Aqueous ink composition for writing instrument, and writing instrument and ink cartridge for writing instrument storing the same

Abstract

To provide an aqueous ink composition for a writing instrument which enables formation of handwriting that has a thick black color, is clear and suppresses bleeding, has good dryness of the handwriting, is excellent in water resistance of the handwriting even if a writing instrument is a writing instrument after the elapse of time, and enables formation of good handwriting over a long period of time, and a writing instrument and an ink cartridge for a writing instrument which store the same.SOLUTION: There are provided an aqueous ink composition for a writing instrument which is composed of at least a self-dispersion type carbon black, a specific surface active agent having an acetylene bond, urethane-based resin emulsion and water, wherein tensile elongation of a resin in the urethane-based resin emulsion is 600% or more; and a writing instrument and an ink cartridge for a writing instrument which store the same.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-based ink composition for a writing instrument, and a writing instrument and an ink cartridge for a writing instrument each containing the same. [Background technology]

[0002] Conventionally, dyes and pigments have been used as colorants in inks contained in writing instruments. In particular, inks using pigments as colorants are widely used because they have better light resistance than dyes and are less likely to fade over time. Studies have been conducted on inks containing pigments to improve the density and water resistance of handwriting (see, for example, Patent Document 1). Patent Document 1 discloses a water-based ink composition for a writing instrument, which comprises self-dispersing carbon black having a specific average particle size and an acrylic resin emulsion having a glass transition temperature of 0° C. or lower. Handwriting formed by a writing instrument containing the ink composition (ink) has a deep black color and is water-resistant.

[0003] However, the above-mentioned inks do not have sufficient penetration into the paper surface, so when the ink is applied to a writing instrument, it is difficult to form handwriting that has excellent drying properties. In particular, when the ink is applied to a writing instrument such as a brush pen in which a large amount of ink is applied to the paper surface, it is even more difficult to form handwriting that has excellent drying properties. Furthermore, if a writing instrument containing the above-mentioned ink is left unused for a long period of time, the water resistance of the handwriting formed with the writing instrument may be impaired, making it difficult to produce an ink that maintains the effect of imparting water resistance to handwriting for a long period of time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5690087 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide an aqueous ink composition for a writing instrument that is capable of forming deep black handwriting, has good drying properties, and provides excellent water resistance to handwriting even after the writing instrument has been aged, as well as a writing instrument and an ink cartridge for a writing instrument that contain the same. [Means for solving the problem]

[0006] The present invention relates to an aqueous ink composition for a writing instrument, which comprises at least self-dispersing carbon black, a surfactant having an acetylene bond represented by the following formula (1), a urethane resin emulsion, and water, and wherein the tensile elongation of the resin in the urethane resin emulsion is 600% or more. [ka] (In the formula, R 1 , R 2 , R 3 , and R 4 are each independently an alkyl group, R 5 is an ethylene group, l and m are each independently an integer of 0 or more. Further, the tensile elongation of the resin in the urethane resin emulsion is 600% or more and 2000% or less, and the content of the resin in the urethane resin emulsion with respect to the total mass of the ink composition is 0.1 to 3 mass%. A further feature is a writing instrument containing the ink composition. Further, the requirements are that the writing instrument is a brush pen, that the brush pen is equipped with a nib, an ink filling mechanism, and an ink supply mechanism, that the ink filling mechanism is equipped with an ink cartridge, that the ink filling mechanism is made of a barrel with an ink storage chamber provided inside, and that the nib and ink filling mechanism are joined via the ink supply mechanism, and that the ink supply mechanism is equipped with a pen core consisting of a number of disks arranged in parallel with comb-like intervals, a slit-shaped ink guide groove running vertically through the disks in the axial direction and a wider air vent groove than the groove, and an ink guide core arranged in the barrel for guiding ink to the nib. A further feature is an ink cartridge containing the ink composition. Effect of the Invention

[0007] The present invention can provide an aqueous ink composition for a writing instrument that can form handwriting that is deep, vivid, and suppressed bleeding, that dries easily, and that provides excellent water resistance to handwriting even after the writing instrument has been aged, allowing good handwriting to be formed over a long period of time, as well as a writing instrument and an ink cartridge for a writing instrument that contain the same. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is an explanatory diagram showing one embodiment of a writing instrument (brush pen) according to the present invention. [Diagram 2] FIG. 1 is an explanatory diagram showing one embodiment of an ink cartridge for a writing instrument (brush pen) according to the present invention. [Diagram 3] FIG. 4 is an explanatory diagram showing another embodiment of the writing instrument (brush pen) according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The water-based ink composition for writing instruments according to the present invention (hereinafter sometimes referred to as "ink composition" or "ink") contains at least self-dispersing carbon black, a surfactant having an acetylene bond represented by the above formula (1), a urethane resin emulsion, and water, and the tensile elongation of the resin in the urethane resin emulsion is 600% or more. Each component constituting the ink composition according to the present invention will be described below.

[0010] The ink composition according to the present invention comprises self-dispersible carbon black. Self-dispersing carbon black refers to carbon black that can be dispersed in an aqueous medium without using a dispersant such as a resin, a surfactant, etc. The aqueous medium is not particularly limited, and examples thereof include water such as tap water, ion-exchanged water, ultrafiltered water, and distilled water. By subjecting carbon black to a physical or chemical treatment to form hydrophilic functional groups (hereinafter sometimes referred to as "hydrophilic groups") on the surface, it becomes possible to disperse the carbon black in an aqueous medium without using a dispersant. Examples of hydrophilic functional groups include -COOM and -SO 3 M, -SO 2 M, -CO-, -COO-, -OM, -SO 2 NH 2 , -RSO 2 M, -PO 3 H.M., -PO 3 M 2 , -SO 2 NHCOR, -NH 3 , -NR 3 Examples include: Each M in the above functional group is independently a hydrogen atom, an alkali metal, ammonium, a phenyl group which may have a substituent, or an organic ammonium. Each R in the functional group is independently an alkyl group having 1 to 12 carbon atoms, or a naphthyl group which may have a substituent. An example of the physical treatment is a vacuum plasma treatment. Examples of chemical treatments include a wet oxidation method in which oxidation is performed in water using an oxidizing agent, and a method in which p-aminobenzoic acid is bonded to the carbon black surface to bond a carboxy group via a phenyl group.

[0011] Ink using a pigment that has excellent paper surface permeability is one in which the pigment easily permeates into the inside of the paper together with the vehicle, but on the other hand, there is a tendency for the color development of handwriting to be easily impaired. However, the ink composition according to the present invention contains self-dispersible carbon black, and while the ink composition has excellent paper surface permeability, it is possible to form a deep black and vivid handwriting. In addition, the use of self-dispersible carbon black can also suppress bleeding of handwriting. This is presumably because the hydrophilic groups present on the surface of the self-dispersed carbon black have a high affinity with the cellulose in the paper fibers, and so when the ink comes into contact with the paper surface, the self-dispersed carbon black is quickly adsorbed to the cellulose on the paper surface via the hydrophilic groups present on its surface, preventing the self-dispersed carbon black from penetrating into the paper and preventing the ink that has come into contact with the paper surface from spreading around the area of ​​contact.

[0012] Specific examples of self-dispersible carbon black include BONJET BLACK CW-1, CW-2, and CW-3 manufactured by Orient Chemical Industries Co., Ltd., CAB-O-JET 200 and 300 manufactured by Cabot Corporation, Aqua-Black 001 and 162 manufactured by Tokai Carbon Co., Ltd., and FUJI JET BLACK A-20, B-15, B-22, and D-12 manufactured by Fuji Pigment Co., Ltd.

[0013] The content of the self-dispersed carbon black relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 5 to 15 mass%, more preferably 6 to 14 mass%. By having the content of the self-dispersed carbon black within the above range, the black color of the handwriting is deep and vivid, while the self-dispersed carbon black can be prevented from adhering to the periphery of the handwriting when the handwriting is rubbed, thereby preventing the paper surface from being contaminated. In addition, when the moisture in the ink evaporates from the pen tip of the writing instrument and dries, it becomes easier to prevent the ink from becoming unable to be rewritten.

[0014] The ink composition according to the present invention further comprises a surfactant having an acetylene bond represented by the following formula (1). [ka] (In the formula, R 1 , R 2 , R 3 , and R 4 are each independently an alkyl group, R 5 is an ethylene group, l and m are each independently an integer of 0 or more.

[0015] The ink composition according to the present invention contains the above-mentioned specific surfactant having an acetylene bond, and therefore the ink composition can have good paper surface penetration properties. For example, a writing instrument such as a brush pen, which has a rich ink tip, tends to impair the drying properties of handwriting when writing on paper because a large amount of ink is applied to the paper. However, the ink composition according to the present invention has excellent paper surface permeability due to the inclusion of the surfactant represented by the above formula (1), and can provide good drying properties of handwriting even when a large amount of ink is applied to the paper. Furthermore, the above-mentioned surfactant enables the ink composition to move smoothly through the ink flow path of a writing instrument equipped with a pen tip, an ink filling mechanism, an ink supply mechanism, etc., as described below, so that the ink composition of the present invention can also improve the ink ejection properties of the writing instrument.

[0016] The surfactant represented by formula (1) preferably has an HLB value of 4 to 18, more preferably 8 to 17, and even more preferably 12 to 16, since this tends to improve the paper surface permeability of the ink composition. The HLB value is a value based on the Griffin method, and is calculated by the following formula (2). The HLB value according to the Griffin method is in the range of 0 to 20, and the larger the value, the more hydrophilic the compound is. HLB value = 20 × (mass % of hydrophilic groups) = 20 × (sum of formula weights of hydrophilic groups / molecular weight of surfactant) (2) Furthermore, the sum of l and m in formula (1), (l+m), is preferably 0≦(l+m)≦30, and more preferably 0≦(l+m)≦20. The above surfactants can be used alone or in combination of two or more.

[0017] Specific examples of surfactants having an acetylene bond represented by formula (1) include Olfin D-10A, D-10PG, E1004, E1010, E1020, E1030W, PD-001, PD-002W, PD-003, PD-004, PD-201, PD-301, EXP.4001, EXP.4200, EXP.4123, and EXP.430, all manufactured by Nissin Chemical Industry Co., Ltd. Examples of the ink composition include Surfynol 82, 104E, 104H, 104A, 104PA, 104-PG50, 104S, 420, 440, 465, 485, and 2502, all manufactured by Nissin Chemical Industry Co., Ltd., Dynol 604 and 607, all manufactured by Nissin Chemical Industry Co., Ltd., and Acetylenol E13T, EX, EL, E40, E60, E81, E100, and 85, all manufactured by Kawaken Fine Chemical Co., Ltd. Among these, Olfine E1010, Olfine E1020, and Surfynol 485 are preferred because they are likely to improve the paper surface permeability and ink dischargeability of the ink composition.

[0018] The ink composition according to the present invention can also be blended with a surfactant other than the above-mentioned surfactant having an acetylene bond, and the ink composition can be adjusted to a desired viscosity and surface tension, and the ink ejection stability can be improved to suppress writing defects, while also suppressing bleeding and show-through of handwriting on the paper surface, resulting in an ink composition that can form better handwriting. Examples of surfactants other than those having an acetylene bond include nonionic surfactants, anionic surfactants, phosphate surfactants, silicone surfactants, etc. Among these, phosphate surfactants are preferred because they are more likely to improve the ink ejection stability.

[0019] The content of the surfactant having an acetylene bond represented by the above formula (1) relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.5 to 3 mass%, more preferably 0.5 to 2.5 mass%. When the surfactant content is within the above range, the paper surface permeability of the ink composition is improved, the drying speed of handwriting is improved, and bleeding of handwriting can be further suppressed.

[0020] The ink composition according to the present invention further comprises a urethane resin emulsion in which the resin has a tensile elongation of 600% or more. A resin emulsion is a resin that is not dissolved in an aqueous medium but is dispersed in the form of particles in the aqueous medium. The aqueous medium is not particularly limited, and examples thereof include water such as tap water, ion-exchanged water, ultrafiltered water, and distilled water. Urethane-based resin emulsions include a forced emulsification type in which a surfactant is used as an emulsifier to forcibly emulsify the resin and disperse it in an aqueous medium, and a self-emulsification type in which hydrophilic groups or hydrophilic segments are imparted to the resin and then dispersed in the aqueous medium. In the present invention, either type may be used as long as the resin is dispersed in particulate form in the aqueous medium.

[0021] The urethane resin constituting the urethane resin emulsion is mainly composed of soft segments, which are amorphous portions of polyol, and hard segments, which are crystalline portions mainly composed of urethane bonds and urea bonds. Polyether polyol copolymer type, polyester polyol copolymer type, polycarbonate polyol copolymer type, etc. can be used as the urethane resin. The urethane resin emulsions can be used alone or in combination of two or more.

[0022] The urethane resin emulsion in the ink composition according to the present invention has the effect of imparting excellent water resistance to handwriting formed by a writing instrument containing the ink composition. This is presumably because, when the ink composition comes into contact with the paper surface, the urethane resin contained in the ink composition interacts with the cellulose on the paper surface, causing the urethane resin to be firmly fixed to the paper surface.

[0023] Furthermore, the urethane resin emulsion of the present invention has a tensile elongation of the resin in the resin emulsion of 600% or more. This provides the effect of imparting excellent water resistance to handwriting formed by a writing instrument containing the ink composition, even after the writing instrument has been left for a long period of time. This is presumably due to the high degree of freedom of the soft segment constituting the urethane resin emulsion. Generally, when a writing instrument containing an ink composition is left for a long period of time, the moisture in the ink composition evaporates, and the particulate urethane resin in the ink composition approaches each other, which makes it easier for the urethane resin to interact with each other. Here, when the tensile elongation of the resin in the urethane resin emulsion is less than 600%, the degree of freedom of the soft segments constituting the urethane resin is low, so that even when the ink composition contained in the writing instrument is brought into contact with the paper surface, the interaction between the urethane resins is stronger. As a result, the urethane resin is less likely to interact with the cellulose on the paper surface, and the urethane resin is less likely to be fixed to the paper surface, so that the water resistance is easily impaired. On the other hand, when the tensile elongation of the resin in the urethane resin emulsion is 600% or more, the degree of freedom of the soft segments constituting the urethane resin is high, so that when the ink composition contained in the writing instrument is brought into contact with the paper surface, not only the interaction between the urethane resins but also the interaction between the urethane resin and the cellulose on the paper surface is easily caused. As a result, it is believed that the urethane resin is firmly fixed to the paper surface, imparting excellent water resistance to handwriting even after the writing instrument has been left for an extended period of time.

[0024] The tensile elongation of the resin in the urethane resin emulsion is not particularly limited as long as it is 600% or more, but is preferably 600% or more and 2000% or less, more preferably 650% or more and 1900% or less, even more preferably 700% or more and 1800% or less, and particularly preferably 700% or more and 1600% or less.

[0025] The tensile elongation of the resin in the urethane resin emulsion according to the present invention can be determined, for example, by preparing a film using the urethane resin emulsion, cutting a test piece from the obtained film, and measuring the elongation in accordance with the measurement method specified in JIS K7161-1 or ISO527-1. Specifically, the measurement can be performed by the following method.

[0026] (Method of measuring tensile elongation) 1. The urethane resin emulsion is pre-dried at room temperature (20°C) for 15 hours, then dried at 80°C for 6 hours and at 120°C for 20 minutes to produce a film with a thickness of 500 μm. 2. A rectangular specimen measuring 150 mm in length and 15 mm in width is cut out from the obtained film to prepare a test specimen, and two parallel lines are marked at 50 mm intervals in the center of the specimen in the direction parallel to the short side of the specimen. The shape and dimensions of the test specimen shall conform to the provisions of JIS K7127. 3. Attach both ends of the test specimen to the tensile testing machine so that the distance between the chucks is 50 mm, i.e., at the position of the marked line on the test specimen, and apply a tensile load at a constant rate (5 mm / min) in a room temperature (20°C) environment until the test specimen breaks. 4. The gauge length (L) at the time when the test piece breaks and the initial gauge length [L 0 (=50mm)], the displacement of the gauge distance [ΔL (=LL 0 ) is calculated from the following formula (3). Tensile elongation (%) = [ΔL (gauge line distance displacement) / L 0 (Initial gauge length) × 100 (3)

[0027] Specific examples of the urethane resin emulsion according to the present invention include Superflex 300, 740, 460, 460S, 500M, E-2000, and E-4800 manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Permarin UA-200 manufactured by Sanyo Chemical Industries, Ltd., and Takelac W-6061 and W-6061T manufactured by Mitsui Chemicals, Inc.

[0028] Furthermore, the ink composition according to the present invention contains a urethane resin emulsion, and therefore the cap-off performance of a writing instrument containing the ink composition is excellent. Generally, when a writing instrument containing an ink composition containing a resin is left in a cap-off state, the resin solidifies and precipitates at the pen tip as moisture evaporates from the pen tip, and writing defects such as smearing tend to occur easily when rewriting. However, the urethane resin emulsion contained in the ink composition according to the present invention is less susceptible to solidification and precipitation of the resin due to moisture evaporation at the pen tip of the writing instrument, and even after the writing instrument containing the ink composition is left in a cap-off state, the occurrence of writing defects such as smearing is suppressed, and good handwriting can be formed. In other words, the urethane resin emulsion in the ink composition of the present invention imparts good water resistance to handwriting formed with a writing instrument containing the ink composition, even after the writing instrument has been left unused for a long period of time, and further provides excellent cap-off performance to the writing instrument containing the ink composition.

[0029] The content of the resin in the urethane resin emulsion relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.1 to 3 mass%, more preferably 0.5 to 2.5 mass%. By having the resin (urethane resin) content within the above range, it is possible to suppress the occurrence of solidification and precipitation of the resin due to evaporation of water at the pen tip of a writing instrument containing the ink composition, while more highly achieving both the water resistance of handwriting formed by the writing instrument after aging and the cap-off performance of the writing instrument.

[0030] The ink composition of the present invention contains self-dispersing carbon black, a specific surfactant having an acetylene bond, and a urethane-based resin emulsion, and thereby achieves a high degree of balance between the color development of black handwriting, the drying properties of the handwriting formed on the paper surface, the water resistance of the handwriting, in particular the water resistance of the handwriting formed on the paper surface by the writing instrument after aging, and the cap-off performance of the writing instrument containing the ink composition, making the writing instrument containing this ink composition, in particular a brush pen, excellent in that it is capable of producing good handwriting over a long period of time.

[0031] The ink composition according to the present invention further comprises water. The water 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 10 to 90 mass %, more preferably 30 to 80 mass %.

[0032] The ink composition according to the present invention can be blended with a water-soluble organic solvent that is compatible with water, and has the effect of suppressing evaporation of water from the pen tip of a writing instrument. Examples of water-soluble organic solvents include glycerin, ethylene glycol, diethylene glycol, propylene glycol, polyethylene glycol, 3-methoxy-3-methyl-1-butanol, monoethanolamine, diethanolamine, triethanolamine, 2-pyrrolidone, etc. Among these, glycerin, ethylene glycol, diethylene glycol, propylene glycol, 3-methoxy-3-methyl-1-butanol, and 2-pyrrolidone are preferred because they can further improve the drying properties of handwriting. The water-soluble organic solvents can be used alone or in combination of two or more kinds. When the ink composition according to the present invention contains a water-soluble organic solvent, the content of the water-soluble organic solvent relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 1 to 40 mass%, more preferably 5 to 30 mass%, and even more preferably 10 to 25 mass%. If the content of the water-soluble organic solvent exceeds 40 mass%, the ink viscosity tends to increase, the ink dischargeability of a writing instrument containing the ink composition decreases, and writing defects tend to occur. On the other hand, if the content is less than 1 mass%, the effect of suppressing water evaporation is poor.

[0033] The ink composition according to the present invention may also contain various other additives as required. Examples of the additives include dyes, pigments other than the above-mentioned self-dispersing carbon black, preservatives, antifungal agents, wetting agents, defoamers, specific gravity adjusters, and pH adjusters.

[0034] The method for producing the ink composition according to the present invention is not particularly limited, and any conventionally known method can be used. Specifically, the ink composition can be produced by stirring a mixture of the above-mentioned components with various stirrers such as a propeller stirrer, a homodisper, or a homomixer, or by dispersing the mixture with various dispersers such as a bead mill.

[0035] The viscosity of the ink composition according to the present invention is not particularly limited, but is preferably 1 to 6 mPa s, and more preferably 2 to 5 mPa s, in an environment of 20° C. By having the viscosity within the above range, it becomes easy to improve the ink dischargeability while increasing the ink penetration into paper and thereby improving the handwriting drying property. The viscosity was measured by placing the ink composition in an environment of 20°C using an EL type rotational viscometer (manufactured by Toki Sangyo Co., Ltd., product name: RE-80L, cone-type rotor: standard type (1°34' x R24)).

[0036] The surface tension of the ink composition according to the present invention is not particularly limited, but is preferably 25 to 45 mN / m, and more preferably 25 to 35 mN / m, in an environment of 20° C. If the surface tension is within the above range, it becomes easy to suppress bleeding of handwriting while improving the paper surface permeability of the ink. The surface tension was measured using a surface tension meter (manufactured by Kyowa Interface Science Co., Ltd., product name: DY-300) by placing the ink composition in an environment of 20°C and using a vertical plate method using a platinum plate.

[0037] The ink composition according to the present invention is contained in a writing instrument when used. Examples of writing implements include various writing implements such as ballpoint pens, marking pens, fountain pens, brush pens, etc. The ink composition according to the present invention is suitable for use in brush pens because it has good drying properties even when applied to a writing implement in which a large amount of ink is applied to a paper surface, and it has excellent water resistance and cap-off performance even after the writing implement has been aged.

[0038] The structure or shape of the brush pen is not particularly limited as long as it has a brush-shaped pen tip, and an example of the brush pen is one that has a brush-shaped pen tip and an ink filling mechanism.

[0039] The pen tip is not particularly limited as long as it is in the form of a brush, and examples thereof include a fiber bundle such as a writing brush in which fibers are closely bundled in the longitudinal direction, a plastic porous body having continuous pores, a heat-fused body or resin-processed body of synthetic resin fibers, or a brush-shaped tip made of an extrusion molded body of a soft resin or elastomer. The chips may be glued with a water-soluble substance such as polyvinyl alcohol, polyvinylpyrrolidone, starch, gum arabic, and the like.

[0040] The ink filling mechanism is not particularly limited, and an example of the mechanism is a barrel having an ink storage chamber inside, into which ink can be directly filled. The material of the barrel is not particularly limited, and examples thereof include synthetic resins such as polyethylene, polypropylene, polymethylpentene, polycarbonate, polyethylene terephthalate, polyacetal, acrylonitrile-butadiene-styrene copolymer (ABS resin), polyurethane, polystyrene, etc., metal, glass, and rubber. Among these, polyethylene or polypropylene is preferable.

[0041] The ink filling mechanism may be an ink reservoir that can be filled with ink, or an ink occlusion body. The ink reservoir may be, for example, a molded body made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon, or a tubular body made of metal. The ink occlusion body is a fiber bundle formed by bundling crimped fibers in the longitudinal direction, and is placed inside a covering such as a plastic cylinder or film, and is configured so that the porosity is adjusted to be in the range of approximately 40 to 90%.

[0042] The ink refilling mechanism may be an ink cartridge, and the ink refilling mechanism of a writing instrument such as a brush pen may be configured to be detachable. In this case, after the ink refilled in the ink cartridge of the writing instrument is used up, the writing instrument can be used again by replacing it with a new ink cartridge. The ink cartridge may be one that also serves as the barrel that constitutes the writing instrument when connected to the writing instrument body, or one that covers and protects the barrel (rear barrel) after being connected to the writing instrument body. In the latter case, the ink cartridge may be connected to the writing instrument body, or it may be housed in the barrel in a disconnected state so that the user of the writing instrument can connect the ink cartridge in the barrel when using the writing instrument and start using it.

[0043] The structure of the ink cartridge is not particularly limited, and may be, for example, a bottomed cylinder whose cross section perpendicular to the longitudinal direction is circular. The cylinder is a hollow, elongated rod-like body. The ink cartridge may have a structure that can be deformed and restored by pressure, or the outer or inner surface of the cylinder may be tapered. Alternatively, the ink cartridge may be an ink cartridge having a structure in which an ink supply mechanism, which will be described later, is provided inside.

[0044] When the ink filling mechanism is configured to directly fill the ink, a stirring body such as a stirring ball for stirring the ink may be built into the ink cylinder or ink reservoir in which the ink is filled in order to facilitate redispersion of the self-dispersing carbon black. Examples of the shape of the stirring body include a spherical body and a rod-shaped body. The material of the stirring body is not particularly limited, and examples thereof include metal, ceramic, resin, and glass.

[0045] A writing implement equipped with a pen tip and an ink filling mechanism may further be equipped with an ink supply mechanism for supplying the ink filled in the ink filling mechanism to the pen tip. The ink supply mechanism is not particularly limited, and examples include: (1) a mechanism that has an ink guide core made of a fiber bundle or the like as an ink flow regulator and supplies ink to the pen tip through this; (2) a mechanism that has a comb-shaped ink flow regulator and supplies ink to the pen tip through this; (3) a mechanism that has a porous body with continuous pores that can be impregnated with ink as an ink flow regulator and supplies ink to the pen tip through this; (4) a mechanism that supplies ink to the pen tip through a pen core consisting of a number of disks arranged in parallel with comb-shaped intervals, with slit-shaped ink guide grooves running vertically through the disks in the axial direction and wider air vent grooves than said grooves, and with an ink guide core arranged in the axial center to guide ink from the ink filling mechanism to the pen tip; and (5) a mechanism that has an ink flow regulator with a valve mechanism and supplies ink to the pen tip by opening the valve.

[0046] The material of the pen core is not particularly limited as long as it is a synthetic resin that can be injection molded into a structure in which multiple disks are arranged in a comb groove shape. Examples of synthetic resins include general-purpose polycarbonate, polypropylene, polyethylene, and acrylonitrile-butadiene-styrene copolymer (ABS resin). In particular, acrylonitrile-butadiene-styrene copolymer (ABS resin) is preferably used because it has high moldability and is easy to obtain pen core performance.

[0047] The valve mechanism may be a conventional, general-purpose pumping type that opens when the tip is pressed, and is preferably set to a spring pressure that can be pressed and opened by the pressure of the writing pen.

[0048] The writing instrument according to the present invention can be made into a capped writing instrument by providing a cap to cover the pen tip, thereby preventing the pen tip from drying out and becoming unable to write, and preventing the writing tip from becoming contaminated or damaged. Furthermore, the form of the writing instrument according to the present invention is not limited to the above-mentioned configuration, and may be a composite writing instrument (double-ended writing instrument) equipped with tips of different shapes.

[0049] A preferred writing instrument according to the present invention is a brush pen that includes a brush-shaped tip as a pen tip, an ink filling mechanism, and an ink supply mechanism. The ink composition of the present invention moves smoothly through the ink flow path of the brush pen of the above configuration, and the ink filled in the ink filling mechanism is stably supplied to the pen tip, so that the brush pen of the above configuration is a writing instrument that can clearly produce black handwriting with excellent color development, and which also has excellent quick-drying and water resistance of handwriting and good cap-off performance, and is therefore suitably used. A more preferred configuration of the brush pen is a brush pen having the above configuration, in which the ink supply mechanism is a mechanism for supplying ink to the pen tip via a pen core having a number of disks arranged in parallel with comb-like intervals, a slit-shaped ink guide groove that runs vertically through the disks in the axial direction and a vent groove that is wider than said groove, and an ink guide core for guiding ink from the ink filling mechanism to the pen tip arranged at the axial center.A brush pen having the above configuration is more suitable because the ink flow rate from the ink filling mechanism is appropriately adjusted, ink is more stably supplied to the pen tip, and ink ejection stability is excellent.

[0050] Among the writing implements according to the present invention, specific examples of a brush pen having a brush-shaped tip as a pen tip, an ink filling mechanism, and an ink supply mechanism include: (1) a brush pen in which the ink filling mechanism is made of a barrel having an ink storage chamber provided inside, and the ink supply mechanism is a mechanism for supplying ink to the pen tip via a pen core having a number of disks arranged in parallel with comb-like intervals, a slit-shaped ink guide groove that runs vertically through the disks in the axial direction and a vent groove that is wider than the groove, and an ink guide core for guiding ink from the ink filling mechanism to the pen tip, which is disposed at the axis center, and the pen tip and the ink filling mechanism are joined via the ink supply mechanism; (2) a brush pen in which the ink filling mechanism is provided with an ink cartridge, and the ink supply mechanism is a mechanism for supplying ink to the pen tip via the ink guide core, Examples of such a mechanism include a brush pen in which the ink is supplied to the pen tip through a porous body having continuous pores that can be impregnated with ink, and the pen tip and the ink filling mechanism are joined via an ink supply mechanism; (3) a brush pen (double-ended brush pen) in which the ink filling mechanism is composed of a barrel with two ink storage chambers on the inside, the ink supply mechanism is composed of a number of disks arranged in parallel with comb-like intervals, the disks are provided with a slit-like ink guide groove that runs vertically in the axial direction and a wider air vent groove than that groove, and the ink guide core is arranged in the barrel to guide ink from the ink filling mechanism to the pen tip, and the pen tip is joined to each of one end and the other end of the barrel via an ink supply mechanism.

[0051] In the above (1), a more specific structure is one in which the pen tip and ink supply mechanism are attached to the front of a barrel consisting of a bottomed cylindrical body, and an ink storage chamber is formed inside the barrel behind the ink supply mechanism. In (2) above, more specific examples of the structure include a structure in which a front barrel equipped with a pen tip and an ink supply mechanism is releasably connected to a rear barrel consisting of an ink cartridge, and a structure in which a front barrel equipped with a pen tip and an ink supply mechanism is releasably connected to an ink cartridge, and the ink cartridge is covered by a rear barrel. In the above (3), a more specific structure is one in which a pen tip and an ink supply mechanism are attached to one end and the other end of a barrel having both ends open, and the barrel has two ink storage chambers formed by providing partitions, and the ink storage chambers are isolated from each other so that ink does not flow between them. The pen tips attached to one end and the other end of the barrel may be tips of different shapes. EXAMPLES

[0052] The following examples are given, but the present invention is not limited thereto. In the examples, "parts" refers to "parts by mass" unless otherwise specified.

[0053] Example 1 Preparation of Ink Composition An ink composition was prepared by mixing 40 parts of self-dispersing carbon black (manufactured by Tokai Carbon Co., Ltd., product name: Aqua-Black 162 (solid content: 20%)), 1 part of a surfactant having an acetylene bond (manufactured by Nissin Chemical Industry Co., Ltd., product name: Olfin E1010), 1 part of a urethane-based resin emulsion (manufactured by Mitsui Chemicals, Inc., product name: Takelac W-6061T (solid content: 30%, tensile elongation: 760%)), 0.5 parts of a phosphate ester-based surfactant (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Plysurf AL), 0.5 parts of triethanolamine, 10 parts of ethylene glycol, 5 parts of glycerin, 0.4 parts of a preservative (manufactured by Arcsada Japan Co., Ltd., product name: Proxel XL-2 (S)), and 41.6 parts of water. The content of the urethane-based resin relative to the total mass of the ink composition is 0.3 mass%.

[0054] Making brush pen A A brush pen having a brush-shaped tip as the pen tip, an ink cartridge as the ink filling mechanism, and an ink supply mechanism, with the ink filling mechanism and the pen tip being joined via the ink supply mechanism, was filled with the ink composition of Example 1 into the ink cartridge of the brush pen and a cap was attached to produce brush pen A. The specific configuration of the brush pen A and the ink cartridge attached to the brush pen A is as described below.

[0055] Configuration of Brush Pen A (see Figure 1) The brush pen A (1) is composed of a rear barrel consisting of an ink cartridge (2) which is a cylindrical bottomed body made of polyethylene and which can be deformed by pressure and restored to its original shape, and a front barrel (3) which is fitted with a nib (4) consisting of a bundle of thermoplastic polyester elastomer and an annular porous body (5) having continuous pores formed therein, which are connected in a releasable manner. A stopper (7) having a central hole (6) is fitted into one end of the ink cartridge (2). The nib (4) is provided with an adhesive layer (8) having a protrusion (9) on its rear end surface, and the annular porous body (5) is loosely inserted around the rear side circumference of the nib (4), so that the protrusion (9) and the front end of the stopper (7) abut against each other while forming an induction gap (10) between the adhesive layer (8) and the front end of the stopper (7).

[0056] Configuration of the ink cartridge attached to brush pen A (see Figure 2) The ink cartridge (2) has a first mounting hole (20) larger in diameter than the central hole (6) and a second mounting hole (21) larger in diameter than the first mounting hole, which are concentrically arranged at the rear of the inside plug (7), and an inner pipe (22) and an outer pipe (23) are fitted into the first mounting hole (20) and the second mounting hole (21).

[0057] Making brush pen B The ink filling mechanism of a brush pen was configured to include a brush-shaped tip as the nib, a barrel with an ink storage chamber inside, and an ink supply mechanism, with the nib and the ink filling mechanism being joined via the ink supply mechanism. The ink composition of Example 1 was filled into the ink filling mechanism of the brush pen, and a cap was attached to produce Brush Pen B. The configuration of the brush pen B is as follows.

[0058] Composition of Brush Pen B The brush pen B (11) is configured such that an ink supply mechanism (13) equipped with a pen tip (14) made of an extrusion molded body of soft resin with a surface coated with polyurethane is attached to the front of a barrel (12) made of a polyethylene bottomed cylinder, and an ink storage chamber (15) is formed inside the barrel behind the ink supply mechanism (13). The ink supply mechanism (13) is configured such that a number of disks (16) are arranged in parallel with comb-like intervals, a slit-like ink guide groove (17) that runs vertically through the disks (16) in the axial direction, and a vent hole (18) that is wider than the groove, an ink guide core (19) is arranged at the axis, and the ink guide core (19) is connected to the pen tip (14).

[0059] Examples 2 to 7 and Comparative Examples 1 to 4 An ink composition was prepared in the same manner as in Example 1, except that the types and amounts of the materials to be blended were changed to those shown in Table 1 below. The content of the urethane resin relative to the total mass of the ink composition is as shown in Table 1. Moreover, the brush pen A and the brush pen B were prepared in the same manner as in Example 1.

[0060] [Table 1]

[0061] The contents of the materials in Table 1 will be explained according to the note numbers. (1) Self-dispersing carbon black A (a dispersion in which carbon black with carboxyl groups bonded to the surface by surface treatment is dispersed; no dispersant is included) [Product name: Aqua-Black 162 (solid content: 20%), manufactured by Tokai Carbon Co., Ltd.] (2) Self-dispersing carbon black B (a dispersion in which carbon black with carboxyl groups bonded to the surface by surface treatment is dispersed; no dispersant is included) [Manufactured by Fuji Color Co., Ltd., product name: FUJI JET BLACK D-12 (solid content: 12.5%)] (3) Resin-dispersed carbon black [dispersion in which carbon black is dispersed in acrylic resin (solid content: 15%)] (4) Surfactant A having an acetylene bond [Manufactured by Nissin Chemical Industry Co., Ltd., product name: Olfin E1010 (HLB value: 13.3)] (5) Surfactant B having an acetylene bond [Manufactured by Nissin Chemical Industry Co., Ltd., product name: Olfin E1020 (HLB value: 15-16)] (6) Urethane resin emulsion A [Manufactured by Mitsui Chemicals, Inc., product name: Takelac W-6061T (solid content: 30%, tensile elongation: 760%)] (7) Urethane resin emulsion B [Manufactured by Mitsui Chemicals, Inc., product name: Takelac W-6061 (solid content: 30%, tensile elongation: 1000%)] (8) Urethane resin emulsion C [Manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Superflex 300 (solid content: 30%, tensile elongation: 1500%)] (9) Urethane Resin Emulsion D [Manufactured by Mitsui Chemicals, Inc., product name: Takelac W-6110 (solid content: 32%, tensile elongation: 550%)] (10) Acrylic resin emulsion [Manufactured by Toagosei Co., Ltd., product name: Julimar AT-210 (solid content: 30%)] (11) Phosphate ester surfactants [Manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Plysurf AL] (12) Preservatives [Product name: Proxel XL-2(S), manufactured by Arcsada Japan Co., Ltd.]

[0062] [Surface tension measurement] For each of the ink compositions prepared in Examples 1 to 7 and Comparative Examples 1 to 4, the surface tension was measured by a vertical plate method using a platinum plate at room temperature (20°C) using an automatic surface tensiometer (manufactured by Kyowa Interface Science Co., Ltd., product name: DY-300). The measurement results are shown in Table 1.

[0063] [Written Exam] The caps were removed from each of the brush pens A and B produced in Examples 1 to 7 and Comparative Examples 1 to 4, and the characters "Komoro naru" were handwritten on an A4-sized test paper (portrait orientation) in a room temperature (20°C) environment. The test paper was a writing paper conforming to JWIMA M 003:2015 (Japan Writing Instruments Manufacturers Association standard for "brush pens") [product name: NPi Form (manufactured by Nippon Paper Industries Co., Ltd.)]. <55> 〕 was used.

[0064] [Handwriting density evaluation] The handwriting of the character "Komoro naru" was visually confirmed for its density, and the density was evaluated according to the following criteria. The evaluation results are shown in Table 2 below, with an evaluation of "A" being a pass. A: The writing was thick and bright black. B: The handwriting was slightly light black or light gray. The lines of the handwriting of "Komoro naru" were set in the measuring area of ​​a fluorescence spectrodensitometer (manufactured by Konica Minolta, Inc., product name: FD-7 type) and the density value of the handwriting was measured from the K value of the fluorescence spectrodensitometer. The evaluation results are shown in Table 2 below. The density value (K value) is the average value of three measurements, and the larger the value, the higher the density of the handwriting.

[0065] [Evaluation of writing drying time] The caps of the brush pens A and B produced in Examples 1 to 7 and Comparative Examples 1 to 4 were removed, and the character "EI" was handwritten on an A4-sized test paper (portrait) in a room temperature (20°C) environment. After a certain time from writing, the character "EI" was rubbed and visually confirmed whether the ink spread around the handwriting. The initial handwriting dryness was evaluated based on the time it took for the handwriting to dry, according to the following criteria. Next, the writing implements used in the test were capped and left to stand in a thermostatic chamber set at 50°C for 60 days with the pen tip facing downward (inverted state). After 60 days, the writing implements were removed from the thermostatic chamber, the writing implements were removed from the caps, and the same test as above was performed, and the handwriting dryness after aging was evaluated according to the following criteria. The evaluation results are shown in Table 2 below, and evaluations "A" and "B" were considered to be acceptable. Kent paper (ream weight: 125 kg) was used as the test paper. A: When the handwriting was rubbed one second after writing, no evidence of ink spreading around the handwriting was observed. B: When the handwriting was rubbed 1 second after writing, the ink spread around the handwriting, but when the handwriting was rubbed 3 seconds after writing, there was no evidence of the ink spreading around the handwriting. C: Even after 4 seconds had passed since writing, when the handwriting was rubbed, there was evidence of ink spreading around the handwriting.

[0066] [Water resistance evaluation of handwriting] The caps of each of the brush pens A and B produced in Examples 1 to 7 and Comparative Examples 1 to 4 were removed, and the character "EI" was handwritten on an A4-sized test paper (portrait) in a room temperature (20°C) environment. One hour after writing, a drop of water was dropped on the character "EI", and then the water was allowed to dry naturally, and it was visually confirmed whether the handwriting had smudged. The initial water resistance of the handwriting was evaluated based on the state of the handwriting according to the following criteria. Next, the writing implements used in the test were capped and left to stand in a thermostatic chamber set at 50°C for 60 days with the pen tip facing downward (inverted state). After 60 days, the writing implements were removed from the thermostatic chamber, the writing implements were removed from the caps, and the same test as above was performed, and the handwriting water resistance after aging was evaluated according to the following criteria. The evaluation results are shown in Table 2 below, and evaluations "A" and "B" were considered to be acceptable. Calligraphy paper was used as the test paper. A: No bleeding was observed in the handwriting. B: Some bleeding was observed in the handwriting, but it was at a level that did not cause any practical problems. C: Significant bleeding was observed in the writing.

[0067] [Cap-off performance evaluation] The caps of each of the brush pens A and B produced in Examples 1 to 7 and Comparative Examples 1 to 4 were removed, and the pens were left to stand in a thermostatic chamber set at a temperature of 20°C and a humidity of 65% for 2 hours in a horizontal position. After 2 hours, the pens were removed from the thermostatic chamber, and the characters "Komoro naru koushiro no hotori kumomo shiroku yuuko kanashimu (20 characters)" were handwritten on an A4-sized test paper (portrait) in a room temperature (20°C) environment. The handwriting obtained was visually confirmed, and the initial cap-off performance was evaluated based on the presence or absence of blurring of the handwriting according to the following criteria. Next, the writing instruments used in the test were capped, and the pens were left to stand in a thermostatic chamber set at 50°C for 60 days with the pen tip facing downward (inverted position). After 60 days, the pens were removed from the thermostatic chamber, the caps of the writing instruments were removed, and the same test as above was performed, and the cap-off performance after aging was evaluated according to the following criteria. The evaluation results are shown in Table 2 below, with ratings of "A" and "B" being considered passing. The test paper was a writing paper conforming to JWIMA M 003:2015 ("Brush Pen" Japan Writing Instruments Manufacturers Association standard) [product name: NPi Form manufactured by Nippon Paper Industries Co., Ltd.] <55> 〕 was used. A: From the start of writing, there was no smudging in the handwriting and good handwriting was obtained. B: There was some smearing in the handwriting from the beginning of writing, but by the time 10 characters had been written, the smearing had disappeared and was at a level that did not cause any problems in practical use. C: The handwriting started to blur from the beginning, and the blurring did not go away by the time the 11 characters were written.

[0068] [Table 2] [Explanation of symbols]

[0069] 1 Brush pen 2 Ink cartridges 3 Front barrel 4. Pen Tip 5 Annular porous body 6 center hole 7 Inner stopper 8. Adhesive Layer 9 Protrusion 10 Induction gap 11 Brush Pen 12 shaft cylinder 13 Ink supply mechanism 14 Pen Tip 15 Ink Containment Room 16 Disk 17 Ink guide hole 18 Ventilation holes 19 Ink guide core 20 First mounting hole 21 Second mounting hole 22 Inner pipe 23 Outer pipe

Claims

1. A water-based ink composition for a writing instrument, comprising at least self-dispersing carbon black, a surfactant having an acetylene bond represented by the following formula (1), a urethane-based resin emulsion, and water, wherein the tensile elongation of the resin in the urethane-based resin emulsion is 600% or more: 【Chemical 1】 (In the formula, R １ , R ２ , R ３ , and R ４ are each independently an alkyl group, R ５ is an ethylene group, l and m are each independently an integer of 0 or greater.

2. 2. The ink composition according to claim 1, wherein the tensile elongation of the resin in the urethane resin emulsion is 600% or more and 2000% or less.

3. 2. The ink composition according to claim 1, wherein the content of the resin in the urethane resin emulsion is 0.1 to 3 mass % relative to the total mass of the ink composition.

4. A writing implement containing the ink composition according to any one of claims 1 to 3.

5. 5. The writing implement according to claim 4, which is a brush pen.

6. 6. The brush pen according to claim 5, comprising a pen tip, an ink filling mechanism, and an ink supply mechanism.

7. 7. The calligraphy pen according to claim 6, wherein the ink filling mechanism comprises an ink cartridge.

8. 7. The brush pen according to claim 6, wherein the ink filling mechanism comprises a barrel having an ink chamber therein, and the nib and the ink filling mechanism are joined via the ink supply mechanism.

9. 7. The brush pen according to claim 6, wherein the ink supply mechanism comprises a pen core having a number of disks arranged in parallel with comb-like intervals, a slit-shaped ink guide groove running vertically through the disks in the axial direction, and a ventilation groove wider than the slit-shaped ink guide groove, and an ink guide core arranged in the axial center to guide ink to the pen tip.

10. An ink cartridge for a writing instrument, which contains the ink composition according to any one of claims 1 to 3.

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