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

Abstract

To provide a water-based ink composition for a ball-point pen capable of effectively improving lubricating performance even in a small amount by using a small amount of a phosphoric acid ester in a range not affecting ink viscosity even in the water-based ink using a polyglycerol isostearic acid ester as a shear thinning property imparting agent, and capable of exhibiting excellent writing performance with a smoother writing feeling over a long period, and to provide the ball-point pen including the same.SOLUTION: The water-based ink composition for the ballpoint pen comprises a pigment, water, a polyglycerol isostearic acid ester as a shear-thinning property imparting agent, a phosphoric acid ester and a chelating agent, wherein the phosphoric acid ester is contained in an amount of <0.5 mass% based on the total amount of the ink composition and the electric conductivity of the ink composition is ≥ 80 μ S / cm, and the ballpoint pen contains the water-based ink composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based ink composition for a ballpoint pen, and more particularly to a water-based ink composition for a ballpoint pen and a ballpoint pen having excellent lubricating properties. [Background technology]

[0002] Water-based ink compositions containing shear-thinning agents such as xanthan gum and welan gum are released from shear force after being transferred to the paper surface and become highly viscous, so they do not suffer from the drawback of bleeding, which is a drawback of conventional low-viscosity water-based ink compositions.Furthermore, they are widely used because they can be used to produce writing instruments with a simple structure that do not require a flow rate adjusting element (a temporary ink retention element such as a comb-like element) to adjust the ink flow rate (see, for example, Patent Document 1). However, in the case of aqueous inks having shear thinning properties, the writing feel can deteriorate, particularly when a pigment is used as a colorant, and the pigment can aggregate over time. Therefore, it is necessary to blend a large amount of multiple additives, which reduces the flexibility of blending.

[0003] Therefore, it has been proposed that a smooth writing feel can be obtained without causing aggregation of pigments by using polyglycerol isostearate as a shear thinning agent (see, for example, Patent Document 2). Since the polyglycerol isostearate also has an effect as an activator, in a system in which it is blended as a shear thinning agent, a smooth writing feel can be obtained without relying on a general-purpose lubricant, and there is an advantage in that it does not require the blending of additives to improve the writing feel. However, when used in a ballpoint pen with a small diameter ball, which results in a relatively small ink ejection volume, or in a ballpoint pen with a tip formed from a straight pipe made of metal such as stainless steel, the feeling of smoothness during writing becomes difficult to sense, and therefore an ink composition with a stronger lubricating effect is desired. Therefore, in order to achieve a higher lubricating effect, a technology has been investigated that combines polyglycerol isostearate esters as shear thinning agents with phosphate esters. However, adding more than a certain amount of phosphate ester weakens the effect of polyglycerol isostearate esters as shear thinning agents, making it difficult to achieve the required ink viscosity. Therefore, it becomes necessary to limit the amount of phosphate ester added, but adding only a small amount that achieves the required ink viscosity has not been able to improve the lubricating effect. This is thought to be due to the fact that, because phosphate esters have chelating properties, adding small amounts only acts to chelate cations in the ink, preventing them from adsorbing to the surfaces of the ball and ball seat, preventing them from achieving lubricating performance. The present inventors discovered the above phenomenon and conducted extensive research to solve it, and as a result, discovered a method in which a small amount of phosphate ester contributes to improving lubricating performance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 4-214782 [Patent Document 2] WO99 / 06494 publication Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides an aqueous ink composition for ballpoint pens that uses a polyglycerol isostearate ester, which provides a smooth writing feel, as a shear thinning agent, and that can effectively improve lubrication performance even with a small amount of phosphate ester, provided that the amount is within a range that does not affect the ink viscosity. This enables the ink to have a smoother writing feel and excellent writing performance over a long period of time, and also provides a ballpoint pen incorporating the same. [Means for solving the problem]

[0006] The present invention provides an aqueous ink composition for a ballpoint pen, which comprises a pigment, water, a polyglycerol isostearate ester as a shear thinning agent, a phosphate ester, and a chelating agent, wherein the content of the phosphate ester is less than 0.5% by mass of the total amount of the ink composition, and the electrical conductivity of the ink composition is 80 μS / cm or more. Furthermore, the ratio of the chelating agent to the phosphate ester is in the range of 0.002 to 1 times, and a nonionic dispersant is contained. Furthermore, the chelating agent is at least one selected from the group consisting of EDTA, NTA, HEDTA, HIDA, GEDTA, DHEG, DTPA, TTHA, PDTA, and salts thereof. Furthermore, the electrical conductivity is required to be 2000 μS / cm or less. Furthermore, the present invention is also required to provide a ballpoint pen containing any of the above-mentioned aqueous ink compositions for ballpoint pens, and a ballpoint pen tip having a ball seat formed by pressing and deforming a metal pipe. [Effects of the Invention]

[0007] According to the present invention, when a polyglycerol isostearate having excellent lubricity is used as a shear thinning agent, the lubrication performance can be dramatically improved while maintaining stable ink properties, and therefore, it is possible to provide an aqueous ink composition for ballpoint pens that can provide a smoother writing feel and excellent writing performance over a long period of time, and a ballpoint pen incorporating the same. DETAILED DESCRIPTION OF THE INVENTION

[0008] In the present invention, when polyglycerol isostearate is used as a shear thinning agent, the use of a small amount of phosphate ester in combination provides higher lubrication performance. However, until now, small amounts of phosphate ester applied within a range that does not affect the ink viscosity have acted to chelate cations in the ink, and have not been effective in improving lubricity. However, the present inventors have discovered that by adding a chelating agent with stronger chelating ability than phosphate ester, the phosphate ester can be prevented from acting as a chelating agent, and further, by setting the electrical conductivity of the ink composition to a specific value or higher, it is possible to achieve both the chelating ability of the chelating agent and the lubricating performance of the phosphate ester, thereby providing a dramatically higher lubrication effect. This allows the phosphate ester to effectively act as a lubricant without exhibiting chelating ability, while maintaining stable ink properties, making it possible to effectively achieve a smoother writing feel while suppressing wear on the ball seat due to writing.

[0009] Examples of the pigment include inorganic pigments such as carbon black and ultramarine, organic pigments such as copper phthalocyanine blue and benzidine yellow, and water-dispersed pigment products that have been stably dispersed in an aqueous medium using a surfactant or resin. Examples include CI Pigment Blue 15:3B (product name: Sandye Super Blue GLL, pigment content 24%, manufactured by Sanyo Pigment Co., Ltd.), CI Pigment Red 146 (product name: Sandye Super Pink FBL, pigment content 21.5%, manufactured by Sanyo Pigment Co., Ltd.), CI Pigment Yellow 81 (product name: TC Yellow FG, pigment content approximately 30%, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), and CI Pigment Red 220 / 166 (product name: TC Red FG, pigment content approximately 35%, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.). As the fluorescent pigment, a fluorescent pigment in the form of fine particles of synthetic resin, in which various fluorescent dyes are solid-dissolved in a resin matrix, can be used. Other examples include pearl pigments, gold and silver metallic pigments, phosphorescent pigments, white pigments such as titanium dioxide used in correction pens, metal powders such as aluminum, thermochromic compositions, photochromic compositions, and capsule pigments obtained by directly or microencapsulating fragrances, etc.

[0010] The thermochromic composition is preferably a reversible thermochromic composition consisting of (i) an electron-donating color-forming organic compound, (ii) an electron-accepting compound, and (iii) a reaction medium that determines the temperature at which the color reaction between the two occurs, and is encapsulated in microcapsules and used as a reversible thermochromic microcapsule pigment. The reversible thermochromic composition may be a heat-discoloring microcapsule pigment, in which a reversible thermochromic composition having a relatively small hysteresis width (ΔH=1 to 7°C) is encapsulated in a microcapsule, and which is described in, for example, Japanese Patent Publication Nos. 51-44706, 51-44707, and 1-29398, and which changes color around a predetermined temperature (color change point), exhibiting a discolored state in a temperature range above the high-temperature color change point and a colored state in a temperature range below the low-temperature color change point, and of these two states, only one specific state exists in the room temperature range, and the other state is maintained while the heat or cold required to manifest that state is applied, but returns to the state exhibited in the room temperature range when the application of heat or cold is removed. Furthermore, there are those exhibiting relatively large hysteresis characteristics (ΔH=8 to 50°C) as described in JP-B-4-17154, JP-A-7-179777, JP-A-7-33997, JP-A-8-39936, etc., and those exhibiting large hysteresis characteristics as described in JP-A-2006-137886, JP-A-2006-188660, JP-A-2008-45062, JP-A-2008-280523, etc. In other words, the shape of the curve plotting the change in color density with temperature changes follows a path that is significantly different when the temperature is increased from a temperature lower than the color-changing temperature range than when the temperature is decreased from a temperature higher than the color-changing temperature range, and the color-developed state in a low-temperature range below the complete color-developing temperature or the color-decolored state in a high-temperature range above the complete color-decoloring temperature can also be applied to heat-decolorizable microcapsule pigments that encapsulate a reversible thermochromic composition that has color memory properties in a specific temperature range. Specifically, the reversible thermochromic composition having color memory properties has a complete color development temperature that is set to a temperature that can only be achieved in a freezer or in a cold region, i.e., -50 to 0°C, preferably -40 to -5°C, more preferably -30 to -10°C, and a complete decolorization temperature that is set to a temperature that can be achieved by frictional heat from a friction body or a familiar heating body such as a hair dryer, i.e., a range of 50 to 95°C, preferably 50 to 90°C, more preferably 60 to 80°C, and a ΔH value of 40 to 100°C, thereby allowing the composition to effectively maintain the color that it exhibits under normal conditions (the temperature range in everyday life).

[0011] Furthermore, if necessary, a dye soluble in an aqueous medium can be used in combination. Examples of the dyes that can be used include acid dyes, basic dyes, and direct dyes. Examples of acid dyes that can be used include New Coccine (CI 16255), Tartrazine (CI 19140), Acid Blue Black 10B (CI 20470), Guinea Green (CI 42085), Brilliant Blue FCF (CI 42090), Acid Violet 6B (CI 42640), Soluble Blue (CI 42755), Naphthalene Green (CI 44025), Eosin (CI 45380), Phloxine (CI 45410), Erythrosine (CI 45430), Nigrosine (CI 50420), and Acid Flavin (CI 56205). Examples of basic dyes that can be used include chrysoidine (CI 11270), methyl violet FN (CI 42535), crystal violet (CI 42555), malachite green (CI 42000), Victoria blue FB (CI 44045), rhodamine B (CI 45170), acridine orange NS (CI 46005), and methylene blue B (CI 52015). Direct dyes include Congo Red (CI 22120), Direct Sky Blue 5B (CI 24400), Violet BB (CI 27905), Direct Deep Black EX (CI 30235), Kayalas Black G Conc (CI 35225), Direct Fast Black G (CI 35255), and Phthalocyanine Blue (CI 74180).

[0012] The colorants containing the pigments can be used alone or in a suitable mixture of two or more, and are used in an amount of 1 to 30% by mass, preferably 2 to 25% by mass, and particularly preferably 2 to 15% by mass in the ink composition.

[0013] The polyglycerol isostearate is added to the aqueous ink as a shear thinning agent, and is a compound represented by the following general formula (1). [ka] [wherein n is an integer of 1 to 8, and R 1 ~R 4 are each independently, R 5 may be the same or different and represent an isostearoyl group or a hydrogen atom, and the number of isostearoyl groups is 1 to 4.

[0014] The polyglycerol isostearate ester has a high lubricating effect, imparts shear thinning properties, and has an evaporation suppressing effect, and therefore has been used as a substitute for polar solvents, lubricants, and viscosity modifiers in ink compositions. In particular, when used as a substitute for a viscosity modifier, it is useful because it does not affect writing performance due to variations in shear thinning properties caused by the batch variations of gums such as welan gum, and it does not deteriorate writing performance due to deterioration of ink stability even when a pigment is used. The amount added is in the range of 1 to 30% by mass, preferably 3 to 20% by mass, and more preferably 5 to 15% by mass, based on the total amount of the ink.

[0015] Furthermore, if necessary, a general-purpose shear-thinning agent can be used in combination. Examples include xanthan gum, welan gum, zeta sea gum, diutan gum, macrophomopsis gum, succinoglycan (average molecular weight: approximately 1,000,000 to 8,000,000), which is an organic acid-modified heteropolysaccharide whose constituent monosaccharides are glucose and galactose, guar gum, locust bean gum and its derivatives, hydroxyethyl cellulose, alginic acid alkyl esters, polymers having a molecular weight of 100,000 to 150,000 and containing an alkyl ester of methacrylic acid as the main component, glucomannan, carbohydrates having gelling ability extracted from seaweed such as agar and carrageenan, cross-linked poly-N-vinyl carboxylic acid amide, benzylidene sorbitol, benzylidene xylitol or derivatives thereof, cross-linked acrylic acid polymers, alkali-thickening acrylic thickeners, inorganic fine particles, nonionic surfactants with an HLB value of 8 to 12, and metal salts and amine salts of dialkyl sulfosuccinic acid.

[0016] Although the aqueous ink composition using the polyglycerol isostearate as a shear thinning agent exhibits a smooth writing feel, when used in a ballpoint pen in which the amount of ink ejected during writing or the amount of ink stored behind the ball is small, the writing may feel less smooth than when used in a ballpoint pen in which a large amount of ink is ejected and stored, and therefore an ink in which the phosphate ester of the present invention is used in combination is more effective. Since the ink properties (viscosity) become unstable when a large amount of phosphate ester is added, the content of the phosphate ester is less than 0.5% by mass of the total amount of the ink composition. Also, if the content is 0.05% by mass or more, high lubrication performance can be achieved with the composition of the present invention even in a ballpoint pen with a small amount of ink as described above.

[0017] The phosphate ester (phosphate ester surfactant) has a phosphate group that easily adsorbs to metals, and therefore eliminates factors that inhibit ball rotation and improves lubricity, thereby suppressing wear on the ball seat and improving the writing feel. Specific examples include polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate monoesters, polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate diesters, phosphate triesters, and derivatives thereof, which may be used alone or in combination of two or more. Commercially available products of the phosphate ester include Plysurf series (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), such as Plysurf A217E, A219B, A215C, A208N, A208B, and AL, and Phosphanol series (manufactured by Toho Chemical Industry Co., Ltd.), such as Phosphanol RB410, RS-410, RS-610, and RS-710.

[0018] The chelating agent is used to sequester metals present in the aqueous ink composition, such as those derived from raw materials contained in water or additives, or those resulting from contact between the aqueous ink and metal components, thereby allowing the phosphate ester to act as a lubricant. Examples of such chelating agents include ethylenediaminetetraacetic acid (EDTA), hydroxyethylenediaminetriacetic acid (HEDTA), glycol ether diaminetetraacetic acid (GEDTA), nitrilotriacetic acid (NTA), hydroxyethyliminodiacetic acid (HIDA), dihydroxyethylglycine (DHEG), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA), and alkali metal salts, ammonium salts, or amine salts thereof. The content of the chelating agent is preferably 0.5% by mass or less, more preferably 0.1% by mass or less, based on the total mass of the ink composition, and specifically, it is optimal to add it in the range of 0.001 to 0.1% by mass.

[0019] In order for the chelating agent to more effectively exhibit the lubrication-improving effect of the phosphate ester, the ratio of the chelating agent to the phosphate ester in the ink is in the range of 0.002 to 1, preferably 0.002 to 0.95, and more preferably 0.002 to 0.9. By using an amount equal to or less than 1, the lubrication effect of the phosphate ester can be made particularly high.

[0020] The present invention relates to an ink that uses water as the main medium, and the water to be used is not particularly limited, and examples thereof include tap water, ion-exchanged water, ultrafiltered water, and distilled water. The content of water relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 45 to 95 mass %, more preferably 50 to 90 mass %.

[0021] Furthermore, if necessary, conventional water-soluble organic solvents that are compatible with water can be used, such as ethanol, propanol, butanol, glycerin, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thiodiethylene 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, sulfolane, 2-pyrrolidone, and N-methyl-2-pyrrolidone. The water-soluble organic solvents can be used alone or in combination of two or more kinds, and are used in the range of 2 to 60% by mass, preferably 5 to 35% by mass.

[0022] Furthermore, a water-soluble resin can be added to impart adhesion and viscosity to the paper surface. Examples of the water-soluble resin include alkyd resin, acrylic resin, styrene-maleic acid copolymer, cellulose derivative, polyvinylpyrrolidone, polyvinyl alcohol, dextrin, etc. One or more of the water-soluble resins can be used in combination, and the ink composition can contain 1 to 100% water-soluble resins. It is used in the range of 30% by mass.

[0023] Other optional additives include inorganic salts such as sodium carbonate, sodium phosphate, and sodium acetate; pH adjusters such as water-soluble amine compounds and other organic basic compounds; rust inhibitors such as benzotriazole, tolyltriazole, and saponin; preservatives or antifungals such as carbolic acid, 1,2-benzthiazolin-3-one sodium salt, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl parahydroxybenzoate, and 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine; antifoaming agents; and fluorine-based surfactants and nonionic surfactants that improve ink penetration. Wetting agents such as urea and sodium pyrophosphate can also be used. Furthermore, a general-purpose lubricant may be added in combination with the phosphate ester, such as metal soap, polyalkylene glycol fatty acid ester, ethylene oxide-added cationic surfactant, dicarboxylic acid surfactant, β-alanine surfactant, 2,5-dimercapto-1,3,4-thiadiazole, its salts and oligomers, 3-amino-5-mercapto-1,2,4-triazole, thiocarbamate, dimethyldithiocarbamate, condensate of N-acyl-L-glutamic acid and L-lysine, and its salt. Additionally, air bubbles can be removed chemically by adding ascorbic acids, erythorbic acids, α-tocopherol, catechins, synthetic polyphenols, kojic acid, alkylhydroxylamines, oxime derivatives, α-glucosylrutin, α-lipoic acid, phosphonates, phosphinates, sulfites, sulfoxylates, dithionites, thiosulfates, thiourea dioxide, or the like. Furthermore, by adding a thickening inhibitor such as an oligomer of N-vinyl-2-pyrrolidone, an oligomer of N-vinyl-2-piperidone, N-vinyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, ε-caprolactam, or an oligomer of N-vinyl-ε-caprolactam, the functionality in the retractable form can be improved.

[0024] A dispersant can also be used to obtain dispersion stability of the pigment. In particular, nonionic dispersants are preferred because they can exert a dispersion effect while maintaining stable ink viscosity when polyglycerol isostearate is used as a shear thinning agent. Examples of nonionic dispersants include ethylene oxide adducts of alkyl ethers, ethylene oxide adducts of glycerin fatty acid esters, polyvinylpyrrolidone and its derivatives, and vinylpyrrolidone copolymers. These dispersants can be used alone or in combination of two or more kinds, and the amount added is preferably 10 to 80 mass %, more preferably 15 to 60 mass %, based on the total mass of the pigment.

[0025] The water-based ink composition having the above-mentioned configuration is intended to exhibit a higher lubrication effect by blending a chelating agent when polyglycerol isostearate ester and phosphate ester are used in combination as shear thinning agents. However, it has been discovered that the electrical conductivity of the ink composition, along with the amount of phosphate ester added, is involved in achieving both ink stability and high lubricity during writing when these components are used. By increasing the electrical conductivity of the water-based ink composition composed of the above-mentioned materials to 80 μS / cm or more, it has become possible to establish the technology of the present invention. If the electrical conductivity is less than 80 μS / cm, even if the composition is as described above, a high lubricating effect is not imparted, and the feeling of smoothness during writing is reduced. Although there is no particular upper limit for the electrical conductivity, it is preferable to set it to 2000 μS / cm or less in consideration of long-term ink stability and the expression of the lubricating effect.

[0026] The ink composition of the present invention is used after adjusting its viscosity to a level suitable for ejection depending on the structure of the ballpoint pen in which it is housed, and exhibits the above-mentioned effects, but it is preferably used as a shear-thinning ink. In this case, the ink composition exhibits excellent effects by adjusting its viscosity to 480 to 2000 mPa s, preferably 500 to 1700 mPa s, measured at 20°C and 1 rpm.

[0027] The water-based ink composition is filled into a ballpoint pen. The structure and shape of the ballpoint pen itself are not particularly limited, and conventional general-purpose ones can be used, for example, a ballpoint pen having an ink reservoir tube filled with an ink composition in a barrel, the ink reservoir tube communicating with a tip having a ball attached to the tip, and an ink backflow preventer in close contact with the end face of the ink. If the ink composition has a low viscosity, it is also possible to use a structure in which an ink retaining member is attached to the front of the barrel and the ink composition is stored directly in the barrel, or a structure in which the ink composition is stored by impregnating a porous body or a processed fiber body.

[0028] To explain the ballpoint pen tip in more detail, it is possible to use a tip in which a ball is held in a ball-holding portion formed by deforming the vicinity of the tip of a straight or stepped metal pipe by pressing inward from the outer surface, or a tip in which a ball is held in a ball-holding portion formed by cutting a metal material with a drill or the like, or a tip formed by cutting a metal pipe or metal material in which the ball held in the tip is biased forward (outward) by an elastic body. The balls may be made of cemented carbide, stainless steel, ruby, ceramic, etc., and preferably have a diameter in the range of 0.1 mm to 2.0 mm. Furthermore, when the outer diameter of the ball held is small, 0.4 mm or less, the amount of ink ejected during writing is relatively small, and in the case of a tip using a straight metal pipe, as the inner diameter becomes smaller, the amount of ink held behind the ball held becomes relatively smaller, making it difficult to feel the lubricity during writing, making the ink composition of the present invention even more useful.

[0029] The ink reservoir tube for containing the water-based ink composition is preferably made of a molded article made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, etc., in terms of low ink evaporation and productivity. Furthermore, by using a transparent, colored transparent, or translucent molded article as the ink reservoir tube, it is possible to check the ink color, remaining ink amount, etc. The ink reservoir may be directly connected to the tip, or may be connected to the tip via a connecting member. Furthermore, the ink reservoir tube may be in the form of a refill, with the refill stored within the barrel, or the barrel itself with a tip attached to the tip may serve as the ink reservoir, with ink being filled directly into the barrel.

[0030] Furthermore, the ink backflow preventer filled into the rear end of the ink composition filled in the ink reservoir tube can be either liquid or solid. Examples of the liquid ink backflow preventer (liquid stopper) include non-volatile media such as polybutene, α-olefin co-oligomer, silicone oil, and refined mineral oil. If desired, silica, aluminum silicate, swellable mica, fatty acid amide, etc. can also be added to the media. Furthermore, examples of solid ink backflow preventers include resin molded products. The liquid and solid ink backflow preventers can also be used in combination.

[0031] The ballpoint pen may be either a cap type or a retractable type, and any retractable ballpoint pen can be used as long as the writing tip provided on the ballpoint pen refill is stored in the barrel (outer barrel) while exposed to the outside air, and the writing tip protrudes from the barrel opening when the retractable mechanism is activated. The method of operating the retractable mechanism includes a knock type, a rotation type, a slide type, and the like. The knock type has a knock portion at the rear end of the barrel or on the side of the barrel, and by pressing the knock portion, the writing tip of the ballpoint pen refill is caused to protrude and retract from the opening at the front end of the barrel, or by pressing a clip portion provided on the barrel, the writing tip of the ballpoint pen refill is caused to protrude and retract from the opening at the front end of the barrel. The rotating type can be exemplified by a configuration in which a rotating part is provided at the rear of the barrel, and the writing tip of the ballpoint pen refill is caused to appear and disappear from the opening at the front end of the barrel by rotating the rotating part. The sliding type can be exemplified by a configuration in which a sliding portion is provided on the side of the barrel, and the writing tip of the ballpoint pen refill is caused to appear and disappear from the front end opening of the barrel by operating the sliding portion, or a configuration in which a clip portion provided on the barrel is slid to cause the writing tip of the ballpoint pen refill to appear and disappear from the front end opening of the barrel. The retractable ballpoint pen may be a composite type retractable ballpoint pen (refill replaceable type) that accommodates a plurality of ballpoint pen refills in the barrel. [Example]

[0032] Examples will be described below, but the present invention is not limited to these examples. The compositions of the water-based inks for ballpoint pens of Examples and Comparative Examples are shown in the following table, where the numerical values ​​for the compositions in the table indicate parts by mass. The ink viscosity was measured at 20°C using an EM-type rotational viscometer (manufactured by Tokyo Keiki Co., Ltd.) at 1 rpm, and the electrical conductivity was measured at 20°C using an electrical conductivity meter (manufactured by Yokogawa Electric Corporation, SC82) using a known measurement method.

[0033] [Table 1]

[0034] [Table 2]

[0035] The contents of the ingredients in the table are explained according to the note numbers. (1) Sanyo Pigment Co., Ltd., trade name: Sandai Super Black C (E), pigment content 30% (contains nonionic dispersant) (2) A dispersion obtained by mixing 10 parts of carbon black, 10 parts of a copolymer of N-vinylpyrrolidone and 1-butene, and 80 parts of water in a ball mill with stirring for 1 hour. (3) Sanyo Pigment Co., Ltd., trade name: Sandai Super Red BS (E), pigment content 32% (contains nonionic dispersant) (4) Sanyo Pigment Co., Ltd., trade name: Sandai Super Green LXB(E), pigment content 30% (contains nonionic dispersant) (5) A microcapsule pigment encapsulating a reversible thermochromic composition consisting of 4.5 parts of 2-(2-chloroanilino)-6-di-n-butylaminofluoran as component (A), 4.5 parts of 1,1-bis(4'-hydroxyphenyl)n-decane and 7.5 parts of 2,2-bis(4'-hydroxyphenyl)hexafluoropropane as components (B), and 50.0 parts of 4-benzyloxyphenylethyl caprate as component (C) (complete color development temperature (t1): -20°C, complete decolorization temperature (t4): 57°C, average particle size: 2.5 μm, color change from black to colorless). (6) Daiichi Kogyo Seiyaku Co., Ltd., trade name: Plysurf AL (7) Daiichi Kogyo Seiyaku Co., Ltd., trade name: Plysurf A219B (8) Arcsada Japan, product name: Proxel XL-2 (9) Hexaglycerin monoisostearate (10) Decaglycerin monoisostearate (11) Decaglycerin diisostearate (12) EDTA tetrasodium salt tetrahydrate, manufactured by Chelest Co., Ltd., trade name: Chelest 3D (13) Trisodium salt of DTPA, manufactured by Chelest Co., Ltd., trade name: Chelest PC-45 (14) Disodium salt of NTA, manufactured by Chelest Co., Ltd., trade name: Chelest NTB

[0036] Ink preparation Each ink was prepared by adding all ingredients except for polyglycerol isostearate to water, mixing and stirring, then adding polyglycerol isostearate, stirring at 1000 rpm in a disper at 60°C for 30 minutes, and filtering.

[0037] Preparation of ink backflow preventer 1.5 parts of fatty acid amide as a thickener was added to 98.5 parts of polybutene as a base oil, and then the mixture was kneaded with a three-roll mill to obtain an ink backflow preventive.

[0038] Making a ballpoint pen A ballpoint pen refill having a stainless steel tip (having a ball-holding portion formed by deforming the vicinity of the tip of a straight pipe inward from the outer surface) fitted onto one end of a polypropylene pipe with 1.5 g of the ink composition of the above Examples and Comparative Examples was filled, and the ink backflow preventive body was then placed at the rear end, after which the ballpoint pen refill was incorporated into a barrel (cap type) to prepare a sample ballpoint pen. The following tests were carried out using the sample ballpoint pen and ink composition.

[0039] Written exam Each sample ballpoint pen that was confirmed to be writable was used in an automatic writing tester to continuously write a spiral circle on JIS P3201 writing paper A, and the condition of the pen tip after consumption was confirmed to be complete. The tester was used under the following conditions: writing load 100 g, writing angle 70°, and writing speed 4 m / min.

[0040] Ink viscosity confirmation test The viscosity of each ink composition was measured at 20°C at 1 rpm using an EM-type rotational viscometer to confirm whether the thickening effect of polyglycerol isostearate was obtained. In this test configuration, the ink was deemed to have passed the test if its viscosity was 500 mPa·s or higher, which is the condition for ink stabilization. The results of the above tests are shown in the table below.

[0041] [Table 3]

[0042] The test results were evaluated as follows: Written exam ○: Writing was possible and no wear was observed on the ball seat. △: I was able to write completely, but there was wear on the ball seat. ×: The ball seat was worn out so much that writing became impossible halfway through. Ink viscosity confirmation test ○: Sufficient viscosity is exhibited. ×: The viscosity is insufficient.

Claims

1. An aqueous ink composition comprising a pigment, water, a polyglycerol isostearate ester as a shear thinning agent, a phosphate ester, and a chelating agent, The water-based ink composition for a ballpoint pen contains the phosphoric acid ester in an amount of less than 0.5 mass % based on the total amount of the ink composition, and the ink composition has an electrical conductivity of 80 μS / cm or more.

2. 2. The water-based ink composition for ballpoint pens according to claim 1, wherein the ratio of the chelating agent to the phosphate ester is in the range of 0.002 to 1.

3. 3. The water-based ink composition for a ballpoint pen according to claim 1, further comprising a nonionic dispersant.

4. 3. The aqueous ink composition for a ballpoint pen according to claim 1, wherein the chelating agent is at least one selected from the group consisting of EDTA, NTA, HEDTA, HIDA, GEDTA, DHEG, DTPA, TTHA, PDTA, and salts thereof.

5. 2. The water-based ink composition for ballpoint pens according to claim 1, wherein the electrical conductivity is 2000 μS / cm or less.

6. A ballpoint pen incorporating the water-based ink composition for ballpoint pens according to any one of claims 1 to 5.

7. 7. The ballpoint pen according to claim 6, wherein the ballpoint pen tip has a ball seat formed by pressing and deforming a metal pipe.

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