JP6626373B2 - Aqueous ink composition for writing implements - Google Patents

Description

  The present invention relates to a water-based ink composition for a writing implement suitable for a writing implement such as an aqueous ball-point pen having excellent writing performance and dry-up resistance without reducing the dispersion stability of resin particles.

  Conventionally, resin particles may be blended for the purpose of imparting a specific function to the aqueous ink composition for writing implements. When a writing instrument using such an ink is left in a state where the cap is removed, a drop in ink ejection property (dry-up), a change in physical properties such as viscosity due to a decrease in dispersion stability of particles, and a decrease in writing property. Tends to occur. These changes in physical properties and decrease in writability were particularly susceptible to the effects of the amount and size of the resin particles.

The mechanism by which dry-up occurs is presumed to be that the dispersion state of the resin particles collapses due to the volatilization of water to cause agglomeration, which lowers the ink dischargeability of the writing portion.
In order to suppress this, a method of creating a state like a “lid” by preventing aggregation or generating loose aggregation can be considered. However, even if it is loose aggregation, if it is “bulky” aggregation, it will be like a lump of ink with high viscosity, and although dry-up resistance will be expressed, this lump is transferred to the drawing line, so the drawing line There are issues such as deterioration of quality.

  On the other hand, as an ink composition for writing implements with improved dry-up resistance, for example, in an ink comprising at least a pigment having a specific range of particle diameter, a humectant, and water, the humectant comprises urea and ethylene urea. A water-based pigment ink composition having a weight ratio of 1: 3 to 5: 1 (for example, see Patent Document 1), a colorant containing colored resin particles, water, and shear-thinning application An aqueous ink composition for ballpoint pens containing an agent and ethylene oxide-modified polyvinyl alcohol (PVA) is known (for example, see Patent Document 2).

  However, the above-mentioned Patent Document 1 has problems such as insufficient dry-up resistance and poor writing such as blurring. In the above-mentioned Patent Document 2, although the non-drying property is certainly improved by blending the ethylene oxide-modified PVA, there is a problem that a lump due to an aggregate of ink may be generated at the beginning of writing after capping off. There is also a problem that the viscosity increases with time.

JP-A-8-127746 (Claims, Examples, etc.) Japanese Patent Application Laid-Open No. 2015-120777 (Claims, Examples, etc.)

  The present invention has been made in view of the above-described problems of the related art, and has been made to solve the problem. Without reducing the dispersion stability of the resin particles, the dry-up resistance, the writing performance is excellent, and the viscosity increases with time. It is an object of the present invention to provide a water-based ink composition for writing implements suitable for writing implements such as water-free ball-point pens and marking pens.

  The present inventors have conducted intensive studies in view of the above-described conventional problems and the like, and as a result, have at least a resin particle having a specific average particle size and content, and a specific modified polyvinyl alcohol in a specific range. As a result, it was found that the aqueous ink composition for a writing instrument of the above object was obtained, and the present invention was completed.

That is, the aqueous ink composition for a writing instrument of the present invention is as follows.
(1) A water-based ink composition for a writing implement comprising 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 a sulfonic acid-modified polyvinyl alcohol. .
(2) The aqueous ink composition for a writing instrument according to the above (1), wherein the resin particles are core-shell type microcapsules.
(3) A writing implement comprising the aqueous ink composition for a writing implement according to (1) or (2).

  According to the present invention, without lowering the dispersion stability of the resin particles, dry-up resistance, excellent writing performance, water-based ballpoint pen with no increase in viscosity over time, water-based water suitable for writing implements such as marking pens An ink composition is provided.

(A)-(c) is each drawing which shows typically the evaluation criteria (the presence or absence of a drawing line lump) of the state of the first writing line in the Example of this invention, and a comparative example, and (a) is a spiral writing. (B) and (c) are enlarged views of the portion A in (a), and (b) is a drawing in which the initial drawing state is good without drawing lump (evaluation: (C) is a drawing showing a drawing line (evaluation: ×) in which there is a drawing line defect and the first brush drawing line state is poor.

Hereinafter, embodiments of the present invention will be described in detail.
The aqueous ink composition for a writing implement of the present invention is characterized by containing at least 5% by mass or more of resin particles having an average particle size of 0.3 μm or more and 0.05 to 10% by mass of a sulfonic acid-modified polyvinyl alcohol. It is assumed that.

<Resin particles>
The functions and types of the resin particles used in the present invention are not particularly limited. For example, resin particles used as a coloring material, resin particles intended for a binder or a sealing effect may be used. Further, the material constituting the resin particles is not limited. For example, acrylic resins, styrene resins, urethane resins, urea resins, epoxy resins, melamine resins, silicone resins and copolymers thereof, and various latex particles are exemplified.

The resin particles used as the coloring material are composed of colored resin particles. For example, (1) Inorganic pigments such as carbon black and titanium oxide, phthalocyanine pigments, azo pigments, etc. Colored resin particles in which a colorant made 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 made of the pigment; (3) dyes and acid dyes directly on the resin particles Resin particles dyed with a coloring agent composed of a dye such as a basic dye or a food dye; (4) colored resin particles that have been rendered thermochromic or photochromic by using a leuco dye, a photochromic dye, or the like. And the like.
Examples of the resin component of the colored resin particles of the above (1) to (3) include at least one selected from the above-mentioned various resins, and have been subjected to a treatment such as crosslinking if necessary. Is also good. Conventional methods for coloring these resins include adding a colorant during polymerization of the resin particles, coating the surface of the resin particles with a colorant by a hybridization method, and dyeing the resin particles with a dye. A known method is used.

As the thermochromic colored resin particles of the above 4), a leuco dye, a color developer which is a component having the ability to develop the leuco dye, and a color change temperature in the coloration of the leuco dye and the color developer are controlled. Thermochromic composition containing at least a color-changing temperature adjusting agent, so that a predetermined average particle size, thermochromic coloring resin particles produced by microencapsulation, also, photochromic As the colored resin particles, photochromic dyes (compounds), which are colorless under indoor lighting environment and are photochromic dyes having the property of developing color under ultraviolet irradiation environment, and photochromic pigments produced by microencapsulating fluorescent pigments Colored resin particles.
Examples of the microencapsulation method include an interfacial polymerization method, an interfacial polycondensation method, an in situ polymerization method, a curing-in-liquid 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 according to the use, the shape and the structural characteristics of the microcapsules.
As preferred 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 the filling effect are not particularly limited, but include, for example, polystyrene resin particles, polyurethane resin particles, acrylic resin particles, polyethylene wax emulsions, olefin wax emulsions such as polypropylene wax emulsions, and the like. At least one selected may be mentioned.

  The resin particles of the present invention, such as the resin particles used as these coloring materials and the resin particles for the purpose of the binder and the sealing effect, exhibit a predetermined function (coloring power, dispersion stability, binder and sealing effect). It is prepared to have a suitable average particle diameter from the viewpoint of achieving a high degree of compatibility with the object of the present invention such as the above-mentioned dry-up.

In the present invention, the greater the content of the resin particles, and the greater the average particle size, the greater the effect on the performance of the ink. The content of the 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 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 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) is a value of D50 calculated on a volume basis using a particle size distribution analyzer HRA9320-X100 (manufactured by Nikkiso Co., Ltd.).

<Sulfonic acid-modified polyvinyl alcohol>
The sulfonic acid-modified polyvinyl alcohol used in the present invention is a polyvinyl alcohol (hereinafter abbreviated as “PVA”) “general formula, — [CH ₂ —CH (OH)] m— [CH ₂ —CH (OCOCH ₃ ] n— ] At least a part of the hydroxyl group, the acetic acid group and the terminal group is modified with a sulfonic acid group, and any vinyl alcohol polymer containing a predetermined amount of a sulfonic acid group can be used without any particular limitation.
As a method of synthesizing a sulfonic acid-modified polyvinyl alcohol, for example, a method of polymerizing a monomer having a sulfonic acid group with vinyl acetate and then saponifying some or all of the vinyl acetate to obtain a vinyl alcohol can be used. Alternatively, it can be synthesized by bonding a compound having a sulfonic acid group to a hydroxyl group of polyvinyl alcohol.
Examples of the monomer having a sulfonic acid group include ethylenesulfonic acid, allylsulfonic acid, methallylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and salts thereof.
The sulfonic acid-modified polyvinyl alcohol may be appropriately synthesized or may be a commercially available product.

According to the present invention, the sulfonic acid-modified polyvinyl alcohol used in the ink composition using the above-described resin particles has the effect of the present invention, that is, dry-up resistance, drawing line without lowering the dispersion stability of the resin particles. It has excellent writing performance with no deterioration in quality and exhibits a function with no increase in viscosity over time. Above all, the degree of saponification {[m / (m + n)] × 100} is preferably 70 mol% or more, and more preferably 85 mol, from the viewpoints of the aging stability and viscosity imparting property of the ink. % Is desirable.
Further, in the sulfonic acid-modified polyvinyl alcohol having the above-mentioned saponification degree, the polymerization degree (m + n) is preferably 1,000 or less, from the viewpoint that the effects of the present invention can be further exerted without impairing the writing feeling and coloring property. Preferably, it is 500 or less, particularly preferably 100 to 300.
Specific examples of sulfonic acid-modified polyvinyl alcohol that can be used include commercially available Nippon Synthetic Chemical Industry Co., Ltd., Gohsenx L-3266, CKS-50, and the like.
These sulfonic acid-modified polyvinyl alcohols may be used alone or in combination of two or more.

The content of the sulfonic acid-modified polyvinyl alcohol used in the present invention is 0.05 to 10% by mass, and 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 intended 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 aqueous ink composition for a writing instrument of the present invention, in addition to the above-mentioned components, a coloring material, the remaining solvent water (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.), and an anionic interface Activators, components commonly used in aqueous ink compositions for writing implements, such as water-soluble organic solvents, thickeners, lubricants, rust inhibitors, preservatives or antibacterial agents, pH adjusters, etc. It can be appropriately contained within a range not to impair.

In the present invention, when the resin particles are used as a coloring material, other coloring materials (coloring agents) other than the colored resin particles can be used in combination as a complementary color component. Can be used for components.
Coloring materials that can be used include dyes that dissolve or disperse in water, conventionally known inorganic and organic pigments such as titanium oxide, and silica or mica as a base material and the surface layer is multi-layer coated with iron oxide or titanium oxide. Pigments and the like can be used in an appropriate amount as long as the effects of the present invention are not impaired.
Examples of the dye include acid dyes such as eosin, fuoxin, water yellow # 6-C, acid red, water blue # 105, brilliant blue FCF, and nigrosine NB; and direct dyes such as direct black 154, direct sky blue 5B and violet B00B Dyes; basic dyes such as rhodamine and methyl violet;

Examples of the organic pigments include azo lakes, insoluble azo pigments, chelated azo pigments, phthalocyanine pigments, perylene and perinone pigments, and nitroso pigments. More specifically, carbon black, titanium black, zinc white, black iron, aluminum, chromium oxide, iron black, cobalt blue, iron oxide yellow, viridian, zinc sulfide, lithopone, cadmium yellow, vermilion, cadmium red, graphite, Inorganic pigments such as molybdated orange, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine, 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 the like.
These coloring materials can be used alone or in combination of two or more.

Examples of the anionic surfactant that can be used include, for example, fatty acid salts, alkyl sulfate salts, alkyl benzene sulfonates, alkyl naphthalene sulfonates, alkyl sulfosuccinates, alkyl diphenyl ether disulfonates, alkyl phosphates, and polyphosphates. Oxyethylene alkyl sulfate, polyoxyethylene alkyl allyl sulfate, naphthalene sulfonic acid formalin condensate, polyoxyethylene alkyl phosphate, and the like. Among these, those having an aromatic ring are preferable, and a salt of formalin condensate of naphthalenesulfonic acid is particularly 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% by mass relative 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. And these can be used alone or in combination of two or more.
The content of these water-soluble organic solvents is appropriately adjusted for each ink composition, and generally ranges from about 10% by mass to 30% by mass based on the total amount of the ink composition.
It is an effective measure to reduce the content of these water-soluble organic solvents to 10% by mass or less in order to exert a function excellent in drawing line drying property, 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 when 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, polyvinyl pyrrolidone, polyvinyl methyl ether, polyacrylic acid and salts thereof, polyethylene oxide, copolymers of vinyl acetate and polyvinyl pyrrolidone, styrene-acrylic acid copolymers and salts thereof.

Examples of the lubricant include nonionics such as fatty acid esters of polyhydric alcohols, higher fatty acid esters of sugar, higher fatty acid esters of polyoxyalkylene, and alkyl sulfonic acids of phosphate esters and higher fatty acid amides, which are also used as surface treatment agents for pigments. Salts, anionic derivatives such as alkyl allyl sulfonates, derivatives of polyalkylene glycols, fluorinated surfactants, and polyether-modified silicones are exemplified.
In addition, as a rust inhibitor, benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, saponins and the like, as a preservative or antiseptic, phenol, sodium omazine, sodium benzoate, benzoisothiazoline, benzimidazole-based And the like.
Examples of the pH adjuster 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, and ammonia. Is mentioned.

  The aqueous ink composition for a writing instrument of the present invention comprises the resin particles having an average particle diameter of 0.3 μm or more, 5% by mass or more, a sulfonic acid-modified polyvinyl alcohol of 0.05 to 10% by mass, and an anionic surfactant. , A water-soluble organic solvent, and other components are appropriately combined according to the use of the ink for writing implements (for ballpoint pens, marking pens, etc.) and stirred and mixed with a stirrer such as a homomixer, a homogenizer, or a disper. The aqueous ink composition for a writing instrument can be prepared, for example, by removing coarse particles in the ink composition by filtration or centrifugation.

The aqueous ink composition for a writing instrument of the present invention is mounted on a ballpoint pen, a marking pen, or the like having a pen tip portion such as a ballpoint pen tip, a fiber tip, a felt tip, and a plastic tip.
As the ballpoint pen in the present invention, the aqueous ink composition for a writing implement having the above composition is accommodated in an ink container for ballpoint pen (refill), and is not compatible with the aqueous ink composition accommodated in the ink container. A substance in which a substance having a smaller specific gravity than the aqueous ink composition, for example, polybutene, silicone oil, mineral oil, or the like is contained as an ink follower.
The structures of the ball-point pen and the marking pen are not particularly limited. For example, 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 writing instrument having the above configuration is filled in the shaft cylinder. It may be a direct liquid type ballpoint pen or marking pen provided.

The aqueous ink composition for a writing implement comprising the resin particles of the present invention thus configured is excellent in writing performance without reducing the dispersion stability of the resin particles, dry-up resistance, and degraded drawing quality. The reason why the aqueous ink composition for writing implements does not increase in viscosity over time is presumed as follows.
Conventionally, when a water-based ink composition for writing implements containing resin particles is used, the dispersed state is broken by the volatilization of water, or resin particles coagulate in the ink, or when coagulation occurs in the writing portion. This causes a problem of dry-up in which ink ejection is hindered and writing is poor. Further, in order to suppress dry-up, there is a method of generating loose aggregation by containing a modified ethylene oxide PVA or the like. Thus, although dry-up resistance is exhibited, the lumps are transferred to the drawn lines, and there is a problem that the quality of the drawn lines is reduced.
In the conventional aqueous ink composition for writing implements, the larger the content of the resin particles used, and the larger the average particle diameter, the more the above-mentioned problems tend to become apparent. By adding 0.05 to 10% by mass of the sulfonic acid-modified polyvinyl alcohol in the ink composition using the resin particles of the above, a loose aggregate having an appropriate bulkiness can be formed even when water evaporates, A material that exhibits excellent dry-up resistance without lowering the dispersion stability of the resin particles, has excellent writing performance without lowering the drawing quality such that the writing line becomes ink, and exhibits a function that does not increase viscosity over time. It becomes.

  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]
Each aqueous ink composition for writing implements was prepared according to the composition shown in Table 1 below.
Thermochromic microcapsule pigments 1 and 2, which are resin particles used as coloring materials in Examples 1 and 2, were obtained by the following production methods 1 and 2. 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)
1 part by mass (hereinafter simply referred to as "parts") of ETAC (manufactured by Yamada Chemical Industry Co., Ltd.) as a leuco dye, 2 parts of bisphenol A as a color developer, and 24 parts of myristyl myristate as a discoloration temperature regulator at 100 ° C. To obtain 27 parts of a homogeneous composition.
To a uniform hot solution of 27 parts of the composition obtained above, 10 parts of an isocyanate and 10 parts of a polyol were added as a capsule film agent, followed by stirring and mixing. Next, a dispersion was prepared by emulsification at 25 ° C. using 60 parts of a 12% aqueous solution of polyvinyl alcohol as a protective colloid. Next, the mixture was treated with 5 parts of 5% polyamine at 80 ° C. for 60 minutes to obtain core-shell type microcapsules.
(Production Example 2: Thermochromic microcapsule pigment 2)
1 part of RED520 (manufactured by Yamada Chemical Industries) dye as a leuco dye, 4,4 '-(2-ethylhexylidene) bisphenol as a color developer, and 4,4' as a color change temperature regulator 24 parts of-(hexafluoroisopropylidene) bisphenol dimyristate was heated and melted at 100 ° C to obtain 27 parts of a homogeneous composition.
Using a uniform hot solution of 27 parts of the composition obtained above as a protective colloid agent, 40 parts of a methyl vinyl ether / maleic anhydride copolymer resin (Gantrez AN-179: manufactured by ISP Co.) was adjusted 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 disperse it in the form of oil droplets having a diameter of about 0.5 to 1.0 μm, and then, as a capsule film agent, a melamine resin (Sumitec Resin) 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 prepared using each of the ink compositions obtained above. Specifically, a ballpoint pen [manufactured by Mitsubishi Pencil Co., Ltd., trade name: SIGNO UM-100] is used, and an ink receiving tube made of polypropylene with an inner diameter of 4.0 mm and a length of 113 mm and a stainless steel tip (a cemented carbide ball, The above water-based ink is filled in a refill consisting of a joint for connecting the storage tube and the chip with a ball having a diameter of 0.7 mm, and an ink follower mainly composed of mineral oil is loaded at the rear end of the ink to produce a water-based ball-point pen. did.

Using each of the obtained water-based ballpoint pens, the dry-up resistance, the state of the first writing line, and the stability over time of the pen body were evaluated by the following evaluation methods. Further, the aging stability (initial viscosity and viscosity after aging) of each of the obtained aqueous ink compositions for writing implements was evaluated.
Table 1 below shows the evaluation results and the like.

[Evaluation method for dry-up resistance]
After leaving each of the obtained water-based ballpoint pens in a constant temperature / humidity bath at 25 ° C. and 60% RH for 10 days with the pen tip exposed, circles having a diameter of about 2 cm are continuously drawn on PPC paper. Twenty spiral writing was performed as described above, and the dry-up resistance was evaluated according to the following evaluation criteria.
Evaluation criteria:
：: Good writing without blurring.
Δ: Blurring occurred within 5 laps.
×: Debris exceeding 5 laps occurred.

[Evaluation method of the first brush line condition]
Regarding the example of the evaluation of o in the above test, the drawing line state at the beginning of writing was evaluated based on the following evaluation criteria and FIG.
：: Line drawing damage (a state in which a lump was dropped due to an initial appearance) was not observed and was uniform (see FIG. 1B).
X: Line lump is recognized (see FIG. 1 (c)).

(Evaluation method of pen body temporal stability)
After storing each of the obtained water-based ballpoint pens at 50 ° C. and 65% RH for one month, the writing speed was measured using a writing tester (Minitech writing tester, Mitsubishi pencil) based on JIS standard: S6039-2001. 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 standard P3201. The density was compared with the drawn line density at an arbitrary position of 300 to 400 m.
：: No difference in drawing line density.
Δ: Slight difference in drawing line density is observed.
X: A clear difference is observed in the drawing line density.

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

As is clear from the results in Table 1 above, the aqueous ink compositions for writing implements of Examples 1 to 9 according to the present invention have higher dispersion stability of the resin particles as compared with Comparative Examples 1 to 5 which are out of the scope of the present invention. It was found that a water-based ink composition for a writing instrument was obtained which was excellent in writing performance without a decrease in dry-up resistance and drawing quality without a decrease in viscosity, and did not increase in viscosity over time.
Looking at Comparative Examples 1 to 5, Comparative Examples 1 to 4 are those containing the same resin particles as Examples 1 to 4, and are aqueous ink compositions for writing implements not containing sulfonic acid-modified polyvinyl alcohol, Comparative Example 5 contained a modified ethylene oxide polyvinyl alcohol copolymer (PVA) described in JP-A-2015-120777 instead of the sulfonic acid-modified polyvinyl alcohol. In these cases, the effect of the present invention was obtained. Was not able to be exhibited.

  A water-based ink composition for writing implements suitable for writing implements such as aqueous ball-point pens and marking pens can be obtained.

Claims (3)

  An aqueous ink composition for a writing implement, comprising 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 a sulfonic acid-modified polyvinyl alcohol.   The aqueous ink composition for a writing instrument according to claim 1, wherein the resin particles are core-shell type microcapsules.   A writing implement, comprising the aqueous ink composition for a writing implement according to claim 1.

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