Ink composition for aqueous ballpoint pen

Abstract

To provide an ink composition for an aqueous ballpoint pen which is excellent in temporal stability, does not degrade writing performance, and prevents occurrence of so-called "direct current phenomenon" such that ink drops and leaks by gravity from a gap between a holder and a ball, even with low viscosity ink.SOLUTION: An ink composition for an aqueous ballpoint pen contains at least a coloring material, and polyester resin emulsion.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an ink composition for aqueous ballpoint pens that has excellent stability over time, does not deteriorate writing performance, and does not exhibit the so-called "direct current phenomenon" where ink drips or leaks due to gravity from the gap between the holder and the ball, even with low-viscosity ink.

Background Art

[0002] Conventionally, in aqueous ballpoint pens, there have been problems such as the occurrence of the so-called "direct current phenomenon" where ink drips or leaks due to gravity from the gap between the holder and the ball.

[0003] As methods for solving this problem, an approach from the structure of the ballpoint pen tip and an approach from the composition of the ink are known. Among them, as the latter approach, for example, in the invention described in Patent Document 1, it is characterized by containing fine particle anhydrous silica so that ink does not leak first from the pen tip. Also, in the invention described in Patent Document 2, it is known to add a water-absorbing and swelling spherical polymer compound having a minimum film-forming temperature of 30°C or lower to prevent ink leakage. Furthermore, in the invention described in Patent Document 3, a ballpoint pen tip that rotatably holds a ball at the tip of the ink storage cylinder is directly attached or attached via a tip holder, and an aqueous ballpoint pen ink composition comprising at least water, a colorant, organic resin particles, and a shear-thinning viscosity-imparting agent is stored in the ink storage cylinder. The aqueous ballpoint pen is characterized in that the axial movement amount of the ball of the ballpoint pen tip is 15 μm or more, and the average particle diameter of the organic resin particles is 15 μm or less. In the invention of Patent Document 4, an ink composition for ballpoint pens characterized by containing at least crystalline cellulose and resin particles is known.

[0004] However, in Patent Document 1 mentioned above, since particles such as silica have a high specific gravity, it is difficult to uniformly maintain their presence in the ink over a long period. In Patent Document 2, there are still several problems such as the formation of a film at the pen tip, which can also be a factor in drying up and the like. In Patent Document 3, it is an approach from the composition and structure of the ink. However, in the case of low-viscosity ink, the current situation is that the problem of a sufficient "direct current phenomenon" has not yet been solved. In Patent Document 4, it is an unprecedented technique using crystalline cellulose, which suppresses the occurrence of the direct current phenomenon. However, as a further need, there is a strong desire for an aqueous ballpoint pen ink composition that has excellent stability over time, does not deteriorate writing performance, and moreover, even in the case of low-viscosity ink, does not exhibit the "direct current phenomenon".

[0005] On the other hand, as a technique of using a resin emulsion or the like in a writing instrument ink, for example, in Patent Document 5, an aqueous ink composition for a fabric marking pen containing a colorant and a resin emulsion, wherein the glass transition point of the resin contained in the resin emulsion is 20°C or higher and 100°C or lower, and the resin emulsion is a colored resin emulsion colored with the colorant is known. In Patent Document 6, an aqueous ink composition for a writing instrument containing a pigment, a guar gum derivative, a hardly water-soluble resin (resin emulsion), and water is known. When the total content of the pigment with respect to the total amount of the ink composition is U, and the total content of the guar gum derivative with respect to the total amount of the ink composition is V, 0.0005 ≦ V / U ≦ 0.05, and when the total content of the hardly water-soluble resin with respect to the total amount of the ink composition is X, 5 ≦ X / V ≦ 75. A writing instrument using such an aqueous ink composition is also known. However, Patent Document 5 aims to improve the bleeding resistance and washability of the handwriting or coating film written on the fabric. Also, Patent Document 6 provides an aqueous ink composition with excellent color development and fixing properties of the handwriting, which can retain the colorant on the fiber surface of the written surface even when writing on the surface of a writing object with large gaps between fibers such as paper or fabric. The present invention is different in the problems to be solved and the technical idea (configuration and its operational effects).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0007] In view of the problems and current situation of the above prior art, the present invention aims to solve these problems, and provides an aqueous ballpoint pen ink composition that is excellent in stability over time, does not reduce writing performance, and does not cause the occurrence of "DC phenomenon" even with a low-viscosity ink, and an aqueous ballpoint pen equipped with the same.

Means for Solving the Problems

[0008] In view of the above conventional problems and the like, the present inventor has conducted intensive research, and as a result, has found that an aqueous ballpoint pen ink composition for the above purpose can be obtained by containing at least a coloring material and a specific resin emulsion, and has thus completed the present invention.

[0009] That is, the aqueous ballpoint pen ink composition of the present invention is characterized by containing at least a colorant and a polyester resin emulsion. Shear rate 383 sec -1 Preferably, the viscosity at 25 °C is 1 to 100 mPa·sec. The above polyester resin emulsion preferably has a number average molecular weight (Mn) of 10,000 or more. The content of the above polyester resin emulsion is preferably 0.5 to 30% by mass in terms of solid content concentration with respect to the total amount of the ink composition. The aqueous ballpoint pen of the present invention is characterized by being equipped with the aqueous ballpoint pen ink composition having the above configuration. Preferably, the amount of movement of the ball in the ball tip in the axial direction is 15 to 60 μm.

Advantages of the Invention

[0010] According to the present invention, there are provided an aqueous ballpoint pen ink composition having excellent stability over time, not reducing writing performance, and not causing the so-called "direct current phenomenon" in which ink drips or leaks due to gravity from the gap between the holder and the ball even with a low-viscosity ink, and an aqueous ballpoint pen equipped with the same. The object and advantages of the present invention are recognized and obtained by using the components and combinations particularly pointed out in the claims. Both the above general description and the following detailed description are exemplary and explanatory, and do not limit the present invention described in the claims.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail. However, note that the technical scope of the present invention is not limited to the embodiments described in detail below, and extends to the invention described in the claims and its equivalents. The ink composition for a water-based ballpoint pen of the present invention is characterized by containing at least a coloring material and a polyester resin emulsion.

[0013] As the coloring material used in the present invention, all dyes that are soluble or dispersed in water, conventionally known inorganic and organic pigment systems such as titanium oxide, resin particle pigments containing pigments, pseudo-pigments obtained by coloring resin emulsions with dyes, white plastic pigments, pigments having a base of silica or mica and having a multilayer coating of iron oxide or titanium oxide on the surface layer, thermochromic pigments, photochromic particles, etc. can be used without limitation. Examples of the dye include acid dyes such as eosin, phloxine, water yellow #6-C, acid red, water blue #105, brilliant blue FCF, nigrosine NB; direct dyes such as direct black 154, direct sky blue 5B, violet BB; 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, nitroso pigments, etc. More specifically, inorganic pigments such as carbon black, titanium black, zinc white, red iron oxide, aluminum, chromium oxide, iron black, cobalt blue, iron oxide yellow, viridian, zinc sulfide, lithopone, cadmium yellow, vermilion, cadmium red, lead yellow, molybdate orange, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine, precipitated barium sulfate, barite powder, calcium carbonate, lead white, ultramarine white, ultramarine blue, manganese violet, aluminum powder, brass powder, etc., and C.I. Pigment Blue 17, C.I. Pigment Blue 15, C.I. Pigment Blue 17, C.I. Pigment Blue 27, C.I. Pigment Red 5, C.I. Pigment Red 22, C.I. Pigment Red 38, C.I. Pigment Red 48, C.I. Pigment Red 49, C.I. Pigment Red 53, C.I. Pigment Red 57, C.I. Pigment Red 81, C.I. Pigment Red 104, C.I. Pigment Red 146, C.I. Pigment Red 245, C.I. Pigment Yellow 1, C.I. Pigment Yellow 3, C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. Pigment Yellow 17, C.I. Pigment Yellow 34, C.I. Pigment Yellow 55, C.I. Pigment Yellow 74, C.I. Pigment Yellow 95, C.I. Pigment Yellow 166, C.I. Pigment Yellow 167, C.I. Pigment Orange 5, C.I. Pigment Orange 13, C.I. Pigment Orange 16, C.I. Pigment Violet 1, C.I. Pigment Violet 3, C.I. Pigment Violet 19, C.I. Pigment Violet 23, C.I. Pigment Violet 50, C.I. Pigment Green 7, etc. can be mentioned.

[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 developer that is a component having the ability to develop the color of the leuco dye, and a discoloration temperature adjuster that can control the discoloration temperature in the color development of the leuco dye and the developer so as to have a predetermined average particle diameter (for example, 0.1 to 6 μm). Examples of photochromic particles include photochromic particles composed of at least one selected from at least photochromic dyes (compounds), fluorescent dyes, etc. and a resin such as terpene phenol resin, and photochromic compositions containing at least one selected from at least photochromic dyes (compounds), fluorescent dyes, etc., an organic solvent, and additives such as antioxidants, light stabilizers, and sensitizers, produced by microencapsulating them so as to have a predetermined average particle diameter (for example, 0.1 to 6 μm).

[0016] In the present invention (including examples, etc.), the "average particle diameter" is the value of D50 measured with a particle size analyzer [Microtrac HRA9320-X100 (manufactured by Nikkiso Co., Ltd.)]. Examples of the method for microencapsulating the thermochromic pigment include, for example, interfacial polymerization method, interfacial polycondensation method, in-situ polymerization method, in-liquid hardening 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 a leuco dye, a developer, and a discoloration temperature adjuster, they are put into an emulsifier solution, heated and stirred to be dispersed in the form of oil droplets, and then, as a capsule film agent, a resin raw material whose wall film is a urethane resin, an epoxy resin, an amino resin, etc. is used. For example, each solution such as an amino resin solution, specifically, an aqueous solution of methylol melamine, a urea solution, a benzoguanamine solution, etc. is gradually added, and then continuously reacted and prepared, and then this dispersion is filtered to produce a thermochromic microcapsule pigment. In this thermochromic pigment, by suitably combining the types and amounts of the leuco dye, the developer, and the discoloration temperature adjuster, the color development temperature and the decoloration temperature of each color can be set to suitable temperatures. In addition, as the method for microencapsulating the photochromic particles, it can be prepared in the same manner as the production of the above-mentioned thermochromic resin particles. By suitably using a photochromic dye (compound), a fluorescent dye, etc. in these photochromic particles, for example, they can be made to be colorless in an indoor lighting environment (lighting fixtures selected from incandescent lamps, fluorescent lamps, lamps, white LEDs, etc. indoors) and have the property of developing color in an ultraviolet irradiation environment (irradiation with a wavelength of 200 to 400 nm, irradiation environment with sunlight containing ultraviolet rays).

[0017] These color materials can be used alone or in combination of two or more. Among these color materials, the average particle diameters of pigments dispersed in water, resin particle pigments, pseudo pigments, white plastic pigments, multi-layer coated pigments, thermochromic pigments, photochromic particles, etc. vary depending on the ball diameter, ink composition, viscosity, etc., but those with an average particle diameter of 0.02 to 6 μm are desirable. The content of these colorants can be appropriately increased or decreased according to the line drawing density of the ink, but it is preferably 0.1 to 40% by mass (hereinafter, "% by mass" is referred to as "%"), more preferably 1 to 10% by mass, based on the total amount of the ink composition.

[0018] The polyester resin emulsion used in the present invention is contained in order to exhibit the effects of the present invention. The polyester resin emulsion to be used can be obtained by using at least a polyhydric alcohol component and a polyvalent carboxylic acid component such as a polyvalent carboxylic acid, a polyvalent carboxylic anhydride, and a polyvalent carboxylic ester. Examples of the polyhydric alcohol component include alkylene glycols having 2 to 36 carbon atoms (ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 1,6-hexanediol, etc.), alkylene ether glycols having 4 to 36 carbon atoms (diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, etc.), alicyclic diols having 6 to 36 carbon atoms (1,4-cyclohexanedimethanol, hydrogenated bisphenol A, etc.), alkylene oxide (ethylene oxide (hereinafter abbreviated as EO), propylene oxide (hereinafter abbreviated as PO), butylene oxide (hereinafter abbreviated as BO)) adducts (addition mole number 1 to 30) of the above alicyclic diols having 2 to 4 carbon atoms or alkylene oxide (EO, PO, BO, etc.) adducts (addition mole number 2 to 30) of bisphenols (bisphenol A, bisphenol F, bisphenol S, etc.). These polyhydric alcohol components may be used alone or in combination of two or more.

[0019] Examples of the polyvalent carboxylic acid component include alkanedicarboxylic acids having 4 to 36 carbon atoms (succinic acid, adipic acid, sebacic acid, etc.), alkenyl succinic acids (dodecenyl succinic acid, etc.), alicyclic dicarboxylic acids having 4 to 36 carbon atoms (dimer acid (dimerized linoleic acid), etc.), alkenedicarboxylic acids having 4 to 36 carbon atoms (maleic acid, fumaric acid, citraconic acid, mesaconic acid, etc.), or carbon It contains aromatic dicarboxylic acids with prime numbers from 8 to 36 (phthalic acid, isophthalic acid, terephthalic acid or their derivatives, naphthalenedicarboxylic acid, etc.). These polycarboxylic acid components may be used alone, only one type, or in combination of two or more types.

[0020] The number average molecular weight (Mn) of the above polyester resin is preferably 10,000 or more, more preferably 10,000 to 100,000. When the number average molecular weight (Mn) of the above polyester resin is 10,000 or more, it has excellent effects in preventing DC phenomena and long-term storage stability. The number average molecular weight (Mn) is a value measured by gel permeation chromatography (GPC). For example, it can be obtained from a calibration curve prepared with a polystyrene standard sample using "RID-6A" manufactured by Shimadzu Corporation (column: "TSK-GEL" manufactured by Tosoh Corporation, solvent: tetrahydrofuran (THF), column temperature: 40°C).

[0021] As the above polyester resin emulsion, commercially available products may be used. Examples of commercially available products of the above polyester resin emulsion include Elite KA-5034, Elite KA-5071S, Elite KA-1449, Elite KA-0134, Elite KA-3556, Elite KA-6137, Elite KZA-6034, Elite KT-8803, Elite KT-8701, Elite KT-9204, Elite KT-8904, Elite KT-0507, Elite KT-9511 (all manufactured by Unitika Ltd.). These may be used alone, only one type, or in combination of two or more types.

[0022] The content of these polyester resin emulsions is preferably 0.5 to 30% in terms of solid content concentration with respect to the total amount of the ink composition, and more preferably 1 to 10%. If the solid content of this polyester resin emulsion is less than 0.5%, the effects of the present invention cannot be exerted. On the other hand, if it exceeds 30%, the stability of the ink over time may decrease, and the ink is likely to solidify at the pen tip, resulting in a decrease in the initial writing performance, which is not preferable.

[0023] 〈Ink Composition for Water-Based Ballpoint Pen〉 The ink composition for water-based ballpoint pen of the present invention is characterized by containing at least the above-described coloring material and polyester resin emulsion. In addition to a water-soluble solvent and water (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.) as the solvent for the balance, dispersants, lubricants, thickeners, pH adjusters, rust preventives, preservatives, or antibacterial agents can be appropriately contained within a range that does not impair the effects of the present invention. Examples of water-soluble solvents that can be used include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, 3-butylene glycol, thiodiethylene glycol, and glycerin, and ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, which can be used alone or in combination. The content of this water-soluble solvent is desirably 5 to 40% based on the total amount of the ink composition.

[0024] As the dispersant that can be used, nonionics, anionic surfactants, and water-soluble resins are used. Preferably, a water-soluble polymer is used. Examples of lubricants that can be used include nonionic types such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugars, polyoxyalkylene higher fatty acid esters, and alkyl phosphate esters, which are also used as surface treatment agents for pigments, and anionic types such as phosphate esters, alkyl sulfonates of higher fatty acid amides, and alkyl allyl sulfonates, as well as derivatives of polyalkylene glycols and polyether-modified silicones. As the thickener that can be used, for example, at least one selected from the group consisting of synthetic polymers, cellulose, and polysaccharides is desirable. Specifically, gum arabic, tragacanth gum, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, xanthan gum, welan gum, succinoglycan, diutan gum, dextran, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, starch glycolic acid and its salts, polyvinyl pyrrolidone, polyvinyl methyl ether, polyacrylic acid and its salts, polyethylene oxide, a copolymer of vinyl acetate and polyvinyl pyrrolidone, styrene-acrylic acid copolymer and its salts, etc. may be mentioned.

[0025] As the pH adjuster, ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, alkali metal salts of carbonic acid and phosphoric acid such as sodium tripolyphosphate and sodium carbonate, hydrates of alkali metals such as sodium hydroxide, etc. may be mentioned. Further, as the rust inhibitor, benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, saponins, etc., and as the preservative or antibacterial agent, phenol, sodium omadine, sodium benzoate, thiazoline-based compounds, benzimidazole-based compounds, etc. may be mentioned. Each component such as the above dispersant, lubricant, thickener, pH adjuster, rust inhibitor, preservative or antibacterial agent may be used alone or in combination of two or more. Also, if there are commercially available products of these, they can be used.

[0026] The aqueous ballpoint pen ink composition of the present invention can be produced without any particular difference compared to the production methods of other aqueous ink compositions. That is, the aqueous ink composition for ballpoint pens of the present invention is prepared by at least mixing a coloring material, a polyester resin emulsion, a water-soluble solvent, and other components using a mixer or the like, and further, for example, using a bead mill, a homomixer, a homogenizer, etc. that can apply strong shear to set the stirring conditions to suitable conditions and then mixing and stirring. Furthermore, if necessary, the aqueous ink composition for ballpoint pens can be manufactured by removing coarse particles in the ink composition by filtration or centrifugation, etc. Also, 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, stability of the ink itself, and matching with the ink container. More preferably, it is desirably set to 6 to 9.5.

[0027] The aqueous ink composition for ballpoint pens of the present invention has a viscosity at a shear rate of 383 sec -1 in the range of 1 to 100 mPa·sec at 25°C. If this viscosity exceeds 100 mPa·s at the above shear rate and becomes too high, the ink flow rate will decrease, the writing feel will become heavy, and it will be difficult to write smoothly. On the other hand, if it is less than 1 mPa·sec, the effect of suppressing bleeding and back-through of the handwriting will not be exhibited, which is not preferable. In the present invention, in order to adjust the viscosity within the above range at the above shear rate, it can be achieved by suitably combining the resin emulsion to be used, water as a solvent, the coloring material, etc., and suitably adjusting the respective contents thereof.

[0028] The aqueous ink composition for ballpoint pens of the present invention is mounted on a ballpoint pen equipped with a pen tip such as a ballpoint pen tip. As the aqueous ballpoint pen in the present invention, for example, the ink composition for aqueous ballpoint pen having the above composition is housed in an ink container (refill) for ballpoint pen equipped with a ball having a diameter of 0.18 to 2.0 mm, and is incompatible with the aqueous ink composition housed in the ink container, and has a specific gravity smaller than that of the aqueous ink composition. Substances such as polybutene, silicone oil, and mineral oil are housed as ink followers. As long as it is equipped with a ball having a diameter within the above range, the structure of the aqueous ballpoint pen to be used is not particularly limited. In particular, it is desirable to fill the above aqueous ink composition into an ink storage tube of a resin tube made of polypropylene and finish it into an aqueous ballpoint pen with a refill having a stainless steel tip (the ball is a super alloy) at the tip. Furthermore, it may be a direct liquid type ballpoint pen having a collector structure (ink holding mechanism) in which the shaft cylinder itself is used as an ink container and the ink composition for aqueous ballpoint pen having the above configuration is filled into the shaft cylinder.

[0029] Figures 1 to 4 are drawings showing an example of an aqueous ballpoint pen when the ink composition for aqueous ballpoint pen of the present invention is used in an ink refill equipped with a ballpoint pen tip such as a metal tip or a resin tip, and when mounted on a ballpoint pen for use. As the ink refill 10 housing the ink composition for aqueous ballpoint pen of the present invention, for example, as shown in FIG. 1, those composed of a ballpoint pen tip 15, a joint member 14, and an ink storage tube 11 can be mentioned. The ink storage tube 11 is a resin tube made of polypropylene or the like, and the aqueous ink composition 12 for aqueous ballpoint pen of the present invention is housed therein. Further, an ink follower 13 is housed at the rear end of the ink composition 12. At the tip of the ink refill 10, a ball pen tip 15 is attached via a joint member 14. As shown in FIGS. 1 and 2, this ball pen tip 15 is composed of a holder 16 and a writing ball 17 made of cemented carbide held by the holder 16. The holder 16 is formed in a columnar shape, and includes a tapered portion 16a whose tip side serves as a ball holding portion with a tapered shape, a connecting portion 16b whose outer circumference at the rear end side has a small diameter, and a back hole 16c formed as an internal space from the rear end of the holder to the middle portion of the tapered portion 16a. The tip portion of the holder 16 that receives the writing ball 17 has, as shown in FIG. 2, a ball house 16d , a caulking portion 16e that holds the writing ball 17, an ink guiding hole 16f and an ink groove 16g that communicate with the back hole 16c, and a ball receiving seat 16h are formed.

[0030] In this embodiment of the aqueous ball pen, the clearance between the writing ball 17 of the ball pen tip 15 and the ball receiving seat 16h, that is, the axial direction (vertical direction) movement amount (movement distance) L of the writing ball 17, is preferably set to 15 to 60 μm from the viewpoints of preventing ink direct flow, appropriately discharging ink containing resin particles with a large particle diameter, and ensuring initial writing performance. Also, it is preferable to use the writing ball 17. The "surface roughness" defined in the present invention refers to the "average surface roughness Ra value" measured by the method defined in JIS B 0601:2013, which is 1 to 5 nm from the viewpoints of appropriately transferring ink containing resin particles with a large particle diameter and ensuring initial writing performance.

[0031] This ink refill 10 is mounted on a click-type aqueous ballpoint pen 20 as shown in FIGS. 3 and 4, for example, and is to be used. This click-type aqueous ballpoint pen 20 is a dual aqueous ballpoint pen in which the writing tips of three (black, red, blue) ink refills 10 for aqueous ballpoint pens can be selectively projected and retracted from the tip 24 of a shaft cylinder 23 where a front shaft 21 and a rear shaft 22 are detachably engaged by screwing. The click mechanism 30 of this aqueous ballpoint pen 20 includes a knock body 32... into which three tubes 10... for each aqueous ballpoint pen are detachably fitted and a spring 31... serving as a return spring is inserted. By knocking one of the knock bodies 32 downward, it can be selectively projected and retracted and used. Reference numeral 25 is a grip portion composed of a rubber member or an elastomer member, and 26 is a clip portion. The inner diameter (diameter) of the ink refill 10 is preferably set to 1.5 to 3.0 mm, and the filling length of the ink follower is preferably set to 5 to 20 mm. Further, as the spring 31 which is a return spring constituting the click mechanism, a spring having a spring multiplier, a load during use, and a load during storage within the above preferable range is used. Furthermore, in FIGS. 3 and 4, a dual aqueous ballpoint pen is shown, but a single aqueous ballpoint pen may also be used.

[0032] Why is the aqueous ballpoint pen ink composition of the present invention configured as described above and the aqueous ballpoint pen equipped with the same excellent in stability over time, without degrading the writing performance, and even for a low-viscosity ink, there is no occurrence of the so-called "direct current phenomenon"? It is presumed that this is because the polyester emulsion is easily dispersed uniformly in the ink and forms a thin, uniform, and flexible film on the surface of the ink droplets accumulated at the pen tip, thus exerting an effect in achieving both stability over time and writing performance. In the aqueous ballpoint pen ink composition of the present invention and the aqueous ballpoint pen equipped with the same, the continuous effect of exerting the effects of the present invention is extremely excellent. Moreover, the period and duration of the manifestation of the effect are long, and furthermore, because it is aqueous, it is also excellent in stability over time.

Examples

[0033] Next, the present invention will be described in more detail with reference to Examples 1 to 8 of the aqueous ballpoint pen ink composition and the aqueous ballpoint pen equipped with the same. However, the present invention is not limited to the following examples and the like.

[0034] 〔Examples 1 to 8〕 According to the formulation shown in Table 1 below, each aqueous ballpoint pen ink composition was prepared by a conventional method. Regarding each of the obtained aqueous ballpoint pen ink compositions (total amount: 100% by mass), the viscosity (mPa·s) at a shear rate of 383 sec -1 (25°C) was measured, and each evaluation of the DC test, writing test (feathering, line breakage), and stability over time was performed. These results are shown in Table 1 below.

[0035] 〔Measurement method of viscosity at a shear rate of 383 sec -1 (25°C)〕 Using an E-type rotational viscometer [VISCOMETER RE215 (manufactured by Toki Sangyo Co., Ltd.)], cone: 1°34’*R24, measurement time: 60 seconds, measurement temperature: 25°C, the ink viscosity (mPa·s) at a shear rate of 383 sec -1 was measured.

[0036] (Evaluation method of DC test) (Aqueous ballpoint pen) Using the shaft of a ballpoint pen [manufactured by Mitsubishi Pencil Co., Ltd., product name: Signo UM-151], an ink storage tube made of polypropylene with an inner diameter of 3.8 mm and a length of 113 mm conforming to FIG. 1, a ballpoint pen tip (holder: made of stainless steel, ball: carbide ball, ball diameter: 0.7 mm), and a refill consisting of a joint connecting the storage tube and the tip, each of the aqueous ballpoint pen inks obtained above was filled, and an ink follower made of polybutene was filled at the rear end of the ink to produce aqueous ballpoint pens (5 each). The axial (vertical) movement amount (movement distance) L of the writing ball 17 was 30 μm, and the surface roughness (Ra value) was 2 nm.

[0037] <DC test> The aqueous ballpoint pen filled with the ink of any of the examples or comparative examples was left with the pen tip facing down for one day with the cap removed in an environment of 25°C and 60% relative humidity, and evaluated according to the following evaluation criteria based on the degree of leakage from the pen tip. Evaluation criteria: A: No leakage at all. A′: No leakage at all or the ballpoint pen tip is slightly soiled. B: Droplets form around the ballpoint pen tip but do not progress further. C: The droplets become larger and are in the process of progressing but do not drip. D: The liquid drips from the ballpoint pen tip.

[0038] <Writing test> Using the aqueous ballpoint pen prepared in the same manner as in the above DC test, the drawn lines obtained by manual spiral writing were evaluated according to the following two items (smudging, line break) based on each evaluation criterion. (Evaluation criteria for smudging) A: No smudging at all. B: There are slightly smudged areas but they are not noticeable. C: There are partially smudged areas. D: The smudging is quite noticeable.

[0039] (Evaluation criteria for line break) A: No line break at all. B: There are slightly cracked areas but they are not noticeable. C: There is a line break but the characters are still recognizable. D: The line break is very noticeable.

[0040] (Evaluation method for stability over time) Each of the aqueous ballpoint pens obtained above was stored for one month with the pen tip facing down with the cap on in an environment of 60°C and 30% relative humidity. Then, it was left at room temperature for 6 hours, and after the ballpoint pen reached the same temperature as room temperature, manual spiral writing was performed and the writing performance was evaluated according to the following evaluation criteria. (Evaluation criteria for stability over time) A: There is no problem with the writing performance. B: There is no problem with writing, but the writing feel is slightly heavy. C: It is inferior in writing quality compared to writing with a copybook. D: Writing is not possible.

[0041]

Table 1

[0042] As is clear from the results in Table 1 above, the ballpoint pens filled with the aqueous ballpoint pen ink compositions of Examples 1 to 8 within the scope of the present invention are excellent in stability over time, without degrading writing performance (feathering, line cracking), and even with low-viscosity ink, it was confirmed that there is no occurrence of the so-called "direct current phenomenon". In particular, it was confirmed that Examples 1 to 3 containing a polyester resin emulsion with a number average molecular weight (Mn) of 10,000 or more are significantly superior compared to Examples 4 to 8.

Industrial Applicability

[0043] An ink composition suitable for an aqueous ballpoint pen can be obtained.

Claims

**Claim 1** An aqueous ballpoint pen ink composition comprising at least a coloring material and a polyester resin emulsion having a number average molecular weight (Mn) of 10,000 or more. **Claim 2** Cutting speed: 383 sec －１ The aqueous ballpoint pen ink composition according to claim 1, characterized in that the viscosity at 25 °C is 1 to 100 mPa·sec. **Claim 3** The aqueous ballpoint pen ink composition according to claim 1 or 2, characterized in that the content of the polyester resin emulsion is 0.5 to 30% by mass based on the total amount of the ink composition. **Claim 4** An aqueous ballpoint pen comprising the aqueous ballpoint pen ink composition according to any one of claims 1 to 3. **Claim 5** The aqueous ballpoint pen according to claim 4, characterized in that the amount of movement of the ball in the axial direction of the ball tip is 15 to 60 μm.

Images