JP2022157128A - Ink composition for aqueous ballpoint pen - Google Patents

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

The present invention has excellent stability over time, does not degrade writing performance, and even low-viscosity ink drips or leaks from the gap between the holder and the ball due to gravity, the so-called "direct current phenomenon". It relates to an ink composition for a water-based ballpoint pen that does not generate

Conventionally, water-based ballpoint pens have had problems such as the so-called "direct current phenomenon" in which ink drips or leaks due to gravity from the gap between the holder and the ball.

Known methods for solving this problem include an approach based on the structure of the tip of the ballpoint pen and an approach based on the composition of the ink. It is characterized by containing fine particles of anhydrous silica so that ink does not leak from the tip, and in the invention described in Patent Document 2, a water-swellable spherical ink with a minimum film-forming temperature of 30 ° C. or less to prevent ink leakage. It is known to add polymeric compounds.
Furthermore, in the invention described in Patent Document 3, a ball-point pen tip holding a ball rotatably is attached to the tip of an ink containing cylinder directly or via a tip holder, and at least water, a coloring agent, A water-based ball-point pen containing an ink composition for a water-based ball-point pen comprising organic resin particles and a shear thinning agent, wherein the amount of movement of the ball-point pen tip in the axial direction of the ball is 15 μm or more, and the average amount of the organic resin particles is An aqueous ball-point pen characterized by having a particle size of 15 μm or less, and an ink composition for a ball-point pen characterized by containing at least crystalline cellulose and resin particles in the invention of Patent Document 4 are known.

However, in Patent Document 1, since particles such as silica have a heavy specific gravity, it is difficult to make them exist uniformly in the ink for a long period of time. There are quite a few problems, such as being a factor such as
In Patent Document 3, the approach is based on the composition and structure of the ink, but in the case of low-viscosity ink, the problem of the "direct current phenomenon" has not yet been fully resolved. In the above Patent Document 4, it is an unprecedented technology using crystalline cellulose, which suppresses the occurrence of the direct current phenomenon. There is a strong demand for an ink composition for water-based ballpoint pens that does not cause the "direct current phenomenon" even with low-viscosity ink.

On the other hand, as a technique using a resin emulsion or the like for writing instrument ink, for example, Patent Document 5 discloses that a coloring material and a resin emulsion are included, and the resin contained in the resin emulsion has a glass transition point of 20° C. or more and 100° C. or less. , the resin emulsion is a water-based ink composition for a cloth marking pen, which is a colored resin emulsion colored with the coloring agent; is a water-based ink composition for writing instruments, wherein U is the total content of pigments relative to the total amount of the ink composition, and V is the total content of guar gum derivatives relative to the total amount of the ink composition, where V/U is 0. 0005≦V/U≦0.05, and X/V is 5≦X/V≦75, where X is the total content of the poorly water-soluble resin with respect to the total amount of the ink composition. and a writing instrument using the same.
However, Patent Document 5 is intended to improve the bleeding resistance and washing resistance of handwritings or coatings written on cloth, and Patent Document 6 is to improve the gaps between fibers such as paper and cloth. To provide a water-based ink composition excellent in color developability and fixability of handwriting, which makes it possible to keep a coloring agent on the fiber surface of a writing surface even when writing on the surface of a writing object having a large surface area. The subject of the invention and the technical idea (configuration and effects thereof) are different from the invention.

Japanese Patent Application Laid-Open No. 2001-40266 (Claims, Examples, etc.) Japanese Patent Application Laid-Open No. 2006-63235 (Claims, Examples, etc.) Japanese Patent Application Laid-Open No. 2016-124179 (Claims, Examples, etc.) Japanese Patent Application Laid-Open No. 2013-103986 (Claims, Examples, etc.) Japanese Patent Application Laid-Open No. 2003-238879 (Claims, Examples, etc.) Japanese Patent Application Laid-Open No. 2019-11397 (Claims, Examples, etc.)

The present invention is intended to solve the above-mentioned problems and current situation of the prior art, and has excellent stability over time without deteriorating writing performance, and even with low-viscosity ink, " An object of the present invention is to provide an ink composition for a water-based ball-point pen which does not cause "direct current phenomenon" and a water-based ball-point pen incorporating the ink composition.

In view of the above-described conventional problems, the present inventors have conducted intensive research and as a result, have obtained an ink composition for a water-based ballpoint pen, etc., for the above-mentioned purpose, by containing at least a coloring material and a specific resin emulsion. The inventors have found that it can be done, and have completed the present invention.

That is, the ink composition for water-based ballpoint pens of the present invention is characterized by containing at least a coloring material and a polyester resin emulsion.
It is preferable that the viscosity at a shear rate of 383 sec ^-1 is 1 to 100 mPa·sec at 25°C.
The polyester resin emulsion preferably has a number average molecular weight (Mn) of 10,000 or more.
The content of the polyester resin emulsion is preferably 0.5 to 30% by mass in terms of solid concentration with respect to the total amount of the ink composition.
The water-based ball-point pen of the present invention is characterized by incorporating the ink composition for a water-based ball-point pen having the above-described structure.
It is preferable that the amount of movement of the ball chip in the axial direction of the ball is 15 to 60 μm.

According to the present invention, it has excellent stability over time, does not degrade writing performance, and even low-viscosity ink drips or leaks from the gap between the holder and the ball due to gravity. Provided are an ink composition for water-based ball-point pens and water-based ball-point pens equipped with the same, which do not cause the phenomenon.
The objects and advantages of the invention may 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, and are not limiting of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view showing an example of an ink refill for a water-based ball-point pen containing the ink composition for a water-based ball-point pen of the present invention; FIG. 2 is an explanatory view showing a main part of a ball-point pen tip in a vertical cross-sectional form for explaining the amount of axial movement of the ball of the ball-point tip in the ink refill of FIG. 1 (clearance between the ball of the ball-point pen tip and the ball receiving seat); . 1 is a longitudinal sectional view showing an example of a water-based ball-point pen of the present invention; FIG. 4 is a front view of the water-based ballpoint pen of FIG. 3; FIG.

Embodiments of the present invention are described in detail below. However, it should be noted that the technical scope of the present invention is not limited to the embodiments detailed below, but extends to the invention described in the claims and equivalents thereof.
The water-based ballpoint pen ink composition of the present invention is characterized by containing at least a coloring material and a polyester resin emulsion.

Coloring materials used in the present invention include all dyes that dissolve or disperse in water, conventionally known inorganic and organic pigments such as titanium oxide, pigment-containing resin particle pigments, and pseudo-pigments obtained by coloring resin emulsions with dyes. , white plastic pigments, silica or mica-based pigments coated with multiple layers of iron oxide or titanium oxide on the surface layer, thermochromic pigments, photochromic particles, and the like can be used without limitation.
Dyes include, for example, acid dyes such as Eosin, Foxin, Water Yellow #6-C, Acid Red, Water Blue #105, Brilliant Blue FCF, Nigrosine NB; Dyes; basic dyes such as rhodamine and methyl violet.

Examples of inorganic pigments include azo lakes, insoluble azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, and nitroso pigments. More specifically, 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, vermillion, cadmium red, yellow lead, Inorganic pigments such as molybdate orange, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine blue, precipitated barium sulfate, barite powder, calcium carbonate, lead white, dark blue, dark blue, manganese violet, aluminum powder, brass powder, etc. , C.I. I. Pigment Blue 17, C.I. I. Pigment Blue 15, C.I. I. Pigment Blue 17, C.I. I. Pigment Blue 27, C.I. I. Pigment Red 5, C.I. I. Pigment Red 22, C.I. I. Pigment Red 38, C.I. I. Pigment Red 48, C.I. I. Pigment Red 49, C.I. I. Pigment Red 53, C.I. I. Pigment Red 57, C.I. I. Pigment Red 81, C.I. I. Pigment Red 104, C.I. I. Pigment Red 146, C.I. I. Pigment Red 245, C.I. I. Pigment Yellow 1, C.I. I. Pigment Yellow 3, C.I. I. Pigment Yellow 12, C.I. I. Pigment Yellow 13, C.I. I. Pigment Yellow 14, C.I. I. Pigment Yellow 17, C.I. I. Pigment Yellow 34, C.I. I. Pigment Yellow 55, C.I. I. Pigment Yellow 74, C.I. I. Pigment Yellow 95, C.I. I. Pigment Yellow 166, C.I. I. Pigment Yellow 167, C.I. I. Pigment Orange 5, C.I. I. Pigment Orange 13, C.I. I. Pigment Orange 16, C.I. I. Pigment Violet 1, C.I. I. Pigment Violet 3, C.I. I. Pigment Violet 19, C.I. I. Pigment Violet 23, C.I. I. Pigment Violet 50, C.I. I. Pigment Green 7 and the like.

The thermochromic pigments include a leuco dye that functions as a color former, a developer that is a component capable of developing the color of the leuco dye, and a color change temperature that can be controlled in the coloration of the leuco dye and the developer. Thermochromic pigments produced by microencapsulating a thermochromic composition containing at least a discoloration temperature adjusting agent to have a predetermined average particle size (e.g., 0.1 to 6 μm). be able to.
As the photochromic particles, for example, photochromic particles composed of at least one or more selected from photochromic dyes (compounds), fluorescent dyes, etc., and resins such as terpene phenolic resins, and at least photochromic dyes (compounds ), a photochromic composition containing one or more selected from fluorescent dyes and the like, an organic solvent, and additives such as antioxidants, light stabilizers, and sensitizers, with a predetermined average particle size (e.g. , 0.1 to 6 μm), and photochromic particles produced by microencapsulation.

In the present invention (including examples, etc.), the "average particle size" is the value of D50 measured with a particle size analyzer [Microtrac HRA9320-X100 (manufactured by Nikkiso Co., Ltd.)].
Examples of the microencapsulation method of the thermochromic pigment include interfacial polymerization method, interfacial polycondensation method, in situ polymerization method, in-liquid curing coating method, phase separation method from aqueous solution, phase separation method from organic solvent, melting A dispersion cooling method, an air suspension coating method, a spray lining method, and the like can be mentioned, and can be appropriately selected according to the application. For example, in the phase separation method from an aqueous solution, a leuco dye, a developer, and a discoloration temperature adjusting agent are heated and melted, then added to an emulsifier solution, heated and stirred to disperse them in the form of oil droplets, and then, as a capsule film agent, Use a resin raw material whose wall film is urethane resin, epoxy resin, amino resin, etc. After reacting and preparing, the thermochromic microcapsule pigment can be produced by filtering the dispersion. In this thermochromic pigment, by appropriately combining the types and amounts of the leuco dye, color developer, and color change temperature adjusting agent, the color developing temperature and color erasing temperature of each color can be set to suitable temperatures.
In addition, as a method for microencapsulation of the photochromic particles, preparation can be performed in the same manner as in the production of the thermochromic resin particles described above.
By suitably using a photochromic dye (compound), a fluorescent dye, or the like, the photochromic particles can be used, for example, in an indoor lighting environment (indoor lighting fixtures selected from incandescent lamps, fluorescent lamps, lamps, white LEDs, etc.). It can be colorless 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).

These coloring materials 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, pseudo pigments, white plastic pigments, multi-layer coated pigments, thermochromic pigments, photochromic particles, etc. Although it varies depending on the diameter, ink composition/viscosity, etc., those having an average particle diameter of 0.02 to 6 μm are desirable.
The content of these coloring materials can be appropriately increased or decreased depending on the density of the drawn line of the ink, but is 0.1 to 40% by mass (hereinafter, "% by mass" is referred to as " %”), preferably 1 to 10% by mass.

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 acid anhydride, or a polyvalent carboxylic acid ester.
Examples of polyhydric alcohol components 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-cyclohexanediol methanol, hydrogenated bisphenol A, etc.), alkylene oxides having 2 to 4 carbon atoms of the above alicyclic diols (ethylene oxide (hereinafter abbreviated as EO), propylene oxide (hereinafter abbreviated as PO), butylene oxide (hereinafter abbreviated as PO), Abbreviated as BO)) adduct (addition mole number 1 to 30) or bisphenols (bisphenol A, bisphenol F, bisphenol S, etc.) with 2 to 4 carbon atoms alkylene oxide (EO, PO, BO, etc.) adduct ( 2 to 30 moles) and the like are included. These polyhydric alcohol components may be used alone or in combination of two or more.

Examples of polyvalent carboxylic acid components include alkanedicarboxylic acids having 4 to 36 carbon atoms (succinic acid, apidic acid, sebacic acid, etc.), alkenylsuccinic acids (dodecenylsuccinic acid, etc.), and alicyclic dicarboxylic acids having 4 to 36 carbon atoms. Acids (dimer acid (dimerized linoleic acid), etc.), alkene dicarboxylic acids with 4 to 36 carbon atoms (maleic acid, fumaric acid, citraconic acid, mesaconic acid, etc.), or aromatic dicarboxylic acids with 8 to 36 carbon atoms (phthalic acid, isophthalic acid, terephthalic acid or derivatives thereof, naphthalenedicarboxylic acid, etc.). These polyvalent carboxylic acid components may be used alone or in combination of two or more.

The number average molecular weight (Mn) of the polyester resin is preferably 10,000 or more, more preferably 10,000 to 100,000. When the number average molecular weight (Mn) of the polyester resin is 10,000 or more, the effect of preventing the direct current phenomenon and the long-term storage stability are excellent. The number average molecular weight (Mn) is a value measured by gel permeation chromatography (GPC). Solvent: tetrahydrofuran (THF), column temperature: 40° C.) can be determined from a calibration curve prepared from polystyrene standard samples.

Commercially available products may be used as the polyester resin emulsion. Examples of commercial products of the above polyester resin emulsions include Elitel KA-5034 manufactured by Unitika Ltd., Elitel KA-5071S, Elitel KA-1449, Elitel KA-0134, Elitel KA-3556, Elitel KA-6137, Elitel KZA- 6034, Elitel KT-8803, Elitel KT-8701, Elitel KT-9204, Elitel KT-8904, Elitel KT-0507, Elitel KT-9511 (manufactured by Unitika Ltd.). These may be used individually by 1 type, and may use 2 or more types together.

The content of these polyester resin emulsions is preferably from 0.5 to 30%, more preferably from 1 to 10%, in terms of solid concentration, based on the total amount of the ink composition.
If the solid content of the polyester resin emulsion is less than 0.5%, the effects of the present invention cannot be exhibited. In addition, the ink tends to solidify at the tip of the pen, resulting in poor initial writing performance, which is not preferable.

<Ink composition for water-based ballpoint pen>
The ink composition for water-based ball-point pens of the present invention is characterized by containing at least the above-described coloring material and a polyester resin emulsion, and additionally, a water-soluble solvent, and the remainder being water (tap water , purified water, distilled water, ion-exchanged water, pure water, etc.), dispersants, lubricants, thickeners, pH adjusters, rust inhibitors, antiseptics or antiseptics to the extent that the effects of the present invention are not impaired. A fungicide and the like can be contained as appropriate.
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, ethylene glycol monomethyl ether and diethylene glycol monomethyl ether. , can be used singly or in combination. The content of the water-soluble solvent is desirably 5 to 40% of the total amount of the ink composition.

As dispersants that can be used, nonionic, anionic surfactants and water-soluble resins are used. A water-soluble polymer is preferably used.
Lubricants that can be used include polyhydric alcohol fatty acid esters, sugar higher fatty acid esters, polyoxyalkylene higher fatty acid esters, alkyl phosphate esters and other nonionic lubricants that are also used as surface treatment agents for pigments, and phosphate esters. , anionic compounds such as higher fatty acid amide alkylsulfonates and alkylarylsulfonates, polyalkylene glycol derivatives and polyether-modified silicones.
As a 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, methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, starch glycolic acid and Its salt, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylic acid and its salt, polyethylene oxide, copolymer of vinyl acetate and polyvinylpyrrolidone, styrene-acrylic acid copolymer and its salt, and the like.

Examples of pH adjusters include ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, alkali metal salts of carbonic acid and phosphoric acid such as sodium tripolyphosphate and sodium carbonate, and alkali metal hydrates such as sodium hydroxide. etc. Examples of rust preventives include benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, and saponins. Examples of antiseptics or antibacterial agents include phenol, sodium omadine, sodium benzoate, thiazoline compounds, and benzimidazole. system compounds and the like.
Each component such as the dispersant, lubricant, thickener, pH adjuster, rust inhibitor, antiseptic or antibacterial agent may be used alone or in combination of two or more. . In addition, if these commercial products are available, they can be used.

The water-based ink composition for ball-point pens of the present invention can be produced without any particular changes compared to other water-based ink compositions.
That is, the ink composition for a water-based ballpoint pen of the present invention is prepared by mixing at least a coloring material, a polyester resin emulsion, a water-soluble solvent, and other components in a mixer, etc. By setting the stirring conditions to suitable conditions using a homomixer, homogenizer, etc., and mixing and stirring, if necessary, coarse particles in the ink composition are removed by filtration or centrifugation. A ballpoint pen ink composition can be produced.
The pH (25° C.) of the water-based ballpoint pen ink composition of the present invention is adjusted to 5 to 10 with a pH adjuster or the like from the viewpoints of usability, safety, stability of the ink itself, and compatibility with the ink container. It is preferably adjusted, more preferably 6 to 9.5.

The water-based ballpoint pen ink composition of the present invention is prepared so that the viscosity at a shear rate of 383 sec ^-1 is in the range of 1 to 100 mPa·sec at 25°C.
If the viscosity exceeds 100 mPa·s at the above shear rate and the viscosity increases, the flow rate of the ink decreases, the feeling of writing becomes heavy, and it becomes difficult to write smoothly. This is not preferable because the effect of suppressing strike-through is not exhibited.
In the present invention, in order to adjust the viscosity within the above range at the above shear rate, it is necessary to suitably combine the resin emulsion to be used, water as a solvent, coloring material, etc., and suitably adjust the content of each of these. and so on.

The ink composition for water-based ball-point pens of the present invention is mounted in a ball-point pen having a pen tip such as a ball-point pen tip.
For the water-based ball-point pen of the present invention, for example, the water-based ball-point pen ink composition having the composition described above is contained in a ball-point pen ink container (refill) having a ball with a diameter of 0.18 to 2.0 mm, and the ink container is Substances that are not compatible with the water-based ink composition contained in the body and have a small specific gravity relative to the water-based ink composition, such as polybutene, silicone oil, and mineral oil, are contained as ink followers. mentioned. The structure of the water-based ball-point pen to be used is not particularly limited as long as it has a ball having a diameter within the above range. A refillable water-based ballpoint pen with a stainless steel tip (ball is super steel alloy) is desirable.
Further, the ballpoint pen may be a direct liquid type ballpoint pen having a collector structure (ink holding mechanism) in which the barrel itself is used as an ink container and the ink composition for a water-based ballpoint pen having the above structure is filled in the barrel. .

FIGS. 1 to 4 show an example of an ink refill having a ballpoint pen tip such as a metal tip or a resin tip, and an aqueous ballpoint pen in which the ink composition for an aqueous ballpoint pen of the present invention is used. Each drawing.
As an ink refill 10 containing the ink composition for water-based ballpoint pens of the present invention, for example, as shown in FIG. . The ink storage tube 11 is a tube made of resin such as polypropylene, and contains therein the ink composition 12 for water-based ballpoint pens of the present invention. A follower 13 is accommodated.
A ball-point pen tip 15 is attached to the tip of the ink refill 10 via a joint member 14 . As shown in FIGS. 1 and 2, the ball-point pen tip 15 is composed of a holder 16 and a writing ball 17 made of cemented carbide held by the holder. The holder 16 is formed in a cylindrical shape, and has a tapered portion 16a that serves as a tapered ball holding portion on the tip side, a connecting portion 16b that has a small diameter on the rear end side, and a tapered portion 16a extending from the rear end of the holder. It is composed of a back hole 16c formed as an internal space up to the middle portion. The tip of the holder 16 for receiving the writing ball 17 has a ball house 16d as shown in FIG.
, a crimped portion 16e for holding the writing ball 17, an ink guide hole 16f and an ink groove 16g communicating with the back hole 16c, and a ball receiving seat 16h.

In this embodiment of the water-based ball-point pen, the clearance between the writing ball 17 of the ball-point pen tip 15 and the ball receiving seat 16h, that is, the movement amount (movement distance) L of the writing ball 17 in the axial direction (vertical direction) is the prevention of direct current flow of the ink. 15 to 60 μm is preferable from the viewpoints of the above points, the point of appropriately ejecting ink containing resin particles having a large particle size, and the point of ensuring initial writing performance.
Also, it is preferable to use the writing ball 17 . In addition, the surface roughness of the "surface roughness" defined in the present invention is 1 to 5 nm from the point of appropriately transferring ink containing resin particles with a large particle diameter and from the point of ensuring initial writing performance. B 0601: Refers to the "average surface roughness Ra value" measured by the method specified in 2013.

For example, the ink refill 10 is mounted on a knock-type water-based ballpoint pen 20 as shown in FIGS. 3 and 4 and used. This knock-type water-based ball-point pen 20 has three (black, red, and blue) water-based ball-point pen ink refills 10 attached to a shaft tip 24 of a barrel 23 in which a front barrel 21 and a rear barrel 22 are detachably attached by screwing a front barrel 21 and a rear barrel 22 together. Therefore, it is a double-type water-based ball-point pen in which each writing tip can be selectively retracted. The knocking mechanism 30 of the water-based ballpoint pen 20 includes knocking bodies 32 into which each of the three water-based ballpoint pen tubes 10 is detachably fitted and springs 31 serving as return springs are inserted. By knocking one of the knock bodies 32 downward, it can be selectively retracted for use. Reference numeral 25 in the figure denotes a grip portion made of a rubber member or an elastomer member, and 26 denotes 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. As 31, the spring multiplier, the load during use, and the load during storage, which are within the above-mentioned preferable ranges, are used. Furthermore, in FIGS. 3 and 4, a dual-type water-based ballpoint pen is used, but a single-type water-based ballpoint pen may be used.

Why is the ink composition for a water-based ball-point pen of the present invention configured as described above and the water-based ball-point pen equipped with the same excellent in stability over time, without deteriorating writing performance, and even with low-viscosity ink, The so-called "direct current phenomenon" does not occur because the polyester emulsion easily disperses evenly in the ink and forms a thin, uniform and flexible film on the surface of the ink droplets that collect on the pen tip, so it is stable over time. It is presumed that this is because it is effective in achieving both compatibility with writing performance.
The ink composition for water-based ball-point pens of the present invention and the Mizushi-e ball-point pens equipped with the same have extremely excellent sustained effects for exhibiting the effects of the present invention, and furthermore, the period and duration of the effects are long. Therefore, the stability over time is also excellent.

Next, the present invention will be described in more detail with reference to Examples 1 to 8 of ink compositions for water-based ballpoint pens and water-based ballpoint pens incorporating the same, but the present invention is not limited to the following examples.

[Examples 1 to 8]
Each water-based ballpoint pen ink composition was prepared according to the formulation shown in Table 1 below.
For each of the obtained ink compositions for water-based ballpoint pens (total amount 100% by mass), the viscosity (mPa s) at a shear rate of 383 sec ^-1 (25 ° C.) was measured by the following methods, and a direct current test, a writing test (blurred , line cracks) and stability over time were evaluated.
These results are shown in Table 1 below.

[Method for measuring 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.)], the ink viscosity (mPa・s) was measured.

(Evaluation method for DC test)
(water-based ballpoint pen)
Using the shaft of a ballpoint pen [manufactured by Mitsubishi Pencil Co., Ltd., product name: Signo UM-151], a polypropylene ink storage tube with an inner diameter of 3.8 mm and a length of 113 mm conforming to Fig. 1 and a ballpoint pen tip (holder: stainless steel, Ball: Cemented carbide ball, ball diameter 0.7 mm) and a joint connecting the storage tube and the tip. Aqueous ball-point pens (five each) were prepared by filling the ink follower consisting of: The movement amount (movement distance) L of the writing ball 17 in the axial direction (vertical direction) was 30 μm, and the surface roughness (Ra value) was 2 nm.

<DC test>
The water-based ballpoint pen filled with the ink of either Example or Comparative Example was left in an environment of 25 ° C. and 60% relative humidity for one day with the writing tip facing downward with the cap removed. The degree of leakage was evaluated according to the following evaluation criteria.
Evaluation criteria:
A: No leakage at all.
A': Absolutely no leakage or the tip of the ballpoint pen is slightly soiled.
B: Droplets formed around the tip of the ballpoint pen, but did not progress any further.
C: The droplet became large and was in the process of progressing, but did not drip.
D: The liquid drips from the tip of the ballpoint pen.

<Written test>
Using a water-based ballpoint pen prepared in the same manner as in the direct current test, the drawn line obtained by hand spiral writing was evaluated according to the following two criteria (blurring, line breakage).
(Evaluation criteria for blurring)
A: There is no fading at all.
B: Slightly faded portions are present, but are not noticeable.
C: Partially blurred.
D: Scratches are conspicuous.

(Evaluation criteria for line cracks)
A: There is no line crack at all.
B: There is a slight line crack, but it is not noticeable.
C: The characters are recognizable although the lines are broken.
D: Line cracks are very conspicuous.

(Method for evaluating stability over time)
Each of the water-based ballpoint pens obtained above was stored for one month in an environment of 60° C. and 30% relative humidity with the tip facing downward while being capped. Then, it was left at room temperature for 6 hours, and after the ballpoint pen reached the same temperature as the room temperature, spiral writing was performed by hand to evaluate the writability according to the following evaluation criteria.
(Evaluation criteria for stability over time)
A: There is no problem in writability.
B: There is no problem in writing, but the feeling of writing is a little heavy.
C: Writability is inferior to that of writing.
D: Not writeable.

As is clear from the results in Table 1 above, the water-based ball-point pens equipped with the ink compositions for water-based ball-point pens of Examples 1 to 8 within the scope of the present invention have excellent stability over time and excellent writing performance (blurring, line cracking). It was confirmed that the so-called "direct current phenomenon" did not occur even with low-viscosity ink. In particular, it was confirmed that Examples 1 to 3 containing polyester resin emulsions having a number average molecular weight (Mn) of 10,000 or more are significantly superior to Examples 4 to 8.

An ink composition suitable for water-based ballpoint pens can be obtained.

Claims (6)

An ink composition for a water-based ballpoint pen, comprising at least a coloring material and a polyester resin emulsion. 2. The ink composition for a water-based ballpoint pen according to claim 1, wherein the viscosity at a shear rate of 383 sec ^-1 is 1 to 100 mPa·sec at 25°C. 3. The ink composition for a water-based ballpoint pen according to claim 1, wherein the polyester resin emulsion has a number average molecular weight (Mn) of 10,000 or more. The water-based ballpoint pen ink composition according to any one of claims 1 to 3, wherein the content of the polyester resin emulsion is 0.5 to 30% by mass with respect to the total amount of the ink composition. object A water-based ball-point pen, comprising the ink composition for a water-based ball-point pen according to any one of claims 1 to 4. 6. The water-based ball-point pen according to claim 5, wherein the amount of movement of the ball tip in the axial direction of the ball is 15 to 60 μm.

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