JP2021134357A - Aqueous ink composition for writing implement and writing implement using the same - Google Patents

Abstract

To provide an aqueous ink composition for a writing implement which stabilizes dispersibility of a colorant (pigment) and resin particles, suppresses precipitation of the colorant (pigment) and the resin particles, does not cause dense handwriting, is excellent in color tone of handwriting, suppresses handwriting blur, and has good writing property, and a writing implement using the same.SOLUTION: An aqueous ink composition for a writing implement contains water, a solvent, a colorant and an urea compound, in which the urea compound is selected from modified urea, urea-modified urethane, and urea-modified polyamide.SELECTED DRAWING: None

Description

The present invention relates to a water-based ink composition for writing instruments, and more specifically, suppresses sedimentation of colorants (pigments), resin particles, etc., has excellent handwriting color tone, suppresses handwriting blurring, and has good writing performance. The present invention relates to a water-based ink composition for writing instruments and a writing instrument using the same.

Conventionally, water-based ink compositions for writing instruments using pigments are well known. In the case of an ink composition for a water-based ballpoint pen using such a pigment, unlike a dye-based water-based ink composition, the use of a pigment having a large difference in specific gravity from the ink causes agglomeration of the pigment and accompanying precipitation. Therefore, there are problems that the shading of the handwriting occurs during long-term storage and that the color tone of the handwriting at the time of writing is affected.
In particular, in inks using metal pigments and pearl pigments, the specific gravity of the pigment is larger than that of the solvent generally used in the ink composition, so that the pigment tends to settle in the ink and the ink stability with time is inferior.

In order to solve these problems, as the pigment dispersant, JP-A-63-152681 “Aqueous black pigment ink for ballpoint pens” using a polymer dispersant and a fatty acid ester of polyoxyethylene diglycerin borate ester were used. Proposals have been made such as JP-A-11-12524 "Aqueous glossy ink composition" and JP-A-7-118592 "Aqueous metallic glossy color ink for ballpoint pens" using seed polysaccharides gargum and locust beinga as gelling agents. ing.

However, for the purpose of setting the water-based ink composition for writing instruments of Patent Documents 1 and 2 to an ink viscosity suitable for marking pen ink, ink for perpetual brush, etc., and by increasing the amount of ink ejected, the color tone of the brush stroke (metal). When the ink is set to a low viscosity for the purpose of improving the glossiness), the metal pigment and the pearl pigment have a large specific gravity, so that there is a problem that pigment precipitation and accompanying hard cake formation occur. there were. Therefore, as a countermeasure against pigment sedimentation and the accompanying hard cake, it is necessary to put a metal stirrer in the ink container and redisperse it.
Further, in Patent Document 3, since the ink viscosity is increased by using a gelling agent and the ink viscosity is set to 1000 to 150,000 (mPa · s), pigment precipitation can be suppressed and the metal can be suppressed. Although it does not require a material stirrer, it is not suitable for low-viscosity inks such as marking pen inks and perpetual brush inks because the ink viscosity is too high, and the amount of ink ejected is small. The glossiness) is not sufficient, and the brush strokes are blurred.

"Japanese Patent Laid-Open No. 63-152681" "Japanese Patent Laid-Open No. 11-12524" "Japanese Patent Laid-Open No. 7-118592"

In view of the above problems, an object of the present invention is to suppress precipitation of colorants (pigments), resin particles, etc., so that it is not necessary to put a stirrer of a metal material in the ink container, and the color tone of handwriting can be further improved. It is an object of the present invention to provide a water-based ink composition for a writing instrument having excellent writing ability, suppressing handwriting blurring, and a writing instrument using the same.

In order to solve the above problems, the present invention
"1. A water-based ink composition for writing utensils, which comprises water, a solvent, a colorant, and a urea compound, wherein the urea compound is selected from modified urea, urea-modified urethane, and urea-modified polyamide.
2. The water-based ink composition for writing instruments according to item 1, wherein the content of the urea compound is 0.01 to 5% by mass with respect to the total amount of the ink composition.
3. 3. The water-based ink composition for writing instruments according to item 1 or 2, wherein the colorant is a metal pigment.
4. The water-based writing instrument according to any one of items 1 to 3, wherein the solvent is selected from a pyrrolidone derivative, a polyalkylene glycol, an aliphatic alcohol, a glycol ether, and a hydrocarbon solvent. Ink composition.
5. A writing instrument characterized in that the water-based ink composition for a writing instrument according to any one of paragraphs 1 to 4 is directly packed in an ink storage cylinder. "
And.

The present invention stabilizes the dispersibility of colorants (pigments) and resin particles in a water-based ink composition for writing instruments, suppresses sedimentation of colorants (pigments), resin particles, etc., and has no shading in handwriting. , The color tone of the handwriting was excellent, the blurring of the handwriting was suppressed, and the effect of good writing property could be achieved.

The feature of the present invention is to select from modified urea, urea-modified urethane, and urea-modified polyamide as the urea compound to prepare a water-based ink composition for writing instruments, which comprises the colorant (pigment) and resin particles. Stabilize dispersibility, suppress sedimentation of colorants (pigments), resin particles, etc., have no shading in the handwriting, have excellent handwriting color tone, suppress handwriting blurring, and achieve good writing performance. Is possible.

The urea compound used in the present invention can disperse and stabilize colorants (pigments) and resin particles and suppress precipitation. This is because the urea compound forms a dense three-dimensional network structure by interacting with water and a solvent, thereby forming a strong network structure, thereby forming a colorant (pigment), resin particles, and the like. This is because the precipitation of colorants (pigments) and resin particles can be suppressed by hooking on the formed three-dimensional network structure, the dispersibility of the pigment having a particularly large specific gravity can be stabilized, and the precipitation of the pigment can be suppressed. It is possible to suppress the sedimentation of the metal pigment even in the case of a metal pigment having a large particle size. Further, by stabilizing the pigment dispersion, it is easy to suppress the precipitation of the pigment, the handwriting is less likely to be shaded, and the color tone (metallic luster) is more likely to be improved. In particular, when a metal pigment containing a metal powder is used, the orientation of the metal powder is easily stable and the metallic luster of the handwriting is easily obtained, which is preferable.
Further, when writing, an impact is applied to the tip of the writing, so that the three-dimensional network structure is easily broken, the viscosity of the ink can be lowered, there is no blurring of the handwriting, and good writing performance can be obtained.

(Urea compound)
Examples of the urea compound are compounds having a urea group, and examples thereof include modified ureas such as modified urea and urea-modified urethane, and urea-modified polyamides such as urea-modified medium-polar polyamide and urea-modified low-polarity polyamide. Among these, by adsorbing on the surface of colorants (pigments) and resin particles by hydrogen bonding force and associative action due to the strong polarity of urethane groups, sedimentation is physically suppressed, and at the time of writing, it is attached to the tip of writing. It is preferable to select from modified urea, urea-modified urethane, and urea-modified polyamide, considering that the impact is applied to reduce the ink viscosity, there is no stroke blurring, and it is easy to obtain good writing performance. Considering this, modified urea and urea-modified urethane are preferable. Furthermore, while stabilizing the dispersibility of colorants (pigments) and resin particles and physically suppressing sedimentation, the ink viscosity is lowered during writing, and there is no handwriting blurring, which facilitates good writing performance. Considering that, modified urea is preferable. In particular, the modified urea is more effective when a metal pigment is used because it can stabilize the dispersion of the pigment having a large specific density and suppress the precipitation of the pigment.
The modified urea is a compound in which a copolymerization or a substituent is introduced into a main chain having one or more urea groups, and the urea-modified urethane is a compound in which a part of the main chain is a urethane chain, urea. Examples of the modified polyamide include compounds in which a part of the main chain is an amide chain. These urea compounds may be used alone or in combination of two or more.

With respect to the urea compound, it is easy to stably form a three-dimensional network structure, and in consideration of improving dispersibility, it is preferable to mix it with a solvent in advance to obtain a mixture with the urea compound. It is preferable to select from among pyrrolidone derivatives, polyalkylene glycols, aliphatic alcohols, aromatic alcohols, glycol ethers and hydrocarbon solvents, and more preferably from among pyrrolidone derivatives and polyalkylene glycols. Is preferable, and most preferably a pyrrolidone derivative.

Further, in each urea compound, by using a specific solvent as a main solvent in each urea compound, each urea compound can easily form a three-dimensional network structure stably and can easily improve dispersibility. ..
Therefore, when using modified urea, it is preferable to use a pyrrolidone derivative in consideration of improving dispersibility. Examples of the pyrrolidone derivative include N-methylpyrrolidone, N-ethylpyrrolidone, N-vinylpyrrolidone, 2-pyrrolidone and the like, but N-methylpyrrolidone is preferably used in consideration of further improvement in dispersibility.
When urea-modified urethane is used, it is preferable to use polyalkylene glycol as well. Examples of the polyalkylene glycol include polyethylene glycol and polypropylene glycol, but polypropylene glycol is preferably used in consideration of improving dispersibility.
When a urea-modified polyamide is used, it is preferable to select from an aliphatic alcohol, a glycol ether, and a hydrocarbon solvent in the same manner. Examples of the aliphatic alcohol include methanol, ethanol, 1-propanol, 2-propanol, isopropanol, isobutanol, t-butanol and the like, and examples of the glycol ether include ethylene glycol monophenyl ether (monophenyl glycol) and propylene glycol monomethyl. Examples thereof include ether, propylene glycol monoethyl ether, diethylene glycol dimethyl ether, 3-methoxybutanol, 3-methoxy-3-methylbutanol, etc. Examples of the hydrocarbon solvent include benzene, toluene, xylene, solvent naphtha, octane, mineral spirit and the like. However, in consideration of improving dispersibility, it is preferable to select from isopropanol, isobutanol, ethylene glycol monophenyl ether (monophenyl glycol), propylene glycol monomethyl ether, solvent naphtha, and mineral spirit. In consideration, it is preferable to use isopropanol, ethylene glycol monophenyl ether (monophenyl glycol), and solvent naphtha.

Regarding the modified urea, urea-modified urethane, and urea-modified polyamide, specifically, BYK-410 (main component: modified urea), BYK-411 (main component: modified urea), BYK-420 manufactured by Big Chemie Japan Co., Ltd. (Main component: modified urea), BYK-425 (main component: urea-modified urethane), BYK-430 (main component: urea-modified medium-polar polyamide), BYK-431 (main component: urea-modified low-polarity polyamide), BYK- 7420 (main component: modified urea) and the like can be mentioned.

Further, if the content of the urea compound is less than 0.01% by mass with respect to the total amount of the ink composition, the desired colorant (pigment) and resin particles cannot be suppressed from settling, and the desired color tone of the writing stroke cannot be obtained. If it exceeds 5, mass%, the ink ejection property tends to be inferior, and the color tone and writing property of the writing tend to be deteriorated. Therefore, 0.01 to 5% by mass is preferable, and more consideration is given, 0.05 to 3% by mass is used. More preferably, more preferably 0.1 to 1.5% by mass, and further preferably 0.1 to 1% by mass.

(Colorant)
The colorant used in the present invention is not particularly limited in pigment and dye, but the water-based ink composition for writing utensils containing the urea compound as in the present invention has an effect of stabilizing the pigment dispersion. The pigment ink is preferable because it is effective, and particularly effective when a metal pigment is used because the dispersion of the pigment having a large specific gravity can be stabilized and the pigment can be suppressed from settling.
Pigments include inorganic, organic, and processed pigments. Specific examples include carbon black, aniline black, ultramarine, chrome yellow, phthalocyanine, azo, quinacridone, quinophthalone, slene, and triphenylmethane. , Perinone type, Perylene type, Gioxazine type, Microcapsules, Metal pigments, Fluorescent pigments, Luminescent pigments, Complementary color pigments and the like. As the dye, direct dyes, acid dyes, basic dyes, gold-containing dyes, various salt-forming type dyes and the like can be adopted. These pigments and dyes may be used alone or in combination of two or more.

In the present invention, when a metal pigment is used as the colorant, the metal pigment is a metal powder such as aluminum, brass, stainless steel, bronze, titanium oxide, iron oxide, aluminum oxide, zinc oxide, or an alloyed metal powder. And pigments containing at least those metals. Specifically, metal powders such as aluminum powder, brass powder, stainless steel powder, bronze powder, and titanium oxide may be used as they are as metal pigments, or metal pigments in which a colorant is adsorbed on these metal pigments may be used. Further, the metal powder pigment such as aluminum powder may be processed in advance with a surfactant, a resin, a solvent or the like and dispersed to obtain a paste-like pigment dispersion or a liquid metal pigment dispersion. Further, the metal powder pigment such as aluminum powder may be processed or dispersed with wax, a surfactant, a resin or the like, or may be a solid metal pigment containing no solvent.
Examples of the metal pigment include aluminum paste-like pigments, aluminum powder pigments, titanium oxide pigments, metal vapor deposition powder pigments (pigments in which a metal thin film is coated with a resin), glass flake pigments, and pearl pigments.

The metal pigment is preferably a metal pigment coated with a coating material such as silica, molybdenum, or a phosphoric acid compound such as a phosphate, a phosphonic acid, or a phosphoric acid ester. This is because by using a metal pigment coated with a coating material such as silica, the three-dimensional network structure formed by the urea compound and the metal pigment are easily entangled in the network structure in a stable manner, so that the metal pigment is precipitated. This is because it is difficult.
Further, a metal pigment coated with a coating material such as silica has low reactivity with water and a solvent and high stability, so that bubble generation and deterioration of metal gloss over time are unlikely to occur. Therefore, the above coating is preferable. Among them, silica coating and phosphoric acid compound coating are preferable from the viewpoint of low reactivity with water and solvent and high stability. Further, more consideration is given, that a phosphoric acid compound coating is preferable.

Regarding the amount of the metal pigment coated with silica or the like, the total amount of the coating material such as silica or the phosphoric acid compound (coating material / metal powder) is relative to the total mass of the metal powder in the total amount of the ink composition. However, it is preferably 0.001 to 0.5 times. If it is less than 0.001 times, it is adsorbed on the entire surface of the metal powder and it is difficult to coat it, and if it exceeds 0.5 times, it is difficult to obtain the above-mentioned effects such as suppression of metal pigment precipitation. This is because the covering material tends to become a surplus with respect to the metal powder, and the surplus tends to precipitate or metal salt precipitates are likely to be generated. More considered, the content ratio is preferably 0.01 to 0.4 times based on the mass, and more preferably 0.01 to 0.1 times.

Among the phosphoric acid compound coatings, a phosphonic acid coating is preferable, and an alkylphosphonic acid coating is further preferable. This is a phosphonic acid compound having an alkyl group, and since both functional groups of the phosphonic acid group and the alkyl group of the alkylphosphonic acid are easily adsorbed on the metal powder, the adsorption is stable for a long period of time, so that it is more stable than the conventional metal pigment. However, the stability over time becomes good for a long period of time, and the above effect can be easily obtained for a long period of time. In particular, in consideration of the dispersibility of the metal pigment, it is preferable to use a metal pigment in which the metal powder is surface-treated with alkylphosphonic acid, and more preferably, a metal pigment in which the metal powder is surface-treated with alkylphosphonic acid in advance is used. Is preferable.

Regarding the alkylphosphonic acid, by improving the adsorptivity to the metal powder, the elution of metal ions is suppressed, the pigment precipitation suppression (dispersity of the metal pigment) is improved, and the metal salt precipitate is suppressed. Therefore, the number of carbon atoms of the alkyl group is preferably 1 to 20 in consideration of the good stability of the ink over time and the metallic glossiness of the brush stroke. The longer the alkyl group, the wider the adsorption area. This is because it is easily adsorbed on metal powder. More considered, the alkyl group preferably has 1 to 12 carbon atoms, more considered, the alkyl group has 6 to 10 carbon atoms, and most preferably the alkyl group has 8 carbon atoms. Further, the alkyl group is not limited to those having a linear structure or a branched chain structure, but an alkyl group having a linear structure is preferable because it has a wider adsorption area and is easily adsorbed on a metal powder. It is preferable because the suppression (dispersability of the metal pigment) tends to be good.

Further, considering that the precipitation suppression of the metal pigment (metal pigment dispersibility), the color tone of the brush stroke (metal glossiness), and the writability are good, it is preferable to use an aluminum paste-like pigment or a metal vapor-deposited powder pigment. For more consideration, it is preferable to use an aluminum paste-like pigment.

Further, among the metal pigments, those using aluminum powder are preferable, because the metallic luster of the handwriting is good, the specific gravity is relatively small among the metals, and the metal powder is less likely to settle. Further, regarding the shape of the metal powder, if it has a scale shape, a square shape, or a plate shape, it is easy to be caught in the three-dimensional network structure formed by the urea compound, and the metal pigment is suppressed from settling, and further, it is said that the shape is that. , It is preferable because the light is easily diffused and the metallic luster becomes clearer. Further, there are types such as a leafing type and a non-leafing type, but the leafing type is more preferable because the metal powder floats and is arranged on the surface layer of the ink film, and the metallic luster of the handwriting tends to be improved.

Further, the size of the metal pigment is preferably one having an average particle diameter of 1 to 50 μm, because if it is in the above range, it is likely to be caught in the three-dimensional network structure formed by the urea compound, and the metal pigment is suppressed from settling. However, it is easy to obtain a good color tone (metallic luster), and moreover, the metal pigment in the ink is less likely to be clogged with the pen tip. In particular, the average particle size is preferably 3 to 20 μm, most preferably 5 to 15 μm, in consideration of suppressing sedimentation of the metal pigment by easily getting caught in the three-dimensional network structure. Here, the average particle size is determined by using a laser diffraction method, specifically, a laser diffraction type particle size distribution measuring machine (trade name "Microtrac HRA9320-X100", Nikkiso Co., Ltd.), and using a standard sample or another measuring method. It can be obtained from the particle size (D50) when the cumulative volume of the particle size distribution measured based on the calibrated value is 50%.
Since the metal powder exerts the above-mentioned action and effect in the dispersed state of the metal powder in the ink composition, it is preferable to determine the particle size in the dispersed state.

Further, in the total amount of the ink composition, the total mass ratio of the urea compound to the total mass of the pigment (the urea compound / pigment) is preferably 0.01 to 3 times. If it is less than 0.01 times, it is difficult to obtain the above-mentioned effects such as pigment precipitation suppression, good handwriting color tone, and writability, and if it exceeds 3 times, the ink viscosity is too high. This is because the amount of ink ejected tends to be small and the color tone of the handwriting is likely to be affected. More considered, the content ratio is preferably 0.01 to 2 times based on the mass, and more preferably 0.1 to 1 times.

Specific examples of metal pigments include WXM0630, WB0230, 400SW, FM4010WG (all manufactured by Toyo Aluminum K.K.) as aluminum paste pigments, and F503RG, F503BG, F500SI, and F500RE as colored aluminum pigments. Examples thereof include F500RE and F500BL (all manufactured by Toyo Aluminum Co., Ltd.), Chromaru series and the like, and solid RotosafeAqua250 042, 250 022, 260 003 and the like (all manufactured by ECKART Co., Ltd.).
As the aluminum powder, AA12, AA8, No. 900, No. 18000 (above, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) and the like can be mentioned.
As metal vapor deposition powder pigments, aluminum was vacuum-deposited on a synthetic resin, and the metal layer was protected by the resin and crushed into pieces. Made) and so on. Further, the resin layer was colored by LG R. Gold # 500, B.I. Gold # 500, R.M. Gold # 325, B.I. Gold # 325, Red # 325, Blue # 325, Green # 325, Violet # 325, Black # 325, Copper # 325, R.M. Gold # 200, B.I. Gold # 200, Red # 200, Blue # 200, Green # 200, Violet # 200, Black # 200, Copper # 200 (all manufactured by Oike Kogyo Co., Ltd.) and the like can be mentioned.
As glass flake pigments, Metashine REFSX-2025PS, -2025PS, -2040PS, RCFSX-5030NS, -5030NB, -5030PS, -5030PS, -5030PS, -5030PS, -5030PS, -5030PS, -5030PS, -5030PS, -5030PS, -5030PS, -5030PS, -5030PS, -5030PS, -5030PS, -5030PS, -5030PS, -5030PS, 5090GG (all manufactured by Nippon Sheet Glass Co., Ltd.) and the like can be mentioned.
Examples of pearl pigments include Iriodin 120 Rutile Satin, 123 Bright Luster Satin, 201 Rutile Fine Gold, 211 Rutile Fine Red, 221 Rutile Fine Blue, 223 Rutile Fine, 223 Rutile Fine, and 223 Rutile Fine. , 323 Royal Gold Satin, 520 Bronze Satin, 522 Red Brown Satin, 524 Red Satin (all manufactured by Merck Japan Co., Ltd.) and the like.
Examples of titanium oxide pigments include Titone SR-1, R-650, R-3L, A-110, A-150, R-5N, and R-7E (Sakai Chemical Industry Co., Ltd.). (Manufactured by), Typake R-580, R-550, R-780, R-780-2, R-930, A-100, A-220, CR-58 (above, Ishihara Sangyo (above, Ishihara Sangyo) Kronos KR-310, KR-380, KR-480, KA-10, KA-20, KA-30 (all manufactured by Titan Kogyo Co., Ltd.), Typure R -900, R-931, R-960, R-960VHG (all manufactured by DuPont Japan Limited) and the like can be mentioned. In addition, LIOFAST WHITE H201, EM WHITE H, EMWHITE FX9048 (all manufactured by Toyo Ink Co., Ltd.), Polx White PC-CR (manufactured by Sumitomo Color Co., Ltd.), FUJISP WHITE 11, 1011 and 1036, same It is preferable to use a commercially available aqueous titanium oxide dispersion such as 1051 (all manufactured by Fuji Dye Co., Ltd.) because the dispersion step on the production side can be omitted and the ink can be easily converted into ink.

Further, when a metal pigment is used, it is preferable to include a black colorant because it is easy to improve the color tone by enhancing the visibility of handwriting on blank paper by containing the black colorant. The content of the black colorant is preferably 0.001 to 1% by mass and preferably 0.01 to 0.5% by mass with respect to the total amount of the ink composition in consideration of the color tone.

Further, if the content of the colorant is less than 0.5% by mass with respect to the total amount of the ink composition, the desired color tone (metal glossiness) of the brush stroke cannot be obtained, and if it is 20% by mass or more, the pigment precipitates. In addition, since it easily affects the stability of the ink with time, 0.5 to 20% by mass is preferable, 1 to 15% by mass is more preferable, and 1 to 8% by mass is most preferable.

Further, as a solvent other than the solvent used for mixing the urea compound with the solvent in advance to form a mixture as described above, the following water-soluble solvent is used in consideration of prevention of moisture evaporation and drying, metal pigment dispersion stability, and the like. Is preferably used. Specifically, polyhydric alcohol solvents such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol and glycerin, methanol, ethanol, 1-propanol, 2-propanol, isopropanol, isobutanol, t-butanol and propanol. Examples thereof include alcoholic solvents such as gil alcohol, allyl alcohol, 3-methyl-1-butin-3-ol, ethylene glycol monomethyl ether acetate and other higher alcohols. Among them, as a pigment dispersion aid, it is easy to suppress the precipitation of the pigment, and when the pen tip dries, the pigment (aluminum powder, stainless steel powder, titanium oxide powder) is a hard particle in the ink, so it is dry. Since it easily affects the writing performance at the time of uploading, the polyhydric alcohol is preferable considering that it can be easily improved by the polyhydric alcohol, and more considering it, at least the polyhydric alcohol having a divalent or trivalent hydroxyl group is used. It is preferable to contain it. A polyhydric alcohol solvent is a solvent in which two or more hydroxyl groups are bonded to different carbon atoms of an aliphatic or alicyclic compound. These may be used alone or in mixture of 2 or more types.

Regarding the content of the water-soluble solvent, considering the solubility, dry-up property, bleeding, etc. of the urea compound and the metal pigment, it is preferably 1 to 40% by mass with respect to the total amount of the ink composition. 3 to 30% by mass is preferable, and 5 to 25% by mass is preferable.

(water)
The water is not particularly limited, and for example, tap water, ion-exchanged water, ultrafiltered water, distilled water, or the like can be used.

(Resin particles)
In the present invention, the inclusion of resin particles is preferable in the case of a ballpoint pen because it causes a physical obstacle in the gap between the ball and the inner wall of the tip of the tip and easily suppresses ink leakage. Furthermore, since the organic resin particles have a lower hardness than the inorganic particles, the particles are partially deformed and adhere to each other to form a structure formed by weak aggregation, so that the particles are allowed to stand still. By forming a structure having a high resistance to ink leakage in the ink, it is easy to suppress high ink leakage, which is preferable. The present invention is effective because the use of the urea compound makes it easy to catch the resin particles on the formed three-dimensional network structure, stabilize the dispersion of the resin particles, and easily suppress the sedimentation.

Regarding resin particles, nitrogen atoms are contained in olefin resin particles such as polyethylene resin and polypropylene resin, and chemical structures such as melamine / formaldehyde resin, benzoguanamine / formaldehyde resin, benzoguanamine / melamine / formaldehyde resin, urea formaldehyde resin, and nylon resin. Examples thereof include nitrogen-containing resin particles, acrylic resin particles, styrene resin particles, epoxy resin particles, urethane resin particles, cellulose resin particles, and the like. These organic resin particles may be used alone or in combination of two or more.

The pH value of the water-based ink composition for writing instruments of the present invention is preferably 6.0 to 10.0 in consideration of the dispersibility of the colorant (pigment) and the resin particles by the urea compound. This is because when the pH value approaches the acidic side of less than 6 or the pH value exceeds 10 and approaches the strong alkaline side, the dispersibility of the metal pigment is affected, the metal pigment is easily corroded, and the metal gloss is easily affected. Therefore, if more consideration is given, the pH value is more preferably 7.0 to 9.0. In particular, when aluminum powder is used, the pH value is more preferably 7.0 to 9.0 in consideration of the corrosion of aluminum. The pH value is a value measured at 20 ° C. using a pH meter HM-30R manufactured by DKK-TOA CORPORATION.

As a pH adjuster, alkanolamines such as monoethanolamine, diethanolamine, triethanolamine, dimethylethanolamine, N-methylethanolamine, N-methyldiethanolamine, diisopropanolamine, ammonia, sodium carbonate, potassium carbonate, sodium acetate, etc. , Alkaline inorganic salts such as potassium acetate, sodium phosphate, potassium phosphate, sodium hydrogen phosphate, potassium hydrogen phosphate and the like, organic acids such as lactic acid, acetic acid and citric acid and the like. Among them, it is preferable to use a weaker basic alkanolamine in consideration of the stability of the ink with time.

The content of the pH adjuster is preferably 0.1 to 10% by mass, more preferably 0.3 to 5% by mass, based on the total amount of the ink composition in consideration of the stability over time of the ink. ..

When a metal pigment is used as the colorant, it is preferable to include a chelating agent because it is easy to suppress precipitates such as metal salts by sealing the metal present in the water-based ink composition for writing instruments.
Further, the water-based ink composition for writing instruments may be contained in a glass ink container such as a glass bottle. Glass bottles are easy to mold and cheaply available, and on the other hand, they can easily obtain the desired strength. On the other hand, when soda-lime glass, which is inexpensive and highly versatile, is used, the ink composition can be stored for a long period of time. If this is the case, there is a high possibility that the alkaline component in the glass will be eluted into the water-based ink composition for writing instruments, and the eluted alkaline component and the component of the water-based ink composition for writing instruments will react with each other to form a precipitate. There is a possibility that
Therefore, it is effective to further use a chelating agent in the water-based ink composition for writing instruments of the present invention, and even when it is stored in a glass ink container, the alkaline component that elutes is supplemented and the alkaline component is used. Prevents the formation of water-insoluble precipitates by reacting with the components in the water-based ink composition for writing instruments, and the generated precipitates block the ink flow path, causing the writing marks to be blurred or making writing impossible. It can be suppressed.

Examples of the chelating agent include ethylenediaminetetraacetic acid (EDTA) such as aminocarboxylic acid, hydroxyethylenediaminetriacetic acid (HEDTA), glycol etherdiaminetetraacetic acid (GEDTA), nitrilotriacetic acid (NTA), and hydroxyethyliminodiacetic acid (HIDA). Examples thereof include dihydroxyethylglycine (DHEG), diethylenetriaminetetraacetic acid (DTPA), triethylenetetraminehexacetic acid (TTHA) and alkali metal salts, ammonium salts or amine salts thereof.
Aminocarboxylic acid is used among the chelating agents in consideration of the fact that the alkaline component can be sufficiently supplemented and that the physical properties of the water-based ink composition for writing instruments before and after blending are not likely to be significantly affected. Of these, ethylenediaminetetraacetic acid (EDTA) and salts thereof are preferably used.

The content of the chelating agent is preferably 0.01 to 1% by mass with respect to the total amount of the ink composition. If it is 1% by mass or less, it does not adversely affect the performance and physical properties of the ink composition such as discoloration of the ink. Further, if it is 0.01% by mass or more, the alkaline component eluted from the glass ink container such as a glass bottle can be supplemented and the generation of precipitates can be suppressed.
Further, by adding an appropriate amount of the chelating agent, there is a tendency that the leakage resistance performance from the pen tip can be further improved. Therefore, in consideration of suppressing the generation of precipitates and further improving the leakage resistance from the pen tip, it is more preferably 0.01 to 0.5% by mass.

When a metal pigment is used as the colorant, it preferably contains a phosphoric acid ester-based surfactant. This is because it contains a phosphoric acid ester-based surfactant, and when a metal pigment is used, it is easy to suppress precipitates such as metal salts by sealing the metal existing in the ink composition. be.
Further, when used for a ball pen, the phosphoric acid group adsorbs metal to further improve the lubricity, suppress the wear of the ball seat, and easily improve the writing quality. Further, the lubricity should be taken into consideration. For example, it is preferable to use a phosphoric acid ester-based surfactant, and it is preferable to use a phosphoric acid ester-based surfactant having an alkyl group.
Examples of the type of phosphoric acid ester-based surfactant having an alkyl group include styrene phenol-based, nonylphenol-based, lauryl alcohol-based, tridecyl alcohol-based, octylphenol-based, and octyl alcohol-based. Among these, if the ink has a phenyl skeleton, the lubricity is likely to be affected by steric damage, and the compatibility with the metal pigment is likely to affect the stability of the ink over time. Therefore, a phosphoric acid ester-based surfactant having no phenyl skeleton It is preferable to use an activator.

Examples of the phosphoric acid ester-based surfactant include a phosphoric acid monoester of a polyoxyethylene alkyl ether or a polyoxyethylene alkyl aryl ether, a phosphoric acid diester of a polyoxyethylene alkyl ether or a polyoxyethylene alkyl aryl ether, and a polyoxyethylene alkyl ether. Alternatively, examples thereof include a phosphoric acid triester of a polyoxyethylene alkylaryl ether, an alkyl phosphoric acid ester, an alkyl ether phosphoric acid ester or a derivative thereof, and these phosphoric acid ester-based surfactants may be used alone or in combination of two or more. You may use it.

The content of the phosphoric acid ester-based surfactant is preferably 0.1 to 5% by mass with respect to the total amount of the ink composition. This is because if it exceeds 5% by mass, the stability of the ink with time tends to be affected, and more consideration is given, preferably 0.1 to 3% by mass.

When a pigment is used as a colorant, when the pen tip dries, the pigment (aluminum powder, stainless steel powder, titanium oxide powder) is hard particles in the ink, which affects the writing performance during dry-up. It is preferable to use a moisturizer because it is easy to use. Specific examples thereof include N, N, N-trialkyl amino acids such as urea, sorbit, trimethylglycine, triethylglycine and tripropylglycine, which have a moisture absorbing effect. Considering that it is easy to obtain, it is preferable to use urea. Further, if left for a long period of time, the pH value tends to shift to the acidic side due to carbon dioxide in the air, but by containing urea as in the present invention, the pH value is less than 7 even after a long period of time. When the pH value is set, it can be used more effectively.

Further, when a metal pigment is used as in the present invention, the black colorant is included because it is easy to improve the color tone by improving the visibility of handwriting on a blank sheet of paper. Is preferable. The content of the black colorant is preferably 0.001 to 1% by mass and preferably 0.01 to 0.5% by mass with respect to the total amount of the ink composition in consideration of the color tone.

An antiseptic may be used, and examples of the rust preventive include benzotriazole and its derivatives, tolyltriazole, dicyclohexylammonium nitrate, diisopropylammonium nitrate, sodium thiosulfate, saponin, and dialkylthiourea.

Preservatives may also be used, and the preservatives include phenol, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, 2,3,5,6-tetrachloro-4- (methylsulfonyl). ) Ppyridine, 2-pyridinethiol-1-oxide sodium, 1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, etc. Can be mentioned.

Further, a pigment dispersant may be used for the purpose of improving the dispersibility of the pigment, suppressing pigment precipitation and aggregation, and improving the fixability of handwriting. Examples of the pigment dispersant include an acidic resin, a basic resin, a nonionic surfactant, and an anionic surfactant. However, in consideration of long-term pigment dispersion stability, it is preferable to use an acidic resin. Examples of the acidic resin include acidic resins having a carboxyl group, a phenyl group, a sulfonic acid group, etc. Specific examples thereof include acrylic resin, styrene-acrylic resin, styrene-maleic acid resin, phenol resin, and polyvinyl-sulfonic acid. Examples thereof include resins, and among the above acidic resins, acidic resins having a carboxyl group are preferable.

If the content of the pigment dispersant is less than 0.1% by mass with respect to the total amount of the ink composition, it is difficult to obtain the desired pigment dispersion effect and the fixability of the brush stroke, and if it is 5.0% by mass or more, the ink is stable over time. 0.1 to 5.0% by mass is preferable because the properties tend to be inferior. More preferably, it is 1.0 to 4.0% by mass.

In addition, when a metal pigment is used, the shape of the metal powder in the metal pigment may be scaly, square, or plate-shaped, and it tends to be difficult for air bubbles caught during ink production to escape, so that air bubbles are absorbed. It is preferable to use an agent. Examples of the bubble absorber include hydroxylamines, ascorbic acids, erythorbic acids, and polyphenols. These bubble absorbers are compounds that exhibit reducing properties, and by absorbing oxygen in the ink, they exert a bubble absorbing effect. Regarding hydroxylamines, ascorbic acids, erythorbic acids, and polyphenols, hydroxylamines, hydroxylamine derivatives, polyphenols, polyphenol derivatives, ascorbic acid, ascorbic acid derivatives, erythorbic acid, erythorbic acid derivatives, and salts thereof. And so on.

As for bubble absorbers, some ascorbic acids have strong acidity (pH value = 2), and reacting with the components in the ink affects the stability of the ink over time, which affects the dispersibility of the metal powder used in the present invention. Ascorbic acids and polyphenols are likely to affect the color tone, so it is preferable to use hydroxylamines and erythorbic acids. Further, since hydroxylamines may generate an amine odor, it is preferable to use erythorbic acids.

The content of the bubble absorber is preferably 0.01 to 5% by mass with respect to the total amount of the ink composition. This is because if it is 0.01% by mass or less, it is difficult to sufficiently absorb oxygen in the ink, and if it exceeds 5% by mass, the stability of the ink with time is likely to be affected. More considered, 0.1 to 3% by mass is preferable, and 0.1 to 1% by mass is most preferable.

Further, in the case of an ink composition for a ballpoint pen, a shear thinning agent may be used in consideration of improving the pigment dispersibility. Examples of the shear thinning agent include polyacrylic acid, xanthan gum, welan gum, succinoglycan, guar gum, locust bean gum, λ-carrageenan, cellulose derivatives, oxidized cellulose, and daiyutan gum. By forming a three-dimensional network structure in the ink, it becomes easy to stabilize the metal pigment dispersion. These shear thinning agents may be used alone or in combination of two or more.

Regarding the ink viscosity, it is preferable that the ink viscosity is 500 (mPa · s) or less at a shear rate of 1.92 (sec ^{-1) (at rest) in an environment of 20 ° C.} This is preferably 300 (mPa · s) or less because it is easy to improve the color tone (metallic luster) of the handwriting by keeping a large amount of ink ejected, and further to suppress the blurring of the handwriting to obtain good writing performance. In consideration of the above, 200 (mPa · s) or less is preferable. Further, considering suppressing sedimentation of colorants (pigments), resin particles and the like, 10 (mPa · s) or more is preferable, and 20 (mPa · s) or more is preferable.
Further, in order to suppress handwriting blurring and facilitate good writing performance, the ink viscosity should be 20 (mPa · s) or less at a ^{shear rate of 384 (sec -1) (at the time of writing) in an environment of 20 ° C.} It is preferable, and more preferably, it is 10 (mPa · s) or less.
Further, considering that the ink ejection amount is maintained, the color tone (metal glossiness) of the handwriting is improved, the handwriting blurring is suppressed, and the precipitation of the metal pigment is suppressed, the viscosity gradient of the ink composition during flow is increased. It is preferable that the ink composition has a certain value or more, that is, the viscosity ratio of the ink composition at the time of high shear and the time of low shear is constant or more.
Thus, at high shear (viscosity at viscosity / shear rate 384sec ^-1 at shear rate of 1.92sec ^-1) viscosity ratio of the ink composition when (writing time) and low shear (at rest) is preferably 3 or more There, more preferably 5 or more, further, the viscosity ratio (viscosity at viscosity / shear rate 384sec ^-1 at shear rate of 1.92sec ^-1) is preferably 30 or less, preferably 20 or less.

(Writing instrument)
The water-based ink composition for writing tools of the present invention can be used for writing tools such as marking pens and ballpoint pens using a pen nib such as a fiber tip, felt tip, plastic tip or a ballpoint pen tip, or a fountain pen using a metal pen tip. Can be used. As in the present invention, even if the ink viscosity is low, pigment precipitation can be suppressed, so that it is effective to use it as an ink composition for marking pens and fountain pens, and it is particularly effective when used for an ink composition for fountain pens. Is.

Further, the ink composition for writing instruments of the present invention can be used for those having a structure in which the ink composition is directly filled, those provided with an ink storage body capable of filling the ink composition, and the like.

The water-based ink composition for writing utensils of the present invention can be introduced into an ink storage body from an ink storage body (ink cartridge) in which the ink storage body can be detachably attached to and detachable from the writing tool body, or from an ink container such as an ink bottle. It can be suitably used for a writing tool provided with an ink storage body (ink inhaler) having a function of directly inhaling ink.
Since the ink storage body as described above may be provided in the barrel of the writing instrument, the inner diameter of the ink storage body is likely to be restricted. Therefore, the ink composition does not easily flow in the ink storage body, and it is necessary to pay particular attention to the ink mobility in the ink storage body. The ink composition of the present invention can suppress a decrease in wettability with respect to the ink storage body when the ink moves, and is excellent in ink transferability in the ink storage body. It can be suitably used for a writing instrument provided with a storage body.
In particular, when the material of the ink storage body is molded from a resin material, the ink storage body tends to have poor wettability with the ink composition, and it is necessary to particularly consider the ink transfer property in the ink storage body. .. Since the ink composition of the present invention can suppress a decrease in wettability when the ink moves with respect to the resin material, it can be suitably used for a writing instrument having a resin ink storage body. ..

Further, it is desired that the ink storage body is made of a translucent or transparent material so that the remaining amount of ink can be known. Examples of such a material include thermoplastic resins such as polyethylene, polypropylene, polymethylpentene, polyethylene terephthalate, polycyclohexane terephthalate, polycarbonate, and nylon.
Further, since the ink composition is stored for a long period of time, it is preferable to use a crystalline resin having excellent chemical resistance as the ink storage body, and therefore, a crystalline olefin resin such as polyethylene, polypropylene, or polymethylpentene should be used. Is more preferable.

Further, the writing instrument to which the water-based ink composition for writing instruments of the present invention can be used includes a cap type having a cap covering the writing tip, a knock type, a rotary type, a sliding type, and the like, and the writing tip is housed in a shaft cylinder. It may be a possible haunting type.

The ink supply mechanism of the writing tool that can be used by the water-based ink composition for writing tools of the present invention is not particularly limited, and for example, an ink guide core made of (mechanism 1) a fiber bundle or the like is provided as an ink flow rate adjusting body. , A mechanism for supplying the ink composition to the pen tip by interposing this, (mechanism 2) a mechanism for providing a comb-shaped ink holding member as an ink flow rate adjusting body and supplying the ink composition to the pen tip, (mechanism 3). ) A mechanism that includes an ink flow rate adjusting body by a valve mechanism and supplies the ink composition to the writing tip, and (mechanism 4) a mechanism that directly supplies the ink composition to the pen tip without the ink flow rate adjusting body.

In the case of a ballpoint pen, the ball material is not particularly limited, and examples thereof include cemented carbide balls containing tungsten carbide as a main component, silicon carbide, alumina, zirconia, and silicon nitride. It is preferable to use silicon carbide balls in consideration of writing taste without being affected by metal corrosion. The size of the ball is determined by the use of the writing instrument, the width of the drawn line required at the time of writing, and the like, but is generally selected from the range of 0.1 to 2.0 mm.

The amount of movement of the ball of the ballpoint pen tip in the vertical axis direction is preferably 15 to 50 μm, less than 15 μm, because the color tone (metallic luster) of the handwriting can be improved by keeping a large amount of ink ejected. This is because the amount of ink consumed tends to be small, the metallic luster of the handwriting tends to be inferior, and when it exceeds 50 μm, the dryness of the handwriting and the suppression of ink leakage tend to be inferior. Considering the color tone (metallic luster) of the handwriting, it is preferably 30 to 50 μm.

<Aqueous ink products>
The water-based ink product according to the present invention may contain the water-based ink composition for writing instruments of the present invention in a glass ink container.
In particular, when the water-based ink composition for writing instruments contains a chelating agent, the alkaline component that elutes is supplemented even when the ink composition is contained in a glass ink container, and the alkaline component is the water-based ink composition for writing instruments. It is easy to prevent the formation of water-insoluble precipitates by reacting with the components inside, and to prevent the ink flow path from being blocked by the generated precipitates, resulting in scratches or inability to write. Therefore, it is effective and preferable. In particular, it is preferable when the water-based ink composition for writing instruments is combined with a glass ink container using soda-lime glass because a particularly high effect is likely to be exhibited.

The glass ink container that houses the ink composition for writing instruments may be made of a single glass product such as a glass bottle, or an exterior (decoration) such as resin, wood, or lacquer may be placed on the outside of the ink container. You can use the applied ones.

(Manufacturing method of water-based ink composition)
The water-based ink composition for writing instruments of the present invention can be produced by any conventionally known method. Specifically, each ink component can be blended in a required amount and mixed with various stirrers such as a propeller stirrer, a homodisper, or a homomixer, or various dispersers such as a bead mill to produce the ink.

Next, the present invention will be described with reference to examples.
(Aqueous ink composition for writing instruments)
Example 1
Metal pigment (65% aluminum powder, 3% octylphosphonic acid, leafing type, mass ratio of alkylphosphonic acid to mass of metal powder: 0.05 times (alkylphosphonic acid / metal powder)) 2.0 Part by mass dye (Direct Black 154) 0.01 part by mass water 68.5 parts by mass polyhydric alcohol (diethylene glycol) 7.0 parts by mass modified urea (nonvolatile component 2.6%, containing pyrrolidone derivative) 20.0 parts by mass pH Adjusting agent (triethanolamine) 1.0 part by mass Aminocarboxylic acid (ethylenediamine tetraacetic acid) 0.5 part by mass Phosphoric acid ester-based surfactant 1.0 part by mass

First, with respect to the metal pigment, the metal powder was surface-treated with alkylphosphonic acid (octylphosphonic acid), and imidazoline and propylene glycol monomethyl ether (SP value 10.2) were mixed to prepare a paste-like metal pigment.
After that, dye, water, polyhydric alcohol, modified urea (a mixture of modified urea and pyrrolidone derivative mixed in advance), pH adjuster, aminocarboxylic acid, and phosphate ester-based surfactant are heated and stirred to make a base ink. The metal pigment prepared above was mixed with the base ink, and the mixture was heated and stirred to prepare a water-based ink composition for writing utensils.

The ink viscosities of Examples 1, 12 to 15 and Comparative Example 1 were measured in an environment of 20 ° C. using a rheometer AR-G2 viscometer (cone plate 40 mm, angle 2 °) manufactured by TA Instruments. The ink viscosity was measured at a shear rate of 1.92 sec ^-1 (rotation speed 0.5 rpm) and a shear rate of 384 sec ^-1 (rotation speed 100 rpm).
^{When the ink viscosity was measured at a shear rate of 1.92 sec -1} (rotational speed 0.5 rpm) in an environment of 20 ° C., Examples 1: 195 (mPa · s) and Example 12: 25 (mPa · s). ), Example 13: 115 (mPa · s), Example 14: 155 (mPa · s), Example 15:50 (mPa · s), Comparative Example 1: 3.2 (mPa · s). ..
^{Further, when the ink viscosity was measured at a shear rate of 384 sec -1} (rotation speed 100 rpm) in an environment of 20 ° C., Examples 1:16 (mPa · s) and Example 12: 4.9 (mPa · s). ), Example 13: 6.7 (mPa · s), Example 14: 8.4 (mPa · s), Example 15: 5.8 (mPa · s), Comparative Example 1: 2.4 (mPa · s). -S).
The viscosity ratio of the ink composition (viscosity at a shear rate of 1.92 sec ^-1 / viscosity at a shear rate of 384 sec ^-1 ) was Example 1: 12.2, Example 12: 5.1, Example 13: 17.2. , Example 14: 18.5, Example 15: 8.6, Comparative Example 1: 1.3.
The pH values of Examples 1 and 12 were measured at 20 ° C. using a pH meter HM-30R manufactured by DKK-TOA CORPORATION, and the pH values were 7.9 and 8.1, respectively. there were.

Examples 2 to 17
Water-based ink compositions for writing instruments of Examples 2 to 17 were obtained in the same procedure as in Example 1 except that the ink composition was changed as shown in the table. The table shows the ink formulation and evaluation results.

Comparative Examples 1 to 3
Water-based ink compositions for writing instruments of Comparative Examples 1 to 3 were obtained in the same procedure as in Example 1 except that the ink composition was changed as shown in the table. The table shows the ink formulation and evaluation results.

<Making test writing instruments>
The water-based ink compositions for writing instruments of Examples 1 to 17 and Comparative Examples 1 to 3 are moved to an ink inhaler made of crystalline olefin resin (polymethylpentene) (a resin that can be moved in the ink inhaler in the front-rear direction). The moving body was injected into the ink inhaler opening facing upward so that the moving body was completely immersed in the ink composition. This ink inhaler is a knock-type haunting writing instrument (Pilot Corporation, fountain pen, FCN-1MR-BM) with a pen tip in the form of a fountain pen, in which a comb-shaped ink holding member is arranged as an ink flow control body. The following tests and evaluations were carried out using the attached writing instrument, and the evaluation of the color tone test and the writing ability test was carried out using JIS P3201 writing paper A as the writing test paper.

Precipitation test (precipitation test of pigment / resin particles): Put the water-based ink composition for each writing instrument in a densely opened / closed glass test tube with a diameter of 15 mm, leave it at room temperature for 7 days, and then visually settle the pigment / resin particles. Was observed.
The supernatant liquid (precipitation of pigments and resin particles) is almost nonexistent and good ... ◎
A part of the supernatant liquid (precipitation of pigments and resin particles) was confirmed, but there was no problem in practical use ... ○
The supernatant liquid (precipitation of pigment / resin particles) was confirmed, but there was no problem in practical use ... △
Pigments, etc. (pigment / resin particles settle) are severely settled and are at a problematic level ... ×

Color tone test: The color tone after handwriting was visually observed.
The color tone (metallic luster) of the handwriting is very good, and there is no shading ... ◎
Good handwriting color (metallic luster) ・ ・ ・ ○
The color tone (metallic luster) of the handwriting is slightly inferior ... △
Handwriting color tone (metallic luster) is inferior and practicality is poor ... ×

Writtenness test: The handwriting after handwriting was visually observed.
Handwriting with no blur ... ◎
Something with a slight blur in the handwriting ... ○
There is cassoulet in the handwriting, but there is no problem in practical use ... △
Handwriting with cassoulet and poor practicality ... ×

From the results in the table, in Examples 1 to 17, good or no problem level performance was obtained in all of the color tone test, the sedimentation test (precipitation test of pigment / resin particles), and the writability test. As in Examples 1 to 17, the water-based ink composition for writing instruments containing a chelating agent is stored in a glass ink container (water-based ink product: glass bottle) using soda-lime glass and brought to room temperature. Three months later, the ink was observed by microscopic observation, and there was no problem in practical use, and good performance was obtained.

From the results shown in the table, in Comparative Examples 1 to 3, since the urea compound was not used, the pigment (metal pigment) was severely settled, resulting in poor writing and blurring of handwriting.

The water-based ink composition for writing instruments of the present invention can be used as various water-based ink compositions for writing instruments such as fountain pens, ballpoint pens, brush pens, calligraphy pens, marking pens, and plate pens. More specifically, it can be widely used as a cap-type, haunting-type writing instrument filled with the water-based ink composition for writing instruments.

Claims (5)

A water-based ink composition for writing utensils, which comprises water, a solvent, a colorant, and a urea compound, wherein the urea compound is selected from modified urea, urea-modified urethane, and urea-modified polyamide. The water-based ink composition for writing instruments according to claim 1, wherein the content of the urea compound is 0.01 to 5% by mass with respect to the total amount of the ink composition. The water-based ink composition for writing instruments according to claim 1 or 2, wherein the colorant is a metal pigment. The water-based ink composition for writing tools according to any one of claims 1 to 3, wherein the solvent is selected from a pyrrolidone derivative, a polyalkylene glycol, an aliphatic alcohol, a glycol ether, and a hydrocarbon solvent. thing. A writing instrument characterized in that the water-based ink composition for a writing instrument according to any one of claims 1 to 4 is directly packed in an ink container.