JP7412896B2 - 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 has excellent dispersion stability of the colorant and storage stability of the ink composition, and even when written, the handwriting does not smear easily, does not cause blurring or line cracking, provides good handwriting, and has a pleasant writing feel. An object of the present invention is to provide an ink composition for a water-based ballpoint pen with good properties and a water-based 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、直鎖または分岐の、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（Ａ）：

（式中、
Ｒ^Ａ１は、それぞれ独立に、水素、メチル基、またはエチル基であり、
Ｒ^Ａ２は、炭素数１０～２２の、直鎖または分岐の、アルキル基であり、かつ
ｘａは、５～２５の整数である）
で表され、ＨＬＢ値が１２～１５である化合物、または
以下の式（Ｂ）：

（式中、
Ｒ^Ｂ１は、それぞれ独立に、水素、メチル基、またはエチル基であり、
Ｒ^Ｂ２は、それぞれ独立に、水素、メチル基、またはエチル基であり、
ｘｂは、５～２５の整数であり、かつ
ｙｂは、１～３の整数である）
で表され、ＨＬＢ値が１２～１６である化合物である、分散剤、および
（ｄ）水
を含んでなる。 The ink composition for a water-based ballpoint pen according to the present invention includes:
(a) a coloring agent;
(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 a linear or branched alkyl group having 1 to 5 carbon atoms)
An acrylic acid copolymer comprising a repeating unit represented by
(c) The following formula (A):

(In the formula,
R ^A1 is each independently hydrogen, a methyl group, or an ethyl group,
R ^A2 is a linear or branched alkyl group having 10 to 22 carbon atoms, and xa is an integer of 5 to 25)
A compound represented by and having an HLB value of 12 to 15, or the following formula (B):

(In the formula,
R ^B1 is each independently hydrogen, a methyl group, or an ethyl group,
R ^B2 is each independently hydrogen, a methyl group, or an ethyl group,
xb is an integer from 5 to 25, and yb is an integer from 1 to 3)
and (d) water.

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 ones, and it does not cause blurred handwriting or 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, since the ink composition contains a specific dispersant, it has excellent dispersion stability not only immediately after preparation but also after aging. When such an ink composition is housed in a transparent ink container, the color of the ink composition can be visually recognized from the ink container evenly, resulting in excellent quality.

Embodiments of the present invention will be described in detail below. In the present invention, "parts", "%", "ratio", etc. indicating formulations are based on mass unless otherwise specified, and content refers to the amount of constituent components based on the mass of the ink composition. Mass%.

<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) a colorant, (b) an acrylic acid copolymer, (c) a specific dispersant, and (d ) Contains water.

(a) Coloring agent The coloring agent used in the present invention is not particularly limited, such as pigments and dyes, and can be appropriately selected and used. The colorant is preferably a pigment, and in particular, when a pigment with a specific structure described below is used, the effect of further improving the dispersibility can be obtained. A dye can also be used in combination with the pigment.

Pigments that can be used in the present invention include inorganic, organic, and processed pigments, and specifically include carbon black, aniline black, ultramarine, yellow lead, titanium oxide, iron oxide, phthalocyanine, azo, Examples include quinacridone series, quinophthalone series, triphenylmethane series, perinone series, perylene series, dioxazine series, aluminum pigments, pearl pigments, fluorescent pigments, phosphorescent pigments, and complementary color pigments. In addition, microcapsule pigments, liquid crystals, which are made by encapsulating or dissolving a colored body formed by dispersing a pigment in a medium as a colored resin particle body in a shell body made of a resin wall-forming substance by a known microencapsulation method, etc. A microcapsule pigment containing a functional material such as a reversible thermochromic composition or a photochromic material may also be used. Furthermore, colored resin particles in which a pigment is covered with a transparent or translucent resin, etc., or colored resin particles or colorless resin particles colored with a pigment or dye can also be used. These dyes and 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 surfactant to be described later, 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. From the above, it is preferable to use a pigment as the colorant. More preferably, it is an organic pigment, even more preferably a phthalocyanine-based organic pigment. Particularly preferred are phthalocyanine green and phthalocyanine blue. Examples of phthalocyanine green include Pigment Green 7, 36, and 58, and examples of phthalocyanine blue include Pigment Blue 16, 15, 15:1, 15:2, and 15: 3, 15:4, 15:6, 75, 79, etc. Pigment Blue 15 is most preferred.

The dye that can be used in the present invention is not particularly limited as long as it can be dissolved or dispersed in an aqueous medium. Examples include various dyes such as acid dyes, basic dyes, reactive dyes, direct dyes, disperse dyes, and food colorings, and these can be used alone or in combination of two or more types. The content of the dye is preferably 0.1 to 20% by mass, more preferably 0.1 to 10% by mass, based on the total mass of the ink composition.

Specifically, as the acid dye, C.I. I. Acid Red 18, C. I. Acid Red 51, C. I. Acid Red 52, C. I. Acid Red 87, C. I. Acid Red 92, C. I. Acid Red 289, C. I. Acid Orange 10, C. I. Acid Yellow 3, C. I. Acid Yellow 7, C. I. Acid Yellow 23, C. I. Acid Yellow 42, C. I. Acid Green 3, C. I. Acid Green 16, C. I. Acid Blue 1, C. I. Acid Blue 9, C. I. Acid Blue 22, C. I. Acid Blue 90, C. I. Acid Blue 239, C. I. Acid Blue 248, C. I. Acid Baolette 15, C. I. Acid Violet 49, C. I. Acid Black 1, C. I. Acid Black 2, basic dyes include C.I. I. Basic Orange 2, C. I. Basic Orange 14, C. I. Basic Green 4, C. I. Basic Blue 9, C. I. Basic Blue 26, C. I. Basic Violet 1, C. I. Basic Violet 3, C. I. Basic Violet 10, direct dyes such as C.I. I. Direct Red 28, C. I. Direct Yellow 44, C. I. Direct Blue 86, C. I. Direct Blue 87, C. I. Direct Violet 51, C. I. Direct Black 19, as food coloring, C. I. Food Yellow 3, C. I. Examples include Food Black 2.

（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、直鎖または分岐の、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 a linear or branched alkyl group having 1 to 5 carbon atoms)
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 acid copolymers can be used alone or in combination of two or more.

Furthermore, R ³ in formula (ii) is a linear or branched alkyl group having 1 to 5 carbon atoms, but when the number of carbon atoms exceeds 5, steric hindrance of the alkyl group becomes large, 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, resulting 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. The weight average molecular weight herein is a weight 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.

(c) Dispersant The dispersant used in the present invention is a compound represented by formula (A) and has an HLB value of 12 to 15, or a compound represented by formula (B) and has an HLB value of 12 to 16. It is.

式中、
Ｒ^Ａ１は、それぞれ独立に、水素、メチル基、またはエチル基であり、
Ｒ^Ａ２は、炭素数１０～２２の、直鎖または分岐の、アルキル基であり、かつ
ｘａは、５～２５の整数である。
好ましくは、
Ｒ^Ａ１が、水素、またはメチル基であり、
Ｒ^Ａ２が、デシル基、イソデシル基、またはトリデシル基であり、かつ
ｘａが、７～１５である。 The compound represented by formula (A) is as follows.

During the ceremony,
R ^A1 is each independently hydrogen, a methyl group, or an ethyl group,
R ^A2 is a linear or branched alkyl group having 10 to 22 carbon atoms, and xa is an integer of 5 to 25.
Preferably,
R ^A1 is hydrogen or a methyl group,
R ^A2 is a decyl group, isodecyl group, or tridecyl group, and xa is 7 to 15.

Specific examples of the compound represented by formula (A) include polyoxyethylene decyl ether (HLB: 14.7), polyoxyethylene isodecyl ether (HLB: 14), and polyoxyethylene tridecyl ether (HLB 14.5). ), polyoxyalkylene isodecyl ether (HLB 14.7, 14.5, 13.8), and the like.

Specifically, the Nougen series (product name, Dai-ichi Kogyo Seiyaku Co., Ltd.), Fine Surf series, Brownon series, Safety Cut series (product name, Aoki Yushi Kogyo Co., Ltd.), Emulgen series (product name, Kao Co., Ltd.), Rheokol series, Rheox series (product name, Lion Specialty Chemicals Co., Ltd.), NIKKOL series (product name, Nikko Chemicals Co., Ltd.), etc., and select HLB, R ^A2 , etc. as appropriate. It can be used as

The HLB value of the compound represented by formula (A) is 12 to 15, more preferably 13 to 15, and even more preferably 14 to 15. When the HLB value is within the above range, dispersion stability is improved. This is because there is a tendency to
The above HLB value is a value calculated by the Griffin method, and is calculated by the following formula.
HLB value = 20 x (mass% of hydrophilic groups) = 20 x (sum of formula weights of hydrophilic groups/molecular weight of surfactant)
Note that the HLB value of the compound represented by formula (B) described later is also calculated in the same manner.

式中、
Ｒ^Ｂ１は、それぞれ独立に、水素、メチル基、またはエチル基であり、
Ｒ^Ｂ２は、それぞれ独立に、水素、メチル基、またはエチル基であり、
ｘｂは、５～２５の整数であり、かつ
ｙｂは、１～３の整数である。
好ましくは、
Ｒ^Ｂ１が、水素、またはメチル基であり、
Ｒ^Ｂ２は、水素、またはメチル基であり、
ｘｂが、１１～１７の整数であり、かつ
ｙｂが、１～３の整数である。 The compound represented by formula (B) is as follows.

During the ceremony,
R ^B1 is each independently hydrogen, a methyl group, or an ethyl group,
R ^B2 is each independently hydrogen, a methyl group, or an ethyl group,
xb is an integer from 5 to 25, and yb is an integer from 1 to 3.
Preferably,
R ^B1 is hydrogen or a methyl group,
R ^B2 is hydrogen or a methyl group,
xb is an integer from 11 to 17, and yb is an integer from 1 to 3.

Specific examples of the compound represented by formula (B) include the compounds exemplified below.

More specifically, examples include the Nougen series (product name, Dai-ichi Kogyo Seiyaku Co., Ltd.), the Brownon series (product name, Aoki Yushi Kogyo Co., Ltd.), the Emulgen series (product name, Kao Corporation), etc. It can be used selectively.

The HLB value of the compound represented by formula (B) is 12 to 16, more preferably 12 to 15, and still more preferably 12 to 14. This is because dispersion stability tends to be improved when the HLB value is within the above range.

In the present invention, by combining component (c) with component (a) and component (b), it is possible to further improve dispersibility while maintaining writing performance, thereby further improving stability over time. . This is presumed to be due to the following reasons. Component (a) and component (b) have high affinity. When these are combined, component (b) may be adsorbed on the surface of component (a), the dispersibility of component (a) may be inhibited, aggregates may be formed, and the number of coarse particles may increase. This may reduce the storage stability of the ink composition. When component (c), which has a higher affinity with component (a) than component (b), is further added, component (c) is adsorbed on the surface of component (a), and component (b) is adsorbed. become less likely to be Therefore, component (a) can be uniformly dispersed in the ink composition. From the above, it is considered that the dispersion stability of component (a) can be further improved while maintaining the writing performance, thereby further improving the storage stability of the ink composition.

The ratio of the mass of component (c) to the mass of component (a) is preferably 1 to 40%, more preferably 5 to 35%.

The content of component (c) is 0.1 to 10% by weight, more preferably 0.3 to 5% 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. It is also possible to contain two or more types of compounds represented by formula (A) (or formula (B)).

(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.

(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 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 are included, and the content of water-soluble organic solvents is determined based on the total weight of the ink composition. The amount is preferably 0.1 to 30% by weight, more preferably 0.1 to 20% by weight, based on .

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. Note that the above-mentioned component (c) is not included in the surfactant herein. 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.

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.

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. .

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.

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, if more consideration is given, 0.05 to 2.0% by mass is preferable, and 0.1 to 1.5% by weight is particularly preferable.

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.

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 total mass of 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 because it improves 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, because if the nitrogen-containing resin particles have an amino group or an imino group, a stable agglomerated structure can be easily maintained for a long period of time, and ink leakage can be easily suppressed. 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 mass 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/cm2=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 170≦A/B≦300. 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.
Further, the ink composition according to the present invention is prepared by mixing component (a) and component (c) to form a dispersion state, and then adding other components to improve dispersion stability. Further improvements can be made.

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.
・Coloring agent (component (a)): Pigment Blue 15 6% 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) 0.3% by mass
・Dispersant (component (c)): Polyoxyalkylene isodecyl ether (Daiichi Kogyo Seiyaku Co., Ltd., HLB value 14.7) 1.5% by mass
・Water (component (d)): 68.87 parts by mass of ion-exchanged water ・Water-soluble organic solvent: 15% by mass of diethylene glycol
・Phosphate ester surfactant: "Plysurf A215C" (Daiichi Kogyo Seiyaku Co., Ltd., HLB value 11.5) 1% by mass
・pH adjuster: triethanolamine 2% by mass
・Rust inhibitor: benzotriazole 0.3% by mass
・Preservative: 1,2-benzisothiazolin-3-one 0.03% by mass
・Polysaccharide: Dextrin (mass average molecular weight 30,000, Sandek series, Sanwa Starch Industries Co., Ltd.) 2% by mass
・Wetting agent: urea 3% by mass

A dispersion was prepared by mixing a colorant, a dispersant, and water. Then, materials other than the acrylic acid copolymer were added to the dispersion, and the mixture was stirred with a disper to prepare a base ink. While heating the prepared base ink, 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.

<Examples 2 to 9, Comparative Examples 1 to 4>
Ink compositions of Examples 2 to 9 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1 except that component (c) was changed to the compound shown in Table 1.

Each of the ink compositions obtained above was placed in a sealed glass test tube with a diameter of 15 mm. The samples immediately after preparation and those left at room temperature for 7 days after preparation were collected on slide glasses and observed using an optical microscope. The dispersion stability of the ink composition was evaluated using the following evaluation criteria. The evaluation was as summarized in Table 1.
A: Good condition with no aggregates observed and uniformly dispersed.
B: A slight amount of aggregate was observed, but it was at a level that caused no practical problems.
C: Aggregates were observed, and the level was of practical concern.
D: Aggregates were confirmed and many coarse particles were observed.

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. When writing was performed using the obtained ballpoint pen as a test ballpoint pen, good handwriting was obtained with all the compositions of the examples, with good color development and no skipped lines or fading.

Claims (8)

(a) 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 a linear or branched alkyl group having 1 to 5 carbon atoms)
The repeating unit indicated by
A non-crosslinked acrylic acid copolymer consisting of
(c) The following formula (A):
(In the formula,
R ^A1 is each independently hydrogen, a methyl group, or an ethyl group,
R ^A2 is a linear or branched alkyl group having 10 to 22 carbon atoms, and xa is an integer of 5 to 25)
An aqueous ballpoint pen ink composition comprising a dispersant, which is a compound represented by the formula and having an HLB value of 12 to 15, and (d) water. R ^A1 is hydrogen or a methyl group,
The ink composition according to claim 1, wherein R ^A2 is a decyl group, an isodecyl group, or a tridecyl group, and xa is from 7 to 15. The ink composition according to claim 1 or 2, wherein the R ³ is a methyl group or an ethyl group. Any one of claims 1 to 3, wherein in the copolymer, the ratio of the number of repeating units of formula (i) to repeating units of formula (ii) is 1:0.1 to 1:5 in terms of number ratio. The ink composition according to item (1). The ink composition according to any one of claims 1 to 4, wherein the amount of the copolymer blended is 0.1 to 2% by mass based on the total mass of the composition. The ink composition according to any one of claims 1 to 5, further comprising a polysaccharide. The ink composition according to claim 6, wherein the polysaccharide is dextrin. An aqueous ballpoint pen containing the composition according to claims 1 to 7.