JP6846195B2 - Aqueous ink composition for writing tools and writing tools using it - Google Patents

Description

The present invention relates to a water-based ink composition for stationery. More specifically, the present invention relates to a water-based ink composition for writing instruments, which is excellent in storage stability of ink and color development of handwriting. The present invention also relates to a writing instrument using the composition.

Conventionally, a water-based ink composition for writing instruments using a white pigment such as titanium oxide has been known in order to obtain a handwriting having a concealing property. Furthermore, it has become known that by using a complementary color pigment or the like in combination with such a highly concealing ink composition, pastel or chromatic handwriting can be obtained while concealing the base, and such a composition. Is being actively considered.

However, when a pigment having a heavy specific gravity such as titanium oxide is used, if the pigment precipitates over time to form a so-called hard cake, redispersion may become difficult. Therefore, attempts have been made to prevent the pigment from settling by modifying various materials used in the composition or by using a dispersant in combination. However, although the conventionally reported technology can slow down the sedimentation rate, it is inevitable that the cake will become a hard cake over a long period of time, and the actual situation is that these measures have not led to sufficient results. Is. Further, measures such as increasing the ink viscosity and developing structural viscosity by using so-called gelling agents and thickeners are also being studied. However, when an ink composition taking these countermeasures is used for a writing instrument using a pen tip such as a fiber core or a porous body, the amount of ink ejected may be reduced. Further, when used in a writing instrument, the pigment may settle at the pen tip, and the writing line may not be visible or faint when writing. As described above, there is room for improvement in the conventional techniques for the stability of ink compositions containing pigments having a heavy specific gravity over time, and further improvement methods are being studied.

Japanese Unexamined Patent Publication No. 2003-138192 Japanese Unexamined Patent Publication No. 11-217532 Japanese Unexamined Patent Publication No. 2004-149681

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to easily create a dispersed state in which various components such as pigments settle over time without forming a hard cake, and a writing instrument using a pen tip such as a fiber core or a porous body. It is an object of the present invention to provide a writing ink composition having excellent handwriting color development and a writing instrument using the same, without the pigment settling on the pen tip even when used in the above.

In the present invention, a water-based ink composition for writing tools (hereinafter, may be referred to as "water-based ink composition", "ink composition", or "composition") contains wet silica, water-containing kaolin, or the like. The above-mentioned problem was solved by doing so.
That is, the present invention
"1. A water-based ink composition for writing instruments, which comprises pigment particles, wet silica, hydrous kaolin, an agglutination control agent, and water.
2. The composition according to item 1, wherein the pigment particles contain titanium oxide.
3. 3. The composition according to item 1 or 2, wherein the aggregation control agent is a cellulose derivative.
4. The composition according to any one of items 1 to 3, further comprising a coagulation dispersant.
5. The composition according to item 4, wherein the coagulation dispersant is an alkylol ammonium salt of a polybasic acid.
6. The composition according to any one of Items 1 to 5, wherein the hydrous kaolin has an average particle size of 0.1 μm to 5.0 μm.
7. A writing instrument comprising the composition according to any one of items 1 to 6. About.

According to the present invention, by blending wet silica into a water-based ink composition for writing instruments, a pigment at a pen tip is maintained while maintaining redispersibility and stability over time of the ink composition as compared with conventional writing instruments. It is possible to suppress the precipitation of ink, which is excellent in writing property, and also exhibits excellent effects such as obtaining a water-based ink composition for writing instruments which is excellent in color development of writing instruments.

Hereinafter, embodiments of the present invention will be described in detail. In addition, in this specification, "part", "%", "ratio", etc. indicating a composition are based on mass unless otherwise specified.

The water-based ink composition for writing instruments according to the present invention comprises pigment particles, wet silica, hydrous kaolin, an agglutination control agent, and water. Hereinafter, each component constituting the water-based ink composition according to the present invention will be described.

(Pigment particles)
In the present invention, the pigment particles can be selected from any conventionally known pigment particles. Examples of pigments include inorganic pigments such as metal oxides or metal salts, and organic pigments such as organic pigments or lake pigments. In the present invention, inorganic pigment particles are preferable, and metal oxide particles are particularly preferable. In particular, since titanium oxide is white, it is preferable because various colors can be realized by combining it with a complementary color pigment or the like described later. Further, it is particularly preferable to use titanium oxide whose surface is treated with alumina because the dispersion stability is improved. Further, as the pigment, a glossy brilliant pigment such as an aluminum pigment can also be used.

The average particle size of the pigment particles is preferably 0.01 μm to 30 μm, more preferably 0.05 μm to 20 μm, and even more preferably 0.1 μm to 10 μm. When the average particle size of the pigment particles is within the above numerical range, the settling of the pigment particles can be suppressed by a pen tip such as a fiber core or a porous body when combined with wet silica, so that good handwriting color development is achieved. Is obtained. As an example, the average particle size of the pigment particles is 50, which is the cumulative volume of the particle size distribution measured by the laser diffraction method using a laser diffraction type particle size distribution measuring machine (trade name "Microtrac HRA9320-X100", Nikkiso Co., Ltd.). It can be measured by the particle size (D50) at%. In the present specification, the "average particle size" refers to a volume-based average particle size unless otherwise specified.

The content of the pigment particles in the water-based ink composition is preferably 1 to 50% by mass, more preferably 10 to 40% by mass, based on the total mass of the water-based ink composition. When the content of the pigment particles is within the above numerical range, it is possible to prevent the ink ejection property from being lowered, and it is possible to maintain the water-based ink composition and the concealing property of the handwriting formed by using the water-based ink composition. ..

(Wet silica)
The water-based ink composition according to the present invention contains wet silica. The wet silica referred to in the present invention is an amorphous silica synthesized by a wet method, in which relatively large primary particles having a diameter of several to several tens of nm are aggregated, and it is difficult to obtain primary particles by dispersion. It is a secondary particle of 10 μm. In the present invention, the wet silica has a higher specific surface area and a large number of silanol groups on the surface as compared with the dry silica, and therefore forms a loose bridging network by interaction with the pigment particles. Then, since a loose and bulky agglomerate can be formed with a coagulation control agent or a coagulation dispersant described later, the inclusion of wet silica in the ink composition improves the dispersion stability of the pigment particles. Furthermore, the redispersibility of the agglomerates can be improved. On the other hand, when dry silica is used, dispersion stability can be maintained, but it is not preferable because structural viscosity is generated and the ink viscosity is increased by adding a small amount.

Further, as for wet silica, when paper is used as the writing surface, the wet silica exerts a strong sealing effect and can prevent pigment particles from entering between the fibers of the paper, and can be used in combination with hydrous kaolin described later. , The effect of enhancing the color development of handwriting can be obtained.

The average particle size of the wet silica is preferably 0.1 μm to 10 μm. When the average particle size of the wet silica is within the above numerical range, stable dispersion is possible in the ink composition, and a high pigment precipitation suppressing effect can be obtained. Further, from the viewpoint of achieving higher color development, it is more preferably 0.5 μm to 7 μm, and further preferably 1 μm to 5 μm. The average particle size of the wet silica is, for example, when the cumulative volume of the particle size distribution measured by the laser diffraction method using a laser diffraction type particle size distribution measuring machine (trade name "Microtrac HRA9320-X100", Nikkiso Co., Ltd.) is 50%. It can be measured by the particle size (D50) of.

Specific examples of the wet silica that can be used in the present invention include NIPSIL series (manufactured by Tosoh Corporation), Mizukasil series (manufactured by Mizusawa Chemical Industry Co., Ltd.), Carplex series (manufactured by DSL. Japan), and Tokusil series (manufactured by Oriental silica). Examples include the Ultrasil series (manufactured by Evonik Degussa Japan), the Zeosil series (manufactured by Rhodia), and the Silica series (manufactured by PPG).

The content of wet silica in the water-based ink composition is preferably 0.1% by mass to 5% by mass, and more preferably 1% by mass to 3% by mass, based on the total mass of the water-based ink composition. preferable. When the content of the wet silica is within the above numerical range, it is possible to prevent the pigment from settling at the pen tip even when it is used for a writing instrument using a pen tip such as a fiber core or a porous body. Further, the concealing property of the water-based ink composition and the handwriting formed by using the water-based ink composition can be maintained.

(Aggregation control agent)
The water-based ink composition according to the present invention comprises an aggregation control agent. The agglomeration control agent binds to the agglomerates having a relatively low density formed by the wet silica described above, and further disperses the water-containing kaolin and the extender, which will be described later, in the water-based ink composition, and is bulky. It is capable of forming aggregates. This agglomeration control agent prevents the water-based ink composition from forming a hard cake and forms bulky agglomerates, so that the redispersibility can be improved. As the aggregation control agent, for example, a cellulose derivative can be used, and two or more kinds of cellulose derivatives can be used in combination.

Examples of the cellulose derivative include carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, hydroxypropyl ethyl cellulose and salts thereof. Of these, carboxymethyl cellulose is preferable because it can prevent the pigment particles from forming a hard cake and reducing the redispersibility. This is because the carboxyl group contained in carboxymethyl cellulose is easily adsorbed on the aggregate having a relatively low density, is uniformly present in the composition, and can inhibit the aggregation of the pigment particles, and as described above. It is considered that this is because the constitutional material, the polyolefin resin particles and the like can be dispersed, and the agglomerates can be made bulky. Further, carboxymethyl cellulose is preferable because it has high thermal stability as compared with other cellulose derivatives and its physical properties do not change even when the composition is heated.

The content of the aggregation control agent in the water-based ink composition is preferably 0.05 to 1.0% by mass, preferably 0.1 to 0.5% by mass, based on the total mass of the water-based ink composition. Is more preferable.

(Water-containing kaolin)
The water-based ink composition according to the present invention comprises hydrous kaolin. The hydrous kaolin referred to in the present invention is a flat or plate-shaped natural clay mineral containing aluminum silicate containing water of crystallization, which is obtained by purifying the natural clay mineral kaolin clay. In the present invention, since the hydrous kaolin has a flat or plate-like particle shape as described above, since the hydrous kaolin is contained in the ink composition, when paper is used as the writing surface, the hydrous kaolin However, it exerts a strong sealing effect, prevents pigment particles from entering between the fibers of the paper, and further enhances the color development of handwriting.

Further, since the hydrous kaolin is uniformly dispersed in the aggregate having a relatively low density formed by the pigment particles, the wet silica and the agglutination control agent in the ink composition, the water-containing kaolin is bulky although the density is relatively low. Since high agglomerates are formed, the redispersibility can be improved as compared with the case where calcined kaolin is used.

Furthermore, because of the flat or plate-like particle shape of kaolin containing water when writing, it is placed parallel to the paper surface when writing, so it does not scratch the paper surface even when overwriting. , It is possible to write without scraping the paper surface.

The average particle size of the hydrous kaolin is preferably 0.1 μm to 5 μm. When the average particle size of the water-containing kaolin is within the above numerical range, the redispersibility of the ink composition and the color development of the handwriting can be enhanced, and the paper surface can be prevented from being scraped. Further, from the viewpoint of achieving higher color development, it is more preferably 0.2 μm to 3 μm, and further preferably 0.5 μm to 2 μm. As an example, the average particle size of hydrous kaolin is measured by a laser diffraction method using a laser diffraction type particle size distribution measuring machine (trade name "Microtrac HRA9320-X100", Nikkiso Co., Ltd.) when the cumulative volume of the particle size distribution is 50%. It can be measured by the particle size (D50) of.

Specific examples of the hydrous kaolin that can be used in the present invention include ASP-G90 (average particle size 0.2 μm), ASP-G92 (average particle size 0.2 μm), and ASP-072 (average particle size 0. 3 μm), ASP-101 (average particle size 0.4 μm), ASP-102 (average particle size 0.4 μm), ASP-170 (average particle size 0.4 μm), ASP-172 (average particle size 0.4 μm) , ASP-200 (average particle size 0.4 μm), ASP-400P (average particle size 3.5 μm), ASP-600 (average particle size 0.6 μm), ASP-602 (average particle size 0.6 μm), ASP -802 (average particle size 2.5 μm), ASP-900 (average particle size 1.5 μm), ASP-RO (average particle size 0.4 μm), ASP-NCX1 (average particle size 0.7 μm) (all are commercial products Name, manufactured by BASF, Hydrote PXN-LCS (average particle size 0.68 μm), Hydrote RS (average particle size 0.77 μm), Hydrote Flat-DS (average particle size 5.0 μm), Barrisurf HX (average particle size 1) .49 μm), Eckalite 1 (average particle size 0.40 μm), Eckalite ED (average particle size 0.32 μm) (trade name, manufactured by Imeris Specialty's Japan Co., Ltd.), KaMin35 (average particle size 4.0 μm) ), KaMin35B (average particle size 4.0 μm), KaMin80 (average particle size 0.5 μm), KaMin80B (average particle size 0.5 μm), KaMin90 (average particle size 0.4 μm), KaMin90B (average particle size 0.4 μm) ) KaMinHG90 (average particle size 0.3 μm), KaMinTEK2001 (average particle size 0.25 μm), Polygloss90 (average particle size 0.2 μm), PolyplatateP (average particle size 0.8 μm), PolyplatateP01 (average particle size 0.8 μm) , Polyplatate HMT (average particle size 1.5 μm) (both are trade names, manufactured by KaMin LLC), and the like.

The content of the water-containing kaolin in the water-based ink composition is preferably 1% by mass to 20% by mass, more preferably 5% by mass to 15% by mass, based on the total mass of the water-based ink composition. When the content of the water-containing kaolin is within the above numerical range, it is possible to prevent the ink viscosity from becoming too high, making a hard cake, and scraping the paper surface when writing. Further, the concealing property of the water-based ink composition and the handwriting formed by using the water-based ink composition can be maintained.

(resin)
The water-based ink composition can further contain a resin. Examples of the resin that can be used in the present invention include acrylic resin, urethane resin, ethylene-vinyl acetate copolymer, etc., and water-soluble resin, resin emulsion in which the resin is dispersed in water, and the like are used. Can be done. By including the acrylic resin in the water-based ink composition, the fixability of the water-based ink composition can be improved, and the scratch resistance of the writing line formed by using the acrylic resin can be further improved.

The acrylic resin used in the present invention is a polymer containing acrylic acid or methacrylic acid as a repeating unit. As this acrylic resin, either one dissolved in any alkali or the like or one dispersed in water may be used.

As the acrylic resin, an acrylic acid ester resin, an acrylic styrene copolymer resin, an acrylic acid ester copolymer resin, a methacrylic acid ester resin, a methacrylic acid ester copolymer resin, or the like can be used. These resins are usually often used as emulsions. The molecular weight of these acrylic resins is not particularly limited, but those having a mass average molecular weight of 1,000 to 100,000 are generally used.

Specific examples of the acrylic resin that can be used in the present invention include JONCRYL series (manufactured by BASF), Primal AC series (manufactured by Roam & Haas Japan Co., Ltd.), JSRAE series (manufactured by JSR Corporation), and Mo. Examples include the vinyl series (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), the Nikazol series (manufactured by Nippon Carbide Industry Co., Ltd.), the Neocryl series (manufactured by DSM), and the Boncoat series (manufactured by DIC).

As the urethane resin that can be used in the present invention, urethane resins such as a polyether polyol copolymer type, a polyester polyol copolymer type, and a polycarbonate polyol copolymer type can be used.

Specifically, as urethane resin, Neorez series (manufactured by DSM), Hydran series (manufactured by DIC), Juliano W series (manufactured by Arakawa Chemical Industry Co., Ltd.), Superflex (manufactured by Daiichi Kogyo Co., Ltd.), Merci series (manufactured by Toyo Polymer) (Made by the company) and so on.

Specific examples of the ethylene-vinyl acetate copolymer that can be used in the present invention include Ayurisol series (manufactured by Showa Denko KK) and Sumikaflex series (manufactured by Sumitomo Chemical Co., Ltd.).

The content of the resin in the water-based ink composition is preferably 0.5 to 15% by mass, more preferably 2 to 8% by mass, based on the total mass of the water-based ink composition.

(Coagulation dispersant)
The water-based ink composition according to the present invention may contain a coagulation dispersant. Here, the coagulation dispersant is capable of adhering to the surface of the pigment particles, keeping the distance between the pigment particles at a certain level or more while separating the pigment particles from each other, and preventing the pigment particles from directly aggregating with each other. is there. As a result, agglomeration of pigment particles is suppressed, and even when agglomerates are formed, agglomerates having a relatively low density are formed. Further, since the above-mentioned effects are exhibited on the pigment particles of the bulky aggregate formed of the pigment particles, the wet silica, the aggregation control agent, and the hydrous kaolin, the redispersibility can be further improved.

As such a coagulation dispersant, an alkylol ammonium salt of a polybasic acid is preferably used. The polybasic acid may have a plurality of acid groups, and examples thereof include acidic polymers having a larger number of acid groups, such as acrylic acid, methacrylic acid, polyvinylsulfonic acid, and polyphosphoric acid. In addition to this, a polymer obtained by polymerizing an unsaturated fatty acid such as crotonic acid is also an example of a polybasic acid. Alkyrol ammonium salts of polybasic acids can be obtained by reacting these polybasic acids with alkyrol ammonium. The salt obtained by such a reaction contains the following partial structure.
-C (= O) -N (-R ¹ ) ( ^{-R 2-} OH)
Here, R ¹ is an alkyl group and R ² is an alkylene group. The dispersion coagulant used in the present invention is preferably a polymer having such a partial structure. Such a polymer may have a plurality of the above structures, and its molecular weight is not particularly limited, but the mass average molecular weight is preferably 1,000 to 100,000, and 5,000 to 20,000. Is more preferable.

Further, depending on the pigment used, an acidic group such as a carboxyl group may exert the same function. That is, polymers containing an acidic group can also be used as the coagulation dispersant.

In the present invention, the coagulation / dispersant is bonded to the surface of the pigment particles by the group as described above, and by hydrogen bonding with other coagulation / dispersant molecules, the main chain structure of the polymer penetrates between the pigment particles, and the pigment particles. It is thought that they are separated from each other.

Such coagulation dispersants are generally commercially available, such as Anti-Terra 203, Anti-Terra 204, Anti-Terra 206, Anti-Terra 250, Anti-Terra U, DISPER BYK-102, DISPER BYK-180, Examples thereof include DISPER BYK-191 (trade name, manufactured by Big Chemie), TEGO Disper630, and TEGO Disper700 (trade name, all manufactured by Evonik Degussa Japan).

(Constitution material)
The water-based ink composition according to the present invention may contain an extender material in addition to wet silica and hydrous kaolin as long as the performance is not affected. In the present invention, the constitutional material can be selected from any conventionally known materials, and specific examples thereof include calcined kaolin, talc, mica, clay, bentonite, calcium carbonate, barium sulfate, and aluminum hydroxide. Be done. In addition, whiskers such as calcium carbonate, potassium titanate, magnesium sulfate, and calcium sulfate can also be used.

The content of the constitutional material in the water-based ink composition is preferably 1% by mass to 20% by mass, more preferably 5% by mass to 15% by mass, based on the total mass of the water-based ink composition. When the content of the constitutional material is within the above numerical range, it is possible to prevent the ink viscosity from becoming too high, making a hard cake, and preventing the ink ejection property from being lowered during writing. Further, the concealing property of the water-based ink composition and the handwriting formed by using the water-based ink composition can be maintained.

(Complementary color pigment)
The water-based ink composition according to the present invention may contain a complementary color pigment in order to adjust the color of the obtained writing line. In particular, when white titanium oxide is selected as the main pigment particles, various colors can be realized by combining with the complementary color pigment. The complementary color pigment is not particularly limited, and pigments of various colors such as red, blue, yellow, green, white, and black can be used. Complementary color pigments include, for example, SP series (manufactured by Fuji Dye Co., Ltd.) Emacol series, Sandye series (manufactured by Sanyo Dye Co., Ltd.), Lumicol series (manufactured by Nippon Fluorescent Chemical Co., Ltd.), EM / Color series (Toyo Ink Co., Ltd.) (Manufactured by Shinroihi), Shinroihi color base series (manufactured by Shinroihi), WA color series (manufactured by Dainichiseika), etc.

The content of the complementary color pigment in the water-based ink composition is preferably 0.01 to 15% by mass, more preferably 0.1 to 10% by mass, based on the total mass of the water-based ink composition.

(Other)
In addition, the water-based ink composition contains, if necessary, a surfactant, a preservative, a wetting agent, a defoaming agent, a rust preventive, a pH adjuster, a bubble suppressant, a bubble absorber, a shear-reducing agent and a viscosity. It may contain a regulator or the like.

(Aqueous ink composition for writing tools)
The viscosity of the aqueous ink composition according to the present invention is preferably low. The viscosity of the composition can be measured using an E-type rotational viscometer (manufactured by Brookfield). Specifically, the viscosity of the aqueous ink composition at 20 ° C. is preferably 1 to 20 mPa · s, preferably 8 to 18 mPa · s, when measured under the condition of ^{a rotation speed of 100 rpm (shear rate 380 sec -1).} Is more preferable. When the viscosity of the water-based ink composition is within the above numerical range, the ink ejection property when used for a writing instrument such as a marker can be improved, and the writing property on a non-permeable recording medium such as a film is improved. To do.

The pH of the aqueous ink composition is preferably 6.0 to 10.0, more preferably 7.0 to 9.0. When the pH of the water-based ink composition is within the above numerical range, the ink can be used without discoloration or increase in ink viscosity and without affecting the ink. In the present invention, the pH value can be measured at 20 ° C. by, for example, an IM-40S type pH meter (manufactured by DKK-TOA CORPORATION).

The reason why the water-based ink composition according to the present invention exhibits excellent redispersibility has not been clarified in detail, but it is presumed to be due to the following mechanism.

As described above, the pigment particles, the wet silica, and the agglomeration control agent form agglomerates having a relatively low density. However, especially when the pigment particles have a large specific gravity such as titanium oxide, the agglomerates gradually become the largest with time. It is densely packed and becomes a hard cake. It is thought that the combined use of hydrous kaolin here will improve the redispersibility by inhibiting the closest packing due to the presence of the flat and plate-like structures of the hydrous kaolin between the agglomerated pigment particles. Eh. Further, since the coagulation dispersant can be adsorbed on the surface of the pigment particles and the distance between the pigment particles can be kept constant, it is considered that the dense packing works more effectively to inhibit the inhibition and the redispersibility is further improved.

The water-based ink composition according to the present invention can be produced by any conventionally known method. Specifically, each of the above components can be blended in a required amount and mixed with various stirrers such as a propeller stirrer, a homodisper, or a homomixer, or various dispersers such as a bead mill to produce the product.

(Writing instrument)
The water-based ink composition of the present invention is used for writing instruments such as marking pens and ballpoint pens with a pen core such as a fiber tip, felt tip, plastic tip or ballpoint pen tip as a writing tip, and a fountain pen using a metal writing tip. Can be done. Among them, when the pen tip is used for a writing instrument having a fiber tip or a felt tip, the settling of pigment particles in the tip can be suppressed, so that the writing performance is improved and the effect is particularly high. The porosity of the pen core is preferably 50 to 80%. When the porosity of the pen core is within the above numerical range, the pigment is not clogged and an appropriate ink ejection amount can be maintained.

The writing tool of the present invention may be configured to be directly filled with the water-based ink composition, or may be provided with an ink container or an ink occlusion body capable of filling the water-based ink composition.

The infestation mechanism of the writing instrument of the present invention is not particularly limited, and examples thereof include a cap type having a cap covering the pen tip, a knock type, a rotary type, and a slide type. Further, it may be a retractable type in which the pen tip can be accommodated in the barrel.

Further, the ink supply mechanism in the writing tool is not particularly limited. For example, (1) a mechanism provided with an ink guide core made of a fiber bundle or the like as an ink flow rate adjusting member and supplying an aqueous ink composition to a pen tip. (2) A mechanism for supplying a water-based ink composition to the pen tip by providing a comb groove-shaped ink flow rate adjusting member, and (3) a mechanism for supplying an ink flow rate adjusting member by a valve mechanism, and a pen for the water-based ink composition. Examples thereof include a mechanism for supplying the ink composition first, and (4) a mechanism for directly supplying the water-based ink composition to the pen tip from the ink container or the barrel provided with the pen tip.

In one embodiment, the writing instrument is a marking pen, and the pen tip is not particularly limited and may be, for example, a fiber tip, a felt tip or a plastic tip, and the shape thereof may be bullet-shaped, chisel-shaped or It may be a brush pen type or the like.

In one embodiment, the writing instrument is a ballpoint pen, preferably a ballpoint pen provided with an ink backflow preventive body.

The present invention will be described below with reference to various examples.
(Example 1)
An ink composition for writing utensils was obtained by stirring and mixing the following raw materials and blending amounts at room temperature for 1 hour. The viscosity of the obtained aqueous ink composition was measured with an E-type rotational viscometer (DV-II + Pro, cone-type rotor CPE-42, manufactured by Brookfield). Specifically, the viscosity at 20 ° C. and a shear rate of 380 sec ^-1 (rotational speed of 100 rpm) was 13 mPa · s.
・ Pigment particles 25% by mass
(Titanium oxide particles whose surface is treated with alumina, average particle size: 0.21 μm, manufactured by TAYCA CORPORATION, trade name: JR-405)
・ Wet silica 2% by mass
(Average particle size 2 μm, trade name: Mizkasil P-527, manufactured by Mizusawa Chemical Industry Co., Ltd.)
・ Hydrous kaolin 10% by mass
(Average particle size 0.6 μm, trade name: ASP-600, manufactured by BASF)
・ Coagulation dispersant 1.5% by mass
(Alchilol ammonium salt of high molecular weight acidic polymer, trade name: Anti-Terra 250, manufactured by Big Chemie)
・ Aggregation control agent 2% by mass
(Carboxymethyl cellulose, 10% aqueous solution, trade name: F-907A, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.)
・ Acrylic resin 7% by mass
(Styrene-acrylic acid copolymer emulsion, solid content 47%, trade name: JONCRYL PDX-7600, manufactured by BASF)
・ Wetting agent 0.4% by mass
(Acetylene glycol, trade name: Dynol 604, manufactured by Nissin Chemical Industry Co., Ltd.)
・ Preservative 0.2% by mass
(1,2-benzoisothiazolin-3-one, trade name: Proxel XL-2, manufactured by Lonza Japan Co., Ltd.)
・ Ion-exchanged water 61.9% by mass

(Examples 2 to 4, Comparative Examples 1 to 6)
The ink compositions of Examples 2 to 4 and Comparative Examples 1 to 6 were obtained by changing the types and amounts of the components to be blended with respect to Example 1 as shown in Table 1. Details of the materials used in these examples are as follows.
-Titanium oxide (1) JR-405 (Al ₂ O ₃ treatment, average particle size: 0.21 μm, manufactured by TAYCA CORPORATION)
-Titanium oxide (2) JR-600E (Al ₂ O ₃ treatment, average particle size: 0.27 μm, manufactured by TAYCA CORPORATION)
-Wet silica (1) (Mizkasil P-527, manufactured by Mizusawa Chemical Co., Ltd.)
-Wet silica (2) (Mizkasil P-763, manufactured by Mizusawa Chemical Co., Ltd.)
・ Dry silica (Aerosil 200, manufactured by Nippon Aerosil)
Hydrous kaolin (1) (ASP-600, average particle size: 0.6 μm, manufactured by BASF)
Hydrous kaolin (2) (ASP-900, average particle size: 1.5 μm, manufactured by BASF)
-Baked kaolin (Satintone 5HB, average particle size: 0.8 μm, manufactured by BASF)
-Coagulation dispersant Anti-Terra 250 (ulchilol ammonium salt of high molecular weight acidic polymer, manufactured by Big Chemie)
・ Aggregation control agent CMC (Carboxymethyl cellulose brand name: F-907A, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.)
-Acrylic resin JONCRYL PDX-7600 (styrene-acrylic acid copolymer emulsion, solid content 47%, manufactured by BASF)
-Urethane resin Neorez R-650 (polyether polyol copolymerized urethane resin emulsion, solid content 38%, manufactured by DSM)

(Evaluation of redispersibility)
The water-based ink composition was placed in a closed glass test tube having a diameter of 15 mm and left at room temperature for 14 days. Then, each glass test tube once settled was shaken up and down, and the redispersion state of the water-based ink composition was visually observed. The agglutination state was evaluated according to the following criteria.
A: Easily redispersed by shaking B: Redispersed by shaking but taking a long time C: Not sufficiently redispersed by shaking D: Not redispersed by shaking

(Evaluation of handwriting color development)
For the pen tip, a bullet-shaped polyester fiber core tip having a porosity of 60% was used. Writing was performed on the writing test paper with this marking pen. The color development of the handwriting at that time was visually observed. Black paper (manufactured by Kishu Paper Co., Ltd., high-quality colored paper, medium-thick mouth) was used as the writing test paper.
A: The handwriting hides the writing surface, and a good handwriting is obtained.
B: Although the handwriting hides the writing surface, it is not enough and the color of the writing surface is slightly transparent.
C: The handwriting is visible, but the writing surface is hardly concealed, and the color of the writing surface is transparent.
D: The handwriting cannot be visually recognized and the writing surface is not concealed at all.

(Evaluation of writing performance)
For the pen tip, a bullet-shaped polyester fiber core tip having a porosity of 60% was used. After writing on the writing test paper using this marking pen, the chip was left facing upward for 30 days, then writing was performed on the writing test paper, and the state of the paper surface at that time was visually observed. Black paper was used as the writing test paper.
A: The handwriting hides the writing surface, and a good handwriting is obtained.
B: Although the handwriting hides the writing surface, it is not enough and the color of the writing surface is slightly transparent.
C: The handwriting cannot be visually recognized and the writing surface is not concealed at all.

As is clear from the results in (Table 1), the water-based ink composition for writing utensils of the present invention was excellent in ink redispersibility and ink storage stability. Further, when writing was performed on the writing instrument with a marker using a bullet-shaped polyester fiber core tip having a porosity of 60% on the pen tip, the handwriting color development was good and the writing performance was also good. In particular, in terms of writing performance, when the ink composition of the example was used, good writing performance was obtained without sedimentation of the pigment in the chip.

Claims (6)

A water-based ink composition for writing instruments containing pigment particles, wet silica, hydrous kaolin, an aggregation control agent, and water , wherein the pigment particles contain titanium oxide, and the content of the aggregation control agent is the above. A water-based ink composition for writing instruments, which is 0.05% by mass to 1.0% by mass based on the total mass of the water-based ink composition for writing instruments. The composition according to claim 1, wherein the aggregation control agent is a cellulose derivative. The composition according to claim 1 or 2 , further comprising a coagulation dispersant. The composition according to claim 3 , wherein the coagulation dispersant is an alkylol ammonium salt of a polybasic acid. The composition according to any one of claims 1 to 4 , wherein the hydrous kaolin has an average particle size of 0.1 μm to 5.0 μm. A writing instrument comprising the composition according to any one of claims 1 to 5.