Aqueous ink composition for ballpoint pen

Abstract

[Problem] To provide: a water-based ink composition for a ballpoint pen, which suppresses ink flow characteristics and has excellent stability over time; and a ballpoint pen. [Solution] The aqueous ink composition for ballpoint pens according to the present invention is characterized by containing at least a colorant, a fermented cellulose, and water, the fermented cellulose forming a soft aggregate having a particle diameter of 5-1000 [mu] m in the ink composition, and the colorant being dispersed in the soft aggregate.

Description

Technical Field

[0001] The present invention relates to a water-based ink composition for a ballpoint pen, and more particularly to a water-based ink composition for a ballpoint pen that suppresses ink straight flow and has excellent stability over time. Background Art

[0002] Conventionally, as a technique for preventing the so-called "direct current phenomenon" in water-based ballpoint pens, which causes ink to drip or leak due to gravity from the gap between the retaining member and the ball, a water-based ink composition for ballpoint pens containing crystalline cellulose is known from the perspective of the ink composition (for example, refer to Patent Document 1 based on the applicant of the present application).

[0003] The technology of the above-mentioned Patent Document 1 is an excellent technology that has never been used before as a technology for preventing the "DC phenomenon". Crystalline cellulose aggregates / exists unevenly over time, and the DC prevention effect is reduced. In order to suppress this phenomenon, the applicant of the present application proposed a ballpoint pen aqueous ink composition that contains crystalline cellulose and resin particles, thereby achieving a high degree of both DC prevention effect and stability over time (for example, refer to Patent Document 2).

[0004] However, the technology of Patent Document 2 has several problems, such as aggregation and uneven distribution of crystalline cellulose at low viscosity, which results in a decrease in writing performance.

[0005] On the other hand, as a technology for water-based ballpoint pens having excellent dry-up performance and pigment dispersibility, the following technologies are known: water-based ballpoint pen inks in which fermented cellulose is blended in terms of ink composition (for example, see Patent Document 3); in addition, a method for improving the quality of water-based inks for ballpoint pens by blending fermented cellulose to improve the quality of water-based inks for ballpoint pens (to suppress blurring, leakage, etc.) (for example, see Patent Document 4); and further, water-based ballpoint pen inks in which organic resin particles and surface-treated polysaccharide fibers are blended in order to suppress ink leakage (for example, see Patent Document 5), etc.

[0006] However, in each of the technologies of Patent Documents 3 to 5, ink leakage is not sufficiently suppressed, and fermented cellulose and polysaccharide fibers are easily mixed with air during stirring and filtering, thereby generating buoyancy, becoming easily unevenly distributed on the upper portion over time, and having poor storage stability.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2010-1381 (claims, etc.)

[0010] Patent Document 2: Japanese Patent Application Publication No. 2013-103986 (claims, etc.)

[0011] Patent Document 3: Japanese Patent Application Publication No. 2013-91730 (claims, etc.)

[0012] Patent Document 4: Japanese Patent Application Publication No. 2009-161624 (claims, etc.)

[0013] Patent Document 5: Japanese Patent Application Publication No. 2017-222113 (claims, etc.) Summary of the invention

[0014] Problem that the invention aims to solve

[0015] The present invention has been made in view of the above-mentioned problems and current situations of the prior art and aims to solve them. Its object is to provide a water-based ink composition for ballpoint pens that has a high degree of both direct current prevention effect and temporal stability without reducing writing performance.

[0016] Solutions for solving problems

[0017] The present inventors have conducted intensive studies in view of the above-mentioned existing problems, and as a result, have found that the above-mentioned target aqueous ink composition for ballpoint pens can be obtained by containing at least a colorant, fermented cellulose and water, and making the soft aggregates composed of the aforementioned fermented cellulose have a predetermined particle size range, etc., thereby completing the present invention.

[0018] That is, the aqueous ink composition for ballpoint pens of the present invention is characterized by comprising at least a colorant, fermented cellulose and water, wherein the fermented cellulose forms soft aggregates with a particle size of 5 to 1000 μm in the ink composition, and the colorant is dispersed in the soft aggregates.

[0019] It is preferred that the aqueous ballpoint pen ink composition further contains a resin emulsion, and the resin emulsion is dispersed in the soft aggregates.

[0020] It is preferred 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 aggregates.

[0021] It is preferred that the aqueous ballpoint pen ink composition further contain a nonionic surfactant having an HLB value of 15 or more.

[0022] The ballpoint pen of the present invention is characterized by being equipped with the aqueous ink composition for ballpoint pens having the above-mentioned structure.

[0023] In the present invention, "soft aggregate" refers to a soft (flexible) aggregate having an amorphous outline shape with a three-dimensional network structure formed by fermented cellulose and a colorant contained in the ink composition, and the particle size (maximum particle size) of the aggregate is within a specified range (5 to 1000 μm). In addition, when the ink composition contains a resin emulsion and fine particles with 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 within the above-mentioned specified range.

[0024] Effects of the Invention

[0025] According to the present invention, there are provided: an aqueous ink composition for a ballpoint pen that has a high degree of both the direct flow prevention effect and the stability over time without reducing the writing performance; and a ballpoint pen.

[0026] The objects and effects of the present invention can be realized and achieved particularly by using the constituent elements and combinations pointed out in the claims.Both the above general description and the following detailed description are for exemplary and illustrative purposes and do not limit the present invention described in the claims. DETAILED DESCRIPTION

[0027] Hereinafter, each embodiment of the present invention is described in detail. However, the protection scope of the present invention is not limited to the embodiments described in detail below, and attention should be paid to the aspects involved in the invention and its equivalents recorded in the claims. In addition, the present invention can be implemented based on the contents disclosed in this specification and the technical common sense in the field (including conventional technical selection and obvious matters).

[0028] The aqueous ink composition for ballpoint pens of the present invention is characterized in that it contains at least: a colorant, fermented cellulose and water, the fermented cellulose is soft aggregated, the particle size of the soft aggregate of the fermented cellulose is 5 to 1000 μm, and the colorant is dispersed in the soft aggregate.

[0029] As the colorant used in the present invention, all dyes that are dissolved or dispersed in water, conventionally known inorganic and organic pigments such as titanium oxide, pigment-containing resin particle pigments, simulated pigments obtained by coloring a resin emulsion with a dye, white plastic pigments, wax particles, hollow resin particles, pigments based on silica or mica and coated with multiple layers of iron oxide, titanium oxide, etc. on the surface, bright pigments such as aluminum, thermochromic pigments, photochromic particles, etc., and composite particles thereof can be used without limitation.

[0030] Examples of the dye include acid dyes such as eosin, fluorescent pink, water yellow #6-C, acid red, water blue #105, brilliant blue FCF, and aniline black NB; direct dyes such as direct black 154, direct sky blue 5B, and purple BB; and basic dyes such as rhodamine and methyl violet.

[0031] Examples of inorganic pigments include azo lakes, insoluble azo pigments, chelated azo pigments, phthalocyanine pigments, perylene and perinone pigments, and nitroso pigments. More specifically, examples include inorganic pigments such as carbon black, titanium black, zinc flower, ferric oxide, aluminum, chromium oxide, iron black, cobalt blue, yellow iron oxide, chrome green, zinc sulfide, lithopone, cadmium yellow, vermilion, cadmium red, yellow lead, molybdenum orange, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine, precipitated barium sulfate, barite powder, calcium carbonate, lead white, navy blue, Prussian blue, manganese violet, aluminum powder, and brass powder, and 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 54, CI Pigment Red 56, CI Pigment Red 57, CI Pigment Red 58, CI Pigment Red 59, CI Pigment Red 60, CI Pigment Red 61, CI Pigment Red 62, CI Pigment Red 63, CI Pigment Red 64, CI Pigment Red 65, CI Pigment Red 66, CI Pigment Red 67, CI Pigment Red 68, CI Pigment Red 69, CI Pigment Red 70, CI Pigment Red 71, CI Pigment Red 72, CI Pigment Red 73, CI Pigment Red 74, CI Pigment Red 75, CI Pigment Red 76, CI Pigment Red 77, CI Pigment Red 78, CI Pigment Red 79, CI Pigment Red 80, CI Pigment Red 81, CI Pigment Red 83, CI Pigment Red 84, CI Pigment Red CI Pigment Red 57, CI 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.

[0032] Examples of thermochromic pigments include thermochromic pigments produced as follows, wherein a thermochromic pigment is produced by microencapsulating a thermochromic composition comprising at least a colorless pigment that functions as a color developer, a color developer that is a component capable of causing the colorless pigment to develop color, and a color change temperature regulator that can control the color change temperature during the coloring of the colorless pigment and the color developer, so as to have a predetermined average particle size (e.g., 0.1 to 6 μm).

[0033] As photochromic particles, for example, there can be mentioned photochromic particles manufactured as follows: the photochromic particles are photochromic particles composed of at least one selected from photochromic pigments (compounds), fluorescent pigments, etc., and resins such as terpene phenol resins; photochromic compositions containing at least one selected from photochromic pigments (compounds), fluorescent pigments, etc., an organic solvent, and additives such as antioxidants, light stabilizers, and sensitizers are microencapsulated in a manner to have a predetermined average particle size (for example, 0.1 to 6 μm).

[0034] In the present invention (including Examples, etc.), the "average particle size" is the value of the volume-based 50% particle size (D50) measured using a particle size analyzer [MICROTRAC HRA9320-X100 (manufactured by Nikkiso Co., Ltd.), refractive index 1.8].

[0035] As the microencapsulation method of the above-mentioned thermochromic pigment, for example, interfacial polymerization, interfacial polycondensation, insitu polymerization, liquid solidification coating, phase separation from aqueous solution, phase separation from organic solvent, melt dispersion cooling, air suspension coating, spray drying, etc. can be cited, which can be suitably selected according to the purpose. For example, in the phase separation from aqueous solution, after the colorless pigment, developer, and color-changing temperature regulator are heated and melted, they are put into emulsifier solution and heated and stirred, dispersed in an oil drop shape, then, the resin raw material of polyurethane resin, epoxy resin, amino resin, etc. is used as capsule agent, for example, each liquid such as amino resin solution, specifically methylol melamine aqueous solution, urea solution, benzoguanamine solution, etc. is slowly put into, then react and prepare, the dispersion is filtered, so that thermochromic microcapsule pigment can be manufactured. In the thermochromic pigment, by the type, amount, etc. of suitable combination of colorless pigment, developer and color-changing temperature regulator, the color developing temperature and the decolorizing temperature of each color can be set to suitable temperature.

[0036] The photochromic particles can be microencapsulated in the same manner as the thermochromic resin particles.

[0037] The photochromic particles can have the property of being colorless in an indoor lighting environment (selected from lighting fixtures such as incandescent lamps, fluorescent lamps, lamps, white LEDs, etc. located indoors) and showing color in an ultraviolet irradiation environment (irradiation with a wavelength of 200 to 400 nm, irradiation environment under sunlight containing ultraviolet rays) by appropriately using photochromic pigments (compounds), fluorescent pigments, etc.

[0038] These colorants can be used alone or in combination of two or more. In addition, among these colorants, the average particle size of pigments dispersed in water, resin particle pigments, simulated pigments, white plastic pigments, multi-layer coated pigments, thermochromic pigments, photochromic particles, etc. varies depending on the ball diameter, ink composition / viscosity, etc., but the average particle size is preferably 0.02 to 6 μm.

[0039] The content of these colorants can be appropriately increased or decreased depending on the line density of the ink, but is desirably 0.1 to 40% by mass (hereinafter, "% by mass" is referred to as "%"), and preferably 1 to 10% based on the total amount of the ink composition.

[0040] The fermented cellulose used in the present invention is used to form flexible aggregates (soft aggregates) having a predetermined particle size in the ink composition.

[0041] It has been known to use xanthan gum and the like as a technique for preventing the so-called "direct current phenomenon" in water-based ballpoint pens, etc., which is to prevent ink from dripping or leaking due to gravity from the gap between the retaining member and the ball. However, in the present invention, the compounding system containing the above-mentioned pigment and other colorants contains fermented cellulose, and soft aggregates (soft aggregates) of a specified particle size are formed in the ink composition, specifically, soft aggregates (soft aggregates) with a particle size of 5 to 1000 μm and colorants dispersed in the soft aggregates are formed, thereby achieving an ink composition that highly combines the anti-direct current effect and the stability over time without reducing the writing performance.

[0042] In the present invention (including the embodiments described later, etc.), the particle size of the soft aggregates based on the aforementioned fermented cellulose is measured by observing the ink with an optical microscope (HIROX digital microscope RH-2000, the same below), and the maximum diameter of the soft aggregates is preferably 5 to 1000 μm, and more preferably 5 to 200 μm.

[0043] If the particle size of the soft aggregate is less than 5 μm, the direct flow prevention effect cannot be achieved. On the other hand, if it exceeds 1000 μm, the flow out during writing is hindered and the effect of the present invention cannot be achieved.

[0044] The fermentable cellulose that can be used is cellulose produced by cellulose-producing bacteria such as bacteria belonging to the genus Acetobacterium, Pseudomonas, Agrobacterium, etc., and there is no particular limitation as long as it is these celluloses. Generally, fermentable cellulose can be produced by culturing cellulose-producing bacteria according to a known method (a culture medium and conditions to be cultured, etc.), and purifying the obtained fermented cellulose as desired.

[0045] The chemical structure of the polysaccharide constituting fermented cellulose is a linear high-molecular polysaccharide based basically on β1-4-bonded glucose.

[0046] The formation of the soft aggregate in the present invention can be obtained by adjusting the content of each component, stirring conditions, such as stirring speed, stirring time, temperature, etc. when preparing an ink containing a mixing system of at least a colorant, fermented cellulose and water.

[0047] The fermented cellulose used in the present invention is water-insoluble and, unlike thickening polysaccharides, has low viscosity and little stickiness, and can be used stably under various ink coexisting components, temperatures, pH, and the like.

[0048] Examples of fermented cellulose that can be used include fermented cellulose obtained in the above-mentioned production, commercially available SAN ARTIST series manufactured by San-Ei Gen FFI, Inc., such as SAN ARTIST H-PN, SAN ARTIST H-PG, and SAN ARTIST H-PX, and CM-NFBC manufactured by Kusano Sakuko Co., Ltd.

[0049] The content of these fermented celluloses can be any amount that forms soft aggregates (soft aggregates) of a specified particle size in the ink composition and can exert the effects of the present invention, as described above. It varies depending on the type of compounding, etc., but is desirably adjusted to 0.01 to 10% by mass, preferably 0.03 to 5% by mass, and particularly preferably 0.05 to 1% by mass, relative to the total amount of the ink composition.

[0050] When the content of the fermented cellulose is 0.01% by mass or more, the effects of the present invention can be exhibited, whereas when the content is 10% by mass or less, the effects of the present invention can be effectively exhibited without increasing the cost.

[0051] The aqueous ink composition for a ballpoint pen of the present invention preferably contains a resin emulsion from the viewpoint of adjusting the ink viscosity and improving the fixing force.

[0052] As the resin emulsion that can be used, specifically, at least one selected from the group consisting of styrene acrylic emulsions, polyolefin emulsions, acrylic emulsions, vinyl acetate emulsions, urethane emulsions, styrene-butadiene emulsions, styrene acrylonitrile emulsions and the like can be cited, and at least one of each can be used, and it is desirable to use a total of two or more.

[0053] As a preferred resin emulsion, a styrene acrylic resin is desirable.

[0054] Examples of commercially available products of the resin emulsion include JONCRYL 352D, JONCRYL 537-E, JONCRYL PDX-7198, JONCRYL 7430, JONCRYL 7538, JONCRYL 7615, JONCRYL 7700, and JONCRYL 7787 (manufactured by BASF Corporation).

[0055] The content of these resin emulsions is preferably adjusted to 0.5 to 15% by mass, preferably 1 to 10% by mass, based on the total amount of the ink composition in terms of solid content.

[0056] When the content of the resin emulsion is 0.05% by mass or more, the effect of the present invention can be further exerted. On the other hand, when it is 15% by mass or less, the effect of the present invention is not changed and the cost is not increased, which is preferred.

[0057] Furthermore, within the range not impairing the effects of the present invention, 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 resins, water-soluble styrene·maleic acid resins, polyvinyl alcohol, polyvinyl pyrrolidone, water-soluble maleic acid resins, water-soluble styrene resins, olefin emulsions, water-soluble ester-acrylic resins, ethylene-maleic acid copolymers, polyethylene oxide, and water-soluble polyurethane resins may be used in combination.

[0058] The aqueous ink composition for a ballpoint pen of the present invention preferably further contains fine particles having a new Mohs hardness of 7 or more. By containing fine particles having such characteristics, the effect of suppressing the wear of the ball socket and the effect of preventing the above-mentioned soft aggregates from floating up are further exhibited.

[0059] The fine particles that can be used are not particularly limited as long as they have a new Mohs hardness of 7 or more.

[0060] The new Mohs hardness of the fine particles is preferably 7 or more and 15 or less in terms of durability and ink outflow.

[0061] The new Mohs hardness is the same as the corrected Mohs hardness. The new Mohs hardness refers to a hardness scale for obtaining the hardness of a mineral by comparing it with 15 minerals that become the benchmark. The benchmark minerals are talc, gypsum, calcite, fluorite, apatite, orthoclase, fused quartz, crystal (quartz), topaz (topaz), garnet, fused zirconium oxide, fused aluminum oxide, silicon carbide, boron carbide and diamond in order from soft (new Mohs hardness 1) to hard (new Mohs hardness 15). In this specification, the new Mohs hardness is measured by rubbing the sample material (particles) whose hardness is to be measured with these benchmark minerals, and the hardness is measured by the presence or absence of scratches. For example, for fused quartz, when there is no scratch and there is a scratch in crystal (quartz), the new Mohs hardness of the sample material (particles) becomes 7.5 (meaning between 7 and 8). It should be noted that in particles with a new Mohs hardness lower than 7, the ball bearing socket cannot be sufficiently subjected to the wear suppression effect, so it is not preferred.

[0062] Examples of the fine particles having a new Mohs hardness of 7 or more include ceramic fine particles such as silicon carbide, aluminum oxide, silicon dioxide, tungsten carbide, and zirconium oxide, and metal fine particles. These can be used alone or in combination of two or more.

[0063] In addition, for the fine particles used, the average particle size is preferably 30 μm or less, preferably 0.07 to 30 μm, and more preferably 0.1 to 10 μm, in order to further suppress the wear of the socket and adjust the specific gravity of the soft aggregate to improve the outflow of the ink.

[0064] Fine particles having an average particle diameter of 30 μm or less preferably have good dispersion stability in the ink and can suppress sedimentation of the fine particles.

[0065] Furthermore, from the perspective of improving writing feel and ink outflow properties, the shape of the fine particles having the above-specified new Mohs hardness and average particle size is preferably spherical, elliptical, plate-like, or rod-like.

[0066] As these fine particles, any fine particles having the above-specified new Mohs hardness and the above-specified average particle size may be used, and commercially available fine particles may be used. In addition, ceramic fine particles, metal fine particles, etc. produced by a known method may be used.

[0067] Furthermore, in the present invention, when the new Mohs hardness of the microparticles is set to (A), the average particle size is set to (B), and the product of (A) and (B) is set to the product value, if the product value is within a prescribed range, then when used in a water-based ink composition for a ballpoint pen, the balance between the wear suppression of the socket and the dispersion stability is further excellent, and the effect of the present invention can be further suitably exerted. The prescribed range of the above-mentioned product value is, for example, not less than 0.2, preferably not less than 0.3, more preferably not less than 0.49, and further preferably not less than 0.7, for example, not more than 450, preferably not more than 210, more preferably not more than 150, and further preferably not more than 70.

[0068] The content of the fine particles having the specified new Mohs hardness and the like is preferably 0.001 to 5% by mass, more preferably 0.1 to 2% by mass, based on the total amount of the ink composition.

[0069] When the content of the fine particles is 0.001% by mass or more, more sufficient socket wear suppression can be achieved. On the other hand, when the content is 5% by mass or less, more sufficient socket wear suppression can be achieved without deteriorating the writing feel.

[0070] Furthermore, in the present invention, it is desirable to contain a nonionic surfactant having an HLB value of 15 or more.

[0071] The "HLB value" in the present invention can be determined by the Griffith method [HLB value = 20 x (MW / M), MW: molecular weight of the hydrophilic part, M: molecular weight].

[0072] The nonionic surfactant having an HLB value of 15 or more is easily compatible with the water system and can effectively form soft aggregates within the above-mentioned specified range (5 to 1000 μm).

[0073] As the nonionic surfactant that can be used, for example, polyoxyethylene polyoxypropylene block polymers, polyoxyethylene polyoxypropylene glycols, polyoxyalkylene adducts of organic amines, diglycerol polyoxyethylene fatty acid esters, polyoxyethylene styrenated phenyl ethers, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, polyoxyethylene alkyl ethers, etc. can be mentioned. Among them, those having an HLB value of 15 or more can be used. In terms of stability over time, polyoxyethylene polyoxypropylene block polymers are more preferably used, and particularly preferably used.

[0074] Among the commercially available nonionic surfactants having an HLB of 15 or higher, for example, one or more of Solsperse 27000 (or more, manufactured by Lubrizol Japan Ltd.), EPAN 680 (or more, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), MM-750, MCA-750, 10G-L (or more, manufactured by Sakamoto Yakuin Kogyo Co., Ltd.), Emulgen 120, Emulgen 1150, Emulgen 1430, Emulgen 1A-500, and Amiet 320 (or more, manufactured by Kao Corporation) can be used.

[0075] The content of these nonionic surfactants is preferably 0.01 to 10% by mass, more preferably 0.2 to 5% by mass, based on the total amount of the ink composition.

[0076] When the content of the nonionic surfactant is 0.01% by mass or more, the dispersion stability of the soft aggregate is improved. On the other hand, when the content is 10% by mass or less, the effect of suppressing the change in viscosity over time can be expected.

[0077] The aqueous ink composition for a ballpoint pen of the present invention is characterized in that it contains at least a colorant, fermented cellulose and water, wherein the fermented cellulose forms soft aggregates with a particle size of 5 to 1000 μm in the ink composition, and the colorant is dispersed in the soft aggregates. Furthermore, it is preferred that the composition further contains at least one of a resin emulsion, fine particles with a new Mohs hardness of 7 or more, and a nonionic surfactant with 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 a solvent as the balance, a water-soluble solvent, a lubricant, a thickener, a pH adjuster, a rust inhibitor, a preservative or an antibacterial agent, etc. may be appropriately contained as needed within a range that does not impair the effects of the present invention.

[0078] The water-soluble solvent that can be used is used for various purposes as ink quality, such as preventing the ink from freezing at low temperatures, preventing the ink from drying at the tip of the pen, etc. Specifically, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, 3-butylene glycol, thiodiethylene glycol, glycerol, ethylene glycol monomethyl ether, and diethylene glycol monomethyl ether can be used alone or in combination. The content of the water-soluble solvent is preferably set to 1 to 40% by mass relative to the total amount of the ink composition.

[0079] As lubricants that can be used, there are fatty acid esters of polyols, which are also used as surface treatment agents for pigments, higher fatty acid esters of sugars, polyoxyalkylene higher fatty acid esters, nonionic systems such as alkyl phosphates, anionic systems such as phosphates, alkyl sulfonates of higher fatty acid amides, alkyl allyl sulfonates, derivatives of polyalkylene glycol, polyether-modified silicones, and the like.

[0080] As the thickener that can be used, known substances can be used, and specifically, at least one selected from the group consisting of alkali-swellable associative emulsions, alkali-swellable emulsions, polysaccharides such as cellulose derivatives, xanthan gum, succinoglycan, cross-linked acrylic acid polymers, crystalline cellulose, xanthan gum, gellan gum, montmorillonite clay minerals and other inorganic thickeners can be mentioned.

[0081] Examples of pH adjusters include ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, sodium tripolyphosphate, alkali metal salts of carbonic acid and phosphoric acid such as sodium carbonate, hydrates of alkali metals such as sodium hydroxide, etc. In addition, examples of rust inhibitors include benzotriazole, tolyltriazole, dicyclohexylamine nitrite, saponins, etc., and examples of preservatives or antibacterial agents include phenol, sodium pyrithione, sodium benzoate, thiazoline compounds, benzimidazole compounds, etc.

[0082] Each component such as the lubricant, thickener, pH adjuster, rust inhibitor, antiseptic or antibacterial agent may be used alone or in combination of two or more. Any commercially available product thereof may be used.

[0083] The aqueous ink composition for a ballpoint pen of the present invention can be produced without any particular change compared to the production method of other aqueous ink compositions.

[0084] That is, the aqueous ink composition for a ballpoint pen of the present invention can be produced as follows: using a mixer, for example, a bead mill, a homomixer, a homogenizer, etc. that can apply strong shearing, setting the stirring conditions to appropriate conditions, at least a colorant, fermented cellulose, water, and preferably each component and other components are mixed and stirred, and then, if necessary, coarse particles in the ink composition are removed by filtration or centrifugal separation, thereby producing an aqueous ink composition for a ballpoint pen.

[0085] In addition, the pH (25° C.) of the aqueous ballpoint pen ink composition of the present invention is preferably adjusted to 5 to 10, more preferably 6 to 9.5, using a pH adjuster or the like for ease of use, safety, stability of the ink itself, and compatibility with the ink container.

[0086] The aqueous ink composition for a ballpoint pen of the present invention is mounted on a ballpoint pen having a pen tip such as a ballpoint pen tip.

[0087] As the ballpoint pen in the present invention, for example, there can be mentioned a ballpoint pen having the above-mentioned aqueous ink composition stored in an ink container (pen core) for a ballpoint pen having a ball with a diameter of 0.18 to 2.0 mm, and a substance that is incompatible with the aqueous ink composition stored in the ink container and has a specific gravity lower than that of the aqueous ink composition, such as polybutene, silicone oil, mineral oil, etc., as an ink follower. As long as the ball has a diameter within the above range, the structure of the aqueous ballpoint pen used is not particularly limited, and it is particularly desirable to fill the above-mentioned aqueous ink composition into an ink container tube made of a polypropylene resin tube, and finish it into a water-based ballpoint pen core having a stainless steel tip (the ball is a super steel alloy) at the front end.

[0088] Furthermore, a straight liquid type ballpoint pen having a collector structure (ink holding mechanism) in which the barrel itself serves as an ink container and the barrel is filled with the aqueous ballpoint pen ink composition having the above-described structure.

[0089] In the present invention, when used in a water-based ballpoint pen having a ball with a diameter of 0.18 to 1.0 mm, the wear of the socket can be expected to be suppressed, and the present invention is suitable.

[0090] The reason why the aqueous ink composition for a ballpoint pen of the present invention having such a configuration is a highly compatible aqueous ink composition for a ballpoint pen with both the anti-flowing effect and the stability over time without deteriorating the writing performance is as follows.

[0091] That is, the aqueous ink composition for ballpoint pens of the present invention contains at least a colorant, fermented cellulose and water, the fermented cellulose forms soft aggregates (soft aggregates) with a particle size of about 5 to 1000 μm in the ink, the colorant is dispersed in the soft aggregates, and the soft aggregates are easily disintegrated and have fluidity when shearing force is applied to the ink between the ball and the tip holder generated during writing. On the other hand, when not writing, that is, when shearing force is not applied to the ink, a three-dimensional network structure is formed, and a large amorphous soft aggregate shape is maintained. Therefore, a ballpoint pen aqueous ink composition is obtained that has an excellent effect of preventing the ink from dripping or leaking from the gap between the holder and the ball under severe conditions such as falling, and the ink has excellent temporal stability without reducing the writing performance, and a ballpoint pen equipped with the ink composition.

[0092] Example

[0093] Next, the present invention will be described in further detail based on 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 and the like.

[0094] [Examples 1 to 12 and Comparative Examples 1 to 5]

[0095] According to the blending recipe shown in Table 1 below (colorant, fermented cellulose, resin emulsion, fine particles, nonionic surfactant, and combination of other components), a stirrer [MAX MIXER manufactured by Inoue Seisakusho Co., Ltd.] was used to appropriately adjust the stirring speed, stirring time, temperature, etc. to prepare each aqueous ink composition for ballpoint pens.

[0096] When soft aggregates were prepared from each of the obtained aqueous ballpoint pen ink compositions (total amount: 100% by mass) according to the above method, the particle sizes thereof were measured using an optical microscope.

[0097] In addition, the temporal stability of the ink and the temporal stability and anti-flowing property of the pen body of a ballpoint pen having the following configuration were evaluated by the following evaluation methods for each of the obtained aqueous ink compositions for ballpoint pens.

[0098] These results are shown in Table 1 below.

[0099] (Evaluation method of ink stability over time)

[0100] Each ink composition was placed in a 500 ml glass mayonnaise bottle at 25°C and 60% relative humidity and stored for 2 months. After that, the ink was sucked out from the uppermost and lowermost parts and observed with an optical microscope. When no soft aggregates were observed in the lowermost part compared to the uppermost part, it was judged that the soft aggregates floated on the upper part and the stability was poor.

[0101] After the above, evaluation was performed according to the following evaluation criteria.

[0102] Evaluation criteria:

[0103] A: No difference between the top and bottom

[0104] B: The soft aggregates at the bottom are slightly less than those at the top

[0105] C: No soft aggregates were observed at all in the lowermost part, but many were observed in the uppermost part.

[0106] (Ballpoint pen composition)

[0107] Ballpoint pen tips of various ball diameters (0.18 mm super alloy ball or 1.0 mm super alloy ball) were mounted on a tube (all PP tubes with an inner diameter of 4.7 mm) and a polypropylene joint member of UMN-103 manufactured by Mitsubishi Pencil Co., Ltd., filled with the above-mentioned aqueous ink compositions and polybutene as an ink follower, and degassed under centrifugal treatment (500 G, 5 minutes). After assembling aqueous ballpoint pens of various ball diameters, the various writing tests shown below were carried out.

[0108] (Temperature stability of the pen body)

[0109] A water-based ballpoint pen stored for 12 weeks at a temperature of 50° C. and a humidity of 65% with the pen tip facing downward was tested in the following manner: Ink was sucked out from the upper and lower parts of the pen core and observed using an optical microscope.

[0110] After the above, evaluation was performed according to the following evaluation criteria.

[0111] Evaluation criteria:

[0112] A: No difference between the top and bottom

[0113] B: The soft aggregates at the bottom are slightly less than those at the top

[0114] C: No soft aggregates were observed at all in the lowermost part, but many were observed in the uppermost part.

[0115] (Evaluation method for DC protection)

[0116] Each of the water-based ballpoint pen bodies obtained above was placed with the writing tip facing downward with the cap removed for one day at 25° C. and a relative humidity of 60%, and the degree of leakage from the writing tip was evaluated according to the following criteria.

[0117] Evaluation criteria:

[0118] A: No leakage at all or the tip of the ballpoint pen is slightly contaminated

[0119] B: A droplet forms around the tip of the ballpoint pen, but does not develop further

[0120] C: The droplet becomes larger and does not fall down in the middle of the process

[0121] D: Liquid dripping from the tip of a ballpoint pen

[0122] [Table 1]

[0123]

[0124] *1 to *5 in the above Table 1 are as follows.

[0125] *1: Made by Mitsubishi Chemical Co., Ltd., average particle size 0.1μm

[0126] *2: Blue colored resin particles, average particle size 1.2 μm

[0127] *3: Red thermochromic particles, average particle size 3.0 μm, decolorization temperature 60°C

[0128] *4: KELZAN AR (manufactured by Sanjing Co., Ltd.)

[0129] *5: RD-510Y (manufactured by Toho Chemical Industry Co., Ltd.)

[0130] It is clearly determined from the results in Table 1 above that two types of water-based ballpoint pens with different ball diameters equipped with water-based ink compositions for ballpoint pens of Examples 1 to 12 that fall within the scope of the present invention are superior in terms of ink stability over time, pen body stability over time, and anti-flowing properties compared to Comparative Examples 1 to 5 that are not within the scope of the present invention.

[0131] If the comparative examples are observed separately, comparative examples 1 and 3 are aqueous ink compositions for ballpoint pens that do not form soft aggregates, and comparative examples 2, 4, and 5 are compositions that form soft aggregates but have a particle size of more than 1000 μm. Any one of the temporal stability of the ink, the temporal stability of the pen body, and the anti-direct current property, which are the effects of the present invention, is significantly poor.

[0132] Industrial Applicability

[0133] Provided are a ballpoint pen aqueous ink composition that has a high degree of both anti-direct current effect and stability over time without reducing writing performance, and a ballpoint pen.

Claims

1. A water-based ink composition for a ballpoint pen, characterized in that: The ink composition contains at least: a colorant, fermented cellulose and water. The fermented cellulose forms soft aggregates with a particle size of 5 to 1000 μm in the ink composition, and the colorant is dispersed in the soft aggregates.

2. The aqueous ink composition for ballpoint pens according to claim 1, characterized in that: The aqueous ink composition for ballpoint pens further comprises a resin emulsion, and the resin emulsion is dispersed in the soft aggregates.

3. The aqueous ink composition for ballpoint pens according to claim 1 or 2, characterized in that: The aqueous ink composition for a ballpoint pen further comprises fine particles having a new Mohs hardness of 7 or more, and the fine particles are dispersed in the soft aggregates.

4. The aqueous ink composition for ballpoint pens according to claim 1 or 2, characterized in that: The aqueous ballpoint pen ink composition further includes a nonionic surfactant having an HLB value of 15 or more.

5. A ballpoint pen, characterized in that: The invention is provided with the aqueous ink composition for ballpoint pens according to claim 1 or 2.

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