Aqueous ink composition for writing instrument

Abstract

To provide an ink excellent in clear drainage, simultaneously excellent in ink adherence on a page space where an aqueous ink is difficult to permeate such as inkjet postcards and lightly coated paper, and difficult to repel.SOLUTION: An aqueous ink composition for writing instruments of the present invention contains at least a luminous pigment, polyoxyalkylene glycol, and a thickening agent, and has a viscosity of 500 to 2000 mPa s when measured under the conditions of 25°C and a shear rate of 3.83 sec-1.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aqueous ink composition for a writing instrument. [Background technology]

[0002] In writing instruments, particularly in ballpoint pens, ink reservoirs (refills) made of transparent or translucent resin are expected to have the ability to visually check the amount of ink remaining, and this ability is generally called "clear drainage." Clear drainage is impaired when ink adheres to and contaminates the ink reservoir, and various means have been proposed to improve this.

[0003] Patent Document 1 discloses an oil-based ballpoint pen ink containing at least a polypropylene glycol monoalkyl ether having a viscosity of 600 mPa·s or more at 25°C, a colorant selected from a dye, a pigment, or a mixture of a dye and a pigment, and a solvent.

[0004] Patent Document 2 discloses an aqueous ink composition to be incorporated in a direct ink writing instrument, which is characterized by containing water, a colorant, and polyoxyethylene polyoxypropylene glycol and / or polyoxyethylene polyoxypropylene alkyl ether.

[0005] In addition, an aqueous ink composition for writing instruments has been proposed that can withstand repeated rubbing of handwriting formed by writing or rubbing with stronger force on a paper surface onto which aqueous inks do not easily penetrate, such as inkjet postcard paper or lightly coated paper.

[0006] Patent Document 3 discloses an aqueous ink composition for a writing instrument, which contains at least a pigment-containing colorant (A), olefin-based resin particles (B), and water, wherein the olefin-based resin particles (B) have a penetration hardness of 1 or more and an average particle size measured by a Coulter counter method of 15 μm or less, and the mass ratio of the solid contents of the colorant (A) to the olefin-based resin particles (B) [(A) / (B)] is in the range of 1 to 100. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2006-348239 A [Patent Document 2] JP 2016-27106 A [Patent Document 3] JP 2023-24288 A Summary of the Invention [Problem to be solved by the invention]

[0008] When an ink containing a glittering pigment such as an aluminum pigment or a pearl pigment is used in an ink composition for a writing instrument, there is a problem that the clear drainage is more likely to be impaired than in an ink not containing a glittering pigment, and this problem cannot always be fully solved even by the measures disclosed in Patent Documents 1 and 2. There is also a demand for inks that adhere well to paper surfaces that are difficult for aqueous inks to penetrate, such as inkjet postcard paper and lightly coated paper, and that are not easily repelled.

[0009] The present invention provides an ink that has good clear drainage properties, and at the same time, has good ink adhesion to paper surfaces that are difficult for aqueous inks to penetrate, such as inkjet postcard paper and lightly coated paper, and is not easily repelled. [Means for solving the problem]

[0010] As a result of intensive research, 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> At least a glittering pigment, a polyoxyalkylene glycol, and a thickener are included, Temperature 25℃, shear rate 3.83sec -1 The viscosity measured under the above conditions is 500 to 2000 mPa s. A water-based ink composition for a writing instrument. <Aspect 2> The aqueous ink composition for a writing instrument according to Aspect 1, wherein the thickener is at least one selected from the group consisting of xanthan gum, succinoglycan, and diutan gum. Aspect 3: The aqueous ink composition for a writing instrument according to Aspect 2, wherein the thickener is a mixture of xanthan gum and at least one selected from the group consisting of succinoglycan and diutan gum, and the ratio of the mass of the solid content of xanthan gum to the total mass of the solid content of the thickener is 0.05 to 0.85. Aspect 4: The aqueous ink composition for a writing instrument according to any one of Aspects 1 to 3, wherein the luster pigment is an aluminum pigment coated with silica. Aspect 5: The aqueous ink composition for a writing instrument according to any one of Aspects 1 to 4, further comprising a phosphate ester having an HLB value of 10 or less. Aspect 6: The aqueous ink composition for a writing instrument according to any one of Aspects 1 to 5, further comprising a bubble inhibitor. Aspect 7: The aqueous ink composition for a writing instrument according to Aspect 6, wherein the bubble inhibitor is N-acetylcysteine. Effect of the Invention

[0011] According to the present invention, it is possible to provide an ink that has good clear drainage properties, and at the same time, has good ink adhesion to lightly coated paper and is not easily repelled. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] <<Water-based ink composition for writing instruments>> The aqueous ink composition for a writing instrument of the present invention comprises: At least the composition contains a glittering pigment, a polyoxyalkylene glycol, and a thickener, Temperature 25℃, shear rate 3.83sec -1 The viscosity measured under the above conditions is 500 to 2000 mPa·s.

[0013] The present inventors have found that the above-mentioned composition makes it possible to provide an ink that has good clear drain properties, and at the same time, has good ink adhesion to lightly coated paper (such as Christmas cards) and is not easily repelled.

[0014] The glittering pigment has a large particle size and is easily attached to the inner wall of the refill of the writing instrument, which can impair the clear drainage, especially the clear drainage when writing quickly. Without wishing to be bound by theory, it is believed that polyoxyalkylene glycol has good adsorption to glittering pigments, especially aluminum pigments, and this can suppress the adhesion of glittering pigments to the inner wall of the refill of the writing instrument. In addition, the presence of polyoxyalkylene glycol can improve the ink flow on the paper surface when writing on lightly coated paper such as Christmas cards.

[0015] Furthermore, the aqueous ink composition for writing instruments of the present invention has a viscosity of 500 mPa·s or more, 600 mPa·s or more, 700 mPa·s or more, 800 mPa·s or more, 900 mPa·s or more, or 1000 mPa·s or more due to the presence of a thickener, thereby making it possible to suppress settling of the glittering pigment. Furthermore, by making the viscosity 2000 mPa·s or less, or 1900 mPa·s or less, good writing properties can be maintained. This viscosity is measured at a temperature of 25°C and a shear rate of 3.83 sec -1 The viscosity was measured under the following conditions.

[0016] In the present invention, the term "aqueous ink composition" refers to an ink composition that contains an aqueous medium as a liquid component.

[0017] The aqueous ink composition for a writing instrument of the present invention preferably contains a bubble inhibitor, from the viewpoint of facilitating the movement of bubbles in the ink and thereby further improving the clear drainage property.

[0018] The aqueous ink composition for a writing instrument of the present invention may contain a coloring material.

[0019] The aqueous ink composition for a writing instrument of the present invention may contain other optional ingredients.

[0020] Each component of the present invention will now be described.

[0021] <Aqueous medium> The aqueous medium contains water and an optional water-soluble organic solvent. In the aqueous medium, the content of water is the highest among the liquid components, and in particular, the content of water may be more than 50 mass%, 60 mass% or more, 70 mass% or more, 75 mass% or more, or 78 mass% or more, and may be 100 mass% or less, 95 mass% or less, or 90 mass% or less, based on the mass of the aqueous medium.

[0022] (water) As the water, for example, tap water, purified water, distilled water, ion-exchanged water, pure water, etc. can be used.

[0023] (Water-soluble organic solvent) Examples of the water-soluble organic solvent that can be used include aromatics, alcohols, polyhydric alcohols, glycol ethers, esters, etc. These solvents may be used alone or in combination.

[0024] As the aromatics, for example, benzyl alcohol, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, propylene glycol monophenyl ether, diethylene glycol monophenyl ether, alkylsulfonic acid phenyl ester, etc. can be used.

[0025] 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, 2-octanol, 2-ethylhexanol, 3,5,5-trimethylhexanol, nonanol, n-decanol, undecanol, n-decanol, trimethylnonyl alcohol, tetradecanol, heptadecanol, cyclohexanol, and 2-methylcyclohexanol.

[0026] 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.

[0027] Examples of glycol ethers that can be used include methyl isopropyl ether, ethyl ether, ethyl propyl ether, ethyl butyl ether, isopropyl ether, butyl ether, hexyl ether, 2-ethylhexyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylbutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, 3-methyl-3-methoxy-1-butanol, 3-methoxy-1-butanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol tertiary butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, and tetrapropylene glycol monobutyl ether.

[0028] Examples of esters include propylene glycol methyl ether acetate, propylene glycol diacetate, 3-methyl-3-methoxybutyl acetate, propylene glycol ethyl ether acetate, ethylene glycol ethyl ether acetate, butyl formate, isobutyl formate, isoamyl formate, propyl acetate, butyl acetate, isopropyl acetate, isobutyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, propyl propionate, isobutyl propionate, isoamyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, propyl isobutyrate, Methyl valerate, ethyl valerate, propyl valerate, methyl isovalerate, ethyl isovalerate, propyl isovalerate, methyl trimethylacetate, ethyl trimethylacetate, propyl trimethylacetate, methyl caproate, ethyl caproate, propyl caproate, methyl caprylate, ethyl caprylate, propyl caprylate, methyl laurate, ethyl laurate, methyl oleate, ethyl oleate, caprylic acid triglyceride, tributyl acetate citrate, octyl oxystearate, propylene glycol monoricinoleate, methyl 2-hydroxyisobutyrate, 3-methoxybutyl acetate, and the like can be used.

[0029] The content of the water-soluble organic solvent may be 3% by mass or more, 5% by mass or more, 7% by mass or more, 10% by mass or more, or 12% 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, based on the total mass of the aqueous ink composition for writing instruments.

[0030] <Brilliant Pigments> Examples of the luster pigment that can be used include metal powder pigments, metal oxide powder pigments, pearl pigments, aluminum pigments, and flake pigments. The flake pigment may be a flake pigment in which a base material of a block flake is coated with a metal or metal oxide, and may be, for example, a flake glass pigment or a flake plastic pigment. These luster pigments can be used alone or in combination. Among them, the use of an aluminum pigment is particularly preferred from the viewpoint of writing properties.

[0031] Aluminum pigments are broadly classified into leafing and non-leafing types depending on the type of grinding aid used. Commercially available products include, for example, the non-leafing types Alpaste 1100MA, CS420, and CS460, the WXM series in which the aluminum surface is treated for rust prevention with a phosphorus compound, the WL series in which the aluminum surface is treated for rust prevention with a molybdenum compound, the EMR series in which the surface of aluminum flakes is coated with high-density silica (all manufactured by Toyo Aluminum Co., Ltd.), and SW-120PM (all manufactured by Asahi Kasei Chemicals Corporation).

[0032] While aluminum pigments are preferable from the viewpoint of writing properties, they are prone to generating air bubbles, which can impair clear drainage properties. However, by using a silica-coated aluminum pigment, which is coated with silica, as the aluminum pigment, the generation of air bubbles can be suppressed.

[0033] The content of the glittering pigment may be 1% by mass or more, 3% by mass or more, or 5% by mass or more, and may be 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, 12% by mass or less, 10% by mass or less, or 8% by mass or less, based on the total mass of the aqueous ink composition for writing instruments.

[0034] <Polyoxyalkylene glycol> Polyoxyalkylene glycols are generally compounds having repeating units based on alkylene oxide monomers, such as ethylene oxide and propylene oxide, which may be used alone or copolymerized.

[0035] As such polyoxyalkylene glycol, for example, polyoxyethylene polyoxypropylene glycol can be used. As the polyoxyethylene polyoxypropylene glycol, commercially available products can be used, for example, Unilube 50MB-2, 50MB-5, 50MB-11, 50MB-26, 50MB-72, 50MB-168, 75DE-25, 75DE-60, 75DE-170 (all NOF Corp.), etc. can be used.

[0036] Polyoxyethylene polyoxypropylene glycol is a compound represented by the general formula (1) in which R is H. RO-(C3H6O) m (C2H4O) n -H (1) [In the formula, R represents an alkyl group, and m and n each independently represent a number from 1 to 40.] The alkyl group represented by R in the general formula may be, for example, an alkyl group having 2 or more or 3 or more carbon atoms and 8 or less, 7 or less, 6 or less, 5 or less, or 4 or less. The number of moles of ethylene oxide or propylene oxide added represented by m and n may each independently be 1 or more, 3 or more, 5 or more, 7 or more, 10 or more, or 12 or more, and may be 40 or less, 35 or less, 30 or less, 27 or less, 25 or less, 24 or less, 22 or less, 20 or less, or 18 or less.

[0037] In particular, it is preferable that the molecular weight of polyoxyethylene polyoxypropylene glycol is 800 to 3,500 from the viewpoint of suppressing an increase in ink viscosity due to its addition.

[0038] The content of polyoxyalkylene glycol may be 0.01% by mass or more, 0.03% by mass or more, 0.05% by mass or more, 0.07% by mass or more, 0.1% by mass or more, or 0.2% by mass or more, and may be 5.0% by mass or less, 4.5% by mass or less, 4.0% by mass or less, 3.0% by mass or less, 3.5% by mass or less, 2.0% by mass or less, 2.5% by mass or less, 1.0% by mass or less, 0.7% by mass or less, 0.6% by mass or less, or 0.5% by mass or less, relative to the mass of the aqueous ink composition for writing instruments.

[0039] <Thickener> The usable thickener is preferably at least one selected from the group consisting of synthetic polymers, cellulose, and polysaccharides, for example.Specific examples include gum arabic, tragacanth gum, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, xanthan gum, welan gum, succinoglycan, diutan gum, dextran, methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, fermented cellulose, oxidized cellulose, crystalline cellulose, starch glycolic acid and its salts, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylic acid and its salts, polyethylene oxide, copolymers of vinyl acetate and polyvinylpyrrolidone, styrene-acrylic acid copolymers and its salts, alkali swelling association type emulsions, alkali swelling type emulsions, etc.

[0040] In particular, the thickening agent is preferably at least one selected from the group consisting of xanthan gum, succinoglycan and diutan gum, and more preferably a mixture of at least one selected from the group consisting of succinoglycan and diutan gum with xanthan gum, from the viewpoint of suppressing sedimentation and the resulting color separation.

[0041] When the thickener is a mixture of at least one selected from the group consisting of succinoglycan and diutan gum and xanthan gum, the ratio of the mass of the solid content of xanthan gum to the total mass of the solid content of the thickener is preferably 0.05 or more, 0.10 or more, 0.15 or more, 0.20 or more, 0.25 or more, 0.30 or more, 0.35 or more, 0.40 or more, or 0.45 or more from the viewpoint of improving writing properties. This ratio is preferably 0.85 or less, 0.80 or less, 0.75 or less, 0.70 or less, 0.65 or less, 0.60 or less, or 0.55 or less from the viewpoint of suppressing sedimentation of the luster pigment.

[0042] <Phosphate ester> The phosphoric acid ester used in the present invention is not particularly limited, and may be, for example, a phosphoric acid ester of polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether. These phosphoric acid esters may be used alone or in combination of two or more kinds.

[0043] From the viewpoint of clear drainage, it is preferable to use a phosphate ester having an HLB value of 10 or less (HLB≦10). The HLB value may be 4 or more, 5 or more, 6 or more, 7 or more, or 8 or more.

[0044] Specific examples of phosphate esters that can be used include Phosphanol RB-410 and RD-510Y (manufactured by Toho Chemical Industry Co., Ltd.).

[0045] These may be used as they are or as salts neutralized with an alkali metal or an organic base, and two or more of them may be used in combination.

[0046] The content of the phosphate ester, relative to the mass of the aqueous ink composition for writing instruments, may be 0.01% by mass or more, 0.03% by mass or more, 0.05% by mass or more, 0.07% by mass or more, 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more, and may be 5.0% by mass or less, 4.5% by mass or less, 4.0% by mass or less, 3.5% by mass or less, 3.0% by mass or less, 2.0% by mass or less, 2.5% by mass or less, 1.0% by mass or less, 0.7% by mass or less, 0.6% by mass or less, or 0.5% by mass or less.

[0047] <Air Foam Inhibitor> As the foam inhibitor, at least one of cysteine ​​and its derivatives, glutathione and its derivatives, hydroxylamine and its derivatives, ascorbic acid and its derivatives, erythorbic acid and its derivatives, and salts thereof, and oligomers of N-vinyl-2-pyrrolidone, can be used.

[0048] In particular, when an aluminum pigment is used as the luster pigment, air bubbles may be generated in the refill during storage, which may cause problems such as obstructing the ink flow path and hindering outflow. In this case, the ink flowability can be improved by further adding an air bubble inhibitor.

[0049] Among them, it is preferable to use a cysteine ​​derivative, especially N-acetylcysteine, as the air bubble suppressor from the viewpoint of suppressing air bubble generation. In particular, when an aluminum pigment, especially a silica-coated aluminum pigment, is used as the glitter pigment, air bubbles are easily generated by the glitter pigment, so the presence of N-acetylcysteine ​​is useful.

[0050] The content of the bubble inhibitor is preferably 0.01% by mass or more, 0.03% by mass or more, 0.05% by mass or more, 0.07% by mass or more, 0.1% by mass or more, or 0.2% by mass or more, based on the mass of the aqueous ink composition for writing instruments, from the viewpoint of adjusting the dissolved oxygen concentration in the ink composition and thereby suppressing bubbles. This content may be 5.0% by mass or less, 4.5% by mass or less, 4.0% by mass or less, 3.5% by mass or less, 3.0% by mass or less, 2.5% by mass or less, 2.0% by mass or less, 1.0% by mass or less, or 0.5% by mass or less.

[0051] <Coloring material> As the coloring material, various coloring materials that can be used in conventional inks can be used, such as dyes, pigments, or mixtures of dyes and pigments, etc. These coloring materials can be used alone or in combination.

[0052] As the dye, any dye that dissolves or disperses in water can be used, for example, acid dyes such as eosin, fuoxin, water yellow #6-C, acid red, water blue #105, brilliant blue FCF, and nigrosine NB; direct dyes such as direct black 154, direct sky blue 5B, and violet BB; and basic dyes such as rhodamine and methyl violet.

[0053] As the pigment, any of the conventionally known inorganic and organic pigments such as titanium oxide, resin particle pigments containing a pigment or dye, pseudopigments in which a resin emulsion is colored with a dye or pigment, white plastic pigments, thermochromic pigments, photochromic particles, and the like can be used without limitation.

[0054] Examples of inorganic pigments that can be used include carbon black, titanium black, zinc oxide, red iron oxide, aluminum, chromium oxide, iron black, cobalt blue, iron 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, Prussian blue, manganese violet, aluminum powder, and brass powder.

[0055] 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 CI Pigment Blue 17, CI Pigment Blue 15, CI Pigment Blue 17, CI Pigment Blue 27, CI Pigment Red 5, CI Pigment Red 22, CI Pigment Red 38, CI Pigment Red 48, CI Pigment Red 49, CI Pigment Red 53, CI Pigment Red 57, CI Pigment Red 81, CI Pigment Red 104, CI Pigment Red 146, CI Pigment Red 245, CI Pigment Yellow 1, CI Pigment Yellow 3, CI Pigment Yellow 12, CI Pigment Red 13, CI Pigment Red 14, CI Pigment Red 15, CI Pigment Red 16, CI Pigment Red 17, CI Pigment Red 18, CI Pigment Red 19, CI Pigment Red 20, CI Pigment Red 21, CI Pigment Red 22, CI Pigment Red 23, CI Pigment Red 24, CI Pigment Red 25, CI Pigment Red 26, CI Pigment Red 27, CI Pigment Red 28, CI Pigment Red 29, CI Pigment Red 30, CI Pigment Red 31, CI Pigment Red 32, CI Pigment Red 33, CI Pigment Red 34, CI Pigment Red 35, CI Pigment Red 36, CI Pigment Red 37, CI Pigment Red 38, CI Pigment Red 39, CI P Examples of pigments include CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 17, CI Pigment Yellow 34, CI Pigment Yellow 55, CI Pigment Yellow 74, CI Pigment Yellow 95, CI Pigment Yellow 166, CI Pigment Yellow 167, CI Pigment Orange 5, CI Pigment Orange 13, CI Pigment Orange 16, CI Pigment Violet 1, CI Pigment Violet 3, CI Pigment Violet 19, CI Pigment Violet 23, CI Pigment Violet 50, and CI Pigment Green 7.

[0056] Examples of thermochromic pigments include those produced by microencapsulating a thermochromic composition containing at least a leuco dye functioning as a color former, a color developer as a component capable of causing the leuco dye to develop color, and a color change temperature regulator capable of controlling the color change temperature in the color development of the leuco dye and the color developer, so as to have a predetermined average particle size (e.g., 0.1 to 6 μm). The 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, and 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.

[0057] As the photochromic particles, for example, 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 can be used. In addition, as the photochromic particles, 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 antioxidants, light stabilizers, and sensitizers, to a predetermined average particle size (for example, 0.1 to 6 μm) can be used.

[0058] 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 coloring in an ultraviolet ray irradiation environment (irradiation with light of a wavelength of 200 to 400 nm, or irradiation with sunlight containing ultraviolet rays).

[0059] In the present invention (including examples), the "average particle size" is appropriately selected depending on the size of the particles to be measured. In the case of particles less than about 1 μm, it is the histogram average particle size (D50) calculated on a volume basis in the scattering intensity distribution measured by the dynamic light scattering method, and in the case of particles of 1 μm or more, it is the median diameter (D50) calculated on a volume basis by the laser diffraction method. The average particle size can be measured using a particle size analyzer [Microtrac HRA9320-X100 (Nikkiso Co., Ltd.)].

[0060] Examples of the microencapsulation method of the thermochromic pigment and the photochromic particle include an interfacial polymerization method, an interfacial polycondensation method, an in situ polymerization method, a liquid hardening coating method, a phase separation method from an aqueous solution, a phase separation method from an organic solvent, a melting dispersion cooling method, an air suspension coating method, and a spray drying method, and can be appropriately selected depending on the application.

[0061] 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 by a method including 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 discoloration temperature regulator to an emulsifier solution, and dispersing the mixture in the form of oil droplets by heating and stirring to prepare a dispersion liquid; (3) A resin raw material capable of forming a wall film, such as a urethane resin, an epoxy resin, or an amino resin, is gradually added to the above dispersion as a capsule film agent, for example, an amino resin solution, specifically, an amino resin solution such as a methylolmelamine aqueous solution, a urea solution, or a benzoguanamine solution, and the resin raw material is reacted to form a capsule film, thereby obtaining a thermochromic microcapsule pigment; and (4) filtering the dispersion containing the thermochromic microencapsulated pigment;

[0062] In this thermochromic pigment, the color-developing temperature and the color-discoloring temperature of each color can be set to an appropriate temperature by appropriately combining the types and amounts of the leuco dye, the color developer, and the color-discoloring temperature regulator.

[0063] These coloring materials can be used alone or in combination of two or more. The average particle diameter of the pigments dispersed in water, resin particle pigments, pseudopigments, white plastic pigments, multi-coated pigments, thermochromic pigments, photochromic particles, etc. among these coloring materials varies depending on the ball diameter, ink composition, viscosity, etc., but it is desirable to have an average particle diameter of 0.02 to 6 μm. The 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, and 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.

[0064] The content of these color materials 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 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.

[0065] Other Ingredients The aqueous ink composition for writing instruments of the present invention may contain other optional components, such as a humectant, a dispersant, a lubricant, a pH adjuster, a rust inhibitor, a preservative, an antibacterial agent, and a fixing resin.

[0066] As the dispersant, a water-soluble resin is used, and preferably, a water-soluble polymer is used.

[0067] As the lubricant, lubricants used in surface treatment agents for pigments can be used, for example, nonionic surfactants such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, polyoxyalkylene higher fatty acid esters, and alkyl phosphate esters; anionic surfactants such as phosphoric acid esters, alkyl sulfonates of higher fatty acid amides, and alkyl aryl sulfonates; derivatives of polyalkylene glycols; and polyether-modified silicones.

[0068] Examples of the pH adjuster include ammonia, urea, amines such as monoethanolamine, diethanolamine, and triethanolamine, alkali metal salts of carbonate and phosphoric acid such as sodium tripolyphosphate and sodium carbonate, and hydrates of alkali metal salts such as sodium hydroxide.

[0069] As the rust inhibitor, benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, saponins, etc. can be used. As the preservative or antibacterial agent, phenol, sodium omadine, sodium benzoate, thiazoline compounds, benzimidazole compounds, etc. can be used.

[0070] The fixing resin is a resin used as necessary to adjust the viscosity and improve the fixing strength. For example, a water-soluble resin and a resin emulsion can be used as the fixing resin.

[0071] Examples of the water-soluble resin that can be used include water-soluble resins having a hydrophobic portion in the molecule, such as polyacrylic acid, water-soluble styrene-acrylic resin, water-soluble styrene-maleic acid resin, polyvinyl alcohol, polyvinylpyrrolidone, water-soluble maleic acid resin, water-soluble styrene resin, water-soluble ester-acrylic resin, ethylene-maleic acid copolymer, polyethylene oxide, and water-soluble urethane resin.

[0072] As the resin emulsion, for example, at least one type selected from polyolefin-based emulsion, acrylic-based emulsion, vinyl acetate-based emulsion, urethane-based emulsion, styrene-butadiene emulsion, styrene-acrylonitrile emulsion, and the like can be used.

[0073] The fixing resin may be used alone or in combination. In particular, it is preferable to use one or more of the above water-soluble resins and resin emulsions, that is, two or more fixing resins in total, from the viewpoint of fixing property.

[0074] The above other components may be used alone or in combination of two or more. In addition, if commercially available products of these are available, they may be used.

[0075] Ballpoint pen The ballpoint pen of the present invention comprises at least an ink storage section, a writing section having a ball, and a holding section, The above-mentioned aqueous ink composition for a writing instrument is stored in the ink storage section. It's a ballpoint pen.

[0076] The ink reservoir and the writing portion may be integrated, that is, the ballpoint pen of the present invention may have a refill having an ink reservoir and a writing portion.

[0077] Ink storage section The ink reservoir stores the above-mentioned aqueous ink composition for a writing instrument.

[0078] Any material can be used for the ink storage section as long as it is capable of storing ink and supplying ink to the writing section. When a hollow ink storage section made of a transparent or translucent resin is used, the excellent clear drainage properties of the aqueous ink composition for a writing instrument of the present invention become particularly useful.

[0079] <Writing Department> The writing part can be a writing part having a ballpoint pen tip at its tip.

[0080] 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 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, a bullet shape, a needle shape, etc.

[0081] Furthermore, from the viewpoint of writing feel, it is preferable that the surface roughness Ra of the ball is less than 10 nm, 8 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, or 3 nm or less. This surface roughness may be 1.0 nm or more, 1.5 nm or more, or 1.7 nm or more.

[0082] In the present invention (including the examples described later), the "surface roughness Ra" was measured using a non-contact surface profiler (NewView7200, Zygo) under the following conditions: lens magnification: 50x, evaluation length: 100 μm, Gaussian filter: 25 μm, and all other conditions were measured in accordance with JIS B0601 (geometric characteristics of products - surface properties).

[0083] From the viewpoint of writing performance, the ball clearance, i.e., the distance that the ball can move in the longitudinal direction of the ballpoint pen tip body, is preferably 30 μm or more, 40 μm or more, 50 μm or more, or 60 μm or more, and 120 μm or less, 110 μm or less, 100 μm or less, or 90 μm or less. This clearance can be measured by measuring the distance between the state where the ball is in contact with the receiving seat of the ballpoint pen tip and the state where the ball is in contact with the crimped portion at the tip of the ballpoint pen tip using a measuring microscope. EXAMPLES

[0084] The present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to these.

[0085] Preparation of Water-Based Ink Composition Examples 1 to 7 and Comparative Examples 1 to 6 The substances shown in Table 1 were mixed in the parts by mass shown in Table 1 to obtain 100 parts by mass of an aqueous ink composition for a writing instrument.

[0086] Details of the substances shown in Table 1 are as follows: Silica A: Silica-coated aluminum pigment (EMERAL EMR-D5660, Toyo Aluminum Co., Ltd.) Silica B: Silica-coated aluminum pigment (EMERAL EMR-D7670, Toyo Aluminum Co., Ltd.) Pearl: pearl pigment (Iriodin 111, Merck) POG-A: Polyoxyethylene polyoxypropylene glycol (Emulgen PP-290, Kao Corporation) POG-B: Pluronic (registered trademark) type nonionic surfactant in which ethylene oxide is added to polypropylene glycol (Newpol PE-108, Sanyo Chemical Industries, Ltd.) AG: Acetylene glycol surfactant (Surfynol 104H, Nissin Chemical Co., Ltd.) Fluorine: Fluorosurfactant (Surflon S-211, AGC Inc.) Silicone: Silicone-based surfactant (BYK-349, BYK) Xanthan gum: KELZAN AR (Sansho Co., Ltd.) Succinoglycan: Leozan SH (Solvay SA) Diutan gum: KELCO-VIS DF-F (Sansho Co., Ltd.) Inorganic salt acrylic acid: Hiviswako 105 (FUJIFILM Wako Pure Chemical Industries, Ltd.) Phosphate ester A: Phosphanol RB-410 (Toho Chemical Industry Co., Ltd.) Phosphate ester B: Phosphanol RD-510Y (Toho Chemical Industry Co., Ltd.) Phosphate ester C: Phosphanol RS-610 (Toho Chemical Industry Co., Ltd.) Foam suppressant: N-acetyl-L-cysteine ​​(FUJIFILM Wako Pure Chemical Corporation) Yellow pigment: Pigment Yellow (Sanyo Pigment Co., Ltd.) Styrene acrylic resin: Joncryl PDX-7615 (BASF)

[0087] The viscosity of the resulting aqueous ink composition for writing instruments was measured at a temperature of 25° C. and a shear rate of 3.83 sec. -1 The measurements were performed under the following conditions.

[0088] The obtained aqueous ink composition for writing instruments was filled into a ballpoint pen to obtain an aqueous ballpoint pen. For Examples 1, 3 to 7 and Comparative Examples 1 to 6, a transparent refill having a ballpoint tip with a clearance of 60±20 μm was used. For Example 2, a transparent refill having a ballpoint tip with a clearance of 90±20 μm was used. The surface roughness of the balls used was in the range of about 1.7 to 2.0 nm.

[0089] "evaluation" <Clear drainage> The prepared water-based ballpoint pen was used to write until the end, and the refill was observed from the outside to visually confirm the state of the refill, thereby evaluating the clear drainage property. The evaluation criteria are as follows. A: No ink was found on the inner wall of the refill. B: Ink was found adhering to the inner wall of the refill, but visibility inside the refill was not a problem at all. C: Ink was attached to the inner wall of the refill to such an extent that it was difficult to see inside the refill.

[0090] <Repellant properties on lightly coated paper> The prepared water-based ballpoint pen was used to write on lightly coated paper, and the appearance of the drawn lines was visually confirmed. The evaluation criteria were as follows: A: A clear, uninterrupted line was obtained. B: Although slightly interrupted, the lines were recognizable. C: The entire line is broken.

[0091] <Sedimentation and color separation> The water-based ballpoint pens thus produced were left with the tip facing down in an environment of 50°C and 30% relative humidity for three months, after which the appearance of the refills was visually inspected. The evaluation criteria are as follows. The appearance of the water-based ballpoint pens immediately after assembly was compared to evaluate sedimentation and color separation. A: There was no change in appearance. B: There was some shading or color separation in the refill. C: Sedimentation of the brilliant pigment and clear color separation were observed.

[0092] <Writability> A mechanical writing test was conducted in which the pen was spirally written until the end under conditions of a load of 100gf, a writing angle of 65 degrees, and a writing speed of 4.5mm / min.

[0093] The evaluation criteria are as follows: A: All five pens wrote without any smudging until the end. B: There were some smudges here and there, but all five pens were able to write to the end. C: There were scattered smudges and breaks in the lines throughout the drawing.

[0094] The configurations and evaluation results of the examples and comparative examples are shown in Tables 1 and 2. [Table 1]

[0095] [Table 2]

[0096] From Tables 1 and 2, it is found that the composition contains at least a photoluminescent pigment, a polyoxyalkylene glycol (POG), and a thickener, and is mixed at a temperature of 25°C and a shear rate of 3.83 sec. -1 It can be seen that the aqueous ink compositions for writing instruments of the Examples, which have a viscosity of 500 to 2000 mPa s measured under the above conditions, were excellent in clear drainage properties, repellency to lightly coated paper, sedimentation / color separation, and writability.

Claims

1. At least the composition contains a glittering pigment, a polyoxyalkylene glycol, and a thickener, Temperature 25℃, shear rate 3.83sec －１ The viscosity measured under the conditions is 500 to 2000 mPa s. A water-based ink composition for a writing instrument.

2. 2. The aqueous ink composition for a writing instrument according to claim 1, wherein the thickener is at least one selected from the group consisting of xanthan gum, succinoglycan, and diutan gum.

3. 3. The aqueous ink composition for a writing instrument according to claim 2, wherein the thickener is a mixture of xanthan gum and at least one selected from the group consisting of succinoglycan and diutan gum, and the ratio of the mass of the solid content of the xanthan gum to the total mass of the solid content of the thickener is 0.05 to 0.

85.

4. 3. The aqueous ink composition for a writing instrument according to claim 1, wherein the luster pigment is an aluminum pigment coated with silica.

5. The aqueous ink composition for a writing instrument according to claim 1 or 2, further comprising a phosphoric acid ester having an HLB of 10 or less.

6. 3. The aqueous ink composition for a writing instrument according to claim 1, further comprising a bubble inhibitor.

7. 7. The aqueous ink composition for a writing instrument according to claim 6, wherein the bubble suppressant is N-acetylcysteine.

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