JP6718259B2 - Aqueous ink composition for ballpoint pen - Google Patents

Description

The present invention, without reducing the dispersion stability of the resin particles, writing performance, of a preferred ballpoint pen water-based ink composition ballpoint pen excellent water etc. dry up resistance.

Conventionally, resin particles may be blended for the purpose of imparting a specific function to an aqueous ink composition for a writing instrument. When a writing instrument using such an ink is left with the cap removed, the ejection property of the ink is lowered (dry-up), the physical properties such as viscosity are changed due to the deterioration of dispersion stability of particles, and the writing property is deteriorated. Tend to occur. These changes in physical properties, deterioration of writing properties, and the like were particularly susceptible to the compounding amount and size of the resin particles.

It is presumed that the mechanism of the dry-up is such that the dispersed state of the resin particles collapses due to the volatilization of water to cause agglomeration, which reduces the ink ejection property of the writing portion.
In order to suppress this, a method of producing a state like a “lid” by not causing aggregation or causing loose aggregation can be considered. However, even if the flocculation is loose, "bulky" flocculation causes a state like a lump of ink with high viscosity, so that although the dry-up resistance is expressed, the lump is transferred to the drawn line, There are problems such as deterioration of quality.

On the other hand, as an ink composition for a writing instrument with improved dry-up resistance, for example, in an ink containing at least a pigment having a particle size in a specific range, a moisturizing agent and water, the moisturizing agent consists of urea and ethylene urea. A weight ratio of the aqueous pigment ink composition is 1:3 to 5:1 (see, for example, Patent Document 1), a coloring agent containing colored resin particles, water, and shear thinning An aqueous ink composition for a ball-point pen, which contains an agent and an ethylene oxide-modified polyvinyl alcohol (PVA) (for example, see Patent Document 2) is known.

However, in the above-mentioned Patent Document 1, there are problems that the dry-up resistance is still insufficient, and writing defects such as scratches are likely to occur. In the above-mentioned Patent Document 2, although the non-dry property is certainly improved by blending the ethylene oxide-modified PVA, there is a problem that lumps may occur due to the agglomerate of the ink at the beginning of writing after the cap-off. There is also a problem that the viscosity increases with time.

JP-A-8-127746 (claims, examples, etc.) JP-A-2015-120777 (claims, examples, etc.)

The present invention has been made in view of the above-mentioned problems of the prior art and is intended to solve this problem, without lowering the dispersion stability of the resin particles, excellent in dry-up resistance, writing performance, and viscosity increase over time. and to provide a suitable ballpoint pen water-based ink composition ballpoint pen of no water.

The present inventors, in view of the above-mentioned conventional problems, as a result of earnest research, at least a specific average particle size and content of the resin particles, the degree of acetalization polyvinyl butyral in a specific range is specified. It was found that the water-based ink composition for a ball-point pen having the above-mentioned object can be obtained by containing it within the range, and the present invention has been completed.

That is, the aqueous ink composition for a ballpoint pen of the present invention is as follows.
(1) An erasability imparting agent containing at least 5% by mass of resin particles having an average particle size of 0.3 μm or more and 0.05 to 10% by mass of polyvinyl butyral having an acetalization degree of 5 to 40 mol %. A water-based ink composition for a ball-point pen, which does not contain
(2) The water-based ink composition for a ballpoint pen according to the above (1), wherein the resin particles are core-shell type microcapsules.
(3) A writing instrument equipped with the water-based ink composition for a ballpoint pen described in (1) or (2) above.

According to the present invention, without reducing the dispersion stability of the resin particles, dry up resistance, excellent writing performance, provided a suitable ballpoint pen water-based ink composition ballpoint pen of no time increase in viscosity aqueous To be done.

(A)-(c) is each drawing which shows typically the evaluation criteria (presence or absence of drawing line slump) of the first stroke drawing line state in the Example and comparative example of this invention, (a) is a spiral writing The drawing showing the first stroke drawing line, (b) and (c) are the enlarged drawings of the portion A of (a), and (b) is the drawing line in which the first stroke drawing line is good without the line drawing lump (evaluation: A drawing showing (○), and (c) is a drawing showing a drawing line (evaluation: ×) in which the drawing stroke is bad and the drawing line state is poor.

Hereinafter, embodiments of the present invention will be described in detail.
The water-based ink composition for a ballpoint pen of the present invention has at least 5% by mass of resin particles having an average particle size of 0.3 μm or more and 0.05 to 10% by mass of polyvinyl butyral having an acetalization degree of 5 to 40 mol %. And does not contain an erasability imparting agent .

<Resin particles>
The function and type of the resin particles used in the present invention are not particularly limited. For example, resin particles used as a coloring material, a binder, or resin particles for the purpose of blocking effect may be used. The material forming the resin particles is also not limited. Examples thereof include acrylic resins, styrene resins, urethane resins, urea resins, epoxy resins, melamine resins, silicone resins and copolymers thereof, and various latex particles.

The resin particles used as the coloring material are composed of colored resin particles. For example, (1) carbon black, an inorganic pigment such as titanium oxide, a phthalocyanine-based pigment, an azo diameter pigment, etc. Colored resin particles in which a colorant composed of a pigment such as an organic pigment is dispersed, (2) colored resin particles in which the surface of the resin particles is coated with the colorant composed of the above pigment, (3) a direct dye or an acid dye on the resin particles Resin particles dyed with a colorant composed of a dye such as a basic dye or food dye, and (4) colored resin particles which are thermochromic or photochromic using a leuco dye, a photochromic dye, or the like. And so on.
As the resin component of the colored resin particles (1) to (3), for example, at least one selected from the above-mentioned various resins can be mentioned, which has been subjected to a treatment such as crosslinking as necessary. Good. As a method for coloring these resins, a method of adding a colorant upon polymerization of the resin particles, a method of coating the surface of the resin particles with a colorant by a hybridization method, a method of dyeing the resin particles with a dye, etc. A known method is used.

As the thermochromic colored resin particles of the above 4), a leuco dye, a developer which is a component having the ability to develop the color of the leuco dye, and a color change temperature in the color development of the leuco dye and the developer are controlled. A thermochromic composition containing at least a color-changing temperature adjuster capable of having a predetermined average particle diameter, thermochromic colored resin particles produced by microencapsulation, and also a photochromic resin. The colored resin particles are photochromic dyes (compounds), which are colorless in indoor lighting environments and become photochromic dyes that have the property of developing color in an ultraviolet irradiation environment, and fluorescent dyes, which are produced by microencapsulation. Colored resin particles.
Examples of the microencapsulation method include an interfacial polymerization method, an interfacial polycondensation method, an in situ polymerization method, a liquid hardening coating method, a phase separation method from an aqueous solution, a phase separation method from an organic solvent, a melt dispersion cooling method, and an airborne method. A suspension coating method, a spray drying method, and the like can be mentioned, and the method can be appropriately selected depending on the application, the shape of the microcapsules, and the structural characteristics.
As the preferable resin particles, core-shell type microencapsulated resin particles are desirable from the viewpoint of exhibiting stability and more fulfilling functions.

The binder and the resin particles for the purpose of sealing effect are not particularly limited, for example, polystyrene resin particles, polyurethane resin particles, acrylic resin particles, polyethylene wax emulsion, olefin wax emulsion such as polypropylene wax emulsion, etc. At least one selected can be mentioned.

The resin particles of the present invention, such as resin particles used as these coloring materials, or resin particles for the purpose of a binder or a sealing effect, exhibit a predetermined function (coloring power, dispersion stability, binder or sealing effect). From the viewpoint of achieving a high degree of resolving the problems of the present invention such as the above-mentioned dry-up, the average particle size is adjusted to a suitable average particle size.

In the present invention, the larger the content of resin particles, and the larger the average particle diameter, the greater the influence on the performance of the ink. The content of resin particles is 5% by mass or more based on the total amount of the ink composition, As the average particle diameter becomes 0.3 μm or more, the problem of the present invention tends to become apparent.
The average particle size of the resin particles to be used and the content thereof vary depending on the function of the resin particles, the type of writing instrument, the application, etc., but the average particle size is 0.3 to 15 μm, and the content thereof is the total amount of the ink composition. On the other hand, it is preferably adjusted to 5 to 30% by mass.
The "average particle size" defined in the present invention (including examples etc.) is a value of D50 calculated on a volume basis using a particle size distribution analyzer HRA9320-X100 (manufactured by Nikkiso Co., Ltd.).

本発明では、アセタール化度が５〜４０ｍｏｌ％となるポリビニルブチラールを用いることにより、上述の樹脂粒子を用いたインク組成物中において、本発明の効果、すなわち、樹脂粒子の分散安定性を低下することなく、耐ドライアップ性、描線品位の低下もなく筆記性能に優れ、経時的な粘度上昇もない機能を発揮するものとなる。
ポリビニルブチラールのアセタール化度が５ｍｏｌ％未満では、本発明の効果が得られず、一方、４０ｍｏｌ％を超えると、水溶性が十分でなく、好ましくない。
本発明において、ポリビニルブチラールのアセタール化度は、ＪＩＳ Ｋ６７２８「ポリビニルブチラール試験方法」に準拠した方法により、算出される。 <Polyvinyl butyral>
The polyvinyl butyral used in the present invention has a degree of acetalization of 5 to 40 mol %.
The molecular structure of polyvinyl butyral is, as represented by the following formula (I), a terpolymer composed of vinyl butyral/vinyl acetate/vinyl alcohol, in which polyvinyl alcohol (PVA) is replaced with butyraldehyde (BA). It is a reaction product and has a structure having a butyral group, an acetyl group, and a hydroxyl group. By changing the ratio of these three types of structures (each ratio of 1, m, and n), the solubility in water, Furthermore, it becomes possible to control the physical properties of the ink when it is contained in the ink formulation components.

In the present invention, the use of polyvinyl butyral having an acetalization degree of 5 to 40 mol% reduces the effect of the present invention, that is, the dispersion stability of the resin particles, in the ink composition using the above resin particles. In addition, it is excellent in writing performance without deterioration in dry-up resistance and drawing quality, and exhibits the function of preventing viscosity increase with time.
If the degree of acetalization of polyvinyl butyral is less than 5 mol%, the effect of the present invention cannot be obtained. On the other hand, if it exceeds 40 mol%, the water solubility is not sufficient, which is not preferable.
In the present invention, the degree of acetalization of polyvinyl butyral is calculated by a method based on JIS K6728 “Polyvinyl butyral test method”.

As a polyvinyl butyral having a degree of acetalization of 5 to 40 mol%, commercially available products include, for example, S-REC K (KW) series, "KW-1", "KW-3", "KW-" manufactured by Sekisui Chemical Co., Ltd. 10" or the like can be used. These may be used alone or in combination of two or more.

The content of polyvinyl butyral having an acetalization degree of 5 to 40 mol% used in the present invention is 0.05 to 10% by mass, preferably 0.1 to 5% by mass based on the total amount of the ink composition.
If the content is less than 0.05%, the effect of the present invention cannot be obtained, while if it exceeds 10% by mass, the viscosity of the ink increases, which is not preferable.

In the water-based ink composition for a ballpoint pen of the present invention, in addition to the above components, a coloring material, the balance water (solvent water, purified water, distilled water, ion-exchanged water, pure water, etc.), and an anionic interface. Activator, each component usually used in writing instrument aqueous ink composition, for example, a water-soluble organic solvent, a thickener, a lubricant, a rust inhibitor, a preservative or antibacterial agent, the pH adjusting agent, etc. It can be appropriately contained within a range that does not impair it.

In the present invention, when the resin particles are used as the coloring material, a coloring material (coloring agent) other than the colored resin particles can be used as a complementary color component, and when the resin particles are not used as the coloring material, coloring of the ink is performed. It can be used as a component.
As a coloring material that can be used, a dye that is soluble or dispersible in water, a conventionally known inorganic type or organic pigment type such as titanium oxide, silica or mica as a base material, and the surface layer is coated with iron oxide or titanium oxide in a multi-layered manner. A pigment or the like can be used in an appropriate amount within a range that does not impair the effects of the present invention.
Examples of the dye include acid dyes such as eosin, fuxine, water yellow #6-C, acid red, water blue #105, brilliant blue FCF, and nigrosine NB; direct black 154, direct sky blue 5B, violet B00B, and the like. Dyes: basic dyes such as rhodamine and methyl violet can be mentioned.

Examples of organic 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, vermilion, 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, navy blue, navy blue, manganese violet, aluminum powder, brass powder, etc. , 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 other organic pigments.
These coloring materials can be used alone or in combination of two or more.

Examples of the anionic surfactant that can be used include fatty acid salts, alkyl sulfate ester salts, alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkyl sulfosuccinates, alkyl diphenyl ether disulfonates, alkyl phosphates, and polyphosphates. Examples thereof include oxyethylene alkyl sulfate ester salt, polyoxyethylene alkyl allyl sulfate salt, naphthalene sulfonic acid formalin condensate salt, and polyoxyethylene alkyl phosphate ester. Among these, those having an aromatic ring are preferable, and particularly naphthalenesulfonic acid formalin condensate salt is preferable. These anionic surfactants have the effect of further stabilizing the physical properties of the ink.
The content of these anionic surfactants is appropriately adjusted within the range of 0.05 to 10 mass% with respect to the total amount of the ink composition.

Examples of the water-soluble organic solvent that can be used include alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, 3-butylene glycol, thiodiethylene glycol and glycerin, and ethylene glycol monomethyl ether and diethylene glycol monomethyl ether. These may be used alone or in admixture of two or more.
The content of these water-soluble organic solvents is appropriately adjusted for each ink composition, and is generally in the range of approximately 10% by mass to 30% by mass with respect to the total amount of the ink composition.
In order to exert a function excellent in drawing line drying property, it is an effective means to set the content of these water-soluble organic solvents to 10% by mass or less, but on the other hand, the dry-up resistance tends to be impaired. According to the present invention, the dry-up resistance is not impaired even if the content is 10% by mass or less, further 7% by mass or less, and further 5% by mass or less.

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 Examples thereof include salts thereof, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylic acid and salts thereof, polyethylene ethoxide, copolymers of vinyl acetate and polyvinylpyrrolidone, styrene-acrylic acid copolymers and salts thereof.

As the lubricant, nonionic compounds such as fatty acid ester of polyhydric alcohol, higher fatty acid ester of sugar, and higher fatty acid ester of polyoxyalkylene, which are also used as a surface treatment agent for pigment, or phosphoric acid ester, alkyl sulfonic acid of higher fatty acid amide Examples thereof include salts, anionic systems such as alkylallyl sulfonates, polyalkylene glycol derivatives, fluorosurfactants, and polyether-modified silicones.
Further, as rust preventives, benzotriazole, tolyltriazole, dicyclohexyl ammonium nitrite, saponins, etc., as preservatives or fungicides, phenol, sodium omazine, sodium benzoate, benzoisothiazoline, benzimidazole series A compound etc. are mentioned.
Examples of the pH adjusting agent include hydroxides of alkali metals such as sodium hydroxide, potassium hydroxide and lithium hydroxide, amine compounds such as triethanolamine, diethanolamine, monoethanolamine, dimethylethanolamine, morpholine and triethylamine, ammonia and the like. Are listed.

The water-based ink composition for a ball-point pen of the present invention has a resin particle having an average particle diameter of 0.3 μm or more in an amount of 5% by mass or more, and a polyvinyl butyral having an acetalization degree of 5 to 40 mol% in an amount of 0.05 to 10% by mass. , an anionic surfactant, a water-soluble organic solvent, suitably combined in accordance with other Lee ink for a ball Rupen components applications, homomixer, by mixing and stirring by a stirrer such as a homogenizer or a disperser, with the necessity Accordingly, the aqueous ink composition for a ballpoint pen can be prepared by removing coarse particles in the ink composition by filtration or centrifugation.

Ballpoint pen water-based ink composition of the present invention is mounted on ballpoint pen having a pen tip portion of the ballpoint pen chip.
The ballpoint pen of the present invention, the ballpoint pen water-based ink composition of the above composition accommodates the ballpoint pen ink container (refill), no compatibility with the ink containing the aqueous ink composition contained in the body, and A substance containing a small specific gravity with respect to the aqueous ink composition, for example, polybutene, silicone oil, mineral oil, etc., as an ink follower.
The structure of the ball-point pen is not particularly limited. For example, a direct structure provided with a collector structure (ink holding mechanism) in which the shaft cylinder itself is used as an ink container and the water-based ink composition for a ball-point pen having the above-mentioned configuration is filled a ballpoint pen of the ink type is intended may be.

The water-based ink composition for a ball-point pen containing the resin particles of the present invention thus constituted is excellent in writing performance without decreasing the dispersion stability of the resin particles, the dry-up resistance, and the drawing quality. The reason why the water-based ink composition for ball-point pens does not increase in viscosity with time is presumed as follows.
Conventionally, when a water-based ink composition for a ballpoint pen containing resin particles is used, the dispersion state is broken due to the evaporation of water, and the resin particles agglomerate with each other in the ink, or when agglomeration occurs in the writing part. There is a problem of dry-up in which the ejection of ink is hindered and the writing becomes defective. Further, in order to suppress dry-up, there is a method of containing modified ethylene oxide PVA or the like to cause loose aggregation. However, even if loose aggregation is “bulky” aggregation, ink with high viscosity is obtained. However, although the dry-up resistance is exhibited, there is a problem in that the line quality is deteriorated because the line is transferred to the line.
In a conventional water-based ink composition for a ballpoint pen , the larger the content of the resin particles used and the larger the average particle diameter, the more the above problems tend to become apparent. By containing 0.05 to 10% by mass of polyvinyl butyral having an acetalization degree of 5 to 40 mol% in the ink composition using the resin particles of 1., a loose coagulation having an appropriate bulkiness even if water is volatilized. Since it can form aggregates, it does not deteriorate the dispersion stability of resin particles, has excellent dry-up resistance, does not deteriorate the drawing quality such that writing lines become ink dampening, has excellent writing performance, and increases viscosity over time. It will have no function.

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples and the like.

[Examples 1 to 9 and Comparative Examples 1 to 5]
Aqueous ink compositions for ballpoint pens were prepared according to the formulations shown in Table 1 below.
As the thermochromic microcapsule pigments 1 and 2 which are resin particles used as the coloring material in Examples 1 and 2, those obtained by the following production methods 1 and 2 were used. The modified ethylene oxide polyvinyl alcohol (PVA) used in Comparative Example 5 was obtained by the following production method 3.
(Production Example 1: Thermochromic microcapsule pigment 1)
As a leuco dye, ETAC (manufactured by Yamada Chemical Industry Co., Ltd.) 1 part by mass (hereinafter, simply referred to as “part”), as a developer, 2 parts of bisphenol A, and as a color-changing temperature adjusting agent, 24 parts of myristyl myristate at 100° C. After heating and melting, 27 parts of a homogeneous composition was obtained.
To a uniform hot solution of 27 parts of the composition obtained above, 10 parts of isocyanate and 10 parts of polyol were added as a capsule film agent and mixed with stirring. Then, 60 parts of a 12% polyvinyl alcohol aqueous solution was used as a protective colloid, and emulsified at 25° C. to prepare a dispersion liquid. Then, 5 parts of a 5% polyvalent amine was used for treatment at 80° C. for 60 minutes to obtain core-shell type microcapsules.
(Production Example 2: Thermochromic microcapsule pigment 2)
As a leuco dye, 1 part of RED520 (manufactured by Yamada Chemical Co., Ltd.), 4,4'-(2-ethylhexylidene)bisphenol as a developer, and 4,4' as a color-changing temperature adjusting agent. 24 parts of -(hexafluoroisopropylidene)bisphenol dimyristate was heated and melted at 100°C to obtain 27 parts of a homogeneous composition.
A uniform hot solution of 27 parts of the composition obtained above was used as a protective colloid agent, and 40 parts of methyl vinyl ether/maleic anhydride copolymer resin [Gantzlets AN-179: manufactured by ISP Co.] was added to pH 4 with NaOH. While gradually adding to 100 parts of the dissolved 90° C. aqueous solution, the mixture is heated and stirred to be dispersed into oil droplets having a diameter of about 0.5 to 1.0 μm, and then, as a capsule film agent, a melamine resin (Sumitex resin) is used. 20 parts of M-3, manufactured by Sumitomo Chemical Co., Ltd. was gradually added and treated at 90° C. for 30 minutes to obtain core-shell type microcapsules.

An aqueous ballpoint pen was produced using each of the ink compositions obtained above. Specifically, using a ballpoint pen [Mitsubishi Pencil Co., Ltd., trade name: CIGNO UM-100], an inner diameter of 4.0 mm, a length of 113 mm, a polypropylene ink storage tube, and a stainless steel tip (a cemented carbide ball, A ball refill having a ball diameter of 0.7 mm) and a joint for connecting the housing tube and the tip is filled with each of the above-described aqueous inks, and an ink follower containing mineral oil as a main component is loaded at the ink trailing end to produce an aqueous ballpoint pen. did.

Using each of the obtained water-based ballpoint pens, the dry-up resistance, the state of the first stroke drawn line, and the pen stability over time were evaluated by the following evaluation methods. In addition, the ink stability over time (initial viscosity and viscosity after aging) of each of the obtained water-based ink compositions for ballpoint pens was evaluated.
The evaluation results and the like are shown in Table 1 below.

[Dry-up resistance evaluation method]
Each of the resulting water-based ballpoint pens was left facing downward in a thermo-hygrostat at 25° C. and 60% RH for 10 days with the pen tip exposed, and then a circle with a diameter of about 2 cm was continuously drawn on a PPC paper. As described above, the spiral writing was performed 20 times, and the dry-up resistance was evaluated according to the following evaluation criteria.
Evaluation criteria:
◯: There is no blurring and good writing is possible.
Δ: Scratching occurred within 5 laps.
X: Scratching occurs over 5 laps.

[Evaluation method for the state of the first stroke stroke]
Regarding the example of ◯ evaluation in the above test, the drawing line state at the beginning of writing was evaluated according to the following evaluation criteria and FIG. 1.
◯: Dulled lines (a state in which the lumps have fallen due to a tendency to come out first) are not recognized and are uniform [see FIG. 1(b)].
X: Dulled lines are observed [see FIG. 1(c)].

[Pen body temporal stability evaluation method]
After storing each of the obtained water-based ballpoint pens under the conditions of 50° C. and 65% RH for 1 month, a writing speed tester (Minitech writing tester, Mitsubishi pencil) based on JIS standard: S6039-2001 was used. Under a writing condition of 4.5 m/min, a writing angle of 60°, and a writing weight of 1.96 N, a writing test is performed by spiral writing on a writing test paper conforming to JIS P3201, and a drawing line at an arbitrary position of 0-100 m is drawn. The density was compared with the density of the drawn line at an arbitrary position of 300 to 400 m.
◯: There is no difference in the line density.
Δ: A slight difference is observed in the drawn line density.
X: A clear difference is observed in the line density.

[Evaluation method of ink stability over time]
Each of the obtained ink compositions was filled in a glass bottle, and the viscosity value (shear rate 3.83/s) after storing for 1 month at 50° C. and 65% RH was compared with the initial value (immediately after production). The smaller the difference between this ink viscosity value and the viscosity value after storage for 1 month, the better the stability of the ink.

As is clear from the results of Table 1 above, the aqueous ink compositions for ball-point pens of Examples 1 to 9 according to the present invention are more stable in dispersion of resin particles than Comparative Examples 1 to 5, which are outside the scope of the present invention. It was found that a water-based ink composition for ball-point pens which does not deteriorate in dry-up resistance and drawing quality, is excellent in writing performance, and does not increase in viscosity over time can be obtained.
Looking at the comparative examples 1 to 5, Comparative Examples 1 to 4, be those containing the same resin particles as in Examples 1-4, ballpoint aqueous acetalization degree does not contain 5 to 40 mol% of polyvinyl butyral Comparative Example 5 was an ink composition, and in place of polyvinyl butyral having an acetalization degree of 5 to 40 mol %, a modified ethylene oxide polyvinyl alcohol copolymer (PVA) described in JP-A-2015-120777 of the related art was contained. It was confirmed that the effects of the present invention could not be exhibited in these cases.

An aqueous ink composition for a ballpoint pen suitable for an aqueous ballpoint pen is obtained.

Claims (3)

It contains at least 5% by mass of resin particles having an average particle size of 0.3 μm or more and 0.05 to 10% by mass of polyvinyl butyral having an acetalization degree of 5 to 40 mol %, and does not contain an erasability imparting agent. An aqueous ink composition for a ballpoint pen, which is characterized in that: The water-based ink composition for a ball-point pen according to claim 1, wherein the resin particles are core-shell type microcapsules. Ballpoint pen characterized by mounting the ballpoint pen water-based ink composition according to claim 1 or 2.

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