JP2013124360A - Water-based ink composition for writing utensil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-based ink composition for writing utensil which uses a plate-like pigment, and can improve the redispsersibility of the plate-like pigment by preventing hard caking in a temporal condition when filled in a direct liquid type writing utensil.SOLUTION: The water-based ink for writing utensil contains the plate-like pigment at least the surface of which is coated with a water-insoluble material, and water.

Description

  The present invention relates to a water-based ink composition for a writing instrument, and prevents hard cake formation with time in a writing instrument such as a marking pen, particularly a water-based ink composition containing a plate-like pigment filled in a direct liquid type writing instrument. The present invention also relates to a water-based ink composition for a writing instrument that can improve the redispersibility of a plate-like pigment.

  Conventionally, when a pearl pigment, an aluminum pigment, or the like is used as a pigment for obtaining glitter as a glittering water-based ink composition for a writing instrument, it is necessary that the particle diameter be at least 3 μm. In an aqueous ink composition for a writing instrument containing such a pigment having a large particle size, the pigment settles and a hard cake is generated. As a result, a stirring member such as a ball or a rod for redispersion is repeatedly applied to the writing instrument several times. Need to stir.

  The pearl pigments, etc., which obtain the luster by reflecting these lights, have a particle size larger than that of ordinary organic pigments and inorganic pigments, and are mainly composed of plate pigments. In the case of water-based ink compositions for writing instruments containing a long period of time or storage in an environment with a large temperature change, the settled plate-like pigment forms a hard hard cake, which causes the phenomenon that the stirring member becomes immobile and The problem of deterioration of dispersibility is likely to occur. This is because the plate-like pigment has a high specific critical particle size, so it is easy to settle, and since it is a flat plate, it has a layered structure in which the flat sides face each other when it settles, so the contact area between the pigments is large and the contact is large. This is because the resistance is increased, and the pigment dispersant is entangled, and the adhesion on the contact surface is further strengthened, so that it is easy to form a hard sediment (hard cake).

  A water-based ink composition for a writing instrument that attempts to solve these problems includes: 1) a glitter that comprises crystalline cellulose, a shear thinning agent, a plate-like particle pigment, and water as constituent components. Water-based ink composition (see, for example, Patent Document 1 by the present applicant), 2) a bottomed cylindrical ink storage container having an inner diameter of less than 15 mm, an ink stirrer enclosed in the ink storage container, and the ink storage A water-based ink composition housed in a writing instrument having a writing tip having an ink outlet slit width of less than 1 mm in front of the opened opening of the container, comprising: a dispersion resin; a first flat pigment; The second tabular pigment having an average particle size less than the average particle size of the first tabular pigment is an addition amount equal to or less than the addition amount of the first tabular pigment, Water containing crystalline cellulose The ink composition (for example, see Patent Document 2 by the present applicant) are known.

  However, in Patent Documents 1 and 2, the redispersibility of the tabular pigment before the aging is good, but the redispersibility of the aqueous ink composition for writing instruments may deteriorate due to the high temperature aging for a long time. There are still some issues, such as there.

JP 2002-285064 A (Claims, Examples, etc.) JP 2011-84661 A (Claims, Examples, etc.)

  The present invention has been made in view of the above-mentioned problems of the prior art, and intends to solve this problem. As a water-based ink composition for writing instruments, the formation of a hard cake over time when a plate-like pigment is contained, and redispersion thereby An object of the present invention is to provide a water-based ink composition for a writing instrument that solves the deterioration of the properties and is excellent in redispersibility, final writing property and writing performance.

  In view of the above-described conventional problems, the present inventors have tried to solve this problem, and tried to inhibit adhesion of plate-like particles by blending a water-insoluble polysaccharide crystal such as crystalline cellulose. However, the cellulose did not pass through the plate-like particles to inhibit adhesion. As a result of such various studies, the water-insoluble substance that can be a steric hindrance that can inhibit the adhesion between the pigments is recrystallized on the particle surface of the plate pigment, thereby suppressing the adhesion between the particles, redispersibility, etc. The inventors have found that the present invention is favorable, and have completed the present invention.

That is, the present invention resides in the following (1) to (8).
(1) A water-based ink composition for a writing instrument, comprising at least a plate-like pigment having a surface coated with a water-insoluble substance and water.
(2) The aqueous ink composition for a writing instrument as described in (1) above, further comprising a resin containing at least an acrylate ester in the molecule.
(3) The aqueous ink composition for a writing instrument as described in (1) or (2) above, further comprising crystalline cellulose.
(4) The above (1), wherein the plate pigment is a pigment selected from one or more of a pearl pigment, an aluminum powder pigment, a metal or metal oxide coated glass flake, and an aluminum coated polyester film. The water-based ink composition for writing instruments as described in any one of-(3).
(5) The writing instrument according to any one of the above (1) to (4), wherein the water-insoluble substance is a polymer selected from cellulose, hemicellulose, lignin, chitin, chitosan, latex, silica, alumina, and silicone. Water-based ink composition.
(6) any viscosity 4~65mPa · s at a shear rate 38.4s ^-1, the viscosity at a shear rate 384S ^-1 is in the range of 4~24mPa · s (1) ~ (5) The water-based ink composition for writing instruments as described in any one.
(7) A water-based ink composition for a writing instrument, comprising 3 to 15% by mass of a plate-like pigment having a surface coated with at least a water-insoluble substance and water, and dispersing the plate-like pigment. Production method.
(8) A resin containing acrylic acid ester in the molecule and / or crystalline cellulose is added, and the viscosity of the aqueous beauty nail composition is 4 to 65 mPa · s when the shear rate is 38.4 s ⁻¹ , the shear rate. The method for producing an aqueous ink composition for a writing instrument according to the above (7), wherein the viscosity at 384 s ^-1 is in the range of 4 to 24 mPa · s.

  According to the present invention, the water-based ink composition for a writing instrument, which has excellent stability over time, is hard to form a hard cake even when the plate-like pigment settles, can be easily redispersed by stirring, and has excellent writing performance, and its A manufacturing method is provided.

It is a fragmentary longitudinal view which shows an example of the writing instrument which accommodates the water-based ink composition for writing instruments of this invention. It is a whole side view of the pen core used for the writing instrument of FIG. FIG. 3 is a cross-sectional view of the pen core along the line II in FIG. 2.

Hereinafter, embodiments of the present invention will be described in detail.
The aqueous ink composition for a writing instrument according to the present invention is characterized by containing a plate-like pigment whose surface is coated with a water-insoluble substance and water.

The plate-like pigment whose surface is coated with at least a water-insoluble substance used in the present invention is a plate pigment such as a pearl pigment, an aluminum powder pigment, a metal or metal oxide-coated glass flake, and an aluminum-coated polyester film, and at least water. The surface of the plate pigment is coated with an insoluble substance.
In the present invention, the “plate pigment” means that the ratio of the average length corresponding to the average diameter to the average thickness (aspect ratio) is usually 5 to 200. It is.

Examples of the water-insoluble substance in the present invention include at least one selected from cellulose, hemicellulose, lignin, chitin, chitosan, latex, silica, alumina, and silicone, which are polymers.
Examples of a method for coating the surface of the plate pigment with the water-insoluble material include, for example, 1) spraying and drying a water slurry in which a water-insoluble substance and a plate pigment are mixed with a spray dryer, A method of adhering a water-insoluble substance to the aqueous solution (hereinafter referred to as “Production Method 1”), 2) Adjusting the pH of a substance soluble in an acidic or basic aqueous solution, dissolving it in water, and adjusting the pH in the direction of insolubilization with acid or base And a method of depositing a water-insoluble substance on the surface of the plate pigment (hereinafter referred to as “Production Method 2”).
If the surface coating amount of this water-insoluble substance is too small, the effect of redispersibility by suppressing hard cake cannot be obtained. On the other hand, if the amount is too large, not only the pearl feeling will be reduced, but the pearl surface will not be in point contact. It becomes contact and the effect of redispersibility cannot be obtained. Therefore, the surface coating amount of the water-insoluble substance is 0.1 to 10%, preferably 0.5 to 8%, more preferably, as the surface coverage of the plate-like pigment (calculated from mass% at the time of surface treatment). Is preferably in the range of 1 to 7%.

The plate-like pigment coated with the water-insoluble substance obtained above used in the present invention can confirm a recrystallized product of the water-insoluble substance on the surface observed with an electron microscope (× 35,000 times).
As a method for distinguishing between a plate-like pigment whose surface is coated with a water-insoluble substance and an uncoated plate-like pigment in the present invention, redispersibility cannot be obtained in a system in which an uncoated plate-like pigment is blended. It can be confirmed that good redispersibility can be obtained in a system in which a water-insoluble substance is used for the surface coating of plate-like particles.

In the present invention, the content of the plate-like pigment coated with the water-insoluble substance is 1 to 20% by mass (hereinafter simply referred to as the “total brightness” and concealment power when using the product with respect to the total amount of the composition). (Referred to as “%”), preferably 3 to 15%.
If the content of the coated plate-like pigment is less than 3%, the glitter and hiding power are poor. On the other hand, if it exceeds 20%, the plate-like pigment is in the applicator pen core, that is, the writing is poor. This is not preferable. In the case of a plate-like pigment that has not been surface-treated, the formation of a hard cake is promoted.

The water-based ink composition for a writing instrument of the present invention preferably further contains a resin containing at least an acrylate ester in the molecule from the viewpoints of adhesion and dispersion stability.
As the resin containing this acrylic ester in the molecule, emulsion type John Krill 790 (manufactured by BASF), Primal AC2235 (manufactured by Rohm and Haas Japan Co., Ltd.), vinylol 1020 (manufactured by Daido Kasei Kogyo Co., Ltd.), Examples include alkali-soluble resins such as Joncrill 62J (manufactured by BASF) and Jurimer AT-210 (manufactured by Nippon Pure Chemicals Co., Ltd.). Preferably, those having an acid group in the composition and capable of being dissolved in water by neutralization are preferable.
Particularly preferred is an alkyl acrylate copolymer. For neutralization, 2-amino-2-methyl-1-propanol, 2-amino-2-methyl-1,3-propanediol, triethanolamine, L-arginine, aqueous ammonia, sodium hydroxide, etc. Particularly preferred is 2-amino-2-methyl-1-propanol which can be used.
Commercially available products include AMPHOMER HC (manufactured by NSC Japan) which is an alkyl acrylate copolymer, Luvimer 100P (manufactured by BASF) which is an alkyl acrylate copolymer, and Yodosol GH800F which is an alkyl acrylate copolymer emulsion ( AKZO NOBEL Co., Ltd.) and Jonkrill 450 (BASF Co.) which is a styrene alkyl resin emulsion.
The content of these resins is preferably 2 to 10%, more preferably 3.5 to 8% in terms of solid content, based on the total amount of the composition, from the viewpoints of adhesion and dispersion stability. .5% is desirable.

The aqueous ink composition for a writing instrument of the present invention preferably further contains crystalline cellulose from the viewpoint of suppressing the precipitation of the pigment.
The crystalline cellulose used functions not only as a thickener but also as a sedimentation inhibitor that prevents hard pigment precipitation, and is specifically obtained by acid hydrolysis or alkali oxidation decomposition of cellulose. It is an aggregate of cellulose crystallites having a substantially constant degree of polymerization. Unlike conventional aqueous solutions of thickening polysaccharides, etc., the cellulose crystallites have the property of forming dispersed particles in water.
Examples of the crystalline cellulose that can be used include those made of colloidal glue obtained by coating the surface of fine cellulose crystals of primary particles with a water-soluble polymer or the like. 591, RC-N81, RC-591NF, CL-611, Theolas cream [manufactured by Asahi Kasei Corporation] and the like.
The content of these crystalline celluloses is preferably 0.5 to 3.5%, more preferably 1.2%, based on the total amount of the composition, from the viewpoint of the viscosity range that can be used for the applicator. It is desirable to set it to -2.0%.

  The aqueous ink composition for a writing instrument of the present invention is prepared with water (purified water, ion-exchanged water, distilled water, pure water, etc.) as a solvent in addition to the above components.

Further, the water-based ink composition for a writing instrument of the present invention does not interfere with the dispersion system with a moisturizer, antibacterial agent, inorganic pigment, organic pigment, dye, surfactant, water-soluble organic solvent, etc. It can be suitably contained within a range not impairing the effects of the invention.
Examples of humectants that can be used include water such as 1,3-butylene glycol, 1,4-butylene glycol, pentylene glycol, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, and glycerin. And soluble glycols.
The content of these humectants is preferably 1 to 30%, more preferably 5 to 20%, based on the total amount of the composition.

  Examples of the antibacterial agent that can be used include parabens, sodium dehydroacetate, phenoxyethanol and the like. The antibacterial agent of the present invention contains a preservative, and parabens that are antiseptics include methyl paraoxybenzoate, ethyl paraoxybenzoate, propyl paraoxybenzoate, butyl paraoxybenzoate, and paraoxybenzoic acid. An appropriate amount of isopropyl or the like can be used.

  In the present invention, in order to obtain a more vivid color, in addition to the above-described coated plate-like pigment, an organic pigment, an AL lake pigment, and a dye can be blended to obtain a vivid color tone. In the case of plate pigments not subjected to the above coating treatment, hard cakes are deteriorated by blending of AL lake pigments, particularly dyes, but hard cakes are generated even with dyes if the plate pigments are surface-treated with the above water-insoluble substances. In addition, the reason why the heart cake is deteriorated when the AL lake pigment is not subjected to the above-described coating treatment is that the lake dye is released from the AL (bleed) and becomes a dye.

  In the present invention, the pH of the ink composition is adjusted by 2-amino-2-methyl-1-propanol, 2-amino-2-methyl-1,3-propanediol, triethanolamine, L-arginine, aqueous ammonia. PH adjusting agents such as sodium hydroxide can be used, and particularly preferable is pH adjustment with 2-amino-2-methyl-1-propanol.

Moreover, if the viscosity of the water-based ink composition for a writing instrument in the present invention is too high, it cannot be ejected from a direct liquid pen, and if it is too low, it is used as a pen, so that the drawn line becomes thick. Therefore, the viscosity at 25 ° C., it is desirable that the viscosity at a shear rate 38.4s ^-1 is 4~65mPa · s, the viscosity at a shear rate of 384S ^-1 in the range of 4~24mPa · s.
The flow rate of the aqueous ink composition for a writing instrument of the present invention is a so-called pen core in which the fibers are hardened with a resin or the like, or the fibers are fused to each other at the predetermined shear rate. Thus, the application like a marker is further facilitated, and the application area is small by applying force, such as application with a thin brush, and the variation of the application area is small.
The viscosity range is adjusted by combining the coated plate-like pigment, water, and a resin containing acrylic acid ester in the molecule and / or crystalline cellulose so as to have a suitable content. be able to.

The water-based ink composition for a writing instrument of the present invention is to mix and disperse the above-described components with a content of each of the above ranges using a mixing and dispersing machine such as a bead mill, a homomixer, a disper, an attritor, a ball mill, or a sand grinder. It is prepared with.
Specifically, 3 to 15% of the above-mentioned plate-like pigment coated on the surface with at least a water-insoluble substance and water are blended, and the plate-like pigment becomes the above preferable viscosity range etc. with the above-mentioned disperser or the like. Thus, it can be prepared by mixing and dispersing.

  The water-based ink composition for a writing instrument of the present invention configured as described above has at least a liquid storage space for storing the water-based ink composition for a writing instrument, and fibers are solidified with a resin or the like, or fibers are fused. A pen tip of a so-called pen core type is suitably housed in a writing instrument (marking pen) housed in the liquid housing space of an applicator for transporting liquid from the liquid housing space to the pen tip by capillary force. Can be used.

Examples of the writing instrument that can be used include writing instruments in which the water-based ink composition for writing instruments having the above-described configuration shown in FIGS.
FIG. 1 is a partial vertical view showing an example of a writing instrument containing the aqueous ink composition for a writing instrument of the present invention, FIG. 2 is an overall side view of a pen tip used in the writing instrument of FIG. 1, and FIG. It is a cross-sectional view of the nib along the II line.

  As shown in FIG. 1, this writing instrument is provided with a valve mechanism 14 on the inner wall surface 12 i of the open end 12 of the bottomed cylindrical main body 10 that houses the water-based ink composition for writing instruments having the above-described configuration. Then, the outer wall surface side 12o of the opening end 12 of the main body 10 and the holder 16 are screwed to each other with male and female screws formed respectively so as to cover the valve mechanism 14. At the same time, the pen core 18 is externally held by a cylindrical elastic resin porous body 20 inside the holder 16, and the pen core 18 is slidably provided. In this case, the application body 18 is moved by pressing the writing portion 18a which is the front end portion of the pen core 18, and the valve stem 24 is pressed by the pen core rear end portion 18b by the movement of the pen core 18. (The inclined surface 24b of the valve stem 24 opens and closes when the valve seat 14a is separated and contacted), and the aqueous ink composition for writing instruments is guided to the writing portion 18a.

  Specifically, in the holder 16, the pen core 18 is in contact with the tip 24 a of the valve stem 24, and an ink passage 26 having an inner groove having a radial cross section as shown in FIG. 2 is formed continuously in the axial direction. A pen core 18 made of a polyacetal resin is provided. As shown in FIG. 2, the pen core 18 is formed by cutting the entire writing portion 18 a, which is a tip portion, into a jet cone shape and is roughly cut into a bullet shape. Further, an aqueous ink composition for a writing instrument is used. Holes 28a and 28b introduced into the ink passage 26 in the writing instrument main body are formed in the pen core rear end portion 18b and the pen core side surface portion 18c. Here, the structure of the pen core 18 made of polyacetal resin is such that one ink introduction hole 28b for introducing the aqueous ink composition for a writing instrument into the ink passage 26 in the writing instrument body is spaced by 1 mm or more from the rear end surface of the pen core 18. The pen core side surface portion 18c is formed so as to surround the entire side surface (or part thereof) in a trapezoidal cross section. In addition, the shape of the ink introduction hole 28b formed in the pen core side surface portion 18c is such that the front end side surface 30a of the ink introduction hole 28b has an obtuse angle of the rearward opening angle α with respect to the axis 32, and the rear end side surface 30b has the axis 32. The forward opening angle β is set to be a right angle or an acute angle. Further, the outer diameter of the pen core 18 made of polyacetal resin is 2 mm or more and 4 mm or less. The valve stem 24 is urged forward by a spring 34 in the holder 16, and always abuts against the pen core 18 to press the pen core 18. Further, in the main body 10, a stirring ball 36 is accommodated in an ink tank of a water-based ink composition for a writing instrument.

For example, the pen core 18 is manufactured by continuously extruding a polyacetal resin to obtain a long molded body having an outer diameter of 3.0 mm and an ink distribution groove inside, and the long body is formed to a length of 500 mm. After cutting, it was further cut to a desired length, and then the pen core tip, rear end, and side ink outflow holes were polished to form a predetermined pen core (see FIG. 3).
A valve mechanism is provided on the inner wall surface side of the open end of a bottomed cylindrical main body having the pen ink obtained by the above-described manufacturing procedure inside with the water-based ink composition for a writing instrument having the above-described configuration. It was attached to the inside of the holder of the writing instrument main body in which the outer wall surface side of the opening end of the main body and the inner wall of the holder were screwed so as to cover. Then, after the application body was pushed and the water-based ink composition for a writing instrument reached the tip of the application body, the writing instrument was shaken back and forth, the number of times until the application body was removed was measured, and the average value was calculated. In addition, as a control, the same test was performed using the same type of pen body and a pen tip for a writing instrument that was changed to a pen core without an ink introduction hole on the side surface.
As a result, the average value of 10 controls showed that the pen lead was removed in less than 10 times, whereas in the pen lead of this example, the pen lead was removed after 200 times or more. Significant differences were obtained.
Furthermore, when writing with a writing instrument filled with this water-based ink composition for writing instruments, beautiful lines and patterns can be drawn easily, and the sedimentation stability with time is excellent, even if the plate pigment settles. It has been confirmed that hard cake hardly occurs, can be easily redispersed by stirring, and has excellent usability.

  In the present invention configured as described above, by containing at least a plate-like pigment whose surface is coated with a water-insoluble substance and water, it has excellent sedimentation stability with time, and even if the plate-like pigment settles, hard cake is generated. It is difficult to obtain a water-based ink composition for writing instruments and a method for producing the same, which can be easily redispersed by stirring, is excellent in usability, and has excellent writing performance.

  EXAMPLES Next, although an Example and a comparative example demonstrate this invention further in full detail, this invention is not restrict | limited by the following Example etc.

(Production Example 1: MP-20 cellulose treatment)
A plate-like pigment (MP-20, manufactured by Merck) is treated with cellulose by the production method 1. 2% surface coverage

(Production Example 2: MP-20 chitosan treatment)
A plate-like pigment (MP-20, manufactured by Merck) was treated with chitosan by production method 2. 2% surface coverage

(Production Example 3: MP-1005 cellulose treatment)
A plate-like pigment (MP-1005, manufactured by Merck) was subjected to cellulose treatment according to production method 1. 2% surface coverage

[Examples 1 to 11 and Comparative Examples 1 to 9]
A water-based ink composition for each writing instrument was prepared by mixing and dispersing with a homomixer or a disper with the formulation shown in Table 1 below.
About the aqueous ink compositions for writing instruments of Examples 1 to 11 and Comparative Examples 1 to 9 obtained above, 25 ° C. at a shear rate of 38.4 (s ⁻¹ ) and 384 (s ⁻¹ ) by the following method. The viscosity, pumping property, final writing property, and ball movement at 50 ° C. were evaluated.
These results are shown in Tables 1 and 2 below.

[Measurement method of viscosity]
About each obtained nail material composition, at a temperature of 25 ° C., a predetermined shear using a cone plate viscometer (among the TV-30 viscometer, EMD viscometer, standard cone plate, manufactured by Tokimec) The viscosity at speed was measured.

[Method for evaluating pumping properties]
Each water-based ink composition for a writing instrument was filled in the applicator shown in FIG. 1, and pumping was performed once per second, and the pumping property was evaluated according to the following evaluation criteria.
Evaluation criteria:
○: The above composition liquid reaches the nib in 1 to 15 times. Δ: The above composition liquid reaches the nib in 16 to 30 times. X: The above composition liquid reaches the nib in 30 times or more.

[Evaluation method of final writing properties]
Each water-based ink composition for a writing instrument was filled in the applicator shown in FIG. 1 and written on a paper surface, and the final writing property was evaluated according to the following evaluation criteria.
Evaluation criteria:
○: The strokes are not blurred, and the final stroke △: The strokes are blurred, but the final stroke ×: The strokes are blurred, impossible to finish

[Evaluation method of ball movement at 50 ° C]
The writing ink shown in FIG. 1 is filled with each water-based ink composition for writing instruments, and is allowed to stand at 50 ° C. for 1 month. This was shaken by hand, the movement of the stirring ball was observed, and evaluated according to the following evaluation criteria.
Evaluation criteria:
○: The stirring ball moves by swinging 1 to 3 times.
Δ: The stirring ball moves with 4 to 9 swings.
X: Must be shaken 10 times or more until the stirring ball moves.

* 1 to * 6 in Tables 1 and 2 are as follows.
* 1: Theolas RC-N81, manufactured by Asahi Kasei Chemicals * 2: Jonkrill-450, manufactured by BASF, solid content 45% by mass
* 3: MP-20, manufactured by Merck * 4: Superseen MP-1001, manufactured by Merck * 5: MP-115, manufactured by Merck * 6: MP-149, manufactured by Merck

  As is clear from the results of Table 1 and Table 2, Examples 1 to 11 of the present invention are pumping properties, final writing properties, and 50 ° C. compared to Comparative Examples 1 to 8 that are outside the scope of the present invention. It was found that the water-based ink composition for writing instruments was excellent in ball movement and re-stirability.

  A water-based ink composition for a writing instrument suitable for a marking pen, particularly a water-based ink filled in a direct liquid-type writing instrument.

10 Main Body 14 Valve Mechanism 18 Pen Core Type Application Body

Claims (8)

  A water-based ink composition for a writing instrument, comprising at least a plate-like pigment having a surface coated with a water-insoluble substance.   The aqueous ink composition for a writing instrument according to claim 1, further comprising a resin containing at least an acrylic ester in the molecule.   Furthermore, crystalline cellulose is contained, The aqueous ink composition for writing instruments of Claim 1 or 2 characterized by the above-mentioned.   The plate-like pigment is a pigment selected from one or more of a pearl pigment, an aluminum powder pigment, a metal or metal oxide-coated glass flake, and an aluminum-coated polyester film. The water-based ink composition for writing instruments as described in any one.   The water-based ink composition for a writing instrument according to any one of claims 1 to 4, wherein the water-insoluble substance is selected from cellulose, hemicellulose, lignin, chitin, chitosan, latex, silica, alumina, and silicone, which are polymers. Viscosity 4~65mPa · s at a shear rate 38.4s ^-1, the viscosity at a shear rate 384S ^-1 is according to any one of claims 1 to 5 in the range of 4~24mPa · s A water-based ink composition for writing instruments.   A method for producing an aqueous ink composition for a writing instrument, comprising mixing 3 to 15% by mass of a plate-like pigment having a surface coated with at least a water-insoluble substance and water, and dispersing the plate-like pigment. A resin containing acrylic acid ester in the molecule and / or crystalline cellulose is added, and the water-based ink composition for writing instruments has a viscosity of 4 to 65 mPa · s and a shear rate of 384 s ⁻¹ when the shear rate is 38.4 s ^−1. The method for producing a water-based ink composition for a writing instrument according to claim 7, wherein the viscosity of the ink is 4 to 24 mPa · s.

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