JP7370241B2 - Ink composition for water-based ballpoint pen and water-based ballpoint pen using the same - Google Patents

Description

The present invention relates to an ink composition for an aqueous ballpoint pen and an aqueous ballpoint pen. More specifically, the present invention relates to an ink composition for an aqueous ballpoint pen and an aqueous ballpoint pen with excellent writing performance.

BACKGROUND ART Conventionally, ink compositions for aqueous ballpoint pens using a crosslinked acrylic acid polymer as a shear thinning agent have been disclosed (eg, Patent Documents 1 to 3).
This type of ink has a high viscosity when standing still without shear stress and is stably held within the mechanism, and when writing, the ink near the ball is eroded by the high shear force generated by the high speed rotation of the ball. The viscosity is lowered, and as a result, the ink is ejected from the gap between the ball and the ball accommodating portion and transferred onto the paper surface. When the ink transferred to the paper surface is released from the shearing force, it becomes highly viscous again, making it possible to improve the occurrence of blurring in handwriting, which is a drawback of conventional water-based ink compositions. In addition, due to the shear thinning property mentioned above, ink can be used until the end without the need for so-called batting to hold the ink, and a flow rate adjusting member (for example, a comb-like member) that adjusts the ink flow rate can be used to temporarily ink the ink. It is widely used because it has many advantages, such as not requiring a storage member (reservoir member), so a writing instrument with a simple structure can be obtained.

However, further improvement is desired in the effect of suppressing the occurrence of bleeding after being transferred to a paper surface. In addition, when using a crosslinked acrylic acid polymer, which is conventionally known as a shear thinning agent, the crosslinked part is chemically bonded, so the viscosity of the ink can be increased when it is left still, but the viscosity can be lowered by shearing force. Because the ink viscosity cannot be lowered below a certain value due to the influence of the cross-linked portion, when used in writing instruments as a water-based ink composition for writing, it causes so-called line cracking, where handwriting becomes blurred or hollow. Improvements were desired.

Japanese Patent Application Publication No. 2000-136340 Japanese Patent Application Publication No. 2001-64559 Japanese Patent Application Publication No. 2002-294132

The present invention makes it possible to obtain good handwriting without blurring or line cracking even when writing, has excellent storage stability of the ink composition, and further improves handwriting drying properties. The present invention provides an ink composition for an aqueous ballpoint pen with good writing taste and an aqueous ballpoint pen using the same.

（式中、Ｒ^１は、水素またはメチル基である）
で示される繰り返し単位と、
以下の式（ｉｉ）：

（式中、
Ｒ^２は、水素またはメチル基であり、かつ
Ｒ^３は、炭素数１～５の、直鎖または側鎖を有するアルキル基である）
で示される繰り返し単位と
を含んでなるアクリル酸共重合体、
（ｃ）以下の式（Ｉ）で示される有機溶剤：

（式中、
Ｒ^Ａは、炭素数３もしくは４の、直鎖または分岐の、アルキル基であり、かつＲ^Ｂは、ヒドロキシ基であるか、またはＲ^Ａは、炭素数１～３の、直鎖または分岐の、アルキル基であり、かつＲ^Ｂは、炭素数１～３の、直鎖または分岐の、アルコキシ基であり、
Ｌは、メチル基によって置換されていてもよいエチレン基（－ＣＨ_２－ＣＨ_２－）、またはトリメチレン基（－ＣＨ_２－ＣＨ_２－ＣＨ_２－）であり、かつ
ｘは、１～５の整数である）、および
（ｄ）水
を含んでなり、
前記成分（ｃ）の含有量が、前記組成物の総質量を基準として、１～３０質量％であるものである。 The ink composition for a water-based ballpoint pen according to the present invention includes:
(a) organic pigment,
(b) The following formula (i):

(In the formula, R ¹ is hydrogen or a methyl group)
A repeating unit indicated by
Formula (ii) below:

(In the formula,
R ² is hydrogen or a methyl group, and R ³ is an alkyl group having 1 to 5 carbon atoms and having a straight chain or a side chain)
An acrylic acid copolymer comprising a repeating unit represented by
(c) Organic solvent represented by the following formula (I):

(In the formula,
R ^A is a straight chain or branched alkyl group having 3 or 4 carbon atoms, and R ^B is a hydroxy group, or R ^A is a straight chain or branched alkyl group having 1 to 3 carbon atoms. , is an alkyl group, and R ^B is a linear or branched alkoxy group having 1 to 3 carbon atoms,
L is an ethylene group (-CH ₂ -CH ₂ -) which may be substituted with a methyl group, or a trimethylene group (-CH ₂ -CH ₂ -CH ₂ -), and x is 1 to 5. an integer), and (d) water;
The content of component (c) is 1 to 30% by weight based on the total weight of the composition.

The water-based ballpoint pen according to the present invention contains the above-described ink composition.

According to the present invention, by using a copolymer with a specific structure, when shear stress is applied, the ink viscosity decreases compared to conventional ink, which prevents blurred handwriting and line cracks. It is possible to maintain good handwriting. On the other hand, in the copolymer, the alkyl groups create reversible physical bonds due to intermolecular forces, which makes it possible to maintain a high ink viscosity at rest, making it difficult for handwriting to smudge and improving the storage stability of the ink. It has excellent effects such as improving
Furthermore, when the ink composition contains a combination of an organic pigment and a specific organic solvent, the drying properties of the handwritten surface can be improved.

<Ink composition for water-based ballpoint pen>
The ink composition for a water-based ballpoint pen according to the present invention (hereinafter referred to as "ink composition" in some cases) comprises (a) an organic pigment, (b) an acrylic acid copolymer, (c) a specific organic solvent, and (d ) Contains water.

(a) Organic pigments Examples of the organic pigments used in the present invention include phthalocyanine-based, azo-based, quinacridone-based, diketopyrrolopyrrole-based, quinophthalone-based, triphenylmethane-based, perinone-based, perylene-based, dioxazine-based, etc. However, phthalocyanine-based, azo-based, quinacridone-based, diketopyrrolopyrrole-based, and perylene-based are preferable, and phthalocyanine-based and azo-based are more preferable.
These pigments may be used alone or in combination of two or more. The content is preferably 1 to 30% by mass based on the total mass of the ink composition.
Furthermore, since pigments have conventionally been dispersed in ink compositions, they tend to have poorer permeability into the writing target than dye-based pigments, making it difficult to improve handwriting drying properties. However, in the present invention, by using a specific organic solvent or surfactant described below, even when a pigment is used as a coloring agent, the handwriting drying property can be further improved. Furthermore, the pigment has excellent water resistance and light resistance, and provides good color development.

（式中、Ｒ^１は、水素またはメチル基である）
で示される繰り返し単位と、
以下の式（ｉｉ）：

（式中、
Ｒ^２は、水素またはメチル基であり、かつ
Ｒ^３は、炭素数１～５の、直鎖または側鎖を有するアルキル基である）
で示される繰り返し単位と
を含んでなる。 (b) Acrylic acid copolymer The acrylic acid copolymer used in the present invention has the following formula (i):

(In the formula, R ¹ is hydrogen or a methyl group)
A repeating unit indicated by
Formula (ii) below:

(In the formula,
R ² is hydrogen or a methyl group, and R ³ is an alkyl group having 1 to 5 carbon atoms and having a straight chain or a side chain)
and a repeating unit represented by.

Component (b) used in the present invention is an acrylic acid copolymer having a specific structure. This acrylic acid copolymer functions as a shear thinning agent. The copolymer used as component (b) in the present invention has a carboxylic acid group and a carboxylic ester group. The alkyl group having 1 to 5 carbon atoms constituting the carboxylic acid ester group of component (b) is a hydrophobic group. Therefore, in the ink composition, aggregation of alkyl groups due to intermolecular forces between hydrophobic groups causes reversible physical bonding to form a network, and this portion acts like a bonding point. As a result, the viscosity of the ink composition at rest increases. When the ink composition flows during writing and is subjected to shear stress, the physical bonds at the portions that act like bonding points dissociate, resulting in a decrease in ink viscosity. As mentioned above, the ink composition according to the present invention has good stability because the viscosity gradient at rest and during flow is larger than that in the past due to the reversible action of aggregation and dissociation of the alkyl group of component (b). It has both functionality and writing ability. That is, when the ink composition is used in a ballpoint pen, the viscosity during writing is lower than that of the conventional ink composition, so that good writing is possible without blurring, line cracking, etc. Furthermore, since the ink viscosity at rest is higher than the viscosity at rest compared to the viscosity at writing, bleeding of handwriting is suppressed when the ink recovers to the resting viscosity after writing. Furthermore, when a solid substance such as a pigment is used in the ink composition, since the dispersion state is maintained stably, sedimentation of the pigment etc. can be prevented. As a result, the storage stability of the ink is improved. On the other hand, cross-linked acrylic acid, which is different from component (b), has irreversible chemical bonds in its cross-linked parts, so the ink viscosity at rest is high, but even when shear stress is applied, the cross-linked parts remain bonded. Since the ink does not break, the viscosity of the ink is less likely to decrease when shear stress is applied, compared to when component (b) is used. Therefore, when the ink composition is used in a ballpoint pen, the handwriting may be affected, such as blurring or line breakage.

This component (b) is a (meth)acrylic acid-(meth)acrylic acid ester copolymer. In the present invention, (meth)acrylic means to include both acrylic and methacrylic. Specifically, acrylic acid-acrylic ester copolymer, methacrylic acid-acrylic ester copolymer, acrylic acid-methacrylic ester copolymer, methacrylic acid-methacrylic ester copolymer, acrylic acid-methacrylic acid - Acrylic ester copolymer, acrylic acid-methacrylic acid-methacrylic ester copolymer, acrylic acid-acrylic ester-methacrylic ester copolymer, methacrylic acid-acrylic ester-methacrylic ester copolymer, acrylic Examples include acid-acrylic ester-methacrylic acid-methacrylic ester copolymer. As the component (b), a random copolymer, a block copolymer, or the like can be used. These non-crosslinked acrylic difference copolymers can be used alone or in combination of two or more.

Furthermore, R ³ in formula (ii) is an alkyl group having a straight chain or a side chain having 1 to 5 carbon atoms, but when the number of carbon atoms exceeds 5, steric hindrance of the alkyl group increases, and the alkyl groups cohesive force decreases. Furthermore, when the number of carbon atoms is greater than 5, the hydrophobicity of the alkyl group increases, so that separation and precipitation may occur in some parts, resulting in non-uniformity. Therefore, the stability in the ink composition tends to be poor. When the number of carbon atoms is in the range of 1 to 5, the alkyl groups have a strong cohesive force and form a physical bond to form an intermolecular network, which is preferable. Furthermore, it is preferable that the alkyl group is a straight chain because steric hindrance is smaller than that of an alkyl group having a side chain. In particular, when R ³ is a methyl group with 1 carbon number or an ethyl group with 2 carbon atoms, the hydrophobicity is not large, so it is possible to design a relatively large amount of alkyl group to be introduced into the molecule. By increasing the amount of alkyl groups introduced, it becomes possible to arrange many physical bonding points between the alkyl groups, which results in effects such as higher viscosity when standing and lower viscosity when sheared. Particularly preferred.

The ratio of the number of repeating units of formula (i) to repeating units of formula (ii) is 1:0.05 to 1:10, more preferably 1:0.1 to 1:5, and more preferably Preferably, the ratio is 1:0.3 to 1:3. If the ratio of the repeating units in formula (ii) is too small, the physical bonding effect of the alkyl group will be insufficient, and the thickening property and viscosity gradient between standing and shearing will tend to become small, and if the ratio of the carboxylic acid ester is too large, If it is too high, the hydrophobicity of the copolymer increases, which may cause some separation or precipitation. If it is within this range, it is particularly preferable because both high static viscosity and low sheared viscosity can be achieved.

Component (b) may contain repeating units other than formulas (i) and (ii), but the ratio of repeating units other than formulas (i) and (ii) is preferably as small as possible. Specifically, the ratio is preferably 5% or less, and more preferably substantially no repeating units other than formulas (i) and (ii) are included. Ideally that proportion is zero.

The mass average molecular weight of component (b) is preferably 1,000 or more, more preferably 5,000 or more, and even more preferably 20,000 or more. If it is smaller than the above, it may be difficult to develop sufficient viscosity. Moreover, it is preferably 1,000,000 or less, more preferably 700,000 or less, and still more preferably 600,000 or less. If it is larger than the above, the viscosity at high shear may become too high. Here, the mass average molecular weight is a mass average molecular weight in terms of polystyrene, and can be measured by gel permeation chromatography using polystyrene as a reference.

The content of component (b) may range from 0.01 to 10% by mass based on the total mass of the ink composition. It is preferably in the range of 0.05 to 5% by weight, more preferably in the range of 0.1 to 2% by weight. If it is larger than this range, the viscosity when standing will be high, the dispersion stability of the ink composition will be improved, and the handwriting will not smear, but the ink viscosity during shearing will tend to be slightly higher, and the writing performance will be slightly reduced. A downward trend can be seen. When it is smaller than this range, the ink viscosity during shearing decreases, and the handwriting does not blur or break lines, but there is a tendency for the handwriting to smear. If it is within the above range, while maintaining the dispersion stability of the ink composition, there will be no blurring or line breakage when writing, the handwriting will not smear, and excellent ink stability and writing performance will be obtained. ,preferable.
The acrylic acid copolymer used as component (b) swells in the composition and has structural viscosity.

式中、
Ｒ^Ａは、炭素数３もしくは４の、直鎖または分岐の、アルキル基であり、かつＲ^Ｂは、ヒドロキシ基または－ＣＯ－Ｎ－Ｒ^Ｃ _２（式中、Ｒ^Ｃはそれぞれ独立に水素またはメチル基である）、好ましくはヒドロキシ基、であるか、
またはＲ^Ａは、炭素数１～３の、直鎖または分岐の、アルキル基（好ましくはメチル基またはエチル基、さらに好ましくはエチル基）であり、かつＲ^Ｂは、炭素数１～３の、直鎖または分岐の、アルコキシ基（好ましくはメトキシ基またはエトキシ基、さらに好ましくはエトキシ基）である。
より好ましくは、Ｒ^Ａは、炭素数３もしくは４の、直鎖または分岐の、アルキル基であり、かつＲ^Ｂは、ヒドロキシ基であり、
Ｌは、メチル基によって置換されていてもよい、エチレン基（－ＣＨ_２－ＣＨ_２－）またはトリメチレン基（－ＣＨ_２－ＣＨ_２－ＣＨ_２－）であり、好ましくは、メチル基によって置換されていてもよいエチレン基、またはトリメチレン基であり、さらに好ましくは、メチル基によって置換されていてもよいエチレン基であり、かつ
ｘは、１～５の整数、好ましくは１～３の整数である。
なお、メチル基によって置換されているエチレン基としては、例えば－ＣＨ（ＣＨ_３）－ＣＨ_２－、－Ｃ（ＣＨ_３）_２－ＣＨ_２－などが挙げられ、－ＣＨ（ＣＨ_３）－ＣＨ_２－が好ましい。 (c) Specific organic solvent The specific organic solvent used in the present invention is represented by the following formula (I).

During the ceremony,
R ^A is a linear or branched alkyl group having 3 or 4 carbon atoms, and R ^B is a hydroxy group or -CO-N-R ^C ₂ (wherein R ^C is each independently hydrogen or methyl group), preferably a hydroxy group, or
or R ^A is a linear or branched alkyl group having 1 to 3 carbon atoms (preferably a methyl group or an ethyl group, more preferably an ethyl group), and R ^B is a linear or branched alkyl group having 1 to 3 carbon atoms; It is a straight-chain or branched alkoxy group (preferably a methoxy group or an ethoxy group, more preferably an ethoxy group).
More preferably, R ^A is a linear or branched alkyl group having 3 or 4 carbon atoms, and R ^B is a hydroxy group,
L is an ethylene group (-CH ₂ -CH ₂ -) or a trimethylene group (-CH ₂ -CH ₂ -CH ₂ -), which may be substituted with a methyl group, and is preferably substituted with a methyl group. an ethylene group or a trimethylene group which may be substituted with a methyl group, more preferably an ethylene group which may be substituted with a methyl group, and x is an integer of 1 to 5, preferably an integer of 1 to 3. .
Examples of ethylene groups substituted with methyl groups include -CH(CH ₃ )-CH ₂ -, -C(CH ₃ ) ₂ -CH ₂ -, and -CH(CH ₃ )-CH _2- is preferred.

Considering handwriting quality and ink stability in addition to handwriting drying properties, R ^A is a linear or branched alkyl group having 1 to 3 carbon atoms, and R ^B is a straight chain or branched alkyl group having 1 to 3 carbon atoms. , a linear or branched alkoxy group is also one of the preferred forms of the present invention. At this time, it is preferable that the number of carbon atoms in both R ^A and R ^B is not 3.
Furthermore, when R ^B is an alkoxy group, x is preferably 1 or 2.

In the present invention, by combining component (a) with component (c), handwriting drying properties are improved while maintaining ink stability. Even if a pigment other than component (a), for example an inorganic pigment such as carbon black, is combined with component (c), such an effect is hardly obtained. On the other hand, even if an organic solvent other than component (c), such as ethylene glycol, is combined with component (a), such an effect is hardly obtained. That is, it was surprisingly found that excellent effects can be obtained only with a combination of specific components. This is presumed to be due to the following reasons. In order to improve handwriting drying properties, it is necessary to increase the permeability of the ink into the writing medium, and to allow the ink on the surface of the writing medium to quickly penetrate into the inside of the writing medium immediately after writing. Conventionally used solvents, such as ethylene glycol and diethylene glycol, have poor permeability into writing media, and even when added to ink, high permeability cannot be obtained. On the other hand, since the organic solvent of component (c) has high permeability into the writing medium, adding it to the ink also improves the permeability of the ink itself into the writing medium.

The ratio of the mass of component (a) to the mass of component (c) is preferably 20 to 600%, more preferably 30 to 120%.

Specific examples of component (c) include ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, diethylene glycol monopropyl ether, diethylene glycol Monoisopropyl ether, triethylene glycol monobutyl ether, triethylene glycol monopropyl ether, triethylene glycol monoisobutyl ether, triethylene glycol monoisopropyl ether, propylene glycol monopropyl ether, propylene glycol monoisopropyl ether, propylene glycol mono-n-butyl ether, Propylene glycol monoisobutyl ether, dipropylene glycol mono-n-butyl ether, dipropylene glycol monoisobutyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monopropyl ether, ethylene glycol dimethyl ether, ethylene glycol methyl ethyl ether, ethylene glycol diethyl ether, Diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether, diethylene glycol isopropyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol methyl ethyl ether, triethylene glycol diethyl ether, propylene glycol dimethyl ether, propylene glycol methyl ethyl ether, propylene glycol diethyl ether, Examples include dipropylene glycol dimethyl ether, dipropylene glycol methyl ethyl ether, dipropylene glycol diethyl ether, tripropylene glycol dimethyl ether, tripropylene glycol methyl ethyl ether, tripropylene glycol diethyl ether, and the like. Preferably, component (c) is selected from the group consisting of ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, propylene glycol monopropyl ether, and propylene glycol mono-n-butyl ether. Preferably component (c) is selected from the group consisting of diethylene glycol diethyl ether, diethylene glycol isopropyl methyl ether, and dipropylene glycol dimethyl ether, more preferably diethylene glycol diethyl ether.

The content of component (c) is 1 to 30% by weight, more preferably 3 to 20% by weight, and even more preferably 5 to 15% by weight, based on the total weight of the ink composition.

These components (c) may be used alone or in combination of two or more.

(d) Water The water used in the present invention is not particularly limited, and for example, ion-exchanged water, ultrafiltrated water, distilled water, etc. can be used. The ink composition in the present invention contains water as a main solvent. The content of water is 50 to 95% by mass, preferably 60 to 90% by mass, based on the total mass of water in the ink composition, component (b), and the water-soluble organic solvent that is included as necessary and will be described later. Mass%.

(Other additives)
The ink composition according to the present invention contains a water-soluble organic solvent, a humectant, a surfactant, a lubricant, a polysaccharide, and a shear thinning agent for the purpose of improving the physical properties and functions of the ink without impairing the performance of the present invention. It may also contain various additives such as a pH adjuster, a rust preventive agent, a preservative, an organic resin particle, and a water-soluble resin.

The ink composition according to the present invention may contain a water-soluble organic solvent other than component (c) for the purpose of dissolution stability, prevention of water evaporation and drying, and the like. Examples of water-soluble organic solvents include (i) glycols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, or glycerin, (ii) methanol, ethanol, 1-propanol, 2-propanol, isopropanol, isobutanol, and -Alcohols such as butanol, propargyl alcohol, allyl alcohol, 3-methyl-1-butyn-3-ol, and other higher alcohols, and the content of water-soluble organic solvents other than component (c) are as follows: The amount is preferably 0.1 to 30% by weight, more preferably 0.1 to 20% by weight, based on the total weight of the ink composition.

The ink composition according to the present invention may contain a humectant such as urea or sorbitol in addition to the above-mentioned water-soluble organic solvent for the purpose of preventing water evaporation. In addition, in this specification, the above-mentioned water-soluble organic solvent is not included in the moisturizer. The content of the humectant is preferably 0.1 to 10% by mass, more preferably 0.1 to 5% by mass, based on the total mass of the ink composition.

The ink composition according to the present invention may contain various surfactants, including nonionic, anionic, and cationic surfactants. Also included are surfactants having an acetylene bond in their structure, silicone surfactants, and the like.

A surfactant having an acetylene bond in its structure or a silicone surfactant may be included to further improve handwriting drying properties.
By using component (b), the shear viscosity of the ink composition during writing tends to be lower than when conventional crosslinked acrylic acid polymers are used. It can be quickly permeated into a writing object (for example, a paper support) made of such materials. When the ink composition further contains a surfactant having an acetylene bond or a silicone surfactant, the ink composition exhibits a synergistic effect with the effect of component (b) due to the penetration promotion effect, and the penetration into the writing target is further improved. It is thought that this will improve. As a result, the above-described components in the ink composition function to reduce the viscosity of the ink composition and improve its permeability, resulting in high handwriting drying properties.

The surfactant having an acetylene bond in its structure used in the ink composition of the present invention preferably has an added mole number of ethylene oxide of 10 or less.
A surfactant having an acetylene bond in its structure in which the number of moles of ethylene oxide added is 10 or less is a surfactant that has an acetylene bond in its structure to which ethylene oxide is added, and the number of moles of ethylene oxide added to the surfactant is 10 or less. The number is 10 or less. Examples include an acetylene glycol surfactant with an added mole of ethylene oxide of 10 or less, an acetylene alcohol surfactant with an added mole of ethylene oxide of 10 or less, and the like.
A surfactant having an acetylene bond in its structure in which the number of moles of ethylene oxide added is 10 or less can significantly improve the permeability to the object to be written. For this reason, an ink composition containing a surfactant with an acetylene bond in its structure can quickly penetrate paper, allowing the handwriting formed on the surface to dry completely. A product with excellent handwriting drying properties that reduces the time it takes to dry the handwriting and prevents the composition from adhering to areas where there was no handwriting or removing the composition from the handwritten area when rubbing the handwritten area. becomes.

The reason for this is not clear, but it is because surfactants with an acetylene bond in their structure that has 10 or less moles of ethylene oxide added exhibit a suitable balance between hydrophobicity and hydrophilicity in order to exhibit a penetration effect. It is believed that there is. Considering the improvement in the effect of a surfactant having an acetylene bond in its structure, the number of moles of ethylene oxide added is preferably 8 or less. Furthermore, the number of moles of ethylene oxide added is preferably 4 or more. When the number of moles of ethylene oxide added is 4 or more, the solubility decreases, making it difficult for the surfactant to exist stably in the ink composition, thereby preventing a decrease in the stability of the effect of the surfactant over time.
In order for the ink composition to quickly penetrate into the object to be written after writing, it is necessary to suitably control the surface tension of the ink composition after writing. The behavior of surfactant molecules in ink is important in order to instantly control the surface tension associated with writing action, so-called dynamic surface tension, and to obtain rapid penetration into the writing target. Under dynamic conditions, surfactant molecules can be quickly arranged at the gas-liquid interface and the surface tension can be controlled instantaneously and effectively by using a surfactant with a specific structure. An ink composition with excellent handwriting drying properties can be obtained.

In addition, surfactants with an acetylene bond in their structure in which the number of moles of ethylene oxide added is 10 or less have the effect of improving the writing quality, such as improving handwriting dryness and providing a smooth writing feel. . This is because the ink composition contains a surfactant that has an acetylene bond in its structure, which improves the lubricity between the ball of the ballpoint pen and the ballpoint pen tip, and suppresses wear on the ball seat. This is because it can be done.
Note that the ink composition according to the present invention containing a surfactant having an acetylene bond in its structure can contain other lubricants, but in particular, among the lubricants, the following phosphorus is preferred. It is preferable to use it in combination with an acid ester surfactant.

Further, the surfactant having an acetylene bond in its structure used in the present invention may further have propylene oxide added thereto. In consideration of further improvement in handwriting drying properties and stability of the ink composition over time, in the present invention, a surfactant having an acetylene bond in which ethylene oxide and further propylene oxide are added in its structure is selected. It is preferable to use This is because when a surfactant having an acetylene bond in its structure has both ethylene oxide and propylene oxide added to it, the balance between hydrophobicity and hydrophilicity is maintained more favorably.
The ratio of the number of moles of ethylene oxide added to the number of moles of propylene oxide added is determined to maintain a suitable balance between hydrophobicity and hydrophilicity of the surfactant having an acetylene bond in its structure, and to further improve handwriting drying properties. The number of moles added: the number of moles added propylene oxide is preferably 1:1 to 5:1.

In addition, in consideration of alignment at the gas-liquid interface, it is preferable that the total number of moles of ethylene oxide added and the number of moles added of propylene oxide is 10 or less. If the number of moles added is too large, the surfactant molecules become too long, which tends to cause steric hindrance when arrayed at the gas-liquid interface. However, if the total number of moles added is 10 or less, the surfactant molecules become too long. This is particularly preferable because it maintains a suitable balance between hydrophobicity and hydrophilicity, and also takes into account the effects of steric hindrance during alignment at the gas-liquid interface.
Furthermore, considering the improvement of handwriting drying properties and the stability of the ink composition over time, a surfactant having an acetylene bond in its structure with 5 moles of ethylene oxide added and 2 moles of propylene oxide added is used. It is more preferable to use

Further, the HLB value of the surfactant having an acetylene bond in its structure is preferably 3 to 14, more preferably 6 to 12, and particularly preferably 7 to 9. It is preferable that the HLB value of the surfactant having an acetylene bond in its structure is 3 or more because it can stably exist in water as a solvent without remaining dissolved, and can obtain effects both initially and over time. , 14 or less is preferable because it tends to be arranged near the gas-liquid interface due to its hydrophobicity, and the effects brought about by the surfactant, such as improved handwriting drying properties, can be obtained instantaneously in a small amount.

Examples of surfactants that have an acetylene bond in their structure include acetylene alcohol surfactants and acetylene glycol surfactants, which improve permeability into the writing target and improve handwriting drying properties. Considering that it is easy to use, it is preferable to use an acetylene glycol surfactant.

Specific examples of surfactants having an acetylene bond in their structure include Olfine series (manufactured by Nissin Chemical Industry Co., Ltd.), Surfynol series, Dynor series (all manufactured by Air Products Japan Co., Ltd.), etc. .

The silicone surfactant is stable in the ink composition, and can act as an active agent by balancing the structure with the Si skeleton, hydrophobic groups such as propylene oxide, and hydrophilic groups such as ethylene oxide. Since the molecules are easily aligned quickly at the air-liquid interface, the surface tension of the ink composition can be quickly controlled during writing, improving permeability and achieving both handwriting drying properties and stability of the ink composition over time. can. Among silicone surfactants, those having a mass average molecular weight of 500 to 3,000 are preferred. This is because when the mass average molecular weight exceeds 3,000, the molecules of the silicone surfactant tend to become too large and the alignment at the gas-liquid interface becomes slow. Because of this, handwriting drying properties may not be sufficient. On the other hand, if the mass average molecular weight is 3,000 or less, the molecules of the silicone surfactant will become relatively small, and the active agent molecules will tend to be quickly aligned at the gas-liquid interface. Easy to improve dryness. Further, if the mass average molecular weight is less than 500, it is difficult to obtain desired handwriting drying properties. Taking the above effects into consideration, it is preferable that the weight average molecular weight is 500 to 3,000, more preferably, the weight average molecular weight is 500 to 2,000, and further considering that the weight average molecular weight is 1, It is preferably from 000 to 2,000.

In addition, silicone surfactants have the effect of improving handwriting dryness and, at the same time, improving the writing quality, such as by providing a smooth writing quality. This is because the ink composition containing the silicone surfactant improves the lubricity between the ball of the ballpoint pen and the ballpoint pen tip, and also suppresses wear on the ball seat. be.
Note that the ink composition according to the present invention containing a silicone surfactant can contain other lubricants, but in particular, among the lubricants, the phosphate ester surfactant described below is preferred. It is preferable to use it together with.

Regarding the solubility parameter (hereinafter referred to as SP value) of the silicone surfactant, if handwriting dryness is considered, it is preferable that the SP value is 8 to 13, and if more considered, the SP value should be 9 to 12. is preferable, and an SP value of 10 to 11 is particularly preferable. The SP value of water, which is the main component of the solvent, is 23.4, and if the SP values of the silicone surfactant are too close, the silicone surfactant will be stabilized in a dissolved state, so the active agent molecules will quickly align at the gas-liquid interface. It tends to be difficult to accomplish. When the SP value is within the above range, the active agent molecules tend to be quickly arranged at the air-liquid interface, and stability in the ink composition is also obtained, which is preferable.

Specifically, silicone surfactants include the Silface series (manufactured by Nissin Chemical Industries, Ltd.), the BYK series (manufactured by BYK Chemie Corporation), the Silsoft Spread series, and the Coatosil series (all manufactured by Momentive Performance Materials). ), etc. These may be used alone or in combination of two or more.

Further, the total content of the surfactant having an acetylene bond in its structure or the silicone surfactant is more preferably 0.01 to 3.0% by mass based on the total mass of the ink composition. This is because if the total content of surfactants having acetylene bonds in their structure or silicone surfactants is less than 0.01% by mass, it is difficult to obtain the desired handwriting drying properties, and 3.0% by mass. This is because if it exceeds this, the stability of the ink composition over time is likely to be affected. Furthermore, in consideration of this, 0.05 to 2.0% by mass is preferred, and 0.1 to 1.5% by mass is particularly preferred.

Moreover, the ink composition according to the present invention can further contain a phosphate ester surfactant. In addition to improving the dispersibility of the ink composition, the phosphate surfactant also acts as a lubricant when the ink composition is used in a ballpoint pen. The lubricant improves the lubricity between the ball of a ballpoint pen and the ballpoint pen tip, making the rotation of the ball smoother, thereby suppressing wear on the ball seat and improving the writing quality. The phosphoric acid ester surfactant used in the present invention has a property that the phosphoric acid group easily adsorbs to metal, so it improves lubricity, suppresses wear of the ball seat, and improves writing quality. Easy to improve. Therefore, when the ink composition according to the present invention is applied to a ballpoint pen, a particularly excellent writing feeling can be achieved. However, since this surfactant contributes not only to lubricity but also to improving dispersibility, it acts effectively even when the ink composition is used in writing instruments other than ballpoint pens.

Furthermore, phosphate ester surfactants also have the effect of adjusting surface tension. For this reason, in particular, in a writing instrument that is equipped with a comb-like ink flow rate adjustment member (described later) and has a supply mechanism that supplies the ink composition to the nib by interposing the comb groove-shaped ink flow rate adjustment member, the ink flow rate adjustment member has excellent wettability. It is preferable because it exhibits the characteristics of Therefore, the ink composition according to the present invention is also preferable for fountain pens, markers, felt-tip pens, ballpoint pens, etc. that have comb-shaped ink flow rate regulating members.

Phosphate ester surfactants include straight chain alcohol, styrenated phenol, nonylphenol, octylphenol and other phosphate ester surfactants, among which straight chain alcohol, styrenated phenol, etc. It is preferable to use a phosphate ester surfactant.

In the present invention, the phosphate ester surfactant preferably has an HLB value of 5 to 15, more preferably 6 to 13. Furthermore, in the present invention, the carbon number of the alkyl group or alkylaryl group contained in the phosphate ester surfactant is preferably 6 to 30, more preferably 8 to 18, and preferably 10 to 14. Particularly preferred. This is because linear phosphate ester surfactants with a specific HLB value and carbon number have excellent writing stability, such as stable handwriting with improved line skipping and blurring. This is because it can synergistically improve the dispersion effect together with the dispersant used in the present invention, and at the same time provide a lubricating effect.

In addition, in the present invention, the HLB value of the phosphate ester surfactant means the HLB value of the raw material nonionic surfactant of the phosphate ester surfactant, and the value calculated by the Kawakami method. It is calculated by the following formula.
HLB=7+11.7log (Mw/Mo), (Mw: molecular weight of hydrophilic group, Mo: molecular weight of lipophilic group)

Specific examples of phosphate ester surfactants include Plysurf series (Daiichi Kogyo Seiyaku Co., Ltd.), and examples of linear alcohol-based phosphate ester surfactants include Plysurf A212C, A208B, A213B, A208F, A215C, A219B, and A208N are listed, examples of styrenated phenol-based phosphate ester surfactants include Plysurf AL, and nonylphenol-based surfactants include Plysurf 207H, A212E, and A217E, and examples of octylphenol include Plysurf A210G.

When the ink composition according to the present invention contains a phosphate ester surfactant, the content thereof is preferably 0.1 to 2.0% by mass, and 0.5 to 1.5% by mass based on the total mass of the ink composition. It is more preferable that it is mass %.
A ballpoint pen can achieve excellent writing performance by forming an appropriate film of an ink composition between the ball and the ball seat at the pen tip. Since a phosphate ester surfactant effectively acts to form such a film, it is preferable to use a phosphate ester surfactant in an ink composition used for a ballpoint pen.
When the ink composition according to the present invention uses a phosphate ester surfactant, the phosphate ester surfactant acts as an extreme pressure agent. In general, extreme pressure agents are substances that easily react with metal surfaces when the temperature rises due to frictional heat, form a solid soft film, and have the effect of increasing lubricity. It is added to obtain a brush feel. The phosphoric acid groups of the phosphoric acid ester, which is a phosphoric acid ester surfactant, are adsorbed onto the metal surface and exert an extreme pressure effect, resulting in a good writing feel even under high writing pressure.
In other words, the lubricating effect of the phosphate ester surfactant is due to the fact that the phosphoric acid group adsorbs to the ball receiving seat of the chip and the metal surface of the ball, and the hydrophobic group extends into the ink, resulting in the physical interaction between the ball and the ball seat. This is thought to occur because it occurs by inhibiting contact. Therefore, it is thought that the cushioning effect of the hydrophobic groups extending between the tip and the ball provides a lubricating effect that is desirable for a ballpoint pen, that is, a smooth and soft writing feel.
In addition, the above-mentioned phosphate ester surfactant can also be used after being suitably neutralized with an alkaline substance such as amines or alkali metals.

In addition to the above-mentioned surfactants, examples of substances that can be used as lubricants include alkylbenzenesulfonic acids, amino acids, N-acylamino acids, aliphatic amide alkylene oxide adducts, terpenoid acid derivatives, and salts thereof. More specifically, oleic acid, stearic acid, linoleic acid, linolenic acid, ricinoleic acid, dodecylbenzenesulfonic acid, alanine, glycine, lysine, threonine, serine, proline, sarcosine, N-acylsarcosine, polyoxyethylene fatty acid amide and their salts.

Ink compositions according to the present invention can include polysaccharides. Polysaccharides bring about various effects, but mainly bring about effects such as adjusting ink viscosity, imparting shear thinning properties, and improving dry-up resistance. Specific examples include dextrin, xanthan gum, welan gum, succinoglycan, guar gum, locust bean gum, λ-carrageenan, cellulose derivatives, and diutan gum.

When an ink composition contains a component such as a pigment that can exist in a state insoluble in water, which is the main solvent, the water evaporates at the nib of a writing instrument containing the ink, and the ink dries and solidifies, causing the ink flow path to flow. etc. may become clogged. When such a phenomenon occurs, the ink ejection performance is affected, and although there is a residual amount of ink in the writing instrument, it may become impossible to write again. Therefore, it is preferable to improve the dry-up resistance. Therefore, it is necessary to consider improving the dry-up resistance at the tip of a ballpoint pen, for example. Dextrin forms a film on the pen tip, which has the effect of preventing the solvent in the ink from evaporating. Therefore, the use of dextrin is effective because an ink composition with excellent dry-up resistance can be obtained.

The mass average molecular weight of the dextrin is preferably 5,000 to 120,000. If it is 120,000 or more, the film formed on the pen tip is hard, and handwriting tends to become blurred when starting to write during dry-up. On the other hand, if it is less than 5,000, it is difficult to change the viscosity enough to improve the dispersion stability over time, and the hygroscopicity of the dextrin tends to increase, and the film formed on the pen tip is soft and does not stabilize on the pen tip. It is difficult to maintain, and it tends to be difficult to suppress evaporation of the solvent in the ink. In further consideration of improving the above effects, it is preferable to use a dextrin having a mass average molecular weight of 20,000 to 100,000.

The content of dextrin is preferably 0.1 to 5% by mass based on the total mass of the ink composition. This is because if it is less than 0.1% by mass, the effect of improving dry-up resistance performance will not be sufficiently achieved, and if it exceeds 5% by mass, it will tend to be difficult to dissolve in the ink. In consideration of dissolution stability in the ink, the amount is preferably 0.1 to 3% by mass, and in consideration of improved dry-up resistance, the amount is most preferably 1 to 3% by mass.

The ink composition according to the present invention may contain two or more types of polysaccharides.

The ink composition according to the invention can include a crosslinking agent. The crosslinking agent used in the present invention is a compound that can form a reversible physical crosslink with the component (b) used in the present invention, and is a compound that can form a reversible physical crosslink with the alkyl group of the ester of component (b). It is a compound that can exhibit Waals' intermolecular cohesive force. When the ink composition is in a stationary state, the crosslinking agent forms a crosslinking point by physical bonding with the alkyl group of the copolymer used in the present invention, and the component (b) and the crosslinking agent form a strong network. It is a compound whose physical bonds at crosslinking points are easily released when shearing force is applied to the ink composition.

Specific examples of the crosslinking agent used in the present invention include alkyl-modified glucose, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene fatty acid ester, alkyl-modified polyethylene oxide, phenyl-modified polyethylene oxide, and phenylalkyl-modified polyethylene oxide. It will be done. The effect can be obtained by using either a high-molecular compound containing an alkyl group or a low-molecular compound as a crosslinking agent, but the viscosity when shearing tends to be lower when using a low-molecular compound, and the viscosity when standing still and when shearing is This is preferable because it can increase the viscosity gradient at the time. The alkyl group used has 1 to 30 carbon atoms, preferably 1 to 22 carbon atoms, and more preferably 1 to 18 carbon atoms. In particular, when the alkyl groups have the same number of carbon atoms, it is preferable to use a compound with less steric hindrance because the effect will be greater.

Examples of pH adjusters include inorganic salts such as ammonia, sodium carbonate, sodium phosphate, sodium hydroxide, and sodium acetate, organic basic compounds such as water-soluble amine compounds such as triethanolamine and diethanolamine, lactic acid, and citric acid. can be mentioned. The content of the pH adjuster is preferably 0.1 to 25% by mass, more preferably 0.5 to 10% by mass, based on the ink composition.

Examples of the rust inhibitor include benzotriazole and its derivatives, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, sodium thiosulfate, saponin, and dialkylthiourea.

The preservatives include 2-methyl-4-isothiazolin-3-one (hereinafter sometimes referred to as MIT), 2-n-octyl-4-isothiazolin-3-one (hereinafter sometimes referred to as OIT), 1 , 2-benzisothiazolin-3-one, 2-methyl-4,5-trimethylene-4-isothiazolin-3-one, N-(n-butyl)-1,2-benzisothiazolin-3-one, 2-pyridinethiol Examples include sodium -1-oxide, sodium 3-iodo-2-propynylbutylcarbamate benzoate, benzotriazole, and phenol. The content of these preservatives is preferably 20 to 200 ppm based on the total mass of the ink composition. Further, among these, it is preferable to use MIT and OIT in combination because the antibacterial properties are improved. In this case, the content of OIT is preferably 1 to 50 ppm based on the total mass of the ink composition, and the blending ratio of OIT and MIT is preferably 1:1 to 10:1 on a mass basis. preferable.

Organic resin particles can be used in the ink composition of the present invention. When organic resin particles are used, ink sag can be suppressed. Examples of organic resin particles that can be used in the present invention include olefin resin particles such as polyethylene resin and polypropylene resin, melamine/formaldehyde resin, benzoguanamine/formaldehyde resin, benzoguanamine/melamine/formaldehyde resin, urea formaldehyde resin, and nylon resin. Examples include nitrogen-containing resin particles containing a nitrogen atom in the chemical structure, acrylic resin particles, styrene resin particles, epoxy resin particles, urethane resin particles, and cellulose resin particles. These organic resin particles may be used alone or in combination of two or more.

Among the organic resin particles, it is preferable to use olefin resin particles and nitrogen-containing resin particles. This is because the olefin resin particles are hydrocarbon compounds and are nonpolar, so they tend to aggregate in water, and this aggregate structure and the copolymer intertwine with each other to further suppress ink leakage. At the same time, it is presumed that this is because it is easy to form an optimized agglomerated structure that does not cause problems such as insufficient ink discharge amount. Furthermore, since olefin resin particles have a high melting temperature, they tend to remain stable even in high-temperature environments, and are easily deformed and difficult to modify in high-pressure environments. It can be suitably used as an ink additive.

Examples of the material for the olefin resin particles include polyolefins such as polyethylene, polypropylene, and polybutene, and mixtures thereof. Among these, it is preferable to use polyethylene in consideration of suppressing ink leakage and improving writing taste. Specifically, polyethylene is used, such as low density polyethylene, high density polyethylene, low molecular weight polyethylene, modified polyethylene, and modified high density polyethylene. Examples include. Among them, low-density polyethylene, low-molecular-weight polyethylene, and modified polyethylene are preferable in consideration of the ink leakage suppressing effect.In particular, low-density polyethylene has a lower melting point and softer properties than other types of polyethylene, so polyethylene particles stick together. Low-density polyethylene is preferred because it is easy to apply, does not easily create gaps between particles, and is difficult to leak ink.Furthermore, low-density polyethylene is soft, so it can be suitably used for improving the writing feel. The olefin resin particles may contain materials other than polyolefin, if necessary.

Among the nitrogen-containing resin particles, it is preferable to have an amino group or an imino group. This is because having an amino group or an imino group makes it easier to maintain a stable agglomerated structure for a long period of time, making it easier to suppress ink leakage. . Note that the nitrogen-containing resin particles having a functional group such as an amino group or an imino group include tertiary amines, quaternary amines, and the like.
Further, among the nitrogen resin particles having an amino group or an imino group, it is preferable to use nitrogen-containing resin particles having a chemically bonded three-dimensional crosslinked structure. This is because when it has a chemically bonded three-dimensional cross-linked structure, it has particularly excellent strength, heat resistance, and solvent resistance, so it is stable without absorbing moisture in water-based ink, so it has excellent stability over time. Therefore, it is preferable. Furthermore, due to the stability of the nitrogen-containing resin particles themselves and the mutual hydrogen bonding properties between the nitrogen-containing resin particles, it is easy to maintain an agglomerated structure for a long period of time, and it is easy to stably suppress ink leakage. In particular, among nitrogen-containing resin particles having a crosslinked structure, resin particles having a heterocyclic structure such as melamine/formaldehyde resin, benzoguanamine/formaldehyde resin, and benzoguanamine/melamine/formaldehyde resin are more difficult to absorb moisture and are more stable. preferable.
Specific examples of the nitrogen-containing resin particles having a crosslinked structure include amino resin particles such as melamine/formaldehyde resin, benzoguanamine/formaldehyde resin, benzoguanamine/melamine/formaldehyde resin, and urea formaldehyde resin. Examples of nitrogen-containing resin particles having amide bonds include nylon resins such as nylon 6 and nylon 12, urethane resin particles such as polycarbonate polyurethane resins, polyether polyurethane resins, polyester polyurethane resins, and urethane urea resins. It will be done.

Regarding the shape of the organic resin particles, spherical or irregularly shaped particles can be used, but spherical resin particles are preferable in consideration of reducing frictional resistance. The spherical resin particles herein are not limited to true spheres, and may be approximately spherical resin particles, approximately ellipsoidal resin particles, or the like.

Further, the content of the organic resin particles is more preferably 0.01 to 10.0% by mass based on the total amount of the ink composition. This is because if the content of organic resin particles is less than 0.01% by mass, it is difficult to suppress ink leakage, and if it exceeds 10.0% by mass, the agglomerated structure tends to become strong, which affects the writing quality and dry-up performance. This is because it is easy to appear. Furthermore, in consideration of this, it is preferably 0.02 to 5.0% by weight, particularly preferably 0.03 to 1.0, and most preferably 0.05 to 0.5% by weight.

Further, according to the present invention, the ink composition can contain a water-soluble resin for the purpose of improving the abrasion resistance of handwriting. As the water-soluble resin, acrylic resin, alkyd resin, cellulose derivative, polyvinylpyrrolidone, polyvinyl alcohol, etc. can be used. Further, as a resin emulsion, an emulsion containing acrylic resin, urethane resin, styrene-butadiene resin, polyester resin, vinyl acetate resin, etc. can be added.

The viscosity gradient of the ink composition according to the invention can be expressed by the viscosity index n at 20°C. Here, the viscosity index n refers to n in the viscosity formula represented by S=αDn. Note that S represents shear stress (dyn/cm ² =0.1 Pa), D represents shear rate (s ⁻¹ ), and α represents viscosity coefficient. The viscosity index n can be calculated by measuring the ink viscosity using an E-type rotational viscometer (DV-II+Pro, cone rotor CPE-42, manufactured by Brookfield).

<Water-based ballpoint pen>
The water-based ballpoint pen according to the present invention contains the above-described ink composition.
Examples of water-based ballpoint pens include retractable writing ballpoint pens, such as ball knock type, rotary type, and sliding type, in which the pen tip can be accommodated in the barrel.

When we studied the specifications of a ballpoint pen when it was filled with the water-based ink composition for writing instruments according to the present invention, we found that when the ink consumption per 100 m of the water-based ballpoint pen is A (mg) and the ball diameter is B (mm). , 150≦A/B≦500, and preferably 250≦A/B≦450. This is because by keeping the above range, the amount of ink consumed is appropriate for the ball diameter, which improves ink fluidity and suppresses handwriting blurring, making it easier to obtain good handwriting. It is.

The ink consumption was measured using five test samples at a writing speed of 4 m/min at 20°C, a writing angle of 65°, and a writing load of 100 g on JIS P3201 writing paper. A written test is conducted, and the average value of the ink consumption per 100 m is defined as the ink consumption per 100 m. Further, the diameter of the ball is not particularly limited, but a ball having a diameter of about 0.1 to 2.0 (mm) is generally used.

Regarding the specifications of the ballpoint pen tip, it is preferable that the movable amount (clearance) of the ball in the ballpoint pen tip in the vertical axis direction be 20 to 50 μm, and 30 to 45 μm at the time of manufacturing or starting use of the ballpoint pen. It is preferable. This is because if the clearance is within the above range, it is easy to obtain good handwriting by appropriately adjusting the ink discharge amount and suppressing line skipping and blurring. Furthermore, if the clearance is within the above range, The ratio A/B mentioned above is also easy to adjust.
The movable amount (clearance) of the ball of the ballpoint pen tip in the vertical axis direction indicates the distance that the ball can move in the vertical axis direction of the ballpoint pen tip body. Here, the movable amount generally increases with use because the ball and ball seat wear out with use. The movable amount is related to the ink ejection amount. Therefore, in general, the movable amount of a ballpoint pen is set within the above range when it is manufactured or when it is first used.In order to achieve stable writing characteristics, the movable amount is set within the above range until the end of use of the ballpoint pen. It is preferable that there be.
When a ballpoint pen tip with a large clearance is used, the amount of ink ejected increases and the density of handwriting can be increased, but it is preferable that the handwriting drying property is excellent. Therefore, the ink composition according to the present invention can be suitably used even when a ballpoint pen tip with a large clearance is used.

<Method for manufacturing ink composition>
The ink composition according to the present invention can be produced by any conventionally known method. Specifically, it can be produced by blending the required amounts of each component and mixing with various stirrers such as propeller stirring, homodisper, or homomixer, various dispersion machines such as bead mills, and the like.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

<Example 1>
An ink composition was obtained using the following formulation and method.
・Organic pigment (component (a)): FUJI SP RED 5615 (25% by mass water dispersion, Fuji Shiki Co., Ltd.) 24.0% by mass
・Acrylic acid copolymer (component (b)): (meth)acrylic acid-methyl (meth)acrylate copolymer (mole ratio of carboxylic acid and methyl ester 1:2.1, repeating unit derived from acrylic acid and Molar ratio of repeating units derived from methacrylic acid 1:0.36 Mass average molecular weight 49,000) 0.45% by mass
・Organic solvent (component (c)): ethylene glycol monopropyl ether 10.0% by mass ・Water (component (d)): ion exchange water 54.35% by mass
・Phosphate ester surfactant: "Plysurf A215C" (Daiichi Kogyo Seiyaku Co., Ltd., HLB value 11.5) 1.0% by mass
・pH adjuster: triethanolamine 3.0% by mass
・Rust inhibitor: benzotriazole 0.5% by mass
・Preservative: 1,2-benzisothiazolin-3-one 0.2% by mass ・Polysaccharide: Dextrin (mass average molecular weight 30,000, Sandek series, Sanwa Starch Industries Co., Ltd.) 1.5% by mass
・Wetting agent: urea 5.0% by mass

A base ink was prepared by stirring an organic pigment, an organic solvent, water, a phosphate ester surfactant, a pH adjuster, a rust preventive, a preservative polysaccharide, and a lubricant using a disper. Thereafter, while heating the base ink prepared above, the acrylic acid copolymer was added and thoroughly mixed and stirred using a homogenizer stirrer until a uniform state was obtained, thereby obtaining the ink composition of Example 1. .

表中、
有機顔料分散体－１：アゾ系顔料（Ｐｉｇｍｅｎｔ Ｒｅｄ １７０）、ＦＵＪＩ ＳＰ ＲＥＤ ５６１５（２５質量％水分散体、冨士色素株式会社）
有機顔料分散体－２：ジケトピロロピロール系顔料（Ｐｉｇｍｅｎｔ Ｒｅｄ ２５４） ２５質量％水分散体
有機顔料分散体－３：ペリレン系顔料（Ｐｉｇｍｅｎｔ Ｒｅｄ １４９） ２５質量％水分散体
有機顔料分散体－４：キナクリドン系顔料（Ｐｉｇｍｅｎｔ Ｒｅｄ １２２） ２５質量％水分散体
有機顔料分散体－５：フタロシアニン系顔料（Ｐｉｇｍｅｎｔ Ｂｌｕｅ １５：３） ２５質量％水分散体
有機顔料分散体－６：フタロシアニン系顔料（Ｐｉｇｍｅｎｔ Ｇｒｅｅｎ ７） ２５質量％水分散体
（メタ）アクリル酸－（メタ）アクリル酸メチル共重合体：（メタ）アクリル酸－（メタ）アクリル酸メチル共重合体（カルボン酸とメチルエステルのモル比１：２．１、アクリル酸由来の繰り返し単位とメタクリル酸由来の繰り返し単位のモル比１：０．３６ 質量平均分子量４９，０００
リン酸エステル系界面活性剤：「プライサーフＡ２１５Ｃ」（第一工業製薬株式会社、ＨＬＢ値１１．５）
デキストリン：質量平均分子量３０，０００、サンデックシリーズ、三和デンプン工業株式会社 <Examples 2 to 19, Comparative Examples 1 to 12>
Ink compositions of Examples 2 to 19 and Comparative Examples 1 to 12 were obtained in the same manner as in Example 1 except that the ink compositions were changed to those shown in Tables 1 and 2. In addition, the numerical value of the composition in a table|surface shows mass %. Note that the ink compositions of Comparative Examples 11 and 12 were not evaluated because they were not uniform.

In the table,
Organic pigment dispersion-1: Azo pigment (Pigment Red 170), FUJI SP RED 5615 (25% by mass water dispersion, Fuji Shiki Co., Ltd.)
Organic pigment dispersion-2: Diketopyrrolopyrrole pigment (Pigment Red 254) 25% by mass water dispersion Organic pigment dispersion-3: Perylene pigment (Pigment Red 149) 25% by mass water dispersion Organic pigment dispersion- 4: Quinacridone pigment (Pigment Red 122) 25% by mass water dispersion Organic pigment dispersion-5: Phthalocyanine pigment (Pigment Blue 15:3) 25% by mass water dispersion Organic pigment dispersion-6: Phthalocyanine pigment ( Pigment Green 7) 25% by mass water dispersion (meth)acrylic acid-methyl (meth)acrylate copolymer: (meth)acrylic acid-methyl (meth)acrylate copolymer (mole ratio of carboxylic acid and methyl ester 1:2.1, molar ratio of repeating units derived from acrylic acid to repeating units derived from methacrylic acid 1:0.36, mass average molecular weight 49,000
Phosphate ester surfactant: "Plysurf A215C" (Daiichi Kogyo Seiyaku Co., Ltd., HLB value 11.5)
Dextrin: Mass average molecular weight 30,000, Sandek series, Sanwa Starch Industries Co., Ltd.

The ink composition (1.0 g) obtained above was applied to a ballpoint pen tip (the amount of movement (clearance) in the vertical axis direction of the ball was 30 μm) that rotatably held a cemented carbide ball with a diameter of 0.7 mm. A refill was prepared, which was filled into the inside of an ink container, and this refill was attached to a gel ink ballpoint pen (trade name: Juice) manufactured by Pilot Corporation to obtain a ballpoint pen. The resulting ballpoint pen was used as a test ballpoint pen, and the following handwriting drying properties were evaluated.

The character "ei" was handwritten using a test ballpoint pen at room temperature on commercially available report paper, and the handwriting was rubbed in one direction with the thumb after 0, 3, and 5 seconds, respectively. The condition of the handwriting at that time was visually confirmed, and the results obtained are as shown in Tables 1 and 2. The evaluation criteria are as follows.
A: Good handwriting was left without staining the surrounding area.
B: Very slight staining occurred.
C: Slight staining occurred.
D: Dirt occurs, but there is no practical problem.
E: Severe staining occurred.
F: Significant staining occurs and characters are difficult to recognize.

Compared to the ink compositions of Examples 1 to 11, the ink compositions of Examples 12 to 19 had better handwriting quality with less line skipping and line cracking in the obtained handwriting. Furthermore, the ink compositions of Examples 12 to 19 had better ink stability than the ink compositions of Examples 1 to 11. When the ink compositions of Examples 12, 18, and 19 were compared, the ink composition of Example 12 was even more excellent in ink stability.

Claims (6)

(a) organic pigment,
(b) The following formula (i):
(In the formula, R ¹ is hydrogen or a methyl group)
A repeating unit indicated by
Formula (ii) below:
(In the formula,
R ² is hydrogen or a methyl group, and R ³ is an alkyl group having 1 to 5 carbon atoms and having a straight chain or a side chain)
An acrylic acid copolymer comprising a repeating unit represented by
(c) Organic solvent represented by the following formula (I):
(In the formula,
R ^A is a straight chain or branched alkyl group having 1 to 3 carbon atoms, and R ^B is a straight chain or branched alkoxy group having 1 to 3 carbon atoms;
L is an ethylene group (-CH ₂ -CH ₂ -) which may be substituted with a methyl group, or a trimethylene group (-CH ₂ -CH ₂ -CH ₂ -), and x is 1 to 5. an integer) and (d) water, the ink composition for an aqueous ballpoint pen comprising:
An aqueous ballpoint pen ink composition, wherein the content of the component (c) is 1 to 30% by mass based on the total mass of the composition. The composition according to claim 1, wherein R ^A is a methyl group or an ethyl group, and R ^B is a methoxy group or an ethoxy group. The composition according to claim 1 or 2, wherein x is 1 to 3, and L is an ethylene group optionally substituted with a methyl group. The composition according to any one of claims 1 to 3, wherein the component (a) is a phthalocyanine, azo, quinacridone, diketopyrrolopyrrole, or perylene pigment. The composition according to any one of claims 1 to 4, further comprising a phosphate ester surfactant. An aqueous ballpoint pen containing the composition according to any one of claims 1 to 5.