Water-based ink composition for writing instruments, and writing instruments using the same

Abstract

To provide a water-based ink composition for writing instruments that can form handwritten characters and the like that are transparent and glossy, and three-dimensional.SOLUTION: A water-based ink composition for writing instruments contains a film-forming polymer with a lowest film-forming temperature of 50°C or lower, an associative thickener, a colorant, and water. The ink composition has a viscosity of 50 mPa s or more at 20°C and a shear rate of 1.92 sec-1.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to an aqueous ink composition for writing instruments and a writing instrument using the same. [Background technology]

[0002] When writing with a writing instrument filled with ink, the ink usually penetrates the paper surface, resulting in flat, two-dimensional writing. By making this writing three-dimensional, it becomes possible to enjoy unusual handwriting and decorate various materials. Furthermore, since three-dimensional writing can be distinguished by touch, there is also demand for it as a social product.

[0003] One method for forming three-dimensional handwriting involves the use of an aqueous ink composition containing a large amount of three-dimensional film-forming components (for example, Patent Document 1). There is a need for an aqueous ink composition that can produce three-dimensional handwriting that is stronger and more stable. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2005-8873 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention solves the above-mentioned problems and provides a water-based ink composition for writing instruments that is transparent, glossy, and capable of forming three-dimensional handwriting. [Means for solving the problem]

[0006] The aqueous ink composition for writing instruments 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 as follows: 20°C, shear rate 1.92 sec. -1Under these conditions, the pressure is 50 mPa·s or higher.

[0007] The writing instrument according to the present invention contains the above-mentioned aqueous ink composition for writing instruments. [Effects of the Invention]

[0008] The present invention provides a water-based ink composition for writing instruments that is transparent, glossy, and capable of forming three-dimensional handwriting. The resulting handwriting has low surface tackiness, excellent stability, minimal cracking, and superior strength. [Brief explanation of the drawing]

[0009] [Figure 1] This is a longitudinal cross-sectional view of an example of a capped pressurized ballpoint pen. [Figure 2] This is a vertical cross-sectional view of the ballpoint pen shown in Figure 1 with the cap removed. [Figure 3] This is an explanatory diagram showing a writing instrument with the cap fitted to the rear end of the barrel (pressurized state). [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described in detail below. In this specification, unless otherwise specified, "parts," "%," and "ratio" used to indicate formulations are based on mass, and the content refers to the mass percentage of the constituent components based on the mass of the ink composition.

[0011] <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 less, an associative thickener, a colorant, and water. The viscosity of the ink composition is measured at 20°C and a shear rate of 1.92 sec. -1Under the condition of (0.5 rpm), the viscosity is 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 also preferably 10000 mPa·s or less, and more preferably 8000 mPa·s or less. If the viscosity is within the above range, it is possible to obtain stable ink ejection from the pen tip and sufficiently three-dimensional handwriting. The solid content ratio of the ink composition is preferably 10 to 50% by mass, and 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, then at 20°C and a shear rate of 1.92 sec, -1 Under these conditions, the ink viscosity can be easily set to 50 mPa·s or higher, allowing for the formation of handwriting with excellent three-dimensionality. Furthermore, the three-dimensionality of the handwriting can be maintained even after the ink dries.

[0012] In order to form three-dimensional writing lines, the ink composition according to the present invention preferably has a higher viscosity and solid content ratio than the ink compositions for writing instruments that are commonly used, as described above.

[0013] The ink composition according to the present invention is used in writing instruments, and a preferred embodiment of the present invention is a ballpoint pen. When a ballpoint pen contains the ink composition according to the present invention, it is preferable to obtain good ink ejection performance during writing. Therefore, the viscosity of the ink composition is determined at 20°C and a shear rate of 192 sec. -1 Under the conditions of (50 rpm), the pressure 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, considering that it is possible to form a three-dimensional handwriting while obtaining better ink ejection performance than that of the pen tip of a ballpoint pen, it is preferable that the viscosity of the ink composition at rest and the viscosity gradient during flow are a certain level or more, that is, the viscosity ratio of the ink composition at high shear and low shear is a certain level or more. Therefore, the viscosity ratio of the ink composition at high shear and low shear (viscosity under the condition of 20°C and shear rate of 1.92 sec -1 / viscosity under the condition of 20°C and shear rate of 192 sec -1 ) is preferably 10 or more, more preferably 20 or more, still more preferably 40 or more, still more preferably 45 or more, and also preferably 100 or less, more preferably 80 or less. Also, when the ink composition of the present invention is used as an ink composition for a ballpoint pen, considering that good ink ejection performance can be obtained from the start of writing and a three-dimensional handwriting can be obtained, the viscosity ratio of the ink composition (viscosity under the condition of 20°C and shear rate of 1.92 sec -1 / viscosity under the condition of 20°C and 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 also preferably 20 or less, more preferably 10 or less.

[0014] [Film-forming polymer] The ink composition according to the present invention includes a film-forming polymer (hereinafter sometimes referred to as a film-forming polymer) having a minimum film-forming temperature of 50°C or less. 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 exists in the form of particles without dissolving in the ink composition, and during writing, water evaporates and the particles bind to each other to form a film.

[0015] The minimum film-forming temperature (MFT) refers to the lowest temperature at which a film-forming polymer forms 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 lower. Furthermore, considering the suppression of crack formation in the resulting handwriting, it is more preferably 30°C or lower, and even more preferably 0°C or lower.

[0016] Examples of film-forming polymers include acrylic resins, urethane resins, vinyl resins, and styrene resins. Among these, acrylic resins or urethane resins are preferred because they have good compatibility with the associated thickeners described later, particularly urethane associated thickeners. More preferably, acrylic resins are preferred, and even more preferably, acrylic resins or styrene-acrylic resins are preferred, as they easily provide an ink thickening effect, improve ink dispersion stability, and enable the stable formation of three-dimensional handwriting. Two or more film-forming polymers can also be combined.

[0017] The mass-average molecular weight of the film-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 thereafter.

[0018] When manufacturing the ink composition according to the present invention, the film-forming polymer may be added in the form of a dispersion, such as an emulsion, dispersed in water (using a dispersant if necessary). Adding the film-forming polymer to the ink composition in the form of an emulsion is also a preferred embodiment.

[0019] 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), and "NeoCryl "XK-190", "NeoCryl XK-12", "NeoCryl XK-16", "NeoCryl XK-30", "NeoCryl XK-36", "NeoCryl XK-188", "NeoCryl XK-240", "NeoCryl A-2092", "NeoCryl BT-62", "NeoCryl BT-20", "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 Kasei Co., Ltd.), "MovinylLDM7582 (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.), "Vinibran 271", "Vinibran 278", "Vinibran 715S", "Vinibran 735", "Vinibran 603EM", "Vinibran 603HA", "Vinibran 603SK", and "Vinibran 603VS" (Nisshin Chemical Industry Co., Ltd.).

[0020] The film-forming polymer content is preferably 1 to 50% by mass, based on the total mass of the ink composition, more preferably 1 to 30% by mass, even more preferably 10 to 30% by mass, even more preferably 15 to 30% by mass, and most preferably 15 to 28% by mass, taking into consideration the discharge properties. If the film-forming polymer content is within the above range, it is possible to form handwriting with excellent three-dimensionality, where the raised appearance of the handwriting can be clearly seen. Multiple types of MFTs can be combined as film-forming polymers.

[0021] [Associative thickeners] The ink composition according to the present invention comprises an associated thickener. The associated thickener has a hydrophilic group as its backbone and hydrophobic groups on its side chains or terminals. In an aqueous medium, the associated thickener remains stable in the aqueous medium due to the interaction between its hydrophilic group and the aqueous medium, while one hydrophobic group associates and adsorbs to film-forming polymers or colorant particles, and the other hydrophobic group further associates and adsorbs to hydrophobic groups of other molecules or to film-forming polymers or colorant particles, thereby forming a weak crosslinked structure and achieving an ink thickening effect.

[0022] Examples of associated thickeners include urethane-based associated thickeners, polyacrylic acid-based associated thickeners, polyvinyl-based associated thickeners, polyether-based associated thickeners, polyglycol-based associated thickeners, maleic anhydride copolymer-based associated thickeners, polyamide-based associated thickeners, polyester-based associated thickeners, hydrophobic cellulose ester-based associated thickeners, and polycarboxylic acid-based associated thickeners. From the viewpoint of improving the glossiness of the film, urethane-based associated thickeners are preferred.

[0023] 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 to hydrophobic groups of other molecules, film-forming polymers, or colorant particles, and by associating the ends of the thickeners with each other. Examples of such urethane-based associative thickeners include compounds having urethane bonds and polyether chains in their molecules, i.e., compounds having both a urethane structure and a polyether structure.

[0024] Examples of commercially available urethane-based association-type thickeners include: "Adekanol UH-756VF", "Adekanol UH-462", "Adekanol UH-420", "Adekanol UH-472", "Adekanol UH-540", "Adekanol 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" (Sunopco Co., Ltd.), "Chixostar" (Nippon Materials Technology Co., Ltd.), "OPTIFLO T1000", "OPTIFLO L1400", "OPTIFLO M2600VF", "OPTIFLO Examples include "H7500VF" (Big Chemie Japan Co., Ltd.).

[0025] Furthermore, when using the ink composition of the present invention as an ink composition for ballpoint pens, it is preferable to use an aggregate thickener that imparts thixotropic viscosity among aggregate thickeners. This is because it is easier to set the viscosity ratio of the ink composition at high shear and low shear to a desired range, and it is possible to form a handwriting with excellent three-dimensionality while maintaining good ink discharge from the pen tip.

[0026] The mass-average molecular weight of the associated thickener is preferably 500 to 500,000, more preferably 800 to 300,000, and even more preferably 1,000 to 100,000.

[0027] The content of the aggregate thickener is preferably 0.01 to 5% by mass, more preferably 0.05 to 1% by mass, and more preferably 0.05 to 0.8% by mass, based on the total mass of the ink composition. When the content of the aggregate thickener is within the above range, it is easy to bring appropriate viscosity to the ink composition, and it is possible to form handwriting with excellent three-dimensionality in which the raised shape of the handwriting can be clearly seen. Furthermore, considering the need to impart sufficient viscosity to the ink composition and obtain handwriting with excellent three-dimensionality, the mass ratio of the associated thickener to the film-forming polymer (associated 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.

[0028] [Coloring agent] The ink composition according to the present invention comprises a coloring agent. Any conventionally known pigment or dye can be used. In particular, the coloring agent is preferably a pigment because it is easier to obtain brushstrokes with good color development and excellent three-dimensionality.

[0029] Examples of pigments include inorganic, organic, and processed pigments. Specifically, examples include carbon black, aniline black, ultramarine, lead yellow, titanium dioxide, iron oxide, phthalocyanine pigments, azo pigments, quinacridone pigments, quinophthalone pigments, styrene pigments, triphenylmethane pigments, perinone pigments, perylene pigments, dioxazine pigments, as well as luminescent pigments, microcapsule pigments, and colored resin pigments. In addition, the pigment may be pre-dispersed in a medium using a pigment dispersant such as a surfactant, or a water-dispersible pigment product may be used.

[0030] Furthermore, among pigments, it is preferable to use colored resin pigments. As described later, since colored resin pigments are resin particles colored with a coloring agent, associated thickeners readily associate and adsorb to them, making it easier to obtain an ink thickening effect. This makes it easier to bring appropriate viscosity to the ink composition, enabling the stable formation of three-dimensional handwriting. Moreover, using colored resin pigments makes it easier to maintain excellent transparency and gloss of the handwriting. In the present invention, colored resin particle pigment refers to resin particles that have been colored with a coloring agent. The coloring agent 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 the thermal environment. Examples of commercially available products containing colored resin particles include the Shinloihi Color series (manufactured by Shinloihi Co., Ltd.), the Lumicol series (manufactured by Nippon Fluorescent Chemicals Co., Ltd.), the LM series (manufactured by Fuji Pigment Co., Ltd.), and the Epocolor series (manufactured by Nippon Shokubai Co., Ltd.). Specifically, examples of the Lumicol series include NKW-2317H, NKW-6307H, NKW-2308H, NKW-2302H, NKW-2305H, and NKW-6305H. Other products in the Shinlohi Color series include Shinlohi Color Base SW-11, SW-12, SW-13, SW-14, SW-15, 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.

[0031] Examples of dyes include phthalocyanine dyes, pyrazolone dyes, nigrosine dyes, anthraquinone dyes, and azo dyes.

[0032] The colorant content varies depending on the type, but is preferably 0.05 to 5% by mass, and more preferably 0.1 to 1% by mass, based on the total mass of the ink composition. Colorants can be used individually or in combination of two or more types as appropriate.

[0033] [water] The ink composition according to the present invention contains water. There are no particular restrictions on the water, and for example, tap water, ion-exchanged water, ultrafiltration water, distilled water, or the like can be used. The water content is preferably 10 to 90% by mass, more preferably 50 to 70% by mass, based on the total mass of the ink composition.

[0034] (Other additives) The ink composition of the present invention essentially comprises the above-described components (film-forming polymer, associative thickener, colorant, and water), but may contain components other than those described above as necessary.

[0035] [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 is not particularly limited as long as it can be dissolved in water, but acrylic resins, polyester resins, polyethylene oxide, and polyvinylpyrrolidone are preferably used, and it is possible to obtain a handwriting with excellent three-dimensionality while maintaining the transparency and glossiness of the handwriting. When the content of the water-soluble resin increases, the three-dimensional shape of the handwriting tends to be better maintained, but the adhesiveness of the handwriting surface tends to increase, and the value of the above viscosity ratio (viscosity under the condition of shear rate 1.92 sec -1 / viscosity under the condition of shear rate 192 sec -1 is likely to decrease. Considering these factors, the content of the water-soluble resin is preferably 0.1 to 10% by mass, more preferably 1 to 5% by mass, based on the total mass of the ink composition. Also, considering obtaining a good balance between maintaining the three-dimensionality of the handwriting and suppressing the adhesiveness of the handwriting surface while improving the ink ejection property, the content of the water-soluble resin is preferably 0.5 to 30% by mass, 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 million, still more preferably 20,000 to 150,000, and even more preferably 20,000 to 80,000.

[0036] [Water-soluble organic solvents] 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 when drying, improve dispersion stability, and further improve the drying properties of the ink and suppress the stickiness of the formed ink. Examples include (i) glycols such as ethylene glycol, butylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, or glycerin; (ii) alcohols such as methanol, ethanol, 1-propanol, isopropanol, isobutanol, t-butanol, propagyl alcohol, allyl alcohol, 3-methyl-1-buty-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, or 3-methoxy-3-methylbutanol. These can be used individually or as mixtures of two or more. Furthermore, considering the improvement of ink drying properties, it is preferable to use a vapor pressure of 3 kPa or higher at 20°C, and more preferably 4 kPa or higher. Specifically, examples include methanol, ethanol, isopropanol, ethylene glycol dimethyl ether, and propylene glycol dimethyl ether.

[0037] Considering the need to maintain the three-dimensional shape while balancing and improving writing performance and ink drying speed, 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.

[0038] Furthermore, 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's physical properties and functions.

[0039] 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.

[0040] Examples of preservatives include phenol, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl parahydroxybenzoate, 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.

[0041] Examples of rust inhibitors include benzotriazole and its derivatives, toltriazole, dicyclohexylammonium nitride, diisopropylammonium nitride, sodium thiosulfate, saponin, or dialkylthiourea.

[0042] Examples of chelating agents include ethylenediaminetetraacetic acid (EDTA), hydroxyethylenediaminetriacetic acid (HEDTA), glycol etherdiaminetetraacetic acid (GEDTA), nitrilotriacetic acid (NTA), hydroxyethyliminodiacetic acid (HIDA), dihydroxyethylglycine (DHEG), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA), and their alkali metal salts, ammonium salts, or amine salts.

[0043] Furthermore, the present invention may also contain humectants other than water-soluble organic solvents. Examples include urea, sorbitol, dextrin, N,N,N-trialkyl amino acids such as trimethylglycine, and hyaluronic acids, which can be suitably used.

[0044] Furthermore, nonionic surfactants, anionic surfactants, cationic surfactants, surfactants containing acetylene bonds in their structure, and fluorinated surfactants can also be added. These features improve wettability to the ink reservoir and ink flow regulator, resulting in smooth ink ejection and thus producing good handwriting. Additionally, defoaming agents can be added. Lubricants such as phosphate ester surfactants and fatty acids can also be added.

[0045] <Method for manufacturing ink composition> The ink composition according to the present invention can be manufactured by any conventionally known method. Specifically, it can be manufactured by blending the required amounts of each component and mixing them using various stirrers such as magnetic hot stirrers, propeller stirrers, homogenizer stirrers, homodispersers, homomixers, and planetary stirrers, as well as various dispersers such as bead mills.

[0046] <Writing instruments> The writing instrument according to the present invention contains the above-mentioned ink composition. The structure and shape of the writing instrument itself that is filled with the aqueous ink composition according to the present invention are not particularly limited, and conventional general-purpose ones can be used, but it is preferable to use it in a ballpoint pen with a ballpoint pen tip or the like as the pen tip. It is even more preferable to use the ink composition according to the present invention in a pressurized ballpoint pen. This is because using the ink composition according to the present invention, which tends to have high viscosity, in a pressurized ballpoint pen results in good dispensing properties and can form handwriting with excellent three-dimensionality. Examples of pressurized ballpoint pens include pressurized ballpoint pens that seal pressurized gas in the ink reservoir and use the pressure of this pressurized gas to push the ink composition toward the tip, retractable pressurized ballpoint pens that compress the space on the rear end of the ink composition through actions such as clicking, attaching a cap, or the movement of the pen tip due to writing pressure, and use the pressure from this compression to push the ink composition toward the tip, cap-type pressurized ballpoint pens equipped with a cap that covers the pen tip, and writing pressure pressurized ballpoint pens. Since the ink composition according to the present invention tends to have a high solid content ratio, a cap-type pressurized ballpoint pen that can seal the pen tip is more preferable when considering resistance to drying out.

[0047] The pressure applied to the ink composition filled inside the ink container from the rear end of the ink container by pressurization is preferably greater than atmospheric pressure, specifically, it is preferably greater than atmospheric pressure and 1.5 times or less. More specifically, if atmospheric pressure is 1000 hPa, it is preferably higher than 1000 hPa and 1500 hPa or less, and more preferably higher than 1000 hPa and 1200 hPa or less. This allows for optimal ink consumption while suppressing ink leakage from the front end of the tip, and improves handwriting quality and density, such as achieving sufficient three-dimensionality.

[0048] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0049] <Example 1> A base ink was prepared by heating and stirring the following materials, excluding the association-type thickener, in the following proportions using a magnetic stirrer at room temperature. Then, the following association-type thickener was added to the prepared base ink in the following proportions, and the mixture was thoroughly mixed and stirred using a homogenizer stirrer until a uniform state was achieved to obtain the ink composition of Example 1. • Acrylic resin A (Acrylic emulsion "NeoCryl XK-190" (Kusumoto Chemical Co., Ltd.), solids content 45% by mass, MFT < 0℃) 55 parts by mass • Urethane-based thickener A (associative thickener "Adekanol 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" (Shinloihi Co., Ltd.)) 2 parts by mass • Triethanolamine 0.5 parts by mass ·Water 42 parts by mass

[0050] <Examples 2-11 and Comparative Examples 1-3> Examples 2-11 and Comparative Examples 1-3 were prepared using the same method as in Example 1, except that the types and amounts of components in the ink composition were changed to those shown in Table 1. The numerical values ​​for composition in the table represent parts by mass.

[0051] [Table 1] In the table, • Acrylic resin A: Acrylic emulsion "NeoCryl XK-190" (Kusumoto Chemical Co., Ltd.), solids content 45% by mass, MFT < 0℃, • Acrylic resin B: Acrylic emulsion "Joncryl PDX-7430" (BASF Japan Ltd.), solids content 38% by mass, MFT 44℃, • Acrylic resin C: Acrylic emulsion "Movinyl LDM7582" (Nippon Synthetic Chemical Industry Co., Ltd.), solids content 46% by mass, MFT 20℃, • Acrylic resin D: Acrylic emulsion "NeoCryl A-550" (Kusumoto Chemical Co., Ltd.), solids content 40% by mass, MFT > 100℃, • Styrene-acrylic resin A: Acrylic emulsion "NeoCryl BT-62" (Kusumoto Chemical Co., Ltd.), solids content 40% by mass, MFT 10℃, • Styrene-acrylic resin B: Acrylic emulsion "NeoCryl A-662" (Kusumoto Chemical Co., Ltd.), solids content 40% by mass, MFT > 90℃, • Urethane-based thickener A: Associative thickener "Adekanol UH-756VF" (ADEKA Corporation), solid content 32% by mass, • Urethane-based thickener B: Associative thickener "SN Thickener 665T" (Sunopco Co., Ltd.), solids content 30% by mass, thixotropic • Urethane-based thickener C: Associative thickener "SN Thickener 660T" (Sunopco Co., Ltd.), solids content 20% by mass, thixotropic • Urethane-based thickener D: Associative thickener "Adekanol UH-462" (ADEKA Corporation), solid content 30% by mass, • Acrylic thickener A: High molecular weight thickener "SN Thickener 618" (Sunopco Co., Ltd.), solids content 13% by mass, • Colored resin particles A: 30% by mass aqueous dispersion of fluorescent colored resin particles (fluorescent pink), "SF-5017" (Shinloihi Co., Ltd.) • Colored resin particles B: 44% by mass aqueous dispersion of fluorescent colored resin particles (fluorescent pink), "Lumicol NKW-2317H" (Nippon Fluorescent Chemicals 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 mass aqueous solution.

[0052] [viscosity] The viscosity of the obtained ink composition was measured using an E-type rotational viscometer (model: DV-II+Pro, rotor: CPE-42, manufactured by Brookfield Corporation) at a shear rate of 1.92 sec in a 20°C environment. -1 The ink viscosity was measured under the condition of a rotation speed of 0.5 rpm. The results are shown in Table 1.

[0053] [Viscosity ratio] The viscosity of the obtained ink composition was measured using an E-type rotational viscometer (model: DV-II+Pro, rotor: CPE-42, manufactured by Brookfield Corporation) at 20°C and a shear rate of 192 sec. -1The ink viscosity was measured under the condition of a rotation speed of 50 rpm. Examples 3, 4, 8, and 10 could not be measured because they exceeded the measurement limit of 128 mPa·s. The above shear rate is 1.92 sec. -1 Viscosity and shear rate at 0.5 rpm (192 sec) -1 The viscosity at 50 rpm was calculated, and the viscosity ratio (0.5 rpm / 50 rpm) was determined. The results are shown in Table 1.

[0054] Furthermore, the viscosity of the obtained ink composition was measured using an E-type rotational viscometer (model: DV-II+Pro, rotor: CPE-42, manufactured by Brookfield Corporation) at 20°C and a shear rate of 19.2 sec. -1 The ink viscosity was measured under the condition of a rotation speed of 5 rpm. The above shear rate is 1.92 sec. -1 Viscosity and shear rate at 0.5 rpm (19.2 sec) -1 The viscosity at (5 rpm) was calculated, and the viscosity ratio (0.5 rpm / 5 rpm) was determined to be 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.

[0055] The ink compositions of the examples and comparative examples were filled into the ballpoint pen refill 7 of the cap-type pressurized ballpoint pen 1, and the ink ejection performance under pressure was confirmed. When the ink composition of Example 10 was used, ejection was not possible, so in subsequent handwriting evaluations, the ink composition was written using a decoration pen. The other ink compositions were able to be written with the above-mentioned pressurized ballpoint pen, and in subsequent handwriting evaluations, the above-mentioned pressurized ballpoint pen was used for writing. Regarding the ink compositions of the examples, the ink compositions of Examples 1, 2, 6, and 7 had the best ejection performance, followed by Examples 3, 5, 8, 9, and 11.

[0056] Figures 1 to 3 show a cap-type pressurized ballpoint pen 1. The cap-type pressurized ballpoint pen 1 has a ballpoint pen refill 7 disposed inside a barrel body which connects a front barrel 2 with a grip member 14 attached to the gripping part and a rear barrel 3. Furthermore, the cap-type pressurized ballpoint pen 1 has a translucent cap 4, obtained by injection molding PP resin, which is detachably attached to the front barrel 2 by fitting a fitting projection formed on the inner wall of the cap 4 over a fitting projection 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 sealing member provided inside the cap.

[0057] At the front end of the ink reservoir 8 of the ballpoint pen refill 7, a ballpoint pen tip 10, which rotatably holds a 1.0 mm diameter ball, is attached via a tip holder 9. Furthermore, a tail plug 11 with an air vent that connects the inside and outside is attached to the rear end of the ink reservoir cylinder 8. The inside of the ink reservoir 8 is filled with a water-based ink composition 12 for writing instruments consisting of the ink mixture described above, and an ink-following body 13. Although not shown in the diagram, a coil spring is installed behind the ball to constantly press the ball against the inner wall of the front end of the tip.

[0058] Furthermore, 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-following body 13 is in communication with the outside air only through the communication hole 3A provided at the rear end of the rear barrel 3, which connects the inside and outside of the writing instrument.

[0059] The pressurizing mechanism, which is activated by the fitting of cap 4, is described in detail below. By fitting the cap 4 onto the rear barrel 3 of the writing instrument body, pressure can be applied to the ink composition 12 filled in the ballpoint pen refill 7 via the ink-following body 13. Specifically, when the rear end of the rear shaft 3 is inserted into the open end of the cap body 5 in the direction of arrow F in the diagram, the inner wall 5A of the cap body 5 and the side wall 3B of the rear shaft 3 first come into contact. At this time, the spaces inside the cap body 5, the rear shaft 3, and the ink reservoir 8 are connected in a sealed state through a communication hole 3A provided at the rear end of the rear shaft 3 that connects the inside and outside. Furthermore, when the cap 4 is advanced in the direction of arrow F in the figure, the sealed space is compressed until the fitting is complete. 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-following body 13. The pressure was 1050 hPa.

[0060] [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 to evaluate three-dimensionality, cracking, gloss, and transparency. The evaluation criteria are as follows. The results obtained are shown in Table 1. Three-dimensional feeling ◎: When the handwriting was touched, a sufficient raised texture could be felt. ○: When the handwriting was touched, a raised texture could be felt. Δ: When touching the handwriting with a finger, a raised texture could be felt, but it was somewhat faint. X: When I touched the handwriting with my finger, I couldn't feel any raised areas. Crack ○: No cracks were found in the handwriting. Δ: Slight cracks were observed in the handwriting. X: Numerous cracks were observed in the handwriting, and it crumbled when touched. Glossy finish ○: Sufficient glossiness was observed in the handwriting. X: Sufficient gloss was not observed in the handwriting. Transparency ○: The handwriting was sufficiently transparent. X: Sufficient transparency could not be confirmed in the handwriting. XX: The handwriting did not exhibit sufficient transparency, and furthermore, cloudiness was observed.

[0061] In the ink composition of Comparative Example 2, the amount of thickener was changed from 4% to only 2% by mass. The evaluation of crack resistance, gloss, and transparency was equivalent to that of Comparative Example 2.

[0062] Regarding the ink compositions of the examples, when the surface tackiness of the handprints was checked by touching them one hour after writing, none of them adhered to the hand, indicating low tackiness. Furthermore, the ink composition of Example 6 showed faster and better drying properties than the ink compositions of the other examples. The resulting writing did not smudge even when rubbed 10 minutes after writing. [Explanation of symbols]

[0063] 1. Capped pressurized ballpoint pen 2 front axle 3 rear axle 3A communication hole 3B Side wall 4 caps 5. Cap body 5A Inner wall 6. Sealing member 7 Ballpoint pen refills 8 ink cartridges 9 Chip holder 10 ballpoint pen tips 11. Tail plug 11A Air vent 12. Ink compositions for writing instruments 13 Ink-following body 14 Grips

Claims

1. A water-based ink composition for writing instruments comprising a film-forming polymer having a minimum film-forming temperature of 50°C or lower, an associate-type thickener, a colorant, and water, The viscosity of the ink composition is 20°C and the shear rate is 1.92 sec. －１ Under these conditions, the pressure is 2,000 mPa·s or higher. Viscosity ratio of the ink composition (at 20°C, shear rate 1.92 sec) －１ Viscosity under the following conditions: 20°C, shear rate 192 sec －１ A water-based ink composition for writing instruments having a viscosity (under certain conditions) of 10 or more and 100 or less.

2. The ink composition according to claim 1, wherein the associated thickener is a urethane-based associated thickener.

3. The ink composition according to claim 1 or 2, wherein the film-forming polymer is an acrylic resin or a urethane resin.

4. The ink composition according to any one of claims 1 to 3, further comprising a water-soluble resin.

5. The ink composition according to any one of claims 1 to 4, wherein the solid content ratio of the ink composition is 10 to 50% by mass.

6. A writing instrument comprising the composition described in any one of claims 1 to 5.

7. The writing instrument according to claim 6, which is a ballpoint pen.

8. A writing instrument according to claim 6 or 7, which is a pressurized ballpoint pen.

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