JP7641114B2 - Water-based ink composition for writing implements and writing implement using same - Google Patents

Description

The present invention relates to an aqueous ink composition for writing instruments and a writing instrument using the same.

When writing with a writing instrument filled with an ink composition, the ink usually penetrates the paper surface, leaving a flat handwriting. By making this handwriting three-dimensional, it is possible to enjoy handwriting that is different from normal handwriting, or to decorate various materials. Furthermore, because three-dimensional handwriting can be distinguished by touch, there is also demand for it as a social product.

As one method for forming three-dimensional handwriting, a water-based ink composition containing a large amount of a three-dimensional film-forming component has been proposed (for example, Patent Document 1). There is a demand for a water-based ink composition that can produce three-dimensional handwriting that is stronger and more stable.

JP 2005-8873 A

The present invention aims to solve the above problems by providing a water-based ink composition for writing instruments that is transparent, glossy, and capable of producing three-dimensional handwriting.

The aqueous ink composition for a writing instrument according to the present invention comprises a film-forming polymer having a minimum film-forming temperature of 50° C. or less, an associative thickener, a colorant, and water;
The viscosity of the ink composition is 50 mPa·s or more under conditions of 20° C. and a shear rate of 1.92 sec ⁻¹ .

The writing instrument according to the present invention contains the above-mentioned aqueous ink composition for writing instruments.

The present invention provides an aqueous ink composition for writing instruments that is transparent, glossy, and capable of forming three-dimensional handwriting. The resulting handwriting has low surface adhesion and excellent stability, is also less prone to cracking, and has excellent strength.

FIG. 2 is a vertical cross-sectional view of an example of a cap-type pressurized ballpoint pen. FIG. 2 is a vertical cross-sectional view of the ballpoint pen of FIG. 1 with the cap removed. 1 is an explanatory diagram showing a writing instrument in a state where a cap is fitted onto the rear end of the barrel (pressurized state). FIG.

The following is a detailed description of an embodiment of the present invention. In this specification, unless otherwise specified, "parts," "%," "ratio," and other units used to indicate the composition are based on mass, and the content is the mass% of the component based on the mass of the ink composition.

<Water-based ink composition for writing instruments>
The aqueous ink composition for writing instruments according to the present invention (hereinafter sometimes referred to as the ink composition) comprises a film-forming polymer having a minimum film-forming temperature of 50° C. or lower, an associative thickener, a colorant, and water.
The viscosity of the ink composition is, under conditions of 20° C. and a shear rate of 1.92 sec ⁻¹ (0.5 rpm), 50 mPa·s or more, preferably 100 mPa·s or more, more preferably 500 mPa·s or more, more preferably 1000 mPa·s or more, 2000 mPa·s or more, more preferably 3000 mPa·s or more, and preferably 10000 mPa·s or less, more preferably 8000 mPa·s or less. If the viscosity is within the above numerical range, the ink is excellent in stable ink discharge from the pen tip, and a sufficiently three-dimensional handwriting can be obtained.
The solid content ratio of the ink composition is preferably 10 to 50% by mass, more preferably 15 to 30% by mass, based on the total mass of the ink composition. If the solid content ratio is within the above range, the ink viscosity can be easily set to 50 mPa·s or more under conditions of 20°C and a shear rate of 1.92 sec ^-1 , and handwritten marks with excellent three-dimensional effect can be formed. In addition, the three-dimensional effect of the handwritten marks can be maintained even after the ink has dried.

In order to enable the formation of three-dimensional handwriting, the ink composition according to the present invention preferably has a higher viscosity and solid content ratio than ink compositions typically used for writing instruments, as described above.

The ink composition according to the present invention is used in a writing instrument, and a preferred embodiment of the present invention is a ballpoint pen. When the ballpoint pen contains the ink composition according to the present invention, it is preferable that good ink discharge properties are obtained during writing.
Therefore, the viscosity of the ink composition, under conditions of 20°C and a shear rate of 192 sec ^-1 (50 rpm), is preferably 500 mPa·s or less, more preferably 200 mPa·s or less, more preferably 150 mPa·s or less, more preferably 120 mPa·s or less, more preferably 110 mPa·s or less, and more preferably 100 mPa·s or less.
Furthermore, in order to obtain better ink ejection properties than the tip of a ballpoint pen while still being able to form three-dimensional handwriting, it is preferable that the ink composition has a viscosity gradient between its static viscosity and its flowing viscosity above a certain level, in other words, that the viscosity ratio of the ink composition between high shear and low shear is above a certain level.
Therefore, the viscosity ratio of the ink composition at high shear to low shear (viscosity at 20°C and a shear rate of 1.92 sec ^-1 /viscosity at 20°C and a shear rate of 192 sec ^-1 ) is preferably 10 or more, more preferably 20 or more, even more preferably 40 or more, even more preferably 45 or more, and is preferably 100 or less, more preferably 80 or less.
Furthermore, when the ink composition of the present invention is used as an ink composition for a ballpoint pen, in order to obtain good ink dischargeability and three-dimensional handwriting from the beginning of writing, the viscosity ratio of the ink composition (viscosity under conditions of 20°C and a shear rate of 1.92 sec ^-1 /viscosity under conditions of 20°C and a shear rate of 19.2 sec ^-1 ) is preferably 1.5 or more, more preferably 3.0 or more, more preferably 5.0 or more, more preferably 5.5 or more, and is preferably 20 or less, more preferably 10 or less.

[Film-forming polymer]
The ink composition according to the present invention contains a film-forming polymer having a minimum film-forming temperature of 50° C. or lower (hereinafter, sometimes referred to as film-forming polymer).
The film-forming polymer used in the present invention is uniformly dispersed in the ink composition, and is preferably emulsified and dispersed in an aqueous medium. Specifically, the film-forming polymer used in the present invention is present in the form of particles without being dissolved in the ink composition, and when writing, water evaporates and the particles bond to each other to form a film.

The minimum film-forming temperature (hereinafter sometimes referred to as MFT) refers to the lowest temperature at which a film-forming polymer can form a smooth, transparent, continuous coating film. MFT can be measured in accordance with JIS K6828-2 (2003).
The MFT of the film-forming polymer used in the present invention is preferably 40° C. or less. Furthermore, in consideration of suppressing the occurrence of cracks in the resulting handwriting, it is more preferably 30° C. or less, and even more preferably 0° C. or less.

Examples of the film-forming polymer include acrylic resins, urethane resins, vinyl resins, and styrene resins. Among them, acrylic resins or urethane resins are preferred because they have good compatibility with the association type thickeners described later, particularly urethane association type thickeners, and acrylic resins are more preferred because they are more likely to provide an ink thickening effect, improve the dispersion stability of the ink, and enable stable formation of three-dimensional handwriting, and acrylic resins or styrene acrylic resins are even more preferred.
Two or more film-forming polymers may also be combined.

The mass average molecular weight of the membrane-forming polymer is preferably 10,000 to 10 million, more preferably 30,000 to 3 million, and even more preferably 100,000 to 1 million. Here, in the present invention, the mass average molecular weight can be measured by a conventional method using gel permeation chromatography. The same applies to the mass average molecular weights described below.

When producing the ink composition according to the present invention, the film-forming polymer may be added in the form of a dispersion, for example an emulsion, in which the film-forming polymer is dispersed in water (using a dispersant if necessary). It is also a preferred embodiment that the film-forming polymer is added to the ink composition in the form of an emulsion.

Examples of commercially available emulsions containing film-forming polymers include "Joncryl JDX-7741", "Joncryl PDX-7734", "Joncryl PDX-7787", "Joncryl PDX-7615", "Joncryl PDX-7775", "Joncryl PDX-7630A", "Joncryl PDX-7356", "Joncryl PDX-7777", "Joncryl PDX-7430", "Joncryl PDX-7326", "Joncryl PDX-7616A", "Joncryl PDX-7732", "Joncryl PDX-7356", "Joncryl PDX-7692", "Joncryl 352D", "Joncryl PDX-7667'', ``Joncryl PDX-7700'', ``Joncryl PDX-7696'' (BASF), ``NeoCryl XK-190'', ``NeoCryl XK-12'', ``NeoCryl XK-16'', ``NeoCryl XK-30'', ``NeoCryl XK-36'', ``NeoCryl XK-188'', ``NeoCryl A-614”, “NeoCryl A-633”, “NeoCryl A-655”, “NeoCryl A-1092", "NeoCryl A-1093", "NeoCryl A-1094", "NeoCryl A-1125", "NeoCryl A-1127", "NeoCryl A-6069", "NeoCryl A-6092" (Kusumoto Chemicals Co., Ltd.), "Mobinil" LDM7582 (Nippon Synthetic Chemical Industry Co., Ltd.), "727", "743N", "745", "752", "801", "940", "1752", "6520", "6720", "7525", "7540", "7820", "8020", "8030", "DM60", "DM772", "DM774", "LDM6740", "LDM7522", "LDM7523", "VDM7410", "ES-85", "109E", "172E", "760H", "DS5", "180E", "761HG", "DC02", "185EK", "987B", "D025N", "711H", "128N", "DLR1", "138N", "168N", "135N", Examples include "FK-900", "BA-10L", "BA-20", "BA-53", "BA-58", "BA-321L", "BA-321H", "DM201P", "DM1645P", "LDM1646P", "D5100P", "DM2072P", "LDM2077P", "LDM7000P", "LDM7100P", "LDM7300P", "LDM7400P" (Japan Coating Resin Co., Ltd.), "Vinyblan 271", "Vinyblan 278", "Vinyblan 715S", "Vinyblan 735", "Vinyblan 603EM", "Vinyblan 603HA", "Vinyblan 603SK", and "Vinyblan 603VS" (Nissin Chemical Industry Co., Ltd.).

The content of the film-forming polymer is preferably 1 to 50% by mass based on the total mass of the ink composition, and taking into consideration the jetting property, it is more preferably 1 to 30% by mass, even more preferably 10 to 30% by mass, still more preferably 15 to 30% by mass, and most preferably 15 to 28% by mass. If the content of the film-forming polymer is within the above range, it is possible to form handwriting with a sufficiently visible raised handwriting and excellent three-dimensionality.
As the film-forming polymer, a plurality of types having different MFTs can also be combined.

[Associative thickener]
The ink composition according to the present invention comprises an associative thickener. The associative thickener has a hydrophilic group as a backbone and a hydrophobic group on a side chain or at an end. The associative thickener exists stably in an aqueous medium due to an interaction between the hydrophilic group and the aqueous medium, while one hydrophobic group associates and adsorbs with a film-forming polymer or colorant particles, and the other hydrophobic group associates and adsorbs with a hydrophobic group of another molecule, a film-forming polymer, or a colorant particle, forming a weak crosslinked structure, thereby achieving an ink thickening effect.

Examples of associative thickeners include urethane-based associative thickeners, polyacrylic acid-based associative thickeners, polyvinyl-based associative thickeners, polyether-based associative thickeners, polyglycol-based associative thickeners, maleic anhydride copolymer-based associative thickeners, polyamide-based associative thickeners, polyester-based associative thickeners, hydrophobized cellulose ester-based associative thickeners, and polycarboxylic acid-based associative thickeners. From the viewpoint of improving the gloss of the film, urethane-based associative thickeners are preferred.

A urethane-based associative thickener is a compound that thickens an ink composition in an aqueous medium by associating and adsorbing urethane bonds present at the ends of the thickener with hydrophobic groups of other molecules, film-forming polymers, colorant particles, etc., and by associating the ends of the thickener with each other. Examples of urethane associative thickeners include compounds that have urethane bonds and polyether chains in the molecule, that is, compounds that have a urethane structure and a polyether structure.

Examples of commercially available urethane-based associative thickeners include "ADEKA NOL UH-756VF", "ADEKA NOL UH-462", "ADEKA NOL UH-420", "ADEKA NOL UH-472", "ADEKA NOL UH-540", "ADEKA NOL UH-814N" (ADEKA CORPORATION), "SN Thickener 660T", "SN Thickener 665T", "SN Thickener 612", "SN Thickener 612NC", "SN Thickener 619", "SN Thickener 621N", "SN Thickener 621TF", "SN Thickener 623N", "SN Thickener 623N", "SN Thickener 625N", "Nopal 700N" (SAN NOPCO LTD.), "Thixostar" (Japan Material Technology Co., Ltd.), "OPTIFLO T1000", "OPTIFLO L1400", "OPTIFLO M2600VF", "OPTIFLO H7500VF" (BYK Japan Co., Ltd.), etc.

When the ink composition of the present invention is used as an ink composition for a ballpoint pen, it is preferable to use, among the associative thickeners, an associative thickener that imparts thixotropic viscosity. This is because it is easy to set the viscosity ratio of the ink composition at high shear and low shear within the desired range, and it is possible to form handwriting with excellent three-dimensionality while improving the ink dischargeability from the pen tip.

The mass average molecular weight of the associative thickener is preferably 500 to 500,000, more preferably 800 to 300,000, and even more preferably 1,000 to 100,000.

The content of the associative thickener is preferably 0.01 to 5 mass %, more preferably 0.05 to 1 mass %, and more preferably 0.05 to 0.8 mass %, based on the total mass of the ink composition. When the content of the associative thickener is within the above range, it is easy to impart appropriate viscosity to the ink composition, and it is possible to form handwriting with excellent three-dimensionality in which the raised handwriting can be sufficiently confirmed.
In addition, in order to impart sufficient viscosity to the ink composition and obtain handwriting with excellent three-dimensional effect, the mass ratio of the associative thickener to the film-forming polymer (associative thickener/film-forming polymer) is preferably 0.001 to 0.2, more preferably 0.001 to 0.1, more preferably 0.001 to 0.05, and more preferably 0.002 to 0.03.

[Coloring agent]
The ink composition according to the present invention contains a colorant. Any pigment or dye known in the art may be used. Among them, the colorant is preferably a pigment, since it is easy to obtain handwriting with good color development and excellent three-dimensional effect.

Examples of pigments include inorganic, organic, and processed pigments, but specific examples include carbon black, aniline black, ultramarine, yellow lead, titanium oxide, iron oxide, phthalocyanine pigments, azo pigments, quinacridone pigments, quinophthalone pigments, styrene pigments, triphenylmethane pigments, perinone pigments, perylene pigments, dioxazine pigments, as well as luster pigments, microcapsule pigments, and colored resin pigments. Note that the pigment may be a water-dispersed pigment product that has been dispersed in a medium using a pigment dispersant such as a surfactant.

Among the pigments, it is preferable to use a colored resin pigment. As described later, since the colored resin pigment is a resin particle colored with a colorant, the association type thickener is easily associated and adsorbed, and the ink thickening effect is easily obtained. Therefore, it is easy to impart an appropriate viscosity to the ink composition, and it is possible to stably form a three-dimensional handwriting. Furthermore, by using the colored resin pigment, it is easy to maintain excellent transparency and gloss of the handwriting.
In the present invention, the colored resin particle pigment refers to resin particles colored with a colorant. The colorant is not particularly limited as long as it can color the resin particles, and any pigment or dye can be used. The resin particles are preferably styrene-acrylonitrile resin particles (hereinafter sometimes referred to as SA resin particles) because they have excellent alkali resistance, acid resistance, and heat resistance, are highly stable even in the presence of various additives, and are not easily affected by thermal environments.
Specific examples of commercially available products containing colored resin particles include the Shinroihi Color series (manufactured by Shinroihi Co., Ltd.), the Lumicol series (manufactured by Nippon Kinko Kagaku Co., Ltd.), the LM series (manufactured by Fuji Pigment Co., Ltd.), and the Epocolor series (manufactured by Nippon Shokubai Co., Ltd.). Specific examples of the Lumicol series include NKW-2317H, NKW-6307H, NKW-2308H, NKW-2302H, NKW-2305H, and NKW-6305H. Further, the Sinrohi Color series includes Sinrohi Color Base SW-11, SW-12, SW-13, SW-14, SW15, SW-16, SW-17, SW-18, SW-27, SW-37, SW-47, SF-1012, SF-1013, SF-1014, SF-1015, SF-1017, SF-1027, SF-1038, and SF-5015.

Examples of dyes include phthalocyanine dyes, pyrazolone dyes, nigrosine dyes, anthraquinone dyes, and azo dyes.

The content of the colorant varies depending on the type, but is preferably 0.05 to 5 mass %, and more preferably 0.1 to 1 mass %, based on the total mass of the ink composition.
The colorants may be used alone or in combination of two or more kinds.

[water]
The ink composition according to the present invention contains water. There are no particular limitations on the water, and examples of the water that can be used include tap water, ion-exchanged water, ultrafiltered water, and distilled water.
The water content is preferably from 10 to 90% by mass, and more preferably from 50 to 70% by mass, based on the total mass of the ink composition.

(Other additives)
The ink composition of the present invention essentially contains the above-mentioned components (film-forming polymer, associative thickener, colorant and water), but may contain other components as necessary.

[Water-soluble resin]
The ink composition according to the present invention may further contain a water-soluble resin. By containing a water-soluble resin, the three-dimensional shape after writing can be maintained.
The water-soluble resin may be any resin that dissolves in water, but acrylic resin, polyester resin, polyethylene oxide, and polyvinylpyrrolidone are preferably used, which can provide handwriting with excellent three-dimensional effect while maintaining the transparency and gloss of the handwriting.
When the content of the water-soluble resin is increased, the three-dimensional shape of the handwriting tends to be better maintained, but the adhesion of the handwriting surface tends to increase, and the above-mentioned viscosity ratio (viscosity under a shear rate of 1.92 sec ^-1 / viscosity under a shear rate of 192 sec ^-1 ) tends to decrease. Taking these factors into consideration, the content of the water-soluble resin is preferably 0.1 to 10 mass %, more preferably 1 to 5 mass %, based on the total mass of the ink composition.
In addition, in order to obtain a good balance between maintaining the three-dimensionality of handwriting and suppressing the adhesion of the handwriting surface while improving the ink dischargeability, the content of the water-soluble resin is preferably 0.5 to 30% by mass, and more preferably 5 to 20% by mass, based on the content of the film-forming polymer.
The mass average molecular weight of the water-soluble resin is preferably 5,000 to 1.5 million, more preferably 10,000 to 1,000,000, even more preferably 20,000 to 150,000, and more preferably 20,000 to 80,000.

[Water-soluble organic solvent]
The ink composition according to the present invention may further contain a water-soluble organic solvent. Depending on the type of water-soluble organic solvent, it is possible to improve the writing performance during drying up, to improve the dispersion stability, to improve the drying property of the handwriting, and to suppress the tackiness of the handwriting formed.
Examples include (i) glycols such as ethylene glycol, butylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and glycerin, (ii) alcohols such as methanol, ethanol, 1-propanol, isopropanol, isobutanol, t-butanol, propargyl alcohol, allyl alcohol, 3-methyl-1-butyn-3-ol, ethylene glycol monomethyl ether acetate, and other higher alcohols, and (iii) glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 3-methoxybutanol, and 3-methoxy-3-methylbutanol. These can be used alone or as a mixture of two or more kinds.
In consideration of improving the drying property of the handwriting, it is preferable to use a liquid having a vapor pressure of 3 kPa or more, and more preferably 4 kPa or more, at 20° C. Specific examples of the liquid include methanol, ethanol, isopropanol, ethylene glycol dimethyl ether, and propylene glycol dimethyl ether.

In order to achieve a good balance between improved writing performance and ink drying speed while maintaining the three-dimensional shape, the content of the water-soluble organic solvent is preferably 0.1 to 10% by mass, and more preferably 1 to 8% by mass, based on the total mass of the ink composition.

In addition, the ink composition of the present invention may contain various additives such as pH adjusters, rust inhibitors, preservatives, and chelating agents for the purpose of improving the ink properties and functions.

Examples of pH adjusters include basic inorganic compounds such as ammonia, sodium carbonate, sodium phosphate, and sodium hydroxide, basic organic compounds such as sodium acetate, triethanolamine, and diethanolamine, lactic acid, acetic acid, and citric acid.

Preservatives include phenol, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine, sodium 2-pyridinethiol-1-oxide, 1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, orthophenylphenol or its salts.

Rust inhibitors include benzotriazole and its derivatives, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, sodium thiosulfate, saponin, or dialkylthiourea.

Chelating agents include ethylenediaminetetraacetic acid (EDTA), hydroxyethylenediaminetriacetic acid (HEDTA), glycol ether diaminetetraacetic acid (GEDTA), nitrilotriacetic acid (NTA), hydroxyethyliminodiacetic acid (HIDA), dihydroxyethylglycine (DHEG), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA), and alkali metal salts, ammonium salts, or amine salts thereof.

In addition, the present invention may further contain a moisturizing agent other than the water-soluble organic solvent. For example, urea, sorbitol, dextrin, N,N,N-trialkylamino acids such as trimethylglycine, and hyaluronic acids can be suitably used.

Furthermore, nonionic surfactants, anionic surfactants, cationic surfactants, surfactants having an acetylene bond in the structure, fluorine-based surfactants, and the like can also be added.
These improve the wettability of the ink reservoir and the ink flow regulator, allowing smooth ink ejection and resulting in good handwriting.
In addition, a defoaming agent can be added, and a lubricant such as a phosphate ester surfactant or a fatty acid can also be added.

<Method of producing ink composition>
The ink composition according to the present invention can be produced by any conventionally known method. Specifically, the ink composition can be produced by blending the required amounts of the above-mentioned components and mixing them with various stirrers such as a magnetic hot stirrer, a propeller stirrer, a homogenizer stirrer, a homodisper, a homomixer, a planetary stirrer, or various dispersing machines such as a bead mill.

<Writing implements>
The writing implement according to the present invention contains the ink composition described above. The structure and shape of the writing implement itself to which the aqueous ink composition according to the present invention is loaded are not particularly limited, and conventional general-purpose ones can be used, but it is preferable that the writing implement is used in a ballpoint pen with a ballpoint pen tip or the like. It is more preferable that the ink composition according to the present invention is used in a pressurized ballpoint pen. This is because, when the ink composition according to the present invention, which tends to have a high viscosity, is used in a pressurized ballpoint pen, the dischargeability is improved and handwriting with excellent three-dimensional effect can be formed.
Examples of pressurized ballpoint pens include pressurized ballpoint pens in which a pressurized gas is enclosed in an ink reservoir and the pressure of the pressurized gas pressurizes the ink composition toward the tip end side, knock-type pressurized ballpoint pens in which a space present at the rear end side of the ink composition is compressed by knocking, attaching a cap, or moving the pen tip due to writing pressure when writing, and the ink composition is pressed toward the tip end side by the pressure caused by this compression, cap-type pressurized ballpoint pens equipped with a cap that covers the pen tip, and pen pressure pressurized ballpoint pens, etc. Since the ink composition according to the present invention tends to have a high solids ratio, a cap-type pressurized ballpoint pen capable of sealing the pen tip is more preferable, taking into account the resistance to dry-up.

The pressure applied to the ink composition filled inside the ink storage tube from the rear end side by pressurization is preferably greater than atmospheric pressure, specifically, greater than atmospheric pressure but not greater than 1.5 times. More specifically, if atmospheric pressure is 1000 hPa, the pressure is preferably greater than 1000 hPa and not greater than 1500 hPa, and more preferably greater than 1000 hPa and not greater than 1200 hPa. This makes it possible to achieve an optimal ink consumption amount while suppressing ink leakage from the front end of the tip, and improves handwriting quality and density, such as providing a sufficient three-dimensional effect.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1
The following materials other than the associative thickener were mixed in the amounts shown below and stirred with a magnetic stirrer while heating at room temperature to prepare a base ink. Thereafter, the following associative thickener was added to the base ink prepared above in the amount shown below and thoroughly mixed and stirred using a homogenizer stirrer until a uniform state was obtained, thereby obtaining the ink composition of Example 1.
Acrylic resin A (acrylic emulsion "NeoCryl XK-190" (Kusumoto Chemicals Co., Ltd.), solid content 45% by mass, MFT < 0 ° C.) 55 parts by mass Urethane-based thickener A (associative thickener "ADEKA NOL UH-756VF" (ADEKA Corporation, solid content 32% by mass) 0.5 parts by mass Colored resin particles A (30% by mass aqueous dispersion of fluorescent colored resin particles (fluorescent yellow), "SF-5017" (Shinroihi Co., Ltd.)) 2 parts by mass Triethanolamine 0.5 parts by mass Water 42 parts by mass

<Examples 2 to 11 and Comparative Examples 1 to 3>
In Examples 2 to 11 and Comparative Examples 1 to 3, water-based ink compositions were obtained in the same manner as in Example 1, except that the types and amounts of components contained in the ink compositions were changed to the compositions shown in Table 1. The numerical values for the compositions in the table indicate parts by mass.

In the table,
Acrylic resin A: acrylic emulsion "NeoCryl XK-190" (Kusumoto Chemical Co., Ltd.), solid content 45% by mass, MFT < 0 ° C.
Acrylic resin B: Acrylic emulsion "Joncryl PDX-7430" (BASF Japan Ltd.), solid content 38% by mass, MFT 44°C,
Acrylic resin C: acrylic emulsion "Movinyl LDM7582" (Nippon Synthetic Chemical Industry Co., Ltd.), solid content 46% by mass, MFT 20°C,
Acrylic resin D: acrylic emulsion "NeoCryl A-550" (Kusumoto Chemical Co., Ltd.), solid content 40% by mass, MFT>100°C,
Styrene acrylic resin A: acrylic emulsion "NeoCryl BT-62" (Kusumoto Chemical Co., Ltd.), solid content 40% by mass, MFT 10°C,
Styrene acrylic resin B: acrylic emulsion "NeoCryl A-662" (Kusumoto Chemical Co., Ltd.), solid content 40% by mass, MFT>90°C,
Urethane thickener A: Associative thickener "ADEKA NOL UH-756VF" (ADEKA Corporation), solid content 32% by mass,
Urethane-based thickener B: Associative thickener "SN Thickener 665T" (San Nopco Ltd.), solid content 30% by mass, thixotropic Urethane-based thickener C: Associative thickener "SN Thickener 660T" (San Nopco Ltd.), solid content 20% by mass, thixotropic Urethane-based thickener D: Associative thickener "ADEKA NOL UH-462" (ADEKA Corporation), solid content 30% by mass,
Acrylic thickener A: Polymer thickener "SN Thickener 618" (San Nopco Ltd.), solid content 13% by mass,
Colored resin particles A: 30% by mass aqueous dispersion of fluorescent colored resin particles (fluorescent pink), "SF-5017" (Shinroihi Co., Ltd.),
Colored resin particles B: 44% by mass aqueous dispersion of fluorescent colored resin particles (fluorescent pink), "Lumicol NKW-2317H" (Japan Fluorescent Chemical Co., Ltd.)
Water-soluble acrylic resin: acrylic resin-containing aqueous solution "Joncryl PDX6124" (BASF Japan Ltd.), solid content 24.5% by mass,
・Polyethylene oxide: "Alcox L-11" (Meisei Chemical Industry Co., Ltd.), molecular weight approximately 110,000,
Polyester resin: "Pluscoat Z-561", 25% by weight aqueous solution.

[viscosity]
The viscosity of the resulting ink composition was measured using an E-type rotational viscometer (model: DV-II+Pro, rotor: CPE-42, manufactured by Brookfield) at a shear rate of 1.92 sec ^-1 (rotation speed: 0.5 rpm) in an environment of 20° C. The results are shown in Table 1.

[Viscosity ratio]
The viscosity of the resulting ink composition was measured using an E-type rotational viscometer (model: DV-II+Pro, rotor: CPE-42, manufactured by Brookfield) at a shear rate of 192 sec ^-1 (rotation speed: 50 rpm) in an environment of 20° C. In Examples 3, 4, 8 and 10, the viscosity exceeded the measurement limit of 128 mPa·s and therefore could not be measured.
The viscosity at the shear rate of 1.92 sec ^-1 (0.5 rpm) and the viscosity at the shear rate of 192 sec ^-1 (50 rpm) were calculated to obtain the viscosity ratio (0.5 rpm/50 rpm). The results are shown in Table 1.

The viscosity of the resulting ink composition was measured using an E-type rotational viscometer (model: DV-II+Pro, rotor: CPE-42, manufactured by Brookfield) at a temperature of 20° C. and a shear rate of 19.2 sec ⁻¹ (rotation speed: 5 rpm).
The viscosity at a shear rate of 1.92 sec ^-1 (0.5 rpm) and the viscosity at a shear rate of 19.2 sec ^-1 (5 rpm) were calculated, and the viscosity ratio (0.5 rpm/5 rpm) was determined. The results were 5.9 for Example 1, 8.1 for Example 2, 3.9 for Example 3, 2.8 for Example 4, 4.5 for Example 5, and 1.0 for Example 10.

The ink compositions of the Examples and Comparative Examples were filled into ballpoint pen refill 7 of capped pressurized ballpoint pen 1, and the ink ejection properties were confirmed when pressure was applied. When the ink composition of Example 10 was used, ejection was not possible, so in the subsequent handwriting evaluation, the ink composition was written using a decoration pen. The other ink compositions could be written with the above pressurized ballpoint pen, and in the subsequent handwriting evaluation, the above pressurized ballpoint pen was used. With regard to the ink compositions of the Examples, the ink compositions of Examples 1, 2, 6, and 7 had the best ejection properties, followed by Examples 3, 5, 8, 9, and 11.

1 to 3 show a cap-type pressure ballpoint pen 1. The cap-type pressure ballpoint pen 1 has a front barrel 2 having a grip member 14 attached to a gripping portion and a rear barrel 3 connected to each other, and a ballpoint pen refill 7 disposed in the barrel body.
In addition, the capped pressurized ballpoint pen 1 has a translucent cap 4 obtained by injection molding of PP resin, which is removably attached by fitting a fitting protrusion formed on the inner wall of the cap 4 over a fitting protrusion formed on the side wall of the front barrel 2. When the cap is attached to the front barrel 2, the ballpoint pen tip 10 is sealed by a seal member provided inside the cap.

A ballpoint pen tip 10 rotatably holding a ball having a diameter of 1.0 mm is attached to the front end of an ink reservoir tube 8 provided in the ballpoint pen refill 7 via a tip holder 9 .
A tail plug 11 having an air hole communicating between the inside and the outside is attached to the rear end of the ink reservoir tube 8.
The ink reservoir 8 is filled with the water-based ink composition 12 for writing instruments having the above-mentioned ink formulation and an ink follower 13 .
Although not shown, a coil spring is provided behind the ball to constantly press the ball against the inner wall at the front end of the tip.

The rear end of the ink reservoir 8 of the ballpoint pen refill 7 is press-fitted into the rear end of the rear barrel 3, and the space following the portion of the ink reservoir 8 filled with the ink composition 12 and the ink follower 13 is only connected to the outside air by the communication hole 3A provided at the rear end of the rear barrel 3, which connects the inside and outside of the writing instrument.

The pressurizing mechanism that operates when the cap 4 is fitted will be described in detail below.
By fitting the cap 4 onto the rear barrel 3 of the writing instrument body, pressure can be applied via the ink follower 13 to the ink composition 12 filled in the ballpoint pen refill 7 .
Specifically, when the rear end of the rear barrel 3 is inserted into the open end of the cap body 5 in the direction of the arrow F in the figure, first the inner wall 5A of the cap body 5 and the side wall 3B of the rear barrel 3 come into contact with each other.
At this time, the spaces inside the cap body 5, the rear barrel 3 and the ink reservoir 8 are communicated in a sealed state through a communication hole 3A provided at the rear end of the rear barrel 3, which communicates the inside and outside.
When the cap 4 is further advanced in the direction of the arrow F in the figure, the sealed space is compressed until the fitting is completed. As a result, pressure can be applied to the water-based ink composition for writing instruments filled in the ballpoint pen refill 7 via the ink follower 13. The pressure was 1050 hPa.

[handwriting]
The ink compositions of the Examples and Comparative Examples were written on writing paper (JIS P 3201 Writing Paper A), and the handwriting was visually observed and evaluated for three-dimensional effect, cracks, glossiness, and transparency. The evaluation criteria were as follows. The results are shown in Table 1.
Three-dimensional effect: When the handwriting was touched with the hand, it felt sufficiently raised.
○: When the handwriting was touched with the hand, it felt raised.
Δ: When the handwriting was touched with a finger, it felt raised, but was rather weak.
X: When I touched the handwriting with my finger, I couldn't feel any raised texture.
Cracks ○: No cracks were found in the handwriting.
Δ: Slight cracks were observed in the writing.
X: Numerous cracks were found in the handwriting and it crumbled when touched.
Glossiness: Good: Sufficient glossiness was observed in the handwriting.
X: The handwriting was not sufficiently glossy.
Transparency: Good: The writing had sufficient transparency.
X: The handwriting was not sufficiently transparent.
XX: The handwriting was not sufficiently transparent, and furthermore, cloudiness was observed.

The ink composition in which the amount of thickener was changed from 4 to only 2% by mass compared to the ink composition in Comparative Example 2 had the same evaluations of cracking, glossiness, and transparency as Comparative Example 2.

When the ink compositions of the Examples were used to check the tackiness of the surface of the handwritten marks one hour after writing, they did not stick to the hand and had low tackiness.
Furthermore, when the ink composition of Example 6 was used, the handwriting was not rubbed off even when rubbed 10 minutes after writing, and the handwriting dried more quickly and favorably than the ink compositions of the other Examples.

REFERENCE SIGNS LIST 1 Cap-type pressurized ballpoint pen 2 Front barrel 3 Rear barrel 3A Communication hole 3B Side wall 4 Cap 5 Cap body 5A Inner wall 6 Sealing member 7 Ballpoint pen refill 8 Ink storage tube 9 Tip holder 10 Ballpoint pen tip 11 Tail plug 11A Air hole 12 Writing instrument ink composition 13 Ink follower 14 Grip

Claims (8)

A water-based ink composition for a writing instrument, comprising a film-forming polymer having a minimum film-forming temperature of 50° C. or less, an associative thickener, a colorant, a water-soluble resin, and water,
The viscosity of the ink composition is 50 mPa·s or more under conditions of 20° C. and a shear rate of 1.92 sec ^-1,
The water-based ink composition for a writing instrument , wherein the content of the water-soluble resin is 0.5 to 30 mass% based on the content of the film-forming polymer, and the mass average molecular weight of the water-soluble resin is 5,000 to 1,500,000. The ink composition according to claim 1, wherein the associative thickener is a urethane-based associative thickener. The ink composition according to claim 1 or 2, wherein the film-forming polymer is an acrylic resin or a urethane resin. The ink composition according to any one of claims 1 to 3 , wherein the solid content of the ink composition is 10 to 50 mass %. The ink composition according to any one of claims 1 to 4, wherein the ink composition has a viscosity ratio (viscosity at 20°C and a shear rate of 1.92 sec ^-1 /viscosity at 20°C and a shear rate of 192 sec ^- 1 ) of 10 or more. A writing instrument containing the composition according to any one of claims 1 to 5 . 7. The writing instrument of claim 6 which is a ballpoint pen. 8. The writing instrument according to claim 6 or 7 , which is a pressurized ballpoint pen.