity of the oil phase appropriate and thereby improving the writing feel and storage stability during writing.

[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 fatty acids, for example, reference can be made to the description of fatty acids having no hydroxyl group mentioned for the estolide of polar lubricating oil.

[0033] The alcohol is an alcohol having 10 or more carbon atoms. As this alcohol, linear alcohols such as n-decanol, undecanol, n-decanol, tetradecanol, heptadecanol, etc., 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, 5,7,7-trimethyl-2-(1,3,3-trimethylbutyl)-octanol, etc. can be used.

[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 with respect to the mass of the oil phase, and may also be 30% by mass or less, 25% by mass or less, 20% by mass or less, or 17% by mass or less. In particular, when the content of the fatty acid is 15% by mass or more, good writing properties can be obtained.

[0035] (Oxygen scavenger) The oxygen scavenger in the oil phase of the present invention may be optional, but it is preferable from the viewpoint of affinity with the components of the oil phase that it is a water-insoluble oxygen scavenger. Also, the oxygen scavenger may be present in a dissolved state in the oil phase or in 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. As such a water-insoluble oxygen scavenger, it is preferable from the viewpoint of not affecting the color of the ink to use an organic water-insoluble oxygen scavenger. As such an organic water-insoluble oxygen scavenger, for example, organic water-insoluble oxygen scavengers such as tocopherol, terpene aldehyde and its derivatives can be used. As the derivative, for example, fatty acid esters such as formate, acetate, and propionate can be used. The water-insoluble oxygen scavenger may be at least one selected from among these.

[0037] The content rate of the oxygen scavenger may be 3% by mass or more and 20% by mass or less with respect to the mass of the oil phase. This content rate may be 3% by mass or more, 4% by mass or more, or 5% by mass with respect to the mass of the oil phase, and may also be 20% by mass or less, 15% by mass or less, 13% by mass or less, 10% by mass or less, 8% by mass or less, or 6% by mass or less.

[0038] (Colorant) As the colorant, various colorants that can be used in conventional inks, such as dyes, pigments, or a mixture of dyes and pigments, can be used. These colorants may be used alone or in combination.

[0039] As the dye, water-insoluble dyes can be used. Water-insoluble dyes are dyes that are insoluble in water at normal temperature, particularly dyes with a solubility in water at 20 °C of 1 g / L or less. As such water-insoluble dyes, for example, salt-forming dyes, disperse dyes, oil-soluble dyes, etc. can be used. Among them, from the viewpoint of color development properties, it is preferable to use salt-forming dyes.

[0040] Examples of salt-forming dyes include dyes having chemical structures such as azo-based, metal complex azo-based, anthraquinone-based, and metal phthalocyanine-based. 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, Valifast (registered trademark) Yellow 1101, etc. of Orient Chemical Industry Co., Ltd. can be used.

[0041] As the disperse dye, for example, at least one dye selected from 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.

[0042] As the oil-soluble dye, for example, Oil Black 860, Oil Blue 613, Oil Brown BB, Oil Green 530, Oil Orange 201, Oil Pink 312, Oil Red 5B, Oil Scarlet 318, Oil Yellow 105, etc. of Orient Chemical Industries, Ltd. can be used.

[0043] As the pigment, conventionally known inorganic and organic pigments such as titanium oxide, resin particle pigments containing pigments or dyes, pseudo-pigments obtained by coloring resin emulsions with dyes or pigments, white plastic pigments, bright pigments, pigments having a substrate of silica or mica and a multilayer coating of iron oxide, titanium oxide, etc. on the surface layer, thermochromic pigments, photochromic particles, etc. can be used without limitation.

[0044] As the inorganic pigment, for example, 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, lead yellow, molybdate orange, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine, precipitated barium sulfate, barite powder, calcium carbonate, lead white, ultramarine white, ultramarine blue, manganese violet, aluminum powder, brass powder, etc. can be used.

[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, for example, 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. Pigment Violet 23, C.I. Pigment Violet 50, C.I. Pigment Green 7, etc.

[0046] Examples of thermochromic pigments include thermochromic pigments produced by microencapsulating a thermochromic composition containing at least a leuco dye that functions as a color former, a developer that is a component having the ability to cause the leuco dye to develop color, and a discoloration temperature adjuster that can control the discoloration temperature in the color development of the leuco dye and the developer so as to have a predetermined average particle diameter (for example, 0.1 to 6 μm). This average particle diameter 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.

[0047] Examples of photochromic particles include photochromic particles composed of at least one selected from photochromic substances such as photochromic dyes (compounds) and fluorescent dyes, and a resin such as terpene phenol resin. Also, examples of photochromic particles include photochromic particles produced by microencapsulating a photochromic composition containing at least one selected from photochromic substances such as photochromic dyes (compounds) and fluorescent dyes, an organic solvent, and additives such as an oxygen scavenger, a light stabilizer, and a sensitizer so as to have a predetermined average particle diameter (for example, 0.1 to 6 μm).

[0048] By suitably using the above photochromic substances, 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 have the property of developing color in an ultraviolet irradiation environment (irradiation with a wavelength of 200 to 400 nm, irradiation environment with sunlight containing ultraviolet rays).

[0049] In the present invention (including examples, etc.), the "average particle diameter" is appropriately selected according to the size of the particles to be measured. In the case of particles with a size of less than approximately 1 μm, it is the value of the histogram average particle diameter (D50) calculated on a volume basis in the scattering intensity distribution measured by the dynamic light scattering method. In the case of particles with a size of 1 μm or more, it is the value of the median diameter (D50) calculated on a volume basis in the laser diffraction method. The measurement of the average particle diameter can be carried out using a particle size analyzer [Microtrac HRA9320-X100 (Nikkiso Co., Ltd.)].

[0050] Examples of the microencapsulation method for the above thermochromic pigment and the above photochromic particles include, for example, an interfacial polymerization method, an interfacial polycondensation method, an in-situ polymerization method, a liquid-phase curing coating method, a phase separation method from an aqueous solution, a phase separation method from an organic solvent, a melt dispersion cooling method, an air suspension coating method, a spray drying method, etc., and can be appropriately selected according to the application.

[0051] For example, in the 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 performing the following steps in this order: (1) Heating and melting a leuco dye, a developer, and a discoloration temperature adjuster. (2) Pouring the heated and melted leuco dye, developer, and discoloration temperature adjuster into an emulsifier solution, heating and stirring to disperse them in the form of oil droplets to prepare a dispersion. (3) As a capsule film agent, a resin raw material capable of forming a wall film such as a urethane resin, an epoxy resin, an amino resin, etc., for example, an amino resin solution, specifically, an amino resin solution such as an aqueous solution of methylol melamine, a urea solution, a benzoguanamine solution, etc., is gradually poured into the above dispersion, and this resin raw material is reacted to form a capsule film, thereby obtaining a thermochromic microcapsule pigment, and (4) Filtering this dispersion containing the thermochromic microcapsule pigment.

[0052] In this thermochromic pigment, by suitably combining the types, amounts, etc. of the leuco dye, the developer, and the discoloration temperature adjuster, the color development temperature and the discoloration temperature of each color can be set to suitable temperatures.

[0053] These colorants can be used alone or in combination of two or more. Among these colorants, the average particle diameters of pigments dispersed in water, resin particle pigments, pseudo pigments, white plastic pigments, pigments with multilayer coatings, thermochromic pigments, photochromic particles, etc. vary depending on the ball diameter, ink composition, viscosity, etc., but those with an average particle diameter of 0.02 to 6 μm are desirable. This average particle diameter can 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 can 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.

[0054] The content of these colorants can be appropriately increased or decreased according to the line drawing density of the ink. However, it can 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, 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 with respect to the mass of the aqueous oil droplet type ink composition for writing instruments.

[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 can be used.

[0056] As the aromatic emulsifier that can be used in the ink composition of the present invention, as long as it has one or more aromatic rings, it is not particularly limited. For example, polyoxyethylene distyrenated phenyl ether, polyoxyethylene monostyrenated phenyl ether, polyoxyethylene cumyl phenyl ether and other polycyclic phenyl type nonionic surfactants, and ionic surfactants such as sulfates thereof can be used.

[0057] From the viewpoint of suppressing the coalescence of oil phase f particles by the long-chain ethylene oxide chain, the number of moles of ethylene oxide (EO) added to the above emulsifier is preferably 40 mol or more, 45 mol or more, or 50 mol or more.

[0058] In addition to the above emulsifier, an emulsifier having a low number of moles of ethylene oxide added and a strong orientation to the oil phase may be further used. Specifically, an emulsifier having 3 mol or more, 4 mol or more, or 5 mol or more of ethylene oxide added and 15 mol or less, 12 mol or less, or 10 mol or less of ethylene oxide added. Combining an emulsifier with a strong orientation to the oil phase and an emulsifier with a strong orientation to the water phase may be preferable from the viewpoint of increasing the micelle concentration at the interface and improving the stability of the emulsion.

[0059] Regarding the HLB value (hydrophilic-lipophilic balance value), for nonionic surfactants, it is preferable to use one or more emulsifiers having an HLB value of at least 15 or more from the viewpoint of suppressing excessive mixing of the emulsifier into the oil phase.

[0060] As the emulsifier component, in addition to the surfactant having an aromatic ring in the molecule, any emulsifier having another 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-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 with respect to 100 parts by mass of the oil phase, 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.

[0062] 〈Aqueous phase〉 The aqueous phase contains at least water. The aqueous phase may contain a coloring agent.

[0063] In the aqueous phase, it is preferable that the resin content is low from the viewpoint of improving the writing performance of the oil-in-water type ink for writing instruments. Specifically, the resin content in the aqueous phase is 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 with respect to the mass of the aqueous phase, or it is preferable that the aqueous phase does not contain resin. Examples of such resins include the resins mentioned for the oil phase.

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

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

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

[0067] As the alcohols, for example, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butyl alcohol, 1-pentanol, isoamyl alcohol, sec-amyl alcohol, 3-pentanol, tert-amyl alcohol, n-hexanol, methyl amyl alcohol, 2-ethylbutanol, n-heptanol, 2-heptanol, 3-heptanol, n-octanol, 2-octanol, 2-ethylhexanol, 3,5,5-trimethylhexanol, nonanol, n-decanol, undecanol, n-decanol, trimethylnonyl alcohol, tetradecanol, heptadecanol, cyclohexanol, 2-methylcyclohexanol, etc. can be used.

[0068] As the polyhydric alcohols, for example, 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, etc. can be used.

[0069] Examples of glycol ethers 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, tetrapropylene glycol monobutyl ether, etc. can be used.

[0070] (Colorant) As the colorant, various colorants that can be used in conventional inks, such as dyes, pigments, or mixtures of dyes and pigments, etc., can be used. These colorants may be used alone or in combination.

[0071] As the dye, a water-soluble dye can be used. As the water-soluble dye, any dye that can be dissolved or dispersed in water can be used. For example, acid dyes such as eosin, phloxine, water yellow #6-C, acid red, water blue #105, brilliant blue FCF, nigrosine NB, etc.; direct dyes such as direct black 154, direct sky blue 5B, violet BB, etc.; basic dyes such as rhodamine, methyl violet, etc.

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

[0073] The content of these colorants can be appropriately increased or decreased according to the line drawing density of the ink. However, it 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, 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 based on the total amount of the water-in-oil droplet type ink composition.

[0074] 〈Other components〉 Examples of other components include a dispersant, a leveling agent, a rust inhibitor, a preservative, a lubricant, a surface conditioner, etc. As the leveling agent, for example, a fluorine-based surfactant, silicone oil, a phosphate ester-based surfactant, etc. can be used. As the surface conditioner, a silicone-based surface conditioner, etc. can be used.

[0075] 《Writing instrument》 The writing instrument contains the above-mentioned water-in-oil droplet type ink composition for writing instruments. The writing instrument may include an ink storage part, a writing part, and a holding part. In this case, the water-in-oil droplet type ink may be stored in the ink storage part. The writing instrument may be a ballpoint pen.

[0076] 〈Ink storage part〉 The above-mentioned water-in-oil droplet type ink composition for writing instruments is stored in the ink storage part.

[0077] The ink storage unit can be any object as long as it can store ink and supply the ink to the writing unit. It may be a direct liquid type equipped with a collector structure (ink holding mechanism), or it may be a cotton core type ink storage unit.

[0078] Also, the ink storage unit may be integrated with the writing unit. In particular, when the writing instrument is a ballpoint pen, the ink storage unit may be a refill for the writing instrument.

[0079] In particular, when the ink storage unit is a refill for a ballpoint pen, the thickness of the outer wall of the ink storage unit, that is, the value of (outer diameter - inner diameter) / 2 of the ink storage unit, 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, which is preferable from the viewpoint of suppressing the intrusion of oxygen into the ink and thereby suppressing the generation of bubbles.

[0080] 〈Writing unit〉 The writing unit can be a writing unit having a ballpoint pen tip at its tip.

[0081] The 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 the ball of a ballpoint pen, for example, stainless steel, cemented carbide, ceramics, etc. Also, the shape of the ballpoint pen tip is not particularly limited, and may be, for example, a bullet shape, a needle shape, etc.

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

[0083] In addition, the "surface roughness Ra" in the present invention (including the embodiments described later) was set under the conditions of a lens magnification of 50 times, an evaluation length of 100 μm, and a Gaussian filter of 25 μm using a non-contact surface shape measuring machine (NewView7200, Zygo Corporation), and the measurement was performed in accordance with JIS B0601 (Geometric Product Specifications - Surface Texture) otherwise.

[0084] 〈Holding part〉 The holding part may be a part that enables the writing instrument of the present invention to be held by hand and may have a hollow structure capable of storing the ink storage part. The holding part may have a shape such as a cylindrical shape or a polygonal cylindrical shape, for example.

Example

[0085] The present invention will be specifically described by way of examples and comparative examples, but the present invention is not limited thereto.

[0086] 《Preparation of an oil-in-water droplet type ink composition for writing instruments》 〈Example 1〉 7.5 parts by mass of a condensed fatty acid ester (Minerazol LB-601, Ito Oil Co., Ltd., Ester A) as a polar lubricating oil, 2 parts by mass of oleic acid (Lunac OV, Kao Corporation) as a fatty acid, and 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 these were heated to a temperature of 50°C to 60°C while stirring to obtain 12 parts by mass of an oily solution in which these were completely dissolved.

[0087] Separately, 5 parts by mass of polyoxyethylene styrenated phenyl ether (Newcol N780 (ethylene oxide 80 mol adduct), Nippon Emulsifier Co., Ltd.) as an emulsifier component was dissolved in 35 parts by mass of purified water while stirring to prepare an emulsifier solution. Next, the emulsifier solution was gradually added to the oily solution to invert the phase from an oil-in-water droplet type (w / o) to an oil-in-water type (o / w) to obtain an oil-in-water droplet type emulsion.

[0088] Thereafter, while stirring, a pigment dispersion was added to this water-in-oil emulsion to obtain 100 parts by mass of the ink composition for writing instruments of Example 1. The pigment dispersion consisted of 6.7 parts by mass of carbon black as a pigment, 2 parts by mass of ethylene glycol as an 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> Except that the types and contents of the respective components were changed as shown in Tables 1 to 4, water-in-oil 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. Details of the components shown in Tables 1 to 4 are as follows. Ester B: Condensed fatty acid ester (Minerazol LB-601, Ito Seiyu Co., Ltd.) Ester C: Ricinoleic acid derivative ester (KF-825E, KF Trading Co., Ltd.) PPG: Polypropylene glycol (Unionol D-4000, NOF Corporation) Paraffin: Liquid paraffin (Liquid Paraffin No. 150-S, Sanko Chemical Industry Co., Ltd.) Silicone: Silicone oil (KF-96, Shin-Etsu Silicone Co., Ltd.) Styrene acrylic: Styrene acrylic resin (Joncryl63J, BASF, Tg: 73°C) Polyester: Polyester resin (Erythel UE-9200, Unitika Ltd., Tg: 65°C) Ketone: Ketone resin (Variplus SK, TEGO, Tg: 90°C) Emulsion: Polyester resin emulsion (Erythel KT8803, Unitika Ltd.)

[0090] <Evaluation> The prepared water-in-oil droplet type ink composition for writing instruments was filled into ballpoint pens respectively to produce ballpoint pens. Specifically, the shaft of a ballpoint pen (Signo UM-100, Mitsubishi Pencil Co., Ltd.) was used, and an ink storage tube made of polypropylene with an outer diameter of 60 mm, an inner diameter of 3.8 mm, and a length of 113 mm, a stainless steel tip (a carbide ball with a ball diameter of 0.38 mm and a surface roughness of less than 10 nm), and a refill consisting of a joint connecting the storage tube and the tip were loaded with the above ink composition and an ink follower at the rear end of the ink. Using these, the following evaluation tests were conducted.

[0091] 〈DC Resistance〉 The produced ballpoint pen was placed in an environment with a temperature of 25°C and a relative humidity of 60%, left downward for one day with the cap removed, and the leakage of ink from the tip of the ballpoint pen was visually observed to evaluate the initial DC resistance. The evaluation criteria are as follows. A: There was no leakage at all. B: There was leakage to the extent that droplets formed around the ballpoint pen tip. C: The liquid was dripping or falling from the ballpoint pen tip.

[0092] Also, after storing the produced ballpoint pen in an environment with a temperature of 25°C and a relative humidity of 60% for one week, the same test as above was conducted to evaluate the DC resistance after long-term storage.

[0093] 〈Writing Feel〉 Writing was carried out, and the writing feel was evaluated by sensory evaluation. The evaluation criteria are as follows. A: It had a smooth writing feel. B: There was a slightly scratchy feeling. C: There was a significant scratchy feeling.

[0094] 〈Scratch of the Drawn Line〉 Under the conditions of a load of 100 gf, a writing angle of 75 degrees, and a writing speed of 4.5 mm / min, a mechanical writing test of spiral writing for 1000 m (ending writing) was conducted, and the appearance of the drawn line was visually evaluated. The evaluation criteria are as follows. A: No scratch was seen on the drawn line. B: Slight blurring was observed in the drawn line. B: Marked blurring was observed in the drawn line.

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

Table 1

[0096]

Table 2

[0097]

Table 3

[0098]

Table 4

[0099] From Tables 1 to 4, it can be understood that the water-in-oil droplet type ink composition for writing instruments of the present invention, that is, the oil phase is contained in the form of oil droplets in water with respect to the aqueous phase, the oil phase contains a resin and a polar lubricating oil, and the content rate of the resin is more than 0.5% by mass with respect to the mass of the oil phase, can improve the DC resistance while suppressing the writing feel and the blurring of the drawn line.

Claims

1. The oil phase is contained in the 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, An oil-in-water type ink composition for writing instruments.

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

3. The fatty acid is a straight-chain fatty acid. The oil-in-water type ink composition for writing instruments according to Claim 2.

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

5. The polar lubricating oil is an ester-based lubricating oil or a polyglycol-based lubricating oil. The oil-in-water type ink composition for writing instruments according to Claim 1 or 2.

6. 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. The oil-in-water type ink composition for writing instruments according to Claim 5.

7. The acid value of the polar lubricating oil is 150 or less. The oil-in-water type ink composition for writing instruments according to Claim 1 or 2.

8. The glass transition temperature of the resin is 100°C or less. The oil-in-water type ink composition for writing instruments according to Claim 1 or 2.

9. The resin is selected from the group consisting of a styrene acrylic resin, a polyester resin, and a ketone resin. The oil-in-water type ink composition for writing instruments according to Claim 1 or 2.

10. The aqueous phase does not contain a resin. The oil-in-water type ink composition for writing instruments according to Claim 1 or 2.

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