JP2020189921A - Aqueous ballpoint pen ink composition - Google Patents

Abstract

To provide an aqueous ballpoint pen ink composition capable of removing a phenomenon (decline of initial writing performance) that ink is reluctant, especially at an initial writing time just after pausing writing, concerning a writing instrument having frequent switching of operations, and great change of shear force, such as a ballpoint pen.SOLUTION: An aqueous ballpoint pen ink composition contains at least colored resin particles having an average particle diameter of 0.5-6 μm, and xanthan gum and polyvinyl pyrrolidone, in which a mass ratio of polyvinyl pyrrolidone/xanthan gum is 1-9.SELECTED DRAWING: None

Description

The present invention relates to an ink composition for a water-based ballpoint pen that can eliminate the phenomenon that ink is reluctant to come out during writing immediately after writing is paused (decrease in first writing property).

Conventionally, colorants such as colored resin particles having a large particle size such as thermochromic microcapsules used in water-based ballpoint pens have lower fluidity in ink than general dyes and pigments. It is a thing. Therefore, the responsiveness from static to dynamic or dynamic to static is somewhat slow.
In writing instruments such as ballpoint pens, where movements are frequently switched and the shearing force changes significantly with respect to ink, the characteristics are likely to appear in the drawn lines, and in particular, the phenomenon that ink is reluctant to write when writing immediately after stopping writing (first writing). (Decreased sex) is seen.

On the other hand, in the conventional ink composition for a water-based ballpoint pen, for example, a colorant, xanthan gum, polyvinyl alcohol, or the like is used.
(1) In a water-based ink for ballpoint pens composed of at least water, a colorant and a resin, the resin is xanthan gum and polyvinylpyrrolidone, and the content ratio of the xanthan gum and polyvinylpyrrolidone is 1: 5.7 to 1: 7.0. A water-based ink for a ballpoint pen (see, for example, Patent Document 1),
(2) An emulsified polymer using at least one or more kinds of vinyl-based monomers as a raw material, which is characterized in that it develops color by containing a color-developing compound and a color-developing agent. Using the polymer and this emulsified polymer as ink, in Example 2, a fine particle dispersion of a clear green emulsified polymer having an average particle diameter of 0.17 μm and a viscosity of 3.9 mPa · s (25 ° C., 150 s ^-1 ). 50 g, 2 g of PVP K-15 (manufactured by ISP Japan Co., Ltd., polyvinylpyrrolidone, decolorizing agent, trade name) and 0.25 g of xanthan gum are added and mixed by stirring for gel ink ball pen ink (see, for example, Patent Document 2). ),
(3) A water-based ink composition for a ballpoint pen containing at least a shear thinning agent selected from xanthan gum or succinoglycan, polyvinylpyrrolidone, a colorant, a water-soluble organic solvent, and water, and said to reduce shear. A water-based ink composition for ballpoint pens having a viscosity-imparting agent and polyvinylpyrrolidone content ratio of 1: 1 to 1: 5.5 (see, for example, Patent Document 3).
(4) At least a colorant, water, a water-soluble organic solvent, a shear-thinning agent selected from xanthan gum, welan gum, and succinoglycan, a thickening inhibitor, and an ionic substance in the ink. The content of the ionic substance is 1% by mass or more with respect to the total amount of the ink composition, the water-soluble organic solvent is 10% by mass or less in the ink composition, and the thickening inhibitor is polyvinyl alcohol, polyvinylpyrrolidone, cellulose. A water-based ink composition for a ballpoint pen selected from a based polymer compound and a polymer compound having a polyalkylene oxide group, and a ballpoint pen containing the composition (see, for example, Patent Document 4).
Etc. are known.

The above-mentioned Patent Documents 1 to 4 disclose proximity techniques and the like of the ink composition for a water-based ballpoint pen of the present invention, while Patent Document 1 uses a fluorescent pigment or the like having a small average particle size and has average particles. There is no description or suggestion that colored resin particles having a diameter exceeding 0.5 μm are used, and the subject of the invention is good by preventing wear and deformation of the ball receiving seat due to the rotation of the ball of the ballpoint pen tip as much as possible. It secures the ejectability of ink and enables a long writing distance, and is different from the present invention in terms of subject matter and configuration.
The above-mentioned Patent Document 2 uses small thermochromic particles having an average particle diameter of 0.17 μm, and there is no description or suggestion that colored resin particles having an average particle diameter of more than 0.5 μm are used. The subject of the present invention is an ink for a ballpoint pen that can utilize not only heating but also an organic solvent as a decoloring means, and the subject and the configuration of the invention are different from the present invention.
The above-mentioned Patent Document 3 uses a pigment or the like having a small average particle size, and there is no description or suggestion of using colored resin particles having an average particle size exceeding 0.5 μm, and the subject of the invention is a pen. Suppresses the drying and solidification of ink in the vicinity of the tip (test to see if good writing can be done after leaving the pen tip sideways at 25 ° C for 30 days with the pen tip exposed: dry-up resistance). The present invention is different from the present invention in terms of subject matter and structure.
In Examples 6 and 7 of Patent Document 4, a reversible thermochromic pigment (thermochromic microcapsules) having an average particle diameter of 2 μm and 3 μm is used, but the subject of the invention is that the cap is removed. Test of whether good writing is possible after leaving at 50 ° C. for 30 days: dry-up resistance), etc. Moreover, the mass ratio of polyvinylpyrrolidone and xanthan gum is outside the scope of the present invention. An invention is one in which the subject and structure of the invention are different.

As described above, Patent Documents 1 to 4 disclose proximity technology and the like of the ink composition for a water-based ballpoint pen of the present invention, but the subject and structure of the invention are different from the present invention. I can say.
An object of the present invention is to suppress drying and solidification of ink in the vicinity of the pen tip after leaving the water-based ballpoint pen for a long period of time with the cap removed, as described in Patent Documents 3 and 4 above (dry-up resistance). This is a phenomenon that occurs when colored resin particles with a large average particle size, such as thermochromic microcapsules, are used instead of (property), and in ballpoint pens with many movement switching and large changes in shearing force. The characteristics are likely to appear in the drawn lines, and in particular, it is a solution to the phenomenon that ink is reluctant to come out when writing immediately after stopping writing (after a few minutes) (decrease in first writing property), and the above-mentioned dry-up resistance and writing of the present invention. Occasionally, the phenomenon that ink is reluctant to come out (decrease in writing ability) can be clearly distinguished by its cause and its solution.

JP-A-10-279875 (Claims, Examples, etc.) Japanese Unexamined Patent Publication No. 2003-221405 (Claims, Examples, etc.) Japanese Unexamined Patent Publication No. 2006-77074 (Claims, Examples, etc.) JP-A-2009-40825 (Claims, Examples, etc.)

The present invention is intended to solve this problem in view of the above-mentioned problems of the prior art and the current situation, and is to solve the phenomenon that ink is reluctant to come out at the time of writing immediately after the writing is paused, that is, the deterioration of the first writing property is solved. An object of the present invention is to provide an ink composition for a water-based ballpoint pen that can be produced.

As a result of diligent research in view of the above-mentioned conventional problems and the like, the present inventors have contained at least colored resin particles having an average particle diameter of 0.5 to 6 μm, xanthan gum and polyvinylpyrrolidone, and the polyvinylpyrrolidone / They have found that the above-mentioned target ink composition for a water-based ballpoint pen can be obtained by setting the mass ratio of xanthan gum to a specific range, and have completed the present invention.

That is, the ink composition for an aqueous ballpoint pen of the present invention contains at least colored resin particles having an average particle diameter of 0.5 to 6 μm, xanthan gum and polyvinylpyrrolidone, and the mass ratio of polyvinylpyrrolidone / xanthan gum is 1 to 9. It is characterized by being.
The K value of the polyvinylpyrrolidone is preferably 10 to 40.
The content of polyvinylpyrrolidone is preferably 0.5 to 5% by mass with respect to the total amount of the ink composition.
The water-based ballpoint pen of the present invention is characterized by being equipped with an ink composition for a water-based ballpoint pen having the above composition.

According to the present invention, there is provided an ink composition for a water-based ballpoint pen capable of eliminating the phenomenon that ink is reluctant to come out during writing immediately after writing is paused (decrease in first writing property), and a water-based ballpoint pen equipped with this ink composition. Will be done.

Hereinafter, embodiments of the present invention will be described in detail.
The ink composition for an aqueous ballpoint pen of the present invention contains at least colored resin particles having an average particle diameter of 0.5 to 6 μm, xanthan gum and polyvinylpyrrolidone, and has a mass ratio of polyvinylpyrrolidone / xanthan gum of 1 to 9. It is characterized by that.

<Colored resin particles>
The colored resin particles used in the present invention are not particularly limited as long as they are composed of colored resin particles. For example, 1) inorganic pigments such as carbon black and titanium oxide, phthalocyanine pigments, etc. in the resin particles. Colored resin particles in which a colorant made of a pigment such as an organic pigment such as an azo pigment is dispersed, 2) Colored resin particles in which the surface of the resin particles is coated with a colorant made of the above pigment, and 3) Dye directly on the resin particles. , Colored resin particles dyed with colorants consisting of dyes such as acidic dyes, basic dyes, food dyes, and fluorescent dyes, 4) Colored resin particles that are thermally discolored using leuco dyes, etc., 5) Photodiscoloration Examples thereof include photochromic dyes (compounds) that serve as sex dyes, colored resin particles that have been made photocolorable by using fluorescent dyes, and the like.
Examples of the resin component of the colored resin particles of 1) to 3) above include polymers such as acrylic acid, methacrylic acid, acrylic acid ester, methacrylic acid ester, styrene, acrylonitrile, and butadiene, or copolymers thereof, benzoguanamine, and the like. At least one selected from phenol resin, epoxy resin, urethane resin and the like can be mentioned, and may be subjected to a treatment such as crosslinking if necessary. As a method for coloring these resins, conventionally known methods such as suspension polymerization and dispersion polymerization are used.

The thermochromic colored resin particles of 4) are an electron donating dye, a leuco dye that functions as a color former, a color developer that is a component having an ability to develop the leuco dye, and the leuco. It was produced by microencapsulating a thermally discolorable composition containing at least a discoloration temperature adjusting agent capable of controlling the discoloration temperature in the color development of a dye and a color developer so as to have a predetermined average particle size. Examples thereof include thermochromic colored resin particles.
Examples of the microencapsulation method include interfacial polymerization method, interfacial polycondensation method, insitu polymerization method, in-liquid curing coating method, phase separation method from aqueous solution, phase separation method from organic solvent, melting dispersion cooling method, and air. Examples thereof include a suspension coating method and a spray drying method, which can be appropriately selected depending on the intended use. For example, in the phase separation method from an aqueous solution, a leuco dye, a color developer, and a discoloration temperature adjuster are heated and melted, then put into an emulsifier solution, heated and stirred to disperse 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. For example, gradually add each solution such as amino resin solution, specifically, methylol melamine aqueous solution, urea solution, benzoguanamine solution, and continue. After the reaction and preparation, the dispersion is filtered to produce thermochromic colored resin particles composed of thermochromic microcapsule pigments. In the heat-discoloring colored resin particles, the color development temperature and decolorization temperature of each color can be set to suitable temperatures by appropriately combining the types and amounts of the leuco dye, the color developer, and the color change temperature adjuster. it can.
The thermally discolorable colored resin particles are preferably those having reversible thermal discoloration. Those with reversible thermal discoloration are a heat decolorization type that decolorizes by heating from the color development state, a color memory retention type that alternately stores the color development state or the decolorization state in a specific temperature range, or a decolorization state. Various types such as a heating color-developing type that develops color by heating and returns to a decolorized state by cooling from the color-developed state can be configured alone or in combination.

The photochromic colored resin particles of 5) above include, for example, at least one selected from at least a photochromic dye (compound), a fluorescent dye, and a resin such as terpenephenol resin. Photochromic composition containing colored resin particles, at least one or more selected from photochromic dyes (compounds), fluorescent dyes, etc., an organic solvent, and additives such as antioxidants, light stabilizers, and sensitizers. Examples thereof include photocolorable colored resin particles produced by microencapsulating an object so as to have a predetermined average particle size. As the microencapsulation method, it can be prepared in the same manner as the above-mentioned production of the heat-discolorable resin particles.
The photochromic colored resin particles and resin particles are selected from indoor lighting environments (incandescent lamps, fluorescent lamps, lamps, white LEDs, etc.) by preferably using photochromic dyes (compounds), fluorescent dyes, and the like. It is possible that the lighting fixture is colorless and has the property of developing color in an ultraviolet irradiation environment (irradiation with a wavelength of 200 to 400 nm, irradiation environment with sunlight including ultraviolet rays).
Each of the colored resin particles 1) to 5) above can be used as a fluorescent pigment, a heat-discoloring pigment, a microcapsule pigment of a photo-discoloring pigment, or the like (coloring material). Further, as each of the resin particles 1) to 5) above, each resin particle produced by each known production method can be used, and if there is a commercially available product, they may be used.
As these colored resin particles, those having an average particle diameter of 0.5 to 6 μm are used, preferably 1 to 5 μm, from the viewpoints of coloring power, dispersion stability and the like.
In the present invention, the "average particle size" is the value of the particle size (D50) when the volume accumulation of the particle size distribution is 50%, which is calculated by the volume standard measured by the laser diffraction method. Here, the measurement of the average particle size by the laser diffraction method can be performed using, for example, the particle size distribution analyzer HRA9320-X100 manufactured by Nikkiso Co., Ltd.

The content of these colored resin particles is preferably 3 to 30%, more preferably 10 to 30%, based on the total amount of the ink composition. If the content of the colored resin particles is less than 3%, a preferable drawing density cannot be obtained, and if it exceeds 30%, the writing feeling becomes heavy and the drawing lines tend to be blurred, which is not preferable.

<Xanthan gum>
The xanthan gum used in the present invention is used as a thickener, and when used in combination with polyvinylpyrrolidone or the like, the effect of the present invention can be exhibited.
Commercially available xanthan gums include KELSAN S, KELSAN AR KELSAN T, KELSAN RD, KELSAN ST, KELSAN M, KELSAN HP, KELSAN ASX, Echo gum manufactured by Dainippon Pharmaceutical Co., Ltd., and Monato gum GS. Etc., and these can be used at least one kind (each alone or a mixture of two or more kinds).
The content of these xanthan gums is set according to the content and ratio of polyvinylpyrrolidone, which will be described later.

<Polyvinylpyrrolidone>
The polyvinylpyrrolidone used in the present invention is a polymer compound obtained by polymerizing N-vinyl-2-pyrrolidone. In the present invention, the effect of the present invention can be exhibited for the first time by using the combination of polyvinylpyrrolidone and xanthan gum and setting the content ratio (mass ratio) thereof within a specific range.
Among the polyvinylpyrrolidones used, those having a K value of 10 to 40 are desirable.
The K value of polyvinylpyrrolidone is a viscosity characteristic value that correlates with the molecular weight. The K value in the present invention refers to a viscosity characteristic value calculated by applying a relative viscosity value (25 ° C.) measured by a capillary viscometer to the following formula (1).
〔formula〕
_{K = (1.5logη rel -1) /} (0.15 + 0.003c) + [300clogη rel + (c + 1.5clogη rel) 2] 1/2 /(0.15c+0.003c 2) ... (1)
η _rel : Relative viscosity of polyvinylpyrrolidone aqueous solution to water c: Polyvinylpyrrolidone concentration (%) in polyvinylpyrrolidone aqueous solution

Among the polyvinylpyrrolidones used, those having a K value of 10 to 40 are preferably used because they suppress the aggregation of colored resin particles and further improve the dispersion stability.
Specific examples of polyvinylpyrrolidone that can be used include PVP K-15 (K value: 13 to 19), PVP K-30 (K value: 26 to 35) manufactured by ASHLAND, and Dai-ichi Kogyo Seiyaku Co., Ltd. Pittscol K-17 (K value: 15-19), Pittscol K-30 (K value: 27-33), Polyvinylpyrrolidone K-30 (K value: 27-33) manufactured by Nippon Shokubai Co., Ltd., etc. At least one of the above (each alone, a mixture of two or more).

The content of these polyvinylpyrrolidones is preferably 0.5 to 5%, more preferably 0.5 to 3.0%, based on the total amount of the ink composition. If the content of this polyvinylpyrrolidone is less than 0.5%, the effect of the present invention cannot be sufficiently exerted, while if it exceeds 5%, the aggregation of the colored resin particles becomes strong and the dispersion stability. Is not preferable because it reduces.

In the present invention, the content ratio of polyvinylpyrrolidone and xanthan gum used, that is, polyvinylpyrrolidone / xanthan gum (mass ratio) needs to be 1 to 9, and preferably 2 to 8.
If this ratio is less than 1 or more than 9, the effect of the present invention cannot be exhibited. The reason for setting the blending ratio (1 to 9) is that polyvinylpyrrolidone and xanthan gum are both ink thickeners, but their physical properties are different. When these are used in combination, good fluidity is maintained by suppressing aggregation of colored resin particles while having shear thinning without canceling each other's physical properties, and the first writing property is improved. It will be used in the above range.

<Ink composition for water-based ballpoint pens>
The ink composition for an aqueous ballpoint pen of the present invention contains at least colored resin particles having an average particle diameter of 0.5 to 6 μm, xanthan gum and polyvinylpyrrolidone, and the mass ratio of polyvinylpyrrolidone / xanthan gum is 1 to 9. In addition to the above-mentioned colored resin particles, a general-purpose colorant and a water-soluble solvent are contained.
As the colorant that can be used, water-soluble dyes and pigments such as inorganic pigments and organic pigments can be used in appropriate amounts as needed without impairing the effects of the present invention.
As the water-soluble dye, any of a direct dye, an acid dye, an edible dye, and a basic dye can be used in an appropriate amount as long as the effects of the present invention are not impaired.

Examples of the water-soluble solvent 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 alone or in combination. The content of this water-soluble solvent is preferably 5 to 40% with respect to the total amount of the ink composition.

The ink composition for an aqueous ball pen of the present invention contains at least the colored resin particles having an average particle diameter of 0.5 to 6 μm, xanthan gum and polyvinylpyrrolidone, and the mass ratio of the polyvinylpyrrolidone / xanthan gum is 1 to 9. In addition to colorants and water-soluble solvents other than the above-mentioned colored resin particles, water as a solvent as a balance (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.) is characterized by the above. In addition, a dispersant, a lubricant, a pH adjuster, a rust preventive, a preservative, an antibacterial agent and the like can be appropriately contained as long as the effects of the present invention are not impaired.

As the dispersant that can be used, nonionic, anionic surfactant and water-soluble resin are used. A water-soluble polymer is preferably used.
As lubricants, nonionics such as fatty acid esters of polyhydric alcohols used as surface treatment agents for pigments, higher fatty acid esters of sugars, polyoxyalkylene higher fatty acid esters, and alkyl phosphate esters, and alkyl sulfonic acids of higher fatty acid amides. Examples thereof include salts, anionic compounds such as alkylallyl sulfonates, derivatives of polyalkylene glycols, fluorine-based surfactants, and polyether-modified silicones.

Acidity regulators include ammonia, urea, monoethanoamine, diethanolamine, triethanolamine, sodium tripolyphosphate, sodium carbonate and other carbonates, alkali metal salts of phosphoric acid, and alkali metal hydrates such as sodium hydroxide. And so on. In addition, rust preventives include benzotriazole, triltriazole, dicyclohexylammonium nitrate, saponins, etc., and preservatives or antibacterial agents include phenol, sodium omadin, sodium benzoate, thiazolin compounds, benzimidazole. Examples include system compounds.
Each component such as the dispersant, the lubricant, the pH adjuster, the rust inhibitor, the preservative or the antibacterial agent may be used alone or in combination of two or more. Also, if you have these commercial products, you can use them.

The water-based ballpoint pen ink composition of the present invention uses at least the colored resin particles having an average particle diameter of 0.5 to 6 μm, xanthan gum, polyvinylpyrrolidone, a water-soluble solvent, and other components as ballpoint pen inks. The polyvinylpyrrolidone / xanthan gum is blended so that the mass ratio of the polyvinylpyrrolidone / xanthan gum is 1 to 9, and the mixture is stirred and mixed with a stirrer such as a homomixer, a homogenizer, or a disper, and further filtered as necessary. An ink composition for an aqueous ballpoint pen can be prepared by removing coarse particles in the ink composition by centrifugation or the like.
A water-based ballpoint pen can be produced by filling the water-based ballpoint pen ink composition into a water-based ballpoint pen body provided with balls having a diameter of 0.18 to 2.0 mm.
The water-based ballpoint pen used is not particularly limited as long as it includes a ball having a diameter in the above range. In particular, the water-based ink composition is filled in an ink storage tube of a polypropylene tube, and a stainless steel tip (ball is a tip). It is desirable to use a refilled water-based ballpoint pen with (super steel alloy).

The ink composition for a water-based ballpoint pen of the present invention can be produced without any particular difference as compared with other methods for producing an water-based ink composition.
That is, the ink composition for an aqueous ballpoint pen of the present invention contains at least the colored resin particles having an average particle diameter of 0.5 to 6 μm, xanthan gum, polyvinylpyrrolidone, and other components, and the mass of the polyvinylpyrrolidone / xanthan gum. By mixing and stirring by setting the stirring conditions to suitable conditions using a mixer or the like so that the ratio is 1 to 9, and further, for example, a bead mill, a homomixer, a homogenizer or the like capable of applying strong shearing. , Aqueous ballpoint pen ink compositions can be produced.
The pH (25 ° C.) of the ink composition for an aqueous ballpoint pen of the present invention can be adjusted to 5 to 10 by a pH adjuster or the like from the viewpoints of usability, safety, stability of the ink itself, and matching with the ink container. It is preferably adjusted, and more preferably 6 to 9.5.

The ink composition for a water-based ballpoint pen of the present invention is mounted on a ballpoint pen provided with a pen tip such as a ballpoint pen tip.
As the water-based ballpoint pen in the present invention, the water-based ballpoint pen ink composition having the above composition is contained in the ballpoint pen ink container (refill) and is not compatible with the water-based ink composition contained in the ink container. Moreover, a substance having a small specific gravity with respect to the water-based ink composition, for example, a substance containing polybutene, silicone oil, mineral oil or the like as an ink follower can be mentioned.
The structure of the water-based ballpoint pen is not particularly limited, and for example, it is provided with a collector structure (ink holding mechanism) in which the shaft cylinder itself is used as an ink container and the shaft cylinder is filled with the ink composition for a water-based ballpoint pen having the above configuration. It may be a direct liquid type ballpoint pen.

The ink composition for an aqueous ballpoint pen of the present invention configured as described above contains at least the colored resin particles having an average particle diameter of 0.5 to 6 μm, xanthan gum and polyvinylpyrrolidone, and contains the polyvinylpyrrolidone /. The mass ratio of xanthan gum is 1 to 9, and for example, in the case of large colored resin particles having an average particle diameter of more than 0.5 μm, such as heat-discoloring microcapsules (heat-discoloring particles). Compared to general dyes and pigments, the fluidity in the ink is low, and the response from static to dynamic or dynamic to static is slightly slower, and the operation like a ballpoint pen is frequently switched. In a writing tool with a large change in shearing force with respect to ink, its characteristics tend to appear in the drawn lines, and in particular, the phenomenon that the ink is reluctant to come out when writing immediately after the writing is stopped, that is, the deterioration of the first writing property is observed. However, in the present invention, it is possible to obtain an ink composition for a water-based ballpoint pen that does not deteriorate the initial writing property, which is a phenomenon in which ink is reluctant to come out at the time of writing.

Next, the present invention will be described in more detail with reference to Production Examples 1 to 3 of the colored resin particles to be used, Examples 1 to 8 and Comparative Examples 1 to 4 of the ink composition for a water-based ballpoint pen. It is not limited to. The average particle size (D50: μm) of the colored resin particles obtained in Production Examples 1 to 3 was measured using a particle size distribution analyzer HRA9320-X100 manufactured by Nikkiso Co., Ltd.

[Production Example 1: Colorable resin particles; Production of thermosetting particles]
1 part by mass of ETAC (manufactured by Yamada Chemical Co., Ltd.) (hereinafter, simply referred to as "part") as a leuco dye, 2 parts of bisphenol A as a color developer, and 24 parts of myristyl myristate as a discoloring temperature adjuster at 100 ° C. The mixture was heated and melted to obtain 27 parts of a homogeneous composition. To a uniform thermal solution of 27 parts of the composition obtained above, 10 parts of isocyanate and 10 parts of polyol were added as a capsule membrane agent and mixed by stirring. Next, 60 parts of a 12% polyvinyl alcohol aqueous solution was used as a protective colloid and emulsified at 25 ° C. to prepare a dispersion. Then, using 5 parts of 5% polyvalent amine, it was treated at 80 ° C. for 60 minutes to obtain core-shell type microcapsules.
The average particle size (D50) of the colored resin particles was 3.5 μm.

[Production Example 2: Colorable resin particles; Urethane-based black particles]
As an oil phase solution, while heating 12.5 parts by mass of ethyl acetate to 60 ° C, 3.5 parts by mass of oil-soluble black dye (Oil Black 860, manufactured by Orient Chemical Industry Co., Ltd.) and terpene phenol resin (YS Polystar N125 Yasuhara Chemical) (Manufactured by the company) 0.5 parts by mass was added and sufficiently dissolved. Next, 8 parts by mass of an isocyanurate-modified product (TLA-100, manufactured by Asahi Kasei Co., Ltd.) of hexamethylene diisocyanate as a prepolymer was added thereto to prepare an oil phase solution.
As the aqueous phase solution, while heating 200 parts by mass of distilled water to 60 ° C., 15 parts by mass of polyvinyl alcohol (PVA-205, manufactured by Kuraray Co., Ltd.) as a dispersant is dissolved therein to prepare an aqueous phase solution. did.
The oil phase solution was added to the aqueous phase solution at 60 ° C., and the mixture was emulsified and mixed by stirring with a homogenizer for 6 hours to complete the polymerization.
Colorable resin particles (urethane-based black particles) were obtained by centrifuging the obtained dispersion. The average particle size (D50) of the colored resin particles was 1.4 μm.

[Production Example 3: Colorable resin particles; Urethane-based white particles]
As an oil phase solution, 9.6 parts of myristyl myristate was heated to 60 ° C., and 2.4 parts of titanium oxide was added and sufficiently dispersed. Next, 9 parts of a trimethylolpropane (1 mol) adduct (D-109, manufactured by Mitsui Chemicals, Inc.) of methylenediphenyl-4,4'-diisocyanate (3 mol) was added, and 2 parts of ethylene glycol monobenzyl ether was further added. It was. As the aqueous phase solution, 15 parts of polyvinyl alcohol (PVA-205, manufactured by Kuraray Co., Ltd.) is dissolved in 600 parts of distilled water, the oil phase solution is added thereto, and the solution is emulsified and mixed with a homogenizer to complete the polymerization. did. The obtained dispersion was centrifuged to recover microcapsules to obtain microcapsule pigments. The average particle size (D50) of the colored resin particles was 0.6 μm.

[Examples 1 to 8 and Comparative Examples 1 to 4]
Each water-based ballpoint pen ink composition was prepared by a conventional method using the colored resin particles of Production Examples 1 to 3 and using xanthan gum, polyvinylpyrrolidone, and the like having the composition shown in Table 1 below.
With respect to the ink compositions for water-based ballpoint pens obtained in Examples 1 to 8 and Comparative Examples 1 to 4, water-based ballpoint pens were produced by the following methods, and the first writing property was evaluated by the following evaluation method.
These results are shown in Table 1 below.

(Making a water-based ballpoint pen)
A water-based ballpoint pen was produced using each ink composition obtained above. Specifically, using the shaft of a ballpoint pen [Mitsubishi Pencil Co., Ltd., trade name: Signo UM-100], a polypropylene ink storage tube with an inner diameter of 4.0 mm and a length of 113 mm and a stainless steel tip (super hard alloy ball) , Ball diameter 0.7 mm) and the refill consisting of the joint connecting the storage pipe and the chip are filled with each of the above water-based inks, and the ink follower containing mineral oil as the main component is loaded at the rear end of the ink to load a water-based ballpoint pen. Made.

[Evaluation method of first writing]
Each of the water-based ballpoint pens obtained above was left uncapped at 25 ° C. and 50% RH for 60 minutes, then a straight line was written on PPC paper, and the first writing property was evaluated according to the following evaluation criteria.
Evaluation criteria:
A: Writing is possible from the beginning of writing without problems B: Blurring of more than 0 mm and less than 5 mm is confirmed from the beginning of writing C: Blurring of 5 mm or more is confirmed from the beginning of writing

As is clear from the results in Table 1 above, the ink compositions for water-based ballpoint pens of Examples 1 to 8 which are within the scope of the present invention are superior in initial writing property as compared with Comparative Examples 1 to 4 which are outside the scope of the present invention. It was confirmed that.
On the other hand, looking at Comparative Examples 1 to 4, Comparative Examples 1 and 2 contained xanthan gum and polyvinylpyrrolidone alone, and Comparative Examples 3 and 4 had a mass ratio of polyvinylpyrrolidone / xanthan gum of 1 to 9. It was confirmed that the writing ability deteriorated from the beginning of writing in these cases when it was out of the range.
Combining the evaluation results of Examples 1 to 8 and Comparative Examples 1 to 4 above, it is the first time that the ink composition for a water-based ballpoint pen of Examples 1 to 8 which is the scope of the present invention is used. It was found that the sex was remarkably improved and a peculiar action and effect could be exhibited.

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

Claims (4)

An ink composition for an aqueous ballpoint pen containing at least colored resin particles having an average particle diameter of 0.5 to 6 μm, xanthan gum and polyvinylpyrrolidone, and having a mass ratio of polyvinylpyrrolidone / xanthan gum of 1 to 9. .. The ink composition for an aqueous ballpoint pen according to claim 1, wherein the K value of polyvinylpyrrolidone is 10 to 40. The ink composition for an aqueous ballpoint pen according to claim 1 or 2, wherein the content of polyvinylpyrrolidone is 0.5 to 5% by mass with respect to the total amount of the ink composition. A water-based ballpoint pen comprising the ink composition for a water-based ballpoint pen according to any one of claims 1 to 3.