Aqueous ink composition for ball point pen

Abstract

To provide: an aqueous ink composition for a ball point pen, which inhibits direct ink flow and has excellent temporal stability; and a ball point pen.SOLUTION: An aqueous ink composition for a ball point pen of the invention includes at least a coloring agent, fermented cellulose, and water. The fermented cellulose becomes a soft aggregate whose particle diameter is 5-1000 μm in the ink composition. The coloring agent is dispersed in the soft aggregate.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aqueous ink composition for a ballpoint pen, and more particularly to an aqueous ink composition for a ballpoint pen which suppresses ink direct current and has excellent stability over time. [Background technology]

[0002] Conventionally, in terms of ink composition, an aqueous ink composition for ballpoint pens containing crystalline cellulose has been known as a technology for preventing the so-called "DC phenomenon" in which ink drips or leaks due to gravity from the gap between the holder and the ball in an aqueous ballpoint pen (see, for example, Patent Document 1 by the applicant of the present application).

[0003] The technology of Patent Document 1 is an unprecedentedly excellent technology for preventing the "DC phenomenon," but there is a phenomenon in which the DC prevention effect is reduced over time due to aggregation and uneven distribution of crystalline cellulose. To suppress this phenomenon, the applicant of the present application has proposed an aqueous ink composition for ballpoint pens that contains crystalline cellulose and resin particles and thus achieves both a high level of DC prevention effect and stability over time (see, for example, Patent Document 2).

[0004] However, the technology of Patent Document 2 above has some problems, such as the fact that, in the case of low viscosity, crystalline cellulose aggregates and is unevenly distributed, resulting in a decrease in writing performance.

[0005] On the other hand, known technologies for aqueous ballpoint pens with excellent drying-up performance and pigment dispersibility include, in terms of ink composition, aqueous ballpoint pen inks containing fermented cellulose (see, for example, Patent Document 3), a method for improving the quality of aqueous ballpoint pen inks by incorporating fermented cellulose to improve the quality of the aqueous ballpoint pen ink (such as suppressing smearing and leakage) (see, for example, Patent Document 4), and aqueous ballpoint pen inks containing organic resin particles and surface-treated polysaccharide fibers to suppress ink leakage (see, for example, Patent Document 5).

[0006] However, the techniques described in Patent Documents 3 to 5 above do not sufficiently prevent ink leakage, and furthermore, fermented cellulose and polysaccharide fibers tend to entrap air during stirring or filtration, which creates buoyancy and makes the ink tend to concentrate at the top over time, resulting in poor storage stability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2010-1381 A (Claims, etc.) [Patent Document 2] JP 2013-103986 A (Claims, etc.) [Patent Document 3] JP 2013-91730 A (Claims, etc.) [Patent Document 4] JP 2009-161624 A (Claims, etc.) [Patent Document 5] JP 2017-222113 A (Claims, etc.) Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in consideration of the above-mentioned problems and current state of the prior art, and aims to solve these problems, and to provide an aqueous ink composition for ballpoint pens that achieves both a high degree of DC prevention effect and stability over time without deteriorating writing performance. [Means for solving the problem]

[0009] In view of the above-mentioned conventional problems, the inventors conducted intensive research and discovered that the above-mentioned aqueous ink composition for ballpoint pens can be obtained by containing at least a colorant, fermented cellulose, and water, and adjusting the particle size of a soft aggregate composed of the fermented cellulose to a predetermined range, thereby completing the present invention.

[0010] That is, the aqueous ink composition for ballpoint pens of the present invention contains at least a colorant, fermented cellulose, and water, and is characterized in that the fermented cellulose is in the form of soft agglomerates having a particle size of 5 to 1000 μm in the ink composition, and the colorant is dispersed in the soft agglomerates. It is preferable that the water-based ink composition for a ballpoint pen further contains a resin emulsion, and the resin emulsion is dispersed in the soft aggregate. It is preferable that the aqueous ink composition for a ballpoint pen further contains fine particles having a new Mohs hardness of 7 or more, and the fine particles are dispersed in the soft aggregate. The aqueous ink composition for ballpoint pens preferably further contains a nonionic surfactant having an HLB value of 15 or more. The ballpoint pen of the present invention is characterized by being equipped with the aqueous ink composition for ballpoint pens having the above-mentioned configuration. In the present invention, the term "soft aggregate" refers to a soft (flexible) aggregate having an irregular contour shape that forms a three-dimensional network structure composed of the fermented cellulose and colorant contained in the ink composition, and the particle size (maximum particle size) of the aggregate is configured in a specific range (5 to 1000 μm). In addition, when the ink composition contains a resin emulsion or fine particles having a new Mohs hardness of 7 or more, the resin emulsion and fine particles are also dispersed in the soft aggregate having a particle size in the above-mentioned specific range. Effect of the Invention

[0011] According to the present invention, there is provided an aqueous ink composition for a ballpoint pen, which achieves both a high level of DC prevention effect and stability over time without deteriorating writing performance, and a ballpoint pen. The objects and advantages of the invention will be realized and obtained by means of the elements and combinations particularly pointed out in the claims. Both the foregoing general description and the following detailed description are exemplary and explanatory but are not restrictive of the invention as claimed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Each embodiment of the present invention will be described in detail below. However, it should be noted that the technical scope of the present invention is not limited to the embodiments described in detail below, but extends to the inventions described in the claims and their equivalents. Furthermore, the present invention can be implemented based on the contents disclosed in this specification and common technical knowledge in the relevant field (including design matters and obvious matters). The aqueous ink composition for ballpoint pens of the present invention contains at least a colorant, fermented cellulose, and water, the fermented cellulose is in a soft agglomerate state, the soft agglomerates of the fermented cellulose have a particle size of 5 to 1000 μm, and the colorant is dispersed in the soft agglomerates.

[0013] The colorants that can be used in the present invention include, without limitation, all dyes that dissolve or disperse in water, conventionally known inorganic and organic pigments such as titanium oxide, resin particle pigments containing pigments, pseudopigments in which resin emulsions are colored with dyes, white plastic pigments, wax particles, hollow resin particles, pigments having a silica or mica base material and a multilayer coating of iron oxide, titanium oxide, etc. on the surface, photochromic pigments such as aluminum, thermochromic pigments, photochromic particles, and composite particles of these. Examples of dyes include acid dyes such as eosin, fuoxin, water yellow #6-C, acid red, water blue #105, brilliant blue FCF, and nigrosine NB; direct dyes such as direct black 154, direct sky blue 5B, and violet BB; and basic dyes such as rhodamine and methyl violet.

[0014] Examples of inorganic pigments include azo lakes, insoluble azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, and nitroso pigments. More specifically, inorganic pigments such as carbon black, titanium black, zinc oxide, red iron oxide, aluminum, chromium oxide, iron black, cobalt blue, iron oxide yellow, viridian, zinc sulfide, lithopone, cadmium yellow, vermilion, cadmium red, yellow lead, molybdate orange, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine blue, precipitated barium sulfate, baryte powder, calcium carbonate, lead white, navy blue, Prussian blue, manganese violet, aluminum powder, and brass powder; CI Pigment Blue 17, CI Pigment Blue 15, CI Pigment Blue 17, CI Pigment Blue 27, CI Pigment Red 5, CI Pigment Red 22, CI Pigment Red 38, CI Pigment Red 48, CI Pigment Red 49, CI Pigment Red 53, CI Pigment Red 57, C I Pigment Red 81, CI Pigment Red 104, CI Pigment Red 146, CI Pigment Red 245, CI Pigment Yellow 1, CI Pigment Yellow 3, CI Pigment Yellow 12, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 17, CI Pigment Yellow 34, CI Pigment Yellow 55, CI Pigment Yellow 74, CI Pigment Yellow 95, CI Pigment Yellow 166, CI Pigment Yellow 167, CI Pigment Orange 5, CI Pigment Orange 13, CI Pigment Orange 16, CI Pigment Violet 1, CI Pigment Violet 3, CI Pigment Violet 19, CI Pigment Violet 23, CI Pigment Violet 50, CI Pigment Green 7, etc.

[0015] Examples of thermochromic pigments include thermochromic pigments produced by microencapsulating a thermochromic composition containing at least a leuco dye that functions as a color former, a color developer that is a component capable of causing the leuco dye to develop color, and a color change temperature regulator that can control the color change temperature in the color development of the leuco dye and the color developer, so as to have a predetermined average particle size (e.g., 0.1 to 6 μm). Examples of photochromic particles include photochromic particles composed of at least one selected from photochromic dyes (compounds), fluorescent dyes, etc., and a resin such as a terpene phenol resin; and photochromic particles produced by microencapsulating a photochromic composition containing at least one selected from photochromic dyes (compounds), fluorescent dyes, etc., an organic solvent, and additives such as an antioxidant, a light stabilizer, and a sensitizer, so as to have a predetermined average particle size (e.g., 0.1 to 6 μm).

[0016] In the present invention (including examples), the "average particle size" is the volume-based 50% particle size (D50) value measured using a particle size analyzer [Microtrac HRA9320-X100 (manufactured by Nikkiso Co., Ltd.), refractive index 1.8]. The above-mentioned microencapsulation method of thermochromic pigment can be, for example, interfacial polymerization method, interfacial polycondensation method, insitu polymerization method, liquid curing coating method, phase separation method from aqueous solution, phase separation method from organic solvent, melt dispersion cooling method, air suspension coating method, spray drying method, etc., and can be appropriately selected according to the application.For example, in the phase separation method from aqueous solution, after heating and melting the leuco dye, developer, and discoloration temperature regulator, put them into an emulsifier solution, heat and stir to disperse them into oil droplets, and then use a resin raw material whose wall film is a urethane resin, epoxy resin, amino resin, etc. as an encapsulation film agent, for example, an amino resin solution, specifically, each liquid such as a methylolmelamine aqueous solution, a urea solution, a benzoguanamine solution, etc. is gradually put in, and then reacted to prepare, and then the dispersion is filtered to produce a thermochromic microencapsulated pigment.In this thermochromic pigment, the type and amount of the leuco dye, developer, and discoloration temperature regulator can be suitably combined to set the color development temperature and decolorization temperature of each color to a suitable temperature. The photochromic particles can be microencapsulated in the same manner as in the production of the thermochromic resin particles. By suitably using photochromic dyes (compounds), fluorescent dyes, etc., the photochromic particles can be made to have the property of being colorless in indoor lighting environments (indoor lighting fixtures selected from incandescent lamps, fluorescent lamps, lamps, white LEDs, etc.) and coloring in ultraviolet irradiation environments (irradiation with light of 200 to 400 nm wavelength, or irradiation with sunlight containing ultraviolet rays).

[0017] These colorants can be used alone or in combination of two or more. Among these colorants, the average particle diameter of water-dispersible pigments, resin particle pigments, pseudopigments, white plastic pigments, multi-layer coated pigments, thermochromic pigments, photochromic particles, etc. varies depending on the ball diameter, ink composition, viscosity, etc., but it is desirable for the average particle diameter to be 0.02 to 6 μm. The content of these colorants can be appropriately increased or decreased depending on the line density of the ink, but it is desirable for the content to be 0.1 to 40 mass % (hereinafter, "mass %" will be referred to as "%"), preferably 1 to 10%, of the total amount of the ink composition.

[0018] The fermented cellulose used in the present invention is used to form soft aggregates (soft aggregates) of a predetermined diameter in the ink composition. It has been known in the past to use xanthan gum or the like as a technique for preventing the so-called "DC phenomenon" in which ink drips or leaks due to gravity from the gap between the holder and the ball in aqueous ballpoint pens and the like. In the present invention, fermented cellulose is added to a formulation system containing a colorant such as the above-mentioned pigment, and soft aggregates of a predetermined diameter are formed in the ink composition; specifically, soft aggregates (soft aggregates) having a particle size of 5 to 1000 μm and in which a colorant is dispersed, thereby resulting in an ink composition that achieves a high degree of both DC prevention effect and stability over time without reducing writing performance.

[0019] In the present invention (including the examples described below), the particle size of the soft agglomerates made from the fermented cellulose is measured as the maximum diameter of the soft agglomerates when the ink is observed with an optical microscope (HIROX Digital Microscope RH-2000, the same applies below), and is preferably 5 to 1000 μm, and more preferably 5 to 200 μm. If the particle size of the soft aggregates is less than 5 μm, the direct current prevention effect will not be achieved, whereas if it exceeds 1000 μm, the outflow during writing will be hindered, and the effect of the present invention will not be achieved.

[0020] The fermented cellulose that can be used is cellulose produced by cellulose-producing bacteria, for example, bacteria belonging to the genus Acetobacter, Pseudomonas, Agrobacterium, etc., and is not particularly limited as long as it is one of these celluloses. Generally, fermented cellulose is cellulose The fermented cellulose can be produced by culturing the producing bacteria according to known methods (culture medium and conditions, etc.) and appropriately purifying the resulting fermented cellulose as desired. The chemical structure of the polysaccharides that make up fermented cellulose is basically a linear polymeric polysaccharide consisting of β1-4-linked glucose. The formation of the soft aggregate in the present invention can be obtained by adjusting the content of each component when preparing an ink containing at least a colorant, fermented cellulose, and water, and the stirring conditions, such as the stirring speed, stirring time, and temperature.

[0021] The fermented cellulose used in the present invention is insoluble in water, and unlike thickening polysaccharides, it has low viscosity and is not sticky, and can be used stably in the presence of various coexisting components of ink, at various temperatures, pH levels, etc. Examples of fermented cellulose that can be used include the fermented cellulose obtained by the above production method, the commercially available Sun Artist series manufactured by San-Ei Gen F.F.I., such as Sun Artist H-PN, Sun Artist H-PG, and Sun Artist H-PX, and CM-NFBC manufactured by Kusano Sakuko Co., Ltd.

[0022] The content of these fermented celluloses may be an appropriate amount that allows them to form flexible aggregates (soft aggregates) of a predetermined size in the ink composition and to exert the effects of the present invention, as described above. Although this varies depending on the blending species, etc., it is desirable to adjust the content to 0.01 to 10 mass %, preferably 0.03 to 5 mass %, and particularly preferably 0.05 to 1 mass %, relative to the total amount of the ink composition. By making the content of this fermented cellulose 0.01% by mass or more, the effects of the present invention can be exerted, while by making it 10% by mass or less, the effects of the present invention can be exerted efficiently without increasing costs.

[0023] The aqueous ink composition for ballpoint pens of the present invention preferably contains a resin emulsion from the viewpoints of adjusting the ink viscosity and improving the ink fixing strength. Specific examples of resin emulsions that can be used include at least one type selected from the group consisting of styrene-acrylic emulsions, polyolefin-based emulsions, acrylic emulsions, vinyl acetate-based emulsions, urethane-based emulsions, styrene-butadiene emulsions, and styrene-acrylonitrile emulsions. It is preferable to use at least one type of each of these, for a total of two or more types. A preferred resin emulsion is a styrene acrylic resin. Examples of commercially available resin emulsions that can be used include JONCRYL 352D, 537-E, PDX-7198, 7430, 7538, 7615, 7700, and 7787 (BASF).

[0024] The content of these resin emulsions is desirably adjusted to 0.5 to 15% by mass, and preferably 1 to 10% by mass, in terms of solid content, based on the total amount of the ink composition. By making the content of this resin emulsion 0.05% by mass or more, the effects of the present invention can be further exerted, while by making it 15% by mass or less, the effects of the present invention remain unchanged but costs are not increased, which is preferable. Furthermore, in addition to the above-mentioned resin emulsions, water-soluble resins having a hydrophobic portion in the molecule, such as polyacrylic acid, water-soluble styrene-acrylic resin, water-soluble styrene-maleic acid resin, polyvinyl alcohol, polyvinylpyrrolidone, water-soluble maleic acid resin, water-soluble styrene resin, olefin-based emulsion, water-soluble ester-acrylic resin, ethylene-maleic acid copolymer, polyethylene oxide, water-soluble urethane resin, and the like, may be used in combination so long as the effects of the present invention are not impaired.

[0025] In the aqueous ink composition for ballpoint pens of the present invention, it is further preferable to use microparticles having a new Mohs hardness of 7 or more. The inclusion of microparticles with this characteristic further exerts the effect of suppressing wear of the ball seat and the effect of preventing the soft aggregates from floating up. The fine particles that can be used are not particularly limited as long as they have a new Mohs hardness of 7 or more.

[0026] The new Mohs hardness of the fine particles is preferably 7 or more and 15 or less from the viewpoints of durability and ink outflow resistance. The new Mohs hardness has the same meaning as the modified Mohs hardness. The new Mohs hardness is a scale of hardness that determines the hardness of a mineral by comparing it with 15 kinds of standard minerals. The standard minerals are, in order from soft (new Mohs hardness 1) to hard (new Mohs hardness 15), talc, gypsum, calcite, fluorite, apatite, orthoclase, fused quartz, crystal (quartz), topaz, garnet, fused zirconia, fused alumina, silicon carbide, boron carbide, and diamond. In this specification, the new Mohs hardness is measured by rubbing a sample material (particle) whose hardness is to be measured with these standard minerals, and measuring the hardness based on the presence or absence of scratches. For example, if fused quartz does not scratch the sample material, but crystal (quartz) does scratch it, the new Mohs hardness of the sample material (particle) is 7.5 (meaning between 7 and 8). Incidentally, fine particles having a new Mohs hardness of less than 7 are not preferred because they do not provide a sufficient wear suppression effect on the ball seat.

[0027] Examples of fine particles having a new Mohs hardness of 7 or more include fine ceramic particles such as silicon carbide, alumina, silica, tungsten carbide, and zirconia, and fine metal particles. These can be used alone or in combination of two or more kinds.

[0028] The fine particles used have an average particle size of 30 μm or less, preferably 0.07 to 30 μm, and more preferably 0.1 to 10 μm, in order to further suppress wear of the receiving seat and adjust the specific gravity of the soft aggregates that enhance the outflow of ink. Fine particles having an average particle size of 30 μm or less are preferable because they have good dispersion stability in the ink and can also suppress sedimentation of the fine particles. Furthermore, the shape of the fine particles having the above-mentioned specified new Mohs hardness and average particle size is preferably spherical, elliptical, plate-like or rod-like in terms of improving the writing feeling and ink outflow properties.

[0029] As these fine particles, commercially available fine particles can be used as long as they have the above-mentioned specified new Mohs hardness and further the above-mentioned average particle diameter, and ceramic fine particles, metal fine particles, etc. produced by known methods can also be used. Furthermore, in the present invention, when the new Mohs hardness of the fine particles is (A), the average particle diameter is (B), and the product of (A) and (B) is the multiplication value, if the multiplication value is within a predetermined range, when used in an aqueous ink composition for a ballpoint pen, both the suppression of wear of the receiving seat and the dispersion stability are more excellent, and the effects of the present invention can be more suitably exhibited. The predetermined range of such multiplication value is, for example, 0.2 or more, preferably 0.3 or more, more preferably 0.49 or more, even more preferably 0.7 or more, and for example, 450 or less, preferably 210 or less, more preferably 150 or less, even more preferably 70 or less.

[0030] The content of these fine particles having the specified new Mohs hardness and the like is desirably 0.001 to 5 mass %, and more desirably 0.1 to 2 mass %, based on the total amount of the ink composition. By making the content of these microparticles 0.001% by mass or more, more sufficient suppression of wear of the receiving seat can be achieved, while if the content is 5% by mass or less, more sufficient suppression of wear of the receiving seat can be achieved without degrading the writing feel.

[0031] Furthermore, in the present invention, it is desirable to contain a nonionic surfactant having an HLB value of 15 or more. The "HLB value" in the present invention can be determined by the Griffin method [HLB value=20×(MW / M), MW: molecular weight of the hydrophilic portion, M: molecular weight]. The nonionic surfactant having an HLB value of 15 or more used is compatible with the aqueous system and can efficiently form soft aggregates in the above-mentioned predetermined range (5 to 1000 μm). Examples of nonionic surfactants that can be used include polyoxyethylene polyoxypropylene block polymers, polyoxyethylene polyoxypropylene glycol, polyalkylene oxide adducts of organic amines, diglycerol polyoxyethylene fatty acid esters, polyoxyethylene styrenated phenyl ethers, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene alkyl ethers, and the like. Of these, those having an HLB value of 15 or more can be used, and it is particularly preferable to use polyoxyethylene polyoxypropylene block polymers, which are more preferable in terms of stability over time.

[0032] As the above-mentioned nonionic surfactants having an HLB of 15 or more, one or more of commercially available products such as Solsperse 27000 (both manufactured by Lubrizol Nippon), Epane 680 (both manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), MM-750, MCA-750, 10G-L (all manufactured by Sakamoto Pharmaceutical Co., Ltd.), Emulgen 120, 150, 430, A-500, and Amit 320 (all manufactured by Kao Corporation) can be used.

[0033] The content of these nonionic surfactants is preferably 0.01 to 10% by mass, and more preferably 0.2 to 5% by mass, based on the total amount of the ink composition. By making the content of this nonionic surfactant 0.01% by mass or more, the effect of enhancing the dispersion stability of the soft aggregates mentioned above can be obtained, while on the other hand, if the content is 5% by mass or less, the effect of suppressing viscosity changes over time can be expected.

[0034] The aqueous ink composition for ballpoint pens of the present invention contains at least a colorant, fermented cellulose, and water, and is characterized in that the fermented cellulose is in the form of soft aggregates with a particle size of 5 to 1000 μm in the ink composition, and the colorant is dispersed in the soft aggregates. It is preferable that the aqueous ink composition further contains at least one of a resin emulsion, fine particles having a new Mohs hardness of 7 or more, and a nonionic surfactant having an HLB value of 15 or more. In addition, in addition to water (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.) as the solvent as the remainder, water-soluble solvents, lubricants, thickeners, pH adjusters, rust inhibitors, preservatives, antibacterial agents, etc. may be appropriately contained as necessary within the range that does not impair the effects of the present invention.

[0035] The water-soluble solvent that can be used is one that is used for various purposes of improving the ink quality, such as preventing the ink from freezing at low temperatures and preventing the ink from drying at the pen tip. Specifically, for example, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, 3-butylene glycol, thiodiethylene glycol, and glycerin, ethylene glycol monomethyl ether, and diethylene glycol monomethyl ether can be used alone or in combination. The content of this water-soluble solvent is preferably 1 to 40% by mass based on the total amount of the ink composition.

[0036] Examples of lubricants that can be used include nonionic lubricants such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, polyoxyalkylene higher fatty acid esters, and alkyl phosphates, which are also used as surface treatment agents for pigments; anionic lubricants such as phosphoric acid esters, alkyl sulfonates of higher fatty acid amides, and alkyl aryl sulfonates; derivatives of polyalkylene glycols; and polyether-modified silicones. The thickener that can be used may be any known thickener, and specifically, at least one selected from the group consisting of alkali swelling association type emulsions, alkali swelling type emulsions, cellulose derivatives, polysaccharides such as xanthan gum and succinoglycan, cross-linked acrylic acid polymers, crystalline cellulose, rheosan gum, gellan gum, and inorganic thickeners such as montmorillonite-based clay minerals, etc. may be used.

[0037] Examples of pH adjusters include ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, alkali metal salts of carbonates and phosphoric acids such as sodium tripolyphosphate and sodium carbonate, and hydrates of alkali metals such as sodium hydroxide. Examples of rust inhibitors include benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, and saponins, while examples of preservatives or antibacterial agents include phenol, sodium omadine, sodium benzoate, thiazoline compounds, and benzimidazole compounds. The above-mentioned lubricants, thickeners, pH adjusters, rust inhibitors, preservatives, antibacterial agents, and other components may be used alone or in combination of two or more. In addition, if commercially available products of these are available, they may be used.

[0038] The water-based ink composition for ballpoint pens of the present invention can be produced in a manner similar to that of other water-based ink compositions. That is, the aqueous ink composition for a ballpoint pen of the present invention can be produced by mixing and stirring at least a colorant, fermented cellulose, water, each of the preferable components and other components using a mixer or the like, and further, for example, a bead mill, homomixer, homogenizer or the like that can apply strong shear, with the stirring conditions set to suitable conditions, and further, if necessary, removing coarse particles in the ink composition by filtration or centrifugation. Furthermore, the pH (25°C) of the aqueous ink composition for ballpoint pens of the present invention is preferably adjusted to 5 to 10 with a pH adjuster or the like from the viewpoints of usability, safety, the stability of the ink itself, and compatibility with the ink container, and is more preferably adjusted to 6 to 9.5.

[0039] The aqueous ink composition for ballpoint pens of the present invention is loaded into a ballpoint pen equipped with a pen tip portion such as a ballpoint pen tip. The ballpoint pen in the present invention may be, for example, a ballpoint pen ink container (refill) containing the above-mentioned aqueous ink composition for ballpoint pens with a ball having a diameter of 0.18 to 2.0 mm, and containing a substance that is incompatible with the aqueous ink composition contained in the ink container and has a small specific gravity relative to the aqueous ink composition, such as polybutene, silicone oil, mineral oil, etc., as an ink follower. The structure of the aqueous ballpoint pen used is not particularly limited as long as it is equipped with a ball having a diameter within the above range, and in particular, it is preferable to fill the above-mentioned aqueous ink composition into an ink container made of a polypropylene resin tube, and finish it into an aqueous ballpoint pen refill with a stainless steel tip (the ball is made of a super steel alloy) at the tip. Furthermore, the present invention may be a direct ink type ballpoint pen having a collector structure (ink retention mechanism) in which the barrel itself serves as an ink container and is filled with the aqueous ink composition for ballpoint pens having the above-mentioned configuration. The present invention is particularly suitable for use in a water-based ballpoint pen having a ball with a diameter of 0.18 to 1.0 mm, as it is expected to suppress wear of the receiving seat.

[0040] The reason why the aqueous ink composition for ballpoint pens of the present invention, which is configured as described above, is an aqueous ink composition for ballpoint pens which achieves both a high degree of DC prevention effect and stability over time without impairing writing performance, is presumed to be as follows. That is, the aqueous ink composition for ballpoint pens of the present invention contains at least a colorant, fermented cellulose, and water, and the fermented cellulose forms soft aggregates (soft aggregates) having a particle size of about 5 to 1000 μm in the ink, and the colorant is dispersed in the soft aggregates. When a shear force is applied to the ink between the ball and the tip holder, which occurs when writing, the soft aggregates easily break down and become fluid. On the other hand, when writing is not being performed, that is, when no shear force is applied to the ink, a three-dimensional mesh structure is formed and the bulky, amorphous soft aggregate shape is maintained. Therefore, even under harsh conditions such as being dropped, an aqueous ink composition for ballpoint pens having excellent direct current prevention effect against dripping or leaking of ink from the gap between the holder and the ball, and having excellent ink stability over time without reducing writing performance, as well as a ballpoint pen equipped with this ink composition can be obtained. EXAMPLES

[0041] Next, the present invention will be described in more detail with reference to Examples 1 to 12 and Comparative Examples 1 to 5 of aqueous ink compositions for ballpoint pens and ballpoint pens equipped with the same, but the present invention is not limited to the following examples.

[0042] [Examples 1 to 12 and Comparative Examples 1 to 5] Each aqueous ink composition for ballpoint pen was prepared according to the formulation shown in Table 1 below (combination of colorant, fermented cellulose, resin emulsion, microparticles, nonionic surfactant, and other ingredients) using a mixer (MAX MIXER, manufactured by Inoue Seisakusho Co., Ltd.) by appropriately adjusting the stirring speed, stirring time, temperature, etc. For each of the obtained aqueous ink compositions for ballpoint pens (total amount 100% by mass), when soft aggregates were produced by the above-mentioned method, the particle size thereof was measured by an optical microscope. In addition, for each of the obtained aqueous ink compositions for ballpoint pens, the ink stability over time was evaluated by the evaluation methods described below. Each ink composition was loaded into a ballpoint pen having the following configuration to evaluate the stability over time of the pen body and resistance to direct current prevention. The results are shown in Table 1 below.

[0043] (Method for evaluating the temporal stability of ink) Each ink composition was stored in a 500 ml glass mayonnaise bottle for two months under an environment of 25°C and 60% relative humidity. After that, ink was extracted from the top and bottom and observed under an optical microscope. When no soft aggregates were observed at the bottom compared to the top, it was judged that the soft aggregates had risen to the top and the stability was poor. After the above, the test was evaluated according to the following criteria. Evaluation criteria: A: There is no difference between the top and bottom B: The amount of soft aggregates at the bottom is slightly less than that at the top. C: No soft aggregates are observed at the bottom, but many are observed at the top.

[0044] (Ballpoint pen configuration) Ballpoint pen tips of each ball diameter (0.18 mm superalloy ball or 1.0 mm superalloy ball) were mounted on tubes (both PP tubes with an inner diameter of 4.7 mm) and polypropylene joint members mounted on Mitsubishi Pencil Co., Ltd. UMN-103, and filled with each of the above aqueous ink compositions and polybutene as an ink follower. After degassing by centrifugation (500G, 5 minutes), the tubes were assembled into aqueous ballpoint pens of each ball diameter, and various writing tests shown below were performed.

[0045] (Stability of the pen over time) The water-based ballpoint pens were stored with the nib facing down at a temperature of 50°C and a humidity of 65% for 12 weeks and then tested using the following method: Ink was extracted from the top and bottom of the refill and observed under an optical microscope. After the above, the test was evaluated according to the following criteria. Evaluation criteria: A: There is no difference between the top and bottom B: The amount of soft aggregates at the bottom is slightly less than that at the top. C: No soft aggregates are observed at the bottom, but many are observed at the top.

[0046] (Method for evaluating DC resistance) Each of the water-based ballpoint pens obtained above was left uncapped with the writing tip facing down for one day in an environment of 25°C and 60% relative humidity, and was evaluated according to the degree of leakage from the writing tip according to the following criteria. Evaluation criteria: A: No leakage at all or only slight staining of the ballpoint pen tip B: Droplets form around the ballpoint pen tip but do not progress any further. C: The droplets are getting bigger and are in the process of progressing, but they are not dripping. D: Liquid drips from the ballpoint pen tip

[0047] [Table 1]

[0048] *1 to *5 in Table 1 above are as follows. *1: Mitsubishi Chemical Corporation, average particle size 0.1 μm *2: Blue colored resin particles, average particle size 1.2μm *3: Red thermochromic particles, average particle size 3.0μm, decolorization temperature 60℃ *4: KELZAN AR (manufactured by Sansho) *5: RD-510Y (manufactured by Toho Chemical Industry Co., Ltd.)

[0049] As is clear from the results in Table 1 above, each of the two types of aqueous ballpoint pens equipped with the aqueous ink compositions for ballpoint pens of Examples 1 to 12, which fall within the scope of the present invention, and which have different ball diameters, was found to be superior in the ink stability over time, the pen body stability over time, and resistance to DC current prevention, as compared to Comparative Examples 1 to 5, which fall outside the scope of the present invention. Looking at the comparative examples individually, Comparative Examples 1 and 3 were aqueous ink compositions for ballpoint pens in which no soft aggregates were formed, while Comparative Examples 2, 4, and 5 were aqueous ink compositions for ballpoint pens in which soft aggregates were formed but had a particle size of more than 1000 μm, and thus showed significantly inferior one or more of the effects of the present invention, namely the ink stability over time, the pen body stability over time, and resistance to DC current.

Claims

1. The aqueous ink composition for a ballpoint pen comprises at least a colorant, fermented cellulose, and water, the fermented cellulose being in the form of soft aggregates having a particle size of 5 to 1000 μm in the ink composition, and the colorant being dispersed in the soft aggregates.

2. 2. The water-based ink composition for a ballpoint pen according to claim 1, further comprising a resin emulsion, the resin emulsion being dispersed in the soft aggregate.

3. 3. The aqueous ink composition for a ballpoint pen according to claim 1, further comprising fine particles having a new Mohs hardness of 7 or more, the fine particles being dispersed in the soft aggregate.

4. 3. The aqueous ink composition for a ballpoint pen according to claim 1, further comprising a nonionic surfactant having an HLB value of 15 or more.

5. A ballpoint pen equipped with the aqueous ink composition for ballpoint pens according to claim 1 or 2.

Images