Aqueous ink composition for writing instrument and writing instrument containing the same

Abstract

To provide an aqueous ink composition for writing instruments which is capable of keeping the ink discharge rate constant during writing, regardless of the structure or form of the writing instrument incorporating the ink, without compounding a variety of compositions, and to provide a writing instrument containing the aqueous ink composition.SOLUTION: The present invention provides an aqueous ink composition for writing instruments that comprises a colorant, water, and two or more discharge stabilizers selected from a hydroxyacetophenone compound represented by general formula (1) and a C5-C8 1,2-alkanediol, and a writing instrument containing the aqueous ink composition. [In the general formula, R represents a substituent selected from hydrogen, 2-methyl, 2-methoxy, 2-hydroxy, 3-methyl, 3-methoxy, 3-chloro, 3-bromo, and 3-methylchloro.]SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous ink composition for writing instruments and a writing instrument. More specifically, the present invention relates to an aqueous ink composition for writing instruments having excellent ink ejection stability during writing and a writing instrument incorporating the same.

Background Art

[0002] Conventionally, in aqueous inks having a higher surface tension than oil-based inks, it has been difficult to stably supply ink to the pen tip. In particular, in writing instruments having a narrow ink flow path structure, blurring or skipping of the writing lines is likely to occur. In order to solve the above problems, a technique has been disclosed in which an alkyl polyglucoside having an alkyl group with 7 to 11 carbon atoms is added to appropriately reduce the surface tension of the ink and obtain ink ejection stability (see, for example, Patent Document 1).

[0003] Furthermore, in the aqueous ink composition of Cited Document 2, by using a diol having 5 to 7 carbon atoms and a diol having 1 to 4 carbon atoms together with a pigment, a polysaccharide, and particulate acrylic resin, a technique is disclosed in which the blending of a highly permeable diol and a low-permeable diol is adjusted to suppress bleeding on the paper surface while maintaining quick-drying properties in the writing. In the examples, it is described that clear writing can be obtained without blurring of the writing lines according to the above composition.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] As a result of intensive studies on improving the discharge stability of aqueous inks such as those in Patent Document 1, the present invention provides an aqueous ink composition for writing instruments that can always keep the ink discharge amount constant during writing, regardless of the structure and form of the writing instrument containing the ink, without blending various compositions. It also provides a writing instrument incorporating the same.

Means for Solving the Problems

[0006] The aqueous ink composition for writing instruments of the present invention is required to contain a colorant, water, a hydroxyacetophenone compound represented by the following general formula (1), and two or more discharge stabilizers selected from 1,2-alkanediols having 5 to 8 carbon atoms.

Chemical formula

Effects of the Invention

[0007] By selecting and using two or more from the hydroxyacetophenone compound represented by the general formula (1) and 1,2-alkanediols having 5 to 8 carbon atoms, the aqueous ink composition for writing instruments of the present invention can obtain ink discharge stability that keeps the ink discharge amount constant over a long period without blending various compositions or greatly changing the physical properties of the ink. Therefore, regardless of the structure and form of the writing instrument containing the ink, it becomes a writing instrument that can form a uniform handwriting without causing handwriting defects such as fading or skipping even after a long period of time.

Mode for Carrying Out the Invention

[0008] The ejection stabilizer used in the present invention is obtained by arbitrarily selecting two or more from a hydroxyacetophenone compound represented by the general formula (1) and a 1,2-alkanediol having 5 to 8 carbon atoms and using them in combination, so that stable ink ejection can be exhibited over a long period of time. This is because the interaction in an aqueous medium between the hydroxyacetophenone compound and the compound selected from 1,2-alkanediol increases the stability of the ejection stabilizer itself in the aqueous ink, and it is presumed that the precipitation phenomenon associated with the physical property change of the composition dissolved in the ink can be suppressed in the long term, and the ink ejection property equivalent to the initial stage can be maintained.

[0009] The ejection stabilizer exhibits its effect by using a plurality of those selected from hydroxyacetophenone compounds, using a plurality of those selected from 1,2-alkanediols, or using in combination those selected from hydroxyacetophenone compounds and those selected from 1,2-alkanediols. In particular, since the effect is high even in a small amount, it is preferable to use in combination those selected from hydroxyacetophenone compounds and those selected from 1,2-alkanediols. In that case, when the 1,2-alkanediol is blended in an amount of 1.1 to 5 times the mass ratio with respect to the hydroxyacetophenone compound, the dissolution stability of the ejection stabilizer becomes particularly excellent, so that a high effect can be exhibited with a small amount of addition, which is more preferable. The 1,2-alkanediol has high permeability, and when blended in an amount exceeding 5 times the mass ratio, bleeding of handwriting is likely to occur on the paper surface.

[0010] Examples of the hydroxyacetophenone compound represented by the general formula (1) include p-hydroxyacetophenone having a substituent selected from hydrogen, 2-methyl, 2-methoxy, 2-hydroxy, 3-methyl, 3-methoxy, 3-chloro, 3-bromo, and 3-methylchloro, and its substituted compounds.

[0011] Examples of the 1,2-alkanediol having 5 to 8 carbon atoms include 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, and 1,2-octanediol.

[0012] The discharge stabilizer composed of two or more of the above-mentioned compounds is added in the range of 0.5 to 20% by mass, preferably 0.7 to 10% by mass, more preferably 0.8 to 8% by mass in the total amount of the aqueous ink composition. In the above range, the ink discharge stabilizing performance is particularly effectively exhibited.

[0013] As the colorant, all dyes and pigments that can be dissolved or dispersed in an aqueous medium can be used, and specific examples thereof are illustrated below. As the dye, acid dyes, basic dyes, direct dyes, etc. can be used. Examples of the acid dye include New Coccine (C.I. 16255), Tartrazine (C.I. 19140), Acid Blue Black 10B (C.I. 20470), Guinea Green (C.I. 42085), Brilliant Blue FCF (C.I. 42090), Acid Violet 6B (C.I. 42640), Soluble Blue (C.I. 42755), Naphthalene Green (C.I. 44025), Eosin (C.I. 45380), Phloxine (C.I. 45410), Erythrosine (C.I. 45430), Nigrosine (C.I. 50420), Acid Flavin (C.I. 56205), etc. Examples of the basic dye include Chrysoidine (C.I. 11270), Methyl Violet FN (C.I. 42535), Crystal Violet (C.I. 42555), Malachite Green (C.I. 42000), Victoria Blue FB (C.I. 44045), Rhodamine B (C.I. 45170), Acridine Orange NS (C.I. 46005), Methylene Blue B (C.I. 52015), etc. Examples of direct dyes include Congo Red (C.I. 22120), Direct Sky Blue 5B (C.I. 24400), Violet BB (C.I. 27905), Direct Deep Black EX (C.I. 30235), Kayarus Black G Conc. (C.I. 35225), Direct Fast Black G (C.I. 35255), Phthalocyanine Blue (C.I. 74180), etc.

[0014] Examples of the pigments include inorganic pigments such as carbon black and ultramarine blue, organic pigments such as copper phthalocyanine blue and benzidine yellow, and water-dispersed pigment products that are finely and stably dispersed in an aqueous medium in advance using surfactants, etc. For example, C.I. Pigment Blue 15:3B [Product Name: S.S. Blue GLL, Pigment Content 22%, Manufactured by Sanyo Color Co., Ltd.], C.I. Pigment Red 146 [Product Name: S.S. Pink FBL, Pigment Content 21.5%, Manufactured by Sanyo Color Co., Ltd.], C.I. Pigment Yellow 81 [Product Name: TC Yellow FG, Pigment Content Approximately 30%, Manufactured by Dainichi Seika Kogyo Co., Ltd.], C.I. Pigment Red 220 / 166 [Product Name: TC Red FG, Pigment Content Approximately 35%, Manufactured by Dainichi Seika Kogyo Co., Ltd.], etc. can be mentioned. As the fluorescent pigment, synthetic resin fine particle-shaped fluorescent pigments in which various fluorescent dyes are solid-solubilized in a resin matrix can be used. In addition, examples include pearl pigments, metallic pigments such as gold and silver, phosphorescent pigments, white pigments such as titanium dioxide, metal powders such as aluminum, and further, capsule pigments in which a thermochromic composition, a photochromic composition, a fragrance, etc. are directly or microencapsulated.

[0015] As the thermochromic composition, a reversible thermochromic composition composed of (a) an electron-donating color-developing organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the color-developing reaction temperature of the above two is suitable, and it is applied as a reversible thermochromic microcapsule pigment by encapsulating it in a microcapsule. As the reversible thermochromic composition, those described in Japanese Patent Publication No. 51-44706, Japanese Patent Publication No. 51-44707, Japanese Patent Publication No. 1-29398, etc., change color before and after a predetermined temperature (color change point), exhibit a decolorized state in a temperature range equal to or higher than the high-temperature-side color change point, and exhibit a colored state in a temperature range equal to or lower than the low-temperature-side color change point. Among these two states, only a specific one of the states exists at room temperature, and the other state is maintained while the heat or cooling heat required for the manifestation of the state is applied, but returns to the state presented at room temperature when the application of the heat or cooling heat ceases. A heat-decolorizing type microcapsule pigment in which a reversible thermochromic composition having a relatively small hysteresis width (ΔH = 1 to 7°C) is encapsulated in microcapsules can be applied. Furthermore, those exhibiting relatively large hysteresis characteristics (ΔH = 8 to 50°C) described in Japanese Patent Publication No. 4-17154, Japanese Patent Laid-Open No. 7-179777, Japanese Patent Laid-Open No. 7-33997, Japanese Patent Laid-Open No. 8-39936, etc., or those exhibiting large hysteresis characteristics described in Japanese Patent Laid-Open No. 2006-137886, Japanese Patent Laid-Open No. 2006-188660, Japanese Patent Laid-Open No. 2008-45062, Japanese Patent Laid-Open No. 2008-280523, etc., that is, the shape of the curve plotting the change in coloring density due to temperature change follows a significantly different path when the temperature is increased from the low-temperature side to the color change temperature range and when the temperature is decreased from the high-temperature side to the color change temperature range, and the colored state in a low-temperature range below the complete coloring temperature or the decolorized state in a high-temperature range above the complete decolorizing temperature has color memory in a specific temperature range. A heat-decolorizing type microcapsule pigment encapsulating a reversible thermochromic composition can also be applied. Incidentally, specifically, as the reversible thermochromic composition having color memory, the complete coloring temperature is a temperature that can only be obtained in a freezer, a cold region, etc., that is, -50 to 0°C, preferably -40 to -5°C, more preferably -30 to -10°C, and the complete decolorizing temperature is a temperature obtained from frictional heat by a friction body, a heating body such as a hair dryer that is close at hand, that is, 50 to 95°C, preferably 50 to 90°C, more preferably 60 to 80°C. By specifying the ΔH value to be 40 to 100°C, it can function effectively to maintain the color presented in the normal state (daily living temperature range).

[0016] The coloring agent can be used by appropriately mixing one kind or two or more kinds thereof, and is used in the range of 1 to 35% by mass, preferably 2 to 30% by mass in the ink composition.

[0017] The ink composition according to the present invention contains water. The water is not particularly limited, and examples thereof include tap water, ion-exchanged water, ultrafiltration water, distilled water and the like. The content rate of water with respect to the total mass of the ink composition is not particularly limited, but is preferably in the range of 35 to 95% by mass, more preferably 40 to 90% by mass.

[0018] In the ink composition according to the present invention, in addition to the above-described essential components, optional components can be blended within a range not impairing the effects of the present invention.

[0019] For example, conventionally widely used water-soluble organic solvents compatible with water can also be used. Examples thereof include ethanol, propanol, butanol, glycerin, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thiodiethylene glycol, hexylene glycol, 1,3-butanediol, neoprene glycol, polyethylene glycol, propylene glycol, butylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, 2-pyrrolidone, N-methyl-2-pyrrolidone and the like. In addition, one kind or two or more kinds of the water-soluble organic solvents can be used in combination, and are used in the range of 2 to 60% by mass, preferably 5 to 35% by mass in the ink composition.

[0020] Furthermore, a water-soluble resin can be added to impart fixability and viscosity to the paper surface. Examples of the water-soluble resin include alkyd resin, acrylic resin, styrene maleic acid copolymer, cellulose derivative, polyvinylpyrrolidone, polyvinyl alcohol, dextrin, etc. The water-soluble resin can be used alone or in combination of two or more kinds, and is used in the range of 1 to 30% by mass in the ink composition.

[0021] In addition, if necessary, rust inhibitors such as benzotriazole, tolyltriazole, 2,5-dimercapto-1,3,4-thiadiazole, saponin, phenol, 1,2-benzisothiazolin-3-one and its sodium salt, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, methylisothiazolinone, 3-iodo-2-propynyl N-butylcarbamate, etc. preservatives or fungicides, wetting agents such as urea, nonionic surfactants, sorbitol, mannitol, sucrose, glucose, reduced starch hydrolyzate, sodium pyrophosphate, In addition, an antifoaming agent, a dispersant, a specific gravity adjuster, etc. may be used. Furthermore, chemically removing bubbles can also be achieved by adding ascorbic acids, erythorbic acids, α-tocopherol, catechins, synthetic polyphenols, kojic acid, alkylhydroxylamine, oxime derivatives, α-glucosylrutin, α-lipoic acid, phosphonates, phosphinates, sulfites, sulfoxylates, dithionites, thiosulfates, thiourea dioxide, etc. Also, by adding a thickening inhibitor such as an oligomer of N-vinyl-2-pyrrolidone, an oligomer of N-vinyl-2-piperidone, N-vinyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, ε-caprolactam, an oligomer of N-vinyl-ε-caprolactam, etc., the function in the emerging form can be enhanced. Furthermore, lubricants can be added in combination. For example, metal soaps, polyalkylene glycol fatty acid esters, ethylene oxide-added cationic surfactants, phosphate ester-based surfactants, β-alanine type surfactants, N-acyl amino acids, N-acyl methyl taurine, 2,5-dimercapto-1,3,4-thiadiazole and its salts and oligomers, 3-amino-5-mercapto-1,2,4-triazole, thiocarbamate, dimethyldithiocarbamate, α-lipoic acid, condensates of N-acyl-L-glutamic acid and L-lysine and their salts, etc. are used.

[0022] Moreover, a shear-thinning viscosity-imparting agent can also be added to the ink composition. For example, water-soluble polysaccharides, polymers with a molecular weight of 100,000 to 150,000 mainly composed of alkyl esters of methacrylic acid, poly-N-vinylcarboxylic acid amide cross-linked products, benzylidene sorbitol and its derivatives, benzylidene xylitol and its derivatives, alkali-thickening type acrylic resins, crosslinkable acrylic acid polymers, inorganic fine particles, nonionic surfactants with an HLB value of 8 to 12, metal salts and amine salts of dialkyl sulfosuccinic acid, etc. can be exemplified. Examples of water-soluble polysaccharides include xanthan gum, welan gum, zeta-sea gum, diutan gum, macrohomoopsis gum, succinoglycan (average molecular weight of about 1 million to 8 million) which is an organic acid-modified heteropolysaccharide whose constituent monosaccharides are glucose and galactose, guar gum, locust bean gum and its derivatives, hydroxyethyl cellulose, alkyl esters of alginic acid, glucomannan, carbohydrates having gelling ability extracted from seaweeds such as agar and carrageenan, etc. The shear-thinning viscosity-imparting agent can be used alone or in combination of two or more. Note that the shear-thinning viscosity of the ink refers to the rheological property that it has a high viscosity and is difficult to flow in a stationary state or when the stress is low, and shows good fluidity with a decrease in viscosity when the stress increases, which means a liquid property also called thixotropy or pseudoplasticity.

[0023] The aqueous ink composition for writing instruments of the present invention is filled in marking pens, ballpoint pens, fountain pens, etc., in which a fiber tip, a felt tip, a plastic tip, or a ballpoint pen tip is attached to the writing tip portion, and which are of the cap type or the retractable type.

[0024] When filling a marking pen, the structure and shape of the marking pen itself are not particularly limited. For example, a pen tip for a marking pen such as a fiber tip, a felt tip, or a plastic tip (bullet type, chisel type, brush pen type, etc.) is attached to the writing tip portion, and an ink reservoir made of a fiber bundle housed inside the shaft cylinder is impregnated with ink, and the ink is supplied to the writing tip portion; a structure in which ink is directly housed inside the shaft cylinder, and a predetermined amount of ink is supplied to the writing tip portion via a comb-shaped ink flow regulating member or an ink flow regulating member made of a fiber bundle; a structure in which ink is directly housed inside the shaft cylinder, and a predetermined amount of ink is supplied to the writing tip portion by a valve mechanism. Further, the ink storage portion can also be a cartridge. In addition to those having one pen tip, a double-headed form having pen tips of different thicknesses and shapes at both ends of the shaft cylinder may also be used. In the double-headed form, one end may be a ballpoint pen.

[0025] When filling a ballpoint pen, the structure and shape of the ballpoint pen itself are not particularly limited. For example, a structure in which an ink reservoir made of a fiber bundle housed inside the shaft cylinder is impregnated with ink and the ink is supplied to the writing tip portion; a structure in which ink is directly housed inside the shaft cylinder and a comb-shaped ink flow regulating member or an ink flow regulating member made of a fiber bundle is interposed; a ballpoint pen having an ink storage tube filled with the ink composition inside the shaft cylinder, the ink storage tube communicating with a tip having a ball attached to the tip portion, and an ink backflow prevention body being in close contact with the end face of the ink.

[0026] As the ink backflow prevention body, either a liquid or a solid can be used. Examples of the liquid ink backflow prevention body include non-volatile media such as polybutene and silicone oil, and silica, aluminum silicate, etc. can be added to the media as desired. In addition, examples of the solid ink backflow prevention body include resin molded articles. Incidentally, the liquid and solid ink backflow prevention bodies can also be used in combination.

Examples

[0027] Examples will be described below, but the present invention is not limited to these examples. Table 1 shows the compositions of the aqueous inks for writing instruments of the examples and comparative examples. Incidentally, the numerical values of the compositions in the table indicate parts by mass.

[0028]

Table 1

[0029] The contents of the raw materials in the table will be described according to the reference numbers. (1) Manufactured by Orient Chemical Industries Co., Ltd., trade name: WATER BLUE 105 (C.I. Acid Blue 90) (2) Manufactured by Sanyo Pigment Co., Ltd., trade name: SANDYE SUPER RED 1326 (3) A microcapsule pigment containing a reversible thermochromic composition composed of 4.5 parts of 2-(2-chloroanilino)-6-di-n-butylaminofluorane as the (a) component, 4.5 parts of 1,1-bis(4'-hydroxyphenyl)n-decane as the (b) component, 7.5 parts of 2,2-bis(4'-hydroxyphenyl)hexafluoropropane, and 50.0 parts of 4-benzyloxyphenylethyl caprate (complete color development temperature (t1): -20 °C, complete decolorization temperature (t4): 57 °C, average particle diameter: 2.5 μm, color change from black to colorless) (4) A microcapsule pigment encapsulating a reversible thermochromic composition composed of 1.0 part of 3,6-bis(diphenylamino) fluoran as component (a), 3.0 parts of 1,1-bis(4-hydroxyphenyl)-2-ethylhexane as component (b), 5.0 parts of 2,2-bis(4'-hydroxyphenyl)-hexafluoropropane as component (b), and 50.0 parts of 4-benzyloxyphenylethyl caprate as component (c) (complete color development temperature (t1): -20 °C, complete decolorization temperature (t4): 55 °C, average particle diameter: 1.8 μm, color change from blue to colorless) (5) p-Hydroxyacetophenone (where R in the formula is hydrogen) (6) 2'-Methoxy-4'-hydroxyacetophenone (where R in the formula is 2-methoxy) (7) 4'-Hydroxy-3'-methylacetophenone (where R in the formula is 3-methyl) (8) Manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., trade name: Presurf AL (9) Manufactured by Arkema Japan Co., Ltd., trade name: GLYCACIL 2000

[0030] Preparation of marking pen ink The raw materials were mixed in the blending amounts of Examples 1 and 2 and Comparative Examples 1 and 2, stirred and dissolved at 20 °C for 1 hour, filtered, and then allowed to stand for 24 hours until the bubbles disappeared to obtain a marking pen ink composition.

[0031] Manufacture of marking pen The marking pen ink composition was impregnated into an ink storage body in which a polyester sliver was coated with a synthetic resin film, housed in a shaft cylinder made of polypropylene resin, and a resin-processed tip (bullet type) of polyester fiber was assembled in a connected state to the tip of the shaft cylinder via a holder, and a cap was attached to obtain a marking pen.

[0032] Preparation of ballpoint pen ink A The raw materials were mixed in the blending amounts of Examples 1 and 2 and Comparative Examples 1 and 2, stirred at 400 rpm for 1 hour with a disper at 20 °C, filtered, and then allowed to stand for 24 hours until the bubbles disappeared to obtain a ballpoint pen ink composition.

[0033] Preparation of Ballpoint Pen A A pen core (comb-tooth ink reservoir) equipped with a stainless steel tip holding a carbide ball with a diameter of 0.7 mm was fitted to the front of the shaft cylinder (opening side). Then, the ink was filled into the outer casing of the pen core type writing instrument with the rear (sealed side) serving as the ink storage part, and the ballpoint pen A was prepared by fitting the cap.

[0034] Preparation of Ballpoint Pen Ink B Each raw material except the thickener was mixed in the blending amounts of Examples 3 to 6 and Comparative Examples 3 to 6, stirred at 400 rpm for 1 hour with a disperser at 20°C, then the thickener was added and stirred for another 1 hour, and then left to stand for 48 hours until the bubbles disappeared to obtain a ballpoint pen ink composition.

[0035] Preparation of Ink Backflow Preventing Body After adding 1.5 parts of fatty acid amide as a thickener to 98.5 parts of polybutene as the base oil, it was kneaded with three rolls to obtain an ink backflow preventing body.

[0036] Preparation of Ballpoint Pen B Each of the ink compositions was filled into a ballpoint pen refill in which a stainless steel tip holding a carbide ball with a diameter of 0.4 mm was fitted to one end of a transparent polypropylene pipe. After disposing the ink backflow preventing body at the rear end, the ballpoint pen refill was incorporated into the shaft cylinder and the cap was attached to prepare the ballpoint pen B.

[0037] The following tests were conducted using the obtained ink compositions and each writing instrument. Ink Stability Test Each ink was sealed in a container, and the state of the ink was visually confirmed when it was left in a thermostat at 30°C for 90 days. Writing Test After leaving each writing instrument confirmed to be capable of writing in an environment at 30°C for 90 days, the handwriting state was visually confirmed when 12 spiral circles were continuously written by hand on JIS P3201 writing paper A. The results of each test are shown below.

[0038]

Table 2

[0039] The evaluation of the test results is as follows. Ink stability test ○: No change compared to before the test. △: Slight precipitation and mild aggregation were confirmed. ×: Ink separation, significant precipitation, or aggregation were confirmed. Writing test Examples 1, 2 and Comparative Examples 1, 2 evaluated two types of marking pens and ball pen A, but no difference in evaluation by writing instruments was observed. Examples 3 to 6 and Comparative Examples 3 to 6 were evaluated with ball pen B. ○: Good handwriting was obtained. ×: Ink ejection was not stable, and line breaks or smearing were confirmed in the handwriting or writing was impossible.

Claims

1. A water-based ink composition for writing instruments comprising a colorant, water, and two or more discharge stabilizers selected from a hydroxyacetophenone compound represented by the following general formula (1) and 1,2-alkanediols having 5 to 8 carbon atoms. 【Chemistry 1】 [In the formula, R is a substituent selected from hydrogen, 2-methyl, 2-methoxy, 2-hydroxy, 3-methyl, 3-methoxy, 3-chloro, 3-bromo, and 3-methylchloro.]

2. The aqueous ink composition for writing instruments according to claim 1, wherein the discharge stabilizer is contained in an amount of 0.5 to 20% by mass in the aqueous ink.

3. The aqueous ink composition for writing instruments according to claim 1, wherein the discharge stabilizer comprises one or more hydroxyacetophenone compounds and one or more 1,2-alkanediols.

4. The aqueous ink composition for writing instruments according to claim 3, wherein a 1,2-alkanediol is blended in an amount of 1.1 to 5 times the mass ratio of the hydroxyacetophenone compound.

5. A writing instrument comprising the aqueous ink composition for writing instruments described in any one of claims 1 to 4.

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