Water-based ink composition for writing instruments and marking pen containing the same.

Abstract

The present invention provides a water-based ink composition for writing instruments and a marking pen containing it, which allows the pigment to maintain excellent redispersibility in the water-based ink even during long-term storage, and suppresses the hard cake formation of the pigment even after a long period of time, thereby enabling the formation of good writing lines with a uniform concentration from the beginning. [Solution] An aqueous ink composition for writing instruments comprising a pigment, water, a polymer flocculant, and a fluid gel with an average particle size of 0.1 to 5 μm, and a marking pen containing the same.

Description

Technical Field

[0001] The present invention relates to an aqueous ink composition for writing instruments and a marking pen. More particularly, the present invention relates to an aqueous ink composition for writing instruments having excellent redispersibility of pigments and a marking pen incorporating the same.

Background Art

[0002] Conventionally, in aqueous inks, various pigments have been widely used because they have higher light resistance than dyes, can provide handwriting with high decorative effects such as metallic luster and pastel colors, and can obtain a hue corresponding to temperature changes. Since the pigments generally have a large specific gravity, they tend to sediment and aggregate, and may harden over time. When applied to writing instruments, writing defects such as streaks and shading in the handwriting or inability to write may easily occur.

[0003] To solve the above problems, techniques for applying additives such as fermented cellulose, hollow resin particles, and polymer flocculants according to the type of pigment have been disclosed (see, for example, Patent Documents 1 to 3).

[0004] In the aqueous ink composition of Cited Document 1, a technique for suppressing the sedimentation of inorganic pigments by using fermented cellulose and a polymer substance for high specific gravity inorganic pigments such as pearl pigments is disclosed, and it is described that the ink is discharged uniformly when incorporated into a marking pen. The aqueous ink composition of Cited Document 2 is a gel ink using hollow resin particles together with titanium oxide having a size of 0.4 μm or less. By reducing the average specific gravity of the solid content in the ink composition with the hollow resin particles, the dispersion stability of the pigment in the gel ink is improved. In the aqueous ink composition of Cited Document 3, by using a polymer flocculant for thermochromic microcapsule pigments, the polymer flocculant has a loose bridging action to make the microcapsule pigments in a loose aggregated state, and suppresses the separation sedimentation of the microcapsule pigments in the capillary gaps of the ink absorber to prevent the occurrence of darkening and lightening of the handwriting.

[0005] While the technologies described in these patent documents maintain the dispersibility of pigments and suppress sedimentation, they may not be sufficiently effective over long periods of time, sometimes resulting in the sedimented pigments aggregating and forming a hard cake. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2016-69564 [Patent Document 2] International Publication No. 2018 / 083782 Brochure [Patent Document 3] Japanese Patent Application Publication No. 11-335613 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The present invention provides a water-based ink composition for writing instruments and a marking pen containing it, which allows the pigment to maintain excellent redispersibility in water-based ink even during long-term storage, and which suppresses the hard cake formation of the pigment even after a long period of time, thereby enabling the formation of good writing lines with a uniform concentration from the beginning. [Means for solving the problem]

[0008] The aqueous ink composition for writing instruments of the present invention is required to comprise a pigment, water, a polymer flocculant, and a fluid gel. Furthermore, the requirements include that the average particle size of the fluid gel is in the range of 0.1 to 5 μm, that the fluid gel is made of duran gum, and that the duran gum is either deacyl or native. Furthermore, the polymer flocculant must be a cellulose derivative. Furthermore, the requirement is a marking pen containing one of the aqueous ink compositions for writing instruments described above, and the requirement is that the marking pen contains an ink absorbent. [Effects of the Invention]

[0009] The aqueous ink composition for writing instruments of the present invention, when using a pigment as a coloring agent, utilizes a polymer flocculant and a fluid gel in combination, thereby maintaining excellent redispersibility of the pigment in the ink even during long-term storage, and suppressing the hard cake formation of the pigment even after a long period of time. As a result, it is possible to form good writing lines with uniform density from the beginning without the occurrence of streaking or differences in density. [Modes for carrying out the invention]

[0010] The polymer flocculant used in this invention interposes itself between pigments, forming loose aggregates and suppressing the aggregation of pigments through contact with each other. Examples of polymeric flocculants include polyvinylpyrrolidone, polyethylene oxide, and water-soluble polysaccharides. Examples of water-soluble polysaccharides include tragacanth gum, guar gum, pullulan, cyclodextrin, and water-soluble cellulose derivatives, with water-soluble cellulose derivatives being preferred. Specific examples of water-soluble cellulose derivatives include methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, and carboxymethylcellulose, which are preferably used.

[0011] Specific examples of commercially available products include the HEC series A, S, and CF grades (manufactured by Sumitomo Seika Co., Ltd.), the HEC Daicel SP, SE, and EE series (manufactured by Daicel Fichem Co., Ltd.), the CELLOSIZE WP, QP, and EP series (manufactured by Dow Chemical Japan Ltd.), SANHEC (manufactured by Sansho Co., Ltd.), and the Selogen series (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.). In the present invention, the content of the polymer flocculant is preferably 0.1 to 3.0% by mass, and more preferably 0.3 to 2.0% by mass, based on the total amount of the ink composition.

[0012] Fluid gel is an aggregate of fine gels that exhibits liquid-like fluidity. In this invention, by using it in combination with a polymer flocculant, the fluid gel penetrates between pigments that have formed loose aggregates due to the polymer flocculant, acting as a buffer. With the three components in the above configuration, the pigment can maintain a state of excellent redispersibility in the ink more efficiently and for a longer period of time, thus suppressing the hard cake formation of the pigment even when the ink is stored for a long period of time. As a result, there will be no smudging or differences in density in the handwriting formed on the paper, and good handwriting will be obtained consistently from the beginning. In particular, when using ink-absorbing materials (cotton pads) or marking pen tips made of fiber bundles or resin-bound fiber bundles, separation of each pigment does not occur in these capillary gaps. Therefore, when left upright or inverted, pigment separation and the darkening or lightening of the handwriting can be suppressed over a long period of time.

[0013] The fluid gel used in this invention preferably has an average particle size in the range of 0.1 to 5 μm, and particularly preferably in the range of 0.4 to 5 μm. If the average particle size is greater than 5 μm, the fluidity deteriorates and inhibits ink discharge from the pen tip, making it difficult to obtain the desired effect. If the average particle size is less than 0.1 μm, the particle size is too small, making it difficult to achieve a sufficient effect in small quantities.

[0014] Fluid gels are formed from synthetic water-soluble polycondensation polymers such as carboxyvinyl polymer, (acrylates / alkyl acrylate (C10-30)) crosspolymer, (ammonium acryloyldimethyltaurate / VP) copolymer, and acrylic acid / alkyl methacrylate copolymer, These are formed from semi-synthetic water-soluble polycondensate polymers such as stearoxyhydroxypropyl methylcellulose, starch-sodium acrylate graft polymer, and hydrophobized hydroxypropyl methylcellulose, It is formed from natural water-soluble polycondensation polymers such as gum arabic, carrageenan, fucoidan, gellan gum, fucogel, and starch, which are polysaccharides composed of several sugars from among monosaccharides such as ribose, xylose, rhamnose, fucose, glucose, mannose, glucuronic acid, and gluconic acid.

[0015] In particular, the fluid gel used in the present invention is preferably a natural water-soluble polycondensation polymer due to its high fluidity between aggregated pigments and its excellent buffering properties, and gellan gum is especially preferred among these. Gellan gum is produced by separating and purifying polysaccharides accumulated outside the cell of microorganisms (Sphingomonas erodea) collected from aquatic plants, using glucose and other nutrients as nutrients. Among these, deacylated gellan gum, which is recovered after removing glyceryl and acetyl groups (deacylation) during the polysaccharide separation process, and native gellan gum, which is recovered without processing, are preferred, and one or both can be used in combination.

[0016] The fluid gel is added in an amount of 0.5 to 30% by mass, preferably 0.7 to 20% by mass, and more preferably 0.8 to 15% by mass, of the total amount of the aqueous ink composition. Within the aforementioned range, particularly high effectiveness can be achieved, making it possible to efficiently maintain a state of excellent pigment redispersibility by polymer flocculants over a long period of time.

[0017] In this invention, a pigment is used as a coloring agent. Specifically, in addition to inorganic pigments such as carbon black and ultramarine blue, and organic pigments such as copper phthalocyanine blue and benzidine yellow, water-dispersed pigment products that have been finely and stably dispersed in an aqueous medium in advance using surfactants or the like are used. For example, C.I. Pigment Blue 15:3B [Product name: S.S. Blue GLL-E, 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.] and the like can be mentioned. As the fluorescent pigment, fluorescent pigment in the form of synthetic resin fine particles 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 obtained by directly encapsulating or microencapsulating thermochromic compositions, photochromic compositions, fragrances, etc.

[0018] As the thermochromic composition, a reversible thermochromic composition comprising (a) an electron-donating color-forming organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color-forming reaction between the two occurs is suitable, and it is applied as a reversible thermochromic microcapsule pigment by encapsulating it in microcapsules. 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). They exhibit a decolorized state in a temperature range above the high-temperature side color change point and a colored state in a temperature range below the low-temperature side color change point. Among these two states, only a specific one exists in the normal temperature range, and the other state is maintained while heat or cooling heat required for its appearance is applied, but returns to the state presented in the normal temperature range 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 showing a relatively large hysteresis characteristic (ΔH = 8 to 50°C) described in Japanese Patent Publication No. 4-1715, Japanese Unexamined Patent Application Publication No. 7-179777, Japanese Unexamined Patent Application Publication No. 7-33997, Japanese Unexamined Patent Application Publication No. 8-39936, etc., and those showing a large hysteresis characteristic described in Japanese Unexamined Patent Application Publication No. 2006-137886, Japanese Unexamined Patent Application Publication No. 2006-188660, Japanese Unexamined Patent Application Publication No. 2008-45062, Japanese Unexamined Patent Application Publication No. 2008-280523, etc., that is, the shape of the curve plotting the change in coloring density due to temperature change greatly differs in the path followed 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. A heat-decolorizing type microcapsule pigment encapsulating a reversible thermochromic composition having color memory in a specific temperature range in a colored state in a low-temperature range below the complete coloring temperature or a decolorized state in a high-temperature range above the complete decolorizing temperature can also be applied. Incidentally, specifically, as the reversible thermochromic composition having color memory, the complete coloring temperature is set to a temperature that can only be obtained in a freezer, 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 set to 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 40 to 100°C, it can function effectively to maintain the color presented in the normal state (daily life temperature range).

[0019] Furthermore, if necessary, dyes soluble in aqueous media can be used in combination, and acid dyes, basic dyes, direct dyes, etc., can be used depending on the desired conditions.

[0020] The colorants containing the aforementioned pigments can be used by mixing one or more of them as appropriate, and are used in an amount of 1 to 30% by mass, preferably 2 to 25% by mass, and particularly preferably 2 to 15% by mass, of the ink composition.

[0021] The ink composition according to the present invention contains water. There are no particular restrictions on the type of water used; for example, tap water, deionized water, ultrafiltered water, and distilled water are examples. The water content relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 35 to 95% by mass, and more preferably in the range of 40 to 90% by mass.

[0022] In addition to the essential components described above, the ink composition according to the present invention may contain optional components as long as they do not impair the effects of the present invention.

[0023] For example, conventional water-soluble organic solvents that are compatible with water can be used, such as 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, etc. Furthermore, the aforementioned water-soluble organic solvent may be used individually or in combination of two or more types, and is used in an amount of 2 to 60% by mass, preferably 5 to 35% by mass, in the ink composition.

[0024] Furthermore, water-soluble resins can be added to impart adhesion and viscosity to the paper surface. Examples of water-soluble resins include alkyd resins, acrylic resins, styrene-maleic acid copolymers, cellulose derivatives, polyvinylpyrrolidone, polyvinyl alcohol, and dextrin. One or more water-soluble resins can be used in combination, and they are used in an amount ranging from 1% to 30% by mass in the ink composition.

[0025] In addition, rust inhibitors such as benzotriazole, toltriazole, 2,5-dimercapto-1,3,4-thiadiazole, and saponins may be used as needed. Preservatives or fungicides such as carbolic acid, 1,2-benzisothiazolin-3-one and its sodium salt, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl parahydroxybenzoate, methylisothiazolinone, and 3-iodo-2-propynyl N-butylcarbamate. Urea, nonionic surfactants, sorbitol, mannitol, sucrose, glucose, reduced starch hydrolysate, sodium pyrophosphate and other humectants, Lubricants such as metal soaps, polyalkylene glycol fatty acid esters, ethylene oxide-additive cationic surfactants, phosphate ester surfactants, β-alanine-type surfactants, N-acyl amino acids, and N-acylmethyl taurine. In addition, defoaming agents, dispersants, specific gravity adjusters, etc., may be used. Furthermore, bubbles can be chemically removed by adding ascorbic acid, erythorbic acid, α-tocopherol, catechins, synthetic polyphenols, kojic acid, alkylhydroxylamines, oxime derivatives, α-glucosylrutin, α-lipoic acid, phosphonates, phosphinates, sulfites, sulfoxylates, dithionites, thiosulfates, thiourea dioxide, etc. Furthermore, the function in the retractable form can be enhanced by adding thickening inhibitors such as N-vinyl-2-pyrrolidone oligomer, N-vinyl-2-piperidone oligomer, N-vinyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, ε-caprolactam, and N-vinyl-ε-caprolactam oligomer.

[0026] Furthermore, shear-thickening agents can be added to the ink composition, provided they do not interfere with the performance of the floyd gel. Examples include water-soluble polysaccharides, polymers with a molecular weight of 100,000 to 150,000 mainly composed of alkyl esters of methacrylic acid, poly-N-vinyl carboxylic acid amide crosslinks, benzylidene sorbitol and its derivatives, benzylidene xylitol and its derivatives, alkali-thickening acrylic resins, crosslinkable acrylic acid polymers, inorganic fine particles, nonionic surfactants with an HLB value of 8 to 12, and metal salts and amine salts of dialkyl sulfosuccinate. Examples of water-soluble polysaccharides include xanthan gum, gellan gum, zeta-C gum, dieutan gum, macrophopsis gum, succinoglycans (average molecular weight of approximately 1 million to 8 million), which are heteropolysaccharides with organic acid modifications of glucose and galactose, guar gum, locust bean gum and its derivatives, hydroxyethylcellulose, alkyl alginates, glucomannan, and gelling carbohydrates extracted from seaweed such as agar and carrageenan.

[0027] The aqueous ink composition for writing instruments of the present invention is filled into a marking pen equipped with a fiber tip, felt tip, or plastic tip at the writing end, and is configured in a capped or retractable form.

[0028] The structure and shape of the marking pen itself are not particularly limited. Examples include a marking pen with a tip such as a fiber tip, felt tip, or plastic tip attached to the writing tip, an ink-absorbing material made of fiber bundles housed inside the barrel impregnated with ink, and ink supplied to the writing tip; a marking pen with ink directly housed inside the barrel and a predetermined amount of ink supplied to the writing tip via a comb-shaped ink flow adjustment member or an ink flow adjustment member made of fiber bundles; and a marking pen with ink directly housed inside the barrel and a predetermined amount of ink supplied to the writing tip by a valve mechanism. Furthermore, the ink storage part can also be a cartridge. In addition to having a single pen tip, a double-ended design may also be available, with pen tips of different thicknesses and shapes at both ends of the barrel. Furthermore, in the aforementioned double-ended design, one end may be a ballpoint pen.

[0029] In the aforementioned marking pen structure, particularly those using an ink-absorbing material (cotton pad) made of a fiber bundle or a resin-bonded fiber bundle, the ink composition of the present invention is stably held in these capillary gaps, thus more effectively suppressing the separation of each pigment. As a result, unlike conventional methods, when the writing instrument is left upright or inverted, the pigment does not separate, preventing the ink from becoming darker or lighter, and allowing for the formation of uniform and good ink over a long period of time. Furthermore, even in marking pen tips made of resin or fiber aggregates, the structure allows the pigment to be stably held in the gaps, thus enabling the ink composition of the present invention to work effectively.

[0030] Examples of the aforementioned pen tip (marking pen tip) include conventional porous materials with interconnected pores selected from a range of approximately 30-70% porosity, such as resin-processed fibers, heat-meltable fiber fused materials, and felt materials. One end is processed into a shape according to the purpose, such as a bullet shape, rectangle, chisel shape, or brush pen shape, for practical use.

[0031] The ink-absorbing material consists of crimped fibers bundled together in the longitudinal direction, which are then embedded within a plastic tube or film or other covering, and the porosity is adjusted to a range of approximately 40-90%. [Examples]

[0032] Examples are described below, but the present invention is not limited to these examples. Table 1 shows the composition of the water-based inks for writing instruments in the examples and comparative examples. The composition values ​​in the table represent parts by mass. The average particle size of each material was measured using a particle size distribution analyzer [Beckman Coulter, Ltd., product name: Multisizer 4e], specifically the particle size (D50) at 50% volume accumulation of the particle size distribution.

[0033] [Table 1]

[0034] The contents of the raw materials listed in the table are explained according to the footnote numbers. (1) Manufactured by Sanyo Shikkei Co., Ltd., Product name: SANDYE SUPER BLUE GLL-E, Active ingredient 22% (2) Manufactured by Teika Co., Ltd., Product name: JR-600E (3) Manufactured by Toyo Aluminum Co., Ltd., Product name: EMR-D6390 (4) A microcapsule pigment containing a reversible thermochromic composition consisting of (a) 4.5 parts of 2-(2-chloroanilino)-6-di-n-butylaminofluorane, (b) 4.5 parts of 1,1-bis(4′-hydroxyphenyl)n-decane and 7.5 parts of 2,2-bis(4′-hydroxyphenyl)hexafluoropropane, and (c) 50.0 parts of 4-benzyloxyphenylethyl caprate (complete color development temperature: -20°C, complete decolorization temperature: 57°C, average particle size: 2.5 μm, changes color from black to colorless). (5) Manufactured by BYK, product name: DISPERBYK-190 (6) Manufactured by Nikko Chemicals Co., Ltd., Product name: NIKKOL PBC-44 (7) Manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Product name: Selogen 5A (8) Manufactured by Dow Chemical Japan Ltd., Product name: Cellosize EP-09 (9) Add 0.2 g of deacyl gellan gum (manufactured by MP Gokyo Food & Chemical Co., Ltd., product name: Kelco Gel) and 0.05 g of calcium chloride to 99.75 g of deionized water, dissolve at 90°C, and then cool to room temperature. Stir in a disper at 1500 rpm for 5 minutes to obtain a fluid gel with an average particle size of 0.7 μm. (10) Add 0.2 g of native gellan gum (manufactured by MP Gokyo Food & Chemical Co., Ltd., product name: Kelcogel HM) to 99.8 g of deionized water, dissolve at 90°C, and then cool to room temperature. Stir in a disperser at 1500 rpm for 5 minutes to obtain a fluid gel with an average particle size of 2.0 μm. (11) A fluid gel with an average particle size of 1.0 μm was obtained by adding 1.0 g of Alkaci gum (manufactured by Hakuto Co., Ltd.) to 74.0 g of ion-exchanged water and 25.0 g of ethylene glycol, and stirring at 25°C in a disper at 3000 rpm for 30 minutes. (12) Rohm & Haas Co., Ltd., Product name: Ropeak SN-1055 (13) Manufactured by Sanei Gen F.F.I. Co., Ltd., Product name: Sun Artist PG (14) Manufactured by Sansho Co., Ltd., Product name: Kelzan (15) Manufactured by Arcsarda Japan, Product name: Proxel XL-2(S)

[0035] Preparation of ink for writing instruments The raw materials were mixed in the proportions specified in the above examples and comparative examples, stirred in a disperser at 20°C for 1 hour, and then allowed to stand for 24 hours until the bubbles disappeared to obtain an ink composition for writing instruments.

[0036] Making a marking pen A marking pen was obtained by impregnating an ink-absorbing body (porosity 80%) made of polyester sliver coated with a synthetic resin film with the aforementioned writing instrument ink composition, housing it in a barrel made of polypropylene resin, assembling it so that a resin-processed tip (bullet shape: porosity 60%) of polyester fiber is connected to the tip of the barrel via a holder, and attaching a cap.

[0037] The following tests were performed using each of the marking pens obtained. Written exam Each marking pen, confirmed to be writable, was used in a running test machine at a room temperature of 20°C with a writing angle of 70°, a load of 100gf, and a speed of 4m / min. The handwriting was visually inspected when a spiral circle was continuously written for 10 minutes on JIS P3201 writing paper A (black paper (manufactured by Kishu Paper Co., Ltd., high-quality colored paper, medium weight) for pens using titanium dioxide as a coloring agent). Ink stability test Each marking pen was left with the tip facing upwards for 30 days in an environment of 40°C and 30% RH. After that, the handwriting quality was visually inspected when 12 spiral circles were continuously written in a single line 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: Written exam ○: Good handwriting was obtained. △: Although slight smudging and breaks were observed in the handwriting, it was still usable for writing. ×: Fading or breaks were observed in the handwriting, or the writing was impossible. Ink stability test ○: There was no difference in color intensity in the handwriting, and there was no change from before the exam. ×: The handwriting becomes uneven in color intensity, making it impossible to write, or it becomes impossible to write from the start.

Claims

1. A water-based ink composition for writing instruments comprising a pigment, water, a polymer flocculant, and a fluid gel.

2. The aqueous ink composition for writing instruments according to claim 1, wherein the average particle size of the fluid gel is in the range of 0.1 to 5 μm.

3. The aqueous ink composition for writing instruments according to claim 1 or 2, wherein the fluid gel is made of duran gum.

4. The aqueous ink composition for writing instruments according to claim 3, wherein the duran gum is of the deacyl or native type.

5. The aqueous ink composition for writing instruments according to claim 1, wherein the polymer flocculant is a cellulose derivative.

6. A marking pen containing the aqueous ink composition for writing instruments described in any one of claims 1 to 5.

7. A marking pen according to claim 6, which contains an ink absorbent.

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