JP3444565B2 - Aqueous ballpoint pen ink composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink composition for water-based ballpoint pens, and more particularly, to an ink composition having excellent storage stability at a high temperature. Water-based ballpoint pen ink compositions.

[0002]

2. Description of the Related Art An aqueous ballpoint pen ink is usually prepared by adding a water-soluble organic solvent such as a polyhydric alcohol or a derivative thereof to an aqueous solution containing a colorant such as a water-soluble dye, a pigment, or a colored resin emulsion.

[0003] In particular, an ink using a pigment or a colored resin emulsion as a coloring agent is inferior in stability over time, and causes storage and separation of the coloring agent when stored for a long period of time. In order to overcome these problems, attempts have been made to blend a water-soluble polymer such as an alkali salt of a styrene-acrylic acid copolymer, polyvinyl alcohol, or polyvinylpyrrolidone as a dispersant for the colorant.

However, inks containing these dispersants have poor high-temperature stability. Therefore, when a ball-point pen is stored under high-temperature conditions in summer, for example, the viscosity of the ink decreases, the colorant precipitates, and chips are formed. This causes a problem that clogging occurs at the tip.

The main object of the present invention is to overcome the above-mentioned drawbacks of the water-based ink for ballpoint pens, and to maintain stable colorant dispersibility not only at room temperature but also for a long time at high temperature. An object of the present invention is to provide an ink composition for an aqueous ball-point pen, which is effective for a ballpoint pen.

[0006]

SUMMARY OF THE INVENTION The present inventor has made extensive studies to solve the problems of the conventional inks for water-based ballpoint pens, and as a result, the inks are composed of pigments and pigment dispersants, and / or colored resin emulsions. Coloring agents, water-soluble organic solvents,
With respect to the aqueous ball-point pen ink composition containing the pseudoplasticity imparting agent and water, the weight of the ink composition is 0.05 to 0.5.
%, When the salt of the crosslinked acrylic acid polymer is blended, it has been found that the above problem is substantially eliminated or greatly reduced by a synergistic effect with the pseudoplasticity imparting agent. .

That is, the present invention provides the following aqueous ink composition for ballpoint pens: (A pigment and a pigment dispersant) and / or a colorant comprising a colored resin emulsion, a water-soluble organic solvent, a pseudoplasticity-imparting agent and water, the aqueous ink basic composition, and 0.05 to 0% by weight of the aqueous ink basic composition. An aqueous ballpoint pen ink composition containing 0.5% by weight of a salt of a crosslinked acrylic acid polymer.

[0008] 2. The viscosity of the ink composition is from 2,000 to
Item 2. The aqueous ball-point pen ink composition according to item 1, which has a molecular weight of 8,000 cps.

3. The molecular weight of the crosslinked acrylic acid polymer is
Item 2. The water-based ink composition for a ballpoint pen according to item 1, which is in the range of 2,000,000 to 6,000,000.

[0010] 4. Item 2. The ink composition for an aqueous ball-point pen according to Item 1, wherein the pseudoplasticity imparting agent is welan gum and / or xanthan gum.

5. Item 2. The aqueous ball-point pen ink composition according to Item 1, further comprising a preservative.

6. Item 6. The aqueous ballpoint pen ink composition according to Item 5, wherein the preservative is 1,2-benzisothiazolin-3-one.

7. Item 2. A ballpoint pen obtained by filling the ink storage section with the ink composition for an aqueous ballpoint pen according to item 1.

Hereinafter, the present invention will be described in detail.

The crosslinked acrylic acid polymer is a polymer in which branched acrylic acid polymers are crosslinked to each other at portions other than the carboxyl group to form a network structure. The polymer itself disperses easily in water but does not dissolve. If the carboxyl group in the polymer is not ionized, an electric double layer will not be formed on the surface of the colorant pigment and / or the colored resin emulsion, and it will not be a protective colloid. It is formed by previously adding an acid value equivalent of a monovalent alkali metal (eg, Na, K) hydroxide, an alkali metal carbonate, an alkali metal bicarbonate, an amine, an alkanolamine, etc. to the crosslinked acrylic acid polymer. Since the carboxyl group in the polymer is ionized, the salt of the polymer is adsorbed on the surface of the pigment as a coloring agent and / or the colored resin emulsion to form a protective colloid.

The salt of the crosslinked acrylic acid polymer may be isolated once in a solid state and dissolved in water, or may be dissolved by adding the above-mentioned alkaline compound in a state of being dispersed in water.

The salt of such a crosslinked acrylic acid polymer is
It is available as a commercial product, for example, “Rheogic 2
50H "(manufactured by Nippon Pure Chemical Co., Ltd.)," Junron PW11
1 "(manufactured by Nippon Pure Chemical Co., Ltd.)," U Jeri-CP "(manufactured by Showa Denko KK)," Carbopol # 934 "(BFGood
It is commercially available under a trade name such as "Rich Company". The degree of polymerization of the crosslinked acrylic acid polymer is preferably about 2,000,000 to 6,000,000. The amount of such an acrylic acid polymer salt used is an aqueous ink containing at least a colorant comprising a (pigment and a pigment dispersant) and / or a colored resin emulsion, a water-soluble organic solvent, a pseudoplasticity-imparting agent and water. It is preferable that the amount is about 0.05 to 0.5% by weight based on the basic composition. If the amount used is too small, sufficient high-temperature stability cannot be obtained, whereas if the amount used is too large, the viscosity of the ink composition increases and the writing quality of a ballpoint pen decreases.

In the present invention, the aqueous ink base composition is a known one. Accordingly, each component of the aqueous ink basic composition and the ratio thereof are not particularly limited, but are usually as follows.

First, as the colorant, various known pigments, pigment dispersants, and colored resin emulsions can be used. More specifically, as the pigment, an azo pigment,
Condensed polyazo pigments, phthalocyanine pigments, quinacridone pigments, anthraquinone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, perinones,
Organic pigments such as perylene pigments and melamine pigments; and inorganic pigments such as titanium oxide, iron oxide and carbon black. As a resin emulsion colored body, an aqueous dispersion of polymer fine particles having an average particle diameter of about 0.1 to 1 μm obtained by emulsion polymerization using a styrene resin, an acrylic resin, an acrylonitrile resin or the like alone or in combination of two or more kinds is used as a base. Substances produced by dyeing with a dye, a fluorescent base dye, a fluorescent brightener, and the like are included. More specifically, examples of the colored resin emulsion include those commercially available under trade names (Nippon Fluorochemicals Co., Ltd.) such as "Lumicol # 2100 series" and "Lumicoll # 3000 series". As the pigment dispersant, at least one of a water-soluble resin, a surfactant and the like generally used in an ink composition is used.
As the water-soluble resin, any of a natural product, a semi-synthetic product and a synthetic product may be used, but from the viewpoint of antifungal property or antiseptic property, viscosity characteristics as a writing instrument ink, a synthetic product is optimal. is there. Examples of the water-soluble synthetic resin include a water-soluble acrylic resin, a water-soluble maleic resin, a water-soluble styrene resin, a water-soluble styrene-acryl resin, and a water-soluble styrene-
Maleic acid resin, polyvinylpyrrolidone, polyvinyl alcohol, water-soluble urethane resin and the like can be mentioned. As the surfactant, at least one of anionic, cationic, nonionic and amphoteric surfactants may be used. These colorants use at least one selected from the group consisting of (pigments and pigment dispersants) and colored resin emulsions.

When a pigment is used as a coloring agent, the amount of the pigment is usually 1 to 3 with respect to the aqueous ink basic composition.
It is about 0% by weight, more preferably about 3 to 15% by weight. The pigment dispersant is used in an amount of 5 to 200% based on the weight of the pigment.
It is used in the range of about% by weight. When a colored resin emulsion is used as the coloring agent, the amount of the resin emulsion is usually about 10 to 50% by weight, more preferably about 25 to 40% by weight, based on the aqueous ink basic composition. . If the amount of the coloring agent is too small, the handwriting becomes thin, and if the amount is too large, the viscosity of the ink composition becomes high and the writing quality decreases. On the other hand, if the amount of the pigment dispersant is too small, the dispersion stability of the pigment decreases, while if it is too large, the viscosity becomes high and the writing quality of the ink composition deteriorates.

Examples of the water-soluble organic solvent include ethylene glycol, diethylene glycol, propylene glycol,
Polyhydric alcohols such as glycerin; glycol ethers such as propylene glycol monomethyl ether;
Glycol ether esters such as propylene glycol monomethyl ether acetate;
Such a water-soluble organic solvent may be used alone.
You may mix and use more than seeds. The amount of the water-soluble organic solvent used is preferably in the range of usually about 1 to 40% by weight based on the aqueous ink basic composition. If the amount of the water-soluble organic solvent is too small, drying of the ink at the tip of the ball-point pen becomes faster, causing blurring of the handwriting, whereas if too much, the drying of the handwriting becomes slower.

As the pseudoplasticity-imparting agent, natural polysaccharides, semi-synthetic cellulosic polymers and the like can be used. Natural polysaccharides include glucose, galactose, rhamnose,
Mannose, welan gum having a high molecular chemical structure composed of monosaccharides, such as glucuronate, xanthan gum, grayed _A Gamu, locust bean gum, etc. rhamsan and the like, is particularly preferred welan gum and xanthan gum Among these. The amount of the pseudoplasticity-imparting agent is usually 0.1 to 0.5 with respect to the aqueous ink base composition.
It is preferable to set it in the range of about weight%. If the amount of the pseudoplasticizer is too small, the dispersion stability of the colorant under high-temperature conditions is not improved, while if too large, the viscosity of the ink composition also increases, and Decrease. The ink composition for a water-based ballpoint pen according to the present invention may optionally contain a known pH adjuster, lubricant, rust inhibitor, preservative, and the like in this type of ink composition. Examples of the pH adjuster include sodium hydroxide, sodium carbonate, alkanolamine, and ammonia. Examples of the lubricant include an alkali salt and an alkanolamine salt of a fatty acid, and a phosphate surfactant. Examples of the rust inhibitor include benzotriazole and its derivatives, dicyclohexylammonium nitrate and the like. As preservatives, potassium sorbate, sodium benzoate, sodium pentachlorophenyl, sodium dihydroacetate, 1,2-
Examples include benzisothiazolin-3-one, and among these, 1,2-benzisothiazolin-3-one is particularly preferable.

Although not particularly limited, the aqueous ink composition according to the present invention is usually used after being filled in a cap-filled ballpoint pen of the type schematically shown in FIG. More specifically, in general, a refill-type ball-point pen accommodates a pipe-shaped ink tank 2 in a main body shaft 1 and is closed at both ends by a tip plug 3 to which a chip 4 is attached and a tail plug 5. An anti-drying agent 9 is accommodated in an inner cylinder provided in the tail plug 5. The ink tank 2 is directly filled with the aqueous ink composition 6, and a backflow prevention member 7 is provided at the rear end. When using, cap 8
And write down.

[0024]

The crosslinked acrylic acid polymer salt used in the present invention is adsorbed on the surface of a pigment and / or a colored resin emulsion as a colorant of the ink composition to form a protective colloid, In addition to increasing the thermal stability of the ink composition and preventing the viscosity of the ink composition from decreasing, even when the ballpoint pen filled with the ink composition is left at a high temperature, the deterioration of the ink properties due to the sedimentation of the colorant is suppressed. it can. Therefore, even after long-term storage at high temperatures,
It does not cause clogging at the tip of the chip.As is clear from the comparison between the following Examples and Comparative Examples, the crosslinked acrylic acid polymer used in the present invention is used in the presence of a pseudoplasticity-imparting agent. The remarkable effect is exhibited for the first time.

[0025]

The present invention will be described in more detail with reference to the following examples. In the following, “part” means
Means "parts by weight".

Example 1 An ink composition of the present invention was prepared using the following materials.

Copper phthalocyanine blue 4.0 parts Sodium salt of styrene-acrylic acid copolymer (pigment dispersant) 1.0 part Diethylene glycol 10.0 parts Glycerin 5.0 parts Na salt of cross-linked acrylic acid copolymer 0 .1 part (trade name "Reogic 250H", manufactured by Nippon Pure Chemical Co., Ltd., number average molecular weight about 2.5 million) 1,2-benzisothiazolin-3-one (preservative) 0.5 part benzotriazole (rust inhibitor) 0.5 part Xanthan gum (pseudoplasticity-imparting agent) 0.3 part Water 78.7 parts In preparing the ink composition, first add xanthan gum little by little to 30 parts of water, dissolve completely with stirring, and add copper Phthalocyanine blue, a sodium salt of a styrene-acrylic acid copolymer, and 48.7 parts of water were added, and the mixture was dispersed in a sand mill for 1 hour. On the other hand, in advance each of the remaining ingredients added, was stirred and dissolved formulation was added to the dispersion liquid, and stirred for 1 hour, adjusted to pH8 with sodium hydroxide solution and filtered to give a blue ink.

Example 2 Copper phthalocyanine green 4.0 parts Sodium salt of styrene-acrylic acid copolymer (pigment dispersant) 1.5 parts Propylene glycol 10.0 parts Glycerin 5.0 parts Cross-linked acrylic acid copolymer Na salt (trademark "Junron PW110", Nippon Pure Chemical Co., Ltd., 3% aqueous solution having a number average molecular weight of about 1.1 million, (NaOH equivalent neutralization)) 5.0 parts Sodium benzoate (preservative) 1.0 part Benzotriazole (rust inhibitor) 0.5 part Welan gum (pseudoplasticity imparting agent) 0.4 part Water 77.6 parts First, welan gum is added little by little to 30 parts of water and completely dissolved with stirring, and copper phthalocyanine is added thereto. Blue, sodium salt of styrene-acrylic acid copolymer and water 4
After 2.6 parts were dispersed in a sand mill for 1 hour, a solution in which the remaining components were previously added and dissolved by stirring was further added.
The mixture was stirred for 1 hour, adjusted to pH 8 with an aqueous sodium hydroxide solution, and filtered to obtain a green ink.

Example 3 Colored yellow resin emulsion (trade name "Lumicoll NKW-2105", manufactured by Nippon Fluorescent Chemical Co., Ltd., including CIBasic Yellow 40) 40.0 parts Glycerin 5.0 parts Propylene glycol 10.0 parts Cross-linked Na salt of acrylic acid copolymer (trade name “Junron PW110”, 3% aqueous solution manufactured by Nippon Pure Chemical Co., Ltd., (NaOH equivalent neutralization)) 6.0 parts Sodium benzoate (preservative) 1.0 part Benzotriazole (rust inhibitor) 0.5 part Xanthan gum (pseudoplasticity-imparting agent) 0.3 part Water 43.2 parts First, xanthan gum was added little by little to 30 parts of water and stirred to dissolve completely. On the other hand, the remaining components were added and stirred in advance, and the dissolved solution was further added to the above xanthan gum solution and stirred for 1 hour. Ink was obtained.

Example 4 Carbon black 4.0 parts Sodium salt of styrene-acrylic acid copolymer (pigment dispersant) 1.0 part Propylene glycol 10.0 parts Ethylene glycol 5.0 parts Crosslinked acrylic acid copolymer Na salt (trade name "Carbopol 940", number average molecular weight: about 4 million, 3% aqueous solution manufactured by BF Goodrich Company, (NaOH equivalent neutralization)) 2.0 parts Sodium benzoate (preservative) 1.0 part Benzo Triazole (rust inhibitor) 0.5 part Xanthan gum (pseudoplasticity imparting agent) 0.2 part Water 78.3 parts First, xanthan gum was added little by little to 30 parts of water, and the mixture was stirred and completely dissolved. On the other hand, carbon black, a sodium salt of a styrene-acrylic acid copolymer and water 46.3
Part was dispersed in a sand mill for 1 hour, the remaining components were added, the above-mentioned aqueous solution of xanthan gum was added to the stirred and dissolved solution, the mixture was stirred for 1 hour, and the pH was adjusted to 8 with an aqueous sodium hydroxide solution. Filtration gave a black ink.

Example 5 Dioxazine violet 3.0 parts Sodium salt of styrene-acrylic acid copolymer (pigment dispersant) 1.0 part Ethylene glycol 10.0 parts Glycerin 5.0 parts Cross-linked acrylic acid polymer Sodium salt 0.2 part (trademark "Reogic 250H", manufactured by Nippon Pure Chemical Co., Ltd.) 1,2-benzisothiazolin-3-one (preservative) 0.5 part Benzotriazole (rust inhibitor) 0.5 part Xanthan gum (pseudoplasticity-imparting agent) 0.3 part Water 79.3 parts First, xanthan gum was added little by little to 30 parts of water, stirred, and completely dissolved. On the other hand, after dioxazine violet, sodium salt of styrene-acrylic acid copolymer and 49.5 parts of water were dispersed in a sand mill for 1 hour, the remaining components were added, stirred and dissolved to prepare a solution,
The above xanthan gum aqueous solution was added thereto, stirred for 1 hour, adjusted to pH 8 with an aqueous sodium hydroxide solution, and filtered to obtain a purple ink.

Example 6 Quinacridone Red 4.0 parts Sodium salt of styrene-acrylic acid copolymer (pigment dispersant) 1.5 parts Ethylene glycol 10.0 parts Glycerin 5.0 parts Crosslinked acrylic acid copolymer Alkanolamine salt (trademark “Junron PW110”, 3% aqueous solution manufactured by Nippon Pure Chemical Co., Ltd., (N (CH ₂ CH ₂ OH) ₃ equivalent neutralization)) 5.0 parts Sodium benzoate (preservative) 0 part Benzotriazole (rust inhibitor) 0.5 part Welan gum (pseudoplasticity imparting agent) 0.3 part Water 78.2 parts First, welan gum was added little by little to 30 parts of water, and stirred to completely dissolve. On the other hand, quinacridone red, sodium salt of styrene-acrylic acid copolymer and water
After dispersing 7 parts by a sand mill for 1 hour, the remaining components are added, stirred, and the above-mentioned welan gum solution is added to a solution obtained by dissolution. The mixture is stirred for 1 hour, and the pH is adjusted with an aqueous sodium hydroxide solution. 8 and filtered to obtain a red ink.

Example 7 Colored red resin emulsion (trade name "Lumicol NKW-2117, manufactured by Nippon Fluorescent Chemical Co., Ltd., containing CIBasic Violet 11 and: CIBasic Red = 1: 1) 40.0 parts glycerin 5 3.0 parts Diethylene glycol 10.0 parts Crosslinked acrylic acid polymer sodium salt (trade name “Junron PW110”, 3% aqueous solution manufactured by Nippon Pure Chemical Industries, Ltd., (NaOH equivalent neutralization)) 3.0 parts 1,2 -Benzisothiazolin-3-one (preservative) 0.5 part Benzotriazole (rust inhibitor) 0.5 part Xanthan gum (pseudoplasticity imparting agent) 0.4 part Water 43.4 parts First, 30 parts of water and a small amount of xanthan gum The remaining components were added and stirred, and the above-mentioned aqueous xanthan gum solution was added to the dissolved solution, and the mixture was stirred for 1 hour, and the pH was adjusted to 7 with an aqueous sodium hydroxide solution. Key After you have to give a fluorescent pink ink was filtered.

Example 8 Purple resin emulsion coloring (trade name "Lumicoll NKW-2367", manufactured by Nippon Fluorescent Chemical Co., Ltd., including CIBasic Violet 7) 40.0 parts Propylene glycol 10.0 parts Glycerin 5.0 parts Crosslinking Na salt of type acrylic acid copolymer (trademark "Carbopol 940", 3% aqueous solution manufactured by BF Goodrich Company, (NaOH equivalent neutralization)) 8.0 parts Sodium benzoate (preservative) 1.0 part Benzotriazole ( Rust inhibitor) 0.5 part Xanthan gum (pseudoplasticity-imparting agent) 0.2 part Water 34.3 parts First, xanthan gum was added little by little to 30 parts of water, and stirred to dissolve completely. On the other hand, the remaining components were added, stirred, and the xanthan gum aqueous solution was added to the dissolved solution, and the mixture was stirred for 1 hour, adjusted to pH 7 with an aqueous sodium hydroxide solution, and then filtered to obtain a purple ink. Obtained.

Comparative Example 1 A blue ink was obtained in the same manner as in Example 1 except that xanthan gum in the ink component of Example 1 was replaced with the same amount of water.

Comparative Example 2 A green ink was obtained in the same manner as in Example 2 except that welan gum in the ink component of Example 2 was replaced with the same amount of water.

Comparative Example 3 A fluorescent yellow ink was obtained in the same manner as in Example 3 except that xanthan gum in the ink component of Example 3 was replaced with the same amount of water.

Comparative Example 4 A black ink was obtained in the same manner as in Example 4 except that the xanthan gum in the ink component of Example 4 was replaced with the same amount of water.

Comparative Example 5 A purple ink was obtained in the same manner as in Example 1 except that the crosslinked acrylic acid polymer in the ink component of Example 1 was replaced with the same amount of water.

Comparative Example 6 A red ink was obtained in the same manner as in Example 2 except that the crosslinked acrylic acid polymer in the ink component of Example 2 was replaced with the same amount of water.

Comparative Example 7 A fluorescent pink ink was obtained in the same manner as in Example 3 except that the crosslinked acrylic acid polymer in the ink component of Example 3 was replaced with the same amount of water.

Comparative Example 8 A purple ink was obtained in the same manner as in Example 3 except that the crosslinked acrylic acid polymer in the ink component of Example 4 was replaced with the same amount of water.

Test Example 1 Stability of the aqueous ink compositions obtained in Examples 1 to 8 and Comparative Examples 1 to 8 at a high temperature and a normal temperature by using a refill ballpoint pen having the structure shown in FIG. Was determined.

That is, the water-based ink composition is directly filled in the polypropylene ink tank 2 made of polypropylene, and the backflow preventing material 7 is attached to the rear end side. The refill obtained by connecting the tip plug 3 thus obtained was defoamed by a centrifuge.

A ballpoint pen having the structure shown in FIG. 1 was assembled using the above-mentioned refill, and the chip was allowed to stand in a constant-temperature bath at 70 ° C. for two weeks with its tip facing down. High temperature stability was determined by examining the number of circles before returning to the original handwriting density.

Further, after leaving a ballpoint pen having the same structure as above with the pen pointed downward at room temperature for 12 months, a continuous circle having a diameter of 2 cm is written by hand and returned to the original handwriting density immediately after production. High temperature stability was determined by examining the number of circles.

The ink viscosity was measured by using a Brookfield viscometer (BL viscometer, manufactured by Tokyo Keiki Co., Ltd.) at 6 rpm with a No. 3 rotor.

Table 1 shows the results.

[0049]

[Table 1] Initial viscosity (cps) after 12 months at room temperature after 2 weeks at 70 ℃ Ink Change in handwriting density Change in handwriting density (20 ℃) (Number of circles) (Number of circles)
Example 1 <1 <1,4,500 Example 2 <1 <17,800 Example 3 <1 <1,4,100 Example 4 <1 <1,2,400 Example 5 <1 <1,3,600 Example 6 <1 <1,4,500 Example 7 <1 <1,5,800 Example 8 <1 <1,3,400 Comparative Example 1 none ^* 53 300 Comparative Example 2 none ^* 45 200 Comparative Example 3 none ^* 53 400 Comparative Example 4 none ^* 45 600 Comparative Example 5 12 36 3,100 Comparative Example 6 8 25 6,100 Comparative Example 7 15 48 4,300 Comparative Example 8 24 63 1,800 Note) *: Ink does not flow out As is clear from the results shown in the above, the aqueous ballpoint pen ink composition according to the present invention using a salt of a crosslinked acrylic acid polymer in the presence of a pseudoplasticity imparting agent is only excellent in long-term stability at room temperature. Not under conditions of accelerated degradation at high temperatures It is also excellent in stability. Therefore, when the aqueous ink composition of the present invention is used, for example, even when the ball-point pen must be stored under high-temperature conditions in the summer, it is possible to effectively prevent the deterioration of the ink and immediately after the preparation. Excellent writing characteristics can be maintained.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing an outline of an example of a ballpoint pen using the aqueous ink composition of the present invention.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C09D 11/18

Claims (7)

(57) [Claims] 1. An aqueous ink basic composition comprising a (pigment and a pigment dispersant) and / or a colorant comprising a colored resin emulsion, a water-soluble organic solvent, a pseudoplasticity imparting agent and water, and a weight of the aqueous ink basic composition. An aqueous ballpoint pen ink composition comprising 0.05 to 0.5% by weight of a salt of a crosslinked acrylic acid polymer. 2. The viscosity of the ink composition is from 2,000 to 8,
The water-based ink composition for a ball-point pen according to claim 1, which has a viscosity of 000 cps. 3. A crosslinked acrylic acid polymer having a molecular weight of 20
The aqueous ball-point pen ink composition according to claim 1, which is in the range of from 10,000 to 6,000,000. 4. The aqueous ball point pen ink composition according to claim 1, wherein the pseudoplasticity imparting agent is welan gum and / or xanthan gum. 5. The aqueous ball-point pen ink composition according to claim 1, further comprising a preservative. 6. The aqueous ball-point pen ink composition according to claim 5, wherein the preservative is 1,2-benzisothiazolin-3-one. 7. A ballpoint pen obtained by filling the ink reservoir with the aqueous ballpoint pen ink composition according to claim 1.