Method for manufacturing writing instruments and aqueous ink compositions for writing instruments

Abstract

To provide a water-based ink composition that allows handwritten characters to be quickly dried and also allows the pen tip to have drought resistance; ensures excellent dispersion stability and temporal stability of a pigment; and gives water-resistant clear handwritten characters.SOLUTION: A water-based ink composition contains black colorants, which are at least carbon black and nigrosine, and also contains 2-methylpentane-2,4-diol and a polyglyceryl fatty acid ester with an HLB of 9.0 or more and 12.0 or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous ink composition that achieves both quick drying of handwriting and dryness resistance of the pen tip, has excellent dispersion stability and stability over time of pigments, and provides clear handwriting with water resistance.

Background Art

[0002] Conventionally, water-soluble dyes have been mainly used as colorants in aqueous inks used for signature pens, marking pens, fountain pens, felt pens, etc. However, the handwriting of these dye inks is inferior in light resistance and water resistance. In particular, the handwriting on postcards, etc. may get wet with water, bleed, or become illegible. Therefore, in recent years, attempts have been made to use pigments with excellent physical properties as colorants, and they are used in various applications.

[0003] In particular, black fountain pens are often used for writing on papers such as Japanese paper that are highly absorbent, in addition to postcards. In recent years, there are many users who are not familiar with pens. Even for fountain pens with pen nibs, there is a demand for inks that have less bleeding, dry quickly after writing like ballpoint pens without soiling the paper surface or hands, and have thick and clear handwriting.

[0004] However, when applying pigment inks to conventional signature pens, marking pens, fountain pens, felt pens, etc., if the ink viscosity cannot be sufficiently reduced, the ink will not flow smoothly from the pen tip or will smear during fast writing, and stable ejection cannot be obtained. Therefore, there are limited pigments that can be dispersed at a low viscosity with a pigment content that can achieve sufficient handwriting density. Also, when adding solvents or surfactants to improve the fluidity of the ink or the quick drying property of the handwriting, the ink penetrates into the paper and the pigment sinks into the paper at the same time. Even if the pigment concentration is increased, the handwriting density does not increase sufficiently or bleeding occurs in the handwriting.

[0005] Patent Document 1 describes a pigment ink for brush pens that uses carbon black, but in order to improve the concentration, it contains a large amount of pigment, resulting in poor drying resistance of the brush tip and the drying of the ink, causing the ink to become faint or smudge easily.

[0006] Patent Document 2 describes an ink for marking pens that uses carbon black and nigrosine as colorants to improve the dispersion stability and concentration of the pigment. However, the amount of pigment that can be stably dispersed is small, and similar to Patent Document 1, the pen tip has poor drying resistance and the ink dries slowly, resulting in faded or easily smudged ink. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2006-241202 [Patent Document 2] Japanese Patent Publication No. 2019-116603 [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention aims to provide a black aqueous ink composition that achieves both quick drying of the ink and drying resistance of the pen tip, while also exhibiting excellent dispersion stability and long-term stability of the pigment, and producing clear, water-resistant ink. [Means for solving the problem]

[0009] The present invention relates to a black aqueous ink composition comprising at least water, a wetting agent, 2-methylpentane-2,4-diol, a polyglycerin fatty acid ester with an HLB of 9.0 to 12.0, and a black coloring agent, wherein the black coloring agent is at least carbon black and nigrosine. The present invention relates to a writing instrument in the form of a brush pen, comprising a brush tip as the writing part and an ink storage part for containing the ink composition, configured such that the ink composition is supplied from the ink storage part to the writing part. The present invention relates to a writing instrument in the form of a brush pen, comprising the step of heating and dissolving at least the nigrosine, the 2-methylpentane-2,4-diol, and the polyglycerin fatty acid ester with an HLB of 9.0 to 12.0, and dispersing them in water. The third main point is a method for producing an aqueous ink composition, and the fourth main point is a method for producing an aqueous ink composition for a writing instrument, comprising a brush tip as a writing part and an ink container for containing the ink composition, wherein the ink composition from the ink container is supplied to the writing part, and the method comprises the steps of heating and dissolving at least the nigrosine, the 2-methylpentane-2,4-diol, and the polyglycerin fatty acid ester with an HLB of 9.0 to 12.0, and then dispersing them in water. [Effects of the Invention]

[0010] The carbon black pigment used in this invention has good lightfastness and water resistance. By adding 2-methylpentane-2,4-diol to the low-viscosity pigment ink composition, the drying of the writing is promoted, the ink retention of the pen tip is increased, and the fluidity of the ink is also improved, so the distance over which continuous writing can be performed without skipping is extended. At the same time, a complex in which polyglycerin fatty acid ester with an HLB of 9.0 to 12.0 is adsorbed on the surface of nigrosine, a black coloring agent, prevents the carbon black from sinking into the paper surface and prevents the pen tip, especially the brush tip, from drying out, resulting in an aqueous ink composition that provides dark, vivid black writing and quick drying of the writing. [Modes for carrying out the invention]

[0011] The details are explained below. Water is used as the main solvent in the ink, and it is preferable to use deionized water or purified water. The amount used is preferably 20% to 65% by weight of the total amount of the ink composition.

[0012] Carbon black can be used as a black pigment. Among black pigments, it is inexpensive, has a high black concentration, and exhibits strong lightfastness of handwriting, allowing for long-term preservation of handwriting. Carbon black can be used as a pigment dispersion prepared by dispersing pigment powder in an aqueous medium using conventionally known methods, or it can be used as a pre-packaged pigment dispersion. As a dispersant, surfactants and pigment dispersion resins are known to be used as known dispersants. Surfactants and pigment dispersion resins can also be used in combination. In particular, using a pigment dispersion resin allows for the production of a dispersion that improves the water resistance of the handwriting and ensures functionality. The amount of carbon black used is preferably 9.0% to 20% by weight of the total amount of ink composition, and particularly preferably 9.0% to 15% by weight for clear handwriting and good ejection. Furthermore, the average particle size of the carbon black in the dispersed ink composition is preferably 0.1 μm to 0.3 μm, and particularly when the average particle size is 0.1 μm to 0.2 μm, the handwriting has appropriate opacity, good color development, and clarity, and is optimal without color fading. Specific examples of usable powdered carbon black include Mitsubishi Carbon Black #10B, #20B, #14, #25, #30, #33, #40, #44, #45, #45L, #50, #55, #95, #260, #900, #970, #1000, #2200B, #2300, #2350, #2400B, #2650, #2700, #4000B, CF9, MA7, MA8, MA11, MA14, and MA77. , MA100, MA100S, MA100R, MA220, MA230, MA600 and MCF88 (all manufactured by Mitsubishi Chemical Corporation), Monarch 120, Monarch 700, Monarch 800, Monarch 880, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, Mogul L, Regal 99R, Regal 250R, Regal 300R, Regal 330R, Regal 400R, Regal 500 and Regal 660R (all manufactured by Cabot)Printex A, Printex G, Printex U, Printex V, Printex 55, Printex 140U, Printex 140V, Printex 35, Printex 40, Printex 45, Printex 85, Ninepex 35, Special Black 4, Special Black 4A, Special Black 5, Special Black 6, Special Black 100, Special Black 250, Special Black 350, Special Black 550, Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160 and Color Black S170 (all from Degussa)(Manufactured by Colombian Carbon Japan Co., Ltd.), Raven 14, Raven 1035, Raven 1040, Raven 7000, Raven 3500, Raven 1255, Raven 1180, Raven 5000 Ultra II, Raven 2500 Ultra, Raven 1250, Raven 760 Ultra, Raven 1100 Ultra, Raven 1080 Ultra, Raven 1060 Ultra (all manufactured by Colombian Carbon Japan Co., Ltd.), TOKABLACK #3800, TOKABLACK #3845, TOKABLACK #3855, TOKABLACK #4400, TOKABLACK #4500, TOKABLACK #5500, TOKABLACK #7270SB, TOKABLACK #7360SB, TOKABLACK #7550SB, TOKABLACK #7550F, TOKABLACK #8500 Examples include F, SeastN (LI-HAF), SeastS (SRF), SeastSP (SRF-LS), SeastSO (FEF), SeastSVH (SRF-HS), SeastTA (FT class), SeastV (GPF), SeastKH (N339), SeastFY (SRF-HS), SeastNH (N351), Seast3 (HAF), Seast3H (HAF-HS), Seast5H (IISAF-HS), Seast6 (ISAF), Seast7 (N234), Seast9 (SAF), Seast9H (SAF-HS), Seast116 (MAF), Seast116HM (MAF-HS), Seast300 (HAF-LS), Seast600 (ISAF-LS) (Tokai Carbon Co., Ltd.), ZAH119 Yellow (manufactured by Dainichi Seika Kogyo Co., Ltd.), etc. Specific examples of pigment dispersions include Pollux Black PM-812C (carbon black content 35% to 45% by weight, manufactured by Sumika Color Co., Ltd.), FUJI SP BLACK 8041 (carbon black content 20% by weight), FUJI SP BLACK 8065 (carbon black content 25% by weight), FUJI SP BLACK 8381 (carbon black content 12% by weight), FUJI SP BLACK 8406 (carbon black content 12% by weight), FUJI SP BLACK 8500 (carbon black content 25% by weight), FUJI SP BLACK 8175 (carbon black content 19-22% by weight), FUJI SP BLACK 8208 (carbon black content 19-22% by weight), FUJI SP BLACK 8871 (carbon black content 10% by weight) (all manufactured by Fuji Pigment Co., Ltd.), WA-H Color Black (carbon black content 15% by weight), WA-H Color Black 03 (carbon black content 10-20% by weight) (all manufactured by Dainichi Seika Kogyo Co., Ltd.), and DWB-B 810KA. Examples include BLACK (carbon black content 12.5-17.5% by weight) (manufactured by Nikko Bigx Co., Ltd.).

[0013] Furthermore, nigrosine is used as a black coloring agent. Specific examples of nigrosine that can be used include CI Solvent Black 5 and CI Solvent Black 7. Specific examples of CI Solvent Black 5 include Orient Spirit Black AB, Orient Spirit Black SB, NUBIAN BLACK NH-805, and NUBIAN BLACK NH-815 (all manufactured by Orient Chemical Industry Co., Ltd.), while specific examples of CI Solvent Black 7 include VALIFAST BLACK 1821, OIL BLACK BS, OIL BLACK NO.5, NUBIAN BLACK TN-870, NUBIAN BLACK TH-807, NUBIAN BLACK AH-807, NUBIAN 6807-25, NUBIAN 6807-40, NUBIAN 7807-25, NUBIAN 7807-40, NUBIAN BLACK PC-0870, NIGROSINE BASE EX, NIGROSINE BASE EEF, NIGROSINE BASE EXBP, NIGROSINE BASE EE, NIGROSINE BASE EEL, and NIGROSINE BASE Examples include EB (manufactured by Orient Chemical Industry Co., Ltd.), Aizen SOT Black 4, and Aizen SOT Black 13Liquid (manufactured by Hodogaya Chemical Co., Ltd.). The amount of nigrosine is preferably 0.03% to 2.00% by weight relative to the total amount of ink. By using 0.05% to 1.50% by weight, the action of the complex with a polyglycerol fatty acid ester with an HLB of 9.0 to 12.0 prevents the carbon black from sinking into the paper surface and prevents the pen tip, especially the brush tip, from drying out, resulting in an aqueous ink composition that produces dark, vivid black lines and quick-drying ink.

[0014] The color tone can be adjusted by using conventionally known dyes and pigments in combination, to the extent that they do not interfere with the color development of carbon black and nigrosine. Usable dyes include the yellow dyes CI Direct Yellow 4, 26, 44, 50, CI Acid Yellow 1, 7, 17, 19, 23, 25, 29, 38, 42, 49, 61, 72, 78, 110, 127, 135, 141, 42, CI Food Yellow 3, etc., and the red dyes CI Food Red 14, CI Acid Red 8, 9, 14, 18, 26, 27, 35, 37, 50, 51, 52, 50. 7, 82, 83, 87, 91, 92, 93, 94, 95, 98, 111, 129, 131, 138, 186, 249, 254, 265, 276, CI Basic Red 1, CI Direct Red 1, 4, 23, 31, 37, 39, 75, 80, 81, 83, 225, 226, 227, and other dyes include Acid Violet 15, 17, 49, Acid Orange 56, etc. For color adjustment, organic pigments are preferred in terms of color development and dispersion stability. Examples of yellow pigments include CI Pigment Yellow 1, 3, 12, 13, 18, 24, 42, 61, 62, 74, 83, 93, 94, 95, 97, 98, 99, 100, 104, 108, 109, 110, 115, 117, 120, 138, 139, 150, 153, 166, 167, 173, 185, etc. Examples of red pigments include CI Pigment Red 2, 3, 5, 17, 22, 38, 41, 48:2, 48:3, 49 Other pigments include CI Pigment Orange 5, 10, 13, 16, 36, 40, 43, CI Pigment Violet 19, 23, 31, 33, 36, 38, 50, 88, 112, 122, 123, 144, 146, 149, 166, 168, 170, 176, 177, 178, 179, 180, 185, 190, 194, 206, 207, 209, 216, 245, etc. Other pigments include CI Pigment Orange 5, 10, 13, 16, 36, 40, 43, CI Pigment Violet 19, 23, 31, 33, 36, 38, 50, etc. The amount of these color-adjusting pigments used is preferably 5% by weight or less of the total amount of the ink composition in order to obtain vivid colors. In addition, conventionally known white pigments, metal powder pigments, lustrous pigments, etc., can be used to add the desired opacity and dispersion stability to the ink or handwriting.

[0015] To disperse the pigment, known water-soluble resin dispersants and various surfactants can be selected and used. Examples of water-soluble resin dispersants include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, and itaconic acid, or their alkyl esters, as well as synthetic polymers polymerized by selecting from a group of monomers such as styrene, acrylonitrile, and vinyl acetate, or synthetic polymers copolymerized by selecting two or more from the aforementioned monomer group, used in the form of alkali metal salts, ammonium salts, and amine salts. Other examples include natural resins such as gum arabic and rosin and their derivatives, hydroxycellulose and its derivatives, polyvinyl alcohol, and polyvinylpyrrolidone. In particular, water-soluble salts of copolymers of styrene and / or α-methylstyrene and acrylic acid and / or methacrylic acid are preferred due to their excellent pigment dispersibility. Commercially available products include the Hyros series from Seikoh PMC Co., Ltd., ARUFON from Toagosei Co., Ltd., as well as Joncryl 52J, 57J, 60J, 61J, and 62 (all manufactured by BASF Japan Ltd.), and the amount used is preferably 10 to 50% by weight relative to the pigment content.

[0016] Polyglycerin fatty acid esters with an HLB of 9.0 to 12.0 can be used to improve the dispersion of nigrosine and the drying resistance of the pen tip. Specifically, these include polyglyceryl-10 stearate (NIKKOL Decaglyn 1-SV: HLB 12), polyglyceryl-10 isostearate (NIKKOL Decaglyn 1-ISV: HLB 12), polyglyceryl-10 stearate, polyglycerin-10 (NIKKOL Decaglyn 1-50SV: HLB 15), polyglyceryl-10 oleate (NIKKOL Decaglyn 1-OV: HLB 12), polyglyceryl-10 distearate (NIKKOL Decaglyn 2-SV: HLB 9.5), and polyglyceryl-10 diisostearate (NIKKOL Decaglyn 2-ISV: HLB 10) (The above are manufactured by Nikko Chemicals Co., Ltd.) and others. In particular, if the constituent fatty acids of the polyglycerin fatty acid ester are at least stearic acid and / or isostearic acid, the solubility of nigrosine is improved and the drying properties of the brush tip are also preferable. The amount used is preferably 0.4 to 2.0% by weight, and if it is 0.6 to 1.0%, an aqueous ink composition with excellent ink discharge properties can be obtained in a brush pen equipped with a brush tip. Polyglycerin fatty acid esters with a degree of polymerization of glycerin of 10 or higher can be particularly suitable for use because they can improve the solubility of nigrosine in 2-methylpentane-2,4-diol and create a stable aqueous dispersion of nigrosine. Furthermore, they provide good ink drying resistance, nigrosine dispersion stability, and long-term stability in the writing section.

[0017] Furthermore, various surfactants can be used, including anionic surfactants such as alkylated sulfonates and alkylallyl sulfonates of higher fatty acid amides, specifically alkyl sulfates, polyoxyethylene alkyl ether sulfates, N-acyl amino acid salts, N-acyl methyl taurate salts, polyoxyethylene alkyl ether acetates, alkyl phosphates, and polyoxyethylene alkyl ether phosphates. Among these, polycarboxylic acid type surfactants such as Demol EP, Homogenol L-18, Poise 520, and Poise 530 (all manufactured by Kao Corporation), naphthalene sulfonate formalin condensate type surfactants such as Demol N (manufactured by Kao Corporation), and Sannol LMT-1430, Sannol TD-3130 (both manufactured by Lion Corporation), Emal 20C, Emal 270J, Emal 20CM, Emal D-3-D, and Emal D Polyoxyethylene alkyl ether sulfates such as -4-D, Emal 20T, Latemul E-118B, Latemul E-150, Latemul WX (all manufactured by Kao Corporation), alkyl sulfate esters such as Sannol EH-1145M, Sannol LM-1130, Sannol LM-1140T (all manufactured by Lion Corporation), and Alscope LN-90PW, Alscope LS-40T, Alscope LS-30, A High-grade alkyl sulfates such as Luscope LS-25B, Alscope NS-230, Alscope TH-330K, Alscope TH-370N, Alscope DA-330S, Alscope N-335T, Alscope A-225B (manufactured by Toho Chemical Industry Co., Ltd.), Emal 0, Emal 0S, Emal 10S, Emal 2FG, Emal 2F-30 (all manufactured by Kao Corporation), and Lypon LS-250, Lypon LH- Alkylbenzenesulfonate sodium such as 200, Lipon S-230, Lipon PS-260, Lipon PS-860, Lipon LH-900 (manufactured by Lion Corporation), and olefin sulfonate sodium such as Liporan PJ-400CJ, Liporan LB-440, Liporan LJ-441, K Liporan PJ-400C, Liporan LB-840, Liporan PB-800CJ (all manufactured by Lion Corporation), and LunoxAlkylbenzene sulfonates such as S-40TD (manufactured by Toho Chemical Industry Co., Ltd.), Neoperex G-15, Neoperex G-25, Neoperex G-65, and Neoperex GS (all manufactured by Kao Corporation) can be preferably used. As nonionic surfactants, for example, polyoxyalkylene higher fatty acid esters, higher fatty acid esters of polyhydric alcohols and their derivatives, higher fatty acid esters of sugars, etc. Specifically, fatty acid esters of glycerin, propylene glycol fatty acid esters, pentaerythritol fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyethylene glycol fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene styrene-phenyl ethers, polyoxyethylene phytosterols, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene alkyl ethers Polyoxyethylene ethers, polyoxyethylene castor oil, polyoxyethylene lanolin, polyoxyethylene lanolin alcohol, polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, polyoxyethylene alkylphenyl formaldehyde condensates, etc. can be used, and among them, acetylene glycol type surfactants such as Surfinol TG and Surfinol 104E (both manufactured by Nisshin Chemical Industry Co., Ltd.), polyoxyethylene alkyl ether type surfactants such as Pegnol O-6 (manufactured by Toho Chemical Industry Co., Ltd.), Neugen P, and Neugen ET (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and polyoxyethylene alkylphenyl ether type surfactants such as Nonal 210 and Nonal 212 (both manufactured by Toho Chemical Industry Co., Ltd.), and NIKKOL Polyoxyethylene sorbitan fatty acid esters such as TL-10, NIKKOL TP-10, NIKKOL TO-10M, NIKKOL TO-10, NIKKOL TI-10 (all manufactured by Nikko Chemicals Co., Ltd.), Leodol TW-L120, Leodol TW-O120V, Leodol Super TW-L120, Leodol TW-P120, Leodol WO120 (all manufactured by Kao Corporation), and NIKKOL MYS-25, NIKKOL MYS-45, NIKKOL MYS-55, NIKKOLPolyoxyethylene glycol fatty acid esters such as CDS-600P (manufactured by Nikko Chemicals Co., Ltd.), Emanone 3199B, Emanone 3299V, Emanone 3299RV (manufactured by Kao Corporation), polyoxyethylene hydrogenated castor oil such as NIKKOL HCO-80, NIKKOL HCO-100 (manufactured by Nikko Chemicals Co., Ltd.), Emulgen 108, Emulgen 120, Emulgen 123P, Emulgen 130K, Emulgen 147, Emulgen 150, Emulgen 210P, Emulgen 220, Emulgen 350, Emulgen 430, Emulgen 4085, Emulgen 2025G (manufactured by Kao Corporation), NIKKOL PBC-34, NIKKOL PBC-44, NIKKOL BL-21, NIKKOL BL-25, NIKKOL Polyoxyalkylene alkyl ethers such as BC-15, NIKKOL BC-20, NIKKOL BC-23, NIKKOL BC-25, NIKKOL BC-30, NIKKOL BC-40, NIKKOL BS-20, NIKKOL BO-15V, NIKKOL BO-20V, NIKKOL BO-50V, NIKKOL BB-20, NIKKOL BB-30, NIKKOL BD-10 (all manufactured by Nikko Chemicals Co., Ltd.), and Ryoto sugar ester S-1570, Ryoto sugar ester S-1670, Ryoto sugar ester P-1570, Ryoto sugar ester P-1670, Ryoto sugar ester M-1695, Ryoto sugar ester O-1570, Ryoto sugar ester Sucrose fatty acid esters such as L-1695 (manufactured by Mitsubishi Chemical Foods Corporation), and Pluronic L10, Pluronic L31, Pluronic L61, Pluronic L62, Pluronic 10R5, Pluronic 17R2, Pluronic 25R2 (manufactured by BASF Japan Kao Corporation), Adeka Pluronic L-23, Adeka Pluronic L-31, Adeka Pluronic L-44, Adeka Pluronic L-61, Adeka Pluronic L-62, Adeka Pluronic L-64, Adeka Pluronic L-71, Adeka Pluronic L-72, Adeka Pluronic L-101, Adeka Pluronic L-121, Adeka PluronicPoly(oxyethylene)poly(oxypropylene) block copolymers such as P-84, ADEKA Pluronic P-85, ADEKA Pluronic P-103, ADEKA Pluronic F-68, ADEKA Pluronic F-88, and ADEKA Pluronic F-108 (all manufactured by ADEKA Corporation) can also be preferably used. In particular, polyoxyethylene distyrenated phenyl ether type surfactants such as Emulgen A-60, A-90, and Emulgen B-66 (all manufactured by Kao Corporation) are suitable as surfactants that do not easily cause color fading because they have low foaming properties for the ink, excellent dispersion stability for the pigment, and low permeability. These surfactants can be used individually or in combination. They can also be used in combination with water-soluble resin dispersants to disperse the pigment, and the amount of surfactant used is preferably 1 to 20% by weight relative to the total amount of aqueous pigment ink. In order to maintain good pigment dispersibility, an amount of 0.5% to 1% by weight is preferable, and furthermore, the amount of these surfactants used is preferably less than the amount of polyglycerin fatty acid ester used. By appropriately adjusting the type and amount of surfactant so that the surface tension of the ink composition is between 25 mN / m and 60 mN / m, the discharge stability is improved, making it even more preferable as an ink composition for use in brush pen-type writing instruments.

[0018] It is possible to use conventionally known wetting agents in combination to prevent ink from drying out in the writing area. Glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, 1,3-butylene glycol, thiodiethylene glycol, glycerin, benzyl glycol, benzyl diglycol, etc., glycol ethers such as ethylene glycol monomethyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monoethyl ether, diethylene glycol monoethyl ether, dipropylene glycol monoethyl ether, etc., urea, ethylene urea, thiourea, sorbitol, sorbitan, etc. can be used as needed. These wetting agents can be used alone or in combination. The amount used can be 5.0% by weight or more and 20.0% by weight or less based on the total amount of the ink composition. Among these wetting agents, it is preferable to combine glycerin, ethylene glycol, urea, and ethylene urea from the viewpoints of pen tip drying property, restoration of the pen nib, and suppression of precipitation. Furthermore, by combining urea, ethylene urea, and glycerin, an aqueous ink composition with good wetting property of the pen nib and difficult bleeding of the handwriting can be obtained.

[0019] 2-Methylpentane-2,4-diol is used to improve the quick drying property and fluidity of the handwriting. The amount used can be 1.0% by weight or more and 20.0% by weight or less based on the total amount of the ink composition. Particularly, when it is 6.0% by weight or more and 10% by weight or less, the fluidity of the handwriting is particularly improved, the ink composition content of the pen nib is good, and a suitable aqueous ink composition that can write long without blurring can be obtained. Although nigrosine does not dissolve even when heated with 2-methylpentane-2,4-diol alone, when used in combination with a polyglycerol fatty acid ester having an HLB of ≥9.0 and ≤12.0, it dissolves when heated, and a nigrosine aqueous dispersion forms a complex of nigrosine and polyglycerol fatty acid ester, and an aqueous ink composition with good wetting property of the pen nib and difficult bleeding of the handwriting can be obtained.

[0020] Furthermore, conventionally known organic solvents can be used in combination to improve various qualities of the ink composition, such as preventing ink freezing at low temperatures. Specific examples of organic solvents include alcohol-based solvents such as ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, diethylene glycol monophenyl ether, propylene glycol monobutyl ether, propylene glycol monophenyl ether, tripropylene glycol monobutyl ether, tripropylene glycol monophenyl ether, benzyl alcohol, α-methylbenzyl alcohol, lauryl alcohol, tridecyl alcohol, isododecyl alcohol, isotridecyl alcohol, isobutanol, and propylene glycol methyl ether acetate, propylene glycol diacetate, phenicelosolve, butyl cellosolve acetate, dibutyl cellosolve, 3-methyl-1,3-butanediol, 2-pyrrolidone, and N-methyl-2-pyrrolidone. These organic solvents can be used individually or in combination. The amount used can be between 5.0% and 50.0% by weight of the total ink composition.

[0021] Water-soluble resins, resin emulsions, and resin dispersions can also be used to fix the colorants. Examples include shellac, styrene-maleic acid copolymers and their salts, styrene-acrylic acid copolymers and their salts, α-methylstyrene-acrylic acid copolymers and their salts, acrylic resins, maleic acid resins, urea resins, polyvinyl butyral, polyvinyl acetal, polyamide resins, epoxy resins, polyvinyl alkyl ethers, coumarone-indene resins, rosin-based resins, urethane resins and their hydrogenated versions, ketone resins, and polyacrylic acid polymethacrylic acid copolymers. These resins can be used alone or in combination of two or more. When added to impart fixing property to the writing surface, the amount used is preferably 0.1% or more and 10.0% by weight or less based on the total amount of the ink composition. They may be used alone or in combination of two or more, and the pigment dispersion resin can also be used as a fixing agent.

[0022] Examples of the acrylic resin emulsion include FK-64S, FK-471, FK-474, FK-285, FK-6100, Mobinyl 952B (manufactured by Nippon Coating Resin Co., Ltd.), Vinzole 1637, 1117, 1008, 1606A, 911 (manufactured by Daido Kasei Kogyo Co., Ltd.), Joncryl HPD-196, HPD-96J, 7100, 711, PDX-7341, PDX-7787, PDX-7734, PDX-7687, 352D, PDX-7164, PDX-7430 (manufactured by BASF Japan Ltd.), etc. In particular, Vinzole 1606A (mentioned above) has a high glass transition point and can be preferably used because it forms a coating film by emulsifying and dispersing an acrylic resin with excellent fastness, thereby improving the water resistance of the handwriting.

[0023] Examples of the urethane resin emulsion include polycarbonate-based urethane resin emulsions such as Evafanol HA-50C and HA170 (manufactured by Nihon Kayaku Co., Ltd.), acrylic resin emulsions such as Acrit WEM-202U and WEM-321U (manufactured by Daisei Fine Chemical Co., Ltd.), polyester-based urethane resin emulsions such as Neosticker 400 and 700 (manufactured by Nihon Kayaku Co., Ltd.), and polyether-based urethane resin emulsions such as Permalin UA-200 (manufactured by Sanyo Chemical Industries, Ltd.) and Acrit WBR-016U (manufactured by Daisei Fine Chemical Co., Ltd.). In particular, the polyester-based urethane resin emulsion of Eucote UWS-145 (mentioned above) has a highly hydrophobic polyester in the polyisocyanate part, and a volatile neutralizing agent can be used when promoting self-emulsification, so it can be preferably used because it improves the water resistance of the handwriting.

[0024] Examples of olefin resin dispersions include Zaixene A, Zaixene L, and Zaixene H (all manufactured by Sumitomo Seika Co., Ltd.). In particular, Zaixene H (mentioned above) is suitable for use because it has a small number of hydrophilic groups in the monomer, improving the water resistance of the writing.

[0025] Water-soluble polymer compounds can be used to obtain suitable flow properties as an aqueous ink composition. For example, gum arabic, tragacanth gum, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, casein, xanthen gum, dextran, welan gum, ramzan gum, alka gum, methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, sodium starch glycolate, sodium alginate, propylene glycol alginate, hydroxypropyl guar gum, methylcellulose, ethylcellulose, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylic acid, carboxyvinyl polymer, polyethylene oxide, copolymer of vinyl acetate and polyvinylpyrrolidone, acrylic resin salts, copolymer of acrylic acid and alkyl methacrylate, or salts thereof can be used and may also be used in conjunction with pigment dispersion resins.

[0026] Resin particles or their aqueous dispersions can be used as anti-bleeding agents. Specifically, polyethylene waxes such as Hi-Tec E-7025P, Hi-Tec E-2213, Hi-Tec E-6500, Hi-Tec E-6314, Hi-Tec E-6400, Hi-Tec E-9460, Hi-Tec E-9015, Hi-Tec E-4A, Hi-Tec E-5403P, and Hi-Tec E-8237, polypropylene waxes such as Hi-Tec P-9018, Hi-Tec P-5300, Hi-Tec P-5800, and Hi-Tec P-5060P, and carboxyl group-containing ethylene copolymers such as Hi-Tec S-3121, Hi-Tec S-3800, Hi-Tec S-9242, Hi-Tec S-9200, Hi-Tec S-8512, and Hi-Tec S-3148K (all manufactured by Toho Chemical Industry Co., Ltd.) can be used. The amount used is preferably 1.0% to 20.0% by weight of the total ink composition. However, if used alone, using an amount sufficient to achieve a sufficient bleed prevention effect will increase the viscosity of the water-based ink composition itself, which may make it difficult to dispense due to its relationship with the writing part of the writing instrument and the flow path of the ink composition. Therefore, it is desirable to adjust the amount used appropriately. If the viscosity of the ink composition becomes too high when used alone, it can be used in combination with other substances that exhibit a bleed prevention effect to achieve a viscosity suitable for dispensing.

[0027] By appropriately adjusting the amounts and types of the above-mentioned resins, water-soluble polymer compounds, and pigment dispersants, the viscosity of the pigment ink composition can be adjusted to 1.0 mPa·s or more and less than 50 mPa·s at 25°C, resulting in a stable discharge for use as an ink composition for writing instruments, which is preferable for producing clearer handwriting.

[0028] To prevent mold growth, preservatives and antifungal agents such as sodium dehydroacetate, 1,2-benzoisothiazolin-3-one, sodium benzoate, morpholine, morpholine derivatives, and omazine-based agents may be added as appropriate, either individually or in combination of two or more.

[0029] To adjust the pH of the aqueous ink composition, basic substances such as sodium hydroxide, lithium hydroxide, triethanolamine, diethanolamine, monoethanolamine, and aminomethylpropanediol, as well as conventionally known acidic substances, can be used. Adjusting the pH of the aqueous ink composition to 7.0 or higher and 11.0 or lower using these adjusting agents is preferable because it further improves the long-term dispersion stability of the pigment, and these can be used individually or in combination of two or more types.

[0030] Furthermore, various additives such as dye dissolving agents, rust inhibitors like benzotriazole, defoaming agents like silicone emulsions, and degassing agents like ascorbic acid and hydroquinone sulfonate can be used as needed.

[0031] Various conventionally known methods can be used to manufacture aqueous ink compositions. For example, they can be produced using equipment such as ball mills, bead mills, roll mills, Henschel mixers, homomixers, propeller agitators, homogenizers, homodispersers, and kneaders. Filtration or centrifugal separation may be performed to remove coarse particles and gases. Heating, cooling, pressurizing, depressurizing, or inert gas displacement may be performed during manufacturing. Power can be supplied by electricity or pressurized air. These methods may be used individually or in combination.

[0032] The aqueous ink composition can be produced by dispersing the above-mentioned wetting agent, 2-methylpentane-2,4-diol, a polyglycerin fatty acid ester with an HLB of 9.0 to 12.0, carbon black, and nigrosine in water. A manufacturing method that includes the step of dispersing nigrosine in water is preferable because it can produce a black aqueous ink composition that achieves both the quick-drying properties of the ink and the drying resistance of the pen tip, which are the objectives of the present invention, and exhibits excellent dispersion stability and aging stability of the pigment, resulting in a clear, water-resistant ink. The specific method involves stirring a polyglycerin fatty acid ester with an HLB of 9.0 to 12.0 in 2-methylpentane-2,4-diol heated to 70-90°C for 30-60 minutes until completely dissolved. Nigrosine is then added and stirred for 120-180 minutes until completely dissolved. At this time, it is preferable to select a stirrer that can stir with high shear force, such as a homodisperser, to promote the dissolution of nigrosine. The completely dissolved nigrosine solution is then dropped into deionized water being stirred in a separate container. Further treatment of the nigrosine aqueous dispersion with a high-pressure homogenizer can be performed to standardize the nigrosine particle size and allow the polyglycerin fatty acid ester to be adsorbed more densely onto the surface. A colorant and additives are added to the nigrosine aqueous dispersion treated with the high-pressure homogenizer to obtain an aqueous ink composition. In this aqueous ink composition, generally known techniques may be used to standardize the particle size of the black colorant. If carbon black is in powder form, it may be dispersed in water beforehand as appropriate and used as a dispersion. While there is no limit to the ratio of nigrosine to polyglycerol fatty acid ester with an HLB of 9.0 to 12.0, it is preferable that the weight of the polyglycerol fatty acid ester with an HLB of 9.0 to 12.0 is 0.5 to 1.0 per unit weight of nigrosine, as this results in good dispersion stability and long-term stability of the nigrosine aqueous dispersion.

[0033] The aqueous ink composition of the present invention can be used in any writing instrument. For example, it can be used in writing instruments in which the ink composition is impregnated into an ink-absorbing material such as a fiber bundle, or in which the ink composition is directly contained in a hollow ink-containing tube. It can also be used in ballpoint pens in which a ball as a writing element is rotatably held in a ball holder made of synthetic resin or metal, brush pens using a brush tip, or fountain pens in which the ink composition passes through a gap in a resin or metal tube or slit. A suitable example of its use is marking pen ink. A marking pen is a writing instrument, also known as a felt pen or sign pen, that has a pen tip made of a fiber bundle, sintered body, or plastic, and an ink storage means inside the casing in which ink is impregnated into a cotton pad made of felt or a fiber bundle. Ink is supplied to the pen tip from this ink storage means using capillary action to enable writing. Alternatively, it can have a direct-ink type structure in which ink is directly stored in a cylindrical ink storage tube or casing, and this ink is supplied to the pen tip by various methods. In particular, an ink composition whose viscosity at 25°C is adjusted to be between 1.0 mPa·s and less than 50 mPa·s, whose pH is between 6.0 and 10.0, and whose surface tension is between 25 mN / m and 60 mN / m is especially suitable for use in a brush pen that has a brush tip made of tapered synthetic fibers, a brush tip diameter of 2.0 to 5.5 mm, and a liquid tank that can be pressed and deformed to assist in the dispensing of the ink composition, and which can supply ink to the brush tip, due to its stability over time and dispensing stability. [Examples]

[0034] Examples and comparative examples are shown below, but they do not limit the present invention in any way.

[0035] [Table 1]

[0036] [Table 2]

[0037] The ink compositions for each example and comparative example were prepared as follows. Examples 1-4 involved dissolving DECAGLYN 1-ISV in 2-methylpentane-2,4-diol heated to 80°C using the materials shown in Table 1, stirring with a homodisperser for 30 minutes until completely dissolved. NIGROSINE BASE EEF was then added and stirred for 180 minutes until completely dissolved. The completely dissolved nigrosine solution was then added dropwise to the entire volume of room-temperature deionized water being stirred in a homomixer in a separate container to prepare a nigrosine aqueous dispersion. Subsequently, the room-temperature nigrosine aqueous dispersion stirred in the homomixer was subjected to a high-pressure homogenizer (model: Starburst Lab, manufactured by Sugino Machine Co., Ltd.) at 245 MPa for three passes. FUJI SP BLACK 8208 and additives were added, stirred in a homomixer at room temperature for 30 minutes, and then subjected to a high-pressure homogenizer (same as above) at 245 MPa for three passes to obtain a black aqueous ink composition. Comparative Example 1 involved adding ethylene glycol, diethylene glycol, and urea to deionized water using the materials shown in Table 2, stirring with a homomixer at room temperature for 30 minutes, then adding nigrosine and carbon black powder, and stirring with a homomixer at room temperature for another 30 minutes to obtain a black aqueous ink composition. Comparative Example 2 was prepared using the materials shown in Table 2, except that FUJI SP BLACK 8208 was omitted from the formulation of Example 1. Comparative Example 3 involved using the materials shown in Table 2. Decaglyn 1-ISV was dissolved in 2-methylpentane-2,4-diol at room temperature by stirring with a homodisperser for 30 minutes until completely dissolved. The completely dissolved Decaglyn 1-ISV solution was then added dropwise to the entire volume of deionized water at room temperature being stirred in a homomixer in a separate container. Fuji SP Black 8208 and additives were added, and the mixture was stirred in a homomixer at room temperature for 30 minutes. The mixture was then subjected to a 3-pass treatment at 245 MPa in a high-pressure homogenizer (same as above) to obtain a black aqueous ink composition. Comparative Example 4 involved adding NIGROSINE BASE EEF to 2-methylpentane-2,4-diol heated to 80°C using the materials shown in Table 2, and stirring for 180 minutes. Although complete dissolution did not occur and some solid matter remained, a nigrosine aqueous dispersion was prepared by dropwise adding it to the entire volume of room-temperature deionized water being stirred in a homomixer in a separate container. Subsequently, the room-temperature nigrosine aqueous dispersion stirred in the homomixer was subjected to a high-pressure homogenizer (same as above) at 245 MPa for three passes. FUJI SP BLACK 8208 and additives were added, stirred in a homomixer at room temperature for 30 minutes, and then subjected to a high-pressure homogenizer (same as above) at 245 MPa for three passes to obtain a black aqueous ink composition. Comparative Example 5 used the materials shown in Table 2. DECAGLYN 1-ISV and NIGROSINE BASE EEF were added to the entire volume of room temperature deionized water being stirred in a homomixer and stirred for 30 minutes. Without going through the solvent dissolution step, the nigrosine aqueous dispersion was subjected to three passes at 245 MPa in a high-pressure homogenizer (same as above). FUJI SP BLACK 8208 and additives were then added, stirred in a homomixer at room temperature for 30 minutes, and subjected to three passes at 245 MPa in a high-pressure homogenizer (same as above) to obtain a black aqueous ink composition. Comparative Example 6 used the materials shown in Table 2. 2-methylpentane-2,4-diol, FUJI SP BLACK 8208, and additives were added to the total volume of deionized water. The mixture was stirred at room temperature for 30 minutes using a homomixer, and then subjected to three passes at 245 MPa using a high-pressure homogenizer (same as above) to obtain a black aqueous ink composition. Comparative Example 7 used the materials shown in Table 2. FUJI SP BLACK 8208 and additives were added to the entire volume of deionized water, stirred at room temperature for 30 minutes using a homomixer, and then subjected to three passes at 245 MPa in a high-pressure homogenizer (same as above) to obtain a black aqueous ink composition. Comparative Example 8 used the materials shown in Table 2. Ethylene glycol, diethylene glycol, urea, and PROXEL GXL(S) were added to deionized water, stirred for 30 minutes, dye was added, and a 25% aqueous NaOH solution was added as a pH adjuster. The mixture was stirred for 4 hours to obtain a black aqueous dye ink composition.

[0038] The materials listed in Tables 1 and 2 are as follows, and the proportions are shown in parts by weight. (1) FUJI SP BLACK 8208 (carbon black pigment dispersion, pigment solids content 19-22% by weight, manufactured by Fuji Pigment Co., Ltd.) (2) Printex G (powdered carbon black, manufactured by Degussa Japan Co., Ltd.) (3) NIGROSINE BASE EEF (CI Solvent Black 7, manufactured by Orient Chemical Industry Co., Ltd.) (4) WATER YELLOW 1 (CI Acid Yellow 23, manufactured by Orient Chemical Industry Co., Ltd.) (5) WATER RED 2 (CI Acid Red 87, manufactured by Orient Chemical Industry Co., Ltd.) (6) WATER BLACK 191L ​​(CI Direct Black 19, manufactured by Orient Chemical Industry Co., Ltd.) (7) WATER BLACK L200 (CI Direct Black 19, manufactured by Orient Chemical Industry Co., Ltd.) (8) 2-Methylpentane-2,4-diol (manufactured by Mitsui Chemicals, Inc.) (9) Glycerin (manufactured by Miyoshi Oil & Fat Co., Ltd.) (10) Ethylene glycol (manufactured by Nippon Alcohol Sales Co., Ltd.) (11) Diethylene glycol (manufactured by Nippon Alcohol Sales Co., Ltd.) (12) Urea (manufactured by Mitsui Chemicals, Inc.) (13) Ethylene urea (manufactured by Kanto Chemical Co., Ltd.) (14) DECAGLYN 1-ISV (Polyglyceryl-10 isostearate, manufactured by Nikko Chemicals Co., Ltd.) (15) PROXEL GXL(S) (1,2-benzoisothiazolin-3-one, manufactured by Lonza Japan Co., Ltd.) (16) San-ai Bac Sodium Omazine (Sodium Omazine, manufactured by San-ai Oil Co., Ltd.)

[0039] The aqueous ink compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 8 were filled into Pentel Pen XFL2L manufactured by Pentel Co., Ltd., which has a flexible ink cartridge part made of polyethylene that can be deformed and pressurized by pressing with the hand, a nib made of nylon fiber with a tapered tip, and a nib diameter of 3.4 mm. After filling and pressing 5 times to allow the ink composition to fully penetrate into the nib, a writing sample was prepared and a confirmation test was conducted.

[0040] Nib resilience test With the ink composition fully penetrated into the nib by pressing the cartridge part of the writing sample, write the character "永" five times in a 2 cm square size. Then, remove the cap and leave it horizontally in an atmosphere at a temperature of 20 ± 5 degrees and a humidity of 65 ± 5 degrees for 15 hours to dry the nib. After putting on the cap and leaving it horizontally in the same atmosphere for another 24 hours, write without pressing. Those with no smudging of the handwriting are marked as 〇, those with smudging during writing but no subsequent smudging are marked as △, and those with irrecoverable smudging are marked as ×.

[0041] Handwriting drying property test With the ink fully penetrated into the nib by pressing the cartridge part of the writing sample, After writing the character "永" five times in a 2 cm square size, write a straight line on high-quality paper with a handwriting length of 4 cm and a handwriting width of 5 mm as a guide. Then, trace the handwriting with a finger at an interval of once per second and measure the time until the handwriting dries.

[0042] Handwriting density test Spread the ink composition on high-quality paper with a rubber spatula and dry for 1 minute. Then, measure the lightness value [L* value] of the test paper by reflection measurement using a color computer (SE7700 manufactured by Nippon Denki Shokai Co., Ltd.).

[0043] Average particle size measurement Dilute the aqueous ink composition with ion-exchanged water so that the absorbance becomes 0.35, and use a particle size distribution meter (nanoWave2 manufactured by Microtrac BEL Co., Ltd.) to measure in terms of volume basis conversion The average particle diameter of a mixture of multiple pigments was measured. The representative diameter was measured by the dynamic light scattering method, and the average particle diameter was calculated by the median diameter. The unit of the average particle diameter is nm.

[0044] Sedimentation rate measurement An ink composition was put into a plastic centrifuge tube (length 9.5 cm, diameter 3 cm) so that the total weight including the centrifuge tube was 55 g, and a centrifuge manufactured by Kokusan Co., Ltd. (H-201FR, BN3 rotor) was used for centrifugation at 7500 rpm, a centrifugal force of 6357 G, and a temperature of 25 °C for 1 hour. After centrifugation, all the supernatant was recovered, the centrifuge tube was inverted and dried for 10 minutes, and then the total weight was measured. The weight of the dry sediment was obtained by subtracting the weight of the empty centrifuge tube from the total weight of the centrifuge tube containing the dry sediment. The sedimentation rate was obtained by dividing the weight of the dry sediment by the ink weight. The unit of the sedimentation rate is %. In the case of the aqueous ink composition mounted on the pen tip, excellent stability over time can be ensured if the sedimentation rate is 2.0% or less.

[0045] Writing distance measurement The cartridge part of the writing sample was pressed to let the ink soak into the pen tip, and the character "永" was written 5 times in a size of 2 cm square. Then, a mechanical writing distance measuring machine was used to measure the writing distance on high-quality paper at a writing speed of 7 centimeters per second, a writing load of 5 grams, and a writing angle of 60 degrees. Those that could write more than 50 m are marked as ○, and if it was less than 50 m, the writing distance is described.

[0046] Water resistance measurement The cartridge part of the writing sample was pressed to let the ink soak into the pen tip, and the character "永" was written 5 times in a size of 2 cm square. The character "永" was handwritten on high-quality paper, and the high-quality paper with the character "永" written on it was immersed in normal-temperature ion-exchanged water for 1 hour after 1 minute, and then taken out to check the state of the writing line. If there is no change in the handwriting, it is marked as ○, If there is a change in the handwriting, it is marked as ×.

[0047] Bleeding property measurement 2.0 μL of the water-based ink composition was dropped onto filter paper No. 2 using a measuring container, allowed to dry for 1 minute, and confirmed that the ink stain did not run when the writing was rubbed with a finger. The area was then confirmed using the area measurement function of a microscope (Keyence Corporation: VHX-6000).

[0048] As described above, the aqueous ink compositions of Examples 1 to 4 contain water, a wetting agent, 2-methylpentane-2,4-diol, a polyglycerin fatty acid ester with an HLB of 9.0 to 12.0, carbon black, and nigrosine. Therefore, we were able to obtain a black aqueous ink composition that achieves both quick drying and drying resistance of the pen tip, has excellent pigment dispersion stability and long-term stability, and produces a clear, water-resistant writing line. In contrast, Comparative Example 1 is the invention described in Patent Document 2, but it does not contain 2-methylpentane-2,4-diol, and because a large amount of humectant is used, the drying properties of the writing are poor, and the ink fluidity is also poor, resulting in a short writing distance. Comparative Example 2 is a formulation in which the black coloring agent carbon black is omitted and only nigrosine is used, but the density of the handwriting became lighter. Comparative Example 3 used a formulation without nigrosine, but the brush tip did not recover in the brush tip recovery test. It was found that polyglycerin fatty acid ester alone is not effective in restoring brush tip recovery. Comparative Example 4 was formulated without polyglycerin fatty acid ester, but the brush tip did not recover in the brush tip recovery test. It was found that nigrosine alone is not effective in restoring brush tip recovery. Comparative Example 5 was formulated without 2-methylpentane-2,4-diol, but the quick-drying properties and fluidity of the ink worsened. Comparative Example 6 was formulated without nigrosine and polyglycerol fatty acid ester, but in the brush tip recovery test, the brush tip did not recover, and the bleeding properties also worsened. Comparative Example 7 was formulated without 2-methylpentane-2,4-diol, nigrosine, and polyglycerin fatty acid ester, but in the brush tip recovery test, the brush tip did not recover, the drying properties of the ink worsened, and the bleeding properties also worsened. Comparative Example 8 used a dye as a coloring agent, but the water resistance, ink drying time, ink density, and bleeding properties deteriorated.

Claims

1. A writing instrument in the form of a brush pen, comprising: a brush tip as a writing part; water; a wetting agent; 2-methylpentane-2,4-diol; a polyglycerin fatty acid ester having an HLB of 9.0 or more and 12.0 or less; and a black coloring agent, wherein the black coloring agent is at least carbon black and nigrosine, and the ink containing part of the writing instrument is configured such that the ink containing part of the writing part is supplied with the writing part.

2. A method for producing an aqueous ink composition comprising carbon black, nigrosine, water, a wetting agent, 2-methylpentane-2,4-diol, and a polyglycerin fatty acid ester having an HLB of 9.0 or more and 12.0 or less, comprising the step of heating and dissolving at least the nigrosine, the 2-methylpentane-2,4-diol, and the polyglycerin fatty acid ester having an HLB of 9.0 or more and 12.0 or less, and then dispersing them in water, wherein the method comprises a brush tip as a writing part and an ink storage part that contains the ink composition, and the ink composition from the ink storage part is supplied to the writing part.

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