Water-based ink composition for ballpoint pens and ballpoint pens containing the same

Abstract

To provide a water-based ink composition for ballpoints that improves ink dischargeability from a pen tip and allows for clear handwriting with reduced blurring and line skipping over the long term, and a ballpoint storing the same.SOLUTION: A water-based ink composition for ballpoints is stored in a ballpoint having a metal ballpoint chip, the ink composition comprising a colorant, a phosphate surfactant, a substance represented by formula (1) and / or a salt thereof, and water, where X and Y each denote a functional group selected from -H, -R, -OH, -OR, -NH2, -NHR and -NR2, and R is an alkyl group, excluding the case where both of X and Y are hydrogen.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous ink composition for ballpoint pens.

Background Art

[0002] Conventionally, in ballpoint pens equipped with metal ballpoint pen tips, studies have been conducted to improve the ink ejection property from the pen tip and form a clear handwriting without ink bleeding or line skipping. A method of adding a lubricant such as a phosphate ester surfactant to the ink to rotate the ball smoothly is widely used. However, even when such an additive is used, it is not easy to maintain good ink ejection, and further studies are being conducted. (For example, see Patent Document 1)

[0003] Patent Document 1 describes an aqueous ink composition using a crosslinked poly-N-vinylcarboxamide or a crosslinked polyacrylic acid or a salt thereof and an alkylbenzenesulfonic acid. This ink exhibits good ink ejection due to smooth ball rotation and is capable of suppressing ink bleeding and line skipping in handwriting.

[0004] However, even in the inks of the prior art, it is not easy to maintain good ink ejection, and there is room for improvement because the ink ejection property may decrease over time.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention relates to an ink contained in a ballpoint pen provided with a metal ballpoint pen tip, which can continuously exhibit good ink ejection properties from the pen tip and can form a clear handwriting with suppressed handwriting streaks and line skips over a long period of time. An object of the present invention is to provide an aqueous ink composition for a ballpoint pen and a ballpoint pen containing the same.

Means for Solving the Problems

[0007] "1. An ink contained in a ballpoint pen provided with a metal ballpoint pen tip, which contains a coloring agent, a phosphate ester surfactant, a substance represented by the following formula (1) and / or its salt, and water. An aqueous ink composition for a ballpoint pen.

Chemical formula

Effects of the Invention

[0008] According to the present invention, there are provided an aqueous ink composition for a ballpoint pen, which is an ink contained in a ballpoint pen having a metal ballpoint pen tip, continuously exhibits good ink ejection property from the pen tip, and can form a clear handwriting with suppressed handwriting blur and ink splashing over a long period of time, and a ballpoint pen containing the same.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described in detail. In this specification, "parts", "%", "ratio", etc. indicating formulation are based on mass unless otherwise specified.

[0010] The aqueous ink composition for a ballpoint pen according to the present invention (hereinafter, may be sometimes referred to as "aqueous ink composition", "ink composition", or "composition") comprises at least a colorant, a phosphate ester surfactant, a substance represented by the formula (1) and / or a salt thereof, and water. Hereinafter, each component constituting the aqueous ink composition according to the present invention will be described.

[0011] (Colorant) The aqueous ink composition for a ballpoint pen of the present invention can use conventional colorants. Examples of pigments include inorganic pigments such as carbon black, metal oxides or metal salts, organic pigments such as organic dye pigments or lake pigments, shiny bright pigments such as aluminum pigments, and fluorescent pigments. Examples of dyes include acid dyes, basic dyes, direct dyes, reactive dyes, vat dyes, sulfur dyes, metal-containing dyes, cationic dyes, and disperse dyes. The content of the coloring material is applied in the range of 0.1 to 30% by mass based on the total mass of the ink composition.

[0012] Furthermore, examples of coloring materials applicable to the ink composition include coloring materials that change color due to frictional heat.

[0013] As the coloring material that changes color due to the frictional heat, those in which the handwriting changes color (hue change, transparency, or decolorization) by rubbing and heating the handwriting with a friction body or the like can be selectively applied regardless of whether they are reversible or irreversible. In addition to those in which the coloring material itself changes hue, those that become transparent (decolorize) and general-purpose coloring materials such as the above-mentioned dyes and pigments can be used in combination to form a configuration in which the hue changes. Examples of the coloring material that changes color upon heating include, for example, reversible types disclosed in JP-A-2012-219160, JP-A-2014-5422, etc., which are cited as references, and irreversible types disclosed in JP-A-2010-229332, etc. In particular, the change in the handwriting is suitable because it can be stably exhibited for a long period without causing a composition change by encapsulating the thermochromic composition in microcapsules. As the thermochromic composition encapsulated in the microcapsule pigment, a reversible thermochromic composition composed of (i) an electron-donating color-developing organic compound, (ii) an electron-accepting compound, and (iii) a reaction medium that determines the color-developing reaction temperature of the two is preferable from the viewpoints of repeatability of use, accuracy of temperature change, etc.

[0014] As the reversible thermochromic composition, there can be applied a heat-decoloring type microcapsule pigment in which a reversible thermochromic composition having a relatively small hysteresis width (ΔH = 1 to 7°C) is encapsulated in microcapsules. The reversible thermochromic composition is described in, for example, Japanese Patent Publication No. 51-44706, Japanese Patent Publication No. 51-44707, Japanese Patent Publication No. 1-29398, etc. It changes color before and after a predetermined temperature (color change point), exhibits a decolorized state in a temperature range equal to or higher than the high-temperature side color change point, and a colored state in a temperature range equal to or lower than the low-temperature side color change point. Among the two states, only a specific one of the states exists at room temperature, and the other state is maintained while heat or cooling heat required for the manifestation of the state is applied, but returns to the state exhibited at room temperature when the application of the heat or cooling heat stops. Furthermore, those showing relatively large hysteresis characteristics (ΔH = 8 to 50°C) described in, for example, Japanese Patent Publication No. 4-17154, Japanese Unexamined Patent Application Publication No. 7-179777, Japanese Unexamined Patent Application Publication No. 7-33997, Japanese Unexamined Patent Application Publication No. 8-39936, etc., and those showing large hysteresis characteristics described in, for example, Japanese Unexamined Patent Application Publication No. 2006-137886, Japanese Unexamined Patent Application Publication No. 2006-188660, Japanese Unexamined Patent Application Publication No. 2008-45062, Japanese Unexamined Patent Application Publication No. 2008-280523, etc., that is, the shape of the curve plotting the change in coloring density due to temperature change significantly differs in the path when the temperature is increased from the low-temperature side of the color change temperature range and when the temperature is decreased from the high-temperature side of the color change temperature range, and changes color following a different path. A heat-decoloring type microcapsule pigment encapsulating a reversible thermochromic composition having color memory properties in a low-temperature range below the complete coloring temperature or a decolorized state in a high-temperature range above the complete decoloring temperature can also be applied. In addition, as the reversible thermochromic composition having the above-described color memory properties and applied to writing instrument ink, specifically, the complete coloring temperature is set to a temperature that can only be obtained in a freezer, a cold region, etc., that is, -50 to 0°C, preferably -40 to -5°C, more preferably -30 to -10°C, and the complete decoloring temperature is set to a temperature obtained from frictional heat by a friction body, a heating body such as a hair dryer that is easily accessible, that is, 50 to 95°C, preferably 50 to 90°C, more preferably 60 to 80°C, and by specifying the ΔH value to 40 to 100°C, it can effectively function to maintain the color exhibited in the normal state (daily living temperature range).

[0015] The microencapsulation of the thermochromic composition includes an interfacial polymerization method, an interfacial polycondensation method, an in-situ polymerization method, a liquid-phase curing coating method, a phase separation method from an aqueous solution, a phase separation method from an organic solvent, a melt dispersion cooling method, an air suspension coating method, a spray drying method, etc., and is appropriately selected according to the application. Furthermore, a secondary resin film can be further provided on the surface of the microcapsule pigment according to the purpose to impart durability or to modify the surface characteristics for practical use.

[0016] Regarding the aqueous ink in which the colorant is a dye and the content of the dye is 2% by mass or less based on the total mass of the ink composition, although the reason is not clear, the ink ejection property tends to decrease easily by repeating writing. Even with such a dye concentration, the ink composition of the present invention can continuously exhibit good ink ejection property from the pen tip and form a clear handwriting with suppressed bleeding and skipping of the writing line over a long period of time.

[0017] (Phosphate ester surfactant) The ink composition contains a phosphate ester surfactant. The phosphate ester surfactant smoothes the rotation of the ball during writing and improves the ink ejection property.

[0018] As the phosphate ester surfactant applicable to the ink composition, known ones can be applied. Specifically, polyoxyethylene alkyl ether phosphate ester, polyoxyethylene alkylene ether phosphate ester, polyoxyethylene aryl ether phosphate ester, polyoxyethylene polyoxypropylene alkyl ether phosphate ester can be exemplified. As the polyoxyethylene aryl ether phosphate ester, polyoxyethylene phenyl ether phosphate ester, polyoxyethylene dodecyl phenyl ether phosphate ester, polyoxyethylene dinonyl phenyl ether phosphate ester, polyoxyethylene monostyryl phenyl ether phosphate ester, polyoxyethylene distyryl phenyl ether phosphate ester, polyoxyethylene tristyryl phenyl ether phosphate ester, polyoxyethylene cumyl phenyl ether phosphate ester, polyoxyethylene naphthyl ether phosphate ester can be exemplified, and all are preferably used. The phosphate ester surfactant may be a sodium salt or an alkanolamine salt such as a monoalkanolamine salt, a dialkanolamine salt, or a trialkanolamine salt. In terms of commercially available products, for example, as the Pricerf series (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), Pricerf A212C, A215C, A208F, M208F, A208N, A208B, A219B, DB-01, A210D, AL can be mentioned. As the Phosphanol series (manufactured by Toho Chemical Co., Ltd.), Phosphanol 2P, ML-200, GF-185, BH-650, ED-200, RA-600, ML-220, ML-240, RD-510Y, RS-410, RS-610, RS-710, RL-210, RL-310, RB-410, RD-710, RP-710, LF-200, RM-410, RM-510, SP-212, CP-120, 720, SC-6103, RD-720.LP -700, LP-500, LB-400 can be mentioned. As the Antestex series (manufactured by Toho Chemical Co., Ltd.), Antestex AK-25, AK-25B, SM-172, GF-339, GF-199, ML-200, GF-185, etc. can be mentioned. The phosphate ester surfactant applicable to the ink composition is not limited to these. The phosphate ester surfactant may be used alone or in combination of multiple types.

[0019] The content of the phosphate ester surfactant in the ink composition is preferably 0.1 to 3% by mass, more preferably 0.5 to 2% by mass, based on the total mass of the ink composition. By setting the content ratio of the phosphate ester surfactant in the ink composition within the above range, while improving the dissolution stability of the phosphate ester surfactant, it is easy to make the ball rotation smooth during writing.

[0020] The aqueous ink composition contains a substance represented by the following formula (1) or a salt thereof.

Chemical formula

[0021] Furthermore, the substance represented by formula (1) and its salts can also enhance the wettability of the members forming the ink supply mechanism of the ballpoint pen described later, and improve the ink supply property from the ink storage part to the pen tip.

[0022] Considering maintaining good ink ejection property during writing, X and Y in formula (1) are preferably functional groups selected from -H, -OH, and -NH2 (except when both X and Y are -H), more preferably functional groups selected from -OH and -NH2, and even more preferably one of X and Y is -OH and the other is -NH2.

[0023] The content of the substance represented by formula (1) and / or its salts is preferably 0.05 to 2% by mass, more preferably 0.1 to 1.5% by mass, and even more preferably 0.1 to 1% by mass based on the total mass of the ink composition. When the content is 0.05% by mass or more, the effect of improving ink ejection property is sufficiently achieved. When it exceeds 2% by mass, the color density due to the substance of formula (1) and its salts becomes high. Therefore, especially when applied to light-colored or white inks, the color tone of the ink may change.

[0024] Also, the relationship between the content A of the phosphate ester surfactant and the content B of the substance represented by formula (1) and / or its salts preferably satisfies 0.01 ≤ B / A ≤ 1, and more preferably 0.05 ≤ B / A ≤ 0.7. When the content ratio is within the above range, good ink ejection property is likely to be maintained.

[0025] The ink composition preferably contains a formalin condensate of naphthalenesulfonic acid. The condensate can further suppress writing blurring and line skipping, and improve the initial writing property after a certain period of time. The formalin condensate of naphthalenesulfonic acid, the substance represented by the formula (1), and its salts have a high affinity because they commonly have a naphthalene ring, and are incorporated into the lubricating layer formed on the inner surface of the ball holding chamber such as the ball surface and the ball seat, which is composed of a phosphate ester surfactant and the substance of the formula (1) and / or its salt. It is presumed that this makes the lubricating layer stronger. The condensate may be an alkali metal salt such as a sodium salt.

[0026] Considering the good initial writing property over time, the content of the formalin condensate of naphthalenesulfonic acid is preferably 0.5 to 5% by mass, more preferably 1 to 3% by mass, and even more preferably 1 to 2% by mass based on the total mass of the ink composition.

[0027] (Thickener) A thickener can be used in the aqueous ink composition. Although conventionally known substances can be used as the thickener, preferably, it is a substance that can impart shear thinning viscosity to the ink composition (shear thinning viscosity imparting agent). The shear thinning viscosity imparting agent can easily lower the viscosity of the ink composition when a shearing force is applied to the ink from the ball while maintaining the high viscosity of the ink during standing. Therefore, it can suppress the sedimentation and aggregation of the pigment in the ink during standing and improve the ink ejection property from the pen tip during writing.

[0028] Specific examples of the shear thinning viscosity imparting agent include tragacanth gum, pullulan, cyclodextrin, succinoglycan, xanthan gum, welan gum, λ-carrageenan, guar gum, locust bean gum and its derivatives, alkyl esters of alginic acid, polymers with a molecular weight of 100,000 to 150,000 mainly composed of alkyl esters of methacrylic acid, glucomannan, carbohydrates having a gelling ability extracted from seaweeds such as carrageenan, poly N-vinyl-carboxylic acid amide cross-linked products, benzylidene sorbitol and benzylidene xylitol or their derivatives, cross-linkable acrylic acid polymers, inorganic fine particles such as smectite and laponite, etc.

[0029] For the ink composition, a conventionally widely used water-soluble organic solvent that is compatible with water can also be used. Examples of the water-soluble organic solvent include ethanol, propanol, butanol, glycerin, sorbitol, triethanolamine, ethylene glycol, diethylene glycol, thiodiethylene glycol, hexylene glycol, 1,3-butanediol, neoprene glycol, polyethylene glycol, propylene glycol, butylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, 2-pyrrolidone, N-methyl-2-pyrrolidone, and the like. In addition, the above water-soluble organic solvents can be used alone or in combination of two or more, and are used in the range of 2 to 60% by weight, preferably 5 to 35% by mass in the ink composition.

[0030] Furthermore, a pH adjuster can also be used to adjust to a desired pH according to the characteristics of the ink composition. As the pH adjuster, conventionally known acidic substances and basic substances can be applied. Examples of the acidic substances include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, carbonic acid, boric acid, lactic acid, citric acid, tartaric acid, malic acid, and the like. Examples of the basic substances include strong alkalis such as sodium hydroxide and potassium hydroxide, or weak alkalis such as sodium carbonate, ammonia, sodium hydrogen phosphate, and potassium hydrogen phosphate. In addition, alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine can also be applied as the basic substances.

[0031] In addition, if necessary, rust inhibitors such as benzotriazole, tolyltriazole, and saponin, phenol, sodium salt of 1,2-benzothiazolin-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine and other preservatives or fungicides, urea, sorbitol, mannitol, sucrose, glucose, reduced starch hydrolyzate, sodium pyrophosphate and other wetting agents, defoaming agents, fluorine-based surfactants and nonionic surfactants that improve the ink permeability may be used. Further, the above-mentioned basic substance can also be used as a neutralizing agent for the substance represented by the formula (1). Furthermore, metal soaps, polyalkylene glycol fatty acid esters, ethylene oxide-added cationic surfactants, N-acyl amino acid-based surfactants, dicarboxylic acid-based surfactants, β-alanine-based surfactants, 2,5-dimercapto-1,3,4-thiadiazole and its salts and oligomers, 3-amino-5-mercapto-1,2,4-triazole, thiocarbamate, dimethyldithiocarbamate, α-lipoic acid, condensates of N-acyl-L-glutamic acid and L-lysine and their salts, etc. are used. In addition, by adding thickening inhibitors such as oligomers of N-vinyl-2-pyrrolidone, oligomers of N-vinyl-2-piperidone, N-vinyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, ε-caprolactam, oligomers of N-vinyl-ε-caprolactam, etc., the function in the emerging form can also be enhanced.

[0032] Furthermore, one or more water-soluble resins such as alkyd resins, acrylic resins, styrene maleic acid copolymers, cellulose derivatives, polyvinylpyrrolidone, polyvinyl alcohol, dextrin, etc. can be added, or one or more wetting agents such as urea, nonionic surfactants, sorbitol, mannitol, sucrose, glucose, reduced starch hydrolyzate, sodium pyrophosphate, etc. can also be added.

[0033] (Physical properties of the aqueous ink composition) The viscosity of the aqueous ink composition is at a shear rate of 384 sec -1The measured viscosity (at 20°C) is preferably from 1 to 100 mPa·s, more preferably from 2 to 70 mPa·s. The viscosity of the ink composition can be measured using a rheometer (DISCOVERY HR-2 manufactured by TA Instruments, cone plate 40 mm, angle 1°). If the viscosity of the aqueous ink composition is within the above numerical range, the ink ejection property is moderately good, so it becomes easy to form a clear handwriting without ink bleeding or line skipping.

[0034] The aqueous ink composition according to the present invention can be produced by any conventionally known method. Specifically, the respective components are blended in required amounts and mixed using various stirrers such as a propeller stirrer, a homodisper, or a homomixer, or various dispersers such as a bead mill, etc., to produce it.

[0035] (Ballpoint pen) A ballpoint pen filled with the aqueous ink composition of the present invention will be described. The ballpoint pen includes a pen tip, an ink filling mechanism, an ink supply mechanism, etc.

[0036] As the pen tip, a metal ballpoint pen tip that rotatably holds a ball in a ball house (ball holding chamber) of a ballpoint pen tip body is used.

[0037] As the ball house, for example, one formed by cutting a metal to form a ball seat and an ink outlet portion inside, or a plurality of inward projecting portions are provided on the inner surface near the tip of a metal pipe by pressing deformation from the outer surface, and an ink outflow gap extending radially outward from the center portion is formed between the inward projecting portions, etc. can be applied. In particular, a ball house provided with inward projecting portions by pressing deformation has a relatively small contact area with the rear end of the ball and can give a smooth writing feeling at a low writing pressure.

[0038] The materials of the ball and the ball house are excellent in strength and wear resistance, and a phosphoric acid ester-based surfactant is easily adsorbed on the surface to smooth the rotation of the ball. Therefore, stainless steel, cemented carbide mainly composed of tungsten carbide, etc. are preferably used.

[0039] As for the ball held by the ball house, balls with an outer diameter of 0.1 to 2.0 mm can be applied. In addition, in the ball pen tip, an elastic member that elastically projects the rear end of the ball forward can be arranged inside the tip. When not writing, the ball is pressed against the inner edge of the tip of the pen tip to be in a close state, and when writing, the ball is retracted by the writing pressure so that the ink can flow out. It is also possible to configure it in this way to suppress ink leakage when not in use. Examples of the elastic member include a spring made of a thin metal wire and one having a straight portion (rod portion) at one end of the spring. It is configured to be pressable and applied with an elastic force of 5 to 40 g.

[0040] The ink filling mechanism may be configured to directly fill an aqueous ink composition, or may include an ink container or an ink storage body capable of filling the aqueous ink composition. When the ball pen includes an ink storage body capable of filling an aqueous ink composition, the ink storage body is preferably a fiber aggregate made of twisted fibers. In addition, the ink filling mechanism may be a cartridge capable of directly filling the ink composition.

[0041] Also, the ink supply mechanism is not particularly limited. For example, (1) a mechanism that includes an ink guiding core made of a fiber bundle or the like as an ink flow rate adjusting member and guides the aqueous ink composition to the pen tip; (2) a mechanism in which a large number of disk bodies are arranged in parallel with a comb-shaped groove interval, and a slit-shaped ink guiding groove that vertically penetrates the disk body in the axial direction and a ventilation groove wider than the groove are provided, and the ink composition is supplied to the pen tip through the ink guiding groove; (3) a mechanism in which a large number of disk bodies are arranged in parallel with a comb-shaped groove interval, a slit-shaped ink guiding groove that vertically penetrates the disk body in the axial direction and a ventilation groove wider than the groove are provided, and an ink guiding core for guiding ink from an ink storage part to the pen tip is arranged at the axial center, and the ink composition is guided to the pen tip through a pen core; (4) a mechanism that directly supplies the aqueous ink composition to the pen tip from an ink container or a shaft cylinder equipped with a pen tip, etc. can be mentioned. As the ink container equipped with a pen tip, it may be an ink refill in which the ball pen tip is provided directly or via a holder at the tip of the ink storage tube, and an ink backflow prevention body made of a viscous liquid such as grease is filled at the rear end of the ink.

[0042] The mechanism of (3) is a preferable ink supply mechanism because it can stably improve the ink supply from the ink storage part to the ball pen tip and improve the ink ejection property from the ball pen tip. Furthermore, as described above, in the ink composition of the present invention, the wettability of the members constituting the ink supply mechanism is enhanced by the substances shown in formula (1) and their salts, so the good ink supply stability exhibited by the ink supply mechanism of (3) can be further enhanced.

[0043] The ball pen may be provided with a pen tip protruding and retracting mechanism. Examples of the pen tip protruding and retracting mechanism include a knock type, a rotary type, and a slide type. Also, it may be a protruding and retracting type in which the pen tip can be accommodated in the shaft cylinder.

[0044] The ball pen that houses the composition of the present invention can be configured by appropriately selecting mechanisms from the above-mentioned pen tip, ink filling mechanism, ink supply mechanism, and pen tip protruding and retracting mechanism.

[0045] Examples of the present invention are as follows. (Example 1) An aqueous ink composition for writing instruments was obtained by stirring and mixing at room temperature for 1 hour with the following raw materials and compounding amounts. · Colorant 0.4% by mass (Blue dye, product name: Water Blue 105, manufactured by Orient Chemical Industries Co., Ltd.) · Phosphate ester surfactant (polyoxyethylene styryl phenyl ether phosphate ester, product name: Plissurf AL, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 1.5% by mass · Compound represented by formula (1) (X: -OH, Y: -NH2) 0.1% by mass · Benzisothiazolin-3-one (preservative, product name: Proxel XL-2, manufactured by Lonza Japan Co., Ltd.) 0.3% by mass · Diethylene glycol 8% by mass · Urea 5% by mass · Triethanolamine 2% by mass · Water 82.7% by mass

[0046] (Examples 2 to 9, Comparative Examples 1 to 4) With respect to Example 1, the types and addition amounts of the components to be blended were changed as shown in Table 1 to obtain the ink compositions of Examples 2 to 9 and Comparative Examples 1 to 4. Details of the materials used in the above examples are as follows. (1) Blue dye (product name: Water Blue 105, manufactured by Orient Chemical Industries Co., Ltd.) (2) Yellow dye (product name: Quinoline Yellow WS300%, manufactured by Daiwa Kasei Co., Ltd.) (3) Blue pigment (product name: Sandaisuper Blue GLL(E), manufactured by Sanyo Shikiso Co., Ltd., 25% by mass dispersion of pigment) (4) Phosphate ester surfactant (polyoxyethylene styryl phenyl ether phosphate ester, product name: Plissurf AL, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (5) Compound represented by formula (1) (X = -OH, Y = -NH2) (6) Compound represented by formula (1) (both X and Y are -OH) (7) Sodium naphthalene sulfonate formalin condensate (Product name: Demol N, manufactured by Kao Corporation) (8) Preservative (benzisothiazolin-3-one, product name: Proxel XL-2, manufactured by Lonza Japan)

[0047]

Table 1

[0048] The prepared aqueous ink composition was evaluated as follows. The obtained results were as shown in Table 2. Also, the ballpoint pen used in the evaluation test was created and used as follows. Ballpoint pen: A metal ballpoint pen tip (material of the ball holding chamber: stainless steel) that rotatably holds a carbide ball with an outer diameter of 0.7 mm, an ink filling mechanism capable of directly filling the ink composition, and a plurality of disk bodies are arranged in parallel with a comb-shaped groove interval therebetween, and an ink guiding groove in the shape of a slit that vertically penetrates the disk body in the axial direction and a ventilation groove wider than the groove are provided, and an ink guiding core for guiding the ink from the ink storage part to the pen tip is arranged at the axial center, and an ink supply mechanism for guiding the ink composition to the ballpoint pen tip through a pen core. The ballpoint pen (manufactured by Pilot Corporation, product name: Hi-Tecpoint V7) was filled with 2 g of the ink obtained in the examples and comparative examples.

[0049] (1) Evaluation of ink ejection stability Continuous round writing was performed on the test paper with the above ballpoint pen, and the handwriting was observed and evaluated. The diameter of one circle was 3 cm, and the writing conditions were set to a writing distance of 1000 m, a writing load of 100 g, a writing angle of 62.5°, and a writing speed of 4 m / min. As the test paper, the product name: NPi form <55> (manufactured by Nippon Paper Industries Co., Ltd.) was used. The evaluation criteria were that S and A were considered qualified and B was considered unqualified. S: No handwriting blur or line skipping was confirmed. A: Slight handwriting blur or line skipping was confirmed, but there was no practical problem. B: There are prominent ink smudges and line skips, which pose practical problems. (2) Evaluation of stability over time 1: Initial writing performance The ballpoint pen with the cap attached was stored at 50 °C for 60 days. After returning the stored ballpoint pen to room temperature, 12 consecutive circles (diameter: 3 cm) were written and the handwriting was observed. The writing conditions were as follows: writing load: 100 g, writing angle: 70°, writing speed: the speed of writing 12 circles in 4 seconds. The same type of paper as the test paper used in the "Evaluation of ink ejection stability" was used for the test paper. The evaluation criteria were that S and A were considered qualified, and B was considered unqualified. S: No ink smudges or line skips were confirmed. A: Slight ink smudges or line skips were confirmed, but there are no practical problems. B: There are prominent ink smudges and line skips, which pose practical problems. (3) Evaluation of stability over time 2: Ink ejection stability Using the ballpoint pen evaluated in "Evaluation of stability over time 1", writing was done on the test paper and the handwriting was observed. The writing conditions and the test paper were the same as those in the "Evaluation of ink ejection stability". The evaluation criteria were that S and A were considered qualified, and B was considered unqualified. S: No ink smudges or line skips were confirmed. A: Slight ink smudges or line skips were confirmed, but there are no practical problems. B: There are prominent ink smudges and line skips, which pose practical problems.

[0050] The test results are shown in Table 2 below.

[0051]

Table 2

Claims

1. An ink contained in a ballpoint pen having a metal ballpoint pen tip, comprising a coloring agent, a phosphate ester surfactant, a substance represented by the following formula (1) and / or a salt thereof, a formalin condensate of naphthalenesulfonic acid, and water, With respect to the total mass of the ink, the content of the phosphate ester surfactant is 0.1 to 3% by mass, and the content of the substance represented by formula (1) and / or a salt thereof is 0.05 to 2% by mass. An aqueous ink composition for a ballpoint pen, wherein the relationship between the content A of the phosphate ester surfactant and the content B of the substance represented by formula (1) and / or a salt thereof satisfies 0.01 ≦ B / A ≦ 1. 【Chemical Formula 1】 In the formula, X and Y are functional groups selected from -H, -R, -OH, -OR, -NH ２ , -NHR and -NR ２ selected from, and R is an alkyl group. However, the case where both X and Y are hydrogen is excluded.

2. The X and Y are functional groups selected from -H, -OH and -NH ２ (however, the case where both X and Y are hydrogen is excluded), the aqueous ink composition according to claim 1.

3. The coloring agent is a dye. The aqueous ink composition according to claim 1 or 2.

4. The content of the dye is 2% by mass or less based on the total mass of the aqueous ink composition. The aqueous ink composition according to claim 3.

5. A ballpoint pen having a metal ballpoint pen tip and containing the aqueous ink composition according to any one of claims 1 to 4.

6. A plurality of disc bodies are arranged in parallel with a comb-shaped groove interval, and a slit-shaped ink guiding groove that vertically penetrates the disc body in the axial direction and a ventilation groove wider than the groove are provided, and an ink guiding core for guiding ink from an ink storage part to a pen tip is arranged at the axial center. A ballpoint pen comprising a pen core.

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