JP2020100730A - Aqueous ink composition for writing instruments - Google Patents

Abstract

To provide an aqueous ink composition for writing instruments that can improve writing dryability.SOLUTION: The present invention provides an aqueous ink composition for writing instruments containing water, a colorant, and an amide compound having a specific structure, and a writing instrument including the same.SELECTED DRAWING: None

Description

The present invention relates to a water-based ink composition for writing instruments. More specifically, it relates to a water-based ink composition for a writing instrument which is excellent in handwriting dryness.

The main solvent of the water-based ink composition for writing instruments is water. Therefore, for example, if the state where the pen tip of the water-based ballpoint pen is exposed to the atmosphere continues, water evaporates from the pen tip, the ink viscosity of the portion increases, and the handwriting may be faint. Therefore, in order to suppress the evaporation of water in the ink composition, it is common practice to add a polyhydric alcohol solvent such as glycerin or ethylene glycol. Although this method can suppress the drying of the pen tip, it takes time to completely dry the obtained handwriting. At this time, if the handwriting that is not dried is touched, the writing surface or the handwriting itself may become dirty.

On the other hand, it has been studied to prevent the writing surface and the like from being soiled by lowering the surface tension of the ink composition and improving the penetrability into a writing target such as a paper support. For example, many proposals have been made to add a specific alcohol or a specific surfactant to an ink composition. However, further improvement is desired to improve the penetrability and handwriting dryness of the ink composition.

JP2012-77102A

The present invention provides an ink composition having improved penetrability into a writing object and excellent handwriting dryness. Furthermore, the present invention provides a writing instrument using the same.

（式中、
Ｒ^１は、炭素数１〜６の、直鎖または分岐の、アルキル基であり、かつ
Ｒ^２およびＲ^３は、それぞれ独立に、水素、または炭素数１〜４の、直鎖もしくは分岐の、アルキル基である）
を含んでなる、筆記具用水性インキ組成物であって、
前記アミド化合物の含有量が、前記組成物の総質量を基準として、１〜３５質量％であることを特徴とするものである。 The aqueous ink composition for a writing instrument according to the present invention,
water and,
A colorant,
An amide compound represented by the formula (1),

(In the formula,
R ¹ is a linear or branched alkyl group having 1 to 6 carbon atoms, and R ² and R ³ are each independently hydrogen or a linear or branched alkyl group having 1 to 4 carbon atoms; It is an alkyl group)
A water-based ink composition for a writing instrument, comprising:
The content of the amide compound is 1 to 35 mass% based on the total mass of the composition.

A writing instrument according to the present invention is characterized by containing the above water-based ink composition.

When the ink composition according to the present invention is used, the penetrability of the composition into a writing target is improved, and as a result, the dryness of the surface of the handwriting can be improved. By using such an ink composition, stains on handwriting are prevented.

Aqueous ink composition for writing instruments The aqueous ink composition for writing instruments according to the present invention (hereinafter sometimes referred to as "ink composition") comprises water, a colorant, and an amide compound having a specific structure.

<Water>
The water used in the present invention is not particularly limited, and for example, ion-exchanged water, ultrafiltered water, distilled water or the like can be used. The ink composition of the present invention contains water as a main solvent. The content of water is 50 to 95% by mass, based on the total mass of water in the ink composition, the amide compound represented by the formula (1), and the water-soluble organic solvent described below, which is optionally contained. It is preferably 60 to 90% by mass.

<Colorant>
The colorant used in the present invention is not particularly limited, such as dyes and pigments, and can be appropriately selected and used.

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 thereof include various dyes such as acid dyes, basic dyes, reactive dyes, direct dyes, disperse dyes and food dyes, and these can be used alone or in combination of two or more kinds. The content of the dye is preferably 0.1 to 20% by mass, and 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. I. Acid Red 51, C.I. I. Acid Red 52, C.I. I. Acid Red 87, C.I. I. Acid Red 92, C.I. I. Acid Red 289, C.I. I. Acid Orange 10, C.I. I. Acid Yellow 3, C.I. I. Acid Yellow 7, C.I. I. Acid Yellow 23, C.I. I. Acid Yellow 42, C.I. I. Acid Green 3, C.I. I. Acid Green 16, C.I. I. Acid Blue 1, C.I. I. Acid Blue 9, C.I. I. Acid Blue 22, C.I. I. Acid Blue 90, C.I. I. Acid Blue 239, C.I. I. Acid Blue 248, C.I. I. Acid Baolet 15, C.I. I. Acid Violet 49, C.I. I. Acid Black 1, C.I. I. Acid Black 2, and basic dyes include C.I. I. Basic Orange 2, C.I. I. Basic Orange 14, C.I. I. Basic Green 4, C.I. I. Basic Blue 9, C.I. I. Basic Blue 26, C.I. I. Basic Violet 1, C.I. I. Basic Violet 3, C.I. I. Basic Violet 10, direct dyes include C.I. I. Direct Red 28, C.I. I. Direct Yellow 44, C.I. I. Direct Blue 86, C.I. I. Direct Blue 87, C.I. I. Direct Violet 51, C.I. I. Direct Black 19, and as food dyes, C.I. I. Food Yellow 3, C.I. I. Food Black 2 and the like can be mentioned.

Examples of the pigment that can be used in the present invention include inorganic, organic and processed pigments. Specifically, carbon black, aniline black, ultramarine blue, yellow lead, titanium oxide, iron oxide, phthalocyanine-based, azo-based, Examples include quinacridone-based, quinophthalone-based, triphenylmethane-based, perinone-based, perylene-based, dioxazine-based, aluminum pigments, pearl pigments, fluorescent pigments, phosphorescent pigments, and complementary color pigments. In addition, a microcapsule pigment in which a colored body obtained by dispersing a pigment as a colored resin particle in a medium is encapsulated or solid-solved in a shell made of a resin wall film forming substance by a known microencapsulation method, liquid crystals, A microcapsule pigment containing a functional material such as a reversible thermochromic composition or a photochromic material may be used. Further, colored resin particles in which a pigment is covered with a transparent or translucent resin or the like, or colored resin particles or colorless resin particles colored with a pigment or a dye can be used. You may use these dyes and pigments individually or in combination of 2 or more types. The content is preferably 1 to 30 mass% based on the total mass of the ink composition.
Further, conventionally, since the pigment is dispersed in the ink composition, the penetrability to a writing target tends to be poor as compared with the dye type, and it is difficult to improve the handwriting dryness. However, in the present invention, handwriting dryness can be improved even when a pigment is used as a colorant. Further, by using a surfactant described below, the handwriting dryness can be further improved. Furthermore, the pigment is excellent in water resistance and light resistance, and good color development can be obtained. From the above, it is preferable to use a pigment as the colorant.

式中、
Ｒ^１は、炭素数１〜６の、直鎖または分岐の、アルキル基であり、かつ
Ｒ^２およびＲ^３は、それぞれ独立に、水素、または炭素数１〜４の、直鎖もしくは分岐の、アルキル基である。 <Amide compound>
The amide compound used in the present invention is represented by the formula (1).

In the formula,
R ¹ is a linear or branched alkyl group having 1 to 6 carbon atoms, and R ² and R ³ are each independently hydrogen or a linear or branched alkyl group having 1 to 4 carbon atoms; It is an alkyl group.

Preferably, R ¹ is a linear alkyl group having 1 to 4 carbon atoms, and R ² and R ³ are both methyl groups.
R ¹ is more preferably methyl or butyl, and even more preferably methyl.

The content of the amide compound represented by the formula (1) may vary depending on the type and content of other additives, but is 1 to 35 mass% based on the total mass of the ink composition. If the amount is less than 1% by mass, the effect is insufficient. If the amount is more than 35% by mass, the amount of the solvent becomes too large, the solubility of various components contained in the ink composition becomes too low, and the dispersion of pigments, resin particles, etc. Stability tends to be compromised. It is preferably 1 to 30% by mass, more preferably 3 to 30% by mass, and particularly preferably 10 to 30% by mass.

Although not bound by theory, it is considered as follows. The main solvent of the water-based ink composition of the present invention is water, and water is known as a characteristic solvent in which a plurality of water molecules have a cluster structure due to a strong hydrogen bond. Water is a low molecular weight substance with a simple chemical structure, but due to its strong hydrogen bonds and cluster structure, it has high surface tension and high heat capacity, and although it is a low molecular weight substance, it is difficult to penetrate and is hard to volatilize. Known as a solvent. It is considered that the amide compound represented by the formula (1) used in the present invention acts so that the amide group contained in the structure effectively breaks the hydrogen bond of water and has the effect of refining the cluster structure. .. Therefore, it is considered that the surface tension is lowered and the permeability is improved. Further, it is considered that the fineness of the cluster structure improves the volatility and more effectively improves the handwriting dryness. For the above reason, the penetrability of the ink composition into the writing target is improved by containing the amide compound of the formula (1) used in the present invention in a specific amount, and as a result, the handwriting dryness becomes remarkable. It is supposed to be improved.

<Other additives>
The ink composition according to the present invention can be used for various writing instruments such as a fountain pen, a ballpoint pen, a writing pen, a calligraphy pen, and various marking pens. Depending on the use of a writing instrument, a water-soluble organic solvent, a humectant, a surfactant, a lubricant, a polysaccharide, a shear thinning agent, and a pH for the purpose of improving the physical properties and functions of the ink within a range that does not impair the performance of the present invention. It may contain various additives such as a regulator, a rust preventive, a preservative, a water-soluble resin, and organic resin particles.

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 the water-soluble organic solvent include (i) ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, or glycols such as glycerin, (ii) methanol, ethanol, 1-propanol, 2-propanol, isopropanol, isobutanol, t. -Butanol, propargyl alcohol, allyl alcohol, 3-methyl-1-butyn-3-ol, alcohols such as ethylene glycol monomethyl ether acetate and other higher alcohols, and (iii) ethylene glycol monomethyl ether, ethylene glycol mono Examples thereof include glycol ethers such as ethyl ether, 3-methoxybutanol, and 3-methoxy-3-methylbutanol. The content of the water-soluble organic solvent 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.
When the ink composition according to the present invention contains the above water-soluble organic solvent, the effect of the present invention may be obtained even if the content of the amide compound is relatively small. In order to obtain such an effect, the total content of the amide compound and the water-soluble organic solvent is preferably 1 to 45 mass% based on the total mass of the ink composition. For example, even if the content of the amide compound is reduced to about ½, a sufficient permeability improving effect may be obtained by using a water-soluble organic solvent such as glycols together. However, the water-soluble organic solvent alone does not exert the effect of the amide compound. Therefore, since the content of the amide compound is generally preferably large, the mass of the amide compound based on the total mass of the amide compound and the water-soluble organic solvent is preferably 10% by mass or more, and more preferably Is 30% by mass or more, and more preferably 70% by mass or more.

The ink composition according to the present invention may contain a humectant such as urea or sorbit in addition to the above water-soluble organic solvent for the purpose of preventing water evaporation. In the present specification, the above water-soluble organic solvent is not included in the humectant. The content of the moisturizing agent is preferably 0.1 to 10% by mass, and 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, and examples thereof include nonionic, anionic and cationic surfactants. Further, a surfactant having an acetylene bond in the structure, a silicone-based surfactant, and the like are also included.

In the present invention, an ink composition having more preferable properties can be obtained by containing a specific surfactant and a specific water-soluble organic solvent. The surfactant contained in the ink composition can remarkably reduce the surface tension of the interface surface such as a gas-liquid interface or a liquid interface by arranging the surfactant molecules at the interface. Further, since the water-soluble organic solvent can break the hydrogen bond of water and reduce the surface tension, the surface tension of the entire ink composition can be lowered regardless of the interface or the inside of the solvent. A synergistic effect can be obtained by combining an amide compound having a different action mechanism as described above and a surfactant. In particular, by combining the specific amide compound used in the present invention and a surfactant having a specific acetylene bond in the structure or a specific silicone-based surfactant, an ink composition having excellent handwriting dryness can be obtained.

A surfactant having an acetylene bond in the structure or a silicone-based surfactant may be included in order to further improve the handwriting dryness.

The surfactant having an acetylene bond in the structure used in the ink composition according to the present invention preferably has an ethylene oxide addition mole number of 10 or less.
The surfactant having an acetylene bond in which the number of moles of ethylene oxide added is 10 or less is a surfactant having an acetylene bond to which ethylene oxide is added in the structure, and the number of moles of ethylene oxide added to the surfactant is ethylene oxide. The number is 10 or less. For example, an acetylene glycol-based surfactant having an ethylene oxide addition mole number of 10 or less and an acetylene alcohol-based surfactant having an ethylene oxide addition mole number of 10 or less can be mentioned.
The surfactant having an acetylene bond in which the number of moles of ethylene oxide added is 10 or less in the structure can remarkably improve the penetrability to the writing target. Therefore, the ink composition containing the surfactant having an acetylene bond in the structure can quickly penetrate into the paper, and thus the handwriting formed on the surface of the writing target is completely dried. The time until the stroke is shortened, and when the handwriting part is rubbed, it is possible to prevent the composition from adhering to the part where there is no handwriting, and to prevent the composition of the handwriting part from being removed. Becomes

The reason for this is not clear, but the surfactant having an acetylene bond in which the number of moles of ethylene oxide added is 10 or less in the structure exhibits a suitable balance between hydrophobicity and hydrophilicity for exerting a penetrating effect. It is believed that there is. Considering the improvement of the effect of the surfactant having an acetylene bond in the structure, the number of moles of ethylene oxide added is preferably 8 or less. Further, 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, it is possible to prevent the solubility from being lowered, and it is possible to prevent the effect of the surfactant from being deteriorated over time due to a state in which it is difficult to stably exist in the ink composition.
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 the ink is important in order to instantaneously control the surface tension associated with the writing operation, so-called dynamic surface tension, and to obtain rapid penetrability into the writing target. In order to control the surface tension in a gas-liquid interface rapidly, and to control the surface tension instantaneously and effectively under dynamic conditions, it is possible to use a surfactant having a specific structure. An ink composition having excellent handwriting dryness can be obtained.

In addition, the surfactant having an acetylene bond in the structure, in which the number of moles of ethylene oxide added is 10 or less, not only improves the handwriting drying property, but also has the effect of improving the writing feel, such as providing a smooth writing feel. .. This is because the ink composition contains a surfactant having an acetylene bond in the structure, so that the lubricity between the ball and the ballpoint pen tip of the ballpoint pen is improved and the abrasion of the ball seat is suppressed. This is because it can be done.
The ink composition according to the present invention containing a surfactant having an acetylene bond in its structure can contain other lubricants. It is preferably used in combination with an acid ester surfactant.

Further, the surfactant having an acetylene bond in the structure used in the present invention may further have propylene oxide added thereto. Considering further improvement in handwriting dryness and stability over time of the ink composition, in the present invention, a surfactant having an acetylene bond to which ethylene propylene oxide and propylene oxide are further added in the structure is selected. It is preferable to use. This is because when the surfactant having an acetylene bond in the structure is added with two of ethylenelen oxide and propylene oxide, the balance between hydrophobicity and hydrophilicity is more preferably maintained.
The ratio of the number of moles of ethylene oxide added and the number of moles of propylene oxide added is such that when the surfactant having an acetylene bond in the structure is kept in a suitable balance of hydrophobicity and hydrophilicity and further improvement in handwriting dryness is considered, ethylene oxide is added. Addition mole number: Propylene oxide addition mole number=1:1 to 5:1 is preferable.

Further, in consideration of the arrangement property to the gas-liquid interface, the total number of moles of ethylene oxide addition and the number of moles of propylene oxide addition is preferably 10 or less. If the number of added moles is too large, the surfactant molecule becomes too long, and steric hindrance is likely to occur at the gas-liquid interface during alignment, but if the total number of added moles is 10 or less, the surfactant It is particularly preferable since the balance between hydrophobicity and hydrophilicity can be maintained in a suitable manner, and the effect in consideration of the influence of steric hindrance at the time of arrangement on the gas-liquid interface can be obtained.
Further, in consideration of the improvement in handwriting dryness and the stability of the ink composition over time, a surfactant having an acetylene bond in which the ethylene oxide addition mole number is 5 and the propylene oxide addition mole number is 2 in the structure 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. When the HLB value of the surfactant having an acetylene bond in the structure is 3 or more, it can exist stably without being left undissolved in water as a solvent, and the effect can be obtained initially and over time, which is preferable. , 14 or less, it is easy to be arranged in the vicinity of the gas-liquid interface due to hydrophobicity, and it is possible to obtain the effect brought by the surfactant such as the improvement of the handwriting drying property in a small amount and instantly, which is preferable.

Examples of the surfactant having an acetylene bond in the structure include, for example, an acetylene alcohol-based surfactant, an acetylene glycol-based surfactant, and the like, which improve the penetrability into a writing target and improve the handwriting dryness. Considering that it is easy to do, it is preferable to use an acetylene glycol-based surfactant.

Specific examples of the surfactant having an acetylene bond in the structure include Olfine series, Surfynol series, Dynol series and the like (all manufactured by Nisshin Chemical Industry Co., Ltd.).

Silicone-based surfactants are stable in the ink composition by being suitable by balancing the Si skeleton in the structure, hydrophobic groups such as propylene oxide and hydrophilic groups such as ethylene oxide, and the surfactants Molecules can be easily arranged at the gas-liquid interface, so that the surface tension of the ink composition can be quickly controlled during writing to improve the penetrability, and both handwriting dryness and stability over time of the ink composition can be achieved. it can. Among the silicone-based surfactants, the mass average molecular weight is preferably 500 to 3,000. This is because when the mass average molecular weight of the above-mentioned surfactant is more than 3,000, the molecules of the silicone-based surfactant become too large and the arrangement at the gas-liquid interface tends to be slow. Therefore, the handwriting dryness may not be sufficient. On the other hand, when the mass average molecular weight is 3,000 or less, the molecules of the silicone-based surfactant become relatively small, so that the molecules of the surfactant tend to be quickly arranged at the gas-liquid interface. Easy to improve the drying property. Further, when the mass average molecular weight is less than 500, it is difficult to obtain desired handwriting dryness. Considering the above effect more, the mass average molecular weight is preferably 500 to 3,000, more preferably the mass average molecular weight is 500 to 2,000, and further considering, the mass average molecular weight is 1. It is preferably 000 to 2,000.

Further, the silicone-based surfactant not only improves the handwriting dryness, but also has the effect of improving the writing feel, such as providing a smooth writing feel. This is because the ink composition contains the silicone-based surfactant, so that the lubricity between the ball and the ballpoint pen tip of the ballpoint pen is improved, and the abrasion of the ball seat can be suppressed. is there.
It should be noted that the ink composition according to the present invention containing a silicone-based surfactant may contain other lubricants, and particularly, among the lubricants, the phosphoric acid ester-based surfactants described later are also included. It is preferable to use together with.

Regarding the solubility parameter (hereinafter referred to as SP value) of the silicone-based surfactant, the SP value is preferably 8 to 13 in consideration of the handwriting drying property, and further considered, the SP value is 9 to 12. Are preferred, and SP values of 10-11 are particularly preferred. The SP value of water, which is the main component of the solvent, is 23.4, and if the SP value of the silicone-based surfactant is too close, it will be stabilized in the dissolved state, so the alignment of the activator molecules on the gas-liquid interface is prompt. It tends to be difficult to do. When the SP value is in the above range, the activator molecules are easily arranged at the gas-liquid interface quickly, and the stability in the ink composition is also obtained, which is preferable.

As for the silicone-based surfactant, specifically, Silface series (manufactured by Nissin Chemical Industry Co., Ltd.), BYK series (manufactured by Big Chemie Co., Ltd.), Silsoft Spread series, Coatosil series (all manufactured by Momentive Performance Materials, Inc. ) And the like. You may use these individually or in mixture of 2 or more types.

Further, the total content of the surfactant having an acetylene bond in the structure or the silicone-based surfactant is more preferably 0.01 to 3.0% by mass based on the total mass of the ink composition. This is because when the total content of the surfactant having an acetylene bond in the structure or the silicone-based surfactant is less than 0.01% by mass, it is difficult to obtain desired handwriting dryness, and 3.0% by mass is preferable. This is because if it exceeds, the temporal stability of the ink composition is likely to be affected. Furthermore, if further considered, 0.05 to 2.0 mass% is preferable, and 0.1 to 1.5 mass% is particularly preferable.

Further, the ink composition according to the present invention may further include a phosphate ester surfactant. In addition to the effect of improving the dispersibility of the ink composition, the phosphate ester-based surfactant also functions as a lubricant when the ink composition is used in a ballpoint pen. The lubricant improves lubricity between the ball and the ball-point pen tip of the ball-point pen, smoothes the rotation of the ball, suppresses wear of the ball seat, and improves writing quality. The phosphoric acid ester-based surfactant having a phosphoric acid group used in the present invention has a property that the phosphoric acid group is easily adsorbed to a metal, and thus improves the lubricity and suppresses the abrasion of the ball seat and the 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 quality can be realized. However, since this surfactant contributes not only to lubricity but also to improvement of dispersibility, it also works effectively when the ink composition is used for writing instruments other than ballpoint pens.

Furthermore, the phosphate ester type surfactant also has the effect of adjusting the surface tension. Therefore, particularly in a writing instrument that includes a comb groove-shaped ink flow rate adjusting member to be described later and has a supply mechanism that interposes the ink flow rate adjusting member and supplies the ink composition to the pen tip, excellent wetting of the ink flow rate adjusting member is achieved. It is preferable because it exhibits a property. Therefore, the ink composition according to the present invention is also preferable for a fountain pen having a comb groove-shaped ink flow rate adjusting member, a marking pen, a felt-tip pen, a ballpoint pen, and the like.

Examples of the phosphoric acid ester-based surfactants include phosphoric acid ester-based surfactants such as linear alcohol-based, styrenated phenol-based, nonylphenol-based, and octylphenol-based surfactants. Among them, linear alcohol-based surfactants and styrenated phenol-based surfactants are included. It is preferable to use the phosphoric acid ester-based surfactant.

In the present invention, the phosphate ester surfactant has an HLB value of preferably 5 to 15, and more preferably 6 to 13. In the present invention, the alkyl group or alkylallyl group of the phosphate ester surfactant preferably has 6 to 30 carbon atoms, more preferably 8 to 18 carbon atoms, and 10 to 14 carbon atoms. Particularly preferred. This is because the straight-chain type phosphoric acid ester-based surfactant having a specific HLB value and carbon number has excellent writing stability such as stable production of good handwriting with improved line skipping and blurring. This is because the dispersion effect can be synergistically improved with the dispersant used in the present invention, and at the same time, the lubricating effect can be provided.

In the present invention, the HLB value of the phosphoric acid ester-based surfactant means the HLB value of the raw material nonionic surfactant of the phosphoric acid ester-based surfactant, and the value calculated from the Kawakami method. And is calculated by the following formula.
HLB=7+11.7 log (Mw/Mo), (Mw; molecular weight of hydrophilic group, Mo; molecular weight of lipophilic group)

Specific examples of the phosphoric acid ester-based surfactant include Plysurf series (Daiichi Kogyo Seiyaku Co., Ltd.), and as the linear alcohol-based phosphoric acid ester-based surfactant, Plysurf A212C, Examples thereof include A208B, A213B, A208F, A215C, A219B, and A208N. As the styrenated phenolic phosphate ester surfactant, Plysurf AL can be mentioned, and as the nonylphenol type, Plysurf. 207H, A212E, and A217E, and Plysurf A210G as an octylphenol system.

When the ink composition according to the present invention contains a phosphoric acid ester-based surfactant, the content thereof is preferably 0.1 to 2.0 mass% based on the total mass of the ink composition, and 0.5 to 1.5. More preferably, it is mass %.
The ballpoint pen can realize excellent writing performance by forming a suitable film of the ink composition between the ball and the ball seat at the pen tip. Since the phosphate ester-based surfactant effectively acts to form such a film, it is preferable to use the phosphate ester-based surfactant in the ink composition used for the ballpoint pen.
When a phosphate ester type surfactant is used in the ink composition according to the present invention, the phosphate ester type surfactant acts as an extreme pressure agent. In general, an extreme pressure agent is a substance that easily reacts on the metal surface when the temperature rises due to frictional heat, forms a solid soft film, and has the effect of enhancing lubricity, and it has a good effect under high writing pressure. It is added to obtain a writing feel. The phosphate group of the phosphate ester, which is a phosphate-based surfactant, is adsorbed on the metal surface and exerts an extreme pressure action, so that good writing feeling can be obtained even under high writing pressure.
That is, the lubricating effect of the phosphoric acid ester-based surfactant is that the phosphoric acid group is adsorbed on the ball receiving seat of the chip and each metal surface of the ball, the hydrophobic group extends into the ink, and the physical property of the ball and the ball seating is increased. It is thought to be manifested by the inhibition of various contacts. Therefore, it is considered that the cushioning effect of the hydrophobic groups extending between the tip and the ball provides a lubricating effect preferable as a ballpoint pen, that is, a smooth and soft writing feeling.
The phosphoric acid ester-based surfactant can be used after being appropriately neutralized with an alkaline substance such as amines and alkali metals.
On the other hand, since there is no friction between the ball and the ball seat in the fountain pen or the marking pen, the ink composition used in the fountain pen or the marking pen may not require the phosphate ester surfactant.

In addition to the above-mentioned surfactants, examples of usable lubricants include alkylbenzene sulfonic acid, amino acids, N-acyl amino 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 salts thereof and the like.

When the ink composition according to the present invention is used for a fountain pen or a marking pen, an ink reversal material capable of maintaining appropriate wettability with respect to the inner wall of the ink tank is used in order to improve ink transfer by reversing the ink tank. be able to. Ink reversal materials include polyether amines, glycyrrhizic acid and/or its salts, oligomeric esters of polyglycerin and dicarboxylic acids, polyoxyethylene/polyoxypropylene alkyl ethers, polyoxyethylene/polyoxypropylene block polymers, etc. The content is preferably 0.01 to 10 mass% based on the total mass of the ink composition.
In addition, the ink reversal material can maintain appropriate wettability not only with the ink tank but also with the ink flow rate adjuster. Therefore, the function of the ink flow rate adjuster can be sufficiently obtained, and the ink dischargeability from the pen tip can be maintained satisfactorily, and excess ink can be applied to the comb-shaped ink retaining member, so-called pen core. Since the ink can flow in smoothly, it is possible to suppress the ink dripping phenomenon.

The ink composition according to the present invention may include a polysaccharide. Polysaccharides bring about various effects, but mainly bring about effects such as adjustment of ink viscosity, addition of shear thinning property, and improvement of dry-up resistance as described later. Specific examples thereof include dextrin, xanthan gum, welan gum, succinoglycan, guar gum, locust bean gum, λ-carrageenan, a cellulose derivative and diutan gum.

When the ink composition contains a component that can exist in a state insoluble in water, which is the main solvent such as a pigment, the water evaporates at the pen tip of the writing instrument that contains the ink, and the ink dries and solidifies to form an ink flow path. May get stuck. When such a phenomenon occurs, the ink dischargeability is affected, and although the writing instrument has a residual amount of ink, it may not be possible to write again. Therefore, it is preferable to improve the dry-up resistance. Therefore, it is necessary to consider the improvement of the dry-up resistance at the tip of the ballpoint pen, for example. Dextrin has the effect of forming a film on the pen tip and preventing evaporation of the solvent in the ink by the film. Therefore, the use of dextrin is effective because an ink composition having excellent dry-up resistance can be obtained.

The mass average molecular weight of dextrin is preferably 5,000 to 120,000. When it is 120,000 or more, the coating film formed on the pen tip is hard, and the handwriting tends to be faint when writing at the time of dry-up. On the other hand, if it is less than 5,000, it is difficult to give a viscosity change to the extent that it improves dispersion stability over time, and the hygroscopicity of dextrin tends to be high, and the film formed on the pen tip is soft and stable at the pen tip. It is difficult to maintain and it is difficult to suppress evaporation of the solvent in the ink. Considering further improvement of the above effects, it is preferable to use dextrin having a mass average molecular weight of 20,000 to 100,000.

The content of dextrin is preferably 0.1 to 5 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 the dry-up resistance tends to be insufficient, and if it exceeds 5% by mass, it tends to be difficult to dissolve in the ink. From the viewpoint of dissolution stability in ink, 0.1 to 3% by mass is preferable, and from the viewpoint of improvement of dry-up resistance, 1 to 3% by mass is most preferable.

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

Particularly when the ink composition according to the present invention is used in a ballpoint pen, it is preferable to use a shear thinning agent in order to adjust the ink viscosity. Keeps the viscosity of the ink composition high when it is standing, and it is easy to maintain a uniform and good dispersion state. At the time of writing, the shearing force due to the rotation of the ball at the tip of the tip is applied to the ink composition, which lowers the viscosity of the ink composition. This is because good ink dischargeability can be obtained, and handwriting with good color development can be obtained without bleeding. In some cases, an ink composition that requires a relatively low viscosity, for example, an ink composition used for a fountain pen or a marking pen, preferably does not contain a shear thinning agent. With such a configuration, it is possible to secure the ink flow and improve the writability.

Examples of the shear thinning agent include non-crosslinked acrylic acid polymers and crosslinked acrylic acid polymers in addition to the above-mentioned polysaccharides. The shear thinning agent may be used alone or in combination of two or more kinds.

（式中、Ｒ^１１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^１２は、水素またはメチル基であり、かつ
Ｒ^１３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
を含んでなる非架橋型アクリル酸共重合体を用いることが好ましい。 The non-crosslinked acrylic acid polymer has the following formula (i):

(In the formula, R ¹¹ is hydrogen or a methyl group.)
And the repeating unit
The following formula (ii):

(In the formula,
R ¹² is hydrogen or a methyl group, and R ¹³ is an alkyl group having 1 to 5 carbon atoms and having a straight chain or a side chain)
It is preferable to use a non-crosslinked acrylic acid copolymer containing a repeating unit represented by:

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

Further, R ¹³ of the non-crosslinked acrylic acid copolymer is an alkyl group having a straight chain or a side chain having 1 to 5 carbon atoms, but when the carbon number is larger than 5, steric hindrance of the alkyl group becomes large, The cohesive force between the alkyl groups is reduced. Further, when the carbon number is larger than 5, the hydrophobicity of the alkyl group increases, so that separation or precipitation is likely to occur in a part of the alkyl group, which may cause 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 cohesive force between the alkyl groups is high, and a physical bond is formed to form an intermolecular network, which is preferable. Further, when the alkyl group is linear, steric hindrance is smaller than that of an alkyl group having a side chain, which is preferable. In particular, when R ¹³ is a methyl group having 1 carbon atom or an ethyl group having 2 carbon atoms, the hydrophobicity is not large, so that it is possible to design a relatively large introduction amount of the alkyl group into the molecule. By increasing the amount of introduction of the alkyl group, it becomes possible to arrange many physical bonding points between the alkyl groups, and it is possible to obtain effects such as higher viscosity at rest and lower viscosity at shear, Particularly preferred.

The ratio of the number of repeating units of formula (i) to the number of repeating units of formula (ii) is a number ratio of 1:0.05 to 1:10, more preferably 1:0.1 to 1:5, and It is preferably 1:0.3 to 1:3. If the ratio of the repeating units of the formula (ii) is too small, the physical bonding effect of the alkyl group becomes insufficient, and the viscosity increase or viscosity gradient between standing and shearing tends to be small, and the ratio of the carboxylic acid ester is large. If it is too much, the hydrophobicity of the copolymer increases, so that some separation or precipitation may occur. Within this range, both high static viscosity and low shear viscosity can be achieved at the same time, which is particularly preferable.

The mass average molecular weight of the non-crosslinked acrylic acid copolymer is preferably 1,000 or more, more preferably 5,000 or more, still more preferably 20,000 or more. If it is smaller than the above range, it may be difficult to develop a sufficient viscosity. Further, it is preferably 1,000,000 or less, more preferably 700,000 or less, and further preferably 600,000 or less. If it is larger than the above range, the viscosity at high shear may be too high. Here, the mass average molecular weight is a polystyrene equivalent mass average molecular weight, and can be measured by gel permeation chromatography with polystyrene as a reference.

The content of the non-crosslinked acrylic acid copolymer may be 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 mass, and more preferably in the range of 0.1 to 2% by mass. When it is larger than this range, the viscosity at rest becomes high, the dispersion stability of the ink composition is improved, and the handwriting does not bleed, but the ink viscosity at shearing tends to be slightly high, and the writing performance is slightly deteriorated. There is a tendency to decrease. If it is less than this range, the ink viscosity at the time of shearing is lowered, and the handwriting is not blurred or broken, but the handwriting tends to be blurred. Within the above range, while maintaining the dispersion stability of the ink composition, it does not cause scratches or line breaks when writing, the handwriting does not bleed, and excellent ink stability and writing performance are obtained. ,preferable.

When the ink composition according to the present invention contains a non-crosslinked acrylic acid copolymer, it may further contain a crosslinking agent. The cross-linking agent used in the present invention is a compound capable of forming a reversible physical cross-link with the above-mentioned non-cross-linking type acrylic acid copolymer, and is an alkyl ester of the non-cross-linking type acrylic acid copolymer. It is a compound capable of expressing intermolecular cohesive force due to groups and van der Waals. When the ink composition is in a stationary state, the cross-linking agent can form a cross-linking point by a physical bond with the alkyl group of the copolymer used in the present invention to form a strong network. It is a compound in which the physical bond at the cross-linking point is easily released when a shearing force is applied to an object.

Specific examples of the cross-linking agent 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. The effect can be obtained by using both a high-molecular compound containing an alkyl group and a low-molecular compound as the cross-linking agent, but the viscosity at shear tends to be lower when a low-molecular compound is used, and the cross-linking agent at standing and shear This is preferable because the viscosity gradient at that time can be increased. The alkyl group has 1 to 30 carbon atoms, preferably 1 to 22 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 having less steric hindrance, because the effect will be greater.

By using a non-crosslinked acrylic acid copolymer, the viscosity of the ink composition at shearing during writing becomes lower than that of a conventional crosslinked acrylic acid polymer, and thus the ink composition is composed of paper fibers or the like. It can be quickly permeated into the written object (for example, a paper support). When the ink composition further contains the above-mentioned surfactant having an acetylene bond or a silicone-based surfactant, the ink composition exhibits a synergistic effect with the effect of the non-crosslinked acrylic acid copolymer due to the penetration promoting effect. It is thought that the permeability to As a result, the above-mentioned components in the ink composition serve to lower the viscosity of the ink composition and to improve the penetrability, and the handwriting dryness becomes high.

When the ink composition according to the present invention is used in a ballpoint pen, the ink viscosity is preferably 500 to 5,000 mPa·s at a shear rate of 1.92 sec ⁻¹ in a 20° C. environment, and the ink viscosity is within the above numerical range. Within the range, ink flowability and dispersion stability are excellent, good ink dischargeability is obtained, and good handwriting without blurring or blurring of handwriting can be obtained. In particular, the ink viscosity is more preferably 1,000 to 3,000 mPa·s in consideration of good ink dischargeability from the pen tip of the ink composition.

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. Are listed. The content of the pH adjuster is preferably 0.1 to 25% by mass, and more preferably 5 to 20% by mass with respect to the ink composition.

Examples of the rust preventive agent include benzotriazole and its derivative, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, sodium thiosulfate, saponin, and dialkylthiourea.

As a preservative, 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 thereof include sodium 1-oxide, sodium 3-iodo-2-propynylbutyl carbamate 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 a combination of MIT and OIT because the antibacterial property is 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 compounding ratio of OIT and MIT is 1:1 to 10:1 by mass. preferable.

In addition, the ink composition according to the present invention may contain a water-soluble resin such as an acrylic resin, an alkyd resin, a cellulose derivative, polyvinylpyrrolidone, or polyvinyl alcohol as a water-soluble resin for the purpose of improving the scratch resistance of handwriting. it can. Further, the resin emulsion may include an emulsion containing an acrylic resin, a urethane resin, a styrene-butadiene resin, a polyester resin, a vinyl acetate resin, or the like.

The ink composition according to the present invention may contain organic resin particles for the purpose of suppressing the dripping of the ink. Examples of the 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. And nitrogen-containing resin particles containing a nitrogen atom in the chemical structure thereof, acrylic resin particles, styrene resin particles, epoxy resin particles, urethane resin particles, cellulose resin particles and the like. You may use these organic resin particles individually or in combination of 2 or more types.

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 a hydrocarbon compound and are likely to aggregate in water because they are non-polar, and this aggregate structure and the above-mentioned non-crosslinked acrylic acid copolymer are entangled with each other, 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 while suppressing ink leakage. Furthermore, since the olefin resin particles have a high melting temperature, they easily exist stably even in a high temperature environment, and when they are in a high pressure environment, they are easily deformed and are not easily modified. 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 a mixture thereof. Among these, polyethylene is preferably used from the viewpoints of suppressing ink leakage and improving writing quality, and specifically, low density polyethylene, high density polyethylene, low molecular weight polyethylene, modified polyethylene, modified high density polyethylene. And so on. Of these, low density polyethylene, low molecular weight polyethylene, and modified polyethylene are preferable in view of the effect of suppressing ink leakage. Especially, since low density polyethylene has a lower melting point and softer properties than other types of polyethylene, polyethylene particles adhere closely. It is preferable to use low-density polyethylene because it is easy to form, gaps between particles are less likely to occur, and ink is less likely to leak. Further, since low-density polyethylene is soft, it can be used preferably because it improves writing. The olefin-based resin particles may contain a material other than polyolefin, if necessary.

Among the nitrogen-containing resin particles, it is preferable to have an amino group or an imino group, because the presence of an amino group or an imino group makes it easy to have a stable aggregate structure for a long period of time and to easily suppress ink leakage. The nitrogen-containing resin particles having a functional group such as an amino group and an imino group include tertiary amine and quaternary amine.
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-linking structure, it is particularly excellent in strength, heat resistance, solvent resistance, etc., so it is stable without absorbing moisture in water-based ink, and therefore has excellent stability over time. Therefore, it is preferable. Furthermore, the stability of the nitrogen-containing resin particles themselves and the mutual hydrogen bonding between the nitrogen-containing resin particles facilitates the formation of an agglomerated structure for a long period of time, which makes it easy to stably suppress ink leakage. In particular, among the nitrogen-containing resin particles having a crosslinked structure, resin particles having a heterocyclic structure such as melamine/formaldehyde resin, benzoguanamine/formaldehyde resin, benzoguanamine/melamine/formaldehyde resin are more difficult to absorb moisture and are 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 an amide bond include nylon resins such as nylon 6 and nylon 12, polycarbonate polyurethane resin, polyether polyurethane resin, polyester polyurethane resin, urethane urea resin particles such as urethane urea resin. To be

Regarding the shape of the organic resin particles, a spherical shape or an irregular shape can be used, but spherical resin particles are preferable from the viewpoint of reducing frictional resistance. The spherical resin particles mentioned here are not limited to true spherical shapes, and may be substantially spherical resin particles, substantially elliptic spherical resin particles, or the like.

Further, the content of the organic resin particles is more preferably 0.01 to 10.0 mass% based on the total mass of the ink composition. This is because if the content of the 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 be strong, which affects the writing quality and dry-up performance. Because it is easy to come out. Furthermore, if further considered, 0.02 to 5.0 mass% is preferable, 0.03 to 1.0 is particularly preferable, and 0.05 to 0.5 mass% is most preferable.

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

<Writing instrument>
The aqueous ink composition for a writing instrument according to the present invention can be contained in various writing instruments. Such a writing instrument can form a handwriting on the surface by writing on a writing target such as a paper support, wood, or a cloth made of a hydrophilic organic material. The structure and shape of the writing instrument filled with the water-based ink composition for a writing instrument according to the present invention are not particularly limited, and conventional ones can be applied, and a fiber tip, a felt tip, a plastic tip, a ballpoint pen tip, or the like can be used as the pen tip. Can be used for various writing instruments such as a marking pen, a ballpoint pen, and a fountain pen using a metal nib.

Further, the writing instrument in which the ink composition according to the present invention can be used may be one in which the ink composition is directly filled, and an ink container or an ink storage which can be filled with the ink composition. It may have a body. Further, the ink container or the ink occlusion body may be an ink cartridge type writing instrument having a structure in which it can be removably attached to the writing instrument body.

Further, a writing instrument that can use the ink composition according to the present invention includes a cap-type writing instrument having a cap that covers the pen tip, and a retractable tip that can accommodate the pen tip in a knock-type, rotary-type, slide-type shaft cylinder, or the like. An example of a writing instrument is a ballpoint pen.

Further, the supply mechanism of the writing instrument which can use the ink composition according to the present invention is not particularly limited. For example, (mechanism 1) an ink guide core made of a fiber bundle or the like is provided as an ink flow rate adjusting member, Mechanism for supplying the composition to the pen tip, (Mechanism 2) Comb groove-shaped ink flow rate adjusting member, a mechanism for interposing this, and supplying the ink composition to the pen tip, (Mechanism 3) Ink flow rate by valve mechanism Examples thereof include a mechanism that includes an adjusting member and supplies the ink composition to the pen tip, and (Mechanism 4) a mechanism that directly supplies the ink composition to the pen tip without the ink flow rate adjusting member.
In particular, when an ink guide core made of fiber bundles like the mechanism 1 utilizing the capillarity is provided or when an ink flow rate adjusting member in the shape of a groove like the mechanism 2 is provided, the capillary force is effectively applied. Therefore, a low-viscosity ink composition is used, and the amount of ink discharged during writing tends to increase. Therefore, since it takes time to completely dry the handwriting, it is preferable that the handwriting drying property is excellent. The ink composition according to the present invention has a mechanism including an ink guide core or a comb groove-shaped ink flow rate adjusting member. When it has, it is used suitably.

When the specifications of the ball-point pen when the ball-point pen was filled with the water-based ink composition for a writing instrument according to the present invention, the ink consumption per 100 m of the water-based ball-point pen was A (mg) and the ball diameter was B (mm). , 150≦A/B≦500, and preferably 250≦A/B≦450. This is because by setting the above range, by making the ink consumption appropriate for the ball diameter, the ink fluidity becomes good, and by suppressing handwriting blurring, it is easy to obtain good handwriting. Is.

Regarding the ink consumption, a spiral of 5 test samples was used at a writing speed of 4 m/min under the conditions of 20° C., a writing paper JIS P3201 writing paper, a writing angle of 65°, and a writing load of 100 g. A writing test is performed, and the average value of the ink consumption per 100 m is defined as the ink consumption per 100 m. Further, the ball diameter is not particularly limited, but a ball of about 0.1 to 2.0 (mm) is generally used.

Regarding the specifications of the ball-point pen tip, the movable amount (clearance) of the ball in the ball-point pen tip in the vertical axis direction is preferably 20 to 50 μm, preferably 30 to 45 μm at the time of manufacturing or starting use of the ball-point pen. It is preferable. This is because in the above range, by properly adjusting the ink discharge amount and suppressing line skipping and blurring, it is easy to obtain good handwriting, and if the clearance is within the above range, The above ratio A/B is also easy to adjust.
The movable amount (clearance) of the ball of the ball-point pen tip in the vertical axis direction indicates the distance that the ball can move in the vertical axis direction of the ball-point pen tip body. Here, the movable amount generally increases with use because the ball and the ball seat wear due to use. Then, the movable amount is related to the ink ejection amount. Therefore, in general, the movable amount at the time of manufacturing or starting to use the ballpoint pen is set within the above range, and therefore, in order to achieve stable writing characteristics, within the above range until the end of use of the ballpoint pen. It is preferable to have.
When a ballpoint pen tip with a large clearance is used, the ink discharge amount increases and the handwriting density can be increased, but it is preferable that the handwriting dryness is excellent. Therefore, the ink composition according to the present invention is preferably used even when a ballpoint pen tip with a large clearance is used. When the ink discharge amount is large, it is preferable to include the above-mentioned organic resin particles for the purpose of preventing dripping.
When the ink composition according to the present invention is combined with such a ballpoint pen,
water and,
A colorant,
An amide compound represented by the formula (1) and a lubricant such as a phosphate ester-based surfactant, the content of which is 1 to 35 mass based on the total mass of the ink composition;
It is preferable to use an ink composition containing

Further, when the aqueous ink composition for a writing instrument according to the present invention is combined with a marking pen, the pen tip is not particularly limited, and may be, for example, a fiber tip, a felt tip, a plastic tip, or the like. It may be a mold, a chisel type, a brush pen type, or the like.
When the water-based ink composition according to the present invention is combined with such a marking pen,
water and,
A colorant,
It is preferable to use an ink composition containing an amide compound represented by the formula (1) and having a content of 1 to 35 mass based on the total mass of the ink composition.

Further, when the water-based ink composition for a writing instrument according to the present invention is combined with a fountain pen, a nib made of metal or ceramic, a shaft having a comb groove mechanism, or the like can be employed. Furthermore, the ink composition according to the present invention can be applied to a fountain pen which can be written by filling a replaceable cartridge or the like with the cartridge. When combining the water-based ink composition according to the present invention with such a fountain pen, based on the total mass of the ink composition,
water and,
A colorant,
An amide compound represented by the formula (1) and an ink reversible material, the content of which is 1 to 35 mass based on the total mass of the ink composition;
It is preferable to use an ink composition containing

<Method for producing ink composition>
The ink composition according to the present invention can be produced by any conventionally known method. Specifically, it can be produced by mixing required amounts of the respective components and mixing them with various stirrers such as a propeller stirrer, homodisper or homomixer, and various dispersers such as a bead mill.

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

<Example 1>
An ink composition was obtained by the following composition and method.
Water: ion-exchanged water 77.8% by mass
Coloring agent: carbon black 8.0% by mass
Amide compound: 3-methoxy-N,N-dimethylpropanamide 10.0% by mass
pH adjuster: triethanolamine 1.0% by mass
Antirust agent: benzotriazole 0.5 mass%
Preservative: 1,2-benzisothiazolin-3-one 0.2% by mass
Phosphate ester surfactant: Prysurf A215C (manufactured by Daiichi Kogyo Co., Ltd.) 1.0% by mass
Polysaccharide: Dextrin (mass average molecular weight 30,000, Sandeck series, Sanwa Starch Industry Co., Ltd.) 1.5% by mass

Water, a colorant, a pH adjuster, a rust preventive, an antiseptic, a phosphoric acid ester surfactant and dextrin were heated and stirred with a disper to prepare a base ink. Then, while heating the base ink, the base ink was sufficiently mixed and stirred using a homogenizer stirrer until a uniform state was obtained, and filtration was performed using filter paper to obtain an ink composition of Example 1.

<Example 2, Comparative Example 1>
0.5% by mass of Surfynol 2502 (manufactured by Nisshin Chemical Industry Co., Ltd.), which is an acetylene glycol-based surfactant, was added to the composition of Example 1 except that water was changed to 77.3% by mass. The ink composition of Example 2 was prepared in the same manner.
An ink composition of Comparative Example 1 was prepared in the same manner as the composition of Example 1 except that the amide compound was set to 0 and water was set to 87.8% by mass.

A ballpoint pen tip rotatably holding a 0.7 mm diameter cemented carbide ball with the ink compositions of Examples 1 and 2 and Comparative Example 1 (1.0 g). ) 30 μm) was filled inside the ink container to prepare a refill, and this refill was attached to a gel ink ballpoint pen (trade name: G-2) manufactured by Pilot Corporation to obtain a ballpoint pen. The obtained ballpoint pen was used as a test ballpoint pen, and the following handwriting dryness evaluation was performed.

The test ballpoint pen was handwritten on a commercially available report paper at room temperature, and the letters “Naga” were written. After 0, 3, 5, 10, and 30 seconds, the handwriting was rubbed in one direction with the thumb. The state of the handwriting at that time was visually confirmed, and the obtained results are shown in Table 1. The evaluation criteria are as follows.
A: Good handwriting was left without staining the surroundings.
B: Staining was slightly generated, but good handwriting was left.
C: Some stains were generated, but good handwriting was left.
D: The entire handwriting was stained.
E: Marked stains were generated on the entire handwriting.

The ink compositions of Examples 1 and 2 and Comparative Example 1 were sampled on a slide glass and observed with an optical microscope to evaluate the ink stability (microscope). Further, the appearance of each ink composition was visually observed to evaluate the ink stability (appearance). The obtained results are shown in Table 1. The evaluation criteria are as follows.
Ink stability A: No agglomerates were confirmed and they were uniformly dispersed.
B: A few agglomerates were confirmed, but it was in a good dispersed state.
C: Agglomerates were confirmed, but there was no problem in practical use.
D: Aggregates were confirmed, which was at a level at which there was practical concern.
Ink stability (appearance)
A: Good fluidity of the ink was obtained.
B: The viscosity of the ink was confirmed, but the fluidity was maintained.
C: Poor fluidity was confirmed due to gelation of the ink.

In Example 2, the acetylene glycol-based surfactant Surfynol 2502 is, for example, acetylene glycol-based surfactant Dynol 604 (manufactured by Nisshin Chemical Industry Co., Ltd.) or silicone-based surfactant BYK345 (Big Chemie). The effect of the present invention can be obtained even if it is changed to (made by a corporation).

インキ安定性（外観）の評価において、比較例１−ｈのインキ組成物では、増粘する様子が確認され、比較例１−ｉのインキ組成物は、析出物が発生する様子が確認された。 <Examples 1-a to 1-g and Comparative Examples 1-h and 1-i>
Example 1-a to 1-g and Comparative Example 1 were performed in the same manner except that the composition of Example 1 was replaced with 10% by mass of the amide compound and the amount of the amide compound shown in Table 2 was included. -H and 1-i ink compositions were prepared.
These ink compositions were evaluated for writing dryness and ink stability in the same manner as above. The obtained results are shown in Table 2.

In the evaluation of ink stability (appearance), the ink composition of Comparative Example 1-h was confirmed to thicken, and the ink composition of Comparative Example 1-i was confirmed to generate a precipitate. ..

For comparison, all of these examples were evaluated by combining them with a ballpoint pen, but the ink compositions of Examples 1, 2 and 1-a to 1-g were used in addition to the ballpoint pen, especially fountain pens and markings. It can also be suitably used for a pen. When used in a fountain pen, the effect of the present invention can be obtained without containing a shear thinning agent such as a polysaccharide.

In particular, when the ink composition according to the present invention is used in a fountain pen, the ink composition of Example 1 does not contain a phosphate ester-based surfactant and a polysaccharide and is polyoxyethylene which is an ink reversal material. An ink composition containing 0.1% by mass of a polyoxypropylene block polymer and having water changed to 80.2% by mass can be used, and this ink composition can obtain the effect according to the present invention. ..

<Examples 3 and 4, and Comparative Example 2>
With respect to the composition of Example 1, (meth)acrylic acid-methyl (meth)acrylate copolymer (molar ratio of carboxylic acid and methyl ester 1:2.1, repeating unit derived from acrylic acid and methacrylic acid derived An ink composition of Example 3 was prepared in the same manner except that 0.21% by mass of the repeating unit molar ratio of 1:0.36) was added and the amount of water was changed to 77.59% by mass.
0.5% by mass of Surfynol 2502 (manufactured by Nisshin Chemical Industry Co., Ltd.), which is an acetylene glycol-based surfactant, was added to the composition of Example 3 except that water was changed to 77.09% by mass. In the same manner, an ink composition of Example 4 was prepared.
An ink composition of Comparative Example 2 was prepared in the same manner as in the composition of Example 3 except that the amide compound was 0 and water was 87.59% by mass.

The ink compositions of Examples 3 and 4 and Comparative Example 2 were evaluated for handwriting dryness and ink stability in the same manner as above. The results obtained are shown in Table 3.

<Examples 4-a to 4-c>
Inks of Examples 4-a to 4-c were prepared in the same manner as in Example 4 except that the amount of the amide compound and diethylene glycol described in Table 2 were included instead of 10% by mass of the amide compound. A composition was prepared.
These ink compositions were evaluated for writing dryness and ink stability in the same manner as above. The results obtained are shown in Table 4.

The ink compositions of Examples 3, 3-a to 3-c and 4 can be particularly preferably used for a ballpoint pen.

<Examples 5 and 6 and Comparative Example 3>
Xanthan gum (manufactured by Sansho Co., Ltd.) was added to the composition of Example 1 in an amount of 0.33% by mass, and water was changed to 77.47% by mass, to prepare an ink composition of Example 5 in the same manner. Prepared.
0.5% by mass of Surfynol 2502 (manufactured by Nisshin Chemical Industry Co., Ltd.), which is an acetylene glycol-based surfactant, was added to the composition of Example 5 except that water was changed to 76.97% by mass. In the same manner, an ink composition of Example 6 was prepared.
An ink composition of Comparative Example 3 was prepared in the same manner as the composition of Example 5 except that the amide compound was 0 and water was 87.47% by mass.

The ink compositions of Examples 5 and 6 and Comparative Example 3 were evaluated for handwriting dryness and ink stability in the same manner as above. The results obtained are shown in Table 5.

The ink compositions of Examples 5 and 6 can be particularly preferably used for ballpoint pens.

<Examples 7 and 8 and Comparative Example 4>
To the composition of Example 1, 0.15% by mass of succinoglycan (manufactured by Sansho Co., Ltd.) was added, and water was changed to 77.65% by mass. Was prepared.
With respect to the composition of Example 7, 0.5% by mass of Surfynol 2502 (manufactured by Nisshin Chemical Industry Co., Ltd.), which is an acetylene glycol-based surfactant, was added, and water was changed to 77.15% by mass. Similarly, the ink composition of Example 8 was prepared.
An ink composition of Comparative Example 4 was prepared in the same manner as in the composition of Example 7 except that the amide compound was 0 and water was 87.65% by mass.

The ink compositions of Examples 7 and 8 and Comparative Example 4 were evaluated for handwriting dryness and ink stability in the same manner as above. The obtained results are shown in Table 6.

The ink compositions of Examples 7 and 8 can be particularly preferably used for ballpoint pens.

<Example 9>
For the composition of Example 1, except that the amide compound was replaced by 10 mass% of 3-methoxy-N,N-dimethylpropanamide, but 10 mass% of 3-butoxy-N,N-dimethylpropanamide was included. Similarly, the ink composition of Example 9 was prepared.
When the handwriting dryness of the obtained ink composition was evaluated in the same manner as above, it was confirmed that the effects of the present invention were obtained. In addition, the ink stability evaluation result was better in Example 1.

Claims (10)

water and,
A colorant,
An amide compound represented by the formula (1),

(In the formula,
R ¹ is a linear or branched alkyl group having 1 to 6 carbon atoms, and R ² and R ³ are each independently hydrogen or a linear or branched alkyl group having 1 to 4 carbon atoms; It is an alkyl group)
A water-based ink composition for a writing instrument, comprising:
The aqueous ink composition for a writing instrument, wherein the content of the amide compound is 1 to 35% by mass based on the total mass of the composition. The composition according to claim 1, wherein R ¹ is a linear alkyl group having 1 to 4 carbon atoms, and R ² and R ³ are both methyl groups. The composition according to claim 1 or 2, further comprising a surfactant having an acetylene bond in the structure or a silicone-based surfactant. The composition according to any one of claims 1 to 3, further comprising a phosphate ester surfactant. The composition according to any one of claims 1 to 4, further comprising a polysaccharide. The composition of claim 5, wherein the polysaccharide is dextrin. The following formula (i):

(In the formula, R ¹¹ is hydrogen or a methyl group.)
And the repeating unit
The following formula (ii):

(In the formula,
R ¹² is hydrogen or a methyl group, and R ¹³ is an alkyl group having 1 to 5 carbon atoms and having a straight chain or a side chain)
The composition according to any one of claims 1 to 6, further comprising a copolymer comprising a repeating unit represented by: The composition according to any one of claims 1 to 6, which is an ink composition for a fountain pen or a marking pen. The composition according to any one of claims 1 to 7, which is an aqueous ink composition for a ballpoint pen. A writing instrument containing the composition according to claim 1.