JP2007154209A - Water-based pigment dispersion for water-based ink composition, method for producing the same and water-based ink composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based pigment dispersion for a water-based ink composition capable of providing a water-based ink composition having excellent water resistance and alkali resistance, and to provide a method for producing the same. <P>SOLUTION: The water-based pigment dispersion for a water-based ink composition which is obtained by dispersing pigments in water by using a pigment disperser comprises a slightly volatile alkali salt of a copolymer of a carboxy group-containing monomer and a hydrophobic monomer, and a water-soluble organic solvent having 7.5 to 11 solubility parameter. After the copolymer is solved in the water-soluble organic solvent, the water-based pigment dispersion for a water-based ink composition is obtained by dispersing pigments in water by using the pigment disperser in which the copolymer is the slightly volatile alkali salt by the use of a slightly volatile alkali substance. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an aqueous pigment dispersion for an aqueous ink composition and a method for producing the same. Furthermore, it is related with the water-based ink composition using the said water-based pigment dispersion for water-based ink compositions. The aqueous pigment dispersion for aqueous ink composition of the present invention can be applied to aqueous ink compositions for various uses. In particular, it is useful as a water-based ink composition for writing instruments such as sign pens, ballpoint pens, felt pens, and brush pens.

  Conventionally, in an aqueous ink using an aqueous pigment dispersion in which a pigment is dispersed in water, an alkali salt of a resin having a carboxyl group is used as a pigment dispersant in the aqueous pigment dispersion. However, the resin having a carboxyl group has poor solubility and tends to become cloudy during alkali chlorination. Such a cloudy pigment dispersant was poorly wetted with the pigment, and was insufficiently mixed with the pigment in the aqueous pigment dispersion. Moreover, the foaming in the defoaming step after mixing is poor, and it takes a long time for defoaming.

  Further, in water-based inks for writing instruments, a volatile alkaline substance such as ammonia is generally used as an alkaline substance for solubilizing the pigment dispersant in order to develop water resistance and alkali resistance against handwriting.

  On the other hand, from the viewpoint of cap-off properties, an aqueous ink containing an aqueous pigment dispersion using a hardly volatile alkali salt of a resin having a carboxyl group as a pigment dispersant is known. However, it cannot be said that the water-based ink has sufficient water resistance and alkali resistance.

  An object of the present invention is to provide an aqueous pigment dispersion for an aqueous ink composition having good wettability with the pigment and having good mixing with the pigment in the aqueous pigment dispersion for an aqueous ink composition, and a method for producing the same. To do.

  The present invention also provides an aqueous pigment dispersion for an aqueous ink composition and a method for producing the same, which can provide an aqueous ink composition excellent in water resistance and alkali resistance even when a hardly volatile alkali salt is used. With the goal.

  Furthermore, it aims at providing the water-based ink composition using the said water-based pigment dispersion for water-based ink compositions.

  The inventors of the present invention have intensively studied to solve the above-mentioned problems. As a result, they have found that the above object can be achieved by the following aqueous pigment dispersion for water-based ink composition and the production method thereof, and have completed the present invention. .

That is, in an aqueous pigment dispersion for an aqueous ink composition in which a pigment is dispersed in water with a pigment dispersant,
The pigment dispersant contains a hardly volatile alkali salt of a copolymer of a carboxyl group-containing monomer and a hydrophobic monomer, and a water-soluble organic solvent having a solubility parameter of 7.5 to 11, and the copolymer is After dissolving in the water-soluble organic solvent, the pigment is dispersed in water using a pigment dispersant in which the copolymer is made into a hardly volatile alkali salt with a hardly volatile alkali substance. The present invention relates to an aqueous pigment dispersion for an aqueous ink composition.

  Since the aqueous pigment dispersion for water-based ink composition of the present invention contains a water-soluble organic solvent having the specific solubility parameter value, it is a copolymer of a carboxyl group-containing monomer and a hydrophobic monomer that becomes a pigment dispersant. The solubility in water is improved, and alkali chlorination is facilitated. The aqueous pigment dispersion for water-based ink compositions of the present invention has good wettability between the pigment dispersant and the pigment, and the water-based pigment for water-based ink compositions has good mixing properties in the water-based pigment dispersion for water-based ink compositions. A dispersion is obtained. Moreover, the foaming out in the defoaming process is also good.

  The water-soluble organic solvent has an appropriate surface tension, and can reduce the surface tension of the aqueous pigment dispersion for aqueous ink composition. Therefore, in a water-based ink for a writing instrument such as a sign pen, a good writing property is usually obtained without adding a surfactant used for securing a capillary phenomenon. In addition, by not adding a surfactant, it is possible to reduce the badness of water-based inks such as blemishes caused by the surfactant. A water-soluble organic solvent is also preferable for improving water resistance and alkali resistance.

  In the aqueous pigment dispersion for an aqueous ink composition, the hardly volatile alkali salt of a copolymer of a carboxyl group-containing monomer and a hydrophobic monomer is a co-polymer of a carboxyl group-containing monomer having an acid value of 30 to 140 KOHmg / g and a hydrophobic monomer. It is preferably a hardly volatile alkali salt of a polymer.

  The hardly volatile alkali salt of a copolymer of a carboxyl group-containing monomer and a hydrophobic monomer used as a pigment dispersant has insufficient water resistance and alkali resistance compared to volatile alkali salts, but has a lower acid value than conventional ones. A water-based ink composition having excellent water resistance and alkali resistance can be provided by using a hardly volatile alkali salt of a copolymer of a carboxyl group-containing monomer and a hydrophobic monomer adjusted to the range. When the acid value of the copolymer of a carboxyl group-containing monomer and a hydrophobic monomer is low, it is generally difficult to dissolve in water. However, in the present invention, as described above, since it contains a water-soluble organic solvent, it has a low acid value. Even when a copolymer of a carboxyl group-containing monomer and a hydrophobic monomer is used, the solubility in water is good and the water resistance and alkali resistance can be satisfied.

  When the acid value of the copolymer of the carboxyl group-containing monomer and the hydrophobic monomer exceeds 140 KOHmg / g, the solubility in water increases and the effect of improving water resistance and alkali resistance is low. The acid value of the copolymer of the carboxyl group-containing monomer and the hydrophobic monomer is 140 KOH mg / g or less, preferably 130 KOH mg / g or less, more preferably 120 KOH mg / g or less. On the other hand, when the acid value is less than 30 KOHmg / g, even when a hardly volatile alkali salt is used, it is difficult to dissolve in water and to function as a pigment dispersant. The acid value of the copolymer of the carboxyl group-containing monomer and the hydrophobic monomer is preferably 30 KOHmg / g or more, more preferably 50 KOHmg / g or more.

  The aqueous pigment dispersion for aqueous ink compositions of the present invention is useful as an aqueous pigment dispersion for aqueous ink compositions applied to aqueous inks for writing instruments. In particular, it exhibits excellent water resistance and alkali resistance against handwriting.

  In the present invention, a copolymer of a carboxyl group-containing monomer and a hydrophobic monomer is dissolved in a water-soluble organic solvent having a solubility parameter of 7.5 to 11, and then the carboxyl group-containing monomer and the hydrophobic monomer are dispersed with a hardly volatile alkaline substance. The present invention relates to a method for producing an aqueous pigment dispersion for an aqueous ink composition, wherein a pigment is dispersed in water using a pigment dispersant in which a carboxyl group of a monomer copolymer is made a hardly volatile alkali salt.

  The aqueous pigment dispersion for an aqueous ink composition of the present invention can be alkali-chlorinated with a hardly volatile alkaline substance after a copolymer of a carboxyl group-containing monomer and a hydrophobic monomer is dissolved in a water-soluble organic solvent. . Therefore, even if it is a copolymer of a carboxyl group-containing monomer having a low acid value and a hydrophobic monomer, an aqueous pigment dispersion for an aqueous ink composition can be efficiently produced with a pigment dispersant having good mixing properties with the pigment.

  Furthermore, the present invention relates to a water-based ink composition using the water-based pigment dispersion for water-based ink composition as the water-based pigment dispersion for water-based ink composition. The aqueous ink composition using the aqueous pigment dispersion for an aqueous ink composition of the present invention is excellent in water resistance and alkali resistance.

  The present invention also provides an aqueous ink using an aqueous pigment dispersion for an aqueous ink composition in which a pigment is dispersed in water with a hardly volatile alkali salt of a copolymer of a carboxyl group-containing monomer and a hydrophobic monomer, which is a pigment dispersant. A water-based ink composition characterized in that the amount of 0.1 mol / liter hydrochloric acid necessary for neutralizing per gram of non-volatile content is 2 to 6.5 ml.

  The water-based ink composition is excellent in water resistance and alkali resistance. In the water-based ink composition, a water-based pigment dispersion for a water-based ink composition using a low-volatility alkali salt of a copolymer of a low acid value carboxyl group-containing monomer and a hydrophobic monomer as a pigment dispersion is used. The water-based ink composition can usually be specified by the amount of hydrochloric acid. The amount of hydrochloric acid is more preferably 4-6 ml.

  Hereinafter, the water-based pigment dispersion for water-based ink composition and the water-based ink composition of the present invention will be described.

  The aqueous pigment dispersion for an aqueous ink composition of the present invention uses a hardly volatile alkali salt of a copolymer of a carboxyl group-containing monomer and a hydrophobic monomer as a pigment dispersant, and the pigment dispersant is used to disperse the pigment in water. It is a thing.

  As the copolymer of the carboxyl group-containing monomer and the hydrophobic monomer, those capable of functioning as a pigment dispersant can be used without particular limitation. Although the acid value of the copolymer of a carboxyl group-containing monomer and a hydrophobic monomer is not particularly limited, as described above, a copolymer of a low acid number carboxyl group-containing monomer and a hydrophobic monomer of 30 to 140 KOHmg / g is preferable. The pigment dispersant usually has a hydrophilic part and a hydrophobic part, and the hydrophilic part has a carboxyl group.

  Examples of the carboxyl group-containing monomer of the copolymer of the carboxyl group-containing monomer and the hydrophobic monomer include monobasic acids such as acrylic acid, methacrylic acid, and crotonic acid, dibasic acids such as itaconic acid and maleic acid, and An anhydride of a dibasic acid, its half ester, etc. are mention | raise | lifted. Examples of the hydrophobic monomer include aromatic monomers such as styrene, α-methylstyrene and vinyltoluene, acrylic acid esters such as methyl acrylate and ethyl acrylate, methacrylic acid esters, α-olefins, vinyl acetate and the like. Examples include vinyl esters. As the copolymer, a copolymer prepared by appropriately combining a carboxyl group-containing monomer and a hydrophobic monomer and adjusting the acid value within the above range is used. Examples of the copolymer include a styrene- (meth) acrylic acid copolymer, a styrene-maleic acid copolymer, a (meth) acrylic acid ester- (meth) acrylic acid copolymer, and a styrene- (meth). An acrylic ester- (meth) acrylic acid copolymer, a styrene- (meth) acrylic ester-maleic acid copolymer, and the like are preferable. In particular, styrene as a hydrophobic monomer represented by styrene- (meth) acrylic acid copolymer and styrene- (meth) acrylic ester- (meth) acrylic acid copolymer, and carboxyl group as a hydrophilic monomer A copolymer containing acrylic acid as the containing monomer is preferred. The copolymer may be either an oligomer or a polymer. The weight average molecular weight is not particularly limited, but is usually about 1500 to 20000.

  As the hardly volatile alkaline substance that alkalily salifies the carboxyl group of the copolymer of the carboxyl group-containing monomer and the hydrophobic monomer, those that do not volatilize at normal temperature (23 ° C.) can be used without particular limitation. For example, those having a boiling point higher than room temperature include alkali hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, and amine compounds such as triethanolamine, diethanolamine, monoethanolamine and dimethylethanolamine.

  In alkali chlorination of the copolymer of the carboxyl group-containing monomer and the hydrophobic monomer, the copolymer of the carboxyl group-containing monomer and the hydrophobic monomer is dissolved in a water-soluble organic solvent having a solubility parameter of 7.5 to 11. In addition, it can be carried out by adding an aqueous solution containing a hardly volatile alkaline substance.

  As the water-soluble organic solvent, those capable of dissolving a copolymer of a carboxyl group-containing monomer and a hydrophobic monomer and exhibiting water solubility can be used without particular limitation. Such a water-soluble organic solvent has a solubility parameter of 7.5 to 11 as described above. Specific examples of the water-soluble organic solvent include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisopropyl ether, alkylene glycol monoalkyl ether such as propylene glycol monomethyl ether, diethylene glycol, diethylene glycol monomethyl ether, Examples include dialkylene glycol such as diethylene glycol monoethyl ether and dipropylene ethylene glycol monomethyl ether, monoalkyl ethers thereof, 3-methoxybutanol and the like. The amount of the water-soluble organic solvent used is not particularly limited, but it is usually preferably 0 to 200 parts by weight, more preferably 50 to 100 parts by weight based on 100 parts by weight of the copolymer of carboxyl group-containing monomer and hydrophobic monomer. It is preferably 150 parts by weight.

  The dissolution temperature of the copolymer of the carboxyl group-containing monomer and the hydrophobic monomer in the water-soluble organic solvent is not particularly limited, but it is usually preferably about 40 to 60 ° C. However, it is desirable to adjust so as not to exceed the glass transition temperature (Tg) of the copolymer. By dissolving a copolymer of a carboxyl group-containing monomer and a hydrophobic monomer in a water-soluble organic solvent, the copolymer of the carboxyl group-containing monomer and the hydrophobic monomer is alkali-chlorinated with a hardly volatile alkaline substance and is dissolved in water. Precipitation of the compound during conversion is suppressed.

  The alkali chlorination alkalizes the carboxyl group to such an extent that the copolymer of the carboxyl group-containing monomer and the hydrophobic monomer can be dissolved in water. Usually, neutralization is carried out by adding an amount of a hardly volatile alkaline substance which can alkalize all the carboxyl groups. After alkali chlorination, water can be added to adjust the concentration of the aqueous solution containing the pigment dispersant as appropriate.

  The aqueous pigment dispersion for an aqueous ink composition is prepared by dispersing the pigment with the pigment dispersant. In preparing the aqueous pigment dispersion for an aqueous ink composition, the viscosity can be adjusted by further adding water. As the pigment, various organic pigments and inorganic pigments can be used without particular limitation. Examples thereof include carbon black, quinacdrine pigment, azo pigment, phthalocyanine pigment, dioxane pigment, anthraquinone pigment, perylene pigment, ansanthrone pigment, perinone pigment, and azomethine pigment. The particle size of the pigment is not particularly limited, but usually it is preferably about 0.02 to 0.5 μm. The amount of the pigment dispersant (solid content) used is usually preferably about 5 to 100 parts by weight, more preferably 10 to 50 parts by weight with respect to 100 parts by weight of the pigment.

  The ratio of the pigment in the aqueous pigment dispersion for an aqueous ink composition is usually about 1 to 50% by weight, preferably 3 to 20% by weight, since the viscosity tends to increase as the ratio increases. The amount of the water-soluble organic solvent is appropriately adjusted according to the copolymer of the carboxyl group-containing monomer and the hydrophobic monomer, but the amount of the water-soluble organic solvent in the aqueous pigment dispersion for the water-based ink composition is not limited. Since the pigment dispersion stability of the aqueous pigment dispersion for water-based ink compositions tends to deteriorate when the ratio increases, it is usually preferably adjusted to about 60% by weight or less, and more preferably 10 to 30% by weight.

  The aqueous pigment dispersion for water-based ink composition can be applied to various water-based ink compositions. In preparing the water-based ink composition, water can be added to adjust the viscosity. Since the water-based ink composition is likely to be clogged with a writing instrument such as a sign pen, the color becomes thin when the ratio is reduced. Therefore, the concentration of the nonvolatile content is usually about 3 to 30% by weight, and further about 5 to 20% by weight. It is preferable to prepare it.

  In preparation of the water-based ink composition, it is dispersed by stirring as appropriate using a disperser or the like according to a conventional method. Additives such as a wetting agent, a pH adjuster, an antiseptic, an antifungal agent, an antioxidant, and a viscosity adjuster are appropriately added to the aqueous pigment dispersion for an aqueous ink composition. In addition, the same additive can be added in the preparation of the aqueous pigment dispersion for an aqueous ink composition.

  Wetting agents include glycerin, diglycerin, triglycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, polypropylene glycol and other glycols, urea, sugar, and further Derivatives and the like. The wetting agent is preferably about 3 to 60% by weight, more preferably about 5 to 50% by weight of the water-based ink composition. Examples of pH adjusters include alkali hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, amine compounds such as triethanolamine, diethanolamine, monoethanolamine, dimethylethanolamine, morpholine and triethylamine, ammonia and the like. .

  In addition, when the aqueous pigment dispersion for aqueous ink compositions containing a water-soluble organic solvent is used in the aqueous ink composition of the present invention, the surface tension of the aqueous ink composition can be reduced, so that a surfactant is added. Is not particularly necessary, but it is optional. Surfactants include anionic surfactants such as alkylbenzene sulfonic acid, alkyl sulfosuccinic acid, alkyl phosphate ester, alkyl sulfate ester, alkyl phenyl phosphate ester, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxy Nonionic surfactants such as ethylene alkyl allyl ether, sorbitan esters, alkyl sulfosuccinic acid, and alkyl phosphate esters are listed. The surfactant is preferably about 3% by weight or less, more preferably 1.5% by weight or less of the water-based ink composition.

Examples of the present invention will be described below with reference to examples. The carboxyl group-containing monomer and hydrophobic monomer copolymer (resin A, resin B, resin C, resin D) used in each example all contain styrene as the hydrophobic monomer and acrylic acid as the hydrophilic monomer. The acid value and the weight average molecular weight are as shown in Table 1.

（顔料分散剤Ａ〜Ｄの調製）
樹脂Ａ〜Ｄに樹脂Ａ〜Ｄと同重量のエチレングリコールモノブチルエーテル（溶解度パラメーター８. ９）を加え、５０℃の加温下で撹拌した。次いで、樹脂Ａのカルボキシル基と等当量の５０重量％濃度の水酸化ナトリウム水溶液を加えてアルカリ塩化を行った。さらに、イオン交換水を加えて、顔料分散剤Ａ〜Ｄを得た。なお、顔料分散剤Ａ〜Ｄ中の各成分の割合（重量％）を表２に示す。

(Preparation of pigment dispersants A to D)
Ethylene glycol monobutyl ether (solubility parameter 8.9) having the same weight as the resins A to D was added to the resins A to D, and the mixture was stirred while heating at 50 ° C. Subsequently, an aqueous solution of sodium hydroxide having a concentration of 50% by weight equivalent to the carboxyl group of the resin A was added to perform alkali chloride. Further, ion-exchanged water was added to obtain pigment dispersants A to D. In addition, Table 2 shows the ratio (% by weight) of each component in the pigment dispersants A to D.

表２中の数値は重量％である。顔料分散剤Ａ〜Ｄはいずれも樹脂が完全溶解し、透明な液が得られた。

The numerical values in Table 2 are% by weight. In all of the pigment dispersants A to D, the resin was completely dissolved, and a transparent liquid was obtained.

(Preparation of pigment dispersants A ′ to D ′)
Alkaline chlorination was performed by adding a 50 wt% sodium hydroxide aqueous solution equivalent to the carboxyl groups of the resins A to D to the resins A to D. Further, ion-exchanged water was added to obtain pigment dispersants A to D. In addition, Table 3 shows the ratio (% by weight) of each component in the pigment dispersants A to D.

表３中の数値は重量％である。顔料分散剤Ａ′は少々白濁を生じた液であった。顔料分散剤Ｂ′は樹脂が少し溶け残りを生じたうえに、少々白濁を生じた液であった。顔料分散剤Ｃ′は樹脂を全く溶解させることができなかった。顔料分散剤Ｄ′は樹脂が完全溶解し、透明な液が得られた。

The numerical values in Table 3 are% by weight. The pigment dispersant A ′ was a liquid that produced a slight cloudiness. The pigment dispersant B ′ was a solution in which the resin slightly melted and a little clouded. The pigment dispersant C ′ could not dissolve the resin at all. In the pigment dispersant D ′, the resin was completely dissolved, and a transparent liquid was obtained.

Example 1 (Preparation of aqueous pigment dispersion for aqueous ink composition)
Using the pigment dispersant A, the composition having the composition shown in Table 4 was mixed and stirred, and then defoamed. Subsequently, the said composition was disperse | distributed and the water-based pigment dispersion A for water-based ink compositions was obtained.

Examples 2 to 7 (Preparation of aqueous pigment dispersion for aqueous ink composition)
In Example 1, aqueous pigment dispersions B to G for aqueous ink compositions were obtained in the same manner as in Example 1, except that the composition of the aqueous pigment dispersion for aqueous ink composition was changed to the formulation shown in Table 4. It was.

Comparative Example 1 (Preparation of aqueous pigment dispersion for aqueous ink composition)
Using the pigment dispersant D ′, the composition having the composition shown in Table 4 was mixed and stirred, and then defoamed. Subsequently, the said composition was disperse | distributed and the water-based pigment dispersion H for water-based ink compositions was obtained. The obtained water-based pigment dispersion H for water-based ink composition had poor pigment wettability and was difficult to mix with the pigment dispersant D ′. Moreover, in the defoaming step after mixing, the foaming was poor, and the defoaming step required a long time compared to the examples.

Comparative Examples 2 to 4 (Preparation of aqueous pigment dispersion for aqueous ink composition)
In Comparative Example 1, aqueous pigment dispersions I to K for aqueous ink composition were obtained in the same manner as in Comparative Example 1, except that the composition of the aqueous pigment dispersion for aqueous ink composition was changed to the formulation shown in Table 4. It was. The obtained water-based pigment dispersions I to K for water-based ink compositions had poor pigment wetting and were difficult to mix with the pigment dispersant D ′. Moreover, in the defoaming step after mixing, the foaming was poor, and the defoaming step required a long time compared to the examples.

  Water resistance and alkali resistance were evaluated using the aqueous pigment dispersions for water-based ink compositions obtained in Examples and Comparative Examples. The results are shown in Table 4.

(water resistant)
It was applied to Kent paper (5 cm × 5 cm) with a doctor-type applicator having a gap of 0.02 mm, and after 1 hour had passed after the application, the test piece was immersed in still water for 1 hour. Subsequently, the test piece was taken out from the water, and the degree of bleeding was evaluated in five levels according to the following criteria. Evaluation was performed 3 times. The average value is shown.
<Evaluation criteria>
5: There is no bleeding.
3: There is bleeding from a part.
1: There is bleeding from the whole.

(Alkali resistance)
A constant thickness was applied to Kent paper (5 cm × 5 cm) with a doctor-type applicator having a gap of 0.02 mm, and one day later, the test piece was immersed in an aqueous ammonia solution (10 wt%) for 24 hours. Subsequently, the test piece was taken out from the aqueous ammonia solution, and the state of the writing line after drying was evaluated in five stages based on the following criteria. Evaluation was performed 3 times. The average value is shown.
<Evaluation criteria>
5: No discoloration.
4: Discolored slightly.
3: The color of the original ink can be read.
2: Completely discolored.
1: Fading and unreadable.

表４中の顔料は、ａ：プリンテックス８０（デグサ（株）製）、ｂ：シムラファーストレッド４１２７（大日本インキ化学工業 (株）製）、ファーストオレンジＲＪＷ−Ａ（山陽色素（株）製）、ファストゲンスーパーマゼンタＲＧ（大日本インキ化学工業 (株）製）、ホスタパームブラウンＨＦＲ０１（クリアラント社製）であり、コートサイドＨ（防カビ剤，武田薬品工業（株）製）、プロクセルＸＬ−２（防腐剤，アビシア（株）製）である。

The pigments in Table 4 are: a: Printex 80 (manufactured by Degussa), b: Shimura First Red 4127 (manufactured by Dainippon Ink and Chemicals), First Orange RJW-A (manufactured by Sanyo Dye) ), Fastgen Super Magenta RG (manufactured by Dainippon Ink and Chemicals), Hosta Palm Brown HFR01 (manufactured by Clearant), Coatside H (anti-mold agent, manufactured by Takeda Pharmaceutical Co., Ltd.), Proxel XL-2 (preservative, manufactured by Avicia Co., Ltd.).

Examples 1-7, Comparative Examples 1-4 (Preparation of water-based ink composition)
Using the water-based pigment dispersions A to K for the water-based ink composition, the compositions having the composition shown in Table 5 were mixed and stirred, and then coarse particles were removed by centrifugation to obtain a water-based ink composition.

  In the comparative example, except that the surfactant shown in Table 5 is not used, the water-based ink composition separately prepared in the same manner as in the comparative example has a remarkably high surface tension and is difficult to flow out from the pen tip. there were. Therefore, a surfactant is used in the comparative example.

  Using the water-based ink compositions obtained in Examples and Comparative Examples, Sigma Pig Pen (registered trademark) was prepared, and the following water resistance and alkali resistance were evaluated. Further, the surface tension and neutralization titration of the water-based ink composition were evaluated. The results are shown in Table 5.

(water resistant)
Using the above-mentioned sign pen, after writing a V-shape four times by hand on Kent paper (6 lines), a brush (Sakura Paintbrush Neo Sebron) lightly impregnated with water every predetermined time (15 seconds, 30 seconds, 60 seconds, 120 seconds) (Registered trademark) flat type-ENF14), the writing line was traced twice in a fixed direction, and the degree of bleeding after drying was evaluated in five stages according to the following criteria. The V-shaped side was 10-15 mm, and the writing speed was 2 V-shaped for about 1 second. Evaluation was performed 3 times. The average value is shown.
<Evaluation criteria>
5: There is no bleeding.
3: There is blur from the start point and end point.
1: There is bleeding from the entire line.

(Alkali resistance)
Using the above sign pen, writing on Kent paper (6 lines) and 1 hour later, the test piece was immersed in an aqueous ammonia solution (10% by weight) for 24 hours. Next, the test piece was taken out from the aqueous ammonia solution, and the state of the writing line after drying was evaluated in five stages according to the following criteria. Evaluation was performed 3 times. The average value is shown.
<Evaluation criteria>
5: No discoloration.
4: Discolored slightly.
3: The color of the original ink can be read.
2: Completely discolored.
1: Fading and unreadable.

(surface tension)
It measured using the platinum plate by CBVP SURFACE TENSIONMETER A3 by Kyowa Interface Science Co., Ltd.

(Surface tension stability)
The surface tension stability after standing for 3 months at room temperature was evaluated according to the following criteria.
○: Within ± 1 mN / m.
X: Over ± 1 mN / m

(Neutralization titration)
5 g of the water-based ink composition was weighed and placed in 100 ml of tetrahydrofuran. While slowly stirring with a stirrer, neutralization titration was performed with 0.1 mol / liter hydrochloric acid. For titration, an automatic titrator (manufactured by Mitsubishi Chemical Co., Ltd., GT-06) was used. Table 5 shows the amount of 0.1 mol / liter hydrochloric acid (ml) required for neutralization. Table 5 shows values obtained by dividing the amount of hydrochloric acid by the weight of nonvolatile content in 5 g of the water-based ink composition to determine the amount of hydrochloric acid necessary to neutralize per 1 g of nonvolatile content. The weight of the non-volatile content of the water-based ink composition refers to the weight when dried in an oven at 110 ° C. for 24 hours.

表５中、サンモリン０Ｔ−７０（界面活性剤，三洋化成工業（株）製）、ホスファノールＰＥ−５１０（界面活性剤，東邦化学（株）製）、コートサイドＨ（防カビ剤，武田薬品工業（株）製）、プロクセルＸＬ−２（防腐剤，アビシア（株）製）、ＮａＯＨ水溶液：水酸化ナトリウム１０重量％水溶液、である。

In Table 5, Sanmoline 0T-70 (surfactant, manufactured by Sanyo Chemical Industries, Ltd.), Phosphanol PE-510 (surfactant, manufactured by Toho Chemical Co., Ltd.), Coatside H (antifungal agent, Takeda Pharmaceutical) Manufactured by Co., Ltd.), Proxel XL-2 (preservative, manufactured by Avicia Co., Ltd.), NaOH aqueous solution: 10% by weight aqueous sodium hydroxide solution.

  From Table 5, it is recognized that the water-based ink compositions of the examples have good water resistance and alkali resistance, and also have good surface tension stability. On the other hand, the water-based ink composition of the comparative example has poor water resistance and alkali resistance. In addition, since the water-based ink composition of the comparative example uses a surfactant, the stability of the surface tension is not good.

Claims (7)

In an aqueous pigment dispersion for an aqueous ink composition in which a pigment is dispersed in water with a pigment dispersant,
The pigment dispersant contains a hardly volatile alkali salt of a copolymer of a carboxyl group-containing monomer and a hydrophobic monomer, and a water-soluble organic solvent having a solubility parameter of 7.5 to 11, and the copolymer is After dissolving in the water-soluble organic solvent, the pigment is dispersed in water using a pigment dispersant in which the copolymer is made into a hardly volatile alkali salt with a hardly volatile alkali substance. An aqueous pigment dispersion for an aqueous ink composition.   The hardly volatile alkali salt of the copolymer of the carboxyl group-containing monomer and the hydrophobic monomer is a hardly volatile alkali salt of the copolymer of the carboxyl group-containing monomer and the hydrophobic monomer having an acid value of 30 to 140 KOHmg / g. The aqueous pigment dispersion for water-based ink compositions according to claim 1, wherein   The aqueous pigment dispersion for water-based ink compositions according to claim 1 or 2, which is applied to a writing instrument.   A copolymer of a carboxyl group-containing monomer and a hydrophobic monomer is dissolved in a water-soluble organic solvent having a solubility parameter of 7.5 to 11, and then the copolymer of the carboxyl group-containing monomer and the hydrophobic monomer with a hardly volatile alkali substance. The aqueous pigment dispersion for an aqueous ink composition according to any one of claims 1 to 3, wherein the pigment is dispersed in water using a pigment dispersant in which the carboxyl group of the above is made a hardly volatile alkali salt. Production method.   The water-based ink composition using the water-based pigment dispersion for water-based ink compositions in any one of Claims 1-3 as a water-based pigment dispersion for water-based ink compositions. A water-based ink composition using a water-based pigment dispersion for a water-based ink composition in which a pigment is dispersed in water with a volatile alkali salt of a copolymer of a carboxyl group-containing monomer and a hydrophobic monomer, which is a pigment dispersant. ,
6. The water-based ink composition according to claim 5, wherein the amount of 0.1 mol / liter hydrochloric acid necessary for neutralizing per gram of nonvolatile content is 2 to 6.5 ml.   The water-based ink composition according to claim 6, wherein the water-based pigment dispersion for water-based ink composition according to claim 1 is used as the water-based pigment dispersion for water-based ink composition.