Aqueous ink composition for writing instrument and writing instrument using the same

Abstract

To provide an aqueous ink composition for a writing instrument and a writing instrument using the same, the ink composition containing a thixotropy-imparting agent capable of exhibiting a stable thickening action without being inhibited in thickening by an ionic material such as a metallic ion, unlike conventional thixotropy-imparting agents, thereby exhibiting a thickening effect, suppressing ink leakage, providing excellent writing feel, suppressing blurred writing, and achieving excellent writing properties.SOLUTION: The present invention provides an aqueous ink composition for a writing instrument comprising a coloring agent, a solvent, and an (acrylic acid / acrylic acid perfluoroalkyl) copolymer, and a writing instrument using the same.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based ink composition for a writing instrument and a writing instrument using the same. [Background technology]

[0002] Conventionally, aqueous ink compositions and oil-based ink compositions have been used as ink compositions for writing instruments, and in particular, ballpoint pens include aqueous ballpoint pens filled with aqueous ink compositions and oil-based ballpoint pen compositions filled with oil-based ink compositions. Among these, gel ink compositions, which are ink compositions imparted with shear thinning properties, are known, and various proposals have been made regarding agents for imparting shear thinning properties thereto.

[0003] As shear thinning agents, polysaccharides such as xanthan gum, welan gum, and diutan gum have been proposed for aqueous ink compositions, while fatty acid amide waxes and hydrogenated castor oil have been proposed for oil-based ink compositions.

[0004] Techniques using xanthan gum, welan gum, and diutan gum as ink compositions for such writing instruments are disclosed in Japanese Patent Publication No. 64-8673, "Oil-based ink composition for writing instruments," Japanese Patent Application Laid-Open No. 4-214782, "Ink composition for aqueous ballpoint pens," and Japanese Patent Application Laid-Open No. 2005-068363, "Aqueous ink composition and aqueous ballpoint pen using the same," and techniques using fatty acid amide wax and hydrogenated castor oil are disclosed in Japanese Patent Application Laid-Open Nos. 7-196972 and 7-268268. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] "Special Publication No. 64-8673" [Patent Document 2] "Unexamined Japanese Patent Publication No. 4-214782" [Patent Document 3] "JP Patent Publication No. 2005-068363" [Patent Document 4] "Unexamined Japanese Patent Publication No. 7-196972" [Patent Document 5] "Unexamined Japanese Patent Publication No. 7-268268" Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Documents 1 to 3, shear thinning properties can be imparted and a certain degree of thickening effect can be obtained, but depending on the type of colorant, type of surfactant, other ink components, and metal material of the ballpoint pen tip, thickening can easily be inhibited by ionic substances (metal ions, etc.) present in the ink, and the desired thickening effect may not be obtained. Furthermore, in Patent Documents 4 and 5, hydrogenated castor oil and fatty acid amide wax can provide a certain degree of thickening effect, but the ink viscosity increases when the ink is stationary, which affects the writing feel, tends to deteriorate ink tracking, and can cause smearing of handwriting, leaving room for improvement.

[0007] The object of the present invention is to provide an aqueous ink composition for a writing instrument having excellent writing properties, which contains a shear thinning agent that, unlike conventional shear thinning agents, is capable of stable thickening without being inhibited by ionic substances (metal ions, etc.), thereby exerting a thickening effect, suppressing ink leakage, improving the writing feel, and suppressing smearing of handwriting, and to provide a writing instrument using the same. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention "1. An ink composition for a writing instrument, comprising a colorant, a solvent, and an (acrylic acid / perfluoroalkyl acrylate) copolymer. 2. The ink composition for a writing instrument according to item 1, wherein the content of the (acrylic acid / perfluoroalkyl acrylate) copolymer is 0.1 to 10% by mass based on the total amount of the ink composition. 3. The ink composition for a writing instrument according to item 1 or 2, wherein the (acrylic acid / perfluoroalkyl acrylate) copolymer has as a constituent an acrylic acid ester represented by the general formula (Chemical Formula 1). [ka] 4. An ink composition for a writing instrument according to any one of items 1 to 3, characterized in that the (acrylic acid / perfluoroalkyl acrylate) copolymer has as a constituent component acrylic acid represented by the general formula (Chemical Formula 2). [ka] 5. The ink composition for a writing instrument according to any one of items 1 to 4, wherein the (acrylic acid / perfluoroalkyl acrylate) copolymer contains a crosslinking agent as a constituent component. 6. The ink composition for a writing instrument according to any one of items 1 to 5, characterized in that the ink composition for a writing instrument contains a surfactant. 7. The ink composition for a writing instrument according to any one of items 1 to 6, characterized in that the ink composition for a writing instrument contains resin particles. 8. A writing instrument characterized by containing the ink composition for a writing instrument according to any one of items 1 to 7. [Effects of the Invention]

[0009] The present invention has made it possible to obtain an aqueous ink composition for a writing instrument that is excellent in writing performance, and a writing instrument using the same, by comprising a colorant, a solvent, and an (acrylic acid / perfluoroalkyl acrylate) copolymer, and by having a stable gel structure even when ionic substances (such as metal ions) are present in the ink, it imparts shear thinning properties, and by increasing the ink viscosity at rest, it suppresses ink leakage from the gap at the writing tip (in the case of a ballpoint pen, ink leakage from the gap between the ball and the tip tip), and by lowering the ink viscosity during writing, it improves the writing feel and suppresses smearing of handwriting. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention is characterized in that the aqueous ink composition for a writing instrument comprises a colorant, a solvent, and an (acrylic acid / perfluoroalkyl acrylate) copolymer.

[0011] It was found that by including a colorant, a solvent, and an (acrylic acid / perfluoroalkyl acrylate) copolymer in an aqueous ink composition for writing instruments, the ink has a stable gel structure, which imparts shear thinning properties, suppresses ink leakage from the gaps at the writing tip, improves the writing feel, suppresses smearing of handwriting, and provides excellent writing properties.

[0012] ((acrylic acid / perfluoroalkyl acrylate) copolymer) The (acrylic acid / perfluoroalkyl acrylate) copolymer used in the present invention is a copolymer having at least an acrylic acid ester and an acrylic acid (methacrylic acid) as constituent components, and having a constituent unit derived from an acrylic acid ester and a constituent unit derived from acrylic acid (methacrylic acid). Unlike conventional shear thinning agents, the (acrylic acid / perfluoroalkyl acrylate) copolymer contains perfluoroalkyl acrylate (an acrylic ester containing fluorine atoms) as a constituent component, and is therefore capable of forming a stable network structure and a gel structure without being inhibited by ionic substances (metal ions) in the ink, making it possible to thicken the ink. Therefore, by forming a stable network structure and a gel structure, the ink viscosity at rest can be set high, and by suppressing the flow of the ink, ink leakage from the gap at the writing tip (in the case of a ballpoint pen, ink leakage from the gap between the ball and the tip tip) can be suppressed, thereby suppressing ink leakage from the gap at the writing tip (ink leakage from the gap between the ball and the tip tip). Furthermore, because it has a weak network structure, the gel structure temporarily dissolves due to impacts such as shearing during writing, thereby lowering the ink viscosity and making it possible to maintain a good writing feel. In particular, when used in a ballpoint pen, it is presumed that the effect of easily improving the writing feel can be obtained due to impacts such as shearing of the ball during writing, and therefore it is preferable to use it as an ink composition for a ballpoint pen because it is effective. Furthermore, the (acrylic acid / perfluoroalkyl acrylate) copolymer is preferably an (acrylic acid / perfluoroalkyl acrylate) crosspolymer. This is effective and preferred because the crosspolymer facilitates the formation of a three-dimensional network structure, and a denser three-dimensional network structure facilitates the formation of a more stable gel structure, and is particularly effective and preferred when used as an ink composition for a ballpoint pen. Furthermore, when a pigment is used as the colorant, the gel structure makes it easier to maintain pigment dispersibility, and therefore the colorant can be used more suitably and is preferable.

[0013] Furthermore, with regard to the (acrylic acid / perfluoroalkyl acrylate) copolymer, it is preferable that the perfluoroalkyl acrylate (acrylic ester having a fluorine atom) component contains an acrylic ester represented by the general formula (Chemical Formula 1). This is because, unlike conventional shear thinning agents, the component is an acrylic ester having a fluorine atom, and therefore, even if ionic substances (metal ions, etc.) such as colorants and surfactants are present in the ink components, the ink is not inhibited from thickening, and a stable network structure is formed, and the ink viscosity can be increased by forming a gel structure. Setting the ink viscosity at rest at a high level has the effect of suppressing ink leakage from the gap at the writing tip (ink leakage from the gap between the ball and the tip tip), and because the network structure is weak, the gel structure temporarily dissolves due to impacts such as shear during writing, thereby lowering the ink viscosity and enabling the ink to write smoothly. [ka]

[0014] In addition, the acrylic ester represented by the general formula (Chemical Formula 1), which is a component of the (acrylic acid / perfluoroalkyl acrylate) copolymer, forms a stable network structure, which makes it easy to stably thicken the ink viscosity. A is preferably a hydrogen atom, and m is preferably 2 to 4, more preferably 2 or 3, and even more preferably 2.

[0015] Specific examples of the acrylic acid ester represented by the general formula (Chemical Formula 1) include 2-perfluorohexylethyl (meth)acrylate, 3-perfluorohexylpropyl (meth)acrylate, 4-perfluorohexylbutyl (meth)acrylate, etc. In the above specific examples, (meth)acrylate means acrylate and / or methacrylate. Furthermore, among the acrylic acid esters represented by the general formula (Chemical Formula 1), 2-perfluorohexylethyl (meth)acrylate is preferred because it forms a more stable network structure, thereby preventing ink leakage from the gaps at the writing tip and making it easier to maintain a good writing feel. From further considerations, 2-perfluorohexylethyl acrylate is more preferred.

[0016] Furthermore, with regard to the (acrylic acid / perfluoroalkyl acrylate) copolymer, it is preferable that the acrylic acid component contains the acrylic acid represented by the general formula (Chemical Formula 2). This is because it is easy to form a more stable network structure and a weak network structure, which makes it easier to suppress ink leakage from the gaps at the writing tip and maintain a good writing feel. In particular, it is effective when used as an ink composition for ballpoint pens, and is therefore preferable. Furthermore, taking the above-mentioned effects into consideration, it is preferable that the R B is preferably a hydrogen atom or an alkyl having 1 to 3 carbon atoms, and further considering, R B is preferably a hydrogen atom or an alkyl having one carbon atom, and in consideration of the ease of forming a more stable network structure, R B is preferably a hydrogen atom. Specific examples of the acrylic ester represented by the general formula (Chemical Formula 2) include acrylic acid and methacrylic acid, and in consideration of the above-mentioned effects, acrylic acid and methacrylic acid are preferred, and in consideration of the above-mentioned effects, acrylic acid is more preferred. [ka]

[0017] The (acrylic acid / perfluoroalkyl acrylate) copolymer used in the present invention is preferably a copolymer having, as constituent components, at least an acrylic acid ester represented by general formula (Chemical Formula 1) and an acrylic acid represented by general formula (Chemical Formula 2), because this makes it easier to obtain the above-mentioned effects, and is preferably a crosspolymer having, as constituent components, at least an acrylic acid ester represented by general formula (Chemical Formula 1) and an acrylic acid represented by general formula (Chemical Formula 2). This is because a three-dimensional network structure is easily formed, and a denser three-dimensional network structure makes it easier to form a more stable gel structure, and is particularly effective when used as an ink composition for a ballpoint pen, and is therefore preferred. Furthermore, the weight ratio of the acrylic acid ester (Chemical Formula 1) to the acrylic acid (Chemical Formula 2) is preferably (Chemical Formula 1) / (Chemical Formula 2)=0.1 to 1, more preferably (Chemical Formula 1) / (Chemical Formula 2)=0.1 to 0.5, and most preferably 0.15 to 0.4, taking into consideration ink thickening properties (ink viscosity development) and stability in the ink.

[0018] The (acrylic acid / perfluoroalkyl acrylate) copolymer used in the present invention preferably contains a crosslinking agent as a constituent component in addition to the acrylic acid and perfluoroalkyl acrylate described above. This is because the inclusion of a crosslinking agent facilitates crosslinking of the acrylic acid and perfluoroalkyl acrylate, which facilitates ink thickening (development of ink viscosity) and the formation of a stable network structure, thereby making it easier to achieve the effects of the present invention. In particular, a copolymer containing an acrylic acid ester (Chemical Formula 1), an acrylic acid (Chemical Formula 2), and a crosslinking agent as constituent components is preferred, and a crosspolymer containing an acrylic acid ester (Chemical Formula 1), an acrylic acid (Chemical Formula 2), and a crosslinking agent as constituent components is preferred. This facilitates the formation of a three-dimensional network structure, and the formation of a denser three-dimensional network structure facilitates the formation of a more stable gel structure. This is particularly effective when used as an ink composition for ballpoint pens, and is therefore preferred.

[0019] Examples of the crosslinking agent include 1,10-decanediol diacrylate, pentaerythritol triallyl ether, diethylene glycol diallyl ether, N,N'-methylenebisacrylamide, dialkylene glycol diallyl ethers such as diethylene glycol diallyl ether, dipropylene glycol diallyl ether, and dibutylene glycol diallyl ether, and polyalkylene glycol diallyl ethers such as polyethylene glycol diallyl ether, polypropylene glycol diallyl ether, and polybutylene glycol diallyl ether. Among these crosslinking agents, 1,10-decanediol diacrylate, pentaerythritol triallyl ether, diethylene glycol diallyl ether, and N,N'-methylenebisacrylamide are preferred in view of their ease of thickening the ink (developing ink viscosity) and of facilitating the formation of a stable network structure, thereby making it easier to achieve the effects of the present invention, and from this perspective, diethylene glycol diallyl ether is even more preferred. Therefore, in the present invention, a crosspolymer containing acrylic acid ester (Chemical Formula 1), acrylic acid (Chemical Formula 2), and diethylene glycol diallyl ether as constituent components is preferably used, and specifically, (acrylic acid / perfluorohexylethyl acrylate) crosspolymer is preferred, with acrylic acid-4,7,10-trioxatrideca-1,12-diene-3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl acrylate copolymer (trade name: Soltrela, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) being most preferred.

[0020] Considering the ink thickening (development of ink viscosity) and the ease of forming a stable network structure, the proportion (weight ratio) of the crosslinking agent in the copolymer of the present invention is preferably 0.0001 to 2 parts by weight, more preferably 0.1 to 1.5 parts by weight, more preferably 0.1 to 1 part by weight, and even more preferably 0.15 to 0.5 parts by weight, relative to 100 parts by weight of the total of the acrylic acid ester and acrylic acid.

[0021] As the constituent components of the (acrylic acid / perfluoroalkyl acrylate) copolymer of the present invention, in addition to the above-mentioned acrylic esters, acrylic acid, and crosslinking agents, (meth)acrylic esters such as methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate may also be used.

[0022] The content of the (acrylic acid / perfluoroalkyl acrylate) copolymer is preferably 0.01 to 10% by mass relative to the total amount of the ink composition. This is because if it is less than 0.01% by mass, it is difficult to achieve the desired ink thickening and to suppress ink leakage, and if it exceeds 10% by mass, the ink viscosity increases, which tends to deteriorate the writing feel and ink followability. From this perspective, 0.01 to 5% by mass is preferable. Furthermore, taking the above effects into consideration, the content is preferably 0.01 to 5 mass% for aqueous ink compositions, more preferably 0.1 to 3 mass% for oil-based ink compositions, and more preferably 0.5 to 5 mass% for oil-based ink compositions, more preferably 0.5 to 4 mass% for oil-based ink compositions, and most preferably 0.8 to 3.5 mass% for oil-based ink compositions.

[0023] (solvent) The solvent used in the aqueous ink composition for writing instruments of the present invention may be water, an organic solvent, or a mixed solvent of water and an organic solvent. It is presumed that the use of a solvent allows the (acrylic acid / perfluoroalkyl acrylate) copolymer to form a stable network structure and a gel structure, thereby making it possible to increase the viscosity of the ink.

[0024] As the water, conventional water such as ion-exchanged water, distilled water, and tap water can be used. Examples of organic solvents include polyhydric alcohol solvents such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, and glycerin; alkylene glycol alkyl ether solvents such as alkylene glycol monoalkyl ethers and alkylene glycol dialkyl ethers; aromatic alcohols such as benzyl alcohol; and aliphatic alcohol solvents such as methanol, ethanol, 1-propanol, 2-propanol, isobutanol, and t-butanol.

[0025] Furthermore, in the case of aqueous ink compositions, the solvent is preferably an (acrylic acid / perfluoroalkyl acrylate) copolymer, and in consideration of stability with water and the formation of a stable network structure, a polyhydric alcohol solvent is preferred, and from this perspective, a polyhydric alcohol having a divalent or trivalent hydroxyl group is even more preferred. In the case of oil-based ink compositions, alkylene glycol alkyl ether solvents are preferred, and alkylene glycol monoalkyl ethers are preferred, in consideration of the formation of a stable network structure with the (acrylic acid / perfluoroalkyl acrylate) copolymer. Furthermore, the number of carbon atoms in the alkylene glycol moiety of the alkylene glycol monoalkyl ether is preferably 2 to 10, more preferably 3 to 8, and even more preferably 5 to 6, in consideration of the ease of thickening the ink with the (acrylic acid / perfluoroalkyl acrylate) copolymer (developing ink viscosity). Regarding the number of carbon atoms in the alkyl ether moiety of the alkylene glycol monoalkyl ether, in consideration of swelling dispersibility with the (acrylic acid / perfluoroalkyl acrylate) copolymer, writing feel, and writing performance (suppression of smearing and blobbing), the shorter the alkyl ether moiety, the better. Therefore, the number of carbon atoms is preferably 1 to 6, and in consideration of easier stability with the (acrylic acid / perfluoroalkyl acrylate) copolymer and easier achievement of the effect, it is 1 to 4, and more preferably 1 to 2. Furthermore, alkylene glycol monoalkyl ethers having a solubility parameter (SP value) of 8 to 13 are preferred.

[0026] Furthermore, in the case of an oil-based ink composition, it is preferable for the solvent to contain a small amount of water. The reason for this is unclear, but water has excellent affinity with the (acrylic acid / perfluoroalkyl acrylate) copolymer, and can impart a stronger thickening effect and stable swelling properties to the swelling dispersion caused by the (acrylic acid / perfluoroalkyl acrylate) copolymer. Furthermore, water improves the slipperiness of the writing tip (ball), improves ink ejection properties, and suppresses uneven dots, smearing, and blurring, thereby improving writing performance. In particular, using an alkylene glycol alkyl ether solvent and water together as the solvent is preferable, as this tends to impart a stronger thickening effect and stable swelling properties.

[0027] If the water content is less than 0.1% by mass of the total ink composition, it is likely to affect the smoothness of the writing tip (ball) and ink dischargeability, and if it exceeds 20% by mass, it is likely to deteriorate the solubility in the ink, so the water content is preferably 0.1 to 20% by mass of the total ink composition. Furthermore, in consideration of solubility in the ink and writing performance (prevention of smearing and bleeding), it is preferably 1 to 10% by mass, and even more preferably 2 to 10% by mass.

[0028] The content of the solvent in the aqueous ink composition for writing instruments is preferably 20 to 90% by mass, and more preferably 30 to 80% by mass, of the total amount of the ink composition. If the solvent content is within the above range, the (acrylic acid / perfluoroalkyl acrylate) copolymer can form a stable network structure and a gel structure, which makes it possible to increase the viscosity of the ink, suppress ink leakage from the gaps at the writing tip, and reduce the ink viscosity during writing, thereby suppressing blurring of handwriting, providing excellent writing performance and facilitating an improved writing feel.

[0029] Furthermore, the blending ratio of the solvent to the (acrylic acid / perfluoroalkyl acrylate) copolymer (solvent / perfluoroalkyl acrylate) is preferably 10 to 1000 times by mass, more preferably 20 to 200 times, and even more preferably 30 to 100 times. This is because within the above ranges, a stable network structure is formed and a gel structure is easily formed, which makes it easier to suppress ink leakage, provide excellent writing properties, and improve the writing feel.

[0030] (coloring agent) The colorant used in the water-based ink composition and oil-based ink composition of the present invention is not particularly limited and may be a dye, pigment, or the like, and may be appropriately selected and used. Dyes and pigments may be used in combination.

[0031] As the dyes used in the aqueous ink composition, direct dyes, acid dyes, basic dyes, metal-containing dyes, various salt-forming dyes, etc. can be used. (a) Direct dyes include Direct Yellow 4, 26, 44, 50, and 85; Direct Red 1, 2, 4, 23, 31, 37, 39, 75, 80, 81, 83, 225, 226, and 227; Direct Blue 1, 3, 15, 41, 71, 86, 106, and 119; and Direct Orange 6. (b) Acid dyes include The colors are Acid Black 1, 2, 24, 26, 31, 52, 107, Acid Orange 56, Acid Yellow 3, 7, 17, 19, 23, 42, 49, 61, 92, Acid Red 8, 9, 14, 18, 51, 52, 73, 87, 92, 94, Acid Blue 1, 7, 9, 22, 62, 90, 103, Acid Green 3, 9, 16, 25, 27, Acid Violet 15, 17, etc.; (c) Basic dyes include CI Basic Yellow 1, 2, 21, 7, 40, CI Basic Orange 2, 14, 32, CI Basic Red 1, 1:1, 2, 9, 14, CI Basic Violet 1, 3, 7, 10, 11:1, CI Basic Blue 3, 7, 26, Basic Green 4, CI Basic Brown 12, CI Basic Black 2, methyl violet, Victoria Blue FB, malachite green, and rhodamine series; (d) Other dyes include disperse dyes such as Disperse Yellow 82, 121, and Disperse Blue 7.

[0032] Dyes that can be used in oil-based ink compositions include oil-soluble dyes, acid dyes, basic dyes, metal-containing dyes, etc., and various salt-forming dyes thereof, such as salt-forming dyes formed from an acid dye and a basic dye, salt-forming dyes formed from an organic acid and a basic dye, salt-forming dyes formed from an acid dye and an organic amine, etc. Considering that the network structure of the (acrylic acid / perfluoroalkyl acrylate) copolymer used in the present invention is not inhibited and the ink viscosity is stably increased, it is preferable to use a salt-forming dye. Dyes include Balifast Black 1802, Balifast Black 1805, Balifast Black 1807, Balifast Violet 1701, Balifast Violet 1704, Balifast Violet 1705, Balifast Blue 1601, Balifast Blue 1605, Balifast Blue 1613, Balifast Blue 1621, Balifast Blue 1631, Balifast Red 1320, Balifast Red 1355, Balifast Red 1360, Balifast Yellow 1101, Balifast Yellow 1151, Nigrosine Base EXBP, Nigrosine Base EX, BASE OF BASIC DYES ROB-B, BASE OF BASIC DYES RO6G-B, BASE OF BASIC DYES VPB-B, BASE OF BASIC DYES VB-B, BASE OF BASIC DYES MVB-3 (all manufactured by Orient Chemical Industries Co., Ltd.), Aizen Spiron Black GMH-Special, and Aizen Spiron Violet C-RH, Aizenspiron Blue GNH, Aizenspiron Blue 2BNH, Aizenspiron Blue C-RH, Aizenspiron Red C-GH, Aizenspiron Red C-BH, Aizenspiron Yellow C-GNH, Aizenspiron Yellow C-2GH, SPT Blue 111, SPT Blue GLSH-Special, SPT Red 533, SPT Orange 6, SBN Yellow 510, SBN Yellow 530, SRC-BH (all manufactured by Hodogaya Chemical Co., Ltd.). Examples of pigments include inorganic, organic, and processed pigments. Specific examples include carbon black, aniline black, ultramarine, yellow lead, titanium oxide, iron oxide, phthalocyanine-based, azo-based, quinacridone-based, diketopyrrolopyrrole-based, quinophthalone-based, threne-based, triphenylmethane-based, perinone-based, perylene-based, dioxazine-based, metallic pigments, pearl pigments, fluorescent pigments, and phosphorescent pigments. These dyes and pigments may be used alone or in combination of two or more.

[0033] It is preferable to use a pigment as the colorant, because in the case of a ballpoint pen, the pigment particles create a physical obstacle in the gap between the ball and the inner wall of the tip, which makes it easy to suppress ink leakage. In addition, pigments are preferable because they provide excellent handwriting fastness, especially excellent light resistance. Furthermore, in the case of ballpoint pens, the use of pigments allows pigment particles to penetrate into the gap between the ball and the tip body, acting like a bearing, and by suppressing metal-to-metal contact, it is possible to improve lubricity, improve writing feel, and reduce wear of the ball seat, making the use of pigments preferable. The use of an (acrylic acid / perfluoroalkyl acrylate) copolymer, as in the present invention, gives the ink a gel structure, reducing the ink viscosity during writing, which makes metal-to-metal contact between the ball and the tip body more likely to occur, improving lubricity and reducing wear of the ball seat, making the use of pigments preferable. Furthermore, the synergistic effect of the lubricating layer formed by the surfactant, described below, and the pigment particles and bearing action makes it easier to maintain lubricity and improve the writing feel, making the use of pigments preferable.

[0034] The content of the colorant is preferably 1 to 30% by mass relative to the total amount of the ink composition. This is because if it is less than 1% by mass, it tends to be difficult to obtain thick handwriting, and if it exceeds 30% by mass, it is likely to affect the solubility and dispersibility in the ink. Taking this into consideration, the content is more preferably 3 to 25% by mass, and even more preferably 5 to 25% by mass.

[0035] (stabilizer) In the present invention, it is preferable to use a stabilizer to stably swell and disperse the (acrylic acid / perfluoroalkyl acrylate) copolymer in the ink, thereby facilitating stable thickening. Furthermore, even when a surfactant such as a phosphate ester surfactant is used, neutralization is preferred because it stabilizes the solution in the ink and improves the writing feel and start-up performance. Examples of stabilizers include basic inorganic compounds such as ammonia, sodium carbonate, sodium phosphate, and sodium hydroxide; alkanolamines such as diethanolamine and triethanolamine; amines containing ethylene oxide such as oxyethylene alkylamines and polyoxyethylene alkylamines; alkylamines such as laurylamine and stearylamine; aliphatic amines such as dimethyl alkylamines such as distearylamine, dimethyl laurylamine, dimethylstearylamine, and dimethyloctylamine; basic organic compounds such as sodium acetate; lactic acid; and citric acid. Among these, basic inorganic compounds are preferred in consideration of stability with the (acrylic acid / perfluoroalkyl acrylate) copolymer, and alkanolamines are even more preferred. In particular, in the case of aqueous ink compositions, alkanolamines are preferred, and it is preferable to use triethanolamine, which is weakly basic. In the case of oil-based ink compositions, amines containing ethylene oxide are preferred. These may be used alone or in combination of two or more.

[0036] The average number of moles of ethylene oxide added (per amine molecule) (EO number) of the amine having ethylene oxide is preferably 1 to 30, and more preferably 4 to 20. By setting the EO number within the above range, the (acrylic acid / perfluoroalkyl acrylate) copolymer is neutralized and stabilized due to stable dissolution in the solvent, and a stable thickening effect is easily obtained.

[0037] Furthermore, in consideration of stability with the solvent, (acrylic acid / perfluoroalkyl acrylate) copolymer, colorant, and other components, the total amine value of the organic amine is preferably 300 (mgKOH / g) or less. This is because if it exceeds 300 (mgKOH / g), the organic amine is highly reactive and easily reacts with the above-mentioned components, which tends to deteriorate the ink's stability over time. Furthermore, in consideration of stability with the solvent and (acrylic acid / perfluoroalkyl acrylate) copolymer, the total amine value is preferably 200 (mgKOH / g) or less, and even more preferably 150 (mgKOH / g) or less. On the other hand, in consideration of the above effects, the lower limit of the total amine value is preferably 30 (mgKOH / g) or more. The total amine value indicates the total amount of primary, secondary, and tertiary amines, and is expressed as the number of milligrams of potassium hydroxide equivalent to the amount of hydrochloric acid required to neutralize 1 g of sample.

[0038] The HLB value of the organic amine is preferably 5 to 17. This is because a stable thickening effect can be obtained by neutralizing and stabilizing the (acrylic acid / perfluoroalkyl acrylate) copolymer and stabilizing the swelling and dispersion with the solvent. In consideration of further neutralization stability and improved swelling and dispersion properties, the HLB value is preferably 7 to 17, and further consideration is more preferably 9 to 16.

[0039] In the present invention, the blending ratio of the stabilizer to the (acrylic acid / perfluoroalkyl acrylate) copolymer (stabilizer / (acrylic acid / perfluoroalkyl acrylate) copolymer) is preferably 0.1 to 15 times by mass, more preferably 0.3 to 10 times, and more preferably 0.5 to 8 times. This is because the (acrylic acid / perfluoroalkyl acrylate) copolymer can be stably swelled and dispersed in the ink, making it easier to obtain a stable thickening effect.

[0040] The content of the stabilizer is preferably 0.1 to 10 mass% of the total amount of the ink composition, taking into consideration the neutralization stability with the (acrylic acid / perfluoroalkyl acrylate) copolymer and the phosphate ester surfactant, and further taking into consideration the neutralization with the phosphate ester surfactant, it is preferably 0.1 to 8 mass%, and more preferably 0.5 to 6 mass%.

[0041] (surfactant) In the present invention, the use of a surfactant is preferred because improving lubricity improves the writing feel and also improves the writing performance when the writing tip is left exposed to the atmosphere and dries. This is because the lubricating layer formed by the surfactant facilitates improving lubricity, and the surfactant can soften the coating formed by drying the writing tip, thereby facilitating improved writing performance. Examples of surfactants include fatty acids, silicone-based surfactants, fluorine-based surfactants, phosphate ester-based surfactants, surfactants with acetylene bonds, fatty acid esters, polyalkylene alkyl ethers, and alkyl alkanolamides. Considering the above effects, it is preferable to use one or more of fatty acids, phosphate ester-based surfactants, and fatty acid esters. In particular, when used in a ballpoint pen, it is preferable to use a phosphate ester surfactant because the phosphate group makes it easy for the surfactant to be adsorbed to the ballpoint pen tip or ball, which are made of metals, and therefore it is easy to obtain a lubricating effect. This is also preferable because it makes it easy to obtain an extreme pressure effect between the metal ball and ball seat, making it easy to further improve lubrication. In the case of aqueous ink compositions, among the phosphate ester surfactants, phosphate ester surfactants such as linear alcohol-based, styrenated phenol-based, nonylphenol-based, and octylphenol-based surfactants can be mentioned. Among these, it is preferable to use linear alcohol-based and styrenated phenol-based phosphate ester surfactants, and in consideration of making it easier to improve the writing feel, it is even more preferable to use linear alcohol-based phosphate ester surfactants. In the case of oil-based ink compositions, among phosphate ester surfactants, in order to facilitate improvement of the writing feel, it is preferable to use a phosphate ester surfactant with an acid value of 180 (mgKOH / g) or less, and from a more particular consideration, it is more preferable to use a phosphate ester surfactant with an acid value of 70 to 160 (mgKOH / g). The acid value is expressed as the number of mg of potassium hydroxide required to neutralize the acidic components contained in 1 g of sample.

[0042] The HLB value of the surfactant is preferably 5 to 17, taking into consideration compatibility with the (acrylic acid / perfluoroalkyl acrylate) copolymer. To further improve swelling dispersibility, lubricity, and writing performance, the HLB value is preferably 6 to 14. Furthermore, taking into consideration lubricity, the HLB value is preferably 12 or less, and an HLB value of 6 to 12 is preferred. The HLB value used in the present invention can be determined by the Griffin method, the Kawakami method, etc. In particular, in retractable writing instruments such as knock-type writing instruments and rotary-propelling writing instruments, the writing tip is always exposed to the outside, unlike cap-type writing instruments, and therefore the writing performance when the writing tip dries is easily affected, so it is more preferable to use a surfactant with the above HLB value.

[0043] Specific examples of the surfactant include fatty acids such as oleic acid, stearic acid, and linoleic acid; silicone surfactants such as dimethyl silicone, methylphenyl silicone, polyether-modified silicone, and higher fatty acid ester-modified silicone; fluorine-containing surfactants such as perfluoro group-containing butyl sulfonate, perfluoro group-containing carboxylate, perfluoro group-containing phosphate, perfluoro group-containing phosphate ester-type compound, perfluoroalkyl betaine, and perfluoroalkylamine oxide compound; and phosphate surfactants such as polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate monoester, polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate diester, polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate triester, alkyl phosphate ester, alkyl ether phosphate ester, and derivatives thereof. Among these, it is preferable to use a phosphate ester surfactant in consideration of lubrication and thickening effects.

[0044] The content of the surfactant is more preferably 0.1 to 5.0% by mass relative to the total amount of the ink composition. This is because if it is less than 0.1% by mass, it is difficult to obtain the desired lubricity, and if it exceeds 5.0% by mass, the ink tends to become unstable over time. Taking this into consideration, the content is preferably 0.3 to 3.0% by mass, and even more preferably 0.5 to 3.0% by mass relative to the total amount of the ink composition.

[0045] (resin) In the present invention, resins may be used as ink viscosity modifiers, ink leakage suppressants, pigment dispersants, and fixing agents. Examples of resins include polyvinyl butyral resins, ketone resins, polyacetal resins, polyvinyl alcohol resins, cellulose resins, terpene resins, alkyd resins, phenoxy resins, polyvinyl acetate resins, polyvinylpyrrolidone resins, ethylene oxide polymers, acrylic resins, styrene-acrylic resins, styrene-maleic acid resins, and resin particles such as olefin-based resin particles, acrylic ester resin particles, amino resin particles, acrylic resin particles, and styrene-butadiene-based resin particles. These may be used alone or in combination of two or more.

[0046] Among these resins, resin particles are preferred when ink leakage is to be suppressed. Even more preferably, organic resin particles are used, and a resin selected from acrylic ester resin particles, olefin-based resin particles, and amino resin particles is preferred. This is because the resin particles create a physical barrier between the gap at the writing tip (the gap between the ball and the tip in the case of a ballpoint pen), thereby suppressing ink leakage. Furthermore, when the particles partially deform and adhere to each other, a structure formed by weak aggregation is generated, forming a structure in the ink that is highly resistant to ink leakage when left stationary, thereby enabling high ink leakage suppression. Meanwhile, because the structure is formed by weak aggregation, the aggregated structure is broken down by physical actions such as the rotation of the ball during writing. This allows for smooth writing without impairing the ink fluidity during writing, resulting in a good writing feel and writing performance with reduced smearing. Furthermore, the (acrylic acid / perfluoroalkyl acrylate) copolymer has a stable network structure that inhibits ink leakage, and the interaction between the resin particles and the physical barriers provides a more effective ink leakage suppression effect, which is particularly advantageous. This is particularly effective when used as an ink composition for ballpoint pens.

[0047] The average particle size of the resin particles is preferably 7 μm or less, more preferably 5 μm or less, because a smaller average particle size allows particles to adhere to each other, forming a weakly aggregated structure and suppressing ink leakage. Furthermore, considering the dispersion stability of the resin particles in the ink (ink stability over time), 3 μm or less is preferable, and even more preferably less than 1 μm. On the other hand, since an average particle size that is too small tends to reduce the ink leakage suppression effect, the average particle size is preferably 0.1 μm or more, more preferably 0.3 μm or more. The average particle size can be determined by the Coulter Counter method using a Coulter Multisizer™3 (a measuring device manufactured by Beckman Coulter) to measure the particle size at 50% cumulative volume (D50) of the particle size distribution measured based on values ​​calibrated using standard samples or other measurement methods.

[0048] Of these resin particles, in consideration of the (acrylic acid / perfluoroalkyl acrylate) copolymer in the ink, stability to solvents, and suppression of ink leakage, it is preferable to select and use from among olefin-based resin particles, acrylic ester resin particles, and amino resin particles, and in consideration of the fact that they are more likely to be stable in the ink and thereby improve suppression of ink leakage, it is preferable to select and use from among polyethylene resin particles, methacrylic ester resin particles, melamine resin particles, and benzoguanamine resin particles, and from these considerations, polyethylene resin particles and methacrylic ester resin particles are preferred. In particular, in the case of aqueous ink compositions, olefin resin particles are preferred, with polyethylene resin particles being more preferred, taking into consideration compatibility with the solvent and the effect of suppressing ink leakage. In the case of oil-based ink compositions, acrylic acid ester resin particles are preferred, with methacrylic acid ester resin particles being more preferred, taking into consideration compatibility with the solvent and the effect of suppressing ink leakage. These resin particles may be used alone or in combination of two or more kinds, and may also be a mixture or copolymer.

[0049] The resin particles may be spherical or irregularly shaped, but spherical resin particles are preferred in view of the ink leakage suppression effect due to the adhesion between the resin particles. The spherical resin particles referred to here are not limited to true spheres, and may be approximately spherical resin particles or approximately oval spherical resin particles.

[0050] Furthermore, among resins, it is preferable to use ketone resins and polyvinyl butyral resins in order to improve the writing feel, suppress blurred handwriting and uneven dots, and facilitate improvement of pigment dispersibility, and it is preferable to use ketone resins in order to improve the writing feel and suppress blurred handwriting and uneven dots (writing performance).

[0051] Furthermore, the content of the resin particles is more preferably 0.01 to 10% by mass of the total amount of the ink composition. This is because if the content of the resin particles is less than 0.01% by mass, it is difficult to prevent ink leakage, and if it exceeds 10% by mass, the aggregate structure tends to become strong, which tends to affect the ink stability over time, writing feel, and writing performance. From further consideration, the content is preferably 0.1 to 5% by mass, particularly preferably 0.3 to 3% by mass, and most preferably 0.5 to 3% by mass.

[0052] Shear thinning agents other than the (acrylic acid / perfluoroalkyl acrylate) copolymer may also be used in combination. This can adjust the viscosity of the ink composition and improve the dispersion stability of the pigment. Specific examples include fatty acid amides, hydrogenated castor oil, polyacrylic acid, xanthan gum, welan gum, succinoglycan, guar gum, locust bean gum, λ-carrageenan, cellulose derivatives, and polysaccharides such as diutan gum.

[0053] Furthermore, in the case of aqueous ink compositions, it is preferable to use dextrin in order to suppress ink leakage and improve writing performance. This is because the use of dextrin causes the ink at the writing tip to form a coating when it dries, thereby suppressing ink leakage from the gap at the writing tip (in the case of a ballpoint pen, ink leakage from the gap between the ball and the tip), and furthermore, by suppressing the writing tip from drying and solidifying, it has the effect of improving writing performance due to drying up.

[0054] The weight-average molecular weight of the dextrin is more preferably 5,000 to 120,000. If the weight-average molecular weight exceeds 120,000, the coating formed on the writing tip becomes hard, and handwriting tends to smudge when writing begins after drying up. On the other hand, if the weight-average molecular weight is less than 5,000, the hygroscopicity tends to be high, and the coating on the writing tip tends to become soft, making it difficult to obtain a sufficient ink leakage suppression effect. Furthermore, if the weight-average molecular weight is less than 20,000, the coating tends to become thin, so a weight-average molecular weight of 20,000 to 120,000 is most preferred.

[0055] Other additives that can be added include antibacterial agents such as 1,2-benzisothiazolin-3-one, rust inhibitors such as benzotriazole, humectants such as urea and sorbitol, chelating agents such as ethylenediaminetetraacetic acid, plasticizers, etc. These can be used alone or in combination of two or more.

[0056] The ink viscosity of the ink composition for a writing instrument of the present invention is not particularly limited, but by imparting shear thinning properties with the (acrylic acid / perfluoroalkyl acrylate) copolymer, the ink viscosity at rest can be increased, making it easier to suppress ink leakage, and the ink viscosity during writing can be decreased, making it easier to improve writing feel and writing performance such as smearing. For water-based ink compositions, 20°C, shear rate 192 sec -1The ink viscosity (when writing) is preferably 300 mPa·s or less, as this tends to improve the writing feel and writing performance such as preventing smearing, and is preferably 200 mPa·s or less in consideration of the writing feel and writing performance. In addition, considering ink leakage prevention and ink tracking, the shear rate is 20°C and 1.92 sec -1 The ink viscosity (at rest) is preferably 100 to 5000 mPa·s, more preferably 200 to 3500 mPa·s, and even more preferably 300 to 3000 mPa·s. The ink viscosity of the aqueous ink composition was measured using a Brookfield DV-II viscometer (CPE-42 rotor). For oil-based ink compositions, 20°C, shear rate 20 sec -1 The ink viscosity (when writing) is preferably 7000 mPa·s or less, and if we take into consideration the writing feel and writing performance, the ink viscosity is preferably 4000 mPa·s or less, and even more preferably 3000 mPa·s or less. Furthermore, if we take into consideration writing performance such as bleeding, smearing, bleed-through, and drying of handwriting, the ink viscosity is preferably 100 mPa·s or more, and even more preferably 200 mPa·s or more, and 500 mPa·s or more. In addition, considering ink followability, 20°C, shear rate 0.18 sec -1 The ink viscosity (at rest) is preferably 50,000 mPa·s or less, more preferably 30,000 mPa·s or less, and even more preferably 20,000 mPa·s or less. In addition, in consideration of suppressing ink leakage, the ink viscosity is preferably 20°C, shear rate 0.18 sec -1 The ink viscosity (at rest) is preferably 1000 mPa·s or more, more preferably 2000 mPa·s or more, and even more preferably 3000 mPa·s or more. Here, the ink viscosity of the oil-based ink composition was measured at 20°C using a Brookfield Viscometer RVDVII+Pro CP-52 spindle. This is also effective for retractable writing instruments such as knock-type writing instruments and rotary-propelling writing instruments, in which it is necessary to give greater consideration to preventing ink leakage.

[0057] In the present invention, the viscosity index n is expressed as S=αD n where S is the shear stress (dyn / cm 2 =0.1 Pa), D is the shear rate (s -1 ), and α represents the viscosity coefficient. The viscosity index n can be calculated by measuring the ink viscosity at 20°C using the viscometer described above. With regard to the viscosity index n, taking into consideration writing properties such as ink leakage prevention, writing feel, and smearing, it is preferable that the viscosity index n = 0.4 to 0.9, and taking into consideration the balance of writing properties such as ink leakage prevention, writing feel, and smearing, it is preferable that the viscosity index n = 0.5 to 0.85, and more particularly, 0.55 to 0.8 is preferable.

[0058] (writing implements) The aqueous ink composition for writing instruments of the present invention can be used in writing instruments such as marking pens and ballpoint pens with pen tips such as fiber tips, felt tips, plastic tips, or ballpoint pen tips. The writing instrument of the present invention may be configured to be filled directly with the aqueous ink composition for a writing instrument, or may be configured to be equipped with an ink reservoir or ink occlusion body that can be filled with the aqueous ink composition for a writing instrument.

[0059] The retractable mechanism of the writing implement of the present invention is not particularly limited, and examples include a cap type with a cap that covers the pen tip, a knock type, a rotation type, and a slide type.It may also be a retractable type that allows the pen tip to be stored in the barrel.

[0060] The ink supply mechanism in the writing instrument is also not particularly limited, and examples include (1) a mechanism that has an ink guide core made of a fiber bundle or the like as an ink flow rate adjusting member and supplies the ink composition to the pen tip, (2) a mechanism that has a comb-shaped ink flow rate adjusting member and supplies the ink composition to the pen tip through this, (3) a mechanism that has an ink flow rate adjusting member with a valve mechanism and supplies the ink composition to the pen tip, and (4) a mechanism that supplies the ink composition directly to the pen tip from an ink reservoir or barrel equipped with a pen tip.

[0061] In one embodiment, the writing instrument is a marking pen, and the pen tip is not particularly limited and may be, for example, a fiber tip, a felt tip, or a plastic tip, and further, the shape may be a bullet type, a chisel type, a brush pen type, or the like. In one embodiment, the writing instrument is a ballpoint pen, preferably a ballpoint pen equipped with an ink backflow preventer.

[0062] (ballpoint pen tip) In the case of a ballpoint pen, the amount of movement of the ball of the ballpoint pen tip in the vertical axis direction is preferably 15 to 50 μm in the case of an aqueous ballpoint pen. This is because if it is less than 15 μm, it becomes difficult to obtain a good writing feel and suppression of blurred handwriting, and if it exceeds 50 μm, it is likely to affect the suppression of ink leakage, blobbing, and ink following performance. From further consideration, it is preferable to set it to 20 to 50 μm, and even more preferably, the amount of movement in the vertical axis direction is 25 to 45 μm. In the case of an oil-based ballpoint pen, it is preferably 3 to 25 μm. This is because if it is less than 3 μm, it becomes difficult to obtain a good writing feel and suppression of handwriting smearing, and if it exceeds 25 μm, it is likely to affect the suppression of ink leakage, blobbing, and ink following performance. From further consideration, it is more preferable to set it to 3 to 20 μm, and from further consideration, it is more preferable to set the amount of movement in the vertical axis direction to 5 to 16 μm. The amount of movement (clearance) of the ball of the ballpoint pen tip in the axial direction refers to the distance that the ball can move in the longitudinal direction of the ballpoint pen tip body.

[0063] Furthermore, to suppress wear of the ball seat and improve the writing feel, the arithmetic mean roughness (Ra) of the ball surface is preferably 0.1 to 10 nm. This is because if the arithmetic mean roughness (Ra) exceeds this range, the ball surface becomes too rough, which tends to increase the rotational resistance between the ball and ball seat, affecting the writing feel and wear of the ball seat. Conversely, if the arithmetic mean roughness (Ra) is below this range, the ink does not adhere sufficiently to the ball surface, which tends to affect writing performance, such as blurring of handwriting. Therefore, to suppress wear of the ball seat, improve the writing feel, and obtain sufficient writing performance, the arithmetic mean roughness (Ra) of the ball surface is preferably 0.1 to 10 nm, more preferably 0.1 to 8 nm, and particularly preferably 0.1 to 6 nm. The arithmetic mean roughness of the ball surface is calculated by taking a reference length from the roughness curve measured using a surface roughness measuring instrument (Seiko Epson model SPI3800N) in the direction of the mean line, and then adding up and averaging the absolute values ​​of the deviations from the mean line of this sampled section to the measurement curve.

[0064] The material used for the balls is not particularly limited, but examples include cemented carbide balls mainly composed of tungsten carbide, metal balls such as stainless steel, ceramic balls such as silicon carbide, silicon nitride, alumina, silica, and zirconia, and ruby ​​balls.

[0065] In addition, materials for ballpoint pen tips include metals such as stainless steel, nickel silver, brass, aluminum bronze, and aluminum, and resins such as polycarbonate, polyacetal, and ABS, but considering wear of the ball seat, stability over time, and cost, it is preferable to use a tip body made of stainless steel.

[0066] <Example> The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0067] Example 1 <Water-based ballpoint pen ink composition> The colorants used were pigment dispersion, water, polyhydric alcohol, stabilizer, organic resin particles, surfactant, and rust inhibitor. Predetermined amounts of these were weighed out, heated to 60°C, and completely dissolved using a disper mixer to prepare a base ink. Then, while heating the base ink, (acrylic acid / perfluorohexylethyl acrylate) crosspolymer was added and thoroughly mixed and stirred using a homogenizer mixer until a uniform state was achieved, yielding the aqueous ballpoint pen ink composition of Example 1. The specific blending amounts are as follows: The blending ratio of the stabilizer to the (acrylic acid / perfluoroalkyl acrylate) copolymer (stabilizer / (acrylic acid / perfluoroalkyl acrylate) copolymer) was 1.33. The ink viscosity of Example 1 was measured at a shear rate of 1.92 sec at 20°C using a Brookfield DV-II viscometer (CPE-42 rotor). -1 The ink viscosity was measured at 1027 mPa·s under the conditions of a rotation speed of 0.5 rpm, a temperature of 20°C, and a shear rate of 192 sec -1 The viscosity was 152 mPa·s at a rotation speed of 50 rpm, and the viscosity index n was 0.59.

[0068] Pigment dispersion (colored resin particles, solid content 34%) 20.0% by mass Water 64.0% by mass Polyhydric alcohol (glycerin) 10.0% by mass (acrylic acid / perfluorohexylethyl acrylate) crosspolymer 1.5% by mass "Constituents: acrylic acid ester (chemical formula 1), acrylic acid (chemical formula 2), diethylene glycol diallyl ether (chemical formula 1) / (chemical formula 2) = 0.3. The ratio of diethylene glycol diallyl ether to 100 parts by weight of the total of acrylic acid ester and acrylic acid: 0.29 parts by weight." Organic resin particles (polyethylene resin, average particle size: 6 μm) 1.0% by mass Stabilizer (triethanolamine) 2.0% by mass Phosphate ester surfactant (HLB value: 11.5) 1.0% by mass Rust inhibitor (benzotriazole) 0.5% by mass

[0069] <Examples 2 to 9 and Comparative Examples 1 to 4> Water-based ink compositions for ballpoint pens of Examples 2 to 9 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1, except that the types and amounts of the components to be blended were changed as shown in the table.

[0070] The aqueous ballpoint pen ink compositions (1.0 g) prepared in Examples 1 to 9 and Comparative Examples 1 to 4 were filled into ballpoint pen refills equipped with ink reservoirs (polypropylene) and ballpoint pen tips (with a coil spring pressing the ball directly against the inner wall of the tip edge, ball longitudinal movement: 30 μm, ball surface arithmetic mean roughness (Ra): 1 nm) that rotatably hold a ball with a ball diameter of φ0.7 mm. The ballpoint pens were prepared by filling the refills with the aqueous ballpoint pen ink compositions (1.0 g) prepared in ink reservoirs (polypropylene). The test paper used was JIS P3201 writing paper, and the following tests and evaluations were carried out.

[0071] Example 11 <Ink composition for oil-based ballpoint pens> A colorant, a solvent, a surfactant, and organic resin particles were used, and a predetermined amount of each was weighed out, heated to 60°C, and then completely dissolved using a disper mixer to prepare a base ink. Then, while heating the base ink prepared above, an (acrylic acid / perfluorohexylethyl acrylate) crosspolymer was added and thoroughly mixed and stirred using a homogenizer mixer until it became uniform, thereby obtaining the oil-based ink of Example 11. The specific blending amounts are as follows: The ink viscosity of Example 11 was measured using a Brookfield Viscometer RVDVII+Pro CP-52 spindle at a shear rate of 0.18 sec at a temperature of 20°C. -1 At 15,000 mPa·s, 20°C, shear rate 20 sec -1The viscosity was 2700 mPa·s at 100°C, and the viscosity index n was 0.64.

[0072] Coloring agent (dye, salt-forming dye of basic dye and acid dye) 10.0% by mass Coloring agent (dye, salt-forming dye of basic dye and organic acid) 10.0% by mass Alkylene glycol monoalkyl ether, number of carbon atoms in alkylene glycol moiety: 6, solubility parameter (SP value): 10.5) 74.7% by mass (acrylic acid / perfluorohexylethyl acrylate) crosspolymer 3.3% by mass "Constituents: acrylic acid ester (chemical formula 1), acrylic acid (chemical formula 2), diethylene glycol diallyl ether (chemical formula 1) / (chemical formula 2) = 0.3. The ratio of diethylene glycol diallyl ether to 100 parts by weight of the total of acrylic acid ester and acrylic acid: 0.29 parts by weight." Phosphate ester surfactant (HLB value: 8.6) 1.0% by mass Organic resin particles (methyl methacrylate resin particles, average particle size: 0.8 μm, 1.0 mass%

[0073] <Examples 12 to 27 and Comparative Examples 11 to 13> Ink compositions for oil-based ballpoint pens of Examples 12 to 27 and Comparative Examples 11 to 13 were obtained in the same manner as in Example 11, except that the types and amounts of the components to be blended were changed as shown in the table.

[0074] The oil-based ballpoint pen ink compositions (0.27 g) prepared in Examples 11 to 27 and Comparative Examples 11 to 13 were filled into ballpoint pen refills equipped with ink reservoirs (polypropylene) and ballpoint pen tips (with a coil spring pressing the ball directly against the inner wall of the tip edge, ball longitudinal movement: 8 μm, ball surface arithmetic mean roughness (Ra): 5 nm) that rotatably hold a ball with a ball diameter of φ0.7 mm. The ballpoint pens were prepared by filling the refills with the oil-based ballpoint pen ink compositions (0.27 g) prepared in Examples 11 to 27 and Comparative Examples 11 to 13 into ink reservoirs (polypropylene). The refills had a ballpoint pen tip that rotatably holds a ball with a ball diameter of φ0.7 mm (the tip had a coil spring inside that pressed the ball directly against the inner wall of the tip edge, ball longitudinal movement: 8 μm, ball surface arithmetic mean roughness (Ra): 5 nm). JIS P3201 writing paper was used as the test paper, and the following tests and evaluations were carried out.

[0075] [Table 1]

[0076] [Table 2]

[0077] [Table 3]

[0078] Writing feel: Evaluation was carried out by a sensory test using handwriting. Very smooth... Smooth ○ Smooth enough for practical use △ Heavy items ×

[0079] (Water-based ballpoint pen) Ink leakage test: A 40g weight was attached to a gel ink ballpoint pen, with the ballpoint pen tip protruding and pointing downwards, and the ball of the ballpoint pen tip was kept in contact with the bottom of a ballpoint pen display case. The pen was left for one day in an environment of 20°C and 65% RH, and the amount of ink leaking from the tip of the ballpoint pen was measured. Ink leakage is less than 5 mg. Ink leakage amount is 5 to 15 mg. Ink leakage amount is more than 15 mg but less than 30 mg △ Ink leakage of 30 mg or more: × (Oil-based ballpoint pen) Ink leakage prevention test: The pen was left in an environment of 30°C and 85% RH with the tip facing downwards for 7 days, and ink leakage from the tip was confirmed. No ink droplets at the tip end... The ink droplet at the tip end is within 1 / 4 of the tapered section. The ink droplet at the tip tip is more than 1 / 4 but less than 1 / 2 of the tapered section. The ink droplet at the tip is more than half the size of the tapered part. ×

[0080] (Water-based ballpoint pen) Writing performance test: The writing was observed after a 100m writing test using a running tester with a load of 100gf, a writing angle of 70°, and a writing speed of 4m / min. (Oil-based ballpoint pen) Writing performance test: The writing was observed after a 100m writing test using a running test machine with a load of 200gf, a writing angle of 70°, and a writing speed of 4m / min. There is little or no blurring in the handwriting. There is some smudge in the writing, but it is not a problem for practical use. The handwriting is smudged, affecting its practical use. The handwriting is smudged... ×

[0081] In Examples 1 to 27, good performance was obtained in the writing feel, ink leakage suppression test, and writing performance. Furthermore, in Examples 1 to 9 and 23 to 27, when the pigment inks were examined under a microscope, the pigment dispersibility was good and no precipitates were observed, which was good. As described above, the viscosity of the inks of Examples 4 and 12 was measured using a viscometer manufactured by Brookfield Co., Ltd., and the viscosity imparting index n was calculated. In Example 4, the shear rate was 1.92 sec in an environment of 20°C. -1 (Rotation speed 0.5 rpm), ink viscosity = 345 mPa·s, 20℃ environment, shear rate 192 sec -1 (Rotation speed: 50 rpm), ink viscosity = 73 mPa·s, viscosity imparting index n was 0.66. In Example 12, the shear rate was 0.18 sec in an environment of 20 ° C. -1 Ink viscosity = 10,000 mPa·s, 20°C environment, shear rate 20 sec -1 The ink viscosity was 2000 mPa·s and the viscosity index n was 0.66. In Example 23, the shear rate was 0.18 sec in an environment of 20 ° C. -1 Ink viscosity = 11000 mPa·s, 20℃ environment, shear rate 20 sec -1 The ink viscosity was 2400 mPa·s and the viscosity index n was 0.71. In Example 24, the shear rate was 0.18 sec in an environment of 20 ° C. -1 Ink viscosity = 6600 mPa·s, 20℃ environment, shear rate 20 sec -1 The ink viscosity was 2200 mPa·s and the viscosity index n was 0.79.

[0082] In Comparative Examples 1, 2, 11, and 13, the (acrylic acid / perfluoroalkyl acrylate) copolymer was not used, and therefore the ink leakage suppression performance and writing performance were poor.

[0083] In Comparative Examples 3, 4, and 12, a shear thinning agent and a resin other than the (acrylic acid / perfluoroalkyl acrylate) copolymer were added, but sufficient ink leakage suppression effect and writing performance were not obtained.

[0084] Furthermore, when a retractable writing instrument (retractable ballpoint pen) such as a knock-type writing instrument or a rotary-advance-type writing instrument is used, ink leakage prevention performance is one of the most important performance characteristics. Therefore, it is effective to use an aqueous ink composition for a writing instrument containing the (acrylic acid / perfluoroalkyl acrylate) copolymer of the present invention, which can prevent ink leakage from the gap at the writing tip (ink leakage from the gap between the ball and the tip tip) and achieve good ink leakage prevention performance, as in the present invention.

[0085] In order to suppress ink leakage and improve writing performance as in the present invention, it is preferable to provide a valve mechanism in which the ball rotatably held at the tip of the ballpoint pen tip is pressed against the inner wall of the tip edge by a coil spring directly or via a pressing body, creating a gap between the inner wall of the tip edge and the ball due to the pressing force during writing, allowing ink to flow out, and also to close the minute gap at the tip when not in use.

[0086] In addition, in this example, for convenience, a ballpoint pen in which a ballpoint pen refill containing a writing instrument ink composition directly in the barrel is exemplified, but the writing instrument of the present invention may also be a direct-fill type ballpoint pen, marking pen, or felt-tip pen in which the barrel serves as an ink storage tube and the writing instrument ink composition is directly contained in the barrel. Furthermore, when the writing instrument ink composition is directly contained in the barrel as a marking pen or felt-tip pen, it is possible to obtain the effect of suppressing ink leakage and ink dripping, and therefore it is preferably used. Furthermore, in this embodiment, for convenience, a ballpoint pen tip formed by cutting a wire material is exemplified, but a ballpoint pen tip formed by pressing a pipe material may also be used. [Industrial Applicability]

[0087] The present invention can be used as a writing instrument, and more specifically, can be widely used as a ballpoint pen, a marking pen, a felt-tip pen, or the like, as a cap-type or retractable writing instrument.

Claims

1. A water-based ink composition for a writing instrument, comprising a colorant, a solvent, and an (acrylic acid / perfluoroalkyl acrylate) copolymer, wherein the (acrylic acid / perfluoroalkyl acrylate) copolymer has as a constituent an acrylic acid ester represented by general formula (Chemical Formula 1), and the content of the acrylic acid ester is 0.01 to 5% by mass based on the total amount of the ink composition; 20℃, shear rate 192sec －１ The ink viscosity is 300 mPa·s or less 20℃, shear rate 1.92sec －１ The ink viscosity is 200 to 3500 mPa·s 1. A water-based ink composition for a writing instrument, comprising: 【Chemical 1】

2. 2. The water-based ink composition for a writing instrument according to claim 1, wherein the solvent is a polyhydric alcohol solvent.

3. 3. The aqueous ink composition for writing instruments according to claim 1, wherein the (acrylic acid / perfluoroalkyl acrylate) copolymer has, as a constituent, acrylic acid represented by the general formula (Chemical Formula 2). 【Chemistry 2】

4. 4. The aqueous ink composition for a writing instrument according to claim 1, wherein the (acrylic acid / perfluoroalkyl acrylate) copolymer contains a crosslinking agent as a constituent component.

5. 5. The water-based ink composition for a writing instrument according to claim 1, wherein the water-based ink composition for a writing instrument contains a pigment.

6. 6. The water-based ink composition for a writing instrument according to claim 1, further comprising a surfactant.

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