Aqueous ink composition for ball-point pen and ball-point pen incorporating the same

Abstract

To provide an aqueous ink composition for a ball-point pen, capable of suppressing abrasion of a ball reception seat generated by use in a thin-character ball-point pen and a ball-point pen of an ink cartridge form, excellent ink inflow properties and drawing line quality, and capable of exhibiting smooth writing feeling for a long period, and to provide a ball-point pen incorporating the same.SOLUTION: An aqueous ink composition for a ball-point pen contains a coloring agent, water, and barium titanate having an average particle diameter of 50 nm or less. A ball-point pen incorporating the composition is also provided. The barium titanate is 0.01-5 mass% in an aqueous ink.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous ink composition for ballpoint pens. Furthermore, the present invention relates to an aqueous ink composition for ballpoint pens having excellent wear resistance of the ball receiving seat of a ballpoint pen tip and a ballpoint pen incorporating the same.

Background Art

[0002] Since a ballpoint pen is a mechanism in which ink is transferred to the writing surface by the rotation of the ball during writing, and thus handwriting can be formed, with long-distance writing, the portion (ball receiving seat) that receives and contacts the ball inside the ballpoint pen tip wears due to the rotation of the ball, causing problems such as clogging of the ink flow holes or the caulked portion holding the ball hitting the paper surface, resulting in writing defects such as smudging or inability to write. Therefore, techniques have been proposed in which fine particles having a particle diameter of 0.1 μm or more and 30 μm or less, such as alumina, silicon carbide, and chromium oxide, having a new Mohs hardness of 4 or more, are added to the aqueous ink composition, and ultra-fine particles having a particle diameter of less than 0.1 μm, such as alumina, titanium oxide, silica, silicon carbide, and tungsten carbide, are added to the ink composition in an amount of 0.002 to 2% by weight (see, for example, Patent Documents 1 and 2).

[0003] However, in the technique of Patent Document 1, there are problems such as a deterioration in writing feel, a phenomenon (directionality) in which the ink outflow amount becomes non-uniform depending on the writing direction, and a phenomenon (skipping) in which the rotation of the ball temporarily stops and the ball slides on the paper surface and the drawn line is interrupted, resulting in a decrease in the quality of the drawn line. In the case of a fine-point ballpoint pen using a ball with a diameter of 0.4 mm or less, since the area of the ball seat is smaller than that of a normal ballpoint pen using a ball with a diameter of 0.48 mm or more, the load per unit area of the seat is large, the frictional resistance is high, and wear is significant. Furthermore, as the ball diameter decreases, the number of rotations of the ball when writing the same distance in the same time increases, so the load on the seat increases, and writing defects and inability to write are more likely to occur. Therefore, in the technology of Patent Document 2, although the problems such as those in Patent Document 1 are solved, there are cases where sufficient effects cannot be obtained for suppressing the wear of the seat. Furthermore, in the case of a cartridge-type ballpoint pen, after the built-in ink is consumed, it can be written again by replacing the ink cartridge, so the pen body can be used repeatedly, leading to a reduction in environmental load. However, compared with disposable-type products, the writing distance is extremely long, so a technology for suppressing wear of the seat due to repeated use is required.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] As a result of further intensive studies on the technology for suppressing wear (seat wear) of the ball seat of a ballpoint pen tip, the present invention provides an aqueous ink composition for a ballpoint pen that can suppress seat wear generated during use even in a fine-point ballpoint pen or a ballpoint pen in the form of an ink cartridge, has excellent ink outflow properties and line drawing quality, and can exhibit a smooth writing feeling over a long period, and a ballpoint pen incorporating the same.

Means for Solving the Problems

[0006] The aqueous ink composition for ballpoint pens of the present invention is required to comprise a colorant, water, and barium titanate having an average particle diameter of 50 nm or less. Furthermore, it is required that the barium titanate is in the range of 0.01 to 5% by mass in the aqueous ink and that it comprises a dispersant. Furthermore, a ballpoint pen incorporating the aqueous ink composition for ballpoint pens is required. It is in the form of an ink cartridge having the aqueous ink incorporated in an ink storage part detachable from the writing instrument body, and it is required to be provided with a ball with a diameter of 0.4 mm or less at the writing tip part.

Effects of the Invention

[0007] According to the present invention, even in a fine-line ballpoint pen or a ballpoint pen in the form of an ink cartridge, wear (seat wear) of the ball receiving seat of the ballpoint pen tip generated during use can be suppressed. Therefore, it becomes an aqueous ink composition for ballpoint pens excellent in ink outflow properties and drawing line quality, capable of expressing a smooth writing feeling over a long period, and a ballpoint pen incorporating the same.

Modes for Carrying Out the Invention

[0008] Barium titanate (BaTiO3) is an artificial mineral having a tetragonal perovskite crystal structure at room temperature. In the present invention, ultrafine particles having an average particle diameter of 50 nm or less are used. Incidentally, as the shape, a true spherical or substantially spherical one is applied. Barium titanate having an average particle diameter of 50 nm or less is presumed to suppress the occurrence of wear by flowing a large number between the ball and the ball receiving seat due to the ink flow during writing and acting as a roller by being stably dispersed in the ink. This effect cannot be sufficiently obtained with other inorganic particles and is an effect peculiar to barium titanate having an average particle diameter of 50 nm or less. Incidentally, since barium titanate does not have hardness like titanium dioxide or silica among inorganic particles, it is not suitable for coating involving pressure, and coating using supercritical carbon dioxide etc. cannot be performed, but surface treatment can also be performed by other methods if necessary.

[0009] In the present invention, those with an average particle diameter of 50 nm or less are applied. However, since a high effect can be exhibited with a small amount of addition, those with an average particle diameter of preferably 40 nm or less, more preferably 35 nm or less are applied. Further, as the lower limit, those with an average particle diameter of 10 nm or more, preferably 20 nm or more can be applied from the viewpoint of availability. The average particle diameter is the average particle diameter calculated by the cumulant analysis method by measuring the particle size distribution based on the dynamic light scattering method. Specifically, it can be measured by a particle size distribution measuring device using the dynamic light scattering method such as the model "Zetasizer Nano ZS ZEN3600" (manufactured by Malvern Instruments). Further, when it cannot be measured by the dynamic light scattering method, a scanning electron microscope (SEM) can be used to take an SEM photograph of the barium titanate fine particles, and 20 arbitrary fine particles are selected from the obtained photograph, and the diameters of the fine particles are measured and averaged. It can also be obtained by

[0010] It is preferable to add the barium titanate in the range of 0.01 to 5% by mass in the total amount of the ink composition. If it is less than 0.01% by mass, it is difficult to obtain a sufficient effect, and even if it is added in excess of 5% by mass, no improvement in the effect is observed, so no further addition is required.

[0011] In order to suppress the aggregation of the barium titanate particles in the ink and maintain a uniformly dispersed state for a long period of time, it is preferable to contain a dispersant. The dispersant is not particularly limited, and one or more kinds can be used as necessary from various known dispersants. Specifically, it may be any of so-called surfactant-type dispersants (also referred to as low-molecular-type dispersants), polymer-type dispersants, inorganic-type dispersants, etc., and may be any of anionic, cationic, amphoteric or nonionic. Incidentally, a surfactant refers to an amphiphilic substance having a hydrophilic site and a lipophilic site in its molecular structure and having a chemical structure in which these are covalently bonded.

[0012] Examples of surfactant-type dispersants include dispersants mainly composed of alkyl sulfonates, dispersants mainly composed of quaternary ammonium salts, dispersants mainly composed of alkylene oxide compounds of higher alcohols, dispersants mainly composed of polyhydric alcohol ester compounds, dispersants mainly composed of alkyl polyamine compounds, and the like. Examples of polymer-type dispersants include dispersants mainly composed of fatty acid salts such as carboxylic acids or polycarboxylic acids, dispersants mainly composed of polycarboxylic acid partial alkyl ester compounds in which hydrogen atoms in some of the carboxylic acid groups are substituted by alkyl groups, dispersants mainly composed of polycarboxylic acid alkylamine salts, dispersants mainly composed of polycarboxylic acid partial alkyl ester compounds having alkyl ester bonds in some parts of the polycarboxylic acids, polystyrene sulfonates, polyisoprene sulfonates, dispersants mainly composed of polyalkylene polyamine compounds, sulfonic acid-based compounds such as naphthalene sulfonates and naphthalene sulfonic acid formalin condensate salts, dispersants mainly composed of hydrophilic polymers such as polyethylene glycol, dispersants mainly composed of polyether compounds, and dispersants mainly composed of poly(meth)acrylic-based compounds such as poly(meth)acrylate and poly(meth)acrylamide. Examples of inorganic-type dispersants include phosphates such as orthophosphate, metaphosphate, polyphosphate, pyrophosphate, tripolyphosphate, hexametaphosphate, and organic phosphate, iron salts such as ferric sulfate, ferrous sulfate, ferric chloride, and ferrous chloride, aluminum salts such as aluminum sulfate, polyaluminum chloride, and sodium aluminate, and dispersants mainly composed of calcium salts such as calcium sulfate, calcium hydroxide, and calcium hydrogen phosphate.

[0013] The dispersant is preferably added in the range of 0.01 to 5% by mass based on the total amount of the ink composition. If it is less than 0.01% by mass, it is difficult to obtain a sufficient dispersion effect. Also, even if it is added in excess of 5% by mass, no improvement in the effect is observed, so further addition is not required.

[0014] As the coloring agent, all dyes and pigments that can be dissolved or dispersed in an aqueous medium can be used, and specific examples thereof are illustrated below. As the dye, an acid dye, a basic dye, a direct dye, etc. can be used. Examples of the acid dye include New Coccine (C.I. 16255), Tartrazine (C.I. 19140), Acid Blue Black 10B (C.I. 20470), Guinea Green (C.I. 42085), Brilliant Blue FCF (C.I. 42090), Acid Violet 6B (C.I. 42640), Soluble Blue (C.I. 42755), Naphthalene Green (C.I. 44025), Eosin (C.I. 45380), Fluorescein (C.I. 45410), Erythrosine (C.I. 45430), Nigrosine (C.I. 50420), Acid Flavin (C.I. 56205), etc. Examples of the basic dye include Chrysoidine (C.I. 11270), Methyl Violet FN (C.I. 42535), Crystal Violet (C.I. 42555), Malachite Green (C.I. 42000), Victoria Blue FB (C.I. 44045), Rhodamine B (C.I. 45170), Acridine Orange NS (C.I. 46005), Methylene Blue B (C.I. 52015), etc. Examples of the direct dye include Congo Red (C.I. 22120), Direct Sky Blue 5B (C.I. 24400), Violet BB (C.I. 27905), Direct Deep Black EX (C.I. 30235), Kayarus Black G Conc. (C.I. 35225), Direct Fast Black G (C.I. 35255), Phthalocyanine Blue (C.I. 74180), etc.

[0015] As the pigment, in addition to inorganic pigments such as carbon black and ultramarine blue, and organic pigments such as copper phthalocyanine blue and benzidine yellow, water-dispersed pigment products finely and stably dispersed in an aqueous medium in advance using a surfactant or the like are used. For example, C.I. Pigment Blue 15:3B [Product name: S.S. Blue GLL, pigment content 22%, manufactured by Sanyo Color Co., Ltd.], C.I. Pigment Red 146 [Product name: S.S. Pink FBL, pigment content 21.5%, manufactured by Sanyo Color Co., Ltd.], C.I. Pigment Yellow 81 [Product name: TC Yellow FG, pigment content approximately 30%, manufactured by Dainichi Seika Kogyo Co., Ltd.], C.I. Pigment Red 220 / 166 [Product name: TC Red FG, pigment content approximately 35%, manufactured by Dainichi Seika Kogyo Co., Ltd.] and the like can be mentioned. As the fluorescent pigment, synthetic resin fine particle-shaped fluorescent pigments in which various fluorescent dyes are solid-solubilized in a resin matrix can be used. In addition, pearl pigments, metallic pigments of gold and silver, phosphorescent pigments, white pigments such as titanium dioxide, metal powders such as aluminum, and further, heat-discolorable compositions, light-discolorable compositions, fragrances, etc. directly or microencapsulated capsule pigments and the like can be exemplified.

[0016] As the heat-discolorable composition, a reversible heat-discolorable composition comprising (a) an electron-donating color-developing organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the color-developing temperature of the two is preferable, and it is applied as a reversible heat-discolorable microcapsule pigment by being encapsulated in a microcapsule. As the reversible thermochromic composition, those described in Japanese Patent Publication No. Sho 51-44706, Japanese Patent Publication No. Sho 51-44707, Japanese Patent Publication No. Hei 1-29398, etc., change color before and after a predetermined temperature (color change point), exhibit a decolorized state in a temperature range equal to or higher than the high-temperature-side color change point, and exhibit a colored state in a temperature range equal to or lower than the low-temperature-side color change point. Only one of the two states exists at room temperature, and the other state is maintained while heat or thermal cooling required for the manifestation of the state is applied, but returns to the state exhibited at room temperature when the application of heat or thermal cooling ceases. A heat-decolorizable microcapsule pigment in which a reversible thermochromic composition having a relatively small hysteresis width (ΔH = 1 to 7°C) is encapsulated in microcapsules can be applied. Furthermore, those exhibiting a relatively large hysteresis characteristic (ΔH = 8 to 50°C) described in Japanese Patent Publication No. Hei 4-17154, Japanese Unexamined Patent Application Publication No. Hei 7-179777, Japanese Unexamined Patent Application Publication No. Hei 7-33997, Japanese Unexamined Patent Application Publication No. Hei 8-39936, etc., and those exhibiting a large hysteresis characteristic described in 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 greatly differs between the case of increasing the temperature from the low-temperature side of the color change temperature range and the case of decreasing the temperature from the high-temperature side of the color change temperature range, and changes color following a greatly different path. A heat-decolorizable microcapsule pigment encapsulating a reversible thermochromic composition having color memory in a low-temperature range below the complete coloring temperature or a decolorized state in a high-temperature range above the complete decolorizing temperature can also be applied. Incidentally, specifically, as the reversible thermochromic composition having color memory, 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 decolorizing 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 function effectively for maintaining the color exhibited in the normal state (daily living temperature range).

[0017] The coloring agent can be used by appropriately mixing one kind or two or more kinds thereof, and is used in the range of 1 to 35% by mass, preferably 2 to 30% by mass in the ink composition. In particular, since carbon black tends to promote seat wear due to writing, the configuration of the present invention becomes particularly useful.

[0018] Furthermore, if necessary, a conventionally general-purpose water-soluble organic solvent compatible with water can be used. Specifically, 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, N-methyl-2-pyrrolidone, etc. can be mentioned. In addition, the water-soluble organic solvent can be used in combination of one kind or two or more kinds, and is used in the range of 2 to 60% by mass, preferably 5 to 35% by mass.

[0019] 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, polyvinyl pyrrolidone, polyvinyl alcohol, dextrin, etc. The water-soluble resin can be used in combination of one kind or two or more kinds, and is used in the range of 1 to 30% by mass in the ink composition.

[0020] Moreover, a shear-thinning viscosity imparting agent can also be added. For example, substances soluble or dispersible in water are effective, such as xanthan gum, welan gum, zeta-sea gum, diutan gum, macrohomo psis gum, succinoglycan (average molecular weight of about 1 million to 8 million) which is an organic acid-modified heteropolysaccharide with constituent monosaccharides of glucose and galactose, guar gum, locust bean gum and its derivatives, hydroxyethyl cellulose, alkyl alginates, polymers with a molecular weight of 100,000 to 150,000 mainly composed of alkyl esters of methacrylic acid, glucomannan, carbohydrates having gelling ability extracted from seaweeds such as agar and 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, nonionic surfactants with an HLB value of 8 to 12, metal salts and amine salts of dialkyl sulfosuccinic acid, etc. can be exemplified.

[0021] In addition, as necessary, pH adjusters such as inorganic salts such as sodium carbonate, sodium phosphate, sodium acetate, and organic basic compounds such as water-soluble amine compounds, rust preventives such as benzotriazole, tolyltriazole, and saponin, preservatives or fungicides such as 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, defoaming agents, fluorine-based surfactants and nonionic surfactants that improve the ink permeability may be used. Also, other wetting agents such as sorbitol, mannitol, sucrose, glucose, reduced starch hydrolyzate, urea, sodium pyrophosphate, etc. can be used in combination. Furthermore, lubricants can be added, and metal soaps, polyalkylene glycol fatty acid esters, ethylene oxide-added cationic surfactants, phosphate ester-based surfactants, dicarboxylic acid-type surfactants, β-alanine-type surfactants, 2,5-dimercapto-1,3,4-thiadiazole and its salts and oligomers, 3-amino-5-mercapto-1,2,4-triazole, thiocarbamate, dimethyldithiocarbamate, condensates of N-acyl-L-glutamic acid and L-lysine and their salts, etc. are used. 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, etc. can also be added to chemically remove bubbles. 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 and disappearing form can also be enhanced.

[0022] The ballpoint pen filled with the above-described aqueous ink composition for ballpoint pens will be described. The ballpoint pen tip at the writing tip portion is, for example, one formed by cutting a metal to form a ball seat and an ink outlet portion inside, or a plurality of inward protrusions are provided on the inner surface near the tip of a metal pipe by pressing and deforming from the outer surface, and an ink outflow gap extending radially outward from the center portion is formed between the inward protrusions. etc. can be applied. In particular, the tip formed 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. The ball held by the ballpoint pen tip is effective for balls with an outer diameter of 0.1 to 2.0 mm, preferably 0.2 to 1.2 mm, more preferably 0.28 to 1.0 mm, such as cemented carbide, stainless steel, ruby, ceramics, etc. In particular, when a ball of 0.4 mm or less is used, seat wear is likely to occur, so the present invention becomes particularly useful. Furthermore, a ballpoint pen tip may be configured such that a resilient member for elastically projecting the rear end of the ball forward is disposed within the tip. When not writing, the ball is pressed against the inner edge of the tip end to be in a close state, and when writing, the ball is retracted by the writing pressure to allow ink to flow out. Ink leakage when not in use can be suppressed. Examples of the resilient member include a spring made of a thin metal wire, one having a straight portion (rod portion) at one end of the spring, a linear plastic processed body, etc. It is configured to be applicable with a resilient force of 5 to 40 g so as to be pressable.

[0023] The shaft cylinder for accommodating the aqueous ink composition is preferably made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, etc. in terms of low ink volatility and productivity. In addition to directly connecting the tip to the shaft cylinder, the tip and the shaft cylinder may be connected via a connecting member. For the ink composition accommodated in the shaft cylinder, when the ink composition has a low viscosity, an ink retention member may be attached to the front part of the shaft cylinder, and methods include directly accommodating the ink composition in the shaft cylinder and impregnating and accommodating the ink composition in a porous body or a fiber processed body. Furthermore, the ink storage portion disposed behind the ink retention member and accommodating the aqueous ink may be in the form of an ink cartridge with a detachable structure with respect to the writing instrument body. In this case, after the previously accommodated ink is used up, it can be replaced with a new ink cartridge and continuously used. Therefore, the writing distance becomes longer and the load on the pen tip is greater than that of a disposable one. Thus, the application of the ink of the present application configuration becomes more useful. As the ink cartridge, those that also serve as the shaft cylinder that constitutes the writing instrument when connected to the writing instrument body, or those that cover and protect the shaft cylinder (rear shaft) after being connected to the writing instrument body can be applied. In the latter case, in addition to being applicable as a single ink cartridge, in a writing instrument before use, it may be one in which the writing instrument body and the ink cartridge are connected, or one that is accommodated in the shaft cylinder in a non-connected state so that the user connects the ink cartridge in the shaft cylinder to start using it when using the writing instrument.

[0024] Furthermore, by using a transparent, colored transparent, or translucent molded body as the barrel, it is possible to check the ink color, the remaining amount of ink, etc. In addition, the barrel may be in the form of a refill for a ballpoint pen that houses the refill inside the outer shaft, or the barrel itself with a tip attached to the tip may be used as an ink container, and the barrel may be directly filled with ink.

[0025] The ballpoint pen using the barrel can be applied in either a cap type or a retractable type. As a retractable ballpoint pen, the writing tip provided on the ballpoint pen refill is housed inside the outer shaft in a state exposed to the outside air, and any structure in which the writing tip protrudes from the outer shaft opening by the operation of the retracting mechanism can be used. Since the pen tip of the retractable ballpoint pen is always exposed to the outside air, the ink composition of the present invention is particularly effective. Examples of the operation method of the retracting mechanism include a knock type, a rotary type, a slide type, etc. The knock type has a knock portion on the rear end portion or the side surface of the outer shaft, and by pressing the knock portion, the writing tip of the ballpoint pen refill is configured to protrude and retract from the front end opening of the outer shaft, or by pressing a clip portion provided on the outer shaft, the writing tip of the ballpoint pen refill is configured to protrude and retract from the front end opening of the outer shaft. The rotary type has a rotating portion (rear shaft, etc.) on the outer shaft, and an example of the configuration is that by rotating the rotating portion, the writing tip of the ballpoint pen refill is protruded and retracted from the front end opening of the outer shaft. The slide type has a slide portion on the side surface of the barrel, and by operating the slide, the writing tip of the ballpoint pen refill is configured to protrude and retract from the front end opening of the outer shaft, or by sliding a clip portion provided on the outer shaft, the writing tip of the ballpoint pen refill is configured to protrude and retract from the front end opening of the outer shaft. In addition, the retractable ballpoint pen may be a composite type retractable ballpoint pen that houses a plurality of ballpoint pen refills, in addition to the one that houses a single ballpoint pen refill inside the outer shaft. Also, the ink storage tube constituting the ballpoint pen refill may be made of resin or metal.

[0026] An ink backflow prevention body can also be filled at the rear end of the ink contained in the ballpoint pen refill. The ink backflow prevention body composition consists of a non-volatile liquid or a hardly volatile liquid. Specifically, there are petrolatum, spindle oil, castor oil, olive oil, refined mineral oil, liquid paraffin, polybutene, α-olefin, an oligomer or a co-oligomer of α-olefin, dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, polyether-modified silicone oil, fatty acid-modified silicone oil, etc., and one kind or two or more kinds can be used in combination.

[0027] It is preferable to add a gelling agent to the non-volatile liquid or hardly volatile liquid to thicken it to a suitable viscosity. Examples of thickening agents include silica with a hydrophobic surface, fine particle silica with a methylated surface, aluminum silicate, swelling mica, clay-based thickening agents such as hydrophobic-treated bentonite and montmorillonite, fatty acid metal soaps such as magnesium stearate, calcium stearate, aluminum stearate, zinc stearate, tribenzylidene sorbitol, fatty acid amide, amide-modified polyethylene wax, hydrogenated castor oil, dextrin-based compounds such as fatty acid dextrin, and cellulose-based compounds. Furthermore, a liquid ink backflow prevention body composition and a solid ink backflow prevention body can also be used in combination.

Examples

[0028] Examples will be described below, but the present invention is not limited to these examples. The compositions of aqueous inks for ballpoint pens in Examples and Comparative Examples are shown in the following table. The numerical values of the compositions in the table indicate parts by mass.

[0029]

Table 1

[0030] The contents of the raw materials in the table will be described according to the footnote numbers. (1) Manufactured by Orient Chemical Industries Co., Ltd., trade name: Water Black 191L (15% by mass aqueous solution) (2) Manufactured by Sumitomo Chemical Co., Ltd., trade name: Acid Blue PG (3) Manufactured by Tokai Carbon Co., Ltd., trade name: Aqua Black 162 (20% by mass aqueous solution) (4) Microcapsule pigment encapsulating a reversible thermochromic composition consisting of 1.0 part of 3,6-bis(diphenylamino)fluorane as component (a), 3.0 parts of 1,1-bis(4-hydroxyphenyl)-2-ethylhexane as component (b), 5.0 parts of 2,2-bis(4'-hydroxyphenyl)-hexafluoropropane, and 50.0 parts of 4-benzyloxyphenylethyl caprate as component (c) (complete color development temperature (t1): -20 °C, complete decolorization temperature (t4): 55 °C, average particle diameter: 1.8 μm, color change from blue to colorless) (5) Average particle diameter: 30 nm (6) Average particle diameter: 40 nm (7) Average particle diameter: 100 nm (8) Rutile type, average particle diameter: 30 - 50 nm (9) Hydrophilic silica, average particle diameter: 30 nm (10) Manufactured by BYK-Chemie Japan Co., Ltd., trade name: DISPER BYK-191 (11) Manufactured by Nikko Chemicals Co., Ltd., trade name: NIKKOL DDP-4 (12) Manufactured by Avecia Japan Co., Ltd., trade name: Proxel XL-2

[0031] Preparation of Ink Water, inorganic fine particles, and a dispersant were mixed and pre-dispersed using a bead mill. Then, components other than the thickener were added to the water, mixed and stirred, and then, those containing the thickener were added, and stirred at 400 rpm for 1 hour using a disper at 20 °C, and each ink was prepared by filtration.

[0032] Preparation of Ink Backflow Preventive After adding 1.5 parts of fatty acid amide as a thickener to 98.5 parts of polybutene as a base oil, it was kneaded using a three-roll mill to obtain an ink backflow preventive.

[0033] Preparation of Ball Pen A 1.0 g of each of the ink compositions of Examples 1 to 5 and Comparative Examples 1 to 3 was filled into two types of ball pen refills in which stainless steel tips holding cemented carbide balls with diameters of 0.4 mm and 0.5 mm were fitted to one end of a polypropylene pipe. After disposing the ink backflow preventer at the rear end of the ink, the ball pen refill was incorporated into the outer shaft, and a cap was attached to prepare sample ball pen A.

[0034] Preparation of Ball Pen B The ink compositions of Examples 6 to 8 and Comparative Examples 4 and 5 were filled with 0.9 g into an ink cartridge having a pen tip with a cemented carbide ball with a diameter of 0.5 mm (manufactured by Pilot Corporation, BXC-V5-BG) and an outer case obtained by replacing the pen tip of a stainless steel tip holding a cemented carbide ball with a diameter of 0.4 mm to prepare sample ball pen B.

[0035] The following tests were conducted using the sample ball pens and the ink compositions. Writing Test Each sample ball pen confirmed to be capable of writing was continuously written with spiral circles on JIS P3201 writing paper A using an automatic writing tester, and it was confirmed whether the filled ink was completely consumed and the condition of the pen tip after consumption. Further, for ball pen B, the cartridge was replaced twice, and it was confirmed whether all could be written out and the condition of the pen tip after writing out. The tester was used under the conditions of a writing load of 100 g, a writing angle of 70°, and a writing speed of 4 m / min. Ink Stability Test Each ink composition was sealed in a glass bottle and left in an environment of 50°C for 30 days. Then, the state of the internal ink was visually confirmed at room temperature. The results of the above tests are shown in the following table.

[0036]

Table 2

[0037] The evaluation of the test results is as follows. Written test ○: It was possible to finish writing, and no wear was observed on the ball seat. △: It was possible to finish writing, but significant wear was observed on the ball seat. ×: Wear on the ball seat was significant, and it became impossible to write midway. Ink stability test ○: No abnormality. ×: Sedimentation is observed.

Claims

1. An aqueous ink composition for ballpoint pens, comprising a colorant, water, and barium titanate having an average particle diameter of 50 nm or less.

2. The aqueous ink composition for ballpoint pens according to Claim 1, wherein the barium titanate is in the range of 0.01 to 5% by mass in the aqueous ink.

3. The aqueous ink composition for ballpoint pens according to Claim 1 or 2, comprising a dispersant.

4. A ballpoint pen containing the aqueous ink composition for ballpoint pens according to any one of Claims 1 to 3.

5. The ballpoint pen according to Claim 4, which is in the form of an ink cartridge having an aqueous ink built in an ink storage part detachable from the writing instrument body.

6. The ballpoint pen according to Claim 4 or 5, having a ball with a diameter of 0.4 mm or less at the writing tip.

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